Image forming apparatus

Abstract

To improve transfer efficiency by effectively supplying fine particles to a surface of a photoconductor drum.SOLUTION: An image forming apparatus has a rotatable developer carrier that carries developer composed of toner particles and transfer promoting particles adhered to the surface of each of the toner particles. When a pressing force pressing the developer carrier to an image carrier is F, and the total number of the transfer promoting particles interposed between the toner particle and the image carrier is N, the relationship between an adhesive force Ft formed between the transfer promoting particles and the toner particle measured when the transfer promoting particles are pressed against the toner particle at a pressing force F / N per unit transfer promoting particle, and an adhesive force Fdr formed between the transfer promoting particles and the image carrier measured when the transfer promoting particles are pressed against the image carrier at the pressing force F / N, satisfies Ft<Fdr. In the direction of movement of a surface of an intermediate transfer belt, discharge is generated on the upstream side of an upstream end of a transfer unit, and the potential difference between the image carrier and the intermediate transfer belt at the transfer unit is reduced compared with the Paschen's discharge threshold.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an image forming apparatus that utilizes an electrophotographic process or the like. [Background technology]

[0002] Image forming devices that use electrophotographic processes to form images have been known for a long time, such as photocopiers and laser printers.

[0003] In this image forming apparatus, as part of the transfer process, a voltage is applied from a voltage power supply to a transfer member positioned opposite the photosensitive drum, which acts as an image carrier, thereby electrostatically transferring the toner image formed on the surface of the photosensitive drum onto an intermediate transfer body or recording material. When forming toner images of multiple colors, this transfer process is repeated for each of the multiple toner images to form toner images of multiple colors on the surface of the intermediate transfer body or recording material. Developer (toner) that was not transferred from the photosensitive drum to the intermediate transfer body or recording material is removed from the photosensitive drum by a cleaning member and stored as waste toner in the waste toner storage section of the cleaning unit.

[0004] However, in recent years, cleanerless systems have been proposed that omit the cleaning system for the surface of the photosensitive drum in order to miniaturize the device. To achieve a cleanerless system, it is preferable to improve the efficiency of transferring the toner image from the photosensitive drum to the intermediate transfer material and to reduce the amount of residual toner remaining on the surface of the photosensitive drum after the toner image has been transferred by the transfer material.

[0005] Patent Document 1 proposes a configuration that improves transfer efficiency by pre-attaching fine particles to the surface of the photosensitive drum and interposing the fine particles between the photosensitive drum and the toner image, thereby reducing the adhesion force between the photosensitive drum and the toner, particularly in order to achieve a cleanerless system.

[0006] Furthermore, Patent Document 1 proposes a configuration in which, as a means of attaching fine particles to the surface of the photosensitive drum, toner with fine particles added externally is used to supply fine particles onto the photosensitive drum from the developing device. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 10-63027 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, in configurations that increase primary transfer efficiency and reduce the amount of toner remaining on the photosensitive drum, as described in Patent Document 1, the following problems existed.

[0009] In the configuration of Patent Document 1, the transfer efficiency may decrease in high-temperature, high-humidity environments or after durability degradation, where the charge amount of the toner tends to be low. In such conditions, if a high transfer voltage is used to increase the transfer efficiency, the electrostatic force acting in the direction of transferring the toner from the photosensitive drum to the intermediate transfer material increases, thereby improving the transfer efficiency. However, when toner already formed on the intermediate transfer material passes through the transfer section where the photosensitive drum and the intermediate transfer material come into contact, image defects may occur due to an increase in so-called re-transfer, where toner is transferred back to the photosensitive drum.

[0010] Therefore, the present invention aims to improve transfer efficiency while reducing re-transfer by effectively supplying fine particles to the surface of the photosensitive drum. [Means for solving the problem]

[0011] As described above, the image forming apparatus of the present invention includes a rotatable image carrier, and a rotatable developer carrier that carries a developer composed of toner particles and transfer promoting 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. An intermediate transfer belt that forms a transfer portion in contact with the image carrier, a current supply unit that supplies a transfer current from the intermediate transfer belt toward the image carrier in the transfer portion by applying a transfer voltage to the intermediate transfer belt, and a control unit that controls the current supply unit. In a state where the image carrier is rotating, in the developing portion, it is an image forming apparatus capable of supplying the transfer promoting particles carried on the surface of the developer carrier 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 transfer promoting particles intervening between the toner particles and the image carrier is N, the adhesive force Ft formed between the transfer promoting particles and the toner particles measured when the transfer promoting particles are pressed against the toner particles with a pressing force of F / N per unit transfer promoting particle, and the adhesive force Fdr formed between the transfer promoting particles and the image carrier measured when the transfer promoting particles are pressed against the image carrier with the F / N satisfy Ft < Fdr. The control unit generates a discharge between the image carrier and the intermediate transfer belt upstream of the upstream end of the transfer portion in the moving direction of the surface of the intermediate transfer belt, and controls the potential difference between the image carrier and the intermediate transfer belt in the transfer portion to be smaller than the Paschen discharge threshold value.

[0012] The image forming apparatus of the present invention further includes a rotatable image carrier, a charging member that charges the surface of the image carrier in a charging portion facing the image carrier, a rotatable developer carrier that holds a developer composed of toner particles and transfer promoting 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, an intermediate transfer belt that forms a transfer portion in contact with the image carrier, a charging voltage applying portion that applies a charging voltage to the charging member, a current supplying portion that supplies a transfer current from the intermediate transfer belt toward the image carrier in the transfer portion by applying a transfer voltage to the intermediate transfer belt, and a control portion that controls the charging voltage applying portion and the current supplying portion. In a state where the image carrier is rotating, the image forming apparatus is capable of supplying the transfer promoting particles carried on the surface of the developer carrier to the surface of the image carrier in the developing portion. When the pressing force for pressing the developer carrier against the image carrier is F and the total number of the transfer promoting particles intervening between the toner particles and the image carrier is N, an adhesive force Ft formed between the transfer promoting particles and the toner particles when the transfer promoting particles are pressed against the toner particles with a pressing force of F / N per unit transfer promoting particle, and an adhesive force Fdr formed between the transfer promoting particles and the image carrier when the transfer promoting particles are pressed against the image carrier with the F / N satisfy Ft < Fdr. When the potential difference between the first potential formed on the surface of the image carrier in the charging portion and the charging voltage is a first potential difference, and the potential difference between the second potential formed on the surface of the image carrier in the transfer portion and the surface potential of the intermediate transfer belt is a second potential difference, the control portion controls so that the second potential difference is smaller than the first potential difference in a state where the image carrier is rotating and the charging voltage is applied.

[0013] Further, the image forming apparatus of the present invention includes a rotatable image carrier, a charging member that charges the surface of the image carrier in a charging portion facing the image carrier, a rotatable developer carrier that carries a developer composed of toner particles and transfer promoting particles attached to the surface of the toner particles, 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, an intermediate transfer belt that forms a transfer portion in contact with the image carrier, a charging voltage applying portion that applies a charging voltage to the charging member, a current supply portion that supplies a transfer current from the intermediate transfer belt toward the image carrier in the transfer portion by applying a transfer voltage to the intermediate transfer belt, and a control portion that controls the charging voltage applying portion and the current supply portion. In a state where the image carrier is rotating, the image forming apparatus is capable of supplying the transfer promoting particles carried on the surface of the developer carrier to the surface of the image carrier in the developing portion. When the pressing force for pressing the developer carrier against the image carrier is F and the total number of the transfer promoting particles intervening between the toner particles and the image carrier is N, an adhesive force Ft formed between the transfer promoting particles and the toner particles when the transfer promoting particles are pressed against the toner particles with a pressing force of F / N per unit transfer promoting particle, and an adhesive force Fdr formed between the transfer promoting particles and the image carrier when the transfer promoting particles are pressed against the image carrier with the F / N satisfy Ft < Fdr. When a potential difference between a first potential formed on the surface of the image carrier in the charging portion and the charging voltage is a first potential difference, and a potential difference between a second potential formed on the surface of the image carrier in the transfer portion and the transfer voltage is a second potential difference, the control portion controls such that the second potential difference is smaller than the first potential difference in a state where the image carrier is rotating and the charging voltage is applied.

[0014] The image forming apparatus of the present invention also includes a rotatable image carrier, and a rotatable developer carrier that carries a developer composed of toner particles and transfer promoting 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. An intermediate transfer belt that forms a transfer portion in contact with the image carrier, and a current supply unit that supplies a transfer current from the intermediate transfer belt toward the image carrier in the transfer portion by applying a transfer voltage to the intermediate transfer belt. A current supply member that supplies current to the intermediate transfer belt in contact with the intermediate transfer belt, and a control unit that controls the current supply unit. In a state where the image carrier is rotating, in the developing portion, it is an image forming apparatus capable of supplying the transfer promoting particles carried on the surface of the developer carrier 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 transfer promoting particles intervening between the toner particles and the image carrier is N, the adhesive force Ft formed between the transfer promoting particles and the toner particles measured when the transfer promoting particles are pressed against the toner particles with a pressing force of F / N per unit transfer promoting particle, and the transfer promoting particles measured when the transfer promoting particles are pressed against the image carrier with the F / N. The relationship between the adhesive force Fdr formed between the image carrier and the image carrier satisfies Ft < Fdr. The intermediate transfer belt has a first layer among a plurality of layers constituting the intermediate transfer belt, which has conductivity in the thickness direction of the intermediate transfer belt, and a second layer having conductivity and a lower electrical resistance than the first layer. By applying a voltage from the current supply unit to the current supply member, a toner image is transferred from the image carrier to the intermediate transfer belt.

Advantages of the Invention

[0015] As described above, according to the present invention, it is possible to improve the transfer efficiency while reducing re-transfer by effectively supplying fine particles to the surface of the photosensitive drum.

Brief Description of the Drawings

[0016] [Figure 1] This is an overview of the image forming apparatus in Example 1. [Figure 2] This is a control block diagram in Example 1. [Figure 3] This is a schematic diagram of the toner surface in Example 1. [Figure 4] This is a schematic diagram of the convex shape of the toner surface in Example 1. [Figure 5] This is a schematic diagram of the convex shape of the toner surface in Example 1. [Figure 6] This is a schematic diagram of the convex shape of the toner surface in Example 1. [Figure 7] This is a schematic diagram of the toner and transfer promoting particles in Example 1. [Figure 8] This is a cross-sectional view of the intermediate transfer belt in Example 1. [Figure 9] This is a schematic diagram at the time of supplying transfer promoting particles in Example 1. [Figure 10] This is a schematic diagram at the time of primary transfer in Example 1. [Figure 11] (a), (b) These are diagrams showing the contact state of the toner in the developing unit in Example 1. [Figure 12] This is a diagram showing the existence state of the toner and transfer promoting particles in the developing unit in Example 1. [Figure 13] (a), (b) These are diagrams showing the state of the transfer promoting particles in the developing unit in Example 1. [Figure 14] This is the result of confirming the effect on the transfer efficiency in Example 1. [Figure 15] This is the result of confirming the coating rate of the transfer promoting particles in Example 1. [Figure 16] This is the result of measuring the adhesion force in Example 1. [Figure 17] This is the result of confirming the effect on re-transfer in Example 1. [Figure 18] This is a flow for examining the discharge in the transfer nip in Example 1. [Figure 19] This is a schematic diagram of the discharge light observation method in Example 1. [Figure 20]This is an overview of the image forming apparatus in other embodiments. [Modes for carrying out the invention]

[0017] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the following embodiments should be appropriately modified depending on the configuration and various conditions of the apparatus to which the present invention is applied. Therefore, unless otherwise specifically stated, the scope of the present invention is not intended to be limited to those embodiments. [Examples]

[0018] 1. Image forming apparatus The present invention particularly relates to an image forming apparatus that uses a so-called drum cleanerless method, which does not have a means for cleaning the image carrier.

[0019] Figure 1 is a schematic diagram showing an example of a color image forming apparatus, and the configuration and operation of the image forming apparatus of this embodiment will be explained using Figure 1. The image forming apparatus of this embodiment is a so-called tandem type printer equipped with image forming stations a to d. The first image forming station a forms a yellow (Y) image, the second image forming station b forms a magenta (M) image, the third image forming station c forms a cyan (C) image, and the fourth image forming station d forms a black (Bk) image. The configuration of each image forming station is the same except for the color of the toner it contains, and the following explanation will use the first image forming station a as an example. Furthermore, unless otherwise specified, a to d for Y, M, C, and K will be omitted and explained in a general manner.

[0020] The first image forming station a comprises a drum-shaped electrophotographic photoreceptor (hereinafter referred to as a photosensitive drum) 1a, a charging roller 2a which is a charging means, an exposure unit 3a, and a developer 4a.

[0021] The photosensitive drum 1a is an image carrier that is rotated by the photosensitive drum drive unit 110 at a peripheral speed (process speed) of 150 mm / sec in the direction of the arrow and carries the toner image. The photosensitive drum 1a has a photosensitive layer 1f and a surface layer 1e (see Figure 12) on an aluminum tube with a diameter of φ20 mm, and the surface layer 1e is a thin film layer with a thickness of 20 μm formed of polyarylate.

[0022] When the control unit 200, such as a controller, receives an image signal, the image forming operation is initiated and the photosensitive drum 1a is driven to rotate. During the rotation process, the photosensitive drum 1a is uniformly charged to a predetermined potential with a predetermined polarity (in this embodiment, the normal polarity is negative polarity) by the charging roller 2a, and is exposed by the exposure unit 3a according to the image signal. 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 the developer (yellow developer) 4a at the development position and visualized as a yellow toner image.

[0023] The charging roller 2a, acting as a charging member, is in contact with the surface of the photosensitive drum 1a at its charged portion with a predetermined pressure, and rotates driven by friction with the surface of the photosensitive drum 1a. In addition, a predetermined DC voltage is applied to the rotation axis of the charging roller 2a from the charging voltage power supply 120 in accordance with the image forming operation. In this embodiment, the charging roller 2a has a metal shaft with a diameter of φ5.5 mm, a thickness of 1.5 mm, and a volume resistivity of 1 × 10⁻¹⁶. 6An elastic layer made of a conductive elastic material with a strength of approximately Ωcm is used. In accordance with the image forming operation, the control unit 200 applies a DC voltage of -1050V as a charging voltage to the rotation axis of the charging roller 2a, charging the surface of the photosensitive drum 1a to a predetermined potential of -500V. The surface potential of the photosensitive drum 1a was measured using a Trek Model 344 surface potential meter. The surface potential of the photosensitive drum 1a at this time, -500V, is the surface potential of the photosensitive drum 1 when not forming an image, and is the dark area potential (Vd) where toner image development does not occur. In addition, the surface of the charging roller 2a is provided with numerous protrusions, and the average height of the protrusions is about 10 μm. The protrusions on the surface of the charging roller 2a act as spacers between the charging roller 2a and the photosensitive drum 1a in the charged area. The role of this component is to prevent the charging roller 2a from becoming contaminated with transfer residue toner when the transfer residue toner, which is toner that remains on the photosensitive drum 1a without being transferred in the primary transfer section described later, enters the charged section, by preventing parts other than the protrusions from touching the transfer residue toner.

