Aminobiphenyl Charge Transporting Materials and Electrophotographic Photoconductors Using the Same

The present invention relates to charge transporting materials and electrophotographic photoconductors using the same, and more particularly, novel aminobiphenyl compounds used as the charge transporting materials, and electrophotographic photoconductors comprising any of the aminobiphenyl compounds as an organic photoconductive material or charge transporting material.

Conventionally a variety of inorganic and organic electrophotographic photoconductors are known. As inorganic photoconductors for use in electrophotography, there are known types in which the photoconductive materials, for instance, selenium, cadmium sulfide, and zinc oxide.

In an electrophotographic process, a photoconductor is first exposed to corona charges in the dark, so that the surface of the photoconductor is electrically charged uniformly to a predetermined polarity. The thus uniformly charged photoconductor is then exposed to original light images and the portions exposed to the original light images selectively become electroconductive so that electric charges dissipate from the exposed portions of the photoconductor, whereby latent electrostatic images corresponding to the original light images are formed on the surface of the photoconductor. The latent electrostatic images are then developed by the so-called toner which comprises a colorant, such as a dye or a pigment, and a binder agent made, for instance, of a polymeric material; thus, visible developed images can be obtained on the photoconductor. It is necessary that the photoconductors for use in electrophotography have at least the following fundamental properties: (1) chargeability to a predetermined potential in the dark; (2) minimum electric charge dissipation in the dark; and (3) quick dissipation of electric charges upon exposure to light.

While the above-mentioned inorganic electrophotographic photoconductors have many advantages over other conventional electrophotographic photoconductors, at the same time they have several shortcomings from the viewpoint of practical use.

For instance, a selenium photoconductor, which is widely used at present and sufficiently meets the above-mentioned requirements (1) to (3), has the shortcoming that its production is difficult and, accordingly, its production cost is high. Further, 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.

Cadmium sulfide photoconductors and zinc oxide photoconductors are prepared by dispersing cadmium sulfide or zinc oxide in a binder resin. They can be produced inexpensively compared with selenium photoconductors and are also used commonly in practice. However, the cadmium sulfide and zinc oxide photoconductors are poor in surface smoothness, hardness, tensile strength and wear resistance. Therefore, they are not suitable as photoconductors for use in plain paper copiers in which the photoconductors are used in quick repetition.

Recently, organic electrophotographic photoconductors, which are said not to have such shortcomings of the inorganic electrophotographic photoconductors, have been proposed, and some of them are in fact used in practice.

Representative examples of such organic electrophotographic photoconductors are an electrophotographic photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluorenon-9-one (U.S. Pat. No. 3,484,237), an electrophotographic photoconductor comprising poly-N-vinylcarbazole which is sensitized by a pyrylium salt type dye (Japanese Patent Publication No. 48-25658), photoconductors containing as the main component organic pigments (Japanese Laid-Open Patent Application No. 47-37543), a photoconductor comprising as the main component an eutectic crystalline complex consisting of a dye and a resin (Japanese Laid-Open Patent Application No. 47-10735), a photoconductor comprising a triphenylamine compound which is sensitized by a dye (U.S. Pat. No. 3,180,730), and a photoconductor comprising as charge transporting materials poly-N-vinyl-carbazole and an amide derivative (Japanese Laid-Open Patent Application No. 58-1155).

Although the above-mentioned organic electrophotographic photoconductors have various advantages over other conventional electrophotographic photoconductors, they do not meet various requirements in view of the practical use thereof.

Furthermore, polyfunctional tertiary amine compounds, in particular, aminobiphenyl derivatives (or benzidine derivatives), are known as excellent photoconductive materials for use in electrophotographic photoconductors, as disclosed in U.S. Pat. No. 3,265,496, Japanese Patent Publication No. 39-11546, and Japanese Laid-Open Patent Application No. 53-27033. These compounds, however, have the shortcoming that they are so slightly soluble in adhesive resins that they tend to be crystallized in a photoconductive layer of an electrophotographic photoconductor. In order to eliminate this shortcoming, it has been tried to use the above compounds in combination with low-molecular weight compounds for minimizing the crystallization of the amine compounds as disclosed in Japanese Laid-Open Patent Application No. 62-11216.

In addition to the above aminobiphenyl compounds, N,N-diphenyl-[1,1-biphenyl]-4-amine (Helv. Chim. Acta. 6 1011P, 1923) and N,N-bis(4-methoxyphenyl)-[1,1'-biphenyl]-4-amine (J. Prakt. Chem. 317 (2) 284P, 1975) are known. These compounds, however, are not useful as organic photoconductive materials for electrophotography.

