Electrophotographic photoreceptor, process cartridge, and electrophotographic device

Abstract

The present invention addresses the problem of providing an electrophotographic photoreceptor that is durable enough for use in an image forming device having a long life. In order to solve this problem, the present invention provides an electrophotographic photoreceptor wherein: when a surface layer thereof is viewed from above, S1 and S2 satisfy 70 ≤ (S1 + S2) ≤ 95 and 0.8 ≤ (S1 / S2) ≤ 2.0, where S1 [%] signifies the ratio of the area occupied by first particles in the entire area of the surface layer, and S2 [%] signifies the ratio of the area occupied by second particles in the entire area of the surface layer; L1 and L2 satisfy 50 ≤ L1 ≤ 300 and 2.0 ≤ L1 / L2 ≤ 10.0, where L1 [nm] signifies the exposure height of the first particles exposed on the surface of the electrophotographic photoreceptor, and L2 [nm] signifies the exposure height of the second particles exposed on the surface of the electrophotographic photoreceptor; the first particles include one or more kinds of particles selected from the group consisting of metal oxide particles, metal particles, and carbon black; and the second particles include silica particles.

Description

Electrophotographic photoreceptor, process cartridge and electrophotographic device

[0001] The present invention relates to an electrophotographic photosensitive member, a process cartridge having the electrophotographic photosensitive member, and an electrophotographic apparatus.

[0002] Conventionally, in electrophotographic or electrostatic recording image forming apparatuses, corona chargers have been used as means for charging electrophotographic photosensitive members such as electrophotographic photosensitive members and electrostatic recording dielectrics. In recent years, contact charging devices have been put to practical use, in which a charging member to which a voltage is applied is brought into contact with the electrophotographic photosensitive member to charge the electrophotographic photosensitive member, due to their advantages such as 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, according to Paschen's law, charging begins when a voltage equal to or greater than a certain threshold voltage is applied.

[0004] Even in such roller charging systems, a discharge phenomenon is utilized to apply a voltage to the electrophotographic photosensitive member, and so discharge products are generated and the surface of the electrophotographic photosensitive member is altered, although to a lesser extent than in charging systems using a corona charger. The discharge products and the altered surface of the electrophotographic photosensitive member become less resistive, particularly in high-temperature and high-humidity environments, and the surface potential of the electrophotographic photosensitive member 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 common configuration is to continue printing while gradually scraping away the discharge products and altered surface of the electrophotographic photosensitive member, thereby simultaneously scraping away the discharge products and altered surface of the electrophotographic photosensitive member. Specifically, the surface of the electrophotographic photosensitive member is scraped off by a cleaning blade that is arranged in contact with the electrophotographic photosensitive member and cleans off the developer remaining on the surface of the electrophotographic photosensitive member, or by a charging member or a developing member.

[0006] However, in recent years, from the viewpoint of reducing the frequency of maintenance and improving usability, there has been a demand for an increase in the number of printable sheets, and accordingly, there is a need for a longer life of the electrophotographic photosensitive member. In other words, for the electrophotographic photosensitive member in a long-life image forming apparatus, it has become difficult to use the above-mentioned measures, which involve continuously scraping the surface of the electrophotographic photosensitive member over a long period of use (throughout the life).

[0007] For these reasons, an injection charging method that does not involve a discharge phenomenon has been proposed as a countermeasure against discharge products and deterioration of the surface of an electrophotographic photosensitive member that does not rely on scraping off the surface of the electrophotographic photosensitive member.Electrophotographic photosensitive members used in image forming apparatuses using the injection charging method are required to be designed using a conductive material on the surface of the electrophotographic photosensitive member in order to realize charge injection from a charging member.

[0008] For example, Patent Document 1 proposes a technology in which conductive powder is contained in the surface of an electrophotographic photosensitive member and the conductive powder has a particle size equal to or larger than the film thickness of the surface layer, thereby exposing the conductive powder from the surface layer and improving injection charging properties.

[0009] Japanese Patent Application Publication No. 11-249493

[0010] However, when the electrophotographic photoreceptor of Patent Document 1 is used in an image forming apparatus that is required to have a long life, there is still room for improvement. For example, there is a need to improve the suppression of the occurrence of mottled images caused by contamination of the surface of the electrophotographic photoreceptor in an image forming apparatus that has a long life.

[0011] 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 condition in the surface layer of the electrophotographic photoreceptor.

[0012] The above object is achieved by the present invention, which provides an electrophotographic photoreceptor having a surface layer, the surface layer containing a binder resin, first particles, and second particles, the surface of the surface layer having convex portions derived from the first particles and convex portions derived from the second particles, and when the surface layer is viewed from above, the ratio of the area occupied by the first particles to the total area of ​​the surface layer is S1 [%], and the ratio of the area occupied by the second particles to the total area of ​​the surface layer is S2 [%], where S1 and S2 satisfy the following formulas (1) and (2): 70≦(S1+S2)≦95 (1) and 0.8≦(S1 / S2)≦2.0 (2). The electrophotographic photosensitive member is characterized in that, when the exposed height of the first particles exposed on the surface of the electrophotographic photosensitive member is L1 [nm] and the exposed height of the second particles exposed on the surface of the electrophotographic photosensitive member is L2 [nm], L1 and L2 satisfy the following formulas (3) and (4): 50≦L1≦300 (3) 2.0≦L1 / L2≦10.0 (4) The first particles comprise one or more particles selected from the group consisting of metal oxide particles, metal particles, and carbon black, and the second particles comprise silica particles. The present invention also relates to a process cartridge that integrally supports the above electrophotographic photosensitive member and at least one unit selected from the group consisting of a charging unit, a developing unit, and a cleaning unit, and is detachably mountable to the main body of an electrophotographic apparatus. The present invention also relates to an electrophotographic apparatus having the above electrophotographic photosensitive member, a charging unit, an exposure unit, a developing unit, and a transfer unit.

[0013] According to the present invention, in the design of the surface layer of an electrophotographic photosensitive member, two types of particles are used to create an appropriate surface state in the surface layer of the electrophotographic photosensitive member, thereby making it possible to provide an electrophotographic photosensitive member that can withstand use in a long-life image forming apparatus.

[0014] 1 is a schematic diagram showing an example of the cross-sectional configuration of an electrophotographic photosensitive member according to the present invention. 2 is a schematic diagram showing an example of the cross-sectional configuration of a surface layer of an electrophotographic photosensitive member according to the present invention. 3 is a schematic diagram showing an example of the schematic configuration of an electrophotographic apparatus having an electrophotographic photosensitive member and a process cartridge equipped with a charging means. 4 is a schematic diagram showing an example of a unit measurement range in a cross-section of the surface layer of an electrophotographic photosensitive member according to the present invention. 5 is a schematic diagram for explaining measurement of a film thickness and an exposed height of particles in a cross-section of the surface layer of an electrophotographic photosensitive member according to the present invention. 6 is an STEM image of niobium-doped titanium oxide contained in the surface layer of an electrophotographic photosensitive member according to the present invention. 7 is a schematic diagram for explaining EDS analysis by STEM.

[0015] One embodiment of the present invention relates to an electrophotographic photoreceptor. As a result of extensive research, the present inventors have discovered a method for designing the surface layer of an electrophotographic photoreceptor that suppresses contamination of the electrophotographic photoreceptor that occurs in long-life image forming apparatuses. This electrophotographic photoreceptor can be used not only in image forming apparatuses using an injection charging method, but also in image forming apparatuses using a discharge charging method. That is, the electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor having a surface layer, the surface layer containing a binder resin, first particles, and second particles, the surface of the surface layer having convex portions derived from the first particles and convex portions derived from the second particles, when the surface layer is viewed from above, the ratio of the area occupied by the first particles to the total area of ​​the surface layer is S1 [%], and the ratio of the area occupied by the second particles to the total area of ​​the surface layer is S2 [%], S1 and S2 satisfy the following formulas (1) and (2): 70≦(S1+S2)≦95 (1) 0.8≦(S1 / S2)≦2.0 (2) When the exposed height of the first particles exposed on the surface of the electrophotographic photosensitive member is L1 [nm] and the exposed height of the second particles exposed on the surface of the electrophotographic photosensitive member is L2 [nm], L1 and L2 satisfy the following formulas (3) and (4): 50≦L1≦300 (3) 2.0≦L1 / L2≦10.0 (4) The present invention is characterized in that the first particles contain one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black, and the second particles contain silica particles. Preferred embodiments of the present invention will now be described.

[0016] [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, a charge transport layer, and a particle-containing surface layer provided on the support. The electrophotographic photoreceptor of the present invention can be used as a cylindrical electrophotographic photoreceptor in which a charge generation layer, a charge transport layer, and a surface layer are formed on a cylindrical support, but it can also be in a belt-like or sheet-like shape. 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.

[0017] The above-described configuration makes it possible to provide an electrophotographic photoreceptor that can withstand use in an image-forming apparatus with a long life. The mechanism by which the configuration of the present invention solves the problems has not been clarified, but is speculated as follows.

[0018] The mottled images that occur in long-life image forming devices become apparent when contaminants such as toner, external additives, and paper dust adhere to the surface of the electrophotographic photosensitive member during the image formation process, causing repeated contamination of the electrophotographic photosensitive member surface and resulting in the accumulation of contaminants on the electrophotographic photosensitive member surface.

[0019] When contaminants accumulate on the surface of an electrophotographic photoreceptor, charges are also stored on the contaminants during the charging process. Because the contaminants are primarily composed of toner and external additives, they are more susceptible to charge-up than the surface layer of an electrophotographic photoreceptor containing conductive particles. Such contaminated areas do not achieve the intended potential on the electrophotographic photoreceptor surface during the image formation process, and are output as mottled images (speckled image defects seen on halftone images).

[0020] The electrophotographic photoreceptor of the present invention has a surface layer containing a binder resin, first particles, and second particles, the surface of which has convex portions derived from the first particles and convex portions derived from the second particles, and when the surface layer is viewed from above, the ratio of the area occupied by the first particles to the total area of ​​the surface layer is S1 [%], and the ratio of the area occupied by the second particles to the total area of ​​the surface layer is S2 [%], where S1 and S2 satisfy the following formulas (1) and (2): 70≦(S1+S2)≦95 (1) and 0.8≦(S1 / S2)≦2.0 (2).

