Electrophotographic photoreceptor

Abstract: An electrophotographic photoreceptor comprising at least a photosensitive layer on a conductive base, said photosensitive layer containing oxytitanium phthalocyanine and dihalogenotin phthalocyanine is disclosed herein. The electrophotographic photoreceptor according to the present invention is very high potential stability in its repeated use and very little change in properties by environment. Therefore, using the electrophotoreceptor according to the present invention, the images can be obtained with stability.

Description: Field of the Invention: The present invention relates to an electrophotographic photoreceptor. More especially, it relates to the electrophotographic photoreceptor having a very high sensitivity and a high potential stability in its repeated use. Background of the Invention: In recent years, electrophotography is applied to copying machines as well as to various printers, because it provides high quality images without delay. A laser beam printer which is excellent in speediness, image quality and silence has been keenly developed and rapidly commercialized. In the laser beam printer, a light source is a semiconductor laser whose oscillation wavelength is about 800 nm. Therefore, the photoreceptor having the high sensitivity in a long wavelength range including about 800 nm is strongly requested. As a photoreceptor which plays an important role in electrophotography, a photoreceptor comprising an inorganic photoconductive material such as selenium, an arsenic-selenium alloy, cadmium sulfide or zinc oxide has been used. More recently, a photoreceptor comprising an organic photoconductive material which has advantages, i.e. it is not a pollutant and it has film-formability and shapability, is proposed. Among known organic photoconductive materials having the high sensitivities in the long wavelength range, phthalocyanine dyes are extensively investigated, because those syntheses are relatively easy and those absorption wavelengths extend to relatively long wavelength range as compared with other dyes. The phthalocyanines have different absorption spectra and photoconductivities, depending on kinds of their coordinated metals and of their crystalline forms. It is reported that among the phthalocyanines having the same coordinated metal, only the phthalocyanine having a specified crystalline form can be applied to the electrophotographic photoreceptor. The known photoreceptors show good properties on their initial uses. However, in their repeated uses, many problems such as the lowering in sensitivity, the increase in residual potential and the lowering in charge-ability are found. As the result, not many copies can be produced. In general, the sensitivity of the photoreceptor is principally determined depending on the photoconductive material used therein. Especially, in the electrophotoreceptor in which the semiconductor laser is used as the light source, an optical strength range which can be controlled in view of an output stability and a life of the light source is often incompatible with the sensitivity of the photoreceptor. In this connection, the lowering in image qualities including a resolution is often found. Thus, it is considered that the photoreceptor can be widely applied, if only its sensitivity can be freely adjusted without impairing other properties. As methods for adjusting the sensitivity of the photoreceptor, an alternation of a binder resin which is used together with a charge generating material and an alternation of a layer configuration such as a layer thickness are known. These known methods are effective to some extent. The methods for adjusting the sensitivity of the photoreceptor by using a mixed phthalocyanines are also known. For example, JP-A-62/272272 describes a mixture of α-type oxytitanium phthalocyanine with β-type oxytitanium phthalocyanine in a proportion to obtain a desired sensitivity. JP-A-02/183261 describes a mixture of oxytitanium phthalocyanine showing diffraction peaks at Bragg angle (2 ± 0.2°) of 9.6°, 11.7°, 24.1° and 27.2° with oxytitanium phthalocyanine showing diffraction peaks of 6.9°, 15.5° and 23.4° in a proportion to obtain a desired sensitivity. Further, JP-A-02/280169 describes a mixture of oxytitanium phthalocyanine with other type of phthalocyanine such as phthalocyanine without a metal and Cu-phthalocyanine in a proportion to adjust the sensitivity. However, the adjustment of the sensitivity of the photoreceptor according to the above methods is limited. The resultant photoreceptor has a limited application, because