Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that can extend its lifespan by simultaneously improving image granularity and density uniformity after long-term use, even when the charge generation layer is made thicker. [Solution] An electrophotographic photoreceptor comprising a conductive substrate, a charge generation layer disposed on the conductive substrate, and a charge transport layer disposed on the charge generation layer, wherein the ratio of the straight-line component to the light transmittance at a wavelength of 780 nm (straight-line component / light transmittance) is 50.0% or more, the thickness of the charge transport layer is 40.0 μm or more and 65.0 μm or less, and the index X of the short-period circumferential unevenness of the thickness of the charge transport layer (the maximum value among the differences between the maximum and minimum values ​​of the thickness in a 45-degree range starting from each of 90 points of thickness measured at 4-degree intervals in the circumferential direction 360 degrees) satisfies the relationship of the following formula (A). Equation (A): Index of short-period circumferential unevenness in the thickness of the charge transport layer X (μm) ≤ -0.02 × thickness of the charge transport layer (μm) + 2

Description

[Technical Field]

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

[0002] Electrophotographic photoreceptors remove surface foreign matter by wearing down their surface with a cleaning blade, and their lifespan (hereinafter also referred to as "life") is primarily determined by wear. Typically, electrophotographic photoreceptors are configured as part of a replaceable unit (i.e., a process cartridge), and the life of the electrophotographic photoreceptor determines when the unit needs to be replaced. For this reason, various methods for extending life are being considered. To extend life, in charge transport layers that do not have a protective layer, wear resistance is improved by incorporating fluororesin particles, such as PTFE particles (polytetrafluoroethylene particles), to improve surface slipperiness, and the thickness of the charge transport layer, which is the surface layer, is being increased.

[0003] Patent Document 1 discloses "an electrophotographic photoreceptor that, by adding a fluoride carbon and a long-chain alkyl amino acid compound, improves wear resistance by improving slipperiness, simultaneously prevents the adhesion of foreign matter by improving release properties, and exhibits excellent durability both initially and after use." [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-265241 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] The object of this disclosure is to provide an electrophotographic photoreceptor that, even when the charge generation layer is made thicker, can achieve improvements in both image granularity and density uniformity after long-term use, thereby extending the lifespan, compared to cases where the ratio of the straight-line component (straight-line component / light transmittance), described later, is less than 50.0%, or where the index X of short-period circumferential unevenness of the film thickness of the charge transport layer, described later, does not satisfy equation (A). [Means for solving the problem]

[0006] The following embodiments are included as specific means for solving the aforementioned problems. <1> A conductive substrate, A charge generation layer disposed on the conductive substrate, A charge transport layer is disposed on the charge generation layer and contains fluororesin particles, wherein the ratio of the straight-traveling component to the light transmittance at a wavelength of 780 nm (straight-traveling component / light transmittance) is 50.0% or more. Equipped with, The thickness of the charge transport layer is 40.0 μm or more and 65.0 μm or less, and the index X of the short-period circumferential unevenness of the thickness of the charge transport layer (the maximum value among the differences between the maximum and minimum values ​​of the thickness within a 45-degree range starting from each of 90 points of thickness measured at 4-degree intervals around 360 degrees in the circumferential direction) satisfies the relationship of equation (A) below. Electrophotographic photoreceptor. Equation (A): Index of short-period circumferential unevenness in the thickness of the charge transport layer X (μm) ≤ -0.02 × thickness of the charge transport layer (μm) + 2 <2> The index X of short-period circumferential unevenness in the thickness of the charge transport layer is 0.70 μm or less. <1> The electrophotographic photoreceptor described above. <3> The ratio of the straight-traveling component to the light transmittance of the charge transport layer at a wavelength of 780 nm (straight-traveling component / light transmittance) is 60.0% or more. <1> or <2> The electrophotographic photoreceptor described above. <4> The electrophotographic photoreceptor according to any one of <1> to <3>, wherein the film thickness of the charge transport layer is 40.0 μm or more and 45.0 μm or less. <5> An electrophotographic photoreceptor according to any one of <1> to <4>, and A charging device having a charging member, applying a voltage obtained by superimposing an alternating voltage on a direct current voltage to the charging member, and charging the surface of the electrophotographic photoreceptor, Comprising, A process cartridge that is detachable from an image forming apparatus. <6> An electrophotographic photoreceptor according to any one of <1> to <4>, and A charging device having a charging member, applying a voltage obtained by superimposing an alternating voltage on a direct current voltage to the charging member, and charging the surface of the electrophotographic photoreceptor, An electrostatic latent image forming device that forms an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image, A transfer device that transfers the toner image onto the surface of a recording medium, An image forming apparatus comprising.

Advantages of the Invention

[0007] According to <1>, in an electrophotographic photoreceptor including a conductive substrate, a charge generation layer, and a charge transport layer containing fluororesin particles and having a film thickness of 40.0 μm or more and 65.0 μm or less, compared with the case where the ratio of the straight-ahead component (straight-ahead component / light transmittance) is less than 50.0% or the index X of the short-period circumferential unevenness of the film thickness of the charge transport layer does not satisfy the formula (A), even if the charge generation layer is thickened, an electrophotographic photoreceptor is provided that can achieve both improvement in image granularity and density unevenness after long-term use and can extend the life. According to <2>, compared with the case where the index X of the short-period circumferential unevenness of the film thickness of the charge transport layer is more than 0.70 μm, even if the charge generation layer is thickened, an electrophotographic photoreceptor is provided that can achieve both improvement in image granularity and density unevenness after long-term use and can extend the life. <3> According to this, compared to cases where the ratio of the straight-linking component to the light transmittance of the charge transport layer at a wavelength of 780 nm (straight-linking component / light transmittance) is less than 60.0%, even if the charge generation layer is made thicker, an electrophotographic photoreceptor is provided that can achieve both improvement in image granularity and density uniformity after long-term use, thereby extending its lifespan. <4> According to this, compared to cases where the thickness of the charge transport layer is less than 40.0 μm or greater than 45.0 μm, an electrophotographic photoreceptor is provided that can extend its lifespan while simultaneously improving both the granularity of the image and the density unevenness after long-term use, even when the charge generation layer is made thicker. <5> or <6> According to the present invention, an electrophotographic photoreceptor comprising a conductive substrate, a charge generation layer, and a charge transport layer containing fluororesin particles and having a film thickness of 40.0 μm to 65.0 μm is provided. Compared to an electrophotographic photoreceptor in which the ratio of the straight-line component (straight-line component / light transmittance) is less than 50.0%, or in which the index X of short-period circumferential unevenness of the film thickness of the charge transport layer does not satisfy formula (A), the present invention provides a process cartridge and an image forming apparatus that can extend the life of an electrophotographic photoreceptor by improving both the granularity of the image and the density unevenness after long-term use, even when the charge generation layer is made thicker. [Brief explanation of the drawing]

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

[0009] The embodiments of this disclosure are described below. The description and embodiments are illustrative and do not limit the scope of this disclosure.

[0010] In this disclosure, numerical ranges indicated using "~" represent a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0011] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0012] In this disclosure, when embodiments are described with reference to the drawings, the configuration of such embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each figure are conceptual, and the relative relationships between the components are not limited thereto.

[0013] In this disclosure, each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition in this disclosure, if there are multiple types of the substance corresponding to each component in the composition, it means the total amount of those multiple types of substances present in the composition unless otherwise specified. In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified.

[0014] In this disclosure, "circumferential direction" of the electrophotographic photoreceptor means the rotational direction of the electrophotographic photoreceptor.

[0015] In this disclosure, "short period" means a period corresponding to 4° in the circumferential direction.

[0016] In this disclosure, the "charge transport layer" of an electrophotographic photoreceptor means the surface layer.

