UV-radiation curing of waterbased urethane-acrylate coatings

A kinetic study of the drying and UV-curing of waterbased urethane-acrylate formulation was conducted by means of infrared spectroscopy. The water rel ease upon heating of the dispersion was shown to depend on the temperature and on the film thickness. The drying of a 30 etam thick coating was comple ted in <2 min upon heating in an oven at 80<degrees>C. The influence of a n umber of critical factors on the polymerization kinetics has been investiga ted, namely the type of photoinitiator, the sample temperature, the chemica l structure of the functionalized oligomer and its acid content. As expecte d, the latter factor has a strong effect on the properties of the UV-cured coatings, in particular their hardness and their hydrophilic character. The water uptake and the softening of coatings placed in a wet atmosphere was found to be directly related to the carboxylic acid content of the urethane -acrylate polymer. This phenomenon is fully reversible and does not affect the long term properties of the UV-cured coatings. (C) 2000 Elsevier Scienc e S.A. All rights reserved.