ELECTROPHOTOGRAPHIC PHOTORECEPTOR, METHOD FOR PRODUCING THE SAME, AND ELECTROPHOTOGRAPHIC DEVICE
20190377274 ยท 2019-12-12
Assignee
Inventors
- Shinjiro SUZUKI (Matsumoto-city, JP)
- Kazuki NEBASHI (Matsumoto-city, JP)
- Fengqiang ZHU (Matsumoto-city, JP)
- Toshiki TAKEUCHI (Shen Zhen, CN)
Cpc classification
G03G15/75
PHYSICS
G03G5/0542
PHYSICS
International classification
Abstract
A method for producing an electrophotographic photoreceptor having a conductive substrate, and a photosensitive layer formed on the conductive substrate. The method includes the steps of preparing a coating liquid containing a charge generating material, and applying the coating liquid on to the conductive substrate, to thereby form the photosensitive layer. An absolute value of a zeta potential of the charge generating material is 5 mV or more, and a half-value width of a zeta potential distribution of the charge generating material is 100 mV or less.
Claims
1. An electrophotographic photoreceptor, comprising: a conductive substrate; and a photosensitive layer formed on the conductive substrate by applying a coating liquid containing a charge generating material, an absolute value of a zeta potential of the charge generating material being 5 mV or more, and a half-value width of a zeta potential distribution of the charge generating material being 100 mV or less.
2. The electrophotographic photoreceptor according to claim 1, wherein the charge generating material includes at least one material selected from a group consisting of titanyl phthalocyanine, hydroxygallium phthalocyanine, chlorogallium phthalocyanine, a metal-free phthalocyanine, and a pigment having an azo bond.
3. The electrophotographic photoreceptor according to claim 1, wherein an absolute value of an electrophoretic mobility of the charge generating material at a time of measuring the zeta potential is 0.01 m.Math.cm/V.Math.s or more.
4. The electrophotographic photoreceptor according to claim 1, wherein the coating liquid is form of a solvent of which a dielectric constant is 30 or less.
5. A method for producing an electrophotographic photoreceptor having a conductive substrate, and a photosensitive layer formed on the conductive substrate, the method comprising steps of: preparing a coating liquid containing a charge generating material, and applying the coating liquid on to the conductive substrate, to thereby form the photosensitive layer, wherein an absolute value of a zeta potential of the charge generating material is 5 mV or more, and a half-value width of a zeta potential distribution of the charge generating material is 100 mV or less.
6. The method of claim 5, wherein the charge generating material includes at least one material selected from a group consisting of titanyl phthalocyanine, hydroxygallium phthalocyanine, chlorogallium phthalocyanine, a metal-free phthalocyanine, and a pigment having an azo bond.
7. The method of claim 5, wherein an absolute value of an electrophoretic mobility of the charge generating material at a time of measuring the zeta potential is 0.01 m.Math.cm/V.Math.s or more.
8. The method of claim 5, wherein preparing the coating liquid including preparing a solvent of which a dielectric constant is 30 or less.
9. An electrophotographic device equipped with the electrophotographic photoreceptor according to claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0026]
[0027]
[0028]
[0029]
MODE FOR CARRYING OUT THE INVENTION
[0030] A specific embodiment of the present invention will be described in detail with reference to drawings, provided that the present invention is not restricted in any way by the following description.
[0031] As described above, electrophotographic photoreceptors are roughly classified into so-called negatively-charged laminated photoreceptors and positively-charged laminated photoreceptors, both as laminated (functionally separated) photoreceptors, and monolayer photoreceptors mainly used as a positively-charged type.
[0032] As illustrated, in a negatively-charged laminated photoreceptor, on a conductive substrate 1, an undercoat layer 2, and a photosensitive layer 6 having a charge generation layer 4 provided with a charge generating function and a charge transport layer 5 provided with a charge transporting function are sequentially layered one on another. In a positively-charged monolayer photoreceptor, on a conductive substrate 1, an undercoat layer 2, and a monolayer photosensitive layer 3 provided with both a charge generating function and a charge transporting function are sequentially layered one on another. Further, in a positively-charged laminated photoreceptor, on a conductive substrate 1, an undercoat layer 2, and a photosensitive layer 7 having a charge transport layer 5 provided with a charge transporting function, and a charge generation layer 4 provided with both a charge generating function and a charge transporting function are layered one on another. In any type of the photoreceptors, an undercoat layer 2 may be provided according to need.
[0033] The photoreceptor of the embodiment of the present invention includes a conductive substrate and a photosensitive layer provided on the conductive substrate, and the photosensitive layer contains a charge generating material. As for the charge generating material, it is important to use one in which an absolute value of a zeta potential is 5 mV or more, and a half-value width of a zeta potential distribution is 100 mV or less in a coating liquid for forming a photosensitive layer for forming the photosensitive layer. In this regard, the half-value width of the zeta potential distribution means a half-value width of a spectrum expressing the intensity on the vertical axis and the zeta potential on the horizontal axis, and the absolute value represents a peak value of the spectrum.
[0034] The reason why an electrophotographic photoreceptor, which is suppressed from deterioration of image quality such as black spots attributable to a charge generating material, and capable of realizing a stable image, can be obtained is as follows.
