Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that suppresses both residual potential accumulation and leakage current, and exhibits excellent charge retention. [Solution] An electrophotographic photoreceptor comprising a conductive substrate, a first undercoat, a second undercoat, and a photosensitive layer in this order, wherein the first undercoat contains at least one electron-transporting material selected from the group consisting of a compound represented by a specific formula (1), a compound represented by a specific formula (2), and a compound represented by the following formula (3), and a binder resin, and the silica particle content in the first undercoat is 0% by mass or 5% by mass or less, and the second undercoat contains at least one electron-transporting material selected from the group consisting of a compound represented by a specific formula (1), a compound represented by a specific formula (2), and a compound represented by the following formula (3), and silica particles and a binder resin, and the silica particle content in the second undercoat is greater than the silica particle content in the first undercoat. JPEG2026058233000027.jpg3265

Description

[Technical Field]

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

[0002] Patent Document 1 discloses an electrophotographic photoreceptor comprising an intermediate layer between a conductive substrate and a photosensitive layer, characterized in that the intermediate layer contains hydrophobic silica fine particles.

[0003] Patent Document 2 discloses an electrophotographic photoreceptor in which a support, an underlayer, a charge generation layer, and a hole transport layer are laminated in this order, wherein the underlayer contains a polymer of a composition comprising an electron transport substance having polar groups selected from the group consisting of hydroxyl groups, thiol groups, amino groups, carboxyl groups, and methoxy groups, and a crosslinking agent, and silica particles, wherein the content of the electron transport substance in the composition is 30% by mass or more and 70% by mass or less based on the total mass of the composition, and the content of the silica particles is 1% by mass or more and 30% by mass or less based on the total mass of the electron transport substance.

[0004] Patent Document 3 discloses an electrophotographic photoreceptor comprising a conductive substrate, an undercoat layer provided on the conductive substrate which contains an electron transport material and silica particles, wherein the silica particle content is 30% by mass or more, and a photosensitive layer provided on the undercoat layer, wherein the condensation rate of the silica particles is 90% or more, and the condensation rate is the ratio of Si-O-Si in the SiO4- bonds in the silica particles.

[0005] Patent Document 4 discloses an electrophotographic photoreceptor having an intermediate layer and a photosensitive layer on a support in that order, characterized in that the intermediate layer contains a polymer of an electron transporting material having a non-hydrolyzable polymerizable functional group.

[0006] Patent Document 5 discloses an electrophotographic photoreceptor having an intermediate layer and a photosensitive layer on a support in that order, characterized in that the intermediate layer contains a specific resin.

[0007] Patent document 6 discloses an electrophotographic photoreceptor containing a specific imide compound in its underlayer.

[0008] Patent Document 7 discloses an electrophotographic photoreceptor comprising an intermediate layer and a photosensitive layer in that order on a conductive support, wherein the intermediate layer contains a specific polyolefin resin and an organic electron transport substance, and the organic electron transport substance is a compound selected from the group consisting of imide compounds, benzimidazole compounds, quinone compounds, cyclopentadienylidene compounds, azo compounds and their derivatives.

[0009] Patent Document 8 describes an electrophotographic photoreceptor having an intermediate layer and a photosensitive layer in that order on a support, wherein the photosensitive layer contains a charge generating material and a charge transporting material, and an electrostatic latent image is formed on the surface by a semiconductor laser, wherein the intermediate layer contains a specific electron transporting material, and the volume resistivity of the intermediate layer at 30°C and 80%RH is 1 × 10⁻¹⁶ 12 An electrophotographic photoreceptor is disclosed, characterized in that it has a roughness of Ω·cm or more, and the ratio of the ten-point average roughness (Rz) of the photosensitive layer side surface of the support to the wavelength (λ) of the semiconductor laser (Rz / λ) is 0.6 or more and 2.5 or less. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Application Publication No. 05-088396 [Patent Document 2] Japanese Patent Publication No. 2016-138931 [Patent Document 3] Patent No. 6946895 [Patent Document 4] Japanese Patent Publication No. 2003-330209 [Patent Document 5] Japanese Patent Publication No. 2003-345044 [Patent Document 6] Patent No. 5147274 [Patent Document 7] Japanese Patent Publication No. 2011-095665 [Patent Document 8] Patent No. 3958154 [Overview of the project] [Problems that the invention aims to solve]

[0011] Conventionally, electrophotographic photoreceptors equipped with an undercoat containing an electron-transporting material, which is an organic compound, tend to generate leakage current when foreign matter from the outside penetrates the surface of the photoreceptor during image formation. When leakage current occurs, point-like image defects are more likely to occur. If silica particles are dispersed with high uniformity in the undercoat to suppress leakage current, residual potential tends to accumulate and charge retention decreases when images are repeatedly formed. The objective of this disclosure is to provide an electrophotographic photoreceptor that suppresses both residual potential accumulation and leakage current, and exhibits excellent charge retention, compared to a case where silica particles are uniformly contained throughout the entire underlayer containing an electron-transporting material. [Means for solving the problem]

[0012] The following embodiments are specific means for solving the aforementioned problem. Each formula is identical to the formula with the same number described later.

[0013] <1> A conductive substrate, A first undercoat layer provided on the conductive substrate, A second lower layer is provided on top of the first lower layer, A photosensitive layer provided on the second undercoat layer, Equipped with, The first undercoat layer contains at least one electron transporting material selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3), and a binder resin, and the content of silica particles in the first undercoat layer is 0% by mass or 5% by mass or less. The second undercoat layer contains at least one electron transporting material selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3), silica particles, and a binder resin, and the content of the silica particles in the second undercoat layer is larger than the content of the silica particles in the first undercoat layer. Electrophotographic photoreceptor.

Chemical formula

[0014] <1> , <4> or <9> According to the invention, compared to the case in which silica particles are uniformly contained throughout the entire underlayer containing an electron-transporting material, an electrophotographic photoreceptor is provided that suppresses both the accumulation of residual potential and leakage current, and has excellent charge retention properties. <2> According to the invention, an electrophotographic photoreceptor is provided in which the second undercoat suppresses both residual potential accumulation and leakage current compared to the case in which the silica particle content in the second undercoat is less than 20% by mass. <3> According to the invention, an electrophotographic photoreceptor is provided in which the second undercoat suppresses both residual potential accumulation and leakage current compared to the case in which the silica particle content in the second undercoat is less than 25% by mass or more than 50% by mass. <5> According to the invention, an electrophotographic photoreceptor is provided in which the specific undercoat suppresses both residual potential accumulation and leakage current compared to a case where the proportion of silica particles in a region within 50% of the thickness-direction cross-section from the interface between the specific undercoat and the photosensitive layer in the direction toward the conductive substrate is less than 25 area % or more than 60 area % of the entire specific undercoat. <6> According to the invention, compared to a case where the proportion of silica particles in a region within 50% of the thickness-direction cross-section of the specific undercoat, from the interface between the specific undercoat and the photosensitive layer toward the conductive substrate, is less than 30 area % or more than 50 area % of the entire specific undercoat, an electrophotographic photoreceptor is provided that suppresses both residual potential accumulation and leakage current, and exhibits excellent charge retention. <7> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention compared to electron transport materials with an average primary particle size of less than 20 nm or greater than 1000 nm. <8> According to the invention, an electrophotographic photoreceptor is provided that suppresses both residual potential accumulation and leakage current, and exhibits excellent charge retention, compared to cases where the average primary particle size of silica particles is less than 50 nm or greater than 500 nm. <10> According to the invention, a process cartridge is provided that has an electrophotographic photoreceptor that suppresses both residual potential accumulation and leakage current, and has excellent charge retention, compared to the case in which silica particles are uniformly contained throughout the entire underlayer containing an electron transport material. <11> According to the invention, an image forming apparatus is provided that has an electrophotographic photoreceptor that suppresses both residual potential accumulation and leakage current, and has excellent charge retention, compared to the case in which silica particles are uniformly contained throughout the entire underlayer containing an electron transport material. [Brief explanation of the drawing]

[0015] [Figure 1] This is a partial cross-sectional view showing an example of the layer structure of an electrophotographic photoreceptor according to this embodiment. [Figure 2] This is a partial cross-sectional view showing another example of the layer configuration of the electrophotographic photoreceptor according to this embodiment. [Figure 3] This is a schematic diagram showing an example of an image forming apparatus according to this embodiment. [Figure 4] This is a schematic diagram showing another example of the image forming apparatus according to this embodiment. [Modes for carrying out the invention]

[0016] The embodiments of this disclosure are described below. These descriptions and embodiments are illustrative and do not limit the scope of the embodiments.

[0017] In this disclosure, the numerical range indicated using "~" represents a range that includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0018] In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.

[0019] In the present disclosure, when an embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Also, the sizes of the members in each drawing are conceptual, and the relative size relationships between the members are not limited thereto.

[0020] In the present disclosure, each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, in the case where there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition. In the present disclosure, the particles corresponding to each component may contain a plurality of types. When there are a plurality of types of particles corresponding to each component in the composition, unless otherwise specified, the particle size of each component means a value for the mixture of the plurality of types of particles present in the composition.

[0021] In the present disclosure, the alkyl group and the alkylene group include linear, branched, and cyclic ones unless otherwise specified.

[0022] In the present disclosure, organic groups, aromatic rings, linking groups, alkyl groups, alkylene groups, aryl groups, aralkyl groups, alkoxy groups, aryloxy groups, etc. may have the hydrogen atoms in the group substituted by halogen atoms.

[0023] In the present disclosure, when a compound is represented by a structural formula, it may be represented by a structural formula in which the symbols (C and H) representing carbon atoms and hydrogen atoms in the hydrocarbon group and / or hydrocarbon chain are omitted.

[0024] In the present disclosure, the "structural unit" of a copolymer or a resin is synonymous with a monomer unit.

[0025] <Electrophotographic photoreceptor> Hereinafter, the electrophotographic photoreceptor is also simply referred to as a "photoreceptor". Hereinafter, when describing the common matters of the first embodiment and the second embodiment, it is referred to as "this embodiment". Hereinafter, the compound represented by formula (1) is also referred to as perinone compound (1), the compound represented by formula (2) is also referred to as perinone compound (2), and the compound represented by formula (3) is also referred to as perylene tetracarboxylic dianhydride.

[0026] The photoreceptor according to the first embodiment includes a conductive substrate, a first undercoat layer provided on the conductive substrate, a second undercoat layer provided on the first undercoat layer, and a photosensitive layer provided on the second undercoat layer. The first undercoat layer contains at least one electron transporting material selected from the group consisting of the compound represented by the following formula (1), the compound represented by the following formula (2), and the compound represented by the following formula (3), and a binder resin, and the content of silica particles in the first undercoat layer is 0% by mass or 5% by mass or less. The second undercoat layer contains at least one electron transporting material selected from the group consisting of the compound represented by the following formula (1), the compound represented by the following formula (2), and the compound represented by the following formula (3), silica particles, and a binder resin, and the content of silica particles in the second undercoat layer is larger than the content of silica particles in the first undercoat layer.

[0027] The photoreceptor according to the second embodiment includes a conductive substrate, a specific undercoat layer provided on the conductive substrate, and a photosensitive layer provided on the specific undercoat layer. The specific undercoat layer contains at least one electron transporting material selected from the group consisting of the compound represented by the following formula (1), the compound represented by the following formula (2), and the compound represented by the following formula (3), silica particles, and a binder resin, and the silica particles are unevenly distributed in a region within 50% from the interface between the specific undercoat layer and the photosensitive layer in the direction of the conductive substrate.

[0028]

Chemical formula

[0029] Conventionally, photoreceptors using a compound represented by formula (1) and / or a compound represented by formula (2) as the undercoat layer have been known to yield good initial electrical properties. Furthermore, as a result of diligent research by the inventors, it has been found that photoreceptors using a compound represented by formula (3) as the undercoat layer also yield excellent initial electrical properties. However, these photoreceptors tend to generate leakage current when foreign objects (such as needle-shaped objects like carbon fibers) from the outside penetrate to the conductive substrate if they pierce the surface of the photoreceptor during image formation. To suppress this leakage current, if silica particles are uniformly dispersed in the underlayer containing the charge-transporting material, the silica particles become less resistive due to polar groups such as hydroxyl groups on the silica surface. When repeated images are formed, the charge retention tends to gradually decrease with repeated exposure and charging. Conversely, in the case of silica particles treated to make the surface hydrophobic, the resistance increases, improving charge retention. However, because they do not participate in charge transport, the conductive paths of the charge-transporting material are obstructed, and sufficient charge transport to the conductive substrate does not occur, leading to a tendency for the residual potential to increase.

[0030] On the other hand, the photoreceptor according to this embodiment, having the above configuration, suppresses both the accumulation of residual potential and leakage current, and exhibits excellent charge retention. The mechanism of action is not entirely clear, but it is presumed to be as follows.

[0031] In the first embodiment, the second undercoat on the photosensitive layer side has a higher silica particle content than the first undercoat on the conductive substrate side. In other words, looking at the undercoat as a whole, silica particles are predominantly concentrated on the interface side with the photosensitive layer. Therefore, even if foreign matter penetrates the surface of the photoreceptor, penetration to the conductive substrate is suppressed, and leakage current to the conductive substrate is suppressed. Furthermore, since the silica particle content in the first undercoat is 0% by mass or 5% by mass or less, even when repeatedly forming images, the contact area between the conductive substrate and the charge transport material is sufficiently maintained, so that charge transport to the conductive substrate is sufficiently maintained and the accumulation of residual potential is suppressed. In other words, obstruction of the conductive path of the charge transport material by silica particles is less likely to occur. In addition, both the first and second undercoat layers contain at least one compound selected from the group consisting of compounds represented by formulas (1) to (3) as a charge transport material with excellent charge retention properties. This ensures sufficient charge transport and charge retention. In the second embodiment, silica particles are unevenly distributed in the specific underlayer within 50% of the interface between the specific underlayer and the photosensitive layer in the direction toward the conductive substrate. Therefore, even if foreign matter penetrates the surface of the photoreceptor, the penetration of the foreign matter is more likely to remain at the interface between the specific underlayer and the photosensitive layer, preventing it from penetrating to the conductive substrate and suppressing local leakage current. Furthermore, even when repeatedly forming images, the accumulation of residual potential is suppressed, and the obstruction of the conductive path of the charge transport material by silica particles is less likely to occur. In addition, the entire specific underlayer contains at least one compound selected from the group consisting of compounds represented by formulas (1) to (3) as a charge transport material with excellent charge retention properties. This ensures that both charge transport and charge retention properties are maintained.

[0032] The layer structure of the photoreceptor according to this embodiment will be described below with reference to the drawings. Figure 1 is a schematic partial cross-sectional view showing an example of the layer structure of a photoreceptor according to this embodiment. The photoreceptor 10A shown in Figure 1 has a stacked photoreceptor layer. The photoreceptor 10A has a structure in which a base layer 2, a charge generation layer 3, and a charge transport layer 4 are stacked in this order on a conductive substrate 1, and the charge generation layer 3 and the charge transport layer 4 constitute the photoreceptor layer 5 (a so-called functionally separated photoreceptor layer). The photoreceptor 10A may have an intermediate layer (not shown) between the base layer 2 and the charge generation layer 3. In the case of the photoreceptor according to the first embodiment, the undercoat 2 shown in Figure 1 has a two-layer structure in which the first undercoat and the second undercoat are stacked in that order from the conductive substrate 1 side. The second undercoat may be provided on at least a portion of the area of ​​the first undercoat, or it may be provided over the entire surface of the first undercoat. In the case of the photoreceptor according to the second embodiment, the undercoat layer 2 shown in Figure 1 is a specific undercoat layer.

