Integral Epoxy Resin–Silane Primer System For Hot-Dip Galvanized Steel

Abstract

This work deals with the development of a non-chromate, one-step finishing system for corrosion protection of hot-dip galvanized steel. Environmental regulations demand that chromate pretreatments and chromate pigments used in primers be replaced. Previously the Silane Research Group has reported on the effectiveness of silane pretreatments and suggested silane formulations for replacing chromate pretreatments. In this project a pretreatment-free, chromate-free one-step finishing system was needed for hot-dip galvanized steel used in automotive coils in cars. Pretreatments act as adhesionpromoters and bind coatings to metals and since silanes, especially systems using bisamino silane and bis-sulfur silane, have been shown as excellent adhesion-promoters by this lab, the idea of incorporating silanes in primers for obtaining adhesion to metals emerged. Whether this also meant increased corrosion protection was investigated. The coating formulation exhibiting the best corrosion resistance is a mixture of hydrolyzed and non-hydrolyzed silanes incorporated into a commercial epoxy resincuring agent system. Salt spray analysis indicated that the coating exhibits good corrosion resistance. Impedance values were significantly higher for the integral resin-silane coating, as compared to the commercial resin. Impedance values of the integral primer coatings increased with time, as secondary curing reactions imparted by the presence of the non-hydrolyzed silane proceed. Due to the presence of the hydrolyzed silanes, the investigated coatings exhibited good adhesion to both the hot-dipped galvanized steel substrate and a polyester coating. Coating characterization was carried out using liquid and solid-state NMR and infra-red spectroscopy. It was found that bis-sulfur silane did not react during curing, it