Electrophotographic photoreceptor, image forming apparatus, and image forming method

Abstract

To provide an electrophotographic photoreceptor, an image forming apparatus, and an image forming method that can improve image quality and prevent a change in image density in continuous printing.SOLUTION: An electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor in which at least a photosensitive layer and a surface protective layer are sequentially laminated on a conductive substrate. The surface protective layer contains metallic oxide fine particles containing Ti atoms and second atoms that are metal atoms or semi-metal atoms other than the Ti atoms. When the average value of the equivalent circle diameters of cross sections of the metallic oxide fine particles appearing on a cross section of the surface protective layer is defined as A, and the standard deviation value of the equivalent circle diameters as B, a coefficient of variation (B / A) is within a range of 0.12-0.35.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electrophotographic photoreceptor, an image forming apparatus, and an image forming method. [Background technology]

[0002] Patent Document 1 discloses the following technology: An electrophotographic photoreceptor having a conductive support, a photosensitive layer, and a protective layer (surface protective layer), the protective layer containing conductive particles, the surfaces of which contain a metal oxide containing titanium and niobium atoms. The atomic concentration ratio of niobium atoms to titanium atoms in the metal oxide is 0.01 or more and 0.20 or less. The conductive particles are surface-treated with a compound containing silicon atoms. The content of the conductive particles in the protective layer is 5% by volume or more and less than 40% by volume with respect to the total volume of the protective layer. The relative concentrations of multiple atoms on the surface of the protective layer, as determined by X-ray photoelectron spectroscopy, satisfy specific conditions. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-57026 Summary of the Invention [Problem to be solved by the invention]

[0004] If the dispersion state of the fine particles contained in the surface protective layer of an electrophotographic photoreceptor (hereinafter simply referred to as "photoreceptor") is not appropriate, local defects may appear in images formed using the photoreceptor, or image density may vary between images during continuous printing. However, the measurement control method described in Patent Document 1 can determine the average state of the surface protective layer as a whole, but cannot predict local defects, nor can it determine the detailed dispersion state of the particles contained in the surface protective layer. The measurement control methods in question include X-ray photoelectron spectroscopy, volume resistivity, and volume ratio, but these methods all have insufficient planar resolution compared to the particle size of the conductive particles.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrophotographic photoreceptor, an image forming apparatus, and an image forming method that can improve image quality and suppress changes in image density during continuous printing. [Means for solving the problem]

[0006] The above-mentioned problems of the present invention can be solved by the following means.

[0007] 1. An electrophotographic photoreceptor having at least a photosensitive layer and a surface protective layer laminated in this order on a conductive support, the surface protective layer contains metal oxide fine particles containing Ti atoms and second atoms which are metal atoms or semi-metal atoms other than Ti atoms, When the average value of the equivalent circle diameters of the cross sections of the metal oxide fine particles appearing on the cross section of the surface protective layer is defined as A and the standard deviation value of the equivalent circle diameters is defined as B, the coefficient of variation (B / A) is within a range of 0.12 to 0.35. Electrophotographic photoreceptor.

[0008] 2. The second atom is a Nb atom; 2. The electrophotographic photoreceptor according to claim 1.

[0009] 3. The surface protective layer contains at least a polymer of a (meth)acrylic monomer having a structure represented by the following general formula (1), or contains at least a compound having a structure represented by the following general formula (1) and a crosslinked (meth)acrylic resin: 2. The electrophotographic photoreceptor according to claim 1.

[0010] [ka]

[0011] [In general formula (1), R 1 , R 2 , and R 3 are each independently a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an allyl group, or an acyl group. 1 , R 2 , and R 3 R may have a substituent. 1 , R 2 , and R 3 At least two of the may form a bond with each other.]

[0012] 4. The average primary particle size of the metal oxide fine particles is within the range of 40 to 140 nm. 2. The electrophotographic photoreceptor according to claim 1.

[0013] 5. An electrophotographic photoreceptor according to any one of items 1 to 4. Image forming device.

[0014] 6. An image is formed using the image forming apparatus described in item 5. Image forming method. [Effects of the Invention]

[0015] According to the present invention, it is possible to improve image quality and suppress changes in image density during continuous printing.

[0016] The mechanism by which the effects of the present invention are manifested or the mechanism of action is not clear, but is presumed as follows.

[0017] The metal oxide microparticles according to the present invention contain a Ti atom and a second atom, which is a metal atom or a semimetal atom other than Ti. The microparticles become crystals in which the second atom is mixed with titanium oxide, thereby releasing excess electrons and acting as conductive carriers. This improves the conductivity of the surface protection layer containing the microparticles, thereby improving the image quality of the formed image.

[0018] In the present invention, the coefficient of variation (B / A) of the equivalent circle diameter of the metal oxide microparticles contained in the surface protective layer is used as an index of the dispersion state of the metal oxide microparticles. The coefficient of variation (B / A) is the ratio of the standard deviation value B to the average value A of the equivalent circle diameter. The smaller the coefficient of variation (B / A), the better the dispersion of the metal oxide microparticles.

[0019] When the coefficient of variation (B / A) is greater than 0.35, the surface protection layer contains metal oxide particles (including secondary particles) with extremely large diameters. In this case, the extremely large metal oxide particles scatter the exposure light, which can degrade image quality, such as fine line reproducibility. Metal oxide particles containing Ti atoms and secondary atoms have a particularly high refractive index, which can significantly affect image quality due to the scattering of exposure light. Furthermore, when the particle size of the metal oxide particles exceeds half the wavelength of the exposure light, the scattering of exposure light can also significantly affect image quality. Furthermore, when the coefficient of variation (B / A) is greater than 0.35, the extremely large metal oxide particles form locally irregular conductive paths. In this case, uniformity in electrical resistance cannot be ensured, and image defects such as leakage are likely to occur, regardless of the resistivity measured by macroanalysis or the element ratio measured by X-ray photoelectron spectroscopy.

[0020] If the coefficient of variation (B / A) is less than 0.12, electronic conductivity depends entirely on "discharge between particles," which is unfavorable for rapid discharge of residual charge. As a result, residual charge accumulates during continuous printing, which can cause instantaneous and sudden changes in image density.

[0021] In contrast, the present invention is characterized in that the variation factor (B / A) is within the range of 0.12 to 0.35. In this case, the surface protective layer contains a very small amount of secondary particles with a small aggregation number, and the particle size of the contained particles is stable. As a result, the surface protective layer of the present invention is less likely to scatter exposure light, despite containing metal oxide fine particles containing Ti atoms and second atoms, making it possible to improve image quality. Furthermore, by containing a very small amount of secondary particles with a small aggregation number, some of the particles contain contact conductivity, stabilizing conductivity and making it possible to suppress changes in image density during continuous printing. [Brief explanation of the drawings]

[0022] [Figure 1] Schematic cross-sectional view showing an example of an electrophotographic photoreceptor [Figure 2] Schematic cross-sectional view showing an example of an image forming apparatus DETAILED DESCRIPTION OF THE INVENTION

[0023] The following description describes embodiments of the present invention. The advantages and features of one or more embodiments of the present invention can be understood from the following detailed description and drawings. It should be noted that the following detailed description and drawings are provided for illustrative purposes only and do not limit the scope of the present invention.

[0024] The following description refers to the drawings and describes one or more embodiments of the invention, although the scope of the invention is not limited to the disclosed embodiments.

[0025] In this application, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0026] [1. Overview of Electrophotographic Photoreceptors] The electrophotographic photoreceptor of the present invention comprises at least a photosensitive layer and a surface protective layer laminated in this order on a conductive support.

[0027] The photosensitive layer has both the function of absorbing light to generate charges and the function of transporting charges. The photosensitive layer is composed of, for example, two layers, a charge generation layer and a charge transport layer. In this case, the charge generation layer and the charge transport layer are arranged in this order from the conductive support side. The photoreceptor of the present invention may further have an intermediate layer between the conductive support and the photosensitive layer, if necessary.

[0028] Examples of the layer structure of the photoreceptor include the layer structures shown in (1) or (2) below.

[0029] (1) A layer structure in which a "photosensitive layer consisting of a charge generating layer containing a charge generating agent and a charge transport layer containing a charge transport agent" and a "surface protective layer" are sequentially laminated on a conductive support. (2) A layer structure in which an "intermediate layer," a "photosensitive layer consisting of a charge generating layer containing a charge generating agent and a charge transport layer containing a charge transport agent," and a "surface protective layer" are laminated in this order on a conductive support.

[0030] The layer structure of the photoreceptor may be either (1) or (2) above, but (2) is particularly preferred.

[0031] The photoreceptor of the present invention is preferably an organic photoreceptor. The organic photoreceptor refers to a photoreceptor in which at least one of the charge generating function and the charge transporting function, which are essential for the construction of the photoreceptor, is exhibited by an organic compound. Examples of organic photoreceptors include photoreceptors having a photosensitive layer containing an organic charge generating agent or an organic charge transporting agent, and photoreceptors having a photosensitive layer containing an organic polymer complex exhibiting the charge generating function and the charge transporting function.

[0032] Fig. 1 is a schematic cross-sectional view showing the layer structure (2) of the photoreceptor of the present invention. In the photoreceptor 1 shown in Fig. 1, an intermediate layer 102, a photosensitive layer 103, and a surface protective layer 104 are laminated on a conductive support 101. The photosensitive layer 103 is composed of a charge generation layer 103a laminated on the intermediate layer 102, and a charge transport layer 103b laminated on the charge generation layer 103a.

[0033] [Surface protective layer] The surface protective layer 104 of the photoreceptor 1 of the present invention contains metal oxide fine particles 104b. The surface protective layer 104 preferably has a form in which the metal oxide fine particles 104b are dispersed in a matrix 104a, which is a continuous phase, as shown in Figure 1. The matrix 104a may be mainly composed of a resin, a charge transport agent, etc.

[0034] The metal oxide microparticles 104b according to the present invention contain a Ti atom and a second atom. The second atom is a metal atom or a metalloid atom other than a Ti atom. Metalloid atoms include boron, silicon, arsenic, tellurium, astatine, germanium, antimony, and polonium. The metal oxide microparticles 104b according to the present invention are crystalline titanium oxide mixed with the second atom, which releases excess electrons and acts as a conductive carrier. This improves the conductivity of the surface protection layer 104 containing the metal oxide microparticles 104b, thereby improving the quality of the formed image.

[0035] From the viewpoint of the conductivity and transparency of the metal oxide particles 104b, the second atoms are preferably Nb atoms or Ta atoms, and particularly preferably Nb atoms.

