JP2018004702A - Electrophotographic photoreceptor, process cartridge, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor that is excellent in sensitivity characteristic and reduces the occurrence of transfer memory.SOLUTION: An electrophotographic photoreceptor comprises a conductive substrate and a photosensitive layer. The photosensitive layer is a single-layer photosensitive layer. The photosensitive layer contains at least a charge generating agent, a hole transport agent, an electron transport agent, and a binder resin. The charge generating agent contains titanyl phthalocyanine. The electron transport agent contains a quinone derivative represented by the formula (2).SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrophotographic photosensitive member, a process cartridge, and an image forming apparatus.

  The electrophotographic photosensitive member is used in an electrophotographic image forming apparatus. The electrophotographic photoreceptor includes a photosensitive layer. The photosensitive layer contains, for example, a charge generator, a charge transport agent (for example, a hole transport agent and an electron transport agent), and a resin (binder resin) that binds them. The photosensitive layer contains a charge generating agent and a charge transport agent in the same layer, and can have both functions of charge generation and charge transport in the same layer. Such an electrophotographic photoreceptor is referred to as a single layer type electrophotographic photoreceptor.

  The photosensitive layer provided in the electrophotographic photoreceptor described in Patent Document 1 contains a phenylbenzofuranone derivative (specifically, a naphthoquinone compound). Patent Document 1 discloses a compound represented by the chemical formula (ET-2).

JP2013-117572A

  However, the electrophotographic photosensitive member described in Patent Document 1 is not sufficient in suppressing sensitivity characteristics and generation of transfer memory.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an electrophotographic photoreceptor excellent in sensitivity characteristics and suppressing generation of a transfer memory. Another object of the present invention is to provide a process cartridge and a process cartridge that suppress the occurrence of image defects (particularly, image defects caused by deterioration of sensitivity characteristics and transfer memory) by including such an electrophotographic photosensitive member. An image forming apparatus is provided.

  The electrophotographic photosensitive member of the present invention includes a conductive substrate and a photosensitive layer. The photosensitive layer is a single-layer type photosensitive layer. The photosensitive layer includes at least a charge generator, a hole transport agent, an electron transport agent, and a binder resin. The charge generator includes titanyl phthalocyanine represented by the following chemical formula (1). The electron transport agent includes a quinone derivative represented by the following general formula (2).

In the general formula (2), R ⁴ and R ⁵ each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

  The process cartridge of the present invention includes the above-described electrophotographic photosensitive member.

  The image forming apparatus of the present invention includes an image carrier, a charging unit, an exposure unit, a developing unit, and a transfer unit. The image carrier is the above-described electrophotographic photosensitive member. The charging unit charges the surface of the image carrier. The charging polarity of the charging unit is positive. The exposure unit exposes the charged surface of the image carrier to form an electrostatic latent image on the surface of the image carrier. The developing unit develops the electrostatic latent image as a toner image. The transfer unit transfers the toner image from the image carrier to a transfer body.

  According to the electrophotographic photosensitive member of the present invention, it has excellent sensitivity characteristics and can suppress the generation of a transfer memory. In addition, according to the process cartridge and the image forming apparatus of the present invention, it is possible to suppress the occurrence of image defects by including such an electrophotographic photosensitive member.

(A), (b), and (c) are schematic sectional views showing the structure of the electrophotographic photosensitive member according to the first embodiment, respectively. It is the schematic which shows the structure of the aspect of the image forming apparatus which concerns on 2nd embodiment.

  Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments. The present invention can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, although description may be abbreviate | omitted suitably about the location where description overlaps, the summary of invention is not limited.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. In addition, when “polymer” is added after the compound name to indicate the polymer name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof.

  Hereinafter, an alkyl group having 1 to 4 carbon atoms has the following meaning unless otherwise specified.

  The alkyl group having 1 to 4 carbon atoms is linear or branched and unsubstituted. Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an s-butyl group, and a t-butyl group.

<First embodiment: electrophotographic photoreceptor>
The first embodiment relates to an electrophotographic photoreceptor (hereinafter sometimes referred to as a photoreceptor). Hereinafter, the photoreceptor of the first embodiment will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view showing the structure of the photoreceptor according to the first embodiment.

  As shown in FIG. 1A, the photoreceptor 1 includes, for example, a conductive substrate 2 and a photosensitive layer 3. The photosensitive layer 3 is provided directly or indirectly on the conductive substrate 2. For example, as shown in FIG. 1A, the photosensitive layer 3 may be provided directly on the conductive substrate 2. As shown in FIG. 1B, the photoreceptor 1 may further include an intermediate layer, and the intermediate layer 4 may be provided between the conductive substrate 2 and the photosensitive layer 3. Further, as shown in FIGS. 1A and 1B, the photosensitive layer 3 may be exposed as the outermost layer. The photoreceptor 1 may further include a protective layer. As shown in FIG. 1C, a protective layer 5 may be provided on the photosensitive layer 3. The structure of the photoreceptor 1 has been described above with reference to FIG.

  The thickness of the photosensitive layer is not particularly limited as long as it can sufficiently function as a photosensitive layer. The thickness of the photosensitive layer is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less.

  The photosensitive layer contains at least a charge generator, a hole transport agent, an electron transport agent, and a binder resin. The charge generating agent contains titanyl phthalocyanine represented by the chemical formula (1) (hereinafter sometimes referred to as titanyl phthalocyanine (1)). The electron transport agent includes a quinone derivative represented by the general formula (2) (hereinafter sometimes referred to as a quinone derivative (2)). The photoconductor according to the first embodiment has excellent electrical characteristics and suppresses the generation of a transfer memory. The reason is presumed as follows.