[0017] <Electrophotographic photoconductor> The electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") of this disclosure comprises a conductive substrate, a charge generation layer disposed on the conductive substrate, and a charge transport layer disposed on the charge generation layer. The electrophotographic photoreceptor contains fluororesin particles. In the charge transport layer, the ratio of the forward-propagating component to the light transmittance at a wavelength of 780 nm (forward-propagating component / light transmittance) is 50.0% or higher. The thickness of the charge transport layer is between 40.0 μm and 65.0 μm, and the index X of short-period circumferential unevenness of the charge transport layer thickness (the maximum value among the differences between the maximum and minimum thicknesses within a 45-degree range, calculated from each of 90 points of thickness measured at 4-degree intervals around 360 degrees in the circumferential direction) satisfies the relationship given by equation (A) below. Equation (A): Index of short-period circumferential unevenness in the thickness of the charge transport layer X (μm) ≤ -0.02 × thickness of the charge transport layer (μm) + 2

[0018] Here, it is easy to imagine that extending the lifespan of the charge transport layer by adding fluororesin particles such as PTFE particles (polytetrafluoroethylene particles) would be beneficial. However, when the charge transport layer with added fluororesin particles is thickened, the exposure light during image formation is scattered within the charge transport layer, reducing the amount that reaches the charge generation layer. As a result, the granularity of the image deteriorates. Furthermore, thickening the charge transport layer tends to increase film thickness unevenness. Initial film thickness unevenness tends to worsen further due to discharge phenomena during the charging process in image formation, and this is detected as density unevenness in the image. As a result, the benefit of extending the lifespan through thickening is difficult to obtain.

[0019] In other words, the use of fluororesin particles in the charge transport layer to improve lubricity in order to extend life reduces the light transmittance of the charge transport layer. This reduces the granularity of the image. Therefore, it is desirable to reduce the amount of fluororesin particles used to compensate for the contribution of lubricity to wear resistance, or to increase the thickness of the charge transport layer even more. However, increasing the thickness of the charge transport layer tends to increase film thickness unevenness. When film thickness unevenness increases, it exacerbates wear unevenness (i.e., uneven wear) and generates density unevenness. In particular, when a photoreceptor is mounted in an image forming apparatus equipped with a charging device that charges the surface of the electrophotographic photoreceptor by applying a voltage obtained by superimposing a DC voltage on a charged member, discharge unevenness occurs during charging according to the initial film thickness unevenness. Therefore, wear unevenness (i.e., uneven wear) is particularly exacerbated. As a result, it is difficult to extend life. Furthermore, the increased thickness of the film can lead to a decrease in the light transmittance of the charge transport layer during exposure and an increase in scattered light, which can also reduce the granularity of the image.

[0020] In contrast, the photoreceptor of this disclosure has a charge transport layer containing fluororesin particles in which the ratio of the straight-traveling component to the light transmittance at a wavelength of 780 nm (straight-traveling component / light transmittance) is set to 50.0% or more. As a result, the transmittance of light is improved even when the film is made thicker by increasing the transmittance of the charge transport layer. This suppresses the decrease in image granularity. Furthermore, by controlling the index X of short-period circumferential unevenness in the film thickness of the charge transport layer to satisfy equation (A), wear unevenness (i.e., uneven wear) can be suppressed. This suppresses the occurrence of concentration unevenness after long-term use. Therefore, the photoreceptor of this disclosure can achieve both improvement in image granularity and density unevenness after long-term use, thereby extending its lifespan.

[0021] The following describes the details of the photoreceptor. Figure 1 is a schematic partial cross-sectional view showing an example of the layer structure of the photoreceptor of this disclosure. The photoreceptor 10A shown in Figure 1 has a stacked photosensitive layer. The photoreceptor 10A has a structure in which a base layer 2, a charge generation layer 3, and a charge transport layer 4 are stacked in this order on a conductive substrate 1, and the charge generation layer 3 and the charge transport layer 4 constitute the photosensitive layer 5 (a so-called functionally separated photosensitive layer). Here, the lower layer 2 is a layer that is provided as needed. The photoreceptor 10A may have an intermediate layer (not shown) between the undercoat layer 2 and the charge generation layer 3.

[0022] The details of each component are explained below. Note that the symbols for each component are omitted.

[0023] (Conductive substrate) Examples of conductive substrates include metal plates, metal drums, and metal belts containing metals (aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, platinum, etc.) or alloys (stainless steel, etc.). Other examples of conductive substrates include paper, resin films, and belts coated, vapor-deposited, or laminated with conductive compounds (e.g., conductive polymers, indium oxide, etc.), metals (e.g., aluminum, palladium, gold, etc.) or alloys. Here, "conductive" refers to a volume resistivity of 10⁻¹⁰. 13 This refers to a value less than Ω·cm.

[0024] When an electrophotographic photoreceptor is used in a laser printer, the surface of the conductive substrate is preferably roughened to a center-line average roughness Ra of 0.04 μm to 0.5 μm in order to suppress interference fringes that occur when irradiated with laser light. While roughening to prevent interference fringes is not particularly necessary when using non-interfering light as the light source, it is beneficial for extending the lifespan by suppressing the occurrence of defects due to surface irregularities of the conductive substrate.

[0025] Methods for roughening a surface include, for example, wet honing, which involves suspending an abrasive in water and spraying it onto a conductive substrate; centerless grinding, which involves pressing a conductive substrate against a rotating grinding wheel and continuously grinding it; and anodizing.

[0026] One method for roughening the surface is to disperse conductive or semiconductive powder in a resin without roughening the surface of the conductive substrate, to form a layer on the surface of the conductive substrate, and then roughen the surface with the particles dispersed in that layer.

[0027] Anodizing roughening treatment involves forming an oxide film on the surface of a conductive substrate (e.g., aluminum) by anodizing it in an electrolyte solution. Examples of electrolyte solutions include sulfuric acid solution and oxalic acid solution. However, the porous anodic oxide film formed by anodizing is chemically active, easily contaminated, and exhibits large resistance fluctuations depending on the environment. Therefore, it is preferable to perform a sealing treatment on the porous anodic oxide film to block the micropores of the oxide film by volume expansion due to a hydration reaction using pressurized steam or boiling water (metal salts such as nickel may be added), thereby converting it into a more stable hydrated oxide.

[0028] The thickness of the anodic oxide film is preferably, for example, 0.3 μm to 15 μm. When the film thickness is within this range, it tends to exhibit barrier properties against injection and tends to suppress the increase in residual potential due to repeated use.

[0029] The conductive substrate may be treated with an acidic treatment solution or with boehmite. Treatment with an acidic solution is carried out, for example, as follows: First, an acidic solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The mixing ratio of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic solution is, for example, in the range of 10% to 11% by mass for phosphoric acid, 3% to 5% by mass for chromic acid, and 0.5% to 2% by mass for hydrofluoric acid, and the total concentration of these acids is preferably in the range of 13.5% to 18% by mass. The treatment temperature is preferably, for example, 42°C to 48°C. The film thickness is preferably 0.3 μm to 15 μm.

[0030] The boehmite treatment is carried out, for example, by immersing the material in pure water at 90°C to 100°C for 5 to 60 minutes, or by contacting it with heated steam at 90°C to 120°C for 5 to 60 minutes. The film thickness is preferably 0.1 μm to 5 μm. This can be further treated with anodic oxidation using an electrolyte solution with low film solubility, such as adipic acid, boric acid, borate, phosphate, phthalate, maleate, benzoate, tartrate, or citrate.

[0031] (Charge generation layer) The charge generation layer is, for example, a layer containing a charge generation material and a binder resin. Alternatively, the charge generation layer may be a vapor-deposited layer of the charge generation material. A vapor-deposited layer of the charge generation material is suitable when using non-coherent light sources such as LEDs (Light Emitting Diodes) or organic EL (Electro-Luminescence) image arrays.

[0032] Examples of charge-generating materials include azo pigments such as bisazo and trisazo; fused aromatic pigments such as dibromoanthonthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0033] Among these, in order to accommodate laser exposure in the near-infrared region, it is preferable to use a metal phthalocyanine pigment or a metal-free phthalocyanine pigment as the charge generating material. Specifically, for example, hydroxygallium phthalocyanine; chlorogallium phthalocyanine; dichlorotin phthalocyanine; and titanyl phthalocyanine are more preferable.