[0036] When the second atom is an Nb atom, the molar ratio of the Nb atoms is preferably 0.1 to 15 mol %, and particularly preferably 1 to 10 mol %, when the molar ratio of the Ti atoms in the metal oxide microparticles 104b is 100 mol %. When the molar ratio of the Nb atoms is equal to or greater than the lower limit, the crystallinity is improved, the free electron ratio is increased, and the conductivity is improved. When the molar ratio of the Nb atoms is equal to or less than the upper limit, the final composition is less likely to deviate from the doped state, thereby improving the conductivity.

[0037] Hereinafter, a production example of the metal oxide fine particles 104b according to the present invention will be described taking as an example a case where the second atom is an Nb atom.

[0038] When the second atom is a Nb atom, the metal oxide microparticles 104b are preferably produced using a precursor solution containing both a Ti source material and a Nb source material, which allows the Ti atoms and Nb atoms to be mixed at the atomic level to create a doped state.

[0039] The manufacturing method using a precursor solution containing both a Ti source material and a Nb source material may be a method of growing core particles by adhering the precursor solution to the surface of the core particles, or a method of growing particles by using the precursor solution alone. From the viewpoint of suppressing the occurrence of internal defects, the method of growing core particles by adhering the precursor solution to the surface of the core particles is preferred.

[0040] The core particle is not particularly limited, and may be, for example, a particle containing an inorganic material such as titanium oxide, alumina, barium sulfate, etc. The core particle is preferably required to have sufficient heat resistance at the temperature of the synthesis process, to be white, and to absorb little ultraviolet light.

[0041] The core particles are particularly preferably titanium oxide particles, which makes it difficult for an elementally heterogeneous interface to form between the core particles and the coating layer formed from the precursor solution, thereby reducing the possibility of breakage due to defects at the interface or strain caused by differences in expansion coefficient.

[0042] Known crystalline forms of titanium dioxide include rutile, anatase, and brookite, with rutile and anatase being the most suitable for mass production. Anatase absorbs less UV light than rutile, and the wavelength range in which it absorbs is narrower. Anatase has particularly low absorbance for many commercially available UV curing LED light sources, making it cost-effective when using UV light to form a surface protection layer. Furthermore, anatase has a low refractive index, making it less likely to scatter exposure light. Therefore, anatase titanium dioxide particles are preferred for use as core particles.

[0043] The method for producing titanium oxide particles used as core particles is not limited and may be a known method. Widely known methods for producing titanium oxide particles include a gas phase synthesis method using a raw material such as titanium tetrachloride and a liquid phase synthesis method using titanium sulfate as a raw material. Hydrothermal synthesis is also known as a liquid phase synthesis method, and either method can be used. From the viewpoint of the robustness required for core particles in order to form a coating layer, it is preferable that titanium oxide particles be synthesized using a broad liquid phase synthesis method (including hydrothermal synthesis).

[0044] Known methods for reacting a precursor solution containing both Ti and Nb source materials include reacting in an aqueous solution and reacting in the gas phase using chemical vapor deposition (CVD). The former method involves normal temperature conditions and hydrothermal synthesis. Hydrothermal synthesis allows synthesis under high-temperature and high-pressure conditions, which is expected to shorten reaction times and stabilize the quality of the finished product. Examples of film formation methods using the latter include the use of a particle-specific atomic layer deposition (ALD) system manufactured by FORGE NANO. Using a CVD system, a volatile organotitanium compound or a volatile organoniobium compound is injected as a precursor under reduced pressure to form a coating layer around the core particle, resulting in the formation of a coating layer with a niobium oxide-containing titanium oxide composition. In particular, the ALD system allows for layer-by-layer growth, which reduces lattice defects and facilitates achieving ideal film quality. In either case, immediately after preparation of the composition containing Ti atoms and Nb atoms, the particles may contain many lattice defects, so it is preferable to perform moderate sintering as necessary to reduce the lattice defects. Reducing the lattice defects can improve the robustness of the metal oxide particles 104b.

[0045] The present invention is characterized in that, when the average value of the equivalent circle diameters of the cross sections of the metal oxide fine particles 104b appearing on the cross section of the surface protective layer 104 is A and the standard deviation value of the equivalent circle diameters is B, the coefficient of variation (B / A) is within the range of 0.12 to 0.35. As a result, the photoreceptor 1 of the present invention, as described above, is capable of improving image quality and suppressing changes in image density during continuous printing.

[0046] The coefficient of variation (B / A) is a numerical value that indicates the degree of variation in the standard deviation value. For example, if all the metal oxide particles 104b have the same shape, the coefficient of variation (B / A) will be zero.

[0047] The coefficient of variation (B / A) is calculated as follows. First, a thin section sample of the cross section of the surface protective layer 104 is prepared. Next, a TEM photograph of the thin section sample is taken using a transmission electron microscope (TEM). At this time, the acceleration voltage is set to, for example, 80 kV. The magnification is adjusted so that the average total number of "secondary particles or independently dispersed primary particles" in one field of view is 30 to 100. The target magnification is 10,000 to 50,000 times. Fine particles that overlap the outer edge of the photograph cannot be used to calculate the circle equivalent diameter, so they are excluded from the count. Twenty TEM photographs are taken at a uniform magnification in random fields of view.

[0048] The TEM photographs are then saved in JPEG format. The TEM photographs are then binarized using the analysis software ImageJ according to the following rules. ImageJ is an image software developed by the National Institutes of Health (NIH). Binarization is the process of distinguishing between fine particle areas and other areas in the TEM photograph. First, open the software "ImageJ". Next, open the image to be analyzed. Select "Binary" from the "Process" menu and perform binarization according to the "Make Binary" menu. At this time, primary particles are binarized as primary particles. Secondary particles are binarized as a single particle, regardless of whether the boundaries of the particles can be distinguished as primary particles. A secondary particle is a particle made up of an aggregate of two or more primary particles, and is a particle in which two or more primary particles are in complete contact at at least one point. Fine particles that overlap the outer edge of the TEM photograph are excluded from the binarization.

[0049] Using the above method, all fine particles in the TEM photographs of multiple fields of view are binarized until the total number of primary particles and secondary particles reaches 150 or more.

[0050] The area S' of each binarized particle image is calculated, and the circle-equivalent diameter L' of the image is calculated using the following formula: L′=√(4S′ / π) L': Equivalent circle diameter in the image S': Area in the image π: Pi

[0051] Taking the scale of the image into consideration, the equivalent circle diameter L at the actual scale is calculated from the equivalent circle diameter L' in the image.

[0052] The average value A and standard deviation value B of the equivalent circle diameters are calculated from the equivalent circle diameter L. The coefficient of variation (B / A), which is the ratio of the standard deviation value B to the average value A, is calculated from the average value A and standard deviation value B of the equivalent circle diameters. The coefficient of variation (B / A) may be an average of the coefficients of variation (B / A) measured at multiple cross sections of the surface protective layer 104.

[0053] The average primary particle size of the metal oxide particles 104b is preferably within a range of 40 to 140 nm. An average primary particle size of 40 nm or more facilitates ensuring an appropriate dispersion state of the metal oxide particles 104b. Oxide particles doped with a different element tend to have higher surface activity than oxide particles without the doping. However, an average primary particle size of 40 nm or more facilitates keeping the coefficient of variation (B / A) within an appropriate range. An average primary particle size of 140 nm or less reduces the scattering of exposure light, improving the fine-line reproducibility of the formed image and improving image quality. In particular, metal oxide particles 104b containing Nb atoms as the second atom tend to easily scatter exposure light due to their high refractive index, so an average primary particle size of 140 nm or less is particularly preferred.

[0054] The average primary particle size of the metal oxide microparticles 104b is measured as follows. When measuring the coefficient of variation (B / A) described above, the ImageJ image is analyzed, and all of the microparticles that fall into the bottom 5% of the particle size distribution are selected, and the number-average particle size of these microparticles is calculated. This value is used as the average primary particle size of the metal oxide microparticles 104b in the surface protective layer 104.

[0055] The average value A of the equivalent circle diameter is preferably within the range of 65 to 200 nm, which improves the dispersion state of the metal oxide fine particles 104b, making it possible to improve image quality and suppress changes in image density during continuous printing to a higher degree.

[0056] The coefficient of variation (B / A) can be adjusted by surface treatment of the metal oxide particles 104b or by adding an additive for the purpose of dispersing the metal oxide particles 104b.

[0057] By performing a surface treatment on the metal oxide particles 104b, the dispersibility of the metal oxide particles 104b in the matrix 104a or in the coating liquid for forming the surface protection layer 104 can be adjusted.

[0058] The surface treatment agent used for the surface treatment is not particularly limited, and may be an organic surface treatment agent or an inorganic surface treatment agent. From the viewpoint of being less likely to cause a decrease in conductivity, an organic surface treatment agent is preferred. The surface treatment agent used may be one type or two or more types.

[0059] Examples of organic surface treatment agents include various silane coupling agents having an alkoxy group, titanium-based coupling agents, nirconium-based coupling agents, aluminum-based coupling agents, alkoxysilane-based surface modifiers, etc. Other examples of organic surface treatment agents include titanium-based chelating agents, zirconium-based chelating agents, aluminum-based chelating agents, metal soaps, etc.

[0060] Examples of inorganic surface treatment agents include alumina and silica.

[0061] The surface treatment may be a treatment in which the metal oxide particles 104b are mixed with a surfactant and kneaded to make the surfactant compatible with the surface of the metal oxide particles 104b. In this case, a nonionic surfactant is preferred as the surfactant because it can act on an untreated surface, can maintain the electrical properties of the photoreceptor 1, and is required to prevent adverse effects on UV curing.

[0062] Examples of nonionic surfactants include the following: Alcohols with a partial glycol structure Compounds partially or completely etherified with alcohols having a glycol partial structure A compound obtained by partially esterifying an alcohol with a glycol partial structure with a fatty acid Compounds obtained by partially or completely etherifying trihydric or higher polyhydric alcohols Compounds obtained by partially esterifying trihydric or higher polyhydric alcohols with fatty acids

[0063] The surface treatment may be a wet method or a dry method, and may be performed by combining two or more types of surface treatment or in two or more stages.

[0064] The wet method is a method of performing surface treatment in a solution. Examples of solvents used in the wet method include water, methanol, ethanol, 2-propanol, methyl ethyl ketone, toluene, etc. The pH of the water may be adjusted with an acid or a base.

[0065] By adjusting the coverage rate by surface treatment, it is possible to adjust the surface free energy and methanol hydrophobicity of the metal oxide particles 104b. Here, the methanol hydrophobicity is the volume concentration of methanol at which the metal oxide particles 104b begin to disperse in a methanol / water mixed solvent. For solvents with a methanol ratio lower than the hydrophobicity value, the metal oxide particles 104b do not disperse in the solvent at all but float on the surface of the solvent.

