Effect of type and content of reactive diluent on the mechanical properties of automotive UV-cured clear coat

Photo induced polymerization is a rapidly expanding technology because of advantages such as high-speed curing, low VOC content, and low energy consumption. In this study we choose different functional acrylate monomers, for investigation the effect of reactive diluent and oligomer/monomer ratio on the mechanical behaviour of UV-cured automotive clear coats. 3 different ratios (%wt) of oligomer/monomer, 25:75, 50:50 and 75:25, was examined. Micro indentation and pendulum hardness shows that samples with higher monomer concentration (lower oligomer/monomer ratio) had lower hardness. Due to the rapid polymerization during UV-curing, more stress induced in the samples and shrinkage caused in defects such as curling and cracking. The surface roughness was determined by using Atomic Force Microscopy (AFM).