[0034] On the other hand, to accommodate laser exposure in the near-ultraviolet region, preferred charge-generating materials include fused aromatic pigments such as dibromoanthoten; thioindigo pigments; porphyrazine compounds; zinc oxide; trigonal selenium; and bisazo pigments.

[0035] The above charge generating material may also be used when using non-coherent light sources such as LEDs and organic EL image arrays, which have a central emission wavelength between 450 nm and 780 nm.

[0036] When n-type semiconductors such as fused aromatic pigments, perylene pigments, and azo pigments are used as charge-generating materials, dark currents are less likely to be generated, and image defects called black spots can be suppressed even in thin films. The n-type is determined using the commonly used time-of-flight method, which is determined by the polarity of the photocurrent that flows, and materials that readily carry electrons as carriers rather than holes are classified as n-type.

[0037] The binder resin used in the charge generation layer can be selected from a wide range of insulating resins, or it may be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, and polysilane. Examples of binder resins include polyvinyl butyral resin, polyarylate resin (polycondensate of bisphenols and aromatic divalent carboxylic 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, "insulating properties" refers to a volume resistivity of 10 13 This refers to a density of Ω·cm or greater. These binder resins can be used individually or in mixtures of two or more types.

[0038] The mixing ratio of the charge-generating material to the binder resin is preferably within the range of 10:1 to 1:10 by mass ratio.

[0039] The charge generation layer may also contain other known additives.

[0040] The formation of the charge generation layer is not particularly limited, and known formation methods can be used. For example, it can be carried out by forming a coating film of a coating solution for forming a charge generation layer by adding the above components to a solvent, drying the coating film, and heating it as necessary. The charge generation layer may also be formed by vapor deposition of a charge generation material. Formation of the charge generation layer by vapor deposition is particularly suitable when using fused ring aromatic pigments or perylene pigments as the charge generation material.

[0041] Solvents for preparing the coating solution for forming the charge generation layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene. These solvents may be used individually or in mixtures of two or more.

[0042] Methods for dispersing particles (e.g., charge-generating material) in a coating solution for forming a charge-generating layer include, for example, media dispersers such as ball mills, vibrating ball mills, attritors, sand mills, and horizontal sand mills, as well as media-less dispersers such as stirrers, ultrasonic dispersers, roll mills, and high-pressure homogenizers. Examples of high-pressure homogenizers include collision methods, in which the dispersion is dispersed by liquid-liquid collisions or liquid-wall collisions under high pressure, and penetration methods, in which the dispersion is dispersed by penetrating fine channels under high pressure. During dispersion, it is effective to set the average particle size of the charge-generating material in the coating solution for forming the charge-generating layer to 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0043] Conventional methods for applying the charge-generating layer forming coating solution onto the undercoat (or intermediate layer) include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0044] The thickness of the charge generation layer is preferably set within the range of 0.1 μm to 5.0 μm, and more preferably within the range of 0.2 μm to 2.0 μm.

[0045] (charge transport layer) -Composition of the charge transport layer- The charge transport layer contains fluororesin particles. Specifically, the charge transport layer is, for example, a layer containing a charge transport material, a binder resin, and fluororesin particles. The charge transport layer may also be a layer containing a polymer charge transport material and fluororesin particles.

[0046] Examples of the charge transport material include quinone compounds such as p-benzoquinone, chloranil, bromanil, and anthraquinone; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone; xanthone compounds; benzophenone compounds; cyanovinyl compounds; and electron transporting compounds such as ethylene compounds. Examples of the charge transport material also include hole transporting compounds such as triarylamine compounds, benzidine compounds, arylalkane compounds, aryl-substituted ethylene compounds, stilbene compounds, anthracene compounds, and hydrazone compounds. These charge transport materials may be used alone or in combination of two or more, but are not limited thereto.

[0047] From the viewpoint of charge mobility, as the charge transport material, a triarylamine derivative represented by the following structural formula (a-1) and a benzidine derivative represented by the following structural formula (a-2) are preferable.

[0048]

Chemical formula

[0049] In the structural formula (a-1), Ar T1 , Ar T2 , and Ar T3 each independently represent a substituted or unsubstituted aryl group, -C6H4-C(R T4 )=C(R T5 )(R T6 ), or -C6H4-CH=CH-CH=C(R T7 )(R T8 ). R T4 , R T5 , R T6 , R T7 , and R T8 each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Substituents for each of the above groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Furthermore, substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms are also examples of substituents for each of the above groups.

[0050] [ka]

[0051] In structural formula (a-2), R T91 and R T92 Each of these independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms. T101 , R T102 , R T111 and R T112 Each of these independently consists of a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an amino group substituted with an alkyl group having 1 to 2 carbon atoms, a substituted or unsubstituted aryl group, and -C(R T12 )=C(R T13 )(R T14 ), or -CH=CH-CH=C(R T15 )(R T16 ) shows R T12 , R T13 , R T14 , R T15 and R T16 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Tm1, Tm2, ​​Tn1, and Tn2 each independently represent an integer between 0 and 2. Substituents for each of the above groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Furthermore, substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms are also examples of substituents for each of the above groups.

[0052] Among the triarylamine derivatives shown in structural formula (a-1) and the benzidine derivatives shown in structural formula (a-2), in particular, "-C6H4-CH=CH-CH=C(R T7 )(RT8 Triarylamine derivatives having ")" and "-CH=CH-CH=C(R T15 )(R T16 A benzidine derivative having ) is preferred from the viewpoint of charge mobility.

[0053] As polymer charge transport materials, known charge transport materials such as poly-N-vinylcarbazole and polysilane can be used. Polyester-based polymer charge transport materials are particularly preferred. Polymer charge transport materials may be used alone or in combination with a binder resin.

[0054] Examples of binder resins used in the charge transport layer include polycarbonate resin, polyester resin, polyarylate resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicone alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin, poly-N-vinylcarbazole, and polysilane. Among these, polycarbonate resin or polyarylate resin is preferred as the binder resin. These binder resins can be used individually or in combination of two or more. The preferred mixing ratio of the charge transport material to the binder resin is between 10:1 and 1:5 by mass.

[0055] Examples of fluororesin particles include polytetrafluoroethylene (PTFE, also known as "tetrafluoroethylene resin"), perfluoroalkoxy fluororesins, polychlorotrifluoroethylene, polyvinylidene fluoride, polydichlorodifluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-perfluoroalkoxyethylene copolymer.

[0056] In particular, from the viewpoint of wear resistance and cleanability of the electrophotographic photoreceptor, polytetrafluoroethylene and copolymer particles of tetrafluoroethylene and perfluoroalkoxyethylene are preferred. Fluororesin particles may be used individually or in combination of two or more types.

[0057] The weight-average molecular weight of the fluororesin constituting the fluororesin particles should, for example, be between 3,000 and 5,000,000. The weight-average molecular weight of fluororesins is measured by gel permeation chromatography (GPC). GPC molecular weight measurement is performed using a Tosoh HLC-8120 analyzer, a Tosoh TSKgel SuperHM-M (15 cm) column, and tetrahydrofuran as the solvent. The weight-average molecular weight is then calculated using a molecular weight calibration curve prepared from monodisperse polystyrene standard samples.

[0058] The average primary particle size of the fluororesin particles is preferably, for example, 0.05 μm or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less, and even more preferably 0.5 μm or more and 1 μm or less. The average primary particle size of fluororesin particles is measured using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by Horiba, Ltd.) at a refractive index of 1.35, with the measurement solution diluted in the same solvent as the dispersion in which the fluororesin particles were dispersed.

[0059] Examples of commercially available fluoropolymer particles include the LeBron® series (manufactured by Daikin Industries, Ltd.), the Teflon® series (manufactured by DuPont), and the Dynion series (manufactured by Sumitomo 3M).

