Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

To provide an electrophotographic photoreceptor that has high photosensitivity and prevents the generation of black spots.SOLUTION: An electrophotographic photoreceptor has a conductive substrate, and a single-layer photosensitive layer that is provided on the conductive substrate and contains a binder resin, a charge generating material, a hole transport material, and an electron transport material. When the ratio of the thickness of the photosensitive layer after wear to the thickness of the photosensitive layer before wear (the thickness of the photosensitive layer after wear / the thickness of the photosensitive layer before wear) is 0.8, the volume resistivity of the photosensitive layer after wear is 5.0×1010 Ω cm or more and 2.0×1011 Ω cm or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In a conventional electrophotographic image forming apparatus, a toner image formed on the surface of an electrophotographic photosensitive member is transferred onto a recording medium through processes of charging, electrostatic latent image formation, development, and transfer.

[0003] For example, Patent Document 1 discloses "an electrophotographic photoreceptor having a conductive substrate and a single-layer photosensitive layer provided on the conductive substrate, the photosensitive layer including a binder resin, a charge generating material, an electron transport material, and a hole transport material, and having a product of volume resistivity (GΩ m) and modulus of elasticity (GPa) of 90 or more."

[0004] Furthermore, Patent Document 2 describes a photoconductive layer that includes a charge generating material, a hole transporting material, an electron transporting material, and an organic binder resin on a conductive support, and the resistivity ρ of the photoconductive layer is ρ<10 11 The document discloses an image forming apparatus equipped with a single-layer positively charged organic photoreceptor having a resistivity of Ωm (where ρ is the resistivity at an electric field strength of 20 V / μm) and a charging member for charging the surface of the photoreceptor, wherein the charging member is a non-contact charging member. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-049149 [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-365818 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to provide an electrophotographic photoreceptor having a single-layer photosensitive layer containing a binder resin, a charge generating material, a hole transport material, and an electron transport material, in which the volume resistivity of the photosensitive layer after abrasion is 5.0×10 when the ratio of the thickness of the photosensitive layer after abrasion to the thickness of the photosensitive layer before abrasion is 0.8. 10 Less than Ωcm or 2.0×10 11 The object of the present invention is to provide an electrophotographic photoreceptor which has high photosensitivity and suppresses the occurrence of black spots, compared to a case where the resistivity exceeds Ωcm, or a case where the ratio of the amount of hole transport material present on the surface of the photosensitive layer to the amount of hole transport material present on the back surface of the photosensitive layer is less than 1 / 6 or more than 1 / 3. [Means for solving the problem]

[0007] The means for solving the above problems include the following aspects. <1> a conductive substrate; a single-layer photosensitive layer provided on the conductive substrate and containing a binder resin, a charge generating material, a hole transport material, and an electron transport material; and When the ratio of the thickness of the photosensitive layer after abrasion to the thickness of the photosensitive layer before abrasion (thickness of the photosensitive layer after abrasion / thickness of the photosensitive layer before abrasion) is 0.8, the volume resistivity of the photosensitive layer after abrasion is 5.0 × 10 10 Ωcm or more 2.0×10 11 An electrophotographic photoreceptor with a resistivity of Ωcm or less. <2> The ratio of the volume resistivity of the photosensitive layer after abrasion to the volume resistivity of the photosensitive layer before abrasion (volume resistivity of the photosensitive layer after abrasion / volume resistivity of the photosensitive layer before abrasion) is 1 / 100 or more and 7 / 100 or less. <1> The electrophotographic photoreceptor according to claim 1. <3> The mass ratio of the hole transport material to the electron transport material (the hole transport material / the electron transport material) is 19 / 5 or more and 28 / 5 or less. <1> or <2> The electrophotographic photoreceptor according to claim 1. <4> The content of the hole transport material relative to the total solid content of the photosensitive layer is 38% by mass or more and 44% by mass or less. <3> The electrophotographic photoreceptor according to claim 1. <5> The hole transport material has a benzidine skeleton. <1> ~ <4> 10. The electrophotographic photoreceptor according to claim 9, wherein the electrophotographic photoreceptor is a <6> The hole transport material having a benzidine skeleton is a hole transport material represented by the following general formula (HT1a): <5> The electrophotographic photoreceptor according to claim 1. [ka] (In the general formula (HT1a), R C21 , R C22 , and R C23 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms. <7> The electron transport material has a diphenoquinone skeleton. <1> ~ <6> 10. The electrophotographic photoreceptor according to claim 9, wherein the electrophotographic photoreceptor is a <8> The electron transport material having a diphenoquinone skeleton is an electron transport material represented by the following general formula (FK): <7> The electrophotographic photoreceptor according to claim 1. [ka] (In the general formula (FK), R k1 ~R k4 each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group. <9> a conductive substrate; a single-layer photosensitive layer provided on the conductive substrate and containing a binder resin, a charge generating material, a hole transport material, and an electron transport material; and an electrophotographic photoreceptor in which the ratio of the amount of the hole transport material present on the surface of the photosensitive layer to the amount of the hole transport material present on the back surface of the photosensitive layer (amount of the hole transport material present on the surface of the photosensitive layer / amount of the hole transport material present on the back surface of the photosensitive layer) is 1 / 6 or more and 1 / 3 or less. <10> <1> ~ <9> The electrophotographic photoreceptor according to any one of the preceding claims is provided, A process cartridge that is detachably attached to an image forming apparatus. <11> <1> ~ <9> the electrophotographic photoreceptor according to any one of the above items; a charging means for charging the surface of the electrophotographic photosensitive member; an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; a developing means for developing an electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing a toner to form a toner image; a transfer means for transferring the toner image onto a surface of a recording medium; An image forming apparatus comprising: <12> <1> ~ <9> the electrophotographic photoreceptor according to any one of the above items; a charging means for charging the surface of the electrophotographic photosensitive member; an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; a developing means for developing an electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing a toner to form a toner image; a direct transfer type transfer means having a transfer member that transfers the toner image directly from the electrophotographic photosensitive member onto a surface of a recording medium; Equipped with An image forming apparatus in which the relationship between the rotation speed P (mm / s) of the electrophotographic photosensitive member, the transfer current value I (μA) for directly transferring the toner image from the electrophotographic photosensitive member to the surface of the recording medium, and the length L (mm) of the transfer member satisfies the following formula (PIL): Formula (PIL):-1.07×10 -3 ≦I / (P×L)≦-4.30×10 -4 [Effects of the Invention]

[0008] <1> According to the invention, in an electrophotographic photoreceptor having a single-layer type photosensitive layer containing a binder resin, a charge generating material, a hole transport material, and an electron transport material, when the ratio of the thickness of the photosensitive layer after abrasion to the thickness of the photosensitive layer before abrasion is 0.8, the volume resistivity of the photosensitive layer after abrasion is 5.0 × 10 10 Less than Ωcm or 2.0×10 11 As compared with a case where the resistivity exceeds Ωcm, an electrophotographic photoreceptor is provided which has high photosensitivity and suppresses the occurrence of black spots. <2> According to the invention, an electrophotographic photoreceptor is provided which has high photosensitivity and suppresses the occurrence of black spots, compared to when the ratio of the volume resistivity of the photosensitive layer after wear to the volume resistivity of the photosensitive layer before wear (volume resistivity of the photosensitive layer after wear / volume resistivity of the photosensitive layer before wear) is less than 1 / 100 or more than 7 / 100. <3> According to the invention, an electrophotographic photoreceptor is provided which has high photosensitivity and suppresses the occurrence of black spots, compared to when the mass ratio of the hole transport material to the electron transport material (the hole transport material / the electron transport material) is less than 19 / 5 or more than 28 / 5. <4> According to the invention, an electrophotographic photoreceptor is provided which has high photosensitivity and suppresses the occurrence of black spots, compared to when the content of the hole transport material is less than 38% by mass or more than 44% by mass with respect to the photosensitive layer.

[0009] <5> , or <6> According to the present invention, an electrophotographic photoreceptor is provided which has high photosensitivity and suppresses the occurrence of black spots, compared to when the hole transport material is HTM-B, which is used in the comparative example described below. <7> , or <8> According to the present invention, an electrophotographic photoreceptor is provided which has high photosensitivity and suppresses the occurrence of black spots, compared to when the electron transport material is ETM-C, which is used in the comparative example described below.

