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替换城市 Principle and influencing factors of special Free of silicone defoamers agents for paints(2)

2023-05-17

Alkyl modified organosiloxane
As mentioned earlier, polyether modified polysiloxanes have some shortcomings; Alkyl modified polysiloxanes have precisely these advantages.
This series of polysiloxane products also belong to the comb structure. The molecular weight of this type of product is relatively small, around 10000, and n+m is about 30-50. The main purpose of modifying with alkyl is to improve thermal stability, compatibility, and unstable foaming, and even to have defoaming functions. However, as the modified alkyl chain increases, its ability to reduce surface tension also decreases

water-based

black

matte

Good paint defoamers not only have a good defoaming effect in paint systems, but also maintain defoaming ability at room temperature and under heating environments. In addition, it cannot be compatible with foam system. If the compatibility is good, it will help to produce foam. While the paint Free of silicone defoamers has good dispersibility in the foaming system, specifically refers to the uniform and smooth diffusion of the defoamer on the surface, which can cover the foam to achieve the elimination effect. Its working principle is to reduce the surface tension of the liquid around the foam, so that small foam can gather into large foam, and finally foam will burst.

Influencing factors of special defoaming agents for paints:

dispersant

anti-delamination

Action mechanism of polysiloxane defoamer
The representative defoaming mechanisms of polysiloxane mainly include "bridging spreading" mechanism, "bridging dehumidifying" mechanism, and "spreading liquid entrainment" mechanism. The "bridging spreading" mechanism mainly starts from the basic point of "polysiloxane has a relatively low tension and is easy to spread on the liquid film." It emphasizes that defoamer droplets are prone to deformation, but this theory cannot explain the defoaming differences between individual polysiloxanes and mixtures of polysiloxanes and solid ions as defoamers. The "bridging dehumidification" mechanism is mainly based on the hydrophobicity of polysiloxanes themselves, but the defoaming effect of polysiloxanes with high viscosity cannot be well explained. The "spreading liquid entrainment" mechanism cannot be confirmed because some facts indicate that polysiloxanes sometimes do not spread on the surface of the foam film, but can also break the foam.

surface tension

替换城市  The level of coating surface tension has a significant impact on defoaming agents. The surface tension of defoaming agents is lower than that of coatings, otherwise they cannot have defoaming and antifoaming effects. The surface tension of a coating is a variable factor, so when selecting defoamers, it is necessary to maintain a constant surface tension, taking into account the surface tension variation factor.

Effects of other additives

metal

Most surfactants used in coatings tend to be functionally incompatible with Free of silicone defoamers. In particular, emulsifiers, wetting and dispersing agents, leveling agents, thickeners, etc. can have an impact on the effectiveness of defoamers. Therefore, when coordinating various additives, it is necessary to pay attention to the relationship between different additives and select a good balance point.