[0060] The content of fluororesin particles is preferably 0.1% by mass or more and 40% by mass or less relative to the charge transport layer, and more preferably 1% by mass or more and 30% by mass or less. However, the amount of fluororesin particles is adjusted so that the ratio of the straight-propagating component to the light transmittance at a wavelength of 780 nm in the charge transport layer (straight-propagating component / light transmittance) falls within the above range.

[0061] Fluororesin particles may also be used in combination with alkyl fluoride copolymers as a dispersant. Examples of commercially available alkyl fluoride copolymers include GF300, GF400 (manufactured by Toagosei Co., Ltd.), Surflon series (manufactured by AGC Seikamikagaku Co., Ltd.), Futergent series (manufactured by Neos Co., Ltd.), PF series (manufactured by Kitamura Chemical Co., Ltd.), Megafac series (manufactured by DIC), and FC series (manufactured by 3M). One alkyl fluoride copolymer may be used alone, or two or more may be used in combination.

[0062] The weight-average molecular weight of the alkyl fluoride copolymer is preferably, for example, 2,000 to 250,000, and more preferably 3,000 to 150,000. The weight-average molecular weight of alkyl fluoride copolymers is measured by gel permeation chromatography (GPC), similar to the weight-average molecular weight of fluororesins.

[0063] The charge transport layer may also contain other known additives.

[0064] The formation of the charge transport layer is not particularly limited, and known formation methods can be used. For example, it can be carried out by forming a coating film of a charge transport layer forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0065] Suitable solvents for preparing the coating solution for forming the charge transport layer include common organic solvents such as aromatic hydrocarbons like benzene, toluene, xylene, and chlorobenzene; ketones like acetone and 2-butanone; halogenated aliphatic hydrocarbons like methylene chloride, chloroform, and ethylene chloride; and cyclic or linear ethers like tetrahydrofuran and ethyl ether. These solvents can be used individually or in mixtures of two or more.

[0066] Conventional methods for applying a charge transport layer forming coating solution onto a charge generation layer include blade coating, wire bar coating, spray coating, immersion coating, bead coating, air knife coating, and curtain coating.

[0067] -Characteristics of the charge transport layer- --Ratio of the forward-propagating component to the light transmittance at a wavelength of 780 nm (forward-propagating component / light transmittance)-- In the charge transport layer, the ratio of the forward-propagating component to the light transmittance at a wavelength of 780 nm (forward-propagating component / light transmittance) is 50.0% or higher. When the ratio (forward-propagating component / light transmittance) is 50.0% or higher, the photodurability of the charge transport layer improves, and the granularity of the image is improved. The ratio (straight-linked component / light transmittance) is preferably 60.0% or higher, and more preferably 70.0% or higher, from the viewpoint of improving the granularity of the image. A ratio (straight-linked component / light transmittance) of 60.0% or higher further improves the photodurability of the charge transport layer, thus making it easier to improve the granularity of the image.

[0068] The ratio of the straight-line component to the light transmittance at a wavelength of 780 nm (straight-line component / light transmittance) can be determined by measuring the collected charge transport layer (i.e., a film-like sample) using a UV-Vis spectrophotometer (Shimadzu UV-2600). Specifically, the charge transport layer is cut out from the photoreceptor to be measured to obtain the measurement sample. For the obtained sample, a reference sample (a white plate filled with barium sulfate) is set in the aperture on the reflective side of the integrating sphere apparatus, and a normal light transmission measurement is performed to measure the light transmittance at a wavelength of 780 nm. Specifically, both the directional and scattering components are detected. With the reflective side of the inlet aperture open, the light transmittance of only the scattering component at a wavelength of 780 nm is measured, and the value obtained by subtracting the scattering component from the light transmittance is defined as the directional component.

[0069] Methods for controlling the ratio of the straight-line component (straight-line component / light transmittance) within the above range include adjusting the content of fluororesin particles and the film thickness of the charge transport layer.

[0070] --Thickness of the charge transport layer and index X-- The thickness of the charge transport layer is between 40.0 μm and 65.0 μm, and the index X of short-period circumferential unevenness of the charge transport layer thickness (the maximum value among the differences between the maximum and minimum thicknesses within a 45-degree range from each of 90 points on the circumferential 360 degrees measured at 4-degree intervals) satisfies the relationship shown in equation (A) below. Equation (A): Index of short-period circumferential unevenness in the thickness of the charge transport layer X (μm) ≤ -0.02 × thickness of the charge transport layer (μm) + 2

[0071] Having a charge transport layer thickness of 40.0 μm or more improves the wear resistance of the charge transport layer, thus extending its lifespan. By keeping the charge transport layer thickness to 65.0 μm or less, the index X for short-period circumferential unevenness decreases, reducing uneven wear of the charge transport layer, making concentration unevenness less likely to occur after long-term use, and extending the lifespan.

[0072] On the other hand, when the index X of short-period circumferential unevenness in the thickness of the charge transport layer satisfies the above equation (A), uneven wear of the charge transport layer is reduced, making it less likely for concentration unevenness to occur after long-term use, and extending the lifespan. Indicator X is preferably 70 μm or less, and more preferably 65 μm or less, from the viewpoint of improving concentration uniformity after long-term use. One method for controlling index X within the above range is to adjust the film thickness formed in each step when forming a charge transport layer by multiple coatings.

[0073] The index X of short-period circumferential unevenness in the thickness of the charge transport layer can be determined by the following method. From 90 points where the film thickness is measured at 4-degree intervals around the 360-degree circumference, the difference between the maximum and minimum film thickness within a 45-degree range from each point is calculated. Then, the maximum value within that range is determined. This maximum value is defined as X, an index of short-period circumferential unevenness in the charge transport layer film thickness. The film thickness can be measured using an overcurrent film thickness gauge (FISCHERSCOPE's "GRUNDEINHEIT MMS 3AM").

[0074] Furthermore, the thickness of the charge transport layer is preferably 40.0 μm to 55.0 μm, more preferably 40.0 μm to 50.0 μm, and even more preferably 40.0 μm to 45.0 μm, from the viewpoint of improving the density unevenness after long-term use as well as the granularity of the image. When the thickness of the charge transport layer is 40.0 μm to 45.0 μm, the ratio of the straight-traveling component to the light transmittance at a wavelength of 780 nm (straight-traveling component / light transmittance) is not too low, and scattered light is also reduced, so the granularity of the image is easily improved.

[0075] The index X for short-period circumferential unevenness in the thickness of the charge transport layer is 0.40 μm or more and 0.60 μm or less, more preferably 0.50 μm or less.

[0076] Methods for adjusting the index X of short-period circumferential unevenness in the thickness of the charge transport layer to the above range include methods such as multi-layer coating of the charge transport layer.

[0077] (subbing layer) The undercoat layer is, for example, a layer containing inorganic particles and a binder resin.

[0078] As for inorganic particles, for example, powder resistance (volume resistivity) 1 × 10 2 Ω cm or more 1×10 11Examples include inorganic particles with a size of Ω·cm or less. Among these, suitable inorganic particles having the above-mentioned resistance values ​​include metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles, with zinc oxide particles being particularly preferred.

[0079] The specific surface area of ​​inorganic particles using the BET method is, for example, 10 m². 2 A value of 1g or more is preferable. The volume-average particle size of the inorganic particles is preferably between 50 nm and 2000 nm (preferably between 60 nm and 1000 nm).

[0080] If the undercoat contains inorganic particles, the inorganic particle content is preferably 60% to 95% by mass, more preferably 70% to 95% by mass, and even more preferably 80% to 90% by mass, relative to the total undercoat.

[0081] The inorganic particles may be surface-treated. Two or more types of inorganic particles with different surface treatments or particle sizes may be mixed and used.

[0082] Examples of surface treatment agents include silane coupling agents, titanate-based coupling agents, aluminum-based coupling agents, and surfactants. Silane coupling agents are particularly preferred, and silane coupling agents having an amino group are more preferred.

[0083] Examples of silane coupling agents having an amino group include, but are not limited to, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane.

