ELECTROPHOTOGRAPHIC PHOTORECEPTOR, PROCESS CARTRIDGE, AND IMAGE FORMING APPARATUS

Abstract

An electrophotographic photoreceptor includes a conductive substrate; and a photosensitive layer disposed on the conductive substrate and including a charge generation layer and a charge transport layer, in which the charge transport layer has an average thickness of 30 μm or greater, the charge transport layer contains a polyarylate resin, and an absorption spectrum measured by peeling off the photosensitive layer and dissolving the photosensitive layer in tetrahydrofuran satisfies Expression (1) and Expression (2),

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2023-095896 filed Jun. 9, 2023.

BACKGROUND

(i) Technical Field

The present invention relates to an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus.

(ii) Related Art

JP2016-031517A discloses an electrophotographic photoreceptor including a support, an undercoat layer, a charge generation layer, and a charge transport layer, in which the charge generation layer contains at least one of a titanyl phthalocyanine pigment or a gallium phthalocyanine pigment, the charge transport layer contains at least one of a polycarbonate resin or a polyarylate resin, and a non-image forming region includes a region a where the film thickness of the charge generation layer is less than the film thickness of the charge generation layer in an image forming region.

JP2021-004948A discloses an electrophotographic photoreceptor including a cylindrical support, a charge generation layer, and a charge transport layer, in which a region of the charge generation layer from a central position of an image forming region to an end position of the image forming region in an axial direction of the cylindrical support is divided into five equal parts, and in a case where the average values of the film thicknesses of the charge generation layer in each of the equally divided regions are respectively defined as d11, d12, d13, d14, and d15 in order from the central position of the image forming region toward the end position of the image forming region, the film thicknesses of the charge generation layer satisfy a relationship of d11<d12<d13<d14<d15, a region of the charge transport layer from a central position of an image forming region to an end position of the image forming region in an axial direction of the cylindrical support is divided into five equal parts, and in a case where the average values of the film thicknesses of the charge transport layer in each of the equally divided regions are respectively defined as d21, d22, d23, d24, and d25 in order from the central position of the image forming region toward the end position of the image forming region, the film thicknesses of the charge transport layer satisfy a relationship of d21>d22>d23>d24>d25.

US2021/0124277A discloses a method of forming a charge generation layer on a photoconductive drum, including preparing a dispersion liquid containing a charge generation composition, dipping an elongated support element in the dispersion liquid, taking out a first portion of the elongated support element from the dispersion liquid at a first speed, coating the first portion with the charge generation composition at a first thickness, taking out a second portion of the elongated support element from the dispersion liquid at a second speed that is higher than the first speed, and coating the second portion with the charge generation composition at a second thickness that is greater than the first thickness.

SUMMARY

Aspects of non-limiting embodiments of the present disclosure relate to an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus that has excellent abrasion resistance and is unlikely to cause charging unevenness, as compared with an electrophotographic photoreceptor which does not satisfy one or both of Expression (1) and Expression (2).

Aspects of certain non-limiting embodiments of the present disclosure address the above advantages and/or other advantages not described above. However, aspects of the non-limiting embodiments are not required to address the advantages described above, and aspects of the non-limiting embodiments of the present disclosure may not address advantages described above.

Specific means for achieving the above-described object includes the following aspects. Each formula representing a compound is the same as the formula having the same number described below.

According to an aspect of the present disclosure, there is provided an electrophotographic photoreceptor including: a conductive substrate; and a photosensitive layer disposed on the conductive substrate and including a charge generation layer and a charge transport layer, in which the charge transport layer has an average thickness of 30 μm or greater, the charge transport layer contains a polyarylate resin, and an absorption spectrum measured by peeling off the photosensitive layer and dissolving the photosensitive layer in tetrahydrofuran satisfies Expression (1) and Expression (2),

$\begin{array}{cc}\mathrm{Iu}\le 0.95\times Im& \mathrm{Expression}\left(1\right)\end{array}$ $\begin{array}{cc}1.05\times Im\le I1& \mathrm{Expression}\left(2\right)\end{array}$

• • in a case where a total length of the electrophotographic photoreceptor in an axial direction is defined as L, Im represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled from a center of the electrophotographic photoreceptor in the axial direction, Iu represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the electrophotographic photoreceptor in the axial direction toward one end, and Il represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the electrophotographic photoreceptor in the axial direction toward the other end.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein:

FIG. 1 is a partial cross-sectional view showing an example of a layer configuration of an electrophotographic photoreceptor according to the present exemplary embodiment;

FIG. 2 is a schematic configuration view showing an example of an image forming apparatus according to the present exemplary embodiment; and

FIG. 3 is a schematic configuration view showing another example of the image forming apparatus according to the present exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will be described. The following descriptions and examples merely illustrate the exemplary embodiments, and do not limit the scope of the exemplary embodiments.

In the present disclosure, a numerical range shown using “to” indicates a range including numerical values described before and after “to” as a minimum value and a maximum value.

In a numerical range described in a stepwise manner in the present disclosure, an upper limit value or a lower limit value described in a certain numerical range may be replaced with an upper limit value or a lower limit value in another numerical range described in a stepwise manner. Further, in a numerical range described in the present disclosure, an upper limit value or a lower limit value described in the numerical range may be replaced with a value shown in examples.

In the present disclosure, the meaning of the term “step” includes not only an independent step but also a step whose intended purpose is achieved even in a case where the step is not clearly distinguished from other steps.

In the present disclosure, in a case where an exemplary embodiment is described with reference to drawings, the configuration of the exemplary embodiment is not limited to the configuration shown in the drawings. In addition, the sizes of members in each drawing are conceptual and the relative relation in the sizes between the members is not limited thereto.

In the present disclosure, each component may include a plurality of kinds of substances corresponding to each component. In the present disclosure, in a case where a plurality of kinds of substances corresponding to each component in a composition are present, the amount of each component in the composition indicates the total amount of the plurality of kinds of substances present in the composition unless otherwise specified.

In the present disclosure, each component may include a plurality of kinds of particles corresponding to each component. In a case where a plurality of kinds of particles corresponding to each component are present in a composition, the particle diameter of each component indicates the value of a mixture of the plurality of kinds of particles present in the composition, unless otherwise specified.

In the present disclosure, an alkyl group and an alkylene group are any of linear, branched, or cyclic unless otherwise specified.

In the present disclosure, a hydrogen atom in an organic group, an aromatic ring, a linking group, an alkyl group, an alkylene group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, or the like may be substituted with a halogen atom.

In the present disclosure, in a case where a compound is represented by a structural formula, the compound may be represented by a structural formula in which symbols (C and H) representing a carbon atom and a hydrogen atom in a hydrocarbon group and/or a hydrocarbon chain are omitted.

In the present disclosure, the term “constitutional unit” of a copolymer or a resin has the same definition as that for a monomer unit.

In the present disclosure, the term “axial direction” of an electrophotographic photoreceptor denotes a direction in which a rotation axis of the electrophotographic photoreceptor extends, and the term “circumferential direction” of the electrophotographic photoreceptor denotes a rotation direction of the electrophotographic photoreceptor.

Electrophotographic Photoreceptor

An electrophotographic photoreceptor (hereinafter, also referred to as “photoreceptor”) according to the present exemplary embodiment includes a conductive substrate, and a photosensitive layer disposed on the conductive substrate and including a charge generation layer and a charge transport layer.

FIG. 1 is a partial cross-sectional view schematically showing an example of a layer configuration of a photoreceptor according to the present exemplary embodiment. A photoreceptor 10A shown in FIG. 1 has a structure in which an undercoat layer 2, a charge generation layer 3, and a charge transport layer 4 are laminated in this order on a conductive substrate 1, and the charge generation layer 3 and the charge transport layer 4 constitute a photosensitive layer 5 (so-called function separation type photosensitive layer). The photoreceptor 10A may include an interlayer (not shown) between the undercoat layer 2 and the charge generation layer 3. The undercoat layer 2 may or may not be present.

In the photoreceptor according to the present exemplary embodiment, the charge transport layer has an average thickness of 30 μm or greater, the charge transport layer contains a polyarylate resin, and an absorption spectrum measured by peeling off the photosensitive layer and dissolving the photosensitive layer in tetrahydrofuran satisfies Expression (1) and Expression (2).

$\begin{array}{cc}\mathrm{Iu}\le 0.95\times Im& \mathrm{Expression}\left(1\right)\end{array}$ $\begin{array}{cc}1.05\times \mathrm{Im}\le I1& \mathrm{Expression}\left(2\right)\end{array}$

In a case where a total length of the photoreceptor in an axial direction is defined as L, Im represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled from a center of the photoreceptor in the axial direction, Iu represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the photoreceptor in the axial direction toward one end, and Il represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the photoreceptor in the axial direction toward the other end.

Since the photoreceptor according to the present exemplary embodiment has the above-described configuration, the photoreceptor has excellent abrasion resistance and is unlikely to cause charging unevenness. The mechanism is assumed as follows.

For example, it is desirable that the photosensitive layer is thick and that the charge transport layer is 30 μm or greater, in order to extend the life of the photoreceptor. Further, from the viewpoint of the abrasion resistance of the photosensitive layer, for example, it is desirable to use a polyarylate resin as the binder resin of the charge transport layer. It is more beneficial that the molecular weight of the polyarylate resin is large in terms of the abrasion resistance.

Meanwhile, the photosensitive layer is typically formed by being dipped and coated with a coating solution under a condition that the axial direction of the conductive substrate is set as the gravity direction. The polyarylate resin is a resin that is likely to be viscous due to the molecular structure thereof (stacking of aromatic rings), and the polyarylate resin is more likely to be viscous as the molecular weight thereof increases. In order to ensure the coating properties of the coating solution, the concentration of the polyarylate resin in the coating solution is adjusted to be relatively low.

Here, the coating solution in which the concentration of the polyarylate resin is adjusted to be relatively low is likely to flow in the gravity direction, and it takes a relatively long time to dry the coating solution. Therefore, the charge transport layer formed by being dipped in and coated with the coating solution tends to have a thin upper end and a thick lower end, and this tendency is more conspicuous as the layer thickness of the charge transport layer is intended to increase. The unevenness in the layer thickness of the charge transport layer in the axial direction of the photoreceptor causes charging unevenness of the photoreceptor.

In order to address the above-described problems, the photoreceptor according to the present exemplary embodiment is formed such that the thickness of the charge generation layer positioned below the charge transport layer is set to be less at one end portion and greater at the other end portion, as compared with the central portion.

In the formation of the charge transport layer by being dipped in and coated with the coating solution on the charge generation layer, it is assumed that the uniformity of the layer thickness of the charge transport layer is enhanced by the following mechanism in a case where the charge transport layer is dipped and coated by setting the end of the charge generation layer with a small thickness to be positioned on the upper side in the gravity direction and the end thereof with a large thickness to be positioned on the lower side in the gravity direction.

It is considered that in a case where the thickness of the upper end portion of the charge generation layer is less than the thickness of the central portion, since the upper end portion with a small thickness is dried at a high speed, the coating solution for forming a charge transport layer easily adheres to the upper end portion, the coating solution is suppressed from flowing down from the upper end portion, and reduction in film thickness of the upper end portion of the charge transport layer is suppressed. Further, it is considered that the coating solution for forming a charge transport layer is likely to remain on the upper end portion even in the case where the thickness of the upper end portion of the charge generation layer is less than the thickness of the central portion, and thus reduction in film thickness of the upper end portion of the charge transport layer is suppressed. It is considered that the coating solution for forming a charge transport layer is likely to flow down in the gravity direction in a case where the thickness of the upper end portion of the charge generation layer is greater than or equal to the thickness of the central portion, and thus the thickness of the upper end portion of the charge transport layer is likely to be reduced.

It is considered that in a case where the thickness of the lower end portion of the charge generation layer is greater than the thickness of the central portion, since the lower end portion with a large thickness is dried at a low speed, the coating solution for forming a charge transport layer easily adheres to the lower end portion, the coating solution flows down from the lower end portion, and an increase in the thickness of the lower end portion of the charge transport layer is suppressed. Further, an increase in the thickness of the lower end portion of the charge transport layer is considered to be suppressed even in the case where the thickness of the lower end portion of the charge generation layer is greater than the thickness of the central portion. It is considered that the coating solution for forming a charge transport layer is likely to remain at a large thickness on the lower end portion in a case where the thickness of the lower end portion of the charge generation layer is less than or equal to thickness of the central portion, and thus the thickness of the lower end portion of the charge transport layer is likely to increase.

According to the above-described mechanism, it is considered that the uniformity of the layer thickness of the charge transport layer is enhanced in a case where the thickness of the charge generation layer is less at one end portion and greater at the other end portion. As a result, it is considered that charging unevenness is unlikely to occur in the photoreceptor.

Here, the charge generation layer is originally a thin layer. The layer thickness of the charge generation layer is typically less than 1 m, and even the maximum layer thickness is several m. Therefore, a difference in the layer thickness of the charge generation layer in the axial direction is small, and thus the difference in the layer thickness is difficult to detect in some cases.

Accordingly, the absorbance of the photosensitive layer at a wavelength of 678 nm in the absorption spectrum is employed as an index of the thickness of the charge generation layer of the photoreceptor according to the present exemplary embodiment. As the charge generation material of the charge generation layer, a charge generation material having absorption at a wavelength of 678 nm is used in many cases. It can be considered that the thickness of the charge generation layer increases as the absorbance at a wavelength of 678 nm increases and that the thickness of the charge generation layer decreases as the absorbance at a wavelength of 678 nm decreases. The thickness of the charge generation layer can be known by comparing the absorbances of the central portion, one end portion, and the other end portion of the photoreceptor at a wavelength of 678 nm.

The absorption spectrum of the photosensitive layer is measured as follows.

The photosensitive layer is peeled off and cut out from a position (M), a position (U), and a position (L) into a square with a size (axial direction×circumferential direction) of 1 cm×1 cm.

The position (M) is the center of the photoreceptor in the axial direction.

The position (U) is a position of 0.40 L from the center of the photoreceptor in the axial direction toward one end. Here, L represents the total length of the photoreceptor in the axial direction.

The position (L) is a position of 0.40 L from the center of the photoreceptor in the axial direction toward the other end. Here, L represents the total length of the photoreceptor in the axial direction.

The photosensitive layer is cut out from four positions at intervals of 90° in the circumferential direction at each of the position (M), the position (U), and the position (L). Therefore, four sheets of films having a square shape with a size of 1 cm×1 cm are obtained at each of the position (M), the position (U), and the position (L).

