Electrophotographic photoreceptor, process cartridge, and electrophotographic apparatus

Abstract

To provide an electrophotographic photoreceptor which can reduce a frictional force with a cleaning blade, exhibits high cleaning performance and is excellent in transferability in use under the high-temperature and high-humidity environment.SOLUTION: Disclosed is an electrophotographic photoreceptor which includes: a support; a photosensitive layer; and a surface layer in this order. The outer surface of the electrophotographic photoreceptor exhibits a wrinkle shape due to its uneven shape. A surface layer contains a binder resin and inorganic particles. At least some of the inorganic particles is exposed in a concave part of the uneven shape.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 having the electrophotographic photoreceptor. [Background technology]

[0002] Organic electrophotographic photoreceptors containing organic photoconductive materials (charge-generating materials) (hereinafter also simply referred to as "electrophotographic photoreceptors" or "photoreceptors") are used as electrophotographic photoreceptors mounted in process cartridges and electrophotographic devices. In recent years, there has been a demand for electrophotographic devices with longer lifespans, and there is a need for electrophotographic photoreceptors with improved image quality and wear resistance (mechanical durability).

[0003] Furthermore, in recent years, electrophotographic devices have been required to improve image quality and reduce waste toner by streamlining the transfer process, in addition to addressing the need for longer lifespan as mentioned above. This is achieved by suppressing toner splatter during transfer.

[0004] As a method to improve the wear resistance of electrophotographic photoreceptors, a technique has been proposed in which a radically polymerizable resin is used for the surface layer of the photoreceptor, and the surface layer of the photoreceptor is cured to increase the mechanical strength of the surface layer.

[0005] Electrophotographic photoreceptors are generally used in electrophotographic image formation processes, which consist of charging, exposure, development, transfer, and cleaning steps. Among these steps, the cleaning step, which removes any remaining toner from the electrophotographic photoreceptor after the transfer step, is a crucial step for obtaining a clear image. A common cleaning method in the cleaning step involves pressing a rubber-like cleaning blade against the electrophotographic photoreceptor to scrape off the toner.

[0006] However, with the above cleaning method, the frictional force between the cleaning blade and the electrophotographic photoreceptor is large, causing the cleaning blade to vibrate, which easily leads to image defects due to inadequate cleaning. This problem in the cleaning process becomes more pronounced as the mechanical strength of the surface layer of the electrophotographic photoreceptor increases, that is, as the peripheral surface of the electrophotographic photoreceptor becomes less prone to wear. In other words, this problem is more likely to occur when the surface layer of the electrophotographic photoreceptor is made into a hardened layer, thereby increasing the mechanical strength of the surface layer, as described above.

[0007] Furthermore, the surface layer of an organic electrophotographic photoreceptor is generally formed by immersion coating, and the surface of the surface layer formed by immersion coating (i.e., the outer surface of the electrophotographic photoreceptor) becomes very smooth. Therefore, the contact area between the cleaning blade and the peripheral surface of the electrophotographic photoreceptor increases, the frictional resistance between the cleaning blade and the peripheral surface of the electrophotographic photoreceptor increases, and the above-mentioned problem becomes more pronounced.

[0008] As a way to overcome the aforementioned problems, a method has been proposed to improve cleaning performance by reducing frictional force and providing an uneven surface on the outer surface of the photoreceptor, thereby reducing the contact area between the outer surface of the electrophotographic photoreceptor and the cleaning blade.

[0009] Patent Document 1 describes a technique for incorporating metal oxide fine particles into the surface layer. It is believed that by including metal oxide fine particles in the surface layer, some of the metal oxide fine particles are exposed on the outer surface of the electrophotographic photoreceptor, forming an uneven surface, which reduces the frictional force between the cleaning blade and the photoreceptor.

[0010] Furthermore, Patent Document 2 describes a technology for a photoreceptor having a groove shape along the circumferential direction on the outer surface of the photoreceptor. In the technology disclosed in Patent Document 2, the contact area between the cleaning blade and the photoreceptor is reduced by providing a groove shape along the circumferential direction on the outer surface of the photoreceptor, thereby reducing frictional force. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2018-128515 [Patent Document 2] Japanese Patent Publication No. 2010-250355 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] In the technology disclosed in Patent Document 1, the reduction of frictional force between the cleaning blade and the photoreceptor was insufficient, and the torque may become excessive when used in low-temperature, low-humidity environments.

[0013] Furthermore, in the technology disclosed in Patent Document 2, cleaning defects sometimes occurred where the toner partially slipped through the groove-shaped areas in low-temperature, low-humidity environments. Moreover, there was room for improvement in the transfer performance of the technology disclosed in Patent Document 2.

[0014] This invention has been made in view of the above-mentioned problems. That is, the object of this invention is to provide a photoreceptor that can reduce frictional force with the cleaning blade when used in low-temperature, low-humidity environments, exhibits high cleaning performance, and has excellent transfer properties. [Means for solving the problem]

[0015] The above objective is achieved by the present invention as follows: That is, the electrophotographic photoreceptor according to the present invention is An electrophotographic photoreceptor having a support, a photosensitive layer, and a surface layer in this order, The outer surface of the electrophotographic photoreceptor has an uneven shape, which gives it a wrinkled appearance. The wrinkled shape is formed by the random and isotropic arrangement of the ridges of the convex parts of the uneven shape. When a square observation area with sides of 200 μm is placed at any position on the outer surface, and a line passing through the center point of the observation area and parallel to the circumferential direction of the electrophotographic photoreceptor is defined as reference line L1, and the 1799 reference lines obtained by rotating reference line L1 at 0.1° intervals around the center point are defined as reference lines L2 to L1800, Each of the reference lines L1 to L1800 intersects with the ridge lines of the concavo-convex shape at a plurality of positions, Applicable and at least two positions selected from the plurality of positions, the intersection angles between each of the reference lines L1 to L1800 and the ridge line have different values from each other. When frequency analysis is performed on the height information of the concavo-convex shape in the observation region and a two-dimensional power spectrum F(r, θ) is obtained with the frequency component as r and the angular component as θ, the one-dimensional radial distribution function p(r) obtained by integrating the two-dimensional power spectrum F(r, θ) in the θ direction has at least one maximum value. Regarding the frequency rp when the one-dimensional radial distribution function p(r) takes the maximum value, when the angular distribution q(θ) is calculated from the two-dimensional power spectrum F(r, θ), the variation in power values in the entire θ range is 15% or less. The surface layer contains a binder resin and inorganic particles, and at least some of the inorganic particles are exposed in the concave portions of the concavo-convex shape. This is the gist.

Advantages of the Invention

[0016] According to the present invention, in use in a low-temperature and low-humidity environment, it is possible to reduce the frictional force with a cleaning blade, exhibit high cleaning performance, and provide an electrophotographic photoreceptor excellent in transferability.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing an example of the concavo-convex shape on the outer surface of the electrophotographic photoreceptor according to the present invention. (A) is a top view of the outer surface of the electrophotographic photoreceptor, and (B) is a graph showing the height information of the concavo-convex shape obtained from the surface observation of the outer surface of the electrophotographic photoreceptor. [Figure 2] ​This figure shows an example of the results obtained by numerical analysis of the electrophotographic photoreceptor according to the present invention. (A) is a figure showing the two-dimensional power spectrum F(r,θ) obtained by frequency analysis of wrinkles on the outer surface of the electrophotographic photoreceptor. (B) is a figure showing the one-dimensional radial distribution function obtained by integrating the two-dimensional power spectrum F(r,θ) in the θ direction. (C) is a figure showing the variation in power values ​​over the entire θ range when the angular distribution q(θ) is calculated from the two-dimensional power spectrum F(r,θ) for the frequency rp at which the one-dimensional radial distribution function p(r) takes its maximum value. [Figure 3] This is a schematic diagram showing a cross-section of the outer surface of an electrophotographic photoreceptor. [Figure 4] This is a schematic diagram showing the exposure of inorganic particles in recesses observed when viewing the outer surface of an electrophotographic photoreceptor from above. [Figure 5] This diagram shows a schematic configuration of an electrophotographic apparatus having a process cartridge equipped with an electrophotographic photoreceptor. [Figure 6] This figure shows the polishing machine used to polish the outer surface of the electrophotographic photoreceptor in the comparative example. [Modes for carrying out the invention]

[0018] The present invention will be described in detail below with reference to preferred embodiments. In the technology described in Patent Document 1, the contact area between the photoreceptor and the cleaning blade cannot be sufficiently reduced, and therefore, it is thought that the reduction of frictional force may not be sufficient when used in low-temperature, low-humidity environments.

