Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge, and image forming apparatus

Abstract

The present invention provides a positively-charged monolayer-type electrophotographic photoreceptor that has an outermost layer, the electrophotographic photoreceptor having excellent mechanical strength, electric characteristics, and adhesiveness, and also provides an electrophotographic photoreceptor cartridge and an image formation device.　The problem described above is solved by providing a positively-charged electrophotographic photoreceptor that has a monolayer-type photosensitive layer and an outermost layer, wherein the Martens hardness of the surface of the photoreceptor satisfies a prescribed condition, and preferably, the contents and molecular weights of a hole transport material and an electron transport material contained in the photosensitive layer satisfy a specific relational expression.

Description

Technical Field

[0001] The present invention relates to an electrophotographic photoreceptor used in a copying machine, a printer, etc., and an image forming apparatus. Specifically, the present invention relates to a single-layer electrophotographic photoreceptor excellent in electrical characteristics, mechanical characteristics, and adhesiveness, and an image forming apparatus including the photoreceptor.

Background Art

[0002] The electrophotographic technology is widely used in the fields of copying machines, printers, multifunction machines, digital printing, etc. because high-speed and high-quality images can be obtained. As for the electrophotographic photoreceptor (hereinafter, also simply referred to as "photoreceptor") which is the core of the electrophotographic technology, a photoreceptor using an organic photoconductive material having advantages such as environmental friendliness, easy film formation, and easy manufacturing is mainly used.

[0003] From the viewpoint of the layer structure, organic electrophotographic photoreceptors include a single-layer electrophotographic photoreceptor (hereinafter, referred to as a single-layer photoreceptor) having a charge generating substance and a charge transporting substance in the same layer, and a charge generating substance and a charge transporting substance separated and laminated in separate layers (a charge generation layer and a charge transport layer), a laminated electrophotographic photoreceptor (hereinafter, referred to as a laminated photoreceptor).

[0004] Among these, the laminated photoreceptor is, from the viewpoint of photoreceptor design, easy to optimize the function for each layer and easy to control the characteristics, so most of the current photoreceptors are of this type. Most of the laminated photoreceptors have a charge generation layer and a charge transport layer on a substrate in this order. In the charge transport layer, there are extremely few suitable electron transport substances, while many materials with good characteristics are known for hole transport substances. For this reason, laminated photoreceptors are usually used in a negative charging method in which a charge generation layer and a charge transport layer are laminated in this order on a substrate and the surface of the photoreceptor is charged negatively. In the negative charging method, compared with the positive charging method in which the surface of the photoreceptor is charged positively, the amount of ozone generated from the charger is large, so there may be a problem of deteriorating the photoreceptor.

[0005] On the one hand, in principle, both the negative charging method and the positive charging method can be used for the single-layer photoreceptor. However, the positive charging method is advantageous because it can suppress the amount of ozone generated, which is a problem in the above-mentioned laminated photoreceptor, and is generally easier to make highly sensitive than the negative charging method. In addition, the single-layer photoreceptor has an advantage in that it has fewer coating steps and is advantageous in terms of resolution. Although it has a disadvantage in terms of electrical characteristics compared to the negative charging laminated photoreceptor, it has been partially put into practical use, and various improvement studies have been conducted up to the present (Patent Documents 1 and 2).

[0006] In addition, since the electrophotographic photoreceptor is repeatedly used in the electrophotographic process, that is, cycles such as charging, exposure, development, transfer, cleaning, and discharging, it deteriorates due to various stresses during that time. In particular, damage due to mechanical deterioration such as abrasion, generation of scratches, and peeling of the film on the surface of the photosensitive layer caused by rubbing with a cleaning blade, magnetic brush, etc., contact with a developer, paper, etc., is likely to appear on the image and directly impair the image quality, so it is a major factor limiting the life of the photoreceptor.

[0007] As a technique for improving the mechanical strength or abrasion resistance of the surface of the photoreceptor, a photoreceptor is disclosed in which a layer containing a compound having a chain polymerizable functional group as a binder resin is formed on the outermost layer of the photoreceptor, and this is polymerized by applying energy such as heat, light, and radiation to form a cured resin layer. (See, for example, Patent Documents 3 and 4).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0009] As described above, the positively charged single-layer photoreceptor has inferior electrical characteristics compared to the negatively charged laminated photoreceptor. However, it is considered effective to increase the contents of the hole transport material and the electron transport material in the single-layer photosensitive layer in order to improve the electrical characteristics.

[0010] However, when the contents of the hole transport material and the electron transport material in the single-layer photosensitive layer are increased, the content of the binder resin relatively decreases, resulting in a problem that the mechanical strength of the photosensitive layer decreases. Moreover, not only that, but the hole transport material and the electron transport material tend to concentrate on the surface of the photosensitive layer. When the outermost layer containing a cured resin is formed, the adhesiveness between the outermost layer and the photosensitive layer in contact therewith significantly deteriorates. Therefore, due to stress such as sliding between members such as a charging roller, a developing roller, a transfer roller, and a cleaning blade arranged in contact with the photoreceptor in the electrophotographic process or with printing paper, there has been a problem that the outermost layer peels off and the mechanical strength is impaired.

[0011] The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a positively charged single-layer electrophotographic photoreceptor excellent in electrical characteristics, mechanical characteristics, and adhesiveness between the photosensitive layer and the outermost layer, an electrophotographic photoreceptor cartridge using the electrophotographic photoreceptor, and an image forming apparatus.

Means for Solving the Problems

[0012] The inventors of the present invention intensively studied an electrophotographic photoreceptor capable of satisfying the above object. As a result, they found that for a positively charged single-layer photoreceptor having an outermost layer containing a cured resin, the above problems can be solved by satisfying a predetermined condition for the Martens hardness of the photoreceptor surface, and thus the present invention was achieved. In addition, even when the contents of the hole transport material and the electron transport material in the photosensitive layer are increased, by satisfying a specific relational expression for the contents and molecular weights of the hole transport material and the electron transport material, and by satisfying a predetermined condition for the Martens hardness of the photoreceptor surface, it was found that the above problems can be solved, and thus the present invention was achieved.

[0013] The gist of the present invention lies in the following [1] to

[14] .

[0014] [1] A positive-charged electrophotographic photoreceptor having at least a photosensitive layer and a topmost layer on a conductive support, wherein the photosensitive layer is a single layer containing at least a binder resin, a charge generating substance, a hole transporting substance, and an electron transporting substance, the topmost layer has a structure formed by polymerizing a compound having a chain polymerizable functional group, and the Martens hardness of the photoreceptor surface is 345 N / mm 2 or more.

[0015] [2] The electrophotographic photoreceptor according to [1], wherein the photosensitive layer satisfies the following formula (1).

[0016] 0.9 ≦ (B / b) / (A / a) ≦ 4.0 (1) (In formula (1), A is the content (parts by mass) of the hole transporting substance with respect to 100 of the content of the binder resin, a is the molecular weight of the hole transporting substance, B is the content (parts by mass) of the electron transporting substance with respect to 100 of the content of the binder resin, and b is the molecular weight of the electron transporting substance)

[0017] [3] The electrophotographic photoreceptor according to [1] or [2], wherein the photosensitive layer satisfies the following formula (2).

[0018] 0.15 ≦ (A / a) + (B / b) (2) (In formula (2), A is the content (parts by mass) of the hole transporting substance with respect to 100 of the content of the binder resin, a is the molecular weight of the hole transporting substance, B is the content (parts by mass) of the electron transporting substance with respect to 100 of the content of the binder resin, and b is the molecular weight of the electron transporting substance)

[0019] [4] A positive-charged electrophotographic photoreceptor having at least a photosensitive layer and a outermost layer on a conductive support, wherein the photosensitive layer is a single layer containing at least a binder resin, a charge generating substance, a hole transporting substance, and an electron transporting substance, the photosensitive layer satisfies the following formulas (1) and (2), the outermost layer has a structure formed by polymerizing a compound having a chain polymerizable functional group, and the Martens hardness of the photoreceptor surface is 350 N / mm 2 or more. The electrophotographic photoreceptor.

[0020] 0.9 ≦ (B / b) / (A / a) ≦ 4.0 (1) 0.15 ≦ (A / a) + (B / b) (2)

[0021] (In formulas (1) and (2), A is the content (parts by mass) of the hole transporting substance with respect to 100 of the content of the binder resin, a is the molecular weight of the hole transporting substance, B is the content (parts by mass) of the electron transporting substance with respect to 100 of the content of the binder resin, and b is the molecular weight of the electron transporting substance)

[0022] [5] The electrophotographic photoreceptor according to any one of [1] to [4], wherein the outermost layer contains metal oxide fine particles.

[0023] [6] The electrophotographic photoreceptor according to [5], wherein the metal oxide fine particles are surface-treated with a surface treatment agent having a polymerizable functional group.

[0024] [7] The electrophotographic photoreceptor according to any one of [1] to [6], wherein the photosensitive layer contains a hole transporting substance having a molecular weight of 700 or more.

[0025] [8] The electrophotographic photoreceptor according to any one of [1] to [7], wherein the compound having a chain polymerizable functional group includes a compound having two or more chain polymerizable functional groups.

[0026] [9] The electrophotographic photoreceptor according to any one of [1] to [8], wherein the compound having a chain polymerizable functional group includes a compound having an acryloyl group or a methacryloyl group.

[0027]

[10] The electrophotographic photoreceptor according to any one of [1] to [9], wherein the compound having a chain polymerization functional group contains urethane acrylate.

[0028]

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

[10] , wherein the photosensitive layer contains an electron transport material having a molecular weight of 400 or more.

[0029]

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

[11] , wherein the electron transport material contained in the photosensitive layer has a structure represented by the following formula (6).

