Waterborne and solvent based coatings should use various additives in their formulations, including additives that help wet and disperse pigments; There are additives that improve the storage stability of finished coatings and additives that adjust the appearance of the coating film to be smooth; There are also some additives that achieve special functions. Most of these additives are surfactants, which can change the surface tension of the coating, resulting in the internal factors of the coating itself that are easy to foam or make the foam stable.
For water-based coatingsDefoamerThe reason is:
Bubbles in water-based coatings have always been a headache for producers 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. Of course, defoaming is also related to the viscosity of the system, as low viscosity naturally leads 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.
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) they have strong defoaming ability; (2) Good stability; (3) Does not affect gloss; (4) It is recommended to use high-speed stirring method to test the defoaming ability of defoamers without obstacles such as recoating. Fix the rotating speed, mixing time, dosage, viscosity and other parameters, and then compare the height of foam and the elimination time.
