JP2009031488A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for suppressing degradation with time of a photoreceptor 4K due to a discharging as compared to a conventional apparatus while suppressing generation of an afterimage due to discharge error of the photoreceptor 4K. <P>SOLUTION: The image forming apparatus is equipped with: a photoreceptor 4K; a charging device 23K uniformly charging the photoreceptor; an optical writing device, not shown in the figure, writing an electrostatic latent image in the photoreceptor 4K after uniformly charged; a developing device 6K developing the electrostatic latent image carried by the photoreceptor 4K with toner; a transfer unit, not shown in the figure, transferring the toner image obtained by development from the photoreceptor 4K onto an intermediate transfer belt; and a discharging means having a discharging lamp 22K discharging the photoreceptor 4K subjected to a transfer process by the transfer unit, wherein the discharging means is configured so that a discharge amount during image formation is smaller than that during a post-process after the image formation to form a toner image on the photoreceptor 4K. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer that discharges a latent image carrier after a transfer process by a transfer unit using a discharging unit.

  In an electrophotographic image forming apparatus, an image is generally formed by the following process. That is, first, a latent image carrier such as a photosensitive member uniformly charged by a charging device is subjected to writing processing by optical scanning or the like to form an electrostatic latent image, and this electrostatic latent image is developed by a developing device. develop. Next, the toner image obtained by development is transferred from the latent image carrier to a transfer member such as a recording paper or an intermediate transfer member. Although there is a residual charge on the latent image carrier after the transfer process, this residual charge is removed by a charge eliminating means such as a charge eliminating lamp.

  The reason why the latent image carrier is neutralized by the neutralizing means is as follows. That is, the latent image carrier after the transfer process has a history of electrostatic latent images. In a state where such a history exists, even if a uniform charging process is performed by the charging unit, the potential of the latent image carrier is unlikely to be uniform. When a subsequent image is formed on a latent image carrier in which the history of the electrostatic latent image remains, an afterimage of the previous image is generated in the solid portion of the image. In order to avoid the occurrence of such an afterimage, the latent image carrier after the transfer process is neutralized.

  As the charge eliminating means, those of a charge eliminating lamp type as described in Patent Document 1, Patent Document 2, Patent Document 3, and the like are known. Also known is a method of applying a neutralizing bias to a neutralizing member disposed in contact with or close to the latent image carrier.

Japanese Patent No. 2618009 JP 2000-181159 A JP 2000-66552 A

  In any of the methods, there is a problem that the latent image carrier is deteriorated with the lapse of time as the charge removal process is repeated.

  The present invention has been made in view of the above background, and an object of the present invention is to provide an image that can suppress deterioration of the latent image carrier over time due to the charge removal process as compared to the conventional technique while suppressing the occurrence of afterimages. A forming apparatus is provided.

In order to achieve the above object, the invention of claim 1 includes a latent image carrier that carries a latent image, a charging means that uniformly charges the latent image carrier, and the latent image carrier that has been uniformly charged. A latent image writing means for writing a latent image on the surface, a developing means for developing the latent image with toner, a transfer means for transferring the toner image obtained by the development from the latent image carrier to a transfer body, and the transfer means In an image forming apparatus comprising a neutralizing unit that neutralizes the latent image carrier after passing through the transfer step, a post-processing operation performed after an image forming operation for forming a toner image on the latent image carrier In comparison, the charge eliminating means is configured to reduce the charge removal amount during the image forming operation.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, as the neutralization unit, a first neutralization unit that neutralizes the latent image carrier during an image forming operation, and the first neutralization unit are separate from the first neutralization unit. And the second static elimination means, and the first static elimination means and the second static elimination means are configured to reduce the total static elimination amount of both static elimination means during the image forming operation as compared with that during the post-processing operation. It is characterized by this.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the static elimination amount is changed so that the static elimination amount is changed as the wear amount of the surface of the latent image carrier increases with time. It is characterized by comprising means.
According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, the second neutralization unit is configured to perform the neutralization process at least during the post-processing operation.
According to a fifth aspect of the present invention, in the image forming apparatus of the first aspect, the neutralization process of the latent image carrier during the image forming operation and the neutralization process of the latent image carrier during the post-processing operation are performed by one neutralization member. The above-described static eliminating means is configured to implement the above.
According to a sixth aspect of the present invention, in the image forming apparatus of the second or fourth aspect, the latent image writing unit functions as the second neutralizing unit that neutralizes the latent image carrier during the post-processing operation. It is characterized by that.
According to a seventh aspect of the present invention, in the image forming apparatus according to the second or fourth aspect, as the second charge eliminating unit, a bias is applied to a biased member disposed in contact with or close to the latent image carrier. The latent image carrier is used to remove static electricity.
According to an eighth aspect of the present invention, in the image forming apparatus of the seventh aspect, as the transfer means, a transfer bias is applied to a transfer member as the biased member to transfer the toner image on the latent image carrier. What is transferred to the body is used, and the transfer means is made to function as the second charge eliminating means during the post-processing operation.
According to a ninth aspect of the present invention, in the image forming apparatus of the seventh aspect, as the charging means, a charging bias is applied to a charging member as the biased member to uniformly charge the latent image carrier. In addition, the charging unit is made to function as the second charge eliminating unit during the post-processing operation.
The invention according to claim 10 is the image forming apparatus according to claim 6, wherein when the latent image carrier is neutralized, the entire surface of the latent image carrier in the direction orthogonal to the moving direction is removed. The latent image writing means is configured to perform the writing process on the entire image forming area to be a latent image writing target in the area.
Further, in the image forming apparatus according to the eighth aspect, in the image forming apparatus according to the eighth aspect, when the latent image carrier is neutralized, the transfer unit is configured to apply a neutralizing bias consisting only of a DC voltage to the transfer member. It is characterized by comprising.
According to a twelfth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the charging member is an image forming target that is an image forming target in the entire region in a direction orthogonal to the moving direction of the surface of the latent image carrier. A charging roller configured to be in non-contact with the region is used.
The invention according to claim 13 is the image forming apparatus according to claim 12, wherein the charging roller is provided with an abutting portion having a larger diameter than the roller portion at both ends in the direction of the rotation axis of the charging roller. By abutting these abutting portions against both end portions in a direction orthogonal to the surface movement direction of the latent image carrier, a gap is formed between the roller portion and the image forming area of the latent image carrier. It is characterized by that.
According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, as the transfer unit, the toner image on the latent image carrier is transferred to an intermediate transfer member and then transferred to a recording member. It is characterized by using what to do.
Further, the invention of claim 15 is the image forming apparatus according to any one of claims 1 to 14, wherein the image is formed while moving the surface of the latent image carrier at a standard speed which is a standard speed. In addition to the operation, a non-standard image forming operation for forming an image while moving the surface at a speed different from the standard speed is performed, and the standard image forming operation and the non-standard image forming operation are used for static elimination. The charge eliminating means is configured to vary the power consumption.
According to a sixteenth aspect of the present invention, in the image forming apparatus according to any one of the first to fifteenth aspects, the latent image carrier includes a surface layer and an organic photosensitive layer formed under the surface layer. It is characterized by using a multi-layered photoreceptor.
The invention according to claim 17 is the image forming apparatus according to claim 16, wherein the surface layer is made of a material in which an additive is dispersed in a resin.
The invention according to claim 18 is the image forming apparatus according to claim 16, wherein the surface layer is made of a material containing a photocurable resin or a thermosetting resin. is there.
According to a nineteenth aspect of the present invention, in the image forming apparatus according to any one of the first to fifteenth aspects, a photosensitive member having a photosensitive portion made of amorphous silicon is used as the latent image carrier. It is.
According to a twentieth aspect of the present invention, in the image forming apparatus according to any one of the first to nineteenth aspects, a lubricant application unit for applying a lubricant to the surface of the latent image carrier is provided. is there.
The invention according to claim 21 is the image forming apparatus according to claim 20, wherein the image forming apparatus adheres to the surface of the latent image carrier after the transfer step by the transfer unit and before entering the charging step by the charging unit. A cleaning means for cleaning the latent image carrier by removing transfer residual toner, and a lubricant for the latent image carrier before entering the charging process after the cleaning process by the cleaning means. The above-mentioned lubricant application means is disposed so as to apply the liquid.
According to a twenty-second aspect of the present invention, in the image forming apparatus according to any one of the first to twenty-first aspects, a plurality of the latent image carriers are provided, and the toner images formed on the latent image carriers are superimposed on the transfer body. The transfer means is configured to transfer the image and the charge eliminating means is configured to individually adjust the charge removal amount for each latent image carrier.
The invention according to claim 23 is the image forming apparatus according to any one of claims 1 to 22, wherein a photosensitive member is used as the latent image carrier, and the charge eliminating means neutralizes the photosensitive member by light irradiation. The charge removing means is configured to change the charge removal amount according to the change in the charge removal amount accompanying the change in the supply voltage to the charge removal lamp.
According to a twenty-fourth aspect of the present invention, in the image forming apparatus according to any one of the first to twenty-second aspects, the photosensitive member is used as the latent image carrier, and the static eliminator discharges the photosensitive member by light irradiation as the neutralizing unit. The charge removing means is configured to change the charge removal amount according to the change in the charge removal amount accompanying the change in the supply current to the charge removal lamp.
According to a twenty-fifth aspect of the present invention, in the image forming apparatus according to any one of the first to twenty-fourth aspects, the latent image carrier and at least a part of the charge eliminating unit are held on a common holding body to form an image. The latent image carrier unit is configured to be integrally attached to and detached from the apparatus main body.

  In these inventions, for the reasons described below, it is possible to suppress the deterioration of the latent image carrier due to the charge removal process with time while suppressing the occurrence of afterimages. That is, the present inventors do not sufficiently discharge the latent image carrier as in the past by experiments to be described later. It has been found that afterimages do not occur if the amount of is relatively small. However, it is understood that if the image forming operation is stopped with the residual charge left on the latent image carrier and the latent image carrier is left as it is for a long time, deterioration of the latent image carrier may be promoted. It was. Therefore, in the present invention, the charge removal amount during the image forming operation is made smaller than during the post-processing operation performed after the image forming operation. In such a configuration, during the post-processing operation, the latent image carrier is less deteriorated over time than before by performing neutralization with a smaller amount of neutralization than in the past so that afterimage generation can be suppressed during the image formation operation. In this case, it is possible to avoid the deterioration of the latent image carrier due to the charge removal performed in the same manner as in the prior art and the remaining charge remaining.

Hereinafter, an embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter simply referred to as a copying machine) as an image forming apparatus will be described.
First, a basic configuration of the copying machine according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram showing the copying machine. The copying machine includes an image forming unit 1, a blank paper supply device 40, and a document conveyance reading unit 50. The document conveying / reading unit 50 includes a scanner 150 serving as a document reading device fixed on the image forming unit 1 and an ADF 51 serving as a document conveying device supported by the scanner 150.

