Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge, and image forming apparatus

Abstract

Provided is a novel negative-charge type electrophotographic photoreceptor which has a cured resin-based protective layer and does not require a heating treatment for enhancing electrical properties. The negative-charge type electrophotographic photoreceptor comprises, on a conductive support body and in this order: a photosensitive layer; and a protective layer containing a cured product obtained by curing a curable compound. The photosensitive layer contains at least a hole transport material (HTM) and a radical acceptor compound or an electron transport material (ETM). The hole transport material (HTM) is a compound in which the energy difference between the HOMO level and LUMO level is 3.60 eV or less, and the HOMO level is -4.50 or less using the vacuum level as a basis.

Description

Technical Field

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

Background Art

[0002] In printers and copying machines, when light is irradiated onto a charged organic photoreceptor (OPC) drum, the irradiated portion is discharged to generate an electrostatic latent image, and an image can be obtained by attaching toner to the electrostatic latent image. In devices using such electrophotographic technology, the photoreceptor is a core member.

[0003] For this type of organic photoreceptor, since there is a large margin for material selection and it is easy to control the characteristics of the photoreceptor, a "function-separated photoreceptor" that distributes the functions of negative charge generation and movement to different compounds has become the mainstream. For example, a single-layer electrophotographic photoreceptor (hereinafter referred to as a single-layer photoreceptor) having a charge generation material (CGM) and a charge transport material (CTM) in the same layer, and a laminated electrophotographic photoreceptor (hereinafter referred to as a laminated photoreceptor) formed by laminating a charge generation layer containing a charge generation material (CGM) and a charge transport layer containing a charge transport material (CTM) are known. Further, as the charging method of the photoreceptor, a negative charging method for charging the surface of the photoreceptor with a negative charge and a positive charging method for charging the surface of the photoreceptor with a positive charge can be mentioned. As combinations of the layer structure and charging method of currently commercialized photoreceptors, a "negatively charged laminated photoreceptor" and a "positively charged single-layer photoreceptor" can be mentioned.

[0004] The "negatively charged laminated photoreceptor" generally has a configuration in which an undercoat layer (UCL) made of resin or the like is provided on a conductive support such as an aluminum tube, a charge generation layer (CGL) made of a charge generation material (CGM) and resin or the like is provided thereon, and further a charge transport layer (CTL) made of a hole transport material (HTM) and resin or the like is provided thereon. In the case of a negatively charged layered photoreceptor, after the surface of the photoreceptor is negatively charged by a corona discharge method or a contact method, the photoreceptor is exposed. This light is absorbed by a charge generation material (CGM) to generate hole and electron charge carriers. Among these, the holes, i.e., the positive charge carriers, move within the charge transport layer (CTL) through a hole transport material (HTM) and reach the surface of the photosensitive layer to neutralize the surface charge. On the other hand, the electrons generated by the charge generation material (CGM), i.e., the negative charge carriers, pass through the undercoat layer (UCL) and reach the conductive support. Thus, in a negatively charged layered photoreceptor, since holes mainly move in the photosensitive layer, it is usually the case that only a hole transport material is contained as the charge transport material in the photosensitive layer. At this time, if a compound with a low hole transport ability such as an electron transport material is further added, the content of the hole transport material in the photosensitive layer decreases, resulting in a problem of deterioration of electrical characteristics. Also, since the content of the binder resin also decreases, there is a concern that the abrasion resistance may decrease. Therefore, except in special cases, an electron transport material has not been contained in the photosensitive layer.

[0005] On the other hand, a "positively charged single-layer photoreceptor" generally has a structure in which an undercoat layer (UCL) made of 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 generation material (CGM), a hole transport material (HTM), an electron transport material (ETM), and resin or the like is provided thereon (see, for example, Patent Document 1). In the case of such a positively charged single-layer photoreceptor, after the surface of the photoreceptor is positively charged by a corona discharge method or a contact method, the photoreceptor is exposed. This light is absorbed by the charge generation material (CGM) near the surface of the photosensitive layer to generate hole and electron charge carriers. Among these, the electrons, i.e., the negative charge carriers, neutralize the surface charge on the surface of the photosensitive layer. On the other hand, the holes generated by the charge generation material (CGM), i.e., the positive charge carriers, pass through the photosensitive layer and the undercoat layer (UCL) and reach the conductive support.

[0006] In any 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. Then, printing is completed through visualization of the latent image with toner (powder colored resin ink) and transfer of the toner to paper or the like and heat melting and fixing.

[0007] As described above, the electrophotographic photoreceptor basically consists of a photosensitive layer formed on a conductive support, but for the purpose of improving wear resistance and the like, a protective layer is also provided on the photosensitive layer.

[0008] For example, Patent Document 1 discloses that a surface protective layer containing a thermoplastic alcohol-soluble resin as a binder resin, an average primary particle diameter of 0.1 to 3 μm, and a filler having a density of 3.0 g / cm 3 is provided on the photosensitive layer. Patent Document 2 describes that a crosslinked surface layer formed by thermally or photocuring a composition containing a trimethylolpropane acrylate crosslinked body, an organosilica cured film, and a thermally or photocurable crosslinked body is provided on the photosensitive layer. Furthermore, Patent Document 3 discloses that a surface protective layer is provided on the surface side of the photosensitive layer, and the surface protective layer is a cured product obtained by photocuring a composition containing a hindered amine compound, a polymerizable compound for a binder, and a charge transport agent.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] When the present inventors conducted studies, they found that in a negatively charged photoreceptor having a cured resin-based protective layer, when the photosensitive layer contains a specific hole transport material (HTM), while an improvement in ozone resistance and strong exposure characteristics can be expected, a problem occurs in that the electrical characteristics deteriorate. When the present inventors conducted further studies, they found that the problem of deterioration of the electrical characteristics is improved by performing a heat treatment immediately after curing the protective layer. However, on the other hand, when performing the heat treatment, it is necessary to introduce a space for the heat treatment process, a heating device, etc., resulting in a high initial cost, and furthermore, a new problem occurs in that the running cost also increases. Further, as a result of the studies by the present inventors, in the case of a positively charged photoreceptor, even when a cured resin-based protective layer is provided, the above-mentioned problem does not occur when the photosensitive layer contains a specific hole transport material (HTM).

[0011] An object of the present invention is to provide a negatively charged electrophotographic photoreceptor having a cured resin-based protective layer, in which the photosensitive layer contains a specific hole transport material (HTM) and the electrical characteristics are good.

Means for Solving the Problems

[0012] The present invention relates to a negatively charged electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer (also referred to as a "cured resin-based protective layer") containing a cured product obtained by curing a curable compound on a conductive support. The curable compound is a photocurable compound, the photosensitive layer contains a hole transport material (HTM), the hole transport material (HTM) is a compound having an energy difference between the HOMO level and the LUMO level of 3.60 eV or less, and the HOMO level is -4.50 eV or less based on the vacuum level, and the photosensitive layer further contains a radical acceptor compound or an electron transport material (ETM) having an electron affinity of 3.50 eV or more. A negatively charged electrophotographic photoreceptor is proposed.

[0013] That is, the gist of the present invention resides in the following [1] to

[13] .

[0014] [1] In a negatively charged electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on a conductive support, the curable compound is a photocurable compound, the photosensitive layer contains a hole transport material (HTM), the hole transport material (HTM) is a compound having an energy difference between the HOMO level and the LUMO level of 3.60 eV or less, and the HOMO level is -4.50 eV or less based on the vacuum level, the photosensitive layer further contains a radical acceptor compound having an electron affinity of 3.50 eV or more. The negatively charged electrophotographic photoreceptor is characterized by this.

[0015] [2] In a negatively charged electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on a conductive support, the curable compound is a photocurable compound, the photosensitive layer contains a hole transport material (HTM), the hole transport material (HTM) is a compound having an energy difference between the HOMO level and the LUMO level of 3.60 eV or less, and the HOMO level is -4.50 eV or less based on the vacuum level, the photosensitive layer further contains an electron transport material (ETM). The negatively charged electrophotographic photoreceptor is characterized by this.

[0016] [3] The negatively charged electrophotographic photoreceptor according to [1] or [2], wherein the photocurable compound is a compound having an acryloyl group or a methacryloyl group. [4] The negatively charged electrophotographic photoreceptor according to any one of [1] to [3], wherein the protective layer is a layer formed from a composition containing a photocurable compound and a polymerization initiator. [5] The photosensitive layer is a laminated photosensitive layer having a structure in which a charge transport layer (CTL) containing a hole transport material (HTM) and a radical acceptor compound or an electron transport material (ETM) having an electron affinity of 3.50 eV or more is laminated on a charge generation layer (CGL) containing a charge generation material (CGM), and is characterized by being the negatively chargeable electrophotographic photoreceptor according to any one of [1] to [4]. [6] The negatively chargeable electrophotographic photoreceptor according to any one of [1] to [5], characterized in that the Martens hardness is 270 N / mm 2 or more.

[0017] [7] The radical acceptor compound or the electron transport material (ETM) is a compound having a diphenoquinone structure or a dinaphthylquinone structure, and is characterized by being the negatively chargeable electrophotographic photoreceptor according to any one of [1] to [6]. [8] The content of the radical acceptor compound or the electron transport material (ETM) is from 0.1 part by mass to 10 parts by mass with respect to 100 parts by mass of the content of the hole transport material (HTM) in the photosensitive layer, and is characterized by being the negatively chargeable electrophotographic photoreceptor according to any one of [1] to [7].

[0018] [9] The hole transport material (HTM) in the photosensitive layer is a compound having a triphenylamine structure, and is characterized by being the negatively chargeable electrophotographic photoreceptor according to any one of [1] to [8].

[10] The protective layer further contains 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 HTM in the photosensitive layer, and is characterized by being the negatively chargeable electrophotographic photoreceptor according to any one of [1] to [9].

[11] The protective layer is a layer cured by irradiation with ultraviolet light or / and visible light, and is characterized by being the negatively chargeable electrophotographic photoreceptor according to any one of [1] to

[10] .

[0019]

[12] A cartridge comprising the negatively chargeable electrophotographic photoreceptor according to any one of [1] to

[11] . An image forming apparatus including the negatively chargeable electrophotographic photoreceptor according to any one of

[13] to

[11] .

Advantages of the Invention

[0020] In a negatively chargeable electrophotographic photoreceptor having a photosensitive layer and a cured resin-based protective layer sequentially provided on a conductive support, when the curable compound is a photocurable compound and the photosensitive layer contains a hole transport material (HTM) satisfying predetermined conditions, it has been found that the photosensitive layer further contains a radical acceptor compound or an electron transport material (ETM) having an electron affinity of 3.50 eV or more, whereby the electrical characteristics can be improved. At this time, the hole transport material (HTM) satisfying predetermined conditions is a case where the hole transport material (HTM) has an energy difference between the HOMO level and the LUMO level of 3.60 eV or less, and the HOMO level is -4.50 eV or less based on the vacuum level.