[0030] [Chemical formula]

[0031] (In formula (6), R 61 ~R 64 each independently represents a hydrogen atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted alkenyl group having 2 to 20 carbon atoms, and R 61 and R 62 with each other, or R 63 and R 64 with each other may be bonded to each other to form a cyclic structure. X represents an organic residue having a molecular weight of 120 or more and 250 or less.)

[0032]

[13] An electrophotographic photoreceptor cartridge having the electrophotographic photoreceptor according to any one of [1] to

[12] .

[0033]

[14] An image forming apparatus having the electrophotographic photoreceptor according to any one of [1] to

[12] . [Advantages of the Invention]

[0034] According to the present invention, it is possible to provide a positive charging single-layer type electrophotographic photoreceptor excellent in electrical characteristics, mechanical characteristics, and adhesiveness, an electrophotographic photoreceptor cartridge using the electrophotographic photoreceptor, and an image forming apparatus.

Brief Description of the Drawings

[0035]

Figure 1

Embodiments for Carrying Out the Invention

[0036] <Electrophotographic Photoreceptor> The electrophotographic photoreceptor of the present invention has, on a conductive support, a single-layer photoreceptive layer having a binder resin, a charge generating substance, a hole transporting substance, and an electron transporting substance in the same layer, and a outermost layer containing a structure formed by polymerizing a compound having a chain polymerizable functional group.

[0037] Hereinafter, each part (conductive support, single-layer photoreceptive layer, outermost layer) constituting the electrophotographic photoreceptor of the present invention will be described.

[0038] <Conductive Support> First, the conductive support used in the photoreceptor of the present invention will be described.

[0039] The conductive support is not particularly limited as long as it supports the single-layer photoreceptive layer and the outermost layer described below and exhibits conductivity. Examples of the conductive support include metal materials such as aluminum, aluminum alloys, 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 having a conductive material such as aluminum, nickel, ITO (indium tin oxide alloy) etc. vapor-deposited or coated on its surface.

[0040] As the form, drum-shaped, sheet-shaped, belt-shaped, etc. are used. It may also be one in which a conductive material having an appropriate resistance value is applied on the conductive support of the metal material for controlling conductivity, surface properties, etc. or covering defects.

[0041] When using a metal material such as an aluminum alloy as the conductive support, it may be used after applying an anodic oxide film to the metal material.

[0042] The average film thickness of the anodic oxide film is usually 20 μm or less, particularly preferably 7 μm or less.

[0043] 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.

[0044] 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.

[0045] <Single-layer photosensitive layer> Hereinafter, materials (charge generating substances, hole transporting substances, electron transporting substances, binder resins, etc.) used for the single-layer photosensitive layer will be described.

[0046] (Charge generating substance) Examples of charge generating substances used in the photosensitive layer include selenium and its alloys, cadmium sulfide, and other inorganic photoconductive materials; phthalocyanine pigments, azo pigments, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, anthraanthrone pigments, benzimidazole pigments, and other organic pigments; and various other photoconductive materials. Among them, organic pigments are particularly preferred, and phthalocyanine pigments and azo pigments are more preferred.

[0047] In particular, when using a phthalocyanine pigment as the charge generating substance, specifically, metal-free phthalocyanine, metals such as copper, indium, gallium, tin, titanium, zinc, vanadium, silicon, germanium, etc., or coordinated phthalocyanines such as their oxides, halides, etc. are used. Examples of ligands to metal atoms with a valence of 3 or more include, in addition to the oxygen atom and chlorine atom shown above, hydroxyl group, alkoxy group, etc. Among them, X-type and τ-type metal-free phthalocyanines with particularly high sensitivity, titanyl phthalocyanines such as A-type, B-type, D-type, vanadyl phthalocyanine, chloroindium phthalocyanine, chlorogallium phthalocyanine, hydroxygallium phthalocyanine, etc. are preferred.

[0048] Among the crystal forms of titanyl phthalocyanine mentioned here, for A-type and B-type, they are shown as phase I and phase II respectively by W. Heller et al. (Zeit. Kristallogr. 159 (1982) 173), and A-type is known as the stable form. D-type is a crystal form characterized by showing a distinct peak at a diffraction angle 2θ±0.2° of 27.3° in powder X-ray diffraction using CuKα radiation.

[0049] When using an azo pigment, various known bisazo pigments and trisazo pigments are preferably used. Examples of preferred azo pigments are shown below.

[0050]

Chemical formula

[0051] The charge generating substance may be used alone, or two or more kinds may be used in combination in any combination and ratio. Further, when two or more kinds of charge generating substances are used in combination, as a mixing method of the charge generating substances to be used in combination, each charge generating substance may be mixed later and used, or may be mixed and used in the manufacturing and processing steps of the charge generating substance such as synthesis, pigmentation, crystallization, etc. Such treatments include acid paste treatment, grinding treatment, solvent treatment, etc. which are known.

[0052] The particle size of the charge generating substance is preferably small. Specifically, usually, 1 μm or less is preferable, and more preferably 0.5 μm or less.

[0053] Furthermore, from the viewpoint of sensitivity, the amount of the charge generating substance in the single-layer photosensitive layer is usually preferably 0.1% by mass or more, and more preferably 0.5% by mass or more. Also, from the viewpoints of sensitivity and chargeability, it is usually preferably 50% by mass or less, and more preferably 20% by mass or less.

[0054] (Charge transporting substance) Charge transporting substances are mainly classified into hole transporting substances having mainly hole transporting ability and electron transporting substances having mainly electron transporting ability. The single-layer photosensitive layer used in the present invention contains both a hole transporting substance and an electron transporting substance.

[0055] [Hole transporting substance] The hole transporting substance is not particularly limited as long as it is a known material. For example, heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, benzofuran derivatives, aniline derivatives, hydrazone derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives, and those in which a plurality of these compounds are bonded, and electron-donating substances such as polymers having a group composed of these compounds in the main chain or side chain, etc. may be mentioned.

[0056] Among these, carbazole derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, enamine derivatives, and those in which a plurality of these compounds are bonded are preferable, and arylamine derivatives and enamine derivatives are more preferable.

[0057] The larger the molecular weight of the hole transporting material, the higher the effect of delocalizing the received holes, and there is a tendency to exhibit good electrical properties. Also, since the larger the molecular weight, the lower the migration property to the surface, it is advantageous from the viewpoint of adhesion to the outermost layer. From this viewpoint, the molecular weight of the hole transporting material is preferably 350 or more, more preferably 450 or more, and even more preferably 700 or more. From the viewpoint of solubility, it is preferably 1500 or less, and more preferably 1000 or less.

[0058] Only one type of hole transporting material may be used alone, or two or more types may be used in any ratio and combination. When two or more types of hole transporting materials are used, from the viewpoints of the aforementioned electrical properties and migration property to the surface, it is preferable to use a hole transporting material having a molecular weight of 700 or more. Further, among two or more types of hole transporting materials contained in the photosensitive layer, it is more preferable that the molecular weight of the hole transporting material having the largest content (parts by mass) in the photosensitive layer is 700 or more. The structures of preferable hole transporting materials are exemplified below.

[0059]

Chemical formula

[0060]

Chemical formula

[0061]

Chemical formula

[0062] Among the above hole transporting materials, from the viewpoint of electrical properties, HTM6, HTM7, HTM8, HTM9, HTM10, HTM12, HTM14, HTM26, HTM31, HTM32, HTM33, HTM34, HTM35, HTM36, HTM37, HTM38, HTM39, HTM40, HTM41, HTM42, HTM43, HTM48 are preferable, HTM31, HTM32, HTM33, HTM34, HTM35, HTM36, HTM37, HTM38, HTM39, HTM40, HTM41, HTM42, HTM43, HTM48 are more preferable, and HTM39, HTM40, HTM41, HTM42, HTM43, HTM48 are even more preferable.

[0063] [Electron transporting material] The electron transporting material is not particularly limited as long as it is a known material. Examples thereof include electron-withdrawing substances such as aromatic nitro compounds such as 2,4,7-trinitrofluorenone, cyano compounds such as tetracyanoquinodimethane, and quinone compounds such as diphenoquinone, as well as known cyclic ketone compounds and perylene pigments (perylene derivatives). In particular, it is preferably a compound represented by the following formula (6).

[0064] [Chemical formula]

[0065] R 61 ~R 64 Each independently represents a hydrogen atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an alkenyl group having 2 to 20 carbon atoms.

[0066] Examples of the optionally substituted alkyl group having 1 to 20 carbon atoms include linear alkyl groups, branched alkyl groups, and cyclic alkyl groups. From the viewpoint of electron transport ability, linear alkyl groups or branched alkyl groups are preferred. The number of carbon atoms of these alkyl groups is usually 1 or more, preferably 4 or more, usually 20 or less, preferably 15 or less from the viewpoint of the versatility of raw materials, more preferably 10 or less, and still more preferably 5 or less from the viewpoint of handleability during production. Specific examples include methyl group, ethyl group, hexyl group, iso-propyl group, tert-butyl group, tert-amyl group, cyclohexyl group, and cyclopentyl group. Among these, a methyl group, a tert-butyl group, or a tert-amyl group is preferred, and a tert-butyl group or a tert-amyl group is more preferred from the viewpoint of solubility in the organic solvent used in the coating solution.

[0067] Examples of the optionally substituted alkenyl group having 2 to 20 carbon atoms include linear alkenyl groups, branched alkenyl groups, and cyclic alkenyl groups. The number of carbon atoms of these alkenyl groups is usually 2 or more, preferably 4 or more, and usually 20 or less, preferably 10 or less from the viewpoint of the light attenuation characteristics of the photoreceptor. Specific examples include ethenyl group, 2-methyl-1-propenyl group, and cyclohexenyl group.

