JP7463221B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that uses an electrophotographic process, etc.

Image forming devices that form images using electrophotographic processes, such as copying machines and laser printers, are known.

In the transfer process, this image forming device applies a voltage from a voltage power source to a transfer member arranged opposite the photosensitive drum 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 a toner image of multiple colors, this transfer process is repeatedly performed for the toner images of multiple colors, thereby forming a toner image of multiple colors on the surface of the intermediate transfer body or recording material. The developer (toner) that is 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 a waste toner storage section in the cleaning unit.

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

In order to achieve a cleanerless system, Patent Document 1 proposes a configuration in which fine particles are attached to the surface of the photosensitive drum in advance, and the fine particles are placed between the photosensitive drum and the toner image, reducing the adhesive force between the photosensitive drum and the toner, thereby improving transfer efficiency.

Furthermore, Patent Document 1 proposes a configuration in which toner with externally added fine particles is used as a means for adhering fine particles to the surface of the photosensitive drum, and the fine particles are supplied from the developing device onto the photosensitive drum.

JP 10-63027 A

However, as in Patent Document 1, when toner with fine particles added thereto is supplied from a developing device onto a photosensitive drum to transfer a toner image onto a recording material in order to improve transfer efficiency, the fine particles migrate to the surface of the recording material together with the transferred toner image. In particular, to improve the transfer efficiency of high-density printing of multiple colors, it is necessary to supply a larger number of fine particles to the surface of the photosensitive drum. As a result, a large amount of fine particles may migrate to the surface of the recording material together with the transferred toner. As a result, when fixing the toner to the recording material, a large amount of fine particles may inhibit heat conduction to the toner, deteriorating fixability.

Therefore, the present invention aims to supply a sufficient amount of fine particles to the photosensitive drum surface to improve transfer efficiency while suppressing image defects caused by the fine particles.

Therefore, the image forming apparatus according to the present invention includes a first image forming section having a rotatable first image carrier, a first developer carrier carrying a first developer composed of first toner particles and carrier particles adhering to the surfaces of the first toner particles, the first developer carrier contacting the first image carrier to form a first developing section and supplying the first developer to form a first developer image on the surface of the first image carrier in the first developing section, a second image forming section having a rotatable second image carrier, a second developer carrier carrying a second developer composed of second toner particles and carrier particles adhering to the surfaces of the second toner particles, the second developer carrier contacting the second image carrier to form a second developing section and supplying the second developer to form a second developer image on the surface of the second image carrier in the second developing section, and an intermediate transfer body that comes into contact with an image carrier of a first type to form a first contact portion and comes into contact with a second image carrier to form a second contact portion, the first developer image being transferred at the first contact portion and the second developer image being transferred at the second contact portion; and a transfer member that comes into contact with the intermediate transfer body to form a transfer portion and transfers the first developer image and the second developer image formed on the surface of the intermediate transfer body to a recording material in the transfer portion, the first image carrier being in a rotating state, the carrier particles carried on the surface of the first developer carrier being capable of being supplied to the surface of the first image carrier in the first developing portion, and the second image carrier being in a rotating state, the carrier particles carried on the surface of the second developer carrier being capable of being supplied to the surface of the second image carrier in the second developing portion, the first image forming unit and the second image forming unit are disposed so that the first contact portion is formed downstream of the transfer unit and upstream of the second contact portion in a moving direction of the surface of the intermediate transfer body, and when a pressing force for pressing the first developer carrier against the first image carrier is F1 and a total number of the carrier particles interposed between the first toner particles and the first image carrier is N1, a relationship between an adhesive force Ft1 formed between the carrier particles and the first toner particles, which is measured when the carrier particles are pressed against the first toner particles with a pressing force per unit carrier particle, F1/N1, and an adhesive force Fdr1 formed between the carrier particles and the first image carrier, which is measured when the carrier particles are pressed against the first image carrier with F1/N1, satisfies Ft1≦Fdr1, a pressing force for pressing the second developer carrier against the second image carrier is F2, When the total number of the carrier particles between the second toner particles and the second image carrier is N2, the adhesive force Ft2 formed between the carrier particles and the second toner particles measured when the carrier particles are pressed against the second toner particles with F2/N2, which is the pressing force per unit carrier particle, and the adhesive force Fdr2 formed between the carrier particles and the second image carrier measured when the carrier particles are pressed against the second image carrier with F2/N2 satisfy Ft2≦Fdr2, and the adhesion area of the carrier particles adhered to the surface of the second image carrier is larger than the adhesion area of the carrier particles adhered to the surface of the first image carrier after the first image carrier and the first developer carrier, and the second image carrier and the second developer carrier are in contact with each other and the first image carrier and the second image carrier are rotated.

As described above, according to the present invention, it is possible to supply a sufficient amount of fine particles to the photosensitive drum surface to improve transfer efficiency while suppressing image defects caused by the fine particles.

5 is a timing chart of a transfer carrier supply operation in the first embodiment. 1 is an outline of an image forming apparatus according to a first embodiment. FIG. 2 is a control block diagram according to the first embodiment. FIG. 2 is a diagram illustrating a developing cartridge according to the first embodiment. FIG. 4 is a diagram illustrating the setting of a developing blade in the first embodiment. 4A and 4B are diagrams illustrating a contact portion between a developing roller and a photosensitive drum in the first embodiment. FIG. 2 is a schematic diagram of a toner surface in Example 1. 3 is a schematic diagram of a convex shape of a toner surface in Example 1. FIG. 3 is a schematic diagram of a convex shape of a toner surface in Example 1. FIG. 3 is a schematic diagram of a convex shape of a toner surface in Example 1. FIG. FIG. 2 is a schematic diagram of a toner and a transfer carrier in the first embodiment. FIG. 4 is a schematic diagram illustrating a transfer carrier supply time in the first embodiment. FIG. 4 is a schematic diagram showing primary transfer in the first embodiment. 4 is a timing chart of an image forming operation in the first embodiment. 5A and 5B are diagrams illustrating a contact state of toner in the developing unit in the first embodiment. FIG. 4 is a diagram showing the state of toner and transfer carrier particles in a developing section in Example 1. 5A and 5B are diagrams illustrating the state of transfer carrier particles in the developing section in the first embodiment. 5 is a timing chart for explaining a supply operation of transfer carrier particles in the first embodiment. 10 is a timing chart for explaining a supply operation of transfer carrier particles in the second embodiment. 13A and 13B are diagrams illustrating a transfer carrier supply mechanism during a non-image forming operation in a development unit according to a second embodiment. 11A and 11B are diagrams illustrating a transfer carrier supply mechanism in an image forming operation in a developing unit according to a second embodiment. 13A and 13B are diagrams illustrating a transfer carrier supply member according to another embodiment.

The following describes in detail preferred embodiments of the present invention by way of example, with reference to the drawings. However, the dimensions, materials, shapes, and relative positions of the components described in the following embodiments should be modified as appropriate depending on the configuration and various conditions of the device to which the present invention is applied. Therefore, unless otherwise specified, it is not intended to limit the scope of the present invention to these alone.

1. Image forming apparatus First, the overall configuration of an electrophotographic image forming apparatus (hereinafter, referred to as an image forming apparatus) according to the present invention will be described. Fig. 2 is a schematic cross-sectional view of an image forming apparatus 100 according to this embodiment. Fig. 3 is a diagram showing the configuration of a control unit 200 that controls the image forming apparatus 100. The configuration, operation, and control of the image forming apparatus 100 according to this embodiment will be described with reference to Figs. 2 and 3.

The image forming apparatus 100 of this embodiment is a full-color laser printer that employs an in-line system and an intermediate transfer system. Example 1 particularly relates to an image forming apparatus that uses a so-called drum cleanerless system that does not have a cleaning means for the image carrier.

The image forming apparatus 100 can form a full-color image on a recording material P (e.g., recording paper, a plastic sheet) according to image information. The image information is input to the image forming apparatus 100 from an image reading device or a host device such as a personal computer that is communicatively connected to the image forming apparatus 100.

The image forming apparatus 100 has a plurality of image forming units, namely, first, second, third and fourth process cartridges Sa, Sb, Sc and Sd for forming images of each color, yellow (Y), magenta (M), cyan (C) and black (K). In this embodiment, the first to fourth process cartridges Sa, Sb, Sc and Sd are arranged in a row in a direction intersecting the vertical direction. In this embodiment, the configurations and operations of the first to fourth process cartridges Sa, Sb, Sc and Sd are substantially the same except for the colors of the images they form. Therefore, hereinafter, unless a particular distinction is required, the suffixes a, b, c and d given to the reference numerals to indicate that the element is provided for one of the colors will be omitted and a general description will be given.

In this embodiment, the image forming apparatus 100 has, as a plurality of image carriers, four drum-shaped electrophotographic photosensitive bodies arranged in a direction intersecting the vertical direction, that is, photosensitive drums 1 (1a, 1b, 1c, 1d). The photosensitive drums 1 are rotated by a photosensitive drum drive unit (drive source) 110. Around the photosensitive drum 1, charging rollers 2 (2a, 2b, 2c, 2d), scanner units (exposure devices) 3 (3a, 3b, 3c, 3d), development units (development devices) 4 (4a, 4b, 4c, 4d), and pre-charge exposure devices 5 (5a, 5b, 5c, 5d) are arranged. The charging roller 2 is a charging means for uniformly charging the surface of the photosensitive drum 1. The scanner unit 3 is an exposure means for irradiating a laser to form an electrostatic image (electrostatic latent image) on the photosensitive drum 1 based on the output calculated by the CPU 150 from image information input from a host device such as a personal computer. The developing unit 4 is a developing means that develops the electrostatic image into a toner image. The pre-charge exposure device 5 is an exposure means for eliminating unevenness in the surface potential of the photosensitive drum 1 after primary transfer. The photosensitive drum 1, the charging roller 2 as a process means acting on the photosensitive drum 1, and the developing unit 4 are integrated to form a process cartridge S. The process cartridge S is detachably attached to the image forming apparatus 100 via attachment means such as an attachment guide and a positioning member provided in the image forming apparatus 100.

In addition, an intermediate transfer belt 10 is disposed opposite the four photosensitive drums 1 as an intermediate transfer body for transferring the toner image on the photosensitive drum 1 to a recording material P. The intermediate transfer belt 10, which is formed as an endless belt, contacts each photosensitive drum 1 and moves (rotates) in a circular motion in the direction of the illustrated arrow R3 (clockwise). The intermediate transfer belt 10 is stretched around a secondary transfer opposing roller 13, a drive roller 11, and a tension roller 12 as multiple support members. In order to move the surface of the intermediate transfer belt 10, the drive roller 11 is driven to rotate in the direction of the illustrated arrow R2.

Four primary transfer rollers 14 (14a, 14b, 14c, 14d) are arranged side by side on the inner peripheral side of the intermediate transfer belt 10 so as to face each photosensitive drum 1. The primary transfer rollers 14 press the intermediate transfer belt 10 against the photosensitive drums 1, forming a primary transfer section where the intermediate transfer belt 10 and the photosensitive drums 1 come into contact.

A secondary transfer roller 20 is disposed on the outer peripheral surface of the intermediate transfer belt 10 at a position facing the secondary transfer opposing roller 13. The secondary transfer roller 20 is pressed against the secondary transfer opposing roller 13 via the intermediate transfer belt 10, forming a secondary transfer section where the intermediate transfer belt 10 and the secondary transfer roller 13 are in contact.

The recording material P onto which the toner image has been transferred is transported to the fixing device 30, which serves as a fixing means. The fixing device 30 applies heat and pressure to the recording material P, thereby fixing the toner image to the recording material P.

In addition, the image forming device 100 can also form a monochromatic or multi-color image using only one desired image forming unit, or using only some (but not all) of the image forming units.

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

The configuration of the control unit 200 that controls the entire image forming apparatus will be described with reference to FIG. 3. As shown in FIG. 3, the control unit 200 includes a CPU circuit unit 150, a ROM 151, and a RAM 152. The CPU circuit unit 150 controls the primary transfer control unit 201, the secondary transfer control unit 202, the development control unit 203, the exposure control unit 204, and the charging control unit 205 in accordance with a control program stored in the ROM 151. The environment table and the paper thickness correspondence table are stored in the ROM 151 and are called and reflected by the CPU 150. The RAM 152 temporarily holds control data and is used as a work area for arithmetic processing associated with the control. The primary transfer control unit 201 and the secondary transfer control unit 202 control the primary transfer voltage power supply 15 and the secondary transfer voltage power supply 21, respectively, and control the voltages output from the primary transfer voltage power supply 15 and the secondary transfer voltage power supply 21 based on the current values detected by current detection circuits (not shown). When the control unit 200 receives image information and a print command from a host computer (not shown), it controls each control unit (primary transfer control unit 201, secondary transfer control unit 202, development control unit 203, exposure control unit 204, and charging control unit 205) to perform the image formation operations required for the printing operation.
2. Image Forming Process Next, the image forming process in the first embodiment will be described. During image formation, the surface of the photosensitive drum 1 is first uniformly charged by the charging roller 2 to which a charging voltage of −1000V is applied by the charging voltage power supply 132. Next, the surface of the charged photosensitive drum 1 is scanned and exposed by laser light (La, Lb, Lc, Ld) emitted from the scanner unit 3 based on the output calculated by the CPU 150 from the image information input from the host device. Thereby, an electrostatic image according to the image information is formed on the photosensitive drum 1. Next, the electrostatic image formed on the photosensitive drum 1 is developed as a toner image by the developing unit 4. Then, a voltage of the opposite polarity to the normal charging polarity of the toner is applied to the primary transfer roller 14 from the primary transfer voltage power supply 15 (high voltage power supply) as a primary transfer voltage application means. As a result, the toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 10. When a full-color image is formed, the above-mentioned process is carried out in sequence in the first to fourth process cartridges Sa, Sb, Sc, and Sd, and the toner images of each color are then primarily transferred onto the intermediate transfer belt 10 in a superimposed manner.

The primary transfer roller 14 is a cylindrical metal roller with an outer diameter of 6 mm, and is made of nickel-plated SUS. The primary transfer roller 14 is positioned 8 mm offset downstream in the direction of movement of the intermediate transfer belt 10 from the center position of the photosensitive drum 1, and the intermediate transfer belt 10 is configured to wrap around the photosensitive drum 1. The primary transfer roller 14 is positioned 1 mm above the horizontal plane formed by the photosensitive drum 1 and the intermediate transfer belt 10 so that the amount of winding of the intermediate transfer belt 10 around the photosensitive drum 1 can be ensured, and it presses the intermediate transfer belt 10 with a force of approximately 200 gf. The primary transfer roller 14 rotates in response to the rotation of the intermediate transfer belt 10.

Then, in synchronization with the movement of the intermediate transfer belt 10, the recording material P is transported to the secondary transfer section. Then, a voltage of the opposite polarity to the normal charging polarity of the toner is applied to the secondary transfer roller 20 from a secondary transfer voltage power source 21 (high voltage power source) as a secondary transfer voltage application means. As a result, the four-color toner image on the intermediate transfer belt 10 is secondarily transferred all at once onto the recording material P transported by the feeding means by the action of the secondary transfer roller 20 that is in contact with the intermediate transfer belt 10 via the recording material P.

