JP7528678B2 - Electrophotographic photoreceptor, process cartridge, and image forming apparatus - Google Patents

Description

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

Electrophotographic photoreceptors are used as image carriers in electrophotographic image forming apparatuses (e.g., printers or multifunction machines). Electrophotographic photoreceptors have a photosensitive layer. The electrophotographic photoreceptor provided in the image forming apparatus described in Patent Document 1 contains a bisphenol Z-type polycarbonate resin as a binder resin at least in the photosensitive layer, which is the surface layer.

Japanese Patent Application Publication No. 8-234538

However, the inventors' investigations revealed that the electrophotographic photoreceptor provided in the image forming apparatus described in Patent Document 1 is insufficient in terms of positive charging ability when positive and negative charging are repeated, and in terms of sensitivity characteristics.

The present invention has been made in consideration of the above problems, and its object is to provide an electrophotographic photoreceptor that can be positively charged well even when positive and negative charging are repeated, and has excellent sensitivity characteristics. Another object of the present invention is to provide a process cartridge and an image forming apparatus that are equipped with such an electrophotographic photoreceptor and are capable of forming good images.

The electrophotographic photoreceptor of the present invention comprises a conductive substrate and a photosensitive layer. The photosensitive layer is a single layer and contains a charge generating agent, an electron transport agent, a binder resin, a hole transport agent, and an n-type pigment. The electron transport agent contains a compound represented by general formula (1).

In the general formula (1), ^R1 and ^R2 each independently represent an aryl group, which may be substituted by 1 to 5 substituents selected from the group consisting of a halogen atom, an alkyl group, and an alkoxy group, a hydrogen atom, an alkyl group, a heterocyclic group, an alkoxy group, an aralkyl group, or an allyl group.

The process cartridge of the present invention includes at least one selected from the group consisting of a charging device, an exposure device, a developing device, a transfer device, a cleaning member, and a static eliminator, and the electrophotographic photosensitive member already described.

The image forming apparatus of the present invention includes an image carrier, a charging device, an exposure device, a developing device, and a transfer device. The charging device charges the surface of the image carrier to a positive polarity. The exposure device exposes the charged surface of the image carrier to light to form an electrostatic latent image on the surface of the image carrier. The developing device develops the electrostatic latent image as a toner image. The transfer device transfers the toner image from the image carrier to a transfer target. The image carrier is the electrophotographic photosensitive member already described.

The electrophotographic photoreceptor of the present invention can be positively charged well even when it is repeatedly positively and negatively charged, and has excellent sensitivity characteristics. Furthermore, the process cartridge and image forming apparatus of the present invention equipped with such an electrophotographic photoreceptor can form good images.

1 is a partial cross-sectional view illustrating an example of an electrophotographic photoreceptor according to a first embodiment of the present invention. 1 is a partial cross-sectional view illustrating an example of an electrophotographic photoreceptor according to a first embodiment of the present invention. 1 is a partial cross-sectional view illustrating an example of an electrophotographic photoreceptor according to a first embodiment of the present invention. FIG. 11 is a cross-sectional view illustrating an example of an image forming apparatus according to a second embodiment of the present invention. 5 is a diagram showing the image carrier and cleaning member shown in FIG. 4, and a control device. FIG. 6 is a time chart showing the control of the cleaning member in a printing mode and a cleaning mode. FIG. FIG. 5 is a flow chart illustrating control of the image forming apparatus shown in FIG. 4 .

The following describes in detail the embodiments of the present invention. However, the present invention is not limited to the following embodiments, and can be practiced with appropriate modifications within the scope of the object of the present invention. Hereinafter, the compound and its derivatives may be collectively referred to by adding "system" after the compound name. In addition, when the compound name is followed by "system" to represent the name of a polymer, it means that the repeating unit of the polymer is derived from the compound or its derivative. "Independently" in the explanation of the general formula means that they may be the same or different. Each component described in the specification may be used alone or in combination of two or more types.

First, the substituents used in this specification will be described. Examples of halogen atoms (halogen groups) include fluorine atoms (fluoro groups), chlorine atoms (chloro groups), bromine atoms (bromo groups), and iodine atoms (iodo groups).

Unless otherwise specified, alkyl groups having 1 to 8 carbon atoms, alkyl groups having 1 to 6 carbon atoms, alkyl groups having 1 to 4 carbon atoms, and alkyl groups having 1 to 3 carbon atoms are each linear or branched and unsubstituted. Examples of alkyl groups having 1 to 8 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl, 2-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, n-hexyl, 1-methylpentyl, 2 ... Examples of alkyl groups include 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethylbutyl, 2-ethylbutyl, and 3-ethylbutyl, linear and branched heptyl groups, and linear and branched octyl groups. Examples of alkyl groups having 1 to 6 carbon atoms, examples of alkyl groups having 1 to 4 carbon atoms, and examples of alkyl groups having 1 to 3 carbon atoms are groups having the corresponding number of carbon atoms among the groups mentioned as examples of alkyl groups having 1 to 8 carbon atoms.

Alkoxy groups having 1 to 8 carbon atoms, alkoxy groups having 1 to 6 carbon atoms, and alkoxy groups having 1 to 3 carbon atoms are each linear or branched and unsubstituted unless otherwise specified. Examples of alkoxy groups having 1 to 8 carbon atoms include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, n-pentoxy, 1-methylbutoxy, 2-methylbutoxy, 3-methylbutoxy, 1-ethylpropoxy, 2-ethylpropoxy, 1,1-dimethylpropoxy, 1,2-dimethylpropoxy, 2,2-dimethylpropoxy, n-hexyloxy, 1-methylpentyloxy, 2 ... Examples of alkoxy groups include alkoxy groups having 1 to 6 carbon atoms, and alkoxy groups having 1 to 3 carbon atoms are groups having the corresponding number of carbon atoms among the groups mentioned as examples of alkoxy groups having 1 to 8 carbon atoms.

Unless otherwise specified, the aryl group having 6 to 14 carbon atoms and the aryl group having 6 to 10 carbon atoms are each unsubstituted. Examples of the aryl group having 6 to 14 carbon atoms include a phenyl group, a naphthyl group, an indacenyl group, a biphenylenyl group, an acenaphthylenyl group, an anthryl group, and a phenanthryl group. Examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

Unless otherwise specified, aralkyl groups having 7 to 20 carbon atoms and aralkyl groups having 7 to 13 carbon atoms are each unsubstituted. An aralkyl group having 7 to 20 carbon atoms is, for example, an alkyl group having 1 to 6 carbon atoms substituted with an aryl group having 6 to 14 carbon atoms. An aralkyl group having 7 to 13 carbon atoms is, for example, an alkyl group having 1 to 3 carbon atoms substituted with an aryl group having 6 to 10 carbon atoms.

The 5- to 14-membered heterocyclic group and the 5- or 6-membered heterocyclic group are each unsubstituted unless otherwise specified. Examples of the 5- to 14-membered heterocyclic group include a 5- or 6-membered monocyclic heterocyclic group containing 1 to 3 heteroatoms other than carbon atoms; a heterocyclic group in which two such monocyclic heterocyclic rings are condensed; a heterocyclic group in which such a monocyclic heterocyclic ring is condensed with a 5- or 6-membered monocyclic hydrocarbon ring; a heterocyclic group in which three such monocyclic heterocyclic rings are condensed; a heterocyclic group in which two such monocyclic heterocyclic rings are condensed with one 5- or 6-membered monocyclic hydrocarbon ring; or a heterocyclic group in which one such monocyclic heterocyclic ring is condensed with two 5- or 6-membered monocyclic hydrocarbon rings. Specific examples of the 5- to 14-membered heterocyclic group include a piperidinyl group, a piperazinyl group, a morpholinyl group, a thiophenyl group, a furanyl group, a pyrrolyl group, an imidazolyl group, a pyrazolyl group, an isothiazolyl group, an isoxazolyl group, an oxazolyl group, an isoxazolyl group, a thiazolyl group, an isothiazolyl group, a furazanyl group, a pyranyl group, a pyridyl group, a pyridazinyl group, a pyrimidinyl group, a pyrazinyl group, an indolyl group, and a 1H-indazolyl group. Examples of the heterocyclic groups include isoindolyl, chromenyl, quinolinyl, isoquinolinyl, purinyl, pteridinyl, triazolyl, tetrazolyl, 4H-quinolizinyl, naphthyridinyl, benzofuranyl, 1,3-benzodioxolyl, benzoxazolyl, benzothiazolyl, benzimidazolyl, carbazolyl, phenanthridinyl, acridinyl, phenazinyl, and phenanthrolinyl. The 5- or 6-membered heterocyclic group is a group having the corresponding number of ring members among the groups mentioned as examples of the heterocyclic group having 5 to 14 members. The above describes the substituents used in this specification.

[First embodiment: electrophotographic photoreceptor]
The first embodiment of the present invention relates to an electrophotographic photoreceptor (hereinafter, may be referred to as a photoreceptor). The structure of a photoreceptor 1 of the first embodiment will be described below with reference to Figures 1 to 3. Each of Figures 1 to 3 shows a partial cross-sectional view of the photoreceptor 1.

As shown in FIG. 1, the photoreceptor 1 includes a conductive substrate 2 and a photosensitive layer 3. The photosensitive layer 3 is a single layer. The photoreceptor 1 is a single-layer electrophotographic photoreceptor that includes a single photosensitive layer 3.

As shown in FIG. 2, the photoreceptor 1 may further include an intermediate layer 4 (undercoat layer) in addition to the conductive substrate 2 and the photosensitive layer 3. The intermediate layer 4 is provided between the conductive substrate 2 and the photosensitive layer 3. As shown in FIG. 1, the photosensitive layer 3 may be provided directly on the conductive substrate 2. Alternatively, as shown in FIG. 2, the photosensitive layer 3 may be provided on the conductive substrate 2 via the intermediate layer 4.

As shown in FIG. 3, the photoreceptor 1 may further include a protective layer 5 in addition to the conductive substrate 2 and the photosensitive layer 3. The protective layer 5 is provided on the photosensitive layer 3. As shown in FIGS. 1 and 2, the photosensitive layer 3 may be provided as the outermost layer of the photoreceptor 1. Alternatively, as shown in FIG. 3, the protective layer 5 may be provided as the outermost layer of the photoreceptor 1.

The thickness of the photosensitive layer 3 is not particularly limited, but is preferably 5 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less. Above, the structure of the photoreceptor 1 has been described with reference to Figures 1 to 3.

