Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge, and image forming apparatus

Abstract

To provide a novel electrophotographic photoreceptor which offers enhanced wear resistance without increasing the thickness of a protective layer and, in particular, prevents wear of ends of the photosensitive photoreceptor when used in an image forming device of a contact charging type.SOLUTION: An electrophotographic photoreceptor is provided, comprising a photosensitive layer and a protective layer containing a cured product obtained by curing a curable compound, arranged on a conductive support body in the described order, the electrophotographic photoreceptor being designed to exhibit a flow-in current of 15 A / m2 or less when a voltage of -3.4 kV is applied.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

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

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

[0004] A "negatively charged laminated photoreceptor" generally has a configuration in which an undercoat layer (UCL) made of resin or the like is provided on a conductive support such as an aluminum tube, a charge generation layer (CGL) made of a charge generation material (CGM) and resin or the like is provided thereon, and further a charge transport layer (CTL) made of a hole transport material (HTM) and resin or the like is provided thereon.

[0005] On the one hand, a "positively charged single-layer photoreceptor" generally has a structure in which an undercoat layer (UCL) made of resin or the like is provided on a conductive support such as an aluminum tube, and a single-layer photosensitive layer made of a charge generation material (CGM), a hole transport material (HTM), an electron transport material (ETM), and resin or the like is provided thereon (see, for example, Patent Document 1).

[0006] In any photoreceptor, after the surface of the photoreceptor is charged by a corona discharge method or a contact method, the photoreceptor is exposed to neutralize the surface charges, thereby forming an electrostatic latent image due to the potential difference with the surrounding surface. Thereafter, toner is brought into contact with the surface of the photoreceptor to form a toner image corresponding to the electrostatic latent image, and this is transferred onto paper or the like and heat-fused and fixed to complete printing.

[0007] As described above, the basic configuration of an electrophotographic photoreceptor is a structure in which a photosensitive layer is formed on a conductive support. However, for the purpose of improving abrasion resistance and the like, a protective layer is provided on the photosensitive layer.

[0008] As a technique for improving the mechanical strength or abrasion resistance of the photoreceptor surface, a layer containing a compound having a chain polymerizable functional group, that is, a curable resin compound, is formed as a binder resin on the outermost layer of the photoreceptor, and this is polymerized by applying energy such as heat, light, or radiation to form a cured resin layer (protective layer). A photoreceptor is disclosed (see, for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] In recent years, from the perspective of suppressing maintenance costs, there has been an increasing demand for improving the lifespan, that is, improving the abrasion resistance, especially for photoreceptors used in multifunctional printers. Among them, in an image forming apparatus using a contact electrification method, how to suppress the abrasion of the photoreceptor end portion that contacts the end of the charging roller has become an issue. In order to solve such problems, it is conceivable to increase the thickness of the protective layer (also referred to as "OCL") to enhance the abrasion resistance of the photoreceptor. However, when the thickness of the protective layer (OCL) is increased, there is a problem that the image characteristics deteriorate.

[0011] Therefore, an object of the present invention is to provide a new electrophotographic photoreceptor capable of enhancing abrasion resistance regardless of the thickness of the protective layer, and more preferably, a new electrophotographic photoreceptor capable of suppressing the abrasion of the photoreceptor end portion when used in an image forming apparatus using a contact electrification method.

Means for Solving the Problems

[0012] To solve such problems, the present invention proposes an electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on a conductive support, - An electrophotographic photoreceptor in which the flowing current when a voltage of -3.4 kV is applied is 15 A / m 2 or less.

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

[13] .

[0014] [1] An electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on a conductive support, wherein the flowing current when a voltage of -3.4 kV is applied is 15 A / m 2 or less.

[0015] [2] The electrophotographic photoreceptor according to [1], wherein the thickness of the photosensitive layer is 10 μm or more. [3] The electrophotographic photoreceptor according to [1] or [2], wherein the thickness of the protective layer is 1 μm or less. [4] The electrophotographic photoreceptor according to any one of [1] to [3], wherein the ratio A / B of the thickness A of the protective layer to the thickness B of the photosensitive layer is 0.002 or more and 0.3 or less.

[0016] [5] The electrophotographic photoreceptor according to any one of [1] to [4], wherein the photosensitive layer contains metal oxide particles having a band gap of 5 eV or more. [6] The electrophotographic photoreceptor according to [5], wherein the metal oxide particles having a band gap of 5 eV or more are silica particles.

[0017] [7] The electrophotographic photoreceptor according to any one of [1] to [6], wherein the protective layer contains metal oxide particles having a band gap of 2 to 4 eV. [8] The electrophotographic photoreceptor according to [7], wherein the content ratio (mass ratio) of the metal oxide particles having a band gap of 5 eV or more in the photosensitive layer to the content of the metal oxide particles having a band gap of 2 to 4 eV in the protective layer is 0.1 to 0.5.

[0018] [9] The electrophotographic photoreceptor according to any one of [1] to [8], wherein the hole transport material contained in the photosensitive layer contains any one or a combination of two or more of the following formulas (1) or (2).

[0019] TIFF0007700486000001.tif49170

[0020] TIFF0007700486000002.tif44170

[0021]

[10] The electrophotographic photoreceptor according to any one of [1] to [9], wherein the curable compound is a photocurable compound.

[0022]

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

[10] , which is used in an image forming apparatus of a contact electrification method.

[0023]

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

[11] .

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

[11] .

Advantages of the Invention

[0024] The electrophotographic photoreceptor of the present invention can enhance the abrasion resistance regardless of the thickness of the protective layer, that is, without increasing the thickness of the protective layer more than before. In particular, when used in an image forming apparatus of the contact electrification method, abrasion at the end of the photoreceptor can be suppressed.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0026] Hereinafter, embodiments for carrying out the present invention (hereinafter, embodiments of the invention) will be described in detail. Note that the present invention is not limited to the following embodiments, and various modifications can be made and implemented within the scope of the gist thereof.

[0027] <<This electrophotographic photoreceptor>> An electrophotographic photoreceptor (also referred to as "this electrophotographic photoreceptor") according to an example of an embodiment of the present invention is an electrophotographic photoreceptor sequentially including a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on a conductive support.

[0028] This electrophotographic photoreceptor may optionally have layers other than the photosensitive layer and this protective layer. Also, the charging method of this electrophotographic photoreceptor may be either a negative charging method for charging the surface of the photoreceptor with negative charges or a positive charging method for charging the surface of the photoreceptor with positive charges.

[0029] In the present electrophotographic photoreceptor, the side opposite the conductive support is the upper side or front side, and the conductive support side is the lower side or back side.

[0030] <Characteristics of the present electrophotographic photoreceptor> This electrophotographic photoreceptor has a current flow of 15 A / m when a voltage of -3.4 kV is applied. 2 It is preferable that: The present inventors investigated the causes of wear on the surface of an electrophotographic photoreceptor, particularly the wear on the surface of the end of the photoreceptor that comes into contact with the end of the charging roller when used in a contact charging type image forming apparatus, and found that one of the causes is that the charge generated by the charging roller flows as a current inside the photoreceptor (hereinafter, this current is also referred to as "inflow current"). In the contact charging type, the electric field is concentrated especially at the end of the photoreceptor, so the inflow current to the end of the photoreceptor is also large, and it was found that the wear of the end becomes severe. The reason why a large current inflow causes the surface of the photoconductor to wear more severely is believed to be as follows: It is believed that a large current inflow causes the binder resin of the protective layer and the photosensitive layer to deteriorate. Specifically, it is believed that when a current inflow flows, the polymer chains of the binder resin of the protective layer and the photosensitive layer are destroyed, which reduces the wear resistance of the protective layer and the photosensitive layer, causing the surface of the photoconductor to wear more severely. Photoconductors, as a necessary characteristic, have the property of allowing electrons and holes to move, but the effect of inflow current on the characteristics of photoconductors has not been examined so far. In addition, the "photoconductor end" refers to the end in the length direction when the photoconductor is drum-shaped (cylindrical), and refers to the end in the width direction when the photoconductor is sheet-shaped or belt-shaped. Also, the end of the charging roller refers to the end in the length direction of the cylindrical roller. From this viewpoint, the inflow current of the electrophotographic photoreceptor is set to 15 A / m 2The following are preferred. When the flowing-in current is within the above range, deterioration of the binder resin of the protective layer and the photosensitive layer is suppressed, and the abrasion resistance of the photoreceptor can be improved. The flowing-in current is, among others, 12 A / m 2 or less, and among others, 10 A / m 2 or less, and among others, 8 A / m 2 or less is even more preferred. On the other hand, although it is preferable that the lower limit value of the flowing-in current is small, from the viewpoint of maintaining chargeability and maintaining photoreceptor performance, it is usually 1 A / m 2 or more.

[0031] In this electrophotographic photoreceptor, as a means for making the flowing-in current 15 A / m 2 or less, for example, methods such as increasing the thickness of the photosensitive layer or incorporating metal oxide particles having a band gap of 5 eV or more (which is also referred to as "insulating metal oxide particles" in the present invention) into the photosensitive layer can be mentioned. Thus, it is surprising and worthy of note that the abrasion resistance can be enhanced by improving the photosensitive layer, which is an intermediate layer, rather than improving the protective layer, which is the outermost layer. However, the specific means for making the flowing-in current 15 A / m 2 or less are not limited to these methods.

[0032] The method for measuring the flowing-in current of the photoreceptor is based on the method described in the examples below. Note that for the flowing-in current of the photoreceptor, it is sufficient if at least one location of the photoreceptor has a value within the above range. However, when it is clear that the value of the flowing-in current varies depending on the location of the photoreceptor, it is preferable that the average value of any location of the photoreceptor is within the above range, and it is more preferable that all locations of the photoreceptor are within the above range. Since the measurement of the flowing-in current is performed in the thickness direction of the photoreceptor, the above-mentioned location of the photoreceptor means an arbitrary position on the plane of the photoreceptor.

[0033] (Thickness of this photosensitive layer) The thickness of the photosensitive layer (also referred to as "the present photosensitive layer") in this electrophotographic photoreceptor is preferably 10 μm or more, more preferably 15 μm or more, still more preferably 19 μm or more, still more preferably 20 μm or more, still more preferably 22 μm or more, and still more preferably 24 μm or more from the viewpoint of suppressing the leakage current. On the other hand, from the viewpoint of chargeability, it is preferably 40 μm or less, more preferably 35 μm or less, and still more preferably 30 μm or less. Here, the thickness of the photosensitive layer refers to the thickness in the case of a single-layer photosensitive layer, and refers to the total thickness of the charge generation layer and the charge transport layer in the case of a laminated photosensitive layer.

