Electrophotographic photoreceptor, process cartridge, and image forming apparatus

Abstract

This electrophotographic photoreceptor comprises an electroconductive substrate (2), a photosensitive layer (3), and a protective layer (5). The protective layer (5) is the outermost layer of the electrophotographic photoreceptor. The protective layer (5) contains a photocurable resin. The photosensitive layer (3) contains a charge generator and a hole transporter. The hole transporter includes a compound having a molecular weight of 580 or more and represented by formula (1), (2), (3), or (4).

Description

[Technical Field]

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

[0002] When images are repeatedly formed using an image forming apparatus equipped with an electrophotographic photoreceptor, the electrophotographic photoreceptor may gradually wear down. To suppress wear and extend the lifespan of the electrophotographic photoreceptor, a hard protective layer may be provided on the surface of the electrophotographic photoreceptor. For example, the electrophotographic photoreceptor described in Patent Document 1 has a photosensitive layer on a conductive support containing a charge generating material and a charge transporting material in the same layer. A protective layer is provided on the photosensitive layer. The volume resistivity of the protective layer is smaller than the volume resistivity of the photosensitive layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-286707 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] However, the electrophotographic photoreceptor described in Patent Document 1 is not intended to contain a photocurable resin in its protective layer. Our research has revealed that when a photocurable resin is included in the protective layer, the electrophotographic photoreceptor is prone to overshoot in its charge potential.

[0005] The present invention has been made in view of the above problems, and its objective is to provide an electrophotographic photoreceptor, a process cartridge, and an image forming apparatus that have excellent wear resistance and can suppress overshoot of the charge potential even when the protective layer contains a photocurable resin. [Means for solving the problem]

[0006] The electrophotographic photoreceptor of the present invention includes a conductive substrate, a photosensitive layer, and a protective layer. The protective layer is the outermost surface layer of the electrophotographic photoreceptor and contains a photocurable resin. The photosensitive layer contains a charge generating agent and a hole transporting agent. The hole transporting agent has a molecular weight of 580 or more and contains a compound represented by formula (1), (2), (3), or (4).

[0007]

Chemical formula

[0008]

Chemical formula

[0009] In the above formula (1), R 41 , R 42 , R 43 , R 44 , R 45 , and R 46 each independently represent an alkyl group having 1 to 8 carbon atoms or a phenyl group, R 47 and R 48 each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group, e1, e2, e3, and e4 each independently represent an integer of 0 to 5, e5 and e6 each independently represent an integer of 0 to 4, and e7 and e8 each independently represent 0 or 1. In the above formula (2), R 50 , R 51 , and R 54 each independently represent an alkyl group having 1 to 8 carbon atoms or a phenyl group, R 52 , and R 53 each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group optionally substituted with an alkyl group having 1 to 8 carbon atoms, and f3, f4, and f5 each independently represent an integer of 0 to 5. In the above formula (3), R 11 , R 12 , R 13 , and R 14Each of these independently represents an alkyl group or phenyl group having 1 to 8 carbon atoms, and each of a1, a2, a3, and a4 independently represents an integer between 0 and 5. In formula (4) above, R 21 , R 22 , R 23 , R 24 , R 25 , and R 26 Each independently represents an alkenyl group having 2 to 6 carbon atoms, or an alkyl group having 1 to 8 carbon atoms, which may be substituted with at least one phenyl group; each independently represents an integer between 0 and 5; and each independently represents an integer between 0 and 4.

[0010] The process cartridge of the present invention comprises at least one selected from the group consisting of a charging device, an exposure device, a developing device, a transfer device, a cleaning member, a rubbing roller, and a static elimination device, and the electrophotographic photoreceptor.

[0011] The image forming apparatus of the present invention comprises an image carrier, a charging device for charging the surface of the image carrier, an exposure device for exposing the charged surface of the image carrier to form an electrostatic latent image on the surface of the image carrier, a developing device for supplying toner to the surface of the image carrier to develop the electrostatic latent image as a toner image, and a transfer device for transferring the toner image from the image carrier to a transfer target. The image carrier is the electrophotographic photoreceptor described above. [Effects of the Invention]

[0012] The electrophotographic photoreceptor, process cartridge, and image forming apparatus of the present invention can suppress overshoot of the charge potential even when the protective layer contains a photocurable resin, and exhibits excellent wear resistance. [Brief explanation of the drawing]

[0013] [Figure 1] This is a partial cross-sectional view of a single-layer electrophotographic photoreceptor, which is an example of an electrophotographic photoreceptor according to the first embodiment of the present invention. [Figure 2]This is a partial cross-sectional view of a single-layer electrophotographic photoreceptor, which is an example of an electrophotographic photoreceptor according to the first embodiment of the present invention. [Figure 3] This is a partial cross-sectional view of a stacked electrophotographic photoreceptor, which is an example of an electrophotographic photoreceptor according to the first embodiment of the present invention. [Figure 4] This is a partial cross-sectional view of a stacked electrophotographic photoreceptor, which is an example of an electrophotographic photoreceptor according to the first embodiment of the present invention. [Figure 5] This is a partial cross-sectional view of a stacked electrophotographic photoreceptor, which is an example of an electrophotographic photoreceptor according to the first embodiment of the present invention. [Figure 6] This is the absorption spectrum of a sample containing a hole transporter (HTM-2) before and after irradiation with a predetermined amount of ultraviolet light, as measured by ultraviolet-visible spectroscopy. [Figure 7] This figure shows an example of an image forming apparatus according to a second embodiment of the present invention. [Figure 8] Figure 7 shows an example of the configuration of a developing apparatus. [Modes for carrying out the invention]

[0014] The embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be implemented with appropriate modifications within the scope of the object of the present invention.

[0015] Acrylic and methacrylate are sometimes collectively referred to as "(meth)acrylic." Acrylate and methacrylate are sometimes collectively referred to as "(meth)acrylate." Acryloyl and methacryloyl are sometimes collectively referred to as "(meth)acryloyl." Unless otherwise specified, viscosity-average molecular weight is measured according to JIS (Japanese Industrial Standards) K7252-1:2016. Unless otherwise specified, hydroxyl value is measured according to JIS (Japanese Industrial Standards) K0070-1992. Unless otherwise specified, number-average primary particle diameter is the number-average value of the equivalent circle diameter (Heywood diameter: the diameter of a circle with the same area as the projected area of ​​the primary particle) of primary particles measured using a scanning electron microscope. Number-average primary particle diameter is, for example, the number-average value of the equivalent circle diameter of 100 primary particles. Unless otherwise specified, the BET specific surface area is the value measured by the BET method using nitrogen adsorption, in accordance with "JIS (Japanese Industrial Standards) Z8830:2001 Method for Measuring Specific Surface Area of ​​Powders (Solids) by Gas Adsorption". The term "system" may be added after the compound name to comprehensively refer to the compound and its derivatives. Also, when "system" is added after the compound name to represent a polymer name, it means that the repeating units of the polymer originate from the compound or its derivative. Furthermore, "general formula" and "chemical formula" are collectively referred to as "formula". In the explanation of a formula, "each independently" means that they may represent the same group or different groups. Unless otherwise specified, each component described in this specification may be used alone or in combination of two or more. Also, for example, "at least one of a, b, and c" and "at least one of a, b, and c" mean "at least one selected from the group consisting of a, b, and c". Note that a, b, and c are examples and can be replaced with other terms as appropriate.

[0016] [First Embodiment: Electrophotographic Photoreceptor] A first embodiment of the present invention relates to an electrophotographic photoreceptor (hereinafter sometimes referred to as a photoreceptor). The photoreceptor of the first embodiment comprises a conductive substrate, a photosensitive layer, and a protective layer. The protective layer is the outermost layer of the photoreceptor and contains a photocurable resin. The photosensitive layer contains a charge generating agent and a hole transporter. The hole transporter includes a compound having a molecular weight of 580 or more and represented by formula (1), (2), (3), or (4). Hereinafter, "a compound having a molecular weight of 580 or more and represented by formula (1), (2), (3), or (4)" may be referred to as a "predetermined hole transporter".

[0017] The photoreceptor of the first embodiment, by having the above configuration, can suppress overshoot of the charge potential even when the protective layer contains a photocurable resin, and has excellent abrasion resistance. The reason for this is presumed to be as follows.

[0018] Overshoot of charging potential is a phenomenon in which, when a photoreceptor is first charged by a charging device, the charging potential rises excessively, and then, as a reaction, the charging potential falls excessively. In image formation, the charging of the photoreceptor and the decharging by decharging light are repeated. If the movement of holes in the photosensitive layer is delayed between the decharging of the photoreceptor and the charging of the next cycle, and holes remain in the photosensitive layer, the charging potential of the photoreceptor will fall below the desired value during the charging of the next cycle. This results in an overshoot of charging potential.

[0019] Overshoot in charge potential is particularly likely to occur when the protective layer contains a photocurable resin. In one example of the protective layer formation process, ultraviolet light is irradiated onto a coating solution for forming the protective layer applied to the photosensitive layer (hereinafter sometimes referred to as the protective layer coating solution). At least a portion of the irradiated ultraviolet light passes through the protective layer coating solution and reaches the photosensitive layer. The ultraviolet light that reaches the layer may decompose common hole transporters. If the hole transporter is decomposed, the movement of holes in the photosensitive layer is delayed from the time the photoreceptor is discharged until the photoreceptor is charged again, making it easier for holes to remain in the photosensitive layer and increasing the likelihood of overshoot in charge potential.

[0020] In this first embodiment, the photosensitive layer contains a predetermined hole transporter. The predetermined hole transporter is a compound with a large molecular weight of 580, and therefore has high charge mobility. Furthermore, because the predetermined hole transporter has a structure represented by the above formulas (1) to (4), it is resistant to decomposition by ultraviolet light.

[0021] When the photoreceptor is negatively charged, holes move within the photosensitive layer toward the surface of the photoreceptor. By containing a predetermined hole transporter in the photosensitive layer, holes move rapidly within the layer, making it difficult for holes to remain in the photosensitive layer after static discharge. This prevents electrons attached to the surface of the photoreceptor during the next charging cycle from being canceled out by remaining holes. As a result, the photoreceptor can be charged to the desired charging potential in the next cycle, and overshoot of the charging potential can be suppressed.

[0022] Furthermore, when the photoreceptor is positively charged, holes and electrons move within the photosensitive layer. If the movement of holes is slow, the movement of electrons tends to be slow as well. By containing a predetermined hole transport agent in the photosensitive layer, holes move rapidly within the layer, and as a result, electrons also move rapidly. This causes electrons to move rapidly within the photosensitive layer toward the surface of the photoreceptor. Therefore, electrons are less likely to remain in the photosensitive layer after static discharge, and the cancellation of holes applied to the surface of the photoreceptor during the next charging cycle by the remaining electrons can be suppressed. As a result, the photoreceptor can be charged to the desired charging potential in the next cycle, and overshoot of the charging potential can be suppressed.

[0023] Furthermore, because it is equipped with a protective layer containing a photocurable resin, the photoreceptor of the first embodiment also exhibits excellent abrasion resistance.

[0024] The above explains why the photoreceptor of the first embodiment suppresses overshoot of the charge potential and has excellent wear resistance. The photoreceptor will be described further below.

[0025] The photoreceptor is, for example, a single-layer electrophotographic photoreceptor (hereinafter sometimes referred to as a single-layer photoreceptor) or a multilayer electrophotographic photoreceptor (hereinafter sometimes referred to as a multilayer photoreceptor).

[0026] The structure of a single-layer photoreceptor 1, an example of a photoreceptor, will be described below with reference to Figures 1 and 2. Figures 1 and 2 show partial cross-sectional views of the single-layer photoreceptor 1, respectively. As shown in Figure 1, the single-layer photoreceptor 1 comprises, for example, a conductive substrate 2, a photosensitive layer 3, and a protective layer 5. The photosensitive layer 3 is a single-layer photosensitive layer (hereinafter sometimes referred to as a single-layer photosensitive layer) 3a. In the example shown in Figure 1, the 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 outermost layer of the single-layer photoreceptor 1.

[0027] As shown in Figure 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 photoreceptor layer 3a, and the protective layer 5. In the example shown in Figure 2, the intermediate layer 4 is provided on the conductive substrate 2, the single-layer photoreceptor layer 3a is provided on the intermediate layer 4, and the protective layer 5 is provided on the single-layer photoreceptor layer 3a. The single-layer photoreceptor layer 3a is provided on the conductive substrate 2 via the intermediate layer 4.

