Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

The invention provides an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus. The electrophotographic photoreceptor includes: 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, the charge transport layer having a specific surface area, when a cross-section of the charge transport layer is observed, the specific surface area is smaller than the specific surface area. The proportion of the individual particles of the metal oxide particles to the total of the individual particles of the metal oxide particles and the aggregated particles is 60% by number or more.

Description

Technical Field

[0001] This invention relates to an electrophotographic photosensitive element, a processing cartridge, and an image forming apparatus. Background Technology

[0002] Patent Document 1 discloses "an electrophotographic photosensitive layer characterized by comprising at least a stacked photosensitive layer having a charge-generating layer containing a charge-generating substance and a charge-transporting layer containing a charge-transporting substance sequentially stacked on a conductive support, or at least the stacked photosensitive layer and a surface protective layer stacked thereon, wherein either or both of the charge-transporting layer and the surface protective layer contain a light absorber, the outermost layer of the electrophotographic photosensitive layer contains a silica filler, has a transmittance of 50% or more relative to light with a wavelength of 600 nm, and the ratio of the transmittance T600 relative to light with a wavelength of 600 nm to the transmittance T550 relative to light with a wavelength of 550 nm, T600 / T550, is 1.10 or more and 2.20 or less."

[0003] Patent document 2 discloses "an electrophotographic photosensitive material, characterized in that it comprises a conductive support and a photosensitive layer formed on the conductive support, the photosensitive layer being composed of one or more layers, the surface layer of the photosensitive layer containing a binding resin, silica particles and a charge transport substance, the ten-point average roughness Rz of the surface layer being 0.08 μm or more and 0.80 μm or less, the average spacing Sm of the unevenness of the surface layer being more than 15 μm and less than 120 μm, and the ratio of the average spacing Sm to the ten-point average roughness Rz, Sm / Rz, being 30 or more and 500 or less."

[0004] Patent Document 1: Japanese Patent Application Publication No. 2023-054576

[0005] Patent Document 2: Japanese Patent Application Publication No. 2023-069379 Summary of the Invention

[0006] The objective of this invention is to provide an electrophotographic photosensitive material with excellent wear resistance and electrical properties, compared to an electrophotographic photosensitive material having a conductive substrate, a charge generating layer disposed on the conductive substrate, and a charge transport layer disposed on the charge generating layer and comprising a binder resin, a charge transport material, and metal oxide particles, wherein when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual and aggregated metal oxide particles is less than 60%.

[0007] The means to solve the above problems include the following methods.

[0008] <1>

[0009] An electrophotographic photosensitive material comprises: a conductive substrate; a charge generating layer disposed on the conductive substrate; and a charge transport layer disposed on the charge generating layer, comprising a binding resin, a charge transport material, and metal oxide particles.

[0010] When the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual and aggregated metal oxide particles is 60% or more.

[0011] <2>

[0012] According to the electrophotographic photosensitive material described in <1>, wherein...

[0013] The proportion of individual metal oxide particles is more than 70%.

[0014] <3>

[0015] According to the electrophotographic photosensitive material described in <1> or <2>, wherein,

[0016] When the cross-section of the charge transport layer is observed, the total area of ​​the individual particles and aggregated particles of the metal oxide particles is more than 60% and less than 95% of the area of ​​the observed cross-section.

[0017] <4>

[0018] According to any one of <1> to <3>, the electrophotographic photosensitive material, wherein,

[0019] The metal oxide particles are silicon dioxide particles.

[0020] <5>

[0021] According to any one of <1> to <4>, the electrophotographic photosensitive material, wherein,

[0022] The metal oxide particles have an average roundness of 0.7 or higher and a hydrophobicity of 60% or higher.

[0023] <6>

[0024] According to the electrophotographic photosensitive material described in <5>, wherein...

[0025] The metal oxide particles have an average roundness of 0.8 or higher and a hydrophobicity of 60% or higher.

[0026] <7>

[0027] According to any one of <1> to <6>, the electrophotographic photosensitive material, wherein,

[0028] The transmittance T of the charge transport layer is above 80%.

[0029] <8>

[0030] The electrophotographic photosensitive material according to any one of <1> to <7> further comprises an inorganic protective layer disposed on the charge transport layer.

[0031] <9>

[0032] A processing cartridge comprising any one of <1> to <8> of an electrophotographic photosensitive element, the processing cartridge being detachable from an image forming apparatus.

[0033] <10>

[0034] 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 apparatus for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor; a developing apparatus for developing the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developing agent containing a toner to form a toner image; and a transfer apparatus for transferring the toner image onto the surface of a recording medium.

[0035] Invention Effects

[0036] According to the invention described in <1>, compared to having a conductive substrate, a charge generating layer disposed on the conductive substrate, and a charge transport layer disposed on the charge generating layer and comprising a binding resin, a charge transport material, and metal oxide particles, when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual and aggregated metal oxide particles is less than 60%, providing an electrophotographic photosensitive material with excellent wear resistance and electrical properties.

[0037] According to the invention described in <2>, an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to cases where the proportion of individual metal oxide particles is less than 70%.

[0038] According to the invention described in <3>, compared to cases where the total area of ​​individual particles and aggregated particles of metal oxide particles is less than 60% or more than 95% of the total area of ​​the observed cross section when observing the cross section of the charge transport layer, an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided.

[0039] According to the invention described in <4>, an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to the case where the metal oxide particles are not silicon dioxide particles.

[0040] According to the invention described in <5> or <6>, an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to cases where the average roundness of the metal oxide particles is less than 0.7 or the degree of hydrophobicity is less than 60%, or the average roundness of the metal oxide particles is less than 0.8 or the degree of hydrophobicity is less than 60%.

[0041] According to the invention described in <7>, an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to the case where the transmittance T of the charge transport layer is less than 80%.

[0042] According to the invention described in <8>, compared to a conductive substrate, a charge generating layer disposed on the conductive substrate, and a charge transport layer disposed on the charge generating layer and comprising a binding resin, a charge transport material, and metal oxide particles, when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual and aggregated metal oxide particles is less than 60%, providing an electrophotographic photosensitive material with excellent crack suppression of the inorganic protective layer and excellent electrical properties.

[0043] According to the invention described in <9> or <10>, compared to an electrophotographic photoreceptor that uses a conductive substrate, a charge generation layer disposed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and comprising a binding resin, a charge transport material, and metal oxide particles, when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual and aggregated metal oxide particles is less than 60%, a processing cartridge or image forming apparatus for an electrophotographic photoreceptor with excellent wear resistance and electrical properties is provided. Attached Figure Description

[0044] The embodiments of the present invention will be described in detail with reference to the following figures.

[0045] Figure 1 This is a partial cross-sectional view showing an example of the layer structure of the electrophotographic photoreceptor according to this embodiment;

[0046] Figure 2 This is a schematic structural diagram illustrating an example of the image forming apparatus according to this embodiment;

[0047] Figure 3 This is a schematic structural diagram showing another example of the image forming apparatus according to this embodiment.

[0048] Symbol Explanation

[0049] 1-Conductive substrate, 2-Undercoat layer, 3-Charge generating layer, 4-Charge transport layer, 5-Photosensitive layer, 6-Inorganic protective layer, 10A-Photoreceptor. 7-Electrophotographic photoreceptor, 8-Charging device, 9-Exposure device, 11-Developing device, 13-Cleaning device, 14-Lubricant, 40-Transfer device, 50-Intermediate transfer material, 100-Image forming device, 120-Image forming device, 131-Cleaning blade, 132-Fiber component (roller), 133-Fiber component (flat brush), 300-Processing box. Detailed Implementation

[0050] The following describes an embodiment as an example of the present invention. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the present invention.

[0051] In this specification, the numerical range represented by “~” indicates the range to be included by taking the values ​​before and after “~” as the minimum and maximum values, respectively.

[0052] In the numerical ranges described in this specification, the upper or lower limit of a numerical range can be replaced with the upper or lower limit of other numerical ranges described in different periods. Furthermore, within the numerical ranges described in this specification, the upper or lower limit of that range can be replaced with the values ​​shown in the embodiments.

[0053] In this specification, the term "process" includes not only individual processes, but also processes that achieve their purpose, even if they cannot be clearly distinguished from other processes.

[0054] In this specification, when embodiments are described with reference to the accompanying drawings, the structure of the embodiments is not limited to the structure shown in the drawings. Furthermore, the sizes of the components in the figures are conceptual, and the relative sizes of the components are not limited thereto.

[0055] In this specification, each component may contain multiple corresponding substances. When referring to the amount of each component in a composition, unless otherwise specified, the amount refers to the total amount of those multiple substances present in the composition, where multiple substances corresponding to each component are present in the composition.

[0056] This specification may include multiple particles corresponding to each component. When multiple particles corresponding to each component are present in the composition, unless otherwise specified, the particle size of each component represents a value with respect to the mixture of the multiple particles present in the composition.

[0057] In this specification, the “axial direction” of an electrophotographic photosensitive element refers to the direction in which the rotation axis of the electrophotographic photosensitive element extends, and the “circumferential direction” of the electrophotographic photosensitive element refers to the rotation direction of the electrophotographic photosensitive element.

[0058] <Electronic Photoreceptor>

[0059] The electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") according to this embodiment has a conductive substrate, a charge generation layer and a charge transport layer.

[0060] The charge generation layer is disposed on a conductive substrate.

[0061] The charge transport layer comprises a binding resin, a charge transport material, and metal oxide particles.

