Electrophotographic photosensitive member, method for manufacturing electrophotographic photosensitive member, process cartridge, and electrophotographic apparatus

The present invention relates to an electrophotographic photosensitive member, a method for manufacturing this electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus incorporating this electrophotographic photosensitive member.

Electrophotographic photosensitive members having a charge transport layer as a surface layer are required to be resistant to wear enough to withstand repeated use. To improve the wear resistance of the charge transport layer, researchers have been studying the structure of resins that are used as binders in the charge transport layer, polycarbonate resins in particular (Japanese Patent Laid-Open Nos. 2011-26574, 5-113680, 4-149557, 6-11877, and 2005-338446).

An aspect of the invention provides an electrophotographic photosensitive member with which fog can be very effectively reduced. Some other aspects of the invention provide a method for manufacturing such an electrophotographic photosensitive member and a process cartridge and an electrophotographic apparatus incorporating such an electrophotographic photosensitive member.

An electrophotographic photosensitive member according to an aspect of the invention has a support, a charge generation layer, and a charge transport layer in this order, the charge transport layer containing a charge transport material. The charge transport layer is a surface layer of the electrophotographic photosensitive member and contains a polycarbonate resin having a structural unit selected from group A and a structural unit selected from group B.

The group A includes structural units represented by formula (103).

(In formula (103), R 231 to R 234 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. R 235 and R 236 are groups of the same kind, representing an alkyl group containing 1 to 9 carbon atoms. i 231 represents an integer of 0 to 3.)

The group B includes structural units represented by formulae (104), (105), and (106).

(In formula (104), R 241 to R 244 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. X represents a single bond or a sulfonyl group.)

(In formula (105), R 251 to R 254 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. R 256 and R 257 each independently represent a hydrogen atom or an alkyl, aryl, or halogenated alkyl group.)

(In formula (106), R 261 to R 264 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. W represents a cycloalkylidene group containing 5 to 12 carbon atoms.)

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

FIG. 1 illustrates an example of a schematic structure of an electrophotographic apparatus installed with a process cartridge that incorporates an electrophotographic photosensitive member.

FIG. 2 is a powder X-ray diffraction pattern of a crystalline hydroxygallium phthalocyanine used in Examples.

FIG. 3 is a powder X-ray diffraction pattern of a crystalline chlorogallium phthalocyanine used in Examples.

FIG. 4 is a powder X-ray diffraction pattern of a crystalline hydroxygallium phthalocyanine used in Examples.

FIG. 5 is a diagram for describing a 1-dot “knight move in chess” pattern image.

Through research, the inventors found the following fact. That is, when an electrophotographic photosensitive member having a charge transport layer as a surface layer is used repeatedly, the charge transport layer becomes thinner due to wear. This leads to increased electric field intensity, causing the technical problem called “fog” on images, i.e., a defect whereby a small amount of toner is developed in unintended areas of the images.

The known electrophotographic photosensitive members according to the aforementioned publications, having a charge transport layer that contains a polycarbonate resin as a binder, help to reduce the fog, but not to the extent that the recent high demand for long-life electrophotographic photosensitive members would be fully satisfied.

An aspect of the invention therefore provides an electrophotographic photosensitive member with which fog can be very effectively reduced. Some other aspects of the invention provide a method for manufacturing such an electrophotographic photosensitive member and a process cartridge and an electrophotographic apparatus incorporating such an electrophotographic photosensitive member.

The following describes certain aspects of the invention by providing some preferred embodiments. Studies conducted by the inventors have revealed that the use of a particular kind of polycarbonate resin in a charge transport layer of an electrophotographic photosensitive member significantly improves the mechanical strength of the photosensitive member and leads to effective reduction of fog. To be more specific, an electrophotographic photosensitive member according to an aspect of the invention has a support, a charge generation layer, and a charge transport layer in this order, the charge transport layer containing a charge transport material. The charge transport layer is a surface layer of the electrophotographic photosensitive member and contains a polycarbonate resin having a structural unit selected from group A and a structural unit selected from group B.

The group A includes structural units represented by formula (103).

In formula (103), R 231 to R 234 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. R 235 and R 236 are groups of the same kind, representing a substituted or unsubstituted alkyl group containing 1 to 9 carbon atoms. i 231 represents an integer of 0 to 3. When i 231 is 0, this site is a single bond.

The group B includes structural units represented by formulae (104), (105), and (106).

In formula (104), R 241 to R 244 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. X represents a single bond or a sulfonyl group.

In formula (105), R 251 to R 254 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. R 256 and R 257 each independently represent a hydrogen atom or an alkyl, aryl, or halogenated alkyl group. The aryl group may be substituted with an alkyl or alkoxy group or a halogen atom.

In formula (106), R 261 to R 264 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. W represents a cycloalkylidene group containing 5 to 12 carbon atoms. The cycloalkylidene group may be substituted with an alkyl group.

This polycarbonate resin having a structural unit selected from group A and a structural unit selected from group B can be synthesized using, for example, one of the following two processes. The first is to allow a bisphenol compound according to formula (109) and at least one bisphenol compound selected from formulae (110) to (112) to react directly with phosgene (a phosgene process). The second is to transesterify the at least two bisphenol compounds and a bisaryl carbonate, such as diphenyl carbonate, di-p-tolyl carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate, or dinaphthyl carbonate (a transesterification process).

In the phosgene process, the at least two bisphenol compounds and phosgene are usually reacted in the presence of an acid-binding agent and a solvent. The acid-binding agent can be pyridine, an alkali metal hydroxide, such as potassium hydroxide or sodium hydroxide, or similar. The solvent can be methylene chloride, chloroform, or similar. A catalyst and/or a molecular-weight modifier may be added in order to accelerate the condensation polymerization. The catalyst can be triethylamine or any other tertiary amine, a quaternary ammonium salt, or similar. The molecular-weight modifier can be phenol, p-cumylphenol, t-butylphenol, a phenol substituted with a long-chain alkyl group, or similar monofunctional compounds.

