Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that improves the light transmittance of a charge transport layer, while ensuring the crack resistance of an inorganic protective layer.SOLUTION: An electrophotographic photoreceptor comprises: a conductive substrate; a charge generating layer provided on the conductive substrate; a charge transport layer provided on the charge generating layer and including inorganic oxide particles; and an inorganic protective layer provided on the photosensitive layer. In cross-sectional observation of the charge transport layer, the inorganic oxide particles included in a surface layer on a surface side, and the inorganic oxide particles included in an inner layer on an inner face side are divided, with 1 / 2 of the film thickness of the charge transport layer as a boundary, and the relationship between the area ratio A of the inorganic oxide particles in the surface layer and the area ratio B of the inorganic oxide particles in the inner layer satisfies area ratio A>area ratio B.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus. [Background technology]

[0002] Patent Document 1 discloses "an electrophotographic photoreceptor having a conductive substrate, an undercoat layer formed on the conductive substrate and consisting of a metal oxide layer, a charge generation layer formed on the undercoat layer, a charge transport layer formed on the charge generation layer and containing a binder resin, a charge transport material, and silica particles, and an inorganic protective layer formed on the charge transport layer and consisting of a metal oxide layer." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-008688 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide an electrophotographic photoreceptor comprising a conductive substrate, a charge generating layer provided on the conductive substrate, a charge transport layer provided on the charge generating layer and containing inorganic oxide particles, and an inorganic protective layer provided on a photosensitive layer, wherein, in cross-sectional observation of the charge transport layer, the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, across half the thickness of the charge transport layer, are the same, while ensuring the crack resistance of the inorganic protective layer, compared to when these are the same. [Means for solving the problem]

[0005] Means for solving the above problems include the following aspects. <1> a conductive substrate; a charge generating layer provided on the conductive substrate; a charge transport layer provided on the charge generating layer and containing inorganic oxide particles; an inorganic protective layer provided on the photosensitive layer; Equipped with An electrophotographic photoreceptor in which, upon cross-sectional observation of the charge transport layer, the relationship between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, with the half film thickness of the charge transport layer as the boundary, satisfies area ratio A>area ratio B. <2> The difference between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 1% or more and 75% or less. <1> The electrophotographic photoreceptor according to claim 1. <3> The difference between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 20% or more and 75% or less. <2> The electrophotographic photoreceptor according to claim 1. <4> the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is 60% or more and 75% or less, The area ratio B of the inorganic oxide particles contained in the inner layer on the inner surface side is less than 60%. <1> ~ <3> 10. An electrophotographic photoreceptor according to any one of claims 1 to 9. <5> the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is 60% or more and 70% or less, The area ratio B of the inorganic oxide particles contained in the inner layer on the inner surface side is less than 60%. <4> The electrophotographic photoreceptor described in <6> The charge transport layer has a light transmittance of 80% or more. <1> ~ <5> 10. The electrophotographic photoreceptor according to claim 9, wherein the electrophotographic photoreceptor is a <7> The Young's modulus of the charge transport layer is 12 GPa or more. <1> ~ <6> 10. The electrophotographic photoreceptor according to claim 9, wherein the electrophotographic photoreceptor is a <8> The inorganic oxide particles are silica particles. <1> ~ <7> 10. The electrophotographic photoreceptor according to claim 9, wherein the electrophotographic photoreceptor is a <9> The inorganic protective layer is a layer containing a metal oxide. <1> ~ <8> 10. The electrophotographic photoreceptor according to claim 9, wherein the electrophotographic photoreceptor is a <10> The inorganic protective layer is a layer containing gallium oxide. <1> ~ <9> 10. The electrophotographic photoreceptor according to claim 9, wherein the electrophotographic photoreceptor is a <11> <1> ~ <10> The electrophotographic photoreceptor according to any one of the preceding claims is provided, A process cartridge that is detachably attached to an image forming apparatus. <12> <1> ~ <10> the electrophotographic photoreceptor according to any one of the above items; a charging device that charges the surface of the electrophotographic photosensitive member; an electrostatic latent image forming device for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing toner to form a toner image; a transfer device that transfers the toner image onto a surface of a recording medium; An image forming apparatus comprising: [Effects of the Invention]

[0006] <1> According to the invention, there is provided an electrophotographic photoreceptor comprising a conductive substrate, a charge generating layer provided on the conductive substrate, a charge transport layer provided on the charge generating layer and containing inorganic oxide particles, and an inorganic protective layer provided on a photosensitive layer, wherein, in cross-sectional observation of the charge transport layer, the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, across half the thickness of the charge transport layer, are the same, while ensuring the crack resistance of the inorganic protective layer, compared to when these are the same. <2> According to the invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the difference between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is less than 1% or more than 75%. <3> According to the invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the difference between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is less than 20% or more than 75%. <4> According to the invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is less than 60% or more than 75%, or when the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 60% or more. <5> According to the invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is less than 60% or exceeds 70%, or when the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is more than 60%. <6> According to the present invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the light transmittance of the charge transport layer is less than 80%. <7> According to the present invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the Young's modulus of the charge transport layer is less than 12 GPa. <8> According to the present invention, an electrophotographic photoreceptor is provided in which the charge transport layer contains silica particles, and the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same, with the half-thickness of the charge transport layer as the boundary. <9> According to the invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer containing a metal oxide, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same, with the half-thickness of the charge transport layer as the boundary. <10> According to the invention, an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer containing gallium oxide, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same, with the half-film thickness of the charge transport layer as the boundary. <11> , or <12> According to the invention, there is provided a process cartridge or an image forming apparatus including an electrophotographic photosensitive member comprising a conductive substrate, a charge generating layer provided on the conductive substrate, a charge transport layer provided on the charge generating layer and containing inorganic oxide particles, and an inorganic protective layer provided on the photosensitive layer, wherein, in cross-sectional observation of the charge transport layer, the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same across the half film thickness of the charge transport layer, while ensuring the crack resistance of the inorganic protective layer, as compared to the case of using an electrophotographic photosensitive member. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a partial cross-sectional view showing an example of a layer structure of the electrophotographic photoreceptor according to the present exemplary embodiment. [Figure 2] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 3] FIG. 10 is a schematic configuration diagram illustrating another example of an image forming apparatus according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, exemplary embodiments of the present disclosure will be described. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the present disclosure.

[0009] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0010] In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0011] When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0012] In the present disclosure, each component may contain multiple corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0013] In the present disclosure, alkyl groups and alkylene groups include any of linear, branched and cyclic groups, unless otherwise specified. In the present disclosure, a hydrogen atom in an organic group, aromatic ring, linking group, alkyl group, alkylene group, aryl group, aralkyl group, alkoxy group, aryloxy group, or the like may be substituted with a halogen atom. In the present disclosure, when a compound is represented by a structural formula, the symbols (C and H) representing carbon atoms and hydrogen atoms in the hydrocarbon group and / or hydrocarbon chain may be omitted.

[0014] In this disclosure, ppm is an abbreviation for parts per million and is based on mass.

[0015] In the present disclosure, the "axial direction" of an electrophotographic photosensitive member means the direction in which the rotation axis of the electrophotographic photosensitive member extends, and the "circumferential direction" of an electrophotographic photosensitive member means the rotation direction of the electrophotographic photosensitive member.

[0016] <Electrophotographic photoreceptor> The electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") according to this embodiment includes a conductive substrate, a charge generation layer provided on the conductive substrate, a charge transport layer provided on the charge generation layer and containing inorganic oxide particles, and an inorganic protective layer provided on the photosensitive layer. In cross-sectional observation of the charge transport layer, the relationship between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, with the boundary being half the film thickness of the charge transport layer, satisfies area ratio A>area ratio B.

[0017] The photoreceptor according to this embodiment has the above-described structure, which ensures the crack resistance of the inorganic protective layer while improving the light transmittance of the charge transport layer. The reason for this is presumed to be as follows.