[0021] By satisfying formula (1), the surface layer of the electrophotographic photosensitive member is largely covered with the first particles and the second particles. As a result, irregularities resulting from the first particles and the second particles are formed on the surface of the surface layer of the electrophotographic photosensitive member. This irregular shape makes point contact with contaminants, so that contaminants are more likely to be released from the surface of the electrophotographic photosensitive member than in a general electrophotographic photosensitive member that does not have an irregular shape.

[0022] By satisfying the formulas (1) and (2), the presence ratio of the first particles, which are conductive particles, on the surface of the electrophotographic photosensitive member is sufficiently ensured, and the injection charging property of the electrophotographic photosensitive member can be exhibited.

[0023] On the other hand, if the ratio 70≦(S1+S2) is not satisfied, the area occupied by the resin relative to the total area when the surface layer of the electrophotographic photosensitive member is viewed from above becomes relatively large, so that the area S1 occupied by the first particles, which are injection sites, decreases, resulting in poor injection characteristics. Also, the area S2 occupied by the second particles, which form the fine uneven shape, decreases, making it impossible to promote the detachment of contaminants, causing the accumulation of contaminants and making it more likely to produce mottled images.

[0024] If (S1+S2)≦95 is not satisfied, the area occupied by the resin on the surface of the electrophotographic photosensitive member becomes small, weakening the function of binding particles to the surface layer of the electrophotographic photosensitive member, and rubbing with a contact member during image formation makes it easy for particles to detach from the surface layer of the electrophotographic photosensitive member. As a result, when the first particles detach from the surface layer of the electrophotographic photosensitive member, injection properties deteriorate due to the disappearance of injection sites, and when the second particles detach, contaminant detachment properties deteriorate due to the disappearance of fine unevenness.

[0025] If 0.8≦(S1 / S2) is not satisfied, the area S1 occupied by the first particles, which are injection sites, decreases, resulting in poor injection charging characteristics. Also, if (S1 / S2)≦2.0 is not satisfied, the area S2 occupied by the second particles, which form the fine irregularities, decreases, failing to promote the removal of contaminants from the surface of the electrophotographic photosensitive member, causing the accumulation of contaminants and making mottled images more likely to occur.

[0026] In the electrophotographic photosensitive member of the present invention, when the exposed height of the first particles exposed on the surface of the electrophotographic photosensitive member is L1 [nm] and the exposed height of the second particles exposed on the surface of the electrophotographic photosensitive member is L2 [nm], L1 and L2 satisfy the following formulas (3) and (4): 50≦L1≦300 (3) 2.0≦L1 / L2≦10.0 (4)

[0027] By satisfying the formula (3), the injection charging characteristics of the electrophotographic photosensitive member are ensured, and even when the electrophotographic photosensitive member is used for a long period of time, the first particles are less likely to be detached from the surface layer of the electrophotographic photosensitive member.

[0028] By satisfying formulas (3) and (4), the first conductive particles form higher convex portions on the surface of the electrophotographic photoreceptor than the second insulating particles, and the second insulating particles form lower convex portions on the surface of the electrophotographic photoreceptor than the first conductive particles. This allows contaminants to adhere more easily to the relatively concave insulating particle surfaces, while the first conductive particles remain exposed on the electrophotographic photoreceptor surface. This maintains the injection charging characteristics even after long-term use of the electrophotographic photoreceptor. Furthermore, the surface formed by the insulating particles, which form the relatively concave portions of the surface layer of the electrophotographic photoreceptor, has a fine uneven shape due to the insulating particles. Furthermore, the second particles have a lower dielectric constant than the first particles. Therefore, not only are contaminants in point contact with the electrophotographic photoreceptor surface, but the electrostatic adhesion is also low, making it easier for contaminants to detach from the electrophotographic photoreceptor surface.

[0029] If 50≦L1 is not satisfied, the exposed height L1 is not formed sufficiently as a conductive site, and the injection charging characteristics are likely to deteriorate due to the accumulation of contaminants. Also, if L1≦300 is not satisfied, the exposed height L1 of the first particles is formed too high, and the first particles are likely to detach from the surface of the electrophotographic photosensitive member due to durability, and the injection charging characteristics of the electrophotographic photosensitive member are likely to deteriorate.

[0030] If 2.0≦L1 / L2 is not satisfied, the first particles cannot form a sufficient exposed height L1, and the accumulation of contaminants tends to deteriorate the injection charging characteristics. If L1 / L2≦10.0 is not satisfied, if the exposed height L1 of the first particles is relatively large, the first particles tend to detach, resulting in deterioration of the injection charging characteristics. If the exposed height L2 of the second particles is relatively small, a fine uneven shape cannot be formed, making it difficult for contaminants to detach, and as a result, contaminants tend to accumulate on the surface of the electrophotographic photosensitive member, making it easy for mottled images to occur.

[0031] In the electrophotographic photosensitive member of the present invention, 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], it is preferable that D1 and D2 satisfy the following formulas (5), (6), and (7): 100≦D1≦350 (5) 30≦D2≦150 (6) 2.0≦D1 / D2≦10.0 (7)

[0032] By doing so, it is possible to design a surface shape of the surface layer of the electrophotographic photosensitive member that is less susceptible to adhesion of contaminants. Furthermore, it is more preferable that formula (5) satisfies 120≦D1≦250, and even more preferable that it satisfies 150≦D1≦220. It is more preferable that formula (6) satisfies 30≦D2≦120, and even more preferable that it satisfies 30≦D2≦100. It is more preferable that formula (7) satisfies 4.0≦D1 / D2≦10.0, and even more preferable that it satisfies 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 photosensitive member. By satisfying formulas (5), (6), and (7), it is possible to form convexities on the surface of the surface layer of the electrophotographic photosensitive member in which the first particles, which are conductive particles, are higher than the second particles, which are insulating particles.

[0033] In the electrophotographic photosensitive member of the present invention, when the thickness of the surface layer is T1 [nm] and the number-based average primary particle diameter of the primary particles is D1 [nm], it is preferable that T1 and D1 satisfy the following formula (8): 1.0≦T1 / D1≦1.8 (8)

[0034] In this way, the surface shape of the surface layer of the electrophotographic photosensitive member can be designed using the primary particle diameter of the particles. It is more preferable that the formula (8) be 1.2≦T1 / D1≦1.5. By doing so, the convex portions formed by the first particles are higher than the film thickness, but the convex portions are not formed by agglomerates of the first particles. Therefore, even when the electrophotographic photosensitive member is used for a long period of time, the injection characteristics can be maintained and detachment of the first particles due to friction with the contact member can be suppressed.

[0035] In the electrophotographic photoreceptor of the present invention, the powder resistivity R1 of the first particles is 1.0×10 ８ The powder resistivity R2 of the second particles is preferably 1.0×10 １０Preferably, the dielectric constant is Ω·cm or more. The first particles, which form higher convexities than the second particles, are conductive particles, and the second particles, which form lower convexities than the first particles, are insulating particles. This allows contaminants to adhere more easily to the relatively concave insulating particle surfaces, while the conductive first particles remain exposed to the surface. Furthermore, the relatively concave portions of the surface layer of the electrophotographic photoreceptor are formed by the insulating particles, resulting in fine irregularities. Furthermore, the second particles have a lower dielectric constant than the first particles. Therefore, not only are contaminants in point contact with the electrophotographic photoreceptor surface, but the electrostatic adhesion is also low, making it easier for the contaminants to detach. As a result, even when the electrophotographic photoreceptor is used for a long period of time, the projections that serve as injection points can be maintained, and the injection characteristics can be easily maintained.

[0036] In the electrophotographic photoreceptor of the present invention, the powder resistivity R2 of the second particles is 1.0×10 １３ It is more preferable that the resistivity be Ω·cm or more. By doing so, the material that affects the injection characteristics can be limited to only the first particles. Furthermore, even if contaminants adhere to the fine unevenness formed by the second particles in the relatively recessed areas of the surface layer of the electrophotographic photosensitive member, the second particles do not affect the injection characteristics, so the injection characteristics of the surface layer of the electrophotographic photosensitive member are unlikely to change. Therefore, even if the electrophotographic photosensitive member is used for a long period of time, changes in the injection characteristics can be minimized. Note that the above mechanism is based on speculation, and this speculation does not affect the technical scope of the present invention.

[0037] <Binder Resin> Examples of the binder resin according to the present invention include polyester resin, acrylic resin, phenoxy resin, polycarbonate resin, polystyrene resin, phenol resin, melamine resin, epoxy resin, etc. Among these, polycarbonate resin, polyester resin, and acrylic resin are preferred.

[0038] The surface layer may also be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction include thermal polymerization, photopolymerization, and radiation-induced polymerization. Examples of the polymerizable functional group possessed by the monomer having a polymerizable functional group include an acryloyl group and a methacryloyl group. A material having charge transport capability may also be used as the monomer having a polymerizable functional group.

[0039] The compound having a polymerizable functional group may have a charge transport structure in addition to the chain polymerizable functional group. As the charge transport structure, a triarylamine structure is preferred in terms of charge transport. As the chain polymerizable functional group, an acryloyl group or a methacryloyl group is preferred. The number of functional groups may be one or more. Among these, it is particularly preferred to form a cured film containing a compound having multiple functional groups and a compound having one functional group, since distortion caused by polymerization between the multiple functional groups is easily eliminated.

[0040] Examples of the compound having one functional group are shown in the following formulas (2-1) to (2-6).

[0041] Examples of the compound having multiple functional groups are shown in the following formulas (3-1) to (3-5).

[0042] The surface layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipping agents, and abrasion resistance improvers. Specific examples of such additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, and silicone oils.

[0043] The surface layer can be formed by preparing a coating solution for the surface layer containing the materials and solvent described below, forming the coating film on the charge transport layer or the single-layer photosensitive layer, and drying and / or curing the coating film. Examples of the solvent used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0044] <First Particles> In the electrophotographic photoreceptor of the present invention, the first particles include at least one selected from the group consisting of metal oxide particles, metal particles, and carbon black. Examples of metal oxide particles include magnesium oxide, aluminum oxide, titanium oxide, iron oxide, copper oxide, zinc oxide, silver oxide, tantalum oxide, behimus oxide, cobalt oxide, indium oxide, tin oxide, and indium tin oxide. Examples of metal particles include magnesium, aluminum, titanium, iron, copper, zinc, silver, tin, platinum, and gold. These particles may be synthetic or commercially available. Furthermore, in order to improve the dispersion stability of the particles, they may be subjected to a hydrophobic treatment, as described below.

[0045] Carbon black can be produced by a furnace method, a channel method, an acetylene method, a thermal method, etc., but carbon black produced by the acetylene method is preferred from the viewpoint of high conductivity and low impurity content.