The synthesis of the polycarbonate resin may involve an antioxidant, such as sodium sulfite or hydrosulfite, and/or a branching agent, such as phloroglucin or isatin bisphenol. The polycarbonate resin can be synthesized at a temperature of 0° C. to 150° C., preferably 5° C. to 40° C. The duration of the reaction depends on the reaction temperature but can typically be in the range of 0.5 minutes to 10 hours, preferably 1 minute to 2 hours. During the reaction, the pH of the reaction system can be 10 or more.

Here are some specific examples of bisphenol compounds that can be used for synthesis.

(1) A bisphenol compound according to formula (109)

In formula (109), R 231 to R 234 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. R 235 and R 236 are groups of the same kind, representing a substituted or unsubstituted alkyl group containing 1 to 9 carbon atoms. i 231 represents an integer of 0 to 3. When i 231 is 0, this site is a single bond.

Examples of bisphenol compounds represented by general formula (109) include 1,1-bis(4-hydroxyphenyl)-3-methyl butane and 1,1-bis(4-hydroxyphenyl)-2-methyl propane. A combination of two or more of these compounds can also be used.

(2) At least one bisphenol compound selected from formulae (110) to (112)

In formula (110), R 241 to R 244 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. X represents a single bond or a sulfonyl group.

In formula (111), R 251 to R 254 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. R 256 and R 257 each independently represent a hydrogen atom or an alkyl, aryl, or halogenated alkyl group. The aryl group may be substituted with an alkyl or alkoxy group or a halogen atom.

In formula (112), R 261 to R 264 each independently represent a hydrogen atom or an alkyl, aryl, or alkoxy group. W represents a cycloalkylidene group containing 5 to 12 carbon atoms. The cycloalkylidene group may be substituted with an alkyl group.

Examples of bisphenol compounds represented by formulae (110) to (112) include 4,4′-dihydroxybiphenyl, 4,4′-dihydroxy-3,3′-dimethyl biphenyl, 4,4′-dihydroxy-2,2′-dimethyl biphenyl, 4,4′-dihydroxy-3,3′,5-trimethyl biphenyl, 4,4′-dihydroxy-3,3′,5,5′-tetramethyl biphenyl, 4,4′-dihydroxy-3,3′-dibutyl biphenyl, 4,4′-dihydroxy-3,3′-dicyclohexyl biphenyl, 3,3′-difluoro-4,4′-dihydroxybiphenyl, 4,4′-dihydroxy-3,3′-diphenyl biphenyl, 1,1-bis(4-hydroxyphenyl)ethane, 1,1-bis(3-methyl-4-hydroxyphenyl)ethane, 1,1-bis(3-fluoro-4-hydroxyphenyl)ethane, 1,1-bis(2-tert-butyl-4-hydroxy-3-methyl phenyl)ethane, 1,2-bis(4-hydroxyphenyl)ethane, 1,2-bis(3-methyl-4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, 2,2-bis(3-phenyl-4-hydroxyphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 2,2-bis(3-fluoro-4-hydroxyphenyl)propane, 2,2-bis(3-chloro-4-hydroxyphenyl)propane, 2,2-bis(3-bromo-4-hydroxyphenyl)propane, 2,2-bis(3,5-difluoro-4-hydroxyphenyl)propane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane, 2,2-bis(2-tert-butyl-4-hydroxy-3-methyl phenyl)propane, 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3-methyl-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3-phenyl-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3-fluoro-4-hydroxyphenyl)hexafluoropropane, 2,2-bis(3-chloro-4-hydroxyphenyl)hexafluoropropane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane, 1,1-bis(3-cyclo-4-hydroxyphenyl)cyclohexane, 1,1-bis(3-phenyl-4-hydroxyphenyl)cyclohexane, 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane, 1,1-bis(3-fluoro-4-hydroxyphenyl)cyclohexane, 1,1-bis(3-chloro-4-hydroxyphenyl)cyclohexane, 1,1-bis(3-bromo-4-hydroxyphenyl)cyclohexane, 1,1-bis(3,5-difluoro-4-hydroxyphenyl)cyclohexane, 1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane, 1,1-bis(3,5-dibromo-4-hydroxyphenyl)cyclohexane, 1,1-bis(2-tert-butyl-4-hydroxy-3-methyl phenyl)cyclohexane, bis(4-hydroxyphenyl)sulfone, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethyl cyclohexane, 1,1-bis(4-hydroxyphenyl)cyclopentane, 1,1-bis(4-hydroxyphenyl)-1-phenyl ethane, bis(4-hydroxyphenyl)diphenyl methane, 9,9-bis(4-hydroxyphenyl)-fluorene, and 2,2-bis(4-hydroxyphenyl)butane. A combination of two or more of these compounds can also be used.

Structural Unit Selected from Group A

The use of a polycarbonate resin having any of the structural units represented by formulae (A-301) to (A-305), as compared to others selected from group A, leads to more effective reduction of fog and better electrical characteristics. Polycarbonate resins having any of these structural units, while in the charge transport layer, will keep a constant intermolecular distance and a constant distance from the charge transport material, improving mechanical strength and electrical characteristics.

Structural Unit Selected from Group B

The use of a polycarbonate resin having any of the structural units represented by formulae (B-103) and (B-110) to (B-112), as compared to others selected from group B, leads to more effective reduction of fog and better electrical characteristics. Polycarbonate resins having any of these structural units, while in the charge transport layer, will keep a constant intermolecular distance and a constant distance from the charge transport material, improving mechanical strength and electrical characteristics.

The use of a polycarbonate resin having any of the structural units represented by formulae (B-201) to (B-205), as compared to others selected from group B, leads to more effective reduction of fog. Polycarbonate resins having any of these structural units will be, while in the charge transport layer, densely packed with short intermolecular distances, improving mechanical strength.