[0018] In electrophotographic photoreceptors having an inorganic protective layer, a technique for improving the hardness of the charge transport layer by incorporating inorganic oxide particles (e.g., silica particles) into the charge transport layer on which the inorganic protective layer is formed has been known to prevent the inorganic protective layer from cracking due to mechanical load. Improving the hardness of the charge transport layer reduces the amount of deformation of the charge transport layer under load, thereby reducing the amount of deformation of the inorganic protective layer and improving crack resistance. On the other hand, it is generally known that the greater the loading of inorganic oxide particles, the greater the hardness of the charge transport layer. However, if the inorganic oxide particle loading is too high, the light transmittance of the charge transport layer decreases. When the light transmittance of the charge transport layer decreases, light is less likely to reach the charge generation layer located below the charge transport layer, and the charge generation efficiency of the charge generation layer decreases. As a result, the electrical properties of the photoreceptor deteriorate.

[0019] In contrast, in the photoreceptor according to this embodiment, when observing a cross section of the charge transport layer, the relationship between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, with the half film thickness of the charge transport layer as the boundary, is set so as to satisfy the relationship area ratio A > area ratio B. This allows a large amount of inorganic oxide particles to be present in the surface layer of the charge transport layer in contact with the inorganic protective layer, improving the hardness of the surface layer, thereby ensuring crack resistance of the inorganic protective layer. On the other hand, the light transmittance of the entire charge transport layer is improved by allowing a small amount of inorganic oxide particles to exist in the inner layer of the charge transport layer that is in contact with the charge generation layer.

[0020] From the above, it is presumed that the photoreceptor according to this embodiment improves the light transmittance of the charge transport layer while ensuring the crack resistance of the inorganic protective layer.

[0021] The photoreceptor according to this embodiment will be described in detail below.

[0022] FIG. 1 is a partial cross-sectional view schematically illustrating an example of the layer structure of a photoreceptor according to this embodiment. Photoreceptor 10A shown in FIG. 1 has a laminated photosensitive layer. Photoreceptor 10A has a structure in which an undercoat layer 2, a charge generation layer 3, a charge transport layer 4, and an inorganic protective layer 6 are laminated in this order on a conductive substrate 1, and the charge generation layer 3 and the charge transport layer 4 constitute a photosensitive layer 5 (a so-called function-separated photosensitive layer). Photoreceptor 10A may have an intermediate layer (not shown) between the undercoat layer 2 and the charge generation layer 3. The undercoat layer 2 may or may not be present.

[0023] (Area ratio of inorganic oxide particles contained in charge transport layer) In cross-sectional observation of the charge transport layer, the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, with the boundary being half the film thickness of the charge transport layer, satisfies the relationship area ratio A > area ratio B. Here, the surface layer of the charge transport layer refers to the region from the surface located at half the thickness of the charge transport layer to the surface where the charge transport layer contacts with the inorganic protective layer. The inner layer of the charge transport layer refers to the region from the surface located at half the thickness of the charge transport layer to the surface where the charge transport layer contacts the charge transport layer.

[0024] From the viewpoint of improving the crack resistance of the inorganic protective layer and the light transmittance of the charge transport layer, the difference between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is preferably 1% or more and 75% or less, more preferably 10% or more and 75% or less, and even more preferably 20% or more and 75% or less.

[0025] From the viewpoint of improving the crack resistance of the inorganic protective layer and the light transmittance of the charge transport layer, the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is preferably 60% or more and 75% or less, more preferably 60% or more and 72% or less, and even more preferably 60% or more and 70% or less. From the viewpoint of improving the crack resistance of the inorganic protective layer and the light transmittance of the charge transport layer, the area ratio B of the inorganic oxide particles contained in the inner layer on the inner surface side is preferably less than 60%, more preferably 55% or less, and even more preferably 50% or less.

[0026] To satisfy the relationship between the area ratio A and the area ratio B of the inorganic oxide particles, that is, area ratio A > area ratio B, there is a method of controlling the drying conditions of the coating film when forming the charge transport layer, for example.Specifically, there are methods such as increasing the temperature of the hot air blown onto the coating film, increasing the liquid viscosity, or changing the solvent to one with a lower boiling point.

[0027] (Method for observing the cross section of the charge transport layer) The cross section of the charge transport layer was observed as follows. The photosensitive layer of the photoreceptor is cut in the thickness direction with a knife or the like, and the exposed cut surface is used as the observation surface to obtain a sample. Next, the observation surface of the sample is observed with a scanning electron microscope (SEM) to obtain a cross-sectional SEM image of the photosensitive layer.

[0028] Then, using a cross-sectional SEM image of the photosensitive layer, the area ratio A of inorganic oxide particles present in the surface layer on the surface side of the boundary line located at half the film thickness of the charge transport layer and the area ratio B of inorganic oxide particles present in the inner layer on the inner side are calculated.

[0029] Specifically, the inorganic oxide particles present in each layer are observed, and the images of the observed inorganic oxide particles are analyzed using image processing analysis software WinRoof (manufactured by Mitani Shoji Co., Ltd.), and the area ratios of all the inorganic oxide particles observed in each layer (i.e., area ratios A and B) relative to each layer of the charge transport layer are calculated.

[0030] (Configuration of inorganic oxide particles contained in charge transport layer) Examples of inorganic oxide particles include silica particles, alumina particles, and titanium oxide particles. Among these, silica particles are preferred as inorganic oxide particles from the viewpoint of suppressing deterioration in the electrical properties of the photoreceptor.

[0031] Examples of silica particles include dry silica particles and wet silica particles. Examples of dry silica particles include combustion silica (fumed silica) obtained by burning a silane compound, and deflagration silica obtained by explosively burning metallic silicon powder. Examples of wet silica particles include wet silica particles obtained by the neutralization reaction of sodium silicate and mineral acid (precipitation silica synthesized and agglomerated under alkaline conditions, and gel-process silica particles synthesized and agglomerated under acidic conditions), colloidal silica particles (silica sol particles) obtained by polymerizing acidic silicic acid in an alkaline state, and sol-gel silica particles obtained by hydrolysis of organic silane compounds (e.g., alkoxysilanes). As the silica particles, from the viewpoint of suppressing image defects due to deterioration of electrical properties, combustion method silica (fumed silica) which has few silanol groups on the surface and a poor void structure is preferred.

[0032] From the viewpoint of dispersibility in the coating liquid for forming the charge transport layer, the inorganic oxide particles are preferably surface-treated with a hydrophobic treatment agent, such as known silane compounds such as chlorosilane, alkoxysilane, and silazane. The hydrophobic treatment agent is preferably a silane compound having a trimethylsilyl group, a decylsilyl group, or a phenylsilyl group, that is, the silica particles preferably have trimethylsilyl groups, decylsilyl groups, or phenylsilyl groups on their surfaces. Examples of silane compounds having a trimethylsilyl group include trimethylchlorosilane, trimethylmethoxysilane, 1,1,1,3,3,3-hexamethyldisilazane, etc. Examples of silane compounds having a decylsilyl group include decyltrichlorosilane, decyltrichlorosilane, decyldimethylchlorosilane, decyltrimethoxysilane, etc. Examples of silane compounds having a phenyl group include triphenylmethoxysilane, triphenylchlorosilane, etc.

[0033] The inorganic oxide particles have an average particle size of preferably 20 nm to 200 nm, more preferably 30 nm to 180 nm, and even more preferably 40 nm to 150 nm, from the viewpoint of improving the crack resistance of the inorganic protective layer and the light transmittance of the photoreceptor.

[0034] The average particle size of the inorganic oxide particles is determined by the following measurement method. The inorganic oxide particles are extracted from the charge transport layer. Methods for extracting the inorganic oxide particles from the charge transport layer include, for example, a method in which the charge transport layer peeled off from the photoreceptor is immersed in an organic solvent that dissolves the binder resin to extract the inorganic oxide particles, and a method in which the charge transport layer peeled off from the photoreceptor is heated to about 800°C to remove the binder resin and extract the inorganic oxide particles. Inorganic oxide particles are observed under a scanning electron microscope, the circle-equivalent diameters of 100 randomly selected primary particles are determined, and the arithmetic mean of the circle-equivalent diameters is taken as the average particle size.

