Stress buildup in ultraviolet-cured coatings: Sample thickness dependence

Stress buildup in ultraviolet radiation-induced coating can vary significan tly as a function of processing conditions. Depending on radiation intensit y and photoinitiator concentration, the average stress in the film may eith er increase or decrease with film thickness. On the basis of the current st udy on trimethylolpropane triacrylate (TMPTA) together with data reported p reviously, we conclude that the two main factors affecting stress in radiat ion curable coatings are (i) degree and distribution of crosslinking and (i i) temperature at solidification point. In certain experimental conditions, an uneven distribution of the conversion within the film may occur, leadin g to a decrease of the average film stress with increasing film thickness. In contrast, the temperature jump in the sample when irradiated may lead to an increase of the ultimate stress with film thickness.