Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor with excellent wear resistance and electrical properties. [Solution] An electrophotographic photoreceptor comprising a conductive substrate, a charge generation layer placed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles, wherein when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual and aggregated metal oxide particles is 60% or more.

Description

[Technical Field]

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

[0002] Patent Document 1 discloses "an electrophotographic photoreceptor comprising at least a laminated photosensitive layer in which a charge generating layer containing a charge generating material and a charge transport layer containing a charge transport material are laminated in this order on a conductive support, or an electrophotographic photoreceptor comprising at least the laminated photosensitive layer and a surface protective layer laminated thereon, wherein both or either of the charge transport layer and the surface protective layer contain a light absorber, the outermost layer of the electrophotographic photoreceptor contains silica filler, has a transmittance of 50% or more for light with a wavelength of 600 nm, and the ratio T600 / T550 of the transmittance T600 for light with a wavelength of 600 nm to the transmittance T550 for light with a wavelength of 550 nm is 1.10 or more and 2.20 or less."

[0003] Patent Document 2 discloses "an electrophotographic photoreceptor comprising a conductive support and a photosensitive layer formed on the conductive support, wherein the photosensitive layer is composed of one or more layers, the surface layer of the photosensitive layer contains a binder resin, silica particles and a charge transport material, the ten-point average roughness Rz of the surface of the surface layer is 0.08 μm or more and 0.80 μm or less, the average spacing Sm of the irregularities on the surface of the surface layer is greater than 15 μm and 120 μm or less, and the ratio Sm / Rz of the average spacing Sm to the ten-point average roughness Rz is 30 or more and 500 or less." [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-054576 [Patent Document 2] Japanese Patent Publication No. 2023-069379 [Overview of the Initiative]

Problems to be Solved by the Invention

[0005] The problem of the present invention is that in an electrophotographic photoreceptor having a conductive substrate, a charge generation layer provided on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles, when the cross-section of the charge transport layer is observed, compared with the case where the ratio of the single particles of the metal oxide particles to the total of the single particles and aggregated particles of the metal oxide particles is less than 60% by number, to provide an electrophotographic photoreceptor excellent in both abrasion resistance and electrical characteristics.

Means for Solving the Problems

[0006] Means for solving the above problems include the following aspects. <1> An electrophotographic photoreceptor having a conductive substrate, a charge generation layer provided on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles, where when the cross-section of the charge transport layer is observed, the ratio of the single particles of the metal oxide particles to the total of the single particles and aggregated particles of the metal oxide particles is 60% or more by number. <2> The electrophotographic photoreceptor according to <1>, wherein the ratio of the single particles of the metal oxide particles is 70% or more by number. <3> The electrophotographic photoreceptor according to <1> or <2>, wherein when the cross-section of the charge transport layer is observed, the ratio of the total area of the single particles and aggregated particles of the metal oxide particles to the area of the entire observed cross-section is 60% to 95% by area. <4> The electrophotographic photoreceptor according to any one of <1> to <3>, wherein the metal oxide particles are silica particles. <5> The electrophotographic photoreceptor according to any one of <1> to <4>, wherein the average circularity of the metal oxide particles is 0.7 or more and the degree of hydrophobization is 60% or more. <6> The electrophotographic photoreceptor according to <5>, wherein the average circularity of the metal oxide particles is 0.8 or more and the degree of hydrophobization is 60% or more. <7> The electrophotographic photoreceptor according to any one of <1> to <6>, wherein the light transmittance T of the charge transport layer is 80% or more. <8> The electrophotographic photoreceptor according to any one of <1> to <7>, further comprising an inorganic protective layer disposed on the charge transport layer. <9> A process cartridge that is detachable from an image forming apparatus and includes the electrophotographic photoreceptor according to any one of <1> to <8>. <10> An image forming apparatus comprising: the electrophotographic photoreceptor according to any one of <1> to <8>; a charging device that charges the surface of the electrophotographic photoreceptor; an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the electrophotographic photoreceptor; a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image; and a transfer device that transfers the toner image onto the surface of a recording medium.

Advantages of the Invention

[0007] According to the invention according to <1>, there are provided a conductive substrate, a charge generation layer provided on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles. When observing the cross-section of the charge transport layer, compared with the case where the ratio of the single particles of the metal oxide particles to the total of the single particles and aggregated particles of the metal oxide particles is less than 60% by number, an electrophotographic photoreceptor having both excellent wear resistance and electrical characteristics is provided. According to the invention according to <2>, compared with the case where the ratio of the single particles of the metal oxide particles is less than 70% by number, an electrophotographic photoreceptor having both excellent wear resistance and electrical characteristics is provided. According to the invention according to <३>, when observing the cross-section of the charge transport layer, compared with the case where the ratio of the total area of the single particles and aggregated particles of the metal oxide particles to the entire area of the observed cross-section is less than 60% by area or exceeds 95% by area, an electrophotographic photoreceptor having both excellent wear resistance and electrical characteristics is provided. <4> According to the invention, an electrophotographic photoreceptor is provided that has superior wear resistance and electrical properties compared to a case where the metal oxide particles are not silica particles. <5> or <6> According to the invention, an electrophotographic photoreceptor is provided that has superior wear resistance and electrical properties compared to cases where the average circularity of the metal oxide particles is less than 0.7 or the degree of hydrophobicity is less than 60%, or where the average circularity of the metal oxide particles is less than 0.8 or the degree of hydrophobicity is less than 60%. <7> According to the invention, an electrophotographic photoreceptor is provided that has superior abrasion resistance and electrical properties compared to a case where the light transmittance T of the charge transport layer is less than 80%. <8> According to the present invention, an electrophotographic photoreceptor is provided having a conductive substrate, a charge generation layer installed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles, wherein when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual and aggregated metal oxide particles is less than 60 percent, compared to the case where both crack suppression of the inorganic protective layer and electrical properties are superior. <9> or <10> According to the present invention, a process cartridge or image forming apparatus is provided that has an electrophotographic photoreceptor having a conductive substrate, a charge generation layer installed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles, wherein when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual and aggregated metal oxide particles is less than 60 percent, and the electrophotographic photoreceptor has superior wear resistance and electrical properties compared to the case in which such an electrophotographic photoreceptor is used. [Brief explanation of the drawing]

[0008] [Figure 1] This is a partial cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor according to this embodiment. [Figure 2] This is a schematic diagram showing an example of an image forming apparatus according to this embodiment. [Figure 3] This is a schematic diagram showing another example of the image forming apparatus according to this embodiment. [Modes for carrying out the invention]

[0009] The following describes an example of the present invention. These descriptions and examples are illustrative and do not limit the scope of the present invention.

[0010] In this specification, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described stepwise within this specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise. Furthermore, in numerical ranges described within this specification, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objective is achieved. When embodiments are described herein with reference to the drawings, the configuration of such embodiments is not limited to that shown in the drawings. Furthermore, the sizes of the components in each figure are conceptual, and the relative relationships between the components are not limited thereto. In this specification, each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition in this specification, if there are multiple types of the substance corresponding to that component in the composition, unless otherwise specified, it means the total amount of those multiple types of substances present in the composition. In this specification, each component may contain multiple types of particles. When multiple types of particles corresponding to each component are present in a composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified.

[0011] In this specification, the "axial direction" of an electrophotographic photoreceptor means the direction in which the axis of rotation of the electrophotographic photoreceptor extends, and the "circumferential direction" of an electrophotographic photoreceptor means the direction of rotation of the electrophotographic photoreceptor.

[0012] <Electrophotographic photoconductor> The electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") according to this embodiment comprises a conductive substrate, a charge generation layer, and a charge transport layer. The charge generation layer is provided on a conductive substrate. The charge transport layer comprises a binder resin, a charge transport material, and metal oxide particles. Furthermore, when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual metal oxide particles and aggregated metal oxide particles must be 60% or more.

[0013] The photoreceptor according to this embodiment, with the above configuration, is an electrophotographic photoreceptor that has excellent abrasion resistance and electrical properties. The reason for this is presumed to be as follows.

[0014] Metal oxide particles tend to aggregate within the charge transport layer, leading to increased particle size and poor dispersion within the layer. This results in reduced light transmittance due to light scattering and variations in the hardness of the charge transport layer surface. Consequently, the wear resistance and electrical properties of the photoreceptor are reduced.

