Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that exhibits excellent charge retention even when operating for extended periods in high-temperature, high-humidity environments. [Solution] An electrophotographic photoreceptor comprising a conductive substrate, a base layer provided on the conductive substrate and containing an electron transport material and a binder resin, a charge generation layer provided on the base layer, and a charge transport layer provided on the charge generation layer, wherein the ratio (X1 / X2) of the content of the electron transport material in the region within 4% in the thickness direction of the base layer from the interface between the base layer and the charge generation layer, and the content of the electron transport material in the region exceeding 4% in the thickness direction of the base layer from the interface between the base layer and the charge generation layer, is 0 or 78 or less.

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 "a functionally separated electrophotographic photoreceptor constructed by sequentially laminating a charge generation layer (CGL) and a charge transport layer (CTL) containing a donor compound having hole transport ability on a conductive substrate, characterized in that an undercoat layer containing a phthalimide compound is provided between the conductive substrate and the CGL." Patent Document 2 discloses "a functionally separated electrophotographic photoreceptor constructed by sequentially laminating a charge generation layer (CGL) and a charge transport layer (CTL) containing a donor compound having hole transport ability on a conductive substrate, characterized in that an undercoat layer containing a pyrazine compound is provided between the conductive substrate and the CGL." Patent Document 3 discloses "a functionally separated electrophotographic photoreceptor constructed by sequentially laminating a charge generation layer (CGL) and a charge transport layer (CTL) containing a donor compound having hole transport ability on a conductive substrate, characterized in that an undercoat layer containing an oxazole compound or a thiazole compound is provided between the conductive substrate and the CGL." Patent Document 4 discloses an electrophotographic photoreceptor having a base layer and a photosensitive layer on a conductive support, wherein the base layer contains crystalline electron-transporting compound particles, the full width at half maximum of the maximum intensity peak in an X-ray diffraction measurement of the base layer measured from the thickness direction is 5° or less, and when the relative integrated intensity of each peak in an X-ray diffraction measurement of the base layer measured from the thickness direction is defined as I1, and the relative integrated intensity of each peak in an X-ray diffraction measurement of the base layer in a powder state with a volume-average particle size of 5 μm or less is defined as I2, the value of the maximum value Nmax in the orientation index N expressed by a specific formula is 1 or more and 3 or less. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 07-175250 [Patent Document 2] Japanese Patent Application Publication No. 07-175251 [Patent Document 3] Patent No. 07-175252 [Patent Document 4] Japanese Patent Publication No. 2023-130151 [Overview of the project] [Problems that the invention aims to solve]

[0004] In electrophotographic photoreceptors mounted in image forming apparatuses, an undercoat is provided on a conductive substrate. In recent years, from the perspective of environmentally friendly manufacturing, organic compounds with electron transport properties (hereinafter referred to as electron transport materials) have been adopted as substitutes for metal oxides in undercoat layers. However, electrophotographic photoreceptors equipped with an undercoat containing electron transport materials tended to have reduced charge retention when operated for long periods in high temperature and high humidity environments. Therefore, the objective of this embodiment is to provide an electrophotographic photoreceptor that exhibits superior charge retention even when operated for long periods in high temperature and high humidity environments (for example, performing 10,000 cycles of charging and exposure of the electrophotographic photoreceptor at 30°C and 80%RH) compared to cases where the content ratio (X1 / X2) exceeds 78 or the area ratio (Y1 / Y2) exceeds 81. [Means for solving the problem]

[0005] The following embodiments are specific means for solving the aforementioned problem. Each formula is identical to the formula with the same number described later.

[0006] <1> A conductive substrate, A base layer provided on the conductive substrate, comprising an electron transport material and a binder resin, A charge generation layer provided on the aforementioned lower layer, A charge transport layer provided on the charge generation layer, Equipped with, The aforementioned lower layer is The content X1 (mass%) of the electron transport material in a region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer, The content X2 (mass%) of the electron transport material in the region exceeding 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer, An electrophotographic photoreceptor in which the ratio (X1 / X2) is 0 or 78 or less. <2> A conductive substrate, A base layer provided on the conductive substrate, comprising an electron transport material and a binder resin, A charge generation layer provided on the aforementioned lower layer, A charge transport layer provided on the charge generation layer, Equipped with, The aforementioned lower layer is In a cross-section in the thickness direction, the area ratio Y1 (%) of the electron transport material in the region within 4% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer, In a cross-section in the thickness direction, the area ratio Y2(%) of the electron transport material in the region exceeding 4% in the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer, An electrophotographic photoreceptor in which the ratio (Y1 / Y2) is 0 or 81 or less. <3> The electron transport material includes an acid anhydride having electron transport properties, <1> or <2> The electrophotographic photoreceptor described above. <4> The electron transport material includes a compound represented by the following formula (P), <3> The electrophotographic photoreceptor described above. [ka] In formula (P), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38Each 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 aforementioned undercoat has an average thickness of 2 nm or more and 15 nm or less. <1> ~ <4> An electrophotographic photoreceptor as described in any one of the following. <6> The aforementioned underlayer has a content X1 of the electron transport material in a region within 4% of the thickness direction of the underlayer from the interface between the underlayer and the charge generation layer, which is 0 or 55% by mass or less. <1> ~ <5> An electrophotographic photoreceptor as described in any one of the following. <7> The aforementioned underlayer has a content X2 of the electron transport material in a region exceeding 4% in the thickness direction of the underlayer from the interface between the underlayer and the charge generation layer, which is 60% by mass or more and 80% by mass or less. <6> The electrophotographic photoreceptor described above. <8> The aforementioned undercoat has an area ratio Y1 of the electron transport material in a region within 4% of the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer in the thickness direction of the undercoat, which is 0 or 63% or less. <1> ~ <7> An electrophotographic photoreceptor as described in any one of the following. <9> The aforementioned undercoat layer has an area ratio Y2 of the electron transport material in the region extending more than 4% in the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer in the thickness direction of the undercoat layer, which is 60% or more and 80% or less. <8> The electrophotographic photoreceptor described above. <10> The aforementioned <1> ~ <9> It comprises an electrophotographic photoreceptor as described in any one of the following: A process cartridge that is attached to and detached from an image forming apparatus. <11> The aforementioned <1> ~ <9> An electrophotographic photoreceptor as described in any one of the following, 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. [Effects of the Invention]

