Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge, and image forming apparatus

Abstract

Provided is an image formation device that makes it possible to print without causing problems relating to ease of electrification, leak resistance, gas resistance, and wear resistance despite said image formation device being a contact charging-type device. Also provided are an electrophotographic photoreceptor provided to the image formation device and an electrophotographic photoreceptor cartridge.　The problem described above is solved by a contact charging-type image formation device comprising a positively charged electrophotographic receptor that has a monolayer-type photosensitive layer and an outermost layer containing a cured product obtained by curing a curable compound.

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic photoreceptor, an electrophotographic photoreceptor cartridge, and an image forming apparatus having a hardened protective layer as the outermost layer, and more particularly to a so-called single-layer electrophotographic photoreceptor, an electrophotographic photoreceptor cartridge, and an image forming apparatus in which the surface of the photoreceptor is positively charged by a contact charger that involves a discharge phenomenon. [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] In organic electrophotographic photoreceptors, from the viewpoint of layer structure, there are known single-layer electrophotographic photoreceptors (hereinafter referred to as single-layer photoreceptors) that have charge generating material and charge transport material in the same layer, and multilayer electrophotographic photoreceptors (hereinafter referred to as multilayer photoreceptors) that separate and stack charge generating material and charge transport material in separate layers (charge generating layer and charge transport layer).

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

[0005] On the other hand, in single-layer photoreceptors, both negative and positive charging methods are theoretically usable, but the positive charging method is advantageous because it can suppress ozone generation, which is a problem in the aforementioned multilayer photoreceptors, and is generally easier to achieve high sensitivity than the negative charging system. Furthermore, positively charged single-layer photoreceptors have the advantage of fewer coating steps and are advantageous in terms of resolution, and although they are inferior to negatively charged multilayer photoreceptors in terms of electrical characteristics, they have been partially put into practical use, and various improvements have been considered to date (Patent Documents 1-5). Generally, when charging a photoreceptor, the photoreceptor is charged to the desired surface potential by rotating it multiple times after applying a voltage to the charging roller, but in the case of positively charged single-layer photoreceptors, for example, there is a problem that charging is not easily performed because hole transport material and electron transport material tend to seep out onto the photoreceptor surface, so-called bleed-out. In other words, some of the charge on the photoreceptor surface is lost from the surface due to the influence of the bleed-out component, which increases the number of rotations required to bring the photoreceptor surface to the desired charging potential. This problem of impaired chargeability is known, and studies are underway to suppress it by adding specific additives (Patent Document 6).

[0006] Furthermore, in recent years, in image forming apparatuses, roller charging methods, which generate less oxidizing gases such as ozone, have been preferred over charging methods such as Corotron and Scorotron, from the perspective of minimizing environmental impact, as a means of charging the photoreceptor. Among roller charging methods, contact roller charging methods are known to suppress the generation of the aforementioned gases even more effectively (Patent Document 7). [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 5-92936 [Patent Document 2] Japanese Patent Application Publication No. 2-228670 [Patent Document 3] Japanese Patent Publication No. 2001-33997 [Patent Document 4] Japanese Patent Publication No. 2005-331965 [Patent Document 5] Japanese Patent Publication No. 2013-231866 [Patent Document 6] International Publication No. 2017 / 170615 [Patent Document 7] Japanese Patent Publication No. 2012-14142 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, applying a positively charged single-layer photoreceptor to a contact roller charging type image forming apparatus was desirable because it could reduce ozone generation as much as possible and minimize environmental impact. However, there were many challenges to practical implementation for the following reasons.

[0009] As mentioned above, in positively charged single-layer photoreceptors, the ease of charging is impaired because the hole transport material and electron transport material tend to seep out onto the photoreceptor surface, requiring the addition of specific additives. However, adding additives not only increases costs but also carries the risk of impairing wear resistance due to the addition of additives that are generally low molecular weight components.

[0010] Furthermore, when the photosensitive layer is a single layer or contains charge-generating material in the photosensitive layer in contact with the outermost layer (for example, an inverted stacked photosensitive layer where the charge transport layer and charge-generating layer are stacked in that order), the charge-generating material forms aggregates and is exposed on the surface of the photoreceptor. In particular, in the case of contact roller charging, the electric field concentrates locally on the large protrusions of the aggregates of charge-generating material, and as a result of overcurrent flowing in those areas, dielectric breakdown of the photosensitive layer is likely to occur. In other words, pinhole-shaped leakage defects are likely to occur on the surface of the photoreceptor, which is significantly disadvantageous in terms of leakage resistance. When pinhole-shaped leakage defects occur on the surface of the photoreceptor, overcurrent flows through the defects, causing a voltage drop in the power supply and resulting in band-shaped charging defects across the entire contact width of the charger. Moreover, if gases such as ozone penetrate from the surface of the photoreceptor, the charge-generating material near the surface is susceptible to influence due to its single-layer structure, which is another disadvantage.

[0011] As mentioned above, the deterioration of charging ease due to bleed-out is not a problem for photoreceptors used with a negatively charged surface. Furthermore, the leakage problem and poor gas resistance caused by the presence and exposure of charge-generating material near the surface were not issues when using a typical sequentially laminated photoreceptor in which the charge-generating layer and charge-transport layer are stacked in that order.

[0012] This invention has been made in view of the above-mentioned problems. Specifically, the object of this invention is to provide an image forming apparatus that does not cause the above-mentioned problems, and an electrophotographic photoreceptor or electrophotographic photoreceptor cartridge to be provided in the image forming apparatus. [Means for solving the problem]

[0013] The present inventors have found that the above problems can be solved by providing a positively charged electrophotographic photoreceptor having a contact charging method, particularly a contact roller charging method, in an image forming apparatus, which comprises a single-layer photosensitive layer and a surface layer containing a cured product obtained by curing a curable compound, such as a photocurable compound. In other words, the gist of the present invention is as follows.

[0014] <1> An image forming apparatus comprising at least an electrophotographic photoreceptor, wherein the charging method of the image forming apparatus is a contact charging method, and the electrophotographic photoreceptor is a positively charged electrophotographic photoreceptor having a single-layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material and an electron transport material, and a top layer containing a cured product formed by the curing of a curable compound.

[0015] <2> The curable compound is characterized in that it is a photocurable compound. <1> The image forming apparatus described above.

[0016] <3> The charging method of the image forming apparatus is a contact roller charging method. <1> or <2> The image forming apparatus described above.

[0017] <4> An image forming apparatus comprising at least an electrophotographic photoreceptor, wherein the charging method of the image forming apparatus is a contact roller charging method, and the electrophotographic photoreceptor is a positively charged electrophotographic photoreceptor having a single-layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material and an electron transport material, and a top layer containing a cured product obtained by curing a photocurable compound. <5> The outermost layer of the electrophotographic photoreceptor is characterized by containing metal oxide particles. <1> ~ <4> An image forming apparatus as described in any of the following.

[0018] <6> The content ratio (mass ratio) of the metal oxide particles to the curable compound is 0.5 or more. <5> The image forming apparatus described above.

[0019] <7> The single-layer photosensitive layer contains 30 parts by mass or more of the electron transport material with respect to 100 parts by mass of the binder resin. <1> ~ <6> An image forming apparatus as described in any of the following.

[0020] <8> The single-layer photosensitive layer contains 70 parts by mass or more of the hole transport material with respect to 100 parts by mass of the binder resin. <1> ~ <7> An image forming apparatus as described in any of the following.

[0021] <9> The single-layer photosensitive layer contains 1.0 part by mass or more of the charge generating material with respect to 100 parts by mass of the binder resin. <1> ~ <8> An image forming apparatus as described in any of the following.

[0022] <10> The thickness of the outermost layer is 0.2 μm or more and 6 μm or less. <1> ~ <9> An image forming apparatus as described in any of the following.

[0023] <11> The single-layer photosensitive layer contains tribenzylamine <1> ~ <10> An image forming apparatus as described in any of the following.

[0024] <12> The charging method of the image forming apparatus is a contact charging method that applies only a DC voltage. <1> ~ <11> An image forming apparatus as described in any of the following.

[0025] <13> An image forming method using an image forming apparatus equipped with at least an electrophotographic photoreceptor, wherein the image forming apparatus is equipped with a contact-type charging device, the electrophotographic photoreceptor has a single-layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material and an electron transport material, and an outermost layer containing a cured product formed by the curing of a curable compound, and the image forming method involves positively charging the electrophotographic photoreceptor and developing it with a developer.

[0026] <14> The curable compound is characterized in that it is a photocurable compound. <13> The image formation method described above.

[0027] <15> The image forming apparatus is a contact-type roller. <13> or <14> The method for creating a painter-monk as described above.

[0028] <16> The electrophotographic photoreceptor is charged by applying only a DC voltage. <13> ~ <15> The image formation method described in any of the following.

[0029] <17> The electrophotographic photoreceptor is charged to a potential of +600V or higher. <13> ~ <16> The image formation method described in any of the following.

[0030] <18> A positively charged electrophotographic photoreceptor used in a contact charging method, having a single-layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material, and an electron transport material, and a top layer containing a cured product formed by the curing of a curable compound.

[0031] <19> The curable compound is characterized in that it is a photocurable compound. <18> A positively charged electrophotographic photoreceptor as described above.

[0032] <20> The aforementioned contact charging method is a contact roller charging method. <18> or <19> A positively charged electrophotographic photoreceptor as described above.

[0033] <21> A positively charged electrophotographic photoreceptor used in a contact roller charging method, having a single-layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material, and an electron transport material, and a top layer containing a cured product formed by curing a photocurable compound.

[0034] <22> <18> ~ <21> An electrophotographic photoreceptor cartridge characterized by comprising an electrophotographic photoreceptor as described in any of the above, and at least one of the following: a charging unit for charging the electrophotographic photoreceptor, an exposure unit for exposing the charged electrophotographic photoreceptor to light to form an electrostatic latent image, a developing unit for developing the electrostatic latent image formed on the electrophotographic photoreceptor, and a cleaning unit for cleaning the electrophotographic photoreceptor.

[0035] <23> <18> ~ <21> An image forming apparatus comprising an electrophotographic photoreceptor as described in any of the above, a charging unit for charging the electrophotographic photoreceptor, an exposure unit for exposing the charged electrophotographic photoreceptor to light to form an electrostatic latent image, and a developing unit for developing the electrostatic latent image formed on the electrophotographic photoreceptor.

