Image forming device

Abstract

To provide an image forming apparatus in which a plurality of image carrier units can be integrally replaced, and to reduce a difference in residual film thickness of a surface layer between image carriers to extend the entire life of the plurality of units that can be integrally replaced.SOLUTION: An image forming apparatus 1 has a belt 12 that sandwiches and conveys a recording material S between a first image carrier 4Y and a second image carrier 4M at a first transfer unit NY and a second transfer unit NM. In the direction of movement of the recording material S, a first image forming unit PY is arranged upstream of a second image forming unit PM. A plurality of members including the first image carrier 4Y and the second image carrier 4M can be integrally mounted on an apparatus body 2 of the image forming apparatus 1. The film thickness of a surface layer of the first image carrier 4Y is larger than the film thickness of a surface layer of the second image carrier 4M.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus, such as a printer, a copying machine, or a facsimile machine, that uses an electrophotographic method. [Background technology]

[0002] Conventionally, there is an image forming apparatus using an electrophotographic method, which transfers toner images formed on a plurality of image carriers such as photosensitive drums to a recording material carried and transported by a recording material carrier to form an image on the recording material. In this image forming apparatus, a charging member for charging the image carrier, a developing device for supplying toner as a developer to the image carrier to form a toner image, and a transfer member for transferring the toner image from the image carrier to the recording material are provided for each image carrier. A transfer belt made of an endless belt is often used as the recording material carrier. Then, toner images are sequentially transferred from a plurality of image carriers arranged in a line along the moving direction of the recording material by the recording material carrier onto the recording material that is electrostatically attracted to the transfer belt and transported. As the transfer member, a transfer roller or the like arranged on the opposite side of the image carrier across the transfer belt is used, and the toner image is transferred by applying a transfer voltage to the transfer member.

[0003] Moreover, the image forming apparatus as described above is provided with a cleaning means for removing the toner (transfer residual toner) remaining on the image carrier without being transferred to the recording material from the image carrier. The following cleaning means are known. A cleaning roller is provided as a cleaning member that contacts the image carrier, and during image formation, the transfer residual toner is caused to adhere to the cleaning roller and temporarily collected. This prevents the transfer residual toner from affecting the next image formation process and causing image defects. In addition, the transfer residual toner temporarily collected by the cleaning roller is discharged from the cleaning roller onto the image carrier at a predetermined timing during non-image formation. Then, the transfer residual toner discharged onto the image carrier is collected into a developing device. The toner collected into the developing device is reused to develop a toner image.

[0004] Furthermore, when the recording material comes into contact with the image carrier, foreign matter generated from the recording material is transferred onto the image carrier. This foreign matter is mainly the fibers and fillers that form the paper (so-called "paper dust"), or dust that adheres to the recording material. If such foreign matter adheres to the image carrier, it may affect the subsequent image formation process, resulting in image defects.

[0005] Patent Document 1 discloses a configuration in which a foreign matter recovery member that attracts and recovers foreign matter from the cleaning roller is provided only for the most upstream image carrier in the direction of movement of the recording material, which is the most affected by foreign matter. In this configuration, foreign matter that has moved to the most upstream image carrier during image formation is recovered by the cleaning roller during non-image formation, and is further recovered by the foreign matter recovery member and stored in a storage section.

[0006] Here, in an electrophotographic image forming apparatus, an image carrier unit equipped with an image carrier may be detachable from the main body of the image forming apparatus and may be replaceable by an operator such as a user or a service representative. Furthermore, in order to improve operability for the operator, there may be a configuration in which a plurality of image carrier units are integrated and replaceable. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2010-165000 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, it was found that conventional image forming apparatuses as described above had a problem in that the amount of wear on the image carrier located most upstream in the direction of movement of the recording material was greater than the amount of wear on image carriers other than the most upstream image carrier.

[0009] The reason why the amount of wear on the most upstream image carrier is large is that the recording material comes into contact with the most upstream image carrier first when forming an image. Most of the foreign matter contained in the recording material and easily moves to the image carrier is collected on the most upstream image carrier. Furthermore, the foreign matter collected on the most upstream image carrier is interposed between the image carrier and the cleaning roller, or between the image carrier and the developer carrier of the developing device, and rubs against the image carrier. This causes the amount of wear on the most upstream image carrier to be large.

[0010] One of the factors that determine the lifespan of an image carrier is the occurrence of vertical streak images (streak-like images extending along the moving direction of the surface of the image carrier) caused by the remaining film thickness of the surface layer of the image carrier decreasing beyond a predetermined value. Therefore, when the same image carrier is used as multiple image carriers, only the most upstream image carrier will reach the end of its life earlier than the image carriers other than the most upstream image carrier.

[0011] In particular, in a configuration in which a plurality of image carrier units, including a most upstream image carrier unit equipped with the most upstream image carrier, are integrated into one replaceable part, the problem becomes more pronounced if the most upstream image carrier is significantly worn down, because in this case, the overall lifespan of the integrated plurality of image carrier units is determined by the lifespan of the most upstream image carrier unit.

[0012] Therefore, the present invention aims to extend the overall life of multiple integrated and replaceable units in an image forming device in which multiple image carrier units are integrated and replaceable, by reducing the difference in remaining film thickness of the surface layer between each image carrier. [Means for solving the problem]

[0013] The above object is achieved by the image forming apparatus according to the present invention. In summary, a typical configuration of the present invention is an image forming apparatus capable of performing an image forming operation for forming an image on a recording material, the image forming apparatus comprising a first image forming section including a first image carrier that is rotatable and has a photosensitive layer, a first charging member that charges the surface of the first image carrier, a first developing device that supplies a first developer to the surface of the first image carrier, a first transfer member that transfers the first developer supplied to the surface of the first image carrier to the recording material, a first cleaning member that comes into contact with the first image carrier to clean the surface of the first image carrier, and a recovery member that recovers foreign matter adhering to the first cleaning member, a second image carrier that is rotatable and has a photosensitive layer, a second charging member that charges the surface of the second image carrier, a second developing device that supplies a second developer to the surface of the second image carrier, and a first image forming section including a second image carrier that is rotatable and has a photosensitive layer, a first charging member that charges the surface of the second image carrier, a first developing device that supplies a second developer to the surface of the second image carrier, and a first transfer member that transfers the first developer supplied to the surface of the first image carrier to the recording material, a first cleaning member that comes into contact with the first image carrier to clean the surface of the first image carrier, and a recovery member that recovers foreign matter adhering to the first cleaning member. a second image forming section including a second transfer member that transfers the second developer supplied to a surface thereof onto a recording material, and a second cleaning member that comes into contact with the second image carrier to clean the surface of the second image carrier; and a belt that comes into contact with the first image carrier to form a first transfer section and comes into contact with the second image carrier to form a second transfer section, the belt nipping and conveying the recording material between the first image carrier and the second image carrier in the first transfer section and the second transfer section, respectively, the first image forming section being disposed upstream of the second image forming section in a moving direction of the recording material, a plurality of members including the first image carrier and the second image carrier being integrated and detachable from a main body of the image forming apparatus, and the film thickness of the surface layer of the first image carrier being larger than the film thickness of the surface layer of the second image carrier. The first developer is yellow and the second developer is black. The image forming apparatus is characterized in that: Effect of the Invention

[0014] According to the present invention, in an image forming device in which multiple image carrier units are integrated and replaceable, the overall life of the multiple integrated and replaceable units can be extended by reducing the difference in remaining film thickness of the surface layer between each image carrier. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic cross-sectional view of an image forming apparatus. [Diagram 2] 2 is a schematic cross-sectional view of the drum unit and the developing cartridge. [Diagram 3] FIG. 2 is a schematic block diagram for explaining a control mode of the image forming apparatus. [Figure 4] 5A and 5B are schematic diagrams for explaining collection of transfer residual toner and foreign matter. [Diagram 5] FIG. 2 is a schematic diagram illustrating an example of a layer structure of a photosensitive drum. [Figure 6] FIG. 2 is a schematic diagram illustrating an example of a driving configuration of a developing device. [Figure 7] 5A and 5B are schematic diagrams illustrating an example of a configuration for determining a contact pressure of a developing roller. [Figure 8] FIG. 2 is a schematic diagram of a developer containing a metal soap. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, the image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

[0017] [Example 1] <Configuration of Image Forming Apparatus> 1 is a schematic cross-sectional view of an image forming apparatus 1 according to this embodiment. The image forming apparatus 1 according to this embodiment is a color laser printer that uses an electrophotographic image forming process, and can form a color image on a recording material S according to image information from an external device such as a personal computer.

[0018] The image forming apparatus 1 has four image forming units (stations) PY, PM, PC, and PK that form images of the colors yellow (Y), magenta (M), cyan (C), and black (K), respectively. Elements having the same or corresponding functions or configurations in the four image forming units PY, PM, PC, and PK may be generally described by omitting the Y, M, C, or K at the end of the reference numerals indicating that the element is for one of the colors.

[0019] In this embodiment, each image forming station P has a photosensitive drum 4, which is a drum-type (cylindrical) photosensitive member (electrophotographic photosensitive member) as a rotatable image carrier, a charging device (charging member) 5 (FIG. 2) as a charging means, and a developing device 8 as a developing means. Also, each image forming station P has a transfer roller 16, which is a roller-type transfer member as a transfer means, a discharging light source 31 (FIG. 2) as a discharging means, and a cleaning mechanism 36 (FIG. 2) as a cleaning means. The four image forming stations PY, PM, PC, and PK are arranged in a line along the moving direction of the recording material S by the transfer belt 12 described later (here, simply referred to as the "moving direction of the recording material S"). Also, in this embodiment, the exposure device 10 used as an exposure means in each image forming station P is configured as one unit. Also, in this embodiment, in each image forming station P, the drum unit 30 having the photosensitive drum 4 and the developing device (developing cartridge, developing unit) 8 are each a replaceable unit as a consumable item.