the usable light is limited, it shows a significant potential change in its repeated use and it shows a significant variation in properties depending on environments. EP-A-409 737 discloses an electrophotosensitive member comprising an electroconductive support and a photosensitive layer, wherein the photosensitive layer comprises an oxytitanium phthalocyanine. EP-A-314 100 discloses an electrophotographic sensitive material having superposed on an electroconductive substrate a sensitive layer comprising an alpha-type titanyl phthalocyanine and a metal-free phthalocyanine. Summary of the Invention The present inventors found that the electrophotographic photoreceptor whose sensitivity can be controlled in a very wide range and which has the high potential stability in its repeated use and an excellent environmental properties can be obtained, by mixing specific phthalocyanines. According to the present invention, the electrophotographic photoreceptor having a photosensitive layer on a conductive base can be provided, characterized in that the photosensitive layer contains oxytitanium phthalocyanine and dihalogenotin phthalocyanine. Detailed Explanation of the Invention As the conductive base, any known conductive base can be used. Examples are a base comprising a metal such as aluminum, stainless steel, copper or nickel as well as a base comprising a insulating material such as polyester film or paper on which a conductive layer such as a layer of aluminum, copper, palladium, tin oxide or indium oxide is provided. A barrier layer as used in the known photoreceptor may be provided between the conductive base and the photosensitive layer. The barrier layer generally comprises a known material, for example an inorganic material such as an anodized film of aluminum, aluminum oxide and aluminum hydroxide and an organic material such as polyvinyl alcohol, casein, polyvinyl pyrrolidone, polyacrylic acid, cellulose, gelatin, starch, polyurethane, polyimide and polyamide. The photosensitive layer which is provided on the conductive base should contain oxytitanium phthalocyanine and dihalogenotin phthalocyanine. It may be a laminated-typ photosensitive layer in which a charge generation layer mainly consisting of a charge generation material and a charge transport layer mainly consisting of a charge transport material and a binder resin are successively laminated; an inverted bilayer-type photosensitive layer in which the charge transport layer and the charge generation layer are successively laminated; and a dispersion-type photoreceptor in which the charge generation material is dispersed in a medium comprising the charge transport material and the binder resin. Oxytitanium phthalocyanine used in the present invention has any crystalline form. Oxytitanium phthalocyanine showing a maximum peak at Bragg angle (29 ± 0.2°) of 27.3° and rather strong peaks of 9.6° and 24.1° in the X-ray diffraction spectrum, oxytitanium phthalocyanine showing major peaks of 9.2°, 13.1°, 20.7°, 26.2° and 27.1°, oxytitanium phthalocyanine showing major peaks of 6.9°, 15.5° and 23.4° and oxytitanium phthalocyanine showing major peaks of 7.6°, 10.2°, 12.6°, 13.2°, 15.2°, 16.2°, 18.4°, 22.5°, 24.2°, 25.4° and 28.7° are preferable. Especially, oxytitanium phthalocyanine showing the maximum peak of 27.3° is preferable. A mixture of oxytitanium phthalocyanines having different crystalline forms in any proportion may be used. Oxytitanium phthalocyanine used in the present invention is, for example, the compound having the following formula (I): wherein X is halogen atom and n is a number from 0 to 1. The compound of the general formula (I) wherein X is chlorine atom and n is the number from 0 to 0.5 is preferable. Oxytitanium phthalocyanine used in the present invention can be easily synthesized, for example, from 1,2-dicyanobenzene (o-phthalodinitrile) and a titanium compound according to the following reaction schemes (1) and (2): Pc= phthalocyanine residue That is, 1,2-dicyanobenzene and titanium halide are reacted with heating in an inert solvent. Examples of the titanium halide include titanium tetrachloride, titanium trichloride and titanium tetrabromide, titanium tetrachloride being preferable. The inert solvent is preferably any solvent being inert to the reaction and having a high boiling point, such as trichlorobenzene, α-chloro naphthalene, β-chloro naphthalene, α-methyl naphthalene, methoxy naphthalene, diphenyl ether, diphenyl methane, diphenyl ethane, ethyleneglycol dialkyl ether, diethyleneglycol dialkyl ether and triethyleneglycol dialkyl ether. The reaction