[0015] Therefore, in this embodiment, the photoreceptor has a metal oxide particle ratio of several percent of 60 particles, as described above. In other words, the metal oxide particles are dispersed in a state that is small in size and nearly uniform, making them less likely to aggregate in the charge transport layer. This suppresses light scattering in the charge transport layer and prevents a decrease in light transmittance.

[0016] In addition, metal oxide particles exhibiting a filler effect are dispersed on the surface of the charge transport layer in a small particle size and nearly uniform manner. This makes it possible to suppress variations in the hardness of the charge transport layer surface.

[0017] For the reasons stated above, it is presumed that the photoreceptor according to this embodiment exhibits excellent abrasion resistance and electrical properties.

[0018] The details of the photoreceptor according to this embodiment will be described below.

[0019] Figure 1 is a schematic partial cross-sectional view showing an example of the layer structure of a photoreceptor according to this embodiment. The photoreceptor 10A shown in Figure 1 has a stacked photoreceptor layer. The photoreceptor 10A has a structure in which a base layer 2, a charge generation layer 3, a charge transport layer 4, and an inorganic protective layer 6 are stacked in this order on a conductive substrate 1, with the charge generation layer 3 and the charge transport layer 4 constituting the photosensitive layer 5 (a so-called functionally separated photosensitive layer). The 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. The inorganic protective layer 6 may or may not be present.

[0020] The following describes each layer of the photoreceptor in detail. However, the symbols will be omitted, and the individual layers of the photoreceptor will be described accordingly.

[0021] [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, and belts 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 volume resistivity of 10⁻¹⁰. 13 This refers to a value less than Ω·cm.

[0022] When an 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 in order to suppress interference fringes that occur when irradiated with laser light. While roughening to prevent interference fringes is not particularly necessary when using non-interfering light as the light source, it is beneficial for extending the lifespan by suppressing the occurrence of defects due to surface irregularities of the conductive substrate.

[0023] Methods for roughening a surface include, for example, wet honing, which involves suspending an abrasive in water and spraying it onto a conductive substrate; centerless grinding, which involves pressing a conductive substrate against a rotating grinding wheel and continuously grinding it; and anodizing.

[0024] One method for roughening the surface is to disperse conductive or semiconductive powder in a resin without roughening the surface of the conductive substrate, to form a layer on the surface of the conductive substrate, and then roughen the surface with the particles dispersed in that layer.

[0025] Anodizing roughening treatment involves forming an oxide film on the surface of a conductive substrate (e.g., aluminum) by anodizing it in an electrolyte solution. Examples of electrolyte solutions include sulfuric acid solution and oxalic acid solution. However, the porous anodic oxide film formed by anodizing is chemically active, 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 to block the micropores of the oxide film by volume expansion due to a hydration reaction using pressurized steam or boiling water (metal salts such as nickel may be added), thereby converting it into a more stable hydrated oxide.

[0026] The thickness of the anodic oxide film is preferably, for example, 0.3 μm to 15 μm. When the film thickness is within this range, it tends to exhibit barrier properties against injection and tends to suppress the increase in residual potential due to repeated use.

[0027] The conductive substrate may be treated with an acidic treatment solution or with boehmite. Treatment with an acidic solution is carried out, for example, as follows: First, an acidic solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The mixing ratio of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic solution is, for example, in the range of 10% to 11% by mass for phosphoric acid, 3% to 5% by mass for chromic acid, and 0.5% to 2% by mass for hydrofluoric acid, and the total concentration of these acids is preferably in the range of 13.5% to 18% by mass. The treatment temperature is preferably, for example, 42°C to 48°C. The film thickness is preferably 0.3 μm to 15 μm.

[0028] The boehmite treatment is carried out, for example, by immersing the material in pure water at 90°C to 100°C for 5 to 60 minutes, or by contacting it with heated steam at 90°C to 120°C for 5 to 60 minutes. The film thickness is preferably 0.1 μm to 5 μm. This can be further treated with anodic oxidation using an electrolyte solution with low film solubility, such as adipic acid, boric acid, borate, phosphate, phthalate, maleate, benzoate, tartrate, or citrate.

[0029] (subbing layer) The undercoat layer is, for example, a layer containing inorganic particles and a binder resin.

[0030] As for inorganic particles, for example, powder resistance (volume resistivity) 10 2 Ω cm or more 10 11 Examples include inorganic particles with a size of Ω·cm or less. Among these, suitable inorganic particles having the above-mentioned resistance values ​​include, for example, 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.

[0031] The specific surface area of ​​inorganic particles using the BET method is, for example, 10 m². 2 A value of 1g or more is preferable. The volume-average particle size of the inorganic particles is preferably between 50 nm and 2000 nm (preferably between 60 nm and 1000 nm).

[0032] The inorganic particle content is preferably 10% by mass or more and 80% by mass or less relative to the binder resin, and more preferably 40% by mass or more and 80% by mass or less.

[0033] The inorganic particles may be surface-treated. Two or more types of inorganic particles with different surface treatments or particle sizes may be mixed and used.

[0034] Examples of surface treatment agents include silane coupling agents, titanate-based coupling agents, aluminum-based coupling agents, and surfactants. Silane coupling agents are particularly preferred, and silane coupling agents having an amino group are more preferred.

[0035] 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.

[0036] Silane coupling agents may be used in combination of two or more types. 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-methacrylateoxypropyl-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.

[0037] The surface treatment method using the surface treatment agent may be any known method, and may be either a dry or wet method.

[0038] The amount of surface treatment agent applied is preferably, for example, 0.5% by mass or more and 10% by mass or less relative to the inorganic particles.

[0039] In this case, it is preferable for the underlayer to contain electron-accepting compounds (acceptor compounds) along with inorganic particles, from the viewpoint of improving the long-term stability of electrical properties and carrier blocking ability.

[0040] Examples of electron-accepting compounds include electron-transporting substances such as compounds having anthraquinone structures; 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, compounds having an anthraquinone structure are preferred as electron-accepting compounds. Examples of compounds having an anthraquinone structure include hydroxyanthraquinone compounds, aminoanthraquinone compounds, and aminohydroxyanthraquinone compounds. Specifically, examples of preferred compounds include anthraquinone, alizarin, quinizalin, anthralphine, purpurin, and their derivatives.

[0041] The electron-accepting compound may be dispersed in the underlayer together with inorganic particles, or it may be present attached to the surface of the inorganic particles.

[0042] Methods for attaching electron-accepting compounds to the surface of inorganic particles include, for example, dry methods or wet methods.

[0043] The dry method involves, for example, adding an electron-accepting compound, either directly or dissolved in an organic solvent, dropwise while stirring inorganic particles with a mixer that has a high shear force, or spraying it with dry air or nitrogen gas, to adhere the electron-accepting compound to the surface of the inorganic particles. When adding or spraying the electron-accepting compound, it is preferable to do so at a temperature below the boiling point of the solvent. After adding or spraying the electron-accepting compound, further exposure may be performed at a temperature of 100°C or higher. The exposure time is not particularly limited as long as the temperature and duration are such that electrophotographic characteristics can be obtained.

[0044] The wet method involves dispersing inorganic particles in a solvent using, for example, a stirrer, ultrasonic disperser, sand mill, attritor, or ball mill, while adding an electron-accepting compound. After stirring or dispersion, the solvent is removed, and the electron-accepting compound adheres to the surface of the inorganic particles. Solvent removal methods include, for example, filtration or distillation. After solvent removal, further baking at 100°C or higher may be performed. The baking temperature and time are not particularly limited as long as electrophotographic characteristics can be obtained. In the wet method, the water content of the inorganic particles may be removed before adding the electron-accepting compound. Examples of this include removing water while stirring and heating in the solvent, or removing water by azeotrope with the solvent.

[0045] Furthermore, the attachment of the electron-accepting compound may be performed before or after surface treatment with a surface treatment agent on the inorganic particles, or it may be performed simultaneously with the attachment of the electron-accepting compound and surface treatment with the surface treatment agent.