[0028] The thickness of the single-layer photosensitive layer 3a is not particularly limited, but is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0029] The thickness of the protective layer 5 is not particularly limited, but is more preferably 0.1 μm to 30.0 μm, even more preferably 0.3 μm to 10.0 μm, and even more preferably 0.5 μm to 2.0 μm. In the examples shown in Figures 1 and 2, the protective layer 5 is a single layer. However, the protective layer 5 may consist of multiple layers. If the protective layer 5 consists of multiple layers, at least the outermost layer of the multiple layers contains a photocurable resin. The structure of a single-layer photoreceptor 1, which is an example of a photoreceptor, has been described above with reference to Figures 1 and 2.

[0030] The structure of a multilayer photoreceptor 10, an example of a photoreceptor, will be described below with reference to Figures 3 to 5. Figures 3 to 5 each show a partial cross-sectional view of the multilayer photoreceptor 10. As shown in Figure 3, the multilayer photoreceptor 10 comprises, for example, a conductive substrate 2, a photosensitive layer 3, and a protective layer 5. The photosensitive layer 3 includes a charge generation layer 3b and a charge transport layer 3c. In the example shown in Figure 3, the charge generation layer 3b is provided on the conductive substrate 2, the charge transport layer 3c is provided on the charge generation layer 3b, and the protective layer 5 is provided on the charge transport layer 3c. However, as shown in Figure 4, in the multilayer photoreceptor 10, the charge transport layer 3c may be provided on the conductive substrate 2, the charge generation layer 3b may be provided on the charge transport layer 3c, and the protective layer 5 may be provided on the charge generation layer 3b. In the examples shown in Figures 3 and 4, the photosensitive layer 3 is provided directly on the conductive substrate 2. The protective layer 5 is the outermost layer of the stacked photoreceptor 10.

[0031] As shown in Figure 5, the stacked photoreceptor 10 may further include an 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 Figure 5, the intermediate layer 4 is provided on the conductive substrate 2, the charge generation layer 3b is provided on the intermediate layer 4, the charge transport layer 3c is provided on the charge generation layer 3b, and the protective layer 5 is provided on the charge transport layer 3c. The photosensitive layer 3 (for example, the charge generation layer 3b) is provided on the conductive substrate 2 via the intermediate layer 4.

[0032] The thickness of the charge generation layer 3b is not particularly limited, but is preferably 0.01 μm or more and 5 μm or less, and more preferably 0.1 μm or more and 3 μm or less. In the examples shown in Figures 3 to 5, the charge generation layer 3b is a single layer. However, the charge generation layer 3b may consist of multiple layers.

[0033] The thickness of the charge transport layer 3c is not particularly limited, but is preferably 2 μm to 100 μm, and more preferably 5 μm to 50 μm. In the examples shown in Figures 3 to 5, the charge transport layer 3c is a single layer. However, the charge transport layer 3c may consist of multiple layers.

[0034] The protective layer 5 of the stacked photoreceptor 10 is the same as the protective layer 5 of the single-layer photoreceptor 1, so its explanation is omitted. The structure of the stacked photoreceptor 10, which is an example of a photoreceptor, has been explained above with reference to Figures 3 to 5.

[0035] <Protective layer> The protective layer contains, for example, a photocurable resin and a metal oxide. The protective layer may further contain, if necessary, one or both of a polymerization initiator and / or an additive.

[0036] (light curing resin) Examples of photocurable resins include (meth)acrylic resins and epoxy resins. (Meth)acrylic resins are preferred as photocurable resins because stopping ultraviolet irradiation in the protective layer formation process described later also stops the photocuring reaction, making it easier to control the progress of the photocuring reaction.

[0037] The photocurable resin preferably has repeating units derived from a compound having two or more polymerizable functional groups. Hereinafter, "repeating units derived from a compound having two or more polymerizable functional groups" may be referred to as "polyfunctional units," and "compounds having two or more polymerizable functional groups" may be referred to as "polyfunctional monomers." Since polyfunctional monomers have two or more polymerizable functional groups, the photocuring reaction in which the polymerizable functional groups react proceeds favorably in the protective layer formation process of photoreceptor manufacturing. As a result, the hardness of the protective layer is increased, and the abrasion resistance of the photoreceptor is improved.

[0038] Examples of polymerizable functional groups in a polyfunctional unit include vinyl groups and epoxy groups. When the photocurable resin is a (meth)acrylic resin, the (meth)acrylic resin has vinyl groups as polymerizable functional groups. When the photocurable resin is an epoxy resin, the epoxy resin has epoxy groups as polymerizable functional groups.

[0039] When the protective layer contains a photocurable resin, and the photocurable resin has repeating units derived from a compound having two or more vinyl groups (i.e., polyfunctional units in which the polymerizable functional group is a vinyl group), ultraviolet light suitable for cleaving the carbon-carbon double bonds of the vinyl groups is irradiated onto the protective layer coating solution during the protective layer formation process. Some of the irradiated ultraviolet light passes through the protective layer coating solution and reaches the photosensitive layer. The ultraviolet light that reaches the photosensitive layer may cleave some of the carbon-carbon double bonds of the hole transporter contained in the photosensitive layer, causing the hole transporter to decompose. However, as already mentioned, a predetermined hole transporter is difficult to decompose by ultraviolet light. Therefore, even when the photocurable resin has repeating units derived from a compound having two or more vinyl groups, the predetermined hole transporter in the photosensitive layer is difficult to decompose. As a result, the sensitivity characteristics of the photoreceptor are improved, and the overshoot of the charge potential is suppressed.

[0040] The polyfunctional group unit is preferably a repeating unit derived from a compound having 2 to 10 polymerizable functional groups, and more preferably a repeating unit derived from a compound having 3 to 6 polymerizable functional groups.

[0041] Examples of polyfunctional monomers for forming polyfunctional units include trimethylolpropane triacrylate, glycerin triacrylate, tris-(2-acryloxyethyl) isocyanurate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate. These polyfunctional monomers may be ethoxylated.

[0042] The polyfunctional monomer is preferably at least one selected from the group consisting of pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate, and more preferably one or two.

[0043] The above-mentioned pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and dipentaerythritol hexaacrylate are compounds represented by the following formulas (EA-1), (EA-2), (EA-3), and (EA-4), respectively. Therefore, the polyfunctional group unit is preferably a repeating unit derived from at least one selected from the group consisting of compounds represented by formulas (EA-1), (EA-2), (EA-3), and (EA-4), and more preferably a repeating unit derived from one or two. It is even more preferable that the polyfunctional group unit is a repeating unit derived from at least one selected from the group consisting of compounds represented by formulas (EA-1) and (EA-2).

[0044] [ka]

[0045] Polyfunctional units are formed by polymerizing the polymerizable functional groups of polyfunctional monomers. For example, by a photocuring reaction (more specifically, an addition polymerization reaction of vinyl groups), repeating units represented by formulas (EA-1a), (EA-2a), (EA-3a), and (EA-4a), which are polyfunctional units, are formed from compounds represented by formulas (EA-1), (EA-2), (EA-3), and (EA-4), which are polyfunctional monomers.

[0046] [ka]

[0047] Y in equation (EA-1a) 1 ~Y 3 At least one of them represents a group represented by formula (Yb), and Y 1 ~Y 3 The remaining part represents the base expressed by equation (Ya). Y in equation (EA-2a) 4 ~Y 7 At least one of them represents a group represented by formula (Yb), and Y 4 ~Y7 The remaining part represents the group expressed by equation (Ya). Y in equation (EA-3a) 8 ~Y 12 At least one of them represents a group represented by formula (Yb), and Y 8 ~Y 12 The remaining part represents the group represented by equation (Ya). Y in equation (EA-4a) 13 ~Y 18 At least one of them represents a group represented by formula (Yb), and Y 13 ~Y 18 The remaining part represents the base expressed by formula (Ya).

[0048] [ka]

[0049] * in equations (Ya) and (Yb) 1 * is a bond that attaches to the carbon atom of the carbonyl group in formulas (EA-1a) to (EA-4a). 2 This is a coupling that connects to other repeating units.

[0050] Through a photocuring reaction (more specifically, an addition polymerization reaction of vinyl groups), the double bond of the group represented by formula (Ya) is cleaved, and the group represented by formula (Yb) is formed. Therefore, as the photocuring reaction (more specifically, the addition polymerization reaction of vinyl groups) proceeds, the number of groups represented by formula (Ya) decreases and the number of groups represented by formula (Yb) increases.

[0051] The polyfunctional monomer is preferably a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate. The content of pentaerythritol triacrylate in the mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate is preferably 40% by mass or more and 60% by mass or less. The polyfunctional monomer is also preferably a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate.

[0052] The hydroxyl value of the polyfunctional group monomer is preferably 1 mg KOH / g or more and 50 mg KOH / g or less, and more preferably 5 mg KOH / g or more and 15 mg KOH / g or less.

[0053] The photocurable resin may have only polyfunctional group units, or it may further have repeating units (monofunctional group units) derived from a compound having one polymerizable functional group in addition to the polyfunctional group units. The content of polyfunctional group units in relation to the total number of repeating units of the photocurable resin is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass. Furthermore, the photocurable resin may have one type of polyfunctional group unit, or it may have two or more types (for example, two or three types) of polyfunctional group units.

[0054] The content of the photocurable resin in the protective layer is preferably 50% by mass or more and 99% by mass or less, and more preferably 70% by mass or more and 90% by mass or less, relative to the mass of the protective layer.

[0055] (Metal oxides) Examples of metal oxides include alumina, zinc oxide, titanium oxide, and tin oxide. The metal oxide does not need to be doped. However, it is preferable that the metal oxide be doped in order to improve the conductivity of the protective layer. Examples of doped metal oxides include phosphorus-doped tin oxide and antimond-doped tin oxide. As the metal oxide, tin oxide is preferred, and phosphorus-doped tin oxide or antimond-doped tin oxide is more preferred. The metal oxide is contained in the protective layer, for example, as metal oxide particles.

[0056] The BET specific surface area of ​​metal oxide particles is 30 m². 2 / g or more 200m 2 It is preferable that it be less than or equal to / g, and 55m 2 / g or more 130m 2It is more preferable that the amount is less than or equal to / g. The number-average primary particle diameter of the metal oxide particles is preferably 5 nm to 50 nm, and more preferably 20 nm to 35 nm.

[0057] The content of metal oxides in the protective layer is preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, relative to the mass of the protective layer.

[0058] (Polymerization initiator) The polymerization initiator is, for example, a photopolymerization initiator. Examples of photopolymerization initiators include acylphosphine oxide compounds, acetophenone compounds, ketal compounds, benzoin ether compounds, anthraquinone compounds, and thioxanthone compounds. Due to their high UV absorption efficiency, acylphosphine oxide compounds are preferred as photopolymerization initiators. Examples of acylphosphine oxide compounds include 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and lithiumphenyl(2,4,6-trimethylbenzoyl)phosphonate. The content of the polymerization initiator in the protective layer is preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 10% by mass or less, relative to the mass of the protective layer.

[0059] (Additives) Examples of additives contained in the protective layer include leveling agents (e.g., UV-curable fluorosilicone-modified acrylic polymers) and silica. Preferably, the protective layer does not contain charge generating agents, hole transporters, or electron transporters.

[0060] <Photosensitive layer> The photosensitive layer contains a charge generating agent, a hole transporter, and a binder resin. If the photoreceptor is a single-layer photoreceptor, the single-layer photosensitive layer contains, for example, a charge generating agent, a hole transporter, a binder resin, and an electron transporter. The single-layer photosensitive layer may further contain additives as needed.

[0061] When the photoreceptor is a multilayer photoreceptor, the charge generation layer included in the photosensitive layer contains, for example, a charge generating agent and a base resin. The charge transport layer included in the photosensitive layer contains, for example, a hole transport agent and a binder resin. The charge generation layer and the charge transport layer may each further contain additives as needed. Since the hole transport agent used in the photoreceptor of the first embodiment is not easily decomposed by ultraviolet light, the charge generation layer and the charge transport layer do not each need to contain a radical acceptor compound.

[0062] (Charge-generating agent) Examples of charge generating agents include phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metallic naphthalocyanine pigments, squaline pigments, indigo pigments, azulenium pigments, cyanine pigments, powders of inorganic photoconductive materials (e.g., selenium, selenium-tellurium, selenium-arsenide, cadmium sulfide, and amorphous silicon), pyryllium pigments, ancencelon pigments, triphenylmethane pigments, surene pigments, toluidine pigments, pyrazoline pigments, and quinacridone pigments.

[0063] Phthalocyanine pigments have a phthalocyanine structure. Examples of phthalocyanine pigments include metallic phthalocyanines and metal-free phthalocyanines. Examples of metallic phthalocyanines include titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine. Titanyl phthalocyanine is preferred as the metallic phthalocyanine. Titanyl phthalocyanine is represented by formula (CG-1). Metal-free phthalocyanines are represented by formula (CG-2).

