Abstract
To elucidate the effect of short-wavelength vacuum UV (VUV) irradiation on the UV curing and matting of acrylate formulations, a real-time (ATR) FTIR 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 μm). 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.
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