Electrophotographic photoreceptor, process cartridge, and electrophotographic device

Abstract

To provide an electrophotographic photoreceptor that can withstand a large amount of prints.SOLUTION: An electrophotographic photoreceptor has a surface layer containing a binder resin and inorganic particles. The surface layer contains a urethane resin as the binder resin. The value of the ratio of the volume of the inorganic particles to the volume of the binder resin in the surface layer is 0.10 or more and 3.0 or less. Projections derived from the inorganic particles are present on the surface of the surface layer. The number-based average primary particle diameter of the inorganic particles contained in the surface layer is 10 nm or more and 500 nm or less. The maximum height roughness Rz of the surface of the surface layer is 10 nm or more and 760 nm or less.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] In recent years, in the field of electrophotographic apparatuses, from the viewpoints of reducing the maintenance frequency and improving the usability, an increase in the number of printable sheets of a copying machine main body or a cartridge and an increase in the printing speed have been demanded. In an electrophotographic apparatus, in order to achieve an increase in the number of printable sheets and an increase in the printing speed, it is necessary to improve the life of the electrophotographic photoreceptor by improving the durability of the electrophotographic photoreceptor. In order to extend the life of the electrophotographic photoreceptor, characteristics contributing to functionality must be stabilized during long-term use from the initial use.

[0003] In the electrophotographic image forming method, there are a charging step, an exposure step, a developing step, a transfer step, and a cleaning step. In recent years, there is also an image forming method from which the cleaning step is removed. In an electrophotographic apparatus, an electrophotographic photoreceptor and a contact member such as an intermediate transfer belt are in contact with each other at an appropriate relative rotation speed.

[0004] Conventional electrophotographic photoreceptors, as the number of printable sheets increases, surface wear due to rubbing against contact members such as charging members, transfer members, and cleaning members, and contamination of the electrophotographic photoreceptor surface by toner and external additives become apparent, and surface properties such as the coefficient of kinetic friction change. That is, the surface characteristics of the electrophotographic photoreceptor, which were uniform at the initial use, change to non-uniform surface characteristics during long-term use. The electrophotographic photoreceptor that is in contact with each contact member at an appropriate relative rotation speed has uniform surface characteristics at the initial use, so it can maintain stable rotation within the printing process. Therefore, an appropriate electrostatic latent image is formed on the surface of the electrophotographic photoreceptor. However, during long-term use, the electrophotographic photoreceptor has non-uniform surface characteristics, so it cannot maintain stable rotation within the printing process, and an inappropriate electrostatic latent image is formed on the surface of the electrophotographic photoreceptor. As a result, horizontal streak images occur in the output image.

[0005] This problem is likely to occur in electrophotographic apparatuses that require a longer lifespan than conventional ones. In particular, it is prominent during the long-term use of electrophotographic apparatuses that require a higher printing speed than conventional ones. As a means to solve this problem, there is an electrophotographic photoreceptor that suppresses changes in surface characteristics from the initial use to the long-term use by suppressing wear on the surface of the electrophotographic photoreceptor. In order to realize these solutions, for example, the following technologies have been proposed. Patent Document 1 proposes a technique for making an electrophotographic photoreceptor highly durable by configuring the surface layer of the electrophotographic photoreceptor with a urethane resin and an inorganic filler and controlling the ten-point average surface roughness (Rz value). Patent Document 2 suppresses deterioration of the electrophotographic photoreceptor due to discharge by changing the charging process of the electrophotographic photoreceptor from a general charging method by discharge to an injection charging method without discharge, and proposes a technique for making the electrophotographic photoreceptor highly durable by using a urethane resin for the protective layer of the electrophotographic photoreceptor.

Prior Art Documents

Patent Documents

[0006] Patent Document 1 Japanese Patent Application Laid-Open No. 2014-174426 Patent Document 2 Japanese Patent Application Laid-Open No. 2001-201874 Summary of the Invention Problems to be Solved by the Invention

[0007] However, in the case of long-term use of an electrophotographic apparatus with a larger number of printable sheets and a higher printing speed than conventional ones, in Patent Document 1, the inorganic filler introduced into the surface layer of the electrophotographic photoreceptor was locally detached from the surface layer, and uniform surface characteristics could not be maintained. From the initial stage to the later stage of printing, stable rotation within the printing process could not be maintained, and inappropriate electrostatic latent image formation occurred during long-term use. As a result, horizontal streak images occurred in the output image. In Patent Document 2, due to the increase in printing speed, stable contact between the electrophotographic photoreceptor and the charging member could not be maintained, and uniform charging could not be ensured in the charging process. As a result, density unevenness occurred in the output image.

[0008] The present invention provides an electrophotographic photoreceptor that suppresses horizontal streak images generated during long-term use of an electrophotographic apparatus with a larger number of printable sheets and a higher printing speed than conventional ones. Means for Solving the Problems

[0009] The above object is achieved by the following present invention. That is, the electrophotographic photoreceptor according to the present invention is an electrophotographic photoreceptor having a surface layer containing a binder resin and inorganic particles, wherein the surface layer contains a urethane resin as the binder resin, the value of the ratio of the volume of the inorganic particles to the volume of the binder resin in the surface layer is 0.10 or more and 3.0 or less, convex portions derived from the inorganic particles are present on the surface of the surface layer, the average primary particle diameter based on the number of the inorganic particles contained in the surface layer is 10 nm or more and 500 nm or less, and the maximum height roughness Rz of the surface of the surface layer is 10 nm or more and 760 nm or less.

[0010] Further, the present invention relates to a process cartridge that integrally supports the electrophotographic photoreceptor and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachable from the electrophotographic apparatus main body.

[0011] Further, the present invention relates to an electrophotographic apparatus comprising the electrophotographic photoreceptor, and a charging means, an exposure means, a developing means, and a transfer means.

Advantages of the Invention

[0012] According to the present invention, in the surface layer design of the electrophotographic photoreceptor, by using a urethane resin and inorganic particles excellent in durability to create an appropriate surface state on the surface layer, it is possible to provide an electrophotographic photoreceptor that suppresses lateral streak images generated during long-term use in an electrophotographic apparatus with a larger number of printed sheets and a higher printing speed than conventional ones.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of the present invention will be described. [Electrophotographic Photoreceptor] The electrophotographic photoreceptor of the present invention has a support, a charge generation layer provided on the support, a charge transport layer, and a surface layer containing particles. The electrophotographic photoreceptor according to the present invention can be used as a cylindrical electrophotographic photoreceptor in which a charge generation layer, a charge transport layer, and a surface layer are formed on a cylindrical support, but a belt-like or sheet-like shape is also possible.

[0015] FIG. 1 is a diagram showing an example of the layer structure of an electrophotographic photoreceptor. In FIG. 1, 101 is a support, 102 is an undercoat layer, 103 is a charge generation layer, and 104 is a charge transport layer. 105 is the surface layer according to the present invention.

[0016] The electrophotographic photoreceptor of the present invention includes a charging step of charging the surface of the electrophotographic photoreceptor, an exposure step of exposing the charged electrophotographic photoreceptor to form an electrostatic latent image, a developing step of supplying toner to the electrophotographic photoreceptor on which the electrostatic latent image is formed to form a toner image, a transfer step of transferring the toner image formed on the electrophotographic photoreceptor, and a cleaning step of removing the toner remaining on the electrophotographic photoreceptor in the transfer step, and can be used in an image forming method having these steps. In addition to the above image forming method, the electrophotographic photoreceptor of the present invention can also be used in an image forming method that does not have a cleaning step in the above image forming method.

[0017] As a method for manufacturing the electrophotographic photoreceptor of the present invention, there is a method of preparing coating liquids for each layer described later, coating them in a desired layer order, and drying them. At this time, examples of the coating method of the coating liquid include dip coating, spray coating, inkjet coating, roll coating, die coating, blade coating, curtain coating, wire bar coating, ring coating, and the like. Among these, dip coating is preferable from the viewpoints of efficiency and productivity.

[0018] The present invention relates to an electrophotographic photoreceptor having a surface layer containing a binder resin and inorganic particles, wherein the surface layer contains a urethane resin as the binder resin, and the value of the volume ratio of the inorganic particles to the volume of the binder resin in the surface layer is 0.10 or more and 3.0 or less, convex portions derived from the inorganic particles are present on the surface of the surface layer, the average primary particle diameter of the inorganic particles contained in the surface layer based on the number is 10 nm or more and 500 nm or less, and the maximum height roughness Rz of the surface of the surface layer is 10 nm or more and 760 nm or less.

[0019] With the above configuration, it is possible to suppress the occurrence of horizontal streak images during long-term use in an electrophotographic apparatus that can print a larger number of sheets than conventional ones and has a high printing speed. Although the mechanism by which the problems are solved by the configuration of the present invention is not clearly understood, the following speculation is made. Horizontal streaks that occur during long-term use in an electrophotographic apparatus that can print a larger number of sheets than conventional ones and has a high printing speed are affected by changes in the surface characteristics of the electrophotographic photoreceptor. There are mainly two reasons for the changes in the surface characteristics of the electrophotographic photoreceptor. The first is the wear of the surface of the electrophotographic photoreceptor. As the electrophotographic photoreceptor undergoes a large number of prints, it rubs against contact members such as cleaning members for a long time. As a result, the surface treatment and the surface shape designed using particles, etc., applied to the surface of the electrophotographic photoreceptor are destroyed, and the initially uniformly designed surface shape gradually changes to a non-uniform surface state as the number of printable sheets increases. This causes the kinetic friction coefficient and tackiness of the surface of the electrophotographic photoreceptor to become non-uniform. The second is the contamination of the surface of the electrophotographic photoreceptor by toner or the like. The surface of the electrophotographic photoreceptor has an increasing chance of coming into contact with contaminants such as toner, external additives, and paper dust due to a large number of prints. As a result, the surface of the electrophotographic photoreceptor is contaminated, and the surface state gradually changes as the number of printable sheets increases. This causes the kinetic friction coefficient and tackiness of the surface of the electrophotographic photoreceptor to change.

