Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge, and image forming apparatus

Abstract

Provided is an electrophotographic photoreceptor characterized by having a protective layer (surface layer), having high Martens hardness, a high modulus of elastic deformation, and excellent adhesive properties between a photosensitive layer and the protective layer (surface layer), the electrophotographic photoreceptor also having at least a photosensitive layer and a protective layer (surface layer) on a conductive supporting body, wherein the protective layer (surface layer) includes a structure obtained by polymerizing a compound having a chain-growth functional group, and the photosensitive layer which is in contact with the protective layer (surface layer) includes a positive hole transport substance that satisfies formula (1) below and an electron transport substance that satisfies formula (2) below.　(1): 600 ≤ a; (2): 400 ≤ b (in formula (1), a is the molecular weight of a hole transport substance, and in formula (2), b is the molecular weight of the electron transport substance.)　

Description

[Technical Field]

[0001] This invention relates to an electrophotographic photoreceptor and an image forming apparatus used in photocopiers, printers, and the like. More specifically, it relates to an electrophotographic photoreceptor with excellent mechanical properties and adhesion, and an electrophotographic photoreceptor cartridge and image forming apparatus equipped with the photoreceptor. [Background technology]

[0002] Electrophotography technology is widely used in fields such as photocopiers, printers, multifunction devices, and digital printing due to its ability to produce high-speed, high-quality images. The electrophotographic photoreceptor (hereinafter also simply referred to as "photoreceptor"), which is the core component of electrophotography technology, primarily uses photoreceptors made of organic photoconductive materials that have advantages such as being non-polluting, easy to form films on, and easy to manufacture.

[0003] From the perspective of layer structure, organic electrophotographic photoreceptors are known to include single-layer electrophotographic photoreceptors (hereinafter referred to as single-layer photoreceptors) that have charge-generating material and charge-transporting material in the same layer, and multilayer electrophotographic photoreceptors (hereinafter referred to as multilayer photoreceptors) that separate and stack charge-generating material and charge-transporting material in separate layers (charge-generating layer and charge-transporting layer).

[0004] Of these, the multilayer photoreceptor type is the most common in current photoreceptors because it allows for easy optimization of the function of each layer in terms of photoreceptor design, and the characteristics can be easily controlled. Most multilayer photoreceptors have a charge generation layer and a charge transport layer on the substrate in that order. While there are very few suitable electron transport materials for charge transport layers, many materials with good properties are known for hole transport. For this reason, multilayer photoreceptors are usually used in a negative charging method, where a charge generation layer and a charge transport layer are stacked on a substrate in that order, and the surface of the photoreceptor is negatively charged. In the negative charging method, compared to the positive charging method which charges the surface of the photoreceptor with a positive charge, a larger amount of ozone is generated from the charger, which can sometimes lead to degradation of the photoreceptor.

[0005] On the one hand, in principle, either a negative charging method or a 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 multilayer photoreceptor, and is generally easier to make highly sensitive than the negative charging method. In addition, the single-layer photoreceptor has the advantage of having fewer coating steps and being advantageous in terms of resolution. Although it has the disadvantage of being inferior to the negative-charged multilayer photoreceptor in terms of electrical characteristics, it has been partially put into practical use, and various improvements have been studied until now (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 under 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, which 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, radiation, etc. 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] In order to improve the electrical properties of a photoreceptor, it is considered effective to increase the contents of a hole transport material (HTM) and an electron transport material (ETM) in a photosensitive layer. However, when the contents of the hole transport material and the electron transport material in the photosensitive layer are increased, the hole transport material and the electron transport material tend to concentrate on the surface of the photosensitive layer. As a result of the study by the present inventors, when a protective layer containing a curable resin is formed (particularly when formed as the outermost layer), the adhesiveness between the protective layer (outermost layer) and the photosensitive layer in contact therewith is significantly deteriorated, and the protective layer (outermost layer) may be peeled off due to stress such as sliding with members such as a charging roller, a developing roller, a transfer roller, and a cleaning blade arranged in contact with the photoreceptor in an electrophotographic process or printing paper. Further, there are also problems such as a decrease in the Martens hardness of the photoreceptor surface and a decrease in the elastic deformation rate of the photoreceptor surface.

[0010] The present invention has been made in view of the above problems. That is, an object of the present invention is to provide an electrophotographic photoreceptor having a high Martens hardness, a high elastic deformation rate, and excellent adhesiveness between a photosensitive layer and a protective layer (outermost layer), an electrophotographic photoreceptor cartridge using the electrophotographic photoreceptor, and an image forming apparatus.

Means for Solving the Problems

[0011] The present inventors intensively studied an electrophotographic photoreceptor that can satisfy the above object, and found that the above problems can be solved if the molecular weights, the ratio of the amounts of substances (molar amounts), or the ratio of the molecular weights of the hole transport material and the electron transport material in the photosensitive layer are within a specific range, and thus the present invention was achieved.

[0012] The gist of the present invention resides in the following [1] to

[19] .

[0013] [1] An electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, The protective layer contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, An electrophotographic photoreceptor characterized in that the photosensitive layer in contact with the protective layer contains a hole transport material that satisfies the following formula (1) and an electron transport material that satisfies the following formula (2). 600 ≤ a (1) 400 ≤ b (2) (In formula (1), a is the molecular weight of the hole transporter. In formula (2), b is the molecular weight of the electron transporter.)

[0014] [2] An electrophotographic photoreceptor having at least a photosensitive layer and an outermost layer on a conductive support, The outermost layer contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, An electrophotographic photoreceptor characterized in that the photosensitive layer in contact with the outermost layer contains a hole transport material that satisfies the following formula (1) and an electron transport material that satisfies the following formula (2). 600 ≤ a (1) 400 ≤ b (2) (In formula (1), a is the molecular weight of the hole transporter. In formula (2), b is the molecular weight of the electron transporter.)

[0015] [3] The electrophotographic photoreceptor according to [1] or [2], characterized in that the photosensitive layer in contact with the outermost layer or the protective layer is a single layer containing at least a binder resin, a charge generating substance, a hole transporting substance and an electron transporting substance.

[0016] [4] The electrophotographic photoreceptor according to any one of [1] to [3] above, characterized in that the hole transport material satisfies the following formula (1'). 600 ≤ a ≤ 1200 (1') (In equation (1'), a is the molecular weight of the hole transporter.)

[0017] [5] The electrophotographic photoreceptor according to any one of [1] to [4] above, characterized in that the electron transport material satisfies the following formula (2'). 400 ≤ b ≤ 1000 (2') (In equation (2'), b is the molecular weight of the electron transport substance.)

[0018] [6] The electrophotographic photoreceptor according to any one of [1] to [5] above, characterized in that the photosensitive layer satisfies the following formula (3). 0.15 ≤ (A / a) + (B / b) (3) (In formula (3), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), a is the molecular weight of the hole transport substance, B is the content of the electron transport substance per 100 units of binder resin (parts by mass), and b is the molecular weight of the electron transport substance.)

[0019] [7] The electrophotographic photoreceptor according to any one of [1] to [6] above, characterized in that the photosensitive layer satisfies the following formula (4). 0.80 ≤ A / B ≤ 3.00 (4) (In formula (4), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), and B is the content of the electron transport substance per 100 units of binder resin (parts by mass).)

[0020] [8] The electrophotographic photoreceptor according to any one of [1] to [7] above, characterized in that the photosensitive layer satisfies the following formula (5). 1.20 ≤ (B / b) / (A / a) ≤ 1.60 (5) (In formula (5), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), a is the molecular weight of the hole transport substance, B is the content of the electron transport substance per 100 units of binder resin (parts by mass), and b is the molecular weight of the electron transport substance.)

[0021] [9] The electrophotographic photoreceptor according to any one of [1] to [8], characterized in that the ratio of the molecular weight a of the hole transport material to the molecular weight b of the electron transport material (a / b) is 1.40 or more and 1.90 or less.

[10] An electrophotographic photoreceptor according to any one of [1] to [9] above, characterized in that it is positively charged.

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

[10] , characterized in that the outermost layer or the protective layer contains a structure obtained by radical polymerization of a compound having a chain polymerizable functional group.

[0022]

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

[11] , characterized in that the outermost layer or the protective layer contains metal oxide fine particles.

[13] The electrophotographic photoreceptor according to

[12] , characterized in that the metal oxide fine particles are surface-treated with a surface treatment agent having polymerizable functional groups.

[0023]

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

[13] , characterized in that the compound having the chain polymerizable functional group is a urethane acrylate.

[0024]

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

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

[0025] JPEG0007852506000001.jpg2682

[0026] In formula (6), R 61 ~R 64 Each of these 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 Both, or R 63 and R 64 These elements may bond to each other to form a cyclic structure. X represents an organic residue with a molecular weight between 120 and 250.

[0027]

[16] An electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, The protective layer contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, The photosensitive layer in contact with the protective layer contains at least a binder resin, a hole transport material, and an electron transport material. An electrophotographic photoreceptor characterized in that the photosensitive layer in contact with the protective layer satisfies the following formula (5). 1.20 ≤ (B / b) / (A / a) ≤ 1.60 (5) (In formula (5), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), a is the molecular weight of the hole transport substance, B is the content of the electron transport substance per 100 units of binder resin (parts by mass), and b is the molecular weight of the electron transport substance.)

[0028]

[17] An electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, The protective layer contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, The photosensitive layer in contact with the protective layer contains at least a hole transport material and an electron transport material, An electrophotographic photoreceptor characterized in that the ratio (a / b) of the molecular weight of the hole transport material to the molecular weight of the electron transport material (b) is 1.40 or more and 1.90 or less.

[0029]

[18] An electrophotographic photoreceptor cartridge having the electrophotographic photoreceptor described in any one of [1] to

[17] above.

[19] An image forming apparatus having an electrophotographic photoreceptor as described in any one of [1] to

[17] above. [Effects of the Invention]

[0030] According to the present invention, it is possible to provide an electrophotographic photoreceptor having high Martens hardness, high elastic deformation rate, and excellent adhesion (also simply referred to as "adhesion") between the photosensitive layer and the outermost layer or the protective layer, an electrophotographic photoreceptor cartridge using the electrophotographic photoreceptor, and an image forming apparatus. [Brief explanation of the drawing]

[0031] [Figure 1] This graph shows the load curve as a function of indenter depth when measuring the Martens hardness and elastic deformation rate of the photoreceptor surface. [Modes for carrying out the invention]

[0032] The embodiments for carrying out the present invention (hereinafter referred to as "embodiments of the invention") will be described in detail below. However, the present invention is not limited to the following embodiments and can be implemented in various ways within the scope of its essence.

