Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge, and image forming apparatus

Abstract

The present invention relates to an electrophotographic photoreceptor which has at least a photosensitive layer and a protective layer on a conductive support. As a novel electrophotographic photoreceptor with which it is possible to improve the electrical characteristics, especially residual potential and potential retention rate of the photoreceptor, the present invention proposes an electrophotographic photoreceptor which has at least a photosensitive layer and a protective layer on a conductive support, wherein: the protective layer contains a hole transporting compound and an electron accepting compound; and the electron accepting compound is a compound that contains a boron atom.

Description

Electrophotographic photoreceptor, electrophotographic photoreceptor cartridge and image forming apparatus

[0001] The present invention relates to an electrophotographic photoreceptor used in a copying machine, a printer, etc., and an electrophotographic photoreceptor cartridge and an image forming apparatus using the same.

[0002] In printers and copiers, when a charged organic photoconductor (OPC) drum is irradiated with light, the part is discharged, an electrostatic latent image is formed, and an image is obtained by attaching toner to the electrostatic latent image. In such devices that use electrophotography, the photoconductor is a key component.

[0003] Because this type of organic photoreceptor offers a wide range of material options and allows for easy control of photoreceptor properties, "function-separated photoreceptors," in which the functions of charge generation and transport are shared by separate compounds, have become mainstream. For example, known electrophotographic photoreceptors include a single-layer electrophotographic photoreceptor (hereinafter referred to as a single-layer photoreceptor) that contains a charge generation material (CGM) and a charge transport material (CTM) in the same layer, and a multi-layer electrophotographic photoreceptor (hereinafter referred to as a multi-layer photoreceptor) that comprises a charge generation layer containing a charge generation material (CGM) and a charge transport layer containing a charge transport material (CTM). Furthermore, photoreceptor charging methods include a negative charging method, in which the photoreceptor surface is negatively charged, and a positive charging method, in which the photoreceptor surface is positively charged. Currently available photoreceptor layer configuration and charging method combinations include a "negatively charged multi-layer photoreceptor" and a "positively charged single-layer photoreceptor."

[0004] A "negatively charged laminated photoreceptor" generally has a structure in which an undercoat layer (UCL) made of a resin or the like is provided on a conductive substrate such as an aluminum tube, on which a charge generation layer (CGL) made of a charge generation material (CGM) and a resin or the like is provided, and on which a charge transport layer (CTL) made of a hole transport material (HTM) and a resin or the like is provided.

[0005] On the other hand, a "positively charged single-layer photoreceptor" generally has a configuration in which an undercoat layer (UCL) made of a resin or the like is provided on a conductive substrate such as an aluminum tube, and a single-layer photosensitive layer made of a charge generating material (CGM), a hole transporting material (HTM), an electron transporting material (ETM), and a resin or the like is provided thereon (see, for example, Patent Document 1).

[0006] In either case, the surface of the photoreceptor is first charged using corona discharge or contact, and then the photoreceptor is exposed to light to neutralize the surface charge, forming an electrostatic latent image due to the potential difference with the surrounding surface. Toner is then brought into contact with the photoreceptor surface to form a toner image corresponding to the electrostatic latent image, which is then transferred to paper or other media and heated to fuse and fix to create a print.

[0007] As described above, the basic structure of an electrophotographic photoreceptor is a photosensitive layer formed on a conductive support, but a protective layer may also be provided on the photosensitive layer for the purpose of improving abrasion resistance, etc.

[0008] As a technique for improving the mechanical strength or abrasion resistance of the surface of a photoreceptor, a photoreceptor has been disclosed in which a layer containing a compound having a polymerizable functional group as a binder resin is formed on the outermost surface of the photoreceptor, and this layer is polymerized by applying energy such as heat, light, or radiation to form a cured resin layer (see, for example, Patent Documents 1 and 2).

[0009] U.S. Patent No. 9,417,538 WO 2010 / 035683 (Patent No. 5,263,296)

[0010] As described above, it has not been easy to improve the electrical properties, particularly the residual potential and potential retention, of an electrophotographic photoreceptor having a photosensitive layer and a protective layer formed on a conductive support. To improve the electrical properties of the photoreceptor, it is necessary for charges (holes or electrons) to move smoothly through each layer of the photoreceptor, and for charges to be smoothly injected between adjacent layers. To this end, attempts have been made to incorporate compounds having a hole transport structure or an electron transport structure into each layer of the photoreceptor, but it has not been easy to improve the electrical properties.

[0011] Therefore, an object of the present invention is to provide a novel electrophotographic photoreceptor that can improve the electrical properties of the photoreceptor, particularly the residual potential and potential retention rate, with respect to an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support.

[0012] In order to solve the above problems, the present inventors propose an electrophotographic photosensitive member, an electrophotographic photosensitive member cartridge, and an image forming apparatus according to the following embodiments.

[0013] [1] A first embodiment of the present invention is an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, the protective layer containing a hole transporting compound and an electron accepting compound, and the electron accepting compound is a compound containing a boron atom.

[0014] [2] A second embodiment of the present invention is the electrophotographic photoreceptor of the first embodiment, wherein the electron accepting compound is a compound represented by the following formula (1) or (2):

[0015]

[0016]

[0017] In the formula (1) or (2), R 11 ~R 13 and R 21 ~R 24 Each of o, p, q, r, s, t, and u independently represents a hydrogen atom, a deuterium atom, a halogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. Each of o, p, q, r, s, t, and u represents an integer of 1 or more and 5 or less. １ , Ph ２ , Ph ３ , Ph ４ are symbols that refer to each benzene ring.

[0018] [3] A third embodiment of the present invention is the electrophotographic photoreceptor according to the first or second embodiment, wherein the hole transporting compound is any one of compounds represented by the following formulas (3) to (5):

[0019]

[0020]

[0021]

[0022] In the formulas (3) to (5), Ar 1 ~Ar 7 , Ar 9 ~Ar 11 each independently represents an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a heteroaryloxy group which may have a substituent, an alkoxycarbonyl group which may have a substituent, a dialkylamino group which may have a substituent, a diarylamino group which may have a substituent, an arylalkylamino group which may have a substituent, an acyl group which may have a substituent, a haloalkyl group which may have a substituent, an alkylthio group which may have a substituent, an arylthio group which may have a substituent, a silyl group which may have a substituent, a siloxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. 8 represents an aromatic hydrocarbon group which may have a substituent or an aromatic heterocyclic group which may have a substituent, and m and n each represent an integer of 1 or more.

[0023] [4] A fourth embodiment of the present invention is the electrophotographic photoreceptor of any one of the first to third embodiments, wherein the hole transporting compound has at least one polymerizable functional group in one molecule.

[0024] [5] A fifth embodiment of the present invention is the electrophotographic photoreceptor of the fourth embodiment, wherein the polymerizable functional group is selected from the following formulae (M1) to (M7):

[0025]

[0026] In the formulae (M1) to (M7), R 110 represents a hydrogen atom or an alkyl group which may have a substituent, and * represents the bonding position.

[0027] [6] A sixth embodiment of the present invention is the electrophotographic photoreceptor according to any one of the first to fifth embodiments, wherein the protective layer has a content mass ratio of the electron accepting compound to the hole transporting compound of 0.001 or more and 1.0 or less.

[0028] [7] A seventh embodiment of the present invention is the electrophotographic photoreceptor according to any one of the first to sixth embodiments, wherein the hole transporting compound and the electron accepting compound in the protective layer satisfy the following formula (I): 0<LUMO dop -HOMO HTM　 ≦ 2.0 (I) (In formula (I), LUMO dop represents the LUMO level (eV) of the electron-accepting compound, and HOMO HTM represents the HOMO level (eV) of the hole transporting compound.

[0029] [8] An eighth embodiment of the present invention is the electrophotographic photoreceptor of the seventh embodiment, further satisfying the following formula (II): |HOMO dop -HOMO HTM　 |≦2.5(II) (in formula (II), HOMO dop represents the HOMO level (eV) of the electron-accepting compound.

[0030] [9] A ninth embodiment of the present invention is the seventh or eighth embodiment, wherein the LUMO dop

[10] A tenth embodiment of the present invention is an electrophotographic photoreceptor according to any one of the seventh to ninth embodiments, wherein the HOMO HTM

[11] The eleventh embodiment of the present invention is an electrophotographic photoreceptor according to the eighth or ninth embodiment, wherein the HOMO dop 8. The electrophotographic photoreceptor according to claim 7, wherein the potential is −7.2 eV or more and −5.5 eV or less.

[0031]

[12] A twelfth embodiment of the present invention is the electrophotographic photoreceptor according to any one of the first to eleventh embodiments, wherein the photosensitive layer contains an arylamine compound.

[0032]

[13] A thirteenth embodiment of the present invention is the electrophotographic photoreceptor of the twelfth embodiment, wherein the arylamine compound contains a compound represented by the following formula (200) or (201):

[0033]

[0034] In the formula (200) or (201), Ar HTM may be the same or different as long as they are groups selected from the following formulae (200-1) to (200-3).

[0035]

[0036] In the formulas (200), (201), and (200-1) to (200-3), each R independently represents a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, an aromatic heterocyclic group which may have a substituent, or a halogen atom. h1 represents an integer of 0 to 5, and h4 represents an integer of 0 to 2. * represents a bonding position.

[0037]

[14] A fourteenth embodiment of the present invention is the electrophotographic photoreceptor of any one of the first to thirteenth embodiments, wherein the photosensitive layer is a laminated photosensitive layer including a charge generating layer and a charge transport layer, and the charge transport layer contains an arylamine compound.

[0038]

[15] A fifteenth embodiment of the present invention is the electrophotographic photoreceptor of any one of the twelfth to fourteenth embodiments, wherein a content mass ratio of the electron accepting compound to the arylamine compound is 0.001 or more and 0.9 or less.

[0039]

[16] A sixteenth embodiment of the present invention is the electrophotographic photoreceptor of any one of the first to fifteenth embodiments, wherein the protective layer further contains a cured product of a curable compound that does not have a hole transport skeleton.

[0040]

[17] A seventeenth embodiment of the present invention is the electrophotographic photoreceptor according to any one of the first to sixteenth embodiments, wherein the electrophotographic photoreceptor contains 0.001% by mass or more of boron atoms relative to the total mass of all layers (excluding the conductive support) of the electrophotographic photoreceptor.

[0041]

[18] An eighteenth embodiment of the present invention is an electrophotographic photosensitive member cartridge having the electrophotographic photosensitive member of any one of the first to seventeenth embodiments.

[19] A nineteenth embodiment of the present invention is an image forming apparatus having the electrophotographic photosensitive member of any one of the first to seventeenth embodiments.

[0042] The electrophotographic photoreceptor proposed by the present invention is an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, and the protective layer contains a hole transporting compound and a compound containing a boron atom as an electron accepting compound, thereby making it possible to improve the electrical properties of the electrophotographic photoreceptor, in particular the residual potential and potential retention rate.

[0043] 1 is a diagram schematically illustrating an example of the configuration of an image forming apparatus that can be configured using an electrophotographic photosensitive member according to an example of the present invention.

[0044] The following describes in detail the mode for carrying out the present invention (hereinafter referred to as "embodiments of the invention"). Note that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention.

[0045] <<Present Electrophotographic Photoreceptor>> An electrophotographic photoreceptor according to one embodiment of the present invention (also referred to as “present electrophotographic photoreceptor”) is an electrophotographic photoreceptor including at least a photosensitive layer (also referred to as “present photosensitive layer”) and a protective layer (also referred to as “present protective layer”) on a conductive support, and the protective layer contains a hole transporting compound and an electron accepting compound.

[0046] The present electrophotographic photoreceptor may optionally have layers other than the present photosensitive layer and the present protective layer. The charging method of the present electrophotographic photoreceptor may be either a negative charging method in which the photoreceptor surface is negatively charged, or a positive charging method in which the photoreceptor surface is positively charged. Of these, the positive charging method is preferred, since it is considered that the effects of the present invention can be more effectively achieved with the positive charging method, which requires the protective layer to have electron transport properties.

[0047] In the present electrophotographic photoreceptor, the side opposite to the conductive support is the upper side or front side, and the conductive support side is the lower side or back side.

[0048] <Protective Layer> From the viewpoint of obtaining the effects of the present invention more effectively, the protective layer is preferably the outermost layer, that is, the outermost layer located on the opposite side from the conductive support. However, the effects of the present invention can be obtained even if the protective layer is not necessarily the outermost layer. For example, in cases where some kind of segregation layer exists on the outermost layer of the photoreceptor, the effects can be obtained even if the protective layer is not the outermost layer.