[0068] The substituent R 61 ~R 64 may be such that R 61 and R 62 are bonded to each other, or R 63 and R 64 are bonded to each other to form a cyclic structure. From the viewpoint of electron mobility, when both R 61 and R 62 are alkenyl groups, it is preferable that they are bonded to each other to form an aromatic ring, and it is more preferable that both R 61 and R 62 are ethenyl groups, are bonded to each other, and have a benzene ring structure.

[0069] In the formula (6), X represents an organic residue having a molecular weight of 120 or more and 250 or less. From the viewpoint of the light attenuation characteristics of the photoreceptor, the compound represented by the formula (6) is preferably a compound represented by any of the following formulas (7) to (10).

[0070]

Chemical formula

[0071] (In formula (7), R 71 ~R 73 each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.)

[0072]

Chemical formula

[0073] (In formula (8), R 81 ~R 84 each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.)

[0074]

Chemical formula

[0075] (In formula (9), R 91 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen atom.)

[0076]

Chemical formula

[0077] (In formula (10), R 101 and R 102 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms.)

[0078] R 71 ~R102 In the formula, examples of the alkyl group having 1 to 6 carbon atoms include linear alkyl groups, branched alkyl groups, and cyclic alkyl groups. The number of carbon atoms of these alkyl groups is usually 1 or more and usually 6 or less. Specifically, examples include methyl group, ethyl group, hexyl group, iso-propyl group, tert-butyl group, tert-amyl group, and cyclohexyl group. Among these, from the viewpoint of electron transport ability, a methyl group, tert-butyl group, or tert-amyl group is preferred.

[0079] Examples of the halogen atom include fluorine, chlorine, bromine, and iodine, and chlorine is preferred from the viewpoint of electron transport ability.

[0080] The number of carbon atoms of the aryl group having 6 to 12 carbon atoms is usually 6 or more and usually 12 or less. Specifically, examples include phenyl group and naphthyl group, and a phenyl group is preferred from the viewpoint of the film physical properties of the photosensitive layer. These aryl groups may be further substituted.

[0081] Among the formulas (7) to (10), formula (6) is preferably formula (7) or formula (8) from the viewpoint of image quality stability when repeatedly forming images, and more preferably formula (7). Further, the compound represented by formula (6) may be used alone, or compounds represented by formula (6) having different structures may be used in combination, and it can also be used in combination with other electron transport materials.

[0082] The larger the molecular weight of the electron transport material, the higher the effect of delocalizing the received electrons, and there is a tendency to exhibit good electrical properties. Further, since the larger the molecular weight, the lower the migration property to the surface, it is also advantageous from the viewpoint of adhesion to the outermost layer. From this viewpoint, the molecular weight of the electron transport material is preferably 300 or more, more preferably 350 or more, still more preferably 400 or more, and particularly preferably 420 or more. From the viewpoint of solubility, it is preferably 1000 or less, more preferably 700 or less.

[0083] The electron transport material may be used alone as only one type, or two or more types may be used in any ratio and combination. When two or more hole transport materials are used, from the viewpoints of the above-described electrical properties and migration properties to the surface, it is preferable to use an electron transport material having a molecular weight of 400 or more. Further, among the two or more electron transport materials contained in the photosensitive layer, it is more preferable that the molecular weight of the electron transport material having the largest content (parts by mass) in the photosensitive layer is 400 or more.

[0084] The structures of preferable electron transport materials are exemplified below.

[0085] [Chemical formula]

[0086] Among the above electron transport materials, from the viewpoint of electrical properties, ET-1, ET-2, ET-3, ET-4, ET-5, ET-6, ET-8, ET-10, ET-11, ET-12, ET15, ET-16, ET-17 are preferable, ET-1, ET-2, ET-3, ET-4, ET-5 are more preferable, and ET-2 is even more preferable.

[0087] [Contents of hole transport material and electron transport material] In the present invention, it is preferable that the single-layer photosensitive layer satisfies the formula (1) or the formula (2). In particular, by satisfying both simultaneously, a photoreceptor having good electrical properties can be obtained.

[0088] When the content of the binder resin contained in the single-layer photosensitive layer in the present invention is set to 100, the content A (parts by mass) of the hole transport material, the content B (parts by mass) of the electron transport material, the molecular weight a of the hole transport material, and the molecular weight b of the electron transport material preferably satisfy the following formulas (1) and (2).

[0089] 0.9 ≦ (B / b) / (A / a) ≦ 4.0 (1) 0.15 ≦ (A / a) + (B / b) (2)

[0090] (A / a) or (B / b) is the content of the hole transport material or the electron transport material divided by the molecular weight, representing the amount of substance, that is, the number of molecules.

[0091] In the case of the positive charging method, it is necessary to transport the holes and electrons generated by charge separation in the single-layer photosensitive layer, with the holes transported to the side of the conductive support and the electrons transported to the side of the photosensitive body surface, both in a well-balanced manner. It is considered that the transport capabilities of the holes and electrons increase in proportion to the number of molecules of the hole transport material and the electron transport material in the photosensitive layer. Therefore, from the perspective of electrical characteristics, there is a suitable range for the total amount of the hole transport material and the electron transport material required for sufficient charge transport, and there is also a suitable range for the amount ratio between the hole transport material and the electron transport material.

[0092] In the present invention, by setting (B / b) / (A / a), which represents the ratio of the amount of substance of the hole transport material to the amount of substance of the electron transport material, within the range of formula (1), it becomes possible to transport both the holes and electrons generated in the single-layer photosensitive layer in a well-balanced manner.

[0093] When (B / b) / (A / a) is 0.9 or less, the number of molecules of the electron transport material is small relative to the hole transport material. At this time, the holes can be sufficiently transported to the side of the conductive support, while the transport of electrons to the side of the photosensitive body surface is hindered due to the small number of molecules responsible for transport. If repeated printing continues in this state, the number of electrons trapped in the photosensitive layer or left behind in the photosensitive layer due to being too slow in mobility increases, forming a negative space charge and weakening the electric field strength in the photosensitive layer. As a result, ultimately, the transport of holes may also be hindered.

[0094] On the one hand, when (B / b) / (A / a) is 4.0 or more, the number of molecules of the hole transport material with respect to the electron transport material is in a small state. At this time, while electrons can be sufficiently transported to the surface side of the photoreceptor, holes are trapped in the photosensitive layer or the number of holes left in the photosensitive layer due to being too slow in mobility increases to form a positive space charge because the number of molecules responsible for transport is small, and the electric field strength in the photosensitive layer is weakened. Therefore, ultimately, electron transport may also be hindered.

[0095] That is, if (B / b) / (A / a) is 0.9 or more, electron transportability in the photosensitive layer is ensured, and if (B / b) / (A / a) is 4.0 or less, hole transportability in the photosensitive layer tends to be ensured.

[0096] The value of (B / b) / (A / a) is usually 0.9 or more from the viewpoint of the above technical idea, preferably 1.1 or more, more preferably 1.3 or more, and still more preferably 1.5 or more. Also, from the viewpoint of the above technical idea, the value of (B / b) / (A / a) is usually 4.0 or less, preferably 3.0 or less, more preferably 2.5 or less, and still more preferably 2.2 or less. When a plurality of types of hole transport materials are contained in the single-layer type photosensitive layer, the value obtained by summing the values obtained by dividing the content of each substance by its molecular weight is taken as (A / a). Similarly, when a plurality of types of electron transport agents are contained in the single-layer type photosensitive layer, the value obtained by summing the values obtained by dividing the content of each substance by its molecular weight is taken as (B / b).

[0097] In the present invention, by setting the value of (A / a)+(B / b), which represents the sum of the amount of substance of the hole transport material and the amount of substance of the electron transport material, within the range of formula (2), the absolute amount of the charge transport material necessary for charge transport in the photosensitive layer can be ensured.

[0098] The value of (A / a)+(B / b) is usually 0.15 or more from the viewpoint of electrical characteristics, preferably 0.17 or more, and more preferably 0.20 or more.

[0099] (Binder resin) Next, the binder resin used in the photosensitive layer will be described. Examples of the binder resin used in the photosensitive layer include vinyl polymers or copolymers thereof such as polymethyl methacrylate, polystyrene, and polyvinyl chloride; butadiene resins; styrene resins; vinyl acetate resins; vinyl chloride resins, acrylate resins; methacrylate resins; vinyl alcohol resins; polymers and copolymers of vinyl compounds such as ethyl vinyl ether; polyvinyl butyral resins; polyvinyl formal resins; partially modified polyvinyl acetal resins; polyarylate resins; polyamide resins; polyurethane resins; cellulose ester resins; silicone-alkyd resins; poly-N-vinylcarbazole resins; polycarbonate resins; polyester resins; polyester carbonate resins; polysulfone resins; polyimide resins; phenoxy resins; epoxy resins; silicone resins; and partially crosslinked cured products thereof. Further, the above resins may be modified with a silicon reagent or the like. These may be used alone or in combination of two or more in any ratio and combination.

[0100] In particular, as the binder resin, it is preferable to contain one or two or more polymers obtained by interfacial polymerization.

[0101] As the binder resin obtained by the above interfacial polymerization, a polycarbonate resin and a polyester resin are preferable, and in particular, a polycarbonate resin or a polyarylate resin is preferable. Further, it is preferably a polymer using an aromatic diol as a raw material, and preferable aromatic diol compounds include compounds represented by the following formula (11).

[0102]

Chemical formula

[0103] In the above formula (11), X 111 represents a linking group represented by any of the following formulas or a single bond.

[0104] [Chemical formula]

[0105] In the above formula, R 111 and R 112 each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group which may be substituted, or a halogenated alkyl group. Z represents a substituted or unsubstituted carbocyclic ring having 4 to 20 carbon atoms.

[0106] In formula (11), Y 111 to Y 118 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, an aryl group which may be substituted, or a halogenated alkyl group.