[0033] <<Electrophotographic photoconductor>> The electrophotographic photoreceptor of the present invention comprises at least a photosensitive layer and a protective layer containing a structure formed by polymerizing a compound having a chain-polymerizable functional group on a conductive support. From the viewpoint of obtaining the effects of the present invention, it is preferable that the protective layer is the outermost layer.

[0034] The charging method for the electrophotographic photoreceptor of the present invention may be either a negative charging method that charges the surface of the photoreceptor with a negative charge, or a positive charging method that charges the surface of the photoreceptor with a positive charge. From the viewpoint of enjoying the effects of the present invention to the fullest extent, a positively charged electrophotographic photoreceptor is preferred.

[0035] The conductive support, photosensitive layer, protective layer (outermost layer), and other components constituting the electrophotographic photoreceptor of the present invention will be described in order below. In this specification, "protective layer (outermost layer)" means either the protective layer or the outermost layer.

[0036] <Conductive support> First, the conductive support used in the photoreceptor of the present invention will be described.

[0037] The conductive support is not particularly limited as long as it supports the single-layer photosensitive layer and protective layer (outermost layer) described later and exhibits conductivity. Examples of conductive support materials mainly used include metal materials such as aluminum, aluminum alloys, stainless steel, copper, and nickel, or resin materials that have been imparted conductivity by coexisting conductive powders such as metal, carbon, and tin oxide, or resins, glass, and paper on which conductive materials such as aluminum, nickel, and ITO (indium tin oxide alloy) have been vapor-deposited or coated.

[0038] Conductive supports can take various forms, such as drum-shaped, sheet-shaped, or belt-shaped. For example, a conductive support made of metal material may be coated with a conductive material having an appropriate resistance value for controlling conductivity and surface properties, or for defect coverage. When using a metal material such as an aluminum alloy as a conductive support, the metal material may be coated with an anodic oxide film before use. The average thickness of the anodic oxide coating is usually 20 μm or less, and preferably 7 μm or less.

[0039] The surface of the conductive support may be smooth, or it may be roughened by using a special cutting method or by polishing. Alternatively, the surface may be roughened by mixing particles of an appropriate particle size into the material constituting the support.

[0040] Furthermore, an undercoat layer, as described later, may be provided between the conductive support and the photosensitive layer to improve adhesion, blocking properties, etc.

[0041] <Photosensitive layer> The photosensitive layer in the electrophotographic photoreceptor of the present invention may be a single layer or a multilayer, and the photosensitive layer in contact with the protective layer (outermost layer) may have the configuration described below. In particular, it is preferable that the photosensitive layer in contact with the protective layer (outermost layer) is a single layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material, and an electron transport material in the same layer.

[0042] As mentioned above, the deterioration of adhesion between the protective layer (outermost layer) and the photosensitive layer in contact with it, as well as the decrease in the Martens hardness of the photoreceptor surface and the elastic deformation rate of the photoreceptor surface, are thought to be due to the concentration of hole transport materials and electron transport materials on the surface of the photosensitive layer. Here, "photosensitive layer surface" refers to the interface on the side where the photosensitive layer is in contact with the protective layer (outermost layer). More specifically, it is presumed that when hole transport materials concentrate on the surface of the photosensitive layer, they create a steric obstruction that hinders the entanglement between the cured film of the protective layer (outermost layer) and the binder resin of the photosensitive layer, thus causing the deterioration of adhesion as described above. Furthermore, it is presumed that when electron transport materials concentrate on the surface of the photosensitive layer, the electron transport materials trap radicals generated in the curing reaction of the protective layer (outermost layer), inhibiting the chain polymerization reaction, i.e., the curing reaction, in the protective layer (outermost layer), thus causing the decrease in the Martens hardness of the photoreceptor surface and the elastic deformation rate of the photoreceptor surface.

[0043] To address these issues, the first embodiment of the present invention involves setting the molecular weight of the hole transport material and electron transport material to a predetermined value or higher. This suppresses the mobility of the hole transport material and electron transport material in the photosensitive layer, thereby suppressing migration to the surface of the photosensitive layer, preventing concentration on the surface of the photosensitive layer, and thus improving adhesion, Martens hardness, and elastic deformation rate.

[0044] Furthermore, a second embodiment of the present invention involves adjusting the ratio of the amount of substance (moles) of hole transport material and the amount of substance (moles) of electron transport material in the photosensitive layer to a predetermined range, thereby suppressing the concentration of hole transport material and electron transport material in a balanced manner, and thus enabling desirable adhesion, Martens hardness, and elastic deformation rate.

[0045] Furthermore, a third embodiment of the present invention involves adjusting the ratio of the molecular weight of the hole transport material to the molecular weight of the electron transport material within a predetermined range, thereby suppressing the concentration of the hole transport material and the electron transport material in a balanced manner, and thus enabling desirable adhesion, Martens hardness, and elastic deformation rate.

[0046] The following describes the materials used in the photosensitive layer that comes into contact with the protective layer (outermost layer), such as a single-layer photosensitive layer (charge generating material, hole transport material, electron transport material, binder resin, etc.).

[0047] (Charge-generating material) Various photoconductive materials can be used as charge-generating materials for the photosensitive layer, such as selenium and its alloys, cadmium sulfide, and other inorganic photoconductive materials; and organic pigments such as phthalocyanine pigments, azo pigments, and perylene pigments. Among these, organic pigments are preferred, phthalocyanine pigments and azo pigments are more preferred, and phthalocyanine pigments are even more preferred.

[0048] In particular, when phthalocyanine pigments are used as charge-generating materials, specific examples include metal-free phthalocyanines, phthalocyanines coordinated with metals such as copper, indium, gallium, tin, titanium, zinc, vanadium, silicon, and germanium, or their oxides and halides. Among these, X-type and τ-type metal-free phthalocyanines, A-type, B-type, and D-type titanyl phthalocyanines, vanadyl phthalocyanines, chloroindium phthalocyanines, chlorogallium phthalocyanines, and hydroxygallium phthalocyanines, which have particularly high sensitivity, are preferred.

[0049] Of the titanylphthalocyanine crystal forms listed here, types A and B have been described as phase I and phase II, respectively, by W. Heller et al. (Zeit. Kristallogr. 159 (1982) 173), with type A being known as the stable form. Type D is a crystal form characterized by a clear peak at a diffraction angle of 2θ ± 0.2° at 27.3° in powder X-ray diffraction using CuKα rays.

[0050] Furthermore, when using azo pigments, various known bis-azo pigments and tris-azo pigments are preferably used.

[0051] Furthermore, the charge-generating material may be used alone, or two or more may be used in any combination and ratio. In addition, when two or more charge-generating materials are used in combination, the charge-generating materials may be mixed afterwards, or they may be mixed during the manufacturing or processing steps of the charge-generating materials, such as synthesis, pigmentation, or crystallization.

[0052] From the viewpoint of electrical properties, it is desirable that the particle size of the charge-generating material be small. Specifically, it is usually preferred to be 1 μm or less, and more preferably 0.5 μm or less. The lower limit is 0.01 μm. Here, the particle size of the charge-generating material refers to the particle size when it is contained in the photosensitive layer.

[0053] Furthermore, the amount of charge-generating material in the photosensitive layer in contact with the protective layer (outermost layer), such as a single-layer photosensitive layer, is preferably 0.1% by mass or more, and more preferably 0.5% by mass or more, from the viewpoint of sensitivity. Also, from the viewpoint of sensitivity and chargeability, it is preferably 50% by mass or less, and more preferably 20% by mass or less.

[0054] (charge transport material) Charge transport materials are classified into two main types: hole transport materials, which primarily possess hole transport ability, and electron transport materials, which primarily possess electron transport ability. The photosensitive layer in contact with the protective layer (outermost layer) used in this invention, for example, a single-layer photosensitive layer, contains both hole transport materials and electron transport materials.

[0055] [Hole transport material] The hole transport material (HTM) can be selected from known materials. Examples include heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, and benzofuran derivatives; aniline derivatives, hydrazone derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, as well as compounds formed by the combination of multiple types of these compounds, and electron-donating materials such as polymers having groups made of these compounds in their main chain or side chain.

[0056] Among these, carbazole derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, as well as compounds formed by combining multiple types of these compounds, are preferred, with arylamine derivatives and enamine derivatives being more preferred.

[0057] In the first embodiment of the present invention, regarding the molecular weight of the hole transport material (HTM), a larger molecular weight of the hole transport material results in lower migration to the photosensitive layer surface. Therefore, it is possible to suppress the concentration of the hole transport material on the photosensitive layer surface, and thus suppress deterioration of adhesion between the photosensitive layer and the protective layer (outermost layer). However, if the molecular weight of the hole transport material is too large, it tends to decrease in solubility in the solvent used in the coating solution and decrease in compatibility with the binder resin, leading to precipitation, which is undesirable. From this viewpoint, the molecular weight a of the hole transporter preferably satisfies the following formula (1), and more preferably satisfies the following formula (1'). 600 ≤ a (1) 600 ≤ a ≤ 1200 (1') Thus, the molecular weight of the hole transporter is preferably 600 or more, more preferably 650 or more, even more preferably 700 or more, and particularly preferably 750 or more. On the other hand, it is preferably 1200 or less, more preferably 1000 or less, and even more preferably 900 or less.

[0058] In the second and third embodiments of the present invention, from the viewpoint of Martens hardness and elastic deformation rate, it is preferable that the photosensitive layer in contact with the protective layer (outermost layer), for example, a single-layer photosensitive layer, further satisfies formula (1), and even more preferably satisfies formula (1'). In other words, the molecular weight a of the hole transport material is preferably 600 or more, more preferably 650 or more, even more preferably 700 or more, and particularly preferably 750 or more. On the other hand, it is preferably 1200 or less, more preferably 1000 or less, and even more preferably 900 or less.

[0059] The hole transporter may be used alone, or two or more may be used in any ratio and combination. When two or more hole transporters are used, it is even more preferable that the molecular weight of the hole transporter with the largest content (parts by mass) in the photosensitive layer is 600 or more.

[0060] The following are examples of preferred hole transporter structures.

[0061] TIFF0007852506000002.tif72170

[0062] TIFF0007852506000003.tif78170

[0063] TIFF0007852506000004.tif114170

[0064] Among the hole transport materials listed above, HTM12, HTM31, HTM32, HTM33, HTM34, HTM35, HTM36, HTM38, HTM39, HTM40, HTM41, HTM42, HTM43, and HTM48 are preferred from the viewpoint of electrical properties, HTM31, HTM32, HTM33, HTM34, HTM35, HTM36, HTM38, HTM39, HTM40, HTM41, HTM42, HTM43, and HTM48 are more preferred, and HTM39, HTM40, HTM41, HTM42, HTM43, and HTM48 are even more preferred.

