Electrophotographic photoreceptor, process cartridge, and electrophotographic apparatus

Abstract

To provide an electrophotographic photoreceptor that controls the distance between particles in a surface layer to reduce an adhesive force of toner, thereby improving transferability, and prevents separation of particles from the surface layer, thereby improving durability.SOLUTION: In an electrophotographic photoreceptor of the present invention, when projections derived from particles PAA and falling within a height range of 10 nm or more and 300 nm or less are defined as projections CA, the projections CA are arranged on a surface of a surface layer. In a top view of the surface layer, the average value of the distance between the gravity centers of the projections CA is 150 nm or more and 500 nm or less, and the standard deviation of the distance between the gravity centers of the projections CA is 250 nm or less. In a top view of the surface layer, when the area occupied by the particles on the surface of the surface layer is defined as S1, and the area occupied by materials other than the particles as S2, S1 / (S1+S2) is 0.70 or more and 1.00 or less.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] In recent years, there has been a demand for longer lifespan and higher image quality during repeated use of electrophotographic photoreceptors used in electrophotographic devices, which necessitates improved mechanical durability of the surface layer of the electrophotographic photoreceptor. Furthermore, electrophotographic devices involve a transfer process in which the latent image exposed to the electrophotographic photoreceptor is developed with toner, and a predetermined transfer bias is applied to the toner to transfer it from the electrophotographic photoreceptor to a transfer material such as paper via an intermediate transfer medium. In the transfer process, it is necessary to efficiently transfer the toner developed on the surface of the electrophotographic photoreceptor to the intermediate transfer medium or transfer material such as paper with virtually no residue remaining on the surface of the electrophotographic photoreceptor. Therefore, significantly reducing the adhesion of toner to the surface layer of the electrophotographic photoreceptor greatly contributes to reducing the amount of residual toner. In addition, reducing residual toner that is not transferred makes it possible to omit cleaning means in the process cartridge of the electrophotographic device, contributing to the miniaturization of the electrophotographic device.

[0003] Reducing the adhesion between the toner and the surface layer of the electrophotographic photoreceptor reduces the transfer bias applied during the transfer process, thus eliminating the need for a high-voltage power supply within the electrophotographic device. Furthermore, it suppresses toner scattering on the transfer material due to discharge caused by high transfer bias, enabling higher image quality. Two factors contribute significantly to the adhesion between the toner and the surface layer of the electrophotographic photoreceptor during the transfer process: non-electrostatic adhesion and electrostatic adhesion. Non-electrostatic adhesion can be reduced by giving the surface layer of the electrophotographic photoreceptor a shape, thereby reducing the contact area with the toner and minimizing point contact as much as possible. Additionally, by causing the toner to roll or rotate in the toner layer sandwiched between the surface layer of the electrophotographic photoreceptor and the transfer material, the mirroring force due to the toner's surface charge can be reduced, thereby reducing electrostatic adhesion. There are several methods for imparting shape to the surface layer of an electrophotographic photoreceptor, and one of them has been conventionally proposed to incorporate particles and a binder resin into the surface layer of the electrophotographic photoreceptor to form protrusions originating from the particles on the surface layer.

[0004] Patent Document 1 describes a technique for incorporating conductive titanium oxide particles into the protective layer of an electrophotographic photoreceptor in order to maintain cleanability and stable potential characteristics even under harsh environments. Patent Document 2 describes a technique for improving cleaning performance by controlling the convex shape of the toner surface and incorporating an inorganic filler in the outermost layer of the electrophotographic photoreceptor. Patent Document 3 describes a technique for increasing wear resistance and suppressing potential rise in the exposed area by placing conductive particles near insulating particles in the protective layer. Patent Document 4 describes a technique for incorporating tin oxide and silica particles treated with a special surface treatment agent into a protective layer in order to increase the surface hardness of the protective layer and improve its abrasion resistance and scratch resistance. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-229495 [Patent Document 2] Japanese Patent Publication No. 2020-071423 [Patent Document 3] Japanese Patent Publication No. 2013-195707 [Patent Document 4] Japanese Patent Publication No. 2014-002364 [Overview of the project] [Problems that the invention aims to solve]

[0006] However, our investigations have shown that in the electrophotographic photoreceptors described in Patent Documents 1 to 4, the contact area between the toner and the surface layer of the electrophotographic photoreceptor is reduced by protrusions originating from particles on the surface layer of the electrophotographic photoreceptor. However, it has been found that the close proximity of the particles makes it difficult to prevent them from detaching from the surface layer. Furthermore, it has been found that increased adhesion of the toner to the surface layer in durability tests of the electrophotographic photoreceptor leads to a deterioration in transferability. Therefore, the object of the present invention is to provide an electrophotographic photoreceptor that improves transferability by controlling the interparticle distance of the surface layer to reduce the adhesion force of the toner, while also improving durability by suppressing the detachment of particles from the surface layer. [Means for solving the problem]

[0007] The above objective is achieved by the present invention as follows: That is, the present invention provides an electrophotographic photoreceptor having a surface layer containing particles and a binder resin, The particles contained in the surface layer include particle A, the particle A is a silica particle, The particles contained in the surface layer 、 In the particle size distribution based on the number of particles, there are multiple peaks. Among the multiple peaks, the peak with the highest frequency of peak tops, where the peak top is 20 nm or greater, is designated as the first peak. 、 theAmong the peaks having a peak top of 20 nm or more among the plurality of peaks, a peak whose peak top frequency is the second highest after that of the first peak is defined as a second peak, when, among the first peak and the second peak, the peak having a larger peak top particle size value is defined as a peak PEA, a peak top particle size DA of the peak PEA is 、 within a range of 80 nm or more and 300 nm or less, among the particles contained in the surface layer, a particle having a particle size within a range of DA ± 20 nm is defined as a particle PAA, 、 the when a convex portion that is derived from the particle PAA and has a height within a range of 10 nm or more and 300 nm or less is defined as a convex portion CA, 、 the the convex portion CA is 、 disposed on the surface of the surface layer, when the surface layer is viewed from above 、 the an average value of inter-center-of-gravity distances of the convex portion CA is 、 150 nm or more and 500 nm or less, and 、 the a standard deviation of the inter-center-of-gravity distances of the convex portion CA is 250 nm or less, when the surface layer is viewed from above , when an area occupied by the particles on the surface of the surface layer is defined as S1 and an area occupied by components other than the particles is defined as S2, S1 / (S1+S2) is 、 0.70 or more and 1.00 or less , when, in a cross-section of the surface layer, T is defined as the average value of the film thickness of the surface layer at a portion not containing the particle PAA, said DA and said T satisfy the following formula (1): DA>T ···Formula (1) is , an electrophotographic photoreceptor characterized by [Figure 1] . The present invention also provides a process cartridge that integrally supports the above electrophotographic photoreceptor and at least one means selected from the group consisting of a charging means, a developing means, and a cleaning means, and is detachably attachable to an electrophotographic apparatus main body. Furthermore, the present invention relates to an electrophotographic apparatus characterized by having the above-mentioned electrophotographic photoreceptor, as well as a charging means, an exposure means, a developing means, and a transfer means. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an electrophotographic photoreceptor that improves transferability by controlling the interparticle distance of the surface layer to reduce the adhesion force of the toner, while also suppressing the detachment of particles from the surface layer and improving durability. [Brief explanation of the drawing]

[0009] [Figure 2] This is a conceptual diagram showing an example of the layer structure of an electrophotographic photoreceptor according to the present invention. [Figure 3] This is a conceptual diagram showing another example of the layer structure of the electrophotographic photoreceptor according to the present invention. [Figure 4] This is a conceptual diagram showing the surface layer of the electrophotographic photoreceptor according to the present invention as observed from above (surface observation). [Figure 5] This is a conceptual diagram illustrating a method for calculating the interparticle distance of particle PAA by observing the surface layer of an electrophotographic photoreceptor from above (surface observation) according to the present invention. [Figure 6] This is a conceptual diagram showing an example of a side view (cross-sectional observation) of the surface layer of an electrophotographic photoreceptor according to the present invention. [Figure 7] This is a conceptual diagram of another example of observing the surface layer of the electrophotographic photoreceptor according to the present invention from the side (cross-sectional observation). [Figure 8] This is an example of an SPM (scanning probe microscope) image of the surface layer of an electrophotographic photoreceptor according to the present invention. [Figure 9] This is an example of a STEM image of conductive particles according to the present invention. [Figure 10] This is a schematic diagram illustrating the STEM image in Figure 8. [Figure 11A] This figure shows an example of a schematic configuration of an electrophotographic apparatus having a process cartridge equipped with an electrophotographic photoreceptor and a charging means. [Figure 11B]This figure shows an example of the particle size distribution of particles contained in the surface layer of an electrophotographic photoreceptor according to the present invention. , Reference Example, This figure shows another example of the particle size distribution of particles contained in the surface layer of the electrophotographic photoreceptor according to the present invention. [Modes for carrying out the invention]

[0010] The present invention will be described in detail below with reference to preferred embodiments. [Electrophotographic photoconductor] The electrophotographic photoreceptor of the present invention is characterized by having a surface layer containing particles and a binder resin. Here, the surface layer refers to the outermost layer in an electrophotographic photoreceptor, and is the layer that comes into contact with the charged material and toner.

[0011] Figures 1 and 2 show an example of the layer structure of an electrophotographic photoreceptor. In Figures 1 and 2, 101 is the support, 102 is the undercoat layer, 103 is the charge generation layer, and 104 is the charge transport layer. 105 is the surface layer according to the present invention, 106 is the particle PAA according to the present invention, and 107 is a particle other than the particle PAA according to the present invention.

[0012] One method for manufacturing the electrophotographic photoreceptor of the present invention is to prepare coating solutions for each layer, as described later, apply them in the desired order, and then dry 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, ring coating, and dispensing. Among these, immersion coating is preferred from the viewpoint of efficiency and productivity. The following explains each layer.

[0013] <Surface layer> The inventors of the present invention have found that the electrophotographic photoreceptor of the present invention is An electrophotographic photoreceptor having a surface layer containing particles and a binder resin, The particles contained in the surface layer have multiple peaks in the particle size distribution based on the number of particles, Among the multiple peaks, the peak with the highest frequency of peak tops among those whose peak tops are 20 nm or greater is designated as the first peak, and among the multiple peaks with the second highest frequency of peak tops among those whose peak tops are 20 nm or greater is designated as the second peak. When the peak with the larger particle size value at the top of the first and second peaks is defined as peak PEA, The particle size DA at the peak top of the peak PEA is within the range of 80 nm to 300 nm. When the particles contained in the surface layer, particles with a particle size in the range of DA ± 20 nm are defined as particle PAA, and protrusions originating from the particle PAA and having a height in the range of 10 nm to 300 nm are defined as protrusions CA, the protrusions CA are arranged on the surface of the surface layer, When the surface layer is viewed from above, the average distance between the centroids of the protrusions CA is 150 nm or more and 500 nm or less, and the standard deviation of the distance between the centroids of the protrusions CA is 250 nm or less. When the surface layer is viewed from above, if S1 is the area occupied by the particles on the surface of the surface layer and S2 is the area occupied by other materials, then S1 / (S1+S2) must be between 0.70 and 1.00.

[0014] The reason why the effects of the present invention can be achieved under the above conditions is not clearly understood, but the inventors speculate as follows. On the other hand, in order to improve transferability in electrophotographic devices, it is necessary to reduce the adhesion force of the toner developed on the electrophotographic photoreceptor. The adhesion force between toner and electrophotographic photoreceptor can be broadly classified into electrostatic adhesion force and non-electrostatic adhesion force. Since non-electrostatic adhesion force is caused by van der Waals forces based on intermolecular forces between objects, imparting a shape to the surface layer of the electrophotographic photoreceptor reduces the contact area between the toner and the surface layer of the electrophotographic photoreceptor, and can greatly contribute to reducing the non-electrostatic adhesion force. Electrostatic adhesion force is mainly influenced by the amount of charge of the toner, and is therefore greatly affected by the amount of charge of the toner. The magnitude of the reflection force is proportional to the amount of charge of the toner and inversely proportional to the square of the distance between the amount of charge of the toner and the surface of the electrophotographic photoreceptor to which it is attached. Therefore, by appropriately setting the height of the protrusions originating from the particles on the surface of the electrophotographic photoreceptor, the distance between the electrophotographic photoreceptor and the toner can be increased, thus reducing the reflection force. Furthermore, imparting a surface shape to the surface layer promotes toner rolling within the toner layer sandwiched between the surface layer of the electrophotographic photoreceptor and the transfer material such as an intermediate transfer medium or paper, thereby reducing the mirroring force of the surface charge on the toner surface. This reduces the adhesion force of the toner and improves the transferability of the toner to the transfer material. Methods for optimizing the protrusions include, for example, controlling the particle size of the introduced particles or increasing the proportion of particles in the surface layer to arrange the particles on the surface layer. Our research showed that mixing multiple particles with different particle sizes in the surface layer makes it easier to control the height of the protrusions originating from the particles.

[0015] The electrophotographic photoreceptor of the present invention is an electrophotographic photoreceptor having a surface layer containing particles and a binder resin, and it is necessary that there are multiple peaks in the particle size distribution based on the number of particles. Among the multiple peaks whose peak tops are 20 nm or larger, the peak with the highest frequency of peak tops is designated as the first peak, and among the multiple peaks whose peak tops are 20 nm or larger, the peak with the second highest frequency of peak tops after the first peak is designated as the second peak. Comparing the first peak and the second peak, the peak with the larger value of the peak top particle size is designated as peak PEA. In the present invention, the peak top particle size DA of peak PEA must be in the range of 80 nm to 300 nm. More preferably, it must be in the range of 85 nm to 250 nm. Even more preferably, it must be in the range of 90 nm to 250 nm. Being within this range makes it easier to obtain the effect of reducing the adhesion between the toner and the surface layer of the electrophotographic photoreceptor during the transfer process.

