Imaging equipment

Abstract

The present disclosure relates to an image forming apparatus including a rotatable image bearing member and a rotatable developing member configured to carry a developer composed of toner particles and carrier particles attached to surfaces of the toner particles. When a pressing force F1 is applied to the developing member against the image bearing member and a total number N1 of carrier particles interposed between the toner particles and the image bearing member, an adhesion force Ft between the carrier particles and the toner particles measured when the carrier particles are pressed against the toner particles at F1 / N1 and an adhesion force Fdr1 between the carrier particles and the image bearing member measured when the carrier particles are pressed against the image bearing member at F1 / N1 satisfy Ft≤Fdr1, where F1 / N1 is the pressing force per unit carrier particle.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus using an electrophotographic process or the like. Background Art

[0002] Conventionally, there are known image forming apparatuses such as copying machines and laser printers that perform image formation by using an electrophotographic process.

[0003] In the transfer step, the imaging device applies a voltage from a voltage source to a transfer member disposed in an area opposite a photoconductor drum serving as an image bearing member, thereby electrostatically transferring the toner image formed on the surface of the photoconductor drum to an intermediate transfer member or recording medium. When forming a multi-color toner image, the transfer step is sequentially performed for each color of the toner image, resulting in a multi-color toner image formed on the surface of the intermediate transfer member or recording medium. The developer (toner) that has not been transferred from the photoconductor drum to the intermediate transfer member or recording medium is removed from the photoconductor drum by a cleaning member and is stored as waste toner in a waste toner storage portion of the cleaning unit.

[0004] In recent years, for the purpose of reducing the size of equipment, a cleaner-less system has been proposed that does not include a cleaning system for the surface of the photoconductor drum. To achieve the cleaner-less system, it is conceivable that the transfer efficiency of the toner image from the photoconductor drum to the intermediate transfer member is improved, thereby reducing the residual toner remaining on the surface of the photoconductor drum after the toner image is transferred by the transfer member.

[0005] Japanese Patent Laid-Open No. 10-063027 proposes a structure for achieving a cleaner-less system by reducing adhesion between a photoconductor drum and a toner in such a manner that fine particles are attached to the surface of the photoconductor drum in advance and placed between the photoconductor drum and the toner image, thereby improving transfer efficiency.

[0006] Japanese Patent Laid-Open No. 10-063027 further proposes a configuration in which fine particles are supplied from a developing device to a photoconductor drum using a toner to which fine particles are externally added as a means of attaching fine particles to the surface of a photoconductor drum.

[0007] It is known that in the primary transfer nip portion, when the peripheral speed of the photoconductor drum is exactly the same as that of the intermediate transfer belt, transfer efficiency decreases, resulting in the appearance of so-called white spots (white spots) in the center of a toner image (e.g., characters or lines). Japanese Patent Laid-Open No. 10-063027 proposes a proactive approach to provide a peripheral speed difference between the peripheral speeds of the photoconductor drum and the intermediate transfer belt. This configuration improves primary transfer efficiency, reduces the occurrence of white spots, and ultimately improves image quality.

[0008] In the above-described imaging apparatus, when the toner image formed on the surface of the photoconductor drum is primarily transferred to the surface of the intermediate transfer belt, the rotation of the photoconductor drum may fluctuate rapidly. This rapid fluctuation in rotation may cause uneven exposure during laser exposure, resulting in image streaks in the toner image subsequently formed on the surface of the photoconductor drum. This is because when the leading edge of the toner image developed on the photoconductor drum without toner in the primary transfer nip enters the primary transfer nip, the frictional force acting on the surface of the photoconductor drum caused by the surface of the intermediate transfer belt rapidly decreases.

[0009] In contrast, it is known that by forming small dot toner images using a toner of yellow or the like on a photoconductor drum in addition to a toner image of an image pattern, fluctuations in the rotation of a photoconductor drum or an intermediate transfer belt can be reduced, thereby preventing various image defects. In the image forming apparatus described in, for example, Japanese Patent Laid-Open No. 11-052758, by forming small dot toner images on a photoconductor drum in a uniformly distributed manner, the occurrence of color deviation in the toner image to be primarily transferred to the intermediate transfer belt is reduced.

[0010] In order to supply only fine particles from the toner in the developing device to the surface of the photoconductor drum, as in Japanese Patent Laid-Open No. 10-063027, the fine particles adhering to the toner need to be separated from the toner and transferred to the drum. With toners to which fine particles of commonly used silica, etc., are externally added, the adhesion between the toner and the fine particles is strong, making it difficult to supply a sufficient amount of fine particles to the surface of the photoconductor drum to improve transfer efficiency.

[0011] To improve transfer efficiency, when a toner containing externally added fine particles is supplied from a developing device to a photoconductor drum and the toner image is then transferred to a recording medium, the fine particles are transferred to the surface of the recording medium along with the transferred toner image. In particular, to improve transfer efficiency for multi-color, high-resolution printing, it is necessary to supply more fine particles to the surface of the photoconductor drum. Consequently, a large amount of fine particles may be transferred to the surface of the recording medium along with the transferred toner particles. As a result, when the toner is fixed to the recording medium, the large amount of fine particles may hinder heat transfer to the toner, thereby impairing fixability. When a processing member is provided that rotates by contact with the photoconductor drum, the fine particles interposed between the two reduce the friction between the photoconductor drum and the processing member. When the friction is reduced, the rotation of the processing member may become unstable. When the rotation of the processing member is unstable, the imaging process may not be performed under the desired processing conditions. This may result in adverse effects on the image.

[0012] The imaging device described in Japanese Patent Laid-Open No. 11-052758 has the following inconvenience. When performing imaging while adding a dot toner image when printing on a type of recording medium such as high-brightness paper, coated paper, and glossy paper, the added dot toner image may be relatively conspicuous on the recording medium, the recording medium may appear yellowish as a whole, and the image quality may be reduced. This is because the recording medium (such as high-brightness paper, coated paper, and glossy paper) has high surface smoothness and high secondary transferability. The yellow dot toner image that is primarily transferred to the intermediate transfer belt, making the surface of the photoconductor drum and the surface of the intermediate transfer belt easy to slide on each other and reducing friction, is faithfully reproduced on the recording medium. Summary of the Invention

[0013] The present disclosure improves transfer efficiency by effectively supplying fine particles from a developing device to the surface of a photoconductor drum to improve transfer efficiency, reduces the occurrence of adverse effects in an image by stabilizing the rotation of a processing member that rotates by contacting the photoconductor drum in a structure that supplies a sufficient amount of fine particles to the surface of the photoconductor drum to improve transfer efficiency, or reduces the occurrence of adverse effects in an image by reducing fluctuations in the rotation of a photoconductor drum or an intermediate transfer belt without increasing a dot colorant image.

[0014] According to one aspect of the present disclosure, an image forming apparatus includes: an image bearing member configured to be rotatable; a developing member configured to be rotatable and to carry a developer composed of toner particles and carrier particles attached to the surfaces of the toner particles, wherein the developing member is further configured to contact the image bearing member to form a developing portion and to supply the developer to the surface of the image bearing member in the developing portion; a developer accommodating portion configured to accommodate the developer; and a transfer member configured to transfer the developer supplied to the surface of the image bearing member to a transfer receiving member, wherein the developer accommodated in the transfer receiving member is transferred to the transfer receiving member while the image bearing member is rotating. Carrier particles in a developer accommodating portion and carried on the surface of the developing member are supplied to the surface of the image bearing member in the developing portion, and wherein, when a pressing force of pressing the developing member against the image bearing member is F1 and the total number of carrier particles between the colorant particles and the image bearing member is N1, an adhesion force Ft between the carrier particles and the colorant particles measured when the carrier particles are pressed against the colorant particles at F1 / N1 and an adhesion force Fdr1 between the carrier particles and the image bearing member measured when the carrier particles are pressed against the image bearing member at F1 / N1 satisfy Ft≤Fdr1, wherein F1 / N1 is a pressing force per unit carrier particle.

[0015] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of the imaging apparatus in the first embodiment.

[0017] Figure 2 It is a control block diagram in the first embodiment.

[0018] Figure 3 is a schematic diagram of the toner particle surface in the first embodiment.

[0019] Figure 4 is a schematic diagram of the shape of protrusions on the surface of the toner particles in the first embodiment.

[0020] Figure 5 is a schematic diagram of the shape of protrusions on the surface of the toner particles in the first embodiment.

[0021] Figure 6 is a schematic diagram of the shape of protrusions on the surface of the toner particles in the first embodiment.

[0022] Figure 7 is a schematic diagram of toner particles and transfer carrier particles in the first embodiment.

[0023] Figure 8A and Figure 8B This is a schematic diagram of supplying transfer carrier particles in the first embodiment.

[0024] Figure 9A and Figure 9B It is a schematic diagram of the primary transfer in the first embodiment.

[0025] Figure 10 is a timing chart of the imaging operation in the first embodiment.

[0026] Figure 11A and Figure 11B is a diagram showing a contact state of toner in the developing portion in the first embodiment.

[0027] Figure 12 is a diagram showing a state in which toner particles and transfer carrier particles exist in a developing portion in the first embodiment.

[0028] Figure 13A and Figure 13B is a diagram showing the state of transfer carrier particles in the developing portion in the first embodiment.

[0029] Figure 14 The effect confirmation test results in the first embodiment are shown.

[0030] Figure 15 The measurement results of the adhesion in the first embodiment are shown.

[0031] Figure 16 is a timing chart of the imaging operation in the second embodiment.

[0032] Figure 17A and Figure 17B 1 is a diagram showing a mechanism for supplying transfer carrier particles in a non-image forming operation in a developing portion in the second embodiment.

[0033] Figure 18A and Figure 18B is a diagram showing a mechanism for supplying transfer carrier particles in an image forming operation in a developing portion in the second embodiment.

[0034] Figure 19 is a timing chart of the transfer carrier particle supply operation in the third embodiment.

[0035] Figure 20 is a schematic diagram of an imaging apparatus in a third embodiment.

[0036] Figure 21 It is a control block diagram in the third embodiment.

[0037] Figure 22 It is a view showing a developing cartridge in the third embodiment.

[0038] Figure 23 It is a diagram showing the setting of the developing blade in the third embodiment.

[0039] Figure 24 is a diagram illustrating a contact portion between the developing roller and the photoconductor drum in the third embodiment.

[0040] Figure 25 is a timing chart showing the transfer carrier particle supply operation in the third embodiment.

[0041] Figure 26 1 is a timing chart showing the transfer carrier particle supply operation in the fourth embodiment.

[0042] Figure 27 1 is a diagram showing a transfer carrier particle supply member in another embodiment.

[0043] Figure 28 is a diagram showing a primary transfer portion in the sixth embodiment.

[0044] Figure 29 is a schematic diagram of an imaging apparatus in a sixth embodiment.

[0045] Figure 30 : are diagrams illustrating the behavior of toner particles in the drum nip portion in the sixth embodiment.

[0046] Figure 31 is a graph showing the relationship between the peripheral speed difference and the primary transfer residual toner amount in the sixth embodiment.

[0047] Figure 32 is a diagram showing an imaging apparatus in a seventh embodiment.

[0048] Figure 33 is a diagram showing an imaging apparatus in an eighth embodiment.

[0049] Figure 34 is a diagram showing a primary transfer portion in the eighth embodiment.

[0050] Figure 35A and Figure 35B Schematic diagram showing the relationship of adhesion of transfer carrier particles in the ninth embodiment.

[0051] Figure 36A and Figure 36B : is a diagram showing the state of transfer carrier particles in the transfer portion in the ninth embodiment.

[0052] Figure 37 The relationship between the combination of the material of the photoconductor drum and the material of the intermediate transfer belt and the adhesion force in the ninth embodiment and other examples is shown.

[0053] Figure 38 The relationship between the material of the intermediate transfer belt and the adhesion force in the ninth embodiment and other examples is shown.

[0054] Figure 39 It is an enlarged view of a primary transfer portion in the tenth embodiment.

[0055] Figure 40 is a schematic diagram of a collecting member of an image forming apparatus in an eleventh embodiment.

[0056] Figure 41 is a schematic diagram of a collecting member of an image forming apparatus in an eleventh embodiment.

[0057] Figure 42A and Figure 42B is a schematic diagram when transfer carrier particles are collected in the image forming apparatus in the eleventh embodiment.

[0058] Figure 43 The measurement results of the adhesion force for the image forming apparatus in the eleventh embodiment are shown.

[0059] Figure 44 Results of effect confirmation tests for the imaging apparatus in the eleventh embodiment are shown.

[0060] Figure 45is a schematic sectional view of a collecting member of an image forming apparatus in a twelfth embodiment.

[0061] Figure 46 is a schematic diagram of a contact portion between a collecting member and a photoconductor drum in the image forming apparatus in the twelfth embodiment.

[0062] Figure 47 is a rough profile at the surface of the collecting member of the image forming apparatus in the twelfth embodiment.

[0063] Figure 48 is an amplitude distribution curve of the surface of the collecting member of the imaging apparatus in the twelfth embodiment.

[0064] Figure 49 is a schematic diagram of an imaging apparatus in a thirteenth embodiment.

[0065] Figure 50 is a schematic sectional view of a collecting member of an image forming apparatus in a thirteenth embodiment.

[0066] Figure 51 is a schematic diagram of a contact portion between a collecting member and a photoconductor drum in the image forming apparatus in the thirteenth embodiment.

[0067] Figure 52 The effect confirmation test results for the imaging apparatus in the thirteenth embodiment are shown.

[0068] Figure 53A and Figure 53B is a schematic diagram when transfer carrier particles are supplied in the image forming apparatus in the fourteenth embodiment.

[0069] Figure 54A and Figure 54B is a schematic diagram when transfer carrier particles are supplied in the image forming apparatus in the fourteenth embodiment.

[0070] Figure 55 It is a view showing the longitudinal width of the processing member in the fifteenth embodiment.

[0071] Figure 56 The measurement results of the adhesion in the fifteenth example are shown.

[0072] Figure 57 is a sectional view of an imaging unit in a sixteenth embodiment.

[0073] Figure 58 is a graph showing the relationship between the adhesion force and the pressing force in the sixteenth embodiment.

[0074] Figure 59 is a view showing the longitudinal width of the processing member in the sixteenth embodiment.

[0075] Figure 60A is a view showing the longitudinal width of the processing member in the seventeenth embodiment.

[0076] Figure 60B is a sectional view of a configuration at each end portion of a development opening of a development roller in a seventeenth embodiment.

[0077] Figure 61 is a cross-sectional view of an imaging unit in another embodiment. Specific embodiments

[0078] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The sizes, materials, and shapes of the components, the relative arrangements of the components, and the like described in the following embodiments should be changed as needed depending on the configuration or various conditions of the device to which the present disclosure is applied. Unless otherwise specified, these embodiments are not intended to limit the scope of the present disclosure to only them.

[0079] First embodiment

[0080] 1. Imaging equipment

[0081] The present invention particularly relates to an image forming apparatus using a so-called drum-less cleaner system having no cleaner for an image bearing member.

[0082] Figure 1 is a schematic diagram showing an example of a color imaging device. Figure 1 The structure and operation of the imaging device of the present embodiment are described. The imaging device of the present embodiment is a so-called tandem printer, in which imaging stations a to d are provided. The first imaging station a forms a yellow (Y) image. The second imaging station b forms a magenta (M) image. The third imaging station c forms a cyan (C) image. The fourth imaging station d forms a black (Bk) image. The structure of each imaging station is the same except for the color of the toner to be contained. Hereinafter, the structure of each imaging station will be described by using the first imaging station a. Hereinafter, a to d in Y, M, C and K will be omitted unless otherwise specifically distinguished from each other, and the structure will be described in general.

[0083] The first image forming station a includes a drum-shaped electrophotographic photoconductive member (hereinafter, referred to as a photoconductive drum) 1 a , a charging roller 2 a serving as a charging device, an exposure unit 3 a , and a developing unit 4 a .

[0084] The photoconductor drum 1a is an image-bearing member that is driven to rotate in the direction of the arrow at a peripheral speed (process speed) of 150 mm / s by a photoconductor drum driver 110 and carries a toner image. The photoconductor drum 1a comprises an aluminum tube with a diameter of 20 mm, a photoconductor layer provided on the tube, and a surface layer. The surface layer is a thin film layer made of polyallylate and has a thickness of 20 μm.

[0085] When the control unit 200, such as a controller, receives an image signal, the imaging operation begins and the photoconductor drum 1a is driven to rotate. During the rotation, the photoconductor drum 1a is uniformly charged to a predetermined potential with a predetermined polarity (in this embodiment, the normal polarity is negative) by the charging roller 2a and then exposed to light by the exposure unit 3a according to the image signal. As a result, an electrostatic latent image corresponding to the yellow component image of the desired color image is formed. The electrostatic latent image is then developed by the developing unit (yellow developing unit) 4a at a development position and visualized as a yellow toner image.

[0086] The charging roller 2a, which serves as a charging member, contacts the surface of the photoconductor drum 1a with a predetermined pressure contact force in the charging portion and is rotated by the photoconductor drum 1a while rubbing against the surface of the photoconductor drum 1a. According to the image forming operation, a predetermined DC voltage is applied from the charging voltage source 120 to the rotating shaft of the charging roller 2a. In the first embodiment, the charging roller 2a is composed of a metal shaft and an elastic layer provided on the metal shaft. The diameter of the metal shaft is 5.5 mm. The elastic layer is composed of a metal shaft having a thickness of 1.5 mm and a volume resistivity of approximately 1×10 6 Ωcm conductive elastic material. According to the imaging operation, the control part 200 charges the surface of the photoconductor drum 1a to -500V as a predetermined potential by applying a DC voltage of -1050V as a charging voltage to the rotating shaft of the charging roller 2a. The surface potential of the photoconductor drum 1a is measured with a surface electrometer 344 type manufactured by TREK, Inc. At this time, the surface potential of the photoconductor drum 1a of -500V is the surface potential of the photoconductor drum 1a during non-imaging, and is the dark potential (Vd) of the undeveloped colorant image. A large number of protrusions are set on the surface layer of the charging roller 2a. The average height of the protrusions is about 10μm. The protrusions set on the surface layer of the charging roller 2a act as spacers between the charging roller 2a and the photoconductor drum 1a in the charging part. The protruding portion functions to suppress the residual toner (which is the toner that is not transferred and remains on the photoconductor drum 1a in the primary transfer portion (described later)) from contaminating the charging roller 2a due to contact of portions other than the protruding portion with the residual toner when the residual toner enters the charging portion.

[0087] The exposure unit 3a includes a laser driver, a laser diode, a polygon mirror, an optical lens system, etc. Figure 2As shown, a time-series electronic digital image signal of image information input from the controller 202 to the control section 200 via the interface 201 and subjected to image processing is input to the exposure unit 3a. In the first embodiment, the exposure amount is adjusted so that the image forming potential V1 at the electrostatic latent image portion of the photoconductor drum 1 exposed by the exposure unit 3a is -100 V. The image forming potential is also called the bright potential.

[0088] The developing unit 4a includes a developing roller 41a serving as a developing member (developing member) and a non-magnetic single-component developer (described later) composed of toner and transfer carrier particles. The developing unit 4a is a developing device that performs a developing action on the photoconductor drum 1 to develop the electrostatic latent image into a toner image, and is also a developer accommodating portion that accommodates the developer. Figure 2 As shown, the developing unit 4a and the imaging device body 100 include a contact and separation mechanism 401 that controls the contact and separation (development and separation) state between the developing roller 41a and the photoconductor drum 1a. The control unit 200 causes the developing roller 41a and the photoconductor drum 1a to contact or separate with each other according to the imaging operation, etc. When the developing roller 41a and the photoconductor drum 1a contact each other, the developing roller 41a contacts with a pressing force of 200 gf. The width of the developing nip portion, which is the contact portion between the developing roller 41a and the photoconductor drum 1a, is such that the width in the rotational direction of the photoconductor drum 1a is 2 mm and the width in the longitudinal direction of the photoconductor drum 1a is 220 mm. The developing roller 41a is driven by the developing roller driver 130 to rotate in the forward direction relative to the surface movement direction of the photoconductor drum 1a so that the surface movement speed (hereinafter, the peripheral speed) is equal to the peripheral speed of the photoconductor drum 1a in the developing nip portion.

[0089] The pre-exposure unit 5a serves as a neutralizing device that eliminates static charge by exposing the surface of the photoconductor drum 1a before the surface of the photoconductor drum 1a is charged by the charging roller 2a. The pre-exposure unit 5a plays a role in neutralizing the surface potential formed on the photoconductor drum 1a by eliminating the static charge on the surface of the photoconductor drum 1a, and plays a role in controlling the discharge amount of discharge occurring in the charging portion.

[0090] When the developing roller 41a and the photoconductor drum 1a are in contact with each other during the image forming operation, the control section 200 causes the developing voltage source 140 to apply a direct current voltage of -300 V to the metal core of the developing roller 41a as a developing voltage from the developing voltage source 140. During the image forming, the toner carried on the developing roller 41a is developed on the image forming potential V1 portion on the photoconductor drum 1a by an electrostatic force generated by a potential difference between the developing voltage Vdc = -300 V and the image forming potential V1 = -100 V of the photoconductor drum 1a.

[0091] In the following description, regarding the potential and the applied voltage, the potential is high when the absolute value is larger toward the negative polarity side (for example, -1000 V compared to -500 V), and the potential is low when the absolute value is smaller toward the negative polarity side (for example, -300 V compared to -500 V). This is because in the first embodiment, the toner having negative chargeability is considered as a reference.

[0092] The voltage in the first embodiment is expressed as a potential difference from the ground potential (0 V). Therefore, the development voltage Vdc = -300 V is interpreted as providing a potential difference of -300 V from the ground potential by the development voltage applied to the metal core of the development roller 41a. This also applies to the charging voltage, transfer voltage, etc.

[0093] Next, the control section 200 will be described. Figure 2 This is a control block diagram illustrating a schematic control scheme for the relevant components of the imaging device 100 in the first embodiment. The controller 202 exchanges various electrical information with the host device and, via the interface 201, generally controls the imaging operation of the imaging device 100 within the control unit 200 according to a predetermined control program and reference table. The control unit 200 comprises a CPU 155, which serves as a central component and performs various calculations, and a memory 154, which serves as a storage element (e.g., ROM and RAM). Sensor detection results, counter counts, and calculation results are stored in the RAM. The control program and data tables obtained through experiments are stored in the ROM. Controlled objects, sensors, counters, and other components of the imaging device 100 are connected to the control unit 200. The control unit 200 controls the predetermined imaging sequence by, for example, exchanging various electrical information signals and controlling the drive timing of each component. For example, the voltages applied by the charging voltage source 120, the developing voltage source 140, the exposure unit 3, the primary transfer voltage source 160, and the secondary transfer voltage source 150, as well as the exposure, are controlled by the control unit 200. The control section 200 also controls the photoconductor drum driver 110, the developing roller driver 130, and the developing contact and separation mechanism 401. The image forming apparatus 100 forms an image on a recording medium P based on an electrical image signal input from a host device to the controller 202. Examples of the host device include an image reader, a personal computer, a fax machine, and a smartphone.

[0094] The toner in the first embodiment is a non-magnetic toner having negative chargeability and manufactured by suspension polymerization. The toner has a volume average particle size of 7.0 μm. When the toner is carried on the developing roller 41a, the toner is charged to a negative polarity. The volume average particle size of the toner is measured using a laser diffraction particle size analyzer LS-230 manufactured by Beckman Coulter Inc. The toner will be described in detail later.

[0095] Intermediate transfer belt 10, serving as an intermediate transfer member, is stretched by a plurality of tension members 11, 12, and 13 and driven to rotate at a constant circumferential speed relative to photoconductor drum 1a in a region opposing and in contact with photoconductor drum 1a. During the primary transfer phase of image formation, a DC voltage of 200 V is applied from a primary transfer voltage source 160 to primary transfer roller 14a, serving as the primary transfer member. The yellow toner image formed on photoconductor drum 1a is electrostatically transferred to intermediate transfer belt 10 while passing through a primary transfer portion, which is a contact portion formed between primary transfer roller 14a and photoconductor drum 1a via intermediate transfer belt 10.

[0096] The primary transfer roller 14a is a cylindrical metal roller with a diameter of 6 mm and is made of nickel-plated SUS. The primary transfer roller 14a is arranged at a position offset 8 mm downstream in the direction of movement of the intermediate transfer belt 10 relative to the center position of the photoconductor drum 1a. The intermediate transfer belt 10 is configured to be wound around the photoconductor drum 1a. The primary transfer roller 14a is arranged at a position raised by 1 mm from the horizontal surface formed by the photoconductor drum 1a and the intermediate transfer belt 10, so that the amount of winding of the intermediate transfer belt 10 around the photoconductor drum 1a can be ensured. The primary transfer roller 14a presses the intermediate transfer belt 10 with a force of approximately 200 gf. The primary transfer roller 14a rotates as the intermediate transfer belt 10 rotates. The primary transfer roller 14b arranged in the second image forming station b, the primary transfer roller 14c arranged in the third image forming station c, and the primary transfer roller 14d arranged in the fourth image forming station d have a similar configuration to the primary transfer roller 14a.

[0097] Hereinafter, similarly, a second color magenta toner image, a third color cyan toner image, and a fourth color black toner image are formed by the second, third, and fourth image forming stations b, c, d, respectively, and are sequentially transferred in layers to the intermediate transfer belt 10. As a result, a combined color image corresponding to the intended color image is obtained.

[0098] During the secondary transfer process, the four-color toner image on the intermediate transfer belt 10 is transferred simultaneously to the surface of the recording medium P fed by the sheet feeding device 50 through the secondary transfer nip formed by the intermediate transfer belt 10 and the secondary transfer roller 15 serving as the secondary transfer member. The secondary transfer roller 15 contacts the intermediate transfer belt 10 with a pressure of 50 N to form the secondary transfer nip. The secondary transfer roller 15 rotates along the intermediate transfer belt 10. When the toner on the intermediate transfer belt 10 is secondary transferred to the recording medium P (e.g., paper), a voltage of 1500 V is applied to the secondary transfer roller 155 from the secondary transfer voltage source 150.

[0099] Then, the recording medium P with the four-color toner image is introduced into the fixing unit 30. The four-color toner is heated and pressurized by the fixing unit 30, melted and mixed, and fixed to the recording medium P. The toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the cleaning device 17.

[0100] The cleaning device 17 has a cleaning blade or the like that contacts the outer circumferential surface of the intermediate transfer belt 10 to scrape off the toner remaining on the intermediate transfer belt 10 and collect the toner into the intermediate transfer belt cleaning device 17. The intermediate transfer belt cleaning device 17 is arranged to collect the toner adhering to the intermediate transfer belt 10 on the downstream side with respect to the secondary transfer portion on the intermediate transfer belt 10 in the rotation direction of the intermediate transfer belt 10.

[0101] Through the above-described operations, a full-color printed image is formed.

[0102] 2. Developer, toner and transfer carrier particles

[0103] Next, the developer, toner, and transfer carrier particles used in the first embodiment will be described in detail.

[0104] In the first embodiment, a mixture of toner and external additive A serving as transfer carrier particles is used as a developer. Transfer carrier particles are particles that, when interposed between the photoconductor drum 1 and a toner image developed on the photoconductor drum 1, reduce the adhesion between the toner image and the photoconductor drum 1, thereby improving the primary transfer efficiency of the toner image. Toner is toner particles. Each toner particle comprises a toner base particle containing a release agent and an organosilicon polymer on the surface of the toner base particle.

[0105] Silicone polymers have R-Si(O 1 / 2 )3 represents a T3 unit structure. R represents an alkyl group having one or more and six or less carbon atoms or a phenyl group. The organosilicon polymer forms a protrusion on the surface of the toner base particle.

[0106] The protrusions are in surface contact with the toner mother particles. Due to the surface contact, the effect of suppressing displacement, detachment, and burial of the protrusions is significantly expected.

[0107] Will refer to Figure 3 、 Figure 4 、 Figure 5 and Figure 6 The schematic diagram of the protruding parts shown in FIG. 1 is used to describe the degree of surface contact.

[0108] Figure 3Reference numeral 61 in the figure represents a cross-sectional image of a toner particle, showing approximately one-quarter of the toner particle. Reference numeral 62 represents a toner particle. Reference numeral 63 represents the surface of the toner mother particle. Reference numeral 64 represents a protrusion. The cross-section of the toner particle can be observed using a scanning transmission electron microscope (hereinafter also referred to as STEM) (described later).

[0109] A cross-sectional image of a toner particle is observed, and a line is drawn along the circumference of the toner base particle surface. The cross-sectional image of the toner particle is converted into a horizontal image with reference to the line along the circumference. In the horizontal image, the length of the line along the circumference in the portion where the protrusion and the toner base particle form a continuous interface is defined as the protrusion width w.

[0110] The maximum length of the protruding portion in a direction orthogonal to the direction of the protrusion width w is defined as a protrusion diameter D, and the length from the vertex of the protruding portion in the line segment forming the protrusion diameter D to a line along the circumference is defined as a protrusion height H.

[0111] exist Figure 4 and Figure 6 In the example, the protrusion diameter D and the protrusion height H are the same. Figure 5 In the embodiment, the protrusion diameter D is greater than the protrusion height H.

[0112] Figure 6 The attached state similar to a bowl-shaped particle obtained by, for example, crushing or cracking a hollow particle is schematically shown, in which the central portion of the hemispherical particle is depressed.

[0113] exist Figure 6 In the embodiment, the protrusion width W is defined as the total length of the silicone polymer in contact with the surface of the toner mother particle. In other words, Figure 6 The protrusion width W in is the sum of W1 and W2.

[0114] The number average of the protrusion height H is greater than or equal to 30 nm and less than or equal to 300 nm, and preferably greater than or equal to 30 nm and less than or equal to 200 nm. When the number average of the protrusion height H is greater than or equal to 30 nm, a spacer effect is achieved between the surface of the toner base particles and the transfer member, resulting in significantly improved transferability. On the other hand, when the number average of the protrusion height H is less than or equal to 300 nm, the effect of suppressing displacement, desorption, and burial is significant, resulting in high transferability even during long-term use. A cumulative distribution of the protrusion height H is obtained for protrusions having a protrusion height H greater than or equal to 30 nm and less than or equal to 300 nm. When the number average of the protrusion heights corresponding to 80% by number, obtained by accumulating the protrusion heights H in ascending order of protrusion height H, is defined as H80, H80 is preferably greater than or equal to 65 nm and less than or equal to 120 nm, and more preferably greater than or equal to 75 nm and less than or equal to 100 nm. When H80 falls within the above range, transferability is further improved.

[0115] The number average particle diameter R of the primary particles of the external additive A is preferably greater than or equal to 30 nm and less than or equal to 1200 nm. When R is greater than or equal to 30 nm, a spacer effect is exhibited on the transfer member, resulting in high transferability. As R increases, transferability tends to improve. On the other hand, when R exceeds 1200 nm, the fluidity of the toner decreases, and image unevenness is likely to occur.

