Image forming apparatus

Abstract

To effectively supply fine particles to a surface of a photoconductor drum to improve transfer efficiency.SOLUTION: An image forming apparatus has a rotatable developer carrier that carries a developer composed of a toner particle and carrier particles adhered to the surface of the toner particle. When a pressing force for pressing the developer carrier against an image carrier is F, and the total number of carrier particles interposed between the toner particle and the image carrier is N, the relationship between an adhesion force Ft formed between the carrier particles and the toner particle measured when the carrier particles are pressed against the toner particle with F / N being a pressing force per unit carrier particle and an adhesion force Fdr formed between the carrier particles and the image carrier measured when the carrier particles are pressed against the image carrier with F / N satisfies Ft≤Fdr.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

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

[0003] In this image forming apparatus, as a transfer step, a voltage is applied from a voltage power source to a transfer member disposed opposite to the photosensitive drum as an image carrier, so that the toner image formed on the surface of the photosensitive drum is electrostatically transferred onto an intermediate transfer body or a recording material. When forming toner images of a plurality of colors, this transfer step is repeatedly executed for the toner images of the plurality of colors to form toner images of the plurality of colors on the surface of the intermediate transfer body or the recording material. The developer (toner) that has not been transferred from the photosensitive drum to the intermediate transfer body or the recording material is removed from the photosensitive drum by a cleaning member and is stored as waste toner in a waste toner storage portion in the cleaning unit.

[0004] However, in recent years, a cleanerless system in which the cleaning system on the surface of the photosensitive drum is omitted for the purpose of downsizing the apparatus has been proposed. In order to achieve the cleanerless system, it is preferable to improve the transfer efficiency of the toner image from the photosensitive drum to the intermediate transfer body and reduce the residual transfer toner remaining on the surface of the photosensitive drum after the toner image is transferred by the transfer member.

[0005] Patent Document 1 proposes a configuration in which, in order to achieve a cleanerless system, fine particles are previously attached to the surface of the photosensitive drum, and the fine particles are interposed between the photosensitive drum and the toner image to reduce the adhesion force between the photosensitive drum and the toner and improve the transfer efficiency.

[0006] Furthermore, Patent Document 1 proposes a configuration in which, as a means for attaching fine particles to the surface of the photosensitive drum, fine particles are supplied onto the photosensitive drum from a developing device by using toner externally added with fine particles.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] However, in order to supply only fine particles from the toner of the developing device to the surface of the photosensitive drum as in Patent Document 1, it is necessary to detach the fine particles attached to the toner from the toner and transfer them to the drum side. In a toner to which fine particles such as silica generally used are externally added, since the adhesion force between the toner and the fine particles is large, it has been difficult to supply a sufficient amount of fine particles to the surface of the photosensitive drum to improve the transfer efficiency.

[0009] Therefore, an object of the present invention is to improve the transfer efficiency by effectively supplying fine particles from the developing device to the surface of the photosensitive drum.

Means for Solving the Problems

[0010] Therefore, the image forming apparatus according to the present invention includes a rotatable image carrier, and a rotatable developer carrier that carries a developer composed of toner particles and carrier particles adhering to the surface of the toner particles. The developer carrier forms a developing portion in contact with the image carrier, and supplies the developer to the surface of the image carrier in the developing portion. The image forming apparatus further includes a developer storage portion that stores the developer. In a state where the image carrier is rotating, in the developing portion, carrier particles carried on the surface of the developer carrier and stored in the developer storage portion can be supplied to the surface of the image carrier. When the pressing force for pressing the developer carrier against the image carrier is F, and the total number of the carrier particles intervening between the toner particles and the image carrier is N, the adhesive force Ft formed between the carrier particles and the toner particles measured when the carrier particles are pressed against the toner particles with a pressing force of F / N per unit carrier particle, and the adhesive force Fdr formed between the carrier particles and the image carrier measured when the carrier particles are pressed against the image carrier with the F / N satisfy Ft ≦ Fdr. The developer has convex portions on the surface of the toner particles, and the carrier particles are arranged on the convex portions. When the closest distance between adjacent convex portions is the convex interval G, the average of the convex intervals G is equal to or less than the average particle diameter of the carrier particles.

Advantages of the Invention

[0011] As described above, according to the present invention, the transfer efficiency can be improved by effectively supplying fine particles from the developing device to the surface of the photosensitive drum.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] Hereinafter, with reference to the drawings, preferred embodiments of the present invention will be described in detail by way of example. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments should be appropriately changed according to the configuration of the apparatus to which the present invention is applied and various conditions. Therefore, unless otherwise specifically stated, the scope of the present invention is not intended to be limited thereto only.

Example

[0014] 1. Image forming apparatus The present invention particularly relates to an image forming apparatus using a so-called drum cleanerless system without a cleaning means for an image carrier.

[0015] FIG. 1 is a schematic diagram showing an example of a color image forming apparatus, and the configuration and operation of the image forming apparatus according to the present embodiment will be described with reference to FIG. 1. The image forming apparatus according to the present embodiment is a so-called tandem type printer provided with image forming stations a to d. The first image forming station a forms an image of each color of yellow (Y), the second image forming station b forms an image of magenta (M), the third image forming station c forms an image of cyan (C), and the fourth image forming station d forms an image of black (Bk). The configurations of the respective image forming stations are the same except for the color of the toner to be accommodated, and hereinafter, the first image forming station a will be used for explanation. Further, hereinafter, when no particular distinction is required, a to d in Y, M, C, K will be omitted and explained generically.

[0016] The first image forming station a includes a drum-shaped electrophotographic photoreceptor (hereinafter referred to as a photosensitive drum) 1a, a charging roller 2a as a charging means, an exposure unit 3a, and a developing device 4a.

[0017] The photosensitive drum 1a is an image carrier that is rotationally driven by a photosensitive drum driving unit 110 at a peripheral speed (process speed) of 150 mm / sec in the direction of the arrow and carries a toner image. The photosensitive drum 1a is provided with a photosensitive layer and a surface layer on an aluminum base tube having a diameter of φ20 mm, and the surface layer uses a thin film layer having a thickness of 20 μm formed of polyarylate.

[0018] When a control unit 200 such as a controller receives an image signal, an image forming operation is started, and the photosensitive drum 1a is rotationally driven. During the rotation of the photosensitive drum 1a, it is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by a charging roller 2a, and is exposed according to the image signal by an exposure unit 3a. As a result, an electrostatic latent image corresponding to the yellow color component image of the target color image is formed. Next, the electrostatic latent image is developed by a developing device (yellow developing device) 4a at the developing position and visualized as a yellow toner image.

[0019] The charging roller 2a as a charging member is in contact with the charging portion on the surface of the photosensitive drum 1a with a predetermined pressure contact force, and is driven to rotate passively with respect to the photosensitive drum 1a by friction with the surface of the photosensitive drum 1a. Also, a predetermined DC voltage is applied from a charging voltage power supply 120 to the rotation axis of the charging roller 2a according to the image forming operation. In this embodiment, the charging roller 2a has an elastic layer made of a conductive elastic body with a thickness of 1.5 mm and a volume resistivity of about 1×10 6 Ωcm provided on a metal shaft with a diameter of φ5.5 mm. Then, according to the image forming operation, the control unit 200 applies a DC voltage of -1050 V as a charging voltage to the rotation axis of the charging roller 2a to charge the surface of the photosensitive drum 1a to -500 V, which is a predetermined potential. The surface potential of the photosensitive drum 1a was measured with a surface potentiometer Model 344 manufactured by Trek. The surface potential of the photosensitive drum 1a at this time, -500 V, is the surface potential of the photosensitive drum 1 during non-image formation and is the dark portion potential (Vd) at which toner image development is not performed. Also, a large number of convex portions are provided on the surface layer of the charging roller 2a, and the average height of the convex portions is about 10 μm. The convex portions provided on the surface layer of the charging roller 2a serve as a spacer between the charging roller 2a and the photosensitive drum 1a in the charging portion. When transfer residual toner, which is toner remaining on the photosensitive drum 1a without being transferred in the primary transfer portion described later, enters the charging portion, it suppresses the charging roller 2a from being contaminated by the transfer residual toner by preventing the portions other than the convex portions from touching the transfer residual toner.

[0020] The exposure unit 3a includes a laser driver, a laser diode, a polygon mirror, an optical lens system, etc. As shown in FIG. 2, the exposure unit 3 inputs, via the interface 201 from the controller 202, into the control unit 200, and the time-series electrical digital pixel signals of the image information that has been image-processed are input. In this embodiment, the exposure amount is adjusted so that the image formation potential Vl of the photosensitive drum 1 of the electrostatic latent image portion after being exposed by the exposure unit 3a becomes -100V. The image formation potential is also referred to as the bright portion potential.

[0021] The developing unit 4a includes a developing roller 41a as a developing member (developer carrier) and a non-magnetic one-component developer composed of toner and transfer carrier particles described later. The developing unit 4a is a developing means for developing the electrostatic latent image into a toner image on the photosensitive drum 1, and is a developer accommodating portion for accommodating the developer. The developing unit 4a and the image forming apparatus main body 100 are provided with a contact / separation mechanism 40 for controlling the contact / separation state (developing separation) between the developing roller 41a and the photosensitive drum 1a as shown in FIG. 2. The control unit 200 causes the developing roller 41a and the photosensitive drum 1a to contact and separate according to the image forming operation and the like. When the developing roller 41a contacts the photosensitive drum 1a, 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 photosensitive drum 1a, is 2 mm in the rotational direction of the photosensitive drum 1 and 220 mm in the longitudinal direction of the photosensitive drum. The developing roller 41a is rotationally driven by the developing roller driving unit 130 in the forward direction of the surface movement direction of the photosensitive drum 1a so that the surface movement speed (hereinafter, circumferential speed) in the developing nip portion becomes equal to the circumferential speed of the photosensitive drum 1a.

[0022] The pre-exposure unit 5a as a charge removing means removes charge by exposing the surface of the photosensitive drum 1a before the surface of the photosensitive drum 1a is charged by the charging roller 2a. By removing the charge on the surface of the photosensitive drum 1a, it has the role of equalizing the surface potential formed on the photosensitive drum 1 and the role of controlling the discharge amount due to discharge occurring in the charged portion.

[0023] Further, during the contact between the developing roller 41a and the photosensitive drum 1a during the image forming operation, the control unit 200 controls to apply a DC voltage of -300V as the developing voltage Vdc from the developing voltage power supply 140 to the shaft of the developing roller 41a. During image formation, the toner carried on the developing roller 41a is developed on the image forming potential Vl portion of the photosensitive drum 1a by the electrostatic force generated by the potential difference between the developing voltage Vdc = -300V and the image forming potential Vl = -100V of the photosensitive drum 1a.

[0024] Here, in the following description, regarding the potential and the applied voltage, when the absolute value is larger on the negative polarity side (for example, -1000V compared to -500V), it is referred to as a high potential, and when the absolute value is smaller on the negative polarity side (for example, -300V compared to -500V), it is referred to as a low potential. This is for considering the toner having a negative charging property in this embodiment as a reference.

[0025] Also, the voltage in this embodiment is expressed as the potential difference from the ground potential (0V). Therefore, the developing voltage Vdc = -300V is interpreted as having a potential difference of -300V due to the developing voltage applied to the shaft of the developing roller 41a with respect to the ground potential. This is the same for the charging voltage, transfer voltage, etc.

