Electrophotographic photoreceptor, process cartridge, and electrophotographic device

Abstract

To provide an electrophotographic photoreceptor that can prevent highlight image deletion under high temperature and high humidity, while maintaining high injection electrification characteristics.SOLUTION: An electrophotographic photoreceptor has a surface layer containing a binder resin and metal oxide particles. The average primary particle diameter of the metal oxide particles measured from a cross section of the surface layer is 20 nm or more and 70 nm or less. The content of the metal oxide particles in the surface layer measured from the cross section of the surface layer is 30 volume% or more and 75 volume% or less based on the total volume of the surface layer.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an electrophotographic photoreceptor, and a process cartridge and an electrophotographic apparatus each having the electrophotographic photoreceptor. [Background technology]

[0002] As electrophotographic photoreceptors mounted in electrophotographic devices, those containing an organic photoconductive substance that serves as a charge generating substance are widely used. In recent years, there has been a demand for improving the mechanical durability, i.e., wear resistance, of electrophotographic photoreceptors in order to extend the life of the electrophotographic photoreceptors and to improve image quality during repeated use.

[0003] On the other hand, in the charging process, oxidizing gases such as ozone and nitrogen oxides are generated by the discharge occurring between the electrophotographic photoreceptor and the charging member, and the oxidizing gases cause the materials used in the surface layer of the electrophotographic photoreceptor to deteriorate, generating discharge products. When these discharge products absorb moisture in the air, the electrostatic latent image formed on the electrophotographic photoreceptor collapses, and a phenomenon called "image deletion" may occur.

[0004] As the wear resistance of the surface of the electrophotographic photosensitive member increases, the substances causing image deletion, such as the discharge products and moisture, are not removed, and image deletion becomes more likely to occur.

[0005] As a technique for improving image deletion, there is a method in which metal oxide particles are contained in the surface layer of the electrophotographic photosensitive member to control the volume resistivity of the surface layer of the electrophotographic photosensitive member.

[0006] A dark potential is formed on the surface of the electrophotographic photoreceptor by applying a voltage from a charging member in a charging process. It is considered that charging for forming this dark potential is performed by two types of processes. One is a process in which the surface of the electrophotographic photoreceptor is charged by dielectric breakdown of the air layer between the charging member and the surface of the electrophotographic photoreceptor according to Paschen's law. The other process is an injection charging process in which charge is transferred directly from the charging member to the electrophotographic photoreceptor at the contact portion between the charging member and the electrophotographic photoreceptor without discharging when the contact potential difference between the electrophotographic photoreceptor and the charging member is sufficiently small.

[0007] By controlling the volume resistivity by including metal oxide particles in the surface layer, the proportion of charging by injection from the charging member to the electrophotographic photosensitive member in the charging step can be increased. In other words, the injection chargeability of the electrophotographic photosensitive member can be increased, thereby suppressing discharge and suppressing the generation of discharge products.

[0008] Patent Document 1 describes a technology that enables stable injection charging properties and prevents scratches on the injection layer and image blurring even with repeated use by controlling the particle size of metal oxide particles, which are conductive fine particles contained in the protective layer, relative to the toner particle size.

[0009] Furthermore, Patent Document 2 describes a technology in which conductive particles in a protective layer protrude 0.2 μm or more from the surface of a photoreceptor, thereby enabling high-quality image characteristics and stable injection charging even with repeated use.

[0010] Furthermore, Patent Document 3 describes a technology that enables improved cleaning performance when the electrophotographic photosensitive member is used for a long period of time by incorporating a component obtained by reacting a curable compound and anatase-type titanium oxide containing niobium atoms into the protective layer (surface layer) of the electrophotographic photosensitive member. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2002-214815 A [Patent Document 2] JP 2001-305775 A [Patent Document 3] JP 2009-229495 A Summary of the Invention [Problem to be solved by the invention]

[0012] According to the study by the present inventors, the techniques disclosed in Patent Documents 1 and 2 contain metal oxide particles in the surface layer, and use a configuration that allows high injection charging, but have a problem in that density is not obtained at low printing rates (highlights) in high temperature and high humidity environments (hereinafter referred to as "highlight image deletion"). Highlight image deletion is a phenomenon in which density decreases when the exposed area at the time of latent image is small at low printing rates, that is, in the reversal development method, as shown in Figure 1.

[0013] While the above-mentioned image deletion is caused by discharge products due to discharge, highlight image deletion is a phenomenon that occurs from the early stage of the development process regardless of the presence or absence of discharge products, and is thought to have a different mechanism of occurrence from image deletion.

[0014] Therefore, an object of the present invention is to provide an electrophotographic photoreceptor capable of suppressing highlight image deletion even under high temperature and high humidity conditions while maintaining high injection charging properties, and further to provide a process cartridge equipped with the electrophotographic photoreceptor, and an electrophotographic apparatus equipped with the process cartridge. [Means for solving the problem]

[0015] The above object can be achieved by the present invention, which is described below. That is, the electrophotographic photoreceptor according to the present invention is an electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles, characterized in that the average primary particle diameter of the metal oxide particles measured from a cross section of the surface layer is 20 nm or more and 70 nm or less, and the content of the metal oxide particles in the surface layer measured from a cross section of the surface layer is 30 vol % or more and 75 vol % or less with respect to the total volume of the surface layer.

[0016] Furthermore, a process cartridge according to another aspect of the present invention is characterized in that it integrally supports the above-mentioned electrophotographic photosensitive member and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably attachable to the main body of the electrophotographic apparatus.

[0017] Furthermore, an electrophotographic apparatus according to still another aspect of the present invention comprises the above electrophotographic photoreceptor, a charging means, an exposing means, a developing means, and a transferring means. Effect of the Invention

[0018] According to the present invention, it is possible to provide an electrophotographic photoreceptor capable of suppressing highlight image deletion even under high temperature and high humidity conditions while maintaining high injection charging properties. [Brief description of the drawings]

[0019] [Figure 1] FIG. 11 is a diagram showing the relationship between the printing rate and the density for explaining highlight image deletion. [Diagram 2] 1 is a schematic diagram illustrating an example of a configuration of an electrophotographic photoreceptor according to the present invention. [Diagram 3] FIG. 2 is a STEM image of an example of niobium-containing titanium oxide used in the present examples. [Figure 4] FIG. 2 is a schematic diagram of an example of niobium-containing titanium oxide used in the present examples. [Diagram 5] FIG. 2 is a diagram showing an example of a comb-shaped electrode used for measuring the volume resistivity of an electrophotographic photosensitive member. [Figure 6]1 is a diagram showing an example of a schematic configuration of a process cartridge in which an electrophotographic photosensitive member according to the present invention is mounted, and an electrophotographic apparatus including the process cartridge; [Figure 7] FIG. 13 is a diagram showing the print pattern of an image used when evaluating the precision of the image. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will be described in detail below with reference to preferred embodiments. The electrophotographic photoreceptor according to the present invention is an electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles, and it is necessary that the average primary particle diameter of the metal oxide particles measured from a cross-section of the surface layer is 20 nm or more and 70 nm or less, and the content of the metal oxide particles in the surface layer measured from a cross-section of the surface layer is 30 vol % or more and 75 vol % or less with respect to the total volume of the surface layer.

[0021] Furthermore, a process cartridge according to another aspect of the present invention integrally supports the electrophotographic photosensitive member and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably attachable to the main body of the electrophotographic apparatus.

[0022] Furthermore, an electrophotographic apparatus according to still another aspect of the present invention comprises the above electrophotographic photoreceptor, a charging unit, an exposing unit, a developing unit, and a transferring unit.

[0023] In order to realize high injection charging property, it is possible to increase the content of metal oxide particles in the surface layer, but this leads to a trade-off in that highlight image deletion worsens. Metal oxide particles receive charges by directly contacting a charging member, and become so-called charge injection points. Therefore, it is considered that a larger content of metal oxide particles in the surface layer can receive more charges from the charging member. On the other hand, when the content of metal oxide particles in the surface layer increases, the metal oxide particles are connected to each other, and the charge on the surface of the electrophotographic photoreceptor is more likely to move along the metal oxide particles. In particular, in a high-temperature and high-humidity environment, the surface layer absorbs moisture, the surface layer has a lower resistance, and the charge transfer is accelerated, so that highlight image deletion is considered to be prominent in a high-temperature and high-humidity environment.

[0024] According to the investigations of the present inventors, the reason why the electrophotographic photoreceptor according to the present invention employing the above-mentioned unique configuration maintains high injection charging performance while suppressing highlight image deletion is presumed to be as follows.

[0025] As described above, in order to maintain high injection chargeability, the content of metal oxide particles in the surface layer must be 30% by volume or more and 75% by volume or less with respect to the total volume of the surface layer. This is because if the content of metal oxide particles is less than 30% by volume, sufficient injection chargeability cannot be maintained, and if it exceeds 75% by volume, cracks will occur in the film of the surface layer due to a lack of binder resin, the strength of the film will be weak, and the metal oxide particles that are the charge injection points will easily come off, resulting in a significant decrease in wear resistance. The content of metal oxide particles in the surface layer is preferably 42% by volume or more and 65% by volume or less with respect to the total volume of the surface layer.

[0026] Meanwhile, the results of an investigation into highlight image deletion revealed that the main cause of highlight image deletion is charge transfer in the film thickness direction of the surface layer. In other words, in order to suppress highlight image deletion, it is necessary to suppress charge transfer within the film of the surface layer. By reducing the primary particle size of the conductive material, the interface area (particle surface area) of the metal oxide particles in the surface layer increases. Since the binder resin penetrates between the metal oxide particles, the increase in interface area also increases the interface resistance, suppressing charge transfer within the surface layer and thus suppressing highlight image deletion.

[0027] If the primary particle diameter of the metal oxide particles exceeds 70 nm, sufficient interface resistance cannot be obtained, and suppression of highlight image deletion cannot be expected. If the primary particle diameter of the metal oxide particles is smaller than 20 nm, the surface of the surface layer (protective layer) is easily covered with the binder resin, and injection charging properties are reduced. The primary particle diameter of the metal oxide particles is preferably 30 nm or more and 60 nm or less.

[0028] A specific configuration of the electrophotographic photoreceptor according to the present invention will now be described. [Electrophotographic photoreceptor] The electrophotographic photoreceptor of the present invention is characterized by having a photosensitive layer and a protective layer which is a surface layer.

[0029] Fig. 2 is a diagram showing an example of the configuration of an electrophotographic photoreceptor according to the present invention. The electrophotographic photoreceptor shown in Fig. 2 has a support 21, an undercoat layer 22, a charge generating layer 23, a charge transport layer 24, and a protective layer 25 as a surface layer.

[0030] FIG. 2 shows an example in which the photosensitive layer of the electrophotographic photoreceptor is a laminated type photosensitive layer consisting of a charge generating layer 23 and a charge transport layer 24, but the photosensitive layer may be a single-layer type photosensitive layer described later.

[0031] The electrophotographic photoreceptor may not have the undercoat layer 22, and may have a conductive layer (described later) between the support 21 and the undercoat layer 22 or the photosensitive layer.

[0032] The method for producing the electrophotographic photoreceptor of the present invention includes a method of preparing the coating liquid for each layer described later, coating the layer on the support in the desired order, and drying the coating liquid. In this case, the coating liquid can be applied by dip coating, spray coating, inkjet coating, roll coating, die coating, blade coating, curtain coating, wire bar coating, ring coating, etc. Among these, dip coating is preferred from the viewpoint of efficiency and productivity.

