JP6319190B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and more particularly, an image that charges a surface of an organic photoreceptor on which an organic photosensitive layer is formed by a contact charging method. The present invention relates to a forming apparatus.

  In recent years, a charging device is used in an image forming apparatus using an electrophotographic process in order to charge the surface of a photoconductor as an image carrier. As a charging device, a photoconductor and a corona wire are arranged in a non-contact manner, and a scorotron charging method in which the surface of the photoconductor is charged by corona discharge, and a contact in which a charging member such as a charging roller is brought into contact with the surface of the photoconductor for charging. A charging method is known. However, in recent years, in order to reduce the amount of ozone that is harmful to the human body, a contact charging method with a smaller amount of ozone emission has been increasingly adopted.

  On the other hand, a photoconductor as an image bearing member is formed by forming a photosensitive layer having a thickness of 10 to several tens of μm on the surface of a cylindrical base material. Divided. Organic photoconductors have the advantage that they are easier to manufacture than inorganic photoconductors, and that the choice of organic materials for forming the photosensitive layer is diverse and the degree of freedom in design is high.

  As the organic photoreceptor, a multilayer photoreceptor in which a charge generation layer containing a charge generation agent and a charge transport layer containing a charge transport agent are laminated, and a charge generation agent as described in Patent Document 1, There is a single-layer type photoreceptor in which a charge transfer agent is dispersed in a single photosensitive layer. Single-layer photoconductors can generate photocarriers near the surface of the photosensitive layer, so that the photosensitive layer can be made thicker, suitable for longer life, and can be manufactured easily and at low cost due to the single-layer coating. It has advantages such as being able to do so. Therefore, it is considered that the electrophotographic process having better environmental compatibility can be designed by combining the single layer type photoreceptor and the contact charging method.

  However, a problem peculiar to the contact charging method is uneven charging caused by local discharge from the irregularities on the surface of the charging member to the photosensitive layer. This charging unevenness is likely to occur particularly in a positively charged single layer type photoreceptor. This is because a single layer type photoreceptor contains a charge generating agent, a charge transport agent, and a binder resin in the same layer, and the voltage at which discharge occurs for each material is different, so it is a place where local discharge is likely to occur. (Discharge site) exists. It is considered that uneven charging occurs when such discharge sites are scattered on the surface of the photosensitive layer. In order to suppress the local discharge, which is a cause of charging unevenness, there is a means for increasing the discharge voltage to promote the discharge even in a place where the local discharge is difficult. However, by increasing the discharge voltage (= photoconductor inflow current), Since the wear is promoted, the life of the photoreceptor is shortened.

  In addition, as shown in FIG. 9, in contrast to a stacked type photoreceptor in which a charge generation layer and a charge transport layer are separated, a single layer type photoreceptor has a charge generation agent CGM added to a resin material that is a main component of a photoconductive layer. And many materials such as a charge transport agent CTM (ETM that transports electrons, HTM that transports holes). With such a configuration, it is considered that the photocarrier generated in the single-layer type photoreceptor passes through various materials existing in the photoconductive layer and tends to be easily trapped. As a change in the photoreceptor characteristics due to the carrier trap, there is a decrease in charging ability (indicated by the charging potential of the drum when a constant current is passed).

  In addition, there is a tendency that the charged potential on the surface of the photoreceptor can be made uniform by applying a superimposed voltage obtained by superimposing an alternating voltage on a direct current voltage to the charging roller. This is also undesirable. Furthermore, increasing the diameter of the charging roller to enlarge the discharge area, or decreasing the drive speed (rotation speed) of the photoconductor to extend the time that the photosensitive layer passes through the discharge area can also suppress charging unevenness. Although there are certain effects, these measures are not desirable in view of the demand for smaller and faster products.

  Therefore, Patent Document 2 includes a positively charged single-layer type photoreceptor and a charging roller made of conductive rubber as a contact charging member, and by setting the rubber hardness and surface roughness of the charging roller within a predetermined range. An image forming apparatus that suppresses carrier trap, film shaving, and charging unevenness of a photosensitive layer is disclosed. On the other hand, Patent Document 3 discloses a positively charged single layer type photoreceptor in which the abrasion resistance of the photosensitive layer is improved by uniformly dispersing a resin or metal filler in the photosensitive layer.

JP 2002-72511 A JP 2012-14141 A JP, 2014-130236, A

  Even if the method of Patent Document 2 is used, the charging unevenness of the positively charged single-layer type photoreceptor is not completely eliminated, and a device on the photoreceptor side is required. In such charging unevenness, the smoother the surface of the photosensitive layer, the more the influence of discharge sites on the surface of the photosensitive layer appears, and local discharge tends to occur. For this reason, it tends to be remarkably likely to occur particularly in an unused photoreceptor where the surface state of the photosensitive layer is relatively smooth. However, since the discharge site on the photosensitive layer surface is eliminated by discharge, scraping or pushing with a cleaning blade, the influence of the discharge site on the photosensitive layer surface as time elapses from the start of use of the positively charged single layer photoreceptor. Is negligible.