[0035] That is, since a charge generating material having a zeta potential with an absolute value of 5 mV or more in a coating liquid for forming a photosensitive layer is used for a photosensitive layer, the repulsive force among particles of the charge generating material dispersed in the coating liquid for forming a photosensitive layer can be increased, and as a result, aggregation of the charge generating material particles in the coating liquid for forming a photosensitive layer can be prevented. By using a charge generating material for photosensitive layer that has a half-value width of the zeta potential distribution in the coating liquid for forming a photosensitive layer of 100 mV or less, the variation in zeta potential among the particles of the charge generating material can be reduced, so that stable dispersion of the charge generating material in the coating liquid for forming a photosensitive layer may be attained, and further aggregation of the charge generating material particles is suppressed even while the coating film of the photosensitive layer is dried. As a consequence, a photoreceptor having superior image quality without black spots can be obtained.
[0036] When the absolute value of the zeta potential of the charge generating material is less than 5 mV, the repulsive force among the charge generating material particles is reduced to generate aggregation, which causes black spots. The absolute value of the zeta potential of the charge generating material is preferably 20 mV or more, and may be, for example, from 25 to 80 mV. The larger the value is, the greater the repulsive force among the charge generating material particles becomes, which is preferable.
[0037] When the half-value width of the zeta potential distribution of the charge generating material exceeds 100 mV, the particles of the charge generating material having a large difference in zeta potential in a coating liquid or at the time of forming a coating film come to aggregate together causing black spots. The half-value width of the zeta potential distribution of the charge generating material is preferably 50 mV or less, and may be, for example, from 20 to 50 mV. The smaller the value is, the smaller the variation in zeta potential among the charge generating material particles becomes, which is preferable.
[0038] The coating film of the photosensitive layer is formed in a solvent vapor atmosphere, and in doing so the coating film is still on the way of drying, and therefore the charge generating material contained in the coating film is movable inside the coating film. Consequently, unless the charge generating material satisfies the requirements relating to the zeta potential and the zeta potential distribution, aggregation of the charge generating material may occur on the way of drying to cause black spots.
[0039] Furthermore, as the absolute value of electrophoretic mobility at the time of measurement of the zeta potential of the charge generating material becomes larger, the repulsive force among the charge generating material particles becomes higher, so that aggregation may be suppressed, which is preferable. The absolute value of the electrophoretic mobility of the charge generating material at the time of measuring the zeta potential is preferably 0.01 m.Math.cm/V.Math.s or more, and more preferably from 0.1 to 1.0 m.Math.cm/V.Math.s. Although it is difficult to predict the movement of particles in the process of forming a coating film merely by simple measurement of the state of aggregation of the charge generating material in a coating liquid for forming a photosensitive layer with a particle size distribution analyzer, or the like, the present inventors have also found that satisfaction of the above requirements is effective for suppression of the phenomenon of black spots or fogging on an image to be caused by aggregation of the charge generating material in the process of forming a coating film.
[0040] In the embodiment of the present invention, the zeta potential can be measured by combining the electrophoresis method and the laser doppler method. This method measures how fast particles move in a liquid when an electric field is applied, namely the velocity of the particles. When the particle velocity and the intensity of the applied electric field are known, the zeta potential can be calculated using two constants of the viscosity and dielectric constant of a sample. When all particles in a suspension liquid composed of a liquid and the particles have a large negative or positive zeta potential, the particles tend to repel each other and aggregation can be suppressed. When the absolute value of the zeta potential of the particles is small, aggregation of the particles cannot be suppressed, and stable dispersion cannot be achieved. The zeta potential is effective in evaluating the status of dispersion, aggregation, ion adsorption, or the like of particles or molecules in the suspension liquid.
[0041] In a conventional measurement of a zeta potential, although the measurement was easy when an aqueous solvent with a high polarity was used as the liquid, it was substantially difficult to perform an accurate measurement when an organic solvent with a low dielectric constant was used. Especially, it was difficult to measure the distribution of zeta potentials. In the embodiment of the present invention, with respect to the measurement of the zeta potential, it has become possible to measure the average zeta potential accurately by reversing at a high rate the cycle of the electric field applied to the electrodes in a measurement cell to suppress the electroosmotic flow, and further to analyze the electrophoretic mobility with high resolution by reversing at a low rate the cycle of the electric field to grasp the influence of the electroosmotic flow. By performing a measurement combining the above, it has become possible to measure the zeta potential of particles and the distribution thereof in a low dielectric constant medium such as an organic solvent with a high sensitivity and high resolution which were not attainable in the past.
[0042] In this regard, in a case where the photoreceptor of the embodiment of the present invention is a laminated photoreceptor, the charge generation layer 4 is a photosensitive layer containing the charge generating material, and in a case where it is a monolayer photoreceptor, the monolayer photosensitive layer 3 is a photosensitive layer including the above-described charge generation layer. In other words, in the case of a laminated photoreceptor, a coating liquid for forming a charge generation layer functions as the coating liquid for forming a photosensitive layer, and in the case of a monolayer photoreceptor, a coating liquid for forming a monolayer photosensitive layer functions as the coating liquid for forming a photosensitive layer.
[0043] There is no particular restriction on the charge generating material used in the embodiment of the present invention, insofar as the zeta potential and the half-value width of the zeta potential distribution when dispersed in the coating liquid for forming a photosensitive layer are within the above range. Specific examples thereof include a pigment having a phthalocyanine skeleton or a pigment having an azo bond. More specifically, the charge generating material preferably contains at least one selected from the group consisting of titanyl phthalocyanine, hydroxygallium phthalocyanine, chlorogallium phthalocyanine, a metal-free phthalocyanine, and a pigment having an azo bond.
