JP2011186013A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which outputs a satisfactory image for a long time by reducing soil of a charging roller and also by preventing abnormal discharge by gradually decreasing a charging gap over time. <P>SOLUTION: The gap holding member abutting parts of gap holding members 103 and photoreceptor 40 are polished, and the charging gap is gradually decreased according to the rotation time of the photoreceptor 40. A polishing blade 90 abuts on only the part of the gap holding members 103 attached to both ends of the charging roller 70. The gap holding members 103 are polished by the rotation of the charging roller 70. The polishing blade 90 is made of polyurethane rubber as its main component, and alumina particles as polishing particles which are dispersed in the polyurethane rubber. Since a polishing agent is dispersed in thick polyurethane rubber, polishing action is sustained even when the polishing blade 90 wears over time. Consequently, the gap holding members 103 can be polished for a long time. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a composite apparatus thereof, and more particularly to an image forming apparatus including a charging roller disposed in a non-contact manner on an image carrier.

  As a charging means of an image forming apparatus, a system using corona discharge has been widely used, but a proximity discharge system that generates less discharge products such as ozone has also been used. A charging roller is used as one of proximity charging type charging means.

  Conventionally, the charging roller has been used in contact with the image carrier, but recently, a non-contact charging roller arranged in non-contact with the image carrier has also been put into practical use. In an image forming apparatus using such a non-contact charging roller, for example, as disclosed in Patent Document 1, wear of the gap holding member is prevented by rotating the charging roller at a constant speed with the photosensitive member. The emphasis was placed on the stable formation of the charging gap.

  On the other hand, as disclosed in Patent Document 2, for example, it has been proposed to adjust the pressure applied to the charging roller according to the environment. This is to cope with a change in the charging gap due to a change in the hardness due to the environment in a rubber roller having a low hardness, and the aim is to keep the charging gap constant regardless of the environment. That is.

  However, with a rubber roller having a relatively low hardness, the charging gap can be adjusted by changing the pressing force. However, if the charging member is made of resin, the hardness is high, so even if the pressing force is changed. The charging gap hardly changes.

  In addition, as the inventors of the present application know, no consideration has been given to the deterioration of the abnormal discharge margin due to deterioration of the charging roller over time.

  That is, the charging method using proximity discharge such as a charging roller has an advantage that the discharge product such as ozone is very small compared to the charging method using corona discharge, but the charging roller is used in contact with the photosensitive member. In this case, toner that has passed through the cleaning slightly, toner external additive, lubricant applied to the photosensitive member, and the like are likely to adhere to the charging roller. When these substances adhere and accumulate, the resistance of the charging roller increases, causing a charging failure. On the other hand, by disposing the charging roller in contact with the photosensitive member, it is possible to prevent the substance that has passed through the cleaning from coming into contact with the charging roller and transferring it, and the life of the charging roller can be improved. .

  However, when the charging roller is arranged in a non-contact manner with respect to the photoreceptor, uneven charging due to abnormal discharge is likely to occur. This is more likely to occur as the charging gap becomes larger. In addition, due to the material, there is an upper limit of the charging gap that allows uniform charging. The upper limit of the charging gap is smaller in the electron conductive material than in the ion conductive material and tends to cause abnormal discharge. For this reason, ionic conductive materials were mainly used for non-contact charging rollers. However, it was found that even with ionic conductive materials, the gap margin decreases with time and charging unevenness due to abnormal discharge tends to occur. .

  Conventional non-contact charging rollers focus on stabilizing the charging gap over time as in Patent Document 1, or adjust the charging gap according to the environment as in the technique of Patent Document 2. No consideration has been given to preventing abnormal discharge that occurs with time of the non-contact charging roller.

  In consideration of such a situation, the present invention reduces the contamination of the charging roller by arranging the charging roller in a non-contact manner, and gradually reduces the charging gap over time to prevent the occurrence of abnormal discharge, and for a long time. An object of the present invention is to provide an image forming apparatus capable of outputting a good image over a wide range.

  The image forming apparatus of the present invention is an image forming apparatus including a charging unit disposed in a non-contact manner with respect to an image carrier via a minute gap. The image gap is formed between the image carrier and the charging unit. It is characterized by having charging gap reduction means that decreases with the rotation time of the carrier.

  In the image forming apparatus of the present invention, the charging unit has a roller shape, and the charging unit includes at least a core metal as a conductive support and a resin material including an ion conductive material. And a gap holding made of an insulating resin material that is disposed at both ends of the charging member and abuts against a non-image portion of the image bearing member to form a gap that forms the minute gap between the image bearing member and the charging member. It consists of members.

In the image forming apparatus according to the aspect of the invention, the charging gap reduction unit polishes a contact position of the gap holding unit or the gap holding member of the image carrier to reduce the minute gap. .

  The image forming apparatus according to the present invention further includes means for generating a rotational speed difference between the image carrier and the gap holding member.

  In the image forming apparatus of the present invention, the image carrier is made of an organic photoreceptor, and a protective layer for reducing the wear of the organic photoreceptor is formed on the outermost layer.

  The image forming apparatus of the present invention is characterized in that the image carrier is made of an inorganic photoreceptor.

  The image forming apparatus of the present invention further includes a lubricant supply unit that supplies a lubricant to the image carrier, and the lubricant supply unit does not supply the lubricant to a position where the gap holding member abuts. Features.

  Further, the image forming apparatus of the present invention is characterized in that at least the image carrier and the charging unit are configured as a process cartridge that can be integrally attached to and detached from the image forming apparatus main body.

  According to the present invention, by increasing the gap between the image carrier, the charging unit, and the charging unit, the charging unit is less likely to be contaminated. Over time, the gap between the image carrier and the charging unit is decreased, so that the charging member is deteriorated. It is also possible to prevent the occurrence of abnormal images due to.

