JPH0588470B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a photoreceptor for electrophotography, and more particularly to a photoreceptor for electrophotography in which a charge generation layer and a charge transport layer are provided on a conductive support. Prior Art Conventionally, a so-called charge generation layer that can generate charge carriers by light absorption is provided on a conductive support, and a so-called charge generation layer that can further move the generated charge carriers by the force of an electric field. Many laminated electrophotographic photoreceptors provided with a charge transport layer have been proposed. In these laminated electrophotographic photoreceptors, the charge generation layer generally includes 1)
A charge generating substance such as Se, Se alloy, a-Si, or organic pigment is provided by vacuum deposition, glow discharge, or the like. (For example, JP-A-48-47838, JP-A-49-48334) 2) Se,
A dispersion of Se alloy, inorganic pigments such as ZnO, TiO ₂ , CdS, etc., and charge generating substances such as organic pigments, with a binder added if necessary, is applied (for example, as described in JP-A-47-18543, 55-79449) 3) A method has been used in which a solution of an organic pigment charge-generating substance dissolved in an organic amine is applied (for example, JP-A-52-55643). On the other hand, the charge transport layer is generally provided by dissolving a charge transport substance together with a binder in a solvent and applying the solution using a suitable coating method. Needless to say, the functions required of the charge transport layer include providing good electrophotographic properties (charging properties, sensitivity, low residual potential, etc.), as well as electrical, thermal, and optical hazards encountered during use. There is little deterioration compared to other materials, and changes in characteristics due to atmosphere and during storage are as small as possible. Furthermore, the coating liquid for forming the charge transport layer has a long pot life, is stable, allows concentration control over a wide range, satisfies various constraints required by coating methods, and has no limitations on coating equipment. Less is required. Various materials have been considered for forming charge transport layers. The charge transport layer basically consists of a charge transport substance, a binder, and optional additives such as a plasticizer and a leveling agent, and is formed by dissolving them in a solvent and using various coating methods. . Examples of the charge transport substance include poly-N-vinylcarbazole and its derivatives, poly-γ-carbazolylethyl glutamate and its derivatives, pyrene-formaldehyde condensate and its derivatives,
Polyvinylpyrene, polyvinylphenanthrene,
oxazole derivatives, oxadiazole derivatives,
Electrons such as imidazole derivatives, 9-(p-diethylaminostyryl)anthracene, 1,1-bis(4-dibenzylaminophenyl)propane, styrylanthracene, styrylpyrazoline, phenylhydrazones, α-phenylstilbene derivatives, etc. Donor substance, or fluorenone derivative, dibenzothiophene derivative, indenothiophene derivative, phenanthrenequinone derivative, indenopyridine derivative, thioxanthone derivative, benzo[e]cinnoline derivative, phenazine oxide derivative, tetracyanoethylene, tetra Electron-accepting substances such as cyanoquinodimethane, bromanil, chloranil, and benzoquinone are being considered. As the binder, various polymeric materials such as polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-
Maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyarylate resin, polyvinylidene chloride, cellulose acetate, ethyl cellulose,
polyvinyl butyral, polyvinyl formal,
Thermoplastic resins such as polyamide, poly-N-vinylcarbazole, polyvinyltoluene, acrylic resin, polycarbonate, silicone resin, epoxy resin, melamine resin, urethane resin, phenolic resin, alkyd resin, thermosetting resin, starch, glue, casein The use of natural products such as these alone or in combination is being considered. Solvents generally include hydrocarbons such as benzene, toluene, and xylene, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, tetrahydrofuran,
Ethers such as dioxane, esters such as ethyl acetate, propyl acetate, butyl acetate, chlorides such as methylene chloride, ethylene dichloride, 1,1,2-trichloroethane, carbon tetrachloride, monochlorobenzene, 0-dichlorobenzene, etc. The use of hydrocarbons and alcohols such as n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, and isobutyl alcohol is being considered. According to studies conducted by the present inventors, the above-mentioned charge transporting substances generally have poor solubility in solvents and poor compatibility with binders. Therefore, the charge transport layer obtained from such a coating solution for forming the charge transport layer changes over time, and the charge transport substance precipitates on the surface, which greatly affects the electrophotographic properties. Furthermore, there are restrictions on the material ratio between the charge transport material and the binder, making it difficult to select a preferable material ratio.
Furthermore, there is a limit to the concentration of the coating solution at a low level, which poses a problem in controlling coating film formation. For this purpose, various solvents are being considered. Among the above-mentioned solvents, hydrocarbons, ethers, and chlorinated hydrocarbons are generally used. According to the studies conducted by the present inventors, the use of chlorinated hydrocarbons is superior in terms of dissolving the charge transporting substance and binder and providing a stable coating solution; When used, it reacts with free chlorine of chlorinated hydrocarbons,
Charge transfer complexes were formed which adversely affected the electrophotographic properties, and free chlorine corroded the equipment. Furthermore, it has been found that when hydrocarbons are used, their solubility is poor, causing problems in controlling the film thickness and uniformity of the coating film. Purpose The present invention relates to a charge transport layer of a laminated electrophotographic photoreceptor, and relates to a charge transport layer that satisfies all of the functions described above, and a coating liquid for forming the charge transport layer that specifically enables the same. The purpose is to provide The present inventors investigated various materials, and by using a specific combination of a charge transport substance, a binder, and a solvent, the required functions as described above, that is, a long pot life, were achieved.
It is possible to obtain a coating liquid for forming a charge transport layer that is stable, allows concentration control over a wide range, satisfies various constraints required by coating methods, and has few restrictions on coating equipment. It has been found that it is possible to provide an electrophotographic photoreceptor that provides extremely good electrophotographic properties by coating the above. Therefore, the present inventors focused on tetrahydrofuran, an ether, which is a solvent with excellent solubility for many substances, and investigated various charge transport substances and binders. First, an α-phenylstilbene compound represented by the following general formula () is used as a charge transporting substance. Although this charge transport material has excellent characteristics as a charge transport function, it has particularly poor compatibility with a commercially available bisphenol A polycarbonate binder having high mechanical strength.