Brief Description of the Drawings

[0021]

Figure 1

Embodiments for Carrying Out the Invention

[0022] Next, the present invention will be described based on embodiment examples. However, the present invention is not limited to the embodiments described below.

[0023] <<This electrophotographic photoreceptor>> An electrophotographic photoreceptor (referred to as "this electrophotographic photoreceptor" or "this photoreceptor") according to an example of an embodiment of the present invention is a negatively chargeable electrophotographic photoreceptor sequentially including a photosensitive layer containing at least a hole transport material (HTM) and a radical acceptor compound (hereinafter, also simply referred to as "the radical acceptor compound") or an electron transport material (ETM) having an electron affinity of 3.50 eV or more, and a cured resin-based protective layer (also referred to as "this protective layer") containing a cured product obtained by curing a curable compound, on a conductive support. The photoreceptor may optionally have layers other than the photosensitive layer and the protective layer.

[0024] In the photoreceptor of the present invention, the side opposite to the conductive support is the upper side or the surface side, and the conductive support side is the lower side or the back side.

[0025] <Photosensitive layer> The photosensitive layer in the photoreceptor contains at least a hole transport material (HTM), and further contains a radical acceptor compound or an electron transport material (ETM) having an electron affinity of 3.50 eV or more. Then, it may be a single-layer photosensitive layer in which the charge generation material (CGM) and the hole transport material (HTM), and the radical acceptor compound or the electron transport material (ETM) are present in the same layer, or it may be a laminated photosensitive layer separated into a charge generation layer and a charge transport layer. Among them, the laminated photosensitive layer described below is more preferable.

[0026] <Laminated photosensitive layer> As the laminated photosensitive layer in the photoreceptor, a configuration in which a charge transport layer (CTL) containing a hole transport material (HTM) and the radical acceptor compound or the electron transport material (ETM) is laminated on a charge generation layer (CGL) containing a charge generation material (CGM) can be cited. At this time, it is also possible to provide other layers other than the charge generation layer (CGL) and the charge transport layer (CTL).

[0027] <Charge generation layer (CGL)> The charge generation layer may contain a charge generation material (CGM) and a binder resin.

[0028] (Charge generation material (CGM)) Examples of the charge generation material include inorganic photoconductive materials such as selenium and its alloys, cadmium sulfide, and organic photoconductive materials such as organic pigments. Among them, organic photoconductive materials are more preferable, and organic pigments are particularly preferable.

[0029] Examples of the organic pigment include phthalocyanine, azo, dithioketopyrrolopyrrole, squalene (squarylium), quinacridone, indigo, perylene, polycyclic quinone, anthraanthrone, benzimidazole, and the like. Among these, phthalocyanine or azo is particularly preferred. Among them, phthalocyanine is most preferred. These all show the skeletal structure of the compound and include a group of compounds having the skeletal structure, that is, derivatives. When an organic pigment is used as the charge generation material, usually fine particles of these organic pigments are used in the form of a dispersion layer bound with various binder resins.

[0030] Specific examples of the phthalocyanine include metal-free phthalocyanine, and those having each crystal form of coordinated phthalocyanines such as metals or their oxides, halides, hydroxides, alkoxides of copper, indium, gallium, tin, titanium, zinc, vanadium, silicon, germanium, aluminum, etc., and phthalocyanine dimers using an oxygen atom or the like as a bridging atom. In particular, X-type, τ-type metal-free phthalocyanine, A-type (also known as β-type), B-type (also known as α-type), D-type (also known as Y-type) and other titanyl phthalocyanines (also known as: oxytitanium phthalocyanine), vanadyl phthalocyanine, chloroindium phthalocyanine, hydroxyindium phthalocyanine, chloro gallium phthalocyanine of type II, etc., hydroxy gallium phthalocyanine of type V, etc., μ-oxo-gallium phthalocyanine dimer of type G, type I, etc., μ-oxo-aluminum phthalocyanine dimer of type II, etc., which are crystal forms with high sensitivity, are suitable.

[0031] Among these phthalocyanines, A-type (also known as β-type), B-type (also known as α-type), and D-type (Y-type) titanyl phthalocyanine characterized by having distinct peaks at diffraction angles 2θ (±0.2°) of 27.1° or 27.3° in powder X-ray diffraction, type II chlorogallium phthalocyanine, type V, and hydroxygallium phthalocyanine characterized by having the strongest peak at 28.1°, having no peak at 26.2° but having a distinct peak at 28.1°, and having a half-value width W of 0.1° ≤ W ≤ 0.4° at 25.9°, G-type μ-oxo-gallium phthalocyanine dimer, and X-type metal-free phthalocyanine are particularly preferred.

[0032] For phthalocyanine, a single compound may be used, or several in a mixed or mixed crystal state may be used. As the mixed or mixed crystal state here, those obtained by mixing each component later may be used, or those in which a mixed state is produced in the manufacturing and processing steps of phthalocyanine compounds such as synthesis, pigmentation, and crystallization may also be used. Such treatments include acid paste treatment, grinding treatment, solvent treatment, etc. are known. To produce a mixed crystal state, as described in JP-A-10-48859, a method can be cited in which two types of crystals are mixed and then mechanically ground and made amorphous, and then converted to a specific crystal state by solvent treatment.

[0033] The particle size of the charge generation material is usually 1 μm or less, preferably 0.5 μm or less.

[0034] (Binder resin) The binder resin used for the charge generation layer can be used without particular limitation. For example, polyvinyl butyral resin, polyvinyl formal resin, partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal or acetal, etc., polyvinyl acetal resins; polyarylate resin, polycarbonate resin, polyester resin, modified ether-based polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyvinyl pyridine resin, cellulose-based resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin, polyvinyl pyrrolidone resin, casein; vinyl chloride-vinyl acetate copolymer, hydroxy-modified vinyl chloride-vinyl acetate copolymer, carboxyl-modified vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, etc., vinyl chloride-vinyl acetate copolymers; styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer; insulating resins such as styrene-alkyd resin, silicone-alkyd resin, phenol-formaldehyde resin; and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinyl anthracene, polyvinyl perylene, etc. Among these resins, polyvinyl acetal resin or polyvinyl acetate resin is preferred in terms of the dispersibility of the pigment, the adhesiveness to the conductive support or the undercoat layer, and the adhesiveness to the charge transport layer. These binder resins may be used singly, or two or more of them may be mixed in any combination.

[0035] (Other components) In addition to the charge generation material and the binder resin, the charge generation layer can contain other components as necessary. For example, for the purpose of improving film-forming properties, flexibility, coatability, stain resistance, gas resistance, light resistance, etc., additives such as known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light blocking agents, fillers, etc. may be contained.

[0036] (Mixing ratio) In the charge generation layer, if the ratio of the charge generation material is too high, the stability of the coating solution may decrease due to aggregation of the charge generation material or the like. On the other hand, if the ratio of the charge generation material is too low, the sensitivity of the photoreceptor may decrease. Therefore, the mixing ratio (by mass) of the binder resin and the charge generation material is preferably such that the charge generation material is contained in an amount of 10 parts by mass or more, more preferably 30 parts by mass or more, based on 100 parts by mass of the binder resin, and is preferably contained in a ratio of 1000 parts by mass or less, more preferably 500 parts by mass or less. From the viewpoint of sensitivity, it is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less.

[0037] (Layer thickness) The thickness of the charge generation layer is preferably 0.1 μm or more, more preferably 0.15 μm or more. On the other hand, it is preferably 10 μm or less, more preferably 0.6 μm or less.

[0038] <Charge transport layer (CTL)> The charge transport layer (CTL) may contain a hole transport material (HTM), the radical acceptor compound or an electron transport material (ETM), and a binder resin.

[0039] (Hole transport material (HTM)) The hole transport material (HTM) contained in the photosensitive layer is preferably a compound having an energy difference between the HOMO level and the LUMO level of 3.60 eV or less and a HOMO level of -4.50 eV or less based on the vacuum level.

[0040] As described above, in a negatively charged photoreceptor having a cured resin-based protective layer (referred to as a "negatively charged OCL photoreceptor"), when the photosensitive layer contains a specific hole transport material (HTM), while improvement in ozone resistance and strong exposure characteristics can be expected, a problem has occurred in that the electrical characteristics deteriorate. It has been found that this problem can be improved by performing a heat treatment immediately after curing the protective layer. However, on the other hand, when performing the heat treatment, it is necessary to introduce a space for the heat treatment process, a heating device, etc., which increases the initial cost, and furthermore, a new problem has occurred in that the running cost also increases. On the other hand, it has been found that the electrical characteristics can be improved by further containing the radical acceptor compound or electron transport material (ETM) in the photosensitive layer, that is, by combining a predetermined hole transport material (HTM) and the radical acceptor compound or electron transport material (ETM) and containing them in the photosensitive layer. From such a viewpoint, the hole transport material (HTM) contained in the photosensitive layer preferably has an energy difference between the HOMO level and the LUMO level of 3.60 eV or less. Among them, from the viewpoint of electrical characteristics, less than or equal to 3.50 eV is more preferable, and less than or equal to 3.40 eV is even more preferable. When the energy difference is less than or equal to the upper limit value, the spread of conjugation is large and the hole mobility is high, so the electrical characteristics are good. On the other hand, from the viewpoint of strong exposure characteristics, the energy difference is preferably 3.10 eV or more, and more preferably 3.20 eV or more. When the energy difference is greater than or equal to the lower limit value, absorption of the light of a fluorescent lamp can be suppressed.

[0041] However, from the test results conducted by the present inventors, it has been found that when the HOMO level of the hole transport material (HTM) is higher than -4.50 eV based on the vacuum level, the electrical characteristics do not deteriorate so much in the first place. Therefore, when containing such a hole transport material (HTM), it is not necessary to contain the radical acceptor compound or electron transport material (ETM) in combination as described above. From such a perspective, the hole transport material (HTM) contained in the photosensitive layer preferably has a HOMO level of -4.50 eV or less based on the vacuum level, more preferably -4.60 eV or less, and even more preferably -4.65 eV or less.

[0042] Examples of compounds having an energy difference between the HOMO level and the LUMO level of 3.60 eV or less and a HOMO level of -4.50 eV or less based on the vacuum level include heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, benzofuran derivatives, etc., aniline derivatives, hydrazone derivatives, aromatic amine derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives, and those in which a plurality of these compounds are bonded, or polymers having a group composed of these compounds as a main chain or a side chain, etc. From among these compounds, compounds corresponding to the above energy levels (HOMO level and LUMO level) can be appropriately selected. Also, two or more compounds corresponding to the above energy levels can be used in combination. In addition, a hole transport material (HTM) that does not correspond to the above energy levels can be contained as long as the effects of the present invention are not impaired.

