| Most of the building's exterior wall in the developed countries are decorated and protected by paint,and the protection of the external walls of buildings in China are mainly decorative tiles.This situation formed a very important factor is that comprehensive performance of emulsion is poor,and the existence of exterior house paint with poor weathering,low anti-contamination,short life,and so on.So to develope a new type of exterior house paint overcome these shortcomings with broad prospects.This paper synthesized a kind of Silica- styrene-acrylic composite emulsion using in-site emulsion polymerization, systematically studied on the main properties of emulsion such as choice and ratio of monomer,silica content, ratio and the amount of compound emulsifier,the ratio of initial emulsifier,the amount of initiator,and so on.At the same time, analyzed the formation of emulsion by FT-IR,and was compared to styrene-acrylic emulsion,Sol/styrene-acrylic blendemulsion and Sol-coupled styrene-acrylic composite emulsion,focused on contamination resistant coating system and its aging properties.As follows:1. Formula design(1) With the increase of soft monomer,Tg reduced,water resistance increased, film-forming declined, the surface was tacky. When the ratio of hard and soft monomers was 2:3,viscosity was the smallest,size was smaller,solid content was larger,Tg=19.6℃;gloss was the largest, water absorption was smaller.(2) The relative content of the hard monomer was more,the response time was longer,the proportion of hard monomer was greater,the contrast ratio of the coating was better. When the ratio of the two hard monomer was 3:2,response time was the shortest,size was smaller,gloss was better.(3) With functional monomer increased, water absorption first reduced then increased. Whenω(AA) =3.0%,conversion rate,Tg and solid content was high, viscosity was lower, water absorption was smallest,and polymerization and chemical of emulsion were all good.(4) The proportion of silica was the greater,conversion rate of the monomer was more white time of coating was shorter,the hardness was greater; silica which was relatively high will cause system instability.Whenω( silica)=25%,the emulsion had good stability,conversal rate was high,white time was long,particle size was smaller,hardness was up to 5H.(5) With composite emulsifier increased, the react stability enhanced,particle size decreased,condensate also greatly reduced, the chemical stability declined, water absorption increased, filming was white and difficult to film. Whenω(emulsifier)= 3.2%,A:B=2:l,the emulsion had good stability, hardness, water resistance, and its cohesion was low.(6) With the initiator C increased, conversion rate of monomer increased, aggregates increased.Whenω(initiator concentration)=0.43-0.47%, the emulsion had higher conversion rate and aggregate stability.2. Polymerization processWhen the emulsion react T=75℃,ν(monomer droplet)=1drop/s,ν(stirring)＞400r/min in the pre-emulsion phase, v(stirring)≈320r/min in the polymerization phase,ν(stirring)≈180r/min in the insulation phase,pH=6-8,using pre-emulsified monomer dropwise method could obtain better emulsion, and its mechanical properties was also superior to the copolymeremulsion.3. The structure and group of latex particles characterizationThe Silica coupled styrene-acrylic compound emulsion distributed more evenly in lowmagnificial TEM;30K times,the composite latex particles arranged evenly into a uniform sphere,formating into a network structure basicly;generating a part of RP-core-shell structural particles which was for silica-shell,and this core-shell structure changed with the amount of silica changed;FT-IR further proved monomer involved in the reaction,and appeared Si-O-C,Si-O-Si (chain) and free Si-OH,Si-(CH3) characteristic absorption peaks in compound emulsion,instructed Silica and organic polymer formed a chemical bond.4. Comparing with the dirt and anti-aging resistance of the coatingThe dirt resistance of the styrene acrylate/silica composite painting improved about 10% than the best silica coupled styrene-acrylic emulsion;analysising and comparing comprehensively anti-aging performance of the four coating systems, Fully instructed emulsion which was prepared in the test had stronger anti-ultraviolet ability. |
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