(180aa) Characterization of UV-Thermal Dual Curable Clearcoats Using Rotational Rheometry: Effect of Thermal Radical Initiator (TRI) and Photo Initiator (PI)

Incorporating UV-thermal dual curable polymers containing hydroxyl groups and unsaturated double bonds for the enhancement of crosslinking network in paints, curing characteristics and rheological properties of automotive clearcoats were systematically investigated by changing process conditions such as UV dose, thermal curing time, and curing temperature. The storage modulus (G’) and loss modulus (G”) were obtained from the frequency sweep test by rotational rheometer. The storage modulus and loss modulus can convert to the loss tangent, tanδ (=G”/G’), determining the gel point which the phase transition occurs. Also, other mechanical properties and scratches were compared using various methods such as rigid-body pendulum tests and nano scratch tests for ensuring the high performance of clearcoats. It is found that the UV-thermal curing process induced a remarkable degree of crosslinking for the cured clearcoats and also the UV-thermal sequence and the contents of thermal radical initiator (TRI) and photo initiator (PI) affected the curing behavior of dual curable clearcoats. From these results, we cared to elucidate the optimal combination of TRI and PI.