ABSTRACT:In radiation-cured acrylate coatings, a high conversion of monomer is generally desired to improve hardness, prevent further slow reaction upon aging, and avoid surface toxicity; however, shrinkage and, consequently, stress in coatings tend to increase with conversion. One route to achieve high conversion while maintaining low coating stress is to promote stress relaxation. In this study, acrylate coatings were cured with a UV lamp that was cycled on and off, varying the period from 2 to 60 min while keeping the total dose constant. All samples reached nearly the same conversion, between 46 and 48% conversion of functional groups, as measured by FTIR spectroscopy. The coating stress (measured with cantilever deflection) at the end of the exposure cycles, however, was lowered from 8 MPa (tension) to less than 3 MPa (tension) as the period was decreased from 60 to 2 min. The cycling had no significant effect on either the coating hardness or the modulus, as measured by a Hysitron triboscope. Stress relaxation and/or slower reaction during the dark periods are the likely causes for the lower coating stress. It was advantageous to introduce dark periods early in the processing.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.