  The blank paper supply device 40 includes two paper feed cassettes 42 arranged in multiple stages in the paper bank 41, a feed roller 43 that feeds recording paper from the paper feed cassette, and separates the sent recording paper into a paper feed path 44. A separation roller 45 to be supplied is provided. In addition, it has a plurality of transport rollers 47 for transporting the recording paper to the paper feed path 37 of the image forming unit 1. Then, the recording paper in the paper feeding cassette is fed into the paper feeding path 37 in the image forming unit 1.

  The image forming unit 1 includes an optical writing device 2, four process units 3K, Y, M, and C that form toner images of K, Y, M, and C, a transfer unit 24, a paper transport unit 28, and a registration roller. A pair 33, a fixing device 34, a switchback device 36, a paper feed path 37, and the like are provided. Note that the subscripts K, Y, M, and C added after the reference numerals indicate specifications for black, yellow, magenta, and cyan.

  The optical writing device 2 is disposed in the optical path of each light source, four laser diodes for K, Y, M, and C (not shown), a set of polygon scanners composed of a six-sided polygon mirror and a polygon motor, etc. It is composed of a lens such as an fθ lens, a long WTL, a mirror, and the like. The laser light L for K, Y, M, C, and K emitted from the laser diode based on the image information is deflected in the main scanning direction (photosensitive member axial direction) by reflection on the rotating polygon mirror surface. Then, the laser beam L is irradiated toward the photoconductors 4K, Y, M, and C. By this irradiation, electrostatic latent images are formed on the surfaces of the photoreceptors 4K, Y, M, and C, and are developed into toner images through a predetermined development process.

  The process units 3K, 3Y, 3C, and 3C support the photosensitive member and the various devices disposed around it as a single unit on a common support, and with respect to the image forming unit 1 main body. Detachable. In the present copying machine, a so-called tandem type in which four process units 3K, Y, M, and C are arranged so as to face an intermediate transfer belt (25 in FIG. 1), which will be described later, along the endless movement direction. It is configured.

  FIG. 2 is an enlarged configuration diagram showing the K process unit 3K. The process unit 3K includes a charging device 23K, a developing device 6K, a drum cleaning device 15K, a static elimination lamp 22K, and the like around the photoreceptor 4K.

  The photoreceptor 4K is obtained by sequentially laminating an organic photosensitive layer and a surface layer on the peripheral surface of a drum-shaped conductive support. The organic photosensitive layer is composed of a charge generation layer, a charge transport layer, and the like.

The drum-shaped conductive support exhibits a conductivity of 10 ¹⁰ [Ωcm] or less in terms of volume resistance. The conductive support is manufactured, for example, as follows. That is, a metal such as aluminum, nickel, chromium, nichrome, copper, silver, gold, platinum, or metal oxide such as tin oxide or indium oxide is deposited on the surface of a film or cylindrical substrate made of plastic or paper. Or it is manufactured by coating by sputtering. A tube material such as aluminum, aluminum alloy, nickel, and stainless steel may be subjected to surface treatment by cutting, superfinishing, polishing, or the like.

  The charge generation layer of the organic photosensitive layer is a layer mainly composed of a charge generation material. The charge generation material may be either an inorganic material or an organic material. Typical examples include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, squaric acid dyes, phthalocyanine pigments, naphthalocyanine pigments, and azurenium. Examples thereof include 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 material is dispersed in a solvent mixture such as tetrahydrofuran, cyclohexanone, dioxane, 2-butanone, dichloroethane, and a binder resin with a ball mill, attritor, sand mill, etc., and then the dispersion is electrically conductively supported. Apply on the body. And a charge generation layer can be obtained by drying the dispersion liquid after application | coating. For applying the dispersion, a dip coating method, a spray coating method, a bead coating method, or the like can be employed. Further, the charge generation layer may be formed by a known vacuum thin film manufacturing method.

  Examples of the binder resin used for the charge generation layer include resins such as polyamide, polyurethane, polyester, epoxy, polyketone, polycarbonate, silicone, acrylic, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polyacryl, and polyamide. . The addition amount of the binder resin is about 0 to 2 parts by weight with respect to 1 part by weight of the charge generation material. The film thickness of the charge generation layer is preferably 0.01 to 5 [μm]. More preferably, it is 0.1 to 2 [μm].

  The charge transport layer of the organic photosensitive layer can be obtained by applying and drying a dispersion obtained by dispersing a charge transport material in a mixed solution of a binder resin and a solvent on a layer formation target. If necessary, a plasticizer or a leveling agent may be added to the dispersion. As the charge transport material, either an electron transport material or a hole transport material may be used. Examples of the electron transport material include chloroanil, bromoanil, 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-trinitrodibenzo An electron accepting substance such as thiophene-5,5-dioxide is exemplified. These electron transport materials may be used alone or in combination of two or more. As hole transport materials, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, 9- (p-diethylaminostyrylanthracene), 1,1-bis- (4-dibenzylaminophenyl) propane, styryl Examples thereof include electron donating substances such as anthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, benzofuran derivatives, benzimidazole derivatives, and thiophene derivatives. These hole transport materials may be used alone or in combination of two or more.

  The binder resin used for the charge transport layer is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, 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. Resin.

  Examples of the solvent used in the production of the charge transport layer 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 the range of 10 to 40 [μm] according to desired photoreceptor characteristics.

  If necessary, a plasticizer or a leveling agent may be added to the above-mentioned dispersion that is a precursor of the charge transport layer. Examples of the plasticizer include general-purpose plasticizers such as dibutyl phthalate and dioctyl phthalate, and the amount used is preferably about 0 to 30% with respect to 1 part by weight of the binder resin. Examples of the leveling agent include silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, polymers or oligomers having a perfluoroalkyl group in the side chain, and the amount used is 1 part by weight of binder. About 0 to 1% is preferable with respect to resin.

  The content of the charge transport material in the organic 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 the high-speed electrophotographic process cannot be obtained in pulse exposure at the time of laser writing on the photoreceptor, which is not preferable.

  An undercoat layer may be formed between the conductive support and the organic photosensitive layer in the photoreceptor 4K as necessary. The undercoat layer is generally composed mainly of a resin. In consideration of obtaining an undercoat layer by applying the resin dissolved or dispersed in a solvent, it is desirable that the resin be highly resistant to dissolution with respect to general organic solvents. Such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine, alkyd-melamine, epoxy, etc., three-dimensional network structure The curable resin etc. which form can be illustrated. In order to prevent moire and reduce residual potential, fine powders of metal oxides such as titanium oxide, silica, alumina, zirconium oxide, tin oxide, and indium oxide may be added. As the solvent, those similar to those used in the organic photosensitive layer can be employed. Moreover, it is possible to apply | coat also about the solution which consists of binder resin, a solvent, etc. by the method similar to the case where an organic photosensitive layer is manufactured.

Further, as the undercoat layer, a metal oxide layer in which a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like is layered by a sol-gel method or the like may be formed. In addition, the as _Al 2 _{O 3} and a layer obtained by anodic oxidation, organic materials such as polyparaxylylene _(parylene), SiO, is stratified by _SnO 2, TiO 2, ITO, CeO vacuum thin layer manufacturing method inorganic substances such as ₂ It may be formed as an undercoat layer. The thickness of the undercoat layer is preferably 0 to 5 [μm].

  In the surface layer laminated on the organic photosensitive layer, fine metal oxide particles such as alumina, silica, titanium oxide, tin oxide, zirconium oxide, and indium oxide are added to the binder resin to improve wear resistance. Made of material. 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 epoxies.

  The amount of the metal oxide fine particles added to these binder resins is preferably 5 to 30% with respect to 1 part by weight of the binder resin. If the amount of the metal oxide fine particles is less than 5%, the required durability cannot be obtained and the surface layer wears significantly. On the other hand, if the amount of metal oxide fine particles exceeds 30 [%], the bright portion potential rises significantly during optical scanning, and the sensitivity drop cannot be ignored.

  As the particle diameter of the metal oxide particles, it is desirable to use those having a particle diameter in the range of 0.1 to 0.8 [μm]. If the particle size is too large, the surface unevenness of the surface layer becomes large and the cleaning property is lowered, and the writing light at the time of optical scanning is easily scattered in the surface layer, thereby reducing the resolution. Degraded image quality. If the particle size is too small, the wear resistance of the surface layer is poor.

  Examples of the method for forming the surface layer include a coating method such as a spray method. The thickness of the surface layer is preferably 1 to 10 [μm]. More preferably, it is about 3 to 8 [μm]. If the thickness of the surface layer is too thin, the durability is inferior. If the thickness is too thick, not only the productivity at the time of producing the photoreceptor is lowered, but also the increase in residual potential with time is increased.

  A dispersion aid may be added to the solution serving as the precursor of the surface layer in order to improve the dispersibility of the metal oxide fine particles in the binder resin. As such a dispersion aid, those commonly used in paints and the like can be used, and the amount thereof is preferably 0.5 to 4% with respect to 1 part by weight of metal oxide fine particles. More preferably, it is 1-2 [%].

  Moreover, you may accelerate | stimulate the movement of an electric charge in a surface layer by adding a charge transport material in the solution used as the precursor of a surface layer. As such a charge transport material, the same material as the charge transport layer can be used.

  Antioxidants, plasticizers, ultraviolet absorbers, leveling agents, and the like may be added to each layer on the conductive support for the purpose of improving environmental resistance, particularly reducing sensitivity and increasing residual potential.

  The charging device 23K includes a charging roller 231K and a cleaning brush roller 236K. FIG. 3 is a longitudinal sectional view showing the charging roller 231K. The charging roller 231K includes a cored bar 232K that is a conductive support, a roller part 233K that is coated on the circumferential surface of the central part in the longitudinal direction thereof, an abutment roller 234K that is fixed to both longitudinal ends of the cored bar 232K, and the like. It is composed of The core metal 232K is made of a metal such as stainless steel. If the mandrel 232K is too thin, the amount of deflection at the time of cutting or assembling of the roller becomes so large that it cannot be ignored, and the required gap accuracy cannot be obtained. On the other hand, if the core bar 232K is too thick, the charging roller 231K is increased in size and weight. Accordingly, the diameter of the cored bar 232K is preferably about 6 to 10 [mm].

The roller portion 233K of the charging roller 232K is configured to exhibit a volume resistance of 10 ⁴ to 10 ⁹ [Ωcm]. If the resistance is too low, it is easy to cause the charging bias to leak to the photoconductor when the photoconductor (4K) has a defect such as an electrical pinhole. On the other hand, if the resistance is too high, a sufficient discharge cannot be generated between the photosensitive member and the non-uniform charging is likely to occur. The material of the roller portion 233K contains an insulating base material such as resin, a conductive material, and the like. Examples of the insulating substrate include resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate. Since these insulating resins have good moldability, they can be molded easily. Examples of the conductive material include an ion conductive material such as a polymer compound having a quaternary ammonium base. Polyolefins having a quaternary ammonium base include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-san vinyl acetate copolymer, ethylene-propylene having a quaternary ammonium base. Examples thereof include polyolefins such as copolymerization and ethylene-hexene copolymerization. It may be a polymer compound other than a polyolefin having a quaternary ammonium base. These ionic conductive materials are mixed singly or in combination of two or more, and mixed with an insulating base material by a biaxial kneader, a kneader or the like. The roller part 233K can be easily molded by subjecting the obtained mixture to injection molding or extrusion molding on the metal core 232K.

