Study On Epoxy Coatings With Lower Surface Treatment And High Adhesion On The Galvanized Steel

In order to extend the service life of components made up of the galvanized steel or corroded galvanized steel,it is usually necessary to prepare epoxy coating on these substrate.Due to the low surface energy of the galvanized steel and the presence of rust on the corroded galvanized steel surface,the adhesion of epoxy coating is very low.So surface pretreatment was applied before coating to improve the adhesion.However,after surface pretreatment,the increase of adhesion was very small.Therefore it is important to develop a kind of coatings with elementary surface treatment process and high adhesion.The key to the method is to add different kinds and concentration of additive to the coatings on the galvanized steel and the corroded galvanized steel with the rust percentage of35-55%.Then according to adhesion and corrosion resistance,the most appropriate additive was obtained.At last,by adding anti-sag agents to the coatings of the optimal additive,it was successful to promote the sag resistance.The main work of this paper including:The coating containing phytic acid,phosphate,tannins,EDTA,KH-560,KH-590 and sulfosalicylic acid was tested the adhesion with the purpose of determining the optimal additive.The analysis of the data showed that regardless of the galvanized steel and the corroded galvanized steel,the coating containing 2% sulfosalicylic acid had higher adhesion.On the basis of sulfosalicylic acid,the impact of concentration of sulfosalicylic acid on adhesion and corrosion resistance was studied.The results showed that the adhesion as well as corrosion resistance increased at the beginning and then decreased with the increase of sulfosalicylic acid content;when the concentration of sulfosalicylic acid was 3%,the composite effect of dhesion and corrosion resistance was best.There were the reasons for the change of adhesion: on one hand,sulfosalicylic acid can react with the coating and substrate;on the other hand,when the concentration of sulfosalicylic acid was too high,the reaction products between sulfosalicylic acid and substrates were loose.At same time,the corrosion inhibition of sulfosalicylic acid on the substrates and the decrease of the coating adhesion as well as the increase of the drops in adhesion caused that the corrosion resistance also increased at the beginning and then decreased with the increase of sulfosalicylic acid content.At last,flowing experiment was conducted.The results showed that the coatingscontaining 3%(the optimal content)sulfosalicylic acid had worse sag resistance.After adding the proper content of nano-silica,modified polyamide wax and CHX-100 to the coatings,the sag resistance was improved.By analyzing the datas of dry adhesion and EIS,we found that the coatings containing 3% sulfosalicylic acid and 1% modified polyamide wax had the best overall performance.