Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge and image forming apparatus

Abstract

Provided is an electrophotographic photosensitive member characterized in that a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound are sequentially provided on a conductive support, the Martens hardness of the photosensitive member is 255 N / mm2or more, the photosensitive layer contains at least a hole transport material (HTM), and the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is larger than 3.6 eV and equal to or less than 4.0 eV.　

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic photoreceptor, an electrophotographic photoreceptor cartridge, and an image forming apparatus for use in a copying machine, a printer, or the like. [Background technology]

[0002] In printers and copiers, when a charged organic photoconductor (OPC) drum is irradiated with light, the part is discharged, creating an electrostatic latent image, to which toner adheres to create an image. In devices that use electrophotography, the photoconductor is a key component.

[0003] Because this type of organic photoreceptor offers a wide range of material options and allows for easy control of photoreceptor properties, "function-separated photoreceptors," in which the functions of negative charge generation and transport are shared between separate compounds, have become mainstream. For example, known electrophotographic photoreceptors include a single-layer electrophotographic photoreceptor (hereinafter referred to as a single-layer photoreceptor) that contains a charge-generating material (CGM) and a charge-transporting material (CTM) in the same layer, and a multilayer electrophotographic photoreceptor (hereinafter referred to as a multilayer photoreceptor) that consists of a charge-generating layer containing a charge-generating material (CGM) and a charge-transporting layer containing a charge-transporting material (CTM). Furthermore, photoreceptor charging methods include a negative charging method, in which the photoreceptor surface is negatively charged, and a positive charging method, in which the photoreceptor surface is positively charged. Combinations of layer structures and charging methods of photoreceptors currently in practical use include "negatively charged multilayer photoreceptors" and "positively charged single layer photoreceptors."

[0004] A "negatively charged laminated photoreceptor" generally has a structure in which an undercoat layer (UCL) made of a resin or the like is provided on a conductive support such as an aluminum tube, on which a charge generation layer (CGL) made of a charge generation material (CGM) and a resin or the like is provided, and on which a charge transport layer (CTL) made of a hole transport material (HTM) and a resin or the like is provided. In the case of negatively charged multilayer photoreceptors, the surface of the photoreceptor is negatively charged using corona discharge or contact methods, and then the photoreceptor is exposed to light. The charge-generating material (CGM) absorbs this light, generating charge carriers (holes and electrons). Of these, the positive holes migrate through the charge-transport layer (CTL) via the hole-transport material (HTM) and reach the surface of the photoreceptor, neutralizing the surface charge. Meanwhile, the negative electrons generated by the CGM pass through the undercoat layer (UCL) and reach the substrate. Because holes are the primary transporters in the photoreceptor layer in negatively charged multilayer photoreceptors, the photoreceptor typically contains only a hole-transport material as the charge-transport material. Adding a compound with low hole-transport capacity, such as an electron-transport material, reduces the content of the hole-transport material in the photoreceptor layer, resulting in poor electrical properties. Furthermore, the binder resin content also decreases, potentially reducing abrasion resistance. For this reason, except in special cases, electron transport materials have not been incorporated into the photosensitive layer.

[0005] On the other hand, a "positively charged single-layer photoreceptor" generally has a configuration in which an undercoat layer (UCL) made of a resin or the like is provided on a conductive support such as an aluminum tube, and a single-layer photosensitive layer made of a charge generating material (CGM), a hole transport material (HTM), an electron transport material (ETM), and a resin or the like is provided on top of that (see, for example, Patent Document 1). In the case of such positively charged single-layer photoreceptors, the surface of the photoreceptor is positively charged using corona discharge or contact methods, and then the photoreceptor is exposed to light. This light is absorbed by the charge-generating material (CGM) near the surface of the photosensitive layer, generating charge carriers (holes and electrons). The electrons, or negative charge carriers, neutralize the surface charge on the photosensitive layer. Meanwhile, the holes, or positive charge carriers, generated by the charge-generating material (CGM) pass through the photosensitive layer and undercoat layer (UCL) to reach the substrate.

[0006] In either type of photoreceptor, the surface charge of the photoreceptor is neutralized, and an electrostatic latent image is formed due to the potential difference with the surrounding surface. The latent image is then visualized using toner (powder colored resin ink), and the toner is transferred to paper or other material and heated to melt and fix it, completing the print.

[0007] As described above, in the electrophotographic photoreceptor, a photosensitive layer is formed on a conductive support, and further, a protective layer may be provided on the photosensitive layer for the purpose of improving abrasion resistance and the like.

[0008] For example, Patent Document 1 discloses a method for forming an outermost layer using a thermoplastic alcohol-soluble resin as a binder resin and a polymer having an average primary particle diameter of 0.1 to 3 μm and a density of 3.0 g / cm. 3 It is disclosed that a surface protective layer containing the following filler is provided on the photosensitive layer. Patent Document 2 discloses a photosensitive layer having a surface protective layer on the surface side thereof, the surface protective layer being a cured product obtained by photocuring a composition containing a hindered amine compound, a polymerizable compound for a binder, and a charge transport agent.

[0009] Furthermore, Patent Documents 3 and 4 disclose electrophotographic photoreceptors having a photosensitive layer containing an enamine compound on a conductive support, as electrophotographic photoreceptors containing a compound having good solubility, high charge mobility, and excellent electrical properties in the photosensitive layer. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-163984 [Patent Document 2] Japanese Patent Application Publication No. 2019-35856 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-20504 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-139649 Summary of the Invention [Problem to be solved by the invention]

[0011] As a result of the inventors' investigations, it was found that photoreceptors having a curable resin-based protective layer may have poor electrical properties immediately after the protective layer is cured. It was also found that in such cases, heat treatment can improve the electrical properties. However, this heat treatment requires the installation of space and heating equipment for the heat treatment process, which increases the initial cost and also increases the running cost. Further investigation by the present inventors revealed that the above problem is likely to occur with negatively charged photoreceptors, whereas in the case of positively charged photoreceptors, even if a cured resin protective layer is provided, the problem of poor electrical characteristics unless heat treatment is performed tends to be less likely to occur.

[0012] An object of the present invention is to provide an electrophotographic photoreceptor having a cured resin-based protective layer with good electrical properties. [Means for solving the problem]

[0013] The present invention provides an electrophotographic photoreceptor having, on a conductive support, a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound (also referred to as a "cured resin-based protective layer") in this order, The Martens hardness of the photoreceptor is 255N / mm 2 That's all, The photosensitive layer contains at least a hole transport material (HTM), and the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is greater than 3.6 eV and less than 4.0 eV.

[0014] The present invention also provides an electrophotographic photoreceptor having, on a conductive support, a photosensitive layer and a cured resin-based protective layer containing a cured product obtained by curing a curable compound, in that order, The present invention proposes an electrophotographic photoreceptor, wherein the photosensitive layer contains a hole transport material (HTM) made of at least a compound represented by formula (I), and the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is greater than 3.6 eV and less than 4.0 eV.

[0015] Formula (I) TIFF0007782451000001.tif44170

[0016] In formula (I), Ar 1 ~Ar 6 may be the same or different and each represents an aryl group which may have a substituent, n represents an integer of 2 or more, Z represents a monovalent organic residue, and m represents an integer of 0 to 4. 1 ~Ar 2 At least one of the groups is a substituted aryl group.

[0017] That is, the gist of the present invention lies in the following [1] to

[19] .

[0018] [1] An electrophotographic photoreceptor having, on a conductive support, a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound, in that order, The Martens hardness of the photoreceptor is 255N / mm 2 That's all, The photosensitive layer of the electrophotographic photoreceptor contains at least a hole transport material (HTM), and the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is greater than 3.6 eV and less than 4.0 eV. [2] The electrophotographic photoreceptor according to [1], wherein the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is 3.8 eV or less. [3] The electrophotographic photoreceptor according to [1] or [2], wherein the protective layer contains inorganic particles, and the content of the inorganic particles in the protective layer is 10 parts by mass or more and 300 parts by mass or less per 100 parts by mass of the curable compound. [4] The electrophotographic photoreceptor according to [3], wherein the inorganic particles are surface-treated with an organosilicon compound.

[0019] [5] The electrophotographic photoreceptor according to [3] or [4], wherein the inorganic particles are metal oxide particles, and the band gap of the metal oxide particles is smaller than the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) of the photosensitive layer. [6] The electrophotographic photoreceptor according to any one of [1] to [5], wherein the curable compound is a photocurable compound. [7] The electrophotographic photoreceptor according to any one of [1] to [6], wherein the protective layer is a layer formed from a composition containing a curable compound, a polymerization initiator, and inorganic particles. [8] The electrophotographic photoreceptor according to any one of [1] to [7], wherein the photosensitive layer is a laminated photosensitive layer in which a charge generating layer and a charge transport layer are laminated in this order on the conductive support. [9] The Martens hardness is 270N / mm 2 The electrophotographic photoreceptor according to any one of [1] to [8] is characterized in that:

[0020]

[10] The electrophotographic photoreceptor according to any one of [1] to [9], wherein the hole transport material (HTM) of the photosensitive layer is an enamine compound.

[11] The electrophotographic photoreceptor according to any one of [1] to

[10] , wherein the hole transport material (HTM) of the photosensitive layer is a compound represented by the above formula (I).

[0021]

[12] The electrophotographic photoreceptor according to any one of [1] to

[11] , wherein the photosensitive layer contains a radical acceptor compound.

[13] The electrophotographic photoreceptor according to

[12] , wherein the energy difference between the HOMO level and the LUMO level of the radical acceptor compound in the photosensitive layer is 3.0 eV or less.

[14] The electrophotographic photoreceptor according to

[12] or

[13] , wherein the content of the radical acceptor compound in the photosensitive layer is 0.1 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the hole transport material (HTM) in the photosensitive layer.

[0022]

[15] The electrophotographic photoreceptor according to any one of [1] to

[14] , which is a negatively charged type.

[0023]

[16] An electrophotographic photoreceptor having, on a conductive support, a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound, in that order, The photosensitive layer contains at least a hole transport material (HTM) made of a compound represented by formula (I) above, and the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is greater than 3.6 eV and less than 4.0 eV.

[0024]

[17] The method for producing an electrophotographic photoreceptor according to any one of [1] to

[16] , wherein the protective layer is cured by irradiation with ultraviolet light and / or visible light.

[0025]

[18] A cartridge including the electrophotographic photosensitive member according to any one of [1] to

[16] .

[19] An image forming apparatus comprising the electrophotographic photosensitive member according to any one of [1] to

[16] . [Effects of the Invention]

[0026] An electrophotographic photoreceptor having a photosensitive layer and a curable resin-based protective layer sequentially formed on a conductive support, the photosensitive layer containing a hole transport material (HTM) that satisfies certain conditions, can improve electrical characteristics. In this case, the hole transport material (HTM) that satisfies the certain conditions is one in which the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is more than 3.6 eV and not more than 4.0 eV, or one that is a compound represented by the above formula (I). Furthermore, when the photosensitive layer contains a radical acceptor compound together with the hole transport material (HTM), the effects of further improving the strong exposure characteristics and ozone resistance can be obtained. [Brief explanation of the drawings]

[0027] [Figure 1] 1 is a diagram schematically illustrating an example of the configuration of an image forming apparatus that can be configured using an electrophotographic photosensitive member according to an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will now be described based on embodiments, although the present invention is not limited to the embodiments described below.

[0029] <<The present electrophotographic photoreceptor>> An electrophotographic photoreceptor according to one embodiment of the present invention (referred to as "the present electrophotographic photoreceptor" or "the present photoreceptor") is an electrophotographic photoreceptor that includes, in order on a conductive support, a photosensitive layer containing at least a predetermined hole transport material (HTM) and a cured resin-based protective layer (also referred to as "the present protective layer") containing a cured product obtained by curing a curable compound. The photoreceptor may optionally have layers other than the photosensitive layer and the protective layer.