[0016] In this case, the peak-top particle size DA of PEA represents the particle size of the particle with the highest particle frequency in the surface layer. When the particle size DA is less than 80 nm, the height of the protrusions that contribute to point contact between the toner and the surface layer of the electrophotographic photoreceptor decreases. This increases the contact area between the toner and the surface layer of the electrophotographic photoreceptor, worsening the toner's adhesion and thus reducing transferability. When the particle size DA exceeds 300 nm, the curvature of the protrusions originating from the particles decreases, increasing the contact area between the toner and the surface layer. This increases the adhesion between the toner and the surface of the electrophotographic photoreceptor, resulting in poor transferability. Furthermore, the first and second peaks are selected from the range where the particle size corresponding to the peak top is 20 nm or larger. That is, among the multiple peaks, the peak with the highest frequency of peak tops among those whose peak tops are 20 nm or larger is designated as the first peak, and the peak with the second highest frequency of peak tops is designated as the second peak. Figure 11A shows an example of particle size distribution based on the number of particles contained in the surface layer of an electrophotographic photoreceptor, where the first peak 201 is located at a particle diameter of 50 nm and the second peak 202 is located at a particle diameter of 170 nm. In this case, the second peak 202, which has a larger particle diameter, becomes peak PEA, and its particle diameter DA is 170 nm. Therefore, the condition 80 nm ≤ DA is satisfied. Also, since the particle diameter of the first peak 201 is 50 nm, the condition that the particle diameter at the peak top is 20 nm or larger is satisfied. Figure 11B shows another example of the particle size distribution of particles contained in the surface layer of an electrophotographic photoreceptor. There is a peak at a particle size of 5 nm, but since the particle size at the peak top is less than 20 nm, this peak is not included in the first and second peaks. Therefore, as in the case of Figure 11A, the peak at a particle size of 50 nm becomes the first peak 201, and the peak at a particle size of 170 nm becomes the second peak 202. The peaks are selected in this way. Here, even with an electrophotographic photoreceptor 1 in which a large number of very small particles are contained in the surface layer 105, it is possible to obtain the effects of the present invention described later. Therefore, as explained with reference to Figures 11A and 11B, by selecting the first peak 201 and the second peak 202 from the peaks with a particle size of 20 nm or more, the effects of the present invention can be stably obtained.

[0017] Next, particles containing a particle size in the range of DA ± 20 nm in the surface layer of the electrophotographic photoreceptor of the present invention are defined as particle PAA. In the present invention, when a protrusion derived from the particle PAA and having a height of 10 nm to 300 nm is defined as protrusion CA, it is necessary that the protrusion CA exists on the surface of the surface layer. If the height of the protrusion CA is less than 10 nm, the height of the protrusion CA becomes too low, so the rotation of the toner is not promoted during contact between the electrophotographic photoreceptor and the toner, and the electrostatic adhesion between the toner and the surface layer of the electrophotographic photoreceptor does not decrease, resulting in poor transferability. If the height of the protrusion CA exceeds 300 nm, the recesses in the surface layer of the electrophotographic photoreceptor become larger, and as a result of the accumulation of toner additives, the contact area between the surface of the surface layer of the electrophotographic photoreceptor and the toner increases, resulting in poor transferability.

[0018] Next, when the surface layer of the electrophotographic photoreceptor of the present invention is viewed from above, the average distance between the centroids of the convex portions CA must be between 150 nm and 500 nm. If the average distance between the centers of gravity of the convex portions CA on the surface layer of the electrophotographic photoreceptor exceeds 500 nm, and the spacing between the convex portions CA originating from particles becomes too wide, the likelihood of the toner and the surface of the electrophotographic photoreceptor's surface layer coming into contact increases. As a result, it becomes impossible to maintain the distance between the toner and the surface of the electrophotographic photoreceptor's surface layer, making it easier for the toner to come into contact with the concave portions of the surface layer, thus worsening transferability. Since the Coulomb force does not decrease, the electrostatic adhesion force does not increase, and therefore transferability cannot be improved.

[0019] On the other hand, if the average distance between the centers of gravity of the convex CAs becomes less than 150 nm, and the distance between the centers of gravity of the convex CAs on the surface layer of the electrophotographic photoreceptor becomes small, the surface layer will be filled with convex CAs, increasing the number of contact points between the toner matrix particles and the surface layer. This increases the contact area between the toner and the surface layer of the electrophotographic photoreceptor, resulting in a greater non-electrostatic adhesion force and worsening transferability. The distance between the centroids of the convex portions CA on the surface of the surface layer of the electrophotographic photoreceptor of the present invention is more preferably 150 nm or more and 450 nm or less, and more preferably 150 nm or more and 400 nm or less.

[0020] Furthermore, in the electrophotographic photoreceptor of the present invention, the standard deviation of the distance between the centroids of the convex portions CA must be 250 nm or less. If the standard deviation of the distance between the centroids of the convex portions CA exceeds 250 nm, there will be widespread variation in the distribution of the convex portions CA on the surface layer, resulting in uneven adhesion between the toner and the surface of the electrophotographic photoreceptor. This uneven adhesion will result in uneven transfer, making the halftone image appear rough. More preferably, the standard deviation of the average value of the distance between the centroids is 200 nm or less, and even more preferably 175 nm or less.

[0021] Similarly, it is preferable that the coefficient of variation obtained by dividing the standard deviation of the distance between the centroids of the convex portions CA by the average value of the distance between the centroids is 50% or less. If the coefficient of variation of the average value of the distance between the centroids exceeds 50%, there will be widespread variation in the distribution of the convex portions CA on the surface layer, resulting in uneven adhesion between the toner and the surface of the electrophotographic photoreceptor. This uneven adhesion will result in uneven transfer, making the halftone image appear rough. More preferably, the coefficient of variation of the average value of the distance between the centroids is 40%, and even more preferably 35% or less.

[0022] Our investigation revealed that by further filling the spaces between the PAA particles with particles other than PAA particles in a near-closest density toward the surface of the drum (electrophotographic photoreceptor), the density between the particles is increased. This is because, when the PAA particles are subjected to an impact tangentially to the drum surface, controlling the distance between the PAA particles to the aforementioned range suppresses the movement of the PAA particles by restraining them with the binding resin and preventing their movement toward the drum surface. As a result, the detachment of PAA particles from the surface layer of the electrophotographic photoreceptor is suppressed even by friction with the charging member, developing member, and transfer member that come into contact with the electrophotographic photoreceptor. Therefore, in this invention, the surface shape of the surface layer of the electrophotographic photoreceptor, which has excellent transferability, can be maintained throughout durability testing. As a result, the surface shape of the surface layer of the electrophotographic photoreceptor becomes more responsive, reducing the contact area with toner and thus reducing adhesion to toner, thus maintaining improved transferability. Furthermore, because the surface layer of the electrophotographic photoreceptor is less susceptible to contamination, it becomes easier to avoid problems such as latent image distortion and reduced density.

[0023] Furthermore, in the surface of the surface layer of the electrophotographic photoreceptor of the present invention, "particles" refer to all particles, such as particle A, particle B, and other particles, as described later. When the area occupied by these particles is S1 and the area occupied by other particles is S2, it is necessary that S1 / (S1+S2) is between 0.70 and 1.00. If S1 / (S1+S2) is less than 0.70, the areas without particles will not be able to form convex portions. In the present invention, a scanning electron microscope (SEM) is used to observe the surface of the surface layer of the electrophotographic photoreceptor of the present invention from above, with an acceleration voltage set to 5kV or higher. In the backscattered electron image of the surface layer, any particles whose images can be confirmed are added to the area occupied by the particles S1. Theoretically, the upper limit of S1 / (S1+S2) is 1.00. More preferably, S1 / (S1+S2) is between 0.80 and 1.00, and even more preferably between 0.85 and 0.95.

[0024] In the cross-section of the surface layer of the electrophotographic photoreceptor of the present invention, if the particles are stacked in a single layer as shown in Figure 5, it is preferable that the following formula (1) is satisfied when the average thickness of the surface layer in the portion not containing the convex portion CA is T. DA > T ···Formula (1) When particles are stacked in multiple layers as shown in Figure 6, it is preferable that the following equation (1)' is satisfied when T is the average thickness of the surface layer in the parts that do not include the convex portion CA. DA × 2 > T ···Formula (1)'

[0025] If DA becomes smaller than the average film thickness T, it becomes difficult to form the convex portion CA as described above, and the reduction in adhesion between the toner matrix particles and the electrophotographic photoreceptor becomes insufficient, increasing the likelihood of poor transferability. The average film thickness T is preferably 50 nm to 500 nm if the particles are stacked in a manner that satisfies equation (1) as shown in Figures 1 and 2. More preferably it is 70 nm to 450 nm, and even more preferably 80 nm to 400 nm.

[0026] Furthermore, in the cross-section of the surface layer of the electrophotographic photoreceptor of the present invention, the peak with the highest frequency of peak tops is defined as the first peak, and the peak with the second highest frequency of peak tops is defined as the second peak. When comparing the first peak and the second peak, the peak with the smaller value of the peak top particle size is defined as peak PEB, and it is preferable that the peak top particle size DB of peak PEB satisfies the following formula (2). DB < T...Formula (2)

[0027] When particles PAB are defined as particles with a particle size in the range of DB ± 20 nm among all particles contained in the surface layer, if DB is less than or equal to the average value T of the film thickness, the tightness between the particles PAA that form the convex portion CA and the particles PAB arranged between the convex portion CA increases, and a clear recess is formed in the surface layer, thereby suppressing particle detachment. If DB is greater than or equal to the average value T of the film thickness, the particles PAB become more easily exposed from the surface layer, and particle detachment progresses more easily.

[0028] Furthermore, in the cross-section of the surface layer of the electrophotographic photoreceptor of the present invention, it is preferable that DA and DB satisfy the following formula (3). DB / DA > 1 / 10 ···Formula (3) The particles PAA form convex portions CA, and the particles PAB fill the spaces between the particles PAA, thereby enabling control of the average value and standard deviation of the distance between the centroids of the convex portions CA. Furthermore, by satisfying the particle sizes of the particles PAA and PAB in equation (3), it is possible to suppress particle detachment against tangential friction on the surface layer of the electrophotographic photoreceptor while maintaining a sufficient height of the convex portions CA. More preferably, DB / DA in equation (3) is greater than 1 / 3, and even more preferably, DB / DA is greater than 1 / 2.

[0029] Next, it is preferable that the proportion of the number of protrusions CA to the total number of protrusions on the surface layer of the electrophotographic photoreceptor of the present invention is 90% or more. If the proportion of protrusions CA is less than 90%, the protrusions that do not originate from particle PAA will have weak mechanical strength due to friction in the developing section of the electrophotographic apparatus, and the protrusions will wear down due to friction in the tangential direction of the electrophotographic photoreceptor. In this state, it becomes difficult to maintain good transferability over long-term use.

[0030] Furthermore, it is preferable that the full width at half maximum (FWHM) of the peak PEA in the surface layer of the electrophotographic photoreceptor of the present invention is 20 nm or more and 50 nm or less. Since the height of the protrusion CA is controlled by the particle size, it is preferable that the FWHM of the peak PEA be within a constant range as much as possible. If the FWHM of PEA exceeds 50 nm, the variation in the height of the protrusion CA will also increase, resulting in variations in the point contact state between the toner matrix particles and the surface layer of the electrophotographic photoreceptor. This prevents the toner from rotating properly and makes it difficult to reduce the electrostatic adhesion between the surfaces. By promoting point contact between the toner and the electrophotographic photoreceptor, the adhesion force of the toner to the electrophotographic photoreceptor is reduced, making it possible to improve transferability.

[0031] In the electrophotographic photoreceptor of the present invention, it is preferable that the maximum height difference Rz of the surface layer is 100 nm or more and 400 nm or less. If the maximum height difference Rz of the surface layer is less than 100 nm, the rotation of the toner is not promoted properly and the transferability does not improve. If the maximum height difference Rz of the surface layer exceeds 400 nm, the external additive will accumulate in the depressions, so the surface of the surface layer of the electrophotographic photoreceptor may become contaminated, causing the latent image to become distorted and making it difficult to obtain density. In addition, the surface shape of the surface layer of the electrophotographic photoreceptor becomes less responsive, so the contact area with the toner increases, and the transferability deteriorates. Furthermore, discharge is more likely to occur during the transfer process, which may cause roughness in the halftone image due to density unevenness. More preferably, the maximum height difference Rz is 125 nm or more and 375 nm or less, and even more preferably 150 nm or more and 350 nm or less. The maximum height difference Rz was measured using an SPM (Scanning Probe Microscope "JSPM-5200", manufactured by JEOL Ltd.), as described later. The surface shape of a 3 μm square photoreceptor was measured at one location for each sample, for a total of 12 locations. In the surface shape analysis image, which was flattened to correct a linear slope across the entire image, the difference between the maximum value Zmax and the minimum value Zmin of height z was defined as the maximum height difference Rz.

[0032] It is preferable that the circularity of the particles PAA contained in the surface layer of the electrophotographic photoreceptor of the present invention is 0.950 or higher. If the circularity of the particles PAA is less than 0.950, the contact area between the toner matrix particles and the surface of the surface layer of the electrophotographic photoreceptor increases. This leads to an increase in non-electrostatic adhesion, and the transferability of the toner tends to deteriorate with long-term use. The circularity of the particles was determined using a scanning electron microscope as follows: The particles to be measured were observed using a scanning electron microscope ("JSM7800F," manufactured by JEOL Ltd.), and the individual particle sizes of 100 particles were measured from the images obtained from the observation. For each particle, the longest side a and shortest side b of the primary particle were measured, and the circularity was defined as b / a. The circularity of the particles was calculated by averaging the circularity of the 100 particles.

[0033] As described above, the particles in the surface layer of the electrophotographic photoreceptor of the present invention preferably contain at least the particles PAA and PAB. Since particle A contributes to contact with the toner, lowering the dielectric constant is effective in reducing the electrostatic adhesion force. The dielectric constant ε(A) of particle A is preferably 5 or less. More preferably 4 or less, and even more preferably 3 or less. Examples of particles A used in the present invention include organic resin particles such as acrylic resin particles and inorganic particles such as silica.

[0034] Acrylic particles contain polymers of acrylic acid esters or methacrylic acid esters. Among these, styrene-acrylic particles are more preferred. The degree of polymerization of the acrylic resin and styrene-acrylic resin, and whether the resin is thermoplastic or thermosetting, are not particularly limited. Examples of organic resin particles include cross-linked polystyrene, cross-linked acrylic resin, phenolic resin, melamine resin, polyethylene, polypropylene, acrylic particles, polytetrafluoroethylene particles, and silicone particles.

[0035] Examples of inorganic particles include silica particles, metal oxide particles, and metal particles. It is preferable to use inorganic particles as the particles in the surface layer of the electrophotographic photoreceptor of the present invention, as these particles have low elasticity and are advantageous in promoting point contact between the toner and the electrophotographic photoreceptor. When using inorganic particles, silica particles are preferred among them. Compared to other insulating particles, silica particles have a lower elastic modulus and a larger average circularity, which is expected to promote point contact between the toner and the electrophotographic photoreceptor, thereby reducing adhesion.