The use of a polycarbonate resin having any of the structural units represented by (B-301) to (B-308), as compared to others selected from group B, is effective in improving the storage stability of the coating liquid for the formation of the charge transport layer, the prevention of photomemories, and electrical characteristics after repeated use. Polycarbonate resins having any of these structural units will exhibit improved solubility in the solvent of the coating liquid for the formation of the charge transport layer. Furthermore, polycarbonate resins having any of these structural units, while in the charge transport layer, will keep a constant distance from the charge transport material, improving electrical characteristics. A photomemory is a defect caused by the retention of light-generated carriers in a photosensitive layer of an electrophotographic photosensitive member and occurs when an electrophotographic photosensitive member is exposed to light, such as from a fluorescent lamp, in association with maintenance of a process cartridge or electrophotographic apparatus after repeated use. If an electrophotographic photosensitive member in this state is used to produce an image, the difference in electrical potential between the exposed and unexposed areas appears as uneven density in the resulting image.

The use of a polycarbonate resin having any of the structural units represented by (B-401) to (B-405), as compared to others selected from group B, is effective in improving the storage stability of the coating liquid for the formation of the charge transport layer, the prevention of photomemories, and electrical characteristics after repeated use. Polycarbonate resins having any of these structural units will exhibit improved solubility in the solvent of the coating liquid for the formation of the charge transport layer. Furthermore, polycarbonate resins having any of these structural units, while in the charge transport layer, will keep a constant distance from the charge transport material, improving electrical characteristics.

The proportion of the structural unit selected from group A in the polycarbonate resin can be 20 mol % or more and 70 mol % or less, preferably 25 mol % or more and 49 mol % or less.

In an embodiment of the invention, the weight-average molecular weight (Mw) of the polycarbonate resin can be 30,000 or more and 100,000 or less, preferably 40,000 or more and 80,000 or less. If the weight-average molecular weight of the polycarbonate resin is less than 30,000, the reduction of fog may be insufficient due to low mechanical strength. If the weight-average molecular weight of the polycarbonate resin is more than 100,000, the coating liquid for the formation of the charge transport layer may lack storage stability. In Examples below, the weight-average molecular weights of the resins are polystyrene equivalents measured using gel permeation chromatography (GPC) [on Alliance HPLC system (Waters)] under the following conditions: two Shodex KF-805L columns (Showa Denko), 0.25 w/v % chloroform solution as sample, chloroform at 1 ml/min as eluent, and UV detection at 254 nm.

The intrinsic viscosity of the polycarbonate resin can be in the range of 0.3 dL/g to 2.0 dL/g.

The relative dielectric constant ∈ of a polycarbonate resin can be determined according to the Clausius-Mossotti equation that follows.

K =(4π/3)×(α/ V )

∈=(1+2 K )/(1− K )

In this equation, V is the volume of the molecule in its stable structure obtained after structural optimization using density functional calculations B3LYP/6-31G(d,p), and α is the polarizability according to a restricted Hartree-Fock calculation (using the basis function 6-31G(d,p)) in this post-optimization stable structure. For polycarbonate resins having multiple structural units (e.g., copolymers), the relative dielectric constant values of the individual structural units multiplied by their respective proportions are totaled up. For example, exemplified compound 1921 has relative dielectric constant values of 2.11 and 2.20 in structural units (A-301) and (B-301), respectively. The relative dielectric constant of exemplified compound 1921 is therefore 2.16 based on the proportions of the structural units. In an embodiment of the invention, the relative dielectric constant ∈ can be 2.15 or less, preferably 2.13 or less.

A relative dielectric constant of 2.15 or less leads to better response at high speeds, presumably for the following reason. The term “response at high speeds” means that the density of an image produced is comparable between normal and faster process speeds in the image formation process. Altering the process speed usually leads to a change in the amount of light the electrophotographic photosensitive member receives. Even if the amount of light is controlled to achieve constant light exposure of the electrophotographic photosensitive member, different process speeds can result in different image densities. This difference in density becomes more significant in faster processes because the time from exposure to development shortens with increasing process speed. One cause is reciprocal failure, which necessitates complicated control in order to equalize the image density. The inventors, however, presume that reciprocal failure is not the only cause. Another cause is, in the opinion of the inventors, a difference in the rate of light decay of the surface potential of the electrophotographic photosensitive member that occurs during development, a stage in the exposure and development process the electrophotographic photosensitive member undergoes to form an image. To be more specific, even if the electrophotographic photosensitive member has equal surface potentials at the time of development, a difference in the rate of light decay of its surface potential will lead to a difference in the ability of the photosensitive member to develop toner, resulting in variations in density between the images produced. Charge generated in a charge generation layer is injected into a charge transport layer and then is transported to the surface of the electrophotographic photosensitive member by travelling in the charge transport layer. Some amount of charge reaches the surface of the electrophotographic photosensitive member in a short time, but some other amount of charge requires a relatively long time to arrive (residual charge). In view of the fact that the light decay during development occurs immediately after the photoresponse in the charging and exposure process, the rate of light decay should be influenced by the behavior of charge carriers in the charge transport layer toward the residual charge at low electric-field intensity. When the relative dielectric constant of the polycarbonate resin is 2.15 or less, the electrophotographic photosensitive member will not greatly change its capacity to put out residual charge at low electric-field intensity over time, and its rate of light decay during development will therefore be low. Furthermore, the inventors believe that when the relative dielectric constant of the polycarbonate resin is 2.15 or less, the ability of the electrophotographic photosensitive member to develop toner is not very sensitive to unevenness in the surface potential of the electrophotographic photosensitive member, and the density of an image produced is thus comparable between normal and faster process speeds in the image formation process.

When the relative dielectric constant of the polycarbonate resin is 2.15 or less, moreover, the intensity of an electric field applied to the charge transport layer will act favorably on the transport of charge through the charge transport layer and the injection of charge from a charge generation layer into the charge transport layer, making the electrophotographic photosensitive member excellent in terms of the prevention of photomemories after repeated use.

Specific Examples of Polycarbonate Resins

Tables 1 to 3 present specific examples of polycarbonate resins having a structural unit selected from group A and a structural unit selected from group B, along with their relative dielectric constant values.

