Electrophotographic photoreceptor, its manufacturing method and electrophotographic device

Abstract

To provide: an electrophotographic photoreceptor that has sufficiently high sensitivity and excellent potential stability during repeated printing in various environments, and does not cause problems, such as deterioration of gradation or generation of memory images, especially when applied to monochrome high-speed printers and small medium-speed tandem color printers; a method of manufacturing the same; and an electrophotographic device.SOLUTION: A positively charged electrophotographic photoreceptor includes a conductive substrate 1, and a photosensitive layer formed on the conductive substrate. The photosensitive layer contains electron transport materials, and at least one of the electron transport materials contains an azoquinone derivative having a structure represented by general formula (ET1) in the figure.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic photoreceptor (hereinafter also simply referred to as "photoreceptor") used in electrophotographic printers, copiers, fax machines, etc., a method for manufacturing the same, and an electrophotographic apparatus. [Background technology]

[0002] The basic structure of an electrophotographic photoreceptor is a photoconductive layer placed on a conductive substrate. In recent years, research and development of organic electrophotographic photoreceptors, which use organic compounds as functional components responsible for generating and transporting electric charges, has been actively pursued due to their advantages such as material versatility, high productivity, and safety, and their application to copiers, printers, and other devices is progressing.

[0003] In general, photoreceptors are required to have the functions of maintaining a surface charge in a dark place, generating a charge by receiving light, and transporting the generated charge. A photosensitive layer fulfills these functions. Photoreceptors are classified into so-called single-layer photoreceptors and multilayer (function-separated) photoreceptors depending on the form of the photosensitive layer. A single-layer photoreceptor has a single photosensitive layer that combines a charge generation function and a charge transport function. A multilayer photoreceptor has a photosensitive layer in which a charge generation layer and a charge transport layer are laminated. The charge generation layer is primarily responsible for generating a charge upon receiving light. The charge transport layer is responsible for maintaining a surface charge in a dark place and transporting the charge generated in the charge generation layer upon receiving light.

[0004] Photoreceptors are classified into positively charged photoreceptors, in which the surface of the photoreceptor is positively charged, and negatively charged photoreceptors, in which the surface is negatively charged. In the positively charged photoreceptor, an electron transport material having electron transport ability is used as the charge transport material constituting the photosensitive layer. Azoquinone derivatives having one chlorine atom at the para-position as a substituent are widely used as such electron transport materials (see Patent Documents 1 to 3).

[0005] However, when an azoquinone derivative having the above-mentioned specific structure is used, the potential stability tends to be insufficient, particularly during repeated use in a low-temperature, low-humidity environment, resulting in ghost images, thickened characters, and other phenomena, making it difficult to obtain stable, good images.

[0006] To solve this problem, it has been proposed to use an azoquinone derivative having the above specific structure in combination with other electron transport materials (see Patent Document 4).

[0007] Furthermore, as a prior art relating to the combined use of electron transport materials in a photoreceptor, for example, there is a technique described in Patent Document 5.

[0008] On the other hand, high-speed monochrome printers and small, medium-speed tandem color printers require highly sensitive photoconductors, and prior art related to photoconductors applicable to high-quality monochrome high-speed machines and tandem color machines (for example, 40 ppm or higher on A4 paper) includes, for example, the technology described in Patent Document 6. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-199979 [Patent Document 2] International Publication No. 2009 / 104571 [Patent Document 3] International Publication No. 2019 / 159342 [Patent Document 4] International Publication No. 2019 / 142342 [Patent Document 5] Japanese Patent Application Publication No. 2018-105972 [Patent Document 6] International Publication No. 2018 / 154740 Summary of the Invention [Problem to be solved by the invention]

[0010] However, even when the azoquinone derivative having the above specific structure is mixed with other electron transport materials, it is not possible to achieve a sufficiently high sensitivity property while obtaining a relatively good repeatability stability, and therefore, when printing is performed repeatedly under various environments, sufficient potential stability is not obtained, and problems such as deterioration of gradation and generation of memory images may occur.

[0011] Therefore, an object of the present invention is to provide an electrophotographic photoreceptor, a manufacturing method thereof, and an electrophotographic apparatus which have sufficiently high sensitivity, excellent potential stability during repeated printing under various environments, and do not cause problems such as deterioration of gradation and generation of memory images, particularly when applied to monochrome high-speed printers and small medium-speed tandem color printers. [Means for solving the problem]

[0012] As a result of extensive investigations, the present inventors have found that the above-mentioned problems can be solved by using, as an electron transport material, an azoquinone derivative having a specific structure different from those conventionally used, and have thus completed the present invention.

[0013] That is, a first aspect of the present invention is a conductive substrate; a photosensitive layer provided on the conductive substrate, the photosensitive layer contains an electron transport material, and the electron transport material contains an azoquinone derivative having a structure represented by the following general formula (ET1) and a naphthalenetetracarboxylic acid diimide compound having a structure represented by the following general formula (ET2), JPEG0007767805000001.jpg28153(In formula (ET1), R 1 and R 2 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent, or a halogenated alkyl group. R 3represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent, or a halogenated alkyl group. 4 ~R 8 At least two of the R represent chlorine atoms, and the remaining R other than the one representing a chlorine atom 4 ~R 8 are the same or different and represent a hydrogen atom, a halogen atom other than a chlorine atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group which may have a substituent, an aralkyl group which may have a substituent, a phenoxy group which may have a substituent, a halogenated alkyl group, a cyano group, or a nitro group. The substituent represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, a cyano group, an amino group, a nitro group, or a halogenated alkyl group. JPEG0007767805000002.jpg28153(In formula (ET2), R 11 and R 12 may be the same or different and represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkylene group, an alkoxy group, an alkyl ester group, a phenyl group which may have a substituent, a naphthyl group which may have a substituent, or a halogen atom; R 11 and R 12 may be bonded to each other to form an aromatic ring which may have a substituent. The azoquinone derivative having a structure represented by the general formula (ET1) is represented by the following structural formula (ET1-4) or (ET1-5): This is an electrophotographic photoreceptor represented by JPEG0007767805000003.jpg59153.

[0014] Among the naphthalenetetracarboxylic acid diimide compounds having the structure represented by the general formula (ET2), those having the following structural formula (ET2-4): The one represented by TIFF0007767805000004.tif34142 is preferred.