[0046] The content of the electron-accepting compound is preferably, for example, 0.01% by mass or more and 20% by mass or less relative to the inorganic particles, and more preferably 0.01% by mass or more and 10% by mass or less.

[0047] Examples of known polymer compounds used as the binder resin for the undercoat include acetal resin (e.g., polyvinyl butyral), polyvinyl alcohol resin, polyvinyl acetal resin, casein resin, polyamide resin, cellulose resin, gelatin, polyurethane resin, polyester resin, unsaturated polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic anhydride resin, silicone resin, silicone-alkyd resin, urea resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, alkyd resin, epoxy resin, 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 include charge-transporting resins having charge-transporting groups, conductive resins (e.g., polyaniline), and the like.

[0048] Among these, a resin insoluble in the coating solvent of the upper layer is preferred as the binder resin used for the undercoat layer. In particular, a resin obtained by the reaction of a curing agent with at least one resin selected from the group consisting of thermosetting resins such as urea resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, unsaturated polyester resin, alkyd resin, and epoxy resin is preferred. When using two or more of these binder resins in combination, the mixing ratio is set as needed.

[0049] The undercoat may contain various additives to improve electrical properties, environmental stability, and image quality. Examples of known additives include electron-transporting pigments such as polycyclic condensation and azo pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. As mentioned above, silane coupling agents are used for surface treatment of inorganic particles, but they may also be added to the undercoat as additives.

[0050] Examples of silane coupling agents used as additives include vinyltrimethoxysilane, 3-methacrylateoxypropyl-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.

[0051] Examples of zirconium chelate compounds include zirconium butoxide, ethyl zirconium acetate, zirconium triethanolamine, acetylacetonate zirconium butoxide, ethyl acetate 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.

[0052] Examples of titanium chelate compounds include tetraisopropyl titanate, tetran-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.

[0053] Examples of aluminum chelating compounds include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

[0054] These additives may be used individually or as a mixture or polycondensate of multiple compounds.

[0055] The underlayer should ideally have a Vickers hardness of 35 or higher. The surface roughness (ten-point average roughness) of the undercoat layer should be adjusted to between 1 / (4n) (where n is the refractive index of the upper layer) and 1 / 2 of the exposure laser wavelength λ used, in order to suppress moiré patterns. Resin particles may be added to the undercoat to adjust the surface roughness. Examples of resin particles include silicone resin particles and cross-linked polymethyl methacrylate resin particles. The surface of the undercoat may also be polished to adjust the surface roughness. Polishing methods include buffing, sandblasting, wet honing, and grinding.

[0056] There are no particular restrictions on the formation of the undercoat layer, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of an undercoat-forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0057] Solvents for preparing the coating solution for forming the undercoat 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. Examples of these solvents include common organic solvents such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene.

[0058] Known methods for dispersing inorganic particles when preparing a coating solution for forming an undercoat include, for example, roll mills, ball mills, vibrating ball mills, attritors, sand mills, colloid mills, and paint shakers.

[0059] Conventional methods for applying the undercoating solution onto a conductive substrate include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0060] The thickness of the undercoat layer is preferably set to a range of 15 μm or more, and more preferably 20 μm to 50 μm.

[0061] (Middle class) Although not shown in the diagram, an intermediate layer may be further provided between the undercoat layer and the photosensitive layer. The intermediate layer is, for example, a layer containing a resin. Examples of resins used in the intermediate layer include polymer compounds such as acetal resin (e.g., polyvinyl butyral), polyvinyl alcohol resin, polyvinyl acetal resin, casein resin, polyamide resin, cellulose resin, gelatin, polyurethane resin, polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic anhydride resin, silicone resin, silicone-alkyd resin, phenol-formaldehyde resin, and melamine resin. The intermediate layer may contain an organometallic compound. Examples of organometallic compounds used in the intermediate layer include those containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon. The compounds used in these intermediate layers may be used individually, as a mixture of multiple compounds, or as polycondensates.

[0062] Among these, the intermediate layer is preferably a layer containing an organometallic compound that contains zirconium atoms or silicon atoms.

[0063] There are no particular restrictions on the formation of the intermediate layer, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of an intermediate layer-forming coating solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary. Conventional methods such as immersion coating, push-up coating, wire bar coating, spray coating, blade coating, air knife coating, and curtain coating are used to form the intermediate layer.

[0064] The thickness of the intermediate layer is preferably set to a range of 0.1 μm to 3 μm, for example. The intermediate layer may also be used as a base layer.

[0065] (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 when using non-coherent light sources such as LEDs (Light Emitting Diodes) or organic EL (Electro-Luminescence) image arrays.

[0066] Examples of charge-generating materials include azo pigments such as bisazo and trisazo; fused aromatic pigments such as dibromoanthonthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0067] Among these, in order to accommodate 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; and titanyl phthalocyanine are more preferable.

[0068] On the other hand, to accommodate laser exposure in the near-ultraviolet region, preferred charge-generating materials include fused aromatic pigments such as dibromoanthoten; thioindigo pigments; porphyrazine compounds; zinc oxide; trigonal selenium; and bisazo pigments.

[0069] The above charge generating material may also be used when using non-coherent light sources such as LEDs and organic EL image arrays, which have a central emission wavelength between 450 nm and 780 nm.

[0070] When n-type semiconductors such as fused aromatic pigments, perylene pigments, and azo pigments are used as charge-generating materials, dark currents are less likely to occur, and image defects called black spots can be suppressed even in thin films. Furthermore, the n-type is determined using the commonly used time-of-flight method, based on the polarity of the photocurrent that flows. Those that are more likely to carry electrons as carriers than holes are classified as n-type.

[0071] The binder resin used in the charge generation layer can be selected from a wide range of insulating resins, or it may 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 (such as polycondensates of bisphenols and aromatic divalent carboxylic acids), 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, and polyvinylpyrrolidone resin. Here, "insulating properties" refer to a volume resistivity of 10¹³ Ω·cm or higher. These binder resins can be used individually or in combination of two or more types.

[0072] Furthermore, the mixing ratio of the charge-generating material to the binder resin is preferably within the range of 10:1 to 1:10 by mass ratio.

[0073] The charge generation layer may also contain other well-known additives.

[0074] The formation of the charge generation layer is not particularly limited, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of a charge generation layer forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it as necessary. The charge generation layer may also be formed by vapor deposition of the charge generation material. Formation of the charge generation layer by vapor deposition is particularly suitable when using fused aromatic pigments or perylene pigments as the charge generation material.

[0075] Solvents for preparing the coating solution for forming the charge generation layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene. These solvents can be used individually or in mixtures of two or more.

[0076] Methods for dispersing particles (e.g., charge-generating materials) in a coating solution for forming a charge-generating layer include, for example, media dispersers such as ball mills, vibrating 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 collision methods, which disperse the dispersion by causing liquid-liquid collisions or liquid-wall collisions under high pressure, and penetration methods, which disperse the dispersion by penetrating fine channels under high pressure. Furthermore, during this dispersion, it is effective to set the average particle size of the charge-generating material in the coating solution for forming the charge-generating layer to 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0077] Conventional methods for applying the charge-generating layer forming solution onto the undercoat (or intermediate layer) include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0078] The thickness of the charge generation layer is preferably set to a range of 0.1 μm to 5.0 μm, more preferably 0.2 μm to 2.0 μm.

[0079] [Charge transport layer] The charge transport layer is a layer containing a binder resin, a charge transport material, and metal oxide particles. The charge transport layer may be a layer containing a binder resin, a polymer charge transport material, and metal oxide particles.

[0080] In the photoreceptor according to this embodiment, when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual metal oxide particles and aggregated metal oxide particles is 60 percent or more. If the proportion of individual metal oxide particles is less than 60%, aggregated particles will inhibit charge transfer, reducing the conductivity of the charge transport layer. The proportion of individual metal oxide particles is preferably 60% or more, more preferably 80% or more, and even more preferably 90% or more.

[0081] When the charge transport layer is observed in cross-section, the proportion of individual metal oxide particles satisfies the above range, resulting in excellent wear resistance and electrical properties of the photoreceptor.