[0043] In the present invention, the energy level E_homo of HOMO and the energy level E_lumo of LUMO can be obtained by performing a structure optimization calculation 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)), which is a type of density functional method, to obtain a stable structure.

[0044] At this time, 6-31G(d,p) obtained by adding polarization functions to the 6-31G basis function system was used (see R. Ditchfield, et.al., J. Chem. Phys. 54, 724 (1971), W. J. Hehre, et.al., J. Chem. Phys. 56, 2257 (1972), P. C. Hariharan et.al., Mol. Phys. 27, 209 (1974), M. S. Gordon, Chem. Phys. Lett. 76, 163 (1980), P. C. Hariharan et.al., Theo. Chim. Acta 28, 213 (1973), J.-P. Blaudeau, et.al., J. Chem. Phys. 107, 5016 (1997), M. M. Francl, et.al., J. Chem. Phys. 77, 3654 (1982), R. C. Binning Jr.et.al., J. Comp. Chem. 11, 1206 (1990), V. A. Rassolov, et.al., J. Chem. Phys. 109, 1223 (1998), and V. A. Rassolov, et.al., J. Comp. Chem. 22, 976 (2001)). In the present invention, the B3LYP calculation using 6-31G(d,p) is described as B3LYP / 6-31G(d,p).

[0045] In the present invention, the program used for the B3LYP / 6-31G(d,p) calculation is Gaussian03, Revision D.01 (M. J. Frisch, et.al., Gaussian, Inc., Wallingford CT, 2004.).

[0046] The hole transport material (HTM) preferably has a high hole mobility, and from this viewpoint, it is preferably a compound having a triphenylamine structure.

[0047] As suitable examples of the hole transport material (HTM), compounds having any of the structures represented by the following general formulas can be mentioned. However, the present invention is not limited thereto. Also, any one of them may be used alone, or two or more of them may be used in combination in any arbitrary combination.

[0048] TIFF0007708094000001.tif44137

[0049] TIFF0007708094000002.tif77102

[0050] TIFF0007708094000003.tif6184

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[0052] TIFF0007708094000005.tif50102

[0053] TIFF0007708094000006.tif64125

[0054] TIFF0007708094000007.tif56100

[0055] TIFF0007708094000008.tif4763

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[0057] TIFF0007708094000010.tif5389

[0058] TIFF0007708094000011.tif5775

[0059] (Electron Transport Material (ETM)) Examples of the electron transport material (ETM) 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 compounds in which a plurality of these compounds are bonded, or polymers having a group composed of these compounds in the main chain or side chain, etc. However, the present invention is not limited thereto, and known electron transport materials can be used. Among these, from the viewpoint of electrical characteristics, the electron transport material (ETM) is preferably a compound having a diphenoquinone structure or a dinaphthylquinone structure. Among them, a compound having a dinaphthylquinone structure is more preferable. Note that any one of the above electron transport materials may be used alone, or two or more thereof may be used in combination in any combination.

[0060] Specific examples of the electron transport material (ETM) 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-2017-09765. In addition, compounds having any of the following structures can be mentioned. However, the present invention is not limited thereto. Also, any one of them may be used alone, or two or more thereof may be used in combination in any combination.

[0061] TIFF0007708094000012.tif71120

[0062] TIFF0007708094000013.tif3876

[0063] TIFF0007708094000014.tif5052

[0064] The content of the electron transport material (ETM) in the photosensitive layer is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and still more preferably 0.5 part by mass or more with respect to 100 parts by mass of the content of the hole transport material (HTM) in the photosensitive layer. On the other hand, it is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and still more preferably 5 parts by mass or less. The content of the hole transport material (HTM) in the photosensitive layer is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and still more preferably 50 parts by mass or more with respect to 1 part by mass of the electron transport material (ETM). On the other hand, it is more preferably 1000 parts by mass or less, more preferably 300 parts by mass or less, and still more preferably 100 parts by mass or less.

[0065] 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 above-mentioned photosensitive layer.

[0066] 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 above-mentioned photosensitive layer.

[0067] (Radical acceptor compound) The "radical acceptor compound" means a compound having the property of being able to accept radicals from the hole transport material (HTM), and more specifically, a compound having an electron affinity of 3.50 eV or more. Here, the electron affinity means the energy generated when a substance takes in one electron, and it can be obtained by performing a structure optimization calculation 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)), which is a kind of the density functional method described above. When determining the electron affinity, the same basis function system and program used in the calculation can be used as described above.

[0068] As described later, when not only the hole transport material (HTM) but also the electron transport material (ETM) is contained in the photosensitive layer, since the ETM is more likely to become a radical than the HTM, even if the HTM radical is generated, the HTM radical immediately extracts a hydrogen atom from the ETM, and the HTM radical is converted into the HTM, thereby expressing the effect of the present invention. Considering this mechanism of action, all of the electron transport materials (ETMs) are included in the "radical acceptor compound", and it is considered that the effect of the present invention can be obtained by the same mechanism of action when the "radical acceptor compound" is used instead of the electron transport material (ETM).

[0069] Since the effect of the present invention can be more enjoyed, the electron affinity of the radical acceptor compound is preferably 3.50 eV or more, more preferably 3.70 eV or more, and even more preferably 3.80 eV or more. On the other hand, the electron affinity of the radical acceptor compound is preferably 4.30 eV or less, more preferably 4.10 eV or less, even more preferably 4.00 eV or less, and particularly preferably 3.90 eV or less.

[0070] When a radical acceptor compound is used instead of the electron transport material (ETM), the preferred embodiments can be similarly applied to the preferred embodiments of the electron transport material (ETM) described above. The radical acceptor compound can be selected from the aforementioned electron transport materials (ETMs). Also, compounds other than those exemplified as ETMs can be used. Furthermore, the compounds exemplified as ETMs and other compounds can be used in combination.

[0071] (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 resin, and various thermosetting compounds. Among these resins, polycarbonate resin or polyarylate resin is preferred in terms of the light attenuation characteristics and mechanical strength as a photoreceptor.

[0072] The viscosity average molecular weight (Mv) of the binder resin is usually in the range of 5,000 to 300,000, preferably 10,000 to 200,000, more preferably 15,000 to 150,000, and particularly preferably 20,000 to 80,000. When the viscosity average molecular weight (Mv) is excessively small, the mechanical strength tends to decrease when a film such as a photoreceptor is formed. Also, when the viscosity average molecular weight (Mv) is excessively large, the viscosity of the coating solution increases, and it tends to be difficult to apply it to an appropriate film thickness.

[0073] The blending ratio of the binder resin constituting the photosensitive layer and the hole transport material (HTM) is usually such that the hole transport material (HTM) is blended at a ratio of 20 parts by mass or more with respect to 100 parts by mass of the binder resin. Among them, from the viewpoint of reducing the residual potential, it is preferable to blend the hole transport material (HTM) at a ratio of 30 parts by mass or more with respect to 100 parts by mass of the binder resin. Further, from the viewpoints of stability and charge mobility when repeatedly used, it is more preferable to blend the hole transport material (HTM) at a ratio of 40 parts by mass or more. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, it is preferable to blend the hole transport material (HTM) at a ratio of 200 parts by mass or less with respect to 100 parts by mass of the binder resin. Further, from the viewpoint of the compatibility between the hole transport material (HTM) and the binder resin, it is more preferable to blend the hole transport material (HTM) at a ratio of 150 parts by mass or less. From the viewpoint of the glass transition temperature, it is particularly preferable to blend it at a ratio of 120 parts by mass or less. When the hole transport material (HTM) is blended at a ratio of 120 parts by mass or less, the glass transition temperature of the photosensitive layer increases, and an improvement in leak resistance characteristics can be expected. In addition, 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 and the hole transport material (HTM) described above.

[0074] The content ratio of the hole transport material (HTM) with respect to the mass of the entire photosensitive layer is usually such that the hole transport material (HTM) is blended at 16 parts by mass or more with respect to 100 parts by mass of the photosensitive layer. Among them, from the viewpoint of reducing the residual potential, it is preferable to blend the hole transport material (HTM) at 22 parts by mass or more with respect to 100 parts by mass of the photosensitive layer. Further, from the viewpoints of stability and charge mobility when repeatedly used, it is more preferable to blend 28 parts by mass or more. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, it is preferable to blend the hole transport material (HTM) at 68 parts by mass or less with respect to 100 parts by mass of the photosensitive layer. From the viewpoint of the uniformity of the photosensitive layer, it is more preferable to blend 59 parts by mass or less. From the viewpoint of the glass transition temperature, it is particularly preferable to blend 53 parts by mass or less. When the hole transport material (HTM) is blended at 53 parts by mass or less, the glass transition temperature of the photosensitive layer increases, and an improvement in leak resistance characteristics can be expected.

[0075] In the charge transport layer (CTL), the blending ratio of the binder resin and the hole transport material (HTM) is preferably such that the hole transport material (HTM) is blended at a ratio of 20 parts by mass or more with respect to 100 parts by mass of the binder resin. Among them, from the viewpoint of reducing the residual potential, it is more preferable to blend the hole transport material (HTM) at a ratio of 30 parts by mass or more with respect to 100 parts by mass of the binder resin. Further, from the viewpoints of stability and charge mobility when repeatedly used, it is more preferable to blend the hole transport material (HTM) at a ratio of 40 parts by mass or more. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, it is preferable to blend the hole transport material (HTM) at a ratio of 200 parts by mass or less with respect to 100 parts by mass of the binder resin. Further, from the viewpoint of the compatibility between the hole transport material (HTM) and the binder resin, it is more preferable to blend the hole transport material (HTM) at a ratio of 150 parts by mass or less. From the viewpoint of the glass transition temperature, it is particularly preferable to blend at a ratio of 120 parts by mass or less. When the hole transport material (HTM) is blended at a ratio of 120 parts by mass or less, the glass transition temperature of the photosensitive layer increases, and an improvement in leak resistance characteristics can be expected.

[0076] (Other components) The charge transport layer can contain other components as necessary in addition to the radical acceptor compound, the electron transport material (ETM), the hole transport material (HTM), and the binder resin. For example, for the purpose of improving film formability, flexibility, coatability, stain resistance, gas resistance, light resistance, etc., additives such as known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light blockers, fillers, etc. may be contained.

[0077] (Layer thickness) The layer thickness of the charge transport layer is not particularly limited. From the viewpoints of electrical characteristics, image stability, and further high resolution, it is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more or 35 μm or less, and still more preferably 15 μm or more or 25 μm or less.

