DE68922083T2 - Photosensitive element for electrophotography. - Google Patents

Description

The invention relates to a photosensitive member for electrophotography, and more particularly to a photosensitive member for electrophotography comprising a low molecular weight organic photoconductor capable of providing improved electrophotographic characteristics.

A large number of organic photoconductive polymers have been proposed to be used for electrophotographic photosensitive members, such as polyvinyl carbazole. These conventional organic polymers are superior to the inorganic photoconductive materials in lightness (weight), film-forming properties, and the like, but they are inferior to the latter in sensitivity, durability, stability against environmental changes, mechanical strength, and the like.

On the other hand, several low molecular weight organic photoconductive materials have been proposed, such as hydiazone compounds (US Patent 4,150,987), triarylpyrazoline compounds (US Patent 3,837,851) and 9-styrylanthracene (Japanese Laid-Open Patent Application (JP-A, KOKAI) Nos. 94828/1976 and 94829/1976). In the case where conventional low molecular weight organic photoconductors represented by those described above are used, the aforementioned weakness in film-forming property, which has conventionally been a problem in the field of organic photoconductive polymers, can be avoided by appropriately selecting a binder used in combination with the photoconductor. However, these conventional organic photoconductors cannot provide sufficient sensitivity.

From this viewpoint, a multilayer type structure in which the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer has recently been proposed. The electrophotographic photosensitive member comprising such a photosensitive layer can be improved in its sensitivity to visible light, ability to stabilize the charge, surface strength and the like.

As the charge transporting compound constituting the above-mentioned charge transport layer, a large number of organic compounds have been proposed so far. Examples thereof include pyrazoline compounds (Japanese Patent Laid-Open No. 72231/1977), hydrazone compounds (US Patent 842431 and Japanese Patent Laid-Open No. 52063/1980), triplienylamine compounds (Japanese Patent Laid-Open Nos. 195254/1982 and 58445/1979), stilbene compounds (Japanese Patent Laid-Open Nos. 151955/1979 and 198043/1983), carbazole compounds (Japanese Patent Laid-Open Nos. 150128/1979 and 58451/1988), benzothiophene compounds (Japanese Patent Laid-Open No. 110835/1979) and the like. EP-A 0161934 discloses an electrophotographic photosensitive member whose charge transport layer contains a charge transporting aromatic amine compound represented by the following general formula:

wherein R₁ and R₂ represent an aromatic group selected from the group consisting of a substituted or unsubstituted phenyl group, naphthyl group and polyphenyl group, and R₃ is selected from the group consisting of a substituted or unsubstituted aryl group, alkyl group having 1 to 18 carbon atoms and cycloaliphatic compounds having 3 to 18 carbon atoms.

However, in the electrophotographic photosensitive member using the conventional low molecular weight organic compound as the charge transporting compound, the sensitivity and other electrophotographic properties are not necessarily sufficient, and the light area potential and the dark area potential tend to show noticeable changes. when charging and exposure operations are performed repeatedly.

Accordingly, there is still room for improvement regarding such an electrophotographic photosensitive element.

An object of the present invention is to provide an electrophotographic photosensitive member which has solved the above-mentioned various problems encountered in conventional photosensitive members.

Another object of the invention is to provide an electrophotographic photosensitive member using a novel organic photoconductor which is easy to manufacture, relatively inexpensive, and has excellent durability.

According to the invention, there is provided a photosensitive member for electrophotography comprising an electrically conductive support and a photosensitive layer provided thereon, the photosensitive layer comprising a triarylamine compound represented by the following general formula (I) or (II):

wherein Ar₁ and Ar₂ each represent a biphenyl group capable of bearing a substituent, Ar₃ a phenyl group capable of bearing a substituent or an aromatic heterocyclic group capable of bearing a substituent, Ar₄ and Ar₅ each represent a benzene ring capable of bearing a substituent or an aromatic condensed ring hydrocarbon group capable of to carry a substituent, R₁ and R₂ each represent a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom and at least one of the two groups Ar₄ and Ar₅ represents an aromatic hydrocarbon group of condensed rings. In patent claim 1 for the contracting state DE, it is specified with regard to earlier national patent rights from DE-A 3835791 that Ar₃ of formula (I) only represents an aromatic heterocyclic group which is capable of carrying a substituent.