[0116] The ratio of the number average particle diameter R of the primary particles of the external additive A to the number average value of the protrusion height H is preferably higher than or equal to 1.00 and lower than or equal to 4.00. When the ratio [(number average particle diameter R of the primary particles of the external additive A) / (number average value of the protrusion height H)] falls within the above range, high transferability and low-temperature fixing ability are possible for a long service life.

[0117] When the number average of the protrusion height H reaches a minimum value of 30 nm, a spacer effect is exhibited on the transfer member, and when R is 30 nm or greater, transferability is improved. This is presumably because the external additive A replaces positions where protrusions are absent due to desorption and other factors, thus exhibiting a spacer effect. In other words, when R is less than 30 nm, the spacer effect is less likely to be exhibited.

[0118] The attachment rate of the external additive A on the toner particle surfaces is preferably greater than or equal to 0% and less than or equal to 20%, and more preferably greater than or equal to 0% and less than or equal to 10%. When the attachment rate falls within this range, the external additive A easily migrates onto the toner particle surfaces, resulting in further improved transferability by acting as a substitute for the protruding portions. During the fixing step of fixing the toner onto the fixing member, a suitable amount of release agent seeps out from the toner base particles, thereby improving the separability between the fixing member and paper.

[0119] The toner surface is observed using a scanning electron microscope to obtain a 1.5-square-micrometer backscattered electron image of the toner surface. When a binary image is obtained in which the organosilicon polymer portion in the backscattered electron image is a bright portion, the area ratio of the bright portion area relative to the total image area (hereinafter referred to as the bright portion area ratio) is greater than or equal to 30.0% and less than or equal to 75.0%. The bright portion area ratio is preferably greater than or equal to 35.0% and less than or equal to 70.0%. As the bright portion area ratio increases, the presence ratio of the organosilicon polymer on the toner base particle surface increases. When the bright portion area ratio is greater than 75.0%, the presence ratio of components derived from the toner base particle on the toner base particle surface is low, making it more difficult for the release agent to ooze out of the toner base particle, and thus thin paper tends to wrap around the fixing unit during low-temperature fixing. On the other hand, when the bright portion area ratio is less than 30.0%, the presence ratio of components derived from the toner base particle on the toner base particle surface is high. In other words, the exposed area of ​​components derived from the toner base particles on the toner base particle surface is high, so the transferability is reduced in the early stage of use. The area ratio of the bright portion area of ​​the image is also referred to as the coverage rate of the silicone polymer on the toner base particle surface.

[0120] There is no limitation on the external additive A as long as the number average particle diameter R of the primary particles is greater than or equal to 30 nm and less than or equal to 1000 nm. Various organic fine particles or inorganic fine particles can be used as the external additive A. From the viewpoint of being easy to impart fluidity and easy to be negatively charged like the toner mother particle, the external additive may contain silica fine particles. The content of silica fine particles in the external additive A is preferably greater than or equal to 50% by mass, and the external additive A may be silica fine particles. The content of the external additive A in the toner is preferably greater than or equal to 0.02% by mass and less than or equal to 5.00% by mass, and more preferably greater than or equal to 0.05% by mass and less than or equal to 3.00% by mass.

[0121] Examples of organic fine particles other than silica fine particles or inorganic fine particles include the following:

[0122] (1) Fluidity-imparting agents: aluminum oxide fine particles, titanium oxide fine particles, carbon black, and carbon fluoride;

[0123] (2) Abrasives: fine particles of metal oxides (such as strontium titanate, cerium oxide, aluminum oxide, magnesium oxide, and chromium oxide), fine particles of nitrides (such as silicon nitride), fine particles of carbides (such as silicon carbide), and fine particles of metal salts (such as calcium sulfate, barium sulfate, and calcium carbonate).

[0124] (3) Lubricants: fine particles of fluororesin (fine particles of vinylidene fluoride, polytetrafluoroethylene, etc.) and fine particles of fatty acid metal salt (fine particles of zinc stearate, calcium stearate, etc.); and

[0125] (4) Charge control fine particles: fine particles of metal oxides (fine particles of tin oxide, titanium oxide, zinc oxide, aluminum oxide, etc.) and carbon black.

[0126] Organic fine particles (eg, silica fine particles) or inorganic fine particles may be subjected to hydrophobic treatment to improve the fluidity of the toner and to equalize the charge of the toner particles.

[0127] Examples of the treating agent used for the hydrophobic treatment include unmodified silicone varnish, various modified silicone varnishes, unmodified silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organic silicon compounds and organic titanium compounds, etc. These treating agents can be used alone or in combination.

[0128] As the silica fine particles, known silica fine particles can be used. The silica fine particles may be either dry silica fine particles or wet silica fine particles. The silica fine particles may be fine particles of wet silica obtained by a sol-gel method (hereinafter also referred to as sol-gel silica).

[0129] Figure 7 FIG is an enlarged view of the developer used in the first embodiment. Figure 7 As shown, the developer of the first embodiment is such that the external additive A composed of transfer carrier particles is arranged on the toner particle surfaces on which a large number of protrusions composed of an organic silicon polymer are formed.

[0130] Figure 7The protrusion gap G and protrusion height H on the toner surface shown can be measured using a scanning transmission electron microscope (hereinafter also referred to as STEM) (described later). The protrusion gap G and protrusion height H can also be measured using a scanning probe microscope (hereinafter referred to as SPM). A scanning probe microscope (hereinafter, SPM) includes a probe, a cantilever supporting the probe, and a displacement measurement system that detects the deflection of the cantilever. The scanning probe microscope observes the shape of the sample surface by detecting the atomic force (attraction or repulsion) between the probe and the sample.

[0131] When the protrusion gap G is larger than the particle diameter of the transfer carrier particles, the transfer carrier particles come into contact with the toner matrix when arranged between the protrusions, and the adhesion force Ft between the transfer carrier particles and the toner increases, with the result that the transfer carrier particles are difficult to transfer from the toner to the photoconductor drum 1. For this reason, the number average value of the protrusion gap G may be smaller than the number average particle diameter of the transfer carrier particles.

[0132] When the protrusion height H is larger than the particle diameter of the transfer carrier particles, the protrusions come into contact with the photoconductor drum 1 before the transfer carrier particles, and the transfer carrier particles have difficulty in coming into contact with the photoconductor drum 1, resulting in difficulty in transferring the transfer carrier particles from the toner to the photoconductor drum 1. For this reason, the number average value of the protrusion height H may be smaller than the number average particle diameter of the transfer carrier particles.

[0133] As described above, the adhesion force Ft between the transfer carrier particles and the toner can be smaller than the adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1. To this end, the material of the transfer carrier particles can be selected so as to reduce the adhesion force Ft between the transfer carrier particles and the toner. For example, as in the case of the first embodiment, when the protrusions on the toner surface are made of a silica-based material (e.g., an organic silica polymer), a silica-based material having a material composition similar to that of the protrusions can be selected as the material of the transfer carrier particles to reduce the adhesion force between the protrusions and the transfer carrier particles.

[0134] From the perspective of supplying transfer carrier particles from the developing roller 41 to the photoconductor drum 1, the number of transfer carrier particles applied to each toner particle can be as large as possible. However, when the amount of transfer carrier particles added is too large, the risk of contamination of components in the image forming apparatus 100 increases, so the amount of transfer carrier particles added can be adjusted according to the desired primary transfer performance.

[0135] Primary transfer performance improves as the coverage of the transfer carrier particles on the photoconductor drum 1 increases. To achieve sufficient primary transfer performance, the transfer carrier particles coating the photoconductor drum 1 preferably have a coverage of 10% or higher. However, as the coverage of the transfer carrier particles on the photoconductor drum 1 increases, the degree of improvement in primary transfer performance slows, and the risk of contamination of various components in the imaging device by the transfer carrier particles increases. Therefore, the coverage of the photoconductor drum 1 by the transfer carrier particles is preferably 50% or lower.

[0136] 3. Methods for measuring the physical properties of developer

[0137] Hereinafter, various measurement methods will be described.

[0138] <Method of Observing Cross Sections of Toner Particles Using a Scanning Transmission Electron Microscope (STEM)>

[0139] A cross section of a toner particle to be observed with a scanning transmission electron microscope (STEM) is prepared as follows.

[0140] Hereinafter, a process of preparing a cross section of a toner particle will be described. When organic fine particles or inorganic fine particles are externally added to a toner, a toner from which the organic fine particles or inorganic fine particles are removed by the following method or the like is used as a sample.

[0141] 160g of sucrose (produced by Kishida Chemical, Co., Ltd.) was added to 100mL of ion exchange water and dissolved while heating in hot water to prepare a heavy sucrose solution. 31g of the heavy sucrose solution and 6mL of Contaminon N (a pH 7 aqueous solution containing 10% by mass neutral detergent for washing precision measuring devices, composed of a nonionic surfactant, anionic surfactant, and an organic builder, produced by Wako Pure Chemical Industries, Ltd.) were added to a centrifuge tube (volume 50mL). 1.0g of toner was added to the solution, and the aggregates of the toner were loosened with a spatula or the like. The centrifuge tube was shaken at 300spm (strokes / minute) for 20 minutes using a shaking table (AS-1N sold by AS ONE Corporation). After shaking, the solution was placed in a swing rotor glass tube (50mL) and separated at 3500rpm for 30 minutes using a centrifuge (H-9R, produced by KOKUSAN Co., Ltd.). This operation separates the toner particles and external additives. Visually inspect the toner particles for sufficient separation from the aqueous solution, and collect the toner particles that have separated to the top layer using a spatula or the like. After filtering the collected toner particles using a vacuum filter, dry them in a dryer for one hour or longer to obtain a test sample. This operation is repeated multiple times to ensure the required amount.

[0142] Elemental analysis using energy dispersive X-ray spectroscopy (EDS) was used to examine whether the protrusions contained silicone polymers.

[0143] A toner layer was applied to a cover glass (Matsunami Glass Ind., Ltd., square cover glass; square No. 1), and an osmium (Os) film (5 nm) and a naphthalene film (20 nm) were applied as protective films using an Os plasma coater (Filgen, Inc., OPC80T). Subsequently, a photocurable resin D800 (JEOL, Ltd.) was filled into a PTFE tube (outer diameter 3 mm (aperture 1.5 mm) × 3 mm), and the cover glass was gently placed on the tube so that the toner and the photocurable resin D800 came into contact. After irradiating light in this state to cure the resin, the cover glass and tube were removed. Thus, a columnar resin with the toner embedded in its outermost surface was formed. The columnar resin is cut from the outermost surface by the length of the toner particle radius (e.g., 4.0 μm when the weight-average particle diameter (D4) is 8.0 μm) at a cutting speed of 0.6 mm / s using an ultrasonic ultramicrotome (Leica Camera, Inc. UC7) to expose a cross section of the toner center portion.

[0144] Subsequently, a slice sample of the cross section of the toner particle is prepared by cutting the resin into a film thickness of 100 nm. By cutting the resin in this manner, a cross section of the center portion of the toner is obtained.

[0145] JEM-2800 manufactured by JEOL, Ltd. was used as a scanning transmission electron microscope (STEM). The probe size of the STEM was 1 nm, and an image with an image size of 1024×1024 pixels was acquired. The image was acquired by adjusting the contrast to 1425 and the brightness to 3750 on the detector control board for bright field images, and adjusting the contrast to 0.0, the brightness to 0.5, and the gamma to 1.00 on the image control board. The image magnification was set to 100,000 times, and the image was acquired so that about one-quarter to one-half of the circumference of the cross section in the toner particle was as shown in FIG. Figure 3Adapted as shown. The obtained STEM image was subjected to image analysis using image processing software (Image J (available at https: / / imagej.nih.gov / ij / )) to measure the protrusions containing the silicone polymer. Measurements were performed on 30 protrusions randomly selected from the STEM image. Whether the protrusions contain silicone polymers was checked by combining observation using a scanning electron microscope (SEM) with elemental analysis using energy dispersive X-ray spectroscopy (EDS). First, a line was drawn along the circumference of the toner master particle using a line drawing tool (select Segmented line on the Straight tab). For portions where the protrusions of the silicone polymer are embedded in the toner master particle, the embedding is ignored and the lines are connected smoothly. The image is converted to a horizontal image with reference to the line (select Selection on the Edit tab, change the line width attribute to 500 pixels, then select Selection on the Edit tab, and apply Straightener). In the horizontal image, the following measurements were performed on one of the protrusions containing the silicone polymer. The length of a line along the circumference of the portion where the protrusion forms a continuous interface with the toner mother particle is defined as the protrusion width w. The maximum length of the protrusion in a direction perpendicular to the direction of the protrusion width w is defined as the protrusion diameter D, and the length from the vertex of the protrusion in the line segment forming the protrusion diameter D to a line along the circumference is defined as the protrusion height H. Measurements were performed on 30 randomly selected protrusions, and the arithmetic mean of the measured values ​​was obtained as the number average of the protrusion heights H.

[0146] <How to calculate H80>

[0147] In a scanning transmission electron microscope (STEM) image of a cross section of a toner particle using a STEM, for protrusion portions having a protrusion height H of greater than or equal to 30 nm and less than or equal to 300 nm, a cumulative distribution of the protrusion height H is obtained. A protrusion height corresponding to 80% by number, obtained by accumulating the protrusion heights H in ascending order of the protrusion heights H, is defined as H80 (nm).

[0148] <Method for Calculating the Area Ratio of the Bright Portion Area in a 1.5 μm Square Backscattered Electron Image of the Toner Particle Surface>

[0149] To determine the bright portion area ratio, observe the toner particle surface using a scanning electron microscope. Obtain a 1.5 μm square backscattered electron image of the toner particle surface. A binarized image is obtained so that the organosilicon polymer portion in the backscattered electron image is the bright portion, and the ratio of the bright portion area to the total image area is calculated. When organic or inorganic fine particles are externally added to the toner, use a toner sample from which the organic or inorganic fine particles have been removed using the following method, etc.

[0150] 160g of sucrose (produced by Kishida Chemical, Co., Ltd.) was added to 100mL of ion exchange water and dissolved while heating in hot water to prepare a heavy sucrose solution. 31g of the heavy sucrose solution and 6mL of Contaminon N (a pH 7 aqueous solution containing 10% by mass neutral detergent for washing precision measuring devices, composed of a nonionic surfactant, anionic surfactant, and an organic builder, produced by Wako Pure Chemical Industries, Ltd.) were added to a centrifuge tube (volume 50mL). 1.0g of toner was added to the solution, and the aggregates of the toner were loosened with a spatula or the like. The centrifuge tube was shaken at 300spm (strokes / minute) for 20 minutes using a shaking table (AS-1N sold by AS ONE Corporation). After shaking, the solution was placed in a swing rotor glass tube (50mL) and separated at 3500rpm for 30 minutes using a centrifuge (H-9R, produced by KOKUSAN Co., Ltd.). This operation separates the toner particles and external additives. Visually inspect the toner particles for sufficient separation from the aqueous solution, and collect the toner particles that have separated to the top layer using a spatula or the like. After filtering the collected toner particles using a vacuum filter, dry them in a dryer for one hour or longer to obtain a test sample. This operation is repeated multiple times to ensure the required amount.

[0151] Whether the protruding portion contains an organic silicon polymer is examined in combination with elemental analysis (described later) using energy dispersive X-ray spectroscopy (EDS).

[0152] The SEM setup and observation conditions are as follows:

[0153] Apparatus used: ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd.;

[0154] Accelerating voltage: 1.0 kV;

[0155] WD: 2.0mm;

[0156] Aperture size: 30.0 μm;

[0157] Detection signal: EsB (energy selective backscattered electrons);

[0158] EsB gate: 800V;

[0159] Visual magnification: 50,000 times;

[0160] Contrast ratio: 63.0±5.0% (reference value);

[0161] Brightness: 38.0±5.0% (reference value);

[0162] Resolution: 1024×768; and

[0163] Pre-treatment: Toner particles are dispersed on the ribbon (without vapor deposition).

[0164] The accelerating voltage and EsB gate were set to obtain structural information about the outermost surface of the toner particles, prevent charging of undeposited samples, and selectively detect high-energy backscattered electrons. The observation field was selected to include an area near the vertex where the toner particles have the smallest curvature. By superimposing an elemental mapping image obtained using energy-dispersive X-ray spectroscopy (EDS) using a scanning electron microscope (SEM) on the backscattered electron image, it was confirmed that the bright portion of the backscattered electron image originates from the organosilicon polymer.

[0165] The SEM / EDS setup and observation conditions are as follows:

[0166] Equipment used (SEM): ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd.;

[0167] Apparatus used (EDS): NORAN System 7, Ultra Dry EDS Detector manufactured by Thermo Fisher Scientific KK;

[0168] Accelerating voltage: 5.0 kV;

[0169] WD: 7.0mm;

[0170] Aperture size: 30.0 μm;

[0171] Detection signal: SE2 (secondary electron);

[0172] Visual magnification: 50,000 times;

[0173] Mode: Spectral Imaging; and

[0174] Pre-treatment: Toner particles are dispersed on a carbon ribbon and platinum sputtering is applied.

[0175] The backscattered electron image and the element mapping image of silicon obtained in this technique were superimposed on each other, and it was confirmed that the silicon atom portion of the mapping image and the bright portion of the backscattered electron image matched each other.

[0176] The area ratio of the bright portion area to the total area of ​​the backscattered electron image is obtained by analyzing the backscattered electron image of the surface of the toner particles obtained by the above technique using image processing software Image J (developed by Wayne Rashand).

[0177] First, convert the backscattered electron image to an 8-bit image by selecting Type from the Image menu. Next, reduce image noise by setting the median diameter to 2.0 pixels from Filters in the Process menu. Estimate the image center while excluding the observation condition display portion displayed below the backscattered electron image, and use the rectangle tool on the toolbar to select a range of 1.5 square microns from the image center of the backscattered electron image. Subsequently, select Threshold from Adjust in the Image menu. Select Default, click Auto, and then click Apply to obtain a binary image. Through this operation, the bright portion of the backscattered electron image is displayed as white. Again, estimate the image center while excluding the observation condition display portion displayed below the backscattered electron image, and use the rectangle tool on the toolbar to select a range of 1.5 square microns from the image center of the backscattered electron image. Subsequently, select Histogram from the Analyze menu. Read the Count value (which corresponds to the total area of ​​the backscattered electron image) from the newly opened Histogram window. In addition, click List and read the Count value with a brightness of 0 (which corresponds to the bright portion area of ​​the backscattered electron image). Based on the above values, calculate the area ratio of the bright portion area to the total area of ​​the backscattered electron image. The above process is performed for 10 fields of view of each toner particle to be evaluated, the numerical average of the area ratio is calculated, and the calculated numerical average is used as the area ratio (%) of the bright portion area of ​​the image to the total area of ​​the image, wherein the image is binarized so that the silicone polymer portion in the backscattered electron image becomes the bright portion.

[0178] <Method for Identifying Silicone Polymers>

[0179] The method of identifying the silicone polymer is performed by combining observation using a scanning electron microscope (SEM) and elemental analysis using energy dispersive X-ray spectroscopy (EDS).

[0180] The toner is observed in a field of view magnified to 50,000 times using a scanning electron microscope "Hitachi Ultra-High Resolution Field EmissionScanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation). While focusing on the surface of the toner particle, the surface is observed. EDS analysis is performed on the particles, etc. present on the surface, and whether the analyzed particles, etc. are organic silicon polymers is judged based on whether there is an Si element peak. When both organic silicon polymers and fine silica particles are contained in the surface of the toner particles, the organic silicon polymer is identified by comparing the ratio of the element content (atomic %) of Si to the element content (atomic %) of O (Si / O ratio) with the sample. Each sample of the organic silicon polymer and the fine silica particles is subjected to EDS analysis under the same conditions, and the element content (atomic %) of each of Si and O is obtained. The Si / O ratio of the organic silicon polymer is defined as A, and the Si / O ratio of the fine silica particles is defined as B. The measurement conditions in which A is significantly greater than B are selected. Specifically, the sample was measured 10 times under the same conditions, and the arithmetic mean of each of A and B was obtained. The obtained mean was selected to satisfy the measurement condition of A / B>1.1. When the Si / O ratio of the particle to be identified is closer to A than (A+B) / 2, the particle is identified as an organic silicon polymer.

[0181] Tosparel 120A (Momentive Performance Materials Japan LLC) was used as a sample of the silicone polymer particles, and HDK V15 (Asahi Kasei Corporation) was used as a sample of the silica fine particles.

[0182] <Method for Measuring the Number Average Particle Diameter R of Primary Particles of External Additive>

[0183] Observation using a scanning electron microscope "Hitachi Ultra-High Resolution Field EmissionScanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation) and elemental analysis using energy dispersive X-ray spectroscopy (EDS) were performed in combination.

[0184] In a visual field magnified 50,000 times, an image of the external additive particles is randomly captured by combining the above-described elemental analysis technique using EDS. 100 external additive particles are randomly selected from the captured image, and the longitudinal diameters of the primary particles of the selected external additive particles are measured, and the arithmetic mean of the longitudinal diameters is used as the number average particle diameter R. The visual magnification is adjusted as necessary depending on the size of the external additive particles.

[0185] <Method for Identifying the Composition and Ratio of the Component Compounds of the Silicone Polymer>

[0186] NMR is used to identify the composition and ratio of the constituent compounds of the organic silicon polymer contained in the toner. When the toner contains an external additive (eg, silica fine particles) in addition to the organic silicon polymer, the following operation is performed.

[0187] 1 g of the toner was put into a vial container, dissolved in 31 g of chloroform, and dispersed. The solution was dispersed for 30 minutes using an ultrasonic homogenizer to prepare a dispersed solution.

[0188] Ultrasonic processor: Ultrasonic homogenizer VP-050 (manufactured by TIETECH Co., Ltd.)

[0189] Microchip: Step microchip with a 2 mm tip diameter

[0190] The top position of the microchip: the center of the glass vial and 5 mm above the bottom of the vial

[0191] Ultrasonic conditions: 30% intensity, 30 minutes

[0192] At this time, ultrasonic waves were applied while cooling the vial with ice water so that the temperature of the dispersed solution did not rise. The dispersed solution was placed in a swing rotor glass tube (50 mL) and separated for 30 minutes at 58.33 rev / sec using a centrifuge (H-9R, produced by KOKUSAN Co., Ltd.). In the glass tube after centrifugation, particles with a high specific gravity (such as fine silica particles) were contained in the lower layer. The chloroform solution containing the organosilicon polymer in the upper layer was collected and vacuum dried (24 hours at 40°C) to remove the chloroform to prepare a sample. By using this sample or the organosilicon polymer, by using a solid 29 Si-NMR measures and calculates the ratio of the amount of the constituent compounds in the organosilicon polymer and the amount of R-Si(O 1 / 2 )3 represents the ratio of T3 unit structure.

[0193] First, by using 13 C-NMR identifies the hydrocarbon group represented by R. 13C-NMR (solid-state) measurement conditions>

[0194] Device: JNM-ECX500 II produced by JEOL RESONANCE

[0195] Sample tube: 3.2mmφ

[0196] Sample: Sample or silicone polymer

[0197] Measurement temperature: room temperature

[0198] Pulse mode: CP / MAS

[0199] Measurement angular frequency: 123.25MHz( 13 C)

[0200] Reference material: Adamantane (external standard: 29.5 ppm)

[0201] Sample speed: 20kHz

[0202] Contact time: 2ms

[0203] Delay time: 2s

[0204] Cumulative number: 1024

[0205] By this method, the silicon atoms are bonded by methyl groups (Si-CH3), ethyl groups (Si-C2H5), propyl groups (Si-C3H7), butyl groups (Si-C4H9), and pentyl groups (Si-C5H 11 ), the combination of hexyl and silicon atoms (Si-C6H 13 ), the combination of phenyl and silicon atoms (Si-C6H 5- ) etc., and identify the hydrocarbon group represented by R. On the other hand, in the solid state 29 In Si-NMR, peaks are detected within different shift ranges depending on the structure of the Si-bonding functional groups in the components of the organosilicon polymer. The Si-bonding structure can be identified by identifying the peak position using a standard sample. The abundance ratio of the component compounds can be calculated from the obtained peak areas. The ratio of the peak area for the T3 unit structure to the total peak area can be calculated.

[0206] Solid State 29 The measurement conditions of Si-NMR are as follows:

[0207] Device: JNM-ECX5002 (JEOL RESONANCE);

[0208] Temperature: room temperature;

[0209] Measurement method: DDMAS method 29 Si 45°;

[0210] Sample tube: Zirconia 3.2mmφ;

[0211] Sample: filled in a test tube in powder form;

[0212] Sample rotation speed: 10kHz;

[0213] Relaxation delay: 180s; and

[0214] Scans: 2000.

[0215] After measurement, multiple silane components with different substituents and different linking groups in the sample or silicone polymer are peak separated by curve fitting into the following X1 structure, X2 structure, X3 structure, and X4 structure, and their respective peak areas are calculated.

[0216] The following X3 structure is a T3 unit structure.

[0217] X1 structure: (Ri)(Rj)(Rk)SiO 1 / 2 (A1)

[0218] X2 structure: (Rg)(Rh)Si(O 1 / 2 )2(A2)

[0219] X3 structure: RmSi(O 1 / 2 )3(A3)

[0220] X4 structure: Si(O 1 / 2 )4(A4)

[0221] X1 structure

[0222]

[0223] X2 structure

[0224]

[0225] X3 structure

[0226]

[0227] X4 structure

[0228]

[0229] In the chemical formulas A1, A2 and A3, Ri, Rj, Rk, Rg, Rh and Rm each represent an organic group bonded to silicon, such as a hydrocarbon group having 1 to 6 carbon atoms, a halogen atom, a hydroxyl group, an acetoxy group or an alkoxy group. When the structure needs to be studied in more detail, it can be determined according to 1 The results of H-NMR measurements were combined 13 C-NMR and 29 The structure was identified by Si-NMR measurements.

[0230] <Quantitative Method for Silicone Polymer or Silica Fine Particles Contained in Toner>

[0231] The toner is dispersed in chloroform as described above, and then the external additives (such as silicone polymer and silica fine particles) are separated by centrifugal separation according to the difference in specific gravity to obtain a sample. Then, the content of the external additives (such as silicone polymer and silica fine particles) is determined.

[0232] Hereinafter, the case where the external additive is silica fine particles will be described. Other fine particles can also be quantified using a similar technique.

[0233] First, the pressed toner is measured by X-ray fluorescence, and analytical processing (such as calibration curve method and FP method) is performed to determine the content of silicon in the toner. Subsequently, for the constituent compounds of the organic silicon polymer and the silica fine particles, the solid 29 Si-NMR, pyrolysis GC / MS, etc. can be used to identify the structure and determine the silicon content in the organic silicon polymer and silica fine particles. 29 The contents of the organosilicon polymer and the silica fine particles in the toner were calculated based on the relationship between the contents of silicon in the organosilicon polymer and the silica fine particles determined by Si-NMR and pyrolysis GC / MS.

[0234] <Method for Measuring the Attachment Rate of External Additives (eg, Silicone Polymer and Silica Fine Particles) to Toner Mother Particles or Toner Particles by Water Washing Method>

[0235] (Water washing step)

[0236] 20 g of Contaminon N (a pH 7 aqueous solution containing 30% by mass of a neutral detergent for washing precision measuring instruments, composed of a nonionic surfactant, an anionic surfactant, and an organic builder) was weighed into a 50 mL vial and mixed with 1 g of toner. The resulting solution was placed in a KM shaker (Model: V.SX) manufactured by Iwaki Industry Co., Ltd. and shaken at a set speed of 50 for 120 seconds. As a result, depending on the adhesion state of the silicone polymer or silica fine particles, external additives (such as silicone polymer or silica fine particles) were transferred from the toner mother particles or toner particle surfaces to the dispersed solution. Thereafter, the toner and external additives (such as silicone polymer or silica fine particles) that had transferred to the supernatant were separated using a centrifuge (H-9R, manufactured by KOKUSAN Co., Ltd.) at 16.67 rpm for five minutes. The settled toner was dried and hardened in a vacuum dryer (at 40° C. for 24 hours) to obtain a washed toner.

[0237] Subsequently, images of the toner not subjected to the water washing process (unwashed toner) and the toner obtained through the water washing step (washed toner) were captured by using a Hitachi Ultra-High Resolution Field Emission Scanning Electron Microscope S-4800 (Hitachi High-Technologies Corporation).

[0238] The object to be measured is identified by elemental analysis using energy dispersive X-ray spectroscopy (EDS).

[0239] The captured toner surface image was analyzed with image analysis software Image-Pro Plus Ver5.0 (Nippon Roper KK), and the coverage ratio was calculated.

[0240] The imaging conditions of S-4800 are as follows.

[0241] (1) Sample preparation

[0242] A light coating of conductive paste was applied to a sample stage (aluminum sample stage, 15 mm x 6 mm), and toner was sprayed onto the paste. Excess toner was removed from the sample stage by blowing air, and the paste was allowed to dry thoroughly. The sample stage was placed in a sample holder, and the height of the sample stage was adjusted to 36 mm using a sample height gauge.

[0243] (2) Setting the S-4800 observation conditions

[0244] When measuring the coverage, the above-mentioned elemental analysis using energy dispersive X-ray spectroscopy (EDS) is performed in advance to identify external additives (such as silicone polymers or silica fine particles) on the toner surface, and then the coverage is measured. Liquid nitrogen is filled into the anti-contamination trap attached to the housing of the S-4800 until it overflows and is left to stand for 30 minutes. The "PC-SEM" of the S-4800 is activated, and flushing (cleaning of the FE chip as an electron source) is performed. Click the acceleration voltage display portion in the control panel on the screen, and press the [Flushing] button to open the flushing execution dialog box. Confirm that the flushing intensity is set to 2, and flushing is performed. Confirm that the emission current for flushing is 20-40μA. Insert the sample holder into the sample cavity in the housing of the S-4800. Press [Origin] on the control panel to move the sample holder to the observation position.

[0245] Click the accelerating voltage display to open the HV setting dialog box. The accelerating voltage is set to [1.1 kV] and the emission current is set to [20 μA]. In the [Basic] tab on the operation panel, the signal selection is set to [SE], and the SE detector is set to observation mode using backscattered electron images by selecting [Up(U)] and [+BSE] and selecting [LA100] in the selection box to the right of [+BSE]. Similarly, in the [Basic] tab on the operation panel, the probe current in the electron optical system condition block is set to [Normal], the focus mode is set to [UHR], and the WD is set to [4.5 mm]. Press the [ON] button on the accelerating voltage display of the control panel to apply the accelerating voltage.

[0246] (3) Calculation of the number average particle size (D1) of toner

[0247] Drag the magnification display portion of the control panel to set the magnification to 5000 (5k) times. Rotate the focus knob [COARSE] on the operation panel, and adjust the aperture alignment at a point where the field of view comes into focus to a certain extent. Click [Align] on the control panel to display the alignment dialog box, and select [Beam]. Rotate the STIGMA / ALIGNMENT knobs (X, Y) on the operation panel to move the display beam to the center of the concentric circles. Then, select [Aperture], and rotate the STIGMA / ALIGNMENT knobs (X, Y) one by one to adjust so that the movement of the image stops or is minimized. Close the aperture dialog box, and focus the field of view by autofocus. Further repeat this operation twice to focus the field of view.

