UV curing of aqueous polyurethane acrylate dispersions. A comparative study by real-time FTIR spectroscopy and pilot scale curing

Real-time FTIR spectroscopy was used to study the chemical and physical fac tors, e.g., photoinitiator and temperature, affecting the UV curing of drie d films from aqueous polyurethane acrylate dispersions. Poor conversion of the acrylate double bonds (67%) observed at room temperature can be overcom e by irradiation at elevated temperatures. At 353 K almost complete convers ion is observed, even with reduced photoinitiator content. Single or multip le UV-light flash experiments were performed to simulate technical paramete rs, e.g., cure speed and number of required UV lamps, with the help of RTIR spectroscopy. The results obtained were confirmed by pilot-scale UV curing experiments: one or, at most, two UV lamps of high intensity are sufficien t for the curing process with respect to the double-bond conversion. The co atings based on the polyurethane acrylate dispersion show low sensitivity t owards oxygen from air. Moreover, in comparison to UV curing under inert ni trogen atmosphere, a small "positive" effect on the conversion in the prese nce of air has been observed, which might be due to the contribution of per oxyl radical or their decomposition products to curing.