[0026] Next, the control unit 200 will be described. FIG. 2 is a control block diagram showing the schematic control mode of the main part of the image forming apparatus 100 in the present embodiment. The controller 202 exchanges various electrical information with the host device, and comprehensively controls the image forming operation of the image forming apparatus 100 through the interface 201 according to a predetermined control program and reference table in the control unit 202. The control unit 202 includes a CPU 155 which is a central element for performing various arithmetic processes, and memories 154 such as a ROM and a RAM which are storage elements. The RAM stores the detection results of sensors, the count results of counters, arithmetic results, etc., and the ROM stores control programs, data tables obtained in advance by experiments, etc. Various control targets, sensors, counters, etc. in the image forming apparatus 100 are connected to the control unit 200. The control unit 200 controls the exchange of various electrical information signals, the driving timing of each part, etc., and performs control of a predetermined image forming sequence. For example, the control unit 200 controls the voltages applied by the charging voltage power supply 120, the developing voltage power supply 140, the exposure unit 3, the primary transfer voltage power supply 160, and the secondary transfer voltage power supply 150, and the exposure amount. In addition, control of the photosensitive drum driving unit 110, the developing roller driving unit 130, and the developing contact separation mechanism 40 is also performed. Then, this image forming apparatus 100 forms an image on the recording material P based on the electrical image signal input from the host device to the controller 202. Examples of the host device include an image reader, a personal computer, a facsimile machine, a smartphone, etc.

[0027] The toner in the present embodiment is a non-magnetic toner having a negative charging property manufactured by the suspension polymerization method, with a volume average particle diameter of 7.0 μm, and is charged negatively when carried on the developing roller 41a. The volume average particle diameter of the toner was measured with a laser diffraction particle size distribution analyzer LS-230 manufactured by Beckman Coulter, Inc. Details of the toner will be described later.

[0028] The intermediate transfer belt 10 as an intermediate transfer member is stretched by a plurality of stretching members 11, 12, and 13, and is rotationally driven at the same peripheral speed as the photosensitive drum 1a in the direction of moving in the circumferential direction at the opposing portion in contact with the photosensitive drum 1a. A DC voltage of 200V is applied from the primary transfer voltage power source 160 to the primary transfer roller 14a as a primary transfer member during primary transfer in the image forming operation. The yellow toner image formed on the photosensitive drum 1a is electrostatically transferred onto the intermediate transfer belt 10 in the process of passing through the primary transfer portion which is the contact portion of the primary transfer roller 14a via the photosensitive drum 1a and the intermediate transfer belt 10.

[0029] The primary transfer roller 14a is a cylindrical metal roller with a diameter of φ6mm, and the material used is nickel-plated SUS. The primary transfer member 14a is arranged at a position offset by 8mm downstream in the moving direction of the intermediate transfer belt 10 with respect to the center position of the photosensitive drum 1a, and the intermediate transfer belt 10 is configured to wrap around the photosensitive drum 1a. The primary transfer roller 14a is arranged at a position lifted by 1mm with respect to the horizontal plane formed by the photosensitive drum 1a and the intermediate transfer belt 10 so as to ensure the amount of winding of the intermediate transfer belt 10 around the photosensitive drum 1a. And the intermediate transfer belt 10 is pressed with a force of about 200 gf. The primary transfer roller 14a rotates in a driven manner as the intermediate transfer belt 10 rotates. Also, the primary transfer rollers 14b arranged at the second image forming station b, the primary transfer rollers 14c arranged at the third image forming station c, and the primary transfer rollers 14d arranged at the fourth image forming station d have the same configuration as the primary transfer roller 14a.

[0030] Hereinafter, in the same manner, a magenta toner image of the second color, a cyan toner image of the third color, and a black toner image of the fourth color are formed by the second, third, and fourth image forming stations b, c, and d, and are sequentially transferred and stacked on the intermediate transfer belt 10. Then, a composite color image corresponding to the target color image is obtained.

[0031] The four-color toner images on the intermediate transfer belt 10 are collectively transferred onto the surface of the recording material P fed by the paper feeding means 50 in the process of the secondary transfer step of passing through the secondary transfer nip portion formed by the intermediate transfer belt 10 and the secondary transfer roller 15 serving as the secondary transfer member. The secondary transfer roller 15 is in contact with the intermediate transfer belt 10 with a pressure of 50 N to form the secondary transfer nip portion. The secondary transfer roller 15 rotates passively with respect to the intermediate transfer belt 10, and when the toner on the intermediate transfer belt 10 is secondarily transferred onto the recording material P such as paper, a voltage of 1500 V is applied from the secondary transfer voltage power supply 150.

[0032] Thereafter, the recording material P carrying the four-color toner images is introduced into the fixing device 30. By being heated and pressurized by the fixing device 30, the four-color toner is melted and mixed and fixed to the recording material P. The toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the cleaning device 17.

[0033] The cleaning device 17 has a cleaning blade or the like that contacts the outer peripheral surface of the intermediate transfer belt 10 to scrape off the toner remaining on the intermediate transfer belt 10 and collect it 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 in the rotation direction of the intermediate transfer belt 10 from the secondary transfer portion of the intermediate transfer belt 10.

[0034] Through the above operations, a full-color printed image is formed.

[0035] 2. Developer, Toner, Transfer Carrier Particles Next, the developer, toner, and transfer carrier particles used in this embodiment will be described in detail.

[0036] In this embodiment, a mixture of toner and external additive A, which is transfer carrier particles, was used as the developer. Here, the transfer carrier particles are particles that are interposed between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1 to reduce the adhesion force between the toner image and the photosensitive drum 1 and improve the primary transfer efficiency of the toner image. The toner is toner particles containing toner mother particles containing a release agent and an organosilicon polymer on the surface of the toner mother particles.

[0037] The organosilicon polymer has a T3 unit structure represented by R-Si(O 1 / 2 )3, where R represents an alkyl group or a phenyl group having 1 to 6 carbon atoms, and the organosilicon polymer forms convex portions on the surface of the toner mother particles.

[0038] The convex portions are characterized by being in surface contact with the surface of the toner mother particles. By being in surface contact, a remarkable inhibitory effect on the movement, detachment, and burial of the convex portions can be expected.

[0039] The degree of surface contact will be described with reference to the schematic diagrams of the convex portions shown in FIGS. 3, 4, 5, and 6.

[0040] 61 shown in FIG. 3 is a cross-sectional image of toner particles where about 1 / 4 of the toner particles can be seen, 62 are toner particles, 63 is the surface of the toner mother particles, and 64 are the convex portions. The cross-section of the toner particles can be observed using a scanning transmission electron microscope (hereinafter also referred to as STEM) described later.

[0041] Observe the cross-sectional image of the toner and draw a line along the circumference of the surface of the toner mother particles. Perform a conversion to a horizontal image based on the line along the circumference. In the horizontal image, the length of the line along the circumference at the portion where the convex portion and the toner mother particle form a continuous interface is defined as the convex width w.

[0042] Also, in the normal direction of the convex width w, the maximum length of the convex portion is defined as the convex diameter D, and the length from the apex of the convex portion to the line along the circumference in the line segment forming the convex diameter D is defined as the convex height H.

[0043] In FIGS. 4 and 6, the convex diameter D and the convex height H are the same, and in FIG. 5, the convex diameter D is larger than the convex height H.

[0044] Further, FIG. 6 schematically shows the adhesion state of particles similar to bowl-shaped particles in which the central portion of the hemispherical particles is recessed, obtained by crushing or cracking the hollow particles.

[0045] In FIG. 6, the convex width W is the total length of the organosilicon polymer in contact with the surface of the toner mother particles. That is, the convex width W in FIG. 6 is the sum of W1 and W2.

[0046] The number average value of the convex height H is 30 nm or more and 300 nm or less, and preferably 30 nm or more and 200 nm or less. When the number average value of the convex height H is 30 nm or more, a spacer effect occurs between the surface of the toner mother particles and the transfer member, and the transferability is remarkably improved. On the other hand, when the number average value of the convex height H is 300 nm or less, the suppression effect on movement, detachment, and burial is remarkable, and high transferability is maintained even in long-term use. In the convex portion where the convex height H is 30 nm or more and 300 nm or less, the cumulative distribution of the convex height H is taken. When the convex height corresponding to 80% by number from the smaller side of the convex height H is defined as H80, H80 is preferably 65 nm or more and 120 nm or less, and more preferably 75 nm or more and 100 nm or less. By H80 being within the above range, the transferability can be further improved.

[0047] The number average particle diameter R of the primary particles of the external additive A is preferably 30 nm or more and 1200 nm or less. By R being 30 nm or more, a spacer effect is exhibited between the transfer member, and high transferability is exhibited. Also, the larger R is, the more the transfer performance 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.

[0048] The ratio of the number average particle diameter R of the primary particles of external additive A to the number average value of the convex height H is preferably 1.00 or more and 4.00 or less. When the ratio [(number average particle diameter R of the primary particles of external additive A) / (number average value of convex height H)] is within the above range, it is possible to achieve both excellent transferability and low-temperature fixability that can withstand extended lifespan.

[0049] When the number average value of the convex height H is 30 nm, which is the minimum value, if R is 30 nm or more, a spacer effect can be exhibited between the transfer member and the external additive A, and the transferability can be improved. It is considered that the external additive A is substituted at a location where there is no convex portion due to the influence of desorption or the like, and the spacer effect is exhibited. That is, if R is less than 30 nm, it is difficult to exhibit the spacer effect.

[0050] The fixation rate of external additive A to the toner particle surface is preferably 0% or more and 20% or less, and more preferably 0% or more and 10% or less. When the fixation rate is within the above range, the external additive A can move more easily on the surface of the toner particles, and the transferability can be further improved by the convex portion substitution effect. In the fixing process of fixing the toner to the fixing member, an appropriate amount of release agent oozes out from the toner mother particles, improving the separation performance between the fixing member and the paper.

[0051] By observing the surface of the toner with a scanning electron microscope, a backscattered electron image of a 1.5 μm square area on the toner surface is obtained. When a binarized image is obtained such that the organosilicon polymer portion in the backscattered electron image becomes the bright part, the area ratio of the bright part area of the image to the total area of the image (hereinafter simply referred to as the area ratio of the bright part area) is 30.0% or more and 75.0% or less. Further, the area ratio of the bright part area of the image is preferably 35.0% or more and 70.0% or less. The higher the area ratio of the bright part area, the higher the proportion of the organosilicon polymer present on the surface of the toner mother particles. When the area ratio of the bright part area is higher than 75.0%, the proportion of the components derived from the toner mother particles present on the surface of the toner mother particles is small, and bleeding of the release agent from the toner mother particles is less likely to occur, but paper wrapping around the fixing device is likely to occur during low-temperature fixing. On the other hand, when the area ratio of the bright part area of the image is less than 30.0%, the proportion of the components derived from the toner mother particles present on the surface of the toner mother particles is large. That is, the exposed area of the components derived from the toner mother particles on the surface of the toner mother particles is large, and the transferability in the initial stage of use decreases. The area ratio of the bright part area of the image is hereinafter also referred to as the coating rate of the organosilicon polymer on the surface of the toner mother particles.

