Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge, and image forming device

Abstract

To provide an electrophotographic photoreceptor capable of improving the image gradation in printing in a high-temperature and high-humidity environment, so that areas printed at low density are printed as intended.SOLUTION: The electrophotographic photoreceptor includes a photosensitive layer and a protective layer in order over a conductive support. The electrophotographic photoreceptor contains the protective layer that is a cured product of a curable compound and a metal oxide particle that is surface-treated with a compound represented by the following formula (a): (In formula (a), R1 represents an alkoxy group having 1 to 3 carbon atoms. R2 represents an alkyl group or a phenyl group having 1 to 3 carbon atoms. R3 represents a phenyl group, an alkyl group having 1 to 10 carbon atoms, or a cycloalkyl group having 3 to 10 carbon atoms. m is 2 or 3)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic photoreceptor used in a copying machine, a printer, etc., and a cartridge and an image forming apparatus using the same. [Background technology]

[0002] In printers and copiers, when a charged organic photoconductor (OPC) drum is irradiated with light, the part is discharged, creating an electrostatic latent image, to which toner adheres to create an image. In devices that use electrophotography, the photoconductor is a key component.

[0003] Because this type of organic photoreceptor offers a wide range of material options and allows for easy control of photoreceptor properties, "function-separated photoreceptors," in which the functions of negative charge generation and transport are shared by separate compounds, have become mainstream. For example, known electrophotographic photoreceptors include a single-layer electrophotographic photoreceptor (hereinafter referred to as a single-layer photoreceptor) that contains a charge-generating material (CGM) and a charge-transporting material (CTM) in the same layer, and a multilayer electrophotographic photoreceptor (hereinafter referred to as a multilayer photoreceptor) that consists of a charge-generating layer containing a charge-generating material (CGM) and a charge-transporting layer containing a charge-transporting material (CTM). Furthermore, photoreceptor charging methods include a negative charging method, in which the photoreceptor surface is negatively charged, and a positive charging method, in which the photoreceptor surface is positively charged. Combinations of layer structures and charging methods of photoreceptors currently in practical use include "negatively charged multilayer photoreceptors" and "positively charged single layer photoreceptors."

[0004] A "negatively charged laminated photoreceptor" generally has a structure in which an undercoat layer (UCL) made of a resin or the like is provided on a conductive support such as an aluminum tube, on which a charge generation layer (CGL) made of a charge generation material (CGM) and a resin or the like is provided, and on which a charge transport layer (CTL) made of a hole transport material (HTM) and a resin or the like is provided.

[0005] On the other hand, a "positively charged single-layer photoreceptor" generally has a structure in which an undercoat layer (UCL) made of a resin or the like is provided on a conductive support such as an aluminum tube, and a single-layer photosensitive layer made of a charge generating material (CGM), a hole transport material (HTM), an electron transport material (ETM), and a resin or the like is provided on top of that (see, for example, Patent Document 1).

[0006] In either photoconductor, the surface of the photoconductor is charged using corona discharge or contact, and then the photoconductor is exposed to light to neutralize the surface charge, forming an electrostatic latent image due to the potential difference with the surrounding surface.Toner is then brought into contact with the photoconductor surface to form a toner image corresponding to the electrostatic latent image, which is then transferred to paper or other material and heated to melt and fix it to create a print.

[0007] As described above, the basic structure of an electrophotographic photoreceptor is a photosensitive layer formed on a conductive support, but in order to improve abrasion resistance, etc., a protective layer is provided on the photosensitive layer.

[0008] As a technique for improving the mechanical strength or abrasion resistance of the photoreceptor surface, a photoreceptor has been disclosed in which a layer containing a compound having a chain-polymerizable functional group, i.e., a curable resin compound, is formed as a binder resin in the outermost layer of the photoreceptor, and this is polymerized by applying energy such as heat, light, or radiation to form a cured resin layer (protective layer) (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 9,417,538 [Patent Document 2] International Publication No. 2010 / 035683 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-170129 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-107696 [Patent Document 5] Japanese Patent Application Laid-Open No. 2014-145891 Summary of the Invention [Problem to be solved by the invention]

[0010] It is known that metal oxide particles are contained in the protective layer provided on the photosensitive layer in order to improve the electrical properties of the protective layer. However, it has been found that when a protective layer containing metal oxide particles such as titanium oxide is formed, the gradation of the image tends to decrease when an image is formed in a high-temperature, high-humidity environment, and low-density printed areas tend to be printed lighter than specified.

[0011] An object of the present invention is to provide an electrophotographic photosensitive member, an electrophotographic photosensitive member cartridge, and an image forming apparatus that can solve the above-mentioned problems. [Means for solving the problem]

[0012] In order to solve these problems, the present invention relates to an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer formed in that order on a conductive support, and aims to provide an electrophotographic photoreceptor that provides good image gradation when printing in a high-temperature, high-humidity environment, and that allows areas printed at low density to be printed as specified.

[0013] The inventors have conducted extensive research to solve the above problem and have discovered that the reduction in image gradation is caused by the movement of charge from unexposed areas to exposed areas, resulting in a reduction in the contrast between exposed and unexposed areas that form the image. The present inventors discovered that by incorporating metal oxide particles that have been surface-treated with a compound having a specific structure into a protective layer, the movement of charge from unexposed areas to exposed areas can be suppressed, and the contrast between exposed and unexposed areas that form an image can be made clear, resulting in good image gradation and making it possible to provide an electrophotographic photoreceptor in which areas printed at low density can be printed as specified, thereby achieving the present invention.

[0014] The gist of the present invention resides in the following [1] to [7].

[0015] [1] An electrophotographic photoreceptor having at least a photosensitive layer and a protective layer sequentially provided on a conductive support, The electrophotographic photoreceptor, wherein the protective layer contains a cured product of a curable compound and metal oxide particles that have been surface-treated with a compound represented by the following formula (a): TIFF2025153628000001.tif43170 (in formula (a), R 1 represents an alkoxy group having 1 to 3 carbon atoms. 2 R represents an alkyl group having 1 to 3 carbon atoms which may have a substituent, or a phenyl group which may have a substituent. 3 represents an optionally substituted phenyl group, an optionally substituted alkyl group having from 1 to 10 carbon atoms, or an optionally substituted cycloalkyl group having from 3 to 10 carbon atoms; and m is 2 or 3.

[0016] [2] In the formula (a), the R 1 is a methoxy group or an ethoxy group.

[0017] [3] The electrophotographic photoreceptor according to [1] or [2], wherein in the formula (a), m is 3.

[0018] [4] The electrophotographic photoreceptor according to any one of [1] to [3], wherein the curable compound is a polyfunctional acrylate or a polyfunctional methacrylate.

[0019] [5] The electrophotographic photoreceptor according to any one of [1] to [4], wherein the metal oxide particles have a band gap of 2 eV or more and 4 eV or less.

[0020] [6] An electrophotographic photosensitive member cartridge comprising the electrophotographic photosensitive member according to any one of [1] to [5] above.

[0021] [7] An image forming apparatus comprising the electrophotographic photoreceptor according to any one of [1] to [5] above. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide an electrophotographic photosensitive member, an electrophotographic photosensitive member cartridge, and an image forming apparatus that have good image gradation and allow areas printed at low density to be printed as set. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a diagram schematically illustrating an example of the configuration of an image forming apparatus that can be configured using an electrophotographic photosensitive member according to an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The following describes in detail the mode for carrying out the present invention (hereinafter, "embodiments of the invention"). Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention.

[0025] <<The present electrophotographic photoreceptor>> An electrophotographic photoreceptor according to one embodiment of the present invention (also referred to as "the present electrophotographic photoreceptor") is an electrophotographic photoreceptor including, on a conductive support, a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound, in that order.

[0026] The electrophotographic photoreceptor may optionally have layers other than the photosensitive layer and the protective layer. The electrophotographic photosensitive member may be charged by either a negative charging method in which the surface of the photosensitive member is negatively charged or a positive charging method in which the surface of the photosensitive member is positively charged.

[0027] In the present electrophotographic photoreceptor, the side opposite to the conductive support is the upper side or front side, and the conductive support side is the lower side or back side.

