Developing roller, process cartridge and electrophotographic image forming apparatus

A process cartridge detachably attachable on a main body of an electrophotographic image forming apparatus,

• the process cartridge comprising at least a developing unit, the developing unit comprising a developing roller,
• the developing roller comprising an electro-conductive mandrel and an electro-conductive layer on the mandrel,
• the developing roller having an outer surface constituted by at least a first region which is electrically insulating, and a second region,
• the second region having higher electro-conductivity than that of the first region,
• the first region being arranged adjacent to the second region,
• the first region being disposed on an outer surface of the electro-conductive layer,
• the first region having a Vickers hardness of 10.0 or more as measured at an outer surface thereof, and the first region having a fracture toughness value of 800 Pa·m0.5 or more as measured at the outer surface thereof by an indentation fracture method.

An electrophotographic image forming apparatus comprising a developing unit,

• the developing unit comprising a developing roller,
• the developing roller comprising an electro-conductive mandrel and an electro-conductive layer on the mandrel,
• the developing roller having an outer surface constituted by at least a first region which is electrically insulating, and a second region,
• the second region having higher electro-conductivity than that of the first region,
• the first region being arranged adjacent to the second region,
• the first region being disposed on an outer surface of the electro-conductive layer,
• the first region having a Vickers hardness of 10.0 or more as measured at an outer surface thereof, and the first region having a fracture toughness value of 800 Pa·m0.5 or more as measured at the outer surface thereof by an indentation fracture method.