is generally carried out at the temperature of 150 to 300°C, preferably 180 to 250°C. After the reaction is completed, the thus produced dichlorotitanium phthalocyanine is filtered out and washed with the solvent identical with that used in the reaction so as to remove impurities produced in the reaction and unreacted materials. Then, a crude dichlorotitanium phthalocyanine is washed with the inert solvent, for example an alcohol such as methanol, ethanol and isopropyl alcohol and an ether such as tetrahydrofuran and diethyl ether, so as to remove the solvent used in the reaction. Finally, the purified dichlorotitanium phthalocyanine is subjected to hydrolysis, thereby oxytitanium phthalocyanine is obtained. The oxytitanium phthalocyanine used in the present invention is not limited to the crystalline oxytitanium phthalocyanine prepared according to the above method. For example, oxytitanium phthalocyanine having the different crystalline form can be prepared by subjecting any other oxytitanium phthalocyanine to a suitable treatment such as an acid paste method or a mechanical grinding method using a sand grinding mill. Dihalogenotin phthalocyanine used in the present invention has also any crystalline form. Dihalogenotin phthalocyanine showing major peaks at Bragg angle (2 ± 0.2°) of 8.4°, 12.2°, 13.8°, 19.1°, 22.4°, 28.2° and 30.0° and dihalogenotin phthalocyanine showing major peaks at Bragg angle (2 ± 0.2°) of 8.4°, 11.2°, 14.5°, 16.9°, 19.6°, 25.7° and 27.1° in the X-ray diffraction spectrum are preferable. Particularly, the use of dihalogenotin phthalocyanine showing major peaks at Bragg angle (2 ± 0.2°) of 8.4°, 11.2°, 14.5°, 16.9°, 19.6°, 25.7° and 21.1° in combination with oxytitanium phthalocyanine showing the maximum peaks at Bragg angle (2 ± 0.2°) of 27.3° and rather strong peaks of 9.6° and 24.1° is preferable. Dihalogenotin phthalocyanine used in the present invention can be prepared in any method. For example, it is prepared according to the following reaction scheme. wherein X is a hydrogen or halogen atom, a lower alkyl, lower alkoxy, aryloxy, nitro, cyano, hydroxy or benzyloxy group, Y is a halogen atom, l is an integer of 2, 3 or 4 and m representing the number of the substituent X on the benzene ring is an integer of 0 to 4. A starting phthalonitrile may be o-dicarboxylic acids, anhydrous phthalic acids, phthalic imides and phthalic acid diamides. An organic solvent used in the above reaction is any inert solvent having a high-boiling point, such as quinoline, α-chloronaphthalene, β-chloronaphthalene, α-methylnaphthalene, methoxynaphthalene, diphenyl ether, diphenyl methane, diphenyl ethane, ethylene glycol, dialkyl ether and high fatty amines. Desirably, the reaction is generally carried out at the temperature of 150 to 300°C. The reaction proceeds in absence of the organic solvent, by heating to 160°C or more. The thus-produced crude dihalogenotin phthalocyanine is purified according to the known method such as sublimation, recrystallization, treatment with an organic solvent, hot suspension, reprecipitation and alkali washing. In general, the X-ray spectra of phthalocyanine are classified several different patterns, depending on difference of raw materials, solvent and catalyst used in its synthesis; reaction conditions such as reaction time, mixing, agitation and rate of increasing temperature; and difference of treatment to be subjected after the reaction such as heat treatment, solvent treatment and mechanical treatment. As SnYl in the above reaction so as to obtain dihalogenotin phthalocyanine having the suitable X-ray diffraction spectrum, SnY 4 which may be combined with other tin compound (such as SnCl 2 , SnBr 2 and SnBr 4 ) and SnY 2 are illustrated. When SnY 4 or a combination of SnY 4 with other tin compound is used, it is preferable that materials other than SnY 4 and the solvent are mixed and heated to 50°C or more, preferably 100°C or more, to which SnY 4 is added with stirring. SnY 4 may be added in the form of a solution. When SnY 2 is used, it is added at room temperature or after heating. In this case, it is preferable to add a catalyst such as a quaternary ammonium salt, crown ether and polyethylene glycol in 0.1 to 10 parts by weight per 10 parts by weight of SnY 2 . As described in the above, the X-ray diffraction spectral pattern is determined by a combination of several factors. Therefore, the conditions to obtain dihalogenotin phthalocyanine having suitable X-ray diffraction spectral pattern are not limited to the above. The proportion in weight of dihalogenotin phthalocyanine to oxytitanium