Patent ID: 7593670
Filing Date: 2009-09-22
Classification: G03G

Abstract:
1. A charging device for electrically charging an image bearing member, comprising: 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 contact charging member, wherein the image bearing member is adapted to carry a toner image of toner which contains an externally added material comprising silica, wherein the silica on said contact charging member is charged to a negative polarity, and wherein said contact member has a work function larger than a work function of the silica, and said contact charging member has a work function smaller than the work function of the silica, wherein the work function of said contact member is the amount of excitation energy that must be applied thereto to free an electron therefrom, wherein the work function of said contact charging member is the amount of excitation energy that must be applied thereto to free an electron therefrom, wherein the work function of said silica is the amount of excitation energy that must be applied thereto to free an electron therefrom, wherein the amount of excitation energy necessary to free an electron from said contact member is larger than the amount of excitation energy necessary to free an electron from said silica, and wherein the amount of excitation energy necessary to free an electron from said contact charging member is smaller than the amount of excitation energy necessary to free an electron from the silica.