Electrophotographic apparatus of retentive type

Claim 1

In an electrophotographic apparatus for printing a plurality of duplicated copies from the same and single electrostatic charge image once formed on the surface of an electrostatic charge retentive member by repeating developing and transferring operations in succession, a magnetic brush development device comprising: an electrically conductive sleeve; an electrically insulating layer applied on said sleeve, said insulating layer having a magnetic flux density in the range of about 600 to 800 Gauss, a surface resistance higher than about 10 10 Ω-cm, and being positioned a distance in the range of about 2 to 5 mm from the surface of the charge retentive member; a magnet device arranged inside said sleeve to form on a surface of said insulating layer a magnetic brush of a two component developing agent consisting of magnetic carriers having a surface resistance lower than about 10 8 Ω-cm and insulating toners, said toners representing greater than 6% of the total weight of said agent; a doctor blade for defining furs of said magnetic brush, said furs for developing said charge image with said toners to form a toner image on the surface of said charge retentive member, each of said furs having a length less than approximately 6 mm, the difference between said fur length and the distance between said sleeve and said surface of the charge retentive member being less than about 2.0 mm; and a device for transferring said toner image onto a record paper to form a copy.