[0036] <24> An image forming apparatus comprising at least an electrophotographic photoreceptor, wherein the charging method of the image forming apparatus is a contact charging method, and the electrophotographic photoreceptor has an outermost layer containing a cured product formed by the curing of a curable compound, and an electrophotographic photoreceptor containing a charge generating material in the photosensitive layer in contact with the outermost layer. [Effects of the Invention]

[0037] The present invention provides an image forming apparatus that can print without causing problems with ease of charging and leakage resistance, even when using a contact charging method, particularly a contact roller charging method, and an electrophotographic photoreceptor or electrophotographic photoreceptor cartridge to be provided for the image forming apparatus. [Brief explanation of the drawing]

[0038] [Figure 1] This is a schematic diagram showing the main components of one embodiment of the image forming apparatus of the present invention. [Modes for carrying out the invention]

[0039] The embodiments of the present invention will be described in detail below, but the present invention is not limited to the following description and can be modified as appropriate without departing from the spirit of the invention.

[0040] ≪Electrophotographic photoconductor≫ The configuration of the electrophotographic photoreceptor of the present invention is described below. The electrophotographic photoreceptor of the present invention may be used with a positive charge or a negative charge, but it is preferable to use it with a positive charge in order to better enjoy the effects of the present invention. Furthermore, it is preferable to have a configuration in which the outermost layer is on a single-layer photosensitive layer that is used with a positive charge.

[0041] <Conductive support> There are no particular restrictions on the conductive support, but commonly used materials include metal materials such as aluminum, aluminum alloys, stainless steel, copper, and nickel; resin materials to which conductive powders such as metal, carbon, and tin oxide have been added to impart conductivity; and resins, glass, and paper to which conductive materials such as aluminum, nickel, and ITO (indium tin oxide) have been deposited or coated on their surface. These may be used individually or in any combination and ratio of two or more types. Conductive support forms include drum-shaped, sheet-shaped, and belt-shaped supports. Furthermore, a conductive material with an appropriate resistance value may be coated onto a metal conductive support for control of conductivity and surface properties, and for defect coverage. When a metal material such as an aluminum alloy is used as the conductive support, it may be used after applying an anodic oxide coating. When an anodic oxide coating is applied, it is desirable to perform a sealing treatment by a known method.

[0042] The surface of the conductive support may be smooth, or it may be roughened by using a special cutting method or by polishing. Alternatively, it may be roughened by mixing particles of an appropriate size into the material constituting the conductive support. Furthermore, for cost reduction, it is possible to use the drawn tube as is without any cutting treatment.

[0043] <Underlayer> An undercoat layer may be provided between the conductive support and the photosensitive layer for purposes such as improving adhesion and blocking properties, and concealing surface defects of the support. The undercoat layer can be made of resin, or a resin in which particles such as metal oxides are dispersed. The undercoat layer may consist of a single layer or multiple layers.

[0044] 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, zinc oxide, and iron oxide, and metal oxide particles containing multiple metal elements such as calcium titanate, strontium titanate, and barium titanate. These may be used individually or in mixtures of multiple types. Among these metal oxide particles, titanium oxide and aluminum oxide are preferred, with titanium oxide being particularly preferred. The titanium oxide particles may have their surface treated with inorganic substances such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, and silicon oxide, or organic substances such as stearic acid, polyol, and silicon. The crystalline form of the titanium oxide particles can be rutile, anatase, brookite, or amorphous. Multiple crystalline states may also be included.

[0045] Furthermore, while various particle sizes of metal oxide particles can be used, from the viewpoint of properties and liquid stability, the average primary particle size is preferably 10 nm to 100 nm, and particularly preferably 10 nm to 50 nm. This average primary particle size can be obtained from TEM images or the like.

[0046] The undercoat layer is preferably formed by dispersing metal oxide particles in a binder resin. Examples of known binder resins used in the undercoat layer include epoxy resin, polyethylene resin, polypropylene resin, acrylic resin, methacrylic resin, polyamide resin, vinyl chloride resin, vinyl acetate resin, phenolic resin, polycarbonate resin, polyurethane resin, polyimide resin, vinylidene chloride resin, polyvinyl acetal resin, vinyl chloride-vinyl acetate copolymer, polyvinyl alcohol resin, polyurethane resin, polyacrylic resin, polyacrylamide resin, polyvinylpyrrolidone resin, polyvinylpyridine resin, water-soluble polyester resin, cellulose ester resins such as nitrocellulose, cellulose ether resin, casein, gelatin, polyglutamic acid, starch, starch acetate, aminostarch, organic zirconium compounds such as zirconium chelate compounds and zirconium alkoxide compounds, organic titanyl compounds such as titanyl chelate compounds and titanium alkoxide compounds, and silane coupling agents. These may be used individually or in any combination and ratio of two or more. It may also be used in a cured form with a curing agent. Among these, alcohol-soluble copolymer polyamides and modified polyamides are preferred because they exhibit good dispersibility and coatability.

[0047] In the single-layer photoreceptor of the present invention, the charge generation layer that generally constitutes a multilayer photoreceptor can be used as a substitute for the undercoat layer. In this case, a phthalocyanine pigment or azo pigment dispersed in a binder resin and coated is preferably used because it may have excellent electrical properties. Among these, the use of a phthalocyanine pigment (phthalocyanine compound) is more preferable from the viewpoint of electrical properties. As the binder resin, polyvinyl acetal resins are preferably used, and polyvinyl butyral resin is particularly preferred. In this case, it is preferable to mix in oxytitanium phthalocyanine, which shows a clear peak at a diffraction angle of 2θ±0.2° at 27.2° in powder X-ray diffraction using CuKα rays.

[0048] The ratio of particles to the binder resin used in the undercoat can be arbitrarily selected, but from the viewpoint of dispersion stability and coatability, it is generally preferable to use a ratio of 10% to 500% by mass relative to the binder resin.

[0049] The thickness of the undercoat layer is arbitrary as long as it does not significantly impair the effects of the present invention, but from the viewpoint of improving the electrical properties, high exposure properties, image properties, repeatability, and coating properties during manufacturing of the electrophotographic photoreceptor, it is usually 0.01 μm or more, preferably 0.1 μm or more, and usually 30 μm or less, preferably 20 μm or less. Known antioxidants and the like may be mixed into the undercoat layer. Pigment particles, resin particles, and the like may be included for the purpose of preventing image defects, etc.

[0050] <Photosensitive layer> The electrophotographic photoreceptor of the present invention comprises a photosensitive layer. Furthermore, the electrophotographic photoreceptor of the present invention contains a charge-generating material in the photosensitive layer in contact with the outermost layer. The photosensitive layer may be a single-layer photosensitive layer in which the charge generating material (CGM) and the hole transport material (HTM) are present in the same layer, or it may be a multilayer photosensitive layer separated into a charge generating layer and a charge transport layer. However, a single-layer photosensitive layer is preferred because it allows for greater enjoyment of the effects of the present invention.

[0051] <Single-layer photosensitive layer> A single-layer photosensitive layer is formed using a charge generating material, a charge transport material, and a binder resin to ensure film strength. Specifically, a coating solution is prepared by dissolving or dispersing the charge generating material, the charge transport material, and various binder resins in a solvent, and then applied to a conductive support (or the undercoat layer if one is provided) and dried. Negative charges generated when the charge generating material is exposed are transported to the surface of the photosensitive layer, and positive charges are transported to the conductive support, according to the electric field formed in the photosensitive layer.

[0052] <Charge-generating materials> Examples of charge-generating materials include inorganic photoconductive materials such as selenium and its alloys and cadmium sulfide, and organic photoconductive materials such as organic pigments. Organic photoconductive materials are preferred, and organic pigments are particularly preferred. Examples of organic pigments include phthalocyanine pigments, azo pigments, dithioketopyrrolopyrrole pigments, squalene (squallium) pigments, quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, anthanthrone pigments, and benzimidazole pigments. Among these, phthalocyanine pigments or azo pigments are particularly preferred. When organic pigments are used as charge-generating materials, they are usually used in the form of a dispersed layer in which fine particles of these organic pigments are bound with various binder resins.

[0053] When using phthalocyanine pigments as charge-generating materials, specifically, metal-free phthalocyanines, phthalocyanines coordinated with metals such as copper, indium, gallium, tin, titanium, zinc, vanadium, silicon, germanium, and aluminum, or their oxides, halides, hydroxides, and alkoxides, are used in various crystalline forms, as well as phthalocyanine dimers using oxygen atoms as bridging atoms. Particularly preferred are metal-free phthalocyanines of type X and τ, which have highly sensitive crystalline forms, titanyl phthalocyanines (also known as oxytitanium phthalocyanine) of type A (also known as type β), type B (also known as type α), and type D (also known as type Y), vanadyl phthalocyanine, chloroindium phthalocyanine, hydroxyindium phthalocyanine, chlorogallium phthalocyanine of type II, hydroxygallium phthalocyanine of type V, μ-oxo-gallium phthalocyanine dimers of type G and type I, and μ-oxo-aluminum phthalocyanine dimers of type II.

[0054] Furthermore, among these phthalocyanines, X-type metal-free phthalocyanine, A-type (also known as β-type), B-type (also known as α-type), D-type (Y-type) titanyl phthalocyanine characterized by a clear peak at a diffraction angle 2θ (±0.2°) of 27.1° or 27.3° in powder X-ray diffraction, II-type chlorogallium phthalocyanine, V-type, and hydroxygallium phthalocyanine characterized by having the strongest peak at 28.1°, having no peak at 26.2° but a clear peak at 28.1°, and having a full width at half maximum W at 25.9° of 0.1°≦W≦0.4°, and G-type μ-oxo-gallium phthalocyanine dimer are particularly preferred.

[0055] The phthalocyanine compound may be a single compound, or a mixture of several compounds or a mixed crystal state. The phthalocyanine compound or the mixed state in the crystalline state may be one in which the constituent elements are mixed afterward, or one in which a mixed state is created during the manufacturing or processing steps of the phthalocyanine compound, such as synthesis, pigmentation, or crystallization. Known such processing methods include acid paste treatment, grinding treatment, and solvent treatment. To create a mixed crystal state, as described in Japanese Patent Publication No. 10-48859, one method is to mix two types of crystals, mechanically grind and shape them, and then convert them to a specific crystalline state by solvent treatment.