Synthesis of the Polycarbonate Resin

The following describes a method for synthesizing exemplified compound 1921 by way of example. The other polycarbonate resins can be synthesized using appropriate group-A and group-B structural raw materials (raw materials from which the structural units selected from group A and group B, respectively, are produced) in appropriate amounts in the method described in Synthesis of exemplified compound 1921 below. The weight-average molecular weight of the resin can be adjusted by controlling the amount of the molecular-weight modifier.

Synthesis of Exemplified Compound 1921

The following materials were dissolved in 1100 ml of a 5% by mass aqueous solution of sodium hydroxide: 47.5 g (0.196 mol) of 1,1-bis(4-hydroxyphenyl)-2-methyl propane (Wako Pure Chemical Industries, product code 131-11331) as group-A structural raw material, 38.0 g (0.204 mol) of 4,4′-dihydroxybiphenyl (Tokyo Chemical Industry, product code B0464) as group-B structural raw material, and 0.1 g of hydrosulfite. After the addition of 500 ml of methylene chloride, 60 g of phosgene was blown into the solution over 60 minutes with stirring, with the temperature maintained at 15° C.

The reaction solution into which the phosgene had been blown was stirred with 1.3 g of p-t-butylphenol (Tokyo Chemical Industry, product code B0383) as a molecular-weight modifier until emulsification. The resulting emulsion was stirred at 23° C. for 1 hour with 0.4 ml of triethylamine for polymerization.

After the completion of polymerization, the reaction solution was separated into aqueous and organic phases. The organic phase was neutralized with phosphoric acid and then repeatedly washed with water until the conductivity of the washing (aqueous phase) was 10 μS/cm or less. The resulting solution of polymer was added dropwise into warm water kept at 45° C., and the solvent was evaporated away. This yielded a white powdery precipitate. This precipitate was collected through filtration and dried at 110° C. for 24 hours. In this way, the exemplified compound 1921 polycarbonate resin was obtained as a copolymer composed of group-A structural unit A-301 and group-B structural unit B-201.

The obtained polycarbonate resin was analyzed using infrared absorption spectroscopy. The spectrum had a carbonyl absorption at around 1770 cm −1 and an ether absorption at around 1240 cm −1 , identifying the product to be a polycarbonate resin.

Electrophotographic Photosensitive Member

An electrophotographic photosensitive member according to an aspect of the invention has a support, a charge generation layer, and a charge transport layer as a surface layer in this order. There may be other layers between the support and the charge transport layer. The details of the individual layers are given below.

This electrophotographic photosensitive member can be manufactured through, for example, preparation of coating liquids for forming the layers described below and subsequent application and drying of these liquids in the desired order of layers. Examples of methods that can be used to apply the coating liquids include dip coating, spray coating, curtain coating, and spin coating. In particular, dip coating provides excellent efficiency and productivity.

Support

In an embodiment of the invention, the support can be a conductive support, i.e., a support having electroconductivity. Examples of conductive supports include supports made of aluminum, iron, nickel, copper, gold, or other metals or alloys and supports composed of an insulating substrate, such as polyester resin, polycarbonate resin, polyimide resin, or glass, and any of the following thin films thereon: a thin film of aluminum, chromium, silver, gold, or similar metals; a thin film of indium oxide, tin oxide, zinc oxide, or similar conductive materials; and a thin film of a conductive ink containing silver nanowires.

The surface of the support may have been treated for the purpose of improved electrical characteristics and reduced interference fringes. Examples of treatments include anodization and other electrochemical processes, wet honing, blasting, and cutting.

With regard to shape, the support can be, for example, a cylinder or a film.

Conductive Layer

In an embodiment of the invention, there may be a conductive layer on the support. Such a conductive layer prevents interference fringes by covering irregularities and defects on the support. The average thickness of the conductive layer can be 5 μm or more and 40 μm or less, preferably 10 μm or more and 30 μm or less.

The conductive layer may contain conductive particles and a binder resin. The conductive particles can be carbon black, metallic particles, metal oxide particles, or similar.

The metal oxide particles can be particles of zinc oxide, white lead, aluminum oxide, indium oxide, silicon oxide, zirconium oxide, tin oxide, titanium oxide, magnesium oxide, antimony oxide, bismuth oxide, tin-doped indium oxide, antinomy- or tantalum-doped tin oxide, or similar. A combination of two or more of these particles can also be used. Particles of zinc oxide, tin oxide, and titanium oxide are preferred. In particular, titanium oxide particles, absorbing little of visible and near-infrared light and white in color, provide high sensitivity. Titanium oxide has several crystal forms, such as rutile, anatase, brookite, and amorphous, and any of these crystal forms can be used, preferably rutile. It is also possible to use needle or granular crystals of titanium oxide. The number-average primary particle diameter of the metal oxide particles can be in the range of 0.05 to 1 μm, preferably 0.1 to 0.5 μm.

The binder resin can be phenolic, polyurethane, polyamide, polyimide, polyamide-imide, polyvinyl acetal, epoxy, acrylic, melamine, polyester, or similar resins. A combination of two or more of these resins can also be used. In particular, curable resins render the conductive layer highly resistant to solvents that can be used in the coating liquids for the formation of other layers and highly adhesive to a conductive support, without compromising the dispersibility and dispersion stability of metal oxide particles. Such a curable resin can be a thermosetting resin. Examples of thermosetting resins include thermosetting phenolic resins and thermosetting polyurethane resins.

Undercoat Layer

In an embodiment of the invention, there may be an undercoat layer on the support or the conductive layer. Such an undercoat layer provides enhanced barrier properties and adhesiveness. The average thickness of the undercoat layer can be 0.3 μm or more and 5.0 μm or less.

The undercoat layer may contain a binder resin and either an electron transport material or metal oxide particles. Such a structure provides a pathway through which electrons generated in a charge generation layer, one of the two kinds of electric charge generated in the charge generation layer, can be transported to the support. This prevents any increase in the occurrence of charge deactivation and trapping in the charge generation layer associated with improving capacity of the charge transport layer to transport charge. As a result, the initial electrical characteristics and the electrical characteristics after repeated use are improved.

