Electrophotographic Photoconductor

1. Field of the Invention

The present invention relates to an electrophotographic photoconductor comprising a photoconductive layer which contains a compound having a specific tetraazaporphyrin skeleton as a charge generation material capable of generating charge carriers when exposed to light.

2. Discussion of Background

Conventionally, inorganic materials such as selenium, cadmium sulfide and zinc oxide are used as photoconductive materials of an electrophotographic photoconductor in the electrophotographic process. The above-mentioned electrophotographic process is one of the image forming processes, through which the surface of the photoconductor is charged uniformly in the dark to a predetermined polarity, for instance, by corona charge. The uniformly charged photoconductor is exposed to a light image to selectively dissipate the electric charge of the exposed areas, so that a latent electrostatic image is formed on the photoconductor. The thus formed latent electrostatic image is developed into a visible image by a toner comprising a coloring agent such as a dye or pigment, and a binder agent such as a polymeric material.

Fundamental characteristics required for the photoconductor for use in such an electrophotographic process are: (1) chargeability to an appropriate potential in the dark, (2) minimum dissipation of electric charge in the dark, and (3) rapid dissipation of electric charge when exposed to light.

However, while the above-mentioned inorganic materials have many advantages, they have several shortcomings in light of practical use.

For instance, a selenium photoconductor has the shortcomings that the manufacturing conditions are difficult and, accordingly, its production cost is high. In addition, it is difficult to work it into the form of a belt due to its poor flexibility, and it is so vulnerable to heat and mechanical shocks that it must be handled with the utmost care.

A cadmium sulfide photoconductor and a zinc oxide photoconductor can be easily obtained by dispersing cadmium sulfide particles and zinc oxide particles respectively in a binder resin, and coating the thus prepared coating liquid on a support. However, they are poor in terms of the mechanical properties, such as surface smoothness, hardness, tensile strength and wear resistance. Therefore, they cannot be used in the repeated operations as they are.

To solve the problems of the inorganic photoconductive materials, various electrophotographic photoconductors employing organic photoconductive materials are proposed in recent years and some are still put to practical use. For example, there are known a photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorene-9-on, as disclosed in U.S. Pat. No. 3,484,237; a photoconductor prepared by sensitizing poly-N-vinylcarbazole with a pigment of pyrylium salt, as disclosed in Japanese Patent Publication 48-25658; a photoconductor comprising as the main component an organic pigment as disclosed in Japanese Laid-Open Patent Application 47-37543; and a photoconductor comprising as the main component a eutectic crystal complex of a dye and a resin, as disclosed in Japanese Laid-Open Patent Application 47-10735.

In particular, a layered photoconductor fabricated by successively overlaying a charge generation layer in the form of a thin film of an organic pigment and a charge transport layer comprising a charge transport material on an electroconductive support has been actively studied because the sensitivity of the photoconductor is high and there are a large variety of materials therefor. Thus, the layered photoconductor has become the mainstream in the field of the copying machine and printer. However, the conventional layered photoconductors are still unsatisfactory in light of such requirements for the advanced photoconductor as to cope with high speed operation of the copying machine and show high sensitivity in the wavelength range of the semiconductor laser.

In recent years, the copying machine is required not only to produce high quality images, but also to be provided with text editing function and composite processing function. In line with the above-mentioned demands, non-impact printing technology has been developed and digital recording apparatus such as a laser printer, a laser facsimile machine and a digital copying machine have been widely utilized.

Most of the above-mentioned digital recording apparatus employ as a light source a semiconductor laser beam because it is compact, cheap and convenient. The wavelength of the currently used semiconductor laser beam is limited to 600 nm or more, so that the electrophotographic photoconductors used in the above-mentioned digital recording apparatus are required to show sufficient photosensitivity in the wavelength range of at least 600 to 850 nm.

The organic photoconductive materials, for example, a phthalocyanine pigment, azo pigment, cyanine pigment, arylene pigment, and squarylium pigment are conventionally known to satisfy the above-mentioned requirements. In particular, the phthalocyanine pigment can show absorption and photosensitivity in the relatively long wavelength range. In addition, a variety of phthalocyanine pigments can be obtained according to the kind of central metal or the type of crystalline form. Therefore, research and development of the phthalocyanine pigment has been actively conducted for obtaining a photoconductive material capable of coping with the semiconductor laser.

There are conventionally known e-type copper phthalocyanine, X-type metal-free phthalocyanine, .tau.-type metal-free phthalocyanine, vanadyl phthalocyanine and titanyloxy phthalocyanine (Japanese Laid-Open Patent Applications 8-231869, 8-66595 and 8-13942). However, any of the above-mentioned phthalocyanine compounds are still insufficient in terms of photosensitivity, chargeability, and the durability in the repeated use.

Accordingly, an object of this invention is to provide an electrophotographic photoconductor which can be employed not only in the high speed copying machine, but also in the laser printer.

The above-mentioned object of the present invention can be achieved by an electrophotographic photoconductor comprising an electroconductive support, and a photoconductive layer formed thereon comprising a charge transport material and a charge generation material which comprises a pigment comprising a compound with a tetraazaporphyrin skeleton represented by formula (I): ##STR2## wherein M is a hydrogen atom, or an atom or compound capable of bonding to tetraazaporphyrin through a covalent bond or a coordinate bond; and R.sup.1 to R.sup.4 are each independently a hydrogen atom, a lower alkyl group which may have a substituent, or an aryl group which may have a substituent.

In this case, it is preferable that the above-mentioned compound with a tetraazaporphyrin skeleton represented by formula (I) be in such a crystalline form that exhibits a major diffraction peak at 24.8.degree..+-.0.2.degree. in terms of a Bragg angle 2.theta..+-.0.2.degree. in an X-ray diffraction spectrum using a Cu-K.alpha. ray with a wavelength of 1.54 .ANG..

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is an IR spectrum of a tetraazaporphyrin pigment obtained in Preparation Example 1.

FIG. 2 is an IR spectrum of a tetraazaporphyrin pigment obtained in Preparation Example 2.

FIG. 3 is an IR spectrum of a tetraazaporphyrin pigment obtained in Preparation Example 3.

FIG. 4 is an X-ray diffraction spectrum of a tetraazaporphyrin pigment obtained in Preparation Example 3.

FIG. 5 is an IR spectrum of a tetraazaporphyrin pigment obtained in Preparation Example 4.

FIG. 6 is an X-ray diffraction spectrum of a tetraazaporphyrin pigment obtained in Preparation Example 4.

FIGS. 7 through 16 are X-ray diffraction spectra of tetraazaporphyrin pigments obtained in Preparation Examples 5 through 14, respectively.

In a pigment comprising a compound with a tetraazaporphyrin skeleton of formula (I), which will also be hereinafter referred to as a tetraazaporphyrin pigment, M represents an atom such as H, Ti, Co, Ni, Cu, Al, Mg, Pb, V, Fe, Zn, Ge, Sn, Ga, Mo, In or Cr; or an oxide, a halide such as a fluoride, chloride, bromide or iodide, or a hydroxide comprising the above-mentioned atom.

R.sup.1 to R.sup.4 in formula (I), which may be the same or different, are each a hydrogen atom, a lower alkyl group which may have a substituent, or an aryl group which may have a substituent.

Examples of the above-mentioned alkyl group represented by R.sup.1 to R.sup.4 are straight-chain or branched lower alkyl groups, such as methyl group, ethyl group, propyl group and butyl group. As the substituent for the alkyl group, a halogen atom such as fluorine atom or chlorine atom can be employed.

Examples of the above-mentioned aryl group represented by R.sup.1 to R.sup.4 are phenyl group, naphthyl group and pyrenyl group. Examples of the substituent for the aryl group include a halogen atom such as fluorine atom or chlorine atom, and an alkyl group such as methyl group or ethyl group.

Specific examples of the tetraazaporphyrin pigment of formula (I) for use in the present invention are shown in TABLE 1.

The tetraazaporphyrin pigment of formula (I) can be synthesized by heating a mixture of a corresponding dinitrile compound and a metallic chloride or an alkoxymetal, with no solvent, or in the presence of a solvent. In this case, there can be employed a halogenated solvent such as .alpha.-chloronaphthalene, dichlorobenzene or trichlorobenzene, an alcohol solvent such as pentanol or octanol, an amine solvent such as N,N-dimethylformamide or N-methylpyrrolidone, or an aromatic solvent such as benzene, toluene or nitrobenzene. The reaction temperature is generally in the range of room temperature to 300.degree. C., preferably in the range of 100 to 250.degree. C. in light of the reaction yield.

Alternatively, the above-mentioned tetraazaporphyrin pigment of formula (I) can also be synthesized by heating a mixture of a corresponding acid anhydride and a metallic chloride in the presence of a catalyst such as an amine compound, for example, urea or ammonium molybdate. In this case, the previously mentioned solvents may be used or not. The reaction temperature is generally in the range of room temperature to 300.degree. C., preferably in the range of 100 to 250.degree. C. in light of the reaction yield.

In the present invention, the aforementioned tetraazaporphyrin pigment of formula (I) is used as a charge generation material in the photoconductive layer of the electrophotographic photoconductor. In this case, it is preferable that the tetraazaporphyrin pigment represented by formula (I) be in a crystalline state, in particular, be in such a specific crystalline form that exhibits a major diffraction peak at 24.8.degree..+-.0.2.degree. in terms of a Bragg angle 2.theta..+-.0.2.degree. in an X-ray diffraction spectrum using a Cu-K.alpha. ray with a wavelength (.lambda.) of 1.54 .ANG..

