This invention relates to a charge stabilization method for a photosensitive member in an electrophotographic process, and more particularly to an electrophotographic process using as photosensitive members amorphous silicon containing hydrogen (a-Si:H). The electrophotographic process includes charging and exposing steps for making latent images on a photosensitive member, developing and transferring steps for making reproductions from images on the photosensitive member, and discharging and cleaning steps.
Generally, the photosensitive member is employed repeatedly in the electrophotgraphic process to obtain a plurality of image reproductions. However, in order to obtain good image quality and reproduction of images continuously, it is desirable that the electrophotographic apparatus have sufficient adaptability relative to the photosensitive member to perform effective charging, exposing, discharging and the like and that any change in performance of the system resulting from fatigue of the photosensitive member resulting from the repeated use thereof, is reduced as much as possible.
Zinc oxide (ZnO), cadmium sulfide (CdS), organic semiconductors (OPC) such as polyvinyl carbazole (PVK), and amorphous selenium (a-Se) system materials have been known as photosensitive materials for electrophotography. However, ZnO has a problem associated with the durability since the photosensitivity is low and the light fatigue effect is high. Because the photosensitive film of CdS is produced by dispersing CdS in a binder, it is difficult to control the characteristics of the film, which results in a lower sensitivity. In addition, CdS films have a durability problem since the surface of the film is made porous to reduce its resistance to humidity. OPCs have had great promise because of the diversity of the available materials. However, they have many disadvantages including lack of stability resulting from the ozone generated by corona discharge, low wear resistance, and lack of stability resulting from external factors such as heat, light and the like. In comparison with these photosensitive materials, a-Se system materials are widely used at present, since they provide the advantages of high sensitivity, low fatigue and long life. However, they have the disadvantages that the glass transition temperature (Tg) and the crystallization temperature (Tc) are quite low, except for photosensitive layers made of As.sub.2 Se.sub.3 materials, and that the light fatigue effect is somewhat high in case of the photosensitive layer of As.sub.2 Se.sub.3 materials.
Recently, a-Si:H materials have been developed (e.g. Japanese Published Application No. 54-78135) as photosensitive films which do not have the above-mentioned disadvantages of known photosensitive materials. Such a-Si:H photosensitive materials are provided with excellent characteristics with respect to the sensitivity, heat resistance and wear resistance.
However, although a-Si:H materials have good performance as described above, there has been little information about the application of such materials in the electrophotographic process. As a result of a careful investigation, the present inventors have found that the charging performance of a-Si:H photosensitive films depends to a large extent upon the irradiation light to be used. That is, such films have the disadvantage that, because the light fatigue of the material resulting from irradiation light is high, the charge acceptance is reduced by repeated use of the photosensitive film, causing the reproduction or image quality to deteriorate.