Overall configuration diagram showing an example applied to a tandem intermediate transfer type full-color copier Diagram showing configuration of image forming unit The figure which shows the example which has arrange | positioned the lubricant supply means downstream of the cleaning blade A diagram showing the configuration of the charging roller (A), a diagram showing an example in which a polishing blade is brought into contact with the charging roller (B)

  The present invention provides, as an embodiment, an image forming apparatus including a charging unit formed in a non-contact manner by forming a minute gap with respect to an image carrier, wherein the gap between the image carrier and the charging unit is an image carrier unit. It is configured to decrease with the rotation time. With this configuration, the charging unit is less likely to be contaminated, and charging failure due to deterioration of the charging unit over time is prevented. That is, by increasing the gap between the image carrier, the charging unit, and the charging unit, the charging unit is less likely to be contaminated. In addition, since the gap between the image carrier and the charging unit decreases with time, the occurrence of abnormal images due to deterioration of the charging member can be prevented.

  According to the present invention, in the image forming apparatus, the charging unit includes at least a core member as a conductive support and a charging member made of a resin material including an ionic conductive material, and an image carrier disposed at both ends of the charging member. A roller holding member made of an insulating resin material that is in contact with a non-image portion of the body and forms a gap between the image carrier and the charging member, and the image carrier and the charging member A stable gap is formed between them. That is, by making the charging member and the gap holding member into a roller shape made of a resin material, it is possible to process with high accuracy and to form a stable charging gap with little environmental fluctuation.

  The present invention further includes a charging gap reducing unit that polishes the gap holding unit of the charging unit or the contact position of the gap holding member of the image carrier to reduce the charging gap. The charging gap is reduced according to the rotation time. According to the present invention, in the above-described image forming apparatus, a speed difference is generated between the image carrier and the gap holding member, and the gap is held by the speed difference between the image carrier and the gap holding member. The image carrier at the contact position of the member or the gap holding member is worn. Thus, it is not necessary to add a polishing member, and the charging gap can be gradually reduced according to the rotation time of the image carrier.

  According to the present invention, in the above-described image forming apparatus, the image carrier is an organic photoconductor, and a protective layer for reducing the wear of the photoconductor is formed on the outermost layer. Improves sex. By forming a protective layer on the surface of the organic photoreceptor, the abrasion resistance of the photoreceptor can be greatly improved, so even if a speed difference is provided between the image carrier and the gap holding member, the photosensitive layer Deterioration of is difficult to occur.

  According to the present invention, in the above-described image forming apparatus, the image carrier is an inorganic photoconductor, and the durability of the image carrier is improved. That is, since the inorganic photoreceptor is very excellent in abrasion resistance, even when a speed difference is provided between the image carrier and the gap holding member, the photosensitive layer is hardly deteriorated.

  Further, according to the present invention, the image forming apparatus includes a lubricant supply unit that supplies a lubricant to the image carrier, and prevents the lubricant from being supplied to a position where the gap holding member abuts. That is, the image carrier is protected by the lubricant in the image region, and the gap holding member and the image carrier are protected by the lubricant at the position where the gap holding member is abutted to prevent the wear from being reduced. If the lubricant is not supplied to the contact position of the gap holding member, the gap holding member can be worn according to the rotation time without protecting the gap holding member.

  In the image forming apparatus described above, the present invention further comprises a process cartridge in which at least the image carrier and the charging unit are integrally removable from the main body, and the amount of reduction in the charging gap depending on the rotation time of the image carrier. To be able to predict. That is, since the image carrier and the charging unit form an integrated process cartridge, the amount of reduction in the charging gap can be predicted by storing the rotation time of the image carrier.

Embodiments of the present invention will be described below with reference to the drawings.
First, the overall configuration and basic operation of the image forming apparatus will be described. FIG. 1 is an overall configuration diagram showing an example applied to a tandem intermediate transfer type full-color copying machine. The full-color copying machine includes a copying machine main body 100, a paper feeding device 200 on which the copying apparatus main body 100 is mounted, a scanner 300 attached on the copying machine main body, an automatic document feeder (ADF) 400 attached on the scanner 300, and the like. Has been.

  In the center of the apparatus main body 1, image forming units 18Y, 18C, 18M, and 18Bk for four colors Y, C, M, and Bk are arranged side by side to constitute a tandem image forming apparatus 20. . Each image forming unit 18 of the tandem image forming apparatus 20 includes photoreceptors 40Y, 40C, 40M, and 40Bk on which toner images of respective colors Y, C, M, and Bk are formed. In the following description, unless there is a need to specify a color, it is simply referred to as the image forming unit 18, the photoreceptor 40, etc., except for the first description. This description is not limited to the image forming unit 18 and the photoreceptor 40, and the same applies to other components and components.

  An exposure device 21 is provided above the tandem image forming apparatus 20. The exposure device 21 is arranged in four laser diode (LD) light sources prepared for each color, a set of polygon scanners composed of a six-sided polygon mirror and a polygon motor, and an optical path of each light source. It is composed of a lens such as an fθ lens, a long WTL, or a mirror. The laser light emitted from the LD in accordance with the image information of each color is deflected and scanned by the polygon scanner and applied to the photoconductor 40 of each color.

  An endless belt-shaped intermediate transfer belt 10 is installed below the tandem image forming apparatus. In the illustrated example, the intermediate transfer belt 10 is wound around three support rollers 14, 15, and 16 and can be rotated and conveyed in the clockwise direction in the figure. The support roller 14 is a driving roller that drives the intermediate transfer belt 10 to rotate. It is as. Further, between the first support roller 14 and the second support roller 15, primary transfer rollers 62Y, 62C, 62M, and 62Bk are used as primary transfer means for transferring the toner image from the photoconductor 40 of each color to the intermediate transfer belt 10. The intermediate transfer belt 10 is provided so as to face the corresponding photoreceptor colors 40 with the intermediate transfer belt 10 interposed therebetween.

  An intermediate transfer belt cleaning device 17 for removing residual toner remaining on the intermediate transfer belt 10 after image transfer is provided on the downstream side of the third support roller 16 in the sheet conveyance direction.

  As the material of the intermediate transfer belt 10, a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, polyethylene terephthalate, etc. can be molded into a seamless belt and used. These materials can be used as they are, or the resistance can be adjusted with a conductive material such as carbon black. Further, using these resins as a base layer, a surface layer may be formed by a method such as spraying or dipping to form a laminated structure.

