Preparation And Characterization Of Waterborne Epoxy Anticorrosion Emulsion

Waterborne epoxy emulsion not only has the advantages such as excellent adhension,corrosion resistance,chemical stability and mechanical properties as it contains epoxy resin,but also has the economic and environmentally friendly superiorities as waterborne emulsion.It has attracted significant attention and has been one of the main development directions in the application of anticorrosion coatings.At present,researches about waterborne epoxy resin focus more on emulsification of epoxy resin by extra emulsifier.However,the emulsion obtained by adding emulsifier presents large particle size,poor stability and difficult to store.Moreover,the emulsifier will transfer to the surface during the process of film formation,which will result in film with worse appearance,water resistance and solvent resistance.Therefore,chemical modification method was used to prepare waterborne epoxy emulsion in this paper.This paper introduces a method for preparing waterborne epoxy resin emulsion by grafting the methacrylic acid(MAA)to the epoxy phosphate.The obtained emulsion can be used in waterborne epoxy anticorrosion coatings.Firstly,the bisphenol A typed epoxy resin was partly esterified by phosphoric acid.Then MAA was used as functional monomer to modify the epoxy resin.Finally,the modified product was neutralized and dispersed in water to form waterborne epoxy resin dispersion.This paper consists the following four parts.Part one,the effects of reaction conditions such as molecular weight of epoxy resin,introduction of phosphoric acid,reaction temperature,solvent and its dosage,neutralizer and reaction time were discussed.The results showed that when E20 was used as matrix,the amount of phosphoric acid was 2%,the reaction temperature was 110-115 ℃,using propanediol methyl ether and n-butanol as solvents and the mass ratio to E20 was 3:4,triethylamine for neutralizer,reaction time maintained 4h,the emulsion was stable with good performance.The polymerization mechanism was proved through FTIR and chemical titration.The results indicated that the unsaturated monomers were grafted onto the aliphatic carbon chain of the epoxy resin and the polymerization reaction was graft copolymerization.Part two,the effects of the initiator BPO,functional monomer MAA on the performance of emulsion and latex film were discussed.The results showed that with increasing amount of BPO,the conversion rate and viscosity firstly increased then decreased,the particle size firstly decreased then increased.The particle size was between 200-300nm and presents monodispersity.When the amount of BPO was 2.5-4%,the emulsion was stable.When the amount of MAA increased,the conversion rate increased,the particle size decreased and the viscosity firstly increased then decreased.The morphology of the latex particles presented regular,nearly spherical and uniformly dispersed.The emulsion was stable when the amount of MAA was 22-25%.The water absorption of latex film increased and Tg decreased with increasing amount of MAA.The modified epoxy resin appeared two thermal weightlessness peaks and the thermal stability decreased.Part three,the waterborne epoxy resin emulsion was cured.The self-curing mechanism was analyzed and the effects of curing conditions were discussed.The results indicated that when the self-curing temperature was 140℃,the film presented higher degree of cross linking,good adhesive force and impact strength,and water resistance of more than 15 days.The film presented good appearance,well adhesive force,impact strength and water resistance of more than 15 days when the amount of WH260 was 25%and the curing temperature was 110℃.Part four,electrochemical methods were used to evaluate the anticorrosion properties of self-cured films.The results showed that the open potential was-0.623V(Vs SCE)when the coating system was immersed into 3.5wt%NaCl solution initially.The coating presented good anticorrosion properties with a maximum resistance of 108Ω and a stable value of 105Ω at the interim immersion,which was slightly lower than the empirical value 106Ω of organic coating at the initial immersion.