[0044] Although there is no particular restriction on the particle diameter of the charge generating material, insofar as it satisfies the requirements concerning the zeta potential and the half-value width of the zeta potential distribution, it is preferably from 10 to 2000 nm when dispersed in a coating liquid for forming a photosensitive layer from the viewpoint of coating appearance and electrical properties, and more preferably from 20 to 1000 nm. In this regard, the particles in the coating liquid for forming a photosensitive layer may be in the form of primary particles, or of a cluster formed from several particles.
[0045] There is no particular restriction on the solvent used for a coating liquid for forming a photosensitive layer, insofar as it is a solvent generally used for forming a photosensitive layer, and the charge generating material satisfies the requirements concerning the zeta potential and the half-value width of the zeta potential distribution. Preferable examples thereof include tetrahydrofuran (THF), 1,3-dioxolane, tetrahydropyran, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, toluene, methylene chloride, 1,2-dichloroethane, chlorobenzene, ethylene glycol, ethylene glycol monomethyl ether, and 1,2-dimethoxyethane. These may be used singly, or in combination, without any limitation thereto.
[0046] The solvent to be contained in a coating liquid for forming a photosensitive layer preferably has a dielectric constant of 30 or less. By using a solvent having a dielectric constant of 30 or less, the solubility of a resin used in combination with the charge generating agent can be secured, which is preferable. The dielectric constant of the solvent is more preferably from 2 to 20.
(Conductive Substrate)
[0047] The conductive substrate 1 serves as an electrode of the photoreceptor and also as a support for each layer constituting the photoreceptor, and may be in any of a cylindrical, plate-like, film-like, or similar form. As a material for the conductive substrate 1, a metal, such as aluminum, a stainless steel, and nickel, or a glass, a resin or the like, which surface has received a conducting treatment, may be used.
(Undercoat Layer)
[0048] The undercoat layer 2 is constituted with a layer mainly composed of a resin, or a metal oxide film such as alumite. The undercoat layer 2 is optionally provided for the purpose of adjusting the inflow property of a charge from the conductive substrate 1 to the photosensitive layer, covering defects on the surface of the conductive substrate, enhancing the adhesion between the photosensitive layer and the conductive substrate 1, or the like. Examples of a resin material to be used for the undercoat layer 2 include an insulating polymer, such as casein, poly(vinyl alcohol), polyamide, a melamine resin, and cellulose, and a conductive polymer, such as polythiophene, polypyrrole, and polyaniline. These resins may be used singly or in combination as appropriate. Further, these resins may be used by adding a metal oxide, such as titanium dioxide and zinc oxide.
[Negatively-Charged Laminated Photoreceptor]
[0049] The photoreceptor of the embodiment of the present invention may have any of the layer configurations shown in
[0050] The charge generation layer 4 in a negatively-charged laminated photoreceptor is formed, for example, by a method to apply a coating liquid in which particles of a charge generating material are dispersed in a resin binder, and receives light to generate charges. It is important for the charge generation layer 4 to have a high charge generation efficiency and at the same time a favorable inflow property of the generated charges into the charge transport layer 5, and is preferable for it to have a low electric field dependence so that the inflow property is good even in a weak electric field.
[0051] More specifically, as the charge generation layer, a phthalocyanine compound, such as X-form metal-free phthalocyanine, -form metal-free phthalocyanine, -form titanyl phthalocyanine, Y-form titanyl phthalocyanine, -form titanyl phthalocyanine, amorphous titanyl phthalocyanine, hydroxygallium phthalocyanine, chlorogallium phthalocyanine, and -form copper phthalocyanine, various azo pigments, an anthanthrone pigment, a thiapyrylium pigment, a perylene pigment, a perinone pigment, a squarylium pigment, a quinacridone pigment, etc. may be used singly or in combination as appropriate, and a suitable substance can be selected corresponding to the light wavelength region of the exposure light source used for image formation. In particular, a phthalocyanine compound can be suitably used. The charge generation layer 4 may be mainly composed of a charge generating material, and a charge transport material or the like may be added thereto for use.
[0052] As a resin binder for the charge generation layer 4, a polycarbonate resin, a polyester resin, a polyamide resin, a polyurethane resin, a vinyl chloride resin, a vinyl acetate resin, a phenoxy resin, a poly(vinyl acetal) resin, a poly(vinyl butyral) resin, a polystyrene resin, a polysulfone resin, a diallyl phthalate resin, a polymer or a copolymer of a methacrylate, and the like may be used singly or in an appropriate combination.
[0053] The content of a charge generating material in a charge generation layer 4 is favorably from 20 to 80% by mass with respect to the solid content in the charge generation layer 4, and more favorably from 30 to 70% by mass. Meanwhile, the content of a resin binder in the charge generation layer 4 is favorably from 20 to 80% by mass with respect to the solid content in the charge generation layer 4, and more favorably from 30 to 70% by mass. Since the charge generation layer 4 is required only to have a charge generating function, its film thickness is generally from 0.01 to 1 m, and favorably from 0.05 to 0.5 m.
[0054] The photoreceptor of the embodiment of the present invention may be produced with a coating liquid for forming a photosensitive layer containing an appropriate combination of a charge generating material satisfying the range of the zeta potential and the aforedescribed composition according to the present invention, and a solvent. The coating liquid for forming a photosensitive layer may contain a resin binder in the above range of the composition.