  On the other hand, as in Patent Document 3, in order to extend the life of the positively charged single layer type photoreceptor, a photoreceptor in which a resin or metal filler is uniformly dispersed in the photosensitive layer and the wear rate by the blade is reduced is used. And the influence of the discharge site on the surface of the photosensitive layer appears remarkably. This is because when the filler is dispersed in the photosensitive layer, the scraping force or pushing force of the discharge site on the outermost surface of the photosensitive layer is reduced due to the reduction of the frictional force of the blade.

  In view of the above problems, the present invention does not cause uneven charging on the surface of the photosensitive layer when the single-layer type photoreceptor is charged using the contact charging method, and also improves the wear resistance of the photosensitive layer. An object is to provide an environment-friendly image forming apparatus.

  In order to achieve the above object, a first configuration of the present invention is an image forming apparatus including a positively charged single layer type photoreceptor and a charging member. In the positively charged single layer type photoreceptor, a photosensitive layer having a single layer structure including a charge generator, a charge transport agent, a filler, and a binder resin is formed on a conductive substrate. The charging member charges the photosensitive layer by applying a charging bias in contact with the photosensitive member. The charging member is a charging roller formed of conductive rubber and applied with a DC voltage as a charging bias, and the photoreceptor has a surface roughness of the photosensitive layer of 80 to 300 μm in terms of an average interval (Sm) of cross-sectional curve irregularities, In addition, the ten-point average roughness (Rz) is 0.45 to 10 μm.

  According to the first configuration of the present invention, in the initial stage of use of the positively charged single layer type photoreceptor, a minute leak from the charging member occurs at the discharge site generated near the surface of the photosensitive layer due to the presence of the charge generating agent that is not deteriorated in discharge. It is possible to effectively suppress a problem that an abnormal discharge image is generated. In addition, when a filler is contained in the photosensitive layer in order to improve the abrasion resistance of the photosensitive layer, the frictional force generated by the cleaning blade is reduced, so the discharge site removal force is also reduced, and charging unevenness continuously occurs for a long time. However, by optimizing the surface roughness of the photosensitive layer, it is possible to achieve both suppression of the occurrence of charging unevenness due to a decrease in the removal ability of the discharge site and an extension of the life of the photoreceptor.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus 100 according to an embodiment of the present invention. Partial enlarged view of the image forming portion Pa in FIG. Schematic diagram showing a discharge state from the charging roller 21 to the surface of the photosensitive drum 1 when the surface of the photosensitive layer is smooth. 3 is a graph showing the surface potential distribution of the photosensitive drum 1 in FIG. Schematic diagram showing a discharge state from the charging roller 21 to the surface of the photosensitive drum 1 when the surface of the photosensitive layer is excessively rough. 5 is a graph showing the surface potential distribution of the photosensitive drum 1 in FIG. Schematic diagram showing a discharge state from the charging roller 21 to the surface of the photosensitive drum 1 when the surface of the photosensitive layer is moderately rough. 7 is a graph showing the surface potential distribution of the photosensitive drum 1 in FIG. The figure which shows the carrier trap in the single layer type photoreceptor and the lamination type photoreceptor typically

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus 100 according to an embodiment of the present invention. In the present embodiment, the image forming apparatus 100 forms images by arranging four photosensitive drums 1a, 1b, 1c, and 1d corresponding to four different colors (magenta, cyan, yellow, and black) in parallel. Consists of a tandem color printer.

  In the apparatus main body of the image forming apparatus 100, four image forming sections Pa, Pb, Pc, and Pd are sequentially arranged from the left side in FIG. These image forming portions Pa to Pd are provided corresponding to images of four different colors (magenta, cyan, yellow, and black), and magenta, cyan, and yellow are respectively subjected to charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Each of the image forming portions Pa to Pd is provided with the above-described photosensitive drums 1a to 1d that carry visible images (toner images) of the respective colors, and further rotate counterclockwise in FIG. An intermediate transfer belt 8 is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1 a to 1 d are sequentially transferred onto the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1 a to 1 d, and then the paper P is transferred by the secondary transfer roller 9. Then, the toner image is transferred onto the sheet P by the fixing device 13 and then discharged from the image forming apparatus 100. While the photosensitive drums 1a to 1d are rotated in the clockwise direction in FIG. 1, an image forming process for the photosensitive drums 1a to 1d is executed.

  The paper P onto which the toner image is transferred is accommodated in a paper cassette 16 disposed in the lower part of the image forming apparatus 100, and is transferred to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b. Be transported. A sheet made of dielectric resin is used for the intermediate transfer belt 8, and a (seamless) belt mainly having no seam is used. The intermediate transfer belt 8 and the secondary transfer roller 9 are rotationally driven at the same linear speed as the photosensitive drums 1a to 1d by a belt drive motor (not shown). A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9 with respect to the rotation direction of the intermediate transfer belt 8.

  Next, the image forming units Pa to Pd will be described. Around the photosensitive drums 1a to 1d disposed rotatably, there are charging devices 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d, and the photosensitive drums 1a to 1d. An exposure unit 5 that performs exposure based on image data, developing devices 3a, 3b, 3c, and 3d that develop the electrostatic latent images formed on the photosensitive drums 1a to 1d with toner, and the photosensitive drums 1a to 1d Are provided with cleaning devices 7a, 7b, 7c and 7d for collecting and removing the developer (toner) remaining after the transfer of the toner image.