[0010] <9> According to the invention, there is provided an electrophotographic photoreceptor having a single-layer photosensitive layer containing a binder resin, a charge generating material, a hole transport material, and an electron transport material, which has high photosensitivity and suppresses the occurrence of black spots, compared to when the ratio of the amount of the hole transport material present on the surface of the photosensitive layer to the amount of the hole transport material present on the back surface of the photosensitive layer (amount of hole transport material present on the surface of the photosensitive layer / amount of hole transport material present on the back surface of the photosensitive layer) is less than 1 / 6 or more than 1 / 3. <10> , or <11> According to the invention, in an electrophotographic photoreceptor having a single-layer type photosensitive layer containing a binder resin, a charge generating material, a hole transport material, and an electron transport material, when the ratio of the thickness of the photosensitive layer after abrasion to the thickness of the photosensitive layer before abrasion is 0.8, the volume resistivity of the photosensitive layer after abrasion is 5.0 × 10 10 Less than Ωcm or 2.0×10 11 A process cartridge or an image forming apparatus is provided that is equipped with an electrophotographic photosensitive member having high photosensitivity and suppresses the occurrence of black spots, compared to a case where an electrophotographic photosensitive member having a resistivity of more than Ωcm is equipped.

[0011] <12> According to the invention, an image forming device is provided in which the afterimage phenomenon (hereinafter also referred to as "ghost") caused by the retention of the history of the previous image is suppressed from the initial stage to the end of the life of the electrophotographic photosensitive member, compared to when formula (PIL) is not satisfied. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic partial cross-sectional view showing an example of a layer structure of an electrophotographic photosensitive member according to an exemplary embodiment. [Figure 2] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 3] FIG. 10 is a schematic configuration diagram illustrating another example of an image forming apparatus according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment of the present invention will be described in detail.

[0014] In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0015] In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Each component may contain multiple types of the corresponding substance. When referring to the amount of each component, if there are multiple substances corresponding to each component, the amount refers to the total amount of the multiple substances unless otherwise specified. An electrophotographic photoreceptor having a single-layer photosensitive layer is also called a “single-layer photoreceptor.” The single-layer photosensitive layer is a photosensitive layer that has charge generation capability as well as hole transport capability and electron transport capability.

[0016] [Electrophotographic photoreceptor] -First embodiment- The electrophotographic photoreceptor according to the first embodiment has a conductive substrate and a single-layer photosensitive layer provided on the conductive substrate and containing a binder resin, a charge generating material, a hole transport material, and an electron transport material. When the ratio of the thickness of the photosensitive layer after abrasion to the thickness of the photosensitive layer before abrasion (thickness of the photosensitive layer after abrasion / thickness of the photosensitive layer before abrasion) is 0.8, the volume resistivity of the photosensitive layer after abrasion is 5.0 × 10 10 Ωcm or more 2.0×10 11 It is less than Ωcm.

[0017] The electrophotographic photoreceptor according to the first embodiment has the above-described structure, and while having high photosensitivity, suppresses the occurrence of black spots. The reason for this is presumed to be as follows. First, when a single-layer photoreceptor is used and images are repeatedly formed, black spots may occur due to cracks in the photosensitive layer. In a single-layer photoreceptor, if the initial single-layer photosensitive layer before wear has the desired volume resistivity and film strength, the occurrence of black spots after the single-layer photosensitive layer has worn can be suppressed. However, black spots caused by factors other than cracks in the single-layer photosensitive layer may occur due to current leakage (hereinafter also referred to as "leak") caused by an increase in the total amount of charge flowing through the single-layer photosensitive layer after repeated image formation.

[0018] On the other hand, after the wear has progressed, that is, when the ratio of the thickness of the photosensitive layer after wear to the thickness of the photosensitive layer before wear (thickness of the photosensitive layer after wear / thickness of the photosensitive layer before wear) is 0.8, the volume resistivity of the photosensitive layer after wear is 5.0 × 10 10 By increasing the resistivity to Ωcm or more, the occurrence of black spots due to leakage caused by an increase in the total amount of charge flowing through the single-layer photosensitive layer after repeated image formation can be suppressed. On the other hand, if the volume resistivity of the photosensitive layer after abrasion is too high, the photosensitivity decreases. Therefore, the volume resistivity of the photosensitive layer after abrasion is set to 2.0 × 10 11 Keep it below Ωcm.

[0019] From the above, it is presumed that the electrophotographic photosensitive member according to the first embodiment has high photosensitivity and suppresses the occurrence of black spots due to the above configuration.

[0020] -Second embodiment- The electrophotographic photoreceptor according to the second embodiment has a conductive substrate and a single-layer photosensitive layer provided on the conductive substrate and containing a binder resin, a charge generating material, a hole transport material, and an electron transport material. The ratio of the amount of hole transport material present on the surface of the photosensitive layer to the amount of hole transport material present on the back surface of the photosensitive layer (amount of hole transport material present on the surface of the photosensitive layer / amount of the hole transport material present on the back surface of the photosensitive layer) is 1 / 6 or more and 1 / 3 or less.

[0021] The electrophotographic photoreceptor according to the second embodiment has the above-described configuration, and while having high photosensitivity, suppresses the occurrence of black spots for the following reasons.

[0022] As described above, when a single-layer photosensitive member is used, black spots may occur due to current leakage (hereinafter also referred to as "leak") caused by an increase in the total amount of charge flowing through the single-layer photosensitive layer after repeated image formation, in addition to black spots caused by cracks in the single-layer photosensitive layer. In response to this, the ratio of the amount of hole transport material present on the surface of the photosensitive layer to the amount of hole transport material present on the back surface of the photosensitive layer is set to 1 / 3 or less, and the hole transport material is unevenly distributed on the conductive substrate side of the photosensitive layer, thereby increasing the volume resistivity of the photosensitive layer after wear and suppressing the occurrence of black spots caused by leakage due to an increase in the total amount of charge flowing through the single-layer photosensitive layer after repeated image formation. On the other hand, the ratio of the amount of hole transport material present on the surface of the photosensitive layer to the amount of hole transport material present on the back surface of the photosensitive layer is set to 1 / 6 or more, thereby preventing excessive uneven distribution of the hole transport material on the conductive substrate side of the photosensitive layer, thereby preventing the volume resistivity of the photosensitive layer after wear from becoming too high and suppressing a decrease in photosensitivity.

[0023] From the above, it is presumed that the electrophotographic photosensitive member according to the second embodiment has high photosensitivity and suppresses the occurrence of black spots due to the above configuration.

[0024] -Implementation-

[0025] Hereinafter, an electrophotographic photosensitive member corresponding to both the electrophotographic photosensitive member according to the first and second embodiments (hereinafter also referred to as "electrophotographic photosensitive member according to the present embodiment") will be described in detail. However, an example of the electrophotographic photosensitive member of the present invention may be an electrophotographic photosensitive member corresponding to either the electrophotographic photosensitive member according to the first or second embodiment.

[0026] The electrophotographic photoreceptor according to this embodiment will be described in detail below.

[0027] In the electrophotographic photosensitive member according to the present embodiment, when the ratio of the thickness of the photosensitive layer after wear to the thickness of the photosensitive layer before wear (thickness of the photosensitive layer after wear / thickness of the photosensitive layer before wear) is 0.8, the volume resistivity of the photosensitive layer after wear is 5.0×10 10 Ωcm or more 2.0×10 11 Ωcm or less, but from the viewpoint of high light sensitivity and suppression of black spots, it is 6.5 × 10 10 Ωcm or more 1.5×10 11 Ωcm or less is preferable, 8.0×10 10 Ωcm or more 1.0×10 11 It is more preferable that the resistance is Ωcm or less.

[0028] The ratio of the volume resistivity of the photosensitive layer after abrasion to the volume resistivity of the photosensitive layer before abrasion (volume resistivity of the photosensitive layer after abrasion / volume resistivity of the photosensitive layer before abrasion) is preferably 1 / 100 or more and 7 / 100 or less, more preferably 1 / 50 or more and 3 / 50 or less, and even more preferably 3 / 100 or more and 2 / 50 or less, from the viewpoints of high photosensitivity and suppressing the occurrence of black spots.

[0029] The volume resistivity of the photosensitive layer before and after abrasion is, for example, 1) The temperature of the coating solution for forming the photosensitive layer (preferably a low temperature), 2) The temperature of the conductive substrate during application of the coating liquid (preferably low temperature) 3) Drying temperature (preferably low) 4) Type of hole transport material (preferably a hole transport material having a benzidine skeleton) 5) Type of electron transport material (preferably an electron transport material having a diphenoquinone skeleton) etc.

[0030] The volume resistivity of the photosensitive layer before and after abrasion is measured as follows. A sample of the photosensitive layer is taken from the photoreceptor to be measured as follows: The photoreceptor is cut into a 6 cm long cylinder, which is then cut in half to form a semicircle. The edges of the photoreceptor slice are clamped in a vice, and force is applied to increase the curvature of the semicircle, lifting the photosensitive layer from the substrate and allowing the photosensitive layer to be sampled.