phthalocyanine is not limited. Preferably, it is in the range of from 95:5 to 10:90 in weight, more preferably 95:5 to 20:8 in weight. In the laminated-type photosensitive layer, the charge generation layer comprises the charge generation material which is a combination of oxytitanium phthalocyanine and dihalogenotin phthalocyanine. The charge generation layer may be of a dispersion type wherein phthalocyanines are dispersed in any binder resin such as polyester resin, polyvinyl acetate, polyacrylate ester, polymethacrylate ester, polycarbonate, polyvinyl acetacetal, polyvinyl propional, polyvinyl butyral, phenoxy resin, epoxy resin, urethane resin, cellulose ester and cellulose ether. The amount of the total phthalocyanines are generally 30 to 500 parts by weight per 100 parts by weight of the binder resin. A coating dispersion used for forming the charge generation layer of the dispersion type is prepared in any method. For example, phthalocyanines are dispersed in a dispersion medium followed by mixing with the binder resin. Alternatively, each of phthalocyanines is dispersed in the dispersion medium, respectively followed by mixing with the binder resin. Examples of the dispersion medium include ethers such as diethyl ether, dimethoxy ethane, tetrahydrofuran and 1,2-dimethoxyethane; ketones such as acetone, methyl ethyl ketone, diethyl ketone and cyclohexanone; esters such as methyl acetate and ethyl acetate; alcohols such as methanol, ethanol and propanol; and a mixture thereof. Phthalocyanines are dispersed in the dispersion medium according to any known method, using for example a ball mill, a sand grinding mill, a planetary mill or a roll mill. The thus-prepared phthalocyanine dispersion is mixed with the binder resin according to any known method. For example, the binder resin as such or as a solution is simultaneously dispersed. The phthalocyanine dispersion may be mixed in a solution of the binder resin. Conversely, the phathalocyanine dispersion is mixed in the solution of the binder resin. Alternatively the charge generation layer may be formed by directly depositing dihalogenotin phthalocyanine and oxytitanium phthalocyanine on the conductive base. If necessary, the charge generation layer may contain various additives, for example a levelling agent such as silicone oil and fluorosilicone oil; an antioxidant such as hindered phenol and hindered amine; and a sensitizer. The thickness of the charge generation layer is generally 0.1 to 2 µm, preferably 0.15 to 0.8 µm. The charge transport layer comprises the charge transport material and the binder resin. The charge transport material used in the charge transport layer is an electron donative material, examples of which include heterocyclic compounds such as carbazole, indole, imidazole, oxazole, pyrazole, oxadiazole, pyrazoline and thiadiazole; aniline derivatives; hydrazone compounds; aromatic amine derivatives; stilbene derivatives and polymers having the above compound in their main chain or their side chain. As the binder resin used together with the charge transport material in the charge transport layer, a vinyl polymer, for example a homopolymer or a copolymer, such as polymethyl methacrylate, polystyrene and polyvinyl chloride and its copolymer, polycarbonate, polyester, polyester carbonate, polysulfone, polyimide, phenoxy resin, epoxy resin and silicone resin can be used. Their partially crosslinked products may be used. If necessary, the charge transport layer may contain various additives such as the antioxidant and the sensitizer. The charge transport layer is usually formed on the charge generation layer according to any of the known methods, preferably the coating method wherein the coating solution or dispersion containing the charge transport material and the binder resin together with any optional additives in a suitable solvent is coated. The thickness of the charge transport layer is generally 10 to 60 µm, preferably 10 to 45 µm. The laminated-type photosensitive layer described in the above has the charge generation layer on which the charge transport layer is provided, but the order of laminating the charge generation layer and the charge transport layer may be changed, if necessary. As mentioned in the above, the dispersion-type photosensitive layer comprises the particulate charge generation material dispersed in the medium comprising the charge transport material and the binder resin. The ratio of the charge transport material to the binder resin is the same as that in the laminated-type photoconductive layer. In the dispersion-type photoconductive