EP4685565A1

EP4685565A1 - Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Info

Publication number: EP4685565A1
Application number: EP24775017.7A
Authority: EP
Inventors: Katsunori TERAOKA; Daisuke Kuboshima; Tomofumi Shimizu; Makoto Shishido; Yoshitaka Imanaka
Original assignee: Kyocera Document Solutions Inc
Current assignee: Kyocera Document Solutions Inc
Priority date: 2023-03-23
Filing date: 2024-05-20
Publication date: 2026-01-28
Also published as: JPWO2024195884A1; WO2024195884A1

Abstract

An electrophotographic photoreceptor includes a conductive substrate (2), a photosensitive layer (3), and a protective layer (5). The photosensitive layer (3) includes a charge generating agent and a hole transporting agent. The protective layer (5) is the top surface layer of the electrophotographic photoreceptor. The protective layer (5) includes a first particle having n-type conductivity and a second particle having no n-type conductivity. Volume resistivity of the second particle is favorably higher than volume resistivity of the first particle.

Description

Technical Field

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

Background Art

When an image forming apparatus including an electrophotographic photoreceptor is used to form images repeatedly, the electrophotographic photoreceptor gradually wears out in some cases. In order to suppress wear and extend the lifetime of the electrophotographic photoreceptor, a hard protective layer is provided on the surface of the electrophotographic photoreceptor in some cases. For example, the protective layer included in the electrophotographic photoreceptor described in Patent Literature 1 includes a composition. This composition is obtained by reacting a silica fine particle having at least a polymerizable unsaturated group with an organic compound having a reactive group capable of forming a chemical bond with the polymerizable unsaturated group.

Citation List

Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No. 2010-14948

Disclosure of Invention

Technical Problem

However, in order to produce the electrophotographic photoreceptor described in Patent Literature 1, it is necessary to react the silica fine particle having a polymerizable unsaturated group with the organic compound having a reactive group capable of forming a chemical bond with the polymerizable unsaturated group. For this reason, the production process of the electrophotographic photoreceptor described in Patent Literature 1 is complicated. Further, the present inventors' study has revealed that the electrophotographic photoreceptor described in Patent Literature 1 leaves room for improvement in terms of sensitivity characteristics and dot reproducibility in a formed image.
The present invention has been made in view of the above problem, and the purpose of the present invention is to provide an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus that can be easily produced, have excellent sensitivity characteristics, and are capable of forming an image with excellent dot reproducibility. Solution to Problem
An electrophotographic photoreceptor according to the present invention includes a conductive substrate, a photosensitive layer, and a protective layer. The photosensitive layer includes a charge generating agent and a hole transporting agent. The protective layer is a top surface layer of the electrophotographic photoreceptor. The protective layer includes a first particle having n-type conductivity and a second particle having no n-type conductivity.
A process cartridge according to the present invention includes at least one selected from the group consisting of a charging device, an exposure device, a development device, a transfer device, a cleaning member, a rubbing roller, and a static elimination device, and the above electrophotographic photoreceptor.
An image forming apparatus according to the present invention includes an image carrier, a charging device that charges a surface of the image carrier, an exposure device that exposes the charged surface of the image carrier to form an electrostatic latent image on the surface of the image carrier, a development device that supplies a toner to the surface of the image carrier to develop the electrostatic latent image as a toner image, and a transfer device that transfers the toner image from the image carrier to a to-be-transferred body. The image carrier is the above electrophotographic photoreceptor.

Advantageous Effects of Invention

The electrophotographic photoreceptor, the process cartridge, and the image forming apparatus according to the present invention can be easily produced, have excellent sensitivity characteristics, and are capable of forming an image with excellent dot reproducibility.

Brief Description of Drawings

[Fig. 1] Fig. 1 is a partial cross-sectional view of a single-layer electrophotographic photoreceptor that is an example of an electrophotographic photoreceptor according to a first embodiment of the present invention.
[Fig. 2] Fig. 2 is a partial cross-sectional view of a single-layer electrophotographic photoreceptor that is an example of the electrophotographic photoreceptor according to the first embodiment of the present invention.
[Fig. 3] Fig. 3 is a partial cross-sectional view of a stacked electrophotographic photoreceptor that is an example of the electrophotographic photoreceptor according to the first embodiment of the present invention.
[Fig. 4] Fig. 4 is a partial cross-sectional view of a stacked electrophotographic photoreceptor that is an example of the electrophotographic photoreceptor according to the first embodiment of the present invention.
[Fig. 5] Fig. 5 is a partial cross-sectional view of a stacked electrophotographic photoreceptor that is an example of the electrophotographic photoreceptor according to the first embodiment of the present invention.
[Fig. 6] Fig. 6 is a diagram showing an example of an image forming apparatus according to a second embodiment of the present invention.
[Fig. 7] Fig. 7 is a diagram showing an example of a configuration of a development device shown in Fig. 6.

Mode(s) for Carrying Out the Invention

Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the present invention.
First, the terms used in the present specification will be described. Acrylic and methacrylic are collectively referred to as "(meth) acrylic" in some cases. Unless otherwise specified, the hydroxyl value is a value measured in accordance with "JIS (Japanese Industrial Standard) K0070-1992". Unless otherwise specified, the number average primary particle size is a number average value of an equivalent circle diameter (Heywood diameter: diameter of a circle having the same area as the projected area of a primary particle) of a primary particle measured using a scanning electron microscope. The number average primary particle size is, for example, a number average value of equivalent circle diameters of 100 primary particles. Unless otherwise specified, the BET specific surface area is a value measured by a BET method using nitrogen adsorption in accordance with "JIS (Japanese Industrial Standard) Z8830:2001 Determination of the specific surface area of powders (solids) by gas adsorption-BET method". The term "-based" is added after the compound name to collectively refer to the compound and derivatives thereof in some cases. Further, in the case of adding the term "-based" after a compound to refer to a polymer name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Further, a "general formula" and a "chemical formula" are collectively referred to as a "formula". The phrase "each independently" in the description of the formula means that they may indicate the same group or different groups. The phrase "at least one of A, B, or C" means "at least one selected from the group consisting of A, B, and C". The phrase "at least one type of A, B, and C" means "at least one selected from the group consisting of A, B, and C". Note that A, B, and C are merely examples and can be replaced with other terms. Unless otherwise specified, the components described in the present specification may each be used alone, or two or more of them may be used in combination. The terms used in the present specification have been described above.

[First embodiment: electrophotographic photoreceptor]

A first embodiment of the present invention relates to an electrophotographic photoreceptor (hereinafter, referred to as a photoreceptor in some cases). The photoreceptor according to the first embodiment includes a conductive substrate, a photosensitive layer, and a protective layer. The photosensitive layer includes a charge generating agent and a hole transporting agent. The protective layer is the top surface layer of the photoreceptor. The protective layer includes a first particle having n-type conductivity and a second particle having no n-type conductivity.
By having the above configuration, the photoreceptor according to the first embodiment has excellent sensitivity characteristics and is capable of forming an image with excellent dot reproducibility. The reasons for this are presumed to be as follows. Note that the dot reproducibility is the characteristic of being capable of printing dots on a recording medium in accordance with the dot positions of an image input to an image forming apparatus.
The protective layer included in the photoreceptor according to the first embodiment includes a first particle having n-type conductivity. In the present specification, the "n-type conductivity" refers to conductivity in which the main charge carrier is an electron. When the protective layer includes a first particle having n-type conductivity, the sensitivity characteristics are improved.
For example, in the case where the photoreceptor is a positively-charged photoreceptor, a charging device charges the outer surface of the protective layer (surface on the side opposite to the inner surface on the conductive substrate side) to positive polarity. In the first embodiment, since the protective layer includes a first particle having n-type conductivity, the first particle transports electrons suitably from the inner surface of the protective layer to the outer surface. Then, the holes on the outer surface of the protective layer, which are given by charging, are cancelled suitably by the transported electrons. As a result, the sensitivity characteristics of the photoreceptor are improved.
Meanwhile, for example, in the case where the photoreceptor is a negatively-charged photoreceptor, a charging device charges the outer surface of the protective layer to negative polarity. In the first embodiment, since the protective layer includes a first particle having n-type conductivity, the electrons on the outer surface of the protective layer, which are given by charging, are accepted by the first particle. This makes it easier for holes to reach the outer surface of the protective layer from the inner surface. Then, the reached holes cancel the electrons on the outer surface of the protective layer suitably. As a result, the sensitivity characteristics of the photoreceptor are improved.
However, in the case where the protective layer includes only the first particle having n-type conductivity as a particle, drift of charges occurs between the first particles in some cases. The drift of charges shifts the dot positions of the electrostatic latent image formed on the surface of the photoreceptor from the dot positions of the image input to the image forming apparatus in some cases. As a result, the dot reproducibility in a formed image deteriorates in some cases. In this regard, in the first embodiment, the protective layer includes a second particle having no n-type conductivity in addition to the first particle. Since the second particle does not have n-type conductivity, drift of charges can be suppressed. As a result, the dot reproducibility in a formed image is improved.
The reason why the photoreceptor according to the first embodiment has excellent sensitivity characteristics and is capable of forming an image with excellent dot reproducibility has been described above. The photoreceptor will be further described below.
The photoreceptor is, for example, a single-layer electrophotographic photoreceptor (hereinafter, referred to as a single-layer photoreceptor in some cases) or a stacked electrophotographic photoreceptor (hereinafter, referred to as a stacked photoreceptor in some cases).
A structure of a single-layer photoreceptor 1 that is an example of a photoreceptor will be described below with reference to Fig. 1 and Fig. 2. Fig. 1 and Fig. 2 are each a partial cross-sectional view of the single-layer photoreceptor 1. As shown in Fig. 1, the single-layer photoreceptor 1 includes, for example, a conductive substrate 2, a photosensitive layer 3, and a protective layer 5. The photosensitive layer 3 is a single layer. Hereinafter, the "photosensitive layer that is a single layer" will be referred to as a "single-layer photosensitive layer" in some cases. In the example shown in Fig. 1, a single-layer photosensitive layer 3a is provided on the conductive substrate 2 and the protective layer 5 is provided on the single-layer photosensitive layer 3a. The single-layer photosensitive layer 3a is provided directly on the conductive substrate 2. The protective layer 5 is the top surface layer of the single-layer photoreceptor 1.
As shown in Fig. 2, the single-layer photoreceptor 1 may further include an intermediate layer 4 (undercoat layer), in addition to the conductive substrate 2, the single-layer photosensitive layer 3a, and the protective layer 5. In the example shown in Fig. 2, the intermediate layer 4 is provided on the conductive substrate 2, the single-layer photosensitive layer 3a is provided on the intermediate layer 4, and the protective layer 5 is provided on the single-layer photosensitive layer 3a. The single-layer photosensitive layer 3a is provided above the conductive substrate 2 via the intermediate layer 4.
The thickness of the single-layer photosensitive layer 3a is not particularly limited, but is favorably 5 µm or more and 100 µm or less, more favorably 10 µm or more and 50 µm or less.
The thickness of the protective layer 5 is not particularly limited, but is favorably 2 µm or more, more favorably 2 µm or more and 30 µm or less, more favorably 2 µm or more and 10 µm or less, and still more favorably 2 µm or more and 4 µm or less. In the examples shown in Fig. 1 and Fig. 2 , the protective layer 5 is one layer. However, the protective layer 5 may include a plurality of layers. In the case where the protective layer 5 includes a plurality of layers, at least the top surface layer, of the plurality of layers, includes a first particle and a second particle. The structure of the single-layer photoreceptor 1 that is an example of a photoreceptor has been described above with reference to Fig. 1 and Fig. 2.
A structure of a stacked photoreceptor 10 that is an example of a photoreceptor will be described below with reference to Fig. 3 to Fig. 5. Fig. 3 to Fig. 5 are each a partial cross-sectional view of the stacked photoreceptor 10. As shown in Fig. 3, the stacked photoreceptor 10 includes, for example, the conductive substrate 2, the photosensitive layer 3, and the protective layer 5. The photosensitive layer 3 includes a charge generating layer 3b and a charge transporting layer 3c. In the example shown in Fig. 3, the charge generating layer 3b is provided on the conductive substrate 2, the charge transporting layer 3c is provided on the charge generating layer 3b, and the protective layer 5 is provided on the charge transporting layer 3c. However, as shown in Fig. 4, in the stacked photoreceptor 10, the charge transporting layer 3c may be provided on the conductive substrate 2, the charge generating layer 3b may be provided on the charge transporting layer 3c, and the protective layer 5 may be provided on the charge generating layer 3b. In the examples shown in Fig. 3 and Fig. 4, the photosensitive layer 3 is provided directly on the conductive substrate 2. The protective layer 5 is the top surface layer of the stacked photoreceptor 10.
As shown in Fig. 5, the stacked photoreceptor 10 may further include the intermediate layer 4 (undercoat layer), in addition to the conductive substrate 2, the photosensitive layer 3, and the protective layer 5. In the example shown in Fig. 5, the intermediate layer 4 is provided on the conductive substrate 2, the charge generating layer 3b is provided on the intermediate layer 4, the charge transporting layer 3c is provided on the charge generating layer 3b, and the protective layer 5 is provided on the charge transporting layer 3c. The photosensitive layer 3 (e.g., the charge generating layer 3b) is provided above the conductive substrate 2 via the intermediate layer 4.
The thickness of the charge generating layer 3b is not particularly limited, but is favorably 0.01 µm or more and 5 µm or less, more favorably 0.1 µm or more and 3 µm or less. In the examples shown in Fig. 3 to Fig. 5, the charge generating layer 3b is one layer. However, the charge generating layer 3b may include a plurality of layers.
The thickness of the charge transporting layer 3c is not particularly limited, but is favorably 2 µm or more and 100 µm or less, more favorably 5 µm or more and 50 µm or less. In the examples shown in Fig. 3 to Fig. 5, the charge transporting layer 3c is one layer. However, the charge transporting layer 3c may include a plurality of layers.
Since the protective layer 5 included in the stacked photoreceptor 10 is similar to the protective layer 5 included in the single-layer photoreceptor 1, description thereof is omitted. The structure of the stacked photoreceptor 10 that is an example of a photoreceptor has been described above with reference to Fig. 3 to Fig. 5.

The protective layer includes a first particle and a second particle. The protective layer favorably further includes a resin. Hereinafter, the "resin included in the protective layer" will be referred to as "protective layer resin" in some cases. The protective layer may further include, as necessary, one or both of a polymerization initiator and an additive.

