The Study On Synthesis, Structure And Properties Of Acrylic Cathodic Electrodeposition Coating

Electrodeposition coating was a new type of coating, originated in1960s. Because of its unique properties, electrodeposition coatings were widely applied, such as large project of car body, little of badge or glass frame. Electrodeposition coating had high technological content, which study and produce were regarded one of the most difficult coating, especially its requirements of use and management were stricter than that of traditional coatings. Therefore, the research and development of elecrtodeposition coating have great significance.Acrylic resin has many incomparable advantages such as good weather resistance, gloss and color retention. In view of that, a series of cationic acrylate oligomer was designed and synthesized. And then the resin water dispersibility, the structure and properties of acrylic cathodic electrodeposition coating were systematically studied.The designed acrylate oligomer used for cathodic electrodeposition was synthesized by free radical solution polymerization, using methacrylate dimethyl ammonia ethyl as a special monomer. The molecular weight and its distribution were controlled by the initiator, chain transfer agent, reaction temperature, feed way. And the GPC results show that the number average molecular weight is3000-4000and its distribution is below2.5. The amino and hydroxyl content were determined by titration method. While its amine value is50-60mgKOH/g, its hydroxyl value is60-70mgKOH/g. And the acrylate oligomer was further characterized by infrared spectroscopy, thermal analyzer, rotating viscometer.The cathodic electrodeposition coating was prepared using the acrylic resin, blocked isocyanate as curing agent and water. The effect of resin structure, the coating formulation, dispersion processes on the water dispersibility of acrylic resin and coating stability was studied. And the amino groups and the neutralization degree are the two most significant factors of which affect the acrylic resin water dispersion and coating stability. The DLS results show that the colloidal particle size is about120nm with PDI0.18below. After stored at room temperature over six months or centrifuge (3500r/min,30min), the coating had no bad changes, which improved its high stability.On the basis of a systematic study on the structure of acylate oligomer and coating stability, The electrodeposition process was studied by the electrophoretic coating device which set up by ourselves. The effect of voltage, time, temperature, electrode spacing and curing conditions on film performance was studied. Finally, the better condition was ensured:coating solid content10-15%; neutralization degree70-80%; voltage80-120V; coating temperature25-30℃; electrode spacing10-12cm; curing temperature180℃; curing time20min. And the resulting films have very good performance:adhesion1grade; pencil hardness3-4H; impact resistance50kg-cm; water resistance over20days. The SEM photos show that the film cured good and have smooth surface. The TG diagrams show the curing films have better heat resistance than the acrylic resin which its initial weight loss temperature increases by70℃. The electrochemical impedance spectroscopy (EIS) effectively evaluate the corrosion resistance of the film, showing that the impedance of the electrophoresis coating film is30times of regular film, improving the excellent corrosion resistance.