JP4146266B2 - Charging device and image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a charging device and an electrophotographic image forming apparatus such as a copying machine, a printer, a plotter, a facsimile, and a printing apparatus using the charging device.
[0002]
[Prior art]
Conventionally, as a charging means used in an electrophotographic image forming apparatus, a charger-type charging device such as Scorotron has been mainstream, but there is a problem that a large amount of discharge products such as ozone are generated. Contact charging devices such as rollers and brushes have been widely used. In such a contact charging device, the occurrence of uneven charging due to dirt such as toner is a major factor that determines the life of the charging device.
[0003]
In order to reduce the contamination of the charging roller, a method has been proposed in which a film is attached to the end of the charging roller to form a minute gap between the photosensitive member and the charging roller (see Patent Document 1). In addition, as a gap holding method other than a film, a method has been proposed in which a step or groove is provided at the end of the charging roller and a spacer member is attached (see Patent Document 2).
In addition, an elastic member such as rubber or sponge is generally used as the material of the charging roller, but a charging member using a resin is also known (see Patent Document 3).
[0004]
[Patent Document 1]
JP 2001-194868 A
[Patent Document 2]
JP 2002-55508 A
[Patent Document 3]
JP 2001-337515 A
[0005]
[Problems to be solved by the invention]
When the charging member constituting the charging roller is rubber, there is a problem that it is difficult to process with high accuracy by cutting, and the gap is likely to fluctuate depending on the environment due to large thermal expansion. On the other hand, the charging member made of resin is easy to process with high hardness and easy to cut, but because of its high hardness, when a film-like member is used as a gap holding member, There was a problem such as wear of the shaped member. When an organic photoreceptor is used as the photoreceptor, the photoreceptor may be damaged at the contact portion of the gap holding member.
[0006]
Therefore, like the charging member described in Patent Document 2, a step is provided at the end of the charging member that constitutes the charging roller, and the gap holding member is formed of an elastic body. It can prevent that the part which a holding member contact | abuts deteriorates. However, simply providing a step may cause the gap holding member to deviate from the step of the charging member when used for a long period of time. Although there is a method of bonding the charging member and the gap holding member, the use of the adhesive is not preferable because the thickness unevenness of the adhesive has a non-negligible influence when forming a minute gap of several tens of μm.
[0007]
Further, by providing a concave groove at the end of the charging roller and attaching the gap holding member to the groove, the gap holding member can be prevented from coming off. However, in this shape, the discharge from the charging member to the image carrier is generated in the area outside the gap holding member as well as the image area inside the gap holding member. May wear out. Due to this local wear of the image carrier, leakage of charging bias occurs, toner fixation due to poor cleaning occurs, the charging gap widens, and uneven charging due to abnormal discharge is likely to occur. There were problems such as.
[0008]
The present invention has been made in view of the above circumstances, and an object of the present invention is to solve the problems in the prior art and provide a low-cost and long-life charging device and an image forming apparatus using the same.
[0009]
[Means for Solving the Problems]
  As a means for solving the above-mentioned problems, the invention according to claim 1 has a charging member for charging the image carrier, provided with a step at both ends of the charging member, and the image carrier at the step. In a charging device having a gap holding member that forms a gap with a body, a step to which the gap holding member is attached includes a first step portion and a second step having a smaller outer diameter than the first step portion. It is comprised by the level | step difference part. Then, the first step portion is positioned at the end of the charging member from the second step portion,The axial width of the first step portion is wider than the axial width of the second step portion,In addition, as a gap holding member attached to the first and second stepped portions, a tube-shaped material having heat shrinkability is used.The cap holding member covers both the first step portion and the second step portion..
  According to a second aspect of the present invention, in addition to the configuration of the charging device according to the first aspect, the portion of the gap holding member that covers the first stepped portion is brought into contact with the surface of the image carrier. .
  According to a third aspect of the present invention, in addition to the configuration of the charging device according to the first or second aspect, a portion that covers the second step portion of the gap holding member does not contact the image carrier. The second stepped portion is inserted and fixed.
[0010]
  Claim4In the invention according to claimAny one of 1-3In addition to the configuration of the charging device described above, the gap holding member covers the end surface of the charging member.
  Claims5In the invention according to claimAny one of 1-4In addition to the configuration of the charging device described above, the outer diameter of the end portion of the first step portion is configured to be smaller than the outer diameter of the portion other than the end portion of the first step portion.
  Further claims6In the invention according to claim 1,5In addition to the structure of the charging device according to any one of the above, the charging member is made of a resin material containing an ion conductive material, and the gap holding member is made of an insulating resin material containing fluorine.
[0011]
  Claim7In this invention, after charging the image carrier, the image carrier is exposed to light to form a latent image, the latent image is developed with a developer to be visualized, and the visible image is used as a transfer material. In an image forming apparatus for transferring and fixing to form an image, the image carrier is charged as means for charging.6It is set as the structure provided with the charging device as described in any one of these.