[0036] 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, wet silica fine particles obtained by the sol-gel method (hereinafter also referred to as sol-gel silica) are preferred. The sol-gel silica used in the particles contained in the surface layer of the electrophotographic photoreceptor of the present invention may be hydrophilic or have a hydrophobic surface treatment. 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.

[0037] 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, i-butyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, i-butyltrimethoxysilane Alkoxysilanes such as tiltriethoxysilane, decyltriethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-chloropropyltrimethoxysilane, γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-(2-aminoethyl)aminopropyltrimethoxysilane, and γ-(2-aminoethyl)aminopropylmethyldimethoxysilane; Silazanes such as hexamethyldisilazane, hexaethyldisilazane, hexapropyldisilazane, hexabutyldisilazane, hexapentyldisilazane, hexahexyldisilazane, hexacyclohexyldisilazane, hexaphenyldisilazane, divinyltetramethyldisilazane, and dimethyltetravinyldisilazane; Silicone oils such as 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 terminally 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. 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.

[0038] The surface layer in the present invention 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, and silicone oils. The surface layer of the present invention can be formed by preparing a coating solution for the surface layer containing the above-mentioned materials and solvents, forming a coating film, and 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.

[0039] In the electrophotographic photoreceptor of the present invention, the volume of particles in the surface layer is preferably 40% to 90% of the total volume of the surface layer. More preferably 45% to 85% of the total volume, and even more preferably 50% to 80% of the total volume. Being within this range ensures that the formation of the protrusions in the surface layer, as described above, is reliably achieved. If it is 40% or less of the volume, the height of the protrusions becomes low, and the transferability does not improve. If it is 90% or more of the volume, particle detachment becomes severe, and in durability tests, the transferability deteriorates and the image density decreases.

[0040] In the present invention, it is preferable that the relative permittivity ε(NA) of particles other than particle A is 5 or greater than ε(A) among the particles contained in the surface layer of the electrophotographic photoreceptor. As mentioned above, particle A will be a particle with a relative permittivity of 5 or less. Therefore, if only particle A is used, the capacitance of the surface layer will be small, and the amount of charge per unit area will be low when the electrophotographic photoreceptor is charged in the charging process. By increasing the relative permittivity of particles other than particle A, it becomes possible to increase the capacitance of the surface layer. This allows for the maintenance of a larger charge per unit area when charging the electrophotographic photoreceptor during the charging process, enabling the formation of a higher-resolution latent image. As a result, it becomes possible to reduce graininess in halftone images.

[0041] To increase the relative dielectric constant of particles other than the particles A, conductive particles can be used. When inorganic particles are used as the conductive particles, it is preferable to use metal oxide particles. Examples of the metal oxide include zinc oxide, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, and bismuth oxide. Examples of the metal include aluminum, nickel, iron, nichrome, copper, zinc, and silver. Among these, it is particularly more preferable to use titanium oxide, tin oxide, and zinc oxide. 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, aluminum, and niobium or oxides thereof. This doping makes it possible to control the relative dielectric constant of the metal oxide. Therefore, in the electrophotographic photoreceptor of the present invention, in X-ray photoelectron spectroscopy analysis of the surface layer, when the sum of the carbon atom concentration d(C), oxygen atom concentration d(O), Ti atom concentration d(Ti), and Si atom concentration d(Si) is taken as 100.0 atomic%, it is preferable that d(Ti) (atomic%) and d(Si) (atomic%) satisfy the following formulas (4) to (6). 0 < d(Ti) ≦ 2.0 ··· Formula (4) d(Si) ≦ 15.0 ··· Formula (5) 0.01 ≦ d(Ti) / d(Si) ≦ 1.0 ··· Formula (6)

[0042] When d(Ti) is 2.0 atomic% or less, a sufficient amount of titanium oxide particles contained in the surface of the electrophotographic photoreceptor's surface layer is present. This makes it possible to increase the capacitance of the surface layer, and maintain a high amount of charge that can be held per unit area when the electrophotographic photoreceptor is charged in the charging step. Therefore, a higher-definition latent image can be formed, which makes it possible to reduce graininess when outputting halftone images. Furthermore, it is preferable that the titanium oxide particles contained in the surface layer of the electrophotographic photoreceptor of the present invention have their surfaces treated with a silane coupling agent. Depending on the degree of treatment, the dispersion state of the titanium oxide particles within the surface layer changes, and the capacitance of the surface layer changes.

[0043] If d(Si) is 15.0 atomic% or less, and d(Ti) / d(Si) is between 0.01 and 1.0, then the surface of the titanium oxide particles is likely to be sufficiently treated with a silane coupling agent, and the titanium oxide particles contained in the surface layer of the electrophotographic photoreceptor will be dispersed within the surface layer. This makes it possible to increase the capacitance of the surface layer. Furthermore, when the electrophotographic photoreceptor is drum-shaped, uneven dispersion of titanium oxide particles in the longitudinal direction of the electrophotographic photoreceptor is suppressed. This allows for the maintenance of a larger charge per unit area during the charging process, enabling the formation of a higher-resolution latent image. As a result, it becomes possible to reduce graininess in halftone images.

[0044] Examples of conductive particles contained in the surface layer include metal oxide particles such as titanium dioxide, zinc oxide, tin oxide, and indium oxide, with titanium dioxide being preferred among them. In particular, anatase-type titanium dioxide facilitates smooth charge transfer within the protective layer and improves charge injection. It is preferable that the degree of anatase in anatase-type titanium dioxide is 90% or higher. The metal oxide particles may be doped with atoms or oxides of niobium, phosphorus, aluminum, etc., and particularly preferred are titanium dioxide particles containing niobium, with the niobium being concentrated near the particle surface. The concentration of niobium near the surface allows for efficient transfer of charge.

[0045] Examples of conductive particles include particles made of metal oxides such as titanium oxide, zinc oxide, tin oxide, and indium oxide, with the surface of which a metal oxide containing titanium atoms and niobium atoms is present. Specifically, for example, particles of a metal oxide containing titanium atoms are doped with niobium atoms or niobium oxide. Particularly preferred conductive particles are titanium oxide particles containing niobium atoms, with the niobium atoms unevenly distributed near the particle surface. This is because the uneven distribution of niobium atoms near the surface allows for efficient transfer of charge. More specifically, titanium oxide particles in which the concentration ratio calculated as "niobium atom concentration / titanium atom concentration" at 5% inside the particle from the surface to the maximum diameter of the particle is 2.0 or higher, compared to the concentration ratio calculated as "niobium atom concentration / titanium atom concentration" at the center of the particle. The niobium atom concentration and titanium atom concentration are obtained by a scanning transmission electron microscope (STEM) connected to an EDS analyzer (energy dispersive X-ray analyzer). Figure 8 shows a TEM image of an example of titanium oxide particles (X1) used in the embodiment of the present invention. Figure 9 shows a schematic diagram illustrating the STEM image in Figure 8. As will be described in detail later, the niobium-containing titanium oxide particles used in the embodiment of the present invention are produced by coating titanium oxide particles with niobium-containing titanium oxide and then firing them. Therefore, it is thought that the coated niobium-containing titanium oxide undergoes crystalline growth as niobium-doped titanium oxide through so-called epitaxial growth along the crystal structure of the core titanium oxide. As shown in Figure 9, the niobium-containing titanium oxide produced in this way has a lower density near the surface compared to the density in the center of the particle, and is controlled to have a core-shell-like morphology.

[0046] In niobium-containing titanium oxide particles as shown in Figure 9, the niobium / titanium atom concentration ratio near the particle surface 32 is greater than the niobium / titanium atom concentration ratio in the particle center 31, indicating that niobium atoms are concentrated near the particle surface. Specifically, the niobium / titanium atom concentration ratio in the 5% interior of the particle from the particle surface to the maximum diameter (hereinafter also referred to as the niobium / titanium atom concentration ratio ratio) is 2.0 or greater, relative to the niobium / titanium atom concentration ratio in the particle center 31. By making the above niobium / titanium atom concentration ratio ratio 2.0 or greater, charge movement within the protective layer becomes easier, and charge injection performance can be improved. If the above niobium / titanium atom concentration ratio ratio is less than 2.0, charge transfer becomes difficult.

[0047] For EDS analysis using STEM, the niobium / titanium atom concentration ratio is measured by observation with a transmission electron microscope and EDS analysis. The niobium / titanium atom concentration ratio in the center 31 of the particle can be measured by electron beam 33, which analyzes the center of the particle. In addition, the niobium / titanium atom concentration ratio in the 5% interior of the particle from the surface to the maximum diameter can be measured by electron beam 34, which analyzes 5% interior of the particle from the surface to the maximum diameter of the particle. Furthermore, the niobium / titanium atom concentration ratio can also be measured directly from the electrophotographic photoreceptor by thinning it using methods such as microtome, Ar milling, or FIB.

[0048] Examples of conductive particles contained in the surface layer of the present invention include metal oxide particles such as titanium dioxide, zinc oxide, tin oxide, and indium oxide, with titanium dioxide being preferred. In particular, anatase-type titanium dioxide facilitates charge transfer within the surface layer and improves charge injection. It is preferable that the degree of anatase in the anatase-type titanium dioxide is 90% or higher. The metal oxide particles may be doped with atoms or oxides of niobium, phosphorus, aluminum, etc., and particularly preferred are titanium dioxide particles containing niobium, with the niobium being unevenly distributed near the particle surface. The uneven distribution of niobium near the surface allows for efficient transfer of charge. By using such conductive particles, it becomes easier for charge to be injected from a charged member in contact with the surface of the conductive particles, and it becomes easier for charge to move within the surface layer, thereby achieving a high effect in suppressing the decrease in the resistivity of the surface of the electrophotographic photoreceptor.

[0049] When metal oxides are used as conductive particles, their average primary particle size is preferably 20 nm to 200 nm, and more preferably 25 nm to 150 nm. The average primary particle size D1 of metal oxide particles was determined using a scanning electron microscope as follows: The particles to be measured were observed using a JEOL Ltd. scanning electron microscope JSM-7800. From the images obtained from the observation, the individual particle sizes of 100 particles were measured, and their arithmetic mean was calculated to determine the average primary particle size D1. The individual primary particle size was defined as (a+b) / 2, where a is the longest side of the primary particle and b is the shortest side. For needle-shaped metal oxide particles or flaky titanium oxide particles, the average particle size was calculated for both the major axis diameter and the minor axis diameter to determine the average primary particle size.

[0050] As described above, by controlling the relative permittivity of particle A and other particles, and performing surface treatment on the particles, it becomes possible to maintain sufficient surface charge on the surface layer of the electrophotographic photoreceptor when charged, while maintaining transferability. Furthermore, charge transport substances may be added to the surface coating solution to improve the charge transport capability of the surface layer. Additives may also be added to improve various functions. Examples of additives include antioxidants, ultraviolet absorbers, plasticizers, and leveling agents. The following embodiments of the binder resin according to the present invention are available. Here, it is preferable that the surface layer contains a charge transport material.

[0051] Examples of binder resins include polyester resins, acrylic resins, phenoxy resins, polycarbonate resins, polystyrene resins, phenolic resins, melamine resins, and epoxy resins. Among these, polycarbonate resins, polyester resins, and acrylic resins are preferred. The surface layer of the present invention may also be formed as a cured film by polymerizing a composition containing a monomer having a polymerizable functional group. Examples of reactions in this case include thermal polymerization, photopolymerization, and radiation polymerization. Examples of polymerizable functional groups in monomers having a polymerizable functional group include acrylic groups and methacrylic groups. Materials with charge transport ability may be used as monomers having a polymerizable functional group. Compounds having polymerizable functional groups may also have charge-transporting structures simultaneously with chain-polymerizable functional groups. Triarylamine structures are preferred as charge-transporting structures. Acryloyl groups and methacryloyl groups are preferred as chain-polymerizable functional groups. The number of functional groups may be one or more. In particular, forming a cured film containing a compound with multiple functional groups and a compound with one functional group is especially preferable because the strain generated by polymerization between the multiple functional groups is easily relieved.

[0052] Examples of compounds having one of the above functional groups are shown in (2-1) to (2-6). [ka]

[0053] Examples of compounds having the above-mentioned multiple functional groups are shown in (3-1) to (3-5). [ka]

[0054] <Support> In the present invention, the electrophotographic photoreceptor preferably has a support. In the present invention, the support is preferably a conductive support. The shape of the support can be cylindrical, belt-shaped, or sheet-shaped. Among these, a cylindrical support is preferred. Furthermore, the surface of the support may be subjected to electrochemical treatments such as anodizing, blasting, or cutting. The support material can be metal, resin, or glass. Examples of metals include aluminum, iron, nickel, copper, gold, stainless steel, or alloys thereof. Among these, an aluminum support is preferred. Furthermore, conductivity may be imparted to resins and glass by processing such as mixing or coating them with conductive materials.

[0055] <Conductive layer> In the present invention, a conductive layer may be provided on the support. By providing a conductive layer, scratches and irregularities on the surface of the support can be concealed, and the reflection of light on the surface of the support can be controlled. Preferably, the conductive layer contains conductive particles and a resin. 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.

[0056] Among these, it is preferable to use metal oxides as conductive particles, and it is more preferable to use titanium oxide, tin oxide, or zinc oxide. When using metal oxides as conductive particles, the surface of the metal oxide may be treated with a silane coupling agent or doped with elements such as phosphorus or aluminum, or their oxides. Furthermore, the conductive particles may have a laminated structure in which uncoated particles such as titanium dioxide, barium sulfate, and zinc oxide are coated with a metal oxide having a different composition from the uncoated particles. Examples of metal oxides used for coating include tin oxide. Furthermore, when using metal oxides as conductive particles, their average primary particle size is preferably 1 nm to 500 nm, and more preferably 3 nm to 400 nm.

[0057] 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.

[0058] The average 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. 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.

[0059] <Underlay layer> In the present invention, an undercoat layer may be provided on the support or conductive layer. The average 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.

[0060] Examples of resins for this undercoat include polyacrylic acid resin, polyvinyl alcohol resin, polyvinyl acetal resin, polyethylene oxide resin, polypropylene oxide resin, ethylcellulose resin, methylcellulose resin, polyamide resin, polyamic acid resin, polyurethane resin, polyimide resin, polyamide-imide resin, polyvinylphenol resin, melamine resin, phenol resin, epoxy resin, and alkyd resin. Alternatively, the resin may have a structure in which a resin having polymerizable functional groups is crosslinked with a monomer having polymerizable functional groups. Furthermore, the undercoat layer may contain inorganic compounds or organic compounds in addition to resin. Examples of inorganic compounds include metals, oxides, and salts. Examples of metals include gold, silver, and aluminum. Examples of oxides 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 salts include barium sulfate and strontium titanate.

