Electrophotographic photosensitive member, process cartridge, and image forming apparatus

An electrophotographic photosensitive member (1) includes a conductive substrate (2) and a photosensitive layer (3). The photosensitive layer (3) is a single-layer photosensitive layer (3c) and contains a charge generating material, a hole transport material, an electron transport material, and a binder resin. The binder resin includes a polyarylate resin represented by general formula (1). In general formula (1), Q1, Q2, Q3, and Q4 each represent a methyl group or a hydrogen atom. r, s, t, and u each represent a number greater than or equal to 15 and less than or equal to 35. X and Y each represent a divalent group represented by chemical formula (2A), chemical formula (2B), chemical formula (2C), or chemical formula (2D), and X and Y are different from each other

TECHNICAL FIELD

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

BACKGROUND ART

Electrophotographic photosensitive members are used as image bearing members of electrophotographic image forming apparatuses (for example, printers and multifunction peripherals). Electrophotographic photosensitive members each include a photosensitive layer. Examples of electrophotographic photosensitive members that are used include single-layer electrophotographic photosensitive members and multi-layer electrophotographic photosensitive members. The single-layer electrophotographic photosensitive members each include a photosensitive layer having a charge generation function and a charge transport function. The multi-layer electrophotographic photosensitive members each include a photosensitive layer including a charge generating layer having a charge generation function and a charge transport layer having a charge transport function.

Patent Literature 1 discloses an electrophotographic photosensitive member containing a specific polyarylate resin.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, the present inventors' study has revealed that the electrophotographic photosensitive member containing a polyarylate resin disclosed in Patent Literature 1 is not sufficient to achieve improved anti-fogging performance.

The present invention was made in consideration of the above problem and an object thereof is to provide an electrophotographic photosensitive member including a photosensitive layer that shows excellent anti-fogging performance. Another object of the present invention is to provide a process cartridge and an image forming apparatus that inhibit occurrence of an image defect.

Solution to Problem

An electrophotographic photosensitive member according to the present invention includes a conductive substrate and a photosensitive layer. The photosensitive layer is a single-layer photosensitive layer and contains a charge generating material, a hole transport material, an electron transport material, and a binder resin. The binder resin includes a polyarylate resin. The polyarylate resin is represented by general formula (1) shown below. The electron transport material is represented by general formula (ETM1), general formula (ETM2), general formula (ETM3), general formula (ETM4), or general formula (ETM5) shown below. A scratch resistant depth of the photosensitive layer is no greater than 0.50 μm. A Vickers hardness of the photosensitive layer is at least 17.0 HV.

In general formula (1), Q1, Q2, Q3, and Q4each represent, independently of one another, a methyl group or a hydrogen atom. r, s, t, and u each represent, independently of one another, a number greater than or equal to 15 and less than or equal to 35. r+s+t+u=100. r+t=s+u. X and Y each represent, independently of one another, a divalent group represented by chemical formula (2A), chemical formula (2B), chemical formula (2C), or chemical formula (2D) shown below, and X and Y are different from each other.

In general formula (ETM1), R1and R4each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6. R2and R3each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6. a and b each represent, independently of one another, an integer of at least 0 and no greater than 4. When a represents an integer of at least 2 and no greater than 4, chemical groups R2may be the same as or different from one another. When b represents an integer of at least 2 and no greater than 4, chemical groups R3may be the same as or different from one another.

In general formula (ETM2), R5represents a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6 and optionally having a halogen atom.

In general formula (ETM3), R6and R7each represent, independently of one another, a hydrogen atom or an aryl group having a carbon number of at least 6 and no greater than 14 and optionally having an alkyl group having a carbon number of at least 1 and no greater than 3.

In general formula (ETM4), R8and R9each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6, and R10represents a halogen atom or a hydrogen atom

In general formula (ETM5), R11, R12, R13, R14, and R15each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6. R16represents a hydrogen atom or an aryl group having a carbon number of at least 6 and no greater than 14 and optionally having a halogen atom. G1and G2each represent, independently of one another, an oxygen atom or a sulfur atom.

A process cartridge according to the present invention includes the above-described electrophotographic photosensitive member.

An image forming apparatus according to the present invention includes an image bearing member, a charger, a light exposure section, a development section, and a transfer section. The image bearing member is the above-described electrophotographic photosensitive member. The charger charges a surface of the image bearing member. The charger has a positive charging polarity. The light exposure section exposes the charged surface of the image bearing member to light to form an electrostatic latent image on the surface of the image bearing member. The development section develops the electrostatic latent image into a toner image. The transfer section transfers the toner image from the image bearing member to a transfer target while bringing the transfer target into contact with the surface of the image bearing member.

Advantageous Effects of Invention

The electrophotographic photosensitive member according to the present invention has excellent anti-fogging performance. The process cartridge and the image forming apparatus according to the present invention can inhibit occurrence of an image defect.

DESCRIPTION OF EMBODIMENTS

The following describes embodiments of the present invention in detail. However, the present invention is not in any way limited by the following embodiments and appropriate changes may be made when practicing the present invention so long as such changes do not deviate from the intended scope of the present invention. Although description is omitted as appropriate in some instances in order to avoid repetition, such omission does not limit the essence of the present invention. In the present description, the term “-based” may be appended to the name of a chemical compound in order to form a generic name encompassing both the chemical compound itself and derivatives thereof. When the term “-based” is appended to the name of a chemical compound used in the name of a polymer, the term indicates that a repeating unit of the polymer originates from the chemical compound or a derivative thereof.

Hereinafter, an alkyl group having a carbon number of at least 1 and no greater than 6, an alkyl group having a carbon number of at least 1 and no greater than 3, an aryl group having a carbon number of at least 6 and no greater than 14, and a halogen atom each refer to the following.

An alkyl group having a carbon number of at least 1 and no greater than 6 as used herein refers to an unsubstituted straight chain or branched chain alkyl group. Examples of the alkyl group having a carbon number of at least 1 and no greater than 6 include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an s-butyl group, a t-butyl group, a pentyl group, an isopentyl group, a neopentyl group, and a hexyl group.

An alkyl group having a carbon number of at least 1 and no greater than 3 as used herein refers to an unsubstituted straight chain or branched chain alkyl group. Examples of the alkyl group having a carbon number of at least 1 and no greater than 3 include a methyl group, an ethyl group, a propyl group, an isopropyl group.

An aryl group having a carbon number of at least 6 and no greater than 14 as used herein refers to an unsubstituted aryl group. Examples of the aryl group having a carbon number of at least 6 and no greater than 14 include an unsubstituted monocyclic aromatic hydrocarbon group having a carbon number of at least 6 and no greater than 14, an unsubstituted condensed bicyclic aromatic hydrocarbon group having a carbon number of at least 6 and no greater than 14, and an unsubstituted condensed tricyclic aromatic hydrocarbon group having a carbon number of at least 6 and no greater than 14. More specific examples of the aryl group having a carbon number of at least 6 and no greater than 14 include a phenyl group, a naphthyl group, an anthryl group, and a phenanthryl group.

A halogen atom is for example a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom.

Hereinafter, a functional group “optionally having a halogen atom” means that some or all of hydrogen atoms of the functional group may each be replaced with a halogen atom. A similar concept applies to a functional group “optionally having an alkyl group having a carbon number of at least 1 and no greater than 3”.

First Embodiment: Electrophotographic Photosensitive Member

The following describes a structure of an electrophotographic photosensitive member (also referred to below as a photosensitive member) according to a first embodiment of the present invention.FIGS. 1, 2, and 3are each a partial cross-sectional view illustrating a structure of a photosensitive member1, which is an example of the first embodiment. As illustrated inFIG. 1, the photosensitive member1includes a conductive substrate2and a photosensitive layer3. The photosensitive layer3is a single-layer photosensitive layer3c. The photosensitive layer3may be disposed directly on the conductive substrate2as illustrated inFIG. 1. Alternatively, the photosensitive member1may for example include the conductive substrate2, an intermediate layer4(for example, an undercoat layer), and the photosensitive layer3as illustrated inFIG. 2. In the example illustrated inFIG. 2, the photosensitive layer3is disposed indirectly on the conductive substrate2with the intermediate layer4therebetween. Alternatively, the photosensitive member1may include a protective layer5as an outermost layer as illustrated inFIG. 3.

The following describes elements of the photosensitive member1(the conductive substrate2, the photosensitive layer3, and the intermediate layer4). The following further describes a method for producing the photosensitive member1.