[0034] (Thickness of this protective layer) The thickness of this protective layer is appropriately selected to an optimal thickness depending on the materials used, etc. From the viewpoint of the service life of the photoreceptor, the thickness of the protective layer is preferably 0.1 μm or more, more preferably 0.2 μm or more, and particularly preferably 0.5 μm or more. From the viewpoint of electrical characteristics, the thickness of the protective layer is preferably 10 μm or less, more preferably 5 μm or less, and particularly preferably 3 μm or less. Among them, from the viewpoint of suppressing ghost generation, the thickness of this protective layer is preferably 1 μm or less, more preferably 0.1 μm or more or 3 μm or less, still more preferably 0.5 μm or more or 2 μm or less, and still more preferably 0.8 μm or more or 1.5 μm or less.

[0035] Here, generally, as a method for improving the abrasion resistance of the photoreceptor, it is conceivable to increase the thickness of the protective layer. On the other hand, it has been found that when the thickness of the protective layer is increased, the image characteristics deteriorate, and problems such as ghosting occur. Ghosting is a phenomenon in which the afterimage of the first rotation image remains and is reflected in the second rotation image without disappearing. In this electrophotographic photoreceptor, the leakage current is 15 A / m 2By being as follows, deterioration of the binder resins of the protective layer and the photosensitive layer is suppressed, and the abrasion resistance of the photoreceptor can be improved. That is, in this electrophotographic photoreceptor, the thickness of the protective layer remains the same, and the abrasion resistance of the photoreceptor can be improved, so that the above-described ghost generation can also be prevented.

[0036] Also, from the viewpoints of suppressing the leakage current and balancing the abrasion resistance and the image characteristics, the ratio A / B of the thickness A of this protective layer to the thickness B of this photosensitive layer is preferably 0.002 or more, more preferably 0.005 or more, still more preferably 0.008 or more, and particularly preferably 0.01 or more. On the other hand, the ratio A / B of the thickness A of this protective layer to the thickness B of this photosensitive layer is preferably 0.3 or less, more preferably 0.2 or less, still more preferably 0.1 or less, and particularly preferably 0.06 or less.

[0037] <This photosensitive layer> The photosensitive layer (this photosensitive layer) in this electrophotographic photoreceptor may be a single-layer photosensitive layer in which a charge generation material (CGM), a hole transport material (HTM), and an electron transport material (ETM) are present in the same layer, or may be a laminated photosensitive layer separated into a charge generation layer and a charge transport layer.

[0038] (Insulating metal oxide particles) Regardless of whether this photosensitive layer is a single-layer type or a laminated type, this photosensitive layer preferably contains metal oxide particles (insulating metal oxide particles) having a band gap of 5 eV or more. Since the resistance of the entire photoreceptor becomes high by this photosensitive layer containing insulating metal oxide particles, it is considered that the above-described leakage current can be suppressed and the abrasion resistance can be enhanced.

[0039] The band gap of the insulating metal oxide particles may be 5 eV or more, preferably 7 eV or more, more preferably 9 eV or more. On the other hand, it is preferably 13 eV or less, more preferably 11 eV or less.

[0040] Examples of metal oxide particles (insulating metal oxide particles) having a band gap of 5 eV or more include silica, alumina, and zirconia. Among them, silica and alumina are preferred from the viewpoints of electrical properties and dispersibility, and silica is more preferred. Note that the band gap of silica particles is generally known to be about 8 to 9 eV.

[0041] From the viewpoint of not reflecting light of a wavelength (for example, 780 nm) irradiated during exposure of the photoreceptor, insulating metal oxide particles having a low refractive index are preferred. From such a viewpoint, the refractive index of the insulating metal oxide particles is preferably 2.00 or less, and more preferably 1.50 or less. Note that the refractive index of silica particles is generally known to be about 1.45 to 1.47 in the case of amorphous silica. Also, from the viewpoint of the stability of the coating liquid, those having a small specific gravity are preferred. From such a viewpoint, the specific gravity of the insulating metal oxide particles is preferably 7 or less, more preferably 5 or less, and even more preferably 3 or less. On the other hand, the specific gravity is preferably 1 or more. From the viewpoints of low refractive index and small specific gravity, among the above-described insulating metal oxide particles, silica particles are particularly preferred.

[0042] The silica particles may be particles composed of silicon dioxide (allowing the inclusion of less than 5 mass% of impurities). The method for producing the silica particles may be either a dry method or a wet method. Among them, from the viewpoint of a sharp particle size distribution, silica particles obtained by a sol-gel method (also referred to as "sol-gel silica") are preferred in the wet method.

[0043] The particle shape of the insulating metal oxide particles is arbitrary. However, from the viewpoint of reducing contamination of the charging roller in contact with the photoreceptor, a spherical shape is preferred. Also, from the perspective of dispersibility, the particle size of the insulating metal oxide particles preferably has an average primary particle size of 1 μm or less, more preferably 0.8 μm or less, and even more preferably 0.6 μm or less. On the other hand, from the perspective of reducing the leakage current, the average primary particle size is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. This average primary particle size is a value obtained by the arithmetic mean of the diameters of the particles directly observed by a transmission electron microscope (hereinafter also referred to as TEM).

[0044] In order to enhance the insulation, the insulating metal oxide particles may be surface-treated with, for example, silicone oil, silane coupling agent, siloxane compound, etc. to make the surface more hydrophobic. Also, in order to enhance the dispersibility in the binder resin, the insulating metal oxide particles may be surface-treated with at least one organic compound selected from the group consisting of siloxane compounds, silane coupling agents, polyhydric alcohols, titanium coupling agents, alkanolamines or their derivatives, and higher fatty acids or their metal salts. Among them, those surface-treated with a silane coupling agent are preferred. Examples of the silane coupling agent include alkoxysilane and silazane. Among them, silazane is preferred from the perspective of electrical properties. Among silazanes, hexamethyldisilazane is preferred.

[0045] From the perspective of suppressing the above-mentioned leakage current, the content of the insulating metal oxide particles is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 15 parts by mass or more with respect to 100 parts by mass of the photosensitive layer. On the other hand, from the perspective of electrical properties, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and even more preferably 30 parts by mass or less.

[0046] From the same perspective, the content of the insulating metal oxide particles is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 15 parts by mass or more with respect to 100 parts by mass of the binder resin of the photosensitive layer. On the other hand, from the perspective of electrical properties, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and still more preferably 30 parts by mass or less.

[0047] From the same perspective, the ratio (mass ratio) of the content of the insulating metal oxide particles to the content of the charge transport material (total content of the hole transport material (HTM) and the electron transport material (ETM)) is preferably 0.05 or more, more preferably 0.1 or more, and still more preferably 0.2 or more. On the other hand, it is preferably 1 or less, more preferably 0.8 or less, and still more preferably 0.6 or less.

[0048] From the same perspective, the ratio (mass ratio) of the content of the insulating metal oxide particles to the content of the hole transport material (HTM) is preferably 0.05 or more, more preferably 0.1 or more, and still more preferably 0.2 or more from the perspective of suppressing the inflow current. On the other hand, from the perspective of preventing contamination of the charging roller, it is preferably 1 or less, more preferably 0.8 or less, and still more preferably 0.6 or less.

[0049] <Laminated photosensitive layer> As the laminated photosensitive layer in this electrophotographic photoreceptor, there can be mentioned a configuration in which a charge transport layer (CTL) containing a hole transport material (HTM) is laminated on a charge generation layer (CGL) containing a charge generation material (CGM), or a configuration in which the charge generation layer (CGL) is laminated on the charge transport layer (CTL). Among them, a configuration in which the charge transport layer (CTL) is laminated on the charge generation layer (CGL) is preferable. At this time, it is also possible to provide other layers other than the charge generation layer (CGL) and the charge transport layer (CTL). Further, the charge transport layer (CTL) may further contain an electron transport material (ETM).

[0050] In the case of a laminated photosensitive layer, it is preferable that the charge generation layer (CGL) or the charge transport layer (CTL) or both contain the insulating metal oxide particles. Among them, since the layer thickness is larger, it is preferable that at least the charge transport layer (CTL) contains the insulating metal oxide particles from the viewpoint of further suppressing the inflow current.

[0051] <Charge generation layer (CGL)> The charge generation layer usually contains a charge generation material (CGM) and a binder resin.

[0052] (Charge generation material (CGM)) Examples of the charge generation material include inorganic photoconductive materials such as selenium and its alloys, cadmium sulfide, and organic photoconductive materials such as organic pigments. Among them, organic photoconductive materials are more preferable, particularly organic pigments are preferable, and among them, phthalocyanine pigments and azo pigments are more preferable, and phthalocyanine pigments are even more preferable. These all show the skeletal structure of the compound and include a group of compounds having that skeletal structure, that is, derivatives.

[0053] When an organic pigment is used as the charge generation material, usually, fine particles of these organic pigments are used in the form of a dispersion layer bound with various binder resins.

[0054] Specific examples of the phthalocyanine pigment include those having each crystal form of phthalocyanines coordinated with metals such as metal-free phthalocyanine, copper, gallium, tin, titanium, or their oxides and halides, phthalocyanine dimers using an oxygen atom or the like as a bridging atom, and the like. In particular, X-type, τ-type metal-free phthalocyanine, A-type (also known as β-type), B-type (also known as α-type), which are crystal forms with high sensitivity, and titanyl phthalocyanine (also known as oxytitanium phthalocyanine) such as D-type (also known as Y-type) characterized by showing distinct peaks at diffraction angles 2θ (±0.2°) of 27.1° or 27.3° in powder X-ray diffraction, chlorogallium phthalocyanine such as type II, and hydroxygallium phthalocyanine such as type V are suitable.

[0055] The charge generation material may be used alone or in combination of two or more kinds in any combination and ratio. Further, when two or more kinds of charge generation materials are used in combination, the charge generation materials to be used in combination may be mixed later, or may be mixed and used in the manufacturing and processing steps of charge generation materials such as synthesis, pigmentation, and crystallization. Such treatments include acid paste treatment, grinding treatment, solvent treatment, and the like.

[0056] The particle size of the charge generation material is usually 1 μm or less, preferably 0.5 μm or less. Furthermore, from the viewpoint of sensitivity, the content of the charge generation material in the photosensitive layer is usually preferably 0.1% by mass or more, more preferably 0.5% by mass or more. Also, from the viewpoints of sensitivity and chargeability, it is usually preferably 50% by mass or less, more preferably 20% by mass or less.

