The effect of additives on the tribocharging of electrophotographic toners

Abstract

Adhesion and transfer of charged toner particles from one surface to another in electrophotography are dominated by electrostatic forces. Charge control agents, CCAs, are included in toner formulations to control the sign and magnitude of the toner charge. The purpose of this work is to discuss the role of CCAs in triboelectrification of two-component electrophotographic developers. Toner particles 12 μm in diameter were made by spray drying of unpigmented polystyrene containing a variety of monomeric and ionomeric phosphonium sulfonate CCAs. Charge-to-mass ratio ( Q M ) of the toners was measured using two types of carriers. One type was coated with poly(vinylidene fluoride) and charged the toners positively. The other was coated with poly(methylmethacrylate) and charge the toners negatively. The charging measurements were compared to the expectations of electronic and ionic mechanisms and to surface state models of tribocharging. A linear correlation was found between Q M of the toners when they were charged positively and Q M of the same toners charged negatively. This observation is shown to be consistent with the surface state model of tribocharging. However, it is concluded that the mechanism of charging is more complex than the simple transfer of electrons or ions of one polarity from one surface to another. Both surfaces must have the capability of accepting and donating electrons or ions of one polarity or else species of both signs are transferred.