[0020] In order to suppress the above changes in the surface characteristics of the electrophotographic photoreceptor, the following methods can be mentioned. That is, it includes suppressing the wear of the surface of the electrophotographic photoreceptor and improving the stain resistance against toner or the like, or the initial surface characteristic design of the electrophotographic photoreceptor considering that even if wear or contamination occurs, the change in surface characteristics does not become non-uniform. In the present invention, in the surface layer of the electrophotographic photoreceptor, a urethane resin excellent in durability is used, and the ratio of the volume of inorganic particles to the volume of the binder resin is set to be 0.10 or more and 3.0 or less, thereby forming convex portions derived from inorganic particles on the surface of the surface layer and achieving a reduction in the contact area. Furthermore, by designing the contact portion between the electrophotographic photoreceptor and the contact member to be convex portions derived from inorganic particles instead of a urethane resin having viscosity, a reduction in tackiness is also achieved. Thereby, a reduction in the coefficient of kinetic friction is realized. If the ratio of the volume of inorganic particles to the volume of the binder resin is less than 0.10, convex portions derived from inorganic particles cannot be formed on the surface of the surface layer, and the contact area with the contact member cannot be reduced. As a result, wear of the surface layer during long-term use cannot be suppressed, non-uniformity of surface characteristics occurs, and image defects occur. Also, if the ratio of the volume of inorganic particles to the volume of the binder resin exceeds 3.0, the ratio of the binder resin having a role of binding inorganic particles to the surface layer decreases, so the function of binding inorganic particles to the surface layer weakens, and during long-term use, detachment of inorganic particles from the surface layer occurs, wear of the surface layer occurs, and as a result, image defects occur.

[0021] Also, by setting the average primary particle diameter based on the number of inorganic particles contained in the surface layer of the electrophotographic photoreceptor to be 10 nm or more and 500 nm or less, the size of the convex portions derived from inorganic particles formed on the surface of the surface layer is controlled. By doing so, the maximum height roughness Rz of the surface of the surface layer becomes 10 nm or more and 760 nm or less, and fine and numerous convex portions derived from inorganic particles are formed. By increasing the convex portions derived from inorganic particles that come into contact with the contact member, the load applied to each convex portion is dispersed, the load on the convex portions is suppressed, and detachment of particles from the surface layer is suppressed. Thereby, non-uniformity of surface characteristics occurring during long-term use can be prevented. If the maximum height roughness Rz of the surface of the surface layer is less than 10 nm, the surface other than the convex portions derived from inorganic particles comes into contact with the contact member, so not only can a reduction in the contact area due to the convex portions not be achieved, but also contact between the binder resin and the contact member occurs, so the tackiness cannot be reduced either. These tend to cause an increase in the coefficient of kinetic friction and wear of the surface layer, resulting in image defects during long-term use. Also, if the maximum height roughness Rz of the surface of the surface layer exceeds 760 nm, the convex portions derived from inorganic particles are likely to detach, resulting in image defects during long-term use.

[0022] Further, it is preferable that the maximum height roughness Rz of the surface layer is 40 nm or more and 760 nm or less, and more preferably 600 nm or less. By doing so, the contact pressure from the contact member applied to the convex portions derived from the inorganic particles can be controlled, and while suppressing the detachment of the inorganic particles from the surface layer, a surface shape excellent in durability can be maintained.

[0023] Furthermore, it is preferable that the average length Rsm of the roughness curve elements of the surface layer is 20 nm or more and 1400 nm or less. Thereby, the interval between the convex portions derived from the inorganic particles can be designed to an interval excellent in durability. Further, it is preferable that the average length Rsm of the roughness curve elements of the surface layer is 25 nm or more and 200 nm or less, and more preferably 25 nm or more and 180 nm or less. Being within this range controls the number of convex portions derived from the inorganic particles formed per unit area, reduces the load applied to each convex portion, and suppresses the detachment of the inorganic particles from the surface layer. When the average length Rsm of the roughness curve elements of the surface layer is less than 20 nm, the interval between the convex portions derived from the inorganic particles becomes narrow, the contact points with the contact member increase, and the effect of point contact is reduced. Further, when the average length Rsm of the roughness curve elements of the surface layer exceeds 1400 nm, the interval between the convex portions derived from the inorganic particles becomes wide, so the pressure applied from the contact member to each convex portion becomes large, and the detachment of the convex portions derived from the inorganic particles is likely to occur.

[0024] Also, it is preferable that the arithmetic mean roughness Ra of the surface layer is 10 nm or more and 500 nm or less. By doing so, it is possible to design the surface shape to suppress the detachment of the protrusions derived from the inorganic particles while realizing a reduction in the contact area. Furthermore, it is preferable that the arithmetic mean roughness Ra is 10 nm or more and 320 nm or less, and more preferably 12 nm or more and 200 nm or less. By being in this range, it is controlled so that fine and numerous protrusions derived from the inorganic particles are formed on the surface of the surface layer, the load applied to each protrusion is reduced, and the detachment of the inorganic particles from the surface layer can be suppressed. When the arithmetic mean roughness Ra of the surface layer is less than 10 nm, the regions other than the protrusions of the surface layer are also likely to come into contact with the contact member, so the contact area does not decrease. Also, when the arithmetic mean roughness Ra of the surface layer exceeds 500 nm, the pressure applied to each protrusion from the contact member becomes large, and the detachment of the protrusions derived from the inorganic particles is likely to occur.

[0025] Furthermore, it is preferable that the kinetic friction coefficient of the surface layer is 0.95 or less in an environment of 25°C and 50% RH. Thereby, the wear of the contact member and the surface layer is suppressed, and it can withstand long-term use. Furthermore, the kinetic friction coefficient of the surface layer is preferably 0.90 or less, and more preferably 0.85 or less. By being in this range, the load applied to the protrusions derived from the inorganic particles formed on the surface of the surface layer can be suppressed, and the detachment of the inorganic particles from the surface layer can be reduced. When the kinetic friction coefficient of the surface layer exceeds 0.95, wear occurs between the contact member and the surface layer, and image defects occur during long-term use. Furthermore, it is preferable that the inorganic particles contained in the surface layer have a functional group reactive with an isocyanate group. Thereby, when the urethane resin is cured, the resin and the inorganic particles react and bond, so that the inorganic particles can be firmly held in the surface layer. Examples of the functional group reactive with the isocyanate group include a hydroxy group and an amino group. Examples of the inorganic particles include silica particles and metal oxide particles. Also, it is preferable that the arithmetic average film thickness of the surface layer is 2.0 μm or less. By doing so, the number of inorganic particles buried in the surface layer can be reduced, and as a result, it becomes easier to form convex portions derived from the particles on the surface of the surface layer. The film thickness of the surface layer can be controlled by the resin solid content of the surface layer coating liquid and the coating speed during impregnation coating. The lower the resin solid content, the thinner the film thickness, and the slower the coating speed, the easier it is for the film thickness to become thinner.

[0026] Also, it is preferable that the Mohs hardness of the inorganic particles contained in the surface layer is 4.0 or more. Further, 7.0 or more is preferable, and 9.0 or more is more preferable. By being in this range, wear of the inorganic particles due to rubbing between the convex portions derived from the inorganic particles formed on the surface of the surface layer and the contact member can be suppressed, and the surface shape can be maintained even in the latter stage of printing. Furthermore, it is preferable that the inorganic particles contained in the surface layer are silica particles or metal oxide particles. Thereby, the particles themselves are hardly worn, and the surface shape can be maintained even in the latter stage of printing. If the Mohs hardness of the inorganic particles contained in the surface layer is less than 4.0, the convex portions derived from the inorganic particles are worn during long-term use, the convex portions are lost, and as a result, image defects occur.

[0027] Also, it is preferable that the urethane resin contained in the surface layer has a nurate structure. Thereby, the wear resistance of the resin itself is improved, and the surface shape can be maintained even in the latter stage of printing. Furthermore, it is preferable that the urethane resin contained in the surface layer is a polymer of an isocyanate compound having 3 or more polymerizable functional groups and a polyol compound. Thereby, a resin having a three-dimensional structure is synthesized, and a tough and wear-resistant resin is obtained. Such a resin can contribute to maintaining the surface shape in the latter stage of printing.

[0028] Also, it is preferable that the urethane resin contained in the surface layer is a polymer of an isocyanate compound having a nurate structure and a polyol compound. Thereby, it becomes easier to introduce the nurate structure into the structure of the urethane resin, the wear resistance of the urethane resin is improved, and the surface shape can be maintained even in the latter stage of printing. Furthermore, it is preferable that the urethane resin contained in the surface layer is a polymer of an isocyanate compound and a polyol having an average molecular weight of 2.0×10 3 or less. Thereby, the viscosity of the urethane resin can be suppressed, and the coefficient of kinetic friction of the surface layer can be made low. In addition, the metal oxide particles contained in the surface layer are preferably titanium oxide doped with niobium atoms. The volume resistivity of the surface layer of the electrophotographic photoreceptor needs to be controlled to an appropriate value. This value varies depending on the configuration of the image forming apparatus. If the volume resistivity of the surface layer of the electrophotographic photoreceptor is too low, the latent image cannot be maintained and image blurring occurs. Conversely, if the volume resistivity of the surface layer is high, ghost images due to residual charge effects occur. The volume resistivity of the surface layer changes due to wear and contamination, and image defects occur when it changes to a volume resistivity at which image blurring or ghost images occur during long-term use of the image forming apparatus. That is, the volume resistivity of the surface layer must be controlled to an appropriate value. Since the volume resistivity of the surface layer depends on the volume resistivity of the contained metal oxide, when a metal oxide is contained in the surface layer, a metal oxide having a suitable volume resistivity must be selected. Titanium oxide doped with niobium atoms can control the volume resistivity depending on the niobium content. That is, the volume resistivity of the surface layer can be finely controlled by the niobium content without changing the content of the metal oxide, and even when conductive particles are used, a surface layer suitable for the electrophotographic photoreceptor can be formed. Note that the above mechanism is based on speculation, and this speculation does not affect the technical scope of the present invention.

