Direct esterification of a hydroxyl functional polyester resin with p-hydroxybenzoic acid. Part B: Coating preparation and evaluation

Comparison of the physical properties of direct esterified, both purified and unpurified, and standard polyester coatings was undertaken. Clear and pigmented baked enamels, both non-cross-linked and cross-linked, were produced. Results indicate that coating binders containing the unpurified direct esterified resin are potentially superior to conventional binders as they exhibit the outstanding feature of being both hard and flexible. This improvement is due to the presence of unreacted p-hydroxybenzoic acid in the resin and is not due to a liquid crystal phase. The improvement in physical properties is dependent upon the bake conditions used, with temperatures of 232 °C causing a marked decrease in coating performance.