[0062] Furthermore, when the cross-section of the charge transport layer is observed, the ratio of individual metal oxide particles to the total number of individual and aggregated metal oxide particles is more than 60%.

[0063] The photoreceptor described in this embodiment possesses excellent wear resistance and electrical properties due to the aforementioned structure. The reasoning is as follows.

[0064] Metal oxide particles tend to aggregate within the charge transport layer, leading to large particle size and poor dispersion. This results in reduced light transmittance due to light scattering and uneven surface hardness in the charge transport layer. Consequently, the photoreceptor's abrasion resistance and electrical properties are reduced.

[0065] Therefore, as described above, the photoreceptor according to this embodiment has a proportion of 60% of individual metal oxide particles. That is, the metal oxide particles are dispersed in the charge transport layer in a state that is not prone to aggregation, has a small particle size, and is nearly uniform. As a result, light scattering within the charge transport layer is suppressed, and the decrease in light transmittance can be suppressed.

[0066] Furthermore, the metal oxide particles that exhibit a filling effect are dispersed on the surface of the charge transport layer in a small-particle-size and nearly uniform manner. This suppresses unevenness in the hardness of the charge transport layer surface.

[0067] Based on the above reasons, it is speculated that the photoreceptor involved in this embodiment has excellent wear resistance and electrical properties.

[0068] The following is a detailed description of the photoreceptor involved in this embodiment.

[0069] Figure 1 This is a partial cross-sectional view that schematically illustrates an example of the layer structure of the photoreceptor involved in this embodiment. Figure 1The photoreceptor 10A shown has a stacked photosensitive layer.

[0070] The photoreceptor 10A has a structure in which a lower coating layer 2, a charge generation layer 3, a charge transport layer 4 and an inorganic protective layer 6 are sequentially stacked on a conductive substrate 1. The charge generation layer 3 and the charge transport layer 4 constitute the photosensitive layer 5 (the so-called functionally separated photosensitive layer).

[0071] The photoreceptor 10A may have an intermediate layer (not shown) between the lower coating layer 2 and the charge generation layer 3. The lower coating layer 2 may or may not be present. The inorganic protective layer 6 may or may not be present.

[0072] The following is a detailed description of each layer of the photoreceptor. Symbols are omitted in the description of each layer of the photoreceptor.

[0073] [Conductive substrate]

[0074] Examples of conductive substrates include metal plates, metal drums, and metal strips containing metals (aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, platinum, etc.) or alloys (stainless steel, etc.). Furthermore, examples of conductive substrates include conductive compounds (e.g., conductive polymers, indium oxide, etc.); paper coated, vapor-deposited, or laminated with metals (e.g., aluminum, palladium, gold, etc.) or alloys; resin films; and tapes. Here, "conductivity" refers to a volume resistivity of less than 10 Ω·cm. 13 Ω·cm.

[0075] When an electrophotographic photosensitive material is used in a laser printer, to suppress interference fringes generated when the laser beam is irradiated, the surface of the conductive substrate is preferably roughened to, for example, 0.04 μm or more and 0.5 μm or less, based on the centerline average roughness Ra. Furthermore, when incoherent light is used as the light source, roughening to prevent interference fringes is not particularly necessary, but suppressing defects caused by unevenness on the conductive substrate surface is beneficial for extending its lifespan.

[0076] Examples of roughening methods include wet grinding, which involves suspending an abrasive in water and spraying it onto a conductive substrate; centerless grinding, which involves pressing a conductive substrate onto a rotating grinding wheel and continuously grinding it; and anodizing.

[0077] As a roughening method, another example is a method in which conductive or semi-conductive powder is dispersed in a resin to form a layer on the surface of the conductive substrate without roughening the surface of the conductive substrate, and roughening is achieved by the particles dispersed in the layer.

[0078] Anodizing-based roughening processes involve anolysing a conductive metallic substrate (e.g., aluminum) in an electrolyte solution, thereby forming an oxide film on the surface of the conductive substrate. Examples of electrolyte solutions include sulfuric acid and oxalic acid. However, the porous anodic oxide film formed by anodizing is chemically active in its original state, easily contaminated, and exhibits significant resistance variations due to environmental factors. Therefore, it is preferable, for example, to perform a sealing treatment on the porous anodic oxide film, blocking the micropores of the oxide film by volume expansion caused by water and reaction in pressurized steam or boiling water (with the addition of metal salts such as nickel), thereby transforming it into a more stable hydrated oxide.

[0079] The thickness of the anodic oxide film is preferably 0.3 μm or more and 15 μm or less. If the film thickness is within the above range, there is a tendency for it to act as a barrier against implantation, and there is a tendency for the rise in residual potential caused by repeated use to be suppressed.

[0080] Conductive substrates can be treated with acidic solutions or boehmite.

[0081] The treatment based on the acidic treatment solution is carried out, for example, as follows. First, an acidic treatment solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The proportions of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic treatment solution are, for example, phosphoric acid in the range of 10% by mass or more and 11% by mass or less, chromic acid in the range of 3% by mass or more and 5% by mass or less, and hydrofluoric acid in the range of 0.5% by mass or more and 2% by mass or less. The concentration of their total acid content is preferably in the range of 13.5% by mass or more and 18% by mass or less. The treatment temperature is preferably, for example, 42°C or more and 48°C or less. The film thickness is preferably, for example, 0.3 μm or more and 15 μm or less.

[0082] Boehmite treatment can be performed, for example, by immersion in pure water at a temperature above 90°C and below 100°C for 5 to 60 minutes, or by contact in heated steam at a temperature above 90°C and below 120°C for 5 to 60 minutes. The film thickness is preferably, for example, 0.1 μm or more and 5 μm or less. Further anodizing can be performed using electrolyte solutions with low film solubility, such as adipic acid, boric acid, borates, phosphates, phthalates, maleates, benzoates, tartrates, and citrates.

[0083] (Undercoat)

[0084] The undercoat layer may be, for example, a layer containing inorganic particles and a binding resin.

[0085] As inorganic particles, examples include powder resistance (volume resistivity) of 10. 2 Ω·cm or more and 10 11 Inorganic particles below Ω·cm.

[0086] Among them, inorganic particles having the above-mentioned resistance values ​​are preferably metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles, and zinc oxide particles are particularly preferred.

[0087] The specific surface area of ​​inorganic particles based on the BET method is preferably, for example, 10 m². 2 / g or more.

[0088] The volume average particle size of the inorganic particles is preferably 50 nm or more and 2000 nm or less (preferably 60 nm or more and 1000 nm or less).

[0089] The content of inorganic particles, relative to the bonding resin, is preferably 10% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 80% by mass or less.

[0090] Inorganic particles can be used for surface treatment. Two or more types of inorganic particles with different surface treatments or different particle sizes can be mixed together.

[0091] Examples of surface treatment agents include silane coupling agents, titanate coupling agents, aluminum coupling agents, and surfactants. In particular, silane coupling agents are preferred, and silane coupling agents having an amino group are more preferred.

[0092] Examples of amino-containing silane coupling agents include 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, but are not limited to these.

[0093] Two or more silane coupling agents can be used in combination. For example, an amino-containing silane coupling agent can be used in combination with other silane coupling agents. Other silane coupling agents include, but are not limited to, vinyltrimethoxysilane, 3-methacryloyloxypropyltris(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.

[0094] Surface treatment methods based on surface treatment agents can be any known method, including either dry or wet methods.

[0095] The amount of surface treatment agent relative to the inorganic particles is preferably 0.5% by mass or more and 10% by mass or less.

[0096] From the viewpoint of improving the long-term stability of electrical properties and the blocking effect of the carrier, the lower coating preferably contains an electron-accepting compound (acceptor compound) together with the inorganic particles.

[0097] Examples of electron-accepting compounds include compounds with anthraquinone structures; quinones such as chloroquinone and tetrabromo-p-benzoquinone; dimethyl tetracyano-p-benzodiquinone; fluorenones such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone; oxadiazoles such as 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; xanthones; thiophene compounds; biphenylquinones such as 3,3',5,5'-tetra-tert-butylbiphenylquinone; benzophenone compounds; and isoelectronic transport substances.

[0098] Especially as electron-accepting compounds, compounds having an anthraquinone structure are preferred, for example. Compounds having an anthraquinone structure are preferably hydroxyanthraquinone compounds, aminoanthraquinone compounds, aminohydroxyanthraquinone compounds, etc., and more specifically, anthraquinones, alizarins, quinone alizarins, anthraquinone oleuropein, rutin, and their derivatives are preferred.

[0099] Electron-accepting compounds can be dispersed in the undercoat along with inorganic particles, or they can be contained in the undercoat in a state of being attached to the surface of inorganic particles.

[0100] Methods for attaching electron-accepting compounds to the surface of inorganic particles include, for example, dry or wet methods.

[0101] Dry methods, for example, involve directly adding an electron-accepting compound or an electron-accepting compound dissolved in an organic solvent by stirring inorganic particles using a mixer with high shear force, and then spraying the compound with dry air or nitrogen to adhere it 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, sintering can be performed at a temperature above 100°C. There are no particular limitations on the temperature and time for sintering, as long as the electron photographic properties are obtained.