[0046] Furthermore, since the first particles are a material responsible for the injection characteristics of the surface layer of the electrophotographic photoreceptor, they preferably have a volume resistivity of medium resistance or less. In addition, from the viewpoints of cost and environmental impact, metal oxide particles such as tin oxide (tin oxide), indium tin oxide, titanium oxide, and zinc oxide are preferred. In the electrophotographic photoreceptor of the present invention, the first particles preferably contain one or more particles selected from the group consisting of tin oxide particles, ITO particles, titanium oxide particles, and zinc oxide particles. By satisfying the requirement that the first particles be any of tin oxide particles, ITO particles, titanium oxide particles, and zinc oxide particles, the function of the electrophotographic photoreceptor is not impaired, and even with a relatively small amount added, the charge injection characteristics into the surface layer of the electrophotographic photoreceptor can be ensured. Titanium oxide particles and zinc oxide particles are particularly preferred. These particles have a higher volume resistivity than tin oxide particles and ITO particles, and a medium resistance, so even if discharge products due to durability in a high-temperature, high-humidity environment accumulate on the drum surface, they can maintain good image formation compared to tin oxide particles and ITO particles.In addition, because electrostatic adhesion is suppressed, dirt adhering to the convex parts can be easily removed, and changes in injection charging properties can be kept small.

[0047] In the electrophotographic photosensitive member of the present invention, the first particles comprise niobium-doped titanium oxide particles, and in EDS analysis of the niobium-doped titanium oxide particles using a scanning transmission electron microscope (STEM), the concentration ratio calculated as 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 as niobium atomic concentration / titanium atomic concentration at the center of the niobium-doped titanium oxide particles. This allows the surface of the titanium oxide particles to have low resistance while maintaining a medium powder resistivity. This makes it easier to maintain a latent image even when a large amount of first particles is added to the surface layer of the electrophotographic photosensitive member, and ensures high injection properties.

[0048] In the present invention, the first particles are preferably particles having an anatase type titanium oxide particle as a core material and titanium oxide that coats the surface of the core material and contains niobium. The niobium is preferably incorporated into the crystal lattice of titanium oxide in a so-called doped form, rather than being contained as an oxide. Doping titanium oxide with niobium increases injection charging properties.

[0049] When the first particles have titanium oxide particles containing niobium, the niobium content in the first particles is preferably 0.5% by mass or more and 15.0% by mass or less, and more preferably 1.0% by mass or more and 10.0% by mass or less. If the niobium content in the first particles is 0.5% by mass or more, the conductivity of the titanium oxide can be increased and the injection chargeability can be improved, and if it is 15.0% by mass or less, the crystal structure of the titanium oxide can be maintained, so the volume resistivity of the surface layer does not become too high.

[0050] Figure 6 shows an STEM image of an example of a metal oxide in which a titanium oxide core is coated with niobium-containing titanium oxide, similar to the titanium oxide particles (conductive particles 1) used in the examples of the present invention. Figure 7 is a diagram schematically illustrating the STEM image of Figure 6. As will be described in detail later, the niobium-containing titanium oxide particles used in the examples are produced by coating a titanium oxide core particle with niobium-containing titanium oxide and then firing the coated titanium oxide. Therefore, it is believed that the coated niobium-containing titanium oxide undergoes crystal growth as niobium-doped titanium oxide along the crystals of the titanium oxide core by so-called epitaxial growth.

[0051] The niobium-containing titanium oxide produced in this manner has a lower density near the surface compared to the density at the center of the particle, indicating a core-shell morphology, as shown in Figure 6. Furthermore, in EDS analysis using STEM, X-rays penetrate the entire particle, so as shown in Figure 7, EDS analysis at the particle center as shown in the direction 33, within 5% of the primary particle diameter from the surface of the particle as shown in the direction 34, is more affected by the vicinity of the surface.

[0052] In other words, in the EDS analysis using STEM as described above, when the niobium / titanium atomic ratio at the particle center within 5% of the particle diameter from the particle surface is 2.0 times or more, this is considered to be a state in which niobium elements are unevenly distributed near the surface. In Figure 7, reference numeral 32 denotes a region of the metal oxide particle within 5% of the particle diameter from the particle surface, and reference numeral 31 denotes a region of the metal oxide particle further inward than the region referenced 32. Reference numeral 33 denotes an X-ray that analyzes the center of the metal oxide particle, and reference numeral 34 denotes an X-ray that analyzes the metal oxide particle within 5% of the particle diameter from the surface.

[0053] In the EDS analysis using STEM, the niobium / titanium ratio is measured by EDS after observation using a transmission electron microscope. Alternatively, the electrophotographic photosensitive member can be sliced ​​using a microtome, Ar milling, FIB, or other means, and the niobium / titanium ratio can be measured directly from the electrophotographic photosensitive member.

[0054] Furthermore, the niobium-containing titanium oxide particles contained in the surface layer preferably have oxygen deficiencies. Oxygen deficiencies improve injection charging properties. While the detailed mechanism is not well understood, it is speculated that oxygen deficiencies in niobium-containing titanium oxide particles improve injection charging properties by making them more likely to accept charge. The oxygen deficiency rate of the niobium-containing titanium oxide particles is preferably 0.1% or more and 2.0% or less. If the oxygen deficiency rate is less than 0.1%, improvement in injection charging properties cannot be expected. If it exceeds 2.0%, the particles become black, the transparency of the surface layer decreases, and the sensitivity of the electrophotographic photoreceptor decreases. Furthermore, when the oxygen deficiency rate in the region within 5% of the primary particle diameter from the surface of the niobium-containing titanium oxide particles is β, and the oxygen deficiency rate in the remaining region of the niobium-containing titanium oxide particles is γ, the following formula (α) is preferably satisfied: β > 10 × γ (α). By doing so, oxygen deficiencies that are more likely to accept charge are unevenly distributed on the surface of the metal oxide particles, thereby enabling effective injection charging.

[0055] Here, the oxygen deficiency rate of metal oxide particles can be expressed as (B - A) / B x 100 (%), where A is the actual oxygen content of the metal oxide particles and B is the theoretical oxygen content of metal oxide particles without oxygen deficiency. The oxygen deficiency rate of metal oxide particles and the ratio of the oxygen deficiency rate in a region within 5% of the primary particle diameter from the surface of the metal oxide particles to the oxygen deficiency rate in other regions can be measured by energy dispersive X-ray analysis (EDS). As described above, in EDS analysis, X-rays penetrate the entire particle, so if the above-mentioned relational expression (α) is satisfied, this means that the oxygen deficiency is concentrated near the particle surface.

[0056] The introduction of oxygen vacancies can be carried out by firing in a reducing atmosphere such as ammonia or hydrogen, or by firing together with an organic substance in a nitrogen atmosphere at 600° C. or higher, which is the decomposition temperature of the organic substance. Although the detailed mechanism is not clear, as mentioned above, it is believed that the reason why injection charging properties are increased by doping with niobium or by introducing oxygen vacancies is that it becomes easier to transfer charges to and from conductive particles such as carbon black and graphite that are commonly used in charging members, facilitating the transfer of charges from the charging member to the electrophotographic photosensitive member.

[0057] <Second Particles> In the electrophotographic photoreceptor of the present invention, the second particles include silica particles. Silica particles have a higher average circularity than other inorganic particles, and are therefore expected to promote point contact between contaminants and the surface of the electrophotographic photoreceptor, thereby reducing adhesive 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. Wet silica fine particles obtained by a sol-gel method (hereinafter also referred to as sol-gel silica) are preferred.

[0058] The sol-gel silica used for the particles contained in the surface layer of the electrophotographic photosensitive member of the present invention may be hydrophilic or may have a hydrophobic surface.

[0059] The hydrophobic treatment method includes a sol-gel method in which the solvent is removed from the silica sol suspension, the suspension is dried, and then the suspension is treated with a hydrophobic treatment agent, and a method in which the hydrophobic treatment agent is directly added to the silica sol suspension and the suspension is treated simultaneously with drying. From the viewpoint of controlling the half-value width of the particle size distribution and the saturated water adsorption amount, the method in which the hydrophobic treatment agent is directly added to the silica sol suspension is preferred.

[0060] Examples of the hydrophobic treatment agent include chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, t-butyldimethylchlorosilane, and vinyltrichlorosilane; tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltrimethoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, i-butyltrimethoxysilane, methyltriethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, vinyltrichloro ... Alkoxysilanes such as ethyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, and γ-(2-aminoethyl)aminopropylmethyldimethoxysilane; Silazanes such as hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexahexyldisilazane, hexacyclohexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, and dimethyltetravinyldisilazane; silicone oils such as dimethylsilicone oil, methylhydrogensilicone oil, methylphenylsilicone 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 terminally reactive silicone oil;Siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, and octamethyltrisiloxane; fatty acids and metal salts thereof include long-chain fatty acids such as undecylic acid, lauric acid, tridecylic acid, dodecylic acid, myristic acid, palmitic acid, pentadecylic acid, stearic acid, heptadecylic acid, arachidic acid, montanic acid, oleic acid, linoleic acid, and arachidonic acid, and salts of the above fatty acids with metals such as zinc, iron, magnesium, aluminum, calcium, sodium, and lithium;

[0061] Among these, alkoxysilanes, silazanes, and silicone oils are preferably used because they are easy to carry out hydrophobic treatment. These hydrophobic treatment agents may be used alone or in combination of two or more.

[0062] <Additives> 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 slipping agent, an abrasion resistance improver, etc. Specific examples include quaternary ammonium salts, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, and silicone oils.

[0063] <Solvent> A solvent that stably disperses or dissolves the binder resin, inorganic particles, and additives may be appropriately selected. Specific examples include the following: 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; and amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Furthermore, a combination of solvents may be used to adjust the drying speed of the film of the curable composition and to adjust the viscosity of the curable composition to a level suitable for application.

[0064] <Surface Layer> The surface layer can be formed by preparing a surface layer coating liquid containing the above-mentioned materials and solvent, forming a coating film from this, and drying and / or curing it. Figure 2 is a diagram showing an example of the surface layer configuration of an electrophotographic photoreceptor. In Figure 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 applied.

[0065] <Support> In the present invention, the electrophotographic photoreceptor preferably has a support. In the present invention, the support is preferably a conductive support having electrical conductivity. The shape of the support may be cylindrical, belt-like, sheet-like, or the like. Of these, a cylindrical support is preferred. The surface of the support may be subjected to electrochemical treatment such as anodizing, blasting, cutting, or the like.