Furthermore, Japanese Laid-Open Patent Application No. 57-195254 discloses N,N-diphenyl[1,1'-biphenyl]-4-amine as a carrier transporting material for use in an electrophotographic photoconductor. However, the electrophotographic photoconductor using the above compound has the shortcomings that the residual potential thereof is built up while in repeated use thereof and accordingly the obtained image quality is degraded while in use, with the production of unclear images.

Japanese Laid-Open Patent Application No. 62-201447 discloses carrier transporting materials such as 4-dimethylamino-4'-diphenylaminobiphenyl and 4-diethylamino-4'-di(m-tolylamino)biphenyl. The electrophotographic photoconductors using these compounds, however, have the shortcomings that the chargeability thereof decreases while in repeated use and accordingly the obtained images become unclear.

It is therefore an object of the present invention to provide charge transporting materials for use in an electrophotographic photoconductor, which charge transporting materials, when used in electrophotographic photoconductors, are capable of providing electrophotographic photoconductors which are excellent in electrostatic durability repetition, in particular, capable of maintaining a minimum residual potential even when used in repetition, and inexpensive.

Another object of the present invention is to provide electrophotographic photoconductors comprising the above charge transporting materials, which are excellent in electrostatic durability, in particular, in the maintenance of a minimum residual potential thereof even when used in repetition, and inexpensive.

A further object of the present invention is to provide aminobiphenyl compounds having the following general formula (I), which can be used as the above-mentioned charge transporting materials: ##STR2## wherein R.sup.1 represents hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, a thioalkoxyl group having 1 to 4 carbon atoms, an aryloxy group such as a phenoxy group and a naphthoxy group, a methylenedioxy group, an aralkyl group such as C.sub.6 H.sub.5 (CH.sub.2).sub.n -- where n is 1 to 4, a nitro group, or an unsubstituted or substituted aryl group such as a phenyl group and a naphthyl group, which may have a substituent such as an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and halogen; R.sup.2 represents hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, halogen; and R.sup.3 and R.sup.4 each represent hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, halogen, a dialkylamino group, an amino group, a thioalkoxy group having 1 to 4 carbon atoms, an aryloxy group such as a phenoxy group and a naphthoxy group, a methylenedioxy group, an aralkyl group such as C.sub.6 H.sub.5 (CH.sub.2).sub.n --, where n is 1 to 4, or an unsubstituted or substituted aryl group such as a phenyl group and a naphthyl group, which may have a substituent such as an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and halogen, k, m and n each represent an integer of 0 to 5, and represents an integer of 0 to 4, provided that R.sup.1, R.sup.2, R.sup.3 and R.sup.4 cannot be hydrogen at the same time.

In the above formula (I), R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may each represent hydrogen, an alkyl group having 1 to 4 carbon atoms, or an alkoxyl group having 1 to 4 carbon atoms, k, m and n may each represent an integer of 0 to 5, and l may represent and integer of 0 to 4, provided that R.sup.1, R.sup.2, R.sup.3 and R.sup.4 cannot be hydrogen at the same time, which provides preferable charge transporting materials for use in the present invention.

The above objects of the present invention are attained by the above biphenyl amino compounds, using the above biphenyl amino compounds as charge transporting material, and by an electrophotographic photoconductor comprising an electroconductive support and a photoconductive layer formed thereon comprising as a charge transporting material at least one aminobiphenyl compound of the above formula (I).

In the drawings,

FIG. 1 is an infrared spectrum of an aminobiphenyl compound No. 2 for use in the present invention.

FIG. 3 is an infrared spectrum of an aminobiphneyl compound No. 21 for use in the present invention.

FIG. 4 is an infrared spectrum of an aminobiphenyl compound No. 35 for use in the present invention.

FIG. 7 is an infrared spectrum of an aminobiphneyl compound No. 109 for use in the present invention.

FIG. 6 is an infrared spectrum of an aminobiphenyl compound No. 67 for use in the present invention.

FIG. 8 is an infrared spectrum of an aminobiphneyl compound No. 134 for use in the present invention.

FIG. 9 is an infrared spectrum of an aminobiphenyl compound No. 135 for use in the present invention.

FIG. 2 is an infrared spectrum of an aminobiphneyl compound No. 4 for use in the present invention.

FIG. 5 is an infrared spectrum of an aminobiphenyl compound No. 43 for use in the present invention.

FIGS. 10 to 14 are enlarged schematic illustrations of embodiments of an electrophotographic photoconductor according to the present invention.

FIG. 15 is a graph showing the residual surface potentials (Vr') of Comparative Electrophotographic Photoconductor No. 1 and Electrophotographic Photoconductor No. 5 according to the present invention for comparison.