No particular limitations are placed on the conductive substrate2so long as the conductive substrate2can be used as a conductive substrate of the photosensitive member1. A conductive substrate of which at least a surface portion thereof is made from a material having conductivity can be used as the conductive substrate2. Examples of the conductive substrate2include a conductive substrate made from a material having conductivity (a conductive material) and a conductive substrate having a conductive material coating. Examples of conductive materials include aluminum, iron, copper, tin, platinum, silver, vanadium, molybdenum, chromium, cadmium, titanium, nickel, palladium, and indium. Any one of the conductive materials listed above may be used independently, or any two or more of the conductive materials listed above may be used in combination. Examples of combinations of two or more conductive materials include alloys (specific examples include aluminum alloy, stainless steel, and brass). Of the conductive materials listed above, aluminum and an aluminum alloy are preferable in terms of favorable charge mobility from the photosensitive layer3to the conductive substrate2.

The shape of the conductive substrate2can be selected as appropriate in accordance with the structure of an image forming apparatus in which the conductive substrate2is to be used. The conductive substrate2is for example a sheet-shaped conductive substrate or a drum-shaped conductive substrate. The thickness of the conductive substrate2can be selected as appropriate in accordance with the shape of the conductive substrate2.

The photosensitive layer3contains a charge generating material, a hole transport material, an electron transport material, and a binder resin. The photosensitive layer3may further contain an additive. No particular limitations are placed on the thickness of the photosensitive layer3so long as the thickness thereof is sufficient to enable the photosensitive layer3to function as a photosensitive layer. Specifically, the photosensitive layer3may have a thickness of at least 5 μm and no greater than 100 μm, and preferably have a thickness of at least 10 μm and no greater than 50 μm.

The Vickers hardness of the photosensitive layer3is measured by a method in accordance with Japanese Industrial Standard (JIS) Z2244. The Vickers hardness is measured using a hardness tester (for example, “MICRO VICKERS HARDNESS TESTER model DMH-1”, product of Matsuzawa Co., Ltd). The Vickers hardness can for example be measured under the following conditions: a temperature of 23° C., a diamond indenter load (test force) of 10 gf, a time to reach the test force of 5 seconds, a diamond indenter approach speed of 2 mm/second, and a test force retention time of 1 second.

The photosensitive layer3has a Vickers hardness of at least 17.0 HV, preferably at least 18.0 HV in terms of further improving anti-fogging performance, and more preferably at least 19.0 HV. No particular limitations are placed on the upper limit of the Vickers hardness of the photosensitive layer3so long as the photosensitive layer3is able to sufficiently function as the photosensitive layer of the photosensitive member1. Preferably, the upper limit of the Vickers hardness of the photosensitive layer3is 25.0 HV in terms of manufacturing costs.

Note that the Vickers hardness can for example be controlled by adjusting values of r, s, t, and u in general formula (1) representing a polyarylate resin (1) described below, types of X and Y in general formula (1); and a type and an amount of an electron transport material described below.

A scratch resistant depth (also referred to below as a scratch depth) of the photosensitive layer3means a depth of a scratch created by scratching the photosensitive layer3under specific conditions described below. The scratch depth is measured through first to fourth steps described below using a scratching apparatus in accordance with JIS K5600-5-5. The scratching apparatus includes a fixture and a scratching stylus. The scratching stylus has a semispherical sapphire tip having a diameter of 1 mm.

In the first step, the photosensitive member1is fixed to an upper surface of the fixture with a longitudinal direction of the photosensitive member1parallel with a longitudinal direction of the fixture. In the second step, the scratching stylus is brought into vertical contact with a surface of the photosensitive layer3. In the third step, the fixture and the photosensitive member1fixed to the upper surface of the fixture are caused to move by 30 mm at a rate of 30 mm/minute in the longitudinal direction of the fixture while a load of 10 g is applied from the scratching stylus to the photosensitive layer3. Through the third step, a scratch is created on the surface of the photosensitive layer3. In the fourth step, the greatest depth of the scratch is measured as a scratch depth.

Through the above, an overview of the measurement method of the scratch depth has been described. The measurement method of the scratch depth will be explained in detail in association with Examples.

The scratch depth of the photosensitive layer3is no greater than 0.50 μm. In terms of further improving anti-fogging performance, the scratch depth of the photosensitive layer3is preferably no greater than 0.45 μm, and more preferably no greater than 0.42 μm. No particular limitations are placed on the lower limit of the scratch depth of the photosensitive layer3so long as the photosensitive layer3is able to function as a photosensitive layer of the photosensitive member1. For example, the lower limit of the scratch depth of the photosensitive layer3may be 0.00 μm. However, in terms of manufacturing costs, the lower limit is preferably 0.10 μm.

Note that the scratch depth can for example be controlled by adjusting the values of r, s, t, and u in general formula (1) representing the polyarylate resin (1) described below; the types of X and Y in general formula (1), and the type and the amount of the electron transport material described below.

The following describes a charge generating material, a hole transport material, an electron transport material, a binder resin, and an additive, which is an optional component.

No particular limitations are placed on the charge generating material other than being a charge generating material that can be used in the photosensitive member. Examples of charge generating materials include phthalocyanine-based pigments, perylene-based pigments, bisazo pigments, tris-azo pigments, dithioketopyrrolopyrrole pigments, metal-free naphthalocyanine pigments, metal naphthalocyanine pigments, squaraine pigments, indigo pigments, azulenium pigments, cyanine pigments, powders of inorganic photoconductive materials (for example, selenium, selenium-tellurium, selenium-arsenic, cadmium sulfide, and amorphous silicon), pyrylium pigments, anthanthrone-based pigments, triphenylmethane-based pigments, threne-based pigments, toluidine-based pigments, pyrazoline-based pigments, and quinacridone-based pigments. One charge generating material may be used independently, or two or more charge generating materials may be used in combination. Examples of phthalocyanine-based pigments include metal-free phthalocyanine and metal phthalocyanine. Examples of metal phthalocyanine include titanyl phthalocyanine, hydroxygallium phthalocyanine, and chlorogallium phthalocyanine. The phthalocyanine-based pigments may be crystalline or non-crystalline. No particular limitations are placed on the crystal structure (for example, α-form, β-form, X-form, Y-form, V-form, and II-form) of the phthalocyanine-based pigments, and phthalocyanine-based pigments having various different crystal structures may be used.

An example of crystalline metal-free phthalocyanine is metal-free phthalocyanine having an X-form crystal structure (also referred to below as X-form metal-free phthalocyanine). Examples of crystalline titanyl phthalocyanine include titanyl phthalocyanines having α-form, β-form, and Y-form crystal structures (also referred to below as α-form titanyl phthalocyanine, β-form titanyl phthalocyanine, and Y-form titanyl phthalocyanine, respectively). An example of crystalline hydroxygallium phthalocyanine is hydroxygallium phthalocyanine having a V-form crystal structure.

In a situation in which the photosensitive member1is used in a digital optical system image forming apparatus, it is preferable to use a charge generating material that is sensitive to a range of wavelengths greater than or equal to 700 nm. An example of a charge generating material that is sensitive to a range of wavelengths greater than or equal to 700 nm is a phthalocyanine-based pigment. In particular, X-form metal-free phthalocyanine is preferable in terms of efficient charge generation. The digital optical system image forming apparatus may for example be a laser beam printer or a facsimile machine in which a light source such as a semiconductor laser is used.

In a situation in which the photosensitive member1is used in an image forming apparatus that employs a short-wavelength laser light source, it is preferable to use, for example, an anthanthrone-based pigment or a perylene-based pigment as a charge generating material. The wavelength of a short-wavelength laser is for example approximately 350 nm to 550 nm.

Examples of charge generating materials include phthalocyanine-based pigments represented by chemical formulae (CGM-1) to (CGM-4) shown below (also referred to below as charge generating materials (CGM-1) to (CGM-4), respectively).

In terms of efficient charge generation, the charge generating material is preferably contained in an amount of at least 0.1 parts by mass and no greater than 50 parts by mass relative to 100 parts by mass of the binder resin, more preferably in an amount of at least 0.5 parts by mass and no greater than 30 parts by mass, and particularly preferably in an amount of at least 0.5 parts by mass and no greater than 4.5 parts by mass.

Examples of hole transport materials include nitrogen-containing cyclic compounds and condensed polycyclic compounds. Examples of nitrogen-containing cyclic compounds and condensed polycyclic compounds include triphenylamine derivatives, diamine derivatives (specific examples include N,N,N′,N′-tetraphenylbenzidine derivatives, N,N,N′,N′-tetraphenylphenylenediamine derivatives, N,N,N′,N′-tetraphenylnaphtylenediamine derivatives, di(aminophenylethenyl)benzene derivatives, and N,N,N′,N′-tetraphenylphenanthrylenediamine derivatives), oxadiazole-based compounds (specific examples include 2,5-di(4-methylaminophenyl)-1,3,4-oxadiazole), styryl-based compounds (specific example include 9-(4-diethylaminostyryl)anthracene), carbazole-based compounds (specific examples include polyvinyl carbazole), organic polysilane compounds, pyrazoline-based compounds (specific examples include 1-phenyl-3-(p-dimethylaminophenyl)pyrazoline), hydrazone-based compounds, indole-based compounds, oxazole-based compounds, isoxazole-based compounds, thiazole-based compounds, thiadiazole-based compounds, imidazole-based compounds, pyrazole-based compounds, and triazole-based compounds. Any one of the hole transport materials listed above may be used independently, or any two or more of the hole transport materials listed above may be used in combination.