[0024] The exposure unit 3a includes a laser driver, laser diode, polygon mirror, optical lens system, etc. As shown in Figure 2, the exposure unit 3 receives a time-series electrical digital pixel signal of image information that has been processed by the controller 202 and input to the control unit 200 via interface 201. In this embodiment, the exposure amount is adjusted so that the image formation potential Vl of the electrostatic latent image area of ​​the photosensitive drum 1 after exposure by the exposure unit 3a becomes -100V. The image formation potential is also called the bright area potential.

[0025] The developing unit 4a comprises a developing roller 41a as a developing member (developer carrier) and a non-magnetic one-component developer composed of toner and transfer-promoting particles (transfer carrier particles) described later. The developing unit 4a is a developing means that performs a developing operation on the photosensitive drum 1 in order to develop the electrostatic latent image as a toner image, and is a developer storage section that houses the developer. The developing unit 4a and the image forming apparatus body 100 are equipped with a contact-separation mechanism 40 that controls the contact-separation (development-separation) state of the developing roller 41a and the photosensitive drum 1a, as shown in Figure 2. The control unit 200 makes the developing roller 41a and the photosensitive drum 1a contact-separate according to the image forming operation, etc. When the developing roller 41a and the photosensitive drum 1a are in contact, the developing roller 41a is in contact with a pressing force of 1.96 N. The width of the developing nip portion, which is the contact point 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 rotated by the developing roller drive unit 130 at a peripheral speed faster than the peripheral speed of the photosensitive drum 1a, such that the surface movement direction of the developing roller 41a is forward of the surface movement direction of the photosensitive drum 1a at the contact point opposite to the photosensitive drum 1a. In this embodiment, the developing roller 41a is rotated at a peripheral speed 140% of that of the photosensitive drum 1a.

[0026] The pre-exposure unit 5a, which serves as a static elimination means, eliminates static electricity by exposing the surface of the photosensitive drum 1a before it is charged by the charging roller 2a. By eliminating static electricity from the surface of the photosensitive drum 1a, it plays a role in leveling the surface potential formed on the photosensitive drum 1 and controlling the amount of discharge caused by discharge in the charged area.

[0027] Furthermore, the control unit 200 controls the application of a DC voltage of -300V as the development voltage Vdc to the core metal of the development roller 41a from the development voltage power supply 140 when the development roller 41a and the photosensitive drum 1a come into contact during the image formation operation. During image formation, the electrostatic force generated by the potential difference between the development voltage Vdc = -300V and the image formation potential Vl = -100V of the photosensitive drum 1a causes the toner carried on the development roller 41a to be developed at the image formation potential Vl of the photosensitive drum 1a.

[0028] In the following explanation, with respect to potential and applied voltage, a large absolute value on the negative side (for example, -1000V compared to -500V) will be referred to as a high potential, and a small absolute value on the negative side (for example, -300V compared to -500V) will be referred to as a low potential. This is because we are considering the negatively charged toner in this embodiment as the reference.

[0029] Furthermore, the voltage in this embodiment is expressed as a potential difference from the ground potential (0V). Therefore, the developing voltage Vdc = -300V is interpreted as having a potential difference of -300V with respect to the ground potential due to the developing voltage applied to the core metal of the developing roller 41a. The same applies to charging voltage, transfer voltage, etc.

[0030] Next, the control unit 200 will be described. Figure 2 is a control block diagram showing the schematic control configuration of the main parts of the image forming apparatus 100 in this 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 via the interface 201 in the control unit 202 according to a predetermined control program and reference table. The control unit 202 is composed of a CPU 155, which is a central element that performs various calculations, and memory 154 such as ROM and RAM, which are memory elements. Sensor detection results, counter count results, calculation results, etc. are stored in the RAM, and control programs, data tables obtained in advance through experiments, etc., are stored in the ROM. Each control target, sensor, counter, etc. in the image forming apparatus 100 is connected to the control unit 200. The control unit 200 controls the exchange of various electrical information signals and the timing of the driving of each part, etc., and controls a predetermined image forming sequence. For example, the control unit 200 controls the voltage and exposure amount applied by the charging voltage power supply 120 as the charging voltage application unit, the developing voltage power supply 140 as the developing voltage application unit, the exposure unit 3, the primary transfer voltage power supply 160 as the current supply unit, and the secondary transfer voltage power supply 150. In addition, it also controls the photosensitive drum drive unit 110, the developing roller drive unit 130, and the developing contact / separation mechanism 40. The image forming apparatus 100 then 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 host devices include image readers, personal computers, facsimile machines, and smartphones.

[0031] The toner used in this embodiment is a negatively charged, non-magnetic toner manufactured by suspension polymerization, with a volume-average particle size of 7.0 μm. It becomes negatively charged when supported on the developing roller 41a. The volume-average particle size of the toner was measured using a Beckman Coulter LS-230 laser diffraction particle size analyzer. Further details about the toner will be described later.

[0032] The intermediate transfer belt 10, which serves as an intermediate transfer body, is stretched by a plurality of tensioning members 11, 12, and 13. The tensioning member 13 is rotated by a motor (not shown) at a peripheral speed of 103% of that of the photosensitive drum 1a, in a direction that moves circumferentially at the part that contacts the photosensitive drum 1a. The tensioning members 11 and 12 are rotated in accordance with the rotation of the intermediate transfer belt 10. A DC voltage of 250V is applied to the primary transfer roller 14a, which serves as a primary transfer member, from a primary transfer voltage power supply 160 during primary transfer in the image forming operation. In this embodiment, a DC voltage is also applied to the tensioning member 13 from the primary transfer power supply 160. Alternatively, the tensioning member 11 and 12 may also be configured to have a DC voltage applied from the primary transfer power supply 160, or the tensioning member 13 may not have a DC voltage applied. The yellow toner image formed on the photosensitive drum 1a is electrostatically transferred onto the intermediate transfer belt 10 as it passes through the primary transfer section, which is the contact area between the photosensitive drum 1a and the primary transfer roller 14a via the intermediate transfer belt 10. In this embodiment, a difference in peripheral speed is provided between the photosensitive drum 1 and the intermediate transfer belt 10. This causes the toner to move on the photosensitive drum 1 in the primary transfer section, reducing adhesion and improving primary transfer efficiency. Here, the developer remaining on the photosensitive drum 1 that is not transferred to the intermediate transfer belt 10 is recovered by the developing roller 41.

[0033] The primary transfer roller 14a is a cylindrical metal roller with a diameter of φ6 mm, and is made of nickel-plated steel. The primary transfer roller 14a is positioned 8 mm downstream of the center of the photosensitive drum 1a in the direction of movement of the intermediate transfer belt 10, and the intermediate transfer belt 10 is configured to wrap around the photosensitive drum 1a. In the multiple photosensitive drums 1 and multiple primary transfer rollers 14, the distance from the axis center of each photosensitive drum 1 to the axis center of each primary transfer roller 14 is equal. The offset amount may be changed for each image forming station. The primary transfer roller 14a is positioned 1 mm above the horizontal plane formed by the photosensitive drum 1a and the intermediate transfer belt 10 in order to ensure the amount of wrapping of the intermediate transfer belt 10 around the photosensitive drum 1a. The intermediate transfer belt 10 is then pressed with a force of approximately 1.96 N. The primary transfer roller 14a rotates in conjunction with the rotation of the intermediate transfer belt 10. The primary transfer roller 14b located at the second image forming station b, the primary transfer roller 14c located at the third image forming station c, and the primary transfer roller 14d located at the fourth image forming station d have the same configuration as the primary transfer roller 14a.

[0034] Similarly, the second, third, and fourth image forming stations b, c, and d form images of the second color (magenta toner), the third color (cyan toner), and the fourth color (black toner), which are then sequentially transferred onto the intermediate transfer belt 10. A composite color image corresponding to the desired color image is then obtained.

[0035] The four toner images on the intermediate transfer belt 10 are transferred collectively to the surface of the recording material P fed by the paper feeding means 50 during the secondary transfer process, which involves passing through a secondary transfer nip formed by the intermediate transfer belt 10 and the secondary transfer roller 15, which acts as a secondary transfer member. The secondary transfer roller 15 contacts the intermediate transfer belt 10 with a pressure of 50N to form the secondary transfer nip. The secondary transfer roller 15 rotates in a driven manner relative to the intermediate transfer belt 10, and a voltage of 1500V is applied from the secondary transfer voltage power supply 150 when the toner on the intermediate transfer belt 10 is being transferred to the recording material P such as paper.

[0036] Subsequently, the recording material P, which carries the four toner images, is introduced into the fuser unit 30. The four toners are heated and pressurized by the fuser unit 30, causing them to melt and mix, and then fix to the recording material P. After secondary transfer, any toner remaining on the intermediate transfer belt 10 is cleaned and removed by the cleaning device 17.

[0037] The cleaning device 17 has a cleaning blade that contacts the outer surface of the intermediate transfer belt 10 to scrape off the toner remaining on the intermediate transfer belt 10 and collect it inside the intermediate transfer belt cleaning device 17. The intermediate transfer belt cleaning device 17 is positioned downstream of the secondary transfer section of the intermediate transfer belt 10 in the rotational direction of the intermediate transfer belt 10 to collect the toner adhering to the intermediate transfer belt 10.

[0038] Through the above steps, a full-color print image is formed.

[0039] 2. Developer, toner, transfer-promoting particles Next, we will describe in detail the developer, toner, and transfer-promoting particles used in this embodiment.

[0040] In this example, a mixture of toner and external additive A, which is transfer-promoting particles, was used as the developer. Here, transfer-promoting particles are particles that, by being interposed between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1, reduce the adhesion between the toner image and the photosensitive drum 1, thereby improving the primary transfer efficiency of the toner image. The toner consists of toner matrix particles containing a release agent and toner particles containing an organosilicon polymer on the surface of the toner matrix particles.

[0041] The organosilicon polymer is R-Si(O 1 / 2 The T3 unit structure is represented by 3, where R represents an alkyl group or phenyl group having 1 to 6 carbon atoms, and the organosilicon polymer forms protrusions on the surface of the toner matrix particles.

[0042] The protrusions are characterized by surface contact with the toner matrix particle surface, and this surface contact is expected to have a significant inhibitory effect on the movement, detachment, and embedding of the protrusions.

[0043] The degree of surface contact is explained using schematic diagrams of the convex parts shown in Figures 3, 4, 5, and 6.

[0044] Figure 3 shows a cross-sectional image of a toner particle, where 61 reveals approximately one-quarter of the particle's surface; 62 is the toner particle, 63 is the surface of the toner matrix particle, and 64 is the convex portion. The cross-section of the toner particle can be observed using a scanning transmission electron microscope (STEM), which will be described later.

[0045] A cross-sectional image of the toner is observed, and a line is drawn along the circumference of the toner matrix particle surface. This line along the circumference is used as a reference to convert the image to a horizontal image. In the horizontal image, the length of the line along the circumference in the portion where the convex portion and the toner matrix particle form a continuous interface is defined as the convex width w.

[0046] Furthermore, the maximum length of the protrusion in the direction normal to the width w of the protrusion is defined as the protrusion diameter D, and the length from the vertex of the protrusion to the line along its circumference in the line segment forming the protrusion diameter D is defined as the protrusion height H.

[0047] In Figures 4 and 6, the convex diameter D and the convex height H are the same, while in Figure 5, the convex diameter D is greater than the convex height H.

[0048] Figure 6 schematically illustrates the state of adhesion of particles similar to bowl-shaped particles, which are obtained by crushing or breaking hollow particles, resulting in hemispherical particles with a concave center.

[0049] In Figure 6, the convex width W is the sum of the lengths of the organosilicon polymers in contact with the toner matrix particle surface. That is, the convex width W in Figure 6 is the sum of W1 and W2.

[0050] The average number of convex heights H is 30 nm to 300 nm, and preferably 30 nm to 200 nm. When the average number of convex heights H is 30 nm or more, a spacer effect occurs between the toner matrix particle surface and the transfer material, significantly improving transferability. On the other hand, when the average number of convex heights H is 300 nm or less, the inhibitory effect on migration, detachment, and embedding is significant, and high transferability is maintained even with long-term use. A cumulative distribution of convex heights H is taken in the convex portions where the convex height H is 30 nm to 300 nm. When the convex height that corresponds to 80 percent of the sum of the convex heights H is taken from the smallest convex height, H80 is preferably 65 nm to 120 nm, and more preferably 75 nm to 100 nm. By having H80 within the above range, transferability can be further improved.

[0051] The number-average particle size R of the primary particles of external additive A is preferably between 30 nm and 1200 nm. A value of 30 nm or greater creates a spacer effect between the additive and the transfer material, resulting in high transferability. Furthermore, the larger the R value, the better the transfer performance tends to be. On the other hand, if R exceeds 1200 nm, the toner's fluidity decreases, making image unevenness more likely.

[0052] The ratio of the number-average particle size 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 this ratio [(number-average particle size R of the primary particles of external additive A) / (number-average value of the convex height H)] is within the above range, it is possible to achieve both excellent transferability and low-temperature fixation that can withstand extended lifespan.

[0053] When the average number of convex heights H is 30 nm, which is the minimum value, if R is 30 nm or greater, a spacer effect can be generated between the transfer material and the R, improving transferability. This is thought to be because the external additive A is substituted in areas where convex parts are not present due to effects such as desorption, thereby generating a spacer effect. In other words, if R is less than 30 nm, the spacer effect is less likely to be generated.

[0054] The adhesion rate of external additive A to the surface of toner particles is preferably 0% to 20%, and more preferably 0% to 10%. When the adhesion rate is within the above range, external additive A can move more easily on the surface of the toner particles, and the transferability can be further improved by its convexity substitution effect. In the fixing process in which the toner is fixed to the fixing member, the separation performance between the fixing member and the paper is improved by allowing an appropriate amount of release agent to seep out from the toner matrix particles.

[0055] A backscattered electron image of a 1.5 μm square area of ​​the toner surface is obtained by observing the surface of the toner using a scanning electron microscope. When an image is obtained by binarizing the backscattered electron image so that the organosilicon polymer portion in the backscattered electron image becomes a bright area, the area ratio of the bright area of ​​the image to the total area of ​​the image (hereinafter also simply referred to as the area ratio of the bright area) is 30.0% or more and 75.0% or less. Furthermore, it is preferable that the area ratio of the bright area of ​​the image is 35.0% or more and 70.0% or less. The higher the area ratio of the bright area, the higher the proportion of organosilicon polymer on the surface of the toner matrix particles. If the area ratio of the bright area is higher than 75.0%, the proportion of components derived from the toner matrix particles on the surface of the toner matrix particles is low, making it less likely for the release agent to seep out from the toner matrix particles, and making it easier for thin paper to wrap around the fuser during low-temperature fixing. On the other hand, if the area ratio of the bright area of ​​the image is less than 30.0%, the proportion of components derived from the toner matrix particles on the surface of the toner matrix particles is high. In other words, the exposed area of ​​components derived from toner matrix particles on the surface of the toner matrix particles is large, resulting in reduced transferability during the initial stages of use. The area ratio of the bright areas in the image will henceforth be referred to as the coverage rate of the organosilicon polymer on the surface of the toner matrix particles.