[0028] (Thickness of the photosensitive layer) The thickness of the photosensitive layer in the present electrophotographic photoreceptor (also referred to as "the present photosensitive layer") is preferably 10 μm or more, more preferably 15 μm or more, even more preferably 19 μm or more, even more preferably 20 μm or more, even more preferably 22 μm or more, and even more preferably 24 μm or more, from the viewpoints of dielectric breakdown resistance, electrical properties, and printing durability. On the other hand, from the viewpoint of chargeability, the thickness is preferably 40 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less. The thickness of the photosensitive layer referred to here refers to the thickness of a single-layer photosensitive layer, and refers to the total thickness of the charge generating layer and the charge transport layer in the case of a multi-layer photosensitive layer.

[0029] (Thickness of this protective layer) The thickness of the protective layer is selected appropriately depending on the material used, etc. From the viewpoint of the service life of the photoreceptor, the thickness of the protective layer is preferably 0.1 μm or more, more preferably 0.2 μm or more, and particularly preferably 0.5 μm or more. From the viewpoint of electrical properties, the thickness of the protective layer is preferably 10 μm or less, more preferably 5 μm or less, and particularly preferably 3 μm or less. In particular, from the viewpoint of suppressing the occurrence of ghosts, the thickness of the protective layer is preferably 1 μm or less, more preferably 0.1 μm or more or 3 μm or less, even more preferably 0.5 μm or more or 2 μm or less, and even more preferably 0.8 μm or more or 1.5 μm or less.

[0030] From the viewpoint of film-forming properties, the ratio A / B of the thickness A of the protective layer to the thickness B of the photosensitive layer is preferably 0.002 or more, more preferably 0.005 or more, even more preferably 0.008 or more, and particularly preferably 0.01 or more. On the other hand, the ratio A / B of the thickness A of the protective layer to the thickness B of the photosensitive layer is preferably 0.3 or less, more preferably 0.2 or less, even more preferably 0.1 or less, and particularly preferably 0.06 or less.

[0031] <Main photosensitive layer> The photosensitive layer in the present electrophotographic photoreceptor (present photosensitive layer) may be a single-layer photosensitive layer in which a charge generating material (CGM), a hole transporting material (HTM), and an electron transporting material (ETM) are present in the same layer, or may be a multi-layer photosensitive layer separated into a charge generating layer and a charge transporting layer.

[0032] <Layered photosensitive layer> The laminated photosensitive layer in the present electrophotographic photoreceptor may have a structure in which a charge transport layer (CTL) containing a hole transport material (HTM) is laminated on a charge generation layer (CGL) containing a charge generation material (CGM), or a structure in which the charge generation layer (CGL) is laminated on the charge transport layer (CTL).Of these, a structure in which the charge transport layer (CTL) is laminated on the charge generation layer (CGL) is preferred. In this case, it is possible to provide layers other than the charge generation layer (CGL) and the charge transport layer (CTL). The charge transport layer (CTL) may further contain an electron transport material (ETM).

[0033] <Charge generation layer (CGL)> The charge generating layer usually contains a charge generating material (CGM) and a binder resin.

[0034] (Charge-Generating Materials (CGM)) Examples of the charge generating material include inorganic photoconductive materials such as selenium and its alloys, cadmium sulfide, etc., and organic photoconductive materials such as organic pigments. Among these, organic photoconductive materials are preferred, and organic pigments are particularly preferred. Among these, phthalocyanine pigments and azo pigments are more preferred, and phthalocyanine pigments are even more preferred. These all refer to the skeletal structures of compounds, and include compounds having these skeletal structures, i.e., derivatives.

[0035] When an organic pigment is used as the charge generating material, fine particles of the organic pigment are usually used in the form of a dispersed layer bound with various binder resins.

[0036] Specific examples of the phthalocyanine pigment include metal-free phthalocyanine, phthalocyanine crystalline forms coordinated with metals such as copper, gallium, tin, and titanium, or their oxides or halides, and phthalocyanine dimers using oxygen atoms or the like as bridging atoms. Particularly preferred are highly sensitive crystalline forms such as X-type, τ-type metal-free phthalocyanine, A-type (also known as β-type), and B-type (also known as α-type), titanyl phthalocyanine (also known as oxytitanium phthalocyanine) such as D-type (also known as Y-type), which exhibits a clear peak at a diffraction angle 2θ (±0.2°) of 27.1° or 27.3° in powder X-ray diffraction, chlorogallium phthalocyanine such as II-type, and hydroxygallium phthalocyanine such as V-type.

[0037] The charge-generating material may be used alone or in any combination and ratio of two or more. Furthermore, when two or more charge-generating materials are used in combination, the materials may be mixed after each other or may be mixed during the manufacturing or processing process of the charge-generating material, such as synthesis, pigmentization, or crystallization. Examples of such processes include acid paste treatment, grinding, and solvent treatment.

[0038] The particle size of the charge generating material is usually 1 μm or less, and preferably 0.5 μm or less. Furthermore, from the viewpoint of sensitivity, the content of the charge generating material in the photosensitive layer is usually preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and from the viewpoint of sensitivity and chargeability, it is usually preferably 50% by mass or less, more preferably 20% by mass or less.

[0039] (binder resin) The binder resin used in the charge generating layer can be used without any particular limitation. Examples include polyvinyl acetal resins such as polyvinyl butyral resin, polyvinyl formal resin, and partially acetalized polyvinyl butyral resin in which butyral is partially modified with formal or acetal; polyarylate resin, polycarbonate resin, polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin; and vinyl chloride-vinyl acetate copolymer. Among these resins, polyvinyl acetal resin or polyvinyl acetate resin is preferred in terms of pigment dispersibility, adhesion to the conductive support or undercoat layer, and adhesion to the charge transport layer. These binder resins may be used either alone or as a mixture of two or more kinds in any combination.

[0040] (Other ingredients) In addition to the charge generating material and the binder resin, the charge generating layer may contain other components as needed. For example, known additives such as antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light shielding agents, and fillers may be added to improve film-forming properties, flexibility, coating properties, stain resistance, gas resistance, light resistance, etc.

[0041] (composition ratio) If the ratio of the charge generating material in the charge generating layer is too high, the stability of the coating liquid may decrease due to aggregation of the charge generating material, etc., while if the ratio of the charge generating material is too low, the sensitivity of the photoreceptor may decrease. Therefore, the compounding ratio (by mass) of the binder resin to the charge generating material is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, of the charge generating material per 100 parts by mass of the binder resin, and is preferably 1000 parts by mass or less, more preferably 500 parts by mass or less. From the viewpoint of film strength, it is more preferably 300 parts by mass or less, and even more preferably 200 parts by mass or less.

[0042] (layer thickness) The thickness of the charge generating layer is preferably 0.1 μm or more, more preferably 0.15 μm or more, and is preferably 10 μm or less, more preferably 0.6 μm or less.

[0043] <Charge transport layer (CTL)> The charge transport layer (CTL) usually contains a hole transport material (HTM) and a binder resin, and may further contain an electron transport material (ETM).

[0044] (Hole Transport Material (HTM)) The hole transport material (HTM) is not particularly limited, and examples thereof include electron-donating substances such as heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, and benzofuran derivatives, aniline derivatives, hydrazone derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, as well as compounds in which a plurality of these compounds are bonded, and polymers having groups composed of these compounds in the main chain or side chain.

[0045] Among these, carbazole derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives, and compounds in which two or more of these compounds are combined are preferred, with arylamine derivatives and enamine derivatives being more preferred, and enamine derivatives being even more preferred because they are less likely to inject electrons.

[0046] Suitable examples of hole transport materials (HTMs) include, but are not limited to, compounds having any of the structures represented by the following general formulas. Any one of these may be used alone, or two or more may be used in any combination.

[0047] TIFF2025153628000002.tif50170

[0048] TIFF2025153628000003.tif60170

[0049] TIFF2025153628000004.tif51170

[0050] TIFF2025153628000005.tif60170

[0051] TIFF2025153628000006.tif49170

[0052] TIFF2025153628000007.tif40170

[0053] TIFF2025153628000008.tif52170

[0054] TIFF2025153628000009.tif42170

[0055] TIFF2025153628000010.tif50170

[0056] Among the above-mentioned exemplary compounds, it is preferable to include the compound represented by the following formula (1) as the hole transport material (HTM) because the effects of the present invention can be more effectively obtained.

[0057] TIFF2025153628000011.tif51170

[0058] Among the hole transport materials (HTM), compounds having two or more nitrogen atoms in one molecule are preferred, and compounds having a bilaterally symmetric structure are also preferred.

[0059] The content of the hole transport material (HTM) in the charge transport layer is preferably 10 parts by weight or more, more preferably 20 parts by weight or more, and even more preferably 30 parts by weight or more, per 100 parts by weight of the binder resin, and is preferably 150 parts by weight or less, more preferably 120 parts by weight or less, and even more preferably 100 parts by weight or less.