Examples of electron transport materials include quinone, imide, benzimidazole, cyclopentadienylidene, fluorenone, xanthone, benzophenone, cyanovinyl, naphthylimide, and peryleneimide compounds. The electron transport material may have a polymerizable functional group, such as a hydroxy, thiol, amino, carboxy, or methoxy group.

For the metal oxide particles and the binder resin, the details are the same as in the foregoing “Conductive layer” section.

Charge Generation Layer

In an embodiment of the invention, there is a charge generation layer between the support and the charge transport layer. The charge generation layer may be contiguous to the charge transport layer. The thickness of the charge generation layer can be 0.05 μm or more and 1 μm or less, preferably 0.1 μm or more and 0.3 μm or less.

In an embodiment of the invention, the charge generation layer may contain a charge generation material and a binder resin.

The charge generation material content of the charge generation layer can be 40% by mass or more and 85% by mass or less, preferably 60% by mass or more and 80% by mass or less.

Examples of charge generation materials include: monoazo, disazo, and trisazo pigments, and other azo pigments; phthalocyanine pigments including metal phthalocyanine complexes and metal-free phthalocyanine; indigo pigments; perylene pigments; polycyclic quinone pigments; squarylium dyes; thiapyrylium salts; quinacridone pigments; azulenium salt pigments; cyanine dyes; xanthene dyes; quinone imine dyes; and styryl dyes. It is preferred that the charge generation material be a phthalocyanine pigment, more preferably crystalline gallium phthalocyanine.

Crystalline hydroxygallium phthalocyanine, crystalline chlorogallium phthalocyanine, crystalline bromogallium phthalocyanine, and crystalline iodogallium phthalocyanine have excellent sensitivity compared to other crystalline gallium phthalocyanines. Crystalline hydroxygallium phthalocyanine and crystalline chlorogallium phthalocyanine are particularly preferred. In crystalline hydroxygallium phthalocyanine, the gallium atom is coordinated by hydroxy groups as axial ligands. In crystalline chlorogallium phthalocyanine, the gallium atom is coordinated by chlorine atoms as axial ligands. In crystalline bromogallium phthalocyanine, the gallium atom is coordinated by bromine atoms as axial ligands. In crystalline iodogallium phthalocyanine, the gallium atom is coordinated by iodine atoms as axial ligands. Particularly high sensitivity is obtained with the use of a crystalline hydroxygallium phthalocyanine that exhibits peaks at Bragg angles 2θ of 7.4°±0.3° and 28.3°±0.3° in its CuKα X-ray diffraction pattern or a crystalline chlorogallium phthalocyanine that exhibits peaks at Bragg angles 2θ±0.2° of 7.4°, 16.6°, 25.5°, and 28.3° in its CuKα X-ray diffraction pattern.

The crystalline gallium phthalocyanine may contain an amide compound represented by the formula below in its crystal structure.

(In this formula, R 81 represents a methyl, propyl, or vinyl group.)

Specific examples of such amide compounds include N-methylformamide, N-propylformamide, and N-vinylformamide.

The amide compound content can be 0.1% by mass or more and 1.9% by mass or less, preferably 0.3% by mass or more and 1.5% by mass or less, with respect to the gallium phthalocyanine complex in the crystalline gallium phthalocyanine. When the amide compound content is 0.1% by mass or more and 1.9% by mass or less, the dark current from the charge generation layer at increased electric field intensity is small in the opinion of the inventors, making the charge transport layer according to this embodiment of the invention more effective in reducing fog. The amide compound content can be measured using 1 H-NMR spectroscopy.

The crystalline gallium phthalocyanine containing an amide compound in its crystal structure can be obtained through a transformation process in which acid-pasted or dry-milled gallium phthalocyanine is wet-milled in a solvent containing the amide compound.

This process of wet milling is performed using a milling apparatus, such as a sand mill or a ball mill, with a dispersant, such as glass beads, steel beads, or alumina balls.

As for the binder resin, examples include resins such as polyester, acrylic resin, polycarbonate, polyvinyl butyral, polystyrene, polyvinyl acetate, polysulfone, acrylonitrile copolymers, and polyvinyl benzal. In particular, polyvinyl butyral and polyvinyl benzal are effective in dispersing crystalline gallium phthalocyanine.

Charge Transport Layer

In an embodiment of the invention, the charge transport layer contains a charge transport material and a polycarbonate resin that has a structural unit selected from group A and a structural unit selected from group B. The charge transport layer may optionally contain additives, such as a release agent for more efficient transfer of toner, an anti-fingerprint agent to reduce soiling or similar, filler to reduce scraping, and lubricant for higher lubricity.

In an embodiment of the invention, the charge transport layer can be formed by preparing a coating liquid for the formation of the charge transport layer by mixing the charge transport material and the polycarbonate resin with a solvent, applying this coating liquid for the formation of the charge transport layer to form a wet coating, and drying this wet coating.

The solvent used in the coating liquid for the formation of the charge transport layer can be, for example, a ketone-based solvent, such as acetone or methyl ethyl ketone; an ester-based solvent, such as methyl acetate or ethyl acetate; an aromatic hydrocarbon solvent, such as toluene, xylene, or chlorobenzene; an ether-based solvent, such as 1,4-dioxane or tetrahydrofuran; or a halogenated hydrocarbon solvent, such as chloroform. A combination of two or more of these solvents can also be used. Solvents having a dipole moment of 1.0 D or less are preferred. Examples of solvents having a dipole moment of 1.0 D or less include o-xylene (dipole moment=0.64 D) and methylal (dipole moment=0.91 D).

The thickness of the charge transport layer can be 5 μm or more and 40 μm or less, preferably 7 μm or more and 25 μm or less.

The charge transport material content of the charge transport layer can be 20% by mass or more and 80% by mass or less, preferably 40% by mass or more and 70% by mass or less for more effective reduction of fog and higher long-term storage stability of the electrophotographic photosensitive member.