[0033] Figure 2 is a schematic partial cross-sectional view showing another example of the layer configuration of the photoreceptor according to this embodiment. The photoreceptor 10B shown in Figure 2 has a single-layer photosensitive layer. The photoreceptor 10B has a structure in which an undercoat layer 2 and a photosensitive layer 5 are stacked in that order on a conductive substrate 1. The photoreceptor 10B may have an intermediate layer (not shown) between the undercoat layer 2 and the photosensitive layer 5. In the case of the photoreceptor according to the first embodiment, the undercoat 2 shown in Figure 2 has a two-layer structure in which the first undercoat and the second undercoat are stacked in that order from the conductive substrate 1 side. The second undercoat may be provided in at least a part of the area of ​​the first undercoat, or it may be provided over the entire surface of the first undercoat. In the case of the photoreceptor according to the second embodiment, the undercoat layer 2 shown in Figure 2 is a specific undercoat layer.

[0034] The layers of the electrophotographic photoreceptor according to this embodiment will be described in detail below. Reference numerals will be omitted in the description.

[0035] [Sublayer] In the first embodiment, the undercoat has a two-layer structure consisting of a first undercoat provided on a conductive substrate and a second undercoat provided on the first undercoat. In the second embodiment, the undercoat layer has a specific undercoat layer provided on the conductive substrate.

[0036] The first undercoat layer contains at least one electron transporting material selected from the group consisting of the compound represented by formula (1), the compound represented by formula (2), and the compound represented by formula (3), and a binder resin, and the content of silica particles in the first undercoat layer is 0% by mass or 5% by mass or less.

[0037] The first undercoat layer preferably has a silica particle content in the first undercoat layer of 0% by mass or 5% by mass or less, more preferably 0% by mass or 3% by mass or less, still more preferably 0% by mass or 2% by mass or less, and even more preferably 0% by mass. When the content of silica particles in the first undercoat layer is 0% by mass or 5% by mass or less, the conductive path of the electron transporting material is less likely to be inhibited, the injection of charges from the conductive substrate during charging is suppressed, and the charge retention property is excellent. In addition, the accumulation of residual potential is suppressed.

[0038] The second undercoat layer contains at least one electron transporting material selected from the group consisting of the compound represented by formula (1), the compound represented by formula (2), and the compound represented by formula (3), silica particles, and a binder resin, and the content of the silica particles in the second undercoat layer is greater than the content of the silica particles in the first undercoat layer.

[0039] The second undercoat layer preferably has a silica particle content in the second undercoat layer of 20% by mass or more, more preferably 20% by mass or more and 50% by mass or less, and still more preferably 25% by mass or more and 45% by mass or less. When the content of silica particles in the second undercoat layer is 20% by mass or more, even when a foreign object pierces the photoreceptor, it is more effectively suppressed from penetrating to the conductive substrate, and the leakage current is more effectively suppressed. When the content of silica particles in the second undercoat layer is 50% by mass or less, the conductive path of the electron transporting material is less likely to be inhibited, and the charge retention property is more excellent. Also, even when a foreign object pierces the photoreceptor, it is more effectively suppressed from penetrating to the conductive substrate, and it is excellent in suppressing leakage current.

[0040] The specific underlayer comprises at least one electron-transporting material selected from the group consisting of a compound represented by formula (1), a compound represented by formula (2), and a compound represented by formula (3), silica particles, and a binder resin, and the silica particles are unevenly distributed in a region within 50% of the interface between the specific underlayer and the photosensitive layer in the direction toward the conductive substrate.

[0041] In the specific undercoat, the proportion of silica particles in the region within 50% of the thickness-direction cross-section from the interface between the specific undercoat and the photosensitive layer toward the conductive substrate is preferably 25% to 60% of the entire specific undercoat, more preferably 30% to 50% of the entire specific undercoat, and even more preferably 35% to 45% of the entire specific undercoat.

[0042] The specific underlayer preferably has a silica particle content of 0% by mass or 5% by mass or less in the region exceeding 50% from the interface between the specific underlayer and the photosensitive layer toward the conductive substrate, more preferably 0% by mass or 3% by mass or less, even more preferably 0% by mass or 2% by mass or less, and even more preferably 0% by mass. When the silica particle content in the region exceeding 50% is 0% by mass or 5% by mass or less, the conductive paths of the electron transport material are less likely to be obstructed, and the accumulation of residual potential is suppressed.

[0043] The specific underlayer preferably contains 5% by mass or less of silica particles in the region within 50% of the interface between the specific underlayer and the photosensitive layer in the direction toward the conductive substrate, more preferably 0% by mass or 3% by mass or less, even more preferably 0% by mass or 2% by mass or less, and even more preferably 0% by mass. If the silica particle content in the region exceeding 50% is 5% by mass or less, the conductive paths of the electron transport material are less likely to be obstructed, and the accumulation of residual potential is suppressed.

[0044] The area ratio of each silica particle is measured by the following method. First, the undercoat obtained by peeling off the photosensitive layer from the photoreceptor is cut in the thickness direction. The resulting cross-section is observed using a scanning electron microscope (SEM). Then, the cross-sectional area S1 of the region within 50% of the interface between the specific undercoat and the photosensitive layer in the direction toward the conductive substrate, the sum of the cross-sectional areas of all silica particles observed in the region within 50%, the cross-sectional area S2 of the region beyond 50% of the interface between the specific undercoat and the photosensitive layer in the direction toward the conductive substrate, and the sum of the cross-sectional areas of all silica particles observed in the region beyond 50% are determined, and the ratio of the cross-sectional area P of the silica particles to the cross-sectional area S is calculated.

[0045] In the first and second embodiments, the total amount of electron-transporting material in the undercoat (i.e., in the first embodiment, the total amount of electron-transporting material in the entire undercoat including the first and second undercoat, and in the second embodiment, the total amount of electron-transporting material in a specific undercoat) is preferably 50% by mass or more and 75% by mass or less, more preferably 55% by mass or more and 70% by mass or less, and even more preferably 60% by mass or more and 65% by mass or less, relative to the solid content of the undercoat excluding the silica particles. When the electron-transporting material content is 75% by mass or less, the film quality becomes brittle, reducing film formation efficiency and suppressing surface roughness in the underlying layer, resulting in superior charge retention. On the other hand, if the content of electron-transporting material is 50% by mass or more, sufficient electron transport capacity is achieved, and the suppression of residual potential accumulation and charge maintenance are adequately ensured.

[0046] The thickness of the first underlayer is preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 10 μm or less, and even more preferably 2 μm or more and 6 μm or less. The thickness of the second underlayer is preferably 1 μm or more and 20 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 1 μm or more and 5 μm or less. The thickness of the specific undercoat is preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less, and even more preferably 2 μm or more and 10 μm or less.

[0047] The following describes a common preferred configuration for the first lower layer, the second lower layer, and the specific lower layer. Hereafter, when referring to matters common to the First Lower Drainage Layer, the Second Lower Drainage Layer, and the Specific Lower Drainage Layer, the term "Lower Drainage Layer" will be used simply.

[0048] [Silica particles] ★↓During the interview, it was mentioned that further details regarding the electrical properties of the silica particle surface may be explored in the future, so this information has been omitted. Examples of silica particles include dry silica particles and wet silica particles. Silica particles may be used individually or in combination of two or more types. Examples of dry silica particles include fumed silica, which is obtained by burning silane compounds, and deflagration silica, which is obtained by explosively burning metallic silicon powder. Examples of wet silica particles include wet silica particles obtained by the neutralization reaction of sodium silicate and mineral acid (sedimentation silica synthesized and aggregated under alkaline conditions, and gel silica particles synthesized and aggregated under acidic conditions), colloidal silica particles (silica sol particles) obtained by polymerizing acidic silicic acid in an alkaline state, and sol-gel silica particles obtained by the hydrolysis of organosilane compounds (e.g., alkoxysilanes).

[0049] Silica particles may have their surfaces treated with a hydrophobic agent. Examples of hydrophobic agents include known silane compounds such as chlorosilane, alkoxysilane, and silazane. As a hydrophobic treatment agent, silane compounds having trimethylsilyl groups, decylsilyl groups, or phenylsilyl groups are preferred. In other words, silica particles preferably have trimethylsilyl groups, decylsilyl groups, or phenylsilyl groups on their surface. Examples of silane compounds having a trimethylsilyl group include trimethylchlorosilane, trimethylmethoxysilane, and 1,1,1,3,3,3-hexamethyldisilazane. Examples of silane compounds having a decylsilyl group include decyltrichlorosilane, decyltrichlorosilane, decyldimethylchlorosilane, and decyltrimethoxysilane. Examples of silane compounds having a phenyl group include triphenylmethoxysilane and triphenylchlorosilane.

[0050] The silica particles preferably have an average primary particle size of 50 nm to 500 nm, more preferably 60 nm to 400 nm, and even more preferably 70 nm to 300 nm. When the average primary particle size of silica particles is 50 nm or larger, even if foreign matter becomes embedded in the surface of the photoreceptor, its penetration from the undercoat to the conductive substrate is suppressed. As a result, leakage current is further suppressed. When the average primary particle size of silica particles is 500 nm or less, even if foreign matter becomes embedded in the surface of the photoreceptor, it is suppressed from penetrating from the undercoat to the conductive substrate.

[0051] The average primary particle size of silica particles is determined by the following measurement method. The average primary particle size of silica particles is measured by the following method. First, the underlayer obtained by peeling off the photosensitive layer from the photoreceptor is cut in the thickness direction. The resulting cross-section is observed using a scanning electron microscope (SEM). For the surface silica particles observed on the cross-section, the diameter of any 50 circles equal in area (i.e., equivalent circle diameter) is taken as the particle size, and the arithmetic mean of these values ​​is taken as the average primary particle size.

[0052] [Inorganic particles other than silica particles] The undercoat preferably contains 10% by mass or less of inorganic particles other than silica particles, more preferably 5% by mass or less, and even more preferably 0% by mass or 3% by mass or less. When the proportion of inorganic particles other than silica particles in the underlayer is 10% by mass or less, the reduction in resistance due to inorganic particles is suppressed, resulting in superior charge retention and reduced image quality defects.

[0053] [Electron transport material] The electron transport material includes at least one compound selected from the group consisting of the compound represented by formula (1), the compound represented by formula (2), and the compound represented by formula (3).

[0054] [ka] In formula (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 11 and R 12 , R 12 and R 13 and R 13 and R 14 Each element may be independent of the others, or they may be connected to each other to form a ring. 15 and R 16 , R 16 and R 17 and R 17 and R 18 These elements may be connected to each other independently to form a ring. In formula (2), R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 21 and R 22 , R 22 and R 23 and R 23 and R 24 Each element may be independent of the others, or they may be connected to each other to form a ring. 25 and R 26 , R 26 and R 27 and R 27 and R 28 These elements may be connected to each other independently to form a ring. In formula (3), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom.

[0055] From the viewpoint of suppressing residual potential accumulation and leakage current, and from the viewpoint of providing superior charge retention, the electron transport material preferably contains at least one selected from the group consisting of the compound represented by formula (1), the compound represented by formula (2), and the compound represented by formula (3). However, in formula (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom, and in formula (2) above, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom, and in formula (3) above, R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom.

[0056] • Perinone compound (1) and Perinone compound (2) Perinone compound (1) is a compound represented by the following formula (1). Perinone compound (2) is a compound represented by the following formula (2).

[0057] [ka]

[0058] In formula (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 11 and R 12 , R 12 and R 13 and R 13 and R 14 Each element may be independent of the others, or they may be connected to each other to form a ring. 15 and R 16 , R 16 and R 17 and R 17 and R 18 These elements may be connected to each other independently to form a ring.

[0059] In formula (2), R21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 21 and R 22 , R 22 and R 23 and R 23 and R 24 Each element may be independent of the others, or they may be connected to each other to form a ring. 25 and R 26 , R 26 and R 27 and R 27 and R 28 These elements may be connected to each other independently to form a ring.

[0060] The compounds represented by formulas (1) and (2) exhibit excellent electron transport properties and low hole transport properties. Therefore, when the underlayer contains the compounds represented by formulas (1) and (2), the underlayer exhibits excellent electron transport properties, ensuring conductive paths within the underlayer and further suppressing leakage current. In addition, it reduces dark attenuation, resulting in superior charge retention.

[0061] In formula (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these elements may independently represent a hydrogen atom, an alkyl group, or a halogen atom, and more preferably a hydrogen atom. In formula (1), R 11 ~R 18When the underlayer is a hydrogen atom, an alkyl group, or a halogen atom (more preferably a hydrogen atom), the underlayer exhibits excellent electron transport properties, ensuring conductive paths within the underlayer and further suppressing leakage current. Furthermore, dark attenuation is reduced, resulting in superior charge retention.

[0062] In formula (2), R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28 Each of these elements may independently represent a hydrogen atom, an alkyl group, or a halogen atom, and more preferably a hydrogen atom. In formula (2), R 21 ~R 28 When the underlayer is a hydrogen atom, an alkyl group, or a halogen atom (more preferably a hydrogen atom), the underlayer exhibits excellent electron transport properties, ensuring conductive paths within the underlayer and further suppressing leakage current. Furthermore, dark attenuation is reduced, resulting in superior charge retention.

[0063] In formula (1), R 11 ~R 18 Examples of alkyl groups represented by include substituted or unsubstituted alkyl groups.

[0064] In formula (1), R 11 ~R 18 Examples of unsubstituted alkyl groups represented by include linear alkyl groups having 1 to 20 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms), branched alkyl groups having 3 to 20 carbon atoms (preferably 3 to 10 carbon atoms), and cyclic alkyl groups having 3 to 20 carbon atoms (preferably 3 to 10 carbon atoms).

[0065] Examples of linear alkyl groups having 1 to 20 carbon atoms include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, tridecyl group, n-tetradecyl group, n-pentadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, and n-icosyl group.

[0066] Examples of branched alkyl groups having 3 to 20 carbon atoms include isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, neopentyl group, tert-pentyl group, isohexyl group, sec-hexyl group, tert-hexyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, isooctyl group, sec-octyl group, tert-octyl group, isononyl group, sec-nonyl group, tert-nonyl group, isodecyl group, sec-decyl group, tert-decyl group, isododecyl group, sec-dodecyl group, tert-dodecyl group, tert-tetradecyl group, and tert-pentadecyl group.

[0067] Examples of cyclic alkyl groups having 3 to 20 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl groups, as well as polycyclic alkyl groups (e.g., bicyclic, tricyclic, spirocyclic) formed by linking these monocyclic alkyl groups.

[0068] Among the above, linear alkyl groups such as methyl groups and ethyl groups are preferred as unsubstituted alkyl groups.