[0030] The electrophotographic photoreceptor may be charged in any manner, and may be either a positively charged electrophotographic photoreceptor or a negatively charged electrophotographic photoreceptor. Among these, a negatively charged electrophotographic photoreceptor is preferred in terms of being able to more effectively enjoy the effects of the present invention. In the present invention, the term "negatively charged electrophotographic photoreceptor" refers to a photoreceptor whose surface is negatively charged, and the term "positively charged electrophotographic photoreceptor" refers to a photoreceptor whose surface is positively charged.

[0031] In the photoreceptor of the present invention, the side opposite to the conductive support is the upper side or front side, and the conductive support side is the lower side or back side.

[0032] <Photosensitive layer> The photosensitive layer in the present photoreceptor may be a single-layer type photosensitive layer in which a charge generating material (CGM) and a hole transport material (HTM) are present in the same layer, or a multi-layer type photosensitive layer separated into a charge generating layer and a charge transport layer. Among these, a multi-layer type photosensitive layer as described below is more preferred.

[0033] <Layered photosensitive layer> A preferred example of the laminated photosensitive layer in the present photoreceptor is a configuration in which a charge generation layer and a charge transport layer are laminated in this order on a conductive support. More specifically, for example, a configuration in which a charge transport layer (CTL) containing a predetermined hole transport material (HTM) is laminated on a charge generation layer (CGL) containing a charge generation material (CGM) can be mentioned. In this case, it is also possible to provide layers other than the charge generation layer (CGL) and the charge transport layer (CTL).

[0034] <Charge generation layer (CGL)> The charge generating layer may contain a charge generating material (CGM) and a binder resin. From the viewpoint of improving ozone resistance, the charge generating layer may further contain a radical acceptor compound, which will be described later.

[0035] (Charge-Generating Materials (CGM)) Examples of the charge generating material include inorganic photoconductive materials such as selenium and its alloys, cadmium sulfide, etc., and organic photoconductive materials such as organic pigments, etc. Among these, organic photoconductive materials are preferred, and organic pigments are particularly preferred.

[0036] Examples of organic pigments include phthalocyanine and azoperylene. Among these, phthalocyanine or azo is particularly preferred. Of these, phthalocyanine is most preferred. These all indicate the skeletal structure of a compound and include compounds having the skeletal structure, i.e., derivatives. When an organic pigment is used as the charge generating material, fine particles of the organic pigment are usually used in the form of a dispersed layer bound with various binder resins.

[0037] Specific examples of the phthalocyanine include metal-free phthalocyanine; phthalocyanine crystal types coordinated with metals such as copper, indium, gallium, tin, titanium, zinc, vanadium, silicon, germanium, and aluminum, or their oxides, halides, hydroxides, and alkoxides; and phthalocyanine dimers using oxygen atoms or the like as bridging atoms. Particularly preferred crystal types with high sensitivity include X-type and τ-type metal-free phthalocyanine, titanyl phthalocyanine (also known as oxytitanium phthalocyanine) such as A-type (also known as β-type), B-type (also known as α-type), and D-type (also known as Y-type), vanadyl phthalocyanine, chloroindium phthalocyanine, hydroxyindium phthalocyanine, chlorogallium phthalocyanine (also known as II-type), hydroxygallium phthalocyanine (also known as V-type), μ-oxo-gallium phthalocyanine dimers (also known as G-type and I-type), and μ-oxo-aluminum phthalocyanine dimers (also known as II-type).

[0038] Among these phthalocyanines, particularly preferred are Type A (also known as Type β), Type B (also known as Type α), Type D (Type Y) titanyl phthalocyanine, Type II chlorogallium phthalocyanine, Type V, which are characterized by exhibiting a clear peak at a diffraction angle 2θ of 27.1° (±0.2°) or 27.3° (±0.2°) in powder X-ray diffraction, and Type V hydroxygallium phthalocyanine, Type G μ-oxo-gallium phthalocyanine dimer, and Type X metal-free phthalocyanine, which are characterized by having the strongest peak at 28.1° (±0.2°), no peak at 26.2° (±0.2°), and a clear peak at 28.1° (±0.2°), with a half-width W at 25.9° (±0.2°) in the range of 0.1°≦W≦0.4°.

[0039] The phthalocyanine may be a single compound, or a mixture or mixed crystal state of several compounds. The mixed or mixed crystal state may be one in which the individual components are mixed afterwards, or one in which a mixed state is generated during the production or processing process of the phthalocyanine compound, such as synthesis, pigmentization, or crystallization. Examples of such treatments include acid paste treatment, grinding treatment, and solvent treatment. A method for generating a mixed crystal state includes, as described in JP-A-10-48859, mixing two types of crystals, mechanically grinding and deforming them, and then converting them into a specific crystalline state by solvent treatment.

[0040] The particle size of the charge generating material is usually 1 μm or less, and preferably 0.5 μm or less.

[0041] (binder resin) The binder resin used in the charge generating layer may be any known binder resin without any particular limitation. Examples thereof include polyvinyl acetal resins such as polyvinyl butyral resin, polyvinyl formal resin, and partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal or acetal; polyarylate resin, polycarbonate resin, polyester resin, modified ether polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin, polyvinylpyrrolidone resin; vinyl chloride-vinyl acetate copolymer; styrene-butadiene copolymer; vinylidene chloride-acrylonitrile copolymer; insulating resins such as styrene-alkyd resin; and organic photoconductive polymers such as poly-N-vinylcarbazole. Among these resins, polyvinyl acetal resins or polyvinyl acetate resins are preferred in terms of pigment dispersibility, adhesion to the conductive support or undercoat layer, and adhesion to the charge transport layer. These binder resins may be used either alone or as a mixture of two or more kinds in any combination.

[0042] (Other ingredients) In addition to the charge generating material and the binder resin, the charge generating layer may contain other components as needed. For example, known additives such as antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light shielding agents, and fillers may be added to improve film-forming properties, flexibility, coating properties, stain resistance, gas resistance, light resistance, etc.

[0043] (composition ratio) If the proportion of the charge generating material in the charge generating layer is too high, the stability of the coating liquid may decrease due to aggregation of the charge generating material, etc., while if the proportion of the charge generating material is too low, the sensitivity of the photoreceptor may decrease. Therefore, the compounding ratio (by mass) of the binder resin to the charge generating material is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, of the charge generating material per 100 parts by mass of the binder resin, and is preferably 1000 parts by mass or less, more preferably 500 parts by mass or less of the charge generating material. From the viewpoint of film strength, it is more preferably 300 parts by mass or less, and even more preferably 200 parts by mass or less.

[0044] (layer thickness) The thickness of the charge generating layer is preferably 0.1 μm or more, more preferably 0.15 μm or more, and is preferably 2.0 μm or less, more preferably 1.0 μm or less, and even more preferably 0.6 μm or less.

[0045] <Charge transport layer (CTL)> The charge transport layer (CTL) may contain a hole transport material (HTM) and a binder resin, and may further contain a radical acceptor compound.

[0046] (Hole Transport Material (HTM)) The hole transport material (HTM) contained in the photosensitive layer preferably contains a compound having an energy difference between the HOMO level and the LUMO level (also referred to as the "HOMO / LUMO energy level difference") of more than 3.6 eV and not more than 4.0 eV.

[0047] As described above, a photoreceptor having a cured resin-based protective layer (referred to as an "OCL photoreceptor") may have poor electrical properties immediately after curing. In contrast, by incorporating a compound having a HOMO / LUMO energy level difference of more than 3.6 eV and not more than 4.0 eV as a hole transport material (HTM) into the photosensitive layer, the electrical properties can be improved.

[0048] When forming a curable resin-based protective layer, curing generally proceeds with the involvement of radicals from polymerization initiators, etc. As a result, radicals propagate to the hole transport material (HTM) in the photosensitive layer, making it easier for HTM radicals to be generated. These HTM radicals are thought to act as charge trap sites, deteriorating electrical properties. Heat treatment improves electrical properties because the HTM radicals disappear during the heat treatment. When the HOMO / LUMO energy level difference is 3.6 eV or less, conjugation tends to spread, and HTM radicals tend to become stable, which leads to the generation of HTM radicals and the deterioration of electrical properties.On the other hand, when the energy difference is more than 4.0 eV, hole mobility tends to decrease, which leads to the deterioration of electrical properties. On the other hand, compounds with an energy difference of more than 3.6 eV and less than 4.0 eV have small conjugation extent and are thought to have unstable radical structures. Therefore, if the photosensitive layer contains a compound with an energy difference of more than 3.6 eV and less than 4.0 eV as a hole transport material (HTM), HTM radicals that serve as charge trap sites are not generated, and good electrical properties can be obtained without performing a heat treatment after curing the protective layer.

[0049] From this perspective, the hole transport material (HTM) contained in the photosensitive layer preferably has a HOMO / LUMO energy level difference of 4.0 eV or less, particularly 4.00 eV or less. From the perspective of electrical properties, it is more preferably 3.8 eV or less, particularly 3.80 eV or less, and even more preferably 3.7 eV or less, particularly 3.70 eV or less. When the energy difference is equal to or less than the upper limit, the conjugation is large and the hole mobility is high, resulting in good electrical properties. On the other hand, from the perspective of strong exposure characteristics, the energy difference is preferably greater than 3.6 eV, particularly more preferably greater than 3.60 eV. Of these, it is more preferably greater than 3.62 eV, and even more preferably greater than 3.64 eV. When the energy difference is greater than the lower limit, absorption of fluorescent light can be suppressed.

[0050] Examples of compounds having a HOMO / LUMO energy level difference of more than 3.6 eV and not more than 4.0 eV include heterocyclic compounds such as enamine derivatives, carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, and benzofuran derivatives, aniline derivatives, hydrazone derivatives, aromatic amine derivatives, stilbene derivatives, butadiene derivatives, and compounds in which two or more of these compounds are bonded. Among these, carbazole derivatives, aromatic amine derivatives, stilbene derivatives, butadiene derivatives and enamine derivatives are preferred, enamine derivatives and butadiene derivatives are more preferred, and enamine derivatives are even more preferred. Among these compounds, compounds corresponding to the above energy levels (HOMO level and LUMO level) can be appropriately selected. Two or more compounds corresponding to the above energy levels can also be used in combination. Furthermore, as the hole transport material (HTM), two or more compounds may be used in combination: a compound having a HOMO / LUMO energy level difference of more than 3.6 eV and not more than 4.0 eV; and a compound having the same level difference of not more than 3.6 eV or more than 4.0 eV.

[0051] In the present invention, the HOMO energy level (E_homo) and the LUMO energy level (E_lumo) can be obtained by finding a stable structure through structural optimization calculations using B3LYP (see A. D. Becke, J. Chem. Phys. 98, 5648 (1993); C. Lee, et al., Phys. Rev. B37, 785 (1988); and B. Miehlich, et al., Chem. Phys. Lett. 157, 200 (1989)), a type of density half-function method.

[0052] In this case, the basis set used was 6-31G(d,p), which is a polarization function added to 6-31G (R. Ditchfield, et al., J. Chem. Phys. 54, 724 (1971), W. J. Hehre, et al., J. Chem. Phys. 56, 2257 (1972), P. C. Ariharan et al., Mol. Phys. 27, 209 (1974), M. S. Gordon, Chem. Phys. Lett. 76, 163 (1980), P. C. Ariharan et.al., Theo.Chim.Acta28,213(1973), J.-P.Blaudeau,et.al.,J.Chem.Phys.107,5016(1997), MMFrancl,et.al.,J.Chem.Phys.77,3654(1982), RCBinning Jr. et.al., J. Comp. Chem. 11, 1206 (1990), VA Rassolov, et. al., J. Chem. Phys. 109, 1223 (1998), and VA Rassolov, et. al., J. Comp. Chem. 22, 976 (2001)). In the present invention, the B3LYP calculation using 6-31G(d,p) is referred to as B3LYP / 6-31G(d,p).