[0033] Each layer will be described below. <Protective layer (surface layer)> The electrophotographic photoreceptor of the present invention has a protective layer containing a binder resin and metal oxide particles as a surface layer. The protective layer contains 30% by volume or more and 75% by volume or less of the metal oxide particles based on the total volume of the protective layer. The protective layer may contain a charge transport material.

[0034] It is preferable that the powder resistivity A (Ω·cm) of the metal oxide particles satisfies the following formula (1). 1.0×10 3 ≦A≦1.0×10 10 (1) The powder resistivity A of metal oxide particles is 1.0×10 3 If the resistivity is lower than Ω·cm, it is difficult to suppress the charge transfer in the protective layer, and highlight image deletion will occur. Also, if the powder resistivity A exceeds 1.0×1010 Ω·cm, the injection charging property will decrease. 5 Ωcm or more 1.0×10 9 It is more preferable that the resistivity is Ω·cm or less.

[0035] In the present invention, the powder resistivity A of the metal oxide particles is measured under an environment of normal temperature and normal humidity (temperature 23.0°C / relative humidity 55%). In the present invention, a resistivity meter Loresta GP manufactured by Mitsubishi Chemical Corporation is used as the measuring device. The metal oxide particles of the present invention to be measured have a powder resistivity A of 500 kg / cm. 2 The mixture was solidified at a pressure of 100 V to form a pellet-shaped sample for measurement.

[0036] Specific examples of the metal oxide particles include particles of metal oxides such as titanium oxide, zinc oxide, tin oxide, indium oxide, etc. The metal oxides may be doped with elements such as phosphorus or aluminum, or the oxides thereof may be added.

[0037] The metal oxide particles may have a laminated structure having a core particle and a coating layer that coats the core particle. Examples of the core particle include metal oxides such as titanium oxide, barium sulfate, and zinc oxide. Examples of the coating layer include metal oxides such as tin oxide.

[0038] The metal oxide particles are preferably titanium oxide particles containing niobium. The niobium-containing titanium oxide particles may be in various shapes, such as spherical, polyhedral, ellipsoidal, flaky, and needle-like. Among these, from the viewpoint of reducing image defects such as black spots, spherical, polyhedral, and ellipsoidal shapes are preferred. In the present invention, the niobium-containing titanium oxide particles are more preferably spherical or polyhedral close to spherical.

[0039] The niobium-containing titanium oxide particles are preferably anatase or rutile titanium oxide particles, and from the viewpoint of improving injection chargeability, are more preferably anatase titanium oxide particles.

[0040] In the present invention, the metal oxide particles are preferably particles having an anatase type titanium oxide particle as a core material and titanium oxide that coats the surface of the core material and contains niobium. The niobium is preferably contained not as an oxide but in a so-called doped form that is incorporated into the crystal lattice of titanium oxide. By doping titanium oxide with niobium, the injection charging property is increased.

[0041] When the metal oxide particles have titanium oxide particles containing niobium, the niobium content in the metal oxide particles is preferably 0.5% by mass to 15.0% by mass, more preferably 2.6% by mass to 10.0% by mass. If the niobium content in the metal oxide particles is 0.5% by mass or more, the conductivity of the titanium oxide can be increased and the injection chargeability can be increased, and if it is 15.0% by mass or less, the crystal structure of the titanium oxide can be maintained, so that the volume resistivity of the protective layer does not become too large.

[0042] In addition, as the metal oxide particles, titanium oxide particles containing niobium and having a configuration in which niobium is unevenly distributed near the particle surface are particularly preferred. This is because the uneven distribution of niobium near the surface allows efficient transfer of electric charges. More specifically, the titanium oxide particles are those in which the niobium / titanium atomic ratio in the interior of 5% of the primary particle diameter from the surface of the metal oxide particles is 2.0 times or more as compared with the niobium / titanium atomic ratio in the center of the metal oxide particles, as determined by EDS analysis using a scanning transmission electron microscope (STEM). FIG. 3 shows a STEM image of an example of a metal oxide in which titanium oxide containing niobium is coated on titanium oxide serving as a core material, similar to the titanium oxide particles (metal oxide particles 1) used in the examples of the present invention. FIG. 4 shows a schematic representation of the STEM image of FIG. 3. The details will be described later, but the titanium oxide particles containing niobium used in the examples of this case are produced by coating titanium oxide particles serving as a core material with titanium oxide containing niobium and then firing the coated titanium oxide particles. Therefore, it is considered that the coated titanium oxide containing niobium grows as niobium-doped titanium oxide along the crystal of the titanium oxide core material by so-called epitaxial growth. The titanium oxide containing niobium thus produced has a lower density near the surface compared to the density at the center of the particle, as shown in Figure 3, and is in a core-shell morphology. In addition, in the EDS analysis by STEM, X-rays penetrate the entire particle, so that the EDS analysis at 5% of the primary particle diameter from the surface of the particle as shown in the direction 34 is more influenced by the surface than the EDS analysis at the center of the particle as shown in the direction 33, as shown in Figure 4. In other words, in the EDS analysis by STEM as described above, when the niobium / titanium atomic ratio at 5% of the primary particle diameter from the surface of the particle is 2.0 times or more compared to the niobium / titanium atomic ratio at the center of the particle, it is considered that the niobium element is unevenly distributed near the surface. In Fig. 4, reference numeral 32 denotes a region of the metal oxide particle within 5% of the primary particle diameter from the surface of the particle, and reference numeral 31 denotes a region of the metal oxide particle further inward than the region of reference numeral 32. Reference numeral 33 denotes an X-ray for analyzing the center of the metal oxide particle, and reference numeral 34 denotes an X-ray for analyzing the interior of the metal oxide particle within 5% of the particle diameter from the surface.

[0043] In the EDS analysis using STEM, the niobium / titanium ratio is measured by EDS after observing the electrophotographic photoreceptor with a transmission electron microscope. It is also possible to measure the ratio directly from the electrophotographic photoreceptor by cutting it into thin slices using a microtome, Ar milling, FIB, or other means.

[0044] In addition, the niobium-containing titanium oxide particles contained in the protective layer preferably have oxygen deficiency. When the titanium oxide particles contain oxygen deficiency, the injection chargeability is improved. Although the detailed mechanism is not well understood, it is speculated that when the titanium oxide particles containing niobium have oxygen deficiency, they are more likely to receive charges, and therefore the injection chargeability is improved. The oxygen deficiency rate of the titanium oxide particles containing niobium is preferably 0.1% or more and 2.0% or less. If the oxygen deficiency rate is less than 0.1%, the injection chargeability cannot be improved, and if it exceeds 2.0%, the color of the particles becomes black, the transparency of the protective layer decreases, and the sensitivity of the electrophotographic photoreceptor decreases. In addition, when the oxygen deficiency rate of the region within 5% of the primary particle diameter from the surface of the titanium oxide particles containing niobium is β, and the oxygen deficiency rate of the other region is γ, it is preferable to satisfy the following formula (α). β > 10×γ (α) This is because oxygen vacancies that are likely to receive charges are unevenly distributed on the surface of the metal oxide particles, allowing for effective injection charging.

[0045] The oxygen deficiency rate of metal oxide particles and the ratio of the oxygen deficiency rate in a region within 5% of the primary particle diameter from the surface of the metal oxide particles to the oxygen deficiency rate in other regions can be measured by energy dispersive X-ray analysis (EDS). As described above, in EDS analysis, X-rays penetrate the entire particle, so if the above-mentioned relational expression (α) is satisfied, it means that the oxygen deficiencies are concentrated near the particle surface.

[0046] In the present invention, the ratio of the oxygen deficiency rate in a region within 5% of the primary particle diameter from the surface of the metal oxide particle to the oxygen deficiency rate in the other region was measured by STEM-EDS analysis of the metal oxide particle.

[0047] The introduction of oxygen vacancies can be carried out by firing in a reducing atmosphere such as ammonia or hydrogen, or by firing together with an organic substance in a nitrogen atmosphere at 600° C. or higher, which is the decomposition temperature of the organic substance.

[0048] Although the detailed mechanism is not clear, as described above, it is believed that the reason why the injection charging property is increased by doping with niobium or introducing oxygen vacancies is that it becomes easier to transfer charges to and from conductive particles such as carbon black and graphite that are generally used in charging members, and this facilitates the transfer of charges from the charging member to the electrophotographic photosensitive member.

[0049] The metal oxide particles are also surface-treated with a compound having silicon atoms, such as a silane coupling agent or silicone resin. This surface treatment increases the hydrophobicity of the metal oxide particles. This surface treatment also keeps high the interface resistance between the metal oxide particles, which suppresses uneven dispersion of the metal oxide particles in the protective layer, thereby suppressing the decrease in resistance due to poor dispersion of the surface layer. As a result, the surface layer is kept high in resistance in a high humidity environment, and highlight image deletion can be suppressed.

[0050] The compound having a silicon atom used for the surface treatment of the metal oxide particles preferably contains an alkyl group having 12 or less carbon atoms.

[0051] A silane coupling agent is preferably used for the surface treatment of the metal oxide particles. As the silane coupling agent, a compound represented by the following formula (A) may be used. [ka] In formula (A), R 1 ~R 3 each independently represents an alkoxy group or an alkyl group. 1 ~R 3 At least two of R are alkoxy groups. 4 is an alkyl group having 12 or fewer carbon atoms.

[0052] Examples of the compound represented by formula (A) include hexyltrimethoxysilane, hexyltriethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, and dodecyltriethoxysilane.

[0053] In addition, as the silane coupling agent, a silane coupling agent other than the compound represented by formula (A), for example, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, (phenylaminomethyl)methyldimethoxysilane, N-2-(aminoethyl)-3-aminoisobutylmethyldimethoxysilane, N-ethylaminoisobutylmethyldiethoxysilane, N-methylaminopropylmethyldimethoxysilane, vinyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, methyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane 3-methacryloxypropyltrimethoxysilane, 3-chloropropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, etc. may be used in combination with the compound represented by formula (A).

[0054] The surface treatment of the metal oxide particles can be carried out by a common method, such as a dry method or a wet method. In the dry method, metal oxide particles are stirred in a mixer capable of high-speed stirring, such as a Henschel mixer, while an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent is added to the metal oxide particles to uniformly disperse them, and then the particles are dried. In the wet method, the metal oxide particles and the surface treatment agent are stirred in a solvent or dispersed in a sand mill using glass beads or the like, and the solvent is removed by filtration or distillation under reduced pressure. After the solvent is removed, it is preferable to further bake the mixture at 100° C. or higher.

[0055] Examples of the charge transport material include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these materials. Among these, triarylamine compounds and benzidine compounds are preferred.

[0056] The thickness of the protective layer as the surface layer is preferably 0.1 μm or more and 2.0 μm or less. If the thickness of the protective layer is less than 0.1 μm, it becomes difficult for the surface layer containing metal oxide particles to cover the entire surface of the electrophotographic photoreceptor, and the injection charging property decreases. If the thickness of the protective layer exceeds 1.0 μm, the shared voltage becomes large, the charge penetrates into the protective layer, and highlight image deletion becomes worse. More preferably, it is 0.1 μm or more and 1.5 μm or less.

[0057] The binder resin used in the protective layer as the surface layer preferably has a volume resistivity B (Ω·cm) at a temperature of 32.5° C. and a humidity of 80% RH (hereinafter also referred to as an “HH environment”) that satisfies the following formula (4). 1.0×10 12 ≦B≦1.0×10 15 (4)

[0058] The surface layer contains a high content of metal oxide particles, and there is a high probability that the binder resin will get into the spaces between the metal oxide particles. Therefore, if the volume resistivity B of the binder resin is high, the charge transfer in the surface layer described above can be suppressed, and highlight image deletion can be suppressed. When the volume resistivity B of the binder resin is 1.0×10 12 If it is less than Ω·cm, the above effect cannot be achieved and highlight image bleeding cannot be sufficiently suppressed.

