Surface microstructure of powder layers influenced by the forces of deposition and adhesion in electrostatic coating process

In the electrostatic powder coating process, several factors affect the deposition of charged polymer paint particles and the adhesion of the deposited particles on the grounded substrate being coated. In this paper, the roles and relative magnitudes of these forces are discussed. A model on the deposition of a charged particle approaching the surface of the substrate is presented. The electrostatic fields that are considered here to be responsible for particle deposition are the following: (1) corona field between gun tip and grounded plane; (2) image field between a particle and its image charge; (3) field due to the space charge of charged particles; and (4) net repulsive field between a charged particle and the powder layer. Once the particle deposits on the surface and the high voltage is turned off, the particle experiences the following forces: (1) the force due to the image charge of the underlying powder layer; (2) the force due to the image charge of the particle; and (3) the repulsive force between the charged particle and the charged powder layer. The model shows criteria on whether the particles will deposit on the substrate and, if deposited, whether they will remain on the surface of the powder layer once the corona field is turned off. These relative forces influence the microstructure of the powder layer and may affect the ultimate appearance or the texture of paint film after curing.