JP2012173406A - Image forming apparatus and method of charging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that suppresses unstable discharge and improves uniformity of charging, and a method of charging.SOLUTION: An image forming apparatus 10 includes a photoreceptor drum 62 that has an electrically-chargeable film formed on the surface thereof and holds an image, and a charger 66 that charges the surface of the film of the photoreceptor drum 62. The charger 66 includes a plurality of charging units having different surface roughness Ra, which is defined by JIS B 0601, for applying a DC voltage to the photoreceptor drum 62, and the charging units having smaller surface roughness Ra are configured to apply a DC voltage as the film thickness of the photoreceptor drum 62 is reduced.

Description

  The present invention relates to an image forming apparatus and a charging method.

  Japanese Patent Application Laid-Open No. H10-228667 discloses a surface layer in a charging roller having a cored bar, a conductive elastic layer formed on the outer peripheral surface of the cored bar, and a surface layer formed on the conductive elastic layer. The average film thickness is 150 nm or more and 600 nm or less, and the minimum film thickness and the maximum film thickness of the surface layer are -50 nm or more and +100 nm or less with respect to the average film thickness of the surface layer, respectively. Furthermore, a charging roller whose outer peripheral surface roughness of the surface layer is 1.5 μm or more and 8 μm or less in terms of an average roughness of 10 areas measured by a scanning white interferometer and a manufacturing method thereof are disclosed.

  Japanese Patent Application Laid-Open No. H10-228707 discloses a surface layer of a charging roller having a cored bar, a conductive elastic layer formed on the outer peripheral surface of the cored bar, and a surface layer formed on the conductive elastic layer. The average film thickness of the surface layer is not less than 8 nm and not more than 100 nm, and the minimum and maximum film thicknesses of the surface layer are 70% or more and 130% or less, respectively, with respect to the average film thickness of the surface layer. Disclosed is a charging roller in which the outer peripheral surface roughness of the surface layer is 1.5 μm or more and 8 μm or less in terms of the 10-point average roughness measured by a scanning white interferometer, and a manufacturing method thereof.

JP 2007-225995 A JP 2008-299118 A

  An object of the present invention is to provide a charging device, an image forming apparatus, and a charging method capable of improving the uniformity of charging while suppressing unstable discharge.

  According to a first aspect of the present invention, there is provided an image holding member for holding an image on which a chargeable film is formed, and charging means for charging the film surface of the image holding member. A plurality of charged portions having different surface roughness Ra specified in JIS B 0601 for applying a DC voltage between the image carrier and the surface roughness as the film thickness of the image carrier decreases. The image forming apparatus is set to be applied by a charging unit having a small thickness Ra.

  The present invention according to claim 2 is the charging device according to claim 1, wherein the charging means is formed in a film shape.

  The present invention according to claim 3 is the charging device according to claim 1, wherein the charging means is formed in a cylindrical cross section.

  In the present invention according to claim 4, a chargeable film is formed on the surface, and the film thickness of an image holding body for holding an image is measured. As the film thickness of the image holding body becomes thinner, JIS B 0601 In this charging method, a charging portion having a specified surface roughness Ra is set so that a DC voltage is applied between the charging portion and the image carrier, and the film surface of the image carrier is charged.

  According to the first aspect of the present invention, it is possible to improve the uniformity of charging while suppressing unstable discharge.

  According to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, the configuration can be simplified as compared with the case where the present configuration is not provided.

  According to the third aspect of the present invention, in addition to the effect of the first aspect of the present invention, the image carrier can be stably charged as compared with the case without this configuration.

  According to the fourth aspect of the present invention, it is possible to improve the uniformity of charging while suppressing unstable discharge.

1 is a cross-sectional view from the side of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic view of an image forming unit and its peripheral structure according to an embodiment of the present invention. It is an example of the schematic diagram of the cross section of the photoreceptor drum which concerns on embodiment of this invention. It is the schematic of the charger which concerns on embodiment of this invention, and its periphery structure. It is a measurement result about the relationship between the surface roughness of the charging unit, the film thickness of the photosensitive drum, and the image defect. It is a measurement result about the relationship between the surface roughness of the charging unit, the film thickness of the photosensitive drum, and the fog. It is the schematic of the charger concerning 2nd embodiment, and its periphery structure. It is the schematic of the charger concerning 3rd embodiment, and its peripheral structure.

[First embodiment]
Embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view from the side of an image forming apparatus 10 as an embodiment of the present invention.

  The image forming apparatus 10 includes an image forming apparatus main body 12, and the upper part of the image forming apparatus main body 12 is used as a discharge unit 14 from which a recording medium on which an image is formed is discharged.

  The image forming apparatus main body 12 is provided with a mounting opening / closing section (not shown) and a paper feeding opening / closing section 24 that can be freely opened and closed with respect to the image forming apparatus main body 12.

  The mounting opening / closing portion is used when mounting the storage containers 30Y, 30M, 30C, and 30K used as the image forming agent storage container in the image forming apparatus main body 12, or when mounting the storage containers 30Y, 30M, 30C, and 30K to the image forming apparatus. Opened when removed from the body 12. The mounting opening / closing unit is closed when image formation is performed.

  The paper feed opening / closing unit 24 is opened when the recording medium is supplied from the front side of the image forming apparatus main body 12.

