Photoconductive materials (charge generation materials and charge transport materials) used for an electrophotographic photosensitive member installed in an electrophotographic apparatus include inorganic photoconductive materials such as selenium, cadmium sulfide and zinc oxide. Recently, however, from the viewpoint of no pollution, high productivity and ease in material design, organic photoconductive materials have been actively developed.
An electrophotographic photosensitive member using an organic photoconductive material (organic electrophotographic photosensitive member) generally has a photosensitive layer formed by applying, on a support, a coating solution obtained by dissolving and dispersing an organic photoconductive material and a binder resin in a solvent and drying the same. Regarding the layer structure of the photosensitive layer, a multi-layer type (regular-layer type) photosensitive layer in which a charge generation layer and a charge transport layer are stacked in that order from the support side is common.
Although electrophotographic photosensitive members using an organic photoconductive material have the above-described advantages, not all properties that electrophotographic photosensitive members are required to possess have been highly satisfied, and further improvement in quality of output images and durability of the electrophotographic photosensitive members are desired.
For improvement in image qualities, in order to further increase the resolution of output images, use of light having a wavelength shorter than conventionally used light as exposure light (image exposure light) for irradiating an electrophotographic photosensitive member has been recently proposed (Japanese Patent Application Laid-Open No. H09-240051, etc.).
In addition, from the fact that transmittance of layers against exposure light influences the sensitivity of an electrophotographic photosensitive member, Japanese Patent Application Laid-Open No. 2000-105471, for example, discloses a technique of forming a charge transport layer of a multi-layer type (regular-layer type) photosensitive layer into a layer having a high transmittance against short wavelength exposure light. More specifically, by using a compound having a specific structure as a charge transport material and polycarbonate resin (bisphenol Z polycarbonate) as a binder resin, a charge transport layer having a high transmittance against short wavelength exposure light is formed.
On the other hand, for improving durability, polycarbonate resins have been commonly used as a binder resin for the surface layer of an electrophotographic photosensitive member. Recently, however, it has been proposed to further improve durability of electrophotographic photosensitive members by using a polyarylate resin which has a higher mechanical strength than polycarbonate resin as a binder resin for the surface layer (Japanese Patent Application Laid-Open No. H10-039521, etc.). Polyarylate resins are examples of aromatic dicarboxylic acid polyester resins.
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