[0084] Silane coupling agents may be used in combination of two or more types. For example, a silane coupling agent having an amino group may be used in combination with another silane coupling agent. Examples of other silane coupling agents include, but are not limited to, vinyltrimethoxysilane, 3-methacrylateoxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

[0085] The surface treatment method using the surface treatment agent may be any known method, and may be either a dry or wet method.

[0086] The amount of surface treatment agent applied is preferably, for example, 0.5% by mass or more and 10% by mass or less relative to the inorganic particles.

[0087] In this case, it is preferable for the underlayer to contain electron-accepting compounds (acceptor compounds) along with inorganic particles, from the viewpoint of improving the long-term stability of electrical properties and carrier blocking ability.

[0088] Examples of electron-accepting compounds include electron-transporting substances such as compounds having anthraquinone structures; quinone compounds such as chloranil and bromoanil; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone; oxadiazole compounds such as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; xanthone compounds; thiophene compounds; diphenoquinone compounds such as 3,3',5,5'-tetra-t-butyldiphenoquinone; and benzophenone compounds. In particular, compounds having an anthraquinone structure are preferred as electron-accepting compounds. Examples of compounds having an anthraquinone structure include hydroxyanthraquinone compounds, aminoanthraquinone compounds, and aminohydroxyanthraquinone compounds. Specifically, examples of preferred compounds include anthraquinone, alizarin, quinizalin, anthralphine, purpurin, and their derivatives.

[0089] The electron-accepting compound may be dispersed in the underlayer together with inorganic particles, or it may be present attached to the surface of the inorganic particles.

[0090] Methods for attaching electron-accepting compounds to the surface of inorganic particles include, for example, dry methods or wet methods.

[0091] The dry method involves, for example, adding an electron-accepting compound, either directly or dissolved in an organic solvent, dropwise while stirring inorganic particles with a mixer that has a high shear force, or spraying it with dry air or nitrogen gas, to adhere the electron-accepting compound to the surface of the inorganic particles. When adding or spraying the electron-accepting compound, it is preferable to do so at a temperature below the boiling point of the solvent. After adding or spraying the electron-accepting compound, further baking at 100°C or higher may be performed. The baking temperature and time are not particularly limited as long as electrophotographic characteristics can be obtained.

[0092] The wet method involves dispersing inorganic particles in a solvent using, for example, a stirrer, ultrasonic disperser, sand mill, attritor, or ball mill, while adding an electron-accepting compound. After stirring or dispersion, the solvent is removed, and the electron-accepting compound adheres to the surface of the inorganic particles. Solvent removal methods include, for example, filtration or distillation. After solvent removal, further baking at 100°C or higher may be performed. The baking temperature and time are not particularly limited as long as electrophotographic characteristics can be obtained. In the wet method, the water content of the inorganic particles may be removed before adding the electron-accepting compound. Examples of this include removing water while stirring and heating in the solvent, or removing water by azeotrope with the solvent.

[0093] The electron-accepting compound may be applied before or after surface treatment with a surface treatment agent to the inorganic particles, or it may be applied simultaneously with the surface treatment with the surface treatment agent.

[0094] The content of the electron-accepting compound is preferably, for example, 0.01% by mass or more and 20% by mass or less relative to the inorganic particles, and more preferably 0.01% by mass or more and 10% by mass or less.

[0095] Examples of known polymer compounds used as the binder resin for the undercoat include acetal resin (e.g., polyvinyl butyral), polyvinyl alcohol resin, polyvinyl acetal resin, casein resin, polyamide resin, cellulose resin, gelatin, polyurethane resin, polyester resin, unsaturated polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic anhydride resin, silicone resin, silicone-alkyd resin, urea resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, alkyd resin, epoxy resin, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. Examples of binder resins used in the undercoat include charge-transporting resins having charge-transporting groups, conductive resins (e.g., polyaniline), and the like.

[0096] Among these, a resin insoluble in the coating solvent of the upper layer is preferred as the binder resin used for the undercoat layer. In particular, a resin obtained by the reaction of a curing agent with at least one resin selected from the group consisting of thermosetting resins such as urea resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, unsaturated polyester resin, alkyd resin, and epoxy resin is preferred. When using two or more of these binder resins in combination, the mixing ratio is set as needed.

[0097] The undercoat may contain various additives to improve electrical properties, environmental stability, and image quality. Examples of known additives include electron-transporting pigments such as polycyclic condensation and azo pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. As mentioned above, silane coupling agents are used for surface treatment of inorganic particles, but they may also be added to the undercoat as additives.

[0098] Examples of silane coupling agents used as additives include vinyltrimethoxysilane, 3-methacrylateoxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

[0099] Examples of zirconium chelate compounds include zirconium butoxide, ethyl zirconium acetate, zirconium triethanolamine, acetylacetonate zirconium butoxide, ethyl acetate zirconium butoxide, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, methacrylate zirconium butoxide, stearate zirconium butoxide, and isostearate zirconium butoxide.

[0100] Examples of titanium chelate compounds include tetraisopropyl titanate, tetran-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetonate, polytitanium acetylacetonate, titanium octylene glycolate, titanium lactate ammonium salt, titanium lactate, titanium lactate ethyl ester, titanium triethanolamine, and polyhydroxytitanium stearate.

[0101] Examples of aluminum chelating compounds include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

[0102] These additives may be used individually or as a mixture or polycondensate of multiple compounds.

[0103] The underlayer should ideally have a Vickers hardness of 35 or higher. The surface roughness (ten-point average roughness) of the undercoat layer should be adjusted to between 1 / (4n) (where n is the refractive index of the upper layer) and 1 / 2 of the exposure laser wavelength λ used, in order to suppress moiré patterns. Resin particles may be added to the undercoat to adjust the surface roughness. Examples of resin particles include silicone resin particles and cross-linked polymethyl methacrylate resin particles. The surface of the undercoat may also be polished to adjust the surface roughness. Polishing methods include buffing, sandblasting, wet honing, and grinding.

[0104] The formation of the undercoat is not particularly limited, and known formation methods can be used. For example, it can be carried out by forming a coating film of an undercoat-forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0105] Solvents for preparing the coating solution for forming the undercoat include known organic solvents such as alcohol-based solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone-based solvents, ketone alcohol-based solvents, ether-based solvents, and ester-based solvents. Specific examples of these solvents include common organic solvents such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene.

[0106] Known methods for dispersing inorganic particles when preparing a coating solution for forming an undercoat include, for example, roll mills, ball mills, vibrating ball mills, attritors, sand mills, colloid mills, and paint shakers.

[0107] Conventional methods for applying the undercoating solution onto a conductive substrate include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0108] The thickness of the undercoat layer is preferably set to a range of 15 μm or more, and more preferably 20 μm to 50 μm.

[0109] (Middle class) Although not shown in the diagram, an intermediate layer may be further provided between the undercoat layer and the photosensitive layer. The intermediate layer is, for example, a layer containing a resin. Examples of resins used in the intermediate layer include polymer compounds such as acetal resin (e.g., polyvinyl butyral), polyvinyl alcohol resin, polyvinyl acetal resin, casein resin, polyamide resin, cellulose resin, gelatin, polyurethane resin, polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic anhydride resin, silicone resin, silicone-alkyd resin, phenol-formaldehyde resin, and melamine resin. The intermediate layer may contain an organometallic compound. Examples of organometallic compounds used in the intermediate layer include those containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon. The compounds used in these intermediate layers may be used individually, as a mixture of multiple compounds, or as polycondensates.

[0110] Among these, the intermediate layer is preferably a layer containing an organometallic compound that contains zirconium atoms or silicon atoms.

[0111] The formation of the intermediate layer is not particularly limited, and known formation methods can be used. For example, it can be carried out by forming a coating film of an intermediate layer-forming coating solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary. Conventional methods such as immersion coating, push-up coating, wire bar coating, spray coating, blade coating, air knife coating, and curtain coating are used to form the intermediate layer.

[0112] The thickness of the intermediate layer is preferably set in the range of 0.1 μm to 3 μm. The intermediate layer may also be used as a base layer.

