A Fundamental Study of Surface Protection by Powder Coating

Abstract

The thesis examines the fundamental factors governing the corrosion protection properties of powder coatings on various steel and aluminium substrates. A corrosion testing programme involving static outdoor roof exposure and salt spray fog testing has been carried out and the results related to potential-time measurements. The powder coatings studied were a polyester, a mixed polymer and various epoxy coatings including a low-bake formulation and a matt-textured coating on substrates in conditions including grit blast, iron and zinc phosphated and chromated. A study of adhesion was carried out and attempts made to develop a good quantitative test for powder coatings. The curing stage in the production of powder coatings was studied with differential thermal analysis and a hot stage microscope technique. The hot stage microscope technique studied the flow behaviour of the molten particles on various substrates and it was found that flow varied according to powder type, the substrate and the condition of the powder. Differential thermal analysis was used to study the differences in curing behaviour between fresh and stale powders, and also as a tool to evaluate the degree of curing in a study on the effects of partial curing. Scanning electron microscopy was used to examine the powders, the substrates and the surface of the cured coating. The discussion brings together these studies with previous studies cited in the literature to elucidate the factors governing the corrosion of powder coated articles.