[0248] Then, the particle diameters of 300 toner particles are measured, and the number average particle diameter (D1) is obtained. The particle diameter of each individual particle is the maximum diameter when the toner particles are observed.

[0249] (4) Focus adjustment

[0250] For the particles having a number average particle size (D1) of ±0.1 μm obtained in (3), the magnification display portion of the control panel is dragged with the center point of the maximum diameter placed at the center of the measurement screen, and the magnification is set to 10,000 (10k) times.

[0251] Rotate the focus knob [COARSE] on the operation panel, and adjust the aperture alignment at a point where the field of view comes into focus to a certain extent. Click [Align] on the control panel to display the alignment dialog box, and select [Beam]. Rotate the STIGMA / ALIGNMENT knobs (X, Y) on the operation panel to move the display beam to the center of the concentric circle. Then, select [Aperture], and rotate the STIGMA / ALIGNMENT knobs (X, Y) one by one to adjust so that the movement of the image stops or is minimized. Close the aperture dialog box, and focus the field of view by autofocus. After that, set the magnification to 50,000 (50k) times, perform focus adjustment using the focus knob and STIGMA / ALIGNMENT knob as in the above case, and focus the field of view again by autofocus. Repeat this operation again to focus the field of view. Here, when the inclination angle of the observation surface is large, the coverage measurement accuracy tends to decrease. Therefore, the tilt angle at which the entire observation surface is simultaneously brought into focus is selected in the focus adjustment to select the tilt angle at which the surface is almost not tilted, and then the observation surface is analyzed.

[0252] (5) Image preservation

[0253] The brightness was adjusted in ABC mode, and a photo of 640×480 pixels was taken and saved. The following analysis was performed using this image file. One photo was taken for each toner particle, and an image for the toner particle was obtained.

[0254] (6) Image analysis

[0255] The image obtained using the above technique was binarized using the following analysis software to calculate the coverage. At this point, one screen was divided into 12 square sections, and each section was analyzed. The analysis conditions for the image analysis software, Image-ProPlus ver. 5.0, were as follows. However, if an external additive (e.g., an organosilicon polymer with a particle size of less than 30 nm or greater than 300 nm, or fine silica particles with a particle size of less than 30 nm or greater than 1200 nm) was placed in a divided section, the coverage in that section was not calculated.

[0256] In the image analysis software Image-Pro Plus 5.0, select "Count / Size" and "Option" from "Measurement" on the toolbar, and set the binarization conditions. In the object extraction options, select eight connections and set the smoothing to 0. In addition, pre-sort, fill holes, do not select included lines, and set "Exclude boundary lines" to "None". Select "Measurement Item" from "Measurement" on the toolbar, and enter 2 to 10 in the area selection range. 7 .

[0257] The coverage calculation is performed by surrounding a square area. At this time, the area (C) of the area is set to 24,000 to 26,000 pixels. Automatic binarization is performed by selecting "Process"-Binarization, and the sum (D) of the areas where no external additives (such as silicone polymers or silica fine particles) are present is calculated. The coverage is determined by the sum D of the areas of the square area C and the areas where no external additives (such as silicone polymers or silica fine particles) are present using the following expression.

[0258] Coverage (%) = 100 - (D / C × 100)

[0259] The arithmetic mean of all obtained data was used as the coverage ratio.

[0260] The coverage ratio of each of the unwashed toner and the washed toner is calculated.

[0261] Then, (coverage ratio of washed toner) / (coverage ratio of unwashed toner)×100 is used as the “attachment ratio” of the present disclosure.

[0262] 4. Method for manufacturing toner particles, external additives and developer

[0263] Next, an example of manufacturing the toner particles, the external additive A, and the developer of the first embodiment will be described.

[0264] <Production Example of Toner Particles>

[0265] (Preparation of aqueous medium)

[0266] 650.0 parts of ion exchange waters and 14.0 parts of sodium phosphate (dodecahydrate, produced by Rasa Industries, Ltd.) are put into the reaction vessel equipped with agitator, thermometer and reflux line, and maintained 1.0 hour at 65 ℃, while purging with nitrogen. While stirring the above-mentioned solution with 15000rpm using TK Homomixer (produced by TOKUSHU KIKAKOGYO Co., Ltd.), a disposable calcium chloride aqueous solution obtained by dissolving 9.2 parts of calcium chloride (dihydrate) in 10.0 parts of ion exchange waters is added in the solution to prepare the aqueous medium containing dispersion stabilizer. In addition, in the aqueous medium, the hydrochloric acid of 10 mass % is added so that the pH is adjusted to 5.0, finally obtaining an aqueous medium.

[0267] (Preparation of polymerizable monomer composition)

[0268] Styrene: 60.0 parts

[0269] CI Pigment Blue 15:3: 6.5 parts

[0270] The above materials were put into an attritor (produced by Mitsui Mitsuike Chemical Engineering Machinery, Co., Ltd.) and dispersed at 220 rpm for 5.0 hours by using zirconium oxide particles having a diameter of 1.7 mm, and then the zirconium oxide particles were removed, and a colorant dispersion solution was prepared.

[0271] Styrene: 20.0 parts

[0272] n-Butyl acrylate: 20.0 parts

[0273] Cross-linking agent (divinylbenzene): 0.3 parts

[0274] Saturated polyester resin: 5.0 parts

[0275] (Polycondensate of propylene oxide-modified bisphenol A (2-mole adduct) and terephthalic acid (molar ratio of 10:12), glass transition temperature (Tg) of 68° C., weight average molecular weight (Mw) of 10,000, and molecular weight distribution (Mw / Mn) of 5.12)

[0276] Fischer-Tropsch wax (melting point 78°C): 7.0 parts

[0277] The above materials were added to the colorant dispersion solution, heated to 65° C., and dissolved and dispersed uniformly with a TK Homomixer (manufactured by TOKUSHU KIKA KOGYO Co., Ltd.) at 500 rpm to prepare a polymerizable monomer composition.

[0278] (Granulation step)

[0279] The temperature of the aqueous medium was adjusted to 70°C. While maintaining the rotation speed of the TK Homomixer at 15,000 rpm, the polymerizable monomer composition was placed in the aqueous medium 1, and 10.0 parts of t-butyl peroxypivalate was added as a polymerization initiator. Then, granulation was directly carried out while maintaining the stirrer at 15,000 rpm for 10 minutes.

[0280] (Polymerization step and distillation step)

[0281] After the granulation step, a propeller stirring blade was set in the stirrer, and polymerization was carried out for 5.0 hours while stirring the solution at 150 rpm and maintaining it at 70°C. The temperature was then raised to 85°C and maintained for 2.0 hours. The reflux line of the reaction vessel was then replaced with a cooling line. The resulting slurry was heated to 100°C and distilled for six hours to distill off unreacted polymerizable monomers, thereby obtaining a resin particle dispersion solution.

[0282] (Step of Forming Silicone Polymer)

[0283] In a reaction vessel equipped with a stirrer and a thermometer, 60.0 parts of ion-exchanged water were weighed and the pH was adjusted to 4.0 using 10% by mass hydrochloric acid. The solution was heated to 40°C while stirring. Then, 40.0 parts of methyltriethoxysilane, an organosilicon compound, was added and stirred for two hours or longer to hydrolyze the mixture. When the oil and water did not separate and form a single layer, the hydrolysis was visually confirmed to be complete, and the oil and water were cooled to obtain a hydrolyzed solution of the organosilicon compound.

[0284] The temperature of the resin particle dispersion solution obtained above was adjusted to 55°C, and 25.0 parts of a hydrolyzed solution of an organosilicon compound (the amount of the organosilicon compound added was 10.0 parts) was added to initiate polymerization of the organosilicon compound. The solution was maintained for 0.25 hours, and the pH was adjusted to 5.5 using a 3.0% sodium bicarbonate solution. After the solution was maintained at 55°C for 1.0 hour while continuously stirring (Condensation Reaction 1), the pH was adjusted to 9.5 using a 3.0% sodium bicarbonate solution and maintained for a further 4.0 hours (Condensation Reaction 2) to obtain a toner particle dispersion solution.

[0285] (Washing step and drying step)

[0286] After the organosilicon polymer formation step is completed, the toner particle dispersion solution is cooled, hydrochloric acid is added to the toner particle dispersion solution to adjust the pH to 1.5 or less, and the solution is allowed to stand for 1.0 hour while stirring. The solution is then subjected to solid-liquid separation using a filter press to obtain a toner filter cake. The resulting toner filter cake is reslurried with ion-exchanged water to form a dispersion solution, and solid-liquid separation is performed using the filter press to obtain a toner filter cake. The resulting toner filter cake is placed in a constant temperature bath at 40°C, dried for 72 hours, and classified to obtain toner particles.

[0287] <Production Example of External Additive A>

[0288] External Additive A was prepared as follows. 150 parts of a 5% aqueous ammonia solution was placed in a 1.5 L glass reaction vessel equipped with a stirrer, a dropper, and a thermometer to obtain an alkaline catalyst solution. After the alkaline catalyst solution was adjusted to 50°C, 100 parts of tetraethoxysilane and 50 parts of 5% aqueous ammonia were simultaneously added dropwise while stirring the solution. The mixture was reacted for eight hours to obtain a dispersion of fine silica particles. The resulting dispersion was then dried by spray drying and pulverized using a pin mill to obtain fine silica particles having a primary particle number average particle diameter of 100 nm as External Additive A.

[0289] <Developer Manufacturing Example>

[0290] 100 parts of toner particles and 1.00 part of external additive A were placed in a Henschel Mixer (FM10C model, manufactured by NIPPON COKE & ENGINEERING Co., Ltd.), with water at 7°C passing through the jacket of the Henschel Mixer. Subsequently, after the temperature of the water in the jacket stabilized at 7°C ± 1°C, mixing was performed for 10 minutes at a rotating blade peripheral speed of 38 m / sec. During the mixing process, the amount of water passing through the jacket was adjusted as needed so that the temperature in the tank of the Henschel Mixer did not exceed 25°C. The resulting mixture was sieved with a mesh having an aperture of 75 μm to obtain a developer.

[0291] Table 1 shows the physical properties of the developer.

[0292] Table 1

[0293]

[0294] In the table, "X" represents the ratio of the number average particle diameter R of primary particles of the external additive A to the number average value of the protrusion height H. When the produced developer was observed with an SEM, it was confirmed that the external additive A was placed as transfer carrier particles on the silicone polymer protrusions of the toner particles, and the average coverage number of the external additive A per toner particle was about 500.

[0295] 5. Supply of transfer carrier particles

[0296] Next, a description will be given of a manner in which transfer carrier particles are supplied to the photoconductor drum 1, which is one of the features of the first embodiment. As described above, the transfer carrier particles refer to particles that, when interposed between the photoconductor drum 1 and the toner image developed on the photoconductor drum 1, play a role in improving the primary transfer efficiency of the toner image by reducing the adhesion between the toner image and the photoconductor drum 1.

[0297] In the first embodiment, before the toner image is developed, transfer carrier particles are previously supplied to the surface of the photoconductor drum 1 by using the toner carried on the developing roller 41. By coating the photoconductor drum 1 with the transfer carrier particles in advance, the transfer carrier particles are placed between the toner image and the photoconductor drum 1.

[0298] Figure 8A Schematic diagram of the developing nip portion when the developing roller 41 and the photoconductor drum 1 are in contact with each other. Figure 8A As shown, the toner particles carried on the developing roller 41 and the photoconductor drum 1 are in contact with each other via transfer carrier particles in the developing nip portion. Figure 8B 4 is a schematic diagram showing a state where the toner carried on the developing roller 41 and the photoconductor drum 1 pass through the developing nip portion. Figure 8B As shown, transfer carrier particles interposed between the toner and the photoconductor drum 1 in the development nip portion are supplied by being transferred from the surface of the toner carried on the development roller 41 to the surface of the photoconductor drum 1 after passing through the development nip portion.

[0299] like Figure 8A As shown, when the adhesion force Ft between the toner and the transfer carrier particles interposed between the toner and the photoconductor drum 1 in the development nip portion is greater than the adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1, the transfer carrier particles are difficult to transfer onto the photoconductor drum 1. Therefore, Ft may be smaller than Fdr.

[0300] Figure 9A is a schematic diagram of a primary transfer portion when a toner image is formed on the surface of the photoconductor drum 1; Figure 9B yes Figure 9AThe diagram shows a state where the primary transfer of the toner image is completed and the photoconductor drum 1 and the intermediate transfer belt 10 are separated from each other. When Ft is less than Fdr, when the toner image is primarily transferred from the photoconductor drum 1 to the surface of the intermediate transfer belt 10, only the toner image is transferred to the intermediate transfer belt 10, and the transfer carrier particles interposed between the toner image and the photoconductor drum 1 remain on the photoconductor drum 1.

[0301] It is assumed that transfer carrier particles interposed between the toner image and the photoconductor drum 1 are primarily transferred to the intermediate transfer belt 10 together with the toner image, and the transfer carrier particles are lost from the surface of the photoconductor drum 1. In this case, no transfer carrier particles are interposed between the photoconductor drum 1 and the toner image to be subsequently developed on the surface of the photoconductor drum 1, and the adhesion between the toner image and the photoconductor drum 1 is large, so the primary transferability is reduced.

[0302] Therefore, from the viewpoint of not only easily supplying transfer carrier particles from the toner carried on the developing roller 41 to the photoconductor drum 1 but also maintaining the transfer carrier particles coated on the photoconductor drum 1 , Ft may be smaller than Fdr.

[0303] Figure 10 1 is a timing chart of the printing operation of the image forming apparatus 100 used in the first embodiment. Figure 10 As shown, during the image forming operation, before the image forming apparatus 100 of the first embodiment starts developing the toner from the developing roller 41 to the photoconductor drum 1, the developing roller 41 and the photoconductor drum 1 are driven to rotate in a contact state. Therefore, time is provided for supplying the transfer carrier particles from the developing roller 41 to the photoconductor drum 1 (transfer carrier particle supply mode).

[0304] In order to improve the primary transfer efficiency of the toner image on the entire surface of the photoconductor drum 1, the entire surface of the photoconductor drum 1 is coated with transfer carrier particles before starting the development of the toner image. For this purpose, the time for supplying the transfer carrier particles can be set to the time for rotating the photoconductor drum 1 one or more times. Therefore, in the first embodiment, in order to be able to coat the entire surface of the photoconductor drum 1 with transfer carrier particles, Figure 10 The length of the transfer carrier particle supply time shown in is set to 500 milliseconds, which is substantially equal to the time it takes for the photoconductor drum 1 to make one rotation.

[0305] In addition, in the first embodiment, Figure 10 In the transfer carrier particle supply timing shown, the surface potential of the photoconductor drum 1 is set to a non-image forming potential Vd = -500 V, at which the toner charged with the normal polarity is not developed. Therefore, in the transfer carrier particle supply timing of the first embodiment, the toner with the normal polarity of negative polarity is not developed from the developing roller 41 to the surface of the photoconductor drum 1, and only the transfer carrier particles are supplied from the developing roller 41 to the photoconductor drum 1.

[0306] When transferring carrier particles are supplied from the toner on the developing roller 41 to the photoconductor drum 1 while a potential difference exists between the developing roller 41 and the photoconductor drum 1, as in the first embodiment, the following inconvenience arises. If the particle size of the transfer carrier particles is too large, the transfer carrier particles are susceptible to the electrostatic force generated by the potential difference between the developing roller 41 and the photoconductor drum 1. Consequently, it becomes difficult to control the supply of the transfer carrier particles from the toner on the developing roller 41 to the photoconductor drum 1. For example, in a configuration in which the transfer carrier particles are supplied at a non-image forming potential, as in the first embodiment, when the transfer carrier particles are negatively charged, they are attracted toward the developing roller 41 by electrostatic force. Consequently, it becomes difficult to supply the transfer carrier particles from the toner on the developing roller 41 to the photoconductor drum 1. The particle size of the transfer carrier particles is preferably set to 1000 nm or less; at or below this particle size, the transfer carrier particles are less susceptible to electrostatic force. In the first embodiment, in order to stably supply transfer carrier particles from the toner on the developing roller 41 to the surface of the photoconductor drum 1 regardless of the potential difference between the developing roller 41 and the photoconductor drum 1 , particles having a particle size of 100 nm are used as the transfer carrier particles.

[0307] The developer used in the first embodiment is a mixture of the above-mentioned toner and transfer carrier particles. Figure 7 FIG is an enlarged view of the developer used in the first embodiment. Figure 7 As shown, the developer of the first embodiment is such that transfer carrier particles are arranged on the toner surface on which a large number of protrusions made of an organic silicon polymer are formed. Figure 7 The protrusion gap G and protrusion height H on the toner surface shown can be measured using a scanning probe microscope (hereinafter referred to as SPM). A scanning probe microscope (hereinafter referred to as SPM) includes a probe, a cantilever supporting the probe, and a displacement measurement system that detects the deflection of the cantilever. The SPM observes the shape of the sample surface by detecting the atomic force (attraction or repulsion) between the probe and the sample.

[0308] When the protrusion gap G is larger than the particle size of the transfer carrier particles, the transfer carrier particles, when arranged between the protrusions, come into contact with the toner base, and the adhesion force Ft between the transfer carrier particles and the toner increases, resulting in difficulty in transferring the transfer carrier particles from the toner to the photoconductor drum 1. To this end, the protrusion gap G can be narrower than the particle size of the transfer carrier particles. Therefore, when the minimum distance between two adjacent protrusions is the protrusion gap G, the average value of the protrusion gap G can be smaller than the average particle size of the transfer carrier particles.

[0309] When the protrusion height H is greater than the particle size of the transfer carrier particles, the protrusions come into contact with the photoconductor drum 1 before the transfer carrier particles. As a result, the transfer carrier particles have difficulty coming into contact with the photoconductor drum 1, and thus, the transfer carrier particles have difficulty transferring from the toner to the photoconductor drum 1. Therefore, the protrusion height H can be smaller than the particle size of the transfer carrier particles. Therefore, when the height of each protrusion from the surface of the toner particle is the protrusion height H, the average value of the protrusion height H can be less than or equal to the average particle size of the transfer carrier particles.

[0310] The protrusions on the toner surface of Example 1 were measured. The average value of the protrusion gap G on the toner surface was about 30 nm, and the average value of the protrusion height H was 50 nm, and both the protrusion gap G and the protrusion height H were smaller than the particle diameter of the transfer carrier particles of 100 nm.

[0311] The transfer carrier particles used in the first embodiment are silica particles with a particle size of 100 nm manufactured by a sol-gel method. In the first embodiment, silica is used as the transfer carrier particles; however, the material of the transfer carrier particles is not limited to silica, and can be various organic or inorganic fine particles. As described above, the adhesion force Ft between the transfer carrier particles and the colorant can be smaller than the adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1. For this reason, the material of the transfer carrier particles can be selected so as to reduce the adhesion force Ft between the transfer carrier particles and the toner. For example, as in the case of the first embodiment, when the protruding portion on the toner surface is made of a silica-based material (such as an organic silica polymer), a silica-based material having a material composition similar to the material composition of the protruding portion can be selected as the material of the transfer carrier particles. From the perspective of reducing the adhesion between the protruding portion and the transfer carrier particles, a silica-based material having a material composition similar to the material composition of the protruding portion can be selected.

[0312] In addition, in the first embodiment, the amount of transfer carrier particles added is adjusted so that the number of transfer carrier particles coated per toner particle is approximately 500. As the number of transfer carrier particles coating the toner particles increases, more transfer carrier particles can be supplied from the developing roller 41 to the surface of the photoconductor drum 1. However, if the amount of transfer carrier particles added is too large, the risk of contamination of components in the image forming apparatus 100 increases, so the amount of transfer carrier particles added can be adjusted according to the desired primary transfer performance.

[0313] In addition, primary transferability improves to a certain extent as the coverage of the transfer carrier particles coating the surface of the photoconductor drum 1 increases. However, as the coverage of the transfer carrier particles coating the surface of the photoconductor drum 1 increases, the degree of improvement in primary transferability slows, and the risk of contamination of various components in the imaging device by the transfer carrier particles increases. Therefore, the coverage of the transfer carrier particles coating the surface of the photoconductor drum 1 is preferably less than or equal to 80%.

[0314] 6. The role of transfer carrier particles

[0315] Next, an effect confirmation test conducted in order to confirm the effect of the manner of supplying transfer carrier particles to the photoconductor drum 1 in the first embodiment will be described.

[0316] Initially, a patch image with a yellow density of 100% is formed by using the image forming apparatus 100 in which a new photoconductor drum 1 not coated with transfer carrier particles is set. Immediately after the primary transfer of the formed yellow patch image is completed, the image forming apparatus 100 is stopped. At this time, the residual toner density of the patch image portion remaining on the surface of the photoconductor drum 1a of the yellow station is checked.

[0317] The measurement of the residual toner density is performed by the following technique. First, a transparent tape (polyester tape 5511, Nichiban Co., Ltd.) is adhered to the residual toner portion of the yellow block image on the surface of the photoconductor drum 1a, and the residual toner is captured by the transparent tape. Afterwards, the transparent tape that has captured the residual toner and peeled off from the surface of the photoconductor drum 1a and a new transparent tape are adhered to high-brightness paper (GFC081 Canon, Inc.). Then, the density D1 of the transparent tape in the residual toner capturing portion and the density D0 of the new transparent tape portion are measured using a reflection densitometer (TC-6DS type reflectometer, produced by Tokyo Denshoku Co., Ltd.). The difference "D0-D1" obtained by the measurement is determined as the residual toner density. The residual toner density means that the residual toner decreases as the numerical value decreases. When this value is less than or equal to 1.0, it can be determined that there is almost no residual toner, and no adverse effects in the image due to adhesion to the charging roller 2a, etc. will occur.

[0318] The surface of the photoconductor drum 1a, for which the residual toner density was measured, was observed under a microscope, and the coverage of the transfer carrier particles coating the surface of the photoconductor drum 1a was calculated. Specifically, the coverage was calculated according to the following steps using an image observed at a magnification of 3000 times using a laser microscope (VK-X200, Keyence Corporation) on the surface of the photoconductor drum 1a. The transfer carrier particle portion and the other portion were binarized, and the total area ratio of the transfer carrier particles to the surface of the photoconductor drum 1a was calculated as the coverage of the transfer carrier particles on the surface of the photoconductor drum 1a.

[0319] The adhesion force between the transfer carrier particles and the toner used in the first embodiment was measured using an SPM. Specifically, the transfer carrier particles were attached to the tip of a lever on a cantilever, and the cantilever was pressed against the toner with a predetermined pressing force. The force required to separate the cantilever from the toner was then measured as the adhesion force Ft between the transfer carrier particles and the toner.

[0320] The predetermined pressing force with which the cantilever is pressed against the toner during adhesion measurement can be set to the force with which the transfer carrier particles interposed between the toner and the photoconductor drum 1 in the developer nip are pressed against the toner. This pressing force is calculated using the calculation method described below. Here, the phrase "transfer carrier particles interposed between the toner and the photoconductor drum 1 in the developer nip" refers to a state in which the transfer carrier particles are in contact with both the toner and the photoconductor drum 1.

[0321] First, to calculate the pressing force, refer to Figure 11A 、 Figure 11B and Figure 12 Describe the hypothesis. Figure 11A Schematic diagram of the development nip portion. It is assumed that the development roller 41 and the photoconductor drum 1 are in contact with each other via the toner in the development nip portion. Figure 11B It is along Figure 11A sectional view taken parallel to the surface of the photoconductor drum 1 along the dotted line XIB-XIB in FIG. It is assumed that the toner in contact with the photoconductor drum 1 is in the densest packing as indicated by the hatched portion. Figure 12 is Figure 11A FIG. 1 is an enlarged schematic diagram of the contact portion between the toner and the photoconductor drum 1, which is surrounded by the dotted line XII. Figure 12 As shown, it is assumed that the toner and the photoconductor drum 1 are in contact with each other via the transfer carrier particles. In addition, it is assumed that the transfer carrier particles have not yet been supplied to the surface of the photoconductor drum 1 and that the transfer carrier particles do not exist on the surface of the photoconductor drum 1 in advance.

[0322] Based on the above assumptions, the total number N of transfer carrier particles interposed between the toner and the photoconductor drum 1 in the development nip portion is calculated as follows. By using the calculated number N and the contact force F between the developing roller 41 and the photoconductor drum 1, F / N, which is the pressing force of each transfer carrier particle against the toner in the development portion, is calculated, and the calculated F / N is used as a predetermined pressing force of the cantilever against the toner when measuring adhesion.

[0323] First, a method of calculating the total number N of transfer carrier particles interposed between the toner and the photoconductor drum 1 in the development nip portion will be described.

[0324] Figure 13A : is a two-dimensional schematic diagram of the contact state between the toner particles, the transfer carrier particles and the photoconductor drum 1 in the developing part. Figure 13B As shown in FIG. 1 , when the particle diameter of the transfer carrier particles is r, when the distance between the photoconductor drum 1 and the surface of the toner particles exceeds r, the transfer carrier particles on the toner particles are almost not in contact with the photoconductor drum 1. Therefore, the toner circumferential portion where the transfer carrier particles that can contact the photoconductor drum 1 are arranged is the arc connecting A and B. In practice, the toner particles need to be considered as Figure 13B The sphere shown, and it is necessary to obtain the surface area obtained by integrating the arc AB in the circumferential direction ( Figure 13B The ratio of the surface area of ​​the toner particles (the shaded area in the figure) to the surface area of ​​the toner particles. The surface area of ​​the shaded area can generally be calculated as the surface area of ​​a spherical cap and is expressed by Expression 2. Therefore, the ratio to the surface area of ​​the toner particles is expressed by Expression 3. The actual value can be calculated from the average particle size R of the toner and the particle size r of the transfer carrier particles.

[0325] The transfer carrier particles can be in contact with the photoconductor drum 1

[0326]

[0327] Average particle size of toner R = 7.0 μm = 7000 nm

[0328] The particle size of the transfer carrier particles is r = 100 nm

[0329] Through the above calculation, in the configuration of the first embodiment, the ratio of the arc AB to the toner circumferential portion is calculated to be approximately 1.43%.

[0330] Therefore, it can be estimated that the area where the transfer carrier particles are interposed between the toner particles and the photoconductor drum 1 in the development nip portion is about 1.43% of the entire toner particle surface. Since the number of transfer carrier particles coated per toner particle is 500, the number M of transfer carrier particles interposed between the toner and the photoconductor drum 1 per toner particle is calculated as 500×1.43%, which is about 7.2.

[0331] The total number of toner particles in contact with the photoconductor drum 1 in the development portion is multiplied by 7.2, where 7.2 is the number of transfer carrier particles interposed between the toner and the photoconductor drum 1 per toner particle. As a result, the total number N of transfer carrier particles interposed between the toner and the photoconductor drum 1 in the development nip portion can be calculated.

[0332] The total number L of toner particles in contact with the photoconductor drum 1 in the development nip portion can be calculated by (area of ​​the development nip portion)×(filling rate of toner) / (maximum cross-sectional area of ​​toner particles).

[0333] (Total number of toner particles in contact with the photoconductor drum 1 in the development nip portion) = (220 [mm] × 2.0 [mm] × π / √12) / (π × (7.0 / 2) 2 ) = approximately 10.37 × 10 6

[0334] (Using π / √12≈0.9069 as the closest packing ratio of two-dimensional circles)

[0335] Therefore, the total number N of transfer carrier particles interposed between the toner and the photoconductor drum 1 in the development nip portion is calculated as follows. The total number N is calculated by multiplying the "total number of toner particles in contact with the photoconductor drum 1 in the development nip portion" by the "number of transfer carrier particles interposed between the toner and the photoconductor drum 1 per toner particle" and is calculated to be approximately 7.47×10 7 .

[0336] Since the pressing force of the developing section 41 on the photoconductor drum 1 is F = 200 gf in the first embodiment, the pressing force F / N of each transfer carrier particle on the toner in the developing section is determined to be 26.3 nN. The F / N value thus determined is used as the predetermined pressing force with which the cantilever is pressed against the toner when measuring adhesion using the SPM. Similar adhesion force measurements are also performed on the photoconductor drum 1, and the adhesion force Fdr between the transfer carrier particles fixed at the tip of the cantilever and the photoconductor drum 1 is measured.

[0337] The results of the effect confirmation test for the first embodiment will be described. Figure 14 As shown, in the configuration of the first embodiment, the residual toner density was 0.8%, and there was almost no residual toner, and it was confirmed that high transferability was obtained. In addition, the transfer carrier coverage on the surface of the photoconductor drum 1 of the first embodiment was 61.7%, and it was confirmed that the photoconductor drum 1 was sufficiently coated with transfer carrier particles. In addition, in the first embodiment, as Figure 15As shown, the adhesion between the transfer carrier particles and the toner is 32.8 (nN), and the adhesion between the transfer carrier particles and the photoconductor drum 1 is 210.1 (nN). In other words, it was confirmed that in the first embodiment, the adhesion between the transfer carrier particles and the toner is smaller than the adhesion between the transfer carrier particles and the photoconductor drum 1.

[0338] On the other hand, in Comparative Example 1, a construction of a developer is adopted in which the adhesion between the transfer carrier particles and the photoconductor drum 1 is greater than the adhesion between the transfer carrier particles and the toner. Specifically, unlike the construction of the first embodiment, the developer is such that the surface of the toner particles is not coated with an organic silica polymer or the like, and the transfer carrier particles are directly added to the surface of the toner particles from the outside. When the developer of Comparative Example 1 is used, the residual toner density is 4.1%. As the residual toner increases, an adverse effect on the image may occur due to a charging failure or the like caused by contamination of the charging roller 2. In addition, in Comparative Example 1, as Figure 15 As shown, the adhesion between the transfer carrier particles and the toner is 304.6 (nN), and the adhesion between the transfer carrier particles and the photoconductor drum 1 is 210.1 (nN). In other words, it was confirmed that in Comparative Example 1, the adhesion between the transfer carrier particles and the toner is greater than the adhesion between the transfer carrier particles and the photoconductor drum 1.

[0339] From the above results, the first embodiment has the following configuration.

[0340] The imaging device 100 includes a rotatable photoconductor drum 1 and a rotatable developing roller 41, which carries a developer composed of toner particles and transfer carrier particles attached to the surface of the toner particles. The developing roller 41 contacts the photoconductor drum 1 to form a developing nip portion, and supplies the developer to the surface of the photoconductor drum 1 in the developing nip portion. The imaging device 100 includes a developer accommodating portion 4 that accommodates the developer. The imaging device 100 includes a transfer roller 14 that transfers the developer supplied to the surface of the photoconductor drum 1 to an intermediate transfer belt 10 serving as a transfer receiving member, a photoconductor drum driver 110 that drives the photoconductor drum 1, and a control portion 200 that controls the photoconductor drum driver 110. In the configuration of the first embodiment, while the photoconductor drum 1 is rotating, the transfer carrier particles carried on the surface of the developing roller 41 can be supplied to the surface of the photoconductor drum 1 in the developing nip portion. Here, the pressing force of the developing roller 41 against the photoconductor drum 1 is defined as F, and the total number of transfer carrier particles between the toner particles and the photoconductor drum 1 is defined as N. The adhesion force between the transfer carrier particles and the toner particles is defined as Ft, and the adhesion force is measured when the transfer carrier particles are pressed against the toner particles at a pressing force F / N per unit carrier particle. The adhesion force between the transfer carrier particles and the photoconductor drum 1 is defined as Fdr, and the adhesion force is measured when the transfer carrier particles are pressed against the photoconductor drum 1 at F / N. The adhesion force Ft and the adhesion force Fdr satisfy Ft<Fdr. The imaging device 100 is capable of performing an imaging mode in which the developer is developed on the electrostatic latent image and a supply mode in which the transfer carrier particles are supplied from the developing roller 41 to the photoconductor drum 1.

