Interfacial spectroscopic studies of UV cured urethane acrylate coatings

Interfacial structural changes of UV cured urethane acrylate coating films were investigated using ATR FTIR spectroscopy. These studies show that at t he film-air (F-A) interface, when photo-initiator levels do not exceed 0.1% w/w, the band area ratio of H-bonding to non-H-bonding carbonyl stretching vibrations is proportional to UV energy density. However, when the initiat or level is increased to 5% w/w, an increase of up to 200 mJ/cm(2) UV power is required in order to achieve a similar band ratio, and at higher photo- initiator levels, the amount of energy levels off. Analysis of the H bonded to non-H-bonded band ratio near the film-substrate (F-S) interface shows t hat the band area ratio increases further away from the interface. At shall ower depths, around 0.84 mu m from the F-S interface, the magnitude of the H-bonding/non-H-bonding is smaller than that observed for the same penetrat ion depths before UV exposure for lower photo-initiator concentration or lo wer energy UV exposure. (C) 1999 Elsevier Science S.A. All rights reserved.