[0065] Among the hole transport materials described above, from the viewpoint of further improving the adhesion between the photosensitive layer and the protective layer (outermost layer), the hole transport material is preferably one having a substituent at at least one ortho position of at least one aromatic group bonded to the nitrogen (N) atom, and more preferably one having substituents at both ortho positions of at least one aromatic group bonded to the nitrogen (N) atom. When the hole transport material has the above structure, it is thought that the aromatic group repels other substituents bonded to the nitrogen atom, resulting in a stereochemistry that is rotated with respect to the plane formed by the nitrogen atom and the other substituents bonded to the nitrogen atom. With such a stereochemistry, it is presumed that the aromatic group exerts an anchoring effect on the binder resin, making it difficult for the hole transport material to concentrate on the surface of the photosensitive layer.

[0066] Examples of the aromatic groups include the benzene ring, naphthyl group, anthracene group, phenanthrene group, biphenyl group, pyrene group, and carbazole group. Among these, the benzene ring, naphthyl group, and biphenyl group are preferred from the viewpoint of solubility, with the benzene ring being more preferred.

[0067] Examples of the ortho substituents include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, sec-butyl group, i-butyl group, tert-butyl group, n-pentyl group, isopentyl group, sec-pentyl group, neopentyl group, 1-methylbutyl group, 2-methylbutyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, vinyl group, 1-propenyl group, 2-propenyl group, isopropenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 1-pentenyl group, 2-pentenyl group, 3-pentenyl group, 4-pentenyl group, ethynyl group, 1-propynyl group, 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3-pentynyl group, and 4-pentynyl group. Among these, methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, sec-butyl group, and i-butyl group are preferred from the viewpoint of ease of substituent introduction, and methyl group, ethyl group, n-propyl group, and i-propyl group are more preferred.

[0068] From this viewpoint, among the hole transport materials mentioned above, HTM48, HTM42, HTM40, HTM43, and HTM41 are preferred, and among them, HTM40 and HTM43 are even more preferred.

[0069] Furthermore, hole transporters with a molecular weight of 600 or more may be used in combination with hole transporters outside that molecular weight range (referred to as "other hole transporters"). However, in that case, it is preferable that the amount of hole transporting material with a molecular weight of 600 or more is greater than the amount of other hole transporting materials, and in particular, it is preferable that the amount of other hole transporting materials is 80 parts by mass or less per 100 parts by mass of hole transporting material with a molecular weight of 600 or more, and more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less.

[0070] Examples of other hole transporting materials include, but are not limited to, those having the following structures.

[0071] TIFF0007852506000005.tif68170

[0072] TIFF0007852506000006.tif74170

[0073] TIFF0007852506000007.tif80170

[0074] TIFF0007852506000008.tif39170

[0075] [Electron transport material] The electron transport material (ETM) can be selected from known materials. Examples include electron-withdrawing substances such as aromatic nitro compounds like 2,4,7-trinitrofluorenone, cyano compounds like tetracyanoquinodimethane, and quinone compounds like diphenoquinone, as well as known cyclic ketone compounds and perylene pigments (perylene derivatives).

[0076] In the first embodiment of the present invention, regarding the molecular weight of the electron transport material (ETM), a larger molecular weight of the electron transport material results in lower migration to the surface. Therefore, it is possible to suppress the concentration of the electron transport material on the surface of the photosensitive layer and further suppress migration to the outermost layer. This prevents the electron transport material from trapping radicals generated in the curing reaction of the protective layer (outermost layer) and inhibiting the curing reaction. Consequently, it is possible to suppress a decrease in the Martens hardness of the photoreceptor surface and a decrease in the elastic deformation rate of the photoreceptor surface. However, if the molecular weight of the electron transport material is too large, it tends to decrease in solubility in the solvent used in the coating solution and decrease in compatibility with the binder resin, leading to precipitation, which is undesirable. From this viewpoint, the molecular weight b of the electron transport material is preferably satisfied by the following formula (2), and more preferably by the following formula (2'). 400 ≤ b (2) 400 ≤ b ≤ 1000 (2') Thus, the molecular weight of the electron transport material is preferably 400 or more, more preferably 410 or more, and even more preferably 420 or more. On the other hand, it is preferably 1000 or less, more preferably 800 or less, and even more preferably 600 or less.

[0077] In the second and third embodiments of the present invention, from the viewpoint of Martens hardness and elastic deformation rate, it is preferable that the photosensitive layer in contact with the protective layer (outermost layer), for example, a single-layer photosensitive layer, further satisfies formula (2), and even more preferably satisfies formula (2'). In other words, the molecular weight b of the electron transport material is preferably 400 or more, more preferably 410 or more, and even more preferably 420 or more. On the other hand, it is preferably 1000 or less, more preferably 800 or less, and even more preferably 600 or less.

[0078] In the first and second embodiments of the present invention, regarding the relationship between the molecular weight of the hole transport material and the molecular weight of the electron transport material, it is preferable that the molecular weight a of the hole transport material is greater than the molecular weight b of the electron transport material, from the viewpoint of Martens hardness, elastic deformation rate, and adhesion between the photosensitive layer and the protective layer (outermost layer). In other words, the ratio (a / b) of the molecular weight a of the hole transport material to the molecular weight b of the electron transport material is preferably 1.00 or more, more preferably 1.40 or more, more preferably 1.50 or more, more preferably 1.60 or more, even more preferably 1.70 or more, and particularly preferably 1.80 or more. On the other hand, from the viewpoint of electrical properties, it is preferably 3.00 or less, more preferably 2.00 or less, even more preferably 1.90 or less, and even more preferably 1.85 or less.

[0079] In a third embodiment of the present invention, by setting the ratio of the molecular weight a of the hole transport material to the molecular weight b of the electron transport material (a / b) to 1.40 or more and 1.90 or less, the concentration of the hole transport material and the concentration of the electron transport material are suppressed in a balanced manner, thereby favorable adhesion, Martens hardness, and elastic deformation rate. If a / b is 1.40 or higher, the molecular weight of the hole transporter is adjusted to be relatively larger, and the migration of the hole transporter to the photosensitive layer surface is reduced, resulting in good adhesion. Furthermore, when the migration of the hole transporter to the photosensitive layer surface is reduced, the migration of the electron transporter to the photosensitive layer surface is also inhibited, resulting in reduced migration of the electron transporter to the photosensitive layer surface, and thus good Martens hardness and elastic deformation rate. Among these, a / b is preferably 1.50 or higher, more preferably 1.60 or higher, even more preferably 1.70 or higher, and particularly preferably 1.80 or higher. If a / b is 1.90 or less, the molecular weight of the electron transport material is adjusted to be relatively larger, and the migration of the electron transport material to the photosensitive layer surface is reduced, resulting in good Martens hardness and elastic deformation. Furthermore, when the migration of the electron transport material to the photosensitive layer surface is reduced, the movement of the hole transport material to the photosensitive layer surface is also inhibited, resulting in low migration of the hole transport material to the photosensitive layer surface and good adhesion. Therefore, a / b is preferably 1.90 or less, and more preferably 1.85 or less.

[0080] The electron transport material may be used alone as only one kind, or two or more kinds may be used in any ratio and combination. When two or more kinds of hole transport materials are used, among the two or more kinds of electron transport materials, 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.

[0081] As a particularly preferable compound as the electron transport material, a compound represented by the following formula (6) can be exemplified.

[0082] TIFF0007852506000009.tif54161

[0083] 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 may be bonded to each other, or R 63 and R 64 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.

[0084] 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. Examples of alkyl groups having 1 to 20 carbon atoms that may be substituted include linear alkyl groups, branched alkyl groups, and cyclic alkyl groups, with linear alkyl groups or branched alkyl groups being preferred in terms of electron transport capacity. The number of carbon atoms in these alkyl groups is usually 1 or more, preferably 4 or more, usually 20 or less, preferably 15 or less in terms of versatility of raw materials, more preferably 10 or less in terms of handling during manufacturing, and even more preferably 5 or less. Specifically, examples include methyl group, ethyl group, hexyl group, iso-propyl group, tert-butyl group, tert-amyl group, cyclohexyl group, and cyclopentyl group. Among these, methyl group, tert-butyl group, or tert-amyl group are preferred, and tert-butyl group or tert-amyl group are more preferred in terms of solubility in organic solvents used in coating solutions.

[0085] Examples of alkenyl groups having 2 to 20 carbon atoms that may be substituted include linear alkenyl groups, branched alkenyl groups, and cyclic alkenyl groups. The number of carbon atoms in these alkenyl groups is usually 2 or more, preferably 4 or more, usually 20 or less, and preferably 10 or less from the viewpoint of the photoattenuation characteristics of the photoreceptor. Specifically, examples include ethenyl groups, 2-methyl-1-propenyl groups, and cyclohexenyl groups.

[0086] The substituent R 61 ~R 64 R 61 and R 62 Both, or R 63 and R 64 They may bond with each other to form a ring structure. From the viewpoint of electron mobility, R 61 and R 62 When both are alkenyl groups, it is preferable that they bond to each other to form an aromatic ring, R 61 and R 62 It is more preferable that both are ethenyl groups, bonded to each other, and have a benzene ring structure.

[0087] In formula (6) above, X represents an organic residue with a molecular weight of 120 to 250, and from the viewpoint of the photoattenuation characteristics of the photoreceptor, the compound represented by formula (6) is preferably a compound represented by any of the following formulas (7) to (10).

[0088] TIFF0007852506000010.tif59170

[0089] In formula (7), R 71 ~R 73 Each of these independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.

[0090] TIFF0007852506000011.tif47170

[0091] In formula (8), R 81 ~R 84 Each of these independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.

[0092] TIFF0007852506000012.tif45170

[0093] In equation (9) above, R 91 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen atom.

[0094] TIFF0007852506000013.tif50170

[0095] In the above equation (10), R 101 and R 102 Each of these 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.

[0096] R 71 ~R 102Examples of alkyl groups having 1 to 6 carbon atoms include linear alkyl groups, branched alkyl groups, and cyclic alkyl groups. The number of carbon atoms in these alkyl groups is usually 1 to 6. Specifically, examples include methyl group, ethyl group, hexyl group, iso-propyl group, tert-butyl group, tert-amyl group, and cyclohexyl group. Among these, methyl group, tert-butyl group, or tert-amyl group are preferred in terms of electron transport capacity.

[0097] Examples of halogen atoms include fluorine, chlorine, bromine, and iodine, with chlorine being preferred in terms of electron transport capability.

[0098] The number of carbon atoms in the aryl group, which is between 6 and 12 carbon atoms, is usually between 6 and 12. Specifically, examples include the phenyl group and the naphthyl group, and from the viewpoint of the film properties of the photosensitive layer, the phenyl group is preferred. These aryl groups may be further substituted.