A solution is prepared by dipping four sheets of films at each position in 100 mL of tetrahydrofuran. The absorption spectrum is measured with an ultraviolet-visible spectrophotometer (for example, Hitachi U2000) using this solution as a sample, and the absorbance at a wavelength of 678 nm is detected.

The absorbance of the photosensitive layer at the position (M) at a wavelength of 678 nm is defined as Im.

The absorbance of the photosensitive layer at the position (U) at a wavelength of 678 nm is defined as Iu.

The absorbance of the photosensitive layer at the position (L) at a wavelength of 678 nm is defined as Il.

In the photoreceptor according to the present exemplary embodiment, Iu and Im have a relationship represented by Expression (1): Iu≤0.95×Im.

In a case where Iu is greater than 0.95×Im, for example, one end portion of the charge generation layer (the upper end portion in a case of formation of the charge transport layer by being dipped and coated) is not as thin as desired, and thus the thickness of the charge transport layer at this site is likely to be decreased. From the viewpoint of suppressing a decrease in the thickness of the charge transport layer at this site, for example, Iu and Im have a relationship represented by Expression (1), preferably a relationship represented by Expression (1-1), more preferably a relationship represented by Expression (1-2), and still more preferably a relationship represented by Expression (1-3).

$\begin{array}{cc}\mathrm{Iu}\le 0.95\times Im& \mathrm{Expression}\left(1\right)\end{array}$ $\begin{array}{cc}0.7\times Im<Iu\le 0.95\times Im& \mathrm{Expression}\left(1-1\right)\end{array}$ $\begin{array}{cc}0.75\times Im\le Iu\le 0.95\times Im& \mathrm{Expression}\left(1-2\right)\end{array}$ $\begin{array}{cc}0.75\times Im<Iu\le 0.95\times Im& \mathrm{Expression}\left(1-3\right)\end{array}$

In the photoreceptor according to the present exemplary embodiment, Il and Im have a relationship represented by Expression (2): 1.05×Im≤Il.

In a case where Il is less than 1.05×Im, for example, since the other end portion of the charge generation layer (the lower end portion in a case where the charge transport layer is formed by being dipped and coated) is not as thick as desired, the thickness of the charge transport layer at this site is likely to be increased. From the viewpoint of suppressing an increase in the thickness of the charge transport layer at this site, for example, Il and Im have a relationship represented by Expression (2), preferably a relationship represented by Expression (2-1), more preferably a relationship represented by Expression (2-2), and still more preferably a relationship represented by Expression (2-3).

$\begin{array}{cc}1.05\times Im\le I1& \mathrm{Expression}\left(2\right)\end{array}$ $\begin{array}{cc}1.05\times Im\le I1<1.3\times Im& \mathrm{Expression}\left(2-1\right)\end{array}$ $\begin{array}{cc}1.05\times Im\le I1\le 1.25\times Im& \mathrm{Expression}\left(2-2\right)\end{array}$ $\begin{array}{cc}1.05\times Im\le I1<1.25\times Im& \mathrm{Expression}\left(2-3\right)\end{array}$

Examples of means for forming the charge generation layer such that the thickness of one end portion is adjusted to be less and the thickness of the other end portion is adjusted to be greater than the thickness of the central portion in order to satisfy Expression (1) and Expression (2) include the following means.

In a case where the charge generation layer is formed by a dip coating method, the speed at which the conductive substrate is pulled upward in the gravity direction from the coating solution for forming a charge generation layer is controlled such that “pull-up speed at upper end portion<pull-up speed at central portion<pull-up speed at lower end portion” is satisfied.

In a case where the charge generation layer is formed by a blade coating method, the blade pressure with respect to the conductive substrate is controlled such that “blade pressure at one end portion>blade pressure at central portion>blade pressure at other end portion” is satisfied.

In a case where the charge generation layer is formed by a spray coating method, the spray amount of the coating solution is controlled such that “spray amount at one end portion<spray amount at central portion<spray amount at other end portion” is satisfied.

In each of the above-described means, for example, it is preferable that “central portion” is a region that occupies a length of 60% or greater and 80% or less of the total length L in the axial direction of the photoreceptor. In the central portion, it is preferable that the pull-up speed, the blade pressure, or the spray amount is, for example, constant.

Hereinafter, the polyarylate resin contained in the charge transport layer and each layer of the photoreceptor will be described in detail.

Polyarylate Resin (1)

As the polyarylate resin that is a binder resin of the charge transport layer, for example, a polyarylate resin (1) having at least a dicarboxylic acid unit (A) and a diol unit (B) is preferable. The polyarylate resin (1) may have other dicarboxylic acid units in addition to the dicarboxylic acid unit (A). The polyarylate resin (1) may have other diol units in addition to the diol unit (B).

The dicarboxylic acid unit (A) is a constitutional unit represented by Formula (A).

In Formula (A), Ar^A1 and Ar^A2 each independently represent an aromatic ring that may have a substituent, L^A represents a single bond or a divalent linking group, and n^A1 represents 0, 1, or 2.

The aromatic ring as Ar^A1 may be any of a monocycle or a polycycle. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring. Among these, for example, a benzene ring and a naphthalene ring are preferable.

The hydrogen atom on the aromatic ring as Ar^A1 may be substituted with an alkyl group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, a halogen atom, or the like. As the substituent in a case where the aromatic ring as Ar^A1 is substituted, for example, an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, and an alkoxy group having 1 or more and 6 or less carbon atoms are preferable.

The aromatic ring of Ar^A2 may be any of a monocycle or a polycycle. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring. Among these, for example, a benzene ring and a naphthalene ring are preferable.

The hydrogen atom on the aromatic ring as Ar^A2 may be substituted with an alkyl group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, a halogen atom, or the like. As the substituent in a case where the aromatic ring as Ar^A2 is substituted, for example, an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, and an alkoxy group having 1 or more and 6 or less carbon atoms are preferable.

In a case where L^A represents a divalent linking group, examples of the divalent linking group include an oxygen atom, a sulfur atom, and —C(Ra¹)(Ra²)—. Here, Ra¹ and Ra² each independently represent a hydrogen atom, an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, or an aralkyl group having 7 or more and 20 or less carbon atoms, and Ra¹ and Ra² may be bonded to each other to form a cyclic alkyl group.

The alkyl group having 1 or more and 10 or less carbon atoms as Ra¹ and Ra² may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or more and 6 or less, more preferably 1 or more and 4 or less, and still more preferably 1 or 2.

The aryl group having 6 or more and 12 or less carbon atoms as Ra¹ and Ra² may be any of a monocycle or a polycycle. The number of carbon atoms of the aryl group is, for example, preferably 6 or more and 10 or less and more preferably 6.

The alkyl group in the aralkyl group having 7 or more and 20 or less carbon atoms as Ra¹ and Ra² may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the aralkyl group having 7 or more and 20 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2.

The aryl group in the aralkyl group having 7 or more and 20 or less carbon atoms as Ra¹ and Ra² may be any of a monocycle or a polycycle. The number of carbon atoms of the aryl group is, for example, preferably 6 or more and 10 or less and more preferably 6.

It is preferable that the dicarboxylic acid unit (A) includes, for example, at least one selected from the group consisting of a dicarboxylic acid unit (A1) represented by Formula (A1), a dicarboxylic acid unit (A2) represented by Formula (A2), a dicarboxylic acid unit (A3) represented by Formula (A3), and a dicarboxylic acid unit (A4) represented by Formula (A4). The dicarboxylic acid unit (A) includes, for example, more preferably at least one selected from the group consisting of a dicarboxylic acid unit (A2), a dicarboxylic acid unit (A3), and a dicarboxylic acid unit (A4), still more preferably at least one selected from the group consisting of a dicarboxylic acid unit (A2) and a dicarboxylic acid unit (A4), and even still more preferably a dicarboxylic acid unit (A2).

In Formula (A1), n¹⁰¹ represents an integer of 0 or greater and 4 or less, and n¹⁰¹ pieces of Ra¹⁰¹'s each independently represent an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, or an alkoxy group having 1 or more and 6 or less carbon atoms.

• • n¹⁰¹ represents, for example, preferably 0, 1, or 2, more preferably 0 or 1, and still more preferably 0.

In Formula (A2), n²⁰¹ and n²⁰² each independently represent an integer of 0 or greater and 4 or less, and n²⁰¹ pieces of Ra²⁰¹'s and n²⁰² pieces of Ra²⁰²'s each independently represent an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, or an alkoxy group having 1 or more and 6 or less carbon atoms.

• • n²⁰¹ represents, for example, preferably 0, 1, or 2, more preferably 0 or 1, and still more preferably 0.
  • n²⁰² represents, for example, preferably 0, 1, or 2, more preferably 0 or 1, and still more preferably 0.

In Formula (A3), n³⁰¹ and n³⁰² each independently represent an integer of 0 or greater and 4 or less, and n³⁰¹ pieces of Ra³⁰¹'s and n³⁰² pieces of Ra³⁰²'s each independently represent an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, or an alkoxy group having 1 or more and 6 or less carbon atoms.

• • n³⁰¹ represents, for example, preferably 0, 1, or 2, more preferably 0 or 1, and still more preferably 0.
  • n³⁰² represents, for example, preferably 0, 1, or 2, more preferably 0 or 1, and still more preferably 0.

In Formula (A4), n⁴⁰¹ represents an integer of 0 or greater and 6 or less, and n⁴⁰¹ pieces of Ra⁴⁰¹'s each independently represent an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, or an alkoxy group having 1 or more and 6 or less carbon atoms.

• • n⁴⁰¹ represents, for example, preferably an integer of 0 or greater and 4 or less, more preferably 0, 1, or 2, and still more preferably 0.

The specific forms and the desired forms of Ra¹⁰¹ in Formula (A1), Ra²⁰¹ and Ra²⁰² in Formula (A2), Ra³⁰¹ and Ra³⁰² in Formula (A3), and Ra⁴⁰¹ in Formula (A4) are the same as each other, and hereinafter, Ra¹⁰¹, Ra²⁰¹, Ra²⁰², Ra³⁰¹, Ra³⁰², and Ra⁴⁰¹ will be collectively referred to as “Ra”.

The alkyl group having 1 or more and 10 or less carbon atoms as Ra may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or more and 6 or less, more preferably 1 or more and 4 or less, and still more preferably 1 or 2.

Examples of the linear alkyl group having 1 or more and 10 or less carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group. Examples of the branched alkyl group having 3 or more and 10 or less carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an isodecyl group, a sec-decyl group, and a tert-decyl group.

Examples of the cyclic alkyl group having 3 or more and 10 or less carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclononyl group, a cyclodecyl group, and polycyclic (for example, bicyclic, tricyclic, or spirocyclic) alkyl groups to which these monocyclic alkyl groups are linked.

The aryl group having 6 or more and 12 or less carbon atoms as Ra may be any of a monocycle or a polycycle. The number of carbon atoms of the aryl group is, for example, preferably 6 or more and 10 or less and more preferably 6.

Examples of the aryl group having 6 or more and 12 or less carbon atoms include a phenyl group, a biphenyl group, a 1-naphthyl group, and a 2-naphthyl group.

The alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms as Ra may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2.

Examples of the linear alkoxy group having 1 or more and 6 or less carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an n-pentyloxy group, and an n-hexyloxy group.

Examples of the branched alkoxy group having 3 or more and 6 or less carbon atoms include an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an isopentyloxy group, a neopentyloxy group, a tert-pentyloxy group, an isohexyloxy group, a sec-hexyloxy group, and a tert-hexyloxy group.

Examples of the cyclic alkoxy group having 3 or more and 6 or less carbon atoms include a cyclopropoxy group, a cyclobutoxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

Hereinafter, dicarboxylic acid units (A1-1) to (A1-9) are shown as specific examples of the dicarboxylic acid unit (A1). The dicarboxylic acid unit (A1) is not limited thereto.

Hereinafter, dicarboxylic acid units (A2-1) to (A2-3) are shown as specific examples of the dicarboxylic acid unit (A2). The dicarboxylic acid unit (A2) is not limited thereto.

Hereinafter, dicarboxylic acid units (A3-1) and (A3-2) are shown as specific examples of the dicarboxylic acid unit (A3). The dicarboxylic acid unit (A3) is not limited thereto.

Hereinafter, dicarboxylic acid units (A4-1) to (A4-3) are shown as specific examples of the dicarboxylic acid unit (A4). The dicarboxylic acid unit (A4) is not limited thereto.

The dicarboxylic acid unit (A) includes, for example, preferably at least one selected from the group consisting of (A1-1), (A1-7), (A2-3), (A3-2), and (A4-3) in the above-described specific examples, more preferably at least one selected from the group consisting of (A2-3), (A3-2), and (A4-3), still more preferably at least one selected from the group consisting of (A2-3) and (A4-3), and most preferably at least (A2-3).

The total mass proportion of the dicarboxylic acid units (A1) to (A4) in the polyarylate resin (1) is, for example, preferably 15% by mass or greater and 60% by mass or less. In a case where the total mass proportion of the dicarboxylic acid units (A1) to (A4) is 15% by mass or greater, the abrasion resistance of the photosensitive layer is enhanced. From this viewpoint, the total mass proportion of the dicarboxylic acid units (A1) to (A4) is, for example, more preferably 20% by mass or greater and still more preferably 25% by mass or greater.

In a case where the total mass proportion of the dicarboxylic acid units (A1) to (A4) is 60% by mass or less, peeling of the photosensitive layer can be suppressed. From this viewpoint, the total mass proportion of the dicarboxylic acid units (A1) to (A4) is, for example, more preferably 55% by mass or less and still more preferably 50% by mass or less. The dicarboxylic acid units (A1) to (A4) contained in the polyarylate resin (1) may be used alone or in combination of two or more kinds thereof.

Examples of other dicarboxylic acid units (A) in addition to the dicarboxylic acid units (A1) to (A4) include aliphatic dicarboxylic acid (such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenyl succinic acid, adipic acid, and sebacic acid) units, alicyclic dicarboxylic acid (such as cyclohexanedicarboxylic acid) units, and lower (for example, having 1 or more and 5 or less carbon atoms) alkyl ester units thereof. These dicarboxylic acid units contained in the polyarylate resin (1) may be used alone or in combination of two or more kinds thereof.

The dicarboxylic acid unit (A) contained in the polyarylate resin (1) may be used alone or in combination of two or more kinds thereof.

