How to Choose a Defoamer

Paint manufacturers continuously ask the question, “Will consumers buy our product?” It is a common belief that the performance of the final product is what drives the customer’s decision. I would argue that this is not the case. I believe that appearance is the ultimate deciding factor. Appearance sells cars, homes, boats, and even kitchen appliances. So what affects appearance? Many factors could have an effect on the final product. One example is the wrong additive. How do you choose a good defoamer? What is the best dispersing agent for maximum pigment performance? Let’s begin by looking at defoamers.

Foam is a dispersion of a gas in a liquid and usually not desirable in a coatings application. It can occur during the paint manufacturing and application process. Foam in a coating can cause structural problems in the dry paint film by weakening it, cause discoloring, the absorption of dirt and pollutants, and clouding or fogging in a transparent coating. None of which are ideal for the consumer. The right defoamer can prevent these from happening.

What is a Defoamer?

What are defoamers? A key feature in all defoamers is their targeted and controlled incompatibility with the medium that is to be defoamed. A defoamer that is too compatible does not migrate into the foam lamella specifically, it is present in the entire coating film; the defoaming effect is then either low or non-existent. Too much incompatibility causes problematic coating defects such as turbidity or cratering. Choosing the correct defoamer is therefore a kind of “balancing act” between compatibility and incompatibility.

Imagine an acrobat trying to keep their balance. One step to the right or left- they will fall! If a defoamer is too compatible or soluble, there will be increased levels of foam. If the defoamer is too incompatible or insoluble, there will be increased surface defects.

This graph demonstrates the relationship between foam and solubility. The optimum level is found when defoaming is achieved without defects.

Graph 1 (BYK USA)

In light of this, selecting a defoamer depends on the time of addition, the duration, and incorporation method (shear forces, and the dosage in the coating formulation. All of these parameters have an impact on the distribution and therefore on the droplet size of the defoamer in the coating formulation. They influence its effectiveness. If the dispersing process is inefficient and causes the formation of droplets that are too large, the coating suffers from surface defects. If dispersion is too great the defoamer droplets are too small and their behavior in the coating formulation is too “compatible”, decreasing the effectiveness.

For defoamers with especially high activity, which are present as concentrate, the defoamer droplets need to be created in situ. This can be caused, for instance, by the defoamer in the coating formulation being finely distributed in the millbase by high shear dispersing equipment. For defoamer emulsions, in which the emulsified droplets are already finely distributed in the water, the defoamer can be added to the coating formulation at the low shear forces that are usually used during the letdown.

Graph 2 (BYK USA)

 

As a result of the multitude of different coating systems, there is no “one” defoamer that is optimally suited for all formulations. To ensure that a suitable product can be provided for any purpose, a range of defoamers is required. The defoaming effect can be finely adjusted by varying the dosage. In general, the more defoamer, used, the better defoaming is achieved. However, this may also increase the defects or allow defects to become more visible. Reducing the dosage prevents film defects, though the defoaming effect may, in some circumstances, not be sufficient.

The term “defoaming” is frequently used to describe the removal of gas bubbles from the coating. However, in certain cases the terms “defoaming” and “air release” should be differentiated. First, the gas bubbles need to reach the surface. Removing the foam bubbles that are at the surface is called defoaming. Defoamers are only effective at the surface where they eliminate air bubbles located there. In comparison, air release agents take effect throughout the coating film.

To conclude, here’s the list of important steps in choosing a defoamer that is well suited for the system:

  • Compatibility:  Mix small amount with the resin if possible. If sample is too clear, the additive is soluble/compatible. It must create some turbidity.
  • High shear stability: Review the additive’s TDS and how it is designed to incorporate.
  • Amount of defoamer: Conduct a ladder study beginning at the recommended level as a guide.
  • Defoaming or air release: Depends upon application

 

Hall Technologies, Inc. is a specialty chemical distributor based in St. Louis, Missouri, that serves the Midwest, Upper Midwest, Southwest, Southeast, and Ohio Valley. Our technical service applications laboratory offers our partners a valuable resource- answers. Do you have a technical or defoamer question for our chemists? Contact us today!

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