[0053] In the present invention, the program used for the B3LYP / 6-31G(d,p) calculations was Gaussian 03, Revision D.01 (MJ Frisch, et al., Gaussian, Inc., Wallingford CT, 2004).

[0054] The charge transport layer (CTL) and photosensitive layer of the present photoreceptor may contain, within the scope of the present invention, a hole transport material (HTM) that does not fall within the energy level difference between the HOMO and LUMO energy levels of more than 3.6 eV and 4.0 eV or less, in addition to the compound having such an energy level difference, provided that the effect of the present invention is not impaired. However, from the viewpoint of maintaining the effect of the present invention, the content of the latter compound in the charge transport layer (CTL) and photosensitive layer is preferably less than 100 parts by weight, more preferably less than 80 parts by weight, even more preferably less than 60 parts by weight, even more preferably less than 50 parts by weight, even more preferably less than 20 parts by weight, per 100 parts by weight of the former compound.

[0055] A suitable example of a hole transport material (HTM) is a compound represented by the following formula (I): That is, a compound having a HOMO / LUMO energy level difference of more than 3.6 eV and not more than 4.0 eV and represented by formula (I) is suitable as a hole transport material (HTM), but is not limited thereto. Any one of the compounds represented by formula (I) may be used alone, or two or more of them may be used in any combination. When two or more compounds represented by formula (I) are used in combination, a compound having a HOMO / LUMO energy level difference of more than 3.6 eV and not more than 4.0 eV may be used in combination with a compound having a level difference of not more than 3.6 eV or more than 4.0 eV. The energy level of the compound represented by formula (I) depends on the structure of the compound, i.e., Ar 1 ~Ar 6 , n, Z, m.

[0056] Formula (I) TIFF0007782451000002.tif44170

[0057] In formula (I), Ar 1 ~Ar 6may be the same or different and each represents an aryl group which may have a substituent, n represents an integer of 2 or more, Z represents a monovalent organic residue, and m represents an integer of 0 to 4. 1 ~Ar 2 At least one of the groups is a substituted aryl group.

[0058] In the formula (I), Ar 1 ~Ar 6 represents an aryl group which may have a substituent, and may be the same or different. Among these, an aryl group having 6 to 20 carbon atoms is preferred, and an aryl group having 6 to 12 carbon atoms is more preferred. Specific examples include a phenyl group, a naphthyl group, a fluorenyl group, an anthryl group, a phenanthryl group, and a pyrenyl group, and preferably a phenyl group, a naphthyl group, and a fluorenyl group. In terms of production costs, an aryl group having 6 to 10 carbon atoms, such as a phenyl group or a naphthyl group, is particularly preferred. Furthermore, when a substituent is present, the substituent preferably has 1 to 10 carbon atoms and a substituent constant σp according to Hammett's rule of 0.20 or less.

[0059] Here, Hammett's rule is an empirical rule used to explain the effect that substituents in aromatic compounds have on the electronic state of the aromatic ring. The substituent constant σp of a substituted benzene can be said to be a value that quantifies the degree of electron donating / withdrawing of the substituent. If the σp value is positive, the substituent is more acidic than the unsubstituted one, that is, it is an electron-withdrawing substituent. Conversely, if the σp value is negative, it is an electron-donating substituent. Table 1 shows the σp values ​​of representative substituents ("Chemical Handbook, Basics II, Revised 4th Edition," edited by the Chemical Society of Japan, Maruzen Co., Ltd., published September 30, 1993, pp. 364-365).

[0060] [Table 1]

[0061] Examples of such substituents include alkyl groups having 1 to 10 carbon atoms, alkoxy groups having 1 to 10 carbon atoms, alkylamino groups having 2 to 10 carbon atoms, and aryl groups having 6 to 10 carbon atoms, and specific examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, methoxy, ethoxy, propoxy, butoxy, N,N-dimethylamino, N,N-diethylamino, phenyl, 4-tolyl, 4-ethylphenyl, 4-propylphenyl, 4-butylphenyl, and naphthyl groups. Among these, from the viewpoint of electrical properties, alkyl groups having 1 to 4 carbon atoms are preferred, and methyl and ethyl groups are particularly preferred.

[0062] In the formula (I), n is usually an integer of 2 or more in order to improve the electrical properties of the electrophotographic photoreceptor, and there is no particular upper limit as long as the electrical properties are not adversely affected, but an integer of 5 or less is preferred, and an integer of 3 or less is more preferred. Considering the compatibility with the photosensitive layer, production costs, and the like comprehensively, n is preferably 2 or 3, and the case where n=2 is particularly preferred.

[0063] In the formula (I), examples of the monovalent organic residue Z include alkyl groups having 1 to 4 carbon atoms, alkoxy groups having 1 to 4 carbon atoms, alkylamino groups having 2 to 4 carbon atoms, and aryl groups having 6 to 10 carbon atoms, and specific examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, methoxy, ethoxy, propoxy, butoxy, N,N-dimethylamino, N,N-diethylamino, phenyl, 4-tolyl, 4-ethylphenyl, 4-propylphenyl, 4-butylphenyl, naphthyl, etc. Among these, alkyl groups having 1 to 4 carbon atoms are particularly preferred in terms of electrical properties. In the formula (I), m is preferably an integer of 0 to 1, but from the viewpoint of production costs, it is particularly preferable for m=0.

[0064] (Radical acceptor compounds) The charge transport layer (CTL) of the present electrophotographic photoreceptor may further contain a radical acceptor compound, if necessary. In the present invention, the term "radical acceptor compound" refers to a compound that has the property of being able to accept radicals from a hole transport material (HTM), and more specifically, refers to a compound that has an electron affinity of 3.5 eV or more. Here, electron affinity refers to the energy generated when a substance absorbs one electron, and can be obtained by determining a stable structure through geometry optimization calculations using B3LYP (see A. D. Becke, J. Chem. Phys. 98, 5648 (1993), C. Lee, et al., Phys. Rev. B37, 785 (1988), and B. Miehlich, et al., Chem. Phys. Lett. 157, 200 (1989)), a type of density half-function method mentioned above. When determining electron affinity, the same basis set and calculation program as those mentioned above can be used.

[0065] The inclusion of a radical acceptor compound in the charge transport layer (CTL) of the present electrophotographic photoreceptor can further improve the strong exposure characteristics and ozone resistance, i.e., the deterioration of performance when the present photoreceptor is exposed to light such as fluorescent light can be further suppressed (strong exposure characteristics), and the deterioration of performance when the present photoreceptor is exposed to an ozone atmosphere can be further suppressed (ozone resistance). The reason for this is unclear, but as mentioned above, HTM within the scope of the present invention has an unstable radical structure and is therefore less likely to form radicals. However, it is possible that a small amount of radicals still exists. It is thought that these radicals are more likely to decompose upon strong exposure, thereby worsening the strong exposure characteristics. When a radical acceptor compound is contained, the radical acceptor compound is more likely to form radicals than the HTM. Therefore, even if there are only a small number of HTM radicals, it is thought that the radicals will transfer to the radical acceptor compound and the HTM will no longer be in a radical state. This is thought to eliminate charge trap sites, further improving the strong exposure characteristics. On the other hand, the ozone resistance is particularly effective after a certain period of time has passed since exposure to an ozone atmosphere (e.g., two days after exposure). This is because ozone reaches the charge generation layer from the surface of the photoreceptor after a certain period of time, causing degradation of the charge generation material (CGM). When a radical acceptor compound is contained, the radical acceptor compound is easily oxidized by ozone, so the ozone is consumed before it reaches the charge generation layer, which is thought to result in suppression of CGM degradation. Furthermore, it is believed that the radical acceptor compound oxidized by ozone does not adversely affect electrical properties. In particular, the strong exposure characteristics can be further improved by dispersing the hole transport material (HTM) and the radical acceptor compound in the same layer.

[0066] Furthermore, when an electron transport material (ETM) described below is incorporated into the photosensitive layer, ETM forms radicals more easily than HTM, and therefore even if an HTM radical is generated, the HTM radical immediately abstracts a hydrogen atom from the ETM, converting the HTM radical to HTM, further improving the strong exposure characteristics and ozone resistance. Considering this mechanism of action, all electron transport materials (ETMs) are included in the category of "radical acceptor compounds," and it is believed that the use of electron transport materials (ETMs) can also achieve further improvements in strong exposure characteristics and ozone resistance through a mechanism similar to that of radical acceptor compounds.

[0067] The radical acceptor compound that can be used in the present electrophotographic photoreceptor is preferably a compound having an energy difference between the HOMO level and the LUMO level of 3.0 eV or less, particularly 3.00 eV or less. If the energy difference of the radical acceptor compound is 3.0 eV or less, the ultraviolet light shielding ability is high, which is preferable. From this viewpoint, the energy difference between the HOMO level and the LUMO level of the radical acceptor compound is preferably 3.0 eV or less, particularly preferably 3.00 eV or less, more preferably 2.8 eV or less, particularly preferably 2.80 eV or less, and even more preferably 2.6 eV or less, particularly preferably 2.60 eV or less. From the viewpoint of the transmittance of exposure light, the lower limit of the energy difference of the radical acceptor compound is preferably 2.0 eV or more, particularly 2.00 eV or more, more preferably 2.1 eV or more, particularly 2.10 eV or more, and even more preferably 2.2 eV or more, particularly 2.20 eV or more.

[0068] In order to enjoy the effects of the present invention more effectively, the electron affinity of the radical acceptor compound is preferably 3.5 eV or more, particularly 3.50 eV or more, more preferably 3.7 eV or more, particularly 3.70 eV or more, and even more preferably 3.8 eV or more, particularly 3.80 eV or more. On the other hand, the electron affinity of the radical acceptor compound is preferably 4.3 eV or less, particularly 4.30 eV or less, more preferably 4.1 eV or less, particularly 4.10 eV or less, even more preferably 4.0 eV or less, particularly 4.00 eV or less, and especially preferably 3.9 eV or less, particularly 3.90 eV or less.

[0069] Preferred embodiments of the radical acceptor compound can be similarly applied to the preferred embodiments of the electron transport material (ETM) described below. The radical acceptor compound can be selected from the electron transport materials (ETM) described below. Compounds other than the compounds exemplified as electron transport materials (ETM) can also be used. Furthermore, compounds exemplified as electron transport materials (ETM) can also be used in combination with other compounds.

[0070] The content of the radical acceptor compound in the photosensitive layer of the electrophotographic photoreceptor is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the hole transport material (HTM) in the photosensitive layer, and is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less. The content ratio of the radical acceptor compound and the hole transport material (HTM) in the photoreceptor is the same as the content ratio of the radical acceptor compound and the hole transport material (HTM) in the photosensitive layer described above. The content ratio of the radical acceptor compound and the hole transport material (HTM) in the charge transport layer (CTL) is the same as the content ratio of the radical acceptor compound and the hole transport material (HTM) in the photosensitive layer described above.

[0071] (Electron transport material (ETM)) As described above, when the charge transport layer (CTL) or photosensitive layer of the present photoreceptor contains an electron transport material (ETM) in addition to the hole transport material (HTM), the strong exposure characteristics and ozone resistance can be further improved.

[0072] As the electron transport material (ETM) that can be used in the present photoreceptor, a compound having an energy difference between the HOMO level and the LUMO level of 3.0 eV or less, particularly 3.00 eV or less, is preferred. If the energy difference of the ETM is 3.0 eV or less, the ultraviolet light shielding ability is high, which is preferable. From this viewpoint, the energy difference between the HOMO level and the LUMO level of the electron transport material (ETM) is preferably 3.0 eV or less, particularly 3.00 eV or less, more preferably 2.8 eV or less, particularly 2.80 eV or less, even more preferably 2.6 eV or less, particularly preferably 2.60 eV or less. From the viewpoint of the transparency of exposure light, the lower limit of the energy difference of the electron transport material (ETM) is preferably 2.0 eV or more, particularly 2.00 eV or more, more preferably 2.1 eV or more, particularly 2.10 eV or more, and even more preferably 2.2 eV or more, particularly 2.20 eV or more.

