Defoamer selection and evaluation methods
The defoamer must be able to spread quickly on the foam surface and penetrate quickly, causing the foam to break quickly. The commonly used defoamer types at present are silicone and polyacrylate.
Silicone defoamers are usually polysiloxane-type. For example, polydimethylsiloxane containing acrylate functional groups and polyether-modified polydimethylsiloxane. Silicone has become a commonly used defoamer because of its high and low temperature resistance, stable physical properties, chemical inertness and low surface tension. It is recommended to use a solvent-based directional defoamer, which can be used for matte coatings, metallic coatings and color coatings. It has the characteristics of fast defoaming speed, small dosage and no effect on recoating. Defoamers such as polyacrylic acid defoamers cause selective incompatibility by changing the polarity and molecular weight of the polymer.
The use of such defoamers requires an evaluation of the effect on gloss. It is recommended that our company’s products are solvent-based non-silicone defoamers, which are particularly suitable for coil coatings and two-component polyurethanes, high-viscosity coatings, polyester coatings and acrylic coatings, and have excellent defoaming ability. In the future, the selection of a suitable defoamer must consider the process of foam generation in the system, the compatibility of the system, the concentration, temperature and viscosity of the system, etc. Each of the above factors will directly affect the selection of defoamers. The evaluation of foam control agents mainly considers the following aspects: spreading rate; compatibility with the system; defoaming stability and cost performance. However, in the formula, the above factors are often contradictory. The defoamer with the best compatibility with the system usually has the worst defoaming stability. The worst compatibility usually has the fastest spreading speed. Due to the diversity of coating raw materials and construction methods, defoamers need to be evaluated based on actual conditions.