The aminobipheny compounds of the following general formula (I), which are novel and used in the present invention, can be prepared, for example, by a known condensation reaction of condensing (a-1) a halobiphenyl derivative of general formula (II), and (b-1) a diphenylamine derivative of general formula (III), or condensing (a-2) an aminobiphenyl derivative of general formula (IV) and (b-2) a halobenzene derivative of general formula (V), in the presence of (c) finely-divided copper, copper oxide or copper halogenide, and (d) a sufficient amount of an alkali or alkali salt for the neutralization of hydrogen halogenide which is produced in the course of this condensation reaction, with or without (e) a reaction solvent, in an atmosphere of nitrogen at temperatures of about 150.degree. C. to about 250.degree. C.: ##STR3## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, k, l, m, and n are respectively the same as defined previously, and X represents halogen.

In the above condensation reaction, as the alkali or alkali salt, for example, sodium hydroxide and potassium hydroxide, sodium carbonate and potassium carbonate can be employed.

Further as the reaction solvent, nitrobenezene, dichlorobenzene, N,N-dimethylformamide, dimethyl sulfoxide, N-methylpyrrolidone, and 1,3-dimethyl-2-imidazolidinone can be employed.

600 ml of nitrobenzene was added to a mixture of 49.90 g (0.253 mol) of 4,4'-dimethyldiphenylamine, 78.00 g (0.278 mol) of 4-iodine biphenyl, 38.42 g (0.278 mol) of potassium carbonate, and 0.10 g of copper powder. The mixture was placed in an ester pipe and azeotropically heated for dehydration, with stirring, at 208.degree. C. to 209.degree. C. for 15 hours as a nitrogen gas was caused to flow over the reaction mixture.

The reaction mixture was then cooled to room temperature and filtered through a sellite filter to obtain a filtrate. The nitrobenzene was distilled away from the filtrate under reduced pressure. The residue was extracted with toluene, washed with water, dried by use of magnesium sulfate, and condensed under reduced pressure, whereby a dark brown oily material was obtained.

The thus obtained product was subjected to a silica gel column chromatography by use of a toluene--n-hexane mixed solvent as an eluent, and recrystallized from a mixed solvent of ethanol and ethyl acetate, whereby N,N-bis(4-methylphenyl)-[1,1'-biphenyl]-4-amine was obtained in the form of colorless needles with a yield of 52.98 g (59.9%). The melting point of the product was 129.5.degree. C. to 130.5.degree. C.

The results of the elemental analysis of the thus obtained N,N-bis(4-methylphenyl)-[1,1'-biphenyl]-4-amine were as follows:

The above calculation was based on the formula for N,N-bis(4-methylphenyl)-[1,1'-biphenyl]-4-amine of C.sub.26 H.sub.23 N.

An infrared spectrum of the N,N-bis(4-methylphenyl)-[1,1'-biphenyl]-4-amine (Aminobiphenyl Compound No. 2 in Table 2), taken by use of a KBr pellet, is shown in FIG. 1.

50 ml of nitrobenzene was added to a mixture of 2.27 g of 4,4'-ditolylamine, 3.38 g of 4-methyl-4'-iodine biphenyl, 1.67 g of potassium carbonate, and 50 mg of copper powder. The mixture was placed in an ester pipe and azeotropically heated for dehydration, with stirring, at 205.degree. C. to 208.degree. C. for 11 hours as a nitrogen gas was caused to flow over the mixture. The reaction mixture was then cooled to room temperature and filtered through a sellite filter to obtain a filtrate. The nitrobenzene was distilled away from the filtrate under reduced pressure. The residue was extracted with toluene, washed with water, dried by use of magnesium sulfate, and condensed under reduced pressure, whereby a dark brown oily material was obtained. The thus obtained product was subjected to a silica gel column chromatography two times, first by use of toluene, and subsequently by a toluene--n-hexane mixed solvent as eluents, and recrystallized from ethanol, whereby 4-methyl-4'-N,N-bis(4-methylphenyl)aminobiphenyl (Aminobiphenyl Compound No. 21 in Table 2) was obtained in the form of colorless needles with a yield of 3.08 g (52%). The melting point of the product was 118.0.degree. C. to 119.0.degree. C.

The results of the elemental analysis of the thus obtained 4-methyl-4'-N,N-bis(4-methylphenly)aminobiphenyl were as follows:

The above calculation was based on the formula for 4-methyl-4'-N,N-bis(4-methylphenyl)aminobiphenyl of C.sub.27 H.sub.25 N.

In addition to the above aminobiphenyl compounds for use in the present invention, the aminobiphenyl compounds listed in Table 1 were synthesized in the same manner as mentioned above.

Further aminobiphenyl compounds for use in the present invention can be synthesized in the same manner as mentioned in the above. Representative examples of the aminobiphenyl compounds for use in the present invention are collectively listed in Table 2:

The above listed novel aminobiphenyl compounds are useful as electrophotoconductive materials for use in electrophoto-graphic photoconductors and can be optically and/or chemically sensitized by dyes and Lewis acids. The above aminobipheny compounds are particularly useful as charge transporting materials for use in the so-called function-separation type photoconductors which include as charge generating materials organic pigments or inorganic pigments.

