Composition of defoamers

Defoamers are mainly composed of active compounds, spreading agents and carriers. Spreading agents are surfactants that help in reducing the surface tension, while carriers are the solvents used to compound the other ingredients. 

The main groups of defoamers for waterhased coatings are mineral oilbased defoamers, silicone defoamers and fluorinated defoamers. 

Mineral oilbased defoamers are composed of 85 % carrier oil (aliphatic or aromatic mineral oil), 10 % hydrophobic particles, with the remainder an emulsifier and other ingredients such as metal stearate and fatty acid derivatives. They are used in flat and semigloss emulsion paints but are not suitable for higher quality aqueous industrial coatings due to possible surface defects and gloss reduction. 

Silicone defoamers are composed mainly of hydrophobic silicone oil (polydimethylsiloxanes). Pure silicone oil is effective, but overdose often leads to surface defects. Therefore, polyether modified poly-siloxanes have been preferably used to give effective defoaming with negligible effect on appearance of the films. MW and side chain modifications are important considerations in their selection. For ease of incorporation, they are often supplied as emulsions. They may also contain hydrophobic silica to make them more effective. Possible adverse effects are poor intercoat adhesion or craters. 

As a recent innovation, some fluorinated compounds and silicones with perfluorinated organic modifications, also known as fluorosi- 

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