  When image data is inputted from a host device such as a personal computer, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d, and then light is irradiated by the exposure unit 5 based on the image data. The electrostatic latent images corresponding to the image data are formed on the respective photosensitive drums 1a to 1d. Each of the developing devices 3a to 3d includes a developing roller (developer carrying member) disposed so as to face the photosensitive drums 1a to 1d, and a predetermined amount of two-component developer containing toners of each color of magenta, cyan, yellow, and black. Filled.

  In addition, when the ratio of the toner in the two-component developer filled in each developing device 3a to 3d falls below a specified value due to the formation of a toner image described later, each developing device 3a to 3d is transferred from the toner container 4a to 4d. Toner is replenished. The toner is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached to form a toner image corresponding to the electrostatic latent image formed by exposure of the exposure unit 5. Is done.

  Then, by applying a predetermined transfer voltage between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by the primary transfer rollers 6a to 6d, magenta, cyan, yellow on the photosensitive drums 1a to 1d and A black toner image is primarily transferred onto the intermediate transfer belt 8. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. The primary transfer rollers 6a to 6d are rotationally driven at the same linear speed as the photosensitive drums 1a to 1d and the intermediate transfer belt 8 by a primary transfer drive motor (not shown). Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning devices 7a to 7d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched over a driven roller 10 and a driving roller 11, and when the intermediate transfer belt 8 starts to rotate counterclockwise as the driving roller 11 is rotated by the belt driving motor, the sheet P is loaded. The sheet is conveyed from the registration roller pair 12b to the nip portion (secondary transfer nip portion) between the secondary transfer roller 9 and the intermediate transfer belt 8 provided adjacent to the intermediate transfer belt 8 at a predetermined timing. A full-color image is secondarily transferred to the image. The sheet P on which the toner image is transferred is conveyed to the fixing device 13.

  The sheet P conveyed to the fixing device 13 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13a to fix the toner image on the surface of the sheet P, and a predetermined full color image is formed. It is formed. The paper P on which the full-color image is formed is distributed in the transport direction by the branching section 14 that branches in a plurality of directions. When an image is formed on only one side of the paper P, it is discharged to the discharge tray 17 by the discharge roller pair 15 as it is.

  On the other hand, when forming images on both sides of the paper P, a part of the paper P that has passed through the fixing device 13 is once projected from the discharge roller pair 15 to the outside of the device. Thereafter, the paper P is distributed to the reverse conveyance path 18 by the branching section 14 by rotating the discharge roller pair 15 in the reverse direction, and is conveyed again to the secondary transfer roller 9 with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the paper P where the image is not formed by the secondary transfer roller 9 and conveyed to the fixing device 13 to fix the toner image, The paper is discharged to the discharge tray 17 by the discharge roller pair 15.

  FIG. 2 is an enlarged sectional view showing the vicinity of the image forming portion Pa in FIG. Around the photosensitive drum 1a, the above-described charging device 2a, developing device 3a, primary transfer roller 6a, and cleaning device 7a are disposed along the rotation direction of the photosensitive drum 1a (clockwise direction in FIG. 2). ing. Among these, the primary transfer roller 6a is disposed at a position facing the photosensitive drum 1a with the intermediate transfer belt 8 interposed therebetween. The photosensitive drum 1a, the charging device 2a, and the cleaning device 7a are unitized. In each of the image forming portions Pa to Pd, units including the photosensitive drums 1a to 1d, the charging devices 2a to 2d, and the cleaning devices 7a to 7d are referred to as drum units 40a to 40d.

  Next, details of each member and apparatus constituting the above-described image forming units Pa to Pd will be described. 2 shows the photosensitive drum 1a disposed in the image forming portion Pa, and the charging device 2a, the developing device 3a, and the cleaning device 7a opposed to the photosensitive drum 1a, but are disposed in the image forming portions Pb to Pd. The configuration and operation of the photosensitive drums 1b to 1d, the charging devices 2b to 2d, the developing devices 3b to 3d, and the cleaning devices 7b to 7d that are opposite to the photosensitive drums 1b to 1d are the same. Reference numerals a to d indicating the photosensitive drums, the charging device, the developing device, and the cleaning device of the portions Pa to Pd are omitted.

  The photosensitive drum 1 is formed by laminating an organic photosensitive layer (OPC) containing a charge generating agent, a charge transport agent, a binder resin (binder), and a filler in the same layer on a conductive substrate (cylinder) such as aluminum. Further, it is a positively charged single layer type photoreceptor. Hereinafter, the conductive substrate and the photosensitive layer will be described in detail.