[0007] <1> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case where the content ratio (X1 / X2) exceeds 78. <2> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case where the area ratio (Y1 / Y2) exceeds 81. <3> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the electron transport material contains an acid anhydride having electron transport properties. <4> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the electron transport material is a perinone compound. <5> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the average thickness of the undercoat layer is less than 2 nm or more than 15 nm. <6> According to the invention, compared to the case where the content X1 of electron transport material in the lower layer within 5% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer exceeds 55% by mass, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high temperature and high humidity environment. <7> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the content X2 of electron transport material in the region exceeding 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer is less than 60% by mass or more than 80% by mass. <8> According to the invention, in the lower layer, compared to the case where the area ratio Y1 of the electron transport material in the region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section exceeds 63%, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high temperature and high humidity environment. <9> According to the invention, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to a case where the area ratio Y2 of the electron transport material in the region exceeding 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section is less than 60% or more than 80%. <10> According to the invention, a process cartridge is provided that exhibits superior static charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the content ratio (X1 / X2) exceeds 78 or the area ratio (Y1 / Y2) exceeds 81. <11> According to the invention, an image forming apparatus is provided that has an electrophotographic photoreceptor that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the content ratio (X1 / X2) exceeds 78 or the area ratio (Y1 / Y2) exceeds 81. [Brief explanation of the drawing]

[0008] [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 schematic diagram showing an example of an image forming apparatus according to this embodiment. [Figure 3] This is a schematic diagram showing another example of the image forming apparatus according to this embodiment. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure are described below. These descriptions and embodiments are illustrative and do not limit the scope of the embodiments.

[0010] 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.

[0011] In this disclosure, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their objectives are achieved.

[0012] When embodiments are described in this disclosure with reference to the drawings, the configuration of such embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each figure are conceptual, and the relative relationships between the components are not limited thereto.

[0013] In this disclosure, each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition in this disclosure, if there are multiple types of the substance corresponding to each component in the composition, it means the total amount of those multiple types of substances present in the composition unless otherwise specified. In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified.

[0014] In this disclosure, alkyl groups and alkylene groups include linear, branched, and cyclic groups unless otherwise specified.

[0015] In this disclosure, organic groups, aromatic rings, linking groups, alkyl groups, alkylene groups, aryl groups, aralkyl groups, alkoxy groups, aryloxy groups, etc., may have hydrogen atoms in the group substituted with halogen atoms.

[0016] In this disclosure, when compounds are shown by structural formulas, the symbols representing carbon atoms and hydrogen atoms (C and H) in the hydrocarbon group and / or hydrocarbon chain may be omitted.

[0017] In this disclosure, the term "constituent unit" of a copolymer or resin is synonymous with "monomer unit."

[0018] <Electrophotographic photoconductor>

[0019] Hereafter, the electrophotographic photoreceptor will also be simply referred to as the "photoreceptor." Hereafter, when describing the common features between the first embodiment and the second embodiment, the term "this embodiment" will be used. Hereinafter, the compound represented by formula (P) is also called perylenetetracarboxylic dianhydride.

[0020] The photoreceptor according to the first embodiment comprises a conductive substrate, a base layer provided on the conductive substrate and containing an electron transport material and a binder resin, a charge generation layer provided on the base layer, and a charge transport layer provided on the charge generation layer, wherein the ratio (X1 / X2) of the content of the electron transport material in the region within 4% in the thickness direction of the base layer from the interface between the base layer and the charge generation layer, and the content of the electron transport material in the region exceeding 4% in the thickness direction of the base layer from the interface between the base layer and the charge generation layer, is 0 or 78 or less.

[0021] The photoreceptor according to the second embodiment comprises a conductive substrate, a base layer provided on the conductive substrate and containing an electron transport material and a binder resin, a charge generation layer provided on the base layer, and a charge transport layer provided on the charge generation layer, wherein the base layer has a ratio (Y1 / Y2) of 0 or 81 or less between the area ratio Y1 (%) of the electron transport material in a region within 4% of the thickness direction of the base layer from the interface between the base layer and the charge generation layer in a cross-section in the thickness direction, and the area ratio Y2 (%) of the electron transport material in a region exceeding 4% of the thickness direction of the base layer from the interface between the base layer and the charge generation layer in a cross-section in the thickness direction.

[0022] In electrophotographic photoreceptors used in image forming apparatuses, an undercoat is provided on a conductive substrate. In recent years, electron-transporting materials have been adopted as an alternative to metal oxides in undercoat layers, from the perspective of environmentally friendly manufacturing. However, when electrophotographic photoreceptors equipped with an undercoat containing electron-transporting materials are operated for a long period in a high-temperature, high-humidity environment (for example, 10,000 cycles of charging and exposure of the electrophotographic photoreceptor at 30°C and 80% RH), the charge generation layer may be electrochemically corroded by factors such as radicals derived from the electron-transporting material contained in the undercoat. As a result, electron transport performance tends to decrease in the corroded region, and charge retention tends to decline.

[0023] On the other hand, the electrophotographic photoreceptor according to this embodiment exhibits excellent charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, due to the above configuration. The mechanism of this action is not entirely clear, but it is presumed to be as follows.

[0024] In the first embodiment, the undercoat layer has a ratio (X1 / X2) of 0 or 78 or less between the content X1 (mass%) of electron transport material in the region within 5% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer, and the content X2 (mass%) of electron transport material in the region exceeding 5% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer. In the second embodiment, the undercoat layer has a ratio (Y1 / Y2) of 0 or 81 or less between the area ratio Y1 (%) of the electron transport material in the region within 5% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer in the thickness direction cross-section, and the area ratio Y2 (%) of the electron transport material in the region exceeding 5% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer in the thickness direction cross-section. In other words, in the undercoat layer according to this embodiment, the content of electron-transporting material is reduced on the interface side between the undercoat layer and the charge generation layer, or the electron-transporting material is not included on the interface side between the undercoat layer and the charge generation layer. Therefore, the penetration of moisture that has entered from the surface layer side into the undercoat layer is suppressed. As a result, even when operated for a long period of time in a high temperature and high humidity environment, the electron-transporting material contained in the undercoat layer is suppressed from being electrochemically corroded by moisture, and the charge retention is excellent.

[0025] 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.

[0026] The layers of the electrophotographic photoreceptor according to this embodiment will be described in detail below. Reference numerals will be omitted in the description.

[0027] [Sublayer] The base layer contains an electron transport material and a binder resin. The base layer may further contain other materials besides the electron transport material and binder resin, if necessary.

[0028] ·Content ratio In the first embodiment, the ratio (X1 / X2) of the content of electron transport material in the region within 4% of the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer, and the content of electron transport material in the region exceeding 4% of the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer, is 0 or 78 or less, preferably 0 or 74 or less, and more preferably 0 or 72 or less. In the second embodiment, the ratio (X1 / X2) of the content of electron transport material in the region within 4% of the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer, and the content of electron transport material in the region exceeding 4% of the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer, is 0 or 78 or less, preferably 0 or 74 or less, and more preferably 0 or 72 or less.