  Further, a secondary transfer device 22 is provided below the intermediate transfer belt 10. In the example shown in the figure, the secondary transfer device 22 is configured by spanning a secondary transfer belt 24 that is an endless belt between two rollers 23, 23, and the third support roller 16 via the intermediate transfer belt 10. The image on the intermediate transfer belt 10 is transferred to a transfer material. As the secondary transfer belt, the same material as that of the intermediate transfer belt 10 can be used.

  A fixing device 25 for fixing the toner image on the transfer material as an image is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt.

  The secondary transfer device 22 also has a sheet conveyance function for conveying the transfer material after image transfer to the fixing device 25. Of course, a transfer roller or a transfer charger may be disposed as the secondary transfer device 22, and in such a case, it is necessary to provide this transfer material conveying function separately.

  In the illustrated example, in order to reversely discharge the transfer material or to form an image on both sides of the transfer material below the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming device 20 described above. A sheet reversing device 28 for reversing the transfer material and refeeding the transfer material is provided.

  When performing a copying operation using this full-color copying machine, a document is set on the document table 30 of the ADF 400. Alternatively, the ADF 400 is opened and a document is set on the contact glass 32 of the scanner, and the ADF 400 is closed and the document is pressed. When the start switch of the operation unit (not shown) is pressed, when the document is set on the ADF 400, the document is transported and moved onto the contact glass 32, and then the scanner is driven. When is set, the scanner is immediately driven to drive the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read. Thereafter, when the mode setting is performed on the operation unit (not shown), or when the automatic mode selection is set on the operation unit, the image forming operation is started in the full color mode or the monochrome mode according to the reading result of the document. .

  When the full color mode is selected, each color photoconductor 40 rotates in the counterclockwise direction in FIG. Then, the surface of each color photoconductor 40 is uniformly charged by a later-described charging roller which is a charging device. Then, each color photoconductor 40 is irradiated with laser light corresponding to the image of each color from the exposure device 21, and a latent image corresponding to the image data of each color is formed. Each latent image is developed with toner of each color by the developing devices 60Y, 60C, 60M, and 60Bk of the respective colors as the photoreceptor 40 rotates. The toner images of the respective colors are sequentially transferred onto the intermediate transfer belt 10 along with the conveyance of the intermediate transfer belt 10 to form a full color image on the intermediate transfer belt 10. After the transfer, the photoreceptor 40 is subjected to light neutralization by a neutralization lamp, and the residual toner is removed by a cleaning unit.

  On the other hand, one of the paper feeding rollers 42 of the paper feeding device 200 is selectively rotated to feed the transfer material from one of the paper feeding cassettes 44 provided in multiple stages on the paper feeding table 43 and separated one by one by the separation roller 45. The paper is put into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the main body, and abutted against the registration roller 49 and stopped. Alternatively, the transfer roller 50 is rotated to feed the transfer material on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped. Then, the registration roller 49 is rotated in synchronization with the full-color image on the intermediate transfer belt 10, the transfer material is fed between the intermediate transfer belt 10 and the secondary transfer device, and the transfer material is transferred by the secondary transfer device. Transfer the toner image on top.

  The transfer material on which the toner image has been transferred is conveyed by the secondary transfer device and sent to the fixing device 25. The fixing device 25 applies heat and pressure to fix the transfer material, and then the switching material is switched by the switching claw 55. The paper is discharged by the discharge roller 56 and stacked on the paper discharge tray 57. Alternatively, it is switched by the switching claw 55 and put into the sheet reversing device 28, where it is reversed and fed again to the transfer position. After the image is also recorded on the back side, it is ejected onto the paper ejection tray by the ejection roller. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is repeated.

  After the predetermined number of images have been formed, the post-image forming process is performed, and then the rotation of the photoconductor 40 is stopped. In the post-image forming process, the photosensitive member 40 is rotated one or more times with the charging bias and the transfer bias turned off. At that time, the charge on the surface of the photosensitive member 40 is discharged by the discharging means, and the photosensitive member 40 remains discharged. This prevents the photoconductor 40 from being left to deteriorate.

  When the monochrome mode is selected, the support roller 15 moves downward to separate the intermediate transfer belt 10 from the photoreceptor 40. Only the Bk photoconductor 40Bk rotates counterclockwise in FIG. 1, the surface of the photoconductor 40Bk is uniformly charged by the charging roller, and a laser beam corresponding to the Bk image is irradiated to form a latent image. , Bk toner develops a toner image. This toner image is transferred onto the intermediate transfer belt 10. At this time, the three-color photoconductors 40Y, 40C, and 40M other than Bk and the developing device 60 are stopped, and unnecessary consumption of the photoconductor 40 and the developer is prevented.

  On the other hand, the transfer material is fed from the paper feed cassette 44 and conveyed by the registration roller 49 at a timing that coincides with the toner image formed on the intermediate transfer belt 10. The transfer material onto which the toner image has been transferred is fixed by the fixing device 25 as in the case of a full-color image, and is processed through a paper discharge system corresponding to a designated mode. Thereafter, when the formation of two or more images is instructed, the above-described image forming process is repeated.

The configuration of the image forming unit 18 is shown in FIG. Around the photosensitive member 40 as an image carrier, a charging roller 70 for uniformly charging the photosensitive member 40, a potential sensor 71 for detecting the potential of the photosensitive member 40, and an electrostatic latent image formed on the photosensitive member 40 are developed. A developing device 60 for discharging, a neutralizing lamp 72 for neutralizing the surface of the photoreceptor 40 after the toner image is transferred, and two brush rollers 73 and 74 and a cleaning blade 75 as a cleaning device for cleaning the transfer residual toner. Has been. The case of the image forming unit 18 is provided with an opening for allowing the exposure light 76 from the exposure device 21 to pass therethrough.
A solid lubricant 78 is in contact with the brush roller 74 and has a function as a lubricant supply member. Examples of solid lubricants include zinc stearate, barium stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, magnesium stearate, zinc oleate, oleic acid Fatty acid metal salts such as cobalt, magnesium oleate, and zinc palmitate, natural waxes such as carnauba wax, and fluorine-based resins such as polytetrafluoroethylene can be used.