[0015] The solubility S of the azoquinone derivative having the structure represented by the general formula (ET1) ETM (THF) (the mass (g) of tetrahydrofuran required to dissolve 1 g of the azoquinone derivative) is calculated by the following formula: S ETM (THF)≦2.0 It is preferable to satisfy the following.

[0019] The photosensitive layer may be a laminated type having a charge transport layer and a charge generation layer laminated in this order, and the charge generation layer may contain the electron transport material. Alternatively, the photosensitive layer may be a single layer type containing the electron transport material.

[0020] In a second aspect of the present invention, in producing the electrophotographic photoreceptor, a step of preparing a coating solution for a photosensitive layer containing an azoquinone derivative having a structure represented by general formula (ET1); forming the photosensitive layer by a dip coating method using the coating liquid for the photosensitive layer; The method for producing an electrophotographic photoreceptor includes the steps of:

[0021] A third aspect of the present invention is an electrophotographic apparatus equipped with the above electrophotographic photoreceptor. [Effects of the Invention]

[0022] According to the present invention, an electrophotographic photoreceptor, a manufacturing method thereof, and an electrophotographic apparatus have been realized which have sufficiently high sensitivity, excellent potential stability during repeated printing under various environments, and do not cause problems such as deterioration of gradation or the occurrence of memory images, particularly when applied to monochrome high-speed printers and small medium-speed tandem color printers. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic cross-sectional view illustrating an example of an electrophotographic photoreceptor according to an embodiment of the present invention. [Figure 2]FIG. 2 is a schematic cross-sectional view showing another example of an electrophotographic photoreceptor according to an embodiment of the present invention. [Figure 3] 1 is a schematic configuration diagram illustrating an example of an electrophotographic apparatus according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] DETAILED DESCRIPTION OF THE INVENTION Specific embodiments of the electrophotographic photoreceptor according to the present invention will be described in detail below with reference to the drawings. The present invention is not limited to the following description.

[0025] 1 is a schematic cross-sectional view showing an example of an electrophotographic photoreceptor according to an embodiment of the present invention, showing a positively charged single-layer electrophotographic photoreceptor. As shown in the figure, in the positively charged single-layer photoreceptor, an undercoat layer 2 and a single-layer positively charged photosensitive layer (single-layer photosensitive layer) 3 having both a charge generating function and a charge transport function are sequentially laminated on the surface of a conductive substrate 1.

[0026] FIG. 2 is a schematic cross-sectional view showing another example of an electrophotographic photoreceptor according to an embodiment of the present invention, illustrating a positively charged laminated electrophotographic photoreceptor. As shown in the figure, the positively charged laminated photoreceptor includes a laminated positively charged photosensitive layer 6. The photosensitive layer 6 is composed of a charge transport layer 4 with a charge transport function and a charge generation layer 5 with a charge generation function, which are sequentially laminated on the surface of a cylindrical conductive substrate 1 via an undercoat layer 2. In both the photoreceptors shown in FIGS. 1 and 2, the undercoat layer 2 may be provided as needed. Although not shown, a surface protective layer may also be provided on the outermost surface of the photoreceptor in both the photoreceptors shown in FIGS. 1 and 2.

[0027] In a photoreceptor according to an embodiment of the present invention, the photosensitive layer contains electron transport materials, at least one of which contains an azoquinone derivative having a structure represented by the following general formula (ET1): Unlike conventional azoquinone derivatives having one chlorine atom at the para-position as a substituent, the azoquinone derivative having two or more soluble chlorine atoms as substituents. The use of such an azoquinone derivative as an electron transport material improves solubility in solvents and compatibility with resins, thereby increasing the content of the electron transport material in the photosensitive layer and achieving dispersion of the electron transport material with a sharp particle size distribution. This allows for the realization of a photoreceptor that simultaneously achieves sufficiently high sensitivity and repetitive potential stability in various environments, even in high-speed monochrome printers and small, medium-speed tandem color printers, thereby producing consistently good image quality. Furthermore, problems such as poor gradation and the occurrence of memory images are eliminated, and image defects due to sebum cracking and mineral oil contamination can be avoided.

[0028] TIFF0007767805000005.tif28153(In formula (ET1), R 1 and R 2 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent, or a halogenated alkyl group. R 3 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent, or a halogenated alkyl group. 4 ~R 8 At least two of the R represent chlorine atoms, and the remaining R other than the one representing a chlorine atom 4 ~R 8are the same or different and represent a hydrogen atom, a halogen atom other than a chlorine atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group which may have a substituent, an aralkyl group which may have a substituent, a phenoxy group which may have a substituent, a halogenated alkyl group, a cyano group, or a nitro group. The substituent represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, a cyano group, an amino group, a nitro group, or a halogenated alkyl group.

[0029] Specific examples of the azoquinone derivative having the structure represented by the above general formula (ET1) as an electron transport material include, but are not limited to, the following: Such azoquinone derivatives can be produced, for example, by the method described in paragraph

[0021] of JP-A No. 2000-199979 (U.S. Pat. No. 6,268,095, column 6, lines 4 to 10).

[0030] TIFF0007767805000006.tif227153

[0031] TIFF0007767805000007.tif145153

[0032] The azoquinone derivative having the structure represented by the general formula (ET1) includes R 4 and R 8 Among the azoquinone derivatives having two or more chlorine atoms as substituents, those having such a specific structure can be used to obtain a photoreceptor superior in terms of sensitivity, repeated potential stability, gradation, and generation of memory images. In addition, the azoquinone derivatives having the structure represented by the above general formula (ET1) include those having R 1 and R 2 is a tertiary butyl group, and R 3is also preferably a hydrogen atom. Among these, the azoquinone derivatives having the structure represented by the general formula (ET1) above are more preferably those represented by the structural formula (ET1-4) or (ET1-5) above. The azoquinone derivatives represented by the structural formula (ET1-4) or (ET1-5) above have excellent solubility and electrical properties, so their use as electron transport materials allows the content of the electron transport material in the photosensitive layer to be increased, which is particularly advantageous for positively charged multilayer photoreceptors, which require a high content of electron transport material to achieve high performance. Furthermore, although the reason is unclear, the azoquinone compound represented by the structural formula (ET1-4) above is more suitable in terms of sensitivity characteristics.