[0056] External additive A is not particularly limited as long as the number-average particle size R of the primary particles is 30 nm or more and 1000 nm or less, and various organic or inorganic fine particles can be used. From the viewpoint of easily imparting fluidity and being easily negatively charged like the toner matrix particles, it is preferable that external additive A contains silica fine particles. The silica fine particle content 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 it is more preferable that it is 0.05% by mass or more and 3.00% by mass or less.

[0057] Examples of organic or inorganic microparticles other than silica microparticles include the following: (1) Fluidity imparting agents: alumina nanoparticles, titanium oxide nanoparticles, carbon black, and carbon fluoride. (2) Abrasives: Fine particles of metal oxides (fine particles of strontium titanate, cerium oxide, alumina, magnesium oxide, and chromium oxide, etc.), fine particles of nitrides (fine particles of silicon nitride, etc.), fine particles of carbides (fine particles of silicon carbide, etc.), fine particles of metal salts (fine particles of calcium sulfate, barium sulfate, and calcium carbonate, etc.). (3) Lubricants: Fine particles of fluororesin (such as vinylidene fluoride and polytetrafluoroethylene), fine particles of fatty acid metal salts (such as zinc stearate and calcium stearate). (4) Charge controllable fine particles: Fine particles of metal oxides (fine particles of tin oxide, titanium oxide, zinc oxide, and alumina, etc.), carbon black.

[0058] Silica microparticles and said organic or inorganic microparticles may be hydrophobized to improve toner fluidity and uniformize the charge of toner particles.

[0059] Examples of treatment agents for the hydrophobic treatment include unmodified silicone varnish, various modified silicone varnishes, unmodified silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organosilicon compounds, and organotitanium compounds. These treatment agents may be used alone or in combination.

[0060] The silica fine particles can be any known silica fine particles, and may be either dry silica fine particles or wet silica fine particles. Preferably, they are wet silica fine particles obtained by the sol-gel method (hereinafter also referred to as sol-gel silica).

[0061] Figure 7 is a magnified view of the developer used in this embodiment. As shown in Figure 7, the developer in this embodiment has an external additive A, which is a transfer-promoting particle, placed on a toner surface on which many protrusions of organosilicon polymer are formed.

[0062] The convex spacing G and convex height H on the toner surface shown in Figure 7 can be measured using a scanning transmission electron microscope (STEM), which will be described later. The convex spacing G and convex height H can also be measured using a scanning probe microscope (SPM). A scanning probe microscope (SPM) is equipped with a probe, a cantilever supporting the probe, and a displacement measurement system for detecting the bending of the cantilever. It detects the interatomic force (attractive or repulsive force) between the probe and the sample to observe the shape of the sample surface.

[0063] If the convex spacing G is larger than that of the transfer-promoting particles, the transfer-promoting particles will come into contact with the toner matrix when positioned between the convex portions, increasing the adhesion force Ft between the transfer-promoting particles and the toner, making it difficult for the transfer-promoting particles to transfer from the toner to the photosensitive drum 1. Therefore, it is preferable that the average number of convex spacing G is smaller than the average number particle size of the transfer-promoting particles.

[0064] Furthermore, if the convex height H is higher than the particle size of the transfer-promoting particles, the convex portion will come into contact with the photosensitive drum 1 before the transfer-promoting particles, making it difficult for the transfer-promoting particles to come into contact with the photosensitive drum 1, and thus making it difficult for the transfer-promoting particles to transfer from the toner to the photosensitive drum 1. For this reason, it is preferable that the number average value of the convex height H is smaller than the number average particle size of the transfer-promoting particles.

[0065] However, as mentioned above, it is preferable that the adhesion force Ft between the transfer-promoting particles and the toner is smaller than the adhesion force Fdr between the transfer-promoting particles and the photosensitive drum 1. Therefore, it is preferable to select a material for the transfer-promoting particles that reduces the adhesion force Ft of the transfer-promoting particles to the toner. For example, as in this embodiment, if the protrusions on the toner surface are formed of a silica-based material such as an organic silica polymer, it is preferable to select a silica-based material for the transfer-promoting particles that has a similar material composition to the protrusions in order to reduce the adhesion force between the protrusions and the transfer-promoting particles.

[0066] A larger number of transfer-promoting particles coating the toner is preferable from the viewpoint of supplying transfer-promoting particles from the developing roller 41 to the photosensitive drum 1. However, if too many transfer-promoting particles are added, the risk of contamination of components within the image forming apparatus 100 increases, so it is preferable to adjust the amount according to the desired primary transferability.

[0067] Primary transferability improves with increasing coverage of the transfer-promoting particles on the photosensitive drum 1, and it is preferable that the coverage of the transfer-promoting particles on the photosensitive drum 1 be 10% or more in order to obtain sufficient primary transferability. However, as the coverage of the transfer-promoting particles on the photosensitive drum 1 increases, the degree of improvement in primary transferability slows down, and the risk of contamination of various components within the image forming apparatus by the transfer-promoting particles increases. For this reason, it is preferable to keep the coverage of the transfer-promoting particles on the photosensitive drum 1 within 50%.

[0068] 3. Method for measuring the physical properties of the developer The following describes various measurement methods.

[0069] <Method for observing the cross-section of toner using a scanning transmission electron microscope (STEM)> The cross-section of the toner observed with a scanning transmission electron microscope (STEM) is prepared as follows.

[0070] The procedure for preparing a cross-section of the toner is described below. If organic or inorganic microparticles are added to the toner, the sample should be prepared by removing the organic or inorganic microparticles using the method described below.

[0071] Add 160g of sucrose (manufactured by Kishida Chemical Co., Ltd.) to 100mL of deionized water and dissolve it while heating in a water bath to prepare a concentrated sucrose solution. Add 31g of the above concentrated sucrose solution and 6mL of Contaminon N (a 10% by mass aqueous solution of pH 7 neutral detergent for cleaning precision measuring instruments, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) to a centrifuge tube (capacity 50mL). Add 1.0g of toner and break up any clumps of toner with a spatula or similar tool. Shake the centrifuge tube in a shaker (AS-1N, sold by AS ONE Corporation) at 300 spm (strokes per min) for 20 minutes. After shaking, transfer the solution to a glass tube for a swing rotor (50mL) and separate the contents using a centrifuge (H-9R, manufactured by Kokusan Co., Ltd.) at 3500 rpm for 30 minutes. This operation separates the toner particles from the external additives. Visually confirm that the toner particles and aqueous solution are sufficiently separated, and collect the separated toner particles from the top layer using a spatula or similar tool. Filter the collected toner particles using a vacuum filter, then dry them in a dryer for at least one hour to obtain a sample for measurement. Repeat this process multiple times to obtain the required amount.

[0072] Furthermore, whether or not the protruding portion contains an organosilicon polymer is confirmed by combining it with elemental analysis using energy-dispersive X-ray spectroscopy (EDS).

[0073] Toner is sprayed in a single layer onto a cover glass (Matsunami Glass Co., Ltd., square cover glass; square No. 1), and an osmium (Os) plasma coater (filgen, OPC80T) is used to apply an Os film (5 nm) and a naphthalene film (20 nm) to the toner as protective films. Next, a PTFE tube (outer diameter 3 mm (inner diameter 1.5 mm) x 3 mm) is filled with photocurable resin D800 (JEOL Ltd.), and the cover glass is gently placed on top of the tube in an orientation such that the toner is in contact with the photocurable resin D800. After curing the resin by irradiating it with light in this state, the cover glass and tube are removed to form a cylindrical resin with toner embedded on the outermost surface. Using an ultrasonic ultramicrotome (Leica, UC7), the toner is cut from the outermost surface of the cylindrical resin at a cutting speed of 0.6 mm / s, to a length equal to the radius of the toner (for example, 4.0 μm if the weight-average particle size (D4) is 8.0 μm), thereby revealing a cross-section of the toner's center.

[0074] Next, the toner is cut to a thickness of 100 nm to create a thin section sample of the toner's cross-section. By cutting in this manner, a cross-section of the toner's center can be obtained.

[0075] 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 an image was acquired at an image size of 1024×1024 pixels. Also, the Contrast of the Detector Control panel for the bright-field image was adjusted to 1425, the Brightness was adjusted to 3750, and the Contrast of the Image Control panel was adjusted to 0.0. Then, the Brightness was adjusted to 0.5 and the Gamma was adjusted to 1.00 to acquire an image. The image magnification was 100,000 times, and the image acquisition was performed so that it covered approximately one-fourth to one-half of the circumference of the cross-section in one toner particle as shown in Figure 3. For the obtained STEM image, 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 this line, conversion to a horizontal image (select Selection in the Edit tab, change the line width to 500 pixels in properties, and 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 in the line segment forming the convex diameter D to the line along the circumference 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.

[0076] <Method for calculating H80> In the STEM image of the toner cross-section obtained using the scanning transmission electron microscope (STEM) described above, the cumulative distribution of the convex height H is taken for convex portions where the convex height H is between 30 nm and 300 nm. The convex height that corresponds to 80 percent of the convex heights, calculated by accumulating from the smallest convex height H, is defined as H80 (unit: nm).

[0077] <Method for calculating the area ratio of bright areas in a 1.5 μm square backscattered electron image of the toner surface> The area ratio of the bright area is determined by observing the surface of the toner using a scanning electron microscope. A 1.5 μm square backscattered electron image of the toner surface is obtained. Then, the image is binarized so that the organosilicon polymer portion in the backscattered electron image becomes the bright area, and the ratio of the bright area to the total area of ​​the image is determined. If organic or inorganic fine particles are added to the toner, the sample is used after removing the organic or inorganic fine particles by the method described below.

[0078] Add 160g of sucrose (manufactured by Kishida Chemical Co., Ltd.) to 100mL of deionized water and dissolve it while heating in a water bath to prepare a concentrated sucrose solution. Add 31g of the above concentrated sucrose solution and 6mL of Contaminon N (a 10% by mass aqueous solution of pH 7 neutral detergent for cleaning precision measuring instruments, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) to a centrifuge tube (capacity 50mL). Add 1.0g of toner and break up any clumps of toner with a spatula or similar tool. Shake the centrifuge tube in a shaker (AS-1N, sold by AS ONE Corporation) at 300 spm (strokes per min) for 20 minutes. After shaking, transfer the solution to a glass tube for a swing rotor (50mL) and separate the contents using a centrifuge (H-9R, manufactured by Kokusan Co., Ltd.) at 3500 rpm for 30 minutes. This operation separates the toner particles from the external additives. Visually confirm that the toner particles and aqueous solution are sufficiently separated, and collect the separated toner particles from the top layer using a spatula or similar tool. Filter the collected toner particles using a vacuum filter, then dry them in a dryer for at least one hour to obtain a sample for measurement. Repeat this process multiple times to obtain the required amount.

[0079] Furthermore, whether or not the protrusions contain organosilicon polymers will be confirmed by combining this with elemental analysis using energy-dispersive X-ray spectroscopy (EDS), as described later.

[0080] The SEM equipment and observation conditions are as follows: Equipment used: ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd. Acceleration voltage: 1.0kV WD: 2.0mm Aperture Size: 30.0 μm Detection signal: EsB (Energy-selective backscattered electrons) EsB Grid: 800V Observation magnification: 50,000x Contrast: 63.0 ± 5.0% (reference value) Brightness: 38.0 ± 5.0% (reference value) Resolution: 1024×768 Pre-treatment: Toner particles are scattered onto carbon tape (no vapor deposition is performed). The acceleration voltage and EsB grid are set to achieve objectives such as acquiring structural information of the outermost surface of toner particles, preventing charge-up of undeposited samples, and selectively detecting high-energy backscattered electrons. The observation field is selected to be near the apex where the curvature of the toner particles is smallest. The origin of the bright areas in the backscattered electron image was confirmed by superimposing the backscattered electron image with an elemental mapping image obtained by energy-dispersive X-ray spectroscopy (EDS) acquired by a scanning electron microscope (SEM).

[0081] The SEM / EDS equipment and observation conditions are as follows: Equipment used (SEM): ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd. Equipment used (EDS): NORAN System 7, Ultra Dry EDS Detector, manufactured by Thermo Fisher Scientific Co., Ltd. Acceleration voltage: 5.0kV WD: 7.0mm Aperture Size: 30.0 μm Detection signal: SE2 (secondary electrons) Observation magnification: 50,000x Mode: Spectral Imaging Pre-treatment: Toner particles are scattered onto carbon tape, and platinum sputtering is performed. The silicon element mapping image obtained by this method is superimposed with the backscattered electron image, and it is confirmed that the silicon atom portion of the mapping image and the bright portion of the backscattered electron image coincide.

[0082] The area ratio of the bright area to the total area of ​​the backscattered electron image was calculated by analyzing the backscattered electron image of the toner particle surface obtained by the above method using the image processing software ImageJ (developed by Wayne Rashand). The procedure is as follows.

[0083] First, convert the backscattered electron image to 8-bit using the Image menu's Type option. Next, reduce image noise by setting the Median diameter to 2.0 pixels using the Process menu's Filters option. Estimate the image center, excluding the observation conditions display at the bottom of the backscattered electron image, and select a 1.5 μm square area from the image center using the Rectangle Tool on the toolbar. Next, select Threshold from the Adjust option in the Image menu. Select Default, click Auto, and then click Apply to obtain a binarized image. This operation will display the bright areas of the backscattered electron image in white. Again, estimate the image center, excluding the observation conditions display at the bottom of the backscattered electron image, and select a 1.5 μm square area from the image center using the Rectangle Tool on 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 brightness is 0 (corresponding to the bright area of ​​the backscattered electron image). From the above values, the area ratio of the bright area to the total area of ​​the backscattered electron image is calculated. The above procedure is performed for 10 fields of view for each toner particle to be evaluated, the average value is calculated, and the area ratio (%) of the bright area of ​​the image to the total area of ​​the image after binarization processing so that the organosilicon polymer portion in the backscattered electron image becomes the bright area is calculated.

[0084] <Method for identifying organosilicon polymers> The identification method for organosilicon polymers involves a combination of observation using a scanning electron microscope (SEM) and elemental analysis using energy-dispersive X-ray spectroscopy (EDS).

[0085] Using a scanning electron microscope, the "Hitachi Ultra-High Resolution Field Emission Scanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation), toner is observed in a field of view magnified up to 50,000 times. The surface is observed by focusing on the toner particle surface. EDS analysis is performed on particles present on the surface, and the presence or absence of Si element peaks is used to determine whether the analyzed particles are organosilicon polymers. If both organosilicon polymers and silica nanoparticles are present on the toner particle surface, the organosilicon polymer is identified by comparing the ratio of the elemental content (atomic%) of Si and O (Si / O ratio) with that of a standard sample. EDS analysis is performed on both the organosilicon polymer and the silica nanoparticles under the same conditions to obtain the elemental content (atomic%) of Si and O, respectively. The Si / O ratio of the organosilicon polymer is denoted as A, and the Si / O ratio of the silica nanoparticles as B. Measurement conditions are selected in which A is significantly larger than B. Specifically, 10 measurements are performed on the standard under the same conditions, and the arithmetic mean values ​​of A and B are obtained. Select measurement conditions such that the obtained average value A / B > 1.1. If the Si / O ratio of the particles to be identified is on the A side of [(A+B) / 2], then those particles are identified as organosilicon polymers.

