In image forming apparatuses using electrophotographic methods, such as copiers and printers, roller members given electric conductivity are used in electrophotographic processes such as development, charging and transfer (toner feeding and cleaning).
As the roller members used as developing rollers, charge rollers, transfer rollers (toner feeding and cleaning) and the like, ones provided with a basic structure having an elastic layer comprising a conductive rubber, polymeric elastomer, polymeric foam or the like given electric conductivity by blending a conductive agent therein, which elastic layer is formed on the outer periphery of the shaft; and further with a single or multiple coating layers on the outer periphery of the layer to attain a desired surface roughness, electric conductivity, hardness and the like; have been conventionally used.
For example, in cases where an elastic layer comprising a polyurethane foam is used, since the surface of the foam has open cells, there are problems such as melting of the surface of the elastic layer caused by a solvent-type paint, so that the surface roughness cannot be controlled. In cases where the surface roughness cannot be controlled, for example, in a developing roller, problems such as roughness of printed images and occurrence of toner filming are caused, so that a method wherein the surface roughness is adjusted by formation of a coating layer with an aqueous paint containing an aqueous resin has been conventionally used for an elastic layer comprising a polyurethane foam. Since coating layers by an aqueous paint have low impacts on the environment unlike solvent-type paints, they can be said to be excellent from the view point of environmental protection.
Examples of an improved technology for a roller member include one for a developing roller disclosed in Patent Document 1 which is constituted by an elastic layer and a single or multiple resin layer(s) laminated sequentially and concentrically on the periphery of a conductive shaft, wherein the major component of at least the surface layer among the resin layers is a polyurethane resin obtained by reacting a polyol, an isocyanate and, as required, a chain elongation agent, wherein one or both of the polyol and the chain elongation agent has/have a polysiloxane skeleton, and the document also discloses to make 100% modulus of the surface layer not less than 5×106 Pa and not more than 30×106 Pa. Further, in Patent Document 2, a conductive member for electrophotography is disclosed, which conductive member comprises in the outer periphery of the conductive support a conductive elastic material mainly constituted by a polymer having a halogen group, which conductive elastic material contains an inorganic compound containing a metallic element whose chloride has a solubility of not more than 30 g, which inorganic compound was hydrophobized, wherein the outermost layer of the conductive elastic material is more highly cross-linked than the inside thereof.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 11-212354 (Claims and the like)    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-338167 (Claims and the like)