A study was conducted on the durability of steel sheet coated with PVC using polyester adhesives that can be activated at a temperature of 180°C. Assuming a case in which the PVC becomes degraded and a corrosive electrolyte reaches the adhesive layer, the corrosion behavior of Zn-Co-Mo electroplated steel sheet coated with polyester adhesive only in 5%NaCl was studyed mainly by the AC impedance method. The film resistance (Rf) of polyester adhesives cured at 180°C was higher than that of conventional acrylic/epoxy adhesives, and the decrease in Rf and the increase in the capacitance (Cf) were smaller than those of conventional acrylic/epoxy adhesives in 5%NaCl immersion tests. It was found that there was good correlation between AC impedance measurement and corrosion resistance and adhesion. It is considered that the excellent corrosion resistance of steel sheet coated with polyester adhesives is due mainly to the addition of silane coupling agent to the polyester adhesives.
