Why do waterproof coatings need to add defoamers?

Generally, waterproof coatings are very prone to producing bubbles without adding any additives. The important reason for bubbles is that the lower the surface tension is, the smaller the free energy required for the system to form foam is, 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.

Firstly, pay attention to whether there are stable foaming 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 acid lotion, polyurethane dispersion 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 film formation.

Defoamers are used to prevent the formation of bubbles in lubricating oil. The principle of action is to change the surface tension of foam to make small bubbles gather into large bubbles, so as to break the bubbles and achieve defoaming.

Waterproof coatings often produce a certain amount of foam when they are prepared, but the production of these foam is very unstable, as mentioned above. Only by adding a certain amount of coating additives can the desired effect be achieved.