[0060] (Electron transport material (ETM)) Examples of electron transport materials (ETMs) include, but are not limited to, electron-withdrawing substances such as aromatic nitro compounds such as 2,4,7-trinitrofluorenone, cyano compounds such as tetracyanoquinodimethane, and quinone compounds such as diphenoquinone and dinaphthylquinone, as well as compounds in which a plurality of these compounds are bonded, and polymers having groups consisting of these compounds in the main chain or side chain. However, the present invention is not limited to these, and known electron transport materials can be used. Among these, quinone compounds and perylene pigments (perylene derivatives) are preferred from the viewpoint of electrical properties, and quinone compounds are more preferred. Among the quinone compounds, diphenoquinone or dinaphthylquinone is preferred from the viewpoint of electrical properties, and among these, dinaphthylquinone is more preferred. The above electron transport materials may be used alone or in any combination of two or more.

[0061] Specific examples of electron transport materials (ETMs) that can be used in the present electrophotographic photoreceptor include compounds represented by general formulas (ET1) to (ET3) exemplified in paragraphs 0043 to 0053 of JP-A No. 2017-09765. Further examples include compounds having any of the following structures:

[0062] TIFF2025153628000012.tif56170

[0063] TIFF2025153628000013.tif44170

[0064] The content of the electron transport material (ETM) in the charge transport layer is preferably 10 parts by weight or more, more preferably 20 parts by weight or more, and even more preferably 30 parts by weight or more, per 100 parts by weight of the binder resin, and is preferably 150 parts by weight or less, more preferably 120 parts by weight or less, and even more preferably 100 parts by weight or less.

[0065] The content of the electron transport material (ETM) in the charge transport layer is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the hole transport material (HTM) in the charge transport layer, and is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, and even more preferably 5 parts by weight or less.

[0066] (binder resin) Examples of the binder resin for the charge transport layer include vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymers thereof, thermoplastic resins such as polycarbonate, polyarylate, polyester, polyester polycarbonate, polysulfone, phenoxy, epoxy, and silicone resins, and various thermosetting compounds. Among these resins, polycarbonate resins and polyarylate resins are preferred in terms of light attenuation characteristics and mechanical strength as a photoreceptor.

[0067] The viscosity average molecular weight (Mv) of the binder resin is usually in the range of 5,000 to 300,000, preferably 10,000 to 200,000, more preferably 15,000 to 150,000, and particularly preferably 20,000 to 80,000. If the viscosity average molecular weight (Mv) is too small, the mechanical strength of the resulting film used in forming a photoreceptor or the like tends to decrease. On the other hand, if the viscosity average molecular weight (Mv) is too large, the viscosity of the coating solution increases, making it difficult to coat the film to an appropriate thickness.

[0068] (Other ingredients) In addition to the hole transport material (HTM), electron transport material (ETM), and binder resin, the charge transport layer may contain other components as needed. For example, known additives such as antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light shielding agents, and fillers may be added to improve film-forming properties, flexibility, coating properties, stain resistance, gas resistance, light resistance, etc.

[0069] (layer thickness) The thickness of the charge transport layer is not particularly limited, but from the viewpoints of electrical properties, image stability, and high resolution, it is preferably 5 μm to 50 μm, more preferably 10 μm to 35 μm, and even more preferably 15 μm to 25 μm.

[0070] <Single-layer photosensitive layer> When the photosensitive layer of the present electrophotographic photoreceptor is a single-layer type photosensitive layer, the binder resin, the charge generating material, the hole transport material, and the electron transport material are usually contained in the same layer.

[0071] The charge generating material, the hole transporting material, and the electron transporting material are the same as those explained for the laminated photosensitive layer.

[0072] The content of the charge generating material in the single-layer photosensitive layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of sensitivity, and is preferably 50% by mass or less, more preferably 20% by mass or less, from the viewpoint of sensitivity and chargeability.

[0073] In a single-layer photosensitive layer, the content ratio of the binder resin and the hole transport material constituting the photosensitive layer is preferably 20 parts by mass or more of the hole transport material per 100 parts by mass of the binder resin, more preferably 30 parts by mass or more from the viewpoint of reducing residual potential, and even more preferably 40 parts by mass or more from the viewpoints of stability and charge mobility during repeated use. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, the content ratio of the hole transport material per 100 parts by mass of the binder resin is preferably 200 parts by mass or less, more preferably 150 parts by mass or less from the viewpoint of compatibility between the hole transport material and the binder resin, and particularly preferably 120 parts by mass or less from the viewpoint of abrasion resistance.

[0074] The content ratio of the binder resin and the electron transport material in the single-layer photosensitive layer is preferably 5 parts by mass or more of the electron transport material per 100 parts by mass of the binder resin. From the viewpoint of reducing the residual potential, 10 parts by mass or more is more preferable, and from the viewpoints of stability during repeated use and charge mobility, 20 parts by mass or more is even more preferable. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, the content of the electron transport material per 100 parts by mass of the binder resin is preferably 100 parts by mass or less. From the viewpoint of compatibility between the electron transport material and the binder resin, 80 parts by mass or less is more preferable, 60 parts by mass or less is even more preferable, and 50 parts by mass or less is particularly preferable.

[0075] In the single-layer photosensitive layer, the ratio (mass ratio) of the electron transport material (ETM) to the hole transport material (HTM) is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more, and is preferably 1 or less, more preferably 0.9 or less, and even more preferably 0.8 or less.

[0076] The content ratio of the binder resin and the charge transport material (electron transport material and hole transport material) constituting the single-layer photosensitive layer is arbitrary, but preferably 25 parts by weight or more of the charge transport material per 100 parts by weight of the binder resin. From the viewpoint of reducing residual potential, 35 parts by weight or more is preferred, and from the viewpoints of stability and charge mobility during repeated use, 45 parts by weight or more is more preferred. From the viewpoint of thermal stability of the photosensitive layer, on the other hand, 200 parts by weight or less of the charge transport material per 100 parts by weight of the binder resin is preferred, and from the viewpoint of compatibility between the charge transport material and the binder resin, 150 parts by weight or less is more preferred, 125 parts by weight or less is even more preferred, and 100 parts by weight or less is particularly preferred.

[0077] <Method of forming each photosensitive layer> In either the laminated type or the single layer type, the above-mentioned layers can be formed as follows. The coating solution obtained by dissolving or dispersing the substance to be contained in a solvent can be applied to a conductive support by a known method such as dip coating, spray coating, nozzle coating, bar coating, roll coating, or blade coating, and the layers can be formed by repeating the coating and drying steps in sequence. However, the method is not limited to this.

[0078] The solvent or dispersion medium used to prepare the coating liquid is not particularly limited. Specific examples include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; aromatic hydrocarbons such as benzene, toluene, xylene, and anisole; and chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichloroethylene. These solvents may be used alone or in any combination and ratio.

[0079] The amount of the solvent or dispersion medium used is not particularly limited, and is preferably adjusted appropriately so that the solids concentration, viscosity, and other physical properties of the coating liquid fall within the desired range, taking into consideration the purpose of each layer and the properties of the selected solvent or dispersion medium. The coating film is preferably dried to the touch at room temperature, and then heated and dried at a temperature in the range of 30° C. to 200° C. for 1 minute to 2 hours, either stationary or with a fan. The heating temperature may be constant, or the temperature may be varied during drying.

[0080] <Main protective layer> The protective layer of the present electrophotographic photoreceptor (present protective layer) is a layer containing a cured product obtained by curing a curable compound and metal oxide particles.

[0081] Examples of the curable compound include photocurable compounds, heat-curable compounds, and radiation-curable compounds. Among these, photocurable compounds are preferred from the viewpoint of improving abrasion resistance.

[0082] The curable compound is preferably, for example, a compound having a chain-polymerizable functional group. From the viewpoint of reactivity, the compound having a chain-polymerizable functional group usually has two or more, preferably three or more, and more preferably four or more chain-polymerizable functional groups, and on the other hand, usually has 20 or less, preferably 10 or less, and more preferably 6 or less chain-polymerizable functional groups. Examples of the chain-polymerizable functional group of the compound having the chain-polymerizable functional group include an acryloyl group, a methacryloyl group, a vinyl group, and an epoxy group. Among these, examples of the chain-polymerizable functional group capable of radical polymerization include an acryloyl group, a methacryloyl group, and a vinyl group, and from the viewpoint of curing speed, an acryloyl group and a methacryloyl group are preferred. The curable compound preferably has two or more chain-polymerizable functional groups, and the functional groups are preferably acryloyl groups or methacryloyl groups, and are preferably polyfunctional acrylates or polyfunctional methacrylates. The compound having a chain-polymerizable functional group is not particularly limited as long as it is a known material, but from the viewpoint of curability, a monomer, oligomer, or polymer having an acryloyl group or a methacryloyl group is preferred.