The diol unit (B) is a constitutional unit represented by Formula (B).

in Formula (B), Ar^B1 and Ar^B2 each independently represent an aromatic ring that may have a substituent, L^B represents a single bond, an oxygen atom, a sulfur atom, or —C(Rb¹)(Rb²)—, n^B1 represents 0, 1, or 2. Rb¹ and Rb² each independently represent a hydrogen atom, an alkyl group having 1 or more and 20 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, or an aralkyl group having 7 or more and 20 or less carbon atoms, and Rb¹ and Rb² may be bonded to each other to form a cyclic alkyl group.

The aromatic ring as Ar^B1 may be any of a monocycle or a polycycle. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring. Among these, for example, a benzene ring and a naphthalene ring are preferable.

The hydrogen atom on the aromatic ring as Ar^B1 may be substituted with an alkyl group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, a halogen atom, or the like. As the substituent in a case where the aromatic ring as Ar^B1 is substituted, for example, an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, and an alkoxy group having 1 or more and 6 or less carbon atoms are preferable.

The aromatic ring as Ar^B2 may be any of a monocycle or a polycycle. Examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, and a phenanthrene ring. Among these, for example, a benzene ring and a naphthalene ring are preferable.

The hydrogen atom on the aromatic ring as Ar^B2 may be substituted with an alkyl group, an aryl group, an aralkyl group, an alkoxy group, an aryloxy group, a halogen atom, or the like. As the substituent in a case where the aromatic ring as Ar^B2 is substituted, for example, an alkyl group having 1 or more and 10 or less carbon atoms, an aryl group having 6 or more and 12 or less carbon atoms, and an alkoxy group having 1 or more and 6 or less carbon atoms are preferable.

The alkyl group having 1 or more and 20 or less carbon atoms as Rb¹ and Rb² may be linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or more and 18 or less, more preferably 1 or more and 14 or less, and still more preferably 1 or more and 10 or less.

The aryl group having 6 or more and 12 or less carbon atoms as Rb¹ and Rb² may be any of a monocycle or a polycycle. The number of carbon atoms of the aryl group is, for example, preferably 6 or more and 10 or less and more preferably 6.

The alkyl group in the aralkyl group having 7 or more and 20 or less carbon atoms as Rb¹ and Rb² may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the aralkyl group having 7 or more and 20 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2.

The aryl group in the aralkyl group having 7 or more and 20 or less carbon atoms as Rb¹ and Rb² may be any of a monocycle or a polycycle. The number of carbon atoms of the aryl group is, for example, preferably 6 or more and 10 or less and more preferably 6.

It is preferable that the diol unit (B) includes, for example, at least one selected from the group consisting of a diol unit (B1) represented by Formula (B1), a diol unit (B2) represented by Formula (B2), a diol unit (B3) represented by Formula (B3), a diol unit (B4) represented by Formula (B4), a diol unit (B5) represented by Formula (B5), a diol unit (B6) represented by Formula (B6), a diol unit (B7) represented by Formula (B7), and a diol unit (B8) represented by Formula (B8).

The diol unit (B) includes, for example, more preferably at least one selected from the group consisting of a diol unit (B1), a diol unit (B2), a diol unit (B4), a diol unit (B5), and a diol unit (B6), still more preferably at least one selected from the group consisting of a diol unit (B1), a diol unit (B2), a diol unit (B5), and a diol unit (B6), even still more preferably at least one selected from the group consisting of a diol unit (B1), a diol unit (B2), and a diol unit (B6), and most preferably at least one selected from the group consisting of a diol unit (B1) and a diol unit (B2).

In Formula (B1), Rb¹⁰¹ represents a branched alkyl group having 4 or more and 20 or less carbon atoms, Rb²⁰¹ represents a hydrogen atom or an alkyl group having 1 or more and 3 or less carbon atoms, and Rb⁴⁰¹, Rb⁵⁰¹, Rb⁸⁰¹, and Rb⁹⁰¹ each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

The number of carbon atoms of the branched alkyl group having 4 or more and 20 or less carbon atoms as Rb¹⁰¹ is, for example, preferably 4 or more and 16 or less, more preferably 4 or more and 12 or less, and still more preferably 4 or more and 8 or less. Specific examples of Rb¹⁰¹ include an isobutyl group, a sec-butyl group, a tert-butyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, an isododecyl group, a sec-dodecyl group, a tert-dodecyl group, a tert-tetradecyl group, and a tert-pentadecyl group.

In Formula (B2), Rb¹⁰² represents a linear alkyl group having 4 or more and 20 or less carbon atoms, Rb²⁰² represents a hydrogen atom or an alkyl group having 1 or more and 3 or less carbon atoms, and Rb⁴⁰², Rb⁵⁰², Rb⁸⁰², and Rb⁹⁰² each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

The number of carbon atoms of the linear alkyl group having 4 or more and 20 or less carbon atoms as Rb¹⁰² is, for example, preferably 4 or more and 16 or less, more preferably 4 or more and 12 or less, and still more preferably 4 or more and 8 or less. Specific examples of Rb¹⁰² include an n-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, a tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group, and an n-icosyl group.

In Formula (B3), Rb¹¹³ and Rb²¹³ each independently represent a hydrogen atom, a linear alkyl group having 1 or more and 3 or less carbon atoms, an alkoxy group having 1 or more and 4 or less carbon atoms, or a halogen atom, d represents an integer of 7 or greater and 15 or less, and Rb⁴⁰³, Rb⁵⁰³, Rb⁸⁰³, and Rb⁹⁰³ each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

The number of carbon atoms of the linear alkyl group having 1 or more and 3 or less carbon atoms as Rb¹¹³ and Rb²¹³ is, for example, preferably 1 or 2 and more preferably 1. Specific examples of such a group include a methyl group, an ethyl group, and an n-propyl group.

The alkyl group in the alkoxy group having 1 or more and 4 or less carbon atoms as Rb¹¹³ and Rb²¹³ may be linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the alkoxy group having 1 or more and 4 or less carbon atoms is, for example, preferably 1 or more and 3 or less, more preferably 1 or 2, and still more preferably 1. Specific examples of such a group include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a cyclopropoxy group, and a cyclobutoxy group.

Examples of the halogen atom as Rb¹¹³ and Rb²¹³ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

In Formula (B4), Rb¹⁰⁴ and Rb²⁰⁴ each independently represent a hydrogen atom, an alkyl group having 1 or more and 3 or less carbon atoms, and Rb⁴⁰⁴, Rb⁵⁰⁴, Rb⁸⁰⁴, and Rb⁹⁰⁴ each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

The alkyl group having 1 or more and 3 or less carbon atoms as Rb¹⁰⁴ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or 2 and more preferably 1. Specific examples of Rb¹⁰⁴ include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and a cyclopropyl group.

In Formula (B5), Ar¹⁰⁵ represents an aryl group having 6 or more and 12 or less carbon atoms or an aralkyl group having 7 or more and 20 or less carbon atoms, Rb²⁰⁵ represents a hydrogen atom or an alkyl group having 1 or more and 3 or less carbon atoms, and Rb⁴⁰⁵, Rb⁵⁰⁵, Rb⁸⁰⁵, and Rb⁹⁰⁵ each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

The aryl group having 6 or more and 12 or less carbon atoms as Ar¹⁰⁵ may be any of a monocycle or a polycycle. The number of carbon atoms of the aryl group is, for example, preferably 6 or more and 10 or less and more preferably 6.

The alkyl group in the aralkyl group having 7 or more and 20 or less carbon atoms as Ar¹⁰⁵ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the aralkyl group having 7 or more and 20 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2. The aryl group in the aralkyl group having 7 or more and 20 or less carbon atoms as Ar¹⁰⁵ may be any of a monocycle or a polycycle. The number of carbon atoms of the aryl group is, for example, preferably 6 or more and 10 or less and more preferably 6. Examples of the aralkyl group having 7 or more and 20 or less carbon atoms include a benzyl group, a phenylethyl group, a phenylpropyl group, a 4-phenylbutyl group, a phenylpentyl group, a phenylhexyl group, a phenylheptyl group, a phenyloctyl group, a phenylnonyl group, a naphthylmethyl group, a naphthylethyl group, an anthracenylmethyl group, and a phenyl-cyclopentylmethyl group.

In Formula (B6), Rb¹¹⁶ and Rb²¹⁶ each independently represent a hydrogen atom, a linear alkyl group having 1 or more and 3 or less carbon atoms, an alkoxy group having 1 or more and 4 or less carbon atoms, or a halogen atom, e represents an integer of 4 or greater and 6 or less, and Rb⁴⁰⁶, Rb⁵⁰⁶, Rb⁸⁰⁶, and Rb⁹⁰⁶ each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

The number of carbon atoms of the linear alkyl group having 1 or more and 3 or less carbon atoms as Rb¹¹⁶ and Rb²¹⁶ is, for example, preferably 1 or 2 and more preferably 1. Specific examples of such a group include a methyl group, an ethyl group, and an n-propyl group.

The alkyl group in the alkoxy group having 1 or more and 4 or less carbon atoms as Rb¹¹⁶ and Rb²¹⁶ may be linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the alkoxy group having 1 or more and 4 or less carbon atoms is, for example, preferably 1 or more and 3 or less, more preferably 1 or 2, and still more preferably 1. Specific examples of such a group include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a cyclopropoxy group, and a cyclobutoxy group.

Examples of the halogen atom as Rb¹¹⁶ and Rb²¹⁶ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

In Formula (B7), Rb⁴⁰⁷, Rb⁵⁰⁷, Rb⁸⁰⁷, and Rb⁹⁰⁷ each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

In Formula (B8), Rb⁴⁰⁸, Rb⁵⁰⁸, Rb⁸⁰⁸, and Rb⁹⁰⁸ each independently represent a hydrogen atom, an alkyl group having 1 or more and 4 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or a halogen atom.

The specific forms and the desired forms of Rb²⁰¹ in Formula (B1), Rb²⁰² in Formula (B2), Rb²⁰⁴ in Formula (B4), and Rb²⁰⁵ in Formula (B5) are the same as each other, and hereinafter, Rb²⁰¹, Rb²⁰², Rb²⁰⁴, and Rb²⁰⁵ will be collectively referred to as “Rb²⁰⁰”

The alkyl group having 1 or more and 3 or less carbon atoms as Rb²⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or 2 and more preferably 1.

The alkyl group having 1 or more and 3 or less carbon atoms includes a methyl group, an ethyl group, an n-propyl group, an isopropyl group, and a cyclopropyl group.

The specific forms and the desired forms of Rb⁴⁰¹ in Formula (B1), Rb⁴⁰² in Formula (B2), Rb⁴⁰³ in Formula (B3), Rb⁴⁰⁴ in Formula (B4), Rb⁴⁰⁵ in Formula (B5), Rb⁴⁰⁶ in Formula (B6), Rb⁴⁰⁷ in Formula (B7), and Rb⁴⁰⁸ in Formula (B8) are the same as each other, and hereinafter, Rb⁴⁰¹, Rb⁴⁰², Rb⁴⁰³, Rb⁴⁰⁴, Rb⁴⁰⁵, Rb⁴⁰⁶, Rb⁴⁰⁷, and Rb⁴⁰⁸ will be collectively referred to as “Rb⁴⁰⁰”.

The alkyl group having 1 or more and 4 or less carbon atoms as Rb⁴⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or more and 3 or less, more preferably 1 or 2, and still more preferably 1. Examples of the linear alkyl group having 1 or more and 4 or less carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an n-butyl group.

Examples of the branched alkyl group having 3 or 4 carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

Examples of the cyclic alkyl group having 3 or 4 carbon atoms include a cyclopropyl group and a cyclobutyl group.

The alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms as Rb⁴⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2. Examples of the linear alkoxy group having 1 or more and 6 or less carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an n-pentyloxy group, and an n-hexyloxy group.

Examples of the branched alkoxy group having 3 or more and 6 or less carbon atoms include an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an isopentyloxy group, a neopentyloxy group, a tert-pentyloxy group, an isohexyloxy group, a sec-hexyloxy group, and a tert-hexyloxy group.

Examples of the cyclic alkoxy group having 3 or more and 6 or less carbon atoms include a cyclopropoxy group, a cyclobutoxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

Examples of the halogen atom as Rb⁴⁰⁰ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The specific forms and the desired forms of Rb⁵⁰¹ in Formula (B1), Rb⁵⁰² in Formula (B2), Rb⁵⁰³ in Formula (B3), Rb⁵⁰⁴ in Formula (B4), Rb⁵⁰⁵ in Formula (B5), Rb⁵⁰⁶ in Formula (B6), Rb⁵⁰⁷ in Formula (B7), and Rb⁵⁰⁸ in Formula (B8) are the same as each other, and hereinafter, Rb⁵⁰¹, Rb⁵⁰², Rb⁵⁰³, Rb⁵⁰⁴, Rb⁵⁰⁵, Rb⁵⁰⁶, Rb⁵⁰⁷, and Rb⁵⁰⁸ will be collectively referred to as “Rb⁵⁰⁰”.

The alkyl group having 1 or more and 4 or less carbon atoms as Rb⁵⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or more and 3 or less, more preferably 1 or 2, and still more preferably 1. Examples of the linear alkyl group having 1 or more and 4 or less carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an n-butyl group.

Examples of the branched alkyl group having 3 or 4 carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

Examples of the cyclic alkyl group having 3 or 4 carbon atoms include a cyclopropyl group and a cyclobutyl group.

The alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms as Rb⁵⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2.

Examples of the linear alkoxy group having 1 or more and 6 or less carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an n-pentyloxy group, and an n-hexyloxy group.

Examples of the branched alkoxy group having 3 or more and 6 or less carbon atoms include an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an isopentyloxy group, a neopentyloxy group, a tert-pentyloxy group, an isohexyloxy group, a sec-hexyloxy group, and a tert-hexyloxy group.

Examples of the cyclic alkoxy group having 3 or more and 6 or less carbon atoms include a cyclopropoxy group, a cyclobutoxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

Examples of the halogen atom as Rb⁵⁰⁰ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The specific forms and the desired forms of Rb⁸⁰¹ in Formula (B1), Rb⁸⁰² in Formula (B2), Rb⁸⁰³ in Formula (B3), Rb⁸⁰⁴ in Formula (B4), Rb⁸⁰⁵ in Formula (B5), Rb⁸⁰⁶ in Formula (B6), Rb⁸⁰⁷ in Formula (B7), and Rb⁸⁰⁸ in Formula (B8) are the same as each other, and hereinafter, Rb⁸⁰¹, Rb⁸⁰², Rb⁸⁰³, Rb⁸⁰⁴, Rb⁸⁰⁵, Rb⁸⁰⁶, Rb⁸⁰⁷, and Rb⁸⁰⁸ will be collectively referred to as “Rb⁸⁰⁰”.