[0059] Specific examples of the binder resin used in the present invention include polyester resin, acrylic resin, phenoxy resin, polycarbonate resin, polyarylate resin, polystyrene resin, phenol resin, melamine resin, epoxy resin, etc. Among them, it is preferable to contain at least one resin selected from the group consisting of polycarbonate resin, polyarylate resin, and acrylic resin.

[0060] The protective layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction include thermal polymerization, photopolymerization, and radiation polymerization. Examples of the polymerizable functional group of the monomer having a polymerizable functional group include an acryloyl group and a methacryloyl group. A material having a charge transport function may be used as the monomer having a polymerizable functional group.

[0061] The protective layer may also contain a resin having silicon atoms. The resin having silicon atoms that the protective layer may contain may be silicone oil. The silicone oil may be, for example, straight silicone oil or modified silicone oil. The straight silicone oil may be dimethyl silicone oil, methylphenyl silicone oil, methylhydrogen silicone oil, etc. The modified silicone oil may be reactive silicone oil such as amino-modified, epoxy-modified, carboxy-modified, carbinol-modified, methacryl-modified, mercapto-modified, or phenol-modified, and non-reactive silicone oil may be polyether-modified, methylstyryl-modified, alkyl-modified, ester-modified, or fluorine-modified. Furthermore, the resin having silicon atoms may be a block polymer or a graft polymer in which a polydimethylsiloxane structure is introduced into a side chain or a main chain.

[0062] The protective layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipping agents, abrasion resistance improvers, etc. Specific examples of such additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0063] Moreover, it is preferable that the volume resistivity C (Ω·cm) of the protective layer as the surface layer at a temperature of 32.5° C. and a humidity of 80% RH (HH environment) satisfies the following formula (2). 1.0×10 11 ≦C≦1.0×10 13 (2) The volume resistivity C of the protective layer is 1.0×10 11 If the resistivity falls below Ω·cm, the potential distribution of the latent image cannot be maintained, the latent image collapses, and highlight image deletion cannot be suppressed. The volume resistivity C is 7.0×10 11 Ω cm or more, 1.0×10 13 It is more preferable that the resistivity is Ω·cm or less.

[0064] Furthermore, it is preferable that the volume resistivity D (Ω·cm) of the protective layer at a temperature of 23.0° C. and a humidity of 55% RH (hereinafter also referred to as an “NN environment”) satisfies the following formula (3). 1.0×10 12 ≦D≦1.0×10 14 (3) The volume resistivity D of the protective layer is 1.0×10 12 If it falls below Ω·cm, the risk of leakage increases.

[0065] Furthermore, it is preferable that the volume resistivity C (Ω·cm) of the protective layer serving as the surface layer at a temperature of 32.5° C. and a humidity of 80% RH and the volume resistivity D of the protective layer serving as the surface layer at a temperature of 23.0° C. and a humidity of 55% RH satisfy the following formula (5). 0.05≦D / C≦1.0 (5) When the volume resistivities C and D of the protective layer serving as the surface layer satisfy the relationship of formula (5), charge migration in the surface layer can be suppressed, and highlight image deletion can be suppressed.

[0066] The volume resistivity of the protective layer and the binder resin can be measured as follows. A pA (picoampere) meter is used to measure the volume resistivity. First, a comb-shaped gold electrode with an interelectrode distance (D) of 180 μm and a length (L) of 59 mm as shown in FIG. 5 is prepared by deposition on a PET film. A protective layer with a thickness (T1) of 2 μm and a binder resin are provided on the prepared comb-shaped gold electrode so as to cover the comb-shaped gold electrode. Next, a DC voltage (I) of 100 V is applied between the comb-shaped gold electrodes in an environment of temperature 23.0° C. / humidity 55% RH (NN) and an environment of temperature 32.5° C. / humidity 80% RH (HH). Using the obtained measured values, the volume resistivity C (temperature 32.5° C. / humidity 80% RH) and the volume resistivity D (temperature 23.0° C. / humidity 55% RH) are calculated by the following formula (6). Volume resistivity ρv(Ω cm)=V(V)×T1(cm)×L(cm) / {I(A)×D(cm)} (6)

[0067] When it is difficult to identify the composition of the metal oxide particles, binder resin, etc. of the protective layer, the surface resistivity of the surface of the electrophotographic photoreceptor is measured and converted into volume resistivity. In other words, when measuring the volume resistivity of the protective layer that exists as the surface layer of the electrophotographic photoreceptor, rather than the protective layer alone, the surface resistivity of the protective layer is measured and the obtained value is converted into volume resistivity.

[0068] Specifically, comb-shaped gold electrodes with an interelectrode distance (D) of 180 μm and length (L) of 59 mm are prepared by gold deposition on the surface of the electrophotographic photoreceptor (surface of the protective layer) as shown in Fig. 5. Next, a DC voltage (V) of 1000 V is applied between the comb-shaped gold electrodes in an environment of 23.0°C temperature / 55% RH (NN) and 32.5°C temperature / 80% RH (HH), and the DC voltage (I) is measured, and the surface resistivity ρs of the protective layer is calculated from the DC voltage (V) / DC voltage (I). Using the obtained surface resistivity ρs and the film thickness t (cm) of the protective layer, the volume resistivity can be calculated according to the following formula (7). ρv=ρs×t (7) (ρv: volume resistivity, ρs: surface resistivity, t: thickness of protective layer)

[0069] In this measurement, since a minute amount of current is measured, it is preferable to use a resistance measuring device capable of measuring minute current. For example, a Hewlett-Packard Picoammeter 4140B is an example of a resistance measuring device capable of measuring minute current. It is preferable to select the comb-shaped electrodes to be used and the voltage to be applied so that an appropriate signal-to-noise ratio is obtained depending on the material and resistance value of the protective layer.

[0070] The protective layer can be formed by preparing a coating solution for the protective layer containing the above-mentioned materials and solvent, forming a coating film of this on the photosensitive layer, and drying and / or curing it. Examples of the solvent used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0071] <Support> In the present invention, the electrophotographic photoreceptor may have a support. In the present invention, the support is preferably a conductive support having electrical conductivity. The shape of the support may be a cylinder, a belt, a sheet, or the like. Among them, a cylindrical support is preferable. The surface of the support may be subjected to electrochemical treatment such as anodization, blasting, cutting, or the like. The support is preferably made of a metal, a resin, or a glass. Examples of the metal include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among them, an aluminum support using aluminum is preferable. Furthermore, the resin or glass may be made conductive by a process such as mixing with or coating with a conductive material.

[0072] <Conductive layer> In the present invention, a conductive layer may be provided on the support. By providing a conductive layer, scratches and irregularities on the surface of the support can be concealed and light reflection on the surface of the support can be controlled. The conductive layer preferably contains conductive particles and a resin.

[0073] The conductive particles may be made of a material such as metal oxide, metal, or carbon black. Examples of metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, etc. Examples of metals include aluminum, nickel, iron, nichrome, copper, zinc, silver, etc. Among these, it is preferable to use metal oxides as the conductive particles, and it is particularly preferable to use titanium oxide, tin oxide, or zinc oxide. When a metal oxide is used as the conductive particles, the surface of the metal oxide may be treated with a silane coupling agent or the like, or the metal oxide may be doped with an element such as phosphorus or aluminum or an oxide thereof. The conductive particles may have a laminated structure having a core particle and a coating layer that covers the core particle. Examples of the core particle include titanium oxide, barium sulfate, zinc oxide, etc. Examples of the coating layer include metal oxides such as tin oxide. When a metal oxide is used as the conductive particles, the volume average particle size is preferably 1 nm or more and 500 nm or less, and more preferably 3 nm or more and 400 nm or less.

[0074] Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, and alkyd resin. The conductive layer may further contain silicone oil, resin particles, a masking agent such as titanium oxide, and the like.

[0075] The average thickness of the conductive layer is preferably from 1 μm to 50 μm, and particularly preferably from 3 μm to 40 μm.

[0076] The conductive layer can be formed by preparing a coating solution for the conductive layer containing the above-mentioned materials and solvent, forming a coating film on a support, and drying the coating solution. Examples of the solvent used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Examples of the dispersion method for dispersing the conductive particles in the coating solution for the conductive layer include a method using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

[0077] <Undercoat layer> In the present invention, an undercoat layer may be provided on the support or the conductive layer. By providing an undercoat layer, the adhesion between layers can be improved and a function of preventing injection charging can be imparted.

[0078] The undercoat layer preferably contains a resin. Alternatively, the undercoat layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group.

[0079] Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinyl phenol resin, alkyd resin, polyvinyl alcohol resin, polyethylene oxide resin, polypropylene oxide resin, polyamide resin, polyamic acid resin, polyimide resin, polyamideimide resin, and cellulose resin.

[0080] Examples of the polymerizable functional group contained in the monomer having a polymerizable functional group include an isocyanate group, a blocked isocyanate group, a methylol group, an alkylated methylol group, an epoxy group, a metal alkoxide group, a hydroxyl group, an amino group, a carboxyl group, a thiol group, a carboxylic anhydride group, and a carbon-carbon double bond group.

[0081] For the purpose of improving electrical properties, the undercoat layer may further contain an electron transporting material, a metal oxide, a metal, a conductive polymer, etc. Among these, it is preferable to use an electron transporting material or a metal oxide. Examples of the electron transport substance include a quinone compound, an imide compound, a benzimidazole compound, a cyclopentadienylidene compound, a fluorenone compound, a xanthone compound, a benzophenone compound, a cyanovinyl compound, an aryl halide compound, a silole compound, a boron-containing compound, etc. An electron transport substance having a polymerizable functional group may be used as the electron transport substance, and the undercoat layer may be formed as a cured film by copolymerizing the electron transport substance with the monomer having the polymerizable functional group described above. Examples of metal oxides include indium tin oxide, tin oxide, indium oxide, titanium oxide, zinc oxide, aluminum oxide, silicon dioxide, etc. Examples of metals include gold, silver, aluminum, etc.

[0082] The metal oxide particles contained in the undercoat layer may be surface-treated with a surface treatment agent such as a silane coupling agent. The method for surface-treating the metal oxide particles is a general method. For example, a dry method or a wet method may be used. In the dry method, metal oxide particles are stirred in a mixer capable of high-speed stirring, such as a Henschel mixer, while an alcohol aqueous solution, an organic solvent solution, or an aqueous solution containing a surface treatment agent is added to the metal oxide particles to uniformly disperse them, and then the particles are dried. In the wet method, the metal oxide particles and the surface treatment agent are stirred in a solvent or dispersed in a sand mill using glass beads or the like, and the solvent is removed by filtration or distillation under reduced pressure. After the solvent is removed, it is preferable to further bake the mixture at 100° C. or higher.

[0083] The undercoat layer may further contain additives, for example, known materials such as metal powder such as aluminum, conductive materials such as carbon black, charge transport materials, metal chelate compounds, and organometallic compounds.

[0084] Examples of the charge transport substance include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, aryl halide compounds, silole compounds, boron-containing compounds, etc. A charge transport substance having a polymerizable functional group may be used as the charge transport substance, and the undercoat layer may be formed as a cured film by copolymerizing the charge transport substance with the monomer having the polymerizable functional group.

