Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

The present application relates to an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus. The electrophotographic photoreceptor has: a conductive base; a charge generating layer provided on the conductive base, containing a charge generating material and a vinyl-based copolymer, the vinyl-based copolymer including a structural unit having chlorine, a structural unit having acyloxy, and a structural unit having an aromatic polycarboxylic acid structure, the proportion of the structural unit having chlorine with respect to all structural units being 80% by mass or more, and the proportion of the structural unit having the aromatic polycarboxylic acid structure with respect to all structural units being 0.5% by mass or more; and a charge transport layer provided on the charge generating layer, containing a charge transport material and a binding resin.

Description

Technical Field

[0001] This invention relates to an electrophotographic photosensitive element, a processing cartridge, and an image forming apparatus. Background Technology

[0002] Japanese Patent Application Publication No. 5-19507 discloses an electrophotographic photosensitive material, which is an electrophotographic photosensitive material having at least a laminated photosensitive layer consisting of a charge generation layer and a charge transport layer on a conductive support. The charge generation layer is characterized by containing a hygroscopic agent consisting of a polyacid compound having two or more carboxyl groups in its molecule. Summary of the Invention

[0003] Regarding an electrophotographic photosensitive material in which a charge generation layer and a charge transport layer are sequentially provided on a conductive substrate, for example, after forming a charge generation layer on the conductive substrate, a coating liquid containing a solvent for forming a charge transport layer is applied to the charge generation layer and then dried to form the charge transport layer. However, if the charge generation layer contains a charge generation material and a vinyl copolymer, applying the coating liquid for forming a charge transport layer to the charge generation layer may cause a portion of the vinyl copolymer in the charge generation layer to dissolve due to the solvent in the coating liquid.

[0004] Furthermore, in the process of applying the coating liquid for forming the charge transport layer onto the charge generation layer, an immersion coating method is typically used. In the immersion coating method, a conductive substrate on which the charge generation layer is formed on its outer peripheral surface is immersed in the coating liquid for forming the charge transport layer with one axial end of the conductive substrate facing downwards, and then pulled up. As a result, the coating liquid for forming the charge transport layer adheres to the charge generation layer.

[0005] Therefore, the coating liquid for forming the charge transport layer adheres to the charge generation layer at different times at the lower and upper ends along the axial direction of the conductive substrate. As a result, electrical characteristics differ between one end and the other end of the electrophotographic photoreceptor, particularly in photosensitivity, which may manifest as an image density difference.

[0006] The object of the present invention is to provide an electrophotographic photosensitive material that, compared with cases where the charge-generating layer contains a charge-generating material and a vinyl copolymer, and the vinyl copolymer contains structural units having chlorine, structural units having acyloxy groups, and structural units derived from maleic acid, where the proportion of structural units having chlorine relative to all structural units is less than 80% by mass, where the proportion of the aforementioned structural units having aromatic polycarboxylic acid structures relative to all structural units is less than 0.5% by mass, or where the solubility of the vinyl copolymer in 100 parts by mass of tetrahydrofuran is greater than 10 parts by mass, the electrophotographic photosensitive material of the present invention can suppress the image density difference along the axial direction of the electrophotographic photosensitive material.

[0007] According to a first aspect of the present invention, an electrophotographic photosensitive material is provided, comprising: a conductive substrate; a charge generating layer disposed on the conductive substrate, comprising a charge generating material and a vinyl copolymer, wherein the vinyl copolymer comprises structural units having chlorine, structural units having acyloxy groups, and structural units having aromatic polycarboxylic acid structures, wherein the proportion of the structural units having chlorine groups relative to all structural units is 80% by mass or more, and the proportion of the structural units having aromatic polycarboxylic acid structures relative to all structural units is 0.5% by mass or more; and a charge transport layer disposed on the charge generating layer, comprising a charge transport material and an adhesive resin.

[0008] According to the second aspect of the present invention, the proportion of the chlorine-containing structural units is 88% by mass or less relative to all structural units constituting the above-mentioned vinyl copolymer.

[0009] According to the third aspect of the present invention, the proportion of the chlorine-containing structural units is 80% by mass or more and 87% by mass or less relative to all structural units constituting the above-mentioned vinyl copolymer.

[0010] According to a fourth aspect of the present invention, an electrophotographic photosensitive material is provided, comprising: a conductive substrate; a charge generating layer disposed on the conductive substrate, comprising a charge generating material and a vinyl copolymer, wherein the vinyl copolymer comprises structural units having chlorine, structural units having acyloxy groups, and structural units having aromatic polycarboxylic acid structures, and the solubility of the vinyl copolymer in 100 parts by mass of tetrahydrofuran at 30°C is 10 parts by mass or less; and a charge transport layer disposed on the charge generating layer, comprising a charge transport material and an adhesive resin.

[0011] According to a fifth aspect of the present invention, when the proportion of the structural unit having the aromatic polycarboxylic acid structure to all structural units constituting the vinyl copolymer is A by mass%, and the content of the charge-generating material to the vinyl copolymer is C by mass%, the value of A / C is 3.00 × 10⁻⁶.-3 Above 1.40×10 -2 the following.

[0012] According to the sixth aspect of the present invention, the above-mentioned chlorine-containing structural unit is represented by the following general formula (1), and the above-mentioned acyloxy-containing structural unit is represented by the following general formula (2).

[0013]

[0014] In the above general formula (1), R 11 ~R 13 Each of the above general formulas (2) independently represents an alkyl group having 1 to 5 hydrogen atoms or carbon atoms, where R 21 ~R 23 Each independently represents an alkyl group having 1 to 5 hydrogen atoms or carbon atoms, R 24 This refers to alkyl groups having 1 to 5 carbon atoms.

[0015] According to the seventh aspect of the present invention, R in the above general formula (1) 11 ~R 13 All are hydrogen atoms, and R in the above general formula (2) 21 ~R 23 All are hydrogen atoms, R 24 It is a methyl group.

[0016] According to the eighth aspect of the present invention, the structural unit having an aromatic polycarboxylic acid structure is a structural unit having an phthalic acid structure.

[0017] According to a ninth aspect of the present invention, a processing cartridge that is mounted and detached in an image forming apparatus is provided, which includes the aforementioned electrophotographic photosensitive element.

[0018] According to a tenth aspect of the present invention, an image forming apparatus is provided, comprising: the aforementioned electrophotographic photosensitive element; a charging mechanism for charging the surface of the aforementioned electrophotographic photosensitive element; an electrostatic latent image forming mechanism for forming an electrostatic latent image on the charged surface of the aforementioned electrophotographic photosensitive element; a developing mechanism for developing the electrostatic latent image formed on the surface of the aforementioned electrophotographic photosensitive element using a developing agent containing a toner, thereby forming a toner image; and a transfer mechanism for transferring the aforementioned toner image onto the surface of a recording medium.

[0019] The effects of the invention

[0020] According to the first embodiment described above, an electrophotographic photosensitive material is provided that, compared with the case where the charge generation layer contains a charge generation material and a vinyl copolymer and the vinyl copolymer contains structural units having chlorine, structural units having acyloxy groups, and structural units derived from maleic acid, the case where the proportion of structural units having chlorine relative to all structural units is less than 80% by mass, or the case where the proportion of structural units having aromatic polycarboxylic acid structures relative to all structural units is less than 0.5% by mass, the electrophotographic photosensitive material of this embodiment can suppress the image density difference along the axial direction of the electrophotographic photosensitive material.

[0021] According to the second scheme mentioned above, compared with the case where the proportion of chlorine structural units is greater than 88% by mass, an electrophotographic photosensitive material with high photosensitivity can be provided.

[0022] According to the third scheme mentioned above, compared with cases where the proportion of chlorine structural units is less than 80% by mass or greater than 87% by mass, an electrophotographic photosensitive material that balances suppression of image density differences along the axial direction and high photosensitivity can be provided.

[0023] According to the fourth scheme mentioned above, compared with the case where the charge generation layer contains charge generation material and vinyl copolymer, and the solubility of the vinyl copolymer in 100 parts by mass of tetrahydrofuran is greater than 10 parts by mass, an electrophotographic photoreceptor in which the image density difference along the axial direction of the electrophotographic photoreceptor is suppressed.

[0024] According to the fifth scheme mentioned above, the value of A / C is less than 3.00 × 10 -3 Compared to the previous case, this provides an electrophotographic photoreceptor in which the image density difference along the axial direction of the photoreceptor is suppressed.

[0025] According to the above-mentioned schemes 6, 7 or 8, compared with the case where the vinyl copolymer contains structural units having chlorine, structural units having acyloxy groups and structural units from maleic acid, an electrophotographic photoreceptor with suppressed image density difference along the axial direction can be provided.

[0026] According to the above-mentioned 9th or 10th scheme, a processing cartridge or image forming apparatus having an electrophotographic photoreceptor can be provided. Compared with the case where the vinyl copolymer contains structural units having chlorine, structural units having acyloxy groups, and structural units from maleic acid, the image density difference along the axial direction of the electrophotographic photoreceptor in the processing cartridge or image forming apparatus of this scheme is suppressed. Attached Figure Description

[0027] Figure 1 This is a schematic partial cross-sectional view illustrating an example of the layer structure of the electrophotographic photoreceptor of this embodiment.

[0028] Figure 2 This is a schematic configuration diagram illustrating an example of the image forming apparatus of this embodiment.

[0029] Figure 3 This is a schematic configuration diagram illustrating another example of the image forming apparatus of this embodiment. Detailed Implementation

[0030] The following description illustrates one embodiment of the present invention. These descriptions and examples are for illustrative purposes only and do not limit the scope of the invention.

[0031] In this specification, the upper or lower limit of a numerical range described in stages can be replaced with the upper or lower limit of other numerical ranges described in other stages. Furthermore, the upper or lower limit of a numerical range described in this specification can be replaced with the values ​​shown in the embodiments.

[0032] Each component may contain two or more corresponding substances.

[0033] When referring to the amount of each component in a composition, if there are two or more substances in the composition corresponding to each component, unless otherwise stated, it refers to the total amount of the two or more substances present in the composition.

[0034] Electrophotographic photosensitive material

[0035] (First Implementation)

[0036] The electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") according to the first embodiment has: a conductive substrate; a charge generating layer provided on the conductive substrate containing a charge generating material and a vinyl copolymer; and a charge transport layer provided on the charge generating layer containing a charge transport material and an adhesive resin.

[0037] Furthermore, the vinyl copolymer comprises structural units having chlorine (hereinafter also referred to as "chlorine-containing components"), structural units having acyloxy groups (hereinafter also referred to as "acyloxy groups"), and structural units having aromatic polycarboxylic acid structures (hereinafter also referred to as "aromatic polycarboxylic acid components"). In addition, in the vinyl copolymer, the proportion of the chlorine-containing component relative to all structural units is 80% or more by mass, and the proportion of the aromatic polycarboxylic acid component relative to all structural units is 0.5% or more by mass.

[0038] Here, "chlorine-containing component (i.e., structural unit with chlorine)" refers to a structural unit that has a chlorine atom but no acyloxy group and two or more carboxyl groups, and may also have other substituents (e.g., alkyl groups). Similarly, "acyloxy group (i.e., structural unit with acyloxy group)" refers to a structural unit that has an acyloxy group but no two or more carboxyl groups, and may also have other substituents (e.g., alkyl groups). Furthermore, "aromatic polycarboxylic acid component (i.e., structural unit with aromatic polycarboxylic acid structure)" refers to a structural unit with aromatic polycarboxylic acid structure, and may also have substituents other than carboxyl groups (e.g., alkyl groups).

[0039] By configuring the photoreceptor of the first embodiment as described above, the image density difference along the axial direction of the photoreceptor can be suppressed. The reason for this is presumably as follows.