[0019] Furthermore, in low-temperature and low-humidity environments, toner and photoreceptor tend to become charged, and the electrostatic adhesion between the toner and photoreceptor tends to increase. In the technology described in Patent Document 2, the direction in which the groove shape extends is parallel to the rotation direction of the photoreceptor. Therefore, as a result of the inventors' investigation, it was found that, especially in low-temperature and low-humidity environments, residual toner on the outer surface of the photoreceptor may slip through the groove shape and pass through the contact area with the cleaning blade, causing streaky image defects. In particular, in recent years, due to the increasing demand for high-definition and high-quality images, small-particle-diameter spherical toner has become mainstream. Small-particle-diameter spherical toner has a strong adhesion force to the outer surface of the photoreceptor, and toner removal by the cleaning blade tends to be insufficient. Therefore, when using small-particle-diameter spherical toner, it is thought that streaky image defects are more likely to occur in the technology described in Patent Document 2.

[0020] Furthermore, in low-temperature, low-humidity environments, as mentioned earlier, the adhesion between the toner and the photoreceptor tends to increase, resulting in a larger amount of residual toner on the outer surface of the photoreceptor after the transfer process. To improve transferability, it is necessary to reduce the adhesion between the toner and the electrophotographic photoreceptor, and reducing the contact area between the toner and the surface of the photoreceptor is effective. Therefore, one possible method is to reduce the contact area between the toner and the surface of the photoreceptor by making the outer surface of the photoreceptor have an uneven shape. However, the uneven shape described in Patent Document 2 was not sufficient to improve transferability.

[0021] As a result of diligent research, the inventors have found that the above problem can be solved by providing the outer surface of the photoreceptor with a predetermined uneven shape described below, and further exposing inorganic particles in the recesses of the uneven shape.

[0022] Specifically, the electrophotographic photoreceptor according to the present invention is An electrophotographic photoreceptor having a support, a photosensitive layer, and a surface layer in this order, The outer surface of the electrophotographic photoreceptor has an uneven shape, which gives it a wrinkled appearance. The wrinkled shape is formed by the random and isotropic arrangement of the ridges of the convex parts of the uneven shape. When a square observation area with sides of 200 μm is placed at any position on the outer surface, and a line passing through the center point of the observation area and parallel to the circumferential direction of the electrophotographic photoreceptor is defined as reference line L1, and the 1799 reference lines obtained by rotating reference line L1 at 0.1° intervals around the center point are defined as reference lines L2 to L1800, Each of the reference lines L1 to L1800 has the uneven shape Applicable It intersects with the ridge of the convex part in multiple places, At least two locations selected from the multiple locations, the intersection angles between each of the reference lines L1 to L1800 and the ridge line are different values. In the observed region, when the height information of the uneven shape is analyzed by frequency analysis to obtain a two-dimensional power spectrum F(r, θ) with frequency component r and angular component θ, the one-dimensional radial distribution function p(r) obtained by integrating the two-dimensional power spectrum F(r, θ) in the θ direction has at least one local maximum. When the angular distribution q(θ) is calculated from the two-dimensional power spectrum F(r, θ) for the frequency rp at which the one-dimensional radial distribution function p(r) takes its maximum value, the variation in power values ​​over the entire θ range is 15% or less. The surface layer contains a binder resin and inorganic particles, At least some of the inorganic particles are exposed in the recesses of the uneven shape.

[0023] The present inventors have not yet clearly defined the mechanism by which the electrophotographic photoreceptor according to the present invention solves the problems in the prior art described above, but they speculate as follows.

[0024] First, the outer surface of the electrophotographic photoreceptor has a predetermined number of protrusions within a certain range, which sufficiently reduces the contact area when the cleaning blade contacts the electrophotographic photoreceptor. This is presumed to sufficiently reduce the frictional force between the cleaning blade and the electrophotographic photoreceptor, even in low-temperature and low-humidity environments. Furthermore, the outer surface of the electrophotographic photoreceptor has an uneven shape, which creates a wrinkled appearance, and the edges of the protrusions of this uneven shape face in various directions. This is presumed to suppress toner leakage through the recesses of the uneven shape when the electrophotographic photoreceptor rotates. As a result, it is believed that a high degree of both frictional force reduction and toner leakage suppression can be achieved.

[0025] Next, we will explain why the electrophotographic photoreceptor according to the present invention has excellent transferability. According to our investigations, when the outer surface of the electrophotographic photoreceptor has only the above-mentioned uneven shape, and inorganic particles are not exposed in the recesses of the uneven shape, the effect of improving transferability is limited. This is thought to be because the toner is pressed into the recesses of the uneven shape, and the adhesion between the toner and the surface of the photoreceptor is increased. As a result of further investigations by our inventors, we found that excellent transferability can be obtained by incorporating inorganic particles into the surface layer of the electrophotographic photoreceptor and exposing the inorganic particles in the recesses of the uneven shape. This is presumed to be because the inorganic particles exposed in the recesses of the uneven shape make point contact with the toner, increasing the distance between the toner and the surface of the photoreceptor and creating a gap, thereby reducing the adhesion between the toner and the surface of the photoreceptor.

[0026] The following describes in more detail the uneven surface shape of the electrophotographic photoreceptor according to the present invention, and the inorganic particles contained in the surface layer of the electrophotographic photoreceptor according to the present invention.

[0027] The uneven surface of the electrophotographic photoreceptor according to the present invention has a certain level of fineness and has a predetermined number of protrusions within a certain range. Specifically, first, on the outer surface of the photoreceptor, an observation area with sides of 200 μm is placed with one side parallel to the circumferential direction of the photoreceptor, with the 76 intersection points of 19 line segments that divide the electrophotographic photoreceptor into 20 equal parts in the axial direction and 4 line segments that divide it into 4 equal parts in the circumferential direction as the center points. Next, in each observation area, a line passing through the center point of the observation area and parallel to the circumferential direction of the photoreceptor is defined as the reference line L1. Furthermore, 1799 reference lines obtained by rotating the reference line L1 by 0.1° around the center point are defined as reference lines L2 to L1800. At this time, the uneven surface of each observation area has a sufficient number of protrusions to intersect each of the reference lines L1 to L1800 at multiple points.

[0028] Furthermore, the uneven surface of the electrophotographic photoreceptor according to the present invention has a complex shape, with the edges of the protrusions facing in various directions. Specifically, for each of the reference lines L1 to L1800, at least two points selected from multiple points where they intersect with the protrusions of the uneven surface have different intersection angles. As a result, the outer surface of the electrophotographic photoreceptor according to the present invention exhibits a wrinkled appearance.

[0029] Figure 1 shows an example of the uneven surface shape of the outer surface of the electrophotographic photoreceptor according to the present invention. Figure 1(A) is a top view of the outer surface of the electrophotographic photoreceptor, and Figure 1(B) is a graph showing the height information of the uneven surface shape obtained from surface observation of the outer surface of the electrophotographic photoreceptor.

[0030] The uneven surface shape on the outer surface of the electrophotographic photoreceptor according to the present invention is a striped uneven surface shape observable on the outer surface of the electrophotographic photoreceptor, as shown in Figure 1(A). The stripe shape is not distributed in a single direction, but consists of curved parts, straight parts, interrupted parts, branched parts, etc., and multiple stripes exist within an observation area that is a square with sides of 200 μm.

[0031] Furthermore, the ridges of the convex parts of the uneven surface refer to the straight or curved lines obtained by connecting the highest points of the convex parts separating adjacent concave parts in a striped uneven surface, as shown in a in Figure 1(A), when observing the outer surface of an electrophotographic photoreceptor.

[0032] There are no particular limitations on the method for identifying protrusions and obtaining ridge lines by surface observation of the outer surface of an electrophotographic photoreceptor. For example, one method is to perform image analysis on height information obtained by measurement using a confocal laser microscope. Figure 1(B) shows an example in which the height information obtained by this method is plotted against a position on an arbitrary straight line placed on the outer surface of the electrophotographic photoreceptor. By identifying the vertex of the convex shape shown as b in Figure 1(B), a curved ridge line like the one shown as a in Figure 1(A) can be obtained.