After the compound with the tetraazaporphyrin skeleton of formula (I) is synthesized by the above-mentioned synthesis method, the tetraazaporphyrin pigment of formula (I) can be turned into the above-mentioned specific crystalline state through a treatment using an acid or a solvent, or milling treatment.

To be more specific, the treatment using an acid is carried out in such a manner that the tetraazaporphyrin pigment is first dissolved in an acid such as sulfuric acid at 50.degree. C. or less, the thus prepared solution of the pigment is added dropwise to ice-cold water to precipitate the crystals of the pigment, and thereafter the thus precipitated crystals are collected, for example, by filtration. In such an acid treatment, sulfuric acid is particularly preferable as the acid in light of cost.

In the treatment using a solvent, the tetraazaporphyrin pigment is suspended in the solvent with stirring at room temperature or under the application of heat.

Examples of the solvent used in such a solvent treatment include aromatic solvents such as benzene, toluene, dichlorobenzene and nitrobenzene; alcohols such as methanol and ethanol; ketones such as cyclohexanone and methyl ethyl ketone; ethers such as n-butyl ether, ethylene glycol n-butyl ether and tetrahydrofuran; amines such as N,N-dimethylformamide, N-methylpyrrolidone and quinoline; and water. Those solvents may be used in combination.

The previously mentioned milling treatment employs a milling apparatus such as sand mill or ball mill, using glass beads, steel beads and alumina balls.

Specific examples of the solvent used in the milling treatment include alcohols such as methanol and ethanol; ketones such as cyclohexanone and methyl ethyl ketone; ethers such as n-butyl ether, ethylene glycol n-butyl ether and tetrahydrofuran; amines such as N,N-dimethylformamide and N-methylpyrrolidone; basic solvents such as quinoline and pyridine; and water.

Further, as mentioned above, it is preferable to employ the compound with the tetraazaporphyrin skeleton of formula (I) in such a crystalline form that exhibits a major diffraction peak at 24.8.degree..+-.0.2.degree. in terms of a Bragg angle 2.theta..+-.0.2.degree. in the X-ray diffraction spectrum using the Cu-K.alpha. ray. The tetraazaporphyrin compound of formula (I) can be treated so as to form the above-mentioned specific crystal structure by adding the pigment of formula (I) to a mixed solvent of a trihaloacetic acid and an alkylene halide to prepare a solution or slurry of the pigment, and further adding the thus prepared solution or slurry to a mixed solvent of a cyclic ether and water to precipitate the crystals, and when necessary, successively washing the precipitated crystals with water and an aliphatic alcohol.

In the above-mentioned treatment, trichloroacetic acid or trifluoroacetic acid can be used as the trihaloacetic acid; and dichloromethane, dichloroethane, chloroform or trichloroethylene can be used as the alkylene halide.

It is preferable that the mixing ratio by volume of the trihaloacetic acid to the alkylene halide be in the range of 1/4 to 1/20, and more preferably in the range of 1/1 to 1/8.

To prepare the above-mentioned solution or slurry of the tetraazaporphyrin compound of formula (I), the tetraazaporphyrin compound may be added to the mixed solvent of a trihaloacetic acid and an alkylene halide at room temperature over a period of 2 to 10 minutes, with stirring, and further, the resultant mixture may be continuously stirred for about 30 minutes to completely dissolve the tetraazaporphyrin compound in the mixed solvent.

Examples of the cyclic ether in the above-mentioned treatment include tetrahydrofuran, 1,4-dioxane, tetrahydropyran, and tetrafurfuryl alcohol.

It is preferable that the mixing ratio by volume of the cyclic ether to water be in the range of 3/1 to 1/3.

While the solution or slurry of the tetraazaporphyrin pigment is added to the mixed solvent of water and the cyclic ether, this mixed solvent may be cooled to a temperature in the range of -5 to 10.degree. C., and the solution or slurry may be added dropwise to the mixed solvent with stirring over a period of 5 minutes to one hour. After completion of the addition, the stirring is continued for about 30 minutes, thereby precipitating the tetraazaporphyrin pigment.

As previously mentioned, when necessary, the precipitated crystals may be successively washed with water and an aliphatic alcohol such as methanol, ethanol, n-propanol, isopropanol, or n-butanol.

Furthermore, a tetraazaporphyrin compound of formula (I) with a specific crystalline form can be obtained by subjecting the tetraazaporphyrin pigment to the above-mentioned acid treatment to prepare a wet cake of the pigment, followed by mixing the wet cake with an organic solvent in the presence of water. In this case, examples of the organic solvent which can be employed in this solvent treatment include aromatic solvents such as benzene, toluene, dichlorobenzene and nitrobenzene; alcohols such as methanol, ethanol, n-propanol, n-butanol and n-pentanol; ketones such as cyclohexanone and methyl ethyl ketone; ethers such as n-butyl ether, ethylene glycol n-butyl ether and tetrahydrofuran; and amines such as N,N-dimethylformamide, N-methylpyrrolidone and quinoline.

In the above-mentioned solvent treatment of the wet cake of the pigment, it is preferable that the volume of the organic solvent be 5 times or more, more preferably 5 to 100 times that of the solid content of the tetraazaporphyrin pigment. By use of the organic solvent in such a sufficient amount, the stirring can be completely carried out so as to obtain uniform crystals. In addition, the organic solvent, water and the tetraazaporphyrin pigment may be placed into a reaction vessel in any order. It may be possible to take a procedure of putting the organic solvent and water into a reaction vessel in advance, and thereafter adding the tetraazaporphyrin pigment to the solvent in which the organic solvent is saturated in water. To change the pigment into a crystalline state, the temperature of the reaction system is controlled so that water may remain as it is in the reaction system, for example, in the range of 0 to 100.degree. C., preferably in the range of 15 to 80.degree. C. The reaction time is not particularly limited, but it is preferable to stir the reaction mixture under a sufficient uniform condition.

By using the organic pigment with the tetraazaporphyrin skeleton of formula (I), serving as a charge generation material, and a charge transport material in combination, an electrophotographic photoconductor with a single-layered photoconductor or a function-separating layered photoconductor can be fabricated.

The single-layered photoconductor is fabricated in such a manner that a photoconductive layer which comprises a binder resin, and a charge generation material comprising the tetraazaporphyrin pigment of formula (I) and a charge transport material dispersed in the binder resin is provided on an electroconductive support. In the case where the function-separating photoconductor is fabricated, a charge generation layer comprising a binder resin and a charge generation material which comprises the aforementioned tetraazaporphyrin pigment is provided on an electroconductive support, and a charge transport layer comprising a binder resin and a charge transport material is overlaid on the charge generation layer. To fabricate the positively chargeable function-separating layered photoconductor, the above-mentioned overlaying order of the charge generation layer and the charge transport layer may be reversed.

For the fabrication of the function-separating layered photoconductive layer, a coating liquid for a charge generation layer is prepared by dispersing or dissolving the charge generation material in an appropriate solvent, with a binder resin being optionally added thereto, using a ball mill, ultrasonic wave, or a homomixer. Then, the above prepared coating liquid may be coated on the electroconductive support by dip coating, blade coating or spray coating, and thereafter dried.

In the case where the charge generation layer is prepared by dispersing the charge generation material therein, it is preferable that the average particle size of the charge generation material be 2 .mu.m or less, and more preferably 1 .mu.m or less in order to upgrade the dispersibility of the charge generation material in the charge generation layer. In addition, when the average particle size of the charge generation material is 0.01 .mu.m or more, aggregation of fine particles can be inhibited, so that the increase of the resistivity of the charge generation layer can be prevented. Further, the deterioration of sensitivity and durability in the repeated use caused by the increase of defective crystallites can be prevented.

In addition to the tetraazaporphyrin compound of formula (I), the following organic pigments can be used as the charge generation materials: azo pigments such as C.I. Pigment Blue 25 (C.I. 21180), C.I. Pigment Red 41 (C.I. 21200), C.I. Acid Red 52 (C.I. 45100), C.I. Basic Red 3 (C.I. 45210), an azo pigment having a carbazole skeleton (Japanese Laid-Open Patent Application 53-95033), an azo pigment having a distyryl benzene skeleton (Japanese Laid-Open Patent Application 53-133445), an azo pigment having a triphenylamine skeleton (Japanese Laid-Open Patent Application 53-132347), an azo pigment having a dibenzothiophene skeleton (Japanese Laid-Open Patent Application 54-21728), an azo pigment having an oxadiazole skeleton (Japanese Laid-Open Patent Application 54-12742), an azo pigment having a fluorenone skeleton (Japanese Laid-Open Patent Application 54-22834), an azo pigment having a bisstilbene skeleton (Japanese Laid-Open Patent Application 54-17733), an azo pigment having a distyryl oxadiazole skeleton (Japanese Laid-Open Patent Application 54-2129) and an azo pigment having a distyryl carbazole skeleton (Japanese Laid-Open Patent Application 54-14967); phthalocyanine pigments such as C.I. Pigment Blue 16 (C.I. 74100) and titanyl phthalocyanine; indigo pigments such as C.I. Vat Brown 5 (C.I. 73410) and C.I. Vat Dye (C.I. 73030); and perylene pigments such as Algol Scarlet B and Indanthrene Scarlet R (made by Bayer Co., Ltd.). Two or more organic pigments mentioned above may be used in combination with the tetraazaporphyrin pigment of formula (I).

