DEVELOPING ROLLER, PROCESS CARTRIDGE AND ELECTROPHOTOGRAPHIC IMAGE FORMING APPARATUS

PROBLEM TO BE SOLVED: To provide a developing roller capable of providing a high-quality electrophotographic image.SOLUTION: A developing roller 1 comprises: a substrate 2; an electro-conductive elastic layer 3 on the substrate; and a plurality of electric insulation domains 4 on the electro-conductive elastic layer 3. The developing roller 1 has a length L of 200 mm or more in a longitudinal direction orthogonal to the circumferential direction thereof. A surface of the developing roller 1 includes surfaces of the domains 4, and an exposed portion of the electro-conductive elastic layer 3, the exposed portion being not covered with the domains 4. The domains 4 generate protrusion parts 5 on the surface of the developing roller 1. The electro-conductive elastic layer 3 has a plurality of protrusion parts 5 at the exposed portion. Asker C hardness of the developing roller 1 is 50 degrees or higher and 90 degrees or lower. A surface potential of the electric insulation domains measured under a specific condition is 10 V or more and 100 V or less, a surface potential at the exposed portion of the electro-conductive elastic layer 3 is 2 V or less, and an area ratio of the exposed portion of the conductive elastic layer 3 is in a specific range.SELECTED DRAWING: Figure 1A 【課題】高品位な電子写真画像を与え得る現像ローラの提供。【解決手段】現像ローラ１は、基体２と、該基体上の導電性弾性層３と、該導電性弾性層３上の複数個の電気絶縁性のドメイン４と、を有し、該現像ローラ１は、その周方向に直交する長手方向の長さＬが２００ｍｍ以上であり、該現像ローラ１の表面は、該ドメイン４の表面と、該ドメイン４で被覆されていない該導電性弾性層３の露出部分とを含み、該ドメイン４が現像ローラ１の表面に凸部５を生じさせており、該導電性弾性層３は、該露出部分において複数個の凸部５を有し、該現像ローラ１のアスカーＣ硬度が、５０度以上、９０度以下である。また、特定条件で測定される電気絶縁性のドメインの表面電位が１０Ｖ以上、１００Ｖ以下であり、導電性弾性層３の露出部分の表面電位が２Ｖ以下であり、導電性弾性層３の露出部分の面積割合が特定範囲内である。【選択図】図１Ａ