[0033] Furthermore, in the present invention, the ridges of the convex parts of the uneven shape have multiple curvatures within those ridges. Curvature is a quantity that represents the degree of curvature of a curve, and the curvature χ is obtained as the reciprocal of the radius R of the circle when the vicinity of any point on the curve is approximated by a circle, as shown in formula (I).

number

[0035] As a result of the inventors' investigation, it was found that the effects of the present invention can be obtained to a high degree when the outer surface of the electrophotographic photoreceptor has an uneven shape, and when this uneven shape has a predetermined periodicity, as shown in Figure 1(A).

[0036] There are no particular limitations on the method for determining the periodicity of the uneven surface, but one example is to obtain height information from surface observation of the outer surface of an electrophotographic photoreceptor, and then analyze the obtained results using a two-dimensional Fourier transform.

[0037] Specifically, when height information for a surface with N1 × N2 data points is obtained, the height at any point (n,m) in the surface is h n,mTherefore, the two-dimensional power spectrum P(k,l) obtained by the discrete Fourier transform is given by the following equation (II).

number

[0038] Here f k,l It is given by the following formula (III).

number

[0039] Furthermore, the two-dimensional power spectrum P(k,l) obtained by equation (II) is transformed from the Cartesian coordinate system (k,l) to the polar coordinate system (r,θ) and expressed as the two-dimensional power spectrum F(r,θ). Here, r and θ satisfy the following equations (IV) and (V), respectively.

number

number

[0040] In this invention, height information obtained by measuring at regular intervals of 0.25 μm or less in two directions parallel to each side of a square observation area with sides of 200 μm is used for analysis.

[0041] Figure 2 shows an example of the results obtained by numerical analysis of the electrophotographic photoreceptor according to the present invention. Figure 2(A) shows the two-dimensional power spectrum F(r,θ) obtained by frequency analysis of the surface irregularities of the outer surface of the electrophotographic photoreceptor. Figure 2(B) shows the one-dimensional radial distribution function obtained by integrating the obtained two-dimensional power spectrum F(r,θ) in the θ direction. Figure 2(C) shows the variation in power values ​​over the entire θ range when the angular distribution q(θ) is calculated from the two-dimensional power spectrum F(r,θ) for the frequency rp at which the one-dimensional radial distribution function p(r) takes its maximum value.

[0042] As shown in Figure 2(B), the electrophotographic photoreceptor according to the present invention has at least one maximum value in the radial distribution function p(r) obtained by converting the two-dimensional power spectrum F(r,θ) into one dimension in the radial direction. This means that the multiple irregularities on the outer surface of the electrophotographic photoreceptor are distributed at regular intervals.

[0043] Furthermore, as shown in Figure 2(C), when calculating the angular distribution q(θ) of F(rp,θ) for the frequency rp at which the radial distribution function p(r) is maximum, it is preferable that the variation in power value is within 15%, as this helps suppress toner leakage. This indicates that when the variation in power value is small, the edges of the convex parts of the uneven shape point in various directions, making it isotropic.

[0044] The frequency rp at which the above radial distribution function p(r) takes its maximum value is 0.05 μm. -1 More than 0.17μm -1 The following is preferable because it suppresses toner leakage and improves transferability: Frequency rp is 0.05 μm -1 If the above is true, the contact area with the cleaning blade will be reduced, and a greater effect in reducing frictional force with the cleaning blade can be obtained. Frequency rp is 0.17 μm -1 Under the following conditions, point contact between the inorganic particles exposed in the recesses and the toner becomes more likely.

[0045] A depth of 1.0 μm or less is preferable, as it allows inorganic particles to make more point contact with the toner. More preferably, the depth of the uneven surface is between 0.1 μm and 1.0 μm. A depth of 0.1 μm or more provides a greater effect in reducing friction with the cleaning blade. The method for measuring the depth of the uneven surface will be described later.

[0046] As shown in Figure 3, the electrophotographic photoreceptor according to the present invention contains inorganic particles in its surface layer, and some of the total inorganic particles in the surface layer are inorganic particles d that are partially exposed in recesses c of the uneven surface formed on the outer surface of the electrophotographic photoreceptor. Inorganic particles have low elasticity, which is advantageous because it can reduce the contact area between the surface of the toner and the surface of the particles when in contact with the toner.

[0047] Examples of inorganic particles contained in the surface layer include magnesium oxide, zinc oxide, lead oxide, tin oxide, tantalum oxide, indium oxide, bismuth oxide, yttrium oxide, cobalt oxide, copper oxide, manganese oxide, selenium oxide, iron oxide, zirconium oxide, germanium oxide, tin oxide, titanium oxide, niobium oxide, molybdenum oxide, vanadium oxide, copper-aluminum oxide, antimony ion-doped tin oxide, hydrotalcite, and other particles. These particles can be used individually or in combination of two or more types. Furthermore, silica particles can be preferably used as the inorganic particles.

[0048] Any known silica particles can be used as the silica particles, and they may be either dry silica particles or wet silica particles. More preferably, the silica particles are wet silica particles obtained by the sol-gel method (hereinafter also referred to as "sol-gel silica").

[0049] Sol-gel silica may have a hydrophilic surface or a hydrophobic surface. Preferably, the sol-gel silica has a hydrophobic surface. Hydrophobic treatment of the silica particle surface is preferable because it makes it easier to disperse in the surface layer and expose to the surface of the surface layer.

[0050] Methods for hydrophobic treatment include the sol-gel method, in which the solvent is removed from the silica sol suspension, dried, and then treated with a hydrophobic agent; and the method in which the hydrophobic agent is directly added to the silica sol suspension and treated simultaneously with drying. From the viewpoint of controlling the full width at half maximum of the particle size distribution and the amount of saturated water adsorbed, the method of directly adding the hydrophobic agent to the silica sol suspension is preferred.

[0051] Examples of hydrophobic treatment agents include the following: Chlorosilanes such as methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, t-butyldimethylchlorosilane, and vinyltrichlorosilane; Tetramethoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, i Alkoxysilanes such as butyltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, and γ-(2-aminoethyl)aminopropyldimethoxysilane; Silazanes such as hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexahexyldisilazane, hexacyclohexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, and dimethyltetravinyldisilazane; Silicone oils such as dimethyl silicone oil, methyl hydrogen silicone oil, methylphenyl 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 oils; Siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexamethyldisiloxane, and octamethyltrisiloxane; Fatty acids and their metal salts include long-chain fatty acids such as undecylic acid, lauric acid, tridecylic acid, dodecylic acid, myristic acid, palmitic acid, pentadecylic acid, stearic acid, heptadecylic acid, arachidic acid, montanic acid, oleic acid, linoleic acid, and arachidonic acid, as well as salts of the above fatty acids with metals such as zinc, iron, magnesium, aluminum, calcium, sodium, and lithium.

[0052] Among these, alkoxysilanes, silazanes, and silicone oils are preferred because they facilitate hydrophobic treatment. These hydrophobic agents may be used individually or in combination of two or more.

[0053] The volume-average particle size of the inorganic particles is preferably between 50 nm and 550 nm. By using inorganic particles with this volume-average particle size, they can be easily partially exposed in the recesses of the uneven surface layer, and because of their high curvature, the contact area with the toner can be easily reduced.

[0054] When the outer surface of the electrophotographic photoreceptor according to the present invention is viewed from above at a predetermined magnification with a scanning electron microscope, inorganic particles d exposed in the recesses c of the uneven shape can be observed, as shown in Figure 4. Here, if S1 is the total area of ​​the exposed inorganic particles in the recesses, and S2 is the total area of ​​the parts of the recesses other than the parts where the inorganic particles are exposed, it is preferable that S1 / (S1+S2) (hereinafter also referred to as "coverage rate") is 0.20 or more and 0.80 or less.

[0055] If the coverage ratio is 0.20 or higher, the contact area between the toner and the parts of the outer surface of the photoreceptor where inorganic particles are not exposed can be reduced, thereby significantly improving the transferability of the photoreceptor by reducing the adhesion of the toner. If the proportion of inorganic particles exposed in the recesses is too high, the distance between the parts where the toner and inorganic particles come into contact becomes shorter, resulting in a larger contact area between the toner and the inorganic particles exposed on the outer surface of the photoreceptor. This increases the adhesion of the toner, limiting the effect of improving transferability. If the coverage ratio is 0.80 or lower, the distance between the parts where the toner and inorganic particles come into contact can be kept at an appropriate level, thereby significantly improving the transferability of the photoreceptor. It is more preferable that the coverage ratio is between 0.25 and 0.60.