  The mixing ratio of the ion conductive material and the insulating base material is preferably 30 to 80 parts by weight of the ion conductive material with respect to 100 parts by weight of the insulating base material. The thickness of the roller portion 233K on the cored bar 232K is preferably in the range of 0.5 to 3 [mm]. When the thickness is too small, in addition to difficulty in molding, there is a risk of poor strength. On the other hand, if the thickness is too large, the charging roller 231K is increased in size, or the charging efficiency is lowered due to the large electric resistance.

  The abutting roller 234K is fixed to the cored bar 232K after the roller portion 233K is formed by press-fitting or bonding, and has an outer diameter larger than that of the roller portion 233K. Such abutting rollers 234K abut against a photoreceptor (not shown) at both ends in the axial direction of the charging roller 231K, whereby a charging gap is formed between the roller portion 233K and the photoreceptor. A charging bias is applied to the cored bar 232K by a power source (not shown). Then, a discharge is generated between the conductive roller portion 233K and the photosensitive member through the above-described charging gap, so that the photosensitive member is uniformly charged. As for the charging roller 231K, after pressing the abutting roller 234K as described above, the outer diameter and the circularity of each roller portion 233 and the abutting roller 234K can be accurately adjusted by cutting or grinding. It is possible to suppress the fluctuation of the charging gap due to the rotation of the roller.

  Examples of the material of the butting roller 234K include resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, acrylonitrile-butadiene-styrene copolymer, and polycarbonate. From the viewpoint of reducing damage to the photoreceptor, it is desirable to use a material having a lower hardness than the roller portion 233K. Examples of the material of the abutting roller 234K that has excellent slidability and hardly damages the photoreceptor include polyacetal, ethylene-ethyl acrylate copolymer, polyvinylidene fluoride, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoro A resin such as an ethylene-hexafluoropropylene copolymer can be exemplified.

  The abutting rollers 234K respectively provided at both ends of the charging roller 231K in the rotation axis direction abut on a non-image forming area that is not an image forming target in the entire area in the rotation axis direction of the photosensitive member (not shown). Thereby, the charging gap between the roller portion 233K of the charging roller 231K and the image forming area in the rotation axis direction of the photosensitive member is accurately maintained.

  A drive receiving gear (not shown) is fixed to an end portion of the cored bar 232K of the charging roller 231K, and meshes with a photosensitive gear (not shown) fixed to the photosensitive member. When the photosensitive member is rotated by driving a drive motor (not shown), the rotational driving force is transmitted from the photosensitive member to the charging roller 231K. The charging roller 231K rotates in the follower direction at a linear speed substantially equal to that of the photosensitive member. Since the above-described charging gap is secured, even when a relatively hard roller portion 233K of the charging roller 231K is used, the photosensitive member is not worn or damaged by the roller portion 233K. For the purpose of improving toner releasability, a surface layer having a thickness of several tens [μm] may be coated on the peripheral surface of the roller portion 233K or the abutting roller 234K.

  If the charging gap is too large, uneven charging due to abnormal discharge is likely to occur. Therefore, the charging gap is preferably set to 100 [μm] or less. Further, as the charging bias, it is desirable to employ a DC voltage superimposed with an AC voltage.

  In FIG. 2, the cleaning brush roller 236K for cleaning the surface of the charging roller 231K is in contact with the roller portion of the charging roller 231K. The cleaning roller 236K includes a metal cored bar and a brush roller unit made of a plurality of conductive fibers electrostatically flocked on the peripheral surface thereof. Then, the toner is scraped off from the roller portion by rotating along with the rotation of the charging roller 231K while contacting the roller portion of the charging roller 231K by its own weight.

  A method in which a charging roller or a charging brush roller as a charging member is brought into contact with the image forming area of the photosensitive member may be employed. Further, a non-contact charging device such as a scorotron charger may be used.

  An electrostatic latent image is formed on the surface of the photoconductor 4K uniformly charged by the charging device 23K by optical scanning with the laser beam L. Thereafter, the surface of the photoconductor 4K passes through a position facing the potential sensor 5K that detects the surface potential of the photoconductor 4K, and then enters a developing region that is a position facing the developing device 6K.

  The developing device 6K develops a latent image using a two-component developer (hereinafter simply referred to as a developer) containing a magnetic carrier and a non-magnetic toner (not shown). A stirrer 7K that conveys the developer contained in the developer while stirring and supplies the developer to the cylindrical developing sleeve 12K, and transfers the toner in the developer carried on the surface of the developing sleeve 12K to the photoreceptor 4K. And a developing unit 11K.

  The stirring unit 7K is provided at a position lower in the direction of gravity than the developing unit 11K. The first conveying screw 8K and the second conveying screw 9K are arranged in parallel to each other, a partition plate and a casing provided between the screws. The toner density sensor 10K is fixed to the bottom surface of the toner.

  The developing unit 11K includes a developing sleeve 12K that faces the photosensitive member 4K through an opening provided in the casing, a magnet roller 13K that is provided in a non-rotatable state inside the developing sleeve 12K, a doctor blade 14K that approaches the developing sleeve 12K, and the like. is doing. The developing sleeve 12K has a non-magnetic rotatable cylindrical shape. The magnet roller 13K has a plurality of magnetic poles that are sequentially arranged from the position facing the doctor blade 14K toward the rotation direction of the sleeve. Each of these magnetic poles applies a magnetic force to the developer on the sleeve at a predetermined position in the rotational direction. As a result, the developer sent from the stirring unit 7K is attracted and carried on the surface of the developing sleeve 13K, and a magnetic brush is formed along the magnetic field lines on the sleeve surface.

  The magnetic brush is transported to the developing region facing the photoreceptor 4K after being regulated to an appropriate layer thickness when passing through the position facing the doctor blade 14K as the developing sleeve 12K rotates. The toner is transferred onto the electrostatic latent image by the potential difference between the developing bias applied to the developing sleeve 12K and the electrostatic latent image on the photosensitive member 4K, thereby contributing to development. Further, as the developing sleeve 12K rotates, the developing sleeve 12K returns to the developing unit 11K again, and after the release from the sleeve surface due to the influence of the repulsive magnetic field formed between the magnetic poles of the magnet roller 13K, the developing sleeve 12K returns to the stirring unit 7K.

  An appropriate amount of toner is supplied to the developer in the stirring unit 7K based on the detection result by the toner density sensor 10K. In addition, as the developing device 6K, a device using a one-component developer not including a magnetic carrier may be employed instead of a device using a developer.

  The photosensitive member 4K on which the K toner image is formed on the surface by development by the developing device 6K enters a K primary transfer nip described later with rotation. In the primary transfer nip, the K toner image on the photoconductor 4K is primarily transferred onto the front surface of an intermediate transfer belt described later. The surface of the photosensitive member 4K after passing through the primary transfer nip is discharged by the discharging lamp 22K and then enters a cleaning position by the drum cleaning device 15K.

  The drum cleaning device 15K includes a cleaning brush roller 16K, an application brush roller 17K, a cleaning blade 18K, a solid lubricant 19K, a recovery coil 20K, a scraper Sc, and the like.

  Each of the cleaning brush roller 16K and the application brush roller 17K has a metal rotating shaft member and a brush roller portion made of a plurality of conductive fibers standing on the peripheral surface thereof. The cleaning brush roller 16K scrapes off transfer residual toner from the surface of the photoconductor 4K by being driven to rotate while the tip of the brush roller portion is in contact with the surface of the photoconductor 4K. The transfer residual toner thus scraped off is temporarily captured in the brush roller portion, and is then ejected from the brush and falls onto the recovery coil 20K due to the flicker effect of the brush by the scraper Sc in contact with the brush roller portion. The recovery coil 20K conveys the transfer residual toner to the end of the drum cleaning device 15K in the direction orthogonal to the drawing sheet surface as it rotates, and discharges it to the outside of the drum cleaning device 15K. The discharged transfer residual toner is collected in a waste toner bottle (not shown).

  The surface of the photoreceptor 4K that has passed through the contact position with the cleaning brush roller 16K enters the contact position with the application brush roller 17K. In the upper right of the application brush roller 17K in the figure, the solid lubricant 17K is urged toward the application brush roller 17K by a spring. The application brush roller 17K scrapes off the lubricant from the solid lubricant 19 in accordance with the rotational drive, and then applies it to the surface of the photoreceptor 4K. By this application, a film made of lubricant powder is formed on the surface of the photoconductor 4K, and the adhesion between the photoconductor 4K and the toner is weakened to improve the cleaning property, or the photoconductor 4K is brought into contact with the photoconductor 4K. The sliding force with various members is weakened to extend the life of the photosensitive member 4K. As described above, the drum cleaning device 15K also functions as a lubricant application unit that applies the lubricant to the photosensitive member 4K as a latent image carrier.

  Examples of the solid lubricant 19K include zinc stearate, barium stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, magnesium stearate, zinc oleate, cobalt oleate, Examples thereof include fatty acid metal salts such as magnesium oleate and zinc palmitate, natural waxes such as carnauba wax, and fluorine resins such as polytetrafluoroethylene.

  The surface of the photoreceptor 4K that has passed the contact position with the application brush roller 17K enters the contact position with the cleaning blade 18K, and further cleaning processing of the transfer residual toner is performed. The transfer residual toner scraped off from the surface of the photoreceptor 4K by the cleaning blade 18K also finally falls on the recovery coil 20K and is recovered in the waste toner bottle.

  FIG. 4 is an enlarged configuration diagram showing another example of the K process unit 3K. In the drum cleaning device 15K of the process unit 3K, after the cleaning process by the cleaning brush roller 16K and the cleaning process by the cleaning blade 18K are performed on the photoconductor 4K, the lubricant application process by the application brush roller 17K is performed. Apply. In such a configuration, since the lubricant is applied to the surface of the photoconductor 4K in a state in which almost no transfer residual toner is removed, the lubricant is applied in a state where the transfer residual toner is adhered to the photoconductor 4K. This makes it possible to avoid poor application of the lubricant. Thus, regardless of fluctuations in the residual toner amount such as the timing when the residual toner after the output of the solid image becomes relatively large, the timing when the residual toner after the output of the character image becomes relatively small, etc. A lubricant film having a stable thickness can be formed on the surface of the photoreceptor 4K.

  In the process unit 3K shown in FIGS. 2 and 4, the photosensitive member 4K after being neutralized by the neutralizing lamp 22K is subjected to a cleaning process by the drum cleaning device 15K. The photosensitive member 4K may be neutralized by a neutralizing unit.

  The photosensitive member 4K that has been subjected to the cleaning process by the drum cleaning device 15K is uniformly charged again by the charging device 23K. Although the process unit 3K for K has been described in detail, the same process is executed in the process units for other colors (for M, C, and K).