[0033] The reason why azoquinone derivatives having the structure represented by the structural formula (ET1-4) have superior solubility compared to other azoquinone derivatives having one or two chlorine atoms is unclear, but it is thought that the balance between steric hindrance and symmetry in the molecular structure may play a role. Furthermore, the superior electrical properties are thought to be due to the combination of excellent dispersibility in films (solubility) due to high solubility and excellent electron transport performance due to the presence of two chlorine atoms, which are electron-withdrawing groups. Azoquinone derivatives having the structure represented by the structural formula (ET1-4) can be well dissolved in films at 40% by weight or more when used alone in, for example, laminated positively charged organic photoreceptors. Therefore, even in devices with short exposure-development times of 60 ms or less, such as high-speed monochrome machines with a φ30 drum and A4 portrait feed of 50 ppm or more, or medium- to high-speed tandem color machines with a φ24 drum and A4 portrait feed of 24 ppm or more, high-sensitivity (low exposed area potential) and ghost-free, high-quality images with excellent gradation can be obtained.

[0034] Furthermore, the azoquinone derivative having the structure represented by the structural formula (ET1-5) has superior electron transport performance due to the presence of three chlorine atoms, which are electron-withdrawing groups, compared with other azoquinone derivatives having one or two chlorine atoms. Furthermore, due to the favorable solubility, which is thought to be due to the balance between steric hindrance and symmetry in the molecular structure, it can be used at a high content. Therefore, particularly in the charge generation layer of a laminated positively charged organic photoreceptor, which requires the use of a large amount of electron transport material, by using a high content, as with the azoquinone derivative having the structure represented by the structural formula (ET1-4), a clear improvement in performance is achieved compared to the use of other electron transport materials in the high-speed monochrome machines and medium- to high-speed tandem color machines, which have short exposure-development times.

[0035] The azoquinone derivative having the structure represented by the general formula (ET1) has a solubility S of the electron transport material, which is expressed as the mass (g) of tetrahydrofuran required to dissolve 1 g of the electron transport material. ETM (THF) is a compound represented by the following formula: S ETM (THF)≦2.0 It is also preferable that the azoquinone derivative satisfies the following condition. By using such an azoquinone derivative, good solubility can be ensured. The solubility S of the azoquinone derivative as the electron transport material is ETM (THF) is represented by the following formula: 0.5≦S ETM (THF)≦2.0 It is more preferable to satisfy the following.

[0036] In the photoreceptor according to the embodiment of the present invention, the electron transport material contained in the photosensitive layer may further contain other electron transport materials in addition to the azoquinone derivative having the structure represented by the above general formula (ET1).

[0037] Such other electron transport materials are not particularly limited, and examples thereof include succinic anhydride, maleic anhydride, dibromosuccinic anhydride, phthalic anhydride, 3-nitrophthalic anhydride, 4-nitrophthalic anhydride, pyromellitic anhydride, pyromellitic acid, trimellitic acid, trimellitic anhydride, phthalimide, 4-nitrophthalimide, tetracyanoethylene, tetracyanoquinodimethane, chloranil, bromanil, o-nitrobenzoic acid, malononitrile, trinitrofluorenone, trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, thiopyran-based compounds, quinone-based compounds, benzoquinone-based compounds, diphenoquinone compounds, naphthoquinone-based compounds, anthraquinone-based compounds, stilbenequinone compounds, azoquinone compounds other than the azoquinone derivatives having the specific structure described above, and naphthalenetetracarboxylic acid diimide compounds.

[0038] In particular, other electron transport materials have an electron mobility of 15×10 when the electric field strength is 20 V / μm. -8 [cm 2 / V·s] or more, especially 17×10 -8 ~35×10 -8 [cm 2 It is preferable to use a material with a conductivity of 50 V / μm. The electron mobility can be measured using a sample prepared from a coating solution obtained by adding 50% by mass of an electron transport material to a resin binder. The ratio of the electron transport material to the resin binder is 50:50. The resin binder can be a bisphenol Z-type polycarbonate resin, such as Iupizeta PCZ-500 (trade name, manufactured by Mitsubishi Gas Chemical Company, Inc.). Specifically, the coating solution is applied to a substrate and dried at 120°C for 30 minutes to form a coating film with a thickness of 7 μm. The electron mobility can then be measured at a constant electric field strength of 20 V / μm using a time-of-flight (TOF) method. The measurement temperature is 300 K.

[0039] Among these, as other electron transport materials to be used in combination with the azoquinone derivative having a structure represented by the general formula (ET1), it is preferable to use a naphthalenetetracarboxylic acid diimide compound having a structure represented by the following general formula (ET2) or a compound having a structure represented by the following structural formula (ET-1): By using these electron transport materials in appropriate combination, it may be possible to improve the contamination resistance of the photoreceptor surface from peripheral members and to easily adjust the sensitivity characteristics when matching with the device process.

[0040] TIFF0007767805000008.tif28153 formula (ET2), R 11 and R 12 may be the same or different and represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkylene group, an alkoxy group, an alkyl ester group, a phenyl group which may have a substituent, a naphthyl group which may have a substituent, or a halogen atom; R 11 and R 12 may be bonded to each other to form an aromatic ring which may have a substituent.

[0041] TIFF0007767805000009.tif26153

[0042] Specific examples of the naphthalenetetracarboxylic acid diimide compound having the structure represented by the above general formula (ET2) include the following.

[0043] TIFF0007767805000010.tif126158

[0044] When an azoquinone derivative having the structure represented by the general formula (ET1) and a naphthalenetetracarboxylic acid diimide compound having the structure represented by the general formula (ET2) are used in combination as electron transport materials, the mass ratio ET1:ET2 is preferably 5:95 to 95:5, more preferably 20:80 to 80:20. When an azoquinone derivative having the structure represented by the general formula (ET1) and a compound having the structure represented by the structural formula (ET-1) are used in combination as electron transport materials, the mass ratio ET1:ET-1 is preferably 5:95 to 95:5, more preferably 20:80 to 80:20. If the amount of the azoquinone derivative having the structure represented by the general formula (ET1) is too small, problems such as poor gradation and memory generation are likely to occur. If the amount of the azoquinone derivative having the structure represented by the general formula (ET1) is too large, the solvent resistance of the photoreceptor may be impaired.

[0045] As described above, in the photoreceptor according to the embodiment of the present invention, the electron transport material contained in the photosensitive layer satisfies the above conditions. The photoreceptor according to the embodiment of the present invention has the layer structure of a positive-charge single-layer electrophotographic photoreceptor shown in Fig. 1 or a positive-charge multi-layer electrophotographic photoreceptor shown in Fig. 2.