For convenience, the transfer memory will be described first. In electrophotographic image formation, for example, an image forming process including the following steps 1) to 4) is performed.
1) a charging step for charging the surface of an image carrier (corresponding to a photoreceptor);
2) an exposure step of exposing the surface of the charged image carrier to form an electrostatic latent image on the surface of the image carrier;
3) a developing step of developing the electrostatic latent image as a toner image, and 4) a transferring step of transferring the formed toner image from the image carrier to the transfer member.
In such an image forming process, since the image carrier is rotated and used, a transfer memory may be generated due to the transfer process. Specifically, it is as follows. In the charging process, the surface of the image carrier is uniformly charged to a constant positive potential. Subsequently, through an exposure process and a development process, in the transfer process, a transfer bias having a polarity opposite to that of charging (negative polarity) is applied to the image carrier through the transfer body. Specifically, the potential of the non-exposure area (non-image area) on the surface of the image carrier may be greatly lowered due to the influence of the applied reverse polarity transfer bias, and the lowered state may be maintained. Under the influence of this potential drop, the non-exposed area is less likely to be charged to a desired positive potential in the charging process of the next circumference with reference to the circumference on which the photoreceptor has formed an image. On the other hand, even when a transfer bias is applied, the toner is attached to the exposed area, and therefore, it is difficult to apply the transfer bias directly to the surface of the photosensitive member. . For this reason, the exposure area is easily charged to a desired positive potential in the charging process of the next circumference. As a result, the charged potential differs between the exposed area and the non-exposed area, and it may be difficult to uniformly charge the surface of the image carrier to a constant positive potential. As described above, there is a case where the charging ability of the non-exposed area is lowered due to the influence of the potential drop due to the transfer bias in the image forming process (image forming process) on the front periphery of the photoconductor. Such a phenomenon in which a potential difference occurs in the charging potential is called a transfer memory.

  The quinone derivative (2) has a π-conjugated system with a relatively large spatial extent. For this reason, the quinone derivative (2) has excellent carrier (electron) acceptability, and the carrier (electron) travel distance in the molecule of the quinone derivative (2) tends to increase. That is, the intramolecular movement distance of carriers (electrons) tends to increase. In addition, the plurality of quinone derivatives (2) in the photosensitive layer are likely to overlap each other in π-conjugated system, and the movement distance of carriers (electrons) between molecules of the plurality of quinone derivatives (2) tends to decrease. That is, the intermolecular movement distance of carriers (electrons) tends to decrease. Therefore, the quinone derivative (2) is considered to improve the carrier (electron) acceptability (injection property) and transport property of the photoreceptor. Therefore, it is considered that the photoconductor according to the first embodiment is excellent in sensitivity characteristics and can suppress generation of a transfer memory.

  The photosensitive layer contains titanyl phthalocyanine (1) as a charge generating agent. Since the lowest unoccupied orbital (LUMO) of titanyl phthalocyanine (1) is slightly larger than the LUMO of quinone derivative (2), titanyl phthalocyanine tends to donate carriers (electrons) to quinone derivative (2). For this reason, it is considered that the photoconductor according to the first embodiment is excellent in sensitivity characteristics.

  Next, the elements of the photoreceptor will be described. Hereinafter, the conductive substrate, the charge generator, the hole transport agent, the electron transport agent, and the binder resin will be described. The photosensitive layer may further contain an additive. Furthermore, an additive, an intermediate | middle layer, and the manufacturing method of a photoreceptor are demonstrated.

[1. Conductive substrate]
The conductive substrate is not particularly limited as long as it can be used as the conductive substrate of the photoreceptor. The conductive substrate may be formed of a material having at least a surface portion having conductivity. An example of the conductive substrate is a conductive substrate formed of a conductive material. Another example of the conductive substrate is a conductive substrate coated with a conductive material. Examples of the conductive material include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, and indium. These materials having conductivity may be used alone or in combination of two or more. Examples of the combination of two or more include alloys (more specifically, aluminum alloy, stainless steel, brass, etc.). Among these materials having conductivity, aluminum or an aluminum alloy is preferable because charge transfer from the photosensitive layer to the conductive substrate is good.

  The shape of the conductive substrate is appropriately selected according to the structure of the image forming apparatus. Examples of the shape of the conductive substrate include a sheet shape or a drum shape. The thickness of the conductive substrate is appropriately selected according to the shape of the conductive substrate.

[2. Charge generator]
The charge generator includes titanyl phthalocyanine (1). Titanyl phthalocyanine (1) is represented by chemical formula (1).

  Examples of the titanyl phthalocyanine crystal include α-type crystal, β-type crystal, and Y-type crystal of titanyl phthalocyanine. Hereinafter, α-type crystal, β-type crystal, and Y-type crystal of titanyl phthalocyanine may be referred to as α-type titanyl phthalocyanine, β-type titanyl phthalocyanine, and Y-type titanyl phthalocyanine, respectively. Y-type titanyl phthalocyanine is preferable among the titanyl phthalocyanines because it has a high quantum yield in the wavelength region of 700 nm or more.

  Y-type titanyl phthalocyanine has a main peak at a Bragg angle 2θ ± 0.2 ° = 27.2 ° in a CuKα characteristic X-ray diffraction spectrum. The main peak is one of two peaks having the first and second largest peak intensities within a range where the Bragg angle 2θ ± 0.2 ° of the CuKα characteristic X-ray diffraction spectrum is 3 ° or more and 40 ° or less. Means the peak.

  The X-ray diffraction spectrum is measured as follows. A dispersion liquid is prepared by dispersing 0.3 g of a sample (Y-type titanyl phthalocyanine) in 5.0 g of tetrahydrofuran. Subsequently, the prepared dispersion is stored in a closed system for 7 days under conditions of normal temperature and normal humidity (for example, temperature 23 ° C. ± 1 ° C. and humidity 50% RH to 60% RH). Subsequently, the dispersion after storage is filled in a sample holder of an X-ray diffraction apparatus (for example, “RINT (registered trademark) 1100” manufactured by Rigaku Corporation), and the X-ray tube Cu, tube voltage 40 kV, tube current 30 mA In addition, an X-ray diffraction spectrum is measured under the condition of a CuKα characteristic X-ray wavelength of 1.542 mm. The measurement range (2θ) is, for example, 3 ° to 40 ° (start angle: 3 °, stop angle: 40 °), and the scanning speed is, for example, 10 ° / min. The main peak is determined from the obtained X-ray diffraction spectrum, and the Bragg angle of the main peak is read.

