Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor, process cartridge, and image forming apparatus that offer excellent wear resistance and can suppress image blurring. [Solution] The electrophotographic photoreceptor comprises a conductive substrate, a photosensitive layer, and a protective layer. The photosensitive layer is provided on the conductive substrate. The protective layer is provided on the photosensitive layer. The protective layer has a substrate made of a graft polymer having the composition of a UV (ultraviolet) curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, n-type conductive fine particles dispersed in the substrate, and metal oxide fine particles dispersed in the substrate, and has a Martens hardness of 400 N / mm². 2 The above and the volume resistivity is 1.0 × 10⁻⁶ 10 It is greater than or equal to Ω·cm.

Description

[Technical Field]

[0001] This technology relates to an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus used in electrophotographic printing. [Background technology]

[0002] Electrophotographic photoreceptors are used as image carriers in electrophotographic image forming devices such as printers. An electrophotographic photoreceptor has a photosensitive layer laminated on a conductive substrate, with the photosensitive layer comprising a thermoplastic binder resin in which a functional material is dispersed. With repeated use, the photosensitive layer wears down, and the electrophotographic photoreceptor reaches its limit thickness, at which point it reaches the end of its lifespan. In contrast, electrophotographic photoreceptors have been reported that dramatically improve wear resistance and achieve a longer lifespan by forming a protective layer on the photosensitive layer using a thermosetting resin or a photocurable resin (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-152701 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in electrophotographic photoreceptors, image blurring (a phenomenon where the image appears blurred) under high-temperature and high-humidity environments due to the effects of discharge products is a problem. The inventors of this invention investigated an electrophotographic photoreceptor that has excellent wear resistance and can suppress image blurring.

[0005] In light of the above circumstances, the objective of this technology is to provide an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus that have excellent wear resistance and can suppress image flow. [Means for solving the problem]

[0006] To achieve the above objective, an electrophotographic photoreceptor according to one embodiment of the present invention comprises a conductive substrate, a photosensitive layer, and a protective layer. The photosensitive layer is provided on the conductive substrate. The protective layer is provided on the photosensitive layer. The protective layer comprises a substrate made of a graft polymer having a composition of UV (ultraviolet) curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, n-type conductive fine particles dispersed in the substrate, and metal oxide fine particles dispersed in the substrate, with a Martens hardness of 400 N / mm². 2 The above and the volume resistivity is 1.0 × 10⁻⁶ 10 It is greater than or equal to Ω·cm.

[0007] According to the above configuration, the protective layer has a substrate made of a graft polymer comprising a curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, thereby increasing the slipperiness and hardness of the surface of the protective layer (i.e., the photoreceptor surface) (Martens hardness of 400 N / mm²). 2 As described above, the wear resistance of the electrophotographic photoreceptor is improved. Furthermore, because the protective layer has n-type conductive fine particles and metal oxide fine particles dispersed in the substrate, the electrical properties of the electrophotographic photoreceptor are ensured by the n-type conductive fine particles, which have excellent electron transport properties, and the resistance of the protective layer is increased by the metal oxide fine particles, which have high electrical resistance (volume resistivity of 1.0 × 10⁻¹⁰). 10 Because it is greater than Ω·cm, it can prevent the occurrence of image blurring.

[0008] The UV-curable polyfunctional monomer may have three or more (meth)acrylic groups.

[0009] The photoreactive group-containing substance may be a graft polymer in which the main chain is an organic chain and the side chains have multiple reactive groups and a fluorine-modified silicone skeleton or a silane skeleton as a release skeleton.

[0010] The photopolymerization initiator may be an acyl phosphine oxide.

[0011] The protective layer may have a thickness of 2 μm or more and 3 μm or less.

[0012] The photosensitive layer may contain an electron transport material containing any of the compounds represented by the following general formulas (1) to (6).

Chemical formula

Chemical formula

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0013] The photosensitive layer may contain a hole transport material containing any of the compounds represented by the following general formulas (7) to (10).

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0014] The photosensitive layer may contain a charge-generating material which is titanyl phthalocyanine or inorganic phthalocyanine.

[0015] The protective layer may be formed by applying a coating solution, which is a mixture of the UV-curable polyfunctional monomer, the photoreactive group-containing substance, the photopolymerization initiator, the n-type conductive fine particles, and the metal oxide fine particles, onto the photosensitive layer, and then irradiating the coating solution with light.

[0016] The aforementioned light may be light with a wavelength of 365 nm.

[0017] To achieve the above objective, a process cartridge according to one embodiment of the present invention comprises a conductive substrate, a photosensitive layer, and a protective layer. The photosensitive layer is provided on the conductive substrate. The protective layer is provided on the photosensitive layer. The protective layer comprises a substrate made of a graft polymer having a composition of UV (ultraviolet) curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, n-type conductive fine particles dispersed in the substrate, and metal oxide fine particles dispersed in the substrate, with a Martens hardness of 400 N / mm². 2 The above and the volume resistivity is 1.0 × 10⁻⁶ 10 It is greater than or equal to Ω·cm.

[0018] To achieve the above objective, an image forming apparatus according to one embodiment of the present invention comprises an electrophotographic photoreceptor, a charging device, an exposure device, a developing device, and a transfer device. The electrophotographic photoreceptor comprises a conductive substrate, a photosensitive layer provided on the conductive substrate, and a protective layer provided on the photosensitive layer. The charging device charges the surface of the electrophotographic photoreceptor. The exposure device exposes the charged surface to form an electrostatic latent image on the surface. The developing device develops the electrostatic latent image as a toner image. The transfer device transfers the toner image from the electrophotographic photoreceptor to the transfer target member. The protective layer is composed of a base material made of a graft polymer having a composition of a UV (ultraviolet) curable polyfunctional monomer, a photoinitiator, and a photoreactive group-containing substance, n-type conductive fine particles dispersed in the base material, and metal oxide fine particles dispersed in the base material, and has a Martens hardness of 400 N / mm 2 or more and a volume resistivity of 1.0×10 10 Ω·cm or more.

[0019] The charging device may include a charging roller.

[0020] The developing device may be a two-component developing system, a one-component developing system, or a rubbing roller system.

Advantages of the Invention

[0021] As described above, the present invention can provide an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus that are excellent in abrasion resistance and can suppress image flow.

Brief Description of the Drawings

[0022] [Figure 1] It is a schematic diagram of a single-layer electrophotographic photoreceptor according to an embodiment of the present invention. [Figure 2] It is a schematic diagram of a single-layer electrophotographic photoreceptor (with an undercoat layer) according to an embodiment of the present invention. [Figure 3] It is a schematic diagram of a multilayer electrophotographic photoreceptor according to an embodiment of the present invention. [Figure 4] It is a schematic diagram of a multilayer electrophotographic photoreceptor (with an undercoat layer) according to an embodiment of the present invention. [Figure 5] It is a schematic diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 6]This is a schematic diagram showing the configuration of the image forming unit included in the image forming apparatus described above. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will now be described. The electrophotographic photoreceptor according to the embodiment of the present invention may be a single-layer electrophotographic photoreceptor having a single photosensitive layer, or it may be a stacked electrophotographic photoreceptor having multiple photosensitive layers.

[0024] <Configuration of a single-layer electrophotographic photoreceptor> Figure 1 is a schematic diagram of an electrophotographic photoreceptor 1 according to one embodiment of the present invention. As shown in the figure, the electrophotographic photoreceptor 1 comprises a conductive substrate 2, a photosensitive layer 3, and a protective layer 4. The photosensitive layer 3 is provided on the conductive substrate 2, and the protective layer 4 is provided on the photosensitive layer 3. The electrophotographic photoreceptor 1 is a single-layer type electrophotographic photoreceptor comprising a single-layer photosensitive layer 3.

[0025] The electrophotographic photoreceptor 1 may further include an undercoat layer. Figure 2 is a schematic diagram of an electrophotographic photoreceptor 1 that includes an undercoat layer 5. As shown in these figures, an undercoat layer 5 is provided between the conductive substrate 2 and the photosensitive layer 3.