The storage containers 30Y, 30M, 30C, and 30K store yellow (Y), magenta (M), cyan (C), and black (K) toners used as image forming agents, respectively.
The storage containers 30Y, 30M, and 30C are similarly configured in shape and size, and store toner of substantially the same volume.
The storage container 30K is configured to be vertically longer than the storage containers 30Y, 30M, and 30C, has a larger volume than the storage containers 30Y, 30M, and 30C, and has a larger volume of toner that is stored than the storage containers 30Y, 30M, and 30C. It is supposed to be.

  Although the storage containers 30Y, 30M, and 30C and the storage container 30K have different volumes of toner that can be stored, they have the same members and functions.

In the image forming apparatus main body 12, an image forming unit 40, a recording medium supply device 42 that supplies a recording medium to the image forming unit 40, and a conveyance path 44 that is used for conveying the recording medium are provided.
The image forming unit 40, the recording medium supply device 42, and the conveyance path 44 constitute an image forming unit that forms an image on a recording medium.

The image forming unit 40 includes, for example, four image forming units 52Y, 52M, 52C, and 52K, a latent image forming device 54, and a transfer device 56. The image forming units 52Y, 52M, 52C, and 52K form developer images using Y, M, C, and K toners, respectively.
The image forming units 52Y, 52M, 52C, and 52K have the same configuration although the corresponding colors are different. Therefore, hereinafter, Y, M, C, and K corresponding to each color are omitted, and the “image forming unit 52” will be described. And may be generically named. The same applies to other configurations corresponding to the respective colors (such as the container 30 and the photosensitive drum 62).

  Each of the image forming units 52 includes a photosensitive drum 62 used as an image carrier, a cleaning device 64 that cleans the surface of the photosensitive drum 62, a charger 66 that charges the photosensitive drum 62, and a latent image forming device. And a developing device 68 that develops the electrostatic latent image formed on the surface of the photosensitive drum 62 by toner with toner to form a toner image.

  Each developing device 68 is supplied with the corresponding color toner from the container 30.

  The transfer device 56 includes a belt-shaped intermediate transfer body 72 used as a transfer medium, primary transfer rolls 74Y, 74M, 74C, and 74K used as a primary transfer device, and secondary transfer rolls used as a secondary transfer device. 76 and a cleaning device 78 for cleaning the surface of the intermediate transfer member 72.

  The intermediate transfer member 72 is transferred such that the toner images formed on the respective photosensitive drums 62 are superimposed. The intermediate transfer body 72 is rotatably supported by, for example, four support rolls 82a, 82b, 82c, and 82d used as support members.

  The primary transfer rolls 74Y, 74M, 74C, and 74K transfer toner images corresponding to the respective colors formed on the photosensitive drums 62Y, 62M, 62C, and 62K to the intermediate transfer body 72, respectively.

  The secondary transfer roll 76 transfers each color toner image transferred to the intermediate transfer body 72 to a recording medium.

  The recording medium supply device 42 includes, for example, a recording medium storage container 92 that stores recording media in a stacked state, an extraction roll 94 that extracts the uppermost recording medium stored in the recording medium storage container 92, and the extraction roll A conveyance roll 96 that conveys the recording medium extracted in 94 toward the image forming unit 40; and a separation roll 98 that contacts the conveyance roll 96 and separates the recording medium from the conveyance roll 96.

  The recording medium storage container 92 can be pulled out, for example, to the front side (left side in FIG. 1) of the image forming apparatus main body 12, and the recording medium is replenished while being pulled out from the image forming apparatus main body 12.

  The conveyance path 44 includes a main conveyance path 100, a reverse conveyance path 102, and an auxiliary conveyance path 104.

  The main conveyance path 100 is a conveyance path that conveys the recording medium supplied from the recording medium supply device 42 toward the discharge unit 14. In the main conveyance path 100, a registration roll 112, a secondary transfer roll 76, a fixing device 114, and a discharge roll 116 are arranged in order from the upstream side in the conveyance direction of the recording medium.

  The registration roll 112 starts to rotate at a predetermined timing from the stopped state, and the recording medium is transferred to the intermediate transfer body 72 and the secondary transfer roll 76 so as to coincide with the timing at which the toner image is transferred to the intermediate transfer body 72. To the contact portion (nip portion).

  The fixing device 114 fixes the toner image on the recording medium onto which the toner image has been transferred by the transfer device 56.

  The discharge roll 116 discharges the recording medium on which the toner image is fixed by the fixing device 114 to the discharge unit 14. Further, when forming images on both sides of the recording medium, the discharge roll 116 rotates in a direction opposite to that when the recording medium is discharged to the discharge unit 14, and removes the recording medium on which the image is formed on one side. It conveys to the reverse conveyance path 102 from the end side.

  The reverse conveyance path 102 is a conveyance path that reverses the recording medium on which an image is formed on one surface and conveys the recording medium toward the upstream side of the registration roll 112 again. In the reverse conveyance path 102, for example, two reverse conveyance rolls 118a and 118b are arranged.

  The auxiliary conveyance path 104 is used when a recording medium is supplied from the front side of the image forming apparatus main body 12 in a state where the paper feeding opening / closing section 24 is opened with respect to the image forming apparatus main body 12. In the auxiliary conveyance path 104, an auxiliary conveyance roll 120 that conveys the recording medium toward the registration roll 112 and a separation roll 122 that contacts the auxiliary conveyance roll 120 and separates the recording medium are arranged.