Of the hole transport materials listed above, in terms of efficient hole transport, a compound represented by general formula (HTM 1) shown below is preferable, and a compound represented by chemical formula (HTM1-1) shown below (also referred to below as a hole transport material (HTM1-1)) is more preferable.

In general formula (HTM1), R20, R21, R22, and R23each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6. c, d, e, and f each represent, independently of one another, an integer of at least 0 and no greater than 5. When c represents an integer of at least 2 and no greater than 5, chemical groups R20may be the same as or different from one another. When d represents an integer of at least 2 and no greater than 5, chemical groups R21may be the same as or different from one another. When e represents an integer of at least 2 and no greater than 5, chemical groups R22may be the same as or different from one another. When f represents an integer of at least 2 and no greater than 5, chemical groups R23may be the same as or different from one another.

In terms of efficient hole transport, the hole transport material is preferably contained in an amount of at least 10 parts by mass and no greater than 200 parts by mass relative to 100 parts by mass of the binder resin, and more preferably in an amount of at least 10 parts by mass and no greater than 100 parts by mass.

The electron transport material is represented by general formula (ETM1), general formula (ETM2), general formula (ETM3), general formula (ETM4), or general formula (ETM5) shown below. These electron transport materials are also referred to below as electron transport materials (ETM1) to (ETM5), respectively. The photosensitive layer3may contain only one of these electron transport materials or may contain two or more of the electron transport materials.

In general formula (ETM1), R1and R4each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6. R2and R3each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6. a and b each represent, independently of one another, an integer of at least 0 and no greater than 4. When a represents an integer of at least 2 and no greater than 4, chemical groups R2may be the same as or different from one another. When b represents an integer of at least 2 and no greater than 4, chemical groups R3may be the same as or different from one another.

In general formula (ETM2), R5represents a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6 and optionally having a halogen atom.

In general formula (ETM3), R6and R7each represent, independently of one another, a hydrogen atom or an aryl group having a carbon number of at least 6 and no greater than 14 and optionally having an alkyl group having a carbon number of at least 1 and no greater than 3.

In general formula (ETM4), R8and R9each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6. R10represents a halogen atom or a hydrogen atom.

In general formula (ETM5), R11, R12, R13, R14, and R15each represent, independently of one another, a hydrogen atom or an alkyl group having a carbon number of at least 1 and no greater than 6. R16represents a hydrogen atom or an aryl group having a carbon number of at least 6 and no greater than 14 and optionally having a halogen atom. G1and G2each represent, independently of one another, an oxygen atom or a sulfur atom.

In terms of further improving anti-fogging performance, preferably, R1and R4in general formula (ETM1) each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6, and more preferably a branched chain alkyl group having a carbon number of at least 1 and no greater than 6. In terms of further improving anti-fogging performance, preferably, a and b in general formula (ETM1) each represent 0. The electron transport material (ETM1) represented by general formula (ETM1) is for example an electron transport material represented by chemical formula (ETM1-1) shown below (also referred to below as an electron transport material (ETM1-1)).

In terms of further improving anti-fogging performance, preferably, R5in general formula (ETM2) represents an alkyl group having a carbon number of at least 1 and no greater than 6 and optionally having a halogen atom, and more preferably an alkyl group having a carbon number of at least 1 and no greater than 6 and having a chlorine atom. The electron transport material (ETM2) represented by general formula (ETM2) is for example an electron transport material represented by chemical formula (ETM2-1) shown below (also referred to below as an electron transport material (ETM2-1)).

In terms of further improving anti-fogging performance, preferably, R6and R7in general formula (ETM3) each represent, independently of one another, an aryl group having a carbon number of at least 6 and no greater than 14 and optionally having an alkyl group having a carbon number of at least 1 and no greater than 3, more preferably a phenyl group optionally having an alkyl group having a carbon number of at least 1 and no greater than 3, and still more preferably a phenyl group having an alkyl group having a carbon number of at least 1 and no greater than 3. The electron transport material (ETM3) represented by general formula (ETM3) is for example an electron transport material represented by chemical formula (ETM3-1) shown below (also referred to below as an electron transport material (ETM3-1)).

In terms of further improving anti-fogging performance, preferably, R8and R9in general formula (ETM4) each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6, and more preferably a branched chain alkyl group having a carbon number of at least 1 and no greater than 6. In terms of further improving anti-fogging performance, preferably. R10in general formula (ETM4) represents a halogen atom, and more preferably a chlorine atom. The electron transport material (ETM4) represented by general formula (ETM4) is for example an electron transport material represented by chemical formula (ETM4-1) shown below (also referred to below as an electron transport material (ETM4-1)).

In terms of further improving anti-fogging performance, preferably, R11, R13, and R15in general formula (ETM5) each represent, independently of one another, an alkyl group having a carbon number of at least 1 and no greater than 6, and more preferably a branched chain alkyl group having a carbon number of at least 1 and no greater than 6. In terms of further improving anti-fogging performance, preferably. R12and R14in general formula (ETM5) each represent a hydrogen atom. In terms of further improving anti-fogging performance, preferably, R16in general formula (ETM5) represents an aryl group having a carbon number of at least 6 and no greater than 14 and optionally having a halogen atom, more preferably a phenyl group optionally having a halogen atom, still more preferably a phenyl group having a chlorine atom, and particularly preferably a phenyl group having a plurality of chlorine atoms. In terms of further improving anti-fogging performance, preferably, G1and G2in general formula (ETM5) each represent an oxygen atom. The electron transport material (ETM5) represented by general formula (ETM5) is for example an electron transport material represented by chemical formula (ETM5-1) shown below (also referred to below as an electron transport material (ETM5-1)).

Of the electron transport materials mentioned above, the electron transport material (ETM1), the electron transport material (ETM2), and the electron transport material (ETM5) are preferable in terms of further improving anti-fogging performance, and the electron transport material (ETM1-1), the electron transport material (ETM2-1), and the electron transport material (ETM5-1) are more preferable.

The photosensitive layer3may contain an additional electron transport material other than the electron transport materials (ETM1) to (ETM5). Examples of additional electron transport materials that can be used include quinone-based compounds, diimide-based compounds, hydrazone-based compounds, malononitrile-based compounds, thiopyran-based compounds, trinitrothioxanthone-based compounds, 3,4,5,7-tetranitro-9-fluorenone-based compounds, dinitroanthracene-based compounds, dinitroacridine-based compounds, tetracyanoethylene, 2,4,8-trinitrothioxanthone, dinitrobenzene, dinitroacridine, succinic anhydride, maleic anhydride, and dibromomaleic anhydride that have different structures from the electron transport materials (ETM1) to (ETM5).

In terms of efficient electron transport, the electron transport material is preferably contained in an amount of at least 5 parts by mass and no greater than 100 parts by mass relative to 100 parts by mass of the binder resin, and more preferably in an amount of at least 10 parts by mass and no greater than 80 parts by mass.

The binder resin includes a polyarylate resin represented by general formula (1) shown below (also referred to below as a polyarylate resin (1)).

In general formula (1), Q1, Q2, Q3, and Q4each represent, independently of one another, a methyl group or a hydrogen atom. r, s, t, and u each represent, independently of one another, a number greater than or equal to 15 and less than or equal to 35. r+s+t+u=100. r+t=s+u. X and Y each represent, independently of one another, a divalent group represented by chemical formula (2A), chemical formula (2B), chemical formula (2C), or chemical formula (2D) shown below. X and Y are different from each other.

In terms of further improving anti-fogging performance, preferably, X and Y in general formula (1) each represent, independently of one another, a divalent group represented by chemical formula (2A), chemical formula (2B), or chemical formula (2D). In terms of further improving anti-fogging performance, more preferably, X in general formula (1) represents a divalent group represented by chemical formula (2D), and Y represents a divalent group represented by chemical formula (2A) or chemical formula (2B). In terms of further improving anti-fogging performance, preferably, Q1, Q2, Q3, and Q4in general formula (1) each represent a methyl group.

In terms of further improving anti-fogging performance and improving formability of the photosensitive layer3, preferably, r, s, t, and u in general formula (1) each represent, independently of one another, a number greater than or equal to 20 and less than or equal to 30.