[0056] The particle size of the charge-generating material is usually 1 μm or less, preferably 0.5 μm or less. The amount of charge-generating material dispersed in the photosensitive layer is usually 0.1 parts by mass or more, preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of the binder resin. Furthermore, from the viewpoint of sensitivity, it is usually 20 parts by mass or less, preferably 15 parts by mass or less, and more preferably 10 parts by mass or less.

[0057] <Binder resin> Examples of binder resins include vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, their copolymers, thermoplastic resins such as polycarbonate, polyarylate, polyester, polyester polycarbonate, polysulfone, phenoxy, epoxy, and silicone resins, and various thermosetting resins. Among these resins, polycarbonate resin or polyarylate resin is preferred in terms of light attenuation characteristics as a photoreceptor and mechanical strength.

[0058] Specific examples of repeating structural units suitable for the binder resin are shown below. These examples are illustrative, and any known binder resin may be mixed and used as long as it does not contradict the spirit of the present invention.

[0059] [ka]

[0060] The viscosity-average molecular weight of the binder resin is typically 20,000 or more, preferably 30,000 or more, more preferably 40,000 or more, and even more preferably 50,000 or more, from the viewpoint of mechanical strength. From the viewpoint of preparing a coating solution for photosensitive layer formation, it is typically 150,000 or less, preferably 120,000 or less, and more preferably 100,000 or less.

[0061] <Charge transport material> [Electron transport material] The photosensitive layer preferably contains a compound represented by the following formula (1e) as an electron transport material.

[0062] [ka]

[0063] (In formula (1e), R 1 ~R 4 Each of these independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may have substituents, or an alkenyl group having 1 to 20 carbon atoms which may have substituents, and R1 and R 2 each other, or R 3 and R 4 each other may be bonded to form a cyclic structure. X represents an organic residue having a molecular weight of 120 or more and 250 or less.)

[0064] R 1 ~R 4 each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may have a substituent, or an alkenyl group having 1 to 20 carbon atoms. Examples of the alkyl group having 1 to 20 carbon atoms which may have a substituent include linear alkyl groups such as a methyl group, an ethyl group and a hexyl group, branched alkyl groups such as an iso-propyl group, a tert-butyl group and a tert-amyl group, and cyclic alkyl groups such as a cyclohexyl group and a cyclopentyl group. Among these, an alkyl group having 1 to 15 carbon atoms is preferable from the viewpoint of general availability of raw materials, an alkyl group having 1 to 10 carbon atoms is more preferable from the viewpoint of handleability during production, and an alkyl group having 1 to 5 carbon atoms is still more preferable. Also, a linear alkyl group or a branched alkyl group is preferable from the viewpoint of electron transport ability, among which a methyl group, a tert-butyl group or a tert-amyl group is more preferable, and a tert-butyl group or a tert-amyl group is still more preferable from the viewpoint of solubility in an organic solvent used for the coating solution.)

[0065] Examples of the alkenyl group having 1 to 20 carbon atoms which may have a substituent include linear alkenyl groups such as an ethenyl group, branched alkenyl groups such as a 2-methyl-1-propenyl group and cyclic alkenyl groups such as a cyclohexenyl group. Among these, a linear alkenyl group having 1 to 10 carbon atoms is preferable from the viewpoint of the light attenuation characteristics of the photoreceptor.)

[0066] The substituent R 1 ~R 4 is that R I 1 and R 2 each other, or R 3 and R 4 each other may be bonded to form a cyclic structure. From the viewpoint of electron mobility, R 1 and R 2When both are alkenyl groups, it is preferable that they bond to each other to form an aromatic ring, R 1 and R 2 It is more preferable that both are ethenyl groups, bonded to each other, and have a benzene ring structure.

[0067] In formula (1e), X represents an organic residue with a molecular weight of 120 to 250. From the viewpoint of the photoattenuation characteristics of the photoreceptor, the compound represented by formula (1e) is preferably a compound represented by any of the following formulas (2e) to (5e).

[0068] [ka]

[0069] (In formula (2e), R 5 ~R 7 Each of these independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.

[0070] [ka]

[0071] (In formula (3e), R 8 ~R 11 Each of these independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 6 carbon atoms.

[0072] [ka]

[0073] (In formula (4e), R 12 (This represents a hydrogen atom, an alkyl group with 1 to 6 carbon atoms, or a halogen atom.)

[0074] [ka]

[0075] (In formula (5e), ​​R 13and R 14 Each of these independently represents a hydrogen atom, an alkyl group with 1 to 6 carbon atoms, or an aryl group with 6 to 12 carbon atoms.

[0076] R 5 ~R 14 Examples of C1-C6 alkyl groups in this formula include linear alkyl groups such as methyl, ethyl, and hexyl groups, branched alkyl groups such as iso-propyl, tert-butyl, and tert-amyl groups, and cyclic alkyl groups such as cyclohexyl groups. From the viewpoint of electron transport capability, methyl, tert-butyl, or tert-amyl groups are more preferred. Examples of halogen atoms include fluorine, chlorine, bromine, and iodine, with chlorine being preferred from the viewpoint of electron transport capability. Examples of C6-C12 aryl groups include phenyl and naphthyl groups, with phenyl or naphthyl groups being preferred from the viewpoint of photosensitive film properties, and phenyl groups being more preferred. Among the compounds represented by formulas (2e) to (5e), ​​the compound represented by formula (1e) is preferably the compound represented by formula (2e) or formula (3e), and more preferably the compound represented by formula (3e), from the viewpoint of image quality stability when repeatedly forming images. Furthermore, the compound represented by formula (1e) may be used alone, or in combination with other compounds represented by formula (1e) that have different structures, or in combination with other electron transport materials. Examples of electron transport material structures are shown below.

[0077] [ka]

[0078] As an alternative electron transport material, it can also be used in combination with pigments that possess electron transport capabilities.

[0079] Examples of pigments with electron transport capabilities include known cyclic ketone compounds, perylene pigments (perylene derivatives), and azo pigments. An example is shown below.

[0080] [ka]

[0081] [ka]

[0082] The ratio of the binder resin to the electron transport material in the photosensitive layer is, from the viewpoint of electrical properties, usually 10 parts by mass or more of the electron transport material per 100 parts by mass of the binder resin, preferably 30 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 60 parts by mass or more, and particularly preferably 100 parts by mass or more. On the other hand, from the viewpoint of compatibility with the binder resin, the electron transport material is usually 300 parts by mass or less, preferably 200 parts by mass or less, and more preferably 150 parts by mass or less.

[0083] <Hole transport materials> There are no restrictions on the structure of the hole transport material, and examples include arylamine derivatives, stilbene derivatives, butadiene derivatives, hydrazone derivatives, carbazole derivatives, aniline derivatives, enamine derivatives, and combinations of multiple of these compounds, or electron-donating materials such as polymers having groups made of these compounds in their main chain or side chains. Among these, arylamine derivatives, stilbene derivatives, hydrazone derivatives, enamine derivatives, and combinations of multiple of these compounds are preferred, with enamine derivatives and combinations of multiple arylamines being more preferred, and enamine derivatives being even more preferred. Furthermore, multiple types of hole transport materials may be used in combination. The ratio of binder resin to hole transport material in the photosensitive layer is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, and particularly preferably 100 parts by mass or more, of the binder resin. On the other hand, it is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and particularly preferably 150 parts by mass or less.

[0084] [ka]

[0085] <Other additives> The photosensitive layer may contain additives such as well-known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light shielding agents, and space fillers for the purpose of improving film-forming properties, flexibility, coatability, stain resistance, gas resistance, and light resistance. As an additive, for example, trybenzylamine can be included as an antioxidant. The ratio of binder resin to additive in the photosensitive layer is 0.1 parts by mass or more, preferably 1 part by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of binder resin. On the other hand, the upper limit is 100 parts by mass or less, preferably 50 parts by mass or less, and more preferably 30 parts by mass or less.

[0086] <Laminated photosensitive layer> As the stacked photosensitive layer, it is preferable that it be an inverse stacked photosensitive layer in which a charge transport layer and a charge generation layer are stacked in that order from the conductive support side. However, even if it is a forward stacked photosensitive layer in which a charge generation layer and a charge transport layer are stacked in that order, the effects of the present invention can be enjoyed as long as the photosensitive layer in contact with the outermost layer, i.e., the charge transport layer, contains a charge generation material. The charge generating material, hole transport material, electron transport material, binder resin, and other additives that may be contained in the multilayer photosensitive layer are the same as those compounds that may be contained in the single-layer photosensitive layer described above. Furthermore, the amount of these materials contained in the multilayer photosensitive layer is not particularly limited and can be any amount.

[0087] <Over Coat Layer, OCL> Next, the outermost layer of the photoreceptor of the present invention will be described. Hereinafter, the outermost layer may be referred to as the Over Coat Layer or, for short, OCL.

[0088] In this invention, by having the outermost layer contain a cured product formed by the curing of a curable compound, such as a photocurable compound, it is possible to solve problems such as adverse effects of ozone during the printing cycle, deterioration of electrostatic chargeability, and leakage. Here, a curable compound refers to a compound that forms a cross-linked structure by light, heat, etc.

[0089] If the outermost layer contains a cured product formed by the hardening of a curable compound, the curable compound forms a dense three-dimensional network structure, which prevents ozone gas from penetrating the single-layer photosensitive layer.

[0090] Furthermore, because molecular movement is difficult within the layer of a curable compound, such as a photocurable polymer, that is densely crosslinked in a three-dimensional network structure, penetration into the outermost layer of hole transport materials and electron transport materials present in the photosensitive layer does not occur. This suppresses the leakage of hole transport materials and electron transport materials onto the photoreceptor surface, known as bleed-out, which worsens the ease of charging. Conventionally, additives have been added to counteract bleed-out of hole transport materials and electron transport materials from single-layer photosensitive layers. However, while this can reduce the amount of bleed-out, it cannot suppress the occurrence of bleed-out itself. The present invention offers a fundamental solution without the addition of additives, which is advantageous because it allows for a relative increase in the amount of other functional materials within the photosensitive layer.