[0064] [ka]

[0065] Phthalocyanine pigments may be crystalline or amorphous. Examples of metal-free phthalocyanine crystals include X-type crystals of metal-free phthalocyanine (hereinafter sometimes referred to as X-type metal-free phthalocyanine). Examples of titanyl phthalocyanine crystals include α-type, β-type, and Y-type crystals of titanyl phthalocyanine (hereinafter sometimes referred to as α-type, β-type, and Y-type titanyl phthalocyanine, respectively).

[0066] For example, in digital optical image forming apparatuses (e.g., laser beam printers or facsimile machines using light sources such as semiconductor lasers), it is preferable to use a photoreceptor that is sensitive to wavelengths of 700 nm or more. As a charge generating agent, phthalocyanine-based pigments are preferred because they have a high quantum yield in the wavelength range of 700 nm or more, with titanyl phthalocyanine or metal-free phthalocyanine being more preferred, and Y-type titanyl phthalocyanine or X-type metal-free phthalocyanine being particularly preferred.

[0067] Y-type titanyl phthalocyanine has a major peak at, for example, 27.2° of the Bragg angle (2θ±0.2°) in its CuKα-characterized X-ray diffraction spectrum. The major peak in a CuKα-characterized X-ray diffraction spectrum is the peak with the first or second highest intensity in the range where the Bragg angle (2θ±0.2°) is between 3° and 40°. Y-type titanyl phthalocyanine does not have a peak at 26.2° in its CuKα-characterized X-ray diffraction spectrum.

[0068] The CuKα characteristic X-ray diffraction spectrum can be measured, for example, by the following method. First, the sample (titanyl phthalocyanine) is placed in the sample holder of an X-ray diffractometer (for example, RIGAK Corporation's "RINT(registered trademark) 1100"), and the X-ray diffraction spectrum is measured under the following conditions: X-ray tube Cu, tube voltage 40kV, tube current 30mA, and CuKα characteristic X-ray wavelength 1.542Å. The measurement range (2θ) is, for example, 3° to 40° (start angle 3°, stop angle 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.

[0069] When the photoreceptor is a single-layer photoreceptor, the content of the charge generating agent in the single-layer photoreceptor layer is preferably 0.1 parts by mass or more and 50 parts by mass or less, and more preferably 0.5 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the binder resin. When the photoreceptor is a multilayer photoreceptor, the content of the charge generating agent in the photoreceptor layer (specifically the charge generating layer) is preferably 10 parts by mass or more and 300 parts by mass or less, and more preferably 100 parts by mass or more and 200 parts by mass or less, per 100 parts by mass of the base resin.

[0070] (Hole transport agent) The hole transporter includes a specified hole transporter. In this specification, a compound having a molecular weight of 580 or more and represented by formula (1), (2), (3), or (4) refers to a compound represented by formula (1), (2), (3), and (4) that has a molecular weight of 580 or more.

[0071] [ka]

[0072] [ka]

[0073] In formula (1), R 41 , R 42 , R 43 , R44 , R 45 , and R 46 Each of these independently represents an alkyl group having 1 to 8 carbon atoms, or a phenyl group. 47 and R 48 Each of these independently represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group. Each of e1, e2, e3, and e4 independently represents an integer between 0 and 5. Each of e5 and e6 independently represents an integer between 0 and 4. Each of e7 and e8 independently represents 0 or 1.

[0074] In equation (1), when e1 represents an integer between 2 and 5, multiple R 41 These may represent the same base or different bases. When e2 represents an integer between 2 and 5, multiple R 42 These may represent the same base or different bases. When e3 represents an integer between 2 and 5, multiple R 43 These may represent the same base or different bases. When e4 represents an integer between 2 and 5, multiple R 44 These may represent the same base or different bases. When e5 represents an integer between 2 and 4, multiple R 45 These may represent the same base or different bases. When e6 represents an integer between 2 and 4, multiple R 46 These may represent the same group or different groups.

[0075] In formula (1), R 41 ~R 46 Each of these groups preferably independently represents an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group or an ethyl group. 47 and R 48e1, e2, e3, and e4 each preferably represent an integer between 0 and 2, with e1 and e2 representing 0 and e3 and e4 representing 2. e5 and e6 preferably represent 0. To further suppress the decomposition of the hole transporter by ultraviolet light, e7 and e8 preferably represent 0.

[0076] In formula (2), R 50 , R 51 , and R 54 Each of these independently represents an alkyl group having 1 to 8 carbon atoms, or a phenyl group. 52 , and R 53 Each of these independently represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms. Each of these independently represents an integer between 0 and 5.

[0077] In equation (2), when f3 represents an integer between 2 and 5, multiple R 50 These may represent the same base or different bases. When f4 represents an integer between 2 and 5, multiple R 51 These may represent the same base or different bases. When f5 represents an integer between 2 and 5, multiple R 54 These may represent the same group or different groups.

[0078] In formula (2), R 50 , R 51 , and R 54 Each of these groups preferably independently represents an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group. 52 and R 53Each independently preferably represents a hydrogen atom, an unsubstituted phenyl group, or a phenyl group substituted with an alkyl group having 1 to 8 carbon atoms. When the phenyl group is substituted with an alkyl group having 1 to 8 carbon atoms, such an alkyl group having 1 to 8 carbon atoms is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group. f3, f4, and f5 each independently preferably represent 0 or 1.

[0079] In formula (3), R 11 R 12 R 13 and R 14 each independently represent an alkyl group having 1 to 8 carbon atoms or a phenyl group. a1, a2, a3, and a4 each independently represent an integer of 0 or more and 5 or less.

[0080] In formula (3), when a1 represents an integer of 2 or more and 5 or less, the plurality of R 11 may represent the same group as each other or different groups. When a2 represents an integer of 2 or more and 5 or less, the plurality of R 12 may represent the same group as each other or different groups. When a3 represents an integer of 2 or more and 5 or less, the plurality of R 13 may represent the same group as each other or different groups. When a4 represents an integer of 2 or more and 5 or less, the plurality of R 14 may represent the same group as each other or different groups.

[0081] In formula (3), R 11 R 12 R 13 and R 14 each independently preferably represent an alkyl group having 1 to 3 carbon atoms, and more preferably represent a methyl group or an ethyl group. a1, a2, a3, and a4 each independently preferably represent an integer of 1 or more and 3 or less, and more preferably represent 1.

[0082] In formula (4), R 21 R 22 R 23 R 24 R25 and R 26 each independently represents an alkenyl group having 2 to 6 carbon atoms which may be substituted with at least one phenyl group, or an alkyl group having 1 to 8 carbon atoms. b1, b2, b4, and b5 each independently represents an integer of 0 or more and 5 or less. b3 and b6 each independently represents an integer of 0 or more and 4 or less.

[0083] In formula (4), when b1 represents an integer of 2 or more and 5 or less, the plurality of R 21 may represent the same group as each other, or may represent different groups. When b2 represents an integer of 2 or more and 5 or less, the plurality of R 22 may represent the same group as each other, or may represent different groups. When b4 represents an integer of 2 or more and 5 or less, the plurality of R 24 may represent the same group as each other, or may represent different groups. When b5 represents an integer of 2 or more and 5 or less, the plurality of R 25 may represent the same group as each other, or may represent different groups. When b3 represents an integer of 2 or more and 4 or less, the plurality of R 23 may represent the same group as each other, or may represent different groups. When b6 represents an integer of 2 or more and 4 or less, the plurality of R 26 may represent the same group as each other, or may represent different groups.

[0084] In formula (4), R 21 , R 23 , R 24 , and R 26 each independently preferably represents an alkyl group having 1 to 8 carbon atoms, more preferably represents an alkyl group having 1 to 3 carbon atoms, and still more preferably represents a methyl group or an ethyl group. R 22 and R 25b1, b2, b4, and b5 each preferably represent 1 or 2 independently. b1 and b4 represent 2, and b2 and b5 represent 1. b3 and b6 preferably represent 0. 24 , R 25 , and R 26 A diphenylaminophenylethenyl group having R 21 , R 22 , and R 23 It is preferable to bond to the para position of the phenyl group with respect to a diphenylaminophenylethenyl group having the characteristic.

[0085] Suitable examples of the specified hole transporter include compounds represented by formulas (HTM-1), (HTM-2), (HTM-3), (HTM-4), (HTM-5), (HTM-6), (HTM-7), and (HTM-8) (hereinafter, these may be referred to as hole transporters (HTM-1), (HTM-2), (HTM-3), (HTM-4), (HTM-5), (HTM-6), (HTM-7), and (HTM-8), respectively).

[0086] [ka]

[0087] [ka]

[0088] [ka]

[0089] To further suppress the decomposition of the hole transporter by ultraviolet light, the specified hole transporter is preferably hole transporter (HTM-1), (HTM-2), or (HTM-3). However, the specified hole transporter may also be, for example, hole transporter (HTM-4), (HTM-5), (HTM-6), (HTM-7), or (HTM-8).

[0090] If Z is the residual rate of a predetermined hole transporter contained in the photosensitive layer after UV irradiation, it is preferable that the residual rate (Z) after UV irradiation is 75% or higher. Hereinafter, "residual rate (Z) after UV irradiation" may be simply referred to as "residual rate Z". In the protective layer formation process, ultraviolet light suitable for promoting a photocuring reaction (e.g., addition polymerization reaction of vinyl groups) is irradiated onto the protective layer coating solution applied to the photosensitive layer. At least a portion of the irradiated ultraviolet light passes through the protective layer coating solution and reaches the photosensitive layer. A predetermined hole transporter with a residual rate Z of 75% or higher is less likely to decompose due to the ultraviolet light irradiated in the protective layer formation process. By including a predetermined hole transporter with a residual rate Z of 75% or higher in the photosensitive layer, the decomposition of the hole transporter due to the ultraviolet light irradiated in the protective layer formation process can be suppressed. As a result, it is possible to improve the sensitivity characteristics of the photoreceptor and suppress the overshoot of the charge potential.

[0091] The survival rate Z is calculated using formula (I). Z = 100 × (A2 / A1) ... (I)

[0092] In formula (I), A1 is the absorbance of the object to be measured at a wavelength of 365 nm before irradiation with the specified ultraviolet light (hereinafter sometimes referred to as "absorbance A1"). A2 is the absorbance of the object to be measured at a wavelength of 365 nm after irradiation with the specified ultraviolet light (hereinafter sometimes referred to as "absorbance A2"). In this specification, the specified ultraviolet light is defined as ultraviolet light with a wavelength of 365 nm and an integrated light intensity of 34200 mW·s. The object to be measured is a sheet in which a hole transporter is dispersed in bisphenol Z type polycarbonate resin. More specifically, the object to be measured is a 3 μm thick sheet in which 33.5 parts by mass of a hole transporter is dispersed in 138.0 parts by mass of bisphenol Z type polycarbonate resin.

[0093] Furthermore, since bisphenol Z-type polycarbonate resin does not have chain-like groups containing carbon-carbon double bonds, it is hardly decomposed by irradiation with a predetermined amount of ultraviolet light. For this reason, bisphenol Z-type polycarbonate resin is used as the substrate for measurement. Also, since bisphenol Z-type polycarbonate resin is hardly decomposed by irradiation with a predetermined amount of ultraviolet light, the remaining percentage Z of the measured material is considered to be the remaining percentage Z of the hole transporter.

[0094] The method for measuring the residual rate Z of the hole transporter will be explained below with reference to Figure 6. Figure 6 shows the absorption spectra of a sample containing the hole transporter (HTM-2), described later, before and after irradiation with a predetermined ultraviolet light. This absorption spectrum is measured by ultraviolet-visible spectroscopy. In Figure 6, the horizontal axis represents wavelength (unit: nm), and the vertical axis represents absorbance. An ultraviolet-visible spectrophotometer is used to measure the ultraviolet-visible light absorption spectra of the sample before and after irradiation with the predetermined ultraviolet light. From the ultraviolet-visible light absorption spectrum measured before irradiation with the predetermined ultraviolet light (shown as a solid line in Figure 6), the absorbance A1 at a wavelength of 365 nm is determined. From the ultraviolet-visible light absorption spectrum measured after irradiation with the predetermined ultraviolet light (shown as a dashed line in Figure 6), the absorbance A2 at a wavelength of 365 nm is determined. Then, the residual rate Z of the hole transporter is calculated from absorbances A1 and A2 according to formula (I). Details of the method for measuring the residual rate Z of the hole transporter will be described later in the examples.

