An effective anti-corrosive chromate-free, low-VOC, water-borne, direct-to-metal primer for hot-dip galvanized steel (HDG) has been developed. This coating is made of a water-borne dispersion containing organofunctional silanes, water-dispersed resins, cross-linkers, minor binders and chromate-free anti-corrosion inhibitors. Typical systems are based on epoxy resins. These primers are unique as they can be applied onto the metal directly after alkaline cleaning. We will discuss the optimization of the superprimer coating for HDG steel. The selection of silanes, resin combinations, cross-linkers and minor binders was systematically optimized for the primers by using a L9 orthogonal array consisting of four factors each having three levels. The corrosion resistance of the coatings was evaluated using electrochemical methods and performance tests. During the study cured superprimer components and also complete coatings were characterized using sophisticated characterization methods. The results provided information on an optimized coating formulation on HDG steel that survives 2000 hours of ASTM B-117 salt spray testing. This coating contains intermediate a mounts of epoxy, acrylate and silane, but no polyurethane.
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