Minority charge separation in falling particles with bipolar charge

Fluidization of polymer powders is used extensively in the powder coating i ndustry. During the fluidization process the paint particles become electri cally charged due to particle-particle and particle-wall interactions. In t he course of this tribocharging, or friction charging process, it has been observed that a bipolarity of charged powder exists. The smaller, or finer, particles tribocharge oppositely to the larger size particles; thus, there exist both positively and negatively charged particles within the fluidize d bed. A simple technique for charge measurement and separation has been de veloped whereby a small sample of bipolar charged powder taken from the flu idized bed is poured from a height and a separation occurs between the majo rity and minority particles of opposite charge. The amount of separation is a function of charge on the individual particles and the height at which t he sample is poured. A computational model, based on techniques of molecula r dynamics, has been developed to simulate the trajectories of individual c harged particles when a sample of bipolar charged powder is poured. The mod el takes into account electrical, drag and gravitational forces acting on e ach particle and confirms the statistically analyzed experimental results. (C) 1998 Elsevier Science B.V. All rights reserved.