[0040] As described above, when a charge transport layer is formed on a charge generation layer disposed on a conductive substrate, a coating solution for forming the charge transport layer is typically applied to the charge generation layer by dip coating and then dried to form the charge transport layer. In this case, a portion of the vinyl copolymer contained in the charge generation layer may dissolve due to the solvent in the coating solution. In the dip coating method, the coating solution for forming the charge transport layer adheres to the charge generation layer for different times at the lower and upper ends along the axial direction of the conductive substrate. Therefore, a difference in photosensitivity may occur at one end and the other end along the axial direction of the photoreceptor, and this difference in photosensitivity manifests as a difference in image density.

[0041] In contrast, in the first embodiment, the proportion of chlorine-containing components in the vinyl copolymer is 80% or more by mass relative to all structural units, and the proportion of aromatic polycarboxylic acid components is 0.5% or more by mass relative to all structural units. It is known that by making the proportion of chlorine-containing components 80% or more by mass and the proportion of aromatic polycarboxylic acid components 0.5% or more by mass, the vinyl copolymer is less likely to dissolve in the solvent of the coating liquid for forming the charge transport layer.

[0042] Specifically, by including aromatic polycarboxylic acid components in vinyl copolymers, compared to cases where structural units from aliphatic polycarboxylic acids such as maleic acid are used instead of those from aromatic polycarboxylic acids, vinyl copolymers exhibit higher compound stability and are less soluble in solvents. Furthermore, it is known that by including more than 0.5% by mass of aromatic polycarboxylic acid components in vinyl copolymers, compared to cases where the proportion of aromatic polycarboxylic acid components is less than 0.5% by mass, vinyl copolymers are also less soluble in solvents. Moreover, it can be considered that by including more than 80% by mass of chlorine-containing components in vinyl copolymers, compared to cases where the chlorine content is less than 80% by mass, the vinyl copolymer exhibits increased hardness and is less soluble in solvents.

[0043] Furthermore, it can be inferred that by making the vinyl copolymer less soluble in solvents, in the dip coating method, even if the coating liquid for forming the charge transport layer adheres to the charge generation layer at different times on the lower and upper ends of the conductive substrate along the axial direction, the difference in photosensitivity is less likely to occur, thus suppressing the resulting image density difference along the axial direction of the photoreceptor.

[0044] Based on the above reasons, it can be inferred that in the photoreceptor of the first embodiment, the image density difference along the axis of the photoreceptor is suppressed.

[0045] It should be noted that by making the adhesive resin of the charge-generating layer easily soluble in a solvent, it is also possible to obtain a photosensitive material with high photosensitivity. Specifically, by making the adhesive resin in the charge-generating layer easily soluble in the solvent in the coating solution used to form the charge transport layer, charge-generating material is more likely to be present at the interface between the charge-generating layer and the charge transport layer. Furthermore, the more charge-generating material present at the interface between the charge-generating layer and the charge transport layer, the easier it is to increase the photosensitivity of the photosensitive material.

[0046] In contrast, in the first embodiment, high photosensitivity can be obtained even if the vinyl copolymer is not easily soluble in a solvent. The reason for this is not yet certain, but it is speculated as follows. Specifically, firstly, it is believed that the acyloxy group contained in the vinyl copolymer can improve the dispersibility of the charge-generating material in the vinyl copolymer. Furthermore, in the first embodiment, it is known that by combining the acyloxy group with an aromatic polycarboxylic acid group, the dispersibility of the charge-generating material in the vinyl copolymer can be further improved. It is also speculated that by improving the dispersibility of the charge-generating material in the vinyl copolymer, even if the vinyl copolymer is not easily soluble in a solvent, the charge-generating material will be dispersed near the interface with the charge transport layer, thereby obtaining higher photosensitivity. That is, the photoreceptor of the first embodiment can achieve high photosensitivity and suppress the image density difference along the axial direction of the photoreceptor.

[0047] (Second Implementation)

[0048] The photoreceptor of the second embodiment includes: a conductive substrate; a charge-generating layer disposed on the conductive substrate containing a charge-generating material and a vinyl copolymer; and a charge-transfer layer disposed on the charge-generating layer containing a charge-transfer material and an adhesive resin.

[0049] Furthermore, the vinyl copolymer contains chlorine-containing components, acyloxy components, and aromatic polycarboxylic acid components, and the solubility of the above vinyl copolymer in 100 parts by mass of tetrahydrofuran at 30°C (hereinafter also referred to as "THF solubility") is less than 10 parts by mass.

[0050] By configuring the photoreceptor of the second embodiment as described above, the image density difference along the axial direction of the electrophotographic photoreceptor can be suppressed. The reason for this is presumably as follows.

[0051] As described above, when a charge transport layer is formed on a charge generation layer disposed on a conductive substrate, a coating solution for forming the charge transport layer is typically applied to the charge generation layer by dip coating and then dried, thereby forming the charge transport layer. In this case, a portion of the vinyl copolymer contained in the charge generation layer may be dissolved by the solvent in the coating solution for forming the charge transport layer. In the dip coating method, the coating solution for forming the charge transport layer adheres to the charge generation layer for different times at the lower and upper ends along the axial direction of the conductive substrate. Therefore, a difference in photosensitivity may occur between one end and the other end along the axial direction of the electrophotographic photoreceptor, and this difference in photosensitivity sometimes manifests as a difference in image density.

[0052] In contrast, in the second embodiment, the vinyl copolymer contains an aromatic polycarboxylic acid component, and its THF solubility is less than 10 parts by mass. Therefore, it can be considered that the vinyl copolymer is not easily soluble in a solvent.

[0053] Furthermore, it can be inferred that by making the vinyl copolymer less soluble in solvents, in the dip coating method, even if the coating liquid for forming the charge transport layer adheres to the charge generation layer at different times on the lower and upper ends of the conductive substrate along the axial direction, the difference in photosensitivity is less likely to occur, thus suppressing the image density difference along the axial direction of the electrophotographic photoreceptor caused by the difference in photosensitivity.

[0054] Based on the above reasons, it can be inferred that in the photoreceptor of the second embodiment, the image density difference along the axis of the electrophotographic photoreceptor is suppressed.

[0055] Furthermore, in the second embodiment, high photosensitivity can be obtained even if the vinyl copolymer is not easily soluble in a solvent. Specifically, it is known that the acyloxy group contained in the vinyl copolymer can improve the dispersibility of the charge-generating material in the vinyl copolymer, and by combining the acyloxy group with an aromatic polycarboxylic acid group, the dispersibility of the charge-generating material in the vinyl copolymer can be further improved. It is also conceivable that by improving the dispersibility of the charge-generating material in the vinyl copolymer, even if the vinyl copolymer is not easily soluble in a solvent, the charge-generating material will be dispersed near the interface with the charge transport layer, thereby obtaining high photosensitivity. That is, the photoreceptor of the second embodiment can obtain high photosensitivity and suppress the image density difference along the axial direction of the photoreceptor.

[0056] The photoreceptor conforming to both the first embodiment and the second embodiment will be described below as "the photoreceptor of this embodiment". However, an example of the photoreceptor of the present invention may be a photoreceptor conforming to at least one of the first embodiment and the second embodiment.

[0057] The electrophotographic photosensitive element of this embodiment will now be described with reference to the accompanying drawings.

[0058] Figure 1 This is a schematic partial cross-sectional view showing an example of the layer structure of the electrophotographic photosensitive element 7A according to this embodiment. Figure 1 The electrophotographic photosensitive element 7A shown has a structure formed by sequentially depositing an undercoat layer 1, a charge generation layer 2, and a charge transport layer 3 on a conductive substrate 4. Furthermore, the charge generation layer 2 and the charge transport layer 3 constitute a photosensitive layer 5.

[0059] It should be noted that the base layer 1 is a layer that is set as needed. That is, the electrophotographic photosensitive material 7A can have the charge generation layer 2 set directly on the conductive substrate 4 (i.e., without the base layer 1).

[0060] Furthermore, other layers can be provided on the electrophotographic photosensitive element 7A as needed. Examples of other layers include a protective layer further provided on the charge transport layer 3.

[0061] The layers of the electrophotographic photoreceptor of this embodiment will now be described in detail. It should be noted that symbols will be omitted in the description.

[0062] (Conductive substrate)

[0063] Examples of conductive substrates include metal plates, metal cylinders, and metal strips containing metals (aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, platinum, etc.) or alloys (stainless steel, etc.). Additionally, examples of conductive substrates include paper, resin films, and strips 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, "conductivity" refers to a volume resistivity of less than 10 Ω·cm. 13 Ωcm.

[0064] When an electrophotographic photosensitive material is used in a laser printer, the conductive substrate surface is preferably roughened to a centerline average roughness Ra of 0.04 μm to 0.5 μm to suppress interference fringes generated during laser irradiation. It should be noted that when non-interference light is used as the light source, roughening to prevent interference fringes is not particularly necessary, but since this roughening can suppress defects caused by the unevenness of the conductive substrate surface, it is suitable for extending the lifespan.

[0065] Examples of roughening methods include wet honing, which involves suspending an abrasive in water and blowing it onto a support; centerless grinding, which involves pressing a conductive substrate onto a rotating grinding stone and continuously grinding; and anodizing.

[0066] As a method of roughening, the following method can also be cited: instead of roughening the surface of the conductive substrate, conductive or semi-conductive powder is dispersed in a resin to form a layer on the surface of the conductive substrate, and the particles dispersed in the layer are used for roughening.

[0067] In the roughening process of anodizing, a conductive substrate made of metal (e.g., aluminum) is used as the anode, and anodizing is performed in an electrolyte solution, thereby forming 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 this state, easily contaminated, and exhibits large resistance variations due to environmental factors. Therefore, for porous anodic oxide films, a sealing treatment is preferred. In this sealing treatment, the micropores of the oxide film are sealed by the volume expansion caused by the hydration reaction in pressurized steam or boiling water (with the addition of metal salts such as nickel), thereby transforming it into a more stable hydrated oxide.

[0068] The thickness of the anodic oxide film is preferably 0.3 μm or more and 15 μm or less. By keeping the film thickness within the above range, it tends to provide barrier properties against injection and to suppress the rise of residual potential due to repeated use.

[0069] Conductive substrates can be treated with acidic solutions or boehmite.

[0070] The treatment based on the acidic treatment solution can be carried out as follows: First, an acidic treatment solution containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. Regarding the mixing ratio of phosphoric acid, chromic acid, and hydrofluoric acid in the acidic treatment solution, for example, phosphoric acid is in the range of 10% to 11% by mass, chromic acid is in the range of 3% to 5% by mass, and hydrofluoric acid is in the range of 0.5% to 2% by mass, and the overall concentration of these acids can be in the range of 13.5% to 18% by mass. The treatment temperature is preferably, for example, 42°C to 48°C. The coating thickness is preferably 0.3 μm to 15 μm.

[0071] Regarding boehmite treatment, it can be performed, for example, by immersion in pure water at a temperature between 90°C and 100°C for 5 to 60 minutes, or by contact with heated steam at a temperature between 90°C and 120°C for 5 to 60 minutes. The coating thickness is preferably between 0.1 μm and 5 μm. The coating can 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.

[0072] (Base coat)

[0073] The base layer is, for example, a layer containing inorganic particles and a binding resin.

[0074] As for inorganic particles, examples include powders with a resistivity (volume resistivity) of 10. 2 Ωcm or more 10 11 Inorganic particles smaller than Ωcm.

[0075] Among these, the inorganic particles having the above-mentioned resistance values ​​can be, for example, 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.

[0076] The specific surface area of ​​inorganic particles based on the BET method can be, for example, 10 m². 2 / g or more.

