Perfect layers: a novel class of waterborne 2 components isocyanate curing resins

摘要

Coalescents are critical in every waterborne paint formulation. Both the concentration and the type of co-solvent can have a profound effect on film properties. By using specially designed solvent free secondary polyol emulsions, so called NOVOS emulsions, the effect of various co-solvents on the film performance of waterborne 2 component polyisocyanate crosslinking coatings could be determined. Especially the evaporation rate of co-solvents has a strong effect on properties such as drying time, chemical resistance and Konig hardness. Coatings with a slowly evaporating coalescent yielded longer tack free times, reduced Konig hardness and in some cases even reduced chemical resistances. When co-solvents with a high evaporation rate were used, tack free times were achieved that were even shorter than that of solvent free formulations. It was shown that evaporation of water is accelerated when using fast solvents. Formulations containing no coalescent at all showed a very promising set of film properties, with high Konig hardness, short tack free times and very good chemical resistances, thus providing the ideal approach to zero-VOC coatings. Because of the nature by which the NOVOS emulsions are prepared, the concentration of acid rich polymer chains is much reduced. This causes the resulting binders to have a significantly improved blister free film thickness (BFFT) compared to traditional secondary emulsions.