  The toner scraped off from the photoreceptor 40 by a brush roller or a cleaning blade made of polyurethane rubber is collected by a toner transport coil 79 and transported to a waste toner storage section (not shown).

  In this embodiment, the photosensitive member 40 that has been discharged after the transfer is cleaned. However, the photosensitive member 40 that has been cleaned after the transfer may be cleaned.

  In the above embodiment, the lubricant supply means is disposed in the cleaning means. However, this configuration has a drawback that the supply of the lubricant is easily affected by the amount of toner input to the cleaning. This is because the lubricant supply means is provided in the cleaning means, so that the amount of toner input to the cleaning (transfer residual toner or reverse transfer toner based on the toner image formed upstream in the full-color image forming apparatus) is reduced. When it fluctuates, the supply efficiency of the lubricant is affected. On the other hand, as shown in FIG. 3, the lubricant 78, the lubricant supply brush 74, and the lubricant application blade 80, which are the lubricant supply means, are arranged downstream of the cleaning blade 75, so that the transfer residue depends on the image area to be formed. Even if the input amount of toner or reverse transfer toner changes, the lubricant can be stably supplied to the image carrier.

  FIG. 4A shows a configuration of a charging roller 70 that can be used in this embodiment. The charging roller 70 includes a cored bar 101 as a conductive support, a resin layer 102 as a charging member, and a gap holding member 103.

A metal such as stainless steel is used for the core metal. If the mandrel is too thin, the influence of deflection when the charging member is cut or when the photosensitive member 40 is pressurized cannot be ignored, and the required gap accuracy is difficult to obtain. Further, when the core bar is too thick, there is a problem that the charging roller 70 becomes large or the mass becomes heavy. Therefore, the diameter of the core bar is preferably about 6 to 10 mm. The resin layer of the charging roller 70 is preferably a material having a volume resistance of 10 ⁴ to 10 ⁹ Ωcm. If the resistance is too low, charging bias leaks easily when there is a defect such as a pinhole in the photoconductor 40. If the resistance is too high, the discharge is not sufficiently generated and a uniform charging potential cannot be obtained. A desired volume resistance can be obtained by blending a conductive material with a resin as a base material. As the base resin, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate can be used. Since these base resins have good moldability, they can be easily molded.

  As the conductive material, an ion conductive material such as a polymer compound having a quaternary ammonium base is preferable. Examples of polyolefins having a quaternary ammonium base include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-vinyl acetate copolymer, ethylene- Polyolefins such as propylene copolymer and ethylene-hexene copolymer. In the present embodiment, the polyolefin having a quaternary ammonium base is exemplified, but a polymer compound other than the polyolefin having a quaternary ammonium base may be used.

  The ion conductive material is uniformly blended with the base resin by using means such as a biaxial kneader or a kneader. The blended material can be easily molded into a roller shape by injection molding or extrusion molding on the core metal. The blending amount of the ion conductive material and the base resin is desirably 30 to 80 parts by weight of the ion conductive material with respect to 100 parts by weight of the base resin. The thickness of the resin layer of the charging roller 70 is desirably 0.5 to 3 mm. If the resin layer is too thin, molding is difficult and there is a problem in terms of strength. If the resin layer is too thick, the charging roller 70 is increased in size and the actual resistance of the resin layer is increased, so that the charging efficiency is lowered.

  After the resin layer is molded, a gap holding member molded in advance on both ends of the resin layer is fixed to the core metal by press-fitting, bonding, or both. In this way, after the charging member and the gap holding member are integrated, the phase of the charging member and the gap holding member can be aligned by adjusting the outer diameter of the charging roller 70 by performing processing such as cutting and grinding. And variation in the charging gap can be reduced.

  As the material of the gap holding member, a resin such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, polycarbonate, and the like can be used in the same manner as the base material of the charging member. However, since the gap holding member is brought into contact with the photosensitive layer, it is desirable to use a grade having a lower hardness than the charging member in order to prevent the photosensitive layer from being damaged. In addition, as a resin material having excellent slidability and hardly damaging the photosensitive layer, polyacetal, ethylene-ethyl acrylate copolymer, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoro A resin such as a propylene copolymer can also be used.

In addition, a surface layer on which the toner or the like is difficult to adhere can be formed on the resin layer or the gap holding member with a thickness of about several tens of micrometers by coating or the like. A gap is formed between the resin layer of the charging roller 70 and the photoconductor 40 by applying the gap holding member outside the image area of the photoconductor 40. In the charging roller 70, the gear attached to the end of the metal core meshes with the gear formed on the flange of the photoconductor 40. When the photoconductor 40 is rotated by the motor that drives the photoconductor 40, the charging roller 70 is also rotated. Rotate in the direction. Since the resin layer and the photosensitive member 40 do not come into contact with each other, even when a hard resin material and an organic photosensitive member are used as the charging roller 70, the photosensitive layer in the image area is not damaged. Further, if the gap is too wide, abnormal discharge occurs and it becomes impossible to uniformly charge, so the maximum gap needs to be suppressed to about 100 μm or less. When such a charging roller 70 having a gap between the photoreceptor 40 and the charging roller 70 is used, it is desirable to superimpose an AC voltage on a DC voltage as a charging bias.
Since the charging member and the gap holding member are made of a resin material, the charging roller 70 can be manufactured with high accuracy and easy processing.

  The charging roller 70 is in contact with a cleaning roller 77 for cleaning the roller surface. This cleaning roller is a roller in which a melamine foam is mounted on a metal mandrel, and is in contact with the charging roller 70 by its own weight. Remove dirt. The cleaning roller may be kept in contact with the charging roller 70 at all times, but it is provided with a cleaning roller contact / separation mechanism so that the cleaning roller is usually separated and periodically brought into contact with the charging roller 70 as necessary. Alternatively, the surface of the charging roller 70 can be cleaned.