[0055] In a negatively-charged laminated photoreceptor, a charge transport layer 5 is composed mainly of a charge transport material, and a resin binder.
[0056] As a resin binder for the charge transport layer 5, various polycarbonate resins, such as a polyarylate resin, a bisphenol A type, a bisphenol Z type, a bisphenol C type, a bisphenol A/biphenyl copolymer, and a bisphenol Z/biphenyl copolymer, may be used singly or in a mixture of plural kinds thereof. Further, the same kind of resins with a different molecular weight may be used in a mixture. Besides the above, a polyphenylene resin, a polyester resin, a poly(vinyl acetal) resin, a poly(vinyl butyral) resin, a poly(vinyl alcohol) resin, a vinyl chloride resin, a vinyl acetate resin, a polyethylene resin, a polypropylene resin, an acrylic resin, a polyurethane resin, an epoxy resin, a melamine resin, a silicone resin, a polyamide resin, a polystyrene resin, a polyacetal resin, a polysulfone resin, a polymer of a methacrylate, and a copolymer thereof may be used.
[0057] The mass average molecular weight of the resin binder in terms of polystyrene according to GPC (gel permeation chromatography) analysis is favorably from 5,000 to 250,000, and more favorably from 10,000 to 200,000.
[0058] As a charge transport material in a charge transport layer 5 various hydrazone compounds, styryl compounds, diamine compounds, butadiene compounds, indole compounds, arylamine compounds, etc. may be used singly or in an appropriate combination. Specific examples of such a charge transport material include the following (II-1) to (II-31) but not limited thereto.
##STR00001## ##STR00002## ##STR00003## ##STR00004## ##STR00005## ##STR00006## ##STR00007## ##STR00008##
[0059] The content of a resin binder in a charge transport layer 5 is favorably from 20 to 90% by mass with respect to the solid content of the charge transport layer 5, and more favorably from 30 to 80% by mass. The content of a charge transport material in a charge transport layer 5 is favorably from 10 to 80% by mass with respect to the solid content of the charge transport layer 5, and more favorably from 20 to 70% by mass.
[0060] The film thickness of a charge transport layer 5 is preferably in a range of 3 to 50 m from the viewpoint of maintenance of a surface voltage effective for practical use, and more preferably in a range of 15 to 40 m.
[Positively-Charged Monolayer Photoreceptor]
[0061] In the case of a positively-charged monolayer photoreceptor a monolayer photosensitive layer 3 is a photosensitive layer containing the charge generating material. In a positively-charged monolayer photoreceptor, a monolayer photosensitive layer 3 is mainly composed of the charge generating material, a positive hole transport material and an electron transport material (acceptor compound) as charge transport materials, and a resin binder.
[0062] As a resin binder in a monolayer photosensitive layer 3, various polycarbonate resins, such as a bisphenol A type, a bisphenol Z type, a bisphenol A/biphenyl copolymer, and a bisphenol Z/biphenyl copolymer, a polyphenylene resin, a polyester resin, a poly(vinyl acetal) resin, a poly(vinyl butyral) resin, a poly(vinyl alcohol) resin, a vinyl chloride resin, a vinyl acetate resin, a polyethylene resin, a polypropylene resin, an acrylic resin, a polyurethane resin, an epoxy resin, a melamine resin, a silicone resin, a polyamide resin, a polystyrene resin, a polyacetal resin, a polyarylate resin, a polysulfone resin, a polymer of a methacrylate, and a copolymer thereof may be used. Further, the same kind of resins with a different molecular weight may be used in a mixture.
[0063] Specifically, as a charge generating material in a monolayer photosensitive layer 3, for example, a phthalocyanine pigment, an azo pigment, an anthanthrone pigment, a perylene pigment, a perinone pigment, a polycyclic quinone pigment, a squarylium pigment, a thiapyrylium pigment, and a quinacridone pigment may be used. The charge generating materials may be used singly, or in a combination of two or more kinds thereof. Especially, as an azo pigment a disazo pigment, and a trisazo pigment; as a perylene pigment N,N-bis(3,5-dimethylphenyl)-3,4:9,10-perylene-bis(carboxyimide); as a phthalocyanine pigment a metal-free phthalocyanine, copper phthalocyanine, and titanyl phthalocyanine may be used preferably in a photoreceptor according to the present invention. Further, it is preferable to use X-form metal-free phthalocyanine, -form metal-free phthalocyanine, -form copper phthalocyanine, -form titanyl phthalocyanine, Y-form titanyl phthalocyanine, amorphous titanyl phthalocyanine, and titanyl phthalocyanine which shows a maximum peak in a CuK X-ray diffraction spectrum at a Bragg angle 2 of 9.6 as described in JPH08-209023, U.S. Pat. Nos. 5,736,282A, and 5,874,570A, hydroxygallium phthalocyanine, or chlorogallium phthalocyanine, because a remarkable improvement effect is exhibited in terms of the sensitivity, durability and image quality.
[0064] As a positive hole transport material in a monolayer photosensitive layer 3, for example, a hydrazone compound, a pyrazoline compound, a pyrazolone compound, an oxadiazole compound, an oxazole compound, an arylamine compound, a benzidine compound, a stilbene compound, a styryl compound, poly(N-vinyl carbazole), and polysilane may be used. The positive hole transport materials may be used singly, or in a combination of two or more kinds thereof. As a positive hole transport material to be used according to the present invention, those being superior in transportation capacity for a positive hole generated during light irradiation, and suitable for a combination with a charge generating material are preferable.