[0057] (Binder resin) The binder resin used in the charge generation layer can be used without particular limitation. For example, polyvinyl acetal resins such as polyvinyl butyral resin, polyvinyl formal resin, and partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal or acetal; polyarylate resin, polycarbonate resin, polyester resin, phenoxy resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl acetate resin, polystyrene resin, acrylic resin, methacrylic resin, polyacrylamide resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin; vinyl chloride-vinyl acetate copolymer, etc. can be mentioned. Among these resins, polyvinyl acetal resin or polyvinyl acetate resin is preferable from the viewpoints of dispersibility of the pigment, adhesiveness to the conductive support or the undercoat layer, and adhesiveness to the charge transport layer. Any one of these binder resins may be used alone, or two or more kinds may be mixed and used in any combination.

[0058] (Other components) The charge generation layer can contain other components as necessary in addition to the charge generation material and the binder resin. For example, for the purpose of improving film-forming properties, flexibility, coatability, stain resistance, gas resistance, light resistance, etc., additives such as known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light blockers, fillers, etc. may be contained.

[0059] (Mixing ratio) In the charge generation layer, if the ratio of the charge generation material is too high, the stability of the coating solution may decrease due to aggregation of the charge generation material, etc. On the other hand, if the ratio of the charge generation material is too low, the sensitivity of the photoreceptor may decrease. Therefore, the mixing ratio (mass) of the binder resin and the charge generation material is preferably such that the charge generation material is contained in an amount of 10 parts by mass or more, more preferably 30 parts by mass or more, per 100 parts by mass of the binder resin, and preferably in a ratio of 1000 parts by mass or less, more preferably 500 parts by mass or less. From the viewpoint of film strength, it is more preferably 300 parts by mass or less, and even more preferably 200 parts by mass or less.

[0060] (Layer thickness) The thickness of the charge generation layer is preferably 0.1 μm or more, more preferably 0.15 μm or more. On the other hand, it is preferably 10 μm or less, more preferably 0.6 μm or less.

[0061] <Charge transport layer (CTL)> The charge transport layer (CTL) usually contains a hole transport material (HTM) and a binder resin. It may further contain an electron transport material (ETM).

[0062] (Hole transport material (HTM)) The hole transport material (HTM) is not particularly limited. For example, heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, benzofuran derivatives, etc., aniline derivatives, hydrazone derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, as well as those in which multiple types of these compounds are bonded, and electron-donating substances such as polymers having groups composed of these compounds in the main chain or side chain, etc. can be mentioned.

[0063] Among these, carbazole derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, as well as those in which multiple types of these compounds are bonded are preferred, arylamine derivatives and enamine derivatives are more preferred, and enamine derivatives are even more preferred because they are less likely to inject electrons.

[0064] As suitable examples of the hole transport material (HTM), compounds having any of the structures represented by the following general formulas can be mentioned. However, it is not limited to these. Also, any one of them may be used alone, or two or more of them may be used in combination in any combination.

[0065] TIFF0007700486000003.tif44137

[0066] TIFF0007700486000004.tif77102

[0067] TIFF0007700486000005.tif6184

[0068] TIFF0007700486000006.tif6594

[0069] TIFF0007700486000007.tif50102

[0070] TIFF0007700486000008.tif64125

[0071] TIFF0007700486000009.tif56100

[0072] TIFF0007700486000010.tif4763

[0073] TIFF0007700486000011.tif6063

[0074] TIFF0007700486000012.tif5389

[0075] TIFF0007700486000013.tif5775

[0076] TIFF0007700486000014.tif41170

[0077] Among the aforementioned exemplary compounds, since the effects of the present invention can be more enjoyed, it is preferable to contain any one or a combination of two or more of the following formula (1) or formula (2) as a hole transport material (HTM).

[0078] TIFF0007700486000015.tif49170

[0079] TIFF0007700486000016.tif44170

[0080] Among the aforementioned hole transport materials (HTMs), from the viewpoint of suppressing the flowing-in current, a compound having two or more nitrogen atoms in one molecule is preferable. Further, it is preferable that the compound has a symmetric structure.

[0081] The content of the hole transport material (HTM) in the charge transport layer is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more with respect to 100 parts by mass of the binder resin. On the other hand, it is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less.

[0082] (Electron transport material (ETM)) The electron transport material (ETM) is not particularly limited. For example, it may include electron-withdrawing substances such as aromatic nitro compounds like 2,4,7-trinitrofluorenone, cyano compounds like tetracyanoquinodimethane, quinone compounds like diphenoquinone and dinaphthylquinone, and substances formed by combining multiple types of these compounds, or polymers having a group composed of these compounds in the main chain or side chain, etc. However, it is not limited to these, and known electron transport materials can be used. Among these, from the viewpoint of electrical properties, quinone compounds and perylene pigments (perylene derivatives) are preferred, and quinone compounds are more preferred. Among the above quinone compounds, from the viewpoint of electrical properties, diphenoquinone or dinaphthylquinone is preferred. Among them, dinaphthylquinone is more preferred. In addition, any one of the above electron transport materials may be used alone, or two or more of them may be used in combination in any combination.

[0083] As specific examples of the electron transport material (ETM) that can be used in this electrophotographic photoreceptor, the compounds represented by general formulas (ET1) to (ET3) exemplified in paragraphs 0043 to 0053 of JP-A No. 2017-09765 can be exemplified. In addition, compounds having any of the following structures can be mentioned.

[0084] TIFF0007700486000017.tif71120

[0085] TIFF0007700486000018.tif38170

[0086] The content of the electron transport material (ETM) in the charge transport layer is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more with respect to 100 parts by mass of the binder resin. On the other hand, it is preferably 150 parts by mass or less, more preferably 120 parts by mass or less, and even more preferably 100 parts by mass or less.

[0087] The content of the electron transport material (ETM) in the charge transport layer is preferably 0.1 part by mass or more, more preferably 0.3 part by mass or more, and even more preferably 0.5 part by mass or more with respect to 100 parts by mass of the content of the hole transport material (HTM) in the charge transport layer. On the other hand, it is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and even more preferably 5 parts by mass or less.

[0088] (Binder resin) Examples of the binder resin for the charge transport layer include vinyl polymers such as polymethyl methacrylate, polystyrene, and polyvinyl chloride, and copolymers thereof, and thermoplastic resins such as polycarbonate, polyarylate, polyester, polyester polycarbonate, polysulfone, phenoxy, epoxy, and silicone resin, and various thermosetting compounds. Among these resins, polycarbonate resin or polyarylate resin is preferred in terms of the light attenuation characteristics and mechanical strength as a photoreceptor.

[0089] The viscosity average molecular weight (Mv) of the binder resin is usually in the range of 5,000 to 300,000, preferably 10,000 to 200,000, more preferably 15,000 to 150,000, and particularly preferably 20,000 to 80,000. When the viscosity average molecular weight (Mv) is excessively small, the mechanical strength of the film obtained as a film for forming a photoreceptor tends to decrease. When the viscosity average molecular weight (Mv) is excessively large, the viscosity of the coating solution increases, and it tends to be difficult to apply it to an appropriate film thickness.

[0090] (Other components) In addition to the hole transport material (HTM), the electron transport material (ETM), and the binder resin, the charge transport layer can contain other components as needed. For example, for the purpose of improving film-forming properties, flexibility, coatability, stain resistance, gas resistance, light resistance, etc., additives such as known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light blocking agents, and fillers may be contained.

[0091] (Layer thickness) The layer thickness of the charge transport layer is not particularly limited. From the viewpoints of electrical properties, image stability, and further high resolution, it is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more or 35 μm or less, and still more preferably 15 μm or more or 25 μm or less.

[0092] <Single-layer photosensitive layer> When the photosensitive layer of the present electrophotographic photoreceptor is a single-layer photosensitive layer, usually, a binder resin, a charge generation material, a hole transport material, and an electron transport material are contained in the same layer.

[0093] For each of the charge generation material, the hole transport material, and the electron transport material, it is the same as that described for the above-mentioned laminated photosensitive layer.

[0094] From the viewpoint of sensitivity, the content of the charge generation material in the single-layer photosensitive layer is usually preferably 0.1% by mass or more, more preferably 0.5% by mass or more. Also, from the viewpoints of sensitivity and chargeability, it is usually preferably 50% by mass or less, and more preferably 20% by mass or less.

[0095] In the single-layer photosensitive layer, the content ratio of the binder resin constituting the photosensitive layer to the hole transport material is preferably 20 parts by mass or more of the hole transport material with respect to 100 parts by mass of the binder resin. Among them, from the viewpoint of reducing the residual potential, 30 parts by mass or more is more preferable, and from the viewpoints of stability and charge mobility when repeatedly used, 40 parts by mass or more is even more preferable. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, it is preferably 200 parts by mass or less of the hole transport material with respect to 100 parts by mass of the binder resin. Further, from the viewpoint of the compatibility between the hole transport material and the binder resin, 150 parts by mass or less is more preferable, and from the viewpoint of abrasion resistance, 120 parts by mass or less is particularly preferable.

[0096] In the single-layer photosensitive layer, the content ratio of the binder resin to the electron transport material is preferably 5 parts by mass or more of the electron transport material with respect to 100 parts by mass of the binder resin. From the viewpoint of reducing the residual potential, 10 parts by mass or more is more preferable, and from the viewpoints of stability and charge mobility during repeated use, 20 parts by mass or more is even more preferable. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, it is preferable that the electron transport material is 100 parts by mass or less with respect to 100 parts by mass of the binder resin. From the viewpoint of the compatibility between the electron transport material and the binder resin, 80 parts by mass or less is more preferable, 60 parts by mass or less is even more preferable, and 50 parts by mass or less is particularly preferable.

[0097] In the single-layer photosensitive layer, the content ratio (mass ratio) of the electron transport material (ETM) to the hole transport material (HTM) is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more. On the other hand, it is preferably 1 or less, more preferably 0.9 or less, and even more preferably 0.8 or less.