[0066] By controlling the surface state of the metal oxide particles 104b through the surface treatment as described above, the coefficient of variation (B / A) can be adjusted.

[0067] Known additives can be used to disperse the metal oxide particles 104b. It is preferable that the additive acts on the untreated surface of the metal oxide particles 104b to suppress the cohesive force between the metal oxide particles 104b. It is also preferable that the additive has low ionicity so as not to increase the residual potential of the photoreceptor 1. Examples of such additives include nonionic surfactants and metal soaps with poor ionization properties.

[0068] Examples of nonionic surfactants include polyhydric alcohols, compounds in which the hydroxy groups of polyhydric alcohols have been partially or completely esterified, and compounds in which the hydroxy groups of polyhydric alcohols have been partially or completely etherified. Examples of polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, butanediol, pentanediol, hexanediol, propylene glycol, dipropylene glycol, tripropylene glycol, polypropylene glycol, copolymers of ethylene glycol and propylene glycol, glycerin, butanetriol, pentanetriol, hexanetriol, sorbitol, xylitol, and polyvinyl alcohol. Examples of acids used for esterification include stearic acid, palmitic acid, myristic acid, lauric acid, behenic acid, montanic acid, melissic acid, oleic acid, erucic acid, linoleic acid, and linolenic acid. Examples of alcohols used for etherification include methanol, ethanol, propanol, isopropanol, butanol, sec-butanol, amyl alcohol, octyl alcohol, decyl alcohol, dodecyl alcohol, lauryl alcohol, myristyl alcohol, and stearyl alcohol.

[0069] It is particularly important that the additive for dispersing the metal oxide microparticles 104b acts on the untreated surface areas. Therefore, rather than simultaneously mixing all of the materials constituting the finished metal oxide microparticles 104b and dispersing them, it is more preferable to knead the metal oxide microparticles 104b in a wet state with the additive and then allow the additive to act on the untreated surface areas first.

[0070] The blending amount of the metal oxide microparticles 104b is preferably in the range of 1 to 20 parts by volume, assuming the total volume of the surface protective layer 104 to be 100 parts by volume. A blending amount of 1 part by volume or more improves the conductivity. A blending amount of 20 parts by volume or less improves the insulation properties when left in a dark place, which is important for the photoreceptor 1. Furthermore, a blending amount of the metal oxide microparticles 104b with high ultraviolet absorption properties of 20 parts by volume or less can reduce the amount of ultraviolet light when ultraviolet light is used in forming the surface protective layer, which is advantageous in terms of cost. A particularly preferred blending amount of the metal oxide microparticles 104b is in the range of 3 to 10 parts by volume, assuming the total volume of the surface protective layer 104 to be 100 parts by volume.

[0071] The surface protective layer 104 preferably contains at least the following compound A, or at least the following compounds B and C. This includes the following cases. The surface protective layer 104 contains only the compound A among the compounds A to C. The surface protective layer 104 contains only the compound A and the compound B among the compounds A to C. The surface protective layer 104 contains only the compound A and the compound C among the compounds A to C. The surface protective layer 104 contains only the compound B and the compound C among the compounds A to C. The surface protective layer 104 contains all of the compounds A to C.

[0072] Compound A: a polymer of a (meth)acrylic monomer having a structure represented by the following general formula (1): Compound B: a compound having a structure represented by the following general formula (1): Compound C: Crosslinked (meth)acrylic resin

[0073] Compound B is responsible for charge transport properties and contributes to stable electrical properties of the photoreceptor 1. Compound C contributes to improving the strength and durability of the surface protective layer 104. Compound A is a compound having the structures of both compounds B and C, and contributes to improving the strength and durability of the surface protective layer 104 and stable electrical properties of the photoreceptor 1.

[0074] [ka]

[0075] [In general formula (1), R 1 , R 2 , and R 3 are each independently a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an allyl group, or an acyl group. 1 , R 2 , and R 3 R may have a substituent. 1 , R 2 , and R 3 At least two of the may form a bond with each other.]

[0076] R 1 , R 2 , and R 3 Examples of the substituent that may be possessed by include various aromatic ring functional groups and various aliphatic functional groups. Examples of aromatic ring functional groups include a phenyl group, a biphenyl group, a naphthyl group, a fluorenyl group, an anthranyl group, etc. Examples of aliphatic functional groups include a methyl group, an ethyl group, a propyl group, etc. These substituents may further have another substituent.

[0077] The (meth)acrylic monomer having the structure represented by the above general formula (1) preferably has a structure represented by the following general formula (A1) or (A2).

[0078] [ka]

[0079] [In general formula (A1), R 1 represents a hydrogen atom or a methyl group. 2 and R 3 each independently represents an alkyl group having 1 to 3 carbon atoms. x and y each independently represent an integer of 0 to 2. n represents an integer of 1 to 3. R 2 If there are multiple R 2 may be the same or different. 3 If there are multiple R 3 may be the same or different.]

[0080] [In general formula (A2), R 1 R each independently represents a hydrogen atom or a methyl group. 2 represents an alkyl group having 1 to 3 carbon atoms. x represents an integer of 0 to 2. n's each independently represent an integer of 1 to 3. R 2 If there are multiple R 2 may be the same or different.]

[0081] Hereinafter, "a compound having a structure represented by general formula (A1)" will also be referred to as "compound (A1)", and "a compound having a structure represented by general formula (A2)" will also be referred to as "compound (A2)".

[0082] Both the compound (A1) and the compound (A2) have the following structural feature (a-1) and structural feature (a-2). Structural feature (a-1): In triphenylamine compounds, one of the phenyl groups is a biphenyl group. Structural feature (a-2): A structure in which the polymerizable functional group is bonded to at least one of the two phenyl groups, rather than to the biphenyl group.

[0083] The polymerizable functional group possessed by Compound (A1) and Compound (A2) is a (meth)acryloyloxy group. In this specification, "(meth)acryloyloxy group" is a general term for acryloyloxy group and methacryloyloxy group. Similarly, "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid.

[0084] In the compounds (A1) and (A2), the biphenyl group has a structure in which a phenyl group that may be substituted with an alkyl group having 1 to 3 carbon atoms is bonded to the 4-position of the phenyl group that is bonded to the nitrogen atom. The alkyl group having 1 to 3 carbon atoms is represented by R 2 It is expressed by x. 2 The number of R in the phenyl group far from the nitrogen atom is 0 to 2. 2 When x is 1, the bonding position of R may be any of the para-position, meta-position, and ortho-position relative to the bonding position of the phenyl group bonded to the nitrogen atom, and the para-position, meta-position, etc. are preferred. When x is 2, R 2 The bonding positions of may be any combination of two selected from the para position, two meta positions, and two ortho positions, and a combination of the para position and the meta position is preferred. 2 is a methyl group, an ethyl group, a propyl group, or an isopropyl group, and a methyl group, an ethyl group, or a propyl group is preferred. When x is 2, two R 2 may be the same or different.

[0085] Compound (A1) has one (meth)acryloyloxy group. The (meth)acryloyloxy group is bonded to the 4-position (para-position) of one of the two phenyl groups bonded to the nitrogen atom via an alkylene group having 3 or less carbon atoms. Hereinafter, "an alkylene group having 3 or less carbon atoms" will be referred to as "an alkylene (C 1-3 (Meth)acryloyloxy group - alkylene (C 1-3 ) group is bonded to a phenyl group, which is a (meth)acryloyloxy group-alkylene (C 1-3 ) group, and has no other substituents. In other words, the remaining four hydrogen atoms bonded to the phenyl group are unsubstituted.1-3 ) group is a methylene group (-CH2-), an ethylene group (-CH2CH2-), a propylene group (-CH2CH2CH2-) or a 1,2-propylene group (-CH(CH3)CH2-). 1-3 ) group is preferably a methylene group (-CH2-), an ethylene group (-CH2CH2-), or a propylene group (-CH2CH2CH2-).

[0086] In the compound (A1), the (meth)acryloyloxy group-alkylene (C 1-3 In the phenyl group to which no R 2 group is bonded, one or two of the five hydrogen atoms other than the hydrogen atom bonded to the nitrogen atom may be substituted with an alkyl group having 1 to 3 carbon atoms. The alkyl group having 1 to 3 carbon atoms is represented by the formula (A1) R 3 That is, R represented by y 3 The number of R in the phenyl group is 0 to 2. 3 When y is 1, the position of R is preferably the para position, meta position, etc. relative to the bonding position with the nitrogen atom. When y is 2, R 2 The bonding positions of R are preferably a combination of para and meta positions. 3 is a methyl group, an ethyl group, a propyl group, or an isopropyl group. 3 is preferably a methyl group. When y is 2, two R 3 may be the same or different.

[0087] The compound (A2) has two (meth)acryloyloxy groups. The (meth)acryloyloxy groups are each formed by attaching an alkylene (C 1-3 ) group. 1-3 Each phenyl group to which a (meth)acryloyloxy group-alkylene (C 1-3 ) group, there are no other substituents. That is, the remaining four hydrogen atoms attached to each phenyl group are unsubstituted. 1-3The (meth)acryloyloxy-alkylene (C) groups bonded to two phenyl groups are preferably methylene (-CH2-), ethylene (-CH2CH2-), and propylene (-CH2CH2CH2-). 1-3 ) groups may be the same or different.

[0088] Specific examples of compound (A1) include compounds having structures shown in the following T-1 to T-35 (compounds T-1 to T-35). Specific examples of compound (A2) include compounds having structures shown in the following T-36 to T-55 (compounds T-36 to T-55).

[0089] [ka]

[0090] [ka]

[0091] [ka]

[0092] [ka]

[0093] [ka]

[0094] [ka]

[0095] Compound (A1) and compound (A2) can be synthesized using known methods. Specifically, compound (A1) is obtained by an esterification reaction between a hydroxyl-containing N,N-diphenyl-N-biphenylamine derivative (b1) and (meth)acrylic acid chloride (c1), as shown in the following reaction formula (F1). Compound (A2) is obtained by an esterification reaction between a hydroxyl-containing N,N-diphenyl-N-biphenylamine derivative (b2) and (meth)acrylic acid chloride (c1), as shown in the following reaction formula (F2).

[0096] [ka]

[0097] [ka]

[0098] R in the above reaction formula (F1) 1 , R 2 , R 3 , x, y, and n are R in general formula (A1). 1 , R 2 , R 3 , x, y, and n are the same as those in the above reaction formula (F2). 1 , R 2 , x and n are R in general formula (A2). 1 , R 2 , x, and n.

[0099] The compound (compound B) having a structure represented by general formula (1) is not particularly limited, but for example, the compound (A1) or compound (A2) having a (meth)acryloyloxy group + alkylene (C 1-3 ) group is replaced with a hydrogen atom.

