How to speed up the UV curing of water-based acrylic coatings

Water-based polyurethane-acrylate (PUA) coatings have been cured, after drying, by a short exposure to UV radiation in the presence of a radical-type photoinitiator. The light induced polymerization has been followed quantitatively by means of real-time infrared spectroscopy, by monitoring continuously the disappearance of the acrylate double bonds. The UV curing of the dry film was markedly accelerated by adding to the PUA formulation a reactive plasticizer (diacrylate monomer), by operating in a humid atmosphere or by raising the temperature. The neutralizer of the carboxylic groups, needed to get a stable dispersion, plays a key role in both the polymerization kinetics and in the hydrophilic character of the UV-cured polymer, the best performance being achieved by using a volatile tertiary amine. Water-based UV-cured PUA coatings combine hardness and flexibility and are, therefore, quite resistant to abrasion and scratching.