Published November 1975
The first application of fusible powders as surface coatings was accomplished by heating an object above the melting point of a particular polymer, such as polyethylene, and dipping it into a bed of the polymer powder. The procedure was of no great industrial interest until the idea of fluidizing the powder bed was conceived and developed in Germany in the 1950s.
In the fluidized bed technique, the piece to be coated is preheated in an oven to a temperature high enough above the fusion point of the polymer so that, after the piece is removed from the oven, it retains sufficient heat at its surface to melt or sinter the polymer particles. The heated piece is then coated by being dipped into the fluidized bed for a brief, specific period of time.
The fluidized bed coating process has several advantages over liquid paint finishing, the main ones being the elimination of a solvent and the capability of applying plastics for which solvents are not 8 readily available--polyvinyl chloride, polyethylene, and Teflon, for example. These advantages led to rapid growth in fluidized bed coating, particularly in Europe.
The next major step in powder coating was the adaptation of electrostatic painting techniques to the use of powders. This development began in the early 1960s. It has led to a variety of applicational equipment from manually operated guns to electrostatic fluidized beds. This report discusses powder coating principles, the resins used, the equipment available, companies active in powder coating, industry prospects, and the economics of powder manufacture and surface finishing by powder coating.
A great deal of help has been received from resin suppliers and equipment vendors and particular contributions are acknowledged at various points in the text. The author especially wishes to thank A. A. Schupbach of the San Francisco office of the 3M Company (Minnesota Mining and Manufacturing); David B. Todd, R. B. Smorodin, and others at Baker Perkins Company, Saginaw, Michigan; P. R. Donnelly of Plastic Applicators, Inc., Houston, Texas; Robert V. Sallquist, Sallco Industries, Menlo Park, California; and M. C. Siminski, The Polymer Corporation, Reading, Pennsylvania.