[0082] Here, the percentage of individual metal oxide particles is calculated by observing the cross-section of the charge transport layer using the following method. A sample of the charge transport layer, cut along the thickness direction, is obtained using the cryomicrotome method. A scanning electron microscope is used to observe the cross-section of the sample at a magnification of 20,000x. Count the number of individual metal oxide particles and aggregated particles within the observation area. Here, a single metal oxide particle is defined as a particle in which the primary metal oxide particle is observed not in contact with or overlapping with other particles. On the other hand, aggregated metal oxide particles are defined as particles in which primary metal oxide particles are observed to be in contact with or overlapping with other particles. The ratio of individual metal oxide particles to the total number of individual and aggregated metal oxide particles in the observed area is calculated. Then, the above operation is performed five times to calculate the average value of the proportion of individual metal oxide particles. Furthermore, in cross-sectional observation of the sample piece, the identification of metal oxide particles is performed by energy-dispersive X-ray spectroscopy (EDX) analysis, based on the presence of the constituent elements of the metal oxide particles (for example, in the case of silica particles, the presence of Si and O).

[0083] Methods for ensuring that the metal oxide particles contained in the charge transport layer meet the above range include adjusting the temperature of the coating environment for the charge transport layer forming coating solution.

[0084] Furthermore, in the photoreceptor according to this embodiment, when the charge transport layer is observed in cross-section, it is preferable that the ratio of the total area of ​​individual metal oxide particles and aggregated metal oxide particles to the total area of ​​the observed cross-section is 60% to 95%. If the total area percentage of metal oxide particles is less than 60 area percentage, the wear resistance of the charge transport layer is insufficient. If the area percentage of individual metal oxide particles exceeds 95%, the metal oxide particles inhibit charge transfer, reducing the conductivity of the charge transport layer. The area percentage of individual metal oxide particles is more preferably 65% ​​to 92% and even more preferably 70% to 90%.

[0085] Here, the area percentage representing the proportion of individual metal oxide particles is calculated by observing the cross-section of the charge transport layer using the following method. A sample of the charge transport layer, cut along the thickness direction, is obtained using the cryomicrotome method. A scanning electron microscope is used to observe the cross-section of the sample at a magnification of 20,000x. The sum of the areas of individual metal oxide particles and aggregated particles in the observation area is calculated. The identification of individual metal oxide particles and aggregated metal oxide particles is as described in the section on the proportion of individual metal oxide particles. The ratio of the total area of ​​individual metal oxide particles and aggregated metal oxide particles to the total area of ​​the observation region is calculated. Then, the above operation is performed five times to calculate the average value of the total area ratio of individual metal oxide particles and aggregated metal oxide particles. Furthermore, the identification of metal oxide particles in the cross-sectional observation of the sample piece is also done in the same way as explained in terms of the proportion of individual metal oxide particles.

[0086] (Types of metal oxide particles) Examples of metal oxide particles used in the charge transport layer include silica particles, alumina particles, and titanium oxide particles.

[0087] Among these, silica particles are preferred as metal oxide particles from the viewpoint of suppressing the deterioration of the photoreceptor's electrical properties.

[0088] Examples of silica particles include dry silica particles and wet silica particles.

[0089] Examples of dry silica particles include fumed silica and deflagration silica. Fumed silica is obtained by burning silane compounds. Deflagration silica is obtained by explosively burning metallic silicon powder. Examples of wet silica particles include sedimentation silica, gel silica, colloidal silica (silica sol particles), and sol-gel silica. Precipitated silica and gel-processed silica particles are obtained by the neutralization reaction of sodium silicate and mineral acid. Silica synthesized and aggregated under alkaline conditions is called precipitated silica, while silica synthesized and aggregated under acidic conditions is called gel-processed silica particles. Colloidal silica particles (silica sol particles) are obtained by polymerizing acidic silicic acid in an alkaline state. Sol-gel silica particles are obtained by hydrolysis of organosilane compounds (e.g., alkoxysilanes).

[0090] It is preferable that the silica particles have their surfaces treated with a hydrophobic treatment agent. This reduces the number of silanol groups on the surface of the silica particles, making it easier to suppress the generation of residual potential. Examples of hydrophobic treatment agents include well-known silane compounds such as chlorosilanes, alkoxysilanes, and silazanes. Among these, silane compounds having a trimethylsilyl group, a decylsilyl group, or a phenylsilyl group are preferable as hydrophobic treatment agents, from the viewpoint of easily suppressing the generation of residual potential. In other words, it is preferable for the surface of silica particles to have a trimethylsilyl group, a decylsilyl group, or a phenylsilyl group. Examples of silane compounds containing a trimethylsilyl group include trimethylchlorosilane, trimethylmethoxysilane, and 1,1,1,3,3,3-hexamethyldisilazane. Examples of silane compounds containing a decylsilyl group include decyltrichlorosilane, decyldimethylchlorosilane, and decyltrimethoxysilane. Examples of silane compounds containing a phenyl group include triphenylmethoxysilane and triphenylchlorosilane.

[0091] -Average circularity of metal oxide particles- In the photoreceptor according to this embodiment, it is preferable that the metal oxide particles are dispersed in the charge transport layer in a small particle size and nearly uniform state. The metal oxide particles contained in the photoreceptor according to this embodiment preferably have an average circularity of 0.7 or higher, more preferably 0.75 or higher, and even more preferably 0.8 or higher.

[0092] When the average circularity is 0.7 or higher, the inter-particle distance tends to be uniform, and the particles tend to disperse uniformly.

[0093] The average circularity of metal oxide particles is calculated using the following method. The average circularity of metal oxide particles can be determined by the formula: (circular equivalent perimeter) / (perimeter) [(perimeter of a circle with the same projected area as the particle image) / (perimeter of the particle projection image)]. Specifically, it is a value measured by the following method: A sample of the charge transport layer, cut along the thickness direction, is obtained using the cryomicrotome method. A scanning electron microscope is used to observe the cross-section of the sample at a magnification of 20,000x. Determine the circularity of the primary particles of the metal oxide particles in the observed region. Then, the above procedure is performed five times to calculate the average value of the circularity of the primary particles of the metal oxide particles. Furthermore, the identification of metal oxide particles in the cross-sectional observation of the sample piece is also done in the same way as explained in terms of the proportion of individual metal oxide particles.

[0094] - Degree of hydrophobicity of metal oxide particles - In the photoreceptor according to this embodiment, if metal oxide particles with a low OH group content are included in the charge transport layer, it becomes more difficult to capture charges, thus preventing a decrease in the electrical function of the charge transport layer.

[0095] As an indicator of a low OH group content, the degree of hydrophobicity of the metal oxide particles is preferably 60% or higher, more preferably 62% or higher, and even more preferably 65% ​​or higher.

[0096] When the degree of hydrophobicity of metal oxide particles is 60 or higher, the amount of OH groups present in the particles that act as charge traps is small, and the function of the charge transport agent is inhibited or suppressed.

[0097] Therefore, by ensuring that the average circularity and hydrophobicity of the metal oxide particles meet the above ranges, both the wear resistance and electrical properties of the photoreceptor are improved.

[0098] Here, silica particles, which are metal oxide particles, are generally surface-treated with a hydrophobic agent to reduce the amount of OH groups remaining on the surface. However, among silica particles, for example, silica particles produced by the sol-gel method have a porous structure, making it difficult for the surface treatment agent to penetrate into the pores, resulting in a large amount of OH groups remaining inside the pores. Therefore, it is preferable that silica particles be hydrophobic treated with a hydrophobic agent.

[0099] The amount of OH groups in a metal oxide is determined by its degree of hydrophobicity. The degree of hydrophobicity of metal oxide particles is calculated using the following method. Add 5g of metal oxide particles to 100mL of water. Add methanol dropwise at a rate of 1mL each time, and the following value when the metal oxide particles settle is defined as the degree of hydrophobicity. [(Volume of methanol added) / {(Volume of methanol added)+(Volume of water)}] ×100 Furthermore, one method for separating metal oxide particles from a photoreceptor is to dissolve the film peeled off the substrate in an organic solvent and separate the particles by sieving the solution.

[0100] -Light transmittance-

[0101] In this embodiment, it is preferable that the photoreceptor is such that the irradiated light is not easily scattered by the charge transport layer and is transmitted to the charge generation layer. In the photoreceptor according to this embodiment, it is preferable that the light transmittance T of the charge transport layer is 80% or more.

