Preparation And Performance Of Silicone-Acrylic Hybrid Polymer Latex And High Dirt Pickup Resistance Coating

It is a technical difficulty that the dirt pickup resistance of architectural facade coatings is improved for architectural coatings,and it is an urgent problem for the coatings industry.Polydimethylsiloxane（D₄）structured silicone polymers have good hydrophobicity and dirt pickup resistance,but D₄ polymer resin coatings have the poor re-coat ability and are more expensive.Acrylic polymer coatings have good properties of film-forming,weathering,and good adhesion to a wide range of surfaces.In this paper,D₄ polymer latex and acrylate polymer latex were combined to produce blended silicone acrylic polymer latex and silicone acrylic graft polymer latex by using the physical blending method and the chemical graft modification method respectively.It is effective to exploit the respective properties of D₄ polymers and acrylate polymers to produce waterborne coatings of highly dirt pickup resistance.1.Silicone copolymer latex was prepared with D₄,ethyl orthosilicate（TEOS）andγ-methacryloxypropyltrimethoxysilane（A174）by semi-continuous emulsion polymerization.Acrylate copolymer latex was prepared with vinyltriethoxysilane（A151）and acrylate monomers by emulsion copolymerization.A mixed copolymer latex was prepared by blending the two latexes in different proportions.The findings showed that the ratio of PSi:PA of2:8 resulted in the film-forming and thermal stability of the obtained latex being comparatively good.Its contact angle was 102.9°±1.1°and the coating’s reflectance reduction rate was 13.60±0.68%less than acrylic coating（20.50±1.02%）.So,the dirt pickup resistance of silicone-acrylic coating was better.Other properties of its coating:water scrubbing resistance was more than10,000 times without leakage;ethanol scrubbing resistance is 1000 times with leakage;hardness was HB.2.The silicone acrylic hybrid latex was synthesized by semi-continuous seed emulsion polymerization.Firstly,the silicone copolymer latex was prepared by emulsion co-polymerization ofγ-methacryloxypropyl dimethoxysilane（ZH571）,tetramethyltetravinylcyclotetrasiloxane（D₄^V）and D₄;Then,this latex was used as the seed latex,and the emulsifier,free radical initiator,acrylate monomer and silane coupling agent（A174）were added to synthesize the core-shell silicone acrylic polymer latex for emulsion graft co-polymerization.The water whitening resistance of the film of the latex was 5levels,and its water absorption was 7.24±0.36 wt.%.The reflectance reduction of the coating was 9.83±0.49%.In addition,the system of self-crosslinking of room temperature of DAAM/ADH was introduced to acrylate monomers.The result showed that the reduction in reflectance of the silicone-acrylic coating further reduced to 3.60±0.17%.3.Three types of silicone acrylic polymer latexes[P（D₄）/P（MMA-BA-MAA-A174）、P（D₄-D₄^V）/P P（MMA-BA-MAA）、P（D₄-D₄^V）/P（MMA-BA-MAA-A174）]were synthesized by the seed emulsion polymerization method.The best overall performance of silicone acrylic polymer latex of P（D₄-D₄^V）/P（MMA-BA-MAA-A174）was finally selected through the study of particle size,stability and film-forming properties.Studies of morphology of latex particles of P（D₄-D₄^V）/P（MMA-BA-MAA-A174）revealed by transmission electron microscopy that latex particles were the structure of core-shell.And the silicone polymer tended to migrate towards the surface of the latex particles as the D₄^V content increased.DSC studies revealed that the glass transition temperature（Tg）of the polymer increased slightly as the D₄^V content increased.It was found that D₄^V had a positive effect on the dirt pickup resistance of coatings.Reflectance reduction of coatings was 2.65±0.18%when D₄^V was added to 23 wt.%with high dirt pickup resistance.Other properties of the coating:water-resistance was 0 S（1）;water scrub resistance was more than10,000 times without leakage;hardness was 2 H.The high dirt pickup resistance of exterior coating has reached.