[Formula, R ¹ is a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom, or a substituted amino group [

[Formula] (wherein R ³ and R ⁴ represent an alkyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted allyl group, and R ³ and R ⁴ may form a ring)], R ² represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted phenyl group, and X represents a benzene ring, a naphthalene ring, or an indole ring. n
is an integer of 0 or 1, and n is an integer of 0, 1, 2, or 3. ) a repeating unit obtained from 4,4'-dihydroxyphenyl-1,1-cyclohexanone and phosgene as a binder;

By using polycarbonate resin (bisphenol Z type polycarbonate) of [formula],
It has been found that a coating liquid for forming a charge transport layer which is extremely stable and has excellent coating properties can be obtained, and by coating it, it is possible to provide an electrophotographic photoreceptor with extremely good electrophotographic properties. The details of why such excellent properties are obtained are not known, but a comparative study showed that, for example, when saturated polyester resin was used as a binder, the stability of the coating solution was excellent, but mechanical If you use bisphenol A type polycarbonate or polyacrylate resin, which has poor strength and low Tg, it will change over time during storage and charge transport substances will precipitate on the surface. As the liquid changes over time, its viscosity changes moment by moment.
Based on the fact that it begins to gel, it is assumed that this is probably because bisphenol Z type polycarbonate resin has excellent structural mechanical strength, high Tg (170-180℃), and is amorphous. There is. Therefore, the coating liquid can be used for a long period of time, which is very advantageous in terms of productivity and cost, and since tetrahydrofuran is used, no special consideration is required in terms of equipment. The charge transport layer of the present invention basically consists of an α-phenylstilbene compound as a charge transport substance and bisphenol Z polycarbonate as a binder, but the material ratio can be used in a very wide range, but it is 10: 1-1:10, preferably 2:1-1:2
The thickness varies depending on the usage conditions of the photoreceptor, but the appropriate thickness is about 5 to 100 μm. Furthermore, if necessary, known plasticizers and leveling agents can be added. The laminated electrophotographic photoreceptor of the present invention basically consists of aluminum, nickel, chromium, tin oxide,
Indium oxide, etc. is vapor-deposited onto a plastic film such as polyester film, polypropylene film, or cellulose acetate film and treated for conductivity, or a metal plate or tube made of aluminum, nickel, iron, etc. is used as a conductive support, and a charge is generated on it. It can be obtained by providing a layer and further laminating a charge transport layer. The charge generation layer used in the present invention includes Se,
Inorganic semiconductors such as Se alloys and a-Si, photoconductive organic pigments such as phthalocyanine pigments, perylene pigments, and indigo pigments are provided by vapor deposition, sputtering, glow discharge, etc., and photoconductive organic pigments such as C.I. Pigment Blue 25 ( Color Index (CI) 21180), CI Pigment Red 41
(CI21200), CI Shit Dred 52 (CI45100),
In addition to CI Basic Cred 3 (CI45210),
Azo pigments having a carbazole skeleton
