Application Of Ketone-Hydrazide And Blocked Isocyanates Double Cross-Linking System In Cathodic Electrodeposition Coating

Cathodic electrophoretic coating has been widely used in the areas of automotive industry, home appliances, auto parts, and high performance decoration applications. However, it has several disadvantages, such as high curing temperature, high consumption of highly toxic curing agents, and poor film performance. This dissertaion aims to solve above-mentioned problems.In this paper, the epoxy-acrylic grafted copolymer, which has the advantages of both epoxy and acrylate resins coating, were firstly synthesized usingfunctional monomer GMA, cross-linking monomer DAAM and other acrylic monomers viasolution polymerization. Then, the copolymer was treated with water to form emulsion. The mechanism of the grafting reaction as well as the effects of the amount of functional monomer, ring opening of epoxy resin, electrical conductivity and the degree of neutralization have been studied in details.. It is found that the introduction of functional monomer GMA effectively improves the self-emulsifying ability and the storage stability of the emulsion.The effects of different curing systems, such as ketone-hydrazine system with self-crosslinking ability at room temperature, water-based blocked isocyanate system, which can takes place crosslinking reaction at relative lower temperature, and the dual crosslinking systems of ketone-hydrazine and water-based blocked isocyanate on the performance of electrophoretic coating have been studied. In addition, the effects of the amount of crosslinking agents, baking temperature, and baking time werealsostudied. It was found that when ketone-hydrazine crosslinking system was used alone, the performance of the cathodic electrodeposition coating can not met requirements of industry application; when water-based blocked isocyanate cross-linking system was used alone, although the coating's overall performance was greatly improved, the dosage of isocyanates is too large, which is almost 20% of resin; while the dual cross-linking system was used, not only the performance of the resin is excellent but also the usage of blocked isocyanates was reduced from 20% to 10% of resin.Finally, formula and the processing technology of the epoxy-acrylic cathodic electrophoretic coating were conducted. After studying the effects of the film-forming additive and the leveling agent on the performance of the coating, the best dosages and ratios were determined, which can ensure a smooth appearance free from shrinkage, orange, peeling defects.. Furtherly, by studying various processing factors affecting the film properties, the optimum processing conditions were determined, and the resultant electrophoretic film have good appearance and excellent performance.