In the photoconductors according to the present invention, at least one aminobiphenyl compound of the formula (I) is contained in the photoconductive layers 2a, 2b, 2c, 2d and 2e. The aminobiphenyl compounds can be employed in different ways, for example, as shown in FIGS. 10 through 14.

In the photoconductor as shown in FIG. 10, a photoconductive layer 2a is formed on an electroconductive support 1, which photoconductive layer 2a comprises an aminobiphenyl compound, a sensitizer dye and a binder agent. In this photoconductor, the aminobiphenyl compound works as a photoconductive material, through which charge carriers which are necessary for the light decay of the photoconductor are generated and transported. However, the aminobiphenyl compound itself scarcely absorbs light in the visible light range and, therefore, it is necessary to add a sensitizer dye which absorbs light in the visible light range in order to form latent electrostatic images by use of visible light.

Referring to FIG. 11, there is shown an enlarged cross-sectional view of another embodiment of an electrophotographic photoconductor according to the present invention. In the figure, reference numeral 1 indicates an electroconductive support. On the electroconductive support 1, there is formed a photoconductive layer 2b comprising a charge generating material 3 dispersed in a charge transporting medium 4 comprising an aminobiphenyl compound and a binder agent. In this embodiment, the aminobiphenyl compound works as a charge transporting material; and the aminobiphenyl and the binder agent in combination constitute the charge transporting medium 4. The charge generating material 3, which is, for example, an inorganic or organic pigment, generates charge carriers. The charge transporting medium 4 accepts the charge carriers generated by the charge generating material 3 and transports those charge carriers.

In this electrophotographic photoconductor, it is basically necessary that the light-absorption wavelength regions of the charge generating material 3 and the aminobiphenyl compound not overlap in the visible light range. This is because, in order that the charge generating material 3 produce charge carriers efficiently, it is necessary that light pass through the charge transporting medium 4 and reach the surface of the charge generating material 3. Since the aminobiphenyl compounds of the previously described general formula (I) do not substantially absorb light in the visible range, they can work effectively as charge transporting materials in combination with the charge generating material 3 which absorbs the light in the visible region and generates charge carriers.

Referring to FIG. 12, there is shown an enlarged cross-sectional view of a further embodiment of an electrophotographic photoconductor according to the present invention. In the figure, there is formed on the electroconductive support 1 a two-layered photoconductive layer 2c comprising a charge generating layer 5 containing the charge generating material 3, and a charge transporting layer 6 containing an aminobiphenyl compound of the previously described formula (I).

In this photoconductor, light which has passed through the charge transporting layer 6 reaches the charge generating layer 5, and charge carriers are generated within the charge generating layer 5. The charge carriers which are necessary for the light decay for latent electrostatic image formation are generated by the charge generating material 3, accepted and transported by the charge transporting layer 6. In the charge transporting layer 6, the aminobiphenyl compound mainly works for transporting charge carriers. The generation and transportation of the charge carriers are performed by the same mechanism as that in the photoconductor shown in FIG. 11.

The electrophotographic photoconductor shown in FIG. 13, the charge generating layer 5 is formed on the charge transporting layer 5 containing the aminobiphenyl compound in the photoconductive layer 2d, thus the overlaying order of the charge generating layer 5 and the charge transporting layer 6 is reversed as compared with the electrophotographic photoconductor as shown in FIG. 12. The mechanism of the generation and transportation of charge carriers is substantially the same as that of the photoconductor shown in FIG. 12.

In the above photoconductor, a protective layer 7 may be formed on the charge generating layer 5 as shown in FIG. 14 for protecting the charge generating layer 5.

When the electrophotographic photoconductor according to the present invention as shown in FIG. 10 is prepared, at least one aminobiphenyl compound of the previously described formula (I) is dispersed in a binder resin solution, and a sensitizer dye is then added to the mixture, so that a photoconductive layer coating liquid is prepared. The thus prepared photoconductive layer coating liquid is coated on an electroconductive support 1 and dried, so that a photoconductive layer 2a is formed on the electroconductive support 1.

It is preferable that the thickness of the photosensitive layer 2a be in the range of 3 .mu.m to 50 .mu.m, more preferably in the range of 5 .mu.m to 20 .mu.m. It is preferable that the amount of the aminobiphenyl compound contained in the photoconductive layer 2a be in the range of 30 wt. % to 70 wt. % of the total weight of the photoconductive layer 2a, more preferably about 50 wt. % of the total weight of the photoconductive layer 2a. Further, it is preferable that the amount of the sensitizer dye contained in the photoconductive layer 2a be in the range of 0.1 wt. % to 5 wt. %, more preferably in the range of 0.5 wt. % to 3 wt. %, of the total weight of the photoconductive layer 2a.

