Electrophotographic photoreceptor, process cartridge, and electrophotographic device

Abstract

To provide an electrophotographic photoreceptor that can withstand the use in a long-life image forming apparatus.SOLUTION: An electrophotographic photoreceptor is such that: in a top view of a surface layer, when the ratio of the area of first particles in the total area of the surface layer is defined as S1(%), and the ratio of the area of second particles in the total area of the surface layer as S2(%), the S1 and the S2 satisfy 70≤(S1+S2)≤95 and 0.8≤(S1 / S2)≤2.0, when the exposure height of the first particles exposed on the surface of the electrophotographic photoreceptor is defined as L1 (mm), and the exposure height of the second particles exposed on the surface of the electrophotographic photoreceptor as L2 (mm), the L1 and the L2 satisfy 50≤L1≤300 and 2.0≤L1 / L2≤10.0, the first particles include any one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black, and the second particles include silica particles.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] Conventionally, in electrophotographic and electrostatic recording image forming apparatuses, corona chargers have been used as a means for charging electrophotographic photoreceptors such as electrophotographic photoreceptors and electrostatic recording dielectrics. In recent years, devices using a contact charging method, in which a charging member with a voltage applied to the electrophotographic photoreceptor is brought into contact with the electrophotographic photoreceptor to charge the electrophotographic photoreceptor, have come into practical use due to their advantages of low ozone and low power consumption.

[0003] In particular, a roller charging system using a charging roller as a charging member is preferably used from the viewpoint of charging stability. In a contact charging device using the roller charging system, a medium resistance elastic roller as a charging member is pressed against an electrophotographic photosensitive member, and a voltage is applied to the roller to charge the electrophotographic photosensitive member. Specifically, charging is performed by discharging from the charging member to the electrophotographic photosensitive member, and therefore charging is initiated by applying a voltage equal to or higher than a certain threshold voltage according to Paschen's law.

[0004] Even in such a roller charging method, since a discharge phenomenon is used to apply a voltage to the electrophotographic photoreceptor, discharge products are generated and the surface of the electrophotographic photoreceptor is altered, although to a lesser extent than in a charging method using a corona charger. The discharge products and the surface of the altered electrophotographic photoreceptor have low resistance, particularly in a high-temperature and high-humidity environment, and the surface potential of the electrophotographic photoreceptor required for image formation is not formed, which may make it difficult to develop a desired image with a developing member.

[0005] To solve this problem, a configuration is generally used in which while continuously printing while gradually scraping off the discharge products on the surface of the electrophotographic photoreceptor and the altered electrophotographic photoreceptor surface, the discharge products and the altered electrophotographic photoreceptor surface are simultaneously scraped off. Specifically, a cleaning blade that cleans the developer remaining on the surface of the electrophotographic photoreceptor disposed in contact with the electrophotographic photoreceptor, or a charging member or a developing member scrapes off the surface of the electrophotographic photoreceptor.

[0006] However, in recent years, from the viewpoints of reducing maintenance frequency and improving usability, an increase in the number of printable sheets has been demanded, and along with this, a longer life of the electrophotographic photoreceptor is required. That is, in the electrophotographic photoreceptor in a long-life image forming apparatus, it has become difficult to use the above countermeasures of continuously scraping the surface of the electrophotographic photoreceptor over a long period of use (throughout its life).

[0007] For these reasons, an injection charging method without a discharge phenomenon has been proposed as a countermeasure against discharge products and alteration of the electrophotographic photoreceptor surface that does not rely on scraping the electrophotographic photoreceptor surface. The electrophotographic photoreceptor used in an image forming apparatus of the injection charging method requires a design using a conductive material on the surface of the electrophotographic photoreceptor in order to achieve charge injection from the charging member.

[0008] For example, Patent Document 1 proposes a technique of improving the injection charging property by including conductive powder in the surface of the electrophotographic photoreceptor and using conductive powder having a particle size equal to or greater than the film thickness of the surface layer to expose the conductive powder from the surface layer.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, when the electrophotographic photoreceptor of Patent Document 1 is used in an image forming apparatus that requires a long life, there is still room for improvement. For example, it is necessary to make improvements to suppress the occurrence of dot images caused by contamination of the surface of the electrophotographic photoreceptor that occurs in a long-life image forming apparatus. Therefore, an object of the present invention is to provide an electrophotographic photoreceptor that can withstand use in a long-life image forming apparatus by using two types of particles in the surface layer design of the electrophotographic photoreceptor to create an appropriate surface state on the surface layer of the electrophotographic photoreceptor.

Means for Solving the Problems

[0011] The above object is achieved by the following present invention. That is, the present invention is an electrophotographic photoreceptor having a surface layer, wherein the surface layer contains a binder resin, first particles, and second particles, the surface of the surface layer has convex portions derived from the first particles and convex portions derived from the second particles, when the surface layer is viewed from above, when the ratio of the area occupied by the first particles in the total area of the surface layer is S1 [%] and the ratio of the area occupied by the second particles in the total area of the surface layer is S2 [%], the S1 and the S2 are 70 ≦ (S1 + S2) ≦ 95 (1) 0.8 ≦ (S1 / S2) ≦ 2.0 (2) satisfy this, when the exposure height of the first particles exposed on the surface of the electrophotographic photoreceptor is L1 [nm] and the exposure height of the second particles exposed on the surface of the electrophotographic photoreceptor is L2 [nm], the L1 and the L2 are 50 ≦ L1 ≦ 300 (3) 2.0 ≦ L1 / L2 ≦ 10.0 (4) satisfy this, the first particles include any one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black, the second particles include silica particles, and is an electrophotographic photoreceptor. The present invention also relates to a process cartridge that integrally supports the above-described electrophotographic photoreceptor and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachable from the electrophotographic apparatus main body. The present invention also relates to an electrophotographic apparatus having the above-described electrophotographic photoreceptor, as well as a charging means, an exposure means, a developing means, and a transfer means.

Advantages of the Invention

[0012] According to the present invention, in the surface layer design of the electrophotographic photoreceptor, by using two kinds of particles to create an appropriate surface state on the surface layer of the electrophotographic photoreceptor, an electrophotographic photoreceptor capable of withstanding use in a long-life image forming apparatus can be provided.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0014] <One Embodiment> One embodiment of the present invention relates to an electrophotographic photoreceptor. As a result of intensive studies, the present inventors have found a method for designing the surface layer of an electrophotographic photoreceptor that suppresses contamination of the electrophotographic photoreceptor occurring in a long-life image forming apparatus. This electrophotographic photoreceptor is applicable not only to an image forming apparatus using an injection charging method but also to an image forming apparatus using a discharge charging method. That is, the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor having a surface layer, wherein the surface layer contains a binder resin, first particles, and second particles, the surface of the surface layer has convex portions derived from the first particles and convex portions derived from the second particles, when the surface layer is viewed from above, and the ratio of the area occupied by the first particles in the total area of the surface layer is S1 [%] and the ratio of the area occupied by the second particles in the total area of the surface layer is S2 [%], the S1 and the S2 are 70 ≦ (S1+S2) ≦ 95 (1) 0.8 ≦ (S1 / S2) ≦ 2.0 (2) satisfy the following, when the exposure height of the first particles exposed on the surface of the electrophotographic photoreceptor is L1 [nm] and the exposure height of the second particles exposed on the surface of the electrophotographic photoreceptor is L2 [nm], the L1 and the L2 are 50 ≦ L1 ≦ 300 (3) 2.0 ≦ L1 / L2 ≦ 10.0 (4) satisfy the following, the first particles include any one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black, and the second particles include silica particles. Hereinafter, preferred embodiments of the present invention will be described.

[0015] [Electrophotographic Photoreceptor] The electrophotographic photoreceptor of the present invention has a surface layer. The electrophotographic photoreceptor of the present invention preferably has a support, a charge generation layer provided on the support, a charge transport layer, and a surface layer containing particles. The electrophotographic photoreceptor according to the present invention can be used as a cylindrical electrophotographic photoreceptor having a charge generation layer, a charge transport layer, and a surface layer formed on a cylindrical support, but a belt-like or sheet-like shape is also possible. FIG. 1 is a diagram showing an example of the layer structure of an electrophotographic photoreceptor. In FIG. 1, the electrophotographic photoreceptor has a support 101, an undercoat layer 102, a charge generation layer 103, a charge transport layer 104, and a surface layer 105 according to the present invention.

[0016] With the above configuration, an electrophotographic photoreceptor capable of withstanding use in a long-life image forming apparatus can be provided. Although the mechanism by which the problems are solved by the configuration of the present invention is not clearly understood, it is speculated as follows.

[0017] In a long-life image forming apparatus, the spotty image generated is caused by the adhesion of contaminants such as toner, externally added agents, and paper dust to the surface of the electrophotographic photoreceptor during the image forming process. Such contamination of the electrophotographic photoreceptor surface is repeated, and the contaminants accumulate on the surface of the electrophotographic photoreceptor, thereby becoming apparent.

[0018] When contaminants accumulate on the surface of the electrophotographic photoreceptor, charges are also stored in the contaminants deposited on the surface of the electrophotographic photoreceptor during the charging process. Since the main components of the contaminants are toner and externally added agents, they are more likely to be charged up compared to the surface layer of the electrophotographic photoreceptor containing conductive particles. Such contaminated portions do not reach the potential of the surface of the electrophotographic photoreceptor as originally intended during the image forming process, and are output as a spotty image (image defect in the form of spots seen on a halftone image).

[0019] The electrophotographic photoreceptor of the present invention has a surface layer containing a binder resin, first particles, and second particles. The surface of the surface layer has protrusions derived from the first particles and protrusions derived from the second particles. When the surface layer is viewed from above, when the ratio of the area occupied by the first particles in the total area of the surface layer is S1 [%] and the ratio of the area occupied by the second particles in the total area of the surface layer is S2 [%], S1 and S2 are 70 ≦ (S1+S2) ≦ 95 (1) 0.8 ≦ (S1 / S2) ≦ 2.0 (2) satisfy the following.

[0020] By satisfying formula (1), most of the surface layer of the electrophotographic photoreceptor is covered by the first particles and the second particles. As a result, irregularities derived from the first particles and the second particles are formed on the surface of the surface layer of the electrophotographic photoreceptor. Since this irregular shape makes point contact with contaminants, the contaminants are more likely to desorb from the surface of the electrophotographic photoreceptor than in a general electrophotographic photoreceptor having no irregular shape.

[0021] By satisfying formula (1) and formula (2), the existence ratio of the first particles, which are conductive particles, on the surface of the electrophotographic photoreceptor is sufficiently ensured, and the injection charging property of the electrophotographic photoreceptor can be exhibited.

[0022] On the other hand, when 70≦(S1+S2) is not satisfied, the area occupied by the resin with respect to the total area when the surface layer of the electrophotographic photoreceptor is viewed from above becomes relatively large. Therefore, the area S1 occupied by the first particles, which are injection sites, decreases, and the injection characteristics deteriorate. In addition, the area S2 occupied by the second particles that form the fine irregular shape decreases, and the desorption of contaminants cannot be promoted, causing the deposition of contaminants and making it easy to generate spot images.

[0023] When (S1 + S2) does not satisfy (S1 + S2) ≤ 95, the area occupied by the resin on the surface of the electrophotographic photoreceptor becomes insufficient, so the function of binding the particles to the surface layer of the electrophotographic photoreceptor weakens, and due to rubbing with the contacting member during image formation, particles are likely to detach from the surface layer of the electrophotographic photoreceptor. As a result, when the first particles detach from the surface layer of the electrophotographic photoreceptor, the injection characteristics deteriorate due to the disappearance of the injection sites, and when the second particles detach, the desorption characteristics of contaminants due to the disappearance of the fine uneven shape are likely to deteriorate.