[0020] FIG. 2 is a schematic cross-sectional view showing the drum unit 30 and the developing cartridge 8. FIG. 2(a) shows the drum unit 30Y and the developing cartridge 8Y of the image forming portion PY, which is the most upstream in the moving direction of the recording material S. FIG. 2(b) shows the drum units 30M, 30C, 30K and the developing cartridges 8M, 8C, 8K of the image forming portions PM, PC, PK, which are downstream (here, simply referred to as the "downstream side") of the most upstream image forming portion PY, in the moving direction of the recording material S. That is, FIG. 2(b) shows the drum units 30M, 30C, 30K and the developing cartridges 8M, 8C, 8K of the image forming portions PM, PC, PK other than the most upstream image forming portion PY in the moving direction of the recording material S, among the multiple image forming portions P provided in the image forming apparatus 1. Note that, with respect to the multiple image forming portions P or their elements, "upstream" and "downstream" refer to the upstream and downstream in the moving direction of the recording material S. 2(a) and 2(b), in this embodiment, the configuration of the cleaning mechanism 36 is different between the most upstream drum unit 30Y and the downstream drum units 30M, 30C, and 30K. The configurations and operations of the drum unit 30 and the developing cartridge 8 will be described in detail later.

[0021] A cartridge tray 3 is detachably provided in an apparatus main body 2 of the image forming apparatus 1. The drum unit 30 and the developing cartridge 8 are each configured to be detachably attached to the cartridge tray 3. The apparatus main body 2 also includes an exposure device 10, an electrostatic transfer device 11, a paper feed unit 18, a fixing device 21, a discharge unit 22, and a front door 40.

[0022] The exposure device 10 is provided above the drum unit 30 and the developing cartridge 8 mounted on the cartridge tray 3, and outputs laser light L corresponding to image information. The exposure device 10 scans and exposes the surfaces of the four photosensitive drums 4Y, 4M, 4C, and 4K with the laser light L.

[0023] The electrostatic transfer device 11 is provided below the drum unit 30 and the developing cartridge 8 mounted on the cartridge tray 3. The electrostatic transfer device 11 has a transfer belt 12, which is an endless belt serving as a recording material carrier, so as to come into contact with the four photosensitive drums 4Y, 4M, 4C, and 4K. The transfer belt 12 is made of a film-like material such as a resin film or a multi-layer film having a resin layer provided on a rubber base layer. The transfer belt 12 is stretched over a driving roller 13 and a driven roller 14 serving as a plurality of tension rollers (support rollers) and stretched with a predetermined tension. The transfer belt 12 electrostatically attracts a sheet-like recording material (recording medium, transfer material, sheet) S such as paper to the outer peripheral surface on the upper side in FIG. 1, and circulates so as to bring the recording material S into contact with the four photosensitive drums 4Y, 4M, 4C, and 4K in sequence. Four transfer rollers 16Y, 16M, 16C, and 16K are arranged on the inner peripheral surface side of the transfer belt 12, corresponding to the four photosensitive drums 4Y, 4M, 4C, and 4K, respectively. In this embodiment, the transfer rollers 16 are arranged facing the corresponding photosensitive drums 4 via the transfer belt 12, and abut against the photosensitive drums 4 via the transfer belt 12. As a result, transfer portions NY, NM, NC, and NK are formed where the photosensitive drums 4Y, 4M, 4C, and 4K come into contact with the transfer belt 12. In this way, the transfer belt 12 comes into contact with each photosensitive drum 4 to form a transfer portion N, and the recording material S is sandwiched and conveyed between the transfer belt 12 and the photosensitive drum 4 at each transfer portion N. During transfer, a predetermined transfer voltage (transfer bias) is applied to each transfer roller 16, and an electric charge is applied to the recording material S via the transfer belt 12. The toner image on the photosensitive drum 4 is transferred to the recording material S in contact with the photosensitive drum 4 by the electric field generated at this time. In this embodiment, the transfer roller 16 is configured by coating a roller shaft (core shaft) made of metal or the like with a sponge layer made of a sponge material (such as a foamed rubber material such as foamed polyurethane) as an elastic layer.

[0024] The paper feed unit 18 is provided below the electrostatic transfer device 11. The paper feed unit 18 has a paper feed tray 19 as a recording material storage section in which the recording material S is stacked and stored, a paper feed roller 20 as a transport member, and the like.

[0025] The fixing device 21 and the discharge unit 22 are provided above the electrostatic transfer device 11. The fixing device 21 fixes the toner image transferred onto the recording material S onto the recording material S. The discharge unit 22 discharges the recording material S that has passed through the fixing device 21 onto a discharge tray 23.

[0026] The cartridge tray 3 has a detachable drum unit 30 provided with a photosensitive drum 4 corresponding to each of the four developing cartridges 8. In this embodiment, the four drum units 30Y, 30M, 30C, and 30K are integrated with the cartridge tray 3 and are a single replaceable part.

[0027] In this embodiment, the apparatus main body 2 corresponds to a portion of the image forming apparatus 1 excluding the cartridge tray 3, the drum unit 30, and the developing cartridges 8.

[0028] As shown in Figs. 2(a) and (b), the drum unit 30 includes a charging device 5, a static electricity removing light source 31, and a cleaning mechanism 36. As shown in Fig. 2(a), the most upstream drum unit 30Y includes a first cleaning mechanism 36a as the cleaning mechanism 36. The first cleaning mechanism 36a includes a cleaning roller 32 as a cleaning member for cleaning the surface of the photosensitive drum 4, and a foreign matter recovery roller 33 as a foreign matter recovery member for recovering foreign matter adhering to the cleaning member 32. The first cleaning mechanism 36a also includes a scraping member 34 as a foreign matter removal member, and a foreign matter recovery container 35 as a storage section. As shown in Fig. 2(b), the downstream drum units 30M, 30C, and 30K include a second cleaning mechanism 36b as the cleaning mechanism 36. The second cleaning mechanism 36b includes a cleaning roller 32 as a cleaning member. In this embodiment, the second cleaning mechanism 36b does not have the foreign matter collection roller 33, scraping member 34, and foreign matter collection container 35 that the first cleaning mechanism 36a has. In this embodiment, in the first cleaning mechanism 36a, the cleaning roller 32 is connected to a cleaning power supply E4 (FIG. 3), and the foreign matter collection roller 33 is connected to a collection power supply E5 (FIG. 3). In the second cleaning mechanism 36b, the cleaning roller 32 is connected to the cleaning power supply E4 (FIG. 3).

[0029] As shown in FIGS. 2(a) and 2(b), the developing cartridge 8 has a developing frame (developing container) 28 that contains toner T as a developer, and a developing roller 6 that is a rotatable developer carrier carrying toner T on its surface. The developing cartridge 8 also has a supply roller 26 as a developer supply member that supplies toner T to the developing roller 6, and a regulating blade 60 as a developer regulating member that contacts the surface of the developing roller 6 to regulate the layer thickness of the toner T carried on the surface of the developing roller 6. The developing cartridge 8 also has a rotatable stirring shaft 50 and a stirring sheet 51 fixed to the stirring shaft 50 as stirring and transporting members for stirring and transporting the toner T in the developing frame 28. In this embodiment, the toner T is a non-magnetic one-component developer.

[0030] <Image formation process> Next, an image forming process in the image forming apparatus 1 of this embodiment will be described with reference to FIGS.

[0031] During the image forming process, the photosensitive drum 4 is rotated in the direction of arrow D (clockwise direction) in FIGS. 1 and 2 at a predetermined peripheral speed by a driving motor (not shown) as a driving means. The transfer belt 12 of the electrostatic transfer device 11 rotates (circulates) in the direction of arrow F (counterclockwise direction) in FIG. 1 at a peripheral speed corresponding to the peripheral speed of the photosensitive drum 4 by the driving roller 13 being rotated by a driving motor (not shown) as a driving means. The surface of the rotating photosensitive drum 4 is uniformly charged to a predetermined potential of a predetermined polarity (positive polarity in this embodiment) by the charging device 5. During the charging process, a predetermined charging voltage (charging bias) is applied to the charging device 5 by a charging power source E1 (FIG. 3) as a charging voltage application unit. In this embodiment, the charging power source E1 applies a positive DC voltage as the charging voltage to the charging device 5. The charged surface of the photosensitive drum 4 is scanned and exposed by the exposure device 10 with laser light L output according to the image signals of each color, and an electrostatic latent image (electrostatic image) according to the image signals of each color is formed on the photosensitive drum 4. In this embodiment, the laser light L is irradiated onto the image area (printed area, image area) on the photosensitive drum 4, which has been uniformly charged and on which a potential (non-image area potential, dark area potential) has been formed in the non-image area (non-printed area, non-image area). As a result, the absolute value of the potential at the location irradiated with the laser light L decreases, and a potential (image area potential, light area potential) is formed in the image area.

[0032] The electrostatic latent image formed on the photosensitive drum 4 is developed (visualized) by supplying toner from the developing cartridge 8, and a toner image (developer image) corresponding to the image signal of each color is formed on the photosensitive drum 4. The toner T in the developing frame 28 is circulated in the developing frame 28 by the stirring sheet 51 fixed to the stirring shaft 50 and conveyed to the supply roller 26. The supply roller 26 supplies the toner T to the developing roller 6. The developing roller 6 is configured by coating a rubber layer formed of a rubber material as an elastic layer around a roller shaft (core shaft) formed of metal or the like. For the rubber layer, for example, a solid rubber member or a sponge member having elasticity is used. In this embodiment, the developing roller 6 abuts against the photosensitive drum 4. The supply roller 26 is configured by coating a sponge layer formed of a sponge material (foamed rubber material such as polyurethane foam) as an elastic layer around a roller shaft (core shaft) formed of metal or the like. In this embodiment, the supply roller 26 abuts against the developing roller 6. The developing roller 6 is rotated in the direction of the arrow E in FIG. 2 (counterclockwise direction) at a predetermined peripheral speed. That is, the developing roller 6 rotates so that the photosensitive drum 4 and the developing roller 6 move in the forward direction at the contact portion between the photosensitive drum 4 and the developing roller 6. In this embodiment, the developing roller 6 is rotated by branching and transmitting the driving force from a driving motor (not shown) that drives the photosensitive drum 4. Note that a driving means for rotating the photosensitive drum 4 and a driving means for rotating the developing roller 6 may be provided separately. The developing roller 6 may be rotated with a peripheral speed difference with respect to the photosensitive drum 4 (for example, the developing roller 6 is faster), or may be rotated at the same peripheral speed as the photosensitive drum 4. The toner T supplied to the developing roller 6 enters between the developing roller 6 and the regulating blade 60 and is carried on the developing roller 6 as a thin layer of a certain thickness. The toner T is charged to a predetermined polarity (positive polarity in this embodiment) by frictional charging between the regulating blade 60 and the developing roller 6 or between the supply roller 26 and the developing roller 6. That is, in this embodiment, the normal charging polarity of the toner T during development ("normal polarity") is positive. The regulating blade 60 is configured by bonding a resin member to a metal plate made of stainless steel or the like.Depending on the shape and material of the resin member, it is possible to control the pressure and the amount of frictional charge applied to the toner T that has entered between the developing roller 6 and the regulating blade 60. Silicone rubber or urethane rubber is used as the resin member.