These and other objects, features and advantages of the invention will become more apparent upon consideration of the following description of the preferred embodiments of the invention taken in conjunction with the accompanying drawings.

Fig. 1 and 2 show infrared absorption spectra of example compounds No. 2 and 26, respectively, recorded using the KBr tablet method.

In the above general formula (I), Ar₁ and Ar₂ each represent a biphenyl group capable of bearing a substituent. Specific examples of such a substituent may include alkyl groups such as a methyl group, an ethyl group and a propyl group, alkoxy groups such as a methoxy group, an ethoxy group and a propoxy group, halogen atoms such as a fluorine atom, a chlorine atom and a bromine atom, and the like. Ar₁ may be different from Ar₂.

Ar₃ represents a phenyl group capable of bearing a substituent, or an aromatic heterocyclic group such as a pyridyl group, a quinolyl group, a thienyl group or a furyl group capable of bearing a substituent. Specific examples of such a substituent may include: alkyl groups such as a methyl group, an ethyl group and a propyl group, alkoxy groups such as a methoxy group, an ethoxy group and a propoxy group, aryloxy groups such as a phenoxy group and a naphthoxy group, aromatic groups such as a phenyl group and a naphthyl group, halogen atoms such as a fluorine atom, a chlorine atom and a bioatom, and the like.

In the above general formula (II), Ar₄ and Ar₅ may each represent an aromatic hydrocarbon group of a benzene ring or of condensed rings (or fused rings) capable of bearing a substituent. At least one of the two groups Ar₄ and Ar₅ is an aromatic hydrocarbon group of condensed rings. Specific examples of such an aromatic hydrocarbon of condensed rings may include naphthalene, anthracene, phenanthrene, chrysene and naphthacene. Specific examples of such a substituent which Ar₄ and Ar₅ include: alkyl groups such as a methyl group, an ethyl group and a propyl group, alkoxy groups such as a methoxy group, an ethoxy group and a propoxy group, halogen atoms such as a fluorine atom, a chlorine atom and a bromine atom, and the like. Ar₄ may be the same as or different from Ar₅.

R₁ and R₂ each represent a hydrogen atom, an alkyl group such as a methyl group, an ethyl group and a propyl group, an alkoxy group such as a methoxy group, an ethoxy group and a propoxy group, a halogen atom such as a fluorine atom, a chlorine atom and a bromine atom, and the like. R₁ may be the same as or different from R₂.

Representative examples of the compound represented by the above formula (I) are described below. Connection examples:

Representative examples of the compound represented by the above formula (II) are described below. Connection examples:

The above compound examples can be synthesized in the following manner.

Synthesis of Example Compound No. 2

23.5 g (83.9 mmol) of 4-iodobiphenyl, 3.0 g (28.0 mmol) of p-toluidine, 11.6 g (83.9 mmol) of anhydrous potassium carbonate and 15 g of copper powder were added to 50 mL of nitrobenzene and refluxed for 12 hours with heating and stirring. After the reaction mixture was cooled, it was filtered by suction and nitrobenzene was removed from the resulting filtrate under reduced pressure. Ethanol was added to the residue, whereby crude crystals were precipitated.

The crude crystals were subjected to separation by means of a silica gel column for purification, whereby 7.80 g (yield = 66.7%) of the desired Example Compound (2) was obtained, which showed a melting point of 187.0 to 188.0 °C. Elemental analysis (C₃₁₁H₂₅N) calculated value observed value

Fig. 1 shows a graphic representation of an infrared absorption spectrum obtained by measuring the thus obtained compound by a KBr tablet method (KBR pellet).

Synthesis of example compound no. 26

35 5.75 g (20.5 mmol) of 4-iodobiphenyl, 3.0 g (13.7 mmol) of N-phenyl-α-naphthylamine, 2.83 g (20.5 mmol) of anhydrous potassium carbonate and 1.5 g of copper powder were added to 30 ml of nitrobenzene and refluxed for 10 hours with heating and stirring. After the reaction mixture was cooled, it was filtered by suction, and nitrobenzene was then removed from the resulting filtrate under reduced pressure. The residue was subjected to separation by means of a silica gel column for purification to obtain 3.3 g (yield = 65%) of the desired Example Compound (26) which showed a melting point of 176.5 to 177.5 °C. Elemental analysis (C₂₈H₂₁N) calculated value observed value

Fig. 2 shows a graphical representation of an infrared absorption spectrum obtained by measuring the thus obtained compound by a KBr tablet method.

