Electrostatic charge acceptance and decay of powder coating particles

Techniques have been developed to measure the acceptance and decay of electrostatic charge on a wide variety of powder coatings. The measurement of the initial charge carried by the powder was affected by the amount of powder deposited. The decay of charge occurred within four time scales: (1) 1 sec, electron loss to air and to the metallic substrate; (2) 1 to 5 sec, electron flow to neutralize induced positive charge; (3) 5 to 100 sec, rapid decay from powder; and (4) 1,000 to 10,000 sec, very long term decay. Since the decay of charge was markedly affected by moisture and composition, the decay properties can be controlled by these parameters. A mathematical model was constructed describing the quantitative charge decay during the time period of 100 to 10,000 sec. There was considerable heterogeneity within the powders with regard to charge acceptance and interaction with moisture. These measurement techniques give information concerning electrostatic effects on particle transport, adhesion, and polymer electrostatic behavior which are very important variables in a powder coating process.