JP5190757B2 - Corona charger and image forming apparatus - Google Patents

Description

  The present invention relates to a corona charger, and more particularly to a corona charger that generates a negative corona and an image forming apparatus equipped with the corona charger.

In general, an electrophotographic apparatus irradiates a uniformly charged photoconductor with writing light modulated by image data to form an electrostatic latent image on the photoconductor, and this electrostatic latent image is formed. Toner is supplied to the photoreceptor by a developing unit, and a toner image is formed on the photoreceptor and developed. The image forming apparatus transfers the toner image on the photosensitive member to transfer paper (recording paper or intermediate transfer member) at the transfer portion, and then heats and pressurizes the toner transferred onto the transfer paper at the fixing portion to fix the toner image. The toner remaining on the body surface is collected by a method such as scraping with a cleaning blade at the cleaning unit. The image forming process as described above is taken.
Here, a corona charger is used as means for charging the photosensitive member which is a member to be charged.

  Corona discharge is a sustained discharge caused by local air breakdown that occurs in a non-uniform electric field. In general, the structure is such that a small diameter wire is stretched in a shield case such as aluminum and a part of the shield case is deleted. Corona ions are released from the deleted region. As the voltage applied to the corona wire is increased, a strong local electric field is formed around the wire, causing partial breakdown of air and sustaining the discharge. This is corona discharge.

  The discharge mode of corona discharge greatly depends on the polarity of the applied voltage. In the case of normal corona discharge, a uniform discharge is formed on the corona wire surface. In the case of negative corona discharge, a discharge form in which streamer discharge is scattered is obtained. The positive corona discharge has fairly good charging uniformity, but the negative corona causes discharge unevenness and is inferior to the positive corona. In addition, the amount of ozone generated by the discharge is about an order of magnitude greater in the negative corona than in the positive corona, and the burden on the environment is greater.

<Corona charger and its features>
(1) Corotron type corona charger FIG. 1A shows the configuration of a corotron type corona charger and a charging method using the same. The corotron-type corona charger has a structure in which a tungsten wire having a diameter of 50 to 100 μm is shielded with a metal about 1 cm apart. A high voltage of 5 to 10 kV is applied to the corona wire in a state where the opening surface is arranged to face the member to be charged, and positive or negative ions generated thereby are moved to the surface of the member to be charged and charged. As shown in FIG. 2 (a), the corotron type corona charger generates a certain amount of charge, and is not necessarily good at uniformly charging the surface of the object to be charged at a constant potential. It is particularly effective as a transfer charger intended to give a constant charge to the recording paper.

(2) Scorotron-type corona charger The scorotron-type corona charger has been devised in order to reduce the unevenness of the charged potential on the surface of the object to be charged. As shown in FIG. 1B, several wires or meshes are arranged as grid electrodes on the opening surface of the corotron. The opening surface of the scorotron charger is made to face the member to be charged, and a bias voltage is applied to the grid electrode.
FIG. 2B shows charging characteristics of the scorotron type corona charger. A feature of the scorotron type corona charger is that the charging potential is regulated by the voltage applied to the grid electrode even when the charging time is long, and the surface potential is saturated. This saturation value can be controlled by the grid applied voltage. The scorotron-type corona charger has a complicated structure and inferior charging efficiency as compared with the corotron-type, but is excellent in uniformity of charging potential and widely used. The grid electrode in the electrophotographic image forming apparatus is called a charging grid.

Various investigations have been made on the alteration of the surface of an object to be charged by nitrogen oxides generated by a corona charger.
In Patent Document 1, a SUS material charging grid of a corona charger is coated with a conductive paint containing graphite particles, nickel particles, aluminum compound particles and an organic resin binder, and corrosion caused by discharge products of the control electrode is prevented. The conductive film absorbs the generated discharge product and suppresses contamination of the object to be charged. The fine particles in the film use the action of absorbing the discharge product, but the amount that can be absorbed is determined by the number of adsorption sites of the particles, so the adsorption sites are quickly buried when used over time. The effect is expected to fade.

  In the present invention, zeolite is mainly used to reduce discharge products. As a similar example, in Patent Document 2, an opening is provided in a corona charger, and ozone adsorption is provided in a finely divided communication opening provided there. Ozone diffusion is suppressed by forming a particle layer. Zeolite and activated carbon are used for the ozone adsorption particles. According to the present invention, it is possible to suppress the diffusion of ozone, but the charged object contamination by the ozone diffusing to the charged object side cannot be suppressed, so that the effect on the image cannot be expected to be effective.

  Further, in Patent Document 3, in addition to the product removal means for adsorbing the discharge product attached to the surface of the member to be charged, the product adhesion preventing means for making the discharge product difficult to attach to the surface of the member to be charged At least one of a resistance reduction preventing means for preventing the discharge product adhering to the resistance from lowering and a product generation preventing means for reducing the amount of discharge product generated near the surface of the charged body. Although there is an example in which an adsorbent such as zeolite is arranged between the charged object and the corona charger, another discharge product adsorbing means may be brought into contact with the charged object. It is essential and a plurality of members are required. Further, when the adsorbent is disposed between the charged body and the corona charger, it is expected that charging of the charged body becomes unstable.