[0052] External additive A is not particularly limited as long as the number average particle diameter R of the primary particles is 30 nm or more and 1000 nm or less, and various organic fine particles or inorganic fine particles can be used. From the viewpoint of being easy to impart fluidity and being easily negatively charged like the toner mother particles, external additive A preferably contains silica fine particles. The content of the silica fine particles in external additive A is preferably 50% by mass or more, and it is more preferable that external additive A is silica fine particles. The content of external additive A in the toner is preferably 0.02% by mass or more and 5.00% by mass or less, and more preferably 0.05% by mass or more and 3.00% by mass or less.

[0053] Examples of the organic fine particles or inorganic fine particles other than the silica fine particles include the following. (1) Fluidity imparting agents: alumina fine particles, titanium oxide fine particles, carbon black, and fluorinated carbon. (2) Abrasive: fine particles of metal oxides (such as strontium titanate, cerium oxide, alumina, 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). (3) Lubricant: fine particles of fluororesins (such as vinylidene fluoride and polytetrafluoroethylene), fine particles of fatty acid metal salts (such as zinc stearate and calcium stearate). (4) Charge control fine particles: fine particles of metal oxides (such as tin oxide, titanium oxide, zinc oxide, and alumina), carbon black.

[0054] For improving the fluidity of the toner and making the charge of toner particles uniform, silica fine particles and the organic or inorganic fine particles may be those subjected to a hydrophobization treatment.

[0055] Examples of the treatment agent for the hydrophobization treatment include unmodified silicone varnish, various modified silicone varnishes, unmodified silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organosilicon compounds, and organic titanium compounds. These treatment agents may be used alone or in combination.

[0056] As the silica fine particles, known silica fine particles can be used, and either dry silica fine particles or wet silica fine particles may be used. Preferably, they are wet silica fine particles obtained by the sol-gel method (hereinafter also referred to as sol-gel silica).

[0057] Figure 7 is an enlarged view of the developer used in this example. As shown in Figure 7, the developer of this example is formed by arranging external additive A, which is a transfer carrier particle, on the toner surface where a large number of convex portions of an organosilicon polymer are formed.

[0058] The convex interval G and convex height H on the toner surface shown in Fig. 7 can be measured using a scanning transmission electron microscope (hereinafter also referred to as STEM) described later. Further, the convex interval G and convex height H can also be measured with a scanning probe microscope (hereinafter SPM). The scanning probe microscope (hereinafter SPM) is equipped with a probe, a cantilever supporting the probe, and a displacement measurement system for detecting the bending of the cantilever, and detects the atomic force (attractive force or repulsive force) between the probe and the sample to observe the shape of the sample surface.

[0059] If the convex interval G is larger than the transfer carrier, when the transfer carrier particles are arranged between the convex portions, they will come into contact with the toner matrix, and the adhesion force Ft between the transfer carrier particles and the toner will increase, making it difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1. Therefore, it is preferable that the number average value of the convex interval G is smaller than the number average particle diameter of the transfer carrier particles.

[0060] Also, if the convex height H is higher than the particle diameter of the transfer carrier particles, the convex portion will contact the photosensitive drum 1 earlier than the transfer carrier particles, making it difficult for the transfer carrier particles to contact the photosensitive drum 1, and making it difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1. Therefore, it is preferable that the number average value of the convex height H is smaller than the number average particle diameter of the transfer carrier particles.

[0061] However, as described above, it is preferable that the adhesion force Ft between the transfer carrier particles and the toner is smaller than the adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1. Therefore, as the material of the transfer carrier particles, it is preferable to select a material that reduces the adhesion force Ft of the transfer carrier particles to the toner. For example, as in this embodiment, when the convex portion on the toner surface is formed of a silica-based material such as an organic silica polymer, it is preferable to select a silica-based material with a material composition close to that of the convex portion as the material of the transfer carrier particles in order to reduce the adhesion force between the convex portion and the transfer carrier particles.

[0062] From the perspective of supplying transfer carrier particles from the developing roller 41 to the photosensitive drum 1, it is preferable to have a larger number of transfer carrier particles covering the toner. However, if the addition amount of the transfer carrier particles is too large, the risk of member contamination within the image forming apparatus 100 increases. Therefore, it is preferable to adjust according to the desired primary transferability.

[0063] The primary transferability improves as the coverage rate of the transfer carrier particles on the photosensitive drum 1 increases. In order to obtain sufficient primary transferability, it is preferable that the coverage rate of the transfer carrier particles on the photosensitive drum 1 is 10% or more. However, as the coverage rate of the transfer carrier particles on the photosensitive drum 1 increases, the degree of improvement in the primary transferability becomes dull, and the risk of various member contaminations of the image forming apparatus due to the transfer carrier particles increases. Therefore, it is preferable to keep the coverage rate of the transfer carrier particles on the photosensitive drum 1 within 50%.

[0064] 3. Method for Measuring Physical Properties of Developer Hereinafter, various measurement methods will be described.

[0065] <Observation Method of Cross-Section of Toner in Scanning Transmission Electron Microscope (STEM)> The cross-section of the toner observed with a scanning transmission electron microscope (STEM) is prepared as follows.

[0066] Hereinafter, the procedure for preparing the cross-section of the toner will be described. When organic fine particles or inorganic fine particles are externally added to the toner, a sample from which the organic fine particles or inorganic fine particles have been removed by the following method or the like is used.

[0067] Add 160 g of sucrose (manufactured by Kishida Chemical Co., Ltd.) to 100 mL of ion-exchanged water, and dissolve it while stirring with a hot water bath to prepare a thick sucrose solution. In a centrifuge tube (capacity 50 mL), put 31 g of the above thick sucrose solution and 6 mL of Contaminon N (a 10% by mass aqueous solution of a neutral detergent for precision measuring instrument cleaning at pH 7 composed of a nonionic surfactant, an anionic surfactant, and an organic builder, manufactured by Wako Pure Chemical Industries, Ltd.). Add 1.0 g of toner here, and loosen the toner lumps with a spatula or the like. Shake the centrifuge tube with a shaker (sold by AS ONE Corporation) at 300 spm (strokes per min) for 20 minutes. After shaking, transfer the solution to a glass tube (50 mL) for a swing rotor, and separate it with a centrifuge (manufactured by Kokusan Co., Ltd., model H-9R) at 3500 rpm for 30 minutes. By this operation, the toner particles and the external additive are separated. Visually confirm that the toner particles and the aqueous solution are sufficiently separated, and collect the separated toner particles in the uppermost layer with a spatula or the like. After filtering the collected toner particles with a vacuum filter, dry them with a dryer for 1 hour or more to obtain a sample for measurement. Repeat this operation a plurality of times to ensure the required amount.

[0068] Also, regarding whether the convex portion contains an organosilicon polymer, it is confirmed by combining elemental analysis by energy dispersive X-ray analysis (EDS).

[0069] Toner is sprayed onto a cover glass (Matsunami Glass Industry Co., Ltd., square No. 1) so as to form a single layer. Using an osmium (Os) plasma coater (Filgen, Inc., OPC80T), an Os film (5 nm) and a naphthalene film (20 nm) are applied to the toner as a protective film. Next, a tube made of PTFE (outer diameter 3 mm (inner diameter 1.5 mm) × 3 mm) is filled with a photocurable resin D800 (JEOL Ltd.). The cover glass is gently placed on the tube in such a way that the toner is in contact with the photocurable resin D800. After irradiating light in this state to cure the resin, the cover glass and the tube are removed to form a cylindrical resin in which the toner is embedded on the outermost surface. Using an ultrasonic ultramicrotome (Leica Microsystems, UC7), at a cutting speed of 0.6 mm / s, the resin is cut by a length equal to the radius of the toner (for example, 4.0 μm when the weight average particle diameter (D4) is 8.0 μm) from the outermost surface of the cylindrical resin to expose the cross section of the center part of the toner.

[0070] Next, it is cut to a thickness of 100 nm to prepare a thin sample of the cross section of the toner. By cutting in such a manner, the cross section of the center part of the toner can be obtained.

[0071] As a scanning transmission electron microscope (STEM), JEM-2800 manufactured by JEOL Ltd. was used. The probe size of the STEM was 1 nm, and images were acquired with an image size of 1024×1024 pixels. Also, the contrast of the Detector Control panel of the bright-field image was adjusted to 1425, the brightness to 3750, the contrast of the Image Control panel to 0.0, the brightness to 0.5, and the gamma to 1.00 to acquire the images. The image magnification was 100,000 times, and image acquisition was performed so that the cross-section of one toner particle was within about one-fourth to one-half of the circumference as shown in Figure 3. For the obtained STEM images, image analysis was performed using image processing software (ImageJ (available from https: / / imagej.nih.gov / ij / )), and convex portions containing the organosilicon polymer were measured. This measurement was performed for 30 convex portions arbitrarily selected from the STEM image. Whether the convex portion contains an organosilicon polymer or not was confirmed by a combination of scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDS). First, a line was drawn along the circumference of the toner mother particle using the line drawing tool (select Segmented line in the Straght tab). For portions where the convex portion of the organosilicon polymer is buried in the toner mother particle, the line was smoothly connected as if there was no burial. Based on that line, conversion to a horizontal image (select Selection in the Edit tab, change the line width to 500 pixels in properties, then select Selection in the Edit tab and perform Straightener) was performed. For one convex portion containing the organosilicon polymer in the horizontal image, the following measurement was performed. The length of the line along the circumference at the portion where the convex portion and the toner mother particle form a continuous interface was defined as the convex width w. The maximum length of the convex portion in the normal direction of the convex width w was defined as the convex diameter D, and the length from the vertex of the convex portion to the line along the circumference in the line segment forming the convex diameter D was defined as the convex height H. This measurement was performed for 30 arbitrarily selected convex portions, and the arithmetic mean value of each measurement value was defined as the number average value of the convex height H.

[0072] <Method for calculating H80> In the STEM image of the cross-section of the toner using the above scanning transmission electron microscope (STEM), for convex portions where the convex height H is 30 nm or more and 300 nm or less, the cumulative distribution of the convex height H is taken. The convex height corresponding to 80 number % when integrated from the smaller side of the convex height H is defined as H80 (unit: nm).

[0073] <Method for calculating the area ratio of the bright area in the 1.5 μm square backscattered electron image of the toner surface> For calculating the area ratio of the bright area, the surface of the toner is observed using a scanning electron microscope. Then, a 1.5 μm square backscattered electron image of the toner surface is obtained. Then, a binarized image is obtained such that the organosilicon polymer portion in the backscattered electron image becomes the bright area, and the ratio of the bright area of the image to the total area of the image is determined. When organic fine particles or inorganic fine particles are externally added to the toner, a sample obtained by removing the organic fine particles or inorganic fine particles by the following method or the like is used.