(First particle and second particle)

The first particle has n-type conductivity. That is, the first particle has conductivity in which the main charge carrier is an electron. Meanwhile, the second particle does not have n-type conductivity. That is, the second particle does not have conductivity in which the main charge carrier is an electron. The second particle has not n-type conductivity but, for example, p-type conductivity, true conductivity, or insulation properties. Note that in the present specification, the p-type conductivity refers to conductivity in which the main charge carrier is a hole.
In order to suitably suppress drift of charges between first particles, the volume resistivity of the second particle is favorably higher than the volume resistivity of the first particle.
In order to suitably suppress drift of charges between first particles, the volume resistivity of a first particle-containing sheet including a first particle is favorably 0.1 Ω·cm or more and less than 12.0Ω·cm, more favorably 9.0 Ω·cm or more and 11.0 Ω·cm or less. The first particle-containing sheet includes 9.3 parts by mass of the first particle, 89.0 parts by mass of a photocurable resin, 10.0 parts by mass of a polymerization initiator, and 1.0 part by mass of a leveling agent.
In order to suitably suppress drift of charges between first particles, the volume resistivity of a second particle-containing sheet including a second particle is favorably 12.0 Ω·cm or more and 50.0 Ω·cm or less, more favorably 12.5 Ω·cm or more and 14.5 Ω·cm or less. The second particle-containing sheet includes 9.3 parts by mass of the second particle, 89.0 parts by mass of a photocurable resin, 10.0 parts by mass of a polymerization initiator, and 1.0 part by mass of a leveling agent.
Regarding the first particle-containing sheet and the second particle-containing sheet, the components other than the first particle and the second particle (e.g., 89.0 parts by mass of a photocurable resin, 10.0 parts by mass of a polymerization initiator, and 1.0 part by mass of a leveling agent) are the same. For this reason, the high-low relationship of the volume resistivity between the first particle-containing sheet and the second particle-containing sheet matches the high-low relationship of the volume resistivity between the first particle and the second particle. For example, when the volume resistivity of the second particle-containing sheet is higher than the volume resistivity of the first particle-containing sheet, the volume resistivity of the second particle is higher than the volume resistivity of the first particle. The volume resistivity is measured by, for example, applying a voltage under the conditions of +100 V and a frequency of 33.3 mHz using an electric resistance meter in the environment of a temperature of 23°C and a relative humidity of 50% RH.
Examples of the first particle include a metal oxide particle having n-type conductivity, more specifically, a zinc oxide particle, a titanium oxide particle, and a tin oxide particle. In order to improve the sensitivity characteristics of the photoreceptor, a tin oxide particle is favorable as the first particle. The tin oxide particle may be undoped. However, in order to increase the n-type conductivity and improve the sensitivity characteristics of the photoreceptor, the tin oxide particle is favorably doped. As the doped tin oxide particle, a phosphorus-doped tin oxide particle or an antimony-doped tin oxide particle is favorable.
In order to improve the dot reproducibility in a formed image, an alumina particle, a silica particle, or a silicone particle is favorable as the second particle.
One or both of the first particle and the second particle do not necessarily need to have a polymerizable functional group capable of reacting with a photocurable resin. Since the protective layer includes a first particle, the photoreceptor according to the first embodiment is capable of improving the sensitivity characteristics even in the case where one or both of the first particle and the second particle do not react with a photocurable resin.
The BET specific surface area of each of the first particle and the second particle is favorably 30 m²/g or more and 200 m²/g or less, more favorably 45 m²/g or more and 130 m²/g or less, and still more favorably 70 m²/g or more and 130 m²/g or less.
The number average primary particle size of each of the first particle and the second particle is favorably 5 nm or more and 500 nm or less, more favorably 30 nm or more and 200 nm or less, and still more favorably 100 nm or more and 200 nm or less.
When the mass of the first particle is represented as M1 and the mass of the second particle is represented as M2, a ratio M1/M2 of the mass (M1) of the first particle to the mass (M2) of the second particle is favorably 1 or more and 10 or less, more favorably 1 or more and 5 or less, and still more favorably 2 or more and 3 or less.
The content ratio of the first particle occupied in the protective layer is favorably 1 mass% or more and 15 mass% or less, more favorably 5 mass% or more and 10 mass% or less, with respect to the mass of the protective layer. The content ratio of the second particle occupied in the protective layer is favorably 1 mass% or more and less than 5 mass% with respect to the mass of the protective layer. The total content ratio of the first particle and the second particle occupied in the protective layer is favorably 1 mass% or more and 20 mass% or less, more favorably 10 mass% or more and 15 mass% or less, with respect to the mass of the protective layer.

(Protective layer resin)

Examples of the protective layer resin include a photocurable resin, a thermoplastic resin, and a thermosetting resin. As the protective layer resin, a photocurable resin is favorable. Examples of the photocurable resin include a (meth)acrylic resin and an epoxy resin. The photocurable resin has a polymerizable functional group. The (meth)acrylic resin has a vinyl group as a polymerizable functional group. The epoxy resin has an epoxy group as a polymerizable functional group. As the photocurable resin, a (meth)acrylic resin is favorable because the photocuring reaction stops when irradiation of ultraviolet rays is stopped, and the progress of the photocuring reaction can be easily controlled.
The photocurable resin favorably includes a repeating unit derived from a compound having two or more polymerizable functional groups and a repeating unit derived from a compound having one polymerizable functional group. Hereinafter, the "compound having two or more polymerizable functional groups" will be referred to as a "multifunctional group monomer" in some cases. Further, the "compound having one polymerizable functional group" will be referred to as a "monofunctional group monomer" in some cases.
As the multifunctional group monomer, a (meth)acrylic acid ester having 2 or more and 6 or less vinyl groups is favorable. Hereinafter, the "(meth)acrylic acid ester having 2 or more and 6 or less vinyl groups" will be referred to as "multifunctional group acrylic acid ester" in some cases. The multifunctional group acrylic acid ester favorably has 3 or more and 6 or less vinyl groups.
Examples of the multifunctional group acrylic acid ester include a trimethylolpropane triacrylate, a glycerin triacrylate, a tris-(2-acryloxyethyl) isocyanurate, a pentaerythritol triacrylate, a pentaerythritol tetraacrylate, a ditrimethylolpropane tetraacrylate, a dipentaerythritol pentaacrylate, and a dipentaerythritol hexaacrylate. These multifunctional group acrylic acid esters may be ethoxylated.
The multifunctional group acrylic acid ester is favorably at least one selected from the group consisting of a pentaerythritol triacrylate, a pentaerythritol tetraacrylate, a dipentaerythritol pentaacrylate, and a dipentaerythritol hexaacrylate, more favorably one or two of them. The multifunctional group acrylic acid ester is favorably a mixture of a pentaerythritol triacrylate and a pentaerythritol tetraacrylate. The content ratio of the pentaerythritol triacrylate occupied in the mixture of the pentaerythritol triacrylate and the pentaerythritol tetraacrylate is favorably 40 mass% or more and 60% or less. The multifunctional group acrylic acid ester is also favorably a mixture of a dipentaerythritol pentaacrylate and a dipentaerythritol hexaacrylate.
The pentaerythritol triacrylate, the pentaerythritol tetraacrylate, the dipentaerythritol pentaacrylate, and the dipentaerythritol hexaacrylate are respectively compounds represented by the formulae (EA-1), (EA-2), (EA-3), and (EA-4).
Repeating units represented by the formulae (EA-1a), (EA-2a), (EA-3a), and (EA-4a) are respectively formed from the compounds represented by the formulae (EA-1), (EA-2), (EA-3), and (EA-4), which are monomers, by the photocuring reaction (more specifically, an addition polymerization reaction of a vinyl group).
At least one of Y¹ to Y³ in the formula (EA-1a) represents a group represented by the formula (Y-b), and the remainder(s) of the at least one of Y¹ to Y³ represent(s) a group represented by the formula (Y-a). At least one of Y⁴ to Y⁷ in the formula (EA-2a) represents a group represented by the formula (Y-b), and the remainder(s) of the at least one of Y⁴ to Y⁷ represent(s) a group represented by the formula (Y-a). At least one of Y⁸ to Y¹² in the formula (EA-3a) represents a group represented by the formula (Y-b), and the remainder(s) of the at least one of Y⁸ to Y¹² represent(s) a group represented by the formula (Y-a). At least one of Y¹³ to Y¹⁸ in the formula (EA-4a) represents a group represented by the formula (Y-b), and the remainder (s) of the at least one of Y¹³ to Y¹⁸ represent(s) a group represented by the formula (Y-a). *¹ in the formulae (Y-a) and (Y-b) represents atomic bonding to be bonded to a carbon atom of a carbonyl group in the formulae (EA-1a) to (EA-4a). *² in the formula (Y-b) represents atomic bonding to be bonded to *² or *³ described below in another repeating unit. That is, *² of the group represented by the formula (Y-b) of one repeating unit and *² of the group represented by the formula (Y-b) or *³ in the formula (EB-1a) described below of another repeating unit are bonded to each other.
The double bond of the group represented by the formula (Y-a) is cleaved by the photocuring reaction (more specifically, an addition polymerization reaction of a vinyl group) to form the group represented by the formula (Y-b). Therefore, as the photocuring reaction (more specifically, an addition polymerization reaction of a vinyl group) progresses, the group represented by the formula (Y-a) decreases and the group represented by the formula (Y-b) increases.
The hydroxyl value of the multifunctional group acrylic acid ester is favorably 1 mgKOH/g or more and 50 mgKOH/g or less, more favorably 5 mgKOH/g or more and 15 mgKOH/g or less.
As the monofunctional group monomer, a (meth)acrylic acid ester having one vinyl group is favorable. Hereinafter, the "(meth)acrylic acid ester having one vinyl group" will be referred to as a monofunctional group acrylic acid ester in some cases.
The monofunctional group acrylic acid ester is favorably a compound represented by the formula (EB-1).
In the formula (EB-1), R¹ represents a group represented by the formula (b1) or (b2). R² represents a hydrogen atom or a methyl group.
In the formula (b1), m represents 0 or 1, and n represents an integer of 1 or more and 3 or less. R³ represents a hydrogen atom or a fluorine atom. In the formula (b2), R⁴ represents an alkyl group having 1 or more and 18 or less carbon atoms. In the formulae (b1) and (b2), * represents atomic bonding.
In the formula (b1), m favorably represents 1. n favorably represents 1 or 3. R³ favorably represents a hydrogen atom. In the formula (b2), R⁴ represents favorably an alkyl group having 10 or more and 18 or less carbon atoms, more favorably an alkyl group having 15 or more and 18 or less carbon atoms, and still more favorably an alkyl group having 18 carbon atoms. R² favorably represents a hydrogen atom.
Suitable examples of the compound represented by the formula (EB-1) include compounds represented by the formulae (EB-11), (EB-12), and (EB-13). The "iso-C₁₈H₃₇" in the formula (EB-13) represents an isooctadecyl group.
The repeating unit represented by the formula (EB-1a) is formed from the compound represented by the formula (EB-1), which is a monomer, by the photocuring reaction (more specifically, an addition polymerization reaction of a vinyl group). *³ in the formula (EB-1a) represents atomic bonding to be bonded to *² or *³ of another repeating unit. R¹ and R² in the formula (EB-1a) are synonymous with R¹ and R² in the formula (EB-1).
In order to promote the photocuring reaction to increase the hardness of the protective layer, a ratio M4/M3 of a mass M4 of the repeating unit derived from a monofunctional group acrylic acid ester to a mass M3 of the repeating unit derived from a multifunctional group acrylic acid ester is favorably 0.1 or more and 0.9 or less, more favorably 0.5 or more and 0.8 or less, and still more favorably 0.6 or more and 0.7 or less.
The content ratio of the repeating unit derived from a multifunctional group acrylic acid ester occupied in all repeating units of the photocurable resin is favorably 50 mass% or more and 90 mass% or less, more favorably 60 mass% or more and 70 mass% or less. The content ratio of the repeating unit derived from a monofunctional group acrylic acid ester occupied in all repeating units of the photocurable resin is favorably 10 mass% or more and 50 mass% or less, more favorably 30 mass% or more and 40 mass% or less. The total content ratio of the multifunctional group acrylic acid ester and the monofunctional group acrylic acid ester occupied in all repeating units of the photocurable resin is favorably 80 mass% or more, more favorably 90 mass% or more, and particularly favorably 100 mass%.
The content ratio of the protective layer resin occupied in the protective layer is favorably 50 mass% or more and 99 mass% or less, more favorably 70 mass% or more and 90 mass% or less, with respect to the mass of the protective layer.

(Polymerization initiator)

The polymerization initiator is, for example, a photopolymerization initiator. Examples of the photopolymerization initiator include an acylphosphine oxide compound, an acetophenone compound, a ketal compound, a benzoinether compound, an anthraquinone compound, and a thioxanthone compound. An acylphosphine oxide compound is favorable as a photopolymerization initiator because it has high ultraviolet absorption efficiency. Examples of the acylphosphine oxide compound include 2,4,6-trimethylbenzoyl-diphenylphosphineoxide, phenylbis(2,4,6-trimethylbenzoyl)phosphineoxide, and lithiumphenyl (2,4, 6-trimethylbenzoyl) phosphonate. The content ratio of the polymerization initiator occupied in the protective layer is favorably 1 mass% or more and 20 mass% or less, more favorably 5 mass% or more and 10 mass% or less, with respect to the mass of the protective layer.

(Additive)

Examples of the additive included in the protective layer include a leveling agent (e.g., silicone oil) and other known additives. Note that it is favorable that the protective layer does not include a charge generating agent, a hole transporting agent, and an electron transporting agent.

The photosensitive layer includes a charge generating agent, a hole transporting agent, and a binder resin. In the case where the photoreceptor is a single-layer photoreceptor, the single-layer photosensitive layer that is a photosensitive layer includes a charge generating agent, a hole transporting agent, and a binder resin. The single-layer photosensitive layer favorably further includes an electron transporting agent. The single-layer photosensitive layer may further include an additive, as necessary.
In the case where the photoreceptor is a stacked photoreceptor, the charge generating layer included in the photosensitive layer includes a charge generating agent. The charge transporting layer included in the photosensitive layer includes a hole transporting agent and a binder resin. The charge generating layer may further include a base resin, as necessary. Each of the charge generating layer and the charge transporting layer may further include an additive, as necessary. Each of the charge generating layer and the charge transporting layer may include a radical acceptor compound. However, each of the charge generating layer and the charge transporting layer does not necessarily need to include a radical acceptor compound.