[0069] Substituents in alkyl groups include alkoxy groups, hydroxyl groups, carboxyl groups, nitro groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As an alkoxy group that substitutes a hydrogen atom in an alkyl group, R in formula (1) 11 ~R 18 Examples of groups similar to the unsubstituted alkoxy group represented by include:

[0070] In formula (1), R 11 ~R 18 Examples of alkoxy groups represented by include substituted or unsubstituted alkoxy groups.

[0071] In formula (1), R 11 ~R 18 Examples of unsubstituted alkoxy groups represented by include linear, branched, or cyclic alkoxy groups having 1 to 10 carbon atoms (preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms).

[0072] Specific examples of linear alkoxy groups include methoxy, ethoxy, n-propoxy, n-butoxy, n-pentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy, n-nonyloxy, and n-decyloxy groups. Examples of branched alkoxy groups include isopropoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, isopentyloxy group, neopentyloxy group, tert-pentyloxy group, isohexyloxy group, sec-hexyloxy group, tert-hexyloxy group, isoheptyloxy group, sec-heptyloxy group, tert-heptyloxy group, isooctyloxy group, sec-octyloxy group, tert-octyloxy group, isononyloxy group, sec-nonyloxy group, tert-nonyloxy group, isodecyloxy group, sec-decyloxy group, and tert-decyloxy group. Examples of cyclic alkoxy groups include cyclopropoxy, cyclobutoxy, cyclopentyloxy, cyclohexyloxy, cycloheptyloxy, cyclooctyloxy, cyclononyloxy, and cyclodecyloxy groups. Among these, linear alkoxy groups are preferred as unsubstituted alkoxy groups.

[0073] Substituents in alkoxy groups include aryl groups, alkoxycarbonyl groups, aryloxycarbonyl groups, hydroxyl groups, carboxyl groups, nitro groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As an aryl group that substitutes a hydrogen atom in an alkoxy group, in formula (1), R 11 ~R 18 Examples include unsubstituted aryl groups represented by . As an alkoxycarbonyl group that substitutes a hydrogen atom in an alkoxy group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include . As an aryloxycarbonyl group that substitutes a hydrogen atom in an alkoxy group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted aryloxycarbonyl group represented by include .

[0074] In formula (1), R 11 ~R 18 Aralkyl groups represented by include substituted or unsubstituted aralkyl groups.

[0075] In formula (1), R 11 ~R 18 The unsubstituted aralkyl group represented by is preferably an aralkyl group having 7 to 30 carbon atoms, more preferably an aralkyl group having 7 to 16 carbon atoms, and even more preferably an aralkyl group having 7 to 12 carbon atoms.

[0076] Examples of unsubstituted aralkyl groups having 7 to 30 carbon atoms include benzyl group, phenylethyl group, phenylpropyl group, 4-phenylbutyl group, phenylpentyl group, phenylhexyl group, phenylheptyl group, phenyloctyl group, phenylnonyl group, naphthylmethyl group, naphthylethyl group, anthratilmethyl group, and phenylcyclopentylmethyl group.

[0077] Substituents in an aralkyl group include alkoxy groups, alkoxycarbonyl groups, aryloxycarbonyl groups, and halogen atoms (such as fluorine, bromine, and iodine atoms). As an alkoxy group that substitutes a hydrogen atom in the aralkyl group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted alkoxy group represented by include: As for the alkoxycarbonyl group that substitutes a hydrogen atom in the aralkyl group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include . As an aryloxycarbonyl group that substitutes a hydrogen atom in the aralkyl group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted aryloxycarbonyl group represented by include .

[0078] In formula (1), R 11 ~R 18 Examples of aryl groups represented by this symbol include substituted and unsubstituted aryl groups.

[0079] In formula (1), R 11 ~R 18 The unsubstituted aryl group represented by is preferably an aryl group having 6 to 30 carbon atoms, more preferably an aryl group having 6 to 14 carbon atoms, and even more preferably an aryl group having 6 to 10 carbon atoms.

[0080] Examples of aryl groups having 6 to 30 carbon atoms include phenyl group, biphenyl group, 1-naphthyl group, 2-naphthyl group, 9-anthuryl group, 9-phenanthryl group, 1-pyrenyl group, 5-naphthacenyl group, 1-indenyl group, 2-azlenyl group, 9-fluorenyl group, biphenylenyl group, indacenyl group, fluoranthenyl group, acenaphthyleneyl group, aceantrilenyl group, phenalenyl group, fluorenyl group, Examples include anthryl group, bianthracenyl group, teranthracenyl group, quarteranthracenyl group, anthraquinolyl group, phenanthryl group, triphenylenyl group, pyrenyl group, chrysenyl group, naphthacenyl group, pleiadenyl group, picenyl group, perilenyl group, pentaphenyl group, pentacenyl group, tetraphenylenyl group, hexaphenyl group, hexacenyl group, rubicenyl group, coronenyl group, etc. Among the above, the phenyl group is preferred.

[0081] Substituents in an aryl group include alkyl groups, alkoxy groups, alkoxycarbonyl groups, aryloxycarbonyl groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As the alkyl group that substitutes the hydrogen atom in the aryl group, in formula (1), R 11 ~R 18 Examples of groups similar to unsubstituted alkyl groups represented by include . As an alkoxy group that substitutes a hydrogen atom in an aryl group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted alkoxy group represented by include: As an alkoxycarbonyl group that substitutes a hydrogen atom in the aryl group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include . As an aryloxycarbonyl group that substitutes a hydrogen atom in the aryl group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted aryloxycarbonyl group represented by include .

[0082] In formula (1), R 11 ~R18 Examples of aryloxy groups represented by -O-Ar (where Ar represents an aryl group) include substituted and unsubstituted aryloxy groups.

[0083] In formula (1), R 11 ~R 18 As the unsubstituted aryloxy group represented by , an aryloxy group having 6 to 30 carbon atoms is preferred, an aryloxy group having 6 to 14 carbon atoms is more preferred, and an aryloxy group having 6 to 10 carbon atoms is even more preferred.

[0084] Aryloxy groups with 6 to 30 carbon atoms include phenyloxy group (phenoxy group), biphenyloxy group, 1-naphthyloxy group, 2-naphthyloxy group, 9-anthryloxy group, 9-phenanthryloxy group, 1-pyrenyloxy group, 5-naphthacenyloxy group, 1-indenyloxy group, 2-azlenyloxy group, 9-fluorenyloxy group, biphenylenyloxy group, indacenyloxy group, fluoranthenyloxy group, acenaphthyleneyloxy group, aceanthrlenyloxy group, phenalenyloxy group, and fluorenyloxy group. Examples include the phenyloxy group, anthryloxy group, bianthrencenyloxy group, teranthrencenyloxy group, quarteranthrencenyloxy group, anthraquinolyloxy group, phenanthryloxy group, triphenylenyloxy group, pyrenyloxy group, crisenyloxy group, naphthacenyloxy group, pleiadenyloxy group, picenyloxy group, perilennyloxy group, pentaphenyloxy group, pentacenyloxy group, tetraphenylenyloxy group, hexaphenyloxy group, hexacenyloxy group, rubicenyloxy group, coronenyloxy group, etc. Among the above, the phenyloxy group (phenoxy group) is preferred.

[0085] Substituents in the aryloxy group include alkyl groups, alkoxycarbonyl groups, aryloxycarbonyl groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As the alkyl group that substitutes the hydrogen atom in the aryloxy group, in formula (1), R 11 ~R 18Examples of groups similar to unsubstituted alkyl groups represented by include . As an alkoxycarbonyl group that substitutes a hydrogen atom in the aryloxy group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include . As an aryloxycarbonyl group that substitutes a hydrogen atom in the aryloxy group, in formula (1), R 11 ~R 18 Examples of groups similar to the unsubstituted aryloxycarbonyl group represented by include .

[0086] In formula (1), R 11 ~R 18 Examples of alkoxycarbonyl groups represented by (-CO-OR, where R represents an alkyl group) include substituted or unsubstituted alkoxycarbonyl groups.

[0087] In formula (1), R 11 ~R 18 The number of carbon atoms in the alkyl chain of the unsubstituted alkoxycarbonyl group represented by is preferably 1 to 20, more preferably 1 to 15, and even more preferably 1 to 10.

[0088] Examples of alkoxycarbonyl groups with 1 to 20 carbon atoms in the alkyl chain include methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, isopropoxycarbonyl group, n-butoxycarbonyl group, sec-butoxybutylcarbonyl group, tert-butoxycarbonyl group, pentaoxycarbonyl group, hexaoxycarbonyl group, heptaoxycarbonyl group, octaoxycarbonyl group, nonaoxycarbonyl group, decaoxycarbonyl group, dodecaoxycarbonyl group, tridecaoxycarbonyl group, tetradecaoxycarbonyl group, pentadecaoxycarbonyl group, hexadecaoxycarbonyl group, heptadecaoxycarbonyl group, octadecaoxycarbonyl group, nonadecaoxycarbonyl group, and eicosaoxycarbonyl group.

[0089] Examples of substituents on an alkoxycarbonyl group include aryl groups, hydroxyl groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As an aryl group that substitutes a hydrogen atom in an alkoxycarbonyl group, in formula (1), R 11 ~R 18 Examples include unsubstituted aryl groups represented by .

[0090] In formula (1), R 11 ~R 18 Examples of aryloxycarbonyl groups represented by -CO-OAr (where Ar represents an aryl group) include substituted and unsubstituted aryloxycarbonyl groups.

[0091] In formula (1), R 11 ~R 18 In the unsubstituted aryloxycarbonyl group represented by , the number of carbon atoms in the aryl group is preferably 6 to 30, more preferably 6 to 14, and even more preferably 6 to 10.

[0092] Examples of aryloxycarbonyl groups having aryl groups with 6 to 30 carbon atoms include phenoxycarbonyl group, biphenyloxycarbonyl group, 1-naphthyloxycarbonyl group, 2-naphthyloxycarbonyl group, 9-anthuryloxycarbonyl group, 9-phenanthryloxycarbonyl group, 1-pyrenyloxycarbonyl group, 5-naphthacenyloxycarbonyl group, 1-indenyloxycarbonyl group, 2-azlenyloxycarbonyl group, 9-fluorenyloxycarbonyl group, biphenylenyloxycarbonyl group, indacenyloxycarbonyl group, fluoranthenyloxycarbonyl group, acenaphthyleneyloxycarbonyl group, aceanthryleneyloxycarbonyl group, phenalenyloxycarbonyl group, fluorenyloxycarbonyl group, Examples include anthryloxycarbonyl group, biantracenyloxycarbonyl group, terantracenyloxycarbonyl group, quarterantracenyloxycarbonyl group, anthraquinolyloxycarbonyl group, phenanthryloxycarbonyl group, triphenylenyloxycarbonyl group, pyrenyloxycarbonyl group, chrysenyloxycarbonyl group, naphthacenyloxycarbonyl group, pleiadenyloxycarbonyl group, picenyloxycarbonyl group, perilennyloxycarbonyl group, pentaphenyloxycarbonyl group, pentacenyloxycarbonyl group, tetraphenylenyloxycarbonyl group, hexaphenyloxycarbonyl group, hexacenyloxycarbonyl group, rubicenyloxycarbonyl group, coronenyloxycarbonyl group, etc. Among the above, the phenoxycarbonyl group is preferred.

[0093] Substituents in the aryloxycarbonyl group include alkyl groups, hydroxyl groups, and halogen atoms (such as fluorine, bromine, and iodine atoms). As an alkyl group that substitutes a hydrogen atom of the aryloxycarbonyl group, in formula (1), R 11 ~R 18 Examples of groups similar to unsubstituted alkyl groups represented by include .

[0094] In formula (1), R 11 ~R 18Alkoxycarbonyl alkyl groups represented by (-(C n H 2n )-CO-OR, where R represents an alkyl group and n represents an integer of 1 or more. Examples of ) include substituted or unsubstituted alkoxycarbonylalkyl groups.

[0095] In formula (1), R 11 ~R 18 In the unsubstituted alkoxycarbonylalkyl group represented by formula (1), the alkoxycarbonyl group (-CO-OR) is R 11 ~R 18 Examples of groups similar to the alkoxycarbonyl group represented by include .

[0096] In formula (1), R 11 ~R 18 The alkylene chain (-C) in an unsubstituted alkoxycarbonylalkyl group represented by n H 2n Examples of alkylene chains include linear alkylene chains having 1 to 20 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms), branched alkylene chains having 3 to 20 carbon atoms (preferably 3 to 10 carbon atoms), and cyclic alkylene chains having 3 to 20 carbon atoms (preferably 3 to 10 carbon atoms).

[0097] Examples of linear alkylene chains having 1 to 20 carbon atoms include methylene group, ethylene group, n-propylene group, n-butylene group, n-pentylene group, n-hexylene group, n-heptylene group, n-octylene group, n-nonylene group, n-decylene group, n-undecylene group, n-dodecylene group, tridecylene group, n-tetradecylene group, n-pentadecylene group, n-heptadecylene group, n-octadecylene group, n-nonadesilene group, and n-icosilene group.

[0098] Examples of branched alkylene chains having 3 to 20 carbon atoms include isopropylene group, isobutylene group, sec-butylene group, tert-butylene group, isopentylene group, neopentylene group, tert-pentylene group, isohexylene group, sec-hexylene group, tert-hexylene group, isoheptylene group, sec-heptylene group, tert-heptylene group, isooctylene group, sec-octylene group, tert-octylene group, isononylene group, sec-nonylene group, tert-nonylene group, isodecylene group, sec-decylene group, tert-decylene group, isododecylene group, sec-dodecylene group, tert-dodecylene group, tert-tetradecylene group, tert-pentadecylene group, and the like.

[0099] Examples of cyclic alkylene chains having 3 to 20 carbon atoms include cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene, cycloheptylene, cyclooctylene, cyclononylene, and cyclodecylene groups.

[0100] Examples of substituents in alkoxycarbonylalkyl groups include aryl groups, hydroxyl groups, and halogen atoms (such as fluorine, bromine, and iodine atoms). As an aryl group that substitutes a hydrogen atom in an alkoxycarbonylalkyl group, in formula (1), R 11 ~R 18 Examples include unsubstituted aryl groups represented by .

[0101] In formula (1), R 11 ~R 18 (-(C) n H 2n )-CO-OAr, where Ar represents an aryl group and n represents an integer of 1 or more.) Examples include substituted or unsubstituted aryloxycarbonylalkyl groups.

[0102] In formula (1), R 11 ~R 18In the unsubstituted aryloxycarbonylalkyl group represented by (1), the aryloxycarbonyl group (-CO-OAr, where Ar represents an aryl group) is R 11 ~R 18 Examples of groups similar to the aryloxycarbonyl group represented by [the symbol] include [the symbol].

[0103] In formula (1), R 11 ~R 18 Alkylene chain (-C) in unsubstituted aryloxycarbonylalkyl groups represented by n H 2n -) In equation (1), R 11 ~R 18 Examples of groups similar to the alkylene chain in the alkoxycarbonylalkyl group represented by include .

[0104] Substituents in aryloxycarbonylalkyl groups include alkyl groups, hydroxyl groups, and halogen atoms (such as fluorine, bromine, and iodine atoms). As the alkyl group that substitutes the hydrogen atom of the aryloxycarbonylalkyl group, in formula (1), R 11 ~R 18 Examples of groups similar to unsubstituted alkyl groups represented by include .