The alkyl group having 1 or more and 4 or less carbon atoms as Rb⁸⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or more and 3 or less, more preferably 1 or 2, and still more preferably 1.

Examples of the linear alkyl group having 1 or more and 4 or less carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an n-butyl group.

Examples of the branched alkyl group having 3 or 4 carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

Examples of the cyclic alkyl group having 3 or 4 carbon atoms include a cyclopropyl group and a cyclobutyl group.

The alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms as Rb⁸⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2.

Examples of the linear alkoxy group having 1 or more and 6 or less carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an n-pentyloxy group, and an n-hexyloxy group.

Examples of the branched alkoxy group having 3 or more and 6 or less carbon atoms include an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an isopentyloxy group, a neopentyloxy group, a tert-pentyloxy group, an isohexyloxy group, a sec-hexyloxy group, and a tert-hexyloxy group.

Examples of the cyclic alkoxy group having 3 or more and 6 or less carbon atoms include a cyclopropoxy group, a cyclobutoxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

Examples of the halogen atom as Rb⁸⁰⁰ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

The specific forms and the desired forms of Rb⁹⁰¹ in Formula (B1), Rb⁹⁰² in Formula (B2), Rb⁹⁰³ in Formula (B3), Rb⁹⁰⁴ in Formula (B4), Rb⁹⁰⁵ in Formula (B5), Rb⁹⁰⁶ in Formula (B6), Rb⁹⁰⁷ in Formula (B7), and Rb⁹⁰⁸ in Formula (B8) are the same as each other, and hereinafter, Rb⁹⁰¹, Rb⁹⁰², Rb⁹⁰³, Rb⁹⁰⁴, Rb⁹⁰⁵, Rb⁹⁰⁶, Rb⁹⁰⁷, and Rb⁹⁰⁸ will be collectively referred to as “Rb⁹⁰⁰”.

The alkyl group having 1 or more and 4 or less carbon atoms as Rb⁹⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group is, for example, preferably 1 or more and 3 or less, more preferably 1 or 2, and still more preferably 1. Examples of the linear alkyl group having 1 or more and 4 or less carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an n-butyl group.

Examples of the branched alkyl group having 3 or 4 carbon atoms include an isopropyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group.

Examples of the cyclic alkyl group having 3 or 4 carbon atoms include a cyclopropyl group and a cyclobutyl group.

The alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms as Rb⁹⁰⁰ may be any of linear, branched, or cyclic. The number of carbon atoms of the alkyl group in the alkoxy group having 1 or more and 6 or less carbon atoms is, for example, preferably 1 or more and 4 or less, more preferably 1 or more and 3 or less, and still more preferably 1 or 2.

Examples of the linear alkoxy group having 1 or more and 6 or less carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an n-butoxy group, an n-pentyloxy group, and an n-hexyloxy group.

Examples of the branched alkoxy group having 3 or more and 6 or less carbon atoms include an isopropoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, an isopentyloxy group, a neopentyloxy group, a tert-pentyloxy group, an isohexyloxy group, a sec-hexyloxy group, and a tert-hexyloxy group.

Examples of the cyclic alkoxy group having 3 or more and 6 or less carbon atoms include a cyclopropoxy group, a cyclobutoxy group, a cyclopentyloxy group, and a cyclohexyloxy group.

Examples of the halogen atom as Rb⁹⁰⁰ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

Hereinafter, diol units (B1-1) to (B1-6) are shown as specific examples of the diol unit (B1). The diol unit (B1) is not limited thereto.

Hereinafter, diol units (B2-1) to (B2-11) are shown as specific examples of the diol unit (B2). The diol unit (B2) is not limited thereto.

Hereinafter, diol units (B3-1) to (B3-4) are shown as specific examples of the diol unit (B3). The diol unit (B3) is not limited thereto.

Hereinafter, diol units (B4-1) to (B4-7) are shown as specific examples of the diol unit (B4). The diol unit (B4) is not limited thereto.

Hereinafter, diol units (B5-1) to (B5-6) are shown as specific examples of the diol unit (B5). The diol unit (B5) is not limited thereto.

Hereinafter, diol units (B6-1) to (B6-4) are shown as specific examples of the diol unit (B6). The diol unit (B6) is not limited thereto.

Hereinafter, diol units (B7-1) to (B7-3) are shown as specific examples of the diol unit (B7). The diol unit (B7) is not limited thereto.

Hereinafter, diol units (B8-1) to (B8-3) are shown as specific examples of the diol unit (B8). The diol unit (B8) is not limited thereto.

The diol unit (B) contained in the polyarylate resin (1) may be used alone or in combination of two or more kinds thereof.

The mass proportion of the diol unit (B) in the polyarylate resin (1) is, for example, preferably 25% by mass or greater and 80% by mass or less.

In a case where the mass proportion of the diol unit (B) is 25% by mass or greater, peeling of the photosensitive layer can be further suppressed. From this viewpoint, the mass proportion of the diol unit (B) is, for example, more preferably 30% by mass or greater and still more preferably 35% by mass or greater.

In a case where the mass proportion of the diol unit (B) is 80% by mass or less, the solubility in a coating solution for forming the photosensitive layer is maintained, and thus the abrasion resistance can be improved. From this viewpoint, the mass proportion of the diol unit (B) is, for example, more preferably 75% by mass or less and still more preferably 70% by mass or less.

Examples of other diol units in addition to the diol unit (B) include aliphatic diol (such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, and neopentyl glycol) units and alicyclic diol (such as cyclohexanediol, cyclohexane dimethanol, and hydrogenated bisphenol A) units. These diol units contained in the polyarylate resin (1) may be used alone or in combination of two or more kinds thereof.

A terminal of the polyarylate resin (1) may be sealed or modified with a terminal-sealing agent, a molecular weight modifier, or the like used in a case of the production. Examples of the terminal-sealing agent or the molecular weight modifier include monohydric phenol, monovalent acid chloride, monohydric alcohol, and monovalent carboxylic acid.

Examples of the monohydric phenol include phenol, o-cresol, m-cresol, p-cresol, o-ethylphenol, m-ethylphenol, p-ethylphenol, o-propylphenol, m-propylphenol, p-propylphenol, o-tert-butylphenol, m-tert-butylphenol, p-tert-butylphenol, pentylphenol, hexylphenol, octylphenol, nonylphenol, a 2,6-dimethylphenol derivative, a 2-methylphenol derivative, o-phenylphenol, m-phenylphenol, p-phenylphenol, o-methoxyphenol, m-methoxyphenol, p-methoxyphenol, 2,3,5-trimethylphenol, 2,3,6-trimethylphenol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xylenol, 3,5-xylenol, 2-phenyl-2-(4-hydroxyphenyl)propane, 2-phenyl-2-(2-hydroxyphenyl)propane, and 2-phenyl-2-(3-hydroxyphenyl)propane.

Examples of the monovalent acid chloride include monofunctional acid halides such as benzoyl chloride, benzoic acid chloride, methanesulfonyl chloride, phenylchloroformate, acetic acid chloride, butyric acid chloride, octyl acid chloride, benzenesulfonyl chloride, benzenesulfinyl chloride, sulfinyl chloride, benzene phosphonyl chloride, and substituents thereof.

Examples of the monohydric alcohol include methanol, ethanol, n-propanol, isopropanol, n-butanol, 2-butanol, pentanol, hexanol, dodecyl alcohol, stearyl alcohol, benzyl alcohol, and phenethyl alcohol.

Examples of the monovalent carboxylic acid include acetic acid, propionic acid, octanoic acid, cyclohexanecarboxylic acid, benzoic acid, toluic acid, phenylacetic acid, p-tert-butylbenzoic acid, and p-methoxyphenylacetic acid.

From the viewpoint of the abrasion resistance of the charge transport layer, the weight-average molecular weight of the polyarylate resin and the polyarylate resin (1) is, for example, preferably 50,000 or greater, more preferably 80,000 or greater, and still more preferably 100,000 or greater.

From the viewpoint of adjusting the concentration of the polyarylate resin in the coating solution for forming a charge transport layer to a certain degree or greater, the weight-average molecular weight of the polyarylate resin and the polyarylate resin (1) is, for example, preferably 300,000 or less, more preferably 250,000 or less, and still more preferably 200,000 or less.

The molecular weight of the polyarylate resin and the polyarylate resin (1) is a molecular weight measured by gel permeation chromatography (GPC) in terms of polystyrene. The GPC is carried out by using tetrahydrofuran as an eluent.

The polyarylate resin (1) can be obtained by polycondensing a monomer providing a dicarboxylic acid unit (A), a monomer providing a diol unit (B), and other monomers as necessary using a method of the related art. Examples of the method of polycondensing monomers include an interfacial polymerization method, a solution polymerization method, and a melt polymerization method. The interfacial polymerization method is a polymerization method of mixing a divalent carboxylic acid halide dissolved in an organic solvent that is incompatible with water and dihydric alcohol dissolved in an alkali aqueous solution to obtain polyester. Examples of documents related to the interfacial polymerization method include W. M. EARECKSON, J. Poly. Sci., XL399, 1959, and JP1965-1959B. Since the interfacial polymerization method enables the reaction to proceed faster than the reaction carried out by the solution polymerization method and also enables suppression of hydrolysis of the divalent carboxylic acid halide, as a result, a high-molecular-weight polyarylate resin can be obtained.

Conductive Substrate

Examples of the conductive substrate include metal plates containing metals (such as aluminum, copper, zinc, chromium, nickel, molybdenum, vanadium, indium, gold, and platinum) or alloys (such as stainless steel), metal drums, metal belts, and the like. Further, examples of the conductive substrate include paper, a resin film, a belt, and the like obtained by being coated, vapor-deposited or laminated with a conductive compound (such as a conductive polymer or indium oxide), a metal (such as aluminum, palladium, or gold) or an alloy. Here, the term “conductive” denotes that the volume resistivity is less than 1×10¹³ Ω·cm.

In a case where the electrophotographic photoreceptor is used in a laser printer, for example, it is preferable that the surface of the conductive substrate is roughened such that a centerline average roughness Ra thereof is 0.04 μm or greater and 0.5 μm or less for the purpose of suppressing interference fringes from occurring during irradiation with laser beams. In a case where incoherent light is used as a light source, roughening of the surface to prevent interference fringes is not particularly necessary, and it is appropriate for longer life because occurrence of defects due to the unevenness of the surface of the conductive substrate is suppressed.

Examples of the roughening method include wet honing performed by suspending an abrasive in water and spraying the suspension to the conductive substrate, centerless grinding performed by pressure-welding the conductive substrate against a rotating grindstone and continuously grinding the conductive substrate, and an anodizing treatment.

Examples of the roughening method also include a method of dispersing conductive or semi-conductive powder in a resin without roughening the surface of the conductive substrate to form a layer on the surface of the conductive substrate, and performing roughening using the particles dispersed in the layer.

The roughening treatment performed by anodization is a treatment of forming an oxide film on the surface of the conductive substrate by carrying out anodization in an electrolytic solution using a conductive substrate made of a metal (for example, aluminum) as an anode. Examples of the electrolytic solution include a sulfuric acid solution and an oxalic acid solution. However, a porous anodized film formed by anodization is chemically active in a natural state, is easily contaminated, and has a large resistance fluctuation depending on the environment. Therefore, for example, it is preferable that a sealing treatment is performed on the porous anodized film so that the micropores of the oxide film are closed by volume expansion due to a hydration reaction in pressurized steam or boiling water (a metal salt such as nickel may be added thereto) for a change into a more stable a hydrous oxide.

The film thickness of the anodized film is, for example, preferably 0.3 μm or greater and 15 μm or less. In a case where the film thickness is in the above-described range, the barrier properties against injection tend to be exhibited, and an increase in the residual potential due to repeated use tends to be suppressed.

The conductive substrate may be subjected to a treatment with an acidic treatment liquid or a boehmite treatment.

The treatment with an acidic treatment liquid is carried out, for example, as follows. First, an acidic treatment liquid containing phosphoric acid, chromic acid, and hydrofluoric acid is prepared. In the blending ratio of phosphoric acid, chromic acid, and hydrofluoric acid to the acidic treatment liquid, for example, the concentration of the phosphoric acid is 10% by mass or greater and 11% by mass or less, the concentration of the chromic acid is 3% by mass or greater and 5% by mass or less, and the concentration of the hydrofluoric acid is 0.5% by mass or greater and 2% by mass or less, and the concentration of all these acids may be 13.5% by mass or greater and 18% by mass or less. The treatment temperature is, for example, preferably 42° C. or higher and 48° C. or lower. The film thickness of the coating film is, for example, preferably 0.3 μm or greater and 15 μm or less.

The boehmite treatment is carried out, for example, by dipping the conductive substrate in pure water at 90° C. or higher and 100° C. or lower for 5 minutes to 60 minutes or by bringing the conductive substrate into contact with heated steam at 90° C. or higher and 120° C. or lower for 5 minutes to 60 minutes. The film thickness of the coating film is, for example, preferably 0.1 m or greater and 5 μm or less. This coating film may be further subjected to the anodizing treatment using an electrolytic solution having low film solubility, such as adipic acid, boric acid, a borate, a phosphate, a phthalate, a maleate, a benzoate, a tartrate, or a citrate.

Undercoat Layer

The undercoat layer is, for example, a layer containing inorganic particles and a binder resin.

Examples of the inorganic particles include inorganic particles having a powder resistance (volume resistivity) of 1×10² Ω·cm or greater and 1×10¹¹ Ω·cm or less. Among these, as the inorganic particles having the above-described resistance value, for example, metal oxide particles such as tin oxide particles, titanium oxide particles, zinc oxide particles, and zirconium oxide particles may be used, and zinc oxide particles are particularly preferable.

The specific surface area of the inorganic particles measured by the BET method may be, for example, 10 m²/g or greater.

The volume average particle diameter of the inorganic particles may be, for example, 50 nm or greater and 2,000 nm or less (for example, preferably 60 nm or greater and 1,000 nm or less).

The content of the inorganic particles is, for example, preferably 10% by mass or greater and 80% by mass or less and more preferably 40% by mass or greater and 80% by mass or less with respect to the amount of the binder resin.

The inorganic particles may be subjected to a surface treatment. As the inorganic particles, inorganic particles subjected to different surface treatments or inorganic particles having different particle diameters may be used in the form of a mixture of two or more kinds thereof.

