| 摘要 |
PROBLEM TO BE SOLVED: To obtain a developing roller that prevents occurrence of image defects due to uneven coating with a toner, caused by wrinkles and undulation on the surface by satisfying a specified relation between the coefficient of linear expansion of a surface layer and that of an elastic layer. SOLUTION: An elastic layer 24b and a surface layer 24c are formed on a core metal 24a, comprising a cylindrical electrically conductive substrate to obtain the developing roller 24. If the coefficient of linear expansion of the surface layer 24c is represented by A [K-1] and that of the elastic layer 24b by B [K-1], the coefficients A and B satisfy the relation 0.1<=A/B<=100 and the coefficient B satisfies B<=2×10-4 (where K is absolute temperature). When the ratio of coefficier of linear expansion A/B<0.1, the surface layer 24c is unable to follow the change in the thermal expansion or shrinkage of the elastic layer 24b. When A/B>100, the core metal 24a is unable to follow a change of the thermal expansion or shrinkage of the surface layer 24c. In both cases, the surface of the developing roller 24 generates fine wrinkles and undulations, uneven coating with a toner is produced and image density is made uniform. |