As described above, the compound of the present invention can be synthesized easily and inexpensively. The other compounds of the present invention can be synthesized in a similar manner as described in the above-mentioned synthesis examples.

In a preferred embodiment of the invention, the photosensitive layer is functionally separated into a charge generation layer and a charge transport layer, and the charge transport layer comprises the compound represented by the above general formulas (I) or (II) as a charge transporting compound.

The charge transport layer of the present invention can preferably be formed by dissolving the above compound of formula (I) or (II) together with a binder in an appropriate solvent, applying the resulting coating liquid as a solution to a specified surface and drying the resulting coating.

Examples of the binder to be used for preparing the charge transport layer may include: polyarylate resins, polysulfone resins, polyamide resins, acrylic resins, acrylonitrile resins, methacrylic resins, vinyl chloride resins, Vinyl acetate resins, phenolic resins, epoxy resins, polyester resins, alkyl resins, polycarbonate, polyurethane or copolymer resins containing two or more repeating units of these resins, such as copolymers of styrene and butadiene, copolymers of styrene and acrylonitrile, copolymers of styrene and maleic acid and the like. Also, insulating polymers other than such, namely organic, photoconductive polymers, such as polyvinylcarbazole, polyvinylanthracene and polyvinylpyrene, can be used.

In the charge transport layer, the charge transporting compound can be used preferably in an amount of 10 to 500 parts by weight and more preferably in an amount of 50 to 200 parts by weight per 100 parts by weight of the binder.

The charge transport layer is electrically connected to the charge generation layer as described below and has a function of receiving charge carriers entering from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface of the charge transport layer. In such an embodiment, the charge transport layer may be coated on the charge generation layer or it may be coated under the charge generation layer. The charge transport layer may preferably be coated on the charge generation layer. It is not preferable that the charge transport layer has too large a thickness because there is a certain limit to its thickness suitable for transporting the charge carriers. In general, the charge transport layer may have a thickness of 5 to 40 µm, and more preferably 10 to 30 µm.

The organic solvent to be used in the above-mentioned preparation of the charge transport layer may vary depending on the type of the binder used therefor and is preferably selected from those which do not substantially dissolve the charge generation layer or a primer layer (or undercoat layer) described below.

Specific examples of such an organic solvent may include: alcohols such as methanol, ethanol and isopropanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N,N-dimethylformamide and N,N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride and trichloroethylene, aromatic compounds such as benzene, toluene, xylene, monochlorobenzene and dichlorobenzene, and the like.

Coating can be carried out by various coating methods such as dip coating, spray coating, wire bar coating and blade bar coating. Drying should preferably be carried out in a sequence of drying at room temperature to a "tack-free" state and then heat drying. In general, heat drying is preferably carried out for a time ranging from 5 minutes to 2 hours at a temperature of 30ºC to 200ºC under a still atmosphere or under blowing.

The charge transport layer of the present invention may further contain an additive selected from various species. Examples of such an additive may include plasticizers such as diphenyl, m-terphenyl and dibutyl phthalates, surface lubricants such as silicone oil, graft-type silicone polymers and various fluorocarbons, potential stabilizing agents such as dicyanovinyl compounds and carbazole derivatives, antioxidants such as β-carotene, Ni complexes and 1,4-diazabicyclo[2,2,2]octane, and the like.

The charge generation layer may comprise a charge generation compound. Specific examples of the charge generation compound may include inorganic charge generation compounds such as selenium, selenium-telurium and amorphous silicon, and organic charge generation compounds including cationic dyes such as pyrylium dye, thiapyrylium dye, azulenium dye, thiacyanine dye and quinocyanine dye, polycyclic quinone pigments such as squarilium salt dye, phthalocyanine pigment, anthanthione pigment, dibenzopyrenequinone pigment and pyranthrone pigment, indigo pigment, quinacridone pigment, azo pigment and the like. These charge generation compounds may be used singly or in a combination of two or more species. The charge generation layer may be formed using a charge generation compound in the form of a vapor-deposited applied layer or a layer applied by coating.