The molecular weight of the charge transport material can be 300 or more and 1,000 or less. For better electrical characteristics after repeated use and higher long-term storage stability, it is preferred that the molecular weight of the charge transport material be 600 or more and 800 or less. For more effective prevention of photomemories and higher long-term storage stability, it is preferred that the molecular weight of the charge transport material be 350 or more and 600 or less.

The charge transport material can be, for example, a triarylamine, hydrazone, stilbene, pyrazoline, oxazole, thiazole, or triallylamine compound, preferably a triarylamine compound. A combination of two or more of these compounds can also be used. The following are some specific examples of charge transport materials, represented by general formulae and exemplified compounds for each general formula.

(In this formula, Ar 101 and Ar 102 each independently represent a substituted or unsubstituted aryl group. R 101 and R 102 each independently represent a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group. Possible substituents for an aryl group are alkyl and alkoxy groups and a halogen atom.)

Here are some exemplified compounds for (CTM-1).

(In this formula, Ar 103 to Ar 106 each independently represent a substituted or unsubstituted aryl group. Z 101 represents a substituted or unsubstituted arylene group or a divalent group in which multiple arylene groups are linked via a vinylene group. There may be a ring formed by two adjacent substituents on Ar 103 to Ar 106 . Possible substituents for an aryl or arylene group are alkyl and alkoxy groups and a halogen atom.)

Here are some exemplified compounds for (CTM-2).

(In this formula, R 103 represents an alkyl group, a cycloalkyl group, or a substituted or unsubstituted aryl group. R 104 represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group. Ar 107 represents a substituted or unsubstituted aryl group. Z 102 represents a substituted or unsubstituted arylene group. n 101 and m are integers of 1 to 3 and 0 to 2, respectively, with m+n 101 =3. When m is 2, the two R 103 groups may be groups of the same kind or different groups, and there may be a ring formed by two adjacent substituents on the two R 103 groups. There may be a ring formed by R 103 and Z 102 . Furthermore, there may be a ring formed by Ar 107 and R 104 involving a linking vinylene group. Possible substituents for an aryl or arylene group are alkyl and alkoxy groups and a halogen atom.)

Here are some exemplified compounds for (CTM-3).

(In this formula, Ar 108 to Ar 111 each independently represent a substituted or unsubstituted aryl group. Possible substituents for an aryl group are an alkyl group, an alkoxy group, a halogen atom, and a 4-phenyl-buta-1,3-dienyl group.)

Here are some exemplified compounds for (CTM-4).

(In this formula, Ar 112 to Ar 117 each independently represent a substituted or unsubstituted aryl group. Z 103 represents a phenylene group, a biphenylene group, or a divalent group in which two phenylene groups are linked via an alkylene group. Possible substituents for an aryl group are alkyl and alkoxy groups and a halogen atom.)

Here are some exemplified compounds for (CTM-5).

(In this formula, R 105 to R 108 each independently represent a monovalent group according to the formula below or an alkyl group or a substituted or unsubstituted aryl group, with at least one being a monovalent group according to the formula below. Z 104 represents a substitute or unsubstituted arylene group or a divalent group in which multiple arylene groups are linked via a vinylene group. n 102 is 0 or 1. Possible substituents for an aryl or arylene group are alkyl and alkoxy groups and a halogen atom.)

(In this formula, R 109 and R 110 each independently represent a hydrogen atom, an alkyl group, or a substituted or unsubstituted aryl group. Ar 118 represents a substituted or unsubstituted aryl group. Z 105 represents a substituted or unsubstituted arylene group. n 2 is an integer of 1 to 3. Possible substituents for an aryl group are alkyl, alkoxy, dialkylamino, and diarylamino groups. Possible substituents for the arylene group are alkyl and alkoxy groups and a halogen atom.)

Here are some exemplified compounds for (CTM-6).

(In this formula, Ar 119 represents a substituted or unsubstituted aryl group or a monovalent group according to formula (7-1) or (7-2). Ar 120 and Ar 121 each independently represent a substituted or unsubstituted aryl group. Possible substituents for an aryl group are alkyl and alkoxy groups and a halogen atom.)

(In this formula, Ar 121 and Ar 123 each independently represent a substituted or unsubstituted aryl group or a substituted or unsubstituted aralkyl group. Possible substituents for an aryl and aralkyl group are alkyl and alkoxy groups and a halogen atom.)

(In this formula, R 111 and R 112 each independently represent a substituted or unsubstituted aryl group. Z 106 represents a substituted or unsubstituted arylene group. Possible substituents for an aryl and arylene group are alkyl and alkoxy groups and a halogen atom.

Here are some exemplified compounds for (CTM-7).

Process Cartridge and Electrophotographic Apparatus

FIG. 1 illustrates an example of a schematic structure of an electrophotographic apparatus installed with a process cartridge that incorporates an electrophotographic photosensitive member according to an aspect of the invention.

A cylindrical (drum-shaped) electrophotographic photosensitive member 1 is driven to rotate around a shaft 2 in the direction of the arrow at a predetermined circumferential velocity (process speed). During rotation, the surface of the electrophotographic photosensitive member 1 is charged to a predetermined positive or negative potential by a charging unit 3 . The charged surface of the electrophotographic photosensitive member 1 is then irradiated with exposure light 4 emitted from an exposure unit (not illustrated). This produces an electrostatic latent image corresponding to the intended image information. The exposure light 4 is, for example, light emitted from an image exposure unit, such as a slit exposure or laser scanning exposure unit, and intensity-modulated according to the time-sequence electric digital pixel signal of the intended image information.

The electrostatic latent image formed on the surface of the electrophotographic photosensitive member 1 is then developed (normal development or reversal development) using toner contained in a development unit 5 . This produces a toner image on the surface of the electrophotographic photosensitive member 1 . The toner image formed on the surface of the electrophotographic photosensitive member 1 is transferred to a transfer medium 7 by a transfer unit 6 . To the transfer unit 6 , a bias power supply (not illustrated) applies a bias voltage having the opposite polarity with respect to the charge the toner has. When the transfer medium 7 is paper, the transfer medium 7 is discharged from a feeding section (not illustrated) in synchronization with the rotation of the electrophotographic photosensitive member 1 and fed into the space between the electrophotographic photosensitive member 1 and the transfer unit 6 .