[0105] In formula (1), R 11 ~R 18 Examples of halogen atoms represented by this formula include fluorine, chlorine, bromine, and iodine atoms.

[0106] In formula (1), R 11 and R 12 , R 12 and R 13 , R 13 and R 14 , R 15 and R 16 , R 16 and R 17 or R 17 and R 18However, examples of ring structures formed by the linking of these rings include benzene rings and condensed rings having 10 to 18 carbon atoms (naphthalene rings, anthracene rings, phenanthrene rings, chrysene rings (benzo[α]phenanthrene rings), tetracene rings, tetrafen rings (benzo[α]anthracene rings), triphenylene rings, etc.). Among the above, benzene rings are preferred as the ring structure formed.

[0107] In formula (2), R 21 ~R 28 The alkyl group represented by is R in formula (1). 11 ~R 18 Examples of groups similar to the alkyl groups represented are shown. In formula (2), R 21 ~R 28 The alkoxy group represented by formula (1) is R 11 ~R 18 Examples of groups similar to the alkoxy group represented by can be cited. In formula (2), R 21 ~R 28 The aralkyl group represented by is R in formula (1). 11 ~R 18 Examples of groups similar to the aralkyl group represented by this symbol include: In formula (2), R 21 ~R 28 The aryl group represented by is R in formula (1). 11 ~R 18 Examples of groups similar to the aryl group represented by include . In formula (2), R 21 ~R 28 The aryloxy group represented by is, in formula (1), R 11 ~R 18 Examples of groups similar to the aryloxy group represented by can be cited. In formula (2), R 21 ~R 28 The alkoxycarbonyl group represented by formula (1) is R 11 ~R 18 Examples of groups similar to the alkoxycarbonyl group represented by include . In formula (2), R 21 ~R 28The aryloxycarbonyl group represented by formula (1) is R 11 ~R 18 Examples of groups similar to the aryloxycarbonyl group represented by [the symbol] include [the symbol]. In formula (2), R 21 ~R 28 As an alkoxycarbonylalkyl group represented by formula (1), R 11 ~R 18 Examples of groups similar to the alkoxycarbonylalkyl groups represented by include . In formula (2), R 21 ~R 28 The aryloxycarbonylalkyl group represented by is, in formula (1), R 11 ~R 18 Examples of groups similar to the aryloxycarbonylalkyl group represented by [the formula shown] include [the formula shown]. In formula (2), R 21 ~R 28 The halogen atom represented by is R in formula (1). 11 ~R 18 Examples of atoms similar to halogen atoms represented by [the symbol] include [the symbol].

[0108] In formula (2), R 21 and R 22 , R 22 and R 23 , R 23 and R 24 , R 25 and R 26 , R 26 and R 27 or R 27 and R 28 However, examples of ring structures formed by the linking of these rings include benzene rings and condensed rings having 10 to 18 carbon atoms (naphthalene rings, anthracene rings, phenanthrene rings, chrysene rings (benzo[α]phenanthrene rings), tetracene rings, tetrafen rings (benzo[α]anthracene rings), triphenylene rings, etc.). Among the above, benzene rings are preferred as the ring structure formed.

[0109] In equation (1), R 11 , R 12 , R 13 , R 14 , R15 , R 16 , R 17 and R 18 Preferably, each of these is independently a hydrogen atom, an alkyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, or an aryloxycarbonylalkyl group. In equation (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these is more preferably a hydrogen atom or an alkyl group, independently of the others. The preferred form of the alkyl group is as described above. In equation (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 It is particularly preferable that it be a hydrogen atom.

[0110] In equation (2), R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28 Preferably, each of these is independently a hydrogen atom, an alkyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, or an aryloxycarbonylalkyl group. In equation (2), R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28 Each of these is more preferably a hydrogen atom or an alkyl group, independently of the others. The preferred form of the alkyl group is as described above. In equation (2), R 21 , R22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28 It is particularly preferable that it be a hydrogen atom.

[0111] Specific examples of perinone compound (1) and perinone compound (2) are shown below, but this embodiment is not limited to these. In the following structural formulas, Ph represents a phenyl group.

[0112] [ka]

[0113] [ka]

[0114] [ka]

[0115] [ka]

[0116] [ka]

[0117] [ka]

[0118] Perinone compounds (2-1) to (2-18) are isomers (cis and trans isomers) of perinone compounds (1-1) to (1-18), respectively. Due to the synthesis methods, perinone compounds tend to yield mixtures of isomers. One of these mixtures can be purified according to known purification methods.

[0119] As an example of an embodiment, the underlayer may contain both perinone compound (1) and perinone compound (2). Whether or not perinone compound (1) and perinone compound (2) are isomers, the mass ratio of perinone compound (1) to perinone compound (2) is preferably perinone compound (1):perinone compound (2) = 3:97 to 97:3, more preferably 5:95 to 95:5, and even more preferably 10:90 to 90:10.

[0120] • Perylenetetracarboxylic acid dianhydride Perylenetetracarboxylic dianhydride is a compound represented by the following formula (3).

[0121] [ka] In equation (3) above, R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom.

[0122] The compound represented by formula (3) has excellent electron transport properties and low hole transport properties. Therefore, when the underlayer contains the compound represented by formula (3), the underlayer exhibits excellent electron transport properties, ensuring conductive paths within the underlayer and further suppressing leakage current. In addition, it reduces dark attenuation, resulting in superior charge retention.

[0123] In equation (3), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38Each of these elements may independently represent a hydrogen atom, an alkyl group, or a halogen atom, and more preferably a hydrogen atom. In formula (3), R 31 ~R 38 When the underlayer is a hydrogen atom, an alkyl group, or a halogen atom (more preferably a hydrogen atom), the underlayer exhibits excellent electron transport properties, ensuring conductive paths within the underlayer and further suppressing leakage current. Furthermore, dark attenuation is reduced, resulting in superior charge retention.

[0124] In formula (3), R 31 ~R 38 Examples of alkyl groups represented by include substituted or unsubstituted alkyl groups.

[0125] In formula (3), R 31 ~R 38 Examples of unsubstituted alkyl groups represented by include linear alkyl groups having 1 to 20 carbon atoms (preferably 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms), branched alkyl groups having 3 to 20 carbon atoms (preferably 3 to 10 carbon atoms), and cyclic alkyl groups having 3 to 20 carbon atoms (preferably 3 to 10 carbon atoms).

[0126] Examples of linear alkyl groups having 1 to 20 carbon atoms include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, tridecyl group, n-tetradecyl group, n-pentadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, and n-icosyl group.

[0127] Examples of branched alkyl groups having 3 to 20 carbon atoms include isopropyl group, isobutyl group, sec-butyl group, tert-butyl group, isopentyl group, neopentyl group, tert-pentyl group, isohexyl group, sec-hexyl group, tert-hexyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, isooctyl group, sec-octyl group, tert-octyl group, isononyl group, sec-nonyl group, tert-nonyl group, isodecyl group, sec-decyl group, tert-decyl group, isododecyl group, sec-dodecyl group, tert-dodecyl group, tert-tetradecyl group, and tert-pentadecyl group.

[0128] Examples of cyclic alkyl groups having 3 to 20 carbon atoms include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl, and cyclodecyl groups, as well as polycyclic alkyl groups (e.g., bicyclic, tricyclic, spirocyclic, etc.) formed by linking these monocyclic alkyl groups.

[0129] Among the above, linear alkyl groups such as methyl groups and ethyl groups are preferred as unsubstituted alkyl groups.

[0130] Substituents in alkyl groups include alkoxy groups, hydroxyl groups, carboxyl groups, nitro groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As an alkoxy group that substitutes a hydrogen atom in an alkyl group, R in formula (3) 31 ~R 38 Examples of groups similar to the unsubstituted alkoxy group represented by include:

[0131] In formula (3), R 31 ~R 38 Examples of alkoxy groups represented by include substituted or unsubstituted alkoxy groups.

[0132] In formula (3), R 31 ~R 38Examples of unsubstituted alkoxy groups represented by include linear, branched, or cyclic alkoxy groups having 1 to 10 carbon atoms (preferably 1 to 6 carbon atoms, more preferably 1 to 4 carbon atoms).

[0133] Specific examples of linear alkoxy groups include methoxy, ethoxy, n-propoxy, n-butoxy, n-pentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy, n-nonyloxy, and n-decyloxy groups. Examples of branched alkoxy groups include isopropoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, isopentyloxy group, neopentyloxy group, tert-pentyloxy group, isohexyloxy group, sec-hexyloxy group, tert-hexyloxy group, isoheptyloxy group, sec-heptyloxy group, tert-heptyloxy group, isooctyloxy group, sec-octyloxy group, tert-octyloxy group, isononyloxy group, sec-nonyloxy group, tert-nonyloxy group, isodecyloxy group, sec-decyloxy group, and tert-decyloxy group. Examples of cyclic alkoxy groups include cyclopropoxy, cyclobutoxy, cyclopentyloxy, cyclohexyloxy, cycloheptyloxy, cyclooctyloxy, cyclononyloxy, and cyclodecyloxy groups. Among these, linear alkoxy groups are preferred as unsubstituted alkoxy groups.

[0134] Substituents in alkoxy groups include aryl groups, alkoxycarbonyl groups, aryloxycarbonyl groups, hydroxyl groups, carboxyl groups, nitro groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As an aryl group that substitutes a hydrogen atom in an alkoxy group, in formula (3), R 31 ~R 38 Examples include unsubstituted aryl groups represented by . As an alkoxycarbonyl group that substitutes a hydrogen atom in the alkoxy group, in formula (3), R 31 ~R 38 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include . As an aryloxycarbonyl group that substitutes a hydrogen atom in the alkoxy group, in formula (3), R 31 ~R 38 Examples of groups similar to the unsubstituted aryloxycarbonyl group represented by include .

[0135] In formula (3), R 31 ~R 38 Aralkyl groups represented by include substituted or unsubstituted aralkyl groups.

[0136] In formula (3), R 31 ~R 38 The unsubstituted aralkyl group represented by is preferably an aralkyl group having 7 to 30 carbon atoms, more preferably an aralkyl group having 7 to 16 carbon atoms, and even more preferably an aralkyl group having 7 to 12 carbon atoms.

[0137] Examples of unsubstituted aralkyl groups having 7 to 30 carbon atoms include benzyl group, phenylethyl group, phenylpropyl group, 4-phenylbutyl group, phenylpentyl group, phenylhexyl group, phenylheptyl group, phenyloctyl group, phenylnonyl group, naphthylmethyl group, naphthylethyl group, anthratilmethyl group, and phenylcyclopentylmethyl group.

[0138] Substituents in an aralkyl group include alkoxy groups, alkoxycarbonyl groups, and halogen atoms (such as fluorine, bromine, and iodine atoms). As an alkoxy group that substitutes a hydrogen atom in the aralkyl group, in formula (3), R 31 ~R 38 Examples of groups similar to the unsubstituted alkoxy group represented by include: As for the alkoxycarbonyl group that substitutes the hydrogen atom in the aralkyl group, in formula (3), R 31 ~R38 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include .

[0139] In formula (3), R 31 ~R 38 Examples of aryl groups represented by this symbol include substituted and unsubstituted aryl groups.

[0140] In formula (3), R 31 ~R 38 The unsubstituted aryl group represented by is preferably an aryl group having 6 to 30 carbon atoms, more preferably an aryl group having 6 to 14 carbon atoms, and even more preferably an aryl group having 6 to 10 carbon atoms.

[0141] Examples of aryl groups having 6 to 30 carbon atoms include phenyl group, biphenyl group, 1-naphthyl group, 2-naphthyl group, 9-anthuryl group, 9-phenanthryl group, 1-pyrenyl group, 5-naphthacenyl group, 1-indenyl group, 2-azlenyl group, 9-fluorenyl group, biphenylenyl group, indacenyl group, fluoranthenyl group, acenaphthyleneyl group, aceantrilenyl group, phenalenyl group, fluorenyl group, Examples include anthryl group, bianthracenyl group, teranthracenyl group, quarteranthracenyl group, anthraquinolyl group, phenanthryl group, triphenylenyl group, pyrenyl group, chrysenyl group, naphthacenyl group, pleiadenyl group, picenyl group, perilenyl group, pentaphenyl group, pentacenyl group, tetraphenylenyl group, hexaphenyl group, hexacenyl group, rubicenyl group, coronenyl group, etc. Among the above, the phenyl group is preferred.

[0142] Substituents in an aryl group include alkyl groups, alkoxy groups, alkoxycarbonyl groups, aryloxycarbonyl groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As the alkyl group that substitutes the hydrogen atom in the aryl group, in formula (3), R 31 ~R 38 Examples of groups similar to unsubstituted alkyl groups represented by include . As an alkoxy group that substitutes a hydrogen atom in the aryl group, in formula (3), R 31 ~R 38 Examples of groups similar to the unsubstituted alkoxy group represented by include: As an alkoxycarbonyl group that substitutes a hydrogen atom in the aryl group, in formula (3), R 31 ~R 38 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include .

[0143] In formula (3), R 31 ~R 38 Examples of alkoxycarbonyl groups represented by include substituted or unsubstituted alkoxycarbonyl groups.

[0144] In formula (3), R 31 ~R 38 The number of carbon atoms in the alkyl chain of the unsubstituted alkoxycarbonyl group represented by is preferably 1 to 20, more preferably 1 to 15, and even more preferably 1 to 10.

[0145] Examples of alkoxycarbonyl groups with 1 to 20 carbon atoms in the alkyl chain include methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, isopropoxycarbonyl group, n-butoxycarbonyl group, sec-butoxybutylcarbonyl group, tert-butoxycarbonyl group, pentaoxycarbonyl group, hexaoxycarbonyl group, heptaoxycarbonyl group, octaoxycarbonyl group, nonaoxycarbonyl group, decaoxycarbonyl group, dodecaoxycarbonyl group, tridecaoxycarbonyl group, tetradecaoxycarbonyl group, pentadecaoxycarbonyl group, hexadecaoxycarbonyl group, heptadecaoxycarbonyl group, octadecaoxycarbonyl group, nonadecaoxycarbonyl group, and eicosaoxycarbonyl group.

[0146] Examples of substituents on an alkoxycarbonyl group include aryl groups, hydroxyl groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As an aryl group that substitutes a hydrogen atom in an alkoxycarbonyl group, in formula (3), R 31 ~R 38 Examples include unsubstituted aryl groups represented by .

[0147] In formula (3), R 31 ~R 38 Examples of halogen atoms represented by this formula include fluorine, chlorine, bromine, and iodine atoms.

[0148] The following are examples of compounds represented by formula (3), but this embodiment is not limited to these. The example compound numbers below will be referred to as example compound (3-number).

[0149] [ka]

[0150] [ka]

[0151] The electron transport material preferably has an average primary particle size of 20 nm to 1000 nm, more preferably 30 nm to 800 nm, and even more preferably 50 nm to 700 nm. When the average primary particle size of the electron-transporting material is 20 nm or larger, aggregation of the electron-transporting material within the underlying layer is suppressed, and it tends to exist with high dispersibility. As a result, electron transport performance is superior, and hole transport performance tends to be lower. Consequently, charge retention performance is superior. Furthermore, it exhibits superior conductive path properties and superior suppression of residual potential accumulation and leakage current. When the average primary particle size of the electron-transporting material is 1000 nm or less, the electron-transporting material is less likely to localize within the underlying layer and is more likely to exist with high dispersibility. As a result, electron transport performance is superior, hole transport performance tends to be lower, and charge retention performance is superior. Furthermore, it is superior in conductive paths and superior in suppressing residual potential accumulation and leakage current.

