Photosensitive member for electrophotography

Abstract: A photosensitive member for electrophotography comprising a photosensitive layer on a conductive substrate, the photosensitive layer containing as a binder resin a modi­ fied polycarbonate resin having the repeating structural units represented by the following general formulae (1) and (2): wherein R¹ and R² are selected from a hydrogen atom, an alkyl group having 1-3 carbon atoms and a halogen atom, at least one of R¹ and R² being the alkyl group, and R³ and R⁴ inde­ pendently represent an alkyl group having 1-3 carbon atoms or a hydrogen atom, and wherein R³ and R⁴ are the same as defined in the above formula (1). The ratio of the structural unit (1) to (2) is at least 20:80. This photosensitive member is highly resistant to mechanical wear and the deterioration of sensitivity and chargeability.

Description: BACKGROUND OF THE INVENTION The present invention relates to an electrophotographic photosensitive member with excellent durability containing particular binder resins. Since electrophotographic technology can provide instantaneous and high-quality images, it has been finding wider applications not only in copiers but also in various types of printers. For photosensitive members which are the core of the electrophotographic technology, conventional inorganic photoconductive materials such as selenium, arsenic-selenium alloys, cadmium sulfide or zinc oxide are being used, and recently development has been made to provide photosensitive members made of organic photoconductive materials because of their advantages such as small weight, good film-forming properties and easiness to production. Known as organic photosensitive members are so-called dispersion-type photosensitive members having photoconductive fine powders dispersed in binder resins, and double layer-type photosensitive members having a charge carrier-generating layer and a charge carrier transfer layer on a conduc tive substrate. Since the latter type is enjoying high sertivity and durability, it is widely used. However, despite the fact that the conventional organic, double layer-type photosensitive members have good electric properties such as sensitivity and chargeability, they are susceptible to mechanical wear and surface damage by such load as abrasion by a cleaning member. The surface wear and damage of a photosensitive member leads to deteriorated copy or print images. Therefore, they have only limited durability when actually used in copiers or printers. Conventionally used for charge carrier transfer layers as binder resins are thermoplastic resins such as polycarbonate resins, acrylic resins, methacrylic resins, polyester resins, polystyrene resins, silicone resins, epoxy resins or polyvinyl chloride resins and various curable resins. Usually, the charge carrier transfer layer is made of a solid solution of the binder resin and a charge carrier transfer material, and the amount of this charge carrier transfer material doped is considerably large. Thus the charge carrier transfer layer does not have a sufficient surface strength. As a result, when it is used for a process employing a blade cleaning method, it provides images deteriorated by surface wear and damage after producing several thousands to about ten thousand of copies, making it inevitable to exchange the photosensitive member. Among these binder resins, polycarbonate resins have relatively excellent mechanical properties, so that they enjoy relatively good durability. However, commercially available polycarbonate resins which are usually employed have poor solution stability because they are crystalline. Accordingly, although it provides a uniform solution in the initial stage, crystallization gradually takes place, resulting in the increase in gelation with time. When such solution is applied for preparing a photosensitive layer, a uniform layer is hard to obtain, resulting in low productivity of the photosensitive layer. In addition, the photosensitive members containing commercially available polycarbonate resins as binders are still unsatisfactory in terms of mechanical durability. JP-A-60-172 045 discloses a photosensitive member for electrophotography comprising a photosensitive layer containing a modified polycarbonate resin selected from the group consisting of Formula A and B wherein R 1 and R 2 are independently hydrogen, substituted or unsubstituted aliphatic, or a substituted or unsubstituted hydrocarbon ring, provided that at least one of R 1 and R 2 has at least 3 carbon atoms, Z represents a group of atoms necessary to constitute a substituted or unsubstituted carbon ring or a substituted or unsubstituted