(Charge generating agent)

Examples of the charge generating agent include a phthalocyanine pigment, a perylene pigment, a bisazo pigment, a trisazo pigment, a dithioketopyrrolopyrrole pigment, a metal-free naphthalocyanine pigment, a metal naphthalocyanine pigment, a squaraine pigment, an indigo pigment, an azulenium pigment, a cyanine pigment, a powder of an inorganic photoconductive material (e.g., selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, and amorphous silicon), a pyrylium pigment, an anthanthron pigment, a triphenylmethane pigment, a threne pigment, a toluidine pigment, a pyrazoline pigment, and a quinacridone pigment.
The phthalocyanine pigment has a phthalocyanine structure. Examples of the phthalocyanine pigment include metal phthalocyanine and metal-free phthalocyanine. Examples of the metal phthalocyanine include titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine. As the metal phthalocyanine, titanyl phthalocyanine is favorable. The titanyl phthalocyanine is represented by the formula (CG-1). The metal-free phthalocyanine is represented by the formula (CG-2).
The phthalocyanine pigment may be crystalline or non-crystalline. Examples of the crystal of the metal-free phthalocyanine include an X-type crystal of the metal-free phthalocyanine (hereinafter, referred to as an X-type metal-free phthalocyanine in some cases). Examples of the crystal of the titanyl phthalocyanine include α-type, β-type, and Y-type crystals of the titanyl phthalocyanine (hereinafter, respectively referred to as α-type, β-type, and Y-type titanyl phthalocyanines in some cases).
For example, for a digital optical image forming apparatus (e.g., a laser beam printer or a facsimile machine using a light source such as semiconductor laser light), it is favorable to use a photoreceptor having sensitivity in a wavelength region of 700 nm or more. As the charge generating agent, a phthalocyanine pigment is favorable, titanyl phthalocyanine or metal-free phthalocyanine is more favorable, and Y-type titanyl phthalocyanine or X-type metal-free phthalocyanine is particularly favorable because they have a high quantum yield in the wavelength region of 700 nm or more.
The Y-type titanyl phthalocyanine has a main peak at, for example, 27.2° of the Bragg angle (2θ ± 0.2°) in the CuKα characteristic X-ray diffraction spectrum. The main peak in the CuKα characteristic X-ray diffraction spectrum is a peak having the first or second highest intensity in the range of the Bragg angle (2θ ± 0.2°) of 3° or more and 40° or less. The Y-type titanyl phthalocyanine does not have a peak at 26.2° in the CuKα characteristic X-ray diffraction spectrum.
The CuKα characteristic X-ray diffraction spectrum can be measured by, for example, the following method. First, a sample holder of an X-ray diffractometer (e.g., "RINT (registered trademark) 1100" manufactured by Rigaku Holdings Corporation and its Global Subsidiaries) is filled with a sample (titanyl phthalocyanine) to measure the X-ray diffraction spectrum under the conditions of an X-ray tube Cu, a tube voltage of 40 kV, a tube current of 30 mA, and a wavelength of CuKα characteristic X-rays of 1.542 Å. The measurement range (2θ) is, for example, 3° or more and 40° or less (start angle of 3°, stop angle of 40°), and the scanning speed is, for example, 10°/min. The main peak is determined from the obtained X-ray diffraction spectrum, and the Bragg angle of the main peak is read.
In the case where the photoreceptor is a single-layer photoreceptor, the content of the charge generating agent in the single-layer photosensitive layer that is a photosensitive layer is favorably 0.1 parts by mass or more and 50 parts by mass or less, more favorably 0.5 parts by mass or more and 30 parts by mass or less, with respect to 100 parts by mass of the binder resin. In the case where the photoreceptor is a stacked photoreceptor, the content of the charge generating agent in the photosensitive layer (specifically, the charge generating layer) is favorably 10 parts by mass or more and 300 parts by mass or less, more favorably 100 parts by mass or more and 200 parts by mass or less, with respect to 100 parts by mass of the base resin.

(Hole transporting agent)

Examples of the hole transporting agent include a triphenylamine derivative, a diamine derivative (e.g., an N,N,N',N'-tetraphenylbenzidine derivative, an N,N,N',N'-tetraphenylphenylenediamine derivative, an N,N,N',N'-tetraphenylnaphthylenediamine derivative, an N,N,N',N'-tetraphenylphenanthrylenediamine derivative, and a di(aminophenylethenyl)benzene derivative)), an oxadiazole compound (e.g., 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole), a styryl compound (e.g., 9-(4-diethylaminostyryl)anthracene), a carbazole compound (e.g., polyvinylcarbazole), an organic polysilane compound, a pyrazoline compound (e.g., 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), a hydrazone compound, an indole compound, an oxazole compound, an isooxazole compound, a thiazole compound, a thiadiazole compound, an imidazole compound, a pyrazole compound, and a triazole compound.
In order to improve the sensitivity characteristics of the photoreceptor, the hole transporting agent favorably includes at least one of compounds represented by the formulae (1), (2), and (3). Hereinafter, the compounds represented by the formulae (1), (2), and (3) will be respectively referred to as hole transporting agents (1), (2), and (3) in some cases.
In the formula (1), R⁴¹, R⁴², R⁴³, R⁴⁴, R⁴⁵, and R⁴⁶ each independently represent an alkyl group having 1 or more and 8 or less carbon atoms or a phenyl group. R⁴⁷ and R⁴⁸ each independently represent a hydrogen atom, an alkyl group having 1 or more and 8 or less carbon atoms, or a phenyl group. e₁, e₂, e₃, and e₄ each independently represent an integer of 0 or more and 5 or less. e₅ and e₆ each independently represent an integer of 0 or more and 4 or less.
In the formula (1), when e₁ represents an integer of 2 or more and 5 or less, a plurality of R₄₁ may represent the same group or different groups. When e₂ represents an integer of 2 or more and 5 or less, a plurality of R₄₂ may represent the same group or different groups. When e₃ represents an integer of 2 or more and 5 or less, a plurality of R₄₃ may represent the same group or different groups. When e₄ represents an integer of 2 or more and 5 or less, a plurality of R₄₄ may represent the same group or different groups. When e₅ represents an integer of 2 or more and 4 or less, a plurality of R₄₅ may represent the same group or different groups. When e₆ represents an integer of 2 or more and 4 or less, a plurality of R₄₆ may represent the same group or different groups.
In the formula (1), R⁴¹ to R⁴⁶ each independently represent favorably an alkyl group having 1 or more and 8 or less carbon atoms, more favorably an alkyl group having 1 or more and 3 or less carbon atoms, and still more favorably a methyl group or an ethyl group. R⁴⁷ and R⁴⁸ favorably each represent a hydrogen atom. It is favorable that e₁, e₂, e₃, and e₄ each independently represent an integer of 0 or more and 2 or less, and it is more favorable that e₁ and e₂ each represent 0 and e₃ and e₄ each represent 2. e₅ and e₆ favorably each represent 0.
In the formula (2), R⁵⁰, R⁵¹, and R⁵⁴ each independently represent an alkyl group having 1 or more and 8 or less carbon atoms or a phenyl group. R⁵² and R⁵³ each independently represent a hydrogen atom, an alkyl group having 1 or more and 8 or less carbon atoms, or a phenyl group that may be substituted with an alkyl group having 1 or more and 8 or less carbon atoms. f₃, f₄, and f₅ each independently represent an integer of 0 or more and 5 or less.
In the formula (2), when f₃ represents an integer of 2 or more and 5 or less, a plurality of R⁵⁰ may represent the same group or different groups. When f₄ represents an integer of 2 or more and 5 or less, a plurality of R⁵¹ may represent the same group or different groups. When f₅ represents an integer of 2 or more and 5 or less, a plurality of R⁵⁴ may represent the same group or different groups.
In the formula (2), R⁵⁰, R⁵¹, and R⁵⁴ each independently represent favorably an alkyl group having 1 or more and 8 or less carbon atoms, more favorably an alkyl group having 1 or more and 3 or less carbon atoms, and still more favorably a methyl group. R⁵² and R⁵³ favorably each independently represent a hydrogen atom, an unsubstituted phenyl group, or a phenyl group substituted with an alkyl group having 1 or more and 8 or less carbon atoms. In the case where the phenyl group is substituted with an alkyl group having 1 or more and 8 or less carbon atoms, as such an alkyl group having 1 or more and 8 or less carbon atoms, an alkyl group having 1 or more and 3 or less carbon atoms is favorable and a methyl group is more favorable. f₃, f₄, and f₅ favorably each independently represent 0 or 1.
In the formula (3), R¹¹, R¹², R¹³, and R¹⁴ each independently represent an alkyl group having 1 or more and 8 or less carbon atoms or a phenyl group. a₁, a₂, a₃, and a₄ each independently represent an integer of 0 or more and 5 or less.
In the formula (3), when a₁ represents an integer of 2 or more and 5 or less, a plurality of R¹¹ may represent the same group or different groups. When a₂ represents an integer of 2 or more and 5 or less, a plurality of R¹² may represent the same group or different groups. When a₃ represents an integer of 2 or more and 5 or less, a plurality of R¹³ may represent the same group or different groups. When a₄ represents an integer of 2 or more and 5 or less, a plurality of R¹⁴ may represent the same group or different groups.
In the formula (3), R¹¹, R¹², R¹³, and R¹⁴ each independently represent favorably an alkyl group having 1 or more and 3 or less carbon atoms, more favorably a methyl group or an ethyl group. a₁, a₂, a₃, and a₄ each independently represent favorably an integer of 1 or more and 3 or less, more favorably 1.
Suitable examples of the hole transporting agent include compounds represented by the formulae (HT-2), (HT-3), and (HT-4) (hereinafter, respectively referred to as hole transporting agents (HT-2), (HT-3), and (HT-4) in some cases).
The content ratio of the hole transporting agents (1) to (3) occupied in all hole transporting agents in the photosensitive layer is favorably 80 mass% or more, more favorably 90 mass% or more, and still more favorably 100 mass%, with respect to the total mass of the hole transporting agent in the photosensitive layer.
In the case where ultraviolet rays are applied in the protective layer forming step, in order to suppress decomposition of the hole transporting agent due to irradiation of ultraviolet rays, the hole transporting agent favorably has two or less (one or two) chain ethene-1,2-diyl groups or no chain ethene-1,2-diyl group. Hereinafter, the "chain ethene-1,2-diyl group" will be referred to as a "predetermined double bond" in some cases. The predetermined double bond is a bond represented by the following formula (DB). In the formula (DB), * represents atomic bonding. The predetermined double bond is an unsubstituted ethene-1,2-diyl group. The predetermined double bond is a double bond forming a chain group because it is chain. The predetermined double bond is not a double bond forming a ring such as a benzene ring because it is chain.
In the case where ultraviolet rays are applied in the protective layer forming step, in order to suppress decomposition of the hole transporting agent due to irradiation of ultraviolet rays, the content ratio of the hole transporting agent having two or less predetermined double bonds or no predetermined double bond occupied in all hole transporting agents in the photosensitive layer is favorably 80 mass% or more, more favorably 90 mass% or more, and still more favorably 100 mass%, with respect to the total mass of the hole transporting agents.
In the case where the photoreceptor is a single-layer photoreceptor, the content of the hole transporting agent in the single-layer photosensitive layer that is a photosensitive layer is favorably 10 parts by mass or more and 200 parts by mass or less, more favorably 80 parts by mass or more and 130 parts by mass or less, with respect to 100 parts by mass of the binder resin.
In order to improve the sensitivity characteristics of the photoreceptor, in the case where the photoreceptor is a single-layer photoreceptor, the total content ratio of the hole transporting agent and the electron transporting agent occupied in the single-layer photosensitive layer is favorably 40 mass% or more, more favorably 40 mass% or more and 60 mass% or less, with respect to the mass of the single-layer photosensitive layer.
In the case where the photoreceptor is a stacked photoreceptor, the content of the hole transporting agent occupied in the photosensitive layer (specifically, the charge transporting layer) is favorably 10 parts by mass or more and 200 parts by mass or less, more favorably 50 parts by mass or more and 100 parts by mass or less, with respect to 100 parts by mass of the binder resin.
In order to improve the sensitivity characteristics of the photoreceptor, in the case where the photoreceptor is a stacked photoreceptor, the content ratio of the hole transporting agent occupied in the charge transporting layer is favorably 40 mass% or more, more favorably 40 mass% or more and 60 mass% or less, with respect to the mass of the charge transporting layer.

(Electron transporting agent)

Examples of the electron transporting agent include a quinone compound, a diimide compound, a hydrazone compound, a malononitrile compound, a thiopyran compound, a trinitrothioxanthone compound, a 3,4,5,7-tetranitro-9-fluorenone compound, a dinitroanthracene compound, a dinitroacridine compound, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. Examples of the quinone compound include a diphenoquinone compound, an azoquinone compound, an anthraquinone compound, a naphthoquinone compound, a nitroanthraquinone compound, and a dinitroanthraquinone compound.
The electron transporting agent favorably includes at least one of compounds represented by the formulae (11), (12), (13), (14), (15), and (16). Hereinafter, the compounds represented by the formulae (11), (12), (13), (14), (15), and (16) will be respectively referred to as electron transporting agents (11), (12), (13), (14), (15), and (16) in some cases.
Q¹ and Q² in the formula (11), Q²¹, Q²², Q²³, and Q²⁴ in the formula (12), Q³¹ and Q³² in the formula (13), Q⁴¹, Q⁴², and Q⁴³ in the formula (14), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ in the formula (15), and Q⁶¹ and Q⁶² in the formula (16) each independently represent a hydrogen atom, a halogen atom, a cyano group, an alkyl group having 1 or more and 6 or less carbon atoms, an alkenyl group having 2 or more and 6 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or an aryl group having 6 or more and 14 or less carbon atoms that may be substituted with at least one substituent group selected from the group consisting of an alkyl group having 1 or more and 6 or less carbon atoms and a halogen atom. Y¹ and Y² in the formula (15) each represent an oxygen atom.
Q¹ and Q² in the formula (11), Q²¹, Q²², Q²³, and Q²⁴ in the formula (12), Q³¹ and Q³² in the formula (13), Q⁴¹, Q⁴², and Q⁴³ in the formula (14), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ in the formula (15), and Q⁶¹ and Q⁶² in the formula (16) favorably each independently represent a hydrogen atom, an alkyl group having 1 or more and 6 or less carbon atoms, or an aryl group having 6 or more and 14 or less carbon atoms that may be substituted with at least one substituent group selected from the group consisting of an alkyl group having 1 or more and 6 or less carbon atoms and a halogen atom.
As the alkyl group having 1 or more and 6 or less carbon atoms represented by Q¹ and Q² in the formula (11), Q²¹, Q²², Q²³, and Q²⁴ in the formula (12), Q³¹ and Q³² in the formula (13), Q⁴¹, Q⁴², and Q⁴³ in the formula (14), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ in the formula (15), and Q⁶¹ and Q⁶² in the formula (16), an alkyl group having 1 or more and 5 or less carbon atoms is favorable, a methyl group, an ethyl group, a propyl group, a butyl group, or a pentyl group is favorable, and a methyl group, a tert-butyl group, or a 1,1-dimethylpropyl group is particularly favorable.
As the aryl group having 6 or more and 14 or less carbon atoms represented by Q¹ and Q² in the formula (11), Q²¹, Q²², Q²³, and Q²⁴ in the formula (12), Q³¹ and Q³² in the formula (13), Q⁴¹, Q⁴², and Q⁴³ in the formula (14), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ in the formula (15), and Q⁶¹ and Q⁶² in the formula (16), an aryl group having 6 or more and 10 or less carbon atoms is favorable and a phenyl group is more favorable. The aryl group having 6 or more and 14 or less carbon atoms may be substituted with at least one substituent group selected from the group consisting of an alkyl group having 1 or more and 6 or less carbon atoms and a halogen atom. As such an alkyl group having 1 or more and 6 or less carbon atoms, an alkyl group having 1 or more and 3 or less carbon atoms is favorable and a methyl group or an ethyl group is more favorable. As the halogen atom that is a substituent group, a fluorine atom, a chlorine atom, or a bromine atom is favorable and a chlorine atom is particularly favorable. In the case where the aryl group having 6 or more and 14 or less carbon atoms is substituted with a substituent group, the number of substituent groups is favorably 1 or more and 5 or less, more favorably 1 or 2. As the aryl group having 6 or more and 14 or less carbon atoms substituted with at least one substituent group selected from the group consisting of an alkyl group having 1 or more and 6 or less carbon atoms and a halogen atom, a chlorophenyl group, a dichlorophenyl group, or an ethylmethylphenyl group is favorable and a 4-chlorophenyl group, a 2,5-dichlorophenyl group, or a 2-ethyl-6-methylphenyl group is more favorable.
Suitable examples of the electron transporting agent include compounds represented by the formulae (ET-1) to (ET-7) (hereinafter, respectively referred to as electron transporting agents (ET-1) to (ET-7) in some cases).
The content ratio of the electron transporting agents (11) to (16) occupied in all electron transporting agents in the photosensitive layer is favorably 80 mass% or more, more favorably 90 mass% or more, and still more favorably 100 mass%, with respect to the total mass of the electron transporting agents in the photosensitive layer.
In the case where the photoreceptor is a single-layer photoreceptor, the content of the electron transporting agent in the single-layer photosensitive layer that is a photosensitive layer is favorably 5 parts by mass or more and 150 parts by mass or less, more favorably 10 parts by mass or more and 50 parts by mass or less, with respect to 100 parts by mass of the binder resin.