Among the above-mentioned charge generating compounds, in particular, the azo pigment includes various types. Representative structures of the azo pigment preferably used in the invention are described below. When the azo pigment is represented by a general formula including the following central skeleton A:

A(N=N-Cp)n

wherein Cp represents a coupler region (or coupler molecule part) and n is two or three, specific examples of the central skeleton A include those comprising the following structures:

Specific examples of the coupler region Cp include those having the following structures: (R: H atom, halogen atom, alkoxy group, alkyl group, nitro group and the like, n = 1 or 2) (R: alkyl group or R' = H atom, halogen atom, alkoxy group, alkyl group, nitro group and the like) (R: H atom, halogen atom, alkoxy group, alkyl group, nitro group and the like) (R: alkyl group, alkyl group and the like) (R₁, R₂: H atom, halogen atom, alkoxy group, alkyl group, nitro group and the like, n=1 or 2)

The above-mentioned central skeleton A and the coupler element Cp can be appropriately combined to form a pigment as a charge-generating compound.

The charge generation layer may be formed, as required, by vapor-depositing a charge generating compound by means of a vacuum deposition device or by applying a dispersion containing such a charge generating compound in a dispersed form together with an appropriate binder.

The binder to be used to form the charge generation layer can be selected from a wide variety of insulating resins or alternatively from organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene and polyvinylpyrene. It can Preferably, an insulating resin is used, such as polyvinyl butyral, polyacrylates (for example a polycondensation product of bisphenol A and phthalic acid), polycarbonate, polyester, phenoxy resin, acrylic resin, polyacrylamide resin, polyamide, polyvinylpyridine, cellulose resin, urethane resin, epoxy resin, casein, polyvinyl alcohol and polyvinylpyrrolidone.

The resin may preferably be contained in the charge generating layer in an amount of 5 to 80 wt%, and more preferably 10 to 40 wt%.

Specific examples of the organic solvent usable in coating the charge generation layer may include alcohols such as methanol, ethanol and isopropanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, amides such as N,N-dimethylformamide and N,N-dimethylacetamide, sulfoxides such as dimethyl sulfoxide, ethers such as tetrahydrofuran, dioxane and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, aliphatic halogenated hydrocarbons such as chloroform, methylene chloride, dichloroethylene, carbon tetrachloride and trichloroethylene, aromatic compounds such as benzene, toluene, xylene, monochlorobenzene and dichlorobenzene, and the like.

The charge generation layer may preferably contain the above-mentioned charge generation compound in an amount as large as possible so that the layer may have a sufficient absorption capacity. Further, the charge generation layer may preferably be a thin layer having a thickness of 5 µm or less, and more preferably 0.01 to 1 µm, so that it can introduce charge carriers generated therein into the charge transport layer within the lifetime of the charge carriers. This may be due to facts such as that most of the amount of incident light can be preferentially absorbed in the charge generation layer to generate a large number of charge carriers, and that the charge carriers thus produced are preferentially introduced into the charge transport layer without deactivation due to recombination or interception of the charge carriers.

The above-mentioned photosensitive layer, which has a multilayer structure comprising a charge generation layer and a charge transport layer, can be applied to an electrically conductive support.

The electrically conductive support may be a support which itself has electrical conductivity, such as aluminum, aluminum alloy, copper, zinc and stainless steel; alternatively, it may be the said metal support or a support made of a plastic coated, for example, with a vacuum-deposited layer of aluminum, aluminum alloy, indium oxide, zinc oxide or indium oxide-tin oxide alloy, or a mixture of an electrically conductive powder (such as aluminum powder, titanium dioxide powder, tin oxide powder, zinc oxide powder, carbon black powder and silver particles) and a suitable binder, a support made of paper or plastic impregnated with electrically conductive particles or a plastic support coated with an electrically conductive polymer layer. The electrically conductive support may have any shape, such as the shape of a sheet, a drum and the like.