[0056] The configuration of the electrophotographic photoreceptor according to the present invention will be described below. [Electrophotographic photoconductor] The electrophotographic photoreceptor according to the present invention has a support, a photosensitive layer, and a surface layer in that order. Furthermore, a conductive layer and an undercoat layer may be further present between the support and the photosensitive layer.

[0057] A method for manufacturing an electrophotographic photoreceptor according to the present invention involves preparing coating solutions for each layer, applying them to a support in the desired layer order, and drying them. Methods for applying the coating solutions include immersion coating, spray coating, inkjet coating, roll coating, die coating, blade coating, curtain coating, wire bar coating, and ring coating. Among these, immersion coating is preferred from the viewpoint of efficiency and productivity.

[0058] The support structure and each layer are described below. <Support> In the present invention, the electrophotographic photoreceptor has a support. The support is preferably a conductive support (conductive support). The shape of the support can be cylindrical, belt-shaped, sheet-shaped, etc. Among these, a cylindrical support is preferred. Furthermore, the surface of the support may be subjected to electrochemical treatment such as anodizing, blast treatment, cutting, etc.

[0059] Suitable materials for the support include metal, resin, and glass. Examples of metals include aluminum, iron, nickel, copper, gold, stainless steel, and alloys thereof. Among these, an aluminum support made of aluminum is preferred. Furthermore, conductivity may be imparted to resins and glass by processes such as mixing or coating them with conductive materials.

[0060] <Conductive layer> In this invention, a conductive layer may be provided on the support. By providing a conductive layer, scratches and irregularities on the surface of the support can be concealed, and the reflection of light on the surface of the support can be controlled. The conductive layer preferably contains conductive particles and a resin.

[0061] Examples of materials for conductive particles include metal oxides, metals, and carbon black. Examples of metal oxides include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, and bismuth oxide. Examples of metals include aluminum, nickel, iron, nichrome, copper, zinc, and silver. Among these, it is preferable to use metal oxides as conductive particles, and more preferably titanium oxide, tin oxide, and zinc oxide. When using metal oxides as 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 elements such as phosphorus or aluminum, or their oxides. Furthermore, the conductive particles may have a laminated structure comprising core material particles and a coating layer covering the particles. Examples of core material particles include titanium oxide, barium sulfate, and zinc oxide. Examples of the coating layer include metal oxides such as tin oxide. Furthermore, when using metal oxides as conductive particles, their volume-average particle size is preferably 1 nm to 500 nm, and more preferably 3 nm to 400 nm.

[0062] Examples of resins include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenolic resin, and alkyd resin. Furthermore, the conductive layer may further contain silicone oil, resin particles, a concealing agent such as titanium dioxide, etc.

[0063] The 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.

[0064] A conductive layer can be formed by preparing a coating solution for a conductive layer containing the above-mentioned materials and solvents, forming a coating film, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Methods for dispersing conductive particles in the coating solution for a conductive layer include using a paint shaker, sand mill, ball mill, or liquid impaction type high-speed disperser.

[0065] <Underlayer> In the present invention, an undercoat layer may be provided on the support or conductive layer. By providing an undercoat layer, the interlayer adhesion function is enhanced and a charge injection prevention function can be provided.

[0066] The undercoat layer preferably contains a resin. Alternatively, the undercoat layer may be formed as a cured film by polymerizing a composition containing a monomer having polymerizable functional groups. Examples of resins include polyester resin, polycarbonate resin, polyvinyl acetal resin, acrylic resin, epoxy resin, melamine resin, polyurethane resin, phenolic resin, polyvinylphenol resin, alkyd resin, polyvinyl alcohol resin, polyethylene oxide resin, polypropylene oxide resin, polyamide resin, polyamic acid resin, polyimide resin, polyamide-imide resin, and cellulose resin. Polymerizable functional groups found in monomers possessing polymerizable functional groups include isocyanate groups, blocked isocyanate groups, methylol groups, alkylated methylol groups, epoxy groups, metal alkoxide groups, hydroxyl groups, amino groups, carboxyl groups, thiol groups, carboxylic acid anhydride groups, and carbon-carbon double bond groups.

[0067] Furthermore, the undercoat layer may further contain electron transport materials, metal oxides, metals, conductive polymers, etc., for the purpose of improving electrical properties. Among these, electron transport materials and metal oxides are preferred. Examples of electron transport materials include quinone compounds, imide compounds, benzimidazole compounds, cyclopentadienylidene compounds, fluorenone compounds, xanthone compounds, benzophenone compounds, cyanovinyl compounds, aryl halides, silole compounds, and boron-containing compounds. An electron transport material having polymerizable functional groups may be used as the electron transport material, and a base layer may be formed as a cured film by copolymerizing it with the above-mentioned monomers having polymerizable functional groups. Examples of metal oxides include indium tin oxide, tin oxide, indium oxide, titanium oxide, zinc oxide, aluminum oxide, and silicon dioxide. Examples of metals include gold, silver, and aluminum. Furthermore, the underlayer may contain additional additives.

[0068] The 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.

[0069] The undercoat can be formed by preparing an undercoat coating solution containing the above-mentioned materials and solvents, forming a coating film, and then drying and / or curing it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, aromatic hydrocarbon-based solvents, and the like.

[0070] <Photosensitive layer> The photosensitive layer of an electrophotographic photoreceptor is mainly classified into (1) a multilayer photosensitive layer and (2) a single-layer photosensitive layer. (1) A multilayer photosensitive layer has a charge generating layer containing a charge generating material and a charge transport layer containing a charge transport material. (2) A single-layer photosensitive layer has a photosensitive layer containing both a charge generating material and a charge transport material. The electrophotographic photoreceptor according to the present invention preferably has a multilayer photosensitive layer.

[0071] (1) Stacked photosensitive layer The stacked photosensitive layer comprises a charge generation layer and a charge transport layer.

[0072] (1-1) Charge generation layer The charge generation layer preferably contains a charge generation material and a resin.

[0073] Examples of charge-generating materials include azo pigments, perylene pigments, polycyclic quinone pigments, indigo pigments, and phthalocyanine pigments. Among these, azo pigments and phthalocyanine pigments are preferred. Among phthalocyanine pigments, oxytitanium phthalocyanine pigments, chlorogallium phthalocyanine pigments, and hydroxygallium phthalocyanine pigments are preferred. The content of the charge generating material in the charge generating layer is preferably 40% to 85% by mass, and more preferably 60% to 80% by mass, relative to the total mass of the charge generating layer.

[0074] Examples of resins include polyester resin, polycarbonate resin, polyvinyl acetal resin, polyvinyl butyral resin, acrylic resin, silicone resin, epoxy resin, melamine resin, polyurethane resin, phenolic resin, polyvinyl alcohol resin, cellulose resin, polystyrene resin, polyvinyl acetate resin, and polyvinyl chloride resin. Among these, polyvinyl butyral resin is more preferred.

[0075] Furthermore, the charge generation layer may further contain additives such as antioxidants and ultraviolet absorbers. Specifically, examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, and the like.

[0076] The thickness of the charge generation layer is preferably 0.1 μm or more and 1 μm or less, and more preferably 0.15 μm or more and 0.4 μm or less.

[0077] The charge generation layer can be formed by preparing a coating solution for the charge generation layer containing the above-mentioned materials and solvents, forming a coating film, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0078] (1-2) Charge transport layer The charge transport layer preferably contains a charge transport material and a resin.

[0079] Examples of charge transport materials 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, and the compound represented by formula (1) is preferably used. [ka] (In formula (1), R 1 ~R10 (Each of these independently represents either a hydrogen atom or a methyl group.)

[0080] Examples of the structure shown by equation (1) are shown in equations (1-1) to (1-10). Among these, the structures shown by equations (1-1) to (1-6) are more preferred. [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka] [ka]

[0081] Thermoplastic resins are used as the resin, including polyester resin, polycarbonate resin, acrylic resin, and polystyrene resin. Among these, polycarbonate resin and polyester resin are preferred. Polyarylate resin is particularly preferred among polyester resins.

[0082] The content of the charge transport material in the charge transport layer is preferably 25% to 70% by mass, and more preferably 30% to 55% by mass, relative to the total mass of the charge transport layer.

[0083] The content ratio (mass ratio) of the charge transport material to the resin is preferably 4:10 to 20:10, and more preferably 5:10 to 12:10.