Examples of the surface treatment agent include a silane coupling agent, a titanate-based coupling agent, an aluminum-based coupling agent, and a surfactant. In particular, for example, a silane coupling agent is preferable, and a silane coupling agent containing an amino group is more preferable.

Examples of the silane coupling agent containing an amino group include 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, but are not limited thereto.

The silane coupling agent may be used in the form of a mixture of two or more kinds thereof. For example, a silane coupling agent containing an amino group and another silane coupling agent may be used in combination. Examples of other silane coupling agents include vinyltrimethoxysilane, 3-methacryloxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane, but are not limited thereto.

The surface treatment method using a surface treatment agent may be any method as long as the method is a known method, and any of a dry method or a wet method may be used.

The treatment amount of the surface treatment agent is, for example, preferably 0.5% by mass or greater and 10% by mass or less with respect to the amount of the inorganic particles.

The undercoat layer may contain an electron-accepting compound (acceptor compound) together with the inorganic particles from the viewpoint of enhancing the long-term stability of the electrical properties and the carrier blocking properties.

Examples of the electron-accepting compound include electron-transporting substances, for example, a quinone-based compound such as chloranil or bromanil; a tetracyanoquinodimethane-based compound; a fluorenone compound such as 2,4,7-trinitrofluorenone or 2,4,5,7-tetranitro-9-fluorenone; an oxadiazole-based compound such as 2-(4-biphenyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, 2,5-bis(4-naphthyl)-1,3,4-oxadiazole, or 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole; a xanthone-based compound; a thiophene compound; a diphenoquinone compound such as 3,3′,5,5′-tetra-t-butyldiphenoquinone; and a benzophenone compound.

In particular, as the electron-accepting compound, for example, a compound having an anthraquinone structure is preferable. As the compound having an anthraquinone structure, for example, a hydroxyanthraquinone compound, an aminoanthraquinone compound, or an aminohydroxyanthraquinone compound is preferable, and specifically, for example, anthraquinone, alizarin, quinizarin, anthrarufin, or purpurin is preferable.

The electron-accepting compound may be contained in the undercoat layer in a state of being dispersed with inorganic particles or in a state of being attached to the surface of each inorganic particle.

Examples of the method of attaching the electron-accepting compound to the surface of the inorganic particle include a dry method and a wet method.

The dry method is, for example, a method of attaching the electron-accepting compound to the surface of each inorganic particle by adding the electron-accepting compound dropwise to inorganic particles directly or by dissolving the electron-accepting compound in an organic solvent while stirring the inorganic particles with a mixer having a large shearing force and spraying the mixture together with dry air or nitrogen gas. The electron-accepting compound may be added dropwise or sprayed, for example, at a temperature lower than or equal to the boiling point of the solvent. After the dropwise addition or the spraying of the electron-accepting compound, the compound may be further baked at 100° C. or higher. The baking is not particularly limited as long as the temperature and the time are adjusted such that the electrophotographic characteristics can be obtained.

The wet method is, for example, a method of attaching the electron-accepting compound to the surface of each inorganic particle by adding the electron-accepting compound to inorganic particles while dispersing the inorganic particles in a solvent by performing stirring or using ultrasonic waves, a sand mill, an attritor, or a ball mill, stirring or dispersing the mixture, and removing the solvent. The solvent removing method is carried out by, for example, filtration or distillation so that the solvent is distilled off. After removal of the solvent, the mixture may be further baked at 100° C. or higher. The baking is not particularly limited as long as the temperature and the time are adjusted such that the electrophotographic characteristics can be obtained. In the wet method, the moisture contained in the inorganic particles may be removed before the electron-accepting compound is added, and examples thereof include a method of removing the moisture while stirring and heating the moisture in a solvent and a method of removing the moisture by azeotropically boiling the moisture with a solvent.

The electron-accepting compound may be attached to the surface before the inorganic particles are subjected to a surface treatment with a surface treatment agent or simultaneously with the surface treatment performed on the inorganic particles with a surface treatment agent.

The content of the electron-accepting compound may be, for example, 0.01% by mass or greater and 20% by mass or less and preferably 0.01% by mass or greater and 10% by mass or less with respect to the amount of the inorganic particles.

Examples of the binder resin used for the undercoat layer include known polymer compounds such as an acetal resin (such as polyvinyl butyral), a polyvinyl alcohol resin, a polyvinyl acetal resin, a casein resin, a polyamide resin, a cellulose resin, gelatin, a polyurethane resin, a polyester resin, an unsaturated polyester resin, a methacrylic resin, an acrylic resin, a polyvinyl chloride resin, a polyvinyl acetate resin, a vinyl chloride-vinyl acetate-maleic anhydride resin, a silicone resin, a silicone-alkyd resin, a urea resin, a phenol resin, a phenol-formaldehyde resin, a melamine resin, a urethane resin, an alkyd resin, and an epoxy resin; a zirconium chelate compound; a titanium chelate compound; an aluminum chelate compound; a titanium alkoxide compound; an organic titanium compound; and known materials such as a silane coupling agent.

Examples of the binder resin used for the undercoat layer include a charge-transporting resin containing a charge-transporting group, and a conductive resin (such as polyaniline).

Among these, as the binder resin used for the undercoat layer, for example, a resin insoluble in a coating solvent of the upper layer is preferable, and a resin obtained by reaction between a curing agent and at least one resin selected from the group consisting of a thermosetting resin such as a urea resin, a phenol resin, a phenol-formaldehyde resin, a melamine resin, a urethane resin, an unsaturated polyester resin, an alkyd resin, or an epoxy resin; a polyamide resin, a polyester resin, a polyether resin, a methacrylic resin, an acrylic resin, a polyvinyl alcohol resin, and a polyvinyl acetal resin is particularly preferable. In a case where these binder resins are used in combination of two or more kinds thereof, the mixing ratio thereof is set as necessary.

The undercoat layer may contain various additives for improving the electrical properties, the environmental stability, and the image quality.

Examples of the additives include known materials, for example, an electron-transporting pigment such as a polycyclic condensed pigment or an azo-based pigment, a zirconium chelate compound, a titanium chelate compound, an aluminum chelate compound, a titanium alkoxide compound, an organic titanium compound, and a silane coupling agent. The silane coupling agent is used for a surface treatment of the inorganic particles as described above, but may be further added to the undercoat layer as an additive.

Examples of the silane coupling agent serving as an additive include vinyltrimethoxysilane, 3-methacryloxypropyl-tris(2-methoxyethoxy)silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, vinyltriacetoxysilane, 3-mercaptopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N,N-bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane, and 3-chloropropyltrimethoxysilane.

Examples of the zirconium chelate compound include zirconium butoxide, ethyl zirconium acetoacetate, zirconium triethanolamine, acetylacetonate zirconium butoxide, ethyl zirconium butoxide acetoacetate, zirconium acetate, zirconium oxalate, zirconium lactate, zirconium phosphonate, zirconium octanoate, zirconium naphthenate, zirconium laurate, zirconium stearate, zirconium isostearate, zirconium butoxide methacrylate, stearate zirconium butoxide, and isostearate zirconium butoxide.

Examples of the titanium chelate compound include tetraisopropyl titanate, tetranormal butyl titanate, a butyl titanate dimer, tetra(2-ethylhexyl) titanate, titanium acetylacetonate, polytitanium acetylacetonate, titanium octylene glycolate, titanium lactate ammonium salt, titanium lactate, titanium lactate ethyl ester, titanium triethanol aminate, and polyhydroxy titanium stearate.

Examples of the aluminum chelate compound include aluminum isopropylate, monobutoxyaluminum diisopropylate, aluminum butyrate, diethylacetoacetate aluminum diisopropylate, and aluminum tris(ethylacetoacetate).

These additives may be used alone or in the form of a mixture or a polycondensate of a plurality of compounds.

The undercoat layer may have, for example, a Vickers hardness of 35 or greater. The surface roughness (ten-point average roughness) of the undercoat layer may be adjusted, for example, to ½ from 1/(4n) (n represents a refractive index of an upper layer) of a laser wavelength k for exposure to be used to suppress moire fringes.

Resin particles or the like may be added to the undercoat layer to adjust the surface roughness. Examples of the resin particles include silicone resin particles and crosslinked polymethyl methacrylate resin particles. Further, the surface of the undercoat layer may be polished to adjust the surface roughness. Examples of the polishing method include buff polishing, a sandblast treatment, wet honing, and a grinding treatment.

The formation of the undercoat layer is not particularly limited, and a known forming method is used. For example, a coating film of a coating solution for forming an undercoat layer in which the above-described components are added to a solvent is formed, and the coating film is dried and, as necessary, heated.

Examples of the solvent for preparing the coating solution for forming an undercoat layer include known organic solvents such as an alcohol-based solvent, an aromatic hydrocarbon solvent, a halogenated hydrocarbon solvent, a ketone-based solvent, a ketone alcohol-based solvent, an ether-based solvent, and an ester-based solvent.

Specific examples of these solvents include typical organic solvents such as methanol, ethanol, n-propanol, iso-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, ethyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene.

Examples of the method of dispersing the inorganic particles when preparing the coating solution for forming an undercoat layer include known methods such as a roll mill, a ball mill, a vibration ball mill, an attritor, a sand mill, a colloid mill, and a paint shaker.

Examples of the method of coating the conductive substrate with the coating solution for forming an undercoat layer include typical methods such as a dip coating method, a blade coating method, a wire bar coating method, a spray coating method, a bead coating method, an air knife coating method, and a curtain coating method.

The average thickness of the undercoat layer is, for example, preferably 10 μm or greater and 40 μm or less, more preferably 14 μm or greater and 36 μm or less, still more preferably 18 μm or greater and 32 μm or less, and even still more preferably 20 μm or greater and 30 μm or less.

Interlayer

An interlayer may be further provided between the undercoat layer and the photosensitive layer.

The interlayer is, for example, a layer containing a resin. Examples of the resin used for the interlayer include a polymer compound, for example, an acetal resin (such as polyvinyl butyral), a polyvinyl alcohol resin, a polyvinyl acetal resin, a casein resin, a polyamide resin, a cellulose resin, gelatin, a polyurethane resin, a polyester resin, a methacrylic resin, an acrylic resin, a polyvinyl chloride resin, a polyvinyl acetate resin, a vinyl chloride-vinyl acetate-maleic anhydride resin, a silicone resin, a silicone-alkyd resin, a phenol-formaldehyde resin, or a melamine resin.

The interlayer may be a layer containing an organometallic compound. Examples of the organometallic compound used for the interlayer include an organometallic compound containing metal atoms such as zirconium, titanium, aluminum, manganese, and silicon.

The compounds used for the interlayer may be used alone or in the form of a mixture or a polycondensate of a plurality of compounds.

Among these, it is preferable that the interlayer is, for example, a layer containing an organometallic compound having a zirconium atom or a silicon atom.

The formation of the interlayer is not particularly limited, and a known forming method is used. For example, a coating film of a coating solution for forming an interlayer in which the above-described components are added to a solvent is formed, and the coating film is dried and, as necessary, heated.

Examples of the coating method of forming the interlayer include typical methods such as a dip coating method, a push-up coating method, a wire bar coating method, a spray coating method, a blade coating method, an air knife coating method, and a curtain coating method.

The thickness of the interlayer is set to be, for example, preferably in a range of 0.1 μm or greater and 3 μm or less. The interlayer may be used as the undercoat layer. Charge Generation Layer

The charge generation layer is, for example, a layer containing a charge generation material and a binder resin. Further, the charge generation layer may be a deposition layer of the charge generation material. The deposition layer of the charge generation material is, for example, appropriate in a case where an incoherent light source such as a light emitting diode (LED) or an organic electro-luminescence (EL) image array is used.

Examples of the charge generation material include an azo pigment such as bisazo or trisazo; a fused ring aromatic pigment such as dibromoanthanthrone; a perylene pigment; a pyrrolopyrrole pigment; a phthalocyanine pigment; zinc oxide; and trigonal selenium.

Among these, for example, a metal phthalocyanine pigment or a metal-free phthalocyanine pigment is preferably used as the charge generation material in order to deal with laser exposure in a near infrared region. Specifically, for example, at least one selected from the group consisting of hydroxygallium phthalocyanine, chlorogallium phthalocyanine, dichlorotin phthalocyanine, and titanyl phthalocyanine is preferable, hydroxygallium phthalocyanine and/or chlorogallium phthalocyanine is more preferable, and hydroxygallium phthalocyanine is still more preferable. Hydroxygallium phthalocyanine has an absorption peak at a wavelength of 678 nm.

For example, a fused ring aromatic pigment such as dibromoanthanthrone; a thioindigo-based pigment; a porphyrazine compound; zinc oxide; trigonal selenium; or a bisazo pigment is preferable as the charge generation material in order to deal with laser exposure in a near ultraviolet region.

The above-described charge generation material may also be used even in a case where an incoherent light source such as an LED or an organic EL image array having a center wavelength of light emission at 450 nm or greater and 780 nm or less is used, but from the viewpoint of the resolution, the electric field intensity in the photosensitive layer is increased, and a decrease in charge due to injection of a charge from the substrate, that is, image defects referred to as so-called black spots are likely to occur when a thin film having a thickness of 20 m or less is used as the photosensitive layer. The above-described tendency is evident when a p-type semiconductor such as trigonal selenium or a phthalocyanine pigment is used as the charge generation material that is likely to generate a dark current.

Meanwhile, in a case where an n-type semiconductor such as a fused ring aromatic pigment, a perylene pigment, or an azo pigment is used as the charge generation material, a dark current is unlikely to be generated, and image defects referred to as black spots can be suppressed even in a case where a thin film is used as the photosensitive layer. The n-type is determined by the polarity of the flowing photocurrent using a typically used time-of-flight method, and a material in which electrons more easily flow as carriers than positive holes is determined as the n-type.

The binder resin used for the charge generation layer is selected from a wide range of insulating resins, and the binder resin may be selected from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, and polysilane.

Examples of the binder resin include a polyvinyl butyral resin, a polyarylate resin (a polycondensate of bisphenols and aromatic divalent carboxylic acid), a polycarbonate resin, a polyester resin, a phenoxy resin, a vinyl chloride-vinyl acetate copolymer, a polyamide resin, an acrylic resin, a polyacrylamide resin, a polyvinylpyridine resin, a cellulose resin, a urethane resin, an epoxy resin, casein, a polyvinyl alcohol resin, and a polyvinylpyrrolidone resin. Here, the term “insulating” denotes that the volume resistivity is 1×10¹³ Ω·cm or greater. These binder resins may be used alone or in the form of a mixture of two or more kinds thereof.