  Claims8In the invention according to claim7In addition to the configuration of the image forming apparatus described above, the gap holding member attached to the charging member of the charging device is brought into contact with the image carrier, whereby a gap is formed between the image carrier and the charging member in the image forming region. The gap between the image carrier and the charging member in the image forming region is 100 μm or less, and an alternating voltage having a peak-to-peak voltage that is at least twice the discharge start voltage between the charging member and the image carrier is applied to the charging device. Apply superimposed charging bias.
  Further claims9In the invention according to claim7Or8In addition to the configuration of the image forming apparatus described above, a unit configuration in which at least the image carrier and the charging device are configured to be detachable integrally with the image forming apparatus main body is adopted.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the configuration, operation, and action of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an overall configuration diagram of an image forming apparatus showing an embodiment of the present invention, and shows an example in which the present invention is applied to a full-color printer. In the apparatus main body 1, photoconductor units 2A, 2B, 2C and 2D, which are four image carrier units, are detachably attached to the apparatus main body 1, respectively. A transfer unit in which the transfer belt 3 is rotatably mounted in a direction indicated by an arrow A between a plurality of rollers is disposed at a substantially center of the apparatus main body 1. Four transfer brushes 57 are provided on the inner side of the transfer belt 3 corresponding to the four photoconductors 5, respectively. The photoconductor 5 provided in each of the photoconductor units 2A, 2B, 2C, and 2D is arranged so as to contact the upper surface of the transfer belt 3. In correspondence with the photoreceptor units 2A to 2D, developing devices 10A to 10D having different toner colors are arranged. The developing devices 10A to 10D are two-component developing type developing devices that have the same configuration and differ only in the color of the toner used. As an example, the developing device 10A uses magenta toner, the developing device 10B uses cyan toner, the developing device 10C uses yellow toner, and the developing device 10D uses black toner. use. Each color developing device contains a developer composed of toner and carrier.
[0013]
The developing devices 10A to 10D include a developing roller facing the photosensitive member 5, a screw for conveying and stirring the developer, a toner replenishing unit and a replenishing device, a toner density sensor, and the like. The developing roller is composed of an outer rotatable sleeve and a magnet fixed on the inner side. The developing device is replenished with toner from a toner replenishing unit by a replenishing device in accordance with the output of the toner density sensor.
[0014]
The toner includes a binder resin, a colorant, and a charge control agent as main components, and other additives are added as necessary. Specific examples of the binder resin include polystyrene, styrene-acrylic acid ester copolymer, polyester resin, and the like. As the colorant (for example, yellow, magenta, cyan and black) used for the toner, those known for toner can be used. The amount of the coloring material is suitably 0.1 to 15 parts by weight with respect to 100 parts by weight of the binder resin.
Specific examples of the charge control agent include nigrosine dyes, chromium-containing complexes, quaternary ammonium salts, and the like, which are properly used depending on the polarity of the toner particles. The amount of the charge control agent is 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.
[0015]
It is advantageous to add a fluidity imparting agent to the toner particles. Examples of the fluidity-imparting agent include fine particles of metal oxides such as silica, titania and alumina, and those obtained by surface treatment with silane coupling agents, titanate coupling agents, etc., polystyrene, polymethyl methacrylate, polyfluoride. Polymer fine particles such as vinylidene are used. These fluidity imparting agents have a particle size in the range of 0.01 to 3 μm. The addition amount of these fluidity-imparting agents is preferably in the range of 0.1 to 7.0 parts by weight with respect to 100 parts by weight of toner particles.
[0016]
As a method for producing the toner for two-component developer according to the present invention, it can be produced by various known methods or a combination thereof. For example, in the kneading and pulverization method, a binder resin, a colorant such as carbon black, and the necessary additives are dry-mixed, heated and melt-kneaded with an extruder or two-roll, three-roll, etc., and after cooling and solidification Then, the toner is pulverized by a pulverizer such as a jet mill and classified by an airflow classifier. In addition, a toner can be directly produced from a monomer, a colorant, and an additive by suspension polymerization or non-aqueous dispersion polymerization.
[0017]
The carrier is generally composed of the core material itself, or a carrier provided with a coating layer on the core material. The core material of the resin-coated carrier that can be used in the present invention is ferrite or magnetite. An appropriate particle size of the core material is about 20 to 60 μm.
Examples of the material used for forming the carrier coating layer include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinyl ether substituted with a fluorine atom, and vinyl ketone substituted with a fluorine atom. As a method for forming the coating layer, a resin may be applied to the surface of the carrier core material particles by a spraying method, a dipping method, or the like, as in the conventional case.
[0018]
A writing unit 6 is disposed above the photoreceptor units 2 </ b> A to 2 </ b> D, and a duplex unit 7 is disposed below the transfer belt 3. In this printer, a reversing unit 8 is mounted on the left side of the apparatus main body 1 for reversing and discharging a transfer material (for example, transfer paper) P after image formation or transporting it to a duplex unit.
The writing unit 6 is arranged in four laser diode (LD) type light sources prepared for each color, a set of polygon scanners composed of a six-sided polygon mirror and a polygon motor, and an optical path of each light source. It is composed of a lens such as an fθ lens, a long WTL, or a mirror. Laser light emitted from the laser diode is deflected and scanned by a polygon scanner and irradiated onto the photosensitive member.