In the image forming apparatus main body 12, a film thickness measuring unit 130 that measures the film thickness (film thickness reduction) of the photosensitive drum 62 is provided.
Regarding the measurement of the film thickness of the photosensitive drum 62, the film thickness measuring unit 130 measures, for example, the number of printed recording media (hereinafter referred to as “number of printed sheets”), the measurement of the rotational speed of the photosensitive drum 62, and the input. The pixel count (pixel count) of the printed image, the rotation number of the toner conveying member (auger) of the developing device 66, the amount of toner used, or a combination thereof are measured. May be.

The image forming apparatus main body 12 includes a movement control unit 140 that drives (moves) the charger 66 and controls a portion where the charger 66 and the photosensitive drum 62 are in contact with each other.
The movement control unit 140 is notified of the measurement result measured by the film thickness measurement unit 130, and the movement control unit 140 controls the charger 66 based on the measurement result of the film thickness measurement unit 130. It is designed to move.

Next, details of the image forming unit 52 will be described.
FIG. 2 shows a schematic diagram of the image forming unit 52 and its peripheral structure.

  Around the photosensitive drum 62, a cleaning device 64, a charger 66, a developing device 68, and a primary transfer roll 74 are arranged via an intermediate transfer body 72.

  The cleaning device 64 includes a cleaning blade 200 that removes toner, paper dust, and the like remaining on the surface of the photosensitive drum 62, a collection container 202 that collects toner and the like removed by the cleaning blade 200, and a collection container 202 that collects the toner and the like. And a leakage prevention member 204 for preventing leakage of toner and the like.

The charger 66 is provided along the rotation direction of the photosensitive drum 62 (hereinafter, simply referred to as “rotation direction”).
A side closer to the developing device 68 with respect to the rotation direction is defined as a downstream side in the rotation direction.

In the present embodiment, the charger 66 is provided downstream of the cleaning device 64 in the rotation direction. The charging device 66 is a charging film (charging film) formed in a film shape (film shape), and is in contact with the photosensitive drum 62 to charge the photosensitive drum 62.
The charger 66 may be close to the photosensitive drum 62 to such an extent that discharge occurs.

The charger 66 is provided with an application unit 210 that applies a voltage to the charger 66.
In the present embodiment, the application unit 210 applies a DC voltage to the charger 66 (DC charging method).
Note that the application unit 210 may apply a method in which an AC voltage is superimposed on a DC voltage (AC + DC charging method).

Next, details of the photosensitive drum 62 will be described.
FIG. 3 shows an example of a schematic diagram of a cross section of the photosensitive drum 62.

  In the photosensitive drum 62, an undercoat layer 172 is provided on a conductive substrate 170, and a charge generation layer 174, a charge transport layer 176, and a protective layer 178 are formed on the undercoat layer 172. Is provided.

Examples of the material of the conductive substrate 170 include, for example, a metal plate, a metal drum, and a metal plate formed using a metal or an alloy such as aluminum, copper, zinc, stainless steel, chromium, nickel, molybdenum, vanadium, indium, gold, and platinum. In addition, a metal belt, or a paper, a plastic film, a belt, or the like on which a conductive compound such as a conductive polymer or indium oxide, a metal or an alloy such as aluminum, palladium, or gold is applied, vapor-deposited, or laminated is used.
Here, the conductivity means that the volume resistivity is less than 10 ¹³ Ωcm.

When the photosensitive drum 62 is used in a laser printer, the surface of the conductive substrate 170 has a centerline average roughness (Ra ₇₅ ) of 0.04 in order to prevent interference fringes generated when laser light is irradiated. Not less than μm and not more than 0.5 μm.
When the center line average roughness (Ra ₇₅ ) is less than 0.04 μm, the interference prevention effect tends to be insufficient, and when it exceeds 0.5 μm, the image quality tends to be coarse.

As a method for adjusting the surface roughness, liquid honing is performed by suspending an abrasive in water and spraying it on the support, centerless grinding in which the support is pressed against a rotating grindstone, and grinding is continuously performed. An oxidation treatment or the like is used.
Further, a method is used in which conductive or semiconductive powder is dispersed in a resin, a layer is formed on the surface of the support, and the surface is roughened by particles dispersed in the layer.

The undercoat layer 172 is a layer that imparts leak resistance and carrier blocking properties.
For example, the undercoat layer 172 is configured to contain inorganic particles in the binder resin.

  Examples of the binder resin used for the undercoat layer 172 include acetal resins such as polyvinyl butyral, polyvinyl alcohol resin, casein, polyamide resin, cellulose resin, gelatin, polyurethane resin, polyester resin, methacrylic resin, acrylic resin, Polymer resin compounds such as vinyl chloride resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic anhydride resin, silicone resin, silicone-alkyd resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, or charge Examples thereof include a charge transporting resin having a transporting group and a conductive resin such as polyaniline.

Various additives may be used in the undercoat layer 172 to improve electrical characteristics, environmental stability, and image quality.
As the additive, polycyclic condensation type, azo type electron transporting pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, silane coupling agents and the like are used.

As the inorganic particles, for example, powder resistance (volume resistivity) of 10 ² Ωcm or more and 10 ¹¹ Ωcm or less is used.
If the volume resistivity is less than 10 ² Ωcm, sufficient leakage resistance cannot be obtained, and if it is higher than 10 ¹¹ Ωcm, a residual potential may be increased.
As the inorganic particles, for example, inorganic particles (conductive metal oxide) such as tin oxide, titanium oxide, zinc oxide, and zirconium oxide are used.