  In FIG. 1 described above, a transfer unit 24 is disposed below the four process units 3K, Y, M, and C. The transfer unit 24 moves the intermediate transfer belt 25 stretched by a plurality of rollers endlessly in the clockwise direction in the drawing while contacting the photoreceptors 4K, Y, M, and C. As a result, primary transfer nips for K, Y, M, and C in which the photoreceptors 4K, Y, M, and C contact the intermediate transfer belt 25 are formed. In the vicinity of the primary transfer nips for K, Y, M, and C, the intermediate transfer belt 25 is moved to the photoreceptors 4K, Y, M, and C by primary transfer rollers 26K, Y, M, and C disposed inside the belt loop. Pressing toward C. A primary transfer bias is applied to the primary transfer rollers 26K, Y, M, and C by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 4K, Y, M, and C toward the intermediate transfer belt 25 is formed in the primary transfer nips for K, Y, M, and C. Has been. In the drawing, a toner image is formed on each of the primary transfer nips on the front surface of the intermediate transfer belt 25 that sequentially passes through the primary transfer nips for K, Y, M, and C with endless movement in the clockwise direction. Are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 25.

  Examples of the intermediate transfer belt 25 include those obtained by molding a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, and polyethylene terephthalate into a seamless belt shape. About the material mentioned above, it is possible to use it as it is or to make it show appropriate electrical resistance by adding conductive materials such as carbon black. Further, the belt base made of the above-described material may have a multilayer structure in which several layers are laminated by means such as spraying or dipping.

  Below the transfer unit 24 in the figure, a paper transport unit 28 is provided between the drive roller 30 and the secondary transfer roller 31 to endlessly move the endless paper transport belt 29. The intermediate transfer belt 25 and the paper transport belt 29 are sandwiched between the secondary transfer roller 31 and the lower stretching roller 27 of the transfer unit 24. As a result, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 25 and the front surface of the paper transport belt 29 come into contact with each other. A secondary transfer bias is applied to the secondary transfer roller 31 by a power source (not shown). On the other hand, the lower stretching roller 27 of the transfer unit 24 is grounded. Thereby, a secondary transfer electric field is formed in the secondary transfer nip.

  A registration roller pair 33 is disposed on the right side of the secondary transfer nip in the drawing, and the secondary transfer nip 33 is arranged at a timing at which the recording paper sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 25. Send to transfer nip. In the secondary transfer nip, the four-color toner images on the intermediate transfer belt 25 are secondarily transferred onto the recording paper under the influence of the secondary transfer electric field and nip pressure, and become a full-color image combined with the white color of the recording paper. The recording paper that has passed through the secondary transfer nip is separated from the intermediate transfer belt 25 and is conveyed to the fixing device 34 along with its endless movement while being held on the front surface of the paper conveying belt 29. Instead of the paper transport unit 28, the secondary transfer roller 31 may be provided alone or a transfer charger may be provided. In this case, a means for conveying the recording paper after passing through the secondary transfer nip to the fixing device may be provided separately.

  On the surface of the intermediate transfer belt 25 that has passed through the secondary transfer nip, residual transfer toner that has not been transferred to the recording paper as a recording member at the secondary transfer nip is attached. This transfer residual toner is scraped off and removed by the belt cleaning device Bc in contact with the intermediate transfer belt 25.

  The recording paper conveyed to the fixing device 34 is fixed to a full color image by pressurization or heating in the fixing device 34, and then sent from the fixing device 34 to the paper discharge roller pair 35, and then to the outside of the apparatus. Discharged.

  A switchback device 36 is disposed below the paper transport unit 28 and the fixing device 34. As a result, the recording paper having undergone the image fixing process on one side is switched by the switching claw to the switchback device side, where it is reversed and enters the secondary transfer transfer nip again. Then, after the secondary transfer process and the fixing process of the image are performed on the other side, the sheet is discharged onto a discharge tray.

  The scanner 150 fixed on the image forming unit 1 includes a fixed reading unit 151 and a moving reading unit 152 as reading means for reading an image of the document MS. A fixed reading unit 151 having a light source, a reflection mirror, an image reading sensor such as a CCD, etc. is disposed immediately below a first contact glass (not shown) fixed to the upper wall of the casing of the scanner 150 so as to contact the document MS. Yes. Then, when a document MS conveyed by the ADF 51 described later passes over the first contact glass, the light emitted from the light source is sequentially reflected on the document surface and received by the image reading sensor via a plurality of reflecting mirrors. To do. Thereby, the document MS is scanned without moving the optical system including the light source and the reflection mirror.

  On the other hand, the moving reading unit 152 is disposed directly below the second contact glass (not shown) fixed to the upper wall of the casing of the scanner 150 so as to come into contact with the document MS, and is disposed on the right side of the fixed reading unit 151 in the drawing. The optical system including the light source and the reflection mirror can be moved in the left-right direction in the figure. Then, in the process of moving the optical system from the left side to the right side in the figure, the light emitted from the light source is reflected by a document (not shown) placed on the second contact glass and then passed through a plurality of reflecting mirrors. The light is received by an image reading sensor 153 fixed to the scanner body. Accordingly, the original is scanned while moving the optical system.

  An ADF 51 disposed on the scanner 150 includes a document placing table 53 for placing a document MS before reading on a main body cover 52, a transport unit 54 for transporting the document MS, and a document MS after reading. A document stack base 55 for stacking is held. The scanner 150 is supported so as to be openable and closable by a hinge (not shown) fixed to the scanner 150. When the ADF 51 is opened, the scanner 150 exposes the first contact glass and the second contact glass on the upper surface thereof. In the case of a single-sided original such as a book in which one corner of the original bundle is bound, the original cannot be separated one by one, so that the original cannot be conveyed by the ADF 51. Therefore, in the case of a single-sided original, the ADF 51 is opened to expose the second contact glass 155. Then, after placing a single-sided original on which the page to be read is opened facing down on the second contact glass, the ADF 51 is closed, and the moving reading unit 152 of the scanner 150 reads the image of the page.

  On the other hand, in the case of an original bundle in which a plurality of independent originals MS are simply stacked, the original MS can be sequentially read by the fixed reading unit 151 of the scanner 150 while being automatically conveyed one by one by the ADF 51. . In this case, after setting the document bundle on the document placing table 53, a copy start button (not shown) is pressed. Then, the ADF 51 sends the originals MS of the original bundle placed on the original placement table 53 into the conveyance unit 54 in order from the top, and conveys the original MS toward the original stack table 55 while inverting it. In the course of this conveyance, immediately after the document MS is reversed, the original MS is passed directly above the fixed reading unit 151 of the scanner 150. At this time, the image of the document MS is read by the fixed reading unit 151 of the scanner 150.

  When making a copy of the document MS using this copying machine, the document is set on the document table 53 of the ADF 51. Alternatively, after the ADF 51 is opened and a document is set on the second contact glass of the scanner 150, the ADF 51 is closed and the document is pressed. When a start switch of an operation unit (not shown) is pressed, a plurality of originals MS are sequentially read by the ADF 51 and read by the fixed reading unit 151. Alternatively, the document MS on the second contact glass is read by the moving reading unit 152. Thereafter, when the mode setting is set in the operation unit or the automatic mode selection is set in 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 MS.

  When the full color mode is selected, the photoreceptors 4K, Y, M, and C of the respective colors rotate in the counterclockwise direction in the drawing. Then, K, Y, M, and C toner images are formed on the photoreceptors 4K, Y, M, and C of the respective colors by the above-described process, and these images are primarily transferred while being superimposed on the front surface of the intermediate transfer belt 25. The On the other hand, the recording paper is sent out from the paper feed cassette 42, passes through the separation roller 45, the paper feed path 44, and the transport roller pair 47, and is sandwiched between the rollers of the registration roller pair 33. Alternatively, the recording sheet fed from the manual feed tray is sandwiched between the rollers of the registration roller pair 33. Then, the toner is fed from the registration roller pair 33 at a timing that can be synchronized with the four-color toner image on the intermediate transfer belt 25 and enters the secondary transfer nip. The four-color toner image secondarily transferred from the intermediate transfer belt 25 to the recording paper at the secondary transfer nip is combined with the white color of the recording paper to form a full-color image. Thereafter, the fuel is discharged out of the apparatus following the route described above. When two or more originals MS are read, the same image forming process is repeated.

  After the image forming operation on the recording paper is finished, a post-processing operation is performed. In this post-processing operation, the photoconductors 4K, Y, M, and C of the respective colors are subjected to charge removal processing while being rotated by one or more rounds. Then, after the neutralization process over the entire circumference is completed, the driving of the photoconductors 4K, Y, M, and C of each color and the intermediate transfer belt 25 is stopped.

  When the monochrome mode is selected, a bracket (not shown) of the transfer unit 24 is moved to move the intermediate transfer belt 25 from the Y, M, and C photoconductors 4Y, M, and C among the four photoconductors. Separate. Then, a K toner image is formed on the photoconductor 4K by the above-described process in the K process unit 3K while rotating only the K photoconductor 4K in the counterclockwise direction in the drawing, and then the intermediate transfer belt 25. Primary transfer on top. At this time, unnecessary wear of the photosensitive member and developer is avoided by stopping the photosensitive members 4Y, 4M, and 4C and the developing devices 6Y, 6M, and 6C that are not necessary in the monochrome mode.

  In the process units 3K, Y, M, and C for the respective colors, the following toner is used. That is, it contains a binder resin, a colorant, a charge control agent, etc., and is made of a material to which other additives are added as necessary.

  Examples of the binder resin constituting the toner particles include polystyrene, styrene-acrylic acid ester copolymer, and polyester resin. Further, as the colorant (yellow, magenta, cyan, black), it is possible to use a known one for toner. The addition amount of the colorant is preferably 0.1 to 15 parts by weight with respect to 100 parts by weight of the binder resin.

  Examples of the charge control agent used for the toner particle material include a nigrosine dye, a chromium-containing complex, a quaternary ammonium salt, and the like, which are properly used according to the polarity of the toner particles. The addition amount of the charge control agent amount is preferably 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 composed of metal oxides such as silica, titania, and alumina, those obtained by surface-treating such fine particles with a silane coupling agent, titanate coupling agent, etc., polystyrene, polymethyl methacrylate, polyvinylidene fluoride. Examples thereof include polymer fine particles. As the fluidity-imparting agent, it is desirable to use one having a particle size in the range of 0.01 to 3 [μm]. The addition amount of the fluidity imparting agent 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.

  The toner can be produced by a conventionally known method or a combination thereof. For example, in the kneading and pulverization method, a binder resin, a colorant such as carbon black, and other additives are dry-mixed and heated and melt-kneaded by means such as an extruder, a two-roll, a three-roll. The kneaded product is cooled and solidified, and then pulverized by a pulverizer such as a jet mill, and further classified by an airflow classifier to obtain a toner. It is also possible to produce toner from monomers, colorants, additives, etc. by suspension polymerization or non-aqueous dispersion polymerization.