[0074] Add 160 g of sucrose (manufactured by Kishida Chemical Co., Ltd.) to 100 mL of ion-exchanged water, and dissolve it while stirring with hot water to prepare a sucrose concentrated solution. Put 31 g of the above sucrose concentrated solution and 6 mL of Contaminon N (a 10 mass% aqueous solution of a neutral detergent for precision measuring instrument cleaning with pH 7 composed of a nonionic surfactant, an anionic surfactant, and an organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) into a centrifuge tube (capacity 50 mL). Add 1.0 g of toner here, and loosen the toner lumps with a spatula or the like. Shake the centrifuge tube with a shaker (sold by AS ONE Corporation) at 300 spm (strokes per min) for 20 minutes. After shaking, transfer the solution to a glass tube (50 mL) for a swing rotor, and separate it with a centrifuge (manufactured by Kokusan Co., Ltd., model H-9R) at 3500 rpm for 30 minutes. By this operation, the toner particles and the external additive are separated. Visually confirm that the toner particles and the aqueous solution are sufficiently separated, and collect the separated toner particles in the uppermost layer with a spatula or the like. After filtering the collected toner particles with a vacuum filter, dry them with a dryer for 1 hour or more to obtain a sample for measurement. Repeat this operation a plurality of times to secure the required amount.

[0075] Regarding whether the convex portion contains an organosilicon polymer, it is confirmed by combining elemental analysis by energy-dispersive X-ray spectroscopy (EDS) described later.

[0076] The SEM apparatus and observation conditions are as follows. Apparatus used: ULTRA PLUS manufactured by Carl Zeiss Microscopy GmbH Acceleration voltage: 1.0 kV WD: 2.0 mm Aperture Size: 30.0 μm Detection signal: EsB (energy-selective backscattered electron) EsB Grid: 800 V Observation magnification: 50,000 times Contrast: 63.0 ± 5.0% (reference value) Brightness: 38.0 ± 5.0% (reference value) Resolution: 1024 × 768 Pretreatment: Sprinkle toner particles on carbon tape (no vapor deposition)

[0077] The acceleration voltage and EsB Grid are set to achieve items such as obtaining the structure information of the outermost surface of the toner particles, preventing charge-up of the unvapor-deposited sample, and selectively detecting high-energy backscattered electrons. The observation field of view is selected near the apex where the curvature of the toner particles is the smallest. That the bright part of the backscattered electron image is derived from the organosilicon polymer was confirmed by superimposing the elemental mapping image by energy-dispersive X-ray spectroscopy (EDS) that can be obtained with a scanning electron microscope (SEM) and the said backscattered electron image.

[0078] The SEM / EDS apparatus and observation conditions are as follows. Apparatus used (SEM): ULTRA PLUS manufactured by Carl Zeiss Microscopy GmbH Apparatus used (EDS): NORAN System 7, Ultra Dry EDS Detecter manufactured by Thermo Fisher Scientific Inc. Acceleration voltage: 5.0 kV WD: 7.0 mm Aperture Size: 30.0 μm Detection signal: SE2 (secondary electron) Observation magnification: 50,000 times Mode: Spectral Imaging Pretreatment: Sprinkle toner particles on carbon tape and platinum sputter

[0079] Overlay the mapping image of the silicon element obtained by this method and the reflection electron image, and confirm that the silicon atom part of the mapping image coincides with the bright part of the reflection electron image.

[0080] The calculation of the area ratio of the bright part area to the total area of the reflection electron image was obtained by analyzing the reflection electron image of the surface of the toner particles obtained by the above method using the image processing software ImageJ (developed by Wayne Rashand). The procedure is shown below.

[0081] First, convert the backscattered electron image to 8-bit from the Type in the Image menu. Next, set the Median diameter to 2.0 pixels from the Filters in the Process menu to reduce image noise. Estimate the image center excluding the observation condition display part shown at the bottom of the backscattered electron image, and select a range of 1.5 μm square from the image center of the backscattered electron image using the Rectangle Tool in the toolbar. Next, select Threshold from Adjust in the Image menu. Select Default, click Auto, and then click Apply to obtain a binary image. By this operation, the bright part of the backscattered electron image is displayed in white. Again, estimate the image center excluding the observation condition display part shown at the bottom of the backscattered electron image, and select a range of 1.5 μm square from the image center of the backscattered electron image using the Rectangle Tool in the toolbar. Next, select Histogram from the Analyze menu. Read the Count value from the newly opened Histogram window (corresponding to the total area of the backscattered electron image). Also, click List and read the Count value when the luminance is 0 (corresponding to the bright part area of the backscattered electron image). Calculate the area ratio of the bright part area to the total area of the backscattered electron image from the above values. Perform the above procedure for 10 fields for the toner particles to be evaluated, calculate the number average value, and use it as the area ratio (%) of the bright part area of the image to the total area of the binary image processed so that the organosilicon polymer part in the backscattered electron image becomes the bright part.

[0082] <Method for Identifying Organosilicon Polymer> The method for identifying an organosilicon polymer is performed by combining observation with a scanning electron microscope (SEM) and elemental analysis by energy-dispersive X-ray analysis (EDS).

[0083] Using a scanning electron microscope, the Hitachi High-Resolution Field Emission Scanning Electron Microscope S-4800 (Hitachi High-Technologies Corporation), observe the toner at a magnification of up to 50,000 times in the field of view. Focus on the surface of the toner particles and observe the surface. Perform EDS analysis on the particles present on the surface, and determine whether the analyzed particles are organosilicon polymers based on the presence or absence of Si element peaks. When both organosilicon polymers and silica fine particles are contained on the surface of the toner particles, identify the organosilicon polymer by comparing the ratio (Si / O ratio) of the elemental contents (atomic%) of Si and O with that of the standard sample. Perform EDS analysis on the standard samples of organosilicon polymers and silica fine particles under the same conditions to obtain the elemental contents (atomic%) of Si and O respectively. Let the Si / O ratio of the organosilicon polymer be A and the Si / O ratio of the silica fine particles be B. Select the measurement conditions under which A becomes significantly larger than B. Specifically, perform 10 measurements on the standard sample under the same conditions to obtain the additive average values of A and B respectively. Select the measurement conditions under which the obtained average value satisfies A / B > 1.1. If the Si / O ratio of the particles to be discriminated is on the A side of [(A + B) / 2], determine that the particles are organosilicon polymers.

[0084] Use Tospearl 120A (Momentive Performance Materials Japan G.K.) as the standard sample of organosilicon polymer particles and HDK V15 (Asahi Kasei) as the standard sample of silica fine particles.

[0085] <Measurement Method for Number-Average Particle Size R of Primary Particles of Externally Added Agents> Perform a combination of a scanning electron microscope, the Hitachi High-Resolution Field Emission Scanning Electron Microscope S-4800 (Hitachi High-Technologies Corporation), and elemental analysis by energy-dispersive X-ray analysis (EDS).

[0086] In a field of view magnified up to 50,000 times, the elemental analysis method by EDS described above is used in combination, and the external additive particles are randomly photographed. From the photographed images, 100 external additive particles are randomly selected, and the major axis length of the primary particles of the target external additive particles is measured, and the arithmetic mean value is defined as the number average particle size R. The observation magnification is appropriately adjusted according to the size of the external additive particles.

[0087] <Method for Identifying Composition and Ratio of Constituent Compounds of Organosilicon Polymer> For identifying the composition and ratio of the constituent compounds of the organosilicon polymer contained in the toner, NMR is used. When the toner contains external additives such as silica fine particles in addition to the organosilicon polymer, the following operations are performed.

[0088] Put 1 g of the toner into a vial and dissolve it in 31 g of chloroform and disperse it. For dispersion, use an ultrasonic homogenizer and treat it for 30 minutes to prepare a dispersion. Ultrasonic treatment device: Ultrasonic homogenizer VP-050 (manufactured by Taitec Corporation) Microchip: Step type microchip, tip diameter φ2 mm Tip position of the microchip: Center of the glass vial and at a height of 5 mm from the bottom of the vial Ultrasonic conditions: Intensity 30%, 30 minutes

[0089] At this time, apply ultrasonic waves while cooling the vial with ice water so that the dispersion does not heat up. Replace the dispersion with a glass tube (50 mL) for a swing rotor and centrifuge it (H-9R; manufactured by Kokusan Co., Ltd.) under the conditions of 58.33S -1 , for 30 minutes. In the glass tube after centrifugation, heavier particles with a higher specific gravity, for example, silica fine particles, are contained in the lower layer. Collect the upper chloroform solution containing the organosilicon polymer and remove the chloroform by vacuum drying (40 °C / 24 hours) to prepare a sample. Using the above sample or the organosilicon polymer, the abundance ratio of the constituent compounds of the organosilicon polymer and the ratio of the T3 unit structure represented by R-Si(O 1 / 2 )3 in the organosilicon polymer are determined as solids 29It is measured and calculated by Si-NMR.

[0090] First, the hydrocarbon group represented by the above R is 13 confirmed by C-NMR. ≪ 13 Measurement conditions for C-NMR (solid)≫ Apparatus: JNM-ECX500II manufactured by JEOL RESONANCE Sample tube: 3.2 mm φ Sample: Sample or organosilicon polymer Measurement temperature: Room temperature Pulse mode: CP / MAS Measured nuclear frequency: 123.25 MHz ( 13 C) Reference substance: Adamantane (external standard: 29.5 ppm) Sample rotation speed: 20 kHz Contact time: 2 ms Delay time: 2 s Number of integrations: 1024 times

[0091] By this method, the hydrocarbon group represented by the above R is confirmed based on the presence or absence of signals caused by methyl groups (Si-CH3), ethyl groups (Si-C2H5), propyl groups (Si-C3H7), butyl groups (Si-C4H9), pentyl groups (Si-C5H 11 ), hexyl groups (Si-C6H 13 ) or phenyl groups (Si-C6H5-), etc., bonded to silicon atoms. On the other hand, in solid 29 Si-NMR, peaks are detected in different shift regions depending on the structure of the functional groups bonded to Si in the constituent compounds of the organosilicon polymer. Each peak position can be used to identify the structure bonded to Si by using a standard sample. Also, the abundance ratio of each constituent compound can be calculated from the obtained peak areas. The ratio of the peak area of the T3 unit structure to the total peak area can be obtained by calculation.

[0092] Solid 29 The measurement conditions for solid Si-NMR are specifically as follows. Apparatus: JNM-ECX5002 (JEOL RESONANCE) Temperature: Room temperature Measurement method: DDMAS method 29 Si 45° Sample tube: Zirconia 3.2 mm φ Sample: Filled in the test tube in powder form Sample rotation speed: 10 kHz Relaxation delay: 180 s Scan: 2000

[0093] After the measurement, a plurality of silane components with different substituents and bonding groups in the sample or the organosilicon polymer are peak-separated into the following X1 structure, X2 structure, X3 structure, and X4 structure by curve fitting, and the peak area is calculated respectively.

[0094] Note that the following X3 structure is the T3 unit structure. X1 structure: (Ri)(Rj)(Rk)SiO 1 / 2 (A1) X2 structure: (Rg)(Rh)Si(O 1 / 2 )2(A2) X3 structure: RmSi(O 1 / 2 )3(A3) X4 structure: Si(O 1 / 2 )4(A4)

[0095]

Chemical formula

[0096] In the formulas (A1), (A2), and (A3), Ri, Rj, Rk, Rg, Rh, and Rm represent organic groups such as hydrocarbon groups with 1 to 6 carbon atoms bonded to silicon, halogen atoms, hydroxy groups, acetoxy groups, or alkoxy groups. When it is necessary to confirm the structure in more detail, the above 13 C-NMR and 29 together with the measurement results of Si-NMR 1 may be identified by the measurement results of H-NMR.