[0102] Wet processes, for example, involve dispersing inorganic particles in a solvent using a mixer, ultrasonic disperser, sand mill, grinder, or ball mill. An electron-accepting compound is added, and the mixture is stirred or dispersed. The solvent is then removed, allowing the electron-accepting compound to adhere to the surface of the inorganic particles. Solvent removal methods include filtration or evaporation. After solvent removal, sintering can be performed at temperatures above 100°C. The temperature and time for sintering are not particularly limited as long as the electron imaging properties are obtained. In wet processes, the moisture content of the inorganic particles can be removed before adding the electron-accepting compound. Examples include removing moisture while stirring and heating in a solvent, or removing it through azeotropic mixing with the solvent.

[0103] In addition, the attachment of electron-receiving compounds can be carried out before or after the surface treatment of inorganic particles based on surface treatment agents, or the attachment of electron-receiving compounds and surface treatment based on surface treatment agents can be carried out simultaneously.

[0104] The content of the electron-accepting compound is preferably 0.01% by mass or more and 20% by mass or less, and more preferably 0.01% by mass or more and 10% by mass or less, relative to inorganic particles.

[0105] Examples of known polymeric compounds used as adhesive resins in the undercoat include acetal resins (such as polyvinyl butyral), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane resins, polyester resins, unsaturated polyester resins, methacrylic acid resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, urea resins, phenolic resins, phenolic-formaldehyde resins, melamine resins, urethane resins, alkyd resins, and epoxy resins; zirconium chelate compounds; titanium chelate compounds; aluminum chelate compounds; titanium alkoxide compounds; organotitanium compounds; and silane coupling agents.

[0106] Examples of adhesive resins used in the undercoat include charge-transporting resins with charge-transporting groups and conductive resins (e.g., polyaniline).

[0107] The adhesive resin used in the lower coating layer is preferably a resin that is insoluble in the coating solvent, and more preferably a resin obtained by reacting a curing agent with at least one resin selected from the group consisting of thermosetting resins such as urea resin, phenolic resin, phenolic-formaldehyde resin, melamine resin, urethane resin, unsaturated polyester resin, alkyd resin, and epoxy resin; polyamide resin, polyester resin, polyether resin, methacrylic resin, acrylic resin, polyvinyl alcohol resin, and polyvinyl alcohol acetal resin.

[0108] When using two or more adhesive resins in combination, the mixing ratio should be set as needed.

[0109] To improve electrical properties, environmental stability, and image quality, various additives can be included in the undercoat.

[0110] Examples of additives include polycyclic condensation pigments, azo pigments, zirconium chelates, titanium chelates, aluminum chelates, titanium alkoxides, organotitanium compounds, and silane coupling agents. As mentioned earlier, silane coupling agents are used for surface treatment of inorganic particles, but they can also be added as additives to undercoatings.

[0111] Examples of silane coupling agents used as additives include vinyltrimethoxysilane, 3-methacryloyloxypropyltris(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.

[0112] Examples of zirconium chelate compounds include zirconium butoxide, ethyl zirconium acetoacetate, zirconium triethanolamine, zirconium acetylacetone butoxide, zirconium acetoacetate butoxide, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, zirconium methacrylate butoxide, zirconium stearate butoxide, and zirconium isostearate butoxide.

[0113] Examples of titanium chelate compounds include tetraisopropyl titanate, tetrabutyl titanate, tetrabutyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetone, polyacetylacetone titanium, octanediol titanium, titanium ammonium lactate, titanium lactate, titanium ethyl lactate, titanium triethanolamine, and titanium polyhydroxystearate.

[0114] Examples of aluminum chelate compounds include aluminum isopropoxide, aluminum monobutoxydiisopropoxide, aluminum butoxide, aluminum diacetoacetate diisopropoxide, and aluminum triacetoacetate.

[0115] These additives can be used alone or as a mixture or condensation polymer of multiple compounds.

[0116] The undercoat is preferably coated with a Vickers hardness of 35 or higher.

[0117] To suppress interference ripples, the surface roughness (ten-point average roughness) of the lower coating is preferably adjusted to, for example, 1 / (4n) to 1 / 2 of the wavelength λ of the laser used for exposure (where n is the refractive index of the upper layer).

[0118] To adjust surface roughness, resin particles can be added to the undercoat. Examples of resin particles include silicone resin particles and cross-linked polymethyl methacrylate resin particles. Furthermore, to adjust surface roughness, the surface of the undercoat can be ground. Examples of grinding methods include polishing, sandblasting, wet grinding, and grinding.

[0119] There are no particular limitations on the formation of the undercoat, and well-known formation methods can be used. However, for example, it can be carried out by forming a coating film of an undercoat forming liquid in which the above-mentioned components are added to a solvent, drying the coating film, and heating as needed.

[0120] As solvents used to prepare coating liquids for forming the undercoat, known organic solvents can be cited, such as alcohol solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone solvents, ketol solvents, ether solvents, ester solvents, etc.

[0121] Specifically, examples of these solvents include, for instance, methanol, ethanol, n-propanol, isopropanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, dichloromethane, chloroform, chlorobenzene, toluene, and other common organic solvents.

[0122] Methods for dispersing inorganic particles during the preparation of coating liquid for forming a lower coating include, for example, known methods such as roller mills, ball mills, vibratory ball mills, grinding mills, sand mills, colloid mills, and paint mixers.

[0123] Methods for applying a coating liquid for forming an undercoat onto a conductive substrate include, for example, scraper coating, wire rod coating, spraying, dip coating, bead coating, air knife coating, and curtain coating.

[0124] The thickness of the lower coating is preferably 15 μm or more, and more preferably set in the range of 20 μm or more and 50 μm or less.

[0125] (Middle layer)

[0126] Illustrations omitted, but an intermediate layer can also be placed between the lower coating layer and the photosensitive layer.

[0127] The intermediate layer may be, for example, a layer containing resin. Examples of resins used in the intermediate layer include acetal resins (such as polyvinyl butyral), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane resins, polyester resins, methacrylic acid resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, phenolic-formaldehyde resins, melamine resins, and other polymeric compounds.

[0128] The intermediate layer can be a layer containing an organometallic compound. Examples of organometallic compounds used as intermediate layers include those containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon.

[0129] The compounds used in these intermediate layers can be used alone or as a mixture of multiple compounds or as condensation polymers.

[0130] The intermediate layer is preferably a layer containing an organometallic compound containing zirconium or silicon atoms.

[0131] There are no particular limitations on the formation of the intermediate layer, and well-known formation methods can be used. However, for example, a coating film of a coating liquid can be formed by forming an intermediate layer in which the above-mentioned components are added to a solvent, drying the coating film, and heating as needed.

[0132] Common methods for forming the intermediate layer include dip coating, push coating, bar coating, spraying, scraper coating, air knife coating, and curtain coating.

[0133] The thickness of the intermediate layer is preferably set in the range of 0.1 μm or more and 3 μm or less. Alternatively, the intermediate layer can be used as the lower coating layer.

[0134] (charge generation layer)

[0135] The charge generation layer is, for example, a layer comprising a charge generation material and a binding resin. Furthermore, the charge generation layer can be a vapor-deposited layer of the charge generation material. Vapor-deposited layers of charge generation material are suitable, for example, for use with incoherent light sources such as LED (Light Emitting Diode) and organic EL (Electro-Luminescence) image arrays.

[0136] Examples of charge-generating materials include azo pigments such as diazo and triazo; fused-ring aromatic pigments such as dibromoanthracene anthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0137] To cope with laser exposure in the near-infrared region, metal phthalocyanine pigments or metal-free phthalocyanine pigments are preferably used as charge-generating materials. Specifically, hydroxy gallium phthalocyanine, gallium chloride phthalocyanine, dichlorotin phthalocyanine, and titanium dioxide phthalocyanine are more preferred.

[0138] On the other hand, in order to cope with laser exposure in the near-ultraviolet region, the preferred charge-generating materials are, for example, fused-ring aromatic pigments such as dibromoanthracene; sulfur-indigo pigments; porphyrin compounds; zinc oxide; trigonal selenium; and diazo pigments.

[0139] The above-mentioned charge-generating materials can be used even when using incoherent light sources such as LEDs and organic EL image arrays with a center wavelength of light emission above 450nm and below 780nm.

[0140] When n-type semiconductors such as fused-ring aromatic pigments, perylene pigments, and azo pigments are used as charge-generating materials, dark currents are not easily generated, and even when set as thin films, image defects known as black spots can be suppressed.

[0141] Furthermore, regarding the determination of n-type, the commonly used time-of-flight method is used, and the determination is made based on the polarity of the flowing photocurrent. Semiconductors that flow more easily than holes, which are carried by electrons, are defined as n-type.

[0142] The adhesive resin used in the charge generation layer is selected from a wide range of insulating resins, and the adhesive resin can be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinyl anthracene, polyvinylpyrene, and polysilane.

[0143] Examples of adhesive resins include polyvinyl butyral resin, polyarylate resins (condensates of bisphenols and aromatic dicarboxylic acids, etc.), polycarbonate resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyamide resin, acrylic resin, polyacrylamide resin, polyvinylpyridine resin, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol resin, and polyvinylpyrrolidone resin. Here, "insulation" refers to a volume resistivity of 10 Ω·cm. 13 Ω·cm or higher.

[0144] These adhesive resins can be used alone or in combination of two or more.

[0145] In addition, the mixing ratio of the charge-generating material to the adhesive resin is preferably in the range of 10:1 to 1:10 by mass, for example.

[0146] Other well-known additives may be included in the charge-generating layer.