The secondary transfer roller 20, which serves as a secondary transfer member, contacts the intermediate transfer belt 10 with a pressure of 50 N, forming a secondary transfer portion (secondary transfer nip). The secondary transfer roller 20 rotates in response to the intermediate transfer belt 10, and a voltage of 1500 V is applied to it from the secondary transfer voltage power source 21 when the toner on the intermediate transfer belt 10 is being secondarily transferred to a recording material P such as paper.

The recording material P onto which the toner image has been transferred is transported to the fixing device 30, which serves as a fixing means. In the fixing device 30, heat and pressure are applied to the recording material P to fix the transferred toner image, and the recording material P is discharged from the image forming apparatus 100.

The primary transfer residual toner remaining on the surface of the photosensitive drum 1 in the primary transfer process is collected by the developing roller 22 (described later) and reused. The primary transfer residual toner remaining on the surface of the photosensitive drum 1 in the primary transfer process is charged to the normal charging polarity, negative, when it passes through the charging roller 2. The primary transfer residual toner is then collected by the developing roller 22 and reused due to an electric field caused by the potential difference between the potential of the photosensitive drum 1 formed by the charging roller 2 and the potential of the developing roller 22 (described later) formed by applying a DC voltage to the developing roller 22.

Furthermore, any residual toner remaining on the surface of the intermediate transfer belt 10 in the secondary transfer process is cleaned and removed by an intermediate transfer belt cleaning device 16 .
3. Structure of the Process Cartridge Next, the overall structure of the process cartridge S to be mounted in the image forming apparatus 100 of this embodiment will be described. The process cartridges S for each color have the same shape, except for an identification portion, etc., not shown. The developing unit (developing device) 4 of the process cartridge S for each color contains toner of each color, namely yellow (Y), magenta (M), cyan (C), and black (K). The developing unit 4, which is the developer containing portion, contains a negative polarity non-magnetic one-component developer (toner) manufactured by a suspension polymerization method.

The process cartridge S is constructed by integrating a photosensitive unit including a photosensitive drum 1 and a rotatable charging roller 2, and a developing unit 4 including a rotatable developing roller 22, etc.

The photosensitive drum 1 is rotatably supported via a bearing (not shown). The photosensitive drum 1 is configured to be rotated in the direction of the arrow R1 (counterclockwise) in response to the image forming operation by transmitting the driving force of the photosensitive drum driving means 110 (driving source) which is the photosensitive drum driving section to the photosensitive unit.

The photosensitive drum 1 is made by providing a photosensitive layer and a surface layer on an aluminum tube having an outer diameter of φ20 mm. The surface layer is a thin film layer made of polyarylate and has a thickness of 20 mm.

The charging roller 2 is configured such that a roller portion, which is provided on a metal shaft having a diameter of 5.5 mm and an elastic layer made of conductive rubber having a thickness of 1.5 mm and a volume resistivity of about 1×10 ⁶ Ωcm, is in pressure contact with the photosensitive drum 1 and rotates driven by the photosensitive drum 1. The surface layer of the charging roller 2 is provided with a large number of protrusions, and the average height of the protrusions is about 10 μm. The protrusions provided on the surface layer of the charging roller 2 serve as spacers between the charging roller 2 and the photosensitive drum 1 in the charging section. When the primary transfer residual toner on the photosensitive drum 1 enters the charging section, the protrusions prevent the charging roller 2 from being soiled with the primary transfer residual toner by contacting the primary transfer residual toner at places other than the protrusions.

As shown in FIG. 4, the developing unit 4 has a developing roller 22 that carries toner T, a developing blade 23 (toner regulating member), a supply roller 26 that supplies toner T, and a developing frame 24 that fixes these. The developing frame 24 has a developing chamber 24a in which the developing roller 22 is disposed, and a blowout prevention sheet 24b that seals a developing opening (opening) that connects the developing chamber 24a to the outside.

The supply of toner to the developing roller 22 is performed by a supply roller 26 that contacts the developing roller 22. The supply roller 26 rotates (in the direction of the arrow R5) while in contact with the developing roller 22 (in the direction of the arrow R4). The supply roller 26 transports the toner T from inside the developing chamber 24a and causes it to adhere to the developing roller 22, and also serves the function of temporarily removing any toner T remaining on the developing roller 22. Furthermore, the toner T that has adhered to the supply roller 26 is given a preliminary frictional charge by rubbing against the developing roller 22.

One end of the developing blade 23 is fixed to a fixed member 25 fixed to the developing frame 24, and the other end of the developing blade 23 is brought into contact with the developing roller 22, enabling the control of the amount of toner coat on the developing roller 22 and the application of electric charge. The developing roller 22 is disposed in the developing opening and is capable of coming into contact with the photosensitive drum 1.

As shown in FIG. 4, the developing roller 22 is a roller having a configuration in which, for example, a base layer 22b made of silicon and a surface layer 22c made of urethane are laminated on a metal core 22a. It is arranged so that it is driven to rotate in the direction R4 indicated by the arrow in the figure by the driving force of the developing roller driving means 130 (driving source) which is the developing roller driving section.

In this embodiment, a predetermined DC voltage (development voltage Vdc) is applied to the development roller 22 from the development voltage power supply 131, and the electrostatic latent image is visualized in the development section where the toner negatively charged by frictional charging contacts the photosensitive drum 1 to form a toner image.

The supply roller 26 is provided with a urethane foam layer 26b around a core metal electrode 26a having an outer diameter of φ5.5 (mm) which is a conductive support. The outer diameter of the entire supply roller 26 including the urethane foam layer 26b is φ11 (mm). The amount of penetration of the developing roller 22 into the supply roller 26 is 1.2 mm. The supply roller 26 rotates in a direction (indicated by the arrow R5 in the figure) such that the supply roller 26 and the developing roller 22 have opposite speeds at the contact portion. The powder pressure of the toner T present around the urethane foam layer 26b acts on the urethane foam layer 26b, and the toner T is taken into the urethane foam layer 26b as the supply roller 26 rotates. A predetermined DC voltage (supply voltage Vrs) is applied to the supply roller 26 from the supply voltage power source 136. The amount of toner supply and the amount of preliminary frictional charge are controlled by controlling the potential difference (supply roller contrast ΔVrs = Vrs - Vdc) with the voltage applied to the developing roller 22.

In this embodiment, a supply voltage Vrs = -500V is applied to the supply roller 26, and a development voltage Vdc = -300V is applied to the development roller 22 from the supply voltage power source 136 and the development voltage power source 131, respectively. As a result, the control unit 200 controls the supply roller 26 so that a potential difference of -200V is created with respect to the development roller 22, stabilizing the amount of toner supply and the amount of preliminary frictional charge.

In the following explanation, a high potential and applied voltage refers to an absolute value that is larger on the negative polarity side (e.g., -1000V compared to -500V), and a low potential refers to an absolute value that is smaller on the negative polarity side (e.g., -300V compared to -500V). This is because the negatively charged toner in this embodiment is considered as the standard.

In addition, the voltage in this embodiment is expressed as a potential difference with respect to the earth potential (0 V). Therefore, the development voltage Vdc = -300 V is interpreted as having a potential difference of -300 V with respect to the earth potential due to the development voltage applied to the core metal of the development roller 22. This is also true for the charging voltage, transfer voltage, etc.

As shown in FIG. 4, the developing blade 23 is in contact with the developing roller 22 in a counter direction, and regulates the amount of toner coated and imparts an electric charge.

In this embodiment, the developing blade 23, which is a toner regulating member, is a support member made of a 50 to 120 μm thick SUS plate, and the surface of the blade portion is brought into contact with the developing roller 22 by utilizing the spring elasticity of the support member. Specifically, the contact is as shown in FIG. 5. If the center of the cross section of the developing roller 22 is set as the zero point, and the XY coordinate axes are determined as shown in FIG. 5, and the contact position is defined by the XY coordinates (x, y), in this embodiment, x = 3.86 mm, y = -0.60 mm. The blade portion of the developing blade 23 is configured such that a blade portion is formed at one end in the short direction, and the other end is fixed to the developing frame 24 and supported. On the other hand, the blade portion is formed by covering the surface of the support member with a thin film made of conductive urethane resin. Furthermore, a predetermined DC voltage is applied to the developing blade 23 from the developing blade voltage power supply 133 (developing blade voltage Vb), and the potential difference with the voltage applied to the developing roller 22 (developing voltage Vdc) (developing blade contrast ΔVb = Vb - Vdc) is controlled. This controls the toner charge amount and toner coat amount.

In this embodiment, a development blade voltage Vb of -500 V is applied to the development blade 23, and a development voltage Vdc of -300 V is applied to the development roller 22. A potential difference (development blade contrast) of -200 V is applied to the development blade 23 relative to the development roller 22 to stabilize the toner charge amount and toner coat amount.

The toner layer formed on the developing roller 22 by the developing blade 23 is transported to the developing section that contacts the photosensitive drum 1, where reversal development is performed. At the contact position A shown in FIG. 6, the amount of penetration of the developing roller 22 into the photosensitive body 1 is set to 40 μm by the rollers (not shown) at the end of the developing roller 22. The surface of the developing roller 22 is deformed by being pressed against the photosensitive drum 1. This forms a development nip, and development can be performed in a stable contact state. In this embodiment, the pressing force of the developing roller 22 against the photosensitive drum 1 is 200 gf. The width of the developing section (hereinafter, the development nip section), which is the contact section between the developing roller 22 and the photosensitive drum 1, is 2.0 mm in the rotation direction of the photosensitive drum 1 and 220 mm in the longitudinal direction of the photosensitive drum 1.

The toner in this embodiment is a negatively charged non-magnetic toner produced by a suspension polymerization method, has a volume average particle diameter of 7.0 μm, and is negatively charged when carried on the developing roller 22. The volume average particle diameter of the toner was measured using a laser diffraction particle size distribution measuring instrument LS230 manufactured by Beckman Coulter, Inc. The toner will be described later.
4. Primary Transfer The primary transfer step described in the section on the image forming process will now be described in detail.

First, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential, i.e., charging potential Vd, by the charging roller 2. Next, the surface of the charged photosensitive drum 1 is scanned and exposed to a laser beam emitted from the scanner unit 3 based on the output calculated by the CPU 150 from the image information input from the host device, and an electrostatic image according to the image information is formed on the photosensitive drum 1. At this time, a post-exposure potential Vl, which is the potential at which the electrostatic image is formed, is formed. Next, the electrostatic image formed on the photosensitive drum 1 is developed as a toner image by the potential difference (development contrast ΔVcont = Vl - Vdc) between the development voltage Vdc and the post-exposure potential Vl. Then, a primary transfer voltage Vtr, which is a predetermined DC voltage of the opposite polarity to the normal charging polarity of the toner, is applied to the primary transfer roller 14 from a primary transfer voltage power supply 15 (high voltage power supply) as a primary transfer voltage application means. At this time, the potential difference between Vtr and Vl (primary transfer contrast ΔVtr = Vtr - Vl) becomes a primary transfer electric field, and the toner image on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 10.

In this embodiment, the potential settings during image formation are: charging potential Vd = -500V, development voltage Vdc = -300V, post-exposure potential Vl = -100V, and primary transfer voltage Vtr = 200V.

The surface potential of the photosensitive drum 1 was measured using a surface potential meter Model 344 manufactured by Trek.
5. Developer, Toner, and Transfer Carrier Particles Next, the developer, toner, and transfer carrier particles used in this embodiment will be described in detail.

In this embodiment, a mixture of toner and external additive A, which is transfer carrier particles, is used as the developer. Here, the transfer carrier particles refer to fine particles that are present between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1, thereby reducing the adhesive force between the toner image and the photosensitive drum 1 and improving the primary transfer efficiency of the toner image. The toner is toner particles that contain toner base particles containing a release agent and an organosilicon polymer on the surface of the toner base particles.

The organosilicon polymer has a T3 unit structure represented by R-Si(O _1/2 ) ₃ , where R represents an alkyl group or a phenyl group having 1 to 6 carbon atoms, and the organosilicon polymer forms convex portions on the surfaces of the toner base particles.

The protrusions are characterized by being in surface contact with the surface of the toner base particle, and this surface contact is expected to have a significant effect in inhibiting the movement, detachment, and embedding of the protrusions.

The degree of surface contact is explained using the schematic diagrams of the protrusions shown in Figures 7, 8, 9, and 10.

In FIG. 7, 61 is a cross-sectional image of a toner particle in which about 1/4 of the toner particle can be seen, 62 is a toner particle, 63 is the surface of the toner base particle, and 64 is a protrusion. The cross section of a toner particle can be observed using a scanning transmission electron microscope (hereinafter also referred to as STEM) described later.

Observe the cross-sectional image of the toner and draw a line along the periphery of the toner base particle surface. Convert the image into a horizontal image based on the line along the periphery. In the horizontal image, the length of the line along the periphery in the part where the convex portion and the toner base particle form a continuous interface is defined as the convex width w.

The maximum length of the convex portion in the normal direction of the convex width w is the convex diameter D, and the length from the apex of the convex portion to a line along the circumference on the line segment that forms the convex diameter D is the convex height H.

In Figures 8 and 10, the convex diameter D and the convex height H are the same, and in Figure 9, the convex diameter D is greater than the convex height H.

Figure 10 shows a schematic representation of the adhesion state of particles similar to bowl-shaped particles, which are hemispherical particles with a concave center, obtained by crushing or breaking hollow particles.

In Figure 10, the convex width W is the total length of the organosilicon polymer in contact with the toner base particle surface. In other words, the convex width W in Figure 10 is the sum of W1 and W2.

The number average value of the convex height H is 30 nm or more and 300 nm or less, and preferably 30 nm or more and 200 nm or less. When the number average value of the convex height H is 30 nm or more, a spacer effect occurs between the surface of the toner base particle and the transfer member, and the transferability is significantly improved. On the other hand, when the number average value of the convex height H is 300 nm or less, the effect of suppressing movement, detachment, and embedding is significant, and high transferability is maintained even during long-term use. A cumulative distribution of the convex height H is taken for the convex portion having a convex height H of 30 nm or more and 300 nm or less. When the convex height H that corresponds to 80% by number of the smallest convex heights H is H80, H80 is preferably 65 nm or more and 120 nm or less, and more preferably 75 nm or more and 100 nm or less. By setting H80 in the above range, the transferability can be further improved.

The number-average particle size R of the primary particles of the external additive A is preferably 30 nm or more and 1200 nm or less. When R is 30 nm or more, a spacer effect is exerted between the transfer member and the external additive A, and high transferability is exhibited. In addition, the larger R is, the more the transferability tends to improve. On the other hand, when R is more than 1200 nm, the fluidity of the toner decreases, and image unevenness is easily generated.