heterocyclic ring, R 3 to R 10 in Formulas A and B are independently hydrogen, halogen, substituted or unsubstituted aliphatic, or a substituted or unsubstituted hydrocarbon ring, and n is a number from 10 to 1000, as a binder resin on a conductive substrate, wherein the binder polymer must have a bulky group on the center carbon atom of the bisphenol A residue constituting the polycarbonate resin. EP-A-0 032 431 discloses a photoconductive composition for electrophotograhic processes comprising a plurality of aggregate photoconductive particles containing an aggregating polymer and a pyrilium dye dispersed in an electrically insulating polymeric binder, wherein the polymeric binder is a blend of (a) 50-99.9 wt.% of a non-aggregating polymer and (b) 0.1-50.0 wt.% of an aggreagting polymer having repeating units according to the structure: wherein R 1 and R 2 , taken separately, are the same or different, ana represent hydrogen or alkyl having from 1 to 4 carbon atoms; or R 1 and R 2 taken together, represent the atoms necessary to form a cyclic hydrocarbon radical having up to 14 ring carbon atoms; and R 3 and R 4 represent hydrogen or alkyl as defined for R 1 and R 2 provided that when R 1 and R 2 are both methyl, R 3 and R 4 must both be alkyl having from 1 to 4 carbon atoms. OBJECT AND SUMMARY OF THE INVENTION An object of the present invention is, therefore to provide an electrophotographic photosensitive member having a photosensitive layer with excellent durability and which can be produced efficiently with extremely few defects. As a result of intense research on binder resins capable of providing such photosensitive layers, the inventors have found that a particular modified polycarbonate resin has sufficient solution stability and good mechanical properties. The present invention has been made based on this finding. That is, the gist of the present invention consists in an electrophotographic photosensitive member comprising a photosensitive layer containing a binder resin composed of a modified polycarbonate resin on a conductive substrate, which is characterized in that the modified polycarbonate resin has the repeating structural unit represented by the following general formula (1) wherein R 1 and R 2 are selected from a hydrogen atom, an alkyl group having 1 to 3 carbon atoms and a halogen atom, at least one of R 1 and R 2 being the alkyl group. DETAILED DESCRIPTION OF THE INVENTION The present invention will be explained in detail below. The photosensitive member according to the present invention is formed on a conductive substrate. The conductive substrates which may be used include metal sheets made, for example, aluminum, stainless steel, copper or nickel, and insulating substrates of polyester films and papers coated with conductive layers of, e.g., aluminum, copper, palladium, tin oxide or indium oxide. Formed on such conductive substrate is a dispersion-type or double layer-type photosensitive layer with a known barrier layer therebetween, if ne-cessary. The barrier layer may be formed from metal oxides such as aluminum oxide and resins such as polyamides, polyurethane, cellulose and casein. In the case of the dispersion-type photosensitive member, the photoconductive materials which may be used include selenium and its alloys, cadmium sulfide and other inorganic photoconductive materials, and organic pigments such as phthalocyanine pigments, azo pigments quinacridone pigments, indigo pigments, perylene pigments, polycyclic quinone pigments and benzimidazole pigments. In the case of the double layer-type photosensitive member, the charge carrier-generating layer may be made of various types of the above-described photoconductive materials, in the form of a uniform layer thereof or a layer of fine particles of these materials bonded together by various binder resins such as polyvinyl acetate, polyacrylates, polymethacrylates, polyesters, polycarbonates, polyvinyl butyral, phenoxy resins, cellulose esters, cellulose ethers, urethane resins and epoxy resins. This layer usually has a thickness of 0.1-1 µm, preferably 0.15-0.6 µm. Usable as the charge carrier transfer materials in the charge carrier transfer layer are electron-attracting compounds such as 2,4,7-trinitrofluorenone and tetracyanoquinodimethane; and electron-donating materials such as heterocyclic compounds such as carbazole, indole, imidazole, oxazole, thiazole, oxadiazole, pyrazole, pyrazoline and thiadiazole, aniline derivatives, hydrazine derivatives, hydrazones, and polymers having these compounds in their backbones or pendant groups. Particularly preferable among them are hydrazone compounds represented by the general formulae (2) and (3): wherein R 5 represents an alkyl group, a substituted alkyl group or an aralkyl group; R 6 represents an alkyl group, an allyl group, a substituted alkyl group, a phenyl group, a naphthyl group or an aralkyl group; and Z 1 represents a hydrogen atom, an alkyl group, an alkoxy group or a halogen atom (see Japanese Patent Laid-Open No. 54-150128), and wherein X 1 , Y 1 and Z 2 respectively represent a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenoxy group or an arylalkoxy group; R 7 represents a hydrogen atom, a lower alkyl group, an allyl group, a phenyl group or an aralkyl group; m and 1 represent 1 or 2; and p represents 0 or 1. They may be used alone or in combination. Further, the charge carrier transfer layer according to the present invention may contain known additives such as plasticizers for improving its film-forming ability, flexibility and mechanical strength, and additives for suppressing the accumulation of a residual potential. The modified polycarbonate resin according to the present invention contains the repeating structural unit represented by the above general formula (1). It may further contain the repeating structural unit represented by the following general formula (4): wherein R 3 and R 4 independently represent an alkyl group having 1 to 3 carbon atoms or a hydrogen atom. The ratio of the repeating structural unit (1) to the repeating structural unit (4) is at least 20:80, preferably at least 30:70. The modified polycarbonate resin usually has a viscosity-average molecular weight of about 10,000 to 50,000. Such modified polycarbonate resin may be advantageously used as a binder resin for the above photosensitive layer. In case where the photosensitive layer is a double layer type, it may be used as a binder for either the charge carrier-generating layer or the charge carrier transfer layer, but it is preferably used as a binder for the charge carrier transfer layer. The modified polycarbonate resin according to the present invention may be synthesized easily by a usual method, using two or more of phenolic compounds selected from the general formulae (5) and (6): wherein R 1 and R 2 are the same as defined above, and at least one of R 1 and R 2 is an alkyl group, and wherein R 3 and R 4 are the same as defined above. The ratio of the phenolic compound represented by the general formula (5) to the phenolic compound represented by the general formula (6) is at least 20:80, preferably at least 30:70, according to the above-described composition of the modified polycarbonate resin to be prepared. Specific examples of the phenolic compound represented by the general formula (5) are bis(hydroxyphenyl)alkanes such as 2,2-bis(4-hydroxy-3-methylphenyl)-propane, 2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,2-bis(4-hydroxy-3-chloro-5-methylphenyl)propane or 2,2-bis[4-hydroxy-3-(2-propyl)-phenyl]propane. Specific examples of the phenolic compound represented by the general formula (6) are bis(hydroxyphenyl) alkanes such as bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxy phenyl)ethane, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)butane. The modified polycarbonate resin according to the present invention may be prepared specifically by adding an alkali aqueous solution or pyridine, as an acid acceptor to the above phenolic compound in the presence of an inert solvent such as methylene chloride or 1,2-dichloroethane and introducing phosgene thereinto to cause a reaction therebetween. In a case where the alkali aqueous solution is used as an acid acceptor, the use of tertiary amines such as trimethylamine and triethylamine or quaternary ammonium compounds such as tetrabuthylammonium chloride and benzyltributylammonium bromide as a catalyst would increase the reaction rate. Monovalent phenol such as phenol and p-t-butylphenol may be included as a molecular weight modifier. The catalyst may exist from the beginning, or it may be added after the formation of an oligomer to polymerize it. The copolymerization of two or more phenolic compounds according to the present invention may be carried out by the following methods: (a) Two or more phenolic compounds are reacted with phosgene simultaneously from the beginning to cause copolymerization thereof; (b) One of them is first reacted with phosgene, and after the reaction has proceeded to some extent the other is introduced thereinto to cause the polymerization reaction; or (c) They are separately reacted with phosgene to prepare oligomers which are in turn reacted with each other to provide the desired copolymer. The modified polycarbonate resin thus prepared according to the present invention is highly soluble