[0100] The crosslinked (meth)acrylic resin (compound C) is not particularly limited, but is, for example, a polymer of polymerizable monomers having structures represented by the following M1 to M11.

[0101] In the following formulas, R represents an acryloyl group (CH2=CHCO-), and R' represents a methacryloyl group (CH2=C(CH3)CO-).

[0102] [ka]

[0103] The surface protective layer 104 may contain components other than those described above. The surface protective layer 104 may contain, for example, antioxidants, polymerization initiators, polymerization accelerators, fine particles for improving the strength of the surface protective layer, and additives for improving the photoreceptor characteristics. Examples of fine particles for improving the strength of the surface protective layer include inorganic fine particles such as silica and alumina, and various resin fine particles having a crosslinked structure. Examples of additives for improving the photoreceptor characteristics include leveling agents and fine particles for reducing surface free energy and friction to improve cleaning properties. Examples of such fine particles include fine particles made of fluorine-based resins, silicone-based resins, polyethylene resins, and the like. When the photoreceptor 1 is a positively charged photoreceptor, the surface protective layer 104 may contain a low-molecular-weight compound such as meta-terphenyl as an additive effective in preventing light fatigue.

[0104] The thickness of the surface protection layer 104 is preferably in the range of 0.2 to 10 μm, and more preferably in the range of 0.5 to 6 μm.

[0105] [Conductive Support] The conductive support 101 may be any support that is conductive. Examples of the conductive support 101 include a drum or sheet formed from a metal such as aluminum, copper, chromium, nickel, zinc, or stainless steel. The conductive support 101 may be a plastic film laminated with a metal foil made of a metal such as aluminum or copper. The conductive support 101 may be a plastic film onto which aluminum, indium oxide, tin oxide, or the like is vapor-deposited. The conductive support 101 may be a metal, plastic film, paper, or the like, on which a conductive layer is provided by applying a conductive substance alone or together with a binder resin.

[0106] [Middle class] The intermediate layer 102 has the function of enhancing the barrier property or adhesiveness between the conductive support 101 and the photosensitive layer 103. Although the intermediate layer 102 is not an essential component of the photoreceptor 1 of the present invention, it is preferable to provide the intermediate layer 102 in consideration of preventing various failures and the like.

[0107] The intermediate layer 102 contains, for example, a binder resin for intermediate layers and, if necessary, conductive particles or metal oxide particles.

[0108] Examples of binder resins for the intermediate layer include casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide resin, polyurethane resin, gelatin, etc. Among these, alcohol-soluble polyamide resins are preferred.

[0109] The intermediate layer may contain various conductive particles or metal oxide particles for the purpose of adjusting resistance. Examples of the metal oxide particles that can be used include alumina, zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, and zirconium oxide. Particles of composite metal oxides such as tin-doped indium oxide and antimony-doped tin oxide may also be used. Particles of composite oxides having a perovskite structure, such as strontium titanate, may also be used.

[0110] The number average primary particle size of the metal oxide particles that can be contained in the intermediate layer is preferably 10 to 300 nm, and more preferably 20 to 100 nm.

[0111] The conductive particles or metal oxide particles may be used singly or in combination of two or more kinds. When two or more kinds are mixed, they may be in the form of a solid solution or fused particles.

[0112] The content of the conductive particles or metal oxide particles is preferably 20 to 400 parts by mass, more preferably 50 to 350 parts by mass, relative to 100 parts by mass of the binder resin.

[0113] The thickness of the intermediate layer is preferably 0.1 to 15 μm, more preferably 0.3 to 10 μm. The intermediate layer may have a laminated structure of two or more layers depending on the function. The intermediate layer may contain an electron transport agent.

[0114] [Charge Generation Layer] The charge generating layer 103a in the photosensitive layer 103 contains a charge generating agent and a binder resin for the charge generating layer.

[0115] Examples of charge generating agents include azo pigments, quinone pigments, indigo pigments, polycyclic quinone pigments, phthalocyanine pigments, etc. Examples of azo pigments include Sudan Red and Diane Blue. Examples of quinone pigments include pyrenequinone and anthanthrone. Examples of indigo pigments include quinocyanine pigments, perylene pigments, indigo, and thioindigo. Examples of polycyclic quinone pigments include pyranthrone and diphthaloylpyrene. Among these, polycyclic quinone pigments and titanyl phthalocyanine pigments are preferred. The charge generating agents may be used alone or in combination of two or more.

[0116] Known resins can be used as the binder resin for the charge generating layer. Examples of binder resins for the charge generating layer include polystyrene resins, polyethylene resins, polypropylene resins, acrylic resins, methacrylic resins, vinyl chloride resins, vinyl acetate resins, polyvinyl butyral resins, epoxy resins, polyurethane resins, phenolic resins, polyester resins, alkyd resins, polycarbonate resins, silicone resins, melamine resins, and copolymer resins containing two or more of these resins (for example, vinyl chloride-vinyl acetate copolymer resins, vinyl chloride-vinyl acetate-maleic anhydride copolymer resins), polyvinyl carbazole resins, etc. Among these, polyvinyl butyral resins are preferred.

[0117] The content of the charge generating agent in the charge generating layer 103a is preferably 1 to 600 parts by mass, and more preferably 50 to 500 parts by mass, per 100 parts by mass of the binder resin for the charge generating layer.

[0118] The thickness of the charge generating layer 103a varies depending on the characteristics of the charge generating material, the characteristics and content of the binder resin for the charge generating layer, etc., but is preferably 0.01 to 5 μm, more preferably 0.05 to 3 μm.

[0119] [Charge transport layer] The charge transport layer 103b in the photosensitive layer 103 contains a charge transport material and a binder resin for the charge transport layer.

[0120] Examples of the charge transport agent include carbazole derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, thiadiazole derivatives, triazole derivatives, imidazole derivatives, imidazolone derivatives, imidazolidine derivatives, bisimidazolidine derivatives, styryl compounds, hydrazone compounds, pyrazoline compounds, oxazolone derivatives, benzimidazole derivatives, quinazoline derivatives, benzofuran derivatives, acridine derivatives, phenazine derivatives, aminostilbene derivatives, triarylamine derivatives, phenylenediamine derivatives, stilbene derivatives, benzidine derivatives, poly-N-vinylcarbazole, poly-1-vinylpyrene, poly-9-vinylanthracene, triphenylamine derivatives, etc. The charge transport agents may be used alone or in combination.

[0121] Known resins can be used as the binder resin for the charge transport layer. Examples of binder resins for the charge transport layer include polycarbonate resins, polyacrylate resins, polyester resins, polyarylate (wholly aromatic polyester) resins, polystyrene resins, styrene-acrylonitrile copolymer resins, polymethacrylate resins, and styrene-methacrylate copolymer resins. Among these, polycarbonate resins are preferred. Furthermore, polycarbonate resins of BPA (bisphenol A), BPZ (bisphenol Z), dimethyl BPA, BPA-dimethyl BPA copolymer, BPC (bisphenol C), and copolymer structures thereof are preferred in terms of crack resistance, abrasion resistance, and charging properties.

[0122] The content of the charge transport material in the charge transport layer 103b is preferably 10 to 500 parts by weight, more preferably 20 to 250 parts by weight, per 100 parts by weight of the binder resin for the charge transport layer.

[0123] The thickness of the charge transport layer 103b varies depending on the characteristics of the charge transport material, the characteristics and content of the binder resin for the charge transport layer, etc., but is preferably 5 to 40 μm, more preferably 10 to 30 μm.

[0124] The charge transport layer 103b may contain an antioxidant, an electron conductive agent, a stabilizer, silicone oil, etc. The antioxidant is preferably one disclosed in JP-A-2000-305291. The electron conductive agent is preferably one disclosed in JP-A-50-137543 or JP-A-58-76483.

[0125] [2. Photoreceptor manufacturing method] The photoreceptor 1 can be manufactured, for example, by sequentially forming each layer constituting the photoreceptor 1 on a conductive support 101. Each layer is formed by a process of forming a coating film made of a coating liquid containing a solvent and solid components (or raw material components) constituting each layer, and a process of curing the coating film. A specific method for manufacturing the photoreceptor 1 will be described below using the photoreceptor 1 shown in FIG. 1 as an example.

[0126] The photoreceptor 1 can be manufactured, for example, through the following steps. Step (1): A step of applying a coating liquid for forming an intermediate layer to the surface of a conductive support 101 and drying the coating liquid to form an intermediate layer 102. Step (2): A step of applying a coating liquid for forming a charge generating layer to the surface of the intermediate layer 102 and drying it to form the charge generating layer 103a. Step (3): A step of applying a coating liquid for forming a charge transport layer to the surface of the charge generation layer 103a and drying it to form the charge transport layer 103b. Step (4): A step of forming the surface protective layer 104 by applying a coating liquid for forming the surface protective layer to the surface of the charge transport layer 103b to form a coating film and curing the coating film.

[0127] [Step (1): Formation of intermediate layer] The intermediate layer 102 can be formed, for example, by the following procedure. A coating liquid for forming an intermediate layer is prepared by dissolving a binder resin for the intermediate layer in a solvent. Conductive particles or metal oxide particles are dispersed in the coating liquid for forming an intermediate layer as needed. The coating liquid for forming an intermediate layer is applied to the conductive support 101 to a certain thickness to form a coating film. The coating film is then dried.

[0128] As a means for dispersing the conductive particles or metal oxide particles in the coating liquid for forming the intermediate layer, an ultrasonic disperser, a ball mill, a sand mill, a homomixer, or the like can be used.

[0129] Examples of methods for applying the coating liquid for forming an intermediate layer include dip coating, spray coating, spinner coating, bead coating, blade coating, beam coating, slide hopper, and circular slide hopper methods. The circular slide hopper method is a method used for coating the outer peripheral surface of a cylindrical or columnar article as the coating surface. The circular slide hopper method can be used as a method for applying the coating liquid for forming an intermediate layer to the outer peripheral surface of a drum-shaped conductive support.

[0130] The method for drying the coating film can be appropriately selected depending on the type of solvent and the thickness of the coating film, but heat drying is preferred.

[0131] The solvent used in the step of forming the intermediate layer 102 may be any solvent that can disperse the conductive particles or metal oxide particles well and dissolve the binder resin for the intermediate layer. Specifically, alcohol solvents having 1 to 4 carbon atoms, such as methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, t-butanol, and sec-butanol, are preferred because they have excellent binder resin solubility and coating performance. Furthermore, examples of co-solvents that can be used in combination with the above solvents to improve storage stability and particle dispersibility and that provide favorable effects include benzyl alcohol, toluene, methylene chloride, cyclohexanone, and tetrahydrofuran.

