The most commonly used degassing agent is benzoin, which acts as a solid solvent to keep the coating film continuously unfolded, long enough for air to escape from the coating film. Benzoin, also known by its chemical name diphenylethanolone, is a white or light yellow crystalline powder.
In epoxy systems, benzoin can reduce the viscosity and surface tension of the melt. However, it can cause yellowing of white or off-white coating films when over-baked because it can be converted to dark biphenyls. For general color coatings, a minimum addition of 0.2% benzoin is recommended (on a total formulation basis).
For white and off-white coatings, the addition should not exceed 0.2% if over-baking is involved.
For black or other dark color systems, the maximum addition can be 0.8%.
And, micronised amide wax rheology modifier is useful as degassing agent for paint&coatings.
The degassing properties of benzoin can be enhanced by the use of auxiliary additives (e.g., non-gassing, non-yellowing polymer additives). Suitable alternatives to benzoin are: stearic acid, which is very effective in degassing and leveling, but its use is limited by storage stability because it lowers the glass transition temperature of the system; hydrogenated castor oil derivatives, which also improve the flow of the film but lower the glass transition temperature; various polyethylene and polypropylene waxes (if they do not have matting capabilities); and single or diamide waxes. In order to obtain better degassing effect, it is better to choose the appropriate degassing agent according to the processing characteristics of different systems, and it is better to combine benzoin with other degassing agents.
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