[0065] Examples of an electron transport material (acceptor compound) in a monolayer photosensitive layer 3 include succinic anhydride, maleic anhydride, dibromosuccinic anhydride, phthalic anhydride, 3-nitrophthalic anhydride, 4-nitrophthalic anhydride, pyromellitic anhydride, pyromellitic acid, trimellitic acid, trimellitic anhydride, phthalimide, 4-nitrophthalimide, tetracyanoethylene, tetracyanoquinodimethane, chloranil, bromanil, o-nitrobenzoic acid, malononitrile, trinitrofluorenone, trinitrothioxanthone, dinitrobenzene, dinitroanthracene, dinitroacridine, nitroanthraquinone, dinitroanthraquinone, a thiopyran compound, a quinone compound, a benzoquinone compound, a diphenoquinone compound, a naphthoquinone compound, an anthraquinone compound, a stilbenequinone compound, and an azoquinone compound. The electron transport materials may be used singly, or in a combination of two or more kinds thereof.
[0066] The content of a resin binder in a monolayer photosensitive layer 3 is favorably from 10 to 90% by mass with respect to the solid content of the monolayer photosensitive layer 3, and more favorably from 20 to 80% by mass. The content of a charge generating material in a monolayer photosensitive layer 3 is favorably from 0.1 to 20% by mass with respect to the solid content of the monolayer photosensitive layer 3, and more favorably from 0.5 to 10% by mass. The content of a positive hole transport material in a monolayer photosensitive layer 3 is favorably from 3 to 80% by mass with respect to the solid content of the monolayer photosensitive layer 3, and more favorably from 5 to 60% by mass. The content of an electron transport material in a monolayer photosensitive layer 3 is favorably from 1 to 50% by mass with respect to the solid content of the monolayer photosensitive layer 3, and more favorably from 5 to 40% by mass.
[0067] The film thickness of a monolayer photosensitive layer 3 is preferably in a range of 3 to 100 m from the viewpoint of maintenance of a surface voltage effective for practical use, and more preferably in a range of 5 to 40 m.
[Positively-Charged Laminated Photoreceptor]
[0068] As described above, a photosensitive layer 7 in a positively-charged laminated photoreceptor has a charge transport layer 5 and a charge generation layer 4. In the case of a positively-charged laminated photoreceptor, a charge generation layer 4 is the outermost layer, and constitutes a photosensitive layer containing the charge generating material. A charge transport layer 5 in a positively-charged laminated photoreceptor is mainly composed of a charge transport material and a resin binder. As such a charge transport material and a resin binder, the same materials as named for a charge transport layer 5 in a negatively-charged laminated photoreceptor may be used. The content of each material and the film thickness of a charge transport layer 5 may be the same as a negatively-charged laminated photoreceptor.
[0069] A charge generation layer 4 to be formed on a charge transport layer 5 is mainly composed of the charge generating material, a positive hole transport material and an electron transport material (acceptor compound) as charge transport materials and a resin binder. As a charge generating material, a positive hole transport material, an electron transport material, and a resin binder, the same materials as named for a monolayer photosensitive layer 3 in a monolayer photoreceptor may be used. The content of each material and the film thickness of a charge generation layer 4 may be the same as the monolayer photosensitive layer 3 in a monolayer photoreceptor.
[0070] In the embodiment of the present invention, into both of laminated and monolayer photosensitive layers, a leveling agent, such as silicone oil, and fluorinated oil, may be added for the purpose of improvement of the levelling property of a formed film, or impartation of lubricity. Further, plural kinds of inorganic oxides may be added for the purpose of adjustment of film hardness, reduction of friction coefficient, impartation of lubricity, etc. Further, a metal oxide, such as silica, titanium oxide, zinc oxide, calcium oxide, alumina, and zirconium oxide; a metal sulfate, such as barium sulfate, and calcium sulfate; a fine particle of a metal nitride, such as silicon nitride, and aluminum nitride; a particle of a fluorocarbon resin such as a tetrafluoroethylene resin; or a fluorinated comb graft polymer resin may be added. Further, if necessary, another publicly known additive may be added to the extent that electrophotographic characteristics are not significantly impaired.
[0071] Further into a photosensitive layer an antidegradant, such as an oxidation inhibitor, and a light stabilizer may be added for the purpose of improvement of environmental resistance, or stability against harmful light. Examples of a compound used for such a purpose include a chromanol derivative and an esterified compound, such as tocopherol, a polyarylalkane compound, a hydroquinone derivative, an etherified compound, a dietherified compound, a benzophenone derivative, a benzotriazole derivative, a thioether compound, a phenylenediamine derivative, a phosphonic acid ester, a phosphite ester, a phenol compound, a hindered phenol compound, a straight chain amine compound, a cyclic amine compound, and a hindered amine compound.
(Method for Producing Photoreceptor)
[0072] The method for producing a photoreceptor of the embodiment of the present invention includes a step of applying a coating liquid for forming a photosensitive layer on to the conductive substrate to form a photosensitive layer in producing the electrophotographic photoreceptor as well as a step of preparing a coating liquid for forming a photosensitive layer containing the charge generating material.