[0024] When 0.8 ≤ (S1 / S2) is not satisfied, the area S1 occupied by the first particles, which are the injection sites, decreases, and the injection charging characteristics deteriorate. Also, when (S1 / S2) ≤ 2.0 is not satisfied, the area S2 occupied by the second particles that form the fine uneven shape decreases, and the desorption of contaminants from the surface of the electrophotographic photoreceptor cannot be promoted, causing the deposition of contaminants and making it easy to generate dot images.

[0025] In the electrophotographic photoreceptor of the present invention, when the exposure height of the first particles exposed on the surface of the electrophotographic photoreceptor is L1 [nm] and the exposure height of the second particles exposed on the surface of the electrophotographic photoreceptor is L2 [nm], L1 and L2 satisfy 50 ≤ L1 ≤ 300 (3) 2.0 ≤ L1 / L2 ≤ 10.0 (4) and satisfy the above conditions.

[0026] By satisfying formula (3), while ensuring the injection charging characteristics of the electrophotographic photoreceptor, even when the electrophotographic photoreceptor is used over a long period, the first particles are less likely to detach from the surface layer of the electrophotographic photoreceptor.

[0027] By satisfying Formula (3) and Formula (4), a first particle which is a conductive particle has a higher convex portion than a second particle which is an insulating particle, and a second particle which is an insulating particle has a lower convex portion than a first particle which is a conductive particle are formed on the surface of the electrophotographic photoreceptor. As a result, contaminants are likely to adhere to the surface of the insulating particles which are relatively concave portions, and the first particles which are conductive particles are maintained in a state of being exposed on the surface of the electrophotographic photoreceptor. Thereby, even when the electrophotographic photoreceptor is used over a long period of time, the injection charging characteristics are maintained. Further, the surface formed by the insulating particles which are relatively concave portions of the surface layer of the electrophotographic photoreceptor has a fine uneven shape due to the insulating particles. Furthermore, the second particle has a smaller relative dielectric constant than the first particle. Therefore, not only does the contact between the contaminant and the surface of the electrophotographic photoreceptor become a point contact, but also the electrostatic adhesion force is low, so that the contaminants are likely to detach from the surface of the electrophotographic photoreceptor.

[0028] When 50≦L1 is not satisfied, a sufficient exposure height L1 is not formed as a conductive site, so that the injection charging characteristics are likely to deteriorate due to the deposition of contaminants. Also, when L1≦300 is not satisfied, since the exposure height L1 of the first particle is formed high, the first particle is likely to detach from the surface of the electrophotographic photoreceptor due to durability, and the injection charging characteristics of the electrophotographic photoreceptor deteriorate.

[0029] When 2.0≦L1 / L2 is not satisfied, the first particle cannot form a sufficient exposure height L1, so that the injection charging characteristics are likely to deteriorate due to the deposition of contaminants. When L1 / L2≦10.0 is not satisfied, when the exposure height L1 of the first particle is relatively large, the first particle is likely to detach, and as a result, the injection charging characteristics deteriorate. When the exposure height L2 of the second particle is relatively small, a minute uneven shape cannot be formed, so that it becomes difficult to detach the contaminants, and as a result, the contaminants accumulate on the surface of the electrophotographic photoreceptor, and a pockmark image is likely to occur.

[0030] Further, in the electrophotographic photoreceptor of the present invention, when the average primary particle diameter based on the number of the first particles is D1 [nm] and the average primary particle diameter based on the number of the second particles is D2 [nm], D1 and D2 are 100 ≦ D1 ≦ 350 (5) 30 ≦ D2 ≦ 150 (6) 2.0 ≦ D1 / D2 ≦ 10.0 (7) It is preferable to satisfy the above conditions. By doing so, the surface shape of the surface layer of the electrophotographic photoreceptor, which is less likely to adhere contaminants, can be designed. Furthermore, it is more preferable that the formula (5) is 120≦D1≦250, and even more preferable that it is 150≦D1≦220. For the formula (6), it is more preferable that 30≦D2≦120, and even more preferable that 30≦D2≦100. For the formula (7), it is more preferable that 4.0≦D1 / D2≦10.0, and even more preferable that 5.5≦D1 / D2≦9.0. In the present invention, the primary particle size of the particles is used to design the surface shape of the surface layer of the electrophotographic photoreceptor. By satisfying the formula (5), the formula (6), and the formula (7), the first particles, which are conductive particles, can form higher protrusions on the surface of the surface layer of the electrophotographic photoreceptor than the second particles, which are insulating particles.

[0031] In addition, for the electrophotographic photoreceptor of the present invention, when the film thickness of the surface layer is T1 [nm] and the average primary particle size based on the number of the first particles is D1 [nm], T1 and D1 satisfy 1.0 ≦ T1 / D1 ≦ 1.8 (8) It is preferable to satisfy the above conditions. By doing so, the surface shape of the surface layer of the electrophotographic photoreceptor using the primary particle size of the particles can be designed. It is more preferable that the formula (8) is 1.2≦T1 / D1≦1.5. By doing so, while the protrusions formed by the first particles become higher than the film thickness, the protrusions are not formed by the aggregates of the first particles, so that even when the electrophotographic photoreceptor is used for a long time, the injection characteristics can be maintained while suppressing the detachment of the first particles caused by the friction with the contact member.

[0032] In addition, for the electrophotographic photoreceptor of the present invention, the powder resistivity R1 of the first particles is preferably 8 1.0×10 10It is preferably at Ω·cm or more. The first particles that form a convex higher than the second particles are conductive particles, and the second particles that form a convex lower than the first particles are insulating particles. As a result, contaminants are likely to adhere to the surface of the insulating particles, which are relatively concave portions, and the first particles, which are conductive particles, are likely to remain exposed on the surface. Further, in relatively concave portions of the surface layer of the electrophotographic photoreceptor, a fine concavo-convex shape due to the insulating particles exists. Furthermore, the second particles have a smaller relative dielectric constant than the first particles. Therefore, not only does the contact between the contaminants and the surface of the electrophotographic photoreceptor become a point contact, but also the electrostatic adhesion force is low, so the contaminants are likely to desorb. As a result, even when the electrophotographic photoreceptor is used over a long period of time, the protrusion of the convex portions serving as injection points can be maintained, and the injection characteristics are likely to be maintained.

[0033] Further, in the electrophotographic photoreceptor of the present invention, the powder resistivity R2 of the second particles satisfies 1.0×10 13 It is more preferably Ω·cm or more. By doing so, the materials that affect the injection characteristics can be limited to only the first particles. Further, even if contaminants adhere to the fine concavo-convex shape portions formed by the second particles in the relatively concave portions of the surface layer of the electrophotographic photoreceptor, the second particles do not affect the injection characteristics, so the injection characteristics of the surface layer of the electrophotographic photoreceptor are unlikely to change. Therefore, even when the electrophotographic photoreceptor is used over a long period of time, the change in the injection characteristics can be reduced. Note that the above mechanism is based on speculation, and this speculation does not affect the technical scope of the present invention.

[0034] <Binder resin> The binder resin according to the present invention includes a polyester resin, an acrylic resin, a phenoxy resin, a polycarbonate resin, a polystyrene resin, a phenol resin, a melamine resin, an epoxy resin, and the like. Among them, a polycarbonate resin, a polyester resin, and an acrylic resin are preferable.

[0035] Alternatively, the surface layer may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction in this case include thermal polymerization reaction, photopolymerization reaction, radiation polymerization reaction, etc. Examples of the polymerizable functional group of the monomer having a polymerizable functional group include acryloyl group, methacryloyl group, etc. As the monomer having a polymerizable functional group, a material having charge transport ability may be used.

[0036] The compound having a polymerizable functional group may have a charge transport structure simultaneously with the chain polymerizable functional group. As the charge transport structure, a triarylamine structure is preferable in terms of charge transport. As the chain polymerizable functional group, an acryloyl group and a methacryloyl group are preferable. The number of functional groups may be one or more. Among them, when a cured film is formed by containing a compound having a plurality of functional groups and a compound having one functional group, it is particularly preferable because the strain generated by the polymerization between the plurality of functional groups is easily eliminated.

[0037] Examples of the compound having one functional group are shown in the following formula (2-1) to the following formula (2-6).

Chemical formula

Chemical formula

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0038] Examples of the compound having a plurality of functional groups are shown in the following formula (3-1) to the following formula (3-5).

Chemical formula

[0039] The surface layer may contain additives such as an antioxidant, an ultraviolet absorber, a plasticizer, a leveling agent, a lubricity-imparting agent, and an abrasion resistance improver. Specifically, examples thereof include a hindered phenol compound, a hindered amine compound, a sulfur compound, a phosphorus compound, a benzophenone compound, a siloxane-modified resin, and silicone oil.

[0040] The surface layer can be formed by preparing a coating liquid for the surface layer containing each of the materials and solvents described below, forming this coating film on the charge transport layer or the single-layer type photosensitive layer, and drying and / or curing it. Examples of the solvent used in the coating liquid include alcohol solvents, ketone solvents, ether solvents, sulfoxide solvents, ester solvents, and aromatic hydrocarbon solvents.

[0041] <First particle> In the electrophotographic photoreceptor of the present invention, the first particle contains any one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black. Examples of the metal oxide particles include magnesium oxide, aluminum oxide, titanium oxide, iron oxide, copper oxide, zinc oxide, silver oxide, tantalum oxide, bismuth oxide, cobalt oxide, indium oxide, tin oxide, and indium tin oxide. Examples of the metal particles include magnesium, aluminum, titanium, iron, copper, zinc, silver, tin, platinum, and gold. These particles may be synthetic products or commercially available products. Further, in order to enhance the dispersion stability of the particles, a hydrophobization treatment described below may be performed. As carbon black, there are production methods such as the furnace method, the channel method, the acetylene method, and the thermal method. From the viewpoint of high conductivity and few impurities, carbon black produced by the acetylene method is preferable.

[0042] In addition, since the first particles are materials responsible for the injection characteristics of the surface layer of the electrophotographic photoreceptor, it is preferable to have a volume resistivity of medium resistance or less. In addition, from the viewpoints of cost and environmental load, metal oxide particles such as tin oxide (stannic oxide), indium tin oxide, titanium oxide, and zinc oxide are preferable. In the electrophotographic photoreceptor of the present invention, it is preferable that the first particles contain any one or more selected from the group consisting of tin oxide particles, ITO particles, titanium oxide particles, and zinc oxide particles. By satisfying that the first particles are any one of tin oxide particles, ITO particles, titanium oxide particles, and zinc oxide particles, the function of the electrophotographic photoreceptor is not inhibited, and even with a relatively small addition amount, the charge injection characteristics into the surface layer of the electrophotographic photoreceptor can be ensured. In particular, titanium oxide particles and zinc oxide particles are preferable. These have a higher volume resistivity than tin oxide particles and ITO particles and are of medium resistance. Therefore, even if discharge products due to durability accumulate on the drum surface in a high-temperature and high-humidity environment, better image formation can be maintained compared to tin oxide particles and ITO particles. Also, since the electrostatic adhesion force can be suppressed, dirt adhering to the convex portions can be easily removed, and changes in the injection charging property can be kept small.

[0043] The electrophotographic photoreceptor of the present invention has first particles containing niobium-doped titanium oxide particles. In the EDS analysis by scanning transmission electron microscope (STEM) of the niobium-doped titanium oxide particles, the concentration ratio calculated by niobium atomic concentration / titanium atomic concentration within 5% of the primary particle diameter of the niobium-doped titanium oxide particles from the surface of the niobium-doped titanium oxide particles is preferably 2.0 times or more the concentration ratio calculated by niobium atomic concentration / titanium atomic concentration at the center of the niobium-doped titanium oxide particles. By doing so, it is possible to lower the resistance of the surface of the titanium oxide particles while maintaining the powder resistivity at a medium resistance. As a result, even if a large amount of the first particles are added to the surface layer of the electrophotographic photoreceptor, it becomes easier to maintain the latent image and high injectability is ensured.