The photoreceptor will be described in more detail below. The photosensitive layer contains a charge generating agent, an electron transport agent, a binder resin, a hole transport agent, and an n-type pigment. The photosensitive layer may contain additives as necessary. The charge generating agent, the electron transport agent, the binder resin, the hole transport agent, the n-type pigment, and the additives will be described below.

(Charge generating material)
Examples of the charge generating agent include phthalocyanine pigments, perylene pigments, bisazo pigments, trisazo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, indigo pigments, azulenium pigments, cyanine pigments, powders of inorganic photoconductive materials (e.g., selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, or amorphous silicon), pyrylium pigments, anthanthrone pigments, triphenylmethane pigments, threne pigments, toluidine pigments, pyrazoline pigments, and quinacridone pigments.

Examples of phthalocyanine pigments include metal-free phthalocyanine and metal phthalocyanine. Examples of metal phthalocyanine include titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine. Metal-free phthalocyanine is represented by the chemical formula (CGM-1). Titanyl phthalocyanine is represented by the chemical formula (CGM-2).

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

For example, in a digital optical image forming device (for example, a laser beam printer or facsimile using a light source such as a semiconductor laser), it is preferable to use a photoreceptor that is sensitive in the wavelength region of 700 nm or more. As the charge generating agent, a phthalocyanine pigment is preferable because it has a high quantum yield in the wavelength region of 700 nm or more, and metal-free phthalocyanine or titanyl phthalocyanine is more preferable, X-type metal-free phthalocyanine or Y-type titanyl phthalocyanine is even more preferable, and Y-type titanyl phthalocyanine is particularly preferable.

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

The CuKα characteristic X-ray diffraction spectrum can be measured, for example, by the following method. First, the sample (titanyl phthalocyanine) is loaded into the sample holder of an X-ray diffraction device (for example, Rigaku Corporation's "RINT (registered trademark) 1100"), and the X-ray diffraction spectrum is measured under the conditions of a Cu X-ray tube, a tube voltage of 40 kV, a tube current of 30 mA, and a wavelength of 1.542 Å for the CuKα characteristic X-rays. The measurement range (2θ) is, for example, 3° to 40° (start angle 3°, stop angle 40°), and the scanning speed is, for example, 10°/min. The main peak is determined from the obtained X-ray diffraction spectrum, and the Bragg angle of the main peak is read.

The content of the charge generating agent is preferably 0.1 parts by weight or more and 50 parts by weight or less, and more preferably 1 part by weight or more and 10 parts by weight or less, relative to 100 parts by weight of the binder resin.

(Electron Transport Agent)
The electron transport material includes a compound represented by general formula (1) (hereinafter, may be referred to as electron transport material (1)).

In general formula (1), ^R1 and ^R2 each independently represent an aryl group which may be substituted with 1 to 5 substituents selected from the group consisting of a halogen atom, an alkyl group, and an alkoxy group; a hydrogen atom; an alkyl group; a heterocyclic group; an alkoxy group; an aralkyl group; or an allyl group.

By containing the electron transport agent (1) in the photosensitive layer, the photosensitive body can be positively charged well even when the photosensitive body is repeatedly positively and negatively charged. Such a photosensitive body is particularly suitable for use in the image forming apparatus of the second embodiment described later. Specifically, in the printing mode, the photosensitive body is particularly suitable for use in an image forming apparatus having a configuration in which the charging device charges the surface of the photosensitive body to a positive polarity and a negative first voltage (a voltage of a polarity opposite to the charging polarity of the toner) is applied to the cleaning member. When such an image forming apparatus is provided with a photosensitive body, in the printing mode, the surface of the photosensitive body is repeatedly charged to a positive polarity by the charging device, and the potential of the photosensitive body is repeatedly lowered to a negative polarity by contact with the cleaning member to which the negative first voltage is applied. For this reason, the photosensitive body is repeatedly positively and negatively charged. As already mentioned, the photosensitive body of the first embodiment is effectively positively charged even when the photosensitive body is repeatedly positively and negatively charged. Therefore, even when the photoconductor of the first embodiment is installed in the image forming apparatus of the second embodiment, it can be suitably charged to the desired positive potential in the charging process of image formation.

The aryl group represented by ^R1 and ^R2 in the general formula (1) is, for example, an aryl group having 6 to 14 carbon atoms. The aryl group having 6 to 14 carbon atoms is preferably a phenyl group or a naphthyl group. The naphthyl group is preferably a 1-naphthyl group or a 2-naphthyl group.

The aryl group represented by R ¹ and R ² may be substituted with 1 to 5 substituents selected from the group consisting of halogen atoms, alkyl groups, and alkoxy groups. The halogen atom as the substituent is preferably a chlorine atom or a bromine atom. The alkyl group as the substituent is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group. The alkoxy group as the substituent is preferably an alkoxy group having 1 to 6 carbon atoms, more preferably an alkoxy group having 1 to 3 carbon atoms, and even more preferably a methoxy group. The group consisting of halogen atoms, alkyl groups, and alkoxy groups is preferably a group consisting of halogen atoms, alkyl groups having 1 to 6 carbon atoms, and alkoxy groups having 1 to 6 carbon atoms, more preferably a group consisting of halogen atoms, alkyl groups having 1 to 3 carbon atoms, and alkoxy groups having 1 to 3 carbon atoms, and particularly preferably a group consisting of chlorine atoms, bromine atoms, methyl groups, and methoxy groups. The number of substituents possessed by the aryl group represented by R ¹ and R ² is preferably 1 or 2.

The alkyl group represented by ^R1 and ^R2 is, for example, an alkyl group having from 1 to 6 carbon atoms. As the alkyl group having from 1 to 6 carbon atoms, an alkyl group having from 1 to 4 carbon atoms is preferable, and a methyl group, an n-propyl group, or a tert-butyl group is more preferable.

The heterocyclic group represented by R ¹ and R ² is, for example, a 5-membered to 14-membered heterocyclic group. As the 5-membered to 14-membered heterocyclic group, a 5-membered to 14-membered heterocyclic group containing at least one heteroatom other than carbon atoms is preferable, a 5-membered to 6-membered heterocyclic group containing at least one heteroatom other than carbon atoms is more preferable, and a 5-membered to 6-membered monocyclic heterocyclic group containing at least one heteroatom other than carbon atoms is even more preferable. The heteroatom is preferably at least one selected from the group consisting of a nitrogen atom, a sulfur atom, and an oxygen atom, more preferably at least one selected from the group consisting of a sulfur atom and an oxygen atom, and even more preferably a sulfur atom or an oxygen atom. As the 5-membered to 14-membered heterocyclic group, a thiophenyl group or a furanyl group is more preferable, and a 2-thiophenyl group or a 2-furanyl group is particularly preferable.

The alkoxy group represented by ^R1 and ^R2 is, for example, an alkoxy group having from 1 to 6 carbon atoms. As the alkoxy group having from 1 to 6 carbon atoms, an alkoxy group having from 1 to 3 carbon atoms is preferable, and a methoxy group is more preferable.

The aralkyl group represented by ^R1 and ^R2 is, for example, an aralkyl group having from 7 to 20 carbon atoms. As the aralkyl group having from 7 to 20 carbon atoms, an aralkyl group having from 7 to 13 carbon atoms is preferable, and a benzyl group, a phenylethyl group, or a naphthylmethyl group is more preferable.

The allyl group represented by R ¹ and R ² is represented by the chemical formula "CH ₂ ═CH-CH ₂ -".

In order to improve the positive chargeability when positive and negative charging are repeated, in the general formula (1), R ¹ and R ² each independently represent an aryl group having 6 to 14 carbon atoms, which may be substituted with one or more and five substituents selected from the group consisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms; an alkyl group having 1 to 6 carbon atoms; or a heterocyclic group having 5 to 14 carbon atoms. For the same reason, in the general formula (1), R ¹ represents an aryl group having 6 to 14 carbon atoms; an alkyl group having 1 to 6 carbon atoms; or a heterocyclic group having 5 to 14 carbon atoms, and R ² more preferably represents an aryl group having 6 to 14 carbon atoms, which may be substituted with one or two substituents selected from the group consisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms; or an alkyl group having 1 to 6 carbon atoms.

In order to improve the positive chargeability when positive and negative charging are repeated, in general formula (1), R ¹ and R ² each preferably independently represent an aryl group having 6 to 14 carbon atoms which may be substituted with one or two halogen atoms; or an alkyl group having 1 to 6 carbon atoms. For the same reason, in general formula (1), it is more preferable that R ¹ represents an aryl group having 6 to 14 carbon atoms; or an alkyl group having 1 to 6 carbon atoms, and R ² represents an aryl group having 6 to 14 carbon atoms which may be substituted with one or two halogen atoms; or an alkyl group having 1 to 6 carbon atoms.

Suitable examples of the electron transport agent (1) for improving the positive chargeability when positive and negative charging are repeated include compounds represented by chemical formulas (ETM1) to (ETM31) (hereinafter, these may be referred to as electron transport agents (ETM1) to (ETM31) respectively).

In order to improve the positive chargeability when positive and negative charging are repeated, more suitable examples of the electron transport agent (1) include electron transport agents (ETM1), (ETM2), (ETM6), (ETM7), (ETM8), (ETM19), (ETM22), (ETM23), (ETM24), (ETM28), and (ETM29).

The content of the electron transport agent is preferably 5 parts by mass or more and 150 parts by mass or less, more preferably 10 parts by mass or more and 80 parts by mass or less, and even more preferably 20 parts by mass or more and 60 parts by mass or less, relative to 100 parts by mass of the binder resin.

The photosensitive layer may contain only the electron transport agent (1) as the electron transport agent. The photosensitive layer may further contain, in addition to the electron transport agent (1), other electron transport agents as the electron transport agent. Examples of electron transport agents other than the electron transport agent (1) include quinone compounds, diimide compounds, hydrazone compounds, malononitrile compounds, thiopyran compounds, trinitrothioxanthone compounds, 3,4,5,7-tetranitro-9-fluorenone compounds, dinitroanthracene compounds, dinitroacridine compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride. Examples of quinone compounds include diphenoquinone compounds, azoquinone compounds, anthraquinone compounds, naphthoquinone compounds, nitroanthraquinone compounds, and dinitroanthraquinone compounds.