The transfer medium 7 carrying the toner image transferred from the electrophotographic photosensitive member 1 is separated from the surface of the electrophotographic photosensitive member 1 and conveyed to a fixing unit 8 , at which the toner image is fixed. As a result, an image-bearing article (a photographic print or copy) is printed out of the electrophotographic apparatus.

The surface of the electrophotographic photosensitive member 1 following transferring the toner image to the transfer medium 7 is cleaned by a cleaning unit 9 to remove any adhering substance, such as toner (residual toner). It is also possible to collect any residual toner directly with the development element or any other component, thanks to the advent of clearnerless systems in recent years. The surface of the electrophotographic photosensitive member 1 is again used to form the image after the charge is removed through irradiation with pre-exposure light 10 emitted from a pre-exposure unit (not illustrated). When the charging unit 3 is a contact charging unit, i.e., a roller-based or similar charging unit, the pre-exposure unit may be unnecessary.

In an embodiment of the invention, two or more of these structural elements including the electrophotographic photosensitive member 1 , the charging unit 3 , the development unit 5 , and the cleaning unit 9 may be integrally held in a container to form a process cartridge. This process cartridge may be configured to be detachably attached to the main body of an electrophotographic apparatus. For example, at least one selected from the charging unit 3 , the development unit 5 , the transfer unit 6 , and the cleaning unit 9 and the electrophotographic photosensitive member 1 are integrally held and assembled into a cartridge, forming a process cartridge 11 that can be detachably attached to the main body of an electrophotographic apparatus using a guiding unit 12 , such as rails, on the main body of the electrophotographic apparatus.

When the electrophotographic apparatus is a photocopier or a printing machine, the exposure light 4 may be a light reflected from or transmitted through the original document, and can also be a light emitted as a result of scanning with a laser beam, driving of an LED array or liquid-crystal shutter array, or similar processes performed according to a signal obtained by scanning the original document with a sensor and converting it into a digital image.

The electrophotographic photosensitive member 1 according to an embodiment of the invention also has a wide range of applications in the field of applied electrophotography, including laser beam printers, CRT printers, LED printers, fax machines, liquid-crystal printers, and laser platemaking.

The following describes certain aspects of the invention in further detail using examples and comparative examples. No aspect of the invention is limited to these examples while within the scope of the invention. The term “parts” in the following examples and comparative examples is based on mass unless otherwise specified.

Synthesis of Crystalline Gallium Phthalocyanines

Crystalline gallium phthalocyanines for use as charge generation materials were synthesized as follows.

Synthesis of Hydroxygallium Phthalocyanine Ga-0

Under a nitrogen flow in a reactor, 5.46 parts of phthalonitrile and 45 parts of α-chloronaphthalene were heated to 30° C. and maintained at this temperature. At the same temperature (30° C.), 3.75 parts of gallium trichloride was added. The water content of the liquid mixture at the addition of gallium trichloride was 150 ppm. The temperature was then increased to 200° C. The mixture was allowed to react at a temperature of 200° C. for 4.5 hours under a nitrogen flow and then cooled. When the temperature reached 150° C., the mixture containing the product was filtered. The residue was washed through dispersion in N,N-dimethylformamide at a temperature of 140° C. for 2 hours, and the obtained liquid dispersion was filtered. The residue was washed with ethanol and dried. This yielded 4.65 parts (71% yield) of chlorogallium phthalocyanine (ClGa).

The obtained ClGa, 4.65 parts, was dissolved in 139.5 parts of concentrated sulfuric acid at a temperature of 10° C. The resulting solution was added dropwise to 620 parts of iced water for reprecipitation, and the resulting mixture was filtered using a filter press. The obtained wet cake (residue) was washed through dispersion in 2% aqueous ammonia, and the resulting liquid dispersion was filtered using a filter press. The obtained wet cake (residue) was then purified through three cycles of dispersion and washing in ion-exchanged water and filtration using a filter press, yielding a hydroxygallium phthalocyanine pigment with a solids content of 23% (wet hydroxygallium phthalocyanine pigment).

Then 6.6 kg of the obtained hydroxygallium phthalocyanine pigment (wet hydroxygallium phthalocyanine pigment) was dried using HYPER-DRY HD-06R drying oven (Biocon (Japan); frequency (oscillation frequency), 2455 MHz±15 MHz) as follows.

A cake of the hydroxygallium phthalocyanine pigment freshly removed from the filter press (the thickness of the wet cake being 4 cm or less) was placed on a dedicated round plastic tray. The far-infrared radiation was off, and the temperature setting for the inner wall of the drying oven was 50° C. During the microwave irradiation, the vacuum pump and the leak valve were adjusted to keep the degree of vacuum in the range of 4.0 to 10.0 kPa.

In step 1, the hydroxygallium phthalocyanine pigment was irradiated with microwaves of 4.8 kW for 50 minutes. The microwaves were then turned off, and the leak valve was closed to make a high degree of vacuum of 2 kPa or less. The solids content of the hydroxygallium phthalocyanine pigment at this point was 88%. In step 2, the leak valve was adjusted to make the degree of vacuum (pressure in the drying oven) fall within the above parameter range (4.0 to 10.0 kPa). Then the hydroxygallium phthalocyanine pigment was irradiated with microwaves of 1.2 kW for 5 minutes. The microwaves were turned off, and the leak valve was closed to make a high degree of vacuum of 2 kPa or less. Step 2 was repeated once more (a total of twice). The solids content of the hydroxygallium phthalocyanine pigment at this point was 98%. In step 3, microwave irradiation was performed in the same way as in step 2 except that the microwave output power was changed from 1.2 kW to 0.8 kW. Step 3 was repeated once more (a total of twice). In step 4, the leak valve was adjusted to make the degree of vacuum (pressure in the drying oven) fall within the above parameter range (4.0 to 10.0 kPa) again. Then the hydroxygallium phthalocyanine pigment was irradiated with microwaves of 0.4 kW for 3 minutes. The microwaves were turned off, and the leak valve was closed to make a high degree of vacuum of 2 kPa or less. Step 4 was repeated seven more times (a total of eight times). This yielded 1.52 kg of a hydroxygallium phthalocyanine pigment (Ga-0) containing 1% or less water, taking a total of 3 hours.