[0102] If the light transmittance T of the charge transport layer is less than 80%, the amount of light that passes through the charge transport layer and reaches the charge generation layer is insufficient, and the function of the photoreceptor deteriorates.

[0103] As the light transmittance T satisfies the above range, the metal oxide particles contained in the charge transport layer are dispersed in a nearly uniform state. Thus, from the viewpoint of preventing light scattering within the layer and allowing light to pass through to the charge generation layer, the light transmittance T of the charge transport layer is preferably 80 or higher, more preferably 85 or higher, and even more preferably 90 or higher.

[0104] The light transmittance of the charge transport layer is calculated by the following method. A coating solution for forming a charge transport layer is applied to a polycarbonate sheet and dried to create a laminate (polycarbonate sheet / composition layer), which is then used as the sample for measurement. The light transmittance in the thickness direction of the sample was measured using a UV-Vis spectrophotometer, from wavelengths of 730 to 830 nm. During measurement, light was incident from the polycarbonate sheet side. The light transmittance of the polycarbonate sheet alone was also measured to determine the transmittance of light incident on the composition layer that passes through the composition layer. The average value of the transmittance at 10 nm intervals from wavelengths of 730 to 830 nm was calculated. Alternatively, peel the film of the charge transport layer from the substrate, attach the film to a glass plate, and measure the light transmittance in the same manner as above. At this time, the light is incident from the glass plate side, and by also measuring the light transmittance of only the glass plate, a measured value of the light transmittance of the charge transport layer alone can be obtained.

[0105] (Charge transport material) Examples of the charge transport material include quinone-based compounds such as p-benzoquinone, chloranil, bromanil, and anthraquinone; tetracyanoquinodimethane-based compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone; xanthone-based compounds; benzophenone-based compounds; cyanovinyl-based compounds; and electron-transporting compounds such as ethylene-based compounds. Examples of the charge transport material also include hole-transporting compounds such as triarylamine-based compounds, benzidine-based compounds, arylalkane-based compounds, aryl-substituted ethylene-based compounds, stilbene-based compounds, anthracene-based compounds, and hydrazone-based compounds. These charge transport materials can be used alone or in combination of two or more, but are not limited thereto.

[0106] From the viewpoint of charge mobility, as the charge transport material, a triarylamine derivative represented by the following structural formula (a-1) and a benzidine derivative represented by the following structural formula (a-2) are preferable.

[0107] [Chemical formula]

[0108] In the structural formula (a-1), Ar T1 , Ar T2 , and Ar T3 each independently represent a substituted or unsubstituted aryl group, -C6H4-C(R T4 )=C(R T5 )(R T6 ), or -C6H4-CH=CH-CH=C(R T7 )(R<​​​​​​​​, and R T8 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Substituents for each of the above groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Furthermore, substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms are also examples of substituents for each of the above groups.

[0109] [ka]

[0110] In structural formula (a-2), R T91 and R T92 Each of these 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 of these independently consists of 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, and -C(R T12 )=C(R T13 )(R T14 ), or -CH=CH-CH=C(R T15 )(R T16 ) shows R T12 , R T13 , R T14 , R T15 and R T16 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. m1 , T m2 , T n1 and T n2 Each of these independently represents an integer between 0 and 2 (inclusive). Substituents for each of the above groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Furthermore, substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms are also examples of substituents for each of the above groups.

[0111] Here, among the triarylamine derivative represented by structural formula (a-1) and the benzidine derivative represented by structural formula (a-2), in particular, "-C6H4-CH=CH-CH=C(R T7 )(R T8 Triarylamine derivatives having ")" and "-CH=CH-CH=C(R T15 )(R T16 A benzidine derivative having ) is preferred from the viewpoint of charge mobility.

[0112] As polymer charge transport materials, known charge transport materials such as poly-N-vinylcarbazole and polysilane can be used. Polyester-based polymer charge transport materials are particularly preferred. The polymer charge transport material may be used alone, or it may be used in combination with a binder resin.

[0113] Examples of binder resins used in the charge transport layer include polycarbonate resin, polyester resin, polyarylate resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicone alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin, poly-N-vinylcarbazole, and polysilane. Among these, polycarbonate resin or polyarylate resin is preferred as the binder resin. These binder resins can be used individually or in combination of two or more. The preferred mixing ratio of the charge transport material to the binder resin is between 10:1 and 1:5 by mass.

[0114] The charge transport layer may also contain other well-known additives.

[0115] The formation of the charge transport layer is not particularly limited, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of a charge transport layer forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0116] Suitable solvents for preparing the coating solution for forming the charge transport layer include common organic solvents such as aromatic hydrocarbons like benzene, toluene, xylene, and chlorobenzene; ketones like acetone and 2-butanone; halogenated aliphatic hydrocarbons like methylene chloride, chloroform, and ethylene chloride; and cyclic or linear ethers like tetrahydrofuran and ethyl ether. These solvents can be used individually or in mixtures of two or more.

[0117] Conventional methods for applying a charge transport layer forming coating solution onto a charge generation layer include blade coating, wire bar coating, spray coating, immersion coating, bead coating, air knife coating, and curtain coating.

[0118] The thickness of the charge transport layer is set, for example, preferably within the range of 5 μm to 50 μm, and more preferably within the range of 10 μm to 30 μm.

[0119] [Protective layer] A protective layer is provided on the charge transport layer as needed. The protective layer is provided, for example, to prevent chemical changes in the photosensitive layer when charged, or to further improve the mechanical strength of the photosensitive layer. Conventionally, a technique for forming an inorganic protective layer on a charge transport layer is known. While the charge transport layer is flexible and easily deformed, the inorganic protective layer is hard but tends to have poor toughness. Therefore, cracks may occur in the inorganic protective layer.

[0120] For example, in the development process, if carrier material is scattered from the developing means and adheres to the electrophotographic photoreceptor, the carrier material will remain attached to the electrophotographic photoreceptor until it reaches the transfer position. At the transfer position, the carrier material is sandwiched between the electrophotographic photoreceptor and the transfer means and subjected to pressing force. As a result, the inorganic protective layer may crack due to friction between the electrophotographic photoreceptor and the transfer means, for example.

[0121] To improve the mechanical strength of the inorganic protective layer, one might consider increasing its thickness. However, increasing the thickness of the inorganic protective layer can lead to an increase in residual potential because it makes it easier for charge to accumulate in the inorganic protective layer.

[0122] In this embodiment, the electrophotographic photoreceptor includes metal oxide particles in its charge transport layer. The metal oxide particles are thought to function as reinforcing materials for the charge transport layer through a filler effect. Therefore, the charge transport layer becomes less prone to deformation, and cracking of the inorganic protective layer is suppressed. In addition, as described above, in the electrophotographic photoreceptor according to this embodiment, metal oxide particles are less likely to aggregate in the charge transport layer and are dispersed in a small particle size and nearly uniform state. As a result, it is possible to suppress light scattering in the charge transport layer and prevent a decrease in light transmittance.

[0123] (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.

[0124] The inorganic protective layer is preferably a layer containing a metal oxide, more preferably a layer containing a group 13 element and an oxygen element, and even more preferably a layer containing gallium oxide or aluminum oxide, from the viewpoint of the photoreceptor's abrasion resistance and electrical properties. The inorganic protective layer may contain one or more metal oxides.

[0125] The volume resistivity of the inorganic protective layer is 1.0 × 10⁻⁶ from the viewpoint of maintaining the electrostatic latent image. 10 It is preferable that the density be Ω·cm or greater, and 1.0 × 10 11 A value of Ω·cm or greater is more preferable.

[0126] The method for measuring the volume resistivity of the inorganic protective layer is as follows: The inorganic protective layer is peeled off from the photoreceptor to prepare the sample. The sample is placed in the sample holder of an impedance analyzer (Toyo Technica), and the resistance value is measured at an AC voltage of 1V and a frequency of 100Hz. The resistance is then calculated based on the electrode area and the thickness of the sample.

[0127] Known vapor deposition methods such as plasma CVD (Chemical Vapor Deposition), organometallic vapor deposition, molecular beam epitaxy, evaporation, and sputtering can be used to form the inorganic protective layer. For example, the plasma CVD deposition apparatus and deposition conditions described in Japanese Patent Application Publication No. 2014-191179 can be used to form the inorganic protective layer.