[0066] The support material is preferably a metal, a resin, or a glass. Examples of the metal include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among these, an aluminum support is preferable. Resins and glass may be made conductive by mixing or coating them with a conductive material.

[0067] <Conductive Layer> In the present invention, a conductive layer may be provided on the support. By providing the conductive layer, scratches and irregularities on the surface of the support can be concealed and light reflection on the surface of the support can be controlled. The conductive layer preferably contains conductive particles and a resin.

[0068] Examples of materials for the conductive particles include metal oxides, metals, carbon black, etc. Examples of metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, etc. Examples of metals include aluminum, nickel, iron, nichrome, copper, zinc, silver, etc.

[0069] Among these, it is preferable to use a metal oxide as the conductive particles, and it is particularly preferable to use 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 an oxide thereof.

[0070] The conductive particles may also have a laminated structure in which pre-coated particles such as titanium oxide, barium sulfate, or zinc oxide are coated with a metal oxide having a different composition from the pre-coated particles. Examples of the coating include metal oxides such as tin oxide. When a metal oxide is used as the conductive particles, the average primary particle size is preferably 1 nm or more and 500 nm or less, and more preferably 3 nm or more and 400 nm or less.

[0071] 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, etc. The conductive layer may further contain silicone oil, resin particles, a masking agent such as titanium oxide, etc.

[0072] 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 the above-mentioned materials and solvent, forming a coating film from this, and drying it. Examples of solvents used in the coating liquid include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Examples of dispersion methods for dispersing the 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.

[0073] <Undercoat Layer> In the present invention, an undercoat layer may be provided on the support or the conductive layer. The average thickness of the undercoat layer is preferably from 0.1 μm to 50 μm, more preferably from 0.2 μm to 40 μm, and particularly preferably from 0.3 μm to 30 μm.

[0074] Examples of resins for the undercoat layer include polyacrylic acid resins, polyvinyl alcohol resins, polyvinyl acetal resins, polyethylene oxide resins, polypropylene oxide resins, ethyl cellulose resins, methyl cellulose resins, polyamide resins, polyamic acid resins, polyurethane resins, polyimide resins, polyamideimide resins, polyvinyl phenol resins, melamine resins, phenolic resins, epoxy resins, and alkyd resins. Furthermore, the undercoat layer may be a resin having a structure in which a resin having a polymerizable functional group is crosslinked with a monomer having a polymerizable functional group.

[0075] The undercoat layer may contain inorganic or organic compounds in addition to resins. Examples of inorganic compounds include metals, oxides, and salts. Examples of metals include gold, silver, and aluminum. Examples of oxides include zinc oxide, white lead, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, indium oxide, tin oxide, and zirconium oxide. Examples of salts include barium sulfate and strontium titanate.

[0076] These inorganic compounds may be present in the film in the form of particles. The number average particle size 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.

[0077] 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, organotitanium compounds, etc. Furthermore, they may be doped with elements such as tin, phosphorus, aluminum, and niobium.

[0078] Examples of the organic compound include an electron transport compound and a conductive polymer, such as polythiophene, polyaniline, polyacetylene, polyphenylene, and polyethylenedioxythiophene.

[0079] Examples of electron transport substances include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, aryl halide compounds, silole compounds, and boron-containing compounds.

[0080] The electron transport material may have polymerizable functional groups and may be crosslinked with a resin having functional groups that can react with the polymerizable functional groups, such as hydroxyl, thiol, amino, carboxyl, vinyl, acryloyl, methacryloyl, and epoxy groups.

[0081] These organic compounds may be present in the film in a particulate state, or may be surface-treated. Various additives, such as a leveling agent such as silicone oil, a plasticizer, or a thickener, may be added to the undercoat layer. The undercoat layer can be obtained by preparing a coating solution for the undercoat layer containing the above materials, applying it to a support or a conductive layer, and then drying or curing the coating.

[0082] Examples of the solvent used to prepare the coating liquid include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, aromatic hydrocarbon-based solvents, etc. Examples of the dispersion method for dispersing particles in the coating liquid include methods using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

[0083] <Photosensitive Layer> The photosensitive layer of an electrophotographic photoreceptor is mainly classified into (1) a multi-layer type photosensitive layer and (2) a single-layer type photosensitive layer. (1) The multi-layer type photosensitive layer is a photosensitive layer having a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material. (2) The single-layer type photosensitive layer is a photosensitive layer containing both a charge generation material and a charge transport material.

[0084] (1) Multilayer Photosensitive Layer The multilayer 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 generation material and a resin. Examples of the charge generation material include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred.

[0085] The content of the charge generating material in the charge generating layer is preferably 40% by mass or more and 85% by mass or less, and more preferably 60% by mass or more and 80% by mass or less, based on the total mass of the charge generating 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, and polyvinyl chloride resin. Among these, polyvinyl butyral resin is more preferred.

[0086] The charge generating layer may further contain additives such as antioxidants and ultraviolet absorbers, etc. Specific examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

[0087] The charge generation layer can be formed by preparing a coating solution for the charge generation layer containing the above-mentioned materials and solvent, forming this coating film on the undercoat layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. The thickness of the charge generation layer is preferably 0.1 μm or more and 1.5 μm or less, and more preferably 0.15 μm or more and 1.0 μm or less.

[0088] (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 materials. Among these, triarylamine compounds and benzidine compounds are preferred.

[0089] The content of the charge transport material in the charge transport layer is preferably 25% by weight to 70% by weight, more preferably 30% by weight to 55% by weight, based on the total weight of the charge transport layer.

[0090] Examples of the resin include polyester resin, polycarbonate resin, acrylic resin, and polystyrene resin. 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, and more preferably 5:10 to 12:10.

[0091] The charge transport layer may also contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, slipping agents, and abrasion resistance improvers. Specific examples of such additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0092] The charge transport layer can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned materials and solvent, forming this coating film on the charge generation layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents and aromatic hydrocarbon-based solvents are preferred.

[0093] The thickness of the charge transport layer is preferably from 3 μm to 50 μm, more preferably from 5 μm to 40 μm, and particularly preferably from 10 μm to 30 μm.

[0094] (2) Single-Layer Photosensitive Layer The single-layer photosensitive layer can be formed by preparing a coating solution for the photosensitive layer containing a charge generating material, a charge transport material, a resin, and a solvent, forming the coating film on the undercoat layer, and drying it. The charge generating material, charge transport material, and resin are the same as those exemplified in "(1) Multilayer Photosensitive Layer" above.

[0095] The thickness of the single-layer photosensitive layer is preferably from 10 μm to 45 μm, and more preferably from 25 μm to 35 μm.

[0096] <Process Cartridge, Electrophotographic Apparatus> The process cartridge of the present invention integrally supports the electrophotographic photosensitive member of the present invention and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably mountable to the main body of the electrophotographic apparatus. The electrophotographic apparatus of the present invention has the electrophotographic photosensitive member of the present invention, a charging means, an exposing means, a developing means, and a transfer means.

[0097] (Configuration of Electrophotographic Apparatus) FIG. 3 shows a schematic example of the configuration of an electrophotographic apparatus having a process cartridge equipped with the electrophotographic photosensitive member of the present invention. The electrophotographic apparatus of this embodiment is a so-called tandem-type electrophotographic apparatus having a plurality of image forming stations a to d. The first image forming station a forms images using toner of each color: yellow (Y), the second image forming station b forms images using toner of each color: magenta (M), the third image forming station c forms images using toner of each color: cyan (C), and the fourth image forming station d forms images using toner of each color: black (Bk). These four image forming stations are arranged in a row at regular intervals, and the configuration of each image forming station is substantially similar in many respects except for the color of the toner they contain. Therefore, the electrophotographic apparatus of this embodiment will be described below using the first image forming station a.

[0098] The first image forming unit a has a photosensitive drum 1a, which is a drum-shaped electrophotographic photosensitive member, a charging roller 2a, which is a charging member, and a developing unit 4a (including a developing roller 41a). The photosensitive drum 1a is an image carrier that carries a toner image and is driven to rotate in the direction of the arrow in the figure at a predetermined peripheral speed (process speed). The developing unit 4a contains yellow toner and develops the yellow toner on the photosensitive drum 1a.

[0099] An image forming operation is initiated when a control unit (not shown), such as a controller, receives an image signal, causing the photosensitive drum 1a to rotate. During rotation, the photosensitive drum 1a is uniformly charged to a predetermined voltage (charging voltage) with a predetermined polarity (negative in this embodiment) by the charging roller 2a and exposed to light by the exposure unit 3a in accordance with the image signal. This forms an electrostatic latent image on the photosensitive drum 1a corresponding to the yellow component of the target color image. The electrostatic latent image is then developed by the developing unit 4a at the development position, becoming a visible yellow toner image on the photosensitive drum 1a. The normal charging polarity of the toner contained in the developing unit 4a is negative, and the electrostatic latent image is reversely developed with 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 can also be applied to an electrophotographic device in which an electrostatic latent image is positively developed with toner charged to the opposite polarity to that of the photosensitive drum 1a.

[0100] Furthermore, the surface layer of the charging roller 2a can be provided with numerous protrusions derived from particles. The protrusions 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 section. When residual toner, which is toner that remains on the photosensitive drum 1a without being transferred in the primary transfer section described below, enters the charging section, the protrusions serve to prevent areas other than the protrusions from coming into contact with the residual toner, thereby contaminating the charging roller 2a with the residual toner.

[0101] The pre-exposure unit 5a as a discharging means discharges the surface of the photosensitive drum 1a by exposing it to light before the surface of the photosensitive drum 1a is charged by the charging roller 2a. By discharging the surface of the photosensitive drum 1a, the pre-exposure unit 5a has the role of leveling the surface potential formed on the photosensitive drum 1a and of controlling the amount of discharge caused by discharge in the charging section.

[0102] The endless, movable intermediate transfer belt 10 is conductive, contacts the photosensitive drum 1a to form a primary transfer portion, and rotates at approximately the same peripheral speed as the photosensitive drum 1a. The intermediate transfer belt 10 is stretched between an opposing roller 13 as an opposing member, and a driving roller 11, a tensioning roller 12, and a metal roller 14a as tensioning members, and is stretched by the tensioning roller 12 with a total tension of 60 N. The intermediate transfer belt 10 can be moved by driving the driving roller 11 to rotate in the direction of the arrow in the figure.