[0029] <Binder resin> The binder resin according to the present invention includes urethane resin. Further, the surface layer of the present invention may be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of the reaction in this case include a thermal polymerization reaction, a polymerization reaction using moisture in the air, and a polymerization reaction in which a main agent and a curing agent are mixed. Examples of the polymerizable functional groups of the urethane resin include a hydroxyl group and an isocyanate group. Examples of the hydroxyl group include a hydroxy group, a carboxyl group, and a phenol group. A compound having a hydroxyl group used in the polymerization reaction of the urethane resin is a polyol. In the present invention, the type of polyol is not particularly limited and can be appropriately selected according to the purpose, but the average molecular weight is 2.0×10 3 The following polyols are preferred. Examples of the polyol include polycaprolactone diol, polycaprolactone triol, polycaprolactone tetraol, lactone-modified polyether polyol, lactone-modified (meth)acrylate, carbonate-modified (meth)acrylate, polycarbonate diol, and the like. These may be used alone or in combination of two or more.

[0030] Examples of the compound having an isocyanate group used in the polymerization reaction of the urethane resin include hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), xylene diisocyanate, trimethylhexamethylene diisocyanate, HDI biuret, HDI trimethylolpropane adduct, and the like.

[0031] The main methods for introducing a nurate structure into a urethane resin include a method of generating a nurate structure during a polymerization reaction and a method of using an isocyanate compound having a nurate structure in the polymerization reaction. When generating a nurate structure during a polymerization reaction, it is common to use a catalyst that promotes the trimerization reaction. Examples of the catalyst include potassium salts and quaternary ammonium salts. Examples of the isocyanate compound having a nurate structure include isocyanurate-type trimers. For example, HDI isocyanurate, IPDI isocyanurate, etc. may be mentioned. These may be used alone or in combination of two or more. As a method for introducing a nurate structure into the urethane resin of the present invention, a method of using an isocyanate compound having a nurate structure in the polymerization reaction is preferable. This is because when using a method of generating a nurate structure during a polymerization reaction, since a catalyst is used, there is a concern about contamination of the abutting member by the catalyst component. The nurate structure contributes to the polymerization reaction as a rigid crosslinking point, resulting in a dense polymerization reaction. Therefore, in the present invention, it is possible to prevent wear resistance of the surface layer of the electrophotographic photoreceptor and bleeding of low molecular components.

[0032] Further, the isocyanate group of the isocyanate compound may be a blocked isocyanate blocked by a blocking agent. Free isocyanate groups are prone to reaction. Therefore, when the surface layer coating solution is prepared and then left at room temperature for a long time, the reaction gradually proceeds and the characteristics of the coating solution may change. To prevent this, blocked isocyanates are used. This is because the blocking agent does not react until it is heated to a temperature above the dissociation temperature. This makes it easier to handle the coating solution. Examples of the blocking agent include phenols such as cresol and phenol, lactams such as ε-caprolactam, and oximes such as methyl ethyl ketoxime. In the present invention, for use in an electrophotographic photoreceptor using a pigment or the like, a blocking agent that dissociates at about 100°C to 130°C is preferable. For example, dimethylal pyrazole may be mentioned.

[0033] <Inorganic particles> Examples of the inorganic particles used in the present invention include silica particles, metal oxide particles, and metal particles. As the particles included in the surface layer of the electrophotographic photoreceptor of the present invention, it is preferable to use inorganic particles that are difficult to be shaved, have low elasticity, and are advantageous in promoting point contact with the contact member. The Mohs hardness of the inorganic particles used in the present invention is preferably 4.0 or more. By doing so, wear of the inorganic particles due to rubbing between the convex portions derived from the inorganic particles formed on the surface of the surface layer and the contact member can be suppressed, and the surface shape can be maintained even in the latter stage of printing. Examples of the inorganic particles having a Mohs hardness of 4.0 or more include magnesium oxide, glass, iron, iron oxide, silicon, titanium oxide, zirconium oxide, and alumina. These may be used alone or in combination of two or more.

[0034] When using inorganic particles, among these, silica particles are preferable. Since silica particles have a larger average circularity compared to other inorganic particles, an effect of promoting point contact between the toner and the photoreceptor and reducing the adhesion force is expected. As the silica particles, known silica fine particles can be used, and either dry silica fine particles or wet silica fine particles may be used. Preferably, they are fine particles of wet silica obtained by the sol-gel method (hereinafter also referred to as sol-gel silica).

[0035] The sol-gel silica used for the particles contained in the surface layer of the electrophotographic photoreceptor of the present invention may be hydrophilic or may have its surface hydrophobized. Examples of the hydrophobization treatment method include a method in which, in the sol-gel method, after removing the solvent from the silica sol suspension and drying it, it is treated with a hydrophobizing agent, and a method in which a hydrophobizing agent is directly added to the silica sol suspension and treated simultaneously with drying. From the viewpoints of controlling the half-value width of the particle size distribution and the saturated moisture adsorption amount, a technique of directly adding a hydrophobizing agent to the silica sol suspension is preferable. Examples of the hydrophobizing agent include the following. Chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, t-butyldimethylchlorosilane, vinyltrichlorosilane; Alkoxysilanes such as tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltrimethoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, i-butyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane; Silazanes such as hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexaphenyldisilazane, hexacyclohexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, dimethyltetravinyldisilazane; Silicone oils such as dimethyl silicone oil, methyl hydrogen silicone oil, methyl phenyl silicone oil, alkyl-modified silicone oil, chloroalkyl-modified silicone oil, chlorophenyl-modified silicone oil, fatty acid-modified silicone oil, polyether-modified silicone oil, alkoxy-modified silicone oil, carbinol-modified silicone oil, amino-modified silicone oil, fluorine-modified silicone oil, and terminal-reactive silicone oil; Siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, and octamethyltrisiloxane; As fatty acids and their metal salts, 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. Among these, alkoxysilanes, silazanes, and silicone oils are preferably used because they are easy to subject to hydrophobic treatment. These hydrophobic treatment agents may be used alone or in combination of two or more.

[0036] <Titanium oxide doped with niobium atoms> The titanium oxide doped with niobium atoms used in the present invention may have its niobium content controlled and adjusted to a volume resistivity suitable for the image forming apparatus to be used. Specifically, the niobium content may be adjusted to 0.5 mass% or more and 15.0 mass% or less. Further, the titanium oxide doped with niobium atoms may have oxygen deficiency. When there is oxygen deficiency, the volume resistivity becomes lower. It is preferable that the oxygen deficiency rate is 2.0% or less when used for the surface layer of the electrophotographic photoreceptor. When the oxygen deficiency rate exceeds 2.0%, the particles become blackened, and the light transmittance of the surface layer decreases. This leads to a decrease in the sensitivity of the electrophotographic photoreceptor. Oxygen deficiency can be introduced into titanium oxide by firing in a reducing atmosphere such as ammonia or hydrogen, or by firing in a nitrogen atmosphere together with an organic substance at 600 °C or higher, which is the decomposition temperature of the organic substance. Physical properties such as the particle diameter and volume resistivity of the titanium oxide doped with niobium atoms can be controlled by adjusting the type of core material particles to be used and the weight ratio of niobium atoms to titanium atoms in the titanium niobium mixed solution with respect to the core material.

[0037] <Additive> The surface layer in the present invention may contain additives such as a catalyst for polymerization reaction, an antioxidant, an ultraviolet absorber, a plasticizer, a leveling agent, a lubricity imparting agent, and an abrasion resistance improver. Specifically, examples include quaternary ammonium salts, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, and silicone oils.

[0038] <Solvent> A binder resin, inorganic particles, and a solvent that stably disperses or dissolves the additive may be appropriately selected. Specifically, the following can be mentioned. · Alcohols such as methanol, ethanol, isopropanol, butanol, and octanol; · Ketones such as acetone and cyclohexanone; · Esters such as ethyl acetate, butyl acetate, ethyl lactate, γ-butyrolactone, propylene glycol monomethyl ether acetate, and propylene glycol monoethyl ether acetate; · Ethers such as ethylene glycol monomethyl ether and diethylene glycol monobutyl ether; · Aromatic hydrocarbons such as benzene, toluene, and xylene; · Amides such as dimethylformamide, dimethylacetamide, and N-methylpyrrolidone. Also, in order to adjust the drying rate of the film of the curable composition and adjust the viscosity suitable for coating of the curable composition, a plurality of solvents may be used in combination.

[0039] <Surface layer> The surface layer can be formed by preparing a coating solution for the surface layer containing each of the above materials and solvents, forming this coating film, and drying and / or curing it. The roughness of the surface layer can be adjusted by the drying temperature after coating, the type of solvent, and the solid content of the coating solution in impregnation coating. For example, by using a solvent type with a high evaporation rate, the convection during drying becomes faster and the roughness tends to increase. For the same reason, the roughness also tends to increase when the drying temperature after coating is raised. When the solid content of the coating solution is increased, the convection is suppressed, so the roughness tends to decrease. Also, by making the surface layer film thickness thinner, the inorganic particles are more likely to be exposed on the surface, so the roughness tends to increase. The film thickness can be made thinner by reducing the coating speed during impregnation coating or by reducing the solid content of the coating solution.

[0040] <Support> In the present invention, the electrophotographic photoreceptor preferably has a support. In the present invention, the support is preferably a conductive support having conductivity. Further, examples of the shape of the support include a cylindrical shape, a belt shape, and a sheet shape. Among them, a cylindrical support is preferable. Further, an electrochemical treatment such as anodic oxidation, a blasting treatment, a cutting treatment, or the like may be performed on the surface of the support. Examples of the material of the support include metal, resin, glass, and the like. Examples of the metal include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among them, an aluminum support using aluminum is preferable. Further, conductivity may be imparted to the resin or glass by a treatment such as mixing or coating a conductive material.

[0041] <Conductive layer> In the present invention, a conductive layer may be provided on the support. By providing the conductive layer, it is possible to conceal scratches and unevenness on the surface of the support and to control light reflection on the surface of the support. The conductive layer preferably contains conductive particles and a resin. Examples of the material of the conductive particles include metal oxides, metals, carbon black, and the like. Examples of the metal oxide include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, and the like. Examples of the metal include aluminum, nickel, iron, nichrome, copper, zinc, silver, and the like. Among these, it is preferable to use a metal oxide as the conductive particles, and particularly, it is more preferable to use titanium oxide, tin oxide, or zinc oxide. When a metal oxide is used as the conductive particles, the surface of the metal oxide may be treated with a silane coupling agent or the like, or the metal oxide may be doped with an element such as phosphorus or aluminum or an oxide thereof. Further, the conductive particles may have a laminated structure in which the pre-coated particles such as titanium oxide, barium sulfate, and zinc oxide are coated with a metal oxide having a composition different from that of the pre-coated particles. Examples of the coating include metal oxides such as tin oxide. When a metal oxide is used as the conductive particle, its 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.