[0152] The average primary particle size of an electron-transporting material is determined as follows. The layered cross-section in the thickness direction of the photoreceptor is observed at a magnification of 100,000x using a scanning electron microscope (SEM) to identify the electron-transporting material. Then, the particle size is determined for 10 arbitrary particles present as primary particles in the electron-transporting material within the obtained SEM image. The arithmetic mean of the obtained particle sizes is taken as the average primary particle size of the electron-transporting material.

[0153] The compound represented by formula (3) preferably has an aspect ratio of 1.0 to 5.0, more preferably 1.1 to 3, and even more preferably 1.2 to 2.5. When the aspect ratio of the compound represented by formula (3) is 2.5 or less, the electron-transporting material tends to exist with high dispersibility within the underlying layer, resulting in superior electron transport and lower hole transport. When the aspect ratio of the electron-transporting material is between 1.0 and 5, the electron-transporting material tends to exist with high dispersibility within the underlying layer, resulting in superior electron transport and easier maintenance of charge retention.

[0154] The aspect ratio of the compound represented by formula (3) refers to the ratio of the length of the major axis of the electron transport material to the length of the minor axis of the electron transport material (length of major axis / length of minor axis). The length in the long axis direction of the electron transport material refers to the longest straight-line distance when connecting one end to the other end in the long axis direction of the electron transport material. The length in the short axis direction of the electron transport material refers to the longest straight-line distance when connecting one end to the other end in a direction perpendicular to the long axis of the electron transport material. The photosensitive layer (and protective layer if necessary) is removed from the photoreceptor, and the underlayer is observed at 3,000 to 100,000x magnification using a field emission scanning electron microscope (JEOL JSM-6700F) to identify the compound represented by equation (3). From the obtained micrographs, the length of the major axis and the length of the minor axis are measured for any 10 electron-transporting materials, and the aspect ratio (length of major axis / length of minor axis) is calculated for each. The arithmetic mean of each aspect ratio is taken as the aspect ratio of the electron-transporting material.

[0155] The method for adjusting the average primary particle size and aspect ratio of the compound represented by formula (3) to the above range is not particularly limited, but examples include grinding using a ball mill, bead mill, mortar and pestle, sand mill, kneader, attritor, etc., and precipitating microcrystals by dissolving in fluoroacetic acid, sulfuric acid, etc., and then contacting with water or a poor solvent.

[0156] The underlayer may further contain other electron-transporting materials other than the compounds represented by formulas (1) to (3), to the extent that the effects of this disclosure are achieved.

[0157] The proportion of the total amount of the compounds represented by formulas (1) to (3) to the total amount of electron transport material in the lower layer is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less.

[0158] The total amount of charge-transporting material containing compounds represented by formulas (1) to (3) in the entire underlayer may be less than 70% by mass relative to the total solid content of the specific underlayer. Here, the entire underlayer refers to the laminate of the first underlayer and the second underlayer in the first embodiment, and to the specific underlayer in the second embodiment. Conventionally, from the viewpoint of charge retention, the content of electron-transporting material was preferably 70% by mass or more relative to the total solid content of the undercoat. In contrast, in this embodiment, since it contains at least one compound represented by formulas (1) to (3) which has excellent electron transport properties as well as low hole transport properties, even if the total amount of electron-transporting material is less than 70% by mass, it exhibits excellent suppression of leakage current and residual potential accumulation and charge retention.

[0159] The total amount of charge-transporting material may be 60% by mass or more, or 60% by mass or more and 75% by mass or less, relative to the total solid content excluding silica particles in the undercoat. When the content of electron-transporting material is 75% by mass or less, the film quality becomes brittle, reducing film formation and suppressing surface roughness in the undercoat, resulting in superior charge retention. On the other hand, when the content of electron-transporting material is 60% by mass or more, sufficient electron transport capacity is achieved, and leakage current suppression and residual potential accumulation suppression are superior. Furthermore, sufficient charge retention is ensured.

[0160] • Binding resin Examples of known polymer compounds used as binders include acetal resins (e.g., polyvinyl butyral), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, diallyl phthalate resins, polyamide resins, nylon resins, nylon polyamide resins, cellulose resins, gelatin, urethane resins, melamine resins, benzoguanamine resins (e.g., methylated benzoguanamine resins), polyester resins, unsaturated polyester resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-alkyd resins, urea resins, phenol resins (e.g., resol-type phenol resins), phenol-formaldehyde resins, alkyd resins, epoxy resins, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. Examples of binder resins include charge-transporting resins having charge-transporting groups, and conductive resins (e.g., polyaniline).

[0161] In this specification, the term "binding resin" is a concept that encompasses resins obtained by the reaction of the resins exemplified above with the curing agent, and resins obtained by the reaction of the curing agent alone.

[0162] In this specification, the resin obtained by the reaction of a urethane resin with a curing agent will be referred to as "curable urethane resin" for convenience.

[0163] The binder resin may be either a thermoplastic resin or a thermosetting resin, but a thermosetting resin is preferred. A thermosetting resin is preferable because it does not cause dissolution or swelling of the film during the formation of the upper coating film.

[0164] Among these, a resin insoluble in the coating solvent of the upper layer is preferred as the binder resin used for the undercoat. The binder resin used for the undercoat is preferably a resin obtained by the reaction of a curing agent with at least one resin selected from the group consisting of diallyl phthalate resin, polyamide resin, nylon resin, urethane resin, melamine resin, benzoguanamine resin, and phenol resin, and is more preferably a resin containing at least one resin selected from the group consisting of urethane resin, melamine resin, and benzoguanamine resin. When the binder resin contains at least one resin selected from the above group, the hole blocking properties are high and the charge retention properties are superior.

[0165] The proportion of at least one resin selected from the group consisting of urethane resin, melamine resin, and benzoguanamine resin in the total amount of binder resin in the undercoat is preferably 80% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less.

[0166] The undercoat may contain various additives to improve electrical properties, environmental stability, and image quality. Examples of known additives include electron-transporting pigments such as polycyclic condensation and azo pigments, zirconium chelate compounds, titanium chelate compounds, aluminum chelate compounds, titanium alkoxide compounds, organic titanium compounds, and silane coupling agents. As mentioned above, silane coupling agents are used for surface treatment of inorganic particles, but they may also be added to the undercoat as additives.

[0167] Examples of silane coupling agents used as additives include vinyltrimethoxysilane, 3-methacrylateoxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

[0168] Examples of zirconium chelate compounds include zirconium butoxide, ethyl zirconium acetate, zirconium triethanolamine, acetylacetonate zirconium butoxide, ethyl acetate zirconium butoxide, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, methacrylate zirconium butoxide, stearate zirconium butoxide, and isostearate zirconium butoxide.

[0169] Examples of titanium chelate compounds include tetraisopropyl titanate, tetran-butyl titanate, butyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetonate, polytitanium acetylacetonate, titanium octylene glycolate, titanium lactate ammonium salt, titanium lactate, titanium lactate ethyl ester, titanium triethanolamine, and polyhydroxytitanium stearate.

[0170] Examples of aluminum chelating compounds include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

[0171] These additives may be used individually or as a mixture or polycondensate of multiple compounds.

[0172] The underlayer should ideally have a Vickers hardness of 35 or higher. The surface roughness (ten-point average roughness) of the undercoat layer should be adjusted to between 1 / (4n) (where n is the refractive index of the upper layer) and 1 / 2 of the exposure laser wavelength λ used, in order to suppress moiré patterns. Resin particles may be added to the undercoat to adjust the surface roughness. Examples of resin particles include silicone resin particles and cross-linked polymethyl methacrylate resin particles. The surface of the undercoat may also be polished to adjust the surface roughness. Polishing methods include buffing, sandblasting, wet honing, and grinding.

[0173] There are no particular restrictions on the formation of the undercoat, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of an undercoat-forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0174] Solvents for preparing the coating solution for forming the undercoat include known organic solvents such as alcohol-based solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone-based solvents, ketone alcohol-based solvents, ether-based solvents, and ester-based solvents. Specific examples of these solvents include common organic solvents such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene.

[0175] Known methods for dispersing inorganic particles when preparing a coating solution for forming an undercoat include, for example, roll mills, ball mills, vibrating ball mills, attritors, sand mills, colloid mills, and paint shakers.

[0176] Conventional methods for applying the undercoating solution onto a conductive substrate include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0177] [Conductive substrate] Examples of conductive substrates include metal plates, metal drums, and metal belts containing metals (aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, platinum, etc.) or alloys (stainless steel, etc.). Other examples of conductive substrates include paper, resin films, and belts coated, vapor-deposited, or laminated with conductive compounds (e.g., conductive polymers, indium oxide, etc.), metals (e.g., aluminum, palladium, gold, etc.) or alloys. Here, "conductive" refers to a volume resistivity of 10⁻¹⁰. 13 This refers to a value less than Ω·cm.

[0178] When an electrophotographic photoreceptor is used in a laser printer, the surface of the conductive substrate is preferably roughened to a center-line average roughness Ra of 0.04 μm to 0.5 μm in order to suppress interference fringes that occur when irradiated with laser light. While roughening to prevent interference fringes is not particularly necessary when using non-interfering light as the light source, it is beneficial for extending the lifespan by suppressing the occurrence of defects due to surface irregularities of the conductive substrate.

[0179] Methods for roughening a surface include, for example, wet honing, which involves suspending an abrasive in water and spraying it onto a conductive substrate; centerless grinding, which involves pressing a conductive substrate against a rotating grinding wheel and continuously grinding it; and anodizing.

[0180] One method for roughening the surface is to disperse conductive or semiconductive powder in a resin without roughening the surface of the conductive substrate, to form a layer on the surface of the conductive substrate, and then roughen the surface with the particles dispersed in that layer.

[0181] Anodizing roughening treatment involves forming an oxide film on the surface of a conductive substrate (e.g., aluminum) by anodizing it in an electrolyte solution. Examples of electrolyte solutions include sulfuric acid solution and oxalic acid solution. However, the porous anodic oxide film formed by anodizing is chemically active, easily contaminated, and exhibits large resistance fluctuations depending on the environment. Therefore, it is preferable to perform a sealing treatment on the porous anodic oxide film to block the micropores of the oxide film by volume expansion due to a hydration reaction using pressurized steam or boiling water (metal salts such as nickel may be added), thereby converting it into a more stable hydrated oxide.

[0182] The thickness of the anodic oxide film is preferably, for example, 0.3 μm to 15 μm. When the film thickness is within this range, it tends to exhibit barrier properties against injection and tends to suppress the increase in residual potential due to repeated use.

[0183] The conductive substrate may be treated with an acidic treatment solution or with boehmite. Treatment with an acidic solution is carried out, for example, as follows: First, an acidic solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The mixing ratio of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic solution is, for example, in the range of 10% to 11% by mass for phosphoric acid, 3% to 5% by mass for chromic acid, and 0.5% to 2% by mass for hydrofluoric acid, and the total concentration of these acids is preferably in the range of 13.5% to 18% by mass. The treatment temperature is preferably, for example, 42°C to 48°C. The film thickness is preferably 0.3 μm to 15 μm.

[0184] The boehmite treatment is carried out, for example, by immersing the material in pure water at 90°C to 100°C for 5 to 60 minutes, or by contacting it with heated steam at 90°C to 120°C for 5 to 60 minutes. The film thickness is preferably 0.1 μm to 5 μm. This can be further treated with anodic oxidation using an electrolyte solution with low film solubility, such as adipic acid, boric acid, borate, phosphate, phthalate, maleate, benzoate, tartrate, or citrate.

[0185] [Middle class] Although not shown in the diagram, an intermediate layer may be further provided between the undercoat layer and the photosensitive layer. The intermediate layer is, for example, a layer containing a resin. Examples of resins used in the intermediate layer include polymer compounds such as acetal resin (e.g., polyvinyl butyral), polyvinyl alcohol resin, polyvinyl acetal resin, casein resin, polyamide resin, cellulose resin, gelatin, polyurethane resin, polyester resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinyl acetate resin, vinyl chloride-vinyl acetate-maleic anhydride resin, silicone resin, silicone-alkyd resin, phenol-formaldehyde resin, and melamine resin. The intermediate layer may contain an organometallic compound. Examples of organometallic compounds used in the intermediate layer include those containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon. The compounds used in these intermediate layers may be used individually, as a mixture of multiple compounds, or as polycondensates.

[0186] Among these, the intermediate layer is preferably a layer containing an organometallic compound that contains zirconium atoms or silicon atoms.

[0187] There are no particular restrictions on the formation of the intermediate layer, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of an intermediate layer-forming coating solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary. Conventional methods such as immersion coating, push-up coating, wire bar coating, spray coating, blade coating, air knife coating, and curtain coating are used to form the intermediate layer.

[0188] The thickness of the intermediate layer is preferably set to a range of 0.1 μm to 3 μm, for example. The intermediate layer may also be used as a base layer.

[0189] [Charge generation layer] The charge generation layer is, for example, a layer containing a charge generation material and a binder resin. Alternatively, the charge generation layer may be a vapor-deposited layer of the charge generation material. A vapor-deposited layer of the charge generation material is suitable when using non-coherent light sources such as LEDs (Light Emitting Diodes) or organic EL (Electro-Luminescence) image arrays.

[0190] Examples of charge-generating materials include azo pigments such as bisazo and trisazo; fused aromatic pigments such as dibromoanthonthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0191] Among these, in order to accommodate laser exposure in the near-infrared region, it is preferable to use a metal phthalocyanine pigment or a metal-free phthalocyanine pigment as the charge generating material. Specifically, for example, hydroxygallium phthalocyanine; chlorogallium phthalocyanine; dichlorotin phthalocyanine; and titanyl phthalocyanine are more preferable.

[0192] On the other hand, to accommodate laser exposure in the near-ultraviolet region, preferred charge-generating materials include fused aromatic pigments such as dibromoanthoten; thioindigo pigments; porphyrazine compounds; zinc oxide; trigonal selenium; and bisazo pigments.

[0193] The above charge generating material may also be used when using non-coherent light sources such as LEDs and organic EL image arrays, which have a central emission wavelength between 450 nm and 780 nm.

[0194] When n-type semiconductors such as fused aromatic pigments, perylene pigments, and azo pigments are used as charge-generating materials, dark currents are less likely to occur, and image defects called black spots can be suppressed even in thin films. Furthermore, the n-type is determined using the commonly used time-of-flight method, based on the polarity of the photocurrent that flows. Those that are more likely to carry electrons as carriers than holes are classified as n-type.

[0195] The binder resin used in the charge generation layer can be selected from a wide range of insulating resins, or it may be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, and polysilane. Examples of binder resins include polyvinyl butyral resin, polyarylate resin (such as polycondensates of bisphenols and aromatic divalent carboxylic acids), polycarbonate resin, polyester resin, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyamide resin, acrylic resin, polyacrylamide resin, polyvinylpyridine resin, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol resin, and polyvinylpyrrolidone resin. Here, "insulating properties" refers to a volume resistivity of 10 13 This refers to a value of Ω·cm or greater. These binder resins can be used individually or in combination of two or more types.