[Conductive substrate]
The conductive substrate is not particularly limited as long as it can be used as a conductive substrate of a positively charged single layer type photoreceptor. Specifically, a material having at least a surface portion made of a conductive material can be used. For example, it may be made of a conductive material, or may be a plastic material or the like whose surface is covered with a conductive material. Examples of the conductive material include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass. Moreover, as a material which has electroconductivity, the material which has electroconductivity may be used by 1 type, and may be used as an alloy etc., for example, combining 2 or more types. As the material for the conductive substrate, among the above materials, it is preferable to use aluminum or an aluminum alloy that can transfer charges from the photosensitive layer to the conductive substrate.

  The shape of the conductive substrate can be appropriately selected according to the structure of the image forming apparatus to be used. For example, a sheet-like or drum-like substrate can be suitably used. Further, the thickness of the conductive substrate can be appropriately selected according to the shape.

[Photosensitive layer]
The photosensitive layer provided in the positively charged single layer type photoreceptor is a photosensitive layer having a single layer structure including a charge generator, a charge transport agent, a filler, and a binder resin, and the filler is made of a group consisting of silica fine particles and resin fine particles. There is no particular limitation as long as it contains one or more selected fine particles. Hereinafter, the charge generating agent, the charge transport agent, the filler, the binder resin, the additive, and the method for producing the positively charged single layer type photoreceptor, which are the components constituting the photosensitive layer, will be described.

(Charge generator)
The charge generating agent is not particularly limited as long as it can be used as a charge generating agent for a positively charged single layer type photoreceptor. Specifically, for example, phthalocyanine pigments, perylene pigments, bisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, trisazo pigments, indigo pigments, azulenium pigments, cyanine pigments, Powders of inorganic photoconductive materials such as selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, amorphous silicon, pyrylium salts, ansanthrone pigments, triphenylmethane pigments, selenium pigments, toluidine pigments, pyrazoline pigments, Examples include quinacridone pigments.

  Moreover, a charge generation agent may be used independently so that it may have an absorption wavelength in a desired area | region, and may be used in combination of 2 or more type. Further, among the above-mentioned charge generating agents, in particular, in a digital optical image forming apparatus such as a laser beam printer or a facsimile using a light source such as a semiconductor laser, a positively charged single layer having sensitivity in a wavelength region of 700 nm or more Since a type electrophotographic photoreceptor is required, for example, phthalocyanine pigments such as metal-free phthalocyanine and oxotitanyl phthalocyanine are preferably used. The crystal form of the phthalocyanine pigment is not particularly limited, and various types can be used.

  Specific examples of the phthalocyanine pigment include X-type metal-free phthalocyanine (x-H2Pc) represented by the following formula (I) and oxo titanyl phthalocyanine such as α-type and Y-type represented by the following formula (II). Can be mentioned.

Among these, (A) the CuKα characteristic X-ray diffraction spectrum has a main peak at a Bragg angle 2θ ± 0.2 ° = 27.2 °, and (B) in the differential scanning calorimetry, In addition to the accompanying peak, oxotitanyl phthalocyanine having one peak in the range of 50 ° C. or more and 270 ° C. or less,
In addition to the characteristics of (A), and (C) in differential scanning calorimetry, oxo titanyl phthalocyanine having no peak in the range of 50 ° C. or higher and 400 ° C. or lower, other than the peak accompanying vaporization of adsorbed water,
In addition to the characteristics of (A), and (D) in differential scanning calorimetry, there is no peak in the range of 50 ° C. or higher and 270 ° C. or lower except for the peak accompanying vaporization of adsorbed water, and 270 ° C. or higher and 400 or higher. Oxo titanyl phthalocyanine having one peak in the range of 0 ° C. or lower is preferred in terms of sensitivity.

(Charge transport agent)
The charge transfer agent used in the present invention includes one or more materials selected from a hole transfer agent (HTM) and an electron transfer agent (ETM). Hereinafter, the hole transport agent and the electron transport agent will be described in order.

  The hole transport agent (HTM) is not particularly limited as long as it can be used as a hole transport agent contained in the photosensitive layer of the positively charged single layer type photoreceptor. Specifically, for example, benzidine derivatives, oxadiazole compounds such as 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole, 9- (4-diethylaminostyryl) anthracene, etc. Styryl compounds, carbazole compounds such as polyvinylcarbazole, organic polysilane compounds, pyrazoline compounds such as 1-phenyl-3- (p-dimethylaminophenyl) pyrazoline, hydrazone compounds, triphenylamine compounds, indole compounds And nitrogen-containing cyclic compounds such as oxazole compounds, isoxazole compounds, thiazole compounds, and triazole compounds, and condensed polycyclic compounds. Among these hole transport agents, triphenylamine compounds having one or more triphenylamine skeletons in the molecule are more preferable. These hole transport agents may be used alone or in combination of two or more.

  The electron transfer agent (ETM) is not particularly limited as long as it can be used as an electron transfer agent contained in the photosensitive layer of the positively charged single layer type photoreceptor. Specifically, for example, quinone derivatives such as naphthoquinone derivatives, diphenoquinone derivatives, anthraquinone derivatives, azoquinone derivatives, nitroantharaquinone derivatives, dinitroanthraquinone derivatives, malononitrile derivatives, thiopyran derivatives, trinitrothioxanthone derivatives, 3, 4, 5, 7-tetranitro-9-fluorenone derivative, dinitroanthracene derivative, dinitroacridine derivative, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, succinic anhydride, maleic anhydride, dibromoanhydride And maleic acid. These electron transfer agents may be used alone or in combination of two or more.

