UV curing and matting of acrylate nanocomposite coatings by 172 nm excimer irradiation, Part 2

To elucidate the effect of short-wavelength vacuum UV (VUV) irradiation on the UV curing and matting of acrylate formulations, a real-time (ATR) FUR spectrometer attached to a UV lamp set-up consisting of a monochromatic 172 nm (Xe-2*) excimer lamp or a polychromatic medium pressure mercury arc lamp has been applied. In the presence of a photoinitiator, both the 172 nm excimer lamp and the mercury lamp yielded a similar degree of acrylic C=C bond conversion, i.e. the wavelength of UV irradiation was found to have no significant impact on acrylate conversion. But, short-wavelength VUV irradiation of acrylates results in radical formation and self-initiation of the photopolymerization, i.e. photoinitiator-free curing of acrylates. Furthermore, real-time (ATR) FTIR spectroscopy showed a decrease of the intensity of C=O vibrations by 172 nm irradiation within thin layers (<1 mu m). This radical formation via C=O bond activation is assumed to occur at the surface of thoroughly cured films yielding a higher network density of the coating via radical recombination reactions. Thus, UV-matted acrylate coatings show enhanced surface hardness and improved chemical resistance. (C) 2010 Elsevier B.V. All rights reserved.