Antifoaming agents used in coatings usually require a lower surface tension than the application system and are incompatible with the application system. Because of its low polarity structure, silicone is incompatible with most coating resin systems, so it is widely used as raw material of coating defoaming agent.
Usually, the relative molecular weight is larger (10 000 ~ 100 000) of polydimethylsiloxane can be used as coating defoamer, at present, this kind of defoamer is widely used in heavy anti-corrosion system. In order to improve the defoaming efficiency, some white carbon black can be added as synergistic component. In addition, because of the high efficiency of silicone defoaming, there is a very good effect at a very low amount of addition. In order to facilitate the addition, the silicone defoaming agent is usually made into a solution with a low concentration to meet the needs of actual production. In solvent coating system, in order to enhance the capacity of coating of defoaming, will use fluorocarbon modified organic silicon, the article introduces the compatibility in the main chain of the organic silicon and fluorine carbon chain segment of lower surface tension, and further reduce the coating system compatibility, greatly improve the effect of defoaming, generally introducing fluorine carbon chain is longer, defoaming effect is better, This type of defoamer is usually the high end of silicone defoamer. In waterborne coating system, due to the high polarity of waterborne resin, the compatibility of conventional polydimethylsiloxane and the system is limited, and it is difficult to be used as defoaming agent directly. It is usually necessary to modify polydimethylsiloxane with polyether, especially in the application of high light system. In general, the higher the degree of modification of polyether, the better the compatibility, but the defoaming effect will also decrease, generally according to the degree of defoaming of the system, select the appropriate modification proportion, under the condition of satisfying the defoaming ability, the lower the silicon content, the better. Water-based silicone defoamer according to its own state, divided into concentrated and emulsion type two categories, concentrated defoamer foam inhibition ability is strong, but not easy to disperse, in use need strong shear; Emulsion type defoamer is obtained by emulsification of concentrated type defoamer, through emulsification, the convenience of use is greatly improved, only simple stirring can be introduced into the system.