[0031] Next, an electrode with an area of ​​1 cm2 was placed on the surface of the photosensitive layer. 2 An Au electrode is formed by sputtering, and an Al electrode is formed on the entire surface of the film on the back side of the photosensitive layer. Next, using a frequency response analyzer (Model 1260, Solartron) in an environment of 30°C temperature and 80% RH, a voltage adjusted to an electric field (applied voltage / measurement sample thickness) of 20 V / μm is applied for 30 seconds under dark conditions, and the current value (A) that flows is measured. Then, the volume resistivity is calculated using the obtained current value using the following formula: The obtained volume resistivity is the volume resistivity of the photosensitive layer before abrasion. ·Formula: Volume resistivity (Ω m) = (10 -4 (m 2 ) × applied voltage (V)) / (current value (A) × measurement sample thickness (m))

[0032] On the other hand, the collected slice sample of the photosensitive layer is fixed with tape to the rotating stage of a friction and wear tester (FPR2100, Rhesca Co., Ltd.) with the surface of the photosensitive layer facing up. A wrapping film sheet (abrasive aluminum oxide, 9 μm grit size) is attached to the indenter part. The photosensitive layer is abraded from the surface side at a rotation speed of 100 rpm. The abrasion amount is adjusted while checking the film thickness after abrasion using a step gauge (Surfcom S1500, manufactured by Tokyo Seimitsu Co., Ltd.). The volume resistivity of the abraded measurement sample is calculated in the same manner as above, and the resulting volume resistivity is taken as the volume resistivity of the abraded photosensitive layer.

[0033] In the electrophotographic photosensitive member according to the present embodiment, the ratio of the amount of hole transport material present on the surface of the photosensitive layer to the amount of hole transport material present on the back surface of the photosensitive layer (amount of hole transport material present on the surface of the photosensitive layer / amount of hole transport material present on the back surface of the photosensitive layer) is from 1 / 6 to 1 / 3, and from the viewpoints of high photosensitivity and suppression of black spots, it is preferably from 1.1 / 6 to 3 / 10, and more preferably from 1 / 5 to 1 / 4.

[0034] The ratio of the amounts of the electron transport materials present is controlled in the same manner as in the volume resistivity of the photosensitive layer before and after abrasion.

[0035] Here, the "surface of the photosensitive layer" refers to the surface of the photosensitive layer facing in the thickness direction opposite to the conductive substrate, while the "rear surface of the photosensitive layer" refers to the surface of the photosensitive layer facing in the thickness direction on the conductive substrate side.

[0036] The ratio of the amount of hole transport material present is determined as follows. First, a sample of the photosensitive layer is taken from the photoreceptor to be measured as follows: A 0.5 cm x 0.5 cm square cut is made in the film with a single-edged knife so that it reaches the substrate, and the 0.5 cm x 0.5 cm square section of the film is naturally peeled off from the substrate. The peeled piece of photosensitive layer is used as the sample.

[0037] Next, the surface of the photosensitive layer in the obtained sample is subjected to Fourier transform infrared analysis by total reflection measurement (i.e., ATR method). Specifically, an infrared spectrometer (NICOLET 6700FT-IR manufactured by Thermo Fisher Scientific) is used as the measurement device, and the measurement area is 650 cm -1 ~4000cm -1 , resolution: 4cm -1 Measurements are performed under the following conditions: number of integrations: 32, refractive index medium: ZnSe, measurement depth: 2 μm. From the infrared absorption spectrum obtained by the above measurement, the area of ​​the absorption peak derived from the hole transport material (for example, when the hole transport material has a benzidine skeleton, the area of ​​the absorption peak derived from the hole transport material is 680 cm -1 More than 720cm -1 The area of ​​the absorption peak of the hole transport material (shown below) and the absorption peak derived from the binder resin (for example, when the binder resin is polycarbonate resin, 1675 cm -1 over 1860cm -1 The area of ​​the absorption peak derived from the C=O bond of the binder resin appearing below is determined, and the amount of the hole transport material present on the surface of the photosensitive layer is calculated as (the above peak area of ​​the hole transport material / the above peak area of ​​the resin)=(the amount of the hole transport material present). On the other hand, the rear surface of the photosensitive layer in the obtained sample is subjected to Fourier transform infrared analysis by total reflection measurement in the same manner as above to determine the amount of hole transport material present on the rear surface of the photosensitive layer.

[0038] Next, the electrophotographic photoreceptor according to the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a portion of an electrophotographic photosensitive member 7 according to this embodiment. The electrophotographic photoreceptor 7 shown in FIG. 1 is configured, for example, by including a conductive substrate 3 on which a single-layer photosensitive layer 2 is provided as the outermost layer. Other layers may be provided as needed, such as an undercoat layer provided between the conductive substrate 3 and the single-layer photosensitive layer 2, and a protective layer provided on the single-layer photosensitive layer 2.

[0039] Hereinafter, each layer of the electrophotographic photoreceptor according to this embodiment will be described in detail, with reference numerals omitted.

[0040] (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, belts, etc. 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 material having a volume resistivity of 10 13 This means that the resistance is less than Ωcm.

[0041] When the 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 inclusive in order to suppress interference fringes that occur when irradiated with laser light. When incoherent light is used as the light source, roughening to prevent interference fringes is not particularly necessary, but it is suitable for extending the life of the conductive substrate by suppressing defects caused by surface irregularities.

[0042] Examples of surface roughening methods include wet honing, which involves spraying an abrasive suspended in water onto the support, centerless grinding, which involves pressing a conductive substrate against a rotating grinding wheel and continuously grinding the substrate, and anodizing.

[0043] As a method for roughening the surface, there may be mentioned a method in which, without roughening the surface of the conductive substrate, conductive or semiconductive powder is dispersed in a resin to form a layer on the surface of the conductive substrate, and the surface is roughened by the particles dispersed in the layer.

[0044] Anodizing is a surface roughening treatment that uses a metallic (e.g., aluminum) conductive substrate as the anode and anodizes it in an electrolyte solution to form an oxide film on the surface of the conductive substrate. Examples of electrolyte solutions include sulfuric acid solution and oxalic acid solution. However, the porous anodic oxide film formed by anodizing is chemically active in its original state, 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, in which the micropores of the oxide film are sealed by volume expansion caused by hydration in pressurized steam or boiling water (with the addition of a metal salt such as nickel), converting the film into a more stable hydrated oxide.

[0045] The thickness of the anodic oxide film is preferably, for example, from 0.3 μm to 15 μm, inclusive, and within this range, the film tends to exhibit barrier properties against injection and also tends to suppress an increase in residual potential due to repeated use.

[0046] The conductive substrate may be subjected to a treatment with an acidic treatment solution or a boehmite treatment. Treatment with an acidic treatment solution is carried out, for example, as follows. First, an acidic treatment solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. The compounding ratios of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic treatment solution are, for example, in the range of 10% by mass to 11% by mass for phosphoric acid, 3% by mass to 5% by mass for chromic acid, and 0.5% by mass to 2% by mass for hydrofluoric acid, with the total concentration of these acids preferably in the range of 13.5% by mass to 18% by mass. The treatment temperature is preferably, for example, 42°C to 48°C. The film thickness of the coating is preferably 0.3 μm to 15 μm.

[0047] The boehmite treatment is carried out, for example, by immersing the steel sheet in pure water at 90°C to 100°C for 5 to 60 minutes, or by contacting the steel sheet with heated steam at 90°C to 120°C for 5 to 60 minutes. The coating film preferably has a thickness of 0.1 μm to 5 μm. This may be further anodized using an electrolyte solution with low coating solubility, such as adipic acid, boric acid, borate, phosphate, phthalate, maleate, benzoate, tartrate, or citrate.

[0048] (single-layer photosensitive layer) The single-layer photosensitive layer contains a binder resin, a charge generating material, a hole transport material, and an electron transport material. The single-layer photosensitive layer may contain other additives as needed. Each component contained in the single-layer photosensitive layer will be described in detail below.

[0049] -Binder resin- The binder resin is not particularly limited, and examples thereof 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. These binder resins may be used alone or in combination of two or more.

[0050] Among the binder resins, polycarbonate resins and polyarylate resins are preferred. From the viewpoint of film-forming properties of the photosensitive layer, it is preferable to use at least one of a polycarbonate resin having a viscosity average molecular weight of 30,000 or more and 80,000 or less, and a polyarylate resin having a viscosity average molecular weight of 30,000 or more and 80,000 or less.