Specific examples of the solvent which is used to prepare a dispersion or solution for the charge generation layer coating liquid and the charge transport layer coating liquid include N,N-dimethylformamide, toluene, xylene, monochlorobenzene, 1,2-dichloroethane, 1,1,1-trichloroethane, dichloromethane, 1,1,2-trichloroethane, trichloroethylene, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate and butyl acetate.

Any binder resin that has good electrically insulating properties and is conventionally used in the preparation of the electrophotographic photoconductor can be employed for the formation of the charge generation layer, the charge transport layer, and the single-layered photoconductive layer.

Specific examples of such a binder resin include addition polymerization-type resins, polyaddition-type resins and polycondensation-type resins such as polyethylene, polyvinyl butyral, polyvinyl formal, polystyrene resin, phenoxy resin, polypropylene, acrylic resin, methacrylic resin, vinyl chloride resin, vinyl acetate resin, epoxy resin, polyurethane resin, phenolic resin, polyester resin, alkyd resin, polycarbonate resin, polyamide resin, silicone resin and melamine resin; copolymer resins comprising as the repeat units two or more monomers for use in the above-mentioned resins, for example, electrically insulating resins such as vinyl chloride--vinyl acetate copolymer resin, styrene--acrylic copolymer resin and vinyl chloride--vinyl acetate--maleic anhydride copolymer resin; and polymeric organic semiconductor such as poly-N-vinylcarbazole. Those binder resins may be used alone or in combination.

In the negatively-chargeable photoconductor comprising the charge generation layer and the charge transport layer which are successively overlaid on the electroconductive support in this order, it is preferable that the amount of charge generation material for use in the charge generation layer be 20 wt. % or more of the total weight of the binder resin for use in the charge generation layer. The thickness of the above-mentioned charge generation layer is preferably in the range of 0.01 to 5 .mu.m. Further, in this case, it is preferable that the amount of charge transport material for use in the charge transport layer be in the range of 20 to 200 wt. % of the binder resin for use in the charge transport layer. The thickness of the charge transport layer is preferably in the range of 5 to 100 .mu.m.

In the positively-chargeable photoconductive layer, it is preferable that the amount of charge transport material for use in the charge transport layer be in the range of 20 to 200 wt. % of the total weight of the binder resin for use in the charge transport layer, and that the thickness of the charge transport layer be in the range of 5 to 100 .mu.m. In the charge generation layer, it is preferable that the amount of charge generation material for use in the charge generation layer be 20 wt. % or more of the total weight of the binder resin for use in the charge generation layer. Further, in such a case, the addition of the charge transport material to the charge generation layer is effective for reducing the residual potential and improving the photosensitivity. When the charge transport material is added to the charge generation layer, it is preferable that the amount of charge transport material for use in the charge generation layer be in the range of 20 to 200 wt. % of the total weight of the binder resin for use in the charge generation layer.

In the single-layered photoconductive layer prepared by dispersing the charge generation material and the charge transport material in the binder resin, it is preferable that the amount of pigment serving as the charge generation material be in the range of 5 to 95 wt. %, and the amount of charge transport material be in the range of 30 to 200 wt. %, of the total weight of the binder resin for use in the photoconductive layer. In this case, the thickness of the photoconductive layer is preferably in the range of 10 to 100 .mu.m.

To improve the chargeability, both the layered photoconductive layer and the single-layered photoconductive layer may further comprise a phenol compound, a hydroquinone compound, a hindered phenol compound, a hindered amine compound, and a compound having a hindered amine and a hindered phenol in a molecule thereof.

For the electroconductive support, there can be employed a metallic plate, drum or foil made of aluminum, nickel, copper, titanium, gold or stainless steel; a plastic film on which an electroconductive material such as aluminum, nickel, copper, titanium, gold, tin oxide or indium oxide is deposited; and a sheet of paper or a plastic film, which may be formed in a drum, coated with an electroconductive material.

The electrophotographic photoconductor of the present invention may further comprise an intermediate layer which is provided between the electroconductive support and the photoconductive layer in order to prevent the charge injection from the electroconductive support to the photoconductive layer in the course of charging step, and improve the adhesion between the support and the photoconductive layer.

The above-mentioned intermediate layer may be a resin layer which comprises, for instance, polyamide resin, polyvinyl alcohol, ethyl cellulose, carboxymethyl cellulose, vinyl chloride--vinyl acetate copolymer, vinyl chloride--vinyl acetate--maleic anhydride copolymer, casein, and N-alkoxymethyl nylon. Further, tin oxide, aluminum oxide, titanium oxide, silicon oxide or indium oxide may be dispersed in the above-mentioned resin layer. Alternatively, aluminum oxide, zinc oxide, titanium oxide or silicon oxide may be deposited on the electroconductive support to provide the intermediate layer on the support.

Furthermore, a protective layer may be provided on the photoconductive layer to improve the wear resistance and the mechanical durability of the photoconductor.

The above-mentioned protective layer may be a resin layer comprising the same resin as employed in the preparation of the intermediate layer. A low-resistivity material such as tin oxide or indium oxide may be dispersed in the above-mentioned resin layer. Alternatively, an organic plasma polymerized film can be used as the protective layer, and in this case, oxygen atom, a halogen atom, or an atom belonging to the group III or V in the periodic table may be added to the plasma polymerized film when necessary.

The charge transport material for use in the present invention include a positive hole transport material and an electron transport material.

There can be employed any conventional positive hole transport materials, for example, poly-N-carbazole and derivatives thereof, poly-.gamma.-carbazolyl ethylglutamate and derivatives thereof, a condensation product of pyrene and formaldehyde and derivatives thereof, polyvinyl pyrene, polyvinyl phenanthrene, oxazole derivatives, imidazole derivatives, triphenylamine derivatives, and the compounds to be described later.

In particular, a stilbene compound of the following formula (II) is preferably employed as the positive hole transport material because of its high charge transporting properties: ##STR4## wherein R.sup.11 and R.sup.12 are each an alkyl group which may have a substituent, or an aryl group which may have a substituent, and R.sup.11 and R.sup.12 may form a ring in combination; R.sup.13 and R.sup.14 are each a hydrogen atom, an alkyl group which may have a substituent, an aryl group which may have a substituent, or a heterocyclic group; and Ar.sup.11 is an arylene group which may have a substituent, or a heterocyclic group.