[0049] (Electron-Accepting Compound) The protective layer preferably contains an electron-accepting compound. By including an electron-accepting compound in the protective layer, the electron-accepting property of the protective layer can be enhanced by the electron-accepting compound, which is presumed to further improve the electrical properties of the electrophotographic photoreceptor, particularly the residual potential and potential holding ratio. This is presumably because the protective layer contains an electron-accepting compound, which reduces the Schottky barrier between adjacent layers and reduces the charge, particularly hole, injection barrier between layers, resulting in improved electrical properties, particularly the residual potential and potential holding ratio.

[0050] The "electron-accepting compound" in the present invention may be any compound capable of accepting electrons into the protective layer. In other words, the "electron-accepting compound" may be any compound capable of reducing the energy barrier during hole transfer in a target compound (hole-transporting compound) in the protective layer by any mechanism, thereby injecting holes into the target compound. The mechanism may be, for example, a mechanism in which holes are transferred directly from the electron-accepting compound to the target compound, a mechanism in which holes are transferred by forming a hydrogen bond between the electron-accepting compound and the target compound, or a mechanism in which the energy barrier during hole transfer is reduced by forming a hydrogen bond between the electron-accepting compound and the target compound, thereby injecting holes transferred from the photosensitive layer into the target compound present in the protective layer.

[0051] (Boron Atom-Containing Compound) The electron-accepting compound is preferably a compound containing a boron atom. From the viewpoint of electron-accepting property, the number of boron atoms in the electron-accepting compound is preferably 1 or more, and is preferably 3 or less, and more preferably 2 or less.

[0052] It is believed that if the protective layer contains a compound containing a boron atom, the compound containing a boron atom functions as an electron-accepting compound, and the boron-containing compound can enhance the electron-accepting properties of the protective layer, thereby further improving the electrical properties of the electrophotographic photoreceptor, particularly the residual potential and potential retention. Regarding this effect, it is believed that the inclusion of a compound containing a boron atom in the protective layer reduces the Schottky barrier between the protective layer and the photosensitive layer, thereby reducing the barrier for charge injection between the layers, particularly for holes, resulting in further improved electrical properties.

[0053] Examples of compounds containing boron atoms include triarylborate compounds, tetraarylborate compounds, etc. Among these, tetraarylborate compounds are preferred from the viewpoints of stability and electron accepting ability.

[0054] The electron-accepting compound is preferably a compound represented by the following formula (1) or (2), and more preferably a compound represented by the following formula (2). The compounds represented by the following formulas (1) and (2) have a structure in which benzene rings are bonded to a boron atom at the center, and since the boron atom has electron-accepting properties, the inclusion of a boron atom is thought to facilitate smooth charge transfer (electron transfer) in the electrophotographic photoreceptor, resulting in good electrical properties. In particular, the compound represented by the following formula (2) is an ionic compound, and therefore, since boron serves as an anion and four benzene rings are bonded, it is thought that electron-accepting properties and stability can be improved.

[0055]

[0056]

[0057] In the above formula (1) or (2), R 11 ~R 13 and R 21 ~R 24 each independently represents a hydrogen atom, a deuterium atom, a halogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. In particular, if an electron-accepting group is bonded to the benzene ring bonded to the boron atom, the transfer of charge (transfer of electrons) becomes even smoother. From this perspective, R 11 ~R 13 and R 21 ~R 24 are each independently preferably a halogen atom or an alkyl group which may have a substituent, more preferably a halogen atom, and even more preferably a fluorine atom. 11 ~R 13 and R 21 ~R 24 is enclosed in parentheses. This means that R 11 ~R 13 and R 21 ~R 24 means that it may or may not exist.

[0058] Also, R 11 ~R 13 and R 21 ~R 24 When R is an alkyl group which may have a substituent or an alkoxy group which may have a substituent, the number of carbon atoms in each group is preferably 1 or more, more preferably 2 or more, from the viewpoint of solubility, and is preferably 8 or less, more preferably 6 or less. 11 ~R 13 and R 21 ~R 24 When represents an aromatic hydrocarbon group which may have a substituent or an aromatic heterocyclic group which may have a substituent, from the viewpoint of stability, the number of carbon atoms in each is preferably 5 or more, more preferably 6 or more, and on the other hand, is preferably 10 or less, more preferably 8 or less.

[0059] In the present invention, the phrase "may have a substituent" means that the group can have a substituent, and includes both the case where the group has a substituent and the case where the group does not have a substituent. 11 ~R 13 and R 21 ~R 24 When has a substituent, examples of the substituent include a halogen atom, an alkyl group, an alkoxy group, etc. Among these, from the viewpoint of electron accepting property, a halogen atom is preferred, and a fluorine atom is more preferred.

[0060] In the above formula (1) or (2), o, p, q, r, s, t, and u each represent an integer of 1 or more and 5 or less. From the viewpoint of electron-accepting property, o, p, q, r, s, t, and u are preferably 2 or more, more preferably 3 or more, and are preferably 5 or less. １ , Ph ２ , Ph ３ , Ph ４ are symbols indicating the respective benzene rings. When o, p, q, r, s, t, and u are integers of 2 or more, there are two or more R 11 ~R 13 and R 21 ~R 24 may be the same or different.

[0061] Specific examples of the electron-accepting compound are shown below, but the invention is not limited to these.

[0062]

[0063]

[0064]

[0065] From the viewpoint of hole transportability, the content of the electron-accepting compound in the protective layer is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1 part by mass or more, relative to 100 parts by mass of the total mass of the protective layer. On the other hand, from the viewpoint of stability, the content is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 15 parts by mass or less, relative to 100 parts by mass of the total mass of the protective layer. The total mass of the protective layer means the total mass of the protective layer after curing, which is equal to the total mass of the solid content in the coating solution for forming the protective layer.

[0066] From the viewpoint of electrical properties, the content of the electron-accepting compound in the electrophotographic photoreceptor is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, relative to 100 parts by mass of the total mass of all layers of the electrophotographic photoreceptor, and on the other hand, from the viewpoint of electrical properties, it is preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the total mass of all layers of the electrophotographic photoreceptor.

[0067] (Boron Atoms) From the viewpoint of electron acceptance, the protective layer preferably contains 0.01% by mass or more of boron atoms relative to the mass (100% by mass) of the protective layer. When the protective layer contains 0.01% by mass or more of boron atoms, the hole injection characteristics from adjacent layers into the protective layer are improved, resulting in improved electrical properties, particularly residual potential and potential retention. From this viewpoint, the protective layer preferably contains 0.01% by mass or more of boron atoms relative to the mass (100% by mass) of the protective layer, more preferably 0.05% by mass or more, even more preferably 0.10% by mass or more, and even more preferably 0.15% by mass or more. On the other hand, from the viewpoint of stability, the upper limit is preferably 10% by mass or less, even more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0068] A preferred example of the protective layer containing a predetermined amount of boron atoms is one in which the protective layer contains an electron-accepting compound containing boron as described above.

[0069] The presence of a predetermined amount of boron atoms in the protective layer can be confirmed by elemental analysis. For example, the mass ratio of each compound contained in the protective layer is determined by quantitative analysis of the protective layer, and the content (mass %) of the electron-accepting compound in the protective layer is determined. The method for preparing a sample for quantitative analysis of the protective layer is not particularly limited, and examples include dissolving the protective layer in any organic solvent. This content refers to the content (mass %) of the electron-accepting compound when the total mass of all compounds contained in the protective layer is taken as 100. The content is then multiplied by the atomic weight of the boron atom / the molecular weight of the electron-accepting compound to determine the content (mass %) of boron atoms in the protective layer.

[0070] Furthermore, the present electrophotographic photoreceptor preferably contains 0.001% by mass or more of boron atoms relative to the total mass (100% by mass) of all layers (excluding the conductive support) of the present electrophotographic photoreceptor. When the present electrophotographic photoreceptor contains 0.001% by mass or more of boron atoms, the charge injection barrier between layers is reduced, resulting in improved electrical properties, particularly residual potential and potential retention. From this perspective, the present electrophotographic photoreceptor preferably contains 0.001% by mass or more of boron atoms relative to the total mass (100% by mass) of all layers of the present electrophotographic photoreceptor, more preferably 0.005% by mass or more, even more preferably 0.010% by mass or more, and even more preferably 0.015% by mass or more. On the other hand, from the viewpoint of stability, the upper limit is preferably 5% by mass or less, even more preferably 3% by mass or less, and even more preferably 1% by mass or less. The above-mentioned "total mass of all layers (excluding the conductive support) of the electrophotographic photoreceptor" means, for example, the total mass of the undercoat layer, charge generation layer, charge transport layer, and protective layer when the electrophotographic photoreceptor has an undercoat layer, charge generation layer, charge transport layer, and protective layer on a conductive support. On the other hand, the "mass of the electrophotographic photoreceptor" means the total mass of the conductive support, undercoat layer, charge generation layer, charge transport layer, and protective layer.

[0071] To determine the mass content of boron atoms in all layers (excluding the conductive support) of the electrophotographic photoreceptor, for example, the mass ratio of each compound contained in each layer is determined by quantitative analysis, and the content (mass%) of the electron-accepting compound in each layer is determined. The method for preparing samples for quantitative analysis of each layer is not particularly limited, and examples include dissolving each layer in an organic solvent. This content refers to the content (mass%) of the electron-accepting compound when the total mass of all compounds contained in each layer is taken as 100. Next, the content (mass%) of boron atoms in each layer is determined by multiplying this content by the atomic weight of the boron atom / the molecular weight of the electron-accepting compound. Furthermore, the mass content of boron atoms in each layer is determined by multiplying the thickness of each layer by the total thickness, and the sum of these values ​​is determined as the mass content of boron atoms in all layers (excluding the conductive support) of the electrophotographic photoreceptor.

[0072] (Hole Transport Compound) The protective layer preferably further contains a hole transport compound. In the present invention, the term "hole transport compound" refers to a compound having hole transport properties, in other words, a compound having a hole transport skeleton. The presence of the hole transport compound in the protective layer activates the hole transport performance, further enhancing the hole transport performance of the protective layer, and improving the electrical properties of the electrophotographic photoreceptor, particularly the residual potential and potential holding ratio. Furthermore, the presence of the hole transport compound in the protective layer together with the electron accepting compound can further improve the electrical properties of the electrophotographic photoreceptor, particularly the residual potential and potential holding ratio.

[0073] Examples of the hole transport compound used in the protective layer include carbazole compounds, dibenzofuran compounds, arylamine compounds, naphthalene compounds, phenanthrene compounds, pyrene compounds, etc. Among these, carbazole compounds, arylamine compounds, and naphthalene compounds are preferred, arylamine compounds are more preferred, and any of the compounds represented by the following formulas (3) to (5) is even more preferred.

[0074] The compounds represented by the following formulas (3) to (5) all have an arylamine structure and are structurally characterized by a shallow HOMO level and high hole transportability. Therefore, when electrons are extracted from the arylamine structure by the electron-accepting compound, the compound becomes a doped cationic salt, which is thought to have good electrical properties. Among these, the compounds represented by formulas (4) and (5) are more preferred, and the compound represented by formula (5) is even more preferred, from the viewpoints of having a shallower HOMO level and high hole transportability than the compound represented by formula (3).

[0075]

[0076]

[0077]

[0078] In the above formulas (3) to (5), Ar 1 ~Ar 7 , Ar 9 ~Ar11 Ar each independently represent an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a heteroaryloxy group which may have a substituent, an alkoxycarbonyl group which may have a substituent, a dialkylamino group which may have a substituent, a diarylamino group which may have a substituent, an arylalkylamino group which may have a substituent, an acyl group which may have a haloalkyl group, an alkylthio group which may have a substituent, an arylthio group which may have a substituent, a silyl group which may have a substituent, a siloxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. Among them, from the viewpoint of hole transport properties, an alkenyl group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent is preferred, and an aromatic hydrocarbon group which may have a substituent is more preferred. 8 represents an aromatic hydrocarbon group which may have a substituent or an aromatic heterocyclic group which may have a substituent. Among them, from the viewpoint of hole transportability, an aromatic heterocyclic group which may have a substituent is preferred. m and n represent integers of 1 or more. From the viewpoint of hole transportability, m is preferably 2 or more, more preferably 3 or more, and on the other hand, it is preferably 6 or less, more preferably 5 or less. From the viewpoint of hole transportability, n is preferably 2 or more, more preferably 3 or more, and on the other hand, it is preferably 6 or less, more preferably 5 or less. When m and n are integers of 2 or more, two or more Ar ８ ~Ar 10 may be the same or different.

[0079] The hole transport compound preferably has at least one polymerizable functional group per molecule. The hole transport compound having a polymerizable functional group can crosslink with other hole transport compounds or with a curable compound that does not have a hole transport structure, thereby further improving the mechanical strength of the protective layer. From the viewpoint of film hardness, the number of polymerizable functional groups per molecule is preferably 2 or more, more preferably 3 or more, and is preferably 8 or less, more preferably 6 or less.