[0085] The undercoat layer can be formed by preparing a coating solution for the undercoat layer containing the above-mentioned materials and solvent, forming a coating film of this on a support or a conductive layer, and drying and / or curing it.

[0086] Examples of the solvent used in the coating solution for the undercoat layer include organic solvents such as alcohols, sulfoxides, ketones, ethers, esters, halogenated aliphatic hydrocarbons, aromatic compounds, etc. In the present invention, it is preferable to use alcohol-based and ketone-based solvents.

[0087] Examples of a dispersion method for preparing a coating solution for the undercoat layer include methods using a homogenizer, an ultrasonic disperser, a ball mill, a sand mill, a roll mill, a vibration mill, an attritor, and a liquid collision type high-speed disperser.

[0088] The average thickness of the undercoat layer is preferably from 0.1 μm to 50 μm, more preferably from 0.2 μm to 40 μm, and particularly preferably from 0.3 μm to 30 μm.

[0089] <Photosensitive layer> The photosensitive layer of an electrophotographic photoreceptor is mainly classified into (1) a multi-layer type photosensitive layer and (2) a single-layer type photosensitive layer. (1) The multi-layer type photosensitive layer has a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. (2) The single-layer type photosensitive layer is a photosensitive layer that contains both a charge generation material and a charge transport material.

[0090] (1) Laminated photosensitive layer The laminated type photosensitive layer has a charge generating layer and a charge transport layer.

[0091] (1-1) Charge generation layer The charge generating layer preferably contains a charge generating material and a resin.

[0092] Examples of the charge generating material include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred. The content of the charge generating material in the charge generating layer is preferably from 40% by mass to 85% by mass, and more preferably from 60% by mass to 80% by mass, based on the total mass of the charge generating layer.

[0093] Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, polyvinyl butyral resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, polyvinyl alcohol resin, cellulose resin, polystyrene resin, polyvinyl acetate resin, polyvinyl chloride resin, etc. Among these, polyvinyl butyral resin is more preferable.

[0094] The charge generating layer may further contain additives such as an antioxidant and an ultraviolet absorbing agent, etc. Specific examples of such additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

[0095] The average thickness of the charge generating layer is preferably from 0.1 μm to 1.0 μm, and more preferably from 0.15 μm to 0.4 μm.

[0096] The charge generating layer can be formed by preparing a coating solution for the charge generating layer containing the above-mentioned materials and solvent, forming the coating film on a support, a conductive layer, or an undercoat layer, and drying it. Examples of the solvent used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0097] (1-2) Charge transport layer The charge transport layer preferably contains a charge transport material and a resin.

[0098] Examples of the charge transport material include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these materials. Among these, triarylamine compounds and benzidine compounds are preferred. The content of the charge transport material in the charge transport layer is preferably from 25% by weight to 70% by weight, and more preferably from 30% by weight to 55% by weight, based on the total weight of the charge transport layer.

[0099] Examples of the resin include polyester resin, polycarbonate resin, acrylic resin, polystyrene resin, etc. Among these, polycarbonate resin and polyester resin are preferable. As the polyester resin, polyarylate resin is particularly preferable. The content ratio (mass ratio) of the charge transport material to the resin is preferably from 4:10 to 20:10, and more preferably from 5:10 to 12:10.

[0100] The charge transport layer may also contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipping agents, and abrasion resistance improvers. Specific examples of such additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0101] The average thickness of the charge transport layer is preferably from 5 μm to 50 μm, more preferably from 8 μm to 40 μm, and particularly preferably from 9 μm to 30 μm.

[0102] The charge transport layer can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned materials and solvent, forming the coating film on the charge generating layer, and drying it. Examples of the solvent used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents or aromatic hydrocarbon-based solvents are preferred.

[0103] (2) Single-layer photosensitive layer The single-layer type photosensitive layer can be formed by preparing a coating solution for the photosensitive layer containing a charge generating material, a charge transporting material, a resin and a solvent, forming a coating film of this, and drying it. The charge generating material, the charge transporting material and the resin are the same as the examples of materials in "(1) Multi-layer type photosensitive layer" above.

[0104] [Process cartridges, electrophotographic devices] The process cartridge of the present invention is characterized in that it integrally supports the electrophotographic photosensitive member described above and at least one means selected from the group consisting of a charging means, a developing means, a transfer means and a cleaning means, and is detachably mountable to the main body of the electrophotographic apparatus.

[0105] The electrophotographic apparatus of the present invention is characterized by having the electrophotographic photosensitive member, charging means, exposure means, developing means and transfer means described above.

[0106] FIG. 6 shows an example of a schematic configuration of an electrophotographic apparatus having a process cartridge equipped with an electrophotographic photosensitive member.

[0107] [Configuration of electrophotographic device] The electrophotographic apparatus of this embodiment is a so-called tandem type electrophotographic apparatus having a plurality of image forming units a to d. The first image forming unit a forms an image using toner of each color, yellow (Y), the second image forming unit b forms an image using toner of each color, magenta (M), the third image forming unit c forms an image using toner of each color, cyan (C), and the fourth image forming unit d forms an image using toner of each color, black (Bk). These four image forming units are arranged in a line at regular intervals, and most of the configurations of the image forming units are substantially the same except for the color of the toner they contain. Therefore, the electrophotographic apparatus of this embodiment will be described below using the first image forming unit a. The first image forming section a has a photosensitive drum 1a which is a drum-shaped electrophotographic photosensitive member, a charging roller 2a which is a charging member, a developing unit 4a, and a drum cleaning unit 5a. The photosensitive drum 1a is an image carrier that carries a toner image, and is rotated in the direction of the arrow R1 in the drawing at a predetermined peripheral speed (process speed). The developing means 4a contains yellow toner and develops the yellow toner on the photosensitive drum 1a. The drum cleaning means 5a is a means for recovering the toner attached to the photosensitive drum 1a. The drum cleaning means 5a has a cleaning blade that comes into contact with the photosensitive drum 1a, and a waste toner box that contains the toner and the like removed from the photosensitive drum 1a by the cleaning blade.

[0108] When a control unit (not shown) such as a controller receives an image signal, an image forming operation is started, and the photosensitive drum 1a is rotated. During the rotation process, the photosensitive drum 1a is uniformly charged to a predetermined voltage (charging voltage) with a predetermined polarity (negative polarity in this example) by the charging roller 2a, and is exposed by the exposure unit 3a according to the image signal. As a result, an electrostatic latent image corresponding to the yellow color component image of the target color image is formed on the photosensitive drum 1a. Next, the electrostatic latent image is developed by the developing unit 4a at the development position, and visualized as a yellow toner image on the photosensitive drum 1a. Here, the normal charging polarity of the toner contained in the developing unit 4a is negative polarity, and the electrostatic latent image is reversely developed by the toner charged to the same polarity as the charging polarity of the photosensitive drum 1a by the charging roller 2a. However, the present invention is not limited to this, and the present invention can also be applied to an electrophotographic device in which an electrostatic latent image is positively developed by the toner charged to the polarity opposite to the charging polarity of the photosensitive drum 1a. The endless movable intermediate transfer belt 10 is conductive, contacts the photosensitive drum 1a to form a primary transfer portion N1a, and rotates at approximately the same peripheral speed as the photosensitive drum 1a. The intermediate transfer belt 10 is stretched by an opposing roller 13 as an opposing member, a driving roller 11 and a tension roller 12 as tension members, and a metal roller 14a, and is stretched by the tension roller 12 with a total tension of 60N. The intermediate transfer belt 10 can be moved by the driving roller 11 being driven to rotate in the direction of the arrow R2 in the figure. Each metal roller 14 and the opposing roller 13 are connected to earth via a Zener diode 15 as a constant voltage element. The yellow toner image formed on the photosensitive drum 1a is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10 while passing through the primary transfer portion N1a. Primary transfer residual toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by the drum cleaning means 5a, and is then used for the image formation process following charging. During the primary transfer, a current is supplied to the conductive intermediate transfer belt 10 from a secondary transfer roller 40 serving as a secondary transfer member that contacts the outer circumferential surface of the intermediate transfer belt 10. The current supplied from the secondary transfer roller 40 flows in the circumferential direction of the intermediate transfer belt 10, thereby performing the primary transfer of the toner image from the photosensitive drum 1a to the intermediate transfer belt 10. At this time, a voltage of a predetermined polarity (positive polarity in this example) opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 40 in the J direction from a transfer power source 41.

[0109] Similarly, a magenta toner image of the second color, a cyan toner image of the third color, and a black toner image of the fourth color are formed and transferred to the intermediate transfer belt 10 in a superimposed manner. As a result, a four-color toner image corresponding to a target color image is formed on the intermediate transfer belt 10. Thereafter, the four-color toner images carried on the intermediate transfer belt 10 are secondarily transferred all at once to the surface of the transfer material P, such as paper or an OHP sheet, fed by the paper feed means 50, in the process of passing through the secondary transfer section N2 formed by the contact between the secondary transfer roller 40 and the intermediate transfer belt 10. The transfer material P to which the four-color toner images have been transferred by the secondary transfer is then heated and pressed by the fixing means 30, whereby the four color toners are melted and mixed and fixed to the transfer material P. The toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by the belt cleaning means 16 provided opposite the opposing roller 13 via the intermediate transfer belt 10. In addition, a path is provided that does not pass through the secondary transfer roller 40, and electrically connects the transfer power source 41 and each metal roller 14 via a constant current diode 42 as a constant current element. When a voltage is applied from the transfer power source 41 to the secondary transfer roller 40, a pinch-off current Id flows through the constant current diode 42 in addition to the current It2 that flows toward the secondary transfer portion N2.

[0110] The electrophotographic photoreceptor of the present invention can be used in laser beam printers, LED printers, copiers, facsimiles, and combination machines thereof. EXAMPLES

[0111] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples without departing from the gist of the present invention. In the following description of the examples, "parts" are by mass unless otherwise specified.

[0112] (Methods of producing anatase type titanium oxide particles 1 to 7) Anatase type titanium oxide particles can be produced by the known sulfuric acid method. In the production of titanium oxide, a solution containing titanium sulfate and titanyl sulfate as titanium compounds is heated and hydrolyzed to produce a hydrous titanium dioxide slurry, which is then dehydrated and fired. This produces anatase type titanium oxide particles with an anatase degree of nearly 100%. In the above-mentioned method, anatase type titanium oxide particles 1 to 7 were produced by controlling the concentration of titanyl sulfate in the solution.

[0113] (Method of producing rutile-type titanium oxide particles 1) 200 parts by mass of ultrafine titanium oxide particles (TTO-55(A): Ishihara Sangyo Kaisha, Ltd.; average primary particle diameter (manufacturer's nominal value): 40 nm) were enclosed in a Teflon (registered trademark) tube together with 10,000 parts by mass of a 17 mol / L potassium hydroxide aqueous solution. This was then sealed in a pressure-resistant glass container and subjected to hydrothermal treatment by maintaining at 110°C for 20 hours. The reaction product was neutralized with a 1 mol / L hydrochloric acid aqueous solution, and then repeatedly washed with ion-exchanged water and centrifuged to obtain a white precipitate. The obtained white precipitate was then dried and subsequently calcined at 650°C for 30 minutes to obtain rutile-type titanium oxide particles 1 having a primary particle diameter of 32 nm. For the rutile-type titanium oxide particles 1, diffraction peaks at 27.4°, 36.1°, 41.2°, and 54.3° attributable to rutile-type titanium oxide were confirmed by X-ray diffraction spectrum (CuKα) measurement using RINT2000 (manufactured by Rigaku Corporation).