[0077] The volume average particle size of the inorganic particles can be, for example, 50 nm or more and 2000 nm or less (preferably 60 nm or more and 1000 nm or less).

[0078] The content of inorganic particles is preferably 10% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 80% by mass or less, relative to the adhesive resin.

[0079] Inorganic particles can undergo surface treatment. Two or more types of inorganic particles with different surface treatments or with different particle sizes can also be mixed and used.

[0080] Examples of surface treatment agents include silane coupling agents, titanate coupling agents, aluminum coupling agents, and surfactants. Silane coupling agents are particularly preferred, and silane coupling agents containing amino groups are more preferred.

[0081] Examples of amino-containing silane coupling agents 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.

[0082] Two or more silane coupling agents can also be used in combination. For example, an amino-containing silane coupling agent can be used in combination with other silane coupling agents. Examples of such other silane coupling agents include vinyltrimethoxysilane, 3-methacryloyloxypropyltris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, 3-chloropropyltrimethoxysilane, etc., but are not limited to these.

[0083] Surface treatment methods based on surface treatment agents can be any known method, including either dry or wet methods.

[0084] The amount of surface treatment agent used is preferably 0.5% by mass or more and 10% by mass or less relative to the inorganic particles.

[0085] Here, from the perspective of improving the long-term stability of electrical properties and carrier blocking properties, the undercoat may contain inorganic particles and electron acceptor compounds (acceptor compounds).

[0086] Examples of electron-accepting compounds include quinone compounds such as chloroquinone and bromoaniline; tetracyanoquinone dimethyl 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-tert-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; biphenylquinone compounds such as 3,3',5,5'-tetratert-butylbiphenylquinone; and isoelectronic transport substances.

[0087] 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; more specifically, anthraquinones, alizarins, quinone alizarins, anthraquinone phenols, and rutins are preferred.

[0088] Electron-accepting compounds can be dispersed in the base coat along with inorganic particles, or they can be included in the base coat in a state of being attached to the surface of inorganic particles.

[0089] Methods for attaching electron-accepting compounds to the surface of inorganic particles include, for example, dry or wet methods.

[0090] A dry method, for example, involves directly adding an electron-accepting compound or an electron-accepting compound dissolved in an organic solvent while stirring the inorganic particles using a high-shear mixer or similar equipment. This is then sprayed with dry air or nitrogen, causing the electron-accepting compound to adhere to the surface of the inorganic particles. The addition or spraying of the electron-accepting compound can be carried out at a temperature below the boiling point of the solvent. After the addition or spraying, calcination can be performed at a temperature above 100°C. There are no particular restrictions on the calcination temperature and time, as long as the electron photographic properties are obtained.

[0091] The wet process includes methods such as dispersing inorganic particles in a solvent using stirring, ultrasound, a sand mill, an ultrafine mill, or a ball mill, and adding an electron-accepting compound. After stirring or dispersion, the solvent is removed, leaving the electron-accepting compound attached to the surface of the inorganic particles. Solvent removal methods include, for example, filtration or distillation. After solvent removal, calcination can be performed at 100°C or higher. There are no particular limitations on the temperature and time of calcination, as long as the electron-photographic properties are obtained. In the wet process, the moisture contained in the inorganic particles can be removed before adding the electron-accepting compound; examples include removing moisture while stirring and heating in a solvent, or removing moisture through azeotropic distillation with the solvent.

[0092] It should be noted that the attachment of electron-accepting compounds can be carried out before or after the surface treatment of inorganic particles based on surface treatment agents, or the attachment of electron-accepting compounds and surface treatment based on surface treatment agents can be carried out simultaneously.

[0093] The content of the electron-accepting compound can be, for example, 0.01% by mass or more and 20% by mass or less relative to the inorganic particles, preferably 0.01% by mass or more and 10% by mass or less.

[0094] Examples of known polymeric resins used as adhesives in the base coating include acetal resins (such as polyvinyl butyral), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane 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-modified alkyd resins, urea resins, phenol resins, phenol-formaldehyde resins, melamine resins, urethane resins, alkyd resins, and epoxy resins; zirconium chelates; titanium chelates; aluminum chelates; titanium alkoxides; organotitanium compounds; and silane coupling agents.

[0095] Examples of adhesive resins used in the base coating include charge-transporting resins with charge-transporting groups and conductive resins (such as polyaniline).

[0096] Among these, the adhesive resin used as the base layer is preferably a resin that is insoluble in the coating solvent of the upper layer, and is particularly suitable for thermosetting resins such as urea resin, phenol resin, phenol-formaldehyde resin, melamine resin, urethane resin, unsaturated polyester resin, alkyd resin, and epoxy resin; and a resin obtained by reacting at least one resin selected from the group consisting of polyamide resin, polyester resin, polyether resin, methacrylic resin, acrylic resin, polyvinyl alcohol resin, and polyvinyl alcohol acetal resin with a curing agent.

[0097] When using two or more of these adhesive resins in combination, the mixing ratio should be set as needed.

[0098] In order to improve electrical properties, environmental stability and image quality, various additives may be included in the base coating.

[0099] Examples of additives include known materials such as electron-transporting pigments (e.g., polycyclic condensation systems, azo compounds), zirconium chelates, titanium chelates, aluminum chelates, titanium alkoxides, organotitanium compounds, and silane coupling agents. Silane coupling agents, as mentioned above, are used for surface treatment of inorganic particles, but they can also be further added as additives to the base coating.

[0100] Examples of silane coupling agents used as additives include vinyltrimethoxysilane, 3-methacryloyloxypropyltris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-epoxypropoxypropyltrimethoxysilane, 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.

[0101] Examples of zirconium chelating compounds include zirconium butoxide, zirconium acetoacetate, zirconium triethanolamine, zirconium acetoacetone butoxide, zirconium acetoacetate butoxide, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, zirconium methacrylate butoxide, zirconium stearate butoxide, and zirconium isostearate butoxide.

[0102] Examples of titanium chelating compounds include tetraisopropyl titanate, tetrabutyl titanate, tetrabutyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetonate, polyacetylacetonate, titanium octylene glycolate, titanium ammonium lactate, titanium lactate, titanium ethyl lactate, titanium triethanolamine, and titanium polyhydroxystearate.

[0103] Examples of aluminum chelating compounds include aluminum isopropionate, aluminum diisopropionate monobutoxy, aluminum butyrate, aluminum diisopropionate diethylacetoacetate, and aluminum tri(ethylacetoacetate).

[0104] These additives can be used alone, or in the form of a mixture or condensation polymer of two or more compounds.

[0105] The Vickers hardness of the primer coating can be above 35.

[0106] Regarding the surface roughness (ten-point average roughness) of the base coating, in order to suppress the moiré pattern, it can be adjusted from 1 / (4n) of the laser wavelength λ used for exposure (where n is the refractive index of the upper layer) to 1 / 2.

[0107] To adjust surface roughness, resin particles can be added to the base coating. Examples of resin particles include silicone resin particles and cross-linked polymethyl methacrylate resin particles. Additionally, to adjust surface roughness, the surface of the base coating can be ground. Examples of grinding methods include polishing, sandblasting, wet honing, and grinding.

[0108] There are no particular limitations on the formation of the primer layer, and known formation methods can be used. For example, a coating film of a primer layer forming liquid can be formed by adding the above-mentioned components to a solvent, drying the coating film, and heating it as needed to form the primer layer.

[0109] As solvents used to prepare coating liquids for base coating formation, well-known organic solvents can be cited, such as alcohol solvents, aromatic hydrocarbon solvents, halogenated hydrocarbon solvents, ketone solvents, ketol solvents, ether solvents, ester solvents, etc.

[0110] Specifically, examples of these solvents include, for instance, methanol, ethanol, n-propanol, isopropanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, dichloromethane, chloroform, chlorobenzene, toluene, and other common organic solvents.

[0111] Methods for dispersing inorganic particles during the preparation of a coating liquid for forming a base layer include, for example, known methods such as roller mills, ball mills, vibratory ball mills, ultrafine grinding mills, sand mills, colloid mills, and coating shakers.

[0112] Methods for applying a base coating liquid to a conductive substrate include, for example, scraper coating, wire-wound bar coating, spraying, dip coating, microsphere coating, air knife coating, curtain coating, and other common methods.

[0113] The thickness of the base coating is set, for example, preferably 15 μm or more, more preferably 20 μm or more and 50 μm or less.

[0114] (Middle layer)

[0115] Although the illustration is omitted, an intermediate layer can be further set between the base layer and the photosensitive layer.

[0116] The intermediate layer may be, for example, a layer containing resin. Examples of resins used in the intermediate layer include acetal resins (such as polyvinyl butyral), polyvinyl alcohol resins, polyvinyl acetal resins, casein resins, polyamide resins, cellulose resins, gelatin, polyurethane resins, polyester resins, methacrylic acid resins, acrylic resins, polyvinyl chloride resins, polyvinyl acetate resins, vinyl chloride-vinyl acetate-maleic anhydride resins, silicone resins, silicone-modified alkyd resins, phenol-formaldehyde resins, melamine resins, and other polymeric compounds.

[0117] The intermediate layer can be a layer containing an organometallic compound. Examples of organometallic compounds used as intermediate layers include those containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon.

[0118] These compounds used in the intermediate layer can be used alone, or in the form of a mixture of two or more compounds or in the form of a condensation polymer.

[0119] Among these, the intermediate layer is preferably a layer containing an organometallic compound containing zirconium or silicon atoms.

[0120] There are no particular limitations on the formation of the intermediate layer. Known formation methods can be used, such as forming a coating film of an intermediate layer forming liquid by adding the above-mentioned components to a solvent, drying the coating film, and heating it as needed to form the intermediate layer.

[0121] Common methods used to form intermediate layers include dip coating, extrusion coating, wire rod coating, spraying, scraper coating, knife coating, and curtain coating.

[0122] The thickness of the intermediate layer is preferably set in the range of 0.1 μm to 3 μm. It should be noted that the intermediate layer can also be used as a base layer.

[0123] (charge generation layer)

[0124] The charge-generating layer is a layer containing a charge-generating material and a vinyl copolymer containing chlorine-containing components, acyloxy components and aromatic polycarboxylic acid components as an adhesive resin, and may also contain other components as needed.

[0125] In the following text, vinyl copolymers containing chlorine-containing components, acyloxy components, and aromatic polycarboxylic acid components will also be referred to as "specific copolymers".

[0126] -Charge-generating materials-

[0127] Examples of charge-generating materials include azo pigments such as diazo and triazo; fused-ring aromatic pigments such as dibromoanthrone; perylene pigments; pyrrolopyrrole pigments; phthalocyanine pigments; zinc oxide; and trigonal selenium.

[0128] Among these, phthalocyanine pigments with high charge-generating capabilities are preferred as charge-generating materials. Examples of phthalocyanine pigments include metallic phthalocyanine pigments and metal-free phthalocyanine pigments. Specifically, examples of phthalocyanine pigments include the gallium hydroxyl phthalocyanine pigment disclosed in Japanese Patent Application Publication Nos. 5-263007 and 5-279591; the gallium chloride phthalocyanine pigment disclosed in Japanese Patent Application Publication Nos. 5-98181; the tin dichlorophthalocyanine pigment disclosed in Japanese Patent Application Publication Nos. 5-140472 and 5-140473; and the titanium oxide phthalocyanine pigment disclosed in Japanese Patent Application Publication No. 4-189873.

[0129] Furthermore, among these, from the perspective of charge generation capability, phthalocyanine pigments are preferably selected from at least one of hydroxy gallium phthalocyanine pigments and gallium chloride phthalocyanine pigments, and more preferably hydroxy gallium phthalocyanine pigments.