[0061] These inorganic compounds may exist in the film in particulate form. The number-average particle size is preferably 1 nm to 500 nm, and more preferably 3 nm to 400 nm. These inorganic compounds may also have a laminated structure comprising core material particles and a coating layer that covers those particles. These inorganic compounds may be treated on the surface with silicone oil, silane compounds, silane coupling agents, other organosilicon compounds, organotitanium compounds, etc. They may also be doped with elements such as tin, phosphorus, aluminum, and niobium.

[0062] Examples of organic compounds include electron transport materials and conductive polymers. Examples of conductive polymers include polythiophene, polyaniline, polyacetylene, polyphenylene, and polyethylenedioxythiophene. 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. The electron transport material may have polymerizable functional groups and may be crosslinked with a resin having functional groups that can react with those functional groups. Examples of polymerizable functional groups include hydroxyl groups, thiol groups, amino groups, carboxyl groups, vinyl groups, acryloyl groups, methacryloyl groups, and epoxy groups. These organic compounds may exist in particulate form within the film, and their surfaces may be treated.

[0063] The base layer may contain various additives such as leveling agents like silicone oil, plasticizers, and thickeners. The undercoat layer is obtained by preparing an undercoat coating solution containing the above-mentioned materials, applying it to a support or conductive layer, and then drying or curing the coating film. Examples of solvents used when preparing coating solutions include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, or aromatic hydrocarbon-based solvents. Dispersion methods for dispersing particles in a coating solution include using a paint shaker, sand mill, ball mill, or liquid impact type high-speed disperser.

[0064] <Photosensitive layer> The photosensitive layers of electrophotographic photoreceptors are mainly classified into (1) multilayer photosensitive layers and (2) single-layer photosensitive layers. (1) A multilayer photosensitive layer is a photosensitive layer having 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 is a photosensitive layer containing both a charge generating material and a charge transport material.

[0065] (1) Stacked photosensitive layer The stacked photosensitive layer comprises a charge generation layer and a charge transport layer. (1-1) Charge generation layer The charge generation layer preferably contains a charge generation material and a resin. Examples of 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.

[0066] 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. Furthermore, the charge generation layer may contain additives such as antioxidants and ultraviolet absorbers. Specifically, these include hindered phenol compounds, hindered amine compounds, sulfur compounds, phosphorus compounds, and benzophenone compounds.

[0067] 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 this coating film on the undercoat layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, sulfoxide-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. The thickness of the charge generation layer is preferably 0.1 μm or more and 1.5 μm or less, and more preferably 0.15 μm or more and 1.0 μm or less.

[0068] (1-2) Charge transport layer The charge transport layer preferably contains a charge transport material and a resin. 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. 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.

[0069] Examples of resins include 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. 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. 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.

[0070] The charge transport layer can be formed by preparing a coating solution for the charge transport layer containing the above-mentioned materials and solvents, forming this coating film on the charge generating layer, and drying it. Examples of solvents used in the coating solution include alcohol-based solvents, ketone-based solvents, ether-based solvents, ester-based solvents, and aromatic hydrocarbon-based solvents. Among these solvents, ether-based solvents or aromatic hydrocarbon-based solvents are preferred. The thickness of the charge transport layer is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, and particularly preferably 10 μm to 30 μm.

[0071] (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 on an undercoat layer, 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. The 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.

[0072] [Process cartridges, electrophotographic equipment] The process cartridge of the present invention is capable of integrally supporting 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. The process cartridge is characterized by being detachable from the electrophotographic apparatus body. Figure 10 shows a schematic example of the configuration of an electrophotographic apparatus having a process cartridge equipped with the electrophotographic photoreceptor of the present invention.

[0073] [Configuration of an electrophotographic device] The electrophotographic apparatus of the present invention may include the above-mentioned electrophotographic photoreceptor, as well as a charging means, an exposure means, a developing means, and a transfer means. The electrophotographic apparatus of this embodiment is a so-called tandem type electrophotographic apparatus, equipped with multiple image forming units a to d. The first image forming unit a forms an image using yellow (Y) toner, the second image forming unit b uses magenta (M) toner, the third image forming unit c uses cyan (C) toner, and the fourth image forming unit d uses black (Bk) toner. These four image forming units are arranged in a line at regular intervals, and the configuration of each image forming unit is substantially common in many ways, except for the color of the toner they contain. Therefore, the electrophotographic apparatus of this embodiment will be described below using the first image forming unit a.

[0074] The first image forming unit a includes a photosensitive drum 1a which is a drum-shaped electrophotographic photoreceptor, a charging roller 2a which is a charging member, a developing means 4a, and a static elimination means 5a. The photosensitive drum 1a is an image carrier that holds the toner image and is driven to rotate at a predetermined peripheral speed (process speed) in the direction of the arrow shown in the figure. The developing means 4a contains yellow toner and develops the yellow toner on the photosensitive drum 1a with the developing roller 41a.

[0075] When a control means (not shown), such as a controller, receives an image signal, the image forming operation is initiated and the photosensitive drum 1a is driven to rotate. During the rotation process, the photosensitive drum 1a is uniformly charged by the charging roller 2a to a predetermined voltage (charging voltage) with a predetermined polarity (negative polarity in this embodiment), 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 development position and visualized as a yellow toner image on the photosensitive drum 1a. Here, the normal charging polarity of the toner contained in the developing means 4a is negative polarity, and the electrostatic latent image is reverse-developed by toner charged with the same polarity as the charging polarity of the photosensitive drum 1a by the charging roller 2a. However, the present invention is not limited to this, and can also be applied to electrophotographic devices in which the electrostatic latent image is positively developed by toner charged with the opposite polarity to the charging polarity of the photosensitive drum 1a. Furthermore, it is possible to provide numerous protrusions originating from particles on the surface of the charging roller 2a. The protrusions on the surface of the charging roller 2a act as spacers between the charging roller 2a and the photosensitive drum 1a in the charging section. When the transfer residue toner, which is toner that remains on the photosensitive drum 1a without being transferred in the primary transfer section described later, enters the charging section, the protrusions prevent the charging roller 2a from being contaminated with the transfer residue toner by contacting areas other than the protrusions with the transfer residue toner. The pre-exposure unit 5a, which serves as a static elimination means, eliminates static electricity by exposing the surface of the photosensitive drum 1a before it is charged by the charging roller 2a. By eliminating static electricity from the surface of the photosensitive drum 1a, it plays a role in leveling the surface potential formed on the photosensitive drum 1 and controlling the amount of discharge caused by discharge in the charged area.

[0076] The endless, movable intermediate transfer belt 10 is conductive, contacts the photosensitive drum 1a to form a primary transfer section, and rotates at approximately the same peripheral speed as the photosensitive drum 1a. The intermediate transfer belt 10 is tensioned by opposing rollers 13 as opposing members, and drive rollers 11 and tension rollers 12 and metal rollers 14a as tensioning members, with a total tension of 60 N exerted by the tension rollers 12. The intermediate transfer belt 10 can be moved by the rotational drive of the drive rollers 11 in the direction of the arrows shown in the figure.

[0077] The yellow toner image formed on the photosensitive drum 1a is transferred from the photosensitive drum 1a to the intermediate transfer belt 10 during the process of passing through the primary transfer section. Furthermore, in Figure 2, the photosensitive drums in the second, third, and fourth image forming sections are 1b, 1c, and 1d, the charging rollers are 2b, 2c, and 2d, the exposure means are 3b, 3c, and 3d, the developing means are 4b, 4c, and 4d, the static elimination means are 5b, 5c, and 5d, the metal rollers are 14b, 14c, and 14d, and the developing rollers are 41b, 41c, and 41d.

[0078] Similarly, the second color magenta toner image, the third color cyan toner image, and the fourth color black toner image are formed and sequentially transferred onto the intermediate transfer belt 10. As a result, four toner images corresponding to the desired color image are formed on the intermediate transfer belt 10. Subsequently, the four toner images supported on the intermediate transfer belt 10 are transferred in one step to the surface of the transfer material P, such as paper or an OHP sheet fed by the paper feeding means 50, as they pass through the secondary transfer section formed by the contact between the secondary transfer roller 15 and the intermediate transfer belt 10. The transfer material P onto which the four toner images have been transferred by secondary transfer is then heated and pressurized in the fixing means 30, causing the four toners to melt and mix, and fix them to the transfer material P. Toner remaining on the intermediate transfer belt 10 after secondary transfer is cleaned and removed by the belt cleaning means 17, which is provided opposite the opposing roller 13 via the intermediate transfer belt 10. The electrophotographic photoreceptor of the present invention can be used in laser beam printers, LED printers, photocopiers, and the like. [Examples]

[0079] The following describes methods for measuring the physical properties of electrophotographic photoreceptors and conductive particles according to the present invention. The present invention is not limited in any way by the following examples, unless it exceeds the scope of the invention. In the following examples, "parts" refers to mass unless otherwise specified.

[0080] [Measurement of physical properties of electrophotographic photoreceptors] <Method for measuring the average primary particle size based on the number of particles according to the present invention> The number-average particle size is measured using a Zetasizer Nano-ZS (MALVERN). This instrument can measure particle size using dynamic light scattering. First, the sample to be measured is diluted and prepared so that the solid-liquid ratio is 0.10% by mass (±0.02% by mass), and then collected in a quartz cell and placed in the measurement section. If the sample is an inorganic fine particle, water or a methyl ethyl ketone / methanol mixed solvent is used as the dispersion medium; if the sample is a resin particle or an external additive for toner, water is used. As measurement conditions, the refractive index of the sample, the refractive index of the dispersion solvent, viscosity, and temperature are input into the control software Zetasizersoftware 6.30 and measurement is performed. Dn is adopted as the number-based average primary particle size.

[0081] The refractive index of the particles is taken from "Refractive Index of Solids" as described on page 517 of Volume II of the Chemical Handbook, Basic Edition, Revised 4th Edition (edited by the Chemical Society of Japan, Maruzen Co., Ltd.). The refractive index of the resin particles is taken from the refractive index of the resin used in the resin particles, which is included in the control software. However, if there is no built-in refractive index, the value listed in the polymer database of the National Institute for Materials Science (NIMS) is used. The refractive index of the toner additive is calculated by taking the weight average of the refractive index of the inorganic fine particles and the refractive index of the resin used in the resin particles. The refractive index, viscosity, and temperature of the dispersion solvent are selected from the values ​​included in the control software. In the case of a mixed solvent, the weight average of the dispersion media to be mixed is taken.

[0082] <Method for measuring the maximum height difference Rz on the surface of the surface layer of an electrophotographic photoreceptor> Surface observation was performed on the electrophotographic photoreceptors prepared in the examples. For the samples to be observed, the electrophotographic photoreceptor was divided into four equal parts in the longitudinal direction, and 5 mm square sample pieces were cut from the electrophotographic photoreceptor at positions 1 / 4, 1 / 2, and 3 / 4 of the way from the end, and at 120° intervals in the circumferential direction. The sample pieces were fixed in a sample holder so that the surface layer of the electrophotographic photoreceptor could be observed. For each sample piece fixed in the sample holder, the surface shape of a 3 μm square area on the surface layer of the electrophotographic photoreceptor was measured at one location on each sample. This measurement was performed on each of the nine sample pieces, and the average of the maximum height difference Rz at these nine locations was taken as the maximum height difference Rz of the electrophotographic photoreceptor of the present invention. SPM can utilize the following scanning probe microscopes: JSPM-5200 (manufactured by JEOL Ltd.), E-sweep scanning probe microscope (manufactured by Hitachi High-Tech Corporation), and AFM5500M medium-sized probe microscope system (manufactured by Hitachi High-Tech Corporation). The measurement method using the scanning probe microscope "JSPM-5200" (manufactured by JEOL Ltd.) is as follows. The scanning operation was performed via WinSPM Scanning, and a data analysis image of the surface shape was output. The maximum height difference Rz on the surface of the surface layer of the electrophotographic photoreceptor of the present invention was measured under the following observation conditions of the "JSPM-5200". Figure 7 shows an example of the results of SPM observation. Figure 7 represents the surface shape. After measurement, the measurement position of the sample was marked, and the measurement described below in <Calculation of particle size distribution and height of protrusions in the surface layer of the electrophotographic photoreceptor> was performed for each sample. Observation conditions for "JSPM-5200" Scanner: 4 SPM Scan: All SPM Mode Cantilever: SI-DF3P2 (manufactured by Hitachi High-Tech Fielding Co., Ltd.) Resonance Frequency Detection: (START) 1.00 kHz (Stop) 100 kHz (if f=67kHz, depending on the cantilever type) Cantilever Autotune:Normal approach Acquisition: 2 Inputs (512) Scan Mode: Normal STM / AFM: AC-AFM Clock: 833.33 μs Scan Size: 3000 nm Offset: 0 Bias [V]:0 Reference / V: Do not change (calibration value already entered) Filter: 1.4 Hz Loop Gain: 16 Surface shape images and associated surface height data were analyzed via WinSPM Scanning, and the difference between the maximum height value Zmax and the minimum height value Zmin of the flattened image was determined as the maximum height difference Rz. Furthermore, the measurement method using the scanning probe microscope "E-sweep" (manufactured by Hitachi High-Tech Corporation) is as follows: It is performed through a scanning operation, and a data analysis image of the surface shape of the electrophotographic photoreceptor can be output. • Observation conditions for "E-sweep" Cantilever: SI-DF20 (with rear aluminum plate) K-A102002771 (manufactured by Hitachi High-Tech Fielding Co., Ltd.) Scanning probe microscope: Manufactured by Hitachi High-Tech Science, Ltd. Measurement unit: E-sweep Measurement mode: DFM (Resonance Mode) shape image Resolution: X data count 512, Y data count 512 Measurement frequency: 127Hz The Q curve measurement magnification, excitation voltage, low-pass filter, and high-pass filter are adjusted to optimize the cantilever's resonance state. By analyzing the surface shape image and the surface height data attached to the image using the accompanying software, the difference between the maximum value Zmax and the minimum value Zmin of height z can be determined as the maximum height difference (maximum height) Rz for the flattened image, based on JIS B0601:2001.