[0080] When the hole transporting compound is a compound represented by any one of the formulas (3) to (5) and has a polymerizable functional group in one molecule, Ar 1 ~Ar 7 , Ar 9 ~Ar 11 or Ar 8 It is preferable that Ar has a substituent, and the substituent contains a polymerizable functional group. 1 ~Ar 7 , Ar 9 ~Ar 11 or Ar 8 The substituents which the group has are preferably groups represented by the following formulae (N1) to (N6), more preferably groups represented by formulae (N1), (N3) and (N5), and even more preferably groups represented by formula (N1).

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087] In formulas (N1) to (N6), R 110 represents a hydrogen atom or an alkyl group which may have a substituent, R １１１ represents an alkyl group which may have a substituent, and * represents the bonding position.

[0088] Specific examples of the hole transporting compound are shown below, but the compound is not limited to these.

[0089]

[0090] Among the above compounds, from the viewpoint of electrical properties, the compounds represented by formula (4-1), formula (4-2), formula (4-3), formula (4-4), formula (4-6), and formula (4-7) are preferred, the compounds represented by formula (4-1), formula (4-2), and formula (4-3) are more preferred, the compounds represented by formula (4-2) and formula (4-3) are even more preferred, and the compound represented by formula (4-2) is particularly preferred.

[0091] The polymerizable functional group can be selected from the following formulae (M1) to (M7). Among them, from the viewpoints of stability and solubility, formulae (M1) and (M2) are preferred, and formula (M1) is more preferred.

[0092]

[0093] In formulas (M1) to (M7), R 110 represents a hydrogen atom or an alkyl group which may have a substituent, and * represents the bonding position.

[0094] (Relationship Between Electron Accepting Compound and Hole Transporting Compound) The hole transporting compound and the electron accepting compound in the protective layer preferably satisfy the following formula (I).

[0095] 0<LUMO dop -HOMO HTM　 ≦2.0 (I)

[0096] In formula (I), LUMO dop represents the LUMO energy level (also referred to as the "LUMO level") of the electron-accepting compound (eV), and HTM　 represents the HOMO energy level (eV) of the hole transporting compound (also referred to as "HOMO level").

[0097] The LUMO level of the electron-accepting compound indicates the lowest energy light absorption, and the energy corresponds to the energy band gap (the difference between the HOMO level and the LUMO level). dop - HOMO HTM　 " indicates a charge transfer barrier from the hole transporting compound to the electron accepting compound. When formula (I) is satisfied, charge transport from the HOMO (highest occupied molecular orbital) of the hole transporting compound to the LUMO (lowest unoccupied molecular orbital) of the electron accepting compound is promoted, resulting in good hole transport properties. From this perspective, "LUMO dop -HOMO HTM　 is preferably 2.0 eV or less, more preferably 1.7 eV or less, and even more preferably 1.2 eV or less. On the other hand, from the viewpoint of charge transfer from the hole transporting compound to the electron accepting compound, it is preferably greater than 0 eV, more preferably 0.1 eV or more, and even more preferably 0.15 eV or more.

[0098] It is more preferable that the protective layer further contains a hole transporting compound and an electron accepting compound satisfying the following formula (II):

[0099] | HOMO dop -HOMO HTM　 |≦2.5 (II)

[0100] In formula (II), HOMO dop represents the HOMO level (eV) of the electron-accepting compound.

[0101] |HOMO of formula (II) dop -HOMO HTM　 | represents the depth of the HOMO level in the doped state after charge transfer from the hole transporting compound to the electron accepting compound. When formula (II) is satisfied, the HOMO of the hole transporting compound after doping with the electron accepting compound does not become too deep, improving hole injection from the photosensitive layer to the protective layer and further improving electrical properties. From this viewpoint, |HOMO dop -HOMO HTM　 is preferably 2.5 eV or less, more preferably 1.5 eV or less, and even more preferably 1.0 eV or less.

[0102] The LUMO in the above formula (I) and formula (II) dop In other words, from the viewpoint of stability, the LUMO energy level of the electron-accepting compound is preferably −4.7 eV or higher, more preferably −4.4 eV or higher, even more preferably −4.1 eV or higher, and even more preferably −3.7 eV or higher. From the viewpoint of doping efficiency, the LUMO energy level is preferably −3.0 eV or lower, even more preferably −3.2 eV or lower, even more preferably −3.4 eV or lower, and even more preferably −3.6 eV or lower.

[0103] The HOMO in the above formula (I) and formula (II) HTM　 In other words, from the viewpoint of hole transportability, the energy level of the HOMO of the hole transport compound is preferably −5.5 eV or more, more preferably −5.3 eV or more, even more preferably −5.1 eV or more, and even more preferably −4.9 eV or more. From the viewpoint of stability in the atmosphere, the energy level is preferably −4.0 eV or less, even more preferably −4.2 eV or less, even more preferably −4.4 eV or less, and even more preferably −4.6 eV or less.

[0104] In addition, the HOMO in the above formula (I) and formula (II) dop In other words, the HOMO level of the electron-accepting compound is preferably −7.2 eV or higher, more preferably −6.5 eV or higher, even more preferably −5.8 eV or higher, and even more preferably −5.7 eV or higher, from the viewpoint of doping efficiency. From the viewpoint of stability, the HOMO level is preferably −5.5 eV or lower, even more preferably −5.6 eV or lower.

[0105] In the present invention, the HOMO energy level (E_homo) and the LUMO energy level (E_lumo) can be obtained by finding a stable structure through a structural optimization calculation using B3LYP (see A.D. Becke, J. Chem. Phys. 98, 5648 (1993); C. Lee, et al., Phys. Rev. B37, 785 (1988); and B. Miehlich, et al., Chem. Phys. Lett. 157, 200 (1989)), which is a type of density half-function method.

[0106] In this case, the basis set used was 6-31G(d,p), which is a polarization function added to 6-31G (R. Ditchfield, et al., J. Chem. Phys. 54, 724 (1971), W. J. Hehre, et al., J. Chem. Phys. 56, 2257 (1972), P. C. Ariharan et al., Mol. Phys. 27, 209 (1974), M. S. Gordon, Chem. Phys. Lett. 76, 163 (1980), P. C. Ariharan (See, e.g., J.-P. Blaudeau, et. al., J. Chem. Phys. 107, 5016 (1997), M. M. Francl, et. al., J. Chem. Phys. 77, 3654 (1982), R. C. Binning Jr. et. al., J. Comp. Chem. 11, 1206 (1990), V. A. R. V. Arsolov, et. al., J. Chem. Phys. 109, 1223 (1998), and V. A. R. V. Arsolov, et. al., J. Comp. Chem. 22, 976 (2001).) In the present invention, the B3LYP calculation using 6-31G(d,p) is referred to as B3LYP / 6-31G(d,p). In the present invention, the program used for the B3LYP / 6-31G(d,p) calculation is the software "Spartan'18 Parallel Suite" (Wavefunction, Inc.).

[0107] In the protective layer, the ratio of the mass content of the electron-accepting compound to the mass content of the hole-transporting compound (electron-accepting compound / hole-transporting compound) is preferably 0.001 or more and 1.0 or less. A mass ratio of 0.001 or more (electron-accepting compound / hole-transporting compound) is preferable because hole transportability can be improved. On the other hand, a mass ratio of 1.0 or less is preferable because hole transportability is not inhibited. From this viewpoint, the mass ratio (electron-accepting compound / hole-transporting compound) is preferably 0.001 or more, more preferably 0.005 or more, even more preferably 0.01 or more, and even more preferably 0.05 or more. On the other hand, it is preferably 1.0 or less, even more preferably 0.8 or less, even more preferably 0.6 or less, and even more preferably 0.4 or less.

[0108] In the present electrophotographic photoreceptor, the ratio of the mass content of the electron-accepting compound to the mass content of the hole-transporting compound (electron-accepting compound / hole-transporting compound) is preferably 0.0001 or more and 1.0 or less. A mass ratio of 0.0001 or more (electron-accepting compound / hole-transporting compound) is preferable because hole transportability can be improved. On the other hand, a mass ratio of 1.0 or less is preferable because hole transportability is not impaired. From this viewpoint, the mass ratio (electron-accepting compound / hole-transporting compound) is preferably 0.0001 or more, more preferably 0.0005 or more, even more preferably 0.001 or more, and even more preferably 0.005 or more. On the other hand, it is preferably 0.1 or less, even more preferably 0.08 or less, even more preferably 0.06 or less, and even more preferably 0.04 or less.

[0109] (Curable Compound Not Having a Hole-Transporting Skeleton) The protective layer preferably further contains a cured product obtained by curing a curable compound, particularly a cured product of a curable compound not having a hole-transporting skeleton. When the protective layer further contains a cured product of a curable compound not having a hole-transporting skeleton, the hardness of the film can be improved. The term "not having a hole-transporting skeleton" means that the structure does not contain a group containing a carbazole skeleton, a dibenzofuran structure, an arylamine structure, a naphthalene structure, a phenanthrene structure, a pyrene structure, or a structure exemplified as a hole-transporting substance described below.

[0110] The curable compound may be a compound having a polymerizable functional group and no hole transport skeleton. Among these, a monomer, oligomer, or polymer having a radical polymerizable functional group is preferred. Among these, a curable compound having crosslinkability, particularly a photocurable compound, is preferred. For example, a curable compound having two or more radical polymerizable functional groups can be mentioned. A compound having one radical polymerizable functional group can also be used in combination. Examples of the radical polymerizable functional group include either an acryloyl group (including an acryloyloxy group) or a methacryloyl group (including a methacryloyloxy group), or both of these groups. Furthermore, from the viewpoint of film hardness, it is preferable that the curable compound does not have a hole transport skeleton.

[0111] Examples of the curable compound having a radical polymerizable functional group include monomers having an acryloyl group or a methacryloyl group, such as trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, glycerol triacrylate, tris(acryloxyethyl)isocyanurate, dipentaerythritol hexaacrylate, dimethylolpropane tetraacrylate, pentaerythritol ethoxy tetraacrylate, EO-modified phosphate triacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, poly(acryloyloxypropyl)methylpropane ...,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, poly(acryloyloxypropyl)methylpropane triacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2,2,5,5-tetrahydroxymethylcyclopentanone tetraacrylate, 2,2,5,5- Examples of the esters include polyethylene glycol diacrylate, polypropylene glycol diacrylate, polytetramethylene glycol diacrylate, EO-modified bisphenol A diacrylate, PO-modified bisphenol A diacrylate, 9,9-bis[4-(2-acryloyloxyethoxy)phenyl]fluorene, tricyclodecane dimethanol diacrylate, decanediol diacrylate, hexanediol diacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, EO-modified bisphenol A dimethacrylate, PO-modified bisphenol A dimethacrylate, tricyclodecane dimethanol dimethacrylate, decanediol dimethacrylate, and hexanediol dimethacrylate.

[0112] Examples of oligomers and polymers having an acryloyl group or a methacryloyl group include urethane acrylate, ester acrylate, acrylic acrylate, epoxy acrylate, etc. Among these, urethane acrylate and ester acrylate are preferred, and ester acrylate is more preferred.

[0113] The above compounds can be used alone or in combination of two or more.

[0114] In the protective layer, the ratio of the mass content of the curable compound to the mass content of the electron-accepting compound (curable compound / electron-accepting compound) is preferably 0.1 or more, more preferably 1 or more, and even more preferably 5 or more, from the viewpoint of film hardness. On the other hand, from the viewpoint of electrical properties, it is preferably 30 or less, more preferably 20 or less, and even more preferably 15 or less. Furthermore, in the protective layer, the ratio of the mass content of the curable compound to the hole-transporting compound (curable compound / hole-transporting compound) is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1 or more, from the viewpoint of film hardness. On the other hand, from the viewpoint of hole-transporting properties, it is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less.

[0115] In the present electrophotographic photoreceptor, the ratio of the mass content of the curable compound to the mass content of the electron-accepting compound (curable compound / electron-accepting compound) is preferably 0.1 or more, more preferably 1 or more, and even more preferably 5 or more, from the viewpoint of film hardness. On the other hand, from the viewpoint of electrical properties, it is preferably 30 or less, more preferably 20 or less, and even more preferably 15 or less. Furthermore, in the present electrophotographic photoreceptor, the ratio of the mass content of the curable compound to the hole-transporting compound (curable compound / hole-transporting compound) is preferably 0.1 or more, more preferably 0.5 or more, and even more preferably 1 or more, from the viewpoint of film hardness. On the other hand, from the viewpoint of hole-transporting properties, it is preferably 10 or less, more preferably 8 or less, and even more preferably 5 or less.