[0042] Examples of the resin include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenol resin, and alkyd resin. Further, the conductive layer may further contain a concealer such as silicone oil, resin particles, and titanium oxide. 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 solution for the conductive layer containing each of the above materials and a solvent, forming this coating film, and drying it. Examples of the solvent used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Examples of the dispersion method for dispersing the conductive particles in the coating solution for the conductive layer include methods using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

[0043] <Undercoat layer> In the present invention, an undercoat layer may be provided on the support or the conductive layer. The average film thickness of the undercoat layer is preferably 0.1 μm or more and 50 μm or less, more preferably 0.2 μm or more and 40 μm or less, and particularly preferably 0.3 μm or more and 30 μm or less. Examples of the resin for the undercoat layer include polyacrylic acid resin, polyvinyl alcohol resin, polyvinyl acetal resin, polyethylene oxide resin, polypropylene oxide resin, ethyl cellulose resin, methyl cellulose resin, polyamide resin, polyamic acid resin, polyurethane resin, polyimide resin, polyamideimide resin, polyvinyl phenol resin, melamine resin, phenol resin, epoxy resin, and alkyd resin. Alternatively, it may be a resin having a structure in which a resin having a polymerizable functional group and a monomer having a polymerizable functional group are crosslinked.

[0044] In addition, the undercoat layer may contain an inorganic compound or an organic compound in addition to the resin. Examples of the inorganic compound include metals, oxides, and salts. Examples of the metal include gold, silver, and aluminum. Examples of the oxide include zinc oxide, lead white, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, indium oxide, tin oxide, and zirconium oxide. Examples of the salt include barium sulfate and strontium titanate. These inorganic compounds may be present in the film in a particulate state. The number average particle diameter of the particles is preferably 1 nm or more and 500 nm or less, and more preferably 3 nm or more and 400 nm or less. These inorganic compounds may have a laminated structure having core particles and a coating layer covering the particles. The surfaces of these inorganic compounds may be treated with silicone oil, silane compound, silane coupling agent, other organosilicon compounds, organic titanium compounds, etc. Also, elements such as tin, phosphorus, aluminum, and niobium may be doped.

[0045] Examples of the organic compound include an electron transport compound and a conductive polymer. Examples of the conductive polymer include polythiophene, polyaniline, polyacetylene, polyphenylene, and polyethylene dioxythiophene. Examples of the electron transport material 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. The electron transport material may have a polymerizable functional group and crosslink with a resin having a functional group capable of reacting with those functional groups. Examples of the polymerizable functional group include a hydroxy group, a thiol group, an amino group, a carboxyl group, a vinyl group, an acryloyl group, a methacryloyl group, and an epoxy group. These organic compounds may be present in the film in a particulate state or may have their surfaces treated.

[0046] Various additives such as a leveling agent such as silicone oil, a plasticizer, and a thickener may be added to the undercoat layer. The undercoat layer is obtained by preparing a coating solution for the undercoat layer containing the above materials, coating the solution on a support or a conductive layer, and then drying or curing the coating film. Examples of the solvent for preparing the coating solution include alcohol solvents, ketone solvents, ether solvents, ester solvents, or aromatic hydrocarbon solvents. Examples of the dispersion method for dispersing particles in the coating solution include methods using a paint shaker, a sand mill, a ball mill, and a liquid collision type high-speed disperser.

[0047] <Photosensitive layer> The photosensitive layer of the electrophotographic photoreceptor is mainly classified into (1) a laminated photosensitive layer and (2) a single-layer photosensitive layer. (1) The laminated photosensitive layer is a photosensitive layer having a charge generation layer containing a charge generation substance and a charge transport layer containing a charge transport substance. (2) The single-layer photosensitive layer is a photosensitive layer containing both a charge generation substance and a charge transport substance.

[0048] (1) Laminated photosensitive layer The laminated photosensitive layer has a charge generation layer and a charge transport layer.

[0049] (1-1) Charge generation layer The charge generation layer preferably contains a charge generating substance and a resin. Examples of the charge generating substance include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, phthalocyanine pigments, etc. Among these, azo pigments and phthalocyanine pigments are preferred. Among the phthalocyanine pigments, oxy titanium phthalocyanine pigments, chloro gallium phthalocyanine pigments, and hydroxy gallium phthalocyanine pigments are preferred. The content of the charge generating substance in the charge generation layer is preferably 40% by mass or more and 85% by mass or less, more preferably 60% by mass or more and 80% by mass or less, based on the total mass of the charge generation layer. Examples of the resin include polyester resins, polycarbonate resins, polyvinyl acetal resins, polyvinyl butyral resins, acrylic resins, silicone resins, epoxy resins, melamine resins, polyurethane resins, phenol resins, polyvinyl alcohol resins, cellulose resins, polystyrene resins, polyvinyl acetate resins, polyvinyl chloride resins, etc. Among these, polyvinyl butyral resin is more preferred.

[0050] In addition, the charge generation layer may further contain additives such as antioxidants and ultraviolet absorbers. Specifically, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, etc. can be mentioned. The charge generation layer can be formed by preparing a coating solution for the charge generation layer containing the above-mentioned various materials and a solvent, forming this coating film on the undercoat layer, and drying it. Examples of the solvent used in the coating solution include alcohol solvents, sulfoxide solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, etc. The film thickness of the charge generation layer is preferably 0.1 μm or more and 1.5 μm or less, more preferably 0.15 μm or more and 1.0 μm or less.

[0051] (1-2) Charge transport layer The charge transport layer preferably contains a charge transport material and a resin. Examples of the charge transport material include polycyclic aromatic compounds, heterocyclic compounds, hydrazone compounds, styryl compounds, enamine compounds, benzidine compounds, triarylamine compounds, and resins having groups derived from these substances. Among these, triarylamine compounds and benzidine compounds are preferred. The content of the charge transport material in the charge transport layer is preferably 25% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 55% by mass or less, based on the total mass of the charge transport layer. Examples of the resin include polyester resins, polycarbonate resins, acrylic resins, polystyrene resins, etc. Among these, polycarbonate resins and polyester resins are preferred. Among the polyester resins, polyarylate resins are particularly preferred. The content ratio (mass ratio) of the charge transport material to the resin is preferably 4:10 to 20:10, more preferably 5:10 to 12:10.

[0052] In addition, the charge transport layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, lubricity imparting agents, and wear resistance improvers. Specifically, hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, boron nitride particles, etc. can be mentioned. The charge transport layer can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned respective materials and a solvent, forming this coating film on the charge generation layer, and drying it. Examples of the solvent used in the coating solution include alcohol solvents, ketone solvents, ether solvents, ester solvents, and aromatic hydrocarbon solvents. Among these solvents, ether solvents or aromatic hydrocarbon solvents are preferred. The film thickness of the charge transport layer is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and particularly preferably 10 μm or more and 30 μm or less.

[0053] (2) Single-layer photosensitive layer The single-layer photosensitive layer can be formed by preparing a coating solution for a photosensitive layer containing a charge generating substance, a charge transporting substance, a resin, and a solvent, forming this coating film on the undercoat layer, and drying it. Examples of the charge generating substance, charge transporting substance, and resin are the same as those exemplified in the above “(1) Laminated photosensitive layer”. The film thickness of the single-layer photosensitive layer is preferably 10 μm or more and 45 μm or less, and more preferably 25 μm or more and 35 μm or less.

[0054] <Process cartridge, electrophotographic apparatus> The electrophotographic photoreceptor described so far can be provided in a process cartridge that integrally supports at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means. The process cartridge is characterized in that it is detachable from the electrophotographic apparatus main body.

[0055] (Configuration of electrophotographic apparatus) FIG. 2 shows an example of the schematic configuration of an electrophotographic apparatus having a process cartridge equipped with the electrophotographic photoreceptor of the present invention. Note that the electrophotographic apparatus of this embodiment is a so-called tandem type electrophotographic apparatus provided with a plurality of image forming units a to d. The first image forming unit a forms an image with yellow (Y) toner, the second image forming unit b forms an image with magenta (M) toner, the third image forming unit c forms an image with cyan (C) toner, and the fourth image forming unit d forms an image with black (Bk) toner. These four image forming units are arranged in a row at regular intervals, and the configurations of the respective image forming units have many substantially common parts except for the color of the toner to be accommodated. Therefore, hereinafter, the electrophotographic apparatus of this embodiment will be described using the first image forming unit a.

[0056] The first image forming unit a includes a photosensitive drum 1a which is a drum-shaped photoreceptor, a charging roller 2a which is a charging member, a developing means 4a, and a drum cleaning means 5a. The photosensitive drum 1a is an image carrier that carries a toner image and is rotationally driven at a predetermined peripheral speed (process speed) in the direction of the illustrated arrow R1. The developing means 4a stores yellow toner and develops the photosensitive drum 1a with the yellow toner. The drum cleaning means 5a is a means for collecting the toner adhering to the photosensitive drum 1a. The drum cleaning means 5a includes a cleaning blade that contacts the photosensitive drum 1a and a waste toner box that stores the toner and the like removed from the photosensitive drum 1a by the cleaning blade. When a control means (not shown) such as a controller receives an image signal, an image forming operation is started and the photosensitive drum 1a is rotationally driven. During the rotation process of the photosensitive drum 1a, it is uniformly charged to a predetermined voltage (charging voltage) with a predetermined polarity (negative polarity in this embodiment) by the charging roller 2a and exposed by the exposure means 3a according to the image signal. As a result, an electrostatic latent image corresponding to the yellow color component image of the target color image is formed on the photosensitive drum 1a. Next, the electrostatic latent image is developed by the developing means 4a at the developing position and visualized as a yellow toner image on the photosensitive drum 1a. Here, the normal charging polarity of the toner stored in the developing means 4a is negative polarity, and the electrostatic latent image is reversely developed by the toner charged to the same polarity as the charging polarity of the photosensitive drum 1a by the charging roller 2a. However, the present invention is not limited to this, and the present invention can also be applied to an electrophotographic apparatus that positively develops an electrostatic latent image with toner charged to the opposite polarity to the charging polarity of the photosensitive drum 1a.