[0033] The toner T carried on the developing roller 6 and positively charged is supplied to the electrostatic latent image formed on the photosensitive drum 4 by the direct contact of the developing roller 6 with the photosensitive drum 4. As a result, the toner T adheres to the image portion of the electrostatic latent image, and a toner image is formed on the photosensitive drum 4. During development, a predetermined development voltage (development bias) is applied to the developing roller 6 by a developing power source E2 (FIG. 3) as a developing voltage application unit. In this embodiment, the developing power source E2 applies a positive DC voltage as the development voltage to the developing roller 6. The development voltage is set to a potential between the image portion potential and the non-image portion potential on the photosensitive drum 4. That is, the potential of the electrostatic latent image formed on the photosensitive drum 4 has a larger absolute value than the voltage applied to the developing roller 6 in the non-image portion where the toner T does not adhere (where no image is formed). On the other hand, the potential of the electrostatic latent image formed on the photosensitive drum 4 has a smaller absolute value than the voltage applied to the developing roller 6 in the image portion where the toner T adheres (where an image is formed). With this setting, the toner T, which is positively charged, moves from the developing roller 6 to the image portion of the electrostatic latent image formed on the photosensitive drum 4. In this manner, in this embodiment, the toner T, which is charged with the same polarity as the charging polarity of the photosensitive drum 4 (positive polarity in this embodiment), adheres to the exposed portion (image portion) on the photosensitive drum 4, which has been uniformly charged and then exposed to light, thereby decreasing the absolute value of the potential (reverse development).

[0034] In this embodiment, the peripheral speed of all four photosensitive drums 4 is 100 mm / sec. Also, in this embodiment, the peripheral speed of all four developing rollers 6 is 150 mm / sec. In this embodiment, the peripheral speed of each developing roller 6 is set faster than the peripheral speed of each photosensitive drum 4. In this embodiment, the peripheral speed of each developing roller 6 is set faster than the peripheral speed of each photosensitive drum 4, and the amount of toner T moving from the developing roller 6 to the photosensitive drum 4 is adjusted, thereby maintaining an appropriate image density.

[0035] Also, the recording material S is separated and fed one by one by the paper feed unit 18 at a predetermined control timing. The recording material S is conveyed to the transfer belt 12 at a predetermined control timing so that the timing when the leading edge of the toner image on the most upstream photosensitive drum 4Y moves to the transfer section NY and the timing when the recording material S is conveyed to the transfer section NY are synchronized (the image formation start positions are the same). The toner images are sequentially transferred from each photosensitive drum 4 to the recording material S conveyed by electrostatically adsorbing it to the transfer belt 12 by an electric field formed between each photosensitive drum 4 and each transfer roller 16. During the transfer, a predetermined transfer voltage (transfer bias) is applied to each transfer roller 16 by a transfer power source E3 (FIG. 3) as a transfer voltage application unit. In this embodiment, the transfer power source E3 applies a DC voltage of negative polarity, which is the opposite polarity to the normal polarity (positive polarity in this embodiment) of the toner T, to the transfer roller 16 as the transfer voltage. This makes it possible to electrically attract the positively charged toner T to the recording material S side.

[0036] The recording material S onto which the four color toner images have been transferred is separated from the transfer belt 12 and conveyed to a fixing device 21. The fixing device 21 applies heat and pressure to the recording material S carrying the unfixed toner image, thereby fixing (melting and bonding) the toner image to the recording material S. Thereafter, the recording material S is discharged (output) by a discharge unit 22 to a discharge tray 23 provided outside the apparatus main body 2.

[0037] On the other hand, after the toner T is transferred onto the recording material S, the surface of the photosensitive drum 4 is irradiated with a discharge light by the discharge light source 31, and discharged until the surface potential is close to 0 V. This stabilizes the surface potential of the photosensitive drum 4, and improves the cleaning performance of the cleaning roller 32 of the toner (transfer residual toner) remaining on the photosensitive drum 4 without being transferred to the recording material S, and the foreign matter that has moved from the recording material S to the photosensitive drum 4. The function of the cleaning roller 32 will be described in detail later. Furthermore, by stabilizing the surface potential of the photosensitive drum 4, the surface of the photosensitive drum 4 can be more uniformly charged by the charging device 5. Discharging includes removing (attenuating) at least a part of the charge.

[0038] <Control mode> 3 is a schematic block diagram showing the control mode of the main parts of the image forming apparatus 1 of this embodiment. The image forming apparatus 1 is provided with a control unit 150. The control unit 150 has a CPU 151 as an arithmetic control means which is a central element for performing arithmetic processing, a memory (storage element) 152 such as a ROM or RAM as a storage means, an input / output unit (not shown) for controlling the transmission and reception of signals between various elements connected to the control unit 150, and the like. The RAM stores the detection results of the sensors, the arithmetic results, and the like, and the ROM stores a control program, a data table obtained in advance, and the like.

[0039] The control unit 150 is a control unit that comprehensively controls the operation of the image forming apparatus 1. The control unit 150 executes a predetermined image forming sequence by controlling the transmission and reception of various electrical information signals and the timing of driving. Each unit of the image forming apparatus 1 is connected to the control unit 150. For example, in relation to this embodiment, the control unit 150 is connected to a charging power source E1, a developing power source E2, a transfer power source E3, a cleaning power source E4, a recovery power source E5, an exposure device 10, and the like. The control unit 150 controls the ON / OFF and output values ​​of these various power sources E1, E2, E3, E4, and E5, the amount of exposure by the exposure device 10, and the like, to control the image forming operation and the operation of a cleaning mechanism 36 described later.

[0040] In this embodiment, the charging power supply E1, the developing power supply E2, the transfer power supply E3, and the cleaning power supply E4 are each provided independently for each image forming unit P. However, at least one of the charging power supply E1, the developing power supply E2, the transfer power supply E3, and the cleaning power supply E4 may be shared by a plurality of image forming units P (or may be shared by all image forming units P). Also, in this embodiment, the recovery power supply E5 is provided only for the most upstream image forming unit PY.

[0041] In this embodiment, the image forming apparatus 1 can execute a job (printing operation) which is a series of operations for forming an image on a single or multiple recording materials S in response to a single start instruction from an external device (not shown) such as a personal computer. A job generally includes an image forming process (printing process), a pre-rotation process, a paper-interval process in the case of forming an image on multiple recording materials S, and a post-rotation process. The image forming process is a period during which an electrostatic image is actually formed on the photosensitive drum 4, the electrostatic image is developed (a toner image is formed), the toner image is transferred, the toner image is fixed, and the image forming time refers to this period. More specifically, the timing during image formation differs depending on the positions at which the electrostatic image is formed, the toner image is formed, the toner image is transferred, the toner image is fixed, and the like. The pre-rotation process is a period during which a preparatory operation is performed before the image forming process. The paper-interval process is a period corresponding to the interval between recording materials S when the image forming process is performed continuously on multiple recording materials S (during continuous image formation). The post-rotation process is a period during which an arranging operation (preparatory operation) is performed after the image forming process. The non-image forming time is a period other than the image forming time, and includes the above-mentioned pre-rotation process, inter-sheet process, post-rotation process, and further the pre-multiple-rotation process which is a preparatory operation when the image forming apparatus 1 is turned on or when returning from a sleep state, etc. In this embodiment, at a predetermined timing during the non-image forming time, an operation of expelling the transfer residual toner adhering to the cleaning roller 32 from the cleaning roller 32 to the photosensitive drum 4, as described later, is executed.

[0042] <Cleaning mechanism> Next, the cleaning mechanism 36 in this embodiment will be described in more detail. FIG. 4 is a schematic diagram for explaining the operation of the cleaning mechanism 36 in this embodiment. FIG. 4(a) shows the surroundings of the photosensitive drum 4Y of the most upstream image forming unit PY for Y and the surroundings of the photosensitive drum 4M of the image forming unit PM for M arranged adjacently on the downstream side when the toner T is transferred to the recording material S (during image formation). FIG. 4(b) shows the surroundings of the photosensitive drum 4Y of the most upstream image forming unit PY for Y and the surroundings of the photosensitive drum 4M of the image forming unit PM for M arranged adjacently on the downstream side when not transferring (during non-image formation). Here, the downstream image forming units PM, PC, and PK will be mainly described with respect to the image forming unit PM for M, but in this embodiment, the configurations and operations of the downstream image forming units PM, PC, and PK are substantially the same except that the colors of the toners used for development are different. In FIG. 4, for simplicity, the suffixes Y and M indicating that the elements are for any color are appropriately omitted. As described above, the most upstream image forming station PY is provided with the first cleaning mechanism 36a as the cleaning mechanism 36. Moreover, the downstream image forming station PM is provided with the second cleaning mechanism 36b as the cleaning mechanism 36.

[0043] - Temporary collection of residual toner from transfer With reference to FIG. 4(a), the operation of the cleaning mechanism 36 when a toner image is being transferred onto the recording material S (during image formation) will be described.