[0091] Furthermore, by including a curable compound, such as a photocurable compound, in the outermost layer, aggregates of charge-generating material that could become leakage points are concealed by the outermost layer, preventing the concentration of the electric field on the aggregates and thus suppressing leakage. Furthermore, the inventors' research has shown that suppressing the penetration of water molecules into the outermost layer is effective in suppressing leakage. The cured product formed by the curing compound contained in the outermost layer of the present invention has a densely crosslinked three-dimensional network structure, and therefore can suppress the penetration of water molecules. On the other hand, in the case of an outermost layer made of a thermoplastic resin such as polyamide, although it is possible to prevent electric field concentration on aggregates of charge-generating materials, it is not possible to suppress the penetration of water molecules because it is water-absorbing. Also, even with a hydrophobic thermoplastic resin, it is considered that it is not possible to completely prevent the penetration of water molecules because it does not have a densely crosslinked three-dimensional network structure.

[0092] In addition, the hardening of the curable compound improves the mechanical strength of the outermost layer, thus enabling both improved wear resistance and mechanical strength.

[0093] The materials used for the outermost layer (curable compounds, charge transport materials, metal oxide particles, polymerization initiators) are described in detail below.

[0094] (curable compound) The outermost layer of the present invention is characterized by containing a curable compound and being formed by curing this compound. Examples of curable compounds include compounds having chain polymerizable functional groups, such as photocurable compounds.

[0095] From the viewpoint of reactivity, the compound having chain polymerizable functional groups used in the outermost layer usually has 2 or more, preferably 3 or more, and more preferably 4 or more chain polymerizable functional groups, while on the other hand, it usually has 20 or fewer, preferably 10 or fewer, and more preferably 6 or fewer. Examples of chain polymerizable functional groups used in the outermost layer of a compound having a chain polymerizable functional group include acryloyl groups, methacryloyl groups, vinyl groups, and epoxy groups. While the compound having a chain polymerizable functional group is not particularly limited as long as it is a known material, from the viewpoint of curability, monomers, oligomers, and polymers having an acryloyl group or a methacryloyl group are preferred.

[0096] The following are examples of preferred compounds. Monomers having an acryloyl group or a methacryloyl group include trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate, HPA-modified trimethylolpropane triacrylate, EO-modified trimethylolpropane triacrylate, PO-modified trimethylolpropane triacrylate, caprolactone-modified trimethylolpropane triacrylate, HPA-modified trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerol triacrylate, ECH-modified glycerol triacrylate, EO-modified glycerol triacrylate, PO-modified glycerol triacrylate, tris(acryloxyethyl) isocyanurate, caprolactone-modified tris(acryloxyethyl) isocyanurate, EO-modified tris(acryloxyethyl) isocyanurate, PO-modified tri Acryloxyethyl isocyanurate, dipentaerythritol hexaacrylate, caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hydroxypentaacrylate, alkyl-modified dipentaerythritol pentaacrylate, alkyl-modified dipentaerythritol tetraacrylate, alkyl-modified dipentaerythritol triacrylate, methylolpropane 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, and hexanediol dimethacrylate.

[0097] 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 urethane acrylates include "EBECRYL8301", "EBECRYL1290", "EBECRYL1830", "KRM8200" (Daicel Ornex Co., Ltd.), "UV1700B", "UV7640B", "UV7605B", "UV6300B", "UV7550B" (Mitsubishi Chemical Corporation), etc. Examples of ester acrylates include "M-7100", "M-7300K", "M-8030", "M-8060", "M-8100", "M-8530", "M-8560", "M-9050" (Toagosei Co., Ltd.), etc. Examples of acrylic acrylates include "8BR-600", "8BR-930MB", "8KX-078", "8KX-089", and "8KX-168" (Taisei Fine Chemical Co., Ltd.).

[0098] These can be used individually or in combination of two or more types.

[0099] In addition to compounds having chain polymerizable functional groups, the outermost layer of the present invention may also contain metal oxide particles or charge transporting materials for the purpose of imparting charge transport ability. Furthermore, a polymerization initiator may be used to promote the polymerization reaction when curing the outermost layer.

[0100] (Charge transport material used in the outermost layer) The charge transport material to be contained in the outermost layer can be the same as the charge transport material used in the photosensitive layer. In addition, from the viewpoint of improving the mechanical strength of the outermost layer, a polymer having a substructure with charge transport ability may be used. Examples of chain polymerizable functional groups in the charge transport material having a chain polymerizable functional group include acryloyl group, methacryloyl group, vinyl group, and epoxy group. Among these, acryloyl group or methacryloyl group are preferred from the viewpoint of curability. Examples of electron-donating materials include heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, and benzofuran derivatives, aniline derivatives, hydrazone derivatives, aromatic amine derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, as well as compounds formed by bonding multiple types of these compounds, and polymers having groups made of these compounds in the main chain or side chain. Among these, from the viewpoint of electrical properties, carbazole derivatives, aromatic amine derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, as well as compounds formed by combining multiple types of these compounds, are preferred.

[0101] As the substructure having charge transport ability, a structure represented by the following formula (3) is preferred.

[0102] [ka]

[0103] In formula (3), Ar 41 ~Ar 43 R is an aromatic group. 41 ~R 43 Each of these is independently a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, an alkyl halide, a halogen group, a benzyl group, or the following formula (4). 41 ~n 43 n is an integer greater than or equal to 1. 41 If R is 1, 41 Equation (4) is given by n41 If R is an integer greater than or equal to 2, 41 These can be the same or different, but at least one of them is equation (4). 42 If R is an integer greater than or equal to 2, 42 Each of them may be the same or different, n 43 If R is an integer greater than or equal to 2, 43 These may be the same or different.

[0104] [ka]

[0105] In formula (4), R 51 R represents a hydrogen atom or a methyl group. 52 , R 53 Each of these independently represents a hydrogen atom, a hydrocarbon group, or an alkoxy group, and R 54 n represents a single bond or oxygen atom. 51 * represents an integer between 0 and 10 (inclusive). 41 ~Ar 43 The bond with is shown, and ** indicates a bond with any atom.

[0106] In formula (3), Ar 41 ~Ar 43 Aromatic groups include monovalent aromatic groups such as phenyl, naphthyl, anthracenyl, phenatrenyl, pyrene, biphenyl, and fluorene groups. Among these, the phenyl group is preferred from the viewpoint of solubility and photocurability. Divalent aromatic groups include phenylene, naphthylene, anthreylene, phenanthrylene, pyrenylene, and biphenylene groups. Among these, the phenylene group is preferred from the viewpoint of solubility and photocurability.

[0107] R 41 ~R 43Each of these is independently a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, a halogenated alkyl group, a halogen group, a benzyl group, or the above formula (4). Of these, the number of carbon atoms in the alkyl group, alkoxy group, aryl group, and halogenated alkyl group is usually 1 or more, while the number of carbon atoms in the alkyl group, alkoxy group, aryl group, and halogenated alkyl group is usually 1 or less, preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less. Specific examples of alkyl groups include methyl group, ethyl group, propyl group, isopropyl group, butyl group, tert-butyl group, isobutyl group, and cyclohexyl group. Specific examples of alkoxy groups include methoxy group, ethoxy group, propoxy group, and cyclohexoxy group. Examples of aryl groups include phenyl group and naphthyl group. Examples of halogenated alkyl groups include chloroalkyl groups and fluoroalkyl groups. Examples of halogen groups include fluoro group, chloro group, and bromo group. More preferably, methyl group, ethyl group, and phenyl group.

[0108] n 41 ~n 43 n is an integer greater than or equal to 1, usually 1 or greater, usually 5 or less, preferably 3 or less, and most preferably 1. However, n 41 If R is 1, 41 Equation (4) is given by n 41 If R is an integer greater than or equal to 2, 41 These can be the same or different, but at least one of them is equation (4). 42 If R is an integer greater than or equal to 2, 42 Each of them may be the same or different, n 43 If R is an integer greater than or equal to 2, 43は They may be the same or different. From the viewpoint of the strength of the cured film, n 41 ~n 43 R is 1, 41 is equation (4) and R 42 and R 43 If either of the following is equation (4), or n 41 ~n 43 R is 1, 41 ~R 43 It is preferable that the formula is (4), and from the viewpoint of solubility, n 41 ~n 43is 1, and R 41 is the formula (4) and R 42 and R 43 it is more preferable that either one of them is the formula (4). R 52 , R 53 is the same as the above R 22 , R 23 and the like can be mentioned.

[0109] n 51 is an integer of 0 or more and 10 or less, usually 0 or more, usually 10 or less, preferably 6 or less, more preferably 4 or less, and still more preferably 3 or less.

[0110] There is no particular limitation on the raw material of the polymer having the structure represented by the formula (3), but it is preferable to obtain it by polymerizing a compound having the structure represented by the following formula (3´).

[0111] ]>

Chemical formula

[0112] In the formula (3´), Ar 41 ~Ar 43 is an aromatic group. R 41 ~R 43 are each independently a hydrogen atom, an alkyl group, an alkoxy group, an aryl group, a halogenated alkyl group, a halogen group, a benzyl group or the following formula (4´). n 41 ~n 43 is an integer of 1 or more. However, when n 41 is 1, R 41 is the formula (4´), and when n 41 is an integer of 2 or more, R 41 may be the same or different from each other, but at least one of them is the formula (4´). When n 42 is an integer of 2 or more, R 42 may be the same or different from each other, and when n 43 is an integer of 2 or more, R 43 may be the same or different from each other.

[0113]

Chemical formula

[0114] In formula (4´), R 51 represents a hydrogen atom or a methyl group, and R 52 , R 53 each independently represents a hydrogen atom, a hydrocarbon group or an alkoxy group, and R 54 represents a single bond or an oxygen atom, and n 51 represents an integer of 0 or more and 10 or less. * indicates the bond with Ar 41 ~Ar 43 The specific examples of the structure of the above formula (3´) are shown below.

[0115] [Chemical formula]

[0116] Among the above compounds, from the viewpoint of electrical characteristics, formula (3-1), formula (3-2), formula (3-3), formula (3-4), formula (3-6), formula (3-7) are preferable, and formula (3-1), formula (3-2), formula (3-3) are more preferable.

[0117] The amount of the charge transport material used in the outermost layer of the electrophotographic photoreceptor according to the present invention is not particularly limited, but it is preferably used in the range of 10 to 300 parts by mass with respect to 100 parts by mass of the binder resin. More preferably, it is 30 to 200 parts by mass, and particularly preferably 50 to 150 parts by mass. If the content of the charge transport material is less than this range, the charge transport performance is insufficient and the electrical characteristics deteriorate. If the content of the charge transport material is more than this range, the surface resistance of the outermost surface decreases and image defects such as image flow occur.