[0083] Preferred examples of the compound are shown below. Monomers which are polyfunctional acrylates or polyfunctional methacrylates having two or more acryloyl groups or methacryloyl groups include trimethylolpropane triacrylate (A-TMPT), trimethylolpropane trimethacrylate (TMPT), ditrimethylolpropane tetramethacrylate (D-TMP), HPA-modified trimethylolpropane triacrylate, EO-modified trimethylolpropane triacrylate, PO-modified trimethylolpropane triacrylate, caprolactone-modified trimethylolpropane triacrylate, HPA-modified trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerol triacrylate, ECH-modified glycerol triacrylate, EO-modified glycerol triacrylate, PO-modified glycerol triacrylate, tris(acryloxyethyl)isocyanurate, caprolactone-modified tris(acryloxyethyl)isocyanurate, EO-modified trimethylolpropane triacrylate, Tris(acryloxyethyl)isocyanurate, PO-modified tris(acryloxyethyl)isocyanurate, dipentaerythritol hexaacrylate (A-DPH), caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hydroxypentaacrylate, alkyl-modified dipentaerythritol pentaacrylate, alkyl-modified dipentaerythritol tetraacrylate, alkyl-modified dipentaerythritol triacrylate, dimethylolpropane tetraacrylate, pentaerythritol ethoxy tetraacrylate, EO-modified phosphate triacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, polytetramethylene glycol diacrylate, EO-modified bisphenol A diacrylate, PO-modified bisphenol A diacrylate, 9,Examples of such an alkyl acrylate include 9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, tricyclodecane dimethanol diacrylate, decanediol diacrylate, hexanediol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, EO-modified bisphenol A dimethacrylate, PO-modified bisphenol A dimethacrylate, tricyclodecane dimethanol dimethacrylate, decanediol dimethacrylate, and hexanediol dimethacrylate.

[0084] As oligomers and polymers having an acryloyl group or a methacryloyl group, known urethane acrylates, ester acrylates, acrylic acrylates, epoxy acrylates, etc. can be used. Examples of the urethane acrylate include "EBECRYL8301", "EBECRYL1290", "EBECRYL1830", and "KRM8200" (Daicel-Allnex Co., Ltd.), "UV1700B", "UV7640B", "UV7605B", "UV6300B", and "UV7550B" (Mitsubishi Chemical Corporation). Examples of the ester acrylate include "M-7100", "M-7300K", "M-8030", "M-8060", "M-8100", "M-8530", "M-8560", and "M-9050" (Toagosei Co., Ltd.). Examples of the acrylic acrylate include "8BR-600", "8BR-930MB", "8KX-078", "8KX-089", and "8KX-168" (Taisei Fine Chemical Co., Ltd.).

[0085] These may be used alone or in combination of two or more. Among these, it is preferable to contain urethane acrylate from the viewpoint of electrical properties.

[0086] In addition to the compound having a chain-polymerizable functional group, the protective layer may contain metal oxide particles or a charge transport material for the purpose of imparting charge transport capability, and may also contain a polymerization initiator for accelerating the polymerization reaction.

[0087] The materials (metal oxide particles, charge transport material, polymerization initiator) used in the protective layer will be described in detail below.

[0088] (metal oxide particles) The protective layer contains metal oxide particles from the viewpoint of imparting charge transport capability to the protective layer and improving mechanical strength. Among the metal oxide particles, it is preferable to contain metal oxide particles having a band gap of 2 eV or more and 4 eV or less (also referred to as "conductive metal oxide particles").

[0089] As the conductive metal oxide particles, any metal oxide particles that can be used in electrophotographic photoreceptors can be used. More specifically, examples of conductive metal oxide particles include metal oxide particles containing one type of metal element such as titanium oxide, tin oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, and metal oxide particles containing multiple metal elements such as indium tin oxide, calcium titanate, strontium titanate, and barium titanate. These conductive metal oxide particles may be used alone or in combination of multiple types of particles. Among these conductive metal oxide particles, titanium oxide, tin oxide, indium tin oxide, aluminum oxide, silicon oxide, and zinc oxide are preferred from the viewpoint of electron transport properties, and titanium oxide and tin oxide are more preferred, with titanium oxide being particularly preferred.

[0090] The titanium oxide particles may be in any of the crystalline forms of rutile, anatase, brookite, and amorphous. The titanium oxide particles may also contain particles in a plurality of crystalline forms, each of which has a different crystalline form. The conductive metal oxide particles may be of one type only, or may be a mixture of a plurality of types.

[0091] Generally, the conductive metal oxide particles preferably have an average primary particle size of 500 nm or less, more preferably 1 nm to 100 nm, and even more preferably 5 to 50 nm. This average primary particle size can be determined from the arithmetic mean value of particle sizes observed directly with a transmission electron microscope (hereinafter also referred to as TEM).

[0092] Among the conductive metal oxide particles of the electrophotographic photoreceptor, specific trade names of titanium oxide particles include ultrafine particle titanium oxide that has not been subjected to surface treatment "TTO-55(N)" and "TTO-51(N)", ultrafine particle titanium oxide that has been coated with Al2O3 "TTO-55(A)" and "TTO-55(B)", ultrafine particle titanium oxide that has been surface-treated with stearic acid "TTO-55(C)", ultrafine particle titanium oxide that has been surface-treated with Al2O3 and organosiloxane "TTO-55(S)", and high-purity titanium oxide. "C-EL", sulfuric acid method titanium dioxide "R-550", "R-580", "R-630", "R-670", "R-680", "R-780", "A-100", "A-220", "W-10", chlorine method titanium dioxide "CR-50", "CR-58", "CR-60", "CR-60-2", "CR-67", conductive titanium dioxide "ET-300W" (all manufactured by Ishihara Sangyo Kaisha, Ltd.), titanium dioxide such as "R-60", "A-110", "A-150", as well as Al2O3 coated titanium dioxide "SR-1 "," "R-GL," "R-5N," "R-5N-2," "R-52N," "RK-1," "A-SP," "R-GX" and "R-7E" coated with SiO2 and Al2O3, "R-650" coated with ZnO, SiO2, and Al2O3, "R-61N" coated with ZrO2 and Al2O3 (all manufactured by Sakai Chemical Industry Co., Ltd.), "TR-700" surface-treated with SiO2 and Al2O3, "TR-840" and "TA-500" surface-treated with ZnO, SiO2, and Al2O3, as well as "TA- Examples include titanium oxides with untreated surfaces such as "TA-100," "TA-200," and "TA-300," "TA-400" with an Al2O3 surface treatment (all manufactured by Fuji Titanium Industry Co., Ltd.), "MT-150W" and "MT-500B" with no surface treatment, "MT-100SA" and "MT-500SA" with SiO2 and Al2O3 surface treatment, and "MT-100SAS" and "MT-500SAS" with SiO2, Al2O3, and organosiloxane surface treatment (manufactured by Teika Corporation).

[0093] Specific examples of the trade name of aluminum oxide particles include "Aluminum Oxide C" (manufactured by Nippon Aerosil Co., Ltd.).

[0094] Specific trade names of silicon oxide particles include "200CF" and "R972" (manufactured by Nippon Aerosil Co., Ltd.), and "KEP-30" (manufactured by Nippon Shokubai Co., Ltd.).

[0095] Specific trade names of tin oxide particles include "SN-100P" and "SN-100D" (manufactured by Ishihara Sangyo Kaisha), "SnO2" (manufactured by CIK Nanotech Co., Ltd.), "S-2000," phosphorus-doped tin oxide "SP-2," antimony-doped tin oxide "T-1," and indium-doped tin oxide "E-ITO" (Mitsubishi Materials Corporation).

[0096] A specific trade name of the zinc oxide particles is "MZ-305S" (manufactured by Teika Corporation), but the conductive metal oxide particles that can be used in the present invention are not limited to this.