As the sensitizer dye, the following can be employed in the present invention: Triarylmethane dyes, such as Brilliant Green, Victoria Blue B, Methyl Violet, Crystal Violet, and Acid Violet 6B; xanthene dyes, such as Rhodamine B, Rhodamine 6G, Rhodamine G Extra, Eosin S, Erythrosin, Rose Bengale, and Fluorescein; thiazine dyes, such as Methylene Blue; cyanin dyes, such as cyanin; and pyrylium dyes, such as 2,6-diphenyl-4-(N,N-dimethylaminophenyl) thiapyrylium perchlorate and benzopyrylium salt (Japanese Patent Publication No. 48-25658); and 2,4,7-trinitro-9-fluorenone and 2,4-dinitro-9-fluorenone. These sensitizer dyes can be used alone or in combination.

An electrophotographic photoconductor according to the present invention as shown in FIG. 11 can be prepared, for example, as follows. A charge generating material in the form of small particles is dispersed in a solution of one or more aminobiphenyl compounds and a binder agent. The thus prepared dispersion is coated on the electroconductive support 1 and then dried, whereby a photoconductive layer 2b is formed on the electroconductive support 1.

It is preferable that the thickness of the photoconductive layer 2b be in the range of 3 .mu.m to 50 .mu.m, more preferably in the range of 5 .mu.m to 20 .mu.m. It is preferable that the amount of the aminobiphenyl compound contained in the photoconductive layer 2b be in the range of 10 wt. % to 95 wt. %, more preferably in the range of 30 wt. % to 90 wt. %, of the total weight of the photoconductive layer 2b. Further, it is preferable that the amount of the charge generating material 3 contained in the photoconductive layer 2b be in the range of 0.1 wt. % to 50 wt. %, more preferably in the range of 1 wt. % to 20 wt. %, of the total weight of the photoconductive layer 2b.

As the charge generating material 3, the following can be employed in the present invention: Inorganic pigments, such as selenium, a selenium-tellurium alloy, cadmium sulfide, a cadmium sulfide--selenium alloy, and .alpha.-silicon; and organic pigments, for example, C.I. Pigment Blue 25 (C.I. 21180), C.I. Pigment Red 41 (C.I. 21200), C.I. Acid Red 52 (C.I. 45100), and C.I. Basic Red 3 (C.I. 45210); azo pigments having a carbazole skeleton (Japanese Laid-Open Patent Application No. 53-95033), azo pigments having a distyrylbenzene skeleton (Japanese Laid-Open Patent Application No. 53-133445), azo pigments having a triphenylamine skeleton (Japanese Laid-Open Patent Application No. 53-132347), azo pigments having a dibenzothiophene skeleton (Japanese Laid-Open Patent Application No. 54-21728), azo pigments having an oxazole skeleton (Japanese Laid-Open Patent Application No. 54-12742), azo pigments having a fluorenone skeleton (Japanese Laid-Open Patent Application No. 54-22834), azo pigments having a bisstilbene skeleton (Japanese Laid-Open Patent Application No. 54-17733), azo pigments having a distyryl oxadiazole skeleton (Japanese Laid-Open Patent Application No. 54-2129), azo pigments having a distyryl carbazole skeleton (Japanese Laid-Open Patent Application No. 54-14967); phthalocyanine-type pigments such as C.I. Pigment Blue 16 (C.I. 74100); Indigo-type pigments such as C.I. Vat Brown 5 (C.I. 73410) and C.I. Vat Dye (C.I. 73030); and perylenetype pigments, such as Algo Scarlet B (made by Bayer Co., Ltd.) and Indanthrene Scarlet R (made by Bayer Co., Ltd). These charge generating materials can be used alone or in combination.

An electrophotographic photoconductor according to the present invention as shown in FIG. 12 can be prepared, for example, as follows. A charge generating material 3 is vacuum-evaporated on the electroconductive support 1, whereby a charge generating layer 5 is formed. Alternatively, a charge generating material 3 in the form of fine particles is dispersed in a solution of a binder agent, and this dispersion is applied to the electroconductive support material 1 and then dried, and, if necessary, the applied layer is subjected to buffing to make the surface smooth or to adjust the thickness of the layer to a predetermined thickness, whereby a charge generating layer 5 is formed. A charge transporting layer 6 is then formed on the charge generating layer 5 by applying a solution of one or more aromatic diethyl compounds and a binder agent to the charge generating layer 5 and then drying the applied solution. In this photoconductor, the charge generating material employed is the same as that employed in the photoconductor in FIG. 11.