[0114] Table 1 shows the number average particle diameters of the anatase type titanium oxide particles 1 to 7 and the rutile type titanium oxide particle 1 produced above.

[0115] [Table 1]

[0116] (Production Example of Metal Oxide Particles 1) Niobium (V) hydroxide was dissolved in concentrated sulfuric acid and mixed with an aqueous titanium sulfate solution to prepare an acidic mixed solution of a niobium salt and a titanium salt (hereinafter referred to as a "titanium-niobium mixed solution"). The anatase type titanium oxide particles 1 were dispersed as core particles in water to form a suspension, which was then heated to 70° C. with stirring. While maintaining the pH at 2.5, a titanium-niobium mixed liquid containing 337 g / kg of Ti and 10.3 g / kg of Nb relative to the weight of anatase-type titanium oxide particles 1 and an aqueous sodium hydroxide solution were added at the same time. After the dropwise addition was completed, the suspension was filtered, washed, and dried at 110°C for 8 hours. This dried material was fired together with the organic matter in a nitrogen atmosphere at 725°C for 1 hour to obtain metal oxide particles 1 in which niobium atoms were unevenly distributed near the surface. When the distribution of oxygen vacancies in the metal oxide particles was confirmed using the method described above, the relationship shown in formula (α) was confirmed, as shown in Table 2.

[0117] (Production of Metal Oxide Particles 2 to 14) In the production of metal oxide particles 1, the type of core particles used in the suspension, the weights of niobium atoms and titanium atoms in the titanium-niobium mixed liquid during coating, and the firing conditions for the dried product after the formation of the coating layer were changed as shown in Table 2. Otherwise, the production was performed in the same manner as for metal oxide particles 1 to obtain powders of metal oxide particles 2 to 14 shown in Table 2. When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the above-mentioned method, as shown in Table 2, the relationship of formula (α) was confirmed for all particles except for metal oxide particle 13.

[0118] (Production of Metal Oxide Particles 15) Water: 500cm 3100g of anatase-type titanium oxide particles 4 and 1g of hexametaphosphoric acid were added to the mixture and dispersed in a bead mill. During dispersion, the pH (pH = 9 to 11) was maintained to avoid the isoelectric point of the titanium oxide used. When the slurry after dispersion was observed with an SEM, it was confirmed that it was approximately monodispersed. In addition, when the median diameter of the slurry after dispersion was measured with a laser diffraction / scattering type particle size distribution measuring device (manufactured by Horiba, Ltd., model number: LA-950), it was 0.02 μm. This slurry was heated to 95°C. To this dispersion, an aqueous tin chloride solution was added so that the amount of tin oxide was 25g, and phosphoric acid was added to the aqueous tin chloride solution so that P was 0.8 mass% relative to the weight of tin oxide, and tin hydroxide crystals were precipitated on the titanium dioxide surface by a hydrolysis reaction. The wet-treated powder was taken out, washed, and dried. The tin chloride added in the wet treatment was substantially entirely hydrolyzed, and a stannic hydroxide compound (stannic hydroxide showing a SnO2 pattern in X-ray diffraction) was precipitated on the powder surface. 20 g of this dry powder was placed in a quartz tube furnace, heated at a rate of 10°C / min, and fired in a nitrogen atmosphere for 2 hours while controlling the temperature within the range of 700±50°C, to obtain metal oxide particles 15. When the distribution of oxygen vacancies in the metal oxide particles was confirmed using the method described above, the relationship shown in formula (α) was confirmed, as shown in Table 2.

[0119] (Production of Metal Oxide Particles 16) Niobium sulfate (a water-soluble niobium compound) was added to a hydrous titanium dioxide slurry obtained by hydrolysis of an aqueous titanyl sulfate solution. The amount of niobium sulfate added was 1.8 mass% in terms of niobium ions relative to the amount of titanium in the slurry (calculated as titanium dioxide). Niobium sulfate was added to an aqueous titanyl sulfate solution at a ratio of 1.8% by mass as niobium ions, and the mixture was hydrolyzed to obtain a hydrous titanium dioxide slurry. Next, the hydrous titanium dioxide slurry containing niobium ions and the like was dehydrated and fired in air at a firing temperature of 1000°C. As a result, metal oxide particles 16 were obtained, which are anatase-type titanium oxide containing 1.8% by mass of niobium element. When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the above-mentioned method, as shown in Table 3, the relationship of formula (α) could not be confirmed.

[0120] (Production of Metal Oxide Particles 17) Metal oxide particles 17 were obtained in the same manner as for metal oxide particles 1, except that the concentration of the titanyl sulfate aqueous solution was adjusted. When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the above-mentioned method, as shown in Table 3, the relationship of formula (α) could not be confirmed.

[0121] (Production of Metal Oxide Particles 18 to 21) Niobium sulfate (a water-soluble niobium compound) was added to a hydrous titanium dioxide slurry obtained by hydrolysis of an aqueous titanyl sulfate solution. The amount of niobium sulfate added was 0.2 mass% in terms of niobium ions relative to the amount of titanium in the slurry (calculated as titanium dioxide). Niobium sulfate was added to an aqueous titanyl sulfate solution at a ratio of 0.2% by mass as niobium ions, and the mixture was hydrolyzed to obtain a hydrous titanium dioxide slurry. Next, the hydrous titanium dioxide slurry containing niobium ions and the like was dehydrated and fired in air at a firing temperature of 850°C. As a result, metal oxide particles 18, which are anatase-type titanium oxide containing 0.2% by mass of niobium element, were obtained. In addition, in the above-mentioned method, anatase type titanium oxide particles 19 to 21 were produced by controlling the concentration of titanyl sulfate in the solution.

[0122] When the distribution of oxygen vacancies in the metal oxide particles was confirmed by the method described above, as shown in Table 3, the relationship of formula (α) was not confirmed for any of the particles.

[0123] Tables 2 and 3 also show the number average particle size, powder resistivity, and the proportion of niobium element present within 5% of the particle size from the outermost surface of the metal oxide particles 1 to 21 produced above.

[0124] [Table 2]

[0125] [Table 3]

[0126] <Manufacture of electrophotographic photoreceptor> (Production Example of Electrophotographic Photoreceptor 1) An aluminum cylinder (JIS-A3003, aluminum alloy) having a diameter of 24 mm and a length of 257.5 mm was used as a support (conductive support).

[0127] Next, the following materials were prepared: Titanium oxide (TiO2) particles coated with oxygen-deficient tin oxide (SnO2) (average primary particle diameter 230 nm): 214 parts Phenolic resin (product name: Plyofen J-325, manufactured by DIC Corporation, resin solid content: 60% by mass): 132 parts 1-Methoxy-2-propanol: 98 parts These were placed in a sand mill using 450 parts of glass beads with a diameter of 0.8 mm, and dispersion treatment was performed under the conditions of rotation speed: 2000 rpm, dispersion treatment time: 4.5 hours, and cooling water set temperature: 18 ° C. to obtain a dispersion liquid. The glass beads were removed from this dispersion liquid using a mesh (opening: 150 μm). Silicone resin particles (trade name: Tospearl 120, manufactured by Momentive Performance Materials, Inc., average particle size 2 μm) were added to the obtained dispersion liquid as a surface roughening agent. The amount of silicone resin particles added was 10 mass % of the total mass of the metal oxide particles and binding material in the dispersion liquid after removing the glass beads. In addition, silicone oil (trade name: SH28PA, manufactured by Dow Toray Co., Ltd.) was added to the dispersion liquid as a leveling agent so that the amount was 0.01 mass % of the total mass of the metal oxide particles and binding material in the dispersion liquid. Next, a mixed solvent of methanol and 1-methoxy-2-propanol (mass ratio 1:1) was added to the dispersion so that the total mass of the metal oxide particles, the binding material, and the surface roughening agent in the dispersion (i.e., the mass of the solid content) was 67 mass% relative to the mass of the dispersion. Then, the mixture was stirred to prepare a coating liquid for a conductive layer. The coating liquid for a conductive layer was dip-coated on a support and heated at 140°C for 1 hour to form a conductive layer with a thickness of 30 μm.

[0128] Next, the following materials were prepared: Electron transport material (compound represented by the following formula (E-1): 3.0 parts Blocked isocyanate (product name: Duranate SBB-70P, manufactured by Asahi Kasei Chemicals Corporation): 6.5 parts Styrene-acrylic resin (product name: UC-3920, manufactured by Toagosei): 0.4 parts ·Silica slurry (product name: IPA-ST-UP, manufactured by Nissan Chemical Industries, solid content concentration: 15% by mass, viscosity: 9mPa·s): 1.8 parts 1-Butanol: 48 parts Acetone: 24 parts These were mixed and dissolved to prepare a coating solution for the undercoat layer, which was then dip-coated onto the conductive layer and heated at 170° C. for 30 minutes to form an undercoat layer with a thickness of 0.7 μm. [ka]

[0129] Next, the following materials were prepared: 10 parts of hydroxygallium phthalocyanine in a crystalline form having peaks at 7.5° and 28.4° in a chart obtained by CuKα characteristic X-ray diffraction Polyvinyl butyral resin (product name: S-LEC BX-1, manufactured by Sekisui Chemical Co., Ltd.) 5 parts These were added to 200 parts of cyclohexanone, and dispersed for 6 hours in a sand mill using glass beads with a diameter of 0.9 mm. This was further diluted with 150 parts of cyclohexanone and 350 parts of ethyl acetate to obtain a coating solution for the charge generating layer. The resulting coating solution was dip-coated onto the undercoat layer and dried at 95° C. for 10 minutes to form a charge generating layer having a thickness of 0.20 μm.

[0130] Next, the following materials were prepared: Charge transport material (hole transport material) represented by the following structural formula (C-1): 6.0 parts Charge transport material (hole transport material) represented by the following structural formula (C-2): 3.0 parts Charge transport material (hole transport material) represented by the following structural formula (C-3): 1.0 part Polycarbonate resin (product name: Iupilon Z400, manufactured by Mitsubishi Engineering Plastics Corporation): 10.0 parts Polycarbonate resin having a copolymerization unit having a structure represented by the following structural formula (C-4) and a structure represented by the following structural formula (C-5) (x / y=0.95 / 0.05: viscosity average molecular weight=20000): 0.02 parts These were dissolved in a mixed solvent of 25 parts of orthoxylene, 25 parts of methyl benzoate, and 25 parts of dimethoxymethane to prepare a coating solution for the charge transport layer. The coating solution for the charge transport layer was dip-coated onto the charge generating layer to form a coating film, and the coating film was dried at 120°C for 30 minutes to form a charge transport layer with a thickness of 22 μm. [ka] [ka] [ka] [ka] [ka]

[0131] Next, the following materials were prepared: ·Metal oxide particles 1:100.0 parts Surface treatment agent 1 (compound represented by the following formula (S-1)) (trade name: trimethoxypropylsilane, manufactured by Tokyo Chemical Industry Co., Ltd.): 6.0 parts [ka] Toluene: 200.0 parts These were mixed and stirred for 4 hours using a stirrer, then filtered, washed, and further heat-treated at 130° C. for 3 hours to obtain surface-treated metal oxide particles 1 with an average primary particle size of 68 nm.