[0097] The conductive metal oxide particles are metal oxide particles whose surfaces have been surface-treated with a compound represented by the following formula (a). TIFF2025153628000014.tif43170 In formula (a), R 1 represents an alkoxy group having 1 to 3 carbon atoms. 2 R represents an alkyl group having 1 to 3 carbon atoms which may have a substituent, or a phenyl group which may have a substituent. 3 represents an optionally substituted phenyl group, an optionally substituted alkyl group having from 1 to 10 carbon atoms, or an optionally substituted cycloalkyl group having from 3 to 10 carbon atoms. m is 2 or 3. In order to improve the dispersibility of the surface-treated metal oxide particles in a coating solution described later, R 1 is preferably a methoxy group or an ethoxy group, and more preferably a methoxy group. 3 is preferably a phenyl group which may have a substituent, or an alkyl group having 1 to 10 carbon atoms which may have a substituent. In order to enhance the reactivity of the surface-treated metal oxide particles, m is preferably 3 in the formula (a).

[0098] The metal oxide particles are surface-treated with the compound represented by formula (a) to improve their dispersibility in the protective layer-forming coating solution. The surface-treated metal oxide particles maintain their dispersibility in the protective layer-forming coating solution, and together with the curable compound, they form a protective layer. The metal oxide particles are dispersed in the protective layer and function as conductive particles in the vertical direction of the thin protective layer, e.g., a thickness of 1 μm to 5 μm. Meanwhile, in the in-plane direction of the protective layer, the curable compound penetrates between the metal oxide particles, suppressing the flow of charge, preventing charge from moving from the unexposed areas to the exposed areas. This results in a clearer contrast between the exposed and unexposed areas forming an image, improving the gradation of the image.

[0099] Furthermore, in a high-temperature, high-humidity environment, metal oxide particles absorb moisture, increasing their conductivity, which causes areas printed at low densities to be printed lighter than intended. The compound represented by formula (a) used for surface treatment of metal oxide particles increases the hydrophobicity of the metal oxide particles and reduces the hygroscopicity of the metal oxide particles. As a result, even in a high-temperature, high-humidity environment, the metal oxide particles contained in the protective layer are less likely to absorb moisture, preventing areas printed at low densities from being printed lighter than intended, allowing printing to be performed as intended. This allows images with good gradation to be printed even in a high-temperature, high-humidity environment.

[0100] Methods for surface treating metal oxide particles with the compound represented by formula (a) include a wet method, a dry method, an integral blend method, etc. By directly treating the surfaces of metal oxide particles with the compound represented by formula (a), the hydrophobicity of the surfaces is improved, which has the effect of improving the dispersibility of the metal oxide particles in a coating solution.

[0101] Specific examples of the compound represented by formula (a) include phenyltrimethoxysilane (Ph-Si(OMe)3: Compound 1), hexyltrimethoxysilane (C6-Si(OMe)3: Compound 2), diphenyldimethoxysilane (Ph2-Si(OMe)2: Compound 3), cyclohexyltrimethoxysilane (Cyclohexyl-Si(OMe)3: Compound 4), methyltrimethoxysilane (Me-Si(OMe)3: Compound 5), propyltrimethoxysilane (Pr-Si(OMe)3: Compound 6), trimethoxysilane (Me-Si(OMe)3: Compound 7), propyltrimethoxysilane (Pr-Si(OMe)3: Compound 8), trimethoxysilane (Me-Si(OMe)3: Compound 9), propyltrimethoxysilane (Pr-Si(OMe)3: Compound 10), trimethoxysilane (Me-Si(OMe)3: Compound 11), trimethoxysilane (Me-Si(OMe)3: Compound 12), trimethoxysilane (Me-Si(OMe)3: Compound 13), trimethoxysilane (Me-Si(OMe)3: Compound 14), trimethoxysilane (Me-Si(OMe)3: Compound 15), trimethoxysilane (Me-Si(OMe)3: Compound 16), trimethoxysilane (Me-Si(OMe)3: Compound 17), trimethoxysilane (Me-Si(OMe)3: Compound 18), trimethoxysilane (Me-Si(OMe)3: Compound 19), trimethoxysilane (Me-Si(OMe)3: Compound 20), trimethoxysilane (Me-Si(OMe)3: Compound 21), trimethoxysilane (Me-Si(OMe)3: Compound 22), trimethoxysilane (Me-Si(OMe)3: Compound 23), trimethoxysilane (Me-Si(OMe)3: Compound 24), trimethoxysilane (Me-Si(OMe)3: Compound 25), trimethoxysilane ( Examples include si(p-tolyl)silane (Tolyl-Si(OMe)3, Compound 7), phenyltriethoxysilane (Ph-Si(OEt)3, Compound 8), trimethoxy(2-phenylethyl)silane (Styly-Si(OMe)3, Compound 9), cyclopentyltrimethoxysilane (cyclopentyl-Si(OMe)3, Compound 10), dimethoxymethylphenylsilane (Ph-Si-Me(OMe)2, Compound 11), and benzyltriethoxysilane (Benzyl-(OEt)3, Compound 12).

[0102] The content of the compound represented by formula (a) in the protective layer relative to the metal oxide particles is not particularly limited. From the viewpoints of dispersibility of the conductive metal oxide particles in the protective layer coating solution and conductivity in the vertical direction within the protective layer, the content is preferably 1 part by mass or more, more preferably 3 parts by mass or more, and particularly preferably 5 parts by mass or more, relative to 100 parts by mass of the metal oxide particles. Furthermore, from the viewpoint of maintaining good surface resistance, the content is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and particularly preferably 10 parts by mass or less.

[0103] The content of the conductive metal oxide particles in the protective layer is not particularly limited. From the viewpoint of electrical properties, it is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more, per 100 parts by mass of the curable compound. Furthermore, from the viewpoint of maintaining good surface resistance, it is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0104] (Polymerization initiator) The polymerization initiator includes a thermal polymerization initiator, a photopolymerization initiator, and the like.

[0105] Examples of the thermal polymerization initiator include peroxide compounds such as 2,5-dimethylhexane-2,5-dihydroperoxide, dicumyl peroxide, benzoyl peroxide, t-butyl peroxide, t-butylcumyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, and lauroyl peroxide, and azo compounds such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(methyl isobutyrate), 2,2'-azobis(isobutylamidine hydrochloride), and 4,4'-azobis-4-cyanovaleric acid.

[0106] Photopolymerization initiators can be classified into direct cleavage type and hydrogen abstraction type based on the radical generation mechanism. Direct cleavage type photopolymerization initiators generate radicals by cleaving some of the covalent bonds within the molecule when they absorb light energy. On the other hand, hydrogen abstraction type photopolymerization initiators generate radicals when the molecule becomes excited by absorbing light energy and abstracts hydrogen from the hydrogen donor.

[0107] Examples of the direct cleavage type photopolymerization initiator include acetophenone or ketal compounds such as acetophenone, 2-benzoyl-2-propanol, 1-benzoylcyclohexanol, 2,2-diethoxyacetophenone, benzyl dimethyl ketal, and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone; benzoin ether compounds such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, and O-tosylbenzoin; acylphosphine oxide compounds such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and lithium phenyl(2,4,6-trimethylbenzoyl)phosphonate; xanthones; and oxime ester compounds.

[0108] Examples of hydrogen abstraction photopolymerization initiators include benzophenone compounds such as benzophenone, 4-benzoylbenzoic acid, 2-benzoylbenzoic acid, methyl 2-benzoylbenzoate, methyl benzoylformate, benzyl, p-anisil, 2-benzoylnaphthalene, 4,4'-bis(dimethylamino)benzophenone, 4,4'-dichlorobenzophenone, and 1,4-dibenzoylbenzene, and anthraquinone or thioxanthone compounds such as 2-ethylanthraquinone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone. Other examples of photopolymerization initiators include camphorquinone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime, acridine compounds, triazine compounds, and imidazole compounds. In particular, when combined with methacrylate, from the viewpoint of photoresponsiveness, it is preferable to use one or a combination of two or more compounds selected from the group consisting of α-hydroxyalkylphenone compounds, benzil ketal compounds, oxime ester compounds, acylphosphine oxide compounds, and α-aminoalkylphenone compounds. In the present invention, the term "based compound", for example, "oxime ester based compound" means oxime ester and its derivatives, and similarly for other compounds, it includes their derivatives. From the viewpoint of photoresponsiveness, the photopolymerization initiator is preferably contained in an amount of 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and even more preferably 1% by mass or more, of the total solid content of the protective layer. On the other hand, from the viewpoint of dispersibility, the photopolymerization initiator is preferably contained in an amount of 4.55% by mass or less, more preferably 4.06% by mass or less, even more preferably 3% by mass or less, and even more preferably 2% by mass or less, of the total solid content of the protective layer.