[0130] It should be noted that in charge-generating materials, especially when using phthalocyanine pigments with high charge-generating capabilities (particularly at least one of gallium chloride phthalocyanine and hydroxy gallium phthalocyanine), the high charge-generating capability leads to an increased amount of accumulated charge when charge traps are present in the charge-generating layer, which can easily cause positive ghosting. However, in this embodiment, as described above, by using a specific copolymer as the binding resin, the amount of charge traps generated is reduced. Therefore, it is conjectured that even when using phthalocyanine pigments as charge-generating materials, and even when at least one of gallium chloride phthalocyanine and hydroxy gallium phthalocyanine is specifically used, positive ghosting can be suppressed.

[0131] Among hydroxy gallium phthalocyanine pigments, V-type hydroxy gallium phthalocyanine pigments are preferred.

[0132] In particular, as a hydroxy gallium phthalocyanine pigment, for example from the viewpoint of obtaining better dispersibility, a hydroxy gallium phthalocyanine pigment having a maximum peak wavelength in the range of 810 nm to 839 nm in the spectroscopic absorption spectrum in the wavelength region of 600 nm to 900 nm is preferred.

[0133] Furthermore, the hydroxyl gallium phthalocyanine pigments with the maximum peak wavelength in the range of 810 nm to 839 nm preferably have 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 or more and 0.15 μm or less. On the other hand, the BET specific surface area is preferably 45 m² / s. 2 / g or more, preferably 50m 2 / g or more, preferably 55m 2 / g or more 120m 2 / g or less. The average particle size was measured using a laser diffraction scattering particle size distribution measuring device (LA-700, manufactured by Horiba Corporation) as the volume average particle size (d50 average particle size). Additionally, the value was measured using a BET-type specific surface area meter (Shimadzu Corporation: Flowsoap II2300) via nitrogen replacement method.

[0134] The maximum particle size (maximum value of 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.

[0135] Hydroxygallium phthalocyanine pigments are preferably characterized by 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 m². 2 / g or more.

[0136] The preferred hydroxy gallium phthalocyanine pigment is a V-type hydroxy gallium phthalocyanine pigment that has diffraction peaks at least at Bragg angles (2θ±0.2°) of 7.3°, 16.0°, 24.9°, and 28.0° in the X-ray diffraction spectrum using CuKα characteristic X-rays.

[0137] Charge-generating materials can be used alone or in combination of two or more.

[0138] The content of the charge-generating material relative to the total charge-generating layer can be, for example, 30% or more and 80% or less by volume. From the perspective of suppressing positive image ghosting, it is more preferably 40% or more and 70% or less by volume, and more preferably 50% or more and 60% or less by volume.

[0139] -Specific copolymers-

[0140] The specific copolymer is a vinyl copolymer containing chlorine-containing components, acyl-oxygen components, and aromatic polycarboxylic acid components.

[0141] It should be noted that, in the first embodiment, the proportion of chlorine-containing components in the specific copolymer relative to all structural units is 80% or more by mass, and the proportion of aromatic polycarboxylic acid components relative to all structural units is 0.5% or more by mass.

[0142] It should be noted that the proportion of each structural unit relative to all structural units is determined by analyzing the specific copolymer using NMR (nuclear magnetic resonance).

[0143] The specific copolymer contains at least a chlorine-containing component, an acyloxy group, and an aromatic polycarboxylic acid component, and may also contain other structural units (e.g., structural units derived from diols). The proportion of other structural units relative to all structural units is preferably 5 mol% or less, more preferably 3 mol% or less, even more preferably 1 mol% or less, and particularly preferably does not contain any other structural units. That is, the specific copolymer is particularly preferably a copolymer formed from a chlorine-containing component, an acyloxy group, and an aromatic polycarboxylic acid component.

[0144] --Chlorine-containing components--

[0145] As mentioned above, the chlorine-containing component is a structural unit that has chlorine atoms but no acyloxy group and two or more carboxyl groups.

[0146] In a specific copolymer, the chlorine-containing component may be only one type or may contain two or more types.

[0147] Examples of the number of chlorine atoms in a chlorine-containing component include 1 to 5, preferably 1 to 3, more preferably 1 or more but less than 2, and even more preferably 1. Furthermore, in the chlorine-containing component, it is preferable that the chlorine atoms are directly bonded to the straight chain.

[0148] Other substituents that chlorine-containing components may have include, for example, alkyl groups, alkoxy groups, and halogen atoms other than chlorine.

[0149] The chlorine-containing component is preferably a structural unit derived from vinyl chloride or a vinyl chloride derivative.

[0150] In addition, the chlorine-containing component is preferably the structural unit represented by the following general formula (1).

[0151]

[0152] In general formula (1), R 11 ~R 13 Each can be independently represented as an alkyl group having 1 to 5 hydrogen atoms or carbon atoms.

[0153] R in general formula (1) 11 ~R 13 Each of the components is preferably a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom.

[0154] R in general formula (1) 11 ~R 13 They can be different from each other, or they can be the same group.

[0155] Among chlorine-containing components, those represented by general formula (1) are preferred, and R in general formula (1) is preferred. 11 ~R 13 All of them are structural units composed of hydrogen atoms.

[0156] --Acyloxy component--

[0157] As mentioned above, the acyloxy group is a structural unit containing an acyloxy group.

[0158] In a specific copolymer, the acyloxy group may contain only one type or more types.

[0159] The number of acyl groups in the acyl group component can be, for example, 1 or more but 2 or less, and more preferably 1. Furthermore, in the acyl group component, it is preferable that the acyl group is directly bonded to the straight chain.

[0160] Other substituents that can be present as acyloxy groups include, for example, alkyl, alkoxy, and halogen atoms.

[0161] The acyl group is preferably a structural unit derived from vinyl acetate or a vinyl acetate derivative.

[0162] In addition, the acyloxy group is preferably a structural unit represented by the following general formula (2).

[0163]

[0164] In general formula (2), R 21 ~R 23 Each independently represents an alkyl group having 1 to 5 hydrogen atoms or carbon atoms, R 24 Alkyl groups having 1 to 5 carbon atoms.

[0165] R in general formula (2) 21 ~R 23 Each of the components is preferably a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom.

[0166] R in general formula (2) 21 ~R 23 They can be different from each other or they can be the same group. Among them, R in general formula (2) is preferred. 21 ~R 23 All are hydrogen atoms.

[0167] R in general formula (2) 24 Preferably, it is an alkyl group having 1 to 5 carbon atoms, more preferably methyl or ethyl, and even more preferably methyl.

[0168] Of the acyl group components, the preferred one is represented by general formula (2), and R in general formula (2) is... 21 ~R 23 All are hydrogen atoms and R in general formula (2) 24 It is a structural unit of the methyl group.

[0169] --Aromatic polycarboxylic acid components--

[0170] As mentioned above, aromatic polycarboxylic acid components are structural units with aromatic polycarboxylic acid structures.

[0171] In a specific copolymer, the aromatic polycarboxylic acid component may contain only one type or more types.

[0172] Aromatic rings, which are components of aromatic polycarboxylic acids, can be exemplified by benzene rings, naphthalene rings, etc., with benzene rings being preferred. These aromatic rings can be directly bonded to the main chain of a specific copolymer, or they can be bonded via linking groups such as alkylene groups, with direct bonding being preferred.

[0173] Examples of aromatic polycarboxylic acid components include 2 to 4 carboxyl groups, preferably 2 to 3, and more preferably 2. Furthermore, in aromatic polycarboxylic acid components, two or more carboxyl groups can be directly bonded to the aromatic ring, or they can be bonded via linking groups such as alkylene groups. Preferably, all two or more carboxyl groups in the aromatic polycarboxylic acid component are directly bonded to the aromatic ring.

[0174] Other substituents that can be present in aromatic polycarboxylic acid components include, for example, alkyl, alkoxy, and halogen atoms.

[0175] Examples of aromatic polycarboxylic acid structures that can be used as aromatic polycarboxylic acid components include phthalic acid, isophthalic acid, terephthalic acid, and naphthalic acid structures. Among these, phthalic acid structures are preferred, and phthalic acid structures without other substituents are more preferred.

[0176] In aromatic polycarboxylic acid components, it is preferred that the aromatic polycarboxylic acid structure is directly bonded to the main chain of a specific copolymer, and more preferably that the phthalic acid structure is directly bonded to the main chain of a specific copolymer.

[0177] The aromatic polycarboxylic acid component is preferably a structural unit derived from phthalic acid, vinyl phthalic acid, or their derivatives.

[0178] The aromatic polycarboxylic acid component can be, for example, a structural unit located at the end of the main chain of a specific copolymer, as shown in formula (3-1), or, for example, a structural unit located outside the end, as shown in formula (3-2). Preferably, the aromatic polycarboxylic acid component is a structural unit located at the end of the main chain of the specific copolymer.

[0179]

[0180] --Combination of ingredients--

[0181] The specific copolymer is preferably a copolymer containing the structural unit represented by general formula (1) as a chlorine-containing component and the structural unit represented by general formula (2) as an acyloxy component, more preferably a copolymer containing the structural unit represented by general formula (1), the structural unit represented by general formula (2), and the structural unit having a phthalic acid structure.

[0182] Furthermore, a particular copolymer is preferably a copolymer that contains, as a chlorine-containing component, R represented by general formula (1) and in general formula (1) 11 ~R 13 All are structural units consisting of hydrogen atoms, and the acyloxy group contains R represented by general formula (2). 21 ~R 23 All are hydrogen atoms, and R in general formula (2) 24 A copolymer of structural units of methyl; particularly preferred are copolymers comprising R represented by general formula (1) and in general formula (1) 11 ~R 13 All are structural units of hydrogen atoms, represented by general formula (2), and R in general formula (2) 21 ~R 23 All are hydrogen atoms, and R in general formula (2) 24It is a copolymer of a methyl structural unit and a phthalic acid structural unit without other substituents.

[0183] --Proportions of each ingredient--

[0184] Regarding the proportion of chlorine-containing components, from the perspective of suppressing the image density difference along the photoreceptor axis, it is preferably 80% by mass or more, more preferably 82% by mass or more, and even more preferably 85% by mass or more relative to all components of the specific copolymer.

[0185] Furthermore, regarding the proportion of chlorine-containing components, from the perspective of obtaining high photosensitivity, it is preferably 88% by mass or less, more preferably 87% by mass or less, and even more preferably 86% by mass or less relative to the total components of a specific copolymer.

[0186] If the chlorine content is 87% by mass or less, the hardness of the vinyl copolymer is less likely to become excessively high compared to cases with excessively high chlorine content, thus reducing the dispersibility of the charge-generating material. Furthermore, if the chlorine content is 87% by mass or less, the proportion of acyloxy groups is relatively higher compared to cases with excessively high chlorine content, making it easier to obtain dispersibility of the charge-generating material. It is speculated that the charge-generating material is more likely to exist near the interface with the charge transport layer, resulting in high photosensitivity.

[0187] From the perspective of balancing the suppression of image density difference along the photoreceptor axis and high sensitivity, the proportion of chlorine-containing components is preferably 80% to 88% by mass, more preferably 82% to 87% by mass, and even more preferably 85% to 86% by mass.

[0188] Regarding the proportion of aromatic polycarboxylic acid components, from the perspective of suppressing the image density difference along the photoreceptor axis, it is preferably 0.5% by mass or more, and more preferably 0.8% by mass or more, relative to all components of a specific copolymer.

[0189] Furthermore, regarding the proportion of aromatic polycarboxylic acid components, from the perspective of obtaining high photosensitivity, it is preferably 2.5% by mass or less, more preferably 1.5% by mass or less, relative to all components of a specific copolymer.