[0083] <Observation of the layering state of particles contained in the surface layer of an electrophotographic photoreceptor, the ratio of the volume of particles to the total volume of the surface layer, the particle size distribution, and the calculation of the height of the convex portion CA> The proportion of particle volume to the total volume of the surface layer was calculated from the amount, density, and true specific gravity of polymerizable functional monomers and particles added to the surface layer coating solution. The specific gravity of the polymerized product and particles after polymerization of polymerizable functional monomers can be referenced from the published values ​​of the manufacturers of each material and the National Institute for Materials Science (NIMS) database, POLYINFO. Furthermore, when determining the properties from an electrophotographic photoreceptor, the following method can be used. Cross-sectional observation was performed on the electrophotographic photoreceptor prepared in the example. It was determined whether the particles were stacked in a single layer within the surface layer as shown in Figure 1 or Figure 5, or in multiple layers as shown in Figure 2 or Figure 6. The samples for cross-sectional observation were taken by dividing the electrophotographic photoreceptor into four equal parts in the longitudinal direction, and taking samples at positions 1 / 4, 1 / 2, and 3 / 4 of the way from the end, with a 120° offset in the circumferential direction. A 5 mm square sample piece was cut from each electrophotographic photoreceptor, and the surface layer was rendered in 3D at 2 μm × 2 μm × 2 μm using FIB-SEM's Slice & View. The conditions for Slice&View were set as follows: Sample preparation for analysis: FIB method Processing and observation equipment: SII / Zeiss NVision40 Slice interval: 10nm (Observation conditions) Acceleration voltage: 1.0kV Sample tilt: 54° WD: 5mm Detector: BSE detector Aperture: 60 μm, high current ABC:ON Image resolution: 1.25nm / pixel The measurement environment was: Temperature: 23°C, Pressure: 1 × 10⁻⁶ -4 The pressure is Pa. Additionally, a Strata400S (sample tilt: 52°) manufactured by FEI can be used as the processing and observation device.

[0084] The analysis area is 2 μm x 2 μm, and information is accumulated for each cross-section, resulting in a surface layer of 2 μm x 2 μm x 2 μm (8 μm). 3 The volume V per unit area was calculated. Image analysis of each cross-section was performed using image processing software: Media Cybernetics' Image-Pro Plus. The particle content relative to the total volume of the surface layer was calculated from the contrast differences in the FIB-SEM Slice&View. Furthermore, based on the information obtained from image analysis, the volume of each of the four sample pieces (2 μm × 2 μm × 2 μm, unit volume: 8 μm) was calculated. 3 Determine the volume V of the particles of the present invention in ) and the particle content [volume %] (=Vμm). 3 / 8μm 3 The formula (×100) was calculated. The average value of the particle content in each sample piece was taken as the content of each particle of the present invention in the surface layer relative to the total volume of the surface layer [volume %]. The particle composition was determined using SEM-EDX functionality.

[0085] In particle size distribution A, where the horizontal axis represents the particle size of the particles contained on the surface of the surface layer and the vertical axis represents the frequency based on the number of particles at each particle size, we check whether multiple peaks exist. In particle distribution A, among the multiple peaks, the peak with the highest frequency of peak tops (where the peak top is 20 nm or larger) is defined as the first peak. Next, in particle distribution A, among the multiple peaks, the peak with the second highest frequency of peak tops (where the peak top is 20 nm or larger) is defined as the second peak. Furthermore, comparing the first and second peaks, the peak with the larger peak top particle size value is defined as peak PEA.

[0086] Then, the particle size of the peak top of peak PEA in the particle size distribution A is defined as DA. Particles with a particle size in the range of DA ± 20 nm among all particles contained in the surface layer are defined as particle PAA. When a protrusion originating from particle PAA and having a height of 10 nm to 300 nm is defined as protrusion CA, the height L of protrusion CA is shown in Figures 5 and 6. If particles with different compositions were present, they were identified using mapping images obtained by EDS. Furthermore, 100 points of the protrusion were measured, and the ratio of protrusion CA originating from particle PAA to all protrusions was calculated. In addition, the average value LV was calculated for the height L.

[0087] Next, in the particle size distribution A, the peak with the highest frequency of peak tops is designated as the first peak, and the peak with the second highest frequency of peak tops is designated as the second peak. Comparing the first and second peaks, the peak with the smaller value of the peak top particle size is designated as peak PEB. The peak top particle size DB of peak PEB is then calculated. Furthermore, in the cross-sectional images of the surface layer, the average thickness of the surface layer excluding the convex portion CA was defined as the average thickness T, as shown in Figures 5 and 6.

[0088] <Method for measuring the average and standard deviation of the distance between the centroids of particles on the surface layer of an electrophotographic photoreceptor> In the electrophotographic photoreceptor of the present invention, when the surface layer is viewed from above, the mean value and standard deviation of the distance between the centroids of the convex portions CA originating from the particles PAA can be calculated as follows. The surface of the surface layer of the electrophotographic photoreceptor was imaged using a scanning electron microscope (SEM) ("S-4800", manufactured by JEOL Ltd.) at an acceleration voltage of 10kV. Photographs of the electrophotographic photoreceptor of the present invention were captured at a magnification of 30,000 using a scanner at 12 locations: 50mm from each end along the longitudinal direction, three locations in the center, and four locations at 90-degree intervals along the circumferential direction. The PAA particles in these photographs were binarized using an image processing and analysis device ("LUZEX AP", manufactured by Nireco Corporation).

[0089] In the mode of measuring the distance between adjacent centroids of particle PAAs, as shown in Figure 4, the distance between the centroids of adjacent particle PAAs is measured, and the average value of the centroid distance is calculated. At this time, the centroid distance is calculated from each centroid of the particle PAA by Voronoi partitioning. The above calculation of centroid distance and standard deviation was performed for a total of 10 fields of view, and the obtained average value and standard deviation of centroid distance were taken as the average value and standard deviation of the centroid distance of particles in the surface layer of the electrophotographic photoreceptor, respectively.

[0090] <Method for measuring the particle coverage ratio S1 / (S1+S2) on the surface layer of an electrophotographic photoreceptor> In the electrophotographic photoreceptor of the present invention, when the surface layer is viewed from above, the particles are, for example, particle A, particle B, and other particles as described in Table 4, and the area of ​​the particles is S1, and the total area of ​​the non-particle area is S2, the coverage ratio S1 / (S1+S2) can be calculated as follows. In the present invention, a scanning electron microscope (SEM) is used to observe the surface of the surface layer of the electrophotographic photoreceptor of the present invention from above, with the acceleration voltage set to 5kV or higher. In the backscattered electron image of the surface layer, for those in which particle images can be confirmed, the area occupied by the particles is added to S1.

[0091] The surface of the surface layer of the electrophotographic photoreceptor was imaged using a scanning electron microscope (SEM) ("S-4800", manufactured by JEOL Ltd.) at an acceleration voltage of 5kV. Photographs of the electrophotographic photoreceptor of the present invention were captured at a magnification of 30,000 using a scanner at 12 locations: 50 mm from each end along the longitudinal direction, three locations in the center, and four locations at 90-degree intervals along the circumferential direction. The particles in these photographs were binarized using an image processing and analysis device ("LUZEX AP", manufactured by Nireco Corporation). Let S1 be the area of ​​the particles and S2 be the total area of ​​the non-particle areas. The coverage rate S1 / (S1+S2)(%) was calculated. The above coverage rate calculation was performed for a total of 10 fields of view, and the average of the obtained coverage rates was taken as the particle coverage rate on the surface layer of the electrophotographic photoreceptor.

[0092] <Method for measuring the circularity of particle PAA on the surface layer of an electrophotographic photoreceptor> The surface of the surface layer of the electrophotographic photoreceptor was imaged using a scanning electron microscope (SEM) ("S-4800", manufactured by JEOL Ltd.) at an acceleration voltage of 10kV. Photographs of the electrophotographic photoreceptor of the present invention were captured at a magnification of 30,000 using a scanner at 12 locations: 50mm from each end along the longitudinal direction, three locations in the center, and four locations at 90-degree intervals along the circumferential direction. Furthermore, image processing was performed on the PAA particles in these photographs using an image processing and analysis device ("LUZEX AP", manufactured by Nireco Corporation), and the average circularity across a total of 10 fields of view was calculated and defined as the circularity of the PAA particles.

[0093] <Measurement of film thickness of each layer> Examples , Reference Example, and 、 The film thickness of each layer in the comparative electrophotographic photoreceptor was determined, except for the surface layer and the charge generation layer, using either an eddy current film thickness meter (Fischerscope, manufactured by Fischer Instruments) or by converting the specific gravity from the mass per unit area. The film thickness of the charge generation layer was measured by converting the Macbeth density value of the electrophotographic photoreceptor using a calibration curve previously obtained from the Macbeth density value measured by pressing a spectrophotometer (product name: X-Rite504 / 508, manufactured by X-Rite) against the surface of the electrophotographic photoreceptor and the film thickness measurement value obtained by cross-sectional SEM image observation.

[0094] <Measurement of the relative concentration of each atom on the surface of the surface layer> X-ray photoelectron spectroscopy analysis of the surface layer can be performed specifically as follows. First, five 5mm square sections are cut from randomly selected locations on the surface of the electrophotographic photoreceptor to prepare five observation sample pieces. Next, X-ray photoelectron spectroscopy (XPS) is performed on the surface layer of each observation sample piece. The XPS apparatus and measurement conditions are as follows. Equipment used: ULVAC-FI Quantum 2000 Analysis method: Narrow analysis X-ray source: Al-Kα X-ray conditions: 100μm, 25W, 15kV Photoelectron acquisition angle: 45° PassEnergy: 58.70eV Measurement range: φ100μm Measurements were performed under the above conditions, and the peak originating from the CC bond of the carbon 1s orbital was corrected to 285 eV. Subsequently, a relative sensitivity factor provided by ULVAC-PHIE was applied to the peak area of ​​atoms whose peak tops were detected between 100 eV and 103 eV. The results obtained from five observation samples were averaged, and integration and conversion were performed for the spectral peaks of carbon, oxygen, titanium, and silicon atoms. When the sum of the relative concentrations of carbon (d(C), oxygen (d(O), titanium (Ti), and silicon (d(Si))) was set to 100.0 atomic%, the relative concentrations of carbon (d(C), oxygen (d(O)), titanium (d(Ti), and silicon (d(Si))) were determined. The atomic concentration ratios d(Ti)(atomic%), d(Si)(atomic%), and d(Ti) / d(Si) in the metal oxide were calculated.

[0095] <Calculation of the niobium atom / titanium atom concentration ratio in conductive particles contained in the surface layer of an electrophotographic photoreceptor> A 5mm square sample piece was cut from an electrophotographic photoreceptor and thin sections were prepared by cutting it to a thickness of 200nm at a cutting speed of 0.6mm / s using an ultrasonic ultramicrotome (Leica, UC7). These thin sections were observed in STEM mode on a scanning transmission electron microscope (JEOL, JEM2800) connected to an EDS analyzer (energy-dispersive X-ray spectrometer) at magnifications ranging from 500,000x to 1,200,000x. From the observed cross-sections of conductive particles, the cross-section of the conductive particle with the largest diameter approximately 0.9 to 1.1 times the primary particle size calculated above was visually selected. Subsequently, the constituent elements of the selected conductive particle cross-section were analyzed using an EDS analyzer to collect spectra and create EDS mapping images. Spectrum collection and analysis were performed using an NSS (Thermo Fischer Scientific) analyzer. The collection conditions were an acceleration voltage of 200kV, a probe size of 1.0nm or 1.5nm selected as appropriate to ensure a dead time of 15 to 30, a mapping resolution of 256×256, and 300 frames. EDS mapping images were acquired for 100 cross-sections of conductive particles.

[0096] By analyzing the EDS mapping image obtained in this way, the ratio of niobium atom concentration (atomic %) (same unit as atomic %) to titanium atom concentration (atomic %) is calculated at the particle center and within 5% of the maximum diameter of the measured particle from the particle surface. Specifically, first, the "Line Extraction" button in NSS is pressed to draw a straight line that corresponds to the maximum diameter of the particle, and information on the atomic concentration (atomic %) along the straight line from one surface through the inside of the particle to the other surface is obtained. If the maximum diameter of the particle obtained at this time is less than 0.9 times or more than 1.1 times the primary particle size calculated above, it is excluded from the subsequent analysis. (Only particles with a maximum diameter in the range of 0.9 times or more but less than 1.1 times the primary particle size were analyzed as shown below.) Next, the niobium atom concentration (atomic %) is read at 5% of the maximum diameter of the measured particle from the particle surface on both particle surfaces. Similarly, the "titanium atom concentration (atomic %) at 5% of the maximum diameter of the measured particle from the particle surface" is obtained. Next, using these values, the following formula is used to obtain the "concentration ratio of niobium atoms to titanium atoms at 5% inside the maximum diameter of the measured particle from the particle surface" on both sides of the particle surface. The concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle, from the particle surface, is given by (niobium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface) / (titanium atom concentration (atomic %) within 5% of the maximum diameter of the measured particle from the particle surface).

[0097] Of the two concentration ratios obtained, the one with the smaller value is adopted as the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface" in this invention. Furthermore, the niobium atom concentration (atomic %) and titanium atom concentration (atomic %) were read at the midpoint of the maximum diameter on the aforementioned straight line. Using these values, the "concentration ratio of niobium atoms to titanium atoms in the center of the particle" was obtained from the following formula. The concentration ratio of niobium atoms to titanium atoms in the center of a particle is given by (concentration of niobium atoms in the center of the particle (atomic %)) / (concentration of titanium atoms in the center of the particle (atomic %)). Furthermore, the "concentration ratio calculated by niobium atom concentration / titanium atom concentration at 5% inside the maximum diameter of the measured particle from the particle surface, compared to the concentration ratio calculated by niobium atom concentration / titanium atom concentration at the center of the particle" is (concentration ratio of niobium atoms to titanium atoms at 5% inside the maximum diameter of the measured particle from the particle surface) / (concentration ratio of niobium atoms to titanium atoms at the center of the particle).