[0029] When the ratio (X1 / X2) is 0 or 78 or less, the content of electron-transporting material is reduced on the interface side between the undercoat and the charge generation layer, or the electron-transporting material is arranged so that it is not included on the interface side between the undercoat and the charge generation layer. As a result, the electron-transporting material contained in the undercoat layer does not penetrate into the charge generation layer. Consequently, the penetration of moisture that has entered from the surface layer side into the undercoat layer is suppressed. As a result, even when operating for a long period of time in a high temperature and high humidity environment, the electron-transporting material contained in the undercoat layer is suppressed from being electrochemically corroded, resulting in excellent charge retention.

[0030] The content X1 of the electron transport material in the region within 4% of the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer is preferably 0 or 55% by mass or less, more preferably 0 or 53% by mass or less, and even more preferably 0 or 50% by mass or less.

[0031] When X1 is 0% by mass or 55% by mass or less, the content of electron-transporting material decreases on the interface side between the undercoat and the charge generation layer, or the electron-transporting material is not present at all on the interface side between the undercoat and the charge generation layer. As a result, the penetration of moisture that has entered from the surface layer into the undercoat is suppressed. Consequently, even when operating for a long period of time in a high-temperature, high-humidity environment, the electron-transporting material contained in the undercoat is suppressed from being electrochemically corroded, resulting in excellent charge retention.

[0032] The content X2 of the electron transport material in the region extending more than 5% in the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer is preferably 60% by mass or more and 80% by mass or less, more preferably 60% by mass or more and 75% by mass or less, and even more preferably 65% ​​by mass or more and 72% by mass or less.

[0033] When X2 is 60% by mass or more, the electron transport material in the lower layer is sufficiently close together, resulting in excellent electron transport performance. When X2 is 80% by mass or less, particle aggregation in the lower layer is suppressed, resulting in superior electrical properties and mechanical strength.

[0034] The methods for setting X1, X2 and the ratio (X1 / X2) within the above range are not particularly limited, but examples include a method of preparing two types of coating solutions for forming the undercoat layer with different concentrations of electron-transporting material, and forming a coating film such that the concentration of electron-transporting material is lower on the interface side with the charge generation layer; and a method of thinly coating the undercoat layer with a resin layer that does not contain electron-transporting material on the interface side with the charge generation layer.

[0035] The method for verifying X1, X2, and the ratio (X1 / X2) is as follows. The electrophotographic photoreceptor is cut along its thickness, along with the substrate, to obtain a test specimen. The test specimen is analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). For quantitative determination of electron transport materials, for example, signals with a molecular weight of 800 or less are considered to originate from electron transport materials, and their proportion of the total is calculated. The content of electron-transporting material X1 in the region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer, and the content of electron-transporting material X2 in the region exceeding 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer are calculated from the measured depth profile, and the ratio (X1 / X2) is determined.

[0036] ·Area ratio In the second embodiment, the ratio (Y1 / Y2) of the area ratio Y1(%) of the electron transport material in the region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section, and the area ratio Y2(%) of the electron transport material in the region exceeding 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section, is 0 or 81 or less, preferably 0 or 79 or less, and more preferably 0 or 77 or less. In the first embodiment, the ratio (Y1 / Y2) of the area ratio Y1 (%) of the electron transport material in the region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section, and the area ratio Y2 (%) of the electron transport material in the region exceeding 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section, is 0 or 81 or less, preferably 0 or 79 or less, and more preferably 0 or 77 or less.

[0037] When the ratio (Y1 / Y2) is 0 or 81% by mass or less, the content of electron-transporting material decreases on the interface side between the undercoat and the charge generation layer, or the electron-transporting material is not present at all on the interface side between the undercoat and the charge generation layer. As a result, the penetration of electron-transporting material contained in the undercoat into the charge generation layer is further suppressed. Consequently, even when operating for a long period in a high-temperature, high-humidity environment, the penetration of moisture that has entered from the surface layer side into the undercoat layer is suppressed. As a result, even when operating for a long period in a high-temperature, high-humidity environment, the electrochemical corrosion of the electron-transporting material contained in the undercoat layer is suppressed, resulting in excellent charge retention.

[0038] The undercoat is preferably such that the area ratio Y1 of the electron transport material in the region within 5% of the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer in the cross-section in the thickness direction of the undercoat is 0 or 63% or less, more preferably 0 or 60% or less, and even more preferably 0 or 58% or less.

[0039] When Y1 is 0 or 63% by mass or less, the content of electron-transporting material decreases on the interface side between the undercoat and the charge generation layer, or the electron-transporting material is not present at all on the interface side between the undercoat and the charge generation layer. As a result, the penetration of moisture that has entered from the surface layer into the undercoat is suppressed. Consequently, even when operating for a long period in a high-temperature, high-humidity environment, the electron-transporting material contained in the undercoat is suppressed from being electrochemically corroded, resulting in excellent charge retention.

[0040] In the lower layer, the area ratio Y2 of the electron transport material in the region extending more than 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section is preferably 60% or more and 80%, more preferably 65% ​​or more and 77%, and even more preferably 70% or more and 75%.

[0041] When Y2 is 60% or more, the electron-transporting material in the lower layer is in sufficient proximity, resulting in excellent electron transport performance. When Y2 is 80% or less, particle aggregation in the lower layer is suppressed, resulting in superior electrical properties and mechanical strength.

[0042] The methods for setting Y1, Y2 and the ratio (Y1 / Y2) within the above range are not particularly limited, but examples include a method of preparing two types of coating solutions for forming the undercoat layer with different concentrations of electron-transporting material, and forming a coating film such that the concentration of electron-transporting material is lower on the interface side with the charge generation layer; and a method of thinly coating the undercoat layer on the charge generation layer interface side without electron-transporting material.

[0043] The method for verifying Y1, Y2, and the ratio (Y1 / Y2) is as follows. An electrophotographic photoreceptor is cut in the thickness direction down to the underlayer to obtain a test specimen with this cross-section as the observation surface. The observation surface of the test specimen is observed with a scanning electron microscope (SEM) (Hitachi, Ltd.: S-4100) with a field of view of 500 nm x 500 nm or larger, and an image is captured. This image is then imported into an image analysis system (LUZEXIII, Nireco Corporation). Image analysis is used to determine the total area of ​​the region within 4% of the thickness of the undercoat layer from the interface between the undercoat layer and the charge generation layer. Next, the observation surface of the specimen is subjected to elemental analysis by energy-dispersive X-ray spectroscopy, and a mapping analysis is performed on the elements on the observation surface. Then, the area where elements abundant in the electron-transporting material (for example, oxygen atoms in compound P-1) are concentrated is defined as the amount of electron-transporting material. The area Y1 of the electron-transporting material within 4% of the thickness of the lower layer from the interface between the lower layer and the charge generation layer, and the area Y2 of the electron-transporting material beyond 4% of the thickness of the lower layer from the interface between the lower layer and the charge generation layer are calculated. The ratio (Y1 / Y2) is then determined.