The polyarylate resin (1) includes a repeating unit represented by general formula (1-1) shown below (also referred to below as a repeating unit (1-1)), a repeating unit represented by general formula (1-2) shown below (also referred to below as a repeating unit (1-2)), a repeating unit represented by general formula (1-3) shown below (also referred to below as a repeating unit (1-3)), and a repeating unit represented by general formula (1-4) shown below (also referred to below as a repeating unit (1-4)).

Q1and Q2in general formula (1-1), X in general formula (1-2), Q3and Q4in general formula (1-3), and Y in general formula (1-4) are respectively the same as defined for Q1, Q2, X, Q3, Q4, and Y in general formula (1).

Note that r in general formula (1) represents a percentage of the number of the repeating units (1-1) relative to a sum of the number of the repeating units (1-1), the number of the repeating units (1-2), the number of the repeating units (1-3), and the number of the repeating units (1-4) in the polyarylate resin (1). s represents a percentage of the number of the repeating units (1-2) relative to the sum of the number of the repeating units (1-1), the number of the repeating units (1-2), the number of the repeating units (1-3), and the number of the repeating units (1-4) in the polyarylate resin (1). t represents a percentage of the number of the repeating units (1-3) relative to the sum of the number of the repeating units (1-1), the number of the repeating units (1-2), the number of the repeating units (1-3), and the number of the repeating units (1-4) in the polyarylate resin (1). u represents a percentage of the number of the repeating units (1-4) relative to the sum of the number of the repeating units (1-1), the number of the repeating units (1-2), the number of the repeating units (1-3), and the number of the repeating units (1-4) in the polyarylate resin (1). Note that each of r, s, t, and u is not a value obtained from one resin chain but a number average obtained from all molecules of the polyarylate resin (1) (a plurality of resin chains) contained in the photosensitive layer3.

The polyarylate resin (1) may have another repeating unit in addition to the repeating units (1-1) to (1-4). A ratio (mole fraction) of a sum of the amounts by mole of the repeating units (1-1) to (1-4) relative to the total amount by mole of all the repeating units included in the polyarylate resin (1) is preferably at least 0.80, more preferably at least 0.90, and still more preferably 1.00.

No particular limitations are placed on the sequence of the repeating units (1-1) to (1-4) in the polyarylate resin (1) so long as a repeating unit derived from an aromatic diol and a repeating unit derived from an aromatic dicarboxylic acid are adjacent to one another. For example, the repeating unit (1-1) is adjacent to and bonded to the repeating unit (1-2) or the repeating unit (1-4). For another example, the repeating unit (1-3) is adjacent to and bonded to the repeating unit (1-2) or the repeating unit (1-4).

Examples of the polyarylate resin (1) include polyarylate resins represented by chemical formulae (R-1) to (R-1) shown below (also referred to below as polyarylate resins (R-1) to (R-11), respectively).

The binder resin preferably has a viscosity average molecular weight of at least 20,000, more preferably at least 25,000, and still more preferably at least 30,000. The viscosity average molecular weight of the binder resin is preferably no greater than 70,000, more preferably no greater than 50,000, and still more preferably no greater than 40,000. As a result of the viscosity average molecular weight of the binder resin being at least 30,000, the binder resin can have improved abrasion resistance, preventing the photosensitive layer3from being easily abraded. As a result of the viscosity average molecular weight of the binder resin being no greater than 40,000, the binder resin dissolves more readily in a solvent in formation of the photosensitive layer3, and thus the photosensitive layer3tends to be readily formed.

As the binder resin, the polyarylate resin (1) may be used independently, or a resin (an additional resin) other than the polyarylate resin (1) may be used. Examples of additional resins include thermoplastic resins (specific examples include polyarylate resins other than the polyarylate resin (1), polycarbonate resins, styrene-based resins, styrene-butadiene copolymers, styrene-acrylonitrile copolymers, styrene-maleate copolymers, styrene-acrylate 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, polyether resins, and polyester resins), thermosetting resins (specific examples include silicone resins, epoxy resins, phenolic resins, urea resins, melamine resins, and other crosslinkable thermosetting resins), and photocurable resins (specific examples include epoxy-acrylate-based resins and urethane-acrylate-based copolymers). Any one of the resins listed above may be used independently, or any two or more of the resins listed above may be used in combination.

(Preparation Method of Binder Resin)

No particular limitations are placed on the method for preparing the binder resin so long as the method enables preparation of the polyarylate resin (1). Examples of preparation methods (synthesis methods) of the polyarylate resin (1) include a method involving polycondensation of an aromatic dicarboxylic acid and an aromatic diol for forming repeating units of the polyarylate resin (1). No particular limitations are placed on the specific synthesis method of the polyarylate resin (1), and a known synthesis method (specific examples include solution polymerization, melt polymerization, and interfacial polymerization) can be employed. The following describes an example of the synthesis method of the polyarylate resin (1).

The polyarylate resin (1) is for example prepared through a method involving a reaction represented by chemical equation (R1) shown below (also referred to below as a reaction (R1)) or through a method conforming therewith. The preparation method of the polyarylate resin for example includes the reaction (R1).

In the reaction (R1), Q1and Q2in general formula (1-11), Q3and Q4in general formula (1-12), X in general formula (1-9), and Y in general formula (1-10) are respectively the same as defined for Q1, Q2, Q3, Q4, X, and Y in general formula (1).

In the reaction (R1), a reaction is caused between an aromatic dicarboxylic acid represented by general formula (1-9) and an aromatic dicarboxylic acid represented by general formula (1-10) (also referred to below as an aromatic dicarboxylic acid (1-9) and an aromatic dicarboxylic acid (1-10), respectively), and an aromatic diol represented by general formula (1-11) and an aromatic diol represented by general formula (1-12) (also referred to below as an aromatic diol (1-11) and an aromatic diol (1-12), respectively) to obtain the polyarylate resin (1).

Preferably, a sum of an amount by mole of the aromatic diol (1-11) and an amount by mole of the aromatic diol (1-12) is at least 0.9 mol and no greater than 1.1 mol relative to 1 mol of a sum of an amount by mole of the aromatic dicarboxylic acid (1-9) and an amount by mole of the aromatic dicarboxylic acid (1-10). As a result of the aromatic diols and the aromatic dicarboxylic acids being in the above-specified amount range, the polyarylate resin (1) is readily purified, and the polyarylate resin (1) is obtained in good yield.

The reaction (R1) may be promoted in the presence of an alkali and a catalyst. Examples of catalysts include tertiary ammoniums (specific examples include trialkylamines) and quaternary ammonium salts (specific examples include benzyltrimethylammoniumbromide). Examples of alkalis include alkali metal hydroxides (specific examples include sodium hydroxide and potassium hydroxide) and alkaline earth metal hydroxides (specific examples include calcium hydroxide). The reaction (R1) may be promoted in a solvent under an inert gas atmosphere. The solvent is for example water or chloroform. The inert gas is for example argon. Preferably, the reaction time of the reaction (R1) is at least 2 hours and no greater than 5 hours. Preferably, the reaction temperature is at least 5° C. and no greater than 25° C.

Examples of the aromatic dicarboxylic acids (1-9) and (1-10) include aromatic dicarboxylic acids having two carboxyl groups each bonded to an aromatic ring (specific examples include 2,6-naphthalene dicarboxylic acid, 4,4′-dicarboxydiphenyl ether, and 4,4′-dicarboxybiphenyl). An additional dicarboxylic acid other than the aromatic dicarboxylic acids (1-9) and (1-10) may be used in the reaction (R1). Note that a derivative of an aromatic dicarboxylic acid (specific examples include aryloyl halide and aromatic dicarboxylic acid anhydride) may be used instead of the aromatic dicarboxylic acid (1-9) or (1-10) in the synthesis of the polyarylate resin (1).

Examples of the aromatic diols (1-11) and (1-12) include 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane and 1,1-bis(4-hydroxy-3-methylphenyl)-3,3,5-trimethylcyclohexane. An additional diol (specific examples include bisphenol A, bisphenol S, bisphenol E, and bisphenol F) other than the aromatic diols (1-11) and (1-12) may be used in the reaction (R1). Note that a derivative such as a diacetate may be used instead of the aromatic diol (1-11) or (1-12) in the synthesis of the polyarylate resin (1).

The preparation of the polyarylate resin (1) may include an optional process (for example, a purification process) as necessary. In the purification process, purification is for example performed by a known method (specific examples include filtration, chromatography, and crystallization).

An additive may be added as an optional component. Examples of additives include antidegradants (specific examples include antioxidants, radical scavengers, quenchers, and ultraviolet absorbing agents), softeners, surface modifiers, extenders, thickeners, dispersion stabilizers, waxes, donors, surfactants, and leveling agents. Any one of the additives listed above may be added independently, or any two or more of the additives listed above may be added in combination.