[0019]
The duplex unit 7 includes a pair of conveyance guide plates 45a and 45b and a pair of (four sets in this example) conveyance rollers 46. In the duplex image formation mode in which images are formed on both sides of a transfer sheet, The transfer paper P on which an image is formed on one side, conveyed to the reversing conveyance path 54 of the reversing unit 8 and switched back is received, and conveyed to the paper feeding unit.
[0020]
The reversing unit 8 includes a plurality of paired transport rollers and a plurality of paired transport guide plates. As described above, the reversing unit 8 reverses the transfer paper P when double-sided image formation is carried out to the double-sided unit 7. The transfer paper P after image formation is discharged out of the machine in the same orientation, or the paper is reversed outside and turned out of the machine.
In addition, the paper feed units provided with the paper feed cassettes 11 and 12 are provided with separate paper feed units 55 and 56 for separating and feeding the transfer paper P one by one.
[0021]
A fixing device 9 is provided between the transfer belt 3 and the reversing unit 8 to fix the image on the transfer paper P onto which the image has been transferred. A reverse paper discharge path 20 is branched and formed on the downstream side of the fixing device 9 in the transfer paper conveyance direction, and the transfer paper P conveyed there can be discharged onto a paper discharge tray 26 by a pair of paper discharge rollers 25. Yes.
[0022]
Further, in the lower part of the apparatus main body 1, paper feed cassettes 11 and 12 that can store transfer papers P having different sizes are arranged in two upper and lower stages. Further, a manual feed tray 13 is provided on the right side surface of the apparatus main body so as to be openable and closable in the direction indicated by the arrow B, and the manual feed tray 13 is opened so that manual feeding can be performed therefrom.
[0023]
The photoconductor units 2A to 2D are units having the same configuration. The photoconductor unit 2A forms an image corresponding to magenta, and the photoconductor unit 2B forms an image corresponding to cyan. 2C forms an image corresponding to the yellow color, and the photoreceptor unit 2D forms an image corresponding to the black color.
[0024]
First, the operation of the image forming apparatus during full color image formation will be described. When the image forming apparatus receives full-color image data, the photoreceptors 5 of the photoreceptor units 2A to 2D rotate in the clockwise direction in FIG. Then, the surface of each photoconductor 5 is uniformly charged by the charging roller 14 shown in FIG. Laser light corresponding to a magenta image is written to the photosensitive member of the photosensitive unit 2A by the writing unit 6, and laser light corresponding to a cyan image is applied to the photosensitive member of the photosensitive unit 2B. The photosensitive member is irradiated with laser light corresponding to a yellow image, and the photosensitive member of the photosensitive member unit 2D is irradiated with laser light corresponding to a black image, thereby forming a latent image corresponding to image data of each color. The When the latent images reach the positions of the developing devices 10A, 10B, 10C, and 10D by the rotation of the photosensitive member, the latent images are developed with magenta, cyan, yellow, and black toners to form four-color toner images. .
[0025]
On the other hand, the transfer paper P is fed from the paper feed cassette 11 (or 12) by the separation paper feeding section 55 (or 56), and each photoconductor is fed by a registration roller pair 59 provided immediately before the transfer belt 3. The toner image is conveyed at the same timing as the toner image formed above. The transfer paper P is charged to a positive polarity by a paper suction roller 58 disposed in the vicinity of the entrance of the transfer belt 3, and thereby electrostatically attracted to the surface of the transfer belt 3. Then, while the transfer paper P is conveyed while adsorbed to the transfer belt 3, magenta, cyan, yellow, and black toner images are sequentially transferred to form a four-color superimposed full-color toner image. The
[0026]
The transfer paper P is melted and fixed by applying heat and pressure by the fixing device 9, and then passes through a paper discharge system corresponding to a designated mode to a paper discharge tray 26 at the top of the main body of the apparatus. When the paper is reversed, discharged straight from the fixing device 9 and straightly discharged through the reversing unit 8, or when the double-sided image forming mode is selected, the reversing conveyance path 54 in the reversing unit 8 described above. Is fed back to the duplex unit 7 and is transported to the duplex unit 7 to be fed again and discharged after an image is formed on the back surface in the image forming unit provided with the photoreceptor units 2A to 2D. . Thereafter, when two or more image formations are instructed, the above-described image forming process is repeated.
[0027]
Next, the operation of the image forming apparatus when forming a monochrome image will be described. When the image forming apparatus receives black and white image data, the driven roller supporting the transfer belt 3 is moved downward so as to face the paper suction roller 58, and the transfer belt 3 is moved from the magenta, cyan, and yellow photoconductors. Separate. Then, the photoconductor of the black photoconductor unit 2D rotates in the clockwise direction in FIG. 1, and the surface of the black photoconductor is uniformly charged by the charging roller. The photosensitive member of the photosensitive unit 2D is irradiated with laser light corresponding to a black image to form a latent image. When the latent image reaches the position of the developing device 10D, the latent image is developed with black toner to become a toner image. At this time, the image forming units for the three colors other than black are stopped, and unnecessary wear is prevented.