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

When the number average value of the convex height H is 30 nm, which is the minimum value, if R is 30 nm or more, a spacer effect can be exerted between the transfer member and the convexity, improving transferability. This is thought to be because the external additive A is substituted in places where there are no convexities due to the effects of detachment, etc., exerting the spacer effect. In other words, if R is less than 30 nm, the spacer effect is difficult to exert.

The adhesion rate of external additive A to the toner particle surface is preferably 0% or more and 20% or less, and more preferably 0% or more and 10% or less. When the adhesion rate is in the above range, external additive A can move easily on the surface of the toner particles, and the transferability can be further improved by the protrusion substitution effect. In the fixing process in which the toner is fixed to the fixing member, an appropriate amount of release agent seeps out from the toner base particles, improving the separation performance between the fixing member and the paper.

By observing the surface of the toner with a scanning electron microscope, a reflected electron image of 1.5 μm square of the toner surface is obtained. When an image is obtained by binarizing the reflected electron image so that the organosilicon polymer portion becomes a bright portion, the area ratio of the bright portion area of the image to the total area of the image (hereinafter also simply referred to as the area ratio of the bright portion area) is 30.0% or more and 75.0% or less. In addition, it is preferable that the area ratio of the bright portion area of the image is 35.0% or more and 70.0% or less. The higher the area ratio of the bright portion area, the higher the presence ratio of the organosilicon polymer on the toner mother particle surface. When the area ratio of the bright portion area is higher than 75.0%, the presence ratio of the components derived from the toner mother particle on the toner mother particle surface is low, the exudation of the release agent from the toner mother particle is difficult to occur, and the thin paper is likely to wrap around the fixing device during low-temperature fixing. On the other hand, when the area ratio of the bright portion area of the image is less than 30.0%, the presence ratio of the components derived from the toner mother particle on the toner mother particle surface is high. In other words, the exposed area of the components derived from the toner base particles on the surface of the toner base particles is large, and the transferability is reduced in the initial stage of use. The area ratio of the bright area of the image is hereafter also referred to as the coverage rate of the organosilicon polymer on the surface of the toner base particles.

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

Examples of organic or inorganic fine particles other than silica fine particles include the following.
(1) Fluidity imparting agents: alumina fine particles, titanium oxide fine particles, carbon black and carbon fluoride.
(2) Abrasives: fine particles of metal oxides (fine particles of strontium titanate, cerium oxide, alumina, magnesium oxide, 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, calcium carbonate, etc.).
(3) Lubricants: fine particles of fluororesin (fine particles of vinylidene fluoride, polytetrafluoroethylene, etc.), fine particles of fatty acid metal salts (fine particles of zinc stearate, calcium stearate, etc.).
(4) Charge-controlling fine particles: fine particles of metal oxides (fine particles of tin oxide, titanium oxide, zinc oxide, alumina, etc.), carbon black.

The silica fine particles and the organic or inorganic fine particles may be subjected to a hydrophobic treatment to improve the flowability of the toner and to uniformly charge the toner particles.

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.

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, the silica fine particles are wet silica fine particles obtained by the sol-gel method (hereinafter, also referred to as sol-gel silica).

Figure 11 is an enlarged view of the developer used in this embodiment. As shown in Figure 11, the developer in this embodiment has external additive A, which is a transfer carrier particle, placed on a toner surface on which numerous protrusions of an organosilicon polymer are formed.

The convex spacing G and convex height H on the toner surface shown in Figure 11 can be measured using a scanning transmission electron microscope (hereinafter referred to as STEM), which will be described later. The convex spacing G and convex height H can also be measured with a scanning probe microscope (hereinafter referred to as SPM). A scanning probe microscope (hereinafter referred to as SPM) is equipped with a probe, a cantilever that supports the probe, and a displacement measurement system that detects the bending of the cantilever, and detects the atomic force (attractive or repulsive force) between the probe and the sample to observe the shape of the sample surface.

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

Furthermore, if the convex height H is greater than the particle size of the transfer carrier particles, the convex portion will come into contact with the photosensitive drum 1 before the transfer carrier particles, making it difficult for the transfer carrier particles to come into contact with the photosensitive drum 1, and making it difficult for the transfer carrier particles to transfer from the toner to the photosensitive drum 1. Therefore, it is preferable that the number-average value of the convex height H is smaller than the number-average particle size of the transfer carrier particles.

However, as mentioned above, it is preferable that the adhesive force Ft between the transfer carrier particles and the toner is smaller than the adhesive force Fdr between the transfer carrier particles and the photosensitive drum 1. Therefore, it is preferable to select a material for the transfer carrier particles that reduces the adhesive force Ft of the transfer carrier particles to the toner. For example, as in this embodiment, when the convex portions 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 with a material composition similar to that of the convex portions as the material for the transfer carrier particles, in order to reduce the adhesive force between the convex portions and the transfer carrier particles.

A larger number of transfer carrier particles covering the toner is preferable from the viewpoint of supplying the transfer carrier particles from the developing roller 22 to the photosensitive drum 1. However, adding too many transfer carrier particles increases the risk of contaminating components inside the image forming device 100, so it is preferable to adjust the amount according to the desired primary transferability.

The primary transferability improves with an increase in the coverage of the transfer carrier particles on the photosensitive drum 1, and in order to obtain sufficient primary transferability, it is preferable that the coverage of the transfer carrier particles on the photosensitive drum 1 is 10% or more. However, as the coverage of the transfer carrier particles on the photosensitive drum 1 increases, the degree of improvement in the primary transferability slows down, and the risk of contamination of various members within the image forming apparatus by the transfer carrier particles increases. Therefore, it is preferable to keep the coverage of the transfer carrier particles on the photosensitive drum 1 within 50%.
6. Methods for Measuring Developer Properties Various measuring methods will be described below.

<Method of observing a cross section of a toner using a scanning transmission electron microscope (STEM)>
A cross section of a toner to be observed with a scanning transmission electron microscope (STEM) is prepared as follows.

The procedure for preparing a cross section of a toner is explained below. If organic or inorganic fine particles are added to the toner, the toner from which the organic or inorganic fine particles have been removed using the method described below or similar is used as the sample.

160 g of sucrose (Kishida Chemical) is added to 100 mL of ion-exchanged water, and dissolved in a hot water bath to prepare a concentrated sucrose solution. 31 g of the concentrated sucrose solution and 6 mL of Contaminon N (a 10% aqueous solution of a neutral detergent for cleaning precision measuring instruments, pH 7, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) are placed in a centrifuge tube (50 mL capacity). 1.0 g of toner is added to this, and the toner clumps are loosened with a spatula or the like. The centrifuge tube is shaken at 300 spm (strokes per minute) for 20 minutes in a shaker (AS-1N, sold by AS ONE Corporation). After shaking, the solution is transferred to a glass tube (50 mL) for a swing rotor, and separated in a centrifuge (H-9R, manufactured by Kokusan Co., Ltd.) at 3,500 rpm for 30 minutes. This operation separates the toner particles from the external additives. Visually check that the toner particles and the aqueous solution are sufficiently separated, and collect the toner particles that have separated to the top layer with a spatula or similar. After filtering the collected toner particles with a vacuum filter, dry them in a dryer for at least one hour to obtain a sample for measurement. This operation is carried out multiple times to ensure the required amount.

In addition, whether or not the convex portion contains an organosilicon polymer will be confirmed by combining elemental analysis using energy dispersive X-ray analysis (EDS).

Toner is spread onto a cover glass (Matsunami Glass Co., Ltd., square cover glass; square No. 1) in a single layer, 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 a protective film. 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 so that the toner is in contact with the photocurable resin D800. In this state, light is irradiated to harden the resin, and then the cover glass and tube are removed to form a cylindrical resin with the toner embedded in the outermost surface. Using an ultrasonic ultramicrotome (Leica, UC7), a cutting speed of 0.6 mm/s is used to cut from the outermost surface of the cylindrical resin to the length of the toner radius (for example, 4.0 μm when the weight average particle size (D4) is 8.0 μm) to expose the cross section of the center of the toner.

Next, the toner is cut to a thickness of 100 nm to produce a thin sample of the toner cross section. By cutting in this manner, a cross section of the center of the toner can be obtained.

A JEM-2800 manufactured by JEOL was used as the scanning transmission electron microscope (STEM). The probe size of the STEM was 1 nm, and images were acquired with an image size of 1024 x 1024 pixels. In addition, the contrast of the Detector Control panel for the bright field image was adjusted to 1425, the brightness to 3750, and the contrast of the Image Control panel to 0.0, the brightness to 0.5, and the gamma to 1.00, to acquire the image. The image magnification was 100,000 times, and the image was acquired so that it covered about one-quarter to one-half of the circumference of the cross section of one toner particle, as shown in Figure 11. The obtained STEM image is subjected to image analysis using image processing software (ImageJ (available from https://imagej.nih.gov/ij/)) and the convex portions containing the organosilicon polymer are measured. The measurement is performed on 30 convex portions arbitrarily selected from the STEM image. Whether or not the convex portions contain the organosilicon polymer is confirmed by a combination of elemental analysis using a scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDS). First, a line is drawn along the periphery of the toner base particle using a line drawing tool (select Segmented line in the Strong tab). Parts where the organosilicon polymer convex portions are buried in the toner base particle are connected smoothly with a line, assuming that they are not buried. The image is converted to a horizontal image based on that line (select Selection on the Edit tab, change line width to 500 pixels in properties, then select Selection on the Edit tab and perform Strengthener). In the horizontal image, the following measurements are performed on one of the convex parts containing the organosilicon polymer. The length of the line along the circumference in the part where the convex part and the toner base particle form a continuous interface is defined as the convex width w. The maximum length of the convex part in the normal direction of the convex width w is defined as the convex diameter D, and the length from the apex of the convex part to the line along the circumference in the line segment that forms the convex diameter D is defined as the convex height H. The measurements are performed on 30 arbitrarily selected convex parts, and the arithmetic average of each measurement value is defined as the number average of the convex height H.

<Calculation method of H80>
In the STEM image of the cross section of the toner obtained by the above-mentioned scanning transmission electron microscope (STEM), a cumulative distribution of the convex height H is taken for convex portions having a convex height H of 30 nm or more and 300 nm or less. The convex height H that is integrated from the smallest convex height H and accounts for 80% by number is defined as H80 (unit: nm).

<Method of calculating the area ratio of bright areas in a 1.5 μm square reflected electron image of a toner surface>
The bright area ratio is determined by observing the toner surface using a scanning electron microscope. A backscattered electron image of a 1.5 μm square area of the toner surface is obtained. An image is then obtained by binarizing the backscattered electron image so that the organosilicon polymer portion becomes the bright area, and the ratio of the bright area of the image to the total area of the image is determined. When organic or inorganic fine particles are externally added to the toner, the organic or inorganic fine particles are removed by the following method or the like, and the sample is used.

160 g of sucrose (Kishida Chemical) is added to 100 mL of ion-exchanged water, and dissolved in a hot water bath to prepare a concentrated sucrose solution. 31 g of the concentrated sucrose solution and 6 mL of Contaminon N (a 10% aqueous solution of a neutral detergent for cleaning precision measuring instruments, pH 7, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) are placed in a centrifuge tube (50 mL capacity). 1.0 g of toner is added to this, and the toner clumps are loosened with a spatula or the like. The centrifuge tube is shaken at 300 spm (strokes per minute) for 20 minutes in a shaker (AS-1N, sold by AS ONE Corporation). After shaking, the solution is transferred to a glass tube (50 mL) for a swing rotor, and separated in a centrifuge (H-9R, manufactured by Kokusan Co., Ltd.) at 3,500 rpm for 30 minutes. This operation separates the toner particles from the external additives. Visually check that the toner particles and the aqueous solution are sufficiently separated, and collect the toner particles that have separated to the top layer using a spatula or similar tool. After filtering the collected toner particles with a vacuum filter, dry them in a dryer for at least one hour to obtain a sample for measurement. This operation is repeated multiple times to ensure the required amount.

Whether or not the convex portions contain an organosilicon polymer will be confirmed by combining this with elemental analysis using energy dispersive X-ray analysis (EDS), which will be described later.

The SEM equipment and observation conditions are as follows.
Equipment used: ULTRA PLUS manufactured by Carl Zeiss Microscopy Co., Ltd.
Acceleration voltage: 1.0 kV
WD: 2.0 mm
Aperture Size: 30.0 μm
Detection signal: EsB (energy selective backscattered electrons)
EsB Grid: 800V
Observation magnification: 50,000 times Contrast: 63.0±5.0% (reference value)
Brightness: 38.0±5.0% (reference value)
Resolution: 1024 x 768
Pretreatment: Toner particles are scattered onto carbon tape (no deposition is performed)
The accelerating voltage and EsB Grid are set to achieve the following: obtaining structural information on the outermost surface of the toner particles, preventing charging up of undeposited samples, and selectively detecting high-energy reflected electrons. The observation field is selected to be near the apex where the curvature of the toner particles is smallest. It was confirmed that the bright areas of the reflected electron image were derived from the organosilicon polymer by superimposing the reflected electron image on an element mapping image obtained by energy dispersive X-ray analysis (EDS) that can be obtained by a scanning electron microscope (SEM).

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: 5.0 kV
WD: 7.0 mm
Aperture Size: 30.0 μm
Detection signal: SE2 (secondary electrons)
Observation magnification: 50,000x Mode: Spectral Imaging
Pretreatment: Toner particles are scattered on carbon tape and platinum sputtered. The mapping image of silicon element obtained by this method is superimposed on the above-mentioned reflected electron image, and it is confirmed that the silicon atom parts of the mapping image match the bright parts of the reflected electron image.

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

First, convert the backscattered electron image to 8-bit from Type in the Image menu. Next, set the Median diameter to 2.0 pixels from Filters in the Process menu to reduce image noise. Estimate the image center after excluding the observation condition display section displayed at the bottom of the backscattered electron image, and select a 1.5 μm square range from the center of the backscattered electron image using the Rectangle Tool on the toolbar. Next, select Threshold from Adjust in the Image menu. Select Default, click Auto, and then click Apply to obtain a binarized image. This operation displays the bright areas of the backscattered electron image in white. Again, estimate the image center after excluding the observation condition display section displayed at the bottom of the backscattered electron image, and select a 1.5 μm square range from the center of the backscattered electron image 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 reflected electron image). Also, click List and read the Count value when the brightness is 0 (corresponding to the bright area of the reflected electron image). From this value, calculate the area ratio of the bright area to the total area of the reflected electron image. The above procedure is carried out for 10 fields of view for the toner particles to be evaluated, and the number average value is calculated to obtain the area ratio (%) of the bright area of the image to the total area of the image that has been binarized so that the organosilicon polymer portion in the reflected electron image becomes the bright area.

<Method of Identifying Organosilicon Polymer>
The organosilicon polymer is identified by a combination of observation with a scanning electron microscope (SEM) and elemental analysis by energy dispersive X-ray analysis (EDS).