layer, the charge generation material should have a small particle size. Its particle size is preferably 1 µm or less, more preferably 0.5 µm or less. The charge generation material dispersed in the medium is preferably in an amount of 0.5 to 50 % by weight, more preferably in an amount of 1 to 20 % by weight based on the medium. If the amount of the charge generation material is less than 0.5 % by weight, the sufficient sensitivity cannot be obtained. On the other hand, if it is above 50 % by weight, the lowering in charge-ability and sensitivity are observed. If necessary, the dispersion-type photosensitive layer may contain various additives such as a plasticizer, a dispersion assistant, a levelling agent and a surfactant. The thickness of the dispersion-type photosensitive layer is generally 10 to 70 µm, preferably 10 to 50 µm. As an outer layer, a known overcoat layer, for example, a layer mainly composed of a thermoplastic or thermosetting polymer can be provided. Each layer is formed using a coating solution or dispersion of the material in the suitable solvent according to any known method, for example a roll coating method, a bar coating method, a dip coating method, a spray coating method or a multinozzle coating method. EFFECT OF THE INVENTION: The electrophotographic photoreceptor according to the present invention comprising oxytitanium phthalocyanine and dihalogenotin phthalocyanine in the photosensitive layer is very high potential stability in its repeated use and very little change in properties by environment. Therefore, using the electrophotoreceptor according to the present invention, the images can be obtained with stability. EXAMPLES: The invention will be better understood by reference to certain reference examples and examples, which are included herein for the purpose of illustration only and are not intended to limit the invention. All parts referred herein are by weight unless otherwise indicated. Reference Example 1 Preparation of oxytitanium phthalocyanine 97.5 g of phthlodinitrite was added to 750 ml of α-chloronaphthalene, to which 22 ml of titanium tetrachloride was added dropwise under a nitrogen atmosphere. After heating, reactants were reacted at 200 to 220°C for 3 hours with stirring, and a reaction mixture was cooled, filtered at the temperature of 100 to 130°C, washed with α-chloronaphthalene (200 ml) heated to 100°C and further treated with N-methylpyrrolidone (200 ml x 3) at 100°C for 1 hour. Then, it was treated with hot methanol (300 ml) at a room temperature followed by treating with methanol (500 ml x 3) for 1 hour. The resultant oxytitanium phthalocyanine was ground using a sand grinding mill for 20 hours followed by introducing a suspension of 400 ml of water and 40 ml of o-dichlorobenzene and heating at 60°C for 1 hour. The X-ray diffraction spectrum of the obtained oxytitanium phthalocyanine in powder form was shown in Fig. 1. Judging from the X-ray diffraction spectra, the product showed the maximum peak at Bragg angle (2 ± 0.2°) of 27.3°. Reference Example 2 Preparation of dihalogenotin phthalocyanine 25 parts of phthalodinitrile and 12.7 parts of tin tetrachloride were added to 160 parts of α-chloronaphthalene and dissolved at 120°C. After the reaction temperature was increased slowly to 210°C, the reactants were reacted with agitating at this temperature for 3.5 hours. After the reaction was completed, the reaction mixture was cooled to the temperature of 100 °C and filtered while it was hot. Then, it was treated with hot methanol, hot water and N-methylpyrrolidone at 150°C for 2 hours and filtered while it was hot. Further, it was treated with hot methanol, filtered and dried under vacuum, thereby 10 parts of dihalogenotin phthalocyanine as a blue powder was obtained. The result of elemental analysis of dihalogenotin phthalocyanine is shown below. C (%) H(%) N(%) Cl(%) Calc. 54.70 2.28 15.95 9.97 Anal. 54.88 2.41 16.13 10.01 The result of IR analysis of dihalogenotin phthalocyanine was similar to Fig. 1 of JP-A-62/119547. Judging from the results of elemental analysis and IR analysis, the product obtained in Reference Example 2 was confirmed to be dichlorotin phthalocyanine. The X-ray diffraction spectrum of the product in powder form is shown in Fig. 2. Reference Example 3 Preparation of dihalogenotin phthalocyanine 25 parts of phthalodinitrile and 9.3 parts of tin dichloride were added to 140 parts of α-chloronaphthalene. The reactants were reacted with agitating while the reaction temperature was increased slowly to 200°C. Then, a mixture of 6.4 parts of tin tetrachloride and 10 parts