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 it can not have the function of defoaming. The surface tension of the coating is a variable factor, so the surface tension should be constant when using defoamer, and the change of surface tension should be taken into account.

 

Most of the surfactants used in coatings are incompatible with the function of defoamers. In particular, emulsifiers, wetting dispersants, leveling agents, thickeners and so on, they will affect the effect of defoamer. Therefore, we must pay attention to the relationship between different auxiliaries and choose the best balance point.

 

When the coating enters high temperature baking from room temperature, the instant viscosity will decrease and the bubble can be moved to the surface. However, due to the volatilization of solvent, the curing of paint and the increase of surface viscosity, the foam will become more stable, intercept on the surface and produce shrinkage holes and pinholes.

 

High solid thickness coating, high viscosity, high elastic coatings are very difficult to defoam, in these coatings, defoamer diffusion is difficult, the speed of changing from microbubble to bubble is slow, foam migration ability to the surface decreases, foam viscoelasticity and other adverse defoaming factors become common. Foam in these coatings is quite difficult to eliminate, it is best to combine defoamer and foam casting agent to use.

 

There are many ways for paint construction, brush coating, roll coating, spray coating, scraping coating, spraying, screen printing and so on. The foaming degree of different coatings is also different. Brush coating, roll coating generate more foam than spray and scratch coating, high temperature generate more foam than low one, but high temperature generated foam is easy to eliminate.