[0026] The thickness of each layer is not particularly limited, but the thickness of the photosensitive layer 3 is preferably 5 μm to 100 μm, and the thickness of the protective layer 4 is preferably 2 μm to 3 μm. The thickness of the undercoat layer 5 is preferably 0.1 μm to 5 μm.

[0027] [Composition of the photosensitive layer] The photosensitive layer 3 transports the negative charge generated by light absorption to the surface of the electrophotographic photoreceptor 1 (hereinafter referred to as the photoreceptor surface). The photosensitive layer 3 contains a charge generating material, a hole transport material, an electron transport material, and a binder resin.

[0028] (Charge-generating material) Examples of charge generating materials include phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free sodium compounds, metallic sodium compounds, squaline pigments, indigo pigments, azulenium pigments, cyanine pigments, powders of inorganic photoconductive materials (e.g., selenium, selenium-tellurium, selenium-arsenide, cadmium sulfide, and amorphous silicon), pyryllium pigments, anthenslon pigments, triphenylmethane pigments, surene pigments, toluidine pigments, pyrazoline pigments, and quinacridone pigments. The photosensitive layer 3 may contain only one type of charge generating material, or it may contain two or more types of charge generating materials.

[0029] Phthalocyanine pigments are pigments having a phthalocyanine structure. Preferred phthalocyanine pigments include titanyl phthalocyanine, shown in formula (CG-1), and phthalocyanine, shown in formula (CG-2).

[0030] [ka]

[0031] [ka]

[0032] The charge generating material content is preferably 0.1 parts by mass or more and 50 parts by mass or less per 100 parts by mass of binder resin, and more preferably 0.5 parts by mass or more and 5 parts by mass or less.

[0033] (Hole transport material) Examples of hole transporters include triphenylamine derivatives, diamine derivatives (e.g., N,N,N',N'-tetraphenylbenzidine derivatives, N,N,N',N'-tetraphenylphenylenediamine derivatives, N,N,N',N'-tetraphenylnaphthylenediamine derivatives, N,N,N',N'-tetraphenylphenantolylenediamine derivatives, and di(aminophenylethenyl)benzene derivatives), oxadiazole compounds (e.g., 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole) Examples include ), styryl compounds (e.g., 9-(4-diethylaminostyryl)anthracene), carbazole compounds (e.g., polyvinylcarbazole), organic polysilane compounds, pyrazoline compounds (e.g., 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), hydrazone compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds. The photosensitive layer 3 may contain only one type of hole transporter, or it may contain two or more types of hole transporters.

[0034] In particular, any of the compounds represented by the following formulas (HTM-1), (HTM-2), (HTM-3), and (HTM-4) are preferred as hole transporters.

[0035] [ka]

[0036] [ka]

[0037] [ka]

[0038] [ka]

[0039] In the above formulas (HTM-1) to (HTM-4), R1 to R 16 Each of the following independently represents a hydrogen atom, an alkyl group with 1 to 8 carbon atoms, or a phenyl group, and n represents a natural number less than or equal to 1.

[0040] Specifically, any of the compounds represented by the following formulas (HT-1), (HT-2), (HT-3), and (HT-4) are preferred as hole transporters.

[0041] [ka]

[0042] [ka]

[0043] [ka]

[0044] [ka]

[0045] The hole transporter content is preferably 10 parts by mass or more and 300 parts by mass or less per 100 parts by mass of binder resin, and more preferably 10 parts by mass or more and 150 parts by mass or less.

[0046] (electron transport material) Examples of electron transport materials include quinone compounds, diimide compounds, hydrazone compounds, malononitrile compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7-tetranitro-9-fluorenone compounds, dinitroanthracene compounds, dinitroacridine compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. Examples of quinone compounds include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds, and dinitroanthraquinone compounds. The photosensitive layer 3 may contain only one type of electron transport material, or it may contain two or more types of electron transport materials.

[0047] In particular, any of the compounds represented by the following formulas (ETM-1), (ETM-2), (ETM-3), (ETM-4), (ETM-5), and (ETM-6) are preferred as electron transport materials.

[0048] [ka]

[0049] [ka]

[0050] [ka]

[0051] [ka]

[0052] [ka]

[0053] [ka]

[0054] In the above formulas (ETM-1) to (ETM-6), R1 to R 28 Each of the following independently represents a hydrogen atom, a halogen atom, a cyano group, or an alkyl group having 1 to 6 carbon atoms; X1 and X2 each independently represent an alkenyl group having 2 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 14 carbon atoms which may have at least one alkyl group having 1 to 6 carbon atoms; and Y1 to Y3 each independently represent a halogen group or an oxygen atom.

[0055] Specifically, any of the compounds represented by the following formulas (ET-1), (ET-2), (ET-3), (ET-4), (ET-5), (ET-6), and (ET-7) are preferred as electron transport materials.

[0056] [ka]

[0057] [ka]

[0058] [ka]

[0059] [ka]

[0060] [ka]

[0061] [ka]

[0062] [ka]

[0063] The content of the electron transport material is preferably 5 parts by mass or more and 150 parts by mass or less per 100 parts by mass of binder resin, and more preferably 10 parts by mass or more and 100 parts by mass or less.

[0064] (Binder resin) Examples of binder resins include polycarbonate resin, polyarylate resin, styrene-based resin, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, styrene-maleic acid copolymer, styrene-acrylic acid copolymer, acrylic copolymer, polyethylene resin, ethylene-vinyl acetate copolymer, chlorinated polyethylene resin, polyvinyl chloride resin, polypropylene resin, ionomer, vinyl chloride-vinyl acetate copolymer, polyester resin, alkyd resin, polyamide resin, polyurethane resin, polysulfone resin, diallyl phthalate resin, ketone resin, polyvinyl butyral resin, polyvinyl acetal resin, and polyether resin, silicone resin, epoxy resin, phenolic resin, urea resin, melamine resin, epoxy-acrylic acid resin, and urethane-acrylic acid copolymer.

[0065] Specifically, a polycarbonate resin can be used as the binder resin, with bisphenol represented by the following formula (R-1) as the monomer and DMP (Dimethyl phthalate) as the end-terminating agent.

[0066] [ka]

[0067] The photosensitive layer 3 has the above-described structure. In addition to the materials described above, the photosensitive layer 3 may also contain additives. Examples of additives include ultraviolet absorbers, antioxidants, radical scavengers, singlet quenchers, softeners, surface modifiers, bulking agents, thickening agents, dispersion stabilizers, waxes, donors, surfactants, plasticizers, sensitizers, and leveling agents. The photosensitive layer 3 may contain one or more of these additives.

[0068] [Composition of the protective layer] The protective layer 4 covers the photosensitive layer 3 and protects the photosensitive layer 3. The protective layer 4 comprises a substrate and n-type conductive fine particles and metal oxide fine particles dispersed in the substrate.

[0069] {base material} The substrate consists of a graft polymer comprising a UV (ultraviolet) curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance.

[0070] (UV-curable polyfunctional monomer) UV-curable polyfunctional monomers are acrylic monomers that are UV-curable and have numerous functional groups. Specifically, any of the compounds represented by the following formulas (B-1), (B-2), and (B-3) can be used as UV-curable polyfunctional monomers.

[0071] [ka] The above compound is called dipentaerythritol polyacrylate, and for example, "A-DPH" (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) can be used. This compound has five or six (meth)acrylic groups.

[0072] [ka] The above compound is called polyethylene glycol diacrylate, and for example, "A-200 (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.)" can be used. This compound has two (meth)acrylic groups.

[0073] [ka]

[0074] The above compound is called pentaerythritol tritetraacrylate, and for example, "A-TMM-3LM-N" (manufactured by Shin-Nakamura Chemical Industry Co., Ltd.) can be used. This compound has three or four (meth)acrylic groups.