[0086] Tospar 120A (Momentive Performance Materials Japan LLC) is used as the standard for organosilicon polymer particles, and HDK V15 (Asahi Kasei) is used as the standard for silica microparticles.

[0087] <Method for measuring the number-average particle size R of primary particles of external additives> The analysis is performed using a combination of a scanning electron microscope, the "Hitachi Ultra-High Resolution Field Emission Scanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation), and elemental analysis using energy-dispersive X-ray spectroscopy (EDS).

[0088] In a field of view magnified up to 50,000 times, the elemental analysis method using EDS described above is used in conjunction with randomly capturing images of external additive particles. From the captured images, 100 external additive particles are randomly selected, and the major axis of the primary particle of the target external additive particle is measured. The arithmetic mean of these measurements is defined as the number-average particle size R. The observation magnification is adjusted as appropriate depending on the size of the external additive particles.

[0089] <Method for identifying the composition and ratio of constituent compounds in organosilicon polymers> NMR is used to identify the composition and ratio of the constituent compounds of the organosilicon polymer contained in the toner. If the toner contains external additives other than organosilicon polymers, such as silica nanoparticles, the following procedure is performed.

[0090] Dissolve 1 g of toner in 31 g of chloroform in a vial and disperse. Prepare the dispersion by treating it with an ultrasonic homogenizer for 30 minutes. Ultrasonic processing equipment: Ultrasonic homogenizer VP-050 (manufactured by Taitec Co., Ltd.) Microchip: Stepped microchip, tip diameter φ2mm Microchip tip position: Center of the glass vial, 5mm above the bottom of the vial. Ultrasound conditions: Intensity 30%, 30 minutes At this time, the dispersion is cooled in the vial with ice water while ultrasonic waves are applied to prevent the dispersion from rising in temperature. The dispersion is then transferred to a 50 mL glass tube for a swing rotor and heated in a centrifuge (H-9R; manufactured by Kokusan Co., Ltd.) to 58.33 S. -1 The mixture is then centrifuged for 30 minutes. After centrifugation, the glass tube contains heavier particles, such as silica nanoparticles, in the lower layer. The chloroform solution containing the organosilicon polymer in the upper layer is collected, and the chloroform is removed by vacuum drying (40°C / 24 hours) to prepare a sample. Using the above sample or the organosilicon polymer, the relative abundance of the constituent compounds of the organosilicon polymer and the R-Si(O) content in the organosilicon polymer are determined. 1 / 2 The proportion of the T3 unit structure represented by )3 is in the solid 29 Measured and calculated using Si-NMR.

[0091] First, the hydrocarbon group represented by R above is 13 confirmed by 13C-NMR.

[0092] ≪ 13 Measurement conditions for 13C-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 13C) 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 By this method, the hydrocarbon group represented by R is confirmed based on the presence or absence of signals due to 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 29Si-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. The structure bonded to Si can be specified by specifying each peak position 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.

[0093] Solid 29 The measurement conditions for 29Si-NMR are specifically as follows. Apparatus: JNM-ECX5002 (JEOL RESONANCE) Temperature: Room temperature Measurement method: DDMAS method 29 Si 45° Sample tube: Zirconia 3.2mmφ Sample: Filled in a test tube in powder form. Sample rotation speed: 10kHz Relaxation delay: 180s Scan: 2000 After the measurement, the peaks of multiple silane components of the sample or organosilicon polymer with different substituents and bonding groups are separated into the following X1, X2, X3, and X4 structures by curve fitting, and the peak area of ​​each is calculated.

[0094] The X3 structure shown below 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] [ka]

[0096] [ka]

[0097] [ka]

[0098] [ka]

[0099] In formulas (A1), (A2), and (A3), Ri, Rj, Rk, Rg, Rh, and Rm represent organic groups such as hydrocarbon groups having 1 to 6 carbon atoms, halogen atoms, hydroxyl groups, acetoxy groups, or alkoxy groups bonded to silicon. If further structural details need to be confirmed, please refer to the above. 13 C-NMR and 29 Along with the Si-NMR measurement results 1 Identification may also be performed based on the results of 1H-NMR measurements.

[0100] <Method for quantifying organosilicon polymers or silica fine particles contained in toner> The toner is dispersed in chloroform as described above, and then centrifugation is used to separate the organosilicon polymer and external additives such as silica microparticles based on the difference in specific gravity, obtaining each sample, and determining the content of the organosilicon polymer or external additives such as silica microparticles.

[0101] The following example illustrates the case where the external additive is silica microparticles. Similar methods can be used for quantitative analysis of other microparticles.

[0102] First, the pressed toner is measured using X-ray fluorescence, and the silicon content in the toner is determined by analytical processing such as the calibration curve method or the fission product method. Next, for each constituent compound that forms the organosilicon polymer and silica nanoparticles, the solid 29 The structure is identified using Si-NMR and pyrolysis GC / MS, and the silicon content in the organosilicon polymer and silica nanoparticles is determined. The silicon content in the toner, determined by X-ray fluorescence, and the solid 29 Based on the relationship between the silicon content in the organosilicon polymer and silica microparticles, determined by Si-NMR and pyrolysis GC / MS, the content of organosilicon polymer and silica microparticles in the toner is calculated.

[0103] <Method for measuring the adhesion rate of external additives such as organosilicon polymers or silica microparticles to toner mother particles or toner particles by water washing method> (Water washing process) Weigh 20g of a 30% by mass aqueous solution of "Contaminon N" (a pH 7 neutral detergent for cleaning precision measuring instruments consisting of a nonionic surfactant, anionic surfactant, and organic builder) into a 50mL vial and mix with 1g of toner. Place the vial in an Iwaki Sangyo Co., Ltd. "KM Shaker" (model: V.SX) and shake for 120 seconds at a speed of 50. Depending on the state of adhesion of the organosilicon polymer or silica microparticles, the external additives such as organosilicon polymer or silica microparticles will migrate from the toner mother particles or the surface of the toner particles to the dispersion. Then, separate the toner from the external additives such as organosilicon polymer or silica microparticles that have migrated to the supernatant using a centrifuge (H-9R; manufactured by Kokusan Co., Ltd.) (5 minutes at 16.67S-1). The settled toner is dried under vacuum (40°C / 24 hours) and then washed with water to obtain the toner.

[0104] Next, using the Hitachi S-4800 ultra-high-resolution field emission scanning electron microscope (Hitachi High-Technologies Corporation), images are taken of the toner without the above-mentioned water washing process (pre-wash toner) and the toner obtained after the above-mentioned water washing process (post-wash toner).

[0105] Furthermore, the identification of the object to be measured is performed by elemental analysis using energy-dispersive X-ray spectroscopy (EDS).

[0106] Then, the captured toner surface image is analyzed using the image analysis software Image-Pro Plus ver.5.0 (Nippon Roper Co., Ltd.) to calculate the coverage rate.

[0107] The image capture conditions for the S-4800 are as follows:

[0108] (1) Sample preparation A thin layer of conductive paste is applied to the sample stage (aluminum sample stage, 15mm x 6mm), and toner is sprayed onto it. Excess toner is then removed from the sample stage by air blowing, and it is allowed to dry completely. The sample stage is then placed in the sample holder, and the sample stage height is adjusted to 36mm using the sample height gauge.

[0109] (2) Setting of S-4800 observation conditions Before measuring the coverage, perform elemental analysis using the energy-dispersive X-ray spectroscopy (EDS) method described above to distinguish between organosilicon polymers or external additives such as silica microparticles on the toner surface before measurement. Fill the anti-contamination trap attached to the S-4800 housing with liquid nitrogen until it overflows and leave it for 30 minutes. Start the "PC-SEM" of the S-4800 and perform flushing (cleaning of the FE tip, which is the electron source). Click on the acceleration voltage display section of the control panel on the screen, press the [Flushing] button, and open the flushing execution dialog. Confirm that the flushing intensity is 2 and execute. Confirm that the emission current due to flushing 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.

[0110] Click the acceleration voltage display to open the HV settings dialog, and set the acceleration voltage to [1.1kV] and the emission current to [20μA]. In the [Basic] tab of the operation panel, set the signal selection to [SE], select [U] and [+BSE] for the SE detector, and select [LA100] in the selection box to the right of [+BSE] to enter the mode for observing backscattered electron images. Also in the [Basic] tab of the operation panel, set the probe current to [Normal], the focus mode to [UHR], and the WD to [4.5mm] in the electron optical system conditions block. Press the [ON] button on the acceleration voltage display of the control panel to apply the acceleration voltage.

[0111] (3) Calculation of the average particle size (D1) of toner Drag within the magnification display area of ​​the control panel to set the magnification to 5000 (5k)x. Rotate the focus knob [COARSE] on the control panel until the image is somewhat in focus, then adjust the aperture alignment. Click [Align] on the control panel to display the alignment dialog and select [Beam]. Rotate the STIGMA / ALIGNMENT knob (X,Y) on the control panel to move the displayed beam to the center of the concentric circle. Next, select [Aperture] and rotate the STIGMA / ALIGNMENT knob (X,Y) one by one to stop or minimize the movement of the image. Close the aperture dialog and focus using autofocus. Repeat this process two more times to achieve focus.

[0112] Next, the particle size of 300 toner particles is measured to determine the number-average particle size (D1). The particle size of each individual particle is defined as the maximum diameter observed when observing the toner particles.

[0113] (4) Focus adjustment For the particles with a number-average particle size (D1) of ±0.1 μm obtained in (3), with the midpoint of the maximum diameter aligned to the center of the measurement screen, drag within the magnification display area of ​​the control panel to set the magnification to 10000 (10k) times.

[0114] Rotate the focus knob [COARSE] on the control panel until the image is somewhat in focus, then adjust the aperture alignment. Click [Align] on the control panel to display the alignment dialog and select [Beam]. Rotate the STIGMA / ALIGNMENT knob (X,Y) on the control panel to move the displayed beam to the center of the concentric circle. Next, select [Aperture] and rotate the STIGMA / ALIGNMENT knob (X,Y) one by one to stop or minimize the movement of the image. Close the aperture dialog and focus using autofocus. Then, set the magnification to 50,000 (50k)x and adjust the focus using the focus knob and STIGMA / ALIGNMENT knob as described above, and focus again using autofocus. Repeat this process to focus. Here, since a large tilt angle of the observation surface tends to lower the accuracy of the coverage measurement, when adjusting the focus, we select a surface that is in focus across the entire observation surface simultaneously, thereby selecting and analyzing a surface with as little tilt as possible.

[0115] (5) Save the image Brightness adjustment is performed using ABC mode, and a photograph is taken and saved at a size of 640 x 480 pixels. The following analysis is performed using this image file. One photograph is taken for each toner, and an image is obtained of the toner particle.

[0116] (6) Image analysis The coverage rate is calculated by binarizing the images obtained using the method described above, using the analysis software described below. At this time, the above screen is divided into 12 squares and each is analyzed. The analysis conditions for the image analysis software Image-Pro Plus ver.5.0 are as follows. However, if an external additive such as organosilicon polymers with particle sizes less than 30 nm and greater than 300 nm, or silica nanoparticles with particle sizes less than 30 nm and greater than 1200 nm is included in the divided section, the coverage rate will not be calculated for that section.

[0117] In the image analysis software Image-Pro Plus 5.0, select "Measurement" from the toolbar, then "Count / Size," and then "Options" to set the binarization conditions. In the object extraction options, select 8-connected and set smoothing to 0. For other options, do not select pre-selection, fill holes, or outlines, and set "Exclude boundary lines" to "None." Select "Measurement Items" from the toolbar and set the area selection range to 2-10 7 Enter the following:

[0118] The coverage rate is calculated by drawing a square area. The area of ​​this area (C) should be between 24,000 and 26,000 pixels. The image is automatically binarized using "Processing" - Binarization, and the sum of the areas (D) of regions without external additives such as organosilicon polymers or silica microparticles is calculated. The coverage rate can be calculated using the following formula from the area C of the square area and the sum D of the areas without external additives such as organosilicon polymers or silica microparticles.

[0119] Coverage rate (%)=100-(D / C×100) The coverage rate is defined as the arithmetic mean of all the data obtained.

[0120] Then, calculate the coverage rate of the toner before and after washing. The "adhesion rate" of this invention is calculated as [toner coverage rate after washing] / [toner coverage rate before washing] × 100.

[0121] 4. Method for manufacturing toner particles, external additives, and developer Next, we will describe manufacturing examples of the toner particles, external additive A, and developer used in this embodiment.

[0122] <Example of toner particle manufacturing> (Preparation of aqueous medium 1) In a reaction vessel equipped with a stirrer, thermometer, and reflux tubing, 650.0 parts of deionized water and 14.0 parts of sodium phosphate (manufactured by Rasa Industries, Ltd., dodecahydrate) were added, and the mixture was kept warm at 65°C for 1.0 hour while purging with nitrogen. Using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), a calcium chloride aqueous solution, prepared by dissolving 9.2 parts of calcium chloride (dihydrate) in 10.0 parts of deionized water, was added all at once while stirring at 15,000 rpm to prepare an aqueous medium containing a dispersion stabilizer. Furthermore, 10% by mass hydrochloric acid was added to the aqueous medium to adjust the pH to 5.0, obtaining aqueous medium 1.

[0123] (Preparation of polymerizable monomer composition) • Styrene: 60.0 parts CI Pigment Blue 15:3 : 6.5 parts The aforementioned materials were placed in an attritor (manufactured by Mitsui Miike Chemical Machinery Co., Ltd.), and then dispersed using 1.7 mm diameter zirconia particles at 220 rpm for 5.0 hours. After that, 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 parts • Saturated polyester resin: 5.0 parts (Polycondensate of propylene oxide-modified bisphenol A (2 molar adduct) and terephthalic acid (molar ratio 10:12), glass transition temperature (Tg) of 68°C, weight-average molecular weight (Mw) of 10000, molecular weight distribution (Mw / Mn) of 5.12) • Fischer-Tropsch wax (melting point 78°C): 7.0 parts The material was added to the above-mentioned colorant dispersion, heated to 65°C, and then uniformly dissolved and dispersed at 500 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a polymerizable monomer composition.

[0124] (granulation process) The temperature of aqueous medium 1 was adjusted to 70°C, and while maintaining the rotation speed of the TK homomixer at 15,000 rpm, the polymerizable monomer composition was added to aqueous medium 1, and 10.0 parts of t-butyl peroxypivalate, a polymerization initiator, were added. Granulation was then carried out for 10 minutes while maintaining a stirring speed of 15,000 rpm with the stirring device.

[0125] (Polymerization process and distillation process) After the granulation process, the stirrer was replaced with a propeller-type stirring blade, and polymerization was carried out for 5.0 hours while stirring at 150 rpm and maintaining a temperature of 70°C. Further polymerization was carried out by raising the temperature to 85°C and maintaining the temperature for another 2.0 hours. Subsequently, the reflux tube of the reaction vessel was replaced with a condenser, and the obtained slurry was heated to 100°C for 6 hours to distillate and remove unreacted polymerizable monomers, obtaining a resin particle dispersion.