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

Among these resins, polycarbonate resin is preferred as the binder resin because it provides a photosensitive layer 3 with an excellent balance of processability, mechanical properties, optical properties, and abrasion resistance. Examples of polycarbonate resins include polycarbonate resins having a repeating unit represented by chemical formula (R1) (hereinafter, sometimes referred to as polycarbonate resin (R1)) and polycarbonate resins having a repeating unit represented by (R2) (hereinafter, sometimes referred to as polycarbonate resin (R2)).

The viscosity average molecular weight of the binder resin is preferably 10,000 or more, more preferably 20,000 or more, and particularly preferably 30,000 or more. When the viscosity average molecular weight of the binder resin is 10,000 or more, the abrasion resistance of the photoreceptor is improved. On the other hand, the viscosity average molecular weight of the binder resin is preferably 80,000 or less, and more preferably 70,000 or less. When the viscosity average molecular weight of the binder resin is 80,000 or less, the binder resin is easily dissolved in a solvent for forming the photosensitive layer.

(Hole Transport Agent)
Examples of the hole transport agent include oxadiazole compounds (e.g., 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole), styryl compounds (e.g., 9-(4-diethylaminostyryl)anthracene), carbazole compounds (e.g., polyvinylcarbazole), organic polysilane compounds, pyrazoline compounds (e.g., 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), hydrazone compounds, indole compounds, oxazole compounds, isoxazole compounds, thiazole compounds, thiadiazole compounds, imidazole compounds, pyrazole compounds, and triazole compounds.

In order to improve the positive chargeability and sensitivity characteristics when positive and negative charging are repeated, the hole transport agent preferably contains a compound represented by general formula (21), (22), (23), (24), (25), (26), or (27). Hereinafter, the compounds represented by general formulas (21) to (27) may be referred to as hole transport agents (21) to (27), respectively.

In the general formula (21), R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , and R ¹⁶ each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group. R ¹⁷ and R ¹⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group. b1, b2, b3, and b4 each independently represent an integer of 0 to 5. b5 and b6 each independently represent an integer of 0 to 4. d and e each independently represent 0 or 1.

In the general formula (21), when b1 represents an integer of 2 or more and 5 or less, the plurality of R ¹¹ may represent the same group or different groups. When b2 represents an integer of 2 or more and 5 or less, the plurality of R ¹² may represent the same group or different groups. When b3 represents an integer of 2 or more and 5 or less, the plurality of R ¹³ may represent the same group or different groups. When b4 represents an integer of 2 or more and 5 or less, the plurality of R ¹⁴ may represent the same group or different groups. When b5 represents an integer of 2 or more and 4 or less, the plurality of R ¹⁵ may represent the same group or different groups. When b6 represents an integer of 2 or more and 4 or less, the plurality of R ¹⁶ may represent the same group or different groups.

In the general formula (21), R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , and R ¹⁶ each independently preferably represent an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group or an ethyl group. R ¹⁷ and R ¹⁸ preferably represent a hydrogen atom. b1 and b2 preferably represent 0. b3 and b4 preferably represent 2. b5 and b6 preferably represent 0. d and e preferably represent 0.

In the general formula (22), ^R20 represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, or a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms. ^R21 , ^R22 , and ^R23 each independently represent an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms. f1, f2, and f3 each independently represent an integer of 0 to 5. f4 represents 0 or 1.

In the general formula (22), when f1 is an integer of 2 or more and 5 or less, the multiple ^R21 may represent the same group or different groups. When f2 is an integer of 2 or more and 5 or less, the multiple ^R22 may represent the same group or different groups. When f3 is an integer of 2 or more and 5 or less, the multiple ^R23 may represent the same group or different groups.

In the general formula (22), R ²⁰ preferably represents a phenyl group. R ²¹ , R ²² , and R ²³ each independently preferably represent an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group. f1 and f2 preferably represent 1. f3 preferably represents 0. As already mentioned, f4 represents 0 or 1.

In formula (23), R ³¹ , R ³² , R ³³ , R ³⁴ , and R ³⁵ each independently represent an alkyl group having 1 to 8 carbon atoms or an alkoxy group having 1 to 8 carbon atoms. g1, g2, g3, g4, and g5 each independently represent an integer of 0 to 5.

In the general formula (23), when g1 represents an integer of 2 or more and 5 or less, the plurality of R ³¹ may represent the same group or different groups. When g2 represents an integer of 2 or more and 5 or less, the plurality of R ³² may represent the same group or different groups. When g3 represents an integer of 2 or more and 5 or less, the plurality of R ³³ may represent the same group or different groups. When g4 represents an integer of 2 or more and 5 or less, the plurality of R ³⁴ may represent the same group or different groups. When g5 represents an integer of 2 or more and 5 or less, the plurality of R ³⁵ may represent the same group or different groups.

In formula (23), R ³¹ , R ³² , R ³³ , R ³⁴ , and R ³⁵ each independently preferably represent an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group. g1, g2, g3, g4, and g5 each preferably represent 1.

In general formula (24), ^R41 , ^R42 , ^R43 , ^R44 , ^R45 , and ^R46 each independently represent an alkyl group having 1 to 8 carbon atoms, a phenyl group, or an alkoxy group having 1 to 8 carbon atoms. h1, h2, h4, and h5 each independently represent an integer of 0 to 5. h3 and h6 each independently represent an integer of 0 to 4.

In the general formula (24), when h1 represents an integer of 2 or more and 5 or less, a plurality of R ⁴¹ may represent the same group or different groups. When h2 represents an integer of 2 or more and 5 or less, a plurality of R ⁴² may represent the same group or different groups. When h4 represents an integer of 2 or more and 5 or less, a plurality of R ⁴⁴ may represent the same group or different groups. When h5 represents an integer of 2 or more and 5 or less, a plurality of R ⁴⁵ may represent the same group or different groups. When h3 represents an integer of 2 or more and 4 or less, a plurality of R ⁴³ may represent the same group or different groups. When h6 represents an integer of 2 or more and 4 or less, a plurality of R ⁴⁶ may represent the same group or different groups.

In general formula (24), R ⁴¹ , R ⁴² , R ⁴³ , R ⁴⁴ , R ⁴⁵ , and R ⁴⁶ each independently preferably represent an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group or an ethyl group. h1, h2, h4, and h5 each independently preferably represent an integer of 0 to 2. h3 and h6 each preferably represent 0.

In formula (25), R ⁷¹ , R ⁷² , R ⁷³ , and R ⁷⁴ each independently represent an alkyl group having 1 to 8 carbon atoms. j1, j2, j3, and j4 each independently represent an integer of 0 to 5.

In the general formula (25), when j1 represents an integer of 2 or more and 5 or less, the multiple R ⁷¹ may represent the same group or different groups. When j2 represents an integer of 2 or more and 5 or less, the multiple R ⁷² may represent the same group or different groups. When j3 represents an integer of 2 or more and 5 or less, the multiple R ⁷³ may represent the same group or different groups. When j4 represents an integer of 2 or more and 5 or less, the multiple R ⁷⁴ may represent the same group or different groups.

In formula (25), R ⁷¹ , R ⁷² , R ⁷³ , and R ⁷⁴ each independently preferably represent an alkyl group having 1 to 3 carbon atoms, more preferably a methyl group or an ethyl group. j1, j2, j3, and j4 each independently preferably represent 0 or 1.

In the general formula (26), R ⁸¹ , R ⁸² , and R ⁸³ each independently represent an alkyl group having 1 to 8 carbon atoms, a phenyl group, or an alkoxy group having 1 to 8 carbon atoms. R ⁸⁴ and R ⁸⁵ each independently represent a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms, a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms. k1, k2, and k3 each independently represent an integer of 0 to 5. k4 and k5 each independently represent 1 or 2.

In the general formula (26), when k1 is an integer of 2 or more and 5 or less, a plurality of R ⁸¹ may represent the same group or different groups. When k2 is an integer of 2 or more and 5 or less, a plurality of R ⁸² may represent the same group or different groups. When k3 is an integer of 2 or more and 5 or less, a plurality of R ⁸³ may represent the same group or different groups.

In the general formula (26), R ⁸¹ , R ⁸² , and R ⁸³ each independently represent an alkoxy group having 1 to 8 carbon atoms, more preferably an alkoxy group having 1 to 6 carbon atoms, and even more preferably an ethoxy group. R ⁸⁴ and R ⁸⁵ each preferably represent a hydrogen atom. k1 and k2 each preferably represent 0. k3 each preferably represents 1. k4 and k5 each preferably represent 1.

In formula (27), R ⁶¹ , R ⁶² and R ⁶³ each independently represent an alkyl group having 1 to 8 carbon atoms. ^{R 64} , R ⁶⁵ and R ⁶⁶ each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.

In general formula (27), R ⁶¹ , R ⁶² and R ⁶³ each independently preferably represent an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a methyl group. R ⁶⁴ , R ⁶⁵ and R ⁶⁶ each preferably represent a hydrogen atom.

More suitable examples of the hole transport agent include compounds represented by chemical formulas (HTM1) to (HTM10) (hereinafter, each of which may be referred to as hole transport agents (HTM1) to (HTM10)).

The content of the hole transport agent is preferably 10 parts by mass or more and 300 parts by mass or less, and more preferably 10 parts by mass or more and 150 parts by mass or less, relative to 100 parts by mass of the binder resin.

(n-type pigment)
An n-type pigment is a pigment in which the main charge carrier is an electron. A p-type pigment is a pigment in which the main charge carrier is a hole. An n-type pigment tends to coordinate to a site represented by the chemical formula "=N-N<" of the electron transport agent (1). Therefore, when the photosensitive layer contains an n-type pigment in addition to the electron transport agent (1), the photosensitive layer improves the sensitivity characteristics of the photosensitive layer in addition to the positive charging property of the photosensitive layer when positive and negative charging are repeated. Furthermore, when the photosensitive layer contains an n-type pigment, the dispersibility of the charge generating agent in the photosensitive layer is improved.

Suitable examples of n-type pigments for improving sensitivity characteristics include azo pigments, perylene pigments, and isoindoline pigments.

Azo pigments are described below. Azo pigments are pigments that have an azo group (-N=N-). Examples of azo pigments include monoazo pigments and polyazo pigments (e.g., bisazo pigments, trisazo pigments, and tetrakisazo pigments). Azo pigments may be tautomers. Azo pigments may also have a chlorine atom (chloro group) in addition to the azo group.

Examples of azo pigments include known azo pigments. Suitable examples of azo pigments include Pigment Yellow (14, 17, 49, 65, 73, 83, 93, 94, 95, 128, 166, and 77), Pigment Orange (1, 2, 13, 34, and 36), and Pigment Red (30, 32, 61, and 144).