[0046] The conductive substrate 1 serves as an electrode for the photoreceptor and also as a support for each layer constituting the photoreceptor, and may be in any shape such as a cylinder, plate, film, etc. Materials that can be used for the conductive substrate 1 include metals such as aluminum, stainless steel, and nickel, as well as glass, resin, etc. whose surfaces have been treated to be conductive.

[0047] The undercoat layer 2 is composed of a layer mainly composed of resin or a metal oxide film such as alumite (anodized). The undercoat layer 2 is provided as needed for purposes such as controlling the injection of charges from the conductive substrate 1 to the photosensitive layer, covering defects on the surface of the conductive substrate 1, and improving the adhesion between the photosensitive layer and the conductive substrate 1. Resin materials used for the undercoat layer 2 include insulating polymers such as casein, polyvinyl alcohol, polyamide, melamine, and cellulose, and conductive polymers such as polythiophene, polypyrrole, and polyaniline. These resins can be used alone or in appropriate combinations. These resins may also contain metal oxides such as titanium dioxide and zinc oxide.

[0048] (Positively charged single-layer photoreceptor) In the case of a positive-charged single-layer photoreceptor, the single-layer photosensitive layer 3 is a photosensitive layer containing the above-mentioned specific electron transport material. In a positive-charged single-layer photoreceptor, the single-layer photosensitive layer 3 is a single-layer positive-charged photosensitive layer containing mainly a charge generating material, a hole transport material, an electron transport material (acceptor compound), and a resin binder in a single layer.

[0049] The charge-generating material of the single-layer photosensitive layer 3 is not particularly limited and can be appropriately selected from known materials. Specifically, the charge-generating material is not particularly limited as long as it is photosensitive to the wavelength of the exposure light source. For example, organic pigments such as phthalocyanine pigments, azo pigments, quinacridone pigments, indigo pigments, perylene pigments, perinone pigments, squarylium pigments, thiapyrylium pigments, polycyclic quinone pigments, anthanthrone pigments, and benzimidazole pigments can be used. In particular, phthalocyanine pigments include metal-free phthalocyanine, titanyl phthalocyanine, chlorogallium phthalocyanine, hydroxygallium phthalocyanine, and copper phthalocyanine. Azo pigments include disazo pigments and trisazo pigments. Perylene pigments include N,N'-bis(3,5-dimethylphenyl)-3,4:9,10-perylene-bis(carboximide). Among these, metal-free phthalocyanine or titanyl phthalocyanine is preferred. Examples of usable metal-free phthalocyanines include X-type metal-free phthalocyanine and τ-type metal-free phthalocyanine, and examples of usable titanyl phthalocyanine include α-type titanyl phthalocyanine, β-type titanyl phthalocyanine, Y-type titanyl phthalocyanine, amorphous titanyl phthalocyanine, and titanyl phthalocyanine having a maximum peak at a Bragg angle 2θ of 9.6° in the CuKα:X-ray diffraction spectrum described in JP-A-8-209023, U.S. Pat. No. 5,736,282, and U.S. Pat. No. 5,874,570. The charge-generating material may be any one of the above, or two or more of them may be used in combination.

[0050] Examples of hole transport materials that can be used in the single-layer photosensitive layer 3 include hydrazone compounds, pyrazoline compounds, pyrazolone compounds, oxadiazole compounds, oxazole compounds, arylamine compounds, benzidine compounds, stilbene compounds, styryl compounds, poly-N-vinylcarbazole, and polysilanes, with arylamine compounds being preferred. These hole transport materials can be used alone or in combination of two or more. Preferred hole transport materials are those that have excellent transport capabilities for holes generated upon light irradiation and are suitable for combination with charge generating materials. Furthermore, preferred hole transport materials have a hole mobility of 15×10 at an electric field strength of 20 V / μm. -6 [cm 2 / V·s] or more, especially 20×10 -6 ~80×10 -6 [cm 2 / V·s]. -6 [cm 2 If the r / V·s is less than [V·s], ghosting is likely to occur. The hole mobility can be measured using a coating solution obtained by adding a hole transport material to a resin binder at a concentration of 50% by mass. The ratio of the hole transport material to the resin binder is 50:50. The resin binder may be a bisphenol Z-type polycarbonate resin. For example, Iupizeta PCZ-500 (trade name, manufactured by Mitsubishi Gas Chemical Company, Inc.) may be used. Specifically, the coating solution is applied to a substrate and dried at 120°C for 30 minutes to form a coating film with a thickness of 7 μm. The hole mobility can then be measured at a constant electric field strength of 20 V / μm using a time-of-flight (TOF) method. The measurement temperature is 300 K.

[0051] Specific examples of hole transport materials include compounds having a structure represented by the following general formula (HT1).

[0052] TIFF0007767805000011.tif60155 formula (HT1), R 21 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms which may have a substituent, and R 22 ~R31 each independently represents a hydrogen atom, a halogen atom, an optionally substituted alkyl group having 1 to 6 carbon atoms, or an optionally substituted alkoxy group having 1 to 6 carbon atoms; l, m, and n are integers of 0 to 4; and R represents a hydrogen atom or an optionally substituted alkyl group having 1 to 3 carbon atoms.

[0053] Specific examples of the compound having the structure represented by the above general formula (HT1) as a hole transport material include the following.

[0054] TIFF0007767805000012.tif199170

[0055] TIFF0007767805000013.tif200170

[0056] TIFF0007767805000014.tif197170

[0057] TIFF0007767805000015.tif197170

[0058] TIFF0007767805000016.tif197170

[0059] TIFF0007767805000017.tif197170

[0060] Further specific examples of the hole transport material include the following compounds.

[0061] TIFF0007767805000018.tif127160

[0062] Examples of resin binders that can be used for the single-layer photosensitive layer 3 include various polycarbonate resins such as bisphenol A, bisphenol Z, bisphenol A-biphenyl copolymer, and bisphenol Z-biphenyl copolymer, polyphenylene resin, polyester resin, polyvinyl acetal resin, polyvinyl butyral resin, polyvinyl alcohol resin, vinyl chloride resin, vinyl acetate resin, polyethylene resin, polypropylene resin, acrylic resin, polyurethane resin, epoxy resin, melamine resin, silicone resin, polyamide resin, polystyrene resin, polyacetal resin, polyarylate resin, polysulfone resin, methacrylic acid ester polymers, and copolymers thereof. Furthermore, resins of the same type but with different molecular weights may be mixed and used.