[0126] (Process for forming organosilicon polymers) 60.0 parts of deionized water were weighed into a reaction vessel equipped with a stirrer and thermometer, and the pH was adjusted to 4.0 using 10% by mass hydrochloric acid. This was heated while stirring to a temperature of 40°C. Then, 40.0 parts of methyltriethoxysilane, an organosilicon compound, were added, and hydrolysis was carried out by stirring for more than 2 hours. The end of the hydrolysis was confirmed by visual inspection when the oil and water did not separate into a single layer, and the mixture was cooled to obtain a hydrolyzed solution of the organosilicon compound.

[0127] 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 (10.0 parts of the organosilicon compound) were added to initiate polymerization of the organosilicon compound. After holding for 0.25 hours, the pH was adjusted to 5.5 with a 3.0% sodium bicarbonate aqueous solution. After holding for 1.0 hour with continued stirring at 55°C (condensation reaction 1), the pH was adjusted to 9.5 using a 3.0% sodium bicarbonate aqueous solution, and then held for a further 4.0 hours (condensation reaction 2) to obtain a toner particle dispersion.

[0128] (Washing and drying processes) After the organosilicon polymer formation process was completed, the toner particle dispersion was cooled, hydrochloric acid was added to adjust the pH to 1.5 or less, and the mixture was left to stand for 1.0 hour while stirring. Then, solid-liquid separation was performed using a pressure filter to obtain a toner cake. The obtained toner cake was re-slurred with deionized water to form a dispersion again, and then solid-liquid separation was performed using the aforementioned filter to obtain another toner cake. The obtained toner cake was transferred to a 40°C constant temperature bath and dried and classified for 72 hours to obtain toner particles.

[0129] <Manufacturing example of external additive A> External additive A was prepared as follows: 150 parts of 5% aqueous ammonia were placed in a 1.5 L glass reaction vessel equipped with a stirrer, dropping nozzle, and 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 added dropwise while stirring, and the mixture was reacted for 8 hours to obtain a silica microparticle dispersion. Subsequently, the obtained silica microparticle dispersion was dried by spray drying and crushed with a pin mill to obtain silica microparticles with a primary particle number average size of 100 nm as external additive A.

[0130] <Examples of developer manufacturing> 100.00 parts toner particles and 1.00 part external additive A were added to a Henschel mixer (FM10C model, manufactured by Nippon Coke Industries Co., Ltd.) with 7°C water flowing through the jacket. Next, after the water temperature in the jacket stabilized at 7°C ± 1°C, the mixture was mixed for 10 minutes at a rotational speed of 38 m / sec. During this mixing, the amount of water flowing through the jacket was appropriately adjusted so that the temperature inside the Henschel mixer tank did not exceed 25°C. The resulting mixture was sieved through a 75 μm mesh to obtain the developer.

[0131] The physical properties of the developer are shown in Table 1.

[0132] [Table 1]

[0133] In the table, "X" represents the ratio of the number-average particle size R of the primary particles of external additive A to the number-average value of the convex height H. When the manufactured developer was observed using SEM, it was confirmed that external additive A was positioned as a transfer-promoting particle on the convex portion of the organosilicon polymer of the toner particles, and the average number of external additive A coatings per toner particle was approximately 500.

[0134] 5. Configuration of the intermediate transfer belt Figure 8 is a schematic diagram showing a cross-section of the intermediate transfer belt 10 in this embodiment, viewed from the axial direction of the primary transfer roller 14. The intermediate transfer belt 10 has a circumference of 700 mm and a thickness of 92 μm, and is formed by a base layer 10a (first layer), an inner layer 10b (second layer), and a surface layer 10c (third layer). The base layer 10a uses endless polyvinylidene fluoride (PVdF) mixed with an ionic conductive agent such as a polyvalent metal salt or a quaternary ammonium salt as the conductive agent. The inner layer 10b uses acrylic resin mixed with carbon as the conductive agent. The surface layer 10c uses acrylic resin mixed with a metal oxide or the like as the conductive agent.

[0135] Here, the base layer 10a is defined as the thickest layer among the layers constituting the intermediate transfer belt 10, with respect to the thickness direction of the intermediate transfer belt 10. In this embodiment, the inner layer 10b is a layer formed on the inner circumferential surface side of the intermediate transfer belt 10. With respect to the thickness direction, which is the direction intersecting the movement direction of the intermediate transfer belt 10, the base layer 10a is formed closer to each photosensitive drum 1a to 1d than the inner layer 10b, and the surface layer 10c is formed closer to each photosensitive drum 1a to 1d than the base layer 10a. In this embodiment, the inner layer 10b of the intermediate transfer belt 10 was formed by spray coating the base layer 10a. If the thickness of the base layer 10a is defined as t1, the thickness of the inner layer 10b as t2, and the thickness of the surface layer 10c as t3, then t1 = 87 μm, t2 = 3 μm, and t3 = 2 μm.

[0136] In this embodiment, polyvinylidene fluoride (PVdF) was used as the material for the base layer 10a, but it is not limited to this, and other materials such as polyimide, polycarbonate, polyarylate, polyester, acrylonitrile-butadiene-styrene copolymer (ABS), and mixed resins thereof may also be used. In this embodiment, acrylic resin was used as the material for the inner layer 10b, but other materials may also be used, such as polyester.

[0137] Furthermore, the conductive agent added to the base layer 10a can be carbon as an electronic conductive agent, or polymer-type and low-molecular-weight conductive agents as ionic conductive agents. For example, polymer-type conductive agents can include polyether ester amides, polyethylene oxide-epichlorohydrin, and polyether esters as nonionic types, quaternary ammonium group-containing acrylate polymers as cationic types, and polystyrene sulfonic acid as anionic types. In addition, low-molecular-weight conductive agents can include derivatives containing ether groups and derivatives containing ether esters as nonionic types. Cationic types can include primary to tertiary ammonium salts and quaternary ammonium salts and their derivatives, and anionic types can include carboxylates, sulfate esters, sulfonates, phosphate esters and their derivatives. These polymer-type or low-molecular-weight ionic conductive agents can be used alone or in combination of two or more, and among them, quaternary ammonium salts, sulfonates, and polyether ester amides are preferably used from the viewpoint of heat resistance and conductivity.

[0138] Furthermore, in this embodiment, an intermediate transfer belt 10 is used in which the electrical resistances of the base layer 10a, the inner layer 10b, and the surface layer 10c are different, with the electrical resistance of the inner layer 10b set lower than that of the base layer 10a and the surface layer 10c.

[0139] Here, with respect to the intermediate transfer belt 10, the surface resistivity measured from the outer circumferential surface side (surface layer 10c side) is defined as the combined electrical resistance of the surface layer 10c and the base layer 10a, and the surface resistivity measured from the inner circumferential surface side (inner layer 10b side) is defined as the electrical resistance of the inner layer 10b. That is, in this embodiment, the intermediate transfer belt 10 has different surface resistivity values ​​when measured from the outer circumferential surface side and when measured from the inner circumferential surface side, with the surface resistivity measured from the inner circumferential surface side being smaller than the surface resistivity measured from the outer circumferential surface side. In a standard environment (temperature 23°C, humidity 50%), the surface resistivity measured from the outer circumferential surface side of the intermediate transfer belt 10 is 2.6 × 10⁻⁶. 11 The ratio is Ω / □, and the surface resistivity measured from the inner circumferential surface of the intermediate transfer belt 10 is 1.0 × 10⁻⁶. 6 It was Ω / □.

[0140] Furthermore, the surface resistivity measured from the outer surface side without the formation of the surface layer 10c was 2.0 × 10⁻⁶. 10 It was Ω / □.

[0141] The surface resistivity of the intermediate transfer belt 10 was measured using Mitsubishi Chemical Corporation's Hiresta-UP (MCP-HT450) under measurement conditions of 23°C and 50% humidity. Surface resistivity was measured using a ring probe type UR100 (model MCP-HTP16) with an applied voltage of 10[V] and a measurement time of 10 seconds. The surface resistivity of the inner circumferential surface of the intermediate transfer belt 10 was measured by applying the probe to the inner layer 10b side, and the surface resistivity of the outer circumferential surface of the intermediate transfer belt 10 was measured by applying the probe to the surface layer 10c side.

[0142] In this embodiment, the inner layer 10b formed on the inner surface of the intermediate transfer belt 10 has a sufficiently low electrical resistance compared to the base layer 10a and the surface layer 10c. Therefore, the primary transfer potential supplied by the primary transfer roller 14, which is positioned offset downstream from the contact position (transfer portion, transfer nip portion) between each photosensitive drum 1 and the intermediate transfer belt 10, is formed on the inner circumferential surface of the intermediate transfer belt 10 as follows: It is formed across the entire inner surface of the intermediate transfer belt 10 by traveling through the inner layer 10b formed on the inner circumferential surface of the intermediate transfer belt 10. In other words, an electric potential surface is formed on the inner surface of the intermediate transfer belt 10, and an almost equipotential surface is formed on the inner surface between the tensioning member 13 and the primary transfer roller 14d in the direction of movement of the surface of the intermediate transfer belt 10.

[0143] 6. Supply of transcription-promoting particles Next, the means for supplying transfer-promoting particles onto the photosensitive drum 1, which is a characteristic of this embodiment, will be described. As mentioned above, transfer-promoting particles are particles that, by being interposed 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, thereby improving the primary transfer efficiency of the toner image.

[0144] In this embodiment, transfer-promoting particles are supplied to the surface of the photosensitive drum 1 in advance using toner carried on the developing roller 41 before the toner image is developed. By pre-coating the photosensitive drum 1 with transfer-promoting particles, transfer-promoting particles are interposed between the toner image and the photosensitive drum 1.

[0145] Figure 9(a) is a schematic diagram of the developing nip section when the developing roller 41 and the photosensitive drum 1 are in contact. As shown in Figure 9(a), in the developing nip section, the toner supported on the developing roller 41 and the photosensitive drum 1 are in contact via transfer-promoting particles. Figure 9(b) is a schematic diagram showing the state after the toner supported on the developing roller 41 and the photosensitive drum 1 shown in Figure 9(a) have passed through the developing nip section. As shown in Figure 9(b), the transfer-promoting particles that were interposed between the toner and the photosensitive drum 1 in the developing nip section are supplied by transferring from the surface of the toner supported on the developing roller 41 to the surface of the photosensitive drum 1 after passing through the developing nip section.

[0146] As shown in Figure 9(a), if the adhesion force Ft between the transfer-promoting particles interposed between the toner and the photosensitive drum 1 in the developing nip section is greater than the adhesion force Fdr between the transfer-promoting particles and the photosensitive drum 1, the transfer-promoting particles are less likely to transfer onto the photosensitive drum 1. Therefore, it is preferable that Ft be smaller than Fdr.

[0147] Figure 10(a) is a schematic diagram of the primary transfer section when the toner image is supported on the surface of the photosensitive drum 1. Figure 10(b) is a schematic diagram of the state after the primary transfer of the toner image shown in Figure 10(a) has been completed and the photosensitive drum 1 and the intermediate transfer belt 10 have been separated.

[0148] From the perspective that transfer-promoting particles, once transferred onto the photosensitive drum 1, are less likely to transfer onto the intermediate transfer belt 10, it is desirable that the relationship between the adhesion force Fi between the transfer-promoting particles and the surface of the intermediate transfer belt 10 and the adhesion force Fdr between the transfer-promoting particles and the photosensitive drum 1 be Fdr1 > Fi. Here, as conditions for adhesion force, we consider the case where the pressing force used to press the photosensitive drum 1 against the intermediate transfer belt 10 is F1, and the total number of transfer-promoting particles interposed between the photosensitive drum 1 and the intermediate transfer belt 10 in the transfer section is N1. Let Fi be the adhesion force formed between the transfer-promoting particles and the intermediate transfer belt 10, measured when the transfer-promoting particles are pressed against the intermediate transfer belt 10 with a pressing force of F1 / N1 per unit transfer-promoting particle. Let Fdr1 be the adhesion force formed between the transfer-promoting particles and the photosensitive drum 1, measured when the transfer-promoting particles are pressed against the photosensitive drum 1 with a pressing force of F1 / N1.

[0149] In this example, the relationship Fdr1 > Fi holds, and the transfer-promoting particles that migrate onto the photosensitive drum 1 in the primary transfer section tend to remain on the photosensitive drum 1.

[0150] Suppose that the transfer promoting particles intervening between the toner image and the photosensitive drum 1 are primarily transferred to the intermediate transfer belt 10 together with the toner image, and the transfer promoting particles are lost from the surface of the photosensitive drum 1. For example, the case where Fdr1≦Fi can be cited. In that case, since there are no transfer promoting particles intervening between the toner image developed next on the surface of the photosensitive drum 1 and the photosensitive drum 1, and the adhesion force between the toner image and the photosensitive drum 1 increases, it is assumed that the primary transfer property will deteriorate. However, if the relationship Ft<Fdr is maintained, even if the transfer promoting particles are lost from the surface of the photosensitive drum 1 by primary transfer, it becomes possible to supply them immediately from the developing roller 41 to the surface of the photosensitive drum 1. Therefore, not only is it easier to supply the transfer promoting particles from the toner carried on the developing roller 41 to the photosensitive drum 1, but also from the viewpoint of maintaining the transfer promoting particles coated on the photosensitive drum 1, it is preferable that Ft is smaller than Fdr.

[0151] From the above, due to this adhesion relationship of Ft<Fdr, the surface of the photosensitive drum 1 is covered with the transfer promoting particles, so that the adhesion force of the toner to the photosensitive drum 1 decreases and the transfer efficiency improves.

[0152] <Supply of Transfer Promoting Particles from Developing Roller 41> In this embodiment, a peripheral speed difference is provided between the developing roller 41 and the photosensitive drum 1. Specifically, as described above, the developing roller 41 is driven at a peripheral speed of 140% of the peripheral speed of the photosensitive drum 1. By providing a peripheral speed difference between the developing roller 41 and the photosensitive drum 1, the toner rolls in the developing nip portion. When the toner rolls in the developing nip portion, the opportunity for the transfer promoting particles on the toner particles that did not contact the photosensitive drum 1 upstream of the developing nip portion to contact the photosensitive drum 1 also increases as the toner rotates, and they can move from the toner to the photosensitive drum 1. As a result, the opportunity for supplying the transfer promoting particles from the toner to the photosensitive drum 1 increases, and it becomes possible to sufficiently cover the surface of the photosensitive drum 1 with the transfer promoting particles.

[0153] Furthermore, in this embodiment, at the timing of supplying transfer-promoting particles, the surface potential of the photosensitive drum 1 is set to a non-image-forming potential Vd = -500V, which prevents toner charged with the normal polarity from developing. Therefore, at the timing of supplying transfer-promoting particles in this embodiment, toner with a normal polarity of negative polarity does not develop on the surface of the photosensitive drum 1 from the developing roller 41, and only the transfer-promoting particles are supplied from the developing roller 41 onto the photosensitive drum 1.