[0044] First, the behavior of the transfer residual toner T1 will be described. In the image forming units PY and PM on the most upstream and downstream sides, the cleaning roller 32 contacts the photosensitive drum 4 and rotates in the direction of the arrow G in the figure (counterclockwise direction). That is, the cleaning roller 32 rotates so that the photosensitive drum 4 and the cleaning roller 32 move in the forward direction at the contact portion between the photosensitive drum 4 and the cleaning roller 32. In this embodiment, the cleaning roller 32 is rotated by branching and transmitting the driving force from a driving motor (not shown) that drives the photosensitive drum 4. Note that a driving means for rotating the photosensitive drum 4 and a driving means for rotating the cleaning roller 32 may be provided separately. The cleaning roller 32 may be rotated with a difference in circumferential speed with respect to the photosensitive drum 4 (for example, the cleaning roller 32 is faster), or may be rotated at the same circumferential speed as the photosensitive drum 4. In this embodiment, the cleaning roller 32 is configured by coating a rubber layer made of a rubber material as an elastic layer around a roller shaft (core shaft) made of metal or the like. The rubber layer is made of, for example, a solid rubber material or a sponge material having elasticity. The surface of the photosensitive drum 4 in contact with the cleaning roller 32 is lowered to a surface potential close to 0 V by the charge removal light source 31. A predetermined cleaning voltage (cleaning bias) is applied to the cleaning roller 32 by the cleaning power source E4. In this embodiment, the cleaning power source E4 applies a negative DC voltage, which is the opposite polarity to the normal polarity of the toner T, to the cleaning roller 32 as the cleaning voltage. Therefore, the transfer residual toner T1, which is positively charged, moves along the electric field from the photosensitive drum 4 to the cleaning roller 32 and is collected by the cleaning roller 32. Note that this cleaning voltage may be a voltage that is higher on the opposite polarity side (negative polarity side in this embodiment) to the normal polarity of the toner with respect to the surface potential of the photosensitive drum 4 at the contact portion between the cleaning roller 32 and the photosensitive drum 4.

[0045] In the most upstream image forming portion PY, the foreign matter collecting roller 33 comes into contact with the cleaning roller 32 and rotates in the direction of the arrow H in the figure (clockwise direction). That is, the foreign matter collecting roller 33 rotates so that the cleaning roller 32 and the foreign matter collecting roller 33 move in the forward direction at the contact portion between the cleaning roller 32 and the foreign matter collecting roller 33. In this embodiment, the foreign matter collecting roller 33 is rotated by branching and transmitting the driving force from the driving motor (not shown) that drives the photosensitive drum 4. The foreign matter collecting roller 33 may be rotated with a circumferential speed difference with respect to the cleaning roller 32 (for example, the foreign matter collecting roller 33 is faster), or may be rotated at the same circumferential speed as the cleaning roller 32. The foreign matter collecting roller 33 may be rotated by being driven by the cleaning roller 32. In this embodiment, the foreign matter collecting roller 33 is made of a metal roller. The foreign matter collecting roller 33 may be made of a roller having an elastic layer similar to that of the cleaning roller 32. A predetermined toner recovery voltage (toner recovery bias) is applied to the foreign matter recovery roller 33 by the recovery power source E5. In this embodiment, the recovery power source E5 applies a positive DC voltage, which is the same polarity as the normal polarity of the toner T, to the foreign matter recovery roller 33 as the toner recovery voltage. Therefore, the positive polarity transfer residual toner T1 recovered by the cleaning roller 32 does not move to the foreign matter recovery roller 33, but is held by the cleaning roller 32. Note that this toner recovery voltage may be a voltage higher on the normal polarity side of the toner (positive polarity side in this embodiment) than the potential of the cleaning roller 32 at the contact portion between the foreign matter recovery roller 33 and the cleaning roller 32.

[0046] Next, the behavior of foreign matter A, such as paper fibers, fillers (so-called "paper powder"), or dust, generated from the recording material S will be described. A large amount of foreign matter A moves to the photosensitive drum 4Y of the most upstream image forming unit PY, and a small amount moves to the photosensitive drum 4M of the downstream image forming unit PM. This is because most of the foreign matter A generated from the recording material S is removed at the transfer unit NY of the most upstream image forming unit PY. For this reason, in this embodiment, the foreign matter collection roller 33, scraping member 34, and foreign matter collection container 35 used for separating and collecting the foreign matter A are provided only in the first cleaning mechanism 36a of the most upstream image forming unit PY. And, these members are not provided in the second cleaning mechanism 36b of the downstream image forming unit PM. This prevents the entire device from becoming large.

[0047] In the most upstream image forming portion PY, a negative transfer voltage, for example, a transfer voltage of about -1000V, is applied to the transfer roller 16Y during transfer. This transfer voltage may be a voltage higher than the surface potential of the image portion on the photosensitive drum 4Y at the transfer portion NY on the opposite polarity side (negative polarity side in this embodiment) of the normal polarity of the toner. As a result, the positively charged toner T on the photosensitive drum 4Y is attracted to the recording material S and transferred onto the recording material S. At this time, the foreign matter A present on or inside the recording material S is charged to the negative polarity by receiving a negative discharge or injection charge due to the transfer voltage. Then, this foreign matter A moves onto the photosensitive drum 4Y along the electric field due to the transfer voltage. During transfer, a cleaning voltage on the negative polarity side is applied to the cleaning roller 32 in contact with the photosensitive drum 4Y with respect to the surface potential of the photosensitive drum 4Y at the contact portion between the cleaning roller 32 and the photosensitive drum 4Y. Therefore, the negatively charged foreign matter A is not collected by the cleaning roller 32.

[0048] In the most upstream image forming portion PY, after transfer, the photosensitive drum 4Y is uniformly charged to a positive polarity by the charging device 5Y. In addition, a developing voltage of a negative polarity side with respect to the surface potential (non-image portion potential) of the photosensitive drum 4Y at the contact portion between the developing roller 6Y and the photosensitive drum 4Y is applied to the developing roller 6Y. Therefore, the negatively charged foreign matter A is not collected by the developing roller 6Y. In addition, a negative transfer voltage is applied to the transfer roller 16Y. Therefore, the negatively charged foreign matter A does not move to the recording material S or the transfer belt 12.

[0049] Therefore, in the above-described settings of the voltages applied to each roller during transfer, the transfer residual toner T1 is collected and held by the cleaning roller 32 in each image forming portion P, and the foreign matter A is carried around on the photosensitive drum 4Y in the most upstream image forming portion PY.

[0050] In this embodiment, the transfer voltage, the developing voltage and the recovery voltage during image formation are set to the same values ​​in all image forming stations P.

[0051] - Collection of residual toner and foreign matter The operation of the cleaning mechanism 36 when not transferring (when not forming an image) will be described with reference to FIG. 4(b).

[0052] In the most upstream and downstream image forming units PY and PM, a predetermined discharge voltage (discharge bias) is applied to the cleaning roller 32 by the cleaning power source E4 at a predetermined timing other than during transfer. In this embodiment, the cleaning power source E4 applies a DC voltage of positive polarity, which is the same polarity as the normal polarity of the toner T, to the cleaning roller 32 as the discharge voltage. Note that this discharge voltage may be a voltage higher on the normal polarity side of the toner (positive polarity side in this embodiment) than the surface potential of the photosensitive drum 4 at the contact portion between the cleaning roller 32 and the photosensitive drum 4. At this time, in the most upstream image forming unit PY, a predetermined foreign matter collection time voltage (foreign matter collection time bias) is applied to the foreign matter collection roller 33 by the collection power source E5. In this embodiment, the collection power source E5 applies a positive DC voltage having an absolute value larger than the discharge voltage applied to the cleaning roller 32 to the foreign matter collection roller 33 as the foreign matter collection time voltage. The voltage during the foreign matter collection may be higher on the normal polarity side of the toner (positive polarity side in this embodiment) than the potential of the cleaning roller 32 at the contact portion between the foreign matter collection roller 33 and the cleaning roller 32 .

[0053] By the above potential setting, the transfer residual toner T1, which is positively charged in the most upstream and downstream image forming units PY and PM, is discharged from the cleaning roller 32 onto the photosensitive drum 4. At this time, a development voltage of negative polarity is applied to the developing roller 6 with respect to the surface potential (non-image portion potential) of the photosensitive drum 4 at the contact portion between the developing roller 6 and the photosensitive drum 4. Therefore, the transfer residual toner T1 discharged onto the photosensitive drum 4 is collected by the developing roller 6 and reused as the toner T during the subsequent image formation (development). Also, by the above potential setting, the foreign matter A on the photosensitive drum 4Y, which is negatively charged in the most upstream image forming unit PY, is collected by the cleaning roller 32 and further collected by the foreign matter collecting roller 33. A scraping member 34 is in contact with the foreign matter collecting roller 33, and the surface of the foreign matter collecting roller 33 is rubbed by the scraping member 34 as the foreign matter collecting roller 33 rotates. An elastic member such as a sponge or felt is used as the scraping member 34. The scraping member 34 may be an elastic rubber blade, a plastic film, etc. The foreign matter A collected by the foreign matter collection roller 33 is scraped off from the foreign matter collection roller 33 by the scraping member 34, and falls into the foreign matter collection container 35 to be collected.

[0054] In this embodiment, the transfer voltage and development voltage are set to the same values ​​for all image forming stations P during image formation and when the transfer residual toner T1 is collected into the development cartridge 8 during non-image formation. Also, in this embodiment, the discharge voltage is set to the same value for all image forming stations P.

[0055] Furthermore, the discharge of the transfer residual toner T1 from the cleaning roller 32 and the collection by the developing cartridge 8 can be performed at any timing, such as an inter-sheet process, not limited to the post-rotation process, so long as the image is not being formed.

[0056] Furthermore, most of the foreign matter A generated from the recording material S is removed at the transfer portion NY of the most upstream image forming portion PY. In this embodiment, the second cleaning mechanism 36b of the downstream image forming portion PM is not provided with a foreign matter collection roller 33 for collecting the foreign matter A. When a small amount of foreign matter A moves to the photosensitive drum 4M of the downstream image forming portion PM, the foreign matter A may be retained on the photosensitive drum 4 or the cleaning roller 32 (FIGS. 4(a) and 4(b)).