Examples of antioxidants include hindered phenol compounds, hindered amine compounds, thioether compounds, and phosphite compounds. Of the antioxidants listed above, hindered phenol compounds and hindered amine compounds are preferable.

As described above, the photosensitive member1according to the present embodiment may have the intermediate layer4(for example, an undercoat layer). The intermediate layer4for example contains inorganic particles and a resin that is used for the intermediate layer (an intermediate layer resin). Provision of the intermediate layer4can facilitate flow of current generated when the photosensitive member1is exposed to light and inhibit increasing resistance, while also maintaining insulation to a sufficient degree so as to inhibit occurrence of leakage current.

Examples of inorganic particles include particles of metals (specific examples include aluminum, iron, and copper), particles of metal oxides (specific examples include titanium oxide, alumina, zirconium oxide, tin oxide, and zinc oxide), and particles of non-metal oxides (specific examples include silica). Any one type of the inorganic particles listed above may be used independently, or any two or more types of the inorganic particles listed above may be used in combination. The inorganic particles may be surface-treated.

No particular limitations are placed on the intermediate layer resin other than being a resin that can be used for forming the intermediate layer.

The following describes a production method of the photosensitive member1. The production method of the photosensitive member1for example includes a photosensitive layer formation process. In the photosensitive layer formation process, an application liquid for formation of the photosensitive layer3(also referred to below as an application liquid for photosensitive layer formation) is prepared. Next, the application liquid for photosensitive layer formation is applied onto the conductive substrate2. Next, drying is performed by an appropriate method to remove at least a portion of a solvent in the applied application liquid for photosensitive layer formation. Thus, the photosensitive layer3is formed. The application liquid for photosensitive layer formation for example contains a charge generating material, a hole transport material, an electron transport material, the polyarylate resin (1) as a binder resin, and a solvent. The application liquid for photosensitive layer formation is prepared by dissolving or dispersing the charge generating material, the hole transport material, the electron transport material, and the polyarylate resin (1) as the binder resin in the solvent. Additives may optionally be added to the application liquid for photosensitive layer formation.

The following describes the photosensitive layer formation process in detail. No particular laminations are placed on the solvent contained in the application liquid for photosensitive layer formation other than that components of the application liquid should be soluble or dispersible in the solvent. Examples of solvents include alcohols (specific examples include methanol, ethanol, isopropanol, and butanol), aliphatic hydrocarbons (specific examples include n-hexane, octane, and cyclohexane), aromatic hydrocarbons (specific examples include benzene, toluene, and xylene), halogenated hydrocarbons (specific examples include dichloromethane, dichloroethane, carbon tetrachloride, and chlorobenzene), ethers (specific examples include dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether), ketones (specific examples include acetone, methyl ethyl ketone, and cyclohexanone), esters (specific examples include ethyl acetate and methyl acetate), dimethyl formaldehyde, dimethyl formamide, and dimethyl sulfoxide. Any one of the solvents listed above may be used independently, or any two or more of the solvents listed above may be used in combination. Of the solvents listed above, a non-halogenated solvent is preferably used.

The application liquid for photosensitive layer formation is prepared by mixing the components to disperse the components in the solvent. Mixing or dispersion can for example be performed using a bead mill, a roll mill, a ball mill, an attritor, a paint shaker, or an ultrasonic disperser.

The application liquid for photosensitive layer formation may for example contain a surfactant or a leveling agent in order to improve dispersibility of the components or improve surface flatness of the resulting photosensitive layer3.

No particular limitations are placed on the method by which the application liquid for photosensitive layer formation is applied so long as the method enables uniform application of the application liquid for photosensitive layer formation. Examples of application methods include dip coating, spray coating, spin coating, and bar coating.

No particular limitations are placed on the method by which at least a portion of the solvent in the application liquid for photosensitive layer formation is removed other than being a method that enables evaporation of at least a portion of the solvent in the application liquid. Examples of methods that can be used to remove the solvent include heating, pressure reduction, and a combination of heating and pressure reduction. One specific example of the method involves heat treatment (hot-air drying) using a high-temperature dryer or a reduced pressure dryer. The heat treatment is for example performed for at least 3 minutes and no greater than 120 minutes at a temperature of at least 40° C. and no greater than 150° C.

Note that the production method of the photosensitive member1may further include an optional process such as a process of forming the intermediate layer4as necessary. The process of forming the intermediate layer4can be carried out by a method selected appropriately from known methods.

The photosensitive member according to the present embodiment described above is excellent in anti-fogging performance, and can therefore be favorably used in various image forming apparatuses.

Second Embodiment: Image Forming Apparatus

The following describes an image forming apparatus according to a second embodiment. The image forming apparatus according to the second embodiment includes an image bearing member, a charger, a light exposure section, a development section, and a transfer section. The image bearing member is the photosensitive member according to the first embodiment described above. The charger charges a surface of the image bearing member. The charger has a positive charging polarity. The light exposure section exposes the charged surface of the image bearing member to light to form an electrostatic latent image on the surface of the image bearing member. The development section develops the electrostatic latent image into a toner image. The transfer section transfers the toner image from the image bearing member to a transfer target while bringing the transfer target into contact with the surface of the image bearing member.

The image forming apparatus according to the second embodiment can inhibit image defects from occurring. The reason for the above is thought to be as follows. The image forming apparatus according to the second embodiment includes the photosensitive member according to the first embodiment as an image bearing member. The photosensitive member according to the first embodiment is excellent in anti-fogging performance. The image forming apparatus according to the second embodiment can therefore inhibit image defects (specific examples include fogging) from occurring.

The following describes a tandem color image forming apparatus as an example of the image forming apparatus according to the second embodiment with reference toFIG. 4.

An image forming apparatus100illustrated inFIG. 4adopts a direct transfer process. Typically, a recording medium serving as a transfer target comes in contact with an image bearing member in an image forming apparatus adopting the direct transfer process. As a result, minute matter from the recording medium is likely to adhere to a surface of the image bearing member and cause an image defect. However, the image forming apparatus100, which is an example of the second embodiment, includes the photosensitive member according to the first embodiment as an image bearing member30. The photosensitive member according to the first embodiment is excellent in anti-fogging performance. Accordingly, as long as the image forming apparatus100includes the photosensitive member according to the first embodiment as the image bearing member30, it is possible to inhibit image defects from occurring even if the image forming apparatus100adopts the direct transfer process.

The image forming apparatus100includes image formation units40a,40b,40c, and40d, a transfer belt50, and a fixing section52. Hereinafter, the image formation units40a,40b,40c, and40dare each referred to as an image formation unit40unless they need to be distinguished from one another.

The image formation unit40includes the image bearing member30, a charger42, a light exposure section44, a development section46, and a transfer section48. The image bearing member30is located at a central location in the image formation unit40. The image bearing member30is rotatable in an arrow direction (counterclockwise). The charger42, the light exposure section44, the development section46, and the transfer section48are located around the image bearing member30in order from upstream in a rotation direction of the image bearing member30relative to the charger42as a reference point. Note that the image formation unit40may further include a cleaning section (not shown) or a static eliminating section (not shown).

The image formation units40ato40drespectively superimpose toner images of a plurality of colors (for example, four colors including black, cyan, magenta, and yellow) in order on a recording medium P on the transfer belt50.

The charger42is a charging roller. The charging roller charges a surface of the image bearing member30while in contact with the surface of the image bearing member30. Typically, image defects easily occur in the case of an image forming apparatus including a charging roller. However, the image forming apparatus100includes the photosensitive member according to the first embodiment as the image bearing member30. The photosensitive member according to the first embodiment is excellent in anti-fogging performance. It is therefore possible to inhibit image defects from occurring even if the image forming apparatus100includes a charging roller as the charger42. As described above, the image forming apparatus100, which is an example of the second embodiment, adopts a contact charging process. Another example of the contact charger is a charging brush. Note that the charger may be a non-contact charger. Examples of the non-contact charger include a corotron charger and a scorotron charger.

No particular limitations are placed on the voltage that is applied by the charger42. The voltage that is applied by the charger42is for example a direct current voltage, an alternating current voltage, or a composite voltage (of an alternating current voltage superimposed on a direct current voltage), among which a direct current voltage is preferable. The direct current voltage is advantageous as described below compared to an alternating current voltage and a composite voltage. In a configuration in which the charger42only applies a direct current voltage, the value of voltage applied to the image bearing member30is constant, and therefore it is easy to uniformly charge the surface of the image bearing member30to a specified potential. The amount of abrasion of the photosensitive layer tends to be smaller in a configuration in which the charger42only applies a direct current voltage. As a result, favorable images can be formed.

