The use of XPS and ToF-SIMS to investigate adhesion failure of a cationic radiation cured coating on galvanized steel

Abstract

Although steel substrates are often galvanized to protect against corrosion, further protection can be achieved by painting the exposed zinc surface. The paint must be durable so as to achieve the maximum possible protection. One of the most important properties of a durable coating system is adhesion, which must not deteriorate over the lifetime of the coating. The use of cationic radiation curing chemistry has shown much promise for the development of high-quality paint systems. The cationic radiation cured coating under investigation showed both good durability and mechanical properties, however, the coating delaminated from the substrate rapidly in a hot, humid environment. XPS and ToF-SIMS analyses of the delaminated interface has shown that the phosphorus hexafluoride anion of the photoinitiator segregates to the interface. On the basis of these results the coating was reformulated with a reduced concentration of the photoinitiator, and the durability was much improved.