[0051] The viscosity average molecular weight of polycarbonate resin and polyarylate resin can be measured, for example, by the following method: 1 g of resin is dissolved in 100 cm of methylene chloride. 3 The specific viscosity ηsp was measured using an Ubbelohde viscometer at 25°C, and the formula ηsp / c=[η]+0.45[η] was used. 2 c relation (where c is the concentration (g / cm 3 ) from the intrinsic viscosity [η] (cm 3 / g) and the formula given by H. Schnell is [η] = 1.23 × 10 -4 Mv 0.83 The viscosity average molecular weight Mv is calculated from the following equation.

[0052] As the binder resin, a polycarbonate resin containing at least one of a structural unit represented by the following general formula (PCA) and a structural unit represented by the following general formula (PCB) is particularly preferred.

[0053] [ka]

[0054] In the general formulas (PCA) and (PCB), R P1 , R P2 , R P3 , and R P4 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 5 to 7 carbon atoms, or an aryl group having 6 to 12 carbon atoms.P1 represents a phenylene group, a biphenylene group, a naphthylene group, an alkylene group, or a cycloalkylene group.

[0055] In the general formulas (PCA) and (PCB), R P1 , R P2 , R P3 , and R P4 The alkyl group represented by the formula (I) includes a linear or branched alkyl group having 1 to 6 carbon atoms (preferably 1 to 3 carbon atoms). Specific examples of the linear alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, and an n-hexyl group. Specific examples of branched alkyl groups include an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, an isohexyl group, a sec-hexyl group, and a tert-hexyl group. Among these, lower alkyl groups such as methyl and ethyl are preferred as the alkyl group.

[0056] In the general formulas (PCA) and (PCB), R P1 , R P2 , R P3 , and R P4 Examples of the cycloalkyl group represented by include cyclopentyl, cyclohexyl, and cycloheptyl.

[0057] In the general formulas (PCA) and (PCB), R P1 , R P2 , R P3 , and R P4 Examples of the aryl group represented by include a phenyl group, a naphthyl group, and a biphenylyl group.

[0058] In the general formulas (PCA) and (PCB), X P1 The alkylene group represented by the formula (I) includes a linear or branched alkylene group having 1 to 12 carbon atoms (preferably 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms). Specific examples of the linear alkylene group include a methylene group, an ethylene group, an n-propylene group, an n-butylene group, an n-pentylene group, an n-hexylene group, an n-heptylene group, an n-octylene group, an n-nonylene group, an n-decylene group, an n-undecylene group, and an n-dodecylene group. Specific examples of branched alkylene groups include an isopropylene group, an isobutylene group, a sec-butylene group, a tert-butylene group, an isopentylene group, a neopentylene group, a tert-pentylene group, an isohexylene group, a sec-hexylene group, a tert-hexylene group, an isoheptylene group, a sec-heptylene group, a tert-heptylene group, an isooctylene group, a sec-octylene group, a tert-octylene group, an isonylene group, a sec-nonylene group, a tert-nonylene group, an isodecylene group, a sec-decylene group, a tert-decylene group, an isoundecylene group, a sec-undecylene group, a tert-undecylene group, a neoundecylene group, an isododecylene group, a sec-dodecylene group, a tert-dodecylene group, and a neododecylene group. Among these, the alkylene group is preferably a lower alkyl group such as a methylene group, an ethylene group, or a butylene group.

[0059] In the general formulas (PCA) and (PCB), X P1 Examples of the cycloalkylene group represented by include cycloalkylene groups having 3 to 12 carbon atoms (preferably 3 to 10 carbon atoms, more preferably 5 to 8 carbon atoms). Specific examples of the cycloalkylene group include a cyclopropylene group, a cyclopentylene group, a cyclohexylene group, a cyclooctylene group, and a cyclododecanylene group. Among these, the cycloalkylene group is preferably a cyclohexylene group.

[0060] In the general formulas (PCA) and (PCB), R P1 , R P2 , R P3 , R P4 , and X P1Each of the above substituents represented by the formula (I) also includes a group having a further substituent. Examples of the substituent include a halogen atom (e.g., a fluorine atom, a chlorine atom), an alkyl group (e.g., an alkyl group having 1 to 6 carbon atoms), a cycloalkyl group (e.g., a cycloalkyl group having 5 to 7 carbon atoms), an alkoxy group (e.g., an alkoxy group having 1 to 4 carbon atoms), and an aryl group (e.g., a phenyl group, a naphthyl group, a biphenylyl group, etc.).

[0061] In the general formula (PCA), R P1 , and R P2 each independently preferably represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and R P1 , and R P2 More preferably, represents a hydrogen atom. In the general formula (PCB), R P3 , and R P4 each independently represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms; X P1 Preferably, represents an alkylene group or a cycloalkylene group.

[0062] Specific examples of the structural unit represented by general formula (PCA) and the structural unit represented by general formula (PCB) include, but are not limited to, the following:

[0063] JPEG0007771519000004.jpg83164

[0064] Furthermore, the binder resin is more preferably a polycarbonate resin containing both a structural unit represented by general formula (PCA) and a structural unit represented by general formula (PCB).

[0065] Specific examples of polycarbonate resins containing both structural units represented by general formula (PCA) and structural units represented by general formula (PCB) include, but are not limited to, the following: In the example compounds, pm and pn represent copolymerization ratios.

[0066] [ka]

[0067] Here, in a polycarbonate resin containing both a structural unit represented by general formula (PCA) and a structural unit represented by general formula (PCB), the content (copolymerization ratio) of the structural unit represented by general formula (PCA) is preferably in the range of 5 mol% to 95 mol% of all structural units constituting the polycarbonate resin, and from the viewpoint of improving the abrasion resistance of the photosensitive layer (charge transport layer), it is preferably in the range of 5 mol% to 50 mol%, more preferably in the range of 15 mol% to 30 mol%. Specifically, in the above-mentioned exemplary compounds of polycarbonate resin, pm and pn indicate the copolymerization ratio (molar ratio), and pm:pn is in the range of 95:5 to 5:95, 50:50 to 5:95, and more preferably 15:85 to 30:70.

[0068] When a polycarbonate resin containing at least one of a structural unit represented by general formula (PCA) and a structural unit represented by general formula (PCB) is used in combination with another binder resin, the content of the other binder resin is preferably 10 mass % (preferably 5 mass % or less) of the total binder resin.

[0069] The content of the binder resin relative to the total solid content of the photosensitive layer is preferably 35% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 35% by mass or less.

[0070] -Charge generating materials- Examples of the charge generating material include azo pigments such as bisazo and trisazo; fused-ring aromatic pigments such as dibromoanthanthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0071] Among these, in order to be compatible with 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 disclosed in JP-A-5-263007 and JP-A-5-279591, chlorogallium phthalocyanine disclosed in JP-A-5-98181, dichlorotin phthalocyanine disclosed in JP-A-5-140472 and JP-A-5-140473, and titanyl phthalocyanine disclosed in JP-A-4-189873 are more preferable.

[0072] On the other hand, in order to accommodate laser exposure in the near-ultraviolet region, preferred charge-generating materials include fused-ring aromatic pigments such as dibromoanthanthrone; thioindigo pigments; porphyrazine compounds; zinc oxide; trigonal selenium; and bisazo pigments disclosed in JP-A-2004-78147 and JP-A-2005-181992.

[0073] That is, as the charge generating material, inorganic pigments are preferred when a light source with an exposure wavelength of 380 nm to 500 nm is used, and metal and non-metal phthalocyanine pigments are preferred when a light source with an exposure wavelength of 700 nm to 800 nm is used.

[0074] Here, the charge generating material is preferably at least one selected from hydroxygallium phthalocyanine pigments and chlorogallium phthalocyanine pigments, more preferably hydroxygallium phthalocyanine pigments, from the viewpoint of increasing the sensitivity of the single-layer photoreceptor.

[0075] The hydroxygallium phthalocyanine pigment is not particularly limited, but a V-type hydroxygallium phthalocyanine pigment is preferred. In particular, a hydroxygallium phthalocyanine pigment having a maximum peak wavelength in the range of 810 nm to 839 nm in its spectral absorption spectrum in the wavelength range of 600 nm to 900 nm is preferred from the viewpoint of obtaining superior dispersibility, and when used as a material for an electrophotographic photoreceptor, it is easy to obtain superior dispersibility, as well as sufficient sensitivity, charging properties, and dark decay characteristics.