[0073] Specifically, in the case of a negatively-charged laminated photoreceptor, firstly a charge generation layer is produced by a method including a step of preparing a coating liquid for forming a charge generation layer, namely the aforedescribed coating liquid for forming a photosensitive layer, by dissolving or dispersing the specific charge generating material and a resin binder in a solvent, and a step of forming a charge generation layer by applying the coating liquid for forming a charge generation layer to the circumference of the conductive substrate, if necessary intercalating an undercoat layer, and drying the same. Next, a charge transport layer is formed by a method including a step of preparing a coating liquid for forming a charge transport layer by dissolving an optional charge transport material and a resin binder in a solvent, and a step of forming a charge transport layer by applying the coating liquid for forming a charge transport layer onto the charge generation layer and drying the same. By such a production method, it is possible to produce the negatively-charged laminated photoreceptor of the embodiment.
[0074] In addition, a positively-charged monolayer photoreceptor may be produced by a method including a step of preparing a coating liquid for forming a monolayer photosensitive layer, namely the aforedescribed coating liquid for forming a photosensitive layer, by dissolving or dispersing an optional positive hole transport material, a resin binder, and an electron transport material, as well as the specific charge generating material in a solvent, and a step of forming a photosensitive layer by applying the coating liquid for forming a monolayer photosensitive layer to the circumference of the conductive substrate, if necessary intercalating an undercoat layer, and drying the same.
[0075] Furthermore, in the case of a positively-charged laminated photoreceptor, firstly a charge transport layer is formed by a method including a step of preparing a coating liquid for forming a charge transport layer by dissolving an optional charge transport material and a resin binder in a solvent, and a step of forming a charge transport layer by applying the coating liquid for forming a charge transport layer to the circumference of the conductive substrate, if necessary intercalating an undercoat layer, and drying the same. Next, a charge generation layer is formed by a method including a step of preparing a coating liquid for forming a charge generation layer, namely the aforedescribed coating liquid for forming a photosensitive layer by dissolving or dispersing an optional positive hole transport material, a resin binder, and an electron transport material, as well as the specific charge generating material in a solvent, and a step of forming a charge generation layer by applying the coating liquid for forming a charge generation layer onto the charge transport layer and drying the same. By such production methods, it is possible to produce the positively-charged laminated photoreceptor of the embodiment.
[0076] In this regard, there is no particular restriction on the type of solvent used for preparing coating liquids, such as the coating liquid for forming a photosensitive layer, coating conditions, drying conditions, etc. and they can be appropriately selected according to the conventional method. Preferably, a dip coating method is used as the coating method. By using the dip coating method, it is possible to produce a photoreceptor having good appearance quality and stable electric characteristics, while securing low cost and high productivity.
[0077] In the embodiment of the present invention, examples of a disperser used for dispersing the charge generating material in a coating liquid for forming a photosensitive layer include a paint shaker, a ball mill, and a sand mill without limitation thereto insofar as the requirements of the zeta potential and the half-value width of the zeta potential distribution can be satisfied. In particular, it is preferable to use a circulating bead mill, and more preferable that the vessel volume of the bead mill, the void volume in the vessel, and the retention time of the coating liquid are in desired ranges. Specifically, the ratio (V1/F1) of the void space V1 (L) in the vessel volume to the flow rate F1 (L/min) of the coating liquid at the time of dispersion is preferably in a range of 0.1 to 10.0, and more preferably in a range of 0.2 to 5.0. If the above ratio (V1/F1) is less than 0.1, there is a risk of increase in the dispersion temperature, or excessive dispersion caused by an excessive load. When it exceeds 10.0, it is feared that the retention time may be too short, or a dispersing medium may be unevenly distributed in the vessel, and sufficient dispersion conditions may not be obtained.
(Electrophotographic Device)
[0078] The electrophotographic photoreceptor of the embodiment of the present invention exhibits an intended effect when applied to various machine processes. Specifically, it is able to exhibit a sufficient effect in a charging process, including a contact charging system using a charging member, such as a roller and a brush, and a noncontact charging system using a charging member, such as a corotron, and a scorotron, and also in a developing process, including a contact developing system, and a noncontact developing system, using a developer material, such as a nonmagnetic one component system, a magnetic one component system, and a two component system.
[0079] An electrophotographic device of the embodiment of the present invention is constituted by mounting the aforedescribed photoreceptor according to the present invention. The electrophotographic device may include a charging process device and a developing process device.
EXAMPLES
[0080] A specific embodiment of the present invention will be described in more detail by way of Examples. The scope of the present invention is not restricted in any way by the following Examples, unless it departs from the gist of the invention.
(Production of Negatively-Charged Laminated Photoreceptor)
Example 1
[0081] A coating liquid for forming an undercoat layer was prepared by dissolving or dispersing 5 parts by mass of an alcohol-soluble nylon (Trade name CM8000, produced by Toray Industries, Inc.), and 5 parts by mass of titanium oxide fine particles treated with an aminosilane in 90 parts by mass of methanol. The coating liquid for forming an undercoat layer was dip-coated as an undercoat layer on the outer circumference of an aluminum-made cylinder with an outer diameter of 30 mm to be used as a conductive substrate 1, and dried at a temperature of 100 C. for 30 min to complete an undercoat layer 2 with a film thickness of 3 m.