[0099] Of the formulas (7) to (10) mentioned above, formula (6) is preferably formula (7) or formula (8), and more preferably formula (7), from the viewpoint of image quality stability when repeatedly forming images. Furthermore, the compound represented by formula (6) may be used alone, or a compound represented by formula (6) with a different structure may be used in combination, or it may be used in combination with other electron transport materials.

[0100] The following are examples of preferred electron transport material structures.

[0101] TIFF0007852506000014.tif113170

[0102] Among the electron transport materials mentioned above, ET-2, ET-5, ET-15, ET-16, and ET-17 are preferred in terms of electrical properties, ET-2 and ET-5 are more preferred, and ET-2 is even more preferred. On the other hand, among the electron transport materials mentioned above, ET-2, ET-5, ET-9, ET-13, ET-14, ET-15, ET-16, and ET-17 are preferred from the viewpoint of suppressing a decrease in the Martens hardness of the photoreceptor surface and suppressing a decrease in the elastic deformation rate of the photoreceptor surface, and among these, ET-2 and ET-5 are even more preferred.

[0103] In addition, other electron transport materials may be used in combination with the preferred electron transport materials exemplified above. However, in that case, it is preferable that the amount of the preferred electron transport material is greater than the amount of other electron transport materials, and in particular, it is preferable that the amount of other electron transport materials is 80 parts by mass or less per 100 parts by mass of the electron transport material, and more preferably 60 parts by mass or less, and even more preferably 40 parts by mass or less.

[0104] Examples of such other electron transport materials include those having the following structures, but are not limited to these.

[0105] TIFF0007852506000015.tif125170

[0106] [Content of hole transporter and electron transporter] In the first, second, and third embodiments of the present invention, it is preferable to further adjust the total amount of moles of hole transporting material and electron transporting material contained in the photosensitive layer, such as a single-layer photosensitive layer, so that the photosensitive layer in contact with the protective layer (outermost layer) satisfies formula (3), thereby ensuring the absolute amount of charge transporting material necessary for charge transport in the photosensitive layer. 0.15 ≤ (A / a) + (B / b) (3)

[0107] In formula (3), and formulas (4) and (5) described later, A represents the content (parts by mass) of hole transport material when the binder resin content in the photosensitive layer in contact with the protective layer (outermost layer), for example, a single-layer photosensitive layer, is set to 100 (parts by mass), B represents the content (parts by mass) of electron transport material, a represents the molecular weight of the hole transport material, and b represents the molecular weight of the electron transport material. Furthermore, (A / a) or (B / b) is the amount of hole transporter or electron transporter divided by its molecular weight, representing the amount of substance, i.e., the number of molecules, i.e., the molar amount.

[0108] From the viewpoint of ensuring the absolute amount of charge transport material necessary for charge transport in the photosensitive layer, (A / a) + (B / b) is preferably 0.15 or more, more preferably 0.17 or more, and even more preferably 0.20 or more. On the other hand, it is preferably 0.60 or less, more preferably 0.40 or less, and even more preferably 0.30 or less.

[0109] Furthermore, in the first, second, and third embodiments of the present invention, it is preferable that the photosensitive layer in contact with the protective layer (outermost layer), for example, a single-layer photosensitive layer, satisfies formula (4). 0.80 ≤ A / B ≤ 3.00 (4)

[0110] In formula (4), "A / B" represents the ratio of hole transport material to electron transport material contained in the photosensitive layer. A ratio of 0.80 or higher is preferable because it provides good electron transport performance, and a ratio of 3.00 or lower is preferable because it provides good hole transport performance. From this perspective, "A / B" is preferably 0.80 or higher, more preferably 1.00 or higher, and even more preferably 1.10 or higher. On the other hand, it is preferably 3.00 or lower, more preferably 2.00 or lower, and even more preferably 1.80 or lower.

[0111] In the first and third embodiments of the present invention, it is preferable that the photosensitive layer in contact with the protective layer (outermost layer), for example, a single-layer photosensitive layer, further satisfies formula (5) from the viewpoint of Martens hardness, elastic deformation rate, and adhesion.

[0112] 1.20 ≤ (B / b) / (A / a) ≤ 1.60 (5)

[0113] In other words, (B / b) / (A / a) is preferably 1.20 or greater, more preferably 1.40 or greater, and even more preferably 1.50 or greater. On the other hand, it is preferably 1.60 or less, more preferably 1.58 or less, and even more preferably 1.55 or less.

[0114] In a second embodiment of the present invention, by adjusting the ratio of the amount of substance (mol) of hole transporting material to the amount of substance (mol) of electron transporting material contained in the photosensitive layer, such as a single-layer photosensitive layer, that is in contact with the protective layer (outermost layer), the concentration of the hole transporting material and the concentration of electron transporting material can be suppressed in a balanced manner, thereby improving the Martens hardness, the elastic deformation rate, and the adhesion.

[0115] As mentioned above, from the viewpoint of further improving both adhesion, Martens hardness, and elastic deformation rate by suppressing the concentration of hole transport material and electron transport material in a balanced manner, (B / b) / (A / a) is preferably 1.20 or higher, more preferably 1.40 or higher, and more preferably 1.50 or higher. On the other hand, it is preferably 1.60 or lower, more preferably 1.58 or lower, and more preferably 1.55 or lower. When the photosensitive layer contains both hole transporters and electron transporters, electron transfer occurs from the hole transporters to the electron transporters, resulting in positively charged hole transporters and negatively charged electron transporters, which are thought to form a charge transfer complex. When a charge transfer complex is formed, an electrostatic attraction acts between the positively charged hole transporters and the negatively charged electron transporters, making it difficult for both to concentrate on the surface of the photosensitive layer. If (B / b) / (A / a) is 1.20 or greater, the number of electron transport molecules is not too small compared to the hole transport molecules, and the hole transport molecules that cannot form charge transfer complexes can be suppressed, thereby more effectively suppressing their concentration on the photosensitive layer surface. If (B / b) / (A / a) is 1.60 or less, the number of hole transport molecules is not too small compared to the electron transport material, and electron transport materials that cannot form charge transfer complexes can be suppressed, thus more effectively suppressing concentration on the photosensitive layer surface. In other words, if (B / b) / (A / a) is between 1.20 and 1.60, it is considered that the hole transport material and the electron transport material can sufficiently form a charge transfer complex.

[0116] (Binder resin) Next, we will explain the binder resin used in the photosensitive layer described above. Examples of binder resins used in the photosensitive layer include vinyl polymers or copolymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride; butadiene resin; styrene resin; vinyl acetate resin; vinyl chloride resin, acrylic acid ester resin; methacrylic acid ester resin; vinyl alcohol resin; polymers and copolymers of vinyl compounds such as ethyl vinyl ether; polyvinyl butyral resin; polyvinyl formal resin; partially modified polyvinyl acetal resin; polyarylate resin; polyamide resin; polyurethane resin; cellulose ester resin; silicone alkyd resin; poly-N-vinylcarbazole resin; polycarbonate resin; polyester resin; polyester carbonate resin; polysulfone resin; polyimide resin; phenoxy resin; epoxy resin; silicone resin; and partially crosslinked cured products thereof. The above resins may also be modified with silicon reagents, etc. These can be used individually or in any ratio and combination.

[0117] Furthermore, it is particularly preferable that the binder resin contains one or more polymers obtained by interfacial polymerization.

[0118] The binder resin obtained by the above interfacial polymerization is preferably a polycarbonate resin or a polyester resin, and is particularly preferably a polycarbonate resin or a polyarylate resin. Furthermore, it is especially preferable that the polymer is derived from an aromatic diol, and a preferred aromatic diol compound is the compound represented by the following formula (11).

[0119] TIFF0007852506000016.tif56170

[0120] In the above equation (11), X 111 represents a linking group or single bond, which can be expressed by any of the following formulas.

[0121] TIFF0007852506000017.tif38170

[0122] In the above formula, R 111 and R 112 Each of these independently represents a hydrogen atom, a C1-C20 alkyl group, an optionally substituted aryl group, or a halogenated alkyl group. Z represents a C4-C20 substituted or unsubstituted carbon ring.

[0123] In formula (11), Y 111 or Y 118 Each of these independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 20 carbon atoms, an optionally substituted aryl group, or a halogenated alkyl group.

[0124] (Other substances) In addition to the materials mentioned above, the photosensitive layer may contain additives such as well-known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, and visible light shielding agents to improve film-forming properties, flexibility, coatability, stain resistance, gas resistance, and light resistance. The photosensitive layer may also contain various additives such as sensitizers, dyes, pigments (excluding those that are charge-generating substances, hole-transporting substances, or electron-transporting substances), and surfactants as needed. Examples of surfactants include silicone oil and fluorine-based compounds. In the present invention, these can be used individually or in any ratio and combination of two or more as appropriate.

[0125] Furthermore, in order to reduce the frictional resistance of the photosensitive layer surface, the photosensitive layer may contain fluororesins, silicone resins, etc., and may also contain particles made of these resins or particles of inorganic compounds such as aluminum oxide.

[0126] (Antioxidant) The antioxidant is a type of stabilizer used to prevent oxidation of the electrophotographic photoreceptor of the present invention.

[0127] The antioxidant can be any agent that functions as a radical scavenger, and specific examples include phenol derivatives, amine compounds, phosphonic acid esters, sulfur compounds, vitamins, vitamin derivatives, etc.

[0128] The amount of the above-mentioned antioxidant used is not particularly limited, but is preferably 0.1 parts by mass or more, and more preferably 1 part by mass or more, per 100 parts by mass of binder resin in the photosensitive layer. Furthermore, in order to obtain good electrical properties and print resistance, it is preferably 25 parts by mass or less, and more preferably 20 parts by mass or less.

[0129] (electron-withdrawing compound) Furthermore, the photosensitive layer may contain an electron-withdrawing compound. Examples of electron-withdrawing compounds include sulfonic acid ester compounds, carboxylic acid ester compounds, organic cyano compounds, nitro compounds, aromatic halogen derivatives, etc. Preferably, sulfonic acid ester compounds and organic cyano compounds are used, and particularly preferably, sulfonic acid ester compounds. One of the above electron-withdrawing compounds may be used alone, or two or more may be used in any ratio and combination.

[0130] The amount of the electron-withdrawing compound used in the electrophotographic photoreceptor in the present invention is not particularly limited. When the electron-withdrawing compound is used in the photosensitive layer, it is preferably 0.01 parts by mass or more, and more preferably 0.05 parts by mass or more, per 100 parts by mass of binder resin contained in the photosensitive layer. Furthermore, 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 even more preferably 30 parts by mass or less.