[0098] <Method for measuring the relative permittivity ε(A) and ε(NA) of particle A and particles other than particle A> The dielectric properties of particle A and particles other than particle A in this invention are measured by the following method. 0.1 g each of particle A and the other particles of the present invention are weighed and molded into a disc-shaped sample with a diameter of 25 mm and a thickness of 0.15 ± 0.01 mm by applying a load of 20 kPa for 1 minute. The other particles are pre-mixed with particle B and the other particles in the ratio of the amounts used in the example, and then weighed. The sample is mounted on an ARES (manufactured by TA Instruments) equipped with a 25mm diameter dielectric constant measuring jig (electrode). Measurement temperature: 40°C, 250 g / cm³. 2Under a loaded condition, using a 4284A Precision LCR Meter (manufactured by Hewlett-Packard Company), the dielectric constant ε is calculated from the measured values of the storage dielectric constant ε' and loss dielectric constant ε'' of the complex dielectric constant at 100 kHz and a temperature of 40°C, and then divided by the dielectric constant of vacuum to calculate the relative dielectric constant ε(A) and relative dielectric constant ε(NA) respectively by the following formula (7). ε=(ε' 2 +ε'' 2 ) 1 / 2 ···Formula (7)

[0099] [Production of Electrophotographic Photoreceptor] A support, a conductive layer, an undercoat layer, a charge generation layer, a charge transport layer, and a surface layer were produced by the following method. <Preparation of Coating Liquid 1 for Conductive Layer> As a base material, anatase-type titanium oxide having an average primary particle diameter of 200 nm was used, and a titanium-niobium sulfuric acid solution containing 33.7 parts of titanium in terms of TiO2 and 2.9 parts of niobium in terms of Nb2O5 was prepared. 100 parts of the base material was dispersed in pure water to obtain 1000 parts of suspension, which was heated to 60°C. The titanium-niobium sulfuric acid solution and 10 mol / L sodium hydroxide were added dropwise over 3 hours so that the pH of the suspension became 2 to 3. After the entire amount was dropped, the pH was adjusted to around neutral, a polyacrylamide-based flocculant was added to precipitate the solid content. The supernatant was removed, followed by filtration, washing, and drying at 110°C, to obtain an intermediate containing 0.1 wt% of flocculant-derived organic matter in terms of C. This intermediate was fired at 750°C for 1 hour in nitrogen, then fired at 450°C in air to produce titanium oxide particles. The average primary particle diameter of the obtained particles measured by the aforementioned particle diameter measurement method using a scanning electron microscope was 220 nm.

[0100] Subsequently, 50 parts of a phenol resin (monomer / oligomer of phenol resin) as a binder material (trade name: Pryophen J-325, manufactured by DIC, resin solid content: 60%, density after curing: 1.3 g / cm 2 ) was dissolved in 35 parts of 1-methoxy-2-propanol as a solvent to obtain a solution. 60 parts of titanium dioxide particles 1 were added to this solution, and this was placed in a vertical sand mill using 120 parts of glass beads with a number average primary particle size of 1.0 mm as the dispersion medium. Dispersion treatment was carried out for 4 hours under the conditions of dispersion temperature 23±3℃ and rotation speed 1500 rpm (peripheral speed 5.5 m / s) to obtain a dispersion. The glass beads were removed from this dispersion using a mesh. To the dispersion after the glass beads had been removed, 0.01 parts of silicone oil (product name: SH28 PAINT ADDITIVE, manufactured by Toray Dow Corning) as a leveling agent and silicone resin particles (product name: KMP-590, manufactured by Shin-Etsu Chemical Co., Ltd., average primary particle size: 2 μm, density: 1.3 g / cm³) as a surface roughening agent were added. 3 )8 parts were added and stirred, and the conductive layer coating solution 1 was prepared by pressure filtration using PTFE filter paper (product name: PF060, manufactured by Advantec Toyo).

[0101] <Preparation of coating solution 1 for the undercoat layer> 100 parts of rutile-type titanium dioxide particles (average primary particle size: 50 nm, manufactured by Teika) were stirred and mixed with 500 parts of toluene. 3.5 parts of vinyltrimethoxysilane (product name: KBM-1003, manufactured by Shin-Etsu Chemical Co., Ltd.) were added, and the mixture was dispersed for 8 hours using a vertical sand mill with 1.0 mm diameter glass beads. After removing the glass beads, the toluene was removed by vacuum distillation, and the mixture was dried at 120°C for 3 hours to obtain rutile-type titanium dioxide particles surface-treated with an organosilicon compound. When the volume of the obtained titanium dioxide particles was a and the average primary particle size of the titanium dioxide particles was b [μm], a / b = 15.6. The value of a was determined from a microscope image of the cross-section of the electrophotographic photoreceptor after its fabrication, using a field emission scanning electron microscope (FE-SEM, product name: S-4800, manufactured by Hitachi High-Technologies Corporation). A dispersion was prepared by adding 18.0 parts of rutile-type titanium dioxide particles surface-treated with the aforementioned organosilicon compound, 4.5 parts of N-methoxymethylated nylon (product name: Trezin® EF-30T, manufactured by Nagase ChemteX), and 1.5 parts of copolymerized nylon resin (product name: Amiran® ​​CM8000, manufactured by Toray) to a mixed solvent of 90 parts methanol and 60 parts 1-butanol. This dispersion was subjected to a vertical sand milling process using 1.0 mm diameter glass beads for 5 hours, and the glass beads were removed to prepare coating solution 1 for the undercoat layer.

[0102] <Synthesis of phthalocyanine pigments> (Synthesis Example 1) Under a nitrogen flow atmosphere, 1000 ml of α-chloronaphthalene was mixed with 100 g of gallium trichloride and 291 g of orthophthalonitrile, and the mixture was reacted at 200°C for 24 hours. The product was then filtered. The resulting wet cake was heated and stirred with N,N-dimethylformamide at 150°C for 30 minutes, and then filtered. The resulting filtrate was washed with methanol and dried to obtain chlorogallium phthalocyanine pigment in 83% yield. 20 g of chlorogallium phthalocyanine pigment obtained by the above method was dissolved in 500 ml of concentrated sulfuric acid, stirred for 2 hours, and then added dropwise to a mixed solution of 1700 ml of ice-cold distilled water and 660 ml of concentrated ammonia water to reprecipitation. This was thoroughly washed with distilled water and dried to obtain hydroxygallium phthalocyanine pigment.

[0103] <Preparation of coating solution 1 for charge generation layer> 0.5 parts of the hydroxygallium phthalocyanine pigment obtained in Synthesis Example 1, 7.5 parts of N,N-dimethylformamide (product code: D0722, manufactured by Tokyo Chemical Industry Co., Ltd.), and 29 parts of 0.9 mm diameter glass beads were milled using a sand mill (BSG-20, manufactured by AIMEX) at a temperature of 25°C for 24 hours. This was carried out under conditions of the disc rotating at 1500 revolutions per minute. The resulting solution was filtered through a filter (product code: N-NO.125T, pore size: 133 μm, manufactured by NBC Meshtec) to remove the glass beads. 30 parts of N,N-dimethylformamide were added to this solution, and it was filtered again. The filter residue on the filter was thoroughly washed with n-butyl acetate. The washed residue was then vacuum dried to obtain 0.45 parts of hydroxygallium phthalocyanine pigment. The obtained pigment contained N,N-dimethylformamide.

[0104] Next, 20 parts of the hydroxygallium phthalocyanine pigment obtained in the milling process, 10 parts of polyvinyl butyral (product name: S-Rec® BX-1, manufactured by Sekisui Chemical Co., Ltd.), 190 parts of cyclohexanone, and 482 parts of 0.9 mm diameter glass beads were dispersed for 4 hours at a cooling water temperature of 18°C ​​using a sand mill (K-800, manufactured by Igarashi Machinery Manufacturing Co., Ltd. (now AIMEX), disc diameter 70 mm, number of discs 5). This was carried out under conditions where the disc rotated at 1800 revolutions per minute. The glass beads were removed from this dispersion, and 444 parts of cyclohexanone and 634 parts of ethyl acetate were added to prepare coating solution 1 for the charge generation layer.

[0105] <Preparation of coating solution 1 for charge transport layer> Next, the following materials were prepared to create a mixed solvent. • Orthoxylene 25 parts by mass Methyl benzoate 25 parts by mass • Dimethoxymethane 25 parts by mass Furthermore, the following materials were dissolved in the mixed solvent to prepare the coating solution 1 for the charge transport layer. • 5 parts by mass of a charge-transporting material (hole-transporting material) represented by the following structural formula (C-1) • 5 parts by mass of a charge-transporting substance (hole-transporting substance) represented by the following structural formula (C-2) • Polycarbonate (product name: Yupiron® Z400, manufactured by Mitsubishi Engineering Plastics Corporation) 10 parts by mass [ka] [ka]

[0106] (Example 1 of fabrication of a surface layer containing particles) The materials shown in Table 1 were prepared as particle A and particle B. [Table 1]

[0107] (Examples of manufacturing anatase-type titanium dioxide particles 1-3) Anatase-type titanium dioxide particles can be produced by the known sulfuric acid method. In the production of titanium dioxide, a solution containing titanium sulfate and titanyl sulfate as titanium compounds is heated and hydrolyzed to produce a hydrated titanium dioxide slurry, which is then dehydrated and calcined. This yields anatase-type titanium dioxide with a degree of anatase of nearly 100%. In the method described above, anatase-type titanium dioxide particles 1-3 were prepared by controlling the solution concentration of titanyl sulfate. Table 2 shows the particle sizes.

[0108] (Example of manufacturing anatase-type titanium dioxide particles 4) Niobium sulfate (a water-soluble niobium compound) was added to a hydrated titanium dioxide slurry obtained by hydrolysis of an aqueous solution of titanyl sulfate. The amount of niobium sulfate added was 1.8% by mass relative to the amount of titanium in the slurry (in terms of titanium dioxide). An aqueous solution of titanyl sulfate was hydrolyzed with 1.8% by mass of niobium sulfate as niobium ions to obtain a hydrated titanium dioxide slurry. Next, the hydrated titanium dioxide slurry containing niobium ions was dehydrated and calcined at a temperature of 1000°C. This yielded anatase-type titanium dioxide particles 4 containing 1.8% by mass of niobium. The particle sizes are shown in Table 2.

[0109] [Table 2]

[0110] <Manufacturing of conductive particles> (Manufacturing of conductive particles 1) Niobium(V) hydroxide was dissolved in concentrated sulfuric acid and mixed with an aqueous solution of titanium sulfate to prepare an acidic mixture of niobium salt and titanium salt (hereinafter referred to as "titanium-niobium mixture"). 100 parts of anatase-type titanium dioxide particles 1 were weighed out, dispersed in water as uncoated particles to form a suspension, and heated to 67°C with stirring as a 1000-part aqueous suspension. While maintaining a pH of 2.5, a titanium-niobium mixture containing 337 g / kg of Ti and 10.3 g / kg of Nb, relative to the weight of anatase-type titanium dioxide particles 1, and an aqueous sodium hydroxide solution were simultaneously added. Furthermore, a titanium-niobium solution was prepared by dissolving 3 parts of niobium pentachloride (NbCl5) in 100 parts of 11.4 mol / l hydrochloric acid, and mixing this solution with 200 parts of titanium sulfate solution containing 12.0 parts of titanium to obtain a titanium-niobium solution (with a weight ratio of niobium atoms to titanium atoms in the solution of 1.0 / 20.0). This titanium-niobium solution and a 10.7 mol / l sodium hydroxide aqueous solution were simultaneously added dropwise (parallel addition) to the above aqueous suspension over 3 hours so that the pH of the aqueous suspension would be 2 to 3. After the addition was complete, the suspension was filtered and washed, and dried at 110°C for 8 hours. The dried material was calcined together with organic matter at 725°C for 1 hour in a nitrogen atmosphere to obtain niobium atom-containing titanium oxide particles 1 in which niobium atoms were unevenly distributed near the surface.

[0111] Next, I prepared the following materials. • Niobium atom-containing titanium oxide particles 1 100.0 parts • Surface treatment agent 1 (compound represented by the following formula (S-1)) (product name: trimethoxypropylsilane, manufactured by Tokyo Chemical Industry Co., Ltd.) 6.0 parts [ka] • Toluene 200.0 parts These were mixed, stirred in a stirring device for 4 hours, filtered, washed, and then heat-treated at 130°C for 3 hours to obtain conductive particles 1. Various physical properties are shown in Table 3.

[0112] <Preparation of conductive particles 2-6> Conductive particles 2-6 were prepared in the same manner as conductive particle 1, except that the type of core material particle used and the weight ratio of niobium atoms to titanium atoms in the titanium-niobium mixture relative to the core material were changed as shown in Table 3. The various physical properties of the obtained conductive particles 2-6 are shown in Table 3.

[0113] [Table 3] Surface treatment agent 1: Trimethoxy(propyl)silane (manufactured by Tokyo Chemical Industry Co., Ltd.) Surface treatment agent 2: Dimethoxy(methyl)-n-octylsilane (manufactured by Tokyo Chemical Industry Co., Ltd.) Front treatment agent 3: Decyltrimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) In the table, C represents the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface," and D represents the "concentration ratio of niobium atoms to titanium atoms in the center of the particle." In other words, C / D is the "concentration ratio calculated by niobium atom concentration / titanium atom concentration within 5% of the maximum diameter of the measured particle from the particle surface to the concentration ratio calculated by niobium atom concentration / titanium atom concentration in the center of the particle as described above."

[0114] <Preparation of coating solution 1 for the surface layer> Particle A: Silica particles ("QSG-170", manufactured by Shin-Etsu Chemical Co., Ltd.) 2.5 parts by mass Particle B: Silica particles ("QSG-80", manufactured by Shin-Etsu Chemical Co., Ltd.) 2.5 parts by mass 0.90 parts by mass of monomer 1 having polymerizable functional groups (structural formula (2-1) above) 0.90 parts by mass of monomer 2 having polymerizable functional groups (structural formula (3-1) above) Siloxane-modified acrylic compound (product name: Cymac US270, manufactured by Toagosei Co., Ltd.) 0.1 part by mass 1-Propanol 100.0 parts by mass Cyclohexane 100.0 parts by mass The above components were mixed and stirred in a stirring device for 6 hours to prepare coating solution 1 for the surface layer.

[0115] <Preparation of coating solutions 2-68 for the surface layer> Surface layer coating solutions 2 to 68 were prepared in the same manner as in the preparation of surface layer coating solution 1, except that the types and amounts of particles A, B, and other particles were changed as shown in Table 4.