[0075] As the UV-curable polyfunctional monomer, compounds having three or more (meth)acrylic groups are more preferable among the above compounds, that is, compounds represented by formulas (B-1) and (B-3) are more preferable. This is because when the UV-curable polyfunctional monomer has three or more (meth)acrylic groups, the hardness of the protective layer 4 increases, and wear can be prevented. The content of the UV-curable polyfunctional monomer is preferably 30 parts by mass or more and 80 parts by mass or less per 100 parts by mass of resin.

[0076] (Photopolymerization initiator) A photopolymerization initiator initiates graft polymerization by photopolymerization of a UV-curable polyfunctional monomer and a photoreactive group-containing substance. An acylphosphine oxide represented by the following formula (P-1) can be used as the photopolymerization initiator.

[0077] [ka]

[0078] For example, "Omnirad TPO-H" (manufactured by Toyotsu Chemiplus Co., Ltd.) can be used as the acyl phosphine oxide. In addition, any photopolymerization initiator capable of initiating the photopolymerization of UV-curable polyfunctional monomers and photoreactive group-containing substances can be used. The content of the photopolymerization initiator is preferably 5 to 15 parts by mass per 100 parts by mass of the substrate.

[0079] (Substances containing photoreactive groups) A photoreactive group-containing substance is a monomer or polymer having a photoreactive group. Specifically, as a photoreactive group-containing substance, a graft polymer can be used in which the main chain is an organic chain and the side chains have multiple reactive groups and a fluorine-modified silicone skeleton or silane skeleton as a release skeleton. More specifically, any of the compounds represented by the following formulas (C-1), (C-2), (C-3), and (C-4) can be used as a photoreactive group-containing substance.

[0080] [ka]

[0081] The above compound is a silicon / fluorine-modified acrylic polymer having an acrylic main chain and fluorine-modified silicone side chains. For example, "8FS-001" (manufactured by Taisei Fine Chemical Co., Ltd.) can be used as this compound. [ka]

[0082] The above compound is a silicon-modified acrylic polymer having an acrylic main chain and silicone side chains. For example, "8SS-723" (manufactured by Taisei Fine Chemical Co., Ltd.) can be used as this compound.

[0083] [ka]

[0084] The above compound is a polyfunctional acrylic silane, having an organic chain, a functional group, and an alkoxysilyl group (Si(OR)3). For example, "X-12-1050 (manufactured by Shin-Etsu Chemical Co., Ltd.)" can be used as this compound.

[0085] [ka]

[0086] The above compound is a silicone having a silane skeleton and acrylate groups at both ends; for example, "KP-423" (manufactured by Shin-Etsu Chemical Co., Ltd.) can be used.

[0087] The content of the photoreactive group-containing substance is preferably 0.1 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the base material.

[0088] {n-type conductive fine particles} n-type conductive fine particles are fine particles made of an n-type conductive material. Examples of n-type conductive materials include phosphorus-doped tin oxide and antimond-doped tin oxide. Preferably, the n-type conductive fine particles have a primary particle diameter of 10 nm to 500 nm. The content of the n-type conductive fine particles is preferably 1 to 10 parts by mass per 100 parts by mass of the substrate.

[0089] {Metal oxide fine particles} Metal oxide fine particles are fine particles composed of metal oxides. Examples of metal oxides include tin oxide, zinc oxide, titanium oxide, alumina, and silica. Preferably, the metal oxide fine particles have a primary particle size of 10 nm to 500 nm. Preferably, the content of metal oxide fine particles is 1 to 10 parts by mass per 100 parts by mass of the base material.

[0090] Table 1 below shows examples of n-type conductive nanoparticles and metal oxide particles.

[0091] [Table 1]

[0092] {Regarding protective layers} As described later, protective layer 4 is formed by irradiating a solution containing a UV-curable polyfunctional monomer, a photopolymerization initiator, a photoreactive group-containing substance, n-type conductive fine particles, and metal oxide fine particles with light to induce photopolymerization. Protective layer 4 has a Martens hardness of 400 N / mm². 2 Therefore, the volume resistivity is 1.0 × 10⁻⁶. 10The hardness is greater than or equal to Ω·cm. Martens hardness is measured according to the measurement method compliant with ISO 14577. Volume resistivity is measured by pressing the electrode probe of a resistivity meter against the protective layer 4 and applying a voltage of 100V for 10 seconds.

[0093] The protective layer 4 has the configuration described above. In addition to the materials described above, the protective layer 4 may also contain additives. Examples of additives include ultraviolet absorbers, antioxidants, softeners, surface modifiers, bulking agents, thickening agents, dispersion stabilizers, and leveling agents. The protective layer 4 may contain one or more of these additives.

[0094] [Composition of the lower layer] The undercoat layer 5 maintains an insulating state sufficient to suppress leakage, while facilitating the flow of charge (charges of the opposite polarity to those transported to the photoreceptor surface) from the photosensitive layer 3 to the conductive substrate 2, thereby suppressing an increase in resistance.

[0095] The undercoat 5 contains, for example, inorganic particles and a binder resin. As inorganic particles, for example, particles made of metal (e.g., aluminum, iron, or copper), metal oxides (e.g., titanium oxide, alumina, zirconium oxide, tin oxide, or zinc oxide), or non-metallic oxides (e.g., silica) can be used. The binder resin can be one of the binder resins listed as the material for the photosensitive layer 3. The inorganic particle content is preferably 1 to 10 parts by mass per 100 parts by mass of binder resin. As shown in Figure 1, the undercoat 5 is not necessarily required.

[0096] <Method for manufacturing a single-layer electrophotographic photoreceptor> A method for manufacturing the electrophotographic photoreceptor 1 will now be described. The electrophotographic photoreceptor 1 can be formed by laminating an undercoat layer 5, a photosensitive layer 3, and a protective layer 4 on a conductive substrate 2 in this order (see Figure 2).

[0097] The undercoat layer 5 can be formed on the conductive substrate 2 by creating a coating solution by mixing a solvent with the inorganic particles and binder resin described above, applying this coating solution to the conductive substrate 2, and then removing the solvent. The materials can be mixed using, for example, a bead mill, roll mill, ball mill, attritor, paint shaker, rod-shaped ultrasonic oscillator, or ultrasonic disperser.

[0098] The solvent can be any solvent capable of dissolving the binder resin, and examples include alcohols (specifically methanol, ethanol, isopropanol, and butanol), aliphatic hydrocarbons (specifically n-hexane, octane, and cyclohexane), aromatic hydrocarbons (specifically benzene, toluene, and xylene), halogenated hydrocarbons (specifically dichloromethane, dichloroethane, carbon tetrachloride, and chlorobenzene), ethers (specifically dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether), ketones (specifically acetone, methyl ethyl ketone, and cyclohexanone), esters (specifically ethyl acetate and methyl acetate), dimethylformaldehyde, dimethylformamide, and dimethyl sulfoxide.

[0099] The coating solution can be applied using a method that allows for uniform application, and one of the following methods can be used: dip coating, spray coating, spin coating, or bar coating. The solvent can be removed by heating, reduced pressure, or a combination of heating and reduced pressure, specifically using a high-temperature dryer or a vacuum dryer.

[0100] The photosensitive layer 3 can be formed on the base layer 5 by preparing a coating solution by mixing a solvent with the aforementioned charge generating material, hole transport material, electron transport material, and binder resin, applying this coating solution to the base layer 5, and then removing the solvent. The method for mixing the materials, the solvent, the application method, and the solvent removal method can be the same as those described in the method for forming the base layer 5.

[0101] The protective layer 4 can be formed on the photosensitive layer 3 by preparing a coating solution by mixing a solvent with the above-mentioned UV-curable polyfunctional monomer, photopolymerization initiator, photoreaction basic containing substance, n-type conductive fine particles, and metal oxide fine particles, applying this coating solution to the photosensitive layer 3, and irradiating the coating solution with light. Upon light irradiation, the UV-curable polyfunctional monomer, photopolymerization initiator, and photoreaction basic containing substance undergo photopolymerization, forming the above-mentioned substrate. The method of mixing the materials, solvent, coating method, and solvent removal method can be the same as those listed in the method of forming the undercoat layer 5. For light irradiation, it is preferable to irradiate with light of a wavelength of 365 nm, and light irradiation can be performed using an LED (light-emitting diode) light source with an emission wavelength of 365 nm.