  The charge generator may contain another charge generator in addition to titanyl phthalocyanine (1). Other charge generators include, for example, phthalocyanine pigments (phthalocyanine pigments other than titanyl phthalocyanine (1)), perylene pigments, bisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squara Line pigments, trisazo pigments, indigo pigments, azurenium pigments, cyanine pigments, inorganic photoconductive materials (more specifically, selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, amorphous silicon, etc.) powders, pyrylium salts, An santhrone pigment, triphenylmethane pigment, selenium pigment, toluidine pigment, pyrazoline pigment, or quinacridone pigment may be mentioned. A charge generating agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  Examples of the phthalocyanine pigment include metal-free phthalocyanine or metal phthalocyanine (metal phthalocyanine other than titanyl phthalocyanine (1)). Examples of the crystal of metal-free phthalocyanine include an X-type crystal of metal-free phthalocyanine (hereinafter sometimes referred to as X-type metal-free phthalocyanine). Metal-free phthalocyanine is represented by, for example, chemical formula (CG-1).

  Examples of the metal phthalocyanine include phthalocyanine coordinated with a metal other than titanium oxide (more specifically, V-type hydroxygallium phthalocyanine or chlorogallium phthalocyanine). The phthalocyanine pigment may be crystalline or non-crystalline. Chlorogallium phthalosinin is represented by the chemical formula (CG-3). V-type hydroxygallium phthalocyanine is represented, for example, by the chemical formula (CG-4).

  A charge generator having an absorption wavelength in a desired region may be used alone, or two or more charge generators may be used in combination. Further, for example, in a digital optical image forming apparatus, it is preferable to use a photoconductor having sensitivity in a wavelength region of 700 nm or more. Examples of the digital optical image forming apparatus include a laser beam printer using a light source such as a semiconductor laser, or a facsimile.

  In the case of applying a photoreceptor to an image forming apparatus using a short wavelength laser light source, an ansanthrone pigment or a perylene pigment is preferably used as a charge generating agent. The wavelength of the short wavelength laser light is, for example, not less than 350 nm and not more than 550 nm.

  The content of the charge generating agent is preferably 0.1 parts by mass or more and 50 parts by mass or less, and 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 in the photosensitive layer. More preferred.

[3. Hole transport agent]
Examples of the hole transport agent include oxadiazole-based compounds such as 2,5-di (4-methylaminophenyl) -1,3,4-oxadiazole; 9- (4-diethylaminostyryl) anthracene Styryl compounds such as carbazole compounds such as polyvinyl carbazole; organic polysilane compounds; pyrazoline compounds such as 1-phenyl-3- (p-dimethylaminophenyl) pyrazoline; hydrazone compounds; triphenylamine compounds; Nitrogen-containing cyclic compounds such as oxazole compounds, isoxazole compounds, thiazole compounds, imidazole compounds, pyrazole compounds, or triazole compounds; nitrogen-containing condensed polycyclic compounds such as indole compounds or thiadiazole compounds Compounds. In addition, a hole transport agent may be used individually by 1 type, and may be used in combination of 2 or more type.

  Among these hole transport agents, hole transport agents represented by the following chemical formulas (HT-1) to (HT-8) (hereinafter referred to as hole transport agents (HT-1) to (HT-8), respectively). May be described).

  Among these hole transport agents, hole transport agents (HT-2) to (HT-6) and (HT-8) are preferable from the viewpoint of improving the charging stability of the photoreceptor. Of these hole transport agents, the hole transport agent (HT-5) is preferred from the viewpoint of improving the sensitivity characteristics of the photoreceptor. Of these hole transport agents, hole transport agents (HT-2) to (HT-8) are preferable from the viewpoint of suppressing the generation of transfer memory.

  The content of the hole transport agent is preferably 10 parts by mass or more and 200 parts by mass or less, and more preferably 10 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the binder resin in the photosensitive layer.

  The content of the triphenylamine derivative (1) in the hole transport agent is preferably 80% by mass or more, more preferably 90% by mass or more based on the total mass of the hole transport agent, It is especially preferable that it is 100 mass%.

[4. Electron transport agent]
The electron transport agent includes a quinone derivative (2). The quinone derivative (2) is represented by the general formula (2).

In General Formula (2), R ¹ and R ² each independently represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.

In general formula (2), it is preferable that each of the alkyl groups having 1 to 4 carbon atoms represented by R ¹ and R ² independently represents a methyl group, an isopropyl group, or a t-butyl group, both of which are methyl groups. , An isopropyl group, or a t-butyl group, more preferably a t-butyl group.

Specific examples of the quinone derivative (2) include the quinone derivative (2) shown in Table 1.

  Among these quinone derivatives (2), quinone derivatives represented by chemical formulas (2-1), (2-8), and (2-17) (hereinafter referred to as quinone derivatives (2-1), (2- 8) and (2-17)) are preferable, and the quinone derivative (2-17) is more preferable from the viewpoint of charge stability.

  The electron transport agent may be used in combination with another electron transport agent other than the quinone derivative (2) in addition to the quinone derivative (2). Another electron transport agent is appropriately selected from known electron transport agents.

  Examples of other electron transporting agents include quinone compounds other than the quinone derivative (2), diimide compounds, hydrazone compounds, malononitrile compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7. -Tetranitro-9-fluorenone compound, dinitroanthracene compound, dinitroacridine compound, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, or dibromoanhydride Maleic acid is mentioned. Examples of quinone compounds other than the quinone derivative (2) include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds, and dinitroanthraquinone compounds. These electron transfer agents may be used alone or in combination of two or more.

  The content of the electron transport agent is preferably 5 parts by mass or more and 100 parts by mass or less, and more preferably 10 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the binder resin in the photosensitive layer.

  The content of the quinone derivative (2) in the electron transfer agent is preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass with respect to the total mass of the electron transfer agent. It is particularly preferred.