  As the magnetic carrier for the developer, a carrier made of only a core material, a core material provided with a coating layer, or the like can be used. Examples of the core material of the magnetic carrier on which the coating layer is formed include ferrite and magnetite. The particle size of the core material is preferably about 20 to 60 [μm]. Examples of the material for the 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. Moreover, as a formation method of a coating layer, the method of spraying the material of a coating layer on the surface of a carrier core material particle, the method of immersing, etc. are employable.

Next, experiments conducted by the present inventors will be described.
The inventors prepared a test machine having the same configuration as the copying machine shown in FIG. Then, while the black test image is output by this testing machine, the input voltage to the static elimination lamp 22K in the K process unit 3K, the static elimination current flowing through the static elimination lamp 22K, and the static electricity on the photoreceptor 4K after static elimination. An experiment was conducted to examine the relationship between the potential of the portion that was a latent image and the state of occurrence of an afterimage resulting from the charge removal failure of the photoconductor 4K. The potential of the portion that was the electrostatic latent image was measured by removing the cleaning brush roller and setting a probe for measuring the surface potential at that position. As for the test image, a black solid test image and a halftone test image were alternately output, and the presence or absence of an afterimage appearing in the halftone test image was examined.

  The photoreceptor 4K is uniformly charged to −750 to −850 [V] by the charging device 23K, and then the electrostatic latent image for black solid image (potential = −− 100 to -200V) and electrostatic latent images for halftone images (potential = -300 to -400V). The photosensitive member 4K for K is made of a material in which the charge transport layer has a thickness of 22 [μm] and alumina fine particles having an average particle diameter of 0.3 [μm] are dispersed in 10 [wt%]. A surface layer having a thickness of 5 [μm] was used. As for the occurrence of afterimages in a halftone image, ○: no afterimages are recognized even if the eyes are closed, Δ: a slight afterimage is recognized even if it is looked closely, x: an afterimage of an unacceptable level Evaluation was made in three stages.

The results of experiments conducted under the above conditions are shown in Table 1 below.

  The amount of static elimination light emitted from the static elimination lamp 22K is proportional to the current flowing through the static elimination lamp 22K. As the amount of charge removal light increases, the charge removal amount of the photoreceptor 4K increases. As shown in Table 1, when the input voltage to the static elimination lamp 22K is turned off (0 V) or when the input voltage is made lower than 13.0 [V], the previous black solid image is added to the halftone image. The positive afterimage (higher density than halftone) was significantly generated (×). On the other hand, when the input voltage is set to 13.0 [V] or higher, it is possible to keep a slight afterimage of an acceptable level (Δ) or to avoid the occurrence of a positive afterimage of a halftone image. (○).

  As shown in Table 1, the potential of the portion corresponding to the black solid electrostatic latent image on the photosensitive member 4K after static elimination when the input voltage is 13.0 [V] (hereinafter referred to as latent image history potential) is shown in Table 1. -225 [V]. Conventionally, the input voltage is set to 24.0 [V] shown in Table 1, and the latent image history potential at this time is −70 [V]. That is, in the prior art, sufficient static elimination was performed to reduce the latent image history potential from −485 [V] to −70 [V] (static elimination amount = 415 V), but the latent image history potential was −225 [V. It was found that the generation of a positive afterimage can be kept within an allowable range if the charge is reduced to about (static charge = 260 V). Conventionally, the latent image history portion has been neutralized by 415 [V], but the generation of positive afterimage can be prevented even with a neutralization amount of about half (260 V). If the amount of charge removal is reduced in this way during image formation, it should be possible to significantly reduce the deterioration over time of the photoconductor 4K due to charge removal while suppressing the occurrence of afterimages as in the prior art.

  However, if the image forming operation is stopped and the photoconductor 4K is left as it is for a long period of time while leaving a certain potential in the latent image history portion, there is a possibility that the deterioration of the photoconductor 4K may be promoted. In addition, there is a risk of causing problems such as carrier adhesion during the next image formation. Specifically, the time from the end of image formation until the start of the next image formation is indefinite because it depends on the usage status of the user. The potential remaining on the photoconductor 4K gradually decreases due to dark decay, but the time until the next image forming operation starts is not constant, so that the photoconductor potential at startup becomes unstable. Then, there is a risk of causing problems such as carrier adhesion. Accordingly, while the image forming operation is performed, the photoconductor 4K is neutralized with a smaller amount of charge than before, while during the post-processing operation after the image forming operation, the photoconductor 4K is decharged with the same amount of charge as before. Then, the machine may be stopped.

  Next, the present inventors conducted an experiment in which black solid images and halftone images were alternately output to 300,000 A4 size papers under conditions 1 and 2, respectively, using the test machine described above.

  As the charge removal lamp 22K, the same one as in the previous experiment was used. The static elimination lamp 22K includes an LED (light emitting diode) that emits static elimination light having a wavelength of 660 nm. As shown in FIG. 5, the larger the input voltage, the larger the current flows (the amount of static elimination light increases). Have

  The photoconductor 4K for K has a surface made of a material in which the charge transport layer has a thickness of 22 [μm] and alumina fine particles having an average particle diameter of 0.5 [μm] are dispersed in 30 [wt%]. A layer having a thickness of 5 [μm] was used.

  In condition 1, the input voltage to the charge removal lamp 22K during the image forming operation was set to 13.5 [V], and the charge removal amount was reduced to the extent that no positive afterimage appeared. After outputting 5 test images having a solid black portion, after performing post-processing operation with the input voltage to the static elimination lamp 22K raised to 24.0 [V], output 5 similar test images This step was repeated. Each time the cumulative number of output sheets reaches 10,000, one aftertone evaluation halftone image is output to check the presence or absence of the afterimage.

  In Condition 2, as in the conventional case, the input voltage to the charge removal lamp 22K during the image forming operation is set to 24.0 [V], and the charge removal is sufficiently performed on the photoconductor 4K. After outputting five test images each having a black solid portion, a post-processing operation was executed at the same input voltage, and the process of outputting five test images again was repeated. Each time the cumulative number of output sheets reaches 10,000, one aftertone evaluation halftone image is output to check the presence or absence of the afterimage.

  FIG. 6 shows the relationship between the latent image history potential (residual potential) and the number of prints under each condition. As is clear from this figure, the rate of increase in the residual potential with time is significantly lower in condition 1 than in condition 2 (conventional example). From this, it was proved that the condition 1 can suppress the deterioration of the photoreceptor 4K with the lapse of time as compared with the condition 2 over time. In both conditions 1 and 2, no positive afterimage was observed in the halftone image when printing out 300,000 sheets.

  In view of the above experimental results, in the copying machine according to the embodiment, the static elimination lamps for K, Y, C, and M in the process units 3K, Y, M, and C of each color, and the static elimination voltages are individually applied to the static elimination lamps. The followings are used as a static elimination means comprising a static elimination power source (not shown) to be supplied and a control unit (not shown). That is, in the process units 3K, Y, M, and C for each color, post-processing operations performed after the image forming operation for forming K, Y, C, and M toner images on the photoreceptors 4K, Y, M, and C, respectively. The amount of charge removal during the image forming operation is reduced compared to the inside. More specifically, during the image forming operation, a potential that does not cause an afterimage in the halftone portion is left in the latent image history portion of the photoconductors 4K, Y, C, and M after the charge removal process. By supplying a static elimination voltage of about 13.5 [V] to the static elimination lamps for K, Y, C, and M, respectively, the static elimination amount for the photoconductors 4K, Y, C, and M is reduced as compared with the prior art. The static elimination like this is realized. As a result, it is possible to significantly suppress the deterioration over time of the photoconductor 4K due to charge removal, while suppressing the occurrence of afterimages as in the conventional case. On the other hand, during the post-processing operation, a neutralization voltage of about 24.0 [V] is supplied to the neutralization lamps for K, Y, C, and M, respectively, so that the photoreceptors 4K, Y, C, and M are the same as in the past. To remove static electricity sufficiently. Thereby, it is possible to avoid the deterioration of the photoconductors 4K, Y, C, and M due to leaving them for a long time while leaving electric charges.

The photoresponsiveness of the photoreceptor is affected by the thickness of the charge transport layer. FIG. 7 is a graph showing the relationship between the optical writing energy and the surface potential in three photoreceptors having different charge transport layer thicknesses (15 μm, 20 μm, and 25 μm). The smaller the thickness of the charge transport layer, the greater the capacitance. For this reason, as shown in the drawing, the smaller the thickness of the charge transport layer, the larger the optical writing energy necessary for optically attenuating the background portion of the same uniformly charged potential (−800 V) to the same potential. This is a phenomenon that occurs in optical writing of an electrostatic latent image, but the same can be said for static elimination. In a conventional image forming apparatus, it is generally set to a static elimination light amount (an area of 0.6 μJ / cm ² or more in the same figure) that can sufficiently neutralize the photoreceptor regardless of the layer thickness of the surface of the photoreceptor. It was the target. On the other hand, in the present copying machine, as described above, during the image forming operation, the amount of charge removal is made smaller than before so that a potential of about −200 [V] is left in the latent image history portion. . As can be seen from the figure, the optical writing energy at which the surface potential is −200 [V] is about 0.4 [μJ / cm ² ] when the thickness of the charge transport layer is 15 [μm]. contrast, in the case of 20 [[mu] m] is about 0.3 [μJ / cm ^2]. Further, 15 [μm] is about 0.25 [μJ / cm ² ]. That is, as the thickness of the charge transport layer is reduced, the charge removal energy (charge removal amount in the case of a charge removal lamp) required to discharge the photosensitive member to the same potential is increased.

  As the photoreceptors 4K, Y, C, and M, those coated with a surface layer are used. Even if the surface layer wears with time due to friction with a cleaning blade, the charge transport layer As in the case of wear, appropriate static elimination energy increases as the amount of wear increases.

  Therefore, in this copying machine, the amount of static elimination (static elimination voltage or current) during the image forming operation by the static elimination lamp and the amount of static elimination during the post-processing operation can be used to increase the wear amount on the surface layer of the photoreceptor over time. The static elimination means is configured to change accordingly. More specifically, an IC chip (not shown) is mounted on each color process unit 3K, Y, C, M, and a unit ID number is stored in the IC chip. When the process units 3K, Y, C, and M are correctly set in the copying machine main body, the IC chip of each unit is electrically connected to a control unit (not shown) via a contact (not shown). A control unit including a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like is based on a change in a unit ID number stored in an IC chip of each unit. Unit replacement can be detected. In addition, the control unit stores the accumulated usage time of each unit as a cumulative operation time, a cumulative number of printed sheets, and the like in a RAM as storage means, and sequentially updates the cumulative usage time according to the operation status of the unit. . And when replacement | exchange of a unit is detected, the accumulated use time about the unit is reset to zero. The accumulated use time stored in the RAM in this way has a correlation with the amount of wear on the surface of the photoreceptor. The longer the cumulative use time, the greater the amount of wear on the photoreceptor surface. Therefore, the control unit stores an algorithm or a data table indicating the relationship between the accumulated usage time and the static elimination voltage or static elimination current corresponding to the residual image non-existing static elimination amount obtained by a previous experiment in the ROM. Further, an algorithm or a data table indicating the relationship between the accumulated usage time and the static elimination voltage or static elimination current corresponding to the sufficient static elimination amount obtained by a previous experiment is stored in the ROM. Then, based on the accumulated usage time stored in the RAM and the algorithm or data table, the static elimination voltage or static elimination current supplied to the static elimination lamp during the image forming operation is individually set for each color. Also, the neutralization voltage or neutralization current supplied to the neutralization lamp during the sound processing operation is individually set for each color. And a control signal is sent with respect to a static elimination power supply so that the static elimination voltage or static elimination current of a setting value may be supplied to a static elimination lamp. With such a configuration, it is possible to avoid improper charge removal processing due to a change in the appropriate value of the remaining image non-generated charge removal amount or sufficient charge removal amount with time due to wear of the surface of the photoreceptor over time.