[0095] To suppress the decomposition of the hole transporter by ultraviolet light, thereby improving the sensitivity characteristics of the photoreceptor and suppressing the overshoot of the charge potential, the remaining percentage Z of the hole transporter is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The remaining percentage Z of the hole transporter is, for example, 100% or less.

[0096] The content of a predetermined hole transporter in the hole transporter is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass, based on the total mass of the hole transporter. When the photoreceptor is a single-layer photoreceptor, the content of the hole transporter in the single-layer photosensitive layer is preferably 10 parts by mass or more and 200 parts by mass or less, and more preferably 30 parts by mass or more and 130 parts by mass or less, based on 100 parts by mass of the binder resin. When the photoreceptor is a multilayer photoreceptor, the content of the hole transporter in the photosensitive layer (specifically the charge transport layer) is preferably 10 parts by mass or more and 200 parts by mass or less, and more preferably 50 parts by mass or more and 100 parts by mass or less, based on 100 parts by mass of the binder resin.

[0097] (Electron transport agent) Examples of electron transport agents include quinone compounds, diimide compounds, hydrazone compounds, malononitrile compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7-tetranitro-9-fluorenone compounds, dinitroanthracene compounds, dinitroacridine compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. Examples of quinone compounds include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds, and dinitroanthraquinone compounds.

[0098] The electron transport agent preferably contains at least one compound represented by formulas (11), (12), (13), (14), (15), and (16), and more preferably contains at least one (preferably two) compounds represented by formulas (11) and (16). Hereinafter, the compounds represented by formulas (11), (12), (13), (14), (15), and (16) may be referred to as electron transport agents (11), (12), (13), (14), (15), and (16), respectively.

[0099] [ka]

[0100] Q in equation (11) 1 and Q 2 Q in equation (12) 21 Q 22 Q 23 , and Q 24 Q in equation (13) 31 and Q 32 Q in equation (14) 41 Q 42 , and Q 43 Q in equation (15) 71 Q 72 Q 73 Q 74 Q 75 , and Q 76 , and Q in equation (16) 61 and Q 62 Each independently represents a hydrogen atom, a halogen atom, a cyano group, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 14 carbon atoms which may be substituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 6 carbon atoms and a halogen atom. In formula (15), Y 1 and Y 2 This represents an oxygen atom.

[0101] Q in equation (11) 1 and Q 2 Q in equation (12) 21 Q 22 Q 23 , and Q 24 Q in equation (13) 31 and Q 32 Q in equation (14) 41 Q 42 , and Q 43 Q in equation (15) 71 Q 72 Q 73 Q 74 Q 75 , and Q 76 , and Q in equation (16) 61and Q 62 Preferably, each of these independently represents an aryl group having 6 to 14 carbon atoms, which may be substituted with a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or at least one substituent selected from the group consisting of an alkyl group having 1 to 6 carbon atoms and a halogen atom.

[0102] Q in equation (11) 1 and Q 2 Q in equation (12) 21 Q 22 Q 23 , and Q 24 Q in equation (13) 31 and Q 32 Q in equation (14) 41 Q 42 , and Q 43 Q in equation (15) 71 Q 72 Q 73 Q 74 Q 75 , and Q 76 , and Q in equation (16) 61 and Q 62 The alkyl group having 1 to 6 carbon atoms represented by is preferably an alkyl group having 1 to 5 carbon atoms, and preferably a methyl group, ethyl group, propyl group, butyl group, or pentyl group, and particularly preferably a methyl group, tert-butyl group, or 1,1-dimethylpropyl group.

[0103] Q in equation (11) 1 and Q 2 Q in equation (12) 21 Q 22 Q 23 , and Q 24 Q in equation (13) 31 and Q 32 Q in equation (14) 41 Q 42 , and Q 43 Q in equation (15) 71 Q 72 Q 73 Q 74 Q 75 , and Q 76 , and Q in equation (16) 61 and Q62 The aryl group having 6 to 14 carbon atoms represented by is preferably an aryl group having 6 to 10 carbon atoms, and more preferably a phenyl group. The aryl group having 6 to 14 carbon atoms may be substituted with at least one substituent selected from the group consisting of alkyl groups having 1 to 6 carbon atoms and halogen atoms. The alkyl group having 1 to 6 carbon atoms is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group or an ethyl group. The halogen atom used as a substituent is preferably a fluorine atom, a chlorine atom, or a bromine atom, and particularly preferably a chlorine atom. When the aryl group having 6 to 14 carbon atoms is substituted with a substituent, the number of substituents is preferably one to five, and more preferably one or two. The aryl group having 6 to 14 carbon atoms substituted with at least one substituent selected from the group consisting of alkyl groups having 1 to 6 carbon atoms and halogen atoms is preferably a chlorophenyl group, a dichlorophenyl group, or an ethylmethylphenyl group, and more preferably a 4-chlorophenyl group, a 2,5-dichlorophenyl group, or a 2-ethyl-6-methylphenyl group.

[0104] More preferred examples of electron transport agents include compounds represented by formulas (ET-1) to (ET-7) (hereinafter, these may be referred to as electron transport agents (ET-1) to (ET-7), respectively). As electron transport agents, at least one of electron transport agents (ET-1) and (ET-6) is more preferred, and both electron transport agents (ET-1) and (ET-6) are even more preferred.

[0105] [ka]

[0106] The content of electron transporters (11) to (16) in the total electron transporters in the photosensitive layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass, based on the total mass of electron transporters in the photosensitive layer. When the photoreceptor is a single-layer photoreceptor, the content of electron transporters in the single-layer photosensitive layer is preferably 5 parts by mass or more and 150 parts by mass or less, and preferably 30 parts by mass or more and 60 parts by mass or less, based on 100 parts by mass of binder resin.

[0107] (Binder resin) Examples of binder resins include thermoplastic resins (more specifically, polyarylate resins, polycarbonate resins, styrene-based resins, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleic acid copolymers, styrene-acrylic acid copolymers, acrylic copolymers, polyethylene resins, ethylene-vinyl acetate copolymers, chlorinated polyethylene resins, polyvinyl chloride resins, polypropylene resins, ionomers, vinyl chloride-vinyl acetate copolymers, polyester resins, alkyd resins, polyamide resins, polyurethane resins, polysulfone resins, diallyl phthalate resins, ketone resins, polyvinyl butyral resins, polyvinyl acetal resins, and polyether resins), thermosetting resins (more specifically, silicone resins, epoxy resins, phenolic resins, urea resins, melamine resins, and other crosslinkable thermosetting resins), and photocurable resins (more specifically, epoxy-acrylic acid resins and urethane-acrylic acid copolymers).

[0108] Among these resins, polycarbonate resin is preferred because it provides a single-layer photosensitive layer and charge transport layer with an excellent balance of processability, mechanical strength, optical properties, and abrasion resistance. Examples of polycarbonate resins include bisphenol Z type polycarbonate resin, bisphenol B type polycarbonate resin, bisphenol ZC type polycarbonate resin, bisphenol C type polycarbonate resin, and bisphenol A type polycarbonate resin. As the binder resin, bisphenol Z type polycarbonate resin or bisphenol B type polycarbonate resin is preferred. Bisphenol Z type polycarbonate resin is a resin having repeating units represented by the formula (BisZ). Bisphenol B type polycarbonate resin is a resin having repeating units represented by the formula (BisB).

[0109] [ka]

[0110] (Base resin) The base resin contained in the charge generation layer is the same as the binder resin contained in the charge transport layer. However, in order to suitably form the charge generation layer and the charge transport layer, it is preferable to select a resin as the base resin that is different from the resin used as the binder resin from the above examples of binder resins. The base resin is, for example, polyvinyl acetal resin.

[0111] (Additives) Additives contained in the photosensitive layer include, for example, UV absorbers, antioxidants, radical scavengers, singlet quenchers, softeners, surface modifiers, bulking agents, thickening agents, dispersion stabilizers, waxes, donors, surfactants, plasticizers, sensitizers, electron acceptor compounds, and leveling agents. Examples of leveling agents include silicone oil, and more specifically, dimethyl silicone oil.

[0112] <Middle class> The presence of an intermediate layer allows for a degree of insulation sufficient to suppress leakage while facilitating the flow of current generated when the photoreceptor is exposed, thereby suppressing an increase in resistance. The intermediate layer (undercoat) contains, for example, one or both of inorganic particles and organic particles, and a resin used in the intermediate layer (hereinafter sometimes referred to as "intermediate layer resin"). Hereinafter, the inorganic particles and organic particles contained in the intermediate layer will be collectively referred to as intermediate layer particles. The ratio of the mass of intermediate layer particles to the mass of intermediate layer resin is, for example, 1 to 4. The thickness of the intermediate layer is, for example, 0.1 μm to 5 μm.

[0113] Examples of inorganic particles for the intermediate layer include white pigments (more specifically, titanium dioxide, zinc oxide, zinc oxide, zinc sulfide, lead white, and lithopone, etc.) and extender pigments (more specifically, alumina, calcium carbonate, and barium sulfate, etc.). Examples of organic particles for the intermediate layer include fluororesin particles, benzoguanamine resin particles, and styrene resin particles. The number-average primary particle size of the intermediate layer particles is preferably 100 nm or less, and more preferably 1 nm to 50 nm. Inorganic particles are preferred for the intermediate layer particles, and titanium dioxide is more preferred. Titanium dioxide may be surface-treated. Surface treatment of titanium dioxide may be performed once or multiple times (for example, twice). Examples of surface treatment agents used for surface treatment of titanium dioxide include alumina, silica, and organosilicon compounds (for example, polysiloxane, more specifically, methylhydrogenpolysiloxane).

[0114] Examples of intermediate layer resins are the same as examples of binder resins contained in the photosensitive layer. However, in order to suitably form the photosensitive layer, it is preferable to select an intermediate layer resin from the above examples of binder resins that is different from the resin used as the binder resin. The intermediate layer resin is, for example, a polyamide resin.

[0115] <Conductive substrate> The conductive substrate is not particularly limited, and only needs to be composed of a material whose surface is conductive. An example of a conductive substrate is a conductive substrate composed of a conductive material. Another example of a conductive substrate is a conductive substrate coated with a conductive material. Examples of conductive materials include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, and indium. Two or more conductive materials may be combined to form an alloy (more specifically, an aluminum alloy, stainless steel, or brass, etc.). Aluminum and aluminum alloys are preferred as conductive materials because they allow for good charge transfer from the photosensitive layer to the conductive substrate. The shape of the conductive substrate is appropriately selected according to the structure of the image forming apparatus. Examples of conductive substrate shapes include sheet-like and drum-like shapes. The thickness of the conductive substrate is appropriately selected according to the shape of the conductive substrate.

[0116] <Method for manufacturing photoreceptors> Next, an example of a method for manufacturing a photoreceptor according to the first embodiment will be described. The method for manufacturing a photoreceptor includes, for example, a photosensitive layer formation step and a protective layer formation step.

[0117] (Photosensitive layer formation process for single-layer photoreceptors) The photosensitive layer formation process for a single-layer photoreceptor is described below. The photosensitive layer formation process for a single-layer photoreceptor includes a single-layer photosensitive layer formation process. In the single-layer photosensitive layer formation process, a coating solution for forming a single-layer photosensitive layer (hereinafter sometimes referred to as a single-layer photosensitive layer coating solution) is prepared. The single-layer photosensitive layer coating solution contains, for example, a charge generating agent, a hole transporter, a binder resin, a solvent, an electron transporter if necessary, and additives if necessary. The single-layer photosensitive layer coating solution is prepared by mixing these. Next, the single-layer photosensitive layer coating solution is applied onto a conductive substrate. Then, at least a portion of the solvent contained in the applied photosensitive layer coating solution is removed to form a single-layer photosensitive layer.

[0118] (Photosensitive layer formation process for stacked photoreceptors) The photosensitive layer formation process for a stacked photoreceptor is described below. The photosensitive layer formation process for a stacked photoreceptor includes a charge generation layer formation process and a charge transport layer formation process.

[0119] In the charge generation layer formation step, a coating solution for forming the charge generation layer (hereinafter sometimes referred to as the charge generation layer coating solution) is prepared. The charge generation layer coating solution contains, for example, a charge generating agent, a base resin, a solvent, and additives as needed. The charge generation layer coating solution is prepared by mixing these components. Next, the charge generation layer coating solution is applied onto a conductive substrate. Then, at least a portion of the solvent contained in the applied charge generation layer coating solution is removed to form the charge generation layer.

[0120] In the charge transport layer formation process, a coating solution for forming the charge transport layer (hereinafter sometimes referred to as the charge transport layer coating solution) is prepared. The charge transport layer coating solution contains a hole transport agent, a binder resin, a solvent, and additives as needed. The charge transport layer coating solution is prepared by mixing these components. Next, the charge transport layer coating solution is applied onto the charge generating layer. Then, at least a portion of the solvent contained in the applied charge transport layer coating solution is removed to form the charge transport layer.