[0073] Examples of electron transport materials (ETMs) that can be used in the present photoreceptor include electron-withdrawing substances such as aromatic nitro compounds such as 2,4,7-trinitrofluorenone, cyano compounds such as tetracyanoquinodimethane, quinone compounds such as diphenoquinone and dinaphthylquinone, and the like, as well as compounds in which a plurality of these compounds are bonded, and polymers having groups consisting of these compounds in the main chain or side chain. However, the present invention is not limited to these, and known electron transport materials can be used. Among these, from the viewpoint of electrical properties, the electron transport material (ETM) is preferably a compound having a diphenoquinone structure or a dinaphthylquinone structure, and among these, a compound having a dinaphthylquinone structure is more preferred. The above electron transport materials may be used alone or in any combination of two or more.

[0074] Specific examples of electron transport materials (ETMs) that can be used in the present photoreceptor include compounds represented by general formulas (ET1) to (ET3) exemplified in paragraphs 0043 to 0053 of JP-A No. 2017-09765.

[0075] Specific examples of the electron transport material (ETM) include compounds having any of the following structures: However, the present invention is not limited to these. Any one of these may be used alone, or two or more of these may be used in any combination.

[0076] TIFF0007782451000004.tif50170

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[0078] TIFF0007782451000006.tif28170

[0079] TIFF0007782451000007.tif34170

[0080] The content of the electron transport material (ETM) in the photosensitive layer is preferably 0.1 parts by weight or more, more preferably 0.3 parts by weight or more, and even more preferably 0.5 parts by weight or more, per 100 parts by weight of the hole transport material (HTM) in the photosensitive layer, and is preferably 10 parts by weight or less, more preferably 7 parts by weight or less, and even more preferably 5 parts by weight or less.

[0081] The content ratio of the electron transport material (ETM) and the hole transport material (HTM) in the photoreceptor is the same as the content ratio of the electron transport material (ETM) and the hole transport material (HTM) in the photosensitive layer described above.

[0082] The content ratio of the electron transport material (ETM) and the hole transport material (HTM) in the charge transport layer (CTL) is the same as the content ratio of the electron transport material (ETM) and the hole transport material (HTM) in the photosensitive layer described above.

[0083] (binder resin) Examples of the binder resin for the charge transport layer include vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymers thereof, thermoplastic resins such as polycarbonate, polyarylate, polyester, polyester polycarbonate, polysulfone, phenoxy, epoxy, and silicone resins, and various thermosetting compounds. Among these resins, polycarbonate resins and polyarylate resins are preferred in terms of light attenuation characteristics and mechanical strength as a photoreceptor.

[0084] The viscosity-average molecular weight (Mv) of the binder resin is typically 5,000 to 300,000, preferably 10,000 or more or 200,000 or less, more preferably 15,000 or more or 150,000 or less, and even more preferably 20,000 or more or 80,000 or less. If the viscosity-average molecular weight (Mv) is too small, the mechanical strength of the resulting film, such as that used to form a photoreceptor, tends to decrease. Furthermore, if the viscosity-average molecular weight (Mv) is too large, the viscosity of the coating solution increases, making it difficult to coat the film to an appropriate thickness.

[0085] The binder resin and hole transport material (HTM) constituting the photosensitive layer are typically blended in a ratio of 20 parts by weight or more of the hole transport material (HTM) per 100 parts by weight of the binder resin. From the viewpoint of reducing residual potential, it is preferable to blend 30 parts by weight or more of the hole transport material (HTM) per 100 parts by weight of the binder resin. Furthermore, from the viewpoints of stability and charge mobility during repeated use, it is more preferable to blend 40 parts by weight or more of the hole transport material (HTM). On the other hand, from the viewpoint of thermal stability of the photosensitive layer, it is preferable to blend 200 parts by weight or less of the hole transport material (HTM) per 100 parts by weight of the binder resin. Furthermore, from the viewpoint of compatibility between the hole transport material (HTM) and the binder resin, it is more preferable to blend 150 parts by weight or less of the hole transport material (HTM). From the viewpoint of glass transition temperature, it is particularly preferable to blend 120 parts by weight or less of the hole transport material (HTM). When the hole transport material (HTM) is blended in an amount of 120 parts by mass or less, the glass transition temperature of the photosensitive layer increases, and improvement in leakage resistance can be expected. The blending ratio of the binder resin constituting the charge transport layer and the hole transport material (HTM) is the same as the blending ratio of the binder resin constituting the photosensitive layer described above and the hole transport material (HTM).

[0086] The hole transport material (HTM) content relative to the total mass of the photosensitive layer is typically 16 parts by mass or more per 100 parts by mass of photosensitive layer. From the perspective of reducing residual potential, it is preferable to incorporate 22 parts by mass or more of the hole transport material (HTM) per 100 parts by mass of photosensitive layer. Furthermore, from the perspective of stability and charge mobility during repeated use, it is more preferable to incorporate 28 parts by mass or more. From the perspective of thermal stability of the photosensitive layer, it is preferable to incorporate 68 parts by mass or less of the hole transport material (HTM) per 100 parts by mass of photosensitive layer. From the perspective of uniformity of the photosensitive layer, it is more preferable to incorporate 59 parts by mass or less. From the perspective of glass transition temperature, it is particularly preferable to incorporate 53 parts by mass or less of the hole transport material (HTM). Incorporation of 53 parts by mass or less of the hole transport material (HTM) increases the glass transition temperature of the photosensitive layer, which is expected to improve leakage resistance.

[0087] In the charge transport layer (CTL), the binder resin and the hole transport material (HTM) are preferably blended in a ratio of 20 parts by weight or more of the hole transport material (HTM) per 100 parts by weight of the binder resin. From the viewpoint of reducing residual potential, it is more preferable to blend 30 parts by weight or more of the hole transport material (HTM) per 100 parts by weight of the binder resin. Furthermore, from the viewpoints of stability during repeated use and charge mobility, it is even more preferable to blend 40 parts by weight or more of the hole transport material (HTM). On the other hand, from the viewpoint of thermal stability of the photosensitive layer, it is preferable to blend 200 parts by weight or less of the hole transport material (HTM) per 100 parts by weight of the binder resin. Furthermore, from the viewpoint of compatibility between the hole transport material (HTM) and the binder resin, it is more preferable to blend 150 parts by weight or less of the hole transport material (HTM), and from the viewpoint of glass transition temperature, it is particularly preferable to blend 120 parts by weight or less. When the hole transport material (HTM) is blended in an amount of 120 parts by mass or less, the glass transition temperature of the photosensitive layer increases, and improvement in leakage resistance can be expected.

[0088] (Other ingredients) In addition to the hole transport material (HTM), electron transport material (ETM), and binder resin, the charge transport layer may contain other components as needed. For example, known additives such as antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light shielding agents, and fillers may be added to improve film-forming properties, flexibility, coating properties, stain resistance, gas resistance, light resistance, etc.

[0089] (layer thickness) The thickness of the charge transport layer is not particularly limited, but from the viewpoints of electrical properties, image stability, and high resolution, it is preferably 5 μm to 50 μm, more preferably 10 μm to 35 μm, and even more preferably 15 μm to 25 μm.

[0090] <Single-layer photosensitive layer> The single-layer photosensitive layer of the present photoreceptor may have a structure in which a charge generating material (CGM) and a hole transporting material (HTM) are present in the same layer. The single-layer photosensitive layer may further contain the radical acceptor compound or the electron transporting material (ETM). The charge generating material (CGM), hole transport material (HTM), radical acceptor compound, and electron transport material (ETM) of the single-layer photosensitive layer can be the same as those of the multi-layer photosensitive layer. The content and content ratio of each of these materials in the single-layer photosensitive layer are also the same as those in the multi-layer photosensitive layer.

[0091] (Method of forming each layer) Each of the above layers can be formed by dissolving or dispersing the substance to be contained in a solvent or dispersion medium, and then coating or dispersing the coating solution onto the conductive support by a known method such as dip coating, spray coating, nozzle coating, bar coating, roll coating, blade coating, etc., and then repeating the steps of coating and drying for each layer, although the formation method is not limited to these.

[0092] The solvent or dispersion medium used to prepare the coating solution is not particularly limited. Specific examples include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol, ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane, esters such as methyl formate and ethyl acetate, ketones such as acetone, methyl ethyl ketone, cyclohexanone, and 4-methoxy-4-methyl-2-pentanone, aromatic hydrocarbons such as benzene, toluene, and xylene, chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichloroethylene, nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, and triethylenediamine, and aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide. These may be used alone or in any combination of two or more of them in any type.

[0093] The amount of the solvent or dispersion medium used is not particularly limited, and is preferably adjusted appropriately so that the solids concentration, viscosity, and other physical properties of the coating liquid fall within the desired range, taking into consideration the purpose of each layer and the properties of the selected solvent or dispersion medium. The coating film is preferably dried to the touch at room temperature, and then heated and dried at a temperature in the range of 30° C. to 200° C. for 1 minute to 2 hours, either stationary or with a fan. The heating temperature may be constant, or the temperature may be varied during drying.

[0094] <Main protective layer> The protective layer is preferably a layer containing a cured product obtained by curing a curable compound. The protective layer can be formed from a composition containing a curable compound and a polymerization initiator. Among these, it is preferable to form the protective layer by thermally curing or photocuring a curable composition containing a curable compound, a polymerization initiator, and inorganic particles, and it is more preferable to form the protective layer by photocuring a photocurable compound that can be photocured.

[0095] (Curable composition) An example of the curable composition is a composition containing a curable compound, a polymerization initiator, inorganic particles, and, if necessary, other materials.

[0096] (curable compound) The curable compound is preferably a monomer, oligomer, or polymer having a radical polymerizable functional group. Among them, a curable compound having crosslinkability, particularly a photocurable compound, is preferred. For example, a curable compound having two or more radical polymerizable functional groups can be used. A compound having one radical polymerizable functional group can also be used in combination. Examples of the radically polymerizable functional group include a vinyl group, an acryloyl group, a methacryloyl group, an acryloyloxy group, a methacryloyloxy group, and an epoxy group.

[0097] Examples of preferred compounds as curable compounds having a radical polymerizable functional group are given below. Examples of monomers having an acryloyl group or a methacryloyl group include trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate, HPA-modified trimethylolpropane triacrylate, EO-modified trimethylolpropane triacrylate, PO-modified trimethylolpropane triacrylate, caprolactone-modified trimethylolpropane triacrylate, HPA-modified trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerol triacrylate, ECH-modified glycerol triacrylate, EO-modified glycerol triacrylate, PO-modified glycerol triacrylate, tris(acryloxyethyl)isocyanurate, caprolactone-modified tris(acryloxyethyl)isocyanurate, EO-modified tris(acryloxyethyl)isocyanurate, PO-modified tris(acryloxyethyl)isocyanurate, and the like. (Acryloxyethyl) isocyanurate, dipentaerythritol hexaacrylate, caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hydroxypentaacrylate, alkyl-modified dipentaerythritol pentaacrylate, alkyl-modified dipentaerythritol tetraacrylate, alkyl-modified dipentaerythritol triacrylate, dimethylolpropane tetraacrylate, pentaerythritol ethoxy tetraacrylate, EO-modified phosphate triacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, polytetramethylene glycol diacrylate, EO-modified bisphenol A diacrylate, PO-modified bisphenol A diacrylate, 9,Examples of such acrylic copolymers include 9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, tricyclodecane dimethanol diacrylate, decanediol diacrylate, hexanediol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, EO-modified bisphenol A dimethacrylate, PO-modified bisphenol A dimethacrylate, tricyclodecane dimethanol dimethacrylate, decanediol dimethacrylate, and hexanediol dimethacrylate.