[0103] The yellow toner image formed on the photosensitive drum 1a is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10 as it passes through the primary transfer section. During the primary transfer, a current is supplied to the conductive intermediate transfer belt 10 from a secondary transfer roller 15, which serves as a secondary transfer member and is in contact with the outer circumferential surface of the intermediate transfer belt 10. The current supplied from the secondary transfer roller 15 flows in the circumferential direction of the intermediate transfer belt 10, thereby primarily transferring the toner image from the photosensitive drum 1a to the intermediate transfer belt 10. At this time, a voltage of a predetermined polarity (positive polarity in this embodiment), which is opposite to the normal charging polarity of the toner, is applied to the secondary transfer roller 15 from a transfer power source (not shown).

[0104] Similarly, a magenta toner image (second color), a cyan toner image (third color), and a black toner image (fourth color) are formed and transferred sequentially onto the intermediate transfer belt 10 in a superimposed manner. As a result, four-color toner images corresponding to the desired color image are formed on the intermediate transfer belt 10. The four-color toner images carried on the intermediate transfer belt 10 are then secondarily transferred en bloc onto the surface of a transfer material P, such as paper or an OHP sheet, fed by a paper feed unit 50 as the toner images pass through a secondary transfer section formed by contact between the secondary transfer roller 15 and the intermediate transfer belt 10. The transfer material P, onto which the four-color toner images have been transferred by the secondary transfer, is then heated and pressurized in a fixing unit 30, whereby the four color toners are melted, mixed, and fixed to the transfer material P. Any toner remaining on the intermediate transfer belt 10 after the secondary transfer is cleaned and removed by a belt cleaning unit 16 provided opposite the opposing roller 13 via the intermediate transfer belt 10. The electrophotographic photoreceptor of the present invention can be used in laser beam printers, LED printers, copiers, and the like.

[0105] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited to the following examples in any way as long as the gist of the invention is not exceeded.

[0106] In the following description of the examples, "parts" are based on mass unless otherwise specified. The film thickness of the electrophotographic photoreceptor other than the surface layer in the examples and comparative examples was measured using an eddy current film thickness meter (product name: Fischerscope, manufacturer: Fisher Instruments) or was calculated by converting the mass per unit area into specific gravity.

[0107] <Production Example (1) of Electrophotographic Photoreceptor 1> An aluminum cylinder (JIS-A3003 aluminum alloy) having a diameter of 20 mm and a length of 257.5 mm 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 methods.

[0108] (Preparation of Coating Solution for Conductive Layer) An anatase type titanium oxide having an average primary particle size of 200 nm was used as a substrate, and titanium was replaced with TiO ２ 33.7 parts of niobium converted to Nb ２O ５ A titanium niobium sulfate solution containing 2.9 parts of titanium niobium sulfate (C equivalent) was prepared. 100 parts of the substrate was dispersed in pure water to prepare a 1,000 parts suspension, which was then heated to 60°C. The titanium niobium sulfate solution and 10 mol / L sodium hydroxide were added dropwise over 3 hours so that the pH of the suspension was 2 to 3. After the entire amount was added dropwise, the pH was adjusted to near neutral, and a polyacrylamide-based flocculant was added to precipitate the solids. The supernatant was removed, filtered, washed, and dried at 110°C to obtain an intermediate containing 0.1 mass% of organic matter derived from the flocculant (C equivalent). This intermediate was calcined in nitrogen at 750°C for 1 hour and then calcined in air at 450°C to produce titanium oxide particles 1. The obtained particles had an average primary particle size of 220 nm, as measured by a particle size measurement method using a scanning electron microscope described below.

[0109] Next, a phenolic resin (monomer / oligomer of phenolic resin) (product name: Plyofen J-325, manufacturer: DIC Corporation, resin solid content: 60%, density after curing: 1.3 g / cm) was used as a binder material. ３ 50 parts of the above-mentioned methylcellulose acetate ester compound were dissolved in 35 parts of 1-methoxy-2-propanol as a solvent to obtain a solution.

[0110] To this solution, 60 parts of titanium oxide particles 1 were added, and the resulting mixture was placed in a vertical sand mill using 120 parts of glass beads having a number-average primary particle size of 1.0 mm as a dispersion medium. The mixture was then subjected to a dispersion treatment for 4 hours at a dispersion temperature of 23±3°C and a rotation speed of 1500 rpm (peripheral speed of 5.5 m / s) to obtain a dispersion. The glass beads were removed from the dispersion using a mesh. The dispersion from which the glass beads had been removed was then mixed with 0.01 parts of silicone oil (product name: SH28PAINT ADDITIVE, manufacturer: Dow Corning Toray Co., Ltd.) as a leveling agent and 0.01 parts of silicone resin particles (product name: KMP-590, manufacturer: Shin-Etsu Chemical Co., Ltd., average primary particle size: 2 μm, density: 1.3 g / cm) as a surface roughness imparting agent. ３ 8 parts of toluene) was added and stirred. Thereafter, the mixture was filtered under pressure using PTFE filter paper (product name: PF060, manufactured by Advantec Toyo Co., Ltd.) to prepare a coating liquid for the conductive layer.

[0111] (Preparation of Coating Solution for Undercoat Layer) 100 parts of rutile-type titanium oxide particles (average primary particle size: 50 nm, manufacturer: Teika Corporation) were mixed with 500 parts of toluene by stirring, and 3.5 parts of vinyltrimethoxysilane (product name: KBM-1003, manufacturer: Shin-Etsu Chemical Co., Ltd.) was added. The mixture was dispersed for 8 hours in a vertical sand mill using glass beads with a diameter of 1.0 mm. After removing the glass beads, the toluene was distilled off under reduced pressure, and the mixture was dried at 120°C for 3 hours to obtain rutile-type titanium oxide particles surface-treated with an organosilicon compound. The volume of the obtained titanium oxide particles was a and the average primary particle size of the titanium oxide particles was b [μm], where a / b = 15.6. The value of a was determined from a microscopic image of a cross section of the electrophotographic photoreceptor after fabrication using a field emission scanning electron microscope (FE-SEM, product name: S-4800, manufacturer: Hitachi High-Technologies Corporation).

[0112] A dispersion was prepared by adding 18.0 parts of the rutile-type titanium oxide particles that had been surface-treated with the organosilicon compound, 4.5 parts of N-methoxymethylated nylon (product name: Toresin (registered trademark) EF-30T, manufacturer: Nagase ChemteX Corporation), and 1.5 parts of copolymer nylon resin (product name: Amilan (registered trademark) CM8000, manufacturer: Toray Industries, Inc.) to a mixed solvent of 90 parts of methanol and 60 parts of 1-butanol. This dispersion was dispersed for 5 hours in a vertical sand mill using glass beads with a diameter of 1.0 mm, and the glass beads were removed to prepare a coating solution for an undercoat layer.

[0113] (Synthesis of Phthalocyanine Pigment) (Synthesis Example) Under a nitrogen flow atmosphere, 100 g of gallium trichloride and 291 g of orthophthalonitrile were added to 1,000 mL of α-chloronaphthalene, and the mixture was reacted at 200°C for 24 hours, and then the product was filtered. The obtained wet cake was heated and stirred in N,N-dimethylformamide at 150°C for 30 minutes, and then filtered. The resulting residue was washed with methanol and dried, yielding a chlorogallium phthalocyanine pigment in a yield of 83% by mass.

[0114] 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 added dropwise to an ice-cooled mixed solution of 1700 mL of distilled water and 660 mL of concentrated aqueous ammonia to reprecipitate it, which was then thoroughly washed with distilled water and dried to obtain a hydroxygallium phthalocyanine pigment.

[0115] (Preparation of Coating Solution for Charge Generating Layer) 0.5 parts of the hydroxygallium phthalocyanine pigment obtained in 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 a temperature of 25°C for 24 hours using a sand mill (product name: BSG-20, manufacturer: Imex Co., Ltd.). This was carried out under conditions of a disk rotation speed of 1,500 revolutions per minute. The solution thus treated was filtered through a filter (product number: N-NO.125T, pore size: 133 μm, manufacturer: NBC Meshtec Co., Ltd.) to remove the glass beads. 30 parts of N,N-dimethylformamide was added to this solution, followed by filtration. The residue on the filter was thoroughly washed with n-butyl acetate. The washed residue was then vacuum dried to obtain 0.45 parts of hydroxygallium phthalocyanine pigment. The resulting pigment contained N,N-dimethylformamide.

[0116] Next, 20 parts of the hydroxygallium phthalocyanine pigment obtained by the milling treatment, 10 parts of polyvinyl butyral (product name: S-LEC (registered trademark) BX-1, manufacturer: Sekisui Chemical Co., Ltd.), 190 parts of cyclohexanone, and 482 parts of glass beads having a diameter of 0.9 mm were dispersed using a sand mill (product name: K-800, manufacturer: Igarashi Machine Manufacturing (now Imex Co., Ltd.), disk diameter: 70 mm, number of disks: 5) at a cooling water temperature of 18°C ​​for 4 hours. The dispersion was carried out at a disk rotation rate of 1800 revolutions per minute. The glass beads were removed from the dispersion, and 444 parts of cyclohexanone and 634 parts of ethyl acetate were added to prepare a coating solution for a charge generating layer.

[0117] (Preparation of Coating Liquid for Charge Transport Layer) (Preparation Example of Charge Transport Layer) Next, the following materials were prepared to prepare a mixed solvent. Orthoxylene 25 parts by weight Methyl benzoate 25 parts by weight Dimethoxymethane 25 parts by weight Furthermore, the following materials were dissolved in the mixed solvent to prepare a coating liquid for a charge transport layer. Charge transport material (hole transport material) represented by the following structural formula (C-1) 5 parts by weight Charge transport material (hole transport material) represented by the following structural formula (C-2) 5 parts by weight Polycarbonate (product name: Iupilon (registered trademark) Z400, manufacturer: Mitsubishi Engineering-Plastics Corporation) 10 parts by weight This Coating Liquid for Charge Transport Layer 1 was dip-coated on the charge generating 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 thickness of 15 μm.

[0118] <Production Example (2) of Electrophotographic Photoreceptor 1> (Support) An aluminum cylinder (standard: JIS-A3003, aluminum alloy) having a diameter of 20 mm and a length of 257.5 mm was used as a support (conductive support).

[0119] (Conductive Layer) The conductive layer coating liquid was dip-coated onto the above support to form a coating film, and the coating film was heated at 150° C. for 30 minutes to be cured, thereby forming a conductive layer having a thickness of 22 μm.