in organic solvents, showing high solubility in non-halogenous solvents such as ethyl acetate, 1,4-dioxane, tetrahydrofuran. Since coating solutions can be prepared therefrom by using these solvents, there would be no problem with respect to safety and health. The present invention will be explained in further detail by means of the following Reference Examples and Examples, but the present invention is not limited thereto. Incidentally, the term "part" used in the following Reference Examples and Examples means "part by weight." Reference Example 1 (a) Preparation of polycarbonate oligomer 2,2-bis(4-hydroxy-3-methylphenyl)propane 100 parts Sodium hydroxide 50 parts Water 870 parts Methylene chloride 530 parts p-t-butylphenol 2.0 parts A mixture of the above components was introduced into a reactor with a stirrer, and stirred at 800rpm. 70 parts of phosgene was blown thereinto over 2 hours to cause the interfacial polymerization. After completion of the reaction, only a solution of the resulting polycarbonate oligomer in methylene chloride was collected. The analysis of the collected solution of the oligomer in methylene chloride provided the following results: The oligomer solution obtained by the above method is called "oligomer solution-A" hereinafter. (b) Preparation of polycarbonate oligomer 16.6 % bisphenol A sodium salt aqueous solution prepared by dissolving bisphenol A in a sodium hydroxide aqueous solution 100 parts p-t-butylphenol 0.23 part Methylene chloride 40 parts Phosgene 7 parts A mixture of the above composition was quantitatively introduced into a pipe reactor to cause an interfacial polymerization. By separating the reaction mixture solution, only a solution of the resulting polycarbonate oligomer in methylene chloride was collected. The oligomer solution in methylene chloride was analized. The results are as follows: Concentration of oligomer 24.5 weight % Concentration of chloroformate end group 1.3 N Concentration of phenolic hydroxyl end group 0.3 N The oligomer solution obtained by the above method is called "oligomer solution-B" hereinafter. Reference Example 2 (a) Preparation of modified polycarbonate copolymer resin Oligomer solution-A 80 parts Oligomer solution-B 180 parts Methylene chloride 100 parts p-t-butylphenol 0.3 part The above components were introduced into a reactor equipped with a stirrer, and subjected to stirring at 550rpm. Further, an aqueous solution of the following composition was charged thereinto to carry out an interfacial polymerization for 3 hours: Sodium hydroxide 14 parts Triethylamine 0.07 part Water 80 parts The reaction mixture was separated to collect a solution of the resulting polycarbonate resin in methylene chloride, which was then washed with water, a hydrochloric acid solution and water in this order. Finally methylene chloride was evaporated to isolate the resin. This resin (Resin No. C) had an average molecular weight of 15,500. And the NMR analysis revealed that the amount of bisphenol A was 70.8 weight %. Incidentally, the average molecular weight was obtained by calculation of the following equations (1) and (2) from ηsp determined by measurement at 20°C of a solution of 6.0 g/l of the polymer in methylene chloride. ηsp/C=[η](1+K′ηsp) [η]=KM α wherein C: Polymer concentration (g/l) [η]: Intrinsic viscosity K′=0.28 K=1.23x10 -5 α=0.83 M: Average molecular weight (b) Preparation of modified polycarbonate resin Oligomer solution-A 260 parts Methylene chloride 100 parts p-t-butylphenol 0.3 part The above components were introduced into a reactor equipped with a stirrer, and subjected to stirring at 550rpm. Further, an aqueous solution of the following composition was charged thereinto to carry out an interfacial polymerization for 3 hours: Sodium hydroxide 14 parts Triethylamine 0.07 part Water 80 parts The reaction mixture was separated to collect a solution of the resulting polycarbonate resin in methylene chloride, which was then washed with water, a hydrochloric acid solution and water in this order. Finally methylene chloride was evaporated to isolate the resin. This resin (Resin No. F) had a viscosity-average molecular weight of 44,200. Example 1 To compare the modified polycarbonates shown in Table 1 with a commercially available polycarbonate (IUPILON S-1000 manufactured by Mitsubishi Gas Chemical Company Inc.) with respect to solution stability, their 10-% solutions in tetrahydrofuran were prepared and left to stand at room temperature for one month to measure their solution viscosities. As a result, the solution of the commercially available polycarbonate became completely cloudy after 10 days, which means that gelation took place. On the