1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor. The invention also is concerned with a method of producing the electrophotographic photoreceptor.
2. Description of the Prior Art
Various organic and inorganic electrophotographic photosensitive materials have been proposed, among which a dual-layer type photoreceptor having a charge generating layer and a charge transport layer is becoming a matter of concern as a photoreceptor having high photosensitivity. In this type of photoreceptor, the charge generating layer is made of a charge generating compound such as a phthalocyanine pigment-type organic compound as disclosed in Japanese Patent Unexamined Publication No. 59-15253 or inorganic compounds of tellurium-arsenic-selenium alloy type as disclosed in Japanese Patent Unexamined Publication No. 50-15137, as well as various other known compounds. On the other hand, various compounds are usable as the charge-transport substance, such as compounds of of poly-N-vinylcarbazole as shown in Japanese Patent Unexamined Publication No. 52-77730 or of pyrazoline derivative type as disclosed in Japanese Patent Unexamined Publication No. 49-105537. These charge generating and charge transport compounds have been actually put into practical use in photoreceptors.
Meanwhile, a high-speed electrophotographic printers making use of a laser beam have been put into practical use. This type of printer is capable of performing printing at a high speed, while reducing the size of the light source unit and, hence, the size of the whole printer, particularly when a laser diode is used as the light source. It is also to be noted that organic photoreceptors are disposable by users themselves.
The known organic photoreceptors, on the other hand, has weak durability to abrasion as compared with inorganic photosensitive materials In consequence, the photoconductive layer is worn down to reduce the thickness thereof, so that the electrophotographic characteristics cannot have a long life. In order to overcome this problem, it has been proposed to form a protective film on the surface of the photoreceptor to protect it from mechanical damaging force For instance, Japanese Patent Unexamined Publication No. 58-83857 discloses a photoreceptor in which a selenium photosensitive layer is covered by a protective layer made of an electron donor and a binder. In this photoreceptor, a polycarbonate resin, polyester resin or a polyurethane resin is used as the binder used in the protective layer. Japanese Patent Unexamined Publication Nos. 61-22345 and 61-27550 propose photoreceptors having protective layers made of alkylether melamine formaldehyde. The protective layers of this material, however, tend to increase the level of the residual potential.
In use, a corona discharge makes the surface of the photosensitive material to cause the surface thereof to hold electric charges. Therefore, the photoreceptor, particularly when it is of organic type, tends to exhibit a degradation (oxidation) at the surface thereof during long use, increasing a tendency for the surface to be wetted with moisture. The wetted surface of the organic photosensitive material tends to allow an easy leakage of electric charges, resulting in a lowered resolution of printed images and other defects.
Photoreceptors using fluorine compounds are also known. For instance, Japanese Patent Unexamined Publication No. 62-206559 discloses an electrophotographic photoreceptor having a surface layer containing a fluorine oligomer compound. Japanese Patent Unexamined Publication No. 55-7762 discloses a photoreceptor made of a material containing a fluorine-containing compound. Japanese Patent Unexamined Publication No. 61-95358 discloses an image forming member provided with a resin layer containing fluorine polymer. Japanese Patent Unexamined Publication No. 58-23031 discloses an image carrier containing a surfactant having long-chain fluorinated alkyl group. An image carrier having a surface layer made of a material including a fluorine-containing silane coupling agent is proposed in Japanese Patent Unexamined Publication No. 61-205950.
The known organic electrophotographic photoreceptors mentioned above generally exhibit inferior wear-resistance characteristics due to small surface hardness as compared with inorganic photosensitive materials. In order to overcome this problem, Japanese Patent Unexamined Publication Nos. 58-83857, 61-22345 and 61-27550 propose to use resins having high levels of surface hardness. Such a countermeasure, however, is still unsatisfactory.
Another problem encountered with the known organic photoreceptors is that surfaces of these materials tend to be wetted due to absorption of water as a result of deterioration (oxidation) of the surfaces caused by a corona discharge during the use, with the result that the resolution of the print image is lowered.
Known photoreceptors containing fluoride component also are still unsatisfactory.
Arts shown in Japanese Patent unexamined Publication Nos. 62-206559 and 61-95358 cannot provide required strength of the coating layer because the mechanical strength of the organic coating layer is lowered as a result of use of a fluorine compound as the material of the binder of the organic coating material.
Arts shown in Japanese Patent Unexamined Publication Nos. 55-7762, 58-23031 and 61-205950 cannot provide sufficient lubrication effect because the fluorine compounds used therein are composed of perfluoroalkyl groups having short fluorine chains.