95033), azo pigments having a styrylstilbene skeleton (described in JP-A-53-133229), azo pigments having a triphenylamine skeleton (described in JP-A-53-132547), dibenzothio Azo pigment with a phene skeleton (Japanese Patent Application Laid-Open No. 54-21728
Azo pigments having an oxadiazole skeleton (described in JP-A-12742-1974), azo pigments having a fluorenone skeleton (described in JP-A-54-12742),
22834), azo pigments having a bisstilbene skeleton (described in JP-A-54-17733), azo pigments having a distyryloxadiazole skeleton (described in JP-A-54-2129), Azo pigments having a distyrylcarbazole skeleton
17734), trisazo pigments having a carbazole skeleton (JP-A-195767, JP-A-57-
195768), as well as phthalocyanine pigments such as CI Pigment Blue 16 (CI74100), CI Butt Brown 5 (CI73410),
Indigo pigments such as CI Butt Dye (CI73030), Argo Scarlet B (manufactured by Bayer),
Indance Lens Scarlet R (manufactured by Bayer)
It is possible to use one or several kinds of perylene pigments such as , etc., disperse them in a solvent together with a binder if necessary, and provide them by coating or the like. As the binder, polyvinyl butyral resin, polyvinyl formal resin, polyester resin, polycarbonate resin, polystyrene, polyvinyl acetate, polyvinyl chloride, polyamide, polyurethane, various celluloses, etc. can be used. Examples of solvents include benzene, toluene, xylene, methylene chloride, dichloroethane, monochlorobenzene, dichlorobenzene, methyl acetate, butyl acetate, methyl ethyl ketone, dioxane, tetrahydrofuran, dimethylformamide, cyclohensanone, methyl cellosolve, ethyl cellosolve, etc. A mixture of the following may be mentioned. The thickness of the charge generation layer formed by these methods is
Appropriately, the thickness is about 0.05 to 20μ, preferably about 0.1 to 2μ. In the present invention, in order to improve the interlayer adhesion and charging characteristics of the photoreceptor, before forming the charge generation layer, an adhesive layer of polyamide, polyvinyl acetate, polyurethane, etc., an intermediate layer, Alternatively, a thin layer of aluminum oxide or the like can be provided with a thickness of about 0.01 to 2.0 μm by a conventional method such as coating or vapor deposition. Examples are shown below. Example 1 A coating solution for forming a charge generation layer was prepared using the following disazo pigment as a photoconductive organic pigment according to the following procedure. disazo pigment

[Chemical] After dispersing 13.6 g of 5% by weight tetrahydrofuran solution of polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.) and 44.2 g of tetrahydrofuran in a ball mill for 48 hours, 22.3 g of tetrahydrofuran and 37.2 g of ethyl cellosolve were further added, and the mixture was dispersed for 1 hour. Dispersed. After dispersion, the millbase was taken out into a container and diluted and stirred so that the weight ratio of tetrahydrofuran and ethyl cellosolve was 4:6 and the solid content concentration was 1% by weight to prepare a dispersion for coating. Next, this dispersion was applied onto a 0.5 mm thick aluminum plate (JIS1070) by dip coating, and dried to form a charge generation layer with a thickness of 0.5 μm. Next, a coating solution for forming a charge transport layer having the following composition was prepared and applied by dip coating to provide a charge transport layer having a thickness of 20 μm after drying, thereby producing a laminated electrophotographic photoreceptor. α-Phenylstilbene compound with the following structural formula