of α-chloronaphthalene was added dropwise to it followed by reacting at 200 to 205°C for 4 hours under nitrogen. After the reaction was completed, a reaction system is cooled to 100°C, filtered while it was hot and worked up as in Reference Example 2. Thereby 29.0 parts of dihalogenotin phthalocyanine as a blue powder were obtained. The result of elemental analysis of dihalogenotin phthalocyanine is shown below. C (%) H(%) N(%) Cl(%) Calc. 54.70 2.28 15.95 9.97 Anal. 54.85 2.31 16.02 10.49 The X-ray diffraction spectrum of the obtained dichlorotin phthalocyanine was shown in Fig. 9. Example 1 10 Parts of oxytitanium phthalocyanine obtained in Reference Example 1 were added to 200 parts of n-propanol and they were subjected to the grinding and dispersion treatment using the sand grinding mill for 10 hours, followed by mixing with 5 parts of a 10 % solution of polyvinyl butyral (#6000-C (trade mark), ex DENKI KAGAKU KOGYO K.K.) in methanol, thereby a dispersion A was prepared. 10 Parts of dichlorotin phthalocyanine obtained in Reference Example 2 were added to 200 parts of n-propanol and they were subjected to the grinding and dispersion treatment using the sand grinding mill for 10 hours, followed by mixing with 5 parts of a 10 % solution of polyvinyl butyral (#6000-C (trade mark), ex DENKI KAGAKU KOGYO K.K.) in methanol, thereby a dispersion B was prepared. The above dispersions A and B were mixed so that a final proportion in weight of oxytitanium phthalocyanine to dichlorotin phthalocyanine was 10/90 (dispersion C), 20/80 (dispersion D), 30/70 (dispersion E) or 50/50 (dispersion F). Each of the dispersions C to F was coated on an aluminum substrate and dried followed by subjecting to X-ray diffraction. The spectra are shown in Figs. 3 to 6. Each of the dispersions C to F was coated using a bar coater on a surface of a polyester film having an aluminium deposited layer followed by drying, thereby a charge generation layer with a dry thickness of 0.4 µm was prepared. On the charge generation layer, a solution of a hydrazone compound having the following formula (1), 14 parts of a hydrazone compound having the following formula (2), 1.5 part of a cyano compound having the following formula (3) and 10 parts of a polycarbonate resin (NOVALEX 7030A (trade name) ex Mitsubishi Chemical Industries) in a mixed solvent of 500 parts of 1,4-dioxane and 500 parts of tetrahydrofuran was coated using a film applicator followed by drying, thereby the charge transport layer with a dry thickness of 17 µm was formed. In this way, the photoreceptors C, D, E and F were prepared. Example 2 10 Parts of oxytitanium phthalocyanine whose X-ray spectrum in powder form was shown in Fig. 7 were added to 200 parts of n-propanol and they were subjected to the grinding and dispersion treatment using the sand grinding mill for 10 hours, followed by mixing with 5 parts of a 10 % solution of polyvinyl butyral (#6000-C (trade mark), ex DENKI KAGAKU KOGYO K.K.) in methanol, thereby a dispersion G was prepared. The above dispersion G and the dichlorotin phthalocyanine dispersion B prepared in Example 1 were mixed so that the final proportion of oxytitanium phthalocyanine to dichlorotin phthalocyanine was 80/20 (dispersion H), 50/50 (dispersion I) or 20/80 (dispersion J). Using each of the dispersions H to J, the procedures described in Example 1 were repeated, thereby photoreceptors H, I and J were prepared. Example 3 10 Parts of oxytitanium phthalocyanine whose X-ray spectrum in powder form was shown in Fig. 8 were added to 200 parts of n-propanol and they were subjected to the grinding and dispersion treatment using the sand grinding mill for 10 hours, followed by mixing with 5 parts of a 10 % solution of polyvinyl butyral (#6000-C (trade mark), ex DENKI KAGAKU KOGYO K.K.) in methanol, thereby a dispersion K was prepared. The above dispersion K and the dichlorotin phthalocyanine dispersion B prepared in Example 1 were mixed so that the final proportion of oxytitanium phthalocyanine to dichlorotin phthalocyanine was 80/20 (dispersion L), 50/50 (dispersion M) or 20/80 (dispersion N). Using each of the dispersions L to N, the procedures described in Example 1 were repeated, thereby photoreceptors L, M and N were prepared. Comparative Example Using each of the dispersions A, B, G and K prepared in Examples 1 to 3, the procedures described in Example 1 were repeated. In this way, photoreceptors A, B, G and K were prepared. Example 4 The procedures in the preparation of the dispersion B were repeated, except that dichlorotin phthalocyanine obtained in Reference Example 3 was