[0028]
On the other hand, the transfer paper P is fed from the paper feed cassette 11 (or 12) by the separation paper feeding section 55 (or 56), and the black photosensitive member is fed by the registration roller pair 59 provided immediately before the transfer belt 3. The toner image is conveyed at the same timing as the toner image formed above. The transfer paper P is charged by a paper suction roller 58 disposed near the entrance of the transfer belt 3, and thereby electrostatically attracted to the surface of the transfer belt 3. Since the transfer paper P is conveyed while adsorbed to the transfer belt 3, even if the transfer belt 3 is separated from the magenta, cyan, and yellow photoconductors, the transfer paper P is conveyed to the black photoconductor and the black toner image. Is transcribed. In order to stably transfer and transfer the transfer paper P, the transfer belt 3 needs to be made of a material having at least a surface layer having a high resistance. The transfer paper P is fixed by the fixing device 9 as in the case of a full-color image, and processed through a paper discharge system corresponding to the designated mode. Thereafter, when two or more image formations are instructed, the above-described image forming process is repeated.
[0029]
In the image forming apparatus having the above configuration, as the material of the transfer belt 3, a resin material such as polyvinylidene fluoride, polyimide, polycarbonate, polyethylene terephthalate, etc. can be molded into a seamless belt and used. These materials can be used as they are, or the resistance can be adjusted with a conductive material such as carbon black. Further, using these resins as a base layer, a surface layer may be formed by a method such as spraying or dipping to form a laminated structure.
[0030]
As shown in FIG. 2, each of the photoreceptor units 2 </ b> A to 2 </ b> D includes a charging roller 14 that forms a charging device, a photoreceptor 5 on which an electrostatic latent image is formed, and a cleaning device that cleans the surface of the photoreceptor 5. The brush roller 15 and the cleaning blade 47 are included. The charging roller 14 is in contact with a cleaning brush (or cleaning roller) 49 for cleaning the roller surface.
[0031]
In the cleaning device, the toner scraped off by the cleaning blade 47 is moved to the toner transport auger 48 side by the brush roller 15, and the waste toner collected by rotating the toner transport auger is stored in the waste toner storage shown in FIG. It is configured to be conveyed to the unit 18. In this embodiment, the diameter of the photoconductor is 30 mm, and the photoconductor 5 of each of the photoconductor units 2A to 2D rotates at 125 mm / sec in the arrow C direction. The brush roller 15 rotates in the clockwise direction in synchronization with the rotation of the photosensitive member 5.
[0032]
The photoreceptor units 2A to 2D are provided with a positioning main reference portion 51 as a reference for attaching and detaching the photoconductor units 2A to 2D, and the near side positioning reference portion 52 and the back side positioning reference portion. 53 are integrally provided on the bracket 50, and when the photoconductor units 2A to 2D are mounted on the apparatus main body 1, the photoconductor units 2A to 2D can be reliably positioned at predetermined mounting positions by the reference portions. I am doing so.
[0033]
In the image forming apparatus having the configuration shown in FIGS. 1 and 2, the photosensitive member 5 and the charging device (the charging roller 14 and the cleaning brush 49) are arranged in one unit. Therefore, the photosensitive member 5 and the charging roller 14 are included in the unit. Since the position is determined and the entire unit is replaced, it is not necessary to adjust the gap, and the user can easily replace it. Further, here, the unit in which the cleaning device (the brush roller 15 and the cleaning blade 47) is integrated in addition to the photosensitive member 5 and the charging device (the charging roller 14 and the cleaning brush 49) has been described, but the cleaning device is a separate unit. The developing device may be a unit integrated with the photosensitive member or the charging device.
[0034]
The photoreceptor 5 is formed by laminating an undercoat layer, a charge generation layer mainly composed of a charge generation material, and a charge transport layer mainly composed of a charge transport material on a conductive support.
Further, a protective layer may be formed on the photoreceptor 5 for the purpose of protecting the photosensitive layer and improving durability as a surface layer.
The conductive support has a volume resistance of 10⁴Those having conductivity of Ωcm or less, for example, a metal tube such as aluminum or stainless steel, or a metal such as nickel processed into an endless belt shape, or the like is used.
[0035]
In general, the undercoat layer is mainly composed of a resin. However, considering that the photosensitive layer is applied using a solvent, the resin is a resin having high resistance to general organic solvents. Is desirable. Examples of such resins include water-soluble resins such as polyvinyl alcohol resins, alcohol-soluble resins such as copolymer nylon, polyurethane resins, alkyd-melamine resins, epoxy resins, and other curable resins that form a three-dimensional network structure. Can be mentioned. Further, a fine powder of metal oxide such as titanium oxide, silica, alumina or the like may be added to the undercoat layer in order to prevent moire and reduce residual potential. This undercoat layer can be formed using an appropriate solvent and coating method. The thickness of the undercoat layer is suitably from 0 to 5 μm.
[0036]
The charge generation layer is a layer mainly composed of a charge generation material, and representative examples include a monoazo pigment, a disazo pigment, a trisazo pigment, and a phthalocyanine pigment. These charge generation materials can be formed by dispersing together with a binder resin such as polycarbonate using a solvent such as tetrahydrofuran or cyclohexanone and applying a dispersion. Application is performed by dip coating, spray coating, or the like. The thickness of the charge generation layer is usually 0.01 to 5 μm.