[0084] Furthermore, the charge transport layer may contain additives such as antioxidants, ultraviolet absorbers, plasticizers, leveling agents, lubrication agents, and wear resistance enhancers. Specifically, examples include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0085] The thickness of the charge transport layer is preferably 5 μm to 50 μm, more preferably 8 μm to 40 μm, and particularly preferably 10 μm to 30 μm.

[0086] (2) Single-layer photosensitive layer A 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, and drying it. The charge generating substance, charge transporting substance, and resin are the same as the examples of materials in "(1) Multilayer Photosensitive Layer" above.

[0087] <Protective layer> The electrophotographic photoreceptor according to the present invention has a protective layer as a surface layer on a photosensitive layer. The protective layer contains a binder resin and inorganic particles as described above. The protective layer is formed as a cured film by polymerizing a compound having polymerizable functional groups in a composition containing such a compound. Here, the binder resin contained in the protective layer includes polymers of compounds having polymerizable functional groups.

[0088] Examples of polymerizable functional groups found in monomers having polymerizable functional groups include acryloyloxy groups and methacryloyloxy groups.

[0089] As monomers having polymerizable functional groups, materials with charge transport ability may be used. Triarylamine structures are preferred as charge transport structures. Preferred polymerizable functional groups in charge transport materials include acryloyloxy groups and methacryloyloxy groups.

[0090] A monomer having polymerizable functional groups may have one or more polymerizable functional groups. In particular, polymerizing a composition containing both a compound having multiple polymerizable functional groups and a compound having one polymerizable functional group to form a cured film is especially preferable because it facilitates the release of strain caused by polymerization between multiple functional groups.

[0091] Examples of compounds having one polymerizable functional group are shown in (2-1) to (2-6). [ka] [ka] [ka] [ka] [ka] [ka]

[0092] Examples of compounds having the above-mentioned multiple polymerizable functional groups are shown in (3-1) to (3-7). [ka] [ka] [ka] [ka] [ka] [ka] [ka]

[0093] The protective layer preferably further contains conductive particles and / or charge transport material and a resin.

[0094] Examples of conductive particles include metal oxide particles such as titanium oxide, zinc oxide, tin oxide, and indium oxide.

[0095] Examples of charge transport materials 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.

[0096] Examples of resins include polyester resin, acrylic resin, phenoxy resin, polycarbonate resin, polystyrene resin, phenolic resin, melamine resin, and epoxy resin. Among these, polycarbonate resin, polyester resin, and acrylic resin are preferred.

[0097] The protective layer may further contain additives such as antioxidants, UV absorbers, plasticizers, leveling agents, lubrication agents, and wear resistance enhancers. Specifically, examples of additives include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, benzophenone compounds, siloxane-modified resins, silicone oils, fluororesin particles, polystyrene resin particles, polyethylene resin particles, silica particles, alumina particles, and boron nitride particles.

[0098] The thickness of the protective layer is preferably 0.2 μm to 5.0 μm in order to form a fine and uniform uneven surface. More preferably, the thickness of the protective layer is 0.2 μm to 4.0 μm, and even more preferably 0.2 μm to 3.0 μm.

[0099] The protective layer can be formed by preparing a protective coating solution containing the above-mentioned materials and solvents, forming this coating film, and then drying and / or curing it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, sulfoxide-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents.

[0100] <Method for forming an uneven surface on the outer surface of an electrophotographic photoreceptor> Methods for forming uneven surfaces on the outer surface of an electrophotographic photoreceptor include, for example, (1) a method of laminating and compressing films with different Young's moduli, and (2) a method of forming a structure by embossing. Method (1) requires a structure in which a relatively hard thin film is in close contact with the surface of a relatively soft object. In this structure, the surface layer buckles (bends) due to compressive stress in the surface direction. Method (2) involves pressing a mold made of metal or the like onto the outer surface of the photoreceptor to form a pattern, and is widely known as a surface shaping technique for photoreceptors. Other means such as laser ablation can also be used.

[0101] The method for forming the uneven shape described in (1) is explained below. In the case of a multilayer photosensitive layer, a protective layer is formed by polymerizing a crosslinkable monomer on a charge transport layer mainly composed of a thermoplastic resin, or in the case of a single-layer photosensitive layer, on a single-layer photosensitive layer mainly composed of a thermoplastic resin. Here, the composition containing a polymerizable functional group compound used to form the protective layer (coating liquid for the protective layer) contains inorganic particles. After the protective layer is formed, a heat treatment is applied to create an uneven surface.

[0102] The mechanism by which the uneven surface is formed is thought to be that during the heat treatment, the difference in the amount of deformation between the protective layer and the charge transport layer or single-layer photosensitive layer causes compressive stress in the surface direction, and the protective layer buckles, forming an uneven surface on the outer surface of the photoreceptor. Because the entire surface of the photoreceptor tries to buckle uniformly, as shown in the example in Figure 1, the ridges of the convex parts of the uneven surface are formed randomly and isotropically, and the outer surface of the electrophotographic photoreceptor exhibits a wrinkled appearance.

[0103] The heating temperature for forming the uneven surface is preferably higher than the boiling point of the residual solvent contained in the photosensitive layer. Furthermore, depending on the boiling point of the solvent used, a temperature of 140°C to 230°C is more preferable. When the heating temperature exceeds the boiling point of the residual solvent, the residual solvent in the photosensitive layer evaporates rapidly, and that area is more likely to become the starting point for buckling due to compressive stress, making it easier to form a fine and uniform uneven surface.

[0104] The photosensitive layer is formed by applying this photosensitive coating solution to form a photosensitive coating film, and then heating and drying the film. Examples of solvents for the photosensitive coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Specifically, examples include toluene, xylene (including at least one selected from the group consisting of o-xylene, m-xylene, and p-xylene), methyl benzoate, cyclohexanone, diethylene glycol monoethyl ether acetate, tetrahydrofuran, and dimethoxymethane. It is preferable to combine a solvent with a boiling point of 140°C or higher with a solvent with a boiling point of 140°C or lower, as this makes it easier to leave an appropriate amount of solvent in the photosensitive layer before heating to form the uneven surface. Known methods can be used to measure the amount of residual solvent, such as gas chromatography.

[0105] The protective coating solution contains a compound having a chain-polymerizable functional group. The protective layer is formed as a cured film by applying this protective coating solution onto the photosensitive layer and polymerizing a compound having a chain-polymerizable functional group.

[0106] Polymerization reactions for compositions containing monomers having polymerizable functional groups include methods using heat, light (ultraviolet light, etc.), or radiation (electron beams, etc.). Among these, radiation is preferred, and electron beams are more preferred. Electron beam irradiation is preferably carried out in a low-oxygen atmosphere to prevent deactivation of the polymerizable functional groups through radicalization. Furthermore, a certain level of high temperature is necessary to ensure sufficient polymerization in a short time and to form a cured film. Heating is preferably carried out in a low-oxygen atmosphere to prevent deactivation of radicalization and to ensure rapid polymerization. The heating temperature should not exceed the boiling point of the residual solvent in the photosensitive layer; specifically, 90°C to 130°C is preferred.

[0107] [Process cartridges, electrophotographic equipment] The process cartridge according to the present invention is characterized in that it integrally supports the electrophotographic photoreceptor described above and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably attached to the main body of an electrophotographic apparatus.

[0108] Furthermore, the electrophotographic apparatus according to the present invention is characterized by having the electrophotographic photoreceptor described above, as well as a charging means, an exposure means, a developing means, and a transfer means.

[0109] Figure 5 shows an example of a schematic configuration of an electrophotographic apparatus having a process cartridge equipped with an electrophotographic photoreceptor according to the present invention.