[0057] The endless and movable intermediate transfer belt 10 has conductivity, forms a primary transfer portion N1a in contact with the photosensitive drum 1a, and rotates at substantially the same peripheral speed as the photosensitive drum 1a. Further, the intermediate transfer belt 10 is stretched by an opposing roller 13 as an opposing member, a driving roller 11 and a stretching roller 12 as stretching members, and a metal roller 14a, and is stretched by the stretching roller 12 with a tension of 60 N. The intermediate transfer belt 10 can be moved when the driving roller 11 is rotationally driven in the direction of the arrow R2 in the figure. Also, each metal roller 14a and the opposing roller 13 are connected to the ground via a Zener diode 15 as a constant voltage element. The yellow toner image formed on the photosensitive drum 1a is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10 in the process of passing through the primary transfer portion N1a. The primary transfer residual toner remaining on the surface of the photosensitive drum 1a is cleaned and removed by the drum cleaning means 5a, and then is used for the image forming process below charging.

[0058] During primary transfer, a current is supplied from a secondary transfer roller 20 as a secondary transfer member that contacts the outer peripheral surface of the intermediate transfer belt 10 to the conductive intermediate transfer belt 10. When the current supplied from the secondary transfer roller 20 flows in the circumferential direction of the intermediate transfer belt 10, the toner image is primarily transferred from the photosensitive drum 1a to the intermediate transfer belt 10. At this time, a voltage J of a predetermined polarity (positive polarity in this embodiment) opposite to the normal charging polarity of the toner is applied from the transfer power source 21 to the secondary transfer roller 20. In the figure, in the second, third, and fourth image forming portions of 2, the photosensitive drums are 1b, 1c, 1d respectively, the charging rollers are 2b, 2c, 2d respectively, the exposure means are 3b, 3c, 3d respectively, the developing means are 4b, 4c, 4d respectively, the drum cleaning means are 5b, 5c, 5d respectively, the metal rollers are 14b, 14c, 14d respectively, and the primary transfer portions are N1b, N1c, N1d respectively.

[0059] Similarly, a magenta toner image of the second color, a cyan toner image of the third color, and a black toner image of the fourth color are formed and sequentially transferred and stacked on the intermediate transfer belt 10. As a result, four-color toner images corresponding to the target color image are formed on the intermediate transfer belt 10. Thereafter, the four-color toner images carried on the intermediate transfer belt 10 are collectively secondarily transferred onto the surface of a transfer material P such as paper or an OHP sheet fed by the paper feeding means 50 in the process of passing through a secondary transfer portion N2 formed by the contact between the secondary transfer roller 20 and the intermediate transfer belt 10. The transfer material P onto which the four-color toner images are transferred by secondary transfer is then heated and pressurized by the fixing means 30, so that the four-color toners are melted and mixed and fixed to the transfer material P. The toner remaining on the intermediate transfer belt 10 after secondary transfer is cleaned and removed by belt cleaning means 16 provided to face the counter roller 13 via the intermediate transfer belt 10. Further, a path is provided that does not pass through the secondary transfer roller 20 and electrically connects the transfer power supply 21 and each metal roller 14 via a constant current diode 22 as a constant current element. Also, when a voltage is applied from the transfer power supply 21 to the secondary transfer roller 20, a pinch-off current Id flows through the constant current diode 22 separately from the current It2 flowing toward the secondary transfer portion N2. The electrophotographic photoreceptor of the present invention can be used in a laser beam printer, an LED printer, a copying machine, etc.

Example

[0060] Hereinafter, the present invention will be described in more detail using examples and comparative examples. The present invention is not limited in any way by the following examples as long as the gist thereof is not exceeded. In the description of the following examples, "parts" means based on mass unless otherwise specified. Also, the film thickness of each layer of the electrophotographic photoreceptor of the examples and comparative examples was determined by an eddy current type film thickness meter (trade name: Fischerscope, manufacturer: Fischer Instruments), or determined by specific gravity conversion from the mass per unit area.

[0061] <Manufacturing Example of Electrophotographic Photoreceptor 1> An aluminum cylinder with a diameter of 20 mm and a length of 257.5 mm (standard: JIS-A3003 aluminum alloy) was used as the support (conductive support). The conductive layer, undercoat layer, charge generation layer, charge transport layer, and surface layer were fabricated by the following method.

[0062] <Preparation of Coating Liquid for Conductive Layer> As the substrate, anatase titanium oxide with an average primary particle size of 200 nm was used, and a titanium niobium sulfate solution containing 33.7 parts of titanium atoms in terms of TiO2 and 2.9 parts of niobium atoms in terms of Nb2O5 was prepared. 100 parts of the substrate was dispersed in pure water to obtain a 1000-part suspension, which was heated to 60 °C. The titanium niobium sulfate solution and 10 mol / L sodium hydroxide were added dropwise to the suspension over 3 hours so that the pH of the suspension became 2 - 3. After the addition of the total amount, the pH was adjusted to near neutrality, and a polyacrylamide-based flocculant was added to precipitate the solids. The supernatant was removed, and the precipitate was filtered, washed, and dried at 110 °C to obtain an intermediate containing 0.1 wt% of organic matter derived from the flocculant in terms of C. This intermediate was calcined in nitrogen at 750 °C for 1 hour and then in air at 450 °C to fabricate titanium oxide particles 1. The obtained particles had an average primary particle size of 220 nm in the particle size measurement method using a scanning electron microscope described later. Subsequently, 50 parts of a phenol resin (monomer / oligomer of phenol resin) (trade name: Pryophen J-325, manufacturer: DIC Corporation, resin solid content: 60%, density after curing: 1.3 g / cm 3 ) was dissolved in 35 parts of 1-methoxy-2-propanol as the solvent to obtain a solution. 60 parts of titanium oxide particles 1 were added to this solution, and it was put into a vertical sand mill using 120 parts of glass beads with a number average primary particle size of 1.0 mm as a dispersion medium. Then, a dispersion treatment was performed for 4 hours under the conditions of a dispersion liquid temperature of 23 ± 3°C and a rotation speed of 1500 rpm (peripheral speed 5.5 m / s) to obtain a dispersion liquid. The glass beads were removed from this dispersion liquid with a mesh. To the dispersion liquid after removing the glass beads, 0.01 part of silicone oil (product name: SH28 PAINT ADDITIVE, manufacturer: Toray Dow Corning Co., Ltd.) as a leveling agent and 8 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 3 ) were added and stirred. Then, a coating liquid for the conductive layer was prepared by pressure filtration using a PTFE filter paper (product name: PF060, manufacturer: Advantec Toyo Co., Ltd.).

[0063] <Preparation of Coating Liquid for Undercoat Layer> 100 parts of rutile-type titanium oxide particles (average primary particle size: 50 nm, manufacturer: Tayca Corporation) were stirred and mixed with 500 parts of toluene, 3.5 parts of vinyltrimethoxysilane (product name: KBM-1003, manufacturer: Shin-Etsu Chemical Co., Ltd.) was added, and a dispersion treatment was performed for 8 hours in a vertical sand mill using glass beads with a diameter of 1.0 mm. After removing the glass beads, toluene was distilled off under reduced pressure and dried at 120°C for 3 hours to obtain rutile-type titanium oxide particles surface-treated with an organosilicon compound. When the volume of the obtained titanium oxide particles was a and the average primary particle size of the titanium oxide particles was b [μm], a / b = 15.6. The value of a was determined from a microscopic image using a field emission scanning electron microscope (FE-SEM, product name: S-4800, manufacturer: Hitachi High-Technologies Corporation) of the cross section of the electrophotographic photoreceptor after manufacturing the electrophotographic photoreceptor. 18.0 parts of rutile titanium oxide particles surface-treated with the above organosilicon compound, 4.5 parts of N-methoxymethylated nylon (trade name: Torelina EF-30T, manufacturer: Nagase ChemteX Corporation), and 1.5 parts of copolymerized nylon resin (trade name: Amilan CM8000, manufacturer: Toray Industries, Inc.) were added to a mixed solvent of 90 parts of methanol and 60 parts of 1-butanol to prepare a dispersion. This dispersion was subjected to dispersion treatment for 5 hours using a vertical sand mill with glass beads having a diameter of 1.0 mm, and the glass beads were removed to prepare a coating liquid for the undercoat layer.

[0064] <Synthesis of phthalocyanine pigment> <Synthesis example> Under a nitrogen flow atmosphere, 100 g of gallium trichloride and 291 g of orthophthalonitrile were added to 1000 mL of α-chloronaphthalene, and after reacting at a temperature of 200 °C for 24 hours, the product was filtered. The obtained wet cake was heated and stirred at a temperature of 150 °C for 30 minutes using N,N-dimethylformamide and then filtered. The obtained filtrate was washed with methanol and then dried to obtain a chlorogallium phthalocyanine pigment in a yield of 83%. 20 g of the chlorogallium phthalocyanine pigment obtained by the above method was dissolved in 500 mL of concentrated sulfuric acid, stirred for 2 hours, and then dropped into a mixed solution of 1700 mL of distilled water cooled with ice and 660 mL of concentrated aqueous ammonia for reprecipitation. This was thoroughly washed with distilled water and dried to obtain a hydroxygallium phthalocyanine pigment.