[0078] <Single-layer photosensitive layer> As the single-layer photosensitive layer in this photoreceptor, a configuration can be cited in which a charge generation material (CGM), a hole transport material (HTM), and the radical acceptor compound or electron transport material (ETM) are present in the same layer. The charge generation material (CGM), hole transport material (HTM), the radical acceptor compound, and electron transport material (ETM) of the single-layer photosensitive layer are the same as those of the laminated photosensitive layer. Also, the respective contents and content ratios in the single-layer photosensitive layer are the same as those of the laminated photosensitive layer.

[0079] <Method for forming each layer> Each of the above layers can be formed by repeating a sequential coating and drying process for each layer by a known method such as dip coating, spray coating, nozzle coating, bar coating, roll coating, blade coating, etc. on a conductive support, using a coating solution obtained by dissolving or dispersing the substance to be contained in a solvent. However, it is not limited to such a forming method.

[0080] The solvent or dispersion medium used for preparing the coating solution is not particularly limited. Specific examples include alcohols such as methanol, ethanol, propanol, 2-methoxyethanol, ethers such as tetrahydrofuran, 1,4-dioxane, dimethoxyethane, esters such as methyl formate, ethyl acetate, ketones such as acetone, methyl ethyl ketone, cyclohexanone, 4-methoxy-4-methyl-2-pentanone, aromatic hydrocarbons such as benzene, toluene, xylene, chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, trichloroethylene, nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, triethylenediamine, and aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, etc. Also, these may be used alone or in any combination and type of two or more.

[0081] The amount of the solvent or dispersion medium used is not particularly limited. It is preferable to appropriately adjust the physical properties such as the solid content concentration and viscosity of the coating solution so that they fall within the desired ranges in consideration of the purpose of each layer and the properties of the selected solvent or dispersion medium. For the drying of the coating film, after touch-drying at room temperature, it is preferably heated and dried under static or blowing conditions for 1 minute to 2 hours in a temperature range of usually 30°C or higher and 200°C or lower. Also, the heating temperature may be constant, or heating may be performed while changing the temperature during drying.

[0082] <This protective layer> This protective layer preferably contains a cured product formed by curing a curable compound. This protective layer can be formed from a composition containing a curable compound and a polymerization initiator. Among them, it is preferably formed by thermally curing or photocuring a curable composition containing a curable compound and a polymerization initiator, and among them, it is more preferably formed by photocuring by irradiation with ultraviolet light or / and visible light.

[0083] (Curable composition) As an example of the curable composition, a composition containing a curable compound, a polymerization initiator, and, if necessary, metal oxide particles and other materials can be mentioned.

[0084] (Curable compound) As the curable compound, a monomer, oligomer or polymer having a radically polymerizable functional group is preferable. Among them, a curable compound having crosslinkability, particularly a photocurable compound, is preferable. For example, a curable compound having two or more radically polymerizable functional groups can be mentioned. A compound having one radically polymerizable functional group can also be used in combination. Examples of the radically polymerizable functional group include a vinyl group, acryloyl group, methacryloyl group, acryloyloxy group, methacryloyloxy group, epoxy group, etc.

[0085] Examples of preferred compounds as curable compounds having a radically polymerizable functional group are shown below. As monomers having an acryloyl group or a methacryloyl group, 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, dipentaerythritol hexaacrylate, caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hydroxypentaacrylate, alkyl-modified dipentaerythritol pentaacrylate, alkyl-modified dipentaerythritol tetraacrylate, alkyl-modified dipentaerythritol triacrylate, dimethylolpropane tetraacrylate, pentaerythritol ethoxytetraacrylate, EO-modified phosphoric acid 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, 9,9 - Bis[4-(2 - acryloyloxyethoxy)phenyl]fluorene, tricyclodecane dimethanol diacrylate, decane diol diacrylate, hexane diol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, EO-modified bisphenol A dimethacrylate, PO-modified bisphenol A dimethacrylate, tricyclodecane dimethanol dimethacrylate, decane diol dimethacrylate, hexane diol dimethacrylate, etc. can be mentioned.,

[0086] In addition, examples of oligomers and polymers having an acryloyl group or a methacryloyl group include urethane acrylate, ester acrylate, acrylic acrylate, epoxy acrylate, etc. Among them, urethane acrylate and ester acrylate are preferable, and urethane acrylate is more preferable.,

[0087] The above compounds can be used alone or in combination of two or more.,

[0088] (Polymerization initiator) The polymerization initiator includes thermal polymerization initiators, photoinitiators, etc., Examples of thermal polymerization initiators include peroxide-based compounds such as 2,5 - dimethylhexane - 2,5 - dihydroperoxide, dicumyl peroxide, benzoyl peroxide, t - butyl peroxide, t - butyl cumyl peroxide, t - butyl hydroperoxide, cumene hydroperoxide, lauroyl peroxide, and azo-based 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(isobutyric acid methyl), 2,2’ - azobis(isobutylamidine hydrochloride), 4,4’ - azobis - 4 - cyanovaleric acid.,

[0089] Photoinitiators can be classified into direct cleavage type and hydrogen abstraction type according to the difference in radical generation mechanisms. When a direct cleavage type photoinitiator absorbs light energy, radicals are generated by cleavage of a part of the covalent bonds within the molecule. On the other hand, when a hydrogen abstraction type photoinitiator absorbs light energy, the excited molecule abstracts hydrogen from a hydrogen donor to generate radicals.

[0090] Examples of direct cleavage type photoinitiators include acetophenone, 2-benzoyl-2-propanol, 1-benzoylcyclohexanol, 2,2-diethoxyacetophenone, benzyldimethylketal, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone, and other acetophenone-based or ketal-based compounds; benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, O-tosylbenzoin, and other benzoin ether-based compounds; diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, lithium phenyl(2,4,6-trimethylbenzoyl)phosphonate, and other acylphosphine oxide-based compounds.

[0091] Examples of hydrogen abstraction type photoinitiators include benzophenone-based compounds such as benzophenone, 4-benzoylbenzoic acid, 2-benzoylbenzoic acid, methyl 2-benzoylbenzoate, methyl benzoylformate, benzyl, p-anisyl, 2-benzoylnaphthalene, 4,4'-bis(dimethylamino)benzophenone, 4,4'-dichlorobenzophenone, 1,4-dibenzoylbenzene; anthraquinone-based or thioxanthone-based compounds such as 2-ethylanthraquinone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone, etc. Other photoinitiators include camphorquinone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime, acridine-based compounds, triazine-based compounds, imidazole-based compounds.

[0092] In order to efficiently absorb light energy and generate radicals, the photoinitiator preferably has an absorption wavelength in the wavelength region of the light source used for light irradiation. On the other hand, among the compounds contained in the outermost layer, if components other than the photoinitiator have absorption in this wavelength region, the photoinitiator may not be able to absorb sufficient light energy, resulting in a decrease in radical generation efficiency. General binder resins, charge transport materials, and metal oxide particles have absorption wavelengths in the ultraviolet region (UV), so this effect is particularly significant when the light source used for light irradiation is ultraviolet light (UV). From the perspective of preventing such problems, it is preferable to contain an acylphosphine oxide-based compound that has an absorption wavelength on the relatively longer wavelength side among photoinitiators. In addition, acylphosphine oxide-based compounds have a photobleaching effect in which the absorption wavelength region changes to the lower wavelength side due to self-cleavage, so they can transmit light to the inside of the outermost layer and are also preferable in terms of good internal curability. In this case, from the perspective of supplementing the curability of the outermost layer surface, it is more preferable to use a hydrogen abstraction type initiator in combination. The content ratio of the hydrogen abstraction type initiator with respect to the acylphosphine oxide compound is not particularly limited. From the viewpoint of supplementing surface curability, 0.1 part by mass or more is preferable with respect to 1 part by mass of the acylphosphine oxide compound, and from the viewpoint of maintaining internal curability, 5 parts by mass or less is preferable.

[0093] Moreover, those having a photopolymerization promoting effect can also be used alone or in combination with the above photopolymerization initiator. For example, triethanolamine, methyldiethanolamine, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, 4,4’-dimethylaminobenzophenone, etc. can be mentioned.

[0094] These polymerization initiators may be used alone or in a mixture of two or more. The content of the polymerization initiator is 0.5 to 40 parts by mass, preferably 1 to 20 parts by mass, with respect to 100 parts by mass of the total content having radical polymerizability.

[0095] (Metal oxide particles) From the viewpoints of imparting charge transport ability and improving mechanical strength, the protective layer may contain metal oxide particles.

[0096] As the metal oxide particles, generally, any metal oxide particles that can be used in an electrophotographic photoreceptor can be used. More specifically, as the metal oxide particles, metal oxide particles containing one kind 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 a plurality of metal elements such as calcium titanate, strontium titanate, barium titanate, etc. can be mentioned. The metal oxide particles may be used with only one kind of particle, or a plurality of kinds of particles may be mixed and used. Among these, from the viewpoint of strong exposure characteristics, metal oxide particles with a band gap smaller than the energy difference between the HOMO level and the LUMO level of the HTM in the photosensitive layer are preferred. When the energy difference is small, the wavelength absorbed by the hole transport material (HTM) can be cut according to the addition amount, so that the strong exposure characteristics are improved. From such a viewpoint, metal oxide particles such as titanium oxide, zinc oxide, tin oxide, calcium titanate, strontium titanate, barium titanate are preferred. Among them, titanium oxide particles are particularly preferred.

[0097] As the crystal form of the titanium oxide particles, any of rutile, anatase, brookite, and amorphous can be used. Also, a plurality of crystal states may be included from those with different crystal states among these.

[0098] The metal oxide particles may be those subjected to various surface treatments on their surfaces. For example, those treated with inorganic substances such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, silicon oxide, or organic substances such as stearic acid, polyol, and organosilicon compounds may also be used. In particular, when using titanium oxide particles, 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 having a chain polymerizable functional group are preferred.

[0099] Note that the outermost surface of these surface-treated particles is treated with such a treating agent. Before such treatment, it may be treated with a treating agent such as aluminum oxide, silicon oxide, or zirconium oxide. For the metal oxide particles, only one type of particle may be used, or a plurality of types of particles may be mixed and used.

[0100] The metal oxide particles to be used are usually preferably those having an average primary particle diameter of 500 nm or less, more preferably those having a diameter of 1 nm to 100 nm, and even more preferably those having a diameter of 5 to 50 nm. This average primary particle diameter can be determined by the arithmetic average value of the diameters of the particles directly observed by a transmission electron microscope (hereinafter also referred to as TEM).

[0101] The content of the metal oxide particles in this 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 with respect to 100 parts by mass of the curable compound. Also, 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.

[0102] (Other materials) This protective layer may contain other materials as necessary. Examples of other materials include stabilizers (such as heat stabilizers, ultraviolet absorbers, light stabilizers, antioxidants, etc.), dispersants, antistatic agents, colorants, lubricants, and the like. These can be used singly as appropriate, or two or more of them can be used in any ratio and combination.

