Abstract:

Waterborne two-component polyurethane （2K-WPU） coatings were prepared from hydrophilically-modifled polyisocyanate reacting respectively with an aqueous hydroxy-polyacrylate emulsion （PAE） and its dispersion （PAD）. Then, the viscosity, hardness, gloss and chemical resistance of the films were measured to investigate the physicochemical behaviours of 2K-WPU during the storage. The results indicate that （ 1 ） with the increase of storage time, the viscosity of PAD-based 2K-WPU slowly decreases, along with an increase in bubbles and micro-foams in the film, the film hardness first decreases and then increases, and the chemical resistance decreases after a storage for 3h; （2） as for PAE-based 2K-WPU, the viscosity disorderly changes, the film hardness gradually decreases, the chemical resistance decreases after a storage for 4 h, and the bubbles in the film even disappear; （3） neither the particle diameter nor the gloss of PAE- and PAD-based 2K-WPU shows obvious change during the storage; and （4） PAD-based 2K-WPU is of better film performance but slightly shorter pot life than the PAE-based one （about 4 h）. It is thus concluded that it is not the viscosity but the chemical resistance and appearance of the film that determine the pot life of 2K-WPU before the application.

Key words: two-component polyurethane coating, pot life, waterborne hydroxy-polyacrylate, hydrophilicallymodified polyisocyanate, curing agent