Charging device and image forming apparatus

An image forming apparatus for forming an image on a recording material, comprising:

• a photosensitive member;
• a charging member for electrically charging the photosensitive member by being supplied with a voltage;
• a supporting member for supporting said charging member so as to press-contact to the photosensitive member;
• and
• a power source for applying a voltage to said charging member,
• wherein said charging member comprises:
• an electroconductive support;
• an elastic base layer supported by said electroconductive support;
• and
• an elastic surface layer, provided on a surface of said elastic base layer, being harder than said elastic base layer;
• wherein said elastic surface layer is provided with projected portions and recessed portions, and wherein the projected portions are elastically deformable in contact with the photosensitive member, leaving electrically dischargeable gaps between the recessed portions of said elastic surface layer and the photosensitive member.

A charging device for electrically charging a photosensitive member, comprising:

• a charging member for electrically charging the photosensitive member by being supplied with a voltage;
• and
• a supporting member for supporting said charging member so as to press-contact to the photosensitive member,
• wherein said charging member comprises:
• an electroconductive support;
• an elastic base layer supported by said electroconductive support;
• and
• an elastic surface layer, provided on a surface of said elastic base layer, being harder than said elastic base layer;
• wherein said elastic surface layer is provided with projected portions and recessed portions, and wherein the projected portions are elastically deformable in contact with the photosensitive member, leaving gaps between the recessed portions of said elastic surface layer and the photosensitive member,
• wherein when a potential difference between a surface of said charging member and a surface of the photosensitive member is V (V), an urging force for urging said charging member toward the photosensitive member is P (N), a height of the projected portions before deformation is L (m), the sum of contact areas where the projected portions contact the photosensitive member is S (m2), and Young's modulus when said elastic base layer and said elastic surface layer are deformed is E (MPa), these parameters satisfy the following relationship:
• ((V−312)/6.2)×10−6(m)>L(1−P/ES)>7.7×10−6(m).

An image forming apparatus for forming an image on a recording material, comprising:

• a photosensitive member;
• a charging member for electrically charging the photosensitive member by being supplied with a voltage;
• a supporting member for supporting said charging member so as to press-contact to the photosensitive member;
• and
• a power source for applying a voltage to said charging member,
• wherein said charging member comprises:
• an electroconductive support;
• an elastic base layer supported by said electroconductive support;
• and
• an elastic surface layer, provided on a surface of said elastic base layer, being harder than said elastic base layer;
• wherein said elastic surface layer is provided with projected portions and recessed portions, and wherein the projected portions are elastically deformable in contact with the photosensitive member, leaving gaps between the recessed portions of said elastic surface layer and the photosensitive member,
• wherein when a potential difference between a surface of said charging member and a surface of the photosensitive member is V (V), an urging force for urging said charging member toward the photosensitive member is P (N), a height of the projected portions before deformation is L (m), the sum of contact areas where the projected portions contact the photosensitive member is S (m2), and Young's modulus when said elastic base layer and said elastic surface layer are deformed is E (MPa), these parameters satisfy the following relationship:
• ((V−312)/6.2)×10−6(m)>L(1−P/ES)>7.7×10−6(m).