  Each developing device 60 has the same configuration, and is a two-component developing type developing device 60 that differs only in the color of the toner to be used. In each color developing device 60, two-component development comprising toner and carrier is performed. The agent is contained. The developing device 60 includes a developing roller 61 facing the photoreceptor 40, screws 63a and 63b for conveying and stirring the developer, a toner concentration sensor 64, and the like. The developing roller 61 includes an outer rotatable sleeve and an inner fixed magnet. A required amount of toner is supplied from a toner supply device (not shown) according to the output of the toner density sensor.

  The toner includes a binder resin, a colorant, and a charge control agent as main components, and other additives are added as necessary. Specific examples of the binder resin include polystyrene, styrene-acrylic acid ester copolymer, polyester resin, and the like. As the colorant (for example, yellow, magenta, cyan and black) used for the toner, those known for toner can be used. The amount of the coloring material is suitably 0.1 to 15 parts by weight with respect to 100 parts by weight of the binder resin.

  Specific examples of the charge control agent include a nigrosine dye, a chromium-containing complex, a quaternary ammonium salt, and the like, which are properly used depending on the polarity of the toner particles. The amount of the charge control agent is 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin. It is advantageous to add a fluidity imparting agent to the toner particles. Examples of the fluidity-imparting agent include fine particles of metal oxides such as silica, titania and alumina, and those obtained by surface-treating these fine particles with a silane coupling agent, titanate coupling agent, etc., polystyrene, polymethyl methacrylate, polyvinylidene fluoride. Polymer fine particles such as are used. These fluidity imparting agents have a particle size in the range of 0.01 to 3 μm. The addition amount of these fluidity-imparting agents is preferably in the range of 0.1 to 7.0 parts by weight with respect to 100 parts by weight of the toner particles.

  As a method for producing a toner for two-component developer, it can be produced by various known methods or a combination thereof. For example, in the kneading and pulverization method, a binder resin, a colorant such as carbon black, and the necessary additives are dry-mixed, heated and melt-kneaded with an extruder or two-roll, three-roll, etc., and after cooling and solidification Then, the toner is pulverized by a pulverizer such as a jet mill and classified by an airflow classifier. In addition, a toner can be directly produced from a monomer, a colorant, and an additive by suspension polymerization or non-aqueous dispersion polymerization.

  The carrier is generally composed of the core material itself, or a carrier provided with a coating layer on the core material. The core material of the resin-coated carrier that can be used in this embodiment is ferrite or magnetite. An appropriate particle size of the core material is about 20 to 60 μm. Examples of the material used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with a fluorine atom, and vinyl ketone substituted with a fluorine atom. As a method for forming the coating layer, a resin may be applied to the surface of the carrier core material particles by a spraying method, a dipping method, or the like, as in the conventional case.

An example of the photoreceptor 40 is a stacked organic photoreceptor comprising a charge generation layer and a charge transport layer, which are photosensitive layers formed on a conductive support. The conductive support has a volume resistance of 10 ¹⁰ Ωcm or less, for example, a metal such as aluminum, nickel, chromium, nichrome, copper, silver, gold, platinum, or a metal oxide such as tin oxide or indium oxide. The film is formed by vapor deposition or sputtering, film- or cylindrical plastic, paper-coated, pipes such as aluminum, aluminum alloy, nickel, and stainless steel are subjected to surface treatment by cutting, superfinishing, polishing, or the like.

  The charge generation layer is a layer mainly composed of a charge generation material. As the charge generation material, an inorganic or organic material is used, and typical examples include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squarics. Examples include acid dyes, phthalocyanine pigments, naphthalocyanine pigments, azulenium salt dyes, selenium, selenium-tellurium alloys, selenium-arsenic alloys, and amorphous silicon. These charge generation materials may be used alone or in combination of two or more. The charge generation layer is obtained by dispersing the charge generation material together with a binder resin, using a solvent such as tetrahydrofuran, cyclohexanone, dioxane, 2-butanone, dichloroethane, or the like by a ball mill, attritor, sand mill, etc., and applying a dispersion. Can be formed. The charge generation layer can be applied by dip coating, spray coating, bead coating, or the like.

  Examples of the binder resin that can be used include resins such as polyamide, polyurethane, polyester, epoxy, polyketone, polycarbonate, silicone, acrylic, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polyacryl, and polyamide. The amount of the binder resin is suitably 0 to 2 parts with respect to 1 part of the charge generating material on a weight basis.

  The charge generation layer can also be formed by a known vacuum thin film manufacturing method. The film thickness of the charge generation layer is usually from 0.01 to 5 μm, preferably from 0.1 to 2 μm. The charge transport layer can be formed by dissolving or dispersing the charge transport material and the binder resin in an appropriate solvent, and applying and drying the solution. Moreover, a plasticizer, a leveling agent, etc. can also be added as needed.

  Among charge transport materials, low molecular charge transport materials include electron transport materials and hole transport materials. Examples of the electron transport material include chloroanil, bromanyl, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2, 4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophene-4-one, 1,3,7-tri Examples thereof include electron accepting substances such as nitrodibenzothiophene-5,5-dioxide. These electron transport materials may be used alone or as a mixture of two or more.

  Examples of hole transport materials include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane. , Styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, thiophene derivatives, and the like. These hole transport materials may be used alone or as a mixture of two or more.

  Examples of the binder resin used in the charge transport layer together with the charge transport material include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, and vinyl chloride. Vinyl acetate copolymer, polyvinyl acetate, polyvinylidene chloride, polyarylate, phenoxy, polycarbonate, cellulose acetate, ethyl cellulose, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, acrylic, silicone, epoxy, melamine, urethane, phenol, alkyd, etc. A thermoplastic or thermosetting resin is mentioned. Examples of the solvent include tetrahydrofuran, dioxane, toluene, 2-butanone, monochlorobenzene, dichloroethane, methylene chloride and the like.

