UV curable polyurethane-based microspheres

Radiation curable polyurethane-based microspheres were prepared by modifying conventional procedures for preparing anionic polyurethane dispersions. Vinyl groups were introduced to the side chains and the ends of the polyurethane main chains. Photoinitiators and multifunctional acrylate oligomers were incorporated into each microsphere. The curing behavior of the films obtained from these microspheres under UV were studied. The MEK resistance of UV cured films without multifunctional acrylate oligomers was raised when the content of vinyl groups is above a certain threshold value. The effect of the incorporation of multifunctional acrylates oligomers on MEK resistance was observed. This effect was remarkable at low UV irradiation intensity. The curing behavior of the films was followed by real time FT-IR spectroscopy. The accelerating effect of the incorporation of multifunctional acrylates became striking particularly at the early stage of curing process. Multifunctional acrylates were found to be effective in raising the extent of the conversion of the double bonds. The curing behavior under UV irradiation was compared with that under EB irradiation. (C) 1999 Elsevier Science B.V. All rights reserved.