[0097] <Method for Quantifying Organosilicon Polymer or Silica Fine Particles Contained in Toner> Disperse the toner in chloroform as described above, and then use centrifugation to separate external additives such as organosilicon polymers and silica fine particles by the difference in specific gravity to obtain each sample, and determine the content of external additives such as organosilicon polymers or silica fine particles.

[0098] Hereinafter, the case where the external additive is silica fine particles will be exemplified. Even for other fine particles, quantification can be performed by the same method.

[0099] First, measure the pressed toner by X-ray fluorescence, and determine the silicon content in the toner by performing analysis processing such as the calibration curve method or the FP method. Next, for each constituent compound forming the organosilicon polymer and silica fine particles, solid 29 Identify the structure using Si-NMR and pyrolysis GC / MS, etc., and determine the silicon content in the organosilicon polymer and silica fine particles. From the relationship between the silicon content in the toner determined by X-ray fluorescence and the silicon content in the organosilicon polymer and silica fine particles determined by solid 29 Si-NMR and pyrolysis GC / MS, calculate the content of the organosilicon polymer and silica fine particles in the toner.

[0100] <Method for Measuring Adhesion Rate of External Additives Such as Organosilicon Polymers or Silica Fine Particles to Toner Mother Particles or Toner Particles by Water Washing Method> (Water washing step) Weigh 20 g of a 30% by mass aqueous solution of "Contaminon N" (a neutral detergent for precision measuring instruments with a pH of 7, consisting of a nonionic surfactant, an anionic surfactant, and an organic builder) into a 50 mL vial, and mix it with 1 g of toner. Set it on the "KM Shaker" (model: V.SX) manufactured by Iwaki Sangyo Co., Ltd., set the speed to 50, and shake for 120 seconds. As a result, depending on the state of adhesion of the organosilicon polymer or silica fine particles, external additives such as organosilicon polymers or silica fine particles migrate from the toner mother particles or the toner particle surface to the dispersion side. Then, using a centrifuge (H-9R; manufactured by Kokusan Co., Ltd.) (at 16.67 S-1 for 5 minutes), separate the toner and the external additives such as organosilicon polymers or silica fine particles that have migrated to the supernatant. The precipitated toner is dried by vacuum drying (40 °C / 24 hours) to obtain a toner after washing with water.

[0101] Next, using the Hitachi high-resolution field emission scanning electron microscope S-4800 (manufactured by Hitachi High-Technologies Corporation), take pictures of the toner before the water washing process (toner before water washing) and the toner obtained through the water washing process (toner after water washing).

[0102] Also, the identification of the measurement object is performed by elemental analysis using energy dispersive X-ray analysis (EDS).

[0103] Then, analyze the photographed toner surface image using the image analysis software Image-Pro Plus ver. 5.0 (manufactured by Nippon Roper Co., Ltd.) to calculate the coverage rate.

[0104] The image shooting conditions of the S-4800 are as follows.

[0105] (1) Sample preparation thinly apply a conductive paste on the sample stage (aluminum sample stage 15 mm × 6 mm), and spray the toner on it. Further blow air to remove excess toner from the sample stage and dry it sufficiently. Set the sample stage in the sample holder, and adjust the sample stage height to 36 mm using the sample height gauge.

[0106] (2) Setting of Observation Conditions for S-4800 When measuring the coating rate, first perform elemental analysis by the above-mentioned energy-dispersive X-ray spectroscopy (EDS) to distinguish additives such as organosilicon polymers or silica fine particles on the toner surface, and then conduct the measurement. Pour liquid nitrogen into the anti-contamination trap attached to the housing of S-4800 until it overflows, and leave it for 30 minutes. Start the "PC-SEM" of S-4800 and perform flashing (cleaning of the FE chip, which is the electron source). Click on the acceleration voltage display part in the control panel on the screen, press the [Flashing] button to open the flashing execution dialog. Confirm that the flashing intensity is 2 and execute it. Confirm that the emission current due to flashing is 20 - 40 μA. Insert the sample holder into the sample chamber of the S-4800 housing. Press [Origin] on the control panel to move the sample holder to the observation position.

[0107] Click on the acceleration voltage display part to open the HV setting dialog, and set the acceleration voltage to [1.1 kV] and the emission current to [20 μA]. In the [Basic] tab of the operation panel, set the signal selection to [SE], select the SE detector [Up (U)] and [+BSE], select [L.A.100] in the selection box to the right of [+BSE], and set it to the mode of observing with a backscattered electron image. Also, in the [Basic] tab of the operation panel, set the probe current in the electron optical system condition block to [Normal], the focus mode to [UHR], and the WD to [4.5 mm]. Press the [ON] button in the acceleration voltage display part of the control panel to apply the acceleration voltage.

[0108] (3) Calculation of the Number-Average Particle Size (D1) of the Toner Drag within the magnification display section of the control panel to set the magnification to 5000 (5k) times. Rotate the focus knob [COARSE] on the operation panel, and when the focus is approximately correct, adjust the aperture alignment. 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 displayed beam to the center of the concentric circles. Next, select [Aperture], and rotate the STIGMA / ALIGNMENT knobs (X, Y) one by one to stop the movement of the image or adjust it to the minimum movement. Close the aperture dialog box and focus using autofocus. Repeat this operation two more times to focus.

[0109] After that, measure the particle size of 300 toner particles and obtain the number average particle size (D1). Note that the particle size of each particle is the maximum diameter when observing the toner particles.

[0110] (4) Focus adjustment For the particles with a number average particle size (D1) within ±0.1 μm obtained in (3), drag within the magnification display section of the control panel with the midpoint of the maximum diameter aligned with the center of the measurement screen to set the magnification to 10000 (10k) times.

[0111] Rotate the focus knob [COARSE] on the operation panel. When the focus is adjusted to a certain extent, adjust the aperture alignment. 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 displayed beam to the center of the concentric circles. Next, select [Aperture], and turn the STIGMA / ALIGNMENT knobs (X, Y) one by one to stop the movement of the image or adjust it to the minimum movement. Close the aperture dialog box and focus using autofocus. Then, set the magnification to 50,000 (50k) times, perform focus adjustment using the focus knob and STIGMA / ALIGNMENT knobs as described above, and focus again using autofocus. Repeat this operation to focus. Here, when the tilt angle of the observation surface is large, the measurement accuracy of the coverage rate tends to be low. Therefore, when adjusting the focus, select an object where the entire observation surface is in focus at the same time, and select and analyze an object with as little surface tilt as possible.

[0112] (5) Image Saving Adjust the brightness in ABC mode, take a photo at a size of 640×480 pixels, and save it. Perform the following analysis using this image file. Take one photo for each toner particle to obtain an image of the toner particles.

[0113] (6) Image Analysis Use the following analysis software to calculate the coverage rate by binarizing the image obtained by the above method. At this time, divide the above single screen into 12 squares and analyze each one. The analysis conditions of the image analysis software Image-Pro Plus ver.5.0 are as follows. However, if external additives such as organosilicon polymers with a particle size of less than 30 nm and more than 300 nm, or silica fine particles with a particle size of less than 30 nm and more than 1200 nm enter the divided section, the coverage rate calculation will not be performed in that section.

[0114] In the image analysis software Image-Pro Plus 5.0, select "Count / Size" and then "Options" in sequence from "Measurement" in the toolbar to set the binarization conditions. Select 8-connectivity in the object extraction options and set the smoothing to 0. Additionally, do not select pre-selection, filling holes, and inclusion lines in advance, and set "Exclude boundary lines" to "None". Select "Measurement items" from "Measurement" in the toolbar and input 2 to 10 in the selection range of the area. 7 and input it.

[0115] The calculation of the coverage rate is performed by enclosing a square area. At this time, the area (C) of the area should be 24,000 to 26,000 pixels. Automatically binarize with "Processing" - Binarization, and calculate the total sum (D) of the areas of the regions without external additives such as organosilicon polymers or silica fine particles. The coverage rate can be obtained from the area C of the square area and the total sum D of the areas of the regions without external additives such as organosilicon polymers or silica fine particles using the following formula. Coverage rate (%) = 100 - (D / C × 100)

[0116] Take the arithmetic mean value of all the obtained data as the coverage rate.

[0117] Then, calculate the respective coverage rates of the toner before washing and the toner after washing, and take [Coverage rate of the toner after washing] / [Coverage rate of the toner before washing] × 100 as the "fixing rate" of the present invention.

[0118] 4. Manufacturing methods of toner particles, external additives, and developers Next, manufacturing examples of the toner particles, external additive A, and developer of this example will be described.

[0119] <Manufacturing example of toner particles> (Preparation of aqueous medium 1) Into a reaction vessel equipped with a stirrer, a thermometer, and a reflux tube, 650.0 parts of ion-exchanged water and 14.0 parts of sodium phosphate (manufactured by Rasa Industries Co., Ltd., 12-hydrate) were charged, and the mixture was kept at 65 °C for 1.0 hour while purging with nitrogen. While stirring at 15000 rpm using a T.K. homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), an aqueous calcium chloride solution prepared by dissolving 9.2 parts of calcium chloride (dihydrate) in 10.0 parts of ion-exchanged water was added all at once to prepare an aqueous medium containing a dispersion stabilizer. Further, 10 mass% hydrochloric acid was added to the aqueous medium to adjust the pH to 5.0, and aqueous medium 1 was obtained.

[0120] (Preparation of polymerizable monomer composition) · Styrene: 60.0 parts · C.I. Pigment Blue 15:3: 6.5 parts

[0121] The above materials were charged into an attritor (manufactured by Mitsui Miike Chemical Machinery Co., Ltd.), and further dispersed at 220 rpm for 5.0 hours using zirconia particles with a diameter of 1.7 mm. Then, the zirconia particles were removed to prepare a colorant dispersion. · Styrene: 20.0 parts · n-Butyl acrylate: 20.0 parts · Crosslinking agent (divinylbenzene): 0.3 part · Saturated polyester resin: 5.0 parts (Polycondensate of propylene oxide-modified bisphenol A (2-mol adduct) and terephthalic acid (molar ratio 10:12), glass transition temperature (Tg) is 68 °C, weight average molecular weight (Mw) is 10000, molecular weight distribution (Mw / Mn) is 5.12) · Fischer-Tropsch wax (melting point 78 °C): 7.0 parts

[0122] The above materials were added to the above colorant dispersion, heated to 65 °C, and then uniformly dissolved and dispersed at 500 rpm using a T.K. homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a polymerizable monomer composition.

[0123] (Granulation process) The temperature of the aqueous medium 1 was adjusted to 70°C, and while maintaining the rotation speed of the T.K. homomixer at 15,000 rpm, the polymerizable monomer composition was introduced into the aqueous medium 1, and 10.0 parts of t-butyl peroxy pivalate, which is a polymerization initiator, was added. While maintaining 15,000 rpm with the stirrer, granulation was carried out for 10 minutes as it was.