[0121] (Protective layer formation process) In the protective layer formation process, a protective layer is formed on the photosensitive layer. First, a protective layer coating solution is prepared. The protective layer coating solution includes, for example, at least one compound for forming a photocurable resin, a metal oxide, a solvent, a polymerization initiator if necessary, and additives if necessary. The protective layer coating solution is prepared by mixing these. Next, the protective layer coating solution is applied onto the photosensitive layer. Then, at least one compound for forming a photocurable resin contained in the protective layer coating solution on the photosensitive layer is polymerized. By polymerization, a photocurable resin polymer is formed.

[0122] By irradiating the protective layer coating solution with ultraviolet light, at least one compound for forming a photocurable resin contained in the protective layer coating solution is polymerized. The ultraviolet light irradiated in the protective layer formation step is, for example, irradiated from a light-emitting diode light source. In order to allow the photocuring reaction to proceed favorably, the wavelength of the ultraviolet light irradiated in the protective layer formation step is preferably 200 nm to 420 nm, more preferably 270 nm to 420 nm, and even more preferably 365 nm. The cumulative amount of ultraviolet light irradiated in the protective layer formation step is preferably 10,000 mW·s to 100,000 mW·s, and more preferably 60,300 mW·s to 86,400 mW·s. If the cumulative amount of ultraviolet light is 10,000 mW·s or more, the photocuring reaction proceeds favorably, and the protective layer can be favorably cured. If the cumulative amount of ultraviolet light is 100,000 mW·s or less, the decomposition of the hole transporter contained in the photosensitive layer can be further suppressed, and the sensitivity characteristics of the photoreceptor can be further improved.

[0123] The photosensitive layer formation process and the protective layer formation process have been described above. The method for manufacturing the photoreceptor will now be described further.

[0124] The solvents contained in the above-mentioned single-layer photosensitive layer coating solution, charge generation layer coating solution, charge transport layer coating solution, and protective layer coating solution (hereinafter, these may be collectively referred to as "coating solution") are not particularly limited, as long as they can dissolve or disperse each component contained in the coating solution. Examples of solvents include alcohols (more specifically methanol, ethanol, isopropanol, and butanol), aliphatic hydrocarbons (more specifically n-hexane, octane, and cyclohexane), aromatic hydrocarbons (more specifically benzene, toluene, and xylene), halogenated hydrocarbons (more specifically methylene chloride, chloroform, ethylene chloride, dichloromethane, dichloroethane, carbon tetrachloride, and chlorobenzene), ethers (more specifically dioxane, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, and diethylene glycol dimethyl ether), ketones (more specifically acetone, methyl ethyl ketone, 2-butanone, and cyclohexanone), esters (more specifically ethyl acetate and methyl acetate), dimethylformaldehyde, dimethylformamide, and dimethyl sulfoxide.

[0125] The coating solution is prepared by mixing each component and dissolving or dispersing them in a solvent. For mixing, for example, a bead mill, ball mill, roll mill, paint shaker, or ultrasonic disperser can be used.

[0126] The method of applying the coating solution is not particularly limited, as long as it allows for uniform application of the coating solution. Examples of application methods include dip coating, spray coating, bead coating, blade coating, and roller coating.

[0127] Methods for removing at least a portion of the solvent contained in the above-mentioned single-layer photosensitive layer coating solution, charge generation layer coating solution, and charge transport layer coating solution include, for example, heating, reduced pressure, or a combination of heating and reduced pressure. More specifically, a method of heat treatment (hot air drying) using a high-temperature dryer or a reduced-pressure dryer is used. The heat treatment temperature is, for example, 40°C to 150°C. The heat treatment time is, for example, 3 minutes to 150 minutes.

[0128] The method for manufacturing a photoreceptor may further include an intermediate layer formation step of forming an intermediate layer on a conductive substrate, if necessary. The intermediate layer formation step may be carried out by appropriately selecting a known method.

[0129] [Second Embodiment: Image Forming Apparatus] Next, with reference to Figure 7, an image forming apparatus 100, which is an example of an image forming apparatus according to a second embodiment of the present invention, will be described. Figure 7 is a diagram showing an example of the configuration of the image forming apparatus 100. The image forming apparatus 100 is, for example, a tandem color printer.

[0130] As shown in Figure 7, the image forming apparatus 100 comprises a control unit 15, an operating unit 20, a paper feeding unit 30, a transport unit 40, a toner supply unit 50, an image forming unit 60, a transfer device 70, a fixing device 80, and a discharge unit 90.

[0131] The control unit 15 controls the operation of each part 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 memory such as semiconductor memory, and may also include an HDD (Hard Disk Drive). The processor controls the operation of the image forming apparatus 100 by executing a control program. The storage unit stores the control program.

[0132] The operation unit 20 receives instructions from the user. Upon receiving instructions from the user, the operation unit 20 transmits a signal indicating the user's instructions to the control unit 15. As a result, the image forming operation by the image forming apparatus 100 is started.

[0133] The paper feeding unit 30 includes a paper feeding cassette 31 and a group of paper feeding rollers 32. The paper feeding cassette 31 can accommodate multiple recording media P (for example, paper). The group of paper feeding rollers 32 feeds the recording media P stored in the paper feeding cassette 31 one sheet at a time to the transport unit 40.

[0134] The transport unit 40 is equipped with rollers and guide members. The transport unit 40 extends from the paper feeding unit 30 to the discharge unit 90. The transport unit 40 transports the recording medium P from the paper feeding unit 30 to the discharge unit 90, passing through the image forming unit 60 and the fixing device 80.

[0135] The toner supply unit 50 supplies toner to the image forming unit 60. The toner supply unit 50 comprises a first mounting unit 51Y, a second mounting unit 51C, a third mounting unit 51M, and a fourth mounting unit 51K.

[0136] The first toner container 52Y is mounted in the first mounting section 51Y. Similarly, the second toner container 52C is mounted in the second mounting section 51C, the third toner container 52M is mounted in the third mounting section 51M, and the fourth toner container 52K is mounted in the fourth mounting section 51K.

[0137] The first toner container 52Y, the second toner container 52C, the third toner container 52M, and the fourth toner container 52K each contain toner. In the second embodiment, the first toner container 52Y contains yellow toner. The second toner container 52C contains cyan toner. The third toner container 52M contains magenta toner. The fourth toner container 52K contains black toner.

[0138] The image forming unit 60 comprises an exposure apparatus 61, a first image forming unit 62Y, a second image forming unit 62C, a third image forming unit 62M, and a fourth image forming unit 62K.

[0139] Each of the first image forming units 62Y to the fourth image forming unit 62K includes a charging device 63, a developing device 64, an image carrier 65, a cleaning device 66, and a static elimination device 67.

[0140] Note that the configurations of the first image forming unit 62Y to the fourth image forming unit 62K are the same except for the type of toner supplied from the toner supply unit 50. Therefore, in Figure 7, the reference numerals are omitted for the components of the second image forming unit 62C to the fourth image forming unit 62K.

[0141] The image carrier 65 is the photoreceptor of the first embodiment (more specifically, the single-layer photoreceptor 1 and the stacked photoreceptor 10). As described in the first embodiment, the photoreceptor of the first embodiment can suppress overshoot of the charge potential and has excellent wear resistance. Therefore, the image forming apparatus 100 of the second embodiment can suppress overshoot of the charge potential and improve the wear resistance of the photoreceptor.

[0142] In the second embodiment, the image carrier 65 rotates in the direction indicated by arrow R1 in Figure 7 (clockwise in Figure 7). The charging device 63, developing device 64, cleaning device 66, and static elimination device 67 are arranged along the circumferential surface of the image carrier 65 in the order listed from the upstream side in the rotational direction of the image carrier 65.

[0143] 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 a predetermined polarity by discharge. The charging device 63 is, for example, a charging roller.

[0144] The exposure apparatus 61 exposes the surface of the charged image carrier 65. More specifically, the exposure apparatus 61 irradiates the surface of the charged image carrier 65 with laser light. As a result, an electrostatic latent image is formed on the surface of the image carrier 65.

[0145] The developing device 64 receives toner from the toner supply unit 50. The developing 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.

[0146] In the second embodiment, the developing device 64 of the first image forming unit 62Y is connected to the first toner container 52Y. Therefore, yellow toner is supplied to the developing device 64 of the first image forming unit 62Y. As a result, a yellow toner image is formed on the surface of the image carrier 65 of the first image forming unit 62Y.

[0147] Similarly, the developing device 64 of the second image forming unit 62C, the developing device 64 of the third image forming unit 62M, and the developing device 64 of the fourth image forming unit 62K are connected to the second toner container 52C, the third toner container 52M, and the fourth toner container 52K, respectively. Therefore, the developing devices 64 of the second image forming unit 62C, the third image forming unit 62M, and the fourth image forming unit 62K are supplied with cyan toner, magenta toner, and black toner, respectively. As a result, cyan toner images, magenta toner images, and black toner images are formed on the surfaces of the image carrier 65 of the second image forming unit 62C, the third image carrier 65 of the third image forming unit 62M, and the fourth image carrier 65 of the fourth image forming unit 62K, respectively.

[0148] The cleaning device 66 includes a cleaning member 661 and a scraping roller 662. After transfer by the primary transfer roller 71, which will be described later, the cleaning member 661 is pressed against the surface of the image carrier 65 to collect toner adhering to the surface of the image carrier 65. The cleaning member 661 is, for example, a cleaning blade. The scraping roller 662 scrapes the surface of the image carrier 65 to polish the surface of the image carrier 65.

[0149] The static elimination device 67 irradiates the surface of the image carrier 65 with static elimination light to eliminate static electricity from the surface of the image carrier 65.

[0150] The transfer device 70 transfers the toner image from the image carrier 65 to the recording medium P, which is the object to be transferred. Specifically, the transfer device 70 transfers each toner image formed on the surface of each image carrier 65 of the first image forming unit 62Y to the fourth image forming unit 62K onto the recording medium P. In the second embodiment, the transfer device 70 transfers each toner image onto the recording medium P using a secondary transfer method (intermediate transfer method). The transfer device 70 has four primary transfer rollers 71, an intermediate transfer belt 72, a drive roller 73, a driven roller 74, and a secondary transfer roller 75.

[0151] The intermediate transfer belt 72 is an endless belt stretched over four primary transfer rollers 71, a drive roller 73, and a driven roller 74. The intermediate transfer belt 72 is driven in accordance with the rotation of the drive roller 73. The intermediate transfer belt 72 rotates counterclockwise in Figure 7. The driven roller 74 is rotationally driven in accordance with the drive of the intermediate transfer belt 72.

[0152] The first image forming unit 62Y to the fourth image forming unit 62K are arranged facing the lower surface of the intermediate transfer belt 72. In the second embodiment, the first image forming unit 62Y to the fourth image forming unit 62K are arranged in the order of the first image forming unit 62Y to the fourth image forming unit 62K from the upstream side to the downstream side in the driving direction D of the lower surface of the intermediate transfer belt 72.

[0153] Each primary transfer roller 71 is positioned opposite each image carrier 65 via an intermediate transfer belt 72 and is pressed toward each image carrier 65. As a result, the toner images formed on the surface of each image carrier 65 are sequentially transferred to the intermediate transfer belt 72 by each primary transfer roller 71. In the second embodiment, yellow toner images, cyan toner images, magenta toner images, and black toner images are transferred to the intermediate transfer belt 72 in this order. Hereinafter, the toner image formed by the superimposition of yellow toner images, cyan toner images, magenta toner images, and black toner images may be referred to as a "layered toner image".

[0154] The secondary transfer roller 75 is positioned opposite 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. As the recording medium P passes through the transfer nip, the secondary transfer roller 75 transfers the laminated toner image on the intermediate transfer belt 72 to the recording medium P. In the second embodiment, the yellow toner image, cyan toner image, magenta toner image, and black toner image are transferred to the recording medium P in this order, from top to bottom. The recording medium P on which the laminated toner image has been transferred is transported toward the fuser 80 by the transport unit 40.

[0155] The fixing device 80 includes a heating element 81 and a pressurizing element 82. The heating element 81 and the pressurizing element 82 are arranged facing each other to form a fixing nip. The recording medium P, transported from the image forming unit 60, is heated to a predetermined fixing temperature and pressurized as it passes through the fixing nip. As a result, the stacked toner image is fixed to the recording medium P. The recording medium P is transported from the fixing device 80 to the discharge unit 90 by the transport unit 40.