[0037]
The charge transport layer can be formed by dissolving or dispersing the charge transport material and the binder resin in a suitable solvent such as tetrahydrofuran, toluene, dichloroethane, and applying and drying the solution. Among charge transport materials, low molecular charge transport materials include electron transport materials and hole transport materials. Examples of the electron transport material include chloroanil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 1, Examples include electron-accepting substances such as 3,7-trinitrodibenzothiophene-5,5-dioxide. Examples of hole transport materials include oxazole derivatives, oxadiazole derivatives, imidazole derivatives, triphenylamine derivatives, phenylhydrazones, α-phenylstilbene derivatives, thiazole derivatives, triazole derivatives, phenazine derivatives, acridine derivatives, thiophene derivatives, etc. These electron donating substances are listed. Binder resins used in the charge transport layer together with the charge transport material include polystyrene resin, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, polyester resin, polyarylate resin, polycarbonate resin, acrylic resin, epoxy resin, melamine Examples thereof include thermoplastic or thermosetting resins such as resins and phenolic resins. The thickness of the charge transport layer may be appropriately selected in the range of 5 to 30 μm according to desired photoreceptor characteristics.
[0038]
FIG. 3 is a schematic cross-sectional view of an essential part showing a configuration example of a charging roller used in the image forming apparatus having the configuration shown in FIGS. 1 and 2, and shows a cross section on one end side of the charging roller 14. The charging roller 14 includes a cored bar 101 that is a conductive support, a resin layer 102 as a charging member formed on the cored bar, and a gap holding member 103.
The metal core 101 is made of metal such as stainless steel. If the mandrel 101 is too thin, the influence of deflection at the time of cutting or pressurizing the photoreceptor cannot be ignored, and it is difficult to obtain the required gap accuracy. Further, when the cored bar 101 is too thick, there is a problem that the charging roller 14 is enlarged or the mass is increased. Therefore, the diameter of the cored bar 101 is preferably about 6 to 10 mm.
[0039]
The resin layer (charging member) 102 of the charging roller 14 is 10⁶-10⁹A material having a volume resistance of Ωcm is preferred. If the resistance is too low, leakage of the charging bias tends to occur when the photoreceptor has a defect such as a pinhole. If the resistance is too high, the discharge is not sufficiently generated and a uniform charging potential cannot be obtained.
The resin layer (charging member) 102 can obtain a desired volume resistance by blending a conductive material with a resin as a base material. As the base resin, resins such as polyethylene, polypropylene, polymethyl methacrylate, polystyrene, ABS (acrylonitrile-butadiene-styrene copolymer), polycarbonate, and the like can be used. Since these base resins have good moldability, they can be easily molded.
[0040]
As the conductive material, an ion conductive material such as a polymer compound having a quaternary ammonium base is preferable. Examples of polyolefins having a quaternary ammonium base include polyethylene, polypropylene, polybutene, polyisoprene, ethylene-ethyl acrylate copolymer, ethylene-methyl acrylate copolymer, ethylene-san vinyl acetate copolymer, ethylene-propylene having a quaternary ammonium base. Polyolefins such as copolymerization and ethylene-hexene copolymerization. In the present embodiment, the polyolefin having a quaternary ammonium base has been exemplified. However, a polymer compound other than a polyolefin having a quaternary ammonium base may be used as long as the object of the present invention is not violated.
[0041]
The ion conductive material is uniformly blended with the base resin by using means such as a biaxial kneader or a kneader. By making the blended material into a cored bar by injection molding or extrusion molding, it can be easily molded into a roller shape. As for the compounding quantity of an ion conductive material and base resin, 30-80 weight part is desirable with respect to 100 weight part of base resin. The thickness of the resin layer 102 of the charging roller 14 is desirably 1 to 3 mm. If the resin layer 102 is too thin, it is difficult to mold and there is a problem in terms of strength. If the resin layer 102 is too thick, the charging roller 14 is increased in size and the actual resistance of the resin layer 102 is increased, so that charging efficiency is lowered. Further, a protective layer to which toner or the like hardly adheres can be formed on the resin layer 102 with a thickness of several tens of μm by coating or the like.
[0042]
When cutting the resin layer 102 to adjust the outer diameter, a step 102b for attaching the gap holding member 103 to the end 102a side of the resin layer 102 is formed. As the gap holding member 103, a heat-shrinkable tube of a fluorine resin material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) or FEP (tetrafluoroethylene-hexafluoropropylene copolymer) can be used. Since these resins are excellent in releasability, toner sticking hardly occurs. Furthermore, by using an insulating fluorine-based resin, no discharge occurs at the position of the gap holding member, so that the discharge product accumulates on the surface of the photoconductor to increase the friction coefficient of the photoconductor, It is also possible to prevent the cleaning blade from being caught. Since these fluorine-based resin materials are excellent in releasability, it is difficult to adhere to the resin. However, by attaching them by heat shrinkage, they can be fixed to the roller without using an adhesive.