[0063] Suitable resin binders include resins having a repeating unit represented by the following general formula (GB1): More specific examples of suitable resin binders include polycarbonate resins having repeating units represented by the following structural formulas (GB1-1) to (GB1-3):

[0064] TIFF0007767805000019.tif30153In formula, R 41 and R 42 is a hydrogen atom, a methyl group, or an ethyl group, and X is an oxygen atom, a sulfur atom, or -CR 43 R 44 and R 43 and R 44 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, or a phenyl group which may have a substituent, or R 43 and R 44 may be bonded to form a cycloalkyl group having 4 to 6 carbon atoms which may have a substituent, and R 43 and R 44 may be the same or different.

[0065] TIFF0007767805000020.tif131153

[0066] The content of the charge generating material in the single-layer photosensitive layer 3 is preferably 0.1 to 5 mass %, more preferably 0.5 to 3 mass %, based on the solid content of the single-layer photosensitive layer 3. The content of the hole transport material in the single-layer photosensitive layer 3 is preferably 3 to 60 mass %, more preferably 10 to 40 mass %, based on the solid content of the single-layer photosensitive layer 3. The content of the electron transport material in the single-layer photosensitive layer 3 is preferably 1 to 50 mass %, more preferably 5 to 20 mass %, based on the solid content of the single-layer photosensitive layer 3. The content ratio of the hole transport material to the electron transport material may be in the range of 4:1 to 3:2. The content of the resin binder in the single-layer photosensitive layer 3 is preferably 20 to 80 mass %, more preferably 30 to 70 mass %, based on the solid content of the single-layer photosensitive layer 3.

[0067] The thickness of the single-layer photosensitive layer 3 is preferably in the range of 3 to 100 μm, more preferably in the range of 5 to 40 μm, in order to maintain a practically effective surface potential.

[0068] (Positively charged multilayer photoreceptor) In the case of a positive-charging multilayer photoreceptor, a multilayer positive-charging photosensitive layer 6 including a charge transport layer 4 and a charge generation layer 5 is a photosensitive layer including the specific electron transport material. The charge transport layer 4 and the charge generation layer 5 are sequentially stacked on a conductive substrate 1. In the positive-charging multilayer photoreceptor, the charge transport layer 4 includes at least a first hole transport material and a resin binder, and the charge generation layer 5 includes at least a charge generation material, a second hole transport material, the specific electron transport material, and a resin binder. In the positive-charging multilayer photoreceptor, the charge transport layer 4 may further include an electron transport material.

[0069] As the first hole transport material and resin binder in the charge transport layer 4, the same materials as those listed for the single-layer type photosensitive layer 3 can be used.

[0070] The content of the first hole transport material in the charge transport layer 4 is preferably 10 to 80% by mass, and more preferably 20 to 70% by mass, based on the solid content of the charge transport layer 4. The content of the resin binder in the charge transport layer 4 is preferably 20 to 90% by mass, and more preferably 30 to 80% by mass, based on the solid content of the charge transport layer 4.

[0071] The thickness of the charge transport layer 4 is preferably in the range of 3 to 50 μm, more preferably in the range of 15 to 40 μm, in order to maintain a practically effective surface potential.

[0072] As the charge generating material, second hole transport material, electron transport material, and resin binder in the charge generating layer 5, the same materials as those listed for the single-layer type photosensitive layer 3 can be used.

[0073] The content of the charge generating material in the charge generating layer 5 is preferably 0.1 to 5% by mass, more preferably 0.5 to 3% by mass, based on the solid content of the charge generating layer 5. The content of the second hole transport material in the charge generating layer 5 is preferably 1 to 30% by mass, more preferably 5 to 20% by mass, based on the solid content of the charge generating layer 5. The content of the electron transport material in the charge generating layer 5 is preferably 5 to 65% by mass, more preferably 10 to 60% by mass, based on the solid content of the charge generating layer 5. When a mixture of multiple electron transport materials is used, the content of the electron transport material may be 50 to 60% by mass, based on the solid content of the charge generating layer 5. The ratio of the contents of the second hole transport material and the electron transport material may be in the range of 1:3 to 1:10. The content of the resin binder in the charge generating layer 5 is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, based on the solid content of the charge generating layer 5.

[0074] The thickness of the charge generating layer 5 can be the same as that of the single-layer photosensitive layer 3 of the single-layer photoreceptor.

[0075] In the photoreceptor according to the present invention, a leveling agent such as silicone oil or fluorine-based oil can be incorporated into either the multilayer or single-layer photosensitive layer to improve the leveling properties of the formed film or to provide lubricity. Furthermore, multiple inorganic oxides can be incorporated to adjust film hardness, reduce the coefficient of friction, provide lubricity, etc. Metal oxides such as silica, titanium oxide, zinc oxide, calcium oxide, alumina, and zirconium oxide, metal sulfates such as barium sulfate and calcium sulfate, metal nitride particles such as silicon nitride and aluminum nitride, fluorine-based resin particles such as tetrafluoroethylene resin, and fluorine-based comb-type graft polymerized resin particles can also be incorporated, if necessary, as long as they do not significantly impair electrophotographic properties.

[0076] The photosensitive layer may contain a deterioration inhibitor such as an antioxidant or a light stabilizer for the purpose of improving environmental resistance and stability against harmful light. Examples of compounds used for such purposes include chromanol derivatives such as tocopherol and esterified compounds, polyarylalkane compounds, hydroquinone derivatives, etherified compounds, dietherified compounds, benzophenone derivatives, benzotriazole derivatives, thioether compounds, phenylenediamine derivatives, phosphonate esters, phosphites, phenol compounds, hindered phenol compounds, linear amine compounds, cyclic amine compounds, and hindered amine compounds.

[0077] (Photoreceptor manufacturing method) A method for producing a photoreceptor according to an embodiment of the present invention includes, in producing the electrophotographic photoreceptor, a step of preparing a coating liquid for a photosensitive layer containing an azoquinone derivative having a structure represented by the general formula (ET1) above, and a step of forming a photosensitive layer by a dip coating method using the prepared coating liquid for a photosensitive layer.