[Chemical] Bisphenol Z polycarbonate 20g Silicone oil (KF50 manufactured by Shin-Etsu Chemical Co., Ltd.) 0.002g Tetrahydrofuran 160g Comparative example 1 Polyarylate resin (U-100 A laminated electrophotographic photoreceptor was produced under exactly the same conditions as in Example 1, except that a photoreceptor (manufactured by Unitika) was used. Example 2 A coating solution consisting of a 0.5 mm thick aluminum plate (JIS1070), 10 g of polyamide resin (copolymerized nylon, Elvamide 8061 manufactured by Dupont), and 190 g of ethyl alcohol was prepared and applied by dip coating, and the film thickness after drying was approximately An intermediate layer of 0.2μ was provided. Next, a coating solution for forming a charge generation layer was prepared using the following disazo pigment as a photoconductive pigment according to the following procedure. disazo pigment

[Chemical formula] After 57 g of cyclohexanone was dispersed in a ball mill for 48 hours, 90 g of cyclohexanone was added and further dispersed for 1 hour.
After dispersion, the millbase was taken out into a container, cyclohexanone was added, and the mixture was diluted and stirred to a solid content concentration of 1% by weight to prepare a dispersion for coating. Next, this dispersion was applied onto the intermediate layer by a dip coating method to provide a charge generation layer having a thickness of 0.5 μm after drying. Next, a coating solution for forming a charge transport layer having the following composition was prepared and applied onto the charge generation layer by a dip coating method to form a charge transport layer with a film thickness of 20 μm after drying. A laminated electrophotographic photoreceptor consisting of a generation layer and a charge transport layer was prepared. α-Phenylstilbene compound with the following structural formula

[Chemical] Bisphenol Z polycarbonate 20g Silicone oil (KF50 manufactured by Shin-Etsu Chemical Co., Ltd.) 0.002g Tetrahydrofuran 160g Comparative example 2 As a coating liquid for forming a charge transport layer, bisphenol A polycarbonate (K- 1300: Manufactured by Teijin Kasei Ltd.)
A laminated electrophotographic photoreceptor was produced using the same materials and conditions as in Example 2, except that . Next, the charge transport layer forming coating solution prepared in each Example and Comparative Example was placed in a container, sealed, and measured using a rotational viscometer (E-type viscometer, type EL; manufactured by Toki Sangyo Co., Ltd.) to determine the viscosity. The changes over time were measured. Table 1 shows the measurement results.
Shown below. Further, the electrophotographic properties of each of the electrophotographic photoreceptors prepared as described above were evaluated using an electrostatic copying paper tester (Model SP428, manufactured by Kawaguchi Denki Seisakusho Co., Ltd.) under the following conditions. Conduct corona discharge for 20 seconds to charge the surface, measure the surface potential Vs (volts), leave it in a dark place for another 20 seconds, measure the surface potential Vo (volts), and then apply 20 lux white tungsten. After irradiation with light, the exposure amount E1/10 (lux seconds) required for Vo to attenuate to 1/10 and the surface potential V 30 seconds after irradiation were measured. The results are shown in Table 2.

【table】

[Table] Effects As can be seen from the above examples, the coating liquid for forming a charge transport layer comprising the α-phenylstilbene compound, bisphenol Z polycarbonate, and tetrahydrofuran of the present invention is extremely stable without changing over time. By using it, an extremely high-quality laminated electrophotographic photoreceptor can be obtained.

Claims (1)

[Scope of Claims] 1. In a laminated electrophotographic photoreceptor in which a charge generation layer and a charge transport layer are provided on a conductive support, the charge transport layer comprises at least an α-F represented by the following general formula (). enylstilbene compound [Formula] (wherein R ¹ is a hydrogen atom, an alkyl group, an alkoxy group, a halogen atom or a substituted amino group [Formula] (wherein R ³ and R ⁴ are an alkyl group, substituted or unsubstituted represents an aralkyl group or a substituted or unsubstituted allyl group, R ³ and R ⁴ may form a ring), R ² represents a hydrogen atom, an alkyl group, or a substituted or unsubstituted phenyl group, and X represents benzene ring,
Indicates a naphthalene ring or an indole ring. n is 0
or an integer of 1, n is an integer of 0, 1, 2, or 3. ) An electrophotographic photoreceptor comprising 4,4'-dihydroxyphenyl-1,1-cyclohexane having the structural formula [Formula] and a polycarbonate resin having the repeating unit [Formula] obtained from phosgene.