[0190] When the proportion of aromatic polycarboxylic acid components is below 2.0% by mass, the proportion of acyloxy components is relatively higher compared to cases where the proportion of aromatic polycarboxylic acid components is too high, making it easier to obtain the dispersion of charge-generating materials. This suggests that charge-generating materials are more likely to exist near the interface with the charge transport layer, resulting in high photosensitivity.

[0191] From the perspective of balancing the suppression of image density difference along the photoreceptor axis and high photosensitivity, the proportion of aromatic polycarboxylic acid components is preferably 0.5% by mass or more and 2.0% by mass or less.

[0192] From the perspective of suppressing the image density difference along the photoreceptor axis, when the proportion of aromatic polycarboxylic acid component relative to all components of a specific copolymer is A (mass%), and the content of charge-generating material relative to the specific copolymer is C (mass%), the preferred value of A / C is 3.00 × 10⁻⁶. -3 The above, and more preferably 5.00×10 -3 above.

[0193] Furthermore, from the perspective of obtaining high sensitivity, the A / C value is preferably 1.40 × 10⁻⁶. -2 The following, or more preferably, is 1.00 × 10 -2 the following.

[0194] From the perspective of balancing the suppression of image density difference along the photoreceptor axis and high sensitivity, the A / C value is preferably 3.00 × 10⁻⁶. -3 Above 1.40×10 -2 The following, or more preferably, is 5.00 × 10 -3 Above 1.00×10 -2 the following.

[0195] The weight-average molecular weights mentioned above were determined by gel permeation chromatography (GPC). In the molecular weight determination using GPC, a Tosoh HLC-8120 GPC (manufactured by Tosoh Corporation) was used as the measuring apparatus, and a Tosoh TSKgel SuperHM-M (15 cm) column (manufactured by Tosoh Corporation) was used. The determination was performed using THF solvent. The weight-average molecular weight and number-average molecular weight were calculated from the determination results using a molecular weight calibration curve prepared from monodisperse polystyrene standard samples.

[0196] From the perspective of suppressing the image density difference along the photoreceptor axis, the solubility of the specific copolymer in 100 parts by mass of tetrahydrofuran at 30°C (hereinafter also referred to as "THF solubility") is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7.5 parts by mass or less.

[0197] The polymer of the test object was added to tetrahydrofuran at 30°C, and after standing for 5 minutes, the mass of the residual polymer was measured, thereby determining the above THF solubility.

[0198] There are no particular limitations on the manufacturing method of a specific copolymer. For example, a method can be given in which monomers corresponding to each structural unit are polymerized by suspension polymerization.

[0199] -Other Additives-

[0200] Other known additives may also be included in the charge generation layer.

[0201] -Formation of the charge generation layer-

[0202] There are no particular limitations on the formation of the charge generation layer. Known formation methods can be used, such as forming a coating film of a charge generation layer forming liquid by adding the above components to a solvent, drying the coating film, and heating it as needed to form the charge generation layer.

[0203] Examples of solvents used in preparing coating solutions for forming charge-generating layers 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, dichloromethane, chloroform, chlorobenzene, and toluene. These solvents can be used individually or in combination.

[0204] Methods for dispersing particles (e.g., charge-generating materials) in a coating liquid for forming a charge-generating layer include, for example, media dispersers such as ball mills, vibratory ball mills, ultrafine mills, sand mills, and horizontal sand mills; and medialess dispersers such as stirring, ultrasonic dispersers, roller mills, and high-pressure homogenizers. Examples of high-pressure homogenizers include collision methods where the dispersion is dispersed by liquid-liquid collisions or liquid-wall collisions under high pressure; and penetration methods where the dispersion is dispersed through a micro-flow path under high pressure.

[0205] It should be noted that, during this dispersion, it is effective to ensure that the average particle size of the charge-generating material in the coating liquid for forming the charge-generating layer is 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

[0206] Methods for applying a coating liquid for forming a charge generation layer onto a base layer (or intermediate layer) include, for example, scraper coating, wire-wound bar coating, spraying, dip coating, microsphere coating, air knife coating, curtain coating, and other common methods.

[0207] The thickness of the charge generation layer is preferably set to be 0.05 μm or more and 5.0 μm or less, more preferably 0.1 μm or more and 2.0 μm or less, even more preferably 0.1 μm or more and 1.0 μm or less, and particularly preferably 0.1 μm or more and 0.5 μm or less.

[0208] (charge transport layer)

[0209] The charge transport layer is a layer containing a charge transport material and an adhesive resin. The charge transport layer can also be a layer containing a polymeric charge transport material.

[0210] Examples of charge transport materials include quinone compounds such as p-benzoquinone, chloroquinone, bromoquinone, and anthraquinone; tetracyanoquinone dimethane compounds; fluorenone compounds such as 2,4,7-trinitrofluorenone; xanthone compounds; benzophenone compounds; cyanovinyl compounds; and ethylene compounds, among other electron transport compounds. Examples of hole transport materials include triarylamine compounds, benzidine compounds, arylalkane compounds, aryl-substituted ethylene compounds, mesodeoxyethylene compounds, anthracene compounds, and hydrazone compounds. These charge transport materials can be used individually or in combination of two or more, but are not limited to these examples.

[0211] From the perspective of charge mobility, the preferred charge transport materials are triarylamine-based charge transport materials represented by the following general formula (a-1) (hereinafter also referred to as "triarylamine-based charge transport materials (a-1)"), charge transport materials represented by the following general formula (CT1) as an example of triarylamine-based charge transport materials (hereinafter also referred to as "butadiene-based charge transport materials (CT1)"), and charge transport materials represented by the following general formula (CT2) (hereinafter also referred to as "benzidine-based charge transport materials (CT2)").

[0212] In addition, butadiene-based charge transport materials (CT1) and benzidine-based charge transport materials (CT2) can be used together as charge transport materials.

[0213] The triarylamine-based charge transport material (a-1) is described.

[0214] The triarylamine-based charge transport material (a-1) is the charge transport material represented by the following general formula (a-1).

[0215]

[0216] In general formula (a-1), Ar T1 Ar T2 And Ar T3 Each independently represents 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 of these elements independently represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group.

[0217] Examples of substituents for the aforementioned groups include halogen atoms, alkyl groups having 1 to 5 carbon atoms, and alkoxy groups having 1 to 5 carbon atoms. Additionally, examples of substituents for the aforementioned groups include substituted amino groups substituted with alkyl groups having 1 to 3 carbon atoms.

[0218] The butadiene-based charge transport material (CT1) is described.

[0219] Butadiene-based charge transport materials (CT1) are charge transport materials represented by the following general formula (CT1).

[0220]

[0221] In general formula (CT1), R C11 R C12 R C13 R C14 R C15 and R C16 Each of the following groups can independently represent a hydrogen atom, a halogen atom, an alkyl group with 1 to 20 carbon atoms, an alkoxy group with 1 to 20 carbon atoms, or an aryl group with 6 to 30 carbon atoms. Two adjacent substituents can bond together to form a hydrocarbon ring structure.

[0222] n and m each independently represent 0, 1, or 2.

[0223] In the general formula (CT1), as R C11 R C12 R C13 R C14 R C15 and R C16 Examples of halogen atoms include fluorine, chlorine, bromine, and iodine. Among these, fluorine and chlorine atoms are preferred as halogen atoms, and chlorine atoms are even more preferred.

[0224] In the general formula (CT1), as R C11 R C12 R C13 R C14 R C15 and R C16 The alkyl group referred to may be a straight-chain or branched alkyl group with 1 to 20 carbon atoms (preferably 1 to 6, more preferably 1 to 4).

[0225] Examples of linear alkyl groups include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecanyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecanyl, and n-eicosyl.

[0226] Specifically, branched alkyl groups include isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, tert-pentyl, isohexyl, sec-hexyl, tert-hexyl, isoheptyl, sec-heptyl, tert-heptyl, isooctyl, sec-octyl, tert-octyl, isononyl, sec-nonyl, tert-nonyl, isodel, sec-decyl, tert-decyl, isoundecyl, sec-undecyl, tert-undecyl, neoundecyl, isododecyl, sec-dodecyl, tert-dodecyl, neododecyl, isotridecyl, sec-tridecyl, tert-tridecyl, neotridecyl, isotetradecyl, and sec-tetradecane. Alkyl, tert-tetradecyl, neotetradecyl, 1-isobutyl-4-ethyloctyl, isopentadecanyl, tert-pentadecanyl, neopentadecanyl, isohexadecanyl, tert-hexadecyl, tert-hexadecyl, neohexadecyl, 1-methylpentadecanyl, isohexadecanyl, tert-hexadecyl, tert-hexadecyl, neohexadecyl, isohexadecan ... 1-methyloctyl, isoeicosyl, tert-hexadecyl, tert-hexadecyl, neohexadecyl, etc.

[0227] Among these, lower alkyl groups such as methyl, ethyl, and isopropyl are preferred as alkyl groups.

[0228] In the general formula (CT1), as R C11 R C12 R C13 R C14 R C15 and R C16 The alkoxy group represented can be a straight-chain or branched alkoxy group with 1 to 20 carbon atoms (preferably 1 to 6, more preferably 1 to 4).

[0229] As linear alkoxy groups, examples include methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, octoxy, nonoxy, decoxy, undecyloxy, dodecyloxy, tridecyloxy, tetradecyloxy, pentadecyloxy, hexadecyloxy, heptadecanyloxy, octadecyloxy, nonadecanyloxy, and eicosyloxy.

[0230] Specifically, branched alkoxy groups include isopropoxy, isobutoxy, sec-butoxy, tert-butoxy, isopentoxy, neopentoxy, tert-pentoxy, isohexoxy, sec-hexoxy, tert-hexoxy, isohexyloxy, sec-heptoxy, tert-heptoxy, isooctoxy, sec-octoxy, tert-octoxy, isononoxy, sec-nonoxy, tert-nonoxy, isodeoxy, sec-decoxy, tert-decoxy, isoundecyloxy, sec-undecyloxy, tert-undecyloxy, neoundecyloxy, isododecyloxy, sec-dodecyloxy, tert-dodecyloxy, neododecyloxy, isotridecyloxy, sec-tridecyloxy, tert-tridecyloxy, neotridecyloxy, isotetradecyloxy, sec-tetradecyloxy Tert-tetradecyloxy, neotetradecyloxy, 1-isobutyl-4-ethyloctyloxy, isopentadecyloxy, tert-pentadecadecyloxy, tert-pentadecadecyloxy, neopentadecadecyloxy, isohexadecadecyloxy, tert-hexadecyloxy, tert-hexadecyloxy, neohexadecyloxy, 1-methylpentadecadecyloxy, isohexadecadecyloxy, tert-hexadecyloxy, tert-hexadecyloxy, neohexadecyloxy, isohexadecadecyloxy, tert-octadecyloxy, tert-octadecyloxy, neooctadecyloxy, isohexadecadecyloxy, tert-octadecyloxy, neooctadecyloxy, isohexadecadecyloxy, tert-octadecyloxy, neooctadecyloxy, isohexadecadecyloxy, tert-octadecyloxy, neooctadecyloxy, etc.

[0231] Of these, methoxy is preferred as an alkoxy group.

[0232] In the general formula (CT1), as R C11 R C12 R C13 R C14 R C15 and R C16 The aryl group represented can be an aryl group with 6 to 30 carbon atoms (preferably 6 to 20, more preferably 6 to 16).

[0233] Specifically, examples of aryl groups include phenyl, naphthyl, phenanthryl, and biphenyl.

[0234] Among these, phenyl and naphthyl are preferred as aryl groups.

[0235] It should be noted that in the general formula (CT1), R C11 R C12 R C13 R C14 R C15 and R C16 The substituents mentioned above also include groups that have further substituents. Examples of such substituents include the atoms and groups exemplified above (e.g., halogen atoms, alkyl groups, alkoxy groups, aryl groups, etc.).

