Abstract
The charging properties of powders for electrostatic coating are essential factors concerning adhesive strength between substrate and powders. Electrostatic charging and decaying behavior of several plastic powders has been examined by surface potential measurement. Water absorbed on the powders affects decay velocity (α) as shown in the next formula
α=α0exp(β⋅m)
α0……decay velocity in dry state, β……constant, m……weight of absorbed water
However, the depth of trap also affects these decay phenomena. Activation energy of epoxy resin powder is 0.88eV. The decay of charge is achieved by the following mechanism. The surface corona charges of the layer move to the inner part and are combined to induced opposite sign charges on the back. Moreover, decay velocity agreed with Inoue's experimental values concerning ZnO-resin mixed films.