JP 2005-227470 A Japanese Utility Model Publication No. 62-089660 JP 2003-43894 A

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a corona charger that can suppress contamination of the environment and an object to be charged by reducing the amount of discharge products generated by discharge.

As a result of diligent investigations to solve the above-mentioned problems, the present inventor has reduced the discharge products generated from the corona charger, thereby preventing air pollution and photosensitivity when used in an electrophotographic electrophotographic apparatus. It has been found that the deterioration of the body can be prevented, the occurrence of density unevenness and image flow directly under the charger can be suppressed, and the reliability of the electrophotographic apparatus can be remarkably improved.
That is, the present invention is a corona charger and an image forming apparatus as described below.

(1) In a corona charger having a corona discharge electrode and a charging grid, the charging grid has a layer containing zeolite, a conductive agent, and a binder resin on the surface , and adjusts the mixing ratio of the zeolite and the conductive agent; and The volume resistivity (ρ _o [Ω · cm]) of the outer layer of the charging grid in which the blending ratio of the conductive agent in the inner layer is larger than the blending ratio of the conductive agent in the outer layer is 1.0 × 10. It is in the range of ^{8 to} 1.0 × 10 ¹⁰ [Ω · cm], and the volume resistivity of the charging grid inner layer is lower than the volume resistivity (ρ _i [Ω · cm]) of the outer layer. Corona charger.
( 2 ) The apparatus main body manufactured by combining the corona charger according to (1) , the electrophotographic photosensitive member, and at least one of image exposure means, development means, transfer or separation means, and cleaning means. A process cartridge ( 3 ) characterized in that the corona charger described in (1) is used.

  In a scorotron type discharge-type corona charger having a charging grid (control electrode) that can easily control the surface potential of an object to be charged, when holding a layer made of zeolite, a conductive agent and a binder resin formed on the surface of the charging grid. By changing the mixing ratio of the components constituting the layers on the front and back of the grid, the charging is efficiently stabilized, the amount of discharge products generated from the corona charger is reduced, and the property of the charged object such as the photoconductor is changed. Suppressing can maintain a stable image.

The present invention will be described below by taking an electrophotographic apparatus as an example.
FIG. 3 is a schematic diagram showing a configuration example of the electrophotographic apparatus. The image carrier 100 is charged with (±) 600 to 1400 V by the charging device 101. After the charge is applied (charged), the image exposure system 102 forms a latent image. In the case of an analog copying machine, the original image irradiated by the exposure lamp is projected onto the photosensitive member in the form of a reverse image by a mirror and formed into an image. In the case of a digital copying machine, it is read by a CCD (charge coupled device). The obtained original image is converted into a digital signal of an LD or LED having a wavelength of 400 to 780 nm, and formed on the photosensitive member. Therefore, the analog and digital wavelength ranges are different. By image formation, charge separation is performed in the photosensitive layer, and a latent image is formed on the photosensitive member.

  The image carrier 100 on which the latent image has been formed according to the document is developed with a developer by the developing device 103, and the document image is visualized (toner image). Next, the toner image on the photoreceptor is transferred to the copy sheet 109 by applying a voltage to the transfer device 104. The voltage applied in the transfer is controlled by constant current so that the current flowing through the photosensitive member is constant. On the other hand, after the image carrier 100 is transferred, the toner image is cleaned and cleaned by a cleaning device 105 (consisting of a cleaning brush 106 and an elastic rubber cleaning blade 107). Since the latent image (original image) after the toner image is formed is held on the photosensitive member after cleaning, the static eliminator (generally using red light) 108 for erasing and uniformizing. Then, the preparation for the next latent image formation is completed and a series of copying processes is completed.

The image forming means may be fixedly incorporated in a copying apparatus, facsimile, or printer, but may be incorporated in these apparatuses in the form of a process cartridge and detachable.
A process cartridge for an image forming apparatus includes an image carrier, and further includes at least one of a charging device, a developing device, a transfer unit, a cleaning unit, and a charge eliminating unit, and is detachable from the image forming apparatus main body. It is a device (part).

[Problems caused by discharge products]
<Environmental impact>
It is known that when a corona charger that performs negative corona discharge is used, a substance in the air reacts by discharge to generate a substance called a discharge product. It contains ozone (O ₃ ) in which oxygen is oxidized, and nitrogen oxides (NOx) such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) in which nitrogen is oxidized by ozone. Ozone is a substance that feels odor at about 0.1 ppm and adversely affects the respiratory system. Nitrogen oxide (NO ₂ ) has an adverse effect on human respiratory organs, and the daily average of hourly values is determined to be 0.04 to 0.06 ppm or less according to environmental standards. In addition, nitrogen oxides are converted into a substance called photochemical oxidant (O _x ) by a photochemical reaction caused by ultraviolet rays, and the environmental standard is also set to 0.06 ppm or less for this substance. The amount of each discharge generated is several tens of ppm for ozone and several ppm for nitrogen oxides. The current copying machine uses a filter such as activated carbon to reduce the amount discharged outside the machine.