[0341] As described above, in the configuration of the first embodiment, by efficiently supplying the transfer carrier particles to the surface of the photoconductor drum 1 , the transfer efficiency is improved.

[0342] In the first embodiment, the developing roller 41 is driven to rotate in the forward direction relative to the surface movement direction of the photoconductor drum 1 so that the peripheral speed of the developing roller 41 in the developing nip portion is equal to the peripheral speed of the photoconductor drum 1. In the second embodiment, a peripheral speed difference is provided between the developing roller 41 and the photoconductor drum 1 by rotating the developing roller 41 at a peripheral speed 40% higher than that of the photoconductor drum 1 in the developing nip portion.

[0343] In addition, in the second embodiment, as Figure 16 As shown, the developing operation is configured to start immediately after the developing contact in the image forming operation, and the time for supplying the transfer carrier particles is not set before the development starts. The other configurations are similar to those of the first embodiment, and thus descriptions are omitted.

[0344] Hereinafter, the operation of the second embodiment will be described.

[0345] Figure 17ASchematic diagram showing the behavior of toner and transfer carrier particles in the development nip portion when the development roller 41 and the photoconductor drum 1 are set in a non-image forming potential relationship. Figure 17A As shown, due to the difference in circumferential speed between the developing roller 41 and the photoconductor drum 1, the following phenomenon occurs. The force parallel to the rotation direction of the developing roller 41 is defined as f1, wherein the toner between the developing roller 41 and the photoconductor drum 1 receives the force from the developing roller 41. The force parallel to the rotation direction of the photoconductor drum 1 is defined as f2, wherein the toner between the developing roller 41 and the photoconductor drum 1 receives the force from the photoconductor drum 1. Under the conditions described in the first embodiment, f1 and f2 are balanced with each other; however, in the construction of the second embodiment, f1 and f2 are not balanced with each other, and the toner rolls in the developing clamping portion. When the toner rolls, the transfer carrier particles on the toner that are not in contact with the photoconductor drum 1 also move as the toner rolls. For this reason, the transfer carrier particles can come into contact with the photoconductor drum 1, thereby increasing the chance of supplying the transfer carrier particles from the toner to the surface of the photoconductor drum 1. Therefore, as Figure 17B As shown, after passing through the development nip, transfer carrier particles larger in number than that of the first embodiment may be supplied from the toner on the developing roller 41 to the surface of the photoconductor drum 1 .

[0346] Figure 18A Schematic diagram showing the behavior of toner and transfer carrier particles in the developing nip portion when the developing roller 41 and the photoconductor drum 1 are set in an image potential relationship. Figure 18A As shown, when the developing roller 41 and the photoconductor drum 1 are also set to an image potential relationship, the following phenomenon occurs due to the peripheral speed difference between the developing roller 41 and the photoconductor drum 1. The toner rolls in the developing nip portion, and the efficiency of supplying transfer carrier particles from the surface of the toner to the surface of the photoconductor drum 1 in the developing nip portion is improved. Figure 18B As shown, the developing roller 41 and the photoconductor drum 1 are set in an image-forming potential relationship. Therefore, after passing through the developing nip portion, the toner is developed from the developing roller 41 onto the surface of the photoconductor drum 1. Since the efficiency of supplying transfer carrier particles from the surface of the toner to the surface of the photoconductor drum 1 when passing through the developing nip portion is improved, a large number of transfer carrier particles can be interposed between the photoconductor drum 1 and the toner developed on the surface of the photoconductor drum 1.

[0347] Therefore, in the second embodiment, unlike the first embodiment, even if the transfer carrier particle supply time is not set before the imaging operation, the transfer carrier particles can coat the surface of the photoconductor drum 1 while developing, and the transfer carrier particles can be placed between the colorant image and the photoconductor drum 1.

[0348] In addition, in the second embodiment, no cleaning member is provided on the surface of the photoconductor drum 1. However, since transfer carrier particles can be supplied simultaneously with development, even if a cleaning member is provided on the surface of the photoconductor drum 1, transfer efficiency can be appropriately improved. Even in a configuration where the transfer carrier particles coating the surface of the photoconductor drum 1 are collected by the cleaning member with each rotation of the photoconductor drum 1, the effect of improving primary transfer efficiency by the transfer carrier particles can be achieved. Of course, as long as the transfer carrier particles are supplied in sufficient quantity, a configuration in which a cleaning member is provided while the developing roller 41 and the photoconductor drum 1 are driven to rotate without a circumferential speed difference, as in the first embodiment, is not excluded.

[0349] Next, the results obtained by confirming the effects of the second embodiment by measuring the residual toner density of the yellow patch image and the coverage of the transfer carrier particles on the surface of the photoconductor drum 1 in the configuration of the second embodiment by a method similar to that of the first embodiment will be described.

[0350] like Figure 14 As shown, in the configuration of the second embodiment, the residual toner density was also 0.7%, and almost no residual toner existed, and it was confirmed that high transferability was obtained. Figure 14 As shown, the transfer carrier coverage on the surface of the photoconductor drum 1 of the second embodiment was 62.2%, and it was confirmed that the photoconductor drum 1 was sufficiently coated with transfer carrier particles.

[0351] According to the above results, the second embodiment provides an imaging apparatus having the following configuration.

[0352] When the photoconductor drum driver 110 is the first driver, the developing roller driver 130 driving the developing roller 41 is the second driver. The control portion 200 controls the second driver so that the surface movement speed of the developing roller 41 is different from that of the photoconductor drum 1 in the developing nip portion.

[0353] As described above, in the configuration of the second embodiment, by further efficiently supplying the transfer carrier particles to the surface of the photoconductor drum 1 , the transfer efficiency is improved.

[0354] In the configuration of the second embodiment, an intermediate transfer system using the intermediate transfer belt 10 is employed; however, a direct transfer system may be employed in which a toner image is directly transferred to the recording medium P. For example, the recording medium P may be placed on a transfer belt, and the toner image may be directly transferred from the photoconductor drum 1 to the recording medium P, or a belt configuration need not be used.

[0355] As described above, according to the present disclosure, by efficiently supplying fine particles from the developing device to the surface of the photoconductor drum, transfer efficiency is improved.

[0356] 1. Imaging equipment

[0357] The overall configuration of an electrophotographic image forming apparatus (hereinafter referred to as an image forming apparatus) according to a third embodiment will be described. Figure 20 is a schematic cross-sectional view of the imaging apparatus 100 of this embodiment. Figure 21 1 is a diagram showing the configuration of the control section 200 that controls the imaging device 100. Figure 20 and Figure 21 The configuration, operation, and control of the imaging apparatus 100 of the present embodiment are described.

[0358] The image forming apparatus 100 of this embodiment is a full-color laser printer employing an inline system and an intermediate transfer system.The third embodiment specifically relates to an image forming apparatus using a so-called drumless cleaner system having no cleaner for an image bearing member.

[0359] The imaging apparatus 100 is capable of forming a full-color image on a recording medium P (e.g., a recording sheet or a plastic sheet) based on image information. The image information is input to the imaging apparatus 100 from an image reading device or a host device, such as a personal computer, connected to the imaging apparatus 100 for communication with the imaging apparatus 100.

[0360] Imaging device 100 comprises first, second, third and fourth process box Sa, Sb, Sc and Sd that are used to form the image of the color of yellow (Y), magenta (M), cyan (C) and black (K) as a plurality of imaging units.In the present embodiment, first to fourth process box Sa, Sb, Sc, Sd are arranged in a row on the direction intersecting with the vertical direction.In the present embodiment, except the color of the image to be formed is different, the construction and operation of first to fourth process box Sa, Sb, Sc, Sd are basically the same.Therefore, unless otherwise specially distinguished from each other, otherwise omitting the suffix a, b, c, d that is assigned to reference numeral to represent the element that is intended to be used for relevant color, and will describe generally.

[0361] In this embodiment, the imaging device 100 includes four drum-shaped electrophotographic photoconductive members (i.e., photoconductive drums 1 (1a, 1b, 1c, 1d)) as a plurality of image bearing members, arranged in a direction intersecting the vertical direction. The photoconductive drums 1 are driven to rotate by a photoconductive drum driver (drive source) 110. Charging rollers 2 (2a, 2b, 2c, 2d), scanning units (exposure units) 3 (3a, 3b, 3c, 3d), developing units (developing devices) 4 (4a, 4b, 4c, 4d), and pre-charge exposure units 5 (5a, 5b, 5c, 5d) are arranged around the corresponding photoconductive drums 1. The charging rollers 2 are charging devices that uniformly charge the surface of the photoconductive drums 1. The scanning units 3 are exposure devices that form an electrostatic image (electrostatic latent image) on the photoconductive drums 1 by irradiating laser light according to an output power calculated by the CPU 155 based on image information input from a host device (e.g., a personal computer). The developing units 4 are developing devices that develop the electrostatic image into a toner image. The pre-charge exposure unit 5 is an exposure device for eliminating uneven surface potential of the photoconductor drum 1 after primary transfer. The photoconductor drum 1, the charging roller 2 serving as a process device affecting the photoconductor drum 1, and the developing unit 4 are combined to form a process cartridge S. The process cartridge S can be detached from the image forming apparatus 100 via an attachment device (e.g., an attachment guide and a positioning member provided in the image forming apparatus 100).

[0362] An intermediate transfer belt 10, serving as an intermediate transfer member for transferring the toner image on the photoconductor drum 1 to the recording medium P, is arranged opposite the four photoconductor drums 1. The intermediate transfer belt 10, which is an endless belt, is in contact with the photoconductor drum 1 and circulates (rotates) in the direction indicated by arrow R3 (clockwise) in the figure. The intermediate transfer belt 10 is looped around a plurality of supporting members, including a secondary transfer counter roller 13, a drive roller 11, and a tension roller 12. To move the surface of the intermediate transfer belt 10, the drive roller 11 is driven to rotate in the direction indicated by arrow R2 in the figure.

[0363] On the inner peripheral surface side of the intermediate transfer belt 10, four primary transfer rollers 14 (14a, 14b, 14c, 14d) are arranged opposite to the associated photoconductor drum 1 as the primary transfer means. Each primary transfer roller 14 presses the intermediate transfer belt 10 against the photoconductor drum 1 to form a primary transfer portion where the intermediate transfer belt 10 and the photoconductor drum 1 are in contact with each other.

[0364] On the outer peripheral surface side of the intermediate transfer belt 10, a secondary transfer roller 15 serving as a secondary transfer device is arranged opposite to the secondary transfer counter roller 13. The secondary transfer roller 15 is in pressure contact with the secondary transfer counter roller 13 via the intermediate transfer belt 10 to form a secondary transfer portion where the intermediate transfer belt 10 and the secondary transfer roller 15 are in contact with each other.

[0365] The recording medium P having the transferred toner image is conveyed to the fixing unit 30 serving as a fixing device. By applying heat and pressure to the recording medium P in the fixing unit 30, the toner image is fixed to the recording medium P.

[0366] The image forming apparatus 100 is also capable of forming a monochrome image by using only a desired one of the image forming units or forming a multi-color image by using only some (not all) of the image forming units.

[0367] The image forming apparatus 100 in this embodiment is a printer having a process speed of 148 mm / sec and compatible with A4 size paper.

[0368] Will refer to Figure 21 The configuration of the control section 200 that generally controls the imaging apparatus will be described. Figure 21 As shown, the control section 200 includes a CPU 155, a ROM 151, and a RAM 152. The CPU 155 generally controls the primary transfer control section 207, the secondary transfer control section 206, the development control section 203, the exposure control section 204, and the charging control section 205 according to a control program stored in the ROM 151. The ROM 151 stores an environmental table and a paper thickness correspondence table. The CPU 155 accesses these tables and reflects the information in them. The RAM 152 temporarily stores control data or serves as a workspace for calculations associated with the control. The primary transfer control section 207 controls the primary transfer voltage source 160 and controls the voltage to be output from the primary transfer voltage source 160 based on the current value detected by a current detection circuit (not shown). The secondary transfer control section 206 controls the secondary transfer voltage source 150 and controls the voltage to be output from the secondary transfer voltage source 150 based on the current value detected by the current detection circuit (not shown). When the control part 200 receives image information and printing instructions from a host computer (not shown), the control part 200 performs the imaging operations required for the printing operation by controlling the control parts (primary transfer control part 207, secondary transfer control part 206, development control part 203, exposure control part 204 and charging control part 205).

[0369] (2) Imaging method

[0370] Next, the imaging process in the third embodiment will be described. During the imaging period, first, the surface of the photoconductive drum 1 is uniformly charged by the charging roller 2 to which a charging voltage of 1000V is applied from the charging voltage source 120. Subsequently, the surface of the charged photoconductive drum 1 is scanned and exposed respectively by the laser beam (La, Lb, Lc, Ld) emitted from the scanner unit 3 according to the output power calculated by the CPU 155 based on the image information input from the host device. In this way, an electrostatic image following the image information is formed on each photoconductive drum 1. Subsequently, the electrostatic image formed on each photoconductive drum 1 is developed into a colorant image by the developing unit 4. Then, a voltage of a polarity opposite to the normal charge polarity of the toner is applied to the primary transfer roller 14 from the primary transfer voltage source 160 (high voltage power supply) serving as a primary transfer voltage applying device. Therefore, the toner image on the photoconductive drum 1 is primarily transferred to the intermediate transfer belt 10. During a period of forming a full-color image, the above-described processes are sequentially performed in the first to fourth process cartridges Sa, Sb, Sc, Sd, and the toner images of the respective colors are sequentially primarily transferred to the intermediate transfer belt 10 superimposed on each other.

[0371] The primary transfer roller 14a is a cylindrical metal roller with an outer diameter of 6 mm and is made of nickel-plated SUS. The primary transfer roller 14 is arranged at a position offset 8 mm downstream in the moving direction of the intermediate transfer belt 10 relative to the center position of the photoconductor drum 1. The intermediate transfer belt 10 is configured to be wound around the photoconductor drum 1. The primary transfer roller 14 is arranged at a position raised by 1 mm from the horizontal surface formed by the photoconductor drum 1 and the intermediate transfer belt 10, so that the amount of winding of the intermediate transfer belt 10 around the photoconductor drum 1 can be ensured. The primary transfer roller 14 presses the intermediate transfer belt 10 with a force of approximately 200 gf. The primary transfer roller 14 rotates by the rotation of the intermediate transfer belt 10.

[0372] Afterwards, the recording medium P is conveyed to the secondary transfer section in synchronization with the movement of the intermediate transfer belt 10. A voltage of a polarity opposite to the normal charge polarity of the toner is then applied to the secondary transfer roller 15 from a secondary transfer voltage source 150 (a high-voltage power source), serving as a secondary transfer voltage applying device. Consequently, the four-color toner image on the intermediate transfer belt 10 is secondary-transferred to the recording medium P being conveyed by the sheet feeding device, by the action of the secondary transfer roller 15, which is in contact with the intermediate transfer belt 10 via the recording medium P.

[0373] A secondary transfer roller 15 serving as a secondary transfer member is brought into contact with the intermediate transfer belt 10 at a pressure of 50 N to form a secondary transfer portion (secondary transfer nip). The secondary transfer roller 15 is rotated by the intermediate transfer belt 10. When the toner on the intermediate transfer belt 10 is secondarily transferred onto a recording medium P (e.g., paper), a voltage of 1500 V is applied to the secondary transfer roller 15 from a secondary transfer voltage source 150.

[0374] The recording medium P with the transferred toner image is conveyed to the fixing unit 30 serving as fixing means. By applying heat and pressure to the recording medium P in the fixing unit 30, the transferred toner image is fixed to the recording medium P, and the recording medium P is discharged from the image forming apparatus 100.

[0375] The primary transfer residual toner on the surface of the photoconductor drum 1 in the primary transfer step is collected by the developing roller 22 (described later) and reused. The residual toner on the surface of the photoconductor drum 1 in the primary transfer step is charged with a negative polarity, which is a normal charge polarity, when passing through the charging roller 2. Thereafter, the primary transfer residual toner is collected by the developing roller 22 under an electric field generated by a potential difference between the potential of the photoconductor drum 1 formed by the charging roller 2 and the potential of the developing roller 22 (described later) formed by applying a DC voltage to the developing roller 22, and reused.

[0376] Secondary transfer residual toner on the surface of the intermediate transfer belt 10 in the secondary transfer step is cleaned and removed by the intermediate transfer belt cleaning device 17 .

[0377] 3. Structure of the processing box

[0378] Next, the overall structure of each process cartridge S to be attached to the image forming apparatus 100 of the third embodiment will be described. The process cartridges S for the respective colors have the same shape except for the identification portion (not shown) and the like. Toner of each color of yellow (Y), magenta (M), cyan (C), and black (K) is accommodated in a corresponding one of the developing units (developing devices) 4 of the process cartridge S for the respective color. A negative-polarity non-magnetic single-component developer (toner) manufactured by suspension polymerization is accommodated in the developing unit 4 as the developer accommodating portion.

[0379] The process cartridge S is formed by combining a photosensitive unit including a photoconductor drum 1 and a rotatable charging roller 2 and a developing unit 4 including a rotatable developing roller 22 and the like.

[0380] The photoconductor drum 1 is rotatably supported via a bearing (not shown). When a driving force of a photoconductor drum driving device 110 (driving source) serving as a photoconductor drum driver is transmitted to the photoconductor unit, the photoconductor drum 1 is configured to be driven and rotated in the direction indicated by arrow R1 in the figure (counterclockwise direction) according to an image forming operation.

[0381] The photoconductor drum 1 is composed of an aluminum tube, a photoconductor layer and a surface layer provided on the aluminum tube. The outer diameter of the aluminum tube is 20 mm. The surface layer is a film made of polyallyl compound with a thickness of 20 μm.

[0382] The charging roller 2 includes a roller portion made of a metal shaft having a diameter of 5.5 mm and a conductive rubber having a thickness of 1.5 mm and a volume resistivity of about 1×106 The roller portion is in pressure contact with the photoconductor drum 1 and is configured to be rotated by the photoconductor drum 1. A large number of protrusions are provided on the surface layer of the charging roller 2. The average height of the protrusions is approximately 10 μm. The protrusions provided on the surface layer of the charging roller 2 function as spacers between the charging roller 2 and the photoconductor drum 1 in the charging section. When primary transfer residual toner on the photoconductor drum 1 enters the charging section, the charging roller 2 is prevented from being contaminated by the residual toner due to contact between portions other than the protrusions and the primary transfer residual toner.

[0383] On the other hand, Figure 22 As shown, the developing unit 4 includes a developing roller 22 that carries the toner T, a developing blade 23 (toner regulating member), a supply roller 26 that supplies the toner T, and a developing frame 24 that fixes these components. The developing frame 24 includes a developing chamber 24a in which the developing roller 22 is arranged, and a spray-proof sheet 24b that seals a developing opening (opening portion) that connects the developing chamber 24a to the outside.

[0384] Toner is supplied to the developing roller 22 by a supply roller 26 in contact with the developing roller 22. The supply roller 26 rotates (in the direction indicated by arrow R5 in the figure) in contact with the developing roller 22 (which rotates in the direction indicated by arrow R4 in the figure). The supply roller 26 is used to convey the toner T from the developing chamber 24a, attach the toner T to the developing roller 22, and remove the toner T remaining on the developing roller 22 at one time. In addition, the toner T attached to the supply roller 26 rubs and slides on the developing roller 22, thereby imparting a preliminary triboelectric charge.

[0385] One end of the developing blade 23 is fixed to a fixing member 25 fixed to the developing frame 24, and the other end of the developing blade 23 is brought into contact with the developing roller 22. Thus, the developing blade 23 is configured to be able to control the amount of toner applied to the developing roller 22 and to apply electric charge. The developing roller 22 is arranged at the developing opening portion and is able to be brought into contact with the photoconductor drum 1.

[0386] like Figure 22 As shown in FIG. 1 , the developing roller 22 is a roller formed by, for example, sequentially laminating a base layer 222 made of silicon and a surface layer 223 made of urethane on a metal core 221. The developing roller 22 is arranged to be driven to rotate in the direction indicated by arrow R4 in the figure by the driving force of a developing roller driving device 130 (driving source) serving as a developing roller driver.

[0387] In the third embodiment, a predetermined DC voltage (development voltage Vdc) is applied to the developing roller 22 by the developing voltage source 140, and the colorant negatively charged by friction charging visualizes the electrostatic latent image in the developing portion in contact with the photoconductor drum 1 to form a colorant image.

[0388] The supply roller 26 is composed of a metal core electrode 261 having an outer diameter of 5.5 (mm) as a conductive support member and a urethane foam layer 262 provided around the metal core electrode 261. The outer diameter of the entire supply roller 26, including the urethane foam layer 262, is 11 (mm). The amount of intrusion of the developing roller 22 into the supply roller 26 is 1.2 mm. The supply roller 26 rotates in a direction in which the developing roller 22 has opposite speeds in the contact portion with the developing roller 22 (in the direction indicated by arrow R5 in the figure). The particle pressure of the toner T present around the urethane foam layer 262 is applied to the urethane foam layer 262. As the supply roller 26 rotates, the toner T is further drawn into the urethane foam layer 262. A predetermined DC voltage (supply voltage Vrs) is applied to the supply roller 26 by the supply voltage source 136. By controlling the potential difference (supply roller contrast ΔVrs=Vrs−Vdc) from the voltage (development voltage Vdc) to be applied to the developing roller 22 , the toner supply amount and the preliminary triboelectric charge amount are controlled.

[0389] In the third embodiment, a supply voltage Vrs=-500 V is applied to the supply roller 26 from the supply voltage source 136, and a development voltage Vdc=-300 V is applied to the development roller 22 from the development voltage source 140. Therefore, the control section 200 controls the supply voltage source 136 and the development voltage source 131 so that the supply roller 26 has a potential difference of -200 V with respect to the development roller 22, thereby stabilizing the toner supply amount and the preliminary triboelectric charge amount.

[0390] In the following description, regarding the potential and the applied voltage, the potential is high when the absolute value is larger toward the negative polarity side (for example, -1000 V compared to -500 V), and the potential is low when the absolute value is smaller toward the negative polarity side (for example, -300 V compared to -500 V). This is because toner having negative chargeability is considered as a reference in this embodiment.

[0391] The voltage in this embodiment is expressed as a potential difference from the ground potential (0 V). Therefore, the development voltage Vdc = -300 V is interpreted as providing a potential difference of -300 V relative to the ground potential by the development voltage applied to the metal core of the development roller 22. This also applies to the charging voltage, transfer voltage, etc.

[0392] like Figure 22 As shown, the developing blade 23 contacts the developing roller 22 so as to face in opposite directions, and regulates the toner coating amount and applies electric charges.

[0393] In the third embodiment, a support member of a leaf spring-shaped SUS plate having a thickness of 50 to 120 μm is used as the developing blade 23 as the toner regulating member, and the surface of the blade portion is brought into contact with the developing roller 22 by utilizing the spring elasticity of the support member. Figure 23 As shown, the surface of the scraper portion is in contact. When the center of the cross section of the developing roller 22 is assumed to be the zero point and the XY coordinate axis is as shown Figure 23 When the diagram is set, the contact position defined as the XY coordinate (x, y) in this embodiment is x = 3.86 mm and y = -0.60 mm. The scraper portion of the developing scraper 23 is constructed so that in the lateral direction, the scraper portion is formed at one end, and the other end is fixed to the developing frame 24 and supported. On the other hand, the scraper portion is formed by coating the surface of the supporting member with a conductive film made of a urethane resin. In addition, a predetermined DC voltage (developing scraper voltage Vb) is applied to the developing scraper 23 from the developing scraper voltage source 133 to control the potential difference (developing scraper contrast ΔVb = Vb-Vdc) relative to the voltage (developing voltage Vdc) to be applied to the developing roller 22. Therefore, the colorant charge amount and the colorant coating amount are controlled.

[0394] In the third embodiment, a developing blade voltage Vb=-500 V is applied to the developing blade 23, and a developing voltage Vdc=-300 V is applied to the developing roller 22. A potential difference of -200 V relative to the developing roller 22 (developing blade contrast) is set for the developing blade 23 to stabilize the toner charge amount and the toner coating amount.

[0395] The toner layer formed on the developing roller 22 by the developing blade 23 is transported to the developing portion in contact with the photoconductor drum 1 and is subjected to reverse development in the developing portion. Figure 24 At the contact position A shown, the amount of intrusion of the developing roller 22 into the photoconductor drum 1 is set to 40 μm by a roller (not shown) at the end portion of the developing roller 22. The surface of the developing roller 22 is deformed by being pressed against the photoconductor drum 1, thereby forming a developing clamping portion, and development can be performed in a stable contact state. In this embodiment, the pressing force of the developing roller 22 on the photoconductor drum 1 is 200 gf. The width of the developing portion (hereinafter referred to as the developing clamping portion) which is the contact portion between the developing roller 22 and the photoconductor drum 1 is such that the width in the rotation direction of the photoconductor drum 1 is 2.0 mm, and the width in the longitudinal direction of the photoconductor drum 1 is 220 mm.

[0396] The toner in the third embodiment is a negatively chargeable non-magnetic toner produced by suspension polymerization. The toner has a volume average particle size of 7.0 μm. The toner is negatively charged when carried on the developing roller 22. The volume average particle size of the toner is measured using a laser diffraction particle size analyzer LS230 manufactured by Beckman Coulter, Inc., as described later.

[0397] 4. Initial transfer

[0398] The primary transfer step described in the image forming process section will be described in detail.

[0399] First, the surface of the photoconductor drum 1 is uniformly charged to a predetermined charge potential Vd by the charging roller 2. Subsequently, the charged surface of the photoconductor drum 1 is scanned and exposed by a laser beam emitted from the scanner unit 3, based on the output power calculated by the CPU 155 based on image information input from the host device. As a result, an electrostatic image based on the image information is formed on the photoconductor drum 1. At this time, an exposure potential V1 is formed, which is the potential for forming the electrostatic image. The electrostatic image formed on the photoconductor drum 1 is then developed into a toner image by the potential difference between the development voltage Vdc and the exposure potential V1 (development contrast ΔVcont = V1 - Vdc). A primary transfer voltage Vtr (a predetermined DC voltage of opposite polarity to the normal charge polarity of the toner) is then applied to the primary transfer roller 14 from a primary transfer voltage source 160 (high voltage power supply), serving as a primary transfer voltage applying device. At this time, the potential difference between Vtr and V1 (primary transfer contrast ΔVtr=Vtr− V1 ) becomes the primary transfer electric field, and the toner image on the photoconductor drum 1 is primarily transferred to the intermediate transfer belt 10 .

[0400] In the third embodiment, the voltage settings during the image forming operation are such that the charging potential Vd=-500V, the developing voltage Vdc=-300V, the post-exposure potential V1=-100V, and the primary transfer voltage Vtr=200V.

[0401] The surface potential of the photoconductor drum 1 was measured using a surface electrometer Model 344 manufactured by TREK, Inc.

[0402] 3. Features and Operation Effects

[0403] Next, the features of the third embodiment will be described below. When the adhesion between the transfer carrier particles and the toner is Ft and the adhesion between the transfer carrier particles and the photoconductor drum 1 is Fdr, Ft<Fdr is satisfied. The amount of transfer carrier particles supplied to the photoconductor drum 1 based on the above relationship is controlled as follows. Between at least two process cartridges in the process cartridge, the supply amount of transfer carrier particles in the process cartridge located downstream in the process cartridge is increased compared to the supply amount of transfer carrier particles in the process cartridge located upstream in the conveying direction of the intermediate transfer belt 10. In the third embodiment, during the preparatory operation accompanying the start-up of the imaging device 100, the contact time between the developing roller 22 and the photoconductor drum 1 is changed for each process cartridge. The operation of supplying transfer carrier particles to the surface of the photoconductor drum 1 is referred to as a transfer carrier particle supply operation.

[0404] As the number of transfer carrier particles coating the photoconductor drum 1 increases, the number of toner particles in direct contact with the drum 1 decreases, thereby improving primary transfer performance. In particular, to improve primary transfer efficiency for multi-color, high-resolution printing, a large number of transfer carrier particles can adhere to the drum 1. By using the developer of the third embodiment, the majority of the transfer carrier particles remain substantially on the drum 1 due to the relationship Ft < Fdr during the primary transfer step. However, when a larger number of transfer carrier particles adhere to the surface of the drum 1, the destination of the transfer carrier particles is determined not by their attachment relationship to the drum 1 but rather by the attachment between the transfer carrier particles. In other words, for some transfer carrier particles, the relationship between Ft and Fdr clearly becomes Ft ≥ Fdr, and the transfer carrier particles can be transferred, either primarily or secondary, to the recording medium P along with the toner. This relationship can be Ft ≥ Fdr when the toner base between protruding portions containing the organosilicon polymer having the partial structure represented by Formula 1 contacts the transfer carrier particles. As a result, some transfer carrier particles are primarily transferred and secondarily transferred together with the toner, and then transferred to the recording medium P. In particular, when the amount of transfer carrier particles on the photoconductor drum 1 is large, the chance of contact with the toner base increases, and thus a larger amount of transfer carrier particles is transferred to the recording medium P. As a result, when fixing high-resolution multi-color toner on a recording medium, there is an inconvenience in that the transfer carrier particles hinder the transfer of heat to the toner and reduce the fixability.

[0405] In the third embodiment, among the plurality of process cartridges, the amount of transfer carrier particles supplied to the photoconductor drum 1 (i.e., the amount of attachment) is increased in the process cartridges located downstream of the process cartridges compared to the process cartridges located upstream of the process cartridges in the conveying direction of the intermediate transfer belt 10. Therefore, by reducing the amount of transfer carrier particles transferred to the recording medium P, the effect on fixability can be reduced, and the primary transferability required for each process cartridge can be met. Since the downstream process cartridge transfers the toner to the toner layer on the intermediate transfer belt 10 printed in the upstream process cartridge, it is difficult for the downstream process cartridge to transfer the toner compared to the upstream process cartridge. Therefore, the downstream process cartridge requires more transfer carrier particles to improve the primary transferability. When the transfer carrier particles are supplied according to the required transferability, both primary transferability and fixability are achieved.

[0406] In the third embodiment, in order to achieve the surface state of the photoconductor drum 1, the following control is performed. During the pre-rotation operation (i.e., during the preparation operation at the start of the image forming apparatus 100), the contact time of the developing roller 22 with the photoconductor drum 1 in the downstream process cartridge in the conveying direction of the intermediate transfer belt 10 is set to be longer than that in the upstream process cartridge. Figure 19 Describe the details.