(Binder resin)

Examples of the binder resin include a thermoplastic resin (more specifically, a polyarylate resin, a polycarbonate resin, a styrene resin, a styrene-butadiene copolymer, a styrene-acrylonitrile copolymer, a styrene-maleic acid copolymer, a styrene-acrylic acid copolymer, an acrylic copolymer, a polyethylene resin, an ethylene-vinyl acetate copolymer, a chlorinated polyethylene resin, a polyvinyl chloride resin, a polypropylene resin, an ionomer, a vinyl chloride-vinyl acetate copolymer, a polyester resin, an alkyd resin, a polyamide resin, a polyurethane resin, a polysulfone resin, a diallylphthalate resin, a ketone resin, a polyvinylbutyral resin, a polyvinylacetal resin, and a polyether resin), a thermosetting resin (more specifically, a silicone resin, an epoxy resin, a phenolic resin, a urea resin, a melamine resin, and a cross-linkable thermosetting resin other than these), and a photocurable resin (more specifically, an epoxy-acrylic acid resin and a urethane-acrylic acid copolymer).
Of these resins, a polycarbonate resin is favorable because a single-layer photosensitive layer and a charge transporting layer having an excellent balance of workability, mechanical strength, optical characteristics, and wear resistance can be obtained. Examples of the polycarbonate resin include a bisphenol Z-type polycarbonate resin, a bisphenol B-type polycarbonate resin, a bisphenol ZC-type polycarbonate resin, a bisphenol C-type polycarbonate resin, and a bisphenol A-type polycarbonate resin. As the binder resin, a bisphenol Z-type polycarbonate resin or a bisphenol B-type polycarbonate resin is favorable. The bisphenol Z-type polycarbonate resin is a resin including a repeating unit represented by the formula (Bis2). The bisphenol B-type polycarbonate resin is a resin including a repeating unit represented by the formula (BisB).

(Base resin)

Examples of the base resin included in the charge generating layer are the same as the examples of the binder resin included in the charge transporting layer. However, in order to suitably form a charge generating layer and a charge transporting layer, it is favorable to select, as a base resin, a resin different from the resin used as the binder resin, of the above examples of the binder resin. The base resin is, for example, a polyvinylacetal resin.

(Additive)

Examples of the additive included in the photosensitive layer include an ultraviolet absorber, an antioxidant, a radical scavenger, a singlet quencher, a softener, a surface modifier, a bulking agent, a thickener, a dispersion stabilizer, a wax, a donor, a surfactant, a plasticizer, a sensitizer, an electron acceptor compound, and a leveling agent. Examples of the leveling agent include silicone oil, more specifically, dimethylsilicone oil.

The presence of the intermediate layer makes the flow of currents generated when the photoreceptor is exposed smooth and makes it possible to suppress an increase in resistance, while maintaining the insulated state to the extent that leakage can be suppressed. The intermediate layer (undercoat layer) includes, for example, one or both of an inorganic particle and an organic particle, and a resin used for the intermediate layer (hereinafter, referred to as an "intermediate layer resin" in some cases). Hereinafter, the inorganic particle and the organic particle included in the intermediate layer will be collectively referred to as an intermediate layer particle. The ratio of the mass of the intermediate layer particle with respect to the mass of the intermediate layer resin is, for example, 1 or more and 4 or less. The thickness of the intermediate layer is, for example, 0.1 µm or more and 5 µm or less.
Examples of the inorganic particle of the intermediate layer particle include a white pigment (more specifically, titanium oxide, zinc oxide, zinc flower, zinc sulfide, white lead, lithopone, and the like), and an extender pigment (more specifically, alumina, calcium carbonate, barium sulfate, and the like). Examples of the organic particle of the intermediate layer particle include a fluoropolymer particle, a benzoguanamine resin particle, and a styrene resin particle. The number average primary particle size of the intermediate layer particle is favorably 100 nm or less, more favorably 1 nm or more and 50 nm or less. As the intermediate layer particle, an inorganic particle is favorable and titanium oxide is more favorable. Titanium oxide may be subjected to surface treatment. The surface treatment of titanium oxide may be performed once or a plurality of times (e.g., twice). Examples of the surface treatment agent used for the surface treatment of titanium oxide include alumina, silica, and an organosilicon compound (e.g., polysiloxane, more specifically, methylhydrogenpolysiloxane).
Examples of the intermediate layer resin are the same as the examples of the binder resin included in the photosensitive layer. However, in order to suitably form a photosensitive layer, it is favorable to select, as an intermediate layer resin, a resin different from the resin used as the binder resin, of the above examples of the binder resin. The intermediate layer resin is, for example, a polyamide resin.

The conductive substrate is not particularly limited, and at least the surface portion thereof only needs to be formed of a material having conductivity. One example of the conductive substrate is a conductive substrate formed of a material having conductivity. Another example of the conductive substrate is a conductive substrate covered with a material having conductivity. Examples of the material having conductivity include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, and indium. Two or more materials having conductivity may be combined and used as an alloy (more specifically, an aluminum alloy, stainless steel, brass, or the like). As the material having conductivity, aluminum and an aluminum alloy are favorable because they provide good charge transfer from the photosensitive layer to the conductive substrate. The shape of the conductive substrate is appropriately selected in accordance with the structure of the image forming apparatus. Examples of the shape of the conductive substrate include a sheet shape and a drum shape. Further, the thickness of the conductive substrate is appropriately selected in accordance with the shape of the conductive substrate.

Next, an example of a method of producing the photoreceptor according to the first embodiment will be described. The method of producing the photoreceptor according to the first embodiment includes, for example, a photosensitive layer forming step and a protective layer forming step.

(Step of forming photosensitive layer of single-layer photoreceptor)

A photosensitive layer forming step in the case where the photoreceptor is a single-layer photoreceptor will be described. The step of forming a photosensitive layer of a single-layer photoreceptor includes a single-layer photosensitive layer forming step. In the single-layer photosensitive layer forming step, a coating liquid for forming a single-layer photosensitive layer (hereinafter, referred to as a coating liquid for a single-layer photosensitive layer in some cases) is prepared. The coating liquid for a single-layer photosensitive layer includes, for example, a charge generating agent, a hole transporting agent, a binder resin, a solvent, an electron transporting agent as necessary, and an additive as necessary. The coating liquid for a single-layer photosensitive layer is prepared by mixing these. Subsequently, the coating liquid for a single-layer photosensitive layer is applied onto the conductive substrate. Subsequently, at least part of the solvent included in the applied coating liquid for a photosensitive layer is removed to form a single-layer photosensitive layer.

(Step of forming photosensitive layer of stacked photoreceptor)

A photosensitive layer forming step in the case where the photoreceptor is a stacked photoreceptor will be described. The step of forming a photosensitive layer of a stacked photoreceptor includes a charge generating layer forming step and a charge transporting layer forming step.
In the charge generating layer forming step, a coating liquid for forming a charge generating layer (hereinafter, referred to as a coating liquid for a charge generating layer in some cases) is prepared. The coating liquid for a charge generating layer includes, for example, a charge generating agent, a base resin, a solvent, and an additive as necessary. The coating liquid for a charge generating layer is prepared by mixing these. Subsequently, the coating liquid for a charge generating layer is applied onto the conductive substrate. Subsequently, at least part of the solvent included in the applied coating liquid for a charge generating layer is removed to form a charge generating layer.
In the charge transporting layer forming step, a coating liquid for forming a charge transporting layer (hereinafter, referred to as a coating liquid for a charge transporting layer in some cases) is prepared. The coating liquid for a charge transporting layer includes a hole transporting agent, a binder resin, a solvent, and an additive as necessary. The coating liquid for a charge transporting layer is prepared by mixing these. Subsequently, the coating liquid for a charge transporting layer is applied onto the charge generating layer. Subsequently, at least part of the solvent included in the applied coating liquid for a charge transporting layer is removed to form a charge transporting layer.

(Protective layer forming step)

In the protective layer forming step, a protective layer is formed on the photosensitive layer. First, a coating liquid for forming a protective layer (hereinafter, referred to as a coating liquid for a protective layer in some cases) is prepared. The coating liquid for a protective layer includes a first particle, a second particle, at least one oligomer and a monomer for forming a protective layer resin, a solvent, a polymerization initiator as necessary, and an additive as necessary. The coating liquid for a protective layer is prepared by mixing these. Hereinafter, the "oligomer and monomer" will be referred to as a "monomer or the like" in some cases. Subsequently, the coating liquid for a protective layer is applied onto the photosensitive layer. Subsequently, the at least one monomer or the like included in the coating liquid for a protective layer on the photosensitive layer is polymerized. The polymerization forms a protective layer resin that is a polymerized product.
In the case where the protective layer resin is a photocurable resin, the at least one monomer or the like included in the coating liquid for a protective layer is polymerized by applying ultraviolet rays to the coating liquid for a protective layer. The ultraviolet rays to be applied in the protective layer forming step are applied from, for example, a light-emitting diode light source. In order to cause the photocuring reaction suitably progress, the wavelength of ultraviolet rays to be applied in the protective layer forming step is favorably 200 nm or more and 420 nm or less, more favorably 270 nm or more and 420 nm or less, still more favorably 270 nm or more and 400 nm or less, and particularly favorably 365 nm. The light energy of the ultraviolet rays to be applied in the protective layer forming step is favorably 10000 mW·s or more and 100000 mW·s or less, more favorably 60300 mW·s or more and 86400 mW·s or less. When the light energy of ultraviolet rays is 10000 mW·s or more, the photocuring reaction progresses sufficiently and the protective layer can be sufficiently cured. When the light energy is 100000 mW·s or less, it is possible to further suppress decomposition of the hole transporting agent included in the photosensitive layer and improve the sensitivity characteristics of the photoreceptor.
In the first embodiment, one or both of the first particle and the second particle do not necessarily need to have a polymerizable functional group. Further, in the production of the photoreceptor according to the first embodiment, it does not necessarily need to react a polymerizable functional group (e.g., a polymerizable unsaturated group) of one or both of the first particle and the second particle with a polymerizable functional group of an organic compound (e.g., a protective layer resin or a monomer or the like for forming a protective layer resin) to form a chemical bond. For this reason, the photoreceptor according to the first embodiment can be easily produced.
The photosensitive layer forming step and the protective layer forming step have been described above. The method of producing the photoreceptor according to the first embodiment will be further described below.
The solvent included in each of the above coating liquid for a single-layer photosensitive layer, coating liquid for a charge generating layer, coating liquid for a charge transporting layer, and coating liquid for a protective layer (hereinafter, collectively referred to as a coating liquid in some cases) is not particularly limited as long as the components included in the coating liquid can be dissolved or dispersed. Examples of the solvent include an alcohol (more specifically, methanol, ethanol, isopropanol, butanol, and the like), an aliphatic hydrocarbon (more specifically, n-hexane, octane, cyclohexane, and the like), an aromatic hydrocarbon (more specifically, benzene, toluene, xylene, and the like), a halogenated hydrocarbon (more specifically, methylene chloride, chloroform, ethylene chloride, dichloromethane, dichloroethane, carbon tetrachloride, chlorobenzene, and the like), an ether (more specifically, dioxane, dimethylan ether, diethylan ether, tetrahydrofuran, ethylene glycol dimethylether, propylene glycol monomethylether, diethylene glycol dimethylether, and the like), a ketone (more specifically, acetone, methyl ethyl ketone, 2-butanone, cyclohexanone, and the like), an ester (more specifically, ethyl acetate, methyl acetate, and the like), dimethylformaldehyde, dimethylformamide, and dimethylsulfoxide.
The coating liquid is prepared by mixing the respective components and dissolving or dispersing them in a solvent. For mixing, for example, a bead mill, a ball mill, a roll mill, a paint shaker, or an ultrasonic disperser can be used.
The method of applying the coating liquid is not particularly limited as long as the coating liquid can be uniformly applied. Examples of the application method include a dip coating method, a spray coating method, a bead coating method, a blade coating method, and a roller coating method.
Examples of the method of removing at least part of the solvent included in each of the above coating liquid for a single-layer photosensitive layer, coating liquid for a charge generating layer, and coating liquid for a charge transporting layer include heating, reduction of pressure, and a combination of heating and reduction of pressure. More specifically, a method of performing heat treatment (hot air drying) using a high-temperature dryer or a reduced-pressure dryer may be used. The temperature of the heat treatment is, for example, 40°C or more and 150°C or less. The time of the heat treatment is, for example, 3 minutes or more and 150 minutes or less.
The method of producing the photoreceptor according to the first embodiment may further include, as necessary, an intermediate layer forming step of forming an intermediate layer on the conductive substrate. Note that the intermediate layer forming step only needs to be performed by appropriately selecting a known method.