Between the electrically conductive support and the photosensitive layer, an undercoat layer may be formed which has a barrier function and an adhesive function. The undercoat layer may comprise, for example, casein, polyvinyl alcohol, nitrocellulose, a copolymer of ethylene and acrylic acid, polyamide (for example, nylon 6, nylon 66, nylon 610, copolymer nylon, alkoxymethylated nylon and the like), polyurethane, gelatin or alumina. The thickness of the undercoat layer should preferably be between 0.1 and 5 µm, particularly between 0.5 and 3 µm.

In the electrophotographic photosensitive member of the present invention, a protective layer may be further coated on the photosensitive layer. Such a protective layer may comprise a resin or a resin and an electrically conductive material dispersed therein.

In another embodiment of the invention, a pigment or dye having photoconductivity can be used as a sensitizer. Examples of such dyes or pigments include the aforementioned diazo pigment, pyrylium dye, thiapyrylium dye, sine pyrylium dye, benzopyrylium dye, benzothiapyrylium dye, naphthopyrylium dye and naphtholthiapyrylium dye as described in U.S. Patents 3,554,745, 3,567,438 and 3,586,500.

In yet another embodiment of the invention, a eutectic (crystalline) complex comprising a pyrylium dye (as disclosed in U.S. Patent 3,684,502) and an electrically insulating polymer comprising an alkylidene-diarylene region can be used as a sensitizer. Such a eutectic complex can be formed by dissolving 4-[4-bis(2-chloroethyl)aminophenyl]-2,6-diphenylthiapyrylium perchorate and poly(4,4)-isopropylidenediphenylene carbonate in a halogenated hydrocarbon type solvent (for example, dichloromethane, chloroform, carbon tetrachloride, 1,1-dichloroethane, 1,2-dichloroethane, 1,1,2-trichloroethane, chlorobenzene, bromobenzene, 1,2-dichlorobenzene and the like) and then adding a non-polar solvent (for example, hexane, octane, decane, 2,2,4-trimethylbenzene, ligroin and the like) to the resulting mixture so that a particulate eutectic complex is prepared. In such an embodiment, the electrophotographic photosensitive member may include a binder such as a copolymer of styrene and butadiene, a silicone resin, a vinyl resin, a copolymer of vinylidene chloride and acrylonitrile, a copolymer of styrene and acrylonitrile, a copolymer of vinyl acetate and vinyl chloride, polyvinyl butyral, polymethyl methacrylate, poly-N-butyl methacrylate, polyester, cellulose ester, and the like.

The electrophotographic photosensitive member of the present invention can be used not only for ordinary copying machines but also in the fields related to electrophotography such as laser printers, CRT printers and electrophotographic plate making.

The present invention will be described in more detail with reference to Examples.

example 1

5 g of a diazo pigment represented by the following formula:

and a solution obtained by dissolving 2 g of a butyral resin (butyral grade: 63 mol%) in 100 ml of cyclohexanone were dispersed for 24 hours by means of a sand mill to prepare a coating liquid. The coating liquid thus prepared was coated on an aluminum sheet by means of a wire bar to form a charge generation layer having a density (after drying) of 0.2 µm.

Then, 10 g of the aforementioned Example Compound No. 6 as a charge-transporting compound and 10 g of a polycarbonate resin (weight average molecular weight = 20,000) were dissolved in 70 g of monochlorobenzene to prepare a coating liquid. The coating liquid was coated on the aforementioned charge generation layer by means of a wire bar to form a charge transporting layer having a thickness (after drying) of 20 µm, thereby preparing an electrophotographic photosensitive member having a layered structure.

The photosensitive member thus prepared was charged using a corona (-5 kV) according to a static method by means of an electrostatic copy paper checker (model: SP-428, manufactured by Kawaguchi Denki K.K.) and kept in a dark place for 1 second. Thereafter, the photosensitive member was exposed to light at a brightness of 20 lux to examine the charging characteristics. To examine the charging characteristics, the surface potential (V0), the potential (V1) obtained after decaying in the dark for 1 second, and the exposure amount (E½) required to reduce the potential V1 to half were measured.