[0236] In the general formula (CT1), as R C11 R C12 R C13 R C14 R C15 and R C16 Two adjacent substituents interact with each other (e.g., R). C11 and R C12 mutual, R C13 and R C14 mutual, R C15 and R C16 Examples of groups that link the substituents in a hydrocarbon ring structure formed by mutual linkage include single bonds, 2,2'-methylene, 2,2'-ethylene, and 2,2'-1,2-vinylene, among which single bonds and 2,2'-methylene are preferred.

[0237] Here, as a hydrocarbon ring structure, specifically, examples include cycloalkane structures, cycloolefin structures, and cycloalkane polyene structures.

[0238] In the general formula (CT1), n ​​and m are preferably 1.

[0239] In general formula (CT1), from the perspective of forming a photosensitive layer (charge transport layer) with high charge transport capability, R is preferred. C11 R C12 R C13 R C14 R C15 and R C16 The radical represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or an alkoxy group having 1 to 20 carbon atoms, where m and n represent 1 or 2, more preferably R. C11 R C12 R C13 R C14 R C15 and R C16 This represents a hydrogen atom, and m and n represent 1.

[0240] That is, butadiene-based charge transport materials (CT1) are more preferably charge transport materials represented by the following structural formula (CT1A) (exemplary compound (CT1-3)).

[0241]

[0242] The following are specific examples of butadiene-based charge transport materials (CT1), but are not limited to them.

[0243]

[0244] It should be noted that the abbreviations in the above-described compounds have the following meanings. Additionally, the numbers preceding substituents indicate the substitution positions on the benzene ring.

[0245] CH3: Methyl

[0246] ·OCH3: Methoxy

[0247] Butadiene-based charge transport materials (CT1) can be used alone or in combination with two or more.

[0248] The benzidine-based charge transport material (CT2) is described.

[0249] The benzidine-based charge transport material (CT2) is the charge transport material represented by the following general formula (CT2).

[0250]

[0251] In general formula (CT2), R C21 R C22 and R C23 Each can independently represent 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.

[0252] In the general formula (CT2), R is used as C21 R C22 and R C23 Examples of halogen atoms include fluorine, chlorine, bromine, and iodine. Among these, fluorine and chlorine atoms are preferred as halogen atoms, and chlorine atoms are even more preferred.

[0253] In the general formula (CT2), R is used as C21 R C22 and R C23 The alkyl group represented can be a straight-chain or branched alkyl group with 1 to 10 carbon atoms (preferably 1 to 6, more preferably 1 to 4).

[0254] Examples of linear alkyl groups include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl.

[0255] Specifically, branched alkyl groups include isopropyl, isobutyl, sec-butyl, tert-butyl, isopentyl, neopentyl, tert-pentyl, isohexyl, sec-hexyl, tert-hexyl, isoheptyl, sec-heptyl, tert-heptyl, isooctyl, sec-octyl, tert-octyl, isononyl, sec-nonyl, tert-nonyl, isodel, sec-decyl, tert-decyl, etc.

[0256] Among these, lower alkyl groups such as methyl, ethyl, and isopropyl are preferred as alkyl groups.

[0257] In the general formula (CT2), R is used as C21 R C22 and R C23 The alkoxy group represented can be a straight-chain or branched alkoxy group with 1 to 10 carbon atoms (preferably 1 to 6, more preferably 1 to 4).

[0258] As linear alkoxy groups, examples include methoxy, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, octoxy, nonoxy, and decoxy.

[0259] As branched alkoxy groups, specific examples include isopropoxy, isobutoxy, sec-butoxy, tert-butoxy, isopentoxy, neopentoxy, tert-pentoxy, isohexoxy, sec-hexoxy, tert-hexoxy, isohexoxy, sec-heptoxy, tert-heptoxy, isooctoxy, sec-octoxy, tert-octoxy, isononoxy, sec-nonoxy, tert-nonoxy, isodeoxy, sec-decoxy, tert-decoxy, etc.

[0260] Of these, methoxy is preferred as an alkoxy group.

[0261] In the general formula (CT2), R is used as C21 R C22 and R C23 The aryl group represented can be an aryl group with 6 or more but less than 10 carbon atoms (preferably 6 or more but less than 9, more preferably 6 or more but less than 8).

[0262] Specifically, examples of aryl groups include phenyl and naphthyl groups.

[0263] Of these, phenyl is preferred as an aryl group.

[0264] It should be noted that in the general formula (CT2), R C21 R C22 and R C23 The substituents mentioned above also include groups that have further substituents. Examples of such substituents include the atoms and groups exemplified above (e.g., halogen atoms, alkyl groups, alkoxy groups, aryl groups, etc.).

[0265] In general formula (CT2), from the perspective of forming a photosensitive layer (charge transport layer) with high charge transport capability, R is preferred. C21 R C22 and R C23 Each of the following independently represents an alkyl group having 1 to 10 hydrogen atoms, more preferably R. C21 and R C23 Represents hydrogen atom, R C22 Alkyl groups (especially methyl groups) have 1 to 10 carbon atoms.

[0266] Specifically, the benzidine-based charge transport material (CT2) is particularly preferred to be the charge transport material represented by the following structural formula (CT2A) (exemplary compound (CT2-2)).

[0267]

[0268] The following examples illustrate benzidine-based charge transport materials (CT2), but are not limited to them.

[0269]

[0270] It should be noted that the abbreviations in the above-described compounds have the following meanings. Additionally, the numbers preceding substituents indicate the substitution positions on the benzene ring.

[0271] CH3: Methyl

[0272] C2H5: Ethyl

[0273] ·OCH3: Methoxy

[0274] ·OC2H5: ethoxy

[0275] Benzidine-based charge transport materials (CT2) can be used alone or in combination with two or more.

[0276] As polymeric charge transport materials, known materials with charge transport properties such as poly-N-vinylcarbazole and polysilane are used. Polyester-based polymeric charge transport materials disclosed in Japanese Patent Application Publication Nos. 8-176293 and 8-208820 are particularly preferred. It should be noted that the polymeric charge transport material can be used alone or in combination with an adhesive resin.

[0277] Examples of adhesive resins used in charge transport layers include polycarbonate resins, polyester resins, polyarylate resins, methacrylic resins, acrylic resins, polyvinyl chloride resins, polyvinylidene chloride resins, polystyrene resins, polyvinyl acetate resins, styrene-butadiene copolymers, vinylidene chloride-acrylonitrile copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinyl acetate-maleic anhydride copolymers, silicone resins, silicone-modified alkyd resins, phenol-formaldehyde resins, styrene-modified alkyd resins, poly-N-vinylcarbazole, and polysilanes. Among these, polycarbonate resins or polyarylate resins are suitable as adhesive resins. These adhesive resins can be used alone or in combination of two or more.

[0278] It should be noted that the mixing ratio of the charge transport material and the adhesive resin is preferably 10:1 to 1:5 by mass.

[0279] The charge transport layer may also contain other known additives.

[0280] There are no particular limitations on the formation of the charge transport layer. Using known formation methods, for example, a coating film of a charge transport layer forming liquid can be formed by adding the above-mentioned components to a solvent, drying the coating film, and heating it as needed, thereby forming the charge transport layer.

[0281] Examples of solvents used in preparing coating solutions for charge transport layer formation include aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; ketones such as acetone and 2-butanone; halogenated aliphatic hydrocarbons such as dichloromethane, chloroform, and vinyl chloride; and cyclic or linear ethers such as tetrahydrofuran and diethyl ether. These solvents can be used alone or in combination of two or more.

[0282] Common methods for coating a charge transport layer onto a charge generation layer include scraper coating, wire rod coating, spraying, dip coating, microsphere coating, air knife coating, and curtain coating.

[0283] The thickness of the charge transport layer is set, for example, preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 45 μm or less, and even more preferably 20 μm or more and 42 μm or less.

[0284] (protective layer)

[0285] A protective layer is applied to the photosensitive layer as needed. This protective layer may be for purposes such as preventing chemical changes in the photosensitive layer during charging or further improving the mechanical strength of the photosensitive layer.

[0286] Therefore, the protective layer can be a layer composed of a cured film (crosslinked film). Examples of such layers include those shown in 1) or 2) below.

[0287] 1) A layer consisting of a cured film of a composition containing a reactive group charge transport material having a reactive group and a charge transport backbone within the same molecule (i.e., a layer containing a polymer or crosslinker of the reactive group charge transport material).

[0288] 2) A layer consisting of a cured film comprising a non-reactive charge transport material and a non-reactive charge transport material containing reactive groups but lacking a charge transport framework (i.e., a layer comprising a polymer or crosslinker of the non-reactive charge transport material containing reactive groups and a layer comprising a non-reactive charge transport material).

[0289] Examples of reactive groups that can be used as charge transport materials include chain polymerizable groups, epoxy groups, -OH, -OR [where R represents alkyl], -NH2, -SH, -COOH, and -SiR. Q1 3-Qn (OR Q2 ) Qn [wherein, R] Q1 R represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group. Q2 [Represents hydrogen atoms, alkyl groups, trialkylsilyl groups, etc. Qn represents an integer from 1 to 3] and other known reactive groups.

[0290] As a chain polymerizable group, there is no particular limitation as long as it is a functional group capable of free radical polymerization, such as a functional group having at least a carbon double bond. Specifically, examples include groups containing at least one of vinyl, vinyl ether, vinyl thioether, vinyl phenyl, acryloyl, methacryloyl, and their derivatives. Among these, due to their excellent reactivity, groups containing at least one of vinyl, vinyl phenyl, acryloyl, methacryloyl, and their derivatives are preferred as chain polymerizable groups.

[0291] As a charge transport framework for charge transport materials containing reactive groups, there are no particular limitations as long as it is a known structure in electron photosensitive materials. For example, the following structures can be cited: the framework is derived from nitrogen-containing hole transport compounds such as triarylamine compounds, benzidine compounds, and hydrazone compounds, and has a structure conjugated with nitrogen atoms. Among these, the triarylamine framework is preferred.

[0292] These reactive charge transport materials, non-reactive charge transport materials, and non-reactive charge transport materials with reactive groups and charge transport frameworks can be selected from known materials.

[0293] The protective layer may contain other known additives.

[0294] There are no particular restrictions on the formation of the protective layer. Known formation methods can be used, such as forming a coating film of a protective layer forming liquid by adding the above-mentioned components to a solvent, drying the coating film, and performing curing treatments such as heating as needed to form the protective layer.

[0295] Examples of solvents used to prepare coating solutions for forming protective layers 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 isopropanol and butanol. These solvents can be used alone or in combination of two or more.

[0296] It should be noted that the coating liquid used to form the protective layer can also be a solvent-free coating liquid.

[0297] Common methods for applying a protective layer coating liquid onto a photosensitive layer (e.g., a charge transport layer) include dip coating, extrusion coating, wire rod coating, spraying, scraper coating, blade coating, and curtain coating.

[0298] The thickness of the protective layer is set, for example, in a range preferably 1 μm to 20 μm, more preferably 2 μm to 10 μm.

[0299] [Image forming apparatus (and processing box)]

[0300] The image forming apparatus of this embodiment includes: an electrophotographic photosensitive element; a charging mechanism for charging the surface of the electrophotographic photosensitive element; an electrostatic latent image forming mechanism for forming an electrostatic latent image on the charged surface of the electrophotographic photosensitive element; a developing mechanism for forming a toner image by developing the electrostatic latent image formed on the surface of the electrophotographic photosensitive element using a developing agent containing a toner; and a transfer mechanism for transferring the toner image to the surface of a recording medium. Furthermore, the electrophotographic photosensitive element of this embodiment described above is suitable as the electrophotographic photosensitive element.