  The thickness of the charge transport layer may be appropriately selected in accordance with desired photoreceptor characteristics within a range of 10 to 40 μm. Examples of the plasticizer that is optionally added to the charge transport layer include dibutyl phthalate, dioctyl phthalate, and other general-purpose plasticizers. The amount used is 0 to 30% based on the weight of the binder resin. The degree is appropriate. Leveling agents added to the charge transport layer as desired include silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having a perfluoroalkyl group in the side chain. About 0 to 1% is appropriate for the binder resin on the basis.

  The content of the charge transport material contained in the photosensitive layer is preferably 30% by weight or more of the charge transport layer. If it is less than 30% by weight, a sufficient light decay time in a high-speed electrophotographic process cannot be obtained in pulsed light exposure in laser writing on the photoreceptor 40, which is not preferable.

  An undercoat layer can also be formed on the photoreceptor 40 between the conductive support and the photosensitive layer. In general, the undercoat layer is mainly composed of a resin. However, considering that the photosensitive layer is applied using a solvent, the resin is a resin having high resistance to general organic solvents. Is desirable. Such resins include water-soluble resins such as polyvinyl alcohol, casein, sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine, alkyd-melamine, epoxy, etc., three-dimensional Examples thereof include a curable resin that forms a network structure.

Further, fine powder of metal oxide such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, and indium oxide may be added to the undercoat layer in order to prevent moire and reduce residual potential. This undercoat layer can be formed by using an appropriate solvent and coating method as in the case of the photosensitive layer. Furthermore, it is also useful to use a metal oxide layer formed by, for example, a sol-gel method using a silane coupling agent, a titanium coupling agent, a chromium coupling agent or the like as the undercoat layer. In addition, the undercoat layer which the _Al 2 _{O 3} was formed by those anodized, organic matter such as polyparaxylylene _{(parylene), SiO, SnO 2, TiO} 2, ITO, Ce0 2 , etc. inorganic It is also effective to form the film by a vacuum thin film manufacturing method. The thickness of the undercoat layer is suitably from 0 to 5 μm.

  Further, a protective layer may be formed on the photosensitive member 40 on the photosensitive layer for the purpose of protecting the photosensitive layer and improving durability. This protective layer has a structure in which metal oxide fine particles such as alumina, silica, titanium oxide, tin oxide, zirconium oxide, and indium oxide are added to the binder resin for the purpose of improving wear resistance. Binder resins include styrene-acrylonitrile copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene copolymer, olefin-vinyl monomer copolymer, chlorinated polyether, allyl, phenol, polyacetal, polyamide, polyamide Imide, polyacrylate, polyallylsulfone, polybutylene, polybutylene terephthalate, polycarbonate, polyethersulfone, polyethine, polyethylene terephthalate, polyimide, acrylic, polymethylpentene, polypropylene, polyphenylene oxide, polysulfone, polyurethane, polyvinyl chloride, polyvinylidene chloride And resins such as epoxy.

  The amount of metal oxide fine particles added to the protective layer is usually 5 to 30% on a weight basis. If the amount of the metal oxide fine particles is less than 5%, the wear is large and the effect of improving the wear resistance is small and the durability is inferior. If it exceeds 30%, the bright portion potential is significantly increased during exposure, and the sensitivity is lowered. Is not desirable because it cannot be ignored. As a method for forming the protective layer, a normal coating method such as a spray method is employed. The thickness of the protective layer is 1 to 10 μm, preferably about 3 to 8 μm. If the protective layer is too thin, the durability is inferior, and if the protective layer is too thick, not only the productivity at the time of manufacturing the photoreceptor 40 is lowered, but also the residual potential increases with time. End up. The particle size of the metal oxide particles added to the protective layer is suitably 0.1 to 0.8 μm. When the particle size of the metal oxide fine particles is too large, the unevenness on the surface of the protective layer becomes large and the cleaning property is deteriorated, and the exposure light is easily scattered by the protective layer, so that the resolution is lowered and the image quality is inferior. If the particle size of the metal oxide fine particles is too small, the wear resistance is poor.

  Further, a dispersion aid can be added to the protective layer in order to improve the dispersibility of the metal oxide fine particles in the base resin. As the added dispersion aid, those used in paints and the like can be used as appropriate, and the amount thereof is usually 0.5 to 4%, preferably 1 to 2 with respect to the amount of metal oxide fine particles contained on a weight basis. %.

  Further, by adding a charge transport material to the protective layer, the movement of charges in the protective layer can be promoted. As the charge transport material added to the protective layer, the same material as the charge transport layer can be used.

  Further, the photoreceptor 40 used in this embodiment has an antioxidant, a plasticizer, an ultraviolet absorber, and leveling for each layer in order to improve environmental resistance, in order to prevent a decrease in sensitivity and an increase in residual potential. An agent or the like can be added.

  When a very small charging gap is formed between the photoconductor 40 and the charging roller 70 as in the present invention, the charging gap always varies within a certain range as the photoconductor 40 and the charging roller 70 rotate. In order to uniformly charge the photoreceptor 40 in such a situation, it is effective to superimpose an AC bias in addition to a DC voltage as a charging bias applied to the charging member.

  Here, when the frequency of the AC bias to be applied is low, stripe-shaped charging unevenness is conspicuous. Therefore, it is desirable to set the frequency [Hz] at least six times the linear velocity [mm / s] of the photoreceptor 40. In addition, when the frequency of the applied AC bias is too high, excessive discharge occurs, and the wear amount of the photoconductor 40 increases, or filming of toner or toner external additives tends to occur on the photoconductor 40. Therefore, it is desirable to set the frequency [Hz] which is 10 times or less the linear velocity [mm / s] of the photoconductor 40. Further, it is known that when the AC bias is superposed, the charging roller 70 disposed in contact with the photoconductor 40 is less susceptible to fluctuations in roller resistance due to the environment by performing constant current control so that the AC current is constant. Yes. However, in the case of the charging roller 70 arranged in a non-contact manner on the photoconductor 40, the charging gap fluctuates with the rotation of the photoconductor 40 and the charging roller 70. Therefore, in AC constant current control, the high voltage power source can follow the charging gap fluctuation. An abnormal image (horizontal stripe-like density unevenness) due to overshoot or undershoot may occur. For this reason, it is desirable that the AC voltage be constant voltage control. At this time, the required AC voltage varies depending on the environmental variation of the roller resistance and the size of the charging gap. The higher the roller resistance and the larger the charging gap, the larger the AC voltage is required. For this reason, the AC current flowing through the charging roller 70 can be detected, the control target value of the AC current is set, and the AC voltage is adjusted so that the detected value of the AC current becomes the control target value. An appropriate AC voltage can be set without being affected by individual differences in the gap. The AC voltage adjustment operation may be performed during non-image formation, or the AC voltage may be changed between sheets by detecting an AC current during the image forming operation.