[0196] Furthermore, the mixing ratio of the charge-generating material to the binder resin is preferably within the range of 10:1 to 1:10 by mass ratio.

[0197] The charge generation layer may also contain other well-known additives.

[0198] The formation of the charge generation layer is not particularly limited, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of a charge generation layer forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it as necessary. The charge generation layer may also be formed by vapor deposition of the charge generation material. Formation of the charge generation layer by vapor deposition is particularly suitable when using fused aromatic pigments or perylene pigments as the charge generation material.

[0199] Solvents for preparing the coating solution for forming the charge generation layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene. These solvents may be used individually or in mixtures of two or more.

[0200] Methods for dispersing particles (e.g., charge-generating materials) in a coating solution for forming a charge-generating layer include, for example, media dispersers such as ball mills, vibrating ball mills, attritors, sand mills, and horizontal sand mills, as well as media-less dispersers such as stirrers, ultrasonic dispersers, roll mills, and high-pressure homogenizers. Examples of high-pressure homogenizers include collision methods, which disperse the dispersion by causing liquid-liquid collisions or liquid-wall collisions under high pressure, and penetration methods, which disperse the dispersion by penetrating fine channels under high pressure. Furthermore, during this dispersion, it is effective to set the average particle size of the charge-generating material in the coating solution for forming the charge-generating layer to 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0201] Conventional methods for applying the charge-generating layer forming coating solution onto the undercoat (or intermediate layer) include, for example, the blade coating method, wire bar coating method, spray coating method, immersion coating method, bead coating method, air knife coating method, and curtain coating method.

[0202] The thickness of the charge generation layer is preferably set to a range of 0.1 μm to 5.0 μm, more preferably 0.2 μm to 2.0 μm.

[0203] [Charge transport layer] The charge transport layer is, for example, a layer containing a charge transport material and a binder resin. The charge transport layer may also be a layer containing a polymer charge transport material.

[0204] Examples of charge transport materials include quinone compounds such as p-benzoquinone, chloranil, bromanil, and anthraquinone; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone; xanthone compounds; benzophenone compounds; cyanovinyl compounds; and ethylene compounds, which are electron transport compounds. Other examples of charge transport materials include hole transport compounds such as triarylamine compounds, benzidine compounds, arylalkane compounds, aryl-substituted ethylene compounds, stilbene compounds, anthracene compounds, and hydrazone compounds. These charge transport materials may be used individually or in combination of two or more, but are not limited to these.

[0205] As charge transport materials, from the viewpoint of charge mobility, the triarylamine derivative shown in the following structural formula (a-1) and the benzidine derivative shown in the following structural formula (a-2) are preferred.

[0206] [ka]

[0207] In structural formula (a-1), Ar T1 Ar T2 , and Ar T3 Each is independently a substituted or unsubstituted aryl group, -C6H4-C(R T4 )=C(R T5 )(R T6 ), or -C6H4-CH=CH-CH=C(R T7 )(RT8 ) indicates R T4 , R T5 , R T6 , R T7 , and R T8 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Substituents for each of the above groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Furthermore, substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms are also examples of substituents for each of the above groups.

[0208] [ka]

[0209] In structural formula (a-2), R T91 and R T92 Each of these independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms, or an alkoxy group having 1 to 5 carbon atoms. T101 , R T102 , R T111 and R T112 Each of these independently consists of a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an amino group substituted with an alkyl group having 1 to 2 carbon atoms, a substituted or unsubstituted aryl group, and -C(R T12 )=C(R T13 )(R T14 ), or -CH=CH-CH=C(R T15 )(R T16 ) shows R T12 , R T13 , R T14 , R T15 and R T16 Each of these independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Tm1, Tm2, ​​Tn1, and Tn2 each independently represent an integer between 0 and 2. Substituents for each of the above groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Furthermore, substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms are also examples of substituents for each of the above groups.

[0210] Here, among the triarylamine derivative represented by structural formula (a-1) and the benzidine derivative represented by structural formula (a-2), in particular, "-C6H4-CH=CH-CH=C(R T7 )(R T8 Triarylamine derivatives having ")" and "-CH=CH-CH=C(R T15 )(R T16 A benzidine derivative having ) is preferred from the viewpoint of charge mobility.

[0211] As polymer charge transport materials, known charge transport materials such as poly-N-vinylcarbazole and polysilane can be used. Polyester-based polymer charge transport materials are particularly preferred. The polymer charge transport material may be used alone, or it may be used in combination with a binder resin.

[0212] Examples of binder resins used in the charge transport layer include polycarbonate resin, polyester resin, polyarylate resin, methacrylic resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polystyrene resin, polyvinyl acetate resin, styrene-butadiene copolymer, vinylidene chloride-acrylonitrile copolymer, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-maleic anhydride copolymer, silicone resin, silicone alkyd resin, phenol-formaldehyde resin, styrene-alkyd resin, poly-N-vinylcarbazole, and polysilane. Among these, polycarbonate resin or polyarylate resin is preferred as the binder resin. These binder resins can be used individually or in combination of two or more. The preferred mixing ratio of the charge transport material to the binder resin is between 10:1 and 1:5 by mass.

[0213] The charge transport layer may also contain other well-known additives.

[0214] The formation of the charge transport layer is not particularly limited, and well-known formation methods can be used. For example, it can be carried out by forming a coating film of a charge transport layer forming solution obtained by adding the above components to a solvent, drying the coating film, and heating it if necessary.

[0215] Suitable solvents for preparing the coating solution for forming the charge transport layer include common organic solvents such as aromatic hydrocarbons like benzene, toluene, xylene, and chlorobenzene; ketones like acetone and 2-butanone; halogenated aliphatic hydrocarbons like methylene chloride, chloroform, and ethylene chloride; and cyclic or linear ethers like tetrahydrofuran and ethyl ether. These solvents can be used individually or in mixtures of two or more.

[0216] Conventional methods for applying a charge transport layer forming coating solution onto a charge generation layer include blade coating, wire bar coating, spray coating, immersion coating, bead coating, air knife coating, and curtain coating.

[0217] The thickness of the charge transport layer is set, for example, preferably within the range of 5 μm to 50 μm, and more preferably within the range of 10 μm to 30 μm.

[0218] [Protective layer] A protective layer is provided on the photosensitive layer as needed. The protective layer is provided, for example, to prevent chemical changes in the photosensitive layer during electrostatic charging, or to further improve the mechanical strength of the photosensitive layer. Therefore, it is preferable to apply a protective layer composed of a cured film (crosslinked film). Examples of such layers include those shown in 1) or 2) below.

[0219] 1) A layer composed of a cured film of a composition containing a reactive group-containing charge transport material having a reactive group and a charge transport skeleton within the same molecule (i.e., a layer containing a polymer or crosslinked form of the reactive group-containing charge transport material). 2) A layer composed of a cured film of a composition comprising a non-reactive charge transport material and a non-charge transport material containing reactive groups that does not have a charge transport skeleton but has reactive groups (i.e., a layer comprising a non-reactive charge transport material and a polymer or crosslinked form of the non-charge transport material containing reactive groups).

[0220] The reactive groups in the reactive group-containing charge transport material include chain polymerizable groups, epoxy groups, -OH, -OR [where R represents an alkyl group], -NH2, -SH, -COOH, and -SiR. Q1 3-Qn (OR Q2 ) Qn [However, R Q1 R represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group. Q2 Examples of well-known reactive groups include hydrogen atoms, alkyl groups, and trialkylsilyl groups. Qn represents an integer from 1 to 3.

[0221] The chain polymerizable group is not particularly limited as long as it is a functional group capable of radical polymerization, for example, a functional group having at least one carbon double bond. Specifically, examples include groups containing at least one selected from vinyl groups, vinyl ether groups, vinyl thioether groups, styryl groups (vinyl phenyl groups), acryloyl groups, methacryloyl groups, and their derivatives. Among these, the chain polymerizable group is preferably a group containing at least one selected from vinyl groups, styryl groups (vinyl phenyl groups), acryloyl groups, methacryloyl groups, and their derivatives, due to its excellent reactivity.

[0222] The charge-transporting skeleton of the reactive group-containing charge-transporting material is not particularly limited as long as it is a known structure in electrophotographic photoreceptors. Examples include skeletons derived from nitrogen-containing hole-transporting compounds such as triarylamine compounds, benzidine compounds, and hydrazone compounds, in which the nitrogen atom is conjugated. Among these, the triarylamine skeleton is preferred.

[0223] These reactive groups and charge-transporting skeletons, including reactive group-containing charge transport materials, non-reactive charge transport materials, and reactive group-containing non-charge transport materials, can be selected from well-known materials.

[0224] The protective layer may also contain other well-known additives.

[0225] There are no particular restrictions on the formation of the protective layer, and well-known formation methods can be used. For example, it can be formed by adding the above components to a solvent to create a protective layer coating solution, drying the coating, and then performing a curing treatment such as heating as necessary.

[0226] Solvents for preparing coating solutions for forming a protective layer include aromatic solvents such as toluene and xylene; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; cellosolve solvents such as ethylene glycol monomethyl ether; and alcohol solvents such as isopropyl alcohol and butanol. These solvents can be used individually or in combination of two or more. Furthermore, the coating solution for forming the protective layer may be a solvent-free coating solution.

[0227] Conventional methods for applying a protective layer-forming coating solution onto a photosensitive layer (e.g., a charge transport layer) include immersion coating, push-up coating, wire bar coating, spray coating, blade coating, air knife coating, and curtain coating.

[0228] The thickness of the protective layer is set, for example, preferably within the range of 1 μm to 20 μm, and more preferably within the range of 2 μm to 10 μm.

[0229] [Single-layer photosensitive layer] A single-layer photosensitive layer (charge generation / charge transport layer) is, for example, a layer comprising a charge generation material, a charge transport material, and, if necessary, a binder resin and other well-known additives. These materials are the same as those described for the charge generation layer and the charge transport layer. Furthermore, the content of the charge-generating material in the single-layer photosensitive layer is preferably 0.1% to 10% by mass, and more preferably 0.8% to 5% by mass, relative to the total solid content. In addition, the content of the charge-transporting material in the single-layer photosensitive layer is preferably 5% to 50% by mass, relative to the total solid content. The method for forming a single-layer photosensitive layer is the same as the method for forming a charge generation layer or a charge transport layer. The thickness of the single-layer photosensitive layer is, for example, preferably 5 μm to 50 μm, and more preferably 10 μm to 40 μm.

[0230] <Image forming apparatus (and process cartridge)> The image forming apparatus according to this embodiment comprises an electrophotographic photoreceptor, a charging device for charging the surface of the electrophotographic photoreceptor, an electrostatic latent image forming device for forming an electrostatic latent image on the charged surface of the electrophotographic photoreceptor, a developing device for developing the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing toner to form a toner image, and a transfer device for transferring the toner image to the surface of a recording medium. The electrophotographic photoreceptor according to this embodiment is used as the electrophotographic photoreceptor.

[0231] The image forming apparatus according to this embodiment includes a fixing device for fixing a toner image transferred to the surface of a recording medium; a direct transfer method apparatus for directly transferring a toner image formed on the surface of an electrophotographic photoreceptor to a recording medium; an intermediate transfer method apparatus for first transferring a toner image formed on the surface of an electrophotographic photoreceptor to the surface of an intermediate transfer body, and secondarily transferring the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium; a cleaning device for cleaning the surface of the electrophotographic photoreceptor after the transfer of the toner image and before it is charged; a static elimination device for irradiating the surface of the electrophotographic photoreceptor with static elimination light to eliminate static charge after the transfer of the toner image and before it is charged; and a well-known image forming apparatus such as an electrophotographic photoreceptor heating member for raising the temperature of the electrophotographic photoreceptor and reducing the relative temperature.

[0232] In the case of an intermediate transfer method apparatus, the transfer apparatus may be configured to include, for example, an intermediate transfer body on which a toner image is transferred; a primary transfer apparatus that first transfers the toner image formed on the surface of an electrophotographic photoreceptor to the surface of the intermediate transfer body; and a secondary transfer apparatus that secondarily transfers the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium.

[0233] The image forming apparatus according to this embodiment may be either a dry developing type image forming apparatus or a wet developing type image forming apparatus (a developing method using a liquid developer).

[0234] In the image forming apparatus according to this embodiment, for example, the part equipped with an electrophotographic photoreceptor may be a cartridge structure (process cartridge) that can be attached to and detached from the image forming apparatus. As the process cartridge, for example, a process cartridge equipped with an electrophotographic photoreceptor according to this embodiment is preferably used. In addition to the electrophotographic photoreceptor, the process cartridge may also include at least one selected from the group consisting of, for example, a charging device, an electrostatic latent image forming device, a developing device, and a transfer device.

[0235] The following is an example of an image forming apparatus according to this embodiment, but it is not limited to this example. The main parts shown in the figure will be described, and other parts will be omitted from the explanation.

[0236] Figure 3 is a schematic diagram showing an example of an image forming apparatus according to this embodiment. As shown in Figure 3, the image forming apparatus 100 according to this embodiment includes a process cartridge 300 equipped with an electrophotographic photoreceptor 7, an exposure device 9 (an example of an electrostatic latent image forming apparatus), a transfer device 40 (a primary transfer device), and an intermediate transfer body 50. In the image forming apparatus 100, the exposure device 9 is positioned to expose the electrophotographic photoreceptor 7 from the opening of the process cartridge 300, and the transfer device 40 is positioned facing the electrophotographic photoreceptor 7 via the intermediate transfer body 50, with a portion of the intermediate transfer body 50 in contact with the electrophotographic photoreceptor 7. Although not shown, the apparatus also includes a secondary transfer device that transfers the toner image transferred to the intermediate transfer body 50 to a recording medium (e.g., paper). The intermediate transfer body 50, the transfer device 40 (primary transfer device), and the secondary transfer device (not shown) are examples of transfer devices.

[0237] In Figure 3, the process cartridge 300 integrally supports an electrophotographic photoreceptor 7, a charging device 8 (an example of a charging device), a developing device 11 (an example of a developing device), and a cleaning device 13 (an example of a cleaning device) within a housing. The cleaning device 13 has a cleaning blade (an example of a cleaning member) 131, which is positioned to contact the surface of the electrophotographic photoreceptor 7. The cleaning member may be a conductive or insulating fibrous member, rather than a cleaning blade 131, and may be used alone or in combination with the cleaning blade 131.

[0238] Figure 3 shows an example of an image forming apparatus equipped with a fibrous member 132 (roll-shaped) for supplying lubricant 14 to the surface of the electrophotographic photoreceptor 7, and a fibrous member 133 (flat brush-shaped) for assisting cleaning. These can be arranged as needed.

[0239] The following describes the various components of the image forming apparatus according to this embodiment.

[0240] -Charging device- As the charging device 8, for example, a contact-type charger using conductive or semiconductive charging rollers, charging brushes, charging films, charging rubber blades, charging tubes, etc. may be used. Non-contact roller chargers, known chargers such as scorotron chargers and corotron chargers that utilize corona discharge may also be used.