[0116] (Other Components) The protective layer may contain, as other components, a polymerization initiator, inorganic particles, and other materials, as necessary.

[0117] (Polymerization initiator) Examples of the polymerization initiator include a thermal polymerization initiator, a photopolymerization initiator, etc. Examples of the thermal polymerization initiator include a peroxide compound such as 2,5-dimethylhexane-2,5-dihydroperoxide, and an azo compound such as 2,2'-azobis(isobutyronitrile).

[0118] Photopolymerization initiators can be classified into direct cleavage type and hydrogen abstraction type based on the radical generation mechanism. Direct cleavage type photopolymerization initiators generate radicals by cleaving some of the covalent bonds within the molecule when they absorb light energy. On the other hand, hydrogen abstraction type photopolymerization initiators generate radicals when the molecule becomes excited by absorbing light energy and abstracts hydrogen from the hydrogen donor.

[0119] Examples of the direct cleavage type photopolymerization initiator include acetophenone or ketal compounds such as acetophenone, 2-benzoyl-2-propanol, 1-benzoylcyclohexanol, 2,2-diethoxyacetophenone, benzyl dimethyl ketal, and 2-methyl-4'-(methylthio)-2-morpholinopropiophenone; benzoin ether compounds such as benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isobutyl ether, benzoin isopropyl ether, and O-tosylbenzoin; and acylphosphine oxide compounds such as diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, and lithium phenyl(2,4,6-trimethylbenzoyl)phosphonate.

[0120] Examples of hydrogen abstraction photopolymerization initiators include benzophenone-based compounds such as benzophenone, 4-benzoylbenzoic acid, 2-benzoylbenzoic acid, methyl 2-benzoylbenzoate, methyl benzoylformate, benzyl, p-anisil, 2-benzoylnaphthalene, 4,4'-bis(dimethylamino)benzophenone, 4,4'-dichlorobenzophenone, and 1,4-dibenzoylbenzene, and anthraquinone- or thioxanthone-based compounds such as 2-ethylanthraquinone, 2-isopropylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, and 2,4-dichlorothioxanthone. Examples of other photopolymerization initiators include camphorquinone, 1-phenyl-1,2-propanedione-2-(o-ethoxycarbonyl)oxime, acridine-based compounds, triazine-based compounds, and imidazole-based compounds.

[0121] In order to efficiently absorb light energy and generate radicals, the photopolymerization initiator preferably has an absorption wavelength in the wavelength region of the light source used for light irradiation. Among these, it is preferable to contain an acylphosphine oxide compound, which has an absorption wavelength on the relatively long wavelength side. Furthermore, from the viewpoint of enhancing the curability of the surface of the protective layer, it is even more preferable to use an acylphosphine oxide compound and a hydrogen abstraction initiator in combination. In this case, the content ratio of the hydrogen abstraction initiator relative to the acylphosphine oxide compound is not particularly limited. From the viewpoint of enhancing surface curability, the content is preferably 0.1 parts by mass or more per part by mass of the acylphosphine oxide compound, and from the viewpoint of maintaining internal curability, it is preferably 5 parts by mass or less.

[0122] Furthermore, a compound having a photopolymerization promoting effect can be used alone or in combination with the above photopolymerization initiator. Examples of compounds having a photopolymerization promoting effect include triethanolamine, methyldiethanolamine, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, (2-dimethylamino)ethyl benzoate, and 4,4'-dimethylaminobenzophenone.

[0123] The polymerization initiator may be used alone or in combination of two or more. The content of the polymerization initiator is 0.5 to 40 parts by mass, preferably 1 to 20 parts by mass, per 100 parts by mass of the total radically polymerizable ingredients. The total radically polymerizable ingredients include the electron transport compound represented by formula (1) and the curable compound.

[0124] (Inorganic Particles) The protective layer may contain inorganic particles from the viewpoint of improving the strong exposure characteristics and mechanical strength, or from the viewpoint of imparting charge transport ability. However, the protective layer does not necessarily need to contain inorganic particles.

[0125] Examples of the inorganic particles include metal powder, metal oxide, metal fluoride, potassium titanate, boron nitride, etc. Generally, any inorganic particles that can be used for electrophotographic photoreceptors can be used. Only one type of inorganic particles may be used, or multiple types of particles may be mixed and used.

[0126] (Other Materials) The protective layer may contain other materials as needed. Examples of other materials include stabilizers (heat stabilizers, UV absorbers, light stabilizers, antioxidants, etc.), dispersants, antistatic agents, colorants, lubricants, etc. These may be used alone or in any combination and ratio.

[0127] (Method of Forming the Present Protective Layer) Next, an example of a method of forming the present protective layer will be described, although the present invention is not limited to this method.

[0128] [Coating liquid for forming protective layer] The protective layer can be formed, for example, by preparing a coating liquid in which a curable composition containing the electron-accepting compound and the hole-transporting compound, and optionally the curable compound, the polymerization initiator, the inorganic particles, and the other materials, is dissolved in a solvent or dispersed in a dispersion medium (referred to as "coating liquid for forming protective layer"), applying the coating liquid for forming protective layer onto the photosensitive layer, and curing the coating liquid. However, the method is not limited to this.

[0129] In addition, when the hole transport compound has a polymerizable functional group, it can also serve as a curable compound. In this case, it is not necessary to contain a curable compound separately from the hole transport compound having a polymerizable functional group. Even when no curable compound is contained or the content of the curable compound is small, by using the hole transport compound having a polymerizable functional group, sufficient mechanical strength of the protective layer can be obtained and deterioration of the residual potential due to the presence of a curable compound can be suppressed. However, this does not exclude the use of a hole transport compound having a polymerizable functional group and a curable compound in combination.

[0130] The hole transport compound used in the present protective layer-forming coating liquid is preferably a compound represented by the above formula (1) or (2). In this case, specific examples of the hole transport compound include, in addition to the compounds listed above as specific examples, compounds having a boron anion and a counter cation, such as those shown below. However, the type of counter cation and the combination of the boron anion and the counter cation are not limited to these. It is presumed that in the present protective layer after curing, the counter cation is neutralized by receiving a radical, for example, a radical from the hole transport substance.

[0131]

[0132]

[0133]

[0134]

[0135]

[0136]

[0137]

[0138]

[0139]

[0140]

[0141]

[0142]

[0143]

[0144] The hole transport compound used in the present protective layer-forming coating liquid is preferably a compound represented by the above formulas (3) to (5). Preferred embodiments of the curable compound, polymerization initiator, inorganic particles, and other materials used in the present protective layer-forming coating liquid are the same as those of the respective materials used in the present protective layer.

[0145] The ratio by mass of the electron-accepting compound to the hole-transporting compound in the protective layer-forming coating liquid (electron-accepting compound / hole-transporting compound) is the same as the ratio by mass of the electron-accepting compound to the hole-transporting compound in the protective layer described above (electron-accepting compound / hole-transporting compound). The ratio by mass of the curable compound to the electron-accepting compound in the protective layer-forming coating liquid (curable compound / electron-accepting compound) is the same as the ratio by mass of the curable compound to the electron-accepting compound in the protective layer described above (curable compound / electron-accepting compound). The ratio by mass of the curable compound to the hole-transporting compound in the protective layer-forming coating liquid (curable compound / hole-transporting compound) is the same as the ratio by mass of the curable compound to the hole-transporting compound in the protective layer described above (curable compound / hole-transporting compound).

[0146] The content of the electron-accepting compound in the protective layer-forming coating liquid is preferably 0.01 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 parts by mass or more, per 100 parts by mass of the solvent, from the viewpoint of improving hole transportability. On the other hand, from the viewpoint of not inhibiting hole transportability, it is preferably 8.0 parts by mass or less, more preferably 7.0 parts by mass or less, and even more preferably 5.0 parts by mass or less, per 100 parts by mass of the solvent. On the other hand, the content of the hole-transporting compound in the protective layer-forming coating liquid is preferably 6.0 parts by mass or more, more preferably 8.0 parts by mass or more, and even more preferably 10.0 parts by mass or more, per 100 parts by mass of the solvent, from the viewpoint of hole transport. On the other hand, from the viewpoint of improving filming properties, it is preferably 18.0 parts by mass or less, more preferably 15.0 parts by mass or less, and even more preferably 13.0 parts by mass or less, per 100 parts by mass of the solvent. The content of the curable compound in the protective layer-forming coating liquid is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 4 parts by mass or more, relative to 100 parts by mass of the solvent, from the viewpoint of film uniformity of the protective layer. On the other hand, from the viewpoint of solubility, it is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 6 parts by mass or less, relative to 100 parts by mass of the solvent. In particular, when the hole transport compound contained in the protective layer-forming coating liquid has a polymerizable functional group, the content of the curable compound in the protective layer-forming coating liquid is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 0 part by mass, relative to 100 parts by mass of the solvent, from the viewpoint of residual potential.

[0147] The solvent used in the protective layer-forming coating liquid may be, for example, an organic solvent. Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, and 2-methoxyethanol; ethers such as tetrahydrofuran, 1,4-dioxane, and dimethoxyethane; esters such as methyl formate and ethyl acetate; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic hydrocarbons such as benzene, toluene, xylene, and anisole; chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,1-trichloroethane, tetrachloroethane, 1,2-dichloropropane, and trichloroethylene; nitrogen-containing compounds such as n-butylamine, isopropanolamine, diethylamine, triethanolamine, ethylenediamine, and triethylenediamine; and aprotic polar solvents such as acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, and dimethyl sulfoxide. Mixed solvents of these solvents may also be used in any combination and in any ratio. Among these, from the viewpoints of solubility and coatability, alcohols, ethers, aromatic hydrocarbons, and aprotic polar solvents are preferred, alcohols, ethers, and aromatic hydrocarbons are more preferred, alcohols and ethers are even more preferred, and alcohols are most preferred. Furthermore, even organic solvents that do not dissolve the electron-accepting compound used in the protective layer alone can be used if they can be dissolved by, for example, mixing with the above-mentioned organic solvents. Generally, using a mixed solvent can reduce coating unevenness. When using a dip coating method as the coating method described below, it is preferable to select a solvent that does not dissolve the lower layer. From this viewpoint, it is particularly preferable to add an alcohol.

[0148] The ratio of the amount of the solvent to the amount of solids used in the coating solution for forming the protective layer varies depending on the coating method for the coating solution for forming the protective layer, and may be appropriately changed so as to form a uniform coating film in the coating method to be used.

[0149] [Coating Method] The method for applying the coating solution to form the protective layer is not particularly limited, and examples thereof include spray coating, spiral coating, ring coating, and dip coating.

[0150] After forming the coating film by the above coating method, the coating film is dried. In this case, the drying temperature and time are not important as long as necessary and sufficient drying is obtained. However, if the protective layer is coated by only air drying after coating the photosensitive layer, it is preferable to carry out sufficient drying by the method described below in the method for forming the photosensitive layer.

[0151] [Method for Curing the Protective Layer] The protective layer can be formed by applying the protective layer-forming coating liquid and then curing it by applying external energy. Examples of the external energy used in this process include heat, light, and radiation.

[0152] Examples of methods for applying heat energy include heating methods using gases such as air and nitrogen, steam, various heat media, infrared rays, and electromagnetic waves. Heating can be carried out from the coated surface side or the support side. The heating temperature is preferably 100°C or higher and 170°C or lower.

[0153] As the light energy, UV irradiation light sources such as high-pressure mercury lamps, metal halide lamps, electrodeless lamp bulbs, and light-emitting diodes, which have emission wavelengths mainly in the ultraviolet (UV) range, can be used. It is also possible to select a visible light source in accordance with the absorption wavelengths of the polymerizable compound and photopolymerization initiator. The light irradiation dose is set to 10 mJ / cm from the viewpoint of curing properties. ２ More than 30 mJ / cm is preferable. ２ More preferably, 100 mJ / cm or more ２ In addition, from the viewpoint of electrical properties, 500 mJ / cm ２ Preferably, 300 mJ / cm or less ２ More preferably, 200 mJ / cm or less ２ The following are particularly preferred: On the other hand, examples of radiation energy include those using electron beams (EB).

[0154] Among these energies, light energy is preferred from the viewpoints of ease of reaction rate control, simplicity of the apparatus, and long pot life.

[0155] After the protective layer is cured, a heating step may be performed from the viewpoints of relieving residual stress, relieving residual radicals, and improving electrical properties. The heating temperature is preferably 60° C. or higher, more preferably 100° C. or higher, and is preferably 200° C. or lower, more preferably 150° C. or lower.