used in place of that obtained in Reference Example 2, thereby a dispersion O was prepared. The dispersion A and the dispersion O were mixed so that a final proportion in weight of oxytitanium phthalocyanine to dichlorotin phthalocyanine was 70/30 (dispersion P), 50/50 (dispersion Q) and 30/70 (dispersion R). Using each of the dispersions P to R, the procedures described in Example 1 were repeated, thereby photoreceptors P, Q and R were prepared. Similarly, photoreceptor O was prepared using only the dispersion O. Test Example 1 Initial characteristics of the photoreceptors A to N prepared in Examples and Comparative Example were tested. Each photoreceptor was placed in an apparatus for determining characteristics of electrostatic copying paper (Model SP 428, ex KAWAGUCHI DENKI SEISAKUSHO K.K.) and charged in a dark so that a corona current was set to be 22 µA. Then, a charged potential (V 0 ) was determined. Next, a white light of 0.5 lux was continuously exposed to the photoreceptor. Then, an exposure amount (E 1/2 ) required to reduce a surface potential of - 450 V to - 225 V and a residual potential (V r ) after 10 seconds after the exposure were determined. The results are shown in Table 1. photoreceptor V 0 (V) E 1/2 (lux.sec) Vr (V) Ex. 1 C - 707 0.28 - 8 " D - 709 0.22 - 7 " E - 718 0.20 - 5 " F - 700 0.16 - 7 2 H - 695 0.30 - 8 " I - 690 0.35 - 5 " J - 710 0.36 - 3 3 L - 705 0.27 - 7 " M - 702 0.32 - 5 " N - 690 0.34 - 5 Comp.Ex. A - 674 0.14 -20 " B - 716 0.36 - 1 " G - 669 0.25 - 8 " K - 695 0.22 -10 As clear from the results in Table 1, the photoreceptor of the present invention had the sensitivity which can be freely controlled in a wide range. Simultaneously, the photoreceptor of the present invention showed the improved sensitivity over the comparative photoreceptor B and the improved residual potential (V r ) over the comparative photoreceptors A, G and K. Test Example 2 The photoreceptors D, I and M were placed in an apparatus for determining characteristics of the photoreceptor (Model EPA-8100, ex KAWAGUCHI DENKI K.K.) and charged using a scorotron at a peripheral speed of 260 mm/sec so that an initial potential was - 700 V, followed by exposing and erasing. Then, initial dark and light potentials were determined. Further, a cycle of charging, exposing and erasing was repeated 300,000 times. Then, the dark and light potentials were determined. The results are shown in Table 2. photoreceptor initial after 300,000 cycles dark potential (V) light potential (V) dark potential (V) light potential (V) D - 700 - 90 - 700 - 100 I - 700 - 100 - 680 - 115 M - 700 - 110 - 670 - 120 As clear from the results in Table 2, the photoreceptor of the present invention showed very little change in dark and light potentials after 300,000 cycles. It is concluded that the photoreceptor of the present invention has stable electrical properties. Test Example 3 The photoreceptors D and the comparative photoreceptor A were placed in the apparatus for determining characteristics of the photoreceptor (Model EPA-8100, ex KAWAGUCHI DENKI K.K.) and charged using a corotron so that a surface potential was - 700 V, followed by standing in the dark for 20 seconds. Again the surface potential was determined, from which a retention percentages of the potential was calculated. Further, the photoreceptor was subjecting to a cycle of charging using a scorotron at the peripheral speed of 260 mm/sec so that the initial potential was - 700 V, exposing and erasing. After the photorceptor was subjected to 20,000 cycles, the retention percentages of the potential was calculated again. The results are shown in Table 3. photoreceptor initial after 20,000 cycles D 89 (%) 87 (%) A 82 30 As clear from the results in Table 3, the photoreceptor of the present invention is excellent in potential retention, as compared with the comparative photoreceptor. Test Example 4 The photoreceptors O to R were subjected to the test described in Test Example 1. The results are shown in Table 4. photoreceptor V 0 (V) E 1/2 (lux.sec) V r (V) invention P - 833 0.15 - 16 " Q - 831 0.19 - 15 " R - 831 0.29 - 15 comparison O - 835 0.94 - 18 Further, spectral sensitivity of each of these photoreceptors was determined as follows. The photoreceptor was corona-charged in the dark and continuously exposed by a monochromatic light having the wavelength of 500 to 900 nm. Then, an exposure amount required to reduce a surface potential from - 700 V to - 350 V was determined and expressed in cm 2 /µJ. The higher the numerical value is, the hither the sensitivity is. The results are shown in Fig. 10.