<Influence on print quality>
(Raindrop unevenness)
In an image forming apparatus using a scorotron charger that performs corona discharge, a raindrop-shaped unevenness as shown in FIG. 4 may occur in the output image (a thin vertical line in the halftone is a raindrop-shaped unevenness). This is due to the presence of large unevenness in the charge amount in a small range in charging the photosensitive member by the charger. This unevenness is caused by, for example, defective discharge due to local adhesion of the toner adhering to the charging wire, silica as its additive, or the discharge product, or a similar substance having high electric resistance adheres to the charging grid and is discharged. The generated charge does not flow through the grid and the amount of movement to the photoconductor increases, or the charged grid itself increases in electrostatic capacity, and the surface potential of the photoconductor rises locally above the voltage applied to the charge grid. It can be considered.

(Image Flow [Image Blur])
In an image forming apparatus using an electrophotographic method such as a copying machine, resolution decreases due to image flow (or image flow, image blur, etc.) as long as a charging method with discharge is used.
Although the image flow depends on the paper dust adhesion and the usage environment, the main factor is the discharge product, and the invention of a charging method that does not discharge ozone, NOx, etc. in order to be released from the image flow. It is almost impossible at present unless it is done. The image flow caused by the above factors can be improved by polishing the causative substance to the minimum necessary or by heating if it cannot be polished, but there are problems such as a decrease in the life of the photoreceptor, power and space, and control means. It becomes. Since the generation of image blur is suppressed by actively shaving the surface of the charged body, it is necessary to remove the discharge products adhering to the surface in order to suppress the image flow. Since a highly durable object has a small amount of wear, it is difficult to remove the causative substance.
In order to improve the image flow, it is necessary to take steps according to the situation. For that purpose, it is important to grasp the situation of the image flow and to solve it by taking appropriate measures.

  The discharge product first adheres in the form of spots (stains) and gradually expands over the entire surface. Even if it adheres, the image does not flow initially, but if it is not removed, the adhesion area gradually increases, and a hygroscopic low-resistance layer is formed on the surface of the photoreceptor. The image flow (or image blur) phenomenon is a phenomenon in which electric charges during image formation are diffused on or near the surface of the photosensitive member, so that a normal electrostatic latent image is not formed, resulting in an image with blurry edges. That is, when an electrostatic latent image is formed, if there is a low resistance layer in the surface layer of the photoreceptor or a layer, electric charge distortion occurs in that region, and this phenomenon occurs when the electrostatic latent image is disturbed. FIG. 5 is a schematic diagram for explaining the image flow phenomenon.

When image exposure is performed after negative charging on the surface of the photoreceptor, hole-electron pairs are formed in the charge generation layer, with electrons (-) going to the conductive support and holes (+) going to the negative charge on the surface. However, if there is a low-resistance layer in the middle of movement, holes do not go straight to the surface layer but leak laterally, or if the surface layer has low resistance, it moves laterally on the free surface. . Accordingly, charge diffusion and dissipation occur, and it is difficult to form a normal electrostatic latent image. The smaller the change in resistance value, the smaller the reduction in resolution because the movement of charges is suppressed. When the change of the resistance value is large and the volume resistivity is 1.0 × 10 ¹² Ω · cm or less, the resolution is lost and the image is clearly displayed, and finally the image is completely lost. At this time, the potential does not become a rectangular wave potential pattern, but becomes a gradual potential pattern, and the charge level is lowered and the image portion potential is raised, indicating a potential pattern with a low contrast potential. These phenomena worsen with time and tend to worsen with increasing humidity.
That is, in order to form a high-resolution image, it is necessary that at least the volume resistivity of the photoreceptor is on the order of 10 ¹³ (Ω · cm) or higher and the surface resistivity is on the order of 10 ¹⁵ (Ω · cm) or higher. .

(Uneven density directly under the corona charger)
As a problem caused by the discharge product generated from the corona charger, first, there is density unevenness directly under the corona charger due to standing after a long discharge. This occurs at the time of discharge during image forming operation, and the discharge product attached to the inner wall of the corona charger gradually contaminates the charged object while the device is stopped. This is a problem in that a difference occurs in the surface potential in this portion, resulting in image density unevenness. This problem occurs more prominently in a low humidity environment of about 20% RH, and gradually recovers when placed in a normal temperature and normal humidity environment. It has been confirmed that the surface of the object to be charged reacts reversibly with the discharge product, and the potential difference is generated because the capacitance increases or the resistance decreases. Although the occurrence has been confirmed in any of the photoreceptors, the occurrence is particularly remarkable in a photoreceptor having a cross-linkable cured film on the surface as a protective layer.
FIG. 6A is a diagram showing the state of an image when density unevenness is generated directly under the corona charger, and FIG. 6B is a diagram showing the photoreceptor surface potential corresponding to the image.

  In order to reduce the discharge products discharged outside the machine, it is effective in the form of being supported by a filter etc. in the path to discharge, but the most contaminated by the discharge products is the charged object directly under the corona charger The corona charger and the member to be charged are often fixed at a fixed interval of about 1 to 2 mm in order to perform stable charging. Therefore, in order to suppress contamination of the object to be charged by the discharge product, a complicated mechanism such as inserting a shield between the corona charger and the object to be charged after discharge or moving the corona charger and object to be charged is necessary. is there. The object of the present invention is to suppress contamination of a charged object without the need for the above mechanism by holding zeolite on a charging grid.

