Volume shrinkage of UV-curable coating formulation investigated by real-time laser reflection method

Volume shrinkage is one of the main drawbacks of UV-cured coatings and can lead to premature coating failures. Due to the rapid polymerization during UV-curing, real-time volume shrinkage has been challenging to measure accurately. In this article, the shrinkage process of UV-curable formulations was systematically investigated by a recently developed laser reflection method. The influence of oligomers, monomers, and photoinitiators on shrinkage process has been evaluated. Compared with the oligomers, the monomer was the main contributor to shrinkage due to the high concentration of double bonds. Polymerization shrinkage could be reduced by increasing the oligomer/monomer ratio. Because monomers were the main contributors of shrinkage, the chemical structure of monomers was important for decreasing shrinkage. Methacrylate monomers decreased the final shrinkage but unfortunately reduced the conversion. Monomers with a high degree of ethoxylation lowered the shrinkage and simultaneously increased the conversion. The concentration of photoinitiators had no obvious effect on the normalized shrinkage. Thus, the low shrinkage caused by the low concentration of photoinitiators was only attributed to the significant drop of the conversion.