[0043]
A gap is formed between the resin layer 102 of the charging roller 14 and the photosensitive member 5 by applying the gap holding member 103 outside the image area of the photosensitive member 5. In the charging roller 14, a gear (not shown) attached to an end of the cored bar 101 is engaged with a gear (not shown) formed on the photosensitive member flange, and when the photosensitive member 5 is rotated by the photosensitive member driving motor. The charging roller 14 also rotates at substantially the same speed as the photoreceptor 5. Gap holding members 103 are provided at both ends of the charging roller 14 so that the resin layer 102 and the photoconductor 5 do not come into contact with each other. Therefore, even when a hard resin material and an organic photoconductor are used as the charging roller 14, The body 5 is not damaged. In addition, if the gap is too wide, abnormal discharge occurs and charging cannot be performed uniformly. Therefore, the maximum gap needs to be suppressed to 100 μm or less. Therefore, both the photoconductor 5 and the charging roller 14 are required to have high accuracy, and the straightness needs to be 20 μm or less.
[0044]
In the charging roller 14 having the configuration shown in FIG. 3, a gap is provided between the charging roller 14 and the photoconductor 5 by the gap holding member 103, so that the load accompanying the rotation of the charging roller 14 is concentrated on the gap holding member 103. Therefore, the gap holding member 103 is required to have high durability. When a heat-shrinkable tube is used as the gap holding member 103, durability can be ensured by increasing the thickness of the heat-shrinkable tube.
[0045]
However, since there is a thickness deviation of about ± 10% of the thickness of a general heat shrinkable tube, gap variation caused by the heat shrinkable tube increases as the thickness increases. The thinner the heat-shrinkable tube, the better. If the step part to be attached when using a thin heat-shrinkable tube is linear as shown in the configuration example of FIG. 3, the heat-shrinkable tube will be slightly extended when used for a long time. When the end portion climbs on the inner step, the gap widens and abnormal discharge occurs, or the heat-shrinkable tube sometimes shifts outward from the step.
[0046]
Therefore, in the present invention, as means for solving the above-described problem, two steps are provided at both ends of the charging member 102 of the charging roller 14 as in the configuration example of the charging roller shown in FIG. In other words, in the present invention, the shape of the stepped portion 102b provided on the charging member (resin layer) 102 of the charging roller 14 has a two-step configuration as shown in FIG. More specifically, the first stepped portion 102b-1 is provided on the end portion 102a side of the charging member 102, and the first stepped portion is formed at the end portion from the central portion of the first stepped portion 102b-1. A groove-like second step 102b-2 having an outer diameter smaller than that of 102b-1 is provided, and the heat-shrinkable gap holding member 103 is attached from the first step 102b-1 to the second step 102b-2. . By doing in this way, since a large force is not applied to the heat-shrinkable tube on the second step portion 102b-2 side having a small outer diameter, even when used for a long period of time, the end portion is extended to the inner step. It is unlikely that problems such as getting on or moving outside will occur. Even if the heat-shrinkable tube is slightly extended at the first step 102b-1, there is almost no influence on the gap if the charging roller 14 is pressed against the photosensitive member 5 with a spring or the like.
[0047]
Next, FIG. 5 shows another configuration example of the charging roller according to the present invention. In this configuration example, the shape of the stepped portion 102b of the charging member 102 is the same as that in FIG. 4, but as shown in FIG. 5, the gap holding member 103 made of a heat-shrinkable tube is covered to the side surface of the end portion of the charging member 102. It is attached as follows. By doing in this way, it becomes more difficult for the heat-shrinkable tube to ride on the inner step. Further, by covering the end surface of the charging member 102 with an insulating heat-shrinkable tube, unnecessary discharge that occurs outside the image area can be prevented, and the photoreceptor is worn at this position. As a result, it is possible to prevent the charging bias from leaking, or the gap from being excessively widened due to poor cleaning, resulting in abnormal discharge.
[0048]
FIG. 6 shows still another configuration example of the charging roller according to the present invention. If the end portion of the first step portion 102b-1 of the charging roller 14 is sharp as shown in FIG. 5, the heat-shrinkable tube may be damaged at this portion. However, as shown in FIG. By processing such as cutting the corner 102c at the end of the portion 102b-1, the outer diameter of the end of the first stepped portion 102b-1 is made smaller than the other portions. The heat shrinkable tube is prevented from being damaged, and the durability of the heat shrinkable tube is further improved.
[0049]
When the charging roller 14 has any one of the configurations shown in FIGS. 4 to 6 and a gap is formed between the charging roller 14 and the photosensitive member 5, the gap is always within a certain range as the photosensitive member 5 and the charging roller 14 rotate. fluctuate. In order to uniformly charge the photosensitive member 5 under such circumstances, as a charging bias applied to the charging roller 14, in addition to a direct current (DC) voltage, the discharge starting voltage between the charging member and the photosensitive member is more than twice. It is effective to superimpose alternating (AC) voltages having peak-to-peak voltages. In this case, if the frequency of the applied AC voltage is low, stripe-shaped charging unevenness corresponding to the frequency of the AC voltage becomes conspicuous even on the image. Therefore, the frequency [Hz] is 7 times or more the photosensitive member linear velocity [mm / s]. ] Is desirable.