[0044] In the present invention, the first particles preferably have, in particular, anatase-type titanium oxide particles as a core material and titanium oxide covering the surface of the core material and containing niobium. As the form of containing niobium, it is preferably contained in a so-called doped form incorporated into the crystal lattice of titanium oxide, rather than being contained as an oxide. By doping niobium into titanium oxide, the injection charging property is enhanced.

[0045] When the first particles have niobium-containing titanium oxide particles, the niobium in the first particles is preferably contained in an amount of 0.5 mass% or more and 15.0 mass% or less, more preferably 1.0 mass% or more and 10.0 mass% or less. If the content of niobium in the first particles is 0.5 mass% or more, the conductivity of titanium oxide can be increased and the injection charging property can be enhanced. If it is 15.0 mass% or less, the crystal structure of titanium oxide can be maintained, so that the volume resistivity of the surface layer does not become too large.

[0046] Similar to the titanium oxide particles (conductive particles 1) used in the examples of the present invention, 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 is shown in FIG. 6. FIG. 7 shows a diagram schematically explaining the STEM image of FIG. 6. Although details will be described later, the titanium oxide particles containing niobium used in this example are produced by firing after coating titanium oxide particles serving as a core material with titanium oxide containing niobium. Therefore, it is considered that the coated titanium oxide containing niobium crystallizes as niobium-doped titanium oxide by so-called epitaxial growth along the crystal of the core titanium oxide.

[0047] The titanium oxide containing niobium produced in this way can be seen to have a lower density near the surface compared to the density at the center of the particle, as shown in FIG. 6, and has a core-shell-like form. In addition, in the EDS analysis by STEM, since X-rays penetrate the entire particle, as shown in FIG. 7, the EDS analysis at the center of the particle as shown in the direction of 33 has a greater influence of the surface near the surface for the EDS analysis within 5% of the primary particle diameter from the surface of the particle as shown in the direction of 34.

[0048] That is, in the EDS analysis by STEM as described above, when the niobium / titanium atomic number ratio at the surface of the particle is 2.0 times or more with respect to the niobium / titanium atomic number ratio at the center of the particle, it is considered that the niobium element is unevenly distributed near the surface. In FIG. 7, reference numeral 32 is a region of the metal oxide particle within 5% of the primary particle diameter from the surface of the particle, and reference numeral 31 is a region of the metal oxide particle inside the region of reference numeral 32. Further, reference numeral 33 indicates X-rays for analyzing the center of the metal oxide particle, and reference numeral 34 indicates X-rays for analyzing the inside within 5% of the particle diameter from the surface of the metal oxide particle.

[0049] As the EDS analysis by STEM, it is observed with a transmission electron microscope, and the niobium / titanium ratio is measured by EDS. In addition, it can also be directly measured from the electrophotographic photoreceptor by thinning the electrophotographic photoreceptor by means such as a microtome, Ar milling, or FIB.

[0050] In addition, the titanium oxide particles containing niobium contained in the surface layer preferably have oxygen deficiency. When having oxygen deficiency, the injection charging property is improved. Although the detailed mechanism is not well understood, it is presumed that when the titanium oxide particles containing niobium have oxygen deficiency, they are more likely to receive charges, so the injection charging property 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%, improvement of the injection charging property cannot be expected. If it exceeds 2.0%, the color of the particles becomes black, the transparency of the surface layer decreases, and the sensitivity of the electrophotographic photoreceptor decreases. Further, when the oxygen deficiency rate in 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 in the other region of the titanium oxide particles containing niobium is γ, it is preferable to satisfy the following formula (α). β > 10×γ (α) By doing so, the oxygen deficiency portions where charges are easily received are unevenly distributed on the surface of the metal oxide particles, so that injection charging can be effectively performed.

[0051] Here, the oxygen deficiency rate of the metal oxide particles can be expressed as (B - A) / B × 100 (%) when the actual oxygen content of the metal oxide particles is A and the theoretical oxygen content of the metal oxide particles without oxygen deficiency is B. The oxygen deficiency rate of the metal oxide particles, and the ratio of the oxygen deficiency rate in the region within 5% of the primary particle diameter from the surface of the metal oxide particles to the oxygen deficiency rate in the other region can be measured by energy dispersive X-ray analysis (EDS). Further, as described above, in the EDS analysis, since X-rays penetrate the entire particle, satisfying the above relational expression (α) means that the oxygen deficiency portions are unevenly distributed in the vicinity of the particle surface.

[0052] The introduction of oxygen deficiency can be carried out by firing in a reducing atmosphere such as ammonia or hydrogen, or by firing in a nitrogen atmosphere together with an organic substance at 600 °C or higher, which is the decomposition temperature of the organic substance. Although the detailed mechanism is not clear, as described above, the injection chargeability is increased by doping niobium and introducing oxygen deficiency because it becomes easier to transfer charges to and from conductive particles such as carbon black and graphite generally used for charging members, and the transfer of charges from the charging member to the electrophotographic photoreceptor becomes smooth.

[0053] <Second particle> In the electrophotographic photoreceptor of the present invention, the second particle contains silica particles. Since silica particles have a larger average circularity compared to other inorganic particles, it is expected to have an effect of promoting point contact between contaminants and the surface of the electrophotographic photoreceptor and reducing the adhesion force. As the silica particles, known silica fine particles can be used, and either dry silica fine particles or wet silica fine particles may be used. Preferably, they are wet silica fine particles obtained by the sol-gel method (hereinafter also referred to as sol-gel silica).

[0054] The sol-gel silica used for the particles contained in the surface layer of the electrophotographic photoreceptor of the present invention may be hydrophilic or may have its surface hydrophobized.

[0055] Examples of the hydrophobization treatment method include a method of removing the solvent from the silica sol suspension in the sol-gel method, drying it, and then treating it with a hydrophobizing agent, and a method of directly adding a hydrophobizing agent to the silica sol suspension and treating it simultaneously with drying. From the viewpoints of controlling the half-value width of the particle size distribution and the saturated moisture adsorption amount, the method of directly adding a hydrophobizing agent to the silica sol suspension is preferable.

[0056] Examples of the hydrophobizing agent include, for example, chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, t-butyldimethylchlorosilane, vinyltrichlorosilane; Alkoxysilanes such as tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltrimethoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, i-butyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane; Silazanes such as hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexahyexyldisilazane, hexacyclohexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, dimethyltetravinyldisilazane; Silicone oils such as dimethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, alkyl-modified silicone oil, chloroalkyl-modified silicone oil, chlorophenyl-modified silicone oil, fatty acid-modified silicone oil, polyether-modified silicone oil, alkoxy-modified silicone oil, carbinol-modified silicone oil, amino-modified silicone oil, fluorine-modified silicone oil, and terminal-reactive silicone oil; Siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, octamethyltrisiloxane; Examples of fatty acids and their metal salts include long-chain fatty acids such as undecanoic acid, lauric acid, tridecanoic acid, dodecanoic acid, myristic acid, palmitic acid, pentadecanoic acid, stearic acid, heptadecanoic acid, arachidic acid, montanic acid, oleic acid, linoleic acid, arachidonic acid, and salts of these fatty acids with metals such as zinc, iron, magnesium, aluminum, calcium, sodium, and lithium.

[0057] Among these, alkoxysilanes, silazanes, and silicone oils are preferably used because they are easy to subject to hydrophobization treatment. These hydrophobization agents may be used alone or in combination of two or more.

[0058] <Additive> The surface layer in the present invention may contain additives such as a polymerization catalyst, an antioxidant, an ultraviolet absorber, a plasticizer, a leveling agent, a slipperiness imparting agent, and an abrasion resistance improving agent. Specifically, examples include quaternary ammonium salts, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, and silicone oils.

[0059] <Solvent> A solvent that stably disperses or dissolves the binder resin, inorganic particles, and additives may be appropriately selected. Specifically, the following can be mentioned. For example, Alcohols such as methanol, ethanol, isopropanol, butanol, and octanol; Ketones such as acetone and cyclohexanone; Esters such as ethyl acetate, butyl acetate, ethyl lactate, γ-butyrolactone, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; Ethers such as ethylene glycol monomethyl ether and diethylene glycol monobutyl ether; Aromatic hydrocarbons such as benzene, toluene, and xylene; Amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Moreover, in order to adjust the drying rate of the film of the curable composition and to adjust the viscosity suitable for coating of the curable composition, a plurality of solvents may be used in combination.

[0060] <Surface layer> The surface layer can be formed by preparing a coating solution for the surface layer containing each of the above materials and solvents, forming this coating film, and drying and / or curing it. FIG. 2 is a diagram showing an example of the surface layer configuration of the electrophotographic photoreceptor. In FIG. 2, the surface layer of the electrophotographic photoreceptor has a binder resin 201, first particles 202, second particles 203, and a lower layer 204 on which the surface layer is coated.

[0061] <Support> In the present invention, the electrophotographic photoreceptor preferably has a support. In the present invention, the support is preferably a conductive support having conductivity. Further, examples of the shape of the support include a cylindrical shape, a belt shape, and a sheet shape. Among them, a cylindrical support is preferable. Further, an electrochemical treatment such as anodic oxidation, a blasting treatment, a cutting treatment, or the like may be performed on the surface of the support.

[0062] As the material of the support, metals, resins, glass, etc. are preferable. Examples of the metal include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among them, an aluminum support using aluminum is preferable. Moreover, conductivity may be imparted to resins and glass by treatments such as mixing or coating with a conductive material.

[0063] <Conductive layer> In the present invention, a conductive layer may be provided on a support. By providing the conductive layer, it is possible to conceal scratches and unevenness on the surface of the support and to control light reflection on the surface of the support. The conductive layer preferably contains conductive particles and a resin.

[0064] Examples of the material of the conductive particles include metal oxides, metals, carbon black, and the like. Examples of the metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, and the like. Examples of the metals include aluminum, nickel, iron, nichrome, copper, zinc, silver, and the like.

[0065] Among these, it is preferable to use a metal oxide as the conductive particles, and more preferably, titanium oxide, tin oxide, or zinc oxide. When using a metal oxide 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 its oxide.

[0066] Further, the conductive particles may have a laminated structure in which pre-coated particles such as titanium oxide, barium sulfate, and zinc oxide are coated with a metal oxide having a composition different from that of the pre-coated particles. Examples of the coating include metal oxides such as tin oxide. When using a metal oxide as the conductive particles, the average primary particle diameter is preferably 1 nm or more and 500 nm or less, and more preferably 3 nm or more and 400 nm or less.

[0067] Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, alkyd resin, and the like. Further, the conductive layer may further contain a concealer such as silicone oil, resin particles, and titanium oxide.

[0068] The average film thickness of the conductive layer is preferably 1 μm or more and 50 μm or less, and particularly preferably 3 μm or more and 40 μm or less. The conductive layer can be formed by preparing a coating liquid for the conductive layer containing each of the above materials and a solvent, forming this coating film, and drying it. Examples of the solvent used in the coating liquid include alcohol solvents, sulfoxide solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, and the like. Examples of the dispersion method for dispersing conductive particles in the coating liquid for the conductive layer include methods using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

[0069] <Undercoat layer> In the present invention, an undercoat layer may be provided on the support or the conductive layer. The average film thickness of the undercoat layer is preferably 0.1 μm or more and 50 μm or less, more preferably 0.2 μm or more and 40 μm or less, and particularly preferably 0.3 μm or more and 30 μm or less.

