3 октября, 2015 
Malyar The presence of surfactant in a water-based medium makes the system susceptible to foaming. The correct choice of defoamer will be dependent upon the compatibihty of the additive. Its efficiency is determined by trial and error and most importantly by experience. Defoamers are most effective when dispersed in the mill base stage of the formulation. Post addition is not to be recommended. Defoamers function by changing the surface tension of the system, thereby allowing the bubbles to burst.
Defoamers perform several functions in the system:
a) To prevent undue foaming during manufacture — this can often be subdivided into defoaming during milling, if pigments and/or extenders are being dispersed, and defoaming during the let down and finishing stages of manufacture.
b) To prevent undue air entrapment during application or whilst in the coating applicator (roller coater, for example).
c) To allow rapid and total air release from the film after application.
It may be necessary to use more than one defoamer to fulfil all the necessary roles. Defoamers tend to be very system specific.
The majority of defoamers work by being incompatible with the system they are in. If defoamers are added towards the end of manufacture, it is necessary to make sure that they are well dispersed as poor dispersal can lead to ‘fish eyes’ and ‘cratering’. It is also possible to use small amounts of aliphatic and aromatic hydrocarbons as defoamers, but care should be exercised in their use as they may affect other properties.
Suppliers include Byk, Dow Coming, Efka, Henkel, Tego, Rhone-Poulenc, and Troy.
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