[0118] (Metal oxide particles) From the viewpoints of imparting charge transport ability and improving mechanical strength, the outermost layer of the present invention may contain metal oxide particles.

[0119] As metal oxide particles, any metal oxide particles that can be used in electrophotographic photoreceptors can be used. More specifically, examples of metal oxide particles include metal oxide particles containing one metal element such as titanium oxide, tin oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, and metal oxide particles containing multiple metal elements such as calcium titanate, strontium titanate, and barium titanate. Among these, metal oxide particles with a band gap of 2 to 4 eV are preferred. Only one type of metal oxide particle may be used, or a mixture of multiple types of particles may be used. Among these metal oxide particles, titanium oxide, tin oxide, aluminum oxide, silicon oxide, and zinc oxide are preferred, and titanium oxide and tin oxide are more preferred. Titanium oxide is particularly preferred.

[0120] Any of the following crystalline forms of titanium dioxide particles can be used: rutile, anatase, brookite, or amorphous. Furthermore, a mixture of these particles in different crystalline states may be included.

[0121] 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, it is preferable that they be surface-treated with organosilicon compounds. 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, vinyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane. In particular, from the viewpoint of improving the mechanical strength of the outermost layer, 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, and vinyltrimethoxysilane, which have chain polymerizable functional groups, are preferred.

[0122] Although the outermost surface of these surface-treated particles is treated with such a treatment agent, it may also be treated with a treatment agent such as aluminum oxide, silicon oxide, or zirconium oxide prior to this treatment. The metal oxide particles may be of a single type or a mixture of multiple types.

[0123] The metal oxide particles used typically have an average primary particle diameter of 500 nm or less, more preferably 1 to 100 nm, and even more preferably 5 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).

[0124] 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 "TTO55(S)", and high-purity titanium dioxide "C-E This includes titanium oxides such as "L", sulfuric acid-processed titanium oxides "R-550", "R-580", "R-630", "R-670", "R-680", "R-780", "A-100", "A-220", "W-10", chlorine-processed titanium oxides "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", and "A-150", and "SR-1" which is coated with Al2O3. "RGL", "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 Examples include untreated titanium oxide such as "-100", "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 are untreated, "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.). In addition, a specific product name for aluminum oxide particles is "Aluminium Oxide C" (manufactured by Nippon Aerosil Co., Ltd.).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.). 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). 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.

[0125] The content of metal oxide particles in the outermost layer of the electrophotographic photoreceptor according to the present invention is not particularly limited, but from the viewpoint of electrical properties, it is preferably 10 parts by mass or more, more preferably 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 20 parts by mass or less, and particularly preferably 100 parts by mass or less. The ratio (mass ratio) of metal oxide particles to the curable compound in the outermost layer of the electrophotographic photoreceptor according to the present invention is not particularly limited, but is preferably 0.1 or more, more preferably 0.5 or more, even more preferably 0.8 or more, and particularly preferably 1.5 or more. It is also preferably 10 or less, more preferably 5 or less, and particularly preferably 3 or less.

[0126] (Polymerization initiator) Polymerization initiators include photopolymerization initiators, etc.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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 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 outermost layer and 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 outermost layer surface. 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.

[0131] 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.

[0132] 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.

[0133] (Method of forming the outermost layer) Next, a method for forming the outermost layer will be described. The method for forming the outermost layer is not particularly limited, but 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 (or dispersed) in a solvent (or dispersion medium), as the outermost layer.

[0134] The solvent or dispersion medium used for forming the outermost layer, and the coating method, will be described below.

[0135] [Solvent used in coating solution for forming the 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 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 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.

[0136] The ratio of organic solvent to solid content used in the surface layer forming coating solution of the present invention varies depending on the application method of the surface layer forming coating solution, and can be appropriately changed to ensure that a uniform coating film is formed in the application method.

[0137] [Application Method] The method of applying the coating solution to form the outermost layer is not particularly limited and includes, for example, spray coating, spiral coating, ring coating, and immersion coating.

[0138] After forming the coating film using the above coating method, the coating film is dried. The temperature and time are not specified as long as sufficient drying is achieved. However, if the outermost layer is coated by air drying only after coating the photosensitive layer, it is preferable to dry it thoroughly using the method described in the [coating method] for the photosensitive layer above.

[0139] The thickness of the outermost layer is selected as optimally as appropriate depending on the materials used, but from the viewpoint of lifespan, 0.1 μm or more is preferred, 0.2 μm or more is more preferred, 0.8 μm or more is even more preferred, and 1.5 μm or more is particularly preferred. From the viewpoint of electrical properties, 10 μm or less is preferred, 6 μm or less is more preferred, and 3 μm or less is particularly preferred.

[0140] [Method for hardening the outermost layer] The outermost layer is formed by applying the coating solution, then applying external energy to cure it, thereby creating a cross-linked surface layer. The external energy used can be heat, light, or radiation, but light energy is preferred. UV irradiation 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 as light energy sources. However, visible light sources can also be selected to match the absorption wavelength of the chain-polymerizable compound or photopolymerization initiator. The light intensity is 100 mJ / cm². 2 More than 20000mJ / cm 2 The following is preferable: 500 mJ / cm 2 More than 10000mJ / cm 2The following is even more preferable: 1000 mJ / cm² 2 More than 4000mJ / cm 2 The following is particularly preferred: 100 mJ / cm² 2 Below 20,000 mJ / cm², the hardening reaction does not proceed sufficiently, resulting in insufficient mechanical strength. 2 Beyond a certain point, the photosensitive layer deteriorates due to excessive light energy, resulting in a worsening of its electrical properties.

[0141] After curing the outermost layer, 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 and 200°C or lower, and more preferably 100°C or higher and 150°C or lower. Below 60°C, the above improvement effect is poor, and above 200°C, the electrical properties deteriorate due to degradation of the photosensitive layer.

[0142] <Method of forming each layer> Each layer constituting the photoreceptor described above is formed by sequentially applying and drying a coating solution, obtained by dissolving or dispersing the substance to be contained in a solvent, onto a conductive support using known methods such as immersion coating, spray coating, nozzle coating, bar coating, roll coating, and blade coating, for each layer.

[0143] There are no particular restrictions on the solvent or dispersion medium used in the preparation of the coating solution, but specific examples include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; esters such as methyl formate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, cyclohexanone, and 4-methoxy-4-methyl-2-pentanone; aromatic hydrocarbons such as benzene, toluene, and xylene; chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichloroethylene; nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, and triethylenediamine; and aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide. Furthermore, these can be used individually or in any combination of two or more types.

[0144] While there are no particular restrictions on the amount of solvent or dispersion medium used, it is preferable to appropriately adjust the solid content concentration, viscosity, and other physical properties of the coating solution to be within the desired range, taking into consideration the purpose of each layer and the properties of the selected solvent / dispersion medium.

[0145] For example, in the case of a single-layer photoreceptor, the solid content concentration of the coating solution is usually 5% by mass or more, preferably 10% by mass or more, and usually 40% by mass or less, preferably 35% by mass or less. Furthermore, the viscosity of the coating solution at the temperature of use is usually 10 mPa·s or more, preferably 50 mPa·s or more, and usually 2000 Pa·s or less, preferably 1000 mPa·s or less, next preferably 700 Pa·s or less, and even more preferably 400 mPa·s or less.

[0146] The coating solution is preferably dried by heating at room temperature for 1 minute to 2 hours, either stationary or under a fan, at a temperature range of 30°C to 200°C. The heating temperature may be constant, or it may be changed during the drying process.

[0147] <Cartridges, Image Forming Apparatus> Next, embodiments of an image forming apparatus using the electrophotographic photoreceptor of the present invention (image forming apparatus of the present invention) will be described with reference to Figure 1, which shows the main components of the apparatus. However, the embodiments are not limited to the following description and can be modified and implemented as such without departing from the spirit of the present invention.

[0148] As shown in Figure 1, the image forming apparatus comprises an electrophotographic photoreceptor 1, a charging device 2, an exposure device 3, and a developing device 4. Furthermore, a transfer device 5, a cleaning device 6, and a fixing device 7 are provided as needed.

[0149] The electrophotographic photoreceptor 1 is not particularly limited as long as it is the electrophotographic photoreceptor of the present invention as described above, but Figure 1 shows, as an example, a drum-shaped photoreceptor in which the above-described photosensitive layer is formed on the surface of a cylindrical conductive support. A charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are arranged along the outer circumferential surface of this electrophotographic photoreceptor 1, respectively.

[0150] The charging device 2 charges the electrophotographic photoreceptor 1, uniformly charging the surface of the electrophotographic photoreceptor 1 to a predetermined potential. Common charging devices include non-contact corona charging devices such as Corotron and Scorotron, or contact-type charging devices (direct charging devices) that charge the photoreceptor surface by bringing a voltage-applied charging member into contact with it. However, in this invention, a contact-type charging roller is used. Figure 1 shows a roller-type charging device (charging roller) as an example of the charging device 2. Typically, charging rollers are manufactured by integrally molding resin and additives such as plasticizers with a metal shaft, and may take a laminated structure as needed.

[0151] Charging rollers typically have a cylindrical outer shape with a diameter of 5 to 20 mm. If the diameter of the charging roller is smaller than the above range, the accuracy during rotation tends to be poor, and if it is larger than the above range, it may be inconvenient for miniaturization and weight reduction. Furthermore, the diameter of the charging roller is preferably 7 mm or more, more preferably 8 mm or more, and more preferably 18 mm or less, and more preferably 16 mm or less. A typical electrostatic roller consists of a conductive core with a semiconductive elastic layer. Hereafter, the elastic layer will refer to the portion of the electrostatic roller other than the conductive core. Typically, metal is used as the conductive core material. The material of the elastic layer provided on the core material is not particularly limited as long as it is semiconducting, but generally, polymer compositions such as vulcanized / crosslinked rubber, thermosetting resins, photocurable resins, and thermoplastic resins with added conductivity are used. Vulcanized / crosslinked rubber and thermoplastic resins are particularly preferred in terms of processability and flexibility.