The blending ratio between the charge generation material and the binder resin is, for example, preferably in a range of 10:1 to 1:10 in terms of the mass ratio.

The charge generation layer may also contain other known additives.

The formation of the charge generation layer is not particularly limited, and a known forming method is used. For example, a coating film of a coating solution for forming a charge generation layer in which the above-described components are added to a solvent is formed, and the coating film is dried and, as necessary, heated. The charge generation layer may be formed by vapor deposition of the charge generation material. The formation of the charge generation layer by vapor deposition is, for example, particularly appropriate in a case where a fused ring aromatic pigment or a perylene pigment is used as the charge generation material.

Examples of the solvent for preparing the coating solution for forming a charge generation layer include methanol, ethanol, n-propanol, n-butanol, benzyl alcohol, methyl cellosolve, ethyl cellosolve, acetone, methyl ethyl ketone, cyclohexanone, methyl acetate, n-butyl acetate, dioxane, tetrahydrofuran, methylene chloride, chloroform, chlorobenzene, and toluene. These solvents are used alone or in the form of a mixture of two or more kinds thereof.

As a method of dispersing particles (for example, the charge generation material) in the coating solution for forming a charge generation layer, for example, a media disperser such as a ball mill, a vibration ball mill, an attritor, a sand mill, or a horizontal sand mill, or a medialess disperser such as a stirrer, an ultrasonic disperser, a roll mill, or a high-pressure homogenizer is used. Examples of the high-pressure homogenizer include a collision type high-pressure homogenizer in which a dispersion liquid is dispersed by a liquid-liquid collision or a liquid-wall collision in a high-pressure state, and a penetration type high-pressure homogenizer in which a dispersion liquid is dispersed by causing the dispersion liquid to penetrate through a micro-flow path in a high-pressure state.

During the dispersion, it is effective to set the average particle diameter of the charge generation material in the coating solution for forming a charge generation layer to 0.5 μm or less, for example, preferably 0.3 μm or less, and more preferably 0.15 μm or less.

Examples of the method of coating the undercoat layer (or the interlayer) with the coating solution for forming a charge generation layer include typical methods such as a dip coating method, a blade coating method, a wire bar coating method, a spray coating method, a bead coating method, an air knife coating method, and a curtain coating method. From the viewpoint of the productivity of continuously forming the charge generation layer and the charge transport layer, for example, a dip coating method is preferable as a method of forming the charge generation layer.

The average thickness of the charge generation layer is, for example, set to be in a range of 0.05 μm or greater and 5.0 μm or less, a range of 0.10 μm or greater and 2.0 μm or less, or a range of 0.15 μm or greater and 1.0 μm or less.

Charge Transport Layer

The charge transport layer is, for example, a layer containing a charge transport material and a binder resin. The charge transport layer may be a layer containing a polymer charge transport material.

Examples of the charge transport material include a quinone-based compound such as p-benzoquinone, chloranil, bromanil, or anthraquinone; a tetracyanoquinodimethane-based compound; a fluorenone compound such as 2,4,7-trinitrofluorenone; a xanthone compound; a benzophenone-based compound; a cyanovinyl-based compound; and an electron-transporting compound such as an ethylene-based compound. Examples of the charge transport material include a positive hole-transporting compound such as a triarylamine-based compound, a benzidine-based compound, an arylalkane-based compound, an aryl-substituted ethylene-based compound, a stilbene-based compound, an anthracene-based compound, or a hydrazone-based compound. These charge transport materials may be used alone or in combination of two or more kinds thereof, but are not limited thereto.

Examples of the polymer charge transport material include known chemical substances having charge transport properties, such as poly-N-vinylcarbazole and polysilane. For example, a polyester-based polymer charge transport material is preferable. The polymer charge transport material may be used alone or in combination with a binder resin.

Examples of the charge transport material or the polymer charge transport material include a polycyclic aromatic compound, an aromatic nitro compound, an aromatic amine compound, a heterocyclic compound, a hydrazone compound, a styryl compound, an enamine compound, a benzidine compound, a triarylamine compound (particularly, a triphenylamine compound), a diamine compound, an oxadiazole compound, a carbazole compound, an organic polysilane compound, a pyrazoline compound, an indole compound, an oxazole compound, an isoxazole compound, a thiazole compound, a thiadiazole compound, an imidazole compound, a pyrazole compound, a triazole compound, a cyano compound, a benzofuran compound, an aniline compound, a butadiene compound, and a resin containing a group derived from any of these substances. Specific examples thereof include compounds described in paragraphs 0078 to 0080 of JP2021-117377A, paragraphs 0046 to 0048 of JP2019-035900A, paragraphs 0052 and 0053 of JP2019-012141A, paragraphs 0122 to 0134 of JP2021-071565A, paragraphs 0101 to 0110 of JP2021-015223A, paragraph 0116 of JP2013-097300A, paragraphs 0309 to 0316 of WO2019/070003A, paragraphs 0103 to 0107 of JP2018-159087A, and paragraphs 0102 to 0113 of JP2021-148818A.

From the viewpoint of the charge mobility, for example, it is preferable that the charge transport material contains at least one selected from the group consisting of a compound (C1) represented by Formula (C1), a compound (C2) represented by Formula (C2), a compound (C3) represented by Formula (C3), and a compound (C4) represented by Formula (C4).

In Formula (C1), Ar^T1, Ar^T2, and Ar^T3 each independently represent an aryl group, —C₆H₄—C(R^T4)═C(R^T5)(R^T6), or —C₆H₄—CH═CH—CH═C(R^T7)(R^T8). R^T4, R^T5, R^T6, R^T7, and R^T8 each independently represent a hydrogen atom, an alkyl group, or an aryl group. In a case where R^T5 and R^T6 represent an aryl group, the aryl groups may be linked via a divalent group of —C(R⁵¹)(R⁵²)— and/or —C(R⁶¹)═C(R⁶²)—, R⁵¹, R⁵², R⁶¹, and R⁶² each independently represent a hydrogen atom or an alkyl group having 1 or more and 3 or less carbon atoms.

The group in Formula (C1) may be substituted with a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, an alkoxy group having 1 or more and 5 or less carbon atoms, or a substituted amino group substituted with an alkyl group having 1 or more and 3 or less carbon atoms.

From the viewpoint of the charge mobility, as the compound (C1), for example, a compound containing at least one of an aryl group or —C₆H₄—CH═CH—CH═C(R^T7)(R^T8) is preferable, and a compound (G′1) represented by Formula (C′1) is more preferable.

In Formula (C′1), R^T111, R^T112, R^T121, R^T122, R^T131, and R^T132 each independently represent a hydrogen atom, a halogen atom, an alkyl group (for example, preferably an alkyl group having 1 or more and 3 or less carbon atoms), an alkoxy group (for example, preferably an alkoxy group having 1 or more and 3 or less carbon atoms), a phenyl group, or a phenoxy group. Tj1, Tj2, Tj3, Tk1, Tk2, and Tk3 each independently represent 0, 1, or 2.

In Formula (C2), R^T201, R^T202, R^T211, and R^T212 each independently represent a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, an alkoxy group having 1 or more and 5 or less carbon atoms, an amino group substituted with an alkyl group having 1 or 2 carbon atoms, an aryl group, —C(R^T21)═C(R^T22)(R^T23), or —CH═CH—CH═C(R^T24)(R^T25). R^T21, R^T22, R^T23, R^T24, and R^T25 each independently represent a hydrogen atom, an alkyl group, or an aryl group. R^T221 and R^T222 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, or an alkoxy group having 1 or more and 5 or less carbon atoms. Tm1, Tm2, Tn1, and Tn2 each independently represent 0, 1, or 2.

The group in Formula (C2) may be substituted with a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, an alkoxy group having 1 or more and 5 or less carbon atoms, or a substituted amino group substituted with an alkyl group having 1 or more and 3 or less carbon atoms.

From the viewpoint of the charge mobility, as the compound (C2), for example, a compound containing at least one of an alkyl group, an aryl group, or —CH═CH—CH═C(R^T24)(R^T25) is preferable, and a compound containing two of an alkyl group, an aryl group, or —CH═CH—CH═C(R^T24)(R^T25) is more preferable.

In Formula (C3), RT³⁰¹, RT³⁰², RT³¹¹, and RT³¹² each independently represent a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, an alkoxy group having 1 or more and 5 or less carbon atoms, an amino group substituted with an alkyl group having 1 or 2 carbon atoms, an aryl group, —C(RT³¹)═C(RT³²)(RT³³), or —CH═CH—CH═C(R^T34)(R^T35). RT³¹, RT³², RT³³, RT³⁴, and RT³⁵ each independently represent a hydrogen atom, an alkyl group, or an aryl group. RT³²¹, RT³²², and RT³³¹ each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, or an alkoxy group having 1 or more and 5 or less carbon atoms. To1, To2, Tp1, Tp2, Tq1, Tq2, and Tr1 each independently represent 0, 1, or 2.

The group in Formula (C3) may be substituted with a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, an alkoxy group having 1 or more and 5 or less carbon atoms, or a substituted amino group substituted with an alkyl group having 1 or more and 3 or less carbon atoms.

In Formula (C4), R^T401, R^T402, R^T411, and R^T412 each independently represent a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, an alkoxy group having 1 or more and 5 or less carbon atoms, an amino group substituted with an alkyl group having 1 or 2 carbon atoms, an aryl group, —C(R^T41)═C(R^T42)(R^T43), or —CH═CH—CH═C(R^T44)(R^T45). R^T41, R^T42, R^T43, R^T44, and R^T45 each independently represent a hydrogen atom, an alkyl group, or an aryl group. R^T421, R^T422, and R^T431 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, or an alkoxy group having 1 or more and 5 or less carbon atoms. Ts1, Ts2, Tt1, Tt2, Tu1, Tu2, and Tv1 each independently represent 0, 1, or 2.

The group in Formula (C4) may be substituted with a halogen atom, an alkyl group having 1 or more and 5 or less carbon atoms, an alkoxy group having 1 or more and 5 or less carbon atoms, or a substituted amino group substituted with an alkyl group having 1 or more and 3 or less carbon atoms.

The content of the charge transport material contained in the charge transport layer is, for example, preferably 20% by mass or greater and 70% by mass or less with respect to the total mass of the charge transport layer.

The charge transport layer contains at least a polyarylate resin as the binder resin and, for example, preferably at least the polyarylate resin (1).

The proportion of the polyarylate resin (1) in the total amount of the binder resin contained in the charge transport layer is, for example, preferably 60% by mass or greater, more preferably 70% by mass or greater, still more preferably 80% by mass or greater, and particularly preferably 90% by mass or greater.

The proportion of the polyarylate resin (1) in the total amount of the binder resin contained in the charge transport layer is, for example, preferably 60% by mass or greater, more preferably 70% by mass or greater, still more preferably 80% by mass or greater, and particularly preferably 90% by mass or greater.

According to an example of the exemplary embodiment, the charge transport layer contains the polyarylate resin and a polycarbonate resin as the binder resin. In this case, the mass ratio of both resins (polyarylate resin:polycarbonate resin) is, for example, preferably in a range of 95:5 to 40:60.

In a case where the polyarylate resin (1) and the polycarbonate resin are used in combination, the mass ratio of both resins (polyarylate resin (1):polycarbonate resin) is, for example, preferably in a range of 95:5 to 40:60.

As the polycarbonate resin, for example, a polycarbonate resin with continuous constitutional units having an aromatic ring is preferable, and specific examples thereof include polycarbonate resins used in examples described below.

The charge transport layer may contain other binder resins in addition to the polyarylate resin and the polycarbonate resin. Examples of other binder resins include a polyester resin other than the polyarylate resin, a methacrylic resin, an acrylic resin, a polyvinyl chloride resin, a polyvinylidene chloride resin, a polystyrene resin, a polyvinyl acetate resin, a styrene-butadiene copolymer, a vinylidene chloride-acrylonitrile copolymer, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinyl acetate-maleic anhydride copolymer, a silicone resin, a silicone alkyd resin, a phenol-formaldehyde resin, a styrene-alkyd resin, poly-N-vinylcarbazole, and polysilane. These binder resins may be used alone or in combination of two or more kinds thereof.

The charge transport layer may also contain other known additives. Examples of the additives include an antioxidant, a leveling agent, an antifoaming agent, a filler, and a viscosity adjuster.

The formation of the charge transport layer is not particularly limited, and a known forming method is used. For example, a coating film of a coating solution for forming a charge transport layer in which the above-described components are added to a solvent is formed, and the coating film is dried and, as necessary, heated.

Examples of the solvent for preparing the coating solution for forming a charge transport layer include typical organic solvents, for example, aromatic hydrocarbons such as benzene, toluene, xylene, and chlorobenzene; ketones such as acetone and 2-butanone; halogenated aliphatic hydrocarbons such as methylene chloride, chloroform, and ethylene chloride; and cyclic or linear ethers such as tetrahydrofuran and ethyl ether. These solvents are used alone or in the form of a mixture of two or more kinds thereof.

Examples of the coating method of coating the charge generation layer with the coating solution for forming a charge transport layer include typical methods such as a dip coating method, a blade coating method, a wire bar coating method, a spray coating method, a bead coating method, an air knife coating method, and a curtain coating method.

From the viewpoint of the productivity of the photoreceptor, for example, a dip coating method is preferable as a method of forming the charge transport layer.

From the viewpoints of extending the life of the photoreceptor, the average thickness of the charge transport layer is, for example, 30 μm or greater, preferably 34 μm or greater, and more preferably 38 μm or greater.

From the viewpoint of suppressing unevenness in the layer thickness, the average thickness of the charge transport layer is, for example, preferably 50 μm or less, more preferably 47 μm or less, and still more preferably 45 μm or less.

The average thickness of the charge transport layer is an arithmetic average of the measured values measured by the optical interference type film thickness meter, and the measurement sites are a total of 12 sites at intervals of 90° in the circumferential direction at the position (M), the position (U), and the position (L).

Protective Layer

A protective layer is provided on the photosensitive layer as necessary. The protective layer is provided, for example, for the purpose of preventing a chemical change in the photosensitive layer during charging and further improving the mechanical strength of the photosensitive layer.

Therefore, for example, a layer formed of a cured film (crosslinked film) may be applied to the protective layer. Examples of these layers include the layers described in the items 1) and 2) below.