[0044] The following describes preferred embodiments common to the undercoat layer in the first embodiment and the undercoat layer in the second embodiment. Hereinafter, when there are matters common to the underlayer in the first embodiment and the underlayer in the second embodiment, the term "underlayer" will be used simply.

[0045] The undercoat preferably has an average thickness of 2 μm or more and 15 μm or less. When the average thickness is 2 μm or more, the opacity of the substrate is ensured and the static charge retention is superior. When the average thickness is 15 μm or less, carriers from the charge generation layer can reach the aluminum substrate within the time required for image formation, resulting in superior initial electron transport capacity. It is also preferable from the standpoint of manufacturing cost.

[0046] [Electron transport material] The lower layer contains an electron transport material. Examples of the electron transporting material include quinone compounds such as chloranil and bromanil; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone; oxadiazole compounds such as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; xanthone compounds; thiophene compounds; diphenoquinone compounds such as 3,3’,5,5’-tetra-t-butyldiphenoquinone; acid anhydrides such as perinone compounds, dibromoansanthrone, and perylene tetracarboxylic dianhydride; and the like electron transporting materials.

[0047] Among them, from the viewpoint of more excellent charge retention property, the electron transporting material preferably contains an acid anhydride having electron transporting performance, and more preferably contains a compound represented by the following formula (P) which is perylene tetracarboxylic dianhydride.

[0048] [Chemical formula] In the above formula (P), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 each independently represents a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group or a halogen atom.

[0049] The compound represented by the formula (P) has excellent electron transporting property and low hole transporting property. Therefore, when the undercoat layer contains the compound represented by the formula (P), the undercoat layer has excellent electron transporting property, it is easy to secure a conductive path in the undercoat layer, and the leakage current is more suppressed. Further, since the dark attenuation is further reduced, the charge retention property is more excellent.

[0050] In equation (P), R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 and R 38 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 (P), R 31 ~R 38 When the undercoat is a hydrogen atom, an alkyl group, or a halogen atom (more preferably a hydrogen atom), the undercoat exhibits superior electron transport properties, ensuring conductive paths within the undercoat, and maintaining charge even during long-term operation in high-temperature, high-humidity environments (for example, 10,000 cycles of charging and exposing an electrophotographic photoreceptor at 30°C and 80%RH).

[0051] In formula (P), R 31 ~R 38 Examples of alkyl groups represented by include substituted or unsubstituted alkyl groups.

[0052] In formula (P), 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).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] Among the above, linear alkyl groups such as methyl groups and ethyl groups are preferred as unsubstituted alkyl groups.

[0057] Substituents in alkyl groups include alkoxy groups, hydroxyl groups, carboxyl groups, nitro groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As for the alkoxy group that substitutes a hydrogen atom in the alkyl group, R in formula (P) 31 ~R 38 Examples of groups similar to the unsubstituted alkoxy group represented by include:

[0058] In formula (P), R 31 ~R 38 Examples of alkoxy groups represented by include substituted or unsubstituted alkoxy groups.

[0059] In formula (P), 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).

[0060] 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.

[0061] 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 for the aryl group that substitutes a hydrogen atom in the alkoxy group, in formula (P), R 31 ~R 38 Examples include unsubstituted aryl groups represented by . As for the alkoxycarbonyl group that substitutes a hydrogen atom in the alkoxy group, in formula (P), R 31 ~R 38 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include . As for the aryloxycarbonyl group that substitutes a hydrogen atom in the alkoxy group, in formula (P), R 31 ~R 38 Examples of groups similar to the unsubstituted aryloxycarbonyl group represented by include .

[0062] In formula (P), R 31 ~R 38 Aralkyl groups represented by include substituted or unsubstituted aralkyl groups.

[0063] In formula (P), 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.

[0064] 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.

[0065] Substituents in an aralkyl group include alkoxy groups, alkoxycarbonyl groups, and halogen atoms (such as fluorine, bromine, and iodine atoms). As for the alkoxy group that substitutes a hydrogen atom in the aralkyl group, in formula (P), R 31 ~R 38 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 (P), R 31 ~R38 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include .

[0066] In formula (P), R 31 ~R 38 Examples of aryl groups represented by this symbol include substituted and unsubstituted aryl groups.

[0067] In formula (P), 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.

[0068] 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.

[0069] 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 alkyl groups that substitute for hydrogen atoms in the aryl group, in formula (P), R 31 ~R 38 Examples of groups similar to the unsubstituted alkyl groups shown include those represented. As for the alkoxy group that substitutes a hydrogen atom in the aryl group, in formula (P), R 31 ~R 38 Examples of groups similar to the unsubstituted alkoxy group represented by include: As for the alkoxycarbonyl group that substitutes a hydrogen atom in the aryl group, in formula (P), R 31 ~R 38 Examples of groups similar to the unsubstituted alkoxycarbonyl group represented by include .

[0070] In formula (P), R 31 ~R 38 Examples of alkoxycarbonyl groups represented by include substituted or unsubstituted alkoxycarbonyl groups.

[0071] In formula (P), 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.

[0072] 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.

[0073] Examples of substituents on an alkoxycarbonyl group include aryl groups, hydroxyl groups, and halogen atoms (fluorine atoms, bromine atoms, iodine atoms, etc.). As for the aryl group that substitutes a hydrogen atom in the alkoxycarbonyl group, in formula (P), R 31 ~R 38 Examples include unsubstituted aryl groups represented by .

[0074] In formula (P), R 31 ~R 38 Examples of halogen atoms represented by this formula include fluorine, chlorine, bromine, and iodine atoms.

[0075] The following are examples of compounds represented by formula (P), but this embodiment is not limited to these examples. The following example compound numbers will be denoted as example compound (P-number).

[0076] [ka]

[0077] [ka]

[0078] 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, it tends to have superior electron transport properties and lower hole transport properties. Consequently, it has superior electron transport properties and lower hole transport properties, and superior charge retention properties. 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 improved, hole transport performance tends to be lower, and charge retention performance is improved.

[0079] 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.

[0080] The compound represented by formula (P) preferably has an aspect ratio of 1.0 or more and 5 or less, more preferably 1.1 or more and 3 or less, and even more preferably 1.2 or more and 2.5 or less. When the aspect ratio of the compound represented by formula (P) 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.

[0081] The aspect ratio of the compound represented by formula (P) 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 formula (P). 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.

[0082] The method for adjusting the average primary particle size and aspect ratio of the compound represented by formula (P) 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.

[0083] The proportion of the total amount of the compound represented by formula (P) 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.

