Preparation Of High Hydroxyl Content Self-emulsifying Polyester And Study On Its Modification Of Polyacrylate

Waterborne coatings have been attracting much attention because of their safety and environmental protection.As representative coatings,waterborne polyester coatings and waterborne polyacrylate coatings are widely used in construction,automobile,wood and other fields.The ester bond of waterborne polyester is easy to hydrolyze,which limits its application.The emulsifiers used in the waterborne polyacrylate emulsion affect the performance of the film,and also cause corrosion to the metal substrate.In this paper,high hydroxyl content self-emulsifying waterborne polyester was synthesized,then polyester was introduced to modify polyacrylate,which solved the problem of residual emulsifier and improved the poor flexibility of polyacrylate film.Hexanediol(HG),neopentyl glycol(NPG),trimethylolpropane(TMP)were used as alcohol components,adipic acid(HA)was used as acid component.Free carboxyl groups were introduced through the end-capping of hexahydrophthalic anhydride(HHPA),and self-emulsifying waterborne polyester was obtained by neutralizing and dispersing in water after salt formation.High content of hydroxyl group was supplied by TMP,and the reaction temperature was 140~180?,the process of stepwise feeding and stage heating method was adopted.It showed that the high hydroxyl content self-emulsifying waterborne saturated polyester(WSP)with good storage stability and water resistance have been successfully synthesized.The selection of monomers,catalyst and reaction temperature was studied experimentally,the optimal polymerization conditions were determined according to the designed resin formula: the mole ratio of alcohol to acid was 1.07,the TMP content was 70% of the total amount of alcohol component and the ratio of the stepwise feed was 1:1,the HHPA content was 12%,the HG/NPG molar ratio was 1/2~1/4.The solid content of prepared waterborne polyester was 50%,the acid value was 45 mgKOH/g,and the hydroxyl value was 217 mgKOH/g.The particle size was 83 nm,PdI was 0.141,the molecular weight was 1780,and the viscosity was 1340 mPa·s.The coating film prepared by self-emulsifying waterborne polyester dispersion with amino resin had excellent comprehensive properties.The waterborne polyester modified polyacrylate emulsions were prepared by modifying the polyacrylate with self-emulsifying waterborne polyester through two methods,physical blending and chemical copolymerization.Waterborne unsaturated polyester(WUP)was prepared by WSP modification.In emulsion polymerization,WSP was used instead of emulsifier,while WUP acted as both emulsifier and reactive monomer.The modified emulsions with good performance and storage stability were obtained by pre-emulsification and seeded semi-continuous emulsion polymerization.It showed that when the chain transfer agent was 1%,the WSP/AC=1:10,the emulsion solid content was 47.5%,the average particle size was 209 nm,PdI was 0.141,the molecular weight was 4410,the viscosity was 385 mPa·s,and the resin had good thermal stability.When WUP/AC=1:5,the emulsion solid content was 47.5%,the average particle size was 173 nm,PdI was 0.043,the molecular weight was 5570,the viscosity was 298 mPa·s,and the emulsion had good comprehensive properties.It showed that compared with polyacrylate emulsion,the molecular weight of the polyester modified emulsion decreased,the viscosity increased,the water resistance and hardness of the film increased.In addition,the thermal stability of WSP-AC decreased slightly,the thermal stability of WUP-AC increased significantly,and the particle size of WUP-AC was smaller and distribution was narrower than that of WSP-AC.The adhesion of amino polyacrylate coating prepared by two modified emulsion was 1 grade,the flexibility was 1 mm,and the water resistance was good.