[0109] These polymerization initiators may be used alone or in combination of two or more. The content of the polymerization initiator is 0.5 to 40 parts by mass, preferably 1 to 20 parts by mass, per 100 parts by mass of the total radically polymerizable components.

[0110] (Other ingredients) The protective layer may contain other materials as needed. Examples of other materials include stabilizers (heat stabilizers, UV absorbers, light stabilizers, antioxidants, etc.), dispersants, antistatic agents, colorants, lubricants, etc. These may be used alone or in any combination and ratio.

[0111] (Method for forming the protective layer) Next, the method for forming the protective layer will be described. The method for forming the protective layer is not particularly limited. For example, the protective layer can be formed by applying a protective layer-forming coating liquid in which a curable compound, a charge transport material, metal oxide particles, and other substances are dissolved in a solvent or dispersed in a dispersion medium.

[0112] The solvent or dispersion medium used in forming the protective layer and the method for applying the coating solution for forming the protective layer will be described below.

[0113] [Solvent used in coating solution for forming protective layer] Examples of organic solvents used in the protective layer-forming coating solution include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; esters such as methyl formate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and anisole; chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichloroethylene; nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, and triethylenediamine; and aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide. Mixed solvents of these solvents can also be used in any combination and in any ratio. Furthermore, even if an organic solvent does not dissolve the material for the protective layer of the electrophotographic photoreceptor by itself, it can be used if it can dissolve the material by, for example, mixing it with the above-mentioned organic solvent. Generally, using a mixed solvent can reduce coating unevenness. When using a dip coating method as the coating method described below, it is preferable to select a solvent that does not dissolve the lower layer. From this perspective, it is preferable to contain alcohols that have low solubility in polycarbonate and polyarylate, which are suitable for use in the photosensitive layer.

[0114] The ratio of the amount of the organic solvent to the amount of the solid content used in the coating solution for forming the protective layer varies depending on the coating method for the coating solution for forming the protective layer, and may be appropriately changed so as to form a uniform coating film in the coating method to be used.

[0115] [Application method] The method for applying the coating solution to form the protective layer is not particularly limited, and examples thereof include spray coating, spiral coating, ring coating, and dip coating.

[0116] After forming a coating film by the above coating method, the coating film is dried. In this case, the drying temperature and time are not important as long as necessary and sufficient drying is obtained. However, if the protective layer is coated by only air drying after coating the photosensitive layer, it is preferable to carry out sufficient drying by the method described above in the [Coating method] for the photosensitive layer.

[0117] [Method for curing the protective layer] The protective layer is formed by applying the coating liquid and then curing it by applying external energy, such as heat, light, or radiation. Heat energy can be applied by heating from the coated surface or the support using air, gases such as nitrogen, steam, various heat transfer media, infrared rays, or electromagnetic waves. The heating temperature is preferably 100°C or higher and 170°C or lower. At temperatures above the lower limit, the reaction speed is sufficient and the reaction proceeds completely. At temperatures below the upper limit, the reaction proceeds uniformly, preventing significant distortion in the protective layer. To ensure uniform curing, it is also effective to heat the protective layer at a relatively low temperature below 100°C, and then further heat the protective layer to 100°C or higher to complete the reaction.

[0118] As for light energy, UV irradiation light sources such as high-pressure mercury lamps, metal halide lamps, electrodeless lamp bulbs, and light-emitting diodes, which mainly emit ultraviolet (UV) light, can be used, but it is also possible to select a visible light source to match the absorption wavelength of the chain-polymerizable compound and photopolymerization initiator. The light irradiation dose is 0.1 J / cm from the viewpoint of curing. 2More than 0.5J / cm is preferable. 2 More preferably, 1 J / cm or more 2 In addition, from the viewpoint of electrical properties, 150 J / cm 2 Less than 100 J / cm is preferable. 2 Less than 50 J / cm is more preferable. 2 The following are particularly preferred: The radiation energy may be an electron beam (EB).

[0119] Among these energies, light energy is preferred from the viewpoints of ease of reaction rate control, simplicity of the apparatus, and long pot life.

[0120] After the protective layer is cured, a heating step may be added from the viewpoints of relieving residual stress, relieving residual radicals, and improving electrical properties. The heating temperature is preferably 60°C or higher, more preferably 100°C or higher, and preferably 200°C or lower, more preferably 150°C or lower.

[0121] <Conductive support> The conductive support of the present electrophotographic photoreceptor is not particularly limited as long as it supports the layer formed thereon and exhibits conductivity. Conductive supports are typically made of metals such as aluminum, aluminum alloys, stainless steel, copper, and nickel; resins made conductive by the coexistence of conductive powders such as metals, carbon, and tin oxide; and resins, glass, and paper with conductive materials such as aluminum, nickel, and ITO (indium oxide tin oxide) vapor-deposited or coated on their surfaces. They can be in the form of a drum, sheet, or belt. A conductive material with an appropriate resistance may be coated on a metallic conductive support to control conductivity and surface properties or to cover defects.

[0122] When a metal material such as an aluminum alloy is used as the conductive support, the metal material may be anodized before use.

[0123] The average thickness of the anodic oxide coating is usually 20 μm or less, and preferably 7 μm or less.

[0124] When forming an anodized film on a metal material, it is preferable to perform a sealing treatment. The sealing treatment can be performed by a known method.

[0125] The surface of the conductive support may be smooth, or may be roughened by using a special cutting method, by polishing, or by mixing particles of an appropriate particle size into the material constituting the support. An undercoat layer, which will be described later, may be provided between the conductive support and the photosensitive layer in order to improve adhesion, blocking properties, etc.

[0126] <Undercoat layer> The present electrophotographic photoreceptor may have an undercoat layer between the present photosensitive layer and the conductive support.

[0127] The undercoat layer may be made of, for example, a resin or a resin in which organic pigments or particles of metal oxides or the like are dispersed. The organic pigments used in the undercoat layer are not particularly limited. Examples thereof include the phthalocyanine pigments and azo pigments used as the charge generating material described above.

[0128] Examples of metal oxide particles used in the undercoat layer include metal oxide particles containing one type of metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, and metal oxide particles containing multiple metal elements such as calcium titanate, strontium titanate, and barium titanate. The undercoat layer may contain only one type of particle, or multiple types of particles may be mixed in any ratio and combination.

[0129] Among the above metal oxide particles, titanium oxide and aluminum oxide are preferred, and titanium oxide is particularly preferred. The titanium oxide particles may have their surfaces treated with any inorganic or organic substance, for example. The crystalline form of the titanium oxide particles may be any of rutile, anatase, brookite, and amorphous. Titanium oxide particles may also be present in a variety of crystalline forms.

[0130] The particle size of the metal oxide particles used in the undercoat layer is not particularly limited, but from the viewpoints of the properties of the undercoat layer and the stability of the solution for forming the undercoat layer, the average primary particle size is preferably 10 nm or more, and 100 nm or less, more preferably 50 nm or less.

[0131] Here, the undercoat layer is preferably formed in a form in which particles are dispersed in a binder resin. Examples of binder resins used in the undercoat layer include polyvinyl acetal resins such as polyvinyl butyral resins, polyvinyl formal resins, and partially acetalized polyvinyl butyral resins in which butyral is partially modified with formal or acetal; and insulating resins such as polyarylate resins, polycarbonate resins, polyester resins, phenoxy resins, acrylic resins, methacrylic resins, polyamide resins, polyurethane resins, epoxy resins, silicone resins, polyvinyl alcohol resins, styrene-alkyd resins, silicone-alkyd resins, and phenol-formaldehyde resins. However, the binder resins are not limited to these polymers. These binder resins may be used alone or in combination, or may be used in a cured form with a curing agent. Among these, polyvinyl acetal resins, alcohol-soluble copolymerized polyamides, modified polyamides, etc. are preferred because they exhibit good dispersibility and coatability, and among these, alcohol-soluble copolymerized polyamides are particularly preferred.

[0132] The mixing ratio of the particles to the binder resin can be selected arbitrarily, but it is preferable to use the particles in the range of 10% by mass to 500% by mass in terms of the stability and coatability of the dispersion.

[0133] The thickness of the undercoat layer can be selected arbitrarily. In consideration of the characteristics of the electrophotographic photoreceptor and the coating properties of the dispersion, it is usually preferable to set the thickness to 0.1 μm or more and 20 μm or less. The undercoat layer may also contain known antioxidants, etc.

