Photonic baking and radiation-curing with the near infrared radiation for fast laser or LED activation coating processes

 
Near infrared (NIR) light between was applied for the curing of coatings accelerating the industrial process. An adequate absorber covers at least two functionalities; generation of initiating species for photopolymerization and providing heat. Thus, these NIR initiators exhibit more features as usual UV photoinitiators by transferring heat within the coating by use of LED or laser light sources. Tests for the influence of the absorber concentration, the radiation intensity, and the dwell time of the exposure were made on blocked isocyanate/hydroxy-polyester coating systems. Surprisingly, a laser exposure of several seconds was sufficient for the curing, which usually requires oven times of 15 minutes at 150°C. Favored is the combination of radiation curing and photonic backing, which was achieved by interpenetrating networks from crosslinked photopolymers and baking varnishes without the use of volatile organic compounds. This also realizes photocuring systems with a high Tg and mechanical properties equal to oven cured processes.