When the n-type pigment includes an azo pigment, suitable examples of the azo pigment include compounds represented by chemical formulas (A1), (A2), (A3), (A4), and (A5) (hereinafter, these may be referred to as azo pigments (A1), (A2), (A3), (A4), and (A5), respectively).

Next, the perylene pigment will be described. The perylene pigment has a perylene skeleton represented by general formula (PI). In general formula (PI), Q ⁴⁰ and Q ⁴¹ each independently represent a divalent organic group.

A first specific example of a perylene pigment is a perylene pigment represented by general formula (P-II).

In formula (P-II), Q ⁴² and Q ⁴³ each independently represent a hydrogen atom or a monovalent organic group, Z ¹ and Z ² each independently represent an oxygen atom or a nitrogen atom.

In general formula (P-II), examples of the monovalent organic group represented by Q and ^Q include an ^aliphatic hydrocarbon group, an alkoxy group, an optionally substituted aralkyl group, an optionally substituted aryl group, and an optionally substituted heterocyclic group.

In the general formula (P-II), the aliphatic hydrocarbon group represented by Q ⁴² and Q ⁴³ may be linear, branched, cyclic, or a combination of these structures. The aliphatic hydrocarbon group is saturated or unsaturated, and is preferably saturated. In the general formula (P-II), the aliphatic hydrocarbon group represented by Q ⁴² and Q ⁴³ is preferably an aliphatic hydrocarbon group having 1 to 20 carbon atoms, more preferably an aliphatic hydrocarbon group having 1 to 10 carbon atoms. As the aliphatic hydrocarbon group having 1 to 10 carbon atoms, preferably an alkyl group having 1 to 8 carbon atoms, more preferably an alkyl group having 1 to 6 carbon atoms, even more preferably an alkyl group having 1 to 3 carbon atoms, and particularly preferably a methyl group or an ethyl group.

In formula (P-II), the alkoxy group represented by Q ⁴² and Q ⁴³ is preferably an alkoxy group having 1 to 6 carbon atoms, more preferably an alkoxy group having 1 to 3 carbon atoms, and further preferably a methoxy group or an ethoxy group.

In formula (P-II), the aralkyl group represented by Q ⁴² and Q ⁴³ is preferably an aralkyl group having from 7 to 13 carbon atoms, more preferably a benzyl group, a phenethyl group, an α-naphthylmethyl group, or a β-naphthylmethyl group, and still more preferably a benzyl group or a phenethyl group.

In formula (P-II), the aryl group represented by Q ⁴² and Q ⁴³ is preferably an aryl group having 6 to 14 carbon atoms, more preferably an aryl group having 6 to 10 carbon atoms, and even more preferably a phenyl group.

In general formula (P-II), the ^heterocyclic group represented by Q and ^Q is preferably a heterocyclic group having 5 to 14 carbon atoms, more preferably a heterocyclic group having 5 to 14 carbon atoms and a nitrogen atom as a heteroatom, and further preferably a pyridyl group.

In general formula (P-II), the ^aralkyl group, aryl group, and heterocyclic group represented by Q and ^Q may be substituted with a substituent. Such a substituent is preferably an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a phenyl group, a halogen atom, a hydroxyl group, a cyano group, a nitro group, or a phenylazo group, and more preferably an alkyl group having 1 to 6 carbon atoms (e.g., a methyl group), a halogen atom (e.g., a chlorine atom), or a phenylazo group.

In the general formula (P-II), Q ⁴² and Q ⁴³ preferably represent an alkyl group having 1 to 6 carbon atoms; a heterocyclic group having 5 to 14 carbon atoms; an aralkyl group having 7 to 13 carbon atoms; an alkoxy group having 1 to 6 carbon atoms; an aryl group having 6 to 14 carbon atoms which may be substituted with an alkyl group having 1 to 6 carbon atoms, a halogen atom, or a phenylazo group; or a hydrogen atom. In the general formula (P-II), Q ⁴² and Q ⁴³ more preferably represent a methyl group, an ethyl group, a pyridyl group, a benzyl group, a phenylethyl group, an ethoxy group, a methoxy group, a phenyl group, a dimethylphenyl group (more preferably a 3,5-dimethylphenyl group), a chlorophenyl group (more preferably a 4-chlorophenyl group), a phenylazophenyl group (more preferably a 4-phenylazophenyl group), or a hydrogen atom. It is preferable that Q ⁴² and Q ⁴³ represent the same group.

In general formula (P-II), Q ⁴² and Q ⁴³ preferably represent an alkyl group having from 1 to 6 carbon atoms; or an aryl group having from 6 to 14 carbon atoms which may be substituted by an alkyl group having from 1 to 6 carbon atoms. In general formula (P-II), Q ⁴² and Q ⁴³ more preferably represent a methyl group, a phenyl group, or a dimethylphenyl group (more preferably a 3,5-dimethylphenyl group). It is preferable that Q ⁴² and Q ⁴³ represent each other the same group. It is preferable that Q ⁴² and Q ⁴³ represent each other the same group.

A second specific example of a perylene pigment is a compound represented by general formula (P-III).

In formula (P-III), ^Q44 to ^Q47 each independently represent a hydrogen atom or a monovalent organic group. ^Q44 and ^Q45 may be bonded to each other to form a ring. ^Q46 and ^Q47 may be bonded to each other to form a ring.

The monovalent organic group represented by Q ⁴⁴ to Q ⁴⁷ in formula (P-III) has the same meaning as the monovalent organic group represented by Q ⁴² and Q ⁴³ in formula (P-II).

Examples of the ring formed by Q ⁴⁴ and Q ⁴⁵ bonding to each other, and the ring formed by Q ⁴⁶ and Q ⁴⁷ bonding to each other include aromatic hydrocarbon rings, aromatic heterocycles, alicyclic hydrocarbon rings, and alicyclic heterocycles. Examples of the ring formed by Q ⁴⁴ and Q ⁴⁵ bonding to each other, and the ring formed by Q ⁴⁶ and Q ⁴⁷ bonding to each other are preferably a benzene ring, a naphthalene ring, a pyridine ring, or a tetrahydronaphthalene ring, and more preferably a benzene ring or a naphthalene ring. The benzene ring and the naphthalene ring formed by Q ⁴⁴ and Q ⁴⁵ bonding to each other are each condensed with the imidazole ring to which Q ⁴⁴ and Q ⁴⁵ are bonded. The benzene ring and the naphthalene ring formed by Q ⁴⁶ and Q ⁴⁷ bonding to each other are each condensed with the imidazole ring to which Q ⁴⁶ and Q ⁴⁷ are bonded.

The ring formed by ^Q44 and ^Q45 bonding to each other, and the ring formed by ^Q46 and ^Q47 bonding to each other may each be substituted by a substituent. Such a substituent is preferably a halogen atom, more preferably a chlorine atom or a fluorine atom.

In general formula (P-III), ^Q44 and ^Q45 preferably bond to each other to form an aromatic hydrocarbon ring having 6 to 10 carbon atoms which may be substituted with a halogen atom. ^Q46 and ^Q47 preferably bond to each other to form an aromatic hydrocarbon ring having 6 to 10 carbon atoms which may be substituted with a halogen atom.

In formula (P-III), Q ⁴⁴ and Q ⁴⁵ preferably bond together to form a benzene ring, a chlorobenzene ring, a fluorobenzene ring, or a naphthalene ring, and Q ⁴⁶ and Q ⁴⁷ preferably bond together to form a benzene ring, a chlorobenzene ring, a fluorobenzene ring, or a naphthalene ring.

More suitable examples of perylene pigments include compounds represented by chemical formulas (P1) to (P17) (hereinafter, each may be referred to as perylene pigments (P1) to (P17)). Note that there are no particular limitations on the substitution positions of the pyridyl group in chemical formula (P5) and the fluoro group in chemical formula (P12).

When the n-type pigment includes a perylene pigment, further suitable examples of the perylene pigment include perylene pigments (P1), (P2), (P3), and (P4).

Next, we will explain about isoindoline pigments. Isoindoline pigments are pigments that have an isoindoline structure. The isoindoline structure is a structure represented by the following chemical formula (IA). A substituent may be bonded to the carbon atom of the structure represented by chemical formula (IA).

When the n-type pigment includes an isoindoline pigment, suitable examples of the isoindoline pigment include compounds represented by chemical formulas (I1) and (I2).

The n-type pigment may include an n-type pigment other than the azo pigment, perylene pigment, and isoindoline pigment described above. Examples of n-type pigments other than azo pigments, perylene pigments, and isoindoline pigments include polycyclic quinone pigments, squarylium pigments, pyranthrone pigments, perinone pigments, quinacrylonitrile pigments, pyrazolone pigments, and benzimidazolone pigments.

The content of the n-type pigment is preferably greater than 0.0 parts by mass, and more preferably 0.5 parts by mass or more, per 100.0 parts by mass of the binder resin. The content of the n-type pigment is preferably 10.0 parts by mass or less, and more preferably 4.0 parts by mass or less, per 100.0 parts by mass of the binder resin.

(Additive)
Examples of the additives include antioxidants, radical scavengers, singlet quenchers, ultraviolet absorbers, softeners, surface modifiers, extenders, thickeners, dispersion stabilizers, waxes, donors, surfactants, plasticizers, sensitizers, electron acceptor compounds, and leveling agents.

(Material Combination)
In order to improve the positive chargeability and sensitivity characteristics when positive and negative charging are repeated, the combination of the hole transport material and the electron transport material is preferably one of the combinations D1 to D26 shown in Table 1. For the same reason, it is preferable that the combination of the hole transport material and the electron transport material is one of the combinations D1 to D26 shown in Table 1, and the binder resin is a polycarbonate resin (R1). For the same reason, it is preferable that the combination of the hole transport material and the electron transport material is one of the combinations D1 to D26 shown in Table 1, and the binder resin is a polycarbonate resin (R2). For the same reason, it is preferable that the combination of the hole transport material and the electron transport material is one of the combinations D1 to D26 shown in Table 1, and the charge generating material is a Y-type titanyl phthalocyanine.

In order to improve the positive chargeability and sensitivity characteristics when positive and negative charging are repeated, it is preferable that the combination of the n-type pigment and the electron transport agent is one of the combinations E1 to E26 shown in Table 1. For the same reason, it is preferable that the combination of the n-type pigment and the electron transport agent is one of the combinations E1 to E26 shown in Table 1, and the binder resin is polycarbonate resin (R1). For the same reason, it is preferable that the combination of the n-type pigment and the electron transport agent is one of the combinations E1 to E26 shown in Table 1, and the binder resin is polycarbonate resin (R2). For the same reason, it is preferable that the combination of the n-type pigment and the electron transport agent is one of the combinations E1 to E26 shown in Table 1, and the charge generating agent is Y-type titanyl phthalocyanine.