[0078] Specifically, the single-layer photoreceptor can be produced by a method including the steps of: preparing a coating solution for forming a single-layer photosensitive layer by dissolving and dispersing an electron transport material containing the specific azoquinone derivative described above, as well as an optional charge generating material, a hole transport material, and a resin binder in a solvent; and applying the obtained coating solution for forming a single-layer photosensitive layer to the outer periphery of a conductive substrate, via an undercoat layer if desired, by a dip coating method, and drying the coating solution to form a photosensitive layer.

[0079] In the case of a multilayer photoreceptor, the charge transport layer is formed by a method including the steps of: first, preparing a coating liquid for forming a charge transport layer by dissolving an optional hole transport material and a resin binder in a solvent; then, applying the coating liquid for forming the charge transport layer to the outer periphery of a conductive substrate by dip coating, optionally via an undercoat layer, and drying to form a charge transport layer; then, dissolving and dispersing an electron transport material containing the specific azoquinone derivative, an optional charge generation material, a hole transport material, and a resin binder in a solvent to prepare a coating liquid for forming the charge transport layer; and then, applying the coating liquid for forming the charge generation layer to the charge transport layer by dip coating and drying to form a charge generation layer. This manufacturing method allows the multilayer photoreceptor according to the present invention to be manufactured. The type of solvent used to prepare the coating liquid, the coating conditions, the drying conditions, and the like can be selected as appropriate according to conventional methods and are not particularly limited.

[0080] The electrophotographic photoreceptor according to the embodiment of the present invention can achieve the desired effects by being applied to various machine processes. Specifically, it can achieve sufficient effects in charging processes such as contact charging methods using charging members such as rollers and brushes, non-contact charging methods using corotrons and scorotrons, and development processes such as contact and non-contact development methods using non-magnetic one-component, magnetic one-component, and two-component developers.

[0081] (electrophotographic device) The electrophotographic apparatus according to the embodiment of the present invention is equipped with the electrophotographic photoreceptor described above. The electrophotographic apparatus according to the embodiment of the present invention has sufficiently high sensitivity, and is excellent in potential stability during repeated printing under various environments, and does not cause problems such as deterioration of gradation and generation of image smears, particularly when applied to a monochrome high-speed printer or a small medium-speed tandem color printer.

[0082] FIG. 3 is a schematic diagram of an example of the configuration of an electrophotographic apparatus of the present invention. The illustrated electrophotographic apparatus 30 is equipped with a photoreceptor 20 according to an embodiment of the present invention, which includes a conductive substrate 1, an undercoat layer 2 coated on the outer peripheral surface thereof, and a photosensitive layer 6 consisting of a charge transport layer 4 and a charge generation layer 5. This electrophotographic apparatus 30 includes a charging electrode 21 (in the illustrated example, a scorotron) disposed on the outer peripheral edge of the photoreceptor 20, a high-voltage power supply 22 that supplies a voltage to the charging electrode 21, an image exposure member 23, a developing unit 24, and a transfer electrode 25. The electrophotographic apparatus 30 may further include a cleaning member 26. The electrophotographic apparatus 30 according to an embodiment of the present invention may also be a color printer. [Example]

[0083] Specific embodiments of the present invention will be described in more detail below using examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.

[0084] <Layered photoreceptor> Example 1 The conductive substrate was an aluminum tube with a thickness of 0.75 mm, measuring φ30 mm, length 252.6 mm, and machined to a surface roughness (Rmax) of 0.2 μm. The conductive substrate had an anodized aluminum layer on its surface.

[0085] [Charge transport layer] A coating solution was prepared by dissolving the compound represented by the structural formula (HT1-5) as a hole transport material and the polycarbonate resin having the repeating unit represented by the structural formula (GB1-1) as a resin binder in tetrahydrofuran according to the blending amounts shown in Table 1. This coating solution was applied to the conductive substrate by dip coating and dried at 100°C for 30 minutes to form a charge transport layer with a thickness of 10 μm.

[0086] [Charge generation layer] The compound represented by the formula (HT1-5) above as a hole-transporting material, the compound represented by the formula (ET1-4) above as an electron-transporting material, and the polycarbonate resin having the repeating unit represented by the formula (GB1-2) above as a resin binder were dissolved in tetrahydrofuran in the amounts shown in Table 1 below. Titanyl phthalocyanine represented by the formula (CG1) below as a charge-generating material was then added. The resulting solution was dispersed in a Willy & Bachofen DYNO-MILL Research Lab model disperser using beads of φ0.4mm ZrO, a filling rate of 70%, a rotation speed of 3000 rpm, and three passes to prepare a coating solution. This coating solution was then applied to the charge-transporting layer by dip coating and dried at 110°C for 30 minutes to form a 15 μm-thick charge-generating layer. This resulted in a multilayer electrophotographic photoreceptor with a 25 μm-thick photosensitive layer.

[0087] Here, the solubility S of this azoquinone derivative, which is expressed as the mass (g) of tetrahydrofuran required to dissolve 1 g of the azoquinone derivative having the structure represented by the above structural formula (ET1-4), is ETM (THF) was 1(g).

[0088] TIFF0007767805000021.tif60153

[0089] (Examples 2 to 24, Reference Examples 1 to 6, and Comparative Examples 1 to 11) Positively charged multilayer electrophotographic photoreceptors were obtained in the same manner as in Example 1, except that the type and amount of each material and the film thickness of each layer were changed according to the conditions shown in the following Tables 1 to 3. The structural formulas of the materials used in the comparative examples are shown below.

[0090] TIFF0007767805000022.tif57153

[0091] Here, among the electron transport materials used in Examples 2 to 24, Reference Examples 1 to 6, and Comparative Examples 1 to 11, the solubility S ETM (THF) is 1(g), and the solubility S of the azoquinone derivative having the structure represented by the above structural formula (ET1-3) ETM (THF) is 1 (g) or less, and the solubility S of the azoquinone derivative having the structure represented by the above structural formula (ET-1) ETM (THF) 3(g), the solubility S of the azoquinone derivative having the structure represented by the above structural formula (ET-2) ETM (THF) is 15(g), and the solubility S of the azoquinone derivative having the structure represented by the above structural formula (ET-3) ETM (THF) was 22(g).

[0092] [Table 1]

[0093] [Table 2]

[0094] [Table 3]

[0095] (Evaluation of liquid state) [Evaluation of solubility] For each of the obtained photoreceptors of the examples, reference examples, and comparative examples, the amount of tetrahydrofuran (THF) solvent required to dissolve 1 g of the electron transport material used (when using a plurality of electron transport agents, the amount is divided according to the ratio to a total of 1 g) was measured. When the amount was 2 g or less, it was evaluated as ◎; when it exceeded 2 g and was 5 g or less, it was evaluated as 〇; when it exceeded 5 g and was 20 g or less, it was evaluated as △; and when it exceeded 20 g, it was evaluated as ×.