[0156] The discharge unit 90 includes a pair of discharge rollers 91 and a discharge tray 93. The pair of discharge rollers 91 transports the recording medium P to the discharge tray 93 via a discharge port 92. The discharge port 92 is formed on the upper part of the image forming apparatus 100.

[0157] Next, the configuration of the developing apparatus 64 will be described in detail with reference to Figure 8. Figure 8 is a diagram showing an example of the configuration of the developing apparatus 64. Specifically, Figure 8 shows the developing apparatus 64 of the first image forming unit 62Y. In Figure 8, the image carrier 65 is shown with a dashed line for ease of understanding. In the second embodiment, the developing apparatus 64 employs a two-component developing method using a two-component developer and a touchdown developing method.

[0158] As already explained with reference to Figure 7, the developing container 640 of the developing device 64 is connected to the first toner container 52Y. Therefore, yellow toner is supplied to the developing container 640 of the developing device 64 through the toner supply port 640h.

[0159] As shown in Figure 8, the developing apparatus 64 has a developing roller 641, a magnetic roller 642, a first stirring screw 643, a second stirring screw 644, and a blade 645 inside the developing container 640. Specifically, the developing roller 641 is positioned opposite the magnetic roller 642. The magnetic roller 642 is positioned opposite the second stirring screw 644. The blade 645 is positioned opposite the magnetic roller 642.

[0160] The developing 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 developing roller 641. The first stirring chamber 640a and the second stirring chamber 640b are in communication with each other at the outer ends of the longitudinal direction of the partition wall 640c.

[0161] The first stirring chamber 640a houses the first stirring screw 643. The first stirring chamber 640a contains a carrier, which is a magnetic material. The first stirring chamber 640a is supplied with toner, which is a non-magnetic material, through the toner supply port 640h. In the example shown in Figure 8, yellow toner is supplied to the first stirring chamber 640a.

[0162] The second stirring chamber 640b houses the second stirring screw 644. The second stirring chamber 640b contains a carrier which is a magnetic material.

[0163] The yellow toner is agitated with the carrier by the first agitation screw 643 and the second agitation screw 644. As a result, a two-component developer containing the carrier and the yellow toner is formed. This two-component developer is then placed in the developing container 640 (more specifically, the first agitation chamber 640a and the second agitation chamber 640b).

[0164] The first stirring screw 643 and the second stirring screw 644 agitate the two-component developer between the first stirring chamber 640a and the second stirring chamber 640b while circulating it. As a result, the toner becomes charged to a predetermined polarity due to friction with the carrier.

[0165] When the image carrier 65 is a single-layer photoreceptor 1, the surface of the image carrier 65 and the toner are charged with, for example, a positive polarity. When the image carrier 65 is a multilayer photoreceptor 10, the surface of the image carrier 65 and the toner are charged with, for example, a negative polarity.

[0166] The magnetic roller 642 consists of a non-magnetic rotating sleeve 642a and a magnet body 642b. The magnet body 642b is fixedly positioned inside the rotating sleeve 642a. The magnet body 642b contains multiple 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, magnetic brushes are formed on the surface of the magnetic roller 642.

[0167] The blade 645 is positioned upstream of the magnetic roller 642 in the direction of rotation of the magnetic roller 642, above the position where the magnetic roller 642 and the developing roller 641 face each other. In the second embodiment, the magnetic roller 642 rotates in the direction indicated by arrow R3 in Figure 8 (counterclockwise in Figure 8). By rotating, the magnetic roller 642 transports the magnetic brush to a position facing the blade 645. The blade 645 is positioned such that a gap is formed between it and the magnetic roller 642. The blade 645 is made of a magnetic material. Therefore, the thickness of the magnetic brush is regulated by the magnetic force of the blade 645.

[0168] 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 developing roller 641. When the predetermined voltage is applied and a predetermined potential difference is reached between the magnetic roller 642 and the developing roller 641, the yellow toner contained in the two-component developer is transferred to the developing roller 641. As a result, a thin layer of yellow toner is formed on the surface of the developing roller 641.

[0169] The developing roller 641 rotates in the direction indicated by arrow R2 in Figure 8 (counterclockwise in Figure 8). This transports the thin layer of toner formed on the surface of the developing roller 641 to a position facing the image carrier 65, where it adheres to the image carrier 65. In this way, the developing device 64 supplies toner, which has been charged by friction with the carrier, to the surface of the image carrier 65.

[0170] The developing device 64 of the first image forming unit 62Y has been described above with reference to Figure 8. The configuration of the developing device 64 of each of the first image forming units 62Y to the fourth image forming unit 62K is the same except for the type of toner supplied from the toner supply unit 50. Therefore, the configuration of the developing device 64 of the second image forming unit 62C to the fourth image forming unit 62K will not be described.

[0171] The image forming apparatus 100, an example of an image forming apparatus of the second embodiment, has been described above with reference to Figures 7 and 8. However, the image forming apparatus of 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 have one image forming unit. The image forming apparatus may employ a rotary system. The charging device may be a charging device other than a charging roller (for example, a scorotron charger, a charging brush, or a scorotron charger). The image forming apparatus may employ a one-component development method using a one-component developer. The image forming apparatus may employ a development method other than the touchdown development method (for example, a development method in which there is no development roller and the magnetic roller also serves as the development roller). The image forming apparatus may employ a direct transfer method. When the image forming apparatus employs a direct transfer method, the toner image is directly transferred from the image carrier to the recording medium while the image carrier is in contact with the recording medium. The image forming apparatus does not need to be equipped with a cleaning device. The image forming apparatus does not need to be equipped with a static elimination device. The image forming apparatus of the second embodiment has been described above.

[0172] [Third Embodiment: Process Cartridge] Next, referring to Figure 7, 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 process cartridges according to the third embodiment of the present invention, will be described. The first to fourth process cartridges 101 to 104 of the third embodiment correspond to the first to fourth image forming units 62Y to 62K, respectively. Each of the first to fourth process cartridges 101 to 104 comprises an image carrier 65. The image carrier 65 is a photoreceptor of the first embodiment (more specifically, a single-layer photoreceptor 1 and a stacked photoreceptor 10).

[0173] As described in the first embodiment, the photoreceptor of the first embodiment can suppress overshoot of the charge potential and has excellent wear resistance. Therefore, the process cartridge of the third embodiment can suppress overshoot of the charge potential and improve the wear resistance of the photoreceptor.

[0174] The process cartridge of the third embodiment may further include, in addition to the image carrier 65, at least one (for example, one to seven) selected from the group consisting of a charging device 63, an exposure device 61, a developing device 64, a transfer device 70 (particularly a primary transfer roller 71), a cleaning member 661, a rubbing roller 662, and a static elimination device 67.

[0175] The first process cartridge 101, second process cartridge 102, third process cartridge 103, and fourth process cartridge 104 shown in Figure 7 each include an image carrier 65, a charging device 63, a developing device 64, a cleaning device 66 having a cleaning member 661 and a rubbing roller 662, and a static elimination device 67, similar to the first image forming unit 62Y, second image forming unit 62C, third image forming unit 62M, and fourth image forming unit 62K. However, the process cartridges of the third embodiment are not limited to the first process cartridge 101 to the fourth process cartridge 104. As described above, the process cartridge of the third embodiment may further include at least one of the exposure device 61 and the transfer device 70, or it may include only one of the cleaning member 661 and the rubbing roller 662 (for example, only the cleaning member 661). In any case, the process cartridge of the third embodiment only needs to include the photoreceptor of the first embodiment as the image carrier 65.

[0176] The process cartridge of the third embodiment is designed to be detachably attached to the image forming apparatus 100. Therefore, the process cartridge is easy to handle, and if the sensitivity characteristics of the image carrier 65 deteriorate, it can be easily and quickly replaced, including the image carrier 65. The process cartridge of the third embodiment has been described above with reference to Figure 7.

[0177] [Substituent] The substituents used in this specification are described below. Examples of halogen atoms (halogen groups) include fluorine atoms (fluoro groups), chlorine atoms (chloro groups), bromine atoms (bromo groups), and iodine atoms (iodine groups).

[0178] Alkyl groups having 1 to 8 carbon atoms, alkyl groups having 1 to 6 carbon atoms, alkyl groups having 1 to 5 carbon atoms, and alkyl groups having 1 to 3 carbon atoms are, unless otherwise specified, linear or branched and unsubstituted. Examples of alkyl groups having 1 to 8 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-ethylpropyl group, 2-ethylpropyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, 2,2-dimethylpropyl group, n-hexyl group, 1-methylpentyl group, and 2-methylpentyl group. Examples include the heptyl group, 3-methylpentyl group, 4-methylpentyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,2-dimethylbutyl group, 2,3-dimethylbutyl group, 3,3-dimethylbutyl group, 1,1,2-trimethylpropyl group, 1,2,2-trimethylpropyl group, 1-ethylbutyl group, 2-ethylbutyl group, 3-ethylbutyl group, linear and branched heptyl groups, and linear and branched octyl groups. Examples of alkyl groups having 1 to 6 carbon atoms, alkyl groups having 1 to 5 carbon atoms, and alkyl groups having 1 to 3 carbon atoms are, respectively, groups having the corresponding number of carbon atoms from the groups described as examples of alkyl groups having 1 to 8 carbon atoms.

[0179] Unless otherwise specified, alkoxy groups having 1 to 6 carbon atoms are linear or branched and unsubstituted. Examples of alkoxy groups having 1 to 6 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, 1-methylbutoxy, 2-methylbutoxy, 3-methylbutoxy, 1-ethylpropoxy, 2-ethylpropoxy, 1,1-dimethylpropoxy, 1,2-dimethylpropoxy, 2,2-dimethylpropoxy, n-hexyloxy, and 1-methylpropoxy. Examples include the methylpentyloxy group, 2-methylpentyloxy group, 3-methylpentyloxy group, 4-methylpentyloxy group, 1,1-dimethylbutoxy group, 1,2-dimethylbutoxy group, 1,3-dimethylbutoxy group, 2,2-dimethylbutoxy group, 2,3-dimethylbutoxy group, 3,3-dimethylbutoxy group, 1,1,2-trimethylpropoxy group, 1,2,2-trimethylpropoxy group, 1-ethylbutoxy group, 2-ethylbutoxy group, and 3-ethylbutoxy group.

[0180] Unless otherwise specified, aryl groups having 6 to 14 carbon atoms and aryl groups having 6 to 10 carbon atoms are unsubstituted. Examples of aryl groups having 6 to 14 carbon atoms include the phenyl group, naphthyl group, indacenyl group, biphenylenyl group, acenaphthyrenyl group, anthryl group, and phenanthryl group. Examples of aryl groups having 6 to 10 carbon atoms are those groups among the examples of aryl groups having 6 to 14 carbon atoms that have the corresponding number of carbon atoms.

[0181] Alkenyl groups having 2 to 6 carbon atoms and alkenyl groups having 2 to 4 carbon atoms are, unless otherwise specified, linear or branched and unsubstituted. Alkenyl groups having 2 to 6 carbon atoms have one to three double bonds. Examples of alkenyl groups having 2 to 6 carbon atoms include ethenyl, propenyl, butenyl, butadienyl, pentenyl, hexenyl, hexadienyl, and hexatrinyl groups. Examples of alkenyl groups having 2 to 4 carbon atoms are those groups among the examples of alkenyl groups having 2 to 6 carbon atoms that have the corresponding number of carbon atoms. The substituents used in this specification have now been explained. [Examples]

[0182] The present invention will be described in more detail below using examples, but the present invention is not limited in any way to the scope of these examples.

[0183] [Manufacturing of single-layer photoreceptors] Single-layer photoreceptors (A-1) to (A-8) and (B-1) to (B-6) were manufactured using the following method. The composition of these single-layer photoreceptors is shown in Table 1 below.

[0184] <Manufacturing of single-layer photoreceptor (A-1)> (Formation of a single-layer photosensitive layer) Mixture b was obtained by mixing 2.85 parts by mass of Y-type titanyl phthalocyanine, 62.00 parts by mass of hole transporter (HTM-1), 33.50 parts by mass of electron transporter (ET-1), 33.50 parts by mass of electron transporter (ET-6), 138.00 parts by mass of bisphenol Z-type polycarbonate resin, 0.02 parts by mass of leveling agent, and 500.00 parts by mass of tetrahydrofuran using a rod-shaped sonic oscillator for 20 minutes. As the bisphenol Z-type polycarbonate resin, "Yupizeta PCZ-200" manufactured by Mitsubishi Gas Chemical Company, Inc. was used. Dimethyl silicone oil ("KF96-50CS" manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the leveling agent. The obtained mixture b was filtered using a 5 μm mesh filter to obtain a coating solution for a single-layer photosensitive layer. A single-layer photosensitive layer (film thickness: 25 μm) was formed on a conductive substrate by a dip-coating method, after which a single-layer photosensitive layer was applied and dried at 110°C for 60 minutes. An aluminum drum-shaped support was used as the conductive substrate.