[0407] Figure 19 1 is a timing chart of the rotation and development contact of the developing roller 22 of each process cartridge during the preparatory operation accompanying the start-up of the image forming apparatus 100, and the contact time of the developing roller 22 is represented by Tb.

[0408] First, the general configuration of a process cartridge will be described. In any process cartridge, rotation of the developing roller 22 begins after the imaging apparatus 100 is activated. During the acceleration period, the rotational speeds of the motors of the photoconductor drum driver 110 and the developing roller driver 130 are unstable. Therefore, after the rotation of the motors and the developing roller 22 stabilizes, the developing roller 22 is brought into contact with the photoconductor drum 1. During the development contact time Tb, the toner layer on the developing roller 22 is stabilized. Thereafter, the developing roller 22 separates from the photoconductor drum 1, and rotation of the developing roller 22 ends.

[0409] Regarding the contact time Tb of the developing roller 22, the contact time of the developing roller 22 of Sd is set to be longer than the contact time of any of the developing rollers 22 of Sa, Sb, and Sc. Therefore, the attachment area (attachment amount) of the transfer carrier particles on the photoconductor drum 1 on the downstream side can be increased compared to the upstream side in the conveying direction of the intermediate transfer belt 10. The transfer carrier particle supply time can be set to the time for the photoconductor drum 1 to rotate one or more turns. In this embodiment, the transfer carrier particles are supplied by bringing the developing roller 22 into contact with the photoconductor drum 1 for Tb = 500 ms (the photoconductor drum 1 rotates one or more turns) in Sa, Sb, and Sc and by bringing the developing roller 22 into contact with the photoconductor drum 1 for Tb = 1000 ms (the photoconductor drum 1 rotates two or more turns) in Sd.

[0410] In the third embodiment, during the pre-rotation operation of the image forming apparatus 100 (i.e., the transfer carrier particle supply time), the surface potential of the photoconductor drum 1 is adjusted so that the toner charged with the normal charge polarity is not developed during the development contact time Tb. The surface potential of the photoconductor drum 1 during the transfer carrier particle supply operation is set to a non-image forming potential Vd = -500 V, and the development voltage Vdc applied to the developing roller 22 is set to -300 V. Therefore, during the transfer carrier particle supply operation of this embodiment, the toner is not developed on the photoconductor drum 1 from the developing roller 22, and only the transfer carrier particles are supplied from the developing roller 22 to the photoconductor drum 1.

[0411] In the third embodiment, in the case where the state in which the transfer carrier particles are attached to the entire surface of the photoconductor drum 1 is 100%, the attachment area ratio is set as follows. By the transfer carrier particle supply operation, the attachment area ratio of the transfer carrier particles on the photoconductor drum 1 in each of Sa, Sb, and Sc is controlled to be 15% to 25%, and the attachment area ratio in Sd is controlled to be approximately 45%.

[0412] The above describes the attachment area ratio of the transfer carrier particles on the photoconductor drum 1. Here, it is desired that the transfer carrier particles are substantially uniformly attached to the photoconductor drum 1. Even if the attachment area ratio of the transfer carrier particles falls within the above range, for example, when the transfer carrier particles are partially attached, some parts do not satisfy the desired primary transferability, so the attachment state needs to be substantially uniform. In this embodiment, the Clark and Evans Index (CEI) is used as a numerical value of the attachment state for evaluation. In this embodiment, the Clark and Evans Index falls within the range of 0.80 to 1.30 in any station.

[0413] When the CEI is less than 1, the distribution is leptokurtic (high degree of polymerization). When the CEI is equal to 1, the distribution is Poisson (random distribution). When the CEI is greater than 1, the distribution is regular (distributed at regular intervals). The extreme value of the CEI is about 2.1.

[0414] The Clark and Evans index is preferably greater than or equal to 0.60 in order to satisfy desired primary transferability at any point on the photoconductor drum 1. When the Clark and Evans index is less than or equal to this value, it is a partially adhered state, and the primary transferability is partially reduced.

[0415] The adhesion area ratio, adhesion status (Clark and Evans index), a method of measuring adhesion, and verification results of adhesion will be described later.

[0416] 4. Methods for measuring and verifying multiple parameters

[0417] Next, methods of measuring and verifying parameters will be described.

[0418] (1) Adhesion area ratio of transfer carrier particles on photoconductor drum 1

[0419] The surface of the photoconductor drum 1 was observed with a microscope, and the coverage of the surface of the photoconductor drum 1 by the transfer carrier particles was calculated. Specifically, the surface of the photoconductor drum 1 was observed with a laser microscope (VK-X200, Keyence Corporation) at a magnification of 3000 times. The image to be observed was binarized at a contrast that was clearly different between a portion of the transfer carrier particles and another portion, and the total area ratio of the transfer carrier particles to the surface of the photoconductor drum 1 was calculated as the coverage of the surface of the photoconductor drum 1 by the transfer carrier particles.

[0420] (2) Adhesion state of transfer carrier particles on the photoconductor drum 1 (Clark and Evans index)

[0421] The surface of the photoconductor drum 1 is observed with a microscope, and the adhesion state of the transfer carrier particles on the surface of the photoconductor drum 1 (Clark and Evans index) is calculated. Specifically, as in the case of (1), the surface of the photoconductor drum 1 is observed with a laser microscope (VK-X200 Keyence Corporation) at a magnification of 3000 times. The image to be observed is binarized at a contrast such that there is a clear difference between a portion of the transfer carrier particles and another portion. The coordinates of each particle in the binarized image are calculated, and then the average value r of the shortest distance between the center of mass of all particles is calculated. When the expected value of the shortest distance between the center of mass of particles whose distribution is a Poisson distribution is E(r), the Clark and Evans index (CEI) is defined as CEI=r / E(r), and this value is calculated as the Clark and Evans index.

[0422] 5. Effect confirmation test

[0423] In order to confirm the effects of the third embodiment, the primary transfer properties and fixing properties of the configuration of the third embodiment and the configuration of Comparative Example 2 were verified under the following conditions. An HP Color LaserJet Pro M452dw (product name of HP, Inc.) was used as the image forming apparatus 100, and a CS-680 (product name of Canon Marketing Japan, Inc.) was used as the recording medium P.

[0424] Verification of primary transferability was performed while removing the cleaning blade of the process cartridge included with the HP Color LaserJet Pro M452dw. This was evaluated based on whether or not an image defect occurred in which the primary transfer residual toner was not sufficiently collected when passing through the developing roller 22 and appeared as a ghost image after one rotation of the photoconductor drum 1 (hereinafter referred to as a "cleanerless ghost"). Verification of fixability was evaluated based on whether or not an image defect occurred in which the toner was not completely fixed to the recording medium P and was offset (hereinafter referred to as a "cold offset"). To simplify verification in each case, evaluation was performed using a solid black image of the secondary color using the cyan (Sc) station and the black (Sd) station.

[0425] As described above, the third embodiment is configured such that the transfer carrier particles of the process cartridge Sc located relatively upstream in the conveying direction of the intermediate transfer belt 10 have a 20% adhesion area ratio on the photoconductor drum 1. The transfer carrier particles of the downstream process cartridge Sd have a 45% adhesion area ratio on the photoconductor drum 1.

[0426] On the other hand, Comparative Example 2 was configured such that the attachment area ratio of the transfer carrier particles of the upstream process cartridge Sc on the photoconductor drum 1 was 45%, and the attachment area ratio of the transfer carrier particles of the downstream process cartridge Sd on the photoconductor drum 1 was 20%. In Comparative Example 3, the attachment area ratio of the transfer carrier particles of each of Sc and Sd on the photoconductor drum 1 was 45%.

[0427] Table 2 shows whether there is cleanerless ghosting (primary transfer property) and whether there is cold offset (fixability) in each of the third embodiment and comparative example 2. In the table, OK indicates the absence of image defects, and NG indicates the presence of image defects.

[0428] Table 2

[0429] Sc Sd Primary transferability Y of Sc station Primary transferability Y of Sd station Fixability Y Third embodiment 20％ 45％ OK OK OK Comparative Example 2 45％ 20％ OK NG OK Comparative Example 3 45％ 45％ OK OK NG

[0430] As shown in Table 2, in the third embodiment, the adhesion area ratio of the transfer carrier particles of the downstream process cartridge Sd on the photoconductor drum 1 is set higher than the adhesion area ratio of the transfer carrier particles of the upstream process cartridge Sc in the transport direction of the intermediate transfer belt 10. The upstream process cartridge Sc only needs to be able to perform the primary transfer of a 100% cyan print volume. Therefore, even when the adhesion area ratio is lower than that of the downstream process cartridge, cleanerless ghosting does not occur, and primary transfer performance is good. On the other hand, the downstream process cartridge Sd needs to transfer black toner onto the solid cyan image already formed on the intermediate transfer belt 10. To this end, the adhesion area ratio of the downstream process cartridge is set higher than that of the upstream process cartridge Sc. Therefore, as in the case of Sc, cleanerless ghosting does not occur, and primary transfer performance is good. Furthermore, with respect to fixability, the third embodiment has a structure that suppresses the transfer of transfer carrier particles, thus preventing cold offset.

[0431] On the other hand, in the configuration of Comparative Example 2, the adhesion area ratio of the transfer carrier particles of the downstream Sd on the photoconductor drum 1 in the transport direction of the intermediate transfer belt 10 is set to be lower than the adhesion area ratio of the transfer carrier particles of the upstream Sc on the photoconductor drum 1. First, with regard to fixability, the total adhesion amount is similar to that of the third embodiment, and therefore, no cold offset occurs. Sc, which has a high adhesion area ratio of the transfer carrier particles, has an adhesion area ratio higher than that of the third embodiment, and therefore does not produce cleanerless ghosting, and the primary transfer performance is good. However, Sd, which has a lower adhesion area ratio than that of the third embodiment, does not exhibit sufficient primary transfer performance, and cleanerless ghosting occurs.

[0432] In the configuration of Comparative Example 3, the adhesion area ratio of the transfer carrier particles on the photoconductor drum 1 in the upstream Sc and downstream Sd directions of transport of the intermediate transfer belt 10 were identical. Furthermore, both adhesion area ratios were set at 45%, suggesting that this configuration improves transferability. The results in Table 2 show that Comparative Example 3 had no issues with transferability, but exhibited cold offset in terms of fixability. This is presumably because transfer carrier particles exceeding the permissible amount were transferred to the recording medium P, hindering fixation.

[0433] The third embodiment has the following configuration.

[0434] The yellow station, which serves as the first imaging unit, includes a rotatable first photoconductor drum 1a and a rotatable first developing roller 22a that carries a first developer composed of first toner particles and carrier particles attached to the surfaces of the first toner particles. The developing roller 22a contacts the first photoconductor drum 1a to form a first developing portion, and supplies the first developer to form a first developer image on the surface of the first photoconductor drum 1a in the first developing portion.

[0435] The magenta station, serving as the second imaging unit, includes a rotatable second photoconductor drum 1b and a rotatable second developing roller 22b that carries a second developer composed of second toner particles and carrier particles attached to the surfaces of the second toner particles. The developing roller 22b contacts the second photoconductor drum 1b to form a second developing portion, and supplies the second developer to form a second developer image on the surface of the second photoconductor drum 1b in the second developing portion.

[0436] An intermediate transfer belt 10 is provided. The intermediate transfer belt 10 contacts the first photoconductor drum 1a to form a primary transfer portion as a first contact portion, and contacts the second photoconductor drum 1b to form a primary transfer portion as a second contact portion. In the intermediate transfer belt 10, the first developer image is transferred in the first contact portion, and the second developer image is transferred in the second contact portion.

[0437] A second transfer roller 15 is provided. The second transfer roller 15 contacts the intermediate transfer belt 10 to form a secondary transfer portion, and transfers the first and second developer images formed on the surface of the intermediate transfer belt 10 to a recording medium in the secondary transfer portion.

[0438] While the first photoconductor drum 1a is rotating, carrier particles carried on the surface of the first developing roller 22a can be supplied to the surface of the first photoconductor drum 1a in the first developing section. While the second photoconductor drum 1b is rotating, carrier particles carried on the surface of the second developing roller 22b can be supplied to the surface of the second photoconductor drum 1b in the second developing section.

[0439] The surface of the intermediate transfer belt 10 is movable, and the first and second image forming units are arranged so that a first contact portion is formed downstream of the secondary transfer portion and upstream of the second contact portion in the moving direction of the intermediate transfer belt 10 .

[0440] The pressing force of the developing roller 22 against the photoconductor drum 1 is defined as F, and the total number of carrier particles interposed between the toner particles and the photoconductor drum 1 is defined as N.

[0441] The adhesion force between the carrier particles and the toner particles measured when the carrier particles are pressed against the toner particles at F / N (pressing force per unit carrier particle) is defined as Ft. The adhesion force between the carrier particles and the photoconductor drum 1 measured when the carrier particles are pressed against the photoconductor drum 1 at F / N is defined as Fdr. Ft and Fdr in this embodiment satisfy Ft≤Fdr.

[0442] After the photoconductor drum 1 rotates in a state where the photoconductor drum 1 and the developing roller 22 respectively contact each other, the attachment area of ​​the carrier particles attached to the surface of the second photoconductor drum 1b is larger than that of the first photoconductor drum 1a.

[0443] In addition, after the photoconductor drum 1 rotates in a state in which the photoconductor drum 1 and the developing roller 22 are respectively in contact with each other, the distribution state of the carrier particles is uniform, and the Clark and Evans index is greater than or equal to 0.6.

[0444] Therefore, as described above, with the configuration of the third embodiment, while a sufficient amount of fine particles are supplied to the surface of the photoconductor drum 1 to improve transfer efficiency, hindrance of fixing by the fine particles is suppressed.

[0445] In the third embodiment, during the preparatory operation accompanying the activation of the imaging apparatus, the contact time of the developing roller 22 with the photoconductor drum 1 is set to be longer on the downstream side in the conveyance direction of the intermediate transfer belt 10 than on the upstream side; however, this configuration is not limited to this embodiment. Specifically, the development contact time can be controlled not only during 1) the preparatory operation accompanying the activation of the imaging apparatus of this embodiment (pre-rotation operation); 2) during the rotation operation before image formation during printing operation; and 3) during the rotation operation after image formation during printing operation (post-rotation operation). Alternatively, the development contact time can be controlled during all of 1), 2), and 3), or during a combination of any two of 1), 2), and 3).

[0446] For example, Figure 25 3) is a timing diagram of rotation and development contact in the case of controlling the development contact time during the rotation operation after image formation in the printing operation. Specifically, Figure 25 It is a timing diagram of the rotation and development contact of the developing roller 22 of the Sc station and the Sd station in the printing operation. In any station, the developing roller 22 starts to rotate after a certain time from when the print signal is received. The development contact starts after the rotation of the motor becomes stable, and the colorant layer on the developing roller 22 is stable by the time imaging starts (Tb1). Thereafter, imaging starts, and imaging ends (Ti). The state of the toner layer on the developing roller 22 after imaging (i.e., the amount of charge and the amount of coating) depends on the image pattern, so the developing roller 22 rotates for a certain time even after the imaging ends to return the state of the toner layer to a uniform state (Ta). The adhesion state of the transfer carrier particles on the photoconductor drum 1 is controlled by changing the time of the rotation operation after imaging. In Figure 25In the embodiment, Ta of Sc is set to 500 ms (the photoconductor drum 1 rotates one or more times), and Ta of Sd is set to 1000 ms (the photoconductor drum 1 rotates two or more times). Therefore, in the conveying direction of the intermediate transfer belt 10, the amount of transfer carrier particles on the photoconductor drum 1 is greater on the downstream side than on the upstream side. In this way, an operational effect similar to that of the third embodiment is obtained.

[0447] In the third embodiment, the attachment area ratio of the transfer carrier particles in Sd is increased compared to Sa, Sb, and Sc; however, the configuration is not limited to that of this embodiment. Depending on the transferability of each individual color toner, the relationship (attachment area ratio of the transfer carrier particles in the upstream process cartridge) < (attachment area ratio of the transfer carrier particles in the downstream process cartridge) need only be satisfied between at least two process cartridges from Sa to Sd. The attachment area ratio of the transfer carrier particles may gradually increase from upstream to downstream, or may be set such that Sa < Sb < Sc < Sd.

[0448] With respect to the configuration of the fourth embodiment, the same reference numerals are assigned to the components and portions common to those of the third embodiment, and description will not be repeated.

[0449] In the fourth embodiment, the amount of transfer carrier particles attached to the toner is varied between stations. The following describes in detail the manner in which transfer carrier particles are supplied by varying the amount of transfer carrier particles attached to the toner between stations, which is one of the characteristics of the fourth embodiment, and also describes in detail the specific operational effects of the fourth embodiment.

[0450] 1. Features and Operation Effects

[0451] The characteristics and operational effects of the fourth embodiment are the following three points.

[0452] The first characteristic is that, as in the third embodiment, the transfer carrier particles are supplied to the surface of the photoconductor drum 1 according to the relationship Ft < Fdr, where the adhesion force between the transfer carrier particles and the toner is Ft, and the adhesion force between the transfer carrier particles and the photoconductor drum 1 is Fdr. With this configuration, the transfer carrier particles can be placed between the surface of the photoconductor drum 1 and the toner, and toner adhesion is reduced by preventing the toner from contacting the photoconductor drum 1. As a result, the primary transfer performance in the primary transfer step is improved.

[0453] The second feature is to adjust the supply amount (attachment amount) of transfer carrier particles so that, in the conveying direction of the intermediate transfer belt 10, the supply amount is greater in downstream stations than in upstream stations. In downstream stations, where higher primary transfer performance is required, primary transfer performance is improved by supplying a larger amount of transfer carrier particles than in upstream stations. On the other hand, in upstream stations, where such high primary transfer performance is not required, the supply amount of transfer carrier particles is reduced. As a result, the total amount of transfer carrier particles in the toner on the recording medium P can be minimized, resulting in an operational effect that reduces the impact on fixability.

[0454] The above two features and their operational effects are similar to those of the third embodiment, and thus detailed description is omitted.

[0455] The third feature is a method of varying the amount of transfer carrier particles supplied between stations to vary the amount of transfer carrier particles attached to the toner between stations. In the third embodiment, the amount of transfer carrier particles added is adjusted so that the number of transfer carrier particles coated on the toner particles is approximately 500, regardless of the station. In the fourth embodiment, as shown in Table 3, the amount of transfer carrier particles added to each toner particle is adjusted station by station, so that the amount added in station Sa is approximately 300, the amount added in station Sb is approximately 400, the amount added in station Sc is approximately 500, and the amount added in station Sd is approximately 600. At this time, as described in the first embodiment, the area where the transfer carrier particles are interposed between the toner particles and the photoconductor drum 1 in the developer nip portion is approximately 1.43% of the entire toner particle surface. Therefore, the total number M of transfer carrier particles interposed between the toner and the photoconductor drum 1 for each toner particle is also shown in Table 3. Therefore, the supply amount of transfer carrier particles to the photoconductor drum 1 is increased in the downstream station compared with the upstream station in the conveying direction of the intermediate transfer belt 10 .

[0456] In the fourth embodiment, the timing of performing the transfer carrier particle feeding operation is as follows: Figure 26 The developer contact time during the printing operation is shown and is common between the stations.

[0457] The operational effect regarding the third feature of the fourth embodiment will be described.

[0458] In the fourth embodiment, the amount of transfer carrier particles supplied to the photoconductor drum 1 is increased at downstream stations compared to upstream stations in the conveyance direction of the intermediate transfer belt 10, without changing the timing of supplying transfer carrier particles between stations. Therefore, the time required for the transfer carrier particle supply operation during a single printing operation can be minimized. As a result, the time required for a single printing operation is reduced, thereby improving productivity.

[0459] Table 3

[0460]

[0461] As described above, while a sufficient amount of fine particles is supplied to the surface of the photoconductor drum 1 to improve transfer efficiency, hindrance of fixing by the fine particles is suppressed.

[0462] In the third and fourth embodiments, no peripheral speed difference is provided during the rotation between the developer roller 22 and the photoconductor drum 1 during contact; however, the configuration is not limited to these embodiments. A peripheral speed difference may be provided during the rotation of the developer roller 22 relative to the rotation of the photoconductor drum 1. This peripheral speed difference serves to stabilize the amount of toner to be developed and to make minor unevenness in the coating on the developer roller 22 less visible on the photoconductor drum 1. This embodiment has the following operation for supplying transfer carrier particles.

[0463] Figure 17A Schematic diagram showing the behavior of toner and transfer carrier particles in the development nip portion when the development roller 22 and the photoconductor drum 1 are set in a non-image forming potential relationship. Figure 17A As shown, due to the circumferential speed difference between the developing roller 22 and the photoconductor drum 1, the following phenomenon occurs. The force parallel to the rotation direction of the developing roller 22 is defined as f1, wherein the toner between the developing roller 22 and the photoconductor drum 1 receives the force from the developing roller 22. The force parallel to the rotation direction of the photoconductor drum 1 is defined as f2, wherein the toner between the developing roller 22 and the photoconductor drum 1 receives the force from the photoconductor drum 1. Under the conditions described in the third and fourth embodiments, f1 and f2 are balanced with each other; however, when a circumferential speed difference is provided in the construction of the third and fourth embodiments, f1 and f2 are unbalanced with each other, and the toner rolls in the developing clamping portion. When the toner rolls, the transfer carrier particles on the toner that are not in contact with the photoconductor drum 1 also move as the toner rolls. For this reason, the transfer carrier particles can come into contact with the photoconductor drum 1, thereby increasing the chance of supplying the transfer carrier particles from the toner to the surface of the photoconductor drum 1. Therefore, as Figure 17B As shown, after passing through the development nip, transfer carrier particles greater in number than those of the third and fourth embodiments can be supplied from the toner on the developing roller 22 to the surface of the photoconductor drum 1 .

[0464] Figure 18A 2 is a schematic diagram showing the behavior of toner and transfer carrier particles in the development nip portion when the development roller 22 and the photoconductor drum 1 are set in an image potential relationship. Figure 18A As shown, when the developing roller 22 and the photoconductor drum 1 are also set to an image potential relationship, the following phenomenon occurs due to the peripheral speed difference between the developing roller 22 and the photoconductor drum 1. The toner rolls in the developing nip portion, and the efficiency of supplying transfer carrier particles from the surface of the toner to the surface of the photoconductor drum 1 in the developing nip portion is improved. Figure 18BAs shown, the developing roller 22 and the photoconductor drum 1 are set in an image-forming potential relationship, so that after passing through the developing nip portion, the toner is developed from the developing roller 22 onto the surface of the photoconductor drum 1. Because the efficiency of supplying transfer carrier particles from the surface of the toner to the surface of the photoconductor drum 1 when passing through the developing nip portion is improved, a large number of transfer carrier particles can be placed between the photoconductor drum 1 and the toner developed on the surface of the photoconductor drum 1.

[0465] As described above, in the fourth embodiment, the first driver 110 for driving the photoconductor drum 1, the second driver 130 for driving the developing roller 22, and the control section 200 for controlling the first driver 110 and the second driver 130 are provided. The control section 200 controls the first driver 110 and the second driver 130 so that the surface movement speed of the developing roller 22 in the developing section is different from the surface movement speed of the photoconductor drum 1.

[0466] With respect to the configuration of the fifth embodiment, the same reference numerals are assigned to the same components and parts as those of the third and fourth embodiments, and description will not be repeated.

[0467] In the fifth embodiment, the amount of toner applied to the developing roller 22 after passing through the developing blade 23 is varied between stations while providing a difference in the peripheral speed of the developing roller. The mechanism capable of controlling the supply amount of transfer carrier particles in the fifth embodiment and the operational effects of the fifth embodiment will be described in detail below.

[0468] 1. Features and Operation Effects

[0469] The characteristics and operational effects of the fifth embodiment are the following three points.

[0470] The first characteristic is that, as in the third embodiment, the transfer carrier particles are supplied to the surface of the photoconductor drum 1 according to the relationship Ft < Fdr, where the adhesion force between the transfer carrier particles and the toner is Ft, and the adhesion force between the transfer carrier particles and the photoconductor drum 1 is Fdr. With this configuration, the transfer carrier particles can be placed between the surface of the photoconductor drum 1 and the toner, and toner adhesion is reduced by preventing the toner from contacting the photoconductor drum 1. As a result, the primary transfer performance in the primary transfer step is improved.

[0471] The second feature is to adjust the supply amount (attachment amount) of transfer carrier particles so that, in the conveying direction of the intermediate transfer belt 10, the supply amount is greater in downstream stations than in upstream stations. In downstream stations, where higher primary transfer performance is required, primary transfer performance is improved by supplying a larger amount of transfer carrier particles than in upstream stations. On the other hand, in upstream stations, where such high primary transfer performance is not required, the supply amount of transfer carrier particles is reduced. As a result, the total amount of transfer carrier particles in the toner on the recording medium P can be minimized, resulting in an operational effect that reduces the impact on fixability.

[0472] The above two features and their operational effects are similar to those of the third and fourth embodiments, and thus detailed descriptions are omitted.

[0473] The third feature is to vary the amount of toner on the surface of the developing roller 22 after passing through the developing blade 23 between stations while providing a difference in the peripheral development speed. In the conveyance direction of the intermediate transfer belt 10, the amount of toner on the surface of the developing roller 22 increases in the downstream stations compared to the upstream stations. At this time, in the conveyance direction of the intermediate transfer belt 10, the amount of transfer carrier particles supplied (adhered) increases in the downstream stations compared to the upstream stations.

[0474] As described in the third embodiment, the following phenomenon occurs due to the circumferential speed difference between the developing roller 22 and the photoconductor drum 1. A force parallel to the rotational direction of the developing roller 22 is defined as f1, where the toner between the developing roller 22 and the photoconductor drum 1 receives this force from the developing roller 22. A force parallel to the rotational direction of the photoconductor drum 1 is defined as f2, where the toner between the developing roller 22 and the photoconductor drum 1 receives this force from the photoconductor drum 1. Due to the circumferential speed difference in development, f1 and f2 are unbalanced, and the toner rolls in the developing nip portion. As the toner rolls, transfer carrier particles on the toner that are not in contact with the photoconductor drum 1 move with the rolling of the toner and are able to come into contact with the photoconductor drum 1. Therefore, the chance of transfer carrier particles being supplied from the toner to the photoconductor drum 1 increases. Due to the rolling, the movement of transfer carrier particles on the toner that are not in contact with the photoconductor drum 1 increases with the amount of toner on the developing roller 22. Therefore, the amount of toner on the developing roller 22 is controlled while the toner is rolled by providing a peripheral speed difference between the developing roller 22 and the photoconductor drum 1. As a result, the supply amount of the transfer carrier particles can be controlled.

[0475] In the fifth embodiment, as shown in Table 4, the amounts of toner on the developing roller 22 in Sa-Sd are adjusted to Sa: 0.28, Sb: 0.30, Sc: 0.32, Sd: 0.34 [mg / cm 2The force of controlling the toner by the developing blade 23 is adjusted by changing the contact position between the developing blade 23 and the developing roller 22. Specifically, as shown in Table 4, the contact position is adjusted so that the distal end of the developing blade 23 is located at positions Sa: 0.70, Sb: 0.60, Sc: 0.50, and Sd: 0.40 [mm] away from the center of the developing roller 22, respectively.

[0476] In the fifth embodiment, the developing roller 22 rotates in the developing nip portion in the same direction as the photoconductor drum 1 at a peripheral speed of 140% of the peripheral speed of the photoconductor drum 1. In other words, the moving speed of the surface of the developing roller 22 is 1.4 times the moving speed of the surface of the photoconductor drum 1.

[0477] Table 4

[0478] <![CDATA[Amount of toner on the developing roller [mg / cm 2 > Distal end position of developing blade [mm] Adhesion area ratio [%] Sa 0.28 0.70 15 Sb 0.30 0.60 20 Sc 0.32 0.50 25 Sd 0.34 0.40 30

[0479] In the fifth embodiment, the timing of performing the transfer carrier particle feeding operation is as follows: Figure 14 The development contact time in the printing operation is shown and is common among the stations. In addition, the amount of transfer carrier particles added is adjusted so that the number of transfer carrier particles coated on the toner particles is about 500, regardless of the station.

[0480] Next, the operational effects of the fifth embodiment will be described.

[0481] In the fifth embodiment, while maintaining the timing of transferring carrier particles between stations, the amount of transfer carrier particles supplied to the photoconductor drum 1 can be increased at downstream stations compared to upstream stations in the conveyance direction of the intermediate transfer belt 10. Consequently, the time required to supply the transfer carrier particles during a single printing operation can be minimized. Consequently, the time required for a single printing operation is reduced, thereby improving productivity. Furthermore, the amount of transfer carrier particles added is reduced, thereby reducing the risk of contamination caused by transfer carrier particles migrating to components in the developer unit (e.g., the developer blade 23 and the supply roller 26).

[0482] As described above, while a sufficient amount of fine particles is supplied to the surface of the photoconductor drum to improve transfer efficiency, hindrance of fixing by the fine particles is suppressed.

[0483] In the third, fourth, and fifth embodiments, the case of four colors, yellow (Y), magenta (M), cyan (C), and black (K), has been described; however, the configuration is not limited to these embodiments. For example, four or more stations may also be employed, each including white toner, metallic toner, or the like. In this case, the effect can also be achieved when the relationship (the attachment area ratio of the transfer carrier particles in the upstream process cartridge) < (the attachment area ratio of the transfer carrier particles in the downstream process cartridge) is satisfied between at least two process cartridges.

[0484] In the third, fourth, and fifth embodiments, the features are described using the adhesion area ratio of the transfer carrier particles; however, when the adhesion force Fc between the transfer carrier particles is less than the adhesion force Ft between the toner and the transfer carrier particles (Fc < Ft), the adhesion amount can be used. In other words, the relationship (adhesion amount of transfer carrier particles in the upstream process cartridge) < (adhesion amount of transfer carrier particles in the downstream process cartridge) can be satisfied. In the case of Fc < Ft, the transfer carrier particles are no longer supplied to the transfer carrier particles supplied to the photoconductor drum 1. For this reason, the transfer carrier particles on the photoconductor drum 1 form a single layer, and the magnitude relationship of the adhesion area ratio is synonymous with the magnitude relationship of the adhesion amount.

[0485] Therefore, after the photoconductor drum 1 rotates in a state where the photoconductor drum 1 and the developing roller 22 are respectively in contact with each other, the amount of carrier particles attached to the surface of the second photoconductor drum 1b is greater than that of the first photoconductor drum 1a.

[0486] In the third, fourth, and fifth embodiments, no cleaning member is provided on the photoconductor drum 1; however, the configuration is not limited to these embodiments. A photoconductor drum cleaning member may be provided. When the cleaning member is provided on the photoconductor drum 1, the transfer carrier particles coating the photoconductor drum 1 are collected by the cleaning member with each rotation of the photoconductor drum 1. However, the transfer carrier particles can be supplied simultaneously with development; it is only necessary to control the area (or amount) of attachment of the transfer carrier particles to the photoconductor drum 1 during the period from the start of development to the primary transfer. For example, the circumferential speed difference between the rotation of the developing roller 22 and the rotation of the photoconductor drum 1 is increased in the downstream process cartridge compared to the upstream process cartridge in the transport direction of the intermediate transfer belt 10. As a result, the downstream process cartridge can cause a greater amount of toner to roll than the upstream process cartridge. As a result, the opportunity to supply transfer carrier particles to the downstream photoconductor drum 1 in the transport direction of the intermediate transfer belt 10 is increased compared to the upstream process cartridge, thereby establishing conditions similar to those of the third, fourth, and fifth embodiments and achieving similar operational effects as those of the third, fourth, and fifth embodiments.