[0076] The hydroxygallium phthalocyanine pigment having a maximum peak wavelength in the range of 810 nm to 839 nm preferably has an average particle size within a specific range and a BET specific surface area within a specific range. Specifically, the average particle size is preferably 0.20 μm or less, more preferably 0.01 μm to 0.15 μm, and the BET specific surface area is preferably 45 μm or less. 2 / g or more is desirable, and 50m 2 / g or more is more preferable, and 55m 2 / g or more 120m 2 / g or less is particularly desirable. The average particle size is the volume average particle size (d50 average particle size) measured using a laser diffraction scattering particle size distribution analyzer (LA-700, manufactured by Horiba, Ltd.). Also, it is a value measured by the nitrogen substitution method using a BET specific surface area analyzer (Shimadzu Corporation: Flowsoap II2300). Here, when the average particle size is larger than 0.20 μm or the specific surface area is 45 m 2 If the content is less than 1 / g, the pigment particles tend to become coarse or aggregates of the pigment particles tend to form, which tends to cause defects in properties such as dispersibility, sensitivity, chargeability, and dark decay characteristics, and this may make the image quality more susceptible to defects.

[0077] The maximum particle size (maximum primary particle size) of the hydroxygallium phthalocyanine pigment is preferably 1.2 μm or less, more preferably 1.0 μm or less, and even more preferably 0.3 μm or less. If the maximum particle size exceeds the above range, black spots are likely to occur.

[0078] The hydroxygallium phthalocyanine pigment has an average particle size of 0.2 μm or less, a maximum particle size of 1.2 μm or less, and a specific surface area of ​​45 m 2 It is desirable that the saturation coefficient be 1 / g or more.

[0079] The hydroxygallium phthalocyanine pigment is preferably a V-type pigment having diffraction peaks at Bragg angles (2θ±0.2°) of at least 7.3°, 16.0°, 24.9°, and 28.0° in an X-ray diffraction spectrum using CuKα characteristic X-rays.

[0080] On the other hand, the chlorogallium phthalocyanine pigment is preferably one that has diffraction peaks at Bragg angles (2θ±0.2°) of 7.4°, 16.6°, 25.5°, and 28.3°, which provides excellent sensitivity as an electrophotographic photosensitive material. The preferred maximum peak wavelength of the spectral absorption spectrum, average particle size, maximum particle size, and specific surface area of ​​the chlorogallium phthalocyanine pigment are the same as those of the hydroxygallium phthalocyanine pigment.

[0081] The content of the charge generating material relative to the total solid content of the photosensitive layer is preferably 1% by mass or more and 5% by mass or less, and more preferably 1.2% by mass or more and 4.5% by mass or less.

[0082] -Hole transport material- The hole transport material is not particularly limited, and examples thereof include oxadiazole derivatives such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole; pyrazoline derivatives such as 1,3,5-triphenyl-pyrazoline and 1-[pyridyl-(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminostyryl)pyrazoline; aromatic tertiary amino compounds such as triphenylamine, N,N'-bis(3,4-dimethylphenyl)biphenyl-4-amine, tri(p-methylphenyl)aminyl-4-amine, and dibenzylaniline; aromatic tertiary diamino compounds such as N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine; 3-(4'-dimethylphenyl)-N,N'-diphenylbenzidine; Examples of hole transport materials include 1,2,4-triazine derivatives such as (aminophenyl)-5,6-di-(4'-methoxyphenyl)-1,2,4-triazine; hydrazone derivatives such as 4-diethylaminobenzaldehyde-1,1-diphenylhydrazone; quinazoline derivatives such as 2-phenyl-4-styryl-quinazoline; benzofuran derivatives such as 6-hydroxy-2,3-di(p-methoxyphenyl)benzofuran; α-stilbene derivatives such as p-(2,2-diphenylvinyl)-N,N-diphenylaniline; enamine derivatives; carbazole derivatives such as N-ethylcarbazole; poly-N-vinylcarbazole and its derivatives; and polymers having a group composed of the above-mentioned compounds in the main chain or side chain. These hole transport materials may be used alone or in combination of two or more.

[0083] Among these, preferred examples of the hole transport material include a hole transport material represented by the following general formula (HT1) and a hole transport material represented by the following general formula (HT1a). In particular, from the viewpoint of controlling the volume resistivity of the photosensitive layer before and after abrasion and the abundance ratio of the electron transport material, thereby suppressing the occurrence of black spots while maintaining high photosensitivity, the hole transport material is preferably a hole transport material having a benzidine skeleton, and more preferably a hole transport material represented by the following general formula (HT1a):

[0084] [ka]

[0085] In the general formula (HT1), Ar T1 , Ar T2 , and Ar T3 are each independently an aryl group or —C6H4—C(R T4 )=C(R T5 )(R T6 ) indicates R T4 , R T5 , and R T6 R each independently represents a hydrogen atom, an alkyl group, or an aryl group. T5 and R T6 may be linked to form a hydrocarbon ring structure.

[0086] In the general formula (HT1), Ar T1 , Ar T2 , and Ar T3 The aryl group represented by the formula (I) includes an aryl group having 6 to 15 carbon atoms (preferably 6 to 9, more preferably 6 to 8). Specific examples of the aryl group include a phenyl group, a naphthyl group, and a fluorene group. Among these, the aryl group is preferably a phenyl group.

[0087] In general formula (HT1), R T4 , R T5 , and R T6 The alkyl group represented by is, for example, the alkyl group represented by R C21 , R C22 , and R C23 The examples of the alkyl group represented by the formula (I) and the preferred ranges thereof are also the same.

[0088] In general formula (HT1), R T4 , R T5 , and R T6 The aryl group represented by Ar T1 , Ar T2 , and Ar T3 The examples of the aryl group represented by the formula (I) and the preferred ranges thereof are also the same.

[0089] In general formula (HT1), Ar T1 , Ar T2 , and Ar T3 , and R T4 , R T5 , and R T6 Each of the above substituents represented by the formula (I) also includes a group having a further substituent. Examples of the substituent include a halogen atom, an alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, and an aryl group having 6 to 10 carbon atoms. Further, examples of the substituents of each of the above substituents include a substituted amino group substituted with an alkyl group having 1 to 3 carbon atoms.

[0090] The triarylamine-based hole transport material (HT1) may be used alone or in combination of two or more kinds.

[0091] Here, from the viewpoint of charge mobility, among the triarylamine-based hole transport materials represented by the general formula (HT1), in particular, "-C6H4-C(R T4 )=C(R T5 )(R T6 Of these, triarylamine-based hole transport materials represented by the specific example (HT1-4) of the triarylamine-based hole transport material (HT1) described later are preferred.

[0092] [ka]

[0093] In the general formula (HT1a), R C21 , R C22 , and R C23 each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

[0094] In general formula (HT1a), R C21 , R C22 , and R C23Examples of the halogen atom represented by include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, etc. Among these, the halogen atom is preferably a fluorine atom or a chlorine atom, and more preferably a chlorine atom.

[0095] In general formula (HT1a), R C21 , R C22 , and R C23 The alkyl group represented by may be a straight-chain or branched alkyl group having 1 to 10 carbon atoms (preferably 1 to 6, more preferably 1 to 4). Specific examples of the linear alkyl group include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group. Specific examples of branched alkyl groups include an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an isodecyl group, a sec-decyl group, and a tert-decyl group. Among these, lower alkyl groups such as methyl, ethyl and isopropyl groups are preferred as the alkyl group.

[0096] In general formula (HT1a), R C21 , R C22 , and R C23 The alkoxy group represented by the formula (I) includes a linear or branched alkoxy group having 1 to 10 carbon atoms (preferably 1 to 6, more preferably 1 to 4). Specific examples of the linear alkoxy group include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an n-pentyloxy group, an n-hexyloxy group, an n-heptyloxy group, an n-octyloxy group, an n-nonyloxy group, and an n-decyloxy group. Specific examples of branched alkoxy groups include an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an isopentyloxy group, a neopentyloxy group, a tert-pentyloxy group, an isohexyloxy group, a sec-hexyloxy group, a tert-hexyloxy group, an isoheptyloxy group, a sec-heptyloxy group, a tert-heptyloxy group, an isooctyloxy group, a sec-octyloxy group, a tert-octyloxy group, an isononyloxy group, a sec-nonyloxy group, a tert-nonyloxy group, an isodecyloxy group, a sec-decyloxy group, and a tert-decyloxy group. Among these, the alkoxy group is preferably a methoxy group.

[0097] In general formula (HT1a), R C21 , R C22 , and R C23 The aryl group represented by the formula (I) includes an aryl group having 6 to 10 carbon atoms (preferably 6 to 9, more preferably 6 to 8). Specific examples of the aryl group include a phenyl group and a naphthyl group. Among these, the aryl group is preferably a phenyl group.

[0098] In general formula (HT1a), R C21 , R C22 , and R C23 Each of the above substituents represented by also includes a group having a further substituent, such as the atoms and groups exemplified above (e.g., halogen atoms, alkyl groups, alkoxy groups, aryl groups, etc.).