[Configuration of photoconductor]
Next, the electrophotographic photosensitive member will be described with reference to the drawings.
FIG. 7 is a cross-sectional view showing an example of the electrophotographic photosensitive member used in the present invention. On the conductive support (31), an intermediate layer (33), a charge generation layer (35) having a charge generation function, This is a photoreceptor having a laminated structure in which a charge transport layer (37) having a charge transport material function is laminated.

<About conductive support>
As the conductive support (31), a material having a volume resistance of 10 ¹⁰ Ω · cm or less, for example, a metal such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, tin oxide, oxidation Metal oxide such as indium is deposited or sputtered to form film or cylindrical plastic, paper coated, or aluminum, aluminum alloy, nickel, stainless steel, etc. After conversion, a tube that has been subjected to surface treatment such as cutting, superfinishing, or polishing can be used. Further, an endless nickel belt and an endless stainless steel belt disclosed in Japanese Patent Application Laid-Open No. 58-86547 can also be used as the conductive support (31).
In addition, the conductive support dispersed in a suitable binder resin and coated on the support can also be used as the conductive support (31) used in the present invention.

  Examples of the conductive powder include carbon black, acetylene black, metal powder such as aluminum, nickel, iron, nichrome, copper, zinc and silver, or metal oxide powder such as conductive tin oxide and ITO. Can be mentioned. The binder resin used at the same time is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer. , Polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, Examples thereof include thermoplastic, thermosetting resins, and photocurable resins such as melamine resin, urethane resin, phenol resin, and alkyd resin. Such a conductive layer can be provided by dispersing and coating these conductive powder and binder resin in a suitable solvent such as tetrahydrofuran, dichloromethane, methyl ethyl ketone, and toluene.

  Furthermore, it is electrically conductive by a heat-shrinkable tube in which the conductive powder is contained in a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, Teflon (registered trademark) on a suitable cylindrical substrate. Those provided with a conductive layer can also be used favorably as the conductive support (31) of the present invention.

<About photosensitive layer>
(About the middle class)
The structure of the intermediate layer (33) that can be provided for the purpose of preventing charge injection from the conductive support (31) to the photosensitive layer or for preventing interference fringes is that the binder resin or particles are contained in the binder resin. The binder resin may be a thermoplastic resin such as polyvinyl alcohol, nitrocellulose, polyamide, or polyvinyl chloride, or a thermosetting resin such as polyurethane or alkyd-melamine resin. As particles to be dispersed in the intermediate layer, titanium oxide, aluminum oxide, tin oxide, zinc oxide, zirconium oxide, magnesium oxide, silica and their surface treatment products are used, and titanium oxide is more preferable in terms of dispersibility and electrical characteristics. Both rutile and anatase types can be used.
In order to form the intermediate layer, for example, the above-described binder resin may be dissolved in an organic solvent, and the above-described particles may be dispersed in the solution by means of a ball mill, a sand mill, or the like, and applied to a support and dried. . The thickness of the intermediate layer is 10 μm or less, preferably 0.1 to 6 μm.

(Charge generation layer)
The charge generation layer (35) is a layer mainly composed of a charge generation material having a charge generation function, and a binder resin can be used in combination as necessary. As the charge generation material, inorganic materials and organic materials can be used.

  Inorganic materials include crystalline selenium, amorphous selenium, selenium-tellurium, selenium-tellurium-halogen, selenium-arsenic compounds, and amorphous silicon. In amorphous silicon, dangling bonds that are terminated with hydrogen atoms or halogen atoms, or those that are doped with boron atoms, phosphorus atoms, or the like are preferably used.

  On the other hand, a known material can be used as the organic material. For example, phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, azulenium salt pigments, squaric acid methine pigments, azo pigments having carbazole skeleton, azo pigments having triphenylamine skeleton, azo pigments having diphenylamine skeleton, dibenzothiophene skeleton Azo pigments having a fluorenone skeleton, azo pigments having an oxadiazole skeleton, azo pigments having a bis-stilbene skeleton, azo pigments having a distyryl oxadiazole skeleton, azo pigments having a distyrylcarbazole skeleton, perylene Pigments, anthraquinone or polycyclic quinone pigments, quinoneimine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and azomethine pigments, Goido based pigments, and bisbenzimidazole pigments. These charge generation materials can be used alone or as a mixture of two or more.

  Binder resins used as necessary for the charge generation layer (35) include polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, poly-N-. Examples thereof include vinyl carbazole and polyacrylamide. These binder resins can be used alone or as a mixture of two or more. In addition to the binder resin described above as a binder resin for the charge generation layer, a polymer charge transport material having a charge transport function, such as an arylamine skeleton, a benzidine skeleton, a hydrazone skeleton, a carbazole skeleton, a stilbene skeleton, a pyrazoline skeleton, etc. Polymer materials such as polycarbonate, polyester, polyurethane, polyether, polysiloxane, and acrylic resin, polymer materials having a polysilane skeleton, and the like can be used.