[0065] <Preparation of coating liquid for charge generation layer> 0.5 part of hydroxygallium phthalocyanine pigment obtained in the synthesis example, 7.5 parts of N,N-dimethylformamide (product code: D0722, manufacturer: Tokyo Chemical Industry Co., Ltd.), and 29 parts of glass beads with a diameter of 0.9 mm were milled at a temperature of 25 °C for 24 hours using a sand mill (product name: BSG-20, manufacturer: Aimax Co., Ltd.). At this time, the milling was carried out under the condition that the disk rotated 1500 times per minute. The liquid thus treated was filtered through a filter (product number: N-NO.125T, pore diameter: 133 μm, manufacturer: NBC Mesh Tech Co., Ltd.) to remove the glass beads. After adding 30 parts of N,N-dimethylformamide to this liquid, it was filtered, and the filtrate on the filter was thoroughly washed with n-butyl acetate. Then, the washed filtrate was vacuum dried to obtain 0.45 part of hydroxygallium phthalocyanine pigment. The obtained pigment contained N,N-dimethylformamide. Subsequently, 20 parts of hydroxygallium phthalocyanine pigment obtained by the above milling treatment, 10 parts of polyvinyl butyral (product name: Esrec BX-1, manufacturer: Sekisui Chemical Co., Ltd.), 190 parts of cyclohexanone, and 482 parts of glass beads with a diameter of 0.9 mm were dispersed at a cooling water temperature of 18 °C for 4 hours using a sand mill (product name: K-800, manufacturer: Igarashi Machinery Manufacturing (now: Aimax Co., Ltd.), disk diameter 70 mm, number of disks 5). At this time, the dispersion was carried out under the condition that the disk rotated 1800 times per minute. The glass beads were removed from this dispersion liquid, and 444 parts of cyclohexanone and 634 parts of ethyl acetate were added to prepare a coating liquid for the charge generation layer.

[0066] <Preparation of Coating Liquid for Charge Transport Layer> (Production Example of Charge Transport Layer) Next, the following materials were prepared to prepare a mixed solvent. · 25 parts by mass of ortho-xylene · 25 parts by mass of methyl benzoate · 25 parts by mass of dimethoxymethane Furthermore, the following materials were dissolved in the above mixed solvent to prepare a coating liquid for the charge transport layer. · 5 parts by mass of a charge transport substance (hole transport substance) represented by the following structural formula (C-1) · 5 parts by mass of a charge transport material (hole transport material) represented by the following structural formula (C-2) · 10 parts by mass of polycarbonate (trade name: Iupilon Z400, manufacturer: Mitsubishi Engineering-Plastics Corporation)

Chemical formula

Chemical formula

[0067] <Manufacturing Example of Electrophotographic Photoconductor 1> <Support> An aluminum cylinder with a diameter of 20 mm and a length of 257.5 mm (standard: JIS-A3003, aluminum alloy) was used as the support (conductive support).

[0068] <Conductive layer> The coating solution for the conductive layer was dip-coated on the above-mentioned support to form a coating film, and the coating film was heated and cured at 150 °C for 30 minutes to form a conductive layer with a film thickness of 22 μm.

[0069] <Undercoat layer> The coating solution for the undercoat layer was dip-coated on the above-mentioned conductive layer to form a coating film, and the coating film was heated and cured at 100 °C for 10 minutes to form an undercoat layer with a film thickness of 1.8 μm.

[0070] <Charge generation layer> The coating solution for the charge generation layer was dip-coated on the above-mentioned undercoat layer to form a coating film, and the coating film was heated and dried at a temperature of 100 °C for 10 minutes to form a charge generation layer with a film thickness of 0.20 μm.

[0071] <Charge transport layer> The coating solution for the charge transport layer was dip-coated on the above-mentioned charge generation layer to form a coating film, and the coating film was heated and dried at a temperature of 120 °C for 30 minutes to form a charge transport layer with a film thickness of 21 μm.

[0072] <Surface layer> · Polyol (trade name: Placcel DC2016, manufacturer: Daicel Chemical Industries, Ltd.) 17.83 parts by mass · Isocyanate (trade name: BI7951, manufacturer: GSICreos) 22.17 parts by mass · Inorganic particles (trade name: QSG-170, manufacturer: Shin-Etsu Chemical Co., Ltd., silica particles) 17.37 parts by mass · Cyclohexane 100 parts by mass · 1-Propanol 100 parts by mass · Additive (trade name: US270, manufacturer: Toagosei Co., Ltd.) 5.38 parts by mass These were mixed and stirred to prepare a coating solution 1 for the surface layer. This coating solution 1 for the surface layer was dip-coated onto the charge transport layer so that the film thickness at completion would be about 1 μm to form a coating film, and the obtained coating film was heat-treated at 130 °C for 60 minutes. Thus, the electrophotographic photoreceptor 1 was produced. The film thickness was 1.1 μm.

[0073] <Electrophotographic photoreceptors 2 to 24> In the production example of the electrophotographic photoreceptor 1, up to the charge transport layer, it was produced in the same manner, and the materials of the coating solutions 2 to 24 for the surface layer used in the production of the surface layer were changed as shown in Table 1 and prepared. Using the prepared coating solutions for the surface layer respectively, electrophotographic photoreceptors 2 to 24 were produced in the same manner as the electrophotographic photoreceptor 1.

[0074] <Production of niobium-doped titanium oxide> To the hydrous titanium dioxide slurry obtained by hydrolyzing an aqueous solution of titanyl sulfate, niobium sulfate (a water-soluble niobium compound) was added. The addition amount was such that niobium sulfate was added at a ratio of 1.8% by mass as niobium ions with respect to the amount of titanium in the slurry (in terms of titanium dioxide). What was obtained by adding niobium sulfate to the aqueous solution of titanyl sulfate at a ratio of 1.8% by mass as niobium ions was hydrolyzed to obtain a hydrous titanium dioxide slurry. Next, the hydrous titanium dioxide slurry containing niobium ions and the like was dehydrated and fired at a firing temperature of 1000 °C. Thereby, anatase-type titanium oxide particles having an average primary particle size of 66 nm containing 1.8% by mass of niobium element were obtained.

[0075]

Table 1

[0076] Hereinafter, the materials used for preparing the coating liquid for the surface layer will be described. Polyol · PTG-1000SN (Manufacturer: Hodogaya Chemical Co., Ltd.) · PTG-2000SN (Manufacturer: Hodogaya Chemical Co., Ltd.) · PTG-2900SN (Manufacturer: Hodogaya Chemical Co., Ltd.) Isocyanate · BI7982 (Manufacturer: GSI Creos) · BI7961 (Manufacturer: GSI Creos) Inorganic particles · KE-P50 (Manufacturer: Nippon Shokubai Co., Ltd., silica particles) · QSG-30 (Manufacturer: Shin-Etsu Chemical Co., Ltd., silica particles) · MgO (Manufacturer: Sigma-Aldrich) · Al2O3 (Manufacturer: Sigma-Aldrich) · MT-700Z (Manufacturer: Teika Co., Ltd., titanium oxide) Additive · Kaolizer No. 25 (Manufacturer: Kao Corporation) The density of the particles can be referred to the published values in the database POLYINFO of the manufacturer of each material and the National Institute for Materials Science. The following values were used for the density of various materials. · The density of PTG-1000SN, PTG-2000SN and PTG-2900SN is 0.98 g / cm 3 · The density of BI7951, BI7961 and BI7982 is 1.05 g / cm 3 · The density of silica particles is 1.8 g / cm 3 · The density of magnesium oxide is 3.65 g / cm 3 · Aluminum oxide, density 3.65 g / cm 3 · Titanium oxide, density 4.0 g / cm 3

[0077] <Comparative Example> In the production example of the electrophotographic photoreceptor 1, up to the charge transport layer, it was produced in the same manner, and the materials of the coating liquids c1 to c9 for the surface layer used in the production of the surface layer were changed as shown in Table 2 and prepared. Using the prepared coating liquids for the surface layer respectively, electrophotographic photoreceptors c1 to c9 were produced in the same manner as the electrophotographic photoreceptor 1.

[0078]

Table 2

[0079] <Evaluation Method> <Derivation of the ratio of the volume of inorganic particles to the volume of the binder resin in the surface layer> The ratio of the volume of inorganic particles to the volume of the binder resin in the surface layer was calculated from the number of parts of the acrylic monomer and the inorganic particles used in the coating liquid for the surface layer. The specific gravities of the acrylic monomer and the inorganic particles can be referred to the published values of each material manufacturer. When obtaining from the electrophotographic photoreceptor, for example, there is the following method. Only the surface layer was peeled off into a plurality of sections with a cutting instrument, and the sections were analyzed by composition analysis such as NMR, ESI-MS, LC-CAD / MS / MSn to identify the polymerizable monomer having a polymerizable functional group that constitutes the composition of the binder resin contained in the surface layer before becoming a polymer. Also, another section was measured for the masses of the binder resin and the inorganic particles contained in the surface layer by thermogravimetric analysis such as TGA. Furthermore, perform compositional analysis such as SEM-EDS or XRF on the sintered inorganic particles to identify the material of the inorganic particles and determine the specific gravity. From these methods, in an electrophotographic photoreceptor having a surface layer containing a binder resin and inorganic particles, calculate the value of the ratio of the volume of the inorganic particles to the volume of the binder resin in the surface layer.

[0080] <Evaluation of the Convex Portions on the Surface Layer of the Electrophotographic Photoreceptor> The convex portions formed on the surface of the surface layer of the electrophotographic photoreceptor can be evaluated by observing the surface of the electrophotographic photoreceptor with an electron microscope. When evaluating in more detail, cross-sectional observation of the convex portions of the surface layer of the electrophotographic photoreceptor is preferred. For example, there are the following methods. A 5 mm square sample piece was cut from the electrophotographic photoreceptor using a tool such as a saw. At this time, the positions where the sample pieces were cut were at the 38 mm position, 128 mm position, and 218 mm position in the longitudinal direction, and a total of 12 sample pieces of 5 mm square were cut every 90° in the circumferential direction. The sample pieces were fixed to a sample holder so that the surface layer could be observed. Cross-sectional observation was performed on the sample holder with the fixed sample pieces using a FIBSEM (product name: Nvision, manufacturer: ZEISS). The measurement conditions of the FIBSEM are as follows. Three-dimensionalization of a 2 μm × 2 μm × 2 μm area of the surface layer was performed using Slice&View of the FIB-SEM. The conditions for Slice&View were as follows. Sample preparation for analysis: FIB method Processing and observation apparatus: NVision40 manufactured by SII / Zeiss Slice interval: 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 Also, the measurement environment was at a temperature of 23°C and a pressure of 1×10 -4It is Pa. As the processing and observation apparatus, Strata400S (sample tilt: 52°) manufactured by FEI can also be used. In the cross-sectional image of the surface layer of the electrophotographic photoreceptor obtained by FIBSEM, the surface layer protrusions were evaluated. This operation was performed on all the protrusions existing in the cross-sectional image and whose overall image was within the cross-sectional image. The same operation was performed on each of the 12 sample pieces. If 90% of the evaluated protrusions were protrusions derived from inorganic particles, it was determined that the protrusions on the surface layer of the electrophotographic photoreceptor were protrusions derived from inorganic particles.