Specific examples of the stilbene compound of formula (II) are shown in TABLE 2. - Comp. No. R.sup.1 R.sup.2 Ar.sup.1 R.sup.3 R.sup.4 1 CH.sub.3 CH.sub.3 ##STR5## ##STR6## ##STR7## 2 H ##STR8## ##STR9## ##STR10## ##STR11## 3 H ##STR12## ##STR13## ##STR14## ##STR15## 4 H ##STR16## ##STR17## ##STR18## ##STR19## 5 H ##STR20## ##STR21## ##STR22## ##STR23## 6 H ##STR24## ##STR25## ##STR26## ##STR27## 7 H ##STR28## ##STR29## ##STR30## ##STR31## 8 H ##STR32## ##STR33## ##STR34## ##STR35## 9 CH.sub.3 ##STR36## ##STR37## ##STR38## ##STR39## 10 H ##STR40## ##STR41## ##STR42## ##STR43## 11 ##STR44## ##STR45## ##STR46## --CH.sub.3 ##STR47## 12 ##STR48## ##STR49## ##STR50## ##STR51## ##STR52## 13 ##STR53## ##STR54## ##STR55## ##STR56## ##STR57## 14 ##STR58## ##STR59## ##STR60## ##STR61## ##STR62## 15 ##STR63## ##STR64## ##STR65## ##STR66## ##STR67## 16 ##STR68## ##STR69## ##STR70## ##STR71## ##STR72## 17 ##STR73## ##STR74## ##STR75## ##STR76## ##STR77## 18 ##STR78## ##STR79## ##STR80## ##STR81## ##STR82## 19 ##STR83## ##STR84## ##STR85## ##STR86## ##STR87## 20 ##STR88## ##STR89## ##STR90## ##STR91## ##STR92## 21 ##STR93## ##STR94## ##STR95## ##STR96## ##STR97## 22 ##STR98## ##STR99## ##STR100## ##STR101## ##STR102## 23 ##STR103## ##STR104## ##STR105## ##STR106## ##STR107## 24 ##STR108## ##STR109## ##STR110## ##STR111## ##STR112## 25 ##STR113## ##STR114## ##STR115## ##STR116## ##STR117## 26 ##STR118## ##STR119## ##STR120## ##STR121## ##STR122## 27 ##STR123## ##STR124## ##STR125## ##STR126## ##STR127## 28 ##STR128## ##STR129## ##STR130## ##STR131## ##STR132## 29 ##STR133## ##STR134## ##STR135## ##STR136## ##STR137## 30 ##STR138## ##STR139## ##STR140## ##STR141## ##STR142## 31 ##STR143## ##STR144## ##STR145## ##STR146## ##STR147## 32 ##STR148## ##STR149## ##STR150## ##STR151## ##STR152## 33 ##STR153## ##STR154## ##STR155## ##STR156## ##STR157## 34 ##STR158## H ##STR159## ##STR160## ##STR161## 35 ##STR162## ##STR163## ##STR164## ##STR165## ##STR166## 36 ##STR167## H ##STR168## ##STR169## ##STR170## 37 ##STR171## ##STR172## ##STR173## ##STR174## 38 ##STR175## ##STR176## ##STR177## ##STR178## 39 ##STR179## ##STR180## ##STR181## ##STR182## 40 ##STR183## ##STR184## ##STR185## ##STR186## 41 ##STR187## ##STR188## ##STR189## ##STR190## ##STR191## 42 ##STR192## ##STR193## ##STR194## ##STR195## ##STR196## 43 ##STR197## ##STR198## ##STR199## ##STR200## ##STR201## 44 ##STR202## ##STR203## ##STR204## ##STR205## ##STR206## 45 ##STR207## ##STR208## ##STR209## ##STR210## ##STR211## 46 ##STR212## ##STR213## ##STR214## ##STR215## ##STR216## 47 ##STR217## ##STR218## ##STR219## ##STR220## ##STR221## 48 ##STR222## ##STR223## ##STR224## ##STR225## ##STR226## 49 ##STR227## ##STR228## ##STR229## ##STR230## ##STR231## 50 ##STR232## ##STR233## ##STR234## ##STR235## ##STR236## 51 ##STR237## ##STR238## ##STR239## ##STR240## ##STR241## 52 ##STR242## ##STR243## ##STR244## ##STR245## ##STR246## 53 ##STR247## ##STR248## ##STR249## ##STR250## ##STR251## 54 ##STR252## ##STR253## ##STR254## ##STR255## ##STR256## 55 ##STR257## ##STR258## ##STR259## ##STR260## ##STR261## 56 ##STR262## ##STR263## ##STR264## ##STR265## ##STR266## 57 ##STR267## ##STR268## ##STR269## ##STR270## ##STR271## 58 ##STR272## ##STR273## ##STR274## ##STR275## ##STR276## 59 ##STR277## ##STR278## ##STR279## ##STR280## ##STR281## 60 ##STR282## ##STR283## ##STR284## ##STR285## ##STR286## 61 ##STR287## ##STR288## ##STR289## ##STR290## ##STR291## 62 ##STR292## ##STR293## ##STR294## --CH.sub.3 --CH.sub.3 63 ##STR295## ##STR296## ##STR297## --C.sub.2 H.sub.5 --C.sub.2 H.sub.5 64 ##STR298## ##STR299## ##STR300## ##STR301## --CH.sub.3 65 ##STR302## ##STR303## ##STR304## ##STR305## ##STR306## 66 ##STR307## ##STR308## ##STR309## ##STR310## ##STR311## 67 ##STR312## ##STR313## ##STR314## ##STR315## ##STR316## 68 ##STR317## ##STR318## ##STR319## ##STR320## ##STR321## 69 ##STR322## ##STR323## ##STR324## ##STR325## ##STR326## 70 ##STR327## ##STR328## ##STR329## ##STR330## ##STR331## 71 ##STR332## ##STR333## ##STR334## ##STR335## ##STR336## 72 ##STR337## ##STR338## ##STR339## ##STR340## ##STR341## 73 ##STR342## ##STR343## ##STR344## ##STR345## ##STR346## 74 ##STR347## ##STR348## ##STR349## ##STR350## ##STR351## 75 ##STR352## ##STR353## ##STR354## ##STR355## ##STR356## 76 ##STR357## ##STR358## ##STR359## ##STR360## ##STR361## 77 ##STR362## ##STR363## ##STR364## ##STR365## ##STR366## 78 ##STR367## ##STR368## ##STR369## ##STR370## ##STR371## 79 ##STR372## ##STR373## ##STR374## ##STR375## ##STR376## 80 ##STR377## ##STR378## ##STR379## ##STR380## ##STR381## 81 ##STR382## ##STR383## ##STR384## ##STR385## ##STR386## 82 ##STR387## ##STR388## ##STR389## ##STR390## ##STR391## 83 ##STR392## ##STR393## ##STR394## ##STR395## ##STR396## 84 ##STR397## ##STR398## ##STR399## ##STR400## ##STR401## 85 ##STR402## ##STR403## ##STR404## ##STR405## ##STR406## 86 ##STR407## ##STR408## ##STR409## ##STR410## ##STR411## 87 ##STR412## ##STR413## ##STR414## ##STR415## ##STR416## 88 ##STR417## ##STR418## ##STR419## ##STR420## ##STR421## 89 ##STR422## ##STR423## ##STR424## ##STR425## ##STR426##

Specific examples of other positive hole transport materials for use in the present invention are as follows:

(1) [Described in Japanese Laid-Open Patent Applications Nos. 55-154955 and 55-156954] ##STR427## wherein R.sup.21 is methyl group, ethyl group, 2-hydroxyethyl group or 2-chloroethyl group; R.sup.22 is methyl group, ethyl group, benzyl group or phenyl group; and R.sup.23 is a hydrogen atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, a dialkylamino group or nitro group.

Examples of the above compound of formula (1) are 9-ethylcarbazole-3-aldehyde-1-methyl-l-phenylhydrazone, 9-ethylcarbazole-3-aldehyde-1-benzyl-1-phenylhydrazone, and 9-ethylcarbazole-3-aldehyde-1,1-diphenylhydrazone.

(2) [Described in Japanese Laid-Open Patent Application No. 55-52063] ##STR428## wherein Ar.sup.31 is a naphthalene ring, anthracene ring or styryl ring, each of which may have a substituent, or a pyridine ring, furan ring, or thiophene ring; and R.sup.31 is an alkyl group or benzyl group.

Examples of the above compound of formula (2) are 4-diethylaminostyryl-p-aldehyde-1-methyl-1-phenylhydrazone, and 4-methoxynaphthalene-1-aldehyde-1-benzyl-1-phenylhydrazone.

(3) [Described in Japanese Laid-Open Patent Application No. 56-81850] ##STR429## wherein R.sup.41 is an alkyl group, benzyl group, phenyl group or naphthyl group; R.sup.42 is a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, an alkoxyl group having 1 to 3 carbon atoms, a dialkylamino group, a diaralkylamino group or a diarylamino group; n is an integer of 1 to 4, and when n is 2 or more, R.sup.42 may be the same or different; and R.sup.43 is a hydrogen atom or methoxy group.

Examples of the above compound of formula (3) are 4-methoxybenzaldehyde-1-methyl-1-phenylhydrazone, 2,4-dimethoxybenzaldehyde-1-benzyl-1-phenylhydrazone, 4-diethylaminobenzaldehyde-1,1-diphenylhydrazone, 4-methoxybenzaldehyde-1-(4-methoxy)phenylhydrazone, 4-diphenylaminobenzaldehyde-1-benzyl-1-phenylhydrazone, and 4-dibenzylaminobenzaldehyde-1,1-diphenylhydrazone.

(4) [Described in Japanese Patent Publication No. 51-10983] ##STR430## wherein R.sup.51 is an alkyl group having 1 to 11 carbon atoms, a substituted or unsubstituted phenyl group, or a heterocyclic group; R.sup.52 and R.sup.53 are each independently a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a hydroxyalkyl group, chloroalkyl group, or a substituted or unsubstituted aralkyl group, and R.sup.52 and R.sup.53 may form a nitrogen-containing heterocyclic ring in combination; and R.sup.54, which may be the same or different, each is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group, or a halogen atom.

Examples of the above compound of formula (4) are 1,1-bis(4-dibenzylaminophenyl)propane, tris(4-diethyl-aminophenyl)methane, 1,1-bis(4-dibenzylaminophenyl)-propane, and 2,2'-dimethyl-4,4'-bis(diethylamino)-triphenylmethane.

(5) [Described in Japanese Laid-Open Patent Application No. 51-94829] ##STR431## wherein R.sup.61 is a hydrogen atom or a halogen atom; and Ar.sup.61 is a substituted or unsubstituted phenyl group, naphthyl group, anthryl group, or carbazolyl group.

Examples of the above compound of formula (5) are 9-(4-diethylaminostyryl)anthracene, and 9-bromo-10-(4-diethylaminostyryl)anthracene.

(6) [Described in Japanese Laid-Open Patent Application No. 52-128373] ##STR432## wherein R.sup.71 is a hydrogen atom, a halogen atom, cyano group, an alkoxyl group having 1 to 4 carbon atoms, or an alkyl group having 1 to 4 carbon atoms; and Ar.sup.71 is ##STR433## in which R.sup.72 is an alkyl group having 1 to 4 carbon atoms; R.sup.73 is a hydrogen atom, a halogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, or a dialkylamino group; n is an integer of 1 or 2, and when n is 2, R.sup.73 may be the same or different; and R.sup.74 and R.sup.75 are each a hydrogen atom, a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, or a substituted or unsubstituted benzyl group.

Examples of the above compound of formula (6) are 9-(4-dimethylaminobenzylidene)fluorene, and 3-(9-fluorenylidene)-9-ethylcarbazole.

(7) [Described in Japanese Laid-Open Patent Application No. 56-29245] ##STR434## wherein R.sup.81 is carbazolyl group, pyridyl group, thienyl group, indolyl group, furyl group, a substituted or unsubstituted phenyl group, a substituted or unsubstituted styryl group, a substituted or unsubstituted naphthyl group, or a substituted or unsubstituted anthryl group, each of which may have a substituent selected from the group consisting of a dialkylamino group, an alkyl group, an alkoxyl group, carboxyl group and an ester group thereof, a halogen atom, cyano group, an aralkylamino group, an N-alkyl-N-aralkylamino group, amino group, nitro group and acetylamino group.