Further, in order to measure the changes in the light region potential and the dark region potential with repeated use, the photosensitive member prepared in this connection was stuck on a cylinder for a photosensitive drum to be used for a plain paper copying machine (PPC machine) (NP-3525, manufactured by Canon K.K.) and subjected to a copying test of 5000 sheets. Thus, the light region potential (VL) and the dark region potential (VD) were measured in the initial state and after copying 5000 sheets to examine its change. The initial potentials VD and VL were set to -700 V and -200 V, respectively.

The results are presented in the following Table 1. Table 1 Initial potential (V) Potential after copying 5000 sheets (V) Example

Example 2

An electrophotographic photosensitive member was prepared in the same manner as in Example 1 except that Example Compound (29) was used as a charge-transporting compound instead of Example Compound (6) used in Example 1.

The electrophotographic properties of the photosensitive member thus obtained were measured in the same manner as in Example 1.

The results are presented in Table 2 below. Table 2 Initial potential (V) Potential after copying 5000 sheets (V) Example

Examples 3 to 11

Nine species of photosensitive members were prepared in the same manner as in Example 1, except that Example Compounds (1), (2), (5), (8), (10), (12), (15), (20) and (23), respectively, were used as the charge-transporting compound in place of Example Compound (6) used in Example 1, and that a pigment having the following formula was used as the charge-generating compound:

The electrophotographic characteristics of the photosensitive members thus obtained were measured in the same manner as in Example 1.

The results are presented in Table 3 below. Table 3 Initial potential Potential after copying 5000 sheets Example Connection example Table 3, continued

Examples 12 to 17

Six species of photosensitive members were prepared in the same manner as in Example 1, except that Example Compounds (26), (28), (33), (39), (43) and (44), respectively, were used as the charge-transporting compound in place of Example Compound (29) used in Example 2, and that the pigment used in Examples 3 to 11 was used as the charge-generating compound.

The electrophotographic properties of the photosensitive member thus obtained were measured in the same manner as in Example 1.

The results are presented in Table 4 below. Table 4 Initial potential Potential after copying 5000 sheets Example Connection example

Comparative examples 1 to 5

For comparison purposes, five species of photosensitive members were prepared in the same manner as in Example 1, except that the following comparative example compounds 1 to 5 were used as the charge-transporting compound, respectively.

The electrophotographic properties of the photosensitive members thus obtained were measured in the same manner as in Example 1.

The results are shown in Table 5 below. Comparative example compounds

disclosed in Japanese Laid-Open Publication No. 195254/1982)

(disclosed in Japanese Laid-Open Patent Application No. 58445/1979)

(disclosed in Japanese Laid-Open Patent Application No. 198043/1983)

(disclosed in Japanese Laid-Open Patent Application No. 195254/1982)

(disclosed in Japanese Laid-Open Patent Application No. 58445/1979) Table 5 Initial potential Potential after copying 5000 sheets Comparison example Comparison compound

As is clear from the results described above, the compounds of the present invention provided photosensitive members having better sensitivity and better potential stability in successive copying compared with those of the comparative examples.

Examples 18 and 19

A coating liquid obtained by dissolving 5 g of a methoxymethylated nylon resin (number average molecular weight = 32,000) and 10 g of an alcohol-soluble copolymeric nylon resin (number average molecular weight = 29,000) in 95 g of methanol was coated on an aluminum support by means of a wire bar to form a primer layer with a thickness of 1 µm (after drying).

Then, 10 g of a charge generating compound represented by the following formula:

a butyral resin (butyral grade: 63 mol%) and 200 g of dioxane were dispersed for 48 hours by means of a ball mill type dispersing device to prepare a dispersion. The dispersion thus prepared was coated on the above primer layer by a blade coating method, thereby forming a charge generation layer having a thickness (after drying) of 0.15 µm.

Then, 10 g of the aforementioned Example Compound No. 3 and 10 g of a polymethyl methacrylate resin (weight average molecular weight = 50,000) were dissolved in 70 g of monochlorobenzene to prepare a coating liquid. The coating liquid was coated on the aforementioned charge generation layer by a blade coating method to form a charge transport layer having a thickness (after drying) of 19 µm, thereby preparing an electrophotographic photosensitive member (Example 18).