[0154] As in this embodiment, when transfer-promoting particles are supplied from the toner on the developing roller 41 to the photosensitive drum 1 while there is a potential difference between the developing roller 41 and the photosensitive drum 1, the following problems arise. If the particle size of the transfer-promoting particles is too large, the transfer-promoting particles are easily 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 transfer-promoting particles from the toner on the developing roller 41 to the photosensitive drum 1. For example, in a configuration where transfer-promoting particles are supplied at a non-image-forming potential, as in this embodiment, if the transfer-promoting particles are negatively charged, they are attracted to the developing roller 41 by electrostatic force. Therefore, it becomes difficult to supply the transfer-promoting particles from the toner on the developing roller 41 to the photosensitive drum 1. Here, it is preferable to keep the particle size of the transfer-promoting particles to 1000 nm or less, so as to be less affected by electrostatic force. In this embodiment, in order to stably supply transfer-promoting 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 transfer-promoting particles.

[0155] 7. Effects of transcription-promoting particles This section describes an effectiveness verification experiment conducted to confirm the effectiveness of the means for supplying transfer-promoting particles to the photosensitive drum 1 in this embodiment. To verify the effect of the transfer-promoting particles, the amount of remaining toner after transfer, the coverage rate of the transfer-promoting particles on the photosensitive drum 1, and the adhesion force between the toner and the photosensitive drum 1 to the transfer-promoting particles were measured. The methods for each measurement will be described below.

[0156] i) Measurement of the amount of toner remaining after transfer First, an image forming apparatus 100 equipped with a new photosensitive drum 1 that is not coated with transfer-promoting particles is used to form a patch image with a yellow density of 100%. 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 residue toner density of the patch image remaining on the surface of the photosensitive drum 1a of the yellow station is checked in relation to the primary transfer bias.

[0157] The transfer residue toner concentration was measured using the following method. First, a transparent tape (polyester tape 5511 Nichiban) was applied to the transfer residue toner area of ​​the yellow patch image on the surface of the photosensitive drum 1a, and the transfer residue toner was collected on the transparent tape. Then, the transparent tape that collected the transfer residue toner, which had been peeled off from the surface of the photosensitive drum 1a, and a new transparent tape were each applied to high-whiteness paper (GFC081 Canon). The concentration D1 of the transparent tape where the transfer residue toner was collected and the concentration D0 of the new transparent tape were then measured using a reflectance densitometer (reflectometer model TC-6DS manufactured by Tokyo Denshoku Co., Ltd.). The difference obtained from the measurement, "D1-D0", was defined as the transfer residue toner concentration. A smaller value for the transfer residue toner concentration means that there is less transfer residue toner, and if the value is 1.0 or less, it can be determined that there is almost no transfer residue toner, and no image defects caused by transfer residue toner adhering to the charging roller 2a will occur.

[0158] ii) Measurement of the coverage rate of the transcription-promoting particles Microscopic observation of the surface of the photosensitive drum 1a, where the residual toner concentration was measured, was performed, and the coverage rate of transfer-promoting particles on the surface of the photosensitive drum 1a was calculated. Specifically, the coverage rate was calculated using the following procedure for observation images of the surface of the photosensitive drum 1a at a magnification of 3000x using a laser microscope (VK-X200 Keyence). Binarization was performed to separate the areas with transfer-promoting particles from the areas without, and the total area ratio of transfer-promoting particles on the surface of the photosensitive drum 1 was calculated as the coverage rate of transfer-promoting particles on the surface of the photosensitive drum 1.

[0159] iii) Measurement of adhesion force The adhesion force between the transfer-promoting particles and the toner used in this embodiment was measured using SPM. Specifically, a cantilever was created by fixing the transfer-promoting particles to the tip of a lever, and the cantilever was pressed against the toner with a predetermined pressing force. Subsequently, the force required to detach the cantilever from the toner was measured as the adhesion force Ft between the transfer-promoting particles and the toner.

[0160] The predetermined pressing force applied to the cantilever when measuring adhesion force is preferably set to the force applied to the toner by the transfer-promoting particles interposed between the toner and the photosensitive drum 1 in the developing nip section. The pressing force was calculated using the calculation method described below. Here, "transfer-promoting particles interposed between the toner and the photosensitive drum 1 in the developing nip section" means a state in which the transfer-promoting particles are in contact with both the toner and the photosensitive drum 1 simultaneously.

[0161] First, the assumed conditions for the calculations will be explained using Figures 11 and 12. Figure 11(a) is a schematic diagram of the developing nip section, where it is assumed that the developing roller 41 and the photosensitive drum 1 are in contact via toner. Figure 11(b) shows a cross-section parallel to the surface of the photosensitive drum 1 along the dotted line AB in Figure 11(a), where it is assumed that the toner in contact with the photosensitive drum 1 is packed in the closest possible density as shown in the shaded area. Figure 12 is a schematic diagram of an enlarged view of the contact area between the toner and the photosensitive drum 1 enclosed by the dotted line in Figure 11. As shown in Figure 12, it is assumed that the toner and the photosensitive drum 1 are in contact via transfer-promoting particles. Furthermore, it is assumed that no transfer-promoting particles have been supplied to the surface of the photosensitive drum 1 yet, and that no transfer-promoting particles are present on the surface of the photosensitive drum 1 beforehand.

[0162] Based on the above assumptions, the total number of transfer-promoting particles N interposed between the toner and the photosensitive drum 1 in the developing nip section was calculated as follows. From the calculated N and the contact force F between the developing roller 41 and the photosensitive drum 1, the pressing force F / N, which is the pressing force on the toner per transfer-promoting particle in the developing section, was calculated, and the calculated F / N was adopted as the predetermined pressing force of the cantilever on the toner when measuring the adhesion force.

[0163] First, we will explain how to calculate the total number N of transfer-promoting particles interposed between the toner and the photosensitive drum 1 in the developing nip section.

[0164] Figure 13(a) is a schematic diagram showing the contact state of toner, transfer-promoting particles, and photosensitive drum 1 in two dimensions in the developing unit. As shown in Figure 13(b), if the particle size of the transfer-promoting particles is r, then when the distance between the photosensitive drum 1 and the toner surface exceeds r, the transfer-promoting particles on the toner almost cease to contact the photosensitive drum 1. Therefore, the portion of the toner circumference in which the transfer-promoting particles arranged on the circumference of the toner can contact the photosensitive drum 1 is the arc connecting A and B. In reality, it is necessary to consider the toner as a sphere, as in Figure 13(b), and it is necessary to determine the ratio of the surface area obtained by integrating the arc AB in the circumferential direction (shaded area in Figure 13(b)) to the toner surface area. The surface area of ​​the shaded area can generally be calculated as the surface area of ​​the spherical cap, as shown in equation (2). Therefore, the ratio to the toner surface area is given by equation (3). The actual value can be calculated from the average particle size R of the toner and the particle size r of the transfer-promoting particles.

[0165]

number

[0166] Based on the above calculations, the ratio of arc AB to the toner circumference in the configuration of this embodiment is calculated to be approximately 1.43%.

[0167] Therefore, it can be considered that the area where transfer-promoting particles are interposed between the toner and the photosensitive drum 1 in the developing nip area is approximately 1.43% of the total surface area of ​​the toner. Since there are 500 transfer-promoting particles covering each toner, the number of transfer-promoting particles M interposed between the toner and the photosensitive drum 1 per toner is calculated as "500 particles × 1.43%", which is approximately 7.2 particles.

[0168] Then, the number of transfer-promoting particles interposed between the toner and the photosensitive drum 1 per toner cartridge (7.2 particles) is multiplied by the total number of toners in contact with the photosensitive drum 1 in the developing unit. This allows us to calculate the total number N of transfer-promoting particles interposed between the toner and the photosensitive drum 1 in the developing nip unit.

[0169] The total amount of toner L in contact with the photosensitive drum 1 at the developing nip can be calculated as (area of ​​the developing nip × toner filling rate) / maximum cross-sectional area of ​​the toner.

[0170] (Total number of toners in contact with photosensitive drum 1 at the developing nip section) =(220[mm]×2.0[mm]×π / √12) / (π×(7.0 / 2) 2 ) = approx. 10.37×10 6 pieces (We used the close-packing ratio of a two-dimensional circle, π / √12 ≈ 0.9069.) Therefore, the "total number N of transfer-promoting particles interposed between the toner and the photosensitive drum 1 in the developing nip" is calculated as follows: It is calculated by multiplying the "total number of toners in contact with the photosensitive drum 1 in the developing nip" by the "number of transfer-promoting particles interposed between the toner and the photosensitive drum 1 per toner," and the total number N is approximately 7.47 × 10⁻⁶. 7 To become an individual.

[0171] In this embodiment, the pressing force of the developing roller 41 against the photosensitive drum 1 is F = 1.96 N, so the F / N ratio, which is the "pressing force on the toner per transfer-promoting particle in the developing section," is calculated to be 26.3 nN. The F / N value obtained above was adopted as the predetermined pressing force used to press the cantilever against the toner during adhesion force measurement using SPM. In addition, a similar adhesion force measurement was performed on the photosensitive drum 1, and the adhesion force Fdr between the transfer-promoting particles fixed to the tip of the cantilever and the photosensitive drum 1 was measured.

[0172] <Results of effectiveness verification> Next, we will describe the measurement results for the amount of remaining toner after transfer, the coverage rate of the transfer-promoting particles on the photosensitive drum, and the adhesion force between the toner and the photosensitive drum 1 to the transfer-promoting particles when the transfer-promoting particles are supplied. The measurements were performed on the toner of this embodiment and the toner of Comparative Example 1, which will be described later. The toner of Comparative Example 1 employs a developer configuration in which the adhesion force between the transfer-promoting particles and the photosensitive drum 1 is greater than the adhesion force between the transfer-promoting particles and the toner. Specifically, the toner surface is not covered with an organic silica polymer or the like, as in the configuration of this embodiment, and the developer is one in which the transfer-promoting particles are directly added to the toner surface.

[0173] i) Measurement results of residual toner from primary transfer Figure 14 shows the results of the experiment to confirm the amount of toner remaining after primary transfer. In both this example and Comparative Example 1, the transfer efficiency tends to improve as the primary transfer voltage increases. In the configuration of this example, under the condition of a primary transfer voltage of 250V, the concentration of toner remaining after transfer was 0.7%, indicating that there was almost no toner remaining after transfer, confirming high transferability. On the other hand, when using the developer of Comparative Example 1, the residual toner concentration was 4.1% under the condition of a primary transfer voltage of 250V. The more residual toner there is, the more image defects occur due to charging failures caused by contamination of the charging roller 2. With the developer of Comparative Example 1, the improvement in primary transfer efficiency was limited even when a higher primary transfer voltage was applied.

[0174] ii) Measurement results of coverage Figure 15 shows the results of measuring the coverage rate of transfer-promoting particles on the surface of the photosensitive drum 1. In this example, the coverage rate of transfer-promoting particles on the surface of the photosensitive drum 1 was 61.7%, confirming that the photosensitive drum 1 was sufficiently coated with transfer-promoting particles. On the other hand, in Comparative Example 1, the coverage rate of transfer-promoting particles was 5.0%.

[0175] iii) Measurement results of adhesion strength Figure 16 shows the results of measuring the adhesion force between the transfer-promoting particles and the toner, and between the transfer-promoting particles and the surface of the photosensitive drum 1. As shown in Figure 16, the adhesion force between the transfer-promoting particles and the toner in this embodiment was 32.8 (nN), and the adhesion force between the transfer-promoting particles and the photosensitive drum 1 was 210.1 (nN). In other words, it was confirmed that the adhesion force between the transfer-promoting particles and the toner in this embodiment was smaller than the adhesion force between the transfer-promoting particles and the photosensitive drum 1.

[0176] On the other hand, the adhesion force between the transfer-promoting particles and the toner in Comparative Example 1 was 304.6 (nN), and the adhesion force between the transfer-promoting particles and the photosensitive drum 1 was 210.1 (nN). In other words, it was confirmed that the adhesion force between the transfer-promoting particles and the toner in Comparative Example 1 was greater than the adhesion force between the transfer-promoting particles and the photosensitive drum 1.

[0177] 8. Effects of the inner layer Next, we will explain another feature of this embodiment: the reduction of retransfer toner amount by the intermediate transfer belt 10. In this embodiment, the amount of retransfer toner is reduced by forming an inner layer 10b on the intermediate transfer belt 10.

[0178] The effect of suppressing retransfer in the primary transfer section will be explained. The relationship between the primary transfer voltage applied to the intermediate transfer belt 10 and retransfer was compared and verified using the intermediate transfer belt 10 of this embodiment and an intermediate transfer belt as Comparative Example 2, which does not have an inner layer 10b. Figure 17 shows the relationship between the applied voltage of the primary transfer power supply and the amount of retransfer toner.

[0179] The measurement of retransfer toner is described below. An image forming apparatus 100 is used to form a patch image with a yellow density of 100%. Immediately after the yellow patch image, which was primary transferred onto the intermediate transfer belt 10, passes through the magenta image forming station b, the image forming apparatus 100 is stopped. At that time, the density of the yellow retransfer toner that was reverse-transferred onto the surface of the photosensitive drum 1b of the magenta image forming station b, which was not performing image formation for the primary transfer voltage, was checked. Here, the vertical axis in Figure 17 is a parameter that shows the amount of retransfer toner that moved from the intermediate transfer belt 10 to the photosensitive drum 1 due to retransfer.

[0180] The retransfer toner remaining on the photosensitive drum 1 was collected on a transparent tape (polyester tape 5511 Nichiban) by applying it to the surface of the photosensitive drum 1. Then, the transparent tape that had collected the retransfer toner, peeled off from the surface of the photosensitive drum 1, and a new piece of transparent tape were each attached to high-whiteness paper (GFC081 Canon). The density D1 of the transparent tape in the toner collection area and the density D0 of the new transparent tape area were then measured using a reflectance densitometer (reflectometer model TC-6DS manufactured by Tokyo Denshoku Co., Ltd.). The difference "D1-D0" obtained from the measurement was defined as the density of the toner retransferred onto the photosensitive drum 1.

[0181] As can be seen from Figure 17, in the intermediate transfer belt of Comparative Example 2, which lacks the inner layer 10b, increasing the applied voltage increases the amount of toner re-transferred. In the intermediate transfer belt 10 of this embodiment, even when the same voltage value is applied as in the intermediate transfer belt of Comparative Example 2, the amount of toner re-transferred tends to be less.

[0182] The reason for this is explained below. Regarding retransfer, it is thought to be caused by a discharge phenomenon occurring in the primary transfer section (transfer nip section) where the intermediate transfer belt 10 and the photosensitive drum 1 of the primary transfer section come into contact, which reduces the charge of the toner or reverses its polarity.

[0183] Regarding electrical discharge, Paschen's law is generally known. Let d be the distance (gap length) between the surface of the photosensitive drum 1 and the intermediate transfer belt 10. Then, let V be the potential difference between the photosensitive drum 1 and the intermediate transfer belt 10. If V exceeds Paschen's threshold voltage V(d), a discharge occurs; if it falls below V, no discharge occurs.

[0184] Therefore, to suppress the occurrence of retransfer, the potential difference V in the primary transfer section should be made smaller than the threshold voltage V(d) to suppress the occurrence of discharge, thereby preventing a decrease in the toner's charge and a reversal of the toner's polarity.

