UV-curable polyurethane dispersion for cationic electrodeposition coating

UV-curable polyurethane dispersions were prepared for cationic electrodeposition coating. Methacrylate groups were introduced to the ends of the polyurethane main chains by a sequential condensation reaction. The neutralized polyurethane polymer containing photoinitiator with or without multifunctional acrylate (pentaerythritol triacrylate, PETA) could be dispersed into a stable dispersion without any phase separation. The size of the particles in these polyurethane dispersions was approximately 100 nm, and increased slightly with the incorporation of PETA. The electrodeposition process was used to introduce UV-curable polyurethane dispersions into the nickel-plated plastic substrate. The drying process of the electrodeposition film was completed in 6 min under infrared radiation, which is comparable to the time taken when using a conventional UV coating system. Studies of the kinetics using real-time FTIR and photo-DSC revealed that the cross-linked films containing PETA gave a higher conversion rate than those without PETA, resulting in better resistance to methyl ethyl ketone.