It is preferable that the thickness of the charge generating layer 5 be 5 .mu.m or less, more preferably 2 .mu.m or less. It is preferable that the thickness of the charge transporting layer 6 be in the range of 3 .mu.m to 50 .mu.m, more preferably in the range of 5 .mu.m to 20 .mu.m. In the case where the charge generating layer 5 comprises a charge generating material in the form of fine particles, dispersed in a binder agent, it is preferable that the amount of the charge generating material in the charge generating layer 5 be in the range of 10 wt. % to 95 wt. %, more preferably in the range of about 50 wt. % to about 90 wt. % of the entire weight of the charge generating layer 5. Further, it is preferable that the amount of the aminobiphenyl compound contained in the charge transporting layer 6 be in the range of 10 wt. % to 95 wt. %, more preferably in the range of 30 wt. % to 90 wt. %, of the total weight of the charge transporting layer 6.

The electrophotographic photoconductor as shown in FIG. 13 can be prepared, for example, by coating a solution of the aminobiphenyl compound and a binder agent on the electroconductive support 1 and drying the same to form a charge transporting layer 4, and then coating on the charge transporting layer 4 a dispersion of finely-divided charge generating material, with addition thereto of a binder agent when necessary, and drying the coated dispersion to form a charge generating layer 5 on the charge transporting layer 4. The thickness of each of the two layers 4 and 5 and the compositions thereof may be the same as those of the photoconductive layer 2c in the photoconductor shown in FIG. 12.

When a protective layer 7 is formed on the charge generating layer 5 of the photoconductive layer by coating an appropriate resin solution, for instance, by performing spray coating, the photoconductor as shown in FIG. 14 can be prepared.

As the electroconductive support 1 for use in the present invention, a metal plate or metal foil, for example, made of aluminum, a plastic film on which a metal, for example, aluminum, is evaporated, or paper which has been treated so as to be electroconductive, can be employed.

As the binder agent for use in the present invention, condensation resins, such as polyamide, polyurethane polyester, epoxy resin, polyketone and polycarbonate; and vinyl polymers such as polyvinylketone, polystyrene, poly-N-vinylcarbazole and polyacrylamide, can be used. These resins can also be employed as a resin component in the above mentioned protective layer 7.

Other conventional electrically insulating and adhesive resins can also be used as the binder agent in the present invention. When necessary, there can be added to the binder resins a plasticizer, for example, halogenated paraffin, polybiphenyl chloride, dimethylnaphthalene and dibutyl phthalate.

In the above described photoconductors according to the present invention, if necessary, an adhesive or barrier layer can be interposed between the electroconductive support and the photoconductive layer. The adhesive layer or the barrier layer can be made of, for example, polyamide, nitrocellulose, or aluminum oxide. It is preferable that the thickness of the adhesive layer or barrier layer be 1 .mu.m or less.

When copying is performed by use of the photoconductors according to the present invention, the surface of the photoconductor is charged uniformly in the dark to a predetermined polarity. The uniformly charge photoconductor is exposed to a light image so that a latent electrostatic image is formed on the photoconductor. The thus formed latent electrostatic image is developed by a developer to a visible image, and, when necessary, the developed image can be transferred to a sheet of paper. The photoconductors according to the present invention have high photosensitivity and excellent flexibility.

Preparation of embodiments of an electrophotographic photoconductor according to the present invention will now be explained in detail by referring to the following examples.

The following components were ground and dispersed in a ball mill to prepare a charge generating layer coating liquid:

This charge generating layer coating liquid was coated by a doctor blade on the aluminum-evaporated surface of an aluminum-evaporated polyester base film, which served as an electroconductive support, so that a charge generating layer was formed on the electroconductive support with a thickness of about 1 .mu.m when dried at room temperature.

Then the following components were mixed and dissolved, so that a charge transporting layer coating liquid was prepared:

The thus prepared charge transporting layer coating liquid was coated on the aforementioned charge generating layer by a doctor blade and dried at 80.degree. C. for 2 minutes and then at 105.degree. C. for 5 minutes, so that a charge transporting layer with a thickness of about 20 .mu.m was formed on the charge generating layer; thus, an electrophotographic photoconductor No. 1 according to the present invention was prepared.

The electrophotographic photoconductor No. 1 was charge negatively in the dark under application of -6 kV of corona charge for 20 seconds and then allowed to stand in the dark for 20 seconds without applying any charge thereto. At this moment, the surface potential V.sub.po (V) of the photoconductor was measured by a Paper Analyzer (Kawaguchi Electro Works, Model SP-428). The photoconductor was then illuminated by a tungsten lamp in such a manner that the illuminance on the illuminated surface of the photoconductor was 20 lux, and the exposure E.sub.1/2 (lux seconds) required to reduce the initial surface potential V.sub.po (V) to 1/2 the initial surface potential V.sub.po (V) was measured. The results showed that V.sub.po (V)=-1100 V and E.sub.1/2 =1.62 lux seconds.