  An example in which the amount of wear on the surface of the photoreceptor is estimated based on the relationship between the accumulated usage time obtained based on the results of previous experiments and the amount of static electricity that has not been generated, and the relationship between the accumulated usage time and the sufficient amount of static elimination. However, the charge removal amount may be adjusted based on the result of actually measuring the wear amount. For example, laser displacement meters that can detect the distance from the surface of the photoconductor with high accuracy are provided in the process units 3K, Y, C, and M of the respective colors, and the surface of the photoconductor surface is detected based on the detection results of the respective laser displacement meters. The amount of wear may be obtained.

  In this copying machine, a standard mode, an image quality priority mode, and a speed priority mode, in which each color photoconductor 4K, Y, C, M, intermediate transfer belt 25 and the like are moved on the surface at a standard linear velocity, are formed. Are switched based on the selection by the user. The image quality priority mode is a mode in which an image is formed while moving the surface of the photoreceptors 4K, Y, C, M of each color, the intermediate transfer belt 25, and the like at a linear velocity slower than the standard mode. The speed priority mode is a mode in which an image is formed while moving the surface of the photoreceptors 4K, Y, C, M of each color, the intermediate transfer belt 25, etc. at a linear velocity faster than the standard mode. The control unit of the copier is configured based on an input operation to an operation unit such as a numeric keypad (not shown) provided in the housing of the image forming unit 1 or printer driver setting information sent from a personal computer or the like. The mode is switched appropriately.

  The charge removal amount of the photoconductor changes in accordance with the amount of discharge light from the charge removal lamp. Further, the irradiation amount of the static elimination light from the static elimination lamp varies according to the linear velocity of the photosensitive member when the static elimination light amount per unit time is constant. For this reason, if the light emission amount of the static elimination light from the static elimination lamp is constant, the static elimination amount changes depending on the mode. Specifically, the charge removal amount gradually decreases in the order of image quality priority mode, standard mode, and speed priority mode.

  Therefore, in the present copying machine, the control unit that is a part of the charge eliminating unit includes a standard mode that is a standard image forming operation, an image quality priority mode that is a non-standard image forming operation, and a speed priority mode that is a non-standard image forming operation. The power consumption for static elimination during the image forming operation is made different. Further, the power consumption for static elimination during the post-processing operation is also made different in the three modes. Specifically, when conditions such as the amount of wear on the surface of the photoconductor are the same, the static elimination voltage or static elimination current to the static elimination lamp is minimized in the image quality priority mode among the three modes. The power consumption is minimized. Further, in the speed priority mode, the static elimination voltage or static elimination current to the static elimination lamp is maximized to maximize the power consumption for static elimination. More specifically, as described above, the control unit removes the charge removal voltage or charge removal for each of the process units 3K, Y, C, and M of each color based on the accumulated usage time of the photosensitive member and the above algorithm or data table. Adjust the current individually. As a result, the residual image non-generated static elimination amount and the sufficient static elimination amount are appropriately set according to the wear amount of the photosensitive member surface. Then, the following three types of algorithms or data tables described above are stored in the ROM. That is, for the image quality priority mode for computing the static elimination voltage or static elimination current as the smallest value among the three modes under the same wear amount condition, for the standard mode for computing as a standard value And for the speed priority mode for calculating as the largest value. These three types of algorithms or data tables are individually stored for determining the amount of static elimination that has not occurred in the image forming operation and for determining the amount of static elimination sufficient in the post-processing operation. These algorithms or data tables are selectively used based on which of the three speed modes is selected, an image forming operation, or a post-processing operation. Thereby, irrespective of the speed mode, it is possible to appropriately set the afterimage non-generated static elimination amount during the image forming operation and the sufficient static elimination amount during the post-processing operation.

  Note that, as described in Patent Document 1, the amount of static electricity necessary to sufficiently neutralize the photoconductor varies depending on the pause time and the continuous operation time, and therefore the charge removal amount depends on the pause time and the continuous operation time. It is desirable to adjust. This charge removal amount corresponds to a sufficient charge removal amount during the post-processing operation in this copying machine. Although not mentioned in Patent Document 1, when the appropriate value of the sufficient static elimination amount during the post-processing operation changes according to the pause time or the continuous operation time, the appropriate value of the afterimage non-generated static elimination amount during the image forming operation accordingly. Also changes. In view of this, the static elimination amount and the residual image non-generated static elimination amount may be changed in accordance with the pause time and the continuous operation time. Specifically, as the above-described algorithm or data table, a memory for obtaining a sufficient charge removal amount or a charge removal amount with no afterimage based not only on the accumulated use time of the photosensitive member but also on the rest time and the continuous operation time is stored. You can do it.

Next, modified examples of the copying machine according to the embodiment will be described. Unless otherwise specified below, the configuration of the copying machine according to each modification is the same as that of the embodiment.
[First Modification]
The copying machine according to the first modification includes a second static elimination unit in addition to the first static elimination unit including a static elimination lamp for neutralizing the photosensitive member during the image forming operation. Specifically, the optical writing device 2 is caused to function as a part of the second static elimination unit that neutralizes the photoconductor during post-processing. In each color process unit, during the post-processing operation, the photosensitive member is neutralized by optical scanning of the optical writing device 2 in addition to the neutralization of the photosensitive member by the neutralizing lamp. During the post-processing operation, when performing static elimination by optical scanning, an image to be a latent image writing target in the entire region in the direction (main scanning direction) perpendicular to the moving direction with respect to the surface of the photoreceptor. The optical writing device 2 and the control unit are configured so that the optical writing process is performed on the entire formation region. That is, the entire surface of the image forming area is exposed by optical scanning.

  During the image forming operation, the photosensitive member is neutralized only by the first neutralizing unit composed of a neutralizing lamp or the like, so the amount of neutralization by the second neutralizing unit composed of the optical writing device 2 or the control unit is zero. On the other hand, during the post-processing operation, in addition to the charge removal by the first charge removal means, the charge removal by the second charge removal means is performed, so the total charge removal amount of the photoconductor is the sum of both charge removals by both charge removal means. During the image forming operation and during the post-processing operation, the charge removal amount by the first charge removal unit is the same, but during the post-processing operation, the charge removal amount by the second charge removal unit is added in addition to the charge removal amount. As a result, the amount of static elimination by both static elimination means during post-processing operation is increased compared to that during image-forming operation, so that the amount of static-elimination is eliminated when the image-forming operation is switched to the post-processing operation. Switch from the amount of electricity to the amount of electricity removed sufficiently.

  In such a configuration, even if a discharge lamp having a relatively low light emission capability is used, the photoreceptor can be sufficiently discharged during the post-processing operation.

[Second Modification]
The copying machine according to the second modification also includes a second charge eliminating unit in addition to the first charge eliminating unit including a charge eliminating lamp for discharging the photosensitive member during the image forming operation. This second static elimination means is composed of a charging device in each color process unit 3K, Y, C, M, a charging power source for individually applying a bias to each charging roller, a control unit for controlling the output voltage in the future, and the like. Yes. In each color process unit 3K, Y, C, M, during the image forming operation, a charging bias is applied to each charging roller, so that each color photoconductor 4K, Y, C, M is set to one. Charge like this. Further, each color photoreceptor 4K, Y, C, M is neutralized by the amount of static electricity that has not been generated afterimages. On the other hand, during the post-processing operation, the process units 3K, Y, C, and M of the respective colors perform the charge removal of the photoreceptor by the charging roller in addition to the charge removal of the photoreceptor by the charge removal lamp. Specifically, as described above, during the image forming operation, a charging bias in which an AC voltage is superimposed on a DC voltage (negative polarity) is applied to the charging roller to uniformly charge the photosensitive member to a negative polarity. On the other hand, during the post-processing operation, a static elimination bias consisting only of an AC voltage is output from the charging power source, and this is applied to the charging roller to neutralize the photosensitive member.

  During the image forming operation, the photosensitive member is neutralized by the first neutralization unit composed of a neutralization lamp or the like with the residual image non-generated neutralization amount. On the other hand, during the post-processing operation, the photosensitive member is neutralized with a sufficient amount of static elimination only by the second static elimination means including a charging roller. In such a configuration, even if a discharge lamp having a relatively low light emission capability is used, the photoreceptor can be sufficiently discharged during the post-processing operation. In addition, it is possible to suppress deterioration due to light fatigue of the photosensitive member by discharging the photosensitive member without using light irradiation by the second static eliminating unit.

  During the post-processing operation, the photosensitive member may be neutralized by the first neutralization unit in addition to the second neutralization unit so that the total neutralization amount by both the neutralization units becomes a sufficient neutralization amount.

[Third Modification]
The copying machine according to the third modification also includes a second static elimination unit in addition to the first static elimination unit including a static elimination lamp for neutralizing the photosensitive member during the image forming operation. The transfer means composed of the transfer unit 24, the paper transport unit 28, etc. also functions as the second charge eliminating means. Specifically, during the image forming operation, a positive primary transfer bias (DC voltage) having a polarity opposite to the normal charging polarity of the toner is applied to each color primary transfer roller 26K, Y, C, M. By applying the toner, the toners on the photoreceptors 4K, Y, C, and M of each color are primarily transferred to the intermediate transfer belt 25. On the other hand, during the post-processing operation, a neutralization bias consisting of a DC voltage having a positive polarity and a value greater than the primary transfer bias is applied to the primary transfer rollers 26K, Y, C, and M of each color. To do.

  During the image forming operation, the photosensitive member is neutralized by the first neutralization unit composed of a neutralization lamp or the like with the residual image non-generated neutralization amount. On the other hand, during the post-processing operation, the photosensitive member is neutralized with a sufficient amount of static elimination only by the second static elimination means including the transfer unit 24 and the like. In such a configuration, even if a discharge lamp having a relatively low light emission capability is used, the photoreceptor can be sufficiently discharged during the post-processing operation. In addition, it is possible to suppress deterioration due to light fatigue of the photosensitive member by discharging the photosensitive member without using light irradiation by the second static eliminating unit.