[0147] There are no particular limitations on the formation of the charge-generating layer, and well-known formation methods can be used. For example, it can be achieved by forming a coating film of a charge-generating layer forming liquid in which the aforementioned components are added to a solvent, drying the coating film, and heating it as needed. Alternatively, the charge-generating layer can be formed by vapor deposition of a charge-generating material. Vapor deposition-based formation of the charge-generating layer is particularly suitable, for example, when using polycyclic aromatic pigments or perylene pigments as the charge-generating material.

[0148] Examples of solvents used in preparing coating solutions for forming charge-generating layers include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, dichloromethane, chloroform, chlorobenzene, and toluene. These solvents can be used alone or in combination of two or more.

[0149] As a method for dispersing particles (e.g., charge-generating materials) in a coating liquid for forming a charge-generating layer, media dispersers such as ball mills, vibratory ball mills, grinders, sand mills, and horizontal sand mills, or medialess dispersers such as mixers, ultrasonic dispersers, roller mills, and high-pressure homogenizers can be used. Examples of high-pressure homogenizers include collision methods that disperse the dispersion by liquid-liquid collisions or liquid-wall collisions under high pressure, and penetration methods that disperse the dispersion through fine flow paths under high pressure.

[0150] In addition, when performing this dispersion, it is effective to set the average particle size of the charge-generating material in the coating liquid for forming the charge-generating layer to 0.5 μm or less, for example, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0151] Methods for applying a coating liquid for forming a charge generation layer onto an underlying layer (or an intermediate layer) include, for example, scraper coating, wire rod coating, spraying, dip coating, bead coating, air knife coating, curtain coating, and other common methods.

[0152] The thickness of the charge generation layer is preferably set in the range of 0.1 μm or more and 5.0 μm or less, and more preferably in the range of 0.2 μm or more and 2.0 μm or less.

[0153] [charge transport layer]

[0154] The charge transport layer is a layer containing a binding resin, a charge transport material, and metal oxide particles.

[0155] The charge transport layer can be a layer containing a binding resin, a polymeric charge transport material, and metal oxide particles.

[0156] In the photoreceptor described in this embodiment, when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual metal oxide particles and aggregated particles is 60% or more.

[0157] If the proportion of individual metal oxide particles is less than 60%, then the aggregated particles hinder charge movement, and the conductivity of the charge transport layer decreases.

[0158] The proportion of individual metal oxide particles is preferably 60% or more, more preferably 80% or more, and even more preferably 90% or more.

[0159] When the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles meets the above range, thus the photoreceptor exhibits excellent wear resistance and electrical properties.

[0160] Here, the percentage of individual particles as metal oxide particles is observed and calculated by the following method to determine the cross-section of the charge transport layer.

[0161] A sample of the charge transport layer, cut along the thickness direction, was obtained using a low-temperature slicing method.

[0162] The cross-section of the sample was observed at 20,000x magnification using a scanning electron microscope.

[0163] Count the number of individual metal oxide particles and condensed particles in the observation area.

[0164] Here, an individual metal oxide particle is defined as a primary metal oxide particle that is observed without contacting or overlapping with other particles.

[0165] On the other hand, condensed particles of metal oxide particles are defined as particles observed when primary particles of metal oxide particles come into contact with or overlap with other particles.

[0166] Calculate the ratio of individual metal oxide particles to the total number of individual and aggregated metal oxide particles in the observation area.

[0167] Then, perform the above operation 5 times to calculate the average of the proportion of individual particles of the metal oxide particles.

[0168] In addition, the specificity of metal oxide particles when observing the cross-section of the sample is determined by energy-dispersive X-ray spectroscopy (EDX) based on the presence of the constituent elements of the metal oxide particles (e.g., Si and O in the case of silicon dioxide particles).

[0169] As a method to ensure that the metal oxide particles contained in the charge transport layer meet the above-mentioned range, examples include adjusting the temperature of the coating environment of the coating solution for forming the charge transport layer.

[0170] Furthermore, in the photoreceptor of this embodiment, when the cross-section of the charge transport layer is observed, the ratio of the total area of ​​individual particles and aggregated particles of the metal oxide particles to the total area of ​​the observed cross-section is preferably 60% or more and 95% or less.

[0171] If the total area of ​​the metal oxide particles is less than 60% of the total area, the wear resistance of the charge transport layer is insufficient.

[0172] If the area percentage of individual metal oxide particles exceeds 95%, the metal oxide particles impede the movement of charge, and the conductivity of the charge transport layer decreases.

[0173] The area % of individual metal oxide particles is more preferably 65% ​​or more and 92% or less, and even more preferably 70% or more and 90% or less.

[0174] Here, the area % of the individual particles, which are metal oxide particles, is observed and calculated by the following method to determine the cross-section of the charge transport layer.

[0175] A sample of the charge transport layer, cut along the thickness direction, was obtained using a low-temperature slicing method.

[0176] The cross-section of the sample was observed at 20,000x magnification using a scanning electron microscope.

[0177] Calculate the total area of ​​individual and aggregated metal oxide particles in the observed region.

[0178] The specificity of individual and aggregated particles of metal oxide particles is the same as that described in terms of the proportion of individual metal oxide particles.

[0179] Calculate the ratio of the total area of ​​individual and aggregated metal oxide particles to the area of ​​the observed region.

[0180] Then, perform the above operation 5 times and calculate the average ratio of the total area of ​​individual particles and aggregated particles of the metal oxide particles.

[0181] Furthermore, the specificity of the metal oxide particles observed in the cross-section of the specimen is the same as that described by the proportion of individual metal oxide particles.

[0182] (Types of metal oxide particles)

[0183] Examples of metal oxide particles used in charge transport layers include silicon dioxide particles, aluminum oxide particles, and titanium oxide particles.

[0184] From the viewpoint of suppressing the reduction of the electrical properties of the photoreceptor, metal oxide particles, for example, are preferably silicon dioxide particles.

[0185] Examples of silica particles include dry silica particles and wet silica particles.

[0186] Examples of dry silica particles include combustion-processed silica (fumed silica) and deflagration-processed silica. Combustion-processed silica is obtained by burning silane compounds. Deflagration-processed silica is obtained by causing metallic silicon powder to explode and burn.

[0187] Examples of wet silica particles include precipitated silica, gel silica particles, colloidal silica particles (silica sol particles), and sol-gel silica particles.

[0188] Precipitated silica and gelled silica particles are obtained through the neutralization reaction of sodium silicate with inorganic acids. Silica synthesized / aggregated under alkaline conditions is called precipitated silica, while silica particles synthesized / aggregated under acidic conditions are called gelled silica particles.

[0189] Colloidal silica particles (silica sol particles) are obtained by converting acidic silicic acid into alkaline and then polymerizing it.

[0190] Sol-gel method silica particles are obtained by hydrolysis of organosilane compounds (e.g. alkoxysilanes).

[0191] Silica particles can be surface-treated, for example, by using a hydrophobic agent.

[0192] As a result, the number of silanol groups on the surface of silica particles is reduced, which makes it easier to suppress the generation of residual potential.

[0193] Examples of hydrophobic treatment agents include well-known silane compounds such as chlorosilanes, alkoxysilanes, and silazanes.

[0194] Among these, from the viewpoint of easily suppressing the generation of residual potential, it is desirable, for example, to use a silane compound having trimethylsilyl, decylsilyl, or phenylsilyl groups as a hydrophobic treatment agent. That is, for example, it is acceptable to have trimethylsilyl, decylsilyl, or phenylsilyl groups on the surface of the silica particles.

[0195] Examples of silane compounds containing a trimethylsilyl group include trimethylchlorosilane, trimethylmethoxysilane, and 1,1,1,3,3,3-hexamethyldisilazane.

[0196] Examples of silane compounds having a decyl silyl group include decyltrichlorosilane, decyldimethylchlorosilane, and decyltrimethoxysilane.

[0197] Examples of silane compounds containing phenyl groups include triphenylmethoxysilane and triphenylchlorosilane.

[0198] -Average roundness of metal oxide particles-

[0199] In the photoreceptor of this embodiment, metal oxide particles are preferably dispersed in the charge transport layer in a small-diameter and nearly uniform manner.

[0200] The average sphericity of the metal oxide particles contained in the photoreceptor according to this embodiment is preferably 0.7 or more, more preferably 0.75 or more. For example, it is even more preferably 0.8 or more.

[0201] If the average roundness is above 0.7, the distance between particles will easily become uniform, thus making it easier for the particles to disperse evenly.

[0202] The average roundness of metal oxide particles is calculated using the following method.

[0203] The average roundness of metal oxide particles is calculated by (circumference of the equivalent circle) / (circumference) [(circumference of a circle with the same projected area as the particle image) / (circumference of the particle projected image)].

[0204] Specifically, it refers to the value determined by the following methods.

[0205] A sample of the charge transport layer, cut along the thickness direction, was obtained using a low-temperature slicing method.

[0206] The cross-section of the sample was observed at 20,000x magnification using a scanning electron microscope.

[0207] Determine the roundness of the primary particles of the metal oxide particles in the observation area.

[0208] Then, perform the above operation 5 times and calculate the calculated average of the roundness of the metal oxide particles.

[0209] Furthermore, the specificity of the metal oxide particles observed in the cross-section of the specimen is the same as that described by the proportion of individual metal oxide particles.

[0210] -Hydrophobicity of metal oxide particles-

[0211] In the photoreceptor of this embodiment, if the charge transport layer contains metal oxide particles with a low amount of OH groups, it is difficult to capture charge, and therefore the electrical function of the charge transport layer is not easily degraded.

