Effect Of Polymer Dispersant On Performance Of Waterborne Epoxy Coating

As an environmental-friendly coating,waterborne epoxy anti-corrosion coating has great significance to its development and research on environmental problems and corrosion protection.However,most of the research was to modified its pigments,fillers and resins to improve the anti-corrosion performance of waterborne epoxy coatings,there are few reports on the study of dispersants.The purpose of this paper is to study the effects of polyhydroxyl,epoxy hydroxyl and ammonia hydroxyl on the adhesion,water resistance and electrochemical failure mechanism of waterborne epoxy coatings.On this basis,the effect of the addition of modified antirust pigment calcium zinc phosphate on the protection of waterborne epoxy coating was evaluated.Firstly,the polyhydroxy waterborne epoxy coating was prepared.On the one hand,the molecular structure characteristics of polyhydroxy can enhance the adhesion between the coating and metal substrate,on the other hand,it can improve the crosslinking density of the coating and enhance the corrosion resistance of the coating.The adhesion test results showed that the polyhydroxy dispersant coating has high dry adhesion,which is about 5 MPa higher than the epoxy varnish system,and the wet adhesion is still as high as 7.8 MPa after 30 days.The electrochemical test results showed that after soaking in 3.5%NaCl solution for 10 days,the|Z|_{10 m Hz} remains above 10⁹Ω·cm²,which is about one order of magnitude higher than that of epoxy varnish coating,and the coating shows excellent corrosion resistance.Secondly,epoxy hydroxyl and ammonia hydroxyl waterborne epoxy coatings were prepared.Epoxy hydroxyl enhanced the adhesion between the coating and metal substrate,and ammonia hydroxyl improved the cross-linking reaction with resin molecules and enhanced the compactness of the coating.The adhesion test results showed that the epoxy hydroxyl coating has high dry adhesion,which is about 3 MPa higher than the epoxy varnish system,and remains about 6 MPa in the wet adhesion process of 60 days.The electrochemical test results showed that the|Z|_{10 m Hz} of ammonia hydroxyl coating after soaking in 3.5%NaCl solution for 10 days is 3.0×10⁹Ω·cm²,about one order of magnitude higher than other coatings,and its coating shows excellent barrier performance.Finally,the effect of ammonia hydroxyl polymer dispersant and antirust pigment calcium zinc phosphate on the performance of waterborne epoxy coating was investigated.The antirust pigment calcium zinc phosphate was added to the ammonia hydroxyl coating to prepare RZCP waterborne epoxy coating.On the one hand,the addition of calcium zinc phosphate destroys the compactness of the ammonia hydroxyl coating.On the other hand,calcium zinc phosphate hydrolyzes in the water environment and reacts slowly with the metal substrate,thus enhancing the wet adhesion between the coating and the metal substrate.The electrochemical test results showed that after soaking in 3.5%NaCl solution for 35 days,RZCP coating has lower impedance modulus compared with ammonia hydroxyl dispersant coating,and its|Z|_{10 m Hz} is about one order of magnitude lower than that of ammonia hydroxyl dispersant coating system,the corrosion morphology of metal substrates in different soaking stages was observed by scanning electron microscope（SEM）.The results showed that there were serious corrosion pits on the metal substrates of RZCP coating,indicating that the protective performance of the coating was poor.However,during wet immersion,RZCP coating maintains relatively high wet adhesion,which is about0.8 MPa higher than that of ammonia hydroxyl coating.