[0131] (Method for forming a photosensitive layer) Next, a method for forming a photosensitive layer in contact with the protective layer (outermost layer), such as a single-layer photosensitive layer, will be described. However, the method for forming the photosensitive layer of the present invention is not particularly limited. For example, the charge generating material can be formed by dispersing the charge generating material in a coating solution obtained by dissolving (or dispersing) a hole transport material, an electron transport material, a binder resin, and other materials in a solvent (or dispersion medium), and then coating the solution onto a conductive support (or onto intermediate layers such as the undercoat layer described later, if such intermediate layers are provided).

[0132] The following describes the solvent or dispersion medium used to form the photosensitive layer in contact with the protective layer (outermost layer), such as a single-layer photosensitive layer, and the coating method.

[0133] [Solvent or dispersion medium] Examples of solvents or dispersion media 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; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and anisole; chlorinated hydrocarbons such as dichloromethane, chloroform, and 1,2-dichloroethane; nitrogen-containing compounds; and aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide. These may be used individually or in combination of two or more in any ratio and combination.

[0134] [Application Method] Methods for applying a coating solution to form a photosensitive layer, such as a single-layer photosensitive layer, that comes into contact with the protective layer (outermost layer), include, for example, spray coating, spiral coating, ring coating, and immersion coating.

[0135] In the immersion 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. It is also preferably 50% by mass or less, and more preferably 35% by mass or less.

[0136] Furthermore, the viscosity of the coating solution or dispersion is preferably 50 mPa·s or higher, more preferably 100 mPa·s or higher. It is also preferably 700 mPa·s or lower, more preferably 500 mPa·s or lower. This allows for a photosensitive layer with excellent film thickness uniformity.

[0137] 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 the necessary and sufficient drying is achieved. The drying temperature is usually 80°C or higher, preferably 100°C or higher, from the viewpoint of suppressing residual solvent. Furthermore, from the viewpoint of preventing bubble formation and electrical properties, it is usually 250°C or lower, preferably 170°C or lower, and even more preferably 140°C or lower, and the temperature may be changed in stages. Drying methods that can be used include hot air dryers, steam dryers, infrared dryers, and far-infrared dryers.

[0138] Furthermore, in this invention, since a protective layer (outermost layer) is provided, after coating the photosensitive layer, only air drying at room temperature may be performed, or heat drying may be performed using the method described above after coating.

[0139] The thickness of the photosensitive layer is selected as optimally as appropriate depending on the materials used. From the viewpoint of electrical properties and dielectric breakdown resistance, a thickness of 5 μm or more is preferred, 10 μm or more is more preferred, and 15 μm or more is particularly preferred. Furthermore, from the viewpoint of electrical properties, a thickness of 100 μm or less is preferred, 50 μm or less is more preferred, and 30 μm or less is particularly preferred.

[0140] <Protective layer (outermost layer)> The protective layer (outermost layer) of the photoreceptor of the present invention has a structure formed by polymerizing a compound having a chain-polymerizable functional group. In particular, the effects of the present invention are even more effectively demonstrated when a protective layer (outermost layer) is formed by radical polymerization of a compound having a chain polymerizable functional group. As described above, according to the present invention, by using a predetermined electron transport material, it is possible to suppress the concentration of the electron transport material on the surface of the photosensitive layer, and thus it is possible to suppress the electron transport material from trapping radicals generated in the curing reaction of the protective layer (outermost layer) and inhibiting the curing reaction by radical polymerization. Therefore, it is possible to suppress the decrease in Martens hardness and elastic deformation rate of the photoreceptor surface.

[0141] Examples of chain polymerizable functional groups in compounds having chain polymerizable functional groups include acryloyl groups, methacryloyl groups, vinyl groups, and epoxy groups. Among these, acryloyl groups, methacryloyl groups, and vinyl groups can be cited as chain polymerizable functional groups that can undergo radical polymerization, and from the viewpoint of curing speed, acryloyl groups and methacryloyl groups are preferred. 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, monomers, oligomers, and polymers having an acryloyl group or a methacryloyl group are preferred.

[0142] The following are examples of preferred compounds. Monomers having an acryloyl group or 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, and PO-modified tris(acryloxyethyl) Liloxyethyl) 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,Examples include 9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, tricyclodecanedimethanol diacrylate, decanediol diacrylate, hexanediol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, EO-modified bisphenol A dimethacrylate, PO-modified bisphenol A dimethacrylate, tricyclodecanedimethanol dimethacrylate, decanediol dimethacrylate, hexanediol dimethacrylate, etc.

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

[0144] These can be used individually or in combination of two or more types. Among these, it is preferable that they contain urethane acrylate from the viewpoint of electrical properties.

[0145] The protective layer (outermost layer) of the electrophotographic photoreceptor according to the present invention may contain, in addition to a compound having a chain polymerizable functional group, metal oxide particles or charge transporting substances for the purpose of imparting charge transport ability. Furthermore, a polymerization initiator may be included to promote the polymerization reaction.

[0146] The following details the materials used in the protective layer (outermost layer) (metal oxide particles, charge transport materials, polymerization initiators).

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

[0148] As the metal oxide particles, any metal oxide particles that are normally usable in electrophotographic photoreceptors can be used. More specifically, metal oxide particles include metal oxide particles containing one metal element such as titanium oxide, tin oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, as well as metal oxide particles containing multiple metal elements such as indium tin oxide, calcium titanate, strontium titanate, and barium titanate. Among these, metal oxide particles with a band gap of 2 to 4 eV are preferred. The metal oxide particles may be of a single type or a mixture of multiple types. Among these metal oxide particles, titanium oxide, tin oxide, indium tin oxide, aluminum oxide, silicon oxide, and zinc oxide are preferred from the viewpoint of electron transport, and titanium oxide and tin oxide are more preferred. Titanium oxide is particularly preferred.

[0149] The titanium oxide particles can be in any of the following crystalline forms: rutile, anatase, brookite, or amorphous. Furthermore, a mixture of these particles in different crystalline states may be included.

[0150] Metal oxide particles may be subjected to various surface treatments. For example, they may be treated with inorganic substances such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, and silicon oxide, or with organic substances such as stearic acid, polyols, and organosilicon compounds. In particular, when titanium oxide particles are used, surface treatment with organosilicon compounds is preferred. Examples of organosilicon compounds 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, and vinyltrimethoxysilane. In particular, from the viewpoint of improving the mechanical strength of the protective layer (outermost layer), 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, and vinyltrimethoxysilane, which have chain polymerizable functional groups, are preferred.

[0151] Furthermore, the metal oxide particles may be pre-treated with an insulating material such as aluminum oxide, silicon oxide, or zirconium oxide before their outermost surface is treated with such a treatment agent. The metal oxide particles may be of a single type or a mixture of multiple types.

[0152] The metal oxide particles typically have an average primary particle diameter of 500 nm or less, are more preferably 1 nm to 100 nm, and even more preferably 5 nm to 50 nm. This average primary particle diameter can be determined by the arithmetic mean of the particle diameters directly observed using a transmission electron microscope (TEM).

[0153] Among the metal oxide particles according to the present invention, specific product names for titanium dioxide particles include: ultrafine titanium dioxide particles without surface treatment "TTO-55(N)" and "TTO-51(N)", ultrafine titanium dioxide particles coated with Al2O3 "TTO-55(A)" and "TTO-55(B)", ultrafine titanium dioxide particles surface-treated with stearic acid "TTO-55(C)", ultrafine titanium dioxide particles surface-treated with Al2O3 and organosiloxane "TTO-55(S)", and high-purity titanium dioxide "C-E L", sulfuric acid-processed titanium oxide "R-550", "R-580", "R-630", "R-670", "R-680", "R-780", "A-100", "A-220", "W-10", chlorine-processed titanium oxide "CR-50", "CR-58", "CR-60", "CR-60-2", "CR-67", conductive titanium oxide "ET-300W" (all manufactured by Ishihara Sangyo Co., Ltd.), as well as titanium oxides such as "R-60", "A-110", "A-150", and Al2O3 coated "SR-1", "R-GL", "R-5N", "R-5N-2", "R-52N", "RK-1", "A-SP", "R-GX" and "R-7E" coated with SiO2 and Al2O3, "R-650" coated with ZnO, SiO2, and Al2O3, "R-61N" coated with ZrO2 and Al2O3 (all manufactured by Sakai Chemical Industry Co., Ltd.), as well as "TR-700" surface-treated with SiO2 and Al2O3, "TR-840" and "TA-500" surface-treated with ZnO, SiO2, and Al2O3, and "TA-1 Examples include untreated titanium oxide such as "00", "TA-200", and "TA-300", "TA-400" which is surface-treated with Al2O3 (all manufactured by Fuji Titanium Industries Co., Ltd.), "MT-150W" and "MT-500B" which have no surface treatment, "MT-100SA" and "MT-500SA" which are surface-treated with SiO2 and Al2O3, and "MT-100SAS" and "MT-500SAS" which are surface-treated with SiO2, Al2O3 and organosiloxane (manufactured by Teika Co., Ltd.).

[0154] Furthermore, specific product names for aluminum oxide particles include "Aluminium Oxide C" (manufactured by Nippon Aerosil Co., Ltd.).

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

[0156] Specific product names for tin oxide particles include "SN-100P," "SN-100D" (manufactured by Ishihara Sangyo Co., Ltd.), "SnO2" (manufactured by CIK Nanotech Co., Ltd.), "S-2000," phosphorus-doped tin oxide "SP-2," antimond-doped tin oxide "T-1," and indium-doped tin oxide "E-ITO" (manufactured by Mitsubishi Materials Corporation).

[0157] While "MZ-305S" (manufactured by Teika Co., Ltd.) is a specific example of zinc oxide particles, the metal oxide particles that can be used in this invention are not limited to these.

[0158] The content of metal oxide particles in the protective layer (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, per 100 parts by mass of binder resin. Furthermore, from the viewpoint of maintaining good surface resistance, it is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0159] (charge transport material) The charge transport material contained in the protective layer (outermost layer) can be the same as the charge transport material used in the photosensitive layer.

[0160] Furthermore, from the viewpoint of improving the Martens hardness of the photoreceptor surface, the protective layer (outermost layer) may contain a structure formed by polymerizing a charge transport material having chain polymerizable functional groups. Examples of chain polymerizable functional groups in charge transport materials having chain polymerizable functional groups include acryloyl groups, methacryloyl groups, vinyl groups, and epoxy groups. Among these, acryloyl groups or methacryloyl groups are preferred from the viewpoint of curability. Examples of structures of the charge transport material portion of charge transport materials having chain polymerizable functional groups include heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, and benzofuran derivatives, as well as aniline derivatives, hydrazone derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, and compounds formed by linking multiple types of these compounds, and electron-donating substances such as polymers having groups made of these compounds in the main chain or side chain. Among these, carbazole derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, and compounds formed by linking multiple types of these compounds are preferred from the viewpoint of electrical properties.