[0096] [Evaluation of Precipitates] For each of the obtained photoreceptors of the examples, reference examples, and comparative examples, precipitates of the electron transport material during the film formation of the charge generation layer were observed visually and with an optical microscope. When no precipitates were observed (the size of the precipitates was less than 1 μm), it was evaluated as 〇; when the size of the precipitates was 1 μm or more and less than 50 μm, it was evaluated as △; and when the size of the precipitates was 50 μm or more, it was evaluated as ×.

[0097] [Evaluation of Particle Size] For each of the obtained photoreceptors of the examples, reference examples, and comparative examples, the presence or absence of coarse particles in the coating solution was evaluated by measuring the median diameter D₅₀. Specifically, the coating solution for the charge generation layer, diluted 20 times with the solvent THF, was measured using a dynamic light scattering particle size distribution measuring device LB-500 (manufactured by Horiba, Ltd.). When D₅₀ ≤ 400 nm, it was evaluated as 〇; when 400 nm < D₅₀ ≤ 500 nm, it was evaluated as △; and when D₅₀ > 500 nm, it was evaluated as ×.

[0098] <舍 (Evaluation of Electrical Characteristics) [Evaluation of Sensitivity] Each of the obtained photoreceptors of the examples, reference examples, and comparative examples was mounted at the positions of the yellow, cyan, magenta, and black (4 colors) toners of a tandem color printer (HL-9310CDW, manufactured by Brother Industries, Ltd.) with a printing speed of 31 ppm. Regarding the average value of the measured post-exposure potential in an environment of temperature 25°C and humidity 40%, when it was less than 120 V, it was evaluated as ◎; when it was 120 V or more and less than 140 V, it was evaluated as 〇; when it was 140 V or more and less than 160 V, it was evaluated as △; and when it was 160 V or more, it was evaluated as ×.

[0099] [Evaluation of Potential Stability] The photoreceptors obtained in each of the Examples, Reference Examples, and Comparative Examples were attached to the four-color toner positions of a tandem color printer (HL-9310CDW, manufactured by Brother Industries, Ltd.) with a printing speed of 31 ppm, and the amount of charge potential decrease after printing 50,000 sheets in an environment of a temperature of 10°C and a humidity of 25% was measured. The average value was evaluated as follows: less than 30 V = ◎; 30 V or more but less than 50 V = ◯; 50 V or more but less than 80 V = △; and more than 80 V = ×.

[0100] (Evaluation of image characteristics) [Evaluation of gradation] The photoreceptors obtained in each of the Examples, Reference Examples, and Comparative Examples were attached to the four-color toner positions of a tandem color printer (HL-9310CDW, manufactured by Brother Industries, Ltd.) with a printing speed of 31 ppm, and four-color monochrome images with 10 area gradation levels ranging from low density to high density were printed. The print density at each gradation level was measured with a densitometer (Gretag Macbeth RD-19I). A difference in density between each gradation level and the gradation before and after it was marked as ◯ if it was 0.05 or more, a difference of less than 0.05 and 0.02 or more was marked as △, and a difference of less than 0.02 was marked as ×.

[0101] [Ghost image evaluation] The photoreceptors obtained in each of the Examples, Reference Examples, and Comparative Examples were mounted in the four-color toner positions of a tandem color printer (HL-9310CDW, manufactured by Brother Industries, Ltd.) with a printing speed of 31 ppm, and a solid image was printed using four monochrome images. A halftone (1-on, 2-off) image was printed one revolution of the photoreceptor from the solid image area, and the print density difference between the halftone area and the ghost area of ​​the solid image that appeared in the halftone area was measured. A density difference of less than 0.02 was marked with a circle, a difference of 0.02 to 0.05 with a triangle, and a difference of 0.05 or more with an x.

[0102] The evaluation results are shown in the following Tables 4 and 5. When the first electron transport material is compared among the compounds represented by the structural formulas (ET1-1), (ET1-3), (ET1-4), and (ET1-5), the results of Examples 4 and 13 and Reference Examples 1 and 6 show that the position of the chlorine element in the general formula (ET1) is R 4and R 8 It can be seen that it is preferable that at least one of the groups is a chlorine atom. In particular, when the first electron-transporting material is a compound represented by structural formula (ET1-4) or (ET1-5), comparison of Examples 1 to 3, 4 to 6, 7 to 9, 10 to 12, 13 to 15, and 16 to 18 reveals that the addition of a second electron-transporting material improves potential stability.

[0103] [Table 4]

[0104] [Table 5]

[0105] <Single-layer photoreceptor> Example 25 The conductive substrate was an aluminum tube with a thickness of 0.75 mm, measuring φ30 mm, length 244.5 mm, and machined to a surface roughness (Rmax) of 0.2 μm. The conductive substrate had an anodized aluminum layer on its surface.

[0106] [Single-layer photosensitive layer] The compound represented by the formula (HT1-5) above as a hole-transporting material, the compound represented by the formula (ET1-3) above as an electron-transporting material, and the polycarbonate resin having the repeating unit represented by the formula (GB1-1) above as a resin binder were dissolved in tetrahydrofuran in the amounts shown in Table 6 below, and titanyl phthalocyanine represented by the formula (CG1) above as a charge-generating material was added. The resulting solution was then dispersed in a Willy & Bachofen DYNO-MILL Research Lab model disperser using beads of φ0.4mm ZrO, a filling rate of 60%, a rotation speed of 3600 rpm, and four passes to prepare a coating solution. This coating solution was then applied to the anodized aluminum layer by dip coating and dried at 100°C for 60 minutes to form a 30 μm-thick single-layer photosensitive layer, yielding a positive-charging single-layer electrophotographic photoreceptor.

[0107] (Example 26, Reference Examples 7 to 12, and Comparative Examples 12 to 16) A positively charged single-layer type electrophotographic photoreceptor was obtained in the same manner as in Example 25, except that the types and blending amounts of each material were changed according to the conditions shown in Table 6 below.