[0120] (Undercoat Layer) The undercoat layer coating liquid was dip coated onto the conductive layer to form a coating film, and the coating film was heated at 100° C. for 10 minutes to be cured, thereby forming an undercoat layer with a thickness of 1.8 μm.

[0121] (Charge Generation Layer) The undercoat layer was dip-coated with the coating liquid for the charge generation layer to form a coating film, and the coating film was dried by heating at a temperature of 100° C. for 10 minutes to form a charge generation layer having a thickness of 0.20 μm.

[0122] (Charge Transport Layer) The charge transport layer coating liquid was dip coated onto the charge generating layer to form a coating film, and the coating film was dried by heating at a temperature of 120° C. for 30 minutes to form a charge transport layer having a thickness of 21 μm.

[0123] (Surface Layer) The binder resin, first particles, second particles, and additives may be commercially available or may be synthesized in-house. The method for producing niobium-doped titanium oxide will be described later. Preparation of Anatase Titanium Oxide Anatase titanium oxide particles can be produced by the known sulfuric acid method. In producing titanium oxide, a solution containing titanium sulfate and titanyl sulfate as titanium compounds is heated and hydrolyzed to produce a hydrous titanium dioxide slurry, which is then dehydrated and fired. This results in an anatase titanium oxide with a degree of anatase conversion of nearly 100%. By controlling the titanyl sulfate solution concentration using the above method, anatase titanium oxide particles 1 to 11, as shown in Table 1, were produced.

[0124]

[0125] Preparation of Conductive Particles 1 Niobium (V) hydroxide was dissolved in concentrated sulfuric acid and mixed with an aqueous titanium sulfate solution to prepare an acidic mixed solution of niobium salt and titanium salt (hereinafter referred to as "titanium-niobium mixed solution"). Anatase-type titanium oxide particles 1 were dispersed in water as core particles to form a suspension, which was then heated to 70°C with stirring.

[0126] While maintaining the pH at 2.5, a titanium-niobium mixed solution containing 337 g / kg of Ti and 10.3 g / kg of Nb relative to the weight of the anatase type titanium oxide particles 1 and an aqueous sodium hydroxide solution were simultaneously added.

[0127] After completion of the dropwise addition, the suspension was filtered, washed, and dried at 110°C for 8 hours. This dried product was calcined in a nitrogen atmosphere at 725°C for 1 hour to obtain niobium-doped titanium oxide in which niobium atoms were unevenly distributed near the surface. 100.0 parts of this niobium-doped titanium oxide was mixed with 6.0 parts of a compound represented by the following formula (S-1) (product name: trimethoxypropylsilane, manufactured by Tokyo Chemical Industry Co., Ltd.) and 200 parts of toluene, stirred for 4 hours with a stirrer, filtered, washed, and then further heat-treated at 120°C for 3 hours. The resulting niobium-doped titanium oxide 1 had an average particle size of 70 nm and was designated as conductive particles 1.

[0128] The obtained niobium-doped titanium oxide was observed using a transmission electron microscope (product name: JEM2800, manufacturer: JEOL Ltd.), and the ratio of niobium atoms to titanium atoms at the particle center and within 5% of the particle diameter from the particle surface was measured using EDS (product name: NORAN SYSTEM 7, manufacturer: Thermo Fisher Scientific). Observation was performed on 10 particles in each thinned sample, and the arithmetic average value was adopted. The obtained ratios of niobium atoms to titanium atoms at the particle center and within 5% of the particle diameter from the particle surface were designated α1 and α2, respectively. When calculated by defining α2 / α1 as the niobium distribution ratio, the value was 7.7. The EDS measurement conditions were an acceleration voltage of 200 kV and a beam diameter of 1.0 nm.

[0129] In producing niobium-doped titanium oxide, the average particle size, volume resistivity, and niobium distribution rate of the niobium-doped titanium oxide can be changed by changing the type of core particles used and the weight ratio of niobium atoms to titanium atoms in the titanium-niobium mixed solution relative to the core material. Details of the niobium-doped titanium oxide produced in this experiment are listed in Table 2. It can be confirmed by EDS that the coating layer is niobium-doped titanium oxide.

[0130] Furthermore, with reference 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 than the density at the center of the particle, and this was listed in Table 2. The oxygen deficiency rate of conductive particle 1 was measured using a thermogravimetric analyzer (product name: Q5000IR, manufacturer: TA Instruments). The temperature rise rate during measurement was 10°C / min, and the measurement was performed in an oxygen stream. The mass at the temperature where the mass began to increase in the range from 300°C to 900°C was taken as the minimum mass, and the oxygen deficiency rate was calculated from the minimum mass and the maximum mass during subsequent heating, and this is listed in Table 2.

[0131] The ratio of the oxygen deficiency rate of the core material to the oxygen deficiency rate of the coating layer of the conductive particle 1 can be measured by energy dispersive X-ray analysis (EDS). The oxygen deficiency rate β in a region within 5% of the primary particle diameter from the surface of the niobium-doped titanium oxide particles and the oxygen deficiency rate γ in other regions were measured by energy dispersive X-ray analysis (EDS) using an STEM, and the value of β / γ is shown in Table 2.

[0132] <Preparation of conductive particles 2 to 17> Conductive particles 2 to 17 were prepared in the same manner as in the preparation of conductive particle 1, except that the type of core particle used and the weights of niobium atoms and titanium atoms in the titanium-niobium mixed solution were changed as shown in Table 2. The average particle diameter, volume resistivity, and niobium uneven distribution rate of the obtained conductive particles 2 to 17 are shown in Table 2.

[0133] <Quantitative Determination of Niobium Atoms Contained in Conductive Particles> The quantitative determination of niobium atoms contained in conductive particles is carried out as follows. Conductive particles are pelletized by the press molding described below to prepare a sample. The prepared sample is measured using an X-ray fluorescence analyzer (XRF), and the niobium atom content of the entire conductive particle is quantified by the FP method. Specifically, the niobium atom content is quantified as niobium pentoxide and converted into the niobium atom content.

[0134] (i) Example of equipment used: X-ray fluorescence analyzer 3080 (Rigaku Denki Co., Ltd.) (ii) Sample preparation: Samples were prepared using a sample press molding machine, MAEKAWA Testing Machine (manufacturer: MFG Co., Ltd.). 0.5 g of conductive particles were placed in an aluminum ring (model number: 3481E1), and the ring was pressed for 1 minute under a load of 5.0 tons to form a pellet. (iii) Measurement conditions: Measurement diameter: 10φ; Measurement potential, voltage: 50 kV, 50 to 70 mA; 2θ angle: 25.12°; Crystal plate: LiF; Measurement time: 60 seconds

[0135]

[0136] The ratio S1 of the area occupied by the first particles to the total area of ​​the surface layer when viewed from above, and the ratio S2 of the area occupied by the second particles to the total area of ​​the surface layer can be adjusted mainly by the mixing ratio of the resin and the particles. For example, the ratio (S1 + S2) can be increased by increasing the mixing ratio of the particles relative to the amount of resin. In addition, (S1 / S2) can be adjusted by adjusting the mixing ratio of the first particles to the second particles.

[0137] The exposed height L1 of the first particles and the exposed height L2 of the second particles exposed on the surface of the electrophotographic photosensitive member can be adjusted by the drying temperature after coating, the type of solvent, and the solid content of the coating liquid. For example, using a solvent type with a high evaporation rate tends to accelerate convection during drying, increasing the exposed height of the particles. For the same reason, increasing the drying temperature after coating also increases the exposed height of the particles. Increasing the solid content of the coating liquid suppresses convection, and therefore tends to decrease the exposed height of the particles.

[0138] The thickness T1 of the surface layer of the electrophotographic photosensitive member can be adjusted by the solid content of the coating liquid and the coating speed during impregnation coating. For example, increasing the solid content of the coating liquid increases the thickness T1. Also, increasing the coating speed during impregnation coating increases the thickness T1.

[0139] <Production Example (3) of Electrophotographic Photoreceptor 1> <Preparation of Surface Layer Coating Liquid 1> 8.40 parts of conductive particles 6 as first particles, 3.78 parts of silica particles ("QSG-80", manufacturer: Shin-Etsu Chemical Co., Ltd.) as second particles, 3.60 parts of a compound represented by the following formula (O-1) as a binder resin, 91 parts of 1-propanol, and 91 parts of cyclohexane were mixed and stirred for 6 hours using a stirring / dispersing device to prepare surface layer coating liquid 1.

[0140] <Production Examples of Electrophotographic Photoreceptors 2 to 52> In the Production Example of the electrophotographic photoreceptor 1, the charge transport layer was produced in the same manner, but the materials for surface layer coating liquids 2 to 52 used in producing the surface layer were changed and prepared as shown in Table 3. At this time, the dispersion step of the surface layer coating liquid was adjusted appropriately. Using each of the prepared surface layer coating liquids, electrophotographic photoreceptors 2 to 52 were produced in the same manner as for the electrophotographic photoreceptor 1. That is, electrophotographic photoreceptors 2 to 52 were produced in the same manner as for the electrophotographic photoreceptor 1, using the surface layer coating liquids 2 to 52, respectively. At this time, the coating conditions in the coating step of the surface layer of the electrophotographic photoreceptor were adjusted appropriately. The results are shown in Table 4. In Table 4, the concentration ratio calculated as niobium atomic concentration / titanium atomic concentration at the center of the niobium-doped titanium oxide particle, calculated as niobium atomic concentration / titanium atomic concentration, from the surface of the niobium-doped titanium oxide particle to within 5% of the primary particle diameter of the niobium-doped titanium oxide particle, was recorded as "Nb concentration / Ti concentration from the surface of the first particle to within 5% of the primary particle diameter, relative to Nb concentration / Ti concentration at the center of the first particle" in EDS analysis of the niobium-doped titanium oxide particle using a scanning transmission electron microscope (STEM).

[0141]

[0142] Details of the first particles and the second particles are as follows: 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 Flowform N990, manufacturer: CanCarb), Indium Tin Oxide, Blue (manufacturer: Corefront Co., Ltd.), ZnO-S05 (manufacturer: Sumitomo Osaka Cement Co., Ltd.).

[0143] (Density) The density of the particles was measured by the pycnometer (liquid phase displacement) method using butanol as the dispersion solvent. The density and specific gravity of the particles can also be determined by referring to the published values ​​in the database POLYINFO of the manufacturer of each material and the National Institute for Materials Science. For example, when 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 the carbon black is 1.8 g / cm ３ is.