A major factor that determines the life of the charging roller 70 is the occurrence of charging failure due to contamination of the charging roller 70 where toner, an external toner additive, a lubricant, etc. adhere to the surface of the charging roller 70. By forming a very small charging gap between the toner and the toner, the toner, the toner external additive, the lubricant, etc. existing on the photosensitive member 40 are not slightly transferred through contact with the charging roller 70. The charging roller 70 is less likely to get dirty, which is advantageous for extending the life of the charging roller 70. However, since the toner on the photoconductor 40, the toner external additive, the lubricant, and the like may fly and adhere to the charging roller 70 due to the charging bias, the charging roller 70 cannot be completely prevented from being contaminated. However, as can be seen by comparing the results of roller numbers 2 and 4 in Tables 1 and 2 below, even if the charging gap is doubled, the required charging bias does not double, so the charging gap is Since the electric field between the charging roller 70 and the photosensitive member 40 becomes weaker as the width increases, the toner, toner external additive, lubricant, etc. on the photosensitive member 40 are less likely to fly to the charging roller 70. The charging roller 70 is less likely to become dirty.

  On the other hand, there is an upper limit of the charging gap caused by the material of the charging roller 70, and there is a problem that even when the charging bias is increased beyond the upper limit, abnormal discharge cannot be eliminated and uniform charging cannot be performed. The upper limit of the charging gap tends to have a larger upper limit of the charging gap when an ion conductive material is used as a conductive agent for the charging roller 70 rather than an electronic conductive material, and it is desirable to use an ion conductive material. This is presumably because the ion conductive material is more easily dispersed uniformly in the base resin, and the microscopic resistance unevenness at the molecular level is smaller.

  Even with the non-contact charging roller 70 using such an ion conductive material, as the charging roller 70 is used for a long time, the charging gap capable of uniform charging may gradually become smaller. found.

  The experiment was performed using the image forming apparatus of FIG. The photoreceptor 40 is an aluminum substrate having a diameter of 60 mm, an undercoat layer of 3.5 μm, a charge generation layer of 0.15 μm, a charge transport layer of 22 μm, and 10% by weight of alumina particles having a particle size of 0.3 μm as the uppermost layer. A protective layer having a thickness of 5 μm is formed. The charging roller 70 is a charging made of a resin composition obtained by blending 40 parts by weight of an ABS resin as a base resin and 60 parts by weight of a polyether ester amide as an ionic conductive material on a 10 mm outer core made of stainless steel. The member was molded by injection molding, and a surface layer made of an acrylic silicon resin, an isocyanate curing agent, and a conductive agent was applied to the surface of the member to produce a charging roller 70 having an outer diameter of 12.7 mm. Gap holding members made of high-molecular polyethylene that form a charging gap are attached to both ends of the charging roller 70. The process linear velocity of this image forming apparatus is 350 mm / s, and the charging bias is a sine wave having a voltage V = −700 V and an AC frequency f = 2.5 kHz as a DC component.

  The charging roller 70 having a different charging gap was manufactured by adjusting the outer diameter of the charging member while keeping the outer diameter of the gap holding member constant. The measurement results of the charging gap of each charging roller 70 are shown in Table 1. The charging gap was measured at seven points in the axial direction, and the maximum value, minimum value, and average value measured while rotating the charging roller 70 and the photoreceptor 40 were described. Here, since the charging gap is also affected by the accuracy of the photoconductor 40, the charging gap is measured by combining the photoconductors 40 used when the paper passing test is performed.

  A paper passing test was performed using these charging rollers 70. Here, the gear attached to the end portion of the charging roller 70 meshes with the gear attached to the end portion of the photosensitive member 40, and the charging roller 70 rotates with the photosensitive member 40 at a substantially constant speed in synchronization with the rotation of the photosensitive member 40. Configured to rotate the way. The paper was passed in a laboratory environment, and the image was confirmed in a low-temperature and low-humidity environment of 10 ° C. and 15%, where every 100,000 sheets were passed, where the charging roller 70 was dirty and abnormal discharge was likely to occur. . Here, the necessary Vpp is the lowest Vpp voltage at which no abnormal discharge occurs. When abnormal discharge cannot be eliminated even when the practical upper limit of Vpp is set to 3.0 kV, x is indicated. As for the charging roller 70 stain, an entire halftone image was output, and the presence or absence of vertical black stripes due to the charging roller 70 was confirmed.

  Since the charging roller 70 is rotated about the photosensitive member 40 at a substantially constant speed, the charging gap was the same as that in the initial stage and remained unchanged after the paper passing test. As shown in Table 2 described above, the Vpp necessary for uniform charging increases as the charging gap increases. Further, the required Vpp becomes larger as the sheet passes, and when the charging gap becomes larger, abnormal discharge occurs with time and uniform charging cannot be performed.

The reason why the upper limit of the charging gap changes with time is presumed to be caused by the fact that the ionic conductive agent moves in the charging member due to the action of the electric field for a long time and the dispersion state changes. On the other hand, when the charging gap is narrow, there is a margin for uniform charging, but when used for a long time, an abnormal image due to contamination of the charging roller 70 occurs. Therefore, in the conventional method of maintaining the charging gap constant, it is difficult to prevent both abnormal discharge and contamination of the charging roller 70, and there is a limit to extending the life of the charging roller 70. However, as in this embodiment, By configuring the charging gap to gradually become smaller according to the rotation time of the photoconductor 40, it is possible to achieve both prevention of abnormal discharge and prevention of contamination of the charging roller 70.