[0102] The electrophotographic photoreceptor 1 can be manufactured as described above. Note that an electrophotographic photoreceptor 1 without an undercoat layer 5 (see Figure 1) can be manufactured by omitting the step of forming the undercoat layer 5 and directly forming the photosensitive layer 3 on the conductive substrate 2.

[0103] <Effects of electrophotographic photoconductors> The effects of the electrophotographic photoreceptor 1 will now be explained. As described above, the electrophotographic photoreceptor 1 has a protective layer 4 that covers the photosensitive layer 3. Because the protective layer 4 has a substrate made of a graft polymer having a composition of a curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, the slipperiness of the surface of the protective layer 4 (i.e., the photoreceptor surface) is increased, and the hardness is also increased (specifically, the Martens hardness is 400 N / mm²). 2 (The above). As a result, the slipperiness and hardness of the photoreceptor surface are increased, thereby improving the wear resistance of the electrophotographic photoreceptor 1.

[0104] Furthermore, the protective layer 4 has n-type conductive fine particles and metal oxide fine particles dispersed in the substrate, which suppresses image flow in the electrophotographic photoreceptor. While the n-type conductive fine particles, which have excellent electron transport properties, can ensure the electrical characteristics of the electrophotographic photoreceptor 1, charging problems occur due to reduced resistance. Therefore, by mixing in metal oxide fine particles, the resistance of the protective layer 4 is increased (specifically, a volume resistivity of 1.0 × 10⁻⁶). 10 This is because it prevents image blurring (above Ω·cm).

[0105] Thus, the electrophotographic photoreceptor 1 exhibits excellent abrasion resistance and suppresses image blurring, making it possible to realize an electrophotographic photoreceptor with suppressed image blurring. In particular, by using a graft polymer having a fluorine-modified silicone skeleton or a silane skeleton in its side chains as the photoreactive group-containing material, the slipperiness of the photoreceptor surface is further improved, making it possible to realize an electrophotographic photoreceptor 1 with even greater abrasion resistance. Furthermore, since the above graft polymer is water-repellent, the protective layer 4 becomes a low-moisture-absorbing film, making it possible to further suppress the occurrence of image blurring.

[0106] <Configuration of a stacked electrophotographic photoconductor> Figure 3 is a schematic diagram of a stacked electrophotographic photoreceptor 6 according to this embodiment. As shown in the figure, the electrophotographic photoreceptor 6 comprises a conductive substrate 2, a photosensitive layer 7, and a protective layer 4, and the photosensitive layer 7 comprises a charge generation layer 8 and a charge transport layer 9. The charge generation layer 8 is provided on the conductive substrate 2, and the charge transport layer 9 is provided on the charge generation layer 8. The protective layer 4 is provided on the charge transport layer 9. The electrophotographic photoreceptor 6 is a stacked electrophotographic photoreceptor comprising a photosensitive layer 7 consisting of two layers: a charge generation layer 8 and a charge transport layer 9. Of the components of the electrophotographic photoreceptor 6, the components other than the photosensitive layer 7 are the same as those of the electrophotographic photoreceptor 1, so the same reference numerals as those used in the electrophotographic photoreceptor 1 are used, and their explanation is omitted.

[0107] The electrophotographic photoreceptor 6 may also include an undercoat layer. Figure 4 is a schematic diagram of an electrophotographic photoreceptor 6 that includes an undercoat layer 5. As shown in these figures, an undercoat layer 5 is provided between the conductive substrate 2 and the charge generation layer 8.

[0108] The thickness of each layer is not particularly limited, but the thickness of the photosensitive layer 7 is preferably 10 μm to 200 μm. Of these, the thickness of the charge generation layer 8 is preferably 5 μm to 100 μm, and the thickness of the charge transport layer 9 is preferably 5 μm to 100 μm.

[0109] [Composition of the photosensitive layer] The photosensitive layer 7 transports the positive charge generated by light absorption to the surface of the electrophotographic photoreceptor 6 (hereinafter referred to as the photoreceptor surface). In the electrophotographic photoreceptor 6, charge is generated in the charge generation layer 8, and the charge transport layer 9 transports the generated charge to the photoreceptor surface.

[0110] The charge generation layer 8 contains a charge generating material and a binder resin. The materials described in the above-described configuration of the photosensitive layer 3 can be used for each of the charge generating material and the binder resin. The charge transport layer 9 contains a hole transport material and a binder resin. The materials described in the above-described configuration of the photosensitive layer 3 can be used for each of the hole transport material and the binder resin.

[0111] The photosensitive layer 7 has the configuration described above. The charge generation layer 8 and the charge transport layer 9 may each contain additives in addition to the materials described above. Examples of additives include ultraviolet absorbers, antioxidants, radical scavengers, singlet quenchers, softeners, surface modifiers, bulking agents, thickening agents, dispersion stabilizers, waxes, donors, surfactants, plasticizers, sensitizers, and leveling agents. The charge generation layer 8 and the charge transport layer 9 may contain one or more of these additives.

[0112] The electrophotographic photoreceptor 6 has the above configuration. The protective layer 4, like the electrophotographic photoreceptor 1, contains a substrate and n-type conductive fine particles and metal oxide fine particles dispersed in the substrate. The substrate consists of a graft polymer having a UV-curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance. The undercoat layer 5, like the electrophotographic photoreceptor 1, also contains inorganic particles and a binder resin.

[0113] <Method for manufacturing a stacked electrophotographic photoreceptor> A method for manufacturing the electrophotographic photoreceptor 6 will now be described. The electrophotographic photoreceptor 6 can be formed by laminating an undercoat layer 5, a charge generation layer 8, a charge transport layer 9, and a protective layer 4 on a conductive substrate 2 in this order (see Figure 4). The undercoat layer 5 can be formed in the same manner as the method for manufacturing the electrophotographic photoreceptor 1 described above.

[0114] The charge generating layer 8 can be formed on the base layer 5 by preparing a coating solution by mixing a solvent with the above-mentioned charge generating material and binder resin, applying this coating solution to the base layer 5, and then removing the solvent. The method for mixing the materials, the solvent, the application method, and the solvent removal method can be the same as those described in the method for forming the base layer 5 above.

[0115] The charge transport layer 9 can be formed on the charge generating layer 8 by preparing a coating solution by mixing a solvent with the hole transport material and binder resin described above, applying this coating solution to the charge generating layer 8, and then removing the solvent. The method for mixing the materials, the solvent, the application method, and the solvent removal method can be the same as those described in the method for forming the undercoat layer 5 described above.

[0116] The protective layer 4 can be formed on the photosensitive layer 3 by preparing a coating solution by mixing a solvent with the above-mentioned UV-curable polyfunctional monomer, photopolymerization initiator, photoreaction basic containing substance, n-type conductive fine particles, and metal oxide fine particles, applying this coating solution onto the charge transport layer 9, and irradiating the coating solution with light. Upon light irradiation, the UV-curable polyfunctional monomer, photopolymerization initiator, and photoreaction basic containing substance undergo photopolymerization, forming the above-mentioned substrate. The method for mixing the materials, the solvent, the application method, and the solvent removal method can be those listed in the method for forming the undercoat layer 5 described above. For light irradiation, it is preferable to irradiate with light of a wavelength of 365 nm, and light irradiation can be performed using an LED (light-emitting diode) light source with an emission wavelength of 365 nm.

[0117] The electrophotographic photoreceptor 1 can be manufactured as described above. Note that the electrophotographic photoreceptor 6 (see Figure 3) without the undercoat layer 5 can be manufactured by directly forming the charge generation layer 8 on the conductive substrate 2, without performing the step of forming the undercoat layer 5.