Examples of the above compound of formula (7) are 1,2-bis(4-diethylaminostyryl)benzene, and 1,2-bis(2,4-dimethoxystyryl)benzene.

(8) [Described in Japanese Laid-Open Patent Application No. 58-58552] ##STR435## wherein R.sup.91 is a lower alkyl group, a substituted or unsubstituted phenyl group, or benzyl group; R.sup.92 is a hydrogen atom, a lower alkyl group, a lower alkoxyl group, a halogen atom, nitro group, or an amino group which may have as a substituent a lower alkyl group or benzyl group; and n is an integer of 1 or 2.

Examples of the above compound of formula (8) are 3-styryl-9-ethylcarbazole, and 3-(4-methoxystyryl)-9-ethylcarbazole.

(9) [Described in Japanese Laid-Open Patent Application No. 57-73075] ##STR436## wherein R.sup.101 is a hydrogen atom, an alkyl group, an alkoxyl group, or a halogen atom; R.sup.102 and R.sup.103 are each an alkyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted aryl group; R.sup.104 is a hydrogen atom, a lower alkyl group, or a substituted or unsubstituted phenyl group; and Ar.sup.101 is a substituted or unsubstituted phenyl group, or a substituted or unsubstituted naphthyl group.

Examples of the above compound of formula (9) are 4-diphenylaminostilbene, 4-dibenzylaminostilbene, 4-ditolylaminostilbene, 1-(4-diphenylaminostyryl)-naphthalene, and 1-(4-diethylaminostyryl)naphthalene.

(10) [Described in Japanese Laid-Open Patent Application No. 58-198043] ##STR437## wherein n is an integer of 0 or 1, and when n=0, A and R.sup.111 may form a ring in combination; R.sup.111 is a hydrogen atom, an alkyl group, or a substituted or unsubstituted phenyl group; Ar.sup.111 is a substituted or unsubstituted aryl group; R.sup.115 is a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; and A is 9-anthryl group, a substituted or unsubstituted carbazolyl group, or ##STR438## in which m is an integer of 0 to 3, and when m is 2 or more, R.sup.112 may be the same or different; and R.sup.112 is a hydrogen atom, an alkyl group, an alkoxyl group, a halogen atom, or ##STR439## in which R.sup.113 and R.sup.114 are each independently an alkyl group, a substituted or unsubstituted aralkyl group, or a substituted or unsubstituted aryl group, and R.sup.113 and R.sup.114 may form a ring in combination.

Examples of the above compound of formula (10) are 4'-diphenylamino-.alpha.-phenylstilbene, and 4'-bis(4-methylphenyl)amino-.alpha.-phenylstilbene.

(11) [Described in Japanese Laid-Open Patent Application No. 49-105537] ##STR440## wherein R.sup.121, R.sup.122 and R.sup.123 are each a hydrogen atom, a lower alkyl group, a lower alkoxyl group, a dialkylamino group, or a halogen atom; and n is an integer of 0 or 1.

Examples of the above compound of formula (11) include 1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)pyrazoline.

(12) [Described in Japanese Laid-Open Patent Application No. 52-139066] ##STR441## wherein R.sup.131 and R.sup.132 are each a substituted or unsubstituted alkyl group, or s substituted or unsubstituted aryl group; and A.sup.131 is a substituted amino group, a substituted or unsubstituted aryl group, or an allyl group.

Examples of the above compound of formula (12) are 2,5-bis(4-diethylaminophenyl)-1,3,4-oxadiazole, 2-N,N-diphenylamino-5-(4-diethylaminophenyl)-1,3,4-oxadiazole, 9 and 2-(4-dimethylaminophenyl)-5-(4-diethylaminophenyl)-1,3,4-oxadiazole.

(13) [Described in Japanese Laid-Open Patent Application No. 52-139065] ##STR442## wherein X is a hydrogen atom, a lower alkyl group, or a halogen atom; R.sup.141 is a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; and A.sup.141 is a substituted amino group, or a substituted or unsubstituted aryl group.

Examples of the above compound of formula (13) are 2-N,N-diphenylamino-5-(N-ethylcarbazole-3-yl)-1,3,4-oxadiazole, and 2-(4-diethylaminophenyl)-5-(N-ethylcarbazole-3-yl)-1,3,4-oxadiazole.

(14) [Described in Japanese Laid-Open Patent Application No. 58-32372] ##STR443## wherein R.sup.151 is a lower alkyl group, a lower alkoxyl group, or a halogen atom; n is an integer of 0 to 4; and R.sup.152 and R.sup.153 are each independently a hydrogen atom, a lower alkyl group, a lower alkoxyl group, or a halogen atom.

Examples of the benzidine compound of formula (14) are N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine, and 3,3'-dimethyl-N,N,N', N'-tetrakis(4-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine.

(15) [Described in Japanese Laid-Open Patent Application No. 2-178669] ##STR444## wherein R.sup.161, R.sup.163 and R.sup.164 are each a hydrogen atom, amino group, an alkoxyl group, a thioalkoxyl group, an aryloxy group, methylenedioxy group, a substituted or unsubstituted alkyl group, a halogen atom, or a substituted or unsubstituted aryl group; R.sup.162 is a hydrogen atom, an alkoxyl group, a substituted or unsubstituted alkyl group, or a halogen atom, provided that R.sup.161, R.sup.162, R.sup.163 and R.sup.164 are not hydrogen atoms at the same time; and k, l, m and n are each an integer of 1 to 4, and when each is an integer of 2, 3 or 4, R.sup.161, R.sup.162, R.sup.163 and R.sup.164 may be independently the same or different.

Examples of the biphenylamine compound of formula (15) are 4'-methoxy-N,N-diphenyl-[1,1'-biphenyl]-4-amine, 4'-methyl-N,N-bis(4-methylphenyl)-[1,1'-biphenyl]-4-amine, and 4'-methoxy-N,N-bis(4-methylphenyl)-[1,1'-biphenyl)-4-amine.

(16) [Described in Japanese Laid-Open Patent Application No. 3-285960] ##STR445## wherein Ar.sup.171 is a condensed polycyclic hydrocarbon group having 18 or less carbon atoms; and R.sup.171 and R.sup.172 are each independently a hydrogen atom, a halogen atom, a substituted or unsubstituted alkyl group, an alkoxyl group, or a substituted or unsubstituted phenyl group.

Examples of the triarylamine compound of formula (16) are 1-diphenylaminopyrene, and 1-di(p-tolylamino)pyrene.

(17) [Described in Japanese Laid-Open Patent Application No. 62-98394]

wherein Ar.sup.181 is a substituted or unsubstituted aromatic hydrocarbon group; and A.sup.181 is ##STR446## in which Ar' is a substituted or unsubstituted aromatic hydrocarbon group; and R.sup.181 and R.sup.182 are each a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group. Examples of the diolefin aromatic compound of formula (17) are 1,4-bis(4-diphenylaminostyryl)benzene, and 1,4-bis[4-di(p-tolyl)aminostyryl]benzene.

(18) [Described in Japanese Laid-Open Patent Application No. 4-230764] ##STR447## wherein Ar.sup.191 is a substituted or unsubstituted aromatic hydrocarbon group; R.sup.191 is a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted aryl group; and n is an integer of 0 or 1, and m is an integer of 1 or 2, and when n=0 and m=1, Ar.sup.191 and R.sup.191 may form a ring in combination.

Examples of the styrylpyrene compound of formula (18) are 1-(4-diphenylaminostyryl)pyrene, and 1-[4-di(p-tolyl)aminostyryl]pyrene.

Examples of the electron transport material for use in the present invention are chloroanil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4,5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-indeno4H-indeno[1,2-b]thiophene-4-one, and 1,3,7-trinitrodibenzothiophene-5,5-dioxide.

In particular, (2,3-diphenyl-1-indenylidene)-malononitrile represented by the following formula (III), and electron transport materials represented by formulas (19) and (20) are preferably employed as the charge transport materials because of their excellent electron transporting capability. ##STR448##

These charge transport materials may be used alone or in combination.

Other features of this invention will become apparent in the course of the following description of exemplary embodiments, which are given for illustration of the invention and are not intended to be limiting thereof.

Preparation Example 1

0.36 g (15 mmol) of magnesium and iodine in such an amount as to work as a catalyst were added to 40 ml of 1-pentanol. The resultant mixture was heated under reflux in a stream of nitrogen with stirring for 2 hours. Then, the reaction mixture was allowed to stand at room temperature.

1.68 g (10 mmol) of 5,6-dihydro-p-dithiin-2,3-dicarbonitrile was added to the above-mentioned reaction mixture at room temperature. With the reaction temperature being maintained at 150.degree. C., the reaction mixture was stirred for 5 hours to carry out the reaction.

After completion of the reaction, the reaction product was separated from the mixture by filtration under the application of heat, and successively washed with ethanol and water, and then dried. Thus, an Mg-tetraazaporphyrin pigment was obtained in a yield of 1.43 g (82%).

FIG. 1 is an IR spectrum of the thus obtained Mg-tetraazaporphyrin pigment.