[0084] The total amount of charge-transporting material containing the compound represented by formula (P) in the entire underlayer may be less than 70% by mass relative to the total solid content of the specific underlayer. 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 a compound represented by formula (P) that has excellent electron transport properties as well as low hole transport properties, excellent charge retention is achieved even if the total amount of electron-transporting material is less than 70% by mass.

[0085] The total amount of charge-transporting material may be 60% by mass or more, or 60% by mass or more and 70% by mass or less, relative to the total solid content of the undercoat. If the content of electron-transporting material is 70% by mass or less, the film quality becomes brittle, the film formation performance decreases, and surface roughness of the undercoat is suppressed, resulting in superior charge retention. On the other hand, if the content of electron-transporting material is 60% by mass or more, sufficient electron transport capacity is maintained, and charge retention is sufficiently ensured.

[0086] • Binding resin Examples of known polymer compounds used as binders include polyarylate resins, polycarbonate resins, 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, phenolic resins (e.g., resol-type phenolic 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).

[0087] 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.

[0088] A binder resin that is insoluble in the coating solvent of the upper layer is preferred for use in the undercoat layer. Preferably, the binder resin used in the undercoat layer is a diallyl phthalate resin, a polyamide resin, a nylon resin, a urethane resin, a melamine resin, a benzoguanamine resin, a phenol resin, or a resin obtained by the reaction of at least one of these resins with a curing agent. When the binder resin contains at least one resin selected from the above group, it exhibits high hole blocking properties and superior charge retention.

[0089] The lower layer may further contain inorganic particles. As for inorganic particles, for example, powder resistance (volume resistivity) 102 Ω cm or more 10 11 Examples include inorganic particles with a size of Ω·cm or less. Among these, suitable inorganic particles having the above-mentioned resistance values ​​include metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles, with zinc oxide particles being particularly preferred.

[0090] The specific surface area of ​​inorganic particles using the BET method is, for example, 10 m². 2 A value of 1g or more is preferable. The volume-average particle size of the inorganic particles is preferably between 50 nm and 2000 nm (preferably between 60 nm and 1000 nm).

[0091] The inorganic particle content is preferably 10% by mass or more and 80% by mass or less relative to the binder resin, and more preferably 40% by mass or more and 80% by mass or less.

[0092] The inorganic particles may be surface-treated. Two or more types of inorganic particles with different surface treatments or particle sizes may be mixed and used.

[0093] Examples of surface treatment agents include silane coupling agents, titanate-based coupling agents, aluminum-based coupling agents, and surfactants. Silane coupling agents are particularly preferred, and silane coupling agents having an amino group are more preferred.

[0094] Examples of silane coupling agents having an amino group include, but are not limited to, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane.

[0095] Silane coupling agents may be used in combination of two or more types. For example, a silane coupling agent having an amino group may be used in combination with another silane coupling agent. Examples of other silane coupling agents include, but are not limited to, 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.

[0096] The surface treatment method using the surface treatment agent may be any known method, and may be either a dry or wet method.

[0097] The amount of surface treatment agent applied is preferably, for example, 0.5% by mass or more and 10% by mass or less relative to the inorganic particles.

[0098] In this case, it is preferable for the underlayer to contain electron-accepting compounds (acceptor compounds) along with inorganic particles, from the viewpoint of improving the long-term stability of electrical properties and carrier blocking ability.

[0099] Examples of electron-accepting compounds include electron-transporting substances such as compounds having anthraquinone structures; quinone compounds such as chloranil and bromoanil; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitro-9-fluorenone; oxadiazole compounds such as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; xanthone compounds; thiophene compounds; diphenoquinone compounds such as 3,3',5,5'-tetra-t-butyldiphenoquinone; and benzophenone compounds. In particular, compounds having an anthraquinone structure are preferred as electron-accepting compounds. Examples of compounds having an anthraquinone structure include hydroxyanthraquinone compounds, aminoanthraquinone compounds, and aminohydroxyanthraquinone compounds. Specifically, examples of preferred compounds include anthraquinone, alizarin, quinizalin, anthralphine, purpurin, and their derivatives.

[0100] The electron-accepting compound may be dispersed in the underlayer together with inorganic particles, or it may be present attached to the surface of the inorganic particles.

[0101] Methods for attaching electron-accepting compounds to the surface of inorganic particles include, for example, dry methods or wet methods.

[0102] The dry method involves, for example, adding an electron-accepting compound, either directly or dissolved in an organic solvent, dropwise while stirring inorganic particles with a mixer that has a high shear force, or spraying it with dry air or nitrogen gas, to adhere the electron-accepting compound to the surface of the inorganic particles. When adding or spraying the electron-accepting compound, it is preferable to do so at a temperature below the boiling point of the solvent. After adding or spraying the electron-accepting compound, further baking at 100°C or higher may be performed. The baking temperature and time are not particularly limited as long as electrophotographic characteristics can be obtained.

[0103] The wet method involves dispersing inorganic particles in a solvent using, for example, a stirrer, ultrasonic disperser, sand mill, attritor, or ball mill, while adding an electron-accepting compound. After stirring or dispersion, the solvent is removed, and the electron-accepting compound adheres to the surface of the inorganic particles. Solvent removal methods include, for example, filtration or distillation. After solvent removal, further baking at 100°C or higher may be performed. The baking temperature and time are not particularly limited as long as electrophotographic characteristics can be obtained. In the wet method, the water content of the inorganic particles may be removed before adding the electron-accepting compound. Examples of this include removing water while stirring and heating in the solvent, or removing water by azeotrope with the solvent.

[0104] Furthermore, the attachment of the electron-accepting compound may be performed before or after surface treatment with a surface treatment agent on the inorganic particles, or it may be performed simultaneously with the attachment of the electron-accepting compound and surface treatment with the surface treatment agent.

[0105] The content of the electron-accepting compound is preferably, for example, 0.01% by mass or more and 20% by mass or less relative to the inorganic particles, and more preferably 0.01% by mass or more and 10% by mass or less.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] Examples of aluminum chelating compounds include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

[0111] These additives may be used individually or as a mixture or polycondensate of multiple compounds.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] [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.

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] [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.

[0126] Among these, the intermediate layer is preferably a layer containing an organometallic compound that contains zirconium atoms or silicon atoms.

[0127] 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.

[0128] 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.

[0129] [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.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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.

[0134] In contrast, 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.

[0135] 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 (polycondensate of bisphenols and aromatic divalent carboxylic acids, etc.), 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.

[0136] 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.

[0137] The charge generation layer may also contain other well-known additives.

[0138] 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.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] [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 contain a polymer charge transport material.

[0144] 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.

[0145] 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.