[0118] <Effects of electrophotographic photoconductors> The electrophotographic photoreceptor 6 has the same effects as the electrophotographic photoreceptor 1. That is, because the surface of the protective layer 4 (i.e., the photoreceptor surface) has high slipperiness and hardness, the electrophotographic photoreceptor 6 has excellent wear resistance. In addition, because the protective layer 4 has n-type conductive fine particles and metal oxide fine particles dispersed in the substrate, the resistance of the protective layer 4 is high, and the occurrence of image blurring is suppressed.

[0119] [Configuration of the image forming apparatus] An image forming apparatus 100 according to an embodiment of the present invention will now be described. Figure 5 is a schematic diagram showing the configuration of the image forming apparatus 100. The image forming apparatus 100 is, for example, a tandem-type color printer.

[0120] As shown in Figure 5, the image forming apparatus 100 comprises a control unit 10, an operation unit 20, a paper feeding unit 30, a transport unit 40, a toner supply unit 50, an image forming unit 60, a transfer device 70, a fixing device 80, and a discharge unit 90.

[0121] The control unit 10 controls the operation of each part of the image forming apparatus 100. The control unit 10 includes an arithmetic processing unit and a storage unit (not shown). The arithmetic processing unit is, for example, a CPU (central processing unit), and the storage unit is, for example, semiconductor memory or an HDD (hard disk drive). The arithmetic processing unit controls the operation of the image forming apparatus 100 by executing a control program. The storage unit stores the control program.

[0122] The control unit 20 receives instructions from the user. Upon receiving instructions from the user, the control unit 20 transmits a signal indicating the user's instructions to the control unit 10. This initiates the image forming operation by the image forming apparatus 100.

[0123] The paper feeding unit 30 includes a paper feeding cassette 31 and a group of paper feeding rollers 32. The paper feeding cassette 31 can accommodate several recording media P. The recording media P is, for example, printing paper. The group of paper feeding rollers 32 feeds the recording media P contained in the paper feeding cassette 31 one sheet at a time to the transport unit 40.

[0124] The transport unit 40 is equipped with rollers and guide members. The transport unit 40 extends from the paper feeding unit 30 to the discharge unit 90. The transport unit 40 transports the recording medium P from the paper feeding unit 30 to the discharge unit 90, passing through the image forming unit 60 and the fixing device 80.

[0125] The toner supply unit 50 supplies toner to the image forming unit 60. The toner supply unit 50 comprises a first mounting unit 51Y, a second mounting unit 51C, a third mounting unit 51M, and a fourth mounting unit 51K. The first mounting unit 51Y is fitted with a first toner container 52Y. The second mounting unit 51C is fitted with a second toner container 52C, the third mounting unit 51M is fitted with a third toner container 52M, and the fourth mounting unit 51K is fitted with a fourth toner container 52K.

[0126] The first toner container 52Y contains yellow toner, the second toner container 52C contains cyan toner, the third toner container 52M contains magenta toner, and the fourth toner container 52K contains black toner. Note that the colors of each toner are not limited to those shown here; other colors may be used. The number of colors may also be one or more.

[0127] The image forming unit 60 comprises an exposure apparatus 61, a first image forming unit 62Y, a second image forming unit 62C, a third image forming unit 62M, and a fourth image forming unit 62K. Figure 6 is a schematic diagram of the image forming unit 62. The first image forming unit 62Y, the second image forming unit 62C, the third image forming unit 62M, and the fourth image forming unit 62K each have the configuration of the image forming unit 62 shown in Figure 6. The image forming unit 62 includes a charging device 63, a developing device 64, a photoreceptor 65, a cleaning device 66, and a static elimination device 67. The charging device 63, the developing device 64, the cleaning device 66, and the static elimination device 67 are arranged along the surface 65a of the photoreceptor 65.

[0128] The exposure apparatus 61 (see Figure 5) irradiates light (dashed line in the figure) onto the surface 65a of the photoreceptor 65 of each image forming unit 62, thereby exposing the surface 65a. Based on the supplied image data, the exposure apparatus 61 irradiates each image forming unit 62 with light for each color, performing exposure. The exposure apparatus 61 can perform exposure using laser light.

[0129] The photoreceptor 65 forms an electrostatic latent image when exposed by the exposure device 61. The photoreceptor 65 can be either the single-layer electrophotographic photoreceptor 1 or the multilayer electrophotographic photoreceptor 6 described above. The surface of the protective layer 4 on the electrophotographic photoreceptor 1 and the electrophotographic photoreceptor 6 is defined as the surface 65a of the photoreceptor 65. The surface 65a is pre-charged positively or negatively. When this surface 65a is exposed by the exposure device 61, the charge attenuates in the irradiated area, forming an electrostatic latent image. The photoreceptor 65 rotates in the direction indicated by the arrow in Figure 6 (clockwise).

[0130] The charging device 63 positively or negatively charges the surface 65a. The charging device 63 comprises a charging roller 631, a charging voltage power supply 632, and a cleaning brush 633. The charging roller 631 contacts the surface 65a to uniformly charge the surface 65a. The charging voltage power supply 632 applies a charging voltage to the charging roller. A DC voltage is preferred for this charging voltage. The cleaning brush 633 contacts the charging roller 631 to clean the charging roller 631.

[0131] The developing device 64 supplies toner supplied from the toner supply unit 50 to the surface 65a. As shown in Figure 6, the developing device 64 is equipped with a developing roller 641. The toner supplied from the toner container is mixed with a magnetic carrier to form a two-component developer. At this time, the toner becomes charged with the same polarity as the surface 65a due to friction with the carrier.

[0132] The two-component developer is attracted to the developing roller 641 by magnetic force and transported to a position opposite the photoreceptor 65. A voltage is applied between the developing roller 641 and the photoreceptor 65, causing the toner in the two-component developer to adhere to the electrostatic latent image on the surface 65a. This forms a toner image on the surface 65a that matches the electrostatic latent image.

[0133] The developing device 64 of the first image forming unit 62Y is connected to the first toner container 52Y, and yellow toner is supplied. As a result, a yellow toner image is formed on the surface of the photoreceptor 65 of the first image forming unit 62Y. Similarly, the developing device 64 of the second image forming unit 62C is connected to the second toner container 52C, and a cyan toner image is formed on the surface of the photoreceptor 65 of the second image forming unit 62C.

[0134] Furthermore, the developing device 64 of the third image forming unit 62M is connected to the third toner container 52M, and a magenta toner image is formed on the surface of the photoreceptor 65 of the third image forming unit 62M. The developing device 64 of the fourth image forming unit 62K is connected to the fourth toner container 52K, and a black toner image is formed on the surface of the photoreceptor 65 of the fourth image forming unit 62K.

[0135] The cleaning device 66 recovers toner adhering to the surface 65a after transfer by the primary transfer roller 71, which will be described later. Specifically, the cleaning device 66 includes a cleaning blade 661 and a static elimination device 67. The cleaning blade 661 is pressed against the surface 65a and cleans the surface 65a by recovering the toner adhering to it. The static elimination device 67 removes static electricity from the surface 65a by irradiating it with static elimination light.

[0136] The transfer device 70 (see Figure 5) transfers the toner image from the photoreceptor 65 to the recording medium P, which is the object to be transferred. Specifically, the transfer device 70 transfers the toner images of each color formed on the surface 65a of the photoreceptor 65 of each image forming unit 62 onto the recording medium P. The transfer device 70 can transfer each toner image onto the recording medium P by a secondary transfer method (intermediate transfer method). For the secondary transfer method, the transfer device 70 has four primary transfer rollers 71, an intermediate transfer belt 72, a drive roller 73, a driven roller 74, and a secondary transfer roller 75.

