Electrographic printing method and apparatus

Abstract

An electrographic printing apparatus for forming a toner image on a recording medium, includes: a) a magnetic brush having a rotatable magnetic core and a stationary outer cylindrical shell; b) an addressable array of transfer electrodes on the outer shell, the array including a plurality of parallel strips of high magnetic permeability, electrically conductive material arranged circumferentially around the shell and disposed under an electrically insulating layer, the insulating layer defining printing gaps over the strips; c) a receiver electrode arranged in spaced relation to the array of transfer electrodes to define a recording region through which a receiver can be moved; d) a developer supply for supplying developer powder having an electrically conductive, magnetic carrier and a first colored toner to the magnetic brush, and e) an electronic circuit adapted to selectively apply voltage pulses to the transfer electrodes to cause the toner to transfer from the developer powder to the receiver in an image-wise pattern. A method, includes the steps of: providing a developer including a toner; forming a plurality of parallel circumferential ridges of developer, the ridges having a length substantially greater than their width; providing a corresponding plurality of printing gaps in the central portions of the ridges of developer, the printing gaps having a length substantially less than the length of the ridges; and selectively transferring toner at the printing gaps from the ridges to a receiver in an image wise manner.