[0152] Vulcanized and crosslinked rubbers are not particularly limited, but examples include EPDM, polybutadiene, natural rubber, polyisoprene rubber, SBR, CR, NBR, silicone rubber, urethane rubber, and epichlorohydrin rubber. Thermoplastic resins are not particularly limited, but examples include polyolefin-based, polystyrene-based, polyester-based, polyamide-based, polyurethane-based, polycarbonate-based, fluorine-based, and silicone-based resins. In particular, thermoplastic resins are preferred from the standpoint of recyclability, which helps reduce waste. Furthermore, materials with lower hardness are even more preferable because they ensure reliable contact with the photoreceptor even if the surface of the elastic layer is rough, thus reducing the likelihood of uneven charging. For this reason, among the thermoplastic resins mentioned above, soft materials such as thermoplastic elastomers are preferred. Among thermoplastic elastomers, styrene-based thermoplastic elastomers are preferred due to their low hardness, and olefin-based thermoplastic elastomers are preferred due to their good toner release properties.

[0153] Generally, the voltage applied during charging can be either a DC voltage alone or a DC voltage superimposed with an AC voltage. Generally, superimposing an AC voltage on a contact-type charging roller in addition to a DC voltage increases damage to the photoreceptor and worsens wear, so the effect of introducing the outermost layer is considered greater in a DC / AC superimposed system. However, a DC voltage-only system is preferable in terms of environmental impact. The benefit of improved ease of charging due to introducing the outermost layer is also considered greater in a DC voltage-only system.

[0154] Furthermore, the surface potential of the charged photoreceptor is usually +400V or higher, preferably +500V or higher, second preferably +600V or higher, more preferably +650V or higher, even more preferably +700V or higher, particularly preferably +750V or higher, and most preferably +800V or higher. The higher the surface potential of the photoreceptor, the greater the difference with the development bias potential, which is preferable in terms of contrast.

[0155] The exposure apparatus 3 is not particularly limited in type, as long as it can expose the electrophotographic photoreceptor 1 to form an electrostatic latent image on the photosensitive surface of the electrophotographic photoreceptor 1. Specific examples include halogen lamps, fluorescent lamps, lasers such as semiconductor lasers and He-Ne lasers, and LEDs. Exposure may also be performed using an internal exposure method for the photoreceptor. The light used for exposure is arbitrary, but for example, exposure can be performed with monochromatic light with a wavelength of 780 nm, monochromatic light with a slightly shorter wavelength of 600 nm to 700 nm, or monochromatic light with a short wavelength of 380 nm to 500 nm.

[0156] The type of toner T used as the developer is arbitrary; in addition to powdered toner, polymerized toners produced by suspension polymerization or emulsion polymerization can be used. In particular, when using polymerized toner, a small particle size of about 4 to 8 μm in diameter is preferred, and the shape of the toner particles can vary from nearly spherical to rod-shaped or other non-spherical shapes. Polymerized toner has excellent charge uniformity and transfer properties, and is suitable for high-image-quality applications.

[0157] The transfer device 5 is not particularly limited in type, and any device using any method such as electrostatic transfer (corona transfer, roller transfer, belt transfer, etc.), pressure transfer, or adhesive transfer can be used. Here, the transfer device 5 is assumed to consist of a transfer charger, transfer roller, transfer belt, etc., arranged opposite the electrophotographic photoreceptor 1. This transfer device 5 applies a predetermined voltage value (transfer voltage) with the opposite polarity to the charging potential of the toner T, and transfers the toner image formed on the electrophotographic photoreceptor 1 to the recording paper (paper, medium) P.

[0158] There are no particular restrictions on the cleaning device 6; any cleaning device can be used, such as a brush cleaner, magnetic brush cleaner, electrostatic brush cleaner, magnetic roller cleaner, or blade cleaner. The cleaning device 6 scrapes off residual toner adhering to the photoreceptor 1 with a cleaning component and recovers the residual toner. However, if there is little or almost no toner remaining on the surface of the photoreceptor, the cleaning device 6 may not be necessary.

[0159] In the electrophotographic apparatus configured as described above, images are recorded as follows. First, the surface (photosensitive surface) of the photoreceptor 1 is charged to a predetermined potential (for example, 600V) by the charging device 2. This charging may be performed using a DC voltage, or by superimposing an AC voltage on a DC voltage.

[0160] Next, the photosensitive surface of the charged photoreceptor 1 is exposed by the exposure device 3 according to the image to be recorded, forming an electrostatic latent image on the photosensitive surface. Then, the electrostatic latent image formed on the photosensitive surface of the photoreceptor 1 is developed by the developing device 4.

[0161] The developing device 4 thins the toner T supplied by the supply roller 43 using a regulating member (developing blade) 45, and triboelectrically charges it to a predetermined polarity (in this case, the same polarity as the charging potential of the photoreceptor 1, which is positive polarity), and then transports it while supported on the developing roller 44 to bring it into contact with the surface of the photoreceptor 1.

[0162] When the charged toner T supported on the developing roller 44 comes into contact with the surface of the photoreceptor 1, a toner image corresponding to the electrostatic latent image is formed on the photosensitive surface of the photoreceptor 1. This toner image is then transferred to the recording paper P by the transfer device 5. After this, any toner remaining on the photosensitive surface of the photoreceptor 1 that was not transferred is removed by the cleaning device 6.

[0163] After the toner image is transferred onto the recording paper P, the toner image is thermally fixed onto the recording paper P by passing it through the fixing device 7, thereby obtaining the final image.

[0164] In addition to the configuration described above, the image forming apparatus may also be configured to perform a static elimination process. The static elimination process involves exposing the electrophotographic photoreceptor to light to remove static electricity, and the static elimination device may be a fluorescent lamp, LED, or the like. The light used in the static elimination process is often light with an exposure energy of three times or more that of the exposure light. From the viewpoint of miniaturization and energy saving, it is preferable not to have a static elimination process.

[0165] Furthermore, the image forming apparatus may be further modified in its configuration. For example, it may be configured to perform processes such as a pre-exposure process and an auxiliary charging process, or to perform offset printing, or it may be configured as a full-color tandem system using multiple types of toner.

[0166] Furthermore, the electrophotographic photoreceptor 1 may be combined with one or more of the charging device 2, exposure device 3, developing device 4, transfer device 5, cleaning device 6, and fixing device 7 to form an integrated cartridge (hereinafter referred to as the "electrophotographic photoreceptor cartridge" as appropriate), and this electrophotographic photoreceptor cartridge may be configured to be detachable from the main body of an electrophotographic device such as a copier or laser beam printer. [Examples]

[0167] The 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.

[0168] <Creation of electrophotographic photoreceptors> [Example 1] Ten parts by mass of Y-type oxytitanium phthalocyanine were added to 150 parts by mass of 1,2-dimethoxyethane, and the mixture was ground and dispersed in a sand grind mill to prepare a pigment dispersion. 160 parts by mass of the resulting pigment dispersion was added to 100 parts by mass of a 5% by mass solution of polyvinyl butyral (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name #6000C) containing 1,2-dimethoxyethane, and an appropriate amount of 4-methoxy-4-methyl-2-pentanone to prepare a base coat with a solid content of 4.0% by mass. A cylinder made of aluminum alloy with a roughly machined surface, an outer diameter of 30 mm, a length of 340 mm, and a wall thickness of 0.75 mm was immersed in this base coat to form a base layer with a film thickness of 0.3 μm after drying.

[0169] Next, 2.2 parts by mass of Y-type oxytitanium phthalocyanine and 1.1 parts by mass of perylene pigment represented by the following structural formula (PIG-1) were mixed and dispersed with 81 parts by mass of toluene using a sand grind mill. A 10% tetrahydrofuran solution containing 0.5 parts by mass of butyral resin (product name: Mobital B14S, manufactured by Kuraray Co., Ltd.) was mixed into this dispersion and stirred to prepare a pigment dispersion. Meanwhile, 70 parts by mass of a hole transport material represented by the following structural formula (H-1), 50 parts by mass of an electron transport material represented by the following structural formula (E-1), and 100 parts by mass of polycarbonate resin [viscosity-average molecular weight: Mv=60,000] represented by the following structural formula (B-1) were dissolved in a mixed solvent of 565 parts by mass of tetrahydrofuran and 61 parts by mass of toluene. 0.05 parts of silicone oil was added as a leveling agent, and the above pigment dispersion was added to this mixture. The mixture was homogenized to prepare a coating solution for a single-layer photosensitive layer. The single-layer photosensitive coating solution prepared in this manner was applied onto the aforementioned undercoat layer so that the film thickness after drying would be 34 μm. The solution was then air-dried at 100°C for 24 minutes to produce a single-layer photoreceptor before the outermost layer coating.

[0170] [ka]

[0171] <Formation of the outermost layer> Titanium dioxide (product name: TTO55N, rutile-type titania manufactured by Ishihara Sangyo Co., Ltd.) and 7% by mass (5% by mass + 2% by mass) of 3-methacryloxypropyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd.) relative to the titanium dioxide were mixed in a Henschel mixer to obtain surface-treated titanium dioxide, which was then dispersed in methanol solvent using a UAM-015 (bead mill device manufactured by Hiroshima Metal & Machinery Co., Ltd.) to obtain a dispersion slurry (solvent: methanol) with a solid content concentration of 25% by mass of surface-treated titania. The dispersion slurry was stirred and mixed with a methanol / 1-propanol mixed solvent, 100 parts by mass of acrylic monomer UV6300B (manufactured by Mitsubishi Chemical Corporation), 1 part by mass of benzophenone, and 2 parts by mass of diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide to dissolve the solids. Afterward, ultrasonic dispersion treatment was performed to prepare a top-layer coating solution with a solid content of 15.0%, containing methanol / 1-propanol in a mass ratio of 7 / 3 and acrylic monomer / surface-treated titanium dioxide in a mass ratio of 1 / 0.6. This coating solution was then immersed and applied to a single-layer photoreceptor before top-layer coating, and dried at 100°C for 10 minutes. From the surface side of this protective layer, a UV light irradiation device equipped with an electrodeless lamp bulb (D-bulb) was used to irradiate it with a light intensity of 8000 mJ / cm². 2 The material was cured by irradiating it with UV light to form a 1 μm thick outermost layer (O-1), and a single-layer photoreceptor (X-1) was obtained.

[0172] [Examples 2-4] Photoreceptors (X-2), (X-3), and (X-4) were prepared by performing the same procedure as in Example 1, except that the thickness of the outermost layer was formed as shown in Table 1.

[0173] [Example 5] A photoreceptor (X-5) was prepared by performing the same procedure as in Example 1, except that the acrylic monomer / surface-treated titanium dioxide content ratio was changed to a mass ratio of 1 / 1 to form the outermost layer (O-2).