The crystals of the Mg-tetraazaporphyrin compound were identified by the elemental analysis shown below:

Preparation Example 2

1.0 g (1.4 mmol) of the Mg-tetraazaporphyrin pigment obtained in Preparation Example 1 was added to 20 ml of trifluoroacetic acid little by little, with the temperature being maintained at 5.degree. C. or less on an ice bath. The resultant mixture was stirred for 9 hours to carry out the reaction.

After completion of the reaction, the reaction mixture was poured into 800 ml of deionized water, and stirred for 2 hours, with the temperature being maintained at 5.degree. C. or less on an ice bath. After the mixture was allowed to stand, the reaction product was separated from the mixture by filtration and successively washed with ethanol and water, and then dried. Thus, a metal-free tetraazaporphyrin pigment was obtained in a yield of 0.70 g (74%).

FIG. 2 is an IR spectrum of the thus obtained metal-free tetraazaporphyrin pigment.

The crystals of the metal-free tetraazaporphyrin compound were identified by the elemental analysis shown below:

[Fabrication of Layered Photoconductor]

(Formation of charge generation layer)

A mixture of one part by weight of the Mg-tetraazaporphyrin pigment obtained in Preparation Example 1, serving as a charge generation material, 50 parts by weight of a butyl acetate solution containing 2 wt. % of a commercially available polyvinyl butyral resin (Trademark "S-Lec BLS", made by Sekisui Chemical Co., Ltd.) and 49 parts by weight of n-butyl acetate was dispersed in a sand mill using 2-mm diameter glass beads for 2 hours, so that a coating liquid for a charge generation layer was prepared.

The thus prepared charge generation layer coating liquid was coated on the aluminum-deposited surface of an aluminum-deposited PET film with a thickness of 75 .mu.m serving as an electroconductive support, and dried at 80.degree. C. for 5 minutes. Thus, a charge generation layer with a thickness of 0.2 .mu.m was provided on the electroconductive support.

(Formation of charge transport layer)

A mixture of 42 parts by weight of a charge transport material represented by the following formula (A), 60 parts by weight of a commercially available polycarbonate resin (Trademark "IUPILON Z200" made by Mitsubishi Gas Chemical Company, Inc.), and 0.001 parts by weight of a commercially available silicone oil (Trademark "KF50", made by Shin-Etsu Chemical Co., Ltd.) was dissolved in 638 parts by weight of dichloromethane, so that a coating liquid for a charge transport layer was prepared. ##STR449## The thus prepared charge transport layer coating liquid was coated on the above prepared charge generation layer and dried at 80.degree. C. for 5 minutes and then 110.degree. C. for 10 minutes, so that a charge transport layer with a thickness of 20 .mu.m was provided on the charge generation layer.

Thus, an electrophotographic photoconductor No. 1 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 1 in Example 1 was repeated except that the charge transport material of formula (A) for use in the charge transport layer coating liquid in Example 1 was replaced by the following charge transport material of formula (B): ##STR450##

Thus, an electrophotographic photoconductor No. 2 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 1 in Example 1 was repeated except that the charge transport material of formula (A) for use in the charge transport layer coating liquid in Example 1 was replaced by the following charge transport material of formula (C): ##STR451##

Thus, an electrophotographic photoconductor No. 3 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 1 in Example 1 was repeated except that the charge transport material of formula (A) for use in the charge transport layer coating liquid in Example 1 was replaced by the following charge transport material of formula (D): ##STR452##

Thus, an electrophotographic photoconductor No. 4 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 1 in Example 1 was repeated except that the Mg-tetraazaporphyrin pigment (obtained in Preparation Example 1) for use in the coating liquid for the charge generation layer in Example 1 was replaced by the metal-free tetraazaporphyrin pigment obtained in Preparation Example 2.

Thus, an electrophotographic photoconductor No. 5 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 2 in Example 2 was repeated except that the Mg-tetraazaporphyrin pigment (obtained in Preparation Example 1) for use in the coating liquid for the charge generation layer in Example 2 was replaced by the metal-free tetraazaporphyrin pigment obtained in Preparation Example 2.

Thus, an electrophotographic photoconductor No. 6 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 3 in Example 3 was repeated except that the Mg-tetraazaporphyrin pigment (obtained in Preparation Example 1) for use in the coating liquid for the charge generation layer in Example 3 was replaced by the metal-free tetraazaporphyrin pigment obtained in Preparation Example 2.

Thus, an electrophotographic photoconductor No. 7 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 4 in Example 4 was repeated except that the Mg-tetraazaporphyrin pigment (obtained in Preparation Example 1) for use in the coating liquid for the charge generation layer in Example 4 was replaced by the metal-free tetraazaporphyrin pigment obtained in Preparation Example 2.

Thus, an electrophotographic photoconductor No. 8 according to the present invention was fabricated.

Each of the electrophotographic photoconductors No. 1 to No. 8 according to the present invention was negatively charged in the dark under application of -6 kV of corona charge for 20 seconds using a commercially available electrostatic copying sheet testing apparatus "Paper Analyzer Model EPA-8200" (Trademark), made by Kawaguchi Electro Works Co., Ltd.

Then, each photoconductor was allowed to stand in the dark for 20 seconds without applying any charge thereto, and the surface potential Vo (-V) of the photoconductor was measured.

Each photoconductor was then illuminated by a light of 20 lux, and the exposure E.sub.1/2 (lux.cndot.sec) required to reduce the initial surface potential Vo (-V) to 1/2 the initial surface potential Vo (-V) was measured.

The results are shown in TABLE 3.

[Fabrication of Layered Photoconductor]

(Formation of charge generation layer)

A mixture of one part by weight of the Mg-tetraazaporphyrin pigment obtained in Preparation Example 1, serving as a charge generation material, 50 parts by weight of a butyl acetate solution containing 2 wt. % of a commercially available polyvinyl butyral resin (Trademark "S-Lec BLS", made by Sekisui Chemical Co., Ltd.) and 49 parts by weight of n-butyl acetate was dispersed in a sand mill using 2-mm diameter glass beads for 2 hours.

Thus, a coating liquid for a charge generation layer was prepared.

The thus prepared charge generation layer coating liquid was coated on the aluminum-deposited surface of an aluminum-deposited PET film with a thickness of 75 .mu.m serving as an electroconductive support, and dried at 80.degree. C. for 5 minutes. Thus, a charge generation layer with a thickness of 0.2 .mu.m was provided on the electroconductive support.

(Formation of charge transport layer)

A mixture of 8 parts by weight of an electron transport material represented by formula (III) shown below, 11 parts by weight of a commercially available Z type polycarbonate resin (made by Teijin Chemicals Ltd.), and 0.02 parts by weight of a commercially available silicone oil (Trademark "KF50", made by Shin-Etsu Chemical Co., Ltd.) was dissolved in 91 parts by weight of tetrahydrofuran, so that a coating liquid for a charge transport layer was prepared. ##STR453##

The thus prepared charge transport layer coating liquid was applied to the above prepared charge generation layer by cast coating method using a doctor blade, and then dried, so that a charge transport layer with a thickness of 20 .mu.m was provided on the charge generation layer.

Thus, an electrophotographic photoconductor No. 9 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 9 in Example 9 was repeated except that the electron transport material of formula (III) for use in the charge transport layer coating liquid in Example 9 was replaced by the following electron transport material of formula (19): ##STR454##

Thus, an electrophotographic photoconductor No. 10 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 9 in Example 9 was repeated except that the electron transport material of formula (III) for use in the charge transport layer coating liquid in Example 9 was replaced by the following electron transport material of formula (20): ##STR455##

Thus, an electrophotographic photoconductor No. 11 according to the present invention was fabricated.

Each of the electrophotographic photoconductors No. 9 to No. 11 according to the present invention was positively charged in the dark under application of +5.3 kV of corona charge for 20 seconds using a commercially available electrostatic copying sheet testing apparatus "Paper Analyzer Model EPA-8200" (Trademark), made by Kawaguchi Electro Works Co., Ltd.

Then, each photoconductor was allowed to stand in the dark for 20 seconds without applying any charge thereto, and the surface potential Vo (V) of the photoconductor was measured.

Each photoconductor was then illuminated by a light of 20 lux, and the exposure E.sub.1/2 (lux.cndot.sec) required to reduce the initial surface potential Vo (V) to 1/2 the initial surface potential Vo (V) was measured.

The results are shown in TABLE 4.

[Fabrication of Single-Layered Photoconductor]

(Formation of single-layered photoconductive layer)

A mixture of 0.5 g of the Mg-tetraazaporphyrin pigment obtained in Preparation Example 1, serving as a charge generation material, 10 g of a solution prepared by dissolving a commercially available Z type polycarbonate resin (made by Teijin Chemicals Ltd.) in tetrahydrofuran so as to have a concentration of 10 wt. %, and 9 g of tetrahydrofuran was dispersed in a ball mill.

Thereafter, a tetrahydrofuran solution containing 10 wt. % of the Z type polycarbonate resin and the same charge transport material of formula (D) as employed in Example 4 were further added to the above-mentioned dispersion so that the amount ratio of pigment might be 2 wt. %, that of Z type polycarbonate resin be 50 wt. %, and that of charge transport material be 28 wt. %.

The thus obtained mixture was thoroughly stirred, so that a coating liquid for a photoconductive layer was prepared.