[0103] (Curing method) As the curing method, any method such as heat curing, photocuring, electron beam curing, radiation curing, etc. is possible, but photocuring, which is excellent in safety and energy saving, is preferred. Among photocuring methods, curing by metal halide light or LED light is preferred, and curing by LED light, which can control the reaction and suppress heat generation, is more preferred. From the viewpoint of curing speed, the wavelength of the LED light is preferably 400 nm or less, and more preferably 385 nm or less.

[0104] (Martens hardness) By providing this protective layer, the Martens hardness of this photoreceptor can be made 270 N / mm 2 or more, and among them, 300 N / mm 2 or more, and among them, 330 N / mm 2 or more. If the Martens hardness is 270 N / mm 2 or more, it can have practically sufficient abrasion resistance. In the present invention, the Martens hardness of the photoreceptor means the Martens hardness measured from the surface side of the photoreceptor.

[0105] (Elastic deformation rate) By providing this protective layer, the elastic deformation rate of this photoreceptor can be made 40% or more, and among them, 45% or more, and among them, 50% or more. If the elastic deformation rate is 40% or more, it can have practically sufficient abrasion resistance and cleaning resistance. In the present invention, the elastic deformation rate of the photoreceptor means the elastic deformation rate measured from the surface side of the photoreceptor.

[0106] (Method for forming this protective layer) This protective layer can be formed, for example, by dissolving a curable composition containing a curable compound, a polymerization initiator, and, if necessary, metal oxide particles, etc. in a solvent, if necessary, to make a coating solution, or by dispersing it in a dispersion medium to make a coating solution, and then curing the coating solution after coating.

[0107] At this time, as the organic solvent used for forming this protective layer, a known organic solvent may be appropriately selected and used. Among them, it is preferable to contain alcohols, which have low solubility in polycarbonate and polyarylate, which are preferably used for the photosensitive layer.

[0108] As the coating method when forming this protective layer, for example, spray coating method, spiral coating method, ring coating method, dip coating method, etc. can be mentioned. However, it is not limited to these methods. After forming a coating film by the above coating method, it is preferable to dry the coating film.

[0109] The curing of the curable composition can be carried out by irradiating the curable composition with heat, light (for example, ultraviolet light or / and visible light), radiation, etc. as external energy.

[0110] As a method of applying heat energy, it is carried out by heating from the coating surface side or the support side using a gas such as air or nitrogen, steam, or various heat media, infrared rays, or electromagnetic waves. The heating temperature is preferably 100°C or higher and 170°C or lower. At a temperature equal to or higher than the lower limit temperature, a sufficient reaction rate can be obtained and the reaction proceeds completely. At a temperature equal to or lower than the upper limit temperature, the reaction can proceed uniformly and the generation of large distortion in the outermost layer can be suppressed. In order to make the curing reaction proceed uniformly, a method of heating at a relatively low temperature below 100°C and then further heating to 100°C or higher to complete the reaction is also effective.

[0111] As the energy of light, mainly UV irradiation light sources such as high-pressure mercury lamps, metal halide lamps, electrodeless lamp bulbs, and light-emitting diodes having an emission wavelength in ultraviolet light (UV) can be used. It is also possible to select a visible light source according to the absorption wavelength of the curable compound and the photoinitiator. The light irradiation amount is preferably 100 mJ / cm 2 or more, more preferably 500 mJ / cm 2 or more, particularly preferably 1000 mJ / cm 2 or more. Also, from the viewpoint of electrical properties, it is preferably 20000 mJ / cm 2 or less, preferably 10000 mJ / cm2 The following is more preferable, 5000 mJ / cm 2 The following is particularly preferable.

[0112] Examples of the radiation energy include those using an electron beam (EB). Among these energies, those using light energy are preferable from the viewpoints of ease of reaction rate control, simplicity of the apparatus, and length of the pot life.

[0113] <Conductive support> The conductive support is not particularly limited as long as it supports the layer formed thereon and exhibits conductivity. Examples of the conductive support include metal materials such as aluminum, aluminum alloy, stainless steel, copper, and nickel, resin materials imparted with conductivity by coexisting conductive powders such as metal, carbon, and tin oxide, and resins, glass, paper, etc. mainly used by vapor-depositing or coating a conductive material such as aluminum, nickel, ITO (indium tin oxide alloy) on its surface. As the form, those such as drum shape, sheet shape, and belt shape are used. A conductive material having an appropriate resistance value may be applied on the conductive support of the metal material for controlling conductivity, surface properties, etc. or covering defects.

[0114] When a metal material such as an aluminum alloy is used as the conductive support, it may be used after applying an anodic oxide film to the metal material. For example, an anodic oxide film is formed on the surface of the metal material by subjecting the metal material to anodic oxidation treatment in an acidic bath such as chromic acid, sulfuric acid, oxalic acid, boric acid, and sulfamic acid. In particular, anodic oxidation treatment in sulfuric acid gives better results.

[0115] In the case of anodic oxidation 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 liquid temperature is usually 15°C or more and 30°C or less, the electrolytic voltage is usually 10 V or more and 20 V or less, and the current density is usually 0.5 A / dm 2 or more and 2 A / dm 2It is preferably set within the following range, but is not limited to the above conditions. The average film thickness of the anodic oxide film is usually 20 μm or less, particularly preferably 7 μm or less.

[0116] When an anodic oxide film is applied to 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.

[0117] The surface of the conductive support may be smooth, or may be roughened by using a special cutting method or performing a polishing treatment. Also, it may be roughened by mixing particles of an appropriate particle size into the material constituting the support. Note that an undercoat layer described later may be provided between the conductive support and the photosensitive layer in order to improve adhesiveness, blocking properties, etc.

[0118] <Undercoat layer> This photoreceptor may have an undercoat layer between the photosensitive layer and the conductive support.

[0119] As the undercoat layer, for example, a resin, a resin in which particles such as an organic pigment or a metal oxide are dispersed, etc. are used. Examples of the organic pigment used for the undercoat layer include phthalocyanine pigments, azo pigments, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, anthraanthrone pigments, benzimidazole pigments, and the like. Among them, phthalocyanine pigments and azo pigments, specifically, the phthalocyanine pigments and azo pigments used as the charge generation materials described above can be mentioned.

[0120] Examples of the metal oxide particles used for the undercoat layer include metal oxide particles containing one kind of metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, iron oxide, etc., and metal oxide particles containing a plurality of metal elements such as calcium titanate, strontium titanate, barium titanate, etc. For the undercoat layer, only one kind of the above particles may be used, or a plurality of kinds of particles may be mixed and used in any ratio and combination.

[0121] Among the above metal oxide particles, titanium oxide and aluminum oxide are preferable, and titanium oxide is particularly preferable. The titanium oxide particles may be treated, for example, with inorganic substances such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, silicon oxide, etc., or organic substances such as stearic acid, polyol, silicone, etc. As the crystal form of the titanium oxide particles, any of rutile, anatase, brookite, and amorphous can be used. Also, those having a plurality of crystal states may be included.

[0122] The particle size of the metal oxide particles used for the undercoat layer is not particularly limited. From the viewpoint 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.

[0123] Here, it is desirable to form the undercoat layer by dispersing particles in a binder resin. Examples of the binder resin used for the undercoat layer include polyvinyl butyral resin, polyvinyl formal resin, and partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal, acetal, etc., i.e., polyvinyl acetal resins; polyarylate resin, polycarbonate resin, polyester resin, modified ether-based polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyvinyl pyridine resin, cellulose-based resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin, polyvinyl pyrrolidone resin, casein; vinyl chloride-vinyl acetate copolymers, hydroxy-modified vinyl chloride-vinyl acetate copolymers, carboxyl-modified vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, etc., i.e., vinyl chloride-vinyl acetate-based copolymers; styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers; insulating resins such as styrene-alkyd resins, silicone-alkyd resins, phenol-formaldehyde resins; and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinyl anthracene, polyvinyl perylene. However, it is not limited to these polymers. Further, these binder resins may be used alone, or two or more of them may be mixed and used, or they may be used in a cured form together with a curing agent. Among them, polyvinyl butyral resin, polyvinyl formal resin, polyvinyl acetal resins such as partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal, acetal, etc., alcohol-soluble copolymer polyamides, modified polyamides, etc. are preferable because they exhibit good dispersibility and coatability. Among them, alcohol-soluble copolymer polyamides are particularly preferable.

[0124] The mixing ratio of the particles to the binder resin can be arbitrarily selected. It is preferable to use in the range of 10% by mass to 500% by mass in terms of the stability and coatability of the dispersion liquid.

[0125] The film thickness of the undercoat layer can be arbitrarily selected. It is preferably usually 0.1 μm or more and 20 μm or less based on the characteristics of the electrophotographic photoreceptor and the coatability of the above dispersion liquid. The undercoat layer may contain a known antioxidant or the like.

[0126] <<This Image Forming Apparatus>> An image forming apparatus ("this image forming apparatus") can be configured using this photoreceptor.

[0127] As shown in FIG. 1, this image forming apparatus includes this photoreceptor 1, a charging device 2, an exposure device 3, and a developing device 4, and further, a transfer device 5, a cleaning device 6, and a fixing device 7 are provided as necessary. This photoreceptor 1 is not particularly limited as long as it is the electrophotographic photoreceptor of the present invention described above. In FIG. 1, as an example thereof, a drum-shaped photoreceptor having the above-described photosensitive layer formed on the surface of a cylindrical conductive support is shown. Along the outer peripheral surface of this photoreceptor 1, a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are respectively arranged.

[0128] The charging device 2 charges this photoreceptor 1 and uniformly charges the surface of this photoreceptor 1 to a predetermined potential. Examples of general charging devices include non-contact corona charging devices such as a corotron and a scorotron, or contact charging devices (direct charging devices) that charge by bringing a charged member to which a voltage is applied into contact with the surface of the photoreceptor. Examples of contact charging devices include a charging roller and a charging brush. In FIG. 1, a roller-type charging device (charging roller) is shown as an example of the charging device 2. Usually, a charging roller is manufactured by integrally molding a resin and additives such as a plasticizer with a metal shaft, and may have a laminated structure as necessary. As the voltage applied during charging, not only a DC voltage but also a DC voltage with an AC voltage superimposed thereon can be used.

[0129] The exposure device 3 is not particularly limited in type as long as it can expose the photosensitive member 1 to form an electrostatic latent image on the photosensitive surface of the photosensitive member 1. Specific examples include halogen lamps, fluorescent lamps, lasers such as semiconductor lasers and He-Ne lasers, and LEDs. Also, exposure may be performed by an internal exposure method of the photosensitive member. The light used for exposure is arbitrary. For example, exposure may be performed with monochromatic light having a wavelength of 780 nm, monochromatic light having a slightly shorter wavelength in the range of 600 nm to 700 nm, or monochromatic light having a short wavelength in the range of 380 nm to 500 nm.