(Filler)
The filler includes one or more fine particles selected from the group consisting of silica fine particles and resin fine particles. The volume average particle diameter of the filler is 5 nm or more and 5 μm or less. By including such a filler in the photosensitive layer, it is possible to obtain a positively charged single layer type photoreceptor excellent in wear resistance.

  The material of the resin fine particles is not particularly limited as long as the object of the present invention is not impaired. Preferable examples of the material of the resin fine particles include silicone rubber, silicone resin such as organopolysiloxane, polyphenylene sulfide resin, and fluorine-containing resin such as polytetrafluoroethylene resin. As the silicone resin, polysilsesquioxane is preferable, and polymethylsilsesquioxane is more preferable.

  The silica fine particles can be appropriately selected from known silica fine particles as long as the object of the present invention is not impaired. As the silica fine particles, those treated with a surface treatment agent such as a silane coupling agent or silicone oil can also be used.

  The volume average particle diameter of the filler is 5 nm or more and 5 μm or less, more preferably 5 nm or more and 1 μm or less, and particularly preferably 5 nm or more and 0.1 μm or less. When the volume average particle diameter of the filler is excessive, the surface of the photoreceptor tends to be hardly charged and it is difficult to obtain a positively charged single layer type photoreceptor excellent in electrical characteristics.

  The filler may contain other types of fine particles other than silica fine particles and resin fine particles as long as the object of the present invention is not impaired. Other types of fine particles other than silica fine particles and resin fine particles are positively charged single layer type electrophotographic photoreceptors obtained from fine particles such as metal oxide fine particles, inorganic metal salt fine particles, and organic metal salt fine particles. It is selected in consideration of the performance. When the filler includes other types of fine particles other than silica fine particles and resin fine particles, the total content of silica fine particles and resin fine particles in the filler is 80% by mass or more based on the mass of the filler. Is preferable, 90 mass% or more is preferable, and 95 mass% or more is particularly preferable.

(Binder resin)
The binder resin is not particularly limited as long as it can be used as the binder resin contained in the photosensitive layer of the positively charged single layer type electrophotographic photosensitive member. Specific examples of the resin suitably used as the binder resin include polycarbonate resin, styrene resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, styrene-acrylic acid copolymer. Polymer, acrylic copolymer, polyethylene resin, ethylene-vinyl acetate copolymer, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer, vinyl chloride-vinyl acetate copolymer, alkyd resin, polyamide resin, polyurethane Resin, polyarylate resin, polysulfone resin, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyether resin, polyester resin, etc .; silicone resin, epoxy resin, phenol resin, urea resin, melamine resin, Thermosetting resin such as cross-linking thermosetting resins, epoxy acrylate resins, urethane - include photocurable resins such as acrylate copolymer resin. These resins may be used alone or in combination of two or more.

  Among these resins, a photosensitive layer having a good balance of processability, mechanical properties, optical properties, and abrasion resistance can be obtained. Therefore, bisphenol Z-type polycarbonate resins, bisphenol ZC-type polycarbonate resins, and bisphenol C-type polycarbonates are obtained. A resin and a polycarbonate resin such as a bisphenol A type polycarbonate resin are more preferable.

(Additive)
In addition to the charge generating agent, hole transporting agent, electron transporting agent, filler, and binder resin, the photosensitive layer of the positively charged single layer type photoreceptor has various additives within a range that does not adversely affect the electrophotographic characteristics. May be included. Additives that can be incorporated into the photosensitive layer include, for example, antioxidants, radical scavengers, singlet quenchers, UV absorbers and other deterioration inhibitors, softeners, plasticizers, surface modifiers, extenders, Examples thereof include a sticking agent, a dispersion stabilizer, a wax, an acceptor, a donor, a surfactant, and a leveling agent.

  Next, a method for manufacturing the photosensitive drum 1 will be described. The method for producing the photosensitive drum 1 which is a positively charged single layer type photoreceptor is not particularly limited as long as the object of the present invention is not impaired. A preferred example of the method for producing the photosensitive drum 1 includes a method in which a photosensitive layer is formed by applying a coating solution for a photosensitive layer on a conductive substrate. Specifically, a coating solution in which a charge generating agent, a hole transporting agent, an electron transporting agent, a filler, a binder resin, and various additives as necessary are dissolved or dispersed in a solvent is applied onto a conductive substrate. Then, the photosensitive layer can be produced by drying. The application method is not particularly limited, and examples thereof include a method using a spin coater, applicator, spray coater, bar coater, dip coater, doctor blade and the like. Moreover, as a drying method of the coating film formed on the electroconductive base | substrate, the method of hot-air drying etc. on the conditions for 15 to 120 minutes at 80 to 150 degreeC are mentioned, for example.