[0137] The intermediate transfer belt 72 is an endless belt stretched over four primary transfer rollers 71, a drive roller 73, and a driven roller 74. The intermediate transfer belt 72 is driven in accordance with the rotation of the drive roller 73. In Figure 5, the intermediate transfer belt 72 rotates in the direction indicated by the arrow in Figure 5 (counterclockwise). The driven roller 74 is rotationally driven in accordance with the driving of the intermediate transfer belt 72.

[0138] Each image forming unit 62 faces the lower surface of the intermediate transfer belt 72 and is arranged in the order of the first image forming unit 62Y to the fourth image forming unit 62K, from the upstream side to the downstream side in the driving direction of the lower surface of the intermediate transfer belt 72.

[0139] Each primary transfer roller 71 is positioned opposite each photoreceptor 65 via an intermediate transfer belt 72 and is pressed toward each photoreceptor 65. As a result, the toner image formed on the surface 65a of each photoreceptor 65 is sequentially transferred to the intermediate transfer belt 72 by each primary transfer roller 71. In the configuration shown in Figure 5, the yellow toner image, cyan toner image, magenta toner image, and black toner image are transferred to the intermediate transfer belt 72 in this order, but the order of the toner images is not limited to this. Hereinafter, the toner image formed by stacking the yellow toner image, cyan toner image, magenta toner image, and black toner image will be referred to as the "stacked toner image".

[0140] The secondary transfer roller 75 is positioned opposite the drive roller 73 via the intermediate transfer belt 72. The secondary transfer roller 75 is pressed toward the drive roller 73. This forms a transfer nip (contact area) between the secondary transfer roller 75 and the drive roller 73, and as the recording medium P passes through the transfer nip, the secondary transfer roller 75 transfers the layered toner image on the intermediate transfer belt 72 to the recording medium P. The layering order of the layered toner image on the recording medium P is the opposite of the layering order of the layered toner image on the intermediate transfer belt 72. The recording medium P on which the layered toner image has been transferred is transported toward the fuser 80 by the transport unit 40.

[0141] The fuser unit 80 fixes the stacked toner image onto the recording medium P. The fuser unit 80 includes a heating member 81 and a pressurizing member 82. The heating member 81 and the pressurizing member 82 are arranged facing each other to form a fuser nip. The recording medium P, transported from the image forming unit 60, is heated and pressurized at a predetermined fixing temperature as it passes through the fuser nip, and the stacked toner image is fixed onto the recording medium P. The recording medium P is transported from the fuser unit 80 to the discharge unit 90 by the transport unit 40.

[0142] The discharge unit 90 discharges the recording medium P on which the stacked toner image has been fixed. The discharge unit 90 has a pair of discharge rollers 91, a discharge port 92, and a discharge tray 93. The pair of discharge rollers 91 transports the recording medium P to the discharge tray 93 via the discharge port 92.

[0143] The image forming method using the image forming apparatus 100 will now be described. When the control unit 10 acquires image data and the operation unit 20 receives a user instruction to start the image forming operation, the photoreceptor 65 in each image forming unit 62 is rotated, and the charging roller 631 uniformly charges the surface 65a. An image forming apparatus in which the surface 65a is positively charged is called a positive charging method, and an image forming apparatus in which the surface 65a is negatively charged is called a negative charging method.

[0144] Next, the exposure apparatus 61 exposes the surface 65a of each image forming unit 62 according to the image data, forming electrostatic latent images for each color on the surface 65a. Specifically, the charge generated by exposure is transported to the surface 65a, and the electrostatic latent image is formed by the attenuation of the charge by that charge. In the positive charging method, electrons generated by exposure are transported to the surface 65a, attenuating the positive charge. In the negative charging method, holes generated by exposure are transported to the surface 65a, attenuating the negative charge.

[0145] Each image forming unit's developing device 64 supplies toner of each color to the surface 65a, which then electrostatically adheres to the electrostatic latent image for each color. This forms a toner image of each color on the surface 65a of each photoreceptor 65. If the amount of toner filled in each developing device 64 falls below a specified value due to the formation of the toner image, toner is replenished to each developing device 64 from the first toner container 52Y to the fourth toner container 52K.

[0146] An electric field is applied between the primary transfer roller 71 and the photoreceptor 65 at a predetermined transfer voltage by the primary transfer roller 71. As a result, the toner images of each color on the surface 65a are primary transferred onto the intermediate transfer belt 72. The toner images of each color are stacked, and a stacked toner image is formed on the intermediate transfer belt 72. Subsequently, in preparation for the formation of a new electrostatic latent image, any toner remaining on the surface 65a after the primary transfer is removed by the cleaning device 66.

[0147] As the intermediate transfer belt 72 rotates counterclockwise in conjunction with the rotation of the drive roller 73, the transport unit 40 transports the recording medium P to the transfer nip between the secondary transfer roller 75 and the drive roller 73 at a predetermined timing, and the laminated toner image on the intermediate transfer belt 72 is secondarily transferred onto the recording medium P. The recording medium P on which the laminated toner image has been secondarily transferred is then transported by the transport unit 40 to the fuser 80.

[0148] The recording medium P, transported to the fixing device 80, is heated and pressurized by the heating element 81 and the pressurizing element 82, causing the laminated toner image to fix to the surface of the recording medium P, and a color image is formed on the recording medium P. The recording medium P on which the color image has been formed is discharged to the discharge tray 93 in the discharge unit 90.

[0149] The image forming apparatus 100 has the configuration described above. The configuration of the image forming apparatus according to the present invention is not limited to that described above, and may include any photoreceptor 65 having the configuration of an electrophotographic photoreceptor 1 or an electrophotographic photoreceptor 6. For example, although the image forming apparatus 100 is an image forming apparatus capable of forming color images, the image forming apparatus according to the present invention may be an image forming apparatus capable of forming monochrome images. In this case, the image forming apparatus may include only one image forming unit.

[0150] Furthermore, although the developing device 64 has been described as a two-component developing system that supplies a two-component developer to the surface 65a, it may also be a one-component developing system that supplies a one-component developer to the surface 65a. A one-component developer is a developer consisting only of toner, without the toner being mixed with a carrier. Moreover, the developing device 64 may also be a sliding roller system equipped with rollers that rub the surface 65a.

[0151] Furthermore, although the image forming apparatus 100 is a tandem type image forming apparatus, the image forming apparatus according to the present invention may be a rotary type image forming apparatus. In addition, although the image forming apparatus 100 is a touchdown development type image forming apparatus, the image forming apparatus according to the present invention may be an image forming apparatus with a development method other than the touchdown development method.

[0152] Furthermore, although the image forming apparatus 100 is an intermediate transfer type image forming apparatus, the image forming apparatus according to the present invention may be a direct transfer type image forming apparatus. In this case, the toner image is directly transferred from the photoreceptor 65 to the recording medium P while the photoreceptor 65 is in contact with the recording medium P.

[0153] [Process Cartridge Configuration] A process cartridge according to an embodiment of the present invention will now be described. The process cartridge according to this embodiment corresponds to part or all of the image forming unit 62 (see Figure 6) described above and comprises at least a photoreceptor 65. In addition, the process cartridge according to this embodiment may also comprise at least one of a charging device 63, a developing device 64, a cleaning device 66, and a static elimination device 67, in addition to the photoreceptor 65.

[0154] The process cartridge is configured to be detachable from the image forming apparatus 100. This allows for easy replacement of the entire process cartridge when the sensitivity characteristics of the photoreceptor 65 deteriorate, for example. [Examples]

[0155] Electrophotographic photoreceptors according to the examples and comparative examples of the present invention were prepared, and various physical properties were measured. Tables 2 to 5 below show the configuration of the electrophotographic photoreceptors according to the examples and comparative examples.

[0156] [Table 2]

[0157] [Table 3]

[0158] [Table 4]

[0159] [Table 5]

[0160] In each table, "A-1" to "A-23" and "B-1," which indicate the composition of the photosensitive layer, correspond to the compositions described in Tables 6 and 7 below. Furthermore, "O-1" to "O-12," which indicate the composition of the protective layer, correspond to the compositions described in Tables 2 and 5. In addition, "B-1" to "B-3," which indicate the main skeleton of the UV-curable polyfunctional monomer, are compounds represented by formulas (B-1) to (B-3) above, and "C-1" to "C-4," which indicate the main skeleton of the photoreactive group-containing substance, are compounds represented by formulas (C-1) to (C-4) above.