  In addition, the inorganic particles may be subjected to a surface treatment, or may be used as a mixture of two or more kinds such as those having different surface treatments or particles having different particle diameters. The volume average particle diameter of the inorganic particles is, for example, in the range of 50 nm to 2000 nm.

As the inorganic particles, for example, those having a specific surface area of 10 m ² / g or more by BET method are used. If the specific surface area value is less than 10 m ² / g, the chargeability tends to be lowered, and it tends to be difficult to obtain good electrophotographic characteristics.

  For example, the undercoat layer 172 has a Vickers hardness of 35 or more.

The undercoat layer 172 is, for example, 15 μm or more and 50 μm or less.
When the thickness of the undercoat layer 172 is less than 15 μm, sufficient leakage resistance cannot be obtained, and when it is 50 μm or more, residual potential tends to remain when used for a long period of time, resulting in an image density abnormality. There is a case.

  The charge generation layer 174 is a layer containing a charge generation material and a binder resin.

Examples of the charge generating material include azo pigments such as bisazo and trisazo, fused aromatic pigments such as dibromoanthanthrone, perylene pigments, pyrrolopyrrole pigments, phthalocyanine pigments, zinc oxide, and trigonal selenium.
As the charge generation material, for example, an inorganic pigment is desirable when the exposure wavelength of the light source is 380 nm or more and 500 nm or less, and a metal or metal-free phthalocyanine pigment is used when the exposure wavelength is 700 nm or more and 800 nm or less.

Examples of the binder resin used for the charge generation layer 174 include an insulating resin or an organic photoconductive polymer such as poly-N-vinylcarbazole, polyvinyl anthracene, polyvinyl pyrene, and polysilane.
Specifically, the binder resin includes polyvinyl butyral resin, polyarylate resin (polycondensate of bisphenols and aromatic divalent carboxylic acid, etc.), polycarbonate resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate. A polymer, polyamide resin, acrylic resin, polyacrylamide resin, polyvinyl pyridine resin, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol resin, polyvinyl pyrrolidone resin, and the like are used.
These binder resins are used singly or in combination of two or more. The mixing ratio of the charge generation material and the binder resin is, for example, in the range of 10: 1 to 1:10 by mass ratio.
Here, “insulating” means that the volume resistivity is 10 ¹³ Ωcm or more.

  The film thickness of the charge generation layer 174 is, for example, not less than 0.1 μm and not more than 5.0 μm.

  The charge generation layer 174 is formed using a coating liquid in which the charge generation material and the binder resin are dispersed in a solvent.

  Solvents used for dispersion include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, and methylene chloride. , Chloroform, chlorobenzene, toluene and the like, and these are used singly or in combination of two or more.

  As a method for dispersing the charge generating material and the binder resin in the solvent, a ball mill dispersion method, an attritor dispersion method, a sand mill dispersion method, or the like is used. By these dispersion methods, changes in the crystal form of the charge generation material due to dispersion are prevented.

  Further, when the charge generation layer 174 is formed, a blade coating method, a Mayer bar coating method, a spray coating method, a dip coating method, a bead coating method, an air knife coating method, a curtain coating method, or the like is used.

  The charge transport layer 176 is formed containing a charge transport material and a binder resin, or containing a polymer charge transport material.

Charge transport materials include quinone compounds such as p-benzoquinone, chloranil, bromanyl, anthraquinone, tetracyanoquinodimethane compounds, fluorenone compounds such as 2,4,7-trinitrofluorenone, xanthone compounds, benzophenone compounds , Electron transport compounds such as cyanovinyl compounds and ethylene compounds, triarylamine compounds, benzidine compounds, arylalkane compounds, aryl-substituted ethylene compounds, stilbene compounds, anthracene compounds, hydrazone compounds, etc. A hole transporting compound is used.
These charge transport materials may be used singly or in combination of two or more, but are not limited thereto.

The binder resin used for the charge transport layer 176 includes polycarbonate resin, polyester resin, polyarylate resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, styrene-butadiene. Copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicone alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin , Poly-N-vinylcarbazole, polysilane and the like.
These binder resins are used singly or in combination of two or more.
The blending ratio of the charge transport material and the binder resin is, for example, 10: 1 to 1: 5 by mass ratio.

  As the polymer charge transport material, poly-N-vinylcarbazole, polysilane, or the like is used. The polymer charge transport material may be formed alone or mixed with a binder resin to form a film.

  The film thickness of the charge transport layer 176 is, for example, 5 μm or more and 50 μm or less.

The charge transport layer 176 is formed using a charge transport layer forming coating solution containing the above-described constituent materials.
Solvents used in the coating solution for forming the charge transport layer include aromatic hydrocarbons such as benzene, toluene, xylene and chlorobenzene, ketones such as acetone and 2-butanone, and halogenation such as methylene chloride, chloroform and ethylene chloride. Organic solvents such as aliphatic hydrocarbons, cyclic ethers such as tetrahydrofuran and ethyl ether, or straight-chain ethers may be used alone or in admixture of two or more.

  Examples of the coating method for applying the charge transport layer forming coating solution on the charge generation layer 174 include a blade coating method, a Mayer bar coating method, a spray coating method, a dip coating method, a bead coating method, an air knife coating method, A curtain coating method or the like is used.