[0107] Furthermore, a bisphenol having the following structural formula or a polycarbonate resin or polyarylate resin containing a bisphenol component is preferable from the viewpoints of the sensitivity and residual potential of the electrophotographic photoreceptor, and among them, the polycarbonate resin is more preferable from the viewpoint of mobility. This exemplification is carried out to clarify the gist and is not limited to the exemplified structures as long as they do not contravene the gist of the present invention.

[0108] [Chemical formula]

[0109] [Chemical formula]

[0110] In particular, in order to maximize the effects of the present invention, a polycarbonate containing a bisphenol derivative having the following structure is preferable.

[0111] [Chemical formula]

[0112] Also, in order to improve mechanical properties, it is preferable to use polyester, particularly polyarylate. In this case, it is preferable to use those having the following structure as the bisphenol component.

[0113]

Chemical formula

[0114] Also, as the acid component, it is preferable to use those having the following structure.

[0115]

Chemical formula

[0116] Also, when using terephthalic acid and isophthalic acid, it is preferable that the molar ratio of terephthalic acid is higher, and it is preferable to use those having the following structure.

[0117]

Chemical formula

[0118] (Other substances) In addition to the above materials, in the photosensitive layer, additives such as well-known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, and visible light blockers may be contained in order to improve film-forming properties, flexibility, coating properties, stain resistance, gas resistance, light resistance, etc. Also, the photosensitive layer may contain various additives such as sensitizers, dyes, pigments (except those which are the charge generation substances, hole transport substances, and electron transport substances described above), and surfactants as required. Examples of surfactants include silicone oil and fluorine-based compounds. In the present invention, these can be used singly or in combination of two or more in any ratio and combination as appropriate.

[0119] Also, for the purpose of reducing the frictional resistance on the surface of the photosensitive layer, the photosensitive layer may contain a fluororesin, a silicone resin, etc., and may also contain particles made of these resins or particles of inorganic compounds such as aluminum oxide.

[0120] (Antioxidant) The antioxidant is a kind of stabilizer used to prevent the oxidation of the electrophotographic photoreceptor of the present invention.

[0121] The antioxidant may be any one having a function as a radical scavenger. Specifically, examples include phenol derivatives, amine compounds, phosphonate esters, sulfur compounds, vitamins, vitamin derivatives, etc. Among these, phenol derivatives, amine compounds, vitamins, etc. are preferable. Also, hindered phenols or trialkylamine derivatives having a bulky substituent near the hydroxy group are more preferable.

[0122] Furthermore, aryl compound derivatives having a t-butyl group at the o-position of the hydroxy group and aryl compound derivatives having two t-butyl groups at the o-position of the hydroxy group are particularly preferable.

[0123] Also, if the molecular weight of the antioxidant is too large, the antioxidant ability may decrease. Compounds having a molecular weight of 1500 or less, particularly 1000 or less, are preferable. The lower limit is usually 100 or more, preferably 150 or more, and more preferably 200 or more.

[0124] The amount of the above antioxidant used is not particularly limited, but is 0.1 part by mass or more, preferably 1 part by mass or more, per 100 parts by mass of the binder resin in the photosensitive layer. Also, in order to obtain good electrical properties and printing durability, it is preferably 25 parts by mass or less, more preferably 20 parts by mass or less.

[0125] (Electron-withdrawing compound) Further, the photosensitive layer may contain an electron-withdrawing compound. Specific examples of the electron-withdrawing compound include sulfonic acid ester compounds, carboxylic acid ester compounds, organic cyano compounds, nitro compounds, aromatic halogen derivatives, etc. Preferably, they are sulfonic acid ester compounds and organic cyano compounds, and particularly preferably sulfonic acid ester compounds. The above electron-withdrawing compound may be used alone as only one kind, or two or more kinds may be used in any ratio and combination.

[0126] Also, it is understood that the electron-withdrawing ability of the electron-withdrawing compound can be predicted by the value of LUMO (hereinafter, appropriately referred to as LUMOcal). In the present invention, among the above, in particular, compounds having a LUMOcal value of 0.5 or more to 5.0 eV or less by structural optimization using semi-empirical molecular orbital calculations using PM3 parameters (hereinafter, this may be simply described as by semi-empirical molecular orbital calculations) are preferably used. By setting the absolute value of LUMOcal to 0.5 eV or more, the effect of electron-withdrawing can be more expected, and by setting it to 5.0 eV or less, better charging can be obtained. The absolute value of LUMOcal is more preferably 1.0 eV or more, still more preferably 1.1 eV or more, and particularly preferably 1.2 eV or more. The above absolute value is preferably 4.5 eV or less, more preferably 4.0 eV or less, and particularly preferably 3.5 eV or less.

[0127] Examples of the compound in which the absolute value of the above LUMOcal is within the above range include the following compounds.

[0128]

Chemical formula

[0129] The amount of the electron-withdrawing compound used in the electrophotographic photoreceptor of the present invention is not particularly limited. However, when the electron-withdrawing compound is used in the photosensitive layer, it is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, per 100 parts by mass of the binder resin contained in the photosensitive layer. Also, in order to obtain good electrical properties, it is usually preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less.

[0130] (Method for forming a single-layer photosensitive layer) Next, the method for forming a single-layer photosensitive layer will be described. The method for forming the single-layer photosensitive layer is not particularly limited. For example, the charge-generating substance can be dispersed in a coating solution in which a charge-transporting substance, a binder resin, and other substances are dissolved (or dispersed) in a solvent (or dispersion medium), and then coated on a conductive support (when an intermediate layer such as an undercoat layer described later is provided, on these intermediate layers).

[0131] Hereinafter, the solvent or dispersion medium used for forming the single-layer photosensitive layer and the coating method will be described.

[0132] [Solvent or dispersion medium] Examples of the solvent or dispersion medium used for forming the photosensitive layer include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; esters such as methyl formate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and anisole; chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichloroethylene; nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, and triethylenediamine; and aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide. These may be used alone or in combination of two or more in any ratio and combination.

[0133] [Coating method] Examples of the coating method of the coating solution for forming a single-layer photosensitive layer include spray coating method, spiral coating method, ring coating method, dipping coating method, etc.

[0134] Examples of the spray coating method include air spray, airless spray, electrostatic air spray, electrostatic airless spray, rotary atomization type electrostatic spray, hot spray, hot airless spray, etc. Considering the atomization degree, adhesion efficiency, etc. for obtaining a uniform film thickness, the rotary atomization type electrostatic spray is preferred, and the conveying method disclosed in Re-Published Japanese Patent Application No. 1-805198, that is, the method of continuously conveying a cylindrical workpiece while rotating it without spacing in the axial direction is preferred. Thereby, a photosensitive layer having high adhesion efficiency and excellent film thickness uniformity can be obtained comprehensively.

[0135] As the spiral coating method, for example, there are a method using an injection coating machine or a curtain coating machine disclosed in JP-A-52-119651, a method of continuously flying paint in a streak shape from a micro opening disclosed in JP-A-1-231966, a method using a multi-nozzle body disclosed in JP-A-3-193161, and the like.

[0136] In the dipping coating method, the total solid content concentration of the coating solution or dispersion is preferably 5% by mass or more, more preferably 10% by mass or more. Further, it is preferably 50% by mass or less, more preferably 35% by mass or less.

[0137] Also, the viscosity of the coating solution or dispersion is preferably 50 mPa·s or more, more preferably 100 mPa·s or more. Further, it is preferably 700 mPa·s or less, more preferably 500 mPa·s or less. Thereby, a photosensitive layer excellent in film thickness uniformity can be obtained.

[0138] After forming a coating film by the above coating method, the coating film is dried, and it is preferable to adjust the drying temperature and time so that necessary and sufficient drying is performed. The drying temperature is usually 80°C or higher, preferably 100°C or higher, from the viewpoint of suppressing residual solvents. Also, from the viewpoints of preventing generation of bubbles and electrical characteristics, it is usually 250°C or lower, preferably 170°C or lower, more preferably 140°C or lower, and the temperature may be changed stepwise. As the drying method, a hot air dryer, a steam dryer, an infrared dryer, a far-infrared dryer, or the like can be used.

[0139] In the present invention, in order to provide the outermost layer, after coating the photosensitive layer, only air drying at room temperature may be performed, and heat drying by the above method may be performed after coating the outermost layer.

[0140] The thickness of the photosensitive layer is appropriately selected as an optimum thickness depending on the materials used, etc. From the viewpoints of electrical characteristics and dielectric breakdown resistance, 5 μm or more is preferable, 10 μm or more is more preferable, and 15 μm or more is particularly preferable. Also, from the viewpoint of electrical characteristics, 100 μm or less is preferable, 50 μm or less is more preferable, and 30 μm or less is particularly preferable.

[0141] <Outermost layer> The outermost layer of the photoreceptor of the present invention is characterized by having a structure formed by polymerizing a compound having a chain polymerizable functional group. From the viewpoint of abrasion resistance, the compound having a chain polymerizable functional group usually has 2 or more, preferably 3 or more, more preferably 4 or more chain polymerizable functional groups. On the other hand, it usually has 15 or less, preferably 10 or less, more preferably 8 or less. Examples of the chain polymerizable functional group of the compound having a chain polymerizable functional group include an acryloyl group, a methacryloyl group, a vinyl group, and an epoxy group. The compound having a chain polymerizable functional group is not particularly limited as long as it is a known material, but from the viewpoint of curability, a monomer, oligomer, or polymer having an acryloyl group or a methacryloyl group is preferable.

