Thin-film powder coatings: Application issues
This is the final article in a three-article series on issues to consider in thin-film powder coating applications. The article focuses on important issues in powder storage and handling, pre-treatment choice, and tribo- and corona charging applications. Although the article primarily addresses the end user, it will also interest powder coatings formulators and manufacturers. The first and second articles in the series were published in February and October 1996.
Virtually all thermoset powder coatings are slightly hygroscopic, or moisture attracting. Some inorganic pigments and fillers that are compounded into the powder show a distinctive affinity to water. The electronegative groups, that is, the hydroxyl and carboxyl groups, in thermoset resins also attract moisture. Formulators, especially, should be aware that the moisture-attracting behaviour of powder coatings increases with higher hydroxyl, or acid, numbers of the resins.