  The contents of the charge generating agent, hole transporting agent, electron transporting agent, and binder resin in the photosensitive layer are appropriately selected and are not particularly limited. Specifically, for example, the content of the charge generating agent is preferably 0.1 parts by mass or more and 50 parts by mass or less, and more preferably 0.5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin. preferable. 5 mass parts or more and 100 mass parts or less are preferable with respect to 100 mass parts of binder resin, and, as for content of an electron transport agent, 10 mass parts or more and 80 mass parts or less are more preferable. The content of the hole transport agent is preferably 5 parts by mass or more and 500 parts by mass or less, and more preferably 25 parts by mass or more and 200 parts by mass or less with respect to 100 parts by mass of the binder resin. Further, the total content of the hole transport agent and the electron transport agent, that is, the content of the charge transport agent is preferably 20 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the binder resin. More preferably, they are 30 to 200 mass parts.

  The thickness of the photosensitive layer is not particularly limited as long as it has a sufficient function as the photosensitive layer. Specifically, for example, it is preferably 5 μm or more and 100 μm or less, and preferably 10 μm or more and 50 μm or less.

  The solvent contained in the coating solution for the photosensitive layer is not particularly limited as long as each component constituting the photosensitive layer can be dissolved or dispersed. Specifically, alcohols such as methanol, ethanol, isopropanol and butanol; aliphatic hydrocarbons such as n-hexane, octane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; dichloromethane, dichloroethane and tetrachloride Halogenated hydrocarbons such as carbon and chlorobenzene; ethers such as dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as ethyl acetate and methyl acetate Aprotic polar organic solvents such as dimethylformaldehyde, dimethylformamide, and dimethyl sulfoxide. These solvents may be used alone or in combination of two or more.

  Next, the charging device 2, the developing device 3, the primary transfer roller 6, and the cleaning device 7 arranged around the photosensitive drum 1 will be described. The charging device 2 is driven to rotate in contact with the photosensitive drum 1 and is driven to rotate in contact with the charging roller 21 for charging the surface of the photosensitive drum 1 to clean the outer peripheral surface of the charging roller 21. And a cleaning brush 23.

  The charging roller 21 has an elastic layer (rubber layer) formed of a semiconductive elastic material on the outer peripheral surface of a metal core. In the present embodiment, a conductive rubber roller is used in which an elastic layer composed of an epichlorohydrin rubber layer and a coating film made of a polyamide resin laminated on the surface of the epichlorohydrin rubber layer is formed on the outer peripheral surface of the core metal. Yes. The charging roller 21 is rotatably supported by the casing of the charging device 2. The charging roller 21 is in pressure contact with the photosensitive drum 1 with a predetermined nip pressure, and is rotated by being driven by the photosensitive drum 1.

  Further, at the time of image formation, a charging bias having the same polarity (positive polarity) as that of the toner is applied to the charging roller 21. Specifically, the core of the charging roller 21 is electrically connected to a bias control circuit and a charging bias power source (not shown), and a charging bias composed of a DC voltage is applied to the charging roller 21 from the charging bias power source. Is done. The photosensitive layer on the surface of the photosensitive drum 1 can be charged by a current that flows according to the resistance of the elastic layer of the charging roller 21 by applying the charging bias.

  The cleaning brush 23 has a brush portion formed of a resin such as conductive nylon protruding on the outer peripheral surface of the rotating shaft, and the charging roller is rotated by rotating the brush portion in contact with the outer peripheral surface of the charging roller 21. Toner and paper dust adhering to 21 are removed. An input gear (not shown) connected to an output gear (not shown) provided on the rotating shaft of the photosensitive drum 1 is fixed to one end of the rotating shaft of the cleaning brush 23. By the rotational driving force, the charging roller 21 rotates (with rotation) in the same direction on the surface facing the charging roller 21 with a predetermined linear velocity difference. In place of the cleaning brush 23, a cleaning roller made of a sponge roller made of rubber or resin may be used.

  The developing device 3 includes two stirring and conveying members 25 including a stirring and conveying screw and a supply and conveying screw, and a magnetic roller 27. The developing device 3 sensitizes a two-component developer (magnetic brush) carried on the surface of the magnetic roller 27. The electrostatic latent image is developed into a toner image in contact with the surface of the body drum 1. The toner is supplied to the developing device 3 from the toner container 4 (see FIG. 1) via an intermediate hopper (not shown).

  The primary transfer roller 6 transfers the toner image formed on the surface of the photosensitive drum 1 to the intermediate transfer belt 8. The primary transfer roller 6 is connected to a transfer bias power source and a bias control circuit (both not shown) for applying a transfer bias having a polarity opposite to that of the toner.

  The cleaning device 7 includes a cleaning roller 30, a cleaning blade 31, and a toner recovery screw 33. The cleaning roller 30 is in pressure contact with the photosensitive drum 1 at a predetermined pressure, and is driven to rotate in the same direction on the contact surface with the photosensitive drum 1 by a drum cleaning motor (not shown). Residual toner on the surface of the drum 1 is removed and the photosensitive layer on the surface of the photosensitive drum 1 is rubbed and polished using the residual toner. Further, the toner supplied from the developing device 3 is a toner containing an abrasive (abrasive toner). The abrasive toner not only adheres to the electrostatic latent image on the photosensitive drum 1 to form a toner image, but also uses the residual toner that has not been transferred by the primary transfer roller 6 to apply the surface of the photosensitive drum 1 to the surface. Used for polishing.

