Preparation and characterization of thermal-resistant epoxy-polyurethane composite coatings

A hydroxy-containing novolac epoxy resin was obtained from bisphenol A epoxy resin after modification by benzoic acid,and then cured with toluene diisocyanate trimer and phthalic anhydride as curing agents to form a thermal resistant epoxy-polyurethane composite coating.The effect of the amount of novolac epoxy resin introduced to polyurethane system on the thermal resistance of coating was studied by changing the ring-opening rate of benzoic acid-modified novolac epoxy resin.The benzoic acidmodified novolac epoxy resin and its curing reaction were studied by Fourier-transform infrared spectroscopy.The thermal stability of the novolac epoxy-modified polyurethane(MPU) was studied by thermogravimetric analysis,and the coating performances were tested.The results showed that the thermal resistance of polyurethane is significantly improvedby introducing the novolac epoxy resin.The novolac epoxymodified polyurethane coatings(MPUs) with various ringopening rates have an initial decomposition temperature over 350 ℃(higher than that of the traditional acrylic polyurethane by 30 ℃),a transition temperature over 380 ℃,and an final decomposition temperature over 430 ℃.The hardness of the coatings with good resistance to water,acid and alkali is up to 3H.The prospective coating performance indexes can be achieved by adjusting the ring-opening rate,because the flexibility,impact resistance,hardness and adhesion of the coating changes with the difference of ringopening rate.The adhesion of the coating becomes poor when the ring-opening rate is above 40%.