[0161] The amount of charge transport material used in the protective layer (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 30 parts by mass or more, and particularly preferably 50 parts by mass or more, per 100 parts by mass of binder resin. Furthermore, 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.

[0162] (Polymerization initiator) Polymerization initiators include thermal polymerization initiators, photopolymerization initiators, and the like.

[0163] Examples of thermal polymerization initiators include peroxide compounds such as 2,5-dimethylhexane-2,5-dihydroperoxide and azo compounds such as 2,2'-azobis(isobutyronitrile).

[0164] Photopolymerization initiators can be classified into direct cleavage type and hydrogen abstraction type based on differences in their radical generation mechanisms. Direct cleavage type photopolymerization initiators generate radicals when they absorb light energy, as some of the covalent bonds within the molecule cleave. On the other hand, hydrogen abstraction type photopolymerization initiators generate radicals when molecules, excited by absorbing light energy, abstract hydrogen from a hydrogen donor.

[0165] Examples of direct cleavage-type photopolymerization initiators include acetophenone-based or ketal-based compounds such as acetophenone, 2-benzoyl-2-propanol, 1-benzoylcyclohexanol, 2,2-diethoxyacetophenone, benzyldimethylketal, and 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, and O-tosylbenzoin; and acylphosphine oxide-based compounds such as diphenyl(2,4,6-trimethylbenzoyl)phosphone oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphone oxide, and lithiumphenyl(2,4,6-trimethylbenzoyl)phosphonate.

[0166] Examples of hydrogen abstraction type photopolymerization initiators 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, and 1,4-dibenzoylbenzene; and anthraquinone or thioxanthone compounds such as 2-ethylanthraquinone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone. Other photopolymerization initiators include camphorquinone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime, acridine compounds, triazine compounds, and imidazole compounds.

[0167] In order to efficiently absorb light energy and generate radicals, it is preferable that the photopolymerization initiator has an absorption wavelength in the wavelength range of the light source used for irradiation. On the other hand, if components other than the photopolymerization initiator among the compounds contained in the protective layer (outermost layer) have absorption in this wavelength range, the photopolymerization initiator may not be able to absorb sufficient light energy, and the radical generation efficiency may decrease. Since general binder resins, charge transport materials, and metal oxide particles have absorption wavelengths in the ultraviolet (UV) region, this effect is particularly pronounced when the light source used for irradiation is ultraviolet (UV) light. From the viewpoint of preventing such problems, it is preferable to include an acylphosphine oxide compound, which has an absorption wavelength on the relatively long wavelength side among photopolymerization initiators. Furthermore, acylphosphine oxide compounds are also preferable because they have a photobleaching effect in which the absorption wavelength range changes to the low wavelength side due to self-cleavage, allowing light to penetrate to the interior of the protective layer (outermost layer), resulting in good internal curing properties. In this case, it is even more preferable to use a hydrogen abstraction type initiator in combination from the viewpoint of supplementing the curing properties of the surface of the protective layer (outermost layer). The proportion of hydrogen abstraction initiator to the acylphosphine oxide compound is not particularly limited, but from the viewpoint of compensating for surface hardening properties, it is preferable to have 0.1 parts by mass or more per 1 part by mass of the acylphosphine oxide compound, and from the viewpoint of maintaining internal hardening properties, it is preferable to have 5 parts by mass or less.

[0168] Furthermore, substances that have a photopolymerization promoting effect can be used alone or in combination with the above-mentioned photopolymerization initiators. Examples include triethanolamine, methyldiethanolamine, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, and 4,4'-dimethylaminobenzophenone.

[0169] These polymerization initiators may be used individually 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, per 100 parts by mass of the total radical polymerizable material.

[0170] (Method for forming the protective layer (outermost layer)) Next, we will explain the method for forming the protective layer (outermost layer). The method for forming the above-mentioned protective layer (outermost layer) is not particularly limited. For example, it can be formed by applying a coating solution in which a binder resin, charge transport material, metal oxide particles, and other substances are dissolved in a solvent or dispersed in a dispersion medium.

[0171] The solvent or dispersion medium used for forming the protective layer (outermost layer), and the application method will be described below.

[0172] [Solvent used in coating solutions for forming a protective layer (outermost layer)] Any organic solvent capable of dissolving the substance according to the present invention can be used as the coating solution for forming the protective layer (outermost layer) of the present invention. Specifically, examples include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; esters such as methyl formate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, 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. Any combination and proportion of these mixed solvents can be used. Furthermore, even organic solvents that do not dissolve the protective layer (outermost layer) material according to the present invention on their own can be used if they become soluble when mixed with, for example, the above-mentioned organic solvents. Generally, using a mixed solvent can reduce uneven coating. When using the immersion 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 include alcohols that have low solubility in polycarbonate and polyarylate, which are suitably used in the photosensitive layer.

[0173] The ratio of organic solvent to solid content used in the protective layer (outermost layer) forming coating solution of the present invention varies depending on the application method of the protective layer (outermost layer) forming coating solution, and should be appropriately changed to ensure that a uniform coating film is formed in the application method.

[0174] [Application Method] The method of applying the coating solution to form the protective layer (outermost layer) is not particularly limited, and examples include spray coating, spiral coating, ring coating, and immersion coating.

[0175] After forming the coating film using the above coating method, the coating film is dried. At this time, the temperature and time of drying are not specified as long as the necessary and sufficient drying is achieved. However, if the protective layer (outermost layer) is applied by air drying only after the photosensitive layer has been applied, it is preferable to perform sufficient drying using the method described in the [coating method] for the photosensitive layer above.

[0176] The thickness of the protective layer (outermost layer) is selected as optimally as appropriate depending on the materials used. From the viewpoint of lifespan, 0.1 μm or more is preferred, 0.2 μm or more is more preferred, and 0.5 μm or more is particularly preferred. From the viewpoint of electrical properties, 10 μm or less is preferred, 5 μm or less is more preferred, and 3 μm or less is particularly preferred.

[0177] [Method for curing the protective layer (outermost layer)] The protective layer (outermost layer) is formed by applying the coating liquid and then curing it by applying energy from an external source. The external energy used at this time can be heat, light, or radiation. Thermal energy can be applied by heating from either the coated surface or the support side using gases such as air or nitrogen, steam, various heat transfer fluids, infrared rays, or electromagnetic waves. The heating temperature is preferably between 100°C and 170°C. Above the lower limit, a sufficient reaction rate is achieved, and the reaction proceeds completely. Below the upper limit, the reaction proceeds uniformly, and the occurrence of large strains in the protective layer (outermost layer) can be suppressed. To ensure a uniform curing reaction, it is also effective to heat at a relatively low temperature below 100°C, and then further heat to above 100°C to complete the reaction.

[0178] For light energy, UV irradiation light sources such as high-pressure mercury lamps, metal halide lamps, electrodeless lamp bulbs, and light-emitting diodes, which emit light at wavelengths primarily in the ultraviolet (UV) range, can be used. Furthermore, it is possible to select a visible light light source that matches the absorption wavelength of the chain polymerization compound or photopolymerization initiator. The light irradiation dose (cumulative light dose) is 0.1 J / cm² from the perspective of curing properties. 2 The above is preferable, 0.5 J / cm 2 The above is even more preferable, 1 J / cm 2 The above is particularly preferable. Also, from the viewpoint of electrical characteristics, 150 J / cm² is preferable. 2 The following is preferable: 100 J / cm² 2 The following is even more preferable: 50 J / cm 2 The following are particularly preferable. One example of radiation energy is the use of electron beams (EB).

[0179] Among these energy sources, light energy is preferred from the viewpoint of ease of reaction rate control, simplicity of apparatus, and long pot life.

[0180] After the protective layer (outermost layer) has hardened, a heating step may be added from the viewpoint of relieving residual stress, relieving residual radicals, and improving 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.

[0181] [Martens hardness] As described above, the first, second, and third embodiments of the present invention suppress the concentration of hole transport materials and electron transport materials on the surface of the photosensitive layer by setting the molecular weight, amount of substance (moles), or ratio of molecular weights of hole transport materials and electron transport materials in the photosensitive layer in contact with the protective layer (outermost layer), for example, a single-layer photosensitive layer, to a specific range. As a result, the decrease in the Martens hardness of the photoreceptor surface can be suppressed.

[0182] The Martens hardness of the photoreceptor surface is 300 N / mm², from the viewpoint of wear resistance. 2 The above is preferable, 350 N / mm 2 The above is more preferable, 400 N / mm 2 The above is even more preferable. The Martens hardness of the photoreceptor surface should be 600 N / mm² from the viewpoint of suppressing residual stress and crack formation. 2 The following is preferable: 450 N / mm2 The following are preferable. In this invention, the Martens hardness of the photoreceptor refers to the Martens hardness measured from the surface side of the photoreceptor. The aforementioned Martens hardness can be measured by the method described in the examples below.

[0183] [elastic deformation rate] As described above, the first, second, and third embodiments of the present invention suppress the concentration of hole transport materials and electron transport materials on the surface of the photosensitive layer by setting the molecular weight, amount of substance (moles), or ratio of molecular weights of hole transport materials and electron transport materials in the photosensitive layer in contact with the protective layer (outermost layer), for example, a single-layer photosensitive layer, to a specific range. As a result, a decrease in the elastic deformation rate of the photoreceptor surface can be suppressed.

[0184] From the viewpoint of wear resistance, the elastic deformation rate of the photoreceptor surface is preferably 30% or more, more preferably 35% or more, and even more preferably 40% or more. From the viewpoint of suppressing residual stress and crack formation, the elastic deformation rate of the photoreceptor surface is preferably 60% or less, and more preferably 55% or less. In this invention, the elastic deformation rate of the photoreceptor refers to the elastic deformation rate measured from the surface side of the photoreceptor. The aforementioned elastic deformation rate can be measured by the method described in the embodiments below.

[0185] <Underlayer> The electrophotographic photoreceptor of the present invention may have an undercoat between the photosensitive layer and the conductive support.

[0186] For the undercoat layer, for example, a resin, or a resin in which particles such as organic pigments or metal oxides are dispersed, can be used. Examples of organic pigments used in the undercoat include phthalocyanine pigments, azo pigments, and perylene pigments. Among these, phthalocyanine pigments and azo pigments, specifically those used as charge-generating materials as mentioned above, are noteworthy.

[0187] Examples of metal oxide particles used in the undercoat include metal oxide particles containing one metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, and zinc oxide, and metal oxide particles containing multiple metal elements such as strontium titanate. The undercoat may use only one type of particle, or it may be a mixture of multiple types of particles in any ratio and combination.

