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替换城市 Principle and influencing factors of special No Foam agents for paints(4)

2023-05-01

varnish

matte

agent

When the paint is baked at high temperature at room temperature, its viscosity will drop at the beginning, and bubbles can move to the surface. However, because of the volatilization of solvent, the curing of paint, and the increase of surface viscosity, the foam will become more stable and retain on the surface, resulting in shrinkage and pinholes. Therefore, the baking temperature, fixing speed, and solvent volatilization rate also have an impact on the effect of defoamer.

The study of foam can be traced back to Plato's time, but for hundreds of years, people have not formed a unified understanding of the definition of foam. American colloid chemist L · I · Osipow and Dow Corning's R · F · Smith defined foam from the density of foam; Japan's Koichi Ito defined foam from the perspective of foam structure, but ignored the correlation between bubbles; Professor Zhao Guoxi, a famous surface physicist in China, defined foam as: foam is a dispersion system in which gas is dispersed in liquid, gas is a dispersed phase (discontinuous phase), and liquid is a dispersion medium (continuous phase). Bubbles in liquid rise to the liquid surface, forming a bubble aggregate composed of a small amount of liquid that separates gas with liquid film. Scholars at home and abroad agree that foam itself is a thermodynamic unstable system. When the gas enters the solution containing surfactant, it will form a long-term stable foam system.

ink

additive

Solid content, viscosity, elasticity of paint

替换城市  High solid thick film, high viscosity and high elasticity coatings are very difficult to defoamer. In these coatings, defoamer diffusion is difficult, microbubbles become larger slowly, foam migration ability decreases, foam viscoelasticity is large and many other adverse defoamer factors. Foam in these coatings is very difficult to eliminate, so defoamer and defoamer should be used together.