[0134] <Other layers> Furthermore, the present electrophotographic photoreceptor may have other layers as needed in addition to the above-mentioned conductive substrate, the present photosensitive layer, the present protective layer and the undercoat layer.

[0135] (Thickness other than the conductive support) The thickness of the electrophotographic photoreceptor excluding the conductive support, i.e., the thickness of the electrophotographic photoreceptor minus the thickness of the conductive support, is preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more, from the viewpoint of leak resistance, while from the viewpoint of chargeability, it is preferably 50 μm or less, more preferably 40 μm or less, and even more preferably 35 μm or less.

[0136] <<This image forming device>> The present electrophotographic photoreceptor can be used to configure an image forming apparatus (the present image forming apparatus).

[0137] As shown in FIG. 1, the image forming apparatus includes an electrophotographic photosensitive member 1, a charging device 2, an exposure device 3, and a developing device 4, and may further include a transfer device 5, a cleaning device 6, and a fixing device 7 as needed. The electrophotographic photoreceptor 1 is not particularly limited as long as it is the above-described electrophotographic photoreceptor. As an example, Fig. 1 shows a drum-shaped photoreceptor in which the above-described photosensitive layer is formed on the surface of a cylindrical conductive support. A charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are arranged along the outer circumferential surface of the electrophotographic photoreceptor 1.

[0138] The charging device 2 charges the electrophotographic photoreceptor 1, uniformly charging the surface of the electrophotographic photoreceptor 1 to a predetermined potential. Typical charging devices include non-contact corona charging devices such as corotrons and scorotrons, and contact charging image forming devices (also called "contact charging devices" or "direct charging devices") that charge the photoreceptor surface by bringing a charging member to which a voltage is applied into contact with the surface (also called "contact charging devices" or "direct charging devices"). Examples of contact charging devices include a charging roller and a charging brush. Note that FIG. 1 shows a roller-type charging device (charging roller) as an example of the charging device 2. The charging may be performed by a DC voltage or by superimposing an AC voltage on the DC voltage.

[0139] The exposure device 3 is not particularly limited in type as long as it can expose the electrophotographic photoreceptor 1 to light and form an electrostatic latent image on the photosensitive surface of the electrophotographic photoreceptor 1. Exposure may also be performed by an internal photoreceptor exposure method. Any light may be used for exposure.

[0140] The type of toner T is arbitrary, and in addition to powder toner, polymerized toner produced by a suspension polymerization method or an emulsion polymerization method can be used.

[0141] There are no particular limitations on the type of transfer device 5, and any device using any method, such as electrostatic transfer methods such as corona transfer, roller transfer, and belt transfer, pressure transfer, and adhesive transfer, can be used. Here, the transfer device 5 is assumed to be composed of a transfer charger, transfer roller, transfer belt, and the like, arranged opposite the electrophotographic photosensitive member 1. The transfer device 5 applies a predetermined voltage value (transfer voltage) with a polarity opposite to the charged potential of the toner T, and transfers the toner image formed on the electrophotographic photosensitive member 1 onto recording paper (paper, medium) P.

[0142] There are no particular limitations on the cleaning device 6, and any cleaning device can be used, such as a brush cleaner, magnetic brush cleaner, electrostatic brush cleaner, magnetic roller cleaner, or blade cleaner. The cleaning device 6 scrapes off residual toner adhering to the photoreceptor 1 with a cleaning member and collects the residual toner. However, if there is little or almost no toner remaining on the photoreceptor surface, the cleaning device 6 may not be necessary.

[0143] In the image forming apparatus configured as described above, an image is recorded as follows: First, the surface (photosensitive surface) of the photoreceptor 1 is charged to a predetermined potential (e.g., 600 V) by the charging device 2. At this time, charging may be performed using a DC voltage, or by superimposing an AC voltage on the DC voltage. Next, the charged photosensitive surface of the photoreceptor 1 is exposed by the exposure device 3 according to the image to be recorded, and an electrostatic latent image is formed on the photosensitive surface. Then, the electrostatic latent image formed on the photosensitive surface of the photoreceptor 1 is developed by the development device 4.

[0144] The developing device 4 thins the toner T supplied by the supply roller 43 using a regulating member (developing blade) 45, frictionally charges it to a predetermined polarity (here, positive polarity, the same polarity as the charging potential of the photosensitive member 1), and transports it while being carried by the developing roller 44, bringing it into contact with the surface of the photosensitive member 1. When the charged toner T carried on the developing roller 44 comes into contact with the surface of the photoreceptor 1, a toner image corresponding to the electrostatic latent image is formed on the photoreceptor surface of the photoreceptor 1. This toner image is then transferred onto the recording paper P by the transfer device 5. After this, the toner remaining on the photoreceptor surface of the photoreceptor 1 without being transferred is removed by the cleaning device 6.

[0145] After the toner image is transferred onto the recording paper P, the recording paper P is passed through a fixing device 7 to thermally fix the toner image onto the recording paper P, thereby obtaining a final image. In addition to the above-described configuration, the image forming apparatus may be configured to be capable of performing, for example, a static elimination process.

[0146] Furthermore, the image forming apparatus may be further modified and configured, for example, to be capable of performing processes such as a pre-exposure process and an auxiliary charging process, or to be configured to perform offset printing, or even to be configured as a full-color tandem system using multiple types of toner.

[0147] <<This electrophotographic cartridge>> The present electrophotographic photoreceptor 1 can be combined with one or more of a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, a cleaning device 6, and a fixing device 7 to form an integrated cartridge (referred to as "the present electrophotographic cartridge").

[0148] The present electrophotographic cartridge can be configured to be detachable from the main body of an electrophotographic apparatus such as a copying machine, a laser beam printer, etc. In this case, for example, when the present electrophotographic photosensitive member 1 or other members deteriorate, the electrophotographic photosensitive member cartridge can be removed from the main body of the image forming apparatus and a new electrophotographic photosensitive member cartridge can be attached to the main body of the image forming apparatus, thereby facilitating maintenance and management of the image forming apparatus.

[0149] <<Explanation of terms>> In the present invention, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more and Y or less," as well as "preferably larger than X" or "preferably smaller than Y." Furthermore, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the intention that "it is preferable that it is greater than X" or "it is preferable that it is less than Y." [Example]

[0150] The present invention is further illustrated by the following examples, which are not intended to limit the invention in any way.

[0151] <Preparation of Coating Solution P1 for Forming Undercoat Layer> 20 parts by weight of D-type titanyl phthalocyanine, which exhibits a clear peak at a diffraction angle 2θ = 27.3° ± 0.2° in powder X-ray diffraction using CuKα radiation, was mixed with 280 parts by weight of 1,2-dimethoxyethane and ground for 2 hours in a sand grinding mill to perform a fine dispersion treatment. 400 parts by weight of a 2.5% 1,2-dimethoxyethane solution of polyvinyl butyral (manufactured by Denki Kagaku Kogyo Co., Ltd., product name "Denka Butyral" #6000C) and 170 parts by weight of 1,2-dimethoxyethane were further added and mixed to prepare coating solution P1 for forming an undercoat layer.

[0152] <Preparation of Coating Solution Q1 for Forming Single-Layer Photosensitive Layer> A single-layer photosensitive layer-forming coating solution Q1 with a solids concentration of 25% by mass was prepared by mixing 2.6 parts by mass of D-type titanyl phthalocyanine, which exhibits a clear peak at a diffraction angle 2θ=27.3°±0.2° in powder X-ray diffraction using CuKα radiation, 1.3 parts by mass of perylene pigment 1 having the following structure, 0.5 parts by mass of polyvinyl butyral resin, 100 parts by mass of the hole transport substance (formula (1), molecular weight 748) shown below, 60 parts by mass of the electron transport substance (formula (2), molecular weight 424.2) shown below, 100 parts by mass of polycarbonate resin having a biphenyl structure, and 0.05 parts by mass of silicone oil (manufactured by Shin-Etsu Silicones Co., Ltd.: trade name KF-96) as a leveling agent with 793.35 parts by mass of a mixed solvent of tetrahydrofuran (hereinafter occasionally abbreviated as THF) and toluene (hereinafter occasionally abbreviated as TL) (THF 80% by mass, TL 20% by mass). TIFF2025153628000015.tif37170 TIFF2025153628000016.tif56170 TIFF2025153628000017.tif50170