[0035] The mass proportion of the inorganic oxide particles in the charge transport layer is preferably 60 mass % or more, more preferably 62.5 mass % or more, and even more preferably 65 mass % or more, from the viewpoint of improving the crack resistance of the inorganic protective layer. The mass proportion of silica particles in the photosensitive layer is preferably 80 mass % or less, more preferably 77.5 mass % or less, and even more preferably 75 mass % or less, from the viewpoint of light transmittance of the photoreceptor.

[0036] (Light transmittance of charge transport layer) The light transmittance of the charge transport layer is preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more. When the light transmittance of the charge transport layer is within the above range, the electrical properties of the photoreceptor are improved.

[0037] The light transmittance of the charge transport layer was measured as follows. The charge transport layer is peeled off from the photoreceptor to prepare a sample. Using an ultraviolet-visible spectrophotometer, the light transmittance in the thickness direction of the sample is measured from wavelengths of 730 to 830 nm, and the average value of the transmittance every 10 nm is calculated and used as the light transmittance.

[0038] (Young's modulus of the charge transport layer) The Young's modulus of the charge transport layer is preferably 12 GPa or more, more preferably 15 GPa or more, and even more preferably 20 GPa or more. When the Young's modulus of the charge transport layer is within the above range, the crack resistance of the inorganic protective layer is improved. However, the Young's modulus of the charge transport layer is, for example, 20 GPa or less due to restrictions imposed by the amount of inorganic oxide particles filled.

[0039] The Young's modulus of the charge transport layer is determined by nanoindentation, and is measured by the following method. The inorganic protective layer is removed from the photoreceptor by, for example, peeling it off with a single-edged knife, and the Young's modulus of the charge transport layer is measured. The photoreceptor from which the inorganic protective layer has been removed and whose outer peripheral surface is the charge transport layer is fixed with the axial direction of the photoreceptor horizontal. Next, in this state, the Young's modulus of the outer peripheral surface of the charge transport layer is measured using a nanoindenter. The measurement positions are the axial center of the photoreceptor, and four positions are measured at 90° intervals around the circumference of the photoreceptor. The Young's moduli measured at the four positions are then arithmetically averaged. The conditions for measuring Young's modulus using a nanoindenter are as follows: Test equipment: Product name HM-500, Fisher Instruments Co., Ltd. Indenter: Diamond triangular indenter with a 115° edge angle Load: 75mN

[0040] Each layer of the photoreceptor will be described in detail below.

[0041] [Conductive substrate] Examples of conductive substrates include metal plates, metal drums, and metal belts containing metals (aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, platinum, etc.) or alloys (stainless steel, etc.). Other examples of conductive substrates include paper, resin films, belts, etc. coated, vapor-deposited, or laminated with conductive compounds (e.g., conductive polymers, indium oxide, etc.), metals (e.g., aluminum, palladium, gold, etc.), or alloys. Here, "conductive" refers to a material having a volume resistivity of 1×10 13 This means that the resistance is less than Ωcm.

[0042] When the electrophotographic photoreceptor is used in a laser printer, the surface of the conductive substrate is preferably roughened to a center line average roughness Ra of 0.04 μm to 0.5 μm inclusive in order to suppress interference fringes that occur when irradiated with laser light. When incoherent light is used as the light source, roughening to prevent interference fringes is not particularly necessary, but it is suitable for extending the life of the conductive substrate by suppressing defects caused by surface irregularities.

[0043] Examples of methods for roughening the surface include wet honing, which involves spraying an abrasive suspended in water onto the conductive substrate; centerless grinding, which involves pressing the conductive substrate against a rotating grinding wheel and continuously grinding the substrate; and anodizing.

[0044] As a method for roughening the surface, there may be mentioned a method in which, without roughening the surface of the conductive substrate, conductive or semiconductive powder is dispersed in a resin to form a layer on the surface of the conductive substrate, and the surface is roughened by the particles dispersed in the layer.

[0045] Anodizing is a surface roughening treatment that uses a metallic (e.g., aluminum) conductive substrate as the anode and anodizes it in an electrolyte solution to form an oxide film on the surface of the conductive substrate. Examples of electrolyte solutions include sulfuric acid solution and oxalic acid solution. However, the porous anodic oxide film formed by anodizing is chemically active in its original state, easily contaminated, and exhibits large resistance fluctuations depending on the environment. Therefore, it is preferable to perform a sealing treatment on the porous anodic oxide film, in which the micropores of the oxide film are sealed by volume expansion caused by hydration in pressurized steam or boiling water (with the addition of a metal salt such as nickel), converting the film into a more stable hydrated oxide.

[0046] The thickness of the anodic oxide film is preferably, for example, from 0.3 μm to 15 μm, inclusive, and within this range, the film tends to exhibit barrier properties against injection and also tends to suppress an increase in residual potential due to repeated use.

[0047] The conductive substrate may be subjected to a treatment with an acidic treatment solution or a boehmite treatment. Treatment with an acidic treatment solution is carried out, for example, as follows. First, an acidic treatment solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The compounding ratios of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic treatment solution are, for example, in the range of 10% by mass to 11% by mass for phosphoric acid, 3% by mass to 5% by mass for chromic acid, and 0.5% by mass to 2% by mass for hydrofluoric acid, with the total concentration of these acids preferably in the range of 13.5% by mass to 18% by mass. The treatment temperature is preferably, for example, 42°C to 48°C. The film thickness of the coating is preferably 0.3 μm to 15 μm.

[0048] The boehmite treatment is carried out, for example, by immersing the steel sheet in pure water at 90°C to 100°C for 5 to 60 minutes, or by contacting the steel sheet with heated steam at 90°C to 120°C for 5 to 60 minutes. The coating film preferably has a thickness of 0.1 μm to 5 μm. This may be further anodized using an electrolyte solution with low coating solubility, such as adipic acid, boric acid, borate, phosphate, phthalate, maleate, benzoate, tartrate, or citrate.

[0049] [Sublayer] The undercoat layer is, for example, a layer containing inorganic particles and a binder resin.

[0050] For example, inorganic particles have a powder resistance (volume resistivity) of 1×10 2 Ωcm or more 1×10 11 Examples include inorganic particles with a particle size of Ωcm or less. Among these, inorganic particles having the above resistance value are preferably metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles, with zinc oxide particles being particularly preferred.

[0051] The specific surface area of ​​inorganic particles measured by the BET method is, for example, 10 m 2 / g or more is preferable. The volume average particle size of the inorganic particles is, for example, 50 nm or more and 2000 nm or less (preferably 60 nm or more and 1000 nm or less).

[0052] The content of the inorganic particles is, for example, preferably 10% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 80% by mass or less, relative to the binder resin.

[0053] The inorganic particles may be surface-treated, and two or more types of inorganic particles having different surface treatments or different particle sizes may be used in combination.

[0054] Examples of the surface treatment agent include a silane coupling agent, a titanate-based coupling agent, an aluminum-based coupling agent, a surfactant, etc. In particular, a silane coupling agent is preferred, and a silane coupling agent having an amino group is more preferred.

[0055] Examples of silane coupling agents having an amino group include, but are not limited to, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane.

[0056] Two or more silane coupling agents may be used in combination. For example, a silane coupling agent having an amino group may be used in combination with another silane coupling agent. Examples of other silane coupling agents include, but are not limited to, vinyltrimethoxysilane, 3-methacryloxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

[0057] The surface treatment method using the surface treatment agent may be any known method, and may be either a dry method or a wet method.

[0058] The amount of the surface treatment agent to be used is preferably, for example, 0.5% by mass or more and 10% by mass or less relative to the inorganic particles.

[0059] Here, it is preferable that the undercoat layer contains an electron-accepting compound (acceptor compound) together with the inorganic particles, from the viewpoint of improving the long-term stability of the electrical properties and the carrier blocking property.

[0060] Examples of the electron-accepting compound include electron-transporting substances such as quinone compounds such as chloranil and bromoanil; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone; oxadiazole compounds such as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole and 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; xanthone compounds; thiophene compounds; diphenoquinone compounds such as 3,3',5,5'-tetra-t-butyldiphenoquinone; and benzophenone compounds. In particular, the electron-accepting compound is preferably a compound having an anthraquinone structure, such as a hydroxyanthraquinone compound, an aminoanthraquinone compound, or an aminohydroxyanthraquinone compound, and specifically, for example, anthraquinone, alizarin, quinizarin, anthrarphine, or purpurin.