[0070] Examples of the resin of this undercoat layer include polyacrylic acid resin, polyvinyl alcohol resin, polyvinyl acetal resin, polyethylene oxide resin, polypropylene oxide resin, ethyl cellulose resin, methyl cellulose resin, polyamide resin, polyamic acid resin, polyurethane resin, polyimide resin, polyamideimide resin, polyvinyl phenol resin, melamine resin, phenol resin, epoxy resin, and alkyd resin. Further, it may be a resin having a structure in which a resin having a polymerizable functional group and a monomer having a polymerizable functional group are crosslinked.

[0071] Further, the undercoat layer may contain an inorganic compound or an organic compound in addition to the resin. Examples of the inorganic compound include metals, oxides, and salts. Examples of the metal include gold, silver, aluminum, etc. Examples of the oxide include zinc oxide, lead white, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, indium oxide, tin oxide, zirconium oxide, etc. Examples of the salt include barium sulfate, strontium titanate.

[0072] These inorganic compounds may be present in the film in a particulate state. The number average particle diameter of the particles is preferably 1 nm or more and 500 nm or less, and more preferably 3 nm or more and 400 nm or less. These inorganic compounds may have a laminated structure having core particles and a coating layer covering the particles. The surfaces of these inorganic compounds may be treated with silicone oil, silane compounds, silane coupling agents, other organosilicon compounds, organic titanium compounds, etc. Further, elements such as tin, phosphorus, aluminum, niobium, etc. may be doped.

[0073] Examples of the organic compound include an electron transport compound and a conductive polymer. Examples of the conductive polymer include polythiophene, polyaniline, polyacetylene, polyphenylene, and polyethylene dioxythiophene.

[0074] Examples of the electron transport substance include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, halogenated aryl compounds, silole compounds, and boron-containing compounds. The electron transport substance has a polymerizable functional group and may crosslink with a resin having a functional group capable of reacting with those functional groups. Examples of the polymerizable functional group include a hydroxy group, a thiol group, an amino group, a carboxyl group, a vinyl group, an acryloyl group, a methacryloyl group, an epoxy group, etc.

[0075] These organic compounds may be present in the film in particulate form or may have a treated surface. Various additives such as a leveling agent such as silicone oil, a plasticizer, and a thickener may be added to the undercoat layer. The undercoat layer is obtained by preparing a coating solution for the undercoat layer containing the above materials, coating it on a support or a conductive layer, and then drying or curing this coating film.

[0076] Examples of the solvent for preparing the coating solution include alcohol solvents, ketone solvents, ether solvents, ester solvents, or aromatic hydrocarbon solvents. Examples of the dispersion method for dispersing particles in the coating solution include methods using a paint shaker, a sand mill, a ball mill, or a liquid collision type high-speed disperser.

[0077] <Photosensitive layer> The photosensitive layer of the electrophotographic photoreceptor is mainly classified into (1) a laminated photosensitive layer and (2) a single-layer photosensitive layer. (1) The laminated photosensitive layer is a photosensitive layer having a charge generation layer containing a charge generating substance and a charge transport layer containing a charge transport substance. (2) The single-layer photosensitive layer is a photosensitive layer containing both a charge generating substance and a charge transport substance.

[0078] (1) Laminated photosensitive layer The laminated photosensitive layer has a charge generation layer and a charge transport layer. (1-1) Charge generation layer The charge generation layer preferably contains a charge generating substance and a resin. Examples of the charge generating substance include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, phthalocyanine pigments, etc. Among these, azo pigments and phthalocyanine pigments are preferred. Among the phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred.

[0079] The content of the charge generating material in the charge generation layer is preferably 40% by mass or more and 85% by mass or less, more preferably 60% by mass or more and 80% by mass or less, based on the total mass of the charge generation layer. 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, and the like. Among these, polyvinyl butyral resin is more preferable.

[0080] Further, the charge generation layer may further contain additives such as an antioxidant and an ultraviolet absorber. Specifically, examples thereof include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, and the like. The charge generation layer can be formed by preparing a coating solution for the charge generation layer containing the above-mentioned respective materials and a solvent, forming this coating film on the 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, aromatic hydrocarbon-based solvents, and the like. The film thickness of the charge generation layer is preferably 0.1 μm or more and 1.5 μm or less, more preferably 0.15 μm or more and 1.0 μm or less.

[0081] (1 - 2) Charge transport layer The charge transport layer preferably contains a charge transport material and a resin. 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 substances. Among these, triarylamine compounds and benzidine compounds are preferable.

[0082] The content of the charge transport material in the charge transport layer is preferably 25% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 55% by mass or less, based on the total mass of the charge transport layer. Examples of the resin include polyester resin, polycarbonate resin, acrylic resin, polystyrene resin, etc. Among these, polycarbonate resin and polyester resin are preferred. As the polyester resin, polyarylate resin is particularly preferred. The content ratio (mass ratio) of the charge transport material to the resin is preferably 4:10 to 20:10, more preferably 5:10 to 12:10.

[0083] In addition, the charge transport layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, lubricity imparting agents, and wear resistance improving agents. Specifically, 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, boron nitride particles, etc. can be mentioned.

[0084] The charge transport layer can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned various materials and a solvent, forming this coating film on the charge generation layer, and drying it. Examples of the solvent used in the coating solution include alcohol solvents, ketone solvents, ether solvents, ester solvents, and aromatic hydrocarbon solvents. Among these solvents, ether solvents or aromatic hydrocarbon solvents are preferred. The film thickness of the charge transport layer is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

[0085] (2) Single-layer type photosensitive layer The single-layer photosensitive layer can be formed by preparing a coating liquid for the photosensitive layer containing a charge generating substance, a charge transporting substance, a resin, and a solvent, forming this coating film on the undercoat layer, and drying it. Examples of the charge generating substance, the charge transporting substance, and the resin are the same as those exemplified in the above "(1) laminated photosensitive layer". The film thickness of the single-layer photosensitive layer is preferably 10 μm or more and 45 μm or less, and more preferably 25 μm or more and 35 μm or less.

[0086] <Process cartridge, electrophotographic apparatus> The process cartridge of the present invention integrally supports the above electrophotographic photoreceptor and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachable from the main body of the electrophotographic apparatus. The electrophotographic apparatus of the present invention includes the above electrophotographic photoreceptor, and a charging means, an exposure means, a developing means, and a transfer means.

[0087] (Configuration of electrophotographic apparatus) FIG. 3 shows an example of the schematic configuration of an electrophotographic apparatus having a process cartridge equipped with the electrophotographic photoreceptor of the present invention. Note that the electrophotographic apparatus of this embodiment is a so-called tandem type electrophotographic apparatus provided with a plurality of image forming units a to d. The first image forming unit a forms an image with yellow (Y) toner, the second image forming unit b forms an image with magenta (M) toner, the third image forming unit c forms an image with cyan (C) toner, and the fourth image forming unit d forms an image with black (Bk) toner. These four image forming units are arranged in a row at a certain interval, and the configurations of the respective image forming units have many substantially common parts except for the color of the toner to be accommodated. Therefore, hereinafter, the electrophotographic apparatus of this embodiment will be described using the first image forming unit a.

[0088] The first image forming unit a includes a photosensitive drum 1a which is a drum-shaped electrophotographic photoreceptor, a charging roller 2a which is a charging member, and a developing means 4a (including a developing roller 41a). The photosensitive drum 1a is an image carrier that carries a toner image and is rotationally driven at a predetermined peripheral speed (process speed) in the direction of the illustrated arrow. The developing means 4a stores yellow toner and develops the photosensitive drum 1a with the yellow toner.

[0089] When control means (not shown) such as a controller receives an image signal, the image forming operation is started and the photosensitive drum 1a is rotationally driven. During the rotation of the photosensitive drum 1a, it is uniformly charged to a predetermined voltage (charging voltage) with a predetermined polarity (negative polarity in this embodiment) by the charging roller 2a, and is exposed by the exposure means 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 means 4a at the developing position and visualized as a yellow toner image on the photosensitive drum 1a. Here, the normal charging polarity of the toner stored in the developing means 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 apparatus that positively develops an electrostatic latent image with toner charged to the opposite polarity to the charging polarity of the photosensitive drum 1a.

[0090] Also, a large number of convex portions derived from particles can be provided on the surface layer of the charging roller 2a. The convex portions provided on the surface layer of the charging roller 2a serve as spacers between the charging roller 2a and the photosensitive drum 1a in the charging portion. When transfer residual toner, which is toner remaining on the photosensitive drum 1a without being transferred in the primary transfer portion described later, enters the charging portion, the convex portions prevent the charging roller 2a from being contaminated by the transfer residual toner by touching the transfer residual toner at locations other than the convex portions.

[0091] The pre-exposure unit 5a as the discharging means discharges by exposing the surface of the photosensitive drum 1a before the surface of the photosensitive drum 1a is charged by the charging roller 2a. By discharging the surface of the photosensitive drum 1a, it has the role of equalizing the surface potential formed on the photosensitive drum 1 and the role of controlling the discharge amount due to discharge occurring in the charging portion.

[0092] The endless and movable intermediate transfer belt 10 has conductivity, contacts the photosensitive drum 1a to form a primary transfer portion, and rotates at substantially the same peripheral speed as the photosensitive drum 1a. Further, the intermediate transfer belt 10 is stretched by an opposing roller 13 as an opposing member, a driving roller 11 and a stretching roller 12 as stretching members, and a metal roller 14a, and is stretched by the stretching roller 12 with a tension of 60 N. The intermediate transfer belt 10 can be moved by rotationally driving the driving roller 11 in the direction of the arrow shown in the figure.

[0093] The yellow toner image formed on the photosensitive drum 1a is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10 in the process of passing through the primary transfer portion. During primary transfer, a current is supplied from a secondary transfer roller 15, which is a secondary transfer member that contacts the outer peripheral surface of the intermediate transfer belt 10, to the conductive intermediate transfer belt 10. When the current supplied from the secondary transfer roller 15 flows in the circumferential direction of the intermediate transfer belt 10, the toner image is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10. At this time, a voltage of a predetermined polarity (positive polarity in this embodiment) opposite to the normal charging polarity of the toner is applied from a transfer power source (not shown) to the secondary transfer roller 15.

[0094] Similarly, a second-color magenta toner image, a third-color cyan toner image, and a fourth-color black toner image are formed and sequentially transferred and superimposed on the intermediate transfer belt 10. As a result, four-color toner images corresponding to the target color image are formed on the intermediate transfer belt 10. Thereafter, the four-color toner images carried on the intermediate transfer belt 10 are collectively secondarily transferred onto the surface of a transfer material P such as a sheet of paper or an OHP sheet fed by the paper feeding means 50 in the process of passing through a secondary transfer portion formed by the contact between the secondary transfer roller 15 and the intermediate transfer belt 10. The transfer material P onto which the four-color toner images are transferred by secondary transfer is then heated and pressurized by the fixing means 30, whereby the four colors of toner are melted and mixed and fixed to the transfer material P. The toner remaining on the intermediate transfer belt 10 after secondary transfer is cleaned and removed by belt cleaning means 16 provided to face the opposing roller 13 via the intermediate transfer belt 10. The electrophotographic photoreceptor of the present invention can be used in a laser beam printer, an LED printer, a copying machine, and the like.

Example

[0095] Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples. The present invention is not limited in any way by the following examples, provided that the gist thereof is not exceeded. In the description of the following examples, "parts" means based on mass unless otherwise specified. In addition, the film thicknesses other than the surface layer of the electrophotographic photoreceptors of the examples and comparative examples were determined using an eddy current type film thickness meter (product name: Fischerscope, manufacturer: Fischer Instruments), or were determined by specific gravity conversion from the mass per unit area.

[0096] <Manufacturing Example (1) of Electrophotographic Photoreceptor 1> An aluminum cylinder having a diameter of 20 mm and a length of 257.5 mm (standard: JIS-A3003 aluminum alloy) was used as a support (conductive support). The support, conductive layer, undercoat layer, charge generation layer, charge transport layer, and surface layer were produced by the following method.