[0098] The content ratio of the binder resin constituting the single-layer photosensitive layer to the above charge transport materials (electron transport material and hole transport material) is arbitrary, but it is preferably 25 parts by mass or more of the charge transport material with respect to 100 parts by mass of the binder resin. Among them, from the viewpoint of reducing the residual potential, 35 parts by mass or more is preferable, and from the viewpoints of stability and charge mobility during repeated use, 45 parts by mass or more is more preferable. On the other hand, from the viewpoint of the thermal stability of the photosensitive layer, it is preferable that the charge transport material is 200 parts by mass or less with respect to 100 parts by mass of the binder resin, and from the viewpoint of the compatibility between the charge transport material and the binder resin, 150 parts by mass or less is more preferable, 125 parts by mass or less is even more preferable, and 100 parts by mass or less is particularly preferable.

[0099] <Method for forming each layer of the photosensitive layer> In both the laminated type and the single-layer type, each of the above layers can be formed as follows. A coating solution obtained by dissolving or dispersing a substance to be incorporated in a solvent is formed by sequentially repeating the coating and drying steps for each layer by a known method such as dip coating, spray coating, nozzle coating, bar coating, roll coating, blade coating, etc. on a conductive support. However, it is not limited to such a forming method.

[0100] The solvent or dispersion medium used for preparing the coating solution is not particularly limited. Specific examples include alcohols such as methanol, ethanol, propanol, 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, dimethoxyethane; aromatic hydrocarbons such as benzene, toluene, xylene, anisole; chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, trichloroethylene, etc. These may be used alone or in combination of two or more in any ratio and combination.

[0101] The amount of the solvent or dispersion medium used is not particularly limited. It is preferable to appropriately adjust so that physical properties such as the solid content concentration and viscosity of the coating solution are within a desired range in consideration of the purpose of each layer and the properties of the selected solvent or dispersion medium. For drying the coating film, after touch drying at room temperature, it is preferably heated and dried for 1 minute to 2 hours at a temperature in the range of usually 30°C or higher and 200°C or lower, either statically or with air blowing. Also, the heating temperature may be constant, or heating may be performed while changing the temperature during drying.

[0102] <This protective layer> The protective layer (this protective layer) of this electrophotographic photoreceptor is a layer containing a cured product formed by curing a curable compound.

[0103] Examples of the curable compound include photocurable compounds, thermosetting compounds, radiation curable compounds, etc. Among them, from the viewpoint of improving abrasion resistance, a photocurable compound is preferably used.

[0104] The curable compound is preferably a compound having a chain polymerizable functional group, for example. From the viewpoint of reactivity, the compound having a chain polymerizable functional group usually has 2 or more, preferably 3 or more, more preferably 4 or more chain polymerizable functional groups, while usually having 20 or less, preferably 10 or less, more preferably 6 or less. Examples of the chain polymerizable functional group of the compound having a chain polymerizable functional group include an acryloyl group, a methacryloyl group, a vinyl group, and an epoxy group. Among them, examples of the chain polymerizable functional group capable of radical polymerization include an acryloyl group, a methacryloyl group, and a vinyl group, and from the viewpoint of the curing rate, an acryloyl group and a methacryloyl group are preferable. The compound having a chain polymerizable functional group is not particularly limited as long as it is a known material, but from the viewpoint of curability, a monomer, oligomer, or polymer having an acryloyl group or a methacryloyl group is preferable.

[0105] Preferred compounds are exemplified below. Examples of monomers having an acryloyl group or a methacryloyl group include trimethylolpropane triacrylate (A-TMPT), trimethylolpropane trimethacrylate, HPA-modified trimethylolpropane triacrylate, EO-modified trimethylolpropane triacrylate, PO-modified trimethylolpropane triacrylate, caprolactone-modified trimethylolpropane triacrylate, HPA-modified trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerol triacrylate, ECH-modified glycerol triacrylate, EO-modified glycerol triacrylate, PO-modified glycerol triacrylate, tris(acryloxyethyl) isocyanurate, caprolactone-modified tris(acryloxyethyl) isocyanurate, EO-modified tris(acryloxyethyl) isocyanurate, PO-modified tris(acryloxyethyl) isocyanurate, dipentaerythritol hexaacrylate (A-DPH), caprolactone-modified dipentaerythritol hexaacrylate, dipentaerythritol hydroxypentaacrylate, alkyl-modified dipentaerythritol pentaacrylate, alkyl-modified dipentaerythritol tetraacrylate, alkyl-modified dipentaerythritol triacrylate, dimethylolpropane tetraacrylate, pentaerythritol ethoxytetraacrylate, EO-modified phosphate triacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, polytetramethylene glycol diacrylate, EO-modified bisphenol A diacrylate, PO-modified bisphenol A diacrylate, 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, tricyclodecane dimethanol diacrylate, decanediol diacrylate, hexanediol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, EO-modified bisphenol A dimethacrylate, PO-modified bisphenol A dimethacrylate, tricyclodecane dimethanol dimethacrylate, decanediol dimethacrylate, hexanediol dimethacrylate, etc. can be mentioned.,

[0106] As the oligomers and polymers having an acryloyl group or a methacryloyl group, known urethane acrylates, ester acrylates, acrylic acrylates, epoxy acrylates, etc. can be used. Examples of the urethane acrylate include "EBECRYL8301", "EBECRYL1290", "EBECRYL1830", "KRM8200" (Daicel Ornex Co., Ltd.), "UV1700B", "UV7640B", "UV7605B", "UV6300B", "UV7550B" (Mitsubishi Chemical Corporation), etc. Examples of the ester acrylate include "M-7100", "M-7300K", "M-8030", "M-8060", "M-8100", "M-8530", "M-8560", "M-9050" (Toagosei Co., Ltd.), etc. Examples of the acrylic acrylate include "8BR-600", "8BR-930MB", "8KX―078", "8KX-089", "8KX-168" (Daiso Fine Chemical Co., Ltd.), etc.

[0107] These may be used alone or in combination of two or more. Among these, from the viewpoint of electrical properties, it is preferable to contain urethane acrylate.

[0108] In addition to the compound having a polymerizable functional group, the protective layer may contain metal oxide particles or a charge transport material for the purpose of imparting charge transport ability. Further, a polymerization initiator may be contained to accelerate the polymerization reaction.

[0109] Hereinafter, the materials (metal oxide particles, charge transport material, polymerization initiator) used for the protective layer will be described in detail.

[0110] (Metal Oxide Particles) From the viewpoint of imparting charge transport ability to the protective layer and from the viewpoint of improving mechanical strength, the protective layer preferably contains metal oxide particles (also referred to as "conductive metal oxide particles") having a band gap of 2 eV or more and 4 eV or less.

[0111] As the conductive metal oxide particles, generally, any metal oxide particles that can be used in an electrophotographic photoreceptor can be used. More specifically, as the conductive metal oxide particles, metal oxide particles containing one kind of metal element such as titanium oxide, tin oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, zinc oxide, iron oxide, etc., and metal oxide particles containing a plurality of metal elements such as indium tin oxide, calcium titanate, strontium titanate, barium titanate, etc. can be mentioned. These conductive metal oxide particles may use only one kind of particle, or may use a mixture of a plurality of kinds of particles. Among these conductive metal oxide particles, from the viewpoint of electron transportability, titanium oxide, tin oxide, indium tin oxide, aluminum oxide, silicon oxide, zinc oxide are preferable, and titanium oxide and tin oxide are more preferable. Particularly, titanium oxide is preferable.

[0112] As the crystal form of the titanium oxide particles, any of rutile, anatase, brookite, and amorphous can be used. Also, a plurality of crystal states may be included from those having different crystal states.

[0113] The conductive metal oxide particles may be subjected to various surface treatments on their surfaces. For example, they may be treated with inorganic substances such as tin oxide, aluminum oxide, antimony oxide, zirconium oxide, silicon oxide, or organic substances such as stearic acid, polyol, and organosilicon compounds. In particular, when using titanium oxide particles, it is preferably surface-treated with an organosilicon compound. Examples of the organosilicon compound include silicone oils such as dimethylpolysiloxane and methylhydrogenpolysiloxane, organosilanes such as methyldimethoxysilane and diphenyldimethoxysilane, silazanes such as hexamethyldisilazane, and silane coupling agents such as 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, vinyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-aminopropyltriethoxysilane. In particular, from the viewpoint of improving the mechanical strength of the protective layer, 3-methacryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, and vinyltrimethoxysilane having a chain polymerizable functional group are preferred.

[0114] Note that the conductive metal oxide particles may be pre-treated with an insulating substance such as aluminum oxide, silicon oxide, or zirconium oxide before treating the outermost surface with such a treating agent. The conductive metal oxide particles may be used alone or in combination of a plurality of types of particles.

[0115] The conductive metal oxide particles are usually preferably those having an average primary particle diameter of 500 nm or less, more preferably those having a diameter of 1 nm to 100 nm, and even more preferably those having a diameter of 5 to 50 nm. This average primary particle diameter can be determined by the arithmetic mean value of the diameters of the particles directly observed by a transmission electron microscope (hereinafter also referred to as TEM).

[0116] Among the conductive metal oxide particles of this electrophotographic photoreceptor, specific product names of titanium oxide particles include ultrafine titanium oxide without surface treatment, "TTO-55(N)", "TTO-51(N)"; ultrafine titanium oxide coated with Al2O3, "TTO-55(A)", "TTO-55(B)"; ultrafine titanium oxide surface-treated with stearic acid, "TTO-55(C)"; ultrafine titanium oxide surface-treated with Al2O3 and organosiloxane, "TTO-55(S)"; high-purity titanium oxide, "C-EL"; titanium oxide by the sulfuric acid method, "R-550", "R-580", "R-630", "R-670", "R-680", "R-780", "A-100", "A-220", "W-10"; titanium oxide by the chlorine method, "CR-50", "CR-58", "CR-60", "CR-60-2", "CR-67"; conductive titanium oxide, "ET-300W" (all of the above are manufactured by Ishihara Sangyo Co., Ltd.), and titanium oxide such as "R-60", "A-110", "A-150", and Al2O3-coated "SR-1", "R-GL", "R-5N", "R-5N-2", "R-52N", "RK-1", "A-SP", SiO2, Al2O3-coated "R-GX", "R-7E", ZnO, SiO2, Al2O3-coated "R-650", ZrO2, Al2O3-coated "R-61N" (all of the above are manufactured by Sakai Chemical Industry Co., Ltd.), and in addition, "TR-700" surface-treated with SiO2, Al2O3, "TR-840", "TA-500" surface-treated with ZnO, SiO2, Al2O3, and untreated titanium oxide such as "TA-100", "TA-200", "TA-300", and "TA-400" surface-treated with Al2O3 (all of the above are manufactured by Fuji Titanium Industry Co., Ltd.), and untreated "MT-150W", "MT-500B", "MT-100SA", "MT-500SA" surface-treated with SiO2, Al2O3, and "MT-100SAS", "MT-500SAS" surface-treated with SiO2, Al2O3 and organosiloxane (manufactured by Teika Co., Ltd.), etc. can be mentioned.