[0057] <Reduction of remaining film thickness difference> As described above, the amount of the foreign matter A generated from the recording material S moving to the photosensitive drum 4 is significantly larger in the most upstream image forming unit PY and smaller in the downstream image forming units PM, PC, and PK. In particular, in a configuration in which the recording material S and the photosensitive drum 4 are in direct contact with each other as in this embodiment, the amount of the foreign matter A generated from the recording material S moving to the photosensitive drum 4 increases. The more the amount of the foreign matter A moving to the photosensitive drum 4 increases, the more the amount of the foreign matter A intervening between the photosensitive drum 4 and the cleaning roller 32 and between the photosensitive drum 4 and the developing roller 6 increases, and the amount of the photosensitive drum 4 scraped by the foreign matter A increases. In other words, the amount of scraping of the photosensitive drum 4Y of the most upstream image forming unit PY becomes larger than the amount of scraping of the photosensitive drums 4M, 4C, and 4K of the downstream image forming units PM, PC, and PK. As a result, the photosensitive drum 4Y of the most upstream image forming unit PY will reach the end of its life before the photosensitive drums 4M, 4C, and 4K of the downstream image forming units PM, PC, and PK. In other words, the most upstream drum unit 30Y will reach the end of its life before the downstream drum units 30M, 30C, and 30K. In particular, in a configuration in which the four drum units 30 are integrated into one replaceable part as in this embodiment, when the most upstream drum unit 30Y reaches the end of its life first, the entire life of the four drum units 30 will also reach the end.

[0058] Therefore, in this embodiment, the thickness (initial, when new) of the surface layer of the photosensitive drum 4Y of the most upstream image forming unit PY is made thicker than the thickness (initial, when new) of the surface layer of the photosensitive drums 4M, 4C, and 4K of the downstream image forming units PM, PC, and PK. This brings the time when the most upstream photosensitive drum 4Y reaches the end of its life closer to the time when the downstream photosensitive drums 4M, 4C, and 4K reach the end of their life, so that each drum unit 30 reaches the end of its life almost at the same time. As a result, the overall life of the four drum units 30, which are integrated into a single replaceable part, can be extended.

[0059] In this embodiment, the photosensitive drums 4Y, 4M, 4C, and 4K in the most upstream and downstream image forming units PY, PM, PC, and PK are single-layered photosensitive drums that are organic photosensitive drums with positive charging polarity. That is, as shown in the cross section of FIGS. 5(a) and (b), in this embodiment, each photosensitive drum 4 is configured by forming a single-layered surface layer 4b, which is a photosensitive layer mainly made of resin, around a cylindrical base body 4a made of a conductive material such as metal. In this embodiment, the photosensitive drums 4Y, 4M, 4C, and 4K in the most upstream and downstream image forming units PY, PM, PC, and PK use the same material as the material of the surface layer 4b. In this embodiment, polycarbonate resin is used as the binder resin material of the surface layer. In this embodiment, the film thickness (initial) B1 of the surface layer 4b of the photosensitive drum 4Y of the most upstream image forming portion PY is larger than the film thickness (initial) B2 of the surface layer 4b of the photosensitive drums 4M, 4C, and 4K of the downstream image forming portions PM, PC, and PK.

[0060] In this embodiment, the thickness (initial) of the surface layer of the photosensitive drum 4Y of the most upstream image forming station PY is 26 μm, and the thickness (initial) of the surface layer of the photosensitive drums 4M, 4C, and 4K of the downstream image forming stations PM, PC, and PK is 24 μm. Note that the thickness of the surface layer of the photosensitive drum 4 is not limited to the value in this embodiment, and can be appropriately adjusted.

[0061] In addition, a photosensitive drum generally has a conductive support (substrate) and a photosensitive layer formed on the support. The photosensitive layer may be a single-layer type photosensitive layer containing a charge transport material and a charge generating material in the same layer, or a laminate type photosensitive layer formed by laminating a charge generating layer containing a charge generating material and a charge transport layer containing a charge transport material. A protective layer may be provided on the photosensitive layer. The surface layer of the photosensitive drum is the layer located on the outermost surface side of the photosensitive drum. In other words, the surface layer of the photosensitive drum is the layer farthest from the support and has a surface that carries toner.

[0062] Here, the definition of the end of the life of the photosensitive drum 4 in this embodiment will be described. The surface layer of the photosensitive drum 4 is rubbed against the cleaning roller 32, the developing roller 6, and the transfer belt 12 as the image forming operation of the image forming apparatus 1 is repeated, and is gradually worn away. As the surface layer of the photosensitive drum 4 is worn away, unevenness in the charging potential caused by the uneven wear causes a large number of vertical streak images (streak-like images extending along the moving direction of the surface of the photosensitive drum 4) to appear on the halftone image. In this embodiment, the timing at which the vertical streak images appear is defined as the end of the life of the photosensitive drum 4.

[0063] A method of notifying the end of the life of the photosensitive drum 4 (drum unit 30) in this embodiment will be described. In this embodiment, as shown in FIG. 3, the control unit 150 accumulates the total driving time for which the photosensitive drum 4 is driven to rotate, and sequentially stores the accumulated time in the counter 70, which is a storage unit. Then, when the total driving time reaches a predetermined threshold, the control unit 150 controls the display of information indicating that the photosensitive drum 4 has reached the end of its life on the operation unit (operation panel) 80 provided in the image forming apparatus 1 to notify an operator such as a user. The predetermined threshold is set in advance as the timing at which a vertical stripe image occurs, and is stored in the memory 152. In this embodiment, the predetermined threshold is set as the timing at which the total driving time of the photosensitive drum 4 reaches the equivalent of 10,000 sheets with two-sheet intermittent paper passing. Two-sheet intermittent paper passing refers to an operation of repeating a job of forming an image on two sheets of recording material S in succession. In addition, in this embodiment, when the four drum units 30 integrated into one replacement part are replaced, the control unit 150 resets the count value of the counter 70 to an initial value (0 in this embodiment).

[0064] The control unit 150 may control an external device, such as a personal computer, connected to the image forming apparatus 1 in a communicable manner to display information indicating that the photosensitive drum 4 has reached the end of its life. In this embodiment, the end of the life of the photosensitive drum 4 is detected based on the total drive time of the photosensitive drum 4, but the present invention is not limited to this embodiment. The end of the life of the photosensitive drum 5 can be detected based on any index that correlates with the amount of use of the photosensitive drum 4. Examples of the index include the total drive time of the photosensitive drum 4, the total number of rotations of the photosensitive drum 4, and the total number of prints made using the photosensitive drum 4. In other words, any index that indicates the degree of friction that the photosensitive drum 4 receives can be used as the index.

[0065] <Evaluation test> In order to confirm the effect of this embodiment, an evaluation test was performed on the configuration of this embodiment and the configuration of Comparative Example 1. As described above, in this embodiment, the film thickness (initial) of the surface layer of the photosensitive drum 4Y of the most upstream image forming unit PY was set to 26 μm, and the film thickness (initial) of the surface layer of the photosensitive drums 4M, 4C, and 4K of the downstream image forming units PM, PC, and PK was set to 24 μm. On the other hand, in Comparative Example 1, the film thickness (initial) of the surface layer of the photosensitive drums 4Y, 4M, 4C, and 4K of all the image forming units PY, PM, PC, and PK was set to 24 μm. The configuration of Comparative Example 1 is substantially the same as the configuration of this embodiment, except that the film thickness of the surface layer of the photosensitive drum 4 is set differently as described above.

[0066] Here, the film thickness of the surface layer of the photosensitive drum was measured using a film thickness measuring device (manufactured by Fisher Instruments, FISCHRSCOPE (registered trademark) mms (registered trademark)).

[0067] Then, in the configurations of this embodiment and Comparative Example 1, a paper passing durability test was performed to check whether or not vertical stripe images occurred in each image forming station P. The recording material S (paper) used for printing was Xerox multipurpose paper (basis weight 75 g / m 2 The printed image was a horizontal line image (lines extending in a direction substantially perpendicular to the moving direction of the surface of the photosensitive drum 4) with a printing rate of 4% for each color. The occurrence of vertical stripe images was judged using a halftone image with a printing rate of 25% for each color.

[0068] The results are shown in Table 1. In Table 1, "◯" indicates no occurrence of vertical streak images, "△" indicates slight occurrence of vertical streak images, and "×" indicates occurrence of vertical streak images. The total drive time of the photosensitive drum 4 is shown with the total drive time corresponding to the above-mentioned threshold value (life end timing) as 100%.

[0069] [Table 1]

[0070] As shown in Table 1, in this embodiment, no vertical streak images were generated until the total drive time of the photosensitive drum 4 reached 100%, which is the end of life timing. On the other hand, in Comparative Example 1, vertical streak images were generated when the total drive time of the photosensitive drum 4 reached 80% of the end of life timing.

[0071] In the configuration of Comparative Example 1, a large amount of foreign matter A was recovered on the most upstream photosensitive drum 4Y, and the amount of wear on the photosensitive drum 4Y was also large, causing vertical streak images to occur earlier in the most upstream image forming station PY than in the downstream image forming stations PM, PC, and PK.

[0072] In contrast, in the configuration of this embodiment, the thickness of the surface layer of the photosensitive drum 4Y of the most upstream image forming unit PY is made thicker than the thickness of the surface layer of the photosensitive drums 4M, 4C, and 4K of the downstream image forming units PM, PC, and PK. As a result, in the configuration of this embodiment, it was possible to suppress the occurrence of vertical stripe images within the set life in all image forming units PY, PM, PC, and PK. Furthermore, a paper passing durability test was performed until the total driving time of the photosensitive drum 4 exceeded 100%, which is the life end timing. As a result, at 120% of the life end timing, vertical stripe images ranked "△" occurred in all image forming units PY, PM, PC, and PK.

[0073] As described above, the image forming apparatus 1 of this embodiment has the belt 12 that contacts the first image carrier 4Y to form the first transfer portion NY and contacts the second image carriers 4M, 4C, 4K to form the second transfer portions NM, NC, NK, and nip and conveys the recording material S between the first image carrier 4Y and the second image carriers 4M, 4C, 4K at the first transfer portion NY and the second transfer portions NM, NC, NK, respectively, and the first image forming portion 4Y is disposed upstream of the second image forming portions 4M, 4C, 4K in the moving direction of the recording material S, and a plurality of members including the first image carrier 4Y and the second image carriers 4M, 4C, 4K are integrated and detachable from the apparatus body 2 of the image forming apparatus 1. In this embodiment, the thickness of the surface layer of the first image carrier 4Y is larger than the thickness of the surface layers of the second image carriers 4M, 4C, 4K.

[0074] According to this embodiment, the thickness of the surface layer of the photosensitive drum 4 at the end of its life can be made substantially the same between the photosensitive drum 4Y on the upstream side and the photosensitive drums 4M, 4C, and 4K on the downstream side. In other words, it is possible to reduce the difference in the remaining thickness of the surface layer between the photosensitive drums 4. This makes it possible to extend the overall life of the multiple drum units 30 that are integrated into a single replaceable part.