[Second embodiment: image forming apparatus]

Next, an image forming apparatus 100 that is an example of an image forming apparatus according to a second embodiment of the present invention will be described with reference to Fig. 6. Fig. 6 is a diagram showing an example of a configuration of the image forming apparatus 100. The image forming apparatus 100 is, for example, a tandem-type color printer.
As shown in Fig. 6, the image forming apparatus 100 includes a control unit 15, an operation unit 20, a paper feed unit 30, a conveying unit 40, a toner supply unit 50, an image forming unit 60, a transfer device 70, a fixing device 80, and an output unit 90.
The control unit 15 controls the operation of the respective units of the image forming apparatus 100. The control unit 15 includes a processor (not shown) and a storage unit (not shown). The processor includes, for example, a CPU (Central Processing Unit). The storage unit includes a memory such as a semiconductor memory and may include an HDD (Hard Disk Drive). The processor executes a control program to control the operation of the image forming apparatus 100. The storage unit stores the control program.
The operation unit 20 accepts an instruction from a user. The operation unit 20 transmits, upon accepting an instruction from a user, a signal indicating the instruction from a user to the control unit 15. As a result, an image forming operation by the image forming apparatus 100 is started.
The paper feed unit 30 includes a paper feed cassette 31 and a paper feed roller group 32. The paper feed cassette 31 is capable of housing a plurality of recording media P (e.g., sheets of paper). The paper feed roller group 32 feeds the recording media P housed in the paper feed cassette 31 to the conveying unit 40 one sheet at a time.
The conveying unit 40 includes a roller and a guide member. The conveying unit 40 extends from the paper feed unit 30 to the output unit 90. The conveying unit 40 conveys the recording medium P from the paper feed unit 30 to the output unit 90 through the image forming unit 60 and the fixing device 80.
The toner supply unit 50 supplies a toner to the image forming unit 60. The toner supply unit 50 includes a first mounting portion 51Y, a second mounting portion 51C, a third mounting portion 51M, and a fourth mounting portion 51K.
A first toner container 52Y is mounted on the first mounting portion 51Y. Similarly, a second toner container 52C, a third toner container 52M, and a fourth toner container 52K are respectively mounted on the second mounting portion 51C, the third mounting portion 51M, and the fourth mounting portion 51K.
A toner is housed in each of the first toner container 52Y, the second toner container 52C, the third toner container 52M, and the fourth toner container 52K. In the second embodiment, a yellow toner is housed in the first toner container 52Y. A cyan toner is housed in the second toner container 52C. A magenta toner is housed in the third toner container 52M. A black toner is housed in the fourth toner container 52K.
The image forming unit 60 includes an exposure device 61, a first image formation unit 62Y, a second image formation unit 62C, a third image formation unit 62M, and a fourth image formation unit 62K.
Each of the first image formation unit 62Y to the fourth image formation unit 62K includes a charging device 63, a development device 64, an image carrier 65, a cleaning device 66, and a static elimination device 67.
Note that regarding the configurations of the first image formation unit 62Y to the fourth image formation unit 62K, only the type of toner to be supplied from the toner supply unit 50 differs and the other configurations are the same. For this reason, in Fig. 6, the configuration of each of the second image formation unit 62C to the fourth image formation unit 62K is shown with the reference symbol omitted.
The image carrier 65 is the photoreceptor according to the first embodiment (more specifically, the single-layer photoreceptor 1 and the stacked photoreceptor 10). As described in the first embodiment, the photoreceptor according to the first embodiment has excellent sensitivity characteristics and is capable of forming an image with excellent dot reproducibility. Therefore, the image forming apparatus 100 according to the second embodiment has excellent sensitivity characteristics and is capable of forming an image with excellent dot reproducibility.
In the second embodiment, the image carrier 65 rotates in the direction indicated by an arrow R1 in Fig. 6 (clockwise direction in Fig. 6). The charging device 63, the development device 64, the cleaning device 66, and the static elimination device 67 are disposed along the circumferential surface of the image carrier 65 in the order described from the upstream side in the rotation direction of the image carrier 65.
The charging device 63 charges the surface (circumferential surface) of the image carrier 65. The charging device 63 uniformly charges the image carrier 65 to predetermined polarity by electric discharge. The charging device 63 is, for example, a charging roller.
The exposure device 61 exposes the charged surface of the image carrier 65. In detail, the exposure device 61 applies laser light to the charged surface of the image carrier 65. In this way, an electrostatic latent image is formed on the surface of the image carrier 65.
A toner is supplied from the toner supply unit 50 to the development device 64. The development device 64 supplies the toner supplied from the toner supply unit 50 to the surface of the image carrier 65. As a result, the electrostatic latent image formed on the surface of the image carrier 65 is developed as a toner image.
In the second embodiment, the development device 64 of the first image formation unit 62Y is connected to the first toner container 52Y. For this reason, a yellow toner is supplied to the development device 64 of the first image formation unit 62Y. Therefore, a yellow toner image is formed on the surface of the image carrier 65 of the first image formation unit 62Y.
Similarly, the development device 64 of the second image formation unit 62C, the development device 64 of the third image formation unit 62M, and the development device 64 of the fourth image formation unit 62K are respectively connected to the second toner container 52C, the third toner container 52M, and the fourth toner container 52K. For this reason, a cyan toner, a magenta toner, and a black toner are respectively supplied to the development device 64 of the second image formation unit 62C, the development device 64 of the third image formation unit 62M, and the development device 64 of the fourth image formation unit 62K. Therefore, a cyan toner image, a magenta toner image, and a black toner image are respectively formed on the surface of the image carrier 65 of the second image formation unit 62C, the surface of the image carrier 65 of the third image formation unit 62M, and the surface of the image carrier 65 of the fourth image formation unit 62K.
The cleaning device 66 includes a cleaning member 661 and a rubbing roller 662. After transfer by a primary transfer roller 71 described below, the cleaning member 661 is pressed against the surface of the image carrier 65 to collect the toner adhering to the surface of the image carrier 65. The cleaning member 661 is, for example, a cleaning blade. The rubbing roller 662 rubs the surface of the image carrier 65 to polish the surface of the image carrier 65.
The static elimination device 67 applies static elimination light to the surface of the image carrier 65 to eliminate static electricity on the surface of the image carrier 65.
The transfer device 70 transfers a toner image from the image carrier 65 to the recording medium P that is a to-be-transferred body. In detail, the transfer device 70 transfers each toner image formed on the surface of each image carrier 65 of the first image formation unit 62Y to the fourth image formation unit 62K onto the recording medium P in a superimposed manner. In the second embodiment, the transfer device 70 transfers each toner image onto the recording medium P in a superimposed manner using a secondary transfer method (intermediate transfer method). The transfer device 70 includes four primary transfer rollers 71, an intermediate transfer belt 72, a drive roller 73, a driven roller 74, and a secondary transfer roller 75.
The intermediate transfer belt 72 is an endless belt stretched over the four primary transfer rollers 71, the drive roller 73, and the driven roller 74. The intermediate transfer belt 72 is driven in accordance with rotation of the drive roller 73. The intermediate transfer belt 72 rotates counterclockwise in Fig. 6. The driven roller 74 is driven to rotate in accordance with the drive of the intermediate transfer belt 72.
The first image formation unit 62Y to the fourth image formation unit 62K are disposed to face the lower surface of the intermediate transfer belt 72. In the second embodiment, the first image formation unit 62Y to the fourth image formation unit 62K are disposed in the order of the first image formation unit 62Y to the fourth image formation unit 62K from the upstream side to the downstream side in a drive direction D of the lower surface of the intermediate transfer belt 72.
Each primary transfer roller 71 is disposed to face the corresponding image carrier 65 via the intermediate transfer belt 72 and is pressed toward the image carrier 65. For this reason, the toner image formed on the surface of each image carrier 65 by each primary transfer roller 71 is sequentially transferred onto the intermediate transfer belt 72. In the second embodiment, a yellow toner image, a cyan toner image, a magenta toner image, and a black toner image are transferred onto the intermediate transfer belt 72 in this order in a superimposed manner. Hereinafter, the toner image obtained by superimposing a yellow toner image, a cyan toner image, a magenta toner image, and a black toner image will be referred to as a "stacked toner image" in some cases.
The secondary transfer roller 75 is disposed to face the drive roller 73 via the intermediate transfer belt 72. The secondary transfer roller 75 is pressed toward the drive roller 73. This forms a transfer nip between the secondary transfer roller 75 and the drive roller 73. When the recording medium P passes through the transfer nip, the stacked toner image on the intermediate transfer belt 72 is transferred onto the recording medium P by the secondary transfer roller 75. In the second embodiment, a yellow toner image, a cyan toner image, a magenta toner image, and a black toner image are transferred onto the recording medium P in this order as the top layer to the bottom layer. The recording medium P onto which the stacked toner image has been transferred is conveyed toward the fixing device 80 by the conveying unit 40.
The fixing device 80 includes a heating member 81 and a pressure member 82. The heating member 81 and the pressure member 82 are disposed to face each other to form a fixing nip. The recording medium P conveyed from the image forming unit 60 is pressurized while being heated at a predetermined fixing temperature by passing through the fixing nip. As a result, the stacked toner image is fixed to the recording medium P. The recording medium P is conveyed from the fixing device 80 to the output unit 90 by the conveying unit 40.
The output unit 90 includes an output roller pair 91 and an output tray 93. The output roller pair 91 conveys the recording medium P to the output tray 93 via an output port 92. The output port 92 is formed in the upper part of the image forming apparatus 100.
Next, a configuration of the development device 64 will be described in detail with reference to Fig. 7. Fig. 7 is a diagram showing an example of a configuration of the development device 64. In detail, Fig. 7 shows the development device 64 of the first image formation unit 62Y. Note that in Fig. 7, the image carrier 65 is illustrated by a two-dot chain line for ease of understanding. In the second embodiment, the development device 64 adopts a two-component development method using a two-component developer and a touch-down development method.
As described above with reference to Fig. 6, a development container 640 of the development device 64 is connected to the first toner container 52Y. Therefore, a yellow toner is supplied to the development container 640 of the development device 64 via a toner supply port 640h.
As shown in Fig. 7, the development device 64 includes, inside the development container 640, a development roller 641, a magnetic roller 642, a first stirring screw 643, a second stirring screw 644, and a blade 645. In detail, the development roller 641 is disposed to face the magnetic roller 642. The magnetic roller 642 is disposed to face the second stirring screw 644. The blade 645 is disposed to face the magnetic roller 642.
The development container 640 is divided into a first stirring chamber 640a and a second stirring chamber 640b by a partition wall 640c. The partition wall 640c extends in the axial direction of the development roller 641. The first stirring chamber 640a and the second stirring chamber 640b communicate with each other on the outside at both ends of the partition wall 640c in the longitudinal direction.
The first stirring screw 643 is disposed in the first stirring chamber 640a. A carrier that is a magnetic material is housed in the first stirring chamber 640a. A toner that is a non-magnetic material is supplied to the first stirring chamber 640a via the toner supply port 640h. In the example shown in Fig. 7, a yellow toner is supplied to the first stirring chamber 640a.
The second stirring screw 644 is disposed in the second stirring chamber 640b. A carrier that is a magnetic material is housed in the second stirring chamber 640b.
The yellow toner is stirred with the carrier by the first stirring screw 643 and the second stirring screw 644. As a result, a two-component developer that includes a carrier and a yellow toner is formed. In this way, the two-component developer is housed in the development container 640 (more specifically, the first stirring chamber 640a and the second stirring chamber 640b) .
The first stirring screw 643 and the second stirring screw 644 stir the two-component developer while circulating it between the first stirring chamber 640a and the second stirring chamber 640b. As a result, the toner is charged to predetermined polarity by friction with the carrier.
Note that in the case where the image carrier 65 is the single-layer photoreceptor 1, the surface of the image carrier 65 and the toner are charged to, for example, positive polarity. In the case where the image carrier 65 is the stacked photoreceptor 10, the surface of the image carrier 65 and the toner are charged to, for example, negative polarity.
The magnetic roller 642 includes a non-magnetic rotating sleeve 642a and a magnet body 642b. The magnet body 642b is fixed to and disposed in the rotating sleeve 642a. The magnet body 642b includes a plurality of magnetic poles. The two-component developer is attracted to the magnetic roller 642 by the magnetic force of the magnet body 642b. As a result, a magnetic brush is formed on the surface of the magnetic roller 642.
The blade 645 is disposed on the upstream side in the rotation direction of the magnetic roller 642 than the position where the magnetic roller 642 and the development roller 641 face each other. In the second embodiment, the magnetic roller 642 rotates in the direction indicated by an arrow R3 in Fig. 7 (counterclockwise direction in Fig. 7). The magnetic roller 642 rotates to convey the magnetic brush to the position facing the blade 645. The blade 645 is disposed such that a gap is formed between the blade 645 and the magnetic roller 642. The blade 645 is formed of a magnetic material. Therefore, the thickness of the magnetic brush is regulated by the magnetic force of the blade 645.
After the thickness of the magnetic brush on the magnetic roller 642 is regulated, a predetermined voltage is applied to the magnetic roller 642 and the development roller 641. When the predetermined voltage is applied to obtain a predetermined potential difference between the magnetic roller 642 and the development roller 641, the yellow toner included in the two-component developer migrates to the development roller 641. As a result, the toner thin layer including the yellow toner is formed on the surface of the development roller 641.
The development roller 641 rotates in a direction indicated by an arrow R2 in Fig. 7 (counterclockwise direction in Fig. 7). This causes the toner thin layer formed on the surface of the development roller 641 to be conveyed to the position facing the image carrier 65 and adhere to the image carrier 65. In this way, the development device 64 supplies the toner charged due to the friction with the carrier to the surface of the image carrier 65.
The development device 64 of the first image formation unit 62Y has been described above with reference to Fig. 7. Regarding the configuration of the development device 64 of each of the first image formation unit 62Y to the fourth image formation unit 62K, only the type of toner to be supplied from the toner supply unit 50 differs and the other configurations are the same. For this reason, description of the configuration of the development device 64 of each of the second image formation unit 62C to the fourth image formation unit 62K is omitted.
The image forming apparatus 100 that is an example of the image forming apparatus according to the second embodiment has been described above with reference to Fig. 6 and Fig. 7. However, the image forming apparatus according to the second embodiment is not limited to the image forming apparatus 100. For example, the image forming apparatus may be a monochrome image forming apparatus. In this case, the image forming apparatus only needs to include one image formation unit. The image forming apparatus may adopt a rotary method. The charging device may be a charging device other than the charging roller (e.g., a scorotron charger, a charging brush, or a corotron charger). The image forming apparatus may adopt a one-component development method using a one-component developer. The image forming apparatus may adopt a development method other than the touch-down development method (e.g., a development method in which no development roller is provided and a magnetic roller serves also as a development roller). The image forming apparatus may adopt a direct transfer method. In the case where the image forming apparatus adopts a direct transfer method, a toner image is directly transferred to a recording medium from an image carrier while the image carrier is in contact with the recording medium. The image forming apparatus does not necessarily need to include a cleaning device. The image forming apparatus does not necessarily need to include a static elimination device. The image forming apparatus according to the second embodiment has been described above.