The photosensitive member thus prepared was charged using a corona discharge (-5 kV) so that it had an initial potential of V0 and left in a dark place for 1 hour, after which its surface potential (V1) was measured. To examine the sensitivity, the amount of exposure (E½, µJ/cm2) required to reduce the potential V1 to half its value after decaying in the dark was measured. The light source used here was a laser light (output 5 mW, radiation wavelength: 780 µm) emitted from a ternary semiconductor comprising gallium/aluminum/arsenic oxide.

The results were the following:

V0 -710V

V1: -693V

E½: 0.51 uJ/cm²

Separately, the above procedure was repeated except that Example Compound No. 41 was used as a charge-transporting compound contained in the charge-transporting layer, thereby preparing another electrophotographic photosensitive member. The photosensitive member thus prepared was examined in the same manner as described above (Example 19). The results were as follows:

V0 -710V

V1: -693V

E½: 0.51 uJ/cm²

Each of the above photosensitive members was installed in a laser beam printer (trade name: LBP-CX, manufactured by Canon K.K.) as an electrophotographic printer equipped with the above semiconductor laser and using a reversal development system, and subjected to actual image formation.

The image formation conditions here were as follows:

Surface potential after primary charge:

-700V

Surface potential after image exposure:

-150 V (exposure quantity: 2.0 uJ/cm²)

Transmission potential:

+ 700V

Polarity of the developer:

negative

Process speed:

50mm/sec

Development conditions (development bias):

-450V

Image exposure scanning system:

Image scanning

Exposure before primary charging: 50 lux sec (full-surface exposure with red light)

The image formation was achieved by scanning the laser beam line by line according to the character and image signals. As a result, good prints were obtained with respect to the characters and images when each of the two photosensitive elements mentioned above was used.

Further, when consecutive image formation of 300 sheets was carried out, good prints were reliably obtained starting from the initial state up to 3000 sheets in a case where each of the two above-mentioned photosensitive members was used.

Examples 20 and 21, Comparative Examples 6 and 7

10 g of oxytitanium phthalocyanine and a solution obtained by dissolving 5 g of a phenoxy resin in 485 g of dioxane were dispersed for 2 hours by means of a ball mill. The dispersion thus prepared was coated on an aluminum sheet by means of a wire bar and then dried at 80°C for 2 hours, thereby forming a charge generation layer having a thickness of 0.5 µm.

Then, 10 g of the above-mentioned Example Compound No. 7 and 10 g of a bisphenol Z type polycarbonate resin (weight average molecular weight 50,000) were dissolved in 70 g of monochlorobenzene to prepare a coating liquid. The coating liquid was coated on the above-mentioned charge generation layer by means of a wire bar and then dried at 110°C for one hour to form a charge transport layer having a thickness of 19 µm, thereby preparing an electrophotographic photosensitive member (Example 20).

The photosensitive member thus obtained was examined in the same manner as in Example 18.

The procedure described was repeated except that Example Compound No. 28 was used to form the charge transport layer, to prepare a photosensitive member (Example 21), which was then examined in the same manner as described above.

Further, the above-mentioned procedure was repeated except that the following comparative example compounds 6 and 7 were used to form the charge transport layer (Comparative Examples 6 and 7), respectively, which was then examined in the same manner as described above. Comparative example compound:

The results obtained are shown in the following Table 6. Table 6 Connection example Example (comparative)

Examples 22 and 23

3 g of 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate and 5 g of Example Compound No. 18 as a charge transporting compound and 5 g of a polyester resin (weight average molecular weight = 49,000) were dispersed with 50 g of a solvent comprising toluene and dioxane (1:1) for 6 hours by means of a ball mill. The dispersion thus obtained was coated on an aluminum sheet by means of a wire bar and then dried at 100°C for 2 hours to form a photosensitive layer having a thickness of 15 µm, thereby preparing an electrophotographic photosensitive member.

The photosensitive element thus obtained was examined in the same manner as in Example 1 (Example 22).

Separately, the procedure just described was repeated except that Example Compound No. 43 was used as a charge-transporting compound contained in the charge-transporting layer, thereby preparing another electrophotographic photosensitive member. The photosensitive members thus prepared were evaluated in the same manner as described above (Example 23).

