It can be created much more bubbles in architectural coatings because of emulsifier, dispersant and thickener. There will be surface defect, if the bubbles can not vanish. So, it is very important of defoamer in the architectural coatings.

The causes of generating bubbles:

①Fillers have large specific surface area, it can creating bubbles by adsorbing air.

②All kinds of surface active substance (emulsifier, dispersant, wetting additive, thickener, and so on ) also can generate bubbles.

③The air will enter into system and form bubble, because of mixing, dispersion, grinding and construction.

④Due to the side effects to produce CO2, resulting in bubbles.

Defoaming mechanism

Defoamer should be combined with the stable surfactant layer and penetrate into the bilayer, then quickly spreading, forming a double thin film, at last replace the film wall of the original foam. Liquid with low surface tension always flows to high surface tension. The local surface tension of the bubble film is reduced because of defoamer, while the remaining part of the membrane surface still maintains a large surface tension. The Unbalanced stress will cause the crack .

How to choose and apply ?

When a defoamer is effective in one system, you can not judge if it is also effective in another system. It is hard to choose a suited defoamer because there are many additives in water-based coatings. A defoamer should be tested to determine whether it suits or not. How to choose a suited defoamer? Surface tension and phase solubility are mainly considered. At the same time, the main film forming material and different additives will affect the use of different foam agent.