Developing roller, process cartridge and electrophotographic image forming apparatus

An electrophotographic process cartridge which is configured to be detachably attachable to a body of an electrophotographic apparatus, comprising a developing apparatus, wherein

• the developing apparatus comprises a developing roller,
• the developing roller comprising:
• a substrate;
• an electro-conductive elastic layer on the substrate;
• and
• a plurality of electrical insulating domains on the electro-conductive elastic layer, wherein
• the developing roller has a length L of 200 mm or more in a longitudinal direction orthogonal to the circumferential direction thereof,
• the surface of the developing roller comprises:
• the surfaces of the domains;
• and
• an exposed portion of the electro-conductive elastic layer, the exposed portion being uncovered with the domains,
• the developing roller has protrusions on the surface thereof, the protrusion being formed by the domains,
• the electro-conductive elastic layer has a plurality of protrusions at the exposed portion,
• the developing roller has an Asker C hardness of 50 degrees or more and 90 degrees or less, and
• the developing roller satisfies the following (1) and (2):
• (1) a surface potential of the developing roller at the domains is 10 V or more and 100 V or less corresponding to a completion of discharge, and a surface potential of the developing roller at the exposed portion of the electro-conductive elastic layer is 2 V or less corresponding to a completion of discharge, the charging of the surface of the developing roller being conducted with a discharge wire which is disposed substantially parallel to the longitudinal direction of the developing roller and so that the discharge wire is apart from the surface of the developing roller by 1 mm, by applying a direct-current voltage of 8 kV between the developing roller and the discharge wire in an environment of a temperature of 23° C. and a relative humidity of 50%, and
• (2) when a nip region having a nip width of 1.0 mm and an area of 1.0 mm×L mm is demarcated by pressing the surface of the developing roller against a flat glass plate, assuming that a square region of 0.3 mm on a side is placed in the nip region, and total sum of areas of contacted portions between the exposed portion of the electro-conductive elastic layer and the flat glass plate in the square region is defined as “ST” mm2, a percentage ratio of ST to the area 0.09 mm2 of the square region, 100*ST/0.09, is 0.50% or more and 10.00% or less.

An electrophotographic image forming apparatus comprising an image bearing member which bears an electrostatic latent image, a charging apparatus which charges the image bearing member, an exposure apparatus which forms an electrostatic latent image on the charged image bearing member, a developing apparatus which develops the electrostatic latent image with toner to form a toner image, and a transfer apparatus which transfers the toner image to a transfer material, wherein

• the developing apparatus comprises a developing roller,
• the developing roller comprising:
• a substrate;
• an electro-conductive elastic layer on the substrate;
• and
• a plurality of electrical insulating domains on the electro-conductive elastic layer, wherein
• the developing roller has a length L of 200 mm or more in a longitudinal direction orthogonal to the circumferential direction thereof,
• the surface of the developing roller comprises:
• the surfaces of the domains;
• and
• an exposed portion of the electro-conductive elastic layer, the exposed portion being uncovered with the domains,
• the developing roller has protrusions on the surface thereof, the protrusion being formed by the domains,
• the electro-conductive elastic layer has a plurality of protrusions at the exposed portion,
• the developing roller has an Asker C hardness of 50 degrees or more and 90 degrees or less, and
• the developing roller satisfies the following (1) and (2):
• (1) a surface potential of the developing roller at the domains is 10 V or more and 100 V or less corresponding to a completion of discharge, and a surface potential of the developing roller at the exposed portion of the electro-conductive elastic layer is 2 V or less corresponding to a completion of discharge, the charging of the surface of the developing roller being conducted with a discharge wire which is disposed substantially parallel to the longitudinal direction of the developing roller and so that the discharge wire is apart from the surface of the developing roller by 1 mm, by applying a direct-current voltage of 8 kV between the developing roller and the discharge wire in an environment of a temperature of 23° C. and a relative humidity of 50%, and
• (2) when a nip region having a nip width of 1.0 mm and an area of 1.0 mm×L mm is demarcated by pressing the surface of the developing roller against a flat glass plate, assuming that a square region of 0.3 mm on a side is placed in the nip region, and total sum of areas of contacted portions between the exposed portion of the electro-conductive elastic layer and the flat glass plate in the square region is defined as “ST” mm2, a percentage ratio of ST to the area 0.09 mm2 of the square region, 100*ST/0.09, is 0.50% or more and 10.00% or less.