[0113] <Image forming apparatus (and process cartridge)> The image forming apparatus of this disclosure comprises an electrophotographic photoreceptor; a charging device having a charging member, which charges the surface of the electrophotographic photoreceptor by applying a voltage obtained by superimposing a DC voltage on the charging member; an electrostatic latent image forming device that forms an electrostatic latent image on the surface of the charged electrophotographic photoreceptor; a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image; and a transfer device that transfers the toner image to the surface of a recording medium. Furthermore, the electrophotographic photoreceptor is to be the photoreceptor described above.

[0114] The image forming apparatus of this disclosure includes known image forming apparatuses such as: an apparatus equipped with a fixing device for fixing a toner image transferred to the surface of a recording medium; a direct transfer apparatus for directly transferring a toner image formed on the surface of an electrophotographic photoreceptor to a recording medium; an intermediate transfer apparatus for first transferring a toner image formed on the surface of an electrophotographic photoreceptor to the surface of an intermediate transfer body, and secondarily transferring the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium; an apparatus equipped with a cleaning device for cleaning the surface of the electrophotographic photoreceptor after the transfer of the toner image and before charging; an apparatus equipped with a static elimination device for irradiating the surface of the electrophotographic photoreceptor with static elimination light to eliminate static charge after the transfer of the toner image and before charging; and an apparatus equipped with an electrophotographic photoreceptor heating member for raising the temperature of the electrophotographic photoreceptor and reducing the relative temperature.

[0115] In the case of an intermediate transfer method apparatus, the transfer apparatus may be configured to include, for example, an intermediate transfer body on which a toner image is transferred; a primary transfer apparatus that first transfers the toner image formed on the surface of an electrophotographic photoreceptor to the surface of the intermediate transfer body; and a secondary transfer apparatus that secondarily transfers the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium.

[0116] The image forming apparatus disclosed herein may be either a dry developing type image forming apparatus or a wet developing type image forming apparatus (a developing method using a liquid developer).

[0117] In the image forming apparatus of this disclosure, for example, the portion comprising an electrophotographic photoreceptor may be a cartridge structure (process cartridge) that can be attached to and detached from the image forming apparatus. As the process cartridge, for example, a process cartridge comprising the electrophotographic photoreceptor of this disclosure is preferably used.

[0118] The process cartridge of the present disclosure preferably comprises an electrophotographic photoreceptor of the present disclosure and a charging device having a charging member, which charges the surface of the electrophotographic photoreceptor by applying a voltage obtained by superimposing a DC voltage on the charging member. The process cartridge is detachable from an image forming apparatus.

[0119] The following is an example of an image forming apparatus according to the disclosure, but is not limited to this example. The main parts shown in the figure will be described, and the descriptions of other parts will be omitted.

[0120] Figure 2 is a schematic diagram showing an example of an image forming apparatus according to the present disclosure. As shown in Figure 2, the image forming apparatus 100 of this disclosure comprises a process cartridge 300 equipped with an electrophotographic photoreceptor 7, an exposure device 9 (an example of an electrostatic latent image forming apparatus), a transfer device 40 (a primary transfer device), and an intermediate transfer body 50. In the image forming apparatus 100, the exposure device 9 is positioned to expose the electrophotographic photoreceptor 7 from the opening of the process cartridge 300, and the transfer device 40 is positioned facing the electrophotographic photoreceptor 7 via the intermediate transfer body 50, with a portion of the intermediate transfer body 50 in contact with the electrophotographic photoreceptor 7. Although not shown, it also includes a secondary transfer device that transfers the toner image transferred to the intermediate transfer body 50 to a recording medium (e.g., paper). The intermediate transfer body 50, the transfer device 40 (primary transfer device), and the secondary transfer device (not shown) are examples of transfer devices.

[0121] In Figure 2, the process cartridge 300 integrally supports an electrophotographic photoreceptor 7, a charging device 8 (an example of a charging device), a developing device 11 (an example of a developing device), and a cleaning device 13 (an example of a cleaning device) within a housing. The cleaning device 13 has a cleaning blade (an example of a cleaning member) 131, which is positioned to contact the surface of the electrophotographic photoreceptor 7. The cleaning member may be a conductive or insulating fibrous member, rather than a cleaning blade 131, and may be used alone or in combination with the cleaning blade 131.

[0122] Figure 2 shows an example of an image forming apparatus that includes a fibrous member 132 (roll-shaped) for supplying lubricant 14 to the surface of the electrophotographic photoreceptor 7, and a fibrous member 133 (flat brush-shaped) for assisting cleaning. These can be arranged as needed.

[0123] The following describes the various components of the image forming apparatus disclosed herein.

[0124] -Charging device- The charging device 8 includes a charging member, and the charging device applies a voltage obtained by superimposing a DC voltage on an AC voltage to the charging member to charge the surface of the electrophotographic photoreceptor. By adopting a charging method in which the photoreceptor is charged by superimposing a DC voltage on an AC voltage (hereinafter also referred to as the "superimposed voltage application method"), uniformity of charging can be easily obtained. As the charging device 8, for example, a contact-type charger is used that uses conductive or semiconductive charging rollers, charging brushes, charging films, charging rubber blades, charging tubes, etc., as charging components.

[0125] The charging conditions are as follows: The peak-to-peak voltage of the AC voltage is preferably 400V to 3000V, more preferably 800V to 2800V, and even more preferably 1200V to 2800V. The frequency of the AC voltage is preferably 50Hz to 20000Hz, more preferably 100Hz to 5000Hz. The DC voltage superimposed on the AC voltage is preferably positive or negative, between 50V and 2000V, and more preferably positive or negative, between 100V and 1500V.

[0126] -Exposure equipment- Examples of exposure devices 9 include optical equipment that exposes the surface of an electrophotographic photoreceptor 7 to a predetermined image using light such as semiconductor laser light, LED light, or liquid crystal shutter light. The wavelength of the light source is within the spectral sensitivity range of the electrophotographic photoreceptor. As for the wavelength of the semiconductor laser, near-infrared lasers with an oscillation wavelength of around 780 nm are the mainstream. However, the wavelength is not limited to this, and lasers with oscillation wavelengths in the 600 nm range or blue lasers with oscillation wavelengths between 400 nm and 450 nm may also be used. Furthermore, for color image formation, surface-emitting laser light sources capable of outputting multiple beams are also effective.

[0127] -Developing equipment- Examples of developing devices 11 include general developing devices that develop by contacting or not contacting the developing agent. There are no particular restrictions on the developing device 11 as long as it has the above-described functions, and it can be selected according to the purpose. For example, known developing devices that have the function of applying a one-component or two-component developing agent to the electrophotographic photoreceptor 7 using a brush, roller, etc. Among these, those that use a developing roller that holds the developing agent on its surface are preferred.

[0128] The developer used in the developing device 11 may be a one-component developer consisting of toner alone, or a two-component developer containing toner and a carrier. Furthermore, the developer may be magnetic or non-magnetic. Known developers can be used.

[0129] -Cleaning device- The cleaning device 13 uses a cleaning blade system equipped with a cleaning blade 131. In addition to the cleaning blade system, a fur brush cleaning system or a developing and cleaning system may also be used.

[0130] -Transfer device- Examples of the transfer device 40 include contact-type transfer chargers using belts, rollers, films, rubber blades, etc., and transfer chargers that are known themselves, such as scorotron transfer chargers and corotron transfer chargers that utilize corona discharge.

[0131] -Intermediate Transcript- As the intermediate transfer body 50, a belt-shaped material (intermediate transfer belt) containing semiconducting polyimide, polyamide-imide, polycarbonate, polyarylate, polyester, rubber, etc. is used. In addition to the belt shape, a drum-shaped intermediate transfer body may also be used.

[0132] Figure 3 is a schematic diagram showing another example of an image forming apparatus according to the present disclosure. The image forming apparatus 120 shown in Figure 3 is a tandem-type multi-color image forming apparatus equipped with four process cartridges 300. In the image forming apparatus 120, the four process cartridges 300 are arranged in parallel on the intermediate transfer body 50, and one electrophotographic photoreceptor is used for each color. The image forming apparatus 120 has the same configuration as the image forming apparatus 100, except that it is a tandem type. [Examples]

[0133] The embodiments of the invention will be described in detail below with reference to examples, but the embodiments of the invention are not limited to these examples. In the following description, "parts" and "%" are based on mass unless otherwise specified.