[0146] [ka]

[0147] In structural formula (a-1), Ar T1 Ar T2 , and Ar T3is each independently a substituted or unsubstituted aryl group, -C6H4-C(R T4 )=C(R T5 )(R T6 ), or -C6H4-CH=CH-CH=C(R T7 )(R T8 ). R T4 , R T5 , R T6 , R T7 , and R T8 each independently represent a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Examples of the substituents of the above groups include a halogen atom, an alkyl group having 1 to 5 carbon atoms, and an alkoxy group having 1 to 5 carbon atoms. Further, examples of the substituents of the above groups also include a substituted amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0148]

Chemical formula

[0149] In structural formula (a-2), R T91 and R T92 each independently represent 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. R T101 , R T102 , R T111 and R T112 each independently represent 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, -C(R T12 )=C(R T13 )(R T14 ), or -CH=CH-CH=C(R T15 )(R T16 ), and R<00000​​​​​​​​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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] The charge transport layer may also contain other well-known additives.

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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.

[0158] [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.

[0159] 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).

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 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.

[0164] The protective layer may also contain other well-known additives.

[0165] 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.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] <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.

[0170] 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.

[0171] 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.

[0172] 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).

[0173] 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.

[0174] 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.

[0175] Figure 2 is a schematic diagram showing an example of an image forming apparatus according to this embodiment. As shown in Figure 2, 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.

[0176] In Figure 2, 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.

[0177] Figure 2 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.

[0178] The following describes the various components of the image forming apparatus according to this embodiment.

[0179] -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.

[0180] -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.

[0181] -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.

[0182] 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.

[0183] -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.

[0184] -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.

[0185] -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.

[0186] Figure 3 is a schematic diagram showing another example of the image forming apparatus according to this embodiment. The image forming apparatus 120 shown in Figure 3 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]

[0187] 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).

[0188] -Preparation of electronic transport materials- The following electron transport materials were prepared.

[0189] • Fabrication of electron transport material (1) 6.4 parts of the above-mentioned electron-transporting material (P-1) in the β-form (CCDC196997), 72 parts of zirconia beads with a diameter of 0.3 mm, and 1.0 part of sodium chloride were placed in a zirconia container and pulverized for 2 hours at 500 rpm using a planetary mill device (manufactured by Fritsch: P-7 Classic Line). After pulverization, the zirconia beads were washed with 500 ml of distilled water while the pigment particles were separated by filtration. The obtained aqueous dispersion of the pigment particles was centrifuged and the supernatant water was removed by decantation to isolate the pigment. The isolated pigment was repeatedly washed with water until the electrical conductivity became 10 μS / cm or less, and then dried in a freeze dryer for 48 hours to obtain the electron-transporting material (P-1).

[0190] · Preparation of Electron-Transporting Material (2) In the preparation of the electron-transporting material (1), it was prepared in the same procedure except that the materials used were changed to the following materials (crystal structure COD8100240).

[0191]

Chemical formula

[0192] · Preparation of Electron-Transporting Material (3) In the preparation of the electron-transporting material (1), it was prepared in the same procedure except that the materials used were changed to the following materials (crystal structure CCDC798609).

[0193]

Chemical formula

[0194] · Preparation of Electron-Transporting Material (4) In the preparation of the electron-transporting material (1), it was prepared in the same procedure except that the materials used were changed to the following materials (crystal structure COD2219436).

[0195]

Chemical formula

[0196] -Preparation for the lower layer- • Preparation of the lower layer (1) A mixture was obtained by mixing 70 parts of the electron transport material of the type shown in Table 1, 13.5 parts of a curing agent (blocked isocyanate Sumijoule 3175, manufactured by Sumitomo Bayern Urethanes Co., Ltd.), 15 parts of butyral resin (Eslec BM-1, manufactured by Sekisui Chemical Co., Ltd.), and 85 parts of methyl ethyl ketone. 38 parts of this mixture was mixed with 25 parts of methyl ethyl ketone, and dispersion was performed for 3 hours using a sand mill with 1 mmφ glass beads to obtain a dispersion. 0.005 parts of dioctyl tin dilaurate was added to the obtained dispersion as a catalyst to obtain undercoat coating solution 1. This undercoat coating solution 1 was applied to a cylindrical aluminum substrate by immersion coating, dried and cured at 160°C for 30 minutes, and a coating film with an average thickness of 9.6 μm was formed. Subsequently, coating solution 2 for the undercoat, which was prepared by dissolving 40 parts of nylon resin (Amilan® CM8000, manufactured by Toray Industries, Inc.) in 600 parts of methanol, was applied onto the cured film formed by coating solution 1 for the undercoat, and dried and cured at 140°C for 30 minutes to form a coating film made of nylon resin with an average thickness of 0.4 μm. As described above, the underlayer (1) with the average thickness shown in Table 1 was obtained.

[0197] ·Sublayer (2) In the preparation of the undercoat layer (1), the undercoat layer with the average thickness shown in Table 1 was prepared using the same procedure, except that the type of nylon resin in the undercoat layer coating liquid 2 was changed to Amilan® CM4000 manufactured by Toray Industries, Inc.

[0198] ·Sublayer (3) A mixture was obtained by mixing 59 parts of the electron transport material of the type shown in Table 1, 13.5 parts of a curing agent (blocked isocyanate, Sumijule 3175, manufactured by Sumitomo Bayern Urethanes, 75% solids), 15 parts of butyral resin (Eslec BM-1, manufactured by Sekisui Chemical Co., Ltd.), and 85 parts of methyl ethyl ketone. 25 parts of methyl ethyl ketone were mixed with 38 parts of this mixture, and dispersion was performed for 3 hours using a sand mill with 1 mmφ glass beads to obtain a dispersion. 0.005 parts of dioctyl tin dilaurate was added to the obtained dispersion as a catalyst to obtain undercoat coating solution 1. This undercoat coating solution was applied to a cylindrical aluminum substrate by immersion coating, dried and cured at 160°C for 30 minutes, and a coating film with an average thickness of 9.6 μm was formed. Subsequently, in the preparation process for the base coat coating solution 1, the amount of electron-transporting material was changed to 25 parts to prepare base coat coating solution 2. Then, base coat coating solution 2 was applied onto the coating film prepared with base coat coating solution 1 and dried and cured at 160°C for 30 minutes to form a coating film made of polyurethane resin with an average thickness of 0.4 μm. As described above, the underlayer with the average thickness shown in Table 1 was obtained.