[0116] <Preparation of coating solution 69 for the surface layer> Particle A: Silica particles ("QSG-170", manufactured by Shin-Etsu Chemical Co., Ltd.) 2.5 parts by mass Particle B: Silica particles ("QSG-80", manufactured by Shin-Etsu Chemical Co., Ltd.) 2.5 parts by mass Polycarbonate (product name: Yupiron Z400, manufactured by Mitsubishi Engineering Plastics Corporation, density 1.2 g / cm³) 3 ) 1.8 parts by mass Siloxane-modified acrylic compound (product name: Cymac US270, manufactured by Toagosei Co., Ltd.) 0.1 part by mass Toluene 200.0 parts by mass The above components were mixed and stirred in a stirring device for 6 hours to prepare a coating solution 69 for the surface layer.

[0117] <Preparation of surface layer coating solution 70> 4 parts by mass of anatase-type titanium dioxide particles Dipentaerythritol 10 parts by mass 1-Hydroxycyclohexyl(phenyl)methanone (IRGACURE184, manufactured by Ciba Specialty Chemicals) 1 part by mass n-propyl alcohol 40 parts by mass The above components were mixed and dispersed using a sand mill for 2 hours to prepare a coating solution 70 for the surface layer.

[0118] <Preparation of coating solution 71 for the surface layer> 10 parts by mass of methanol Tin oxide (number average primary particle size: 100 nm) 5 parts by mass The mixture was dispersed at room temperature for 30 minutes using a US homogenizer. Next, to the above dispersion 3-Methacryloxypropyltrimethoxysilane (KBM-503, manufactured by Shin-Etsu Chemical Co., Ltd.) 0.25 parts by mass Toluene 10 parts by mass The mixture was added and stirred at room temperature for 60 minutes. After removing the solvent with an evaporator, the mixture was heated at 120°C for 60 minutes to obtain tin oxide particles 1 surface-treated with a reactive surface treatment agent. Next, 15 parts by mass of surface-treated tin oxide particles 2-Butanol 40 parts by mass The mixture was dispersed at room temperature for 60 minutes using a US homogenizer. Next, 0.15 g of a linear silicone surface treatment agent ("KF-9908," manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and the mixture was dispersed using a US homogenizer at room temperature for 60 minutes. After dispersion, the solvent was evaporated at room temperature, and the mixture was dried at 120°C for 60 minutes to produce surface-treated particles 1. Trimethylolpropane trimethacrylate 120 parts by mass Surface-treated particles 1: 100 parts by mass Polymerization initiator (manufactured by BASF Japan Ltd., IRGACURE® 819) 10 parts by mass 2-Butanol 400 parts by mass The above components were mixed to prepare a coating solution 71 for the surface layer.

[0119] <Preparation of coating solution 72 for the surface layer> Trimethylolpropane triacrylate (manufactured by Tokyo Chemical Industry Co., Ltd.) 70 parts by mass Alumina particles AA-05 (manufactured by Sumitomo Chemical Co., Ltd., average primary particle size of 500 nm) 20 parts by mass Zinc oxide particles (Aluminum-doped. Average primary particle size is 165 nm) 10 parts by mass 1-Hydroxycyclohexylphenyl ketone (IRGACURE184, manufactured by Ciba Specialty Chemicals) 3.5 parts by mass Isopropyl alcohol 860 parts by mass The above components were mixed to obtain a coating solution 72 for the surface layer.

[0120] <Preparation of coating solution 73 for the surface layer> tin oxide (Manufactured by CIK Nanotech Co., Ltd., number average primary particle size: 20 nm, volume resistivity: 1.05 × 10⁻⁶) 5 (Ω ·cm)) 100 parts by mass 3-Methacryloxypropyltrimethoxysilane ("KBM-503" manufactured by Shin-Etsu Chemical Co., Ltd.) 30 parts by mass Toluene 150 parts by mass Isopropyl alcohol 150 parts by mass Zirconia beads 300 parts by mass The above components were mixed and stirred in a sand mill at 40°C and a rotation speed of 1500 rpm. The tin oxide particles were then surface-treated with a surface treatment agent containing reactive organic groups. Furthermore, the above-treated mixture was removed, placed in a Henschel mixer, stirred at a rotation speed of 1500 rpm for 15 minutes, and then dried at 120°C for 3 hours to obtain surface-treated tin oxide particles 2. next, 50 parts by mass of surface-treated tin oxide particles Silica particles ("Aerosil® RX-50", manufactured by Nippon Aerosil Co., Ltd.) 10 parts by mass Pentaerythritol 100 parts by mass 15 parts by mass of the charge-transporting material (hole-transporting material) represented by the above structural formula (C-1) 320 parts by mass of sec-butyl alcohol 80 parts by mass of tetrahydrofuran The components listed above were mixed and dispersed in a sand mill at a rotational speed of 1500 rpm to obtain a coating liquid 73 for the surface layer.

[0121] [Table 4]

[0122] <Example of fabrication of electrophotographic photoreceptor 1> (Support) An aluminum cylinder with a diameter of 24 mm and a length of 257 mm was used as the support (cylindrical support). (Conductive layer) A conductive layer with a thickness of 22 μm was formed by immersion coating of the conductive layer coating liquid 1 onto the above-mentioned support, and then curing the coating by heating it at 150°C for 30 minutes. (Underwater layer) The undercoating liquid 1 for the undercoat layer was applied to the conductive layer described above by immersion to form a coating film, and the coating film was heated at 100°C for 10 minutes to cure it, thereby forming an undercoat layer with a thickness of 1.8 μm. (Charge generation layer) A charge generation layer with a thickness of 0.20 μm was formed by immersion coating liquid 1 for the charge generation layer onto the aforementioned undercoat layer to form a coating film, and then heating and drying the coating film at 100°C for 10 minutes. (charge transport layer) A charge transport layer coating solution 1 was applied to the charge generation layer by immersion to form a coating film, and the coating film was heated and dried at 120°C for 30 minutes to form a charge transport layer with a thickness of 21 μm. (Surface layer) The surface layer coating liquid 1 was immersed and applied onto the charge transport layer to form a coating film, and the coating film was heated at 50°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 2.0 seconds under the conditions of an acceleration voltage of 65 kV and a beam current of 5.0 mA. The dose was 15 kGy. After that, the temperature of the coating film was raised to 120°C under a nitrogen atmosphere. The oxygen concentration from electron beam irradiation to the subsequent heat treatment was 10 ppm. Next, the coating film was allowed to cool naturally in air until its temperature reached 25°C, and then heat-treated for 30 minutes under conditions that brought the coating film temperature to 120°C to form a surface layer with a thickness of 1.0 μm. The physical properties of the resulting electrophotographic photoreceptor are shown in Table 5.

[0123] <Examples of fabrication of electrophotographic photoreceptors 2-68> Electrophotographic photoreceptors 2 to 68 were fabricated in the same manner as electrophotographic photoreceptor 1, except that the surface layer coating solution 1 was changed according to the conditions in Table 5. The physical properties of the obtained electrophotographic photoreceptors 1 to 68 are shown in Table 5.

[0124] <Example of fabrication of electrophotographic photoreceptor 69> In the preparation of electrophotographic photoreceptor 1, electrophotographic photoreceptor 69 was prepared in the same manner as electrophotographic photoreceptor 1, except that surface layer coating solution 1 was changed to surface layer coating solution 69. The physical properties of the obtained electrophotographic photoreceptor are shown in Table 5.

[0125] <Example of fabrication of electrophotographic photoreceptor 70> In the fabrication of the electrophotographic photoreceptor 1, the process is carried out in the same manner as for the electrophotographic photoreceptor 1 up to the formation of the charge transport layer. After that, the surface layer coating solution 70 is applied to the charge transport layer, and then ultraviolet light is applied using a metal halide lamp at 16 mW / cm². 2 Irradiation for 1 minute (cumulative light intensity 960 mJ / cm²) 2 The electrophotographic photoreceptor 70 was fabricated using the following method. The physical properties of the obtained electrophotographic photoreceptor 70 are shown in Table 5.

[0126] <Example of fabrication of electrophotographic photoreceptor 71> In the fabrication of the electrophotographic photoreceptor 1, the process is carried out in the same manner as for the electrophotographic photoreceptor 1 up to the formation of the charge transport layer. After that, the surface layer coating liquid 71 is applied to the charge transport layer, and then ultraviolet light is irradiated for 1 minute using a metal halide lamp (irradiation intensity: 15 mW / cm²). 2 The electrophotographic photoreceptor 71 was fabricated by drying it at 80°C for 120 minutes. The physical properties of the obtained electrophotographic photoreceptor 71 are shown in Table 5.

[0127] <Example of fabrication of electrophotographic photoreceptor 72> In the fabrication of the electrophotographic photoreceptor 1, the process is carried out in the same manner as for the electrophotographic photoreceptor 1 up to the formation of the charge transport layer. After that, the surface layer coating liquid 72 is applied to the charge transport layer, and then the photoreceptor is irradiated with a metal halide lamp at an intensity of 500 mW / cm². 2 The electrophotographic photoreceptor 72 was fabricated by irradiating it with ultraviolet light for 20 seconds and drying it at 130°C for 30 minutes. The physical properties of the obtained electrophotographic photoreceptor 72 are shown in Table 5.

[0128] <Example of fabrication of electrophotographic photoreceptor 73> In the fabrication of the electrophotographic photoreceptor 1, the process is carried out in the same manner as for the electrophotographic photoreceptor 1 up to the formation of the charge transport layer. After that, the surface layer coating solution 73 is applied to the charge transport layer, and then ultraviolet light is applied using a metal halide lamp at 16 mW / cm². 2 Irradiation for 1 minute (cumulative light intensity 960 mJ / cm²) 2 ) and an electrophotographic photoreceptor 73 was fabricated. The physical properties of the obtained electrophotographic photoreceptor 73 are shown in Table 5.

[0129] [Table 5-1] [Table 5-2]

[0130] In the table, C represents the "concentration ratio of niobium atoms to titanium atoms within 5% of the maximum diameter of the measured particle from the particle surface," and D represents the "concentration ratio of niobium atoms to titanium atoms in the center of the particle." In other words, C / D is the "concentration ratio calculated by niobium atom concentration / titanium atom concentration within 5% of the maximum diameter of the measured particle from the particle surface to the concentration ratio calculated by niobium atom concentration / titanium atom concentration in the center of the particle as described above."

[0131] <Example of toner particle 1 manufacturing> (Preparation of aqueous medium 1) In a reaction vessel equipped with a stirrer, thermometer, and reflux tubing, 650.0 parts of deionized water and 14.0 parts of sodium phosphate (manufactured by Rasa Industries, dodecahydrate) were added, and the mixture was kept at 65°C for 1.0 hour while purging with nitrogen. Using a TK homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.), a calcium chloride aqueous solution, prepared by dissolving 9.2 parts of calcium chloride (dihydrate) in 10.0 parts of ion-exchanged water, was added all at once while stirring at 15,000 rpm to prepare an aqueous medium containing a dispersion stabilizer. Furthermore, 10% by mass hydrochloric acid was added to the aqueous medium to adjust the pH to 5.0 to obtain aqueous medium 1.

[0132] (Preparation of polymerizable monomer compositions) • Styrene 60.0 parts by mass CI Pigment Blue 15:3 6.5 parts by mass The aforementioned materials were placed in an attritor (manufactured by Mitsui Miike Chemical Machinery Co., Ltd.), and then dispersed using 1.7 mm diameter zirconia particles at 220 rpm for 5.0 hours. After that, the zirconia particles were removed to prepare a colorant dispersion. on the other hand, • Styrene: 20.0 parts by mass • n-butyl acrylate: 20.0 parts by mass • Crosslinking agent (divinylbenzene): 0.3 parts by mass • Saturated polyester resin: 5.0 parts by mass (polycondensate of propylene oxide-modified bisphenol A (2-mol adduct) and terephthalic acid (molar ratio 10:12), having a glass transition temperature (Tg) of 68°C, a weight average molecular weight (Mw) of 10000, and a molecular weight distribution (Mw / Mn) of 5.12) • Fischer-Tropsch wax (melting point: 78°C): 7.0 parts by mass The material was added to the above colorant dispersion, heated to 65°C, then uniformly dissolved and dispersed at 500 rpm using a T.K. Homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to prepare a polymerizable monomer composition.

[0133] (Granulation step) The temperature of aqueous medium 1 was adjusted to 70°C, and while maintaining the rotation speed of the T.K. Homomixer at 15000 rpm, the polymerizable monomer composition was charged into aqueous medium 1, and 10.0 parts by mass of t-butyl peroxypivalate serving as a polymerization initiator was added. Granulation was carried out for 10 minutes while maintaining 15000 rpm with the stirring device as it was.

[0134] (Polymerization step and distillation step) After the granulation step, the stirrer was changed to a propeller stirring blade, and polymerization was carried out for 5.0 hours while maintaining 70°C with stirring at 150 rpm. Polymerization was further carried out by raising the temperature to 85°C and holding for 2.0 hours. Thereafter, the reflux tube of the reaction vessel was replaced with a cooling tube, and the obtained slurry was heated to 100°C to perform distillation for 6 hours, unreacted polymerizable monomers were distilled off, and toner particle dispersion liquid 1 was obtained.

[0135] (Filtration step, washing step, drying step, and classification step) Hydrochloric acid was added to the obtained toner particle dispersion liquid 1 to adjust the pH to 1.4 or lower, the dispersion stabilizer was dissolved, and filtration, washing, drying, and classification were performed to obtain toner particles 1. The number average particle diameter (D1) of toner particles 1 was 6.2 µm, and the weight average particle diameter (D4) was 6.7 µm.

[0136] <Production Example of Toner 1> 100.0 parts by mass of the obtained toner particles 1, and 100.0 parts by mass of silica fine particles (hydrophobized with hexamethyldisilazane, number average particle diameter of primary particles: 8 nm, BET specific surface area: 160 m 2 / g) were mixed with 1.0 part by mass using a Henschel mixer (manufactured by Mitsui Miike Machinery Co., Ltd.). The obtained mixture was sieved through a mesh with an opening of 75 µm to obtain Toner 1.

[0137] [Evaluation Method] Examples The particles contained in the surface layer include particle A, and 、 Comparative Examples were evaluated by the following evaluation methods. <Evaluation of Transferability (Evaluation Method 1)> A modified commercially available Canon laser beam printer i-SENSYS LBP 673 Cdw was used. The modification was that the applied bias in the transfer step can be changed by modifying the main body of the evaluation apparatus and the software.