[0134] <Example 1> -Preparation of conductive substrate- An aluminum cylindrical tube was prepared as the conductive substrate.

[0135] -Formation of the lower layer- Zinc oxide (average particle size 70 nm, specific surface area 15 m²) 2 100 parts of (Teika Co., Ltd.) were mixed with 500 parts of toluene and stirred. 1.3 parts of a silane coupling agent (product name: KBM603, Shin-Etsu Chemical Co., Ltd., N-2-(aminoethyl)-3-aminopropyltrimethoxysilane) were added and the mixture was stirred for 2 hours. The toluene was then removed by distillation under reduced pressure, and the mixture was baked at 120°C for 3 hours to obtain zinc oxide surface-treated with the silane coupling agent.

[0136] 110 parts of surface-treated zinc oxide was mixed with 500 parts of tetrahydrofuran by stirring. 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 solids were then filtered off by vacuum filtration, and the mixture was dried under reduced pressure at 60°C to obtain alizarin-treated zinc oxide.

[0137] A solution was obtained by dissolving 60 parts of alizarin-modified zinc oxide, 13.5 parts of a curing agent (blocked isocyanate, trade name: Sumijule 3175, manufactured by Sumitomo Bayern Urethanes), and 15 parts of butyral resin (trade name: Esrec BM-1, manufactured by Sekisui Chemical Co., Ltd.) in 68 parts of methyl ethyl ketone. 100 parts of this solution were mixed with 5 parts of methyl ethyl ketone, and the mixture was dispersed for 2 hours using a sand mill with 1 mmφ glass beads to obtain a dispersion. To the dispersion, 0.005 parts of dioctyl tin dilaurate as a catalyst and 4 parts of silicone resin particles (trade name: Tospar 145, manufactured by Momentive Performance Materials) were added to obtain a coating solution for forming an undercoat. The undercoat solution was applied to the outer surface of a conductive substrate by immersion coating, and dried and cured at 170°C for 40 minutes to form an undercoat with a film thickness of 25 μm.

[0138] -Formation of a charge generation layer- A mixture was prepared consisting of 15 parts of hydroxygallium phthalocyanine (having diffraction peaks at Bragg angles (2θ±0.2°) of at least 7.5°, 9.9°, 12.5°, 16.3°, 18.6°, 25.1°, and 28.3° in its X-ray diffraction spectrum using CuKα characteristic X-rays), 10 parts of vinyl chloride / vinyl acetate copolymer resin (trade name: VMCH, manufactured by Nippon Unicar Co., Ltd.) as a binder resin, and 200 parts of n-butyl acetate. The mixture was dispersed for 4 hours using glass beads with a diameter of 1 mm in a sand mill. 175 parts of n-butyl acetate and 180 parts of methyl ethyl ketone were added to the dispersion and stirred to obtain a coating solution for forming the charge generation layer. This coating solution was immersion coated onto a conductive substrate and dried at room temperature to form a charge generation layer with a thickness of 0.2 μm.

[0139] -Formation of a charge transport layer- A mixed solvent consisting of 270 parts tetrahydrofuran and 30 parts toluene was used to dissolve 60 parts of polycarbonate resin (1) (viscosity-average molecular weight 40,000, the values ​​in the structural formula below are molar ratios) and 40 parts of the charge transport material CTM-1. PTFE particles were added in an amount equal to 5.5% by mass relative to the solid content of the coating solution to obtain a coating solution for forming a charge transport layer. This coating solution was immersed and applied onto a charge generating layer to form a charge transport layer with a thickness of 42.5 μm. Specifically, a charge transport layer was formed by two immersion coatings: the first to a thickness of 20 μm and the second to a thickness of 22.5 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.63 μm. This resulted in obtaining a photoreceptor for electrophotography. The ratio of the straight-line component to the light transmittance at a wavelength of 780 nm in the charge transport layer (straight-line component / light transmittance) and the index X of short-period circumferential unevenness of the film thickness were measured and calculated using the methods described above.

[0140] [ka]

[0141] -evaluation- The resulting electrophotographic photoreceptor was mounted as the photoreceptor in an image forming apparatus (a modified DocuColor-7171P, manufactured by Fujifilm Business Innovation Co., Ltd.). This image forming apparatus has a charging roll and employs a contact-type charging device that charges the surface of the photoreceptor by applying a voltage to the charging roll that is a DC voltage of 900V superimposed with an AC voltage of 2.1kV peak voltage and 2,800Hz wavenumber. Then, the following evaluations were performed using this image forming apparatus.

[0142] (Image granularity) Using the image forming apparatus described above, halftone images with cyan color and image densities ranging from 5% to 100% in 5% increments were formed on A3-sized plain paper under conditions of 23°C and 55% relative humidity. The graininess of the resulting images was visually evaluated according to the following criteria. The results are shown in Table 1. A: The image does not appear grainy. B: A slight graininess can be felt in low-density images. C: A slight graininess can be felt in low-density and medium-density images. D: A grainy texture can be perceived across the range from low-density to high-density images.

[0143] (Uneven concentration) Using the image forming apparatus described above, 260,000 halftone images with an image density of 20% were printed on A4 paper under low temperature and low humidity conditions (10°C, 15%RH). Then, one halftone image with an image density of 60% was printed on A4 paper. Finally, the level of image quality unevenness that occurred on the single printed halftone image with an image density of 60% was evaluated according to the following criteria. The results are shown in Table 1. A: No unevenness in concentration has occurred. B: The unevenness in concentration is slight and at an acceptable level. C: Although there are variations in concentration, it is at an acceptable level. D: The unevenness in concentration is very noticeable and unacceptable.

[0144] <Example 2> An electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that the amount of PTFE particles added to the coating solution for forming the charge transport layer was 6.5% by mass. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.63 μm.

[0145] <Example 3> A charge transport layer with a thickness of 64.0 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that three immersion coatings were performed: the first time to 21.3 μm, the second time to 18.0 μm, and the third time to 24.7 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.70 μm.

[0146] <Example 4> A charge transport layer with a thickness of 40.5 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that two immersion coatings were performed, with the first being 20 μm and the second being 20.5 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.50 μm.

[0147] <Example 5> A charge transport layer with a thickness of 42.5 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that two immersion coatings were performed, one to a thickness of 10 μm and the other to a thickness of 32.5 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 1.10 μm.

[0148] <Example 6> A charge transport layer with a thickness of 42.5 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that two immersion coatings were performed, one to a thickness of 14 μm and the other to a thickness of 28.5 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.85 μm.

[0149] <Comparative Example 1> The amount of PTFE particles added to the coating solution for forming the charge transport layer was set to 7.3% by mass, and a charge transport layer with a thickness of 66.0 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that three immersion coatings were performed: the first time to 20 μm, the second time to 20 μm, and the third time to 26 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.80 μm.

[0150] <Comparative Example 2> A charge transport layer with a thickness of 38.5 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that two immersion coatings were performed, with the first being 20 μm and the second being 18.5 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.46 μm.

[0151] <Comparative Example 3> The amount of PTFE particles added to the coating solution for forming the charge transport layer was set to 7.3% by mass, and a charge transport layer with a thickness of 42.5 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that two immersion coatings were performed, with the first being 20 μm and the second being 22.5 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.63 μm.

[0152] <Comparative Example 4> A charge transport layer with a thickness of 66.0 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that three immersion coatings were performed: the first time to 22 μm, the second time to 22 μm, and the third time to 22 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.65 μm.

[0153] <Comparative Example 5> A charge transport layer with a thickness of 38.5 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that two immersion coatings were performed, with the first being 20 μm and the second being 18.5 μm. The index X for short-period circumferential unevenness of the charge transport layer thickness was 0.46 μm.

