| Due to the pollution of light environment and changes in people's aesthetic concepts,the market share of low-gloss coatings has increased year by year.Silica has been widely used as matting agent in coatings because of its excellent extinction property and chemical stability.Fumed silica has good dispersibility and excellent matting effect in the coating matrix,but its fabrication process is rigorous and costly.Precipitated silica has disadvantages such as easy aggregation,poor compatibility with organic polymers due to its plenty of hydroxyl groups and high surface activity.In recent years,a series of surface modified silica have been prepared by liquid phase in situ surface-modification technique in our group,which has good dispersion stability and high reinforcement in a variety of polymer materials.In this thesis,the extinction property of surface modified silica in coatings is studied.Based on the relationship between the surface parameters and the extinction properties of silica,the silica matting agent with large pore volume and high dispersion is further synthesized.The specific research contents include the following three parts:1.Silica is incorporated into polyurethane coatings through mechanical blending to obtain extinction coatings,the performance of which is investigated by rotational viscometers,double-slot scraper fineness meters,multi-angle gloss meters and solar film testers.First,the influence rules of the oil absorption value and pore volume of silica on the matting properties of the coatings are studied.Results indicate that the increase in oil absorption value and pore volume is beneficial to improving the extinction performance of silica.After addition of DNS-3,the gloss of coatings decreases from 7.2 to 1.0;the increase in the addition amount could also increase the extinction performance within a certain range,e.g.increasing the amount of DNS-3 from 1% to 3% leads to the extinction ratio of the coatings increased from 52.8 % to 86.1 %.Second,the effect of SiO2 particle size(indicated by the D50 value)on the properties of the coatings is investigated.Since the films are thin,the gloss tends to decrease as the particle size decreases,e.g.from 3.5 in 17.7 ?m to 1.5 in 5.6 ?m.Third,the influence of silica treated at different temperatures is explored on the performance of the coatings.Annealing at 200 °C can further improve the dispersion of silica in coatings and increase the transparency of the film.2.Silica is uniformly dispersed into acrylic acryl paint by mechanical blending to obtain low-gloss paint.The effect of the amount of silica on the extinction performance of coatings is investigated.Results demonstrate that the increase in the amount of silica can effectively improve the extinction performance within a certain range.As the amount of DNS-3 is increased to 4.5 %,the extinction ratio is 95.4 %,which is comparable to OK520,but the effect on transparency and viscosity of coatings are inferior to OK520.Moreover,SiO2 particles with various sizes(represented by D50 value)from 6.7 ?m to 17.7 ?m are prepared to investigate the influence of particle size on the extinction performance of the matting agent.Results show that the gloss of the coating tends to decrease with the increase of particle size.For 6.7 ?m SiO2,it exhibits comparable extinction effect with OK520,yet higher transparency,which is capable to replace the commercially available imported OK520.Silica treated at 200 °C improves the extinction performance without affecting other properties.3.The large pore volume and high dispersive silica matting agent S-XGJ is prepared by the precipitation method and azeotropic distillation.SiO2 particles with sizes of 5.9 ?m and 6.9 ?m are incorporated into above-mentioned two coatings by mechanical blending,respectively.The extinction effect of S-XGJ is comparable to C803 in polyurethane and higher than OK520 in baking paint.Thus,as-prepared S-XGJ is promising to replace the commercially available imported precipitated silica matting agent C803 and OK520. |
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