[0199] ·Sublayer (4)~(20) In preparing the undercoat layer (3), the type and composition of the charge transport material in undercoat layer coating solution 1 and undercoat layer coating solution 2 were changed and adjusted to prepare undercoat layers such that X1, X2, Y1, Y2 and X1 / X2, Y1 / Y2 were the values ​​shown in Table 1. However, in Example 11, the film thickness with undercoating solution 1 was 16.3 μm, and the film thickness with undercoating solution 2 was 0.7 μm, resulting in the undercoat layers with the average thickness shown in Table 1. In Example 12, the film thickness with undercoating solution 1 was 0.6 μm, and the film thickness with undercoating solution 2 was 0.4 μm, resulting in the undercoat layers with the average thickness shown in Table 1.

[0200] ·Sublayer (C1) A mixture was obtained by mixing 59 parts of the electron transport material of the type shown in Table 1, 13.5 parts of a curing agent (blocked isocyanate, Sumijule 3175, manufactured by Sumitomo Bayern Urethanes, 75% solids), 15 parts of butyral resin (Eslec BM-1, manufactured by Sekisui Chemical Co., Ltd.), and 85 parts of methyl ethyl ketone. 25 parts of methyl ethyl ketone were mixed with 38 parts of this mixture, and dispersion was performed for 3 hours using a sand mill with 1 mmφ glass beads to obtain a dispersion. 0.005 parts of dioctyl tin dilaurate was added to the obtained dispersion as a catalyst to obtain coating solution 1 for the undercoat. This coating solution was applied to a cylindrical aluminum substrate by immersion coating, and dried and cured at 160°C for 30 minutes. As described above, a base layer with an average thickness as shown in Table 1 was obtained.

[0201] ·Sublayer (C2)~(C3) Each undercoat was obtained with the same specifications as undercoat (1), except that the type of electron-transporting material in the undercoat (C1) was as shown in Table 1.

[0202] Table 1 shows the values ​​of X1, X2, ratio (X1 / X2), Y1, Y2, ratio (Y1 / Y2), and the type, particle size, and aspect ratio of the electron transport material in each underlayer. In Table 1, "X1" refers to the content X1 (mass%) of electron-transporting material in a region within 4% of the thickness direction of the underlayer from the interface between the underlayer and the charge generation layer. In Table 1, "X2" refers to the content X2 (mass%) of electron-transporting material in the region exceeding 4% in the thickness direction of the underlayer from the interface between the underlayer and the charge generation layer. In Table 1, "Y1" refers to the area ratio Y1(%) of the electron transport material in the region within 4% of the thickness direction of the undercoat layer, from the interface between the undercoat layer and the charge generation layer in the thickness direction cross-section. In Table 1, "Y2" refers to the area ratio Y2(%) of the electron transport material in the region exceeding 4% in the thickness direction of the lower layer, from the interface between the lower layer and the charge generation layer in the thickness direction cross-section. In Table 1, "average thickness" refers to the average thickness of the entire underlayer.

[0203] <Examples 1 to 20 and Comparative Examples C1 to C3> (Formation of Charge Generation Layer) 15 parts by mass of hydroxygallium phthalocyanine having diffraction peaks at positions where the Bragg angles (2θ ± 0.2°) of the X-ray diffraction spectrum using CuKα characteristic X-rays as a charge generating substance are at least 7.3°, 16.0°, 24.9°, and 28.0°, 10 parts by mass of a 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 were stirred and dispersed in a sand mill for 4 hours using glass beads with a diameter of 1 mmφ. 175 parts by mass of n-butyl acetate and 180 parts by mass of methyl ethyl ketone were added to the obtained dispersion, and the mixture was stirred to obtain a coating solution for forming a charge generation layer. This coating solution for forming a charge generation layer was dip-coated on the outer peripheral surface of the undercoat layer of the type 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.

[0204] (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), 52 parts by mass of the following polycarbonate resin (A) (viscosity average molecular weight: 46,000, the numerical values in the formula indicate molar ratios), and 0.3 parts by mass of a fluorine-containing graft polymer (manufactured by Toagosei Co., Ltd.: GF-500) as a dispersion aid were added to 800 parts by mass of tetrahydrofuran and dissolved. 8 parts by mass of tetrafluoroethylene resin (manufactured by Daikin Industries, Ltd.: Rubron L5 average particle diameter 300 nm) was added, and the mixture was dispersed at 5500 rpm for 2 hours using a homogenizer (manufactured by IKA: Ultra Turrax) to obtain a coating solution for forming a charge transport layer. This coating solution was applied on 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.

[0205] [Chemical Formula]

[0206] [Chemical Formula]

[0207] <Evaluation of static charge retention during long-term operation in high-temperature, high-humidity environments> Each example of an electrophotographic photoreceptor was mounted in a laser printer-modified scanner (XP-15 modified) manufactured by Fujifilm Business Innovation Co., Ltd. The electrophotographic photoreceptor was charged using a Scorotron charger with a grid voltage of -700V under conditions of 30°C and 85% RH, and the initial charging potential M1 was measured. Next, the electrophotographic photoreceptor was charged using a Scorotron charger with a grid voltage of -800V under conditions of 30°C and 85% RH, and the charging potential was measured at 4 mJ / cm². 2 The exposure cycle was repeated 100,000 times, and the potential M2 was measured 100 msec after charging in the last cycle. The difference ΔM=(M1-M2) between the obtained initial potential M1 and the potential M2 after long-term use was calculated, and the charge retention performance was evaluated according to the following criteria. The acceptable range is A to C. -Evaluation Criteria- A: The measured potential difference ΔM is less than 15V. B: Measured potential difference ΔM is 15V or more and less than 25V. C: Measured potential difference ΔM is 25V or more and less than 35V. D: Measured potential difference ΔM is 35V or higher.

[0208] <Evaluation of initial sensitivity> Each example of the electrophotographic photoreceptor was mounted in a laser printer-modified scanner (XP-15 modified model) manufactured by Fujifilm Business Innovation Co., Ltd. Under conditions of 20°C and 40% RH relative humidity, the electrophotographic photoreceptor was charged using a scorotron charger with a grid voltage of -700V, and then charged at 4 mJ / cm using a semiconductor laser with a wavelength of 780 nm. 2 After exposure, the potential M3 was measured at a position corresponding to 70 msec after charging. The initial sensitivity of the obtained potential M3 was evaluated according to the following criteria. The acceptable range is A to C. -Evaluation Criteria- A: The measured potential M3 is less than -50V. B: Measured potential M3 is between -50V and -57V. C: Measured potential M3 is between -57V and -65V. D: Measured potential M3 is -65V or higher.

[0209] [Table 1]

[0210] As shown in Table 1, the electrophotographic photoreceptor of the example was found to have superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment compared to the electrophotographic photoreceptor of the comparative example.

[0211] The electrophotographic photoreceptor, process cartridge, and image forming apparatus of this disclosure include the following embodiments.