The light exposure section44exposes the charged surface of the image bearing member30to light. As a result, an electrostatic latent image is formed on the surface of the image bearing member30. The electrostatic latent image is formed based on image data input into the image forming apparatus100.

The development section46supplies toner to the surface of the image bearing member30to develop the electrostatic latent image into a toner image. The development section46may develop the electrostatic latent image into a toner image while in contact with the surface of the image bearing member30.

The development section46is capable of cleaning the surface of the image bearing member30. That is, the image forming apparatus100may adopt a cleaner-less process, which is a process without a cleaner. According to this configuration, the development section46is capable of removing residual matter on the surface of the image bearing member30. A typical image forming apparatus including a cleaning section (for example, a cleaning blade) and an image bearing member scrapes away residual matter on a surface of the image bearing member using the cleaning section. However, the image forming apparatus adopting the cleaner-less process does not scrape away residual matter on the surface of the image bearing member. The image forming apparatus adopting the cleaner-less process therefore tends to leave the residual matter on the surface of the image bearing member. However, the image forming apparatus100includes the photosensitive member according to the first embodiment, which is excellent in anti-fogging performance, as the image bearing member30. As long as the image forming apparatus100includes such a photosensitive member, residual matter, particularly minute matter (for example, paper dust) from the recording medium P, tends not to be left on the surface of the photosensitive member even if the image forming apparatus100adopts the cleaner-less process. As a result, the image forming apparatus100is capable of inhibiting image defects (for example, fogging) from occurring.

In order that the development section46efficiently cleans the surface of the image bearing member30as well as performing development, the following conditions (a) and (b) are preferably satisfied.

Condition (a): A contact development process is adopted, and a peripheral speed (rotation speed) of the image bearing member30and a peripheral speed (rotation speed) of the development section46are different.

Condition (b): A surface potential of the image bearing member30and a potential of development bias satisfy relation (b-1) and relation (b-2) shown below.

0 (V) < Potential (V) of development bias < Surface potential (V)(b-1)of non-exposed region of image bearing member 30Potential (V) of development bias > Surface potential (V) of(b-2)exposed region of image bearing member 30 > 0 (V)

When the condition (a) is satisfied, that is, in a configuration in which the contact development process is adopted, and the peripheral speed of the image bearing member30and the peripheral speed of the development section46are different, the surface of the image bearing member30is in contact with the development section46, and matter adhering to the surface of the image bearing member30is removed by rubbing against the development section46. Preferably, the peripheral speed of the development section46is greater than the peripheral speed of the image bearing member30.

The condition (b) is on the assumption that a reversal development process is adopted. Preferably, in order to improve electrical characteristics of the image bearing member30that has a positive charging polarity, all of the charging polarity of the toner, the surface potential of the non-exposed region of the image bearing member30, the surface potential of the exposed region of the image bearing member30, and the potential of the development bias are of positive polarity. Note that the surface potential of the non-exposed region of the image bearing member30and the surface potential of the exposed region of the image bearing member30are measured after toner image transfer from the image bearing member30to the recording medium P by the transfer section48and before charging of the surface of the image bearing member30by the charger42.

When the relation (b-1) of the condition (b) is satisfied, an electrostatic repulsion between remaining toner (also referred to below as residual toner) on the image bearing member30and the non-exposed region of the image bearing member30is greater than an electrostatic repulsion between the residual toner and the development section46. As a result, the residual toner in the non-exposed region of the image bearing member30moves from the surface of the image bearing member30to the development section46to be collected.

When relation (b-2) of the condition (b) is satisfied, an electrostatic repulsion between the residual toner and the exposed region of the image bearing member30is smaller than an electrostatic repulsion between the residual toner and the development section46. As a result, the residual toner in the exposed region of the image bearing member30is kept on the surface of the image bearing member30. The toner kept in the exposed region of the image bearing member30is then used for image formation.

The transfer belt50conveys the recording medium P to a location between the image bearing member30and the transfer section48. The transfer belt50is an endless belt. The transfer belt50is rotatable in an arrow direction (clockwise).

After the toner image has been formed through development by the development section46, the transfer section48transfers the toner image from the surface of the image bearing member30to the recording medium P. The toner image is transferred from the image bearing member30to the recording medium P while the image bearing member30is in contact with the recording medium P. The transfer section48is for example a transfer roller.

The fixing section52applies either or both of heat and pressure to the unfixed toner image transferred to the recording medium P by the transfer section48. The fixing section52is for example either or both of a heating roller and a pressure roller. The toner image is fixed to the recording medium P through application of either or both of heat and pressure to the toner image. As a result, an image is formed on the recording medium P.

An example of the image forming apparatus according to the second embodiment has been described above. However, the image forming apparatus according to the second embodiment is not limited to the image forming apparatus100described above. For example, the image forming apparatus according to the second embodiment may be a monochrome image forming apparatus. In this case, for example, it is only necessary that the image forming apparatus includes at least one image formation unit. For another example, the image forming apparatus according to the second embodiment is not limited to the above-described tandem image forming apparatus100and may alternatively be a rotary image forming apparatus. The image forming apparatus according to the second embodiment may adopt an intermediate transfer process. In a configuration in which the image forming apparatus according to the second embodiment adopts an intermediate transfer process, the transfer target is an intermediate transfer belt.

Third Embodiment: Process Cartridge

A process cartridge according to a third embodiment includes the photosensitive member according to the first embodiment as an image bearing member. The following describes an example of the process cartridge according to the third embodiment with reference toFIG. 4.

The process cartridge according to the third embodiment is for example equivalent to each of the image formation units40ato40d(FIG. 4). Each of the process cartridges has a unitized configuration. The unitized configuration includes the image bearing member30. The unitized configuration may include, in addition to the image bearing member30, at least one selected from the group consisting of the charger42, the light exposure section44, the development section46, and the transfer section48. The process cartridge may further include a static eliminating section (not shown). The process cartridge is for example designed to be freely attachable to and detachable from the image forming apparatus100. Accordingly, the process cartridge is easy to handle and can be easily and quickly replaced, together with the image bearing member30, when properties such as sensitivity of the image bearing member30deteriorate.

The process cartridge according to the third embodiment described above includes the photosensitive member according to the first embodiment as an image bearing member, and thus is capable of inhibiting image defects from occurring.

EXAMPLES

The following provides more specific description of the present invention through use of Examples. Note that the present invention is not limited to the scope of the Examples.

<Materials Used in Examples and Comparative Examples>

A charge generating material, a hole transport material, electron transport materials, and binder resins described below were prepared as materials for production of single-layer photosensitive members.

The charge generating material (CGM-1) described in association with the first embodiment was prepared. The charge generating material (CGM-1) was metal-free phthalocyanine represented by chemical formula (CGM-1) having an X-form crystal structure. That is, the charge generating material (CGM-1) was X-form metal-free phthalocyanine.

The hole transport material (HTM1-1) described in association with the first embodiment was prepared.

The electron transport materials (ETM1-1), (ETM2-1), (ETM3-1), (ETM4-1), and (ETM5-1) described in association with the first embodiment were prepared. Furthermore, electron transport materials (ETM6-1) and (ETM7-1) were also prepared. The electron transport materials (ETM6-1) and (ETM7-1) are respectively electron transport materials represented by chemical formulae (ETM6-1) and (ETM7-1) shown below.

The polyarylate resins (R-1) to (R-9) described in association with the first embodiment and polyarylate resins (R-12) to (R-17) were prepared as the binder resins. The resins (R-12) to (R-17) are resins including repeating units represented by chemical formulae (R-12) to (R-17) shown below, respectively.

The following describes synthesis methods of the polyarylate resins (R-1) to (R-9) that were used in the Examples.

A three-necked flask was used as a reaction vessel. The reaction vessel was a three-necked flask having a capacity of 1 L and equipped with a thermometer, a three-way cock, and a dripping funnel. Into the reaction vessel, 25.63 g (82.86 mmol) of 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 0.124 g (0.826 mmol) of t-butylphenol, 7.84 g (196 mmol) of sodium hydroxide, and 0.240 g (0.768 mmol) of benzyltributylammonium chloride were added. Next, the reaction vessel was purged with argon. Thereafter, 600 mL of water was added into the reaction vessel. The internal temperature of the reaction vessel was kept at 20° C., and the reaction vessel contents were stirred for 1 hour. Thereafter, the internal temperature of the reaction vessel was reduced to 10° C. As a result, an alkaline aqueous solution was obtained.

Separately from the alkaline aqueous solution, 9.84 g (38.9 mmol) of 2,6-naphthalenedicarboxylic acid dichloride and 11.47 g (38.9 mmol) of 4,4′-oxybisbenzoic acid dichloride were dissolved in 300 g of chloroform. As a result, a chloroform solution was obtained.