[0132] The concentration of the binder resin for the intermediate layer in the coating liquid for forming the intermediate layer is appropriately selected in accordance with the thickness of the intermediate layer 102 and the production speed.

[0133] [Step (2): Formation of Charge Generation Layer] The charge generation layer 103a can be formed, for example, by the following procedure. A coating liquid for forming the charge generation layer is prepared by dispersing a charge generation agent in a solution prepared by dissolving a binder resin for the charge generation layer in a solvent. The coating liquid for forming the charge generation layer is applied to a certain thickness on the intermediate layer 102 to form a coating film. The coating film is then dried.

[0134] As a means for dispersing the charge generating agent in the coating liquid for forming the charge generating layer, for example, an ultrasonic disperser, a ball mill, a sand mill, a homomixer, or the like can be used.

[0135] Examples of methods for applying the coating liquid for forming the charge generating layer include dip coating, spray coating, spinner coating, bead coating, blade coating, beam coating, slide hopper coating, and circular slide hopper coating.

[0136] The method for drying the coating film can be appropriately selected depending on the type of solvent and the thickness of the coating film, but heat drying is preferred.

[0137] Examples of solvents used in forming the charge generating layer 103a include toluene, xylene, methylene chloride, 1,2-dichloroethane, methyl ethyl ketone, cyclohexane, ethyl acetate, t-butyl acetate, methanol, ethanol, propanol, butanol, methyl cellosolve, 4-methoxy-4-methyl-2-pentanone, ethyl cellosolve, tetrahydrofuran, 1-dioxane, 1,3-dioxolane, pyridine, and diethylamine.

[0138] [Step (3): Formation of Charge Transport Layer] The charge transport layer 103b can be formed, for example, by the following procedure. A coating solution for forming the charge transport layer is prepared by dissolving a binder resin for the charge transport layer and a charge transport agent in a solvent. The coating solution for forming the charge transport layer is applied to a certain thickness on the charge generation layer 103a to form a coating film. The coating film is then dried.

[0139] Examples of methods for applying the coating solution for forming the charge transport layer include dip coating, spray coating, spinner coating, bead coating, blade coating, beam coating, slide hopper coating, and circular slide hopper coating.

[0140] The method for drying the coating film can be appropriately selected depending on the type of solvent and the thickness of the coating film, but heat drying is preferred.

[0141] Examples of solvents used to form the charge transport layer 103b include toluene, xylene, methylene chloride, 1,2-dichloroethane, methyl ethyl ketone, cyclohexanone, ethyl acetate, butyl acetate, methanol, ethanol, propanol, butanol, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, pyridine, and diethylamine.

[0142] [Step (4): Formation of Surface Protection Layer] The surface protective layer 104 can be formed, for example, by the following procedure. A coating liquid for forming the surface protective layer is prepared, containing at least metal oxide fine particles 104b, which are an essential component of the surface protective layer 104. The coating liquid for forming the surface protective layer may contain a charge transport agent, a polymerizable monomer, a polymerization initiator, a solvent, etc. as appropriate. The coating liquid for forming the surface protective layer is applied to a certain thickness on the charge transport layer 103b to form a coating film. The reactive components in the coating film are reacted to harden the coating film.

[0143] The coating liquid for forming the surface protective layer can be prepared, for example, by mixing the components using an ultrasonic disperser, a ball mill, a sand mill, a homomixer, or the like.

[0144] The solvent that can be contained in the coating liquid for forming a surface protective layer is preferably one that can dissolve or disperse the above-mentioned components. Examples of such solvents include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, t-butanol, sec-butanol, benzyl alcohol, toluene, xylene, dichloromethane, methyl ethyl ketone, cyclohexane, ethyl acetate, butyl acetate, methyl cellosolve, ethyl cellosolve, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, pyridine, and diethylamine. Examples of co-solvents that can be used in combination with the solvent to improve the storage stability and particle dispersibility of the coating liquid for forming a surface protective layer and that provide favorable effects include benzyl alcohol, toluene, methylene chloride, cyclohexanone, and tetrahydrofuran.

[0145] Examples of methods for applying the coating solution for forming the surface protective layer include dip coating, spray coating, spinner coating, bead coating, blade coating, beam coating, slide hopper, and circular slide hopper methods.

[0146] Coating using the circular slide hopper method can be performed using a circular slide hopper coater. In a circular slide hopper coater, the coating solution is shared across the slide surface of the device, and coating is achieved by the coating solution flowing down in a band from the end of the slide surface toward the surface to be coated. In coating methods using a circular slide hopper coater, the end of the slide surface and the surface to be coated are positioned with a certain gap between them, allowing the coating solution to be applied without damaging the surface. The circular slide hopper method requires a much shorter time in the solvent than the dip coating method, so the components of the lower layer hardly leach into the upper layer and can be applied without leaching into the coating tank. Therefore, the circular slide hopper method is preferred as a coating method for subsequent layers when forming multiple layers with different properties that dissolve in the same solvent.

[0147] The coating film may be cured without being dried, but it is preferable to carry out the curing treatment after natural drying or heat drying.

[0148] Drying conditions can be appropriately selected depending on the type of solvent, film thickness, etc. The drying temperature is preferably within the range of room temperature (25° C.) to 180° C., and particularly preferably within the range of 80 to 140° C. The drying time is preferably 1 to 200 minutes, and particularly preferably 5 to 100 minutes.

[0149] In the curing process of the coating film, the coating film is irradiated with ultraviolet light to generate radicals, which polymerize polymerizable monomers such as (meth)acrylic monomers. If the polymerizable monomer is crosslinkable, a three-dimensional network structure is introduced into the matrix 104a by the crosslinking reaction. This results in a surface protection layer 104 with high crosslink density, high hardness, and high elasticity.

[0150] Any light source that generates ultraviolet light can be used without limitation as the ultraviolet light source, including, for example, a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, and a flash (pulse) xenon lamp.

[0151] The irradiation conditions vary depending on the lamp. The UV irradiation dose is usually 5 to 500 mJ / cm 2 in the range of 5 to 100 mJ / cm 2 The lamp power is preferably in the range of 0.1 to 5 kW, and particularly preferably in the range of 0.5 to 3 kW. The irradiation time to obtain the required amount of ultraviolet light is, for example, preferably 0.1 seconds to 10 minutes, and from the viewpoint of work efficiency, more preferably 0.1 seconds to 5 minutes.

[0152] In the process of forming the surface protection layer 104, drying can be carried out before, after, or during irradiation with ultraviolet rays, and the timing of drying can be selected appropriately by combining these.

[0153] [3. Image forming device] The image forming apparatus of the present invention includes the above-described electrophotographic photoreceptor 1. The image forming apparatus of the present invention preferably further includes a first charging unit, an exposure unit, a developing unit, a transfer unit, a second charging unit, and a cleaning unit. The first charging means is a means for charging the surface of the photoreceptor 1. The exposure means is a means for irradiating the surface of the photoreceptor 1 with light to form an electrostatic latent image. The developing means is a means for developing the electrostatic latent image with toner to form a toner image. The transfer means is a means for transferring the toner image onto a transfer material, which is an image support that carries the image, such as plain paper or a transparent sheet. The second charging means is a means for charging the surface of the photoreceptor 1 after the toner image has been transferred onto the transfer material. The cleaning means is a means for removing residual toner from the photoreceptor 1 .

[0154] FIG. 2 is a schematic diagram showing an example of the image forming apparatus of the present invention. The image forming apparatus 100 is a so-called tandem color image forming apparatus, and is equipped with four sets of image forming units 10Y, 10M, 10C, and 10Bk, an intermediate transfer unit 7, a paper feeding means 21, a fixing means 24, etc. An original image reading device SC is disposed on top of the device main body A of the image forming apparatus 100.

[0155] The image forming unit 10Y that forms a yellow image has a first charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y, a second charging unit 9Y, and a cleaning unit 6Y, which are arranged in this order along the rotation direction of the photoreceptor 1Y, around the drum-shaped photoreceptor 1Y.

[0156] Image forming unit 10M, which forms a magenta image, has a first charging unit 2M, an exposure unit 3M, a developing unit 4M, a primary transfer roller 5M, a second charging unit 9M, and a cleaning unit 6M, which are arranged in this order along the rotation direction of photoreceptor 1M, around the drum-shaped photoreceptor 1M.

[0157] Image forming unit 10C, which forms a cyan image, has a first charging unit 2C, an exposure unit 3C, a developing unit 4C, a primary transfer roller 5C, a second charging unit 9C, and a cleaning unit 6C, which are arranged in this order along the rotation direction of photoreceptor 1C, around drum-shaped photoreceptor 1C.

[0158] Image forming unit 10Bk, which forms black images, has a drum-shaped photoconductor 1Bk and includes a first charging unit 2Bk, an exposure unit 3Bk, a developing unit 4Bk, a primary transfer roller 5Bk, a second charging unit 9Bk, and a cleaning unit 6Bk, which are arranged in this order along the rotation direction of photoconductor 1Bk.

[0159] The photoreceptor 1 of the present invention described above is used as the photoreceptors 1Y, 1M, 1C, and 1Bk.

[0160] Image forming units 10Y, 10M, 10C, and 10Bk are configured similarly, except for the colors of the toner images formed on photoreceptors 1Y, 1M, 1C, and 1Bk. Therefore, image forming unit 10Y will be described in detail as an example, and descriptions of image forming units 10M, 10C, and 10Bk will be omitted.

[0161] The image forming unit 10Y has a first charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, a primary transfer roller 5Y, a second charging unit 9Y, and a cleaning unit 6Y arranged around the photoreceptor 1Y, which is an image forming body, and forms a yellow (Y) toner image on the photoreceptor 1Y. In this embodiment, at least the photoreceptor 1Y, the first charging unit 2Y, the developing unit 4Y, the second charging unit 9Y, and the cleaning unit 6Y of the image forming unit 10Y are provided integrally.

[0162] The first charging means 2Y is a means for applying a uniform potential to the photosensitive member 1Y. As the first charging means 2Y, for example, a corona discharge type charger is used.

[0163] The exposure unit 3Y is a unit that exposes the photoreceptor 1Y, which has been given a uniform potential by the first charging unit 2Y, based on an image signal (yellow), to form an electrostatic latent image corresponding to the yellow image. As the exposure unit 3Y, for example, a unit consisting of an LED in which light-emitting elements are arranged in an array in the axial direction of the photoreceptor 1Y and an imaging element, or a laser optical system is used.

[0164] The developing means 4Y is composed of, for example, a developing sleeve that incorporates a magnet and rotates while holding a developer, and a voltage application device that applies a DC and / or AC bias voltage between the photoreceptor 1Y and the developing sleeve.