[0082] As a charge generating material 1.5 parts by mass of Y-form titanyl phthalocyanine (Y-TiOPc), and as a resin binder 1 part by mass of a poly(vinyl butyral) resin (Trade name S-LEC BM-1, produced by Sekisui Chemical Co., Ltd.) were dissolved in 60 parts by mass of dichloromethane (dielectric constant 9.1). After preparing 5 L of this solution, a circulating bead mill with a vessel volume of 300 mL was filled with 0.64 zirconia beads up to 90% of the vessel volume in terms of bulk volume (void ratio 33%). A coating liquid for a charge generation layer (coating liquid for forming a photosensitive layer) was prepared by circulating the solution at a circulating flow rate of 50 mL/min for 1 hour in the bead mill for dispersion. The ratio (V1/F1) at this time was 2.0. The coating liquid for a charge generation layer was dip-coated on the undercoat layer 2 and dried at a temperature of 80 C. for 30 min to form a charge generation layer 4 having a thickness of 0.3 m.
[0083] As a positive hole transport material (CTM), 8 parts by mass of a compound represented by the following Formula:
##STR00009##
and as a resin binder, 12 parts by mass of a resin having a repeating unit represented by the following Formula:
##STR00010##
were dissolved in 80 parts by mass of tetrahydrofuran to prepare a coating liquid for forming a charge transport layer. The coating liquid for forming a charge transport layer was dip-coated onto the above charge generation layer 4, and dried at a temperature of 120 C. for 60 min to form a charge transport layer 5 having a thickness of 20 m to produce a negatively-charged laminated photoreceptor.
Example 2
[0084] A photoreceptor was produced in the same manner as in Example 1 except that the filled volume of the bead mill with the zirconia beads at the time of dispersing the charge generating material in Example 1 was changed to 50% of the vessel volume (void ratio 63%). The ratio (V1/F1) at this time was 4.0.
Example 3
[0085] A photoreceptor was produced in the same manner as in Example 1 except that the vessel volume of the bead mill at the time of dispersing the charge generating material in Example 1 was changed to 1400 mL. The ratio (V1/F1) at this time was 9.2.
Example 4
[0086] A photoreceptor was produced in the same manner as in Example 1 except that the charge generating material used in Example 1 was changed to -form titanyl phthalocyanine (-TiOPc).
Example 5
[0087] A photoreceptor was produced in the same manner as in Example 1 except that the charge generating material used in Example 1 was changed to hydroxygallium phthalocyanine (OHGaPc).
Comparative Example 1
[0088] A photoreceptor was produced in the same manner as in Example 1 except that the circulating flow rate at the time of dispersing the charge generating material in Example 1 was changed to 1000 mL/min. The ratio (V1/F1) at this time was 0.099.
Comparative Example 2
[0089] A photoreceptor was produced in the same manner as in Example 3 except that the circulating flow rate at the time of dispersing the charge generating material in Example 3 was changed to 40 mL/min. The ratio (V1/F1) at this time was 11.5.
Comparative Example 3
[0090] A photoreceptor was produced in the same manner as in Example 1 except that the charge generating material in Example 1 was changed to -form titanyl phthalocyanine. The ratio (V1/F1) at this time was 11.5.
(Production of Positively-Charged Monolayer Photoreceptor)
Example 6
[0091] A coating liquid for forming an undercoat layer prepared by dissolving with stirring 0.2 parts by mass of a vinyl chloride/vinyl acetate/vinyl alcohol copolymer (Trade name SOLBIN TASR, produced by Nissin Chemical Industry Co., Ltd.) in 99 parts by mass of methyl ethyl ketone was dip-coated on the outer circumference of an aluminum-made cylinder having an outer diameter of 24 mm serving as the conductive substrate 1, and dried at a temperature of 100 C. for 30 min to form an undercoat layer 2 having a thickness of 0.1 m.
[0092] As a charge generating material 0.1 parts by mass of an X-form metal-free phthalocyanine (X-H2Pc), as a positive hole transport material 7 parts by mass of the same compound as used in Example 1, as an electron transport material 3.5 parts by mass of a compound represented by the following Formula:
##STR00011##
[0093] and as a resin binder 8 parts by mass of the same resin as the resin used for the charge transport layer of Example 1 were dissolved in 90 parts by mass of tetrahydrofuran (dielectric constant 11.0) and mixed. After preparing 5 L of this solution, a circulating bead mill with a vessel volume of 300 mL was filled with 1.04 zirconia beads up to 85% of the vessel volume in terms of bulk volume (void ratio 37%). A coating liquid for forming a monolayer photosensitive layer (coating liquid for forming a photosensitive layer) was prepared by circulating the solution at a circulating flow rate of 50 mL/min for 1 hour in the bead mill for dispersion. The ratio (V1/F1) at this time was 2.2. The coating liquid for forming a monolayer photosensitive layer was dip-coated on the undercoat layer 2 and dried at a temperature of 100 C. for 60 min to form a monolayer photosensitive layer 3 having a thickness of 25 m, thereby completing a monolayer photoreceptor.
Comparative Example 4
[0094] A photoreceptor was produced in the same manner as in Example 6 except that the circulating flow rate at the time of dispersing the charge generating material in Example 6 was changed to 1200 mL/min. The ratio (V1/F1) at this time was 0.093.