[Third embodiment: process cartridge]

Next, a first process cartridge 101, a second process cartridge 102, a third process cartridge 103, and a fourth process cartridge 104, which are examples of a process cartridge according to a third embodiment of the present invention, will be described with reference to Fig. 6. The first process cartridge 101 to the fourth process cartridge 104 according to the third embodiment respectively correspond to the first image formation unit 62Y to the fourth image formation unit 62K. Each of the first process cartridge 101 to the fourth process cartridge 104 includes the image carrier 65. The image carrier 65 is the photoreceptor according to the first embodiment (more specifically, the single-layer photoreceptor 1 and the stacked photoreceptor 10).
As described in the first embodiment, the photoreceptor according to the first embodiment has excellent sensitivity characteristics and is capable of forming an image with excellent dot reproducibility. Therefore, the process cartridge according to the third embodiment, which includes the photoreceptor according to the first embodiment, has excellent sensitivity characteristics and is capable of forming an image with excellent dot reproducibility.
The process cartridge according to the third embodiment may further include at least one (e.g., 1 or more and 7 or less) selected from the group consisting of the charging device 63, the exposure device 61, the development device 64, the transfer device 70 (particularly, the primary transfer roller 71), the cleaning member 661, the rubbing roller 662, and the static elimination device 67, in addition to the image carrier 65.
Each of the first process cartridge 101, the second process cartridge 102, the third process cartridge 103, and the fourth process cartridge 104 shown in Fig. 6 includes the image carrier 65, the charging device 63, the development device 64, the cleaning device 66 including the cleaning member 661 and the rubbing roller 662, and the static elimination device 67, similarly to the first image formation unit 62Y, the second image formation unit 62C, the third image formation unit 62M, and the fourth image formation unit 62K. However, the process cartridge according to the third embodiment is not limited to the first process cartridge 101 to the fourth process cartridge 104. As described above, the process cartridge according to the third embodiment may further include at least one of the exposure device 61 or the transfer device 70 and may include only one of the cleaning member 661 and the rubbing roller 662 (e.g. only the cleaning member 661). In any case, the process cartridge according to the third embodiment only needs to include the photoreceptor according to the first embodiment as the image carrier 65.
The process cartridge according to the third embodiment is designed to be attachable/detachable to/from the image forming apparatus 100. For this reason, the process cartridge is easy to handle, and can be easily and quickly replaced together with the image carrier 65 in the case where the sensitivity characteristics or the like of the image carrier 65 deteriorate. The process cartridge according to the third embodiment has been described above with reference to Fig. 6.

[Substituent group]

The substituent group used in the present specification will be described below. Examples of the halogen atom (halogen group) include a fluorine atom (fluoro group), a chlorine atom (chloro group), a bromine atom (bromo group), and an iodine atom (iodo group).
Unless otherwise specified, each of the alkyl group having 1 or more and 18 or less carbon atoms, the alkyl group having 10 or more and 18 or less carbon atoms, the alkyl group having 15 or more and 18 or less carbon atoms, the alkyl group having 18 carbon atoms, the alkyl group having 1 or more and 8 or less carbon atoms, the alkyl group having 1 or more and 6 or less carbon atoms, the alkyl group having 1 or more and 5 or less carbon atoms, and the alkyl group having 1 or more and 3 or less carbon atoms is linear or branched chain and unsubstituted. Examples of the alkyl group having 1 or more and 18 or less carbon atoms include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, a 1-methylbutyl group, a 2-methylbutyl group, a 3-methylbutyl group, a 1-ethylpropyl group, a 2-ethylpropyl group, a 1,1-dimethylpropyl group, a 1,2-dimethylpropyl group, a 2,2-dimethylpropyl group, an n-hexyl group, a 1-methylpentyl group, a 2-methylpentyl group, a 3-methylpentyl group, a 4-methylpentyl group, a 1,1-dimethylbutyl group, a 1,2-dimethylbutyl group, a 1,3-dimethylbutyl group, a 2,2-dimethylbutyl group, a 2,3-dimethylbutyl group, a 3,3-dimethylbutyl group, a 1,1,2-trimethylpropyl group, a 1,2,2-trimethylpropyl group, a 1-ethylbutyl group, a 2-ethylbutyl group, a 3-ethylbutyl group, linear and branched heptyl groups, linear and branched octyl groups, linear and branched nonyl groups, linear and branched decyl groups, linear and branched undecyl groups, linear and branched dodecyl groups, linear and branched tridecyl groups, linear and branched tetradecyl groups, linear and branched pentadecyl groups, linear and branched hexadecyl groups, linear and branched heptadecyl groups, and linear and branched octadecyl groups. Examples of the alkyl group having 10 or more and 18 or less carbon atoms, the alkyl group having 15 or more and 18 or less carbon atoms, the alkyl group having 18 carbon atoms, the alkyl group having 1 or more and 8 or less carbon atoms, the alkyl group having 1 or more and 6 or less carbon atoms, the alkyl group having 1 or more and 5 or less carbon atoms, and the alkyl group having 1 or more and 3 or less carbon atoms are groups having the corresponding number of carbon atoms, of the groups mentioned as the examples of the alkyl group having 1 or more and 18 or less carbon atoms.
Unless otherwise specified, the alkoxy group having 1 or more and 6 or less carbon atoms is linear or branched chain and unsubstituted. Examples of the alkoxy group having 1 or more and 6 or less carbon atoms include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a sec-butoxy group, a tert-butoxy group, an n-pentoxy group, a 1-methylbutoxy group, a methylbutoxy group, a 3-methylbutoxy group, a 1-ethylpropoxy group, a 2-ethylpropoxy group, a 1,1-dimethylpropoxy group, a 1,2-dimethylpropoxy group, a 2,2-dimethylpropoxy group, an n-hexyloxy group, a 1-methylpentyloxy group, a 2-methylpentyloxy group, a 3-methylpentyloxy group, a 4-methylpentyloxy group, a 1,1-dimethylbutoxy group, a 1,2-dimethylbutoxy group, a 1,3-dimethylbutoxy group, a 2,2-dimethylbutoxy group, a 2,3-dimethylbutoxy group, a 3,3-dimethylbutoxy group, a 1,1,2-trimethylpropoxy group, a 1,2,2-trimethylpropoxy group, a 1-ethylbutoxy group, a 2-ethylbutoxy group, and a 3-ethylbutoxy group.
Unless otherwise specified, each of the aryl group having 6 or more and 14 or less carbon atoms and the aryl group having 6 or more and 10 or less carbon atoms is unsubstituted. Examples of the aryl group having 6 or more and 14 or less carbon atoms include a phenyl group, a naphthyl group, an indacenyl group, a biphenylenyl group, an acenaphthylenyl group, an anthryl group, and a phenanthryl group. Examples of the aryl group having 6 or more and 10 or less carbon atoms are groups having the corresponding number of carbon atoms, of the groups mentioned as the examples of the aryl group having 6 or more and 14 or less carbon atoms.
Unless otherwise specified, the alkenyl group having 2 or more and 6 or less carbon atoms is linear or branched chain and unsubstituted. The alkenyl group having 2 or more and 6 or less carbon atoms has 1 or more and 3 or less double bonds. Examples of the alkenyl group having 2 or more and 6 or less carbon atoms include an ethenyl group, a propenyl group, a butenyl group, a butadienyl group, a pentenyl group, a hexenyl group, a hexadienyl group, and a hexatrienyl group. The substituent group used in the present specification has been described above.

(Examples)

Although the present invention will be further specifically described using Examples, the present invention is not limited to the scope of the Examples.

[First particle and second particle]

As a first particle and a second particle, the particle shown below were used. The conductive mechanism of these particles are shown in Table 1.

·Tin oxide: "S-2000" manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd. (undoped tin oxide, a BET specific surface area of 52.5 ± 7.5 m²/g)
·Phosphorus-doped tin oxide: "SP-2" manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd. (BET specific surface area of 105 ± 25 m²/g)
·Antimony-doped tin oxide: "T-1" manufactured by Mitsubishi Materials Electronic Chemicals Co., Ltd. (a BET specific surface area of 77.5 ± 7.5m²/g, a number average primary particle size of 200 nm)
·Zinc oxide: "NanoTek ZnO" manufactured by CIK-Nano Tek (number average primary particle size of 65.9 nm)
·Titanium oxide: "MT-500B" manufactured by TAYCA Co., Ltd. (number average primary particle size of 40 nm)
·Alumina: "Nanotek Al₂O₃" manufactured by CIK-Nano Tek (a BET specific surface area of 55 m²/g, a number average primary particle size of 31 nm)
·Silica: "Nanotek SiO₂" manufactured by CIK-Nano Tek (a BET specific surface area of 110 m²/g, a number average primary particle size of 11 nm)
·Silicone: " MSP-N050" manufactured by NIKKO RICA CORPORATION (number average primary particle size of 500 nm)

Sheets including the above eight types of particles are prepared by the following method, and the volume resistivity of each of the prepared eight types of sheets was measured. The measurement results are shown in Table 1. Note that since the components other than the particle in the eight types of sheets are the same, the volume resistivity of the eight types of particle-containing sheets and the volume resistivity of the particle included in each sheet are correlated. For example, the higher the volume resistivity of the particle-containing sheet, the higher the volume resistivity of the particle included in the sheet.

(Preparation of particle-containing sheet)

9.3 parts by mass of the particle (one of the above tin oxide, phosphorus-doped tin oxide, antimony-doped tin oxide, zinc oxide, titanium oxide, alumina, silica, and silicone), 56.0 parts by mass of a multifunctional group acrylic acid ester, 33.0 parts by mass of a monofunctional group acrylic acid ester, 1.0 part by mass of a leveling agent, 10.0 parts by mass of a polymerization initiator, and 110.0 parts by mass of methanol were mixed using a bead mill for 10 hours to obtain a mixed solution s. As the multifunctional group acrylic acid ester, "A-DPH" manufactured by SHIN-NAKAMURA CHEMICAL CO, LTD. was used. As the monofunctional group acrylic acid ester, "Viscoat 8F" manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD. was used. As the leveling agent, dimethylsilicone oil ("KF96-50CS" manufactured by Shin-Etsu Chemical Co., Ltd.) was used. As the polymerization initiator, 2,4,6-trimethylbenzoyl-diphenylphosphineoxide ("OMNIRAD TPO" manufactured by IGM Resins B.V.) was used. The obtained mixed solution s was filtered with a filter with an opening of 5 µm to obtain a coating liquid for a sample. Subsequently, the coating liquid for a sample was applied onto the conductive substrate by a dip coating method. Ultraviolet rays having a wavelength of 365 nm were applied to the applied coating liquid for a sample from a light-emitting diode light source under the condition of light energy of 86400 mW·s. The application of ultraviolet rays polymerized (photocuring reaction) the multifunctional group acrylic acid ester and the monofunctional group acrylic acid ester in the coating liquid for a sample to form a photocurable resin. In this way, a particle-containing sheet (film thickness of 3 µm) was formed on the conductive substrate. The particle-containing sheet included the photocurable resin cured by the photocuring reaction, the above particle, the leveling agent, and the polymerization initiator. A circular mask with a diameter of 5 mm was placed on the formed particle-containing sheet and silver paste was applied to obtain a sample for volume resistivity measurement.

(Measurement of volume resistivity of particle-containing sheet)

The volume resistivity was measured in the environment of a temperature of 23°C and a relative humidity of 50% RH. First, a high voltage power amplifier ("MODEL 677B" manufactured by TREK), a function generator ("AG2062F" manufactured by OWON Technology Inc.), and a picoammeter ("MODEL 485" manufactured by Keithley Instruments, Inc.) were connected in series to the measurement sample. Subsequently, a voltage was applied between both electrodes at +100 V and a frequency of 33.3 mHz, and the electrical resistance value one minute after the start of application was measured. Then, the volume resistivity of the particle-containing sheet was obtained on the basis of the measured value of the electric resistance and the dimensions of the particle-containing sheet in accordance with the following formula.

Volume resistivity [Ω·cm] = electrical resistance value × cross-sectional area of current path / length of current path

(Table 1)

First/second particle	Conductive mechanism	Particle-containing sheet volume resistivity (Ω · cm)
Tin oxide	n-type	10.6
Phosphorus-doped tin oxide	n-type	9.4
Antimony-doped tin oxide	n-type	9.8
Zinc oxide	n-type	15.2
Titanium oxide	n-type	14.1
Alumina	Non-n-type	12.5
Silica	Non-n-type	13.5
Silicon	Non-n-type	14.2

[Multifunctional group acrylic acid ester]

Those described below were used as the multifunctional group acrylic acid ester.

·EA-3/EA-4: "A-DPH" manufactured by SHIN-NAKAMURA CHEMICAL CO, LTD. (mixture of a dipentaerythritol pentaacrylate and a dipentaerythritol hexaacrylate, the dipentaerythritol pentaacrylate having the number of polymerizable functional groups of 5, the dipentaerythritol hexaacrylate having the number of polymerizable functional groups of 6, a hydroxyl value of 10 mgKOH/g)
·EA-1/EA-2: "A-TMM-3LM-N" manufactured by SHIN-NAKAMURA CHEMICAL CO, LTD. (mixture of a pentaerythritol triacrylate and a pentaerythritol tetraacrylate, the pentaerythritol triacrylate having the number of polymerizable functional groups of 3, the pentaerythritol tetraacrylate having the number of polymerizable functional groups of 4, the content ratio of the pentaerythritol triacrylate occupied in the mixture being 57 mass%)

[Monofunctional group acrylic acid ester]

Those described below were used as the monofunctional group acrylic acid ester.

·Compound in which R¹ in the formula (EB-1) represents - CH₂-(CF₂)₃CHF₂ and R² represents H: "Viscoat 8F" manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD. (compound represented by the formula (EB-12))
·Compound in which R¹ in the formula (EB-1) represents - iso-C₁₈H₃₇ and R² represents H: "ISTA" manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD. (compound represented by the formula (EB-13))
·Compound in which R¹ in the formula (EB-1) represents - CH₂-(CF₂)CHF₂ and R² represents H: "Viscoat 4F" manufactured by OSAKA ORGANIC CHEMICAL INDUSTRY LTD. (compound represented by the formula (EB-11))

[Production of single-layer photoreceptor]

Single-layer photoreceptors (P-A1) to (P-A49) and (P-B1) to (P-B8) were produced by the following method. The configurations of these single-layer photoreceptors are shown in Table 2 to Table 6 described below. Further, the configurations of the single-layer photosensitive layers (A-1) to (A-23) shown in Table 2 to Table 6 are shown in Table 7 described below.