[0212] As an indicator of the low amount of OH groups, the hydrophobicity of the metal oxide particles is preferably 60% or more, more preferably 62% or more, and even more preferably 65% ​​or more.

[0213] If the hydrophobicity of metal oxide particles is above 60%, the amount of OH groups present in the particles that become charge traps is small, thereby inhibiting their function as charge transporters.

[0214] Therefore, by satisfying the above-mentioned ranges in the average roundness and hydrophobicity of the metal oxide particles, the wear resistance and electrical properties of the photoreceptor are improved.

[0215] Here, in order to reduce the residual OH groups on the surface, silica particles, as metal oxide particles, are typically surface-treated with a hydrophobicating agent. However, silica particles, for example, those prepared 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 number of OH groups remaining inside the pores. Therefore, it is preferable, for example, to perform a hydrophobication treatment based on a hydrophobicating agent on the silica particles.

[0216] The amount of OH groups in a metal oxide is determined based on its degree of hydrophobicity.

[0217] The degree of hydrophobicity of metal oxide particles is calculated using the following method.

[0218] Add 5g of metal oxide particles to 100mL of water. Add methanol dropwise in 1mL increments, and use the following value as the degree of hydrophobicity when the metal oxide particles precipitate.

[0219] [Volume of methanol added / (Volume of methanol added + Volume of water)] × 100

[0220] In addition, as a method for separating metal oxide particles from a photoreceptor, the particles can be separated by dissolving the membrane peeled off from the substrate in an organic solvent and sieving the solution.

[0221] -Light transmittance-

[0222] As the photoreceptor involved in this embodiment, it is preferably one in which the irradiated light is not easily scattered in the charge transport layer and transmitted to the charge generation layer.

[0223] In the photoreceptor of this embodiment, the transmittance T of the charge transport layer is preferably 80% or more.

[0224] If the transmittance T of the charge transport layer is less than 80%, the amount of light transmitted through the charge transport layer to the charge generation layer is insufficient, thus reducing its function as a photoreceptor.

[0225] By ensuring that the transmittance T meets the aforementioned range, the metal oxide particles contained within the charge transport layer are dispersed in a nearly uniform state. Thus, from the viewpoint that light is less likely to be scattered and transmitted to the charge generation layer within the layer, as described above, the transmittance T of the charge transport layer is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.

[0226] The transmittance of the charge transport layer is calculated using the following method.

[0227] A charge transport layer forming coating liquid is applied to a polycarbonate sheet and dried to create a laminate (polycarbonate sheet / composition layer), which is then used as a test sample.

[0228] The transmittance in the thickness direction of the test sample was measured using a UV-Vis spectrophotometer within the wavelength range of 730 to 830 nm. During the measurement, light was incident from the polycarbonate sheet side. The transmittance of light incident on the polycarbonate sheet was also measured only, and the transmittance of light passing through the composite layer was calculated. The average transmittance was calculated for every 10 nm intervals within the wavelength range of 730 to 830 nm.

[0229] Alternatively, the charge transport layer film can be peeled off from the substrate, adhered to a glass plate, and its transmittance measured using the same method as described above. In this case, light is incident from the glass plate side, and the transmittance of the charge transport layer monomer is obtained by measuring only the transmittance of the glass plate.

[0230] (charge transport materials)

[0231] Examples of charge transport materials include quinone compounds such as p-benzoquinone, chloroquinone, tetrabromobenzoquinone, and anthraquinone; tetracyanophenyl dimethyl ether compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone; anthrone compounds; benzophenone compounds; cyanoethylene compounds; and ethylene compounds, all of which are electron transport compounds. Examples of hole transport materials include triarylamine compounds, benzidine compounds, arylalane compounds, aryl-substituted ethylene compounds, piracene compounds, anthracene compounds, and hydrazone compounds, all of which are hole transport compounds. These charge transport materials can be used alone or in combination, but are not limited to this.

[0232] From the viewpoint of charge mobility, the preferred charge transport materials are, for example, triarylamine derivatives represented by the following structural formula (a-1) and benzidine derivatives represented by the following structural formula (a-2).

[0233] [Chemical Formula 1]

[0234]

[0235] In structural formula (a-1), Ar T1 Ar T2 and Ar T3 Each independently represents a substituted or unsubstituted aryl group, -C6H4-C(R) T4 )=C(R T5 (R) T6 ) or -C6H4-CH=CH-CH=C(R T7 (R) T8 R T4 R T5 R T6 R T7 and R T8 Each of the following can be independently represented: a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group.

[0236] Examples of substituents for the aforementioned groups include halogen atoms, alkyl groups having 1 or more but 5 or fewer carbon atoms, and alkoxy groups having 1 or more but 5 or fewer carbon atoms. Furthermore, examples of substituents for the aforementioned groups include substituted amino groups substituted with alkyl groups having 1 or more but 3 or fewer carbon atoms.

[0237] [Chemical Formula 2]

[0238]

[0239] In structural formula (a-2), R T91 and R T92 Each of the following can be independently represented: a hydrogen atom, a halogen atom, an alkyl group having 1 or more but less than 5 carbon atoms, or an alkoxy group having 1 or more but less than 5 carbon atoms. R T101 R T102 R T111 and R T112 Each of the following can be independently represented: a halogen atom, an alkyl group having 1 or more but less than 5 carbon atoms, an alkoxy group having 1 or more but less than 5 carbon atoms, an amino group substituted with an alkyl group having 1 or more but less than 2 carbon atoms, a substituted or unsubstituted aryl group, or a -C(R) group. T12 )=C(R T13 (R) T14 ) or -CH=CH-CH=C(R T15 (R) T16 ), R T12 R T13 R T14 R T15 and R T16Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. T m1 T m2 T n1 and T n2 Each of the following can be used to represent an integer greater than 0 and less than 2.

[0240] Examples of substituents for the aforementioned groups include halogen atoms, alkyl groups having 1 or more but 5 or fewer carbon atoms, and alkoxy groups having 1 or more but 5 or fewer carbon atoms. Furthermore, examples of substituents for the aforementioned groups include substituted amino groups substituted with alkyl groups having 1 or more but 3 or fewer carbon atoms.

[0241] Here, from the viewpoint of charge mobility, among the triarylamine derivatives represented by structural formula (a-1) and the benzidine derivatives represented by said structural formula (a-2), in particular, for example, those having "-C6H4-CH=CH-CH=C(R)" are preferred. T7 (R) T8 Triarylamine derivatives with "-CH=CH-CH=C(R)" and those with "-CH=CH-CH=C(R)" T15 (R) T16 )" benzidine derivatives.

[0242] Examples of polymeric charge transport materials include poly-N-vinylcarbazole, polysilane, and other known materials with charge transport properties. Polyester-based polymeric charge transport materials are particularly preferred. Furthermore, polymeric charge transport materials can be used alone or in combination with binder resins.

[0243] Examples of binder resins used in the charge transport layer include polycarbonate resins, polyester resins, polyarylate resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl acetate resins, styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, silicone resins, silicone alkyd resins, phenol-formaldehyde resins, styrene-alkyd resins, poly-N-vinylcarbazole, and polysilanes. Among these, polycarbonate resins or polyarylate resins are preferred as binder resins. These binder resins may be used alone or in combination with two or more other resins.

[0244] Furthermore, the mixing ratio of the charge transport material to the binder resin is preferably 10:1 to 1:5 by mass, for example.

[0245] Other well-known additives may be included in the charge transport layer.

[0246] There are no particular limitations on the formation of the charge transport layer, and well-known formation methods can be used. However, for example, it can be carried out by forming a coating film of a charge transport layer forming liquid in which the above-mentioned components are added to a solvent, drying the coating film, and heating as needed.

[0247] Examples of solvents used in preparing coating solutions for charge transport layer formation include aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; ketones such as acetone and 2-butanone; halogenated aliphatic hydrocarbons such as dichloromethane, chloroform, and dichloroethane; and cyclic or linear ethers such as tetrahydrofuran and diethyl ether. These solvents can be used alone or in combination of two or more.

[0248] Common methods for applying a coating liquid for forming a charge transport layer onto a charge generation layer include scraper coating, wire rod coating, spraying, dip coating, bead coating, air knife coating, and curtain coating.

[0249] The thickness of the charge transport layer is preferably set in the range of 5 μm or more and 50 μm or less, and more preferably in the range of 10 μm or more and 30 μm or less.

[0250] [Protective Layer]

[0251] 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.

[0252] Previously, techniques for forming inorganic protective layers on charge transport layers were known. Charge transport layers are flexible and prone to deformation, while inorganic protective layers, although rigid, tend to have poor toughness. Therefore, cracks sometimes occur in inorganic protective layers.

[0253] For example, in the developing process, when the carrier scatters from the developing member and adheres to the electrophotographic photoreceptor, the carrier reaches the transfer position while still attached to the electrophotographic photoreceptor. Furthermore, at the transfer position, the carrier is subjected to pressure while being held between the electrophotographic photoreceptor and the transfer member. Therefore, the inorganic protective layer may sometimes crack due to friction between the carrier and the electrophotographic photoreceptor and the transfer member.

[0254] To improve the mechanical strength of the inorganic protective layer, one could consider increasing its thickness. However, increasing the thickness of the inorganic protective layer can lead to the accumulation of charge within it, sometimes resulting in an increase in residual potential.