Example P-1 was repeated except that the charge generating material and the aminobiphenyl compound working as the charge transporting material employed in Example P-1 were respectively replaced by the charge generating materials and the aminodiphenyl compounds as listed in Table 3, whereby electrophotographic photoconductors No. 2 through No. 27 according to the present invention were prepared. Charge Trans- porting Material (Aminodiphenyl Photo- compound in Conductor Charge Generating Material Table 2) No. 2 ##STR10## No. 21 No. 3 ##STR11## No. 21 No. 4 ##STR12## No. 21 No. 5 ##STR13## No. 21 No. 6 ##STR14## No. 21 No. 7 .beta. type copper phthalocyanine No. 2 No. 8 ##STR15## No. 2 No. 9 CG-2 2 No. 10 CG-3 2 No. 11 CG-5 2 No. 12 CG-3 20 No. 13 CG-5 20 No. 14 CG-3 3 No. 15 CG-5 3 No. 16 CG-3 22 No. 17 CG-5 22 No. 18 CG-3 30 No. 19 CG-5 30 No. 20 CG-3 34 No. 21 CG-5 34 No. 22 CG-3 8 No. 23 CG-5 8 No. 24 CG-3 28 No. 25 CG-5 28 No. 26 CG-3 36 No. 27 CG-5 36 No. 28 CG-3 37 No. 29 CG-5 37 No. 30 CG-3 39 No. 31 CG-5 39 No. 32 CG-3 48 No. 33 CG-5 48 No. 34 CG-3 62 No. 35 CG-5 62 No. 36 CG-3 63 No. 37 CG-5 63 No. 38 CG-3 64 No. 39 CG-5 64 No. 40 CG-3 66 No. 41 CG-5 66 No. 42 CG-3 104 No. 43 CG-5 104 No. 44 CG-3 105 No. 45 CG-5 105 No. 46 CG-3 106 No. 47 CG-5 106 No. 48 CG-3 108 No. 49 CG-5 108

Selenium was vacuum-evaporated with a thickness of about 1.0 .mu.m on an about 300 .mu.m thick aluminum plate so that a charge generating layer was formed on the aluminum plate.

A charge transporting layer coating liquid was prepared by mixing and dispersing the following components:

The thus prepared charge transporting layer coating liquid was coated on the aforementioned selenium charge generating layer by a doctor blade, dried at room temperature and further dried under reduced pressure, so that a charge transporting layer about 10 .mu.m thick was formed on the charge generating layer; thus, an electrophotographic photoconductor No. 50 according to the present invention was prepared.

A perylene pigment C.I. Vat Red 23 (C.I. 71130) of the following formula was vacuum-evaporated with a thickness of about 0.3 .mu.m on an about 300 .mu.m thick aluminum plate so that a charge generating layer was formed on the aluminum plate: ##STR16##

A charge transporting layer coating liquid was prepared by mixing and dispersing the following components:

The thus prepared charge transporting layer coating liquid was coated on the aforementioned charge generating layer by a doctor blade, dried at room temperature and further dried under reduced pressure, so that a charge transporting layer about 10 .mu.m thick was formed on the charge generating layer; thus, an electrophotographic photoconductor No. 51 according to the present invention was prepared.

One part by weight of Diane Blue (C.I. Pigment Blue 25, C.I. 21180) which was the same as that employed in Example P-1 was added to 158 parts by weight of tetrahydrofuran, and the mixture was ground and dispersed in a ball mill. To this mixture, 12 parts by weight of the aminobiphenyl compound No. 21 in Table 2 and 18 parts by weight of a polyester resin (Polyester Adhesive 49000 made by Du Pont Co.) were added and mixed, whereby a photoconductive layer coating liquid was prepared.

The thus prepared photoconductive layer coating liquid was coated on an aluminum-evaporated polyester film by a doctor blade and dried at 100.degree. C. for 30 minutes, so that a photoconductive layer with a thickness of about 16 .mu.m was formed on the aluminum-evaporated polyester film, thus, an electrophotographic photoconductor No. 52 according to the present invention was prepared.

The same charge transporting layer coating liquid as that prepared in Example 1 was coated by a doctor blade on the aluminum-evaporated surface of an aluminum-evaporated polyester base film, which served as an electroconductive support, so that a charge transporting layer was formed on the electroconductive support, with a thickness of about 20 .mu.m when dried at room temperature.

Then the following components were ground and dispersed in a ball mill to prepare a dispersion:

To the above dispersion, 1700 parts by weight of ethyl cellosolve were further added and the mixture was dispersed, whereby a charge generating layer coating liquid was prepared.