[0061] The electron-accepting compound may be contained in the undercoat layer in a dispersed state together with the inorganic particles, or may be contained in a state of being attached to the surface of the inorganic particles.

[0062] The electron-accepting compound can be attached to the surface of the inorganic particles by, for example, a dry method or a wet method.

[0063] The dry method is a method in which, while stirring inorganic particles using a mixer or the like with high shear force, an electron-accepting compound is added dropwise, either directly or dissolved in an organic solvent, or sprayed together with dry air or nitrogen gas to adhere the electron-accepting compound to the surface of the inorganic particles. The electron-accepting compound is preferably added dropwise or sprayed at a temperature below the boiling point of the solvent. After the electron-accepting compound has been added dropwise or sprayed, baking may be performed at 100°C or higher. The baking temperature and time are not particularly limited as long as they achieve electrophotographic properties.

[0064] The wet method is a method in which inorganic particles are dispersed in a solvent using, for example, a stirrer, ultrasonic disperser, sand mill, attritor, or ball mill, while an electron-accepting compound is added, followed by stirring or dispersion, and then the solvent is removed to adhere the electron-accepting compound to the surfaces of the inorganic particles. The solvent can be removed, for example, by filtration or distillation. After solvent removal, baking may be performed at 100°C or higher. The baking temperature and time are not particularly limited as long as electrophotographic properties are obtained. In the wet method, moisture contained in the inorganic particles may be removed before adding the electron-accepting compound. Examples of such methods include a method in which the inorganic particles are removed by stirring and heating in a solvent, and a method in which the inorganic particles are removed by azeotropy with the solvent.

[0065] The attachment of the electron-accepting compound may be carried out before or after the inorganic particles are surface-treated with a surface-treating agent, or the attachment of the electron-accepting compound and the surface treatment with a surface-treating agent may be carried out simultaneously.

[0066] The content of the electron-accepting compound is, for example, 0.01% by mass or more and 20% by mass or less, and preferably 0.01% by mass or more and 10% by mass or less, based on the inorganic particles.

[0067] Examples of binder resins used in the undercoat layer include known polymer compounds such as acetal resins (e.g., polyvinyl butyral, etc.), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane resins, polyester resins, unsaturated polyester resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, urea resins, phenolic resins, phenol-formaldehyde resins, melamine resins, urethane resins, alkyd resins, and epoxy resins; zirconium chelate compounds; titanium chelate compounds; aluminum chelate compounds; titanium alkoxide compounds; organic titanium compounds; and silane coupling agents. Examples of binder resins used in the undercoat layer include charge transporting resins having charge transporting groups, conductive resins (such as polyaniline), and the like.

[0068] Among these, the binder resin used in the undercoat layer is preferably a resin that is insoluble in the coating solvent of the upper layer, and in particular, a resin obtained by reacting at least one resin selected from the group consisting of thermosetting resins such as urea resins, phenolic resins, phenol-formaldehyde resins, melamine resins, urethane resins, unsaturated polyester resins, alkyd resins, and epoxy resins, and polyamide resins, polyester resins, polyether resins, methacrylic resins, acrylic resins, polyvinyl alcohol resins, and polyvinyl acetal resins with a curing agent is preferred. When two or more of these binder resins are used in combination, the mixing ratio is set as necessary.

[0069] The undercoat layer may contain various additives to improve electrical properties, environmental stability, and image quality. Examples of additives include known materials such as polycyclic condensation and azo electron transport pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. Silane coupling agents are used for the surface treatment of inorganic particles as described above, and may also be added to the undercoat layer as an additive.

[0070] Examples of silane coupling agents as additives include vinyltrimethoxysilane, 3-methacryloxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

[0071] Examples of zirconium chelate compounds include zirconium butoxide, zirconium ethyl acetoacetate, zirconium triethanolamine, acetylacetonate zirconium butoxide, ethyl acetoacetate zirconium butoxide, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, methacrylate zirconium butoxide, stearate zirconium butoxide, and isostearate zirconium butoxide.

[0072] Examples of titanium chelate compounds include tetraisopropyl titanate, tetra-normal-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetonate, polytitanium acetylacetonate, titanium octylene glycolate, titanium lactate ammonium salt, titanium lactate, titanium lactate ethyl ester, titanium triethanolamine, and polyhydroxytitanium stearate.

[0073] Examples of aluminum chelate compounds include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

[0074] These additives may be used alone or as a mixture or polycondensate of a plurality of compounds.

[0075] The undercoat layer preferably has a Vickers hardness of 35 or more. The surface roughness (ten-point average roughness) of the undercoat layer is preferably adjusted to between 1 / (4n) (n is the refractive index of the upper layer) and 1 / 2 of the wavelength λ of the exposure laser used to suppress moire images. Resin particles or the like may be added to the undercoat layer to adjust the surface roughness. Examples of resin particles include silicone resin particles and crosslinked polymethyl methacrylate resin particles. The surface of the undercoat layer may be polished to adjust the surface roughness. Examples of polishing methods include buffing, sandblasting, wet honing, and grinding.

[0076] The formation of the undercoat layer is not particularly limited, and a known formation method can be used. For example, the undercoat layer can be formed by forming a coating film of a coating liquid for forming an undercoat layer in which the above components are added to a solvent, drying the coating film, and heating it as necessary.

[0077] Examples of solvents for preparing the coating liquid for forming the undercoat layer include known organic solvents, such as alcohol-based solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone-based solvents, ketone alcohol-based solvents, ether-based solvents, and ester-based solvents. Specific examples of these solvents include ordinary organic solvents such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene.

[0078] Examples of a method for dispersing inorganic particles when preparing a coating liquid for forming an undercoat layer include known methods such as using a roll mill, a ball mill, a vibrating ball mill, an attritor, a sand mill, a colloid mill, and a paint shaker.

[0079] Examples of methods for applying the coating liquid for forming the undercoat layer onto the conductive substrate include conventional methods such as blade coating, wire bar coating, spray coating, dip coating, bead coating, knife coating, and curtain coating.

[0080] The thickness of the undercoat layer is preferably set to 15 μm or more, more preferably in the range of 20 μm to 50 μm.

[0081] [Middle layer] The intermediate layer is, for example, a layer containing a resin. Examples of the resin used in the intermediate layer include polymer compounds such as acetal resins (such as polyvinyl butyral), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane resins, polyester resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, phenol-formaldehyde resins, and melamine resins. The intermediate layer may be a layer containing an organometallic compound. Examples of the organometallic compound used in the intermediate layer include organometallic compounds containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon. The compounds used in the intermediate layer may be used alone or as a mixture or polycondensation product of a plurality of compounds.

[0082] Among these, the intermediate layer is preferably a layer containing an organometallic compound containing zirconium atoms or silicon atoms.

[0083] The formation of the intermediate layer is not particularly limited, and a known formation method can be used. For example, the intermediate layer can be formed by forming a coating film of a coating liquid for forming an intermediate layer in which the above components are added to a solvent, drying the coating film, and heating it if necessary. The intermediate layer can be formed by any of the usual coating methods, such as dip coating, push-up coating, wire bar coating, spray coating, blade coating, air knife coating, and curtain coating.

[0084] The thickness of the intermediate layer is preferably set in the range of 0.1 μm to 3 μm, and the intermediate layer may also be used as an undercoat layer.

[0085] [Charge generation layer] The charge generation layer is, for example, a layer containing a charge generation material and a binder resin. Alternatively, the charge generation layer may be a vapor-deposited layer of the charge generation material. A vapor-deposited layer of the charge generation material is suitable for use with an incoherent light source such as an LED (Light Emitting Diode) or an organic EL (Electro-Luminescence) image array.

[0086] Examples of the charge generating material include azo pigments such as bisazo and trisazo; fused-ring aromatic pigments such as dibromoanthanthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0087] Among these, in order to be compatible with laser exposure in the near-infrared region, it is preferable to use a metal phthalocyanine pigment or a metal-free phthalocyanine pigment as the charge generating material, specifically, for example, hydroxygallium phthalocyanine, chlorogallium phthalocyanine, dichlorotin phthalocyanine, or titanyl phthalocyanine.