  In order to gradually reduce the charging gap over time, gear driving is performed so that a speed difference is generated between the charging roller 70 and the photoreceptor 40. Thus, the gap holding member or the photoreceptor 40 can be worn. In this case, the charging gap is narrowed by the sum of the wear amount of the gap holding member and the wear amount of the photoreceptor 40. As a speed difference between the charging roller 70 and the photoreceptor 40, it is desirable to rotate the charging roller 70 at a speed 1.2 to 2.5 times the speed of the photoreceptor 40. Since the reduction amount of the charging gap is desirably 5 to 20 μm per 100,000 sheets of output, the speed difference between the charging roller 70 and the photosensitive member 40 is set so that the reduction amount of the charging gap falls within the target range. What is necessary is just to select the material of a gap holding member. If the photoconductor 40 is excessively worn, a charging bias leak occurs. Therefore, in the case of an organic photoconductor, it is desirable to use a photoconductor having a protective layer and having excellent wear resistance. In addition, when an inorganic photoconductor such as amorphous silicon is used as the photoconductor, the mechanical strength is so high that the gap holding member can be worn without wearing the photoconductor.

  As another method for gradually reducing the charging gap over time, a polishing means for polishing the gap holding member or the position where the gap holding member of the photoreceptor 40 abuts can be used. As a polishing means, a wrapping film in which abrasive particles are coated on a plastic film, a polishing blade in which abrasive particles are dispersed in polyurethane rubber, or the like is brought into contact so that the charging gap is gradually increased according to the rotation time of the photoreceptor 40. Can be small. As the abrasive particles, inorganic particles such as aluminum oxide, titanium oxide, and silicon carbide can be used. The particle size is about 0.01 to 0.5 μm, and the dispersion amount is preferably 10 to 50% by weight. By adjusting the material of the gap holding member and the contact pressure of the polishing member, the polishing amount can be adjusted.

  FIG. 4B shows an embodiment in which a polishing blade is brought into contact with the charging roller 70. The polishing blade 90 is in contact with only the gap holding member 103 attached to both ends of the charging roller 70, and the gap holding member 103 is polished by the rotation of the charging roller 70. The polishing blade 90 is mainly made of polyurethane rubber having a thickness of 2 mm, and 40% by weight of alumina particles having a particle diameter of 0.1 μm are dispersed therein. Since the abrasive is dispersed in the thick polyurethane rubber, even if the polishing blade 90 is worn over time, the polishing action is maintained, and the gap holding member 103 can be polished over a long period of time.

  In FIG. 4B, the polishing blade 90 is brought into contact with the gap holding member 103 of the charging roller 70. However, the polishing blade 90 is arranged at the contact position of the gap holding member 103 of the photosensitive member 40, and the photosensitive member 40 is moved. Polishing can also reduce the charging gap over time, and a polishing blade 90 can be disposed on both the charging roller 70 and the photoreceptor 40.

100: apparatus main body 200: paper feeder 300: scanner 400: automatic document feeder (ADF)
10: Intermediate transfer belt 14, 15, 16: Support roller 17: Intermediate transfer belt cleaning device 18Y, 18C, 18M, 18Bk: Image forming unit 20: Tandem image forming device 21: Exposure device 22: Secondary transfer device 23: Roller 24: secondary transfer belt 25: fixing device 26: fixing belt 27: pressure roller 28: sheet reversing device 30: document table 32: contact glass 33: first traveling body 34: second traveling body 35: imaging lens 36 : Read sensor 40Y, 40C, 40M, 40Bk: Photoconductor 42: Paper feed roller 43: Paper feed table 44: Paper feed cassette 45: Separation roller 46: Paper feed path 47: Carriage roller 48: Paper feed path 49: Registration roller 50: paper feed roller 51: manual feed tray 52: separation roller 53: manual paper feed path 55: switching claw 56: Output roller 57: Paper discharge tray 60Y, 60C, 60M, 60Bk: Development device 61: Development roller 62Y, 62C, 62M, 62Bk: Primary transfer roller 63a, 63a: Screw 64: Toner density sensor 70: Charging roller 71: Potential sensor 72: Static elimination lamp 73, 74: Brush roller 75: Cleaning blade 76: Exposure light 78: Lubricant 79: Toner transfer coil 80: Lubricant application blade 101: Core metal 102: Resin layer as charging member 103: Gap holding member

JP 2001-350321 A JP 2002-139893 A

Claims (8)

In an image forming apparatus including a charging unit disposed in a non-contact manner with respect to an image carrier via a minute gap,
An image forming apparatus comprising: a charging gap reducing unit that reduces the minute gap between the image carrier and the charging unit with a rotation time of the image carrier. The image forming apparatus according to claim 1.
The charging means has a roller shape;
The charging means is at least
A charging member made of a core metal which is a conductive support and a resin material containing an ion conductive material;
A gap holding member made of an insulating resin material that is disposed at both ends of the charging member and forms a gap forming the minute gap between the image carrier and the charging member by contacting a non-image portion of the image carrier. When,
An image forming apparatus comprising: The image forming apparatus according to claim 1 or 2,
The charging gap reducing means is
Polishing the contact position of the gap holding member or the gap holding member of the image carrier to reduce the minute gaps;
An image forming apparatus. The image forming apparatus according to claim 3.
Means for generating a rotational speed difference between the image carrier and the gap holding member;
An image forming apparatus. 5. The image forming apparatus according to claim 1, wherein:
The image carrier is composed of an organic photoreceptor, and a protective layer for reducing abrasion of the organic photoreceptor is formed on the outermost layer.
An image forming apparatus. 5. The image forming apparatus according to claim 1, wherein:
The image carrier is made of an inorganic photoreceptor;
An image forming apparatus. The image forming apparatus according to claim 1,
Lubricant supply means for supplying a lubricant to the image carrier,
The lubricant supply means does not supply a lubricant to a position where the gap holding member abuts.
An image forming apparatus. The image forming apparatus according to claim 1,
At least the image carrier and the charging unit are configured as a process cartridge that can be integrally attached to and detached from the image forming apparatus main body.
An image forming apparatus.