[0142] Preferred compounds are exemplified below. Examples of monomers having an acryloyl group or a methacryloyl group include trimethylolpropane triacrylate (A-TMPT), 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 (A-DPH), caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hydroxypentaacrylate, alkyl-modified dipentaerythritol pentaacrylate, alkyl-modified dipentaerythritol tetraacrylate, alkyl-modified dipentaerythritol triacrylate, dimethylolpropane tetraacrylate, pentaerythritol ethoxytetraacrylate, EO-modified phosphate triacrylate, 2,2,5,5,-tetrahydroxymethylcyclopentanone tetraacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, polytetramethylene glycol diacrylate, EO-modified bisphenol A diacrylate, PO-modified bisphenol A diacrylate, 9,9 - Bis[4-(2 - acryloyloxyethoxy)phenyl]fluorene, tricyclodecane dimethanol diacrylate, decanediol diacrylate, hexanediol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, EO - modified bisphenol A dimethacrylate, PO - modified bisphenol A dimethacrylate, tricyclodecane dimethanol dimethacrylate, decanediol dimethacrylate, hexanediol dimethacrylate, etc. may be mentioned.,

[0143] As the oligomers and polymers having an acryloyl group or a methacryloyl group, known urethane acrylates, ester acrylates, acrylic acrylates, epoxy acrylates, etc. can be used. Examples of urethane acrylates include "EBECRYL8301", "EBECRYL1290", "EBECRYL1830", "KRM8200" (Daicel Ornex Co., Ltd.), "UV1700B", "UV7640B", "UV7605B", "UV6300B", "UV7550B" (Mitsubishi Chemical Corporation), etc. Examples of ester acrylates include "M - 7100", "M - 7300K", "M - 8030", "M - 8060", "M - 8100", "M - 8530", "M - 8560", "M - 9050" (Toagosei Co., Ltd.), etc. Examples of acrylic acrylates include "8BR - 600", "8BR - 930MB", "8KX―078", "8KX - 089", "8KX - 168" (Daiso Fine Chemical Co., Ltd.), etc.,

[0144] These may be used alone or in combination of two or more. Among these, from the viewpoint of electrical properties, it is preferable to contain a urethane acrylate.,

[0145] The outermost layer of the electrophotographic photoreceptor according to the present invention may contain metal oxide particles or a charge - transporting substance in addition to the compound having a chain - polymerizable functional group for the purpose of imparting charge - transporting ability. Also, a polymerization initiator may be contained to promote the polymerization reaction.,

[0146] The materials used for the outermost layer (metal oxide particles, charge transport materials, polymerization initiators) will be described in detail below.

[0147] (Metal oxide particles) From the viewpoint of imparting charge transport ability and improving mechanical strength, it is preferable to contain metal oxide particles in the outermost layer of the present invention.

[0148] 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, indium oxide, silicon oxide, zirconium oxide, zinc oxide, iron oxide, etc., and metal oxide particles containing a plurality of metal elements such as indium tin oxide, calcium titanate, strontium titanate, barium titanate, etc. can be mentioned. Among these, metal oxide particles having a band gap of 2 to 4 eV are preferable. The metal oxide particles may be used alone or in combination of a plurality of types. Among these metal oxide particles, from the viewpoint of electron transport property, titanium oxide, tin oxide, indium tin oxide, aluminum oxide, silicon oxide, zinc oxide are preferable, and titanium oxide and tin oxide are more preferable. Particularly, titanium oxide is preferable.

[0149] 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 having different crystal states.

[0150] The metal oxide particles may be subjected to various surface treatments on their surfaces. For example, they may be 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. In particular, when using titanium oxide particles, it is preferably surface-treated with an organosilicon compound. 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 preferable.

[0151] Note that although the outermost surface of these surface-treated particles is treated with such a treatment agent, it may be treated with a treatment agent such as aluminum oxide, silicon oxide, or zirconium oxide before the treatment. The metal oxide particles may use only one type of particle or a mixture of multiple types of particles.

[0152] 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 mean value of the diameters of the particles directly observed by a transmission electron microscope (hereinafter also referred to as TEM).

[0153] Among the metal oxide particles according to the present invention, specific product names of titanium oxide particles include ultrafine titanium oxide without surface treatment, "TTO-55(N)", "TTO-51(N)", Al 2 O 3 coated ultrafine titanium oxide "TTO-55(A)", "TTO-55(B)", ultrafine titanium oxide surface-treated with stearic acid "TTO-55(C)", Al 2 O 3 and ultrafine titanium oxide surface-treated with organosiloxane "TTO55(S)", high-purity titanium oxide "C-EL", sulfuric acid process titanium oxide "R-550", "R-580", "R-630", "R-670", "R-680", "R-780", "A-100", "A-220", "W-10", chlorine process titanium oxide "CR-50", "CR-58", "CR-60", "CR-60-2", "CR-67", conductive titanium oxide "ET-300W" (all of the above are manufactured by Ishihara Sangyo Co., Ltd.), and titanium oxides such as "R-60", "A-110", "A-150", Al 2 O 3 coated "SR-1", "RGL", "R-5N", "R-5N-2", "R-52N", "RK-1", "A-SP", SiO 2 、Al 2 O 3 coated "R-GX", "R-7E", ZnO, SiO 2 、Al 2 O 3 coated "R-650", ZrO 2 、Al 2 O 3 coated "R-61N" (all of the above are manufactured by Sakai Chemical Industry Co., Ltd.), and also SiO 2 、Al 2 O 3 surface-treated "TR-700", ZnO, SiO 2 、Al 2 O 3 surface-treated "TR-840", "TA-500", and in addition, surface-untreated titanium oxides such as "TA-100", "TA-200", "TA-300", Al 2 O 3"TA-400" (manufactured by Fuji Titanium Industry Co., Ltd.) with surface treatment, "MT-150W" and "MT-500B" without surface treatment, SiO 2 , Al 2 O 3 -treated "MT-100SA" and "MT-500SA", SiO 2 , Al 2 O 3 and "MT-100SAS" and "MT-500SAS" (manufactured by Teika Corporation) surface-treated with organosiloxane, etc.

[0154] Specific product names of aluminum oxide particles include "Aluminium Oxide C" (manufactured by Nippon Aerosil Co., Ltd.), etc.

[0155] Specific product names of silicon oxide particles include "200CF", "R972" (manufactured by Nippon Aerosil Co., Ltd.), "KEP-30" (manufactured by Nippon Shokubai Co., Ltd.), etc.

[0156] Specific product names of tin oxide particles include "SN-100P", "SN-100D" (manufactured by Ishihara Sangyo Co., Ltd.), "SnO 2 " (manufactured by CIK Nanotech Co., Ltd.), "S-2000", Lindop tin oxide "SP-2", antimony-doped tin oxide "T-1", indium-doped tin oxide "E-ITO" (Mitsubishi Materials Corporation), etc.

[0157] Specific product names of zinc oxide particles include "MZ-305S" (manufactured by Teika Corporation), but the metal oxide particles that can be used in the present invention are not limited to these.

[0158] The content of the metal oxide particles in the outermost layer of the electrophotographic photoreceptor according to the present invention is not particularly limited. 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 binder resin. Also, from the viewpoint of favorably maintaining the surface resistance, it is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0159] (Charge transport material) As the charge transport material to be contained in the outermost layer, the same materials as those used in the photosensitive layer can be used.

[0160] Also, from the viewpoint of improving the Martens hardness of the photoreceptor surface, a structure formed by polymerizing a charge transport material having a chain polymerizable functional group may be contained. Examples of the chain polymerizable functional group of the charge transport material having a chain polymerizable functional group include an acryloyl group, a methacryloyl group, a vinyl group, and an epoxy group. Among these, from the viewpoint of curability, an acryloyl group or a methacryloyl group is preferable. Examples of the structure of the charge transport material portion of the charge transport material having a chain polymerizable functional group include heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, benzofuran derivatives, aniline derivatives, hydrazone derivatives, aromatic amine derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, and those in which a plurality of these compounds are bonded, and electron-donating substances such as polymers having a group composed of these compounds in the main chain or side chain. Among these, from the viewpoint of electrical properties, carbazole derivatives, aromatic amine derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, and those in which a plurality of these compounds are bonded are preferable.

[0161] As the partial structure having the charge transport ability, a structure represented by the following formula (4) is preferable.

[0162] [Chemical formula]

[0163] In formula (4), Ar 41 ~Ar 43 is an aromatic group. R 41 ~R 43 are each independently a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, a halogenated alkyl group, a halogen group, a benzyl group or the following formula (5). n 41 ~n 43 is an integer of 1 or more. However, when n 41 is 1, R 41 is formula (5), and when n 41 is an integer of 2 or more, R 41 may be the same or different from each other, but at least one is formula (5). When n 42 is an integer of 2 or more, R 42 may be the same or different from each other, and when n 43 is an integer of 2 or more, R 43 may be the same or different from each other.

[0164]

Chemical formula

[0165] In formula (5), R 51 represents a hydrogen atom or a methyl group, R 52 , R 53 each independently represent a hydrogen atom, a hydrocarbon group or an alkoxy group, R 54 represents a single bond or an oxygen atom, and n 51 represents an integer of 0 or more and 10 or less. * represents a bond to Ar 41 ~Ar 43 and ** represents a bond to any atom.

[0166] In formula (4), Ar 41 ~Ar 43is an aromatic group. Examples of monovalent aromatic groups include phenyl group, naphthyl group, anthracenyl group, phenanthrenyl group, pyrene group, biphenyl group, and fluorene group. Among these, from the viewpoints of solubility and photocurability, the phenyl group is preferred. Examples of divalent aromatic groups include phenylene group, naphthylene group, anthrylene group, phenanthrylene group, pyrenylene group, and biphenylene group. Among these, from the viewpoints of solubility and photocurability, the phenylene group is preferred.