  During the post-processing operation, the photosensitive member may be neutralized by the first neutralization unit in addition to the second neutralization unit so that the total neutralization amount by both the neutralization units becomes a sufficient neutralization amount. Further, in this copying machine, since the image is formed by reversal development in which the uniform charging polarity of the photosensitive member and the charging polarity of the toner are the same, primary transfer for performing primary transfer is performed. The polarity of the bias and the neutralizing bias applied to the primary transfer roller in order to neutralize the photosensitive member can be the same polarity. As a result, it is not necessary to use a power source that outputs a bipolar bias, thereby realizing a reduction in cost. On the other hand, in the normal development system in which the charging polarity of the photoconductor and the charging polarity of the toner are different from each other, the polarity of the primary transfer bias for performing the primary transfer and the primary transfer roller for discharging the photoconductor The neutralizing bias applied to the first and second biases have opposite polarities. For this reason, it is necessary to use a power supply that outputs a bipolar bias, resulting in an increase in cost.

[Fourth Modification]
In the copying machine according to the fourth modified example, the surface layer made of a material containing a photo-curing resin or a thermosetting resin on the organic photosensitive layer as the photoconductors 4K, Y, C, and M of the respective colors. Is used. In such a configuration, the wear resistance of the surface of the photoreceptor can be improved by the surface layer obtained by curing the photocurable resin or the thermosetting resin by light irradiation or heat. Further, since the rate of change with time of the wear amount of the photosensitive member is reduced, it is possible to suppress the change with time of the residual image non-generated static charge or the sufficient static charge removed.

[Fifth Modification]
In the copying machine according to the fourth modified example, the photosensitive members 4K, Y, C, and M for the respective colors have an inorganic photosensitive layer made of amorphous silicon. In such a photoreceptor, the inorganic photosensitive layer has a very high hardness, excellent wear resistance, and non-polluting. By using such a photoreceptor, the wear resistance of the photoreceptor surface can be improved. Further, since the rate of change with time of the wear amount of the photosensitive member is reduced, it is possible to suppress the change with time of the residual image non-generated static charge or the sufficient static charge removed.

[Sixth Modification]
In the copying machine according to the sixth modified example, in the process units 3K, Y, C, and M of the respective colors, the amount of static elimination is changed by the change in the static elimination voltage with respect to the static elimination lamp, so It is supposed to change. In such a configuration, it is possible to simplify the configuration as compared with a configuration in which the amount of static elimination is changed by passing the static elimination light through the slit and then applying it to the photoreceptor and changing the width of the slit.

[Seventh Modification]
In the copier according to the seventh modified example, in the process units 3K, Y, C, and M of the respective colors, the amount of static elimination is changed by the change of the static elimination current with respect to the static elimination lamp, so It is supposed to change. Even in such a configuration, the configuration can be simplified as compared with the configuration in which the charge removal light is applied to the photosensitive member after passing through the slit and the width of the slit is changed to change the charge removal amount. Further, by controlling the current flowing through the static elimination lamp, the quantity of static elimination can be controlled more directly.

  Up to now, a copying machine of a type in which a photosensitive member is discharged by a discharging lamp has been described as a discharging unit or a first discharging unit. However, a discharging unit or a first discharging unit of a type in which a photosensitive member is discharged by other means is used. The present invention can also be applied to an image forming apparatus. For example, the present invention can also be applied to an image forming apparatus in which a static elimination bias is applied to a rotatable static elimination brush roller that is in contact with a photosensitive member, and the photosensitive member is neutralized during an image forming operation. However, the bias static elimination method may cause a discharge product to lower the image quality, but the static elimination lamp is advantageous in that it does not cause such image quality degradation.

  As described above, in the copier according to the first modified example, the first charge eliminating unit that removes the photoconductor as the latent image carrier during the image forming operation and the second charge eliminating unit different from this are provided as the charge eliminating unit. In addition, the first static elimination unit and the second static elimination unit are configured to increase the total amount of static elimination by both the static elimination units during the post-processing operation performed after the imaging operation compared to during the imaging operation. . In such a configuration, as already described, even when a static elimination lamp having a relatively low light emission capability is used as the static elimination lamp of the first static elimination means, the photosensitive member can be sufficiently eliminated in the post-processing operation.

  Further, in the copying machine according to the embodiment and each of the modified examples, the neutralizing unit is configured to change the residual image non-generated static elimination amount or the sufficient static elimination amount as the static elimination amount as the wear amount of the photosensitive member surface increases with time. Is configured. In such a configuration, as already described, depending on the change in the proper amount of the residual image non-generated static charge or sufficient static charge removed due to the wear of the surface of the photosensitive member, the image is exposed during the image forming operation and the post-processing operation. The body can be removed with an appropriate charge removal amount.

  In the copying machine according to the first modification, since the second static elimination unit is configured to perform the static elimination process at least during the post-processing operation, the post-processing operation is being performed by the static elimination by the second static elimination unit. It is possible to increase the total amount of static elimination.

  In the copying machine according to the embodiment, the neutralization process of the photoconductor during the image forming operation and the neutralization process of the photoconductor during the post-processing operation are performed by one neutralization lamp as one neutralization member. I have to. In such a configuration, the charge removal amount can be switched between an afterimage non-generation charge removal amount during the image forming operation and a sufficient charge removal amount during the post-processing operation without using a plurality of charge removal members.

  In the copying machine according to the first modification, the optical writing device 2 as the latent image writing means is caused to function as the second charge removing means for discharging the photosensitive member during the post processing operation. It is possible to increase the amount of static electricity removed by the optical writing process.

  In the copying machine according to the second modification or the third modification, a bias is applied to a primary transfer roller or a charging roller, which is a biased member disposed in contact with or close to the photosensitive member, as the second charge eliminating unit. The one that removes the charge of the photosensitive member by application is used. In such a configuration, it is possible to suppress deterioration of the photosensitive member due to light fatigue by discharging the photosensitive member without using light irradiation by the second discharging unit.

  In the copying machine according to the second modification, as the transfer unit 24 serving as a transfer unit, an intermediate transfer belt serving as a transfer member that applies a primary transfer bias to a primary transfer roller serving as a transfer member to transfer a toner image on the photoreceptor. 25 is used, and the transfer unit 24 is caused to function as a second charge eliminating unit during the post-processing operation. In such a configuration, even if a static elimination lamp having a relatively low light emission capability is used as the static elimination lamp of the first static elimination means, the photosensitive member can be sufficiently eliminated in the post-processing operation.

  In the copying machine according to the third modification, as the charging device as the charging means, one that applies a charging bias to the charging roller as the charging member to uniformly charge the photosensitive member is used, and the charging device is subjected to post-processing operation. It is made to function as the 2nd static elimination means in the inside. In such a configuration, it is possible to suppress deterioration of the photosensitive member due to light fatigue by discharging the photosensitive member without using light irradiation by the second discharging unit.

  In the copying machine according to the first modification, when the photosensitive member is neutralized, the latent image is out of the entire region in the direction (main scanning direction) perpendicular to the moving direction with respect to the surface of the photosensitive member. The optical writing device 2 is configured so as to perform writing processing on the entire image forming area to be written. In such a configuration, the entire surface of the image forming area in the latent image carrier can be neutralized by the optical writing device 2.

  In the copying machine according to the third modification, the transfer unit 24 is configured to apply a neutralizing bias consisting of only a DC voltage to the primary transfer roller when neutralizing the photosensitive member. In such a configuration, the photosensitive member can be discharged by the transfer unit 24 while avoiding an increase in cost due to the use of an AC power source.

  In the copier according to the embodiment or the second modification, the charging member is non-contact with respect to the image forming area as the image forming target among all the areas in the direction orthogonal to the moving direction of the surface of the photosensitive member. A charging roller configured to be used is used. In such a configuration, as described above, it is possible to suppress a decrease in charging performance and charge removal performance caused by fixing toner on the surface of the charging roller.

  Further, in the copying machine according to the embodiment and the second modified example, a charging roller having an abutting roller that is an abutting portion having a larger diameter than the roller portion at both ends in the direction of the rotation axis is used. The abutting rollers are abutted against both end portions in the direction orthogonal to the surface movement direction of the photosensitive member, so that a gap is formed between the roller portion and the image forming area of the photosensitive member. In this configuration, as described above, the charging gap between the roller portion of the charging roller and the surface of the photosensitive member is accurately maintained regardless of the rotation of the roller, so that the charging unevenness of the photosensitive member due to the fluctuation of the charging gap is maintained. Can be suppressed.

  Further, in the copying machine according to the embodiment and each modification, the toner image on the photosensitive member is transferred to the intermediate transfer belt 25 as the transfer unit 24 or the paper transport unit 28 as transfer means, and then transferred to the recording paper. , Is used. In this configuration, as described above, fluctuations in the charging potential of the photosensitive member due to resistance changes around the photosensitive member due to paper passing can be suppressed. Specifically, the potential of the photoreceptor is greatly affected by the transfer. In the system in which the toner image on the photosensitive member is directly transferred to the recording paper without using the intermediate transfer belt 25, the electrical resistance at the primary transfer nip changes greatly as the thickness or size of the recording paper changes. Thus, the uniform charging potential of the photosensitive member is likely to fluctuate. On the other hand, in the intermediate transfer system, since the recording paper is not brought into contact with the photoconductor, such fluctuations can be avoided and the photoconductor can be uniformly charged with a stable potential.

  In addition, in the copying machine according to the embodiment and each modification, in addition to the standard mode which is a standard image forming operation for forming an image while moving the surface of the photosensitive member at a standard speed which is a standard speed, The image quality priority mode and speed priority mode, which are non-standard image forming operations that form images while moving at different speeds, are performed, and the power consumption for static elimination in the standard mode, image quality priority mode, and speed priority mode The static elimination means is configured so as to be different. In such a configuration, as described above, it is possible to appropriately set the after-image non-generated static elimination amount during the image forming operation and the sufficient static elimination amount during the post-processing operation, regardless of the speed mode.

  In the copying machine according to the embodiment, a photosensitive member having a multilayer structure including a surface layer and an organic photosensitive layer formed thereunder is used. In such a configuration, by suppressing the wear of the photoconductor by the surface layer, it is possible to keep the rate of change over time of the remaining image non-generated static elimination amount or the appropriate value of the sufficient static elimination amount low. Further, the cost can be reduced as compared with the inorganic photoconductor.

  In the copying machine according to the embodiment, a surface layer made of a material in which an additive is dispersed in a resin is used. In such a configuration, the wear resistance of the surface layer can be improved by the additive in the resin.

  In the copying machine according to the fourth modified example, the surface layer of each color photoconductor 4K, Y, C, M is made of a material containing a photocurable resin or a thermosetting resin. . In such a configuration, the wear resistance of the surface of the photoreceptor can be improved by the surface layer obtained by curing the photocurable resin or the thermosetting resin by light irradiation or heat. Further, since the rate of change with time of the wear amount of the photosensitive member is reduced, it is possible to suppress the change with time of the residual image non-generated static charge or the sufficient static charge removed.

  In the copying machine according to the fifth modification, a photosensitive member having a photosensitive layer made of amorphous silicon is used as the photosensitive member. With this configuration, the wear resistance of the surface of the photoreceptor can be improved. Furthermore, since the rate of change with time of the wear amount of the photoconductor is reduced, it is possible to suppress the change with time of the residual image non-generated charge removal amount or the sufficient charge removal amount.