[0188] Among the metal oxide particles mentioned above, titanium oxide and aluminum oxide are preferred, with titanium oxide being particularly preferred. The titanium oxide particles may have their surfaces treated with inorganic or organic materials, for example. Furthermore, any of the following crystalline forms of titanium oxide particles can be used: rutile, anatase, brookite, or amorphous. Multiple crystalline states may also be included.

[0189] The particle size of the metal oxide particles used in the undercoat is not particularly limited. From the standpoint of the properties of the undercoat and the stability of the solution for forming the undercoat, the average primary particle size is preferably 10 nm or more, and more preferably 100 nm or less, and more preferably 50 nm or less.

[0190] In this case, it is desirable to form the undercoat layer by dispersing particles in the binder resin. As the binder resin used for the undercoat, for example, polyvinyl butyral resin, polyvinyl formal resin, polyvinyl acetal resin, polyarylate resin, polycarbonate resin, polyester resin, modified ether polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyvinylpyridine resin, cellulose resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin, polyvinylpyrrolidone resin, casein, or insulating resins such as vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, and silicone-alkyd resin, or organic photoconductive polymers such as poly-N-vinylcarbazole can be selected and used, but the polymers are not limited to these. Furthermore, these binder resins may be used individually, mixed in combination of two or more types, or used in a cured form with a curing agent. Among these, polyvinyl butyral resin, polyvinyl formal resin, polyvinyl acetal resin, alcohol-soluble copolymer polyamides, and modified polyamides are preferred because they exhibit good dispersibility and coatability.

[0191] The mixing ratio of particles to the binder resin can be arbitrarily selected. Using a ratio in the range of 10% to 500% by mass is preferable in terms of dispersion stability and coatability. The film thickness of the undercoat can also be arbitrarily selected, but it is generally preferable to have a thickness of 0.1 μm or more and 20 μm or less, considering the characteristics of the electrophotographic photoreceptor and the coatability of the dispersion. The undercoat may also contain known antioxidants, etc.

[0192] <Other layers> Furthermore, in addition to the conductive support, photosensitive layer, protective layer (outermost layer), and undercoat layer described above, the electrophotographic photoreceptor of the present invention may have other layers as needed.

[0193] <Explanation of terms> In this invention, when expressed as "X~Y" (where X and Y are any numbers), unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as the meaning of "preferably greater than X" or "preferably less than Y." Furthermore, when we use expressions like "greater than or equal to X" (where X is any number) or "less than or equal to Y" (where Y is any number), we also imply that "greater than X is preferable" or "less than Y is preferable." [Examples]

[0194] Embodiments of the present invention will be described in more detail below with reference to examples. However, the following examples are provided to illustrate the present invention in detail, and the present invention is not limited to the examples shown below, and can be modified and implemented as desired, without departing from the spirit of the invention. In addition, in the following examples and comparative examples, the term "parts" refers to "parts by mass" unless otherwise specified.

[0195] [Example 1] <Fabrication of the photoreceptor> The photoreceptor was prepared using the following procedure.

[0196] (Formation of the underlayer) Powder X-ray diffraction using CuKα rays showed a clear peak at a diffraction angle of 2θ±0.2° at 27.3°. 20 parts of D-type titanyl phthalocyanine and 280 parts of 1,2-dimethoxyethane were mixed and ground in a sand grind mill for 2 hours to perform micronization and dispersion. Further, 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 to prepare a coating solution for the undercoat layer. This coating solution was applied to a 0.3 mm thick aluminum plate using a wire bar to achieve a film thickness of 0.4 μm after drying, and then air-dried to form the undercoat layer.

[0197] (Formation of a single-layer photosensitive layer) Powder X-ray diffraction using CuKα rays showed a clear peak at a diffraction angle of 2θ±0.2° at 27.3°. 2.6 parts of D-type titanyl phthalocyanine, 1.3 parts of perylene pigment 1 with the structure shown below, 60 parts of the hole transporter (HTM48, molecular weight 748), 50 parts of the electron transporter (ET-2, molecular weight 424.2), 100 parts of the binder resin 1, and 0.05 parts of silicone oil (Shin-Etsu Silicone Co., Ltd.: product name KF-96) as a leveling agent were mixed with 974 parts of a mixed solvent of tetrahydrofuran (hereinafter abbreviated as THF as appropriate) and toluene (hereinafter abbreviated as TL as appropriate) (80% THF by mass, 20% TL by mass) to prepare a coating solution for a single-layer photosensitive layer. This coating solution was applied to the above undercoat layer using a bar coater so that the film thickness after drying would be approximately 20 μm, and dried at 100°C for 20 minutes to form a single-layer photosensitive layer.

[0198] TIFF0007852506000018.tif45170

[0199] TIFF0007852506000019.tif63170

[0200] TIFF0007852506000020.tif81170

[0201] (Formation of a protective layer (outermost layer)) A protective layer (outermost layer) coating solution was prepared by mixing 100 parts of urethane acrylate UV6300B (Mitsubishi Chemical Corporation), 55 parts of titanium dioxide particles surface-treated with 7% by mass of 3-methacryloyloxypropyltrimethoxysilane (TTO55N, Ishihara Sangyo Co., Ltd.), 1 part of benzophenone and 2 parts of diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide as photopolymerization initiators, and 745 parts of a mixed solvent of methanol, 1-propanol, and toluene (70% by mass methanol, 10% by mass 1-propanol, 20% by mass toluene). This coating solution was applied to the above-mentioned single-layer photosensitive layer using a wire bar so that the film thickness after curing would be 1 μm, and heated at 115°C for 20 minutes. From the surface side of this coating film, a UV light irradiation device equipped with a UV-LED lamp with a peak at a wavelength of 385 nm was used to irradiate the film with an integrated light intensity of 25.5 J / cm².2 UV light was irradiated to achieve the desired result. Furthermore, after heating at 125°C for 10 minutes, it was allowed to cool to 25°C to form a protective layer (outermost layer).

[0202] [Examples 2-5, Comparative Examples 1-4] Table 1 shows the hole transport material and electron transport material used in the single-layer photosensitive layer, their content, and the compound having a chain-polymerizable functional group used in the protective layer (outermost layer). The structure of each compound used is shown below. Photoreceptors for Examples 2-5 and Comparative Examples 1-4 were prepared using the same procedure as in Example 1.

[0203] TIFF0007852506000021.tif54170

[0204] TIFF0007852506000022.tif47170

[0205] TIFF0007852506000023.tif42170

[0206] TIFF0007852506000024.tif40170

[0207] TIFF0007852506000025.tif43170

[0208] TIFF0007852506000026.tif44170

[0209] TIFF0007852506000027.tif39170

[0210] TIFF0007852506000028.tif41170

[0211] <Martens hardness and elastic deformation rate of the photoreceptor surface> The Martens hardness and elastic deformation rate of the photoreceptor surface were measured using a Fischer Microhardness Tester FISCHERSCOPEHM2000 under conditions of 25°C and 50% relative humidity. A Vickers square pyramidal diamond indenter with a face-to-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 and X axes, respectively, to obtain the profile shown in Figure 1. Applying a load to the indenter transitions it from A to B in Figure 1, and removing the load transitions it from B to C in Figure 1. The results are shown in Table 1. • Measurement conditions Maximum pushing load 0.2mN Load time 10 seconds Required time for unloading: 10 seconds

[0212] The Martens hardness is a value defined by the following formula, based on the indentation depth at that time. Martens hardness (N / mm 2 ) = Test load (N) / Surface area of ​​Vickers indenter under test load (mm²) 2 ) The elastic deformation rate is a value defined by the following formula, and represents the ratio of the work done by the membrane elastically during unloading to the total work required for indentation. Elastic deformation rate (%) = (We / Wt) × 100

[0213] In the above formula, the total work Wt (nJ) represents the area enclosed by ABDA in Figure 1, and the work of elastic deformation We (nJ) represents the area enclosed by CBDC. The larger the elastic deformation rate, the less residual deformation remains under load, and an elastic deformation rate of 100 means that no deformation remains.

[0214] <Adhesion Test> On the single-layer photoreceptors prepared in the examples and comparative examples, six vertical and six horizontal cuts were made at 2 mm intervals using an NT cutter (manufactured by NT Corporation) to create 25 5x5 grids. Cellophane tape (manufactured by 3M Corporation) was then tightly applied over these grids, and the adhesion between the photosensitive layer and the protective layer (outermost layer) was tested by pulling the tape up at a 90° angle to the adhesive surface. The percentage of squares of the protective layer (outermost layer) remaining on the photosensitive layer was evaluated as the retention rate (%). A higher number of remaining squares indicates a higher retention rate and better adhesion. In all tests, no delamination was observed between the aluminum plate support and the photosensitive layer; if delamination occurred, it occurred near the interface between the photosensitive layer and the protective layer (outermost layer). The results are shown in Table 1.

[0215] [Table 1]

[0216] <Measurement results> Comparative Examples 1 and 2 showed significantly low adhesion. This is thought to be because the small molecular weight of the hole transport material (HTM) used in Comparative Examples 1 and 2 caused the HTM to concentrate on the surface, resulting in steric hindrance and inhibiting the entanglement between the outermost cured film and the binder resin of the photosensitive layer. On the other hand, Comparative Examples 3 and 4 showed significantly lower Martens hardness and elastic deformation rates in the protective layer (outermost layer), confirming that curing had not progressed sufficiently. This is thought to be because the electron transport material (ETM) used in Comparative Examples 3 and 4 had a small molecular weight, causing the electron transport material (ETM) to concentrate on the protective layer (outermost layer) side and further migrate to the protective layer (outermost layer), thereby inhibiting the curing reaction in the protective layer (outermost layer).

[0217] Compared to Comparative Examples 1 to 4, Examples 1 to 5 exhibited high Martens hardness, high elastic deformation rate, and excellent adhesion between the photosensitive layer and the protective layer (outermost layer). This is thought to be because the molecular weight a of the hole transport material (HTM) and the molecular weight b of the electron transport material (ETM) in the photosensitive layer were both within the specified range, satisfying the following formulas (1) and (2). 600 ≤ a (1) 400 ≤ b (2) (In formula (1), a is the molecular weight of the hole transporter. In formula (2), b is the molecular weight of the electron transporter.)

[0218] Therefore, it can be considered that an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer (outermost layer) on a conductive support, wherein the protective layer (outermost layer) contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, and the photosensitive layer in contact with the protective layer (outermost layer) contains a hole transport material satisfying formula (1) and an electron transport material satisfying formula (2), can be made to have a high Martens hardness, a high elastic deformation rate, and excellent adhesion between the photosensitive layer and the protective layer (outermost layer).

