Adhesive Properties of Different Powder Resins
Q. Is there a difference in the adhesion between a super-durable polyester and a regular TGIC polyester or a TGIC-free polyester when applied to a galvanized material?—G.S.
A. In general, there is no difference in the adhesive properties of the different technologies you asked about on galvanized steel. The key to adhesion is how you prepare the substrate. This is true of any substrate. They all have unique properties in their raw condition, and you must have the right steps in cleaning and preparation to ensure the powder will bond to the surface.
The zinc coating has a layered structure that includes a thin layer of alloyed iron-zinc coating adjacent to the steel interface with a layer of zinc coating proper on the outer surface. Various elemental impurities or additives may tend to segregate to the grain boundaries of the spangles because of their limited solubility in the solidifying matrix, while other elements, such as aluminum, tend to diffuse into the entire surface of the zinc coating. Galvanized steel should be brush blasted to remove deposits of minerals and oxidation, and be free of these organic soils. In some cases, the galvanized surface is chemically cleaned and treated after blasting, but the blasting does a great job of removing inorganic soils and leaves a corrosion resistant surface with a lot of profile that provides a good anchoring of the powder. The different powder resin systems should adhere well over a good surface, no matter what technology you use.
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