[0098] Examples of oligomers and polymers having an acryloyl group or a methacryloyl group include urethane acrylate, ester acrylate, acrylic acrylate, epoxy acrylate, etc. Among these, urethane acrylate and ester acrylate are preferred, and urethane acrylate is more preferred.

[0099] The above compounds can be used alone or in combination of two or more.

[0100] (Polymerization initiator) The polymerization initiator includes a thermal polymerization initiator, a photopolymerization initiator, and the like. Examples of the thermal polymerization initiator include peroxide compounds such as 2,5-dimethylhexane-2,5-dihydroperoxide, dicumyl peroxide, benzoyl peroxide, t-butyl peroxide, t-butylcumyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, and lauroyl peroxide, and azo compounds such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(methyl isobutyrate), 2,2'-azobis(isobutylamidine hydrochloride), and 4,4'-azobis-4-cyanovaleric acid.

[0101] Photopolymerization initiators can be classified into direct cleavage type and hydrogen abstraction type based on the radical generation mechanism. Direct cleavage type photopolymerization initiators generate radicals by cleaving some of the covalent bonds within the molecule when they absorb light energy. On the other hand, hydrogen abstraction type photopolymerization initiators generate radicals when the molecule becomes excited by absorbing light energy and abstracts hydrogen from the hydrogen donor.

[0102] Examples of the direct cleavage type photopolymerization initiator include acetophenone or ketal compounds such as acetophenone, 2-benzoyl-2-propanol, 1-benzoylcyclohexanol, 2,2-diethoxyacetophenone, benzyl dimethyl ketal, and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone; benzoin ether compounds such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, and O-tosylbenzoin; and acylphosphine oxide compounds such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and lithium phenyl(2,4,6-trimethylbenzoyl)phosphonate.

[0103] Examples of hydrogen abstraction photopolymerization initiators include benzophenone compounds such as benzophenone, 4-benzoylbenzoic acid, 2-benzoylbenzoic acid, methyl 2-benzoylbenzoate, methyl benzoylformate, benzyl, p-anisil, 2-benzoylnaphthalene, 4,4'-bis(dimethylamino)benzophenone, 4,4'-dichlorobenzophenone, and 1,4-dibenzoylbenzene, and anthraquinone or thioxanthone compounds such as 2-ethylanthraquinone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone. Other examples of photopolymerization initiators include camphorquinone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime, acridine compounds, triazine compounds, and imidazole compounds.

[0104] In order to efficiently absorb light energy and generate radicals, the photopolymerization initiator preferably has an absorption wavelength in the wavelength range of the light source used for light irradiation. On the other hand, if any component other than the photopolymerization initiator among the compounds contained in the outermost layer has absorption in this wavelength range, the photopolymerization initiator may not be able to absorb sufficient light energy, resulting in reduced radical generation efficiency. Because common binder resins, charge transport materials, and metal oxide particles have absorption wavelengths in the ultraviolet (UV) range, this effect is particularly pronounced when the light source used for light irradiation is ultraviolet (UV). To prevent such problems, it is preferable to use an acylphosphine oxide-based compound, which has an absorption wavelength relatively toward the long wavelength side among photopolymerization initiators. Furthermore, acylphosphine oxide-based compounds exhibit a photobleaching effect, in which the absorption wavelength range shifts to the short wavelength side upon self-cleavage, allowing light to penetrate deep into the outermost layer and providing good internal curing properties. In this case, it is even more preferable to use a hydrogen abstraction initiator in combination with the compound to enhance the curing properties of the outermost layer surface. The content ratio of the hydrogen abstraction initiator relative to the acylphosphine oxide compound is not particularly limited, but from the viewpoint of supplementing surface curability, it is preferably 0.1 parts by mass or more relative to 1 part by mass of the acylphosphine oxide compound, and from the viewpoint of maintaining internal curability, it is preferably 5 parts by mass or less.

[0105] In addition, a photopolymerization accelerator may be used alone or in combination with the photopolymerization initiator, such as triethanolamine, methyldiethanolamine, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, or 4,4'-dimethylaminobenzophenone.

[0106] These polymerization initiators may be used alone or in combination of two or more. The content of the polymerization initiator is preferably 0.5 to 40 parts by mass, more preferably 1 part by mass or more or 20 parts by mass or less, relative to 100 parts by mass of the radically polymerizable curable composition.

[0107] (Inorganic particles) The protective layer preferably contains inorganic particles as needed, but does not necessarily contain inorganic particles. The inclusion of inorganic particles in the protective layer not only enhances charge transportability but also increases hardness and abrasion resistance, and furthermore, when the protective layer is photocured, it has the effect of suppressing photodegradation of the photosensitive layer.

[0108] As the inorganic particles, metal oxide particles are preferred from the viewpoint of imparting charge transportability and improving mechanical strength.

[0109] As the metal oxide particles, any metal oxide particles that can be used for an electrophotographic photoreceptor can be used. More specifically, as the metal oxide particles, metal oxide particles containing one type of metal element such as titanium oxide, tin oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, iron oxide, etc., and metal oxide particles containing multiple metal elements such as calcium titanate, strontium titanate, barium titanate, etc. As the metal oxide particles, only one type of particles may be used, or multiple types of particles may be mixed and used.

[0110] Among these inorganic particles, metal oxide particles having a band gap smaller than the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) in the photosensitive layer are preferred from the viewpoint of strong exposure characteristics. When multiple types of HTM are used in the photosensitive layer, the energy difference between the HOMO level and the LUMO level of the HTM with the smaller energy difference is used as the reference, within the range specified by the present invention. When the band gap of the metal oxide particles is smaller than the energy difference, the wavelength absorbed by the hole transport material (HTM) can be cut depending on the amount added, resulting in good strong exposure characteristics. From this viewpoint, metal oxide particles such as titanium oxide, zinc oxide, tin oxide, calcium titanate, strontium titanate, and barium titanate are preferred. Among these, titanium oxide, tin oxide, and zinc oxide are more preferred, and titanium oxide particles are particularly preferred.

[0111] The crystalline form of the titanium oxide particles may be any of rutile, anatase, brookite, and amorphous. Also, the titanium oxide particles may have different crystalline forms, and may contain a plurality of crystalline forms.

[0112] The metal oxide particles may be surface-treated with various methods. For example, they may be treated with an inorganic substance such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, or silicon oxide, or with an organic substance such as stearic acid, polyol, or an organosilicon compound. In particular, when titanium oxide particles are used, those surface-treated with an organosilicon compound are preferred. Examples of the organosilicon compound include silicone oils such as dimethylpolysiloxane and methylhydrogenpolysiloxane, organosilanes such as methyldimethoxysilane and diphenyldimethoxysilane, silazanes such as hexamethyldisilazane, and silane coupling agents such as 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, vinyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane. In particular, from the viewpoint of improving the mechanical strength of the outermost layer, 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, and vinyltrimethoxysilane, which have a chain-polymerizable functional group, are preferred.

[0113] Before treating the outermost surface of the metal oxide particles with such a treatment agent, the particles may be pretreated with an insulating material such as aluminum oxide, silicon oxide or zirconium oxide.

[0114] The inorganic particles may be of one type only, or may be a mixture of multiple types of particles.

[0115] In general, inorganic particles having an average primary particle size of 500 nm or less are preferably used, more preferably 1 nm to 100 nm, and even more preferably 5 to 50 nm. This average primary particle size can be determined from the arithmetic mean value of particle sizes observed directly with a transmission electron microscope (hereinafter also referred to as TEM).

[0116] The content of inorganic particles in the protective layer is not particularly limited. For example, from the viewpoint of electrical properties, it is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more, relative to 100 parts by mass of the curable compound. Furthermore, from the viewpoint of maintaining good surface resistance, it is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and particularly preferably 100 parts by mass or less.

[0117] (Other ingredients) The protective layer may contain other materials as needed. Examples of other materials include stabilizers (heat stabilizers, UV absorbers, light stabilizers, antioxidants, etc.), dispersants, antistatic agents, colorants, lubricants, etc. These may be used alone or in any combination and ratio.

[0118] (Curing method) The curing method can be any of heat curing, photocuring, electron beam curing, radiation curing, etc., but photocuring is preferred because of its safety and energy saving. Among photocuring methods, curing with ultraviolet light and / or visible light, especially metal halide light and LED light, is preferred, and curing with LED light, which allows for reaction control and suppression of heat generation, is more preferred. The wavelength of the LED light is preferably 400 nm or less, more preferably 385 nm or less, from the viewpoint of curing speed.

[0119] (Martens hardness) The Martens hardness of this photoconductor is 255N / mm 2 It is preferable that the strength is 270N / mm or more. 2 Above all, 300N / mm 2 Above all, 320N / mm 2 Above all, 330N / mm 2 It is more preferable that the Martens hardness is 255 N / mm or more. 2 If the thickness is equal to or greater than this, sufficient wear resistance can be provided for practical use. On the other hand, in order to prevent cracks from occurring, the Martens hardness of this photoreceptor is 500N / mm 2 Preferably, it is less than 400N / mm 2 More preferably, it is 350N / mm or less. 2 It is more preferable that: In the present invention, the Martens hardness of the photoreceptor means the Martens hardness measured from the surface side of the photoreceptor. The Martens hardness can be measured by the method described in the Examples below.

[0120] (Elastic deformation rate) By providing this protective layer, the elastic deformation rate of the photoreceptor can be increased to 40% or more, preferably 45% or more, and more preferably 50% or more. If the elastic deformation rate is 40% or more, the photoreceptor can have sufficient wear resistance and cleaning resistance for practical use. In the present invention, the elastic deformation rate of the photoreceptor means the elastic deformation rate measured from the surface side of the photoreceptor. The elastic deformation rate can be measured in the same manner as the Martens hardness.

[0121] (Method for forming the protective layer) The protective layer can be formed, for example, by dissolving a curable composition containing a curable compound and a polymerization initiator, and optionally inorganic particles, in a solvent as needed to form a coating liquid, or by dispersing the curable composition in a dispersion medium to form a coating liquid, applying the coating liquid, and then curing the coating liquid.

[0122] In this case, the organic solvent used in forming the protective layer may be appropriately selected from known organic solvents, and among them, it is preferable to use alcohols, which have low solubility in polycarbonate and polyarylate, which are preferably used in the photosensitive layer.

[0123] Examples of coating methods for forming the protective layer include spray coating, spiral coating, ring coating, and dip coating, but the method is not limited to these. After forming the coating film by the above coating method, it is preferable to dry the coating film.

[0124] The curable composition can be cured by irradiating it with external energy such as heat, light (e.g., ultraviolet light and / or visible light), radiation, etc. Among these, curing by light irradiation is preferred.

[0125] Heat energy can be applied by heating from the coated surface or the support using air, gases such as nitrogen, steam, various heat transfer media, infrared rays, or electromagnetic waves. The heating temperature is preferably 100°C or higher and 170°C or lower. At temperatures above the lower limit, the reaction speed is sufficient and the reaction proceeds completely. At temperatures below the upper limit, the reaction proceeds uniformly, preventing significant distortion in the outermost layer. To ensure uniform curing reaction, it is also effective to heat at a relatively low temperature below 100°C, and then further heat to 100°C or higher to complete the reaction.

[0126] As for light energy, UV irradiation light sources that emit light mainly in the ultraviolet (UV) range, such as high-pressure mercury lamps, metal halide lamps, electrodeless lamp bulbs, and light-emitting diodes, can be used. Visible light sources can also be selected to match the absorption wavelengths of the curable compound and photopolymerization initiator. The light irradiation dose is 100 mJ / cm from the viewpoint of curing. 2 More than 500mJ / cm is preferable. 2 More preferably, 1000 mJ / cm or more 2 In addition, from the viewpoint of electrical properties, 20,000 mJ / cm 2 or more is particularly preferable. 2 Preferably less than 10000mJ / cm 2 More preferably, 5000 mJ / cm 2 The following are particularly preferred:

[0127] The radiation energy used may be electron beam (EB). Among these energies, light energy is preferred from the viewpoints of ease of reaction rate control, simplicity of the device, and long pod life.