[0124] (Polymerization step and distillation step) After the granulation step, the stirrer was replaced with a propeller stirring blade, and polymerization was carried out for 5.0 hours while maintaining 70°C with stirring at 150 rpm, and further, polymerization was carried out by raising the temperature to 85°C and holding for 2.0 hours. Thereafter, the reflux pipe of the reaction vessel was replaced with a cooling pipe, and distillation was carried out for 6 hours by heating the obtained slurry to 100°C to distill off the unreacted polymerizable monomer, and a resin particle dispersion was obtained.

[0125] (Formation step of organosilicon polymer) 60.0 parts of ion-exchanged water was weighed into a reaction vessel equipped with a stirrer and a thermometer, and the pH was adjusted to 4.0 using 10 mass% hydrochloric acid. This was heated with stirring to a temperature of 40°C. Thereafter, 40.0 parts of methyltriethoxysilane, which is an organosilicon compound, was added and hydrolysis was carried out by stirring for 2 hours or more. The end point of hydrolysis was confirmed visually by the fact that the oil and water did not separate and became a single layer, and it was cooled to obtain a hydrolysis solution of the organosilicon compound.

[0126] After adjusting the temperature of the resin particle dispersion obtained above to 55°C, 25.0 parts of the hydrolysis solution of the organosilicon compound (the addition amount of the organosilicon compound was 10.0 parts) was added to initiate the polymerization of the organosilicon compound. After holding for 0.25 hour as it was, the pH was adjusted to 5.5 with a 3.0% aqueous sodium hydrogen carbonate solution. While continuing stirring at 55°C, after holding for 1.0 hour (condensation reaction 1), the pH was adjusted to 9.5 using a 3.0% aqueous sodium hydrogen carbonate solution, and further held for 4.0 hours (condensation reaction 2) to obtain a toner particle dispersion.

[0127] (Washing step and drying step) After the formation step of the organosilicon polymer was completed, the toner particle dispersion was cooled, hydrochloric acid was added to the toner particle dispersion to adjust the pH to 1.5 or less, and the mixture was allowed to stand with stirring for 1.0 hour. Thereafter, solid-liquid separation was performed using a pressure filter to obtain a toner cake. The obtained toner cake was reslurried with ion-exchanged water to form a dispersion again, and then solid-liquid separation was performed using the aforementioned filter to obtain a toner cake. The obtained toner cake was transferred to a constant temperature bath at 40°C, and drying and classification were performed over 72 hours to obtain toner particles.

[0128] <Production Example of Exterior Additive A> Exterior additive A was produced as follows. 150 parts of 5% aqueous ammonia was placed in a 1.5 L glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer to prepare an alkaline catalyst solution. After adjusting the alkaline catalyst solution to 50°C, 100 parts of tetraethoxysilane and 50 parts of 5% aqueous ammonia were simultaneously dropped while stirring, and the mixture was reacted for 8 hours to obtain a silica fine particle dispersion. Thereafter, the obtained silica fine particle dispersion was dried by spray drying and pulverized with a pin mill to obtain silica fine particles having a number average particle diameter of primary particles of 100 nm as exterior additive A.

[0129] <Production Example of Developer> 100.00 parts of toner particles 1 and 1.00 part of exterior additive A were charged into a Henschel mixer (Model FM10C manufactured by Nippon Coke & Engineering Co., Ltd.) through which water at 7°C was passed in the jacket. Next, after the water temperature in the jacket was stabilized at 7°C ± 1°C, the mixture was mixed for 10 minutes with the peripheral speed of the rotating blades set to 38 m / sec. In this mixing, the amount of water passed through the jacket was appropriately adjusted so that the temperature inside the tank of the Henschel mixer did not exceed 25°C. The obtained mixture was sieved through a mesh with an opening of 75 μm to obtain a developer.

[0130] The physical properties of the developer are shown in Table 1.

[0131]

Table 1

[0132] In the table, "X" represents the ratio of the number average value of the convex height H to the number average particle diameter R of the primary particles of the external additive A. When the developed developer was observed using SEM, it was confirmed that the external additive A was arranged as transfer carrier particles on the convex portions of the organosilicon polymer of the toner particles, and the average number of coatings of the external additive A per toner particle was about 500.

[0133] 5. Supply of Transfer Carrier Next, the supply means of the transfer carrier particles onto the photosensitive drum 1, which is a feature of this example, will be described. As described above, transfer carrier particles are particles that, by intervening between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1, reduce the adhesion force between the toner image and the photosensitive drum 1 and improve the primary transfer efficiency of the toner image.

[0134] In this example, before the toner image is developed, transfer carrier particles are supplied in advance to the surface of the photosensitive drum 1 using the toner carried on the developing roller 41. By previously coating the surface of the photosensitive drum 1 with transfer carrier particles, transfer carrier particles are interposed between the toner image and the photosensitive drum 1.

[0135] Fig. 8(a) is a schematic diagram of the developing nip portion when the developing roller 41 is in contact with the photosensitive drum 1. As shown in Fig. 8(a), in the developing nip portion, the toner carried on the developing roller 41 and the photosensitive drum 1 are in contact via transfer carrier particles. Fig. 8(b) is a schematic diagram showing the state after the toner carried on the developing roller 41 shown in Fig. 8(a) and the photosensitive drum 1 have passed through the developing nip portion. As shown in Fig. 8(b), the transfer carrier particles that were interposed between the toner and the photosensitive drum 1 in the developing nip portion are supplied by transferring from the surface of the toner carried on the developing roller 41 to the surface of the photosensitive drum 1 after passing through the developing nip portion.

[0136] As shown in Fig. 8(a), when the adhesion force Ft between the transfer carrier particles and the toner intervening between the toner and the photosensitive drum 1 at the developing nip portion is greater than the adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1, it is difficult for the transfer carrier particles to transfer onto the photosensitive drum 1. Therefore, it is preferable that Ft is smaller than Fdr.

[0137] Fig. 9(a) is a schematic diagram of the primary transfer portion when the toner image is carried on the surface of the photosensitive drum 1. Fig. 9(b) is a schematic diagram of the state where the primary transfer of the toner image shown in Fig. 9(a) is completed and the photosensitive drum 1 and the intermediate transfer belt 10 are separated. When Ft is smaller than Fdr, when the toner image is primarily transferred from the photosensitive drum 1 onto the surface of the intermediate transfer belt 10, only the toner image is primarily transferred onto the intermediate transfer belt 10, and the transfer carrier particles intervening between the toner image and the photosensitive drum 1 remain on the photosensitive drum 1.

[0138] Suppose a case where the transfer carrier particles intervening between the toner image and the photosensitive drum 1 are primarily transferred onto the intermediate transfer belt 10 together with the toner image and the transfer carrier particles are lost from the surface of the photosensitive drum 1. In that case, since there are no transfer carrier particles intervening between the toner image developed on the surface of the photosensitive drum 1 next and the photosensitive drum 1 and the adhesion force between the toner image and the photosensitive drum 1 is large, the primary transferability will decrease.

[0139] Therefore, not only is it easier to supply the transfer carrier particles from the toner carried on the developing roller 41 to the photosensitive drum 1, but also from the viewpoint of maintaining the transfer carrier particles coated on the photosensitive drum 1, it is preferable that Ft is smaller than Fdr.

[0140] Figure 10 is a timing chart of the printing operation of the image forming apparatus 100 used in this embodiment. As shown in Figure 10, during the image forming operation of the image forming apparatus 100 of this embodiment, before starting the development of toner from the developing roller 41 to the photosensitive drum 1, the developing roller 41 and the photosensitive drum 1 are rotationally driven in a contacting state. Thereby, a timing (transfer carrier supply mode) for supplying transfer carrier particles from the developing roller 41 to the photosensitive drum 1 is provided.

[0141] In order to improve the primary transfer efficiency of the toner image over the entire surface of the photosensitive drum 1, before starting the development of the toner image, the entire surface of the photosensitive drum 1 is coated with transfer carrier particles. Therefore, it is preferable to set the time of the supply timing of the transfer carrier particles to a time for rotating the photosensitive drum 1 more than once. Therefore, in this embodiment, in order to coat the entire surface of the photosensitive drum 1 with transfer carrier particles, the length of the transfer carrier particle supply timing shown in Figure 10 is set to approximately 500 msec, which is the same as the time for the photosensitive drum 1 to make one rotation.

[0142] Also, in this embodiment, at the transfer carrier particle supply timing shown in Figure 10, the surface potential of the photosensitive drum 1 is set to the non-image forming potential Vd = -500 V at which toner charged to the normal polarity does not develop. Therefore, at the supply timing of the transfer carrier particles of this embodiment, toner having a normal polarity of negative polarity does not develop from the developing roller 41 onto the surface of the photosensitive drum 1, and only the transfer carrier particles are supplied from the developing roller 41 onto the photosensitive drum 1.

[0143] When supplying transfer carrier particles from the toner on the developing roller 41 to the photosensitive drum 1 in a state where there is a potential difference between the developing roller 41 and the photosensitive drum 1 as in this embodiment, there are the following problems. If the particle size of the transfer carrier particles is too large, the transfer carrier particles are liable to be affected by the electrostatic force generated by the potential difference between the developing roller 41 and the photosensitive drum 1. Therefore, it becomes difficult to control the supply of the transfer carrier particles from the toner on the developing roller 41 to the photosensitive drum 1. For example, in the configuration of supplying transfer carrier particles at the non-image forming potential as in this embodiment, when the transfer carrier particles are charged negatively, the transfer carrier particles are attracted by the electrostatic force to the developing roller 41 side. Therefore, it becomes difficult to supply the transfer carrier particles from the toner on the developing roller 41 to the photosensitive drum 1. Here, it is preferable that the particle size of the transfer carrier particles is 1000 nm or less, which is hardly affected by the electrostatic force. In this embodiment, in order to stably supply the transfer carrier particles from the toner on the developing roller 41 to the surface of the photosensitive drum 1 regardless of the potential difference between the developing roller 41 and the photosensitive drum 1, particles with a particle size of 100 nm are used as the transfer carrier particles.

[0144] The developer used in this embodiment is a mixture of the toner and the transfer carrier particles described above. FIG. 7 is an enlarged view of the developer used in this embodiment. As shown in FIG. 7, the developer of this embodiment is configured such that the transfer carrier particles are arranged on the surface of the toner on which a large number of convex portions of the organosilicon polymer are formed. The convex interval G and the convex height H of the toner surface shown in FIG. 7 can be measured by a scanning probe microscope (hereinafter referred to as SPM). The scanning probe microscope (hereinafter referred to as SPM) includes a probe, a cantilever that supports the probe, and a displacement measurement system that detects the bending of the cantilever, and detects the atomic force (attractive force or repulsive force) between the probe and the sample to observe the shape of the sample surface.

[0145] If the convex interval G is larger than the transfer carrier, when transfer carrier particles are disposed between the convex portions, they will come into contact with the toner matrix, increasing the adhesion force Ft between the transfer carrier particles and the toner and making it difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1. Therefore, it is preferable that the convex interval G is narrower than the particle size of the transfer carrier particles. Accordingly, when the closest distance between adjacent convex portions is defined as the convex interval G, it is preferable that the average of the convex interval G is equal to or less than the average particle size of the transfer carrier particles.