[5. Binder resin]
The binder resin disperses and fixes a charge generating agent or the like in the photosensitive layer. Examples of the binder resin include a thermoplastic resin, a thermosetting resin, and a photocurable resin. Examples of the thermoplastic resin include polycarbonate resins (more specifically, bisphenol Z type, bisphenol ZC type, bisphenol C type, or bisphenol A type), polyarylate resins, styrene-butadiene resins, styrene-acrylonitrile resins, Styrene-maleic acid resin, acrylic acid resin, styrene-acrylic acid resin, polyethylene resin, ethylene-vinyl acetate resin, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer resin, vinyl chloride-vinyl acetate resin, Examples include alkyd resins, polyamide resins, polyurethane resins, polysulfone resins, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, and polyether resins. Examples of the thermosetting resin include silicone resins, epoxy resins, phenol resins, urea resins, melamine resins, and other crosslinkable thermosetting resins. Examples of the photocurable resin include epoxy-acrylic acid resins and urethane-acrylic acid resins. Of these binder resins, polycarbonate resins are preferable, and bisphenol Z-type polycarbonate resins are more preferable. Bisphenol Z-type polycarbonate resin has a repeating unit represented by the chemical formula (Resin-1). Hereinafter, the binder resin having a repeating unit represented by the chemical formula (Resin-1) may be referred to as a bisphenol Z-type polycarbonate resin (Resin-1). In addition, a binder resin may be used individually by 1 type, and may be used in combination of 2 or more type.

  The viscosity average molecular weight of the binder resin is preferably 40,000 or more, and more preferably 40,000 or more and 52,500 or less. When the viscosity average molecular weight of the binder resin is 40,000 or more, the abrasion resistance of the binder resin can be sufficiently increased, and the photosensitive layer is hardly worn. Further, when the viscosity average molecular weight of the binder resin is 52,500 or less, the binder resin is easily dissolved in the solvent at the time of forming the photosensitive layer, and the viscosity of the coating solution for the photosensitive layer does not become too high. As a result, it becomes easy to form a photosensitive layer.

[6. Additive]
The photosensitive layer may contain various additives as long as the electrophotographic characteristics of the photoreceptor are not adversely affected. Examples of the additive include a deterioration inhibitor (more specifically, an antioxidant, a radical scavenger, a quencher, or an ultraviolet absorber), a softener, a surface modifier, a bulking agent, a thickener, A dispersion stabilizer, wax, acceptor, donor, surfactant, plasticizer, sensitizer, or leveling agent may be mentioned. Examples of the antioxidant include hindered phenol, hindered amine, paraphenylenediamine, arylalkane, hydroquinone, spirochroman, spiroidanone, or a derivative thereof, an organic sulfur compound, or an organic phosphorus compound.

[7. Middle layer]
An intermediate | middle layer contains an inorganic particle and resin (resin for intermediate | middle layers), for example. The presence of the intermediate layer makes it easy to suppress a rise in resistance by smoothing the flow of current generated when the photosensitive member is exposed while maintaining an insulating state to the extent that leakage can be suppressed.

  Examples of the inorganic particles include metal (more specifically, aluminum, iron, copper, etc.) particles, metal oxide (more specifically, titanium oxide, alumina, zirconium oxide, tin oxide, or zinc oxide). Etc.) or non-metal oxide (more specifically, silica etc.) particles. These inorganic particles may be used individually by 1 type, and may use 2 or more types together.

  The resin for the intermediate layer is not particularly limited as long as it is used as a resin for forming the intermediate layer.

  The intermediate layer may contain various additives as long as the electrophotographic characteristics of the photoreceptor are not adversely affected. The additive is the same as the additive for the photosensitive layer.

[8. Photoconductor manufacturing method]
Next, an example of a method for manufacturing the photoreceptor 1 will be described with reference to FIG. The method for manufacturing the photoreceptor 1 includes, for example, a photosensitive layer forming step. In the photosensitive layer forming step, the photosensitive layer coating solution is applied onto the conductive substrate 2, and the solvent contained in the applied photosensitive layer coating solution is removed to form the photosensitive layer 3. The photosensitive layer coating solution contains at least titanyl phthalocyanine (1) as a charge generating agent, a hole transport agent, a quinone derivative (2) as an electron transport agent, a binder resin, and a solvent. The photosensitive layer coating solution is obtained by dissolving or dispersing in a solvent a titanyl phthalocyanine (1) as a charge generating agent, a hole transporting agent, a quinone derivative (2) as an electron transporting agent, and a binder resin. Prepared. You may add an electron transport agent and various additives to the coating liquid for photosensitive layers as needed.

  The solvent contained in the photosensitive layer coating solution is not particularly limited as long as each component contained in the photosensitive layer coating solution can be dissolved or dispersed. Examples of the solvent include alcohols (more specifically, methanol, ethanol, isopropanol, butanol, etc.), aliphatic hydrocarbons (more specifically, n-hexane, octane, cyclohexane, etc.), aromatics, and the like. Hydrocarbons (more specifically, benzene, toluene, xylene, etc.), halogenated hydrocarbons (more specifically, dichloromethane, dichloroethane, carbon tetrachloride, etc.), ethers (more specifically, , Dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, or diethylene glycol dimethyl ether), ketones (more specifically, acetone, methyl ethyl ketone, cyclohexanone, etc.), esters (more specifically, ethyl acetate, or acetic acid) Me Le etc.), dimethyl formaldehyde, N, N-dimethylformamide (DMF), or dimethylsulfoxide. These solvents may be used alone or in combination of two or more. Of these solvents, solvents other than halogenated hydrocarbons are preferred in order to improve the workability during production of the photoreceptor 1.

  The photosensitive layer coating solution is prepared by mixing each component and dispersing in a solvent. For mixing or dispersing, for example, a bead mill, a roll mill, a ball mill, an attritor, a paint shaker, or an ultrasonic disperser is used.

  The photosensitive layer coating solution may contain, for example, a surfactant or a leveling agent in order to improve the dispersibility of each component or the surface smoothness of each formed layer.

  The method for applying the photosensitive layer coating solution is not particularly limited as long as it is a method that can uniformly apply the photosensitive layer coating solution onto the conductive substrate 2. Examples of the coating method include a dip coating method, a spray coating method, a spin coating method, and a bar coating method.