The charge generation layer (35) may contain a low molecular charge transport material.
Low molecular charge transport materials that can be used in combination with the charge generation layer (35) include hole transport materials and electron transport materials.
Examples of the electron transporting material include chloroanil, bromanyl, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophen-4-one, 1,3,7-tri Examples thereof include electron-accepting substances such as nitrodibenzothiophene-5,5-dioxide and diphenoquinone derivatives. These electron transport materials can be used alone or as a mixture of two or more.

  Examples of the hole transporting material include the electron donating materials shown below and are used favorably. As hole transport materials, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, benzidine derivatives, diarylmethane derivatives, triaryls Other known materials such as methane derivatives, 9-styrylanthracene derivatives, pyrazoline derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, and the like can be given. These hole transport materials can be used alone or as a mixture of two or more.

As a method of forming the charge generation layer (35), a vacuum thin film preparation method and a casting method from a solution dispersion system are mainly exemplified.
As the former method, a vacuum deposition method, a glow discharge decomposition method, an ion plating method, a sputtering method, a reactive sputtering method, a CVD method, or the like is used, and the above-described inorganic materials and organic materials can be satisfactorily formed.
In addition, in order to provide a charge generation layer by the casting method described later, if necessary, the inorganic or organic charge generation material, together with a binder resin, tetrahydrofuran, dioxane, dioxolane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, cyclohexane. Can be formed by dispersing with a ball mill, attritor, sand mill, bead mill, etc. using a solvent such as pentanone, anisole, xylene, methyl ethyl ketone, acetone, ethyl acetate, butyl acetate, etc. . Moreover, leveling agents, such as a dimethyl silicone oil and a methylphenyl silicone oil, can be added as needed. The application can be performed by dip coating, spray coating, bead coating, ring coating, or the like.
The thickness of the charge generation layer provided as described above is suitably about 0.01 to 5 μm, preferably 0.05 to 2 μm.

(Charge transport layer)
The charge transport layer (37) is a layer having a charge transport function. A charge transport material having a charge transport function and a binder resin are dissolved or dispersed in an appropriate solvent, and this is coated on the charge generation layer (35) and dried. To form. As the charge transport material, the electron transport material, hole transport material and polymer charge transport material described in the charge generation layer (35) can be used.

  As the binder resin, polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, Polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin And thermoplastic or thermosetting resins such as phenol resins and alkyd resins.

The amount of the charge transport material is appropriately 20 to 300 parts by weight, preferably 40 to 150 parts by weight, based on 100 parts by weight of the binder resin. However, when a polymer charge transport material is used, it can be used alone or in combination with a binder resin.
As the solvent used for coating the charge transport layer, the same solvent as that used for the charge generation layer can be used, but a solvent that dissolves the charge transport material and the binder resin well is suitable. These solvents may be used alone or in combination of two or more. The charge transport layer (37) can be formed by the same coating method as the charge generation layer (35).

If necessary, a plasticizer and a leveling agent can be added.
As a plasticizer that can be used in combination with the charge transport layer, those used as plasticizers for general resins such as dibutyl phthalate and dioctyl phthalate can be used as they are, and the amount used is 0 with respect to 100 parts by weight of the binder resin. About 30 parts by weight is appropriate.
Leveling agents that can be used in combination with the charge transport layer include silicone oils such as dimethyl silicone oil and methylphenyl silicone oil, and polymers or oligomers having a perfluoroalkyl group in the side chain. The amount used is a binder resin. About 0 to 1 part by weight is appropriate for 100 parts by weight.
The thickness of the charge transport layer is suitably about 5 to 40 μm, preferably about 10 to 30 μm.

(Protective layer)
By providing the protective layer (39) on the charge transport layer, wear resistance and durability against scratches can be improved. The protective layer includes those in which conductive fine particles are dispersed, those in which lubricating fine particles such as a fluorine-containing resin and an acrylic resin are dispersed, and those made of a crosslinked film having excellent mechanical strength. Examples of this resin are preferably phenol resin, urethane resin, melamine resin, curable acrylic resin, siloxane resin, and the like. Further, the protective layer preferably contains a charge transport material in order to improve its electrical characteristics. In addition, as a charge transport material, what was mentioned as a constituent material of the said charge transport layer can be used, for example.

[Charging grid of corona charger]
<Charging grid substrate>
As the base material of the charging grid which is the control electrode of the corona charger, those conventionally used can be used. As a material of the charging grid, a metal which is a conductor is used to function as an electrode. Most of the metals such as aluminum, nickel, iron, nichrome, copper, zinc, and silver can be used as the electrode function, but the charger is exposed to ozone, NOx, etc. generated by corona discharge. A metal having high corrosion resistance is preferable, and stainless steel containing chromium or nickel is used. As the shape, it is necessary to move the charge generated by corona discharge onto the photoconductor and to have a function as a control electrode, so that a metal thin plate is provided with an opening by punching, etching or the like, or metal wires are arranged Is usually used.
As a base material for the control electrode used this time, a SUS304 plate having a thickness of 0.1 mm, a length of 285 mm, and a width of 40 mm is used, and an opening length of 250 mm and a width of 36 mm is formed by a 0.1 mm grid at an angle of 45 degrees. Used at intervals of 0.5 mm.
The appearance of the charging grid used in the example is shown in FIG.