[0185] (Formation of a protective layer) 4.4 parts by mass of phosphorus-doped tin oxide, 45.0 parts by mass of polyfunctional monomer, 5.0 parts by mass of polymerization initiator, and 76.0 parts by mass of methanol were mixed using a bead mill for 12 hours to obtain mixture c. As phosphorus-doped tin oxide, Mitsubishi Materials Electronic Chemicals Co., Ltd.'s "SP-2" (BET specific surface area 105 ± 25 m²) was used. 2A polyfunctional monomer was used. As the polyfunctional monomer, "A-TMM-3LM-N" manufactured by Shin Nakamura Chemical Industry Co., Ltd. was used (a mixture of compounds represented by formulas (EA-1) and (EA-2) as described in the first embodiment, with 3 polymerizable functional groups in the compound represented by formula (EA-1) and 4 polymerizable functional groups in the compound represented by formula (EA-2), and a content of 57% by mass of the compound represented by formula (EA-1) in the mixture). As the polymerization initiator, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide ("OMNIRAD TPO" manufactured by IGM RESINS) was used. The obtained mixture c was filtered using a 5 μm mesh filter to obtain a protective layer coating solution. Next, the protective layer coating solution was applied to a single-layer photosensitive layer by dip coating. The applied protective layer coating solution was exposed to UV light at a wavelength of 365 nm and an intensity of 2400 mW / cm². 2 The sample was irradiated with ultraviolet light for 36 seconds. Upon irradiation with ultraviolet light, the polyfunctional group monomers in the protective layer coating solution polymerized (photocuring reaction), forming a photocurable resin. In this way, a protective layer (film thickness: 1.0 μm) was formed on the single-layer photosensitive layer, and a single-layer photoreceptor (A-1) was obtained. The protective layer contained the photocurable resin cured by the photocuring reaction, phosphorus-doped tin oxide, and a polymerization initiator.

[0186] <Manufacturing of single-layer photoreceptors (A-2) to (A-8) and (B-1) to (B-5)> Single-layer photoreceptors (A-2) to (A-8) and (B-1) to (B-5) were manufactured in the same manner as single-layer photoreceptor (A-1), except that the hole transporter shown in Table 1 was used. The hole transporters (HTM-9) to (HTM-13) used in the comparative examples in Table 1 are represented by the following formulas (HTM-9) to (HTM-13), respectively.

[0187] [ka]

[0188] <Manufacturing of single-layer photoreceptor (B-6)> A single-layer photoreceptor (B-6) was manufactured in the same manner as the single-layer photoreceptor (A-1), except that the hole transport agent shown in Table 1 was used and the formation of the above protective layer was not carried out.

[0189] [Measurement of Single-Layer Photoreceptor] The residual ratio Z of each single-layer photoreceptor was measured by the following method. The measurement results are shown in Table 1.

[0190] [Residual Ratio Z of Hole Transport Agent] 33.5 parts by mass of a hole transport agent (more specifically, any one of hole transport agents (HTM-1) to (HTM-13)), 138.0 parts by mass of a bisphenol Z type polycarbonate resin ("Yupizer PCZ-200" manufactured by Mitsubishi Gas Chemical Company, Inc., viscosity average molecular weight 21,500, glass transition point 174 °C), and 3322.0 parts by mass of tetrahydrofuran were mixed using a bead mill for 12 hours to obtain a coating solution for residual ratio measurement. Next, using a wire bar, the coating solution for residual ratio measurement was applied onto an overhead projector (OHP) film and heated at 100 °C for 60 minutes. In this way, a sheet (film thickness 3 μm) containing the hole transport agent and the like to be measured was formed on the OHP film. A sample comprising the sheet containing the hole transport agent and the like and the OHP film was cut into two equal parts to obtain two samples S1 and S2.

[0191] Sample S1 was set in the film holder of an ultraviolet-visible spectrophotometer ("U-3010" manufactured by Hitachi, Ltd.). Using the above ultraviolet-visible spectrophotometer, Sample S1 was measured under the following measurement conditions. And an ultraviolet-visible light absorption spectrum (spectrum before ultraviolet irradiation) was obtained.

[0192] Next, a predetermined ultraviolet ray with a wavelength of 365 nm and an integrated light amount of 34200 mW·s was irradiated onto the measurement sample S2. After irradiating the predetermined ultraviolet ray, sample S2 was set in the film holder of the above ultraviolet-visible spectrophotometer. Using the above ultraviolet-visible spectrophotometer, the measurement sample S2 after irradiating the predetermined ultraviolet ray was measured under the following measurement conditions to obtain an ultraviolet-visible light absorption spectrum (spectrum after UV irradiation).

[0193] From the spectrum before ultraviolet irradiation, the absorbance A1 at a wavelength of 365 nm was determined. The determined absorbance A1 was regarded as the absorbance A1 of the measurement object before ultraviolet irradiation. Next, from the spectrum after ultraviolet irradiation, the absorbance A2 at a wavelength of 365 nm was determined. The determined absorbance A2 was regarded as the absorbance A2 of the measurement object after ultraviolet irradiation. Based on the calculation formula (I) described in the first embodiment, the residual rate Z of the hole transport agent was calculated from the absorbance A1 of the measurement object before ultraviolet irradiation and the absorbance A2 of the measurement object after ultraviolet irradiation. Since the bisphenol Z-type polycarbonate resin is hardly decomposed by the irradiation of the predetermined ultraviolet light, the residual rate Z of the measurement object was regarded as the residual rate Z of the hole transport agent.

[0194] (Measurement conditions for ultraviolet-visible light absorption spectrum) Measurement wavelength range: Range from 320.00 nm to 600.00 nm Sampling interval: 1.00 nm Slit width: 1 nm Scanning speed: 300 nm / min

[0195] [Evaluation of single-layer photoreceptor] For each of the single-layer photoreceptors (A-1) to (A-8) and (B-1) to (B-6), the abrasion resistance, the suppression of overshoot, and the sensitivity characteristics were evaluated by the following method.

[0196] [Evaluation machine and evaluation paper] For the evaluation of the abrasion resistance and the suppression of overshoot of the single-layer photoreceptor, a modified machine of a color multifunction machine ("Taskalfa 356ci" manufactured by Kyocera Document Solutions Co., Ltd.) was used as the evaluation machine. This evaluation machine was equipped with a charging roller composed of an epichlorohydrin resin in which conductive carbon was dispersed. The charging polarity of the charging roller was positive, and the applied voltage of the charging roller was a DC voltage. This evaluation machine was of a two-component development system. This evaluation machine was equipped with a cleaning blade, a rubbing roller, and a charge removal device. For the evaluation of the abrasion resistance, copy paper ("Multi Paper Super Economy +" sold by Ascl Co., Ltd.) was used as the paper.

[0197] <Abrasion Resistance> The film thickness T1 of the photosensitive layer of the photoreceptor was measured. Next, the photoreceptor was mounted on an evaluation machine. Under normal temperature and humidity conditions of 23°C and 50% RH, image I (a pattern image with a print density of 1%) was printed on 10,000 sheets of paper using the evaluation machine. Next, under high temperature and high humidity conditions of 32°C and 85% RH, image I was printed on 10,000 sheets of paper using the evaluation machine. Next, under low temperature and low humidity conditions of 10°C and 15% RH, image I was printed on 10,000 sheets of paper using the evaluation machine. After that, the film thickness T2 of the photosensitive layer of the photoreceptor was measured. Then, the amount of abrasion (T1-T2, unit: μm), which is the change in the film thickness of the photosensitive layer before and after printing, was determined. The measured amounts of abrasion are shown in Table 1. The criteria for determining the abrasion resistance of the photoreceptor are shown below.

[0198] (Abrasion resistance standards) Good: The amount of wear is 0.5 μm or less. Defective: The amount of wear exceeds 0.5 μm.

[0199] <Suppressing overshoot> A photoreceptor was mounted in the evaluation machine. Under normal temperature and humidity conditions (23°C and 50% RH), a blank image was printed using the evaluation machine in paperless mode. The charge potential of the photoreceptor surface was measured from the start of printing (i.e., the first pass of the photoreceptor) to the tenth pass. The charge potential at the first pass of the photoreceptor was defined as V001 (unit: +V), and the charge potential at the tenth pass was defined as V010 (unit: +V). The overshoot potential Vos (unit: V) was calculated using the formula "Vos = |V001| - |V010|". |V001| and |V010| represent the absolute values ​​of V001 and V010, respectively. Since the charge polarity of the single-layer photoreceptor was set to positive polarity, both V001 and V010 were positive values. A positive value for Vos indicates that the absolute value of V001 is higher than the absolute value of V010. Furthermore, a larger positive value for Vos indicates a greater degree of increase in the charging potential (e.g., the charging potential V001 after the first cycle) and subsequent decrease in the charging potential (e.g., the charging potential V010 after the tenth cycle) when the photoreceptor begins to be charged by the charging device. The measured Vos values ​​are shown in Table 1. Note that all Vos values ​​in Table 1 are positive. The criteria for determining the suppression of overshoot in a single-layer photoreceptor are shown below.

[0200] (Criteria for suppressing overshoot) Good: Vos is between 0V and 20V. Failure: Vos is over 20V.

[0201] <Sensitivity Characteristics> The sensitivity characteristics of the photoreceptor were evaluated using a drum sensitivity tester (manufactured by Gentec) under conditions of 23°C and 50% RH relative humidity. The surface of the photoreceptor was charged to +550V using the drum sensitivity tester. Then, monochromatic light (wavelength: 780nm, exposure: 1.0 μJ / cm²) was used. 2 The monochromatic light was extracted from the halogen lamp using a bandpass filter and irradiated onto the surface of the photoreceptor. The surface potential of the photoreceptor was measured 50 milliseconds after the end of monochromatic light irradiation. The measured surface potential was defined as the post-exposure potential VL (unit: +V) of the photoreceptor. The measured VL values ​​are shown in Table 1. The criteria for determining the sensitivity characteristics of the photoreceptor are shown below.

[0202] (Sensitivity characteristic criteria) Good: The absolute value of VL is 140 V or less. Bad: The absolute value of VL exceeds 140 V.

[0203] [Table 1]

[0204] In Table 1, "Act" indicates an example, "Comp" indicates a comparative example, and "HTM" indicates a hole transport agent.

[0205] As shown in Table 1, the hole transport agents contained in the single-layer photosensitive layers of the single-layer photoreceptors (B-1) to (B-5) were not the predetermined hole transport agents. The single-layer photoreceptors (B-1) to (B-5) could not suppress the overshoot of the charging potential.

[0206] As shown in Table 1, the single-layer photoreceptor (B-6) did not have a protective layer. The single-layer photoreceptor (B-6) was inferior in abrasion resistance.

[0207] On the other hand, as shown in Table 1, the hole transport agents contained in the single-layer photosensitive layers of the single-layer photoreceptors (A-1) to (A-8) were the predetermined hole transport agents. The single-layer photoreceptors (A-1) to (A-8) had a protective layer. The single-layer photoreceptors (A-1) to (A-8) suppressed the overshoot of the charging potential and were excellent in abrasion resistance. Furthermore, the single-layer photoreceptors (A-1) to (A-8) were also excellent in sensitivity characteristics.

[0208] [Manufacture of multilayer photoreceptor] The multilayer photoreceptor (C-1) was manufactured by the following method. The configuration of this multilayer photoreceptor is shown in Table 2 described later.

[0209] [Manufacture of multilayer photoreceptor (C-1)] (Formation of intermediate layer) Two parts by mass of titanium dioxide, one part by mass of polyamide resin, ten parts by mass of methanol, one part by mass of butanol, and one part by mass of toluene were mixed using a bead mill for 5 hours to obtain mixture a. As titanium dioxide, prototype "SMT-A" manufactured by Teika Co., Ltd. (number average particle size 10 nm, titanium dioxide primary surface-treated with alumina and silica, and then secondary surface-treated with methylhydrogenpolysiloxane) was used. As polyamide resin, "Amiran® ​​CM8000" manufactured by Toray Industries, Inc. (a quaternary copolymer polyamide resin of polyamide 6, polyamide 12, polyamide 66, and polyamide 610) was used. The obtained mixture a was filtered using a 5 μm mesh filter to obtain an intermediate layer coating solution. Next, the intermediate layer coating solution was applied to the surface of a conductive substrate by dip coating. An aluminum drum-shaped support was used as the conductive substrate. Next, the applied intermediate layer coating solution was dried at 130°C for 30 minutes to form an intermediate layer (film thickness: 0.5 μm) on the conductive substrate.