  The method for removing the solvent contained in the photosensitive layer coating solution is not particularly limited as long as it is a method capable of evaporating the solvent in the photosensitive layer coating solution. Examples of the method for removing the solvent include heating, reduced pressure, or combined use of heating and reduced pressure. More specifically, a method of heat treatment (hot air drying) using a high-temperature dryer or a vacuum dryer can be mentioned. The heat treatment conditions are, for example, a temperature of 40 ° C. or higher and 150 ° C. or lower and a time of 3 minutes or longer and 120 minutes or shorter.

  In addition, the manufacturing method of the photoreceptor 1 may further include a step of forming the intermediate layer 4 and / or a step of forming the protective layer 5 as necessary. In the step of forming the intermediate layer 4 and the step of forming the protective layer 5, a known method is appropriately selected.

  For example, the photoreceptor 1 is used as an image carrier in an image forming apparatus. The image forming apparatus described later in the second embodiment includes a charging unit that contacts the image carrier and applies a DC voltage to the image carrier.

  Heretofore, the photoreceptor 1 according to the first embodiment has been described with reference to FIG. The photoreceptor 1 according to the first embodiment is excellent in sensitivity characteristics and can suppress the generation of a transfer memory.

<Second Embodiment: Image Forming Apparatus>
The second embodiment relates to an image forming apparatus. The image forming apparatus according to the second embodiment includes an image carrier, a charging unit, an exposure unit, a developing unit, and a transfer unit. The charging unit charges the surface of the image carrier. The exposure unit exposes the surface of the charged image carrier to form an electrostatic latent image on the surface of the image carrier. The developing unit develops the electrostatic latent image as a toner image. The transfer unit transfers the toner image from the image carrier to the transfer body. The image carrier is the electrophotographic photosensitive member according to the first embodiment. The charging polarity of the charging unit is positive.

  The image forming apparatus according to the second embodiment can suppress image defects. Examples of such an image defect include an image defect caused by a decrease in sensitivity characteristics and the generation of a transfer memory. The reason is presumed as follows. The image forming apparatus according to the second embodiment includes the photoconductor according to the first embodiment as an image carrier. The photoreceptor according to the first embodiment has excellent sensitivity characteristics and can suppress the generation of a transfer memory. Therefore, the image forming apparatus according to the second embodiment can suppress image defects.

  Hereinafter, the image forming apparatus 100 according to the second embodiment will be described with reference to FIG. FIG. 2 is a schematic diagram illustrating a configuration of one aspect of the image forming apparatus 100 according to the second embodiment.

  The image forming apparatus 100 is not particularly limited as long as it is an electrophotographic image forming apparatus. The image forming apparatus 100 may be, for example, a monochrome image forming apparatus or a color image forming apparatus. When the image forming apparatus 100 is a color image forming apparatus, the image forming apparatus 100 employs, for example, a tandem method. Hereinafter, the tandem image forming apparatus 100 will be described as an example.

  The image forming apparatus 100 includes image forming units 40a, 40b, 40c, and 40d, a transfer belt 50, and a fixing unit 52. Hereinafter, when it is not necessary to distinguish, each of the image forming units 40a, 40b, 40c, and 40d is referred to as an image forming unit 40.

  The image forming unit 40 includes an image carrier, a charging unit 42, an exposure unit 44, a developing unit 46, and a transfer unit 48. An image carrier is provided at the center position of the image forming unit 40. The image carrier is provided to be rotatable in the arrow direction (counterclockwise). Around the image carrier, a charging unit 42, an exposure unit 44, a developing unit 46, and a transfer unit 48 are provided in this order from the upstream side in the rotation direction of the image carrier with reference to the charging unit 42. The image forming unit 40 may further include one or both of a cleaning unit (not shown) and a charge removal unit (not shown).

  The charging unit 42 charges the surface of the image carrier. The charging polarity of the charging unit is positive. The charging unit 42 is a non-contact type or contact type charging unit. Examples of the non-contact charging unit 42 include a corotron charger and a scorotron charger. Examples of the contact-type charging unit 42 include a charging roller or a charging brush.

  The exposure unit 44 exposes the surface of the charged image carrier. As a result, an electrostatic latent image is formed on the surface of the image carrier. The electrostatic latent image is formed based on image data input to the image forming apparatus 100.

  The developing unit 46 supplies toner to the surface of the image carrier and develops the electrostatic latent image as a toner image.

  The transfer belt 50 conveys the recording medium P between the image carrier and the transfer unit 48. The transfer belt 50 is an endless belt. The transfer belt 50 is provided to be rotatable in the arrow direction (clockwise).

  The transfer unit 48 transfers the toner image developed by the developing unit 46 from the surface of the image carrier to the recording medium P. When the toner image is transferred from the image carrier to the recording medium P, the image carrier is in contact with the recording medium P. That is, the image forming apparatus 100 employs a so-called direct transfer method. An example of the transfer unit 48 is a transfer roller.

  Each of the image forming units 40a to 40d sequentially superimposes toner images of a plurality of colors (for example, four colors of black, cyan, magenta, and yellow) on the recording medium P on the transfer belt 50. When the image forming apparatus 100 is a monochrome image forming apparatus, the image forming apparatus 100 includes an image forming unit 40a, and the image forming units 40b to 40d are omitted.

  The fixing unit 52 heats and / or pressurizes the unfixed toner image transferred to the recording medium P by the transfer unit 48. The fixing unit 52 is, for example, a heating roller and / or a pressure roller. The toner image is fixed on the recording medium P by heating and / or pressurizing the toner image. As a result, an image is formed on the recording medium P.

  The image forming apparatus 100 can include a charging roller as the charging unit 42. When charging the surface of the image carrier, the charging roller comes into contact with the surface of the image carrier. Usually, in an image forming apparatus including a charging roller, a transfer memory is likely to occur. However, the image forming apparatus 100 includes the photoconductor according to the first embodiment as an image carrier. The photoconductor according to the first embodiment can suppress the generation of a transfer memory. Therefore, the image forming apparatus according to the second embodiment can suppress the occurrence of image defects due to the generation of the transfer memory even when the charging unit 42 includes a charging roller.