[0117] In addition, specific product names of aluminum oxide particles include "Aluminium Oxide C" (manufactured by Nippon Aerosil Co., Ltd.), etc.

[0118] Specific product names of silicon oxide particles include "200CF", "R972" (manufactured by Nippon Aerosil Co., Ltd.), "KEP-30" (manufactured by Nippon Shokubai Co., Ltd.), and the like.

[0119] Specific product names of tin oxide particles include "SN-100P", "SN-100D" (manufactured by Ishihara Sangyo Co., Ltd.), "SnO2" (manufactured by CIK Nanotech Co., Ltd.), "S-2000", Lindop tin oxide "SP-2", antimony-doped tin oxide "T-1", indium-doped tin oxide "E-ITO" (Mitsubishi Materials Corporation), and the like.

[0120] A specific product name of zinc oxide particles can be "MZ-305S" (manufactured by Teika Co., Ltd.), but the conductive metal oxide particles usable in the present invention are not limited thereto.

[0121] The content of the conductive metal oxide particles in the present protective layer is not particularly limited. From the viewpoint of electrical properties, it is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and particularly preferably 30 parts by mass or more with respect to 100 parts by mass of the binder resin. Further, from the viewpoint of maintaining good surface resistance, it is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and particularly preferably 120 parts by mass or less.

[0122] The content ratio (mass ratio) of the insulating metal oxide particles in the present photosensitive layer to the content of the conductive metal oxide particles in the present protective layer is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more from the viewpoint of suppressing the inflow current. On the other hand, from the viewpoint of electrical properties, it is preferably 0.5 or less, more preferably 0.45 or less, and even more preferably 0.4 or less.

[0123] This protective layer may further contain metal oxide particles (insulating metal oxide particles) with a band gap of 5 eV or more. As the insulating metal oxide particles contained in this protective layer, those similar to the insulating metal oxide particles contained in the aforementioned photosensitive layer can be used. By including insulating metal oxide particles in this protective layer in addition to the photosensitive layer, it is presumed that the inflow current can be further suppressed and the abrasion resistance can be further enhanced.

[0124] From the perspective of imparting charge transport ability to this protective layer, the content of the insulating metal oxide particles in this protective layer is preferably less than the content of the conductive metal oxide particles in this protective layer. The content ratio (mass ratio) of the conductive metal oxide particles to the insulating metal oxide particles in this protective layer is preferably 0.1 or more, more preferably 0.2 or more, and even more preferably 0.3 or more. On the other hand, it is preferably 0.7 or less, more preferably 0.6 or less, and even more preferably 0.5 or less.

[0125] (Charge transport material) As the charge transport material to be contained in this protective layer, those similar to the charge transport material used in the aforementioned photosensitive layer can be used.

[0126] The content of the charge transport material in this protective layer is not particularly limited. From the perspective of electrical properties, it is preferably 10 parts by mass or more, more preferably 30 parts by mass or more, and particularly preferably 50 parts by mass or more with respect to 100 parts by mass of the binder resin. Also, from the perspective of maintaining good surface resistance, it is preferably 300 parts by mass or less, more preferably 200 parts by mass or less, and particularly preferably 150 parts by mass or less.

[0127] Also, from the perspective of imparting charge transport ability to the protective layer, the protective layer may contain a structure formed by polymerizing a charge transport material having a chain polymerizable functional group. Examples of the chain polymerization functional group of the charge transport material having a chain polymerization functional group include an acryloyl group, a methacryloyl group, a vinyl group, and an epoxy group. Among these, from the viewpoint of curability, an acryloyl group or a methacryloyl group is preferable. Examples of the structure of the charge transport material portion of the charge transport material having a chain polymerization functional group include heterocyclic compounds such as carbazole derivatives, indole derivatives, imidazole derivatives, oxazole derivatives, pyrazole derivatives, thiadiazole derivatives, benzofuran derivatives, aniline derivatives, hydrazone derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, and those in which a plurality of these compounds are bonded, and electron-donating materials such as polymers having a group composed of these compounds in the main chain or side chain. Among these, from the viewpoint of electrical characteristics, carbazole derivatives, arylamine derivatives, stilbene derivatives, butadiene derivatives, and enamine derivatives, and those in which a plurality of these compounds are bonded are preferable.

[0128] (Polymerization initiator) The polymerization initiator includes a thermal polymerization initiator, a photopolymerization initiator, and the like.

[0129] Examples of the thermal polymerization initiator include peroxide-based compounds such as 2,5-dimethylhexane-2,5-dihydroperoxide, dicumyl peroxide, benzoyl peroxide, t-butyl peroxide, t-butylcumyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, lauroyl peroxide, and azo-based compounds such as 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(cyclohexanecarbonitrile), 2,2'-azobis(isobutyric acid methyl), 2,2'-azobis(isobutylamidine hydrochloride), 4,4'-azobis-4-cyanovaleric acid.

[0130] Photoinitiators can be classified into direct cleavage type and hydrogen abstraction type according to the difference in radical generation mechanisms. When a direct cleavage type photoinitiator absorbs light energy, radicals are generated by cleavage of a part of the covalent bonds within the molecule. On the other hand, when a hydrogen abstraction type photoinitiator absorbs light energy, the excited molecule abstracts hydrogen from a hydrogen donor to generate radicals.

[0131] Examples of direct cleavage type photoinitiators include acetophenone-based or ketal-based compounds such as acetophenone, 2-benzoyl-2-propanol, 1-benzoylcyclohexanol, 2,2-diethoxyacetophenone, benzyldimethylketal, 2-methyl-4'-(methylthio)-2-morpholinopropiophenone; benzoin ether-based compounds such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, O-tosylbenzoin; and acylphosphine oxide-based compounds such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, lithium phenyl(2,4,6-trimethylbenzoyl)phosphonate.

[0132] Examples of hydrogen abstraction type photoinitiators include benzophenone-based compounds such as benzophenone, 4-benzoylbenzoic acid, 2-benzoylbenzoic acid, methyl 2-benzoylbenzoate, methyl benzoylformate, benzyl, p-anisyl, 2-benzoylnaphthalene, 4,4'-bis(dimethylamino)benzophenone, 4,4'-dichlorobenzophenone, 1,4-dibenzoylbenzene; anthraquinone-based or thioxanthone-based compounds such as 2-ethylanthraquinone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-dichlorothioxanthone. Other photoinitiators include camphorquinone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime, acridine-based compounds, triazine-based compounds, and imidazole-based compounds.

[0133] The photoinitiator preferably has an absorption wavelength in the wavelength region of the light source used for light irradiation in order to efficiently absorb light energy and generate radicals. On the other hand, among the compounds contained in this protective layer, if components other than the photoinitiator have absorption in this wavelength region, the photoinitiator may not be able to absorb sufficient light energy, and the radical generation efficiency may decrease. General binder resins, charge transport materials, and metal oxide particles have absorption wavelengths in the ultraviolet region (UV), so this effect is particularly prominent when the light source used for light irradiation is ultraviolet light (UV). From the viewpoint of preventing such problems, it is preferable to contain an acylphosphine oxide-based compound having an absorption wavelength on the relatively longer wavelength side among photoinitiators. In addition, the acylphosphine oxide-based compound has a photobleaching effect in which the absorption wavelength region changes to the shorter wavelength side due to self-cleavage, so it can transmit light to the inside of the protective layer and is also preferable from the viewpoint of good internal curability. In this case, from the viewpoint of supplementing the curability of the surface of the protective layer, it is more preferable to use a hydrogen abstraction type initiator in combination. The content ratio of the hydrogen abstraction type initiator to the acylphosphine oxide-based compound is not particularly limited, but from the viewpoint of supplementing the surface curability, 0.1 part by mass or more is preferable with respect to 1 part by mass of the acylphosphine oxide-based compound, and from the viewpoint of maintaining the internal curability, 5 parts by mass or less is preferable.

[0134] In addition, those having a photo-polymerization promoting effect can be used alone or in combination with the above photoinitiator. For example, triethanolamine, methyldiethanolamine, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, 4,4'-dimethylaminobenzophenone, etc. can be mentioned.

[0135] These polymerization initiators may be used alone or in a mixture of two or more. The content of the polymerization initiator is 0.5 to 40 parts by mass, preferably 1 to 20 parts by mass, based on 100 parts by mass of the total radical polymerizable components.

[0136] (Other materials) This protective layer may contain other materials as necessary. Examples of other materials include stabilizers (such as heat stabilizers, ultraviolet absorbers, light stabilizers, antioxidants, etc.), dispersants, antistatic agents, colorants, lubricants, and the like. These can be used singly as appropriate, or two or more of them can be used in any ratio and combination.

[0137] (Method for forming this protective layer) Next, the method for forming this protective layer will be described. The method for forming this protective layer is not particularly limited. For example, it can be formed by applying a coating solution in which a binder resin, a charge transport material, metal oxide particles, and other substances are dissolved in a solvent or a coating solution dispersed in a dispersion medium.

[0138] Hereinafter, the solvent or dispersion medium used for forming this protective layer and the coating method will be described.

[0139] [Solvent used for the coating solution for forming the protective layer] Examples of the organic solvent used in the coating liquid for forming the protective layer include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; esters such as methyl formate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and anisole; chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichlorethylene; 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. A mixed solvent of any combination and any ratio can be used from these. Also, even if it is an organic solvent that does not dissolve the substance for the protective layer of the electrophotographic photoreceptor alone, it can be used as long as it can be dissolved by, for example, being a mixed solvent with the above organic solvent. Generally, using a mixed solvent can reduce coating unevenness. When using the dip coating method in the coating method described later, it is preferable to select a solvent that does not dissolve the lower layer. From this viewpoint, it is preferable to contain alcohols that have low solubility in polycarbonate and polyarylate, which are preferably used for the photosensitive layer.

[0140] The amount ratio of the organic solvent used in the coating liquid for forming the protective layer to the solid content varies depending on the coating method of the coating liquid for forming the protective layer, and it may be appropriately changed and used so that a uniform coating film is formed in the applicable coating method.

[0141] [Coating method] The coating method of the coating liquid for forming the protective layer is not particularly limited, and examples thereof include a spray coating method, a spiral coating method, a ring coating method, and a dip coating method.