[0099] The triarylamine-based hole transport material represented by the general formula (HT1) may be used singly or in combination of two or more kinds.

[0100] Specific examples (HT1-1) to (HT1-10) of the triarylamine-based hole transport material (HT1) and the benzidine-based hole transport material (HT1a) are shown below, but the present invention is not limited thereto.

[0101] [ka]

[0102] [ka]

[0103] [ka]

[0104] [ka]

[0105] The content of the hole transport material relative to the total solid content of the photosensitive layer is preferably 20% by mass or more and 45% by mass or less, more preferably 34% by mass or more and 44% by mass or less, more preferably 38% by mass or more and 44% by mass or less, and even more preferably 38% by mass or more and 42% by mass or less, from the viewpoints of high photosensitivity and suppression of the occurrence of black spots.

[0106] From the viewpoints of achieving high photosensitivity and suppressing the occurrence of black spots, the mass ratio of the hole transport material to the electron transport material (hole transport material / electron transport material) is preferably 19 / 5 or more and 28 / 5 or less, more preferably 20 / 5 or more and 26 / 5 or less, and even more preferably 21 / 5 or more and 24 / 5 or less.

[0107] -Electron transport material- The electron transport material is not particularly limited, and examples thereof include quinone compounds such as chloranil and bromoanil; tetracyanoquinodimethane compounds; fluorenone compounds such as 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, and 9-dicyanomethylene-9-fluorenone-4-octyl carboxylate; 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, and the like. Examples of suitable electron transport materials include oxadiazole compounds such as 1,5-bis(4-diethylaminophenyl)1,3,4-oxadiazole; xanthone compounds; thiophene compounds; dinaphthoquinone compounds such as 3,3'-di-tert-pentyl-dinaphthoquinone; diphenoquinone compounds such as 3,3'-di-tert-butyl-5,5'-dimethyldiphenoquinone and 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone; and polymers having a group composed of any of the above compounds in the main chain or side chain. These electron transport materials may be used alone or in combination of two or more.

[0108] Among these, from the viewpoint of controlling the volume resistivity of the photosensitive layer before and after abrasion and the abundance ratio of the electron transport material, thereby suppressing the occurrence of black spots while maintaining high photosensitivity, an electron transport material having a diphenoquinone skeleton is preferred as the electron transport material, and an electron transport material represented by the following general formula (FK) is more preferred.

[0109] [ka] In the general formula (FK), R k1 ~R k4 each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group. In addition, R k1 is R k2 ~R k4 It is preferable that the group is different from at least one of the above.

[0110] R k1 and R k3 are each independently preferably an alkyl group having 3 to 12 carbon atoms, an alkoxy group having 3 to 12 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group from the viewpoint of suppressing cracking of the photosensitive layer accompanying crystallization of the electron transport material, more preferably a branched alkyl group having 3 to 12 carbon atoms, a branched alkoxy group having 3 to 12 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group, still more preferably a branched alkyl group having 3 to 8 carbon atoms or a branched alkoxy group having 3 to 8 carbon atoms, and particularly preferably a t-butyl group. Also, R k1 and R k3 are preferably the same group.

[0111] R k2 and R k4 are each independently preferably a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms, more preferably a hydrogen atom, a linear alkyl group having 1 to 4 carbon atoms, or a linear alkoxy group having 1 to 4 carbon atoms, still more preferably a linear alkyl group having 1 to 3 carbon atoms or a linear alkoxy group having 1 to 3 carbon atoms, and particularly preferably a methyl group. Also, R k2 and R k4 are preferably the same group. Furthermore, R k1 and R k2 are preferably different groups, and also, R k3 and R k4 are preferably different groups.

[0112] Examples of the electron transport material represented by the general formula (FK) are shown below, but it is not limited thereto. The following example compound numbers are denoted as example compound (1-number). Specifically, for example, example compound 5 is denoted as "example compound (1-5)".

[0113]

Chemical formula

[0114] The abbreviations in the above exemplary compounds have the following meanings. t-C4H9: t-butyl group CH3O: methoxy group t-C4H9O: t-butoxy group c-C6H 12 : Cyclohexyl group C6H5: Phenyl group C6H5CH2: benzyl group

[0115] The content of the electron transport material relative to the total solid content of the photosensitive layer is preferably 4% by mass or more and 20% by mass or less, more preferably 6% by mass or more and 18% by mass or less, and even more preferably 8% by mass or more and 16% by mass or less.

[0116] -Other additives- The single-layer photosensitive layer may contain other well-known additives such as an antioxidant, a light stabilizer, a heat stabilizer, etc. Furthermore, when the single-layer photosensitive layer serves as a surface layer, it may contain fluororesin particles, silicone oil, etc.

[0117] - Formation of a single-layer photosensitive layer - The single-layer type photosensitive layer is formed using a coating liquid for forming a photosensitive layer in which the above components are added to a solvent. Examples of the solvent include ordinary organic solvents such as aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene, ketones such as acetone and 2-butanone, halogenated aliphatic hydrocarbons such as methylene chloride, chloroform, and ethylene chloride, and cyclic or linear ethers such as tetrahydrofuran and ethyl ether. These solvents may be used alone or in combination.

[0118] Methods for dispersing particles (e.g., charge generating material) in a coating liquid for forming a photosensitive layer include media dispersers such as ball mills, vibration ball mills, attritors, sand mills, and horizontal sand mills, and medialess dispersers such as stirrers, ultrasonic dispersers, roll mills, and high-pressure homogenizers. Examples of high-pressure homogenizers include a collision type in which the dispersion liquid is dispersed by liquid-liquid collision or liquid-wall collision under high pressure, and a penetration type in which the dispersion liquid is dispersed by passing through a fine flow path under high pressure.

[0119] Examples of methods for applying the coating solution for forming the photosensitive layer onto the undercoat layer include dip coating, push-up coating, wire bar coating, spray coating, blade coating, knife coating, and curtain coating.

[0120] The thickness of the single-layer photosensitive layer is preferably set in the range of 5 μm to 60 μm, more preferably 5 μm to 50 μm, and even more preferably 10 μm to 40 μm.

[0121] [Image forming device (and process cartridge)] The image forming apparatus according to the present embodiment includes an electrophotographic photosensitive member, a charging unit that charges the surface of the electrophotographic photosensitive member, an electrostatic latent image forming unit that forms an electrostatic latent image on the surface of the charged electrophotographic photosensitive member, a developing unit that develops the electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing toner to form a toner image, and a transfer unit that transfers the toner image to the surface of a recording medium.The electrophotographic photosensitive member according to the present embodiment is used as the electrophotographic photosensitive member.

[0122] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as an apparatus equipped with a fixing means for fixing a toner image transferred onto the surface of a recording medium; an apparatus of a direct transfer type for directly transferring a toner image formed on the surface of an electrophotographic photosensitive member onto a recording medium; an apparatus of an intermediate transfer type for primarily transferring a toner image formed on the surface of an electrophotographic photosensitive member onto the surface of an intermediate transfer member, and then secondarily transferring the toner image transferred onto the surface of the intermediate transfer member onto the surface of a recording medium; an apparatus equipped with a cleaning means for cleaning the surface of an electrophotographic photosensitive member after transfer of a toner image but before charging; an apparatus equipped with a charge eliminating means for irradiating the surface of an electrophotographic photosensitive member with charge eliminating light to eliminate charges after transfer of a toner image but before charging; and an apparatus equipped with an electrophotographic photosensitive member heating member for increasing the temperature of the electrophotographic photosensitive member and reducing the relative temperature.

[0123] In the case of an intermediate transfer type device, the transfer means may be configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means which primarily transfers the toner image formed on the surface of the electrophotographic photosensitive body onto the surface of the intermediate transfer body, and a secondary transfer means which secondarily transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0124] The image forming apparatus according to this embodiment may be either a dry development type image forming apparatus or a wet development type image forming apparatus (a development type using a liquid developer).

[0125] In the image forming apparatus according to the present embodiment, for example, a portion including an electrophotographic photosensitive member may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge including the electrophotographic photosensitive member according to the present embodiment is preferably used. In addition to the electrophotographic photosensitive member, the process cartridge may also include at least one selected from the group consisting of a charging unit, an electrostatic latent image forming unit, a developing unit, and a transfer unit.

[0126] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. Note that only the main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0127] FIG. 2 is a schematic diagram showing an example of the configuration of an image forming apparatus according to this embodiment. 2, the image forming apparatus 100 according to this embodiment includes a process cartridge 300 having an electrophotographic photosensitive member 7, an exposure device 9 (an example of an electrostatic latent image forming means), and a transfer device 40 (an example of a transfer means). In the image forming apparatus 100, the exposure device 9 is disposed at a position where it can expose the electrophotographic photosensitive member 7 through the opening of the process cartridge 300, and the transfer device 40 is disposed at a position facing the electrophotographic photosensitive member 7 across a recording medium transport belt 50.