  The voltage applied by the charging unit 42 is not particularly limited, and examples thereof include a DC voltage, an AC voltage, or a superimposed voltage obtained by superimposing a DC current on an AC current. When the charging unit 42 applies only a DC voltage, the voltage value applied to the image carrier is constant, so that the surface of the image carrier is easily charged uniformly to a constant potential. Further, when the charging unit 42 applies only a DC voltage, the wear amount of the photosensitive layer 3 tends to decrease. As a result, a suitable image can be formed.

  Usually, a direct-current voltage tends to generate a transfer memory as compared with an alternating-current voltage. However, the image forming apparatus 100 according to the second embodiment includes the photoconductor according to the first embodiment as an image carrier. The photoconductor according to the first embodiment can suppress the generation of a transfer memory. Therefore, the image forming apparatus 100 according to the second embodiment can suppress the occurrence of image defects due to the transfer memory even if the charging unit that applies a DC voltage in contact with the image carrier is provided.

  The image forming apparatus 100 employs a direct transfer method. Usually, in an image forming apparatus that employs a direct transfer method, an image carrier is likely to be affected by a transfer bias, and thus a transfer memory is usually easily generated. However, the image forming apparatus 100 according to the second embodiment includes the photoreceptor 1 according to the first embodiment as an image carrier. The photoconductor according to the first embodiment can suppress the generation of a transfer memory. Therefore, when the photoreceptor 1 according to the first embodiment is provided as an image carrier, it is considered that the occurrence of image defects caused by the transfer memory can be suppressed even when the image forming apparatus 100 adopts the direct transfer method. It is done.

  The image forming apparatus according to the second embodiment has been described above. The image forming apparatus according to the second embodiment can suppress the occurrence of image defects by including the photoconductor according to the first embodiment as an image carrier.

<Third embodiment: Process cartridge>
The third embodiment relates to a process cartridge. A process cartridge according to the third embodiment includes the photoconductor according to the first embodiment. Next, the process cartridge according to the third embodiment will be described with reference to FIG. The process cartridge includes a unitized image carrier. The process cartridge employs a configuration in which at least one selected from the group consisting of a charging unit 42, an exposure unit 44, a developing unit 46, and a transfer unit 48 is unitized in addition to the image carrier. The process cartridge corresponds to each of the image forming units 40a to 40d, for example. The process cartridge may further include one or both of a cleaning device (not shown) and a static eliminator (not shown). The process cartridge is designed to be detachable from the image forming apparatus 100. Therefore, the process cartridge is easy to handle, and when the sensitivity characteristics and the like of the image carrier are deteriorated, the process cartridge including the image carrier can be easily and quickly replaced.

  The process cartridge according to the third embodiment has been described above. The process cartridge according to the third embodiment can suppress the occurrence of image defects by including the photoconductor according to the first embodiment as an image carrier.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the scope of the examples.

<1. Photosensitive Material>
(1-1. Charge generator)
The following charge generator, hole transport agent, electron transport agent, and binder resin were prepared as materials for forming the photosensitive layer of the photoreceptor. As the charge generating agent, the charge generating agents (CG-1) to (CG-4) described in the first embodiment were prepared. The charge generating agent (CG-1) was a metal-free phthalocyanine represented by the chemical formula (CG-1) (hereinafter sometimes referred to as metal-free phthalocyanine (CG-1)). The crystal structure of metal-free phthalocyanine (CG-1) was X-type.

  The charge generating agent (CG-2) is titanyl phthalocyanine (1). The crystal structure of titanyl phthalocyanine (1) was Y-type. The X-ray diffraction spectrum had peaks at 9.7 °, 11.7 °, 15.0 °, 23.5 °, and 27.3 °. The main peak was 27.3 °.

  The charge generating agent (CG-3) was chlorogallium phthalocyanine represented by the chemical formula (CG-3) (hereinafter sometimes referred to as chlorogallium phthalocyanine (CG-3)). The main peaks in the X-ray diffraction spectrum were 7.4 °, 16.6 °, 25.5 ° and 28.3 °, and the maximum peak was 7.4 °.

  The charge generating agent (CG-4) was hydroxygallium phthalocyanine represented by the chemical formula (CG-4) (hereinafter sometimes referred to as hydroxygallium phthalocyanine (CG-4)). The crystal structure of hydroxygallium phthalocyanine (CG-4) was V-type. The main peaks in the X-ray diffraction spectrum are 7.5 °, 9.9 °, 12.5 °, 16.3 °, 18.6 °, 25.1 °, 28.3 °, and the maximum peak is 7. It was 5 °.

(1-2. Hole transport agent)
Among the hole transport agents described in the first embodiment, hole transport agents (HT-1) to (HT-8) were prepared as the hole transport agents.

(1-3. Electron transport agent)
Among the quinone derivatives (2) described in the first embodiment, quinone derivatives (2-1), (2-8), and (2-17) were prepared as electron transport agents. In addition, a compound represented by the chemical formula (ET-2) (hereinafter sometimes referred to as compound (ET-2)) was prepared as an electron transport agent.

(1-4. Binder resin)
As the binder resin, the bisphenol Z-type polycarbonate resin (Resin-1) described in the first embodiment was prepared.

<2. Manufacture of photoconductor>
Photoconductors (A-1) to (A-12) and (B-1) to (B-8) were produced using the material for forming the photosensitive layer of the prepared photoconductor.

(2-1. Production of Photosensitive Member (A-1))
In the container, 5 parts by mass of a charge generating agent (CG-2), 50 parts by mass of a hole transporting agent (HT-1), 35 parts by mass of an electron transporting agent (2-1), and a binder resin (Resin-1) ) 100 parts by mass and 750 parts by mass of tetrahydrofuran as a solvent were added. The contents of the container were mixed and dispersed for 50 hours using a ball mill to prepare a photosensitive layer coating solution.

  Using a dip coating method, a coating solution for a photosensitive layer was applied on a conductive substrate to form a coating film on the conductive substrate. Then, it was made to dry for 40 minutes at 100 degreeC, and tetrahydrofuran was removed from the coating film. As a result, a photoreceptor (A-1) having a 35 μm-thick photosensitive layer on a conductive substrate was obtained.