The protective layer 178 is the outermost surface layer of the photosensitive drum 62, and is a layer provided to give resistance to abrasion, scratches, etc. on the outermost surface and to increase toner transfer efficiency.
As the protective layer 178, conductive particles dispersed in a binder resin, lubricant particles such as fluororesin and acrylic resin dispersed in a normal charge transport layer material, a hard coating agent such as silicone or acrylic, or In view of strength, electrical characteristics, image quality maintenance, etc., those having a crosslinked structure, those containing a charge transporting material that is easily oxidized, and the like are used.
As what forms a crosslinked structure, a phenol resin, a urethane resin, a siloxane resin etc. are used, for example.

  Thus, the photosensitive drum 62 has a structure in which a chargeable film is formed on the surface.

The photosensitive drum 62 is not limited to the above configuration, and an undercoat layer 172 is provided on the conductive substrate 170, and a charge transport layer 176, a charge generation layer 174, and a protective layer 178 are sequentially formed on the undercoat layer 172. An exposed photosensitive layer may be provided.
Further, the charge generation material and the charge transport material may be formed as the same layer (single layer type photosensitive layer).
Note that the undercoat layer 172 may not be provided.

Next, details of the charger 66 will be described.
FIG. 4 shows a schematic diagram of the charger 66 and its peripheral structure.

The charger 66 includes a film-like base material 216, and a contact portion 218 that is formed (coated) on one surface of the base material 216 and contacts the photosensitive drum 62.
The charger 66 is provided with a moving unit 220 that moves the charger 66, and the moving unit 220 is controlled by the movement control unit 140.

The base material 216 is made of, for example, a plastic film that has been subjected to a conductive treatment. As a material of the base material 216, polyester, polyethylene, polypropylene, polycarbonate, polyimide, cellulose, nylon, or the like is used.
For example, the substrate 216 is configured to have a surface resistivity of about 10 ⁰ Ω / □ or more and 10 ⁶ Ω / □ or less when a current is passed in the lateral direction.

As a method of conducting a conductive treatment on a plastic film, a method of dispersing a conductive material in a plastic film, a method of applying a conductive paint containing a conductive material to a plastic film, a method of depositing metal on a plastic film, etc. Is used.
Examples of the metal used for vapor deposition include aluminum, gold, copper, titanium, silver, brass, and chromium.
In addition, you may make it comprise the base material 216 with thin plates, such as aluminum, stainless steel, and nickel.

The contact portion 218 is formed so that the surface roughness varies depending on the portion.
Specifically, in this embodiment, the contact part 218 includes a first contact part 218a used as a first charging part, a second contact part 218b used as a second charging part, and a third charging part. And a third contact portion 218c used as a portion.
The surface roughness decreases in the order of the first contact portion 218a, the second contact portion 218b, and the third contact portion 218c.

  Here, the surface roughness is indicated by an arithmetic average roughness (Ra), a ten-point average roughness (Rzjis), a maximum height roughness (Rz) or the like defined by JIS B 0601-2001.

The contact part 218 is composed of, for example, an elastic material and a conductive agent. The resistance of the contact portion 218 is adjusted by the conductive agent.
Further, the contact portion 218 contains an additive as necessary.

  Examples of the elastic material for the contact portion 218 include rubber materials such as polyurethane rubber, epichlorohydrin rubber, chlorosulfonated polyethylene, fluorine rubber, vinyl nitrile rubber, and styrene-butadiene rubber, or polycarbonate, acrylic resin, polyamide, and polyimide. Polystyrene, silicone resin, polyvinyl butyral, polyester, phenol resin, melamine resin and the like are used.

  As the conductive agent, an electronic conductive agent or an ionic conductive agent is used.

  Examples of the electronic conductive agent include carbon black such as ketjen black and acetylene black, pyrolytic carbon, graphite, or conductive metals or alloys such as aluminum, copper, nickel, and stainless steel, or tin oxide and indium oxide. In addition, conductive metal oxides such as titanium oxide, tin oxide-antimony oxide solid solution, tin oxide-indium oxide solid solution, or the like, which are obtained by conducting the surface of an insulating substance, are used.

Examples of the ionic conductive agent include perchloric oxygen salts or chlorates such as tetraethylammonium and lauryltrimethylammonium, or perchloric oxygen salts or chlorates of alkali metals such as lithium and magnesium, or alkaline earth. These include perchloric oxygen salts or chlorates of similar metals.
A conductive agent may be used independently and may be used in combination of 2 or more type.

  Examples of additives that can be used include softeners, plasticizers, curing agents, vulcanizing agents, vulcanization accelerators, antioxidants, surfactants, coupling agents, fillers (silica, calcium carbonate), and the like.

  As a method for adjusting the surface roughness, a method of adding roughness-imparting particles for imparting a predetermined surface roughness, a polishing method for polishing the surface, or the like is used.

As the roughness-imparting particles, conductive particles or non-conductive particles are used.
Here, “conductive” indicates that the volume resistivity is less than 10 ¹³ Ωcm, and “non-conductive” indicates that the volume resistivity is 10 ¹³ Ωcm or more.

  As the conductive particles, the above-described electronic conductive agents, ionic conductive agents, and the like are used.

  Non-conductive particles include resin particles (polyimide resin particles, methacrylic resin particles, polystyrene resin particles, fluorine resin particles, silicone resin particles, etc.), inorganic particles (clay particles, kaolin particles, talc particles, silica particles, alumina particles, etc.) ), And ceramic particles.

  As a method for polishing the surface, buffing, sandblasting, liquid honing or the like is used.