In order to improve the positive chargeability and sensitivity characteristics when positive and negative charging are repeated, it is preferable that the combination of the n-type pigment, the hole transport agent, and the electron transport agent is one of the combinations No. F1 to F42 shown in Table 2. For the same reason, it is preferable that the combination of the n-type pigment, the hole transport agent, and the electron transport agent is one of the combinations No. F1 to F42 shown in Table 2, and the binder resin is polycarbonate resin (R1). For the same reason, it is preferable that the combination of the n-type pigment, the hole transport agent, and the electron transport agent is one of the combinations No. F1 to F42 shown in Table 2, and the binder resin is polycarbonate resin (R2). For the same reason, it is preferable that the combination of the n-type pigment, the hole transport agent, and the electron transport agent is one of the combinations No. F1 to F42 shown in Table 2, and the charge generating agent is Y-type titanyl phthalocyanine.

The meanings of the terms in Tables 1 and 2 below are as follows: "No." indicates the combination number. "HTM" indicates a hole transport material. "ETM" indicates an electron transport material.

(Conductive Substrate)
The conductive substrate is not particularly limited as long as it can be used as the conductive substrate of the photoreceptor. The conductive substrate may be made of a conductive material at least on the surface. An example of the conductive substrate is a conductive substrate made of a conductive material. Another example of the conductive substrate is a conductive substrate coated with a conductive material. Examples of conductive materials include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, indium, stainless steel, and brass. These conductive materials may be used alone or in combination of two or more (for example, as an alloy). Among these conductive materials, aluminum and aluminum alloys are preferred because they have good charge transfer from the photosensitive layer to the conductive substrate.

The shape of the conductive substrate is appropriately selected according to the structure of the image forming device. Examples of the shape of the conductive substrate include a sheet shape and a drum shape. The thickness of the conductive substrate is appropriately selected according to the shape of the conductive substrate.

(Middle class)
The intermediate layer (undercoat layer) contains, for example, inorganic particles and a resin (intermediate layer resin) used in the intermediate layer. The presence of the intermediate layer makes it possible to maintain an insulating state sufficient to suppress leakage, while smoothing the flow of current generated when the photoconductor is exposed to light, thereby suppressing an increase in resistance.

Inorganic particles include, for example, particles of metals (e.g., aluminum, iron, and copper), particles of metal oxides (e.g., titanium oxide, alumina, zirconium oxide, tin oxide, and zinc oxide), and particles of non-metal oxides (e.g., silica).

Examples of the resin for the intermediate layer are the same as the examples of the base resin described above. In order to form the intermediate layer and the photosensitive layer well, it is preferable that the resin for the intermediate layer is different from the base resin and the binder resin contained in the photosensitive layer. The intermediate layer may contain additives. Examples of the additives contained in the intermediate layer are the same as the examples of the additives contained in the photosensitive layer.

(Method of Manufacturing Photoreceptor)
An example of a method for manufacturing a photoreceptor will be described. The method for manufacturing a photoreceptor includes a photosensitive layer forming step. In the photosensitive layer forming step, a coating liquid for forming a photosensitive layer (hereinafter, sometimes referred to as a coating liquid for a photosensitive layer) is prepared. The coating liquid for a photosensitive layer is applied onto a conductive substrate. Then, at least a part of the solvent contained in the applied coating liquid for a photosensitive layer is removed to form a photosensitive layer. The coating liquid for a photosensitive layer contains, for example, a charge generating agent, an electron transport agent, a hole transport agent, a binder resin, an n-type pigment, and a solvent. The coating liquid for a photosensitive layer is prepared by dissolving or dispersing the charge generating agent, the electron transport agent, the hole transport agent, the binder resin, and the n-type pigment in a solvent. The coating liquid for a photosensitive layer may further contain an additive as necessary.

The solvent contained in the coating solution for the photosensitive layer is not particularly limited, but examples thereof include alcohols (more specifically, methanol, ethanol, isopropanol, butanol, etc.), aliphatic hydrocarbons (more specifically, n-hexane, octane, cyclohexane, etc.), aromatic hydrocarbons (more specifically, benzene, toluene, xylene, etc.), halogenated hydrocarbons (more specifically, dichloromethane, dichloroethane, carbon tetrachloride, chlorobenzene, etc.), ethers (more specifically, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.), ketones (more specifically, acetone, methyl ethyl ketone, cyclohexanone, etc.), esters (more specifically, ethyl acetate, methyl acetate, etc.), dimethylformaldehyde, dimethylformamide, and dimethylsulfoxide.

The coating solution for the photosensitive layer is prepared by mixing each component and dispersing it in a solvent. For example, a bead mill, roll mill, ball mill, attritor, paint shaker, or ultrasonic disperser can be used for mixing or dispersing.

The method for applying the coating solution for the photosensitive layer is not particularly limited, but examples include dip coating, spray coating, spin coating, and bar coating.

Methods for removing at least a portion of the solvent contained in the coating solution for the photosensitive layer include, for example, heating, reducing pressure, or a combination of heating and reducing pressure. More specifically, a method for heat treatment (hot air drying) using a high-temperature dryer or a reduced-pressure dryer can be used. The temperature for the heat treatment is, for example, 40°C or higher and 150°C or lower. The time for the heat treatment is, for example, 3 minutes or higher and 120 minutes or lower.

The method for manufacturing the photoreceptor may further include a step of forming an intermediate layer, if necessary. The step of forming the intermediate layer may be appropriately selected from known methods.

[Second embodiment: Image forming apparatus]
Next, an image forming apparatus 110, which is an example of an image forming apparatus according to a second embodiment of the present invention, will be described with reference to Fig. 4. Fig. 4 is a cross-sectional view of the image forming apparatus 110.

The image forming device 110 shown in FIG. 4 includes a control device 10 (see FIG. 5), a feed unit 20, a conveying unit 30, image forming units 40Y, 40M, 40C, and 40K, a transfer unit 60, a belt cleaning unit 70, a fixing unit 80, and a paper discharge unit 90. The belt cleaning unit 70 will be described in detail in the explanation of the <printing mode and cleaning mode> below.

The control device 10 controls the operation of each part of the image forming device 110 (more specifically, the feeding section 20, the conveying section 30, the image forming units 40Y, 40M, 40C, and 40K, the transfer section 60, the belt cleaning section 70, the fixing section 80, and the paper discharge section 90). The control device 10 is disposed at an appropriate position within the main body housing. The control device 10 includes, for example, a Central Processing Unit (CPU), a Random Access Memory (RAM), a Read Only Memory (ROM), and an input/output interface (not shown). The control device 10 executes control by performing various calculation processes based on the detection results of various sensors and preset programs.

The feeding unit 20 includes a cassette 22. The cassette 22 stores multiple sheets of recording medium P. The feeding unit 20 feeds the recording medium P from the cassette 22 to the transport unit 30. The recording medium P is, for example, a sheet made of paper, cloth, or synthetic resin.

The transport unit 30 transports the recording medium P to the image forming units 40Y, 40M, 40C, and 40K.

The image forming units 40Y, 40M, 40C, and 40K each include a corresponding image carrier 100Y, 100M, 100C, and 100K, a charging device 42Y, 42M, 42C, and 42K, an exposure device 44Y, 44M, 44C, and 44K, a developing device 46Y, 46M, 46C, and 46K, a cleaning device 48Y, 48M, 48C, and 48K, and a charge removing device 50Y, 50M, 50C, and 50K. In the following description, the suffixes "Y", "M", "C", and "K" attached to each member of the image forming device 110 will be omitted unless it is necessary to distinguish them. For example, when it is necessary to distinguish them, each of the image forming units 40Y, 40M, 40C, and 40K will be described as an image forming unit 40.

The transfer unit 60 includes four transfer devices 62Y, 62M, 62C, and 62K, a drive roller 64, an endless transfer belt 66, a driven roller 67, and a tension roller 68. The transfer devices 62Y, 62M, 62C, and 62K are each disposed on the inner periphery of the transfer belt 66, and face the image carriers 100Y, 100M, 100C, and 100K via the transfer belt 66. The transfer belt 66 is stretched across the drive roller 64, the driven roller 67, and the tension roller 68. The transfer belt 66 rotates in the direction of the arrow (clockwise in FIG. 4) as the drive roller 64 rotates.

An image carrier 100 is provided at the center of the image forming unit 40. The image carrier 100 is provided so as to be rotatable in the direction of the arrow (counterclockwise in FIG. 4). Around the image carrier 100, in the order listed from the upstream side in the direction of rotation of the image carrier 100, a charging device 42, an exposure device 44, a developing device 46, a transfer device 62, a cleaning device 48, and a charge removing device 50 are provided.

The image carrier 100 is the photoreceptor 1 of the first embodiment. As already mentioned, the photoreceptor 1 of the first embodiment can be positively charged well even when it is repeatedly positively and negatively charged, and has excellent sensitivity characteristics. Therefore, by providing such a photoreceptor 1 as the image carrier 100, the image forming device 110 can form a good image on the recording medium P.

The charging device 42 charges the surface (e.g., the peripheral surface) of the image carrier 100 to a positive polarity. The charging device 42 is, for example, a scorotron charger.

The exposure device 44 exposes the charged surface of the image carrier 100. This causes an electrostatic latent image to be formed on the surface of the image carrier 100. The electrostatic latent image is formed based on image data input to the image forming device 110.

The developing device 46 supplies toner to the surface of the image carrier 100 and develops the electrostatic latent image into a toner image. The toner is a positively charged toner. The developing device 46 is in contact with the surface of the image carrier 100. In other words, the image forming device 110 employs a contact development method. The developing device 46 is, for example, a developing roller.

When the developer is a one-component developer, the developing device 46 supplies toner, which is a one-component developer, to the electrostatic latent image formed on the image carrier 100. When the developer is a two-component developer, the developing device 46 supplies toner, of the toner and carrier contained in the two-component developer, to the electrostatic latent image formed on the image carrier 100. The toner image formed by the supplied toner is carried by the image carrier 100.