[0097] (Preparation of Coating Liquid for Conductive Layer) As the substrate, anatase titanium oxide with an average primary particle size of 200 nm was used, and a titanium niobium sulfate solution containing 33.7 parts of titanium in terms of TiO2 and 2.9 parts of niobium in terms of Nb2O5 was prepared. 100 parts of the substrate was dispersed in pure water to form a 1000-part suspension, which was heated to 60 °C. The titanium niobium sulfate solution and 10 mol / L sodium hydroxide were added dropwise to the suspension over 3 hours so that the pH of the suspension became 2 - 3. After the total amount was added dropwise, the pH was adjusted to near neutrality, and a polyacrylamide-based flocculant was added to precipitate the solid content. The supernatant was removed, filtered and washed, and dried at 110 °C to obtain an intermediate containing 0.1% by mass of organic matter derived from the flocculant in terms of C. This intermediate was calcined in nitrogen at 750 °C for 1 hour and then in air at 450 °C to produce titanium oxide particles 1. The obtained particles had an average primary particle size of 220 nm in the particle size measurement method using the aforementioned scanning electron microscope.

[0098] Subsequently, 50 parts of a phenol resin (monomer / oligomer of the phenol resin) (product name: Pryophen J-325, manufacturer: DIC Corporation, resin solid content: 60%, density after curing: 1.3 g / cm2) as a binder material was dissolved in 35 parts of 1-methoxy-2-propanol as a solvent to obtain a solution.

[0099] 60 parts of titanium oxide particles 1 was added to this solution, and the mixture was put into a vertical sand mill using 120 parts of glass beads with an average primary particle size of 1.0 mm as a dispersion medium. Then, a dispersion treatment was carried out for 4 hours under the conditions of a dispersion liquid temperature of 23 ± 3 °C and a rotation speed of 1500 rpm (peripheral speed 5.5 m / s) to obtain a dispersion liquid. The glass beads were removed from this dispersion liquid with a mesh. To the dispersion liquid after removing the glass beads, 0.01 part of silicone oil (product name: SH28PAINTADDITIVE, manufacturer: Toray Dow Corning Co., Ltd.) as a leveling agent and silicone resin particles (product name: KMP-590, manufacturer: Shin-Etsu Chemical Co., Ltd., average primary particle size: 2 μm, density: 1.3 g / cm 3)Eight parts were added and stirred. Then, a coating solution for the conductive layer was prepared by pressure filtration using a PTFE filter paper (product name: PF060, manufacturer: Advantec Toyo Co., Ltd.).

[0100] (Preparation of the coating solution for the undercoat layer) 100 parts of rutile-type titanium oxide particles (average primary particle size: 50 nm, manufacturer: Teika Co., Ltd.) were stirred and mixed with 500 parts of toluene. 3.5 parts of vinyltrimethoxysilane (product name: KBM-1003, manufacturer: Shin-Etsu Chemical Co., Ltd.) were added, and dispersion treatment was carried out for 8 hours using a vertical sand mill with glass beads having a diameter of 1.0 mm. After removing the glass beads, toluene was distilled off under reduced pressure and dried at 120 °C for 3 hours to obtain rutile-type titanium oxide particles surface-treated with an organosilicon compound. When the volume of the obtained titanium oxide particles was a and the average primary particle size of the titanium oxide particles was b [μm], a / b = 15.6. The value of a was determined from a microscopic image of the cross-section of the electrophotographic photoreceptor using a field emission scanning electron microscope (FE-SEM, product name: S-4800, manufacturer: Hitachi High-Technologies Corporation) after the electrophotographic photoreceptor was produced.

[0101] 18.0 parts of the rutile-type titanium oxide particles surface-treated with the organosilicon compound, 4.5 parts of N-methoxymethylated nylon (product name: Torelina (registered trademark) EF-30T, manufacturer: Nagase ChemteX Corporation), and 1.5 parts of a copolymer nylon resin (product name: Amilan (registered trademark) CM8000, manufacturer: Toray Industries, Inc.) were added to a mixed solvent of 90 parts of methanol and 60 parts of 1-butanol to prepare a dispersion. This dispersion was subjected to dispersion treatment for 5 hours using a vertical sand mill with glass beads having a diameter of 1.0 mm, and the glass beads were removed to prepare a coating solution for the undercoat layer.

[0102] (Synthesis of phthalocyanine pigment) (Synthesis example) In an atmosphere of nitrogen flow, 100 g of gallium trichloride and 291 g of orthophthalonitrile were added to 1000 mL of α-chloronaphthalene, and after reacting at 200 °C for 24 hours, the product was filtered. The obtained wet cake was heated and stirred at 150 °C for 30 minutes using N,N-dimethylformamide, and then filtered. The obtained filtrate was washed with methanol and then dried to obtain a chlorogallium phthalocyanine pigment in a yield of 83% by mass. 20 g of the chlorogallium phthalocyanine pigment obtained by the above method was dissolved in 500 mL of concentrated sulfuric acid, stirred for 2 hours, and then dropped into a mixed solution of 1700 mL of distilled water cooled with ice and 660 mL of concentrated aqueous ammonia for reprecipitation. This was thoroughly washed with distilled water and dried to obtain a hydroxygallium phthalocyanine pigment.

[0103] (Preparation of coating liquid for charge generation layer) 0.5 part of the hydroxygallium phthalocyanine pigment obtained in the synthesis example, 7.5 parts of N,N-dimethylformamide (product code: D0722, manufacturer: Tokyo Chemical Industry Co., Ltd.), and 29 parts of glass beads with a diameter of 0.9 mm were milled at 25 °C for 24 hours using a sand mill (product name: BSG-20, manufacturer: Aimax Co., Ltd.). At this time, it was carried out under the condition that the disk rotates 1500 times per minute. The liquid thus treated was filtered through a filter (product number: N-NO.125T, pore diameter: 133 μm, manufacturer: NBC Mesh Tech Co., Ltd.) to remove the glass beads. 30 parts of N,N-dimethylformamide was added to this liquid, and then filtered. The filtrate on the filter was thoroughly washed with n-butyl acetate. Then, the washed filtrate was vacuum dried to obtain 0.45 part of the hydroxygallium phthalocyanine pigment. The obtained pigment contained N,N-dimethylformamide.

[0104] Subsequently, 20 parts of hydroxygallium phthalocyanine pigment obtained by the milling process, 10 parts of polyvinyl butyral (product name: Esrec (registered trademark) BX-1, manufacturer: Sekisui Chemical Co., Ltd.), 190 parts of cyclohexanone, and 482 parts of glass beads with a diameter of 0.9 mm were dispersed at a cooling water temperature of 18°C for 4 hours using a sand mill (product name: K-800, manufacturer: Igarashi Machinery Manufacturing (now: Aimax Co., Ltd.), disk diameter 70 mm, number of disks 5). At this time, it was carried out under the condition that the disk rotated 1800 times per minute. The glass beads were removed from this dispersion, and 444 parts of cyclohexanone and 634 parts of ethyl acetate were added to prepare a coating solution for the charge generation layer.

[0105] (Preparation of Coating Solution for Charge Transport Layer) (Production Example of Charge Transport Layer) Next, the following materials were prepared to prepare a mixed solvent. o-Xylene 25 parts by mass Methyl benzoate 25 parts by mass Dimethoxymethane 25 parts by mass Furthermore, the following materials were dissolved in the above mixed solvent to prepare a coating solution for the charge transport layer. 5 parts by mass of a charge transport substance (hole transport substance) represented by the following structural formula (C-1) 5 parts by mass of a charge transport substance (hole transport substance) represented by the following structural formula (C-2) Polycarbonate (product name: Iupilon (registered trademark) Z400, manufacturer: Mitsubishi Engineering-Plastics Corporation) 10 parts by mass This coating solution 1 for the charge transport layer was dip-coated on the charge generation layer 1 to form a coating film, and the coating film was dried at a drying temperature of 40°C for 5 minutes to form a charge transport layer 1 with a film thickness of 15 μm.

Chemical formula

Chemical formula

[0106] (Production Example of Electrophotographic Photoconductor 1 (2)) (Support) An aluminum cylinder with a diameter of 20 mm and a length of 257.5 mm (standard: JIS - A3003, aluminum alloy) was used as the support (conductive support).

[0107] (Conductive layer) The coating solution for the conductive layer was dip - coated on the above - mentioned support to form a coating film, and the coating film was heated and cured at 150 °C for 30 minutes to form a conductive layer with a film thickness of 22 μm.

[0108] (Undercoat layer) The coating solution for the undercoat layer was dip - coated on the above - mentioned conductive layer to form a coating film, and the coating film was heated and cured at 100 °C for 10 minutes to form an undercoat layer with a film thickness of 1.8 μm.

[0109] (Charge - generating layer) The coating solution for the charge - generating layer was dip - coated on the above - mentioned undercoat layer to form a coating film, and the coating film was heated and dried at a temperature of 100 °C for 10 minutes to form a charge - generating layer with a film thickness of 0.20 μm.

[0110] (Charge - transporting layer) The coating solution for the charge - transporting layer was dip - coated on the above - mentioned charge - generating layer to form a coating film, and the coating film was heated and dried at a temperature of 120 °C for 30 minutes to form a charge - transporting layer with a film thickness of 21 μm.

[0111] (Surface layer) For the binder resin, the first particles, the second particles, and the additives, commercially available products or those synthesized by oneself may be used. The method for producing niobium - doped titanium oxide will be described later. · Preparation of anatase - type titanium oxide Anatase - type titanium oxide particles can be produced by a 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 hydrated titanium dioxide slurry, and the titanium dioxide slurry is dehydrated and calcined. Thereby, anatase - type titanium oxide with an anatase degree of almost 100% can be obtained. In the above method, by controlling the solution concentration of titanyl sulfate, anatase-type titanium oxide particles 1 to 11 as shown in Table 1 were prepared.

[0112]

Table 1

[0113] · Preparation of conductive particles 1 Niobium(V) hydroxide was dissolved in concentrated sulfuric acid and mixed with an aqueous solution of titanyl sulfate to prepare an acidic mixed solution of niobium salt and titanium salt (hereinafter referred to as "titanium-niobium mixed solution"). Using anatase-type titanium oxide particles 1 as core particles, they were dispersed in water to form a suspension, and heated to 70 °C while stirring. While maintaining the pH at 2.5, an aqueous solution of sodium hydroxide and a titanium-niobium mixed solution containing 337 g / kg of Ti and 10.3 g / kg of Nb were simultaneously added with respect to the weight of anatase-type titanium oxide particles 1.

[0114] After the dropping was completed, the suspension was filtered, washed, and dried at 110 °C for 8 hours. This dried product was calcined at 725 °C for 1 hour in a nitrogen atmosphere to obtain titanium oxide doped with niobium with niobium atoms unevenly distributed near the surface. 100.0 parts of this niobium-doped titanium oxide was mixed with 6.0 parts of the compound represented by the following formula (S-1) (product name: trimethoxypropylsilane, manufactured by Tokyo Chemical Industry Co., Ltd.) and 200 parts of toluene, stirred with a stirrer for 4 hours, filtered, washed, and then heat-treated at 120 °C for 3 hours to obtain conductive particles 1 of niobium-doped titanium oxide with an average particle diameter of 70 nm.

[0115] The obtained niobium-doped titanium oxide was observed with a transmission electron microscope (product name: JEM2800, manufacturer: JEOL Ltd.), and the ratios of niobium atoms to titanium atoms in the center of the particles and within 5% of the particle diameter from the particle surface were measured by EDS (product name: NORAN SYSTEM7, manufacturer: Thermo Fisher Scientific). The observation was performed on 10 particles in each sliced sample, and the arithmetic mean value was adopted. The ratios of niobium atoms to titanium atoms in the obtained particle centers and within 5% of the particle diameter from the particle surface were designated as α1 and α2, respectively. When α2 / α1 was defined as the niobium segregation ratio and calculated, the value was 7.7. The measurement conditions for EDS were an acceleration voltage of 200 kV and a beam diameter of 1.0 nm.