[0165] The primary transfer roller 5Y is a means for transferring the toner image formed on the photosensitive member 1Y onto the endless belt-like intermediate transfer member 70. The primary transfer roller 5Y is disposed in contact with the intermediate transfer member 70.

[0166] The second charging means 9Y is a discharging means that charges (discharges) the surface of the photoreceptor 1Y after the toner image is transferred to the intermediate transfer body 70, and is provided as a pre-cleaning member. As the second charging means 9Y, for example, a corona discharge type charger is used.

[0167] The cleaning means 6Y is composed of a cleaning blade and a brush roller provided upstream of the cleaning blade.

[0168] The intermediate transfer unit 7 has an endless belt-like intermediate transfer member 70 as a second image carrier in the form of a semiconductive endless belt that is wound around and rotatably supported by a plurality of rollers 71, 72, 73, and 74. The intermediate transfer unit 7 is provided with a cleaning means 6b that removes toner from the intermediate transfer member 70.

[0169] The image forming units 10Y, 10M, 10C, and 10Bk and the intermediate transfer unit 7 constitute a housing 8. The housing 8 is configured so as to be able to be pulled out from the apparatus main body A via support rails 82L and 82R.

[0170] The image forming apparatus 100 includes a secondary transfer roller 5b that transfers a color image formed on the intermediate transfer body 70 onto a transfer material P. The paper feed means 21 is a means for supplying the transfer material P to the secondary transfer roller 5b. The paper feed means 21 includes a paper feed cassette 20 that stores the transfer material P, a plurality of intermediate rollers 22A, 22B, 22C, and 22D that transport the transfer material P to the secondary transfer roller 5b, and a registration roller 23.

[0171] The fixing means 24 is a means for fixing the color image transferred onto the transfer material P onto the transfer material P. The fixing means 24 may be, for example, a heat roller fixing type that is composed of a heating roller equipped with a heat source inside and a pressure roller that is placed in pressure contact with the heating roller so as to form a fixing nip portion.

[0172] The image forming apparatus 100 has a paper discharge tray 26 for removing the transfer material P on which an image has been formed. The image forming apparatus 100 also has a paper discharge roller 25 downstream of the fixing means 24 for transporting the transfer material P that has been subjected to the fixing process to the paper discharge tray 26.

[0173] In the above embodiment, the image forming apparatus 100 is a color laser printer. However, the image forming apparatus 100 may also be a monochrome laser printer, a copier, a multifunction peripheral, or the like.

[0174] [4. Image forming method] In the image forming method of the present invention, an image is formed using the image forming apparatus 100 equipped with the above-described photoreceptor 1. The steps of the image forming method are not particularly limited, but are, for example, as follows.

[0175] First, first charging devices 2Y, 2M, 2C, and 2Bk discharge the surfaces of photoconductors 1Y, 1M, 1C, and 1Bk to a negative charge. Next, exposure devices 3Y, 3M, 3C, and 3Bk expose the surfaces of photoconductors 1Y, 1M, 1C, and 1Bk based on an image signal to form electrostatic latent images. Next, developing devices 4Y, 4M, 4C, and 4Bk apply toner to the surfaces of photoconductors 1Y, 1M, 1C, and 1Bk to develop them into toner images.

[0176] Next, the toner images of each color formed on the photoreceptors 1Y, 1M, 1C, and 1Bk are sequentially transferred (primary transfer) by primary transfer rollers 5Y, 5M, 5C, and 5Bk onto the rotating intermediate transfer body 70. This forms a color image on the intermediate transfer body 70.

[0177] Next, the surfaces of photoconductors 1Y, 1M, 1C, and 1Bk are neutralized by second charging devices 9Y, 9M, 9C, and 9Bk. After that, any toner remaining on the surfaces of photoconductors 1Y, 1M, 1C, and 1Bk is removed by cleaning devices 6Y, 6M, 6C, and 6Bk. Finally, in preparation for the next image formation process, photoconductors 1Y, 1M, 1C, and 1Bk are negatively charged by charging devices 2Y, 2M, 2C, and 2Bk.

[0178] Meanwhile, a transfer material P is fed from a paper feed cassette 20 by a paper feed means 21 and transported to a secondary transfer roller 5b via a plurality of intermediate rollers 22A, 22B, 22C, and 22D and a registration roller 23. Then, a color image is transferred (secondary transfer) onto the transfer material P by the secondary transfer roller 5b.

[0179] The transfer material P onto which the color image has been transferred is subjected to a fixing process by fixing means 24. Next, the transfer material P is nipped by paper discharge rollers 25 and discharged to the outside of the apparatus, and placed on a paper discharge tray 26. After the transfer material P is separated from the intermediate transfer body 70, the remaining toner on the intermediate transfer body 70 is removed by cleaning means 6b.

[0180] An image can be formed on the transfer material P through the above steps.

[0181] Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are for purposes of illustration and example only and not for purposes of limitation, and the scope of the present invention should be interpreted by the following claims. [Example]

[0182] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following examples, unless otherwise specified, operations were performed in a standard environment of 25°C and 50% RH. Furthermore, unless otherwise specified, "%", "ppm", and "parts" mean "% by mass", "ppm by mass", and "parts by mass", respectively.

[0183] [1. Preparation of metal oxide particles] [1-1. Formation of core particles] A solution containing titanium sulfate and titanyl sulfate was heated and hydrolyzed to produce a hydrous titanium dioxide slurry. This titanium dioxide slurry was dehydrated and fired. By controlling the titanyl sulfate solution concentration, core particles 1 to 3 with different average primary particle sizes were obtained. Core particles 1 to 3 are composed of anatase-type titanium oxide with a degree of anatase conversion of nearly 100%.

[0184] The average primary particle sizes of the core particles 1 to 3 are as follows. Average primary particle size of core particle 1: 35nm Average primary particle size of core particle 2: 75nm Average primary particle size of core particle 3: 130 nm

[0185] The average primary particle size was measured using the following method. Core particles were observed at 40,000x magnification using a scanning electron microscope "JSM-7401F" (manufactured by JEOL Ltd.). The longest and shortest diameters of each primary particle were measured using image analysis. The median value of the longest and shortest diameters was taken as the primary particle size. The average value of the particle sizes of 100 primary particles measured randomly was taken as the average primary particle size.

[0186] [1-2. Formation of metal oxide particles] Niobium (V) hydroxide was dissolved in concentrated sulfuric acid and mixed with an aqueous titanium sulfate solution to prepare an acidic mixed solution of niobium salt and titanium salt (hereinafter referred to as "titanium-niobium mixed solution").

[0187] Core particles 1 (100 parts by mass) were dispersed in hydrochloric acid (900 parts by mass) with a pH of 2.5±0.3 and heated to 670°C in an autoclave while stirring. While maintaining the pH at 2.5±0.3, a titanium-niobium mixed solution and an aqueous sodium hydroxide solution were simultaneously added. The amount of titanium-niobium mixed solution added was adjusted so that the mass of Ti relative to the mass of core particles 1 was 168.5 g / kg and the mass of Nb relative to the mass of core particles 1 was 5.15 g / kg. This prepared suspension A.

[0188] A titanium niobate solution was prepared by mixing a niobium solution prepared by dissolving 3 parts by mass of niobium pentachloride (NbCl5) in 100 parts by mass of 11.4 mol / L hydrochloric acid with 200 parts by mass of titanium sulfate solution containing 12.0 parts by mass of titanium. The mass ratio of niobium atoms to titanium atoms in the titanium niobate solution was 1.0 / 20.0.

[0189] This titanium niobate solution and a 10.7 mol / L aqueous sodium hydroxide solution were simultaneously added dropwise (parallel addition) to the above aqueous suspension A under stirring conditions over a period of 5 hours so that the pH of the suspension A became 2-3.

[0190] After the dropwise addition, the suspension was filtered and washed. The washed material was dried at 120°C under 1 atmosphere for 7 hours. This dried material and the organic material were then calcined in a nitrogen atmosphere. The initial temperature was 115°C, and the temperature was maintained at 115°C for the first 30 minutes. The temperature was then increased to 700°C at a rate of 20°C per minute, and the calcination was continued at 700°C for 1.5 hours.

[0191] As a result, microparticles with Nb atoms unevenly distributed near the surface were obtained. These microparticles were washed until the pH of the washing solution fell within the range of 6 to 8. Next, the microparticles were dried under conditions of 0.1 atmospheric pressure and 120°C for 1 hour. As a result, metal oxide microparticles 1 were obtained.

[0192] Metal oxide microparticles 2 were prepared in the same manner as in the preparation of metal oxide microparticles 1, except that core particles 1 were changed to core particles 2.

[0193] Metal oxide microparticles 3 were prepared in the same manner as in the preparation of metal oxide microparticles 1, except that core particles 1 were replaced with core particles 3.

[0194] The average primary particle diameters of the metal oxide fine particles 1 to 3 were measured in the same manner as in measuring the average primary particle diameter of the core particles. The average primary particle diameters of the metal oxide fine particles 1 to 3 were as follows. Average primary particle size of metal oxide particles 1: 40nm Average primary particle size of metal oxide particles 2: 80nm Average primary particle size of metal oxide microparticles 3: 135 nm

[0195] [1-3. Surface treatment for metal oxide particles 1-3] In the surface treatment of the metal oxide fine particles 1 to 3, the following surface treatment agents 1 to 5 were used. Surface treatment agent 1: X-12-1303MS manufactured by Shin-Etsu Chemical Co., Ltd. Surface treatment agent 2: Shin-Etsu Chemical Co., Ltd., KBM-502 Surface treatment agent 3: Shin-Etsu Chemical Co., Ltd., KBM-503 Surface treatment agent 4: Shin-Etsu Chemical Co., Ltd., KBM-403 Surface treatment agent 5: Shin-Etsu Chemical Co., Ltd., KBM-402

[0196] (Preparation of metal oxide particles 11) Metal oxide microparticles 1 (100 parts by mass) were added to hydrochloric acid (600 parts by mass) with a pH range of 2.5 to 3.5. Dispersion treatment was performed using an ultrasonic homogenizer US-600AT while controlling the liquid temperature to a range of 15±3°C. The resulting dispersion was stirred at 800 rpm, and 300 parts by mass of an aqueous solution of surface treatment agent was added dropwise to the dispersion over 20 minutes. The aqueous solution of surface treatment agent used here was a transparent solution obtained by adding 2 parts by mass of surface treatment agent 1 and 1.5 parts by mass of surface treatment agent 3 dropwise to 100 parts by mass of an aqueous acetic acid solution with a pH of 4±0.3, stirring for 15 minutes, and filtering off the insoluble matter. The mixture after the addition of the aqueous solution of surface treatment agent was stirred for an additional hour and then filtered. The powder obtained by filtration was washed with 2000 parts by mass of hydrochloric acid with a pH of 4 and then with 2000 parts by mass of pure water. Metal oxide microparticles 11 were thus obtained.