As described above, the movement control unit 140 is notified of the measurement result from the film thickness measurement unit 130. In this way, the movement control unit 140 controls the photosensitive drum 62 to be charged by the contact portion 218 having a surface roughness corresponding to the measurement result (film thickness) based on the measurement result of the film thickness measurement unit 130. To do.
The movement control unit 140 and the moving unit 220 constitute a surface roughness setting unit that sets the surface roughness of a charging unit (contact unit that contacts the photosensitive drum 62) applied to the photosensitive drum 62.

Based on the measurement result of the film thickness measurement unit 130, the movement control unit 140 controls the movement unit 220 so that any one of the first to third contact units 218 a to 218 c is brought into contact with the photosensitive drum 62.
Hereinafter, the contact portion 218 (contact portion that generates electric discharge) that contacts the photosensitive drum 62 and charges the photosensitive drum 62 may be referred to as a “discharge contact portion”.

  In this embodiment, as the film thickness of the photosensitive drum 62 becomes thinner, the surface roughness of the charging portion (surface roughness of the discharging portion) that applies a voltage to the photosensitive drum 62 is set to be smaller. ing.

A member that guides the movement of the charger 66 and a contact portion other than the discharge contact portion (for example, when the discharge contact portion is the first contact portion 218a, the second contact portion 218b and the third contact portion 218c). ) And the photosensitive drum 62 may be provided with a member covering a contact portion other than the discharge contact portion.
Further, the charger 66 may be moved so as to be wound around the moving unit 220.

Next, discharge characteristics will be described using the photosensitive drum 62 and the charger 66.
If the charging of the photosensitive drum 62 by the charger 66 is defective (charging failure), the quality of the formed image is deteriorated. Here, “charging failure” includes phenomena such as unstable discharge and uneven charging.

If the discharge is unstable, a defect (image defect: for example, a horizontal stripe defect) occurs in image formation.
Unstable discharge is more likely to occur as the film thickness of the photosensitive drum 62 is larger, and is more likely to occur as the surface roughness of the charger 66 is smaller.

  Therefore, for example, when the surface roughness of the charger 66 is relatively small, even if an image defect occurs if the film thickness of the photosensitive drum 62 is relatively large, an image is generated if the film thickness of the photosensitive drum 62 is relatively small. Sometimes there are no defects.

FIG. 5 shows the measurement results regarding the relationship between the surface roughness of the discharge contact portion of the charger 66, the film thickness of the photosensitive drum 62, and image defects.
“Image defect level” in FIG. 5 indicates that the greater the value, the greater the degree of image defect. If the level value is “2” or less, no image defect occurs (no problem in image formation). Means.

  As shown in FIG. 5, the image defect level decreases as the surface roughness (Ra) of the discharge contact portion of the charger 66 increases.

Further, when the surface roughness (Ra) of the discharge contact portion is relatively small, 0.5 μm, an image defect occurs when the film thickness of the photosensitive drum 62 is relatively large, 25 μm (the image defect level is “5”). On the other hand, when the film thickness of the photosensitive drum 62 is 15 μm, which is relatively small, no image defect occurs (the image defect level is a small value “1”).
Thus, even when the surface roughness (Ra) of the discharge contact portion is relatively small, image defects are suppressed when the film thickness of the photosensitive drum 62 is relatively small.

On the other hand, if the charge is not uniform, “fogging” occurs. “Fog” is a phenomenon in which toner is transferred to a non-image forming portion and image quality is lowered.
The fog is more likely to occur as the film thickness of the photosensitive drum 62 is smaller, and the fog is more likely to occur as the surface roughness of the discharge contact portion is larger.

  For this reason, for example, when the surface roughness of the discharge contact portion is relatively large, fogging does not occur if the film thickness of the photosensitive drum 62 is relatively large, but fogging occurs if the film thickness of the photosensitive drum 62 is relatively small. Sometimes occurs.

FIG. 6 shows the measurement results regarding the relationship between the surface roughness of the discharge contact portion of the charger 66, the film thickness of the photosensitive drum 62, and the fog.
In FIG. 6, “fogging level” indicates that the greater the numerical value, the greater the degree of fogging. If the level value is “2” or less, it means that there is no fogging (no problem in image quality). .

  As shown in FIG. 6, the fogging level increases as the surface roughness (Ra) of the discharge contact portion increases.

Further, when the surface roughness (Ra) of the discharge contact portion is relatively large, 2.5 μm, fogging does not occur when the film thickness of the photosensitive drum 62 is relatively large (25 μm) (the image defect level is “1”). On the other hand, when the film thickness of the photosensitive drum 62 is 15 μm, which is relatively small, fogging occurs (the image defect level is a large value of “5”).
Thus, even when the surface roughness (Ra) of the discharge contact portion is relatively large, the fogging is suppressed when the film thickness of the photosensitive drum 62 is relatively large.

  However, the film thickness of the photosensitive drum 62 decreases (the film decreases) as the amount of image formation increases (the number of printed sheets increases). For this reason, the appropriate surface roughness (where image defects and fog do not occur) change depending on the usage state of the photosensitive drum 62.

  Next, an experimental result when charging is performed by changing the surface roughness will be described.

  Table 1 shows the occurrence of image defects and fog when the photosensitive drum 62 is rotated up to a predetermined number of times (image formation is continued up to a predetermined number of printed sheets) and image formation is performed according to Example 1 and Comparative Examples 1 to 3. Indicates presence or absence.