[0301] The image forming apparatus of this embodiment is applicable to the following known image forming apparatuses: an apparatus having a fixing mechanism for fixing a toner image transferred to the surface of a recording medium; an apparatus for a direct transfer method that directly transfers a toner image formed on the surface of an electrophotographic photosensitive body to the recording medium; an apparatus for an intermediate transfer method that first transfers a toner image formed on the surface of an electrophotographic photosensitive body to the surface of an intermediate transfer body, and then transfers the toner image transferred to the surface of the intermediate transfer body to the surface of the recording medium a second time; an apparatus having a cleaning mechanism for cleaning the surface of an electrophotographic photosensitive body before charging after the toner image transfer; an apparatus having a static removal mechanism for removing static electricity by irradiating static removal light onto the surface of an electrophotographic photosensitive body before charging after the toner image transfer; an apparatus having an electrophotographic photosensitive body heating member for increasing the temperature of the electrophotographic photosensitive body and decreasing the relative humidity; and so on.

[0302] In the case of an intermediate transfer method apparatus, the transfer mechanism may be configured as follows: an intermediate transfer body that transfers a toner image onto a surface, a primary transfer mechanism that transfers a toner image formed on the surface of an electrophotographic photosensitive body to the surface of the intermediate transfer body in one step, and a secondary transfer mechanism that transfers the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium in a second step.

[0303] The image forming apparatus of this embodiment can be either a dry developing image forming apparatus or a wet developing image forming apparatus (a developing method using liquid developer).

[0304] It should be noted that in the image forming apparatus of this embodiment, the portion including the electrophotographic photosensitive element can be a detachable cartridge structure (processing cartridge) relative to the image forming apparatus. For example, a processing cartridge including the electrophotographic photosensitive element of this embodiment can be suitably used as the processing cartridge. It should also be noted that, in addition to the electrophotographic photosensitive element, the processing cartridge may include at least one of, for example, selected from the group consisting of a charging mechanism, an electrostatic latent image forming mechanism, a developing mechanism, and a transfer mechanism.

[0305] The following shows an example of the image forming apparatus of this embodiment, but it is not limited thereto. It should be noted that only the main parts shown in the figure are described, and the description of other parts is omitted.

[0306] Figure 2 This is a schematic configuration diagram illustrating an example of the image forming apparatus of this embodiment.

[0307] like Figure 2 As shown, the image forming apparatus 100 of this embodiment includes: a processing cartridge 300 with an electrophotographic photosensitive element 7; an exposure apparatus 9 (an example of an electrostatic latent image forming mechanism); a transfer apparatus 40 (a primary transfer apparatus); and an intermediate transfer body 50. It should be noted that in the image forming apparatus 100, the exposure apparatus 9 is positioned to expose the electrophotographic photosensitive element 7 through the opening of the processing cartridge 300, and the transfer apparatus 40 is positioned opposite the electrophotographic photosensitive element 7 across the intermediate transfer body 50. The intermediate transfer body 50 is arranged such that a portion of it contacts the electrophotographic photosensitive element 7. Although not shown, a secondary transfer apparatus is also included to transfer the toner image transferred to the intermediate transfer body 50 to a recording medium (e.g., paper). It should be noted that the intermediate transfer body 50, the transfer apparatus 40 (a primary transfer apparatus), and the secondary transfer apparatus (not shown) are examples of transfer mechanisms.

[0308] Figure 2 The processing cartridge 300 integrally houses the electrophotographic photosensitive element 7, the charging device 8 (an example of a charging mechanism), the developing device 11 (an example of a developing mechanism), and the cleaning device 13 (an example of a cleaning mechanism) within a housing. The cleaning device 13 has a cleaning blade (an example of a cleaning component) 131, which is arranged to contact the surface of the electrophotographic photosensitive element 7. It should be noted that the cleaning component may also be a conductive or insulating fibrous component, rather than the cleaning blade 131, and may be used alone or in conjunction with the cleaning blade 131.

[0309] It should be noted that, in Figure 2 In the example shown, as an image forming apparatus, there is a fibrous component 132 (roller-shaped) for supplying lubricating material 14 to the surface of the electrophotographic photosensitive element 7 and a fibrous component 133 (flat brush-shaped) for assisting in cleaning, but these components are configured as needed.

[0310] The components of the image forming apparatus of this embodiment will be described below.

[0311] -Charging device-

[0312] As a charging device 8, for example, a contact charger is used, which utilizes conductive or semi-conductive charging rollers, charging brushes, charging films, charging rubber scrapers, charging tubes, etc. Alternatively, non-contact roller chargers, corona wire chargers utilizing corona discharge, or corona tube chargers, and other known chargers, can also be used.

[0313] -Exposure device-

[0314] Examples of exposure devices 9 include optical systems that use semiconductor lasers, LED light, liquid crystal shutter light, etc., to expose the surface of an electrophotographic photosensitive object 7 according to a given image. The wavelength of the light source is set within the spectrophotometric sensitivity range of the electrophotographic photosensitive object. Near-infrared wavelengths with oscillations around 780 nm are predominantly used for semiconductor lasers. However, this is not limited to this wavelength; lasers with oscillations around 600 nm or blue lasers with oscillations between 400 nm and 450 nm can also be used. Furthermore, for color image formation, surface-emitting laser sources capable of outputting multiple beams are also effective.

[0315] -Developing apparatus-

[0316] As a developing apparatus 11, common developing apparatuses that use contact or non-contact developing agents can be cited as examples. There are no particular limitations on the developing apparatus 11 as long as it has the aforementioned functions, and it can be selected according to the purpose. For example, known developing devices that use brushes, rollers, etc., to adhere single-component or two-component developing agents to the electrophotographic photosensitive element 7 can be cited. Among these, a developing roller with developing agent retained on its surface is preferred.

[0317] The developer used in the developing apparatus 11 can be a single-component developer containing only toner, or a two-component developer containing both toner and carrier. Furthermore, the developer can be magnetic or non-magnetic. Known developers can be used.

[0318] -Cleaning Device-

[0319] The cleaning device 13 is a device that uses a cleaning scraper with a cleaning scraper 131.

[0320] It should be noted that in addition to the cleaning scraper method, brush cleaning and simultaneous development and cleaning methods can also be used.

[0321] -Transfer Device-

[0322] As a transfer device 40, examples include contact type transfer chargers that use belts, rollers, films, rubber squeegees, etc., corona wire transfer chargers that utilize corona discharge, or corona tube transfer chargers, which are all known transfer chargers.

[0323] -Intermediate Transfer Material-

[0324] As the intermediate transfer body 50, a strip-shaped transfer body (intermediate transfer tape) containing polyimide, polyamide-imide, polycarbonate, polyarylate, polyester, rubber, etc., which imparts semi-conductivity, is used. In addition to the strip shape, a drum-shaped transfer body can also be used as the intermediate transfer body.

[0325] Figure 3 This is a schematic configuration diagram illustrating another example of the image forming apparatus of this embodiment.

[0326] Figure 3 The image forming apparatus 120 shown is a multicolor image forming apparatus equipped with four processing cartridges 300 arranged in series. In the image forming apparatus 120, the four processing cartridges 300 are each arranged side by side on the intermediate transfer body 50, forming a configuration where one electrophotographic photosensitive element is used for each color. It should be noted that, except for being arranged in series, the image forming apparatus 120 has the same configuration as the image forming apparatus 100.

[0327] [Example]

[0328] The following examples provide a detailed description of this implementation method, but this implementation method is not limited to these examples in any way. It should be noted that, unless otherwise stated, "parts" and "%" in the following description refer to mass.

[0329] <Example 1>

[0330] 100 parts by weight of zinc oxide (trade name: MZ 300, manufactured by TAYCA Co., Ltd.), 10 parts by weight of a 10% by weight toluene solution of N-2-(aminoethyl)-3-aminopropyltriethoxysilane as a silane coupling agent, and 200 parts by weight of toluene were mixed and stirred, and refluxed for 2 hours. Then, the toluene was removed by vacuum distillation at 10 mmHg, and the surface was calcined at 135°C for 2 hours for surface treatment.

[0331] 33 parts by mass of surface-treated zinc oxide, 6 parts by mass of end-capped isocyanate (trade name: Sumidur 3175, manufactured by Sumitomo-Bayer Urethane Co., Ltd.), 1 part by mass of the compound represented by the following structural formula (AK-1) as an electron acceptor compound, and 25 parts by mass of methyl ethyl ketone were mixed for 30 minutes. Then, 5 parts by mass of butyral resin (trade name: S-LECBM-1, manufactured by Sekisui Chemicals Co., Ltd.), 3 parts by mass of organosilicon microspheres (trade name: TOSPEARL120, manufactured by Momentive Performance Materials Co., Ltd.), and 0.01 parts by mass of silicone oil (trade name: SH29PA, manufactured by Dow Corning Co., Ltd.) as a leveling agent were added and dispersed in a sand mill for 3 hours to obtain a coating liquid for forming a base coating.

[0332]

[0333] Furthermore, the base coating liquid was applied to an aluminum substrate with a diameter of 30 mm, a length of 365 mm, and a thickness of 1 mm using an immersion coating method, and then dried and cured at 180°C for 30 minutes to obtain a base coating with a thickness of 25 μm.

[0334] Next, a mixture consisting of a hydroxyl gallium phthalocyanine pigment (HOGaPc) as a charge-generating material, the following specific copolymer (1) as an adhesive resin, and acetone is mixed with... Glass beads (50% filling rate) were simultaneously placed into a 100mL glass bottle and dispersed using a coating shaker for 2.5 hours to obtain a coating liquid for forming a charge generation layer.

[0335] Specific copolymer (1): a vinyl copolymer composed of the following structural units in proportions as shown in Table 1: a chlorine-containing copolymer represented by the above general formula (1) and R 11 ~R 13 All are structural units of hydrogen atoms; the acyloxy group is represented by the above general formula (2) and R 21 ~R 23 All are hydrogen atoms, R 24 The structural unit is the methyl group; and the structural unit is the phthalic acid ring without other substituents, which is a component of aromatic polycarboxylic acids and is directly bonded to the main chain.

[0336] It should be noted that the weight-average molecular weight and THF solubility of a specific copolymer (1) are shown in Table 1.

[0337] Here, relative to the total amount of hydroxy gallium phthalocyanine pigment and specific copolymer (1) contained in the coating solution for forming the charge generation layer, the content of hydroxy gallium phthalocyanine pigment is 60% by mass and the concentration of solid components in the coating solution for forming the charge generation layer is 6.0% by mass.

[0338] It should be noted that the above-mentioned hydroxy gallium phthalocyanine pigment is a V-type hydroxy gallium phthalocyanine pigment (with a maximum peak wavelength of 820 nm, average particle size of 0.12 μm, maximum particle size of 0.2 μm, and specific surface area of ​​60 m² in the spectroscopic absorption spectrum in the wavelength region of 600 nm to 900 nm). 2 The V-type hydroxy gallium phthalocyanine pigment has diffraction peaks at least at Bragg angles (2θ±0.2°) of 7.3°, 16.0°, 24.9°, and 28.0° in the X-ray diffraction spectrum of the characteristic X-rays using Cukα.

[0339] The obtained charge generation layer was impregnated and coated onto the base layer with a coating solution and dried at 150°C for 5 minutes to form a charge generation layer with a film thickness of 0.14 μm.

[0340] Next, 12 parts by mass of the charge transport material represented by the following structural formula (CT1A), 28 parts by mass of the charge transport material represented by the following structural formula (CT2A), and 60 parts by mass of bisphenol Z-type polycarbonate resin (molecular weight 40,000) were added to 340 parts by weight of tetrahydrofuran for dissolution to obtain a coating solution for forming a charge transport layer.