[0110] The cylindrical electrophotographic photoreceptor 1 is rotated at a predetermined peripheral speed in the direction of the arrow around the axis 2. The surface of the electrophotographic photoreceptor 1 is charged to a predetermined positive or negative potential by the charging means 3. Although Figure 5 shows a roller charging method using a roller-type charging member, other charging methods such as corona charging, proximity charging, and injection charging may be employed. Exposure light 4 is irradiated onto the surface of the charged electrophotographic photoreceptor 1 from an exposure means (not shown), and an electrostatic latent image corresponding to the desired image information is formed. The electrostatic latent image formed on the surface of the electrophotographic photoreceptor 1 is developed with toner contained in the developing means 5, and a toner image is formed on the surface of the electrophotographic photoreceptor 1. The toner image formed on the surface of the electrophotographic photoreceptor 1 is transferred to a transfer material 7 by the transfer means 6. The transfer material 7 with the transferred toner image is transported to a fixing means 8, undergoes toner image fixing treatment, and is printed out outside the electrophotographic device. The electrophotographic device may also have a cleaning means 9 for removing toner and other deposits remaining on the surface of the electrophotographic photoreceptor 1 after transfer. Alternatively, a so-called cleanerless system may be used in which the above-mentioned adhering substances are removed by the developing means 5, etc., without providing a separate cleaning means 9. The electrophotographic apparatus may also have a static elimination mechanism that removes static electricity from the surface of the electrophotographic photoreceptor 1 with pre-exposure light 10 from a pre-exposure means (not shown). In addition, guide means 12 such as rails may be provided for attaching and detaching the process cartridge 11 to the electrophotographic apparatus body.

[0111] The electrophotographic photoreceptor according to the present invention can be used in laser beam printers, LED printers, copiers, facsimile machines, and multifunction devices thereof.

[0112] [Evaluation methods for uneven surfaces and inorganic particles] The following describes the evaluation method for the uneven surface shape of the outer surface of the electrophotographic photoreceptor according to the present invention, and the inorganic particles contained in the surface layer.

[0113] <Method for evaluating the surface irregularities of a photoreceptor, and method for measuring the depth of these irregularities> The outer surface of the electrophotographic photoreceptor is magnified and observed using a laser microscope (VK-X200, manufactured by Keyence Corporation) to obtain height information about the uneven surface. The observation area is a square observation area with sides of 200 μm, centered at 76 intersection points of 19 line segments that divide the electrophotographic photoreceptor into 20 equal parts axially and 4 line segments that divide it into 4 equal parts circumferentially. The sides of the observation area are oriented so that they are parallel to the circumferential direction of the electrophotographic photoreceptor. The height information is corrected for surface tilt to correct the cylindrical shape of the photoreceptor to a planar shape.

[0114] Next, a reference line L1 is established in the image containing the uneven shape obtained by observation, passing through the center point of the observation area and parallel to the circumferential direction of the electrophotographic photoreceptor. Furthermore, reference lines L1 to L1800 are established by rotating the reference line L1 in 0.1° increments around the center point of the observation area.

[0115] Subsequently, for each of the reference lines L1 to L1800, it is confirmed that they intersect with the edges of the convex parts of the uneven shape at multiple points, and that the intersection angles between each of the reference lines L1 to L1800 and the edges at at least two points selected from these multiple intersection points are different values.

[0116] The depth of the uneven surface is measured by analyzing the line roughness (JIS B 0601-2001) at the reference line L1 established in the observation area from the height information to determine the maximum valley depth Rv. The arithmetic mean of the Rv values ​​obtained at each of the 76 observation areas is taken as the depth of the uneven surface.

[0117] <Method for measuring the frequency rp and power value variations of the surface irregularities on the outer surface of a photoreceptor> The height information of the uneven shape obtained above is subjected to frequency analysis to obtain a two-dimensional power spectrum F(r,θ). Next, the radial distribution function p(r) is calculated by converting the two-dimensional power spectrum F(r,θ) into a one-dimensional function in the radial direction, and the frequency rp at which p(r) is maximized is found. Furthermore, for the frequency rp at which p(r) is maximized, we determine the angular distribution q(θ) of F(rp,θ) and calculate the variation in power values ​​over the entire θ range.

[0118] <Method for measuring the volume-average particle size of inorganic particles> The volume-average particle size is measured using a Zetasizer Nano-ZS (MALVERN). This instrument can measure particle size using dynamic light scattering. First, the inorganic particles to be measured are diluted and prepared so that the solid-liquid ratio is 0.10 mass% (±0.02 mass%), collected in a quartz cell, and placed in the measurement section. Water or a methyl ethyl ketone / methanol mixed solvent is used as the dispersion medium. As measurement conditions, the refractive index of the inorganic particles, the refractive index of the dispersion solvent, viscosity, and temperature are input into the control software Zetasizersoftware 6.30 and the measurement is performed. Dn is adopted as the number-average particle size. The refractive index of inorganic particles is taken from "Refractive Index of Solids" on page 517 of Volume II of the Chemical Handbook, Basic Edition, 4th Revised Edition (edited by the Chemical Society of Japan, Maruzen Co., Ltd.). The refractive index, viscosity, and temperature of the dispersion solvent are selected from the values ​​built into the control software. In the case of mixed solvents, the weight average of the dispersion media to be mixed is taken.

[0119] <Method for confirming the exposure state of inorganic particles in recesses of an uneven surface, and method for measuring coverage rate> From the height information of the 200 μm square observation area obtained above, the total height H, which is the height from the highest point to the lowest point of the uneven shape, is determined. As shown in Figure 3, the portion of the uneven shape that is less than half the total height H is defined as the recess c. The setting of the recess c of the uneven shape is set for each of the above observation areas.

[0120] When viewing the outer surface of an electrophotographic photoreceptor from above, it is determined whether inorganic particles are exposed in the recesses of the uneven surface. The coverage rate is calculated by taking S1 as the total area occupied by the exposed inorganic particles in the recesses of the uneven surface, and S2 as the total area of ​​the recesses other than those occupied by the exposed inorganic particles, and then calculating S1 / (S1+S2).

[0121] For the purpose of confirming the exposure state of inorganic particles and measuring the coverage rate, 10 points (10 in total) are selected from the 19 points in the same axis direction out of the 76 central points of the observation area mentioned above. A scanning electron microscope (SEM) ("S-4800", manufactured by JEOL Ltd.) is used to observe a 15 μm square area with each of the 10 points as the center, with one side parallel to the circumferential direction of the electrophotographic photoreceptor.

[0122] Next, a photographic image of the photoreceptor taken using a scanning electron microscope is scanned. Image analysis is performed using image processing software (ImageJ (available from https: / / imagej.nih.gov / ij / )) and the particles in the photographic image are binarized. The recesses of the uneven surface are identified in advance using a laser microscope. The coverage rate S1 / (S1+S2) is calculated by taking S1 as the total area of ​​the parts where particles are exposed in the recesses of the uneven surface and S2 as the total area of ​​the parts where particles are not exposed. The coverage rate is calculated in the same way for a total of 10 locations, and the arithmetic mean of the obtained coverage rates is taken as the particle coverage rate in the recesses of the uneven surface on the outer surface of the photoreceptor. [Examples]

[0123] The present invention will be described in more detail below using examples and comparative examples. The present invention is not limited in any way by the following examples, unless it exceeds the gist of the invention. In the following descriptions of examples, "parts" refers to mass unless otherwise specified. The film thickness of each layer of the electrophotographic photoreceptor in the examples and comparative examples was determined using an eddy current film thickness gauge (Fischerscope, manufactured by Fischer Instruments) or by specific gravity conversion from the mass per unit area.

[0124] (particle) Table 1 shows the particles 1 to 7 used to form the protective layer (surface layer) in the examples and comparative examples. Particles 1 to 6 are silica particles (inorganic particles), and particle 7 is a silicone resin particle. In addition, particles 4 to 6 have a hydrophobic surface treatment.

[0125] [Table 1]

[0126] (Preparation of surface-treated particles 1) The following materials were prepared. 10 parts methanol • Five copies of particle 1 (listed in Table 1) These were mixed and dispersed at room temperature for 30 minutes using a US homogenizer. Next, 0.25 parts by mass of n-propyltrimethoxysilane (KBM-3033, manufactured by Shin-Etsu Chemical Co., Ltd.), a reactive surface treatment agent, and 10 parts by mass of toluene were added, and the mixture was stirred at room temperature for 60 minutes. After removing the solvent with an evaporator, surface-treated particles 1, which had been surface-treated with the reactive surface treatment agent, were prepared by heating at 140°C for 60 minutes.

[0127] (Preparation of surface-treated particles 2) Surface-treated particles 2 were prepared in the same manner as surface-treated particles 1, except that particle 1 was replaced with particle 2.

[0128] (Preparation of surface-treated particles 3) In the preparation of surface-treated particle 1, surface-treated particle 3 was prepared in the same manner as surface-treated particle 1, except that particle 1 was changed to particle 3.

[0129] <Fabrication of electrophotographic photoreceptors> [Example 1] An aluminum cylinder (JIS-A3003, aluminum alloy) with a diameter of 24 mm and a length of 257.5 mm was used as the support (conductive support).