(2-2. Production of photoconductors (A-2) to (A-15), (A-22) to (A-30) and (B-1) to (B-24))
Except for the following changes, the photoconductors (A-2) to (A-15), (A-22) to (A-30), and (B-1) to (B-24) were produced. To the compound represented by the quinone derivative (2-1) as the charge generating agent (CG-2), the hole transporting agent (HT-1), and the electron transporting agent used for the production of the photoreceptor (A-1) Instead, the types of charge generating agents (CGM), hole transporting agents (HTM), and electron transporting agents (ETM) shown in Tables 2 and 3 were used.

<3. Evaluation of photoconductor>
(3-1. Evaluation of charging stability)
For each of the photoreceptors (A-1) to (A-15), (A-22) to (A-30) and (B-1) to (B-24), the stability of the surface potential during charging (Charging stability) was evaluated.

  The photoreceptor was mounted on an image forming apparatus (“FS-C5250DN” manufactured by Kyocera Document Solutions Inc.). This image forming apparatus includes a contact-type charging roller that applies a DC voltage as a charging unit. The chargeable sleeve is formed of a chargeable rubber in which conductive carbon is dispersed in epichlorohydrin resin. The charging voltage of the charging unit was set to +1.4 kV.

The charging voltage was continuously applied to the photoreceptor using the charging unit for 30 minutes. During the application of the charging voltage for 30 minutes to the photoconductor, the surface potential of the photoconductor was continuously measured. The surface potential of the photoreceptor immediately after the start of the application of the charging voltage was + 570 ± 30V. The maximum value of the surface potential of the photoconductor measured in applying the charging voltage was V ₀ (unit: V), and the minimum value was V ₁ (unit: V). The measurement environment was a temperature of 23 ° C. and a relative humidity of 50% RH.

From the measured maximum value V ₀ and minimum value V ₁ of the surface potential of the photoreceptor, a difference in surface potential ΔV ₀ was obtained using the formula “ΔV ₀ = V ₁ −V ₀ ”. Table 2 shows the difference ΔV ₀ in the surface potential of the photoconductor. The smaller the absolute value of the surface potential difference ΔV ₀ of the photoconductor, the more stable the surface potential of the photoconductor during charging.

(3-2. Evaluation of sensitivity characteristics and transfer memory)
The charging stability of each of the photoreceptors (A-1) to (A-15), (A-22) to (A-30), and (B-1) to (B-24) was evaluated. .

  The photoreceptor was mounted on an image forming apparatus (“FS-C5250DN” manufactured by Kyocera Document Solutions Inc.). This image forming apparatus includes a contact-type charging roller that applies a DC voltage as a charging unit. Further, this image forming apparatus employs a direct transfer system in which a toner image is directly placed on an intermediate transfer belt. The charging sleeve is provided on the surface of the charging roller, and is formed of a charging rubber whose main constituent material is epichlorohydrin resin. The charging voltage of the charging unit was adjusted, and the charging potential (blank portion potential Vs) of the photosensitive member corresponding to the developing unit position during non-exposure was set to 570V ± 10V.

Next, monochromatic light was extracted from the white light of the halogen lamp using a bandpass filter. The extracted monochromatic light was measured for the charged potential of the photoreceptor corresponding to the development position when exposed to laser light having a wavelength of 780 nm, a half width of 20 nm, and a light energy of 1.16 μJ / cm ² . The surface potential of the measured exposure area was defined as a sensitivity potential V _L (unit: V). The measured surface potential of the non-exposed area was defined as the blank portion potential V ₃ (unit: V). Incidentally, the sensitivity potential V _L and the blank portion potential V ₃ was measured in a state of turning off the transfer bias. Subsequently, a transfer bias of −2 kV was applied, and the surface potential of the non-exposed area (blank area) was measured with the transfer bias turned on. The surface potential of the obtained non-exposed area (white paper portion) was defined as a white paper portion potential V ₄ . A transfer memory potential ΔVtc (unit: V) was obtained from the obtained V ₃ and V _{4 using the} mathematical expression “transfer memory potential ΔVtc = V ₄ −V ₃ ”. The measurement environment was a temperature of 23 ° C. and a relative humidity of 50% RH.

The obtained sensitivity potential V _L and transfer memory potential ΔVtc are shown in Tables 2 and 3. In addition, it shows that the sensitivity characteristic of a photoreceptor is excellent, so that the value of the sensitivity potential _VL is small. The smaller the absolute value of the transfer memory potential ΔVtc, the lower the occurrence of the transfer memory.

  In Tables 2 and 3, “CGM”, “HTM”, and “ETM” in the “Material” column respectively represent a charge generating agent, a hole transporting agent, and an electron transporting agent.

  As shown in Table 2, in the photoreceptors (A-1) to (A-15) and (A-22) to (A-30), the photosensitive layer has a quinone derivative (2-1) as an electron transport agent, Any of (2-8) and (2-17) is included. The quinone derivatives (2-1), (2-8), and (2-17) are quinone derivatives represented by the general formula (2). In the photoreceptors (A-1) to (A-15) and (A-22) to (A-30), the photosensitive layer contains a charge generating agent (CG-2). The charge generating agent (CG-2) is titanyl phthalocyanine represented by the chemical formula (1).

As shown in Table 2, in the photoreceptors (A-1) to (A-15) and (A-22) to (A-30), the sensitivity potential (V _L ) is + 82V or more and + 122V or less. The difference (ΔVtc) in the transfer memory potential is −45V or more and −28V or less.

  As shown in Table 3, in the photoreceptors (B-1) to (B-24), the photosensitive layer contains a quinone derivative (2-17) or a compound (ET-2) as an electron transport agent, and is a charge generator. (CG-1), (CG-2), (CG-3), or (CG-4) is included. Specifically, in the photoreceptors (B-1) to (B-5), (B-7) to (B-18), and (B-20) to (B-24), the photosensitive layer is used as an electron transport agent. Including compound (ET-2). The compound (ET-2) is not a quinone derivative represented by the general formula (2). In the photoconductors (B-1) to (B-6), the photosensitive layer contains a charge generating agent (CG-1). In the photoconductors (B-12) to (B-13) and (B-23), the photosensitive layer contains a charge generating agent (CG-3). In the photoreceptors (B-14) to (B-15) and (B-24), the photosensitive layer contains a charge generating agent (CG-4). The charge generators (CG-1) and (CG-3) to (CG-4) are not charge generators represented by the chemical formula (1).

