Anyone watching a child blow bubbles through a straw into their drink can observe that a pure liquid, like water, will not form foam. A mixture, like milk, will form a stable foam on top of the drink. Gas trapped in the liquid will form bubbles, which move to the top of the drink and eventually pop. In a coating, gas entrapped in the liquid medium, either during processing or application, will cause defects when the coating is applied. Foam in production can make processing and filling challenging, while foam in a final coating will not only cause visual defects but weaken the coating.
Foam in coatings can be affected by many different factors: the composition of the coating itself, the way the coating is made and the way the coating is applied. With so many different influences at play, it is not surprising that there is no silver bullet defoamer on the market that can eliminate foam in every system. Understanding the choices of defoamers available in the market, along with the advantages and drawbacks of each, allows formulators to choose optimal chemical and processing conditions for coatings without defects caused by foam.