[0075] [Example 2] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0076] In this embodiment, the peripheral speed of the developing roller 6Y of the most upstream image forming section PY is set slower than the peripheral speeds of the developing rollers 6M, 6C, and 6K of the downstream image forming sections PM, PC, and PK. In this embodiment, the surface layer thicknesses of the most upstream and downstream photosensitive drums 4Y, 4M, 4C, and 4K are all the same at 24 μm. By lowering the peripheral speed of the developing roller 6Y of the most upstream image forming section PY, the amount of wear of the most upstream photosensitive drum 4Y can be suppressed. This is because, when the peripheral speed of the developing roller 6Y is lowered, the force with which the photosensitive drum 4Y is rubbed by the foreign matter A present between the developing roller 6Y and the photosensitive drum 4Y is weakened.

[0077] According to the configuration of this embodiment, the amount of wear on the most upstream photosensitive drum 4Y can be suppressed to match the amount of wear on the downstream photosensitive drums 4M, 4C, and 4K. In other words, the time when the most upstream photosensitive drum 4Y reaches the end of its life approaches the time when the downstream photosensitive drums 4M, 4C, and 4K reach the end of their life, and each drum unit 30 reaches the end of its life almost at the same time. As a result, the overall life of the four drum units 30, which are integrated into a single replaceable part, can be extended.

[0078] In this embodiment, the peripheral speed of the developing roller 6Y of the most upstream image forming unit PY is 120 mm / sec, and the peripheral speed of the developing rollers 6M, 6C, and 6K of the downstream image forming units PM, PC, and PK is 150 mm / sec. That is, in this embodiment, the peripheral speeds of the developing rollers 6M, 6C, and 6K of the downstream image forming units PM, PC, and PK are the same as in Example 1, and the peripheral speed of the developing roller PY of the most upstream image forming unit PY is slower than that in Example 1.

[0079] Here, a configuration for changing the circumferential speed of the developing roller 6 in this embodiment will be described. FIG. 6 is a schematic diagram showing a driving configuration of the developing roller 6. In this embodiment, the image forming apparatus 1 has a driving means for rotating the developing roller 6, which is a first driving means and a second driving means, as follows. First, the first driving means is a first developing drive motor 90a that drives the developing roller 6Y of the most upstream image forming section PY. Also, the second driving means is a second developing drive motor 90b that drives the developing rollers 6M, 6C, and 6K of the downstream image forming sections PM, PC, and PK. This allows the circumferential speeds of the developing roller 6Y of the most upstream image forming section PY and the developing rollers 6M, 6C, and 6K of the downstream image forming sections PM, PC, and PK to be changed by the respective developing drive motors 90a and 90b.

[0080] The configuration for changing the circumferential speed of the developing roller 6 is not limited to the configuration of this embodiment. For example, the driving motor for the developing roller 6 can be shared, while the gear ratio of the gear from the driving motor to the developing roller 6 can be different between the most upstream image forming unit PY and the downstream image forming units PM, PC, and PK. This also makes it possible to change the circumferential speed between the developing roller 6Y of the most upstream image forming unit PY and the developing rollers 6M, 6C, and 6K of the downstream image forming units PM, PC, and PK.

[0081] In order to confirm the effect of this embodiment, an evaluation test was performed on the configuration of this embodiment and the configuration of Comparative Example 2. As described above, in this embodiment, the peripheral speed of the developing roller 6Y of the most upstream image forming unit PY was set to 120 mm / sec, and the peripheral speeds of the developing rollers 6M, 6C, and 6K of the downstream image forming units PM, PC, and PK were set to 150 mm / sec. On the other hand, in Comparative Example 2, the peripheral speeds of the developing rollers 6Y, 6M, 6C, and 6K of all image forming units PY, PM, PC, and PK were set to 150 mm / sec. The configuration of Comparative Example 2 is substantially the same as the configuration of this embodiment, except that the peripheral speed setting of the developing roller 6 is different as described above.

[0082] Then, in the configurations of this embodiment and Comparative Example 2, a paper passing durability test was performed to check whether or not vertical stripe images occurred in the most upstream image forming station PY. The recording material S (paper) used for printing was Xerox multipurpose paper (basis weight 75 g / m 2 The size of the paper was 128 x 1024 x 720 mm (LTR size). The printed image was a horizontal line image with a printing rate of 4% for each color. The occurrence of vertical stripe images was judged using a secondary color halftone image with a printing rate of 25% for each of yellow and magenta.

[0083] The results are shown in Table 2. In Table 2, "◯" indicates no occurrence of vertical streak images, "△" indicates slight occurrence of vertical streak images, and "×" indicates occurrence of vertical streak images. The total drive time of the photosensitive drum 4 is shown with the total drive time corresponding to the threshold value (life end timing) described in the first embodiment as 100%.

[0084] [Table 2]

[0085] As shown in Table 2, in this embodiment, no vertical streak images were generated until the total drive time of the photosensitive drum 4 reached 100%, which is the end of life timing. On the other hand, in Comparative Example 2, vertical streak images were generated when the total drive time of the photosensitive drum 4 reached 80% of the end of life timing.

[0086] In the configuration of Comparative Example 2, the amount of foreign matter A collected at the most upstream photosensitive drum 4Y was large, and the amount of scraping of the photosensitive drum 4Y was large, so that vertical streak images occurred at the most upstream image forming portion PY.

[0087] In contrast, in the configuration of this embodiment, the peripheral speed of the developing roller 6Y of the most upstream image forming station PY is made slower than the peripheral speeds of the developing rollers 6M, 6C, and 6K of the downstream image forming stations PM, PC, and PK. As a result, in the configuration of this embodiment, the amount of wear on the most upstream photosensitive drum 4Y is reduced, and the occurrence of vertical streak images can be suppressed.

[0088] In this embodiment, the amount of wear on the most upstream photosensitive drum 4Y is suppressed by lowering the peripheral speed of the developing roller 6Y of the most upstream image forming station PY, but the present invention is not limited to this embodiment.

[0089] For example, the amount of wear on the most upstream photosensitive drum 4Y can be suppressed by lowering the contact pressure of the developing roller 6Y in the most upstream image forming portion PY against the photosensitive drum 4Y. This is because the force of the foreign matter A interposed between the developing roller 6Y and the photosensitive drum 4Y rubbing against the photosensitive drum 4Y is also weakened. In other words, the contact pressure when the developing roller 6Y in the most upstream image forming portion PY is in contact with the photosensitive drum 4Y is made smaller than the contact pressure when the developing rollers 6M, 6C, and 6K in the downstream image forming portions PM, PC, and PK are in contact with the photosensitive drums 4M, 4C, and 4K. This suppresses the amount of wear on the most upstream photosensitive drum 4Y and makes it possible to match the amount of wear on the downstream photosensitive drums 4M, 4C, and 4K.

[0090] Specifically, the contact pressure of the developing roller 6 against the photosensitive drum 4 can be changed by changing the axial distance between the photosensitive drum 4 and the developing roller 6, which determines the contact pressure of the developing roller 6 against the photosensitive drum 4. That is, the axial distance in the most upstream image forming unit PY is made wider than the axial distance in the downstream image forming units PM, PC, and PK. The axial distance can be determined, for example, as follows. FIG. 7 is a schematic cross-sectional view showing an example of a configuration for determining the axial distance. The developing cartridge 8 is biased by a spring (not shown) or the like, which is a biasing member serving as a biasing means, so that the developing roller 6 is pressed against the photosensitive drum 4. In addition, rollers 65 are provided at both ends of the roller shaft of the developing roller 6 in the longitudinal direction as regulating members that come into contact with the photosensitive drum 4 and determine the depth to which the rubber layer of the developing roller 6 penetrates into the photosensitive drum 4. The outer diameter Q1 of roller 65Y as the first regulating member of the most upstream image forming unit PY (FIG. 7(a)) is made larger than the outer diameter Q2 of rollers 65M, 65C, 65K as the second regulating members of the downstream image forming units PM, PC, PK (FIG. 7(b)). The above-mentioned inter-axis distance can also be determined by providing a positioning portion, as part of the developing cartridge 8, on the developing frame 28, for example, which abuts against the photosensitive drum 4 and determines the depth to which the rubber layer of the developing roller 6 penetrates into the photosensitive drum 4.

[0091] As described above, the image forming apparatus 1 of this embodiment has a driving means for rotating the first developer carrier 6Y and the second developer carriers 6M, 6C, and 6K. This driving means rotates the first image carrier 4Y and the first developer carrier 6Y so that they move in the same direction at the opposing portion between the first image carrier 4Y and the first developer carrier 6Y, and rotates the second image carriers 4M, 4C, and 4K and the second developer carriers 6M, 6C, and 6K so that they move in the same direction at the opposing portion between the second image carriers 4M, 4C, and 4K and the second developer carriers 6M, 6C, and 6K. In this embodiment, a first peripheral speed ratio, which is a ratio of the peripheral speed of the first developer carrier 6Y to the peripheral speed of the first image carrier 4Y, is smaller than a second peripheral speed ratio, which is a ratio of the peripheral speed of the second developer carrier 6M, 6C, 6K to the peripheral speed of the second image carrier 4M, 4C, 4K. For example, the gear ratio of the first gear provided between the first developer carrier 6Y and the driving means and the gear ratio of the second gear provided between the second developer carrier 6M, 6C, 6K and the driving means may be different. Alternatively, the driving means may have a first driving means for rotating the first developer carrier 6Y and a second driving means for rotating the second developer carriers 6M, 6C, and 6K separately, and the driving speed of the first developer carrier 6Y by the first driving means may be different from the driving speed of the second developer carriers 6M, 6C, and 6K by the second driving means.