[0132] Next, the following materials were prepared: Surface-treated metal oxide particles 1:197.5 parts The binder resin is represented by the following structural formula (O-1), and has a resistivity of 3.6×10 at a temperature of 32.5°C and a humidity of 80% (HH). 12 Compound with Ω·cm: 79.0 parts 1-Propanol (1-PA): 100.0 parts Cyclohexane (CH): 100.0 parts The above was mixed and stirred for 6 hours using a stirrer to prepare protective layer coating solution 1. [ka] This protective layer coating solution 1 was applied onto the charge transport layer by dip coating to form a coating film, and the resulting coating film was dried at 50°C for 6 minutes. Thereafter, under a nitrogen atmosphere, the coating film was irradiated with an electron beam for 1.6 seconds while rotating the support (irradiated body) at a speed of 300 rpm under conditions of an acceleration voltage of 70 kV and a beam current of 5.0 mA. The dose at the position of the protective layer was 15 kGy. Thereafter, under a nitrogen atmosphere, the temperature of the coating film was raised to 117°C. The oxygen concentration from the electron beam irradiation to the subsequent heat treatment was 10 ppm. Next, the coating film was naturally cooled in the atmosphere until the temperature of the coating film reached 25° C., and then heat treatment was performed for 1 hour under conditions such that the temperature of the coating film reached 120° C., thereby forming a protective layer with a thickness of 0.5 μm. In this manner, an electrophotographic photoreceptor 1 having a protective layer containing metal oxide particles 1 was produced. In addition, the resistivity of the binder resin was measured by forming a film using the binder resin coating solution 1, which does not contain surface-treated metal oxide particles, in the same manufacturing method as for the protective layer coating solution 1, and measuring the volume resistivity as described above.

[0133] (Production Examples of Electrophotographic Photoreceptors 2 to 20) Electrophotographic photoreceptors 2 to 20 were produced in the same manner as electrophotographic photoreceptor 1, except that the thickness of the protective layer was changed as shown in Table 4 by adjusting the type, number of parts, and amount of solvent of the metal oxide.

[0134] (Manufacturing Example of Electrophotographic Photoreceptor 21) In the manufacturing example of the electrophotographic photoreceptor 1, the types and amounts of the binder resin and mixed solvent used in preparing the protective layer coating liquid were changed as follows to prepare a protective layer coating liquid 21. Binder resin: 33.7 parts of compound represented by (CTM-1), 3.7 parts of compound represented by formula (CTM-2) was dissolved in a mixed solution of 59.25 parts of ortho-xylene and 98.75 parts of methyl benzoate. The weight average molecular weight (Mw) is 100,000 and the volume resistivity at a temperature of 32.5°C and a humidity of 80% RH (HH environment) is 7.8×10 14 41.6 parts of polyester resin with a viscosity of Ω·cm; Mixed solvent: 948 parts chlorobenzene / 632 parts dimethoxymethane, Surface-treated metal oxide particles 1:112.9 parts was added to the above mixed solution, and stirred for 6 hours with a stirrer to obtain protective layer coating solution 21. The obtained protective layer coating solution 21 was dip-coated on the charge transport layer to form a coating film, and the coating film was dried for 30 minutes at 120° C. to form a protective layer having a thickness of 0.5 μm. Except for this, the electrophotographic photoreceptor 21 was produced in the same manner as the electrophotographic photoreceptor 1.

[0135] In addition, the resistivity of the binder resin was measured by forming a film using the binder resin coating solution 21 without containing the surface-treated metal oxide particles 1 in the above-mentioned protective layer coating solution 21, in the same manufacturing method as for the protective layer coating solution 21, and using the above-mentioned method for measuring volume resistivity. [ka] [ka] [ka] [ka]

[0136] (Production Examples of Electrophotographic Photoreceptors 22 to 68 and 70) Electrophotographic photoreceptors 22 to 68 and 70 were produced in the same manner as electrophotographic photoreceptor 21, except that the type of metal oxide particles, whether or not the metal oxide particles were surface-treated, and the number of parts were changed as shown in Tables 4 and 5.

[0137] (Production Example of Electrophotographic Photoreceptor 69) The metal oxide particles to be added to the protective layer and the amount of added particles were determined by comparing the amount of tin oxide particles (product name: SP-2, powder resistance 1×10 3 An electrophotographic photoreceptor 69 was prepared in the same manner as in the electrophotographic photoreceptor 23, except that 196.1 parts of the toner (Ω·cm average primary particle diameter 20 nm, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.) was used.

[0138] (Manufacturing Example of Electrophotographic Photoreceptor 71) Instead of the polyester resin, a polyester resin having a structure represented by formula (PC-I) is used. The polyester resin has a viscosity average molecular weight of 40,000 and a volume resistivity of 2.5×10 13 An electrophotographic photoreceptor 71 was produced in the same manner as the electrophotographic photoreceptor 23, except that a polycarbonate resin (1) having a resistivity of Ω·cm was used. [ka]

[0139] (Production Examples of Electrophotographic Photoreceptors 72 and 73) Electrophotographic photoreceptors 72 and 73 were produced in the same manner as electrophotographic photoreceptor 71, except that the type, number of parts, and protective layer thickness of the metal oxide were as shown in Table 5.

[0140] (Manufacturing Example of Electrophotographic Photoreceptor 74) In the manufacturing example of the electrophotographic photoreceptor 1, the types and amounts of the binder resin and mixed solvent used in preparing the protective layer coating liquid 74 were changed as follows to prepare a protective layer coating liquid 74. 263.3 parts of surface-treated metal oxide particles 1, 59.25 parts of N-methoxymethylated 6 nylon (methoxymethylation rate: 28 to 33%), 19.75 parts of copolymer nylon resin (product name: Amilan CM8000, manufactured by Toray) were mixed with a mixed solvent of 1,185 parts of methanol and 790 parts of 1-butanol, and the mixture was stirred for 6 hours using a stirring device to prepare coating solution 74 for protective layer. The obtained protective layer coating solution 74 was dip-coated on the charge transport layer to form a coating film, and the coating film was dried at 100° C. for 30 minutes to form a protective layer having a thickness of 0.5 μm. Except for this, electrophotographic photoreceptor 74 was produced in the same manner as electrophotographic photoreceptor 1.

[0141] The resistivity of the binder resin was measured by forming a film using the binder resin coating solution 74 not containing the surface-treated metal oxide particles 1 in the protective layer coating solution 74 in the same manufacturing method as the protective layer coating solution 74, and measuring the volume resistivity as described above. The volume resistivity of the binder resin in an environment of a temperature of 32.5°C and a humidity of 80% RH (HH) was 6.1×10 11 The value was Ω·cm.

[0142] (Method of Manufacturing Electrophotographic Photoreceptor 75) Electrophotographic photoreceptor 75 was produced in the same manner as in electrophotographic photoreceptor 1, except that the protective layer was formed in the following manner. Titanium oxide (M-1; primary particle size 350 nm, manufactured by Ishihara Sangyo Kaisha) 18.2 parts Polyvinyl butyral resin 7.8 parts (XYHL; UCC) Cyclohexanone (Kanto Chemical) 122.2 parts The mixture was placed in a ball mill pot and milled for 48 hours using a φ10 mm SUS ball, then the milling liquid was taken out, and 10.2 parts of a 10% cyclohexanone solution of toluene-2,4-diisocyanate, 171.1 parts of cyclohexanone (Kanto Chemical), and 114.1 parts of methyl ethyl ketone (Kanto Chemical) were added and mixed and stirred to prepare a coating liquid for a protective layer. This coating liquid was spray-coated on the charge transport layer, and then dried at 130° C. for 15 minutes to form a protective layer with a thickness of 2.5 μm.

[0143] (Manufacturing Method of Electrophotographic Photoreceptor 76) Except for changing the material of the protective layer coating solution as follows and changing the film thickness to 0.2 μm, electrophotographic photoreceptor 76 was manufactured in the same manner as electrophotographic photoreceptor 75. The average particle diameter of the protective layer coating solution was measured with a centrifugal automatic particle size distribution measuring device CAPA-700 (Horiba, Ltd.) and found to be 0.4 μm. Metal oxide particles 22:18 parts Alcohol-soluble nylon: 8 parts (product name: Amilan CM8000, manufactured by Toray) Methanol: 50 parts Butanol: 20 parts

[0144] (Manufacturing Method of Electrophotographic Photoreceptor 77) Titanium oxide (ET-500W; primary particle size 250 nm, manufactured by Ishihara Sangyo Kaisha) 18.2 parts 3 parts of a naphthalene carboxylic acid derivative represented by the formula (CTM-3) (manufactured by Ricoh) as a charge transport material, Polyvinyl butyral resin (XYHL; UCC) 7.8 parts Cyclohexanone (Kanto Chemical) 122.2 parts The mixture was placed in a ball mill pot and ball milled for 48 hours using a Φ10 mm SUS ball, and the milling liquid was taken out and mixed with 10.2 g of a 10% cyclohexanone solution of toluene-2,4-diisocyanate, 171.1 g of cyclohexanone (Kanto Chemical), and 114.1 g of methyl ethyl ketone (Kanto Chemical) to prepare a protective layer coating liquid. This protective layer coating liquid was spray-coated on the charge transport layer and dried at 130° C. for 15 minutes to form a 2 μm thick protective layer, and the electrophotographic photoreceptor 77 was produced in the same manner as the electrophotographic photoreceptor 1. [ka]

[0145] (Method of Manufacturing Electrophotographic Photoreceptor 78) Electrophotographic photoreceptor 78 was produced in the same manner as electrophotographic photoreceptor 68, except that the metal oxide particles added to the protective layer and the number of parts added were 196.1 parts of non-surface-treated tin oxide particles (product name: S-2000, powder resistance 3 × 10 Ω cm, average primary particle diameter 20 nm, manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd.).

[0146] (Manufacturing method of electrophotographic photoreceptor 79) Electrophotographic photoreceptor 79 was produced in the same manner as electrophotographic photoreceptor 1, except that the material for the protective layer coating solution and the method for forming the protective layer were the materials and the method shown below, and the film thickness was 3.0 μm. 20 parts of the compound represented by the above structural formula (O-1) was mixed with a mixed solvent of 130 parts of 2-propanol and 14 parts of tetrahydrofuran, and 40 parts of anatase-type titanium oxide (AMT600, manufactured by Teika Corporation (particle size 30 nm)) and 2.00 parts of an organic salt represented by the following structural formula (A-1) were added to this solution and stirred. [ka] These were placed in a vertical sand mill using 200 parts of glass beads with an average particle size of 1.0 mm, and dispersed for 2 hours at a dispersion temperature of 23±3° C. and a rotation speed of 1500 rpm (circumferential speed 5.5 m / s) to obtain a dispersion. The glass beads were removed from this dispersion using a mesh, and the resulting dispersion was pressure filtered using PTFE filter paper (product name: PF060, manufactured by Advantec Toyo) to prepare a coating solution for the protective layer. Next, the protective layer coating liquid was applied on the charge transport layer by dip coating to form a coating film, and the obtained coating film was dried at 50°C for 6 minutes. Thereafter, under a nitrogen atmosphere, the support (irradiated body) was rotated at a speed of 300 rpm under conditions of an acceleration voltage of 70 kV and a beam current of 2.0 mA, and the coating film was irradiated with an electron beam for 1.6 seconds. The oxygen concentration during electron beam irradiation was 810 ppm. Next, the coating film was naturally cooled in the atmosphere until the temperature reached 25°C, and then heat-treated for 1 hour under conditions that the temperature of the coating film reached 120°C, forming a protective layer with a thickness of 3.0 μm. In this manner, a cylindrical (drum-shaped) electrophotographic photoreceptor 79 having a protective layer was produced.