1) A layer formed of a cured film of a composition containing a reactive group-containing charge transport material having a reactive group and a charge-transporting skeleton in an identical molecule (that is, a layer containing a polymer or a crosslinked body of the reactive group-containing charge transport material)

2) A layer formed of a cured film of a composition containing a non-reactive charge transport material and a reactive group-containing non-charge transport material containing a reactive group without having a charge-transporting skeleton (that is, a layer containing the non-reactive charge transport material and a polymer or crosslinked body of the reactive group-containing non-charge transport material)

Examples of the reactive group of the reactive group-containing charge transport material include known reactive groups such as a chain polymerizable group, an epoxy group, —OH, —OR [here, R represents an alkyl group], —NH₂, —SH, —COOH, and —SiR^Q1_3-Qn(OR^Q2)_Qn [here, R^Q1 represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group, R^Q2 represents a hydrogen atom, an alkyl group, or a trialkylsilyl group, and Qn represents an integer of 1 to 3].

The chain polymerizable group is not particularly limited as long as the group is a functional group capable of radical polymerization and is, for example, a functional group containing a group having at least a carbon double bond. Specific examples thereof include a vinyl group, a vinyl ether group, a vinyl thioether group, a phenyl vinyl group, a vinyl phenyl group, an acryloyl group, a methacryloyl group, and a group containing at least one selected from derivatives thereof. Among these, from the viewpoint that the reactivity is excellent, for example, a vinyl group, a phenylvinyl group, a vinylphenyl group, an acryloyl group, a methacryloyl group, and a group containing at least one selected from derivatives thereof are preferable as the chain polymerizable group.

The charge-transporting skeleton of the reactive group-containing charge transport material is not particularly limited as long as the skeleton is a known structure in the electrophotographic photoreceptor, and examples thereof include a structure conjugated with a nitrogen atom, which is a skeleton derived from a nitrogen-containing positive hole-transporting compound such as a triarylamine-based compound, a benzidine-based compound, or a hydrazone-based compound. Among these, for example, a triarylamine skeleton is preferable.

The reactive group-containing charge transport material having the reactive group and the charge-transporting skeleton, the non-reactive charge transport material, and the reactive group-containing non-charge transport material may be selected from known materials.

The protective layer may also contain other known additives.

The formation of the protective layer is not particularly limited, and a known forming method is used. For example, a coating film of a coating solution for forming a protective layer in which the above-described components are added to a solvent is formed, and the coating film is dried and, as necessary, subjected to a curing treatment such as heating.

Examples of the solvent for preparing the coating solution for forming a protective layer include an aromatic solvent such as toluene or xylene; a ketone-based solvent such as methyl ethyl ketone, methyl isobutyl ketone, or cyclohexanone; an ester-based solvent such as ethyl acetate or butyl acetate; an ether-based solvent such as tetrahydrofuran or dioxane; a cellosolve-based solvent such as ethylene glycol monomethyl ether; and an alcohol-based solvent such as isopropyl alcohol or butanol. These solvents are used alone or in the form of a mixture of two or more kinds thereof.

The coating solution for forming a protective layer may be a solvent-less coating solution.

Examples of the method of coating the photosensitive layer (such as the charge transport layer) with the coating solution for forming a protective layer include typical methods such as a dip coating method, a push-up coating method, a wire bar coating method, a spray coating method, a blade coating method, an air knife coating method, and a curtain coating method.

The thickness of the protective layer is set to be, for example, preferably in a range of 1 μm or greater and 20 μm or less and more preferably in a range of 2 μm or greater and 10 μm or less.

Image Forming Apparatus and Process Cartridge

An image forming apparatus according to the present exemplary embodiment includes the electrophotographic photoreceptor, a charging device that charges a surface of the electrophotographic photoreceptor, an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the electrophotographic photoreceptor, a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner to form a toner image, and a transfer device that transfers the toner image to a surface of a recording medium. Further, the electrophotographic photoreceptor according to the present exemplary embodiment is employed as the electrophotographic photoreceptor.

As the image forming apparatus according to the present exemplary embodiment, known image forming apparatuses such as an apparatus including a fixing device that fixes the toner image transferred to the surface of a recording medium; a direct transfer type apparatus that transfers the toner image formed on the surface of the electrophotographic photoreceptor directly to the recording medium; an intermediate transfer type apparatus that primarily transfers the toner image formed on the surface of the electrophotographic photoreceptor to the surface of the intermediate transfer member and secondarily transfers the toner image transferred to the surface of the intermediate transfer member to the surface of the recording medium; an apparatus including a cleaning device that cleans the surface of the electrophotographic photoreceptor after the transfer of the toner image and before the charging; an apparatus including a charge erasing device that erases the charges on the surface of the electrophotographic photoreceptor by applying the charge erasing light after the transfer of the toner image and before the charging; and an apparatus including an electrophotographic photoreceptor heating member for increasing the temperature of the electrophotographic photoreceptor and decreasing the relative temperature are employed.

In a case of the intermediate transfer type apparatus, the transfer device is, for example, configured to include an intermediate transfer member having a surface onto which the toner image is transferred, a primary transfer device primarily transferring the toner image formed on the surface of the electrophotographic photoreceptor to the surface of the intermediate transfer member, and a secondary transfer device secondarily transferring the toner image transferred to the surface of the intermediate transfer member to the surface of the recording medium.

The image forming apparatus according to the present exemplary embodiment may be any of a dry development type image forming apparatus or a wet development type (development type using a liquid developer) image forming apparatus.

In the image forming apparatus according to the present exemplary embodiment, for example, the portion including the electrophotographic photoreceptor may have a cartridge structure (process cartridge) that is attachable to and detachable from the image forming apparatus. As the process cartridge, for example, a process cartridge including the electrophotographic photoreceptor according to the present exemplary embodiment is preferably used. The process cartridge may include, for example, at least one selected from the group consisting of a charging device, an electrostatic latent image forming device, a developing device, and a transfer device in addition to the electrophotographic photoreceptor.

Hereinafter, an example of the image forming apparatus according to the present exemplary embodiment will be described, but the present exemplary embodiment is not limited thereto. Further, main parts shown in the figures will be described, but description of other parts will not be provided.

FIG. 2 is a schematic configuration view showing an example of the image forming apparatus according to the present exemplary embodiment.

As shown in FIG. 2, an image forming apparatus 100 according to the present exemplary embodiment includes a process cartridge 300 including an electrophotographic photoreceptor 7, an exposure device 9 (an example of an electrostatic latent image forming device), a transfer device 40 (primary transfer device), and an intermediate transfer member 50. In the image forming apparatus 100, the exposure device 9 is disposed at a position that can be exposed to the electrophotographic photoreceptor 7 from an opening portion of the process cartridge 300, the transfer device 40 is disposed at a position that faces the electrophotographic photoreceptor 7 via the intermediate transfer member 50, and the intermediate transfer member 50 is disposed such that a part of the intermediate transfer member 50 is in contact with the electrophotographic photoreceptor 7. Although not shown, the image forming apparatus also includes a secondary transfer device that transfers the toner image transferred to the intermediate transfer member 50 to a recording medium (for example, paper). The intermediate transfer member 50, the transfer device 40 (primary transfer device), and the secondary transfer device (not shown) correspond to an example of the transfer device.

The process cartridge 300 in FIG. 2 integrally supports the electrophotographic photoreceptor 7, a charging device 8 (an example of the charging device), a developing device 11 (an example of the developing device), and a cleaning device 13 (an example of the cleaning device) in a housing. The cleaning device 13 has a cleaning blade (an example of the cleaning member) 131, and the cleaning blade 131 is disposed to come into contact with the surface of the electrophotographic photoreceptor 7. The cleaning member may be a conductive or insulating fibrous member instead of the aspect of the cleaning blade 131, and may be used alone or in combination with the cleaning blade 131.

FIG. 2 shows an example of an image forming apparatus including a fibrous member 132 (roll shape) that supplies a lubricant 14 to the surface of the electrophotographic photoreceptor 7 and a fibrous member 133 (flat brush shape) that assists cleaning, but these are disposed as necessary.

Hereinafter, each configuration of the image forming apparatus according to the present exemplary embodiment will be described.

Charging Device

As the charging device 8, for example, a contact-type charger formed of a conductive or semi-conductive charging roller, a charging brush, a charging film, a charging rubber blade, a charging tube, or the like is used. Further, a known charger such as a non-contact type roller charger, or a scorotron charger or a corotron charger using corona discharge is also used.

Exposure Device

Examples of the exposure device 9 include an optical system device that exposes the surface of the electrophotographic photoreceptor 7 to light such as a semiconductor laser beam, LED light, and liquid crystal shutter light in a predetermined image pattern. The wavelength of the light source is within the spectral sensitivity region of the electrophotographic photoreceptor. As the wavelength of a semiconductor laser, near infrared, which has an oscillation wavelength in the vicinity of 780 nm, is mostly used. However, the wavelength is not limited thereto, and a laser having an oscillation wavelength of approximately 600 nm or a laser having an oscillation wavelength of 400 nm or greater and 450 nm or less as a blue laser may also be used. Further, a surface emission type laser light source capable of outputting a multi-beam is also effective for forming a color image.

Developing Device

Examples of the developing device 11 include a typical developing device that performs development in contact or non-contact with the developer. The developing device 11 is not particularly limited as long as the developing device has the above-described functions, and is selected depending on the purpose thereof. Examples of the developing device include known developing machines having a function of attaching a one-component developer or a two-component developer to the electrophotographic photoreceptor 7 using a brush, a roller, or the like. Among these, for example, a developing device formed of a developing roller having a surface on which a developer is held is preferably used.

The developer used in the developing device 11 may be a one-component developer containing only a toner or a two-component developer containing a toner and a carrier. Further, the developer may be magnetic or non-magnetic. Known developers are employed as these developers.

Cleaning Device

As the cleaning device 13, a cleaning blade type device including the cleaning blade 131 is used. In addition to the cleaning blade type device, a fur brush cleaning type device or a simultaneous development cleaning type device may be employed.

Transfer Device

Examples of the transfer device 40 include a known transfer charger such as a contact type transfer charger using a belt, a roller, a film, or a rubber blade, and a scorotron transfer charger or a corotron transfer charger using corona discharge.

Intermediate Transfer Member

As the intermediate transfer member 50, a belt-like intermediate transfer member (intermediate transfer belt) containing semi-conductive polyimide, polyamide-imide, polycarbonate, polyarylate, polyester, rubber, or the like is used. Further, as the form of the intermediate transfer member, a drum-like intermediate transfer member may be used in addition to the belt-like intermediate transfer member.

FIG. 3 is a schematic configuration view showing another example of the image forming apparatus according to the present exemplary embodiment.

An image forming apparatus 120 shown in FIG. 3 is a tandem type multicolor image forming apparatus on which four process cartridges 300 are mounted. The image forming apparatus 120 is formed such that four process cartridges 300 are arranged in parallel on the intermediate transfer member 50, and one electrophotographic photoreceptor is used for each color. The image forming apparatus 120 has the same configuration as the image forming apparatus 100 except that the image forming apparatus 120 is of a tandem type.

EXAMPLES

Hereinafter, exemplary embodiments of the invention will be described in detail based on examples, but the exemplary embodiments of the invention are not limited to the examples. In the following description, “parts” and “%” are on a mass basis unless otherwise specified.

In the following description, the synthesis, the production, the treatment, the measurement, and the like are carried out at room temperature (25° C.±3° C.) unless otherwise specified.

Synthesis of Polyarylate Resin (1)

The polyarylate resins (1-1) to (1-3) listed in Table 1 are synthesized.

A2-3 listed in Table 1 is a specific example of the dicarboxylic acid unit (A) described above.

B1-4 and the like listed in Table 1 are specific examples of the diol unit (B) described above.

TABLE 1
Polyarylate resin	Dicarboxylic acid unit (A)	Diol unit (B)
(1-1)	A2-3	B1-4
(1-2)	A2-3	B1-2
(1-3)	A2-3	B2-6

Production of Photoreceptor

Example 1

Formation of Undercoat Layer

A cylindrical aluminum tube having an outer diameter of 30 mm, a length of 250 mm, and a thickness of 1 mm is prepared as a conductive substrate.

100 parts of zinc oxide (average particle diameter of 70 nm, specific surface area of 15 m²/g, manufactured by Tayca Corporation) is stirred and mixed with 500 parts of toluene, 1.3 parts of a silane coupling agent (trade name: KBM603, manufactured by Shin-Etsu Chemical Co., Ltd., N-2-(aminoethyl)-3-aminopropyltrimethoxysilane) is added thereto, and the mixture is stirred for 2 hours. Thereafter, toluene is distilled off under reduced pressure and baked at 120° C. for 3 hours to obtain zinc oxide subjected to a surface treatment with a silane coupling agent.

110 parts of the surface-treated zinc oxide is stirred and mixed with 500 parts of tetrahydrofuran, a solution obtained by dissolving 0.6 parts of alizarin in 50 parts of tetrahydrofuran is added thereto, and the mixture is stirred at 50° C. for 5 hours. Thereafter, the solid content is separated by filtration by carrying out filtration under reduced pressure and dried at 60° C. under reduced pressure, thereby obtaining zinc oxide with alizarin.

100 parts of a solution obtained by dissolving 60 parts of the zinc oxide with alizarin, 13.5 parts of a curing agent (blocked isocyanate, trade name: SUMIDUR 3175, manufactured by Sumitomo Bayer Urethane Co., Ltd.), and 15 parts of a butyral resin (trade name: S-LEC BM-1, manufactured by Sekisui Chemical Co., Ltd.) in 68 parts of methyl ethyl ketone is mixed with 5 parts of methyl ethyl ketone, and the solution is dispersed in a sand mill for 2 hours using 1 mmφ glass beads, thereby obtaining a dispersion liquid. 0.005 parts of dioctyltin dilaurate as a catalyst and 4 parts of silicone resin particles (trade name: TOSPEARL 145, manufactured by Momentive Performance Materials Inc.) are added to the dispersion liquid, thereby obtaining a coating solution for forming an undercoat layer. The outer peripheral surface of the conductive substrate is coated with the coating solution for forming an undercoat layer by a dip coating method, and the coating solution is dried and cured at 170° C. for 40 minutes, thereby forming an undercoat layer with an average thickness of 20 μm.

Formation of Charge Generation Layer

A mixture of 15 parts of hydroxygallium phthalocyanine as a charge generation material (having diffraction peaks at positions where Bragg angles (2θ±0.2°) in the X-ray diffraction spectrum using Cuka characteristic X-rays are at least 7.5°, 9.9°, 12.5, 16.3°, 18.6°, 25.1°, and 28.3°), 10 parts of a vinyl chloride-vinyl acetate copolymer resin (trade name: VMCH, Nippon Unicar Company Limited) as a binder resin, and 200 parts of n-butyl acetate is dispersed in a sand mill for 4 hours using glass beads having a diameter of 1 mm. 175 parts of n-butyl acetate and 180 parts of methyl ethyl ketone are added to the dispersion liquid, and the mixture is stirred, thereby obtaining a coating solution for forming a charge generation layer.

