Influencing factors and selection of defoamer in paint formulation
Factor 1: Surface tension
The surface tension of the coating has a great influence on the defoamer. The surface tension of the defoamer must be lower than that of the coating. Otherwise, the defoaming and anti-foaming effect can not be achieved. Surface tension of coatings is a variable factor, so when choosing defoamer, the surface tension should be constant, and then the factors of surface tension change should be taken into account.
Factor 2: The influence of other additives
Most surfactants used in coatings are incompatible with defoamers tending to function. Especially emulsifier, wetting dispersant, leveling agent, thickener and so on will affect the effect of defoamer. So we must pay attention to the relationship between different auxiliaries and choose the best equilibrium point when compounding various auxiliaries.
Factor 3: Baking temperature
When the coating enters the high temperature baking at normal temperature, the viscosity will decrease immediately, and the bubbles can move to the surface. However, due to the evaporation of the solvent, the solidification of the coating and the increase of the surface viscosity, the foam will become more stable, and it will be trapped on the surface, resulting in shrinkage holes and pinholes, so the baking temperature, fixed speed and solvent evaporation rate will be eliminated. The effect of foaming agent is also affected.
Factor 4: Solid content, viscosity and elasticity of coatings
Coatings with high solid content, high viscosity and high elasticity are very difficult to defroster. In these coatings, defoamer diffuses difficultly, the bubble speed is slow, the migration of foam to the surface decreases, and the viscoelasticity of foam is large. The foam in these paints is quite difficult to remove. It is best to choose defoamer and defoaming agent.
Factor 5: Painting Method and Construction Temperature
There are many methods of coating construction, such as brushing, roll coating, spraying, scraping, spraying, screen printing and so on. The foaming degree of different coatings with different coating methods is also different. Brush and roller coated foam is more than spray and scraping. When the temperature is higher than the temperature, foam will be more, but when the temperature is high, the foam will be eliminated.
Selection of defoamers for different applications
There are many kinds of defoamers with different characteristics, so the defoamers selected in different formulations are also different.
From the Global Coatings Ecosphere