The thus prepared photoconductive layer coating liquid was applied to the aluminum-deposited surface of an aluminum-deposited polyester film serving as an electroconductive support by cast coating method using a doctor blade, and then dried. Thus, a photoconductive layer with a thickness of 15 .mu.m was provided on the electroconductive support.

Thus, an electrophotographic photoconductor No. 12 of a single-layered type according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 12 in Example 12 was repeated except that the Mg-tetraazaporphyrin pigment (obtained in Preparation Example 1) for use in the coating liquid for the photoconductive layer in Example 12 was replaced by the metal-free tetraazaporphyrin pigment obtained in Preparation Example 2.

Thus, an electrophotographic photoconductor No. 13 of a single-layered type according to the present invention was fabricated.

Each of the electrophotographic photoconductors No. 12 and No. 13 according to the present invention was positively charged in the dark under application of +6 kV of corona charge for 20 seconds using a commercially available electrostatic copying sheet testing apparatus "Paper Analyzer Model EPA-8200" (Trademark), made by Kawaguchi Electro Works Co., Ltd.

Then, each photoconductor was allowed to stand in the dark for 20 seconds without applying any charge thereto, and the surface potential Vo (V) of the photoconductor was measured.

Each photoconductor was then illuminated by a light of 20 lux, and the exposure E.sub.1/2 (lux.cndot.sec) required to reduce the initial surface potential Vo (V) to 1/2 the initial surface potential Vo (V) was measured.

The results are shown in TABLE 5.

Preparation Example 3

A mixture of 6.3 g (0.04 mol) of 5,6-dihydro-1,4-dithiin-2,3-dicarbonitrile, 0.99 g (0.01 mol) of copper(I) chloride, 1.2 g (0.02 mol) of urea, and 60 ml of 1-octanol was stirred, and gradually heated to 160.degree. C. in a stream of nitrogen. With the reaction temperature being maintained in the range of 150 to 160.degree. C., the reaction mixture was stirred for 5 hours to carry out the reaction.

After completion of the reaction, the reaction mixture was allowed to stand at room temperature. When the temperature of the reaction mixture was decreased to 130.degree. C., the reaction product was separated from the mixture by filtration. The reaction product thus obtained was successively washed with dimethylformamide and methanol, and further washed with hot water of 80.degree. C. and ethanol several times, and then dried. Thus, a Cu-tetraazaporphyrin pigment was obtained in a yield of 4.2 g (58%) as a crude product.

FIG. 3 is an IR spectrum of this compound.

The results of the elemental analysis of the above-mentioned Cu-tetraazaporphyrin pigment were as follows:

FIG. 4 is an X-ray diffraction spectrum of the thus obtained Cu-tetraazaporphyrin pigment.

Preparation Example 4

A mixture of 5.1 g (0.03 mol) of 5,6-dihydro-1,4-dithiin-2,3-dicarbonitrile, 2.6 g (7.6 mol) of titanium tetrabutoxide, 0.9 g (0.015 mol) of urea, and 50 ml of 1-octanol was stirred, and gradually heated to 160.degree. C. in a stream of nitrogen. With the reaction temperature being maintained in the range of 150 to 160.degree. C., the reaction mixture was stirred for 5 hours to carry out the reaction.

After completion of the reaction, the reaction mixture was allowed to stand at room temperature. When the temperature of the reaction mixture was decreased to 130.degree. C., the reaction product was separated from the mixture by filtration. The reaction product was successively washed with dimethylformamide and methanol, and further washed with hot water of 80.degree. C. and ethanol several times, and then dried. Thus, a TiO-tetraazaporphyrin pigment was obtained in a yield of 4.2 g (76%) as a crude product.

FIG. 5 is an IR spectrum of this compound.

The results of the elemental analysis of the above-mentioned TiO-tetraazaporphyrin pigment were as follows:

FIG. 6 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 5

3 g of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 4 was gradually dissolved in 60 g of 98% sulfuric acid at 5.degree. C. The thus obtained solution was stirred for about one hour with the temperature being maintained at 5.degree. C. or less, and thereafter, slowly poured into 800 ml of ice-cold water which was vigorously stirred, so that crystals were precipitated. The resultant crystals were separated by filtration, and repeatedly washed with distilled water until the obtained filtrate became neutral, and then dried. Thus, 2.9 g of TiO-tetraazaporphyrin pigment was obtained.

FIG. 7 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 6

1 g of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 5 was placed into a 200-ml conical flask, and refluxed with stirring for 8 hours together with 50 ml of methanol under application of heat thereto.

Thereafter, the above-mentioned mixture was cooled to room temperature and subjected to filtration. The resultant residue was dried, so that 0.97 g of a TiO-tetraazaporphyrin pigment was obtained in a crystalline form.

FIG. 8 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 7

1 g of the Tio-tetraazaporphyrin pigment obtained in Preparation Example 5 was placed into a 200-ml conical flask, and refluxed with stirring for 8 hours together with 50 ml of cyclohexanone under application of heat thereto.

Thereafter, the above-mentioned mixture was cooled to room temperature and subjected to filtration. The resultant residue was dried, so that 0.97 g of a TiO-tetraazaporphyrin pigment was obtained in a crystalline form.

FIG. 9 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 8

1 g of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 5 was placed into a 200-ml conical flask, and refluxed with stirring for 8 hours together with 50 ml of tetrahydrofuran under application of heat thereto.

Thereafter, the above-mentioned mixture was cooled to room temperature and subjected to filtration. The resultant residue was dried, so that 0.91 g of a TiO-tetraazaporphyrin pigment was obtained in a crystalline form.

FIG. 10 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 9

1 g of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 5 was placed into a 200-ml conical flask, and refluxed with stirring for 8 hours together with a mixed solvent of 36 ml of methyl ethyl ketone and 4 ml of water under application of heat thereto.

Thereafter, the above-mentioned mixture was cooled to room temperature and subjected to filtration. The resultant residue was dried, so that 0.93 g of a TiO-tetraazaporphyrin pigment was obtained in a crystalline form.

FIG. 11 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 10

1 g of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 5 was placed into a 200-ml conical flask, and refluxed with stirring for 8 hours together with 50 ml of N,N-dimethylformamide under application of heat thereto.

Thereafter, the above-mentioned mixture was cooled to room temperature and subjected to filtration. The resultant residue was dried, so that 0.93 g of a TiO-tetraazaporphyrin pigment was obtained in a crystalline form.

FIG. 12 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 11

1 g of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 5 was placed into a 200-ml conical flask, and refluxed with stirring for 8 hours together with 50 ml of nitrobenzene under application of heat thereto.

Thereafter, the above-mentioned mixture was cooled to room temperature and subjected to filtration. The resultant residue was dried, so that 0.97 g of a TiO-tetraazaporphyrin pigment was obtained in a crystalline form.

FIG. 13 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 12

1 g of the TiO-tetraazaporphyrin pigment obtained as a crude product in Preparation Example 4 was dissolved in a mixed solvent of 2 ml of trifluoroacetic acid and 8 ml of dichloromethane. The thus obtained solution was added dropwise to a mixed solvent of 25 ml of tetrahydrofuran and 25 ml of water which was cooled to 5.degree. C. on an ice bath, with stirring, thereby precipitating the crystals. The thus obtained mixture was further stirred for 30 minutes, and thereafter allowed to stand.

After the crystals were allowed to settle, the supernatant solution was removed. With the addition of 50 ml of methanol to the above-prepared crystals, the mixture was stirred for 30 minutes and subjected to filtration. The resultant residue in the form of a solid material was dispersed in 100 ml of hot water and filtered off several times, so that a wet cake of TiO-tetraazaporphyrin pigment was obtained.

The thus obtained wet cake was washed with methanol and dried, whereby 0.95 g of a TiO-tetraazaporphyrin pigment was obtained.

FIG. 14 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 13

The procedure for preparation of the TiO-tetraazaporphyrin pigment in Preparation Example 5 was repeated except that the obtained TiO-tetraazaporphyrin pigment was not dried, thereby obtaining a wet cake of the pigment.

To 4.89 g of the thus obtained wet cake of the pigment (with a solid content of 21 wt. %), 6.1 g of deionized water and 40.1 g of tetrahydrofuran were successively added. The resultant mixture was stirred at room temperature for 6 hours, and subjected to filtration. The thus obtained crystals were washed with methanol and dried, so that 0.93 g of a TiO-tetraazaporphyrin pigment was obtained.

FIG. 15 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Preparation Example 14

The procedure for preparation of the TiO-tetraazaporphyrin pigment in Preparation Example 5 was repeated except that the obtained TiO-tetraazaporphyrin pigment was not dried, thereby obtaining a wet cake of the pigment.

To 4.89 g of the thus obtained wet cake of the pigment (with a solid content of 21 wt. %), 6.1 g of deionized water and 40.1 g of dimethylformamide were successively added. The resultant mixture was stirred at room temperature for 6 hours, and subjected to filtration.

The thus obtained crystals were washed with methanol and dried, so that 0.98 g of a TiO-tetraazaporphyrin pigment was obtained.

FIG. 16 is an X-ray diffraction spectrum of the thus obtained TiO-tetraazaporphyrin pigment.