[0128] 2 integrally supports within a housing an electrophotographic photosensitive member 7, a charging device 8 (an example of a charging means), a developing device 11 (an example of a developing means), and a cleaning device 13 (an example of a cleaning means). The cleaning device 13 has a cleaning blade (an example of a cleaning member) 131, which is disposed so as to come into contact with the surface of the electrophotographic photosensitive member 7. The cleaning member may not be in the form of the cleaning blade 131, but may be a conductive or insulating fibrous member, which may be used alone or in combination with the cleaning blade 131.

[0129] Note that FIG. 2 shows an example of an image forming apparatus equipped with a fibrous member 132 (roll-shaped) that supplies lubricant 14 to the surface of electrophotographic photosensitive member 7, and a fibrous member 133 (flat brush-shaped) that assists cleaning, but these may be arranged as needed.

[0130] Hereinafter, each configuration of the image forming apparatus according to this embodiment will be described.

[0131] -Charging device- The charging device 8 may be, for example, a contact-type charger using a conductive or semi-conductive charging roller, charging brush, charging film, charging rubber blade, charging tube, etc. Also usable are non-contact type roller chargers, scorotron chargers and corotron chargers that utilize corona discharge, and other known chargers.

[0132] -Exposure equipment- The exposure device 9 may be, for example, an optical system that exposes the surface of the electrophotographic photosensitive member 7 to light such as semiconductor laser light, LED light, or liquid crystal shutter light in a predetermined image. The wavelength of the light source is within the spectral sensitivity range of the electrophotographic photosensitive member. The wavelength of semiconductor lasers is mainly near-infrared, with an oscillation wavelength around 780 nm. However, this wavelength is not limited to this, and lasers with an oscillation wavelength in the 600 nm range or blue lasers with an oscillation wavelength of 400 nm to 450 nm may also be used. Furthermore, for color image formation, a surface-emitting laser light source capable of outputting multiple beams is also effective.

[0133] -Developing device- The developing device 11 may be, for example, a general developing device that develops by contact or non-contact application of a developer. The developing device 11 is not particularly limited as long as it has the above-mentioned functions, and may be selected depending on the purpose. For example, it may be a known developing device that has a function of applying a one-component developer or a two-component developer to the electrophotographic photosensitive member 7 using a brush, roller, or the like. Among these, a developing roller that holds a developer on its surface is preferred.

[0134] The developer used in the developing device 11 may be a one-component developer containing only toner, or a two-component developer containing toner and a carrier. The developer may be magnetic or non-magnetic. Well-known developers are used.

[0135] -Cleaning device- The cleaning device 13 is a cleaning blade type device equipped with a cleaning blade 131 . In addition to the cleaning blade system, a fur brush cleaning system or a simultaneous development and cleaning system may also be used.

[0136] -Transfer device- Examples of the transfer device 40 include a contact type transfer charger using a belt, roller, film, rubber blade, etc., and a known transfer charger such as a scorotron transfer charger or corotron transfer charger that utilizes corona discharge.

[0137] -Recording medium transport belt- The recording medium transport belt 50 is a belt (intermediate transfer belt) made of semiconductive polyimide, polyamideimide, polycarbonate, polyarylate, polyester, rubber, or the like.

[0138] FIG. 3 is a schematic diagram showing another example of the configuration of the image forming apparatus according to the present embodiment. The image forming apparatus 120 shown in Fig. 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 member 50, and one electrophotographic photosensitive member is used per color. The image forming apparatus 120 has the same configuration as the image forming apparatus 100, except that it is a tandem-type apparatus.

[0139] Here, in the image forming apparatus according to the present embodiment, when the image forming apparatus is an image forming apparatus equipped with a direct transfer type transfer means having a transfer member that transfers the toner image directly from the electrophotographic photosensitive member to the surface of a recording medium, it is preferable that the relationship between the rotation speed P (mm / s) of the electrophotographic photosensitive member, the transfer current value I (μA) for directly transferring the toner image from the electrophotographic photosensitive member to the surface of a recording medium, and the length L (mm) of the transfer member satisfies the following formula (PIL): Formula (PIL):-1.07×10 -3 ≦I / (P×L)≦-4.30×10 -4

[0140] The I / (P×L) value indicates the amount of charge that the electrophotographic photoreceptor theoretically receives from the transfer member during direct transfer. The rotation speed P of the electrophotographic photosensitive member is the amount of movement per unit time (1 second) of the surface of the electrophotographic photosensitive member in the circumferential direction (also referred to as the "process speed"). The transfer current value is the current value applied to the transfer member when the toner image is transferred directly from the electrophotographic photosensitive member to the surface of the recording medium. The length of the transfer member is the length in the axial direction of the electrophotographic photosensitive member in the region facing the photosensitive layer of the electrophotographic photosensitive member. The transfer member is preferably a contact type transfer member such as a transfer roll.

[0141] When the electrophotographic photosensitive member according to the present embodiment is used and direct transfer is performed under conditions where the I / (P×L) value falls within the above range, excessive charge injection from the transfer member to the electrophotographic photosensitive member during transfer is suppressed, thereby suppressing negative ghosts in which the image portion of the previous image stands out pale, and insufficient charge injection from the transfer member to the electrophotographic photosensitive member during transfer is suppressed, thereby suppressing negative ghosts in which the image portion of the previous image stands out dark. As a result, ghosts (an afterimage phenomenon caused by the retention of the history of the previous image) are suppressed from the initial stage to the end of the life of the electrophotographic photosensitive member.

[0142] From the viewpoint of ghost suppression, the I / (P×L) value is -8.60×10 -4 Over -3.43 x 10 -4 The following is more preferable: -6.40×10 -4 Over - 4.30 x 10 -4 The following is even more preferred: [Example]

[0143] The present invention will be described in more detail below based on examples and comparative examples, but the present invention is not limited to the following examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0144] <Examples 1 to 17, Comparative Examples 1 to 7> -Production of coating solution for forming photosensitive layer- A mixture of bisphenol Z polycarbonate resin (polycarbonate resin represented by the formula PC-1 above, pm: 25, pn: 75, viscosity average molecular weight 50,000), a charge generating material shown in Table 1 ("CGM" in Table 1), a hole transport material shown in Table 1 ("HTM" in Table 1), an electron transport material shown in Table 1 ("ETM" in Table 1), and tetrahydrofuran in an amount to give a solids concentration shown in Table 1 was dispersed using a high-pressure homogenizer to obtain a coating liquid for forming a photosensitive layer.

[0145] - Formation of photosensitive layer - An aluminum substrate having a diameter of 30 mm, a length of 244.5 mm, and a thickness of 1 mm was prepared as a conductive substrate. Next, the coating solution for forming a photosensitive layer was applied to the aluminum substrate by dip coating under the photosensitive layer formation conditions shown in Table 1, and then dried and cured to form a single-layer photosensitive layer with a thickness of 30 μm on the aluminum substrate.

[0146] In this way, the photoreceptors of each example were obtained.

[0147] <Characteristics> The following characteristics of the photoreceptor of each example were measured according to the methods already described. The volume resistivity of the photosensitive layer after abrasion when the ratio of the thickness of the photosensitive layer after abrasion to the thickness of the photosensitive layer before abrasion (thickness of the photosensitive layer after abrasion / thickness of the photosensitive layer before abrasion) is 0.8 Volume resistivity of the photosensitive layer before wear The ratio of the amount of electron transport material present on the surface of the photosensitive layer to the amount of electron transport material present on the back surface of the photosensitive layer (referred to as "ETM amount ratio between the surface and back surfaces of the photosensitive layer" in the table).

[0148] <Evaluation> The photoreceptors of the respective examples were used to carry out the following evaluations.

[0149] (Evaluation of electrostatic chargeability) Using an electrostatic copying paper testing device (Electrostatic Analyzer EPA 8100, manufactured by Kawaguchi Electric Works Co., Ltd.), the surface potential was measured 0.5 seconds after positive charging by corona discharge of 6.0 kV. The chargeability is evaluated as good when the surface potential is 780 V or more.