[0128] 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, from the viewpoint of the abrasion resistance and electrical properties of the photoreceptor.

[0129] The film thickness of each layer of the photosensitive material is the arithmetic mean of the measurements taken with an electromagnetic film thickness gauge. The measurements were taken at four points in the circumferential direction at 90° intervals, centered in the axial direction of the photosensitive material.

[0130] [Image forming apparatus (and process cartridge)] The image forming apparatus according to this embodiment comprises an electrophotographic photoreceptor, a charging device for charging the surface of the electrophotographic photoreceptor, an electrostatic latent image forming device for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor, a developing device for developing the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image, and a transfer device for transferring the toner image to the surface of a recording medium. The electrophotographic photoreceptor according to this embodiment is used as the electrophotographic photoreceptor.

[0131] The image forming apparatus according to this embodiment includes a fixing device for fixing a toner image transferred to the surface of a recording medium; a direct transfer method apparatus for directly transferring a toner image formed on the surface of an electrophotographic photoreceptor to a recording medium; an intermediate transfer method apparatus for first transferring a toner image formed on the surface of an electrophotographic photoreceptor to the surface of an intermediate transfer body, and secondarily transferring the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium; a cleaning device for cleaning the surface of the electrophotographic photoreceptor after the transfer of the toner image and before it is charged; a static elimination device for irradiating the surface of the electrophotographic photoreceptor with static elimination light to eliminate static charge after the transfer of the toner image and before it is charged; and a well-known image forming apparatus such as an electrophotographic photoreceptor heating member for raising the temperature of the electrophotographic photoreceptor and reducing the relative temperature.

[0132] In the case of an intermediate transfer method apparatus, the transfer apparatus may be configured to include, for example, an intermediate transfer body on which a toner image is transferred; a primary transfer apparatus that first transfers the toner image formed on the surface of an electrophotographic photoreceptor to the surface of the intermediate transfer body; and a secondary transfer apparatus that secondarily transfers the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium.

[0133] The image forming apparatus according to this embodiment may be either a dry developing type image forming apparatus or a wet developing type image forming apparatus (a developing method using a liquid developer).

[0134] In the image forming apparatus according to this embodiment, for example, the part equipped with an electrophotographic photoreceptor may be a cartridge structure (process cartridge) that can be attached to and detached from the image forming apparatus. As the process cartridge, for example, a process cartridge equipped with an electrophotographic photoreceptor according to this embodiment is preferably used. In addition to the electrophotographic photoreceptor, the process cartridge may also include at least one selected from the group consisting of, for example, a charging device, an electrostatic latent image forming device, a developing device, and a transfer device.

[0135] The following is an example of an image forming apparatus according to this embodiment, but it is not limited to this example. The main parts shown in the figure will be described, and other parts will be omitted from the explanation.

[0136] Figure 2 is a schematic diagram showing an example of an image forming apparatus according to this embodiment. As shown in Figure 2, the image forming apparatus 100 according to this embodiment includes a process cartridge 300 equipped with an electrophotographic photoreceptor 7, an exposure device 9 (an example of an electrostatic latent image forming apparatus), a transfer device 40 (a primary transfer device), and an intermediate transfer body 50. In the image forming apparatus 100, the exposure device 9 is positioned to expose the electrophotographic photoreceptor 7 from the opening of the process cartridge 300, and the transfer device 40 is positioned facing the electrophotographic photoreceptor 7 via the intermediate transfer body 50, with a portion of the intermediate transfer body 50 in contact with the electrophotographic photoreceptor 7. Although not shown, the apparatus also includes a secondary transfer device that transfers the toner image transferred to the intermediate transfer body 50 to a recording medium (e.g., paper). The intermediate transfer body 50, the transfer device 40 (primary transfer device), and the secondary transfer device (not shown) are examples of transfer devices.

[0137] In Figure 2, the process cartridge 300 integrally supports an electrophotographic photoreceptor 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 positioned to contact the surface of the electrophotographic photoreceptor 7. The cleaning member may be a conductive or insulating fibrous member, rather than a cleaning blade 131, and may be used alone or in combination with the cleaning blade 131.

[0138] Figure 2 shows an example of an image forming apparatus equipped with a fibrous member 132 (roll-shaped) for supplying lubricant 14 to the surface of the electrophotographic photoreceptor 7, and a fibrous member 133 (flat brush-shaped) for assisting cleaning. These can be arranged as needed.

[0139] The following describes the various components of the image forming apparatus according to this embodiment.

[0140] -Charging device- As the charging device 8, for example, a contact-type charger using conductive or semiconductive charging rollers, charging brushes, charging films, charging rubber blades, charging tubes, etc. may be used. Non-contact roller chargers, known chargers such as scorotron chargers and corotron chargers that utilize corona discharge may also be used.

[0141] -Exposure equipment- Examples of exposure devices 9 include optical equipment that exposes the surface of an electrophotographic photoreceptor 7 to a predetermined image using light such as semiconductor laser light, LED light, or liquid crystal shutter light. The wavelength of the light source is within the spectral sensitivity range of the electrophotographic photoreceptor. As for the wavelength of the semiconductor laser, near-infrared lasers with an oscillation wavelength of around 780 nm are the mainstream. However, the wavelength is not limited to this, and lasers with oscillation wavelengths in the 600 nm range or blue lasers with oscillation wavelengths between 400 nm and 450 nm may also be used. Furthermore, for color image formation, surface-emitting laser light sources capable of outputting multiple beams are also effective.

[0142] -Developing equipment- Examples of developing devices 11 include general developing devices that develop by contacting or not contacting the developing agent. There are no particular restrictions on the developing device 11 as long as it has the above-described functions, and it can be selected according to the purpose. For example, known developing devices that have the function of applying a one-component or two-component developing agent to the electrophotographic photoreceptor 7 using a brush, roller, etc. Among these, those that use a developing roller that holds the developing agent on its surface are preferred.

[0143] The developer used in the developing device 11 may be a one-component developer consisting of toner alone, or a two-component developer containing toner and a carrier. Furthermore, the developer may be magnetic or non-magnetic. Well-known developers are applicable.

[0144] -Cleaning device- The cleaning device 13 is a cleaning blade type device equipped with a cleaning blade 131. In addition to the cleaning blade method, a fur brush cleaning method or a developing-simultaneous cleaning method may also be used.

[0145] -Transfer device- Examples of the transfer device 40 include contact-type transfer chargers using belts, rollers, films, rubber blades, etc., and transfer chargers that are known themselves, such as scorotron transfer chargers and corotron transfer chargers that utilize corona discharge.

[0146] -Intermediate Transcript- As the intermediate transfer body 50, a belt-shaped material (intermediate transfer belt) containing semiconducting polyimide, polyamide-imide, polycarbonate, polyarylate, polyester, rubber, etc. is used. In addition to the belt shape, the intermediate transfer body may also be in the form of a drum.

[0147] Figure 3 is a schematic diagram showing another example of the image forming apparatus according to this embodiment. The image forming apparatus 120 shown in Figure 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 body 50, and one electrophotographic photoreceptor is used for each color. The image forming apparatus 120 has the same configuration as the image forming apparatus 100, except that it is a tandem type. [Examples]

[0148] The embodiments of the invention will be described in detail below with reference to examples, but the embodiments of the invention are not limited to these examples. In the following explanation, unless otherwise specified, "parts" and "%" refer to mass. In the following descriptions, unless otherwise specified, synthesis, manufacturing, processing, and measurement were performed at room temperature (25°C ± 3°C).

[0149] <Example 1> [Formation of the lower layer] As a conductive substrate, an aluminum cylindrical tube with an outer diameter of 30 mm, a length of 250 mm, and a wall thickness of 1 mm was prepared.

[0150] Zinc oxide (average particle size 70 nm, specific surface area 15 m²) 2100 parts of (Teika Co., Ltd.) were mixed with 500 parts of toluene and stirred. 1.3 parts of a silane coupling agent (product name: KBM603, Shin-Etsu Chemical Co., Ltd., N-2-(aminoethyl)-3-aminopropyltrimethoxysilane) were added and the mixture was stirred for 2 hours. Then, the toluene was removed by distillation 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.