[0255] In this embodiment, the electrophotographic photoreceptor contains metal oxide particles in the charge transport layer.

[0256] It is believed that metal oxide particles function as reinforcing materials in the charge transport layer through a filler effect. Therefore, it is assumed that the charge transport layer is not easily deformed and can suppress the cracking of the inorganic protective layer.

[0257] Furthermore, in the electrophotographic photoreceptor according to this embodiment, as described above, the metal oxide particles in the charge transport layer do not easily agglomerate, but are dispersed in a small-particle-size and nearly uniform state. Therefore, it is possible to suppress light scattering within the charge transport layer and also to suppress the decrease in light transmittance.

[0258] (Inorganic protective layer)

[0259] 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, hydrogen / fluorinated amorphous carbon, amorphous silicon carbide, hydrogenated amorphous silicon carbide, amorphous silicon, and hydrogenated amorphous silicon; their mixed crystals; etc.

[0260] From the viewpoint of the photoreceptor's wear resistance and electrical properties, the inorganic protective layer is preferably a layer containing metal oxides, more preferably a layer containing group 13 elements and oxygen, and even more preferably a layer containing gallium oxide or a layer containing aluminum oxide. The inorganic protective layer may contain one or more metal oxides.

[0261] From the viewpoint of maintaining the electrostatic latent image, the volume resistivity of the inorganic protective layer is preferably, for example, 1.0 × 10⁻⁶. 10 Ω·cm or higher, more preferably 1.0×10 11 Ω·cm or higher.

[0262] The method for determining the volume resistivity of inorganic protective layers is as follows.

[0263] The inorganic protective layer was peeled off from the photoreceptor and used as a sample. The sample was held in the sample holder of an impedance analyzer (TOYO Corporation), and the resistance value was measured under AC voltage of 1V and frequency of 100Hz. The resistance value was calculated based on the electrode area and the thickness of the sample.

[0264] Methods for forming inorganic protective layers include known vapor deposition methods such as plasma CVD (Chemical Vapor Deposition), organometallic vapor growth, molecular beam epitaxy, evaporation, and sputtering. For example, the plasma CVD film-forming apparatus and film-forming conditions described in Japanese Patent Application Publication No. 2014-191179 can be used to form inorganic protective layers.

[0265] From the viewpoint of the wear resistance and electrical properties of the photoreceptor, the thickness of the inorganic protective layer is preferably 0.2 μm or more and 10 μm or less, more preferably 0.4 μm or more and 8 μm or less, and even more preferably 0.6 μm or more and 6 μm or less.

[0266] The film thickness of each layer of the photosensitive layer is the arithmetic mean of the measured values ​​obtained by an electromagnetic film thickness gauge. The measurement sites are four points along the circumferential direction at 90° intervals, located at the center of the photoreceptor along the axial direction.

[0267] [Image forming apparatus (and processing box)]

[0268] The image forming apparatus according to this embodiment includes an electrophotographic photosensitive body, a charging device for charging the surface of the electrophotographic photosensitive body, an electrostatic latent image forming device for forming an electrostatic latent image on the surface of the charged electrophotographic photosensitive body, a developing device for developing the electrostatic latent image formed on the surface of the electrophotographic photosensitive body using a developing agent containing a toner to form a toner image, and a transfer device for transferring the toner image onto the surface of a recording medium. Furthermore, the electrophotographic photosensitive body according to this embodiment described above is applicable as the electrophotographic photosensitive body.

[0269] The image forming apparatus according to this embodiment is applicable to the following known image forming apparatuses: a fixing apparatus having a fixing device for transferring a toner image 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 photosensitive body to the recording medium; an intermediate transfer method apparatus for transferring a toner image formed on the surface of an electrophotographic photosensitive body to the surface of an intermediate transfer body in one step, and transferring the toner image transferred to the surface of the intermediate transfer body to the surface of the recording medium in a second step; a cleaning apparatus having a cleaning device for cleaning the surface of an electrophotographic photosensitive body before it is charged after the toner image is transferred; an antistatic apparatus having an antistatic device for irradiating the surface of an electrophotographic photosensitive body with antistatic light after the toner image is transferred and before it is charged; and an electrophotographic photosensitive body heating member having an antistatic member for raising the temperature of the electrophotographic photosensitive body and lowering the relative temperature, etc.

[0270] In the case of an intermediate transfer method apparatus, the transfer apparatus may have a structure that includes an intermediate transfer body for transferring a toner image onto a surface, a primary transfer apparatus for transferring a toner image formed on the surface of an electrophotographic photosensitive body to the surface of the intermediate transfer body in one step, and a secondary transfer apparatus for transferring the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium in a second step.

[0271] The image forming apparatus described in this embodiment can be either a dry developing image forming apparatus or a wet developing image forming apparatus (a developing method that utilizes liquid developer).

[0272] Furthermore, in the image forming apparatus according to this embodiment, for example, the portion including the electrophotographic photosensitive element can be a cassette structure (processing cassette) that is detachable from the image forming apparatus. As the processing cassette, for example, a processing cassette including the electrophotographic photosensitive element according to this embodiment is preferably used. In addition to the electrophotographic photosensitive element, the processing cassette may also include at least one selected from the group consisting of a charging device, an electrostatic latent image forming apparatus, a developing apparatus, and a transfer apparatus.

[0273] The following describes an example of the image forming apparatus according to this embodiment, but it is not limited thereto. Furthermore, the main parts shown in the figures will be described, while descriptions of other parts will be omitted.

[0274] Figure 2 This is a schematic structural diagram illustrating an example of the image forming apparatus according to this embodiment.

[0275] like Figure 2 As shown, the image forming apparatus 100 according to this embodiment includes a processing cartridge 300 having an electrophotographic photosensitive element 7, an exposure apparatus 9 (an example of an electrostatic latent image forming apparatus), a transfer apparatus 40 (a primary transfer apparatus), and an intermediate transfer body 50. Furthermore, in the image forming apparatus 100, the exposure apparatus 9 is positioned to expose the electrophotographic photosensitive element 7 through the opening of the processing cartridge 300, and the transfer apparatus 40 is positioned opposite the electrophotographic photosensitive element 7 across the intermediate transfer body 50, with a portion of the intermediate transfer body 50 in contact with the electrophotographic photosensitive element 7. Although not shown, a secondary transfer apparatus is also included to transfer the toner image transferred to the intermediate transfer body 50 to a recording medium (e.g., paper). The intermediate transfer body 50, the transfer apparatus 40 (a primary transfer apparatus), and the secondary transfer apparatus (not shown) are examples of transfer apparatuses.

[0276] Figure 2 The processing cartridge 300 integrally supports the electrophotographic photoreceptor 7, the charging device 8 (an example of the charging device), the developing device 11 (an example of the developing device), and the cleaning device 13 (an example of the cleaning device) within the housing. The cleaning device 13 has a cleaning blade (an example of a cleaning component) 131, which is configured to contact the surface of the electrophotographic photoreceptor 7. Alternatively, the cleaning component may be a conductive or insulating fibrous component instead of the cleaning blade 131, and can be used alone or in conjunction with the cleaning blade 131.

[0277] In addition, Figure 2 In the example shown, as an image forming apparatus, a fibrous component 132 (roller-shaped) is provided for supplying lubricant 14 to the surface of the electrophotographic photosensitive element 7, and a fibrous component 133 (flat brush-shaped) is provided for auxiliary cleaning, but they can be configured as needed.

[0278] The structure of the image forming apparatus according to this embodiment will be described below.

[0279] -Electrified devices-

[0280] As the charging device 8, contact-type charging devices such as charging rollers, charging brushes, charging films, charging rubber scrapers, and charging hoses that utilize conductive or semi-conductive properties can be used. Furthermore, non-contact roller charging devices, grid corona tube charging devices that utilize corona discharge, or corona tube charging devices, and other charging devices known in themselves, can also be used.

[0281] -Exposure device-

[0282] Examples of exposure devices 9 include optical systems that expose semiconductor lasers, LED lights, liquid crystal shutter lights, etc., onto the surface of an electrophotographic photosensitive object 7 to form a predetermined pattern. The wavelength of the light source is set within the spectral sensitivity range of the electrophotographic photosensitive object. Near-infrared light with an oscillation wavelength around 780 nm is the most common wavelength for semiconductor lasers. However, it is not limited to this wavelength; lasers with an oscillation wavelength in the 600 nm band or blue lasers, or lasers with an oscillation wavelength in the range of 400 nm to 450 nm, can be used. Furthermore, surface-emitting laser sources capable of outputting multiple beams for forming color images are also effective.

[0283] -Developing apparatus-

[0284] As a developing apparatus 11, examples include conventional developing apparatuses that perform development by contact or non-contact with the developer. There are no particular limitations on the developing apparatus 11 as long as it possesses the aforementioned functions, and it can be selected according to the purpose. For example, known developing machines that use brushes, rollers, etc., to adhere single-component or two-component developers to the electrophotographic photosensitive element 7 can be cited. Among these, a developing machine that uses a developing roller to hold the developer on the surface is preferred, for example.

[0285] The developer used in the developing apparatus 11 can be a single-component developer containing only a toner, or a two-component developer containing both a toner and a carrier. Furthermore, the developer can be magnetic or non-magnetic. Well-known developers are applicable.

[0286] -Cleaning Device-

[0287] The cleaning device 13 is a device that uses a cleaning scraper with a cleaning scraper 131.