[0092] Alternatively, the first contact pressure when the first image carrier 4Y and the first developer carrier 6Y are in contact with each other may be smaller than the second contact pressure when the second image carriers 4M, 4C, and 4K and the second developer carriers 6M, 6C, and 6K are in contact with each other. In this embodiment, the first developer carrier 6Y and the second developer carriers 6M, 6C, 6K are each rollers having an elastic layer formed around a core axis, and the distance between the first image carrier 4Y and the core axis of the first developer carrier 6Y when the first image carrier 4Y and the first developer carrier 6Y are in contact with each other is greater than the distance between the second image carrier 4M, 4C, 4K and the core axis of the second developer carrier 6M, 6C, 6K when the second image carrier 4M, 4C, 4K and the second developer carrier 6M, 6C, 6K are in contact with each other. For example, the first contact pressure may be determined by a first regulating member 65Y arranged at both ends of the first developer carrier 6Y in the longitudinal direction abutting against the first image carrier 4Y, and the second contact pressure may be determined by a second regulating member 65M, 65C, 65K arranged at both ends of the second developer carriers 6M, 6C, 6K in the longitudinal direction abutting against the second image carriers 4M, 4C, 4K. Alternatively, the first contact pressure may be determined by a first positioning portion provided on a frame 28Y constituting the first developing device 8Y abutting against the first image carrier 4Y, and the second contact pressure may be determined by a second positioning portion provided on a frame 28M, 28C, 28K constituting the second developing devices 8M, 8C, 8K abutting against the second image carriers 4M, 4C, 4K.

[0093] According to this embodiment, the amount of wear on the upstream photosensitive drum 4Y can be suppressed to match the amount of wear on the downstream photosensitive drums 4M, 4C, and 4K. This makes it possible to extend the overall life of the multiple drum units 30 that are integrated into one replaceable part. Furthermore, according to this embodiment, compared to the configuration of embodiment 1, it is possible to suppress the amount of wear on the most upstream photosensitive drum 4Y while suppressing a decrease in density of the yellow image formed by the most upstream image forming station PY.

[0094] [Example 3] Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the image forming apparatus of embodiment 1. Therefore, in the image forming apparatus of this embodiment, elements having the same or corresponding functions or configurations as those of the image forming apparatus of embodiment 1 are given the same reference numerals as those of embodiment 1, and detailed explanations are omitted.

[0095] First, the structure of the developer T used in this embodiment will be described with reference to FIG. 8. FIG. 8 is a diagram showing an example of the cross-sectional structure of the developer T. In FIG. 8, the main components of the developer (toner) T are shown in a schematic manner to facilitate understanding of the structure of the developer T. The size, number, shape, etc. of each component shown in FIG. 8 may differ from the actual size due to the convenience of drawing. The developer T shown in FIG. 8 includes developer base particles (toner base particles) T0 and metal soap (metal soap particles) X attached to the surface of the developer base particles T0.

[0096] As the metal soap, higher fatty acid salts of various metals suitable as an external additive for the developer base particles T0 can be used. The metal soap is generally a general term for metal salts of long-chain fatty acids and metals other than sodium and potassium. Specifically, metal salts of fatty acids such as stearic acid, myristic acid, lauric acid, ricinoleic acid, and octylic acid and metal species such as lithium, magnesium, calcium, barium, and zinc can be mentioned. In this embodiment, zinc stearate is externally added as the metal soap. The type of metal soap is not limited to this, and lead stearate, cadmium stearate, barium stearate, calcium stearate, aluminum stearate, zinc stearate, magnesium stearate, zinc laurate, and zinc myristate can also be used as appropriate. At least one of these can be selected and used. Typically, the average particle size of the metal soap X is smaller than the average particle size of the developer base particles T0. For example, the average particle size of the developer base particles T0 is typically about 5 μm or more and 8 μm or less. The average particle size of the metal soap is typically about 0.15 μm or more and 2.0 μm or less. The metal soap X may be a single component or a combination of two or more components.

[0097] In this embodiment, only the developer T contained in the most upstream developing cartridge 8Y contains the metal soap X, and the developer T contained in the downstream developing cartridges 8M, 8C, and 8K does not contain the metal soap X. In this embodiment, the surface layer thicknesses of the most upstream and downstream photosensitive drums 4Y, 4M, 4C, and 4K are all the same at 24 μm. By making the developer T contained in the most upstream developing cartridge 8Y contain the metal soap X, the amount of wear on the most upstream photosensitive drum 4Y can be suppressed. This is due to the following action. That is, when the developer T moves to the photosensitive drum 4Y, the metal soap X attached to the surface of the developer T moves to the photosensitive drum 4Y and functions as a lubricant. This can weaken the force with which the photosensitive drum 4Y is rubbed by the foreign matter A.

[0098] According to the configuration of this embodiment, the amount of wear on the most upstream photosensitive drum 4Y can be suppressed to match the amount of wear on the downstream photosensitive drums 4M, 4C, and 4K. In other words, the time when the most upstream photosensitive drum 4Y reaches the end of its life approaches the time when the downstream photosensitive drums 4M, 4C, and 4K reach the end of their life, and each drum unit 30 reaches the end of its life almost at the same time. As a result, the overall life of the four drum units 30, which are integrated into a single replaceable part, can be extended.

[0099] In this embodiment, the content of metal soap X in developer T (developer mother particles T0, metal soap X) (the ratio (mass ratio) of the mass of metal soap X per unit mass of developer T) was set as follows. That is, the content was 0.05 mass% in developer T contained in the most upstream developing cartridge 8Y, and 0 mass% in downstream developing cartridges 8M, 8C, and 8K. Although not limited to this, the content of metal soap X in developer T is preferably about 0.05 mass% or more and 0.6 mass% or less. If the content of metal soap in developer T is too low, it is difficult to achieve the effect of reducing the amount of scraping of the photosensitive drum 4, but if it is too high, there is a possibility that the fluidity of developer T will be reduced.

[0100] The content of metal soap X was measured using a wavelength dispersive X-ray fluorescence analyzer "Axios" (PANalytical). The measurement conditions were set and the measurement data was analyzed using the accompanying dedicated software "SuperQ ver.4.0F" (PANalytical).

[0101] In order to confirm the effect of this embodiment, an evaluation test was performed on the configuration of this embodiment and the configuration of Comparative Example 3. As described above, in this embodiment, the content of metal soap X in developer T is 0.05 mass % in the most upstream developing cartridge 8Y, and 0 mass % in the downstream developing cartridges 8M, 8C, and 8K. On the other hand, in Comparative Example 3, the content of metal soap X in developer T is 0 mass % in all developing cartridges 8Y, 8M, 8C, and 8K. The configuration of Comparative Example 3 is substantially the same as the configuration of this embodiment, except that the configuration of developer T is different as described above.

[0102] Then, in the configurations of this embodiment and Comparative Example 3, a paper passing durability test was performed to check whether or not vertical stripe images occurred in the most upstream image forming station PY. The recording material S (paper) used for printing was Xerox multipurpose paper (basis weight 75 g / m 2 The size of the paper was 128 x 1024 x 720 mm (LTR size). The printed image was a horizontal line image with a printing rate of 4% for each color. The occurrence of vertical stripe images was judged using a secondary color halftone image with a printing rate of 25% for each of yellow and magenta.

[0103] The results are shown in Table 3. In Table 3, "◯" indicates no occurrence of vertical streak images, "△" indicates slight occurrence of vertical streak images, and "×" indicates occurrence of vertical streak images. The total drive time of the photosensitive drum 4 is shown with the total drive time corresponding to the threshold value (life end timing) described in the first embodiment as 100%.

[0104] [Table 3]

[0105] As shown in Table 3, in this embodiment, no vertical streak images were generated until the total drive time of the photosensitive drum 4 reached 100%, which is the end of life timing. On the other hand, in Comparative Example 3, vertical streak images were generated when the total drive time of the photosensitive drum 4 reached 80% of the end of life timing.

[0106] In the configuration of Comparative Example 3, the amount of foreign matter A collected on the most upstream photosensitive drum 4Y was large, and the amount of scraping of the photosensitive drum 4Y was large, so that vertical streak images occurred in the most upstream image forming portion PY.

[0107] In contrast, in the configuration of this embodiment, the amount of metal soap X per unit mass of developer T contained in the most upstream developing cartridge 8Y is made greater than the amount of metal soap X per unit mass of developer T contained in the downstream developing cartridges 8M, 8C, and 8K. As a result, in the configuration of this embodiment, the amount of scraping of the most upstream photosensitive drum 4Y is reduced, making it possible to suppress the occurrence of vertical streak images.

[0108] In this embodiment, the developer T contained in the downstream developing cartridges 8M, 8C, and 8K does not contain the metal soap X, but the present invention is not limited to this embodiment. For example, the content of the metal soap X in the developer T contained in the most upstream developing cartridge 8Y may be greater than the content of the metal soap X in the developer T contained in the downstream developing cartridges 8M, 8C, and 8K. Depending on the amount of the metal soap X, which is a lubricant, moving to the photosensitive drum 4, it is sufficient to increase the effect of weakening the force of the most upstream photosensitive drum 4Y being rubbed by the foreign matter A more than the effect of weakening the force of the downstream photosensitive drums 4M, 4C, and 4K being rubbed by the foreign matter A. In other words, it is sufficient to suppress the amount of scraping of the most upstream photosensitive drum 4Y and match it to the amount of scraping of the downstream photosensitive drums 4M, 4C, and 4K.

[0109] As described above, in this embodiment, the first developer contained in the first developing device 8Y includes developer base particles and metal soap attached to the surfaces of the developer base particles, and the second developer contained in the second developing devices 8M, 8C, and 8K includes at least developer base particles among the developer base particles and the metal soap, and the first mass ratio, which is the ratio of the mass of the metal soap per unit mass of the first developer, is greater than the second mass ratio, which is the ratio of the mass of the metal soap per unit mass of the second developer. In particular, in this embodiment, the first developer includes the metal soap, and the second developer does not include the metal soap.

[0110] According to this embodiment, the amount of wear on the upstream photosensitive drum 4Y can be suppressed to match the amount of wear on the downstream photosensitive drums 4M, 4C, and 4K, thereby extending the overall life of the multiple drum units 30 that are integrated into a single replaceable part.

[0111] [others] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-mentioned embodiments.

[0112] In the above embodiment, the foreign matter recovery member is provided only in the most upstream image forming unit, but the foreign matter recovery member may be provided in the downstream image forming unit. Even in such a configuration, most of the foreign matter that easily moves to the image carrier is recovered in the most upstream image carrier, so the same problems as in the above embodiment may occur. Therefore, even in such a configuration, by applying the present invention, it is possible to obtain the same effects as in the above embodiment.