[0142] After forming a coating film by the above coating method, the coating film is dried. At this time, as long as necessary and sufficient drying is obtained, the drying temperature and time are not limited. However, when the protective layer is applied only by air drying after the photosensitive layer is applied, it is preferable to perform sufficient drying by the method described in the [coating method] of the aforementioned photosensitive layer.

[0143] [Method for curing this protective layer] This protective layer is formed by applying such a coating liquid and then applying energy from the outside to cure it. The external energy used at this time includes heat, light, and radiation. As a method of applying heat energy, it is performed by heating from the coating surface side or the support side using a gas such as air or nitrogen, steam, various heat media, infrared rays, or electromagnetic waves. The heating temperature is preferably 100 °C or higher and 170 °C or lower. At a temperature equal to or higher than the lower limit temperature, a sufficient reaction rate is achieved and the reaction proceeds completely. At a temperature equal to or lower than the upper limit temperature, the reaction proceeds uniformly and the generation of large distortions in the protective layer can be suppressed. In order to advance the curing reaction uniformly, a method of heating at a relatively low temperature below 100 °C and then further heating to 100 °C or higher to complete the reaction is also effective.

[0144] As the light energy, mainly UV irradiation light sources such as high-pressure mercury lamps, metal halide lamps, electrodeless lamp bulbs, and light-emitting diodes having emission wavelengths in ultraviolet light (UV) can be used, but it is also possible to select a visible light source according to the absorption wavelengths of the chain polymerizable compound and the photoinitiator. The light irradiation amount is preferably 0.1 J / cm 2 or more, more preferably 0.5 J / cm 2 or more, particularly preferably 1 J / cm 2 or more. Also, from the viewpoint of electrical characteristics, it is preferably 150 J / cm 2 or less, more preferably 100 J / cm 2 or less, particularly preferably 50 J / cm 2 or less. As the radiation energy, those using an electron beam (EB) can be mentioned.

[0145] Among these energies, those using light energy are preferred from the viewpoints of ease of reaction rate control, simplicity of the apparatus, and length of pot life.

[0146] After curing the protective layer, a heating step may be added from the viewpoints of relaxation of residual stress, relaxation of residual radicals, and improvement of electrical characteristics. The heating temperature is preferably 60°C or higher, more preferably 100°C or higher, and preferably 200°C or lower, more preferably 150°C or lower.

[0147] <Conductive support> The conductive support of this electrophotographic photoreceptor is not particularly limited as long as it supports the layer formed thereon and exhibits conductivity. Examples of the conductive support include metal materials such as aluminum, aluminum alloy, stainless steel, copper, and nickel, resin materials imparted with conductivity by coexisting conductive powders such as metal, carbon, and tin oxide, and resins, glass, paper, etc. on which a conductive material such as aluminum, nickel, ITO (indium tin oxide alloy) is vapor-deposited or coated on the surface. As the form, drum-shaped, sheet-shaped, belt-shaped, etc. are used. A conductive material having an appropriate resistance value may be coated on the conductive support of the metal material for controlling conductivity, surface properties, etc. or for covering defects.

[0148] When a metal material such as an aluminum alloy is used as the conductive support, it may be used after applying an anodic oxide film to the metal material.

[0149] The average film thickness of the anodic oxide film is usually 20 μm or less, particularly preferably 7 μm or less.

[0150] When applying an anodic oxide film to a metal material, it is preferable to perform a sealing treatment. The sealing treatment can be performed by a known method.

[0151] The surface of the above conductive support may be smooth, or may be roughened by using a special cutting method or performing a polishing treatment. Also, it may be roughened by mixing particles of an appropriate particle size into the material constituting the support. Note that an undercoat layer described later may be provided between the above conductive support and the photosensitive layer in order to improve adhesiveness, blocking property, etc.

[0152] <Undercoat layer> This electrophotographic photoreceptor may have an undercoat layer between the photosensitive layer and the conductive support.

[0153] As the undercoat layer, for example, a resin, a resin in which particles such as an organic pigment or a metal oxide are dispersed, etc. can be used. The organic pigment used for the undercoat layer is not particularly limited. For example, phthalocyanine pigments and azo pigments in the case of using them as the charge generation material described above can be mentioned.

[0154] Examples of the metal oxide particles used for the undercoat layer include metal oxide particles containing one kind of metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, iron oxide, etc., and metal oxide particles containing a plurality of metal elements such as calcium titanate, strontium titanate, barium titanate, etc. For the undercoat layer, only the above one kind of particles may be used, or a plurality of kinds of particles may be mixed and used in an arbitrary ratio and combination.

[0155] Among the above metal oxide particles, titanium oxide and aluminum oxide are preferable, and titanium oxide is particularly preferable. Note that the titanium oxide particles may have their surfaces treated with an arbitrary inorganic substance or an arbitrary organic substance, etc. Also, as the crystal form of the titanium oxide particles, any of rutile, anatase, brookite, and amorphous can be used. Also, those having a plurality of crystal states may be included.

[0156] The particle size of the metal oxide particles used for the undercoat layer is not particularly limited. From the viewpoints of the properties of the undercoat layer and the stability of the solution for forming the undercoat layer, the average primary particle size is preferably 10 nm or more, and preferably 100 nm or less, more preferably 50 nm or less.

[0157] Here, it is desirable that the undercoat layer is formed in a form in which particles are dispersed in a binder resin. Examples of the binder resin used for the undercoat layer include polyvinyl acetal resins such as polyvinyl butyral resin, polyvinyl formal resin, and partially acetalized polyvinyl butyral resin in which a part of butyral is modified with formal or acetal; polyarylate resin, polycarbonate resin, polyester resin, phenoxy resin, acrylic resin, methacrylic resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, polyvinyl alcohol resin, styrene-alkyd resin, silicone-alkyd resin, phenolic-formaldehyde resin, and other insulating resins, and the like can be selected and used. However, it is not limited to these polymers. Further, these binder resins may be used alone, or two or more kinds may be mixed and used, or they may be used in a cured form together with a curing agent. Among them, polyvinyl acetal resins, alcohol-soluble copolymer polyamides, modified polyamides, etc. are preferable because they exhibit good dispersibility and coatability. Among them, alcohol-soluble copolymer polyamides are particularly preferable.

[0158] The mixing ratio of the particles with respect to the above binder resin can be arbitrarily selected. It is preferable to use in the range of 10% by mass to 500% by mass from the viewpoints of the stability and coatability of the dispersion liquid.

[0159] The film thickness of the undercoat layer can be arbitrarily selected. From the viewpoints of the properties of the electrophotographic photoreceptor and the coatability of the above dispersion liquid, it is preferably 0.1 μm or more and 20 μm or less. Further, the undercoat layer may contain a known antioxidant or the like.

[0160] <Other Layers> In addition, the electrophotographic photoreceptor may optionally have other layers as needed, in addition to the above-described conductive support, photosensitive layer, protective layer, and undercoat layer.

[0161] (Thickness other than the conductive support) In terms of leakage resistance, the thickness of the electrophotographic photoreceptor excluding the conductive support, that is, the thickness obtained by subtracting the thickness of the conductive support from the thickness of the electrophotographic photoreceptor, is preferably 10 μm or more, more preferably 15 μm or more, and still more preferably 20 μm or more. On the other hand, from the viewpoint of chargeability, it is preferably 50 μm or less, more preferably 40 μm or less, and still more preferably 35 μm or less.

[0162] <<This image forming apparatus>> An image forming apparatus (``this image forming apparatus'') can be configured using this electrophotographic photoreceptor.

[0163] As shown in FIG. 1, this image forming apparatus includes an electrophotographic photoreceptor 1, a charging device 2, an exposure device 3, and a developing device 4, and further includes a transfer device 5, a cleaning device 6, and a fixing device 7 as needed. The electrophotographic photoreceptor 1 is not particularly limited as long as it is the above-described electrophotographic photoreceptor. In FIG. 1, as an example, a drum-shaped photoreceptor in which the above-described photosensitive layer is formed on the surface of a cylindrical conductive support is shown. Along the outer peripheral surface of this electrophotographic photoreceptor 1, a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, and a cleaning device 6 are respectively arranged.

[0164] The charging device 2 charges the electrophotographic photoreceptor 1 and uniformly charges the surface of the electrophotographic photoreceptor 1 to a predetermined potential. As common charging devices, there can be mentioned non-contact corona charging devices such as a corotron and a scorotron, or an image forming apparatus of a contact charging method (also referred to as a "contact type charging device" or a "direct type charging device") that charges by bringing a charged member to which a voltage is applied into contact with the photoreceptor surface. Examples of the contact type charging device include a charging roller and a charging brush. In FIG. 1, a roller type charging device (charging roller) is shown as an example of the charging device 2. In charging, it may be charged by a DC voltage, or may be charged by superimposing an AC voltage on the DC voltage.

[0165] The exposure device 3 is not particularly limited in type as long as it can perform exposure on the electrophotographic photoreceptor 1 to form an electrostatic latent image on the photosensitive surface of the electrophotographic photoreceptor 1. Also, exposure may be performed by an internal photoreceptor exposure method. The light at the time of exposure is arbitrary.

[0166] The type of the toner T is arbitrary, and in addition to a powder toner, a polymer toner using a suspension polymerization method, an emulsion polymerization method, or the like can be used.

[0167] The transfer device 5 is not particularly limited in type, and a device using any method such as an electrostatic transfer method such as corona transfer, roller transfer, or belt transfer, a pressure transfer method, or an adhesion transfer method can be used. Here, it is assumed that the transfer device 5 is composed of a transfer charger, a transfer roller, a transfer belt, etc. arranged to face the electrophotographic photoreceptor 1. This transfer device 5 applies a predetermined voltage value (transfer voltage) with a polarity opposite 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.

[0168] There are no particular restrictions on the cleaning device 6, and any cleaning device such as a brush cleaner, a magnetic brush cleaner, an electrostatic brush cleaner, a magnetic roller cleaner, a blade cleaner, etc. can be used. The cleaning device 6 scrapes off the residual toner adhering to the photoreceptor 1 with a cleaning member and collects the residual toner. However, if there is little or almost no toner remaining on the surface of the photoreceptor, the cleaning device 6 may not be necessary.