[0108]

Table 6

[0109] (Evaluation of liquid state) [Evaluation of precipitate] Regarding the photoreceptors obtained in each of the Examples, Reference Examples, and Comparative Examples, the precipitates of the electron transport material during the formation of the single-layer photoreceptive layer were observed visually and with an optical microscope. When no precipitate was observed (the size of the precipitate was less than 1 μm), it was evaluated as ○; when the size of the precipitate was 1 μm or more and less than 50 μm, it was evaluated as △; when the size of the precipitate was 50 μm or more, it was evaluated as ×.

[0110] [Evaluation of particle size] Regarding the photoreceptors obtained in each of the Examples, Reference Examples, and Comparative Examples, the presence or absence of coarse particles in the coating solution was evaluated by measuring the median diameter D50. Specifically, the coating solution for the single-layer photoreceptive layer, diluted 20-fold with the solvent THF, was measured using a dynamic light scattering type particle size distribution measuring device LB-500 (manufactured by Horiba, Ltd.). When the median diameter D50 was D50 ≤ 400 nm, it was evaluated as ○; when 400 nm < D50 ≤ 500 nm, it was evaluated as △; when D50 > 500 nm, it was evaluated as ×.

[0111] (Evaluation of electrical properties) [Evaluation of sensitivity] Regarding the photoreceptors obtained in each of the Examples, Reference Examples, and Comparative Examples, when mounted on a monochrome printer (HL-5200DW, manufactured by Brother Industries, Ltd.) with a printing speed of 40 ppm and the average value of the post-exposure potential measured in an environment of temperature 25°C and humidity 40% was less than 120 V, it was evaluated as ◎; when it was 120 V or more and less than 140 V, it was evaluated as ○; when it was 140 V or more and less than 160 V, it was evaluated as △; when it was 160 V or more, it was evaluated as ×.

[0112] [Evaluation of potential stability] The photoreceptors obtained in each of the Examples, Reference Examples, and Comparative Examples were mounted in a monochrome printer (HL-5200DW, manufactured by Brother Industries, Ltd.) with a printing speed of 40 ppm, and the amount of decrease in charging potential after printing 50,000 sheets in an environment of 10°C temperature and 25% humidity was measured. The average value was evaluated as follows: less than 30 V = ◎; 30 V or more but less than 50 V = ◯; 50 V or more but less than 80 V = △; and 80 V or more = ×.

[0113] The evaluation results are shown in Table 7 below. When the first electron transport material is compared with each compound represented by the structural formulas (ET1-1), (ET1-3), (ET1-4), and (ET1-5), it is found from the results of Reference Examples 7, 9, 10, and 11 that the position of the chlorine element in the general formula (ET1) is R 4 and R 8 It can be seen that it is preferable that at least one of the groups is a chlorine atom. In particular, when the first electron-transporting material is a compound represented by structural formula (ET1-4) or (ET1-5), comparison of Examples 25 and 26 and Reference Examples 9 and 10 reveals that the addition of a second electron-transporting material improves potential stability.

[0114] [Table 7]

[0115] From the above, it has been confirmed that by using an electron transport material that satisfies the conditions of the present invention, an electrophotographic photoreceptor can be obtained that has sufficiently high sensitivity, is excellent in potential stability during repeated printing under various environments, and does not cause problems such as deterioration of gradation and generation of memory images. [Explanation of symbols]

[0116] 1. Conductive substrate 2 Undercoat layer 3 Single-layer photosensitive layer 4 Charge transport layer 5. Charge generation layer 6 Photosensitive layer 20 Photoreceptor 21 Charged electrode 22 High voltage power supply 23 Image exposure member 24 Developer 25 Transfer pole 26 Cleaning material 30 Electrophotographic device

Claims

1. a conductive substrate; a photosensitive layer provided on the conductive substrate, the photosensitive layer contains an electron transport material, and the electron transport material contains an azoquinone derivative having a structure represented by the following general formula (ET1) and a naphthalenetetracarboxylic acid diimide compound having a structure represented by the following general formula (ET2), (In formula (ET1), R １ and R ２ are the same or different and represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent, or a halogenated alkyl group. ３ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group which may have a substituent, a cycloalkyl group, an aralkyl group which may have a substituent, or a halogenated alkyl group. ４ ~R ８ At least two of R represent chlorine atoms, and the remaining R other than the one representing a chlorine atom ４ ~R ８ are the same or different and represent a hydrogen atom, a halogen atom other than a chlorine atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryl group which may have a substituent, an aralkyl group which may have a substituent, a phenoxy group which may have a substituent, a halogenated alkyl group, a cyano group, or a nitro group. The substituent represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a hydroxyl group, a cyano group, an amino group, a nitro group, or a halogenated alkyl group. (In formula (ET2), R １１ and R １２ may be the same or different and represent a hydrogen atom, an alkyl group having 1 to 10 carbon atoms, an alkylene group, an alkoxy group, an alkyl ester group, a phenyl group which may have a substituent, a naphthyl group which may have a substituent, or a halogen atom; R １１ and R １２ may be bonded to each other to form an aromatic ring which may have a substituent. The azoquinone derivative having the structure represented by the general formula (ET1) is represented by the following structural formula (ET1-4) or (ET1-5): An electrophotographic photoreceptor represented by the formula:

2. The naphthalenetetracarboxylic acid diimide compound having the structure represented by the general formula (ET2) is represented by the following structural formula (ET2-4):

2. The electrophotographic photoreceptor according to claim 1, wherein the formula is:

3. The solubility S of the azoquinone derivative having the structure represented by the general formula (ET1) ＥＴＭ (THF) (the mass (g) of tetrahydrofuran required to dissolve 1 g of the azoquinone derivative) is expressed by the following formula: S ＥＴＭ (THF)≦2.0 3. The electrophotographic photoreceptor according to claim 1, which satisfies the following:

4. the photosensitive layer is a laminated type having a charge transport layer and a charge generation layer laminated in this order, 4. The electrophotographic photoreceptor according to claim 1, wherein the charge generating layer contains the electron transport material.

5. 4. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer is a single layer type and contains the electron transport material.

6. In producing the electrophotographic photoreceptor according to any one of claims 1 to 5, preparing a coating solution for a photosensitive layer, the coating solution containing an azoquinone derivative having a structure represented by general formula (ET1); forming the photosensitive layer by a dip coating method using the coating liquid for the photosensitive layer; A method for producing an electrophotographic photoreceptor, comprising:

7. An electrophotographic apparatus equipped with the electrophotographic photoreceptor according to any one of claims 1 to 5.

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