[0487] In the third, fourth, and fifth embodiments, the transfer carrier particles are supplied to the photoconductor drum 1 via the toner according to the relationship Ft<Fdr; however, the configuration is not limited to these embodiments. The transfer carrier particle supply member may be provided separately from the developing unit 4. In this case, Fdr and the adhesion force Fs between the transfer carrier particles and the transfer carrier particle supply member may be set to the relationship Fs<Fdr to supply the transfer carrier particles to the photoconductor drum 1. The transfer carrier particle supply member only needs to satisfy the relationship in adhesion. For example, Figure 27 As shown in FIG. 1 , the transfer carrier particles can be supplied to the photoconductor drum 1 using a brush member as a transfer carrier particle supply member. Figure 27 In the process, transfer carrier particles are supplied via a transfer carrier particle supply roller 6. The transfer carrier particle supply roller 6 is a brush roller that plays a role in supplying transfer carrier particles to the photoconductor drum 1 and has a brush layer on its surface. The transfer carrier particle supply roller 6 is driven to rotate in a direction opposite to the rotation direction of the photoconductor drum 1 and is supplied with transfer carrier particles from a transfer carrier particle container that contains transfer carrier particles to the brush. The transfer carrier particles are supplied from the brush to the photoconductor drum 1 at the contact portion between the transfer carrier particle supply roller 6 and the photoconductor drum 1.

[0488] In the third, fourth and fifth embodiments, a SUS plate is used as a support member for the developing blade 23; however, the configuration is not limited to these embodiments. For example, a metal film (such as phosphor bronze and aluminum) can be used. In these embodiments, a film made of a conductive urethane resin is used to coat the surface of the supporting member; however, the configuration is not limited to these embodiments. A film made of a conductive resin made of a polyamide elastomer or urethane rubber can be used to coat the surface of the supporting member. Alternatively, the conductive support member itself can contact the developing roller 22 as the developing blade 23.

[0489] In the third, fourth, and fifth embodiments, the toner charge, toner supply, and toner coating amounts are stabilized by applying a -200V potential difference to the supply roller 26 and the development blade 23 relative to the development roller 22; however, the configuration is not limited to these embodiments. When the toner charge, toner supply, and toner coating amounts are stable regardless of the voltage, applying a potential difference is unnecessary. In this case, by setting the same potential as the development roller 22, the high-voltage power supply can be reduced, thereby reducing the size and cost of the device.

[0490] In the third, fourth, and fifth embodiments, the primary transferability of each station can be controlled by utilizing the attachment state of the transfer carrier particles. Therefore, there is no need to change the primary transfer voltage between stations, and the primary transfer voltage source for applying the primary transfer voltage can be shared by all stations, thereby reducing the size and cost of the device.

[0491] Even when a primary transfer voltage source is individually provided at each station, an optimal primary transfer voltage can be set based on the primary transfer performance required at each station. Consequently, image scattering and retransfer can be reduced in the primary transfer section. Retransfer refers to a phenomenon in which an image formed at an upstream station is transferred to the intermediate transfer belt 10, receives an electrical discharge by passing through the primary transfer section of a downstream station, and is then transferred again to the photoconductor drum 1 at the downstream station.

[0492] Next, a sixth embodiment will be described. The intermediate transfer belt 10 according to the sixth embodiment is stretched by a plurality of stretching members 11, 12, 13 and driven to rotate at a specific circumferential speed difference relative to the photoconductor drum 1a in a direction of circumferential movement in a region opposing and contacting the photoconductor drum 1a. Figure 28 As shown, the intermediate transfer belt 10 has a two-layer structure consisting of a coating layer 10a and a base layer 10b, and has a circumference of 700 mm. The coating layer 10a has a high smoothness by applying a 2 μm thick acrylic resin coating solution to the surface. On the other hand, the base layer 10b is made of a material containing polyester as a main component and has a thickness of 100 μm. The film thickness of the coating layer 10a is smaller than that of the base layer 10b, so the influence on the resistance value of the intermediate transfer belt 10 is small; however, if necessary, the resistance can be adjusted by adding a conductive agent (such as carbon black). From the perspective of smoothness and production, the thickness of the coating layer 10a is preferably within the range of 0.5 to 4.0 μm.

[0493] The resin material used for the coating layer 10a is not particularly limited and may be, for example, a material such as polyester, polyether, polycarbonate, polyallylate, urethane, silicone, or fluororesin. The material of the base layer 10b may be any other material as long as it is a thermoplastic resin. For example, a material such as polyimide, polycarbonate, polyallylate, acrylonitrile butadiene styrene copolymer (ABS), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVdF), or a mixed resin of some of these resins.

[0494] The yellow toner image formed on the photoconductor drum 1a is electrostatically transferred to the intermediate transfer belt 10 via the intermediate transfer belt 10 serving as an intermediate transfer member during the primary transfer portion as a contact portion between the primary transfer roller 14a and the photoconductor drum 1a. During the image forming operation, a DC voltage of 500 V is applied from the primary transfer voltage source 160 to the primary transfer roller 14a serving as the primary transfer member. Figure 29 As shown, the primary transfer residual toner remaining on the surface of the photoconductor drum 1 a is cleaned and removed by the cleaning unit 55 a and is subjected to processing after charging in the image forming process.

[0495] Similarly, a second magenta toner image, a third cyan toner image, and a fourth black toner image are formed by the second, third, and fourth imaging stations b, c, and d, respectively. The yellow toner image, the magenta toner image, the cyan toner image, and the black toner image are sequentially transferred in layers to the intermediate transfer belt 10. Thus, a combined color image corresponding to the desired color image is obtained.

[0496] Subsequently, the four-color toner image on the intermediate transfer belt 10, as described above, is transferred simultaneously to the surface of a recording medium P fed by a sheet feeding device 50, while passing through a secondary transfer nip formed by the intermediate transfer belt 10 and a secondary transfer roller 15 serving as a secondary transfer member (secondary transfer). The secondary transfer roller 15 contacts the intermediate transfer belt 10 with a pressure of 5 kgf to form a secondary transfer nip in the secondary transfer portion. The secondary transfer roller 15 rotates as the intermediate transfer belt 10 rotates. When the toner on the intermediate transfer belt 10 is secondary transferred onto a recording medium P (e.g., paper), a voltage of 2500 V is applied to the secondary transfer roller 15 from a secondary transfer voltage source 150. The intermediate transfer belt 10 of the sixth embodiment can reduce the small space from the recording medium P by using the high-smoothness coating 10a, thereby suppressing interference of the electric field in the secondary transfer nip, resulting in improved secondary transfer efficiency.

[0497] Then, the recording medium P bearing the four-color toner image is introduced into the fixing unit 30 and is heated and pressurized. As a result, the four-color toner is melted and mixed and fixed to the recording medium P. The toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the cleaning unit 17.

[0498] Through the above-described operations, a full-color printed image is formed.

[0499] Figure 28 It is an enlarged view of the primary transfer portion in the first image forming station a.

[0500] The primary transfer roller 14a is composed of a metal core 141a with an outer diameter of 6 mm and an elastic member 142a with a thickness of 3 mm and having rubber elasticity. The elastic member 142a is wound around the metal core 141a. In the primary transfer section, the primary transfer roller 14a is arranged opposite to the photoconductor drum 1a via the intermediate transfer belt 10, and the intermediate transfer belt 10 is pressed against the photoconductor drum 1a with 500 gf, thereby clamping the intermediate transfer belt 10 with the photoconductor drum 1a. The intermediate transfer belt 10 is wound around the photoconductor drum 1a to a predetermined length so as to contact the photoconductor drum 1a. The contact area forms a drum clamping portion in the transfer section. At this time, the drum clamping portion width, which is the contact width of the drum clamping portion, is defined as Q.

[0501] The photoconductor drum 1a is driven to rotate at a surface movement speed Vdr as a predetermined circumferential speed. The intermediate transfer belt 10 rotates at a movement speed Vb as a predetermined circumferential speed. In this state, the toner T is sequentially transferred to the intermediate transfer belt 10 within the width of the drum nip. The primary transfer roller 14a rotates together with the intermediate transfer belt 10. The circumferential speed Vdr of the photoconductor drum 1a is the movement speed of the surface of the photoconductor drum 1a. The circumferential speed Vb of the intermediate transfer belt 10 is the movement speed of the surface of the intermediate transfer belt 10. Here, in the configuration of the sixth embodiment, the surface of the intermediate transfer belt 10 is moved by the photoconductor drum driver 110 to provide a surface movement speed difference between the photoconductor drum 1a and the intermediate transfer belt 10. Alternatively, the driver that drives the intermediate transfer belt 10 may be provided separately from the photoconductor drum driver 110, or the intermediate transfer belt 10 may be driven by another driver.

[0502] Next, we will refer to Figure 30 A mechanism for improving the primary transfer efficiency by applying a peripheral speed difference to the drum nip portion is described.

[0503] Figure 30 The drum nip portion is schematically shown, and is a diagram illustrating the behavior of the toner T when a peripheral speed difference is applied between the photoconductor drum 1 a and the intermediate transfer belt 10 .

[0504] In the drum nip portion, the photoconductor drum 1a rotates at a peripheral speed Vdr, and the intermediate transfer belt 10 rotates at a peripheral speed Vb, thereby applying a peripheral speed difference Vdr-Vb. In the sixth embodiment, the relationship between Vdr and Vb is Vdr<Vb, and the primary transfer configuration is such that the peripheral speed Vb of the intermediate transfer belt 10 is higher than the peripheral speed Vdr of the photoconductor drum 1a.

[0505] Each of the lowest-layer toner particles T in the latent image-forming portion attached to the photoconductor drum 1a through the development process has a contact point with the photoconductor drum 1a. Most of the toner particles T, each having a contact point with the photoconductor drum 1a, have a stable contact point with a strong adhesion force. The toner particles T tend to adhere to points with a strong adhesion force that varies depending on the surface profile and surface charge state. Toner particles T attached to points with a strong adhesion force are difficult to transfer, and in order to improve primary transfer efficiency, transfer conditions that exhibit a force greater than or equal to the adhesion force are required.

[0506] First, when a toner particle T enters the drum nip portion, it rotates like a bearing due to the circumferential speed difference, moving from state A to state B. As this movement occurs, the contact point Pt between the toner particle T and the photoconductor drum 1a moves to point Pt'. Therefore, before entering the drum nip portion, the toner particle T separates from the contact point Pt, where it is already in contact with the photoconductor drum 1a and has a relatively high adhesion force. As a result, the adhesion force between the toner particle T and the photoconductor drum 1a decreases. Because the adhered surface of the toner particle T separates from the photoconductor drum 1a at the contact point Pt due to the circumferential speed difference, the magnitude relationship between the circumferential speed Vdr of the photoconductor drum 1a and the circumferential speed Vb of the intermediate transfer belt 10 does not need to conform to the relationship Vdr < Vb, and the effect can be achieved even when the magnitude relationship is reversed.

[0507] As described above, by applying a peripheral speed difference between the photoconductor drum 1a and the intermediate transfer belt 10, the adhesion between the toner T and the photoconductor drum 1a is reduced, and the toner T can be easily peeled off from the photoconductor drum 1a. Therefore, the effect of improving the primary transfer efficiency is exhibited.

[0508] Next, we will describe the range of the peripheral speed difference that achieves improved primary transfer efficiency. First, the relative movement amount between the photoconductor drum 1a and the intermediate transfer belt 10 in the drum nip is defined as the amount of toner T rolling due to the peripheral speed difference. The nip width Q and the peripheral speed difference ratio of the drum nip are set so that the rolling amount falls within a preset range, optimizing the balance between transfer efficiency and image quality degradation.

[0509] Hereinafter, the rolling amount of the toner T, which is a specific parameter defined in the sixth embodiment, will be described.

[0510] The rolling amount of the toner T is the relative movement amount between the photoconductor drum 1 a and the intermediate transfer belt 10 in the drum nip portion due to the peripheral speed difference, and is defined as follows in the present embodiment.

[0511] Rolling amount (R) = circumferential speed difference ratio (Vr) × drum clamping width (Q) (4)

[0512] Peripheral velocity difference ratio (Vr) = |Vdr-Vb| / Vdr×100(5)

[0513] Here, in Expression 4, the peripheral speed difference ratio (peripheral speed ratio or speed ratio) Vr is defined as the percentage of the peripheral speed difference |Vdr-Vb| between the peripheral speed Vdr of the photoconductor drum 1a and the peripheral speed Vb of the intermediate transfer belt 10 to the peripheral speed Vdr.

[0514] Table 5 shows the rolling amount R when the drum nip portion and the peripheral speed difference ratio Vr are changed. As shown in Table 5, the rolling amount R is a parameter that increases as the peripheral speed difference ratio Vr increases or as the drum nip width Q increases.

[0515] Table 5

[0516]

[0517] Figure 31 The present invention shows the measurement results of the residual toner amount remaining on the surface of the photoconductor drum 1 after the primary transfer by changing the peripheral speed difference ratio Vr when the drum clamping portion width Q is 1500μm. The vertical axis in the graph represents the measurement results of the residual toner amount after the primary transfer based on the reflectivity corresponding to the reflection density. A solid image is printed in the M color station, and after the solid image is printed (transferred) in the downstream C color station, the residual toner image after transfer on the surface of the C color photoconductor drum 1c is taped. The reflectivity of the tape-taping result is measured using a reflection densitometer (TC-6DS type, produced by Tokyo Denshoku Co., Ltd.). As a result, it is confirmed that as the peripheral speed difference ratio Vr increases, the amount of residual toner after the primary transfer decreases and the primary transfer efficiency improves. Regarding the effect of improving primary transfer efficiency due to the peripheral velocity difference ratio Vr, this effect begins to appear rapidly at a peripheral velocity difference ratio Vr of approximately 0.75%, and almost no residual toner remains after primary transfer within a peripheral velocity difference ratio Vr range of 2% or higher. This indicates that the effect of the peripheral velocity difference is fully exerted. In the construction of the sixth embodiment, the drum nip width Q is 1500μm. Therefore, the rolling amount (R) of the toner T is 11.25μm at a peripheral velocity difference ratio (Vr) of 0.75%, and the effect of improving primary transfer efficiency begins to appear at a peripheral velocity difference ratio of 0.75%.

[0518] As described above, in the sixth embodiment, toner particles T having a weight-average particle diameter (D) of 7.0 μm are used, and when the toner particles T are assumed to be spherical, the circumference of each toner particle T is 21.98 μm. Here, the rolling amount R, around which the effect of improving the primary transfer efficiency begins to appear, is 11.25 μm. This is the length of an arc approximately half the circumference of each toner particle T. In other words, when the toner particle T rolls approximately half the circumference, the initial contact point of the toner particle T with the photoconductor drum 1a shifts toward the intermediate transfer belt 10, and a sufficient distance from the photoconductor drum 1a is ensured to reduce adhesion, so it can be inferred that the primary transfer efficiency is improved. As can be seen from the above, in the sixth embodiment, the value of half the average circumference calculated based on the weight-average particle diameter of the toner T to be used is set as the lower limit of the rolling amount R.

[0519] Next, the upper limit of the rolling amount R will be described. From the viewpoint of image quality degradation, the upper limit of the rolling amount R is based on the amount of toner movement in the drum nip portion. Figure 30 As shown, when the toner particles T rotate and move a distance L from state A to state B, the relative movement distance between the photoconductor drum 1a and the intermediate transfer belt 10 is L×2 due to the toner particles T moving the distance L. In other words, the toner particles T slide in the drum nip portion by half the circumference of the toner particles T relative to the relative movement distance (i.e., the rolling amount R) between the photoconductor drum 1a and the intermediate transfer belt 10. If the toner particles slide, the height and width of the toner image will change, resulting in a worsened roughness.

[0520] Therefore, corresponding to a size of about 1 Dot of 600 DPI as a resolution of a general image forming apparatus, the allowable range of the sliding amount of the toner T is within a range of about 50 μm, and thus the upper limit of the rolling amount R is 100 μm.

[0521] As can be seen from the above, the range of the rolling amount R that strikes a balance between primary transfer efficiency and image quality degradation is from the length of the arc of half the circumference of the toner particle T to 100 μm. When the toner weight-average particle diameter D, the drum nip width Q, and the peripheral speed difference ratio Vr are used, a configuration that satisfies the range shown in Expression 6 is desirable.

[0522] 1 / 2×D(μm)×π≤Vr(%)×Q(μm) / 100≤100μm (6)

[0523] In the configuration of the sixth embodiment, the drum nip width Q=1500 μm and the peripheral speed difference ratio Vr=2.5% are used.

[0524] In the sixth embodiment, the toner particles are assumed to be spherical; however, the toner particles are not limited to spherical. As long as the toner particles have a shape that allows the toner particles to roll due to the peripheral speed difference, the effect of improving the primary transfer property can be obtained.

[0525] 3. Image blur mechanism

[0526] In the image forming apparatus 100 in which the above-described peripheral speed difference is applied between the photoconductor drum 1 and the intermediate transfer belt 10, rapid fluctuations in the rotation of the photoconductor drum 1 may occur when the toner image formed on the surface of the photoconductor drum 1 is primarily transferred to the intermediate transfer belt 10. It has been found that, due to the fluctuations in the rotation, uneven exposure occurs in laser exposure, followed by the appearance of image streaks in the toner image formed on the surface of the photoconductor drum 1, and this leads to deterioration in the image quality of the final image.

[0527] Hereinafter, reference will be made to an enlarged view showing a primary transfer portion in the first imaging station a. Figure 28To describe the detailed description.

[0528] During the printing operation, the intermediate transfer belt 10 is driven to rotate at a surface peripheral speed that is approximately 2.5% higher than that of the photoconductor drum 1a, which is driven to rotate. This is because, by applying a peripheral speed difference between the photoconductor drum 1a and the intermediate transfer belt 10 as described above, the adhesion between the toner T and the photoconductor drum 1a is reduced, the toner T can be easily peeled off the photoconductor drum 1a, and as a result, the primary transfer efficiency is improved.

[0529] In this case, in the state where there is no toner T in the drum clamping portion, the friction force F acts on the surface of the photoconductor drum 1a from the surface of the intermediate transfer belt 10 toward the downstream side in the tangential direction (sub-scanning direction). When the leading edge of the toner image developed on the surface of the photoconductor drum 1a enters the drum clamping portion, the friction force F decreases sharply (F→F≈0). This is because, when the toner T is supplied to the drum clamping portion, the surface of the photoconductor drum 1a and the surface of the intermediate transfer belt 10 become easy to slide relative to each other. For this reason, spontaneous fluctuations of rotation occur in the photoconductor drum 1a, and as a result, uneven writing occurs in the laser exposure of the surface of the photoconductor drum 1a. This then becomes image stripes in the main scanning direction on the toner image formed on the surface of the photoconductor drum 1a, and the image stripes also appear in the final image.

[0530] Image streaks in the final image on the recording medium P appear on the toner image at a position offset from the front portion of the toner image arranged in the image pattern in the sub-scanning direction toward the downstream side in the sub-scanning direction by the distance between the laser exposure unit and the drum nip (for example, 30 mm in the sixth embodiment). In particular, when a halftone toner image portion susceptible to uneven laser exposure is present at this position, significant image streaks appear.

[0531] As described above, due to intermittent temporary fluctuations in the friction force F according to the image pattern desired by the user, image stripes due to fluctuations in the rotation of the photoconductor drum 1 a appear on the final image.

[0532] As a measure against image streaks, a method is known in which, in addition to the toner image of the image pattern desired by the user, a small dot toner image is additionally formed on the photoconductor drum using toner (e.g., yellow) to reduce fluctuations in the rotation of the photoconductor drum 1a or the intermediate transfer belt 10. It is generally known that various image defects can be prevented; however, the added dot toner image may appear yellowish on the recording medium P and may be noticeable.

[0533] As can be seen from the above, by reducing the friction force F between the photoconductor drum 1a and the intermediate transfer belt 10 in the drum nip portion differently than with the dot toner images, it is possible to reduce image streaks due to fluctuations in the rotation of the photoconductor drum 1 even when the leading edge of the toner image enters the drum nip portion. In addition, color variations on the recording medium P can be reduced.

[0534] (Operation of Sixth Embodiment)

[0535] Next, the operation of the sixth embodiment will be described by using a comparative example.

[0536] In the sixth embodiment, before developing a toner image, fine particles are supplied from the toner carried on the developing roller 41 to the photoconductor drum 1, and the fine particles adhere to the photoconductor drum 1. To this end, the adhesion force Ft between the fine particles and the toner is set to be smaller than the adhesion force Fdr between the fine particles and the photoconductor drum 1. Therefore, by reducing the friction force F between the photoconductor drum 1 and the intermediate transfer belt 10, color variations on the recording medium P can be reduced while also reducing image streaks caused by fluctuations in the rotation of the photoconductor drum 1.

[0537] Hereinafter, description will be made by using the configuration of the first imaging station a.

[0538] First, to explain the effect of coating a certain amount or more of fine particles on the photoconductor drum 1 a according to the sixth embodiment, adhesion Ft between the fine particles and toner and adhesion Fdr between the fine particles and the photoconductor drum 1 a were measured.

[0539] Specifically, the adhesion force is measured using an SPM. Fine particles are fixed to the tip of a lever of a cantilever and the cantilever is pressed against the toner with a predetermined pressing force. The force used to separate the cantilever from the toner is then measured as the adhesion force Ft between the fine particles and the toner.

[0540] The predetermined pressing force used to press the cantilever against the toner when measuring adhesion can be set to the force with which fine particles interposed between the toner and the photoconductor drum 1a in the developer nip are pressed against the toner. The predetermined pressing force is calculated using the following calculation method. Here, the state in which fine particles are interposed between the toner and the photoconductor drum 1a in the developer nip refers to a state in which the fine particles are in contact with both the toner and the photoconductor drum 1a.

[0541] Specifically, it is assumed that the developing roller 41a and the photoconductor drum 1a are in contact with each other via the toner in the developing nip portion, and that the toner in contact with the photoconductor drum 1a is in the densest packing. It is assumed that the toner and the photoconductor drum 1a are in contact with each other via fine particles at the contact portion between the toner and the photoconductor drum 1a.

[0542] Based on the above assumptions, the total number N of fine particles interposed between the toner and the photoconductor drum 1a in the development nip portion is calculated. By using the calculated number N and the contact force F between the developing roller 41a and the photoconductor drum 1a, F / N is calculated as the pressing force of the fine particles against the toner in the development portion, and the calculated F / N is adopted as the predetermined pressing force of the cantilever against the toner when measuring the adhesion force.

[0543] Since the pressing force F between the developing roller 41a and the photoconductor drum 1a is 200 gf in the sixth embodiment, (the pressing force of the fine particles on the toner in the developing nip portion) = F / N is approximately 4.5 (nN). In the sixth embodiment, this 4.5 (nN) is adopted as the predetermined pressing force of the cantilever on the toner when measuring the adhesion force using the SPM.

[0544] A similar adhesion measurement is also performed for the photoconductor drum 1 a , and the adhesion Fdr between the fine particles fixed at the tip of the cantilever and the photoconductor drum 1 a is measured.

[0545] As a result, in the sixth embodiment, the adhesion force Ft between the fine particles and the toner was 32.8 (nN), and the adhesion force Fdr between the fine particles and the photoconductor drum 1a was 210.1 (nN), and it was confirmed that the adhesion force Ft between the fine particles and the toner was smaller than the adhesion force Fdr between the fine particles and the photoconductor drum 1a. Even when the measurement was performed with the pressing force of the cantilever within the range of 3.0 (nN) to 50 (nN), the magnitude relationship did not change.

[0546] Next, the results of evaluations conducted to confirm the effects of the manner of supplying fine particles to the photoconductor drum 1 a in the sixth embodiment will be described.

[0547] In the evaluation, measurement of the presence or absence of image streaks and color changes was performed on the recording medium P for the sixth embodiment, other embodiments, Comparative Example 4, Comparative Example 5, and Comparative Example 6.

[0548] Regarding image streaks, the portion of the halftone toner image that is susceptible to uneven laser exposure tends to be prominent, so determination was made using a 25% density halftone image. A level at which image streaks were clearly visually recognized even on the halftone image was defined as a C grade, a level at which image streaks were slightly visually recognized on the halftone image was defined as a B grade, and a level at which image streaks were not visually recognized even on the halftone image was defined as an A grade.

[0549] Regarding the color change on the recording medium P, the density D1 of the blank portion after printing on high-brightness paper (GFC081 Canon, Inc.) and the density D0 of the high-brightness paper on which printing was not performed were measured using a reflection densitometer (TC-6DS type reflectometer, manufactured by Tokyo Denshoku Co., Ltd.). The difference D0-D1 was defined as the color change on the recording medium P. When the difference D0-D1 in the reflection density was higher than or equal to 3.5%, the level was evaluated as Class C, where the color change on the recording medium P was clearly visually recognized. When the difference D0-D1 in the reflection density was higher than or equal to 2.5%, the level was evaluated as Class B, where the color change on the recording medium P was slightly visually recognized. When the difference D0-D1 in the reflection density was lower than 2.5%, the level was evaluated as Class A, where the color change on the recording medium P could not be visually recognized.

[0550] In the sixth embodiment, as a configuration in which fine particles are coated on the photoconductor drum 1a to reduce the frictional force F between the photoconductor drum 1a and the intermediate transfer belt 10, the amount of fine particles added is adjusted to approximately 0.5% by weight of the toner, and the number of fine particles coated per toner particle is adjusted to approximately 500. The coverage of the fine particles on the photoconductor drum 1a is 30%.

[0551] In another configuration, as a configuration in which fine particles are coated on the photoconductor drum 1a to reduce the frictional force F between the photoconductor drum 1a and the intermediate transfer belt 10, the amount of fine particles added is adjusted to approximately 0.2% by weight of the toner, and the number of fine particles coated per toner particle is adjusted to approximately 200. The coverage of the fine particles on the photoconductor drum 1a is 10%.

[0552] In the configuration of Comparative Example 4, as a configuration in which fine particles are coated on the photoconductor drum 1a, the amount of fine particles added is adjusted to about 0.1% by weight of the toner, and the number of fine particles coated per toner particle is adjusted to about 100. The coverage of the fine particles on the photoconductor drum 1a is 5%.

[0553] In the configuration of Comparative Example 5, fine particles or toner are not used as a means of reducing the frictional force F between the photoconductor drum 1 a and the intermediate transfer belt 10 .

[0554] In the configuration of Comparative Example 6, a yellow dot toner image is used as a means of reducing the frictional force F between the photoconductor drum 1 a and the intermediate transfer belt 10 , and the coverage of the toner on the photoconductor drum 1 a is 5%.

[0555] Next, the evaluation results will be described with reference to Table 6.

[0556] Table 6

[0557] Ways to reduce friction Coverage on drum Image stripes Color change of transfer material Sixth embodiment fine particles 30％ A A Modify the example fine particles 10％ A A Comparative Example 4 fine particles 5％ B A Comparative Example 5 none 0％ C A Comparative Example 6 Yellow toner 5％ B B

[0558] In the configuration of Comparative Example 4, the coverage of fine particles on the photoconductor drum 1a, which is used to reduce friction, is 5%. In the absence of toner in the drum nip, a slight frictional force F acts on the surface of the photoconductor drum 1a in the tangential direction (sub-scanning direction) from the surface of the intermediate transfer belt 10 toward the downstream side. When the leading edge of the toner image of the halftone image developed on the photoconductor drum 1a enters the drum nip, the frictional force F decreases. Consequently, spontaneous fluctuations in the rotation of the photoconductor drum 1a occasionally occur, resulting in uneven writing during laser exposure of the surface of the photoconductor drum 1a. Consequently, streaks form in the main scanning direction on the toner image subsequently formed on the surface of the photoconductor drum 1a, and image streaks appear on the halftone image. On the other hand, in order to address color variations on the recording medium P, fine particles are used instead of toner to reduce the frictional force F between the photoconductor drum 1a and the intermediate transfer belt 10, so color variations do not occur.

[0559] In the configuration of Comparative Example 5, there are no fine particles or toner on the photoconductor drum 1a to reduce friction. Therefore, when the leading edge of the toner image of the halftone image developed on the photoconductor drum 1a enters the drum nip, the friction force F decreases sharply. As a result, spontaneous fluctuations occur in the rotation of the photoconductor drum 1a, and as a result, uneven writing occurs during laser exposure of the surface of the photoconductor drum 1a. As a result, clearly visible image streaks appear on the halftone image. On the other hand, toner or fine particles are not used as a means of reducing the friction force F between the photoconductor drum 1a and the intermediate transfer belt 10 to address color shifts on the recording medium P, and therefore, no color shifts occur.

[0560] In the construction of Comparative Example 6, 5% of the photoconductor drum 1a is coated with yellow dot toner to reduce friction. As in the case of Comparative Example 4, when the leading edge of the toner image of the halftone image developed on the photoconductor drum 1a enters the drum clamping portion, image stripes appear on the halftone image. In addition, with respect to the color change on the recording medium P, the difference D0-D1 in reflection density is higher than or equal to 2.5%, and this level makes the color change visually slightly recognizable. When the conditions of Comparative Example 6 are changed in the direction of increasing coverage (i.e., in the direction of reducing image stripes), the color change further deteriorates; however, when the conditions are changed in the direction of reducing coverage (i.e., in the direction of reducing color change), the image stripes deteriorate.

[0561] In contrast, to reduce friction, in the sixth embodiment, 30% of the photoconductor drum 1a is coated with fine particles, or in another embodiment (modified example), 10% is coated with fine particles. In either case, even when the leading edge of the toner image of a halftone image developed on the photoconductor drum 1a enters the drum nip portion, spontaneous fluctuations in the rotation of the photoconductor drum 1a do not occur, and thus image streaks do not occur. Furthermore, considering the results of Comparative Example 4, the coverage of the fine particles supplied to the photoconductor drum 1a, which is necessary to reduce friction, is preferably greater than or equal to 10%.

[0562] On the other hand, similarly for color variation on the recording medium P, fine particles are used instead of toner as a means of reducing the friction F between the photoconductor drum 1 a and the intermediate transfer belt 10 , so that color variation does not occur.

[0563] As described above, in the configuration of the sixth embodiment, fine particles are preliminarily supplied from the toner carried on the developing roller 41 to the photoconductor drum 1 before the toner image is developed, and the fine particles adhere to the photoconductor drum 1. Consequently, by interposing the fine particles between the photoconductor drum 1 and the intermediate transfer belt 10, the frictional force F in the drum nip portion is reduced. Furthermore, to supply the fine particles to the photoconductor drum 1, the adhesion force Ft between the fine particles and the toner is set to be smaller than the adhesion force Fdr between the fine particles and the photoconductor drum 1, and the particle size of the fine particles is set to be less than or equal to 1000 nm. With this configuration, the fine particles are supplied to the photoconductor drum 1 without the influence of static electricity.