[0116] In the production of niobium-doped titanium oxide, by changing the type of core particles used and the weight ratio of niobium atoms to titanium atoms in the titanium-niobium mixed solution with respect to the core material, the average particle diameter, volume resistivity, and niobium segregation ratio of niobium-doped titanium oxide can be varied. The details of the niobium-doped titanium oxide prototype produced this time are described in Table 2. Note that it can be confirmed by EDS that the coating layer is niobium-doped titanium oxide.

[0117] Also, referring to the obtained STEM images, the film thickness of the coating layer was estimated from the thickness of the portion where the density near the surface was lower compared to the density at the center of the particles and described in Table 2. In addition, the oxygen deficiency rate of the conductive particle 1 was measured using a thermogravimetric analyzer (product name: Q5000IR, manufacturer: TA Instruments). The heating rate during measurement was 10 °C / min, and the measurement was performed under an oxygen stream. In the range from 300 °C to 900 °C, the mass at the temperature at which the mass started to increase was taken as the minimum mass, and the oxygen deficiency rate was determined from the minimum mass and the maximum mass during subsequent heating and described in Table 2.

[0118] Also, the ratio of the oxygen deficiency rate of the core material of the conductive particle 1 to the oxygen deficiency rate of the coating layer can be measured by energy-dispersive X-ray analysis (EDS). Also, the oxygen deficiency rate β in the region within 5% of the primary particle diameter and the oxygen deficiency rate γ in the other regions were measured by energy dispersive X-ray analysis (EDS) using STEM from the surface of the niobium-doped titanium oxide particles, and the values of β / γ are shown in Table 2. [Chemical formula]

[0119] <Production of Conductive Particles 2 to 17> In the production of conductive particle 1, except that the type of core material particles used and the weights of niobium atoms and titanium atoms in the titanium-niobium mixed solution were changed as shown in Table 2, conductive particles 2 to 17 were produced in the same manner as in the production of conductive particle 1. The average particle diameters, volume resistivities, and niobium segregation ratios of the obtained conductive particles 2 to 17 are shown in Table 2.

[0120] <Quantification of Niobium Atoms Contained in Conductive Particles> The quantification of niobium atoms contained in conductive particles is performed as follows. The conductive particles are pelletized by the following press molding to prepare a sample. Using the prepared sample, measurement is performed with a fluorescence X-ray analyzer (XRF), and the niobium atom content of the entire conductive particles is quantified by the FP method. Specifically, quantification is performed as niobium pentoxide and converted to the niobium atom content contained.

[0121] (i) Example of Equipment Used Fluorescence X-ray Analyzer 3080 (Rigaku Corporation) (ii) Sample Preparation For sample preparation, a sample press molding machine MAEKAWA Testing Machine (manufacturer: MFG Co, LTD) is used. 0.5 g of conductive particles are placed in an aluminum ring (model number: 3481E1), set to a load of 5.0 tons, and pressed for 1 minute to pelletize. (iii) Measurement Conditions Measurement diameter: 10φ Measurement potential, voltage: 50 kV, 50 - 70 mA 2θ angle: 25.12° Crystal plate: LiF Measurement time: 60 seconds

[0122]

Table 2

[0123] The ratio S1 of the area occupied by the first particles to the total area when viewing the surface layer from above, and the ratio S2 of the area occupied by the second particles can be mainly adjusted by the mixing ratio of the resin and the particles. For example, by increasing the mixing ratio of the particles with respect to the resin amount, the ratio of (S1 + S2) can be increased. Also, (S1 / S2) can be adjusted by adjusting the mixing ratio of the first particles and the second particles.

[0124] The exposed height L1 of the first particles and the exposed height L2 of the second particles exposed on the surface of the electrophotographic photoreceptor can be adjusted by the drying temperature after coating, the type of solvent, and the solid content of the coating liquid. For example, by using a solvent type with a high evaporation rate, the convection during drying becomes faster and the exposed height of the particles tends to increase. For the same reason, even if the drying temperature after coating is increased, the exposed height of the particles increases. When the solid content of the coating liquid is increased, the convection is suppressed, so the exposed height of the particles tends to decrease.

[0125] The film thickness T1 of the surface layer of the electrophotographic photoreceptor can be adjusted by the solid content of the coating liquid and the coating speed during impregnation coating. For example, when the solid content of the coating liquid is increased, the film thickness T1 becomes thicker. Also, by increasing the coating speed during impregnation coating, the film thickness T1 becomes thicker.

[0126] <Manufacturing Example (3) of Electrophotographic Photoreceptor 1> <Preparation of Coating Liquid 1 for Surface Layer> 68.40 parts of conductive particles 6 as the first particles 3.78 parts of silica particles ("QSG-80", manufacturer: Shin-Etsu Chemical Co., Ltd.) as the second particles 3.60 parts of the compound represented by the following formula (O-1) as the binder resin 91 parts of 1-propanol 91 parts of cyclohexane They were mixed and stirred with a stirring and dispersing device for 6 hours to prepare the coating liquid 1 for the surface layer.

Chemical formula

[0127] <Manufacturing examples of electrophotographic photoreceptors 2 to 52> In the manufacturing example of the electrophotographic photoreceptor 1, up to the charge transport layer, it was produced in the same manner, and the materials of the coating liquids 2 to 52 for the surface layer used in the production of the surface layer were changed as shown in Table 3 and prepared. At this time, the dispersion process of the coating liquid for the surface layer was appropriately adjusted. Using the prepared coating liquids for the surface layer respectively, electrophotographic photoreceptors 2 to 52 were produced in the same manner as electrophotographic photoreceptor 1. That is, electrophotographic photoreceptors 2 to 52 were each produced in the same manner as electrophotographic photoreceptor 1 using the coating liquids 2 to 52 for the surface layer. At this time, the coating conditions in the coating process of the surface layer of the electrophotographic photoreceptor were appropriately adjusted. The results are shown in Table 4. In Table 4, in the EDS analysis by scanning transmission electron microscope (STEM) of niobium-doped titanium oxide particles, the concentration ratio calculated by niobium atomic concentration / titanium atomic concentration at the center of the niobium-doped titanium oxide particles, with respect to the concentration ratio calculated by niobium atomic concentration / titanium atomic concentration within 5% of the primary particle diameter of the niobium-doped titanium oxide particles from the surface of the niobium-doped titanium oxide particles, was described as "Nb concentration / Ti concentration at the center of the first particle with respect to Nb concentration / Ti concentration within 5% of the primary particle diameter from the surface of the first particle".

[0128]

Table 3

[0129] Details about the first particle and the second particle are QSG-10 (Manufacturer: Shin-Etsu Chemical Co., Ltd.) QSG-30 (Manufacturer: Shin-Etsu Chemical Co., Ltd.) QSG-80 (Manufacturer: Shin-Etsu Chemical Co., Ltd.) QSG-100 (Manufacturer: Shin-Etsu Chemical Co., Ltd.) QSG-170 (Manufacturer: Shin-Etsu Chemical Co., Ltd.) KE-P30 (Manufacturer: Nippon Shokubai Co., Ltd.) KE-P150 (Manufacturer: Nippon Shokubai Co., Ltd.) Carbon Black (Product Name: Thermax Flow Foam N990, Manufacturer: CanCarb) Indium Tin Oxide, Blue (Manufacturer: Core Front Co., Ltd.) ZnO-S05 (Manufacturer: Sumitomo Osaka Cement Co., Ltd.).

[0130] (Density) The density of the particles was measured by the pycnometer (liquid phase replacement) method using butanol as the dispersion solvent. Also, the density and specific gravity of the particles can be referred to the published values in the database POLYINFO of the manufacturer of each material and the National Institute for Materials Science. For example, the density of silica particles is 1.8 g / cm 3 and the density of magnesium oxide is 3.65 g / cm 3 and the density of aluminum oxide is 3.65 g / cm 3 and the density of titanium oxide is 4.0 g / cm 3 and the density of zinc oxide is 5.6 g / cm 3 and the density of carbon black is 1.8 g / cm 3 and

[0131]

Table 4

[0132] <Comparative Example> In the manufacturing example of the electrophotographic photoreceptor 1, up to the charge transport layer, it was fabricated in the same manner, and the materials of the coating liquids C1 to C18 for the surface layer used in the fabrication of the surface layer were changed as shown in Table 5 and prepared. Using each of the prepared coating liquids for the surface layer, electrophotographic photoreceptors C1 to C18 were fabricated in the same manner as the electrophotographic photoreceptor 1. That is, electrophotographic photoreceptors C1 to C18 were each fabricated in the same manner as the electrophotographic photoreceptor 1 using the coating liquids C1 to C18 for the surface layer. The results are shown in Table 6. In Table 6, in the EDS analysis by scanning transmission electron microscope (STEM) of niobium-doped titanium oxide particles, the concentration ratio calculated by niobium atomic concentration / titanium atomic concentration at the center of the niobium-doped titanium oxide particles, with respect to the concentration ratio calculated by niobium atomic concentration / titanium atomic concentration within 5% of the primary particle diameter of the niobium-doped titanium oxide particles from the surface of the niobium-doped titanium oxide particles, is described as "Nb concentration / Ti concentration at the center of the first particle with respect to Nb concentration / Ti concentration within 5% of the primary particle diameter from the surface of the first particle".

[0133]

Table 5

[0134]

Table 6

[0135] [Evaluation method] <Measurement of the ratio S1 of the area occupied by the first particles and the area S2 occupied by the second particles with respect to the total area when viewing the surface layer from above>[ An electrophotographic photoreceptor with a total length of 257.5 mm in the longitudinal direction was cut into 5 mm square sample pieces using an instrument such as a saw. At this time, the cut positions were at 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, and 5 mm square sample pieces were cut at 90° intervals in the circumferential direction, for a total of 12 points. The sample pieces were fixed to a sample holder so that the surface layer could be observed. The sample holder with the sample pieces fixed was subjected to surface observation using a scanning electron microscope (hereinafter also referred to as "SEM", product name: JSM7800F, manufacturer: JEOL Ltd.). Image processing was performed on the surface image of the electrophotographic photoreceptor surface obtained by SEM, and the total area of the insulating particle portion and the total area of the conductive particle portion with respect to the total observed area were designated as s1 [%] and s2 [%], respectively (see Figure 3). The conductive particles and the insulating particles were distinguished using the SEM-EDX function. The above operations were performed on 12 sample pieces, and the respective s1 and s2 were obtained. The arithmetic mean of s1 for 12 points was defined as S1 of the electrophotographic photoreceptor, and the arithmetic mean of s2 for 12 points was defined as S2 of the electrophotographic photoreceptor.

[0136] <Measurement of the exposure height L1 of the first particle and the exposure height L2 of the second particle> L1 and L2 were determined by FIBSEM observation as follows. An electrophotographic photoreceptor with a total length of 257.5 mm in the longitudinal direction was cut into 5 mm square sample pieces using an instrument such as a saw. At this time, the cut positions were at 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, and 5 mm square sample pieces were cut at 90° intervals in the circumferential direction, for a total of 12 points. The sample pieces were fixed to a sample holder so that the surface layer could be observed. The sample holder with the sample pieces fixed was subjected to cross-sectional observation using FIBSEM (product name: Nvision, manufacturer: ZEISS). The measurement conditions will be described later. In the cross-sectional image of the surface layer of the electrophotographic photoreceptor obtained by FIBSEM, numbers were sequentially assigned to the first particles from the left side of the image.