[0088] On the other hand, in order to accommodate laser exposure in the near ultraviolet region, preferred charge generating materials include fused ring aromatic pigments such as dibromoanthanthrone; thioindigo pigments; porphyrazine compounds; zinc oxide; trigonal selenium; and bisazo pigments.

[0089] The above charge generating material may also be used when an incoherent light source such as an LED or organic EL image array having a central emission wavelength of 450 nm or more and 780 nm or less is used.

[0090] In contrast, when n-type semiconductors such as fused-ring aromatic pigments, perylene pigments, and azo pigments are used as charge-generating materials, dark current is less likely to occur, and image defects known as black spots can be suppressed even in thin films. The n-type is determined by the polarity of the photocurrent that flows using the commonly used time-of-flight method, and materials that more easily pass electrons as carriers than holes are considered n-type.

[0091] The binder resin used in the charge generating layer may be selected from a wide range of insulating resins, and may also be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, and polysilane. Examples of binder resins include polyvinyl butyral resin, polyarylate resin (polycondensation product of bisphenols and aromatic dicarboxylic acids, etc.), polycarbonate resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyamide resin, acrylic resin, polyacrylamide resin, polyvinylpyridine resin, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol resin, polyvinylpyrrolidone resin, etc. Here, "insulating" means a resin having a volume resistivity of 1013 These binder resins are used alone or in combination of two or more.

[0092] The compounding ratio of the charge generating material to the binder resin is preferably within the range of 10:1 to 1:10 by mass.

[0093] The charge generating layer may contain other known additives.

[0094] The formation of the charge generation layer is not particularly limited, and a known formation method can be used. For example, the charge generation layer can be formed by forming a coating film of a coating liquid for forming the charge generation layer by adding the above components to a solvent, drying the coating film, and heating it as necessary. The charge generation layer can also be formed by vapor deposition of the charge generation material. Formation of the charge generation layer by vapor deposition is particularly suitable when a fused ring aromatic pigment or a perylene pigment is used as the charge generation material.

[0095] Examples of solvents for preparing the coating liquid for forming the charge generating layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, toluene, etc. These solvents may be used alone or in combination of two or more.

[0096] Methods for dispersing particles (e.g., charge-generating material) in the coating liquid for forming a charge-generating layer include media-based dispersers such as ball mills, vibration ball mills, attritors, sand mills, and horizontal sand mills, as well as media-less dispersers such as stirrers, ultrasonic dispersers, roll mills, and high-pressure homogenizers. Examples of high-pressure homogenizers include a collision method in which the dispersion liquid is dispersed by liquid-liquid collision or liquid-wall collision under high pressure, and a penetration method in which the dispersion liquid is dispersed by passing through a fine flow path under high pressure. During dispersion, it is effective to adjust the average particle size of the charge-generating material in the coating liquid for forming a charge-generating layer to 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0097] Examples of methods for applying the coating liquid for forming the charge generating layer onto the undercoat layer (or onto the intermediate layer) include conventional methods such as blade coating, wire bar coating, spray coating, dip coating, bead coating, air knife coating, and curtain coating.

[0098] The thickness of the charge generating layer is preferably set within the range of 0.1 μm to 5.0 μm, more preferably 0.2 μm to 2.0 μm.

[0099] [Charge transport layer] The charge transport layer is, for example, a layer containing a binder resin, a charge transport material, and inorganic oxide particles, or may be a layer containing a polymer charge transport material.

[0100] Examples of charge transport materials include electron transport compounds such as quinone compounds such as p-benzoquinone, chloranil, bromanil, and anthraquinone; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone; xanthone compounds; benzophenone compounds; cyanovinyl compounds; and ethylene compounds. Examples of charge transport materials also include hole transport compounds such as triarylamine compounds, benzidine compounds, arylalkane compounds, aryl-substituted ethylene compounds, stilbene compounds, anthracene compounds, and hydrazone compounds. These charge transport materials may be used alone or in combination, but are not limited to these.

[0101] As the charge transport material, triarylamine derivatives represented by the following structural formula (a-1) and benzidine derivatives represented by the following structural formula (a-2) are preferred from the viewpoint of charge mobility.

[0102] [ka]

[0103] In structural formula (a-1), Ar T1, Ar T2 , and Ar T3 each independently represents a substituted or unsubstituted aryl group, -C6H4-C(R T4 )=C(R T5 )(R T6 ), or -C6H4-CH=CH-CH=C(R T7 )(R T8 ) indicates R T4 , R T5 , R T6 , R T7 , and R T8 each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Examples of the substituents on each of the above groups include halogen atoms, alkyl groups having from 1 to 5 carbon atoms, and alkoxy groups having from 1 to 5 carbon atoms. Examples of the substituents on each of the above groups also include substituted amino groups substituted with alkyl groups having from 1 to 3 carbon atoms.

[0104] [ka]

[0105] In structural formula (a-2), R T91 and R T92 R each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms. T101 , R T102 , R T111 and R T112 each independently represents a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an amino group substituted with an alkyl group having 1 to 2 carbon atoms, a substituted or unsubstituted aryl group, -C(R T12 )=C(R T13 )(R T14 ), or -CH=CH-CH=C(R T15 )(R T16 ) and R T12 , R T13 , R T14 , R T15 and R T16each independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Tm1, Tm2, ​​Tn1, and Tn2 each independently represent an integer of 0 or more and 2 or less. Examples of the substituents on each of the above groups include halogen atoms, alkyl groups having from 1 to 5 carbon atoms, and alkoxy groups having from 1 to 5 carbon atoms. Examples of the substituents on each of the above groups also include substituted amino groups substituted with alkyl groups having from 1 to 3 carbon atoms.

[0106] Among the triarylamine derivatives represented by the structural formula (a-1) and the benzidine derivatives represented by the structural formula (a-2), in particular, "-C6H4-CH=CH-CH=C(R T7 )(R T8 )" and triarylamine derivatives having "-CH=CH-CH=C(R T15 )(R T16 ) is preferred from the viewpoint of charge mobility.

[0107] As the polymer charge transport material, known materials having charge transport properties such as poly-N-vinylcarbazole and polysilane are used. In particular, polyester polymer charge transport materials are particularly preferred. The polymer charge transport material may be used alone or in combination with a binder resin.

[0108] Examples of binder resins used in the charge transport layer include polycarbonate resins, polyester resins, polyarylate resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl acetate resins, styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, silicone resins, silicone alkyd resins, phenol-formaldehyde resins, styrene-alkyd resins, poly-N-vinylcarbazole, and polysilanes. Among these, polycarbonate resins or polyarylate resins are preferred as binder resins. These binder resins may be used alone or in combination of two or more. The compounding ratio of the charge transport material to the binder resin is preferably from 10:1 to 1:5 by mass.

[0109] The charge transport layer may contain other known additives.

[0110] The charge transport layer is formed by coating. An embodiment of the coating method includes, for example, preparing a coating liquid for forming the charge transport layer by dissolving or dispersing a binder resin, a charge transport material, and inorganic oxide particles in a solvent, applying the coating liquid for forming the charge transport layer to the surface of the charge generation layer to form a coating film, and drying the coating film.

[0111] Examples of solvents for preparing the coating solution for forming the charge transport layer include ordinary organic solvents such as aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; ketones such as acetone and 2-butanone; halogenated aliphatic hydrocarbons such as methylene chloride, chloroform, and ethylene chloride; and cyclic or linear ethers such as tetrahydrofuran and ethyl ether. These solvents may be used alone or in combination.

[0112] As a method for dispersing inorganic oxide particles in the coating liquid for forming the charge transport layer, for example, a media disperser such as a ball mill, a vibration ball mill, an attritor, a sand mill, or a horizontal sand mill, or a medialess disperser such as a stirrer, an ultrasonic disperser, a roll mill, or a high-pressure homogenizer, may be used.

[0113] Examples of a coating method for applying the coating liquid for forming the charge transport layer onto the charge generating layer include common methods such as blade coating, wire bar coating, spray coating, dip coating, bead coating, air knife coating, and curtain coating.