[0156] (Layer Thickness) From the viewpoint of abrasion resistance, the thickness of the protective layer is preferably 0.5 μm or more, more preferably 1 μm or more. On the other hand, from the viewpoint of electrical properties, it is preferably 5 μm or less, more preferably 3 μm or less. From the same viewpoint, the thickness of the protective layer is preferably 1 / 50 or more of the thickness of the photosensitive layer, more preferably 1 / 40 or more, and even more preferably 1 / 30 or more. On the other hand, it is preferably 1 / 5 or less, more preferably 1 / 10 or less, and even more preferably 1 / 20 or less.

[0157] <Present Photosensitive Layer> The photosensitive layer (present photosensitive layer) in the present electrophotographic photoreceptor may be any layer containing a charge generating material (CGM) and a charge transport material, and preferably contains at least an arylamine compound.

[0158] As described above, the protective layer contains an electron-accepting compound and the photosensitive layer contains an arylamine compound, whereby the arylamine compound and the electron-accepting compound interact with each other at the interface between the photosensitive layer and the protective layer, improving the hole transport properties in the photosensitive layer and further reducing the hole injection barrier between the photosensitive layer and the protective layer, thereby improving the electrical properties.

[0159] (Arylamine Compound) The arylamine compound may be any amine having an aryl group. Among them, compounds containing a compound represented by the following formula (200) or (201) are particularly preferred from the viewpoint of further reducing the hole injection barrier between the present photosensitive layer and the present protective layer. All of the compounds represented by the following formula (200) or (201) have a common feature that the HOMO orbital expands around the N atom, resulting in excellent hole transport properties.

[0160]

[0161]

[0162] In formula (200) or (201), Ar HTM may be the same or different as long as they are groups selected from the following formulae (200-1) to (200-3).

[0163]

[0164] In formulas (200), (201), and (200-1) to (200-3), each R independently represents a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, an aromatic heterocyclic group which may have a substituent, or a halogen atom. h1 represents an integer of 0 to 5, and h4 represents an integer of 0 to 2. * represents the bonding position to formula (200) or (201).

[0165] From the viewpoint of hole transportability, the content of the arylamine compound in the present photosensitive layer is preferably 10 parts by mass or more, more preferably 20 parts by mass or more, and even more preferably 30 parts by mass or more, relative to 100 parts by mass of the total mass of the present photosensitive layer. On the other hand, from the viewpoint of solubility, it is preferably 65 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less, relative to 100 parts by mass of the total mass of the present photosensitive layer. The total mass of the photosensitive layer means the total mass of the photosensitive layer after curing, which is the same as the total mass of the solids in the coating solution for forming the photosensitive layer.

[0166] In the present electrophotographic photoreceptor, the ratio of the mass content of the electron-accepting compound to the mass content of the arylamine compound (electron-accepting compound / arylamine compound) is preferably 0.001 or more and 0.9 or less. A ratio (electron-accepting compound / arylamine compound) of 0.001 or more is preferred from the viewpoint of electrical properties. On the other hand, a ratio of 0.9 or less is preferred from the viewpoint of film hardness and image bleeding under high temperature and high humidity. From these viewpoints, the ratio (electron-accepting compound / arylamine compound) is more preferably 0.002 or more, more preferably 0.005 or more, and even more preferably 0.01 or more, even more preferably 0.05 or more, and even more preferably 0.1 or more. On the other hand, it is more preferably 0.8 or less, even more preferably 0.6 or less, even more preferably 0.4 or less, and even more preferably 0.3 or less.

[0167] <Configuration of the present photosensitive layer> The present photosensitive layer may be a single-layer type photosensitive layer containing a charge transport material, a charge generating material, and, if necessary, other charge transport materials in the same layer, or may be a multi-layer type photosensitive layer separated into a charge generating layer and a charge transport layer. The present photosensitive layer is preferably a multi-layer type photosensitive layer, as this allows the effects of the present invention to be more effectively enjoyed.

[0168] <Single-Layer Photosensitive Layer> When the present photosensitive layer is a single-layer photosensitive layer, it is preferred that at least a charge generating material (CGM), an electron transporting material (ETM), and, if necessary, other hole transporting materials (HTM), and a binder resin are contained in the same layer. In the single-layer photosensitive layer, for example, a preferred example is a layer containing an arylamine compound that functions as a charge transporting material.

[0169] (Charge-Generating Material) As the charge-generating material used in the photosensitive layer, for example, various photoconductive materials such as inorganic photoconductive materials and organic pigments can be used. Among them, organic pigments are particularly preferred, and phthalocyanine pigments and azo pigments are more preferred.

[0170] In particular, when a phthalocyanine pigment is used as the charge generating material, specific examples include metal-free phthalocyanine, and phthalocyanines coordinated with metals such as copper, indium, gallium, tin, titanium, zinc, vanadium, silicon, and germanium, or oxides or halides thereof. Among these, titanyl phthalocyanine such as A-type, B-type, and D-type, chlorogallium phthalocyanine, and hydroxygallium phthalocyanine are preferred.

[0171] When an azo pigment is used, various known bisazo pigments and trisazo pigments are preferably used.

[0172] The charge generating material may be used alone or in any combination of two or more kinds in any ratio.

[0173] From the viewpoint of electrical properties, it is desirable that the particle diameter of the charge generating material is small. Specifically, the particle diameter of the charge generating material is preferably 1 μm or less, more preferably 0.5 μm or less. The lower limit is 0.01 μm or more. Here, the particle diameter of the charge generating material means the particle diameter in a state in which it is contained in the photosensitive layer.

[0174] The amount of the charge generating substance in the single-layer photosensitive layer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of sensitivity, and is preferably 50% by mass or less, more preferably 20% by mass or less, from the viewpoint of sensitivity and chargeability.

[0175] (Charge transport material) Charge transport materials are classified into hole transport materials having mainly hole transport ability and electron transport materials having mainly electron transport ability. However, when the present photosensitive layer is a single-layer type photosensitive layer, it is preferable that at least a hole transport material and an electron transport material are contained in the same layer.

[0176] [Hole Transport Material] The hole transport material (HTM) can be selected from known materials. For example, a material containing at least one selected from the group consisting of heterocyclic structures such as carbazole, indole, imidazole, oxazole, pyrazole, thiadiazole, and benzofuran, aniline, hydrazone, stilbene, butadiene, and enamine structures is preferred. Other examples include electron donating materials such as compounds containing a combination of multiple of these structures, and polymers having a group containing these structures in the main chain or side chain. Among these, preferred are carbazole, stilbene, butadiene, and enamine structures, as well as compounds containing a combination of multiple of these structures, with compounds containing an enamine structure being more preferred. One or more hole transport materials may be used alone, or two or more may be used in any ratio and combination.

[0177] Since the arylamine compound also functions as a hole transport material (HTM), the composition may contain only an arylamine compound as the hole transport material (HTM), or may contain another hole transport material (HTM) other than the arylamine compound. In this case, the other hole transport material (HTM) can be selected from the above-mentioned known materials.

[0178] [Electron Transporting Material] The electron transporting material (ETM) can be selected from known materials. Examples include electron-withdrawing substances such as aromatic nitro compounds such as 2,4,7-trinitrofluorenone, cyano compounds such as tetracyanoquinodimethane, and quinone compounds such as diphenoquinone, as well as known cyclic ketone compounds and perylene pigments (perylene derivatives). Among these, from the viewpoint of electrical properties, quinone compounds and perylene pigments (perylene derivatives) are preferred, and quinone compounds are more preferred. Among the quinone compounds, from the viewpoint of electrical properties, diphenoquinone or dinaphthylquinone are preferred. Of these, dinaphthylquinone is more preferred. The electron transporting material may be used alone or in any combination and ratio.

[0179] (Binder Resin) Next, the binder resin used in the present photosensitive layer will be described. Examples of binder resins used in the present photosensitive layer include vinyl polymers or copolymers thereof, such as polymethyl methacrylate, polystyrene, and polyvinyl chloride; vinyl alcohol resins; polyvinyl butyral resins; polyvinyl formal resins; partially modified polyvinyl acetal resins; polyarylate resins; polyamide resins; polyurethane resins; polycarbonate resins; polyester resins; polyester carbonate resins; polyimide resins; phenoxy resins; epoxy resins; silicone resins; and partially crosslinked cured products thereof. The above resins may also be modified with a silicon reagent or the like. These may be used alone or in any combination and ratio. Among these, polycarbonate resins, polyarylate resins, and polyester resins are preferred, with polycarbonate resins and polyarylate resins being particularly preferred.

[0180] (Other Substances) In addition to the materials described above, the photosensitive layer may contain additives such as well-known antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, and visible light shielding agents in order to improve film-forming properties, flexibility, coating properties, contamination resistance, gas resistance, light resistance, and the like. The photosensitive layer may also contain various additives, such as sensitizers, dyes, pigments (excluding the charge-generating materials, hole-transporting materials, and electron-transporting materials described above), and surfactants, as needed. Examples of surfactants include silicone oils and fluorine-based compounds. In the present invention, these may be used alone or in any combination of two or more types in any ratio.

[0181] Furthermore, for the purpose of reducing frictional resistance on the surface of the photosensitive layer, the photosensitive layer may contain a fluorine-based resin, a silicone resin, or the like, or may contain particles made of these resins or particles of an inorganic compound such as aluminum oxide.

[0182] (Layer Thickness) When the present photosensitive layer is a single-layer type photosensitive layer, the thickness of the present photosensitive layer is preferably 20 μm or more, more preferably 25 μm or more, from the viewpoint of dielectric breakdown resistance, and is preferably 50 μm or less, more preferably 40 μm or less, from the viewpoint of electrical properties.

[0183] <Laminated Photosensitive Layer> When the present electrophotographic photoreceptor is a laminated photosensitive layer, for example, a configuration in which a charge transport layer (CTL) containing a charge transport material is laminated on a charge generation layer (CGL) containing a charge generation material (CGM) can be mentioned. In this case, it is also possible to provide layers other than the charge generation layer (CGL) and the charge transport layer (CTL). In the laminated photosensitive layer, a preferred example is a case in which the charge transport layer contains the above-mentioned arylamine compound.

[0184] <Charge Generation Layer (CGL)> The charge generation layer usually contains a charge generation material (CGM) and a binder resin. The charge generation material (CGM) and the binder resin are the same as those described above for the single-layer type photosensitive layer.

[0185] (Other Components) In addition to the charge generating material and the binder resin, the charge generating layer may contain other components as needed. For example, known additives such as antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light shielding agents, and fillers may be contained in order to improve film-forming properties, flexibility, coating properties, contamination resistance, gas resistance, light resistance, etc.

[0186] (Composition ratio) In the charge generation layer, if the ratio of the charge generation material is too high, the stability of the coating liquid may decrease due to aggregation of the charge generation material, etc., while if the ratio of the charge generation material is too low, the sensitivity of the photoreceptor may decrease. Therefore, the composition ratio (by mass) of the binder resin to the charge generation material is preferably 10 parts by mass or more of the charge generation material per 100 parts by mass of the binder resin, and more preferably 30 parts by mass or more. On the other hand, it is preferably 1,000 parts by mass or less, and more preferably 500 parts by mass or less. From the viewpoint of film strength, it is more preferably 300 parts by mass or less, and even more preferably 200 parts by mass or less.

[0187] (Layer Thickness) The thickness of the charge generating layer is preferably 0.1 μm or more, more preferably 0.15 μm or more, and is preferably 10 μm or less, more preferably 0.6 μm or less.

[0188] <Charge Transport Layer (CTL)> The charge transport layer (CTL) usually contains a charge transport material and a binder resin. The charge transport material and binder resin are the same as those described for the single-layer photosensitive layer, and the charge transport layer preferably contains the above-mentioned arylamine compound as the charge transport material, particularly as the hole transport material (HTM).

[0189] In the charge transport layer (CTL), the blending ratio of the binder resin and the hole transport material (HTM) is preferably 20 parts by mass or more of the hole transport material (HTM) per 100 parts by mass of the binder resin, more preferably 30 parts by mass or more from the viewpoint of reducing residual potential, and even more preferably 40 parts by mass or more from the viewpoints of stability during repeated use and charge mobility. On the other hand, from the viewpoint of thermal stability of the photosensitive layer, the blending ratio of the hole transport material (HTM) per 100 parts by mass of the binder resin is preferably 200 parts by mass or less, and from the viewpoint of compatibility between the hole transport material (HTM) and the binder resin, more preferably 150 parts by mass or less, and especially preferably 120 parts by mass or less from the viewpoint of glass transition temperature.

[0190] (Other Components) The charge transport layer may contain other components as needed in addition to the electron transport material (ETM), hole transport material (HTM), and binder resin. For example, known additives such as antioxidants, plasticizers, ultraviolet absorbers, electron-withdrawing compounds, leveling agents, visible light shielding agents, and fillers may be contained for the purpose of improving film-forming properties, flexibility, coating properties, contamination resistance, gas resistance, light resistance, etc.