Using a scanning electron microscope "Hitachi Ultra High Resolution Field Emission Scanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation), the toner is observed in a field of view magnified up to 50,000 times. The surface is observed by focusing on the surface of the toner particle. EDS analysis is performed on the particles present on the surface, and the presence or absence of an Si element peak determines whether the analyzed particles are organosilicon polymers or not. If both organosilicon polymers and silica fine particles are present on the surface of the toner particle, the organosilicon polymer is identified by comparing the ratio of the elemental contents (atomic%) of Si and O (Si/O ratio) with a standard. EDS analysis is performed on the standard specimens of the organosilicon polymer and the silica fine particles under the same conditions to obtain the elemental contents (atomic%) of Si and O. The Si/O ratio of the organosilicon polymer is designated as A, and the Si/O ratio of the silica fine particles is designated as B. Measurement conditions are selected under which A is significantly larger than B. Specifically, 10 measurements are performed on the standard specimen under the same conditions, and the arithmetic mean values of A and B are obtained. Select the measurement conditions that result in an average value of A/B>1.1. If the Si/O ratio of the particle to be identified is on the A side of [(A+B)/2], the particle is determined to be an organosilicon polymer.

Tospearl 120A (Momentive Performance Materials Japan, LLC) is used as a sample of organosilicon polymer particles, and HDK V15 (Asahi Kasei) is used as a sample of silica microparticles.

<Method of measuring number average particle size R of primary particles of external additive>
This is performed in combination with a scanning electron microscope "Hitachi Ultra-High Resolution Field Emission Scanning Electron Microscope S-4800" (Hitachi High-Technologies Corporation) and elemental analysis using energy dispersive X-ray analysis (EDS).

In a field of view magnified up to 50,000 times, the external additive particles are randomly photographed using the EDS elemental analysis method described above. From the photographed image, 100 external additive particles are randomly selected, the major axis of the primary particles of the target external additive particles is measured, and the arithmetic average value is taken as the number-average particle size R. The observation magnification is adjusted appropriately depending on the size of the external additive particles.

<Method for identifying the composition and ratio of constituent compounds of organosilicon polymer>
The composition and ratio of the constituent compounds of the organosilicon polymer contained in the toner are identified using NMR. When the toner contains an external additive such as silica fine particles in addition to the organosilicon polymer, the following procedure is carried out.

1 g of the toner is placed in a vial, dissolved in 31 g of chloroform, and dispersed in the vial by treating with an ultrasonic homogenizer for 30 minutes to prepare a dispersion liquid.
Ultrasonic treatment device: Ultrasonic homogenizer VP-050 (manufactured by Taitec Co., Ltd.)
Microchip: Step type microchip, tip diameter φ2mm
Tip position of the microchip: Center of the glass vial, and 5 mm above the bottom of the vial. Ultrasonic conditions: Intensity 30%, 30 minutes. At this time, ultrasonic waves are applied while cooling the vial with ice water so that the temperature of the dispersion does not rise. The dispersion is transferred to a glass tube for a swing rotor (50 mL) and centrifuged in a centrifuge (H-9R; manufactured by Kokusan Co., Ltd.) at 58.33 S ^-1 for 30 minutes. After centrifugation, the lower layer of the glass tube contains particles with a high specific gravity, such as silica fine particles. 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 abundance ratio of the constituent compounds of the organosilicon polymer and the proportion of the T3 unit structure represented by R-Si(O _1/2 ) ₃ in the organosilicon polymer are measured and calculated by solid-state ²⁹ Si-NMR.

First, the hydrocarbon group represented by R is confirmed by ¹³ C-NMR.
< ^13C -NMR (solid) measurement conditions>
Equipment: JEOL RESONANCE JNM-ECX500II
Sample tube: 3.2 mm diameter
Sample: Sample or organosilicon polymer Measurement temperature: Room temperature Pulse mode: CP/MAS
Measurement nuclear frequency: 123.25MHz ( ^13C )
Reference substance: Adamantane (external standard: 29.5 ppm)
Sample rotation speed: 20 kHz
Contact time: 2 ms
Delay time: 2s
Number of integrations: 1024 times. Using this method, the presence or absence of signals due to methyl groups (Si-CH ₃ ), ethyl groups (Si-C ₂ H ₅ ), propyl groups (Si-C ₃ H ₇ ), butyl groups (Si-C ₄ H ₉ ), pentyl groups (Si-C ₅ H ₁₁ ), hexyl groups (Si-C ₆ H ₁₃ ), or phenyl groups (Si-C ₆ H ₅ -) bonded to silicon atoms is used to confirm the presence or absence of the hydrocarbon group represented by R. On the other hand, in solid-state ²⁹ Si-NMR, peaks are detected in different shift regions depending on the structure of the functional groups bonded to Si in the constituent compounds of the organosilicon polymer. The structure bonded to Si can be identified by identifying the position of each peak using a standard sample. Furthermore, the abundance ratio of each constituent compound can be calculated from the obtained peak area. The ratio of the peak area of the T3 unit structure to the total peak area can be calculated.

The specific measurement conditions for solid-state ^29Si -NMR are as follows.
Apparatus: JNM-ECX5002 (JEOL RESONANCE)
Temperature: Room temperature Measurement method: DDMAS method ²⁹ Si 45°
Sample tube: Zirconia 3.2 mm diameter
Sample: Powdered sample filled in test tube Sample rotation speed: 10 kHz
Relaxation delay: 180s
Scan: 2000
After the measurement, the peaks of a plurality of silane components having different substituents and bonding groups of the sample or organosilicon polymer are separated into the following X1, X2, X3, and X4 structures by curve fitting, and the peak areas of each are calculated.

The following X3 structure is a T3 unit structure.
X1 structure: (Ri) (Rj) (Rk) SiO _1/2 (A1)
X2 structure: (Rg)(Rh)Si(O1 _/2 ) ₂ (A2)
X3 structure: RmSi(O1 _/2 ) ₃ (A3)
X4 structure: Si(O1 _/2 ) ₄ (A4)

In the formulae (A1), (A2) and (A3), Ri, Rj, Rk, Rg, Rh and Rm each represent an organic group such as a hydrocarbon group having 1 to 6 carbon atoms, a halogen atom, a hydroxyl group, an acetoxy group or an alkoxy group, which is bonded to a silicon atom. When it is necessary to confirm the structure in more detail, it may be identified by the results of ¹ H-NMR measurement together with the results of ¹³ C-NMR and ²⁹ Si-NMR measurement.

<Method for quantifying organosilicon polymer or silica fine particles contained in toner>
The toner is dispersed in chloroform as described above, and then centrifugal separation is used to separate the external additives such as the organosilicon polymer and silica fine particles based on the difference in specific gravity to obtain samples, and the content of the external additives such as the organosilicon polymer or silica fine particles is determined.

The following is an example of an external additive that is silica microparticles. Other microparticles can also be quantified using the same method.

First, the pressed toner is measured by fluorescent X-rays, and the silicon content in the toner is determined by performing analytical processing such as the calibration curve method or FP method. Next, the structures of the constituent compounds forming the organosilicon polymer and the silica fine particles are identified using solid-state ^29Si -NMR and pyrolysis GC/MS, and the silicon content in the organosilicon polymer and the silica fine particles is determined. The content of the organosilicon polymer and the silica fine particles in the toner is calculated from the relationship between the silicon content in the toner determined by fluorescent X-rays and the silicon content in the organosilicon polymer and the silica fine particles determined by solid-state ^29Si -NMR and pyrolysis GC/MS.

<Method of measuring the adhesion rate of external additives such as organosilicon polymers or silica fine particles to toner base particles or toner particles by water washing method>
(Water washing process)
20 g of a 30% by weight aqueous solution of "Contaminon N" (a neutral detergent for cleaning precision measuring instruments, consisting of a nonionic surfactant, an anionic surfactant, and an organic builder, with a pH of 7) is weighed out and placed in a 50 mL vial, and mixed with 1 g of toner. The vial is then set in a "KM Shaker" (model: V.SX) manufactured by Iwaki Sangyo Co., Ltd., and shaken for 120 seconds at a speed of 50. Depending on the adhesion state of the organosilicon polymer or silica fine particles, the external additives such as the organosilicon polymer or silica fine particles will migrate from the toner base particles or toner particle surfaces to the dispersion liquid. Thereafter, the toner and the external additives such as the organosilicon polymer or silica fine particles that have migrated to the supernatant liquid are separated using a centrifuge (H-9R; manufactured by Kokusan Co., Ltd.) (16.67 S-1 for 5 minutes). The precipitated toner is dried by vacuum drying (40°C/24 hours) and is used as a toner after washing with water.

Next, a Hitachi ultra-high resolution field emission scanning electron microscope S-4800 (Hitachi High-Technologies Corporation) was used to photograph the toner that was not subjected to the above-mentioned washing process (toner before washing) and the toner obtained through the above-mentioned washing process (toner after washing).

The measurement target is identified by elemental analysis using energy dispersive X-ray analysis (EDS).

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

The image capturing conditions for the S-4800 are as follows.
(1) Sample preparation: Apply a thin layer of conductive paste to a sample stage (aluminum sample stage 15 mm x 6 mm), then spray toner onto the paste. Then, use air to remove excess toner from the sample stage and allow it to dry thoroughly. Set the sample stage in the sample holder, and adjust the sample stage height to 36 mm using the sample height gauge.
(2) Setting the S-4800 observation conditions When measuring the coverage, perform elemental analysis by the energy dispersive X-ray analysis (EDS) described above in advance to distinguish between external additives such as organosilicon polymers or silica fine particles on the toner surface before carrying out the measurement. Pour liquid nitrogen into the anti-contamination trap attached to the S-4800 housing until it overflows, and leave it for 30 minutes. Start the S-4800's "PC-SEM" and perform flushing (cleaning the FE chip, which is the electron source). Click on the accelerating voltage display area on the control panel on the screen, press the [Flushing] button, and open the flushing execution dialog. Check that the flushing intensity is 2 and execute it. Check that the emission current due to flushing is 20 to 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.

Click on the acceleration voltage display to open the HV setting dialog, and set the acceleration voltage to [1.1 kV] and the emission current to [20 μA]. In the [Basic] tab of the operation panel, set the signal selection to [SE], select the SE detector to [Upper (U)] and [+BSE], and select [L.A. 100] in the selection box to the right of [+BSE] to set the mode to observation with backscattered electron images. In the same [Basic] tab of the operation panel, set the probe current in the electron optical system condition block to [Normal], the focus mode to [UHR], and the WD to [4.5 mm]. Press the [ON] button on the acceleration voltage display of the control panel to apply the acceleration voltage.
(3) Calculation of toner number average particle diameter (D1) Drag within the magnification display area of the control panel to set the magnification to 5000 (5k). Rotate the focus knob [COARSE] on the operation panel to adjust the aperture alignment when the image is in focus to a certain extent. Click [Align] on the control panel to display the alignment dialog and select [Beam]. Rotate the STIGMA/ALIGNMENT knobs (X, Y) on the operation panel to move the displayed beam to the center of the concentric circle. Next, select [Aperture] and rotate the STIGMA/ALIGNMENT knobs (X, Y) one by one to stop the image movement or adjust it so that the movement is minimized. Close the aperture dialog and adjust the focus with autofocus. Repeat this operation two more times to adjust the focus.

Thereafter, the particle diameters of 300 toner particles are measured to obtain the number average particle diameter (D1). The particle diameter of each particle is the maximum diameter observed when the toner particles are observed.
(4) Focus Adjustment For the particles obtained in (3) with a number average particle diameter (D1) of ±0.1 μm, align the midpoint of the maximum diameter with the center of the measurement screen, and drag within the magnification display section of the control panel to set the magnification to 10,000 (10k) times.

Rotate the focus knob [COARSE] on the operation panel, and adjust the aperture alignment when the image is in focus to some extent. Click [Align] on the control panel to display the alignment dialog, and select [Beam]. Rotate the STIGMA/ALIGNMENT knobs (X, Y) on the operation panel to move the displayed beam to the center of the concentric circle. Next, select [Aperture], and rotate the STIGMA/ALIGNMENT knobs (X, Y) one by one to stop the image movement or adjust it so that it moves as little as possible. Close the aperture dialog, and adjust the focus with autofocus. Then, set the magnification to 50,000 (50k) times, and adjust the focus using the focus knob and STIGMA/ALIGNMENT knob in the same way as above, and adjust the focus again with autofocus. Repeat this operation to adjust the focus. Here, if the inclination angle of the observation surface is large, the measurement accuracy of the coverage rate is likely to be low, so when adjusting the focus, select an observation surface with as little surface inclination as possible for analysis by selecting one that can simultaneously bring the entire observation surface into focus.
(5) Image storage Adjust the brightness in ABC mode, take a photograph with a size of 640 x 480 pixels, and save it. Use this image file to perform the following analysis. Take one photograph for each toner particle to obtain an image of the toner particles.
(6) Image Analysis The image obtained by the above-mentioned method is binarized using the following analysis software to calculate the coverage. 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 an organosilicon polymer with a particle size of less than 30 nm and more than 300 nm, or silica fine particles with a particle size of less than 30 nm and more than 1200 nm is included in a divided section, the coverage is not calculated for that section.

In the image analysis software Image-Pro Plus 5.0, select "Count/Size" from "Measurement" on the toolbar, then "Options", and set the binarization conditions. Select 8 connectivity in the object extraction options, and set smoothing to 0. In addition, do not select pre-sort, fill holes, or encompass lines, and set "Exclude boundaries" to "None". Select "Measurement item" from "Measurement" on the toolbar, and enter 2 to ¹⁰⁷ as the selection range for area.

The coverage rate is calculated by enclosing a square region. In this case, the area of the region (C) should be between 24,000 and 26,000 pixels. Automatic binarization is performed using "Processing" - Binarization, and the total area (D) of regions free of 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 region and the total area D of regions free of external additives such as organosilicon polymers or silica microparticles.

Coverage rate (%) = 100 - (D / C x 100)
The arithmetic mean value of all the data obtained is taken as the coverage rate.

Then, the coverage of the toner before and after washing is calculated,
[Toner coverage after washing]/[Toner coverage before washing]×100 is defined as the “adhesion rate” in the present invention.
7. Methods for Producing Toner Particles, External Additives, and Developer Next, examples of producing the toner particles, external additive A, and developer of this embodiment will be described.

<Production Example of Toner Particles>
(Preparation of aqueous medium 1)
In a reaction vessel equipped with a stirrer, a thermometer, and a reflux tube, 650.0 parts of ion-exchanged water and 14.0 parts of sodium phosphate (12-hydrate, manufactured by Rasa Kogyo Co., Ltd.) were charged, and the mixture was kept warm at 65 ° C. for 1.0 hours while purging with nitrogen. A calcium chloride aqueous solution in which 9.2 parts of calcium chloride (dihydrate) was dissolved in 10.0 parts of ion-exchanged water was charged all at once using a T.K. homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) while stirring at 15,000 rpm, to prepare an aqueous medium containing a dispersion stabilizer. Furthermore, 10% by mass of hydrochloric acid was charged into the aqueous medium, and the pH was adjusted to 5.0, to obtain aqueous medium 1.