[0146] Also, if the convex height H is higher than the particle size of the transfer carrier particles, the convex portion will contact the photosensitive drum 1 before the transfer carrier particles, making it difficult for the transfer carrier particles to contact the photosensitive drum 1. Therefore, since it becomes difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1, it is preferable that the convex height H is lower than the particle size of the transfer carrier particles. Accordingly, when the height from the surface of the toner particles of the convex portion is defined as the convex height H, it is preferable that the average of the convex height H is equal to or less than the average particle size of the transfer carrier particles.

[0147] When the convex portions on the surface of the toner of this example were measured, the average of the convex intervals G on the surface of the toner was about 30 nm, and the average of the convex heights H was 50 nm. Both the convex interval G and the convex height H were smaller than the particle size of the transfer carrier, which was 100 nm.

[0148] The transfer carrier particles used in this example are silica particles with a particle size of 100 nm produced by the sol-gel method. In this example, silica was used as the transfer carrier particles, but the material of the transfer carrier particles is not limited to silica and may be various organic or inorganic fine powders. However, as described above, it is preferable that the adhesion force Ft between the transfer carrier particles and the toner is smaller than the adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1. Therefore, as the material of the transfer carrier particles, it is preferable to select a material that reduces the adhesion force Ft of the transfer carrier particles to the toner. For example, when the convex portions on the toner surface are formed of a silica-based material such as an organic silica polymer as in this example, it is advisable to select a silica-based material with a material composition similar to that of the convex portions as the material of the transfer carrier particles. Selecting a silica-based material with a material composition similar to that of the convex portions is preferable from the viewpoint of reducing the adhesion force between the convex portions and the transfer carrier particles.

[0149] Also, in this example, the addition amount of the transfer carrier particles was adjusted so that the number of coating particles per toner of the transfer carrier particles was about 500. The larger the number of transfer carrier particles coating the toner, the more transfer carrier particles can be transferred from the developing roller 41 to the surface of the photosensitive drum 1. However, if the addition amount of the transfer carrier particles is too large, the risk of member contamination in the image forming apparatus 100 increases, so it is preferable to adjust according to the desired primary transferability.

[0150] Also, the primary transferability improves to some extent as the coverage rate of the transfer carrier particles covering the surface of the photosensitive drum 1 increases. However, as the coverage rate of the transfer carrier particles covering the surface of the photosensitive drum 1 increases, the degree of improvement in the primary transferability becomes dull, and the risk of various member contaminations in the image forming apparatus due to the transfer carrier particles increases. Therefore, it is preferable to keep the coverage rate of the transfer carrier particles covering the surface of the photosensitive drum 1 within 80%.

[0151] 6. Effects of Transfer Carrier Particles Next, an effect confirmation experiment conducted to confirm the effect of the supply means of the transfer carrier particles to the photosensitive drum 1 of this example will be described.

[0152] First, using an image forming apparatus 100 with a new photosensitive drum 1 not coated with transfer carrier particles, a patch image with a yellow density of 100% is formed. Then, immediately after the primary transfer of the formed yellow patch image is completed, the image forming apparatus 100 is stopped. At that time, the transfer residual toner density of the patch image portion remaining on the surface of the photosensitive drum 1a of the yellow station is confirmed.

[0153] The measurement of the transfer residual toner density was performed by the following method. First, a transparent tape (polyester tape 5511 Nichiban) was attached to the transfer residual toner portion of the yellow patch image on the surface of the photosensitive drum 1a to collect the transfer residual toner on the transparent tape. Then, the transparent tape collecting the transfer residual toner peeled from the surface of the photosensitive drum 1a and a new transparent tape were each attached to high white paper (GFC081 Canon). And the density D1 of the transparent tape of the transfer residual toner collection portion and the density D0 of the new transparent tape portion were each measured using a reflectance densitometer (Reflectometer Model TC-6DS manufactured by Tokyo Denshoku Co., Ltd.). The difference "D0 - D1" obtained by the measurement was taken as the transfer residual toner density. The lower the value of the transfer residual toner density, the less the transfer residual toner. If the value is 1.0 or less, it can be determined that there is almost no transfer residual toner, and image defects caused by adhesion to the charging roller 2a or the like do not occur.

[0154] In addition, microscopic observation of the surface of the photosensitive drum 1a where the transfer residual toner density was measured was performed, and the coating rate of the transfer carrier particles on the surface of the photosensitive drum 1a was calculated. Specifically, the coating rate was calculated by the following procedure for an observation image at a magnification of 3000 times by a laser microscope (VK-X200 Keyence) on the surface of the photosensitive drum 1a. Binarization processing was performed between the portion of the transfer carrier particles and the other portion, and the total area ratio of the transfer carrier particles on the surface of the photosensitive drum 1 was calculated as the coating rate of the transfer carrier particles on the surface of the photosensitive drum 1.

[0155] Also, the adhesion force between the transfer carrier particles and the toner used in this embodiment was measured using an SPM. Specifically, a cantilever with transfer carrier particles fixed to the tip of the lever was fabricated, and the cantilever was pressed against the toner with a predetermined pressing force. Then, the force required to detach the cantilever from the toner was measured as the adhesion force Ft between the transfer carrier particles and the toner.

[0156] The predetermined pressing force for pressing the cantilever against the toner during the adhesion force measurement is preferably set to the force with which the transfer carrier particles intervening between the toner and the photosensitive drum 1 are pressed against the toner in the developing nip portion. The pressing force was calculated by the calculation method described below. Here, "transfer carrier intervenes between the toner and the photosensitive drum 1 in the developing nip portion" means a state in which the transfer carrier particles are in contact with both the toner and the photosensitive drum 1 simultaneously.

[0157] First, the assumed conditions for the calculation will be described with reference to FIGS. 11 and 12. FIG. 11(a) is a schematic diagram of the developing nip portion, and it is assumed that the developing roller 41 and the photosensitive drum 1 are in contact via the toner in the developing nip portion. FIG. 11(b) shows a cross-section parallel to the surface of the photosensitive drum 1 along the dotted line AB in FIG. 11(a), and it is assumed that the toner in contact with the photosensitive drum 1 is most densely packed as shown by the hatched portion. FIG. 12 is an enlarged schematic diagram of the contact portion between the toner and the photosensitive drum 1 surrounded by the dotted line in FIG. 11. As shown in FIG. 12, it is assumed that the toner and the photosensitive drum 1 are in contact via the transfer carrier particles. Also, no transfer carrier particles have been supplied onto the surface of the photosensitive drum 1, and it is assumed that there are no transfer carrier particles on the surface of the photosensitive drum 1 in advance.

[0158] After making the above assumptions, the total number N of transfer carrier particles intervening between the toner and the photosensitive drum 1 at the developing nip portion was calculated as follows. From the calculated N and the contact force F between the developing roller 41 and the photosensitive drum 1, F / N, which is the pressing force on the toner per transfer carrier in the developing portion, was calculated, and the calculated F / N was adopted as the predetermined pressing force on the toner of the cantilever at the time of measuring the adhesive force.

[0159] First, a method for calculating the total number N of transfer carrier particles intervening between the toner and the photosensitive drum 1 at the developing nip portion will be described.

[0160] FIG. 13(a) is a schematic diagram showing the contact state of the toner, transfer carrier particles, and photosensitive drum 1 in the developing portion in two dimensions. As shown in FIG. 13(b), when the particle diameter of the transfer carrier particles is r, the transfer carrier particles on the toner hardly come into contact with the photosensitive drum 1 when the distance between the photosensitive drum 1 and the toner surface exceeds r. Therefore, the toner circumferential portion where the transfer carrier particles arranged on the toner circumference can contact the photosensitive drum 1 is on the arc connecting A and B. Actually, as shown in FIG. 13(b), it is necessary to consider the toner as a sphere, and it is necessary to obtain the ratio of the surface area obtained by integrating the arc AB in the circumferential direction (the hatched portion in FIG. 13(b)) to the toner surface area. The surface area of the hatched portion can generally be obtained as the surface area of a spherical cap and is as shown in Equation (2). Therefore, the ratio to the toner surface area is as shown in Equation (3). The actual numerical values can be calculated from the average particle diameter R of the toner and the particle diameter r of the transfer carrier particles.

[0161]

Equation

[0162] By the above calculation, the ratio of the arc AB in the configuration of this embodiment to the toner circumferential portion is calculated to be approximately 1.43%.

[0163] Therefore, it can be considered that in the developing nip portion, the transfer carrier particles are interposed between the toner and the photosensitive drum 1 in an area of about 1.43% of the entire surface of the toner. 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 photosensitive drum 1 per toner particle is calculated as "500 particles × 1.43%", resulting in approximately 7.2 particles.

[0164] Then, the total number of transfer carrier particles in the developing nip portion is calculated by multiplying the number of transfer carrier particles (7.2 particles) interposed between the toner and the photosensitive drum 1 per toner particle by the total number of toner particles in contact with the photosensitive drum 1 in the developing section.

[0165] The total number L of toner particles in contact with the photosensitive drum 1 in the developing nip portion can be calculated as "(the area of the developing nip portion × the filling rate of the toner) / the maximum cross-sectional area of the toner". (Total number of toner particles in contact with the photosensitive drum 1 in the developing nip portion) =(220 [mm] × 2.0 [mm] × π / √12) / (π × (7.0 / 2) 2 ) = approximately 10.37 × 10 6 particles (The closest packing ratio of two-dimensional circles, π / √12 ≈ 0.9069, is used.)

[0166] Therefore, "the total number N of transfer carriers interposed between the toner and the photosensitive drum 1 in the developing nip portion" is calculated as follows. It is calculated by multiplying "the total number of toner particles in contact with the photosensitive drum 1 in the developing nip portion" by "the number of transfer carrier particles interposed between the toner and the photosensitive drum 1 per toner particle", and the total number N is approximately 7.47 × 10 7 particles.

[0167] Since the pressing force of the developing roller 41 against the photosensitive drum 1 in this embodiment is F = 200 gf, F / N, which is the "pressing force on the toner per transfer carrier in the developing unit", is found to be 26.3 nN. The value of F / N obtained above was adopted as the predetermined pressing force for pressing the cantilever against the toner during the adhesion force measurement by SPM. Also, the same adhesion force measurement was performed on the photosensitive drum 1, and the adhesion force Fdr between the transfer carrier particles fixed to the tip of the cantilever and the photosensitive drum 1 was measured.

[0168] The results of the effect confirmation experiment of this embodiment will be described. As shown in FIG. 14, in the configuration of this embodiment, the transfer residual toner concentration is 0.8%, and it was confirmed that there is almost no transfer residual toner and that it has high transferability. Also, the transfer carrier coverage rate on the surface of the photosensitive drum 1 of this embodiment is 61.7%, and it was confirmed that the photosensitive drum 1 could be sufficiently coated with transfer carrier particles. Also, as shown in FIG. 15, the adhesion force between the transfer carrier particles and the toner in this embodiment was 32.8 (nN), and the adhesion force between the transfer carrier particles and the photosensitive drum 1 was 210.1 (nN). That is, it was confirmed that in this embodiment, the adhesion force between the transfer carrier particles and the toner is smaller than the adhesion force between the transfer carrier particles and the photosensitive drum 1.