[0185] As described above, in this embodiment, the intermediate transfer belt 10 has an inner layer 10b with low electrical resistance, so that the back surface potential of the intermediate transfer belt 10 is formed along the circumferential direction of the intermediate transfer belt 10. In particular, the inner surface between the tensioning member 13 and the primary transfer roller 14d is approximately equipotential in the direction of movement of the surface of the intermediate transfer belt 10. Therefore, discharge occurs even on the upstream side of the primary transfer section. At that time, the toner that has already been primary transferred to the intermediate transfer belt 10 at the upstream image forming station is discharged on the upstream side of the primary transfer section of the next image forming station. Also, the surface of the photosensitive drum 1 is negatively charged, and a positive potential is formed on the surface of the intermediate transfer belt 10. Therefore, negatively charged electrons from the photosensitive drum 1 collide with the toner on the intermediate transfer belt 10, causing the toner on the intermediate transfer belt 10 to become more negatively charged. When examining the charge per unit weight of toner (toner particle charge amount ÷ toner particle weight) before and after the toner transferred onto the intermediate transfer belt 10 passes through the primary transfer section of the downstream image forming section, it was found that the negative charge shifts to a higher value after passing through the photosensitive drum 1.

[0186] On the other hand, the potential on the surface of the photosensitive drum 1 decreases when it receives a discharge (because it becomes charged on the positive side), so the potential difference formed between the surface of the photosensitive drum 1 and the intermediate transfer belt 10 becomes smaller. Therefore, the degree of decrease in the potential difference between the intermediate transfer belt 10 and the photosensitive drum 1 is large from the time it receives a discharge in the rotational direction of the photosensitive drum 1 until it reaches the primary transfer section. As a result, the potential difference formed in the primary transfer section becomes below the Paschen discharge threshold. Therefore, discharge is less likely to occur in the primary transfer section.

[0187] In Comparative Example 2, the intermediate transfer belt lacks an inner layer 10b with low electrical resistance. As a result, the inner surface between the tensioning member 13 and the primary transfer roller 14d is not approximately equipotential in the direction of movement of the surface of the intermediate transfer belt 10. Therefore, although discharge occurs upstream of the primary transfer section in the intermediate transfer belt of Comparative Example 2, the discharge is not large enough to lower the potential difference between the intermediate transfer belt potential and the surface of the photosensitive drum below the discharge threshold. When discharge occurs, the potential of the photosensitive drum decreases accordingly, but in the intermediate transfer belt of Comparative Example 2, this decrease is small because there is little discharge upstream of the primary transfer section. Therefore, discharge continues even in the primary transfer section.

[0188] Here, we will explain, using Figures 18 and 19, how to actually confirm whether an electrical discharge is occurring between the intermediate transfer belt 10 and the photosensitive drum 1.

[0189] Figure 18 shows a system for visualizing whether a discharge is actually occurring between the intermediate transfer belt 10 and the photosensitive drum 1. Figure 18 shows a cross-sectional view of the surrounding structure of the photosensitive drum 1 when cut in a cross section perpendicular to the rotation axis direction of the photosensitive drum 1. In both Figures 18 and 19, items without a description of the conditions under consideration are assumed to be the same as those in this embodiment. First, yellow toner is transferred to the intermediate transfer belt 10. Then, the aforementioned yellow toner is passed between the magenta photosensitive drum 1b, which is located downstream of the yellow image forming section a in the direction of movement of the intermediate transfer belt 10, and the intermediate transfer belt 10. When the yellow toner passes through the transfer section, the charging voltage is turned OFF before the area of ​​the photosensitive drum 1b that forms the transfer section reaches the charged section, which is the contact section with the charging roller 2b. If re-transfer toner is to be re-transferred to the photosensitive drum 1, it is preferable to clean the re-transfer toner with a cleaning device beforehand. Here, by turning OFF the charging voltage, the surface potential (post-transfer potential) of the area of ​​the photosensitive drum 1b that the yellow toner has passed through is maintained as it was after the primary transfer. While maintaining that state, a developing voltage of -500V is applied to develop magenta toner in the area of ​​the photosensitive drum 1b where the yellow toner has passed through, using the developing roller 41b. Then, the magenta toner developed on the surface of the photosensitive drum 1b is observed. Alternatively, the magenta toner transferred to the surface of the intermediate transfer belt 10 is observed again. If a discharge occurs at the transfer nip, a spotted toner image will be developed. On the other hand, if a discharge occurs upstream of the transfer nip and no discharge occurs within the transfer nip, toner equivalent to the potential difference between the developing voltage and the post-transfer potential will be developed, but it will not be spotted. When the system in Figure 18 was examined using the intermediate transfer belt 10 of Comparative Example 2, a spotted toner image was observed. On the other hand, when the same examination was performed using the intermediate transfer belt 10 of this embodiment, a spotted toner image was not observed.

[0190] Next, actual discharge light observation was performed using Figure 19. Figure 19 is a system for observing a model that simulates the transfer nip portion, which is the contact area between the intermediate transfer belt 10 and the photosensitive drum 1, from the outside using a high-sensitivity camera (Photron, FASTCAM MAX II). On the intermediate transfer belt 10 side, for example, a piece of the intermediate transfer belt 10 from Comparative Example 2 is cut off, and electrodes are connected to the back and grounded. On the other hand, on the photosensitive drum 1 side, the surface layer 1e of the photosensitive drum 1 of this embodiment is coated onto a transparent conductive ITO (Indium Tin Oxide) glass substrate, and a voltage is applied to the ITO. With toner transferred onto the surface of a piece of the intermediate transfer belt 10, a transfer portion is formed between the surface layer 1e and the piece of the intermediate transfer belt 10, sandwiching the toner. The gap between the surface layer 1e and the piece of the intermediate transfer belt 10 at this time was set to 6 to 15 μm. The discharge light generated when a pulse voltage was applied in this state was confirmed with a high-sensitivity camera. When a toner layer was laminated on one side of the intermediate transfer belt 10 and sandwiched between the surface layer 1e, and a pulse voltage was applied while varying the pulse voltage value, no spotted discharge light was observed at voltages below the discharge threshold, but spotted discharge light was observed at pulse voltages above the discharge threshold. Therefore, it was found that spotted discharge occurs when discharge occurs within the transfer nip. From this result, it was found that the spotted toner image that occurred when using the intermediate transfer belt 10 of Comparative Example 2 with the system in Figure 18 was caused by discharge within the transfer nip. Normally, when discharge occurs continuously, the above-mentioned spotted discharge does not occur. Spotted discharge often occurs when discharge occurs intermittently from a portion of the transfer nip that locally exceeds the discharge threshold. In other words, when incomplete discharge (including no discharge) occurs upstream of the transfer nip, the surface potential of the photosensitive drum 1 cannot be completely reduced (increased to the opposite polarity side of the normal polarity of the toner) by that incomplete discharge. Therefore, it is thought that the discontinuous, spot-like discharges described above occur when the surface of the photosensitive drum 1, which is in an intermittent discharge state, enters the transfer nip area.

[0191] From the above findings, it was confirmed that in the configuration using the intermediate transfer belt 10 of this embodiment, a solid discharge (discharge based on Paschen's law according to a predetermined gap) occurs upstream of the transfer nip. This effectively suppresses discharge at the transfer nip. On the other hand, in the configuration using the intermediate transfer belt 10 of Comparative Example 2, it was confirmed that not much discharge occurred upstream of the transfer nip, and discharge occurred at the transfer nip. Therefore, from the above phenomena, it can be said that the intermediate transfer belt 10 of this embodiment effectively suppresses the generation of retransfer toner.

[0192] Thus, with the configuration of this embodiment, the amount of re-transfer toner can be reduced by performing the primary transfer process by supplying current from the primary transfer power supply 160 to the photosensitive drum 1 via the intermediate transfer belt 10 which has an inner surface layer 10b with low electrical resistance.

[0193] Furthermore, from the perspective of reducing the amount of discharge within the primary transfer section and decreasing the amount of toner to be re-transferred, a smaller charge on the photosensitive drum 1 is advantageous. Configurations that achieve this include, for example, a thicker film thickness and a lower dielectric constant on the surface of the photosensitive drum 1. Also, from the perspective of setting the potential for image formation, a low charging potential is desirable.

[0194] As described above, the present embodiment is an image forming apparatus having the following configuration and features. It includes a rotatable photosensitive drum 1, a charging roller 2 that charges the surface of the photosensitive drum 1 in a charging portion facing the photosensitive drum 1, and a rotatable developing roller 41 that carries a developer composed of toner particles and transfer promoting particles attached to the surface of the toner particles. The developing roller 41 contacts the photosensitive drum 1 to form a developing portion, and supplies the developer to the surface of the photosensitive drum 1 in the developing portion. It has an intermediate transfer belt 10 that contacts the photosensitive drum 1 to form a transfer portion. It has a charging voltage application unit 120 that applies a charging voltage to the charging roller 2, and a primary transfer voltage power supply 160 that is a current supply unit that supplies a transfer current from the intermediate transfer belt 10 to the photosensitive drum 1 in the transfer portion by applying a transfer voltage to the intermediate transfer belt 10. And it has a control unit 200 that controls the charging voltage application unit 120 and the primary transfer voltage power supply 160. A developer composed of toner particles and transfer promoting particles attached to the surface of the toner particles is carried on the developing roller 41. And in the developing nip portion, the transfer promoting particles carried on the surface of the developing roller 41 are supplied to the surface of the photosensitive drum 1. Consider the case where the pressing force pressing the developing roller 41 against the photosensitive drum 1 is F, and the total number of transfer promoting particles intervening between the toner particles and the photosensitive drum 1 is N. Let the adhesive force Ft formed between the transfer promoting particles and the toner particles measured when the transfer promoting particles are pressed against the toner particles with a pressing force of F / N per unit transfer promoting particle. Let the adhesive force Fdr formed between the transfer promoting particles and the photosensitive drum 1 measured when the transfer promoting particles are pressed against the photosensitive drum 1 with F / N. By satisfying the relationship Ft < Fdr between the adhesive force Ft and the adhesive force Fdr, the primary transfer efficiency can be improved by reducing the adhesive force between the surface of the photosensitive drum and the toner particles.

[0195] Furthermore, by forming an inner layer 10b with low electrical resistance on the inner surface of the intermediate transfer belt 10, a discharge is generated from the surface of the intermediate transfer belt 10 to the photosensitive drum 1 upstream of the primary transfer section. This reduces the potential difference between the photosensitive drum 1 and the surface of the intermediate transfer belt 10 in the primary transfer section. This suppresses the decrease in toner charge formed on the intermediate transfer belt 10 in the primary transfer section, the reversal of toner polarity, and the re-transfer of toner transferred to the surface of the intermediate transfer belt 10. As a result, the amount of toner remaining on the photosensitive drum 1 is reduced, and image defects caused by residual toner can be suppressed.

[0196] Furthermore, the control unit 200 is configured to control the generation of a discharge between the photosensitive drum 1 and the intermediate transfer belt 10 upstream of the upstream end of the transfer section in the direction of movement of the surface of the intermediate transfer belt 10. It is also configured to control the potential difference between the photosensitive drum 1 and the intermediate transfer belt 10 in the transfer section so that it is smaller than Paschen's discharge threshold. Here, the first potential difference is defined as the potential difference between the first potential formed on the surface of the photosensitive drum 1 in the charging section and the charging voltage. The second potential difference is defined as the potential difference between the second potential formed on the surface of the photosensitive drum 1 in the transfer section and the surface potential of the intermediate transfer belt 10. Then, when the photosensitive drum 1 is rotating and a charging voltage is applied, the control unit 200 controls the system so that the second potential difference is smaller than the first potential difference. Here, the second potential difference may be, for example, the potential difference between the second potential formed on the surface of the photosensitive drum 1 in the transfer section and the primary transfer voltage when the resistance of the intermediate transfer belt 10 is sufficiently small.

[0197] Furthermore, it has a primary transfer roller 14 that contacts the intermediate transfer belt 10 and supplies current to the intermediate transfer belt 10. The primary transfer roller 14 is a cylindrical metal roller. The intermediate transfer belt 10 has, in the thickness direction of the intermediate transfer belt 10, a base layer 10a as the first layer among a plurality of layers constituting the intermediate transfer belt 10 which is conductive, and an inner layer 10b as the second layer which is conductive and has lower electrical resistance than the base layer 10a. By applying a voltage from the primary transfer voltage power supply 160 to the primary transfer roller 14, a transfer current flows in the circumferential direction of the intermediate transfer belt 10 and the toner image is transferred from the photosensitive drum 1 to the intermediate transfer belt 10. The intermediate transfer belt 10 is configured such that the base layer 10a is the thickest of the plurality of layers constituting the intermediate transfer belt 10. Furthermore, the intermediate transfer belt 10 has a surface layer 10c as the third layer which has higher electrical resistance than the base layer 10a, and the surface layer 10c is conductive and contacts the photosensitive drum 1. Here, the base layer 10a may be configured to contact the photosensitive drum 1. With respect to the thickness direction of the intermediate transfer belt, the inner layer 10b is formed at a position further away from the photosensitive drum 1 than the base layer 10a and contacts the primary transfer roller 14. The current flowing in the circumferential direction of the intermediate transfer belt 10 from the primary transfer roller 14 toward the photosensitive drum 1 flows through the inner layer 10b and then flows to the photosensitive drum 1 via the base layer 10a. Multiple photosensitive drums 1 and primary transfer rollers 14 are provided with respect to the direction of movement of the intermediate transfer belt 10, and each of the multiple primary transfer rollers 14 is provided corresponding to a multiple photosensitive drum 1. Furthermore, a secondary transfer roller 15 is provided to transfer the toner image formed on the surface of the intermediate transfer belt 10 from the surface of the intermediate transfer belt 10 to the recording material. Each of the multiple primary transfer rollers 14 is positioned downstream in the direction of movement of the intermediate transfer belt 10 from the position where the primary transfer roller 14 contacts the corresponding photosensitive drum 1 and the intermediate transfer belt 10, with respect to the direction of movement of the intermediate transfer belt 10. And it is positioned upstream from the position where the secondary transfer roller 15 contacts the intermediate transfer belt 10. Multiple photosensitive drums 1 and multiple primary transfer rollers 14 are arranged such that the distance from the axis center of each photosensitive drum 1 to the axis center of each primary transfer roller 14 is equal.

[0198] Also, the moving speed of the surface of the intermediate transfer belt 10 is set to be higher than the moving speed of the surface of the photosensitive drum 1.

[0199] Consider a case where the pressing force for pressing the photosensitive drum 1 against the intermediate transfer belt 10 is F1, and the total number of transfer promoting particles intervening between the photosensitive drum 1 and the intermediate transfer belt 10 in the transfer section is N1. Let the adhesive force formed between the transfer promoting particles and the intermediate transfer belt 10 measured when the transfer promoting particles are pressed against the intermediate transfer belt 10 with a pressing force of F1 / N1 per unit transfer promoting particle be Fi. Let the adhesive force Fdr1 formed between the transfer promoting particles and the photosensitive drum 1 measured when the transfer promoting particles are pressed against the photosensitive drum 1 with F1 / N1 be defined. In that case, it is preferable that the relationship between Fi and Fdr1 satisfies Fi < Fdr1.

[0200] In this embodiment, a tandem-type image forming apparatus in which a plurality of image forming stations are arranged in series has been described as an example. However, the same effect is obtained in a rotary-type image forming apparatus 200 that forms toner images of a plurality of colors at one image forming station as shown in FIG. 20.