[0174] [Example 6] A photoreceptor (X-6) was prepared by performing the same procedure as in Example 1, except that the acrylic monomer / surface-treated titanium dioxide content ratio was changed to a mass ratio of 1 / 2 to form the outermost layer (O-3).

[0175] [Example 7] A photoreceptor (X-7) was prepared by performing the same procedure as in Example 1, except that the acrylic monomer / surface-treated titanium dioxide content ratio was changed to a mass ratio of 1 / 0.2 to form the outermost layer (O-4).

[0176] [Example 8] A photoreceptor (X-8) was prepared by performing the same procedure as in Example 1, except that 100 parts by mass of the hole transport material represented by structural formula (H-1) and 60 parts by mass of the electron transport material represented by structural formula (E-1) were changed to prepare a single-layer photoreceptor before coating the outermost layer.

[0177] [Example 9] Photoreceptor (X-9) was prepared by performing the same procedure as in Example 1, except that 90 parts by mass of the hole transport material represented by structural formula (H-1) and 70 parts by mass of the electron transport material represented by structural formula (E-1) were changed, and 40 parts by mass of the electron transport material represented by structural formula (E-2) below were added to prepare a single-layer photoreceptor before coating the outermost layer.

[0178] [ka]

[0179] [Example 10] Photoreceptor (X-10) was prepared by performing the same procedure as in Example 1, except that 90 parts by mass of the hole transport material represented by structural formula (H-1) and 70 parts by mass of the electron transport material represented by structural formula (E-1) were changed, and 40 parts by mass of the electron transport material represented by structural formula (E-2) and 30 parts by mass of tripenzylamine (A-1) as an additive were added to prepare a single-layer photoreceptor before coating the outermost layer.

[0180] [Example 11] A photoreceptor (X-11) was fabricated by performing the same procedure as in Example 1, except that the surface-treated titanium oxide was replaced with phosphorus-doped tin oxide (product name: SP-2, phosphorus-doped tin oxide nanopowder manufactured by Mitsubishi Materials Electronic Chemicals, Inc.) to form the outermost layer (O-5).

[0181] [Example 12] A photoreceptor (X-12) was prepared by performing the same procedure as in Example 1, except that the binder resin of the single-layer photoreceptor before the outermost layer coating was changed to a polycarbonate resin [viscosity-average molecular weight: Mv=50,000] shown in structural formula (B-2).

[0182] [ka]

[0183] [Example 13] A photoreceptor (X-13) was prepared by performing the same procedure as in Example 1, except that the binder resin of the single-layer photoreceptor before the outermost layer coating was changed to a polycarbonate resin [viscosity-average molecular weight: Mv=60,000] shown by structural formula (B-3).

[0184] [ka]

[0185] [Example 14] A photoreceptor (X-14) was prepared by performing the same procedure as in Example 1, except that the binder resin of the single-layer photoreceptor before the outermost layer coating was changed to a polyarylate resin shown in structural formula (B-4) [viscosity-average molecular weight: Mv = 43,000].

[0186] [ka]

[0187] [Comparative Example 1] Except for not forming the outermost layer, the same procedure as in Example 1 was performed to prepare a single-layer photoreceptor before coating the outermost layer as in Example 1, and this was designated as photoreceptor (Y-1).

[0188] [Comparative Example 2] The same procedure as in Example 8 was followed, except that the outermost layer was not formed, to produce a single-layer photoreceptor before coating the outermost layer as in Example 8, which was designated as photoreceptor (Y-2).

[0189] [Comparative Example 3] Except for not forming the outermost layer, the same procedure as in Example 9 was performed to produce a single-layer photoreceptor before coating the outermost layer as in Example 9, and this was designated as photoreceptor (Y-3).

[0190] [Comparative Example 4] The same procedure as in Example 10 was followed, except that the outermost layer was not formed, to produce a single-layer photoreceptor before coating the outermost layer as in Example 10, which was designated as photoreceptor (Y-4).

[0191] [Comparative Example 5] ·Dispersion liquid for forming the outermost layer 1 The dispersion for forming the outermost layer was prepared as follows: Rutile-type titanium dioxide with an average primary particle size of 40 nm ("TTO55N" manufactured by Ishihara Sangyo Co., Ltd.) and 3% by weight of methyldimethoxysilane ("TSL8117" manufactured by Toshiba Silicone Co., Ltd.) relative to the titanium dioxide were placed in a high-speed fluid mixing and kneading machine ("SMG300" manufactured by Kawata Co., Ltd.). The surface-treated titanium dioxide obtained by high-speed mixing at a rotational peripheral speed of 34.5 m / sec was dispersed in a mixed solvent with a methanol / 1-propanol weight ratio of 7 / 3 using a ball mill to obtain a dispersion slurry of hydrophobically treated titanium dioxide. The dispersion slurry, a mixed solvent of methanol / 1-propanol / toluene, and a copolymer polyamide pellet consisting of ε-caprolactam / bis(4-amino-3-methylcyclohexyl)methane / hexamethylenediamine / decamethylenedicarboxylic acid / octadecamethylenedicarboxylic acid in molar ratios of 60% / 15% / 5% / 15% / 5% were heated and stirred and mixed to dissolve the polyamide pellet. Subsequently, ultrasonic dispersion treatment was performed to prepare a top-surface layer forming dispersion 1 with a solid content of 18.0%, containing methanol / 1-propanol / toluene in a weight ratio of 7 / 1 / 2 and hydrophobically treated titanium dioxide / copolymer polyamide in a weight ratio of 3 / 1.

[0192] A single-layer photoreceptor, prepared in the same manner as in Example 1, was immersed in the dispersion solution prepared for forming the outermost layer, and dried at 100°C for 24 minutes to form an outermost layer (O-6) with a thickness of 1 μm, thereby producing a photoreceptor (Y-5).

[0193] [Comparative Example 6] A photoreceptor (Y-6) was prepared by performing the same procedure as in Comparative Example 5, except that the weight ratio of hydrophobically treated titanium oxide / polymerized polyamide was changed to 1 / 1 to form the outermost layer (O-7).

[0194] The compositions of the photoreceptors used in the above examples and comparative examples are shown in Table 1.

[0195] [Table 1]

[0196] [Evaluation of photoreceptors in Examples 1-14 and Comparative Examples 1-6] <Evaluation of ease of charging> Photoreceptors (X-1) to (X-14) and (Y-1) to (Y-6) were charged at 32°C and 85% RH by the following charging method while rotating the photoreceptors at 200 rpm. The surface potential after the first rotation of the photoreceptor after the start of voltage application to the charging method was defined as Vcyc1, and the surface potential after the tenth rotation was defined as Vcyc10. The time from charging to potential measurement was set to 90 milliseconds. When a voltage was applied so that Vcyc10 was +850V, the ease of charging was evaluated using the following formula. Ease of charging (%) = (Vcyc1 / Vcyc10) × 100 (%) In the above formula, a larger percentage value indicates that the target charging potential was reached immediately after the start of charging, and that charging was performed easily. The results are shown in Table 2.

[0197] -Charging means- A charging roller (roller charger) with a diameter of 8 mm is used as a means to uniformly charge the circumferential surface of the electrophotographic photoreceptor. This charging roller has both ends of its core metal rotatably held by bearing members, and is biased toward the electrophotographic photoreceptor by a compression spring, pressing against the surface of the electrophotographic photoreceptor with a predetermined pressing force, and rotates in accordance with the rotation of the electrophotographic photoreceptor. When a charging bias voltage of predetermined conditions is applied to the core metal of the charging roller, the circumferential surface of the rotating photosensitive drum is contact-charged to a predetermined polarity and potential.

[0198] <Electrical Characteristics Evaluation> An electrophotographic characteristic evaluation apparatus manufactured in accordance with the electrophotographic society measurement standard (described on pages 404 - 405 of "Fundamentals and Applications of Electrophotography, Continued", edited by the Electrophotographic Society, Corona Publishing Co., Ltd.) was used. While rotating the photoreceptor at 200 rpm, it was charged using a contact charging roller so that the initial surface potential became +850 V. The light of a halogen lamp was made into monochromatic light of 780 nm using an interference filter, and the attenuation behavior of the surface potential was measured by changing the light amount using ND filters with different transmittances. At that time, after exposure at each light amount, once exposed to 660 nm LED light as the discharging light, most of the residual charges were cancelled. As the measurement value, the surface potential (bright potential; referred to as VL1) when exposed to 780 nm monochromatic light was obtained. When measuring VL, the time required from exposure to potential measurement was set to 30 ms. The measurement environment was at a temperature of 10 °C and a relative humidity of 15%. The measurement results are shown in Table - 2. 2 The surface potential (bright potential; referred to as VL1) when exposed was determined. When measuring VL, the time required from exposure to potential measurement was set to 30 ms. The measurement environment was at a temperature of 10 °C and a relative humidity of 15%. The measurement results are shown in Table - 2.

[0199] <Leakage characteristic evaluation> Regarding the photoreceptors (X - 1) to (X - 14) and (Y - 1) to (Y - 6), the leakage characteristics were evaluated by the following charging, potential measurement, and discharging cycle process in an environment of 32 °C and 80% humidity. That is, the photoreceptor was installed in an electrophotographic characteristic evaluation apparatus manufactured in accordance with the electrophotographic society measurement standard (described on pages 404 - 405 of "Fundamentals and Applications of Electrophotography, Continued", edited by the Electrophotographic Society, Corona Publishing Co., Ltd.), charged so that the initial surface potential of the photoreceptor became +850 V, and its surface potential was measured. At that time, the charging (contact roller charging) conditions were fixed so that the initial surface potential of the photoreceptor became approximately +850 V at the beginning of the test. At this time, the time from exposure to potential measurement was set to a high speed of 30 milliseconds. The photoreceptor was rotated at a constant rotational speed of 200 rpm, and after repeating the cycle of charging, potential measurement, and discharging 100,000 times, the surface of the photoreceptor was observed to determine the presence or absence of leakage marks. The evaluation results are shown in Table - 2 in the following notation. ○···No leakage marks, good △···Slight leakage marks ×···Many leakage marks

[0200] <Gas resistance evaluation> For the photoreceptors (X-1) to (X-14) and (Y-1) to (Y-6), gas resistance evaluation was carried out by the following cycle process of charging, potential measurement, and discharging at 32°C and 85% RH environment. That is, the photoreceptor was mounted on an electrophotographic characteristic evaluation apparatus (described in "Fundamentals and Applications of Electrophotography," edited by the Electrophotographic Society, Corona Publishing Co., Ltd., pages 404-405) fabricated according to the measurement standards of the Electrophotographic Society, charged so that the initial surface potential of the photoreceptor became +850 V, and its surface potential was measured. At this time, the time from exposure to potential measurement was set to a high speed of 30 milliseconds. The photoreceptor was rotated at 200 rpm, and the cycle of charging, potential measurement, and discharging was repeated 70,000 times, and the observed surface potential (V0) was measured. At that time, the charging (scorotron charger) conditions were fixed so that the initial surface potential of the photoreceptor became approximately +850 V at the beginning of the test. When V0-ini was the surface potential at the beginning of the test and V0-70k was the surface potential after 70,000 repetitions, the degree of decrease in the surface potential of the photoreceptor caused by the gas and ionic substances generated from the scorotron charger was expressed as the surface potential retention rate (%) = [(V0-70k) / (V0ini)] × 100 (%), and was used as an evaluation of gas resistance. That is, a large value indicates that the surface potential is unchanged and retained before and after the repeated test. The results are shown in Table-2. In addition, in this evaluation, the gas resistance evaluation was carried out under more severe conditions by using the scorotron charging method, which generates more gas than the contact roller charging method.