[0147] (Method of Manufacturing Electrophotographic Photoreceptor 80) In the manufacturing method of the electrophotographic photoreceptor 79, the type of metal oxide particles is rutile type titanium oxide (SC150, manufactured by Teika Co., Ltd. (particle size 50 nm), powder resistance 1.3 × 10 10 Electrophotographic photoreceptor 80 was prepared in the same manner as electrophotographic photoreceptor 79, except that the resistivity was changed to 1.0 Ω·cm and the type of the organic salt was changed to an organic salt represented by the following structural formula (A-2). [ka]

[0148] [Table 4]

[0149] [Table 5]

[0150] (Examples 1 to 73 and Comparative Examples 1 to 8) The electrophotographic photoreceptor manufactured as above was subjected to measurement of physical properties, evaluation of the precision of the output image, and evaluation of the injectability. Examples 1 to 73 are the cases where electrophotographic photoreceptors 1 to 59, 61 to 63, 68 to 74, and 78 to 80 were used, and Comparative Examples 1 to 8 are the cases where electrophotographic photoreceptors 60, 64 to 67, and 75 to 77 were used.

[0151] <Measurement of physical properties of electrophotographic photoreceptors> Hereinafter, methods for measuring various physical properties of the electrophotographic photoreceptor according to the present invention will be described.

[0152] <Calculation of primary particle size of metal oxide particles> First, the entire electrophotographic photoreceptor was placed in methyl ethyl ketone (MEK) in a graduated cylinder and irradiated with ultrasonic waves to peel off the resin layer, and then the substrate of the electrophotographic photoreceptor was taken out. Next, the insoluble matter that does not dissolve in MEK (photosensitive layer and protective layer containing metal oxide particles) was filtered and dried in a vacuum dryer. Furthermore, the obtained solid was suspended in a mixed solvent of tetrahydrofuran (THF) / methylal at a volume ratio of 1:1, the insoluble matter was filtered, and the filtrate was collected and dried in a vacuum dryer. This operation obtained metal oxide particles and the resin of the protective layer. Furthermore, the filtrate was heated to 500°C in an electric furnace so that the solid was only metal oxide particles, and the metal oxide particles were collected. In order to secure the amount of metal oxide particles required for measurement, the same treatment was performed on multiple electrophotographic photoreceptors. A part of the collected metal oxide particles was dispersed in isopropanol (IPA), and the dispersion was dropped onto a grid mesh with a support membrane (Cu150J, manufactured by JEOL Co., Ltd.), and the metal oxide particles were observed in STEM mode of a scanning transmission electron microscope (JEM2800, manufactured by JEOL Co., Ltd.). The observation was performed at a magnification of 500,000 to 1.2 million times to make it easier to calculate the particle diameter of the metal oxide particles, and STEM images of 100 metal oxide particles were taken. At this time, the accelerating voltage was set to 200 kV, the probe size was set to 1 nm, and the image size was set to 1024 x 1024 pixels. Using the obtained STEM image, the primary particle diameter was measured using the image processing software "Image-Pro Plus (Media Cybernetics)". First, the straight line tool (Straight Line) on the toolbar was used to select the scale bar displayed at the bottom of the STEM image. In this state, when Set Scale is selected from the Analyze menu, a new window opens and the pixel distance of the selected straight line is entered in the Distance in Pixels field. Enter the scale bar value (e.g., 100) in the Known Distance field of the window, enter the unit of the scale bar (e.g., nm) in the Unit of Measurement field, and click OK to complete the scale setting. Next, using the straight line tool, a straight line was drawn to be the maximum diameter of the metal oxide particles, and the particle diameter was calculated. The same operation was performed for 100 metal oxide particles, and the number average value of the obtained value (maximum diameter) was taken as the primary particle diameter of the metal oxide particles.

[0153] <Calculation of niobium atom / titanium atom concentration ratio> A sample piece measuring 5 mm square was cut from the photoreceptor and cut to a thickness of 200 nm using an ultrasonic ultramicrotome (Leica, UC7) at a cutting speed of 0.6 mm / s to prepare a thin sample. This thin sample was observed at magnifications of 500,000 to 1.2 million times using a scanning transmission electron microscope (JEM2800, JEOL) in STEM mode connected to an EDS analyzer (energy dispersive X-ray analyzer). Among the observed metal oxide particles, metal oxide particles having a maximum diameter of approximately 0.9 times or more the primary particle diameter calculated above were visually selected. Next, the constituent elements of the selected metal oxide particles were collected using an EDS analyzer to prepare an EDS mapping image. Spectral collection and analysis were performed using an NSS (Thermo Fisher Scientific). The collection conditions were an acceleration voltage of 200 kV, a probe size of 1.0 nm or 1.5 nm appropriately selected so that the dead time was 15 to 30, a mapping resolution of 256 × 256, and 300 frames. EDS mapping images were obtained for 100 metal oxide particles. By analyzing the EDS mapping image obtained in this way, the ratio of the niobium atomic concentration (atomic %) to the titanium atomic concentration (atomic %) at the center of the particle and within 5% of the maximum diameter of the measured particle from the particle surface is calculated. Specifically, the "Line Extraction" button of the NSS is pressed first, a straight line is drawn to the maximum diameter of the particle, and information on the atomic concentration (atomic %) on the straight line from one surface through the inside of the particle to the other surface is obtained. If the maximum diameter of the particle obtained at this time is less than 0.9 times the primary particle diameter of the particle calculated above, it is excluded from the subsequent analysis. In other words, the analysis shown below is performed only on particles with a maximum diameter of 0.9 times or more of the primary particle diameter. Next, the niobium atomic concentration (atomic %) is read at the particle surfaces on both sides within 5% of the maximum diameter of the measured particle from the particle surface, and the average of the two values ​​obtained is calculated to obtain the "niobium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface". In the same manner, the "titanium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface" is obtained. Next, using these values, the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" is calculated according to the following formula. Concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface = (Niobium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface) / (Titanium atom concentration (atomic %) within 5% of the maximum diameter of the measured atom from the particle surface) Also, the niobium atom concentration (atomic %) and titanium atom concentration (atomic %) are read at the position on the straight line that is the midpoint of the maximum diameter. Using these values, the "concentration ratio of niobium atoms to titanium atoms at the center of the particle" is calculated using the following formula. Concentration ratio of niobium atoms to titanium atoms in the particle center = (Niobium atom concentration at the center of the particle (atomic %)) / (Titanium atom concentration at the center of the particle (atomic %)) The "concentration ratio calculated as niobium atomic concentration / titanium atomic concentration at a portion 5% inside the maximum diameter of the measured particle from the particle surface to the concentration ratio calculated as niobium atomic concentration / titanium atomic concentration at the particle center" is calculated by the following formula. (The ratio of the concentration calculated as niobium atom concentration / titanium atom concentration at the center of the particle to the concentration calculated as niobium atom concentration / titanium atom concentration at 5% inside the maximum diameter of the measured particle from the particle surface) = (Ratio of concentration of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface) / (Ratio of concentration of niobium atoms to titanium atoms in the particle center)

[0154] <Calculation of metal oxide particle content> Next, four sample pieces of 5 mm square were cut out from the electrophotographic photoreceptor, and the protective layer was three-dimensionalized to 2 μm x 2 μm x 2 μm using FIB-SEM Slice & View. The content of metal oxide particles in the total volume of the protective layer was calculated from the difference in contrast of FIB-SEM Slice & View. The conditions for Slice & View were as follows. Sample processing for analysis: FIB method Processing and observation equipment: SII / Zeiss NVision40 Slice spacing: 5 nm Observation conditions: Accelerating voltage: 1.0 kV Sample tilt: 54° WD: 5mm Detector: BSE detector Aperture: 60μm, high current ABC:ON Image resolution: 1.25nm / pixel The analysis area was 2 μm long x 2 μm wide, and the information for each cross section was integrated to obtain a 2 μm long x 2 μm wide x 2 μm thick (8 μm 3 ) was measured. The measurement environment was a temperature of 23°C and a pressure of 1x10-4 Pa. Note that the processing and observation device can also be FEI's Strata400S (sample inclination: 52°). Information on each cross section was obtained by image analysis of the area of ​​the metal oxide particles. Image analysis was performed using image processing software: Media Cybernetics' Image-Pro Plus.

[0155] Based on the obtained information, a volume of 2 μm × 2 μm × 2 μm (unit volume: 8 μm 3 The volume V of the metal oxide particles in the sample was calculated. 3 / 8μm 3 × 100) was calculated. 3 / 8μm 3 × 100) was taken as the content [volume %] of metal oxide particles in the protective layer relative to the total volume of the protective layer.

[0156] In addition, for all four sample pieces, the protective layer was processed up to the boundary between the protective layer and the layer immediately below it to measure the thickness t (μm) of the protective layer, and the volume resistivity ρ v The thickness of the protective layer was used as the value for the calculation of The results are shown in Tables 6 and 7.

[0157] <Quantitative determination of niobium atoms contained in metal oxide particles> The amount of niobium atoms contained in the metal oxide particles is determined as follows. The metal oxide particles recovered from the electrophotographic photoreceptor in the above <Calculation of primary particle diameter of metal oxide particles> are pelletized by the press molding described below to prepare a sample. Using the prepared sample, measurement is performed with an X-ray fluorescence analyzer (XRF) and the niobium atom content of the entire metal oxide particles is quantified by the FP method. Specifically, the amount of niobium pentoxide is determined and converted into the niobium atom content. (i) Examples of equipment used X-ray fluorescence analyzer 3080 (Rigaku Electric Co., Ltd.) (ii) Sample preparation The sample is prepared using a sample press molding machine, MAEKAWA Testing Machine (manufactured by MFG Co, LTD.) 0.5 g of metal oxide particles are placed in an aluminum ring (model number: 3481E1), and the load is set to 5.0 tons, and the sample is pressed for 1 minute to form a pellet. (iii) Measurement conditions Measurement diameter: 10φ Measurement potential, voltage 50kV, 50~70mA 2θ angle 25.12° Crystal plate LiF Measurement time: 60 seconds

[0158] <Method for measuring volume resistivity of protective layer> In the present invention, a pA (picoampere) meter was used to measure the volume resistivity. First, a comb-shaped gold electrode with an interelectrode distance (D) of 180 μm and length (L) of 59 mm shown in FIG. 5 was prepared by deposition on a PET film, and a protective layer with a thickness (T1) of 2 μm was provided on top of the electrode. Next, a DC voltage (V) of 100 V was applied between the comb-shaped electrodes in environments of temperature 23°C / humidity 50% RH and temperature 32.5°C / humidity 80% RH. The DC voltage (I) was measured, and the volume resistivity ρ was calculated by the following formula (6). v (Ω·cm) was obtained. Volume resistivity ρ v (Ω cm)=V(V)×T1(cm)×L(cm) / {I(A)×D(cm)}(6)

[0159] When it is difficult to identify the composition of the metal oxide particles, binder resin, etc. of the protective layer, the surface resistivity is measured on the surface of the electrophotographic photoreceptor and converted into volume resistivity. When measuring the volume resistivity of the protective layer in a state in which it is coated on the surface of the photoreceptor, rather than the protective layer alone, it is desirable to measure the surface resistivity of the protective layer and convert it into volume resistivity. In the present invention, comb-shaped electrodes having an interelectrode distance (D) of 180 μm and a length (L) of 59 mm as shown in Fig. 5 are formed by gold deposition on the surface of the protective layer of the electrophotographic photoreceptor. Next, a DC voltage (I) of 1000 V is applied between the comb-shaped electrodes in an environment of a temperature of 23°C and a humidity of 50% RH, and the DC voltage (I) is measured. The surface resistivity ρ of the protective layer is calculated from the DC voltage (V) / DC voltage (I). s was calculated. Furthermore, the volume resistivity ρ v (Ω·cm) was calculated. ρ v =ρ s ×t (7) (ρ v : Volume resistivity, ρ s : surface resistivity, t: thickness of protective layer) In this measurement, since a minute amount of current is measured, it is preferable to use a device capable of measuring minute currents as the resistance measurement device. For example, a picoammeter 4140B manufactured by Hewlett-Packard can be used. It is preferable to select the comb-shaped electrode to be used and the voltage to be applied so that an appropriate signal-to-noise ratio is obtained according to the material and resistance value of the charge injection layer.

