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Defoamers use the principle of incompatibility and ground surface tension to achieve defoaming effects. If an additive is compatible with the system being used, it is usually stable in foaming. Only when it is incompatible can it have the effect of defoaming. However, excessive incompatibility can improve the defoaming effect. But it may also cause many problems with the paint film, such as shrinkage, fisheye, turbidity, and loss of gloss, such as orange peel, poor leveling, and so on. So the selection of defoamers must pay attention to balancing. To achieve the desired defoaming effect without causing paint film defects.

In addition, the compatibility of the same defoamer varies in different resin systems, and some differences can be significant. Therefore, the selection of defoamers for different resin systems may be completely different and cannot be fully applied based on experience. If a good defoamer is used in one system, I can directly apply it to another resin system, which may cause major problems.

Because defoamers are incompatible in the system, the addition of defoamers must be thoroughly stirred and then dispersed into small droplets to avoid local accumulation caused by the excessive size of the defoamer droplets, which can lead to shrinkage and paint film defects. We recommend high-speed dispersion or grinding after adding all defoamers. We can add this defoamer in stages, such as during the grinding stage, which requires a defoamer with strong anti foaming ability. Usually, we choose a highly effective defoamer with poor compatibility to prevent the generation of bubbles.

In the paint mixing stage, we need defoamers with good bubble breaking ability and compatibility to eliminate existing bubbles and avoid shrinkage. The amount of digestive agent added is usually between 0.05% and 0.5% of the total formula. Excessive addition may cause problems such as shrinkage or floating oil. This is not absolute either. We have some systems with high viscosity and thick paste, such as screen printing. The amount of defoamer added reaches 3% to 4% of the total formula, and it cannot be eliminated without adding enough defoamer. However, the use of digestive agents in conventional systems is not necessarily better. Excessive addition can cause shrinkage, oil droplets, and affect interlayer adhesion.

The fourth factor is that the construction method also has a significant impact on the selection of defoamers. For example, brushing and rolling can easily trap bubbles. Require defoamers to have stronger defoaming ability.

The coating process has higher requirements for the defoaming ability of defoamers. If it’s a regular air spray, we know that at the moment of atomization, even if there is a bubble, it will break. So for car repair paint and some industrial paints that have been sprayed, this defoamer is often rarely added.

The fifth one is thick paste coatings, which often have relatively difficult defoaming. In addition, defoaming in high viscosity systems is relatively difficult. This is because the bubble must rise to the surface in order to break. If we break or bubble inside the liquid, the bubble is the whole gas wrapped inside the liquid, and the foam must rise from the bottom to the top.

But the process of rising is related to the viscosity, film thickness, and bubble size of the system. These types of coatings often require stronger consumables, and the amount added may also be slightly higher. Many other factors can affect the defoaming effect, and we must pay attention to them.

For example, thickening system directly affects the stability of foam and the difficulty of defoaming. Like low shear thickeners, due to their strong thixotropy or pseudoplasticity, they can cause difficulty in defoaming. Most substrate wetting agents and leveling agents can also stabilize foam and cause difficulties in defoaming. Choosing a wetting agent for unstable foam substrates is beneficial for solving defoaming problems. In addition, the pH value of the system is too high, which is detrimental to defoaming. The addition of organic pigment pastes such as carbon black and phthalocyanine blue also increases the difficulty of defoaming.

Conventional pigments, when not properly dispersed, have a flocculent or semi flocculent system, which is also detrimental to defoaming. Those containing silicon dioxide. The digestion of this system is relatively more difficult than other fillers. This dispersant of polyacrylates causes more foam, such as sodium salt and ammonium salt, which may affect the digestion effect. When considering defoaming issues, we must take into account other influencing factors in the formula.