Preparation And Properties Of Water-based High Hydroxyl Acrylate/Isocyanate Composite Coatings

Hydroxyl is the main functional groups in acrylic resin molecular chain.Acrylic resin coating which has excellent advantages in weather,chemical and heat,is an essential part of water-based coating field.Since acrylic resin has various modification methods,it can meet the performance requirements of different industry and widely used in outdoor buildings,furniture and other fields.But due to the disadvantages of low solid content and hydroxy1 content of hydroxy acrylic resin,the problems such as low crosslinking density,low fullness,insufficient salt spray resistance and weatherability of paint film will exist.Therefore,by optimizing the synthesis process and adjusting the monomer ratio,the preparation of water-based high-hydroxyl acrylic resin with high solid content,low viscosity and high crosslinking degree will greatly improve the application space of acrylic resin coatings.In this paper,a series of water-based high-hydroxyl acrylic(WHPA)emulsions with core-shell structure were synthesized by reverse emulsion polymerization.The influence of polymerization temperature and fractional acrylate monomer polymerization ratio at step 1 and step 2 on the performance of WHPA emulsion was investigated.At the same time,by adjusting the dosage of functional monomers such as HPA,AA and GMA,the basic performance of WHPA emulsion was analyzed and the appearance,roughness and other aspects of morphology were observed and characterized,so as to obtain the best synthesis scheme.Thermal stability,TEM and IR spectra of WHPA emulsion show that WHPA emulsion with core-shell structure has been successfully prepared by reverse emulsion polymerization.Among them,there is a certain cross-linked structure between the core and the shell,the core is hydrophobic polymer molecular chain and the shell is hydrophilic polymer molecular chain.When the optimal reaction temperature for the preparation of WHPA is 130?,the cooperative conversion rate of initiator is moderate and the conversion efficiency is the best.When the polymerization ratio of step 1 and step 2 of functional monomers is 3:1,the thermal stability of the latex film is good.When the ratio of hard and soft monomer is 20:54,the dosage of functional monomer AA is 2.9 wt.%,the dosage of GMA is 0.9 wt.%and the dosage of HPA is 12.9 wt.%,the viscosity of the obtained WHPA emulsion is 343 mPa·s,the solid content is 47%,the particle size of the latex particles is 143.3 nm and the stability of WHPA emulsion is the best.WHPA emulsions with different hydroxyl values were also synthesized successfully by changing the dosage of functional monomer HPA.According to rheological,appearance morphology analysis and other basic performance analysis,WHPA emulsions showed a viscous behavior when the HPA dosage is 11.3 wt.%,12.9 wt.%and 14.5.%.The series of WHPA emulsions has high stability and low viscosity.WHPA emulsion was cross-linked with HDI trimer to prepare WHPA/NCO composite coatings.The water resistance,impact resistance and fl exibility of the WHPA/NCO composite coatings with different HDI trimer,TiO2 and paint mixing agent dosage were investigated.The results showed that-OH can combine well with-NCO to prepare a precipitation-free composite coating with excellent performance.The addition of titanium dioxide paste can make the composite coating more compact.The appropriate amount of defoaming agent can reduce the amount of side reaction foam and reduce the shrinkage phenomenon on the coating surface.When the hydroxyl value is 132.3 mgKOH/g,HDI trimer dosage was 12 wt.%,TiO2 dosage was 30 wt.%and defoaming agent dosage was 0.075 wt.%,the water resistance,salt spray resistance and impact resistance of composite coatings and composite coatings were optimized.The water absorption of the film is 6.0%,the surface gloss of the film was 92.6°,the adhesion was 1 grade,the impact resistance was excellent,the sample water resistance was up to 48 h,WHPA/NCO composite coating showed good comprehensive performance.In conclusion,WHPA emulsion with high hydroxyl content,core-shell structure and excellent stability can be successfully prepared by the method of reverse emulsion polymerization and step by step addition.WHPA/NCO can be used to improve the impact resistance,water resistance and corrosion resistance of outdoor light anticorrosive composite coating.