[0114] The thickness of the charge transport layer is set, for example, preferably in the range of 5 μm to 50 μm, more preferably 10 μm to 30 μm.

[0115] [Inorganic protective layer] The inorganic protective layer is an inorganic material layer. Examples of inorganic materials include metal oxides such as gallium oxide, aluminum oxide, zinc oxide, titanium oxide, indium oxide, tin oxide, and boron oxide; metal nitrides such as gallium nitride, aluminum nitride, zinc nitride, titanium nitride, indium nitride, tin nitride, and boron nitride; carbon-based and silicon-based inorganic materials such as diamond-like carbon, amorphous carbon, hydrogenated amorphous carbon, hydrogenated-fluorinated amorphous carbon, amorphous silicon carbide, hydrogenated amorphous silicon carbide, amorphous silicon, and hydrogenated amorphous silicon; and mixed crystals thereof.

[0116] From the viewpoint of the abrasion resistance and electrical properties of the photoreceptor, the inorganic protective layer is preferably a layer containing a metal oxide, more preferably a layer containing gallium oxide. The metal oxide contained in the inorganic protective layer may be one type or two or more types.

[0117] The volume resistivity of the inorganic protective layer is set to 1.0×10 10 It is preferable that the resistance is Ω·cm or more, and 1.0×10 11 It is more preferable that the resistivity is Ω·cm or more.

[0118] The volume resistivity of the inorganic protective layer was measured by the following method. The inorganic protective layer is peeled off from the photoreceptor to prepare a sample. The sample is clamped in the sample holder of an impedance analyzer (Toyo Corporation), and the resistance is measured at an AC voltage of 1 V and a frequency of 100 Hz, and calculated based on the electrode area and sample thickness.

[0119] Examples of methods for forming the inorganic protective layer include known vapor phase film formation methods such as plasma CVD (Chemical Vapor Deposition), metalorganic vapor phase epitaxy, molecular beam epitaxy, vapor deposition, sputtering, etc. For example, the inorganic protective layer can be formed using the plasma CVD film formation apparatus and film formation conditions described in JP 2014-191179 A.

[0120] From the viewpoint of the abrasion resistance and electrical properties of the photoreceptor, the thickness of the inorganic protective layer is preferably 0.2 μm to 10 μm, more preferably 0.4 μm to 8 μm, and even more preferably 0.6 μm to 6 μm.

[0121] The thickness of each layer of the photoreceptor is the arithmetic mean of the values ​​measured with an electromagnetic film thickness meter, and the measurement points are four points at 90° intervals around the circumference of the axial center of the photoreceptor.

[0122] [Single-layer photosensitive layer] The single-layer photosensitive layer (charge generation / charge transport layer) is a layer containing, for example, a binder resin, a charge generation material, a charge transport material, and inorganic oxide particles. These materials are the same as those described for the charge generation layer and the charge transport layer.

[0123] The content of the charge generating material in the single-layer photosensitive layer is preferably 0.1% by mass to 10% by mass, and more preferably 0.8% by mass to 5% by mass, based on the total solid content. The content of the charge transport material in the single-layer photosensitive layer is preferably 5% by mass to 50% by mass, based on the total solid content.

[0124] The single-layer photosensitive layer is formed by coating. An embodiment of the coating method includes, for example, dissolving or dispersing a binder resin, a charge generating material, a charge transport material, and inorganic oxide particles in a solvent to prepare a coating liquid for forming a single-layer photosensitive layer, applying the coating liquid for forming a single-layer photosensitive layer to the surface of an undercoat layer or a conductive substrate to form a coating film, and drying the coating film. The details of the preparation method and application method for the coating liquid for forming a single-layer photosensitive layer are the same as those of the preparation method and application method for the coating liquid for forming a charge transport layer.

[0125] The thickness of the single-layer photosensitive layer is, for example, 5 μm or more and 50 μm or less, and preferably 10 μm or more and 40 μm or less.

[0126] <Image forming apparatus, process cartridge> The image forming apparatus according to the present embodiment includes an electrophotographic photosensitive member, a charging device that charges the surface of the electrophotographic photosensitive member, an electrostatic latent image forming device that forms an electrostatic latent image on the surface of the charged electrophotographic photosensitive member, a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing toner to form a toner image, and a transfer device that transfers the toner image to the surface of a recording medium. The electrophotographic photosensitive member according to the present embodiment is used as the electrophotographic photosensitive member.

[0127] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as an apparatus including a fixing device that fixes a toner image transferred onto the surface of a recording medium; an apparatus of a direct transfer type that directly transfers a toner image formed on the surface of an electrophotographic photosensitive member onto a recording medium; an apparatus of an intermediate transfer type that primarily transfers a toner image formed on the surface of an electrophotographic photosensitive member onto the surface of an intermediate transfer member, and then secondarily transfers the toner image transferred onto the surface of the intermediate transfer member onto the surface of a recording medium; an apparatus including a cleaning device that cleans the surface of an electrophotographic photosensitive member after transfer of a toner image but before charging; an apparatus including a static elimination device that irradiates the surface of an electrophotographic photosensitive member with static elimination light to eliminate static electricity after transfer of a toner image but before charging; and an apparatus including an electrophotographic photosensitive member heating member that increases the temperature of the electrophotographic photosensitive member and reduces the relative temperature.

[0128] In the case of an intermediate transfer type device, the transfer device is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer device that performs primary transfer of the toner image formed on the surface of the electrophotographic photosensitive body onto the surface of the intermediate transfer body, and a secondary transfer device that performs secondarily transfer of the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0129] The image forming apparatus according to this embodiment may be either a dry development type image forming apparatus or a wet development type image forming apparatus (a development type using a liquid developer).

[0130] In the image forming apparatus according to the present embodiment, for example, a portion including an electrophotographic photosensitive member may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge including the electrophotographic photosensitive member according to the present embodiment is preferably used. In addition to the electrophotographic photosensitive member, the process cartridge may include, for example, at least one selected from the group consisting of a charging device, an electrostatic latent image forming device, a developing device, and a transfer device.

[0131] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. The main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0132] FIG. 2 is a schematic diagram showing an example of the configuration of an image forming apparatus according to this embodiment. As shown in FIG. 2, the image forming apparatus 100 according to this embodiment includes a process cartridge 300 having an electrophotographic photosensitive member 7, an exposure device 9 (an example of an electrostatic latent image forming device), a transfer device 40 (a primary transfer device), and an intermediate transfer member 50. In the image forming apparatus 100, the exposure device 9 is disposed at a position where it can expose the electrophotographic photosensitive member 7 through the opening of the process cartridge 300, and the transfer device 40 is disposed at a position facing the electrophotographic photosensitive member 7 via the intermediate transfer member 50, with a portion of the intermediate transfer member 50 being in contact with the electrophotographic photosensitive member 7. Although not shown, the image forming apparatus 100 also includes a secondary transfer device that transfers the toner image transferred onto the intermediate transfer member 50 onto a recording medium (e.g., paper). The intermediate transfer member 50, the transfer device 40 (a primary transfer device), and the secondary transfer device (not shown) correspond to examples of transfer devices.

[0133] 2 integrally supports an electrophotographic photosensitive member 7, a charging device 8 (an example of a charging device), a developing device 11 (an example of a developing device), and a cleaning device 13 (an example of a cleaning device) within a housing. The cleaning device 13 has a cleaning blade (an example of a cleaning member) 131, which is disposed so as to come into contact with the surface of the electrophotographic photosensitive member 7. The cleaning member may not be in the form of the cleaning blade 131, but may be a conductive or insulating fibrous member, which may be used alone or in combination with the cleaning blade 131.

[0134] FIG. 2 shows an example of an image forming apparatus that includes a fibrous member 132 (roll-shaped) that supplies lubricant 14 to the surface of electrophotographic photosensitive member 7, and a fibrous member 133 (flat brush-shaped) that assists cleaning, but these are arranged as needed.

[0135] Hereinafter, each configuration of the image forming apparatus according to this embodiment will be described.