Synthesis of Crystalline Gallium Phthalocyanine Ga-1

In a ball mill, 0.5 parts of the obtained hydroxygallium phthalocyanine Ga-0 and 10 parts of N-methylformamide were milled with 20 parts of 0.8-mm diameter glass beads at room temperature (23° C.) and 120 rpm for 300 hours. Crystalline gallium phthalocyanine removed from this liquid dispersion using N,N-dimethylformamide was collected through filtration, and the surface of the filter was thoroughly washed with tetrahydrofuran. The residue was dried in vacuum, yielding 0.45 parts of crystalline hydroxygallium phthalocyanine Ga-1. FIG. 2 is a powder X-ray diffraction pattern of the obtained crystals.

1 H-NMR spectroscopy was performed using deuterated sulfuric acid as solvent [on AVANCE III 500 spectrometer (Bruker)], confirming that crystals of Ga-1 contained 0.9% by mass N-methylformamide.

Synthesis of Crystalline Gallium Phthalocyanine Ga-2

Crystalline gallium phthalocyanine was synthesized in the same way as in the synthesis of crystalline gallium phthalocyanine Ga-1, except that 10 parts of N-methylformamide was changed to 10 parts of N,N-dimethylformamide and the duration of milling was changed from 300 hours to 400 hours. This yielded 0.40 parts of crystalline hydroxygallium phthalocyanine Ga-2. The powder X-ray diffraction pattern of Ga-2 was similar to that in FIG. 2 . NMR measurement demonstrated that crystals of Ga-2 contained 1.4% by mass N,N-dimethylformamide, as determined from the relative abundance of protons.

Synthesis of Crystalline Gallium Phthalocyanine Ga-3

Crystalline gallium phthalocyanine was synthesized in the same way as in the synthesis of crystalline gallium phthalocyanine Ga-1, except that 10 parts of N-methylformamide was changed to 10 parts of N,N-propylformamide and the duration of milling was changed from 300 hours to 500 hours. This yielded 0.40 parts of crystalline hydroxygallium phthalocyanine Ga-3. The powder X-ray diffraction pattern of Ga-3 was similar to that in FIG. 2 . NMR measurement demonstrated that crystals of Ga-3 contained 1.4% by mass N-propylformamide, as determined from the relative abundance of protons.

Synthesis of Crystalline Gallium Phthalocyanine Ga-4

Crystalline gallium phthalocyanine was synthesized in the same way as in the synthesis of crystalline gallium phthalocyanine Ga-1, except that 10 parts of N-methylformamide was changed to 10 parts of N,N-vinylformamide and the duration of milling was changed from 300 hours to 100 hours. This yielded 0.40 parts of crystalline hydroxygallium phthalocyanine Ga-4. The powder X-ray diffraction pattern of Ga-4 was similar to that in FIG. 2 . NMR measurement demonstrated that crystals of Ga-4 contained 1.8% by mass N-vinylformamide, as determined from the relative abundance of protons.

Synthesis of Crystalline Gallium Phthalocyanine Ga-5

In a ball mill, 0.5 parts of the chlorogallium phthalocyanine (ClGa) obtained above was dry-milled with 20 parts of 0.8-mm diameter glass beads at room temperature (23° C.) for 40 hours. Ten parts of N,N-dimethylformamide was added, and wet-milling was performed at room temperature (23° C.) for 100 hours. Crystalline gallium phthalocyanine removed from this liquid dispersion using N,N-dimethylformamide was collected through filtration, and the surface of the filter was thoroughly washed with tetrahydrofuran. The residue was dried in vacuum, yielding 0.44 parts of crystalline chlorogallium phthalocyanine Ga-5. FIG. 3 is a powder X-ray diffraction pattern of the obtained crystals.

1 H-NMR spectroscopy was performed using deuterated sulfuric acid as solvent [on AVANCE III 500 spectrometer (Bruker)], confirming that crystals of Ga-5 contained 1.0% by mass N,N-dimethylformamide.

Synthesis of Crystalline Gallium Phthalocyanine Ga-6

Crystalline gallium phthalocyanine was synthesized in the same way as in the synthesis of crystalline gallium phthalocyanine Ga-2, except that the duration of milling was changed from 400 hours to 48 hours. This yielded 0.46 parts of crystalline hydroxygallium phthalocyanine Ga-6. NMR measurement demonstrated that crystals of Ga-6 contained 2.1% by mass N,N-dimethylformamide, as determined from the relative abundance of protons.

Synthesis of Crystalline Gallium Phthalocyanine Ga-7

Crystalline hydroxygallium phthalocyanine was synthesized in the same way as in the synthesis of crystalline gallium phthalocyanine Ga-1, except that 10 parts of N-methylformamide was changed to 10 parts of N,N-dimethylformamide and the duration of milling was changed from 300 hours to 100 hours. This yielded 0.40 parts of crystalline hydroxygallium phthalocyanine Ga-7. FIG. 4 is a powder X-ray diffraction pattern of the obtained crystals. NMR measurement demonstrated that crystals of Ga-7 contained 2.2% by mass N,N-dimethylformamide, as determined from the relative abundance of protons.

Production of Electrophotographic Photosensitive Members

In the following, the thickness of the individual layers of the electrophotographic photosensitive members is a measured value obtained using Fischerscope eddy-current coating thickness gauge (Fischer Instruments) or a calculated result based on the mass per unit area and the specific gravity.