替换城市 Principle and influencing factors of special paint defoamer agents for paints(2)

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Polyether polyester modified organosiloxane
An organic polysiloxane with a comb like structure. N+m is about 50-250, and the molecular weight is controlled between 1000-150000. Its compatibility is adjusted by polyethers and polyesters, and the longer the chain, the better the phase compatibility. Polyether modifications are the most common in this category, typically using ethylene oxide and propylene oxide. With the increase of the content of ethoxy groups, their compatibility with water also improves, so it is also possible to synthesize water-soluble siloxane type leveling agents. Ethylene oxide and propylene oxide can be used alone or mixed to control hydrophilicity and lipophilicity. If both ethoxy and propoxy groups are contained, a silicone based leveling agent for both water and oil use is prepared,

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 paint defoamer 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.

Stability factors of foam
The direct cause of foam is the presence of surfactant, which reduces the surface tension of the solution. Under the combined effect of this reason and the attenuation mechanism of foam, different foam systems show different stability properties, which are mainly related to the following factors: the surface tension of foaming solution, the surface viscosity of foam, the viscosity of solution, the self-healing effect of surface tension (i.e. Gibbs surface elasticity and Marangoni effect) "The surface double layer repulsion and entropy repulsion forces of liquid membranes, the hydrophobic end structure of surfactants, and the steric hindrance effect are not independent factors, and changes in one factor can cause other factors to also change.". The most important factors affecting the stability of foam are the elasticity of the liquid film and the liquid discharge rate. From this perspective, it can be seen that the main factors affecting the stability of foam are different in different foam systems, and sometimes several factors exist at the same time and work together.
In addition to the above factors, some other factors will also affect the stability of foam, such as the size of foam, the coordination of solute and solvent, temperature, pH value, the evaporation rate of solvent, the impact degree of foam and the adsorption rate of surfactant

Influencing factors of special defoaming agents for paints:

anti-cratering

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

Most surfactants used in coatings tend to be functionally incompatible with paint defoamer. 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.