  The linear velocity of the cleaning roller 30 is controlled to be faster (1.2 times here) than the linear velocity of the photosensitive drum 1. Examples of the cleaning roller 30 include a structure in which a foam layer made of EPDM rubber and having an Asker C hardness of 55 ° is formed as a roller body around a metal shaft. The material of the roller body is not limited to EPDM rubber, but may be a rubber or foamed rubber body of another material, and those having an Asker C hardness of 10 to 90 ° are preferably used.

  A cleaning blade 31 is fixed in contact with the photoconductive drum 1 on the surface of the photoconductive drum 1 downstream of the contact surface with the cleaning roller 30 in the rotation direction. As the cleaning blade 31, for example, a polyurethane rubber blade having a JIS (Japanese Industrial Standards) hardness of 78 ° is used, and is attached at a predetermined angle with respect to the tangential direction of the photoreceptor at the contact point. The material, hardness and dimensions of the cleaning blade 31, the amount of biting into the photosensitive drum 1, the pressure contact force, and the like are appropriately set according to the specifications of the photosensitive drum 1.

  The toner collecting screw 33 discharges the residual toner removed from the surface of the photosensitive drum 1 by the cleaning roller 30 and the cleaning blade 31 to the outside of the cleaning device 7.

  In the image forming apparatus 100 that charges the photosensitive drum 1, which is a positively charged single-layer type photosensitive member, with the charging roller 21 as described above, attention is paid to the relationship between the surface roughness of the photosensitive layer of the photosensitive drum 1 and the charging unevenness. . FIG. 3 is a diagram showing a discharge state from the charging roller 21 to the surface of the photosensitive drum 1 when the surface of the photosensitive layer is smooth, and FIG. 4 is a graph showing a surface potential distribution in FIG. FIG. 5 is a diagram showing a discharge state from the charging roller 21 to the surface of the photosensitive drum 1 when the surface of the photosensitive layer is excessively rough (there is unevenness), and FIG. 6 shows the surface potential distribution in FIG. It is a graph.

  As shown in FIG. 3, when the surface of the photosensitive layer is smooth, the charges moving from the charging roller 21 to the photosensitive drum 1 tend to selectively flow into the discharge sites S existing on the surface of the photosensitive layer. That is, the smoother the photosensitive layer surface, the more concentrated the discharge is at the discharge site S. As shown in FIG. 4, the surface potential unevenness increases, leading to image defects.

  On the other hand, as shown in FIG. 5, when the surface of the photosensitive layer is excessively rough (unevenness is too conspicuous), the charge tends to selectively flow into the convex portions T on the surface of the photosensitive layer. That is, as the unevenness on the surface of the photosensitive layer increases, the discharge concentrates on the convex portion T. Therefore, the surface potential unevenness increases as shown in FIG. 6, leading to an image defect.

  That is, the smoother the surface of the photosensitive layer, the more local discharge due to the influence of the discharge site S of the photosensitive layer becomes. However, as the unevenness of the surface of the photosensitive layer increases, the photosensitive layer becomes more affected than the influence of the discharge site S. It can be seen that the local discharge according to the surface irregularities (air gap distance) becomes dominant.

  FIG. 7 is a diagram showing a discharge state from the charging roller 21 to the surface of the photosensitive drum 1 when the surface of the photosensitive layer is moderately rough (having moderate irregularities), and FIG. 8 is a surface potential distribution in FIG. It is a graph which shows. As shown in FIG. 7, when the surface of the photosensitive layer is moderately rough, the discharge due to the influence of the discharge site and the discharge corresponding to the surface unevenness (air gap distance) are mixed, and in addition to the discharge site S Thus, since the flow of electric charge also occurs in the convex portion T, it can be seen that the unevenness of the surface potential is eliminated as shown in FIG.

  Therefore, in the present invention, the surface of the photosensitive layer is appropriately roughened to create a portion where the gap distance is narrow, and both local discharge due to the influence of the discharge site of the photosensitive layer and local discharge due to surface unevenness (void gap distance) are performed. It was decided to generate. Specifically, if the surface roughness of the photosensitive layer surface is 80 to 300 μm in terms of the average interval (Sm) of the cross-sectional curve irregularities and 0.45 to 10 μm in terms of the ten-point average roughness (Rz), It has been found that uneven charging can be suppressed to a level at which no image defect occurs.

  The surface roughness of the photosensitive layer can be obtained by controlling the surface roughness of the conductive substrate. The surface roughness of the conductive substrate is 50 to 150 μm in Sm and 1.4 to 15 μm in Rz. Then, it was found that the desired surface roughness of the photosensitive layer (Sm of 80 to 300 μm and Rz of 0.45 to 10 μm) can be obtained.