[0201] In this embodiment, a metal roller has been described as an example of the primary transfer roller 14. However, a primary transfer roller having an elastic layer on a metal core also acts in the same manner. Also, a configuration in which four metal rollers 14 are arranged on the inner surface of the intermediate transfer belt 10 corresponding to each image forming station has been adopted, but the number thereof may be increased or decreased. For example, a configuration in which only one metal roller 14 is arranged only between the second image forming station b and the third image forming station c may be adopted.

[0202] Furthermore, regarding the intermediate transfer belt 10, in this embodiment, a transfer electric field is formed upstream of the primary transfer section by forming an inner surface layer 10b having a low electric resistance. However, if the electric resistance of the base layer 10a is sufficiently low, it is not necessarily required to have the inner surface layer 10b. For example, an intermediate transfer belt having a configuration in which a high-resistance surface layer is provided on a base layer having a low electric resistance may be used.

[0203] In this embodiment, a configuration for reducing the toner remaining on the photosensitive drum 1 has been described by taking the drum cleanerless configuration as an example. However, the same effect can be obtained even with a configuration having a cleaner member for cleaning the toner remaining on the photosensitive drum 1.

[0204] Also, in this embodiment, a DC voltage is applied from the primary transfer voltage power supply 160 to the primary transfer roller 14. However, by applying a DC voltage from the secondary transfer voltage power supply 150 to the primary transfer roller 14, it may be configured to reduce the primary transfer voltage power supply. Further, a voltage maintaining element capable of maintaining a predetermined voltage may be provided between the primary transfer voltage power supply 160 and the primary transfer roller 14. As the voltage maintaining element, a Zener diode is typically cited. A Zener diode is an element that maintains a predetermined voltage (hereinafter referred to as the Zener voltage) when a current flows, and a Zener voltage is generated on the cathode side when a current of a certain level or more flows. That is, one end side (anode side) of the Zener diode is connected to the ground, the other end side (cathode side) is connected to the primary transfer roller 14, and the primary transfer voltage is maintained at the Zener voltage. All of the above configurations are applicable to a configuration in which, like this embodiment, the relationship between the adhesive force Ft formed between the transfer promoting particles and the toner particles and the adhesive force Fdr formed between the transfer promoting particles and the surface of the photosensitive drum 1 satisfies Ft < Fdr, so that the transfer efficiency can be increased even when the primary transfer voltage is lowered. Also, in the moving direction of the surface of the intermediate transfer belt 10, a discharge is generated between the photosensitive drum 1 and the intermediate transfer belt 10 upstream of the transfer portion, and the potential difference at the transfer portion is made smaller than the Paschen discharge threshold, which is suitable for the configuration of this embodiment for suppressing re-transfer. That is, in the configuration of this embodiment in which the primary transfer voltage can be lowered more than before, an image forming system capable of obtaining the above effects with the minimum power can be constructed.

Description of Reference Numerals

[0205] 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 transfer-promoting particles adhering to the surface of the toner particles, wherein the developer carrier contacts the image carrier to form a developing section, and the developing section supplies the developer to the surface of the image carrier, An intermediate transfer belt that contacts the image carrier to form a transfer portion, A current supply unit that supplies a transfer current from the intermediate transfer belt to the image carrier in the transfer unit by applying a transfer voltage to the intermediate transfer belt, It includes a control unit that controls the current supply unit, An image forming apparatus capable of supplying the transfer-promoting particles supported on the surface of the developer carrier to the surface of the image carrier in the developing unit while the image carrier is rotating, When the pressing force used to press the developer carrier against the image carrier is F, and the total number of transfer-promoting particles interposed between the toner particles and the image carrier is N, The adhesion force Ft formed between the transfer-promoting particles and the toner particles is measured when the transfer-promoting particles are pressed against the toner particles with a pressing force F / N per unit transfer-promoting particle, The relationship between the transfer-promoting particles and the image carrier, measured when the transfer-promoting particles are pressed against the image carrier at the F / N ratio, and the adhesion force Fdr formed between the transfer-promoting particles and the image carrier is as follows: Ft < Fdr Satisfying the conditions, The control unit is characterized by generating a discharge between the image carrier and the intermediate transfer belt upstream of the upstream end of the transfer section in the direction of movement of the surface of the intermediate transfer belt, and controlling the potential difference between the image carrier and the intermediate transfer belt in the transfer section to be smaller than Paschen's discharge threshold.

2. A rotatable image carrier, A charging member that charges the surface of the image carrier in the charging portion facing the image carrier, A rotatable developer carrier that carries a developer composed of toner particles and transfer-promoting particles adhering to the surface of the toner particles, wherein the developer carrier contacts the image carrier to form a developing section, and the developing section supplies the developer to the surface of the image carrier, An intermediate transfer belt that contacts the image carrier to form a transfer portion, A charging voltage application unit that applies a charging voltage to the charging member, A current supply unit that supplies a transfer current from the intermediate transfer belt to the image carrier in the transfer unit by applying a transfer voltage to the intermediate transfer belt, The system includes a control unit that controls the charging voltage application unit and the current supply unit, An image forming apparatus capable of supplying the transfer-promoting particles supported on the surface of the developer carrier to the surface of the image carrier in the developing unit while the image carrier is rotating, When the pressing force used to press the developer carrier against the image carrier is F, and the total number of transfer-promoting particles interposed between the toner particles and the image carrier is N, The adhesion force Ft formed between the transfer-promoting particles and the toner particles is measured when the transfer-promoting particles are pressed against the toner particles with a pressing force F / N per unit transfer-promoting particle, The relationship between the transfer-promoting particles and the image carrier, measured when the transfer-promoting particles are pressed against the image carrier at the F / N ratio, and the adhesion force Fdr formed between the transfer-promoting particles and the image carrier is as follows: Ft < Fdr Satisfying the conditions, If the potential difference between the first potential formed on the surface of the image carrier in the charging section and the charging voltage is defined as the first potential difference, and the potential difference between the second potential formed on the surface of the image carrier in the transfer section and the surface potential of the intermediate transfer belt is defined as the second potential difference, The image forming apparatus is characterized in that the control unit controls the second potential difference to be smaller than the first potential difference when the image carrier is rotating and the charging voltage is applied.

3. A rotatable image carrier, A charging member that charges the surface of the image carrier in the charging portion facing the image carrier, A rotatable developer carrier that carries a developer composed of toner particles and transfer-promoting particles adhering to the surface of the toner particles, wherein the developer carrier contacts the image carrier to form a developing section, and the developing section supplies the developer to the surface of the image carrier, An intermediate transfer belt that contacts the image carrier to form a transfer portion, A charging voltage application unit that applies a charging voltage to the charging member, A current supply unit that supplies a transfer current from the intermediate transfer belt to the image carrier in the transfer unit by applying a transfer voltage to the intermediate transfer belt, The system includes a control unit that controls the charging voltage application unit and the current supply unit, An image forming apparatus capable of supplying the transfer-promoting particles supported on the surface of the developer carrier to the surface of the image carrier in the developing unit while the image carrier is rotating, When the pressing force used to press the developer carrier against the image carrier is F, and the total number of transfer-promoting particles interposed between the toner particles and the image carrier is N, The adhesion force Ft formed between the transfer-promoting particles and the toner particles is measured when the transfer-promoting particles are pressed against the toner particles with a pressing force F / N per unit transfer-promoting particle, The relationship between the transfer-promoting particles and the image carrier, measured when the transfer-promoting particles are pressed against the image carrier at the F / N ratio, and the adhesion force Fdr formed between the transfer-promoting particles and the image carrier is as follows: Ft < Fdr Satisfying the conditions, If the potential difference between the first potential formed on the surface of the image carrier in the charging section and the charging voltage is defined as the first potential difference, and the potential difference between the second potential formed on the surface of the image carrier in the transfer section and the transfer voltage is defined as the second potential difference, The image forming apparatus is characterized in that the control unit controls the second potential difference to be smaller than the first potential difference when the image carrier is rotating and the charging voltage is applied.

4. The system includes a current supply member that contacts the intermediate transfer belt and supplies current to the intermediate transfer belt, The intermediate transfer belt comprises, with respect to the thickness direction of the intermediate transfer belt, a first layer which is conductive and is one of a plurality of layers constituting the intermediate transfer belt, and a second layer which is conductive and has lower electrical resistance than the first layer. The image forming apparatus according to any one of claims 1 to 3, characterized in that a toner image is transferred from the image carrier to the intermediate transfer belt by applying a voltage from the current supply unit to the current supply member.

5. A rotatable image carrier, A rotatable developer carrier that carries a developer composed of toner particles and transfer-promoting particles adhering to the surface of the toner particles, wherein the developer carrier contacts the image carrier to form a developing section, and the developing section supplies the developer to the surface of the image carrier, An intermediate transfer belt that contacts the image carrier to form a transfer portion, A current supply unit that supplies a transfer current from the intermediate transfer belt to the image carrier in the transfer unit by applying a transfer voltage to the intermediate transfer belt, A current supply member that contacts the intermediate transfer belt and supplies current to the intermediate transfer belt, It includes a control unit that controls the current supply unit, An image forming apparatus capable of supplying the transfer-promoting particles supported on the surface of the developer carrier to the surface of the image carrier in the developing unit while the image carrier is rotating, When the pressing force used to press the developer carrier against the image carrier is F, and the total number of transfer-promoting particles interposed between the toner particles and the image carrier is N, The adhesion force Ft formed between the transfer-promoting particles and the toner particles is measured when the transfer-promoting particles are pressed against the toner particles with a pressing force F / N per unit transfer-promoting particle, The relationship between the transfer-promoting particles and the image carrier, measured when the transfer-promoting particles are pressed against the image carrier at the F / N ratio, and the adhesion force Fdr formed between the transfer-promoting particles and the image carrier is as follows: Ft < Fdr Satisfying the conditions, The intermediate transfer belt comprises, with respect to the thickness direction of the intermediate transfer belt, a first layer which is conductive and is one of a plurality of layers constituting the intermediate transfer belt, and a second layer which is conductive and has lower electrical resistance than the first layer. An image forming apparatus characterized by transferring a toner image from the image carrier to the intermediate transfer belt by applying a voltage from the current supply unit to the current supply member.

6. The image forming apparatus according to claim 5, characterized in that the control unit generates a discharge between the image carrier and the intermediate transfer belt upstream of the upstream end of the transfer section in the direction of movement of the surface of the intermediate transfer belt, and controls the potential difference between the image carrier and the intermediate transfer belt in the transfer section to be smaller than Paschen's discharge threshold.

7. A charging member that charges the surface of the image carrier in the charging portion facing the image carrier, It has a charging voltage application unit that applies a charging voltage to the charging member, If the potential difference between the first potential formed on the surface of the image carrier in the charging section and the charging voltage is defined as the first potential difference, and the potential difference between the second potential formed on the surface of the image carrier in the transfer section and the surface potential of the intermediate transfer belt is defined as the second potential difference, The image forming apparatus according to claim 5 or 6, characterized in that the control unit controls the second potential difference to be smaller than the first potential difference when the image carrier is rotating and the charging voltage is applied.

8. The image forming apparatus according to any one of claims 4 to 7, characterized in that an electric current is passed in the circumferential direction of the intermediate transfer belt to transfer a toner image from the image carrier to the intermediate transfer belt.

9. The image forming apparatus according to any one of claims 4 to 8, characterized in that the first layer among the plurality of layers constituting the intermediate transfer belt is the thickest.

10. The image forming apparatus according to any one of claims 4 to 9, characterized in that the first layer is in contact with the image carrier.

11. The image forming apparatus according to any one of claims 4 to 9, characterized in that the intermediate transfer belt has a third layer having higher electrical resistance than the first layer, and the third layer is in contact with the image carrier.

12. The image forming apparatus according to claim 11, characterized in that the third layer is electronically conductive.

13. The image forming apparatus according to any one of claims 4 to 12, characterized in that, with respect to the thickness direction, the second layer is formed at a position further away from the image carrier than the first layer and is in contact with the current supply member.

14. The image forming apparatus according to claim 13, characterized in that the current flowing from the current supply member toward the image carrier in the circumferential direction of the intermediate transfer belt flows through the second layer and then flows to the image carrier via the first layer.

15. The image forming apparatus according to any one of claims 4 to 14, comprising a voltage maintaining element capable of maintaining a predetermined voltage by supplying current from the current supply unit, wherein one end of the voltage maintaining element is connected to earth and the other end of the voltage maintaining element is connected to the current supply member.

16. The image forming apparatus according to any one of claims 4 to 15, wherein a plurality of the image carriers and the current supply members are provided with respect to the direction of movement of the intermediate transfer belt, and each of the plurality of current supply members is provided in accordance with the plurality of image carriers.

17. The system includes a transfer member that transfers a toner image formed on the surface of the intermediate transfer belt from the surface of the intermediate transfer belt to a recording material. The image forming apparatus according to any one of claims 4 to 16, characterized in that each of the plurality of current supply members is positioned downstream in the direction of movement of the intermediate transfer belt with respect to the direction of movement of the intermediate transfer belt, on the side of the direction of movement of the surface of the intermediate transfer belt, from the position where the current supply member contacts the corresponding image carrier and the intermediate transfer belt, and upstream from the position where the transfer member and the intermediate transfer belt contact.

18. The image forming apparatus according to claim 16, characterized in that, in a plurality of image carriers and a plurality of current supply members, the distance from the axial center of each image carrier to the axial center of each current supply member is equal.

19. The image forming apparatus according to any one of claims 4 to 18, characterized in that the current supply member is a metal roller.

20. The image forming apparatus according to any one of claims 1 to 19, characterized in that the moving speed of the surface of the intermediate transfer belt is faster than the moving speed of the surface of the image carrier.

21. When the pressing force used to press the image carrier against the intermediate transfer belt is F1, and the total number of transfer-promoting particles interposed between the image carrier and the intermediate transfer belt in the transfer section is N1, the relationship between the adhesion force Fi formed between the transfer-promoting particles and the intermediate transfer belt, measured when the transfer-promoting particles are pressed against the intermediate transfer belt with a pressing force of F1 / N1 per unit transfer-promoting particle, and the adhesion force Fdr1 formed between the transfer-promoting particles and the image carrier, measured when the transfer-promoting particles are pressed against the image carrier with a pressing force of F1 / N1, is as follows: Fi < Fdr1 An image forming apparatus according to any one of claims 1 to 20, characterized in that it satisfies the following conditions.

22. The image forming apparatus according to any one of claims 1 to 21, characterized in that it has protrusions formed from fine particles containing an organosilicon polymer having a structure represented by the following formula (1) on the surface of the toner particles, and the fine particles are arranged on the protrusions. R-Si(O １／２ ) ３ (1) (The R in the above-mentioned R represents a hydrocarbon group having 1 to 6 carbon atoms.)

23. The developer carrier is provided with a developer storage section that supplies the developer and stores the developer, The image forming apparatus according to any one of claims 1 to 22, characterized in that the developer remaining on the image carrier without being transferred to the intermediate transfer belt is recovered by the developer carrier.

24. The image forming apparatus according to any one of claims 1 to 23, characterized in that the developer is a one-component developer.

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