[0130] Next, I prepared the following materials. 214 parts of titanium oxide (TiO2) particles (average primary particle size 230 nm) coated with oxygen-deficient tin oxide (SnO2) as a metal oxide particle. • Phenolic resin as a binding material (phenolic resin monomer / oligomer) (product name: Priofen J-325, manufactured by DIC Corporation, resin solids content: 60% by mass) 132 parts 98 parts of 1-methoxy-2-propanol as a solvent These materials were placed in a sand mill using 450 glass beads with a diameter of 0.8 mm, and dispersed under the following conditions: rotation speed: 2000 rpm, dispersion processing time: 4.5 hours, and cooling water temperature set at 18°C ​​to obtain a dispersion. The glass beads were removed from this dispersion using a mesh (mesh opening: 150 μm). Silicone resin particles (product name: Tospearl 120, manufactured by Momentive Performance Materials Co., Ltd., average particle size 2 μm) were added to the obtained dispersion as a surface roughening agent. The amount of silicone resin particles added was set to 10% by mass relative to the total mass of metal oxide particles and binder material in the dispersion after the glass beads were removed. In addition, silicone oil (product name: SH28PA, manufactured by Toray Dow Corning Co., Ltd.) was added to the dispersion as a leveling agent at a concentration of 0.01% by mass relative to the total mass of metal oxide particles and binder material in the dispersion. Next, a mixed solvent of methanol and 1-methoxy-2-propanol (mass ratio 1:1) was added to the dispersion so that the total mass of metal oxide particles, binder, and surface roughening agent (i.e., the mass of solids) in the dispersion was 67% by mass relative to the mass of the dispersion. After that, the mixture was stirred to prepare a coating solution for the conductive layer. This coating solution for the conductive layer was applied to a support by immersion, and the support was heated at 140°C for 1 hour to form a conductive layer with a film thickness of 30 μm.

[0131] Next, I prepared the following materials. • 4 parts of electron transport material represented by the following formula E-1 • Blocked isocyanate (product name: Duranate SBN-70D, manufactured by Asahi Kasei Chemicals Corporation) 5.5 parts • Polyvinyl butyral resin (S-Rec KS-5Z, manufactured by Sekisui Chemical Co., Ltd.) 0.3 parts • Zinc(II) hexanoate (manufactured by Mitsuwa Chemical Co., Ltd.) as a catalyst: 0.05 parts These were dissolved in a mixed solvent of 50 parts tetrahydrofuran and 50 parts 1-methoxy-2-propanol to prepare a coating solution for the undercoat layer. This undercoat solution was applied to the conductive layer by immersion, and the mixture was heated at 170°C for 30 minutes to form an undercoat layer with a thickness of 0.7 μm. [ka]

[0132] Next, I prepared the following materials. 10 parts of crystalline hydroxygallium phthalocyanine having peaks at 7.5° and 28.4° in the chart obtained from CuKα characteristic X-ray diffraction. • Polyvinyl butyral resin (product name: S-Rec BX-1, manufactured by Sekisui Chemical Co., Ltd.) 5 parts These were added to 200 parts of cyclohexanone and dispersed for 6 hours using a sand mill apparatus with glass beads with a diameter of 0.9 mm. Further dilution was performed by adding 150 parts of cyclohexanone and 350 parts of ethyl acetate to obtain a coating solution for the charge generation layer. The obtained coating solution was applied to the undercoat layer by immersion and dried at 95°C for 10 minutes to form a charge generation layer with a film thickness of 0.20 μm.

[0133] The X-ray diffraction measurements were performed under the following conditions. [Powder X-ray diffraction measurement] Measurement equipment used: RINT-TTRII X-ray diffractometer, manufactured by Rigaku Electric Co., Ltd. X-ray tube:Cu Tube voltage: 50KV Tube current: 300mA Scanning method: 2θ / θ scan Scan speed: 4.0° / min Sampling interval: 0.02° Starting angle (2θ): 5.0° Stop angle (2θ): 40.0° Attachment: Standard sample holder Filter: Not used Incident Monochrome: Used Counter monometer: Not used Divergent slit: Open Divergence vertical limiting slit: 10.00 mm Scattering slit: Open Light-receiving slit: Open Planar monochromator: Used Counter: Scintillation counter

[0134] Next, I prepared the following materials. • 5 parts of the charge-transporting material (hole-transporting material) represented by the above formula (1-2) • 5 parts of the charge-transporting material (hole-transporting material) represented by the above formula (1-3) • Polycarbonate (product name: Yupiron Z400, manufactured by Mitsubishi Engineering Plastics Corporation) 10 pieces • 0.02 parts of polycarbonate resin having copolymer units consisting of the structure shown in formula (C-4) and the structure shown in formula (C-5) below (x / y=0.95 / 0.05: viscosity-average molecular weight=20000) These were dissolved in a mixed solvent of 60 parts toluene, 20 parts methyl benzoate, and 20 parts dimethoxymethane to prepare a coating solution for the charge transport layer. This coating solution for the charge transport layer was applied to the charge generating layer by immersion to form a coating film for the charge transport layer, and this coating film was dried at 120°C for 30 minutes to form a charge transport layer with a thickness of 16 μm. [ka] [ka]

[0135] Next, I prepared the following materials. ·436 parts of particles • 14 parts of the compound represented by the above formula (2-2) • 10 parts of the compound represented by the above formula (3-1) • 0.1 part of siloxane-modified acrylic compound (Cymac US270, manufactured by Toagosei Co., Ltd.) These were mixed with 58 parts cyclohexane and 25 parts 1-propanol and stirred. In this way, a protective coating solution was prepared.

[0136] The protective coating solution was immersed and applied onto the charge transport layer to form a protective coating film, and the resulting film was dried at 40°C for 5 minutes. Then, under a nitrogen atmosphere, the support (irradiated object) was rotated at a speed of 300 rpm while the electron beam was irradiated onto the coating film for 1.6 seconds under the conditions of an acceleration voltage of 70 kV and a beam current of 5.0 mA. The dose at the outermost layer was 15 kGy. Subsequently, under a nitrogen atmosphere, the temperature was raised from 25°C to 100°C over 20 seconds to perform the first heating, forming a cured film with a thickness of 1.5 μm. The oxygen concentration from electron beam irradiation to the subsequent first heating treatment was 10 ppm or less. Next, the coating film was allowed to cool naturally in air until its temperature reached 25°C, and then a second heating was performed in air at 160°C for 15 minutes to form a protective layer with an uneven surface and a wrinkled appearance. In this way, the electrophotographic photoreceptor according to Example 1 was fabricated.

[0137] The shape of the surface irregularities on the outer surface of the electrophotographic photoreceptor, the depth of the irregularities, the frequency rp, the power value variation, the presence or absence of exposed inorganic particles in the recesses of the irregularities, and the coverage rate of inorganic particles were measured using the method described above. The results are shown in Table 3.

[0138] Regarding the shape of the bumps and dips, we determined that cases meeting the following conditions were classified as A, and cases not meeting the following conditions were classified as B. Condition: For each of the reference lines L1 to L1800, the reference lines intersect with the edges of the convex parts of the concave shape at multiple points, and at least two of the points selected from these multiple intersections, the angles of intersection between each of the reference lines L1 to L1800 and the edges are different values.

[0139] Furthermore, for the frequency rp at which p(r) is maximized, the angular distribution q(θ) of F(rp,θ) was determined, and it was determined that if the variation in power values ​​over the entire θ range was 15% or less, it was classified as A, and if it was greater than 15%, it was classified as B. Furthermore, if exposed inorganic particles were present in the recesses of the uneven surface, it was determined as A, and if they were not present, it was determined as B.

