Improvement Of Alkyd Resin Emulsion Stability And Coating Performance

Volatile organic compounds(VOCs)in solvent-based coatings have caused serious environmental pollution.It is absolutely necessary to develop the water-borne coating for paint industry.The phase inversion method is an important way to prepare water-borne coating.However,there are some insufficient on the emulsion stability and coating performance of the prepared alkyd emulsions now.Thus the further improvement is needed to promote the industrial production.In order to improve the emulsion stability and the coating performance,protective colloid was introduced into the phase inversion process during emulsion preparation.In view of the poor water resistance of coatings and loss of dry upon storage of emulsions,the effect of drier on emulsion drying and storage process was studied.A solvent-based drier suitable for alkyd emulsions was developed.The mechanism of loss of dry upon storage of emulsion was investigated by infrared spectroscopy(FTIR),gel penetration chromatography(GPC)and X-ray photoelectron spectroscopy(XPS).Specific research contents and results are as follows:Arabic gum,oxidized starch and polyvinyl alcohol(PVA)were selected as protective colloid.The influence of protective colloid on the phase inversion process,the performance and stability of emulsions,the microstructure of emulsions and the coating performance were studied.Using the simplex lattice point mixture design,optimized the protective colloid formula,and got the optimal formula: 1.20% Arabic gum,0.50% oxidized starch,0.30% PVA 1788(The alkyd resin quality as the benchmark,similarly hereinafter),the viscosity of emulsions was 43.11 Pa·s.,the average particle size was 0.561 ?m,water absorption was 5.30%.By the stability test of emulsions,there was no delamination,flocculation phenomenon.The 60° gloss of the coating was 86.2 GU,reaching the standard of bright finish(>60 GU).There was no significant difference between the validation experiment and the predicted value(p>0.05),and the accuracy and reliability of the model were excellent.Compared with emulsions without protective colloid,the dilution,freeze-thaw,storage stability,gloss and water resistance of the coating are improved obviously.Different types of driers were used to affect the drying process of the coating.When the metal ratio of the drier was 0.05%Co,0.3%Zr,0.2%Ca,and the addition amount of 2,2'-bipyridine was 0.5%,the surface-drying time was 3 h,the through-drying time was 6 h,the roughness of film Ra was 2.59 nm,and the 60° gloss was 85.6 GU.After 72 h water resistance test,the surface of film was normal.The traditional solvent-based drier had been successfully applied to water-borne coatings.The drying effect is better than that of water-borne drier in the market,and the cost is lower.At same time,the water resistance of coatings and the anti-drying of emulsions is also improved.Upon the process of emulsion storage,hydrolysis of alkyd resin will happen,and produce a part of carboxyl group,which will lead to the decrease of p H value of emulsions,the decrease of system stability and the increase of viscosity.The content of O-C=O and C-O-C valence bond structure in the coating decrease,which indicates that the hydrolysis of alkyd resin and the decrease of the drier activity may be the main reasons for loss of dry upon storage of emulsions.