[0564] Therefore, with a simple configuration, color variations on the recording medium P are reduced, while image streaks due to fluctuations in the rotation of the photoconductor drum 1 are reduced.

[0565] In the configuration of the imaging apparatus applied to the seventh embodiment, the same reference numerals are assigned to the same components as those of the first and sixth embodiments, and description thereof is omitted.

[0566] In the configuration of the sixth embodiment, in order to reduce color variations on the recording medium P while reducing image streaks due to fluctuations in the rotation of the photoconductor drum 1 , a method of supplying fine particles added to the toner to the photoconductor drum 1 is described.

[0567] In contrast, in the seventh embodiment, a so-called drum-less cleaner configuration is adopted in which cleaning units 55a, 55b, 55c, 55d are not provided on the photoconductor drums 1a, 1b, 1c, 1d, respectively. With this configuration, fine particles can be maintained on the photoconductor drums 1a, 1b, 1c, 1d for a long time.

[0568] Below, we will refer to Figure 32 The configuration of the seventh embodiment will be described.

[0569] In the above drumless cleaner system, if Figure 32 As shown, no cleaning unit is provided on the photoconductor drums 1a, 1b, 1c, 1d. Therefore, the toner remaining on the photoconductor drums 1a, 1b, 1c, 1d during the primary transfer needs to be collected by the developing units 4a, 4b, 4c, 4d.

[0570] Hereinafter, a method of collecting the toner remaining on the photoconductor drums 1 a , 1 b , 1 c , 1 d will be described by using the fourth image forming station d.

[0571] Of the toner that was not primarily transferred to the intermediate transfer belt 10 in the primary transfer portion and remains on the photoconductor drum 1d (primary transfer portion and retransfer residual toner), positive polarity toner adheres to the charging roller 2d. As the photoconductor drum 1d rotates, negative polarity toner is transferred to the area opposite the developing unit 4d through the contact portion with the charging roller 2d. At this time, the surface of the photoconductor drum 1d is again charged and exposed, and an electrostatic latent image based on the image information is formed. Most of the residual toner transferred to the area opposite the developing unit 4d has a negative polarity. To this end, a portion of the residual toner is collected by the developing unit 4d due to the electric field formed by the difference between the surface potential of the photoconductor drum 1d (-500V in the non-exposed area and -100V in the exposed area) and the voltage applied to the developing roller 41d (-300V). In the non-exposed area, the electric field is oriented in a direction to move the negative polarity toner from the photoconductor drum 1d to the developing roller 41d, so the residual toner on the photoconductor drum 1d moves to the developing roller 41d and is collected in the developing unit 4d.

[0572] On the other hand, in the exposure area, the electric field is oriented in a direction that moves the negative polarity toner from the developing roller 41d to the photoconductor drum 1d. Therefore, the negative polarity toner on the developing roller 41d moves to the photoconductor drum 1d and develops the electrostatic latent image on the photoconductor drum 1d. At this time, the residual toner on the photoconductor drum 1d also contributes to the development of the electrostatic latent image. In this way, the developing unit 4d is configured to develop the electrostatic latent image formed on the photoconductor drum 1d into a toner image and to collect the toner adhering to the photoconductor drum 1d.

[0573] Through the above-described operations, the residual toner on the photoconductor drum 1 d is collected in the drum-less cleaner system.

[0574] The other configuration is similar to that of the sixth embodiment, and thus description is omitted.

[0575] Next, the operation of the seventh embodiment will be described.

[0576] In the configuration of the seventh embodiment, as in the case of the sixth embodiment, fine particles are supplied to the photoconductor drum 1 from the toner carried on the developing roller 41 before developing the toner image. In order to supply the fine particles to the photoconductor drum 1, the adhesion force Ft between the fine particles and the toner is set to be smaller than the adhesion force Fdr between the fine particles and the photoconductor drum 1. With this configuration, as Figure 9A and Figure 9B As shown, when the toner image is primarily transferred from the photoconductor drum 1 to the intermediate transfer belt 10, only the toner image is primarily transferred to the intermediate transfer belt 10. Fine particles interposed between the toner image and the photoconductor drum 1 remain on the photoconductor drum 1. In this situation, in the sixth embodiment, a cleaning unit 55 disposed on the photoconductor drum 1 collects the fine particles remaining on the photoconductor drum 1. For this reason, each image formation operation requires the supply of fine particles from the toner carried on the developing roller 41. On the other hand, in the seventh embodiment, no cleaning unit is provided on the photoconductor drum 1, so fine particles supplied to the photoconductor drum 1 continuously remain on the photoconductor drum 1. This also applies to operations in which toner is collected by the developing unit 4 in a drum-less cleaner system. In other words, since the particle size of the fine particles is set to 1000 nm or less, the fine particles are less susceptible to static electricity and remain on the photoconductor drum 1 without being collected by the developing unit 4. With this configuration, the state in which the fine particles are attached to the photoconductor drum 1 can be maintained, and a stable image can be provided for a long period of time.

[0577] In the configuration of the sixth embodiment, the time for supplying fine particles during image formation needs to be set to be equal to or greater than the time it takes for the portion of the photoconductor drum 1 that the developing roller 41 contacts to reach the drum nip portion. In the drumless cleaner configuration of the seventh embodiment, as described above, the supply of fine particles to the photoconductor drum 1 can be maintained, so the developing roller 41 can start development while it is in contact with the photoconductor drum 1. Consequently, the time it takes from the time the image forming apparatus receives image data to the time the image forming apparatus prints out can be shortened, resulting in a reduction in user stress.

[0578] As described above, in a so-called drumless cleaner configuration in which the cleaning unit 55 is not provided on the photoconductor drum 1, fine particles can be stably maintained on the photoconductor drum 1. Therefore, stable images can be provided over a long period of time. Furthermore, the time taken from when the imaging device receives image data until when the imaging device prints it can be shortened.

[0579] In the configuration of the imaging apparatus applied to the eighth embodiment, the same reference numerals are assigned to the same components as those of the sixth and seventh embodiments, and descriptions thereof are omitted.

[0580] In the configuration of the sixth embodiment, in order to reduce color variations on the recording medium P while reducing image streaks due to fluctuations in the rotation of the photoconductor drum 6 , a method of supplying fine particles added to the toner to the photoconductor drum 1 is described.

[0581] In contrast, in the eighth embodiment, the metal roller 40 is arranged opposite to the photoconductor drum 1 via the intermediate transfer belt 10 with a predetermined amount of offset in the transfer portion. With this configuration, the friction force F between the photoconductor drum 1 and the intermediate transfer belt 10 is reduced, thereby reducing image streaks.

[0582] Below, we will refer to Figure 33 and Figure 34 The configuration of the eighth embodiment will be described.

[0583] Figure 33 is a diagram of an imaging apparatus according to an eighth embodiment. Figure 34 yes Figure 33 An enlarged view of the structure of the first imaging station a in FIG. Figure 34 In the embodiment, the metal roller 40a is arranged at a position offset 8 mm downstream in the moving direction of the intermediate transfer belt 10 relative to the center position of the photoconductor drum 1a. The metal roller 40a is arranged at a position elevated 1.0 mm from the horizontal surface formed by the photoconductor drum 1a and the intermediate transfer belt 10, so that the amount of intermediate transfer belt 10 wrapped around the photoconductor drum 1a can be ensured. The metal roller 40 is arranged as close to the photoconductor drum 1 as possible without contacting the photoconductor drum 1 to avoid scratches caused by contact with the photoconductor drum 1. The arrangement of the metal roller 40 on the downstream side in the moving direction of the intermediate transfer belt 10 is advantageous for preventing scattering caused by the transfer electric field formed on the upstream side of the primary transfer nip.

[0584] In the eighth embodiment, when the offset distance of the metal roller 40a is K, the height of the metal roller 40a relative to the intermediate transfer belt 10 is Z, and the drum nip width is Nk, where K = 8 mm, Z = 1.0 mm, and Nk = 1500 μm. The metal roller 40a is made of a straight nickel-plated SUS round rod with an outer diameter of 6 mm. The metal roller 40a rotates with the rotation of the intermediate transfer belt 10. The metal roller 40b arranged in the second imaging station b, the metal roller 40c arranged in the third imaging station c, and the metal roller 40d arranged in the fourth imaging station d also have a configuration similar to that of the metal roller 40a.

[0585] The other configuration is similar to that of the seventh embodiment, and thus description is omitted.

[0586] Next, the operation of the eighth embodiment will be described.

[0587] As described above, in the eighth embodiment, the metal roller 40 is arranged opposite to the photoconductor drum 1 via the intermediate transfer belt 10 with a predetermined amount of offset in the transfer portion. As described in the sixth embodiment, in order to achieve the effect of improving the primary transfer efficiency due to the peripheral speed difference between the photoconductor drum 1 and the intermediate transfer belt 10, the drum nip width Nk is set to 1500 μm as in the case of the sixth embodiment.

[0588] With this configuration, the pressure to be applied to the drum nip portion is reduced with respect to the configuration in which the primary transfer roller 14 directly presses the photoconductor drum 1 via the intermediate transfer belt 10 to form the drum nip portion as in the case of the sixth embodiment. In other words, the friction force F is the product of the normal reaction force and the friction coefficient, and the pressure applied to the drum nip portion corresponding to the normal reaction force also results in a reduction in the friction force F of the drum nip portion.

[0589] In order to reduce the friction force F of the drum nip portion, the adhesion force Ft between the fine particles and the toner is set to be smaller than the adhesion force Fdr between the fine particles and the photoconductor drum 1. The effect of reducing image streaks and color variations on the recording medium P due to fluctuations in the rotation of the photoconductor drum 1 by supplying fine particles to the photoconductor drum 1 is similar to that of the sixth and seventh embodiments.

[0590] As described above, in the eighth embodiment, the metal roller 40 is arranged opposite to the photoconductor drum 1 via the intermediate transfer belt 10 with a predetermined amount of offset in the transfer portion. With this configuration, the friction force F between the photoconductor drum 1 and the intermediate transfer belt 10 is reduced, thereby reducing image streaks.

[0591] Furthermore, in the eighth embodiment, a configuration has been described in which fine particles are supplied and attached to the photoconductor drum 1 associated with each imaging station. For example, when printing only black in monochrome mode, a low friction force F can be maintained between the photoconductor drum 1 and the intermediate transfer belt 10 even when the primary transfer members of the color (yellow, magenta, and cyan) imaging stations a, b, and c are not separated. In other words, there is no need to provide a contact and separation mechanism for the primary transfer members, thereby further reducing the size and cost of the main unit.

[0592] As described above, according to the present disclosure, by reducing fluctuations in the rotation of the photoconductor drum or in the rotation of the intermediate transfer belt without increasing dot toner images, the occurrence of adverse effects in the image is suppressed.

[0593] (Relationship between the Adhesion of Transfer Carrier Particles to the Photoconductor Drum and the Adhesion of Transfer Carrier Particles to the Intermediate Transfer Belt)

[0594] Next, the relationship between the adhesion force of the transfer carrier particles to the photoconductor drum 1 and the adhesion force of the transfer carrier particles to the intermediate transfer belt 10, which is one of the characteristics of the ninth embodiment, will be described. In the ninth embodiment, transfer efficiency is improved by performing the image formation operation while the transfer carrier particles are adhered to the surface of the photoconductor drum 1. To this end, it is necessary to stop the transfer of the transfer carrier particles from the photoconductor drum 1 to the surface of the intermediate transfer belt 10 in contact with the photoconductor drum 1 as much as possible during the transfer portion. In the configuration of the ninth embodiment, the adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1 and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 are set to the relationship Fdr>Fi.

[0595] Next, a method of calculating the adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1 and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 will be described. The adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1 and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 are calculated by Expression 7.

[0596]

[0597] Where A1 (Hamkel constant): 6.58E-20 (J), Z0 (separation distance): 4.00E-10 (m), and R (composite diameter): 5.00E-8 (m). α is the particle deformation amount. The particle deformation amount α can be calculated by using Expression 8.

[0598]

[0599] f is the pressing force (N) on the transfer carrier particles. E* is calculated from the relationship 9 between E (Young's modulus (Pa)) and ν (Poisson's ratio).

[0600]

[0601] Therefore, it is found from Expression 8 and Expression 9 that the adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1 and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10 depend on the pressing force of the material on the transfer carrier particles, Young's modulus and Poisson's ratio.

[0602] Therefore, it is found from Expression 7, Expression 8, and Expression 9 that when the Young's modulus and Poisson's ratio of the surface material of the photoconductor drum 1 are small, the adhesion force when the photoconductor drum 1 is pressed and the adhesion force when the intermediate transfer belt 10 is pressed increase. Therefore, in order to achieve the relationship of Fdr>Fi, the Young's modulus and Poisson's ratio of the material used for the photoconductor drum 1 can be lower than the Young's modulus and Poisson's ratio of the material used for the intermediate transfer belt 10.

[0603] The adhesion force when pressing the photoconductor drum 1 and the adhesion force when pressing the intermediate transfer belt 10 increase according to the pressing force. To achieve the relationship Fdr>Fi, the force pressing the transfer carrier particles against the photoconductor drum 1 can be increased, and the force pressing the transfer carrier particles against the intermediate transfer belt 10 can be reduced.

[0604] In the ninth embodiment, the polycarbonate of the surface layer of the photoconductor drum 1 has a Young's modulus of 2.20 (GPa) and a Poisson's ratio of 0.37, and the acrylic of the surface layer of the intermediate transfer belt 10 has a Young's modulus of 3.00 (GPa) and a Poisson's ratio of 0.38. For this reason, the Young's modulus and Poisson's ratio of the material used for the photoconductor drum 1 are lower than those of the material used for the intermediate transfer belt 10.

[0605] Furthermore, the pressing force of the intermediate transfer belt 10 against the photoconductor drum 1 in the transfer portion was 220 gf. Figure 35A Schematic diagram of the transfer nip portion when the photoconductor drum 1 and the intermediate transfer belt 10 are in contact. Figure 35A As shown, in the transfer nip portion, the transfer carrier particles receive an adhesion force Fdr from the photoconductor drum 1 and an adhesion force Fi from the intermediate transfer belt 10 . Figure 35B It shows that Figure 35A The transfer carrier particles carried on the photoconductor drum 1 and the intermediate transfer belt 10 are shown in FIG. Figure 35B As shown, when the relationship Fdr>Fi is satisfied for the transfer carrier particles interposed between the photoconductor drum 1 and the intermediate transfer belt 10 in the transfer portion, transfer of the transfer carrier particles from the photoconductor drum 1 to the intermediate transfer belt 10 is suppressed.

[0606] Alternatively, another pressing member may be installed that contacts the photoconductor drum 1 and presses the transfer carrier particles against the surface of the photoconductor drum 1. The pressing member can apply additional pressing force to the photoconductor drum 1, thereby further maintaining the relationship Fdr > Fi. The relationship between the adhesion force of the pressing member to the transfer carrier particles and the adhesion force of the photoconductor drum 1 to the transfer carrier particles is similarly configured as the relationship between the adhesion force of the photoconductor drum 1 to the transfer carrier particles and the adhesion force of the intermediate transfer belt 10 to the transfer carrier particles. With this configuration, the effect of enabling the transfer carrier particles to adhere to the photoconductor drum 1 can be appropriately achieved.

[0607] In the ninth embodiment, the developing roller 41 not only supplies transfer carrier particles to the photoconductor drum 1 but also presses the transfer carrier particles against the photoconductor drum 1. The developing roller 41 presses the transfer carrier particles against the surface of the photoconductor drum 1 and increases the pressing force of the photoconductor drum 1, thereby maintaining the relationship Fdr>Fi. The developing roller 41 can function as a pressing member. The developing roller 41 can also function as a transfer carrier particle supply member.

[0608] In the construction of the ninth embodiment, transfer carrier particles are supplied from the developing roller 41 to the photoconductor drum 1; however, another transfer carrier particle supply member in contact with the photoconductor drum 1 may be provided. When the transfer carrier particle supply member presses the transfer carrier particles against the surface of the photoconductor drum 1, the adhesion of the transfer carrier particles to the photoconductor drum 1 increases, thereby maintaining the relationship Fdr>Fi. The transfer carrier particle supply member may also serve as a pressing member. Furthermore, to maintain the relationship Fdr>Fi, the pressing force of the transfer carrier particles on the transfer carrier particle supply member or the pressing member against the photoconductor drum 1 may be greater than the pressing force of the photoconductor drum 1 in the transfer section. In the ninth embodiment, the photoconductor drum 1 is pressed with 200 gf in the developing section, and the width of the developing nip is 2 mm. On the other hand, the photoconductor drum 1 is pressed with 220 gf in the transfer section, and the nip width in the primary transfer section is 3 mm. Therefore, the pressing force applied to the transfer carrier particles per unit area in the developing section is 100 gf / mm, and in the primary transfer section it is 73.3 gf / mm. Therefore, in the ninth embodiment, the pressing force of the transfer carrier particles in the developing section is greater than the pressing force of the transfer carrier particles in the transfer section.

[0609] In addition, the primary transferability is improved to a certain extent as the coverage of the transfer carrier particles on the photoconductor drum 1 increases. In order to obtain sufficient primary transferability, the coverage of the transfer carrier particles on the photoconductor drum 1 is preferably higher than or equal to 10%, where the entire surface of the photoconductor drum is 100%. However, as the coverage of the transfer carrier particles on the photoconductor drum 1 increases, the following inconveniences may occur. When there are too many transfer carrier particles on the surface of the photoconductor drum 1, the risk of contamination of the components in contact with the surface of the photoconductor drum 1 due to the transfer carrier particles increases. For this reason, the coverage of the transfer carrier particles on the photoconductor drum 1 is preferably lower than or equal to 50%. From the observation results of the surface of the photoconductor drum 1, it is confirmed in the ninth embodiment that the coverage of the transfer carrier particles on the surface of the photoconductor drum 1 is higher than or equal to 10%.

[0610] (Effects of Setting the Adhesion Force Fi to the Intermediate Transfer Belt)

[0611] Next, in the ninth embodiment, an effect confirmation test was performed to confirm the effect of suppressing the transfer of transfer carrier particles from the photoconductor drum 1 to the intermediate transfer belt 10. The test method will be described below. First, the method of confirming the transfer of transfer carrier particles from the photoconductor drum 1 to the intermediate transfer belt 10 will be described.

[0612] An imaging device of the ninth embodiment including a photoconductor drum 1 to which transfer carrier particles are added is prepared, and the photoconductor drum 1 and the intermediate transfer belt 10 are pressed against each other with a primary transfer pressure of 220 gf. The surface of the pressed photoconductor drum 1 is observed with a microscope, and the coverage of the transfer carrier particles on the surface of the photoconductor drum 1 is calculated. Specifically, first, the surface of the photoconductor drum 1 is observed with a laser microscope (VK-X200 Keyence Corporation) at a magnification of 3000 times, and an observed image is obtained. Thereafter, the surface of the photoconductor drum 1 in the observed image is binarized into a portion coated with transfer carrier particles and a portion not coated with transfer carrier particles, and the area ratio of the transfer carrier particles on the surface of the photoconductor drum 1 is calculated.

[0613] To capture an observed image, the imaging apparatus is stopped while transfer carrier particles are being supplied to the surface of the photoconductor drum 1. The photoconductor drum 1 is observed both upstream and downstream of the transfer nip position where the photoconductor drum 1 and the intermediate transfer belt 10 contact each other. Therefore, an area ratio is calculated for each of the upstream and downstream sides of the transfer nip. The value obtained by using the upstream area ratio as the denominator and the change obtained by subtracting the downstream area ratio from the upstream area ratio as the numerator is defined as the rate of change in the coverage of the photoconductor drum 1 by the transfer carrier particles.

[0614] If the transfer carrier particles are not newly supplied, when the rate of change in the coverage of the transfer carrier particles on the photoconductor drum 1 is higher than or equal to 50%, the transfer carrier particles almost disappear from the surface of the photoconductor drum 1 after about 10 rotations of the photoconductor drum 1. The rate of change in the coverage of the transfer carrier particles on the photoconductor drum 1 is preferably lower than 20%.

[0615] Next, a method for calculating Fdr and Fi will be described. The calculation method of the adhesion force is performed by using the above-mentioned Expression 7, Expression 8, and Expression 9. In the ninth embodiment, the elastic force of the material is focused on, the adhesion force of the material is calculated according to Expression 7, Expression 8, and Expression 9, and the material is screened. Therefore, it is assumed that the constant independent of the elastic force does not depend on the material, and the measured adhesion force (described later) obtained in some combination from the results obtained by the calculation screening is used as the accurate adhesion force. In the ninth embodiment, by using Figure 37Adhesion was calculated using the Young's modulus and Poisson's ratio of each material shown. Furthermore, the adhesion between the transfer carrier particles and the toner used in the ninth embodiment was measured using an SPM. Specifically, a cantilever was pressed against the toner with a predetermined pressing force, and the force separating the cantilever from the toner was then measured as the adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1, and the adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10. The cantilever was made of silicon coated with a silicon oxide film and had a rounded tip with a tip diameter of 100 nm. When the cantilever's surface material was SiO2, the same as the transfer carrier particles, and the tip diameter was set to 100 nm, which is equal to the number-average particle size of the transfer carrier particles, the adhesion to the transfer carrier particles could be accurately reproduced. The predetermined pressing force applied to the photoconductor drum 1 or the intermediate transfer belt 10 during adhesion measurement can be set to the force with which the transfer carrier particles interposed between the photoconductor drum 1 and the intermediate transfer belt 10 are pressed in the transfer section. The pressing force is calculated by the calculation method described below. Here, the phrase "transfer carrier particles are interposed between the photoconductor drum 1 and the intermediate transfer belt 10" in the transfer portion means a state where the transfer carrier particles are in contact with both the photoconductor drum 1 and the intermediate transfer belt 10 simultaneously.

[0616] First, refer to Figure 36A and Figure 36B Describe the assumptions used for the calculations. Figure 36A Schematic diagram of the transfer portion. It is assumed that the photoconductor drum 1 and the intermediate transfer belt 10 are in contact with each other via transfer carrier particles in the transfer portion. Figure 36B It is along Figure 36A 1 is a cross-sectional view taken along the dashed line XXXVIIB-XXXVIIB in FIG. FIG. 2 is a cross-sectional view parallel to the surface of the photoconductor drum 1 taken along the dashed line XXXVIIB-XXXVIIB in FIG. It is assumed that the transfer carrier particles in contact with the intermediate transfer belt 10 are in the closest packing as indicated by the shaded area. The total number N of transfer carrier particles interposed between the intermediate transfer belt 10 and the photoconductor drum 1 can be calculated from the area of ​​the nip portion between the intermediate transfer belt 10 and the photoconductor drum 1 in the transfer section and the maximum cross-sectional area of ​​the transfer carrier particles.

[0617] The total number Nt of transfer carrier particles in contact with the photoconductor drum 1 in the transfer portion can be calculated by (area of ​​the transfer portion)×(coverage of transfer carrier particles) / (maximum cross-sectional area of ​​transfer carrier particles) and is approximately 6.6×10 9 Based on the above calculation results and the fact that the pressing force F of each of the primary transfer roller 14 and the photoconductor drum 1 in the ninth embodiment is 220 gf, (pressing force of the transfer carrier particles on the toner in the transfer portion) = F / Nt is approximately 0.33 (nN). This 0.33 (nN) is adopted as the predetermined pressing force of the cantilever on the toner in the transfer portion when measuring adhesion using the SPM.

[0618] Next, the results of the effect confirmation test of the ninth embodiment will be described. First, the materials of the photoconductor drum 1 and the intermediate transfer belt 10 subjected to the effect confirmation test will be described in order.

[0619] In the ninth embodiment, a thin film layer made of polycarbonate with a film thickness of 20 μm is used as the surface layer of the photoconductor drum 1. The Young's modulus is 2.20 (GPa), and the Poisson's ratio is 0.37. The maximum roughness Rz of the intermediate transfer belt 10 is less than or equal to 0.12 μm. An acrylic coating is used as the surface layer, and the film thickness of the surface layer is 2.3 μm. The Young's modulus is 3.00 (GPa), and the Poisson's ratio is 0.38. Below, variations 1 to 5 and comparative examples 7 to 10 will be described. The description of the same components as those of the ninth embodiment is omitted.

[0620] Variant 1

[0621] A thin film layer made of polyallylate with a film thickness of 23 μm was used as the surface layer of the photoconductor drum 1. The Young's modulus was 2.15 (GPa), the Poisson's ratio was 0.37, and the Rz was 0.1 μm.

[0622] Variant 2

[0623] A single-layer belt made of polyimide with a film thickness of 65 μm was used as the intermediate transfer belt 10. The Young's modulus was 2.65 (GPa), and the Poisson's ratio was 0.30.

[0624] Variant 3

[0625] A 23 μm thick film layer made of polyallylate was used as the surface layer of the photoconductor drum 1. A 65 μm thick single-layer belt made of polyimide was used as the intermediate transfer belt 10. The Young's modulus was 2.65 (GPa), and the Poisson's ratio was 0.30.

[0626] Variant 4

[0627] A single-layer belt made of polyetheretherketone (PEEK) with a film thickness of 55 μm was used as the intermediate transfer belt 10. The Young's modulus was 3.70 (GPa), and the Poisson's ratio was 0.40.

[0628] Variant 5

[0629] A 23 μm thick film layer made of polyallylate was used as the surface layer of the photoconductor drum 1. A 55 μm thick single-layer belt made of polyetheretherketone (PEEK) was used as the intermediate transfer belt 10. The Young's modulus was 3.70 (GPa), and the Poisson's ratio was 0.40.

[0630] Comparative Example 7

[0631] A surface layer made of urethane with a film thickness of about 2 μm was used as the intermediate transfer belt 10. The Young's modulus was 1.50 (GPa) and the Poisson's ratio was 0.48. The material of the elastic layer was silicone rubber with a thickness of about 350 μm, and the material of the base layer was polyimide with a thickness of about 60 μm.

[0632] Comparative Example 8

[0633] A surface layer made of Si with a film thickness of 1.2 μm was formed on the surface of the photoconductor drum 1. The Young's modulus was 185 (GPa), and the Poisson's ratio was 0.28.

[0634] Comparative Example 9

[0635] A single-layer belt made of polybutylene terephthalate (PBT) with a thickness of about 80 μm was used as the intermediate transfer belt 10. The Young's modulus was 2.20 (GPa), and the Poisson's ratio was 0.38.

[0636] Comparative Example 10

[0637] A 23 μm thick film layer made of polyallylate was used as the surface layer of the photoconductor drum 1. A single-layer belt made of polybutylene terephthalate (PBT) with a thickness of about 80 μm was used as the intermediate transfer belt 10. The Young's modulus was 2.20 (GPa), and the Poisson's ratio was 0.38.

[0638] exist Figure 37 1 and 2 show, together with the configurations of the ninth embodiment, modifications 1 to 5, and comparative examples 7 to 10, a pressing force of 220 gf, an adhesion force Fdr between the transfer carrier particles and the photoconductor drum 1 in a state where a pressure of 0.33 nN is applied to the transfer carrier particles, and an adhesion force Fi between the transfer carrier particles and the intermediate transfer belt 10. By applying a pressure of 220 gf to the photoconductor drum 1 to which the transfer carrier particles are attached, it was examined whether the transfer carrier particles were transferred to the intermediate transfer belt 10. Figure 37 The change rate of the coverage of the transfer carrier particles on the photoconductor drum 1 is shown. In addition, Figure 37 The calculated adhesion Fdr, Fi of the materials and the adhesion Fdr, Fi measured with SPM are shown.

[0639] like Figure 37 As shown in the variation rate of the coverage of the transfer carrier particles on the photoconductor drum 1, in the combinations of the material of the photoconductor drum 1 and the material of the intermediate transfer belt 10 according to the ninth embodiment and variations 1 to 5, the variation rate of the coverage of the transfer carrier particles on the photoconductor drum 1 is less than 20%. On the other hand, in comparative examples 7, 9, and 10, the variation rate of the coverage of the transfer carrier particles on the photoconductor drum 1 is higher than or equal to 20% and lower than 50%. In comparative example 8, the variation rate of the coverage of the transfer carrier particles on the photoconductor drum 1 is higher than or equal to 50%. When the Figure 37 When the calculation results are compared with each other, in the ninth embodiment and modifications 1 to 5 (in which the relationship between the adhesion force of the photoconductor drum 1 and the adhesion force of the intermediate transfer belt 10 is Fdr>Fi), the transfer of the transfer carrier particles is suppressed, and the transfer efficiency is maintained. In comparative examples 7 to 10 (in which the relationship between the adhesion force of the photoconductor drum 1 and the adhesion force of the intermediate transfer belt 10 is Fdr<Fi), the transfer of the transfer carrier particles occurs, and the transfer efficiency decreases.

[0640] Figure 38 The relationship between the pressing force and adhesion force measured by SPM is shown. Figure 38 As shown in Figure 1, in any material, the adhesion force depends on the pressing force of the transfer carrier particles. Therefore, in order to reduce Fi, the pressing force can be reduced as much as possible.

[0641] From the above results, the ninth embodiment has the following configuration.

[0642] Assume that the pressing force of the photoconductor drum 1 against the intermediate transfer belt 10 is F1, and the total number of transfer carrier particles interposed between the photoconductor drum 1 and the intermediate transfer belt 10 in the transfer section is N1. The adhesion force between the transfer carrier particles and the intermediate transfer belt 10 measured when the transfer carrier particles are pressed against the intermediate transfer belt 10 at F1 / N1 (being the pressing force per unit of transfer carrier particles) is defined as Fi. The adhesion force between the transfer carrier particles and the photoconductor drum 1 measured when the transfer carrier particles are pressed against the photoconductor drum 1 at F1 / N1 is defined as Fdr1. Fi and Fdr1 satisfy Fi<Fdr1.

[0643] The imaging device includes a developing unit 4, which contains a developer composed of colorant particles and transfer carrier particles attached to the surface of the toner particles. The developing roller 41 carries the developer. The developing roller 41 is in contact with the photoconductor drum 1 to form a developing portion, and the developer is supplied in the developing portion. Assume that the pressing force of pressing the developing roller 41 against the photoconductor drum 1 is F2, and the total number of transfer carrier particles between the toner particles and the photoconductor drum 1 in the developing portion is N2. The adhesion force between the transfer carrier particles and the toner particles measured when the transfer carrier particles are pressed against the toner particles at F2 / N2 (the pressing force per unit transfer carrier particles) is defined as Ft. The adhesion force between the transfer carrier particles and the photoconductor drum 1 measured when the transfer carrier particles are pressed against the photoconductor drum 1 at F2 / N2 is defined as Fdr2. Ft and Fdr2 satisfy Ft≤Fdr2.

[0644] The imaging device may include a pressing member that presses transfer carrier particles attached to the surface of the photoconductor drum 1. Here, it is assumed that the pressing force of pressing the pressing member against the photoconductor drum 1 is F3, and the total number of transfer carrier particles between the photoconductor drum 1 and the pressing member in the pressing portion is N3. The adhesion force between the transfer carrier particles and the pressing member measured when the transfer carrier particles are pressed against the photoconductor drum 1 with F3 / N3 (which is the pressing force per unit transfer carrier particle) is defined as Fp. The adhesion force between the transfer carrier particles and the photoconductor drum 1 measured when the transfer carrier particles are pressed against the photoconductor drum 1 with F3 / N3 is defined as Fdr3. Fp and Fdr3 satisfy Fp<Fdr3.