[0136] -Charging device- The charging device 8 may be, for example, a contact-type charger using a conductive or semi-conductive charging roller, charging brush, charging film, charging rubber blade, charging tube, etc. Also usable are non-contact type roller chargers, scorotron chargers and corotron chargers that utilize corona discharge, and other known chargers.

[0137] -Exposure equipment- The exposure device 9 may be, for example, an optical system that exposes the surface of the electrophotographic photosensitive member 7 to light such as semiconductor laser light, LED light, or liquid crystal shutter light in a predetermined image. The wavelength of the light source is within the spectral sensitivity range of the electrophotographic photosensitive member. The wavelength of semiconductor lasers is mainly near-infrared, with an oscillation wavelength around 780 nm. However, this wavelength is not limited to this, and lasers with an oscillation wavelength in the 600 nm range or blue lasers with an oscillation wavelength of 400 nm to 450 nm may also be used. Furthermore, for color image formation, a surface-emitting laser light source capable of outputting multiple beams is also effective.

[0138] -Developing device- The developing device 11 may be, for example, a general developing device that develops by contact or non-contact application of a developer. The developing device 11 is not particularly limited as long as it has the above-mentioned functions, and may be selected depending on the purpose. For example, it may be a known developing device that has a function of applying a one-component developer or a two-component developer to the electrophotographic photosensitive member 7 using a brush, roller, or the like. Among these, a developing roller that holds a developer on its surface is preferred.

[0139] The developer used in the developing device 11 may be a one-component developer containing only toner, or a two-component developer containing toner and a carrier. The developer may be magnetic or non-magnetic. Known developers are used.

[0140] -Cleaning device- The cleaning device 13 is a cleaning blade type device equipped with a cleaning blade 131. In addition to the cleaning blade type, a fur brush cleaning type or a simultaneous development cleaning type may also be used.

[0141] -Transfer device- Examples of the transfer device 40 include a contact type transfer charger using a belt, roller, film, rubber blade, etc., and a known transfer charger such as a scorotron transfer charger or corotron transfer charger that utilizes corona discharge.

[0142] -Intermediate transfer body- A belt-like intermediate transfer belt containing semiconductive polyimide, polyamideimide, polycarbonate, polyarylate, polyester, rubber, etc. is used as the intermediate transfer body 50. The intermediate transfer body may be in the form of a drum other than a belt.

[0143] FIG. 3 is a schematic diagram showing another example of the configuration of the image forming apparatus according to the present embodiment. 3 is a tandem-type multi-color image forming apparatus equipped with four process cartridges 300. In the image forming apparatus 120, the four process cartridges 300 are arranged in parallel on the intermediate transfer member 50, and one electrophotographic photosensitive member is used per color. The image forming apparatus 120 has the same configuration as the image forming apparatus 100, except that it is a tandem-type apparatus. [Example]

[0144] Hereinafter, the embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are by mass. In the following description, unless otherwise specified, synthesis, production, treatment, measurement, etc. were carried out at room temperature (25°C ± 3°C).

[0145] Example 1 [Formation of undercoat layer] As a conductive substrate, an aluminum cylindrical tube having an outer diameter of 30 mm, a length of 250 mm, and a wall thickness of 1 mm was prepared.

[0146] Zinc oxide (average particle size 70 nm, specific surface area 15 m 2100 parts of a silane coupling agent (trade name: KBM603, Shin-Etsu Chemical Co., Ltd., N-2-(aminoethyl)-3-aminopropyltrimethoxysilane) was added and stirred for 2 hours. The toluene was then distilled off under reduced pressure, and the mixture was baked at 120°C for 3 hours to obtain zinc oxide surface-treated with the silane coupling agent.

[0147] 110 parts of the surface-treated zinc oxide was mixed with 500 parts of tetrahydrofuran by stirring, and a solution of 0.6 parts of alizarin dissolved in 50 parts of tetrahydrofuran was added thereto, followed by stirring for 5 hours at 50° C. Next, the solid content was filtered off under reduced pressure and dried under reduced pressure at 60° C. to obtain zinc oxide with alizarin added thereto.

[0148] A solution of 60 parts alizarin-modified zinc oxide, 13.5 parts blocked isocyanate (product name: Sumidur 3175, Sumitomo Bayer Urethane Co., Ltd.), and 15 parts butyral resin (product name: S-LEC BM-1, Sekisui Chemical Co., Ltd.) dissolved in 68 parts methyl ethyl ketone was mixed with 5 parts methyl ethyl ketone and dispersed in a sand mill using 1 mm diameter glass beads for 2 hours to obtain a dispersion. To the dispersion, 0.005 parts dioctyltin dilaurate as a catalyst and 4 parts silicone resin particles (product name: Tospearl 145, Momentive Performance Materials Co., Ltd.) were added to obtain a coating solution for forming an undercoat layer. The coating solution for forming the undercoat layer was applied to the outer surface of a conductive substrate by dip coating and dried and cured at 170°C for 40 minutes to form a 20 μm thick undercoat layer.

[0149] [Formation of charge generation layer] A mixture consisting of 15 parts of hydroxygallium phthalocyanine (a charge-generating material) (having diffraction peaks at Bragg angles (2θ±0.2°) of at least 7.5°, 9.9°, 12.5°, 16.3°, 18.6°, 25.1°, and 28.3° in the X-ray diffraction spectrum using CuKα characteristic X-rays), 10 parts of vinyl chloride-vinyl acetate copolymer resin (trade name: VMCH, manufactured by Nippon Unicar Co., Ltd.) as a binder resin, and 200 parts of n-butyl acetate was dispersed in a sand mill using 1 mm diameter glass beads for 4 hours. 175 parts of n-butyl acetate and 180 parts of methyl ethyl ketone were added to the dispersion and stirred to obtain a coating solution for forming a charge-generating layer. The coating solution for forming the charge-generating layer was dip-coated onto the undercoat layer and dried at room temperature to form a 0.25 μm thick charge-generating layer.

[0150] [Formation of charge transport layer] Binder resin: Polycarbonate resin (1) (viscosity average molecular weight 40,000, the numerical value in the structural formula indicates the molar ratio (mol%)) 20 parts ·Charge transport material: CTM-1 ···15 parts Silica particles (average particle size 40 nm) hydrophobized with 1,1,1,3,3,3-hexamethyldisilazane 65 parts Solvent: tetrahydrofuran (THF) 600 parts The above materials were mixed and stirred for 12 hours to obtain a coating solution for forming a charge transport layer. The coating solution for forming a charge transport layer was dip-coated onto the charge generation layer. Hot air at 135°C was then blown onto the coating film to dry it, forming a charge transport layer with a thickness of 30 μm.

[0151] [ka]

[0152] [Formation of inorganic protective layer] Using trimethylgallium as the film-forming material, an amorphous layer containing gallium oxide was formed as an inorganic protective layer by plasma CVD. The layer thickness was 1 μm.

[0153] Through the above steps, a photoreceptor was obtained.

[0154] <Examples 2 to 17, Comparative Examples 1 and 2> A photoreceptor was obtained in the same manner as in Example 1, except that the average particle size and amount of silica particles used in forming the charge transport layer were changed according to Table 1, and the drying temperature of the coating film was adjusted to achieve the area ratio shown in Table 1. However, in Examples 15 and 16, the film-forming material used in forming the inorganic protective layer was changed to dimethyl zinc or trimethyl aluminum.

[0155] <Photoreceptor characteristic measurement> The following characteristics of the photoreceptor of each example were measured according to the methods already described. Cross-sectional observation of the charge transport layer shows that the area ratio A of silica particles contained in the surface layer on the surface side and the area ratio B of silica particles contained in the inner layer on the inner side are measured at half the thickness of the charge transport layer. Light transmittance of the charge transport layer Young's modulus of the charge transport layer

[0156] <Photoreceptor performance evaluation> [Crack resistance of inorganic protective layer] The load at which the inorganic protective layer breaks was measured as follows, and the crack resistance of the inorganic protective layer was evaluated. Measurements were made using a microhardness tester, with the load being increased from 0 mN to 5 mN increments. Observations were made with an optical microscope each time a load was applied, and the load at which the inorganic protective layer broke was taken as the crack initiation load. The measurement conditions were as follows. The measurement results are shown in Table 1. Test equipment: Product name DUH-201, Shimadzu Corporation Indenter: Diamond spherical indenter

[0157] [Table 1]

[0158] The abbreviations listed in Table 1 represent the following compounds. GaO: Gallium oxide ZnO: Zinc oxide AlO: Aluminum oxide

[0159] From the above results, it can be seen that the photoreceptor of this example ensures crack resistance of the inorganic protective layer while improving the light transmittance of the charge transport layer, and thus provides images of excellent quality, compared to the photoreceptor of the comparative example.