[0169] In the image forming apparatus configured as described above, image recording is performed as follows. That is, first, the surface (photosensitive surface) of the photoreceptor 1 is charged to a predetermined potential (for example, 600 V) by the charging device 2. At this time, it may be charged by a DC voltage, or it may be charged by superimposing an AC voltage on the DC voltage. Subsequently, the charged photosensitive surface of the photoreceptor 1 is exposed by the exposure device 3 according to the image to be recorded, and an electrostatic latent image is formed on the photosensitive surface. Then, the development of the electrostatic latent image formed on the photosensitive surface of the photoreceptor 1 is performed by the developing device 4.

[0170] The developing device 4 thins the toner T supplied by the supply roller 43 with a regulating member (developing blade) 45, triboelectrically charges it to a predetermined polarity (here, the same polarity as the charging potential of the photoreceptor 1, positive polarity), conveys it while being carried on the developing roller 44, and brings it into contact with the surface of the photoreceptor 1. When the charged toner T carried on the developing roller 44 comes into contact with the surface of the photoreceptor 1, a toner image corresponding to the electrostatic latent image is formed on the photosensitive surface of the photoreceptor 1. Then, this toner image is transferred to the recording paper P by the transfer device 5. After that, the toner remaining on the photosensitive surface of the photoreceptor 1 without being transferred is removed by the cleaning device 6.

[0171] After the transfer of the toner image onto the recording paper P, the toner image is thermally fixed onto the recording paper P by passing it through the fixing device 7, and finally an image is obtained. In addition to the above-described configuration, the image forming apparatus may be configured to be able to perform, for example, a discharging process.

[0172] Furthermore, the present image forming apparatus may be configured with further modifications. For example, it may be configured to perform processes such as a pre-exposure process and an auxiliary charging process, or to be configured to perform offset printing, or further to be configured in a full-color tandem system using a plurality of types of toner.

[0173] <<This electrophotographic cartridge>> The electrophotographic photoreceptor 1 can be combined with one or two or more of a charging device 2, an exposure device 3, a developing device 4, a transfer device 5, a cleaning device 6, and a fixing device 7 to be configured as an integrated cartridge (referred to as "this electrophotographic cartridge").

[0174] This electrophotographic cartridge can be configured to be detachable from the main body of an electrophotographic apparatus such as a copying machine or a laser beam printer. In that case, for example, when the electrophotographic photoreceptor 1 or other members deteriorate, this electrophotographic photoreceptor cartridge can be removed from the main body of the image forming apparatus, and another new electrophotographic photoreceptor cartridge can be attached to the main body of the image forming apparatus, facilitating the maintenance and management of the image forming apparatus.

[0175] <<Explanation of terms>> In the present invention, when expressed as "X to Y" (X and Y are arbitrary numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as the meaning of "preferably greater than X" or "preferably less than Y". Also, when expressed as "X or more" (X is an arbitrary number) or "Y or less" (Y is an arbitrary number), it also includes the intention of "preferably greater than X" or "preferably less than Y".

Examples

[0176] The present invention will be further described by the following examples. However, the examples are not intended to limit the present invention in any way.

[0177] <Manufacture of the coating liquid for forming the undercoat layer> (Coating liquid A for forming the undercoat layer) The surface of rutile-type titanium oxide (manufactured by Ishihara Sangyo Co., Ltd., "TTO55N", average primary particle diameter of 40 nm) was treated with methyldimethoxysilane (manufactured by Toshiba Silicone Co., Ltd., "TSL8117"), and the titanium oxide particles were mixed with a copolymer polyamide having the following composition ratio in a mixed solvent (mass ratio of methanol / 1-propanol / toluene of 7 / 1 / 2) while heating and stirring to dissolve the copolymer polyamide. Subsequently, ultrasonic dispersion treatment was performed for 1 hour using an ultrasonic generator with an output of 1200 W, and then filtration was carried out to obtain a coating liquid A for forming a subbing layer with a mass ratio of surface-treated titanium oxide / copolymer polyamide of 3 / 1 and a solid content concentration of 18.0% by mass. Composition ratio (molar ratio) of copolymer polyamide: ε-caprolactam / bis(4-amino-3-methylcyclohexyl)methane / hexamethylenediamine / decamethylenedicarboxylic acid / octadecamethylenedicarboxylic acid = 75 / 9.5 / 3 / 9.5 / 3

[0178] <Manufacture of coating liquid for forming charge generation layer> (Coating liquid B for forming charge generation layer) The coating liquid for forming the charge generation layer was prepared as follows. As a charge generation material, 20 parts of D-type (Y-type) oxytitanium phthalocyanine A and 280 parts of 1,2-dimethoxyethane were mixed and pulverized for 1 hour using a sand grinder to perform fine dispersion treatment. Subsequently, 10 parts of polyvinyl butyral (manufactured by Denki Kagaku Kogyo Co., Ltd., "Denka Butyral" #6000C) was added to the fine dispersion treatment liquid, dissolved in a mixed liquid of 255 parts of 1,2-dimethoxyethane and 85 parts of 4-methoxy-4-methyl-2-pentanone to obtain a binder liquid, and 230 parts of 1,2-dimethoxyethane were mixed to prepare a coating liquid B1 for forming a charge generation layer.

[0179] On the other hand, as a charge generation material, 20 parts of A-type (β-type) oxytitanium phthalocyanine B and 280 parts of 1,2-dimethoxyethane were mixed and pulverized with a sand grinder for 4 hours to perform a micronization dispersion treatment. Subsequently, 10 parts of polyvinyl butyral (manufactured by Denki Kagaku Kogyo Co., Ltd., "Denka Butyral" #6000C) were dissolved in a mixed solution of 255 parts of 1,2-dimethoxyethane and 85 parts of 4-methoxy-4-methyl-2-pentanone to obtain a binder solution, and 230 parts of 1,2-dimethoxyethane were mixed to prepare a coating solution B2 for forming a charge generation layer.

[0180] The coating solution B1 for forming a charge generation layer and the coating solution B2 for forming a charge generation layer were mixed at a mass ratio of 7:3 to prepare a coating solution B for forming a charge generation layer used in this example.

[0181] <Manufacture of Coating Solution for Forming Charge Transport Layer> (Coating Solution C1 for Forming Charge Transport Layer) 66.64 parts of a polycarbonate resin (resin X1, viscosity average molecular weight 50,000) represented by the following repeating structure, 33.33 parts of HTM1 as a charge transport material, and 0.03 part of a leveling agent silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., KF96-10CS) were heated and stirred in a mixed solvent of tetrahydrofuran and toluene at a ratio of 8:2 to dissolve, and a coating solution C1 for forming a charge transport layer with a solid content concentration of 18% by mass was obtained.

[0182] Resin X1 is a resin having the following chemical structure.

[0183] TIFF0007700486000019.tif27170

[0184] HTM1 is a compound having the following chemical structure.

[0185] TIFF0007700486000020.tif47170

[0186] (Coating Solution C2 for Forming Charge Transport Layer) Silica (silicon dioxide) particles (KE-S30HG, manufactured by Nippon Shokubai Co., Ltd., average primary particle diameter 0.25 μm, specific gravity 2.2, spherical) were surface-treated with hexamethyldisilazane. These surface-treated silica particles were placed in a tetrahydrofuran solvent and ultrasonic dispersion was carried out for 4 hours to obtain a surface-treated silica particle slurry. Next, 66.64 parts of the resin X1, 33.33 parts of HTM1 as a charge transport material, and 0.03 parts of silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd., KF96-10CS) as a leveling agent were heated and stirred in a mixed solvent of tetrahydrofuran and anisole at a ratio of 9:1 to be dissolved, and an intermediate liquid was prepared. To this intermediate liquid, the surface-treated silica particle slurry was added so that the number of parts of the surface-treated silica particles was 0.3 times the number of parts of HTM1. Thereafter, heating and stirring were carried out to obtain a coating liquid C2 for forming a charge transport layer having a solid content concentration of 18% by mass. Note that the concentration of silica particles in the surface-treated silica particle slurry and the mixing ratio of tetrahydrofuran and anisole in the intermediate liquid were determined so that the mixing ratio of tetrahydrofuran and anisole in the entire liquid after adding the surface-treated silica particle slurry to the intermediate liquid was 9:1.

[0187] (Coating liquid C3 for forming a charge transport layer) Regarding the addition amount of the surface-treated silica particle slurry used in the coating liquid C2 for forming a charge transport layer, a coating liquid C3 for forming a charge transport layer was obtained in the same manner as the coating liquid C2 for forming a charge transport layer, except that the surface-treated silica particles were added so that the number of parts was 0.1 times the number of parts of HTM1.

[0188] (Manufacture of coating liquid for forming a protective layer) (Coating liquid S1 for forming a protective layer) Rutile-type white titanium oxide with an average primary particle diameter of 40 nm (TTO55N, manufactured by Ishihara Sangyo Co., Ltd.) and 7 parts by mass of 3-methacryloxypropyltrimethoxysilane with respect to 100 parts by mass of the titanium oxide were stirred with a shear force using a super mixer until the temperature in the mixer reached 150°C to perform surface treatment of the titanium oxide. Next, 1000 g of a raw material slurry obtained by mixing 250 g of the surface-treated titanium oxide and 750 g of methanol was dispersed using zirconia beads (manufactured by Nikkato Corporation, YTZ) with a diameter of about 50 μm as a dispersion medium in an Ultra Apex Mill (manufactured by Kotobuki Industries Co., Ltd., UAM-015 type) with a mill volume of about 0.15 L. The mixture was subjected to dispersion treatment for 30 minutes in a circulating state at a rotor peripheral speed of 9 m / sec and a liquid flow rate of 2.8 g / sec to prepare a surface-treated titanium oxide dispersion liquid.

[0189] The surface-treated titanium oxide dispersion liquid was mixed with a urethane acrylate oligomer (manufactured by Mitsubishi Chemical Corporation, UV6300B) previously dissolved in a mixed solvent of methanol / 1-propanol / toluene, and benzophenone and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (manufactured by IGM RESINS, Omnirad TPO H) as a polymerization initiator. The mass ratio of urethane acrylate oligomer / surface-treated titanium oxide / benzophenone / 2,4,6-trimethylbenzoyl-diphenylphosphine oxide was 100 / 55 / 1 / 2, the solvent composition was methanol / 1-propanol / toluene = 7 / 1 / 2, and a coating liquid S1 for forming a protective layer with a solid content concentration of 18.0% was obtained.