Each of the tetraazaporphyrin pigments obtained in Preparation Examples 3 to 14 was subjected to measurement of the X-ray diffraction spectrum under the following conditions:

(Fabrication of Layered Photoconductor]

(Formation of charge generation layer)

A mixture of one part by weight of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 4, serving as a charge generation material, 50 parts by weight of butyl acetate solution containing 2 wt. % of a commercially available polyvinyl butyral resin (Trademark "BM-S", made by Sekisui Chemical Co., Ltd.) and 49 parts by weight of n-butyl acetate was dispersed in a sand mill using 2-mm diameter glass beads for 2 hours. Thus, a coating liquid for a charge generation layer was prepared.

The thus prepared charge generation layer coating liquid was coated on the aluminum-deposited surface of an aluminum-deposited PET film with a thickness of 75 .mu.m serving as an electroconductive support, and dried at 80.degree. C. for 5 minutes. Thus, a charge generation layer with a thickness of 0.2 .mu.m was provided on the electroconductive support.

(Formation of charge transport layer)

A mixture of 42 parts by weight of a positive hole transport material represented by the following formula (D), 60 parts by weight of a commercially available polycarbonate resin (Trademark "IUPILON Z200" made by Mitsubishi Gas Chemical Company, Inc.), and 0.001 parts by weight of a commercially available silicone oil (Trademark "KF50", made by Shin-Etsu Chemical Co., Ltd.) was dissolved in 638 parts by weight of dichloromethane, so that a coating liquid for a charge transport layer was prepared. ##STR456##

The thus prepared charge transport layer coating liquid was coated on the above prepared charge generation layer and dried at 80.degree. C. for 2 minutes and then 110.degree. C. for 10 minutes, so that a charge transport layer with a thickness of 20 .mu.m was provided on the charge generation layer.

Thus, an electrophotographic photoconductor No. 14 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 5.

Thus, an electrophotographic photoconductor No. 15 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 6.

Thus, an electrophotographic photoconductor No. 16 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 7.

Thus, an electrophotographic photoconductor No. 17 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the Tio-tetraazaporphyrin pigment obtained in Preparation Example 8.

Thus, an electrophotographic photoconductor No. 18 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 9.

Thus, an electrophotographic photoconductor No. 19 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 10.

Thus, an electrophotographic photoconductor No. 20 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 11.

Thus, an electrophotographic photoconductor No. 21 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 12.

Thus, an electrophotographic photoconductor No. 22 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 13.

Thus, an electrophotographic photoconductor No. 23 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the TiO-tetraazaporphyrin pigment (obtained in Preparation Example 4) for use in the coating liquid for the charge generation layer in Example 14 was replaced by the TiO-tetraazaporphyrin pigment obtained in Preparation Example 14.

Thus, an electrophotographic photoconductor No. 24 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the positive hole transport material of formula (D) for use in the charge transport layer coating liquid in Example 14 was replaced by the following positive hole transport material of formula (C): ##STR457##

Thus, an electrophotographic photoconductor No. 27 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the positive hole transport material of formula (D) for use in the charge transport layer coating liquid in Example 14 was replaced by the following charge transport material of formula (A): ##STR458##

Thus, an electrophotographic photoconductor No. 26 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 14 in Example 14 was repeated except that the positive hole transport material of formula (D) for use in the charge transport layer coating liquid in Example 14 was replaced by the following charge transport material of formula (B): ##STR459##

Thus, an electrophotographic photoconductor No. 27 according to the present invention was fabricated.

Each of the electrophotographic photoconductors No. 14 to No. 27 according to the present invention was negatively charged in the dark under application of -6 kV of corona charge for 20 seconds using a commercially available electrostatic copying sheet testing apparatus "L:Paper Analyzer Model EPA-8200" (Trademark), made by Kawaguchi Electro Works Co., Ltd.

Then, each photoconductor was allowed to stand in the dark for 20 seconds without applying any charge thereto, and the surface potential Vo (-V) of the photoconductor was measured.

Each photoconductor was then illuminated by a light of 20 lux, and the exposure E.sub.1/2 (lux.cndot.sec) required to reduce the initial surface potential Vo (-V) to 1/2 the initial surface potential Vo (-V) was measured.

The results are shown in TABLE 6.

[Fabrication of Layered Photoconductor]

(Formation of charge generation layer)

A mixture of one part by weight of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 4, serving as a charge generation material, 50 parts by weight of a butyl acetate solution containing 2 wt. % of a commercially available polyvinyl butyral resin (Trademark "BM-S", made by Sekisui Chemical Co., Ltd.) and 49 parts by weight of n-butyl acetate was dispersed in a sand mill using 2-mm diameter glass beads for 2 hours. Thus, a coating liquid for a charge generation layer was prepared.

The thus prepared charge generation layer coating liquid was coated on the aluminum-deposited surface of an aluminum-deposited PET film with a thickness of 75 .mu.m serving as an electroconductive support, and dried at 80.degree. C. for 5 minutes. Thus, a charge generation layer with a thickness of 0.2 .mu.m was provided on the electroconductive support.

(Formation of charge transport layer)

A mixture of 8 parts by weight of an electron transport material represented by formula (III) shown below, 11 parts by weight of a commercially available Z type polycarbonate resin (made by Teijin Chemicals Ltd.), and 0.02 parts by weight of a commercially available silicone oil (Trademark "KF50", made by Shin-Etsu Chemical Co., Ltd.) was dissolved in 91 parts by weight of tetrahydrofuran, so that a coating liquid for a charge transport layer was prepared. ##STR460##

The thus prepared charge transport layer coating liquid was applied to the above prepared charge generation layer by cast coating method using a doctor blade, and then dried, so that a charge transport layer with a thickness of 20 .mu.m was provided on the charge generation layer.

Thus, an electrophotographic photoconductor No. 28 according to the present invention was fabricated.

The procedure for fabrication of the electrophoto-graphic photoconductor No. 28 in Example 28 was repeated except that the electron transport material of formula (III) for use in the charge transport layer coating liquid in Example 28 was replaced by the following electron transport material of formula (19): ##STR461##

Thus, an electrophotographic photoconductor No. 29 according to the present invention was fabricated.

Each of the electrophotographic photoconductors No. 28 and No. 29 according to the present invention was positively charged in the dark under application of +5.3 kV of corona charge for 20 seconds using a commercially available electrostatic copying sheet testing apparatus "Paper Analyzer Model EPA-8200" (Trademark), made by Kawaguchi Electro Works Co., Ltd.

Then, each photoconductor was allowed to stand in the dark for 20 seconds without applying any charge thereto, and the surface potential Vo (V) of the photoconductor was measured.

Each photoconductor was then illuminated by a light of 20 lux, and the exposure E.sub.1/2 (lux.cndot.sec) required to reduce the initial surface potential Vo (V) to 1/2 the initial surface potential Vo (V) was measured.

The results are shown in TABLE 7.

[Fabrication of Single-Layered Photoconductor]

(Formation of single-layered photoconductive layer)

A mixture of 0.5 g of the TiO-tetraazaporphyrin pigment obtained in Preparation Example 4, serving as a charge generation material, 10 g of a solution prepared by dissolving a commercially available Z type polycarbonate resin (made by Teijin Chemicals Ltd.) in tetrahydrofuran so as to have a concentration of 10 wt. %, and 9 g of tetrahydrofuran was dispersed in a ball mill.

Thereafter, a tetrahydrofuran solution containing 10 wt. % of the Z type polycarbonate resin and a charge transport material of the following formula (D) were further added to the above-mentioned dispersion so that the amount ratio of pigment might be 2 wt. %, that of Z type polycarbonate resin be 50 wt. %, and that of charge transport material be 28 wt. %. ##STR462##

The thus obtained mixture was thoroughly stirred, so that a coating liquid for a photoconductive layer was prepared.

The thus prepared photoconductive layer coating liquid was applied to the aluminum-deposited surface of an aluminum-deposited polyester film serving as an electroconductive support by cast coating method using a doctor blade, and then dried. Thus, a photoconductive layer with a thickness of 15 .mu.m was provided on the electroconductive support.

Thus, an electrophotographic photoconductor No. 30 of a single-layered type according to the present invention was fabricated.

The electrophotographic photoconductor No. 30 according to the present invention was negatively charged in the dark under application of -6 kV of corona charge for 20 seconds using a commercially available electrostatic copying sheet testing apparatus "Paper Analyzer Model EPA-8200" (Trademark), made by Kawaguchi Electro Works Co., Ltd.

Then, the photoconductor was allowed to stand in the dark for 20 seconds without applying any charge thereto, and the surface potential Vo (-V) of the photoconductor was measured.

Each photoconductor was then illuminated by a light of 20 lux, and the exposure E.sub.1/2 (lux.cndot.sec) required to reduce the initial surface potential Vo (-V) to 1/2 the initial surface potential Vo (-V) was measured.

The results are shown in TABLE 8.

As previously mentioned, when the tetraazaporphyrin pigment of formula (I), in particular, in a specific crystalline form, is used as the charge generation material in the layered or single-layered electrophotographic photoconductor, the chargeability and the sensitivity of the obtained photoconductor is improved.

When the above-mentioned tetraazaporphyrin pigment is used in combination with a charge transport material such as a positive hole transport material or an electron transport material, there can be obtained a layered photoconductor with high sensitivity. In this case, when a specific positive hole transport material or a specific electron transport material is employed, the sensitivity of the obtained photoconductor can be further improved.

Japanese Patent Application No. 10-097572 filed Apr. 9, 1998, Japanese Patent Application No. 10-297940 filed Oct. 20, 1998, and Japanese Patent Application filed Apr. 1, 1999 are hereby incorporated by reference.