[0050]
As a member for cleaning the charging roller 14, a cleaning brush 49 is disposed above the charging roller 14 as shown in FIG. The cleaning brush 49 is obtained by electrostatically implanting conductive fibers having a bristle length of 0.5 mm on a roller-shaped cored bar having a diameter of 6 mm. The cleaning brush 49 is in free contact with the charging roller 14 by its own weight, and cleans the surface of the charging roller while rotating in the follower direction as the charging roller 14 rotates. In this case, since the contact is made only by its own weight without using a pressurizing means such as a spring, the deflection does not become a problem even if the diameter of the cored bar is thin. Here, by making the length of the cleaning brush 49 longer than the length of the charging roller 14 including the portion covered with the heat shrinkable tube constituting the gap holding member 103, the surface of the heat shrinkable tube can be cleaned at the same time. it can. Although there is a difference in the outer diameter of the charging roller 14 between the image forming region and the heat shrinkable tube covering portion, it is only about several tens of μm and at most 100 μm or less, which is sufficiently smaller than the bristle of the cleaning brush 49. The cleaning property of the formation region is not lowered.
[0051]
【Example】
Next, specific examples and comparative examples of the present invention will be described.
[0052]
(Example)
In this example, the charging roller 14 was produced as follows. First, as a charging member (resin layer) 102, a resin composition (volume resistivity 10) obtained by blending 100 parts by weight of an ABS resin and 60 parts by weight of an ionic conductive agent into a core metal 101 made of stainless steel and having a diameter of 8 mm.⁶Ωcm) was formed by injection molding, and then the surface was cut to a diameter of 12 mm. Here, as shown in FIG. 5 or FIG. 6, two-level stepped portions 102 b having a width of 8 mm were formed at both ends of the resin layer 102. The stepped portion includes a first stepped portion 102b-1 and a second stepped portion 102b-2, and the depth of the stepped portion is a first stepped portion having a width of about 6.5 mm from the end portion toward the central portion. The portion 102b-1 has a depth of 50 μm, and the portion having a width of 1.5 mm from the center side end portion of the first step portion further toward the center portion has a depth of 150 μm as the second step portion 102b-2. A heat-shrinkable tube (in this case, a PFA tube) having a thickness of 100 μm was attached to the first and second stepped portions as the gap holding member 103 with a length of 10 mm. The tube was contracted by heating in an atmosphere of 120 ° C. for 20 minutes. In this embodiment, since the length of the heat shrinkable tube is longer than that of the stepped portion, the tube after shrinkage is covered up to the side surface 102a of the charging member 102 as shown in FIG.
[0053]
The charging roller 14 was set on a photosensitive unit of a Ricoh color printer (Ipsiocolor 8000) having the configuration shown in FIG. 1, and a paper passing test was conducted at a photosensitive member linear velocity of 125 mm / s. The charging bias was a sine wave with a DC component of −700 V, an AC component with a peak-to-peak voltage of 2.2 kV, and a frequency of 900 Hz.
When a 50,000 sheet passing test was performed under the above conditions, the image was good throughout the test, and the state of the heat-shrinkable tube after 50,000 sheets was slightly swollen at the center, but both ends were There was no abnormal image.
[0054]
(Comparative example)
Next, as a comparative example, as shown in FIG. 3, the entire stepped portion 102b of the resin layer 102 to which the heat shrinkable tube 103 is attached has a depth of 50 μm, and the length of the heat shrinkable tube to be attached is 8 mm. A similar charging roller was produced.
When a paper passing test of 50,000 sheets was performed under the same conditions as in the example, the initial image was good, but fine dot-like stains appear on a part of the image from around 40,000 sheets. Became. Therefore, when the photoconductor unit was checked, the above-mentioned problem was due to the heat shrinkable tube extending, and the heat shrinkable tube protruded from the stepped portion and stepped on the step inside the charging roller, resulting in an abnormal discharge due to the gap becoming too wide. It was because of the occurrence.
[0055]
【The invention's effect】
  As explained above, claim 1To ~ 3In the charging device described above, the step for attaching the gap holding member includes a first step portion and a second step portion having an outer diameter smaller than the first step portion, and the first step portion is the second step portion. So that it is located at the end of the charging member from the step ofThe axial width of the first step portion is wider than the axial width of the second step portion,In addition, a heat-shrinkable gap retaining member is used.The cap holding member covers both the first step portion and the second step portion, and the image holding portion covers the first step portion of the gap holding member. Further, the portion of the gap holding member that covers the second stepped portion enters the second stepped portion and is fixed so as not to contact the image carrier. Was configuredThis prevents the gap holding member from coming off the step even when used for a long time without using adhesive because the gap holding member enters and is fixed to the second step with a small outer diameter. Therefore, it is possible to realize a charging device with a low cost and a long life.
  Claims4The charging device as claimed in claimAny one of 1-3Configuration andeffectIn addition, since the gap holding member covers the side surface of the charging member, unnecessary discharge outside the image forming area can be prevented, and photoconductor abrasion and toner sticking outside the image forming area can be prevented. Can do. Further, the gap holding member can be prevented from being displaced toward the charging region inside the charging member by covering the side surface.