The transfer belt 66 transports the recording medium P between the image carrier 100 and the transfer device 62. The transfer device 62 transfers the toner image developed by the developing device 46 from the surface of the image carrier 100 to the recording medium P, which is the receiving body. During transfer, the surface of the image carrier 100 and the recording medium P are in contact with each other. In other words, the image forming device 110 employs a direct transfer method. The transfer device 62 is, for example, a transfer roller.

Toner images of multiple colors (e.g., four colors: yellow, magenta, cyan, and black) are sequentially superimposed on the recording medium P on the transfer belt 66 by each of image forming unit 40Y and transfer device 62Y, image forming unit 40M and transfer device 62M, image forming unit 40C and transfer device 62C, and image forming unit 40K and transfer device 62K to form an unfixed toner image.

Cleaning devices 48Y, 48M, 48C, and 48K each include a corresponding housing 481Y, 481M, 481C, and 481K, and cleaning members 482Y, 482M, 482C, and 482K. The cleaning member 482 is disposed in the housing 481. The cleaning member 482 is in contact with the surface of the image carrier 100. The cleaning member 482 polishes the surface of the image carrier 100, and collects the toner adhering to the surface of the image carrier 100 into the housing 481. In this way, the cleaning device 48 collects the toner adhering to the surface of the image carrier 100. The cleaning member 482 is, for example, a cleaning roller.

The static eliminator 50 eliminates static electricity from the surface of the image carrier 100.

The recording medium P on which the unfixed toner image has been formed is transported to the fixing unit 80. The fixing unit 80 includes a pressure member 82 and a heating member 84. The pressure member 82 and the heating member 84 apply pressure and heat to the recording medium P, and the unfixed toner image is fixed to the recording medium P.

The recording medium P with the fixed toner image is discharged from the paper discharge section 90.

<Printing mode and cleaning mode>
Next, the operation of the image forming apparatus 110 executed in the print mode and cleaning mode will be described with further reference to Fig. 5 and Fig. 6 in addition to Fig. 4. Fig. 5 is a diagram showing the image carrier 100 and cleaning member 482 shown in Fig. 4, and the control device 10. Fig. 6 is a time chart showing the control of the cleaning member 482 in the print mode and cleaning mode. The horizontal axis in Fig. 6 indicates time, and the vertical axis indicates the voltage applied to the cleaning member 482. On the vertical axis in Fig. 6, "+" indicates that a positive voltage is applied, "0" indicates that no voltage is applied, and "-" indicates that a negative voltage is applied.

As already described with reference to FIG. 4, the image forming apparatus 110 includes a control device 10 and a belt cleaning unit 70. As shown in FIG. 5, the image forming apparatus 110 further includes voltage application devices 200Y, 200M, 200C, and 200K, and contact/separation mechanisms 300Y, 300M, 300C, and 300K. As already described, the suffixes "Y", "M", "C", and "K" attached to each component of the image forming apparatus 110 will be omitted when no distinction is necessary.

The control device 10 controls the voltage application device 200 to control the voltage applied to the cleaning member 482.

In the cleaning mode, the belt cleaning unit 70 collects toner that has moved from the image carrier 100 to the transfer belt 66. The belt cleaning unit 70 includes a belt cleaning roller 72, a toner collection container 74, and a backup roller 76. The belt cleaning unit 70 is provided below the transfer belt 66. The belt cleaning roller 72 contacts the surface (e.g., the outer peripheral surface) of the transfer belt 66. The backup roller 76 is disposed so as to sandwich the transfer belt 66 between itself and the belt cleaning roller 72. The belt cleaning roller 72 polishes the surface (the outer peripheral surface that is the contact surface) of the transfer belt 66, and collects the toner adhering to the surface of the transfer belt 66 into the toner collection container 74.

Voltage application devices 200Y, 200M, 200C, and 200K are connected to cleaning members 482Y, 482M, 482C, and 482K, respectively. Voltage application device 200 applies a voltage to cleaning member 482.

The contact/separation mechanisms 300Y, 300M, 300C, and 300K respectively contact or separate the corresponding developing devices 46Y, 46M, 46C, and t from the image carriers 100Y, 100M, 100C, and 100K.

(Print Mode)
The control by the control device 10 in the print mode and the operation of the image forming device 110 will be described below. When a print job including image data is input from an external device (not shown, for example a personal computer), the control device 10 executes the print mode. In the print mode, an image is printed on the recording medium P.

Specifically, as shown in FIG. 6, at time t11 when printing in the print mode starts, the control device 10 controls the voltage application device 200 to apply a negative first voltage to the cleaning member 482. Also, at time t11, the control device 10 starts the rotational driving of the image carrier 100, the cleaning member 482, and the transfer belt 66. The toner (positively charged toner) remaining on the image carrier 100 after transfer is electrostatically collected by the cleaning member 482 to which the negative first voltage is applied.

In more detail, in the print mode, the control device 10 applies a positive voltage to the charging device 42. The charging device 42 then charges the surface of the image carrier 100 to a positive polarity. As a result, the positively charged toner is electrostatically moved from the positively charged surface of the image carrier 100 to the cleaning member 482 to which a negative voltage is applied, and is then collected.

While continuing to collect toner by the cleaning member 482 to which the negative first voltage has been applied, the control device 10 causes the image carrier 100, which is rotating, to be charged by the charging device 42, exposed by the exposure device 44, developed by the developing device 46, transferred by the transfer device 62, and discharged by the discharge device 50. Then, after the unfixed toner image is transferred to the recording medium P transported between the image carrier 100 and the transfer device 62, the control device 10 causes the fixing unit 80 to fix the unfixed toner image, forming an image, which is a fixed toner image, on the recording medium P.

When image formation for all image data included in the print job is completed, that is, at time t12 when the print mode ends, the control device 10 controls the voltage application device 200 to stop applying the negative polarity first voltage to the cleaning member 482. Also, at time t12, the control device 10 stops the rotational driving of the image carrier 100, the cleaning member 482, and the transfer belt 66. This ends the print mode.

As described in the first embodiment, the photoconductor 1, which is the image carrier 100, is positively charged well even when it is repeatedly positively and negatively charged. Therefore, even if in the printing mode the surface of the image carrier 100 is repeatedly charged to a positive polarity by the charging device 42, and the potential of the image carrier 100 is repeatedly lowered to a negative polarity by contact with the cleaning member 482 to which a negative first voltage is applied, the photoconductor 1, which is the image carrier 100, is preferably charged to the desired positive potential in the charging process. As a result, even when it is repeatedly positively and negatively charged, the image forming apparatus 110 having the photoconductor 1 as the image carrier 100 can form a good image.

(Cleaning mode)
The following describes the control by the control device 10 in the cleaning mode and the operation of the image forming apparatus 110. When the print mode ends, the control device 10 executes the cleaning mode. In the cleaning mode, the toner that adheres to the cleaning member 482 after the print mode ends is collected.

Specifically, during the first predetermined time T1 (time t12 to t13) in the cleaning mode, the control device 10 controls the contact/separation mechanism 300 to separate the developing device 46 from the image carrier 100 in the separation direction D1. The separation direction D1 is the direction in which the developing device 46 separates from the image carrier 100.

After the developing device 46 is separated, at time t13 in the cleaning mode, the control device 10 controls the voltage application device 200 to apply a second voltage of positive polarity (a voltage of the same polarity as the charge polarity of the toner) to the cleaning member 482. Also, at time t13, the control device 10 starts the rotational driving of the image carrier 100, the cleaning member 482, and the transfer belt 66. As a result, the toner (positively charged toner) adhering to the cleaning member 482 is electrostatically moved from the cleaning member 482 to which the second voltage of positive polarity has been applied, to the image carrier 100. The toner that has moved to the image carrier 100 moves to the transfer belt 66 as the image carrier 100 rotates. The toner that has moved to the transfer belt 66 is collected by the belt cleaning unit 70 as the transfer belt 66 rotates.

During the second predetermined time T2 (times t13 to t14) in the cleaning mode, a second voltage of positive polarity is applied to the cleaning member 482. Then, at time t14, the control device 10 controls the voltage application device 200 to stop the application of the second voltage of positive polarity to the cleaning member 482.

In addition, during the second predetermined time T2 (time t13 to t14) in the cleaning mode, the control device 10 may not apply a voltage to the charging device 42, or may apply a positive voltage to the charging device 42. When applying a positive voltage to the charging device 42, it is preferable that the positive voltage applied to the charging device 42 is lower than the second positive voltage applied to the cleaning member 482. This is to electrostatically move the positively charged toner from the cleaning member 482 to the charging device 42 in an appropriate manner.

During the third predetermined time T3 (times t14 to t15) in the cleaning mode, the control device 10 continues to rotate the image carrier 100, the cleaning member 482, and the transfer belt 66. Also, during the third predetermined time T3, the control device 10 controls the contact/separation mechanism 300 to move the developing device 46 in the approach direction D2. The approach direction D2 is the direction in which the developing device 46 approaches the image carrier 100. Then, at time t15, the control device 10 brings the developing device 46 into contact with the image carrier 100. Also, at time t15, the control device 10 stops the rotation of the image carrier 100, the cleaning member 482, and the transfer belt 66. Time t15 can be defined as the time when the toner that moved from the cleaning member 482 to the image carrier 100 immediately before the application of the second voltage of positive polarity was stopped moves from the image carrier 100 to the transfer belt 66, and is then collected from the transfer belt 66 by the belt cleaning unit 70. The cleaning mode ends when the rotational drive of the image carrier 100, the cleaning member 482, and the transfer belt 66 is stopped.

As described in the first embodiment, the photoconductor 1, which is the image carrier 100, is well-charged to a positive polarity even when it is repeatedly charged positively and negatively. Such an image carrier 100 is not easily affected by fluctuations in surface potential. Therefore, even if the potential of the photoconductor rises to a positive polarity due to contact with a cleaning member to which a positive second voltage is applied, the image carrier 100 can be well-charged to the desired positive polarity potential when the printing mode is executed again after the cleaning mode ends.

The above describes the control by the control device 10 in the printing mode and cleaning mode, and the operation of the image forming device 110. Below, the control by the control device 10 in the printing mode and cleaning mode will be described in more detail with reference to FIG. 7. FIG. 7 is a flow chart showing the control of the image forming device 110 shown in FIG. 4.

The control device 10 repeatedly executes the process of the flowchart shown in FIG. 7. Specifically, the control device 10 determines whether a print job has been input (S101). If a print job has not been input (No in S101), the process of the flowchart shown in FIG. 7 ends. If a print job has been input (Yes in S101), the print mode is executed. In the print mode, the control device 10 controls the voltage application device 200 to apply a negative first voltage to the cleaning member 482 (S102). At this time, as already described, the positively charged toner remaining on the image carrier 100 is collected by the cleaning member 482 to which the negative first voltage has been applied.

