Adhesion and scratch resistance of polycarbonate films on ferroplate substrates:: Effect of γ-APS primers

The influence of gamma-aminopropyltriethoxysilane (gamma-APS) primers on the adhesion and scratch resistance of polycarbonate (PC) films on ferroplate substrates was determined from the critical normal loads at which debonding of the films from the substrates occurred during scratch testing. The critical load was a strong function of the concentration of the aqueous solutions from which the gamma-APS primers were adsorbed and of the thickness of the primer films. Thus, the critical normal load increased from 0.09 +/- 0.02N to 0.31 +/- 0.07N as the concentration of the gamma-APS solutions increased from 0.05% to 0.2%, respectively. However, the critical load increased only slightly as the solution concentration increased beyond 0.2%. The increase in critical load as concentration of gamma-APS solutions increased was related to the formation of an interphase involving chemical reaction and physical entanglement of PC and gamma-APS molecules. The critical load for debonding of PC films from the substrates also depended strongly on the temperature at which the gamma-APS films were dried before application of the PC films. Thus, the critical normal loads for debonding were 0.31 +/- 0.07, 0.20 +/- 0.02, and 0.05 +/- 0.01N for gamma-APS films that were dried for 15 min at room temperature, 60 degrees C, or 110 degrees C, respectively. The decrease in critical load with increasing drying temperature was attributed to the greater cross-link density in gamma-APS films that were dried at elevated temperatures, which limited interdiffusion and physical entanglement of PC and gamma-APS molecules. High reaction temperature of gamma-APS and PC induced a fragmentation of amine. However, it also increased the probability of amines to react with carbonate because of increasing mobility of PC chains. Optimization of these two factors was required to obtain the greatest adhesion and scratch resistance. Chemical reactions occurring between PC films and gamma-APS primers were investigated by reflection - absorption infrared spectroscopy (RAIR) and X-ray photoelectron spectroscopy (XPS) using diphenyl carbonate (DPC) as a model compound. The carbonyl absorption band of neat DPC was observed at 1780 cm(-1). However, two carbonyl bands were observed at 1738 and 1652 cm(-1) in RAIR spectra of gamma-APS films that were reacted with DPC and were assigned to urethane and urea groups, respectively. XPS results revealed that urethane was the main reaction product between DPC and gamma-APS. It was concluded that urethane groups formed by the reaction of PC with gamma-APS were responsible for adhesion and scratch resistance of PC to ferroplate substrates that were primed with gamma-APS.