[0167] R 41 ~R 43 are each independently a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, a halogenated alkyl group, a halogen group, a benzyl group, or the formula (5). Among these, the carbon number of the alkyl group, alkoxy group, and halogenated alkyl group is usually 1 or more, while usually 10 or less, preferably 8 or less, more preferably 6 or less, and still more preferably 4 or less. Specific examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group, butyl group, tert-butyl group, isobutyl group, cyclohexyl group, etc. Specific examples of the alkoxy group include methoxy group, ethoxy group, propoxy group, cyclohexoxy group, etc. Examples of the halogenated alkyl group include chloroalkyl group, fluoroalkyl group, etc. Examples of the halogen group include fluoro group, chloro group, bromo group, etc. More preferably, they are methyl group, ethyl group, and phenyl group.

[0168] n 41 ~n 43 is an integer of 1 or more, usually 1 or more, usually 5 or less, preferably 3 or less, and most preferably 1. However, when n 41 is 1, R 41 is the formula (5), and when n 41 is an integer of 2 or more, R 41 may be the same or different from each other, but at least one is the formula (5). When n 42 is an integer of 2 or more, R 42 may be the same or different from each other, and when n 43 is an integer of 2 or more, R 43はThey may be the same or different. From the viewpoint of the strength of the cured film, n 41 ~n 43 is 1, R 41 is formula (5) and either R 42 or R 43 is formula (5), or when n 41 ~n 43 is 1 and R 41 ~R 43 is formula (5), it is preferable. From the viewpoint of solubility, when n 41 ~n 43 is 1, R 41 is formula (5) and either R 42 or R 43 is formula (5), it is more preferable.

[0169] R 52 and R 53 are the same as the above R 22 and R 23 .

[0170] n 51 is an integer of 0 or more and 10 or less, usually 0 or more, usually 10 or less, preferably 6 or less, more preferably 4 or less, and still more preferably 3 or less.

[0171] There is no particular limitation on the raw material of the polymer having the structure represented by the formula (4), but it is preferable to obtain it by polymerizing a compound having the structure represented by the following formula (4´).

[0172]

Chemical formula

[0173]

Chemical formula

[0174] In formula (5´), R 51 represents a hydrogen atom or a methyl group, and R 52 and R 53Each independently represents a hydrogen atom, a hydrocarbon group, or an alkoxy group, and R 54 represents a single bond or an oxygen atom, and n 51 represents an integer of 0 or more and 10 or less. * represents Ar 41 ~Ar 43 indicates a bond to.

[0175] Examples of the compound having the structure represented by the formula (4´) are shown below.

[0176]

Chemical formula

[0177] Among the above compounds, from the viewpoint of electrical properties, the formulas (4-1), (4-2), (4-3), (4-4), (4-6), and (4-7) are preferable, and the formulas (4-1), (4-2), and (4-3) are more preferable.

[0178] The amount of the charge transport material used in the outermost layer of the electrophotographic photoreceptor according to the present invention is not particularly limited, but from the viewpoint of electrical properties, it is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and particularly preferably 50 parts by mass or more with respect to 100 parts by mass of the binder resin. Also, from the viewpoint of maintaining good surface resistance, it is preferably 300 parts by mass or less, more preferably 20 parts by mass or less, and particularly preferably 150 parts by mass or less.

[0179] (Polymerization initiator) The polymerization initiator includes a thermal polymerization initiator, a photopolymerization initiator, and the like.

[0180] Examples of the thermal polymerization initiator include peroxide compounds such as 2,5-dimethylhexane-2,5-dihydroperoxide, dicumyl peroxide, benzoyl peroxide, t-butyl peroxide, t-butyl cumyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, lauroyl peroxide, and azo compounds such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(isobutyric acid methyl), 2,2'-azobis(isobutylamidine hydrochloride), 4,4'-azobis-4-cyanovaleric acid.

[0181] Photoinitiators can be classified into direct cleavage type and hydrogen abstraction type according to the difference in the radical generation mechanism. When the direct cleavage type photoinitiator absorbs light energy, radicals are generated by cleavage of a part of the covalent bond in the molecule. On the other hand, when the hydrogen abstraction type photoinitiator absorbs light energy, the excited molecule extracts hydrogen from a hydrogen donor to generate radicals.

[0182] Examples of the direct cleavage type photoinitiator include acetophenone-based or ketal-based compounds such as acetophenone, 2-benzoyl-2-propanol, 1-benzoylcyclohexanol, 2,2-diethoxyacetophenone, benzyldimethyl ketal, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone, benzoin ether-based compounds such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, O-tosylbenzoin, and acylphosphine oxide-based compounds such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, lithium phenyl(2,4,6-trimethylbenzoyl)phosphonate.

[0183] Examples of hydrogen abstraction type photoinitiators include benzophenone 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 or thioxanthone compounds such as 2-ethylanthraquinone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone. Other photoinitiators include camphorquinone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime, acridine compounds, triazine compounds, and imidazole compounds.

[0184] The photoinitiator preferably has an absorption wavelength in the wavelength region of the light source used for light irradiation in order to efficiently absorb light energy and generate radicals. 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, and the radical generation efficiency may decrease. 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 viewpoint of preventing such problems, it is preferable to contain an acylphosphine oxide-based compound having an absorption wavelength on the relatively longer wavelength side among photoinitiators. In addition, the acylphosphine oxide-based compound has a photobleaching effect in which the absorption wavelength region changes to the shorter wavelength side due to self-cleavage, and thus can transmit light to the inside of the outermost layer, and is also preferable from the viewpoint of good internal curability. In this case, from the viewpoint 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 to the acylphosphine oxide-based compound is not particularly limited, but from the viewpoint of supplementing the surface curability, 0.1 part by mass or more is preferable with respect to 1 part by mass of the acylphosphine oxide-based compound, and from the viewpoint of maintaining the internal curability, 5 parts by mass or less is preferable.

[0185] In addition, those having a photo-polymerization promoting effect can be used alone or in combination with the above photoinitiator. For example, triethanolamine, methyldiethanolamine, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, 4,4'-dimethylaminobenzophenone, etc. can be mentioned.

[0186] 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, based on 100 parts by mass of the total radical polymerizable components.

[0187] (Method for forming the outermost layer) Next, a method for forming the outermost layer will be described. The method for forming the outermost layer is not particularly limited. For example, it can be formed by applying a coating solution in which a compound having a chain-polymerizable functional group, a charge transport material, metal oxide particles, and other substances are dissolved in a solvent or a coating solution dispersed in a dispersion medium.

[0188] Hereinafter, the solvent or dispersion medium used for forming the outermost layer and the coating method will be described.

[0189] [Solvent used for the coating solution for forming the outermost layer] As the organic solvent used for the coating solution for forming the outermost layer of the present invention, any organic solvent that can dissolve the substances according to the present invention can be used. Specifically, alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; esters such as methyl formate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and anisole; chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichlorethylene; nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, and triethylenediamine; aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide, etc. can be mentioned. A mixed solvent of any combination and any ratio can be used from these. Also, an organic solvent that does not dissolve the substance for the outermost layer according to the present invention alone can be used if it can be dissolved, for example, as a mixed solvent with the above organic solvent. Generally, using a mixed solvent can reduce coating unevenness. When using the dip coating method in the coating method described later, it is preferable to select a solvent that does not dissolve the lower layer. From this viewpoint, it is preferable to contain alcohols that have low solubility in polycarbonate and polyarylate, which are preferably used for the photosensitive layer.

[0190] The quantitative ratio between the organic solvent used in the coating liquid for forming the outermost layer of the present invention and the solid content varies depending on the coating method of the coating liquid for forming the outermost layer, and may be appropriately changed and used so that a uniform coating film is formed in the applicable coating method.

[0191] [Coating method] The coating method of the coating liquid for forming the outermost layer is not particularly limited, and examples thereof include a spray coating method, a spiral coating method, a ring coating method, a dip coating method, and the like.

[0192] After forming a coating film by the above coating method, the coating film is dried, and the temperature and time are not limited as long as necessary and sufficient drying is obtained. However, when the outermost layer is coated only by air drying after coating the photosensitive layer, it is preferable to perform sufficient drying by the method described in the [coating method] of the aforementioned photosensitive layer.

[0193] The thickness of the outermost layer is appropriately selected as an optimum thickness depending on the materials used, etc. From the viewpoint of lifespan, 0.1 μm or more is preferable, 0.2 μm or more is more preferable, and 0.5 μm or more is particularly preferable. From the viewpoint of electrical characteristics, 10 μm or less is preferable, 5 μm or less is more preferable, and 3 μm or less is particularly preferable.

[0194] [Curing method of the outermost layer] The outermost layer is formed by applying such a coating liquid and then applying energy from the outside to cure it. The external energy used at this time includes heat, light, and radiation. As a method of applying the energy of heat, it is performed 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 is achieved and the reaction proceeds completely. At a temperature equal to or lower than the upper limit temperature, the reaction proceeds 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.

[0195] As the light energy, for example, high-pressure mercury lamps, metal halide lamps, electrodeless lamp bulbs, light-emitting diodes, etc. having emission wavelengths mainly in ultraviolet light (UV) can be used as UV irradiation light sources, but it is also possible to select a visible light source according to the absorption wavelengths of the chain polymerizable compound and the photoinitiator. From the viewpoint of curability, the light irradiation amount is preferably 0.1 J / cm 2 or more, more preferably 0.5 J / cm 2 or more, and particularly preferably 1 J / cm 2 or more. Also, from the viewpoint of electrical properties, it is preferably 150 J / cm 2 or less, more preferably 100 J / cm 2 or less, and particularly preferably 50 J / cm 2 or less.

[0196] As the radiation energy, those using an electron beam (EB) can be mentioned.

[0197] Among these energies, those using light energy are preferred from the viewpoints of ease of reaction rate control, simplicity of the apparatus, and length of the pot life.