other hand, none of the modified polycarbonates (A-D) of the present invention became cloudy even after one month, meaning that no gelation took place, and no change was observed in their solution viscosities. Example 2 The comparison of the modified polycarbonates shown in Table 2 with the commercially available polycarbonate (IUPILON S-1000 manufactured by Mitsubishi Gas Chemical Company Inc.) was carried out with respect to solution stability. Their 10-% solutions in tetrahydrofuran were prepared and left to stand at room temperature for one month to measure their solution viscosities. As a result, the solution of the commercially available polycarbonate became completely cloudy after 10 days, which means that gelation took place. On the other hand, none of the modified polycarbonates (E and F) of the present invention became cloudy even after one month, meaning that no gelation took place, and no change was observed in their solution viscosities. Example 3 10 parts of a bisazo compound having the structure shown below, 5 parts of a phenoxy resin (PKHH manufactured by Union Carbide) and 5 parts of a polyvinyl butyral resin (BH-3 manufactured by Sekisui Chemical Co., Ltd.) were mixed with 100 parts of 4-methoxy-4-methylpentanone-2, and subjected to a pulverization and dispersion treatment by a sand grind mill. The resulting dispersion was applied in a dry thickness of 0.4 g/m 2 by a film applicator to an aluminum vapor deposition layer formed on a 100-µm-thick polyester film, and dried. The charge carrier-generating layer thus obtained was coated with a solution of 90 parts of N-methylcarbazole-3-aldehydediphenylhydrazone, 100 parts of the modified polycarbonate resin A shown in Table 1 and 4.5 parts of a cyano compound having the following structure: in 900 parts of 1,4-dioxane, in a dry thickness of 17 µm to form a charge carrier transfer layer. Thus the double layer-type photosensitive member 2-A was prepared. The photosensitive member thus prepared was measured with respect to their properties. First, the photosensitive member moving at a constant velocity of 150 mm/sec was subjected to corona discharge in the dark so that corona current of 22 A flew in the photosensitive member, and the potential of the charged photosensitive member was measured to determine an initial charge voltage V 0 . It was then exposed to a white light of 5 lux to determine the amount of light exposure (E 1/2 ) necessary for reducing the surface potential of the photosensitive member by half from the initial charge voltage. The results are shown in Table 3. Examples 4 to 6 Example 3 was repeated except for using the modified polycarbonate resins B, C and D shown in Table 1 in place of the modified polycarbonate resin used in Example 3 to prepare photosensitive members 3-B, 4-C and 5-D. Their properties were measured as in Example 3. The results are shown in Table 3. Comparative Example 1 Example 3 was repeated except for using a commercially available polycarbonate (IUPILON S-1000 manufactured by Mitsubishi Gas Chemical Co., Inc.) in place of the modified polycarbonate in Example 3 to prepare a photosensitive member 1-I. The properties of this photosensitive member was measured as in Example 3. The results are shown in Table 3. As is clear from Table 3, the photosensitive members of the present invention are superior to the photosensitive member containing the commercially available polycarbonate in terms of electric properties. Examples 7 and 8 Example 3 was repeated except for using the modified polycarbonate resins E and F shown in Table 2 in place of the modified polycarbonate resin used in Example 3 to prepare photosensitive members 6-E and 7-F. Their properties were measured as in Example 3. The results are shown in Table 4. As is clear from Table 4, the photosensitive members of the present invention are superior to the photosensitive member containing the commercially available polycarbonate in terms of electric properties. Example 9 A mirror-finished aluminum cylinder was dipped in the pigment dispersion in Example 3 so that a charge carrier-generating layer of 0.4µm in dry thickness was prepared. This was then dipped in a solution of the charge carrier transfer material and the modified polycarbonate resin A in 1,4-dioxane used in Example 3, so that it was coated with a charge carrier transfer layer of 20µm in dry thickness. The drum-shaped photosensitive member thus prepared is called 10-A. To evaluate the durability of this photosensitive member, this photosensitive member was installed in a commercially available copier utilizing a blade cleaning system, and subjected to a copy test. As a result, even after producing 