[0128] From the viewpoint of improving electrical properties, a heat treatment may be performed after the cured composition is cured. The present invention does not exclude heat treatment after curing, but it is not necessary. When heat treatment is performed after curing, it is preferable to keep the temperature at or below 130°C and the heating time at or below 20 minutes.

[0129] <Conductive support> The conductive support is not particularly limited as long as it supports the layer formed thereon and exhibits electrical conductivity. Examples of conductive supports include metal materials such as aluminum, aluminum alloys, stainless steel, copper, and nickel; resin materials imparted with electrical conductivity by the coexistence of conductive powders such as metal, carbon, and tin oxide; and resins, glass, and paper on whose surfaces conductive materials such as aluminum, nickel, and ITO (indium oxide tin oxide alloy) are vapor-deposited or coated. The supports may be in the form of a drum, sheet, or belt. A conductive material with an appropriate resistance may be coated on a metallic conductive support to control electrical conductivity and surface properties or to cover defects.

[0130] When a metal material such as an aluminum alloy is used as the conductive support, the metal material may be anodized before use. For example, an anodic oxide film is formed on the surface of a metal material by anodizing the metal material in an acid bath such as chromic acid, sulfuric acid, oxalic acid, boric acid, sulfamic acid, etc. Anodizing in sulfuric acid, in particular, gives better results.

[0131] For anodizing in sulfuric acid, the sulfuric acid concentration is usually 100 g / L or more and 300 g / L or less, the dissolved aluminum concentration is usually 2 g / L or more and 15 g / L or less, the solution temperature is usually 15°C or more and 30°C or less, the electrolysis voltage is usually 10 V or more and 20 V or less, and the current density is usually 0.5 A / dm 2 Above, 2A / dm 2 It is preferable to set it within the following range, but it is not limited to the above conditions. The average thickness of the anodic oxide coating is usually 20 μm or less, and preferably 7 μm or less.

[0132] When forming an anodized film on a metal material, it is preferable to perform a sealing treatment. The sealing treatment can be performed by a known method. For example, it is preferable to perform a low-temperature sealing treatment in which the metal material is immersed in an aqueous solution containing nickel fluoride as a main component, or a high-temperature sealing treatment in which the metal material is immersed in an aqueous solution containing nickel acetate as a main component.

[0133] The surface of the conductive support may be smooth, or may be roughened by using a special cutting method, by polishing, or by mixing particles of an appropriate particle size into the material constituting the support. An undercoat layer, which will be described later, may be provided between the conductive support and the photosensitive layer in order to improve adhesion, blocking properties, etc.

[0134] <Undercoat layer> The photoreceptor may have an undercoat layer between the photosensitive layer and the conductive support.

[0135] The undercoat layer may be made of, for example, a resin or a resin in which organic pigments or particles of metal oxides are dispersed. Examples of organic pigments used in the undercoat layer include phthalocyanine pigments, azo pigments, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, anthanthrone pigments, and benzimidazole pigments. Among these, phthalocyanine pigments and azo pigments, specifically, the phthalocyanine pigments and azo pigments used as the charge generating material described above, can be mentioned.

[0136] Examples of metal oxide particles used in the undercoat layer include metal oxide particles containing one type of metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, and metal oxide particles containing multiple metal elements such as calcium titanate, strontium titanate, and barium titanate. The undercoat layer may contain only one type of particle, or multiple types of particles may be mixed in any ratio and combination.

[0137] Among the above metal oxide particles, titanium oxide and aluminum oxide are preferred, and titanium oxide is particularly preferred. Note that the surface of the titanium oxide particles may be treated with, for example, inorganic substances such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, silicon oxide, or organic substances such as stearic acid, polyol, silicone, etc. Furthermore, the crystalline form of the titanium oxide particles may be any of rutile, anatase, brookite, and amorphous. Furthermore, titanium oxide particles may contain particles in multiple crystalline states.

[0138] The particle size of the metal oxide particles used in the undercoat layer is not particularly limited, but from the viewpoints of the properties of the undercoat layer and the stability of the solution for forming the undercoat layer, the average primary particle size is preferably 10 nm or more, and 100 nm or less, more preferably 50 nm or less.

[0139] Here, the undercoat layer is preferably formed in a state in which particles are dispersed in a binder resin.The binder resin used in the undercoat layer may be, for example, a polyvinyl acetal resin such as a polyvinyl butyral resin, a polyvinyl formal resin, or a partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal or acetal, etc.; a polyarylate resin, a polycarbonate resin, a polyester resin, a modified ether polyester resin, a phenoxy resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, a polyvinyl acetate resin, a polystyrene resin, an acrylic resin, a methacrylic resin, a polyacrylamide resin, a polyamide resin, a polyvinylpyridine resin, a cellulose resin, a polyurethane resin, an epoxy resin, or a silicone resin. , polyvinyl alcohol resin, polyvinylpyrrolidone resin, casein; vinyl chloride-vinyl acetate copolymers such as vinyl chloride-vinyl acetate copolymer, hydroxy-modified vinyl chloride-vinyl acetate copolymer, carboxyl-modified vinyl chloride-vinyl acetate copolymer, and vinyl chloride-vinyl acetate-maleic anhydride copolymer; styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer; insulating resins such as styrene-alkyd resin, silicone-alkyd resin, and phenol-formaldehyde resin; and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinyl anthracene, and polyvinylperylene. However, the binder resin is not limited to these polymers. Furthermore, these binder resins may be used alone or in combination, or may be used in a cured form with a curing agent. Among these, polyvinyl butyral resins, polyvinyl formal resins, polyvinyl acetal resins such as partially acetalized polyvinyl butyral resins in which butyral is partially modified with formal or acetal, alcohol-soluble copolymerized polyamides, modified polyamides, etc. are preferred because they exhibit good dispersibility and coatability. Of these, alcohol-soluble copolymerized polyamides are particularly preferred.

[0140] The mixing ratio of the particles to the binder resin can be selected arbitrarily, but it is preferable to use the particles in the range of 10% by mass to 500% by mass in terms of the stability and coatability of the dispersion.

[0141] The thickness of the undercoat layer can be selected arbitrarily. In consideration of the characteristics of the electrophotographic photoreceptor and the coating properties of the dispersion, it is usually preferable to set the thickness to 0.1 μm or more and 20 μm or less. The undercoat layer may also contain known antioxidants, etc.

[0142] <<This image forming device>> The present photoreceptor can be used to configure an image forming apparatus (the present image forming apparatus).

[0143] As shown in FIG. 1, the image forming apparatus is configured with a photoreceptor 1, a charging device 2, an exposure device 3, and a developing device 4, and may further include a transfer device 5, a cleaning device 6, and a fixing device 7 as needed. There are no particular limitations on the present photoreceptor 1 as long as it is the above-described present electrophotographic photoreceptor. Figure 1 shows, as an example, a drum-shaped photoreceptor in which the above-described photosensitive layer is formed on the surface of a cylindrical conductive support. A charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are arranged along the outer circumferential surface of the present photoreceptor 1.

[0144] The charging device 2 charges the photoreceptor 1, uniformly charging the surface of the photoreceptor 1 to a predetermined potential. Typical charging devices include non-contact corona charging devices such as corotrons and scorotrons, and contact-type charging devices (direct-type charging devices) that charge the photoreceptor surface by bringing a charging member to which a voltage is applied into contact with the surface. Examples of contact charging devices include a charging roller and a charging brush. Note that FIG. 1 shows a roller-type charging device (charging roller) as an example of the charging device 2. Normally, charging rollers are manufactured by molding resin and additives such as plasticizers integrally with a metal shaft, and may have a laminated structure as needed. The voltage applied during charging can be DC voltage alone, or DC voltage superimposed with AC voltage.

[0145] There are no particular limitations on the type of exposure device 3, as long as it can expose the photoreceptor 1 to light and form an electrostatic latent image on the photosensitive surface of the photoreceptor 1. Specific examples include halogen lamps, fluorescent lamps, lasers such as semiconductor lasers and He-Ne lasers, and LEDs. Alternatively, exposure may be performed using an internal photoreceptor exposure method. Any light may be used for exposure. For example, exposure may be performed using monochromatic light with a wavelength of 780 nm, monochromatic light with a slightly shorter wavelength of 600 nm to 700 nm, or monochromatic light with a short wavelength of 380 nm to 500 nm.

[0146] The type of toner T is arbitrary, and in addition to powder toner, polymerized toners produced by suspension polymerization or emulsion polymerization can be used. In particular, when using polymerized toner, small particle diameters of about 4 to 8 μm are preferred, and the shape of the toner particles can vary from nearly spherical to rod-shaped or other non-spherical shapes. Polymerized toners have excellent charging uniformity and transferability, and are therefore suitable for achieving high image quality.

[0147] There are no particular limitations on the type of transfer device 5, and any device using any method, such as electrostatic transfer methods such as corona transfer, roller transfer, or belt transfer, pressure transfer, or adhesive transfer, can be used. Here, the transfer device 5 is assumed to be composed of a transfer charger, transfer roller, transfer belt, etc., arranged opposite the photoreceptor 1. The transfer device 5 applies a predetermined voltage value (transfer voltage) with a polarity opposite to the charged potential of the toner T, and transfers the toner image formed on the photoreceptor 1 to recording paper (paper, medium) P.

[0148] There are no particular limitations on the cleaning device 6, and any cleaning device can be used, such as a brush cleaner, magnetic brush cleaner, electrostatic brush cleaner, magnetic roller cleaner, or blade cleaner. The cleaning device 6 scrapes off residual toner adhering to the photoreceptor 1 with a cleaning member and collects the residual toner. However, if there is little or almost no toner remaining on the photoreceptor surface, the cleaning device 6 may not be necessary.

[0149] In the electrophotographic apparatus configured as described above, an image is recorded as follows: First, the surface (photosensitive surface) of the photoreceptor 1 is charged to a predetermined potential (e.g., 600 V) by the charging device 2. At this time, charging may be performed using a DC voltage, or by superimposing an AC voltage on the DC voltage. Next, the charged photosensitive surface of the photoreceptor 1 is exposed by the exposure device 3 according to the image to be recorded, and an electrostatic latent image is formed on the photosensitive surface. Then, the electrostatic latent image formed on the photosensitive surface of the photoreceptor 1 is developed by the development device 4.

[0150] The developing device 4 thins the toner T supplied by the supply roller 43 using a regulating member (developing blade) 45, frictionally charges it to a predetermined polarity (here, positive polarity, the same polarity as the charging potential of the photosensitive member 1), and transports it while being carried by the developing roller 44, bringing it into contact with the surface of the photosensitive member 1. When the charged toner T carried on the developing roller 44 comes into contact with the surface of the photoreceptor 1, a toner image corresponding to the electrostatic latent image is formed on the photoreceptor surface of the photoreceptor 1. This toner image is then transferred onto the recording paper P by the transfer device 5. After this, the toner remaining on the photoreceptor surface of the photoreceptor 1 without being transferred is removed by the cleaning device 6.

[0151] After the toner image is transferred onto the recording paper P, the recording paper P is passed through a fixing device 7 to thermally fix the toner image onto the recording paper P, thereby obtaining a final image. In addition to the above-described configuration, the image forming apparatus may be configured to be capable of performing, for example, a static elimination process.

[0152] Furthermore, the image forming apparatus may be further modified and configured, for example, to be capable of performing processes such as a pre-exposure process and an auxiliary charging process, or to be configured to perform offset printing, or even to be configured as a full-color tandem system using multiple types of toner.

