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Centrifuge measurements and electrostatic charge measurements have shown that the force of adhesion of xerographic toner particles to carrier beads can be described by an electrostatic model. In this model the triboelectric charge on the toner particle is attracted by its countercharge residing on the bead surface and during the process of electrostatic development this force of attraction between toner and carrier must be overcome by a competing process. In this paper it is suggested that the applied field lowers the Coulomb barrier that normally constrains the toner to the bead surface, so that under the combined effects of the mechanical impulse and the applied electric field, the less tightly held particles are stripped from the carrier bead surface. A calculation has been made on the potential function adjacent to the bead surface in the presence of an electric field, and an equation is derived for toner detachment. Measurements have been made on xerographic toner of the efficiency of toner release for various drop heights, with field applied, and without field. The results are somewhat difficult to interpret because of the wide distribution in toner mass and charge. Nonetheless, a comparison can be made between theory and experiment, and there is reasonable agreement.
Donald et al. (Sat,) studied this question.