[0191] (Layer Thickness) The layer thickness of the charge transport layer is not particularly limited. From the viewpoints of electrical characteristics, image stability, and high resolution, the layer thickness is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more or 35 μm or less, and even more preferably 15 μm or more or 25 μm or less.

[0192] <Method of Forming Photosensitive Layer> In both the multilayer type and the single-layer type, each of the above layers can be formed as follows. A coating liquid obtained by dissolving or dispersing a substance to be contained in a solvent can be applied to a conductive support by a known method such as dip coating, spray coating, nozzle coating, bar coating, roll coating, or blade coating, and the layers can be formed by repeating the steps of coating and drying sequentially for each layer. However, the formation method is not limited to this.

[0193] The solvent or dispersion medium used to prepare the coating liquid is not particularly limited. Specific examples include alcohols, ethers, aromatic hydrocarbons, chlorinated hydrocarbons, etc. These may be used alone or in any combination of two or more of them.

[0194] The amount of solvent or dispersion medium used is not particularly limited. It is preferable to appropriately adjust the solids concentration, viscosity, and other physical properties of the coating solution so that they fall within the desired range, taking into account the purpose of each layer and the properties of the selected solvent or dispersion medium. The coating film is preferably dried by heating, usually at a temperature of 30°C or higher and 200°C or lower, for 1 minute to 2 hours, either stationary or under airflow. The heating temperature may be constant, or the temperature may be varied during drying.

[0195] <Conductive Support> The conductive support (also referred to as the "conductive support") of the electrophotographic photoreceptor is not particularly limited as long as it supports the layer formed thereon and exhibits conductivity. Examples of the conductive support include metal materials such as aluminum, aluminum alloys, stainless steel, copper, and nickel, resin materials imparted with conductivity by the coexistence of metals, carbon, and conductive powders such as tin oxide, and resins, glass, and paper on whose surfaces conductive materials such as aluminum, nickel, and ITO (indium oxide tin oxide alloy) are vapor-deposited or coated. The conductive support may be in the form of a drum, cylinder, sheet, belt, or the like. The conductive support may also be a metal conductive support coated with a conductive material having an appropriate resistance value for controlling conductivity, surface properties, and the like, or for covering defects.

[0196] The surface of the conductive support may be smooth or may be roughened by using a special cutting method or by polishing. Alternatively, the surface may be roughened by mixing particles of an appropriate particle size into the material constituting the support. An undercoat layer, which will be described below, may be provided between the conductive support and the photosensitive layer to improve adhesion, blocking resistance, etc.

[0197] <Present Undercoat Layer> The present electrophotographic photoreceptor may have an undercoat layer (also referred to as "present undercoat layer") between the present photosensitive layer and the present conductive support.

[0198] The undercoat layer may be made of, for example, a resin, a resin in which organic pigments or particles of metal oxides are dispersed, etc. Examples of organic pigments used in the undercoat layer include phthalocyanine pigments, azo pigments, and perylene pigments.

[0199] Examples of metal oxide particles used in the present undercoat layer include metal oxide particles containing one type of metal element such as titanium oxide, aluminum oxide, silicon oxide, zirconium oxide, zinc oxide, and iron oxide, and metal oxide particles containing multiple metal elements such as calcium titanate, strontium titanate, and barium titanate. The undercoat layer may contain only one type of particle, or multiple types of particles may be mixed in any ratio and combination.

[0200] Among the above metal oxide particles, titanium oxide and aluminum oxide are preferred, with titanium oxide being particularly preferred.

[0201] The particle size of the metal oxide particles used in the present undercoat layer is not particularly limited. From the viewpoints of the properties of the undercoat layer and the stability of the solution for forming the undercoat layer, the average primary particle size is preferably 10 nm or more, and 100 nm or less, more preferably 50 nm or less.

[0202] The binder resin used in the present undercoat layer can be selected from, for example, polyvinyl acetal resins such as polyvinyl butyral resins; and insulating resins such as polyarylate resins, polycarbonate resins, polyester resins, phenoxy resins, acrylic resins, methacrylic resins, polyamide resins, polyurethane resins, epoxy resins, silicone resins, polyvinyl alcohol resins, and styrene-alkyd resins. However, the binder resin is not limited to these polymers. Furthermore, these binder resins may be used alone or in combination with two or more types, or may be used in a cured form with a curing agent. Among these, polyvinyl acetal resins, alcohol-soluble copolymer polyamides, modified polyamides, and the like are preferred because of their good dispersibility and coatability. Of these, alcohol-soluble copolymer polyamides are particularly preferred.

[0203] The mixing ratio of the particles to the binder resin can be selected arbitrarily, but it is preferable to use the particles in the range of 10% by mass to 500% by mass in terms of the stability and coatability of the dispersion.

[0204] The thickness of the undercoat layer can be selected arbitrarily. In view of the characteristics of the electrophotographic photoreceptor and the coating properties of the dispersion, the thickness is preferably 0.1 μm or more, and more preferably 20 μm or less. The undercoat layer may also contain a known antioxidant.

[0205] <Other Layers> The electrophotographic photoreceptor may have other layers as needed, in addition to the conductive support, photosensitive layer, protective layer, and undercoat layer described above.

[0206] <<Present Image Forming Apparatus>> An image forming apparatus ("present image forming apparatus") can be configured using the present electrophotographic photoreceptor.

[0207] As shown in Figure 1, the image forming apparatus is configured to include an electrophotographic photoreceptor 1, a charging device 2, an exposure device 3, and a developing device 4, and may further include a transfer device 5, a cleaning device 6, and a fixing device 7 as needed. There are no particular limitations on the electrophotographic photoreceptor 1 as long as it is the electrophotographic photoreceptor described above. Figure 1 shows, as an example, a drum-shaped photoreceptor in which the above-described photosensitive layer is formed on the surface of a cylindrical conductive support. The charging device 2, exposure device 3, developing device 4, transfer device 5, and cleaning device 6 are arranged along the outer circumferential surface of the electrophotographic photoreceptor 1, respectively.

[0208] Examples of the charging device 2 include a non-contact corona charging device such as a corotron or scorotron, or a contact-type charging device (direct charging device) that charges the photosensitive member by bringing a charging member to which a voltage is applied into contact with the surface of the photosensitive member. Examples of contact charging devices include a charging roller and a charging brush. Note that FIG. 1 shows a roller-type charging device (charging roller) as an example of the charging device 2.

[0209] The type of exposure device 3 is not particularly limited as long as it can expose the electrophotographic photoreceptor 1 to light and form an electrostatic latent image on the photosensitive surface of the electrophotographic photoreceptor 1. Furthermore, exposure may be performed by an internal photoreceptor exposure method. Any light may be used for exposure.

[0210] The type of toner T is arbitrary, and in addition to pulverized toner, polymerized toner produced by a suspension polymerization method or an emulsion polymerization method can be used.

[0211] The type of transfer device 5 is not particularly limited, and any device using an arbitrary method such as electrostatic transfer such as corona transfer, roller transfer, or belt transfer, pressure transfer, or adhesive transfer can be used.

[0212] There are no particular limitations on the cleaning device 6. Any cleaning device can be used, such as a brush cleaner, a magnetic roller cleaner, or a blade cleaner. If there is little or almost no toner remaining on the photoreceptor surface, the cleaning device 6 may be omitted. In addition to the above-described configuration, the image forming apparatus may also be configured to be capable of performing, for example, a static elimination process.

[0213] Furthermore, the image forming apparatus may be further modified and configured, for example, to be capable of performing processes such as a pre-exposure process and an auxiliary charging process, to be configured to perform offset printing, or to be configured as a full-color tandem system using multiple types of toner.

[0214] <<Present Electrophotographic Cartridge>> The present electrophotographic photosensitive member 1 can be combined with one or more of the charging device 2, the exposure device 3, the developing device 4, the transfer device 5, the cleaning device 6, and the fixing device 7 to form an integrated cartridge (referred to as the present electrophotographic cartridge).

[0215] The electrophotographic cartridge can be configured to be detachable from the main body of an electrophotographic apparatus such as a copying machine, a laser beam printer, etc. In this case, for example, when the electrophotographic photosensitive member 1 or other members deteriorate, the electrophotographic photosensitive member cartridge can be removed from the main body of the image forming apparatus and a new electrophotographic photosensitive member cartridge can be mounted in the main body of the image forming apparatus, thereby facilitating maintenance and management of the image forming apparatus.

[0216] <<Explanation of Terms>> In the present invention, when "X to Y" (X and Y are any numbers) is expressed, unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as "preferably larger than X" or "preferably smaller than Y". Furthermore, when "X or more" (X is any number) or "Y or less" (Y is any number) is expressed, it also includes the meaning of "preferably larger than X" or "preferably smaller than Y".

[0217] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples. However, the following examples are provided to explain the present invention in detail, and the present invention is not limited to the examples shown below, and can be practiced by modifying it as desired, as long as it does not deviate from the gist of the present invention. Furthermore, in the following examples and comparative examples, "parts" refers to "parts by mass" unless otherwise specified.

[0218] <<Test Example 1>> In Test Example 1, the following electron-accepting compounds 1 and 2 were used as the electron-accepting compounds.

[0219] <Electron Accepting Compound 1> Electron accepting compound 1 represented by the following structural formula, manufactured by Tokyo Chemical Industry Co., Ltd., was used.

[0220]

[0221] <Electron Accepting Compound 2> Electron accepting compound 2 represented by the following structural formula, manufactured by Tokyo Chemical Industry Co., Ltd., was used.

[0222]

[0223] <Hole Transporting Compound 1> As the hole transporting compound 1 represented by the following structural formula, a compound represented by the following structure was used.

[0224]

[0225] <Hole Transporting Compound 2> A synthesis scheme of hole transporting compound 2 represented by the following structural formula is shown below: Compound 2-1 represented by the following structural formula was synthesized according to the method described in JP-A-2019-532495.

[0226]

[0227]

[0228] The synthesis procedure of the hole transporting compound 2 is shown below.

[0229] Under a nitrogen atmosphere, 150 mL of anhydrous dichloromethane and triethylamine (7.48 mL, 54.0 mmol) were added to compound 2-1 (4.00 g, 9.00 mmol) and 4-methoxyphenol (0.05 g), and the mixture was cooled on ice. Compound 2-2 (9.36 g, 27.0 mmol) dissolved in 50 mL of anhydrous dichloromethane was added dropwise, and the mixture was stirred under ice cooling for 1 hour and at room temperature for 2 hours. The reaction solution was poured into 100 mL of water, extracted with dichloromethane, and the organic layer was washed with water and then dried over magnesium sulfate. The resulting solid was filtered, and the solvent in the filtrate was distilled off under reduced pressure. The residue was subjected to silica gel column chromatography to obtain hole-transporting compound 2 (yield: 5.0 g, 52%).

[0230] <Preparation of Electrophotographic Photoreceptor> (Preparation of Coating Solution P1 for Forming Undercoat Layer) Titanium oxide particles, the surfaces of which had been treated with methyldimethoxysilane ("TSL8117" manufactured by Toshiba Silicones Co., Ltd.) using rutile titanium oxide ("TTO55N" manufactured by Ishihara Sangyo Kaisha, Ltd., average primary particle diameter 40 nm), and a copolymeric polyamide having the following composition ratio were mixed with stirring in a mixed solvent (methanol / 1-propanol / toluene in a mass ratio of 7 / 1 / 2) while heating to dissolve the copolymeric polyamide. Subsequently, ultrasonic dispersion treatment was performed using an ultrasonic oscillator with an output of 1200 W for 1 hour, and the mixture was filtered to obtain Coating Solution P1 for forming an undercoat layer, in which the mass ratio of surface-treated titanium oxide / copolymeric polyamide was 3 / 1 and the solids concentration was 18.0 mass%. Composition ratio (molar ratio) of copolymerized polyamide: ε-caprolactam / bis(4-amino-3-methylcyclohexyl)methane / hexamethylenediamine / decamethylenedicarboxylic acid / octadecamethylenedicarboxylic acid=75 / 9.5 / 3 / 9.5 / 3

[0231] (Preparation of Coating Solution Q1 for Forming Charge Generating Layer) 20 parts of D-type (Y-type) oxytitanium phthalocyanine A as a charge generating material and 280 parts of 1,2-dimethoxyethane were mixed and ground for 1 hour in a sand grinding mill to perform a fine particle dispersion treatment. Subsequently, this fine particle treatment solution was mixed with a binder solution obtained by dissolving 10 parts of polyvinyl butyral (manufactured by Denki Kagaku Kogyo Co., Ltd., "Denka Butyral" #6000C) in a mixture of 255 parts of 1,2-dimethoxyethane and 85 parts of 4-methoxy-4-methyl-2-pentanone, and 230 parts of 1,2-dimethoxyethane to prepare Coating Solution B1 for forming a charge generating layer. On the other hand, 20 parts of Type A (β-type) oxytitanium phthalocyanine B was mixed with 280 parts of 1,2-dimethoxyethane as a charge generating material and ground for 4 hours in a sand grinding mill to perform a fine particle dispersion treatment. Subsequently, this finely ground solution was mixed with a binder solution obtained by dissolving 10 parts of polyvinyl butyral (Denka Butyral #6000C, manufactured by Denki Kagaku Kogyo Co., Ltd.) in a mixture of 255 parts of 1,2-dimethoxyethane and 85 parts of 4-methoxy-4-methyl-2-pentanone, and 230 parts of 1,2-dimethoxyethane to prepare Charge Generating Layer Forming Coating Solution B2. Charge Generating Layer Forming Coating Solution B1 and Charge Generating Layer Forming Coating Solution B2 were mixed in a mass ratio of 3:7 to obtain Charge Generating Layer Forming Coating Solution Q1.