[0160] [evaluation] (Evaluation of the resolution of the output image) A modified Hewlett-Packard laser beam printer Color LaseJet Enterprise M552 was used as the electrophotographic device for evaluation. The modification was to change the charging conditions and the laser exposure amount to operate variably. Each of the electrophotographic photoreceptors manufactured above was mounted in a process cartridge for black color and attached to the station of the process cartridge for black color, so that the laser beam printer could operate without mounting the process cartridges for other colors (cyan, magenta, yellow) on the main body of the laser beam printer. When outputting an image, only the process cartridge for black color was mounted on the main body of the laser beam printer, and a monochromatic image was output using only black toner. In addition, the laser intensity was adjusted so that the dark area potential Vd was -600V and the light area potential Vl was -250V, and the developing bias Vdc applied to the charging member was adjusted to -450V.

[0161] The definition of the output image was evaluated by the density of the output image when an image pattern (isolated dot pattern) exposed with an interval of 3 dots per exposed dot as shown in FIG. 7 was output in an environment of 32.5°C temperature / 80% relative humidity. If the latent image of the isolated dot pattern is clearly formed on the electrophotographic photoreceptor, the image of the isolated dot pattern is clearly output on the paper, resulting in an output with a high image density. On the other hand, if the latent image of the isolated dot pattern is not clearly formed on the electrophotographic photoreceptor, the image of the isolated dot pattern is not clearly output on the paper, resulting in an output with a low image density. Therefore, the definition of the output image can be evaluated from the level of density of the output image obtained.

[0162] The density of the output image was calculated from the difference in whiteness between the part of the output image where the exposed image pattern was formed and the part (white background) where the exposed image pattern was not formed. The density of the output image was measured using a Tokyo Denshoku white light meter TC-6DS / A with an amber filter. In the present invention, when the density of the output image obtained was 8.0% or more, it was determined that the definition of the output image was high. The results are shown in Tables 6 and 7.

[0163] (Evaluation of injectability) For the evaluation of the injection property, a modified electrophotographic device (laser beam printer) (product name: HP LaserJet Enterprise Color M553dn, manufactured by Hewlett-Packard Co.) was used. The electrophotographic device used for the evaluation was modified so that the voltage applied to the charging roller could be adjusted and measured. In addition, the cyan process cartridge of the electrophotographic device was modified to attach a potential probe (model 6000B-8, manufactured by Trek Japan Co., Ltd.) to the development position. Next, the surface potential of the center part of the electrophotographic photosensitive member was measured using a surface potential meter (model 344, manufactured by Trek Japan Co., Ltd.). The electrophotographic photoreceptors according to the Examples and Comparative Examples were mounted in an environment of 23.0°C temperature and 55% RH humidity, and a direct current of -500V was applied to the charging roller to charge the electrophotographic photoreceptor while rotating it at 60 rpm. The potential A of the electrophotographic photoreceptor surface at this time was measured, and the injection property = A / -500 was determined. The results are shown in Tables 6 and 7.

[0164] [Table 6]

[0165] [Table 7]

[0166] The disclosure of this embodiment includes the following configuration. (Configuration 1) An electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles, the average primary particle diameter of the metal oxide particles measured from a cross section of the surface layer is 20 nm or more and 70 nm or less; a content of the metal oxide particles in the surface layer measured from a cross section of the surface layer is 30 vol% or more and 75 vol% or less with respect to the total volume of the surface layer; 1. An electrophotographic photoreceptor comprising: (Configuration 2) 2. The electrophotographic photoreceptor according to claim 1, wherein the surface layer has a thickness of 0.1 μm or more and 1.5 μm or less. (Configuration 3) 3. The electrophotographic photoreceptor according to claim 1, wherein the content of the metal oxide particles in the surface layer is 42 vol % or more and 65 vol % or less with respect to the total volume of the surface layer. (Configuration 4) 4. The electrophotographic photoreceptor according to any one of configurations 1 to 3, wherein the powder resistivity A (Ω·cm) of the metal oxide particles satisfies the following formula (1): 1.0×10 3 ≦A≦1.0×10 10 (1) (Configuration 5) 5. The electrophotographic photoreceptor according to any one of Configurations 1 to 4, wherein the volume resistivity C (Ω·cm) of the surface layer at 32.5° C. and a humidity of 80% RH satisfies the following formula (2): 1.0×10 11 ≦C≦1.0×10 13 (2) (Configuration 6) 6. The electrophotographic photoreceptor according to any one of configurations 1 to 5, wherein the volume resistivity D (Ω·cm) of the surface layer at 23.0° C. and a humidity of 55% RH satisfies the following formula (3): 1.0×10 12 ≦D≦1.0×10 14 (3) (Configuration 7) The electrophotographic photoreceptor according to any one of Configurations 1 to 6, wherein the volume resistivity B (Ω·cm) of the binder resin at a temperature of 32.5° C. and a humidity of 80% RH satisfies the following formula (4): 1.0×10 12 ≦B≦1.0×10 15 (4) (Configuration 8) The electrophotographic photoreceptor according to any one of configurations 1 to 7, wherein the metal oxide particles are titanium oxide particles containing niobium. (Configuration 9) 9. The electrophotographic photoreceptor according to claim 8, wherein, in an EDS analysis of the metal oxide particles using a scanning transmission electron microscope (STEM), the niobium / titanium atomic ratio at the center of the metal oxide particle within 5% of the primary particle diameter from the surface of the metal oxide particle is 2.0 times or more. (Configuration 10) The electrophotographic photoreceptor according to any one of Configurations 1 to 9, wherein a volume resistivity C (Ω cm) of the surface layer at a temperature of 32.5° C. and a humidity of 80% RH and a volume resistivity D of the surface layer at a temperature of 23.0° C. and a humidity of 55% RH satisfy the following formula (5): 0.05≦D / C≦1.0 (5) (Configuration 11) 11. The electrophotographic photoreceptor according to any one of configurations 1 to 10, wherein the metal oxide particles are surface-treated with a compound having a silicon atom. (Configuration 12) 13. The electrophotographic photoreceptor according to any one of Configurations 1 to 12, wherein the surface layer contains, as the binder resin, at least one resin selected from the group consisting of a polyarylate resin, a polycarbonate resin, and an acrylic resin. (Configuration 13) A process cartridge which integrally supports the electrophotographic photosensitive member according to any one of configurations 1 to 12 and at least one means selected from the group consisting of a charging means, a developing means, a transfer means and a cleaning means, and is detachably mountable to a main body of an electrophotographic apparatus. (Configuration 14) 13. An electrophotographic apparatus comprising: an electrophotographic photoreceptor according to any one of configurations 1 to 12; a charging unit, an exposing unit, a developing unit, and a transferring unit. [Explanation of symbols]

[0167] 1a, 1b, 1c, 1d Electrophotographic photoreceptor 2a, 2b, 2c, 2d Charging means 3a, 3b, 3c, 3d exposure light 4a, 4b, 4c, 4d developing means 5a, 5b, 5c, 5d Cleaning means N1a, N1b, N1c, N1d Primary transfer means 10 Intermediate transfer belt P Transfer material N2 Secondary transfer means 30 Fixing Method 10 Pre-exposure light

Claims

1. An electrophotographic photoreceptor having a surface layer containing a binder resin and metal oxide particles, the average primary particle diameter of the metal oxide particles measured from a cross section of the surface layer is 20 nm or more and 70 nm or less; the content of the metal oxide particles in the surface layer, as measured from a cross section of the surface layer, is 30% by volume or more and 75% by volume or less, based on the total volume of the surface layer; An electrophotographic photoreceptor characterized by:

2. An electrophotographic photosensitive member as described in claim 1, wherein the metal oxide particles are titanium oxide particles containing niobium.

3. An electrophotographic photosensitive member as described in claim 2, wherein the titanium oxide particles containing niobium have oxygen deficiencies, and the oxygen deficiency rate of the titanium oxide particles containing niobium is 0.1% or more and 2.0% or less.

4. The electrophotographic photoreceptor according to claim 3, wherein the oxygen deficiency is introduced by baking together with an organic substance in a nitrogen atmosphere at a temperature of 600°C or higher, which is the decomposition temperature of the organic substance.

5. An electrophotographic photosensitive member as described in claim 2, wherein, in EDS analysis of the niobium-containing titanium oxide particles using a scanning transmission electron microscope (STEM), the niobium / titanium atomic ratio at a distance of 5% of the primary particle diameter from the surface of the niobium-containing titanium oxide particles is 2.0 times or more higher than the niobium / titanium atomic ratio at the center of the niobium-containing titanium oxide particles.

6. 2. The electrophotographic photoreceptor according to claim 1, wherein the surface layer has a thickness of 0.1 [mu]m or more and 1.5 [mu]m or less.

7. 2. The electrophotographic photoreceptor according to claim 1, wherein the content of the metal oxide particles in the surface layer is 42% by volume or more and 65% by volume or less with respect to the total volume of the surface layer.

8. 2. The electrophotographic photoreceptor according to claim 1, wherein the powder resistivity A (Ω·cm) of the metal oxide particles satisfies the following formula (1): 1.0×10 ３ ≦A≦1.0×10 １０ (1)

9. 2. The electrophotographic photoreceptor according to claim 1, wherein the surface layer has a volume resistivity C (Ω·cm) at 32.5° C. and a humidity of 80% RH that satisfies the following formula (2): 1.0×10 １１ ≦C≦1.0×10 １３ (2)

10. 2. The electrophotographic photoreceptor according to claim 1, wherein the surface layer has a volume resistivity D (Ω·cm) at 23.0° C. and a humidity of 55% RH that satisfies the following formula (3): 1.0×10 １２ ≦D≦1.0×10 １４ (3)

11. 2. The electrophotographic photoreceptor according to claim 1, wherein the binder resin has a volume resistivity B (Ω·cm) at a temperature of 32.5° C. and a humidity of 80% RH that satisfies the following formula (4): 1.0×10 １２ ≦B≦1.0×10 １５ (4)

12. 2. The electrophotographic photoreceptor according to claim 1, wherein a volume resistivity C (Ω cm) of the surface layer at a temperature of 32.5° C. and a humidity of 80% RH and a volume resistivity D of the surface layer at a temperature of 23.0° C. and a humidity of 55% RH satisfy the following formula (5): 0.05≦D / C≦1.0 (5)

13. 2. The electrophotographic photoreceptor according to claim 1, wherein the metal oxide particles are surface-treated with a compound having a silicon atom.

14. 2. The electrophotographic photoreceptor according to claim 1, wherein the surface layer contains, as the binder resin, at least one resin selected from the group consisting of polyarylate resin, polycarbonate resin, and acrylic resin.

15. 15. A process cartridge which integrally supports the electrophotographic photosensitive member according to any one of claims 1 to 14 and at least one means selected from the group consisting of a charging means, a developing means, a transfer means, and a cleaning means, and is detachably mountable to a main body of an electrophotographic apparatus.

16. 15. An electrophotographic apparatus comprising: the electrophotographic photosensitive member according to claim 1; a charging unit; an exposing unit; a developing unit; and a transferring unit.

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