In Example 1, the surface roughness (Ra) of each of the first contact portion 218a, the second contact portion 218b, and the third contact portion 218c is 2.5 μm, 1.5 μm, and 0.5 μm, and the photosensitive drum 62 is used. The surface roughness of the charging portion applied to the photosensitive drum 62 was changed in accordance with the film thickness.
Specifically, as the film thickness of the photosensitive drum 62 becomes thinner (the amount of image formation increases), the surface roughness of the contact portion 218 brought into contact with the photosensitive drum 62 becomes smaller ( It was set so that the surface roughness of the discharge contact portion was reduced.

In Comparative Examples 1 to 3, charging was performed with the surface roughness of the discharge contact portion constant regardless of the film thickness of the photosensitive drum 62.
In Comparative Example 1, the surface roughness (Ra) of the discharge contact portion was kept constant at 2.5 μm.
In Comparative Example 2, the surface roughness (Ra) of the discharge contact portion was constant at 1.5 μm.
In Comparative Example 3, the surface roughness (Ra) of the discharge contact portion was constant at 0.5 μm.

As shown in Table 1, in Example 1, even when the film thickness of the photosensitive drum 62 decreased, the occurrence of image defects and fogging was not confirmed (indicated by “◯” in Table 1).
In contrast, in Comparative Example 1, the occurrence of fogging was confirmed as the film thickness of the photosensitive drum 62 decreased (indicated by “x”).
In Comparative Example 2, image defects were confirmed when the film thickness of the photosensitive drum 62 was relatively large (22 μm or more), and fogging was confirmed when the film thickness was relatively small (less than 17 μm).
In Comparative Example 3, image defects were confirmed when the film thickness of the photosensitive drum 62 was relatively large (17 μm or more).

  Thus, by adopting a configuration in which the surface roughness (Ra) of the discharge contact portion is changed according to the film thickness of the photosensitive drum 62, charging failure (non-existence) is less than in the case without this configuration. Stable discharge and non-uniform charging) are suppressed.

[Second Embodiment]
Next, a second embodiment will be described.
The first embodiment uses a film-like charger 66, whereas the second embodiment differs in that a charger 226 having a cylindrical cross section (roll shape) is used.
FIG. 7 shows a schematic diagram of the charger 226 and its peripheral structure according to the second embodiment.

The charger 226 is formed as a roll, and is configured as a charging roll that is charged in contact with (or close to) the photosensitive drum 62. The charger 226 is provided as a fixed type that does not follow the rotation of the photosensitive drum 62.
The charger 226 is provided with a moving unit 228 that rotates and moves the charger 226, and the moving unit 228 is controlled by the movement control unit 140.

The charger 226 includes a cored bar (shaft) 230, an elastic layer 232 disposed on the outer peripheral surface of the cored bar 230, and a contact portion 234 disposed on the outer peripheral surface of the elastic layer 232. The
The charger 226 is not limited to the above configuration, and an adhesive layer (primer layer) is provided between the core metal 230 and the elastic layer 232, and a resistance adjusting layer or a prevention layer is provided between the elastic layer 232 and the contact portion 234. A protective layer (coating layer) may be provided outside the contact portion 234.

  The moving unit 228 is fixed to the cored bar 230, and the cored bar 230 is rotated by the moving unit 228 so that the charger 226 is rotated.

The core metal 230 is formed in a rod shape by a conductive member. The core metal 230 may be a hollow (tubular) member or a non-hollow member.
As a material of the core metal 230, for example, a metal such as iron, copper, brass, stainless steel, aluminum, nickel, or a member (for example, resin or ceramic) whose outer peripheral surface is plated is dispersed. A member or the like is used.

  The elastic layer 232 is composed of, for example, an elastic material and a conductive agent. Further, the elastic layer 232 contains an additive as necessary.

Examples of the elastic material of the elastic layer 232 include isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, polyurethane, silicone rubber, fluorine rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, and epichlorohydrin. -Ethylene oxide copolymer rubber, epichlorohydrin-ethylene oxide-allyl glycidyl ether copolymer rubber, ethylene-propylene-diene terpolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber (NBR), natural rubber, and blended rubbers thereof Is used.
The elastic material may be foamed or non-foamed.

  As the conductive agent, the same conductive particles as those described above are used.

The elastic layer 232 has a thickness of, for example, about 1 mm to 10 mm and a volume resistivity of about 10 ³ Ωcm to 10 ¹⁴ Ωcm.

The contact portion 234 is formed so that the surface roughness varies depending on the portion.
Specifically, in the present embodiment, the contact portion 234 includes a first contact portion 234a used as a first charging portion, a second contact portion 234b used as a second charging portion, and a third charging portion. And a third contact portion 234c used as a portion.
The surface roughness decreases in the order of the first contact portion 234a, the second contact portion 234b, and the third contact portion 234c.

  The contact part 234 is comprised with resin, for example. The contact portion 234 includes a conductive agent and an additive as necessary.

  Resins include acrylic resin, cellulose resin, polyamide resin, copolymer nylon, polyurethane resin, polycarbonate resin, polyester resin, polyethylene resin, polyvinyl resin, polyarylate resin, styrene butadiene resin, melamine resin, epoxy resin, urethane resin, silicone A resin, a fluororesin (for example, a tetrafluoroethylene perfluoroalkyl vinyl ether copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a polyvinylidene fluoride, or the like), a urea resin, or the like is used.