[0153] <Preparation of Coating Solution for Forming Protective Layer> (Protective layer forming coating solution S1) Rutile-type white titanium dioxide (TTO55N, manufactured by Ishihara Sangyo Kaisha Ltd.) having an average primary particle size of 40 nm and 5.6 parts by mass of Compound 1 in Table 1 were added to 100 parts by mass of the titanium dioxide, and the mixture was stirred for 2 hours in a super mixer. The particles were then heated at 150°C to perform a surface treatment on the titanium dioxide. Next, 2.5 g of this surface-treated titanium oxide was mixed with 7.5 g of dispersion medium (methanol, 1-propanol) to prepare 10 g of raw material slurry, which was dispersed using zirconia beads (Nikkato Corporation, YTZ) as dispersion medium in a paint shaker (Asada Iron Works Co., Ltd.) to adjust the average particle size (D50) to approximately 100 nm, to prepare a surface-treated titanium oxide dispersion. The average particle size (D50) was measured using a dynamic light scattering method using a particle size distribution analyzer (FPAR-1000, Otsuka Electronics Co., Ltd.). The surface-treated titanium oxide dispersion was mixed with methacrylate 1 represented by the following structure as a photocurable compound, which had been dissolved in advance in a mixed solvent of methanol and 1-propanol, and an oxime ester initiator (OXE03, manufactured by BASF Japan Ltd.) as a polymerization initiator, to obtain a protective layer-forming coating solution S1 having a mass ratio of methacrylate 1 / surface-treated titanium oxide / OXE03=100 / 100 / 3, a solvent composition of methanol / 1-propanol=7 / 3, and a solids concentration of 18.0%. TIFF2025153628000018.tif43170

[0154] (Coating liquid for protective layer formation S2~S17) Coating solutions S2 to S17 for forming a protective layer were obtained in the same manner as coating solution S1 for forming a protective layer, except that compounds 2 to 12 or comparative compounds 1 to 5 listed in Table 1 were used instead of compound 1 as the surface treatment agent for titanium oxide, and the amount of compound added was changed to the content of each compound in Table 2.

[0155] [Table 1]

[0156] <Photosensitive drum manufacturing> [Example 1] An aluminum cylinder with a machined surface, 30 mm in diameter and 244 mm in length, was dip-coated with Coating Solution P1 for forming an undercoat layer to form a 0.3 μm film thickness after drying. Coating Solution Q1 for forming a single-layer photosensitive layer was dip-coated onto the undercoat layer and dried at 125°C for 24 minutes to form a single-layer photosensitive layer to form a 30 μm film thickness after drying. Coating Solution S1 for forming a protective layer was ring-coated onto the single-layer photosensitive layer and dried at room temperature for 1 minute. After that, the photoreceptor was rotated at 60 rpm in a nitrogen atmosphere and 365 nm LED light was applied at 1.1 W / cm. 2 for 2 minutes at an intensity of 132 J / cm 2 ) to provide a protective layer so that the thickness of the layer after curing would be 2 μm, thereby producing a photoreceptor.

[0157] [Examples 2 to 12] Photoreceptors of Examples 2 to 12 were prepared in the same manner as in Example 1, except that the composition of the protective layer-forming coating liquid S1 was changed to S2 to S12 as shown in Table 2.

[0158] [Comparative Examples 1 to 5] Photoreceptors of Comparative Examples 1 to 5 were prepared in the same manner as in Example 1, except that the composition of the protective layer-forming coating liquid S1 was changed to S13 to S17 as shown in Table 2.

[0159] <Evaluation of dispersibility> For the protective layer-forming coating solutions S1 to S17, the average particle size D50 of the filler in the solution (particle size of aggregated particles) was measured by the following method. 1 g of each protective layer-forming coating solution was weighed and mixed with 49 g of methanol to prepare a diluted solution. The diluted solution was subjected to particle size distribution measurement using a particle size distribution analyzer UPA-EX150 (manufactured by Microtrac). The particle diameter at which the cumulative value of the obtained volume average particle diameter was 50% was defined as the average particle diameter D50 (nm). The smaller the D50 value, the better the dispersibility. In the present invention, a particle size of 150 nm or less was considered "pass." The results are shown in Table 2. Regarding Comparative Examples 1, 2, and 4, since the dispersibility was extremely poor, the average particle diameter could not be measured.

[0160] <Evaluation of residual potential> The photoreceptors obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were left standing for 16 hours in an environment (LL environment) at a temperature of 10°C and a relative humidity of 20%, and then mounted on an electrophotographic characteristic evaluation apparatus (described in "Fundamentals and Applications of Electrophotography," edited by The Electrophotographic Society of Japan, Corona Publishing Co., Ltd., pages 404 - 405) prepared according to the electrophotographic society measurement standard. The electrical characteristics were measured as follows by the cycle of charging, exposure, potential measurement, and discharging. First, in an environment (LL environment) at a temperature of 10°C and a relative humidity of 20%, the grid voltage was adjusted to charge the photoreceptor so that the initial surface potential (V0) was +850V. Next, exposure light was irradiated at 0.7 μJ / cm 2 and the residual potential (VL) 30 milliseconds after irradiation was measured. The exposure light used was the light of a halogen lamp made into monochromatic light of 780 nm with an interference filter. The smaller the absolute value of the residual potential (VL), the better the electrical characteristics. In the present invention, 65V or less was regarded as "qualified." The results are shown in Table 2. Regarding Comparative Examples 1, 2, and 4, since the dispersibility was extremely poor, the residual potential was not measured.

[0161] <Evaluation of HH gradation> The photoreceptors obtained in Examples 1 to 12 and Comparative Examples 1 to 5 were mounted on a photoreceptor cartridge of a positively charged color printer, and the following printing pattern was printed in an environment at a temperature of 32°C and a relative humidity of 80%. The printing pattern is a pattern in which square patches with an input density varying in 5 - step increments from 0 to 100 are arranged in the printing vertical or horizontal direction. The image density of the patch with an input density of 5 in this pattern was measured. In the present invention, those with the image density of 0.03 or more were evaluated as "qualified." The results are shown in Table 2. Regarding Comparative Examples 1, 2, and 4, since the dispersibility was extremely poor, the HH gradation was not evaluated.

[0162] [Table 2]

[0163] <Consideration> From the results of the above examples, it was found that an electrophotographic photoreceptor having a protective layer containing a cured product of a polyfunctional acrylate or polyfunctional methacrylate and metal oxide particles surface-treated with a compound represented by formula (a) exhibits good image gradation when printing under a high-temperature, high-humidity environment. Furthermore, in this example, the effect of using titanium oxide as the metal oxide particles was demonstrated, but by treating with the compound represented by formula (a), the dispersibility in the coating liquid before curing is improved, and by constructing a protective layer with the curable compound while maintaining this dispersibility in the coating liquid, the movement of charge from the unexposed areas to the exposed areas is suppressed when printing as an electrophotographic photosensitive member, the contrast between the exposed and unexposed areas that form the image is clear, and the gradation of the image is improved. Therefore, it is believed that the type of metal oxide microparticles is not limited to a specific one.

Claims

1. An electrophotographic photoreceptor having at least a photosensitive layer and a protective layer sequentially provided on a conductive support, The protective layer of the electrophotographic photoreceptor comprises a cured product of a curable compound and metal oxide particles that have been surface-treated with a compound represented by the following formula (a): (In formula (a), R １ represents an alkoxy group having 1 to 3 carbon atoms. ２ R represents an alkyl group having 1 to 3 carbon atoms which may have a substituent, or a phenyl group which may have a substituent. ３ represents an optionally substituted phenyl group, an optionally substituted alkyl group having from 1 to 10 carbon atoms, or an optionally substituted cycloalkyl group having from 3 to 10 carbon atoms; and m is 2 or 3.

2. In the formula (a), the R １ 2. The electrophotographic photoreceptor according to claim 1, wherein is a methoxy group or an ethoxy group.

3. 3. The electrophotographic photoreceptor according to claim 1, wherein m is 3 in formula (a).

4. 3. The electrophotographic photoreceptor according to claim 1, wherein the curable compound is a polyfunctional acrylate or a polyfunctional methacrylate.

5. 3. The electrophotographic photoreceptor according to claim 1, wherein the metal oxide particles have a band gap of 2 eV or more and 4 eV or less.

6. An electrophotographic photosensitive member cartridge comprising the electrophotographic photosensitive member according to claim 1 or 2.

7. An image forming apparatus comprising the electrophotographic photosensitive member according to claim 1 or 2.

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