Charging member, method for producing same, process cartridge and electrophotographic image forming apparatus
It is intended to provide a charging member capable of maintaining high charging performance even when used over a long period. The charging member has an electroconductive support and an electroconductive elastic layer as a surface layer, wherein the electroconductive elastic layer has a roughened surface, and the electroconductive elastic layer has an average Martens' hardness Mc of 2 N/mm 2 or larger and 20 N/mm 2 or smaller measured with an indentation strength of 0.04 mN at a core surface defined according to a three dimensional surface texture standard (ISO 25178-2:2012), and has an average viscosity Vc of 70×10 −3 V or smaller measured in a square of 2 μm long×2 μm wide field of view under a scanning probe microscope.
1. A method for producing a charging roller comprising an electroconductive support and an electroconductive elastic layer as a surface layer whose outer surface is roughened with insulating particles, the insulating particles being exposed to the outer surface, the method comprising:
(a) preparing an unvulcanized rubber composition comprising a polymer having a butadiene skeleton and insulating particles;
(b) supplying the electroconductive support and the unvulcanized rubber composition to a crosshead extrusion molding machine provided with a die having an inner diameter of “D”, and molding an unvulcanized rubber roller having a layer of the unvulcanized rubber composition on the periphery of the electroconductive support, wherein a percentage value of (d−d0)/(D−d0) exceeds 100% where “d” is an outer diameter of the unvulcanized rubber roller and “d 0 ” is an outer diameter of the electroconductive support;
(c) vulcanizing the layer of the unvulcanized rubber composition in air, and obtaining a layer of a vulcanized rubber composition having an oxidatively cured topmost surface; and
(d) ultraviolet irradiating said oxidatively cured topmost surface of the layer of the vulcanized rubber composition.
2. The method according to claim 1 , wherein said polymer having a butadiene skeleton is at least one polymer selected from the group consisting of butadiene rubber, isoprene rubber, chloroprene rubber, acrylonitrile-butadiene rubber, styrene-butadiene rubber, and styrene-butadiene-styrene rubber.