[0197] (Preparation of metal oxide microparticles 21) Metal oxide particles 21 were prepared in the same manner as in the preparation of metal oxide particles 11, except for the following changes. Metal oxide particles 1 has been changed to Metal oxide particles 2. In the aqueous solution of surface treatment agents, surface treatment agent 1 (2 parts by mass) and surface treatment agent 3 (1.5 parts by mass) were changed to surface treatment agent 2 (1.5 parts by mass) and surface treatment agent 4 (1 part by mass).

[0198] (Preparation of metal oxide microparticles 31) Metal oxide microparticles 3 (100 parts by mass) were added to hydrochloric acid (600 parts by mass) with a pH range of 3.0 to 3.5. Dispersion treatment was performed using an ultrasonic homogenizer US-600AT while controlling the liquid temperature to a range of 10 to 20°C. The resulting dispersion was stirred at 800 rpm, and 100 parts by mass of an aqueous solution of a surface treatment agent was added dropwise to the dispersion over 20 minutes. The aqueous solution of the surface treatment agent used here was a transparent aqueous solution obtained by adding 3 parts by mass of surface treatment agent 1 dropwise to 100 parts by mass of an aqueous acetic acid solution with a pH of 4±0.3, stirring for 15 minutes, and filtering off the insoluble matter. The mixture after the addition of the aqueous solution of the surface treatment agent was stirred for an additional hour and then filtered. The powder obtained by filtration was washed with hydrochloric acid (700 parts by mass) with a pH of 4 and then with pure water (2,000 parts by mass). This yielded metal oxide microparticles 31.

[0199] (Preparation of metal oxide microparticles 12) Ethanol (special reagent grade, unopened) [100 parts by mass] and pure water [0.5 parts by mass] were mixed to prepare water-in-ethanol. Surface treatment agent 2 [5.4 parts by mass] and surface treatment agent 4 [2.1 parts by mass] were mixed and completely dissolved in toluene [350 parts by mass] to prepare a surface treatment agent toluene solution. Metal oxide microparticles 1 [100 parts by mass] were mixed with the prepared water-in-ethanol [100 parts by mass] to form a suspension. This suspension was mixed with the surface treatment agent toluene solution [350 parts by mass] and stirred in a stirrer for 8 hours, then filtered. The filter cake was washed and further heated at 0.1 atmosphere and 130°C for 2 hours. This yielded metal oxide microparticles 12.

[0200] (Preparation of metal oxide microparticles 13) Metal oxide particles 13 were prepared in the same manner as in the preparation of metal oxide particles 12, except that the surface treatment agent 4 was not used.

[0201] (Preparation of metal oxide microparticles 22) Metal oxide particles 22 were prepared in the same manner as in the preparation of metal oxide particles 12, except for the following changes. Metal oxide particles 1 has been changed to Metal oxide particles 2. Surface treatment agent 2 (5.4 parts by mass) and surface treatment agent 4 (2.1 parts by mass) in the toluene solution were changed to surface treatment agent 2 (3.2 parts by mass) and surface treatment agent 3 (1.8 parts by mass).

[0202] (Preparation of metal oxide microparticles 32) Metal oxide particles 32 were prepared in the same manner as in the preparation of metal oxide particles 12, except for the following changes. Metal oxide particles 1 has been changed to Metal oxide particles 3. Surface treatment agent 2 (5.4 parts by mass) and surface treatment agent 4 (2.1 parts by mass) in the toluene solution were changed to surface treatment agent 2 (1.8 parts by mass) and surface treatment agent 5 (1.1 parts by mass).

[0203] (Preparation of metal oxide microparticles 33) Metal oxide fine particles 33 were prepared in the same manner as in the preparation of metal oxide fine particles 32, except that the surface treatment agent 5 was not used.

[0204] [2. Preparation of Electrophotographic Photoreceptor] The photoreceptors of Examples 1 to 12 and Comparative Examples 1 to 4 were manufactured according to the following procedure. The layer structure of each photoreceptor was the same as that of the photoreceptor shown in FIG.

[0205] [2-1. Preparation of conductive support] The surface of the cylindrical aluminum support was machined to form a conductive support.

[0206] [2-2. Formation of the intermediate layer]

[0207] The components of the composition below were mixed and dispersed batchwise for 10 hours using a sand mill as a disperser to obtain a coating liquid for forming an intermediate layer.

[0208] (Composition of Coating Solution for Forming Intermediate Layer) Polyamide resin X1010 (manufactured by Daicel Degussa Co., Ltd.) 10 parts by mass Titanium oxide SMT500SAS (manufactured by Teika Co., Ltd.) 11 parts by mass Ethanol 200 parts by mass

[0209] The coating solution for forming the intermediate layer was applied onto the conductive support by dip coating, and the resulting coating was dried at 110°C for 20 minutes to form an intermediate layer having a thickness of 2 µm after drying.

[0210] [2-3. Formation of Charge Generation Layer] The components of the following composition were mixed and dispersed using a circulation ultrasonic homogenizer "RUS-600TCVP (manufactured by Nippon Seiki Seisakusho Co., Ltd.)" to prepare a coating solution for forming a charge generating layer. The dispersion conditions were 19.5 kHz, 600 W, a circulation flow rate of 40 L / H, and 0.5 hours.

[0211] (Composition of the Charge Generating Layer Forming Composition) Charge-generating material (a mixed crystal of a 1:1 adduct of titanyl phthalocyanine and (2R,3R)-2,3-butanediol, with clear peaks at 8.3°, 24.7°, 25.1°, and 26.5° in Cu-Kα characteristic X-ray diffraction spectrum measurement, and unadducted titanyl phthalocyanine) 24 parts by mass Polyvinyl butyral resin "S-LEC BL-1 (manufactured by Sekisui Chemical Co., Ltd.)" 12 parts by weight 3-methyl-2-butanone / cyclohexanone=4 / 1 (V / V) 400 parts by mass

[0212] The coating solution for forming the charge generating layer was applied onto the intermediate layer by dip coating, and the resulting coating was dried to form a charge generating layer having a thickness of 0.3 μm after drying.

[0213] [2-4. Formation of Charge Transport Layer] The components of the following composition were mixed and dissolved to prepare a coating liquid for forming a charge transport layer.

[0214] (Composition of Coating Solution for Forming Charge Transport Layer) Charge transport agent (compound CTM-(1)) 60 parts by mass Polycarbonate resin "Z300 (Mitsubishi Gas Chemical Company, Inc.)" 100 parts by mass Antioxidant "Irganox 1010 (manufactured by Ciba Specialty Chemicals)" 4 parts by mass

[0215] [ka]

[0216] The charge transport layer forming coating solution was applied onto the charge generation layer by dip coating, and the resulting coating was dried at 120°C for 70 minutes to form a charge transport layer having a dry thickness of 24 μm.

[0217] [2-5. Formation of surface protection layer] In forming the surface protective layer, the following additives 1 to 6 were used. Additive 1: Polyethylene glycol dimethyl ether (number average molecular weight Mn ≒ 500) Additive 2: Polyethylene glycol dimethyl ether (number average molecular weight Mn ≒ 1000) Additive 3: Polyethylene glycol monolaurate (average polymerization number of ethylene glycol: 12) Additive 4: Ethylene glycol distearate Additive 5: Sorbitan monostearate Additive 6: Pentadecanoic acid monoglyceride

[0218] The various surface-treated metal oxide microparticles (100 parts by mass) prepared were mixed with ethanol (special grade) (50 parts by mass), the first additive, and the second additive. The type of surface-treated metal oxide microparticles, the type of the first additive, the amount of the first additive mixed, the type of the second additive mixed, and the amount of the second additive mixed are as shown in Table I. Zirconia balls (30 μm diameter) (50 parts by mass) were mixed with the mixture and kneaded in a sealed container at 30°C for 2 hours. After kneading, the zirconia balls were separated using a sieve. Ethanol (special grade) was sprinkled on the obtained microparticles to wash away unused additives and residual solvent. Next, the microparticles were dried at 0.1 atmosphere and 60°C for 3 hours. This yielded "pre-treated metal oxide microparticles."

[0219] The components of the following composition were mixed and stirred to be sufficiently dissolved and / or dispersed to prepare a coating liquid for forming a surface protective layer.

[0220] (Composition of Coating Solution for Forming Surface Protective Layer) Charge transport agent (compound T-3) 60 parts by mass Polymerizable monomer (compound M1) 40 parts by mass Pre-treated metal oxide fine particles 50 parts by mass Photopolymerization initiator: Omnirad819 (manufactured by IGM Resins BV) 5 parts by mass 2-butanol 150 parts by mass Tetrahydrofuran 50 parts by mass Third additive as specified in Table I Amount as specified in Table I

[0221] [ka]

[0222] In the compound M1, R represents an acryloyl group (CH2=CHCO-).

[0223] The surface protection layer forming coating solution was applied onto the charge transport layer using a circular slide hopper coater. The coating film was irradiated with ultraviolet light using a metal halide lamp for 1 minute, and then dried at 110°C for 70 minutes. This resulted in a surface protection layer with a dry thickness of 4.0 μm.

[0224] Photoreceptors of Examples 1 to 12 and Comparative Examples 1 to 4 were prepared according to the above procedure.

[0225] The amounts of various additives mixed shown in Table I are the amounts [parts by mass] mixed relative to 100 parts by mass of metal oxide fine particles.

[0226] [3. Measurement of the coefficient of variation (B / A) of the equivalent circle diameter of metal oxide fine particles] The prepared photoreceptor was cut into three equal parts along the longitudinal direction, together with the conductive support. The cut sample was cut at a depth of 2±1 μm from the outermost surface of the surface protection layer to prepare a 200 nm thick thin section sample of the cross section of the surface protection layer. An ultrasonic ultramicrotome (Leica, UC7) was used for cutting. The cutting speed was 0.6 mm / s. The cutting direction was parallel to the surface of the surface protection layer (a tilt of ±5° was allowed).

[0227] TEM photographs of the thin-section samples were taken using a transmission electron microscope "JEM-2000FX" (manufactured by JEOL Ltd.) at an accelerating voltage of 80 kV. The magnification was adjusted so that the average total number of "secondary particles or independently dispersed primary particles" in one field of view was 30 to 100. Fine particles that overlapped the outer edge of the TEM photograph were excluded from the count. 20 TEM photographs were taken at a uniform magnification in random fields of view.

