Selection and dosage of defoamers

The lower the surface tension of water-based paint, the smaller the 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, for defoamer, first pay attention to whether there are foam stabilizing ingredients in the system, and then select appropriate defoamer. Generally, silicon containing defoamer will have a better effect, but pay attention to 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 that have strong defoaming ability, but their anti foaming ability is poor, and they have little effect on the horizontal foaming generated during use. In this case, it is necessary to consider using a mixture of two or more defoamers.

1. Selection of defoamers 

There are many types of defoamers, roughly divided into organic compounds, silica, organosilicon, etc., and further divided into emulsified and unemulsified. When choosing defoamers for water-based coatings, it is important to note that they have strong defoaming ability; Good stability; Does not affect gloss; There are no obstacles such as repainting. It is suggested to use the high-speed stirring method to test the defoaming ability of defoamer, fix the rotational speed, stirring time, dosage, viscosity and other parameters, and then compare the height of foam and the elimination time.

2. The 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 numbers 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.