[0151] 110 parts of 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. The mixture was stirred at 50°C for 5 hours. The solids were then filtered off by vacuum filtration, and the mixture was dried under reduced pressure at 60°C to obtain alizarin-treated zinc oxide.

[0152] 60 parts of alizarin-modified zinc oxide, 13.5 parts of a curing agent (blocked isocyanate, trade name: Sumijule 3175, Sumitomo Bayer Urethane Co., Ltd.), and 15 parts of butyral resin (trade name: Esrec BM-1, Sekisui Chemical Co., Ltd.) were dissolved in 68 parts of methyl ethyl ketone. 100 parts of this solution were mixed with 5 parts of methyl ethyl ketone, and the mixture was dispersed for 2 hours using a sand mill with 1 mm diameter glass beads to obtain a dispersion. To the dispersion, 0.005 parts of dioctyl tin dilaurate and 4 parts of silicone resin particles (trade name: Tospar 145, Momentive Performance Materials, Inc.) were added as catalysts to obtain a coating solution for forming an undercoat. The undercoat solution was applied to the outer surface of a conductive substrate by immersion coating, and dried and cured at 170°C for 40 minutes to form an undercoat with a thickness of 20 μm.

[0153] [Formation of charge generation layer] A mixture consisting of 15 parts of hydroxygallium phthalocyanine (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 its X-ray diffraction spectrum using CuKα characteristic X-rays), 10 parts of vinyl chloride / vinyl acetate copolymer resin (product name: VMCH, manufactured by Nippon Unicar Co., Ltd.) as a binder resin, and 200 parts of n-butyl acetate was dispersed for 4 hours using glass beads with a diameter of 1 mm in a sand mill. 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 the charge generation layer. The coating solution for forming the charge generation layer was immersed and coated onto the undercoat, and dried at room temperature to form a charge generation layer with a thickness of 0.25 μm.

[0154] [Formation of charge transport layer] • Binding resin: Polycarbonate resin (1) (viscosity-average molecular weight 40,000, the values ​​in the structural formula indicate the molar ratio) ... 20 parts ·Charge transport material: CTM-1...15 parts • Metal oxide particles: Silica particles hydrophobized with 1,1,1,3,3,3-hexamethyldisilazane (average particle size 150 nm, average circularity 0.85, degree of hydrophobicity 65%)... Amount equal to the volume (%) shown in Table 1 • Solvent: Tetrahydrofuran (THF) ... 600 copies The above materials were stirred and mixed for 12 hours to obtain a coating solution for forming a charge transport layer. The coating solution for forming a charge transport layer was applied to the charge generating layer by immersion under room temperature conditions of 28°C. Then, hot air was blown onto the coating film to dry it, forming a charge transport layer with a thickness of 30 μm. [ka]

[0155] A photoreceptor was obtained through the above process.

[0156] <Example 2> A photoreceptor was obtained in the same manner as in Example 1, except that the charge transport layer was formed by immersion coating under room temperature conditions of 30°C.

[0157] <Example 3> A photoreceptor was obtained in the same manner as in Example 1, except that the charge transport layer was formed by immersion coating under room temperature conditions of 32°C.

[0158] <Example 4> A photoreceptor was obtained in the same manner as in Example 1, except that the amount of silica particles added in the charge transport layer was changed as shown in Table 1, and the stirring and mixing time of the materials was set to 6 hours. <Example 5> A photoreceptor was obtained in the same manner as in Example 1, except that the amount of silica particles added in the charge transport layer was changed as shown in Table 1, and the stirring and mixing time of the materials was set to 8 hours. <Example 6> A photoreceptor was obtained in the same manner as in Example 1, except that the amount of silica particles added in the charge transport layer was changed as shown in Table 1, and the stirring and mixing time of the materials was set to 14 hours. <Example 7> A photoreceptor was obtained in the same manner as in Example 1, except that the amount of silica particles added in the charge transport layer was changed as shown in Table 1, and the stirring and mixing time of the materials was set to 16 hours. <Example 8> A photoreceptor was obtained in the same manner as in Example 1, except that the silica particles in the charge transport layer were replaced with zinc oxide particles having an average circularity of 0.6 and a hydrophobicity of 65%. <Example 9> A photoreceptor was obtained in the same manner as in Example 1, except that the average circularity of the silica particles was 0.6 in the formation of the charge transport layer. <Example 10> A photoreceptor was obtained in the same manner as in Example 1, except that the average circularity of the silica particles was 0.7 in the formation of the charge transport layer. <Example 11> A photoreceptor was obtained in the same manner as in Example 1, except that the average circularity of the silica particles was 0.8 in the formation of the charge transport layer. <Example 12> A photoreceptor was obtained in the same manner as in Example 1, except that the degree of hydrophobicity of the silica particles was 55% in the formation of the charge transport layer. <Example 13> A photoreceptor was obtained in the same manner as in Example 1, except that 200 parts of the 600 parts of THF in the solvent were replaced with 200 parts of toluene in the formation of the charge transport layer. <Example 14> A photoreceptor was obtained in the same manner as in Example 1, except that 100 parts of the 600 parts of THF in the solvent were replaced with 100 parts of toluene in the formation of the charge transport layer.

[0159] <Example 15> A photoreceptor was obtained in the same manner as in Example 1, except that an inorganic protective layer was formed on the charge transport layer as described below. -Formation of an inorganic protective layer- Trimethylgallium was used as the film deposition material, and an amorphous layer containing gallium oxide was formed as an inorganic protective layer by plasma CVD. The layer thickness was 3 μm.

[0160] <Comparative Example 1> In Example 1, the room temperature during immersion coating was changed to 22°C to prepare each photoreceptor.

[0161] <Various Measurements> The following items were measured using the method described above. • Percentage of individual metal oxide particles (number of particles) contained within the charge transport layer: Indicated as "A1 / (A1+A2)" in Table 1. • Percentage of total area of ​​individual and aggregated metal oxide particles contained within the charge transport layer (%) • Average circularity and hydrophobicity of metal oxide particles

[0162] <Evaluation of photoreceptor performance> [hardness] The hardness of the charge transport layer in each example was evaluated as follows. The hardness of the outer surface of the photoreceptor is determined by the Young's modulus (MPa) obtained by nanoindentation. The hardness was measured at the vertex of the photoreceptor's axial center, with the axial direction of the photoreceptor fixed horizontally. The Young's modulus was measured at four positions at 90° intervals around the circumference of the photoreceptor, and the arithmetic mean of the Young's modulus at the four positions was calculated. The measurement conditions using the nanoindenter are as follows: The measurement results are shown in Table 1. • Test equipment: Product name HM-500, Fischer Instruments Co., Ltd. • Indenter: Diamond triangular indenter with a 115° edge angle • Load: 75mN

[0163] [Abrasion resistance] The abrasion resistance of the photoreceptor in each example was evaluated as follows. Each photoreceptor was mounted in an electrophotographic image forming apparatus (ApeosC4570, manufactured by Fujifilm Business Innovation Co., Ltd.), and 100,000 images with 1% solid image and 1% image density (area coverage) were formed on A3-sized paper under conditions of 30°C and 85% relative humidity. Subsequently, 100,000 solid images with 100% solid image and 100% image density (area coverage) were formed on A3-sized paper under conditions of 10°C and 15% relative humidity. The above image formation process (i.e., 100,000 images formed under conditions of 30°C and 85% relative humidity, and 100,000 images formed under conditions of 10°C and 15% relative humidity, for a total of 200,000 images) was repeated five times. The average thickness of the charge transport layer was determined before and after the above image formation process (i.e., a total of 1,000,000 images), and the difference in average thickness before and after image formation was defined as the amount of wear (nm). A Permascope manufactured by Fischerscope was used as the film thickness measuring instrument. The wear levels were classified as follows. The results are shown in Table 1. G1: Wear amount less than 500 nm G2: Wear amount is 500nm or more, but less than 1000nm. G3: Wear amount between 1000nm and 1500nm G4: Wear amount between 1500nm and 2000nm