[0201]

Table 2

[0202] It can be seen from Table-2 as follows. From the evaluation results of charging easiness and electrical characteristics, it can be seen that the image forming apparatus having the configuration of the present invention has good charging easiness and electrical characteristics. Also, from the evaluation result (VL1) of the electrical characteristics, when the content ratio of titanium oxide in the outermost layer is the same, it can be seen that the photoreceptor using the outermost layer (O-2) containing a cured product formed by curing a curable compound has better electrical characteristics than the outermost layer (O-7) containing polyamide.

[0203] Furthermore, evaluation results of the leakage characteristics show that in a photoreceptor incorporating a top layer containing a cured product formed by the curing of a curable compound, no leakage marks occur even with a contact charging method, indicating a significant improvement in leakage resistance. Since leakage marks cause image defects in which streaky image noise occurs in a manner corresponding to the longitudinal direction of the photoreceptor including the leakage area, it is believed that an image forming apparatus of the present invention using a photoreceptor with high leakage resistance that prevents leakage marks from occurring on the photoreceptor will continuously produce images free from leakage-related image defects throughout the lifespan of the photoreceptor.

[0204] Furthermore, the evaluation results of gas resistance (surface potential retention rate) show that the electrophotographic photoreceptor of the present invention exhibits significantly improved gas resistance even when using the scorotron charging method, which generates more gas than the contact roller charging method.

[0205] <Withstand Voltage Evaluation> The photoreceptors (X-1) and (Y-1) were evaluated for withstand voltage under a temperature and humidity of 25°C and 50% by the following charging and potential measurement cycle. Specifically, the photoreceptors were mounted on an electrophotographic characteristic evaluation device manufactured according to the measurement standards of the Electrophotographic Society (described in "Fundamentals and Applications of Electrophotographic Technology, Continued," edited by the Electrophotographic Society, Corona Publishing Co., Ltd., pp. 404-405). While rotating the photoreceptors at a constant rotation speed of 200 rpm, the applied voltage to the contact roller charger was varied to 1.1 kV, 1.35 kV, and 1.6 kV, and the surface potential of the photoreceptor and the current flowing through the photoreceptor (inflow current) were measured. The time from exposure to potential measurement was set to a high speed of 30 milliseconds. A smaller inflow current value indicates better withstand voltage characteristics. The evaluation results are shown in Table 3.

[0206] [Table 3]

[0207] The results in Table 3 show that the difference in incoming current increases with and without the presence of the outermost layer containing the cured compound, as the applied voltage increases, i.e., as the surface potential of the photoreceptor increases. In other words, the improvement in dielectric strength due to the introduction of the outermost layer containing the cured compound is more pronounced as the surface potential of the photoreceptor increases, and is particularly useful when charged to +600V or higher. Here, to improve the contrast of printed images, it is effective to increase the applied voltage to raise the surface potential of the photoreceptor. Therefore, the image forming apparatus of the present invention, which has good voltage resistance characteristics even when the applied voltage is high, is considered advantageous when printing images with good contrast.

[0208] <Preparation of photosensitive sheet> [Example 15] The undercoat solution prepared in Example 1 was applied to a polyethylene terephthalate sheet with aluminum vapor deposition on its surface, so that the film thickness after drying was 0.4 μm, and then dried to form an undercoat layer. Next, the single-layer photosensitive coating solution prepared in Example 1 was applied to the aforementioned undercoat using an applicator so that the film thickness after drying would be 30 μm. The sheet was then dried at 100°C for 24 minutes to prepare a single-layer photosensitive sheet before the outermost layer coating. Next, the outermost coating solution prepared in Example 1 was applied to this photosensitive layer using a wire bar so that the film thickness after drying would be 1 μm. After drying this photosensitive sheet at 100°C for 10 minutes, a UV light irradiation device equipped with an electrodeless lamp bulb (D bulb) was used to irradiate the outermost layer from the surface side with a light intensity of 8000 mJ / cm². 2 A photoreceptor sheet was fabricated by curing it with UV light, resulting in a 30 μm photosensitive layer with a 1 μm outermost layer. This photoreceptor sheet is designated as (SX1).

[0209] [Comparative Example 7] Except for not forming the outermost layer, the same procedure as in Example 15 was performed to prepare a single-layer photoreceptor sheet before coating the outermost layer as in Example 15, and this was designated as photoreceptor sheet (SY-1).

[0210] [Comparative Example 8] On the single-layer photoreceptor sheet before the outermost layer coating prepared in the same manner as in Example 15, the dispersion for forming the outermost layer used in Comparative Example 6 was applied with a wire bar so that the film thickness after drying would be 1 μm. This photoreceptor sheet was dried at 100 °C for 10 minutes to provide an outermost layer with a film thickness of 1 μm, and a photoreceptor sheet (SY-2) was produced.

[0211] <Abrasion Resistance Evaluation>[ The photoreceptor sheets (SX-1), (SY-1), and (SY-2) were cut into a circular shape with a diameter of 10 cm, and abrasion evaluation was performed using a Taber abrasion tester (manufactured by Toyo Seiki Co., Ltd.). The test conditions were as follows: in an atmosphere of 25 °C and 50% RH, using an abrasion wheel CS-10F, the abrasion amount after 700 rotations with a load of 1000 g was measured by comparing the masses before and after the test. The smaller the value, the better the abrasion resistance. The results are shown in Table-4. Note that this evaluation is a pseudo-evaluation of the abrasion resistance of the photoreceptor when used in an image forming apparatus with a contact roller charging method.

[0212]

Table 4

[0213] From the results of SX-1 and SY-1 in Table-4, it can be seen that the outermost layer (O-1) containing the cured product formed by curing the curable compound of the present invention greatly improves the abrasion resistance of the photoreceptor. Also, it can be seen that this effect of improving abrasion resistance is greater than the effect of the outermost layer (O-7) containing polyamide.

Explanation of Reference Numerals

[0214] 1 Electrophotographic photoreceptor 2 Charging device 3 Exposure device 4 Developing device 5 Transfer device 6 Cleaning device 7 Fixing device

Claims

1. An image forming apparatus comprising at least an electrophotographic photoreceptor, wherein the charging method of the image forming apparatus is a contact charging method, and the electrophotographic photoreceptor is a positively charged electrophotographic photoreceptor having a single-layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material and an electron transport material, and an outermost layer containing a cured product formed by the curing of a curable compound. The outermost layer contains metal oxide particles, and the metal oxide particles are treated with a silane coupling agent having a chain-polymerizable functional group. An image forming apparatus comprising, as the electron transport material, a compound represented by the following structural formula (E-1) and a compound represented by the following structural formula (E-2). (E-1) (E-2)

2. The image forming apparatus according to claim 1, characterized in that the curable compound is a photocurable compound.

3. The image forming apparatus according to claim 1 or 2, wherein the charging method of the image forming apparatus is a contact roller charging method.

4. An image forming apparatus comprising at least an electrophotographic photoreceptor, wherein the charging method of the image forming apparatus is a contact roller charging method, and the electrophotographic photoreceptor is a positively charged electrophotographic photoreceptor having a single-layer photosensitive layer containing at least a binder resin, a charge generating material, a hole transport material and an electron transport material, and a top surface layer containing a cured product obtained by curing a photocurable compound. The outermost layer contains metal oxide particles, and the metal oxide particles are treated with a silane coupling agent having a chain-polymerizable functional group. An image forming apparatus comprising, as the electron transport material, a compound represented by the following structural formula (E-1) and a compound represented by the following structural formula (E-2). (E-1) (E-2)

5. The image forming apparatus according to any one of claims 1 to 4, wherein the content ratio (mass ratio) of the metal oxide particles to the curable compound is 0.5 or more.

6. The image forming apparatus according to any one of claims 1 to 5, wherein the single-layer photosensitive layer contains 30 parts by mass or more of the electron transport material with respect to 100 parts by mass of the binder resin.

7. The image forming apparatus according to any one of claims 1 to 6, wherein the single-layer photosensitive layer contains 70 parts by mass or more of the hole transport material with respect to 100 parts by mass of the binder resin.

8. The image forming apparatus according to any one of claims 1 to 7, wherein the single-layer photosensitive layer contains 1.0 part by mass or more of the charge generating material with respect to 100 parts by mass of the binder resin.

9. The image forming apparatus according to any one of claims 1 to 8, wherein the thickness of the outermost layer is 0.2 μm or more and 6 μm or less.

10. The image forming apparatus according to any one of claims 1 to 9, wherein the single-layer photosensitive layer contains tripenzylamine.

11. The image forming apparatus according to any one of claims 1 to 10, wherein the charging method of the image forming apparatus is a contact charging method in which only a DC voltage is applied.

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

13. The image forming apparatus according to any one of claims 1 to 12, wherein the outermost layer comprises an acyl phosphine oxide compound and a hydrogen abstraction type initiator.

14. The image forming apparatus according to claim 13, wherein the apparatus contains 0.1 parts by mass or more and 5 parts by mass or less of the hydrogen abstraction initiator with respect to 1 part by mass of the acylphosphine oxide compound.

Images