Selection and evaluation of defoamers

DefoamerIt must be able to spread rapidly on the surface of foam and penetrate rapidly, so that foam can burst rapidly. The commonly used types currently include organosilicon and polyacrylate.

Organosilicon defoamers have high temperature resistance, low temperature resistance, stable physical properties, chemical inertness, and very low surface tension. They are commonly used defoamers, usually of the polysiloxane type. For example, polydimethylsiloxane containing acrylate functional groups and polyether modified polydimethylsiloxane.

Organic silicone based polyacrylic acid and other defoamers cause selective incompatibility and defoaming by changing the polarity and molecular weight of the polymer. The use of such defoamers requires an evaluation of their impact on gloss.

The selection of appropriate defoamer must take into account the process of foam production in the system, the compatibility and concentration of the system, temperature and viscosity.

The evaluation of foam control agent mainly considers the following aspects: spreading rate; Compatibility with the system; Stability and cost-effectiveness of defoaming. Due to the diversity of coating raw materials and construction methods, defoamers need to be evaluated based on the actual situation.

1. Add the defoamer to be compared into the varnish in a certain proportion, put it into a glass bottle, shake it in a shaker for 5 minutes, take it out for observation, and preliminarily determine the defoaming ability of the defoamer according to the amount of foam; After placing for 10 minutes/30 minutes, observe the height of foam again and compare the defoaming speed;

2. Use a scraper fineness meter to scrape the paint solution to determine the compatibility between the defoamer and the system (with or without shrinkage);

3. After the foam of the system is eliminated, observe the clarity of the system, whether there is turbidity, stratification, oil slick and other phenomena;

4. Storage stability: After being left for half a month, repeat steps 1, 2, and 3 of the experiment to determine the long-term effectiveness of the defoamer;

5. Determine the amount to be added.