Mechanism of action and development trend of defoaming agent for waterborne coatings
                        
                        Bubble control is necessary in many industries, such as papermaking, water treatment, pharmaceuticals, dyes and coatings.With the continuous upgrading of national environmental protection regulations and the continuous improvement of residents' environmental awareness, water-based coatings have made great progress.Emulsifying agent and wetting dispersant in waterborne coating formula reduce the surface tension of the system and stabilize the bubbles in the system easily.The existence of bubbles will have a negative effect on the production and coating of coatings.During the grinding process of paint, the "air bag" formed by bubbles around the filler reduces the transfer efficiency of shear force and increases the grinding time.After coating, the residual dry foam on the surface will not only affect the appearance of the coating, but also become the center of corrosion, reducing the durability of the coating.In order to eliminate these problems, almost all waterborne coatings need to add defoaming agent.The active component of defoaming agent can achieve the purpose of defoaming by interfering with and destroying the stabilizing effect of bubbles.Different types of defoaming agents act in different ways, so understanding the mechanism of action of defoaming agents can help to systematically adjust the key physical and chemical parameters, so that the main steps in the mechanism can be controlled to achieve the best defoaming efficiency. 1, the stability of bubbles Water - based coatings in the production process, mechanical mixing is easy to bring air into the system.In the process of coating construction, brush, roller and spray are easy to bring gas into the wet film.Other porous substrates, such as wood panels and cement, release gases into the film as the paint wets and penetrates.The gas brought into the coating system is surrounded by the liquid phase and forms a bubble, and relies on electrostatic action and surface tension gradient to maintain stability. 1.1 Electrostatic Action Water-based coating formula contains a variety of surfactant substances, the special point is that the molecule contains a polar or charged hydrophilic end base and a hydrophobic hydrocarbon chain.This unique molecular structure makes it easy for surface activators to form micelles in a directional arrangement at the gas-liquid interface, as shown in Figure 1, with the hydrophilic end facing the water phase and the hydrophobic end facing the air. Because the density of air is less than the paint, so once the bubble will rise to the paint interface.According to Stokes' law, the bubble rising rate depends on the radius of the bubble and the viscosity of the paint [4].The larger the half diameter of the bubble, the lower the viscosity of the coating, the faster the bubble rise.Microbubbles usually exist in coatings with large specific surface area, resulting in high surface freedom energy.Thermodynamically, microbubbles are so unstable that they spontaneously fuse wit...
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