[0645] The image forming apparatus may include a transfer carrier particle supply member that supplies transfer carrier particles to the surface of the photoconductor drum 1. Here, it is assumed that the pressing force of the transfer carrier particle supply member against the photoconductor drum 1 is F4, and the total number of transfer carrier particles between the photoconductor drum 1 and the supply member in the supply portion is N4. The adhesion force between the transfer carrier particles and the supply member measured when the transfer carrier particles are pressed against the photoconductor drum 1 at F4 / N4 (which is the pressing force per unit transfer carrier particle) is defined as Fs. The adhesion force between the transfer carrier particles and the photoconductor drum 1 measured when the transfer carrier particles are supplied to the photoconductor drum 1 at F4 / N4 is defined as Fdr4. Fs and Fdr4 satisfy Fs<Fdr4.

[0646] As described above, with the configuration of the ninth embodiment, the transfer carrier particles can be maintained on the surface of the photoconductor drum 1 while a sufficient amount of transfer carrier particles for improving transfer efficiency is supplied to the photoconductor drum 1 .

[0647] A roller may be inserted into the end portion of the primary transfer roller 14. The roller is a rigid body having a diameter larger than that of the primary transfer roller 14. By inserting the roller into the end portion of the primary transfer roller 14, the primary transfer roller 14 does not directly press the photoconductor drum 1, and thus the pressing force in the transfer portion is reduced.

[0648] In the ninth embodiment, the primary transfer roller 14 is used as the primary transfer member. Alternatively, a sheet-like or brush-like primary transfer member may be arranged.

[0649] In the configuration of the imaging apparatus applied to the tenth embodiment, the same reference numerals are assigned to the same components as those of the first and ninth embodiments, and description thereof is omitted.

[0650] In the tenth embodiment, unlike the first or ninth embodiment, a metal roller is used as the primary transfer roller 51, so the contact pressing force between the intermediate transfer belt 10 and the photoconductor drum 1 is stable and the relationship in adhesion can be further maintained for a long time.

[0651] The configuration of the tenth embodiment will be described. Figure 39 Specifically, the portion of the schematic diagram of the imaging device used in the tenth embodiment that has been changed relative to the first embodiment is shown in an enlarged view. The primary transfer roller 51a is a cylindrical metal roller with a diameter of 6 mm and is made of nickel-plated SUS. The primary transfer roller 51a is arranged at a position offset 7 mm downstream in the surface movement direction of the intermediate transfer belt 10 relative to the center position of the photoconductor drum 1a. The intermediate transfer belt 10 is configured to be wound around the photoconductor drum 1a. The primary transfer roller 51a is arranged at a position raised by 0.3 mm from the horizontal surface formed by the photoconductor drum 1a and the intermediate transfer belt 10, so that the winding amount of the intermediate transfer belt 10 around the photoconductor drum 1a can be ensured. At this time, the primary transfer roller 51a presses the intermediate transfer belt 10 with a force of approximately 200 gf. The primary transfer roller 51a rotates as the intermediate transfer belt 10 rotates. The primary transfer roller 51b arranged in the second image forming station b, the primary transfer roller 51c arranged in the third image forming station c, and the primary transfer roller 51d arranged in the fourth image forming station d have a similar configuration to the primary transfer roller 51a.

[0652] Hereinafter, the operation of the tenth embodiment will be described.

[0653] like Figure 38 As shown, the adhesion force Fi between the intermediate transfer belt 10 and the transfer carrier particles varies depending on the pressure applied to the intermediate transfer belt 10 during the transfer process. Therefore, to suppress the transfer of transfer carrier particles from the photoconductor drum 1 to the intermediate transfer belt 10 by maintaining Fdr > Fi, the pressure applied to the intermediate transfer belt 10 during the transfer process can be reduced. In the tenth embodiment, the photoconductor drum 1 is not directly pressed by the primary transfer roller 51. Therefore, the pressure applied to the intermediate transfer belt 10 during the transfer process can be reduced compared to the first embodiment. Consequently, the adhesion force Fdr > Fi relationship can be maintained for a long period of time.

[0654] (Carrier particle collecting member)

[0655] Next, the manner of collecting the transfer carrier particles, which is one of the characteristics of the eleventh embodiment, will be described. Figure 40As shown, in the imaging apparatus of the eleventh embodiment, a collection roller 7 and a scraping roller 8 are arranged downstream of the primary transfer portion in the rotational direction of the photoconductor drum 1. The collection roller 7 collects transfer carrier particles from the photoconductor drum 1. Before the transfer carrier particles on the photoconductor drum 1 become contaminated by toner, external additives, corona generators, etc., they are collected on the collection roller 7. This prevents contamination of the photoconductor drum 1 with transfer carrier particles and the associated reduction in primary transfer efficiency. The scraping roller 8 is a sponge roller having a porous elastic layer. The scraping roller 8 is driven to rotate in the opposite direction to the collection roller 7 in the portion in contact with the collection roller 7. With this configuration, the scraping roller 8 scrapes the transfer carrier particles collected on the collection roller 7 while retaining them in the porous elastic layer. The collection roller 7 is an elastic roller composed of a metal core, a base layer made of silicone rubber on the metal core, and a surface layer made of acrylic acid, which are sequentially laminated. The collecting roller 7 is pressed against the photoconductor drum 1 at 1000 gf and is driven to rotate in a forward direction relative to the rotation direction of the photoconductor drum 1 at a peripheral speed of 100% relative to the photoconductor drum 1. The contact portion between the collecting roller 7 and the photoconductor drum 1 has a width of approximately 220 mm in the axial direction of the collecting roller 7 and a width of approximately 1 mm in the rotation direction of the collecting roller 7. Therefore, the contact area between the collecting roller 7 and the photoconductor drum 1 is approximately 2.2×10 -4 (m 2 ).

[0656] like Figure 41 As shown, a large number of dot-shaped transfer carrier particle collecting portions, which are small protrusions, are formed on the surface layer of the collecting roller 7. The transfer carrier particle collecting portions are composed of a urethane resin applied to an acrylic resin on the surface layer of the collecting roller 7. The transfer carrier particle collecting portion 70 has a function of collecting transfer carrier particles from the photoconductor drum 1 to the collecting roller 7 when in contact with the photoconductor drum 1.

[0657] Figure 42A and Figure 42B : is a schematic diagram showing a state in which transfer carrier particles are collected from the photoconductor drum 1 by the transfer carrier particle collecting portion 70 of the collecting roller 7. Urethane resin softer than polycarbonate used for the surface layer of the photoconductor drum 1 is used as a material for the transfer carrier particle collecting portion 70. Figure 42AAs shown, when the transfer carrier particle collecting portion 70 is pressed by the transfer carrier particles on the photoconductor drum 1, the transfer carrier particle collecting portion 70 deforms more than the surface of the photoconductor drum 1. With this configuration, the contact area between the transfer carrier particle collecting portion 70 and the transfer carrier particles increases. As the contact area between the transfer carrier particle collecting portion 70 and the transfer carrier particles increases, the adhesion between the transfer carrier particle collecting portion 70 and the transfer carrier particles increases, so that the transfer carrier particles are easily transferred from the photoconductor drum 1 to the transfer carrier particle collecting portion 70.

[0658] The surface of the collecting roller 7 except the transfer carrier particle collecting portion 70 is composed of an acrylic resin harder than the polycarbonate used for the surface layer of the photoconductor drum 1. Figure 42A As shown, the adhesion between the collecting roller 7 and the transfer carrier particles is weaker than that between the photoconductor drum 1 and the transfer carrier particles, as opposed to the transfer carrier particle collecting portion 70. Therefore, the transfer carrier particles are less likely to be transferred to the surface of the collecting roller 7 other than the transfer carrier particle collecting portion 70.

[0659] From the above, we can see that Figure 42B As shown, after the collecting roller 7 passes through the contact portion with the photoconductor drum 1, the transfer carrier particles adhere to the transfer carrier particle collecting portion 70 of the collecting roller 7 and are collected. On the other hand, the transfer carrier particles do not adhere to the surface of the collecting roller 7 other than the transfer carrier particle collecting portion 70, and remain on the photoconductor drum 1 without being collected. If each of the transfer carrier particle collecting portions 70 on the surface of the collecting roller 7 is too large, there is a problem of reduced primary transfer efficiency due to uneven collection of transfer carrier particles from the photoconductor drum 1 by the collecting roller 7. For this reason, the diameter of each of the transfer carrier particle collecting portions 70 provided on the surface of the collecting roller 7 preferably falls substantially within a circumference of 200 μm.

[0660] When the distribution of the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7 is also too biased, there is a problem in that the primary transfer efficiency is reduced due to uneven collection of the transfer carrier particles from the photoconductor drum 1 by the collecting roller 7. For this reason, a large number of transfer carrier particles may be provided on the surface of the collecting roller 7 with high dispersion.

[0661] Next, measurement results related to the collecting roller 7 of the eleventh embodiment will be described.

[0662] In order to calculate the area ratio of the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7, the surface of the collecting roller 7 was observed with a laser microscope (VK-X200 Keyence Corporation). An observation image was obtained by observing the surface of the collecting roller 7 with the laser microscope at a magnification of 100 times, the observation image was binarized into the transfer carrier particle collecting portion 70 and a portion other than the transfer carrier particle collecting portion 70, and then the area ratio of the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7 was calculated. In the eleventh embodiment, the calculated area ratio of the transfer carrier particle collecting portion 70 on the surface of the transfer roller 7 was 8.2%.

[0663] Subsequently, Fdr2 (the aforementioned Fdr) at the contact portion between the collecting roller 7 and the photoconductor drum 1 is measured. Simultaneously, the adhesion force Fr1 between the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7 and the transfer carrier particles, and the adhesion force Fr2 between the transfer carrier particles and portions of the surface of the collecting roller 7 other than the transfer carrier particle collecting portion 70 are measured. The measurements are performed using a method similar to the measurement of the adhesion force Ft between the toner and the transfer carrier particles described above, and each adhesion force is measured a plurality of times while varying the pressing force of the cantilever against the relevant member of the components. Figure 43 The results of adhesion measurement are shown in Figure 2. Figure 43 As shown, regardless of the pressing force of the cantilever on the horizontal axis, the adhesion force is in the relationship of Fr1 > Fdr2 > Fr2. In other words, (the adhesion force between the transfer carrier particles and the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7) > (the adhesion force between the transfer carrier particles and the surface of the photoconductor drum 1) > (the adhesion force between the transfer carrier particles and the portion of the surface of the collecting roller 7 other than the transfer carrier particle collecting portion 70). This means that the transfer carrier particles are collected from the photoconductor drum 1 to the transfer carrier particle collecting portion 70 on the surface of the collecting roller, and that it is difficult for the transfer carrier particles to be collected from the photoconductor drum 1 to the surface of the collecting roller other than the transfer carrier particle collecting portion 70.

[0664] In the measurement of the eleventh embodiment, as described above, regardless of the pressing force of the cantilever on the horizontal axis, the adhesion forces follow the relationship of Fr1 > Fdr2 > Fr2. However, depending on the materials used for the collection roller 7, the transfer carrier particles, and the photoconductor drum 1, etc., the magnitude relationship of the adhesion forces may vary depending on the pressing force of the cantilever on the horizontal axis. Therefore, when comparing the magnitude relationships of the adhesion forces, the adhesion forces can be compared with the horizontal axis representing the pressing force received by the transfer carrier particles held between the collection roller 7 and the photoconductor drum 1 in the actual contact portion between the collection roller 7 and the photoconductor drum 1.

[0665] The pressing force received by the transfer carrier particles held between the collecting roller 7 and the photoconductor drum 1 in the contact portion between the collecting roller 7 and the photoconductor drum 1 can be calculated as follows. Figure 36A A description is given in which the intermediate transfer belt 10 is replaced by the collecting roller 7. Here, as Figure 36A As shown, it is assumed that the collecting roller 7 and the photoconductor drum 1 are in contact with each other via the transfer carrier particles. The pressing force received by the transfer carrier particles held between the collecting roller 7 and the photoconductor drum 1 in the contact portion between the collecting roller 7 and the photoconductor drum 1 can be calculated by the following expression 10.

[0666] (Pressure of the collecting roller 7 against the photoconductor drum 1) / (Number of transfer carrier particles present in the contact portion between the collecting roller 7 and the photoconductor drum 1) (10)

[0667] “The number of transfer carrier particles present in the contact portion between the collecting roller 7 and the photoconductor drum 1 ” in Expression 10 is calculated by the following Expression 11.

[0668] (Area of ​​the contact portion between the collecting roller 7 and the photoconductor drum 1)×(coverage of the transfer carrier particles on the surface of the photoconductor drum 1) / (cross-sectional area of ​​the transfer carrier particles) (11)

[0669] The pressing force of the collecting roller 7 on the photoconductor drum 1 is 1000 (gf). The area of ​​the contact portion between the collecting roller 7 and the photoconductor drum 1 is 2.2×10 -4 (m 2 ). The coverage of the transfer carrier particles on the surface of the photoconductor drum 1 was 14.8%. By using these values, the cross-sectional area of ​​the transfer carrier particles can be calculated from the average particle size of the transfer carrier particles.

[0670] By substituting the above values ​​into Expression 10 and Expression 11, in the eleventh embodiment, the pressing force received by the transfer carrier particles held between the collecting roller 7 and the photoconductor drum 1 in the contact portion therebetween is calculated to be 2.36 (nN).

[0671] like Figure 43 As shown, even near 2.36 (nN) on the horizontal axis, the adhesion force is in the relationship of Fr1>Fdr2>Fr2. This means that (adhesion force between the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7 and the transfer carrier particles)>(adhesion force between the surface of the photoconductor drum 1 and the transfer carrier particles)>(adhesion force between the portion of the surface of the collecting roller 7 other than the transfer carrier particle collecting portion 70 and the transfer carrier particles).

[0672] In order to form a state in which the transfer carrier particles are collected from the photoconductor drum 1 to the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7 and are difficult to be collected from the photoconductor drum 1 to the surface of the collecting roller 7 other than the transfer carrier particle collecting portion 70, the following relationship may be set. As described above, it is only necessary to satisfy the relationship Fr1>Fdr2>Fr2 in the vicinity of the pressing force received by the transfer carrier particles held between the collecting roller 7 and the photoconductor drum 1 in the contact portion between the collecting roller 7 and the photoconductor drum 1.

[0673] Next, a technique for confirming the effect of the transfer carrier particle collecting portion 70 in the configuration of the eleventh embodiment will be described. First, the imaging apparatus of the eleventh embodiment is caused to form a patch image having a yellow density of 100%. Immediately after the primary transfer of the formed yellow patch image is completed, the imaging apparatus is stopped. The residual toner density on the patch image portion remaining on the photoconductor drum 1a at the yellow station is checked. The measurement of the residual toner density is performed according to the following technique. First, a transparent tape (polyester tape 5511, Nichiban Co., Ltd.) is adhered to the residual toner portion of the yellow patch image on the surface of the photoconductor drum 1a, and the residual toner is captured by the transparent tape. Thereafter, the transparent tape that has captured the residual toner and been peeled off from the photoconductor drum 1a and a new transparent tape are adhered to high-brightness paper (GFC081 Canon, Inc.). Then, the density D1 of the transparent belt of the residual colorant capturing portion and the density D0 of the new transparent belt portion were measured using a reflection densitometer (TC-6DS type reflectometer, produced by Tokyo Denshoku Co., Ltd.). A method was used in which the difference D0-D1 was used as the residual colorant density. The residual colorant density means that the residual colorant decreases as the numerical value decreases. When the value is less than or equal to 1.0, it can be determined that there is almost no residual colorant. The above-mentioned measurement of the residual colorant amount was performed when the imaging device was new, printing at a print ratio of 1% was performed on 1,000 sheets, and then similar measurements were performed again. The surface of the photoconductor drum 1 on which the residual colorant density was measured was observed with an electron microscope, and the presence or absence of melt adhesion of the transfer carrier particles was checked when observing the adhesion state of the transfer carrier particles on the surface of the photoconductor drum 1.

[0674] An image forming apparatus using a collecting roller 7 having no transfer carrier particle collecting portion 70 on the surface of the collecting roller 7 was used as Comparative Example 11 and subjected to an effect confirmation test similar to that of the eleventh embodiment. Other configurations are similar to those of the eleventh embodiment, and thus descriptions thereof are omitted.

[0675] Next, the results of the effect confirmation test for the eleventh embodiment will be described. Figure 44As shown, in the configuration of the eleventh embodiment, the initial residual toner density was 0.3, and the residual toner density after printing 1000 sheets was 0.5. Both the initial residual toner density and the residual toner density after printing 1000 sheets were less than or equal to 1.0, indicating that there was almost no residual toner, and the primary transfer performance was good. Furthermore, after printing 1000 sheets, no melt adhesion of transfer carrier particles was observed on the photoconductor drum 1.

[0676] On the other hand, in the configuration of Comparative Example 11, the initial residual toner density was 0.2; however, the residual toner density after printing 1,000 sheets was 4.5, and the presence of residual toner was confirmed after printing 1,000 sheets. In addition, after printing 1,000 sheets, melt adhesion of transfer carrier particles was observed on the photoconductor drum 1.

[0677] As described above, in the eleventh embodiment, the small transfer carrier particle collecting portion 70 that collects the transfer carrier particles on the photoconductor drum 1 is provided on the surface of the collecting roller 7. In this state, the adhesion force is set to the following relationship: (Adhesion force between the transfer carrier particle collecting portion 70 on the surface of the collecting roller 7 and the transfer carrier particles) > (Adhesion force between the surface of the photoconductor drum 1 and the transfer carrier particles) > (Adhesion force between the portion of the surface of the collecting roller 7 other than the transfer carrier particle collecting portion 70 and the transfer carrier particles). By using the above-described configuration, a decrease in the primary transfer efficiency due to contamination of the transfer carrier particles supplied to the surface of the photoconductor drum 1 is suppressed.

[0678] Therefore, the eleventh embodiment has the following configuration.

[0679] Assume that the pressing force of the developing roller 41 against the photoconductor drum 1 is F1, and the total number of transfer carrier particles interposed between the toner particles and the photoconductor drum 1 in the developing portion is N1. The adhesion force between the transfer carrier particles and the toner particles measured when the transfer carrier particles are pressed against the toner particles at F1 / N1 (which is the pressing force per unit of the transfer carrier particles) is defined as Ft. The adhesion force between the transfer carrier particles and the photoconductor drum 1 measured when the transfer carrier particles are pressed against the photoconductor drum 1 at F1 / N1 is defined as Fdr1. Ft and Fdr1 are ...

Claims

1. An imaging device, comprising: an image bearing member configured to be rotatable; a developing member configured to be rotatable and to carry a developer composed of toner particles and external additive particles attached to surfaces of the toner particles, wherein the developing member is further configured to contact the image bearing member to form a developing portion and to supply the developer to the surface of the image bearing member in the developing portion; a developer accommodating portion configured to accommodate the developer; as well as a transfer member configured to transfer the developer supplied to the surface of the image bearing member to a transfer receiving member, wherein, in a state in which the image bearing member is rotated, external additive particles contained in the developer containing portion and carried on the surface of the developing member are supplied to the surface of the image bearing member in the developing portion, and Wherein, in a case where the pressing force of the developing member against the image bearing member is F1 and the total number of external additive particles interposed between the toner particles and the image bearing member is N1, An adhesion force Ft between the external additive particles and the toner particles measured when the external additive particles are pressed against the toner particles at F1 / N1, and an adhesion force Fdr1 between the external additive particles and the image bearing member measured when the external additive particles are pressed against the image bearing member at F1 / N1, satisfy Ft≤Fdr1, wherein F1 / N1 is a pressing force per unit external additive particle.

2. The imaging device according to claim 1, wherein The developer has protrusions made of fine particles containing an organic silicon polymer, the protrusions being present on the surface of each toner particle, the external additive particles being arranged on the protrusions, and the organic silicon polymer having a composition represented by the following Formula 1, R-Si(O 1 / 2 )3(1) wherein R represents a hydrocarbon group having a carbon number greater than or equal to one and less than or equal to six.

3. The imaging device according to claim 2, wherein In the case where the shortest distance between two adjacent protrusions among the protrusions is a protrusion gap G, the average protrusion gap of the protrusion gaps G is smaller than or equal to the average particle size of the external additive particles.

4. The imaging device according to claim 2, wherein In a case where the height of each of the protruding portions from the surface of each of the toner particles is a protrusion height H, an average protrusion height of the protrusion heights H is less than or equal to an average particle diameter of the external additive particles.

5. The imaging device according to claim 1, wherein The developing member is configured to collect the developer that is not transferred to the transfer-receiving member and remains on the image bearing member.

6. The imaging device according to claim 1, wherein The developer is a single-component developer.

7. The imaging device according to claim 1, further comprising: a first driver configured to drive the image bearing member; a second driver configured to drive the developing member; as well as a control section configured to control the first driver and the second driver, wherein the control portion is configured to control the second driver so that, in the developing portion, a surface movement speed of the developing member and a surface movement speed of the image bearing member are different from each other.

8. The imaging device according to claim 7, further comprising: a charging member configured to be in contact with the image bearing member and to charge a surface of the image bearing member; a charging voltage source configured to apply a charging voltage to the charging member; as well as an exposure unit configured to form an electrostatic latent image by exposing the surface of the image bearing member, Here, the image forming apparatus is capable of executing an image forming mode in which the developer is developed on the electrostatic latent image, and executing a supply mode in which the external additive particles are supplied from the developing member to the image bearing member.

9. The imaging device according to claim 8, wherein The control portion is configured to control the first driver so that the image bearing member rotates one or more times in the feeding mode.

10. The image forming apparatus according to claim 8, further comprising a developing voltage source configured to apply a developing voltage to the developing member, in, In the supply mode and in order to prevent the developer charged with the normal polarity from being developed from the developing member to the image bearing member, the control portion is configured to control the surface potential formed on the surface of the image bearing member in the developing portion so that the surface potential is higher toward the normal polarity than the developing voltage to be applied to the developing member in the developing portion.

11. The imaging device according to claim 1, wherein The external additive particles are silicon dioxide.

12. The imaging device according to claim 1, wherein The external additive particles are organic silica polymers.

13. The imaging device according to claim 1, wherein The external additive particles have an average particle size of greater than or equal to 30 nm and less than or equal to 1000 nm.

14. The imaging device according to claim 1, further comprising: an intermediate transfer member configured to be in contact with the image bearing member to form a contact portion in which the developer is transferred to a surface of the intermediate transfer member; and a driver configured to drive the image bearing member and the intermediate transfer member so that there is a speed difference between a moving speed of a surface of the image bearing member and a moving speed of a surface of the intermediate transfer member, wherein, in a case where a second pressing force of pressing the developing member against the image bearing member is F and a second total number of external additive particles interposed between the toner particles and the image bearing member is N, A second adhesion force Ft between the external additive particles and the toner particles measured when the external additive particles are pressed against the toner particles at F / N and a third adhesion force Fdr between the external additive particles and the image bearing member measured when the external additive particles are pressed against the image bearing member at F / N satisfy Ft≤Fdr, wherein F / N is the second pressing force per unit external additive particles.

15. The imaging device according to claim 14, wherein The speed ratio between the moving speed Vdr of the image bearing member and the moving speed Vb of the intermediate transfer member is defined as Vr=|Vdr-Vb| / Vdr×100, In a transfer portion formed by contact between the transfer member and the intermediate transfer member, a nip width of a nip formed by the image bearing member and the intermediate transfer member is defined as Q, and The weight average particle size of the toner particles is defined as D, Vr and Q satisfy the following relationship, 1 / 2×D(μm)×π≤Vr(%)×Q(μm) / 100≤100(μm).

16. The imaging device according to claim 14, wherein The transfer member is arranged at a position shifted from a position where the image bearing member is arranged in a moving direction of the surface of the intermediate transfer member.

17. The image forming apparatus according to claim 1, further comprising a collecting member configured to be in contact with the image bearing member to form a contact portion and to collect the external additive particles from a surface of the image bearing member in the contact portion, in, the collecting member includes an external additive particle collecting portion at a surface of the collecting member, wherein the external additive particle collecting portion is configured to collect the external additive particles, wherein, in a state in which the image bearing member is rotated, external additive particles carried on the surface of the developing member and accommodated in the developer accommodating portion are supplied to the surface of the image bearing member in the developing portion, and wherein, in a case where the pressing force of pressing the collecting member against the image bearing member is F2 and the second total number of external additive particles interposed between the toner particles and the image bearing member in the contact portion is N2, The adhesion force Fr between the external additive particles and the external additive particle collecting portion measured when the external additive particles are pressed against the external additive particle collecting portion at F2 / N2 and the adhesion force Fdr2 between the external additive particles and the image bearing member measured when the external additive particles are pressed against the image bearing member at F2 / N2 satisfy Fr≥Fdr2, where F2 / N2 is the pressing force per unit external additive particle.

18. The imaging device according to claim 17, wherein The external additive particle collecting portion has a size such that the external additive particle collecting portion falls within a circle having a diameter less than or equal to 200 μm.

19. The imaging device according to claim 17, in, F1=F2, N1=N2, and Herein, the developing member also serves as a collecting member.

20. The imaging device according to claim 19, wherein A value obtained by multiplying an area ratio of the external additive particle collecting portion to an area of ​​the surface of the collecting member by a peripheral speed ratio represented by a ratio between a surface moving speed of the collecting member and a surface moving speed of the image bearing member is higher than or equal to 1.0%.

21. The image forming apparatus according to claim 20, further comprising a rotating member configured to be in contact with the image bearing member to form a contact portion and to be rotated by rotation of the image bearing member, in, A carrying region of the developing member that carries the developer in a rotational axis direction of the developing member is shorter than the contact portion in the rotational axis direction.

22. The imaging device according to claim 21, wherein The end amount of the external additive particles attached to the surface of the image bearing member at the end portion of the image bearing member in the direction of the rotation axis is smaller than the center amount of the external additive particles attached to the surface of the image bearing member in the center area at the center portion of the image bearing member in the direction of the rotation axis.

23. The imaging device according to claim 22, wherein An end region at the end portion of the image bearing member is a non-image forming region that is not used for image formation.

24. The imaging device according to claim 22, further comprising: The collecting member is configured to collect external additive particles attached to the area at the end portion of the image bearing member in a collecting portion.

25. The imaging device according to claim 24, wherein The collecting member is configured to be in contact with the image bearing member to form the collecting portion.

26. The imaging device according to claim 24, wherein The collecting member is configured to be in contact with the developing member to form the collecting portion.

27. The imaging device according to claim 25, wherein In a case where the pressing force of the collecting member against the image bearing member is F2 and the total number of external additive particles interposed between the image bearing member or the developing member and the collecting member in the collecting portion is N2, An adhesion force Fr between the external additive particles and the collecting member measured when the external additive particles are pressed against the toner particles at F2 / N2 and an adhesion force Fdr2 between the external additive particles and the collecting member measured when the external additive particles are pressed against the collecting member at F2 / N2 satisfy Fr≥Fdr2, where F2 / N2 is a pressing force per unit external additive particle.

28. The image forming apparatus according to claim 21, further comprising a bearing member that supports the rotating member so that the rotating member can rotate and is arranged at an end portion of the image bearing member in the rotation axis direction, in, In a state where the image bearing member and the rotating member rotate and (i) a torque generated by friction between the image bearing member and the rotating member is T1 and (ii) a torque generated by sliding between the rotating member and the bearing member is T2, T1>T2 is satisfied.

29. The imaging device according to claim 21, wherein The rotating member is a charging member configured to charge the surface of the image bearing member.

30. The imaging device according to claim 21, wherein The rotating member is a foreign matter collecting member configured to collect foreign matter from the surface of the image bearing member, wherein the foreign matter includes at least one of a developer and paper dust.

31. An imaging device, comprising: a first imaging unit including a first image bearing member configured to be rotatable and a first developing member configured to be rotatable and to carry a first developer composed of first toner particles and first external additive particles attached to surfaces of the first toner particles, wherein the first developing member is further configured to contact the first image bearing member to form a first developing portion and to supply the first developer to a surface of the first image bearing member in the first developing portion to form a first developer image on the surface of the first image bearing member; a second imaging unit including a second image bearing member configured to be rotatable and a second developing member configured to be rotatable and to carry a second developer composed of second toner particles and second external additive particles attached to surfaces of the second toner particles, wherein the second developing member is further configured to contact the second image bearing member to form a second developing portion, and to supply the second developer to a surface of the second image bearing member in the second developing portion to form a second developer image on the surface of the second image bearing member; an intermediate transfer member configured to contact the first image bearing member to form a first contact portion in which the first developer is transferred to a surface of the intermediate transfer member, and to contact the second image bearing member to form a second contact portion in which the second developer is transferred to the surface of the intermediate transfer member; as well as a transfer member configured to be in contact with the intermediate transfer member to form a transfer portion and to transfer the first developer image and the second developer image formed on the surface of the intermediate transfer member to a recording medium in the transfer portion, wherein, in a state in which the first image bearing member is rotated, first external additive particles carried on the surface of the first developing member in the first developing portion are supplied to the surface of the first image bearing member, and in a state in which the second image bearing member is rotated, second external additive particles carried on the surface of the second developing member in the second developing portion are supplied to the surface of the second image bearing member, wherein the surface of the intermediate transfer member is movable, and the first imaging unit and the second imaging unit are arranged so that the first contact portion is formed downstream of the transfer portion and upstream of the second contact portion in the moving direction of the surface of the intermediate transfer member, in, In a case where the pressing force of pressing the first developing member against the first image bearing member is F1 and the total number of the first external additive particles interposed between the first toner particles and the first image bearing member is N1, an adhesion force Ft1 between the first external additive particles and the first toner particles measured when the first external additive particles are pressed against the first toner particles at F1 / N1, which is a pressing force per unit external additive particle, and an adhesion force Fdr1 between the first external additive particles and the first image bearing member measured when the first external additive particles are pressed against the first image bearing member at F1 / N1, satisfying Ft1≤Fdr1, in, In a case where the pressing force of pressing the second developing member against the second image bearing member is F2 and the total number of the second external additive particles interposed between the second toner particles and the second image bearing member is N2, an adhesion force Ft2 between the second external additive particles and the second toner particles measured when the second external additive particles are pressed against the second toner particles at F2 / N2, which is a pressing force per unit external additive particle, and an adhesion force Fdr2 between the second external additive particles and the second image bearing member measured when the second external additive particles are pressed against the second image bearing member at F2 / N2, satisfying Ft2≤Fdr2, and wherein, after each of the first image-bearing member and the second image-bearing member rotates in a state in which the first image-bearing member and the first developing member are in contact with each other and the second image-bearing member and the second developing member are in contact with each other, an attachment area of ​​the second external additive particles attached to the surface of the second image-bearing member is greater than an attachment area of ​​the first external additive particles attached to the surface of the first image-bearing member.

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