[0169] On the other hand, in Comparative Example 1, a developer configuration was adopted in which the adhesion force between the transfer carrier particles and the photosensitive drum 1 is greater than the adhesion force between the transfer carrier particles and the toner. Specifically, the toner surface was not covered with an organic silica polymer or the like as in the configuration of Example 1, and the transfer carrier particles were directly externally added to the toner surface to form the developer. When the developer of Comparative Example 1 was used, the transfer residual toner concentration was 4.1%. The more transfer residual toner there is, the more image defects such as charging defects due to contamination of the charging roller 2 occur. Also, as shown in FIG. 15, the adhesion force between the transfer carrier particles and the toner in Comparative Example 1 was 304.6 (nN), and the adhesion force between the transfer carrier particles and the photosensitive drum 1 was 210.1 (nN). That is, it was confirmed that in Comparative Example 1, the adhesion force between the transfer carrier particles and the toner is greater than the adhesion force between the transfer carrier particles and the photosensitive drum 1.

[0170] From the above results, this embodiment has the following features.

[0171] It has a rotatable photosensitive drum 1 and a rotatable developing roller 41 that carries a developer composed of toner particles and transfer carrier particles adhering to the surface of the toner particles. The developing roller 41 contacts the photosensitive drum 1 to form a developing nip portion, and supplies the developer to the surface of the photosensitive drum 1 at the developing nip portion. And it has a developer storage portion 4 that stores the developer. A transfer roller 14 that transfers the developer supplied to the surface of the photosensitive drum 1 to the intermediate transfer belt 10 as a transfer medium, a photosensitive drum driving portion 110 that drives the photosensitive drum 1, and a control portion 200 that controls the photosensitive drum driving portion 110. In the configuration of this embodiment, with the photosensitive drum 1 rotating, at the developing nip portion, it is possible to supply the transfer carrier particles carried on the surface of the developing roller 41 to the surface of the photosensitive drum 1. Also, define the pressing force for pressing the developing roller 41 against the photosensitive drum 1 as F, and the total number of transfer carrier particles intervening between the toner particles and the photosensitive drum 1 as N. Let the adhesive force Ft formed between the carrier particles and the toner particles measured when the transfer carrier particles are pressed against the toner particles with a pressing force of F / N per unit carrier particle. Let the adhesive force Fdr formed between the transfer carrier particles and the photosensitive drum 1 measured when the transfer carrier particles are pressed against the photosensitive drum 1 with F / N. Make the relationship between the adhesive force Ft and the adhesive force Fdr satisfy Ft ≦ Fdr. And it is an image forming apparatus 100 capable of executing an image forming mode of developing an electrostatic latent image with a developer and a supply mode of supplying transfer carrier particles from the developing roller 41 to the photosensitive drum 1.

[0172] As described above, in the configuration of this embodiment, by effectively supplying transfer carrier particles to the surface of the photosensitive drum 1, the transfer efficiency can be improved.

Embodiment

[0173] In Example 1, the developing roller 41 was rotationally driven in the forward direction of the surface movement direction of the photosensitive drum 1 so that the peripheral speed of the developing roller 41 at the developing nip portion became equal to the peripheral speed of the photosensitive drum 1. In this example, the developing roller 41 is rotationally driven at a peripheral speed 40% faster than that of the photosensitive drum 1 at the developing nip portion, thereby providing a peripheral speed difference between the developing roller 41 and the photosensitive drum 1.

[0174] Further, in this example, as shown in FIG. 16, in the image forming operation, the developing operation is set to start immediately after the development contact, and the supply timing of the transfer carrier particles is not provided before the start of the development. Other configurations are the same as those in Example 1 and are therefore omitted.

[0175] The operation of this example will be described below.

[0176] FIG. 17(a) is a schematic diagram showing the behavior of toner and transfer carrier particles at the developing nip portion when the non-image forming potential relationship is set between the developing roller 41 and the photosensitive drum 1. As shown in FIG. 17(a), by providing a peripheral speed difference between the developing roller 41 and the photosensitive drum 1, the following phenomenon occurs. Let the force parallel to the rotational direction of the developing roller 41 received by the toner intervening between the developing roller 41 and the photosensitive drum 1 be f1. Let the force parallel to the rotational direction of the photosensitive drum 1 received by the toner intervening between the developing roller 41 and the photosensitive drum 1 be f2. Under the conditions described in Example 1, f1 and f2 were in balance, whereas in the configuration of this example, the balance between f1 and f2 is broken, and the toner rolls at the developing nip portion. Then, as the toner rolls, the transfer carrier particles on the toner that are not in contact with the photosensitive drum 1 also move along with the rolling of the toner. Therefore, since it becomes possible to come into contact with the photosensitive drum 1, the opportunity to supply the transfer carrier particles from the toner onto the surface of the photosensitive drum 1 increases. Therefore, as shown in FIG. 17(b), more transfer carrier particles can be supplied from the toner on the developing roller 41 onto the surface of the photosensitive drum 1 after passing through the developing nip as compared with Example 1.

[0177] FIG. 18(a) is a schematic diagram showing the behavior of toner and transfer carrier particles in the developing nip portion when the potential relationship for image formation is set between the developing roller 41 and the photosensitive drum 1. As shown in FIG. 18(a), even when the potential relationship for image formation is set between the developing roller 41 and the photosensitive drum 1, the following phenomenon occurs due to the provision of a peripheral speed difference between the developing roller 41 and the photosensitive drum 1. The toner rolls in the developing nip portion, and the supply efficiency of the transfer carrier particles from the surface of the toner in the developing nip portion to the surface of the photosensitive drum 1 is improved. Then, as shown in FIG. 18(b), since the potential relationship for image formation is set between the developing roller 41 and the photosensitive drum 1, after passing through the developing nip portion, the toner is developed from the developing roller 41 onto the surface of the photosensitive drum 1. However, since the supply efficiency of the transfer carrier particles from the surface of the toner at the time of passing through the developing nip portion to the surface of the photosensitive drum 1 is improved, a large number of transfer carrier particles can be interposed between the toner developed on the surface of the photosensitive drum 1 and the photosensitive drum 1.

[0178] Therefore, in this embodiment, even if the supply timing of the transfer carrier particles is not provided before the image forming operation as in the first embodiment, the transfer carrier particles can be coated on the surface of the photosensitive drum 1 simultaneously with development, and the transfer carrier particles can be interposed between the toner image and the photosensitive drum 1.

[0179] Further, in this embodiment, although a cleaning member is not provided on the surface of the photosensitive drum 1, since the transfer carrier particles can be supplied simultaneously with development, even if a cleaning member is provided on the surface of the photosensitive drum 1, the transfer efficiency can be preferably improved. Even in a configuration in which the transfer carrier particles coated on the surface of the photosensitive drum 1 are collected by the cleaning member every one rotation of the photosensitive drum 1, the effect of improving the primary transfer efficiency by the transfer carrier particles can be obtained. Of course, a configuration in which a cleaning member is provided in the case of driven rotation without a peripheral speed difference between the developing roller 41 and the photosensitive drum 1 as in the first embodiment is not excluded as long as the transfer carrier particles are sufficiently supplied.

[0180] Next, in the configuration of this embodiment, the transfer residual toner density of the yellow patch image was measured in the same manner as in Example 1, and the coverage rate of the transfer carrier particles on the surface of the photosensitive drum 1 was measured to explain the results of confirming the effects of this embodiment.

[0181] As shown in FIG. 14, it was confirmed that even in the configuration of this embodiment, the transfer residual toner density was 0.7%, indicating that there was almost no transfer residual toner and high transferability. Also, as shown in FIG. 14, the transfer carrier coverage rate on the surface of the photosensitive drum 1 of this embodiment was 62.2%, confirming that the surface of the photosensitive drum 1 was sufficiently coated with transfer carrier particles.

[0182] From the above results, Example 2 is characterized by an image forming apparatus having the following configuration.

[0183] When the photosensitive drum driving unit 110 is used as the first driving unit, the developing roller driving unit 130 that drives the developing roller 41 is used as the second driving unit. The control unit 200 controls the second driving unit so that the surface moving speed of the developing roller 41 and the surface moving speed of the photosensitive drum 1 are different in the developing nip portion.

[0184] As described above, in the configuration of this embodiment, the transfer efficiency can be improved by more effectively supplying transfer carrier particles to the surface of the photosensitive drum 1.

[0185] Note that in the configuration of this embodiment, an intermediate transfer method using the intermediate transfer belt 10 is adopted, but a direct transfer method that directly transfers to the recording material P may also be adopted. For example, the recording material P may be placed on the transfer belt and directly transferred from the photosensitive drum 1, or the belt configuration may not be used.

Explanation of Reference Numerals

[0186] 1 Photosensitive drum 2 Charging roller 3 Exposure unit 4 Developing unit 14 Transfer roller 41 Developing roller 62 Toner particles

Claims

1. A rotatable image carrier; a rotatable developer carrier that carries a developer composed of toner particles and carrier particles adhering to the surfaces of the toner particles, the developer carrier being in contact with the image carrier to form a development section and supplying the developer to the surface of the image carrier in the development section; a developer storage section that stores the developer, an image forming apparatus capable of supplying the carrier particles carried on the surface of the developer carrier and accommodated in the developer accommodating section to the surface of the image carrier in the developing section while the image carrier is rotating, the image forming apparatus comprising: When the pressing force with which the developer carrying body is pressed against the image carrying body is F and the total number of the carrier particles interposed between the toner particles and the image carrying body is N, an adhesive force Ft formed between the carrier particles and the toner particles, the adhesive force Ft being measured when the carrier particles are pressed against the toner particles with a pressing force F / N per unit carrier particle; and an adhesive force Fdr formed between the carrier particles and the image carrier, the adhesive force Fdr being measured when the carrier particles are pressed against the image carrier at the F / N, Ft≦Fdr Fulfilling the developer has convex portions present on the surfaces of the toner particles, the carrier particles being disposed on the convex portions, When the closest distance between adjacent convex portions is defined as a convex interval G, the average of the convex interval G is equal to or smaller than the average particle size of the carrier particles.

2. 2. The image forming apparatus according to claim 1, wherein the convex portions are formed from fine particles present on the surface of the toner particles and containing an organosilicon polymer having a structure represented by the following formula (1): R-Si(O １／２ ) ３ (1) (The above R represents a hydrocarbon group having 1 to 6 carbon atoms.)

3. a transfer member that transfers the developer supplied to the surface of the image carrier to a transfer target; 2. The image forming apparatus according to claim 1, wherein the developer remaining on the image carrier without being transferred to the transfer medium is collected by the developer carrier.

4. 4. The image forming apparatus according to claim 3, wherein the developer is a one-component developer.

5. A first drive unit that drives the image carrier; A second drive unit that drives the developer carrier; a control unit that controls the first drive unit and the second drive unit, 2. The image forming apparatus according to claim 1, wherein the control unit controls the second drive unit so that, in the development unit, a surface movement speed of the developer carrier and a surface movement speed of the image carrier are different from each other.

6. 2. The image forming apparatus according to claim 1, wherein, when a height H of the convex portion from the surface of the toner particle is taken as a convex height, an average of the convex height H is equal to or smaller than an average particle size of the carrier particles.

7. 7. The image forming apparatus according to claim 1, wherein the carrier particles are silica.

8. 7. The image forming apparatus according to claim 1, wherein the carrier particles are made of an organic silica polymer.

9. 7. The image forming apparatus according to claim 1, wherein the average particle size of the carrier particles is 30 nm or more and 1000 nm or less.

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