What is the role of coating wetting agents?

In general, the interaction between the wetting agent and the specified polymer dispersion is critical in order to achieve good adhesion and appearance. Wetting agents not only affect the wetting performance by reducing the surface tension, but also have a significant effect on film formation and leveling. In addition, they also have an effect on foam stabilization. Of all the wetting agents tested, the overall effect of the fluorinated propylene-containing polymer was very good. Product 3370 had good wettability while having little effect on adhesion and defoaming.

According to the formula, the pressure at the boundary of the Plateau is less than the pressure in the liquid film, that is, the pressure at the liquid film P is less than the pressure at A. Due to the existence of this pressure difference, the liquid will automatically flow from A to P for drainage, making the liquid film thinner. When the thickness of the liquid film is lower than a certain critical value, the liquid film will rupture. According to the Laplace formula, the pressure difference between the boundary of the liquid film and the flat film is proportional to the surface tension, that is, when the surface tension is low, the pressure difference is small. Therefore, the slower discharge speed will extend the foam life L3.42.

Some scholars believe that in high-viscosity coatings, it is very important to dissolve spherical bubbles into dissolved substances by controlling the diffusion of air into the liquid phase. This should be buy polyethylene wax considered as a mechanism to further remove stable bubbles. According to the opinion of Epstein and Plesset, for the spherical bubbles surrounded by the liquid phase to dissolve, the required time increases with the third power of the spherical bubble radius, which means that especially small spherical bubbles (<5pm) will be preferred Dissolved and disappeared.

The above is just an explanation from the nature of the bubble. However, it takes a long time for a relatively stable foam system to achieve the above-mentioned natural defoaming, which is unrealistic for industrial production, so defoamers are always used in most cases.