(Preparation of Polymerizable Monomer Composition)
The above materials were put into an attritor (manufactured by Mitsui Miike Chemical Engineering Co., Ltd.), and further dispersed at 220 rpm for 5.0 hours using zirconia particles having a diameter of 1.7 mm, and then the zirconia particles were removed to prepare a colorant dispersion.
Styrene: 20.0 parts n-Butyl acrylate: 20.0 parts Crosslinking agent (divinylbenzene): 0.3 parts Saturated polyester resin: 5.0 parts (polycondensate of propylene oxide modified bisphenol A (2 mole adduct) and terephthalic acid (molar ratio 10:12), glass transition temperature (Tg) 68°C, weight average molecular weight (Mw) 10,000, molecular weight distribution (Mw/Mn) 5.12)
Fischer-Tropsch wax (melting point 78° C.): 7.0 parts This material was added to the colorant dispersion and heated to 65° C., and then dissolved and dispersed uniformly at 500 rpm using a T.K. homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a polymerizable monomer composition.

(Granulation process)
The temperature of the aqueous medium 1 was adjusted to 70° C., and the polymerizable monomer composition was charged into the aqueous medium 1 while maintaining the rotation speed of the T.K. homomixer at 15,000 rpm, and 10.0 parts of t-butyl peroxypivalate as a polymerization initiator was added. Granulation was continued for 10 minutes while maintaining the rotation speed at 15,000 rpm with the stirring device.

(Polymerization process and distillation process)
After the granulation step, the agitator was replaced with a propeller agitator blade, and polymerization was carried out for 5.0 hours while stirring at 150 rpm and maintaining the temperature at 70° C., and then the temperature was raised to 85° C. and maintained at that temperature for 2.0 hours. Thereafter, the reflux tube of the reaction vessel was replaced with a cooling tube, and the obtained slurry was heated to 100° C. to carry out distillation for 6 hours, thereby distilling off the unreacted polymerizable monomer, and a resin particle dispersion was obtained.

(Organosilicon Polymer Formation Step)
In a reaction vessel equipped with a stirrer and a thermometer, 60.0 parts of ion-exchanged water was weighed, and the pH was adjusted to 4.0 using 10% by mass hydrochloric acid. This was heated while stirring, and the temperature was set to 40°C. Then, 40.0 parts of methyltriethoxysilane, an organosilicon compound, was added, and the mixture was stirred for 2 hours or more to carry out hydrolysis. The end point of hydrolysis was confirmed by visual observation that the oil and water were not separated and became one layer, and the mixture was cooled to obtain a hydrolyzed liquid of an organosilicon compound.

After adjusting the temperature of the resin particle dispersion obtained above to 55°C, 25.0 parts of the hydrolyzed liquid of the organosilicon compound (addition amount of organosilicon compound was 10.0 parts) was 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% aqueous sodium bicarbonate solution. With continued stirring at 55°C, the mixture was held for 1.0 hour (condensation reaction 1), after which the pH was adjusted to 9.5 with a 3.0% aqueous sodium bicarbonate solution and held for a further 4.0 hours (condensation reaction 2) to obtain a toner particle dispersion.

(Washing process and drying process)
After the organosilicon polymer formation process was completed, the toner particle dispersion was cooled, and hydrochloric acid was added to the toner particle dispersion to adjust the pH to 1.5 or less, and the mixture was left for 1.0 hour while stirring. Thereafter, the mixture was subjected to solid-liquid separation using a pressure filter to obtain a toner cake. The obtained toner cake was reslurried with ion-exchanged water to form a dispersion again, and then subjected to solid-liquid separation using the aforementioned filter to obtain a toner cake. The obtained toner cake was transferred to a thermostatic chamber at 40°C, and dried and classified for 72 hours to obtain toner particles.

<Production Example of External Additive A>
The external additive A was produced as follows. 150 parts of 5% aqueous ammonia was added to a 1.5 L glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer to prepare an alkaline catalyst solution. After adjusting the alkaline catalyst solution to 50°C, 100 parts of tetraethoxysilane and 50 parts of 5% aqueous ammonia were dropped simultaneously while stirring, and reacted for 8 hours to obtain a silica microparticle dispersion. The obtained silica microparticle dispersion was then dried by spray drying and crushed with a pin mill to obtain silica microparticles with a number average particle size of 100 nm as the external additive A.

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

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

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 height H of the protrusions. When the manufactured developer was observed using an SEM, it was confirmed that external additive A was arranged as transfer carrier particles on the protrusions of the organosilicon polymer of the toner particles, and the average number of external additive A particles coated per toner particle was about 500.

As described above, the developer used in this embodiment is a mixture of toner and transfer carrier particles. The primary transferability improves to a certain extent with an increase in the coverage of the transfer carrier particles occupying the surface of the photosensitive drum 1. However, as the coverage of the transfer carrier particles occupying the surface of the photosensitive drum 1 increases, the degree of improvement in the primary transferability slows down, and the risk of contamination of various members within the image forming apparatus by the transfer carrier particles increases. Therefore, it is preferable to keep the coverage of the transfer carrier particles occupying the surface of the photosensitive drum 1 within 80%.
8. Supply of Transfer Carrier Next, a means for supplying transfer carrier particles onto the photosensitive drum 1 will be described.

As described above, transfer carrier particles are particles that are present between the toner image developed on the photosensitive drum 1 and the photosensitive drum 1, thereby reducing the adhesive force between the toner image and the photosensitive drum 1 and improving the primary transfer efficiency of the toner image.

In this embodiment, before the toner image is developed, transfer carrier particles are supplied to the surface of the photosensitive drum 1 in advance using the toner carried by the developing roller 22. By coating the photosensitive drum 1 with transfer carrier particles in advance, the transfer carrier particles are interposed between the toner image and the photosensitive drum 1.

Figure 12(a) is a schematic diagram of the development nip when the development roller 22 and the photosensitive drum 1 are in contact with each other. As shown in Figure 12(a), in the development nip, the toner carried on the development roller 22 and the photosensitive drum 1 are in contact with each other via the transfer carrier particles. Figure 12(b) is a schematic diagram showing the state after the toner carried on the development roller 22 and the photosensitive drum 1 shown in Figure 12(a) have passed through the development nip. As shown in Figure 12(b), the transfer carrier particles that were interposed between the toner and the photosensitive drum 1 in the development nip are transferred from the surface of the toner carried on the development roller 22 to the surface of the photosensitive drum 1 after passing through the development nip, and are supplied.

As shown in FIG. 12(a), if the adhesive force Ft between the transfer carrier particles and the toner present between the toner and the photosensitive drum 1 in the development nip portion is greater than the adhesive force Fdr between the transfer carrier particles and the photosensitive drum 1, the transfer carrier particles are less likely to be transferred onto the photosensitive drum 1. Therefore, it is preferable that Ft is smaller than Fdr.

Figure 13(a) is a schematic diagram of the primary transfer section when a toner image is carried on the surface of the photosensitive drum 1. Figure 13(b) is a schematic diagram of the state in which the photosensitive drum 1 and intermediate transfer belt 10 are separated after the primary transfer of the toner image shown in Figure 13(a) is completed. If Ft is smaller than Fdr, when the toner image is primarily transferred from the photosensitive drum 1 onto the surface of the intermediate transfer belt 10, only the toner image is primarily transferred onto the intermediate transfer belt 10, and the transfer carrier particles interposed between the toner image and the photosensitive drum 1 remain on the photosensitive drum 1.

Let us consider a case where the transfer carrier particles interposed between the toner image and the photosensitive drum 1 are transferred to the intermediate transfer belt 10 together with the toner image, and the transfer carrier particles are lost from the surface of the photosensitive drum 1. In that case, the transfer carrier particles are not interposed between the toner image developed next on the surface of the photosensitive drum 1 and the photosensitive drum 1, and the adhesive force between the toner image and the photosensitive drum 1 is large, so the primary transferability is reduced.

Therefore, it is preferable that Ft is smaller than Fdr, not only because this makes it easier to supply transfer carrier particles from the toner carried by the developing roller 22 to the photosensitive drum 1, but also from the viewpoint of maintaining the transfer carrier particles coated on the photosensitive drum 1.

Figure 14 is a timing chart of the print operation of the image forming apparatus 100 used in this embodiment. As shown in Figure 14, during image formation operation, the image forming apparatus 100 of this embodiment rotates while the developing roller 22 and the photosensitive drum 1 are in contact with each other before starting to develop toner from the developing roller 22 to the photosensitive drum 1. This provides a timing (transfer carrier supply mode) for supplying transfer carrier particles from the developing roller 22 to the photosensitive drum 1. The transfer carrier supply mode may be executed at any time other than image formation, for example, during a pre-rotation operation performed before an image formation operation or a post-rotation operation performed after an image formation operation.

In order to improve the primary transfer efficiency of the toner image over the entire surface of the photosensitive drum 1, the entire surface of the photosensitive drum 1 is coated with transfer carrier particles before the development of the toner image begins. For this reason, it is preferable to set the time for supplying the transfer carrier particles to the time it takes for the photosensitive drum 1 to rotate one or more revolutions. For this reason, in this embodiment, the length of the transfer carrier particle supply timing shown in FIG. 14 is set to 500 msec, which is approximately the same as the time it takes for the photosensitive drum 1 to rotate one revolution, so that the entire surface of the photosensitive drum 1 can be coated with the transfer carrier particles.

In addition, in this embodiment, at the timing of supplying transfer carrier particles shown in FIG. 14, the surface potential of the photosensitive drum 1 is set to a non-image forming potential Vd = -500 V at which toner charged to the normal polarity is not developed. Therefore, at the timing of supplying transfer carrier particles in this embodiment, toner whose normal polarity is negative is not developed on the surface of the photosensitive drum 1 from the developing roller 22, and only the transfer carrier particles are supplied from the developing roller 22 onto the photosensitive drum 1.

When the transfer carrier particles are supplied from the toner on the developing roller 22 to the photosensitive drum 1 in a state where there is a potential difference between the developing roller 22 and the photosensitive drum 1 as in this embodiment, the following problem occurs. If the particle size of the transfer carrier particles is too large, the transfer carrier particles are easily affected by electrostatic force caused by the potential difference between the developing roller 22 and the photosensitive drum 1. Therefore, it becomes difficult to control the supply of the transfer carrier particles from the toner on the developing roller 22 to the photosensitive drum 1. For example, in a configuration in which the transfer carrier particles are supplied at a non-image forming potential as in this embodiment, when the transfer carrier particles are negatively charged, the transfer carrier particles are attracted to the developing roller 22 side by electrostatic force. Therefore, it becomes difficult to supply the transfer carrier particles from the toner on the developing roller 22 to the photosensitive drum 1. Here, it is preferable that the particle size of the transfer carrier particles is 1000 nm or less, which is less susceptible to electrostatic force. In this embodiment, in order to stably supply the transfer carrier particles from the toner on the developing roller 22 to the surface of the photosensitive drum 1 regardless of the potential difference between the developing roller 22 and the photosensitive drum 1, particles with a particle size of 100 nm are used as the transfer carrier particles.
9. Features and Effects Next, the features of this embodiment are described below. In the adhesive force Ft between the transfer carrier particles and the toner, and the adhesive force Fdr between the transfer carrier particles and the photosensitive drum 1, Ft<Fdr is satisfied. The amount of transfer carrier particles supplied to the photosensitive drum 1 according to the above relationship is controlled as follows. Between at least two process cartridges, the amount of transfer carrier particles supplied to the downstream process cartridge is made greater than the upstream process cartridge in the transport direction of the intermediate transfer body 10. The first embodiment is characterized in that the contact time between the developing roller 22 and the photosensitive drum 1 during the preparation operation accompanying the start-up of the image forming apparatus 100 is changed for each process cartridge. The operation of supplying the transfer carrier particles to the surface of the photosensitive drum 1 is called the transfer carrier supply operation.

The more transfer carrier particles that cover the photosensitive drum 1, the fewer the number of direct contacts between the toner and the photosensitive drum 1, which is preferable from the viewpoint of improving primary transferability. In particular, in order to improve the primary transfer efficiency of high-printing multiple colors, it is preferable for a large number of transfer carrier particles to adhere to the photosensitive drum 1. By using the developer of this embodiment, in the primary transfer process, many transfer carrier particles remain on the photosensitive drum 1 due to the relationship Ft<Fdr. However, if even more transfer carrier particles are adhered to the surface of the photosensitive drum 1, the destination of the transfer carrier particles is determined not by the relationship of adhesion with the photosensitive drum 1, but by the adhesion between the transfer carriers themselves. In other words, the relationship between Ft and Fdr appears to be Ft≧Fdr for some of the transfer carrier particles, and the transfer carrier particles may be transferred to the recording material P after being subjected to primary and secondary transfer together with the toner. In addition, when the toner matrix between the convex portions containing the organosilicon polymer having the partial structure represented by the above-mentioned formula (1) comes into contact with the transfer carrier particles, Ft≧Fdr may be satisfied. Then, some of the transfer carrier particles are primarily transferred and secondarily transferred together with the toner, and move onto the recording material P. In particular, when there are many transfer carrier particles on the photosensitive drum 1, the opportunities for contact with the toner matrix increase, and more of them move onto the recording material P. As a result, when fixing high-density multi-color toner on the recording material, the transfer carrier particles impede the thermal conduction to the toner, causing a problem of poor fixability.

Therefore, in this embodiment, the amount of transfer carrier particles supplied to the photosensitive drum 1 (i.e., the amount of adhesion) is made greater in downstream process cartridges than in upstream process cartridges in the transport direction of the intermediate transfer body 10 between the process cartridges. This reduces the amount of transfer carrier particles transferred onto the recording material P, reducing the impact on fixability, and making it possible to satisfy the primary transferability required for each process cartridge. Since downstream process cartridges need to transfer toner onto the toner layer on the intermediate transfer belt 10 printed by the upstream process cartridge, transfer is more difficult than with upstream process cartridges. Therefore, the more downstream the process cartridge, the more transfer carrier particles are required to improve primary transferability. By supplying transfer carrier particles according to the required transferability, it becomes possible to achieve both primary transferability and fixability.

In this embodiment, the following control is performed to achieve the above-described surface condition of the photosensitive drum 1. During the pre-rotation operation, which is a preparatory operation at the start of the image forming apparatus 100, the contact time of the developing roller 22 of the downstream process cartridge with the photosensitive drum 1 in the transport direction of the intermediate transfer body 10 is made longer than that of the upstream process cartridge. A detailed explanation will be given using FIG. 1.

FIG. 1 is a timing chart of the rotational drive and development contact of the developing roller 22 of each process cartridge during preparatory operations accompanying the start-up of the image forming apparatus 100, and the contact time of the developing roller 22 is represented _by Tpre.