[0137] Lines A1 and B1 were drawn that are perpendicular to the lower layer interface and touch the end of the first particle numbered 1. Lines A1 and B1 are perpendicular to the lower layer interface and parallel to each other, and line A1 is always located to the left of line B1. This operation was performed on all the first particles that exist within the cross-sectional image and whose overall image is contained within the cross-sectional image. Then, the intersection of line A1 and the lower layer interface was designated as a1, the intersection of line A2 and the lower layer interface as a2, and the length of the line connecting intersection a1 and intersection a2 was defined as the unit measurement range C1. The unit measurement range was determined for all lines AX (X = 1, 2, 3, ···), and they were respectively designated as unit measurement ranges CX (X = 1, 2, 3, ···). In each unit measurement range CX, the longest line that is perpendicular to the lower layer interface and intersects the surface layer surface boundary line was defined as the film thickness tX (X = 1, 2, 3, ···) of the unit measurement range CX, and the shortest line was defined as the recess vX (X = 1, 2, 3, ···) of the unit measurement range CX.

[0138] Furthermore, the longest line that is perpendicular to the lower layer interface and intersects the surface layer surface boundary line formed by the second particles was defined as the small protrusion wX (X = 1, 2, 3, ···) of the unit measurement range CX. Then, the difference between the length of line tX and the length of line vX was defined as the exposure height l1-X (X = 1, 2, 3, ···) of the first particle, and the difference between the length of line wX and the length of line vX was defined as the exposure height l2-X (X = 1, 2, 3, ···) of the second particle. The arithmetic mean value of the obtained exposure height l1 of the first particle was defined as the average exposure height of the first particle in the cross-sectional image, and the arithmetic mean value of the exposure height l2 of the second particle was defined as the average exposure height of the second particle in the cross-sectional image. The arithmetic mean of the exposure heights l1 and l2 of each of the 12 sample pieces was further defined as the exposure height L1 of the first particle and the exposure height L2 of the second particle on the surface layer of the electrophotographic photoreceptor.

[0139] The measurement conditions of the FIBSEM are as follows. Three-dimensionalization of a 2μm × 2μm × 2μm area of the surface layer was performed using Slice&View of the FIB-SEM. The conditions of Slice&View were as follows. Sample processing for analysis: FIB method Processing and observation apparatus: NVision40 manufactured by SII / Zeiss Slice interval: 10nm (Observation conditions) Accelerating voltage: 1.0 kV Specimen tilt: 54° WD: 5 mm Detector: BSE detector Aperture: 60 μm, high current ABC: ON Image resolution: 1.25 nm / pixel Also, the measurement environment is temperature: 23°C, pressure: 1×10 -4 Pa. As for the processing and observation apparatus, Strata400S (specimen tilt: 52°) manufactured by FEI can also be used. The analysis area is 2 μm in length × 2 μm in width, and information for each cross-section is integrated to obtain the volume V per 2 μm in length × 2 μm in width × 2 μm in thickness (8 μm 3 ) of the surface layer on the surface. Also, image analysis for each cross-section was performed using image processing software (product name: Image-Pro Plus, manufacturer: Media Cybernetics).

[0140]

[0141] <Measurement of the average primary particle size D1 of the first particle and the average primary particle size D2 of the second particle> First, the entire electrophotographic photoreceptor was dipped into methyl ethyl ketone (MEK) in a female cylinder and irradiated with ultrasonic waves to peel off the resin layer. Then, the substrate of the electrophotographic photoreceptor was taken out. Next, the insoluble components (photosensitive layer and surface layer containing metal oxide particles) that were insoluble in MEK were filtered and dried in a vacuum dryer. Further, the obtained solid was suspended in a mixed solvent of tetrahydrofuran (THF) / methylal with a volume ratio of 1:1. After filtering the insoluble components, the filtrate was collected and dried in a vacuum dryer. By this operation, the first particles, the second particles, and the resin of the surface layer were obtained. Further, the filtrate was heated to 500 °C in an electric furnace so that only the first particles and the second particles remained as solids, and the first particles and the second particles were recovered. To ensure the required amount for measurement, the same treatment was applied to a plurality of electrophotographic photoreceptors for the first particles and the second particles.

[0142] A part of the recovered metal oxide particles was dispersed in isopropanol (IPA), and the dispersion was dropped onto a grid mesh with a support film (product name: Cu150J, manufacturer: JEOL Ltd.). Observation of the first particles and the second particles was performed in the STEM mode of a scanning transmission electron microscope (product name: JEM2800, manufacturer: JEOL Ltd.). The observation was carried out at a magnification of 500,000 to 1,200,000 times so that the first particles and the second particles could be easily calculated, and 100 STEM images of each of the first particles and the second particles were taken. The first particles and the second particles were distinguished using the EDX function of a scanning electron microscope. At this time, the acceleration voltage was set to 200 kV, the probe size was 1 nm, and the image size was 1024 × 1024 pixels.

[0143] Using the obtained STEM images, the primary particle size was measured with the image processing software "Image-Pro Plus (manufacturer: Media Cybernetics)". First, using the straight line tool (Straight Line) on the toolbar, select the scale bar displayed at the bottom of the STEM image. In this state, select Set Scale in the Analyze menu, and a new window will open. The pixel distance of the selected straight line will be entered in the Distance in Pixels column. Enter the value of the scale bar (e.g., 100) in the Known Distance column of the window, enter the unit of the scale bar (e.g., nm) in the Unit of Mesurement column, and click OK to complete the scale setting. Next, using the straight line tool, draw a straight line so that it represents the maximum diameter of the metal oxide particles, and calculate the particle size. The same operation was performed on 100 metal oxide particles, and the arithmetic mean value of the obtained values (maximum diameter) was taken as the primary particle size of the metal oxide particles. However, for the sample using carbon black as the first particle, the average primary particle size of the first particle was measured by the following method.

[0144] An electrophotographic photoreceptor with a total length of 257.5 mm in the longitudinal direction was cut into 5 mm square sample pieces using an instrument such as a saw. At this time, the cutting positions were at 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, and 5 mm square sample pieces were cut at 90° intervals in the circumferential direction, for a total of 12 points. The sample pieces were fixed in a sample holder so that the surface layer could be observed. Cross-sectional observation of the sample holder with the fixed sample pieces was performed using FIBSEM (product name: [Nvision], manufacturer: ZEISS). The measurement conditions were the same as described above. In the cross-sectional image of the surface layer of the electrophotographic photoreceptor obtained by FIBSEM, the particle size of the first particle was measured. This operation was performed on all the first particles present in the cross-sectional image and whose entire image was within the cross-sectional image. The arithmetic mean value of the obtained particle sizes of the first particles was taken as the average particle size of the sample piece, and the arithmetic mean of the average particle sizes of each of the 12 sample pieces was taken as the average primary particle size D1 of the first particles in the surface layer of the electrophotographic photoreceptor.

[0145] <Measurement of powder resistivity R1 and powder resistivity R2> <Press the first particles into a pellet-shaped measurement sample at a pressure of 300 kg / cm 2 and measure the powder resistivity R1 with an applied voltage of 100 V using a four-probe resistivity measuring device (product name: Loresta (registered trademark), manufacturer: Mitsubishi Chemical Corporation). The powder resistivity R2 was also measured in the same manner for the second particles.

[0146] <Measurement of film thickness T1> An electrophotographic photoreceptor with a total length of 257.5 mm in the longitudinal direction was cut into 5 mm square sample pieces using a tool such as a saw. At this time, the cutting positions were 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, and 5 mm square sample pieces were cut at 90° intervals in the circumferential direction, for a total of 12 points. The sample pieces were fixed to a sample holder so that the surface layer could be observed. Cross-sectional observation of the sample holder with the sample pieces fixed was performed using FIBSEM (product name: Nvision, manufacturer: ZEISS). The measurement conditions were the same as described above.

[0147] Figures 4 and 5 show cross-sections of the surface layer of the electrophotographic photoreceptor. As shown in Figure 4, in the cross-sectional image of the surface layer of the electrophotographic photoreceptor obtained by FIBSEM, the first particles were numbered sequentially from 1 from the left side of the image. Straight lines A1 and B1 were drawn in contact with the end of the first particle numbered 1 and perpendicular to the lower layer interface. Straight lines A1 and B1 are perpendicular to the lower layer interface and parallel to each other, and straight line A1 is always located on the left side of straight line B1. This operation was performed on all the first particles existing within the cross-sectional image and whose entire image was within the cross-sectional image. Then, the intersection of straight line A1 and the lower layer interface was designated as a1, the intersection of straight line A2 and the lower layer interface was designated as a2, and the length of the straight line connecting intersection a1 and intersection a2 was defined as the unit measurement range C1. The unit measurement range was obtained for all straight lines AX (X = 1, 2, 3, ···), and they were respectively designated as unit measurement ranges CX (X = 1, 2, 3, ···).

[0148] As shown in FIG. 5, in each unit measurement range CX, the longest line that is orthogonal to the lower interface and intersects the surface boundary line of the surface layer is defined as the film thickness tX (X = 1, 2, 3, ···) of the unit measurement range CX. The arithmetic mean value of the obtained film thicknesses tX is defined as the average film thickness of the cross-sectional image, and the arithmetic mean of the average film thicknesses of each of the 12 sample pieces is defined as the film thickness T1 of the surface layer of the electrophotographic photoreceptor.

[0149] <Calculation of the niobium atom / titanium atom concentration ratio in the conductive particles contained in the electrophotographic photoreceptor> A 5 mm square sample piece was cut out from the electrophotographic photoreceptor and sliced into a 200 nm thick slice at a cutting speed of 0.6 mm / s using an ultrasonic ultramicrotome (product name: UC7, manufacturer: Leica) to prepare a thin sample. This thin sample was observed in the STEM mode of a scanning transmission electron microscope (product name: JEM2800, manufacturer: JEOL) connected to an EDS analyzer (energy dispersive X-ray analyzer) at a magnification of 500,000 to 1,200,000 times.

[0150] Among the cross-sections of the observed conductive particles, the cross-sections of the conductive particles having a maximum diameter approximately 0.9 times or more and 1.1 times or less of the primary particle diameter calculated above were visually selected. Subsequently, the constituent elements of the cross-sections of the selected conductive particles were collected using an EDS analyzer to create an EDS mapping image. The collection and analysis of the spectra were performed using NSS (manufacturer: Thermo Fisher Scientific). The collection conditions were: an acceleration voltage of 200 kV, a probe size of 1.0 nm or 1.5 nm was appropriately selected so that the dead time was 15 or more and 30 or less, the mapping resolution was 256 × 256, and the number of frames was 300. The EDS mapping images were obtained for 100 cross-sections of the conductive particles.

[0151] By analyzing the EDS mapping image thus obtained, the ratio of the niobium atom concentration (atomic %) to the titanium atom concentration (atomic %) in the central part of the particle and within 5% of the maximum diameter of the measured particle from the particle surface is calculated. Specifically, first, press the "Line Extraction" button of NSS, draw a straight line so as to be the maximum diameter of the particle, and obtain information on the atomic concentration (atomic %) on the straight line passing through the inside of the particle from one surface to the other surface. If the maximum diameter of the particle obtained at this time is less than 0.9 times or exceeds 1.1 times the primary particle diameter calculated above, it is excluded from the subsequent analysis. (Only for particles having a maximum diameter in the range of 0.9 times or more and less than 1.1 times the primary particle diameter, the analysis shown below was performed.) Next, at the particle surfaces on both sides, read the niobium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface. Similarly, obtain the "titanium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface".

[0152] Next, using these values, from the following formula, obtain the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" at the particle surfaces on both sides, respectively. 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 particle from the particle surface) Of the two obtained concentration ratios, the smaller value is adopted as the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" in the present invention.