[0138] The toner in the cyan cartridge of the evaluation apparatus i-SENSYS LBP 673 Cdw is removed, and a required amount of Toner 1 is loaded therein. The refilled cyan toner cartridge was left to stand for 24 hours in a normal temperature and normal humidity environment (25°C, 50% RH; hereinafter also referred to as N / N). After being left to stand for 24 hours in the environment, the cyan toner cartridge was attached to the above-mentioned apparatus, and under the N / N environment, 50 mm margins were provided on the left and right sides, and an image with a printing rate of 2.0% was output on up to 30 sheets of A4 paper in the landscape orientation. The paper used was plain paper CS-680 (68 g / m 2 ) (manufactured by Canon Marketing Japan Inc.). Next, a solid image with a width of 30 mm was output in the longitudinal direction of the sheet on plain paper CS-680, the output during solid image formation was stopped, and residual toner on the electrophotographic photoreceptor after transfer was collected using a transparent polyester adhesive tape (Polyester Tape 5511, manufactured by Nichiban). The density of residual toner was measured using the following method. A transparent tape containing residual toner peeled from the surface of an electrophotographic photoreceptor and a new transparent tape were each attached to high-whiteness paper (GFC081 Canon). The density D1 of the transparent tape containing the residual toner and the density D0 of the new transparent tape were then measured using an X-Rite color reflectance densitometer (X-rite 500 Series). The difference "D1-D0" obtained from the measurement was defined as the concentration of the remaining toner after transfer. A smaller value for the remaining toner after transfer indicates less toner remaining. The following criteria were used for evaluation. The obtained transcription residue concentrations were ranked on a five-point scale from A to E based on the following standards. Of the rankings, A to D were considered to indicate that the effects of the present invention were evident. The evaluation results are shown in Table 6. (Evaluation Criteria) A: Transcription residue concentration is less than 0.02 B: Transcription residue concentration is 0.02 or higher but less than 0.05 C: Transcription residue concentration is 0.05 or higher and less than 0.10 D: Transcription residue concentration is 0.10 or higher

[0139] <Evaluation of transferability under durable conditions (Evaluation method 2)> As part of the durability evaluation, after performing the taping evaluation of residual toner in the <Transferability Evaluation> described above, under N / N conditions, an image with a print density of 2.0% was printed in the center of an A4 sheet with a 50mm margin on both sides, up to 5000 copies. Then, the residual toner was evaluated by taping in the same manner as in the <Transferability Evaluation (Evaluation Method 1)> described above. The same evaluation criteria were also used.

[0140] <Evaluation of sloppiness (Evaluation method 3)> As part of the durability evaluation, the modified machine was subjected to a 30°C, 80% RH environment. After printing 10,000 character images with a print ratio of 1%, a halftone (20H) image was formed, and the roughness (density uniformity) of this image was evaluated based on the following criteria. The paper used was plain paper CS-680 (68g / m²). 2(Canon Marketing Japan Inc.) was used. Note that a 20H image is a value that represents 256 gradations in hexadecimal, and is a halftone image where 00H is solid white (no image) and FFH is solid black (full image). The following criteria were used to evaluate the roughness of the surface. Density measurements were taken at 20 locations, and the uniformity of the surface was determined based on the difference between the maximum and minimum density values ​​(density uniformity). The density was measured using an X-Rite color reflectance densitometer (X-rite 500 Series). (Evaluation Criteria) A: Concentration uniformity is less than 0.04 B: Concentration uniformity is 0.04 or higher and less than 0.06 C: Concentration uniformity is 0.06 or higher and less than 0.08. D: Concentration uniformity is 0.08 or higher

[0141] <Evaluation of the change in endurance concentration (Evaluation method 4)> As part of the durability evaluation, the modified machine was subjected to a durability test under conditions of 30°C and 80% RH, and the density changes during the durability test were evaluated. An original image with five 20mm square solid black patches placed within the development zone was printed, and the development bias was set so that the initial reflectance density was 1.3. Next, a durability test was conducted by printing 10,000 text images with a print ratio of 1%. The paper used was plain paper CS-680 (68g / m²). 2 Canon Marketing Japan Inc. was used. Durability was evaluated by comparing the density difference between the initial image density and the image density after the durability test, using the 5-point average density of the solid black patch. Image density was measured relative to the white areas of the original image using a Macbeth RD918 reflectance densitometer (manufactured by Macbeth). (Evaluation Criteria) A: Concentration difference is less than 0.10 B: Concentration difference is 0.10 or more but less than 0.15 C: Concentration difference is 0.15 or more and less than 0.20 D: Concentration difference is 0.20 or greater The results are shown in Table 6 below.

[0142] [Table 6]

[0143] The disclosure of the present embodiment includes the following configurations. (Configuration 1) An electrophotographic photoreceptor having a surface layer containing particles and a binder resin, the particle A is a silica particle, the the particles contained in the surface layer 、 having a plurality of peaks in a number-based particle size distribution, among the plurality of peaks having a peak top of 20 nm or more, a peak having the maximum frequency of the peak top is defined as a first peak 、 the among the plurality of peaks having a peak top of 20 nm or more, a peak whose peak top frequency is the second highest after that of the first peak is defined as a second peak, when, of the first peak and the second peak, the peak having a larger particle size value at the peak top is designated as peak PEA, the particle size DA at the peak top of the peak PEA 、 is within the range of 80 nm or more and 300 nm or less, among the particles contained in the surface layer, particles having a particle size within the range of DA ± 20 nm are designated as particles PAA 、 the when a convex portion derived from the particle PAA and having a height within the range of 10 nm or more and 300 nm or less is defined as a convex portion CA 、 the the convex portions CA are arranged on the surface of the surface layer, when the surface layer is viewed from above 、 the the average value of the inter-center-of-gravity distances of the convex portions CA is 、 150 nm or more and 500 nm or less, 、 , the standard deviation of the inter-center-of-gravity distances of the convex portions CA is 250 nm or less, the surface layer viewed from above, When the area occupied by the particles on the surface of the surface layer is S1, and the area occupied by other particles is S2, 、 S 1 / (S1+S2) 、 Between 0.70 and 1.00 when, in a cross-section of the surface layer, T is defined as the average value of the film thickness of the surface layer at a portion not containing the particle PAA, said DA and said T satisfy the following formula (1): DA>T ···Formula (1) that satisfies the above-mentioned , An electrophotographic photoreceptor characterized by the following features. (composition 2 ) Of the first and second peaks, the peak with the smaller particle size value at the peak top is defined as Peak PEB. The particle size of the peak top of the peak PEB is DB. DB < T ···Formula (2) At that time, The DB and in 1 T 、 The following formula (2) : DB / DA > 1 / 10 ···Formula (3) Configuration that satisfies the above-mentioned The electrophotographic photoreceptor described. (composition 3 ) The DA and DB 、 The following formula (3) : 0<d(Ti)≦ 2.0 ···Formula (4) Configuration that satisfies 2 The electrophotographic photoreceptor described above. (composition 4 ) The ratio of the number of protrusions CA to the total number of protrusions on the surface of the surface layer is 90% or more, configuration 1~ 3 An electrophotographic photoreceptor as described in any one of the following. (composition 5 ) The full width at half maximum of the aforementioned peak PEA is 、 The configuration is between 20nm and 50nm. 4 An electrophotographic photoreceptor as described in any one of the following. (composition 6 ) The maximum height difference Rz of the surface layer is 100 nm or more and 400 nm or less, configuration 1~ 5 An electrophotographic photoreceptor as described in any one of the following. (composition 7 ) The circularity of the aforementioned particle PAA is 0.950 or greater, configuration 1~ 6 An electrophotographic photoreceptor as described in any one of the following. (composition 8 ) The surface layer contained d(Si)≦ 15.0 ···Formula (5) The relative permittivity ε(A) of particle A is 、 It is 5 or less, The relative permittivity ε(NA) of particles other than particle A contained in the surface layer is 、 ε(A) is 5 or greater 0.01≦d(Ti) / d(Si)≦ 1.0 ···Formula (6) , Configuration 1~ 7 An electrophotographic photoreceptor as described in any one of the following. (composition 9 ) The particles other than the PAA particles contained in the surface layer are conductive particles obtained by treating the surface of metal oxide particles with a Si-containing compound. In X-ray photoelectron spectroscopy analysis, when the sum of the relative concentrations of carbon atoms d(C), oxygen atoms d(O), titanium atoms d(Ti), and silicon atoms d(Si), as determined by X-ray photoelectron spectroscopy, is set to 100.0 atomic%, the values ​​of d(Ti) (atomic%) and d(Si) (atomic%) are given by the following equations (4) to (6). : ​ ​ ​ Configuration that satisfies 8 The electrophotographic photoreceptor described above. (composition 10 ) The conductive particles are configured such that, in energy-dispersive X-ray analysis (EDS analysis) connected to a scanning transmission electron microscope (STEM), the niobium atom / titanium atom concentration ratio in the area from the surface of the conductive particles to 5% inside the maximum diameter of the conductive particles is 2.0 or greater, relative to the niobium atom / titanium atom concentration ratio in the center of the conductive particles. 9 The electrophotographic photoreceptor described above. (composition 11 ) Configuration 1~ 10 A process cartridge characterized by integrally supporting an electrophotographic photoreceptor as described in any one of the above, 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 main body of an electrophotographic apparatus. (composition 12 ) Configuration 1~ 10 An electrophotographic apparatus characterized by comprising an electrophotographic photoreceptor as described in any one of the above, a charging means, an exposure means, a developing means, and a transfer means. [Explanation of symbols]

[0144] 100 Electrophotographic devices a, b, c, d Image forming section 1a, 1b, 1c, 1d Electrophotographic photoreceptor 2a, 2b, 2c, 2d Charging rollers 3a, 3b, 3c, 3d exposure means 4a, 4b, 4c, 4d developing means 5a, 5b, 5c, 5d Static elimination means 41a, 41b, 41c, 41d Developing means 10 Intermediate transfer belt 11 Drive rollers 12 tension rollers 13 Opposing rollers 14a, 14b, 14c, 14d Metal rollers 15. Secondary transfer roller 17. Belt cleaning method 30 Fixing means 50 Paper feeding means P Transfer Material 101 Support 102 Lower layer 103 Charge generation layer 104 Charge transport layer 105 Surface layer 106 Insulating particles 107 Conductive particles 108 Binding resin 31 The center of the conductive particle 32 Near the surface of conductive particles 33. Electron beams used to analyze the core of conductive particles. 34. Electron beam analysis of conductive particles, from the surface to 5% inside the primary particle size. 201 First Peak 202 Second Peak

Claims

1. An electrophotographic photoreceptor having a surface layer containing particles and a binder resin, The particles contained in the surface layer include particle A, The particle A is a silica particle, The particles contained in the surface layer have multiple peaks in the particle size distribution based on the number of particles, Among the multiple peaks, the peak with the highest frequency of peak tops, where the peak top is 20 nm or greater, is designated as the first peak. Among the multiple peaks, the peak whose peak top is 20 nm or more is designated as the second peak, which has the second highest frequency of peak tops after the first peak. When the peak with the larger particle size value at the top of the first and second peaks is defined as peak PEA, The particle size DA at the peak top of the peak PEA is within the range of 80 nm to 300 nm. Of the particles contained in the surface layer, those with a particle size in the range of DA ± 20 nm are defined as particle PAA. When a protrusion originating from the particle PAA and having a height within the range of 10 nm to 300 nm is defined as protrusion CA, The protrusion CA is arranged on the surface of the surface layer, When the surface layer is viewed from above, The average distance between the centroids of the convex portion CA is 150 nm or more and 500 nm or less. The standard deviation of the distance between the centroids of the convex portion CA is 250 nm or less. When the surface layer is viewed from above, and the area occupied by the particles on the surface of the surface layer is denoted as S1, and the area occupied by other particles is denoted as S2, S1 / (S1+S2) is between 0.70 and 1.00, When the average thickness of the surface layer in the portion that does not contain the PAA particles in the cross-section of the surface layer is taken as T, The DA and T are given by the following formula (1): DA>T...Formula (1) Satisfying An electrophotographic photoreceptor characterized by the following features.

2. Of the first and second peaks, the peak with the smaller particle size value at the peak top is defined as peak PEB. When the particle size at the peak top of the peak PEB is denoted as DB, The DB and the T are given by the following formula (2): DB<T...Formula (2) An electrophotographic photoreceptor according to claim 1, satisfying the requirements.

3. The DA and DB are given by the following formula (3): DB / DA>1 / 10...Formula (3) An electrophotographic photoreceptor according to claim 2, satisfying the requirements.

4. The electrophotographic photoreceptor according to claim 1, wherein the ratio of the number of protrusions CA to the total number of protrusions present on the surface of the surface layer is 90% or more.

5. The electrophotographic photoreceptor according to claim 1, wherein the full width at half maximum of the peak PEA is 20 nm or more and 50 nm or less.

6. The electrophotographic photoreceptor according to claim 1, wherein the maximum height difference Rz of the surface layer is 100 nm or more and 400 nm or less.

7. The electrophotographic photoreceptor according to claim 1, wherein the circularity of the particle PAA is 0.950 or greater.

8. The relative permittivity ε(A) of the particles A contained in the surface layer is 5 or less. The relative permittivity ε(NA) of particles other than particle A contained in the surface layer is 5 or more greater than ε(A). The electrophotographic photoreceptor according to claim 1.

9. The particles other than the PAA particles contained in the surface layer are conductive particles obtained by treating the surface of metal oxide particles with a Si-containing compound. In X-ray photoelectron spectroscopy analysis, when the sum of the relative concentrations of carbon atoms d(C), oxygen atoms d(O), titanium atoms d(Ti), and silicon atoms d(Si), as determined by X-ray photoelectron spectroscopy, is 100.0 atomic%, the values ​​of d(Ti) (atomic%) and d(Si) (atomic%) are given by the following equations (4) to (6): 0<d(Ti)≦2.0...Formula (4) d(Si)≦15.0...Formula (5) 0.01≦d(Ti) / d(Si)≦1.0...Formula (6) Satisfying The electrophotographic photoreceptor according to claim 8.

10. The electrophotographic photoreceptor according to claim 9, wherein, in energy-dispersive X-ray analysis (EDS analysis) connected to a scanning transmission electron microscope (STEM), the niobium atom / titanium atom concentration ratio in the area from the surface of the conductive particle to 5% inside the maximum diameter of the conductive particle is 2.0 or more, relative to the niobium atom / titanium atom concentration ratio in the center of the conductive particle.

11. A process cartridge characterized by integrally supporting an electrophotographic photoreceptor according to any one of claims 1 to 10 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 main body of an electrophotographic apparatus.

12. An electrophotographic apparatus characterized by comprising an electrophotographic photoreceptor according to any one of claims 1 to 10, a charging means, an exposure means, a developing means, and a transfer means.

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