Developing roller having specific surface layer, developing device provided with the developing roller and image-forming apparatus provided with developing device equipped with the developing roller

1. A developing roller, having a surface layer comprising;

a binder resin having a solubility parameter (SP) value in the range of 7.5 to 9.0; and

roughness-imparting particles made of a resin having an SP value that has a difference from the SP value of said binder resin of no more than 2 or less in the absolute value thereof,

the roughness-imparting particles being dispersed in the binder resin.

2. The developing roller according to claim 1 , wherein the roughness-imparting particles have an average degree of roundness of 0.94 or more.

3. The developing roller according to claim 1 , wherein the roughness-imparting particles have an SP value in the range of 7 to 11.

4. The developing roller according to claim 1 , wherein the roughness-imparting particles have an average particle size in the range from 10 to 50 μm.

5. The developing roller according to claim 1 , wherein the surface layer has a surface roughness (Ra) in the range from 0.8 to 3.0 μm.

6. The developing roller according to claim 1 , wherein the binder resin has an SP value in the range of 8.0 to 9.0.

7. The developing roller according to claim 1 , wherein the roughness-imparting particles have an average degree of roundness of 0.97 or more.

8. A developing device provided with a developing roller, wherein the developing roller has a surface layer comprising;

a binder resin having a solubility parameter (SP) value in the range of 7.5 to 9.0; and

roughness-imparting particles made of a resin having an SP value that has a difference from the SP value of said binder resin of no more than 2 or less in the absolute value thereof,

the roughness-imparting particles being dispersed in the binder resin.

9. The developing device according to claim 8 , wherein the roughness-imparting particles have an average degree of roundness of 0.94 or more.

10. The developing device according to claim 8 , wherein the roughness-imparting particles have an SP value in the range of 7 to 11.

11. The developing device according to claim 8 , wherein the roughness-imparting particles have an average particle size in the range from 10 to 50 μm.

12. The developing device according to claim 8 , wherein the surface layer has a surface roughness (Ra) in the range from 0.8 to 3.0 μm.

13. The developing device according to claim 8 , wherein the roughness-imparting particles have an average degree of roundness of 0.97 or more.

14. An image-forming apparatus provided with a developing device, equipped with a developing roller, wherein the developing roller has a surface layer comprising;

a binder resin having a solubility parameter (SP) value in the range of 7.5 to 9.0; and

roughness-imparting particles made of a resin having an SP value that has a difference from the SP value of said binder resin of no more than 2 or less in the absolute value thereof,

the roughness-imparting particles being dispersed in the binder resin.

15. The image-forming apparatus according to claim 14 , wherein the roughness-imparting particles have an average degree of roundness of 0.94 or more.

16. The image-forming apparatus according to claim 14 , wherein the roughness-imparting particles have an SP value in the range of 7 to 11.

17. The image-forming apparatus according to claim 14 , wherein the roughness-imparting particles have an average particle size in the range from 10 to 50 μm.

18. The image-forming apparatus according to claim 14 , wherein the surface layer has a surface roughness (Ra) in the range from 0.8 to 3.0 μm.

19. The image-forming apparatus according to claim 14 , wherein the roughness-imparting particles have an average degree of roundness of 0.97 or more.