The thus prepared charge generating layer coating liquid was coated on the aforementioned charge transporting layer by spray coating and dried at 100.degree. C. for 10 minutes, whereby a charge generating layer having a thickness of about 0.2 .mu.m was formed on the charge transporting layer.

Then a methanol/n-buthanol solution of a polyaminde resin (Trademark "CM-8000" made by Toray Industries, Inc.) was coated on the charge generating layer by spray coating and dried at 120.degree. C. for 30 minutes, whereby a protective layer having a thickness of about 0.5 .mu.m was formed on the charge generating layer. Thus an electrophotographic photoconductor No. 53 according to the present invention was prepared.

The thus prepared electrophotographic photoconductors No. 2 to No. 53 were charge negatively or positively in the dark under application of -6 kV or +6 kV of corona charge for 20 seconds and then allowed to stand in the dark for 20 seconds without applying any charge thereto. At this moment, the surface potential V.sub.po (V) of each photoconductor was measured by a Paper Analyzer (Kawaguchi Electro Works, Model SP-428). Each photoconductor was then illuminated by a tungsten lamp in such a manner that the illuminance on the illuminated surface of the photoconductor was 20 lux, wo that the exposure E.sub.1/2 (lux seconds) required to reduce the initial surface potential V.sub.po (V) to 1/2 the initial surface potential V.sub.po (V) was measured.

The results are shown in Table 4.

Each of the above electrophotographic photoconductors No. 1 through No. 53 was incorporated in a commercially available electrophotographic copying machine and a latent electrostatic image was formed thereon by being exposed to a light image. The latent electrostatic image was developed with a dry type developer to a visible toner image, electrostatically transferred to a transfer sheet made of plain paper and fixed thereto. As a result, a clear transferred image was obtained by each of the photoconductors. When a liquid developer was employed instead of the dry type developer, clear transfer images were obtained likewise.

The following components were ground and dispersed in a ball mill to prepare a charge generating layer coating liquid:

This charge generating layer coating liquid was coated by a doctor blade on the aluminum-evaporated surface of an aluminum-evaporated polyester base film, which served as an electroconductive support, so that a charge generating layer was formed on the electroconductive support with a thickness of about 1 .mu.m when dried at room temperature.

Then the following components were mixed and dissolved, so that a charge transporting layer coating liquid was prepared:

The thus prepared charge transporting layer coating liquid was coated on the aforementioned charge generating layer by a doctor blade and dried at 80.degree. C. for 2 minutes and then at 105.degree. C. for 5 minutes, so that a charge transporting layer with a thickness of about 20 .mu.m was formed on the charge generating layer, whereby a comparative electrophotographic photoconductor No. 1 was prepared.

Comparative Example 1 was repeated except that N,N-diphenyl-[1,1'-biphenyl]-4-amine employed as charge transporting material was replaced by 4,4',4"-trimethyltriphenylamine of the following formula: whereby a comparative electrophotographic photoconductor No. 2 was prepared. ##STR19##

The thus prepared comparative electrophotographic photoconductors No. 2 and No. 3 were charged negatively in the dark under application of -6 kV of corona charge for 20 seconds and then allowed to stand in the dark for 20 seconds without applying any charge thereto. At this moment, the surface potential V.sub.po (V) of each photoconductor was measured by a Paper Analyzer (Kawaguchi Electro Works, Model SP-428). Each photoconductor was then illuminated by a tungsten lamp in such a manner that the illuminance on the illuminated surface of the photoconductor was 20 lux, so that the exposure E.sub.1/2 (lux.seconds) required to reduce the initial surface potential V.sub.po (V) to 1/2 the initial surface potential V.sub.po (V) was measured.

Furthermore, the surface potential of each comparative electrophotoconductor 30 seconds after the initiation of the exposure to the light was also measured, which surface potential is referred to as Vr. For comparison, V.sub.po (V), E.sub.1/2 (lux.second) and Vr (V) of Photoconductor No. 5 prepared in Example P-5 were also measured in the same manner.

The results are shown in the following Table 5

In order to investigate the fatigue characteristics of Photoconductor No. 5 and Comparative Photoconductor No. 1 after repeated use (hereinafter referred to as the repeated-use fatigue characteristics), the two photoconductors were subjected to the charging at -7.5 kV and exposure of 30 lux in repetition, so that the changes in the residual surface potential (Vr') of each photoconductor were measured. The results are shown in FIG. 15.

The results shown in Table 5 and in FIG. 15 indicate that Comparative Photoconductor No. 1 is inferior to Photoconductor No. 5 in E.sub.1/2 which represents photosensitivity, and the residual surface potential (Vr') of Comparative Photoconductor No. 1 increases while in repeated use. Comparative Photoconductor No. 2 is also lower in E.sub.1/2 than Photoconductor No. 5, and has a relatively high residual potential (Vr) in the initial stage before its repeated use.