[0150] (Evaluation of light sensitivity) The photosensitivity of the photoconductor was evaluated as the half-life exposure when charged to +800 V. Specifically, using an electrostatic copying paper tester (Electrostatic Analyzer EPA 8100, manufactured by Kawaguchi Electric Works Co., Ltd.), the photoconductor was charged to +800 V in an environment of 20°C and 40% RH, and then the light from a tungsten lamp was converted to monochromatic light of 780 nm using a monochromator, and the light was measured at 1 μW / cm on the surface of the photoconductor. 2 The irradiation was carried out after adjusting the exposure time so that the exposure time was 100 s. The surface potential of the photosensitive member immediately after charging is V0 (V), and the half-life exposure E at which the surface potential becomes 1 / 2 × VO (V) due to light irradiation of the photosensitive member surface. 1 / 2 (μJ / cm 2 ) was measured. The photosensitivity is 0.15 μJ / cm 2 When the half-life exposure value below is obtained, it is evaluated as being high sensitivity.

[0151] (Black dot rating) To evaluate black spots, Brother's HL5340D was used to print 30,000 images specified in ISO / IEC 19752 on A4 paper under high temperature and humidity conditions of 30°C and 80% RH, and then a 50% halftone was printed.The black spots of the images were evaluated according to the following criteria. A rating of 3 indicates that there may be practical problems. -Evaluation criteria- 1: No black spots 2: There are black spots, but they are not a problem 3: Problematic area with black spots

[0152] (Ghost Rating) The photoreceptor of each example was mounted in an image forming apparatus "HL-L5200DW manufactured by Brother (a direct transfer type apparatus equipped with a transfer roll having a length L of 235 mm)". The transfer conditions of the process speed and transfer current value were set to the transfer conditions 1+3, 2+3, 1+4, and 2+4 shown in Table 3, and images were formed as follows. At high temperature and humidity of 32.5°C and 80% RH, a 20mm x 20mm image with 100% image density was printed, and then a full-page A4 halftone image with 30% density was printed in succession. The density fluctuation on the halftone after one revolution of the photosensitive drum was visually evaluated. The occurrence of ghosting on the 10th printed sheet (referred to as "initial ghosting" in the table) and the 500,000th printed sheet (referred to as "ghosting after 50 kpv" in the table) was evaluated according to the following criteria. In the ghost column in Table 3, the notation "number / number / number / number" means the evaluation result of transfer conditions 1+3 / the evaluation result of transfer conditions 2+3 / the evaluation result of transfer conditions 1+4 / the evaluation result of transfer conditions 2+4. When the image output section with 100% image density is on an A4 halftone section with 30% density, if the density becomes darker it is expressed as 1 to 3, and if the density becomes lighter it is expressed as -1 to -3. -Evaluation criteria- 3: There is a clear density fluctuation, and the image quality is unacceptable. 2: Concentration fluctuates, but no problems in actual use 1: Slight fluctuation in density, no problem in actual use 0: No density fluctuation -1: Slight density fluctuation, no problem in actual use -2: Concentration fluctuates, but no problems in actual use -3: Obvious density fluctuations, unacceptable in terms of image quality

[0153] [Table 1]

[0154] [Table 2]

[0155] [Table 3]

[0156] From the above results, it can be seen that the photoreceptor of this example has higher photosensitivity and suppresses the occurrence of black spots compared to the photoreceptor of the comparative example. It is also apparent that the photoreceptor of this example has good charging properties. In addition, when an image is formed under conditions that satisfy formula (PIL) using a direct transfer type image forming apparatus equipped with the photosensitive member of this embodiment, it is also clear that the occurrence of ghosts is suppressed from the initial stage to the end of the life of the photosensitive member.

[0157] The abbreviations in Table 1 refer to the following compounds. -Charge generating materials- CGM-A: V-type hydroxygallium phthalocyanine. The X-ray diffraction spectrum using CuKα characteristic X-rays has diffraction peaks at Bragg angles (2θ±0.2°) of at least 7.3°, 16.0°, 24.9°, and 28.0°. The maximum peak wavelength in the spectral absorption spectrum in the wavelength range of 600nm to 900nm is 820nm, the average particle size is 0.12μm, the maximum particle size is 0.2μm, and the BET specific surface area is 60m 2 / g.

[0158] -Hole transport material- HTM-A: Compound of the structure, an exemplary compound (HT1-1) of a hole transport material represented by the general formula (HT1a), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1']biphenyl-4,4'-diamine [ka] HTM-B: Compound with the following structure [ka]

[0159] -Electron transport material- ETM-A: a compound with the following structure, an exemplary compound (1-1) of the electron transport material represented by general formula (FK), 3,3'-di-tert-butyl-5,5'-dimethyldiphenoquinone. [ka]

[0160] ETM-B: Compound with the following structure [ka] ETM-C: Compound with the following structure [ka] [Explanation of symbols]

[0161] 2 Photosensitive layer, 3 Conductive substrate, 7 Electrophotographic photosensitive member, 8 Charging device, 9 Exposure device, 11 Developing device, 13 Cleaning device, 14 Lubricant, 40 Transfer device, 50 Recording medium conveying belt, 100 Image forming apparatus, 120 Image forming apparatus, 131 Cleaning blade, 132 Fibrous member, 133 Fibrous member, 300 Process cartridge

Claims

1. a conductive substrate; a single-layer photosensitive layer provided on the conductive substrate and containing a binder resin, a charge generating material, a hole transport material, and an electron transport material; and the content of the hole transport material relative to the total solid content of the photosensitive layer is 38% by mass or more and 44% by mass or less, When the ratio of the thickness of the photosensitive layer after abrasion to the thickness of the photosensitive layer before abrasion (thickness of the photosensitive layer after abrasion / thickness of the photosensitive layer before abrasion) is 0.8, the volume resistivity of the photosensitive layer after abrasion is 5.0 × 10 １０ Ωcm or more 2.0 x 10 １１ Ωcm or less, a ratio of the volume resistivity of the photosensitive layer after abrasion to the volume resistivity of the photosensitive layer before abrasion (volume resistivity of the photosensitive layer after abrasion / volume resistivity of the photosensitive layer before abrasion) is 1 / 100 or more; a ratio of the amount of the hole transport material present on the surface of the photosensitive layer to the amount of the hole transport material present on the back surface of the photosensitive layer (amount of the hole transport material present on the surface of the photosensitive layer / amount of the hole transport material present on the back surface of the photosensitive layer) is 1 / 6 or more and 3 / 10 or less, the mass ratio of the hole transport material to the electron transport material (the hole transport material / the electron transport material) is 19 / 5 or more and 28 / 5 or less; Electrophotographic photoreceptor.

2. 2. The electrophotographic photoreceptor according to claim 1, wherein a ratio of the volume resistivity of the photosensitive layer after abrasion to the volume resistivity of the photosensitive layer before abrasion (volume resistivity of the photosensitive layer after abrasion / volume resistivity of the photosensitive layer before abrasion) is 1 / 100 or more and 7 / 100 or less.

3. 3. The electrophotographic photoreceptor according to claim 1, wherein the hole transport material has a benzidine skeleton.

4. 4. The electrophotographic photoreceptor according to claim 3, wherein the hole transport material having a benzidine skeleton is a hole transport material represented by the following general formula (HT1a): 【Chemistry 1】 (In the general formula (HT1a), R Ｃ２１ , R Ｃ２２ , and R Ｃ２３ each independently represents a hydrogen atom, a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms.

5. 5. The electrophotographic photoreceptor according to claim 1, wherein the electron transport material is an electron transport material having a diphenoquinone skeleton.

6. 6. The electrophotographic photoreceptor according to claim 5, wherein the electron transporting material having a diphenoquinone skeleton is an electron transporting material represented by the following general formula (FK): 【Chemistry 2】 (In the general formula (FK), R ｋ１ ~R ｋ４ each independently represents a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group.

7. An electrophotographic photoreceptor according to any one of claims 1 to 6, A process cartridge that is detachably attached to an image forming apparatus.

8. The electrophotographic photoreceptor according to any one of claims 1 to 6, a charging means for charging the surface of the electrophotographic photosensitive member; an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; a developing means for developing an electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing a toner to form a toner image; a transfer means for transferring the toner image onto a surface of a recording medium; An image forming apparatus comprising:

9. The electrophotographic photoreceptor according to any one of claims 1 to 6, a charging means for charging the surface of the electrophotographic photosensitive member; an electrostatic latent image forming means for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive member; a developing means for developing an electrostatic latent image formed on the surface of the electrophotographic photosensitive member with a developer containing a toner to form a toner image; a direct transfer type transfer means having a transfer member that transfers the toner image directly from the electrophotographic photosensitive member onto a surface of a recording medium; Equipped with An image forming apparatus in which the relationship between the rotation speed P (mm / s) of the electrophotographic photosensitive member, the transfer current value I (μA) for directly transferring the toner image from the electrophotographic photosensitive member to the surface of the recording medium, and the length L (mm) of the transfer member satisfies the following formula (PIL): Formula (PL): -1.07 × 10 －３ ≦I / (P×L)≦-4.30×10 －４

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