[0056]
  Claim5The charging device as claimed in claimAny one of 1-4Configuration andeffectIn addition, by treating the end shape of the attachment portion of the gap holding member so that the outer diameter is smaller than the other portions, it is possible to prevent the gap holding member from being damaged due to concentration of force on the end portion. It is possible to improve the durability of the gap holding member.
  Claim6The charging device as claimed in claimAny one of 1-5Configuration andeffectIn addition, the charging member is made of a resin material, so that processing is easy and accuracy is easily obtained. In addition, the ion conductive material contained in the resin material of the charging member is less likely to cause abnormal discharge when there is a gap than the electron conductive material. Furthermore, since the fluorine-based resin constituting the gap holding member is excellent in releasability, it is difficult for toner or the like to adhere to the gap holding member. In addition, since an insulating fluororesin is used, no discharge is generated at the gap holding portion, so that the amount of discharge products adhering to the image carrier at this position can be reduced, and the image carrier is cleaned by increasing the friction coefficient. Involvement of the blade is unlikely to occur.
[0057]
  Claim7,8In the described image forming apparatus,A charging device according to any one of claims 1 to 6, comprising:By forming a gap between the image carrier and the charging member, the charging member is hardly contaminated with toner or the like. Further, by setting the maximum value of the gap to 100 μm or less, abnormal discharge hardly occurs and uniform charging can be obtained. Furthermore, by superimposing an alternating voltage having a peak-to-peak voltage more than twice the discharge start voltage of the image carrier and the charging member on the charging bias, the charging potential is uniform when the gap changes, and the stability against environmental fluctuations Improves.
  Claims9In the described image forming apparatus,In addition to the configuration and effect of claim 7 or 8,By adopting a unit configuration in which the image carrier and charging device can be integrated and removed from the image forming apparatus body, adjustment is not required even when a high-accuracy gap is required, and the user can easily replace it. It becomes.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of an image forming apparatus showing an embodiment of the present invention.
2 is a schematic cross-sectional view illustrating a configuration example of a photoreceptor unit of the image forming apparatus illustrated in FIG.
FIG. 3 is a schematic cross-sectional view showing a main part of a conventional configuration example of a charging roller.
FIG. 4 is a schematic cross-sectional view of an essential part showing a configuration example of a charging roller according to the present invention.
FIG. 5 is a schematic cross-sectional view of an essential part showing another configuration example of a charging roller according to the present invention.
FIG. 6 is a schematic cross-sectional view of an essential part showing still another configuration example of the charging roller according to the present invention.
[Explanation of symbols]
1: Image forming apparatus main body
2A to 2D: Photosensitive unit
3: Transfer belt
5: Photoconductor (image carrier)
6: Writing unit
9: Fixing device
10A to 10D: developing device
14: Charging roller (charging device)
15: Brush roller
47: Cleaning blade
49: Cleaning roller
101: Metal core
102: Resin layer (charging member)
102a: Charging member end
102b: Stepped portion
102b-1: First step portion
102b-2: second stepped portion
103: Gap holding member

Claims (9)

Charging having a charging member for charging the image carrier, provided with a step at both ends of the charging member, and a gap holding member for forming a gap with the image carrier at the step. In the device
The step for attaching the gap holding member includes a first step portion and a second step portion having an outer diameter smaller than that of the first step portion, and the first step portion is charged from the second step portion. The axial width of the first stepped portion is wider than the axial width of the second stepped portion, and the gap holding member has a tube shape having heat shrinkability. Ah is, the cap holding member, a charging device, characterized in that covering both said second stepped portion and the first step portion. The charging device according to claim 1.
A charging device , wherein a portion of the gap holding member covering the first step portion is brought into contact with the surface of the image carrier . The charging device according to claim 1 or 2,
The charging device according to claim 1, wherein a portion of the gap holding member covering the second step portion enters and is fixed to the second step portion so as not to contact the image carrier . The charging device according to any one of claims 1 to 3,
The charging device , wherein the gap holding member also covers a side surface of an end portion of the charging member . The charging device according to any one of claims 1 to 4 ,
The charging device according to claim 1, wherein an outer diameter of an end of the first step portion is smaller than an outer diameter of a portion other than the end . In the charging device according to any one of claims 1 to 5 ,
The charging device, wherein the charging member is made of a resin material containing an ionic conductive material, and the gap holding member is made of an insulating resin material containing fluorine . After charging the image carrier, the image carrier is exposed to light to form a latent image, the latent image is developed with a developer to be visualized, and the developed image is transferred to a transfer material and fixed. In an image forming apparatus for forming an image by
An image forming apparatus comprising the charging device according to claim 1 as means for charging the image carrier . The image forming apparatus according to claim 7.
  A gap is formed between the image carrier in the image forming region and the charging member by bringing a gap holding member attached to the charging member of the charging device into contact with the image carrier, and the image carrier in the image forming region. And the charging member has a gap of 100 μm or less, and a charging bias in which an alternating voltage having a peak-to-peak voltage more than twice the discharge start voltage between the charging member and the image carrier is applied to the charging device. An image forming apparatus. The image forming apparatus according to claim 7 or 8, wherein
  An image forming apparatus, wherein at least the image carrier and the charging device are configured to be detachable integrally with the image forming apparatus main body.

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