First, the contents common to each process cartridge will be described. In each process cartridge, the development roller 22 starts to rotate after the image forming apparatus 100 is started. During the start-up of the rotation drive, the rotation speed of the motor, which is the photosensitive drum drive unit 110 and the development drive unit 130, is unstable, so the development roller 22 is brought into contact with the photosensitive drum 1 after the rotation of the motor and the rotation of the development roller 22 have stabilized. _Before this development contact time T, the toner layer on the development roller 22 is stabilized. Thereafter, the development roller 22 is separated from the photosensitive drum 1, and the rotation drive of the development roller 22 is terminated.

The contact time T of the developing roller 22 is set to be _longer for the developing roller 22 Sd than for the developing rollers Sa, Sb, and Sc. This allows the adhesion area (amount) of the transfer carrier particles on the photosensitive drum 1 to be greater downstream than upstream in the transport direction of the intermediate transfer belt 10. It is preferable to set the time for the transfer carrier particles to be supplied to a time that is longer than the time it takes for the photosensitive drum 1 to make one revolution. In this embodiment, the transfer carrier particles are supplied by making the contact time T _for Sa, Sb, and Sc of 500 ms (the photosensitive drum 1 makes one revolution or more) and for Sd of 1000 ms (the photosensitive drum 1 makes two revolutions or more).

In this embodiment, during the pre-rotation operation of the image forming apparatus 100, which is the timing for supplying transfer carrier particles, the surface potential of the photosensitive drum 1 is adjusted so that the toner charged to the normal charging polarity is not developed during the _pre- development contact time T. The surface potential of the photosensitive drum 1 during the transfer carrier supply operation is set to a non-image forming potential Vd = -500 V, and the development voltage Vdc applied to the development roller 22 is set to -300 V. Therefore, during the transfer carrier supply operation of this embodiment, the toner is not developed from the development roller 22 onto the photosensitive drum 1, and only the transfer carrier particles are supplied from the development roller 22 onto the photosensitive drum 1.

In this embodiment, the adhesion area ratio is as follows, assuming that the case where transfer carrier particles are attached to the entire surface of the photosensitive drum 1 is 100%. By the transfer carrier supply operation, the adhesion area ratio of transfer carrier particles on the photosensitive drum 1 at Sa, Sb, and Sc is controlled to 15-25%, and the adhesion area ratio at Sd is controlled to about 45%.

The above describes the adhesion area ratio of transfer carrier particles on the photosensitive drum 1. It is desirable that the transfer carrier particles adhere approximately uniformly to the photosensitive drum 1. Even if the adhesion area ratio itself is within the range of values described above, if the particles adhere locally, there will be areas that do not satisfy the desired primary transfer properties, so the adhesion state must be approximately uniform. Therefore, in this embodiment, the Clark-Evans Index (CEI) is used to evaluate the adhesion state as a numerical value. The Clark-Evans Index in this embodiment was in the range of 0.80 to 1.30 at all stations.

When the CEI is less than 1, the distribution is concentrated (high degree of aggregation), when the CEI is equal to 1, the distribution is Poisson (random), and when the CEI is greater than 1, the distribution is regular (distributed at regular intervals). The limit value of the CEI is about 2.1.

In order to achieve the desired primary transferability at any point on the photosensitive drum 1, the Clark-Evans index is preferably 0.60 or more. If it is less than that, localized adhesion occurs, which is undesirable as it reduces the primary transferability in some areas.

The adhesion area rate, adhesion state (Clark Evans Index), measurement method for adhesion, and verification results of adhesion will be described later.
10. Methods for Measuring and Verifying Various Parameters Next, methods for measuring and verifying parameters will be described.
(1) Adhesion area ratio of transfer carrier particles on photosensitive drum 1 The surface of the photosensitive drum 1 was observed under a microscope, and the coverage ratio of the transfer carrier particles on the surface of the photosensitive drum 1 was calculated. Specifically, the surface of the photosensitive drum 1 was observed under a laser microscope (VK-X200, Keyence) at a magnification of 3000 times. The observed image was subjected to binarization processing with a contrast that clearly showed a difference between the transfer carrier particle portion and the other portion, and the total area ratio of the transfer carrier particles on the surface of the photosensitive drum 1 was calculated as the coverage ratio of the transfer carrier particles on the surface of the photosensitive drum 1.
(2) Adhesion state of transfer carrier particles on the photosensitive drum 1 (Clark-Evans index)
The surface of the photosensitive drum 1 was observed under a microscope, and the adhesion state (Clark-Evans index) of the transfer carrier particles on the surface of the photosensitive drum 1 was calculated. Specifically, similarly to (1), the surface of the photosensitive drum 1 was observed under a laser microscope (VK-X200, Keyence) at a magnification of 3000 times. The image to be observed was binarized with a contrast that clearly differentiated the transfer carrier particle portion from the other portion. After calculating the coordinates of each particle in the binarized image, the average r of the closest center-of-gravity distance of all particles was calculated. The Clark-Evans index (CEI) is defined as CEI=r/E(r), where E(r) is the expected value of the closest center-of-gravity distance of particles having a Poisson distribution, and this value was calculated as the Clark-Evans index.
(3) Adhesion force measurement method The adhesion force between the transfer carrier particles and the toner used in this embodiment was measured using an SPM. Specifically, a cantilever was prepared with a transfer carrier particle fixed to the tip of the lever, and the cantilever was pressed against the toner with a predetermined pressure. After that, the force required to detach the cantilever from the toner was measured as the adhesion force Ft between the transfer carrier particles and the toner.

The specified pressure with which the cantilever is pressed against the toner during adhesion measurement is preferably set to the force with which the transfer carrier particles interposed between the toner and the photosensitive drum 1 in the development nip are pressed against the toner. The pressing force was calculated using the calculation method described below. Here, "transfer carrier interposed between the toner and the photosensitive drum 1 in the development nip" refers to a state in which the transfer carrier particles are in contact with both the toner and the photosensitive drum 1 at the same time.

First, the conditions assumed for the calculation will be explained using Figures 15 and 16. Figure 15(a) is a schematic diagram of the development nip portion, and it is assumed that the development roller 22 and the photosensitive drum 1 are in contact with each other through the toner in the development nip portion. Also, Figure 15(b) shows a cross section parallel to the surface of the photosensitive drum 1 at the dotted line AB in Figure 15(a), and it is assumed that the toner in contact with the photosensitive drum 1 is closest packed as shown in the hatched area. Figure 16 is a schematic diagram showing an enlarged contact area between the toner and the photosensitive drum 1 surrounded by the dotted line in Figure 15. As shown in Figure 16, it is assumed that the toner and the photosensitive drum 1 are in contact with each other through the transfer carrier particles. Also, it is assumed that the transfer carrier particles have not yet been supplied to the surface of the photosensitive drum 1, and that there are no transfer carrier particles on the surface of the photosensitive drum 1 in advance.

Based on the above assumptions, the total number N of transfer carrier particles present between the toner and the photosensitive drum 1 in the development nip was calculated as follows. From the calculated N and the contact force F between the development roller 22 and the photosensitive drum 1, F/N, which is the pressing force on the toner per transfer carrier particle in the development section, was calculated, and the calculated F/N was used as the specified pressing force of the cantilever on the toner when measuring the adhesion force.

First, we will explain how to calculate the total number N of transfer carrier particles present between the toner and the photosensitive drum 1 in the development nip.

Figure 17(a) is a schematic diagram showing the contact state of the toner, transfer carrier particles, and photosensitive drum 1 in the development section in two dimensions. As shown in Figure 17(b), if the particle size of the transfer carrier particles is r, when the distance between the photosensitive drum 1 and the toner surface exceeds r, the transfer carrier particles on the toner will hardly contact the photosensitive drum 1. Therefore, the toner circumferential portion where the transfer carrier particles arranged on the toner circumference can contact the photosensitive drum 1 is on an arc connecting A to B. In reality, it is necessary to consider the toner as a sphere as shown in Figure 17(b), and it is necessary to find the ratio of the surface area (shaded area in Figure 17(b)) obtained by integrating the arc AB in the circumferential direction to the toner surface area. The surface area of the shaded area can generally be found as the surface area of a spherical crown, as shown in formula (2). Therefore, the ratio of the toner surface area is as shown in formula (3). The actual value can be calculated from the average particle size R of the toner and the particle size r of the transfer carrier particles.

From the above calculations, the ratio of the arc AB in the configuration of this embodiment to the toner circumference is calculated to be approximately 1.43%.

Therefore, it can be said that the area of the transfer carrier particles between the toner and the photosensitive drum 1 in the development nip portion is approximately 1.43% of the entire toner surface. The number of transfer carrier particles coated on one toner particle is 500. From the above, the number M of transfer carrier particles between the toner and the photosensitive drum 1 per toner particle is calculated as "500 particles x 1.43%", which is approximately 7.2 particles.

Then, multiply the number of transfer carrier particles between the toner and the photosensitive drum 1 per toner particle (7.2) by the total number of toner particles in contact with the photosensitive drum 1 in the development section. Then, the total number N of transfer carrier particles between the toner and the photosensitive drum 1 in the development nip can be calculated.

The total amount of toner L in contact with the photosensitive drum 1 in the development nip can be calculated by (area of the development nip x toner filling rate) / maximum cross-sectional area of the toner.

(Total number of toner particles in contact with the photosensitive drum 1 at the development nip)
= (220 [mm] × 2.0 [mm] × π / √12) / (π × (7.0 / 2) ² )
= approx. 10.37 x ¹⁰⁶ (The closest packing rate of a two-dimensional circle, π/√12 ≒ 0.9069, was used.)
Therefore, the "total number N of transfer carrier particles present between the toner and the photosensitive drum 1 in the development nip" is calculated as follows: The total number N is calculated by multiplying the "total number of toner particles in contact with the photosensitive drum 1 in the development nip" calculated so far by the "number of transfer carrier particles present between the toner and the photosensitive drum 1 per toner particle", and is approximately 7.47 x ¹⁰⁷ particles.

In this embodiment, the pressing force of the developing roller 22 against the photosensitive drum 1 is F=200 gf, so that F/N, which is the "pressing force against the toner per transfer carrier particle in the developing section", is calculated as 26.3 nN. The value of F/N calculated above was adopted as the predetermined pressing force for pressing the cantilever against the toner when measuring the adhesion force by SPM. The adhesion force between the transfer carrier particles and the convex portion of the toner at the predetermined pressure for pressing the cantilever against the toner was 32.8 (nN). Furthermore, the adhesion force between the transfer carrier particles and the photosensitive drum 1 was 210.1 (nN), and the adhesion force between the transfer carrier particles and the base of the toner was 250.7 (nN). In other words, it was confirmed that the adhesion force between the transfer carrier particles and the convex portion of the toner was smaller than the adhesion force between the transfer carrier particles and the photosensitive drum 1, and the adhesion force between the transfer carrier particles and the base of the toner was larger than the adhesion force between the transfer carrier particles and the photosensitive drum 1.
11. Effect Confirmation In order to confirm the effect of this embodiment, the primary transfer property and fixation property of the configuration of this embodiment and the configuration of Comparative Example 1 were verified under the following conditions. An HP Color LaserJet Pro M452dw (product name, HP) was used as the image forming apparatus 100, and CS-680 (product name, Canon Marketing Japan) was used as the recording material P.

The primary transferability was verified by removing the cleaning blade from the process cartridge included with the HP Color LaserJet Pro M452dw. This was to evaluate whether or not an image defect (hereinafter referred to as cleanerless ghost) occurred, in which the primary transfer residual toner could not be completely collected when passing through the developing roller 22 and appears as a ghost image after one revolution of the photosensitive drum 1. The fixability was verified by whether or not an image defect (hereinafter referred to as cold offset), in which the toner was not completely fixed to the recording material P and offset, occurred. Note that in both cases, evaluation was performed using a secondary color solid black image using the cyan (Sc) station and black (Sd) station to simplify the verification.

As described above, in the configuration of Example 1, the adhesion area ratio of transfer carrier particles on the photosensitive drum 1 of Sc, which is the upstream process cartridge relatively to the transport direction of the intermediate transfer belt 10, is 20%. And the adhesion area ratio of transfer carrier particles on the photosensitive drum 1 of Sd, which is the downstream process cartridge, is 45%.

On the other hand, in the configuration of Comparative Example 1, the adhesion area ratio of transfer carrier particles on the photosensitive drum 1 of the upstream process cartridge Sc is 45%, and the adhesion area ratio of transfer carrier particles on the photosensitive drum 1 of the downstream process cartridge Sd is 20%. In Comparative Example 2, the adhesion area ratio of transfer carrier particles on the photosensitive drum 1 of both Sc and Sd is 45%.

Table 2 summarizes the occurrence of cleanerless ghost (primary transferability) and cold offset (fixability) for Example 1 and Comparative Example 1. In the table, OK indicates no image defects, and NG indicates image defects.

In Example 1, as shown in Table 2, the adhesion area ratio of the transfer carrier particles on the photosensitive drum 1 of the downstream process cartridge Sd is higher than the adhesion area ratio of the transfer carrier particles on the photosensitive drum 1 of the upstream process cartridge Sc with respect to the conveying direction of the intermediate transfer belt 10. The upstream process cartridge Sc only needs to perform primary transfer of 100% of the print amount of the cyan single color. Therefore, even if the adhesion area ratio is lower than that of the downstream process cartridge Sd, the cleanerless ghost did not occur and the primary transferability was good. On the other hand, the downstream process cartridge Sd needs to transfer black toner onto the solid black image of cyan already formed on the intermediate transfer belt 10. Therefore, the adhesion area ratio of the downstream process cartridge is higher than that of the upstream process cartridge Sc. As a result, like Sc, the cleanerless ghost did not occur and the primary transferability was good. In addition, in Example 1, with regard to fixability, since the configuration is such that the transfer carrier particles are suppressed from being transferred, cold offset did not occur.

On the other hand, in the configuration of Comparative Example 1, the adhesion area rate of transfer carrier particles on the photosensitive drum 1 of Sd, which is downstream, is lower than the adhesion area rate of transfer carrier particles on the photosensitive drum 1 of Sc, which is upstream, in the transport direction of the intermediate transfer belt 10. First, regarding fixability, since the total adhesion amount is similar to that of Example 1, no cold offset occurred. Also, since Sc, which has a high adhesion area rate of transfer carrier particles, has a higher adhesion area rate than Example 1, no cleanerless ghost occurred and the primary transferability was good. However, since Sd has a lower adhesion area rate than Example 1, it was unable to exhibit sufficient primary transferability, resulting in the occurrence of cleanerless ghost.

In addition, in the configuration of Comparative Example 2, the adhesion area ratio of the transfer carrier particles on the photosensitive drum 1 Sc upstream in the transport direction of the intermediate transfer belt 10 is the same as the adhesion area ratio of the transfer carrier particles on the photosensitive drum 1 Sd downstream. Furthermore, since both adhesion area ratios are 45%, it can be said that this configuration enhances transferability. From the results in Table 2, Comparative Example 2 had no problems with transferability, but cold offset occurred in fixability. This is thought to be due to the transfer of more than the allowable amount of transfer carrier particles to the recording material P, inhibiting fixation.