[0160] This embodiment includes the following aspects. (((1))) a conductive substrate; a charge generating layer provided on the conductive substrate; a charge transport layer provided on the charge generating layer and containing inorganic oxide particles; an inorganic protective layer provided on the photosensitive layer; Equipped with An electrophotographic photoreceptor in which, upon cross-sectional observation of the charge transport layer, the relationship between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, with the half film thickness of the charge transport layer as the boundary, satisfies area ratio A>area ratio B. (((2))) The electrophotographic photoreceptor according to (((1))), wherein a difference between an area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and an area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 1% or more and 75% or less. (((3))) The electrophotographic photoreceptor according to (((2))), wherein a difference between an area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and an area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 20% or more and 75% or less. (((4))) the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is 60% or more and 75% or less, The electrophotographic photoreceptor according to any one of (((1))) to (((3))), wherein the area ratio B of the inorganic oxide particles contained in the inner layer on the inner surface side is less than 60%. (((5))) the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is 60% or more and 70% or less, The electrophotographic photoreceptor according to (((4))), wherein the area ratio B of the inorganic oxide particles contained in the inner layer on the inner surface side is less than 60%. (((6))) The electrophotographic photoreceptor according to any one of (((1))) to (((5))), wherein the charge transport layer has a light transmittance of 80% or more. (((7))) The electrophotographic photoreceptor according to any one of (((1))) to (((6))), wherein the charge transport layer has a Young's modulus of 12 GPa or more. (((8))) The electrophotographic photoreceptor according to any one of (((1))) to (((7))), wherein the inorganic oxide particles are silica particles. (((9))) The electrophotographic photoreceptor according to any one of (((1))) to (((8))), wherein the inorganic protective layer is a layer containing a metal oxide. (((10))) The electrophotographic photoreceptor according to any one of ((1))) to (((9))), wherein the inorganic protective layer is a layer containing gallium oxide. (((11))) The electrophotographic photoreceptor according to any one of (((1))) to (((10))) is provided, A process cartridge that is detachably attached to an image forming apparatus. (((12))) The electrophotographic photoreceptor according to any one of (((1))) to (((10))), a charging device that charges the surface of the electrophotographic photosensitive member; an electrostatic latent image forming device for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing toner to form a toner image; a transfer device that transfers the toner image onto a surface of a recording medium; An image forming apparatus comprising:

[0161] The effects of the above embodiment are as follows. According to the invention of (((1))), there is provided an electrophotographic photoreceptor comprising a conductive substrate, a charge generating layer provided on the conductive substrate, a charge transport layer provided on the charge generating layer and containing inorganic oxide particles, and an inorganic protective layer provided on a photosensitive layer, wherein, in cross-sectional observation of the charge transport layer, the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side, across half the thickness of the charge transport layer, are the same, while ensuring the crack resistance of the inorganic protective layer, compared to when these are the same. According to the invention related to (((2))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the difference between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is less than 1% or more than 75%. According to the invention related to (((3))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the difference between the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is less than 20% or more than 75%. According to the invention related to (((4))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is less than 60% or more than 75%, or when the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 60% or more. According to the invention related to (((5))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is less than 60% or exceeds 70%, or when the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is more than 60%. According to the invention related to (((6))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the light transmittance of the charge transport layer is less than 80%. According to the invention (((7))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the Young's modulus of the charge transport layer is less than 12 GPa. According to the invention of (((8))), there is provided an electrophotographic photoreceptor in which the charge transport layer contains silica particles, and the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same, with the half-thickness of the charge transport layer as the boundary. According to the invention of (((9))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer containing a metal oxide, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same, with the half-thickness of the charge transport layer as the boundary. According to the invention of (((10))), an electrophotographic photoreceptor is provided in which the light transmittance of the charge transport layer is improved while ensuring the crack resistance of the inorganic protective layer containing gallium oxide, compared to when the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same, with the half-thickness of the charge transport layer as the boundary. According to the invention pertaining to (((11))) or (((12))), there is provided a process cartridge or an image forming apparatus equipped with an electrophotographic photosensitive member which comprises a conductive substrate, a charge generating layer provided on the conductive substrate, a charge transport layer which is provided on the charge generating layer and contains inorganic oxide particles, and an inorganic protective layer which is provided on the photosensitive layer, and in cross-sectional observation of the charge transport layer, the area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and the area ratio B of the inorganic oxide particles contained in the inner layer on the inner side are the same, with the half film thickness of the charge transport layer as the boundary. [Explanation of symbols]

[0162] 1 Conductive substrate, 2 Undercoat layer, 3 Charge generation layer, 4 Charge transport layer, 5 Photosensitive layer, 6 Inorganic protective layer, 10A photoreceptor, 10B photoreceptor

[0163] 7 electrophotographic photosensitive member, 8 charging device, 9 exposure device, 11 developing device, 13 cleaning device, 14 lubricant, 40 transfer device, 50 intermediate transfer body, 100 image forming apparatus, 120 image forming apparatus, 131 cleaning blade, 132 fibrous member (roll-shaped), 133 fibrous member (flat brush-shaped), 300 process cartridge

Claims

1. a conductive substrate; a charge generating layer provided on the conductive substrate; a charge transport layer provided on the charge generating layer and containing inorganic oxide particles; an inorganic protective layer provided on the photosensitive layer; Equipped with an electrophotographic photoreceptor in which, upon cross-sectional observation of the charge transport layer, a relationship between an area ratio A of the inorganic oxide particles contained in a surface layer on a surface side and an area ratio B of the inorganic oxide particles contained in an inner layer on an inner side, with a boundary being half the film thickness of the charge transport layer, satisfies area ratio A>area ratio B.

2. 2. The electrophotographic photoreceptor according to claim 1, wherein a difference between an area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and an area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 1% or more and 75% or less.

3. 3. The electrophotographic photoreceptor according to claim 2, wherein a difference between an area ratio A of the inorganic oxide particles contained in the surface layer on the surface side and an area ratio B of the inorganic oxide particles contained in the inner layer on the inner side is 20% or more and 75% or less.

4. an area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is 60% or more and 75% or less; 2. The electrophotographic photoreceptor according to claim 1, wherein the area ratio B of the inorganic oxide particles contained in the inner layer on the inner surface side is less than 60%.

5. an area ratio A of the inorganic oxide particles contained in the surface layer on the surface side is 60% or more and 70% or less; 5. The electrophotographic photoreceptor according to claim 4, wherein the area ratio B of the inorganic oxide particles contained in the inner layer on the inner surface side is less than 60%.

6. 2. The electrophotographic photoreceptor according to claim 1, wherein the charge transport layer has a light transmittance of 80% or more.

7. 2. The electrophotographic photoreceptor according to claim 1, wherein the charge transport layer has a Young's modulus of 12 GPa or more.

8. 2. The electrophotographic photoreceptor according to claim 1, wherein the inorganic oxide particles are silica particles.

9. 2. The electrophotographic photoreceptor according to claim 1, wherein the inorganic protective layer is a layer containing a metal oxide.

10. 2. The electrophotographic photoreceptor according to claim 1, wherein the inorganic protective layer is a layer containing gallium oxide.

11. An electrophotographic photoreceptor according to any one of claims 1 to 10, A process cartridge that is detachably attached to an image forming apparatus.

12. The electrophotographic photoreceptor according to any one of claims 1 to 10, a charging device that charges the surface of the electrophotographic photosensitive member; an electrostatic latent image forming device for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing toner to form a toner image; a transfer device that transfers the toner image onto a surface of a recording medium; An image forming apparatus comprising:

Images