<Charging grid coating film>
(Zeolite)
In the present invention, zeolite is used to remove discharge products. Zeolite is a crystal like crystal, mainly composed of aluminum and silicon. The crystals are very small and cannot be seen visually in shape or size. When enlarged, it can be confirmed that there are many pores called pores. More than 40 types of zeolite having this unique structure have been discovered in nature.
In order to make the most of the characteristics of zeolite, which is represented by the adsorption / decomposition function, industrially produced zeolite is called synthetic zeolite. Synthetic zeolites have many types that are high in performance and are not found in natural zeolites, but their cost is a disadvantage.
Artificial zeolite has emerged as the third zeolite. By treating materials that were considered waste such as coal ash, it is converted into a zeolite that is beneficial to the earth and mankind. Moreover, because of its low cost, it is a material that is currently attracting a great deal of attention.

・ Adsorption function Zeolite functions to adsorb various substances, and its mechanism is similar to that of deodorizers and desiccants. By making use of this function, it is possible to adsorb harmful substances and remove malodors.
・ Cation exchange function Zeolite has a high cation exchange function of about 2 to 3 times that of natural zeolite. By utilizing this function, soil improvement to neutralize acidity and removal of ammonium ions in sewage / drainage Etc. are possible.
-Catalytic function Zeolite has a function as a catalyst, and decomposition of nitrogen oxides (NOx) and the like have been studied using this function.

  The type of zeolite used in the present invention is not limited, but the size of pores varies depending on the crystal form and the type of cation, so that the molecules that can be adsorbed are different. Therefore, effective removal is possible by selecting the crystal form and cation species according to the target substance. Crystal types include A type, X type, Y type, L type, mordenite type, ferrierite type, ZSM-5 type, beta type, and cation species include potassium, sodium, calcium, ammonium, hydrogen, etc. is there. Further, the adsorption ability and catalytic ability change depending on the ratio of aluminum and silicon constituting the zeolite, and the target substance can be efficiently removed by setting the optimum ratio.

(Binder resin)
In the present invention, a binder resin is used to hold the zeolite on the charging grid. The binder resin used is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, poly Vinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin, Examples thereof include thermoplastic or thermosetting resins such as phenol resins and alkyd resins. In some cases, two or more of the above resins may be mixed and used.
The binder ratio that the discharge product removal function does not deteriorate due to the binder resin covering the zeolite was normally about 10 wt%, but the evaluation was performed even when the binder resin ratio was around 30 wt%. It has been confirmed that the function is not lowered and compatibility with adhesion is possible.

(Conductive agent)
Although the charged grid base material, which is a processed product of a wire or a metal plate, is inherently conductive, it is covered with zeolite and a binder resin, so that the electric resistance increases and does not play a role in controlling the surface potential. Therefore, a conductive agent is mixed for the purpose of imparting conductivity. Here, conductive particles such as activated carbon and tin oxide can be used as the conductive agent. In some cases, two kinds of conductive agents can be used.

It has been confirmed that a charged grid having a coating film containing only a zeolite and a binder and not containing a conductive agent does not play a role of controlling the surface potential of an object to be charged.
This is because the electrical resistance of the coating film is high, and electrons and ions generated by corona discharge accumulate on the grid, causing the grid potential to rise above the applied voltage. This is considered to be caused by a higher than
The lower the electrical resistance of the coating film, the more stable the chargeability. However, the amount of the conductive agent cannot be extremely increased considering the amount of zeolite for protecting the discharge product from the object to be charged.
Therefore, the membrane resistance on the wire side is lowered to stabilize the charging, and the membrane containing the insulating zeolite is held on the charging grid by increasing the zeolite ratio of the coating film on the charged object side to such an extent that it does not affect the charging property. In this case, it is considered that the charging property can be stabilized and the discharge product removal effect can be efficiently performed.

