UV-Radiation curing of waterborne acrylate coatings

A kinetic study of the ultrafast curing of water-based acrylate resins upon UV irradiation was conducted by means of infrared spectroscopy. Under intense illumination, the crosslinking polymerization was found to occur in the dried film within less than one second to generate a totally insoluble polymer. The influence of a number of critical factors on the polymerization rate and cure extent has been investigated, namely the type of photoinitiator, the chemical structure of the acrylate functionalized oligomer, and the sample temperature. Coating obtained from emulsions undergo a faster and more extensive polymerization than coatings obtained from dispersions, because of a greater molecular mobility in the soft low-modulus polymer formed. Very hard coatings were produced by the UV curing of dispersion-type acrylate resins, especially when the UV irradiation was performed at 80°C on the sample emerging from the drying oven. Tg values up to 120°C were reached when such resins were UV-cured at ambient temperature as 1-mm thick plates, because of the large amount of heat released during such ultrafast polymerization. UV-cured coatings made of aliphatic polyurethane-acrylates proved to be very resistant to accelerated weathering in the presence of adequate light stabilizers.