(Formation of intermediate layer)

2 parts by mass of titanium oxide, 1 part by mass of a polyamide resin, 10 parts by mass of methanol, 1 part by mass of butanol, and 1 part by mass of toluene were mixed for 5 hours using a bead mill to obtain a mixed solution a. As the titanium oxide, a prototype "SMT-A" manufactured by TAYCA Co., Ltd. (a number average primary particle size of 10 nm, obtained by performing primary surface treatment on titanium oxide using alumina and silica and performing secondary surface treatment on the titanium oxide subjected to the primary surface treatment using methylhydrogenpolysiloxane) was used. As the polyamide resin, "Amilan (registered trademark) CM8000" manufactured by TORAY INDUSTRIES, INC. (quaternary copolymerized polyamide resin of polyamide 6, polyamide 12, polyamide 66, and polyamide 610) was used. The obtained mixed solution a was filtered with a filter with an opening of 5 µm to obtain a coating liquid for an intermediate layer. Subsequently, the coating liquid for an intermediate layer was applied onto the surface of the conductive substrate by a dip coating method. As the conductive substrate, a drum-shaped support formed of aluminum was used. Subsequently, the applied coating liquid for an intermediate layer was dried at 130°C for 30 minutes to form an intermediate layer (film thickness: 2 µm) on the conductive substrate.

(Formation of single-layer photosensitive layer)

Next, a single-layer photosensitive layer shown in the column of the single-layer photosensitive layer (A-1) in Table 7 was formed. In detail, 1.31 parts by mass of a Y-type titanyl phthalocyanine, 36.70 parts by mass of a hole transporting agent (HT-2), a total of 30.80 parts by mass of electron transporting agents (more specifically, 15.40 parts by mass of an electron transporting agent (ET-1) and 15.40 parts by mass of an electron transporting agent (ET-6)), 100.00 parts by mass of a bisphenol Z-type polycarbonate resin, and 500.00 parts by mass of tetrahydrofuran were mixed for 20 minutes using a rod-shaped sonic oscillator to obtain a mixed solution b. The obtained mixed solution b was filtered with a filter with an opening of 5 µm to obtain a coating liquid for a single-layer photosensitive layer. Subsequently, the coating liquid for a single-layer photosensitive layer was applied onto the intermediate layer on the conductive substrate by a dip coating method. The applied coating liquid for a single-layer photosensitive layer was dried at 110°C for 60 minutes to form a single-layer photosensitive layer (film thickness: 25 µm) on the intermediate layer. The total content ratio of the hole transporting agent and the electron transporting agent occupied in the single-layer photosensitive layer was 40 mass% with respect to the mass of the single-layer photosensitive layer.

(Formation of protective layer)

Next, a protective layer shown in the column of the protective layer of the single-layer photoreceptor (P-A1) in Table 2 was formed on the single-layer photosensitive layer (A-1). In detail, 9.3 parts by mass of tin oxide that is a first particle, 3.5parts by mass of alumina that is a second particle, 56.0 parts by mass of a multifunctional group acrylic acid ester (EA-3/EA-4), 34.0 parts by mass of a monofunctional group acrylic acid ester (compound in which R¹ in the formula (EB-1) represents -CH₂-(CF₂)₃CHF₂ and R² represents H), 10.0parts by mass of a polymerization initiator, 1.0 part by mass of a leveling agent, and 110.0 parts by mass of methanol were mixed for 10 hours using a bead mill to obtain a mixed solution c. As the polymerization initiator, the compound represented by the following formula (ST-1), i.e., 2,4,6-trimethylbenzoyl-diphenylphosphineoxide ("OMNIRAD TPO" manufactured by IGM Resins B.V.), was used. As the leveling agent, dimethylsilicone oil ("KF96-50CS" manufactured by Shin-Etsu Chemical Co., Ltd.) was used. The obtained mixed solution c was filtered with a filter with an opening of 5 µm to obtain a coating liquid for a protective layer. Subsequently, the coating liquid for a protective layer was applied onto the single-layer photosensitive layer by a dip coating method. Ultraviolet rays having a wavelength of 365 nm were applied from a light-emitting diode light source to the applied coating liquid for a protective layer under the condition of light energy of 86400 mW·s. The application of ultraviolet rays polymerized (photocuring reaction) the multifunctional group acrylic acid ester and the monofunctional group acrylic acid ester in the coating liquid for a protective layer to form a photocurable resin. In this way, a protective layer (film thickness: 3 µm) was formed on the single-layer photosensitive layer. The protective layer includes the photocurable resin cured by the photocuring reaction, tin oxide, alumina, the polymerization initiator, and the leveling agent.

Single-layer photoreceptors (P-A2) to (P-A49) and (P-B1) to (P-B8) were produced in the same manner as in the production of the single-layer photoreceptor (P-A1) except that the following points were changed.

(Formation of single-layer photosensitive layer in each of single-layer photoreceptors (P-A2) to (P-A49) and (P-B1) to (P-B8))

In the formation of a single-layer photosensitive layer, the single-layer photosensitive layer shown in each of the columns of the single-layer photosensitive layer in Table 2 to Table 6 was formed. For the formation of these single-layer photosensitive layers, the charge generating agent, the hole transporting agent, the electron transporting agent, and the binder resin shown in table 7 were used. Further, the hole transporting agent and the electron transporting agent were added in the amount that would make the total content ratio of the hole transporting agent and the electron transporting agent occupied in the single-layer photosensitive layer with respect to the mass of the single-layer photosensitive layer the value shown in Table 7. For example, in the case where the above-mentioned total content ratio of the hole transporting agent and the electron transporting agent is 40 mass% with respect to the mass of the single-layer photosensitive layer, a total of 36.70 parts by mass of the hole transporting agent and a total of 30.80 parts by mass of the electron transporting agent were used. In the case where the above-mentioned total content ratio of the hole transporting agent and the electron transporting agent is 60 mass% with respect to the mass of the single-layer photosensitive layer, a total of 84.00 parts by mass of the hole transporting agent and a total of 70.30 parts by mass of the electron transporting agent were used. Note that in the case where two types of hole transporting agents (HT-2) and (HT-3) were used, each hole transporting agent was used in the amount that would make the mass ratio HT-2/HT-3 1/1. In the case where two types of electron transporting agents (ET-1) and (ET-6) were used, each electron transporting agent was used in the amount that would make the mass ratio ET-1/ET-6 1/1.

(Formation of protective layer in single-layer photoreceptors (P-B1) to (P-B3))

In the formation of a protective layer in each of single-layer photoreceptors (P-B1) to (P-B3), the first particle show in Table 2 was used. No second particle was added.

(Formation of protective layer in single-layer photoreceptors (P-B4) to (P-B6))

In the formation of a protective layer in each of single-layer photoreceptors (P-B4) to (P-B6), no first particle was added. The second particle shown in Table 2 was used.

(Formation of protective layer in single-layer photoreceptors (P-A2) to (P-A49) and (P-B7) to (P-B8))

In the formation of a protective layer in each of single-layer photoreceptors (P-A2) to (P-A49) and (P-B7) to (P-B8), the first particle, the second particle, the multifunctional group acrylic acid ester, and the monofunctional group acrylic acid ester shown in Table 2 to Table 6 were used.

[Evaluation of single-layer photoreceptor]

The dot reproducibility and sensitivity characteristics of each single-layer photoreceptor were evaluated by the following method. The evaluation results are shown in Table 2 to Table 6.

For evaluation of dot reproducibility and sensitivity characteristics, a modified machine of a color multifunction device ("Taskalfa 356ci" manufactured by KYOCERA Document Solutions Inc.) was used as an evaluation device. This evaluation device was equipped with a charging roller including an epichlorohydrin resin in which conductive carbon was dispersed. The charge polarity of the charging roller was positive polarity, and the applied voltage of the charging roller was a direct current voltage. The development method was a two-component development method. The transfer method was an intermediate transfer method. This evaluation device was equipped with a cleaning blade, a rubbing roller, and a static elimination device. For evaluation of these, copy paper ("Multipaper Super Economy+" sold by ASKUL Corporation) was used as a sheet of paper.

The dot reproducibility was evaluated in a high-temperature and high-humidity environment of a temperature of 32°C and a relative humidity of 80% RH. The single-layer photoreceptor was mounted on the evaluation device. An image G1 (image with image density of 1.6%) was printed on a sheet of paper using the evaluation device. The image density (ID) at each of 10 positions randomly selected of the printed dots was measured and the number average value thereof was used as an evaluation value. For the measurement of image density, a reflection densitometer ("TC-6MC" manufactured by TokyoDenshoku. co., Ltd.) was used.

(Criteria for dot reproducibility)

Good (A): The evaluation value is 0.01 or more and less than 0.02.
Poor (B): The evaluation value is less than 0.01.

The sensitivity characteristics were evaluated in a low-temperature and low-humidity environment of a temperature of 10°C and a relative humidity of 10% RH. The single-layer photoreceptor was mounted on the evaluation device. The evaluation device was set such that the charging potential of the single-layer photoreceptor was +500 V. The exposure amount of the exposure device when printing a solid image was set to 1.08 µJ/cm². An image G2 (solid image) was printed on a sheet of paper using the evaluation device, and the surface potential of the single-layer photoreceptor after exposure (post-exposure potential VL) was measured. Then, the sensitivity characteristics of the single-layer photoreceptor were evaluated from the post-exposure potential in accordance with the following criteria.

(Criteria for sensitivity characteristics) Particularly good: VL is +200 V or less.

Good: VL exceeds +200 V and is less than +270 V.

Poor: VL is +270 V or more.

(Table 2)

	Single-layer photoreceptor	Single-layer photsensitive layer	Protective layer						Dot reproducibility	VL (+V)
			First particle	Second particle	Photocurable resin
					Multifunctional group		Monofunctional group
					Type	Polymerizable functional group (pieces)	R1	R2
Comp 1	P-B1	A-1	Tin oxide	-	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	B	140
Comp 2	P-B2	A-1	PT0	-	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	B	120
Comp 3	P-B3	A-1	AT0	-	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	B	129
Comp 4	P-B4	A-1	-	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	270
Comp 5	P-B5	A-1	-	Silica	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	280
Comp 6	P-B6	A-1	-	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	300
Comp 7	P-B7	A-1	Silica	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	290
Ex 1	P-A1	A-1	Tin oxide	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	222
Ex 2	P-A2	A-1	PT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	169
Ex 3	P-A3	A-1	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	165
Ex 4	P-A4	A-1	Zinc oxide	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	230
Ex 5	P-A5	A-1	Titanium oxide	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	210

(Table 3)

	Single-layer photoreceptor	Single-layer photosensitive - layer	Protective layer						Dot reproducibility	VL (+V)
			First particle	Second particle	Photocurable resin
					Multifunctional group		Monofunctional group
					Type	Polymenzable functional group (pieces)	R1	R2
Comp 8	P-B8	A-11	Silica	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	300
Ex 6	P-A6	A-11	Tin oxide	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	200
Ex 7	P-A7	A-11	PT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	170
Ex 8	P-A8	A-11	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	150
Ex 9	P-A9	A-11	Zinc oxide	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	220
Ex 10	P-A10	A-11	Titanium oxide	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	204
Ex 11	P-A11	A-1	Tin oxide	Silica	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	221
Ex 12	P-A12	A-1	PT0	Silica	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	160
Ex 13	P-A13	A-1	AT0	Silica	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	155
Ex 14	P-A14	A-1	Zinc oxide	Silica	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	223
Ex 15	P-A15	A-1	Titanium oxide	Silica	EA-3/EA-4	5/6	-CH₂-(CF₂)₃OHF₂	H	A	210
Ex 16	P-A16	A-1	Tin oxide	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	230

(Table 4)

	Single-layer photoreceptor	Single-layer photosensitive layer	Protective layer						Dot reproducibility	VL (+V)
			First particle	Second particle	Photocurable resin
					Multifunctional group		Monofunctional group
					Type	Polymerizable functional group (pieces)	R1	R2
Ex 17	P-A17	A-1	PT0	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	197
Ex 18	P-A18	A-1	AT0	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	163
Ex 19	P-A19	A-1	Zinc oxide	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	220
Ex 20	P-A20	A-1	Titanium oxide	Silicone	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	210
Ex 21	P-A21	A-1	PT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)CHF₂	H	A	169
Ex 22	P-A22	A-1	PT0	Alumina	EA-3/EA-4	5/6	-iso-C₁₈H₃₇	H	A	162
Ex 23	P-A23	A-1	PT0	Alumina	EA-1/EA-2	3/4	-CH₂-(CF₂)CHF₂	H	A	164
Ex 24	P-A24	A-1	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	160
Ex 25	P-A25	A-1	AT0	Alumina	EA-3/EA-4	5/6	-iso-C₁₈H₃₇	H	A	159
Ex 26	P-A26	A-1	AT0	Alumina	EA-1/EA-2	3/4	-CH₂-(CF₂)₃CHF₂	H	A	157
Ex 27	P-A27	A-2	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	160
Ex 28	P-A28	A-3	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	162

(Table 5)

	Single-layer photoreceptor	Single-layer pholosensitive layer	Protective layer						Dot reproduciblity	VL (+V)
			First particle	Second particle	Photocurable resin
					Multifunctional group		Monofunctional group
					Type	Polymerizable functional group (pieces)	R1	R2
Ex 29	P-A29	A-4	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	164
Ex 30	P-A30	A-5	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	170
Ex 31	P-A31	A-6	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	176
Ex 32	P-A32	A-7	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	165
Ex 33	P-A33	A-8	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	163
Ex 34	P-A34	A-9	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	180
Ex 35	P-A35	A-10	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	172
Ex 36	P-A36	A-11	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	176
Ex 37	P-A37	A-12	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	169
Ex 38	P-A38	A-12	PT0	Alumira	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	174
Ex 39	P-A39	A--14	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	180
Ex 40	P-A40	A-15	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	182

(Table 6)

	Photoreceptor	photosensitive Single-layer layer	Protective layer						Dot reproducibility	VL (+V)
			First particle	Second particle	Photocurable resin
					Multifunctional group		Monofunctional group
					Type	Polymerizable functional group (pieces)	R1	R2
Ex 41	P-A41	A-16	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	181
Ex 42	P-A42	A-17	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	182
Ex 43	P-A43	A-18	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	183
Ex44	P-A44	A-19	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	181
Ex 45	P-A45	A-20	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	180
Ex 46	P-A46	A-21	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	175
Ex 47	P-A47	A-22	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	173
Ex 48	P-A48	A-23	AT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	165
Ex 49	P-A49	A-23	PT0	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	162

(Table 7)

Single-layer photosensitive layer	CGM	HTM	ETM	HTM + ETM ratio (mass%)	Resin
A-1	CG-1	HT-2	ET-1/ET-6	40	BisZ
A-2	CG-1	HT-3	ET-1/ET-6	40	BisZ
A-3	CG-1	HT-4	ET-1/ET-6	40	BisZ
A-4	CG-1	HT-2	ET-1	40	BisZ
A-5	CG-1	HT-2	ET-2	40	BisZ
A-6	CG-1	HT-2	ET-3	40	BisZ
A-7	CG-1	HT-2	ET-4	40	BisZ
A-8	CG-1	HT-2	ET-5	40	BisZ
A-9	CG-1	HT-2	ET-6	40	BisZ
A-10	CG-1	HT-2	ET-7	40	BisZ
A-11	CG-1	HT-2/HT-3	ET-1/ET-6	60	BisZ
A-12	CG-2	HT-2	ET-1/ET-6	40	BisZ
A-13	CG-2	HT-3	ET-1/ET-6	40	BisZ
A-14	CG-2	HT-4	ET-1/ET-6	40	BisZ
A-15	CG-2	HT-2	ET-1	40	BisZ
A-16	CG-2	HT-2	ET-2	40	BisZ
A-17	CG-2	HT-2	ET-3	40	BisZ
A-18	CG-2	HT-2	ET-4	40	BisZ
A-19	CG-2	HT-2	ET-5	40	BisZ
A-20	CG-2	HT-2	ET-6	40	BisZ
A-21	CG-2	HT-2	ET-7	40	BisZ
A-22	CG-2	HT-2/HT-3	ET-1/ET-6	40	BisZ
A-23	CG-1	HT-2/HT-3	ET-1/ET-6	60	BisB

The terms shown in Table 2 to Tabel 7 are as follows.