[0210] (Formation of a charge generation layer) 1.5 parts by mass of Y-type titanyl phthalocyanine, 1.0 part by mass of polyvinyl acetal resin (Sekisui Chemical Co., Ltd.'s "Eslec BX-5") as a base resin, 40.0 parts by mass of propylene glycol monomethyl ether, and 40.0 parts by mass of tetrahydrofuran were mixed using a bead mill for 12 hours to obtain mixture d. The obtained mixture d was filtered using a 3 μm mesh filter to obtain a coating solution for the charge generation layer. Next, the coating solution for the charge generation layer was applied to the intermediate layer on a conductive substrate by dip coating. The applied coating solution for the charge generation layer was dried at 50°C for 5 minutes to form a charge generation layer (film thickness: 0.3 μm) on the intermediate layer.

[0211] (Formation of charge transport layer) 62.00 parts by mass of hole transporter (HTM-1), 100.00 parts by mass of bisphenol Z type polycarbonate resin, 0.05 parts by mass of 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 solution for the charge transport layer. As the bisphenol Z type polycarbonate resin, "Yupizeta PCZ-200" manufactured by Mitsubishi Gas Chemical Company, Inc. was used. Dimethyl silicone oil ("KF96-50CS" manufactured by Shin-Etsu Chemical Co., Ltd.) was used as the leveling agent. Next, the coating solution for the charge transport layer was applied to the charge generation layer by the dip-coating method. The applied coating solution for the charge transport layer was dried at 120°C for 40 minutes to form a charge transport layer (film thickness: 25 μm) on the intermediate layer.

[0212] (Formation of a protective layer) The protective layer of the stacked photoreceptor (C-1) was formed in the same manner as the protective layer of the single-layer photoreceptor (A-1), except that the protective coating solution was applied to the charge transport layer instead of the single-layer photoreceptor layer.

[0213] [Measurement of stacked photoreceptors] The hole transporter retention rate Z of the multilayer photoreceptor (C-1) was measured using the same method as for measuring the hole transporter retention rate Z of the single-layer photoreceptor. The measurement results are shown in Table 2.

[0214] [Evaluation of stacked photoreceptors] The wear resistance, overshoot suppression, and sensitivity characteristics of the stacked photoreceptor (C-1) were evaluated using the following method.

[0215] <Abrasion Resistance> The wear resistance of the multilayer photoreceptor was evaluated using the same method as for evaluating the wear resistance of a single-layer photoreceptor, except that a color printer (OKI DATA C711dn) was used as the evaluation machine. The charging polarity of the charging device in this evaluation machine was negative. The measured wear amounts are shown in Table 2.

[0216] <Suppressing overshoot> An evaluation apparatus that was used for evaluating the suppression of overshoot of a single-layer photoreceptor as an evaluation apparatus was modified to a negative charging polarity, and the suppression of overshoot of the multilayer photoreceptor was evaluated by the same method as the evaluation of the suppression of overshoot of the single-layer photoreceptor, except for this. The charging potential of the first circumference of the photoreceptor was taken as V001 (unit: -V), and the charging potential of the tenth circumference of the photoreceptor was taken as V010 (unit: -V). Since the charging polarity of the multilayer photoreceptor was modified to a negative polarity, both V001 and V010 were negative values. The measured Vos is shown in Table 2. Note that the Vos shown in Table 2 is a positive value.

[0217] <Sensitivity characteristics> The sensitivity characteristics of the multilayer photoreceptor were evaluated by the same method as the evaluation of the sensitivity characteristics of the single-layer photoreceptor, except that the surface of the photoreceptor was charged to -550V instead of +550V. The measured VL is shown in Table 2.

[0218]

Table 2

[0219] In Table 2, "Actual" and "HTM" are synonymous with the explanations of the terms in Table 1 above.

[0220] As shown in Table 1, the hole transport agent contained in the charge transport layer of the multilayer photoreceptor (C-1) was a predetermined hole transport agent. The multilayer photoreceptor (C-1) was provided with a protective layer. The overshoot of the charging potential of the multilayer photoreceptor (C-1) was suppressed, and it was excellent in abrasion resistance. Furthermore, the multilayer photoreceptor (C-1) was also excellent in sensitivity characteristics.

[0221] [[ID=二十六]]From the above, it was shown that the photoreceptors of the present invention including the single-layer photoreceptors (A-1) to (A-8) and the multilayer photoreceptor (C-1) suppress the overshoot of the charging potential and are excellent in abrasion resistance. In addition, since such a photoreceptor is provided, it is judged that the process cartridge and the image forming apparatus of the present invention suppress the overshoot of the charging potential of the photoreceptor and are excellent in the abrasion resistance of the photoreceptor.

Industrial applicability

[0222] 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

1. An electrophotographic photoreceptor comprising a conductive substrate, a photosensitive layer, and a protective layer, The protective layer is the outermost layer of the electrophotographic photoreceptor and contains a photocurable resin. The photosensitive layer contains a charge generating agent and a hole transporting agent, The hole transporter comprises a compound having a molecular weight of 580 or more and represented by formula (2), (3), or (4). An electrophotographic photoreceptor in which the residual rate of the hole transporter contained in the photosensitive layer after ultraviolet irradiation is 80% or more, and the residual rate after ultraviolet irradiation is calculated by formula (I). Z=100×(A2 / A1)...(I) (In the above formula (I), Z is the residual rate after UV irradiation, A1 is the absorbance at a wavelength of 365 nm of the object to be measured before irradiation with a predetermined ultraviolet light with a wavelength of 365 nm and an integrated light intensity of 34,200 mW·s. A2 is the absorbance at a wavelength of 365 nm of the object to be measured after irradiation with the predetermined ultraviolet light. The object of measurement is a sheet in which the hole transport agent is dispersed in bisphenol Z-type polycarbonate resin. 【Chemistry 1】 【Chemistry 2】 (In formula (2) above, R ５０ , R ５１ , and R ５４ Each independently represents an alkyl group having 1 to 8 carbon atoms, or a phenyl group, R ５２ , and R ５３ Each independently represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms, and f ３ , f ４ , and f ５ Each of these independently represents either 0 or 1. In the formula (3), R １１ , R １２ , R １３ , and R １４ each independently represent an alkyl group having 1 to 8 carbon atoms or a phenyl group, and a １ , a ２ , a ３ , and a ４ each independently represent an integer of 0 or more and 5 or less. In the above formula (4), R ２１ , R ２３ , R ２４ , and R ２６ Each of the following independently represents an alkenyl group having 2 to 6 carbon atoms, or an alkyl group having 1 to 8 carbon atoms, which may be substituted with at least one phenyl group; R22 and R25 represent alkenyl groups having 2 to 6 carbon atoms, which may be substituted with at least one phenyl group; b1, b2, b4, and b5 each independently represent an integer between 0 and 5; and b3 and b6 each independently represent an integer between 0 and 4.

2. An electrophotographic photoreceptor comprising a conductive substrate, a photosensitive layer, and a protective layer, The protective layer is the outermost layer of the electrophotographic photoreceptor and contains a photocurable resin. The photosensitive layer contains a charge generating agent and a hole transporting agent, The hole transporter comprises a compound having a molecular weight of 580 or more and represented by the formula (HTM-1), (HTM-2), (HTM-3), (HTM-4), (HTM-5), (HTM-6), (HTM-7), or (HTM-8), and is an electrophotographic photoreceptor. 【Transformation 3】 【Chemistry 4】 【Transformation 5】

3. An electrophotographic photoreceptor comprising a conductive substrate, a photosensitive layer, and a protective layer, The protective layer is the outermost layer of the electrophotographic photoreceptor and contains a photocurable resin. The photosensitive layer contains a charge generating agent and a hole transporting agent, The hole transporter comprises a compound having a molecular weight of 580 or more and represented by formula (1), (2), (3), or (4). The photocurable resin contained in the protective layer has repeating units derived from a compound having two or more vinyl groups, An electrophotographic photoreceptor in which the repeating unit derived from the compound having two or more vinyl groups is derived from at least one compound selected from the group consisting of compounds represented by formulas (EA-1) and (EA-2). 【Transformation 6】 【Transformation 7】 (In formula (1) above, R 41, R 42, R 43, R 44, R 45, and R 46 each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group; R 47 and R 48 each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group; e 1, e 2, e 3, and e 4 each independently represent an integer between 0 and 5; e 5 and e 6 each independently represent an integer between 0 and 4; In formula (2), R 50, R 51, and R 54 each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group; R 52 and R 53 each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms; and f 3, f 4, and f 5 each independently represent an integer between 0 and 5. In formula (3) above, R11, R12, R13, and R14 each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group, and a1, a2, a3, and a4 each independently represent an integer between 0 and 5. In formula (4), R21, R22, R23, R24, R25, and R26 each independently represent an alkenyl group having 2 to 6 carbon atoms, or an alkyl group having 1 to 8 carbon atoms, which may be substituted with at least one phenyl group; b1, b2, b4, and b5 each independently represent an integer between 0 and 5; and b3 and b6 each independently represent an integer between 0 and 4. 【Transformation 8】

4. An electrophotographic photoreceptor comprising a conductive substrate, a photosensitive layer, and a protective layer, The protective layer is the outermost layer of the electrophotographic photoreceptor and contains a photocurable resin. The photosensitive layer contains a charge generating agent and a hole transporting agent, The hole transporter comprises a compound having a molecular weight of 580 or more and represented by formula (1), (2), (3), or (4). The aforementioned photosensitive layer is a single layer, The aforementioned photosensitive layer further contains an electron transport agent, The electron transport agent comprises at least one of the compounds represented by formulas (11) and (16) in an electrophotographic photoreceptor. 【Chemistry 9】 【Chemistry 10】 (In formula (1) above, R 41, R 42, R 43, R 44, R 45, and R 46 each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group; R 47 and R 48 each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group; e 1, e 2, e 3, and e 4 each independently represent an integer between 0 and 5; e 5 and e 6 each independently represent an integer between 0 and 4; In formula (2), R 50, R 51, and R 54 each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group; R 52 and R 53 each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms; and f 3, f 4, and f 5 each independently represent an integer between 0 and 5. In formula (3) above, R11, R12, R13, and R14 each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group, and a1, a2, a3, and a4 each independently represent an integer between 0 and 5. In formula (4), R21, R22, R23, R24, R25, and R26 each independently represent an alkenyl group having 2 to 6 carbon atoms, or an alkyl group having 1 to 8 carbon atoms, which may be substituted with at least one phenyl group; b1, b2, b4, and b5 each independently represent an integer between 0 and 5; and b3 and b6 each independently represent an integer between 0 and 4. 【Chemistry 11】 (Q1 and Q2 in formula (11), and Q61 and Q62 in formula (16) each independently represent a hydrogen atom, a halogen atom, a cyano group, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 14 carbon atoms which may be substituted with at least one substituent selected from the group consisting of an alkyl group having 1 to 6 carbon atoms and a halogen atom.)

5. The electrophotographic photoreceptor according to claim 2, wherein the hole transporter contained in the photosensitive layer is a compound represented by formula (HTM-4), (HTM-5), (HTM-6), (HTM-7), or (HTM-8).

6. The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the thickness of the protective layer is 0.5 μm or more and 2.0 μm or less.

7. The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the charge generating agent contained in the photosensitive layer comprises titanylphthalocyanine.

8. The photosensitive layer includes a charge generation layer and a charge transport layer. The charge generating layer contains the charge generating agent, The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the charge transport layer contains the hole transport agent.

9. At least one selected from the group consisting of a charging device, an exposure device, a developing device, a transfer device, a cleaning member, a friction roller, and a static elimination device, A process cartridge comprising an electrophotographic photoreceptor according to any one of claims 1 to 4.

10. Image carrier and, A charging device for charging the surface of the image carrier, An exposure apparatus for exposing the surface of the charged image carrier to form an electrostatic latent image on the surface of the image carrier, A developing apparatus that supplies toner to the surface of the image carrier and develops the electrostatic latent image as a toner image, The system comprises a transfer device for transferring the toner image from the image carrier to the transfer target, An image forming apparatus wherein the image carrier is an electrophotographic photoreceptor according to any one of claims 1 to 4.

11. A cleaning member for collecting the toner adhering to the surface of the image carrier, A friction roller for rubbing the surface of the image carrier, and A static elimination device for removing static electricity from the surface of the image carrier. The image forming apparatus according to claim 10, further comprising at least one selected from the group consisting of the following.

12. The image forming apparatus according to claim 10, wherein the charging device is a charging roller.

13. The image forming apparatus according to claim 10, wherein the developing apparatus supplies the toner, which has been charged by friction with the carrier, to the surface of the image carrier.

Images