Rheology and curing characteristics of dual-curable clearcoats with hydroxyl functionalized urethane methacrylate oligomer: Effect of blocked isocyanate thermal crosslinkers

Rheological and mechanical properties of dual-curable automotive clearcoats containing different blocked isocyanate thermal crosslinkers (HDI, IPDI, and SMBI) have been compared by changing dual-curing sequences, i.e., UV-thermal dual curing and thermal-UV dual curing. Real-time elastic modulus data of clearcoats measured during several curing procedures have been correlated with the formation of crosslinked networks inside clearcoats. Clearcoat with SMBI shows increased modulus data due to the more reactive nature of functional groups in SMBI. Difference of rheological data of clearcoats under different curing temperatures during dual-curing sequences has been interpreted with the transition of chemical reactions inside clearcoats with different chemical structured crosslinkers. It turns out that scratch properties of cured clearcoats are also affected by the dual-curing sequence.