The configuration of Example 1 has the following characteristics:

The yellow station, which is the first image forming section, has a rotatable first photosensitive drum 1a and a rotatable first developing roller 22a that carries a first developer composed of first toner particles and carrier particles adhering to the surface of the first toner particles. The developing roller 22a contacts the first photosensitive drum 1a to form a first developing section, and supplies the first developer to form a first developer image on the surface of the first photosensitive drum 1a in the first developing section.

The magenta station, which is the second image forming section, has a rotatable second photosensitive drum 1b and a rotatable second developing roller 22b that carries a second developer composed of second toner particles and carrier particles adhering to the surface of the second toner particles. The developing roller 22b contacts the second photosensitive drum 1b to form a second developing section, and supplies the second developer to form a second developer image on the surface of the second photosensitive drum 1b in the second developing section.

The intermediate transfer belt 10 contacts the first photosensitive drum 1a to form a first contact portion, which is a primary transfer portion, and contacts the second photosensitive drum 1b to form a second contact portion, which is a primary transfer portion. The intermediate transfer belt 10 transfers a first developer image at the first contact portion, and a second developer image at the second contact portion.

It has a secondary transfer roller 20 that contacts the intermediate transfer belt 10 to form a secondary transfer section and transfers the first developer image and the second developer image formed on the surface of the intermediate transfer belt 10 to a recording material in the secondary transfer section.

When the first photosensitive drum 1a is rotating, in the first developing section, the carrier particles carried on the surface of the first developing roller 22a can be supplied to the surface of the first photosensitive drum 1. When the second photosensitive drum 1b is rotating, in the second developing section, the carrier particles carried on the surface of the second developing roller 22b can be supplied to the surface of the second photosensitive drum 1b.

The surface of the intermediate transfer belt 10 is movable, and the first image forming unit and the second image forming unit are arranged so that the first contact portion is formed downstream of the secondary transfer unit and upstream of the second contact portion in the direction of movement of the intermediate transfer belt 10.

Let F be the pressure applied by the developing roller 22 against the photosensitive drum 1, and N be the total number of carrier particles between the toner particles and the photosensitive drum 1.

The adhesive force formed between the carrier particles and the toner particles measured when the carrier particles are pressed against the toner particles with F/N, which is the pressing force per unit carrier particle, is defined as Ft. The adhesive force formed between the carrier particles and the photosensitive drum 1 measured when the carrier particles are pressed against the photosensitive drum 1 with F/N is defined as Fdr. In this embodiment, the relationship between Ft and Fdr satisfies Ft≦Fdr.

After the photosensitive drum 1 rotates while the photosensitive drum 1 and the developing roller 22 are in contact with each other, the adhesion area of the carrier particles adhered to the surface of the second photosensitive drum 1b is larger than the adhesion area of the carrier particles adhered to the surface of the first photosensitive drum 1a.

In addition, when the photosensitive drum 1 and the second developing roller 22 are in contact with each other, the distribution of the carrier particles after the photosensitive drum 1 rotates is uniform, and the Clark-Evans index is 0.6 or more.

Therefore, as described above, in the configuration of this embodiment, it is possible to supply a sufficient amount of fine particles to the surface of the photosensitive drum 1 to improve transfer efficiency, while suppressing fixing inhibition caused by the fine particles.

In this embodiment, during the preparatory operation accompanying the start-up of the image forming apparatus, the contact time of the developing roller 22 with the photosensitive drum 1 is longer downstream than upstream in the transport direction of the intermediate transfer belt 10, but this is not limited to the above embodiment. Specifically, the development contact time may be controlled not only during (a) the preparatory operation accompanying the start-up of the image forming apparatus (pre-rotation operation) in this embodiment, but also during (b) the rotation operation before image formation during a print operation and (c) the rotation operation after image formation during a print operation (post-rotation operation). Alternatively, all or a combination of (a), (b), and (c) may be used.

For example, FIG. 18 shows a timing chart of rotation drive and development contact in the case of controlling the development contact time in the rotation operation after image formation during the print operation (c). Specifically, the timing chart shows the rotation drive and development contact of the development roller 22 of the Sc station and the Sd station during the print operation. In each station, the rotation drive of the development roller 22 starts a certain time after receiving the print signal. The development contact starts after the rotation drive of the motor is stabilized, and the toner layer on the development roller 22 is stabilized before the image formation starts ( _before T). After that, the image formation starts and ends (T _{image formation} ). Since the state of the toner layer on the development roller 22 after the image formation differs depending on the image pattern in both the charge amount and the coat amount, the development roller 22 is rotated for a certain time even after the image formation ends in order to return to a uniform state ( _after T). By changing the time of this rotation operation after the image formation, the adhesion state of the transfer carrier particles on the photosensitive drum 1 can be controlled. 18, the time _after T of Sc is set to 500 ms (one revolution or more of the photosensitive drum 1), and the time _after T of Sd is set to 1000 ms (two revolutions or more of the photosensitive drum 1). This makes the amount of transfer carrier particles on the photosensitive drum 1 greater downstream than upstream with respect to the transport direction of the intermediate transfer belt 10. In this way, it is possible to obtain the same effect as in this embodiment.

In this embodiment, the adhesion area ratio of the transfer carrier particles of Sd is higher than that of Sa, Sb, and Sc, but the configuration is not limited to the above embodiment. It is sufficient that the relationship (transfer carrier particle adhesion area ratio of the upstream process cartridge) < (transfer carrier particle adhesion area ratio of the downstream process cartridge) is satisfied between at least two process cartridges among Sa to Sd in accordance with the transfer performance of each color toner alone. The adhesion area ratio of the transfer carrier particles may be gradually increased from upstream to downstream, and may be Sa < Sb < Sc < Sd.

In the configuration of Example 2, the same components and parts as in Example 1 are given the same reference numerals and will not be described again.

The feature of this embodiment is that the amount of transfer carrier particles adhering to the toner is changed for each station. The means for changing the amount of transfer carrier particles adhering to the toner for each station, which is a feature of the second embodiment, and the unique functions and effects of the second embodiment will be described in detail below.
1. Features, Functions and Effects The second embodiment has three features, functions and effects.

The first feature is that, as in Example 1, the transfer carrier particles are supplied to the surface of the photosensitive drum 1 based on the relationship Ft<Fdr, where "adhesion force Ft between the transfer carrier particles and the toner" and "adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1". In this way, the transfer carrier particles can be interposed on the surface of the photosensitive drum 1, and the adhesion force of the toner is reduced by preventing the toner from contacting the photosensitive drum 1. As a result, an effect of improving the primary transferability in the primary transfer process is obtained.

The second feature is that the supply amount (adhesion amount) of transfer carrier is adjusted so that it is greater at downstream stations than at upstream stations in the transport direction of the intermediate transfer belt 10. At downstream stations where high primary transfer performance is required, more transfer carrier particles are supplied than at upstream stations to improve primary transfer performance. On the other hand, at upstream stations where high primary transfer performance is not required, the supply amount of transfer carrier particles is reduced. As a result, the total amount of transfer carrier particles in the toner on the recording material P can be kept to the minimum necessary, which has the effect of reducing the impact of fixation.

The above two features and effects are the same as those in Example 1, so detailed explanations will be omitted.

The third feature is that the means for changing the supply of transfer carrier particles for each station changes the amount of transfer carrier particles attached to the toner for each station. In Example 1, the amount of transfer carrier particles added was adjusted so that the number of transfer carrier particles coated per toner particle of the transfer carrier particles was about 500 regardless of the station. In Example 2, the amount of transfer carrier particles added per toner particle for each station was adjusted so that the number of transfer carrier particles coated per toner particle of the transfer carrier particles was about 300 for the Sa station, 400 for the Sb station, 500 for the Sc station, and 600 for the Sd station, as shown in Table 3 below. At this time, as explained in Example 1, the transfer carrier particles interposed between the toner and the photosensitive drum 1 in the development nip portion account for about 1.43% of the total toner surface. Therefore, the number M of transfer carrier particles interposed between the toner and the photosensitive drum 1 per toner particle is also as shown in Table 3. As a result, the amount of transfer carrier particles supplied to the photosensitive drum 1 can be made greater at the downstream station than at the upstream station in the conveying direction of the intermediate transfer belt 10.

In this embodiment, the timing for executing the transfer carrier supply operation is the development contact time during the print operation, as shown in Figure 19, and is common to each station.

The effect of the third feature of this embodiment will be described below.

In this embodiment, the amount of transfer carrier particles supplied onto the photosensitive drum 1 is greater at downstream stations than at upstream stations in the transport direction of the intermediate transfer belt 10, without changing the supply time of the transfer carrier particles for each station. This makes it possible to minimize the operation time of supplying transfer carrier particles for one printing operation. As a result, it becomes possible to reduce the time required for one printing operation and improve productivity.

As explained above, it is possible to supply a sufficient amount of fine particles to the surface of the photosensitive drum 1 to improve transfer efficiency while suppressing the fixing interference caused by the fine particles.

In Examples 1 and 2, there is no difference in the circumferential speed of the developing roller 22 when it comes into contact with the photosensitive drum 1, but this is not limited to the above examples, and a difference in the circumferential speed of the developing roller 22 relative to the rotation of the photosensitive drum 1 may be provided. Such a difference in circumferential speed has the role of stabilizing the amount of toner to be developed and of hiding minute unevenness in the coat on the developing roller 22 on the photosensitive drum 1, making it difficult to see. In addition, the supply of transfer carrier particles in this embodiment also has the following effects.

Figure 20(a) is a schematic diagram showing the behavior of the toner and transfer carrier particles in the development nip when the developing roller 22 and the photosensitive drum 1 are set to a non-image forming potential relationship. As shown in Figure 20(a), by providing a peripheral speed difference between the developing roller 22 and the photosensitive drum 1, the following phenomenon occurs. The force that the toner interposed between the developing roller 22 and the photosensitive drum 1 receives from the developing roller 22 is parallel to the rotation direction of the developing roller 22. The force that the toner interposed between the developing roller 22 and the photosensitive drum 1 receives from the photosensitive drum 1 is parallel to the rotation direction of the photosensitive drum 1 is f2. In the conditions described in Examples 1, 2, and 3, f1 and f2 were balanced, whereas in the configurations of Examples 1, 2, and 3, the balance between f1 and f2 is lost, and the toner rolls in the development nip. And, as the toner rolls, the transfer carrier particles on the toner that are not in contact with the photosensitive drum 1 also move with the toner rolling. Therefore, by being able to come into contact with the photosensitive drum 1, the opportunity for transfer carrier particles to be supplied from the toner to the surface of the photosensitive drum 1 increases. Therefore, as shown in FIG. 18(b), more transfer carrier particles can be supplied from the toner on the developing roller 22 to the surface of the photosensitive drum 1 after passing through the development nip, even compared to Examples 1, 2, and 3.

21(a) is a schematic diagram showing the behavior of the toner and transfer carrier particles in the development nip when the developing roller 22 and the photosensitive drum 1 are set to an image formation potential relationship. As shown in FIG. 21(a), even when the developing roller 22 and the photosensitive drum 1 are set to an image formation potential relationship, the following phenomenon occurs due to the difference in peripheral speed between the developing roller 22 and the photosensitive drum 1. The toner rolls in the development nip, and the efficiency of supplying the transfer carrier particles from the surface of the toner in the development nip to the surface of the photosensitive drum 1 is improved. Then, as shown in FIG. 21(b), since the developing roller 22 and the photosensitive drum 1 are set to an image formation potential relationship, the toner is developed from the developing roller 22 onto the surface of the photosensitive drum 1 after passing through the development nip. However, since the efficiency of supplying the transfer carrier particles from the surface of the toner to the surface of the photosensitive drum 1 when passing through the development nip is improved, it is possible to interpose a large number of transfer carrier particles between the toner developed on the surface of the photosensitive drum 1 and the photosensitive drum 1.

In view of the above, Example 2 has a first drive unit 110 that drives the photosensitive drum 1, a second drive unit 130 that drives the developing roller 22, and a control unit 200 that controls the first drive unit and the second drive unit. The control unit 200 is characterized by controlling the first drive unit and the second drive unit so that the surface movement speed of the developing roller 22 and the surface movement speed of the photosensitive drum 1 have different surface movement speeds in the developing unit.

In the configuration of Example 3, the same components and parts as in Examples 1 and 2 are designated by the same reference numerals and will not be described again.

The feature of this embodiment is that, while providing a difference in developing peripheral speed, the amount of toner coated on the developing roller 22 after passing the developing blade 23 is changed for each station. In the third embodiment, the mechanism by which the supply amount of the transfer carrier can be controlled and the effects of the third embodiment will be described in detail below.
1. Features and Effects The third embodiment has three features and effects.

The first feature is that, as in Example 1, the transfer carrier particles are supplied to the surface of the photosensitive drum 1 based on the relationship Ft<Fdr, where "adhesion force Ft between the transfer carrier particles and the toner" and "adhesion force Fdr between the transfer carrier particles and the photosensitive drum 1". In this way, the transfer carrier particles can be interposed on the surface of the photosensitive drum 1, and the adhesion force of the toner is reduced by preventing the toner from contacting the photosensitive drum 1. As a result, an effect of improving the primary transferability in the primary transfer process is obtained.

The second feature is that the supply amount (adhesion amount) of transfer carrier is adjusted so that it is greater at downstream stations than at upstream stations in the transport direction of the intermediate transfer belt 10. At downstream stations where high primary transfer performance is required, more transfer carrier particles are supplied than at upstream stations to improve primary transfer performance. On the other hand, at upstream stations where high primary transfer performance is not required, the supply amount of transfer carrier particles is reduced. As a result, the total amount of transfer carrier particles in the toner on the recording material P can be kept to the minimum necessary, achieving the effect of reducing the impact of fixation.

The above two features and effects are the same as those in Examples 1 and 2, so detailed explanations will be omitted.

The third feature is that the amount of toner coated on the surface of the developing roller 22 after passing through the developing blade 23 is changed for each station while providing a difference in developing peripheral speed. The amount of toner coated on the surface of the developing roller 22 is made greater at downstream stations than at upstream stations in the transport direction of the intermediate transfer belt 10. At this time, the supply amount (adhesion amount) of the transfer carrier can be made greater at downstream stations than at upstream stations in the transport direction of the intermediate transfer belt 10.

As described in the second embodiment, when a difference in peripheral speed is provided between the developing roller 22 and the photosensitive drum 1, the following phenomenon occurs. The force that the toner interposed between the developing roller 22 and the photosensitive drum 1 receives from the developing roller 22 is parallel to the rotation direction of the developing roller 22. The force that the toner interposed between the developing roller 22 and the photosensitive drum 1 receives from the photosensitive drum 1 is parallel to the rotation direction of the photosensitive drum 1. The balance between f1 and f2 is lost due to the difference in development peripheral speed, and the toner rolls in the development nip. Then, as the toner rolls, the transfer carrier particles on the toner that are not in contact with the photosensitive drum 1 also move with the toner rolling, and can come into contact with the photosensitive drum 1. Therefore, the opportunity to supply transfer carrier particles from the toner to the photosensitive drum 1 increases. The movement of transfer carrier particles on the toner that is not in contact with the photosensitive drum 1 due to rolling increases according to the amount of toner coated on the developing roller 22. Therefore, by controlling the amount of toner coated on the developing roller 22 while creating a peripheral speed difference between the developing roller 22 and the photosensitive drum 1 to cause the toner to roll, it is possible to control the amount of transfer carrier particles supplied.