[0288] In addition to the cleaning scraper method, brush cleaning and simultaneous development and cleaning methods can also be used.

[0289] -Transfer Device-

[0290] As a transfer device 40, examples include contact transfer belt appliances that use belts, rollers, films, rubber squeegees, etc.; grid corona tube transfer belt appliances that utilize corona discharge; and corona tube transfer belt appliances, which are known in themselves.

[0291] -Intermediate Transfer Material-

[0292] As the intermediate transfer body 50, a strip-shaped transfer body (intermediate transfer belt) comprising polyimide, polyamide-imide, polycarbonate, polyarylate, polyester, rubber, etc., which are endowed with semi-conductivity, is used. Furthermore, in addition to strip-shaped transfer bodies, roller-shaped transfer bodies can also be used as intermediate transfer bodies.

[0293] Figure 3 This is a schematic structural diagram showing another example of the image forming apparatus according to this embodiment.

[0294] Figure 3 The image forming apparatus 120 shown is a multicolor image forming apparatus equipped with four processing cartridges 300 arranged in series. In the image forming apparatus 120, four processing cartridges 300 are arranged side by side on the intermediate transfer body 50, and a structure is formed in which one electrophotographic photosensitive element is used for each color. In addition, the image forming apparatus 120 has the same structure as the image forming apparatus 100 except that it is arranged in series.

[0295] Example

[0296] Hereinafter, the embodiments of the invention will be described in detail with reference to the examples, but the embodiments of the invention are not limited to these examples.

[0297] Unless otherwise specified, “parts” and “%” are quality standards in the following description.

[0298] Unless otherwise specified, the following instructions shall be followed by synthesis, manufacturing, processing, and measurement at room temperature (25℃±3℃).

[0299] <Example 1>

[0300] [Formation of the undercoat]

[0301] 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 as the conductive substrate.

[0302] Zinc oxide (average particle size 70 nm, specific surface area 15 m²) was used. 2100 parts of zinc oxide (manufactured by TAYCA CORPORATION) were mixed with 500 parts of toluene and stirred. 1.3 parts of a silane coupling agent (trade name: KBM603, manufactured by Shin-Etsu Chemical Co., Ltd., N-2-(aminoethyl)-3-aminopropyltrimethoxysilane) were added, and the mixture was stirred for 2 hours. Next, the toluene was subjected to vacuum distillation, and sintered at 120°C for 3 hours to obtain zinc oxide surface-treated with the silane coupling agent.

[0303] 110 parts of surface-treated zinc oxide were mixed with 500 parts of tetrahydrofuran and stirred. A solution of 0.6 parts of alizarin dissolved in 50 parts of tetrahydrofuran was added, and the mixture was stirred at 50°C for 5 hours. The solid components were then filtered off by vacuum filtration and dried under reduced pressure at 60°C to obtain zinc oxide conferred with alizarin.

[0304] A mixture of 60 parts zinc oxide (for imparting alizarin), 13.5 parts curing agent (terminated isocyanate, trade name: SUMIDUR3175, manufactured by Sumitomo Bayer Urethane Co., Ltd.), and 15 parts butyral resin (trade name: S-LEC BM-1, manufactured by SEKISUI CHEMICALCO., LTD.) dissolved in 100 parts of a solution containing 68 parts methyl ethyl ketone and 5 parts methyl ethyl ketone was dispersed in a sand mill using 1 mm diameter glass beads for 2 hours to obtain a dispersion. 0.005 parts dioctyltin dilaurate and 4 parts silicone resin particles (trade name: Tospearl145, Momentive Performance Materials Inc.) were added to the dispersion as a catalyst to obtain a coating solution for forming a lower coating layer. This coating solution was applied to the outer peripheral surface of a conductive substrate using an dip-coating method and dried and cured at 170°C for 40 minutes to form a lower coating layer with a thickness of 20 μm.

[0305] [Formation of the charge generation layer]

[0306] A mixture consisting of 15 parts of hydroxygallium phthalocyanine (which exhibits 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 X-ray diffraction spectra using CuKα characteristic X-rays), 10 parts of vinyl chloride-vinyl acetate copolymer resin (trade name: VMCH, manufactured by Nippon Unicar Company Limited) and 200 parts of n-butyl acetate was dispersed using glass beads with a diameter of 1 mm and milled in a sand mill for 4 hours. 175 parts of n-butyl acetate and 180 parts of methyl ethyl ketone were added to the dispersion, and the mixture was stirred to obtain a coating solution for forming a charge-generating layer. The coating solution for forming the charge-generating layer was impregnated onto a lower coating layer and dried at room temperature to form a charge-generating layer with a thickness of 0.25 μm.

[0307] [Formation of the charge transport layer]

[0308] • Adhesive resin: Polycarbonate resin (1) (viscosity-average molecular weight 40,000, the values ​​in the structural formula represent molar ratios)... 20 parts

[0309] • Charge transport material: CTM-1…15 parts

[0310] • Metal oxide particles: Silica particles hydrophobically treated with 1,1,1,3,3,3-hexamethyldisilazane (average particle size 150 nm, average roundness 0.85, hydrophobicity 65%)... constitute the amount by volume (%) shown in Table 1.

[0311] Solvent: Tetrahydrofuran (THF) ... 600 parts

[0312] The above materials were stirred and mixed for 12 hours to obtain a coating solution for forming a charge transport layer. The coating solution was then applied to the charge generation layer at room temperature (28°C). Hot air was then blown onto the coating to dry it, forming a charge transport layer with a thickness of 30 μm.

[0313] [Chemical Formula 3]

[0314]

[0315] The above process yields a photoreceptor.

[0316] <Example 2>

[0317] In the formation of the charge transport layer, the photoreceptor was obtained in the same manner as in Example 1, except that impregnation coating was performed at room temperature of 30°C.

[0318] <Example 3>

[0319] In the formation of the charge transport layer, the photoreceptor was obtained in the same manner as in Example 1, except that impregnation coating was performed at room temperature of 32°C.

[0320] <Example 4>

[0321] In the formation of the charge transport layer, the amount of silica particles added was changed as shown in Table 1, and the stirring and mixing time of the material was set to 6 hours. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0322] <Example 5>

[0323] In the formation of the charge transport layer, the amount of silica particles added was changed as shown in Table 1, and the stirring and mixing time of the material was set to 8 hours. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0324] <Example 6>

[0325] In the formation of the charge transport layer, the amount of silica particles added was changed as shown in Table 1, and the stirring and mixing time of the material was set to 14 hours. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0326] <Example 7>

[0327] In the formation of the charge transport layer, the amount of silica particles added was changed as shown in Table 1, and the stirring and mixing time of the material was set to 16 hours. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0328] <Example 8>

[0329] In the formation of the charge transport layer, the silicon dioxide particles were replaced with zinc oxide particles with an average roundness of 0.6 and a hydrophobicity of 65%. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0330] <Example 9>

[0331] In the formation of the charge transport layer, the average sphericity of the silicon dioxide particles was 0.6. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0332] <Example 10>

[0333] In the formation of the charge transport layer, the average sphericity of the silicon dioxide particles was 0.7. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0334] <Example 11>

[0335] In the formation of the charge transport layer, the average sphericity of the silicon dioxide particles was 0.8. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0336] <Example 12>

[0337] In the formation of the charge transport layer, the degree of hydrophobicity of the silicon dioxide particles was 55%, otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0338] <Example 13>

[0339] In the formation of the charge transport layer, 200 parts of the 600 parts of THF solvent were replaced with 200 parts of toluene. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0340] <Example 14>

[0341] In the formation of the charge transport layer, 100 parts of the 600 parts of THF solvent were replaced with 100 parts of toluene. Otherwise, the photoreceptor was obtained in the same manner as in Example 1.

[0342] <Example 15>

[0343] An inorganic protective layer was formed on the charge transport layer in the following manner, otherwise a photoreceptor was obtained in the same manner as in Example 1.

[0344] -Formation of the inorganic protective layer-

[0345] Trimethylgallium was used in the film-forming material, and an amorphous layer containing gallium oxide was formed as an inorganic protective layer by plasma CVD. The layer thickness was set to 3 μm.

[0346] <Comparative Example 1>

[0347] In Example 1, the room temperature during impregnation coating was changed to 22°C, and photoresists were made accordingly.

[0348] <Various Measurements>

[0349] The following items were determined using the methods described above.

[0350] • The proportion (number %) of individual metal oxide particles contained within the charge transport layer: denoted as “A1 / (A1+A2)” in Table 1.

[0351] • The percentage of the total area of ​​individual and aggregated metal oxide particles contained within the charge transport layer (%)

[0352] • Average roundness and hydrophobicity of metal oxide particles

[0353] <Performance Evaluation of Photoreceptors>

[0354] [hardness]

[0355] The hardness of the charge transport layer in each example was evaluated below.

[0356] The hardness of the outer peripheral surface of the photoreceptor was determined by the Young's modulus (GPa) using the nanoindentation method. The axis of the photoreceptor was fixed in the horizontal direction, and the hardness was measured at the vertex at the center of the axis of the photoreceptor.

[0357] Four positions were measured along the circumference of the photoreceptor at 90° intervals, and the Young's modulus at the four positions was arithmetically averaged.

[0358] The measurement conditions based on the nanoindentation instrument are as follows.

[0359] The measurement results are shown in Table 1.

[0360] • Test apparatus: Product name HM-500, FISCHER INSTRUMENTS KK

[0361] • Indenter: A diamond triangular indenter with a 115° angle.