[0144]

[0145] Comparative Example In the production example of the electrophotographic photoreceptor 1, the charge transport layer was produced in the same manner, and the materials for surface layer coating liquids C1 to C18 used in producing the surface layer were changed and prepared as shown in Table 5. Using the prepared surface layer coating liquids, electrophotographic photoreceptors C1 to C18 were produced in the same manner as for the electrophotographic photoreceptor 1. That is, electrophotographic photoreceptors C1 to C18 were produced in the same manner as for the electrophotographic photoreceptor 1, using the surface layer coating liquids C1 to C18, respectively. The results are shown in Table 6. In Table 6, the concentration ratio calculated as niobium atomic concentration / titanium atomic concentration at the center of the niobium-doped titanium oxide particle, calculated as niobium atomic concentration / titanium atomic concentration, from the surface of the niobium-doped titanium oxide particle to within 5% of the primary particle diameter of the niobium-doped titanium oxide particle, was recorded as "Nb concentration / Ti concentration from the surface of the first particle to within 5% of the primary particle diameter, relative to Nb concentration / Ti concentration at the center of the first particle" in EDS analysis of the niobium-doped titanium oxide particle using a scanning transmission electron microscope (STEM).

[0146]

[0147]

[0148] [Evaluation Method] <Measurement of the Ratio S1 of the Area Occupied by the First Particles to the Total Area When the Surface Layer is Viewed from the Top and the Area S2 Occupied by the Second Particles> An electrophotographic photoreceptor having 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. The cutting positions were 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, at 90° intervals in the circumferential direction, for a total of 12 5 mm square sample pieces. The sample pieces were fixed to a sample holder so that the surface layer of the sample pieces could be observed. The sample holder to which the sample pieces were fixed was subjected to surface observation using a scanning electron microscope (hereinafter also referred to as "SEM," product name: JSM7800F, manufacturer: JEOL Ltd.). The surface image of the electrophotographic photoreceptor surface obtained by SEM was subjected to image processing, and the total area of ​​the insulating particle portion and the total area of ​​the conductive particle portion relative to the total observed area were defined as s1 [%] and s2 [%], respectively (see Figure 3). Conductive particles and insulating particles were distinguished using SEM-EDX. The above-mentioned operation was performed on 12 sample pieces to determine s1 and s2 for each, and the arithmetic mean of s1 for the 12 points was defined as S1 for the electrophotographic photosensitive member, and the arithmetic mean of s2 for the 12 points was defined as S2 for the electrophotographic photosensitive member.

[0149] <Measurement of Exposed Height L1 of First Particles and Exposed Height L2 of Second Particles> L1 and L2 were determined by FIBSEM observation as follows. An electrophotographic photoreceptor having 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. The cutting positions were 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, and circumferentially at 90° intervals, for a total of 12 5 mm square sample pieces. The sample pieces were fixed to a sample holder so that the surface layer could be observed. The sample holder to which the sample pieces were fixed was subjected to cross-sectional observation using a FIBSEM (product name: Nvision, manufacturer: ZEISS). The measurement conditions are described below. In a cross-sectional image of the surface layer of the electrophotographic photoreceptor obtained by FIBSEM, the first particles were numbered sequentially, starting from 1, from the left side of the image.

[0150] Lines A1 and B1 were drawn tangent to the end of the first particle numbered 1 and perpendicular to the lower layer interface. Lines A1 and B1 are parallel to each other and perpendicular to the lower layer interface, with line A1 always located to the left of line B1. This procedure was performed for all first particles that existed in the cross-sectional image and whose entire images were contained within the cross-sectional image. The intersection of line A1 and the lower layer interface was designated a1, and the intersection of line A2 and the lower layer interface was designated a2. The length of the line connecting intersection a1 and intersection a2 was designated as unit measurement range C1. The unit measurement range was determined for all lines AX (X = 1, 2, 3, ...), and each was designated as unit measurement range CX (X = 1, 2, 3, ...). In each unit measurement range CX, the longest straight line perpendicular to the lower layer interface and intersecting with the surface boundary line of the surface layer was defined as the film thickness tX (X = 1, 2, 3, ...) of the unit measurement range CX, and the shortest straight line was defined as the recess vX (X = 1, 2, 3, ...) of the unit measurement range CX.

[0151] Furthermore, the longest straight line perpendicular to the lower layer interface and intersecting the surface boundary line of the surface layer formed by the second particles was defined as the small convex portion wX (X = 1, 2, 3, ...) of the unit measurement range CX. The difference between the length of line tX and the length of line vX was defined as the exposed 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 exposed height l2-X (X = 1, 2, 3, ...) of the second particle. The arithmetic mean value of the obtained exposed heights l1 of the first particles was defined as the average exposed height of the first particles in the cross-sectional image, and the arithmetic mean value of the exposed heights l2 of the second particles was defined as the average exposed height of the second particles in the cross-sectional image. The arithmetic mean values ​​of the exposed heights l1 and l2 of the 12 sample pieces were further defined as the exposed height L1 of the first particles and the exposed height L2 of the second particles in the surface layer of the electrophotographic photosensitive member.

[0152] The measurement conditions for the FIBSEM are as follows: The surface layer was three-dimensionalized to 2 μm x 2 μm x 2 μm using the Slice & View function of the FIB-SEM. The conditions for Slice & View were as follows: Processing of sample for analysis: FIB method Processing and observation device: NVision 40 manufactured by SII / Zeiss Slice spacing: 10 nm (Observation conditions) Acceleration voltage: 1.0 kV Sample tilt: 54° WD: 5 mm Detector: BSE detector Aperture: 60 μm, high current ABC: ON Image resolution: 1.25 nm / pixel The measurement environment was temperature: 23°C, pressure: 1 x 10 －４ Pa. As the processing and observation device, a Strata 400S (sample tilt: 52°) manufactured by FEI can also be used.

[0153] The analysis area was 2 μm long x 2 μm wide, and the information for each cross section was integrated. ３ The volume V per cross section was calculated. Image analysis of each cross section was performed using image processing software (product name: Image-Pro Plus, manufacturer: Media Cybernetics).

[0154] Furthermore, the surface shape was measured using a scanning probe microscope (JSPM-5200, manufactured by JEOL Ltd.), and it was confirmed that the results were consistent with the measurement results using FIBSEM. Particles in the measurement using the scanning probe microscope were distinguished by marking the measurement position after the measurement and using the EDX function of a scanning electron microscope (product name: JSM7800F, manufactured by JEOL Ltd.).

[0155] <Measurement of the Average Primary Particle Size D1 of the First Particles and the Average Primary Particle Size D2 of the Second Particles> First, the entire electrophotographic photoreceptor was immersed in methyl ethyl ketone (MEK) in a measuring cylinder and irradiated with ultrasonic waves to remove the resin layer. The substrate of the electrophotographic photoreceptor was then removed. The insoluble matter (photosensitive layer and surface layer containing metal oxide particles) that did not dissolve in MEK was then filtered and dried in a vacuum dryer. The resulting solid was then suspended in a 1:1 volumetric ratio mixed solvent of tetrahydrofuran (THF) and methylal. The insoluble matter was then filtered, and the filtered residue was collected and dried in a vacuum dryer. This procedure yielded the first particles, the second particles, and the resin of the surface layer. The filtered residue was then heated to 500°C in an electric furnace until the solid consisted only of the first particles and the second particles. The first particles and the second particles were then collected. To ensure the necessary amounts of the first particles and the second particles for measurement, multiple electrophotographic photoreceptors were subjected to the same treatment.

[0156] A portion 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.). The first particles and second particles were observed using the STEM mode of a scanning transmission electron microscope (product name: JEM2800, manufacturer: JEOL Ltd.). The observations were performed at magnifications of 500,000 to 1,200,000 times to facilitate calculation of the first particles and second particles, and 100 STEM images of the first particles and 100 STEM images of the second particles were taken. The first particles and second particles were distinguished using the EDX function of the scanning electron microscope. The acceleration voltage was set to 200 kV, the probe size to 1 nm, and the image size to 1024 x 1024 pixels.

[0157] Using the obtained STEM image, the primary particle diameter was measured using 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 that state, if you select Set Scale from the Analyze menu, a new window will open and the pixel distance of the selected straight line will be entered in the Distance in Pixels field. Enter the scale bar value (e.g., 100) in the Known Distance field of the window, enter the scale bar unit (e.g., nm) in the Unit of Measurement field, and click OK to complete the scale setting. Next, using the straight line tool, draw a straight line to represent the maximum diameter of the metal oxide particles, and the particle diameter was calculated. The same procedure was performed for 100 metal oxide particles, and the number average of the obtained values ​​(maximum diameter) was taken as the primary particle diameter of the metal oxide particles. However, for samples using carbon black as the first particles, the average primary particle diameter of the first particles was measured by the following method.

[0158] An electrophotographic photoreceptor having 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. The cutting positions were 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, with a total of 12 5 mm square sample pieces cut at 90° intervals in the circumferential direction. The sample pieces were fixed to a sample holder so that the surface layer could be observed. The sample holder with the fixed sample pieces was subjected to cross-sectional observation using a FIBSEM (product name: [Nvision], manufacturer: ZEISS). The measurement conditions were the same as those described above. The particle size of the first particles was measured in a cross-sectional image of the surface layer of the electrophotographic photoreceptor obtained by FIBSEM. This procedure was performed on all first particles that were present in the cross-sectional image and whose entire image was within the cross-sectional image. The arithmetic mean value of the particle diameters of the obtained first particles was taken as the average particle diameter of the sample piece, and the arithmetic mean of the average particle diameters of each of the 12 sample pieces was further taken as the average primary particle diameter D1 of the first particles in the surface layer of the electrophotographic photosensitive member.

[0159] <Measurement of powder resistivity R1 and powder resistivity R2> The first particles were subjected to a pressure of 300 kg / cm ２ The powder resistivity R1 was measured using a four-probe resistivity measurement device (product name: Loresta (registered trademark), manufacturer: Mitsubishi Chemical Corporation) at an applied voltage of 100 V. The powder resistivity R2 of the second particles was also measured in the same manner.

[0160] <Measurement of film thickness T1> An electrophotographic photoreceptor having 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. The cutting positions were 38 mm, 128 mm, and 218 mm from one end in the longitudinal direction, and 12 sample pieces were cut out at 90° intervals in the circumferential direction. The sample pieces were fixed to a sample holder so that the surface layer could be observed. The sample holder to which the sample pieces were fixed was subjected to cross-sectional observation using a FIBSEM (product name: Nvision, manufacturer: ZEISS). The measurement conditions were the same as those described above.