[0198] After curing the outermost layer, a heating step may be added from the viewpoints of relaxation of residual stress, relaxation of residual radicals, and improvement of electrical properties. The heating temperature is preferably 60°C or higher, more preferably 100°C or higher, preferably 200°C or lower, and more preferably 150°C or lower.

[0199] [Martens hardness of the photoreceptor surface] In the present invention, for example, when a single-layer type photosensitive layer simultaneously satisfies the formulas (1) and (2), a sufficient number of hole transport substances and electron transport substances for charge transport can be ensured, and a photoreceptor having good electrical properties can be obtained. On the other hand, in the single-layer type photosensitive layer, when the number of molecules of the hole transport substance or the electron transport substance becomes too large, the number of molecules entering the gaps between the polymer chains of the binder resin increases, so the entanglement between the polymer chains is inhibited, and as a result, the molecules easily pass through between the polymer chains and concentrate on the surface of the photosensitive layer.

[0200] However, the inventors have found that by setting the Martens hardness of the photoreceptor surface to 345 N / mm 2 or higher, good adhesion can be maintained between the photosensitive layer and the outermost layer. Also, even when the contents of the hole transport material and the electron transport material in the photosensitive layer are increased, by setting the Martens hardness of the photoreceptor surface to 350 N / mm 2 or higher, the same effect can be obtained. Although the reason for this is under intensive investigation, by setting the Martens hardness of the photoreceptor surface to 345 N / mm 2 or higher, the cured resin contained in the outermost layer can have sufficient mechanical strength, and the anchor effect can work sufficiently at the interface with the single-layer photosensitive layer, so it is speculated that the adhesion is improved. More specifically, when the Martens hardness of the photoreceptor surface is less than 345 N / mm 2 , the interface between the outermost layer and the single-layer photosensitive layer is soft, and the penetration of both layers at the interface is weak, so the anchor effect becomes weak and the adhesion between the two layers deteriorates. On the other hand, when the Martens hardness of the photoreceptor surface is 345 N / mm 2 or higher, the interface between the outermost layer and the single-layer photosensitive layer is hard, and the penetration of both layers at the interface is strong, so the anchor effect becomes strong and the adhesion between the two layers is considered to be good. Also, when the Martens hardness of the photoreceptor surface is less than 345 N / mm 2 , the adhesion at the interface between the outermost layer and the single-layer photosensitive layer is poor, and it becomes difficult to transfer charges at the interface, so the charge transport from the single-layer photosensitive layer to the outermost layer is inhibited and the electrical characteristics deteriorate. On the other hand, when the Martens hardness of the photoreceptor surface is 345 N / mm 2 or higher, the adhesion at the interface between the outermost layer and the single-layer photosensitive layer becomes good, and the charge transfer at the interface can be performed smoothly, so the charge transport from the single-layer photosensitive layer to the outermost layer is carried out without hindrance and the electrical characteristics become good.

[0201] From the viewpoint of adhesion, the Martens hardness of the photoreceptor surface is preferably 350 N / mm 2 or higher, more preferably 370 N / mm 2 or higher, and even more preferably 390 N / mm 2The above is more preferable. From the viewpoint of suppressing residual stress and crack generation, the martensite hardness of the photoreceptor surface is 600 N / mm 2 or less, preferably 500 N / mm 2 or less, and more preferably.

[0202] The martensite hardness of the photoreceptor surface can be measured using a microhardness tester FISCHERSCOPE HM2000 manufactured by Fischer. The measurement is carried out at an arbitrary location on the photoreceptor surface under an environment of a temperature of 25°C and a relative humidity of 50% using a Vickers square pyramid diamond indenter with an included angle of 136°. The measurement conditions are set as follows. The load applied to the indenter and the indentation depth under that load are continuously read, and a profile as shown in FIG. 1 plotted on the Y-axis and X-axis respectively is obtained. ·Measurement conditions Maximum indentation load 0.2 mN Loading time required 10 seconds Unloading time required 10 seconds

[0203] The martensite hardness is a value defined by the following formula from the indentation depth at that time. Martensite hardness (N / mm 2 ) = Test load (N) / Surface area of the Vickers indenter under the test load (mm 2 )

[0204] <Undercoat layer> The electrophotographic photoreceptor of the present invention may have an undercoat layer between the above-described photosensitive layer and the conductive support.

[0205] As the undercoat layer, for example, a resin, a resin in which particles such as an organic pigment or a metal oxide are dispersed, or the like is 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 generating substances described above, can be mentioned.

[0206] Examples of the metal oxide particles used for the undercoat layer include metal oxide particles containing one 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 the above-mentioned one type of particles may be used, or a plurality of types of particles may be mixed and used in any ratio and combination.

[0207] Among the above metal oxide particles, titanium oxide and aluminum oxide are preferred, and titanium oxide is particularly preferred. 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.

[0208] The particle size of the metal oxide particles used for the undercoat layer is not particularly limited, but from the viewpoints of the characteristics of the undercoat layer and the stability of the solution for forming the undercoat layer, it is preferably 10 nm or more as the average primary particle size, and also 100 nm or less, more preferably 50 nm or less.

[0209] Here, it is desirable to form the undercoat layer in a form in which particles are dispersed in a binder resin. Examples of the binder resin used for the undercoat layer include polyvinyl butyral resin, polyvinyl formal resin, partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal, acetal, etc., polyvinyl acetal resins such as partially acetalized polyvinyl butyral resin, 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-based copolymers, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, styrene-alkyd resin, silicone-alkyd resin, phenolic-formaldehyde resin, etc., insulating resins, and organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinyl anthracene, polyvinyl perylene, etc. These can be selected and used, but are 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 polyamide, modified polyamide, etc. are preferable because they exhibit good dispersibility and coatability.

[0210] The mixing ratio of the particles to the binder resin can be arbitrarily selected, but it is preferably used in the range of 10% by mass to 500% by mass in terms of the stability and coatability of the dispersion. Also, the film thickness of the undercoat layer can be arbitrarily selected, but it is preferably 0.1 μm or more and 20 μm or less from the characteristics of the electrophotographic photoreceptor and the coatability of the above dispersion. Further, the undercoat layer may contain a known antioxidant or the like.

[0211] <Other layers> In addition, the electrophotographic photoreceptor of the present invention may have other layers as appropriate in addition to the above-described conductive support, photosensitive layer, outermost layer, and undercoat layer.

Examples

[0212] Hereinafter, the embodiments of the present invention will be described more specifically with reference to examples. However, the following examples are shown for the purpose of explaining the present invention in detail, and the present invention is not limited to the following examples as long as it does not deviate from the gist thereof, and can be arbitrarily modified and implemented. In addition, the description of "parts" in the following examples and comparative examples indicates "parts by mass" unless otherwise specified.

[0213] [Example 1] <Production of single-layer photoreceptor> A single-layer photoreceptor was produced according to the following procedure.

[0214] (Formation of undercoat layer) In powder X-ray diffraction using CuKα rays, 20 parts of D-type titanyl phthalocyanine showing a distinct peak at a diffraction angle 2θ ± 0.2° of 27.3° and 280 parts of 1,2-dimethoxyethane were mixed and pulverized with a sand grinder for 2 hours to obtain a dispersion. Subsequently, 400 parts of a 2.5% 1,2-dimethoxyethane solution of polyvinyl butyral (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name "Denka Butyral" #6000C) and 170 parts of 1,2-dimethoxyethane were mixed with the dispersion to prepare a coating solution for the undercoat layer. This coating solution was applied onto an aluminum plate (conductive support) having a thickness of 0.3 mm with a wire bar so that the film thickness after drying was 0.4 μm, and air-dried to form an undercoat layer.

[0215] (Formation of single-layer photosensitive layer) In powder X-ray diffraction using CuKα radiation, 2.6 parts of D-type titanyl phthalocyanine showing a distinct peak at a diffraction angle 2θ ± 0.2° of 27.3°, 1.3 parts of perylene pigment 1 having the following structure, 60 parts of the aforementioned hole transport material (HTM48), 50 parts of an electron transport material (ET-2), 100 parts of the following binder resin 1, 0.05 part of silicone oil (trade name KF-96, manufactured by Shin-Etsu Silicone Co., Ltd.) as a leveling agent, and 974 parts of a mixed solvent of tetrahydrofuran (hereinafter abbreviated as THF as appropriate) and toluene (hereinafter abbreviated as TL as appropriate) (80% by mass of THF and 20% by mass of TL) were mixed to prepare a coating solution for a single-layer photosensitive layer. This coating solution was applied onto the undercoat layer with a bar coater so that the film thickness after drying was about 20 μm, and dried at 100°C for 20 minutes to form a single-layer photosensitive layer.

[0216] [Chemical formula]

[0217] (Formation of outermost layer) 100 parts of urethane acrylate UV7600B (Mitsubishi Chemical Corporation), 55 parts of titanium oxide particles surface-treated with 3-methacryloyloxypropyltrimethoxysilane at 7% by mass with respect to the particles (TTO55N, Ishihara Sangyo Co., Ltd.), 1 part of benzophenone and 2 parts of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide as a photopolymerization initiator, and 745 parts of a mixed solvent of methanol, 1-propanol, and toluene (70% by mass of methanol, 10% by mass of 1-propanol, 20% by mass of toluene) were mixed to prepare a coating solution for the outermost layer. This coating solution was applied onto the above single-layer photosensitive layer with a wire bar so that the film thickness after curing was 1 μm, and heated at 125°C for 20 minutes. From the surface side of this coating film, UV light was irradiated using a UV light irradiation device equipped with a UV-LED lamp having a peak at a wavelength of 385 nm so that the integrated light amount was 25.5 J / cm 2 ². After further heating at 125°C for 10 minutes and then cooling to 25°C, the outermost layer was formed.