Claims: An electrophotographic photoreceptor comprising at least a photosensitive layer on a conductive base, said photosensitive layer containing oxytitanium phthalocyanine and dihalogenotin phthalocyanine. The photoreceptor according to claim 1, wherein oxytitanium phthalocyanine shows a maximum peak at Bragg angle (2 ± 0.2°) of 27.3° in the X-ray diffraction spectrum. The photoreceptor according to claim 1, wherein oxytitanium phthalocyanine shows major peaks at Bragg angle (2 ± 0.2°) of 9.2°, 13.1°, 20.7°, 26.2° and 27.1° in the X-ray diffraction spectrum. The photoreceptor according to claim 1, wherein oxytitanium phthalocyanine shows major peaks of 7.6°, 10.2°, 12.6°, 13.2°, 15.2°, 16.2°, 18.4°, 22.5°, 24.2°, 25.4° and 28.7° in the X-ray diffraction spectrum. The photoreceptor according to any one of claims 1 to 4, wherein dihalogenotin phthalocyanine shows major peaks at Bragg angle (2 ± 0.2°) of 8.4°, 12.2°, 13.8°, 19.1°, 22.4°, 28.2° and 30.0° in the X-ray diffraction spectrum. The photoreceptor according to any one of claims 1 to 4, wherein dihalogenotin phthalocyanine shows major peaks at Bragg angle (2 ± 0.2°) of 8.4°, 11.2°, 14.5°, 16.9°, 19.6°, 25.7° and 27.1° in the X-ray diffraction spectrum. The photoreceptor according to claim 1, wherein the photosensitive layer comprises at least a charge generation layer and a charge transport layer, oxytitanium phthalocyanine and dihalogenotin phthalocyanine being contained in the charge generation layer. The photoreceptor according to claim 7, wherein the thickness of the charge generation layer is 0.1 to 2 µm. The photoreceptor according to claim 7 or 8, wherein the thickness of the charge transport layer is 10 to 60 µm. The photoreceptor according to claim 1, wherein the photosensitive layer is a layer comprising a charge transport material, a binder resin, oxytitanium phthalocyanine and dihalogenotin phthalocyanine, oxytitanium phthalocyanine and dihalogenotin phthalocyanine being dispersed in the binder resin. The photoreceptor according to claim 10, wherein the thickness of the photosensitive layer is 10 to 70 µm. The photoreceptor according to claim 11, wherein a proportion of dihalogenotin phthalocyanine to oxytitanium phthalocyanine is 95:5 to 10:90 in weight.

Inventors: NOTSU SHUSUKE, NOZOMI MAMORU, NOTSU, SHUSUKE, NOZOMI, MAMORU, NOZOMI, MAMORU, A-301 SAKURADAI-APAATO,
Applicants: MITSUBISHI CHEM CORP, MITSUBISHI CHEMICAL CORPORATION
Application year: 1992
Main classification: G03G5
IPC codes: C09B67, G03G5