Next, the temperature of the alkaline aqueous solution was adjusted to 10° C., and subsequently the chloroform solution was gradually dripped into the alkaline aqueous solution through the dripping funnel over 110 minutes to initiate a polymerization reaction. The polymerization reaction was caused to proceed for 3 hours while the reaction vessel contents were stirred and the internal temperature of the reaction vessel was kept at 13±3° C.

Thereafter, decantation was performed to remove an upper layer (a water layer) from the reaction vessel contents to collect an organic layer. Next, 500 mL of ion exchanged water was added into a three-necked flask having a capacity of 2 L, and then the collected organic layer was added into the flask. Furthermore, 300 g of chloroform and 6 mL of acetic acid were added into the flask. The three-necked flask contents were stirred at room temperature (25° C.) for 30 minutes. Thereafter, decantation was performed to remove an upper layer (a water layer) from the three-necked flask contents to collect an organic layer. The collected organic layer was washed with 500 mL of ion exchanged water using a separatory funnel. Washing with ion exchanged water was repeated eight times, and thus the water-washed organic layer was obtained.

Next, the water-washed organic layer was filtered to collect a filtrate. Into a conical flask having a capacity of 3 L, 1.5 L of methanol was added. The collected filtrate was gradually dripped into the conical flask to give a precipitate. The precipitate was filtered off. The thus collected precipitate was vacuum dried for 12 hours at 70° C. As a result, the polyarylate resin (R-1) was obtained. The mass yield of the polyalylate resin (R-1) was 35.3 g, and the percentage yield thereof was 88.7%.

Each of the polyarylate resins (R-2) to (R-7) was synthesized according to the same method as for the polyarylate resin (R-1) in all aspects other than that 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane was changed to an aromatic diol that was a starting material of the polyarylate resin, and/or at least one of 2,6-naphthalenedicarboxylic acid dichloride and 4,4′-oxybisbenzoic acid dichloride was changed to an aryloyl halide that was a starting material of the polyarylate resin. Each of the polyarylate resins (R-8) and (R-9) was synthesized according to the same method as for the polyarylate resin (R-1) in all aspects other than that the ratio of the amount by mole of each starting material was changed to the ratio of the amount by mole of the corresponding repeating unit.

Next, a proton nuclear magnetic resonance spectrometer (product of JASCO Corporation, 300 MHz) was used to measure1H-NMR spectra of the polyarylate resins (R-1) to (R-9) synthesized as described above. CDCl3was used as a solvent. Tetramethylsilane (TMS) was used as an internal standard sample. Of these polyarylate resins, the polyarylate resin (R-1) will be described as a representative example.

FIG. 9shows a1H-NMR spectrum of the polyarylate resin (R-1). InFIG. 9, the horizontal axis represents chemical shift (unit: ppm) and the vertical axis represents signal intensity (unit: arbitrary unit). Chemical shifts of the polyarylate resin (R-1) are shown below.

The1H-NMR spectrum and the chemical shifts were used to confirm that the polyarylate resin (R-1) had been obtained. Likewise, the1H-NMR spectra and chemical shifts of the other polyarylate resins (R-2) to (R-9) were used to confirm that the polyarylate resins (R-2) to (R-9) had been obtained.

The following describes a production method of a photosensitive member (A-1) according to Example 1. A vessel was charged with 2 parts by mass of the charge generating material (CGM-1), 65 parts by mass of the hole transport material (HTM1-1), 35 parts by mass of the electron transport material (ETM3-1), 100 parts by mass of the polyarylate resin (R-1) as a binder resin, and 300 parts by mass of tetrahydrofuran as a solvent. A rod-shaped ultrasonic vibrator was used to mix the materials and the solvent in the vessel for 2 minutes to disperse the materials in the solvent. The materials and the solvent in the vessel were further mixed for 50 hours using a ball mill to disperse the materials in the solvent. Thus, an application liquid for single-layer photosensitive layer formation was obtained. The application liquid for single-layer photosensitive layer formation was applied onto a conductive substrate—an aluminum drum-shaped support—by dip coating. The applied application liquid for single-layer photosensitive layer formation was hot-air dried at 100° C. for 40 minutes. Thus, a single-layer photosensitive layer (film thickness: 25 μm) was formed on the conductive substrate. As a result, the single-layer photosensitive member (A-1) was obtained.

[Photosensitive Members (A-2) to (A-19) and (B-1) to (B-10)]

Photosensitive members (A-2) to (A-19) and (B-1) to (B-10) were obtained according to the same method as the above-described production method of the photosensitive member (A-1) in all aspects other than that the binder resins and the electron transport materials shown in Tables 1 and 2 were used. Note that R-1 to R-9 under “Type” in the column titled “Binder resin” in Tables 1 and 2 respectively represent the polyarylate resins (R-1) to (R-9). R-12 to R-17 under “Type” in the column titled “Binder resin” respectively represent the resins (R-12) to (R-17). “Molecular weight” in the column titled “Binder resin” represents the viscosity average molecular weight of the binder resins. ETM1-1 to ETM7-1 under “Type” in the column titled “Electron transport material” respectively represent the electron transport materials (ETM1-1) to (ETM7-1).

<Measurement Method and Evaluation Method>

With respect to each of the photosensitive members (A-1) to (A-19) and (B-1) to (B-10) obtained as described above, the scratch depth of the photosensitive layer (single-layer photosensitive layer) of the photosensitive member was measured. The scratch depth was measured according to a method described below using a scratching apparatus200(seeFIG. 5) in accordance with Japanese Industrial Standard (JIS) K5600-5-5 (K5600: testing methods for paints, Part 5: mechanical property of film, Section 5: scratch hardness (stylus method)).

The following describes the scratching apparatus200in accordance with JIS K5600-5-5 with reference toFIG. 5.FIG. 5is a diagram illustrating an example of a configuration of the scratching apparatus200. The scratching apparatus200includes a fixture201, a retainer202, a scratching stylus203, a support arm204, two shaft supports205, a base206, two rails207, a weight pan208, and a constant speed motor (not shown). A weight209is placed on the weight pan208.

InFIG. 5, an X axis direction and a Y axis direction are each a horizontal direction, and a Z axis direction is a vertical direction. The X axis direction indicates a longitudinal direction of the fixture201. The Y axis direction indicates a direction orthogonal to the X axis direction on a plane parallel with an upper surface (loading surface)201aof the fixture201. Note that an X axis direction, a Y axis direction, and a Z axis direction inFIGS. 6 to 8described below are the same as defined inFIG. 5.

The fixture201is equivalent to a test piece fixture according to JIS K5600-5-5. The fixture201has the upper surface201a, an end201b, and an opposite end201c. The upper surface201aof the fixture201is a horizontal surface. The end201bfaces toward the two shaft supports205.

The retainer202is disposed on the upper surface201aof the fixture201in a position closer to the opposite end201cthan to the end201b. The retainer202fixes a measurement target (the photosensitive member1) to the upper surface201aof the fixture201.

The scratching stylus203has a tip203b(seeFIG. 6). The tip203bhas a semispherical structure having a diameter of 1 mm. The tip203bis made from sapphire.

The support arm204supports the scratching stylus203. The support arm204pivots about a shaft204ain directions that the scratching stylus203moves toward and away from the photosensitive member1.

The two shaft supports205pivotally support the support arm204.

The base206has an upper surface206a. The two shaft supports205are disposed at an end of the upper surface206a.

The two rails207are disposed at an opposite end of the upper surface206a. The two rails207are opposed in parallel with each other. The two rails207are parallel with the longitudinal direction (X axis direction) of the fixture201. The fixture201is disposed between the two rails207. The fixture201is horizontally movable along the rails207in the longitudinal direction (X axis direction) of the fixture201.

The weight pan208is disposed on the scratching stylus203with the support arm204therebetween. The weight209is placed on the weight pan208.

The constant speed motor causes the fixture201to move along the rails207in the longitudinal direction (X axis direction) thereof.

The following describes a measurement method of the scratch depth. The measurement method of the scratch depth includes first to fourth steps. A surface property tester (“HEIDON TYPE 14”, product of Shinto Scientific Co., Ltd.) was used as the scratching apparatus200. The scratch depth was measured under environmental conditions of a temperature of 23° C. and a relative humidity of 50%. The photosensitive member was drum-shaped (cylindrical).

In the first step, the photosensitive member1was fixed to the upper surface201aof the fixture201with a longitudinal direction of the photosensitive member1parallel with the longitudinal direction of the fixture201. The photosensitive member1was loaded such that a direction of a central axis L2(rotation axis) of the photosensitive member1was parallel with the longitudinal direction of the fixture201.

