Preparation And Properties Of UV-Curable Waterborne Polyurethane Cathodic Electrophoretic Coating

Cathodic electrodeposition coating is one of the waterborne coatings. It has many advantages, such as high throwing power, compact and even films, high coating usage and so on. The traditional cathodic electrodeposition coatings are cured by heated. The heating temperature is generally higher than 150℃, and the curing process is commonly longer than 20 minutes. During the curing process, large amount of energy is wasted. Also, these heat curing cathodic electrodeposition coatings are not suitable for the heat sensitive materials. Ultraviolet(UV) curing cathodic electrodeposition coatings are cured by UV radiation. This curing process is not necessary of heating, and the curing speech is fast. Compared to the heat curing traditional cathodic electrodeposition coatings, UV curing cathodic electrodeposition coatings are not only energy-saving, but also suitable for the heat sensitive materials. In the available literatures about polyurethane-type UV curing cathodic electrodeposition coatings, cationic hydrophilic monomers are very rare, nearly all of them used N-Methyldiethanolamine(MDEA) as the hydrophilic monomer. When MDEA was used to synthesize the polyurethane, the hydrophilic groups were distributed in the backbone of the molecules. So, they had low freedom degree, and caused poor hydrophilcity.In order to solve the above problem, novel cationic hydrophilic diol monomers: DDDOD and MPDP bearing pendant tertiary amine groups were synthesized by the reaction between 1,4-Butanediol diglycidyl ether(BDDGE), diglycidyl ether(BADGE) and DEA, respectively. DDDOD, MPDP and MDEA were used as cationic hydrophilic monomers respectively to synthesize polyurethanes in the same way. The hydrophilicities of these three cationic monomers were compared by the content of the tertiary amine and the dispersibility of the dispersions. The experiment results showed that monomer DDDOD had the best hydrophilicity.Polyurethane emultifying epoxy acrylate type UV curing cathodic electrodeposition coatings were synthesized by the reaction between DDDOD, PCL1000 and IPDI. When the polymerization was complete, the tertiary amine groups were neutralized by lactic acid, UV curable monomers were added and dispersed with the pre-polymer together. The influences of different content and types of the UV curable monomers on the emulsions and films were studied. The results indicated that, with the increase of the content of UV curable monomers, the mean particle size was increased, the distribution ranges of the particles were broadened, Zeta potentials were decreased. When the content of UV curable monomers increased, the pencil hardness and alcohol resistance of the films were increased, and water absorption decreased. When used the epoxy acrylate as the UV curable monomers, most of the properties of the films were better than the films that using DPHA or PETA as the UV curable monomers. DSC graphs of the films showed that the cured films had two glass transition temperatures, which corresponding to the polyurethane and the crosslink structure of the polyacrylate.Meanwhile, aceylate modifying polyurethane type UV curing cathodic electrodeposition coatings were synthesized by the reaction between DDDOD, PCL1000, TMPDA, EA and IPDI. After neutralization, the polymer was dispersed with deionized water and formed dispersion. The properties of the coatings were measured by laser particle size analyzer, TEM analysis and TG analysis, also, the effect of hydrophilic monomer content and different blocking monomers on the properties of the coatings were studied.