1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and to a process cartridge and an electrophotographic apparatus that include the electrophotographic photosensitive member.
2. Description of the Related Art
An electrophotographic photosensitive member including an organic photoconductive material is the most widely used electrophotographic photosensitive member installed in electrophotographic apparatuses.
In an electrophotographic process, the surface of the electrophotographic photosensitive member installed in an electrophotographic apparatus is brought into contact with various members such as a developer, a charging member, a cleaning blade, paper, and a transfer member (hereafter, also referred to as “contact members and the like”). Therefore, the electrophotographic photosensitive member becomes abraded and thus damaged due to the contact with these contact members and the like, which may cause degradation of image quality. Thus, a surface layer of the electrophotographic photosensitive member is required to have an enhanced mechanical strength.
In order to enhance the mechanical strength of the surface layer of an electrophotographic photosensitive member, a method in which the mechanical strength of a resin constituting the surface layer is increased has been proposed. Japanese Patent Laid-Open Nos. 10-20514 and 2006-53549 disclose that the mechanical strength of the surface layer of an electrophotographic photosensitive member may be enhanced when the surface layer includes a particular polyester resin.
As a result of studies, the inventors of the present invention have found that the use of the polyester resin that are disclosed in Japanese Patent Laid-Open Nos. 10-20514 and 2006-53549 and the charge-transporting substance having a particular structure enhance the mechanical strength of the surface layer, but on the other hand, may cause degradation of image quality when the electrophotographic photosensitive member is used repeatedly in a high-temperature, high-humidity environment and thus there is still room for further improvement.