Film Formation And Coating Performance For Styrene-acrylic Latex

The most distinguish difference between water-based coating and solvent based coating is the status of polymers. In water-based system, polymers disperse instead of being dissolved in the water, with the help of emulsifiers. Therefore, some differences occur in the process of film formation, which ultimately lead to difference in the film performances. In order to solve the problems of mechanical properties and processing, the study of film formation is necessary.In this article, UV-visible spectrophotometer (UV-vis), weight loss and other methods were used to explore the whole film forming process of styrene-acrylic emulsion. Furthermore, some properties of emulsion and film forming conditions were discussed. The article could be divided into three parts:The first session focus on the whole process of film formation. Particle deformed in wet sintering mechanism which is confirmed by AFM picture, when styrene-acrylic emulsion (Tg=17.8℃) drying in the temperature of 26℃ with relative humidity of 53%. Moreover, there are still some defects in the film though the coating exhibits optically transparent, water vapor transmission rate and the weight gained in re-immersion of water could be reduced by increasing drying time.The second session is about influence of emulsion properties. Tg and particle size were changed by changing monomer ration and amount of emulsifier. It’s found that, with the increase of Tg, Pe constant decrease, λ increase, performance of adhesion and impact strength deteriorated. However, the particle size influences the scattering coefficient, not the evaporation rate and mechanical properties.The third session is about influence of film forming conditions. Light transmittance cure move left as relative humidity decrease. And temperature affect deformation mechanism of particles, film will crack well below Tg. As for coalescent, it has more impact on the particle deformation than water evaporation. Deformation mechanism of particle move from cracking to dry sintering, capillary, skinning, more and more likely to form a uniform film. Moreover, the compactness of dry film enhance as the amount of coalescent increase.