Brief Introduction of Defoamer for Waterborne Coatings


The bubble of water-based paint has always been a headache for producers and users. First, we talk about the generation and stability of bubbles. Simply speaking, the lower the surface tension is, the smaller the free energy required for the formation of the foam, the easier it is to produce bubbles. However, such a bubble is not necessarily stable. Only when the system contains surfactant, which can form elastic film, such as dispersant, thickener, leveling agent, can the foam stabilize.


Understanding the basic principle of foam stabilization, it is easy to defoam. First of all, we should pay attention to whether there is any component of foam stabilization in the system, and then choose the appropriate defoamer. Generally, silicon-containing defoamers have better effect, but we should pay attention to other properties. It should also be noted that different systems use different types of defoamers, such as acrylic emulsion, polyurethane dispersions, water-soluble resins and so on. The defoamers used in different systems are different. Many defoamers have strong defoaming ability, but their anti-foaming ability is poor, and they have little effect on the bubbles generated in the process of use. At this time, two or more defoamers should be considered, and they should be added twice. When grinding, defoamers with good anti-foaming effect should be added, and defoamers with good defoaming effect should be added when lacquering.


Of course, defoaming and system viscosity are also related, low viscosity defoaming naturally fast.


In addition, defoaming is also related to the volatility of the system. The quickly volatilized paint will dry up the surface. When the bubbles float to the surface before they burst, they will be fixed and accumulate more and more.


1. Selection of defoamer


There are many kinds of defoamers, such as organics, silica, organosilicon and so on. They are also divided into emulsified and non-emulsified. When choosing defoamers for waterborne coatings, we should pay attention to the following points:


(1) Strong defoaming ability; (2) good stability; (3) no influence on gloss; (4) no barriers such as re-painting.


It is suggested that the defoaming ability of defoamer should be tested by high-speed stirring method. Fixed speed, mixing time, dosage, viscosity and other parameters, then the height of foam and the time of elimination were compared.


2. The dosage of defoamer


Generally high viscosity latex paint, due to the difficulty of defoaming, foam stabilization factors are also more, a little more, generally 0.3-1.0%. Low viscosity latex paint or water-soluble paint, especially water-soluble paint, due to the presence of a certain amount of cosolvent, can be appropriately reduced, generally 0.01-0.2%. Other waterborne coatings or resins, generally about 0.1%. Anyway, the higher the dosage, the better. More will cause shrinkage, oil and other paint diseases. More silicon-containing defoamers will also affect the re-coatability.


3. Addition Method


Most defoamers can not be directly added to diluted waterborne coatings. Generally, they should be added when the viscosity of resin or coatings is high and have good dispersion. In addition, it is better to add two times, one time in abrasive and the other time in lacquering, adding half in each stage.


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