| 摘要 |
A developing roller is provided which is soft enough to enable toners to be kept from deteriorating with time and cannot easily cause permanent set. The developing roller includes a mandrel, an elastic-material layer and a cover layer as a surface layer which covers the elastic-material layer. Asker-C hardness at the surface of the cover layer is from 40° to 85°. The cover layer has a thickness of from 15 nm to 5,000 nm. Martens hardness H1 (N/mm 2 ) at the surface of the developing roller, Martens hardness H2 (N/mm 2 ) of the elastic-material layer and the thickness d (mm) of the cover layer satisfy the relationship of the following expression (1): 400 ‰¤ H �¢ 1 - H �¢ 2 / d ‰¤ 2 , 000 |
