Electrostatic Powder Coatings

Abstract

SummaryThis paper describes two new electrostatic processes, used for dry painting, plastic coating, talcing, aluminium coating, applying rust inhibitors, applying electrical insulation and vitreous enamelling of sheet steel and castings. These applications are discussed, a wide range of plastic powders being commercially available for use with the processes. In terms of physical chemistry, the main advantages of dry powder spraying are that unfavourable chemical reactions between the liquid vehicle and the solids, or between the liquid and the metal surfaces, can no longer occur, and that the permeability of the final film can be considerably lower, since there are no solvents to boil off during the stoving operation. These factors have recently led to the formulation of interesting materials—particularly some unique epoxide resins. For ideal combination of good anti-corrosion properties, mechanical strength and low cost plastic coatings, there is an optimum thickness of coating. With epoxy coatings, for example, thicknesses of 0.002 to 0.004 in are required. Coatings of this order may be applied automatically by electrostatic powder coating. The process is flexible and coatings of from 0.0005 to 0.04 in can be obtained. For the application of special chemicals, light dustings having a few particlcs/cm2 can be applied.