After the print mode is completed, the cleaning mode is executed. In the cleaning mode, the control device 10 separates the developing device 46 from the image carrier 100 (S103). Next, the control device 10 controls the voltage application device 200 to apply a second voltage of positive polarity to the cleaning member 482 (S104). At this time, as already described, the positively charged toner adhering to the cleaning member 482 moves to the image carrier 100. Next, the toner that has moved to the image carrier 100 is collected by the belt cleaning unit 70 via the transfer belt 66. Next, the control device 10 returns the position of the developing device 46 to bring the developing device 46 into contact with the image carrier 100 (S105). Then, the control device 10 ends the processing of the flowchart shown in FIG. 7.

(Modification)
The image forming apparatus 110 already described can be modified as shown below: In a multi-color printing mode for printing a multi-color image, the printing mode and cleaning mode already described are executed.

On the other hand, unlike the multi-color printing mode, the monochrome printing mode for printing monochrome images can be executed as follows. In the monochrome printing mode (times t11 to t12 in FIG. 6), the control device 10 controls the voltage application device 200K (voltage application device for black) to apply a first voltage of negative polarity to the cleaning member 482K (cleaning member for black). In the monochrome printing mode (times t11 to t12 in FIG. 6), the control device 10 controls the voltage application devices 200Y, 200M, and 200C (voltage application devices for yellow, magenta, and cyan) to apply a third voltage of positive polarity to the cleaning members 482Y, 482M, and 482C (cleaning members for yellow, magenta, and cyan). Microcomponents (e.g., paper dust) of the negatively charged recording medium P may adhere to the image carriers 100Y, 100M, and 100C (yellow, magenta, and cyan image carriers) that are not used in the monochrome printing mode. Therefore, by applying a third voltage (positive polarity voltage) to the cleaning members 482Y, 482M, and 482C, the microcomponents of the negatively charged recording medium P are electrostatically collected by the cleaning members 482Y, 482M, and 482C.

In addition, during the second predetermined time T2 (times t13 to t14 in FIG. 6) in the cleaning mode after the monochrome printing mode, the control device 10 controls the voltage application device 200K to apply a second voltage of positive polarity to the cleaning member 482K. As a result, the positively charged toner adhering to the cleaning member 482K moves onto the image carrier 100K (black image carrier). During the second predetermined time T2 (times t13 to t14 in FIG. 6) in the cleaning mode after the monochrome printing mode, the control device 10 controls the voltage application devices 200Y, 200M, and 200C to apply a fourth voltage of negative polarity to the cleaning members 482Y, 482M, and 482C. As a result, the negatively charged microcomponents of the recording medium P adhering to the cleaning members 482Y, 482M, and 482C move onto the image carriers 100Y, 100M, and 100C. Next, the toner that has moved onto the image carrier 100K, and the minute components of the recording medium P that have moved onto the image carriers 100Y, 100M, and 100C are collected by the belt cleaning unit 70 via the transfer belt 66. This concludes the description of the modified example.

Although an example of an image forming apparatus has been described above, the image forming apparatus is not limited to the image forming apparatus 110, and can be further modified in the following ways, for example. The image forming apparatus 110 is a color image forming apparatus, but the image forming apparatus may be a monochrome image forming apparatus. In this case, the image forming apparatus may have only one image forming unit. In addition, the image forming apparatus 110 employs a tandem system, but the image forming apparatus may employ, for example, a rotary system. Although a scorotron charger has been described as an example of the charging device 42, the charging device may be a charging device other than a scorotron charger (for example, a charging roller, a charging brush, or a corotron charger). The image forming apparatus 110 employs a contact development system, but the image forming apparatus may employ a non-contact development system. The image forming apparatus 110 employs a direct transfer system, but the image forming apparatus may employ an intermediate transfer system.

[Third embodiment: process cartridge]
Next, a process cartridge according to a third embodiment of the present invention will be described with reference to Fig. 4. The process cartridge according to the third embodiment corresponds to each of the image forming units 40Y, 40M, 40C, and 40K. The process cartridge includes an image carrier 100.

The image carrier 100 is the photoreceptor 1 of the first embodiment. As already mentioned, the photoreceptor 1 of the first embodiment can be positively charged well even when it is repeatedly positively and negatively charged, and has excellent sensitivity characteristics. Therefore, by having such a photoreceptor 1 as the image carrier 100, the process cartridge of the third embodiment can form a good image on the recording medium P.

In addition to the image carrier 100, the process cartridge may further include at least one selected from the group consisting of a charging device 42, an exposure device 44, a developing device 46, a transfer device 62, a cleaning member 482, and a static eliminator 50. The process cartridge is designed to be detachable from the image forming apparatus 110. Therefore, the process cartridge is easy to handle, and when the sensitivity characteristics of the image carrier 100 deteriorate, the process cartridge can be easily and quickly replaced including the image carrier 100. The process cartridge of the third embodiment has been described above with reference to FIG. 4.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the scope of the examples.

First, the following charge generating material, electron transport material, hole transport material, binder resin, and n-type pigment were prepared as materials for forming the photosensitive layer of the photoreceptor.

(Charge generating material)
As the charge generating material, the Y-type titanyl phthalocyanine described in the first embodiment was prepared.

(Electron Transport Agent)
As the electron transport materials, the electron transport materials (ETM1), (ETM2), (ETM6), (ETM7), (ETM8), (ETM19), (ETM22), (ETM23), (ETM24), (ETM28), and (ETM29) described in the first embodiment were prepared. In addition, as the electron transport materials used in the comparative examples, compounds represented by the following chemical formulas (ETM32-C) to (ETM37-C) (hereinafter, these may be referred to as electron transport materials (ETM32-C) to (ETM37-C), respectively) were prepared.

(Hole Transport Agent)
As the hole transport material, the hole transport materials (HTM1) to (HTM10) described in the first embodiment were prepared.

(Binder resin)
As the binder resin, the polycarbonate resins (R1) and (R2) described in the first embodiment were prepared. The viscosity average molecular weight of each of the polycarbonate resins (R1) and (R2) was 35,000.

(n-type pigment)
As n-type pigments, the azo pigments (A1) to (A5), the perylene pigments (P1) to (P4), and the isoindoline pigments (I1) to (I2) described in the first embodiment were prepared.

<Production of photoreceptor>
Photoreceptors (A-1) to (A-31) and (B-1) to (B-7) were produced using the above charge generating material, electron transport material, hole transport material, binder resin, and n-type pigment.

(Production of Photoreceptor (A-1))
3 parts by mass of Y-type titanyl phthalocyanine as a charge generating agent, 70 parts by mass of a hole transporting agent (HTM1), 100 parts by mass of a polycarbonate resin (R1) as a binder resin, 35 parts by mass of an electron transporting agent (ETM1), 3 parts by mass of an azo pigment (A1) as an n-type pigment, and 800 parts by mass of a solvent, tetrahydrofuran, were mixed for 50 hours using a ball mill to obtain a coating liquid for a photosensitive layer. The coating liquid for a photosensitive layer was applied onto a conductive substrate (aluminum drum-shaped support) by a dip coating method. The applied coating liquid for a photosensitive layer was dried with hot air at 120° C. for 60 minutes. In this way, a photosensitive layer (film thickness 30 μm) was formed on the conductive substrate to obtain a photoreceptor (A-1). In the photoreceptor (A-1), a single layer of a photosensitive layer was provided directly on the conductive substrate.

(Production of Photoreceptors (A-2) to (A-31) and (B-1) to (B-7))
Photoreceptors (A-2) to (A-31) and (B-2) to (B-7) were each produced in the same manner as for the production of photoreceptor (A-1), except that an n-type pigment, a hole transport material, an electron transport material, and a binder resin were used as shown in Tables 3 and 4. Photoreceptor (B-1) was produced in the same manner as for the production of photoreceptor (A-1), except that an n-type pigment was not used.

<Evaluation of Positive Charging Properties When Positive and Negative Charging Are Repeated>
The positive charging property of the photoconductor was evaluated when the photoconductor was repeatedly charged positively and negatively in an environment of 25°C temperature and 50% RH. A drum sensitivity tester (manufactured by Gentec) was used for this evaluation. The photoconductor was set in the drum sensitivity tester. The drum sensitivity tester was equipped with a first charging device, a probe, a second charging device, and a static eliminator from the upstream side of the rotation direction of the photoconductor. The first charging device charges the surface of the photoconductor to a positive polarity. The first charging device is a scorotron charger, and the grid voltage was set to +700V. The probe is provided at the development position and measures the surface potential of the photoconductor. The second charging device is provided at the cleaning position and charges the surface of the photoconductor to a negative polarity. The second charging device is a corotron charger, and the applied voltage was set to -5kV. The static eliminator eliminates static electricity from the surface of the photoconductor.

The photoconductor was rotated 10 times at a rotation speed of 200 mm/sec with the first charging device for positive charging turned on, the static eliminator turned on, and the second charging device for negative charging turned off. In this manner, the photoconductor was repeatedly positively charged and statically eliminated. During the 10 rotations, the surface potential of the photoconductor was continuously measured using a probe. The average value of the surface potential of the photoconductor for these 10 rotations was taken as the charging potential V1 (unit: +V) of the photoconductor before the repeated positive and negative charging.

Next, the photoconductor was rotated 200 times at a rotation speed of 200 mm/sec with the first charging device for positive charging, the static eliminator, and the second charging device for negative charging all turned on. In this way, the photoconductor was repeatedly positively charged, static eliminator, and negatively charged. Using a probe, the surface potential of the photoconductor was continuously measured for 10 revolutions from the 191st revolution to the 200th revolution. The average value of the surface potential of the photoconductor for these 10 revolutions was taken as the charging potential V2 (unit: +V) of the photoconductor after repeated positive and negative charging.

Then, the amount of charge potential drop (unit: V) of the photoconductor before and after repeated positive and negative charging was calculated from the formula "charge potential drop = V1 - V2". From the amount of charge potential drop, whether the photoconductor could be satisfactorily positively charged when positive and negative charging was repeated was evaluated based on the following criteria. The measured amount of charge potential drop and the evaluation results of positive chargeability when positive and negative charging was repeated are shown in Tables 3 and 4.