[0153] <<This electrophotographic cartridge>> The present photoreceptor 1 can be combined with one or more of a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, a cleaning device 6, and a fixing device 7 to form an integrated cartridge (referred to as "the present electrophotographic cartridge").

[0154] The electrophotographic cartridge can be configured to be detachable from the main body of an electrophotographic apparatus such as a copying machine, a laser beam printer, etc. In this case, for example, when the photoreceptor 1 or other members deteriorate, the electrophotographic photoreceptor cartridge can be removed from the main body of the image forming apparatus and a new electrophotographic photoreceptor cartridge can be installed in the main body of the image forming apparatus, thereby facilitating maintenance and management of the image forming apparatus.

[0155] <<Explanation of terms>> In the present invention, when the expression "X to Y" (X and Y are any numbers) is used, unless otherwise specified, it means "X or more and Y or less," as well as "preferably larger than X" or "preferably smaller than Y." Furthermore, when it is expressed as "X or more" (X is any number) or "Y or less" (Y is any number), it also includes the intention that "it is preferable that it is greater than X" or "it is preferable that it is less than Y." In the present invention, when a numerical range is specified, the upper and lower limits are values ​​taking into consideration significant figures. For example, when written as "3.6 eV," the value that is obtained by rounding to two decimal places is included. For example, 3.55 eV and 3.64 eV are included in 3.6 eV. [Example]

[0156] The present invention is further illustrated by the following examples, which are not intended to limit the invention in any way.

[0157] [Coating liquid P1 for forming undercoat layer] A coating solution P1 for forming an undercoat layer was used, which contained rutile-type white titanium oxide surface-treated with methyldimethoxysilane and a copolymer polyamide having a composition molar ratio of ε-caprolactam / bis(4-amino-3-methylcyclohexyl)methane / hexamethylenediamine / decamethylenedicarboxylic acid / octadecamethylenedicarboxylic acid of 60 / 15 / 5 / 15 / 5 (mass ratio of titanium oxide to copolymer polyamide: 3 / 1) in a mixed solvent (mass ratio of methanol / 1-propanol / toluene: 7 / 1 / 2) at a solids concentration of 18%.

[0158] [Coating liquid Q1 for forming charge generating layer] As a charge generating material, 10 parts of oxytitanium phthalocyanine, which shows a characteristic peak at a Bragg angle (2θ±0.2°) of 27.3° in a powder X-ray spectrum pattern using CuKα radiation, 5 parts of polyvinyl acetal resin (manufactured by Denki Kagaku Kogyo Co., Ltd., product name DK31) as a binder resin, and 500 parts of 1,2-dimethoxyethane were mixed, and the mixture was ground and dispersed in a sand grind mill to obtain a coating solution Q1 for forming a charge generating layer.

[0159] [Coating liquid R1 for forming charge transport layer] 100 parts of a polyarylate resin (viscosity average molecular weight 43,000) represented by the following structural formula (A) as a binder resin, 40 parts of a hole transport material (HTM) represented by the following structural formula (B), 4 parts of a hindered phenol-based antioxidant (manufactured by BASF under the trade name of Irg1076), and 0.05 parts of silicone oil (manufactured by Shin-Etsu Silicones under the trade name of KF-96) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8:2, and the mixture was stirred to obtain a charge transport layer-forming coating solution R1 with a solids concentration of 16.5%.

[0160] Formula (A) TIFF0007782451000008.tif28170

[0161] Formula (B) TIFF0007782451000009.tif38170

[0162] [Coating solution R2 for forming charge transport layer] 100 parts of polyarylate resin (viscosity average molecular weight 43,000) represented by structural formula (A), 40 parts of hole transport material (HTM) represented by structural formula (C) below, 4 parts of hindered phenol-based antioxidant (manufactured by BASF under the trade name of Irg1076), and 0.05 parts of silicone oil (manufactured by Shin-Etsu Silicones under the trade name of KF-96) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8:2, and the mixture was stirred to obtain coating solution R2 for forming a charge transport layer with a solids concentration of 16.5%.

[0163] Formula (C) TIFF0007782451000010.tif59170

[0164] [Coating solution R3 for forming charge transport layer] 100 parts of polyarylate resin (viscosity average molecular weight 43,000) represented by structural formula (A), 60 parts of hole transport material (HTM) represented by structural formula (D) below, 4 parts of hindered phenol-based antioxidant (manufactured by BASF under the trade name of Irg1076), and 0.05 parts of silicone oil (manufactured by Shin-Etsu Silicones under the trade name of KF-96) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8:2, and the mixture was stirred to obtain coating solution R3 for forming a charge transport layer with a solids concentration of 18.0%.

[0165] Formula (D) TIFF0007782451000011.tif48170

[0166] [Coating solution R4 for forming charge transport layer] 100 parts of polyarylate resin (viscosity average molecular weight 43,000) represented by structural formula (A), 60 parts of hole transport material (HTM) represented by the following structural formula (E), 4 parts of hindered phenol-based antioxidant (manufactured by BASF under the trade name of Irg1076), and 0.05 parts of silicone oil (manufactured by Shin-Etsu Silicones under the trade name of KF-96) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8:2, and mixed by stirring to obtain coating solution R4 for forming a charge transport layer with a solids concentration of 18.0%.

[0167] Formula (E) TIFF0007782451000012.tif36170

[0168] [Coating solution R5 for forming charge transport layer] 100 parts of polyarylate resin (viscosity average molecular weight 43,000) represented by structural formula (A), 40 parts of hole transport material (HTM) represented by structural formula (F) below, 4 parts of hindered phenol-based antioxidant (manufactured by BASF under the trade name of Irg1076), and 0.05 parts of silicone oil (manufactured by Shin-Etsu Silicones under the trade name of KF-96) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8:2, and mixed with stirring to obtain coating solution R5 for forming a charge transport layer with a solids concentration of 16.5%.

[0169] Formula (F) TIFF0007782451000013.tif44170

[0170] [Coating liquid R6 for forming charge transport layer] 100 parts of a polyarylate resin (viscosity average molecular weight: 43,000) represented by structural formula (A), 40 parts of a hole transport material represented by structural formula (F), 1 part of a radical acceptor compound (electron transport material, indicated as "G" in the table, electron affinity: 3.83 eV) represented by structural formula (G) below, 4 parts of a hindered phenol-based antioxidant (manufactured by BASF under the trade name Irg1076), and 0.05 parts of silicone oil (manufactured by Shin-Etsu Silicones under the trade name KF-96) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8:2, and the mixture was stirred to obtain a charge transport layer-forming coating solution R6 with a solids concentration of 16.5%. The energy difference between the HOMO level and the LUMO level of the radical acceptor compound G was 2.39 eV.

[0171] Formula (G) TIFF0007782451000014.tif47170

[0172] [Coating solution S1 for forming protective layer] Rutile-type white titanium dioxide (product name TTO55N, manufactured by Ishihara Sangyo Kaisha, Ltd.) with an average primary particle size of 40 nm was surface-treated by stirring 100 parts by weight of the titanium dioxide with 7 parts by weight of 3-methacryloxypropyltrimethoxysilane in a supermixer using shear force until the temperature inside the mixer reached 150°C. Next, 250 g of this surface-treated titanium dioxide was mixed with 750 g of methanol to obtain 1000 g of raw slurry. This was dispersed for 30 minutes using an Ultra Apex Mill (UAM-015, manufactured by Kotobuki Industries Co., Ltd.) with a mill volume of approximately 0.15 L and zirconia beads (YTZ, manufactured by Nikkato Corporation) with a diameter of approximately 50 μm as dispersion medium, at a rotor peripheral speed of 9 m / s and a liquid flow rate of 2.8 g / s, in a circulation state, to produce a titanium dioxide dispersion. A urethane acrylate oligomer (manufactured by Mitsubishi Chemical Corporation, product name UV6300B) previously dissolved in a mixed solvent of methanol / 1-propanol / toluene was mixed with benzophenone and Omnirad TPO H (2,4,6-trimethylbenzoyl-diphenylphosphine oxide) as a polymerization initiator to obtain a protective layer-forming coating solution S1 having a solvent composition of UV6300B / surface-treated titania / benzophenone / Omnirad TPO H=100 / 55 / 1 / 2, a solvent composition of methanol / 1-propanol / toluene=7 / 1 / 2, and a solids concentration of 18.0%.

[0173] <Comparative Example 1> Coating Solution P1 for forming an undercoat layer was dip-coated onto a 30 mm diameter, 248 mm long aluminum cylinder with a machined surface, to form an undercoat layer with a dry film thickness of 1.5 μm. Coating Solution Q1 for forming a charge generation layer was dip-coated onto the undercoat layer to form a charge generation layer with a dry film thickness of 0.3 μm. Coating Solution R1 for forming a charge transport layer was dip-coated onto the charge generation layer to form a charge transport layer with a dry film thickness of 20.0 μm. Coating Solution S1 for forming a protective layer was ring-coated onto the charge transport layer and dried at room temperature for 20 minutes. After that, the photoreceptor was rotated at 60 rpm in a nitrogen atmosphere (oxygen concentration 1% or less) and heated with a metal halide lamp at an illuminance of 140 mW / cm. 2 The photosensitive member was irradiated with light for 2 minutes, thereby forming a protective layer having a cured film thickness of 1.0 μm, thereby producing photosensitive member D1.

[0174] <Comparative Example 2> Photoreceptor D2 was prepared in the same manner as photoreceptor D1, except that charge transport layer forming coating liquid R1 was changed to charge transport layer forming coating liquid R2.

[0175] <Comparative Example 3> Photoreceptor D3 was prepared in the same manner as photoreceptor D1, except that charge transport layer forming coating liquid R1 was replaced with charge transport layer forming coating liquid R3.

[0176] <Comparative Example 4> The charge transport layer forming coating liquid R1 was changed to the charge transport layer forming coating liquid R5, and the irradiation conditions of the metal halide lamp when curing the protective layer were changed to an illuminance of 140 mW / cm 2 Photoreceptor D4 was produced in the same manner as photoreceptor D1, except that the irradiation time was changed to 10 seconds.

[0177] <Comparative Example 5> The irradiation conditions of the metal halide lamp when curing the protective layer were set at an illuminance of 140 mW / cm 2 Photoreceptor D5 was produced in the same manner as photoreceptor D1, except that the irradiation time was changed to 10 seconds.

[0178] Example 1 Photoreceptor D6 was prepared in the same manner as photoreceptor D1, except that charge transport layer forming coating liquid R1 was changed to charge transport layer forming coating liquid R4.

[0179] <Example 2> Photoreceptor D7 was produced in the same manner as photoreceptor D1, except that charge transport layer forming coating liquid R1 was changed to charge transport layer forming coating liquid R5.

[0180] Example 3 Photoreceptor D8 was prepared in the same manner as photoreceptor D1, except that charge transport layer forming coating liquid R1 was changed to charge transport layer forming coating liquid R6.

[0181] Example 4 The charge transport layer forming coating liquid R1 was changed to the charge transport layer forming coating liquid R5, and the irradiation conditions of the metal halide lamp when curing the protective layer were changed to an illuminance of 140 mW / cm 2 Photoreceptor D9 was prepared in the same manner as photoreceptor D1, except that the irradiation time was changed to 20 seconds.

[0182] [Energy difference between the HOMO and LUMO levels of hole transport materials (HTM)] Table 2 shows the energy differences between the HOMO level and the LUMO level of the hole transport materials used in the present examples, comparative examples, and reference examples.

[0183] [Table 2]

[0184] [Martens hardness evaluation] Photoreceptors D1 to D9 were measured from the surface side of the photoreceptor using a microhardness tester (Fischer: FISCHERSCOPE HM2000) under the following conditions at a temperature of 25°C and a relative humidity of 50%. The Martens hardness of each sample is shown in Table 3.