[0219] Furthermore, from the results of the above examples and comparative examples, as well as from the test results conducted by the inventors to date, it has been found that when the ratio of the amount of substance (mol) of hole transporting material to the amount of substance (mol) of electron transporting material contained in the photosensitive layer is within an appropriate range, the concentration of the hole transporting material and the concentration of the electron transporting material are suppressed in a balanced manner, resulting in further improvements in the Martens hardness, the elastic deformation rate, and the adhesion. This is thought to be because, when both hole transporting material and electron transporting material are contained in the photosensitive layer, electron transfer occurs from the hole transporting material to the electron transporting material, resulting in the formation of a charge transfer complex between the positively charged hole transporting material and the negatively charged electron transporting material. Since an electrostatic attraction acts between the hole transporting material and the electron transporting material that form the charge transfer complex, it is thought that this has the effect of suppressing the concentration of both on the photosensitive surface. 1.20 ≤ (B / b) / (A / a) ≤ 1.60 (5) (In formula (5), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), a is the molecular weight of the hole transport substance, B is the content of the electron transport substance per 100 units of binder resin (parts by mass), and b is the molecular weight of the electron transport substance.)

[0220] Therefore, it can be considered that an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer (outermost layer) on a conductive support, wherein the protective layer (outermost layer) contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, the photosensitive layer in contact with the protective layer (outermost layer) contains at least a binder resin, a hole transporter, and an electron transporter, and the photosensitive layer in contact with the protective layer (outermost layer) satisfies the above formula (5), can be made to have an electrophotographic photoreceptor with high Martens hardness, high elastic deformation rate, and excellent adhesion between the photosensitive layer and the protective layer (outermost layer).

[0221] Furthermore, from the results of the above examples and comparative examples, as well as from the test results conducted by the inventors to date, it has been found that when the ratio of the molecular weight a of the hole transporting material to the molecular weight b of the electron transporting material contained in the photosensitive layer (a / b) is 1.40 or more and 1.90 or less, the concentration of the hole transporting material and the concentration of the electron transporting material are suppressed in a balanced manner, and the Martens hardness, the elastic deformation rate, and the adhesiveness are further improved. This is thought to be because when a / b is 1.40 or more, the migration of the hole transporting material to the surface of the photosensitive layer is reduced, and consequently the movement of the electron transporting material to the surface of the photosensitive layer is also inhibited, resulting in a low migration of the electron transporting material to the surface of the photosensitive layer. On the other hand, when a / b is 1.90 or less, the migration of the electron transporting material to the surface of the photosensitive layer is reduced, and consequently the movement of the hole transporting material to the surface of the photosensitive layer is also inhibited, resulting in a low migration of the hole transporting material to the surface of the photosensitive layer. Therefore, it can be considered that an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer (outermost layer) on a conductive support, wherein the protective layer (outermost layer) contains a structure formed by polymerizing a compound having a chain polymerizable functional group, the photosensitive layer in contact with the protective layer (outermost layer) contains at least a hole transporter and an electron transporter, and the ratio of the molecular weight a of the hole transporter to the molecular weight b of the electron transporter (a / b) is 1.40 or more and 1.90 or less, can be made to have an electrophotographic photoreceptor with high Martens hardness, high elastic deformation rate, and excellent adhesion between the photosensitive layer and the protective layer (outermost layer).

[0222] Furthermore, from the test results conducted by the inventors to date, as well as the results of the above examples and comparative examples, it has been found that, from the viewpoint of further improving the adhesion between the photosensitive layer and the protective layer (outermost layer), the hole transport material is preferably a structure having a substituent at least one ortho position of at least one aromatic group bonded to a nitrogen (N) atom, and among these, a structure having substituents at both ortho positions of at least one aromatic group bonded to a nitrogen (N) atom is even more preferable. For example, looking at the above examples, the hole transporters (HTM48 and HTM42) used in Examples 1 and 3, respectively, have substituents at one ortho position of the aromatic group bonded to the nitrogen (N) atom. On the other hand, the hole transporters (HTM40 and HTM43) used in Examples 2 and 4, respectively, have substituents at two ortho positions of one aromatic group bonded to the nitrogen (N) atom, and show even better adhesion. This is thought to be because the aromatic group with substituents at two ortho positions exhibits stronger steric repulsion with respect to the other substituents bonded to the N atom, resulting in a stereochemistry that is rotated relative to the plane formed by the N atom and the other substituents bonded to the N atom. Furthermore, it is thought that the aromatic group with a rotated stereochemistry exhibits an anchoring effect with respect to the binder resin, thereby suppressing the concentration of the hole transporter on the photosensitive layer surface.

[0223] Although the photoreceptors in the above embodiments are all positively charged single-layer electrophotographic photoreceptors, as mentioned above, the problems of the present invention can be solved by improving the configuration of the photoreceptor layer in contact with the protective layer (outermost layer). Therefore, it can be understood that even photoreceptors other than positively charged single-layer electrophotographic photoreceptors can solve the same problems as in the embodiments, as long as they have such a configuration.

Claims

1. An electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, The protective layer contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, The photosensitive layer in contact with the protective layer satisfies the following formulas (4) and (5), and contains a binder resin, a hole transport material satisfying the following formula (1), and an electron transport material satisfying the following formula (2). The ratio (a / b) of the molecular weight a of the hole transport material to the molecular weight b of the electron transport material is 1.40 or more and 1.90 or less. The hole transport material includes a structure having a substituent at the ortho position of at least one aromatic group bonded to a nitrogen (N) atom, The electron transport material is a compound represented by the following formula (6): An electrophotographic photoreceptor characterized in that the compound represented by formula (6) is a compound represented by the following formula (7) or (8). 600 ≦ a ≦ 1200 (1) 400≦b≦1000 (2) (In formula (1), a is the molecular weight of the hole transporter. In formula (2), b is the molecular weight of the electron transporter. However, if two or more electron transporters are included, b is the molecular weight of the electron transporter with the largest content (parts by mass) in the photosensitive layer among the two or more electron transporters.) 0.80 ≤ A / B ≤ 3.00 (4) (In formula (4), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), and B is the content of the electron transport substance per 100 units of binder resin (parts by mass).) 1.20≦(B / b) / (A / a)≦1.60 (5) (In formula (5), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), a is the molecular weight of the hole transport substance, B is the content of the electron transport substance per 100 units of binder resin (parts by mass), and b is the molecular weight of the electron transport substance.) (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, R ６１ and R ６２ Fellow, or R ６３ and R ６４ These elements may bond to each other to form a cyclic structure. (X represents an organic residue with a molecular weight of 120 to 250.) (In formula (7), R ７１ ~R ７３ Each of these independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms. (In formula (8), R ８１ to R ８４ each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.)

2. An electrophotographic photoreceptor having at least a photosensitive layer and an outermost layer on a conductive support, The outermost layer contains a structure formed by polymerizing a compound having a chain-polymerizable functional group, The photosensitive layer in contact with the outermost layer satisfies the following formulas (4) and (5), and contains a binder resin, a hole transport material that satisfies the following formula (1), and an electron transport material that satisfies the following formula (2). The ratio (a / b) of the molecular weight a of the hole transport material to the molecular weight b of the electron transport material is 1.40 or more and 1.90 or less. The hole transport material includes a structure having a substituent at the ortho position of at least one aromatic group bonded to a nitrogen (N) atom, The electron transport material is a compound represented by the following formula (6): An electrophotographic photoreceptor characterized in that the compound represented by formula (6) is a compound represented by the following formula (7) or (8). 600 ≦ a ≦ 1200 (1) 400≦b≦1000 (2) (In formula (1), a is the molecular weight of the hole transporter. In formula (2), b is the molecular weight of the electron transporter. However, if two or more electron transporters are included, b is the molecular weight of the electron transporter with the largest content (parts by mass) in the photosensitive layer among the two or more electron transporters.) 0.80≦A / B≦3.00 (4) (In formula (4), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), and B is the content of the electron transport substance per 100 units of binder resin (parts by mass).) 1.20≦(B / b) / (A / a)≦1.60 (5) (In formula (5), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), a is the molecular weight of the hole transport substance, B is the content of the electron transport substance per 100 units of binder resin (parts by mass), and b is the molecular weight of the electron transport substance.) (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, R ６１ and R ６２ Fellow, or R ６３ and R ６４ These elements may bond to each other to form a cyclic structure. (X represents an organic residue with a molecular weight of 120 to 250.) (In formula (7), R ７１ ~R ７３ Each of these independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms. (In formula (8), R ８１ ~R ８４ Each of these independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.

3. The electrophotographic photoreceptor according to claim 1 or 2, characterized in that the photosensitive layer in contact with the outermost layer or the protective layer is a single layer containing at least a binder resin, a charge generating substance, a hole transporting substance, and an electron transporting substance.

4. The electrophotographic photoreceptor according to any one of claims 1 to 3, characterized in that the value of A is 60.

5. The electrophotographic photoreceptor according to any one of claims 1 to 4, characterized in that the value of B is 50.

6. The electrophotographic photoreceptor according to any one of claims 1 to 5, characterized in that the photosensitive layer satisfies the following formula (3). 0.15≦(A / a)+(B / b) (3) (In formula (3), A is the content of the hole transport substance per 100 units of binder resin (parts by mass), a is the molecular weight of the hole transport substance, B is the content of the electron transport substance per 100 units of binder resin (parts by mass), and b is the molecular weight of the electron transport substance.)

7. An electrophotographic photoreceptor according to any one of claims 1 to 6, characterized in that it is positively charged.

8. The electrophotographic photoreceptor according to any one of claims 1 to 7, characterized in that the outermost layer or the protective layer contains a structure obtained by radical polymerization of a compound having a chain polymerizable functional group.

9. The electrophotographic photoreceptor according to any one of claims 1 to 8, characterized in that the outermost layer or the protective layer contains metal oxide fine particles.

10. The electrophotographic photoreceptor according to claim 9, characterized in that the metal oxide fine particles are surface-treated with a surface treatment agent having polymerizable functional groups.

11. The electrophotographic photoreceptor according to any one of claims 1 to 10, characterized in that the compound having the chain polymerizable functional group is a urethane acrylate.

12. The photosensitive layer in contact with the protective layer contains at least a binder resin, a hole transport material, and an electron transport material. The electrophotographic photoreceptor according to claim 1, characterized in that the electron transport material is at least one compound from among the compounds represented by the following formula.

13. The electrophotographic photoreceptor according to any one of claims 1 to 12, wherein, in the photosensitive layer, there are two or more types of hole transporting materials, and the molecular weight of the hole transporting material with the largest content (parts by mass) in the photosensitive layer satisfies formula (1).

14. An electrophotographic photoreceptor cartridge having an electrophotographic photoreceptor according to any one of claims 1 to 13.

15. An image forming apparatus having an electrophotographic photoreceptor according to any one of claims 1 to 13.

Images