[0113] In the above embodiment, the charging voltage and the developing voltage are described as DC voltage components, but the charging voltage and the developing voltage may be oscillating voltages in which a DC voltage (DC component) and an AC voltage (AC component) are superimposed. The same applies to the collecting voltage and the discharging voltage.

[0114] In the above embodiment, the static elimination light source is used as the static elimination means, but when, for example, a charging means with sufficiently small charging unevenness is used, the static elimination means does not need to be provided.

[0115] In addition, in the above-described embodiment, a one-component non-magnetic contact development method is adopted, but the present invention is not limited to such an embodiment, and a two-component non-magnetic contact development method, a non-contact development method, a magnetic development method, etc. may also be adopted.

[0116] In the above embodiment, the cleaning member is a rotatable roller-shaped member, but it may be, for example, a rotatable brush-shaped member (brush roller), etc. In the above embodiment, the foreign matter collection member is a rotatable roller-shaped member, but it may be, for example, a rotatable brush-shaped member (brush roller), etc.

[0117] In the above embodiment, the image carrier is a rotatable drum-shaped member, but may be, for example, an endless belt. In the above embodiment, the transfer member is a rotatable roller-shaped member, but is not limited to this. For example, the transfer member may be a pad-shaped member, a sheet-shaped member, a brush-shaped member (such as a fixed brush or a rotatable brush roller), a rotatable endless belt (a pressing member that contacts the photoconductor via the belt may be provided), etc. In addition, the charging member may be a rotatable roller-shaped member, a brush-shaped member (such as a rotatable brush roller), a rotatable endless belt, etc.

[0118] In addition, in the above-described embodiment, the image forming device has four image forming units, but the number of image forming units is not limited to 4. The number of image forming units may be two or more depending on the number of colors to be used, and may be, for example, three or five or more. [Explanation of symbols]

[0119] 1. Image forming device 4 Photosensitive drum 5. Charging device 6 Developing roller 8 Developing device (developing cartridge) 10 Exposure equipment 12 Transfer belt 16 Transfer roller 30 Drum unit 32 Cleaning roller 33 Foreign object collection roller 34 Scraping member 35 Foreign matter collection container A Foreign body S recording material T Developer (toner) T0 developer base particles T1 Residual toner X Metal soap

Claims

1. An image forming apparatus capable of performing an image forming operation for forming an image on a recording material, a first image forming section including a rotatable first image carrier having a photosensitive layer, a first charging member for charging a surface of the first image carrier, a first developing device for supplying a first developer to the surface of the first image carrier, a first transfer member for transferring the first developer supplied to the surface of the first image carrier to a recording material, a first cleaning member for contacting the first image carrier to clean the surface of the first image carrier, and a recovery member for recovering foreign matter adhering to the first cleaning member; a second image forming section including a rotatable second image carrier having a photosensitive layer, a second charging member for charging the surface of the second image carrier, a second developing device for supplying a second developer to the surface of the second image carrier, a second transfer member for transferring the second developer supplied to the surface of the second image carrier to a recording material, and a second cleaning member for contacting the second image carrier to clean the surface of the second image carrier; a belt that contacts the first image carrier to form a first transfer portion and contacts the second image carrier to form a second transfer portion, the belt nipping and conveying a recording material between the first image carrier and the second image carrier in the first transfer portion and the second transfer portion, respectively; the first image forming unit is disposed upstream of the second image forming unit in a moving direction of a recording material, and a plurality of members including the first image carrier and the second image carrier are integrated and detachably attached to a main body of the image forming apparatus, a thickness of a surface layer of the first image carrier is greater than a thickness of a surface layer of the second image carrier; 13. An image forming apparatus, comprising: said first developer being yellow; and said second developer being black.

2. An image forming apparatus capable of performing an image forming operation for forming an image on a recording material, a first image forming section including a rotatable first image carrier, a first charging member for charging a surface of the first image carrier, a first developing device for supplying a first developer to the surface of the first image carrier by a first developer carrier, a first transfer member for transferring the first developer supplied to the surface of the first image carrier to a recording material, a first cleaning member for contacting the first image carrier to clean the surface of the first image carrier, and a recovery member for recovering foreign matter adhering to the first cleaning member; a second image forming section including a rotatable second image carrier, a second charging member for charging a surface of the second image carrier, a second developing device for supplying a second developer to the surface of the second image carrier by a second developer carrier, a second transfer member for transferring the second developer supplied to the surface of the second image carrier to a recording material, and a second cleaning member for contacting the second image carrier to clean the surface of the second image carrier; a belt that contacts the first image carrier to form a first transfer portion and contacts the second image carrier to form a second transfer portion, the belt nipping and conveying a recording material between the first image carrier and the second image carrier in the first transfer portion and the second transfer portion, respectively; a driving means for rotating the first developer carrier and the second developer carrier, the driving means rotating the first image carrier and the first developer carrier so that they move in the same direction at a portion where the first image carrier and the first developer carrier face each other, and the driving means for rotating the second image carrier and the second developer carrier so that they move in the same direction at a portion where the second image carrier and the second developer carrier face each other, the first image forming unit is disposed upstream of the second image forming unit in a moving direction of a recording material, and a plurality of members including the first image carrier and the second image carrier are integrated and detachably attached to a main body of the image forming apparatus, an image forming apparatus, characterized in that a first peripheral speed ratio, which is a ratio of the peripheral speed of the first developer carrier to the peripheral speed of the first image carrier, is smaller than a second peripheral speed ratio, which is a ratio of the peripheral speed of the second developer carrier to the peripheral speed of the second image carrier.

3. 3. The image forming apparatus according to claim 2, wherein a gear ratio of a first gear provided between the first developer carrier and the driving means is different from a gear ratio of a second gear provided between the second developer carrier and the driving means.

4. 3. The image forming apparatus according to claim 2, wherein the driving means comprises a first driving means for rotating the first developer carrier and a second driving means for rotating the second developer carrier, and the driving speed of the first developer carrier by the first driving means is different from the driving speed of the second developer carrier by the second driving means.

5. An image forming apparatus capable of performing an image forming operation for forming an image on a recording material, a first image forming section including a rotatable first image carrier, a first charging member for charging a surface of the first image carrier, a first developing device for supplying a first developer to the surface of the first image carrier by a first developer carrier contacting the surface of the first image carrier, a first transfer member for transferring the first developer supplied to the surface of the first image carrier to a recording material, a first cleaning member for contacting the first image carrier to clean the surface of the first image carrier, and a recovery member for recovering foreign matter adhering to the first cleaning member; a second image forming section including a rotatable second image carrier, a second charging member for charging a surface of the second image carrier, a second developing device for supplying a second developer to the surface of the second image carrier by a second developer carrier contacting the surface of the second image carrier, a second transfer member for transferring the second developer supplied to the surface of the second image carrier to a recording material, and a second cleaning member for contacting the second image carrier to clean the surface of the second image carrier; a belt that contacts the first image carrier to form a first transfer portion and contacts the second image carrier to form a second transfer portion, the belt nipping and conveying a recording material between the first image carrier and the second image carrier in the first transfer portion and the second transfer portion, respectively; the first image forming unit is disposed upstream of the second image forming unit in a moving direction of a recording material, and a plurality of members including the first image carrier and the second image carrier are integrated and detachably attached to a main body of the image forming apparatus, an image forming apparatus, characterized in that a first contact pressure when the first image carrier and the first developer carrier are in contact with each other is smaller than a second contact pressure when the second image carrier and the second developer carrier are in contact with each other.

6. 6. The image forming apparatus according to claim 5, wherein the first developer carrier and the second developer carrier are rollers having an elastic layer formed around a core axis, and a distance between the first image carrier and the core axis of the first developer carrier when the first image carrier and the first developer carrier are in contact with each other is greater than a distance between the second image carrier and the core axis of the second developer carrier when the second image carrier and the second developer carrier are in contact with each other.

7. 7. The image forming apparatus according to claim 6, wherein the first contact pressure is determined by a first regulating member arranged at both longitudinal ends of the first developer carrier abutting against the first image carrier, and the second contact pressure is determined by a second regulating member arranged at both longitudinal ends of the second developer carrier abutting against the second image carrier.

8. The image forming apparatus of claim 6, wherein the first contact pressure is determined by a first positioning portion provided on a frame body constituting the first developing device abutting against the first image carrier, and the second contact pressure is determined by a second positioning portion provided on a frame body constituting the second developing device abutting against the second image carrier.

9. An image forming apparatus capable of performing an image forming operation for forming an image on a recording material, a first image forming section including a rotatable first image carrier, a first charging member for charging a surface of the first image carrier, a first developing device for supplying a first developer to the surface of the first image carrier, a first transfer member for transferring the first developer supplied to the surface of the first image carrier to a recording material, a first cleaning member for contacting the first image carrier to clean the surface of the first image carrier, and a recovery member for recovering foreign matter adhering to the first cleaning member; a second image forming section including a rotatable second image carrier, a second charging member for charging a surface of the second image carrier, a second developing device for supplying a second developer to the surface of the second image carrier, a second transfer member for transferring the second developer supplied to the surface of the second image carrier to a recording material, and a second cleaning member for contacting the second image carrier to clean the surface of the second image carrier; a belt that contacts the first image carrier to form a first transfer portion and contacts the second image carrier to form a second transfer portion, the belt nipping and conveying a recording material between the first image carrier and the second image carrier in the first transfer portion and the second transfer portion, respectively; the first image forming unit is disposed upstream of the second image forming unit in a moving direction of a recording material, and a plurality of members including the first image carrier and the second image carrier are integrated and detachably attached to a main body of the image forming apparatus, An image forming apparatus characterized in that the first developer comprises developer base particles and a metal soap adhered to the surfaces of the developer base particles, and the second developer comprises at least the developer base particles among the developer base particles and the metal soap, and a first mass ratio which is a ratio of the mass of the metal soap per unit mass of the first developer is larger than a second mass ratio which is a ratio of the mass of the metal soap per unit mass of the second developer.

10. 10. The image forming apparatus according to claim 9, wherein the first developer contains the metal soap, and the second developer does not contain the metal soap.

11. An image forming apparatus as described in any one of claims 1 to 10, characterized in that when the recovery member is a first recovery member, the second image forming unit does not include a second recovery member for recovering foreign matter adhering to the second cleaning member.

Images