[0228] The TEM images were saved in JPEG format. The TEM images were binarized using the analysis software ImageJ according to the following rules: First, open the software "ImageJ". Next, open the image to be analyzed. Select "Binary" from the "Process" menu and perform binarization according to the "Make Binary" menu. At this time, primary particles are binarized as primary particles. Secondary particles are binarized as a single particle, regardless of whether the boundaries of primary particles can be distinguished. Fine particles that overlap the outer edge of the TEM photograph are excluded from the binarization.

[0229] Using the above method, all fine particles in the TEM photographs of multiple fields of view were binarized until the total number of primary particles and secondary particles reached 150 or more.

[0230] The area S' of each binarized image of each fine particle was determined, and the circle-equivalent diameter L' of the image was calculated using the following formula: L′=√(4S′ / π) L': Equivalent circle diameter in the image S': Area in the image π: Pi

[0231] Taking the scale of the image into consideration, the equivalent circle diameter L at the actual scale was calculated from the equivalent circle diameter L' in the image.

[0232] The mean value A and standard deviation value B of the equivalent circle diameter were calculated from the equivalent circle diameter L. The coefficient of variation (B / A) of the equivalent circle diameter was calculated from the mean value A and standard deviation value B of the equivalent circle diameter.

[0233] The calculation of the coefficient of variation was carried out twice on three different cross sections of the photoreceptor. The two coefficients of variation for each photoreceptor (the value for N=1 and the value for N=2) and their average values ​​are shown in Table II.

[0234] The measurement of the coefficient of variation required cutting out the photoreceptor, and was therefore carried out after the image evaluation described below.

[0235] [4. Measurement of the average primary particle size of metal oxide fine particles] In measuring the coefficient of variation in "3" above, when analyzing the ImageJ image, all of the fine particles in the bottom 5% of the particle size distribution were selected, and the number-average particle size of these fine particles was calculated. This value was used as the average primary particle size of the metal oxide fine particles in the surface protective layer. The average primary particle size of the metal oxide fine particles in each photoreceptor was as shown in Table II. Table II also shows the average primary particle size of the metal oxide fine particles before surface treatment in the production of each photoreceptor.

[0236] [5. Image Evaluation] A drum unit was assembled using the prepared photoreceptor. This drum unit was installed in the black position of a Konica Minolta Bizhub C750i copier, and various image evaluations were performed. Unless otherwise noted, image evaluations were performed in an environment with a temperature of 20°C and a relative humidity of 50%. The drum unit and copier used for image evaluation were conditioned for at least 12 hours in the environment used for evaluation. For drum units other than those in the black position, a commercially available drum unit for the Bizhub C750i was used as is. For the black drum unit, a new, unused drum unit was opened and reassembled with only the photoreceptor replaced with the prepared photoreceptor. In each example, a new, unused black drum unit was used. New, unused, genuine commercially available toner for the Bizhub C750i was used as is. Unless otherwise noted, the printing speed was set to the plain paper setting (maximum speed).

[0237] [5-1. Operation check and evaluation of density difference within the image] First, image stabilization was performed. Next, using A3-sized Konica Minolta CF paper, three consecutive prints were made on one side with a black image at density 0, with black monochrome specified. Next, two consecutive prints were made on one side with a black halftone image at density 64 and hyper (with image quality correction), with black monochrome specified. Finally, two consecutive prints were made on one side with a solid black image at density 255, with black monochrome specified. This confirmed operation.

[0238] The printed solid black image with a density of 255 was divided into three equal parts vertically and horizontally, for a total of nine sections, and five sections were randomly selected from each section to measure image density. The image density measurement device used was an RD-918 (Macbeth). The measurement environment was 20°C and 50% relative humidity. The device was calibrated immediately before measurement using a standard calibration plate. After calibration, the device was recalibrated every hour. The difference between the maximum and minimum image densities of the 45 sections was calculated as the "intra-image density difference." The intra-image density difference was measured for two solid black images with a density of 255, and the larger value was used. The intra-image density difference was evaluated based on the intra-image density difference value and the following criteria. The evaluation results are shown in Table I. Grades A, B, and C were considered acceptable.

[0239] A: Density difference within the image is less than 0.02 B: Density difference within the image is 0.02 or more and less than 0.03 C: Density difference within the image is 0.03 or more and less than 0.04 D: Density difference within the image is 0.04 or more and less than 0.05 E: Density difference within the image is 0.05 or more

[0240] [5-2. Evaluation of thin line reproducibility] After printing in "5-1" above, two consecutive prints of a grid image consisting of black lines with a density of 255 were made on one side of an A3-sized J paper (Konica Minolta) in single-sided mode with full color settings. The line width of the grid image was 2 dots. The spacing between the lines of the grid image was 6 mm in the longitudinal direction of the drum unit and 6 mm in the paper transport direction. The grid image was visually observed. The thin line reproducibility was evaluated based on the observation results and the following criteria. The evaluation results are shown in Table III. A, B, and C were considered acceptable.

[0241] A: No defects can be identified. B: Slight defects can be observed, but are within the acceptable range. C: Defects can be confirmed and are at the minimum acceptable level. D: Defects were confirmed and were at a level that was unacceptable.

[0242] [5-3. Evaluation of local image abnormalities and image density fluctuations] After printing in "5-2" above, a black halftone image with density 64 and hyper (image quality correction) was printed in double-sided continuous printing mode with black monochrome settings. A3-size J Paper (Konica Minolta) was used as the printing paper. 1,000 prints (500 sheets in total) were made.

[0243] Immediately after the above printing was completed, a black halftone image with density 64 and hyper (image quality correction) was printed on A3-size CF paper (Konica Minolta) in single-sided continuous printing mode. 500 prints (500 sheets) of this printing were made. Then, one A3 solid black image with density 255 was printed on A3-size CF paper (Konica Minolta).

[0244] The number of defects per photoreceptor cycle was counted for the last 500 sheets of black halftone images printed on CF paper. Local image abnormalities were evaluated based on the number of defects counted and the following criteria. The evaluation results are shown in Table III. A, B, and C were considered pass.

[0245] A: The number of defects per photoconductor cycle is 0 B: The number of defects per photoconductor cycle is greater than 0 and less than or equal to 1 C: The number of defects per photoconductor cycle is more than 1 and not more than 3 D: The number of defects per photoconductor cycle is more than 3 and 10 or less E: More than 10 defects per photoconductor cycle

[0246] For the first sheet of a black halftone image printed on CF paper, the image density was measured at a total of 45 locations in the same manner as in "5-1" above, and the average value of the image densities at the 45 locations was calculated. For the last 500 sheets of a black halftone image printed on CF paper, the image density was measured at a total of 45 locations in the same manner as in "5-1" above, and the average value of the image densities at the 45 locations was calculated. The difference in the average image densities between the two black halftone images was calculated as the inter-image density difference. The image density variation in the printing of the black halftone image was evaluated based on the inter-image density difference and the following criteria. The evaluation results are shown in Table III. A, B, and C were considered acceptable.

[0247] A: Density difference between images is less than 0.02 B: Density difference between images is 0.02 or more and less than 0.03 C: Inter-image density difference is 0.03 or more and less than 0.04 D: Inter-image density difference is 0.04 or more and less than 0.05 E: Density difference between images is 0.05 or more

[0248] For the first black solid image printed in "5-1" above, the image density was measured at a total of 45 locations in the same manner as in "5-1" above, and the average value of the image densities at the 45 locations was calculated. For the last black solid image printed in "5-3," the image density was measured at a total of 45 locations in the same manner as in "5-1" above, and the average value of the image densities at the 45 locations was calculated. The difference in the average image densities between the two black solid images was calculated as the inter-image density difference. The image density variation in the printing of the black solid image was evaluated based on the inter-image density difference and the following criteria. The evaluation results are shown in Table III. A, B, and C were rated as passing.

[0249] A: Density difference between images is less than 0.02 B: Density difference between images is 0.02 or more and less than 0.03 C: Inter-image density difference is 0.03 or more and less than 0.04 D: Inter-image density difference is 0.04 or more and less than 0.05 E: Density difference between images is 0.05 or more

[0250] [Table 1]

[0251] [Table 2]

[0252] [Table 3]

[0253] From the above results, it was confirmed that the electrophotographic photoreceptor of the present invention can improve image quality and suppress changes in image density during continuous printing. [Explanation of symbols]

[0254] 101: Conductive support 102: Middle class 103: Photosensitive layer 103a: Charge generation layer 103b: Charge transport layer 104: Surface protective layer 104a: Matrix 104b: Metal oxide fine particles 100: Image forming device 1, 1Y, 1M, 1C, 1Bk: Photoconductor 2Y, 2M, 2C, 2Bk: 1st charging means 3Y, 3M, 3C, 3Bk: Exposure means 4Y, 4M, 4C, 4Bk: Developing means 5Y, 5M, 5C, 5Bk: Primary transfer roller 5b: Secondary transfer roller 6Y, 6M, 6C, 6Bk, 6b: cleaning means 7: Intermediate transfer unit 8: Housing 9Y, 9M, 9C, 9Bk: second charging means 10Y, 10M, 10C, 10Bk: Image forming units 21:Paper feeding means 20: Paper cassette 22A, 22B, 22C, 22D: Intermediate rollers 23: Resist roller 24: Fixing means 25: Paper ejection roller 26: Paper output tray 70: Intermediate transfer body 71, 72, 73, 74: Roller 82L, 82R: Support rail P: Transfer material

Claims

1. An electrophotographic photoreceptor having at least a photosensitive layer and a surface protective layer laminated in this order on a conductive support, the surface protective layer contains metal oxide fine particles containing Ti atoms and second atoms which are metal atoms or semimetal atoms other than Ti atoms, When the average value of the equivalent circle diameters of the cross sections of the metal oxide fine particles appearing on the cross section of the surface protective layer is defined as A and the standard deviation value of the equivalent circle diameters is defined as B, the coefficient of variation (B / A) is within a range of 0.12 to 0.

35. Electrophotographic photoreceptor.

2. the second atom is a Nb atom; The electrophotographic photoreceptor according to claim 1 .

3. The surface protective layer contains at least a polymer of a (meth)acrylic monomer having a structure represented by the following general formula (1), or contains at least a compound having a structure represented by the following general formula (1) and a crosslinked (meth)acrylic resin: The electrophotographic photoreceptor according to claim 1 . 【Chemical 1】 [In general formula (1), R １ , R ２ , and R ３ are each independently a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an allyl group, or an acyl group. １ , R ２ , and R ３ may have a substituent. １ , R ２ , and R ３ At least two of them may form a bond with each other.]

4. The average primary particle size of the metal oxide fine particles is within the range of 40 to 140 nm. The electrophotographic photoreceptor according to claim 1 .

5. An electrophotographic photoreceptor comprising the electrophotographic photoreceptor according to any one of claims 1 to 4. Image forming device.

6. An image is formed using the image forming apparatus according to claim 5. Image forming method.

Images