[0185] (Martens hardness measurement conditions) Indenter: Vickers square pyramidal diamond indenter with a facing angle of 136° Maximum pressing force: 0.2mN Load duration: 10 seconds Unloading time: 10 seconds The Martens hardness is calculated by the following formula. Martens hardness (N / mm 2 ) = Maximum indentation load / Indentation area at maximum indentation load

[0186] [Evaluation of electrical characteristics] Next, two of each of the photoreceptors D1 to D9 prepared in the examples and comparative examples were prepared, and one of each was left as is ("without heating" in the table), while the other was heated at 125°C for 10 minutes. After the photoreceptor temperature returned to room temperature ("with heating" in the table), each was mounted in an electrophotographic property evaluation device prepared in accordance with the standards of the Society of Electrophotography (see pages 404-405 of "Continued Fundamentals and Applications of Electrophotography Technology," edited by the Society of Electrophotography, Corona Publishing Co., Ltd.), and the electrical properties were evaluated in an environment of 25°C / 50% RH by a cycle of charging (negative polarity), exposure, potential measurement, and de-electrification, according to the following procedure. The photoconductor was charged so that the initial surface potential was -700 V, and the light from the halogen lamp was converted to monochromatic light of 780 nm through an interference filter and emitted at 1.0 μJ / cm 2 The surface potential (VL) after 60 milliseconds of exposure and before aging was measured when irradiated with an intensity of 1000 kJ / s (unit: -V, "Surface potential VL before HH aging" in the table). The results are shown in Table 3. The smaller the absolute value of the surface potential (VL), the better the electrical properties.

[0187] After measuring the electrical properties, these drums were left in an environment of 35°C / 85% for 24 hours, then returned to room temperature, and the above evaluations were performed again. The surface potential (VL) after exposure and aging was measured (unit: -V, "Surface potential VL after HH aging" in the table). The results are shown in Table 3. The smaller the absolute value of the surface potential (VL), the better the electrical properties.

[0188] [Wear resistance evaluation] The photoreceptors D4, D5, D7, and D9 prepared in the examples and comparative examples were evaluated for abrasion resistance. The photoreceptors were mounted in an electrophotographic printer, and a printing test was conducted on 20,000 sheets with a 5% print ratio at an ambient temperature of 25°C and a relative humidity of 50%. The total film thickness of the photoreceptor (the film thickness of all layers formed on the conductive support) was measured before and after the printing test, and the amount of film thickness reduction (film loss) due to the printing test was calculated. The results are shown in Table 3. The smaller the film loss, the better the abrasion resistance.

[0189] [Table 3]

[0190] [Evaluation of strong exposure characteristics] The photoreceptors D7 and D8 prepared in Examples 2 and 3 were mounted on an electrophotographic property evaluation device prepared in accordance with the measurement standards of the Electrophotographic Society (described in "Continued Fundamentals and Applications of Electrophotographic Technology," edited by the Electrophotographic Society, Corona Publishing, pp. 404-405), and the electrical properties were measured by a cycle of charging, exposure, potential measurement, and static elimination as follows. First, under an environment of 25°C temperature and 50% humidity, the grid voltage was adjusted to charge the photoreceptor so that the initial surface potential (V0) was -700 V. Next, the exposure light was 1.0 μJ / cm 2 The surface potential (VL) was measured 60 milliseconds after irradiation. The exposure light was a halogen lamp light converted to monochromatic light of 780 nm using an interference filter. Next, each photoconductor was irradiated for 10 minutes with light from a white fluorescent lamp (Neolumi Super FL20SS W / 18 manufactured by Mitsubishi Osram) adjusted so that the light intensity on the surface of the photoconductor was 2000 lux. After that, similar measurements were made at the initial grid voltage immediately after irradiation, 10 minutes after irradiation, and 60 minutes after irradiation to measure V0 and VL. Table 4 shows ΔV0 and ΔVL. ΔV0 is the value obtained by subtracting V0 before irradiation with a white fluorescent lamp from V0 after irradiation with a white fluorescent lamp. ΔVL is the value obtained by subtracting VL before irradiation with a white fluorescent lamp from VL after irradiation with a white fluorescent lamp. The smaller the absolute values ​​of ΔV0 and ΔVL, the smaller the change in each potential even when irradiated with a strong white light, indicating better strong exposure characteristics.

[0191] [Table 4]

[0192] [Evaluation of ozone resistance] The photoreceptors D7 and D8 prepared in Examples 2 and 3 were mounted on an electrophotographic property evaluation device prepared in accordance with the measurement standards of the Electrophotographic Society (described in "Continued Fundamentals and Applications of Electrophotographic Technology," edited by the Electrophotographic Society, Corona Publishing, pp. 404-405), and the electrical properties were measured by a cycle of charging, exposure, potential measurement, and static elimination as follows. First, the photosensitive member was charged to an initial surface potential (V0) of -700V by adjusting the grid voltage in an environment of a temperature of 25°C and a humidity of 50%. Next, each photoreceptor was placed in a chamber connected to an ozone generator (OZONIZER UNIT MODEL-0U65B, manufactured by Ebara Jitsugyo Co., Ltd.), and the ozone generator was activated. After the ozone concentration in the chamber reached 200 ppm, the photoreceptor was left for 5 hours. The ozone generator was then stopped, the ozone in the chamber was evacuated, and the photoreceptor was removed from the chamber. Immediately after removal from the chamber and two days later, similar measurements were performed at the initial grid voltage to measure V0. Table 5 shows ΔV0. ΔV0 is the value obtained by subtracting V0 before ozone exposure from V0 after ozone exposure. The smaller the absolute value of ΔV0, the smaller the change in potential even when exposed to ozone, indicating better ozone resistance.

[0193] [Table 5]

[0194] (Consideration) From the above examples and the results of the tests conducted by the present inventors, it has been found that the photoreceptor of the present invention has good electrical properties even when it has a cured resin protective layer. In this case, it has been found that the hole transport material (HTM) is preferably a compound having a HOMO / LUMO energy level difference of more than 3.6 eV and not more than 4.0 eV, or a compound represented by formula (I).

[0195] When forming a curable resin-based protective layer, curing generally proceeds with the involvement of radicals from polymerization initiators, etc. As a result, radicals propagate to the hole transport material (HTM) in the photosensitive layer, making it easier for HTM radicals to be generated. These HTM radicals are thought to act as charge trap sites, deteriorating electrical properties. The reason electrical properties improve with heating is thought to be because the HTM radicals disappear during heat treatment. Here, compounds with an HTM HOMO / LUMO energy level difference of more than 3.6 eV and less than 4.0 eV, or compounds represented by formula (I), are thought to be less likely to generate HTM radicals due to their small conjugation and unstable radical structure, and therefore, it is believed that deterioration of electrical properties can be prevented in such HTMs.

[0196] It was also found that the photoreceptor of the present invention exhibits small film loss and good abrasion resistance. Furthermore, it was also found that the inclusion of a radical acceptor compound in the photosensitive layer can further improve strong exposure characteristics and ozone resistance. In particular, it is presumed that if the energy difference between the HOMO level and the LUMO level of the radical acceptor compound is 3.0 eV or less, the radical acceptor compound will absorb light with a wavelength that could damage the hole transport material (HTM) preferentially over the hole transport material (HTM), thereby suppressing damage to the hole transport material (HTM). In other words, it is believed that a radical acceptor compound with an energy difference between the HOMO level and the LUMO level of 3.0 eV or less will provide the same effects as the radical acceptor compound G. When the same test as in the above example was carried out by changing the type of binder in the photosensitive layer, the same results were obtained.

Claims

1. An electrophotographic photoreceptor including, on a conductive support, a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound, in that order, the curable compound is a photocurable compound, The Martens hardness of the photoreceptor is 255 N / mm ２ That's all, the photosensitive layer contains at least a hole transport material (HTM), the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is greater than 3.6 eV and less than or equal to 4.0 eV; An electrophotographic photoreceptor, wherein the hole transport material (HTM) is a compound represented by formula (I): Formula (I) (In formula (I), Ar 1 to Ar 6 may be the same or different and each represents an aryl group which may have a substituent; n represents an integer of 2 or greater; Z represents a monovalent organic residue; and m represents an integer of 0 to 4, provided that at least one of Ar 1 to Ar 2 is an aryl group which has a substituent.)

2. 2. The electrophotographic photoreceptor according to claim 1, wherein the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is 3.8 eV or less.

3. 3. The electrophotographic photoreceptor according to claim 1, wherein the protective layer contains inorganic particles, and the content of the inorganic particles in the protective layer is 10 parts by mass or more and 300 parts by mass or less with respect to 100 parts by mass of the curable compound.

4. 4. The electrophotographic photoreceptor according to claim 3, wherein the inorganic particles are surface-treated with an organosilicon compound.

5. 5. The electrophotographic photoreceptor according to claim 3, wherein the inorganic particles are metal oxide particles, and the band gap of the metal oxide particles is smaller than the energy difference between the HOMO level and the LUMO level of a hole transport material (HTM) of the photosensitive layer.

6. 6. The electrophotographic photoreceptor according to claim 1, wherein the protective layer is a layer formed from a composition containing a curable compound, a polymerization initiator, and inorganic particles.

7. 7. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer is a laminated type photosensitive layer in which a charge generating layer and a charge transporting layer are laminated in this order on the conductive support.

8. The Martens hardness is 270 N / mm ２ 8. The electrophotographic photoreceptor according to claim 1, wherein the electrophotographic photoreceptor is one of the above.

9. 9. The electrophotographic photoreceptor according to claim 1, wherein the hole transport material (HTM) of the photosensitive layer is an enamine compound.

10. 10. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer contains a radical acceptor compound.

11. 11. The electrophotographic photoreceptor according to claim 10, wherein the energy difference between the HOMO level and the LUMO level of the radical acceptor compound in the photosensitive layer is 3.0 eV or less.

12. The electrophotographic photoreceptor according to claim 10, wherein the photosensitive layer contains a compound having a dinaphthylquinone structure as the radical acceptor compound.

13. 13. The electrophotographic photoreceptor according to claim 10, wherein the content of the radical acceptor compound in the photosensitive layer is 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the hole transport material (HTM) in the photosensitive layer.

14. 14. The electrophotographic photoreceptor according to claim 1, which is of a negative charging type.

15. An electrophotographic photoreceptor including, on a conductive support, a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound, in that order, the curable compound is a photocurable compound, the photosensitive layer contains at least a hole transport material (HTM) made of a compound represented by formula (I) and a compound having a dinaphthylquinone structure, and the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is greater than 3.6 eV and less than 4.0 eV. Formula (I) (In formula (I), Ar １ ~Ar ６ may be the same or different and each represents an aryl group which may have a substituent, n represents an integer of 2 or more, Z represents a monovalent organic residue, and m represents an integer of 0 to 4. １ ~Ar ２ At least one of these is a substituted aryl group.

16. An electrophotographic photoreceptor according to claim 1, wherein the protective layer contains an acylphosphine oxide compound.

17. The electrophotographic photoreceptor according to claim 1, wherein the protective layer contains an acylphosphine oxide compound and a hydrogen abstraction initiator.

18. An electrophotographic photosensitive member described in any of claims 1 to 15, wherein the protective layer contains an acylphosphine oxide compound and a hydrogen abstraction initiator, and contains 0.1 parts by mass or more and 5 parts by mass or less of the hydrogen abstraction initiator per 1 part by mass of the acylphosphine oxide compound.

19. An electrophotographic photoreceptor according to claim 1, wherein the photocurable compound comprises a urethane acrylate.

20. 20. The method for producing an electrophotographic photoreceptor according to claim 1, wherein the protective layer is cured by irradiation with ultraviolet light and / or visible light.

21. A cartridge comprising the electrophotographic photosensitive member according to any one of claims 1 to 19.

22. An image forming apparatus comprising the electrophotographic photosensitive member according to any one of claims 1 to 19.

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