[0140] [Examples 2-16] In forming the protective layer in Example 1, the type and amount of each compound used, the type and amount of particles, the film thickness, and the treatment conditions for the second heating were changed as shown in Table 2. Otherwise, electrophotographic photoreceptors according to Examples 2 to 16 were prepared in the same manner as in Example 1. The obtained electrophotographic photoreceptors were measured and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0141] [Table 2]

[0142] [Comparative Example 1] In the formation of the protective layer in Example 1, the film thickness and the treatment conditions for the second heating were changed as shown in Table 2. Otherwise, an electrophotographic photoreceptor according to Comparative Example 1, which does not have an uneven surface, was fabricated in the same manner as in Example 1. The obtained electrophotographic photoreceptor was measured and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0143] [Comparative Example 2] An electrophotographic photoreceptor without an uneven surface was fabricated in the same manner as in Comparative Example 1. The outer surface of this photoreceptor was polished using the polishing machine shown in Figure 6 under the following conditions. As a result, an electrophotographic photoreceptor according to Comparative Example 2 was fabricated, having multiple parallel grooves extending in the circumferential direction on the outer surface of the electrophotographic photoreceptor. Abrasive sheet feed speed: 400 mm / min Electrophotographic photoreceptor rotation speed: 240 rpm Abrasive grains: Silicon carbide Average particle size of abrasive grains: 3 μm Polishing time: 20 seconds The polishing method involved feeding a polishing sheet 1-1, which had a layer of abrasive particles dispersed in a binder resin on a sheet-like substrate, in the direction of the arrow, while rotating an electrophotographic photoreceptor 1-7 in the direction of the arrow and pressing it against the sheet for 20 seconds to roughen the surface. Here, 1-2 to 1-5 are guide rollers, 1-6 is a backup roller, 1-8 is a feed roller, and 1-9 is a wind-up roller. The resulting electrophotographic photoreceptor was measured and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0144] [Comparative Examples 3-5] In the formation of the protective layer in Example 1, the types and amounts of each compound used, the types and amounts of inorganic particles, the film thickness, and the treatment conditions for the second heating were changed as shown in Table 2. Otherwise, the electrophotographic photoreceptors for Comparative Examples 3 to 5 were prepared in the same manner as in Example 1. The obtained electrophotographic photoreceptors were measured and evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0145] [Table 3]

[0146] <Rating> The following evaluations were performed using the electrophotographic photoreceptors prepared in Examples 1-16 and Comparative Examples 1-5. [Torque Evaluation] A modified Hewlett-Packard laser beam printer, model number HP LaserJet Enterprise Color M553dn, was used as the electrophotographic device. The modifications included the ability to measure the drive current of the photoreceptor's rotation motor, as well as the ability to adjust and measure the voltage applied to the charging roller, the image exposure light intensity, and the voltage applied during the transfer process. The photoreceptor according to each example and comparative example was mounted in the cyan-colored cartridge of the image forming apparatus.

[0147] Subsequently, in an environment of low temperature and low humidity of 15°C and 10% RH, 100 image outputs were performed on A4-size plain paper using a test chart with a printing ratio of 5%. As the charging condition, the dark potential was -500 V, and as the exposure condition, the image exposure light amount was adjusted to 0.25 μJ / cm 2 2 . The drive current value (current value A) at the time of 100 outputs was read. The larger the obtained current value, the greater the frictional force between the electrophotographic photoreceptor and the cleaning blade.

[0148] Furthermore, an electrophotographic photoreceptor serving as a control for the torque relative value was produced as follows. In Example 1, except for Particle 4, the second heating step was set to a treatment at 100°C for 10 minutes, and an electrophotographic photoreceptor was produced in the same manner as in Example 1 except that no concavo-convex shape was formed. In this way, a control electrophotographic photoreceptor having no concavo-convex shape on the outer surface and not containing inorganic particles in the surface layer was produced. Using the produced control electrophotographic photoreceptor, the drive current value (current value B) of the rotation motor of the electrophotographic photoreceptor was measured in the same manner as in Example 1.

[0149] The ratio between the drive current value (current value A) of the rotation motor of the electrophotographic photoreceptor thus obtained and the drive current value (current value B) was calculated. The obtained numerical value of (current value A) / (current value B) was compared as the relative value of torque. The smaller the relative value, the more the frictional force between the electrophotographic photoreceptor and the cleaning blade is reduced. The results are shown in Table 4.

[0150] [Evaluation of Cleaning Property] In a low temperature and low humidity environment of 15°C and 10% RH, the retrofitted machine output 500 image outputs with a printing ratio of 5% on A4-size plain paper. As the charging condition, the dark potential was -500 V, and as the exposure condition, the image exposure light amount was adjusted to 0.25 μJ / cm 2 2 . Subsequently, 10 solid white images were continuously printed out, and evaluation was performed using the halftone image immediately after 10 solid black images were output. Specifically, the streaks in the halftone image caused by toner leakage due to poor cleaning were visually counted and evaluated according to the following criteria. A: There are no visible lines in the image quality, and the image quality is good. B: Very minor streaks may appear. C: Minor streaks may occur. D: Streaks appear in part of the image. E: Streaks appear across the entire image. The results are shown in Table 4.

[0151] [Evaluation of transcriptional properties] The modified machine was subjected to a low-temperature, low-humidity environment of 15°C and 10%RH, and 500 images were printed on A4-sized plain paper with a print ratio of 5%. The charging conditions were a dark area potential of -500V, and the exposure conditions were an image exposure light intensity of 0.25 μJ / cm². 2 The settings were adjusted accordingly. For evaluation, after printing 500 sheets, a solid black image was output, and the residual toner transfer on the outer surface of the photoreceptor during solid black image formation was taped off using transparent polyester adhesive tape. The density difference was calculated by subtracting the density of the paper with only the adhesive tape attached from the density of the paper with the peeled-off adhesive tape attached. Density measurements were taken at five locations, and the arithmetic mean was calculated. Then, the transferability was evaluated from this density difference value (referred to as the residual transfer density) according to the following criteria. The density was measured using an X-Rite color reflectance densitometer (X-rite 500 Series, manufactured by X-rite). (Evaluation Criteria) A: Transcription residue concentration is less than 0.2 B: Transcription residue concentration is 0.2 or higher but less than 0.5 C: Transcription residue concentration is 0.5 or higher but less than 1.0 D: Transcription residue concentration is 1.0 or higher The results are shown in Table 4.

[0152] [Table 4]

Claims

1. An electrophotographic photoreceptor having a support, a photosensitive layer, and a surface layer in this order, The outer surface of the electrophotographic photoreceptor has an uneven shape, which gives it a wrinkled appearance. The wrinkled shape is formed by the random and isotropic arrangement of the ridges of the convex parts of the uneven shape. When a square observation area with sides of 200 μm is placed at any position on the outer surface, and a line passing through the center point of the observation area and parallel to the circumferential direction of the electrophotographic photoreceptor is defined as reference line L1, and the 1799 reference lines obtained by rotating reference line L1 at 0.1° intervals around the center point are defined as reference lines L2 to L1800, Each of the reference lines L1 to L1800 intersects with the ridges of the protrusions of the uneven shape at multiple points. At least two locations selected from the plurality of locations, the intersection angles between each of the reference lines L1 to L1800 and the ridge line are different values. In the observation region, when the height information of the uneven shape is analyzed by frequency analysis to obtain a two-dimensional power spectrum F(r, θ) with frequency component r and angular component θ, the one-dimensional radial distribution function p(r) obtained by integrating the two-dimensional power spectrum F(r, θ) in the θ direction has at least one local maximum. When the angular distribution q(θ) is calculated from the two-dimensional power spectrum F(r, θ) for the frequency rp at which the one-dimensional radial distribution function p(r) takes its maximum value, the variation in power values ​​over the entire θ range is 15% or less. The surface layer contains a binder resin and inorganic particles, At least some of the inorganic particles are exposed in the recesses of the uneven shape. An electrophotographic photoreceptor characterized by the following features.

2. The frequency rp is 0.05 μm －１ 0.17 μm or more －１ The following is the electrophotographic photoreceptor according to claim 1.

3. The electrophotographic photoreceptor according to claim 1 or 2, wherein the depth of the uneven shape is 1.0 μm or less.

4. The electrophotographic photoreceptor according to any one of claims 1 to 3, characterized in that the inorganic particles have a volume-average particle size of 50 nm or more and 550 nm or less.

5. The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein when the outer surface is viewed from above, S1 is the total area of ​​the exposed portion of the inorganic particles in the recess, and S2 is the total area of ​​the portion of the recess other than the portion in which the inorganic particles are exposed, and S1 / (S1+S2) is 0.20 or more and 0.80 or less.

6. The electrophotographic photoreceptor according to any one of claims 1 to 5, wherein the surface of the inorganic particles is hydrophobic.

7. A process cartridge characterized by integrally supporting an electrophotographic photoreceptor according to any one of claims 1 to 6 and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and being detachably attached to the body of an electrophotographic apparatus.

8. An electrophotographic apparatus characterized by comprising an electrophotographic photoreceptor according to any one of claims 1 to 6, and a charging means, an exposure means, a developing means, and a transfer means.

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