(Production of Positively-Charged Laminated Photoreceptor)
Example 7
[0095] As a resin binder 5 parts by mass of the same resin as the resin used for the charge transport layer of Example 1 and as a positive hole transport material 5 parts by mass of the same compound as used in Example 1 were dissolved in 80 parts by mass of tetrahydrofuran to prepare a coating liquid for forming a charge transport layer. The coating liquid for forming a charge transport layer was dip-coated on the outer circumference of an aluminum-made cylinder with an outer diameter of 24 mm to be used as a conductive substrate 1, and dried at a temperature of 120 C. for 60 min to form a charge transport layer with a film thickness of 15 m.
[0096] As a charge generating material 0.1 parts by mass of Y-form titanyl phthalocyanine, as a positive hole transport material 2 parts by mass of the same compound as used in Example 1, as an electron transport material 5 parts by mass of the same compound as used in Example 6, and as a resin binder 13 parts by mass of the same resin as used for the charge transport layer in Example 1 were dissolved in 120 parts by mass of 1,2-dichloroethane (dielectric constant 10.4) and mixed. After preparing 5 L of this solution, a circulating bead mill with a vessel volume of 300 mL was filled with 1.04 zirconia beads up to 85% of the vessel volume in terms of bulk volume (void ratio 37%). A coating liquid for forming a charge generation layer (coating liquid for forming a photosensitive layer) was prepared by circulating the solution at a circulating flow rate of 50 mL/min for 1 hour in the bead mill for dispersion. The ratio (V1/F1) at this time was 2.2. The coating liquid for forming a charge generation layer was dip-coated on the charge transport layer and dried at a temperature of 100 C. for 60 min to form a charge generation layer having a thickness of 15 m, thereby completing a positively-charged laminated photoreceptor.
Comparative Example 5
[0097] A photoreceptor was produced in the same manner as in Example 7 except that the circulating flow rate at the time of dispersing the charge generating material in Example 7 was changed to 1200 mL/min. The ratio (V1/F1) at this time was 0.093.
<Zeta Potential Measurement>
[0098] The zeta potential and the half-value width of the zeta potential distribution of the charge generating material in each coating liquid for forming photosensitive layers of Examples 1 to 7 and Comparative Examples 1 to 5 were measured using a Zetasizer Nano ZSP manufactured by Spectris plc. Each coating liquid was diluted 100 times with a solvent used in such each coating liquid, and used as the measurement sample. A measurement of the zeta potential was carried out under two conditions of fast and slow reversal (M3 measurement) using the applied voltage of 10 V, and DiP cell type electrodes compatible with an organic solvent.
<Properties in Actual Use>
[0099] Each photoreceptor produced in Examples 1 to 5 and Comparative Examples 1 to 3 was mounted on a printer LJ 4250 manufactured by Hewlett Packard, and printing was performed in an environment of high temperature and high humidity (35 C., and 85%). Fogging and black spot on a white sheet were observed. In a case where neither fogging nor black spot was observed, it was rated as good (O), and in a case where fogging and a black spot were observed it was rated as poor (x).
[0100] Each photoreceptor produced in Example 6 and 7, and Comparative Example 4 and 5 was mounted on a printer HL-2040 manufactured by Brother Industries, Ltd., and printing was performed in an environment of high temperature and high humidity (35 C., and 85%). Fogging and black spot on a white sheet were observed. In a case where neither fogging nor black spot was observed, it was rated as good (O), and in a case where fogging and a black spot were observed it was rated as poor (x).
[0101] The rating results are shown in the following table.
TABLE-US-00001 TABLE 1 Measurement result of zeta potential Half-value Absolute width of zeta Image Charge Charging value of zeta potential Electrophoretic rating generating condition of potential distribution mobility HH black material photoreceptor (mV) (mV) (mcm/V .Math. S) spot Example 1 Y-TiOPc Negative 40 40 0.65 Example 2 Y-TiOPc Negative 38 45 0.53 Example 3 Y-TiOPc Negative 30 65 0.15 Example 4 -TiOPc Negative 35 45 0.45 Example 5 OHGaPc Negative 25 70 0.35 Comparative Y-TiOPc Negative 9 110 0.008 x Example 1 Comparative Y-TiOPc Negative 12 120 0.009 x Example 2 Comparative -TiOPc Negative 4 48 0.008 x Example 3 Example 6 X-H.sub.2Pc Positive 35 50 0.21 Comparative X-H.sub.2Pc Positive 8 130 0.111 x Example 4 Example 7 Y-TiOPc Positive 42 40 0.08 Comparative Y-TiOPc Positive 4 115 0.09 x Example 5
[0102] As shown in the above table, in each Example in which the zeta potential and the half-value width of the zeta potential distribution satisfy the specific ranges, a black spot was not detected in the image to demonstrate that good image quality was obtained.
DESCRIPTION OF SYMBOLS
[0103] 1 Conductive substrate [0104] 2 Undercoat layer [0105] 3 Positively-charged monolayer photosensitive layer [0106] 4 Charge generation layer [0107] 5 Charge transport layer [0108] 6 Negatively-charged laminated photosensitive layer [0109] 7 Positively-charged laminated photosensitive layer [0110] 8 Photoreceptor [0111] 21 Charging member [0112] 22 High-voltage power supply [0113] 23 Image exposure member [0114] 24 Developer [0115] 241 Developing roller [0116] 25 Paper feed member [0117] 251 Paper feed roller [0118] 252 Paper feed guide [0119] 26 Transfer charging unit (direct charging type) [0120] 27 Cleaning device [0121] 271 Cleaning blade [0122] 28 Destaticizing member [0123] 60 Electrophotographic device [0124] 300 Photosensitive layer