[0362] • Load: 75mN

[0363] [Abrasion Resistance]

[0364] The abrasion resistance of the photoreceptors in each example was evaluated below.

[0365] Each photoreceptor was mounted in an image forming apparatus (manufactured by FUJIFILM Business Innovation Co., Ltd., Apeos C4570) of an electrophotographic system. 100,000 images with a 1% solid content and an image density (area coverage) of 1% were formed on A3-sized paper at an environment of 30°C and 85% relative humidity. Then, 100,000 solid images with a 100% image density (area coverage) were formed on A3-sized paper at an environment of 10°C and 15% relative humidity. This image forming process was repeated five times (i.e., a total of 200,000 images formed, including 100,000 images formed at 30°C and 85% relative humidity and 100,000 images formed at 10°C and 15% relative humidity). The average thickness of the charge transport layer was calculated before and after the image forming (i.e., a total of 1 million images formed), and the difference in average thickness before and after image forming was defined as the wear amount (nm). As the film thickness measuring instrument, the PERMASCOPE manufactured by Fisher Instruments KK was used.

[0366] The wear levels are categorized as follows. The results are shown in Table 1.

[0367] G1: Wear level less than 500nm

[0368] G2: Wear level is above 500nm and below 1000nm

[0369] G3: Wear level is above 1000nm and below 1500nm

[0370] G4: Wear level above 1500nm

[0371] [Electrical properties]

[0372] The electrical properties of the charge transport layer in each example are evaluated below.

[0373] In an environment with a temperature of 22℃ and a relative humidity of 55%, the photoreceptor was rotated at a speed of 40 rpm. While scanning the surface of the photoreceptor, the exposure light (light source: semiconductor laser, wavelength 780nm, output 5mW) was irradiated with an electrical device using a grid corona tube with a negative charge of -700V. The residual potential on the surface of the photoreceptor was then measured.

[0374] In the potential measurement, a surface potential probe of a surface potentiometer (manufactured by TREQ INC., TREK334) was used, which was positioned at the axial center of the photoreceptor and 1 mm from the surface of the photoreceptor.

[0375] The measured residual potentials were classified into G1 to G4 as follows, and the effectiveness of the suppression of residual potential rise was evaluated. A value less than 40V was considered acceptable. The evaluation results are shown in Table 1.

[0376] G1: Less than 15V

[0377] G2: 15V or higher and less than 30V

[0378] G3: 30V or higher and less than 40V

[0379] G4: 40V and above

[0380] [Fragility resistance of the inorganic protective layer]

[0381] The fracture load of the inorganic protective layer was measured and its fracture resistance was evaluated.

[0382] For the hardness tests conducted using a microhardness tester, the measurements were repeated while increasing the load by 5 mN from 0 mN. After each load application, observation was performed using an optical microscope, and the load at which failure occurred in the inorganic protective layer was defined as the fracture initiation load. The measurement conditions are as follows.

[0383] • Test apparatus: Trade name DUH-201, SHIMADZU CORPORATION

[0384] • Indenter head: Diamond spherical indenter head

[0385]

[0386] As can be seen from the above results, the photoreceptor of the embodiment has higher wear resistance and electrical properties compared with the photoreceptor of the comparative example.

[0387] This implementation includes the following methods. (1)

[0389] An electrophotographic photosensitive material comprises: a conductive substrate; a charge generating layer disposed on the conductive substrate; and a charge transport layer disposed on the charge generating layer, comprising a binding resin, a charge transport material, and metal oxide particles.

[0390] When the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual and aggregated metal oxide particles is 60% or more. (2)

[0392] According to the electrophotographic photosensitive material described in (1), wherein,

[0393] The proportion of individual metal oxide particles is more than 70%. (3)

[0395] According to the electrophotographic photosensitive material described in (1) or (2), wherein,

[0396] When the cross-section of the charge transport layer is observed, the total area of ​​the individual particles and aggregated particles of the metal oxide particles is more than 60% and less than 95% of the area of ​​the observed cross-section. (4)

[0398] According to any one of (1) to (3), the electrophotographic photosensitive material, wherein,

[0399] The metal oxide particles are silicon dioxide particles. (5)

[0401] According to any one of (1) to (4), the electrophotographic photosensitive material, wherein,

[0402] The metal oxide particles have an average roundness of 0.7 or higher and a hydrophobicity of 60% or higher. (6)

[0404] According to the electrophotographic photosensitive material described in (5), wherein,

[0405] The metal oxide particles have an average roundness of 0.8 or higher and a hydrophobicity of 60% or higher. (7)

[0407] According to any one of (1) to (6), the electrophotographic photosensitive material, wherein,

[0408] The transmittance T of the charge transport layer is above 80%. (8)

[0410] The electrophotographic photoreceptor according to any one of (1) to (7) further comprises an inorganic protective layer disposed on the charge transport layer. (9)

[0412] A processing cartridge comprising any one of (1) to (8) an electrophotographic photosensitive element, the processing cartridge being detachable from an image forming apparatus. (10)

[0414] 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 apparatus for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor; a developing apparatus for developing the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developing agent containing a toner to form a toner image; and a transfer apparatus for transferring the toner image onto the surface of a recording medium.

[0415] The effects of the above methods are as follows.

[0416] According to the invention involved in (1), compared with a conductive substrate, a charge generating layer disposed on a conductive substrate, and a charge transport layer disposed on the charge generating layer and comprising a bonding resin, a charge transport material and metal oxide particles, when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual metal oxide particles and aggregated particles is less than 60%, providing an electrophotographic photosensitive material with excellent wear resistance and electrical properties.

[0417] According to the invention involved in (2), an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to the case where the proportion of individual metal oxide particles is less than 70%.

[0418] According to the invention involved in (3), compared with the case where the total area of ​​individual particles and aggregated particles of metal oxide particles is less than 60% or more than 95% of the total area of ​​the observed cross section when the cross section of the charge transport layer is observed, an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided.

[0419] According to the invention involved in (4), an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to the case where the metal oxide particles are not silicon dioxide particles.

[0420] According to the invention involved in (5) or (6), an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to the case where the average roundness of the metal oxide particles is less than 0.7 or the degree of hydrophobicity is less than 60%, or the average roundness of the metal oxide particles is less than 0.8 or the degree of hydrophobicity is less than 60%.

[0421] According to the invention involved in (7), an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided, compared to the case where the transmittance T of the charge transport layer is less than 80%.

[0422] According to the invention involved in (8), compared with a conductive substrate, a charge generating layer disposed on a conductive substrate, and a charge transport layer disposed on a charge generating layer and comprising a bonding resin, a charge transport material and metal oxide particles, when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual metal oxide particles and aggregated particles is less than 60%, providing an electrophotographic photosensitive material with excellent crack suppression of inorganic protective layer and electrical properties.

[0423] According to the invention involved in (9) or (10), compared with an electrophotographic photosensitive material that uses a conductive substrate, a charge generation layer disposed on the conductive substrate, and a charge transport layer disposed on the charge generation layer and comprising a bonding resin, a charge transport material and metal oxide particles, when the cross-section of the charge transport layer is observed, the proportion of individual metal oxide particles to the total number of individual metal oxide particles and aggregated particles is less than 60%, a processing box or image forming apparatus of an electrophotographic photosensitive material with excellent wear resistance and electrical properties is provided.

[0424] The embodiments of the present invention described above are provided for illustrative purposes. Furthermore, these embodiments do not encompass the entirety of the invention, nor do they limit the invention to the disclosed methods. It will be apparent to those skilled in the art that various modifications and variations will be readily understood. These embodiments were chosen and described to most readily explain the principles and applications of the invention. Thus, those skilled in the art can understand the invention through various modifications that are assumed to be optimized for specific uses of various embodiments. The scope of the invention is defined by the foregoing claims and their equivalents.

Claims

1. An electrophotographic photoreceptor, having: an electroconductive base; a charge generating layer provided on the electroconductive base; and a charge transport layer disposed on the charge generating layer, and containing a binding resin, a charge transport material, and metal oxide particles, a proportion of individual particles of the metal oxide particles with respect to a total of the individual particles and agglomerated particles of the metal oxide particles is 60% by number or more when a cross section of the charge transport layer is observed.

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

3. The electrophotographic photoreceptor according to claim 1 or 2, wherein a total of areas of the individual particles and agglomerated particles of the metal oxide particles with respect to an area of the entire observation cross section is 60% by area or more and 95% by area or less when the cross section of the charge transport layer is observed.

4. The electrophotographic photoreceptor according to any one of claims 1 to 3, wherein the metal oxide particles are silica particles.

5. The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein an average circularity of the metal oxide particles is 0.7 or more, and a degree of hydrophobization is 60% or more.

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

8. The electrophotographic photoreceptor according to any one of claims 1 to 7, further having an inorganic protective layer disposed on the charge transport layer.

9. A process cartridge, provided with the electrophotographic photoreceptor according to any one of claims 1 to 8, the process cartridge being detachably attached to an image forming apparatus.

10. An image forming apparatus, provided with: the electrophotographic photoreceptor according to any one of claims 1 to 8; a charging device that charges a surface of the electrophotographic photoreceptor; an electrostatic latent image forming device that forms an electrostatic latent image on the surface of the electrophotographic photoreceptor that has been charged; a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner to form a toner image; and a transfer device that transfers the toner image onto a surface of a recording medium. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Images