Neutralization of electrophotographic developer

Abstract

In many electrophotographic development systems, the developer consists of toner particles (∼10 μ) triboelectrically charged by carrier beads (∼100–250 μ). Since development onto a photoconductor continually removes charged toner from the development system, the carrier-bead charge would continue to increase with use unless, as happens, the developer net charge is limited by some neutralization mechanism. From a series of measurements on typical developer materials, we rule out electrical conduction and air breakdown as straightforward dominant neutralization mechanisms and find that the neutralization of developer is a multistep process. When the net-charged developer is agitated, toner migrates through the developer, reducing the net charge in its bulk and leaving a toner-starved bead layer adhering to any conducting boundary surface. When the developer is further agitated, the surface layer of highly charged adhering beads can be released by either of two charge neutralizing mechanisms. If the beads have conducting cores coated with a polymer, the carrier beads are neutralized by triboelectric charging in the presence of the high electric field due to the net charge on the beads. But if the bead coating integrity is poor, the beads can be neutralized by charge flow from the boundary surface to the conducting bead cores.