[0241] -Exposure equipment- Examples of exposure devices 9 include optical equipment that exposes the surface of an electrophotographic photoreceptor 7 to a predetermined image using light such as semiconductor laser light, LED light, or liquid crystal shutter light. The wavelength of the light source is within the spectral sensitivity range of the electrophotographic photoreceptor. As for the wavelength of the semiconductor laser, near-infrared lasers with an oscillation wavelength of around 780 nm are the mainstream. However, the wavelength is not limited to this, and lasers with oscillation wavelengths in the 600 nm range or blue lasers with oscillation wavelengths between 400 nm and 450 nm may also be used. Furthermore, for color image formation, surface-emitting laser light sources capable of outputting multiple beams are also effective.

[0242] -Developing equipment- Examples of developing devices 11 include general developing devices that develop by contacting or not contacting the developing agent. There are no particular restrictions on the developing device 11 as long as it has the above-described functions, and it can be selected according to the purpose. For example, known developing devices that have the function of applying a one-component or two-component developing agent to the electrophotographic photoreceptor 7 using a brush, roller, etc. Among these, those that use a developing roller that holds the developing agent on its surface are preferred.

[0243] The developer used in the developing device 11 may be a one-component developer consisting of toner alone, or a two-component developer containing toner and a carrier. Furthermore, the developer may be magnetic or non-magnetic. Well-known developers are applicable.

[0244] -Cleaning device- The cleaning device 13 is a cleaning blade type device equipped with a cleaning blade 131. In addition to the cleaning blade method, a fur brush cleaning method or a developing-simultaneous cleaning method may also be used.

[0245] -Transfer device- Examples of the transfer device 40 include contact-type transfer chargers using belts, rollers, films, rubber blades, etc., and transfer chargers that are known themselves, such as scorotron transfer chargers and corotron transfer chargers that utilize corona discharge.

[0246] -Intermediate Transcript- As the intermediate transfer body 50, a belt-shaped material (intermediate transfer belt) containing semiconducting polyimide, polyamide-imide, polycarbonate, polyarylate, polyester, rubber, etc. is used. In addition to the belt shape, a drum-shaped intermediate transfer body may also be used.

[0247] Figure 4 is a schematic diagram showing another example of an image forming apparatus according to this embodiment. The image forming apparatus 120 shown in Figure 4 is a tandem-type multi-color image forming apparatus equipped with four process cartridges 300. In the image forming apparatus 120, the four process cartridges 300 are arranged in parallel on the intermediate transfer body 50, and one electrophotographic photoreceptor is used for each color. The image forming apparatus 120 has the same configuration as the image forming apparatus 100, except that it is a tandem type. [Examples]

[0248] The embodiments of the invention will be described in detail below with reference to examples, but the embodiments of the invention are not limited to these examples. In the following explanation, unless otherwise specified, "parts" and "%" refer to mass. In the following descriptions, unless otherwise specified, synthesis, manufacturing, processing, and measurements were performed at room temperature (25°C ± 3°C).

[0249] -Preparation for the first lower layer- (Preparation of the first lower layer 1) A solution was prepared by dissolving 14 parts by mass of a curable urethane resin (blocked isocyanate Coronate 2507, manufactured by Tosoh Corporation, 80% solids content) and 5.1 parts by mass of butyral resin (Eslec BL-S, manufactured by Sekisui Chemical Co., Ltd.) in 160 parts by mass of methyl ethyl ketone. 25 parts by mass of electron transport material (1-1) was mixed into this solution, and the mixture was dispersed using 1 mmφ glass beads in a sand mill for 200 minutes to obtain a dispersion. After filtering off the glass beads, 0.005 parts by mass of bismuth carboxylate (K-KAT XK-640) manufactured by King Industries Co., Ltd. was added to the resulting dispersion as a catalyst to obtain a coating solution for forming the undercoat layer. This coating solution was applied to an aluminum substrate (conductive substrate) by immersion coating, and dried and cured at 160°C for 60 minutes to obtain a first undercoat layer 1 with a thickness of 4 μm.

[0250] (Preparation of the first lower layer 2) The first underlayer 2 was fabricated with the same specifications as the first underlayer 1, except that the type and amount of electron transport material shown in Table 1 was used instead of the electron transport material (1-1) in the fabrication of the first underlayer 1.

[0251] (Preparation of the first lower layer 3) 20 parts by mass of benzoguaramine resin (methylated benzoguaramine resin BL-60, manufactured by Sanwa Chemical Co., Ltd., solids content 60%) and 4.3 parts by mass of melamine (Nicalac MW-390, manufactured by Sanwa Chemical Co., Ltd.) were dissolved in 160 parts by mass of methyl ethyl ketone. 25 parts by mass of electron transport material (2-1) were mixed into this solution, and the mixture was dispersed using 1 mmφ glass beads in a sand mill for 180 minutes to obtain a dispersion. After filtering off the glass beads, 0.005 parts by mass of Nacure5925 (manufactured by King Industries) was added to the resulting dispersion as a catalyst to obtain a coating solution for forming the undercoat layer. This coating solution was applied to an aluminum substrate by immersion coating, and dried and cured at 160°C for 60 minutes to obtain a first undercoat layer 3 with a thickness of 4 μm.

[0252] (Preparation of the first lower layer 4) The first underlayer 4 was fabricated in the same manner as the first underlayer 3, except that the type and amount of electron transport material shown in Table 1 was used instead of the electron transport material (2-1) in the fabrication of the first underlayer 3.

[0253] (Preparation of the first lower layer 5) 30 parts by mass of phenolic resin (PR-53123, manufactured by Sumitomo Bakelite, 45% solids content) and 2.8 parts by mass of butyral resin (Eslec BM-1, manufactured by Sekisui Chemical Co., Ltd.) were dissolved in a mixed solvent of 100 parts by mass of methyl ethyl ketone and 60 parts by mass of ethanol. 25 parts by mass of electron transport materials of the type shown in Table 1 were mixed into this solution, and the mixture was dispersed using 1 mmφ glass beads in a sand mill for 200 minutes to obtain a dispersion. The glass beads were filtered off to obtain a coating solution for forming the undercoat. This coating solution was applied to an aluminum substrate by immersion coating, and dried and cured at 150°C for 60 minutes to obtain a first undercoat 5 with a thickness of 4 μm.

[0254] (Preparation of the first lower layer 6) Each first underlayer was prepared with the same specifications as the first underlayer 1, except that the silica particles in the mixture before dispersion treatment were in the same content as shown in Table 1.

[0255] (Preparation of the first lower layers 7-14) Each first underlayer was fabricated with the same specifications except that the type and amount of charge-transporting material in the first underlayer 1 were as shown in Table 1.

[0256] (Preparation of the first lower layer C1-1 for comparative example) In the first lower layer 1, silica particles (RX50, manufactured by Nippon Aerosil Co., Ltd., average particle size 40 nm) were added to the mixture before dispersion treatment in the quantities shown in Table 1. This was prepared in the same manner as the first lower layer 1 and designated as the comparative first lower layer C1-1.

[0257] (Preparation of the first lower layer C1-2 for comparative example) In the first underlayer 1, the electron transport material (1-1) was replaced with the imide compound (A) described below, but otherwise the underlayer was prepared in the same manner as the first underlayer 1, and this was designated as the comparative first underlayer 2 (C1-2).

[0258] [ka]

[0259] -Preparation for the second lower layer- (Preparation of the second lower layer 1) A solution was prepared by dissolving 14 parts by mass of a curable urethane resin (blocked isocyanate Coronate 2507, manufactured by Tosoh Corporation, 80% solids) and 5.1 parts by mass of butyral resin (Eslec BL-S, manufactured by Sekisui Chemical Co., Ltd.) in 200 parts by mass of methyl ethyl ketone. 20 parts by mass of an electron transport material of the type shown in Table 2 and 16.3 parts by mass of silica particles of the type shown in Table 2 (RX50, manufactured by Nippon Aerosil Co., Ltd., average particle size 40 nm) were mixed into this solution. The mixture was then dispersed using 1 mmφ glass beads in a paint shaker for 240 minutes to obtain a dispersion. After filtering off the glass beads, 0.005 parts by mass of bismuth carboxylate (K-KAT XK-640) manufactured by King Industries Co., Ltd. was added to the resulting dispersion as a catalyst to obtain a coating solution for forming the undercoat layer. This coating solution was applied to an aluminum substrate by immersion coating, and dried and cured at 160°C for 60 minutes to obtain a second undercoat layer 1 with a thickness of 3 μm.

[0260] (Preparation of the second lower layer 2) The second underlayer 2 was fabricated in the same manner as the second underlayer 1, except that silica particles of the type shown in Table 2 (MSP-016, manufactured by Teika, average particle size 80 nm) were used instead of RX50 for the second underlayer 1.

[0261] (Preparation of the second lower layer 3) In the preparation of the second underlayer 1, the second underlayer 2 was prepared in the same manner as the second underlayer 1, except that silica particles of the type shown in Table 2 (MSL-005L, manufactured by Teika, average particle size 80 nm) were used instead of RX50 silica particles.

[0262] (Preparation of the second lower layer 4) 20 parts by mass of benzoguanamine resin (methylated benzoguanamine resin BL-60, manufactured by Sanwa Chemical Co., Ltd., solids content 60%) and 4.3 parts by mass of melamine (Nicalac MW-390, manufactured by Sanwa Chemical Co., Ltd.) were dissolved in 200 parts by mass of methyl ethyl ketone. 20 parts by mass of electron transport material (3-1) and 16.3 parts by mass of silica particles of the type shown in Table 2 (MSP-002, manufactured by Teika, average particle size 16 nm) were mixed into this solution. The mixture was then dispersed using 1 mmφ glass beads in a paint shaker for 240 minutes to obtain a dispersion. After filtering off the glass beads, 0.005 parts by mass of Nacure5925 (manufactured by King Industries) was added to the resulting dispersion as a catalyst to obtain a coating solution for forming the undercoat layer. This coating solution was applied to an aluminum substrate by immersion coating, and dried and cured at 160°C for 60 minutes to obtain a second undercoat layer 4 with a thickness of 3 μm.

[0263] (Preparation of the second lower layer 5) 30 parts by mass of phenolic resin (PR-53123, manufactured by Sumitomo Bakelite, 45% solids content) and 2.8 parts by mass of butyral resin (Eslec BM-1, manufactured by Sekisui Chemical Co., Ltd.) were dissolved in a mixed solvent of 120 parts by mass of methyl ethyl ketone and 80 parts by mass of ethanol. 20 parts by mass of electron transport material (1-1) and 16.3 parts by mass of silica particles of the type shown in Table 2 (NX90G, manufactured by Nippon Aerosil, average particle size 20 nm) were mixed into this solution. The mixture was then dispersed using 1 mmφ glass beads in a paint shaker for 240 minutes to obtain a dispersion. The glass beads were filtered off to obtain a coating solution for forming the undercoat. This coating solution was applied to an aluminum substrate by immersion coating, and dried and cured at 150°C for 60 minutes to obtain a second undercoat layer 5 with a thickness of 3 μm.

[0264] (Preparation of the second lower layer 6-11) Each second lower layer was fabricated with the same specifications except that the type and amount of charge-transporting material used in the second lower layer 1 were as shown in Table 2.

[0265] (Preparation of the second lower layer 12-13) Each second underlayer was fabricated with the same specifications as the second underlayer 1, except that the charge transport material used had the average primary particle size and aspect ratio shown in Table 2.

[0266] (Preparation of the second lower layer 14) In the second undercoat 1, the silica particles were manufactured with the same specifications as shown in Table 2, except that the type of silica particles was changed to the specifications shown in Table 2 so that the proportion of silica particles in the region within 50% of the interface between the second undercoat and the photosensitive layer in the direction toward the conductive substrate (hereinafter referred to as "IN R50") was as shown in Table 3.

[0267] (Preparation of the second lower layer 15) The product was manufactured with the same specifications as shown in Table 2, except that the type of silica particles was changed to the specifications shown in Table 2 so that the proportion of silica particles in the region exceeding 50% in the direction from the interface between the second undercoat layer and the photosensitive layer towards the conductive substrate (hereinafter referred to as "OUT R50") matches the specifications shown in Table 3.

[0268] (Preparation of the second lower layer 16-18) Each second underlayer was fabricated with the same specifications as shown in Table 2, except that the silica particle content in the second underlayer 1 was set to the specifications shown in Table 2.

[0269] (Preparation of the second lower layers C2-1 to C2-3 for comparative examples) The second lower layers C2-1 to C2-3 for comparative examples were prepared using the same specifications as the first lower layers 1, 4, and 5, except that silica particles were not added.

[0270] <Examples 1-26 and Comparative Examples 1-5> (Formation of a charge generation layer) A mixture consisting of 15 parts by mass of hydroxygallium phthalocyanine, which has diffraction peaks at Bragg angles (2θ±0.2°) of at least 7.3°, 16.0°, 24.9°, and 28.0° in its X-ray diffraction spectrum using Cukα characteristic X-rays, 10 parts by mass of vinyl chloride / vinyl acetate copolymer resin (VMCH, manufactured by Nippon Unicar Co., Ltd.) as a binder resin, and 200 parts by mass of n-butyl acetate was dispersed by stirring in a sand mill for 4 hours using glass beads with a diameter of 1 mmφ. To the obtained dispersion, 175 parts by mass of n-butyl acetate and 180 parts by mass of methyl ethyl ketone were added and stirred to obtain a coating solution for forming a charge generation layer. This coating solution for forming a charge generation layer was immersed and applied to the outer surface of the undercoat layers of the types shown in Table 1, and dried at 150°C for 15 minutes to form a charge generation layer with a film thickness of 0.2 μm.

[0271] (Formation of charge transport layer) 38 parts by mass of the following charge transport agent (HT-1), 10 parts by mass of the following charge transport agent (HT-2), and 52 parts by mass of the following polycarbonate resin (A) (viscosity-average molecular weight: 46,000, values ​​in the structural formula are molar ratios), along with 0.3 parts by mass of fluorine-containing graft polymer (Toagosei: GF-500) as a dispersion aid, were dissolved in 800 parts by mass of tetrahydrofuran. 8 parts by mass of tetrafluoroethylene resin (Daikin Industries: Rubron L5, average particle size 300 nm) were added, and the mixture was dispersed at 5500 rpm for 2 hours using a homogenizer (IKA: Ultra-Turrax) to obtain a coating solution for forming a charge transport layer. This coating solution was applied to the charge generation layer, and dried at 140°C for 40 minutes to form a charge transport layer with a film thickness of 30 μm. This was used as an electrophotographic photoreceptor.

[0272] [ka]

[0273] [ka]

[0274] <Rating> The electrophotographic photoreceptors of each example or comparative example were mounted in a modified Fujifilm Business Innovation DocuCentre C5570 image forming apparatus, and the following evaluations were performed.

[0275] -Evaluation of residual potential accumulation- An image formation test was conducted by continuously printing 500,000 images with 10% halftone under conditions of 30°C and 85% humidity. The residual potential on the photoreceptor surface was measured immediately after the first print and immediately after the 500,000th print, and the increase was calculated from the difference. The residual potential was measured by placing a surface potential measurement probe behind the static elimination lamp in the image forming apparatus and reading the surface potential of the photoreceptor surface. The obtained difference in the increase of residual potential was defined as the accumulated residual potential and evaluated according to the following criteria. The acceptable range is A to D. The results are shown in the table below. A: Less than 15V. B: 15V or more and less than 25V. C: 25V or more and less than 35V. D: 35V or more and less than 45V. E: 45V or higher, which is a problematic level.