[0130] The type of toner T is arbitrary, and in addition to powder toner, polymer toner using suspension polymerization method, emulsion polymerization method, etc. can be used. In particular, when using polymer toner, those with a small particle size of about 4 to 8 μm in diameter are preferred, and the shape of the toner particles can be variously used from those close to spherical to those deviated from spherical such as rod-shaped. Polymer toner is excellent in charge uniformity and transferability and is suitably used for high image quality.

[0131] The transfer device 5 is not particularly limited in type, and a device using any method such as electrostatic transfer method including corona transfer, roller transfer, belt transfer, pressure transfer method, adhesive transfer method, etc. can be used. Here, it is assumed that the transfer device 5 is composed of a transfer charger, a transfer roller, a transfer belt, etc. arranged to face the photosensitive member 1. This transfer device 5 applies a predetermined voltage value (transfer voltage) with the opposite polarity to the charging potential of the toner T and transfers the toner image formed on the photosensitive member 1 to the recording paper (paper, medium) P.

[0132] There are no particular restrictions on the cleaning device 6, and any cleaning device such as a brush cleaner, a magnetic brush cleaner, an electrostatic brush cleaner, a magnetic roller cleaner, a blade cleaner, etc. can be used. The cleaning device 6 scrapes off the 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 surface of the photoreceptor, the cleaning device 6 may not be necessary.

[0133] In the electrophotographic apparatus configured as described above, image recording is performed as follows. That is, first, the surface (photosensitive surface) of the photoreceptor 1 is charged to a predetermined potential (for example, 600 V) by the charging device 2. At this time, it may be charged by a DC voltage, or it may be charged by superimposing an AC voltage on the DC voltage. Subsequently, 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 development of the electrostatic latent image formed on the photosensitive surface of the photoreceptor 1 is performed by the developing device 4.

[0134] The developing device 4 thins the toner T supplied by the supply roller 43 with a regulating member (developing blade) 45, triboelectrically charges it to a predetermined polarity (here, the same polarity as the charging potential of the photoreceptor 1, positive polarity), conveys it while being carried on the developing roller 44, and brings it into contact with the surface of the photoreceptor 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 photosensitive surface of the photoreceptor 1. Then, this toner image is transferred to the recording paper P by the transfer device 5. After that, the toner remaining on the photosensitive surface of the photoreceptor 1 without being transferred is removed by the cleaning device 6.

[0135] After the transfer of the toner image onto the recording paper P, the recording paper P is passed through the fixing device 7 to thermally fix the toner image onto the recording paper P, thereby obtaining the final image. In addition, the image forming apparatus may be configured to be able to perform, for example, a discharging process in addition to the above-described configuration.

[0136] Further, the image forming apparatus may be configured in a further modified manner. For example, it may be configured to perform processes such as a pre-exposure process and an auxiliary charging process, or may be configured to perform offset printing, or may further be configured in a full-color tandem system using a plurality of types of toner.

[0137] <<This electrophotographic cartridge>> This photoreceptor 1 can be combined with one or two 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 be configured as an integrated cartridge (referred to as "this electrophotographic cartridge").

[0138] This electrophotographic cartridge can be configured to be detachable from the electrophotographic apparatus main body such as a copying machine or a laser beam printer. In that case, for example, when this photoreceptor 1 or other members deteriorate, this electrophotographic photoreceptor cartridge is removed from the image forming apparatus main body, and another new electrophotographic photoreceptor cartridge is attached to the image forming apparatus main body, so that maintenance and management of the image forming apparatus become easy.

[0139] <<Explanation of terms>> In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less" and also the meaning of "preferably larger than X" or "preferably smaller than Y". Further, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the intention of "preferably larger than X" or "preferably less than Y".

Examples

[0140] The present invention will be further described by the following examples, but the examples are not intended to limit the present invention in any way.

[0141] <Preparation of dispersion liquid for undercoat layer coating formation> [Coating liquid P1 for undercoat layer formation] Rutile-type white titanium oxide with an average primary particle diameter of 40 nm (manufactured by Ishihara Sangyo Co., Ltd., product name TTO55N) and 3 parts by mass of methyldimethoxysilane with respect to 100 parts by mass of the titanium oxide were stirred with a shear force using a super mixer until the temperature in the mixer reached 160 °C to perform surface treatment. Next, 1000 g of a raw material slurry obtained by mixing 250 g of the surface-treated titanium oxide and 750 g of methanol was dispersed using zirconia beads (YTZ manufactured by Nikkato Corporation) with a diameter of about 50 μm as a dispersion medium, and an ultra apex mill (UAM-015 type) manufactured by Kotobuki Industry Co., Ltd. with a mill volume of about 0.15 L was used. The dispersion treatment was performed for 28 minutes in a circulating state with a rotor peripheral speed of 10 m / s and a liquid flow rate of 6 g / s to prepare a dispersion liquid of titanium oxide. This titanium oxide dispersion liquid was stirred and mixed with a copolymer polyamide solution in which the composition molar ratio of ε-caprolactam / bis(4-amino-3-methylcyclohexyl)methane / hexamethylenediamine / decamethylenedicarboxylic acid / octadecamethylenedicarboxylic acid was 60% / 15% / 5% / 15% / 5% and which was previously dissolved in a mixed solvent of methanol / 1-propanol / toluene. Thereafter, ultrasonic dispersion treatment was performed for 1 hour using an ultrasonic generator with a frequency of 25 kHz and an output of 1200 W. This was filtered through a PTFE membrane filter (Advantec's Miteks LC) with a pore diameter of 5 μm to obtain a coating liquid P1 for forming a subbing layer in which the mass ratio of titanium oxide / copolymer polyamide was 3 / 1, the mass ratio of the mixed solvent of methanol / 1-propanol / toluene was 7 / 1 / 2, and the concentration of the contained solid content was 18%.

[0142] [Coating Liquid Q1 for Forming Charge Generation Layer] 10 parts of oxytitanium phthalocyanine showing a characteristic peak at a Bragg angle (2θ ± 0.2°) of 27.3° in the powder X-ray spectrum pattern by CuKα rays and 5 parts of polyvinyl acetal resin (manufactured by Denki Kagaku Kogyo Co., Ltd., product name DK31) were mixed with 500 parts of 1,2-dimethoxyethane, and pulverized and dispersed using a sand grind mill to obtain a coating liquid Q1 for forming a charge generation layer.

[0143] [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), 40 parts of a hole transport material represented by the following structural formula (B), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of a silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R1 for forming a charge transport layer with a solid content concentration of 16.5%.

[0144] The structural formula (A) is as follows.

[0145] TIFF0007708094000015.tif38147

[0146] The structural formula (B) is as follows.

[0147] TIFF0007708094000016.tif59170

[0148] [Coating solution R2 for forming a charge transport layer] 100 parts of a polyarylate resin (viscosity average molecular weight 43,000) represented by the following structural formula (A), 40 parts of a hole transport material represented by the following structural formula (B), 1 part of an electron transport material represented by the following structural formula (C), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of a silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R2 for forming a charge transport layer with a solid content concentration of 16.5%. Regarding the electron transport material represented by the following structural formula (C), when the electron affinity was determined by the aforementioned method, it was 3.83 eV.

[0149] The structural formula (C) is as follows.

[0150] TIFF0007708094000017.tif5960

[0151] [Coating solution R3 for forming a charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 40 parts of a hole transport material represented by the following structural formula (D), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R3 for forming a charge transport layer with a solid content concentration of 16.5%.

[0152] Structural formula (D) is as follows.

[0153] TIFF0007708094000018.tif8397

[0154] [Coating solution R4 for forming a charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 40 parts of a hole transport material represented by structural formula (D), 1 part of an electron transport material represented by structural formula (C), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R4 for forming a charge transport layer with a solid content concentration of 16.5%.

[0155] [Coating solution R5 for forming a charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 60 parts of a hole transport material represented by the following structural formula (E), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R5 for forming a charge transport layer with a solid content concentration of 18.0%.

[0156] Structural formula (E) is as follows.

[0157] TIFF0007708094000019.tif6387

[0158] [Coating solution R6 for forming charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 60 parts of a hole transport material represented by structural formula (E), 1 part of an electron transport material represented by structural formula (C), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R6 for forming a charge transport layer with a solid content concentration of 18.1%.

[0159] [Coating solution R7 for forming charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 60 parts of a hole transport material represented by the following structural formula (F), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R7 for forming a charge transport layer with a solid content concentration of 18.0%.

[0160] Structural formula (F) is as follows.

[0161] TIFF0007708094000020.tif48107

[0162] [Coating solution R8 for forming charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 60 parts of a hole transport material represented by structural formula (F), 1 part of an electron transport material represented by structural formula (C), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R8 for forming a charge transport layer with a solid content concentration of 18.1%.

[0163] [Coating Liquid R9 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 the following Structural Formula (G), 4 parts of a hindered phenol-based antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain Coating Liquid R9 for Forming Charge Transport Layer with a solid content concentration of 16.5%.

[0164] Structural Formula (G) is as follows.

[0165] TIFF0007708094000021.tif56109

[0166] [Coating Liquid R10 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 (G), 1 part of an electron transport material represented by Structural Formula (C), 4 parts of a hindered phenol-based antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain Coating Liquid R10 for Forming Charge Transport Layer with a solid content concentration of 16.5%.

[0167] [Coating Liquid R11 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 the following Structural Formula (H), 4 parts of a hindered phenol-based antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain Coating Liquid R11 for Forming Charge Transport Layer with a solid content concentration of 16.5%.

[0168] The structural formula (H) is as follows.

[0169] TIFF0007708094000022.tif5898

[0170] [Coating liquid R12 for forming charge transport layer] 100 parts of a polyarylate resin (viscosity average molecular weight 43,000) represented by the structural formula (A), 40 parts of a hole transport material represented by the structural formula (H), 1 part of an electron transport material represented by the structural formula (C), 4 parts of a hindered phenol-based antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating liquid R12 for forming a charge transport layer with a solid content concentration of 16.5%.