In the second step, the scratching stylus203was brought into vertical contact with a surface3aof a photosensitive layer3. The following describes how the scratching stylus203was brought into vertical contact with the surface3aof the photosensitive layer3of the drum-shaped photosensitive member1with reference toFIGS. 6 and 7in addition toFIG. 5.

FIG. 6is a cross-sectional view of the photosensitive member1in contact with the scratching stylus203, taken along line IV-IV inFIG. 5.FIG. 7is a side view of the fixture201, the scratching stylus203, and the photosensitive member1illustrated inFIG. 5.

The scratching stylus203was moved toward the photosensitive member1such that an extension of a central axis A1of the scratching stylus203was perpendicular to the upper surface201aof the fixture201. Next, the tip203bof the scratching stylus203was brought into contact with a point (contact point P2) on the surface3aof the photosensitive layer3of the photosensitive member1. The location of the contact point P2was farthest from the upper surface201aof the fixture201in the vertical direction (Z axis direction) among possible locations on the surface3a. Thus, the tip203bof the scratching stylus203was brought into contact with the photosensitive member1such that the central axis A1of the scratching stylus203was perpendicular to a tangent A2. In such an arrangement, a line connecting a contact point P1in contact with the upper surface201aand the contact point P2in contact with the tip203bwas perpendicular to the central axis L2of the photosensitive member1. The tangent A2touches, at the contact point P2, a perimeter circle of a cross-section of the photosensitive member1taken in a direction perpendicular to the central axis L2.

The following describes the third step with reference toFIGS. 5 and 6. In the third step, a load W of 10 g was applied from the scratching stylus203to the photosensitive layer3with the scratching stylus203in vertical contact with the surface3aof the photosensitive layer3. Specifically, the weight209, which weighed 10 g, was placed on the weight pan208. With the load W being applied to the photosensitive layer3, the fixture201was caused to move. Specifically, the constant speed motor was driven to cause the fixture201to horizontally move in the longitudinal direction thereof (X axis direction) along the rails207. That is, the end201bof the fixture201moved from a first position N1to a second position N2. The second position N2was located downstream of the first position N1in terms of a direction that the fixture201moves away from the two shaft supports205in the longitudinal direction of the fixture201. The photosensitive member1horizontally moved in the longitudinal direction of the fixture201as the fixture201moved in the longitudinal direction. The fixture201and the photosensitive member1moved at a rate of 30 mm/minute. The fixture201and the photosensitive member1moved by a distance of 30 mm. The distance by which the fixture201and the photosensitive member1moved was equal to a distance D1-2between the first position N1and the second position N2. As a result of the fixture201and the photosensitive member1moving, the scratching stylus203created a scratch S on the surface3aof the photosensitive layer3of the photosensitive member1.

The following describes the scratch S with reference toFIG. 8in addition toFIGS. 5 to 7.FIG. 8illustrates the scratch S created on the surface3aof the photosensitive layer3. The thus created scratch S had a depth in a direction perpendicular both to the upper surface201aof the fixture201and to the tangent A2. The scratch S followed a line L3illustrated inFIG. 7. The line L3included a plurality of the contact points P2. The line L3was parallel with the upper surface201aof the fixture201and with the central axis L2of the photosensitive member1. The line L3was perpendicular to the central axis A1of the scratching stylus203.

In the fourth step, the scratch depth was measured, which is a greatest value of a depth Ds of the scratch S. Specifically, the photosensitive member1was removed from the fixture201. A three-dimensional interference microscope (“WYKO NT-1100”, product of Bruker Corporation) was used to observe the scratch S created on the photosensitive layer3of the photosensitive member1at a magnification of 5× to measure the depth Ds of the scratch S. The depth Ds of the scratch S was defined as a distance between the tangent A2and a bottom of the scratch S. The greatest value of the measured values of the depth Ds of the scratch S was taken to be the scratch depth. Tables 1 and 2 show the scratch depth measured as described above.

With respect to each of the photosensitive members (A-1) to (A-19) and (B-1) to (B-10) obtained as described above, the Vickers hardness of the photosensitive layer (single-layer photosensitive layer) of the photosensitive member was measured. The Vickers hardness of the photosensitive layer was measured by a method in accordance with Japanese Industrial Standard (JIS) Z2244. The Vickers hardness was measured using a hardness tester (“MICRO VICKERS HARDNESS TESTER model DMH-1”, product of Matsuzawa Co., Ltd). The Vickers hardness was measured under the following conditions: a temperature of 23° C., a diamond indenter load (test force) of 10 gf, a time to reach the test force of 5 seconds, a diamond indenter approach speed of 2 mm/second, and a test force retention time of 1 second. Tables 1 and 2 show the Vickers hardness measured as described above.

With respect to each of the photosensitive members (A-1) to (A-19) and (B-1) to (B-10) obtained as described above, anti-fogging performance was evaluated in an image formed using the photosensitive member. An image forming apparatus (modified version of “MONOCHROME PRINTER FS-1300D”, product of KYOCERA Document Solutions Inc.) was used as an evaluation apparatus. The image forming apparatus adopts a direct transfer process, a contact development process, and a cleaner-less process. In the image forming apparatus, a development section cleans toner remaining on a photosensitive member. A charger of the image forming apparatus is a charging roller. “KYOCERA Document Solutions-brand paper VM-A4” sold by KYOCERA Document Solutions Inc. (A4 size) was used. A one-component developer (test sample) was used in the evaluation using the evaluation apparatus.

The evaluation apparatus was used to print an image 1 on 12,000 successive sheets of the paper under conditions of a photosensitive member rotational speed of 168 mm/second and a charge potential of +600 V. The image 1 had a coverage of 1%. Subsequently, a blank image was printed on a sheet of the paper. The printing was performed under environmental conditions of a temperature of 32.5° C. and a relative humidity of 80%. An image density of each of three sections in the printed blank image was measured using a reflectance densitometer (“RD914”, product of X-Rite Inc.). A sum of the image densities of the three sections of the blank image was divided by the number of the measured sections. Thus, a number average image density of the blank image was obtained. A value calculated by subtracting an image density of the paper that was not subjected to printing from the number average image density of the blank image was taken to be a fogging density. The thus obtained fogging density was rated in accordance with the following rating standard. Anti-fogging performance of the photosensitive member was evaluated as good if the image fogging density thereof was rated as A or B. Anti-fogging performance of the photosensitive member was evaluated as poor if the image fogging density thereof was rated as C. The fogging density (FD) and the rating results are shown in Tables 1 and 2.

As shown in Table 1, each of the photosensitive members (A-1) to (A-19) contained one of the polyarylate resins (R-1) to (R-9) each having repeating units encompassed by general formula (1). Each of the photosensitive members (A-1) to (A-19) contained one of the electron transport materials (ETM1-1) to (ETM5-1), which are each encompassed by general formula (ETM1), general formula (ETM2), general formula (ETM3), general formula (ETM4), or general formula (ETM5). The scratch depth of the photosensitive layer of each of the photosensitive members (A-1) to (A-19) was from 0.10 μm to 0.42 μm. The Vickers hardness of the photosensitive layer of each of the photosensitive members (A-1) to (A-19) was from 19.0 HV to 22.6 HV. Anti-fogging performance of each of the photosensitive members (A-1) to (A-19) was evaluated as good with a rating “A”.

As shown in Table 2, each of the photosensitive members (B-1) to (B-6), (B-9), and (B-10) contained one of the resins (R-12) to (R-17), which are not encompassed by general formula (1). Each of the photosensitive members (B-5) to (B-8) contained one of the electron transport materials (ETM6-1) and (ETM7-1), which are not encompassed by any of general formula (ETM1), general formula (ETM2), general formula (ETM3), general formula (ETM4), and general formula (ETM5). The scratch depth of the photosensitive layer of each of the photosensitive members (B-1) to (B-6), (B-9), and (B-10) was greater than 0.50 μm. The Vickers hardness of the photosensitive layer of each of the photosensitive members (B-1), (B-2), and (B-5) to (B-8) was less than 17.0 HV. Anti-fogging performance of each of the photosensitive members (B-1) to (B-10) was evaluated as poor with a rating “C”.

As evident from Tables 1 and 2, the photosensitive members (A-1) to (A-19) showed higher anti-fogging performance than the photosensitive members (B-1) to (B-10). The image forming apparatus showed higher anti-fogging performance when the image forming apparatus included any of the photosensitive members (A-1) to (A-19) than when the image forming apparatus included any of the photosensitive members (B-1) to (B-10).

INDUSTRIAL APPLICABILITY

The electrophotographic photosensitive member according to the present invention is applicable to image forming apparatuses such as multifunction peripherals.