[0081] <Evaluation of the average primary particle size based on the number of inorganic particles contained in the surface layer> The average primary particle size based on the number of inorganic particles contained in the surface layer can be referred to from the published values of each material manufacturer of the inorganic particles used. When evaluating from the electrophotographic photoreceptor, for example, there are the following methods. First, the entire electrophotographic photoreceptor was immersed in methyl ethyl ketone (MEK) in a graduated cylinder and irradiated with ultrasonic waves to peel off the resin layer, and then the substrate of the electrophotographic photoreceptor was taken out. Next, the insoluble matter (photosensitive layer and protective layer containing metal oxide particles) that did not dissolve in MEK was filtered and dried in a vacuum dryer. Further, the obtained solid was suspended in a mixed solvent with a volume ratio of tetrahydrofuran (THF) / methylal of 1:1, and after filtering the insoluble matter, the filtrate was collected and dried in a vacuum dryer. By this operation, inorganic particles and the resin of the surface layer were obtained. Further, the filtrate was heated to 500 °C in an electric furnace so that the solid became only inorganic particles, and the inorganic particles were recovered. In order to ensure the amount of inorganic particles required for measurement, the same treatment was performed on a plurality of electrophotographic photoreceptors. A part of the recovered inorganic particles was dispersed in isopropanol (IPA), and the dispersion was dropped onto a grid mesh with a support film (product name: Cu150J, manufacturer: JEOL Ltd.). Observation of the inorganic particles was carried out in the STEM mode of a scanning transmission electron microscope (product name: JEM2800, manufacturer: JEOL). The observation was performed at a magnification of 500,000 to 1,200,000 times so as to easily calculate the inorganic particles, and 100 STEM images of the inorganic particles were taken each. The inorganic particles were distinguished using the EDX function of the scanning electron microscope. At this time, the acceleration voltage was set to 200 kV, the probe size was 1 nm, and the image size was set to 1024×1024 pixels. Using the obtained STEM images, the primary particle diameter was measured with image processing software "Image-Pro Plus (manufacturer: Media Cybernetics)". First, select the scale bar displayed at the bottom of the STEM image using the straight line tool in the toolbar. In this state, select Set Scale in the Analyze menu, and a new window will open. The pixel distance of the selected straight line is entered in the Distance in Pixels column. Enter the value of the scale bar (for example, 100) in the Known Distance column of the window, enter the unit of the scale bar (for example, nm) in the Unit of Mesurement column, and click OK to complete the scale setting. Next, draw a straight line using the straight line tool so as to obtain the maximum diameter of the inorganic particle, and calculate the particle diameter. The same operation was performed for 100 inorganic particles, and the average value of the obtained values (maximum diameter) was taken as the primary particle diameter of the inorganic particles. However, for samples using carbon black or the like as the inorganic particles, the average primary particle diameter of the particles was measured by the following method. An electrophotographic photoreceptor was cut into 5 mm square sample pieces using a tool such as a saw. At this time, the cut positions were at the 38 mm position, 128 mm position, and 218 mm position in the longitudinal direction, and 12 sample pieces of 5 mm square were cut every 90° in the circumferential direction. The sample pieces were fixed to a sample holder so that the surface layer of the sample pieces could be observed. Cross-sectional observation was performed on the sample holder with the sample pieces fixed using a FIBSEM (product name: Nvision, manufacturer: ZEISS). The measurement conditions were the same as those described above. In the cross-sectional image of the surface layer of the electrophotographic photoreceptor obtained by FIBSEM, the particle size of the particles was measured. This operation was performed on all the particles that existed within the cross-sectional image and whose overall image was contained within the cross-sectional image. The arithmetic mean value of the particle sizes of the obtained particles was taken as the average particle size of the sample piece, and the arithmetic mean of the average particle sizes of each of the 12 sample pieces was taken as the average primary particle size of the particles contained in the surface layer of the electrophotographic photoreceptor.

[0082] <Evaluation of maximum height roughness Rz, arithmetic mean roughness Ra, and mean length Rsm> An electrophotographic photoreceptor was cut into 5 mm square sample pieces using a tool such as a saw. At this time, the cut positions were at the 38 mm position, 128 mm position, and 218 mm position in the longitudinal direction, and a total of 12 5 mm square sample pieces were cut every 90° in the circumferential direction. The sample pieces were fixed to a sample holder so that the surface layer of the sample pieces could be observed. The sample holder with the sample pieces fixed was observed with a scanning probe microscope SPM. This observation was performed for each of the 12 sample pieces, and the arithmetic mean of their maximum height roughness Rz was taken as the maximum height roughness Rz of the electrophotographic photoreceptor. The arithmetic mean roughness Ra and the mean length Rsm were also measured in the same manner as the maximum height roughness Rz, and the arithmetic means of the 12 sample pieces were taken as the arithmetic mean roughness Ra and the mean length Rsm of the electrophotographic photoreceptor. As the SPM, a scanning probe microscope "JSPM-5200" (manufacturer: JEOL Ltd.), a scanning probe microscope "E-sweep" (manufacturer: Hitachi High-Tech Corporation), a medium-sized probe microscope system AFM5500M (manufacturer: Hitachi High-Tech Corporation), etc. can be used. As a specific measurement method, the observation conditions for each of "JSPM-5200" and "E-sweep" are described below. In this case, the observation was performed with JSPM-5200. The measurement results are shown in Tables 3 and 4.

[0083] · Observation with "JSPM-5200" Scanner:4 SPM Scan:All SPM Mode Cantilever:SI-DF3P2 (manufacturer: Hitachi High-Tech Fielding Co., Ltd.) Resonance Frequency Detection: (START)1.00 kHz (Stop)100 kHz (depending on the cantilever type when f = 67kHz) Cantilever Autotune:Normal approach Aquisition :2 Inputs (512) Scan Mode :Normal STM / AFM:AC-AFM Clock:833.33 μs Scan Size: 3.00 nm Offset: 0 Bias [V]: 0 Reference / V: Do not change (calibration value already entered) Filter: 1.4 Hz Loop Gain: 16

[0084] Regarding the data image of the surface shape, analysis was performed using the attached WinSPM Processing, and the mode for analyzing the surface roughness was used. The difference between the maximum value Zmax and the minimum value Zmin of the height z of each of the above samples was obtained, and the average values of the maximum height roughness Rz, the arithmetic mean roughness Ra, and the average length of the elements Rsm were calculated.

[0085] Also, the measurement method using the scanning probe microscope "E-sweep" (manufacturer: Hitachi High-Tech Corporation) is as follows. It was performed through a scan operation, and an analysis image of the data surface shape was output. · Observation with "E-sweep" Cantilever: SI-DF20 (with Al on the back) K-A102002771 (manufacturer: Hitachi High-Tech Fielding Co., Ltd.) Scanning probe microscope: manufactured by Hitachi High-Tech Science Corporation Measurement unit: E-sweep Measurement mode: DFM (resonance mode) shape image Resolution: Number of X data 512, Number of Y data 512 Measurement frequency: 127 Hz The Q curve measurement magnification, excitation voltage, low-pass filter, high-pass filter, etc. were adjusted so that the resonance state of the cantilever could be optimized. The surface shape image and the surface height data attached to the image were analyzed using the attached software, and the difference between the maximum value Zmax and the minimum value Zmin of the height z was obtained, and the average values of the maximum height roughness Rz, the arithmetic mean roughness Ra, and the average length of the elements Rsm were calculated.

[0086] <Evaluation of dynamic friction coefficient> For the evaluation of the coefficient of kinetic friction, a surface property measuring instrument (model: 14FW, manufacturer: Shin-Tech Co., Ltd.) was used, and the evaluation was carried out under normal temperature and humidity environment (25 °C, 50% RH; hereinafter also referred to as "N / N"). The electrophotographic photoreceptor was attached to the surface property measuring instrument so as to be horizontal, and a urethane piece with a thickness of 2 mm and a right angle cut with a side length of 10.0 mm was brought into contact with the electrophotographic photoreceptor at an angle of 22.5°. The trial production example of the urethane will be described later. A 10 g weight was placed as the contact pressure of the urethane, and the electrophotographic photoreceptor was moved at a speed of 100 mm / min in the longitudinal direction. Thereby, the frictional force was measured. Similar frictional force measurements were performed except that the weight of the weight was changed to 20 g and 50 g. The coefficient of kinetic friction was calculated from the relationship between the frictional force and the contact pressure obtained by the frictional force measurement, and the value was taken as the coefficient of kinetic friction of the electrophotographic photoreceptor. The measurement results are shown in Tables 3 and 4.

[0087] The method for trial-producing urethane is shown below. 27.7 parts by mass of 4,4'-diphenylmethane diisocyanate (trade name: Millionate MT, manufacturer: Tosoh Corporation) and a polybutylene adipate polyester polyol (trade name: Nipolan 4010, manufacturer: Nippon Polyurethane Industry Co., Ltd.) with a molecular weight of 2.0×10 3 were reacted at 80 °C in a nitrogen atmosphere for 3 hours to obtain a prepolymer with NCO 8.8%. Also, 14.9 parts by mass of PBA with a molecular weight of 1000 (trade name: Nipolan 4009, manufacturer: Nippon Polyurethane Industry Co., Ltd.), 2.6 parts by mass of 1,4-butanediol (manufacturer: Tokyo Chemical Industry Co., Ltd.), 2.1 parts by mass of trimethylolpropane (manufacturer: Tokyo Chemical Industry Co., Ltd.), and 80 ppm of an isocyanurate-forming catalyst (trade name: P15, manufacturer: Air Products Japan) and 340 ppm of a urethanization catalyst (trade name: DABCO crystal, Air Products Japan) as a curing catalyst were mixed. Thereby, a curing agent was prepared. The prepolymer and the curing agent were mixed and stirred for 70 seconds while degassing. The mixed solution obtained by stirring was poured into a mold heated to 135°C and pressed with a vise. At this time, as the mold, an aluminum split mold for forming a square sheet with a thickness of 2 mm and a side length of 200 mm was used. It was left standing while being heated to 135°C for 90 seconds under pressure with a vise. Then, the urethane resin sheet formed into a square sheet with a thickness of 2 mm and a side length of 200 mm was taken out of the mold.

