The mechanism of toner display based on an electrical movement of black and white charged particles has been investigated. Two types of black toner and white particles charged in the different electric polarity are enclosed between two electrodes. The particle movement is controlled by the external electric field applied between two transparent electrodes. The toner is collected to the electrode by an electrostatic force across the insulating layer to display a black image. The toners can be put back to the counter electrode by applying a reverse electric field, and white solid image is displayed. The threshold and driving voltage to move the particle depend on the electric charge and fluidity of particles.
Daisuke Takahashi, Tetsuya Yamamoto, Sakiko Nakamura, Takashi Kitamura, "Driving Voltage for Electrical Particle Movement in Toner Display" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP21), 2005, pp 62 - 64, https://doi.org/10.2352/ISSN.2169-4451.2005.21.1.art00021_1