  According to the above configuration, in the initial stage of use of the photosensitive drum 1, a minute leak is generated from the charging roller 21 at the discharge site generated near the surface of the photosensitive layer due to the presence of the charge generating agent that is not deteriorated in discharge, and an abnormal discharge image is generated. The problem of occurring can be effectively suppressed. In addition, when a filler is contained in the photosensitive layer in order to improve the abrasion resistance of the photosensitive layer, the frictional force by the cleaning blade 31 is reduced, so that the discharge site removal force is also reduced, and charging unevenness occurs continuously for a long time. However, by optimizing the surface roughness of the photosensitive layer, it is possible to achieve both the generation of charging unevenness due to the reduction of the removal ability of the discharge sites and the extension of the life of the photosensitive drum 1.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, the material and shape of the charging roller 21 shown in the above embodiment, the charging bias applied to the charging roller 21, and the like are examples, and can be appropriately changed according to the specification of the photosensitive layer of the photosensitive drum 1.

Further, the image forming apparatus of the present invention is not limited to the color printer as shown in FIG. 1, and may be other image forming apparatuses such as monochrome and color copiers, digital multifunction peripherals, monochrome printers, and facsimiles. . Hereinafter, the effects of the present invention will be described in more detail with reference to test examples.
[Test example]

(Production of photosensitive drum)
Charge generator (metal-free phthalocyanine) 5 parts by mass, hole transport agent 50 parts by mass, electron transport agent 35 parts by mass, binder resin (viscosity average molecular weight 67000) 100 parts by mass, filler 5 parts by mass with tetrahydrofuran 800 parts by mass A ball mill was used for mixing and dispersing for 50 hours to prepare a photoreceptor coating solution. This coating solution is applied to an aluminum conductive substrate having a diameter of 30 mm with a different surface roughness by dip coating, followed by hot air drying at 100 ° C. for 40 minutes, and a photosensitive layer having a film thickness of 36 μm and a different surface roughness. 10 types of photosensitive drums 1 (Inventions 1 to 4 and Comparative Examples 1 to 6) were produced.

  The surface roughness of the conductive substrate and the photosensitive layer was measured using a surface roughness measuring instrument (SURFCOM 1500DX, manufactured by Tokyo Seimitsu Co., Ltd.), and the roughness was determined based on the standard of JIS B0601-1994 (the surface of the charging roller). The roughness was determined in the same way).

  The prepared photosensitive drums and charging rollers of the present inventions 1 to 4 and comparative examples 1 to 6 are mounted on a testing machine (FS-C5300DN, manufactured by Kyocera Document Solutions), and test images with a printing rate of 10% to 25% are obtained. The charging unevenness in the case of printing was evaluated by visual observation. The case where no charging unevenness was observed was marked with ◯, and the case where there was charging unevenness was marked with x. The charging roller is made of rubber mainly composed of epichlorohydrin rubber, and has a hardness of 71 °, a diameter of 12 mm, a thickness of the conductive rubber layer of mm, a surface roughness of Rz of 12 μm, and an Sm of 100 μm, and the surface potential of the photoreceptor is 520V. The charging roller application voltage was set so that The evaluation results are shown in Table 1 together with the surface roughness of the conductive substrate and the surface roughness of the photosensitive layer.

  As is apparent from Table 1, the photosensitive drums of the present inventions 1 to 4 have surface roughness of the photosensitive layer of 0.45 to 10 in terms of Rz (μm) and 80 to 300 in terms of Sm (μm). It was confirmed that the occurrence of charging unevenness can be effectively suppressed when using.

  The present invention can be used in an image forming apparatus including a positively charged single layer type photoreceptor and a charging member that is charged in contact with the photoreceptor. By utilizing the present invention, when charging a single-layer type photoreceptor using a charging member, the charging layer does not cause uneven charging, and the abrasion resistance of the photosensitive layer is improved, and the environment is excellent. An image forming apparatus can be provided.

Pa to Pd Image forming portions 1a to 1d, 1 photoconductor drum (positively charged single layer type photoconductor)
2a to 2d, 2 charging device 3a to 3d, 3 developing device 5 exposure unit 6a to 6d, 6 primary transfer roller 7a to 7d, 7 cleaning device 13 fixing device 21 charging roller (charging member)
23 Cleaning brush 30 Cleaning roller 31 Cleaning blade 100 Image forming apparatus

Claims (2)

A positively charged single layer type photoreceptor in which a photosensitive layer having a single layer structure including a charge generating agent, a charge transport agent, a filler, and a binder resin is formed on a conductive substrate;
A charging member that charges the photosensitive layer by applying a charging bias in contact with the photoreceptor;
In an image forming apparatus comprising:
The charging member is a charging roller formed of conductive rubber, to which a DC voltage is applied as a charging bias,
The photosensitive member is characterized in that the surface roughness of the photosensitive layer is 80 to 300 μm in terms of an average interval (Sm) of cross-sectional curve irregularities and 0.45 to 10 μm in terms of a ten-point average roughness (Rz). Image forming apparatus.   The photosensitive member is characterized in that the surface roughness of the conductive substrate is 50 to 150 μm in terms of an average interval (Sm) of cross-sectional curve irregularities and 1.4 to 15 μm in terms of a ten-point average roughness (Rz). The image forming apparatus according to claim 1.

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