[0171] [Coating liquid S1 for forming protective layer] Rutile-type white titanium oxide with an average primary particle diameter of 40 nm (manufactured by Ishihara Sangyo Co., Ltd., product name TTO55N) and 7 parts by mass of 3-methacryloxypropyltrimethoxysilane were stirred in a super mixer by shear force until the temperature in the mixer reached 150 °C with respect to 100 parts by mass of the titanium oxide, and surface treatment was performed. Next, 1000 g of a raw material slurry obtained by mixing 250 g of the surface-treated titanium oxide and 750 g of methanol was used with zirconia beads (YTZ manufactured by Nikkato Corporation) having a diameter of about 50 μm as a dispersion medium, and an Ultra Apex Mill (UAM-015 type) manufactured by Hisako Industry Co., Ltd. with a mill volume of about 0.15 L was used. In a circulating state with a rotor peripheral speed of 9 m / s and a liquid flow rate of 2.8 g / s, dispersion treatment was performed for 30 minutes to prepare a dispersion liquid of titanium oxide. A urethane acrylate oligomer (product name UV6300B manufactured by Mitsubishi Chemical Corporation) previously dissolved in a mixed solvent of methanol / 1-propanol / toluene and benzophenone and Omnirad TPO H (2,4,6-trimethylbenzoyl-diphenylphosphine oxide) as a polymerization initiator were mixed so that UV6300B / surface-treated titania / benzophenone / Omnirad TPO H = 100 / 55 / 1 / 2, the solvent composition was methanol / 1-propanol / toluene = 7 / 1 / 2, and a coating liquid S1 for forming a protective layer with a solid content concentration of 18.0% was obtained.

[0172] <Comparative Example 1> The coating liquid P1 for forming an undercoat layer was dip-coated on an aluminum cylinder with a surface machined to 30 mmφ and a length of 248 mm, and an undercoat layer was provided so that the dry film thickness was 1.5 μm. The coating liquid Q1 for forming a charge generation layer was dip-coated on the undercoat layer, and a charge generation layer was provided so that the dry film thickness was 0.3 μm. The coating liquid R1 for forming a charge transport layer was dip-coated on the charge generation layer, and a charge transport layer was provided so that the dry film thickness was 20.0 μm. The coating liquid S1 for forming a protective layer was ring-coated on the charge transport layer, dried at room temperature for 20 minutes, and then, in a nitrogen atmosphere (oxygen concentration 1% or less), while rotating the photoreceptor at 60 rpm, a metal halide lamp was used with an illuminance of 140 mW / cm 2By irradiating for 2 minutes, a protective layer with a cured film thickness of 1.0 μm was formed, and a negatively charged photoreceptor D1 was produced.

[0173] <Example 1> A photoreceptor produced in the same manner as the negatively charged photoreceptor D1, except that the coating solution R1 for forming the charge transport layer was changed to the coating solution R2 for forming the charge transport layer, is designated as the negatively charged photoreceptor D2.

[0174] <Comparative Example 2> A negatively charged photoreceptor produced in the same manner as the negatively charged photoreceptor D1, except that the coating solution R1 for forming the charge transport layer was changed to the coating solution R3 for forming the charge transport layer, is designated as the photoreceptor D3.

[0175] <Example 2> A photoreceptor produced in the same manner as the negatively charged photoreceptor D1, except that the coating solution R1 for forming the charge transport layer was changed to the coating solution R4 for forming the charge transport layer, is designated as the negatively charged photoreceptor D4.

[0176] <Comparative Example 3> A photoreceptor produced in the same manner as the negatively charged photoreceptor D1, except that the coating solution R1 for forming the charge transport layer was changed to the coating solution R5 for forming the charge transport layer, is designated as the negatively charged photoreceptor D5.

[0177] <Example 3> A photoreceptor produced in the same manner as the negatively charged photoreceptor D1, except that the coating solution R1 for forming the charge transport layer was changed to the coating solution R6 for forming the charge transport layer, is designated as the negatively charged photoreceptor D6.

[0178] <Reference Example 1> A photoreceptor produced in the same manner as the negatively charged photoreceptor D1, except that the coating solution R1 for forming the charge transport layer was changed to the coating solution R7 for forming the charge transport layer, is designated as the negatively charged photoreceptor D7.

[0179] <Reference Example 2> A photoreceptor produced in the same manner as the negatively charged photoreceptor D1, except that the coating solution R1 for forming the charge transport layer was changed to the coating solution R8 for forming the charge transport layer, is designated as the negatively charged photoreceptor D8.

[0180] [Reference Example 3] A photoreceptor produced in the same manner as the negatively chargeable photoreceptor D1 except that the coating liquid R1 for forming the charge transport layer was changed to the coating liquid R9 for forming the charge transport layer is designated as the negatively chargeable photoreceptor D9.

[0181] [Reference Example 4] A photoreceptor produced in the same manner as the negatively chargeable photoreceptor D1 except that the coating liquid R1 for forming the charge transport layer was changed to the coating liquid R10 for forming the charge transport layer is designated as the negatively chargeable photoreceptor D10.

[0182] [Reference Example 5] A photoreceptor produced in the same manner as the negatively chargeable photoreceptor D1 except that the coating liquid R1 for forming the charge transport layer was changed to the coating liquid R11 for forming the charge transport layer is designated as the negatively chargeable photoreceptor D11.

[0183] [Reference Example 6] A photoreceptor produced in the same manner as the negatively chargeable photoreceptor D1 except that the coating liquid R1 for forming the charge transport layer was changed to the coating liquid R12 for forming the charge transport layer is designated as the negatively chargeable photoreceptor D12.

[0184] [HOMO Level of Hole Transport Material (HTM) and Energy Difference between HOMO Level and LUMO Level] The HOMO level of the hole transport material (HTM) used in this example, comparative examples, and reference examples, and the energy difference between the HOMO level and the LUMO level are shown in Table-1.

[0185] [Table-1]

[0186] [Evaluation of Electrical Characteristics] Next, two of each of these negatively charged electrophotographic photoreceptors D1 to D12 were fabricated. One of each pair was left as is (without heat treatment), and the other was heat-treated at 125°C for 10 minutes. After the temperature of the photoreceptor returned to room temperature, it was mounted on an electrophotographic characteristic evaluation apparatus (described on pages 404 - 405 of "Fundamentals and Applications of Electrophotography," edited by the Electrophotography Society and published by Corona Publishing Co., Ltd.) fabricated according to the standards of the Electrophotography Society. The electrical characteristics were evaluated in an environment of 25°C / 50% according to the following procedure: charging (negative polarity), exposure, potential measurement, and discharging cycles. The photoreceptor was charged so that the initial surface potential was -700 V, and the light from a halogen lamp was made into monochromatic light of 780 nm with an interference filter and irradiated at an intensity of 1.0 μJ / cm 2 The surface potential after exposure (VL) 60 milliseconds later (-V) was measured. These electrical characteristics are shown in Table - 2 and Table - 3.

[0187] After measuring the electrical characteristics, these drums were left in an environment of 35°C / 85% for 24 hours, then returned to room temperature, and the above evaluation was performed again to measure the surface potential after exposure (VL) (-V). These characteristics are shown in Table - 4 and Table - 5.

[0188] [Table - 2]

[0189] [Table - 3]

[0190] [Table - 4]

[0191] [Table - 5]

[0192] [Measurement of Martens hardness and elastic deformation rate] The negatively charged photoreceptors D1 to D12 (without heat treatment) were measured under the following measurement conditions from the surface side of the negatively charged photoreceptor using a microhardness tester (FISCHERSCOPE HM2000, manufactured by Fischer) in an environment of a temperature of 25°C and a relative humidity of 50%. The Martens hardness and elastic deformation rate of each sample are shown in Table-6 and Table-7.

[0193] (Measurement conditions for Martens hardness and elastic deformation rate) Indenter: Vickers square pyramid diamond indenter with an included angle of 136° Maximum indentation load: 0.2 mN Loading time required: 10 seconds Unloading time required: 10 seconds The Martens hardness is obtained from the following formula. Martens hardness (N / mm 2 ) = Maximum indentation load / Indentation area at the maximum indentation load

[0194]

Table-6

[0195]

Table-7

[0196] [Coating solution R13 for forming charge transport layer] 100 parts of a polyarylate resin (viscosity average molecular weight 43,000) represented by structural formula (A), 75 parts of a hole transport material represented by structural formula (B), 4 parts of a hindered phenol-based antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R13 for forming a charge transport layer with a solid content concentration of 16.5%.

[0197] [Coating solution R14 for forming charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 75 parts of a hole transport material represented by structural formula (B), 5 parts of an electron transport material represented by structural formula (C), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R14 for forming a charge transport layer with a solid content concentration of 16.5%.

[0198] [Coating solution R15 for forming a charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 75 parts of a hole transport material represented by structural formula (B), 5 parts of an electron transport material represented by structural formula (I), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R15 for forming a charge transport layer with a solid content concentration of 16.5%. Regarding the electron transport material represented by the following structural formula (I), when the electron affinity was determined by the aforementioned method, it was 3.97 eV.

[0199] Structural formula (I) is as follows.

[0200] TIFF0007708094000030.tif5248

[0201] [Coating solution R16 for forming a charge transport layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 75 parts of a hole transport material represented by structural formula (B), 5 parts of an electron transport material represented by structural formula (J), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R16 for forming a charge transport layer with a solid content concentration of 16.5%. Regarding the electron transport material represented by the following structural formula (J), when the electron affinity was determined by the aforementioned method, it was 3.60 eV.

[0202] The structural formula (J) is as follows.

[0203] TIFF0007708094000031.tif6469

[0204] [Coating Liquid R17 for Forming Charge Transport Layer] 100 parts of a polyarylate resin (viscosity average molecular weight 43,000) represented by structural formula (A), 75 parts of a hole transport material represented by structural formula (B), 0.2 part of an electron transport material represented by structural formula (C), 4 parts of a hindered phenol-based antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating liquid R17 for forming a charge transport layer with a solid content concentration of 16.5%.

[0205] [Coating Liquid R18 for Forming Charge Transport Layer] 100 parts of a polyarylate resin (viscosity average molecular weight 43,000) represented by structural formula (A), 75 parts of a hole transport material represented by structural formula (B), 0.5 part of an electron transport material represented by structural formula (C), 4 parts of a hindered phenol-based antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating liquid R18 for forming a charge transport layer with a solid content concentration of 16.5%.

[0206] [Coating Liquid R19 for Forming Charge Transport Layer] 100 parts of a polyarylate resin represented by structural formula (A) (viscosity average molecular weight 43,000), 75 parts of a hole transport material represented by structural formula (B), 1 part of an electron transport material represented by structural formula (C), 4 parts of a hindered phenol antioxidant (trade name Irg1076, manufactured by BASF), and 0.05 part of a silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) were dissolved in a mixed solvent of tetrahydrofuran:toluene = 8 / 2 and stirred and mixed to obtain a coating solution R19 for forming a charge transport layer with a solid content concentration of 16.5%.