[0232] (Preparation of Coating Solution Q2 for Forming Charge Transport Layer) 100.00 parts of a polycarbonate resin (viscosity average molecular weight 30,000) represented by the following repeating structure, 50.00 parts of a compound (HTM48) represented by the following structure as a charge transport material, 4.0 parts of an antioxidant (Irganox 1076, manufactured by BASF Japan Ltd.), and 0.02 parts of silicone oil (KF96-10CS, manufactured by Shin-Etsu Chemical Co., Ltd.) as a leveling agent were dissolved in a mixed solvent of 8:2 tetrahydrofuran and toluene with heating and stirring to obtain Coating Solution Q2 for Forming Charge Transport Layer with a solids concentration of 30% by mass.

[0233] (Polycarbonate Resin) A polycarbonate resin represented by the following repeating structure was used as the polycarbonate resin.

[0234]

[0235] (Charge Transport Material) An arylamine compound (HTM48) represented by the following structure was used as the charge transport material.

[0236]

[0237] (Preparation of Protective Layer-Forming Coating Liquid S1) The hole-transporting compound 1, a curable compound not having a hole-transporting skeleton (dipentaerythritol polyacrylate: product name "NK Ester A-DPH" manufactured by Shin-Nakamura Chemical Co., Ltd.) previously dissolved in a mixed solvent of toluene and 2-propanol, the electron-accepting compound 1, and Omnirad TPO H (2,4,6-trimethylbenzoyl-diphenylphosphine oxide) and benzophenone (BP) as polymerization initiators were mixed to obtain a protective layer-forming coating liquid S1 (solids concentration: approximately 25%) having a ratio of hole-transporting compound / A-DPH / electron-accepting compound / TPO+BP=35 / 65 / 3.5 / 3 (mass ratio) and a solvent composition of toluene / 2-propanol=3 / 7 (mass ratio).

[0238] (Preparation of Protective Layer-Forming Coating Liquids S2 to S13) Protective layer-forming coating liquids S2 to S13 were obtained in the same manner as for protective layer-forming coating liquid S1, except that the type and amount of the hole transporting compound, the type and amount of the electron accepting compound, and the type and amount of the curable compound not having a hole transporting skeleton were changed as shown in Table 1. Note that "M-9050" in Table 1 refers to polyester acrylate: product name "Aronix M-9050" manufactured by Toagosei Co., Ltd.

[0239] <Preparation of Multilayer Photoreceptor> A multilayer photoreceptor was prepared by the following procedure.

[0240] Example 1-1: An aluminum cylinder with a machined surface, 30 mm in diameter, 357.4 mm in length, and 0.75 mm in thickness, was dip-coated with Coating Solution P1 for forming an undercoat layer and air-dried to form an undercoat layer with a film thickness of 1.5 μm after drying. Coating Solution Q1 for forming a charge generation layer was dip-coated on the undercoat layer and air-dried to form a charge generation layer with a film thickness of 0.4 μm after drying. Coating Solution Q2 for forming a charge transport layer was dip-coated on the charge generation layer and dried at 125°C for 24 minutes to form a charge transport layer with a film thickness of 17 μm after drying. Next, Coating Solution S1 for forming a protective layer was ring-coated on the charge transport layer, and the photoreceptor was rotated at 60 rpm in a nitrogen atmosphere (oxygen concentration 0.1% or less) while irradiating the photoreceptor with 365 nm LED light at an illuminance of 0.5 mW / cm. ２ for 2 minutes (accumulated light amount: 19 mJ / cm ２ ), a protective layer was provided so that the thickness after curing would be 3.0 μm, thereby preparing photoreceptor A1.

[0241] Examples 1-2 to 1-9 and Comparative Examples 1-1 to 1-4 Photoreceptors A2 to A13 were produced in the same manner as photoreceptor A1, except that protective layer-forming coating liquid S1 was changed to protective layer-forming coating liquids S2 to S13.

[0242] <Boron Atom Content> The content (mass %) of the electron-accepting compound in the protective layer was determined using the amount of each compound charged in the protective layer-forming coating solutions S1 to S13. Next, the content was multiplied by the atomic weight of the boron atom divided by the molecular weight of the electron-accepting compound to determine the content (mass %) of boron atoms in the protective layer. Similarly, the content (mass %) of boron atoms in each layer other than the protective layer was determined. The content (mass %) of boron atoms in each layer was multiplied by the film thickness of each layer divided by the total film thickness to determine the mass content of boron atoms in each layer, and the sum of these values ​​was determined to be the mass content of boron atoms in all layers (excluding the conductive support) of the electrophotographic photoreceptor.

[0243] <Electrical Properties: Evaluation of Residual Potential> The photoreceptors A1 to A13 obtained in the examples and comparative examples were mounted on an electrophotographic property evaluation device manufactured in accordance with the measurement standards of the Electrophotographic Society (described in "Continued Fundamentals and Applications of Electrophotographic Technology," edited by the Electrophotographic Society, Corona Publishing, pp. 404-405), and the electrical properties were measured through a cycle of charging, exposure, potential measurement, and neutralization as follows. First, the grid voltage was adjusted to charge the photoreceptor so that the initial surface potential (V0) was -700 V. Next, the exposure light was applied at 1.3 μJ / cm ２ The residual potential (VL) was measured 60 milliseconds after irradiation. The exposure light was a halogen lamp light converted to monochromatic light of 780 nm using an interference filter. The measurement was performed in an N / N environment at a temperature of 25°C and a relative humidity of 50%.

[0244] The residual potentials (VL) are shown in Table 1. The smaller the absolute value of the residual potential (VL), the more sufficiently the charge was transported and the potential was lowered, which is considered to be a good result. Table 1 also shows the results of calculating the VL difference depending on the presence or absence of an electron-accepting compound, i.e., [(electron-accepting compound present; VL value of Example) - (no electron-accepting compound; VL value of Comparative Example)]. When the VL difference is a negative value, it can be said that the inclusion of the electron-accepting compound lowered the VL value, i.e., improved the electrical properties.

[0245] <Evaluation of Electrical Properties: Potential Retention Rate> The photoreceptors A1 to A13 obtained in the examples and comparative examples were mounted on an electrophotographic property evaluation device manufactured in accordance with the measurement standards of the Society of Electrophotography (described in "Continued Fundamentals and Applications of Electrophotography Technology," edited by the Society of Electrophotography, Corona Publishing, pp. 404-405), and the electrical properties were measured as follows, using a cycle of charging, exposure, potential measurement, and neutralization. First, the grid voltage was adjusted to charge the photoreceptor so that the initial surface potential (V0) was -700 V. The potential retention rate (dark decay, DDR) (%) was measured after leaving it for 5 seconds after charging. The measurement was performed in an environment of 25°C temperature and 50% relative humidity (N / N environment).

[0246] The potential retention rates are shown in Table 1. The potential retention rate represents the surface potential retention rate (%) when a photoreceptor with a charged surface is left for a certain period of time. A higher surface potential retention rate (%) indicates better results, since the potential is maintained over time and chargeability is good. Table 1 also shows the results of calculating the VL difference between the presence and absence of an electron-accepting compound, i.e., [(electron-accepting compound: value of potential retention rate in Example) - (no electron-accepting compound: value of potential retention rate in Comparative Example)]. If the difference in potential retention rate is a positive value, it can be said that the inclusion of an electron-accepting compound increased the value of the potential retention rate, i.e., improved electrical properties.

[0247]

[0248] <Discussion> From the results of the above Examples and Comparative Examples, as well as the results of tests conducted by the present inventors, it has been found that in an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, if the protective layer contains an electron-accepting compound, the electron-accepting property of the protective layer can be enhanced by the electron-accepting compound, thereby further improving the electrical properties of the electrophotographic photoreceptor, particularly the residual potential and potential retention. This is thought to be because, when the protective layer contains an electron-accepting compound, the electron-accepting compound functions as an electron-accepting compound, thinning the Schottky barrier between the protective layer and the photosensitive layer and reducing the barrier for injection of charges, particularly holes, between the layers, thereby further improving the electrical properties.

[0249] Furthermore, it is believed that when an electrophotographic photosensitive member contains a certain amount of boron atoms, the electron-accepting properties of the boron atoms can reduce the charge injection barrier between adjacent layers, thereby improving the electrical properties, particularly the residual potential and potential retention rate.

[0250] Among electron-accepting compounds, it has been found that compounds represented by the above formula (1) or (2) are particularly preferred. Both compounds represented by the above formula (1) or (2) have a structure in which a benzene ring is bonded to a boron atom at the center. Since the boron atom has electron-accepting properties, the inclusion of a boron atom is thought to facilitate smooth charge transfer (electron transfer) in the electrophotographic photoreceptor, resulting in improved electrical properties. Furthermore, since the compound represented by the above formula (2) is an ionic compound, boron becomes an anion, allowing four benzene rings to be bonded, which is thought to improve electron-accepting properties and stability. Therefore, it is thought that the desired effects can be achieved if the electron-accepting compound is a compound represented by the above formula (1) or (2).

[0251] Furthermore, as described above, it has been found that when the protective layer contains an electron-accepting compound and the photosensitive layer contains an arylamine compound, the hole injection barrier between the photosensitive layer and the protective layer is further reduced, resulting in better electrical properties. Among these, it has been found that it is particularly preferable for the arylamine compound to contain a compound represented by the above formula (200) or (201). This is thought to be because both of the compounds represented by the above formula (200) and (201) have a structural feature in which the highest unoccupied molecular orbital (HOMO orbital) is widely delocalized around a nitrogen atom.

[0252] It has also been found that the presence of a hole transport compound together with the electron-accepting compound in the protective layer can improve the electrical properties of the electrophotographic photosensitive member, particularly the residual potential and potential holding ratio. This is presumably because the presence of a hole transport compound together with the electron-accepting compound in the protective layer increases the hole density, activating its performance, i.e., hole transport performance, and further improving the hole transport performance of the protective layer, thereby further improving the electrical properties of the electrophotographic photosensitive member, particularly the residual potential and potential holding ratio.

[0253] All of the compounds represented by the above formulas (3) to (5) have an arylamine structure and are structurally characterized by a shallow HOMO level and high hole transportability. Therefore, when electrons are extracted from the arylamine structure by the electron-accepting compound, the compound becomes a doped cationic salt, which is thought to have good electrical properties. Therefore, it is thought that the compounds represented by the above formulas (3) to (5) can achieve the desired effect. Among these, the compounds represented by formulas (4) and (5) are more preferable from the viewpoint of having a shallower HOMO level and high hole transportability than the compound represented by formula (3).

[0254] Furthermore, it is preferable that the protective layer contains a curable compound having no hole-transporting skeleton or a cured product thereof together with the electron-accepting compound. It is presumed that the hardness of the film can be improved by further containing a cured product of a curable compound having no hole-transporting skeleton in the protective layer.

[0255] Furthermore, from the results of the above Examples and Comparative Examples, as well as the results of tests conducted by the present inventors, it has been found that, in an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, the electrical properties of the electrophotographic photoreceptor, particularly the residual potential and potential holding ratio, can be improved as long as the electrophotographic photoreceptor contains 0.001% by mass or more of boron atoms relative to the total mass (100% by mass) of all layers of the electrophotographic photoreceptor. This is thought to be because, when the electrophotographic photoreceptor contains a certain amount of boron atoms, the charge injection barrier between adjacent layers can be reduced due to the electron-accepting effect of the boron atoms, and as a result, the electrical properties, particularly the residual potential and potential holding ratio, can be improved.