[0153] Also, read the niobium atom concentration (atomic %) and the titanium atom concentration (atomic %) at the position on the above straight line that is the midpoint of the maximum diameter. Using these values, obtain the "concentration ratio of niobium atoms to titanium atoms in the central part of the particle" from the following formula. Concentration ratio of niobium atoms to titanium atoms in the central part of the particle = (Niobium atom concentration (atomic %) in the particle core) / (Titanium atom concentration (atomic %) in the particle core)

[0154] Note that the "concentration ratio calculated by niobium atom concentration / titanium atom concentration within 5% of the maximum diameter of the measured particle from the particle surface with respect to the concentration ratio calculated by niobium atom concentration / titanium atom concentration in the particle core" is calculated by the following formula. (Concentration ratio of niobium atoms and titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface) / (Concentration ratio of niobium atoms and titanium atoms in the particle core)

[0155] <Evaluation of dot images> For the evaluation of dot images, a modified laser beam printer (electrophotographic apparatus) (product name: i-SENSYS LBP673Cdw, manufacturer: Canon Inc.) and a toner cartridge equipped with the electrophotographic photoreceptor used in this case were used. The electrophotographic apparatus was modified so that the applied voltage to the charging roller could be adjusted.

[0156] To output an evaluation image, first, the applied voltage to the charging roller was set so that the surface potential of the electrophotographic photoreceptor became -550 V. Further, during image formation, the applied voltage was adjusted so that the ground current connected to the electrophotographic photoreceptor became constant. First, as an evaluation image at the initial use, a halftone image with a 5.0 mm margin on the top, bottom, left, and right (toner loading amount: 0.2 mg / cm 2 ) was printed in cyan for one sheet. Next, after printing 10,000 full-color 5.0% images, as an evaluation image during long-term use, the same halftone image as that at the initial use was printed for one sheet. The dot image evaluation of the halftone image was performed according to the following criteria. From evaluation criteria A to C, there are no practical problems. The evaluation results are shown in Tables 7 and 8.

[0157] (Evaluation criteria) A: When observed with a loupe, no dot image is observed. B: When observed visually, no dot image is observed, but when observed with a loupe, a dot image is slightly observed in some places. C: Visually observed, slightly pockmark images are observed in some places. D: Visually observed, pockmark images are observed in multiple places. E: Visually observed, pockmark images are observed in the entire area of the image.

[0158] <Evaluation of Injection Charging Property> For the measurement of injection charging property, a modified machine of a laser beam printer (electrophotographic apparatus) (product name: i-SENSYS LBP673Cdw, manufacturer: Canon Inc.) was used. The modified machine used for evaluation was modified so that the image exposure amount, the current flowing from the charging roller to the support of the electrophotographic photoreceptor (hereinafter also referred to as the total current), and the applied voltage to the charging roller could be adjusted and measured respectively.

[0159] Also, the process cartridge for cyan color of the above modified machine was modified, and a potential probe (product name: model6000B-8, manufacturer: Trek Japan Co., Ltd.) was installed at the development position. Next, the surface potential of the central part of the electrophotographic photoreceptor was made measurable using a surface potentiometer (product name: model344, manufacturer: Trek Japan Co., Ltd.).

[0160] Under the environment of temperature 30°C and humidity 80%RH, the electrophotographic photoreceptor was mounted on the modified machine, 600V was applied to the charging roller with a direct current, and the electrophotographic photoreceptor was charged while rotating at 60 rpm. The surface potential of the electrophotographic photoreceptor at this time was defined as VC, and the injection charging rate (=-VC / 600) was calculated. Ranking was performed in five grades from A to E according to the value of the injection charging rate. The evaluation criteria from A to C are at a level with no practical problems. The evaluation results are shown in Table 7 and Table 8.

[0161] (Evaluation Criteria) A: The injection charging rate is 80% or more. B: The injection charging rate is 70% or more and less than 80%. C: The injection charging rate is 60% or more and less than 70%. D: The injection charging rate is 50% or more and less than 60%. E: The injection charging rate is less than 50%.

[0162] Also, 10,000 prints were made in the same manner as the above <evaluation of dot images>, the injection charging rate of the electrophotographic photoreceptor during long-term use was measured, and the ratio to the initial injection charging rate was defined as the injection charge retention and is shown in Tables 7 and 8. (Evaluation Criteria) A: The injection charging rate after durability with respect to the initial injection charging rate is 80% or more. B: The injection charging rate after durability with respect to the initial injection charging rate is 70% or more and less than 80%. C: The injection charging rate after durability with respect to the initial injection charging rate is 60% or more and less than 70%. D: The injection charging rate after durability with respect to the initial injection charging rate is 50% or more and less than 60%. E: The injection charging rate after durability with respect to the initial injection charging rate is less than 50%.

[0163]

Table 7

[0164]

Table 8

[0165] The disclosure of this embodiment includes the following configurations. (Configuration 1) An electrophotographic photoreceptor having a surface layer, wherein the surface layer contains a binder resin, first particles, and second particles, the surface of the surface layer has protrusions derived from the first particles and protrusions derived from the second particles, when the surface layer is viewed from above, when the ratio of the area occupied by the first particles in the total area of the surface layer is S1 [%] and the ratio of the area occupied by the second particles in the total area of the surface layer is S2 [%], the S1 and the S2 satisfy 70 ≦ (S1 + S2) ≦ 95 (1) 0.8 ≦ (S1 / S2) ≦ 2.0 (2) and satisfy the above conditions, When the exposed height of the first particles exposed on the surface of the electrophotographic photoreceptor is L1 [nm] and the exposed height of the second particles exposed on the surface of the electrophotographic photoreceptor is L2 [nm], the L1 and the L2 are 50 ≦ L1 ≦ 300 (3) 2.0 ≦ L1 / L2 ≦ 10.0 (4) satisfy the following, the first particles include any one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black, the second particles include silica particles, and the electrophotographic photoreceptor is characterized by this. (Configuration 2) When the number-based average primary particle diameter of the first particles is D1 [nm] and the number-based average primary particle diameter of the second particles is D2 [nm], the D1 and the D2 are 100 ≦ D1 ≦ 350 30 ≦ D2 ≦ 150 2.0 ≦ D1 / D2 ≦ 10.0 and satisfy the above, and the electrophotographic photoreceptor according to Configuration 1. (Configuration 3) When the film thickness of the surface layer is T1 [nm] and the number-based average primary particle diameter of the first particles is D1 [nm], the T1 and the D1 are 1.0 ≦ T1 / D1 ≦ 1.8 and satisfy the above, and the electrophotographic photoreceptor according to Configuration 1 or 2. (Configuration 4) The powder resistivity R1 of the first particles is 1.0×10 8 Ω·cm or less, The powder resistivity R2 of the second particles is 1.0×10 10 Ω·cm or more, and the electrophotographic photoreceptor according to any one of Configurations 1 to 3. (Configuration 5) The powder resistivity R2 of the second particles is 1.0×10 13 Ω·cm or more, and the electrophotographic photoreceptor according to any one of Configurations 1 to 4. (Configuration 6) The electrophotographic photoreceptor according to any one of Configurations 1 to 5, wherein the first particles include any one or more selected from the group consisting of tin oxide particles, ITO particles, titanium oxide particles, and zinc oxide particles. (Configuration 7) The first particles include titanium oxide particles doped with niobium, In the EDS analysis by scanning transmission electron microscope (STEM) of the titanium oxide particles doped with niobium, the concentration ratio calculated by niobium atom concentration / titanium atom concentration within 5% of the primary particle diameter of the titanium oxide particles doped with niobium from the surface of the titanium oxide particles doped with niobium is 2.0 times or more with respect to the concentration ratio calculated by niobium atom concentration / titanium atom concentration at the center of the titanium oxide particles doped with niobium. The electrophotographic photoreceptor according to any one of Configurations 1 to 6. (Configuration 8) A process cartridge that integrally supports the electrophotographic photoreceptor according to any one of Configurations 1 to 7 and at least one means selected from the group consisting of charging means, developing means, and cleaning means, and is detachable from the main body of the electrophotographic apparatus. (Configuration 9) An electrophotographic apparatus having the electrophotographic photoreceptor according to any one of Configurations 1 to 7, as well as charging means, exposure means, developing means, and transfer means.

Explanation of Signs

[0166] 1 Electrophotographic photoreceptor 2 Charging roller 3 Exposure unit 4 Developing means 41 Developing roller 5 Pre-exposure unit 10 Intermediate transfer belt 11 Driving roller 12 Tension roller 13 Opposing roller 14 Metal roller 15 Secondary transfer roller 16 Belt cleaning means 30 Fixing means 50 Paper feeding means 101 Support 102 Underlying layer 103 Charge generation layer 104 Charge transport layer 105 Surface layer 201 Binder resin 201 First particle 202 Second particle 203 Lower layer coated with surface layer

Claims

1. An electrophotographic photoreceptor having a surface layer, wherein the surface layer contains a binder resin, first particles, and second particles, the surface of the surface layer has protrusions derived from the first particles and protrusions derived from the second particles, when the surface layer is viewed from above, when the ratio of the area occupied by the first particles in the total area of the surface layer is S1 [%] and the ratio of the area occupied by the second particles in the total area of the surface layer is S2 [%], the S1 and the S2 are, 70 ≦ (S1 + S2) ≦ 95 (1) 0.8 ≦ (S1 / S2) ≦ 2.0 (2) satisfy the above, when the exposure height of the first particles exposed on the surface of the electrophotographic photoreceptor is L1 [nm] and the exposure height of the second particles exposed on the surface of the electrophotographic photoreceptor is L2 [nm], the L1 and the L2 are, 50 ≦ L1 ≦ 300 (3) 2.0 ≦ L1 / L2 ≦ 10.0 (4) satisfy the above, the first particles contain any one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black, the second particles contain silica particles, characterized in that the electrophotographic photoreceptor.

2. When the number-average primary particle diameter of the first particles is D1 [nm] and the number-average primary particle diameter of the second particles is D2 [nm], the D1 and the D2 are, 100 ≦ D1 ≦ 350 30 ≦ D2 ≦ 150 2.0 ≦ D1 / D2 ≦ 10.0 satisfy the above, the electrophotographic photoreceptor according to claim 1.

3. When the film thickness of the surface layer is T1 [nm] and the number-average primary particle diameter of the first particles is D1 [nm], the T1 and the D1 are, 1.0 ≦ T1 / D1 ≦ 1.8 satisfy the above, the electrophotographic photoreceptor according to claim 1.

4. The powder resistivity R1 of the first particles is 1.0×10 ８ Ω·cm or less, The powder resistivity R2 of the second particles is 1.0×10 １０ Ω·cm or more, and the electrophotographic photoreceptor according to claim 1.

5. The powder resistivity R2 of the second particles is 1.0×10 １３ Ω·cm or more. The electrophotographic photoreceptor according to claim 1.

6. The electrophotographic photoreceptor according to claim 1, wherein the first particles contain any one or more selected from the group consisting of tin oxide particles, ITO particles, titanium oxide particles, and zinc oxide particles.

7. The first particles contain niobium-doped titanium oxide particles, In the EDS analysis by a scanning transmission electron microscope (STEM) of the niobium-doped titanium oxide particles, the concentration ratio calculated by niobium atom concentration / titanium atom concentration within 5% of the primary particle diameter of the niobium-doped titanium oxide particles from the surface of the niobium-doped titanium oxide particles is 2.0 times or more with respect to the concentration ratio calculated by niobium atom concentration / titanium atom concentration at the center of the niobium-doped titanium oxide particles. The electrophotographic photoreceptor according to claim 1.

8. A process cartridge that integrally supports the electrophotographic photoreceptor according to any one of claims 1 to 7 and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachable from the main body of the electrophotographic apparatus.

9. An electrophotographic apparatus having the electrophotographic photoreceptor according to any one of claims 1 to 7, as well as a charging means, an exposure means, a developing means, and a transfer means.

Images