[0088] The obtained urethane resin sheet was measured based on JIS K6253 using a Wallace microhardness tester (manufacturer: H.W, WALLACE). The measurement was performed at 9 points that are the intersections of the horizontal 50 mm position, 100 mm position, 150 mm position and the vertical 50 mm position, 100 mm position, 150 mm position of the urethane resin sheet, and the average value of these was taken as the hardness of the urethane resin sheet. The hardness obtained at this time was 68 (IRHD°). The urethane resin sheet was cut at right angles to form a square sheet with a side length of 10.0 mm, and urethane pieces with a thickness of 2 mm and a side length of 10.0 mm cut at right angles were obtained.

[0089] <Horizontal streak evaluation> To evaluate the horizontal streak image due to the slip of the electrophotographic photoreceptor, an electrophotographic apparatus (product name: i-SENSYS MF754Cdw, manufacturer: Canon Inc.) was used and the evaluation was carried out in an N / N environment. The image forming apparatus was modified so that the conveyance speed of the recording material, the peripheral speed of the intermediate transfer body, and the peripheral speed of the electrophotographic photoreceptor could be adjusted. The image forming apparatus, the toner cartridge used in the image forming apparatus, the electrophotographic photoreceptor, and a recording material of LETTER size (product name: XEROX Vitality, manufacturer: XEROX, basis weight: 75 g / m 2 ) were left in an N / N environment for 24 hours. Then, the electrophotographic photoreceptor was attached to the toner cartridge and attached to the image forming apparatus. The conveyance speed of the recording material was set at 300 mm / second, the peripheral speed of the intermediate transfer member was set at 300 mm / second, and the peripheral speed of the electrophotographic photoreceptor was set at 291 mm / second. That is, the peripheral speed difference between the intermediate transfer member and the electrophotographic photoreceptor was set at 3%. Note that the same electrophotographic photoreceptor was used for all toner cartridges of yellow, magenta, cyan, and black. To output an evaluation image, first, a halftone image (toner loading amount: 0.2 mg / cm 2 ) with a 5.0 mm margin on the top, bottom, left, and right was printed in cyan as an initial print. After printing 50,000 full-color 1.0% images, a halftone image similar to the initial print was printed as an evaluation image during long-term use. The horizontal streak evaluation of the halftone image was performed according to the following criteria. Up to evaluation criterion C is a level with no practical problems. The evaluation results are shown in Tables 3 and 4. (Evaluation Criteria) A: No horizontal streaks are observed by observation using a loupe. B: No horizontal streaks are observed by visual observation, but slight horizontal streaks are observed by observation using a loupe. C: Slight horizontal streaks are observed by visual observation. D: Horizontal streaks are observed by visual observation.

[0090]

Table 3

[0091]

Table 4

[0092] The disclosure of this embodiment includes the following configurations. (Configuration 1) An electrophotographic photoreceptor having a surface layer containing a binder resin and inorganic particles, wherein the surface layer contains a urethane resin as the binder resin, the value of the ratio of the volume of the inorganic particles to the volume of the binder resin in the surface layer is 0.10 or more and 3.0 or less, and convex portions derived from the inorganic particles are present on the surface of the surface layer. The average primary particle diameter of the inorganic particles contained in the surface layer is 10 nm or more and 500 nm or less based on the number, and the maximum height roughness Rz of the surface of the surface layer is 10 nm or more and 760 nm or less. An electrophotographic photoreceptor characterized by the above. (Configuration 2) The electrophotographic photoreceptor according to Configuration 1, wherein the maximum height roughness Rz of the surface layer is 40 nm or more and 760 nm or less. (Configuration 3) The electrophotographic photoreceptor according to Configuration 1 or 2, wherein the average length Rsm of the roughness curve elements of the surface layer is 20 nm or more and 1400 nm or less. (Configuration 4) The electrophotographic photoreceptor according to any one of Configurations 1 to 3, wherein the arithmetic mean roughness Ra of the surface layer is 10 nm or more and 500 nm or less. (Configuration 5) The electrophotographic photoreceptor according to any one of Configurations 1 to 4, wherein the coefficient of kinetic friction of the surface layer is 0.95 or less in an environment of 25 °C and 50% RH. (Configuration 6) The electrophotographic photoreceptor according to any one of Configurations 1 to 5, wherein the inorganic particles contained in the surface layer have a functional group reactive with an isocyanate group. (Configuration 7) The electrophotographic photoreceptor according to any one of Configurations 1 to 6, wherein the arithmetic mean film thickness of the surface layer is 2.0 μm or less. (Configuration 8) The electrophotographic photoreceptor according to any one of Configurations 1 to 7, wherein the Mohs hardness of the inorganic particles contained in the surface layer is 4.0 or more. (Configuration 9) The electrophotographic photoreceptor according to any one of Configurations 1 to 8, wherein the inorganic particles contained in the surface layer are silica particles or metal oxide particles. (Configuration 10) The electrophotographic photoreceptor according to any one of Configurations 1 to 9, wherein the urethane resin contained in the surface layer has a nurate structure. (Configuration 11) The electrophotographic photoreceptor according to any one of Configurations 1 to 10, wherein the urethane resin contained in the surface layer is a polymer of an isocyanate compound having 3 or more polymerizable functional groups and a polyol compound. (Configuration 12) The electrophotographic photoreceptor according to any one of Configurations 1 to 11, wherein the urethane resin contained in the surface layer is a polymer of an isocyanate compound having a nurate structure and a polyol compound. (Configuration 13) The electrophotographic photoreceptor according to any one of Configurations 1 to 12, wherein the urethane resin contained in the surface layer is a polymer of an isocyanate compound and a polyol having an average molecular weight of 2.0×10 3 or less. (Configuration 14) The electrophotographic photoreceptor according to Configuration 8, wherein the metal oxide particles contained in the surface layer are titanium oxide doped with niobium atoms. (Configuration 15) A process cartridge that integrally supports the electrophotographic photoreceptor according to any one of Configurations 1 to 14 and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachable from the main body of the electrophotographic apparatus. (Configuration 16) An electrophotographic apparatus having the electrophotographic photoreceptor according to any one of Configurations 1 to 14, and a charging means, an exposure means, a developing means, and a transfer means.

Explanation of Signs

[0093] 101 Support 102 Undercoat layer 103 Charge generation layer 104 Charge transport layer 105 Surface layer 1a, 1b, 1c, 1d Electrophotographic photoreceptor 2a, 2b, 2c, 2d Charging roller 3a, 3b, 3c, 3d Exposure means 4a, 4b, 4c, 4d Developing means 5a, 5b, 5c, 5d Drum cleaning means 10 Intermediate transfer belt 20 Secondary transfer roller 30 Fixing means

Claims

1. An electrophotographic photoreceptor having a surface layer containing a binder resin and inorganic particles, wherein the surface layer contains a urethane resin as the binder resin, the value of the ratio of the volume of the inorganic particles to the volume of the binder resin in the surface layer is 0.10 or more and 3.0 or less, protrusions derived from the inorganic particles are present on the surface of the surface layer, the average primary particle diameter of the inorganic particles contained in the surface layer is 10 nm or more and 500 nm or less based on the number, and the maximum height roughness Rz of the surface of the surface layer is 10 nm or more and 760 nm or less. An electrophotographic photoreceptor characterized by this.

2. The electrophotographic photoreceptor according to claim 1, wherein the maximum height roughness Rz of the surface layer is 40 nm or more and 760 nm or less.

3. The electrophotographic photoreceptor according to claim 1, wherein the average length Rs m of the roughness curve elements of the surface layer is 20 nm or more and 1400 nm or less.

4. The electrophotographic photoreceptor according to claim 1, wherein the arithmetic mean roughness Ra of the surface layer is 10 nm or more and 500 nm or less.

5. The electrophotographic photoreceptor according to claim 1, wherein the coefficient of kinetic friction of the surface layer is 0.95 or less in an environment of 25 °C and 50% RH.

6. The electrophotographic photoreceptor according to claim 1, wherein the inorganic particles contained in the surface layer have a functional group having reactivity with an isocyanate group.

7. The electrophotographic photoreceptor according to claim 1, wherein the arithmetic average film thickness of the surface layer is 2.0 μm or less.

8. The electrophotographic photoreceptor according to claim 1, wherein the Mohs hardness of the inorganic particles contained in the surface layer is 4.0 or more.

9. The electrophotographic photoreceptor according to claim 1, wherein the inorganic particles contained in the surface layer are silica particles or metal oxide particles.

10. The electrophotographic photoreceptor according to claim 1, wherein the urethane resin contained in the surface layer has a nurate structure.

11. The electrophotographic photoreceptor according to claim 1, wherein the urethane resin contained in the surface layer is a polymer of an isocyanate compound and a polyol compound having 3 or more polymerizable functional groups.

12. The electrophotographic photoreceptor according to claim 1, wherein the urethane resin contained in the surface layer is a polymer of an isocyanate compound having a nurate structure and a polyol compound.

13. The urethane resin contained in the surface layer is a polymer of an isocyanate compound and a polyol compound having an average molecular weight of 2.0×10 ３ or less, and the electrophotographic photoreceptor according to claim 1.

14. The electrophotographic photoreceptor according to claim 8, wherein the metal oxide particles contained in the surface layer are titanium oxide doped with niobium atoms.

15. A process cartridge that integrally supports the electrophotographic photoreceptor according to any one of claims 1 to 14 and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachable from the main body of the electrophotographic apparatus.

16. An electrophotographic apparatus having the electrophotographic photoreceptor according to any one of claims 1 to 14, and a charging means, an exposure means, a developing means, and a transfer means.

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