[0256] <<Test Example 2>> In Test Example 2, in addition to the electron-accepting compounds 1 and 2 used in Test Example 1, the following electron-accepting compounds 3 and 4 were used as the electron-accepting compounds. In addition, the hole-transporting compounds 1 and 2 used in Test Example 1 were used as the hole-transporting compounds.

[0257] <Electron Accepting Compound 3> Electron accepting compound 3 represented by the following structural formula, manufactured by Tokyo Chemical Industry Co., Ltd., was used.

[0258]

[0259] <Electron Accepting Compound 4> Furthermore, as a comparative object not containing a boron atom, electron accepting compound 4 (manufactured by Tokyo Chemical Industry Co., Ltd.) represented by the following structural formula was used.

[0260]

[0261] <LUMO Level (eV) and HOMO Level (eV) of Electron-Accepting Compound, and LUMO Level (eV) and HOMO Level (eV) of Hole-Transporting Compound> LUMO Levels (LUMO) of Electron-Accepting Compounds 1 to 4 dop ) and HOMO level (HOMO dop ), and the LUMO levels of the hole transporting compounds 1 and 2 (LUMO HTM ) and HOMO level (HOMO HTM　 ) are shown in Table 2 below.

[0262]

[0263] (Preparation of coating liquid for forming undercoat layer and coating liquid for forming charge generation layer) In Test Example 2, similarly to Test Example 1, coating liquid P1 for forming undercoat layer, coating liquid Q1 for forming charge generation layer, and coating liquid Q2 for forming charge transport layer were prepared.

[0264] (Preparation of Protective Layer-Forming Coating Liquid S1) The hole-transporting compound 1, a curable compound not having a hole-transporting skeleton (dipentaerythritol polyacrylate: product name "NK Ester A-DPH" manufactured by Shin-Nakamura Chemical Co., Ltd.) previously dissolved in a mixed solvent of toluene and 2-propanol, the electron-accepting compound 1, and Omnirad TPO H (2,4,6-trimethylbenzoyl-diphenylphosphine oxide) and benzophenone (BP) as polymerization initiators were mixed to obtain a protective layer-forming coating liquid S1 (solids concentration: approximately 25%) having a ratio of hole-transporting compound / A-DPH / electron-accepting compound / TPO+BP=35 / 65 / 3.5 / 3 (mass ratio) and a solvent composition of toluene / 2-propanol=3 / 7 (mass ratio).

[0265] (Preparation of protective layer-forming coating liquids S2 to S4, S12, S14, and S15) Protective layer-forming coating liquids S2 to S4, S12, S14, and S15 were obtained in the same manner as the protective layer-forming coating liquid S1, except that the type and amount of the hole transporting compound, the type and amount of the electron accepting compound, and the type and amount of the curable compound not having a hole transporting skeleton were changed as shown in Table 3.

[0266] <Preparation of Multilayer Photoreceptor> A multilayer photoreceptor was prepared by the following procedure.

[0267] Example 2-1: An aluminum cylinder with a machined surface, 30 mm in diameter, 357.4 mm in length, and 0.75 mm in thickness, was dip-coated with Coating Solution P1 for forming an undercoat layer and air-dried to form an undercoat layer with a film thickness of 1.5 μm after drying. Coating Solution Q1 for forming a charge generation layer was dip-coated on the undercoat layer and air-dried to form a charge generation layer with a film thickness of 0.4 μm after drying. Coating Solution Q2 for forming a charge transport layer was dip-coated on the charge generation layer and dried at 125°C for 24 minutes to form a charge transport layer with a film thickness of 17 μm after drying. Next, Coating Solution S1 for forming a protective layer was ring-coated on the charge transport layer, and the photoreceptor was rotated at 60 rpm in a nitrogen atmosphere (oxygen concentration 0.1% or less) while irradiating the photoreceptor with 365 nm LED light at an illuminance of 0.5 mW / cm. ２ for 2 minutes (accumulated light intensity: 19 mJ / cm ２ ), a protective layer was provided so that the thickness after curing would be 3.0 μm, thereby preparing photoreceptor B1.

[0268] [Examples 2-2 to 2-6 and Comparative Example 2-1] Photoreceptors B2 to B7 were produced in the same manner as photoreceptor B1, except that protective layer-forming coating liquid S1 was changed to a protective layer-forming coating liquid having a coating liquid number listed in Table 3.

[0269] <Electrical Properties: Evaluation of Residual Potential> The photoreceptors B1 to B7 obtained in the examples and comparative examples were mounted on an electrophotographic property evaluation device manufactured in accordance with the measurement standards of the Society of Electrophotography (described in "Continued Fundamentals and Applications of Electrophotography Technology," edited by the Society of Electrophotography, Corona Publishing, pp. 404-405), and the electrical properties were measured through a cycle of charging, exposure, potential measurement, and neutralization as follows. First, the grid voltage was adjusted to charge the photoreceptor so that the initial surface potential (V0) was -700 V. Next, the exposure light was applied at 1.3 μJ / cm ２ The residual potential (VL) was measured 60 milliseconds after irradiation. The exposure light was a halogen lamp light converted to monochromatic light of 780 nm using an interference filter. The measurement was performed in an N / N environment at a temperature of 25°C and a relative humidity of 50%.

[0270] The residual potential (VL) is shown in Table 3. The smaller the absolute value of the residual potential (VL), the better the result, since it means that the charge has been transported sufficiently and the potential has decreased.

[0271] <Evaluation of Electrical Properties: Potential Retention Rate> Photoreceptors B1 to B7 obtained in the examples and comparative examples were mounted on an electrophotographic property evaluation device manufactured in accordance with the measurement standards of the Society of Electrophotography (described in "Continued Fundamentals and Applications of Electrophotography Technology," edited by the Society of Electrophotography, Corona Publishing, pp. 404-405), and the electrical properties were measured as follows, using a cycle of charging, exposure, potential measurement, and neutralization. First, the grid voltage was adjusted to charge the photoreceptor so that the initial surface potential (V0) was -700 V. After charging, the potential retention rate (dark decay, DDR) (%) was measured after leaving it for 5 seconds. The measurement was performed in an environment of 25°C temperature and 50% relative humidity (N / N environment).

[0272] The potential retention rate is shown in Table 3. The potential retention rate represents the surface potential retention rate (%) when the photoconductor with a charged surface is left for a certain period of time. A higher surface potential retention rate (%) is considered a good result, since the potential is maintained even over time and the charging properties are good.

[0273]

[0274] <Discussion> From the results of Test Example 2 above and the results of tests conducted by the present inventors up to now, it has been found that an electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support has good electrical properties when it contains a hole transporting compound and an electron accepting compound that satisfy the following formula (I). This is thought to be because, when formula (I) is satisfied, charge transport from the HOMO (highest occupied molecular orbital) of the hole transporting compound to the LUMO (lowest unoccupied molecular orbital) of the electron accepting compound is promoted, resulting in good hole transport properties. 0<LUMO dop -HOMO HTM　 ≦2.0 (I) (In formula (I), LUMO dop represents the LUMO level (eV) of the electron-accepting compound, and HOMO HTM　 represents the HOMO level (eV) of the hole-transporting compound.) In contrast, the comparative example using an electron-accepting compound not containing a boron atom did not satisfy formula (I) and had poor electrical properties.

[0275] Furthermore, it has been found that the electrical properties are further improved when the hole transporting compound and the electron accepting compound satisfying the following formula (II) are contained. This is thought to be because, when formula (II) is satisfied, the HOMO of the hole transporting compound after doping with the electron accepting compound does not become too deep, resulting in good hole injection properties from the photosensitive layer to the protective layer. |HOMO dop -HOMO HTM　 |≦2.5 (II) (In formula (II), HOMOdop represents the HOMO level (eV) of the electron-accepting compound.)

Claims

1. An electrophotographic photoreceptor having at least a photosensitive layer and a protective layer on a conductive support, wherein the protective layer contains a hole transporting compound and an electron accepting compound, and the electron accepting compound is a compound containing a boron atom.

2. The electrophotographic photoreceptor according to claim 1, wherein the electron-accepting compound is a compound represented by the following formula (1) or (2): (In formula (1) or formula (2), R 11 ~R 13 and R 21 ~R 24 Each of o, p, q, r, s, t, and u independently represents a hydrogen atom, a deuterium atom, a halogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. Each of o, p, q, r, s, t, and u represents an integer of 1 or more and 5 or less. １ , Ph ２ , Ph ３ , Ph ４ are symbols that refer to each benzene ring.) 3. The electrophotographic photoreceptor according to claim 1 or 2, wherein the hole transporting compound is any one of compounds represented by the following formulas (3) to (5): (In formulas (3) to (5), Ar 1 ~Ar 7 , Ar 9 ~Ar 11 each independently represents an alkyl group which may have a substituent, an alkenyl group which may have a substituent, an alkoxy group which may have a substituent, an aryloxy group which may have a substituent, a heteroaryloxy group which may have a substituent, an alkoxycarbonyl group which may have a substituent, a dialkylamino group which may have a substituent, a diarylamino group which may have a substituent, an arylalkylamino group which may have a substituent, an acyl group which may have a substituent, a haloalkyl group which may have a substituent, an alkylthio group which may have a substituent, an arylthio group which may have a substituent, a silyl group which may have a substituent, a siloxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or an aromatic heterocyclic group which may have a substituent. 8 represents an aromatic hydrocarbon group which may have a substituent or an aromatic heterocyclic group which may have a substituent; and m and n each represent an integer of 1 or more.

4. The electrophotographic photoreceptor according to claim 3, wherein the hole transporting compound has at least one polymerizable functional group in one molecule.

5. The electrophotographic photoreceptor according to claim 4, wherein the polymerizable functional group is selected from the following formulae (M1) to (M7): (In formulas (M1) to (M7), R 110 represents a hydrogen atom or an alkyl group which may have a substituent, and * represents the bonding position.

6. The electrophotographic photoreceptor according to claim 1 or 2, wherein the mass ratio of the electron-accepting compound to the hole-transporting compound in the protective layer is 0.001 or more and 1.0 or less.

7. The electrophotographic photoreceptor according to claim 1 or 2, wherein the hole transporting compound and the electron accepting compound in the protective layer satisfy the following formula (I): 0<LUMO dop -HOMO HTM　 ≦ 2.0 (I) (In formula (I), LUMO dop represents the LUMO level (eV) of the electron-accepting compound, and HOMO HTM represents the HOMO level (eV) of the hole transporting compound.

8. The electrophotographic photoreceptor according to claim 7, further satisfying the following formula (II): |HOMO dop -HOMO HTM　 |≦2.5(II) (in formula (II), HOMO dop represents the HOMO level (eV) of the electron-accepting compound.

9. The aforementioned LUMO dop 8. The electrophotographic photoreceptor according to claim 7, wherein the potential is −4.7 eV or more and −3.0 eV or less.

10. The aforementioned HOMO HTM　 8. The electrophotographic photoreceptor according to claim 7, wherein the potential is −5.5 eV or more and −4.0 eV or less.

11. The aforementioned HOMO dop 9. The electrophotographic photoreceptor according to claim 8, wherein the potential is −7.2 eV or more and −5.5 eV or less.

12. The electrophotographic photoreceptor according to claim 1 or 2, wherein the photosensitive layer contains an arylamine compound.

13. The electrophotographic photoreceptor according to claim 12, wherein the arylamine compound comprises a compound represented by the following formula (200) or (201): (In formula (200) or (201), Ar HTM are groups selected from the following formulae (200-1) to (200-3), and may be the same or different. (In formulas (200), (201), and (200-1) to (200-3), each R independently represents a hydrogen atom, an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aromatic hydrocarbon group which may have a substituent, an aromatic heterocyclic group which may have a substituent, or a halogen atom. h1 represents an integer of 0 to 5, and h4 represents an integer of 0 to 2. * represents a bonding position.) 14. The electrophotographic photoreceptor according to claim 12, wherein the photosensitive layer is a laminated type photosensitive layer including a charge generating layer and a charge transporting layer, and the charge transporting layer contains an arylamine compound.

15. The electrophotographic photoreceptor according to claim 12, wherein the mass ratio of the electron-accepting compound to the arylamine compound is 0.001 or more and 0.9 or less.

16. The electrophotographic photoreceptor according to claim 1 or 2, wherein the protective layer further contains a cured product of a curable compound having no hole transporting skeleton.

17. The electrophotographic photoreceptor according to claim 1 or 2, which contains boron atoms in an amount of 0.001% by mass or more based on the total mass of all layers (excluding the conductive support) of the electrophotographic photoreceptor.

18. An electrophotographic photoreceptor cartridge comprising the electrophotographic photoreceptor according to claim 1 or 2.

19. An image forming apparatus having the electrophotographic photosensitive member according to claim 1 or 2.

Images