As shown in Table 3, in the photoreceptors (B-1) to (B-24), the sensitivity potential (V _L ) is + 142V or more and + 176V or less. In the photoconductors (B-1) to (B-24), the difference (ΔVtc) in the transfer memory potential is −82 V or more and −45 V or less.

Therefore, the photoreceptors (A-1) to (A-15) and (A-22) to (A-30) have a sensitivity potential V _{L as} compared with the photoreceptors (B-1) to (B-24). It is clear that the absolute value of the difference ΔVtc in the transfer memory potential is small. From the above, it is clear that the photoreceptor according to the present invention has excellent sensitivity characteristics and suppresses the generation of a transfer memory.

As shown in Table 2, in the photoreceptor (A-15), the photosensitive layer contains a quinone derivative (2-17) as an electron transport agent. The surface potential difference ΔV ₀ is −46V.

As shown in Table 2, in the photoreceptors (A-13) and (A-14), the photosensitive layer contains a quinone derivative (2-1) or (2-8) as an electron transport agent. The surface potential difference ΔV ₀ is −75 V and −50 V, respectively.

  The tendency of such photoconductors (A-13) to (A-15) is as follows: photoconductors (A-1) to (A-3), (A-4) to (A-6), (A-7). ) To (A-9), (A-10) to (A-12), (A-22) to (A-24), (A-25) to (A-27), and (A-28) It is also confirmed in (A-30).

  From the above, it is clear that the quinone derivative (2-17) has excellent charging stability compared to the quinone derivatives (2-1) and (2-8).

As shown in Table 2, in the photoreceptors (A-4) to (A-15), (A-22) to (A-24), and (A-28) to (A-30), hole transport is performed. Agents (HT-2), (HT-3), (HT-4), (HT-5), (HT-6), or (HT-8). The surface potential difference ΔV ₀ is −82 V or more and −40 V or less.

As shown in Table 2, in the photoreceptors (A-1) to (A-3) and (A-25) to (A-27), the hole transport agent (HT-1) or (HT-7) is used. Including. The surface potential difference ΔV ₀ is −120 V or more and −103 V or less.

  From the above, photoconductors (A-4) to (A-15), (A-22) to (A-24) containing hole transporting agents (HT-2) to (HT-6) or (HT-8). ), And (A-28) to (A-30) are photoconductors (A-1) to (A-3) and (A-) containing a hole transport agent (HT-1) or (HT-7). It is clear that the charging stability is excellent as compared with 25) to (A to 27).

  As shown in Table 2, in the photoreceptors (A-4) to (A-15) and (A-22) to (A-30), the photosensitive layer is formed of the hole transport agents (HT-2) to (HT). -8). In the photoconductors (A-4) to (A-15) and (A-22) to (A-30), the potential difference (ΔVtc) of the transfer memory is −39V or more and −28V or less.

  As shown in Table 2, in the photoreceptors (A-1) to (A-3), the photosensitive layer contains a hole transport agent (HT-1). In the photoconductors (A-1) to (A-3), the potential difference (ΔVtc) of the transfer memory is −45V or more and −42V or less.

  From the above, the photoreceptors (A-4) to (A-15) and (A-22) to (A-30) containing the hole transporting agents (HT-2) to (HT-8) are transported by holes. It is apparent that the generation of the transfer memory is further suppressed as compared with the photoconductors (A-1) to (A-3) containing the agent (HT-1).

  The photoreceptor according to the present invention can be suitably used as an electrophotographic photoreceptor.

1 electrophotographic photoreceptor 2 conductive substrate 3 photosensitive layer

Claims (10)

An electrophotographic photosensitive member comprising a conductive substrate and a photosensitive layer,
The photosensitive layer is a single-layer type photosensitive layer,
The photosensitive layer includes at least a charge generator, a hole transport agent, an electron transport agent, and a binder resin,
The charge generator includes titanyl phthalocyanine represented by the following chemical formula (1):
The electron transport agent is an electrophotographic photoreceptor containing a quinone derivative represented by the following general formula (2).

In the general formula (2),
R ¹ and R ² each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. In the general formula (2),
The electrophotographic photoreceptor according to claim ^1, wherein R ¹ and R ² each represent a methyl group, an isopropyl group, or a t-butyl group. In the general formula (2),
The electrophotographic photosensitive member according to claim ^1, wherein R ¹ and R ² both represent a t-butyl group. The hole transport agent has chemical formula (HT-1), chemical formula (HT-2), chemical formula (HT-3), chemical formula (HT-4), chemical formula (HT-5), chemical formula (HT-6), chemical formula. The electrophotographic photoreceptor according to any one of claims 1 to 3, comprising a compound represented by (HT-7) or a chemical formula (HT-8).

  The hole transport agent may be the compound (HT-2), (HT-3), (HT-4), (HT-5), (HT-6), (HT-7), or (HT-8). The electrophotographic photosensitive member according to claim 4, comprising the compound represented by:   The hole transport agent is represented by the chemical formula (HT-2), (HT-3), (HT-4), (HT-5), (HT-6), or (HT-8). The electrophotographic photoreceptor according to claim 4 or 5, comprising a compound.   A process cartridge comprising the electrophotographic photosensitive member according to claim 1. An image carrier;
A charging unit that charges the surface of the image carrier;
An exposure unit that exposes the surface of the charged image carrier to form an electrostatic latent image on the surface of the image carrier;
A developing unit for developing the electrostatic latent image as a toner image;
A transfer unit that transfers the toner image from the image carrier to a transfer body,
The charging polarity of the charging part is positive.
The image forming apparatus according to claim 1, wherein the image carrier is the electrophotographic photosensitive member according to claim 1.   The image forming apparatus according to claim 8, wherein the charging unit is in contact with the image carrier and applies a DC voltage to the image carrier.   The image forming apparatus according to claim 8, wherein the transfer body is a recording medium.

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