Influence of functional group content in hydroxyl-functionalized urethane methacrylate oligomers on the crosslinking fea
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Influence of functional group content in hydroxyl-functionalized urethane methacrylate oligomers on the crosslinking features of clearcoats Young-Gun June, Kevin Injoe Jung, Dong Geun Lee, Subin Jeong, Tae-Hee Lee, Young Il Park, Seung Man Noh, Hyun Wook Jung
American Coatings Association 2020 Abstract Crosslinking characteristics and surface mechanical properties of radical and urethane dualcurable clearcoats were investigated by changing quantities of C=C bonds and OH groups in hydroxylfunctionalized urethane methacrylate oligomer (HFUMO) resins. The isocyanate blocked with a thermal radical initiator (BL-Tri-cHD) was utilized as a hybrid dual-curable thermal crosslinker to expedite the crosslinking of the main resin. The dual reactions between various HFUMO resins and BL-Tri-cHD were efficiently monitored via Fourier transform infrared spectroscopy to measure the peaks before and after curing. The influence of each functional group (C=C bond or OH group) in HFUMO on the initiation and development of crosslinking in dualcurable clearcoats was investigated by real-time measurements using rotational rheometer and rigid body pendulum tester. Temperature-dependent mechanical properties of cured films were confirmed through dynamic mechanical analysis. The surface mechanical properties of cured clearcoat films were also evaluated via the nanoindentation and nanoscratch tests, demonstrating the variation in surface resistance with respect to the C=C bond content and the OH value. Thus, the low-temperature curing and desired mechanical properties of clearcoats can be optimized by adjusting the Young-Gun June and Kevin Injoe Jung have contributed equally to this work. Y.-G. June, K. I. Jung, D. G. Lee, H. W. Jung (&) Department of Chemical and Biological Engineering, Korea University, Seoul 02841, Republic of Korea e-mail: [email protected] S. Jeong, T.-H. Lee, Y. I. Park, S. M. Noh (&) Research Center for Green Fine Chemicals, Korea Research Institute of Chemical Technology, Ulsan 44412, Republic of Korea e-mail: [email protected]
content of the functional groups in a HFUMO and using a dual-curable crosslinker to simultaneously generate both radical and urethane crosslinking reactions. Keywords Low-temperature curing, Clearcoat, HFUMO binder, Dual-curable crosslinker, Crosslinking dynamics, Surface resistanceYoung-Gun June and Kevin Injoe Jung have contributed equally to this work.
Introduction Automotive coatings play an important role in modulating the energy efficiency of the coating process. Exterior coatings of car bodies consist of multiple layers, such as the electrocoat, primer, basecoat, and clearcoat. The outermost layer is known as the clearcoat. It protects the car body and the inner coatings against surface defects, harmful chemicals, acid rains, scratches, UV rays, and bird droppings.1,2 To form a dense crosslinked network in the clearcoat layer, a rather high curing temperature greater than 150C in an oven is required for 25–35 min. Recent studies in energy-saving, low-temperature curing tec
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