The copolymerized nylon includes nylon 610, nylon 11, nylon 12, and one or more of these as polymerized units. Further, this copolymer may contain nylon 6 or nylon 66 as a polymerization unit.
Further, an elastic material used for the elastic layer 232 may be applied as the resin.

In the present embodiment, the movement control unit 140 is configured to control the rotational movement of the charger 226 based on the measurement result of the film thickness measurement unit 130.
Based on the measurement result of the film thickness measurement unit 130, the movement control unit 140 is a portion of the surface roughness corresponding to the measurement result (film thickness) of the contact unit 234 (first to third contact units 234 a-234 c). ) To control the photosensitive drum 62 to be charged.

  Specifically, the movement control unit 140 rotates and moves the charger 226 by the moving unit 228 so that the surface roughness of the discharge contact unit decreases as the film thickness of the photosensitive drum 62 decreases. Control.

  As described above, the surface roughness of the charging portion (surface roughness of the discharge contact portion) for applying a voltage to the photosensitive drum 62 is set to become smaller as the film thickness of the photosensitive drum 62 becomes thinner. Yes.

[Third embodiment]
Next, a third embodiment will be described.
In the first embodiment, a film-like charger 66 is used, whereas in the third embodiment, a cylindrical (belt-like) charger 246 is used.
FIG. 8 is a schematic view of the charger 246 and its peripheral structure according to the second embodiment.

In the third embodiment, the charger 246 is formed as a belt, and is configured as a charging belt that is charged in contact with (or in proximity to) the photosensitive drum 62.
The charger 246 is rotatably supported by the moving unit 250 and the driven unit 252.
The charger 246 is configured to be rotationally moved by the moving unit 250, and the moving unit 250 is controlled by the movement control unit 140.

The contact portion 254 that contacts the photosensitive drum 62 of the charger 246 is formed to have six different surface roughnesses for each portion.
Specifically, in this embodiment, the contact portion 254 includes a first contact portion 254a, a second contact portion 254b having a surface roughness smaller than that of the first contact portion 254a, and the second contact portion. A third contact portion 254c having a surface roughness smaller than that of 254b, a fourth contact portion 254d having a surface roughness smaller than that of the third contact portion 254c, and a surface roughness smaller than that of the fourth contact portion 254d. The fifth contact portion 254e having a small surface roughness and the sixth contact portion 254f having a surface roughness smaller than that of the fifth contact portion 254e.

In the present embodiment, the movement control unit 140 is configured to control the rotational movement of the charger 246 based on the measurement result of the film thickness measurement unit 130.
Based on the measurement result of the film thickness measurement unit 130, the movement control unit 140 is a portion of the surface roughness corresponding to the measurement result (film thickness) of the contact unit 254 (first to sixth contact units 254 a-254 f). ), The photosensitive drum 62 is controlled to be charged.

  Specifically, the movement control unit 140 rotates and moves the charger 246 by the moving unit 250 so that the surface roughness of the discharge contact portion decreases as the film thickness of the photosensitive drum 62 decreases. Control.

  As described above, the surface roughness of the charging portion (surface roughness of the discharge contact portion) for applying a voltage to the photosensitive drum 62 is set to become smaller as the film thickness of the photosensitive drum 62 becomes thinner. Yes.

  In the above-described embodiment, the case where a plurality of charging members having different surface roughness are used as a single unit has been described. However, the present invention is not limited thereto, and a plurality of charging members having different surface roughnesses may be provided separately. .

Moreover, although the structure which the movement control part 140 sets the surface roughness of a discharge contact part according to the film thickness of the photosensitive drum 62 was demonstrated, not only this but an operator sets the surface roughness of a discharge contact part. It is good also as a structure to set.
Specifically, the charger 66 may be detachable, and the operator may mount the charger 66 having a predetermined surface roughness according to the film thickness of the photosensitive drum 62.

  The threshold value of the film thickness of the photosensitive drum 62 for changing the surface roughness of the discharge contact portion, the value of the surface roughness, the number of contact portions having different surface roughnesses, the configuration, and the like are not limited to these embodiments. It can be changed as appropriate according to the situation.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming apparatus main body 40 Image forming part 42 Recording medium supply apparatus 44 Conveyance path 52 Image forming unit 54 Latent image forming apparatus 56 Transfer device 62 Photosensitive drum 64 Cleaning device 66 Charger 68 Developing device 72 Intermediate transfer body 114 Fixing device 116 Discharge roll 130 Film thickness measurement unit 140 Movement control unit 210 Application unit 216 Base material 218 Contact unit 220 Movement unit

Claims (4)

A chargeable film formed on the surface and holding an image;
Charging means for charging the film surface of the image carrier;
Have
The charging means has a plurality of charging portions having different surface roughness Ra defined in JIS B 0601 for applying a DC voltage to the image carrier,
An image forming apparatus that is set to be applied by a charging unit having a small surface roughness Ra as the film thickness of the image carrier decreases.   The charging device according to claim 1, wherein the charging unit is formed in a film shape.   The charging device according to claim 1, wherein the charging unit is formed in a cylindrical shape in cross section. A chargeable film is formed on the surface, and the thickness of the image carrier that holds the image is measured.
As the film thickness of the image carrier decreases, the image holding unit is set so that a DC voltage is applied between the image carrier and a charged portion having a small surface roughness Ra specified in JIS B 0601. A charging method for charging the surface of a body membrane.

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