Decreasing adhesion of prepainted steel sheet and decreasing mechanism analysis for UV ageing characterisation

The aim of this study is to analyse the decreasing adhesion mechanism of polyurethanes prepainted steel sheet for UV ageing to simulate nature environment by means of T-bend, FTIR, SEM, EIS. After 2000 hours of ageing in the UV chamber we observed the adhesion decline of polyurethanes prepainted steel sheet by the T-bend test. Taking into account the characteristic peak position and intensity of FTIR spectroscopy was Hardly any change during the ageing period, there is no chemistry reaction on the organic coatings. However, After 2000 hours ageing the electrochemical impedance spectroscopy (EIS) of the prepainted steel sheet showed lower impedance. SEM result indicated that larger defects were found on the film surface, which it is easy that the outside corrosive substances to meet metal substrate. In this way, the corrosive medium accelerated corrosion electrochemical reaction on the metal. growing corrosion products diffused between the metal substrate and the organic coating to destroy their binding. At last, the increscent corrosive area on metal interface caused the adhesion decline.