(Evaluation criteria for positive chargeability when positive and negative charging are repeated)
Evaluation A: The amount of decrease in charged potential is less than 90V.
Evaluation B: The amount of decrease in charged potential is 90V or more and less than 110V.
Evaluation C: The amount of decrease in charged potential is 110 V or more.

<Evaluation of sensitivity characteristics>
The sensitivity characteristics of the photoconductor were evaluated using a drum sensitivity tester (manufactured by Gentec) under an environment of 10°C temperature and 15% RH. Specifically, the surface of the photoconductor was charged to +750V using the drum sensitivity tester. Then, monochromatic light (wavelength: 780 nm, exposure: 0.4 μJ/cm ² ) was extracted from the light of a halogen lamp using a bandpass filter and irradiated onto the surface of the photoconductor. The surface potential of the photoconductor was measured 70 milliseconds after the end of the monochromatic light irradiation. The measured surface potential was taken as the post-exposure potential (unit: +V) of the photoconductor. The sensitivity characteristics of the photoconductor were evaluated based on the post-exposure potential according to the following criteria. The measured post-exposure potential and the evaluation results of the sensitivity characteristics are shown in Tables 3 and 4.

(Evaluation criteria for sensitivity characteristics)
Evaluation A: The potential after exposure is less than +130V.
Evaluation B: The potential after exposure is +130V or more and less than +150V.
C: The potential after exposure is +150 V or more.

The meanings of the terms in Tables 3 and 4 are as follows. "HTM" refers to a hole transport material. "ETM" refers to an electron transport material. "Resin" refers to a binder resin. The "Value" in the "Sensitivity" column indicates the potential after exposure (unit: +V). The "Evaluation" in the "Sensitivity" column indicates the evaluation result of the sensitivity characteristics. The "Value" in the "V1-V2" column indicates the amount of charge potential drop (unit: V) of the photoconductor before and after repeated positive and negative charging. The "Evaluation" in the "V1-V2" column indicates the evaluation result of the positive chargeability when positive and negative charging is repeated.

As shown in Table 4, the photosensitive layer of the photoreceptor (B-1) did not contain an n-type pigment. Therefore, as shown in Table 4, the sensitivity characteristics of the photoreceptor (B-1) were evaluated as C, which was poor.

As shown in Table 4, the photosensitive layers of the photoreceptors (B-2) to (B-7) did not contain the electron transport agent (1). Therefore, as shown in Table 4, the positive chargeability of the photoreceptors (B-2) to (B-7) when they were repeatedly positively and negatively charged was rated C, which was poor.

On the other hand, as shown in Table 3, the photosensitive layers of the photoreceptors (A-1) to (A-31) contained an electron transport agent (1) (more specifically, an electron transport agent (ETM1), (ETM2), (ETM6), (ETM7), (ETM8), (ETM19), (ETM22), (ETM23), (ETM24), (ETM28), or (ETM29)) and an n-type pigment (more specifically, one of azo pigments (A1) to (A5), perylene pigments (P1) to (P4), and isoindoline pigments (I1) to (I2)). Therefore, as shown in Table 3, the positive chargeability of the photoreceptors (A-1) to (A-31) when they were repeatedly positively and negatively charged was rated A or B, which was good. Furthermore, as shown in Table 3, the sensitivity characteristics of photoreceptors (A-1) to (A-31) were rated A or B and were good.

From the above, it has been shown that the photoreceptors of the present invention, including photoreceptors (A-1) to (A-31), can be positively charged well even when repeatedly positively and negatively charged, and have excellent sensitivity characteristics. Furthermore, it is considered that the process cartridge and image forming apparatus of the present invention equipped with such photoreceptors can form good images.

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

1: Photoconductor (electrophotographic photoconductor)
2: Conductive substrate 3: Photosensitive layer 10: Control device 42Y, 42M, 42C, 42K: Charging device 44Y, 44M, 44C, 44K: Exposure device 46Y, 46M, 46C, 46K: Development device 50Y, 50M, 50C, 50K: Discharge device 62Y, 62M, 62C, 62K: Transfer device 100Y, 100M, 100C. 100K: Image carrier 110: Image forming device 482Y, 482M, 482C, 482K: Cleaning member

Claims (15)

A conductive substrate and a photosensitive layer are provided.
the photosensitive layer is a single layer and contains a charge generating material, an electron transport material, a binder resin, a hole transport material, and an n-type pigment;
The electron transport agent includes a compound represented by general formula (1) ,
the content of the electron transport agent is 20 parts by mass or more and 60 parts by mass or less with respect to 100.0 parts by mass of the binder resin,
The content of the n-type pigment is 4.0 parts by mass or less with respect to 100.0 parts by mass of the binder resin .

(In the general formula (1),
^R1 and ^R2 each independently represent an aryl group, a hydrogen atom, an alkyl group, a heterocyclic group, an alkoxy group, an aralkyl group, or an allyl group, which may be substituted with 1 to 5 substituents selected from the group consisting of a halogen atom, an alkyl group, and an alkoxy group. In the general formula (1), R ¹ and R ² each independently represent
an aryl group having 6 to 14 carbon atoms which may be substituted by one to five substituents selected from the group consisting of a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an alkoxy group having 1 to 6 carbon atoms;
The electrophotographic photoreceptor according to claim 1 , wherein the alkyl group has 1 to 6 carbon atoms, or a heterocyclic group having 5 to 14 members. The electrophotographic photoreceptor according to claim 1 or 2, wherein the compound represented by the general formula (1) is a compound represented by the chemical formula (ETM1), (ETM2), (ETM6), (ETM7), (ETM8), (ETM19), (ETM22), (ETM23), (ETM24), (ETM28), or (ETM29).

The electrophotographic photoreceptor according to any one of claims 1 to 3, wherein the n-type pigment includes an azo pigment, a perylene pigment, or an isoindoline pigment. The n-type pigment includes an azo pigment,
The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the azo pigment is a compound represented by chemical formula (A1), (A2), (A3), (A4), or (A5).

The n-type pigment comprises a perylene pigment,
The electrophotographic photoreceptor according to any one of claims 1 to 4, wherein the perylene pigment is a compound represented by chemical formula (P1), (P2), (P3), or (P4).

The n-type pigment comprises an isoindoline pigment;
5. The electrophotographic photoreceptor according to claim 1, wherein the isoindoline pigment is a compound represented by chemical formula (I1) or (I2).

The electrophotographic photoreceptor according to any one of claims 1 to 7, wherein the hole transport agent comprises a compound represented by general formula (21), (22), (23), (24), (25), (26), or (27).

(In the general formula (21), R ¹¹ , R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , and R ¹⁶ each independently represent an alkyl group having 1 to 8 carbon atoms, or a phenyl group; R ¹⁷ and R ¹⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or a phenyl group; b1, b2, b3, and b4 each independently represent an integer of 0 to 5; b5 and b6 each independently represent an integer of 0 to 4; d and e each independently represent 0 or 1;
In the general formula (22), R ²⁰ represents a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, an alkoxy group having 1 to 8 carbon atoms, or a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms; R ²¹ , R ²² , and R ²³ each independently represent an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms; f1, f2, and f3 each independently represent an integer of 0 to 5; and f4 represents 0 or 1;
In the general formula (23), R ³¹ , R ³² , R ³³ , R ³⁴ , and R ³⁵ each independently represent an alkyl group having 1 to 8 carbon atoms or an alkoxy group having 1 to 8 carbon atoms; g1, g2, g3, g4, and g5 each independently represent an integer of 0 to 5;
In the general formula (24), R ⁴¹ , R ⁴² , R ⁴³ , R ⁴⁴ , R ⁴⁵ , and R ⁴⁶ each independently represent an alkyl group having 1 to 8 carbon atoms, a phenyl group, or an alkoxy group having 1 to 8 carbon atoms; h1, h2, h4, and h5 each independently represent an integer of 0 to 5; h3 and h6 each independently represent an integer of 0 to 4;
In the general formula (25), R ⁷¹ , R ⁷² , R ⁷³ , and R ⁷⁴ each independently represent an alkyl group having 1 to 8 carbon atoms; j1, j2, j3, and j4 each independently represent an integer of 0 to 5;
In the general formula (26), R ⁸¹ , R ⁸² , and R ⁸³ each independently represent an alkyl group having 1 to 8 carbon atoms, a phenyl group, or an alkoxy group having 1 to 8 carbon atoms; R ⁸⁴ and R ⁸⁵ each independently represent a phenyl group which may be substituted with an alkyl group having 1 to 8 carbon atoms, a hydrogen atom, an alkyl group having 1 to 8 carbon atoms, or an alkoxy group having 1 to 8 carbon atoms; k1, k2, and k3 each independently represent an integer of 0 to 5; k4 and k5 each independently represent 1 or 2;
In the general formula (27), R ⁶¹ , R ⁶² , and R ⁶³ each independently represent an alkyl group having 1 to 8 carbon atoms, and R ⁶⁴ , R ⁶⁵ , and R ⁶⁶ each independently represent a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. The electrophotographic photoreceptor according to any one of claims 1 to 8, wherein the hole transport agent comprises a compound represented by chemical formula (HTM1), (HTM2), (HTM3), (HTM4), (HTM5), (HTM6), (HTM7), (HTM8), (HTM9), or (HTM10).

The electrophotographic photoreceptor according to any one of claims 1 to 9, wherein the charge generating agent contains Y-type crystals of titanyl phthalocyanine. At least one selected from the group consisting of a charging device, an exposure device, a developing device, a transfer device, a cleaning member, and a static eliminator;
A process cartridge comprising the electrophotographic photoreceptor according to any one of claims 1 to 10. An image carrier;
a charging device for charging the surface of the image carrier to a positive polarity;
an exposure device that exposes the charged surface of the image carrier to light to form an electrostatic latent image on the surface of the image carrier;
a developing device for developing the electrostatic latent image into a toner image;
a transfer device that transfers the toner image from the image carrier to a transfer medium,
An image forming apparatus, wherein the image bearing member is the electrophotographic photoreceptor according to any one of claims 1 to 10. a cleaning member that comes into contact with the surface of the image carrier and collects toner adhering to the surface of the image carrier;
a control device that controls a voltage applied to the cleaning member,
The image forming apparatus according to claim 12 , wherein the control device applies a first voltage of negative polarity to the cleaning member in a printing mode. The image forming apparatus according to claim 13, wherein the control device applies a second voltage of positive polarity to the cleaning member in a cleaning mode. The image forming apparatus according to any one of claims 12 to 14, further comprising a charge removing device that removes charge from the surface of the image carrier.

Images