In Example 3, the toner amounts on the developing roller 22 from Sa to Sd were adjusted to Sa: 0.28, Sb: 0.30, Sc: 0.32, and Sd: 0.34 [mg/ ^cm2 ], respectively, as shown in Table 4. As an adjustment means, the force with which the developing blade 23 restricts the toner was adjusted by changing the contact position between the developing blade 23 and the developing roller 22. Specifically, as shown in Table 4, the tip of the developing blade 23 was adjusted to be located at positions Sa: 0.70, Sb: 0.60, Sc: 0.50, and Sd: 0.40 [mm] from the center of the developing roller 22, respectively.

In addition, in Example 3, the developing roller 22 rotates in the same direction as the photosensitive drum 1 at the development nip with the photosensitive drum 1, with a peripheral speed ratio of 140% to the photosensitive drum 1. In other words, the moving speed of the surface of the developing roller 22 is 1.4 times faster than the moving speed of the surface of the photosensitive drum 1.

In Example 3, the timing for executing the transfer carrier supply operation is the development contact time during the print operation as shown in FIG. 14, and is common to each station. In addition, regardless of the station, the amount of transfer carrier particles added was adjusted so that the number of transfer carrier particles coated per toner particle was about 500.

Next, the effects of Example 3 will be described.

In the third embodiment, the supply of transfer carrier particles to the surface of the photosensitive drum 1 can be increased at downstream stations relative to the transport direction of the intermediate transfer belt 10, without changing the supply time of the transfer carrier particles for each station. Therefore, the operation time of supplying transfer carrier particles for one printing operation can be minimized. As a result, it is possible to reduce the time required for one printing operation and improve productivity. Furthermore, since the amount of transfer carrier particles added can be reduced, the risk of contamination caused by the transfer carrier particles migrating to parts inside the developing unit (e.g., the developing blade 23 and the supply roller 26) can be reduced.

As explained above, it is possible to supply a sufficient amount of fine particles to the photosensitive drum surface to improve transfer efficiency while suppressing the fixing interference caused by the fine particles.

In addition, in the first, second and third embodiments, four colors, yellow (Y), magenta (M), cyan (C) and black (K), are described, but the present invention is not limited to the above embodiments and may be applied to four or more stations including white toner and metallic toner. In this case, too, it is effective if the relationship (transfer carrier particle adhesion area ratio of the upstream process cartridge) < (transfer carrier particle adhesion area ratio of the downstream process cartridge) is satisfied between at least two process cartridges.

In the first, second and third embodiments, the characteristics are described in terms of the "adhesion area ratio" of the transfer carrier particles. However, if the "adhesion force between transfer carrier particles Fc" is smaller than the "adhesion force between the toner and the transfer carrier Ft" (Fc<Ft), the "adhesion amount" may be used. In other words, the relationship (adhesion amount of transfer carrier particles in the upstream process cartridge) < (adhesion amount of transfer carrier particles in the downstream process cartridge) may be established. In the case of Fc<Ft, no further transfer carrier particles are supplied on top of the transfer carrier particles supplied onto the photosensitive drum 1. Therefore, the transfer carrier particles on the photosensitive drum 1 form a single layer, and the magnitude relationship of the "adhesion area ratio" is synonymous with the magnitude relationship of the "adhesion amount".

Therefore, after the photosensitive drum 1 rotates with the photosensitive drum 1 and the developing roller 22 in contact with each other, the amount of carrier particles adhering to the surface of the second photosensitive drum 1b is greater than the amount of carrier particles adhering to the surface of the first photosensitive drum 1a.

In the first, second and third embodiments, a cleaning member is not provided on the photosensitive drum 1, but a photosensitive drum cleaning member may be provided without being limited to the above embodiments. If a cleaning member is provided on the photosensitive drum 1, the transfer carrier particles coated on the photosensitive drum 1 are collected by the cleaning member every time the photosensitive drum rotates. However, since the transfer carrier particles can be supplied simultaneously with the development, it is sufficient to control the adhesion area (or amount) of the transfer carrier particles on the photosensitive drum 1 from the start of development to the primary transfer. For example, the difference in the peripheral speed of the rotation of the developing roller 22 with respect to the rotation of the photosensitive drum 1 is made larger in the downstream process cartridge than in the upstream process cartridge with respect to the transport direction of the intermediate transfer belt 10. Then, the downstream process cartridge can roll more toner than the upstream process cartridge. As a result, the opportunity to supply the transfer carrier particles to the photosensitive drum 1 downstream in the transport direction of the intermediate transfer belt 10 increases compared to the upstream process cartridge, so that the same state as in the first, second and third embodiments can be achieved, and the same effect as in the first, second and third embodiments can be obtained.

In the first, second and third embodiments, the transfer carrier particles are supplied to the photosensitive drum 1 via the toner in the relationship Ft<Fdr. However, this is not limited to the above embodiments, and a transfer carrier particle supply member may be provided separately from the developing unit 4. In that case, the relationship between the "adhesive force Fs between the transfer carrier particles and the transfer carrier particle supply member" and "Fdr" is set to Fs<Fdr, and the transfer carrier particles are supplied to the photosensitive drum 1. The transfer carrier particle supply member only needs to satisfy this adhesive force relationship. For example, as shown in FIG. 22, a brush member may be used as the transfer carrier supply member to supply the transfer carrier particles onto the photosensitive drum 1. In FIG. 22, the transfer carrier particles are supplied via the transfer carrier particle supply roller 6. The transfer carrier particle supply roller 6 has the role of supplying the transfer carrier particles onto the photosensitive drum 1, and is a brush roller with a brush layer on its surface. The transfer carrier particle supply roller 6 is driven to rotate in the direction opposite to the rotation direction of the photosensitive drum 1, and the transfer carrier is replenished onto the brush from a transfer carrier particle container carrying the transfer carrier particles. Then, at the contact point between the transfer carrier particle supply roller 6 and the photosensitive drum 1, the transfer carrier particles are supplied from the brush onto the photosensitive drum 1.

In Examples 1, 2, and 3, the developing blade 23 uses a SUS plate as the support member, but this is not limited to the above examples, and a thin metal plate such as phosphor bronze or aluminum may also be used. Also, in the above examples, the surface of the support member is coated with a thin film of conductive urethane resin, but this is not limited to the above examples, and a thin film of conductive resin made of polyamide elastomer or urethane rubber may be used. Alternatively, the conductive support member itself may be brought into contact with the developing roller 22 as the developing blade 23.

In Examples 1, 2, and 3, the supply roller 26 and the developing blade 23 are provided with a potential difference of -200V with respect to the developing roller 22 to stabilize the toner charge amount, toner supply amount, and toner coat amount, but this is not limited to the above examples. If the toner charge amount, toner supply amount, and toner coat amount are stable regardless of voltage, there is no need to provide a potential difference. In that case, by setting them at the same potential as the developing roller 22, it is possible to reduce the high-voltage power supply, and to achieve a smaller and less expensive device.

In Examples 1, 2, and 3, the primary transfer performance of each station can be controlled by the adhesion state of the transfer carrier particles. This eliminates the need to change the primary transfer voltage at each station, and makes it possible to share the primary transfer power supply that applies the primary transfer voltage at each station, thereby realizing a smaller, less expensive device.

Even if each station has its own primary transfer power supply, it is possible to set the optimal primary transfer voltage according to the primary transfer characteristics required for each station. This makes it possible to suppress image scattering and retransfer at the primary transfer section. Retransfer refers to the phenomenon in which an image formed at an upstream station is transferred to the intermediate transfer belt 10, discharges as it passes through the primary transfer section of the downstream station, and is then retransferred to the photosensitive drum 1 of the downstream station.

1 Photosensitive drum (photoconductor)
2 Charging roller 3 Exposure unit 4 Development unit 10 Intermediate transfer belt 14 Primary transfer roller 22 Development roller 62 Toner particles 100 Image forming apparatus

Claims (19)

a first image forming section including a rotatable first image carrier and a rotatable first developer carrier carrying a first developer composed of first toner particles and carrier particles adhering to the surfaces of the first toner particles, the first developer carrier coming into contact with the first image carrier to form a first developing section and supplying the first developer to form a first developer image on a surface of the first image carrier in the first developing section;
a second image forming section including a rotatable second image carrier and a rotatable second developer carrier carrying a second developer composed of second toner particles and carrier particles adhering to the surfaces of the second toner particles, the second developer carrier contacting the second image carrier to form a second developing section and supplying the second developer to form a second developer image on the surface of the second image carrier in the second developing section;
an intermediate transfer body that comes into contact with the first image carrier to form a first contact portion and that comes into contact with the second image carrier to form a second contact portion, the first developer image being transferred at the first contact portion and the second developer image being transferred at the second contact portion;
a transfer member that contacts the intermediate transfer body to form a transfer section and transfers the first developer image and the second developer image formed on the surface of the intermediate transfer body to a recording material in the transfer section;
an image forming apparatus capable of supplying the carrier particles carried on a surface of the first developer carrier to a surface of the first image carrier in a first developing section while the first image carrier is rotating, and capable of supplying the carrier particles carried on a surface of the second developer carrier to a surface of the second image carrier in a second developing section while the second image carrier is rotating,
a surface of the intermediate transfer body is movable, and the first image forming unit and the second image forming unit are disposed so that the first contact portion is formed downstream of the transfer unit and upstream of the second contact portion in a moving direction of the surface of the intermediate transfer body;
When a pressing force for pressing the first developer carrier against the first image carrier is F1 and a total number of the carrier particles interposed between the first toner particles and the first image carrier is N1,
an adhesive force Ft1 formed between the carrier particles and the first toner particles, the adhesive force Ft1 being measured when the carrier particles are pressed against the first toner particles with a pressing force F1/N1 per unit carrier particle;
and an adhesive force Fdr1 formed between the carrier particles and the first image carrier, the adhesive force Fdr1 being measured when the carrier particles are pressed against the first image carrier at F1/N1,
Ft1≦Fdr1
The filling,
When a pressing force for pressing the second developer carrier against the second image carrier is F2 and a total number of the carrier particles interposed between the second toner particles and the second image carrier is N2,
an adhesive force Ft2 formed between the carrier particles and the second toner particles, the adhesive force Ft2 being measured when the carrier particles are pressed against the second toner particles with a pressing force F2/N2 per unit carrier particle;
and an adhesive force Fdr2 formed between the carrier particles and the second image carrier, the adhesive force Fdr2 being measured when the carrier particles are pressed against the second image carrier at F2/N2,
Ft2≦Fdr2
The filling,
An image forming apparatus characterized in that, after the first image carrier and the first developer carrier, and the second image carrier and the second developer carrier are respectively in contact with each other and the first image carrier and the second image carrier are respectively rotated, the adhesion area of the carrier particles adhered to the surface of the second image carrier is larger than the adhesion area of the carrier particles adhered to the surface of the first image carrier. 2. The image forming apparatus according to claim 1, wherein the first developer and the second developer have convex portions formed from fine particles containing an organosilicon polymer having a structure represented by the following formula (1), which are present on both the surfaces of the first toner particles and the surfaces of the second toner particles, and the carrier particles are disposed on the convex portions.
R-Si(O1 _/2 ) ₃ (1)
(The above R represents a hydrocarbon group having 1 to 6 carbon atoms.) The image forming apparatus according to claim 1 or 2, characterized in that the first developer remaining on the first image carrier without being transferred to the intermediate transfer body is collected by the first developer carrier, and the second developer remaining on the second image carrier without being transferred to the intermediate transfer body is collected by the second developer carrier. The image forming apparatus according to claim 3, characterized in that the first developer and the second developer are one-component developers. The image forming apparatus according to any one of claims 1 to 4, characterized in that after the first image carrier and the first developer carrier, and the second image carrier and the second developer carrier are in contact with each other and the first image carrier and the second image carrier are rotated, the first distribution of the carrier particles adhering to the surface of the first image carrier on the surface of the first image carrier and the second distribution of the carrier particles adhering to the surface of the second image carrier on the surface of the second image carrier are both in a uniform distribution state. The image forming apparatus according to claim 5, characterized in that the first distribution state and the second distribution state have a Clark-Evans index of 0.6 or more. The image forming apparatus according to any one of claims 1 to 6, characterized in that after the first image carrier and the first developer carrier, and the second image carrier and the second developer carrier are in contact with each other and the first image carrier and the second image carrier are rotated, the amount of carrier particles adhering to the surface of the second image carrier is greater than the amount of carrier particles adhering to the surface of the first image carrier. The image forming apparatus according to any one of claims 1 to 7, capable of executing an image forming mode in which the first developer is developed by the first developer carrier and the second developer is developed by the second developer carrier, and a supply mode in which the carrier particles are supplied from the first developer carrier to the first image carrier and the carrier particles are supplied from the second developer carrier to the second image carrier. a first drive unit that drives the first image carrier;
a second drive unit that drives the first developer carrier;
A control unit that controls the first drive unit and the second drive unit,
9. The image forming apparatus according to claim 8, wherein the control unit controls the first drive unit and the second drive unit so that a surface movement speed of the first developer carrier and a surface movement speed of the first image carrier are different in the first developing unit. The image forming apparatus according to claim 9, characterized in that in the supply mode, the first drive unit is controlled so as to rotate the first image carrier and the second image carrier one or more revolutions. The image forming apparatus according to claim 9 or 10, characterized in that in the supply mode, the first drive unit and the second drive unit are controlled so that the rotation time of the second image carrier is longer than the rotation time of the first image carrier. The image forming apparatus according to any one of claims 8 to 11, characterized in that the supply mode is performed during a pre-rotation operation performed before the image forming mode. The image forming apparatus according to any one of claims 8 to 12, characterized in that the supply mode is performed during a post-rotation operation performed after the image forming mode. The image forming apparatus according to any one of claims 1 to 13, characterized in that the amount of carrier particles adhering to the surface of the second toner particles is greater than the amount of carrier particles adhering to the surface of the first toner particles. The image forming device according to claim 2, characterized in that, when the closest distance between adjacent convex portions is defined as a convex interval G, the average of the convex interval G is equal to or smaller than the average particle size of the carrier particles. The image forming apparatus according to claim 2, characterized in that, when the height of the convex portion from the surface of the first toner particle is defined as a convex height H, the average of the convex height H is equal to or less than the average particle size of the carrier particles. The image forming apparatus according to any one of claims 1 to 16, characterized in that the carrier particles are silica. The image forming apparatus according to any one of claims 1 to 17, characterized in that the carrier particles are organic silica polymers. The image forming apparatus according to any one of claims 1 to 18, characterized in that the average particle size of the carrier particles is 30 nm or more and 1000 nm or less.

Images