[0218] [Examples 2 to 21, Comparative Examples 1 to 7] Except that the hole transport material and electron transport material used in the single-layer photosensitive layer, their contents, and the compound having a chain polymerizable functional group used in the outermost layer were as shown in Tables 1 and 2, photoconductors of Examples 2 to 21 and Comparative Examples 1 to 7 were prepared by the same procedure as in Example 1.

[0219] <Electrical Property Test> Using EPA8200 manufactured by Kawaguchi Electric Co., the photoconductors obtained in the examples and comparative examples were charged positively by applying a current of +30 μA to a scorotron charger, and the surface potential was designated as V0 (+V). The charged photoconductor was irradiated with light of 55 nw as monochromatic light through a 780 nm monochromatic light filter for 10 seconds with the light of a halogen lamp. At this time, the surface potential was defined as the residual potential Vr (+V), and the half-exposure amount at which the surface potential decayed from V0 to half of V0 was defined as the sensitivity E1 / 2 (μJ / cm 2 )). Further, the retention rate of the surface potential after charging and leaving in the dark for 5 seconds was defined as DDR-5 (%). The measurement environment was at a temperature of 25 °C and a relative humidity of 50%. A smaller absolute value of Vr indicates that the photoconductor has a smaller residual potential and better electrical properties. Also, a smaller absolute value of E1 / 2 indicates that the photoconductor has better sensitivity to light. The results are shown in Tables 1 and 2.

[0220] <Martens Hardness of Photoconductor Surface> The Martens hardness and elastic deformation rate of the photoconductor surface were measured using a Fischer microhardness tester FISCHERSCOPE HM2000 manufactured by Fischer in an environment of 25 °C and 50% relative humidity. A Vickers square pyramid diamond indenter with a face angle of 136° was used for the measurement. The measurement conditions were set as follows, and the load applied to the indenter and the indentation depth under that load were continuously read and plotted on the Y-axis and X-axis respectively to obtain a profile as shown in Fig. 1. By applying a load to the indenter, it shifts from A to B in Fig. 1, and by removing the load, it shifts from B to C in Fig. 1. The results are shown in Tables 1 and 2. ·Measurement Conditions Maximum indentation load 0.2 mN Loading time: 10 seconds Unloading time: 10 seconds

[0221] The martensite hardness is a value defined by the following formula from the indentation depth at that time. Martensite hardness (N / mm 2 ) = Test load (N) / Surface area of Vickers indenter under test load (mm 2 ) The elastic deformation rate is a value defined by the following formula, and is the ratio of the work done by the film elastically during unloading to the total work required for indentation. Elastic deformation rate (%) = (We / Wt) × 100

[0222] In the above formula, the total work Wt (nJ) represents the area enclosed by A - B - D - A in Figure 1, and the elastic deformation work We (nJ) represents the area enclosed by C - B - D - C. The larger the elastic deformation rate, the less likely the deformation due to loading remains. When the elastic deformation rate is 100, it means that no deformation remains.

[0223] <Adhesion test> On the single - layer photoreceptors prepared in the examples and comparative examples, using an NT cutter (manufactured by NT Co., Ltd.), six cuts were made vertically and six cuts were made horizontally at 2 - mm intervals to create 25 squares of 5×5. A cellophane tape (manufactured by 3M Co., Ltd.) was closely adhered on it, and by pulling it up at 90° with respect to the adhesion surface, the adhesion between the photosensitive layer and the outermost layer was tested. The ratio of the number of squares of the outermost layer remaining on the photosensitive layer was evaluated as the remaining rate. The higher the remaining rate, the better the adhesion. In all tests, no peeling was observed between the aluminum plate as the support and the photosensitive layer. When peeling occurred, it all peeled near the interface between the photosensitive layer and the outermost layer. The results are shown in Tables 1 and 2.

[0224]

Table 1

[0225]

Table 2

[0226] <Measurement results> From the results shown in Tables 1 and 2, it can be seen that when the outermost layer contains a structure formed by polymerizing a compound having a chain polymerizable functional group and the Martens hardness of the photoreceptor surface is 345 N / mm 2 or more, the residual potential Vr is small and the number of masses remaining in the adhesion test is also large. That is, it can be seen that the photoreceptor has excellent electrical characteristics, mechanical characteristics, and adhesion between the photosensitive layer and the outermost layer. On the other hand, in the comparative example, since the Martens hardness of the photoreceptor surface is low, it can be seen that the residual potential Vr is large or the result of the adhesion test is poor.

Claims

1. A positively charged electrophotographic photoreceptor having at least a photosensitive layer and a outermost layer on a conductive support, wherein the photosensitive layer is a single layer containing at least a binder resin, a charge generating substance, a hole transporting substance, and an electron transporting substance, the hole transporting substance is an arylamine derivative having a molecular weight of 350 or more and 1500 or less, the electron transporting substance contains a structure represented by the following formula (6), and the compound represented by the formula (6) is a compound represented by the following formula (7) or (8), It has a structure formed by polymerizing a compound having a radically polymerizable functional group, and the Martens hardness of the photoreceptor surface is 345 N / mm ２ or more and 500 N / mm2 or less. An electrophotographic photoreceptor. (In formula (6), R61 to R64 each independently represent a hydrogen atom, an optionally substituted alkyl group having 1 to 20 carbon atoms, or an optionally substituted alkenyl group having 2 to 20 carbon atoms, and R61 and R62, or R63 and R64 may be bonded to each other to form a cyclic structure. X represents an organic residue having a molecular weight of 120 or more and 250 or less.) (In formula (7), R71 to R73 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.) (In formula (8), R81 to R84 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.)

2. The electrophotographic photoreceptor according to claim 1, wherein the photosensitive layer satisfies the following formula (1). 0.9 ≦ (B / b) / (A / a) ≦ 4.0 (1) (In formula (1), A is the content (parts by mass) of the hole transporting substance with respect to 100 of the content of the binder resin, a is the molecular weight of the hole transporting substance, B is the content (parts by mass) of the electron transporting substance with respect to 100 of the content of the binder resin, and b is the molecular weight of the electron transporting substance)

3. The electrophotographic photoreceptor according to claim 1 or 2, wherein the photosensitive layer satisfies the following formula (2). 0.15 ≦ (A / a) + (B / b) (2) (In formula (2), A is the content (parts by mass) of the hole transporting substance with respect to 100 of the content of the binder resin, a is the molecular weight of the hole transporting substance, B is the content (parts by mass) of the electron transporting substance with respect to 100 of the content of the binder resin, and b is the molecular weight of the electron transporting substance)

4. A positively charged electrophotographic photoreceptor having at least a photosensitive layer and a outermost layer on a conductive support, wherein the photosensitive layer is a single layer containing at least a binder resin, a charge generating substance, a hole transporting substance, and an electron transporting substance, the hole transporting substance is an arylamine derivative having a molecular weight of 350 or more and 1500 or less, The electron transport material contains a structure represented by the following formula (6), and the compound containing the structure represented by the formula (6) is a compound represented by the following formula (7) or (8). The photosensitive layer satisfies the following formulas (1) and (2), the outermost layer has a structure formed by polymerizing a compound having a polymerizable functional group, and the Martens hardness on the surface of the photoreceptor is 350 N / mm ２ or more and 500 N / mm 2 or less, an electrophotographic photoreceptor. 0.9 ≤ (B / b) / (A / a) ≤ 4.0 (1) 0.15 ≤ (A / a) + (B / b) (2) (In formula (1) and formula (2), A represents the content (parts by mass) of the hole transport material with respect to 100 of the content of the binder resin, a represents the molecular weight of the hole transport material, B represents the content (parts by mass) of the electron transport material with respect to 100 of the content of the binder resin, and b represents the molecular weight of the electron transport material.) (In formula (6), R61 to R64 each independently represent a hydrogen atom, an optionally substituted alkyl group having 1 or more and 20 or less carbon atoms, or an optionally substituted alkenyl group having 2 or more and 20 or less carbon atoms, and R61 and R62, or R63 and R64 may be bonded to each other to form a cyclic structure. X represents an organic residue having a molecular weight of 120 or more and 250 or less.) (In formula (7), R71 to R73 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 or more and 6 or less carbon atoms.) (In formula (8), R81 to R84 each independently represent a hydrogen atom, a halogen atom, or an alkyl group having 1 or more and 6 or less carbon atoms.)

5. The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the outermost layer contains metal oxide fine particles.

6. The electrophotographic photoreceptor according to claim 5, wherein the metal oxide fine particles are surface-treated with a surface treatment agent having a polymerizable functional group.

7. The electrophotographic photoreceptor according to any one of claims 1 to 6, wherein the photosensitive layer contains a hole transport material having a molecular weight of 700 or more.

8. The electrophotographic photoreceptor according to any one of claims 1 to 7, wherein the compound having a chain polymerizable functional group includes a compound having 2 or more chain polymerizable functional groups.

9. The electrophotographic photoreceptor according to any one of claims 1 to 8, wherein the compound having a chain polymerizable functional group includes a compound having an acryloyl group or a methacryloyl group.

10. The electrophotographic photoreceptor according to any one of claims 1 to 9, wherein the compound having a chain polymerizable functional group includes urethane acrylate.

11. The electrophotographic photoreceptor according to any one of claims 1 to 10, wherein the photosensitive layer contains an electron transport material having a molecular weight of 400 or more.

12. The electrophotographic photoreceptor according to any one of claims 1 to 11, wherein the outermost layer contains an acylphosphine oxide compound.

13. The electrophotographic photoreceptor according to any one of claims 1 to 12, wherein the outermost layer contains an acylphosphine oxide compound and a hydrogen abstraction type initiator.

14. The negative charge type electrophotographic photoreceptor according to claim 13, which contains 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 compound.

15. An electrophotographic photoreceptor cartridge having the electrophotographic photoreceptor according to any one of claims 1 to 14.

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

Images