[0207] <Comparative Example 4> The coating solution P1 for forming an undercoat layer was dip-coated on an aluminum cylinder with a diameter of 30 mm and a length of 248 mm whose surface was machined to provide an undercoat layer with a dry film thickness of 1.5 μm. The coating solution Q1 for forming a charge generation layer was dip-coated on the undercoat layer to provide a charge generation layer with a dry film thickness of 0.3 μm. The coating solution R13 for forming a charge transport layer was dip-coated on the charge generation layer to provide a charge transport layer with a dry film thickness of 20.0 μm. The coating solution S1 for forming a protective layer was ring-coated on the charge transport layer and dried at room temperature for 20 minutes. Then, in a nitrogen atmosphere (oxygen concentration 1% or less), while rotating the photoreceptor at 60 rpm, a metal halide lamp was irradiated at an illuminance of 140 mW / cm 2 for 2 minutes to form a protective layer with a cured film thickness of 3.0 μm, and a negatively charged photoreceptor D13 was produced.

[0208] <Example 4> A photoreceptor produced in the same manner as the negatively charged photoreceptor D13 except that the coating solution R13 for forming a charge transport layer was changed to the coating solution R14 for forming a charge transport layer was designated as the negatively charged photoreceptor D14.

[0209] <Example 5> A photoreceptor produced in the same manner as the negatively charged photoreceptor D13 except that the coating solution R13 for forming a charge transport layer was changed to the coating solution R15 for forming a charge transport layer was designated as the negatively charged photoreceptor D15.

[0210] <Example 6> A photoreceptor produced in the same manner as the negatively charged photoreceptor D13 except that the coating liquid R13 for forming the charge transport layer is changed to the coating liquid R16 for forming the charge transport layer is defined as the negatively charged photoreceptor D16.

[0211] <Example 7> A photoreceptor produced in the same manner as the negatively charged photoreceptor D13 except that the coating liquid R13 for forming the charge transport layer is changed to the coating liquid R17 for forming the charge transport layer is defined as the negatively charged photoreceptor D17.

[0212] <Example 8> A photoreceptor produced in the same manner as the negatively charged photoreceptor D13 except that the coating liquid R13 for forming the charge transport layer is changed to the coating liquid R18 for forming the charge transport layer is defined as the negatively charged photoreceptor D18.

[0213] <Example 9> A photoreceptor produced in the same manner as the negatively charged photoreceptor D13 except that the coating liquid R13 for forming the charge transport layer is changed to the coating liquid R19 for forming the charge transport layer is defined as the negatively charged photoreceptor D19.

[0214] [Evaluation of Electrical Characteristics] Two of each of these negatively charged electrophotographic photoreceptors D13 to D19 were produced. One of each was used as it was (without heat treatment), and the other was heat-treated at 125 °C for 10 minutes. After the photoreceptor temperature returned to room temperature, the electrical characteristics were evaluated by the method described above in an environment of 25 °C / 50%. The results are shown in Table 8.

[0215] After the above evaluation, for D13, D17 to D19 among the negatively charged electrophotographic photoreceptors, after leaving them standing for 24 hours in an environment of 35 °C / 85% and then returning them to room temperature, the above evaluation was performed again. The results are shown in Table 9.

[0216]

Table 8

[0217]

Table 9

[0218] (Investigation) From the above examples and the test results obtained by the present inventors, it has been found that even in a negatively charged OCL photoreceptor having a cured resin-based protective layer, by combining a predetermined hole transport material (HTM) with the radical acceptor compound or electron transport material (ETM) and containing them in the photosensitive layer, the electrical characteristics can be improved without performing heat treatment after curing the protective layer. At that time, it has been found that the hole transport material (HTM) preferably has an energy difference between the HOMO level and the LUMO level of 3.60 eV or less.

[0219] In addition, it has also been found that when the HOMO level of the hole transport material (HTM) is higher than -4.50 eV based on the vacuum level and when the energy difference between the HOMO level and the LUMO level is 3.60 eV or more, the electrical characteristics do not particularly deteriorate in the first place. That is, it has been found that it is necessary to combine a predetermined hole transport material (HTM) with the radical acceptor compound or electron transport material (ETM) and contain them in the photosensitive layer when the hole transport material (HTM) has a HOMO level of -4.50 eV or less based on the vacuum level and an energy difference between the HOMO level and the LUMO level of 3.60 eV or less.

[0220] The present invention also formed any one of 1) a photosensitive layer containing only a binder resin and an HTM of structural formula (B) satisfying the conditions of claim 1 of the present application, 2) a photosensitive layer containing only a binder resin and an ETM of structural formula (C), and 3) a photosensitive layer containing a binder resin, an ETM of structural formula (C), and an HTM of structural formula (B), provided a cured resin-based protective layer on the photosensitive layer, and performed ESR measurement. As a result, from 1), a spectrum considered to be a radical of the HTM of structural formula (B) satisfying the conditions of claim 1 of the present application was obtained, and from 2) and 3), a spectrum considered to be a radical of the ETM of structural formula (C) was obtained. From this result, it has been found that at least the ETM is more likely to become a radical than the HTM satisfying the conditions of claim 1 of the present application. Based on such test results, the mechanism of action when a hole transport material (HTM) and the radical acceptor compound or electron transport material (ETM) are combined and contained in the photosensitive layer can be considered as follows.

[0221] When forming a cured resin-based protective layer, it is common for curing to proceed due to the involvement of radicals by a polymerization initiator or the like. Therefore, radicals also propagate to the hole transport material (HTM) in the photosensitive layer, making it easier to generate HTM radicals. It is considered that these HTM radicals become charge trap sites and deteriorate the electrical characteristics. The improvement of the electrical characteristics by heating is considered to be because the HTM radicals disappear due to the heat treatment. Here, when not only the hole transport material (HTM) but also the radical acceptor compound or electron transport material (ETM) is contained in the photosensitive layer, since ETM is more likely to become a radical than HTM, even if HTM radicals are generated, the HTM radicals immediately extract hydrogen atoms from the ETM, and it is considered that the HTM radicals are converted back to HTM. On the other hand, ETM is considered to be converted to ETM radicals. However, as a result of the study of the present invention, it is considered that this phenomenon occurs only when the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is 3.60 eV or less, and the HOMO level is -4.50 eV or less based on the vacuum level. The reason is speculated as follows.

[0222] When the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is 3.60 eV or more, the HTM radicals are unstable and difficult to generate. Also, when the HOMO level of the hole transport material (HTM) is -4.50 eV or more based on the vacuum level, since the original HOMO level of the HTM is shallow, even if HTM radicals are generated, the HOMO level of the HTM radicals is less likely to become shallower than the original HOMO level. When the HOMO level of the HTM radicals and the original HOMO level of the HTM are in such a relationship, the HTM radicals are less likely to become charge trap sites. Therefore, in the case of such HTM, it is considered that the electrical characteristics are good even without using ETM in combination. On the other hand, in the case of a hole transport material (HTM) in which the energy difference between the HOMO level and the LUMO level is 3.60 eV or less and the HOMO level is -4.50 eV or less based on the vacuum level, an HTM radical that becomes a charge trap site is likely to be generated and is also likely to become a charge trap site. Therefore, it is considered that an ETM is required to remove the generated HTM radical. Therefore, when the photosensitive layer contains a hole transport material (HTM) and the radical acceptor compound or electron transport material (ETM), and the energy difference between the HOMO level and the LUMO level of the hole transport material (HTM) is 3.60 eV or less, and the HOMO level is -4.50 eV or less based on the vacuum level, it can be considered that HTM radicals that adversely affect the electrical characteristics are not generated, or even if they are generated, they immediately change to ETM radicals, so the electrical characteristics can be improved without heat treatment.

[0223] In addition, when the same test as in the above example was conducted by changing the type of the binder resin in the photosensitive layer, the same results were obtained.

Claims

1. In a negatively charged electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on an electrically conductive support, the curable compound is a photocurable compound, the photosensitive layer contains a hole transport material (HTM), the hole transport material (HTM) is a compound having an energy difference between the HOMO level and the LUMO level of 3.60 eV or less, and the HOMO level is at -4.50 eV or less based on the vacuum level, the photosensitive layer further contains a radical acceptor compound having an electron affinity of 3.50 eV or more, the protective layer further contains metal oxide particles, and the metal oxide particles are surface-treated with a silane coupling agent. The negatively charged electrophotographic photoreceptor is characterized by this.

2. In a negatively charged electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on a conductive support, the curable compound is a photocurable compound, the photosensitive layer contains a hole transport material (HTM), the hole transport material (HTM) is a compound having an energy difference between the HOMO level and the LUMO level of 3.60 eV or less, and the HOMO level is at -4.50 eV or less based on the vacuum level, the photosensitive layer further contains an electron transport material (ETM), the protective layer further contains metal oxide particles, and the metal oxide particles are surface-treated with a silane coupling agent. The negatively charged electrophotographic photoreceptor is characterized by this.

3. The negatively charged electrophotographic photoreceptor according to claim 1 or 2, wherein the photocurable compound is a compound having an acryloyl group or a methacryloyl group.

4. The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 3, wherein the protective layer is a layer formed from a composition containing a photocurable compound and a polymerization initiator.

5. The photosensitive layer is a laminated photosensitive layer having a structure in which a charge transport layer (CTL) containing a hole transport material (HTM) and the radical acceptor compound or an electron transport material (ETM) is laminated on a charge generation layer (CGL) containing a charge generation material (CGM). The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 4 is characterized by this.

6. The martensite hardness is 270 N / mm 2 The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 5, characterized in that the above is satisfied.

7. The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 6, wherein the radical acceptor compound or electron transport material (ETM) is a compound having a diphenoquinone structure or a dinaphthylquinone structure.

8. The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 7, wherein the content of the radical acceptor compound or electron transport material (ETM) is from 0.1 part by mass to 10 parts by mass with respect to 100 parts by mass of the content of the hole transport material (HTM) in the photosensitive layer.

9. The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 8, wherein the hole transport material (HTM) in the photosensitive layer is a compound having a triphenylamine structure.

10. The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 9, wherein the band gap of the metal oxide particles is smaller than the energy difference between the HOMO level and the LUMO level of the HTM in the photosensitive layer.

11. The negatively charged electrophotographic photoreceptor according to claim 4, containing a photopolymerization initiator as the polymerization initiator, wherein the photopolymerization initiator contains an acylphosphine oxide-based compound.

12. The negatively charged electrophotographic photoreceptor according to claim 4, containing a photopolymerization initiator as the polymerization initiator, wherein the photopolymerization initiator contains an acylphosphine oxide-based compound and a hydrogen abstraction type initiator.

13. The negatively charged electrophotographic photoreceptor according to claim 12, containing 0.1 part by mass or more and 5 parts by mass or less of the hydrogen abstraction type initiator with respect to 1 part by mass of the acylphosphine oxide-based compound.

14. The negatively charged electrophotographic photoreceptor according to any one of claims 1 to 13, wherein the protective layer is a layer cured by irradiation with ultraviolet light or / and visible light.

15. A cartridge comprising the negatively charged electrophotographic photoreceptor according to any one of claims 1 to 14.

16. An image forming apparatus comprising the negatively charged electrophotographic photoreceptor according to any one of claims 1 to 14.

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