  Further, in the copying machine according to the embodiment and each modified example, the drum cleaning device in each color process unit is provided with a lubricant applying means for applying a lubricant to the surface of the photoreceptor. In such a configuration, it is possible to suppress wear on the surface of the photoconductor by applying the lubricant and to suppress toner adhesion to the surface of the photoconductor.

  Further, in the process unit 3K shown in FIG. 4, after the primary transfer step, the transfer residual toner adhering to the surface of the photoreceptor 4K before entering the charging step by the charging device 23K is removed, and The drum cleaning device 15K is configured so that the lubricant is applied to the photoconductor 4K after the cleaning process and before entering the charging process. In such a configuration, regardless of fluctuations in the amount of residual toner after transfer, such as when the amount of residual toner after output of a solid image becomes relatively large and when the amount of residual toner after output of a character image becomes relatively small, etc. A lubricant film having a stable thickness can be formed on the surface of the photoreceptor 4K.

  In the copying machine according to the embodiment and each modification, a plurality of photoconductors are provided, and a transfer unit is provided so that the toner image formed on each photoconductor is transferred onto the intermediate transfer belt 25 that is a transfer body. The charge eliminating means is configured so as to individually adjust the remaining image non-generated charge removal amount and the sufficient charge removal amount for each photoconductor. In such a configuration, even if the respective photoconductors are replaced at different timings, it is possible to appropriately adjust the residual image non-generated static elimination amount and the sufficient static elimination amount according to the wear amount of each surface.

  Further, in the copying machine according to the sixth modification or the second modification, as the charge removal means, a charge removal unit that removes the photosensitive member by light irradiation is used, and a charge removal voltage that is a supply voltage to the charge removal lamp, or The static elimination means is configured to change the residual image non-generated static elimination amount or the sufficient static elimination amount by the change of the static elimination light amount accompanying the change of the static elimination current. In such a configuration, it is possible to simplify the configuration as compared with a configuration in which the amount of static elimination is changed by passing the static elimination light through the slit and then applying it to the photoreceptor and changing the width of the slit.

  In the copying machine according to the embodiment and each modification, the photosensitive member and the charge eliminating lamp that is at least a part of the charge eliminating unit are held by a common holder (casing) with respect to the image forming unit 1. It is configured as a process unit which is a latent image carrier unit that is integrally attached and detached. With such a configuration, it is possible to suppress the occurrence of inadequate charge removal due to contamination of the charge removal lamp. Specifically, if the static elimination lamp is used for a long period of time, the lamp may become dirty due to adhesion of toner or the like, and the quantity of static elimination may be reduced. Conventionally, the light emission amount of the static elimination lamp has been set to be quite large so that the photosensitive member can be sufficiently neutralized even if such contamination occurs. This spurred deterioration of the photoreceptor. On the other hand, in this copying machine, it is possible to control the amount of static elimination more delicately to suppress the deterioration of the photoconductor, but a decrease in the amount of light due to dirt leads to problems such as afterimages. However, when the life of the photosensitive member comes to an end, it is possible to suppress a decrease in the amount of light due to contamination by integrally replacing it as a process unit together with a static elimination lamp. Since the life of the static elimination lamp is sufficiently longer than that of the photoreceptor, resources are not wasted if the static elimination lamp of the collected process unit is cleaned and reused.

1 is a schematic configuration diagram showing a copier according to an embodiment. FIG. 2 is an enlarged configuration diagram showing a process unit for K in the copier. The longitudinal cross-sectional view which shows the charging roller of the process unit. The expanded block diagram which shows the other example of the process unit for K. The graph which shows the output characteristic of a static elimination lamp. 6 is a graph showing the relationship between a latent image history potential (residual potential) and the number of printed sheets. 6 is a graph showing the relationship between optical writing energy and photoreceptor surface potential.

Explanation of symbols

Optical writing device (latent image writing means)
3K, Y, C, M: Process unit (latent image carrier unit)
4K, Y, C, M: photoconductor (latent image carrier)
6K: Developing device (developing means)
16K: Cleaning brush roller (part of cleaning means)
17K: Application brush roller (part of lubricant application means)
18K: Cleaning blade (part of cleaning means)
22K: Static elimination lamp (static elimination means, part of first static elimination means)
23K: Charging device (part of charging means)
24: Transfer unit (part of transfer means)
25: Intermediate transfer belt (intermediate transfer member)
26K, Y, C, M: Primary transfer roller (bias applied member)
28: Paper transport unit (part of transfer means)
231K: Charging roller (bias applied member)
233K: Roller part 234K: Butting roller (butting part)

Claims (25)

A latent image carrier that carries a latent image, a charging unit that uniformly charges the latent image carrier, a latent image writing unit that writes a latent image on the latent image carrier after uniform charging, and the latent image Developing means for developing the toner image with toner, transfer means for transferring the toner image obtained by development from the latent image carrier to the transfer body, and discharging the latent image carrier after the transfer process by the transfer means. In an image forming apparatus comprising a static eliminating unit,
The charge eliminating unit is configured to reduce the charge removal amount during the image forming operation compared to the post processing operation performed after the image forming operation for forming the toner image on the latent image carrier. An image forming apparatus. The image forming apparatus according to claim 1.
As the charge eliminating means, there are provided a first charge eliminating means for eliminating the latent image carrier during the image forming operation and a second charge eliminating means different from the first charge eliminating means, and both the charge eliminating means during the image forming operation. An image forming apparatus characterized in that the first static elimination unit and the second static elimination unit are configured such that the total static elimination amount due to is smaller than that during post-processing operation. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the charge eliminating unit is configured to change the charge eliminating amount as the wear amount on the surface of the latent image carrier increases with time. The image forming apparatus according to claim 2.
An image forming apparatus, wherein the second static elimination unit is configured to perform static elimination processing at least during the post-processing operation. The image forming apparatus according to claim 1.
The neutralization unit is configured to perform the neutralization process on the latent image carrier during the image forming operation and the neutralization process on the latent image carrier during the post-processing operation by one neutralization member. Image forming apparatus. The image forming apparatus according to claim 2 or 4,
An image forming apparatus, wherein the latent image writing unit functions as the second neutralizing unit that neutralizes the latent image carrier during the post-processing operation. The image forming apparatus according to claim 2 or 4,
An image characterized in that as the second charge eliminating means, a means for applying a bias to a biased application member disposed in contact with or approaching the latent image carrier to neutralize the latent image carrier is used. Forming equipment. The image forming apparatus according to claim 7.
As the transfer means, a transfer bias is applied to the transfer member as the biased member to transfer the toner image on the latent image carrier to the transfer body, and the transfer means is in the post-processing operation. An image forming apparatus characterized in that the image forming apparatus functions as the second charge eliminating unit. The image forming apparatus according to claim 7.
As the charging means, one that applies a charging bias to the charging member as the bias applying member to uniformly charge the latent image carrier, and the charging means is used as the second charge eliminating means during the post-processing operation. An image forming apparatus characterized in that the image forming apparatus is made to function. The image forming apparatus according to claim 6.
When neutralizing the latent image carrier, writing is performed on the entire surface of the latent image carrier on the surface of the latent image carrier in the entire image forming area as a latent image writing target. An image forming apparatus characterized in that the latent image writing means is configured to perform an embedding process. The image forming apparatus according to claim 8.
An image forming apparatus, wherein the transfer unit is configured to apply a neutralizing bias consisting of only a DC voltage to the transfer member when neutralizing the latent image carrier. The image forming apparatus according to claim 9.
As the charging member, a charging roller configured to be in non-contact with the image forming area to be image formed out of all the areas in the direction orthogonal to the moving direction of the surface of the latent image carrier is used. An image forming apparatus characterized by comprising: The image forming apparatus according to claim 12.
As the charging roller, a roller having an abutting portion having a larger diameter than the roller portion at both ends in the direction of the rotation axis of the charging roller is used, and the abutting portion is orthogonal to the surface movement direction of the latent image carrier. An image forming apparatus characterized in that a gap is formed between the roller section and the image forming area of the latent image carrier by abutting against both ends of the image forming apparatus. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that as the transfer means, a toner image on the latent image carrier is transferred to an intermediate transfer member and then transferred to a recording member. The image forming apparatus according to any one of claims 1 to 14,
In addition to a standard image forming operation for forming an image while moving the surface of the latent image carrier at a standard speed, which is a standard speed, an image is formed while moving the surface at a speed different from the standard speed. An image forming apparatus configured to perform the non-standard image forming operation, and to configure the charge eliminating unit so that the power consumption for charge elimination differs between the standard image forming operation and the non-standard image forming operation. . The image forming apparatus according to any one of claims 1 to 15,
An image forming apparatus comprising: a photosensitive member having a multilayer structure comprising a surface layer and an organic photosensitive layer formed under the surface layer as the latent image carrier. The image forming apparatus according to claim 16.
An image forming apparatus using the surface layer made of a material in which an additive is dispersed in a resin. The image forming apparatus according to claim 16.
An image forming apparatus using the surface layer made of a material containing a photocurable resin or a thermosetting resin. The image forming apparatus according to any one of claims 1 to 15,
An image forming apparatus comprising a photosensitive member having a photosensitive portion made of amorphous silicon as the latent image carrier. The image forming apparatus according to claim 1,
An image forming apparatus comprising a lubricant applying means for applying a lubricant to the surface of the latent image carrier. The image forming apparatus according to claim 20, wherein
Cleaning for cleaning the latent image carrier by removing the transfer residual toner adhering to the surface of the latent image carrier before entering the charging step by the charging unit after the transfer step by the transfer unit. And the lubricant application means is disposed so as to apply the lubricant to the latent image carrier before entering the charging process after the cleaning process by the cleaning means. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 21,
A plurality of the latent image carriers are provided, and the transfer means is configured to transfer the toner image formed on each latent image carrier so as to be superimposed on the transfer member. An image forming apparatus, wherein the charge eliminating unit is configured to individually adjust a charge removal amount. The image forming apparatus according to any one of claims 1 to 22,
A photosensitive member is used as the latent image bearing member, and the neutralizing unit is a unit equipped with a neutralizing lamp that neutralizes the photosensitive member by light irradiation. By the change in the amount of static electricity with the change in the supply voltage to the neutralizing lamp, An image forming apparatus characterized in that the charge eliminating unit is configured to change the charge eliminating amount. The image forming apparatus according to any one of claims 1 to 22,
A photosensitive member is used as the latent image bearing member, and the neutralizing unit is a unit equipped with a neutralizing lamp that neutralizes the photosensitive member by light irradiation. By the change in the amount of static electricity accompanying the change in the supply current to the neutralizing lamp, An image forming apparatus characterized in that the charge eliminating unit is configured to change the charge eliminating amount. 25. The image forming apparatus according to claim 1, wherein:
The latent image carrier and at least a part of the charge eliminating unit are held by a common holder and configured as a latent image carrier unit that is integrally attached to and detached from the image forming apparatus main body. An image forming apparatus.

Images