Efficient drying and crosslinking of water-borne PUADs with near infrared radiation in one step

 
Increasing sustainability is one of the greatest challenges for development of new coating systems because of demands of the society and industry. Switching to water-based radiation-curable coatings is one approach to address this motivation. The overall CO2-footprint of water-borne coatings is in general already lower compared to conventional solvent-borne coatings. Water-based systems still have a big problem in energy consumption, costs, and CO2-emission because of the greater difficulty in the drying step considering time and temperature. This is often powered by natural gas. A solution is the combination of NIR radiation and cyanines to generate efficient heat inside of the coating to accelerate physical drying. These cyanines can also operate as sensitizer in a type II PI-system with iodonium salts. It is possible to incorporate a sulfonate functionalized cyanine with a barbituric substituent in the meso position and the iodonium lactate into a curable water-borne white coating without the need to use any further cosolvent. Upon irradiation (820 nm LED at 1 W/cm2) and purging with N2 it is possible to dry and crosslink the coating efficiently one process.