[0161] <Fabrication of a single-layer electrophotographic photoreceptor> The electrophotographic photoreceptors used in Examples 1-29 and Comparative Examples 1-6 were single-layer electrophotographic photoreceptors, and were manufactured as follows.

[0162] First, an undercoat was formed on the conductive substrate as follows: 2 parts by weight of titanium oxide "SMT-A" (manufactured by Teika Co., Ltd., number mean primary particle size 10 nm), which had been surface-treated with alumina and silica and then wet-dispersed with methylhydrogenpolysiloxane, and 1 part by weight of 6,12,66,610 quaternary copolymer polyamide resin "Amilan® CM8000" (manufactured by Toray Industries, Inc.) were dispersed in a solvent using a ball mill. The dispersion time was 5 hours. The solvent consisted of 10 parts by weight of methanol, 1 part by weight of butanol, and 1 part by weight of toluene. The prepared dispersion was filtered using a 5 μm mesh filter to prepare a coating solution. The coating solution was applied to the conductive substrate by dip-coating, and the coating film was dried at 130°C for 30 minutes to form an undercoat. The thickness of the undercoat layer was 2 μm.

[0163] Next, a photosensitive layer was formed on the undercoat layer as follows. Table 6 below shows the composition of the photosensitive layer. 2.85 parts by weight of charge generating material (CGM), 80 parts by weight of hole transport material (HTM), 68 parts by weight of electron transport material (ETM), 0.02 parts by weight of dimethyl silicone oil ("KF96-50CS" manufactured by Shin-Etsu Chemical Co., Ltd.) as a leveling agent, and 70 parts by weight of polycarbonate resin as a binder resin were dispersed in a solvent using a rod-shaped sonic oscillator. The dispersion time was 2 minutes. The solvent was 500 parts by weight of tetrahydrofuran. The polycarbonate resin used was a polycarbonate resin (molecular weight 50000) with bisphenol represented by the above formula (R-1) as the monomer and DMP (Dimethyl phthalate) as the end-stopping agent. The types of charge generating material (CGM), hole transport material (HTM), and electron transport material (ETM) are as shown in Table 6. Note that "HT-2 / HT-3" refers to 40 parts by weight of the compound represented by formula (HT-2) and 40 parts by weight of the compound represented by formula (HT-3).

[0164] [Table 6]

[0165] The prepared dispersion was filtered using a 5 μm mesh filter to prepare the coating solution. The coating solution was applied to the undercoat using the dip-coating method, and the coating film was dried at 110°C for 60 minutes to form a photosensitive layer. The thickness of the photosensitive layer was 25 μm.

[0166] Next, a protective layer was formed on the photosensitive layer as follows: 3.5 parts by weight of metal oxide fine particles, 9.3 parts by weight of n-type conductive fine particles, a variable amount of UV-curable polyfunctional monomer, a variable amount of photoreactive group-containing substance, and 10 parts by weight of photopolymerization initiator were dispersed in a solvent using a bead mill. The dispersion time was 10 hours. The solvent was 110 parts by weight of methanol. The types of metal oxide fine particles, n-type conductive fine particles, UV-curable polyfunctional monomer, and photoreactive group-containing substance are as shown in Tables 2 to 5 above. The total content of UV-curable polyfunctional monomer and photoreactive group-containing substance was 91 parts by weight, and the ratio of each amount is shown in Tables 2 to 5 above. The photopolymerization initiator was acyl phosphine oxide (formula (P-1) above).

[0167] The prepared dispersion was filtered using a filter with a mesh size of 5 μm to prepare a coating solution. The coating solution was applied to the photosensitive layer by dip-coating, and a protective layer was formed by irradiating the coating solution with light from an LED light source with an emission wavelength of 365 nm. The thickness of the protective layer was set to 3 μm. The electrophotographic photoreceptors for Example 1-29 and Comparative Example 1-6 were prepared in the manner described above.

[0168] <Fabrication of stacked electrophotographic photoreceptors> The electrophotographic photoreceptor according to Example 30 is a stacked electrophotographic photoreceptor, and was manufactured as follows. First, an undercoat layer was formed on a conductive substrate. The undercoat layer was formed by the same process as the undercoat layer formation process in the single-layer electrophotographic photoreceptor described above.

[0169] Next, a photosensitive layer was formed on the undercoat layer as follows. Table 7 below shows the composition of the photosensitive layer. First, a charge generation layer was formed on the undercoat layer as follows. As a method for forming the charge generation layer, 1.5 parts by weight of charge generation material (CGM) and 1 part by weight of polyvinyl acetal resin ("Eslec® BX-5", manufactured by Sekisui Chemical Co., Ltd.) as a binder resin were dispersed in a solvent using a bead mill. The dispersion time was 12 hours. The solvent was a mixture of 40 parts by weight of propylene glycol monomethyl ether and 40 parts by weight of tetrahydrofuran. The types of charge generation material (CGM) are as shown in Table 7. The prepared dispersion was filtered using a 3 μm mesh filter to prepare a coating solution. The coating solution was applied to the undercoat layer by the dip-coat method, and the coated film was dried at 50°C for 5 minutes to form a charge generation layer. The thickness of the charge generation layer was 0.2 μm.

[0170] [Table 7]

[0171] Next, a charge transport layer was formed on the charge generation layer as follows: 60 parts by weight of the compound represented by formula (HT-2) above, 30 parts by weight of the compound represented by formula (HT-3) above, 100 parts by weight of polycarbonate resin as a binder resin, various pigments, and 0.05 parts by weight of dimethyl silicone oil ("KF96-50CS" manufactured by Shin-Etsu Chemical Co., Ltd.) as a leveling agent were dispersed in a solvent using a roll mill. The solvent was a mixture of 340 parts by weight of tetrahydrofuran and 60 parts by weight of toluene. The prepared dispersion was filtered using a 3 μm mesh filter to prepare a coating solution. The coating solution was applied to the charge generation layer by dip-coating, and the coated film was dried at 120°C for 40 minutes to form a hole transport layer. The thickness of the charge generation layer was 25 μm.

[0172] Next, a protective layer was formed on the hole transport layer. The protective layer was formed by the same process as the protective layer formation process in the single-layer electrophotographic photoreceptor described above.

[0173] <Measurement and Evaluation> Various measurements and evaluations were performed on the electrophotographic photoreceptors according to the examples and comparative examples prepared as described above. The measurement and evaluation results are shown in Tables 8 and 9 below.

[0174] [Table 8]

[0175] [Table 9]

[0176] <Martens hardness measurement> The Martens hardness of the electrophotographic photoreceptors in the examples and comparative examples was measured on the surface of the photoreceptor, i.e., the surface of the protective layer. The Martens hardness was measured according to the measurement method in accordance with ISO 14577. Specifically, a hardness tester ("FISCHERSCOPE® HM2000XYp" manufactured by Fischer Instruments) was used, with a diamond square pyramidal indenter (face angle 135 degrees), and the load was gradually applied at a rate of 0.4 μm or 0.1 μm / 20 seconds, held for 5 seconds, and then the load was removed 20 seconds after holding. The environment was set to a temperature of 23°C and a humidity of 50%. The measurement results are shown as "Martens hardness" in Tables 8 and 9.

[0177] <Volume resistivity measurement> The volume resistivity was measured for the electrophotographic photoreceptors according to the examples and comparative examples. Volume resistivity was measured by pressing the electrode probe of a resistivity meter against the surface of the protective layer and applying a voltage of 100V for 10 seconds. A Hiresta-UX MCP-HT800 (manufactured by MITUSBISHI CHEMICAL ANALYTECH) was used as the resistivity meter. The measurement results are shown as "volume resistivity" in Tables 8 and 9.