[0212] (((1))) Conductive substrate and, A base layer provided on the conductive substrate, comprising an electron transport material and a binder resin, A charge generation layer provided on the aforementioned lower layer, A charge transport layer provided on the charge generation layer, Equipped with, The aforementioned lower layer is The content X1 (mass%) of the electron transport material in a region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer, The content X2 (mass%) of the electron transport material in the region exceeding 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer, An electrophotographic photoreceptor in which the ratio (X1 / X2) is 0 or 78 or less. (((2))) Conductive substrate and, A base layer provided on the conductive substrate, comprising an electron transport material and a binder resin, A charge generation layer provided on the aforementioned lower layer, A charge transport layer provided on the charge generation layer, Equipped with, The aforementioned lower layer is In a cross-section in the thickness direction, the area ratio Y1 (%) of the electron transport material in the region within 4% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer, In a cross-section in the thickness direction, the area ratio Y2(%) of the electron transport material in the region exceeding 4% in the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer, An electrophotographic photoreceptor in which the ratio (Y1 / Y2) is 0 or 81 or less. (((3))) The electron transport material comprises an acid anhydride having electron transport properties, as described in (((1))) or (((2))) above, for the electrophotographic photoreceptor. (((4))) The electron transport material comprises a compound represented by the following formula (P), as described in (((3))) above, for the electrophotographic photoreceptor. [ka] In formula (P), 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 any one of (((1))) to (((4))) above, wherein the undercoat has an average thickness of 2 nm or more and 15 nm or less. (((6))) The electrophotographic photoreceptor according to any one of (((1))) to (((5))), wherein the content X1 of the electron transport material in a region within 4% in the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer is 0 or 55% by mass or less. (((7))) The electrophotographic photoreceptor according to (((6))), wherein the undercoat is such that the content X2 of the electron transport material in a region exceeding 4% in the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer is 60% by mass or more and 80% by mass or less. (((8))) The electrophotographic photoreceptor according to any one of (((1))) to (((7))) above, wherein the undercoat layer has an area ratio Y1 of the electron transport material in a region within 4% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer in a cross-section in the thickness direction, which is 0 or 63% or less. (((9))) The electrophotographic photoreceptor according to (((8))), wherein the undercoat is such that the area ratio Y2 of the electron transport material in the region extending more than 4% in the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer in the thickness direction cross-section is 60% or more and 80% or less. (((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.

[0213] According to the invention of (((1))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case where the content ratio (X1 / X2) exceeds 78. According to the invention of (((2))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case where the area ratio (Y1 / Y2) exceeds 81. According to the invention of (((3))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case in which the electron transport material contains an acid anhydride having electron transport properties. According to the invention of (((4))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case where the electron transport material is a perinone compound. According to the invention of (((5))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the average thickness of the undercoat layer is less than 2 nm or greater than 15 nm. According to the invention of (((6))), compared to the case where the content X1 of electron transport material in the lower layer within 5% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer exceeds 55% by mass, an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high temperature and high humidity environment. According to the invention of (((7))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the content X2 of electron transport material in the region exceeding 4% in the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer is less than 60% by mass or more than 80% by mass. According to the invention of (((8))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case where the area ratio Y1 of the electron transport material in the region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section exceeds 63%. According to the invention of (((9))), an electrophotographic photoreceptor is provided that exhibits superior charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to the case where the area ratio Y2 of the electron transport material in the region exceeding 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in the thickness direction cross-section is less than 60% or more than 80%. According to the invention of (((10))), a process cartridge is provided that exhibits superior static charge retention even when operated for a long period of time in a high-temperature, high-humidity environment, compared to cases where the content ratio (X1 / X2) exceeds 78 or the area ratio (Y1 / Y2) exceeds 81. According to the invention of (((11))), an image forming apparatus is provided that has an electrophotographic photoreceptor that exhibits superior charge retention even when operated for a long period of time in a high temperature and high humidity environment, compared to the case where the content ratio (X1 / X2) exceeds 78 or the area ratio (Y1 / Y2) exceeds 81. [Explanation of Symbols]

[0214] 1 Conductive substrate, 2 Undercoat layer, 3 Charge generation layer, 4 Charge transport layer, 5 Photosensitive layer, 10A photoreceptor, 10B electrophotographic photoreceptor

[0215] 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 base layer provided on the conductive substrate, comprising an electron transport material and a binder resin, A charge generation layer provided on the aforementioned lower layer, A charge transport layer provided on the charge generation layer, Equipped with, The aforementioned lower layer is The content X1 (mass%) of the electron transport material in a region within 4% of the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer, The content X2 (mass%) of the electron transport material in the region exceeding 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer, An electrophotographic photoreceptor in which the ratio (X1 / X2) is 0 or 78 or less.

2. A conductive substrate, A base layer provided on the conductive substrate, comprising an electron transport material and a binder resin, A charge generation layer provided on the aforementioned lower layer, A charge transport layer provided on the charge generation layer, Equipped with, The aforementioned lower layer is In a cross-section in the thickness direction, the area ratio Y1 (%) of the electron transport material in the region within 4% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer, In a cross-section in the thickness direction, the area ratio Y2 (%) of the electron transport material in the region exceeding 4% in the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer, An electrophotographic photoreceptor in which the ratio (Y1 / Y2) is 0 or 81 or less.

3. The electron transport material comprises an acid anhydride having electron transport properties, as described in claim 1 or claim 2, for the electrophotographic photoreceptor.

4. The electrophotographic photoreceptor according to claim 3, wherein the electron transport material comprises a compound represented by the following formula (P). 【Chemistry 1】 In formula (P), 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 claim 1 or claim 2, wherein the undercoat has an average thickness of 2 nm or more and 15 nm or less.

6. The electrophotographic photoreceptor according to claim 1 or claim 2, wherein the content X1 of the electron transport material in a region within 4% in the thickness direction of the undercoat from the interface between the undercoat and the charge generation layer is 0 or 55% by mass or less.

7. The electrophotographic photoreceptor according to claim 6, wherein the content X2 of the electron transport material in the region exceeding 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer is 60% by mass or more and 80% by mass or less.

8. The electrophotographic photoreceptor according to claim 1 or claim 2, wherein the area ratio Y1 of the electron transport material in a region within 4% of the thickness direction of the undercoat layer from the interface between the undercoat layer and the charge generation layer in a cross-section in the thickness direction is 0 or 63% or less.

9. The electrophotographic photoreceptor according to claim 8, wherein the area ratio Y2 of the electron transport material in the region extending more than 4% in the thickness direction of the lower layer from the interface between the lower layer and the charge generation layer in a cross-section in the thickness direction is 60% or more and 80% or less.

10. The electrophotographic photoreceptor is provided according to claim 1 or claim 2, A process cartridge that is attached to and detached from an image forming apparatus.

11. An electrophotographic photoreceptor according to claim 1 or claim 2, 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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