<Coating method on the charging grid>
The coating liquid was first prepared by adding a binder resin to a ratio of about 5 to 10 wt% with respect to the solvent, and adding zeolite particles and a conductive agent while stirring. In the case of spray coating, the solid concentration of the coating liquid is 30 wt% or less.
In the present invention, a layer made of zeolite, a conductive agent and a binder resin is formed on the surface of the charging grid.
Then, a layer having a volume resistivity (ρ _o ) in the range of 1.0 × 10 ^{8 to} 1.0 × 10 ¹⁰ [Ω · cm] is formed as an outer layer of the charging grid, and a volume is formed as an inner layer of the charging grid. A layer having a lower resistivity (ρ _i ) than the outer layer is formed.
In the present invention, the outer side of the charging grid means the charged object side, and the inner side of the charging grid means the charging wire side as described with reference to FIG.
The coating method used in the examples will be described below.
In order to obtain coating films having different volume resistivity after the coating film formation, two types of coating liquids are prepared, one applied to the outside of the charging grid and the other to the inside of the charging grid.
As a method for coating the prepared liquid on the charging grid, there are a dipping method, a roller coating method, an electrophoretic electrodeposition method, and the like, but this time, the spray method with the least coating unevenness was used. A charging grid is tensioned from both ends in the long axis direction and installed in the longitudinal direction of a cylindrical base having a diameter of 30 mm, and the cylinder is rotated at a speed of 170 rpm in the circumferential direction and sprayed in the horizontal direction at 10 mm / sec. Coating was carried out by scanning at a speed of. In order to coat both sides, a charging grid was installed about 3 mm above the base. After the coating on one side was completed, the coating was left for 10 minutes, the coating solution was changed, and the other side was coated. After spray coating, the membrane was fixed by heating at 130 ° C. for 30 minutes and drying. The coating film thickness was 30 μm for each of the outer layer and the inner layer.
In the embodiment, the SUS plate is used as the charging grid base material. However, when the charging grid is made of a wire, a layer is formed around the wire. The facing layer is called the outer layer, and the layer facing the wire side is called the inner layer.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example. The “parts” used in the photoconductor production examples all represent parts by weight.

<Example of photoconductor preparation>
By coating and drying an undercoat layer coating solution, a charge generation layer coating solution, and a charge transport layer coating solution in the following order on a φ100 mm aluminum cylinder in sequence, an undercoat layer of 3.5 μm Then, a 0.2 μm charge generation layer and a 32 μm charge transport layer were formed to obtain a photoreceptor 1.

[Coating liquid for undercoat layer]
Alkyd resin 6 parts (Beckosol 1307-60-EL, manufactured by Dainippon Ink & Chemicals, Inc.)
Melamine resin 4 parts (Super Becamine G-821-60, manufactured by Dainippon Ink & Chemicals, Inc.)
Titanium oxide 40 parts Methyl ethyl ketone 50 parts

[Coating liquid for charge generation layer]
Y-type titanyl phthalocyanine 6 parts Silicone resin solution 70 parts (KR5240, 15% xylene-butanol solution: Shin-Etsu Chemical Co., Ltd.)
2-butanone 200 parts

[Coating liquid for charge transport layer]
Charge transport material (Structural formula A below) 25 parts Bisphenol Z-type polycarbonate 30 parts (Iupilon Z300: manufactured by Mitsubishi Gas Chemical Company)
1,2-dichloroethane 200 parts

<Example of charging grid preparation>
A charging grid was prepared by the coating method. In addition, the liquid solid content in that case was 30%. Table 1 shows other coating conditions.

[Example 1]
A coating solution was prepared using the materials shown below. This time, the blending ratio was changed for each side of the grid, but in both cases, the binder resin was 25 wt% of the whole, and the ratio of zeolite / conductive agent was 5/5 inside and 8/2 outside: 8/2.
The solid content concentration of the liquid was adjusted to 30 wt%.
Zeolite ・ ・ ・ β-type zeolite (980HOA manufactured by Tosoh Corporation)
Conductive agent: Activated carbon (RP-20, made by Kuraray Chemical)
Binder resin ... Butyral resin: (BM-5 Sekisui Chemical)
Dispersion medium: methanol The above coating solution was applied to a charging grid of a corona charger by spraying, and the following evaluation was performed.

[Evaluation method of corona charger]
(1) Evaluation of charge controllability The charge grid was attached to an imagio Neo 1050pro having a process cartridge placed in an environment of 10 ° C and 15% RH. Corona discharge was performed by applying a voltage so that a constant current would flow through the charging wire, and the surface potential of the photoreceptor to be charged when -900 V was applied to the charging grid was measured. After that, a halftone image was output, and the presence or absence of raindrop-like discharge unevenness that occurred at the time of local charging failure was confirmed.
◎ ・ ・ ・ Drain-like discharge unevenness does not occur
○ ・ ・ ・ Drain-like discharge unevenness occurs slightly, but acceptable level × ・ ・ ・ Drain-like discharge unevenness occurs

(2) Evaluation of discharge product removal function The charged grid was attached to an imagio Neo 1050pro having a process cartridge placed in a 32 ° C. and 90% RH environment. By performing the image forming operation, the corona charger was discharged for 3 hours, and then the machine was turned off and left for 15 hours. The machine was then turned on, and the presence of white spots and image flow immediately below the corona charger was confirmed by outputting halftone images and full-text images.
◎ ・ ・ ・ No density unevenness directly under the corona charger
○ ・ ・ ・ Slightly uneven density just below the corona charger, but acceptable level × ・ ・ ・ Uneven density level just below the corona charger, unacceptable level

(3) Grid coating film volume resistivity measuring method The volume resistivity of the grid coating film was measured as follows.
Measuring instrument: Mitsubishi Yuka Co., Ltd. Hiresta MODEL HT-201
Measurement conditions: A voltage of 100 V was applied at a bifurcated high voltage application terminal, and the value 10 seconds after the start of measurement was taken as the measurement value. The average value of the three measured values was taken as the volume resistance value.
Measurement method: Two forked high voltage application terminals (each φ2 mm) were brought into contact with the charged grid coating film part and the base part one by one, and the volume resistivity was calculated from the flowing current. At this time, the center between both terminals was arranged to be the boundary between the part holding the composition and the part not holding it.
The volume resistivity of each of the inner and outer layers of the charging grid was measured.
In the embodiment, the one shown in FIG. 8 is used, but when a wire is used as the charging grid, the volume resistivity is a value converted per unit area (1 cm ² ).
The evaluation results for the above evaluation are shown in Table 2.