[0276] -Evaluation of static charge retention- Under conditions of 10°C and 15% RH, an electrophotographic photoreceptor was charged with an applied voltage of -710V, and 30,000 50% halftone images were printed. The initial charge potential V1 (i.e., before image output) and the charge potential V2 (i.e., the surface potential of the photoreceptor immediately after the charging process) on the outer surface of the electrophotographic photoreceptor were measured. The potential difference V1-V2 was calculated and evaluated according to the following criteria. The acceptable range is A to D. The results are shown in the table below. A: Less than 20V. B: 20V or more and less than 25V. C: 25V or more and less than 30V. D: 30V or more and less than 35V. E: 35V or higher, which is a problematic level.

[0277] -Evaluation of leakage current- The effectiveness of suppressing foreign object penetration was evaluated by utilizing the phenomenon where current flows and point-like image defects occur when carbon fibers penetrate the photosensitive layer and undercoat to reach the conductive substrate. The charging potential was typically set to -760V. Carbon fibers (average diameter 7μm, average length 30μm) were mixed into the developer in an amount equal to 0.2% by mass, and 20,000 images with a 20% density were continuously printed on A4 paper. Next, 10 images with a 20% density were printed on A4 paper. The presence or absence of point-like image defects in the 10th image was visually observed, and the degree of image defects was classified into A to E below. The acceptable range is A to D. The results are shown in the table below.

[0278] A: There are no point-like image defects. B: Fewer than 3 point-like image defects. C: Fewer than 5 point-like image defects. D: There are 5 to 10 point-like image defects. E: There are 10 or more point-like image defects, which is a problematic level.

[0279] [Table 1]

[0280] [Table 2]

[0281] [Table 3]

[0282] As shown in the table, the electrophotographic photoreceptor of the example was found to have suppressed both residual potential accumulation and leakage current, and to have excellent charge retention, compared to the electrophotographic photoreceptor of the comparative example.

[0283] The electrophotographic photoreceptor, process cartridge, and image forming apparatus of this disclosure include the following embodiments. Each formula is identical to the formula with the same number described above.

[0284] (((1))) Conductive substrate and, A first undercoat layer provided on the conductive substrate, A second lower layer is provided on top of the first lower layer, A photosensitive layer provided on the second undercoat layer, Equipped with, The first undercoat comprises at least one electron-transporting material selected from the group consisting of a compound represented by formula (1), a compound represented by formula (2), and a compound represented by formula (3), and a binder resin, and the silica particle content in the first undercoat is 0% by mass or 5% by mass or less. The second underlayer comprises at least one electron-transporting material selected from the group consisting of a compound represented by formula (1), a compound represented by formula (2), and a compound represented by formula (3), silica particles, and a binder resin, and the silica particle content in the second underlayer is greater than the silica particle content in the first underlayer. Electrophotographic photoreceptor. [ka] In formula (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 11 and R 12 , R 12 and R 13 and R 13 and R 14 Each element may be independent of the others, or they may be connected to each other to form a ring. 15 and R 16 , R 16 and R 17 and R 17 and R18 These elements may be connected to each other independently to form a ring. In formula (2), R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 21 and R 22 , R 22 and R 23 and R 23 and R 24 Each element may be independent of the others, or they may be connected to each other to form a ring. 25 and R 26 , R 26 and R 27 and R 27 and R 28 These elements may be connected to each other independently to form a ring. In formula (3), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom. (((2))) The electrophotographic photoreceptor according to (((1))), wherein the second underlayer contains 20% by mass or more of silica particles. (((3))) The electrophotographic photoreceptor according to (((2))), wherein the second underlayer contains silica particles in the second underlayer of 25% by mass or more and 50% by mass or less. (((4))) Conductive substrate and, A specific underlayer provided on the conductive substrate, A photosensitive layer provided on the aforementioned specific undercoat layer, Equipped with, The specified underlayer comprises at least one electron-transporting material selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3), silica particles, and a binder resin, and the silica particles are unevenly distributed in a region within 50% of the interface between the specified underlayer and the photosensitive layer in the direction toward the conductive substrate. [ka] In formula (1), R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 11 and R 12 , R 12 and R 13 and R 13 and R 14 Each element may be independent of the others, or they may be connected to each other to form a ring. 15 and R 16 , R 16 and R 17 and R 17 and R 18 These elements may be connected to each other independently to form a ring. In formula (2), R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. 21 and R 22 , R 22 and R 23 and R 23 and R 24 Each element may be independent of the others, or they may be connected to each other to form a ring. 25 and R 26 , R 26 and R 27 and R 27 and R 28 These elements may be connected to each other independently to form a ring. In formula (3), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom. (((5))) The electrophotographic photoreceptor according to (((4))), wherein the specific undercoat is such that the proportion of silica particles in the region within 50% of the thickness cross-section from the interface between the specific undercoat and the photosensitive layer in the direction toward the conductive substrate is 25% or more and 60% or less of the entire specific undercoat. (((6))) The electrophotographic photoreceptor according to (((5))), wherein the specific undercoat is such that the proportion of silica particles in the region within 50% of the thickness-direction cross section from the interface between the specific undercoat and the photosensitive layer in the direction toward the conductive substrate is 30% or more and 50% or less of the entire specific undercoat. (((7))) The electron transport material is an electrophotographic photoreceptor according to any one of (((1))) to (((6))) above, wherein the average primary particle size is 20 nm or more and 1000 nm or less. (((8))) The electrophotographic photoreceptor according to any one of (((1))) to (((7))) above, wherein the silica particles have an average primary particle size of 50 nm or more and 500 nm or less. (((9))) The electron transport material includes at least one selected from the group consisting of the compound represented by formula (1), the compound represented by formula (2), and the compound represented by formula (3), (however, In equation (1) above, R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 and R 18 Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom. In equation (2) above, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , R 27 and R 28 Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom. In the above equation (3), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom. The electrophotographic photoreceptor described in (((1))) or (((4))) above. (((10))) comprising an electrophotographic photoreceptor as described in any one of (((1))) to (((9))), A process cartridge that is attached to and detached from an image forming apparatus. (((11))) An electrophotographic photoreceptor as described in any one of (((1))) to (((9))) above, A charging device for charging the surface of the electrophotographic photoreceptor, An electrostatic latent image forming apparatus for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing apparatus that develops an electrostatic latent image formed on the surface of an electrophotographic photoreceptor using a developer containing toner to form a toner image, A transfer device for transferring the toner image onto the surface of a recording medium, An image forming apparatus equipped with the following features.

[0285] According to the inventions of (((1))), (((4))), or (((9))), compared to the case in which silica particles are uniformly contained throughout the entire underlayer containing an electron-transporting material, an electrophotographic photoreceptor is provided that suppresses both the accumulation of residual potential and leakage current, and has excellent charge retention properties. According to the invention of (((2))), an electrophotographic photoreceptor is provided in which the second underlayer suppresses both residual potential accumulation and leakage current compared to the case in which the silica particle content in the second underlayer is less than 20% by mass. According to the invention of (((3))), an electrophotographic photoreceptor is provided in which the second underlayer suppresses both residual potential accumulation and leakage current compared to the case in which the silica particle content in the second underlayer is less than 25% by mass or more than 50% by mass. According to the invention of (((5))), an electrophotographic photoreceptor is provided in which the specific undercoat is such that the proportion of silica particles in a region within 50% of the thickness cross-section from the interface between the specific undercoat and the photosensitive layer toward the conductive substrate is less than 25 area % or more than 60 area % of the entire specific undercoat, thereby suppressing both residual potential accumulation and leakage current. According to the invention of (((6))), compared to the case where the proportion of silica particles in the region within 50% of the thickness-direction cross-section of the specific undercoat, from the interface between the specific undercoat and the photosensitive layer toward the conductive substrate, is less than 30 area % or more than 50 area % of the entire specific undercoat, an electrophotographic photoreceptor is provided that suppresses both residual potential accumulation and leakage current, and has excellent charge retention. According to the invention of (((7))), an electrophotographic photoreceptor is provided that exhibits superior charge retention compared to cases where the electron transport material has an average primary particle size of less than 20 nm or more than 1000 nm. According to the invention of (((8))), an electrophotographic photoreceptor is provided that suppresses both residual potential accumulation and leakage current, and exhibits excellent charge retention, compared to cases where the average primary particle size of silica particles is less than 50 nm or greater than 500 nm. According to the invention of (((10))), a process cartridge is provided which has an electrophotographic photoreceptor that suppresses both residual potential accumulation and leakage current, and has excellent charge retention, compared to the case in which silica particles are uniformly contained throughout the entire underlayer containing an electron transport material. According to the invention of (((11))), an image forming apparatus is provided that has an electrophotographic photoreceptor that suppresses both the accumulation of residual potential and leakage current, and has excellent charge retention, compared to the case in which silica particles are uniformly contained throughout the entire underlayer containing an electron transport material. [Explanation of Symbols]

[0286] 1 Conductive substrate, 2 Undercoat layer, 3 Charge generation layer, 4 Charge transport layer, 5 Photosensitive layer, 10A photoreceptor, 10B electrophotographic photoreceptor

[0287] 7 Electrophotographic photoreceptor, 8 Charging device, 9 Exposure device, 11 Developing device, 13 Cleaning device, 14 Lubricant, 40 Transfer device, 50 Intermediate transfer body, 100 Image forming device, 120 Image forming device, 131 Cleaning blade, 132 Fibrous material (roll type), 133 Fibrous material (flat brush type), 300 Process cartridge

Claims

1. A conductive substrate, A first undercoat layer provided on the conductive substrate, A second lower layer is provided on top of the first lower layer, A photosensitive layer provided on the second undercoat layer, Equipped with, The first undercoat comprises at least one electron-transporting material selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3), and a binder resin, and the silica particle content in the first undercoat is 0% by mass or 5% by mass or less. The second underlayer comprises at least one electron-transporting material selected from the group consisting of a compound represented by formula (1), a compound represented by formula (2), and a compound represented by formula (3), silica particles, and a binder resin, and the content of the silica particles in the second underlayer is greater than the content of the silica particles in the first underlayer. Electrophotographic photoreceptor. 【Chemistry 1】 In formula (1), R １１ 、R １２ 、R １３ 、R １４ 、R １５ 、R １６ 、R １７ and R １８ each independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group or a halogen atom. R １１ and R １２ 、R １２ and R １３ and R １３ and R １４ each independently may be linked to each other to form a ring. R １５ and R １６ 、R １６ [[ID= 34]]and R １７ and R １７ and R １８ each independently may be linked to each other to form a ring. In formula (2), R ２１ , R ２２ , R ２３ , R ２４ , R ２５ , R ２６ , R ２７ and R ２８ Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. ２１ and R ２２ , R ２２ and R ２３ and R ２３ and R ２４ Each element may be independent of the others, or they may be connected to each other to form a ring. ２５ and R ２６ , R ２６ and R ２７ and R ２７ and R ２８ These elements may be connected to each other independently to form a ring. In formula (3), R ３１ , R ３２ , R ３３ , R ３４ , R ３５ , R ３６ , R ３７ and R ３８ Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom.

2. The electrophotographic photoreceptor according to claim 1, wherein the second undercoat layer contains 20% by mass or more silica particles.

3. The electrophotographic photoreceptor according to claim 2, wherein the second undercoat layer contains silica particles in an amount of 25% by mass or more and 50% by mass or less.

4. A conductive substrate, A specific underlayer provided on the conductive substrate, A photosensitive layer provided on the aforementioned specific undercoat layer, Equipped with, The specified underlayer comprises at least one electron-transporting material selected from the group consisting of a compound represented by the following formula (1), a compound represented by the following formula (2), and a compound represented by the following formula (3), silica particles, and a binder resin, and the silica particles are unevenly distributed in a region within 50% of the interface between the specified underlayer and the photosensitive layer in the direction of the conductive substrate. 【Chemistry 2】 In formula (1), R １１ , R １２ , R １３ , R １４ , R １５ , R １６ , R １７ and R １８ Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. １１ and R １２ , R １２ and R １３ and R １３ and R １４ Each element may be independent of the others, or they may be connected to each other to form a ring. １５ and R １６ , R １６ and R １７ and R １７ and R １８ These elements may be connected to each other independently to form a ring. In formula (2), R ２１ , R ２２ , R ２３ , R ２４ , R ２５ , R ２６ , R ２７ and R ２８ Each of these independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom. ２１ and R ２２ , R ２２ and R ２３ and R ２３ and R ２４ Each element may be independent of the others, or they may be connected to each other to form a ring. ２５ and R ２６ , R ２６ and R ２７ and R ２７ and R ２８ These elements may be connected to each other independently to form a ring. In formula (3), R ３１ , R ３２ , R ３３ , R ３４ , R ３５ , R ３６ , R ３７ , and R ３８ each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom.

5. The electrophotographic photoreceptor according to claim 4, wherein the proportion of silica particles in the region within 50% of the thickness-direction cross-section from the interface between the specific undercoat and the photosensitive layer in the direction toward the conductive substrate is 25% or more and 60% or less of the entire specific undercoat.

6. The electrophotographic photoreceptor according to claim 5, wherein the proportion of silica particles in the region within 50% of the thickness-direction cross-section from the interface between the specific undercoat layer and the photosensitive layer in the direction toward the conductive substrate is 30% or more and 50% or less of the entire specific undercoat layer.

7. The electron transport material has an average primary particle size of 20 nm or more and 1000 nm or less, as described in claim 1 or claim 4, for the electrophotographic photoreceptor.

8. The electrophotographic photoreceptor according to claim 1 or claim 4, wherein the silica particles have an average primary particle size of 50 nm or more and 500 nm or less.

9. The electron transport material includes at least one selected from the group consisting of the compound represented by formula (1), the compound represented by formula (2), and the compound represented by formula (3), (however, In the formula (1), R １１ , R １２ , R １３ , R １４ , R １５ , R １６ , R １７ and R １８ each independently represents a hydrogen atom, an alkyl group, or a halogen atom, In the above formula (2), R ２１ , R ２２ , R ２３ , R ２４ , R ２５ , R ２６ , R ２７ and R ２８ Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom. In the above formula (3), R ３１ , R ３２ , R ３３ , R ３４ , R ３５ , R ３６ , R ３７ and R ３８ Each of these independently represents a hydrogen atom, an alkyl group, or a halogen atom. The electrophotographic photoreceptor according to claim 1 or claim 4.

10. The electrophotographic photoreceptor is provided according to claim 1 or claim 4, A process cartridge that is attached to and detached from an image forming apparatus.

11. An electrophotographic photoreceptor according to claim 1 or claim 4, A charging device for charging the surface of the electrophotographic photoreceptor, An electrostatic latent image forming apparatus for forming an electrostatic latent image on the surface of the charged electrophotographic photoreceptor, A developing apparatus that develops an electrostatic latent image formed on the surface of an electrophotographic photoreceptor using a developer containing toner to form a toner image, A transfer device for transferring the toner image onto the surface of a recording medium, An image forming apparatus equipped with the following features.

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