Development And Research Of New Cationic Acrylic Resins Used As Cathodic Electrophoretic Coating

With the gradual strengthening of people’s awareness of environmentalprotection, especially in the two sessions held this year, both from the central to localenvironmental protection has gone beyond GDP as the most concerned about the topic.Therefore, the coatings were gradually developed in the direction of lowenvironmental toxicity and high automation. Electrophoretic coating is an aqueouscoating using water as major. And it is considered as a promising coating species fromsafety, environmental or cost. Electrophoretic coatings are widely used as primercoatings in automobile, electrical equipment, instrument, etc. Cathodicelectrodeposition coatings also have the advantages of high usage and less corrosiveto small parts except above mentioned advantages.Acrylic resin series cathodic electrodeposition coatings have higher decorativethan other cathodic electrophoretic coating. They have been received more and moreattention used in the field of hardware, home appliances, and other metal partsindustry. An acrylic resin series cathodic electrophoretic paints were developed in thispaper. The performance of the acrylic resins and the stability of the electrophoreticcoating emulsions were studied in detail.A series of acrylic resins with a solids content of50%, which have side hydroxylgroups and tertiary amino groups, were synthesized by free radical solutionpolymerization using methyl methacrylate,2-hydroxylethyl methacrylate,dimethylamino ethyl methacrylate,2-ethylhexyl acrylate and butyl acrylate asmonomers. The molecular weights of the synthesized resins were studied from theinitiator, the reaction temperature and the polymerization process, etc. The numberaverage molecular weight of the resins were about20000Dalton and the molecularweight distributions were about2.12, which were tested by GPC. And the glasstransition temperature was about49.4℃. The structure and properties of the resinswere characterized. From amine value, hydroxyl value, solid content and the infraredabsorption spectrum.The blocked isocyanate curing agents were synthesized using methyl ethylketone oxime as blocking agent and isophorone diisocyanate trimer as a curing agent,it was proved that NCO groups are completely blocked because the characteristicabsorption peaks between2000cm-1and2500cm-1in IR spectrum have disappeared. The cathodic electrodeposition coating emulsion was prepared using abovesynthesized blocked curing agent and acrylic resin. Its neutralization degree wasbetween40%and100%, and its solid content was between10%and15%. It wasstudied that the relationship between the intrinsic viscosity and composition,neutralization degree and the preparation process of the resin and the freeze-thawstability, electrolyte stability, mechanical stability of the emulsion. The results showedthat the mechanical stability of the emulsion was increased with the decreases of thespecialty viscosity of the resin and with the decreases of the soft monomer content ofthe resin. And the stability of the emulsion prepared by phase transfer method washigher than that prepared by no phase transfer method.Finally, the upper and lower phase emulsion extracts were characterized byinfrared absorption and elemental analysis. It was found that the phase separationreasons for electrophoretic coating emulsion was the binding power was poor betweenthe molecular chain of the resin and curing agent, and so the upper phase was mainlyacrylic resin and the lower precipitation phase was mainly blocked isocyanate curingagent.