[0341] The obtained charge transport layer was coated onto the charge generation layer by immersion in a coating solution and dried at 150°C for 40 minutes, thereby forming a charge transport layer with a film thickness of 40 μm.

[0342]

[0343] After the above steps, the electrophotographic photosensitive material of Example 1 is obtained.

[0344] <Examples 2-7>

[0345] As shown in Table 1, the proportions of each structural unit in a specific copolymer (1) were changed, and the resulting specific copolymers (2) to (7) were used. Otherwise, an electron photosensitive material was obtained in the same manner as in Example 1.

[0346] It should be noted that the weight-average molecular weight and THF solubility of specific copolymers (2) to (7) are shown in Table 1.

[0347] <Examples 8-14>

[0348] Except for changing the type of charge-generating material used in the preparation of the coating liquid for forming the charge-generating layer to gallium chloride phthalocyanine pigment (ClGaPc), each electron photosensitive material was obtained in the same manner as in Examples 1 to 7.

[0349] <Examples 15-21>

[0350] Except for changing the type of charge-generating material used in the preparation of the coating liquid for forming the charge-generating layer to titanium phthalocyanine pigment (TiOPc), each electron photosensitive material was obtained in the same manner as in Examples 1 to 7.

[0351] <Comparative Example 1>

[0352] The adhesive resin used in the preparation of the coating liquid for forming the charge generation layer is a vinyl copolymer (C1) as described above, otherwise the same as in Example 1 is used to obtain the electrophotographic photosensitive material.

[0353] Vinyl copolymer (C1): A vinyl copolymer composed of the following components in proportions shown in Table 1: a chlorine-containing component represented by the above general formula (1) and R 11 ~R 13 All are structural units of hydrogen atoms; the acyloxy group is represented by the above general formula (2) and R 21 ~R 23 All are hydrogen atoms, R 24 The structural unit of methyl; and components derived from maleic acid as other polycarboxylic acid components.

[0354] It should be noted that the weight-average molecular weight and THF solubility of the vinyl copolymer (C1) are shown in Table 1.

[0355] <Comparative Examples 2-7>

[0356] As shown in Table 1, the proportions of each structural unit in the vinyl copolymer (C1) were changed to use the obtained vinyl copolymers (C2) to (C7). Otherwise, the same electron photosensitive material as in Comparative Example 1 was obtained.

[0357] It should be noted that the weight-average molecular weight and THF solubility of the vinyl copolymers (C2) to (C7) are shown in Table 1.

[0358] <Comparative Examples 8-9>

[0359] As shown in Table 1, the proportions of each structural unit in a specific copolymer (1) were changed to obtain specific copolymers (8) to (9), and an electron photosensitive material was obtained in the same manner as in Example 1.

[0360] It should be noted that the weight-average molecular weight and THF solubility of specific copolymers (8) to (9) are shown in Table 1.

[0361] <Comparative Example 10>

[0362] The adhesive resin used in the preparation of the coating liquid for forming the charge generation layer is the following vinyl copolymer (C8), otherwise the same as in Example 1 is used to obtain the electrophotographic photosensitive material.

[0363] Vinyl copolymer (C8): A vinyl copolymer composed of the following components in proportions shown in Table 1: a chlorine-containing component represented by the above general formula (1) and R 11 ~R 13 All are structural units of hydrogen atoms; the acyloxy group is represented by the above general formula (2) and R 21 ~R 23 All are hydrogen atoms, R 24 The structural unit is methyl; and the components derived from hydroxybutyl acrylate as other polycarboxylic acid components.

[0364] <Comparative Example 11>

[0365] As the adhesive resin used in the preparation of the coating liquid for forming the charge generation layer, the proportion of each structural unit in the vinyl copolymer (C8) was changed as shown in Table 1, and the resulting vinyl copolymer (C9) was used. Otherwise, the same as in Comparative Example 10, an electron photosensitive material was obtained.

[0366] It should be noted that the weight-average molecular weight and THF solubility of the vinyl copolymer (C9) are shown in Table 1.

[0367] <Comparative Examples 12-18>

[0368] Except for changing the type of charge-generating material used in the preparation of the coating liquid for forming the charge-generating layer to gallium chloride phthalocyanine pigment (ClGaPc), each electron photosensitive material was obtained in the same manner as in Comparative Examples 1 to 7.

[0369] <Comparative Examples 19-25>

[0370] Except for changing the type of charge-generating material used in the preparation of the coating liquid for forming the charge-generating layer to titanium phthalocyanine pigment (TiOPc), each electron photosensitive material was obtained in the same manner as in Comparative Examples 1 to 7.

[0371] [Table 1]

[0372]

[0373] <Evaluation>

[0374] (Evaluation of image density difference)

[0375] The electrophotographic photosensitive elements obtained in each example were mounted in an electrophotographic image forming apparatus (manufactured by Fuji Xerox: ApeosPort-V C7776), and 1000 full-page halftone images (cyan color full-page halftone images) with an image density of 70% were output on A3-sized paper. It should be noted that all image output was carried out in an environment of 10°C and 15% RH.

[0376] For the 1000th full-screen halftone image, image density was measured at five locations on each side of the region corresponding to one end and the other end of the electrophotographic sensor's axis using an image density meter (X-Rite 938: manufactured by X-Rite). The values ​​were averaged, and the image density difference (i.e., the absolute value of "average image density at one end" - "average image density at the other end") was calculated. The results were then evaluated according to the following criteria. The results are shown in Tables 2 and 3. It should be noted that G2 represents the permissible range.

[0377] -Evaluation Criteria-

[0378] G0: 0 ≤ image density difference ≤ 0.05

[0379] G1: 0.05 < image density difference ≤ 0.1

[0380] G2: 0.1 < image density difference ≤ 0.2

[0381] G3: 0.2 < image density difference ≤ 0.25

[0382] G4: 0.25 < image density difference ≤ 0.3

[0383] G5: 0.3 < image density difference ≤ 0.35

[0384] G6: 0.35 < Image density difference

[0385] (Evaluation of ISO sensitivity)

[0386] The evaluation of photosensitivity in each example of an electrophotographic sensor is in the form of half-attenuation exposure when the electrophotographic sensor is charged to +800V.

[0387] Specifically, firstly, using an electrostatic photocopying paper testing apparatus (EPA-8100 electrostatic analyzer, manufactured by Kawaguchi Electric Co., Ltd.), the electrophotographic photoresists of each example were charged to +800V at an environment of 20°C and 40% relative humidity. Subsequently, a monochromator was used to convert tungsten lamp light into 800nm ​​monochromatic light, at a concentration of 1μW / cm² on the surface of the electrophotographic photoresist.2 The amount of light was adjusted for irradiation. Furthermore, the surface potential Vo (V) of the electrophotographic photoreceptor immediately after charging was measured and reduced to half the half-attenuation exposure (μJ / cm²) upon light irradiation. 2 The obtained half-attenuation exposure values ​​are classified according to the following criteria. The results are shown in Tables 2 and 3.

[0388] G1: Half-attenuation exposure is 0.10 μJ / cm 2 the following.

[0389] G2: Half-attenuation exposure greater than 0.10 μJ / cm 2 And it is 0.13 μJ / cm 2 the following.

[0390] G3: Half-attenuation exposure greater than 0.13 μJ / cm 2 And it is 0.15 μJ / cm 2 the following.

[0391] G4: Half-attenuation exposure greater than 0.15 μJ / cm 2 And it is 0.18 μJ / cm 2 the following.

[0392] G5: Half-attenuation exposure greater than 0.18 μJ / cm 2 .

[0393] In each example, the A / C values ​​when the proportion of the polycarboxylic acid component relative to all components of a particular copolymer or vinyl copolymer is A by mass% and the content of the charge-generating material relative to the particular copolymer or vinyl copolymer is C by mass% are shown together in Tables 2-3.

[0394] [Table 2]

[0395]

[0396] [Table 3]

[0397]

[0398] As can be seen from the above results, compared with the electrophotographic photoreceptor of the comparative example, the image density difference along the axial direction of the electrophotographic photoreceptor in this embodiment is suppressed.

Claims

1. An electrophotographic photosensitive material having a conductive substrate, a charge generation layer, and a charge transport layer, The charge-generating layer is disposed on the conductive substrate and contains a charge-generating material and a vinyl copolymer. The vinyl copolymer contains structural units having chlorine, structural units having acyloxy groups, and structural units having aromatic polycarboxylic acid structures. The proportion of the structural units having chlorine relative to all structural units is 80% by mass or more, and the proportion of the structural units having aromatic polycarboxylic acid structures relative to all structural units is 0.5% by mass or more. The charge transport layer is disposed on the charge generation layer and contains charge transport material and adhesive resin.

2. The electrophotographic photosensitive material as described in claim 1, wherein, The proportion of the chlorine-containing structural units is 88% by mass or less relative to all the structural units constituting the above-mentioned vinyl copolymer.

3. The electrophotographic photosensitive material as described in claim 2, wherein, The proportion of the chlorine-containing structural units is 80% to 87% by mass relative to all the structural units constituting the vinyl copolymer.

4. An electrophotographic photosensitive material having a conductive substrate, a charge generation layer, and a charge transport layer, The charge-generating layer is disposed on the conductive substrate and contains a charge-generating material and a vinyl copolymer. The vinyl copolymer contains structural units having chlorine, structural units having acyloxy groups, and structural units having aromatic polycarboxylic acid structures. The solubility of the vinyl copolymer in 100 parts by mass of tetrahydrofuran at 30°C is less than 10 parts by mass. The charge transport layer is disposed on the charge generation layer and contains charge transport material and adhesive resin.

5. The electrophotographic photosensitive material as described in any one of claims 1 to 4, wherein, Let A be the mass percentage of the structural unit having the aromatic polycarboxylic acid structure relative to all structural units constituting the vinyl copolymer, and let C be the mass percentage of the charge-generating material relative to the vinyl copolymer, then the value of A / C is 3.00 × 10⁻⁶. -3 Above 1.40×10 -2 the following.

6. The electrophotographic photosensitive material as described in any one of claims 1 to 5, wherein, The above-mentioned chlorine-containing structural unit is represented by the following general formula (1), and the above-mentioned acyl-oxygen-containing structural unit is represented by the following general formula (2). In the above general formula (1), R 11 ~R 13 Each of the above general formulas (2) independently represents an alkyl group having 1 to 5 hydrogen atoms or carbon atoms, where R 21 ~R 23 Each independently represents an alkyl group having 1 to 5 hydrogen atoms or carbon atoms, R 24 Alkyl groups having 1 to 5 carbon atoms.

7. The electrophotographic photosensitive material as described in claim 6, wherein, In the above general formula (1), R 11 ~R 13 All are hydrogen atoms, and R in the above general formula (2) 21 ~R 23 All are hydrogen atoms, R 24 It is a methyl group.

8. The electrophotographic photosensitive material as described in any one of claims 1 to 7, wherein, The structural unit with the aromatic polycarboxylic acid structure mentioned above is a structural unit with the phthalic acid structure.

9. A processing cartridge that is mounted and dismounted in an image forming apparatus, comprising the electrophotographic photosensitive element according to any one of claims 1 to 8.

10. An image forming apparatus comprising: Electrophotographic photosensitive material as described in any one of claims 1 to 8; The charging mechanism charges the surface of the aforementioned electrophotographic photosensitive material. An electrostatic latent image forming mechanism forms an electrostatic latent image on the surface of the aforementioned charged electrophotographic photosensitive material; The developing unit uses a developer containing a toner to develop the electrostatic latent image formed on the surface of the aforementioned electrophotographic photoreceptor, thereby forming a toner image; as well as The transfer mechanism transfers the toner image onto the surface of the recording medium.

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