Novel Photoinitiator System for Simultaneous Physical drying and Free Radical Polymerization of Water-Borne Dispersions with Near-Infrared Excitation

Abstract

Energy efficient processes in industry represent a key factor to realize a fast transition to renewable energy sources. In the coatings industry, oven technologies applied for drying and curing, mainly contribute to energy consumption. Substitution of these wasting technologies by near infrared radiation (NIR) in combination with a NIR-absorber represents a promising alternative to reduce the energy use. Here, combining of a NIR-LED with a heptamethine cyanine operating as absorber can significantly accelerate the drying process of a water borne coating as measured by Laser Speckle Imaging (LSI). The combination of cyanine and bis(tert-butyl)iodonium salts as radical initiator results in an initiation system that efficiently works in combination with a NIR-LED to dry the coating followed by crosslinking in the same step. photo-DSC and FTIR measurements confirmed the results obtained. The use of a water compatible photoinitiator system based on a cyanine with sulfonate groups and bis(tertbutyl)iodonium lactate as water soluble coinitiator opened the possibility to eliminate the cosolvent needed for film formation and to create a complete VOC free formulation.