[0178] <Evaluation of film-forming properties> The film-forming properties of the protective layer were evaluated for the electrophotographic photoreceptors in the examples and comparative examples. After applying the protective coating solution to the photoreceptor layer during the manufacturing process, the surface was observed. The surface was visually inspected for defects (removal of the coating), and those without defects were evaluated as "good (○)," while those with defects were evaluated as "poor (×)." The evaluation results are shown in Tables 8 and 9 as "film-forming properties."

[0179] <Image flow evaluation> The electrophotographic photoreceptors according to the examples and comparative examples were mounted on an evaluation machine, and printing was performed. The evaluation machine was a modified "Taskalfa356ci" printer (manufactured by Kyocera Document Solutions Corporation) and uses an intermediate transfer method. The evaluation machine is equipped with a charging roller made of electrostatically charged rubber (epichlorohydrin resin with dispersed conductive carbon). When a single-layer electrophotographic photoreceptor (Examples 1-29 and Comparative Example 1-6) was mounted on the evaluation machine, the charging polarity of the photoreceptor was set to the positive electrode, and the applied voltage was a DC voltage. When a stacked electrophotographic photoreceptor (Example 30) was mounted on the evaluation machine, the charging polarity of the photoreceptor was set to the negative electrode, and the applied voltage was a DC voltage.

[0180] Using the evaluation machine described above, 600 prints were performed at a print image density of 1.6%. The printing paper used was "Askul Multipaper Super Economy+", and the environment was set to a temperature of 32°C and a humidity of 80%. The printed image of the final page was observed under a microscope. If each dot and character was properly reproduced, it was evaluated as "Good (〇)", and if each dot and character was missing or could not be identified, it was evaluated as "Poor (×)". The evaluation results are shown as "Image Flow" in Tables 8 and 9.

[0181] <Abrasion resistance evaluation> After printing the 600 sheets mentioned above, the surface of the electrophotographic photoreceptor was visually inspected to check for scratches. If no scratches were found, it was evaluated as "no scratches," and if scratches were found, it was evaluated as "scratches present." The evaluation results are shown in Tables 8 and 9 as "wear resistance."

[0182] <Regarding the evaluation results> As shown in Tables 8 and 9, all of the electrophotographic photoreceptors according to the examples showed good film formation and image flow evaluation (○), and no scratches occurred on the surface of the electrophotographic photoreceptors. On the other hand, the electrophotographic photoreceptors according to the comparative examples showed poor evaluation of at least one of film formation and image flow (○), or scratches occurred on the surface of the electrophotographic photoreceptors. Therefore, it can be said that the electrophotographic photoreceptors according to the above embodiments have excellent wear resistance and can suppress image flow. [Explanation of Symbols]

[0183] 10…Control Unit 20...Operation unit 30…Paper feed section 40…Conveyor Unit 50... Toner Refill Unit 60…Image forming unit 65...Photoreceptor 70…Transfer device 80… Fixing device 90…Discharge section 100…Image forming apparatus

Claims

1. A conductive substrate, A photosensitive layer provided on the conductive substrate, A protective layer provided on the photosensitive layer and Equipped with, The protective layer comprises a substrate made of a graft polymer having a composition of a UV (ultraviolet) curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, n-type conductive fine particles dispersed in the substrate, and metal oxide fine particles dispersed in the substrate, and has a Martens hardness of 400 N / mm². ２ The above and the volume resistivity is 1.0 × 10⁻⁶ １０ It is greater than or equal to Ω·cm. Electrophotographic photoreceptor.

2. The electrophotographic photoreceptor according to claim 1, The UV-curable polyfunctional monomer has three or more (meth)acrylic groups. Electrophotographic photoreceptor.

3. The electrophotographic photoreceptor according to claim 1, The aforementioned photoreactive group-containing substance is a graft polymer in which the main chain is an organic chain and the side chains have multiple reactive groups and a fluorine-modified silicone skeleton or a silane skeleton as a release skeleton. Electrophotographic photoreceptor.

4. The electrophotographic photoreceptor according to claim 1, The aforementioned photopolymerization initiator is acyl phosphine oxide. Electrophotographic photoreceptor.

5. The electrophotographic photoreceptor according to claim 1, The protective layer has a thickness of 2 μm or more and 3 μm or less. Electrophotographic photoreceptor.

6. An electrophotographic photoreceptor according to any one of claims 1 to 5, The photosensitive layer contains an electron transport material comprising any of the compounds represented by the following general formulas (1) to (6). Electrophotographic photoreceptor. 【Chemistry 1】 【Chemistry 2】 【Transformation 3】 【Chemistry 4】 【Transformation 5】 【Transformation 6】 (In general formulas (1) to (6), R １ ~R ２８ Each of these independently represents a hydrogen atom, a halogen atom, a cyano group, or an alkyl group having 1 to 6 carbon atoms, X １ and X ２ Each independently represents an alkenyl group having 2 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 14 carbon atoms which may have at least one alkyl group having 1 to 6 carbon atoms, Y １ ~Y ３ Each of these independently represents either a halogen group or an oxygen atom.

7. An electrophotographic photoreceptor according to any one of claims 1 to 5, The photosensitive layer contains a hole transport material comprising any of the compounds represented by the following general formulas (7) to (10). Electrophotographic photoreceptor. 【Transformation 7】 【Transformation 8】 【Chemistry 9】 【Chemistry 10】 (In general formulas (7) to (10), R １ to R １６ each independently represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group, and n represents a natural number of 1 or less.)

8. An electrophotographic photoreceptor according to any one of claims 1 to 5, The photosensitive layer contains a charge-generating material which is titanyl phthalocyanine or inorganic phthalocyanine. Electrophotographic photoreceptor.

9. The electrophotographic photoreceptor according to claim 1, The protective layer is formed by applying a coating solution, which is a mixture of the UV-curable polyfunctional monomer, the photoreactive group-containing substance, the photopolymerization initiator, the n-type conductive fine particles, and the metal oxide fine particles, onto the photosensitive layer, and then irradiating the coating solution with light. Electrophotographic photoreceptor.

10. The electrophotographic photoreceptor according to claim 9, The aforementioned light has a wavelength of 365 nm. Electrophotographic photoreceptor.

11. A conductive substrate, A photosensitive layer provided on the conductive substrate, A protective layer provided on the photosensitive layer and It comprises an electrophotographic photoreceptor, The protective layer comprises a substrate made of a graft polymer having a composition of a UV (ultraviolet) curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, n-type conductive fine particles dispersed in the substrate, and metal oxide fine particles dispersed in the substrate, and has a Martens hardness of 400 N / mm². ２ The above and the volume resistivity is 1.0 × 10⁻⁶ １０ It is greater than or equal to Ω·cm. Process cartridge.

12. An electrophotographic photoreceptor comprising a conductive substrate, a photosensitive layer provided on the conductive substrate, and a protective layer provided on the photosensitive layer, A charging device for charging the surface of the electrophotographic photoreceptor, An exposure apparatus that exposes the charged surface to form an electrostatic latent image on the surface, A developing apparatus that develops the electrostatic latent image as a toner image, A transfer device for transferring the toner image from the electrophotographic photoreceptor to a transfer target, It is equipped with, The protective layer comprises a substrate made of a graft polymer having a composition of a UV (ultraviolet) curable polyfunctional monomer, a photopolymerization initiator, and a photoreactive group-containing substance, n-type conductive fine particles dispersed in the substrate, and metal oxide fine particles dispersed in the substrate, and has a Martens hardness of 400 N / mm². ２ The above and the volume resistivity is 1.0 × 10⁻⁶ １０ It is greater than or equal to Ω·cm. Image forming apparatus.

13. An image forming apparatus according to claim 12, The charging device comprises a charging roller. Image forming apparatus.

14. An image forming apparatus according to claim 12 or 13, The developing apparatus is a two-component developing system, a one-component developing system, or a friction roller system. Image forming apparatus.

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