Improved developing device for two-color electrophotographic copying

Abstract

An improved two-color electrophotographic copying apparatus comprising a non-magnetic sleeve for supplying magnetic toner to latent electrostatic images formed on a photoconductor, for the development of said images, for use in one or both of the development section for the two colors, whereby, by means of the so-called counter electrode effect, two-color copies can be obtained in which the so-called edge effect has been completely or substantially eliminated. In one category of embodiments, a series of ridges and grooves are formed on the outer peripheral surface of the non-magnetic sleeve. The peaks of those ridges serve to decrease the effective distance between the non-magnetic sleeve and the surface of the photoconductor, which decrease in distance is advantageous in enhancing the counter electrode effect. At the same time, the grooves provide means for the carrying of sufficient toner past a doctor in the apparatus, whereas, heretofore, getting sufficient toner past said doctor was the difficulty in decreasing the aforesaid distance from the non-magnetic sleeve to the photoconductor. In another category of embodiments, the ridges and grooves are formed spirally or in some similar orientation around the surface of the magnetic sleeve, with the effect that toner carried by the sleeve and deposited on the photoconductor is also moved in a lateral direction (axially along the surface of the sleeve), which movement serves to dislodge toner lightly held in unwanted fringe portions of the image due to incomplete, though enhanced, operation of the counter electrode effect, whereby the final traces of the edge effect are eliminated.