40,000 copies, no deep damage was appreciated on the surface of the photosensitive member, and the copy images suffered from substantially no black streaks which were considered to be caused by the damage of the photosensitive member. Thus good copy images were obtained. Further, it had extremely stable potential properties as shown in Table 5, which means that it has sufficient durability. Photosensitive Member 10-A Voltage in Dark Area (V D ) Voltage in Light Area (V L ) At start 650V 115V After Producing 40,000 Copies 590V 95V Example 10 A mirror-finished aluminum cylinder was dipped in the pigment dispersion in Example 3 so that a charge carrier-generating layer of 0.4µm in dry thickness was prepared. This was then dipped in a solution of the charge carrier transfer material and the modified polycarbonate resin F in 1,4-dioxane used in Example 7, so that it was coated with a charge carrier transfer layer of 20µm in dry thickness. The drum-shaped photosensitive member thus prepared is called 11-F. To evaluate the durability of this photosensitive member, this photosensitive member was installed in a commercially available copier utilizing a blade cleaning system, and subjected to a copy test. As a result, even after producing 40,000 copies, substantially no wear by the cleaning blade and no deep damage were appreciated on the surface of the photosensitive member, and the copy images suffered from substantially no black streaks which were considered to be caused by the damage of the photosensitive member. Thus good copy images were obtained. Therefore, it may be concluded that it has excellent mechanical properties. It also had extremely stable potential properties as shown in Table 6, which means that it has sufficient durability. Photosensitive Member 11-F Voltage in Dark Area (V D ) Voltage in Light Area (V L ) At start 700V 120V After Producing 40,000 Copies 670V 100V As is clear from the above results, the modified polycarbonate of the present invention has excellent properties as a binder resin for photosensitive members for electrophotography. Specifically, the modified polycarbonate resin used according to the present invention has excellent solubility and solution stability, so that the photosensitive member with extremely few coating defects can be provided by applying a solution thereof. Thus, the productivity of the photosensitive member is greatly increased. And even if the photosensitive member containing the modified polycarbonate resin of the present invention is used repeatedly, it hardly suffers from the deterioration of sensitivity and chargeability. Therefore, it can enjoy extremely good durability. Further, the photosensitive member of the present invention may be used for wide varieties of applications not only in electrophotographic copiers but also in printers using as light sources laser, LED, LCD, CRT, etc.

Claims: An electrophotographic photosensitive member comprising a photosensitive layer containing a binder resin composed of a modified polycarbonate resin on a conductive substrate, characterized in that the modified polycarbonate resin has the repeating structural unit represented by the following general formula (1) wherein R 1 and R 2 are selected from a hydrogen atom, an alkyl group having 1 to 3 carbon atoms and a halogen atom, at least one of R 1 and R 2 being the alkyl group. The electrophotographic photosensitive member according to claim 1, characterized in that said modified polycarbonate resin further contains the repeating structural unit represented by the following general formula (2) wherein R 3 and R 4 independently represent an alkyl group having 1 to 3 carbon atoms or a hydrogen atom, the ratio of the repeating structural unit of the general formula (1) to that of the general formula (2) being at least 20:80. The electrophotographic photosensitive member according to claim 1 or 2, characterized in that said modified polycarbonate resin has a viscosity-average molecular weight of 10,000-50,000. The electrophotographic photosensitive member according to claim 1 or 2, characterized in that said photosensitive member is constituted by a charge carrier-generating layer and a charge carrier transfer layer, and said modified polycarbonate resin is contained as a binder resin in said charge carrier transfer layer.

Inventors: NOZOMI MAMORU, NUKUI MASAHIRO, OHTSUKA SHIGENORI, SASAKAWA SETSUKO, URABE HIROSHI, NOZOMI, MAMORU, NUKUI, MASAHIRO, OHTSUKA, SHIGENORI, SASAKAWA, SETSUKO, URABE, HIROSHI, URABE, HIROSHI 201 DAINI-YURIGAOKAAPARTMENT 8-12,
Applicants: MITSUBISHI CHEM CORP, MITSUBISHI CHEMICAL CORPORATION
Application year: 1987
Main classification: G03G5
IPC codes: G03G5