Charging apparatus, process cartridge, and image forming apparatus

A process cartridge detachably mountable to a main assembly of an image forming apparatus, said process cartridge comprising:

• an image bearing member;
• a contact charging member contactable to the image bearing member to charge the image bearing member, said contact charging member being supplied only with a DC voltage;
• a developing device for developing a toner image on said image bearing member with toner comprising an externally added material, wherein the externally added material comprising silica;
• wherein said charging device includes a contact charging member contactable to the image bearing member to charge the image bearing member, said contact charging member being supplied only with a DC voltage, and a contact member contacted to said charging member,
• wherein work functions of said charging member, said contact member and the silica satisfy,
• (the work function of said contact member)>(the work function of the silica)>(the work function of said charging member).

An image forming apparatus comprising:

• an image bearing member;
• a charging device for electrically charging said image bearing member;
• a latent image forming device for forming an electrostatic latent image on said image bearing member charged electrically;
• a developing device for developing a toner image on said image bearing member with toner comprising an externally added material, wherein the externally added material comprising silica;
• a transferring device for transferring a toner image formed on said image bearing member onto a recording material;
• a cleaning device for removing the toner remaining on said image bearing member after transfer of the image,
• wherein said charging device includes a contact charging member contactable to the image bearing member to charge the image bearing member, said contact charging member being supplied only with a DC voltage, and a contact member contacted to said charging member,
• wherein work functions of said charging member, said contact member and the silica satisfy,
• (the work function of said contact member)>(the work function of the silica)>(the work function of said charging member).