Preparation And Properties Of Polyurethane Acrylate For UV Curable Cathodic Electrophoretic Paint

An acrylic copolymer with pendant hydroxyl was synthesized by using acrylic monomers in methyl ethyl ketone, and the synthesized acrylic copolymer was modified by the half adduct of isophorone di-isocyanate and β-hydroxyethyl methacrylate to prepare the modified acrylic resin containing both N, A'-dimethyl amino group and vinyl group applicable for UV curable cathodic electrophoretic paint. After neutralized by acid, the UV curable cathodic electrophoretic paint was prepared. The factors that influenced the dispersibility of the modified acrylic resin in water, and the film thickness of the electrodeposition were studied. And the parameters that influenced the curing time and properties of the cured film were also discussed.¹³C-NMR results showed that the half adduct of isophorone di-isocyanate and P-hydroxyethyl methacrylate could be obtained using dibutyltin dilaurate as the catalyst. It was found that the concentration of dibutyltin dilaurate, temperature and molar ratio of the reactants influenced the reaction time. Infrared spectroscopy results showed that both the unsaturated vinyl group and N, N-dimethyl amino group had been introduced into the modified acrylic resin, indicating that the modified acrylic resin could be applied to UV curable cathodic electrophoretic paint. Catalyst, temperature, influenced the reaction time of isocyanate in the half adduct with hydroxyl in the acrylic copolymer. The presence of catalyst accelerated the progress of the reaction, and the complexed catalyst exhibited higher efficiency due to its synergic effect.It was founded that the contents of N, N-dimethyl amino group and hydroxyl group in the resin, the neutralizing agent, and the neutralization degree, solid content influenced the dispersibility of the modified acrylic resin in water. The dispersibility of resin in water was improved with the increase of the contents of N, N-dimethyl amino group and the neutralization degree, and the viscosity of the electrophoretic paint increased. The dispersibility of the resin neutralized by lactic acid was muchbetter than that neutralized by acetic acid.The solid content of the electrophoretic paint, voltage, electrodeposition time, pH, and temperature had great effect on the thickness and appearance of the film.The contents of N, N-dimethyl amino group and hydroxyl group, and vinyl group had great effect on the properties of the film. The multifunctional monomers and photoinitiators influenced both the UV curing time and the properties of the film. With increasing the multifunctional monomer content, UV curing time of the film was shorted, and the pencil hardness, solvent resistance, adherence with the matrix were improved. In comparison with di-funtional monomer TPGDA, tri-funtional monomer TMPTA could improve the properties of the film. The photoinitiator content has great effect on both the UV curing speed and the properties of the film.