The results obtained are presented in the following Table 7. Table 7 Initial potential Potential after copying 5000 sheets Example Connection example

Examples 24 and 25

An aqueous ammonia solution of casein (comprising 11.2 g of casein, 1 g of 28% ammonia water and 222 ml of water) was coated on an aluminum plate by means of a wire bar to form a primer layer having a thickness of 1 µm (after drying). On the primer layer, a charge transport layer and a charge generation layer were sequentially coated in the same manner as in Example 4, thereby preparing an electrophotographic photosensitive member in the same manner as in Example 1 except that the laminate structure was different (Example 24).

The charge characteristics of the photosensitive member thus obtained were examined in the same manner as in Example 1, except that the charge polarity was positive.

The above procedure was repeated except that the charge transport layer was formed in the same manner as in Example 13 (Example 25).

The results obtained are presented in the following Table 8. Table 8 Example connection example

Examples 26 and 27

A 5% methanol solution of a soluble nylon species (6-66-610-12, quaternary copolymeric nylon) was coated on an aluminum support to obtain a to form a primer layer having a thickness of 0.5 µm (after drying).

Then 5 g of a pigment represented by the following formula:

in 95 ml of tetrahydrofuran for 20 hours using a sand mill to prepare a dispersion.

Separately, 5 g of the above-mentioned Example Compound No. 14 as a charge-transporting compound and 10 g of a bisphenol Z type polycarbonate resin (weight average molecular weight = 50,000) were dissolved in 30 ml of monochlorobenzene to prepare a solution. The solution was then added to the above-mentioned dispersion and further dispersed by means of a sand mill for 2 hours to prepare a coating liquid. The coating liquid thus prepared was applied to the above-mentioned primer layer by means of a wire bar and dried to form a photosensitive layer having a thickness of 20 µm (after drying), thereby preparing an electrophotographic photosensitive member.

The electrophotographic properties of the photosensitive member thus obtained were examined in the same manner as in Example 1 (Example 26).

The procedure described was repeated, except that Example Compound No. 32 was used as the charge transporting compound (Example 27).

The results obtained are presented in the following Table 9. Table 9 Example connection example

Claims (11)

1. A photosensitive member for electrophotography comprising an electrically conductive support and a photosensitive layer provided thereon, wherein the photosensitive layer comprises a triarylamine compound represented by the following general formula (I) or (II): wherein Ar₁ and Ar₂ each represent a biphenyl group capable of bearing a substituent, Ar₃ represents an aromatic heterocyclic group capable of bearing a substituent, Ar₄ and Ar₅ each represent a benzene ring capable of bearing a substituent or an aromatic condensed ring hydrocarbon group capable of bearing a substituent, R₁ and R₂ each represent a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom, and at least one of the two groups Ar₄ and Ar₅ represents an aromatic condensed ring hydrocarbon group. 2. The element of claim 1, wherein the photosensitive layer has a laminate structure comprising a charge generation layer and a charge transport layer. 3. The element of claim 2, comprising an electrically conductive support and the charge generation layer and the charge transport layer in that order on the support. 4. The element of claim 2, comprising an electrically conductive support and the charge transport layer and the charge generation layer in that order on the support. 5. The element of claim 2, wherein the charge transport layer comprises the compound represented by formula (I) or (II) and an insulating polymer or an organic photoconductive polymer. 6. The element of claim 2, wherein the charge transport layer comprises the compound represented by formula (I) or (II) and an insulating polymer or an organic photoconductive polymer and at least one species selected from the group consisting of a plasticizer, a surface lubricant, a potential stabilizing agent and an antioxidant. 7. The element of claim 2, wherein the charge generation layer comprises an organic charge generating compound and an insulating resin. 8. The element of claim 1 further comprising a primer layer disposed between the electrically conductive support and the photosensitive layer. 9. The element of claim 1 further comprising a protective layer disposed on the photosensitive layer. 10. The element of any one of claims 1 to 9, wherein the triarylamine compound is represented by formula (I). 11. The element of any one of claims 1 to 9, wherein the triarylamine compound is represented by formula (II).