The nature of defects in polyester powder films on zinc coated steel substrates

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Abstract
Investigations of defects in polyester powder films on zinc coated steel substrates produced commercially and in the laboratory have confirmed two distinct types—cratering and pinholes. Corrosion products, dirt or entrapped gases appear to impede flow of molten polymer resulting in craters. Pinholes are the result of entrapped gases, probably from the dehydration of the conversion coating, and their incidence is very sensitive to the thickness of the polymer film and roughness of the substrate.