Bubbles of water-based paint have always been a headache for production and users. First, let's talk about the generation and stability of bubbles. In brief, the lower the surface tension, the less free energy required for the system to form foam, and the easier it is to produce foam. However, such foam is not necessarily stable. Only when the system contains surfactant that can form an elastic film, such as dispersant, thickener, leveling agent, etc., can foam be stable.

After understanding the basic principle of foam stabilization, it is easy to remove foam. First, pay attention to whether there are any foam stabilizing components in the system, and then choose a suitable defoamer. Generally, defoamers containing silicon have better effects, but it should be noted that they may affect other properties. It should also be noted that different types of defoamers should be used for different systems, such as acrylic lotion, polyurethane dispersion, water soluble resin and other systems. The type of defoamer applicable to each system is different, which should be verified through experiments. There are many defoamers with strong defoaming ability, but their defoaming ability is poor and they have little effect on the bubbles generated during use. In this case, it is necessary to consider mixing two or more defoamers and adding them in two batches. The defoamer with good defoaming effect should be added during grinding, and the defoamer with good defoaming effect should be added during painting.

Defoaming is also related to the viscosity of the system, with low viscosity naturally leading to faster defoaming.

In addition, defoaming is also related to the volatility of the system. Paint that evaporates quickly will dry out on the surface, and when bubbles float to the surface without bursting, they will be fixed and accumulate more and more.

1. Selection of defoamers
There are many types of defoamers, roughly including organic compounds, silica, organosilicon, etc., which are further divided into emulsified and unemulsified. When choosing defoamers for water-based coatings, it is important to note that,
(1) Strong defoaming ability;
(2) Good stability;
(3) Does not affect gloss;
(4) There are no obstacles such as repainting.
It is recommended to use high-speed stirring method to test the defoaming ability of defoamers. Fix the rotating speed, mixing time, dosage, viscosity and other parameters, and then compare the height of foam and the elimination time.

2. Dosage of defoamer
Generally, for high viscosity latex paints, due to the difficulty of defoaming and the presence of multiple stabilizing factors, the dosage should be slightly higher, usually 0.3-1.0%. Low viscosity latex paint or water-soluble coatings, especially water-soluble coatings, can be reduced appropriately due to the presence of a certain amount of cosolvents, usually 0.01-0.2%. Other water-based coatings or resins are generally around 0.1%. Anyway, the higher the dosage, the better. Too much can cause paint diseases such as shrinkage and oil stains. Too many defoamers containing silicon can also affect recoating properties.

3. Method of joining
Most defoamers cannot be directly added to diluted water-based coatings. They are usually added when the viscosity of the resin or coating is high and have good dispersion. It is also best to add it in two stages, one in the grinding material and the other during painting, with each stage adding half.

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