The selection and application of defoamer is a very important technology for the formulation of waterborne industrial paint. The selectivity of defoamer to the system is very strong, and different systems have different requirements for defoamer. Improper selection or application of defoamer can result in:


1. Pinhole/shrinkage of the paint film, which greatly affects the appearance and luster




2. Paint film gap, seriously affect the water resistance and corrosion resistance






In order to better eliminate or suppress bubbles, we must first understand some basic principles of bubble stability.


one Surface tension


When the foam is formed, the total surface area of the system increases and the energy of the system increases accordingly. When the bubble burst, the total surface area of the system decreases and the energy of the system decreases accordingly. Therefore, the surface tension of the liquid is one of the factors affecting the stability of the foam.
2. Surface viscosity


The experiment and theory show that the key factor to determine the stability of the foam is the strength of the liquid film, and the strength of the liquid film depends on the solidity of the adsorption film at the interface, which can be measured by the surface viscosity.
3. Solution viscosity


When the foam is generated by a high-viscosity solution, the viscosity of the liquid film is inevitably large, which improves the stability of the foam. Another reason is that the bulk phase liquid has large viscosity and is not easy to flow, which hinders the liquid film drainage, slows down the thickness reduction rate, delays the liquid film rupture, and thus increases the stability of the foam.
4. The "repairing" effect of surface tension


Due to the large tension on the thin surface, it has the effect of shrinking the surface, and finally the surface tension is restored, the thickness of the liquid film is restored, and the strength is also restored. Then the foam shows good stability. This is called the "repair" effect of surface tension.
5. The diffusion of the gas inside the bubble through the liquid film


The bubbles are large and small, and the pressure of the small bubbles is higher than that of the large bubbles, and the gas can spontaneously diffuse and transfer from the small bubbles to the large bubbles. As a result, the small bubble gradually becomes smaller and disappears, while the large bubble gradually increases and eventually bursts.
6. Liquid film charge


If the liquid film of the foam has the same electrical charge, the two liquid surfaces of the liquid film repel each other, which can prevent the liquid film from thinning and breaking.