In a case where a conductive substrate having an undercoat layer is dipped in the coating solution and the conductive substrate is pulled upward from the coating solution in the gravity direction, the pull-up speed is controlled such that the absorbance ratio listed in Table 2 is obtained, the pull-up speed on the upper end side is controlled to be slower than that in the central portion, and the pull-up speed on the lower end side is controlled to be faster than that in the central portion. Here, the term “central portion” denotes a region that occupies a length of 50% of the total length L of the photoreceptor in the axial direction.

Formation of Charge Transport Layer

60 parts of the polyarylate resin (1-1) as a binder resin and 40 parts of CTM-1 as a charge transport material are dissolved in 270 parts of tetrahydrofuran and 30 parts of toluene, thereby obtaining a coating solution for forming a charge transport layer. The charge generation layer is dipped in and coated with the coating solution for forming a charge transport layer. Next, the coating solution is dried at 145° C. for 30 minutes, thereby forming a charge transport layer. The average thickness of the charge transport layer is as listed in Table 2.

Examples 2 to 5 and Comparative Example 1

Each photoreceptor is prepared in the same manner as in Example 1 except that the speed ratio of the pull-up speed from the coating solution is changed in a case where the charge generation layer is dipped in and coated with the coating solution.

Examples 6 and 7

Each photoreceptor is prepared in the same manner as in Example 1 except that the kind of the polyarylate resin in the formation of the charge transport layer is changed to the kind listed in Table 2.

Examples 8 and 9

Each photoreceptor is prepared in the same manner as in Example 1 except that a part of the polyarylate resin in the formation of the charge transport layer is replaced with a polycarbonate resin. The structures of the polycarbonate resins (1) and (2) are as shown below.

In the formulae, the numerical values denote the polymerization molar ratios (mol %).

Performance Evaluation of Photoreceptor

Each photoreceptor of the examples and the comparative examples is mounted on an electrophotographic image forming apparatus DocuCentre-V C7775 (manufactured by FUJIFILM Business Innovation Corporation).

Abrasion Resistance

Full-surface halftone images with a density of 30% of a yellow color, a magenta color, a cyan color, and a black color are continuously output onto A3 size plain paper such that 10,000 sheets of images of each color, that is, a total of 40,000 sheets of images are output, under a low-temperature and low-humidity environment of a temperature of 10° C. and a relative humidity of 15%. The average thicknesses (nm) of the charge transport layer before and after the image formation are measured, and a difference between the average thicknesses before and after the image formation is defined as the amount of abrasion (nm). PERMASCOPE (manufactured by Fischer Instruments K.K.) is used as a film thickness measuring device. The amount of abrasion is classified as follows. The results are listed in Table 2.

• • A: The amount of abrasion is less than 800 nm
  • B: The amount of abrasion is 800 nm or greater and less than 1,600 nm
  • C: The amount of abrasion is 1,600 nm or greater and less than 2,400 nm
  • D: The amount of abrasion is 2,400 nm or greater

Charging Unevenness

Surface potential probes connected to a surface potential meter (Trek 334, manufactured by Trek) are installed at positions corresponding to the position (U) and the position (L) and separated from the surface of the photoreceptor by 1 mm. 100,000 sheets of full-surface halftone images with an image density of 30% are output onto A3 size plain paper in an environment of a temperature of 24° C. and a relative humidity of 55%. In the formation of an image on the last sheet of paper, the charging potential of the photoreceptor is measured, a difference between the charging potential at the position (U) and the charging potential at the position (L) is calculated, and the results are classified as follows. The results are listed in Table 2.

• • A: The difference in charging potential is less than 10 V
  • B: The difference in charging potential is 10 V or greater and less than 20 V
  • C: The difference in charging potential is 20 V or greater.

“Iu/Im/Il” in Table 2 denotes a relative value in a case where the value of Im is set to 1.

	TABLE 2
	Photosensitive
	Charge transport layer	layer
	Mixing ratio	Absorbance	Performance of
	between	at wavelength	photoreceptor
	Average			Polycarbonate	polyarylate and	of 678 nm	Abrasion	Charging
	thickness	Polyarylate resin		resin	polycarbonate	Iu/Im/II	resistance	unevenness
	μm	Type	Mw	Type	Mass ratio	—	—	—
Comparative	42	(1-1)	110 × 103	—	100:0	1.00/1/1.00	A	C
example 1
Example 5	42	(1-1)	110 × 103	—	100:0	0.95/1/1.05	A	B
Example 4	42	(1-1)	110 × 103	—	100:0	0.90/1/1.10	A	B
Example 3	42	(1-1)	110 × 103	—	100:0	0.85/1/1.15	A	A
Example 1	42	(1-1)	110 × 103	—	100:0	0.80/1/1.20	A	A
Example 2	42	(1-1)	110 × 103	—	100:0	0.75/1/1.25	A	B
Example 6	42	(1-2)	112 × 103	—	100:0	0.80/1/1.20	B	A
Example 7	42	(1-3)	109 × 103	—	100:0	0.80/1/1.20	B	A
Example 8	42	(1-1)	110 × 103	(1)	50:50	0.90/1/1.10	B	A
Example 9	42	(1-1)	110 × 103	(2)	50:50	0.80/1/1.20	A	A

The electrophotographic photoreceptor, the process cartridge, and the image forming apparatus of the present disclosure include the following aspects. Each formula representing a compound is the same as the formula having the same number described below.

(((1)))

An electrophotographic photoreceptor comprising:

• • a conductive substrate; and
  • a photosensitive layer disposed on the conductive substrate and including a charge generation layer and a charge transport layer,
  • wherein the charge transport layer has an average thickness of 30 μm or greater,
  • the charge transport layer contains a polyarylate resin, and
  • an absorption spectrum measured by peeling off the photosensitive layer and dissolving the photosensitive layer in tetrahydrofuran satisfies Expression (1) and Expression (2),

$\begin{array}{cc}\mathrm{Iu}\le 0.95\times Im& \mathrm{Expression}\left(1\right)\end{array}$ $\begin{array}{cc}1.05\times Im\le I1& \mathrm{Expression}\left(2\right)\end{array}$

• • in a case where a total length of the electrophotographic photoreceptor in an axial direction is defined as L,
  • Im represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled from a center of the electrophotographic photoreceptor in the axial direction,
  • Iu represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the electrophotographic photoreceptor in the axial direction toward one end, and
  • Il represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the electrophotographic photoreceptor in the axial direction toward the other end.(((2)))

The electrophotographic photoreceptor according to (((1))), wherein the absorption spectrum measured by peeling off the photosensitive layer and

• • dissolving the photosensitive layer in tetrahydrofuran satisfies Expression (1-3) and Expression (2-3),

$\begin{array}{cc}0.75\times Im<Iu\le 0.95\times Im& \mathrm{Equation}\left(1-3\right)\end{array}$ $\begin{array}{cc}1.05\times Im\le I1<1.25\times Im& \mathrm{Equation}\left(2-3\right)\end{array}$

• • in a case where a total length of the electrophotographic photoreceptor in an axial direction is defined as L,
  • Im represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled from a center of the electrophotographic photoreceptor in the axial direction,
  • Iu represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the electrophotographic photoreceptor in the axial direction toward one end, and
  • Il represents an absorbance of the photosensitive layer at a wavelength of 678 nm, which is peeled at a position of 0.40 L from the center of the electrophotographic photoreceptor in the axial direction toward the other end.(((3)))

The electrophotographic photoreceptor according to (((1))) or (((2))),

• • wherein the charge generation layer contains hydroxygallium phthalocyanine.(((4)))

The electrophotographic photoreceptor according to any one of (((1))) to (((3))),

• • wherein the polyarylate resin contained in the charge transport layer has a weight-average molecular weight of 80,000 or greater.(((5)))

The electrophotographic photoreceptor according to any one of (((1))) to (((4))),

• • wherein the charge transport layer further contains a polycarbonate resin.(((6)))

The electrophotographic photoreceptor according to any one of (((1))) to (((5))),

• • wherein the polyarylate resin includes a polyarylate resin (1) having a dicarboxylic acid unit (A) represented by Formula (A) and a diol unit (B) represented by Formula (B).(((7)))

The electrophotographic photoreceptor according to (((6))),

• • wherein the polyarylate resin (1) has the dicarboxylic acid unit (A) having at least one selected from the group consisting of a dicarboxylic acid unit (A1) represented by Formula (A1), a dicarboxylic acid unit (A2) represented by Formula (A2), a dicarboxylic acid unit (A3) represented by Formula (A3), and a dicarboxylic acid unit (A4) represented by Formula (A4).(((8)))

The electrophotographic photoreceptor according to (((6))) or (((7))),

• • wherein the polyarylate resin (1) has the diol unit (B) having at least one selected from the group consisting of a diol unit (B1) represented by Formula (B1), a diol unit (B2) represented by Formula (B2), a diol unit (B3) represented by Formula (B3), a diol unit (B4) represented by Formula (B4), a diol unit (B5) represented by Formula (B5), a diol unit (B6) represented by Formula (B6), a diol unit (B7) represented by Formula (B7), and a diol unit (B8) represented by Formula (B8).(((9)))

The electrophotographic photoreceptor according to any one of (((6))) to (((8))),

• • wherein the polyarylate resin (1) has the dicarboxylic acid unit (A) having at least one selected from the group consisting of a dicarboxylic acid unit (A2) represented by Formula (A2) and a dicarboxylic acid unit (A4) represented by Formula (A4).(((10)))

The electrophotographic photoreceptor according to any one of (((6))) to (((9))),

• • wherein the polyarylate resin (1) has the diol unit (B) having at least one selected from the group consisting of a diol unit (B1) represented by Formula (B 1) and a diol unit (B2) represented by Formula (B2).(((11)))

A process cartridge comprising:

• • the electrophotographic photoreceptor according to any one of (((1))) to (((10))),
  • wherein the process cartridge is attachable to and detachable from an image forming apparatus.(((12)))

An image forming apparatus comprising:

• • the electrophotographic photoreceptor according to any one of (((1))) to (((10)));
  • a charging device that charges a surface of the electrophotographic photoreceptor;
  • an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the electrophotographic photoreceptor;
  • a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner to form a toner image; and
  • a transfer device that transfers the toner image to a surface of a recording medium.

The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

1. An electrophotographic photoreceptor comprising: a conductive substrate; anda photosensitive layer disposed on the conductive substrate and including a charge generation layer and a charge transport layer,wherein the charge transport layer has an average thickness of 30 μm or greater,the charge transport layer contains a polyarylate resin, andan absorption spectrum measured by peeling off the photosensitive layer and dissolving the photosensitive layer in tetrahydrofuran satisfies Expression (1) and Expression (2),

2. The electrophotographic photoreceptor according to claim 1, wherein the absorption spectrum measured by peeling off the photosensitive layer and dissolving the photosensitive layer in tetrahydrofuran satisfies Expression (1-3) and Expression (2-3),

3. The electrophotographic photoreceptor according to claim 1, wherein the charge generation layer contains hydroxygallium phthalocyanine.

4. The electrophotographic photoreceptor according to claim 1, wherein the polyarylate resin contained in the charge transport layer has a weight-average molecular weight of 80,000 or greater.

5. The electrophotographic photoreceptor according to claim 1, wherein the charge transport layer further contains a polycarbonate resin.

6. The electrophotographic photoreceptor according to claim 1, wherein the polyarylate resin includes a polyarylate resin (1) having a dicarboxylic acid unit (A) represented by Formula (A) and a diol unit (B) represented by Formula (B),

7. The electrophotographic photoreceptor according to claim 6, wherein the polyarylate resin (1) has the dicarboxylic acid unit (A) having at least one selected from the group consisting of a dicarboxylic acid unit (A1) represented by Formula (A1), a dicarboxylic acid unit (A2) represented by Formula (A2), a dicarboxylic acid unit (A3) represented by Formula (A3), and a dicarboxylic acid unit (A4) represented by Formula (A4),

8. The electrophotographic photoreceptor according to claim 6, wherein the polyarylate resin (1) has the diol unit (B) having at least one selected from the group consisting of a diol unit (B1) represented by Formula (B1), a diol unit (B2) represented by Formula (B2), a diol unit (B3) represented by Formula (B3), a diol unit (B4) represented by Formula (B4), a diol unit (B5) represented by Formula (B5), a diol unit (B6) represented by Formula (B6), a diol unit (B7) represented by Formula (B7), and a diol unit (B8) represented by Formula (B8),

9. The electrophotographic photoreceptor according to claim 6, wherein the polyarylate resin (1) has the dicarboxylic acid unit (A) having at least one selected from the group consisting of a dicarboxylic acid unit (A2) represented by Formula (A2) and a dicarboxylic acid unit (A4) represented by Formula (A4),

10. The electrophotographic photoreceptor according to claim 6, wherein the polyarylate resin (1) has the diol unit (B) having at least one selected from the group consisting of a diol unit (B1) represented by Formula (B1) and a diol unit (B2) represented by Formula (B2),

11. A process cartridge comprising: the electrophotographic photoreceptor according to claim 1,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

12. A process cartridge comprising: the electrophotographic photoreceptor according to claim 2,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

13. A process cartridge comprising: the electrophotographic photoreceptor according to claim 3,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

14. A process cartridge comprising: the electrophotographic photoreceptor according to claim 4,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

15. A process cartridge comprising: the electrophotographic photoreceptor according to claim 5,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

16. A process cartridge comprising: the electrophotographic photoreceptor according to claim 6,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

17. A process cartridge comprising: the electrophotographic photoreceptor according to claim 7,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

18. A process cartridge comprising: the electrophotographic photoreceptor according to claim 8,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

19. A process cartridge comprising: the electrophotographic photoreceptor according to claim 9,wherein the process cartridge is attachable to and detachable from an image forming apparatus.

20. An image forming apparatus comprising: the electrophotographic photoreceptor according to claim 1;a charging device that charges a surface of the electrophotographic photoreceptor;an electrostatic latent image forming device that forms an electrostatic latent image on the charged surface of the electrophotographic photoreceptor;a developing device that develops the electrostatic latent image formed on the surface of the electrophotographic photoreceptor with a developer containing a toner to form a toner image; anda transfer device that transfers the toner image to a surface of a recording medium.