[0161] 4 and 5 show cross sections of the surface layer of an electrophotographic photoreceptor. As shown in FIG. 4, in a cross-sectional image of the surface layer of an electrophotographic photoreceptor obtained by FIBSEM, first particles were numbered sequentially from the left side of the image, starting with 1. Lines A1 and B1 were drawn tangent to the end of the first particle numbered 1 and perpendicular to the lower layer interface. Lines A1 and B1 are perpendicular to the lower layer interface and parallel to each other, with line A1 always located to the left of line B1. This procedure was performed for all first particles present in the cross-sectional image whose entire image was within the cross-sectional image. The intersection of line A1 and the lower layer interface was designated a1, and the intersection of line A2 and the lower layer interface was designated a2. The length of the line connecting intersections a1 and a2 was designated the unit measurement range C1. The unit measurement range was determined for all lines AX (X = 1, 2, 3, ...), and each was designated the unit measurement range CX (X = 1, 2, 3, ...).

[0162] 5, in each unit measurement range CX, the longest line that intersects the lower layer interface at right angles and with the surface boundary line of the surface layer is taken as the film thickness tX (X = 1, 2, 3, ...) of the unit measurement range CX. The arithmetic mean value of the obtained film thickness tX is taken as the average film thickness of the cross-sectional image, and the arithmetic mean of the average film thicknesses of the 12 sample pieces is taken as the film thickness T1 of the surface layer of the electrophotographic photosensitive member.

[0163] <Calculation of niobium atom / titanium atom concentration ratio in conductive particles contained in electrophotographic photosensitive member> A 5 ​​mm square sample piece was cut out from the electrophotographic photosensitive member, and cut to a thickness of 200 nm 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 at a magnification of 500,000 to 1,200,000 times using a scanning transmission electron microscope (product name: JEM2800, manufacturer: JEOL) in STEM mode connected to an EDS analyzer (energy dispersive X-ray analyzer).

[0164] Among the cross sections of the observed conductive particles, cross sections of conductive particles having a maximum diameter of approximately 0.9 to 1.1 times the primary particle diameter calculated above were visually selected. Subsequently, spectra of the constituent elements of the cross sections of the selected conductive particles were collected using an EDS analyzer, and EDS mapping images were produced. Spectral collection and analysis were performed using an 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 appropriately selected so that the dead time was 15 to 30, a mapping resolution of 256 × 256, and a frame number of 300. EDS mapping images were obtained for 100 cross sections of conductive particles.

[0165] The EDS mapping image obtained in this way was analyzed to calculate the ratio of niobium atomic concentration (atomic %) to titanium atomic concentration (atomic %) at the particle center and within 5% of the maximum diameter of the measured particle from the particle surface. Specifically, the "Line Extraction" button in NSS was first pressed to draw a line corresponding to the maximum diameter of the particle, and information on the atomic concentration (atomic %) along the line from one surface through the particle interior to the other surface was obtained. If the maximum diameter of the particle obtained was less than 0.9 or more than 1.1 times the calculated primary particle diameter, it was excluded from further analysis. (Only particles with a maximum diameter between 0.9 and 1.1 times the primary particle diameter were analyzed below.) Next, the niobium atomic concentration (atomic %) was read on both particle surfaces within 5% of the maximum diameter of the measured particle from the particle surface. In a similar manner, the "titanium atomic concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface" was obtained.

[0166] Next, using these values, the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" on both particle surfaces is calculated using the following formula: Concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface = (Niobium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface) / (Titanium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface) Of the two concentration ratios obtained, 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.

[0167] Also, the niobium atomic concentration (atomic %) and titanium atomic concentration (atomic %) are read at the midpoint of the maximum diameter on the above straight line. Using these values, the "concentration ratio of niobium atoms to titanium atoms at the particle center" is calculated using the following formula: Concentration ratio of niobium atoms to titanium atoms at the particle center = (niobium atomic concentration (atomic %) at the particle center) / (titanium atomic concentration (atomic %) at the particle center)

[0168] The "concentration ratio calculated as niobium atom concentration / titanium atom concentration at the particle center, calculated as niobium atom concentration / titanium atom concentration at the particle center, within 5% of the maximum diameter of the measured particle from the particle surface" is calculated by the following formula: (concentration ratio of niobium atoms to titanium atoms at the particle center, within 5% of the maximum diameter of the measured particle from the particle surface) / (concentration ratio of niobium atoms to titanium atoms at the particle center).

[0169] <Evaluation of Dot Images> For the evaluation of dot images, a modified laser beam printer (electrophotographic device) (product name: i-SENSYS LBP673Cdw, manufacturer: Canon Inc.) and a toner cartridge equipped with the electrophotographic photosensitive member implemented in this study were used. The electrophotographic device was modified so that the voltage applied to the charging roller could be adjusted.

[0170] In order to output an evaluation image, the voltage applied to the charging roller was first set so that the surface potential of the electrophotographic photosensitive member would be −550 V, and further, the applied voltage was adjusted so that the earth current connected to the electrophotographic photosensitive member would be constant during image formation. First, as an evaluation image during initial use, a halftone image (toner loading amount: 0.2 mg / cm) with margins of 5.0 mm on the top, bottom, left, and right was printed. ２ ) was printed in cyan. Next, after printing 10,000 full-color 5.0% images, one halftone image similar to that used in the initial use was printed as an evaluation image for long-term use. The dot image evaluation of the halftone image was performed according to the following criteria. Evaluation criteria A to C are levels that are practically acceptable. The evaluation results are shown in Tables 7 and 8.

[0171] (Evaluation criteria) A: When observed with a magnifying glass, no dot images are observed. B: When observed with the naked eye, no dot images are observed, but when observed with a magnifying glass, slight dot images are observed in some places. C: When observed with the naked eye, slight dot images are observed in some places. D: When observed with the naked eye, dot images are observed in multiple places. E: When observed with the naked eye, dot images are observed over the entire area of ​​the image.

[0172] <Evaluation of Injection Charging Properties> To measure the injection charging properties, a modified laser beam printer (electrophotographic device) (product name: i-SENSYS LBP673Cdw, manufacturer: Canon Inc.) was used. The modified machine used for the evaluation was modified so that the image exposure amount, the amount of current flowing from the charging roller to the support of the electrophotographic photosensitive member (hereinafter also referred to as total current), and the voltage applied to the charging roller could be adjusted and measured.

[0173] Furthermore, the cyan process cartridge of the modified machine was modified so that a potential probe (product name: model 6000B-8, manufacturer: Trek Japan Co., Ltd.) was attached to the development position. Next, the potential at the center of the electrophotographic photosensitive member was measured using a surface potential meter (product name: model 344, manufacturer: Trek Japan Co., Ltd.).

[0174] An electrophotographic photosensitive member was mounted on the modified machine in an environment of a temperature of 30°C and a humidity of 80% RH, and a direct current of 600 V was applied to the charging roller to charge the electrophotographic photosensitive member while rotating it at 60 rpm. The potential of the surface of the electrophotographic photosensitive member at this time was taken as VC, and the injection charge rate (=-VC / 600) was calculated. The injection charge rate value was ranked on a five-level scale of A to E. Evaluation criteria A to C are levels that present no practical problems. The evaluation results are shown in Tables 7 and 8.

[0175] (Evaluation Criteria) A: The injection charge rate is 80% or more. B: The injection charge rate is 70% or more and less than 80%. C: The injection charge rate is 60% or more and less than 70%. D: The injection charge rate is 50% or more and less than 60%. E: The injection charge rate is less than 50%.

[0176] Further, in the same manner as in the above <Evaluation of dot images>, 10,000 sheets were printed, and the injected charge rate of the electrophotographic photosensitive member after long-term use was measured, and the ratio to the initial injected charge rate was taken as the injected charge retention property and is shown in Tables 7 and 8. (Evaluation criteria) A: The injected charge rate after the endurance test is 80% or more relative to the initial injected charge rate. B: The injected charge rate after the endurance test is 70% or more but less than 80% relative to the initial injected charge rate. C: The injected charge rate after the endurance test is 60% or more but less than 70% relative to the initial injected charge rate. D: The injected charge rate after the endurance test is 50% or more but less than 60% relative to the initial injected charge rate. E: The injected charge rate after the endurance test is less than 50% relative to the initial injected charge rate.

[0177]

[0178]

[0179] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0180] This application claims priority based on Japanese Patent Application No. 2023-219761, filed December 26, 2023, the entire contents of which are incorporated herein by reference.

[0181] REFERENCE SIGNS LIST 1 Electrophotographic photosensitive member 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 Undercoat layer 103 Charge generating layer 104 Charge transport layer 105 Surface layer 201 Binder resin 202 First particles 203 Second particles 204 Underlayer 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 [%], S1 and S2 satisfy the following formula (1) and the following formula (2), 70 ≤ (S1 + S2) ≤ 95 (1) 0.8 ≤ (S1 / S2) ≤ 2.0 (2) 4. The powder resistivity R1 of the first particle is 1.0×10 ８ The powder resistivity R2 of the second particles is 1.0×10 １０ The electrophotographic photoreceptor according to any one of claims 1 to 3, which has a resistivity of Ω·cm or more.

5. The powder resistivity R2 of the second particles is 1.0×10 １３ Ω·cm or more. The electrophotographic photoreceptor according to any one of claims 1 to 4. 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 the following formula (3) and the following formula (4), 50 ≤ L1 ≤ 300 (3) 2.0 ≤ L1 / L2 ≤ 10.0 (4) The first particles include any one or more selected from the group consisting of metal oxide particles, metal particles, and carbon black, The electrophotographic photoreceptor, wherein the second particles contain silica particles.

2. The electrophotographic photoreceptor according to claim 1, 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], D1 and D2 satisfy the following formula (5), the following formula (6), and the following formula (7). 100 ≤ D1 ≤ 350 (5) 30 ≤ D2 ≤ 150 (6) 2.0 ≤ D1 / D2 ≤ 10.0 (7) 3. The electrophotographic photoreceptor according to claim 1 or 2, 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], T1 and D1 satisfy the following formula (8). 1.0 ≤ T1 / D1 ≤ 1.8 (8) 6. The electrophotographic photoreceptor according to any one of claims 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.

7. The first particles include niobium-doped titanium oxide particles, and 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 any one of claims 1 to 6.

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 charging means, developing means, and 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 charging means, exposure means, developing means, and transfer means.

Images