[0190] <Manufacture of Photoconductor Drum> [Example 1] A cylinder (conductive support) made of an aluminum alloy with an outer diameter of 30 mm, a length of 357.4 mm, and a wall thickness of 0.75 mm, whose surface was rough-cut, was coated with the undercoat layer-forming coating liquid A prepared in the production example of the coating liquid by dip coating, and air-dried to form an undercoat layer with a film thickness of 1.5 μm. Next, the charge generation layer-forming coating liquid B was coated on the undercoat layer by dip coating and air-dried to form a charge generation layer with a film thickness of 0.4 μm. Finally, the charge transport layer-forming coating liquid C1 was coated on the charge generation layer by dip coating and dried at 125°C for 24 minutes to form a charge transport layer with a film thickness of 24 μm, obtaining a photoconductor before coating the protective layer.

[0191] Subsequently, before applying the protective layer, the coating liquid S1 for forming the protective layer was applied in a ring shape onto the photoreceptor, dried at room temperature for 20 minutes, and then, in a nitrogen atmosphere (oxygen concentration of 1% or less), while rotating the photoreceptor at 60 rpm, a metal halide lamp was used to irradiate it at an illuminance of 140 mW / cm 2 for 2 minutes to form a protective layer with a film thickness of 1.0 μm after curing. Thereafter, by performing a heat treatment at 125°C for 10 minutes, the photoreceptor of Example 1 was obtained.

[0192] [Example 2] In Example 1, except that the coating liquid C2 for forming the charge transport layer was used instead of the coating liquid C1 for forming the charge transport layer and the film thickness of the charge transport layer was set to 19 μm, the photoreceptor of Example 2 was obtained in the same manner as in Example 1.

[0193] [Example 3] In Example 1, except that the coating liquid C3 for forming the charge transport layer was used instead of the coating liquid C1 for forming the charge transport layer and the film thickness of the charge transport layer was set to 19 μm, the photoreceptor of Example 3 was obtained in the same manner as in Example 1.

[0194] [Comparative Example 1] In Example 1, except that the film thickness of the charge transport layer was set to 19 μm and the protective layer was not formed, the photoreceptor of Comparative Example 1 was obtained in the same manner as in Example 1.

[0195] [Comparative Example 2] In Example 1, except that the film thickness of the charge transport layer was set to 19 μm, the photoreceptor of Comparative Example 2 was obtained in the same manner as in Example 1.

[0196] [Comparative Example 3] In Example 1, except that the film thickness of the charge transport layer was set to 19 μm and the film thickness of the protective layer was set to 3 μm, the photoreceptor of Comparative Example 3 was obtained in the same manner as in Example 1.

[0197] <Measurement Method of Inflow Current> After sticking aluminum foil on one side of the Scotch brand conductive double-sided tape manufactured by 3M, it was cut into a 1.2 cm × 1.2 cm square, and the adhesive surface without the aluminum foil attached was pasted onto the surface (the side opposite to the conductive support) at a position 250 mm from the end of the photoreceptor obtained in Examples 1 to 3 and Comparative Examples 1 to 3 respectively to form an electrode. On top of this electrode, a brass electrode with a 1.0 cm diameter cylinder and a 0.3 cm diameter cylinder connected was placed with the 1.0 cm diameter cylinder surface facing down and fixed with insulating tape. Note that the surface of the part where the 1.0 cm diameter cylinder contacts the aluminum foil was processed so as to contact the curved surface of the photoreceptor.

[0198] As shown in Figure 2, the above electrode was connected to a high-voltage power supply (Trek, model 610D), and the photoreceptor was connected to ground. At this time, an ammeter was connected between the photoreceptor and ground. In this state, a voltage of -3.4 kV was applied to the photoreceptor by the high-voltage power supply. The current values from 10 to 15 seconds after the application were averaged, and the result was divided by the area of the electrode on the photoreceptor surface (1.2 cm × 1.2 cm) to obtain the inflow current (A / m 2 ). The results are shown in Table 1. When measuring the inflow current for a positive-charged type photoreceptor, the inflow current (A / m 2 ) can be measured by applying a voltage of +3.4 kV to the photoreceptor by the high-voltage power supply.

[0199] <Evaluation of Photoreceptor Life (1)> The photoreceptors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were mounted on the photoreceptor cartridges of a commercially available contact charging type monochrome copier, and continuous printing was performed in an environment of 25°C and 50% relative humidity for 20,000 sheets, then in an environment of 32°C and 80% relative humidity for 20,000 sheets, then in an environment of 10°C and 15% relative humidity for 20,000 sheets, and further in an environment of 25°C and 50% relative humidity until the base of the bare tube of each photoreceptor appeared. The number of continuous printed sheets when the end of the photoreceptor wore out and the base of the bare tube appeared after printing was taken as the photoreceptor life. The results are shown in Table 1. Note that in Table 1, K means 1000.

[0200] <Evaluation of Image Characteristics (Ghost Generation)> The photoreceptors obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were mounted in the photoreceptor cartridge of the above copier, and continuous printing of 5,000 sheets was performed in an environment of a temperature of 32 °C and a relative humidity of 80%. Next, using the photoreceptor after continuous printing of 5,000 sheets, a printing pattern as described below was printed in an environment of a temperature of 32 °C and a relative humidity of 80%. The printing pattern is one in which characters are drawn above the printing medium, and a solid print of a halftone (printing density: 0.5%) is drawn under the characters. Visually evaluated how strongly the characters in the first rotation were printed on the halftone in the printing pattern of the second rotation. The results are shown in Table 1.

[0201] =Evaluation Criteria for Image Characteristics= ○(very good): No characters are printed at all in the second rotation. △ (good): Characters are weakly printed in the second rotation, but it is acceptable. × (poor): Characters are strongly printed in the second rotation and it is unacceptable.

[0202]

Table 1

[0203] <Evaluation of Photoreceptor Life (2)> Photoreceptors with a protective layer film thickness of 1.0 μm (the photoreceptors obtained in Examples 1 to 3 and Comparative Example 2) were mounted in the photoreceptor cartridge of the above copier, and continuous printing was performed. The film thickness of the entire photoreceptor (hereinafter referred to as the photoreceptor film thickness) was measured every 30,000 sheets of printing. The continuous printing was performed in an environment of a temperature of 25 °C and a relative humidity of 50% up to 20,000 sheets, a temperature of 32 °C and a relative humidity of 80% from 20,001 to 40,000 sheets, a temperature of 10 °C and a relative humidity of 15% from 40,001 to 60,000 sheets, and a temperature of 25 °C and a relative humidity of 50% after 60,001 sheets. A graph was created with the photoreceptor film thickness on the vertical axis and the number of continuous printed sheets on the horizontal axis, and from the decrease behavior of the film thickness, the number of printed sheets required until the protective layer was completely worn out was determined. The results are shown in Table 2. In Table 2, K means 1000.

[0204]

Table 2

[0205] <Investigation> From the results of the above examples and the test results that the inventor has conducted so far, the inflow current when a voltage of -3.4 kV is applied is 15 A / m 2 By setting it as follows, it was found that the wear resistance can be improved, and in particular, when used in an image forming apparatus of the contact electrification type, wear at the end of the photoreceptor can be suppressed. Also, the inflow current when a voltage of -3.4 kV is applied is 15 A / m 2 As a method of setting it as follows, it was found that increasing the thickness of the photosensitive layer, specifically, making it 20 μm or more, is effective. Furthermore, the inflow current when a voltage of -3.4 kV is applied is 15 A / m 2 As another method of setting it as follows, it was found that a method of making the photosensitive layer contain insulating metal oxide particles having a band gap of 5 eV or more is also effective. Furthermore, from the results of Table 2, it was found that by improving the photosensitive layer, which is the intermediate layer, rather than the protective layer, which is the outermost layer, the wear resistance of the protective layer can be improved.

[0206] Note that the above examples are for a negatively charged type (laminated structure) photoreceptor, but even for a positively charged type (single-layer structure) photoreceptor, since the surface of the photoreceptor is charged for image formation and it is not a perfect insulator, the same results are considered to be obtained. Rather, it can be considered that the positively charged type photoreceptor can enjoy the effects of the present invention more. The reason is that since the positively charged type contains an electron transport material in the photosensitive layer, the photosensitive layer easily transports electrons, that is, easily conducts current, so the inflow current is likely to increase and it is likely to wear.

[0207] In addition, in the above embodiment, as a result of containing silica particles, i.e., silicon dioxide particles, in the photosensitive layer, it was confirmed that the leakage current could be suppressed and the abrasion resistance could be improved. This is presumably because the silica particles are insulating particles, so the resistance of the entire photoreceptor increases, suppressing the leakage current. From such a mechanism, it is considered that when using metal oxide particles having an insulating property with a band gap of 5 eV or more instead of the silica particles, the same effect as that of the silica particles can be obtained.

Claims

1. In an electrophotographic photoreceptor sequentially provided with a photosensitive layer and a protective layer containing a cured product formed by curing a curable compound on a conductive support, the photosensitive layer contains metal oxide particles having a band gap of 5 eV or more, - When a voltage of -3.4 kV is applied, the flowing current is 1 A / m ２ or more and 15 A / m or less ２ An electrophotographic photoreceptor for an image forming apparatus using a contact electrification method, which is as described above.

2. The electrophotographic photoreceptor according to claim 1, wherein the thickness of the photosensitive layer is 10 μm or more.

3. The electrophotographic photoreceptor according to claim 1 or 2, wherein the thickness of the protective layer is 1 μm or less.

4. The electrophotographic photoreceptor according to any one of claims 1 to 3, wherein the ratio A / B of the thickness A of the protective layer to the thickness B of the photosensitive layer is 0.002 or more and 0.3 or less.

5. The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the metal oxide particles having a band gap of 5 eV or more are silica particles.

6. The electrophotographic photoreceptor according to any one of claims 1 to 5, wherein the protective layer contains metal oxide particles having a band gap of 2 to 4 eV.

7. The electrophotographic photoreceptor according to claim 6, wherein the content ratio (mass ratio) of the metal oxide particles having a band gap of 5 eV or more in the photosensitive layer to the content of the metal oxide particles having a band gap of 2 to 4 eV in the protective layer is 0.1 to 0.

5.

8. The electrophotographic photoreceptor according to any one of claims 1 to 7, wherein the hole transport material contained in the photosensitive layer includes any one or a combination of two or more of the following formulas (1) or (2).

9. The electrophotographic photoreceptor according to any one of claims 1 to 8, wherein the curable compound is a photocurable compound.

10. An electrophotographic photoreceptor cartridge having the electrophotographic photoreceptor according to any one of claims 1 to 9.

11. An image forming apparatus having the electrophotographic photoreceptor according to any one of claims 1 to 9.

Images