Introduction to defoaming agents for water-based coatings
Bubbles in water-based paint have always been a headache for production and users. Let’s first talk about the generation and stability of bubbles. Simply put, the lower the surface tension, the smaller the free energy required for the system to form foam, and the easier it is to generate foam. However, such foam is not necessarily very stable. Only when the system contains surface-active substances that can form an elastic film, such as dispersants, thickeners, leveling agents, etc., can the foam be stable.
Once you understand the basic principles of foam stabilization, defoaming is easy. First, you must pay attention to whether there are foam stabilizing ingredients in the system, and then choose a suitable defoamer. Generally, silicon-containing defoamer will be better, but Be aware that it will affect other performance. It should also be noted that different systems require different types of defoaming agents, such as acrylic emulsion, polyurethane dispersion, water-soluble resin, etc. The types of defoaming agents applicable to each system are different, and the details must be verified through experiments. There are many defoaming agents that have strong foam-breaking ability, but poor foam-suppressing ability and have little effect on the bubbles generated during use. At this time, it is necessary to consider the mixed use of two or more defoaming agents, and they should be separated. Add it twice. When grinding, add a defoaming agent with good foam-suppressing effect. When painting, add a defoaming agent with good foam-breaking effect.
Of course, defoaming is also related to the viscosity of the system. Defoaming will naturally be faster if the viscosity is small.
In addition, defoaming is also related to the volatility of the system. Paint liquid that volatilizes quickly will dry up on the surface. When the bubbles float to the surface and have no time to burst, they are fixed and accumulate more and more.
1. Selection of defoaming agent
There are many types of defoaming agents, including organic matter, silica, and organic silicon, which are further divided into emulsified and non-emulsified. What everyone should pay attention to when choosing defoamer for water-based coatings is:
(1) Strong defoaming ability; (2) Good stability; (3) Does not affect gloss; (4) No obstacles such as recoatability.
It is recommended that you use high-speed stirring method to test the defoaming ability of the defoaming agent. Fix the parameters such as rotation speed, stirring time, dosage, viscosity, etc., and then compare the height of the foam and the elimination time.
2. Dosage of defoaming agent
Generally, for high-viscosity latex paints, due to difficulty in defoaming and many factors for stabilizing foam, the dosage is slightly larger, generally 0.3-1.0%. Low viscosity latex paint or water-soluble paint, especially water-soluble paint, contains a certain amount of co-solvent, so the dosage can be appropriately reduced, generally 0.01-0.2%. Other water-based coatings or resins are generally around 0.1%. Anyway, the higher the dosage, the better. Too much will cause paint problems such as shrinkage, oil blooms, etc. Too much silicon-containing defoaming agent will also affect the recoatability.
3. Joining method
Most defoaming agents cannot be added directly to diluted water-based paints. They must be added when the viscosity of the resin or paint is high and have good dispersion. In addition, it is best to add it in two times, one time in the grinding material and the other time when the paint is made, adding half at each stage.
