UV-Curable Acrylic Urethane Coatings for Weatherable Applications
The cure speed and film properties can be tailored to the application by varying the hardness (Tg) and functionality (EW or OH number) of the acrylic polyol; the isocyanate and solvents used; and by the addition of amine, tin or zirconium catalysts and activators. Heat can also be applied to accelerate the cure. Generally, the faster the cure, the shorter the pot life and the higher the VOCs. This is a significant limitation of 2K urethane coatings since one has to trade productivity for compliance, cost and ease of use.
UV-curable formulations typically contain an acrylated oligomer based on a polyether, polyester or epoxy resin. These oligomers are more difficult to prepare than the acrylic polyols used in 2K urethanes, which contributes to the high cost of UV-curable formulations. It is even more difficult to prepare acrylated urethane oligomers based on acrylic polyols because their high functionality often leads to gelling or high viscosities. We believe this has contributed to the slow growth of UV-curable coatings in applications where excellent UV stability is required, such as automotive clearcoats. Other limitations of UV-curable coatings include the absence of a dark cure mechanism, difficulty in spraying and curing 3D parts, and poor adhesion and flexibility due to shrinkage during the curing process.