Studies On Synthesis And Curing Behavior Of Acrylic Anodic Electrophoretic Coating With High Hardness

Electrophoretic coating was a new type of environment-friendly water-borne coating, in which main film forming composition was ionized water-soluble resin. The principle of electrophoretic coating based on phenomenon of electrophoresis. In terms of the polarity of the electrodes acted by workpiece, the electrophoretic coating was divided into two kinds: anodic electrophoretic coating and cathodic electrophoretic coating. Because it can provide excellent corrosion protection, higher paint utilization and low environmental contamination, electrophoretic coating is now widely used in many fields, such as automobile industry, construction material, household appliances and hardware.There are some critical shortcomings existing in domestic products, such as low film hardness(2H~3H), bad film plummy degree, high curing temperature. At present, products of electrophoretic paint manufactured independently in our country were few and most of products were manufactured depending on foreign techniques. Therefore, it is necessary to do research on synthesis of new anodic electrophoretic coatings.Considering the low acid value and low hydroxy value in present anodic electrophoretic coating, acrylic resin having high acid value and high hydroxy value was prepared and characterized. Factors such as water solubility, molecular weight, cross-linked group and glass transition temperature were selected to adjust the formula and technics. The factors affecting the resin water-solubility were studied. Effects of initiator, reaction temperature, monomer concentration, feeding speed on molecular weight and its distribution were discussed. It was found that good resin water solubility and good film water resistance were achieved when the acid value ranged from 50 mgKOH/g to 110mgKOH/g and high hydroxy value ranged from 50 mgKOH/g to 150 mgKOH/g. In synthesis process of acrylic resin mentioned above, a little iso-bornyl methacrylate monomer was introduced. The results shows that this monomer not only decreased the viscosity of acrylate resin, but also improved film appearance and increased the film plummy degree, and this phenomenon was tried to explain from the structure of the monomer.The electrophoretic coating process was systemically studied. Considering the occurrence of dissolution current, the kinetic equation of film growth was revised as follow:...