1.  Technical Field
The present invention relates to an electrophotographic photoreceptor, a process cartridge and an image forming apparatus. 
2.  Related Art
Image formation by an electrophotographic system is widely used in the fields of copying machines, laser beam printers, and the like, since this technique has such advantages as high speed and high quality printing.  As an electrophotographic photoreceptor used in an image forming apparatus (hereinafter sometimes simply referred to as a “photoreceptor”), electrophotographic photoreceptors employing an organic photoconductive material, having such advantages as low cost, high productivity and disposability, have become the mainstream of electrophotographic photoreceptors, as compared with electrophotographic photoreceptors employing an inorganic photoconductive material.  In particular, function-separate type organic photoreceptors, having a charge generation layer that generates charges upon exposure to light and a charge transport layer that transports the charges, exhibit excellent electrophotographic characteristics, and therefore, various proposals have been made for such function-separate type organic photoreceptors, putting them to practical use. 
Incidentally, organic photoreceptors, which are generally inferior to inorganic photoreceptor in mechanical strength, are prone to being subjected to scratches or wear upon application of an external mechanical force by a cleaning blade, a developing brush, a recording medium or the like, and therefore have a short operating life.  Further, in a system employing a contact charging system which has come into use in recent years from the viewpoint of ecological concerns, there is a problem in that the amount of wear of the photoreceptor is significantly increased, as compared with photoreceptors employing a non-contact charging system using a corotoron.  Such insufficient durability of a photoreceptor may become a cause of decrease in image density due to reduced sensitivity, occurrence of fogging in an image due to a reduced charge potential, or the like. 
In order to avoid the above-mentioned phenomena, methods of improving durability of a photosensitive layer have been studied.  For example, a method of reducing a surface energy of a surface layer of a photoreceptor by dispersing fluorine-based resin particles in the surface layer has been proposed. 
Since fluorine-based resin particles have a low dispersibility and a high cohesive force, the fluorine-based resin particles contained in a surface layer of an electrophotographic photoreceptor tend to be unevenly distributed in the surface layer.  Consequently, there is a problem in that it may be difficult to obtain a favorable image in a stable manner, owing to abnormalities in image quality such as black spots, white spots, uneven density or the like caused by defects formed in a coated layer due to aggregation of the fluorine-based resin particles.