Ex: Example
Comp: Comparative Example
-: no corresponding component is included
PTO: phosphorus-doped tin oxide
ATO: antimony-doped tin oxide
Multifunctional group: multifunctional group acrylic acid ester
Monofunctional group: monofunctional group acrylic acid ester
R1: group represented by R¹ in the formula (EB-1)
R2: group represented by R² in the formula (EB-1)
CGM: charge generating agent
HTM: hole transporting agent
ETM: electron transporting agent
HTM + ETM ratio: the total content ratio (unit: mass%) of the hole transporting agent and the electron transporting agent occupied in the single-layer photosensitive layer with respect to the mass of the single-layer photosensitive layer
CG-1: Y-type titanyl phthalocyanine
CG-2: X-type metal-free phthalocyanine
BisZ: bisphenol Z-type polycarbonate resin
BisB: bisphenol B-type polycarbonate resin

As shown in Table 2, the protective layer of each of the single-layer photoreceptors (P-B1) to (P-B3) included no second particle. The dot reproducibility of each of the single-layer photoreceptors (P-B1) to (P-B3) was evaluated as poor.
As shown in Table 2, the protective layer of each of the single-layer photoreceptors (P-B4) to (P-B6) included no first particle. The sensitivity characteristics of each of the single-layer photoreceptors (P-B4) to (P-B6) were evaluated as poor.
As shown in Table 2 to Table 3, the protective layer of each of the single-layer photoreceptors (P-B7) to (P-B8) included silica as a first particle, but silica did not have n-type conductivity as shown in Table 1. The sensitivity characteristics of each of the single-layer photoreceptors (P-B7) to (P-B8) were evaluated as poor.
On the other hand, as shown in Table 2 to Table 6, the protective layer of each of the single-layer photoreceptors (P-A1) to (P-249) included a first particle having n-type conductivity and a second particle having no n-type conductivity. The dot reproducibility of each of the single-layer photoreceptors (P-A1) to (P-A49) was evaluated as good, and the sensitivity characteristics were evaluated as good or particularly good.

[Production of stacked photoreceptor]

A stacked photoreceptor(P-Cl) was produced by the following method. The configuration of this stacked photoreceptor is shown in Table 8 described below.

<Production of stacked photoreceptor (P-Cl)> (Formation of intermediate layer)

An intermediate layer of the stacked photoreceptor (P-Cl) was formed in the same manner as in the formation of an intermediate layer of the single-layer photoreceptor (P-A1) except that the application conditions of the dip coating method (speed at which the conductive substrate is pulled up from the coating liquid for an intermediate layer) were changed to change the film thickness of the intermediate layer to 0.5 µm.

(Formation of charge generating layer)

1.5 parts by mass of a Y-type titanyl phthalocyanine, 1 part by mass of a polyvinylacetal resin ("S-LEC BX-5" manufactured by SEKISUI CHEMICAL CO., LTD.) as a base resin, 40 parts by mass of propylene glycol monomethylether, and 40 parts by mass of tetrahydrofuran were mixed using a bead mill for 12 hours to obtain a mixed solution d. The obtained mixed solution d was filtered with a filter with an opening of 3 µm to obtain a coating liquid for a charge generating layer. Subsequently, the coating liquid for a charge generating layer was applied onto the intermediate layer on the conductive substrate by a dip coating method. The applied coating liquid for a charge generating layer was dried at 50°C for 5 minutes to form a charge generating layer (film thickness: 0.3 µm) on the intermediate layer.

(Formation of charge transporting layer)

A total of 68.00 parts by mass of hole transporting agents (more specifically, 45.30 parts by mass of a hole transporting agent (HT-2) and 22.70 parts by mass of a hole transporting agent (HT-3)), 100.00 parts by mass of a bisphenol Z-type polycarbonate resin, 0.05 parts by mass of a leveling agent, 340.00 parts by mass of tetrahydrofuran, and 60.00 parts by mass of toluene were mixed using a roll mill for 24 hours to obtain a coating liquid for a charge transporting layer. As the leveling agent, dimethylsilicone oil ("KF96-50CS" manufactured by Shin-Etsu Chemical Co., Ltd.) was used. Subsequently, the coating liquid for a charge transporting layer was applied onto the charge generating layer by a dip coating method. The applied coating liquid for a charge transporting layer was dried at 120°C for 40 minutes to form a charge transporting layer (film thickness: 25 µm) on the charge generating layer. The total content ratio of the hole transporting agent occupied in the charge transporting layer was 40 mass% with respect to the mass of the charge transporting layer.

(Formation of protective layer)

A protective layer of the stacked photoreceptor (P-Cl) was formed in the same manner as in the formation of a protective layer of the single-layer photoreceptor (P-A1) except that the coating liquid for a protective layer was applied onto the charge transporting layer instead of onto the single-layer photosensitive layer and the tin oxide was changed to phosphorus-doped tin oxide.

[Evaluation of stacked photoreceptor]

The dot reproducibility and sensitivity characteristics of each stacked photoreceptor were evaluated by the following method. The evaluation results are shown in Table 8.

An evaluation device similar to that used to evaluate the single-layer photoreceptor except that the charge polarity of the charging roller was modified from the positive polarity to the negative polarity was used to evaluate the stacked photoreceptor. Evaluation paper similar to that used to evaluate the single-layer photoreceptor was used to evaluate the stacked photoreceptor.

The dot reproducibility of the stacked photoreceptor was evaluated in the same manner as in the evaluation of dot reproducibility of the single-layer photoreceptor.

The sensitivity characteristics of the stacked photoreceptor were evaluated in the same manner as in the evaluation of sensitivity characteristics of the single-layer photoreceptor except that the evaluation device was set such that the charging potential of the stacked photoreceptor was -500 V and the evaluation criteria were changed as follows.

(Criteria for sensitivity characteristics)

Particularly good: VL is -200 V or more.
Good: VL exceeds -270 V and is less than -200 V.
Poor: VL is -270 V or less.

(Table 8)

	Stacked photoreceptor	Protective layer						Dot reproducibility	VL (-V)
		First particle	Second particle	Photocurable resin
				Multifunctional group monomer		Monofunctional group monomer
				Type	Polymerizable functional group (pieces)	R1	R2
Ex 50	P-C1	PTO	Alumina	EA-3/EA-4	5/6	-CH₂-(CF₂)₃CHF₂	H	A	170

In Table 8, "Ex" and "PTO" are synonymous with the terms described in the above Table 2 to Table 7.
As shown in Table 8, the protective layer of the stacked photoreceptor (P-Cl) included the first particle having n-type conductivity and the second particle having no n-type conductivity. The dot reproducibility of the stacked photoreceptor (P-Cl) was evaluated as good, and the sensitivity characteristics were evaluated as particularly good.
From the above, it has been shown that the photoreceptor according to the present invention, which includes the single-layer photoreceptors (P-A1) to (PA49) and the stacked photoreceptor (P-C1), has excellent sensitivity characteristics and is capable of forming an image with excellent dot reproducibility. Further, it can be judged that the process cartridge and image forming apparatus according to the present invention have excellent sensitivity characteristics of the photoreceptor and are capable of forming an image with excellent dot reproducibility because they include such a photoreceptor.

Industrial Applicability

The photoreceptor according to the present invention can be used in an image forming apparatus. The process cartridge and image forming apparatus according to the present invention can be used to form an image on a recording medium.

Claims

An electrophotographic photoreceptor, comprising:
a conductive substrate;

a photosensitive layer; and

a protective layer,

the photosensitive layer including a charge generating agent and a hole transporting agent,

the protective layer being a top surface layer of the electrophotographic photoreceptor,

the protective layer including a first particle having n-type conductivity and a second particle having no n-type conductivity.
The electrophotographic photoreceptor according to claim 1, wherein
volume resistivity of the second particle is higher than volume resistivity of the first particle.
The electrophotographic photoreceptor according to claim 1, wherein
the first particle is a metal oxide particle.
The electrophotographic photoreceptor according to claim 1, wherein
the first particle is a tin oxide particle.
The electrophotographic photoreceptor according to claim 1, wherein
the first particle is a phosphorus-doped tin oxide particle or an antimony-doped tin oxide particle.
The electrophotographic photoreceptor according to claim 1, wherein
the second particle is an alumina particle, a silica particle, or a silicone particle.
The electrophotographic photoreceptor according to claim 1, wherein
the protective layer further include a photocurable resin, and

the photocurable resin includes a repeating unit derived from a compound having two or more polymerizable functional groups and a repeating unit derived from a compound having one polymerizable functional group.
The electrophotographic photoreceptor according to claim 7, wherein
the compound having a two or more polymerizable functional groups is at least one selected from the group consisting of compounds represented by the following formulae (EA-1), (EA-2), (EA-3), and (EA-4):
The electrophotographic photoreceptor according to claim 7, wherein
the compound having one polymerizable functional group is a compound represented by the following formula (EB-1):

(wherein, in the formula (EB-1), R¹ represents a group represented by the following formula (bl) or (b2) and R² represents a hydrogen atom or a methyl group;

wherein, in the formula (bl), m represents 0 or 1, n represents an integer of 1 or more and 3 or less, and R³ represents a hydrogen atom or a fluorine atom; and

wherein, in the formula (b2), R⁴ represents an alkyl group having 1 or more and 18 or less carbon atoms.)
The electrophotographic photoreceptor according to claim 1, wherein
a thickness of the protective layer is 2 µm or more.
The electrophotographic photoreceptor according to claim 1, wherein
the hole transporting agent included in the photosensitive layer includes at least one of compounds represented by the following formulae (1), (2), and (3):

(wherein, in the formula (1), R⁴¹, R⁴², R⁴³, R⁴⁴, R⁴⁵, and R⁴⁶ each independently represent an alkyl group having 1 or more and 8 or less carbon atoms or a phenyl group, R⁴⁷ and R⁴⁸ each independently represent a hydrogen atom, an alkyl group having 1 or more and 8 or less carbon atoms, or a phenyl group, e₁, e₂, e₃, and e₄ each independently represent an integer of 0 or more and 5 or less, and e₅ and e₆ each independently represent an integer of 0 or more and 4 or less;

wherein, in the formula (2), R⁵⁰, R⁵¹, and R⁵⁴ each independently represent an alkyl group having 1 or more and 8 or less carbon atoms or a phenyl group, R⁵² and R⁵³ each independently represent a hydrogen atom, an alkyl group having 1 or more and 8 or less carbon atoms, or a phenyl group that may be substituted with an alkyl group having 1 or more and 8 or less carbon atoms, and f₃, f₄, and f₅ each independently represent an integer of 0 or more and 5 or less; and

wherein, in the formula (3), R¹¹, R¹², R¹³, and R¹⁴ each independently represent an alkyl group having 1 or more and 8 or less carbon atoms or a phenyl group, and a₁, a₂, a₃, and a₄ each independently represent an integer of 0 or more and 5 or less.)
The electrophotographic photoreceptor according to claim 1, wherein
the charge generating agent included in the photosensitive layer includes titanyl phthalocyanine or metal-free phthalocyanine.
The electrophotographic photoreceptor according to claim 1, wherein
the photosensitive layer is a single layer,

the photosensitive layer further includes an electron transporting agent, and

the electron transporting agent includes at least one of compounds represented by the following formulae (11), (12), (13), (14), (15), and (16):

(wherein Q¹ and Q² in the formula (11), Q²¹, Q²², Q²³, and Q²¹ in the formula (12), Q³¹ and Q³² in the formula (13), Q⁴¹, Q⁴², and Q⁴³ in the formula (14), Q⁷¹, Q⁷², Q⁷³, Q⁷⁴, Q⁷⁵, and Q⁷⁶ in the formula (15), and Q⁶¹ and Q⁶² in the formula (16) each independently represent a hydrogen atom, a halogen atom, a cyano group, an alkyl group having 1 or more and 6 or less carbon atoms, an alkenyl group having 2 or more and 6 or less carbon atoms, an alkoxy group having 1 or more and 6 or less carbon atoms, or an aryl group having 6 or more and 14 or less carbon atoms that may be substituted with at least one substituent group selected from the group consisting of an alkyl group having 1 or more and 6 or less carbon atoms and a halogen atom; and

wherein Y¹ and ^y2 in the formula (15) each represent an oxygen atom.)
A process cartridge, comprising:
at least one selected from the group consisting of a charging device, an exposure device, a development device, a transfer device, a cleaning member, a rubbing roller, and a static elimination device; and

the electrophotographic photoreceptor according to claim 1.
An image forming apparatus, comprising:
an image carrier;

a charging device that charges a surface of the image carrier;

an exposure device that exposes the charged surface of the image carrier to form an electrostatic latent image on the surface of the image carrier;

a development device that supplies a toner to the surface of the image carrier to develop the electrostatic latent image as a toner image;

a transfer device that transfers the toner image from the image carrier to a to-be-transferred body,

the image carrier being the electrophotographic photoreceptor according to claim 1.