Foam is a major adversary in almost every coating formulation; it alters the density and viscosity of the liquid, causing cause defects on surface coatings and reducing their effectiveness. Foams can form in a number of ways, so formulators must do their best to suppress them as early as possible.
Defoamer additives work to eliminate spherical foam bubbles in coating formulations, either by breaking down the lamella walls or by preventing foam’s formation in the first place. There are multiple defoamer options available for a wide variety of industries.
Different defoamers have distinct capabilities and methods of reducing and eliminating foam, so it’s important to choose the best one for your application.
BASF’s unique line of FOAMSTAR® defoamers break down foam at a molecular level, boosting their effectiveness and improving the quality and consistency of the final coating formulation.
Foam formation
Foam is a coarse dispersion of a gas in a liquid, where the volume fraction of gas is greater than that of the liquid. Its lower density compared to the surrounding liquid causes it to rise to the surface where it collects and eventually breaks.
Foam can form in several different ways, including agitation during production and application, air displacement during pigment wetting, or gas formation in the chemical curing process.
“Foam is usually caused by air or gas that makes its way into a dispersant or resin and creates bubbles at the surface of the coating,” says Erin Moore, Marketing Manager at BASF. “One main reason for foam formation is the presence of other materials in the dispersion or resin that reduce the surface tension.”
Once the foam reaches the surface, it can break and inhibit the effectiveness of the coating and its adhesion to the substrate.
“You don't want to have any bubbles, craters or ripples in a coating, because that will create defects and lead to the breakdown of the coating,” says Moore. “Defoamers help prevent those defects and improve the longevity and the durability of the coating.”
The debrief on defoaming
Traditional silicone or mineral oil defoamers work to remove foam by destabilizing the film lamellas by virtue of their insolubility in the medium and their surface-active properties. This ruptures the bubbles and breaks down surface foams.
BASF’s FOAMSTAR defoamers are different. They feature a star-shaped polymer molecule with both hydrophilic and hydrophobic elements, which work on a molecular level to act as a unique surfactant and pair with foam stabilizing surfactants to destabilize foam bubbles more effectively. Combined with conventional defoamer types, this provides faster bubble break times and improves overall efficiency of the formulation.
“With a star-shape polymer, the active molecule acts as an inverse surfactant, where the hydrophilic portion is inside and the hydrophobic portion is on the outside,” explains Moore. “The hydrophilic portion is protected by the hydrophobic molecules, and this keeps the mass of the surfactant and the water-based mixture low. The molecule is able to migrate to the foam and disrupt foam formation and foam stabilization more effectively than other defoamers.”
Foam in architectural coatings
Reducing foam in architectural coatings is particularly important as these coatings must be able to effectively withstand exterior forces for elongated periods of time, and appearances often play a greater role in this area than coatings in other applications.
“Aside from negatively impacting the finished appearance of a coating, foam in architectural coatings creates gaps and holes in the film that can reduce the overall performance of the coating properties,” says Moore. “By reducing foam, we're creating a tighter, more impenetrable film. This results in better protection of the substrate, including increased resistance from staining and improved water resistance.”
There are a few FOAMSTAR defoamers that can play a useful role in architectural coatings.
“A defoamer for architectural coatings that I would recommend is FOAMSTAR SI 2240,” says Moore. “This is a silicone-based defoamer with broad compatibility in a variety of different systems, including architectural coatings, industrial coatings and automotive refinishes. It’s also well-suited for pigment concentrates because it maintains its stability under high shear conditions.”
For low-VOC formulations, FOAMSTAR ST 2420 is a great choice with broad applicability to different types of coatings. It features hyper branch polymer defoamer technology delivered in an essentially emission-free hydrocarbon matrix.
“One of the key highlights of FOAMSTAR ST 2420 is that it's very effective against microfoam and it has a very fast bubble break time,” says Moore. “It’s very efficient, and you can actually use about 30 to 50 percent less of it than you would a normal conventional defoamer.”
A defoamer for any coating
FOAMSTAR defoamers are well-known in the coatings industry for their effectiveness and versatility, with over a dozen solutions designed to meet the needs of any coating formulation.
FOAMSTAR SI 2299 is an industry favorite defoamer that works well within industrial coatings including as a deaerator and a defoamer for spray applications, removing microfoam from water-based spray coatings.
Although foam will continue to remain a challenge for any formulator, capabilities to supress it are growing as technologies improve and more effective defoaming solutions become widespread.
“The great thing about FOAMSTAR technology is our applicability to coating systems that helps deliver a perfect balance between foam suppression, microfoam removal and high compatibility,” says Moore. “All of these attributes lead to easier handling for manufacturers and consumers, environmental compliance, and long-term efficiency and protection.”
Looking for the best defoamer for your application? Click Here to learn more about BASF’s award-winning FOAMSTAR line.