[0154] <Comparative Example 6> A charge transport layer with a thickness of 42.5 μm was formed. Specifically, an electrophotographic photoreceptor was obtained and evaluated in the same manner as in Example 1, except that a 42.5 μm immersion coating was performed in a single step. The index X for short-period circumferential unevenness of the charge transport layer thickness was 1.45 μm.

[0155] [Table 1]

[0156] As shown in Table 1, the electrophotographic photoreceptor of this embodiment shows improvements in image granularity and density unevenness after long-term use. Furthermore, in this embodiment, it is possible to extend the lifespan of the electrophotographic photoreceptor by increasing the thickness of the charge generation layer while simultaneously improving both the granularity of the image and the density unevenness after long-term use.

[0157] The electrophotographic photoreceptor, process cartridge, and image forming apparatus of this disclosure include the following embodiments:

[0158] (((1))) A conductive substrate, A charge generation layer disposed on the conductive substrate, A charge transport layer is disposed on the charge generation layer and contains fluororesin particles, wherein the ratio of the straight-traveling component to the light transmittance at a wavelength of 780 nm (straight-traveling component / light transmittance) is 50.0% or more. Equipped with, The thickness of the charge transport layer is 40.0 μm or more and 65.0 μm or less, and the index X of the short-period circumferential unevenness of the thickness of the charge transport layer (the maximum value among the differences between the maximum and minimum values ​​of the thickness within a 45-degree range starting from each of 90 points of thickness measured at 4-degree intervals around 360 degrees in the circumferential direction) satisfies the relationship of equation (A) below. Electrophotographic photoreceptor. Equation (A): Index of short-period circumferential unevenness in the thickness of the charge transport layer X (μm) ≤ -0.02 × thickness of the charge transport layer (μm) + 2 (((2))) The electrophotographic photoreceptor according to (((1))), wherein the index X of short-period circumferential unevenness in the thickness of the charge transport layer is 0.70 μm or less. (((3))) The electrophotographic photoreceptor according to (((1))) or (((2))), wherein the ratio of the straight-propagating component to the light transmittance of the charge transport layer at a wavelength of 780 nm (straight-propagating component / light transmittance) is 60.0% or more. (((4))) An electrophotographic photoreceptor according to any one of (((1))) to (((3))), wherein the thickness of the charge transport layer is 40.0 μm or more and 45.0 μm or less. (((5))) An electrophotographic photoreceptor described in any one of (((1))) to (((4))), A charging device having a charging member, which charges the surface of the electrophotographic photoreceptor by applying a voltage obtained by superimposing a DC voltage on the charging member, Equipped with, A process cartridge that is attached to and detached from an image forming apparatus. (((6))) An electrophotographic photoreceptor described in any one of (((1))) to (((4))), A charging device having a charging member, which charges the surface of the electrophotographic photoreceptor by applying a voltage obtained by superimposing a DC voltage on the charging member, An electrostatic latent image forming apparatus for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing apparatus that develops an electrostatic latent image formed on the surface of an electrophotographic photoreceptor using a developer containing toner to form a toner image, A transfer device for transferring the toner image onto the surface of a recording medium, An image forming apparatus comprising:

[0159] According to (((1))), an electrophotographic photoreceptor comprising a conductive substrate, a charge generation layer, and a charge transport layer containing fluororesin particles and having a film thickness of 40.0 μm to 65.0 μm is provided. Compared to the case where the ratio of the straight-line component (straight-line component / light transmittance) is less than 50.0%, or where the index X of short-period circumferential unevenness of the film thickness of the charge transport layer does not satisfy equation (A), an electrophotographic photoreceptor is provided that can extend its life by improving both the granularity of the image and the density unevenness after long-term use, even when the charge generation layer is made thicker. According to (((2))), compared to the case where the index X of short-period circumferential unevenness of the charge transport layer thickness is greater than 0.70 μm, an electrophotographic photoreceptor is provided that can extend its lifespan by improving both the granularity of the image and the density unevenness after long-term use, even when the charge generation layer is made thicker. According to (((3))), compared to the case where the ratio of the straight-linking component to the light transmittance of the charge transport layer at a wavelength of 780 nm (straight-linking component / light transmittance) is less than 60.0%, even if the charge generation layer is made thicker, an electrophotographic photoreceptor is provided that can achieve both improvement in image granularity and density uniformity after long-term use, and extend its lifespan. According to (((4))), compared to cases where the thickness of the charge transport layer is less than 40.0 μm or greater than 45.0 μm, an electrophotographic photoreceptor is provided that can extend its lifespan while simultaneously improving both the granularity of the image and the density unevenness after long-term use, even when the charge generation layer is made thicker. According to (((5))) or (((6))), an electrophotographic photoreceptor comprising a conductive substrate, a charge generation layer, and a charge transport layer containing fluororesin particles and having a film thickness of 40.0 μm or more and 65.0 μm or less is provided. Compared to an electrophotographic photoreceptor in which the ratio of the straight-line component (straight-line component / light transmittance) is less than 50.0%, or the index X of short-period circumferential unevenness of the film thickness of the charge transport layer does not satisfy formula (A), an electrophotographic photoreceptor is provided that, even with a thicker charge generation layer, can achieve improvements in both image granularity and density unevenness after long-term use, thereby extending the lifespan. [Explanation of Symbols]

[0160] 1 conductive substrate, 2 subbing layer, 3 charge generation layer, 4 charge transport layer, 5 photosensitive layer, 10A photoreceptor

[0161] 7 Electrophotographic photoreceptor, 8 Charging device, 9 Exposure device, 11 Developing device, 13 Cleaning device, 14 Lubricant, 40 Transfer device, 50 Intermediate transfer body, 100 Image forming device, 120 Image forming device, 131 Cleaning blade, 132 Fibrous material (roll type), 133 Fibrous material (flat brush type), 300 Process cartridge

Claims

1. A conductive substrate, A charge generation layer disposed on the conductive substrate, A charge transport layer is disposed on the charge generation layer and contains fluororesin particles, wherein the ratio of the straight-propagating component to the light transmittance at a wavelength of 780 nm (straight-propagating component / light transmittance) is 50.0% or more. Equipped with, The thickness of the charge transport layer is 40.0 μm or more and 65.0 μm or less, and the index X of short-period circumferential unevenness of the thickness of the charge transport layer (the maximum value among the differences between the maximum and minimum values ​​of the thickness within a 45-degree range starting from each of 90 points of thickness measured at 4-degree intervals in the circumferential direction of 360 degrees) satisfies the relationship of the following formula (A). Electrophotographic photoreceptor. Equation (A): Index of short-period circumferential unevenness in the thickness of the charge transport layer X (μm) ≤ -0.02 × thickness of the charge transport layer (μm) + 2

2. The electrophotographic photoreceptor according to claim 1, wherein the index X of short-period circumferential unevenness in the thickness of the charge transport layer is 0.70 μm or less.

3. The electrophotographic photoreceptor according to claim 1, wherein the ratio of the straight-propagating component to the light transmittance at a wavelength of 780 nm of the charge transport layer (straight-propagating component / light transmittance) is 60.0% or more.

4. The electrophotographic photoreceptor according to claim 1, wherein the thickness of the charge transport layer is 40.0 μm or more and 45.0 μm or less.

5. An electrophotographic photoreceptor according to any one of claims 1 to 4, A charging device having a charging member, which charges the surface of the electrophotographic photoreceptor by applying a voltage obtained by superimposing a DC voltage on the charging member, Equipped with, A process cartridge that is attached to and detached from an image forming apparatus.

6. An electrophotographic photoreceptor according to any one of claims 1 to 4, A charging device having a charging member, which charges the surface of the electrophotographic photoreceptor by applying a voltage obtained by superimposing a DC voltage on the charging member, An electrostatic latent image forming apparatus for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing apparatus that develops an electrostatic latent image formed on the surface of an electrophotographic photoreceptor using a developer containing toner to form a toner image, A transfer device for transferring the toner image onto the surface of a recording medium, An image forming apparatus comprising:

Images