[0164] [Electrical characteristics] The electrical characteristics of the charge transport layer in each example were evaluated as follows. Under conditions of 22°C and 55% relative humidity, the photoreceptor was rotated at a rotation speed of 40 rpm, and while scanning the surface of the photoreceptor, it was negatively charged to -700V using a scorotron charger and irradiated with exposure light (light source: semiconductor laser, wavelength 780 nm, output 5 mW), and the residual potential of the photoreceptor surface was measured. For potential measurement, a surface potential probe of a surface potential meter (Trek 334, manufactured by Trek) was used, which was positioned at the axial center of the photoreceptor and 1 mm away from the surface of the photoreceptor. The measured residual potentials were classified into four categories (G1 to G4) below, and the effectiveness of suppressing the rise in residual potential was evaluated. A value of less than 40V was considered acceptable. The evaluation results are shown in Table 1. G1: Less than 15V G2: 15V or higher, less than 30V G3: 30V or higher, less than 40V G4: 40V or more

[0165] [Crack resistance of the inorganic protective layer] The cracking load of the inorganic protective layer was measured as follows, and its crack resistance was evaluated. Hardness tests using a microhardness tester were repeated, increasing the load from 0 mN in increments of 5 mN. Observations were made using an optical microscope after each load application, and the load at which fracture occurred in the inorganic protective layer was defined as the fracture initiation load. The measurement conditions were as follows: • Test equipment: Product name DUH-201, Shimadzu Corporation • Indenter: Diamond-made spherical indenter [Table 1]

[0166] From the above results, it can be seen that the photoreceptor of the example has higher wear resistance and electrical properties compared to the photoreceptor of the comparative example.

[0167] This embodiment includes the following aspects. (((1))) The device comprises a conductive substrate, a charge generation layer placed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles. An electrophotographic photoreceptor in which, when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual metal oxide particles and aggregated metal oxide particles is 60% or more. (((2))) The electrophotographic photoreceptor according to (((1))), wherein the proportion of individual metal oxide particles is 70% or more. (((3))) The electrophotographic photoreceptor according to (((1))) or (((2))), wherein, when the cross-section of the charge transport layer is observed, the ratio of the total area of ​​individual metal oxide particles and aggregated metal oxide particles to the total area of ​​the observed cross-section is 60 area% or more and 95 area% or less. (((4))) The electrophotographic photoreceptor according to any one of (((1))) to (((3))), wherein the metal oxide particles are silica particles. (((5))) The electrophotographic photoreceptor according to any one of the items (((1))) to (((4))), wherein the metal oxide particles have an average circularity of 0.7 or more and a degree of hydrophobicity of 60% or more. (((6))) The electrophotographic photoreceptor according to (((5))), wherein the metal oxide particles have an average circularity of 0.8 or more and a degree of hydrophobicity of 60% or more. (((7))) The electrophotographic photoreceptor according to any one of (((1))) to (((6))), wherein the light transmittance T of the charge transport layer is 80% or more. (((8))) The electrophotographic photoreceptor according to any one of (((1))) to (((7))), further comprising an inorganic protective layer disposed on the charge transport layer. (((9))) A process cartridge for attaching to and detaching from an image forming apparatus, comprising an electrophotographic photoreceptor as described in any one of items (((1))) to (((8))). (((10))) An image forming apparatus comprising: an electrophotographic photoreceptor as described in any one of (((1))) to (((8))); a charging device for charging the surface of the electrophotographic photoreceptor; an electrostatic latent image forming device for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor; a developing device for developing the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image; and a transfer device for transferring the toner image to the surface of a recording medium.

[0168] The effects of the above embodiment are as follows: According to the invention of (((1))), an electrophotographic photoreceptor is provided which has a conductive substrate, a charge generation layer installed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles, and when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual metal oxide particles and aggregated metal oxide particles is less than 60 percent, compared to the case in which both abrasion resistance and electrical properties are superior. According to the invention of (((2))), an electrophotographic photoreceptor is provided that has superior wear resistance and electrical properties compared to the case in which the proportion of individual metal oxide particles is less than 70 percent. According to the invention of (((3))), when the cross-section of the charge transport layer is observed, an electrophotographic photoreceptor is provided that has superior abrasion resistance and electrical properties compared to cases where the ratio of the total area of ​​individual metal oxide particles and aggregated metal oxide particles to the total area of ​​the observed cross-section is less than 60 area% or more than 95 area%. According to the invention of (((4))), an electrophotographic photoreceptor is provided that has superior wear resistance and electrical properties compared to the case where the metal oxide particles are not silica particles. According to the invention of (((5))) or (((6))), an electrophotographic photoreceptor is provided that has superior wear resistance and electrical properties compared to cases where the average circularity of the metal oxide particles is less than 0.7 or the degree of hydrophobicity is less than 60%, or where the average circularity of the metal oxide particles is less than 0.8 or the degree of hydrophobicity is less than 60%. According to the invention of (((7))), an electrophotographic photoreceptor is provided that has superior abrasion resistance and electrical properties compared to the case where the light transmittance T of the charge transport layer is less than 80%. According to the invention of (((8))), an electrophotographic photoreceptor is provided which has a conductive substrate, a charge generation layer installed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material, and metal oxide particles, and when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual metal oxide particles and aggregated metal oxide particles is less than 60 percent, compared to the case in which both crack suppression of the inorganic protective layer and electrical properties are superior. According to the invention of (((9))) or (((10))), a process cartridge or image forming apparatus is provided that has an electrophotographic photoreceptor that is superior in both wear resistance and electrical properties compared to an electrophotographic photoreceptor that has a conductive substrate, a charge generation layer installed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and containing a binder resin, a charge transport material and metal oxide particles, wherein when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual and aggregated metal oxide particles is less than 60 percent. [Explanation of Symbols]

[0169] 1 conductive substrate, 2 subbing layer, 3 charge generation layer, 4 charge transport layer, 5 photosensitive layer, 6 inorganic protective layer, 10A photoreceptor

[0170] 7 Electrophotographic photoreceptor, 8 Charging device, 9 Exposure device, 11 Developing device, 13 Cleaning device, 14 Lubricant, 40 Transfer device, 50 Intermediate transfer body, 100 Image forming device, 120 Image forming device, 131 Cleaning blade, 132 Fibrous material (roll type), 133 Fibrous material (flat brush type), 300 Process cartridge

Claims

1. A conductive substrate, A charge generation layer is placed on the conductive substrate, A charge transport layer is disposed on the charge generation layer and includes a binder resin, a charge transport material, and metal oxide particles. It has, An electrophotographic photoreceptor in which, when the charge transport layer is observed in cross-section, the ratio of individual metal oxide particles to the total of individual metal oxide particles and aggregated metal oxide particles is 60 percent or more.

2. The electrophotographic photoreceptor according to claim 1, wherein the proportion of individual metal oxide particles is 70% or more.

3. The electrophotographic photoreceptor according to claim 1, wherein when the cross-section of the charge transport layer is observed, the ratio of the total area of ​​individual metal oxide particles and aggregated metal oxide particles to the total area of ​​the observed cross-section is 60% or more and 95% or less.

4. The electrophotographic photoreceptor according to claim 1, wherein the metal oxide particles are silica particles.

5. The electrophotographic photoreceptor according to claim 1, wherein the metal oxide particles have an average circularity of 0.7 or more and a degree of hydrophobicity of 60% or more.

6. The electrophotographic photoreceptor according to claim 5, wherein the metal oxide particles have an average circularity of 0.8 or more and a degree of hydrophobicity of 60% or more.

7. The electrophotographic photoreceptor according to claim 1, wherein the light transmittance T of the charge transport layer is 80% or more.

8. The electrophotographic photoreceptor according to claim 1, further comprising an inorganic protective layer disposed on the charge transport layer.

9. The electrophotographic photoreceptor is provided according to any one of claims 1 to 8, A process cartridge that is attached to and detached from an image forming apparatus.

10. An electrophotographic photoreceptor according to any one of claims 1 to 8, A charging device for charging the surface of the electrophotographic photoreceptor, An electrostatic latent image forming apparatus for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing apparatus that develops an electrostatic latent image formed on the surface of an electrophotographic photoreceptor using a developer containing toner to form a toner image, An image forming apparatus comprising a transfer device for transferring the toner image onto the surface of a recording medium.

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