(Example 2)
The same evaluation as in Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 1/9 and the zeolite / conductive agent weight ratio of the outer coating film was 8/2.
(Example 3)
Evaluation similar to Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 7/3 and the zeolite / conductive agent weight ratio of the outer coating film was 8/2.
Example 4
The same evaluation as in Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 3/7 and the zeolite / conductive agent weight ratio of the outer coating film was 9/1.
(Example 5)
The same evaluation as in Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 1/9 and the zeolite / conductive agent weight ratio of the outer coating film was 9/1.
(Example 6)
The same evaluation as in Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 7/3 and the zeolite / conductive agent weight ratio of the outer coating film was 9/1.

(Comparative Example 1)
Evaluation similar to Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 3/7 and the zeolite / conductive agent weight ratio of the outer coating film was 7/3.
(Comparative Example 2)
The same evaluation as in Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 1/9 and the zeolite / conductive agent weight ratio of the outer coating film was 7/3.
(Comparative Example 3)
The same evaluation as in Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 7/3 and the zeolite / conductive agent weight ratio of the outer coating film was 7/3.
(Comparative Example 4)
The same evaluation as in Example 1 was performed except that the zeolite / conductive agent weight ratio of the inner coating film was 3/7 and the zeolite / conductive agent weight ratio of the outer coating film was 9.5 / 0.5.
(Comparative Example 5)
Evaluation was performed in the same manner as in Example 1 except that the zeolite / conductive agent weight ratio of the inner coating film was 1/9 and the zeolite / conductive agent weight ratio of the outer coating film was 9.5 / 0.5.
(Comparative Example 6)
Evaluation similar to Example 1 was performed using the grid which has not performed coating.

Zeolite capable of removing discharge products by adjusting the amount of the conductive agent so that the volume resistivity of the outer coating film is in the range of 1.0 × 10 ^{8 to} 1.0 × 10 ¹⁰ [Ω · cm]. Therefore, the generation of abnormal images associated therewith is suppressed. Moreover, charge controllability is also improved by making the volume resistivity of the inner coating film lower than that of the outer coating film, and the sum of the volume resistivity of the inner coating film and the outer coating film is 1.0 × 10 ¹³ to 1. By adjusting to 0 × 10 ¹⁵ [Ω · cm], discharge that has become slightly unstable in order to enhance the discharge product removal function on the charged object side, and lower the resistance of the coating film on the wire side It can be considered that the charge controllability is stabilized and the discharge product removal effect is improved.

  Since the corona charger of the present invention can reduce the amount of discharge products, it can be used in an image forming apparatus or the like to suppress the deterioration of a charged body such as a photoconductor and maintain a stable image. be able to.

It is a schematic diagram which shows the structure of a corotron type corona charger and a scorotron type corona charger. It is a figure which shows the charging characteristic of a corotron type corona charger and a scorotron type corona charger. 1 is a diagram illustrating a configuration example of an image forming apparatus of the present invention. It is a schematic diagram which shows a raindrop-like nonuniformity. It is a schematic diagram explaining an image flow phenomenon. It is a figure which shows the density non-uniformity right under a corona charger. It is a schematic diagram which shows the cross section of an electrophotographic photoreceptor. It is a figure which shows an example of the structure of a charging grid.

Explanation of symbols

1 Charger 2 Casing 3 End block (insulating)
4 End block (insulating)
6 Charging grid 8 Claw for stretching grid 9 Grid bias application electrode 9a Claw for stretching grid (bias application electrode and grid are connected)
31 conductive support 33 intermediate layer 35 charge generation layer 37 charge transport layer 100 photoconductor 101 charging device 102 image exposure system 103 developing device 104 transfer device 105 cleaning device 106 cleaning brush 107 elastic rubber cleaning blade 108 static elimination device 109 copy sheet

Claims (3)

In a corona charger having a corona discharge electrode and a charging grid, the charging grid has a layer containing zeolite, a conductive agent, and a binder resin on the surface, and the mixing ratio of the zeolite and the conductive agent is adjusted, and in the inner layer The volume resistivity (ρ _o [Ω · cm]) of the outer layer of the charging grid in which the blending ratio of the conductive agent is larger than the blending ratio of the conductive agent in the outer layer is 1.0 × 10 ⁸ to 1 0.0 × 10 ¹⁰ [Ω · cm], and the volume resistivity of the inner layer of the charging grid is lower than the volume resistivity (ρ _i [Ω · cm]) of the outer layer. .   The corona charger according to claim 1, an electrophotographic photosensitive member, and at least one of at least one of an image exposure unit, a developing unit, a transfer or separation unit, and a cleaning unit, and is detachable from the apparatus main body. A process cartridge that is installed in   An image forming apparatus using the corona charger according to claim 1.