Aqueous coatings are complex blends that may have foaming issues. Here are some ways to control foaming. Aqueous coatings are complex blends with the typical formula consisting of styrene/acrylic co-polymers, amines, water, plasticizer, waxes, surfactant, and an anti-foamer. The balance of each material portion to the total is important and enables a given target performance result to be achieved.
One key component is the amine used to solubilize acrylic resin, which is also the primary determinant of a coating’s pH, or acidity/alkalinity balance. The amine component will evaporate from an open container reducing a coating’s pH. As evaporation takes place a coating’s viscosity will rise. This is to be avoided because viscosity is very important to a coating’s running characteristics. Remember, it is always recommended that a container of coating be covered while in use. Cork typically recommends that coatings be used as received. This recommendation is made because it is too easy to upset the chemical balance of a formula when making field adjustments. Once compromised, both running and final film properties of a coating can be effected.
Considering the subject of “foaming”, improper pH can contribute! Therefore, take care to maintain the pH of a coating as formulated and as received.
Blending or thorough continuous mixing during use is important to maintain a coatings chemical mixture. Cork’s recommendation is that a container of coating be stirred, rocked or rolled before use. Room temperature, 72 degrees F storage will assure that furnished coating viscosity goes to press.
Foaming Can Be Controlled
- Diaphragm pumps are recommended to pump and circulate coating from the supply container to the coater and back. Gear pumps are not recommended since high shear can break down a coating and cause foam.
- The pump should be run only at a rate that satisfies coater demand and does not recirculate coating excessively. The return line must not be allowed to suck and pump air into the coating supply. The coating level in the supply fountain must never be allowed to drop too low.
- The pump set-up should be properly maintained with pump seals and line connections regularly checked to avoid air leaks.
- A loop formed in the return line will slow coating flow speed, allowing any entrained air picked up in the fountain overflow vortex to escape.
- When using a drum or kit as a supply container direct the return line flow through a perforated pipe extending from the container cover to the bottom of the supply container. Don’t return a stream of splashing, foam creating coating to the container.
- If your pump has a flow by-pass, make sure that the exit line also extends below the lowest level of coating ever expected in the container.
- Watch out for detergent/soap wash-up solutions that will cause foam in a coating if all traces are not thoroughly rinsed away after use.
Beware Of Adding Defoamers
Sometimes a bad foaming situation may be remedied by the addition of a defoamer solution press side under the advice of a Cork representative. While this situation will rarely occur, follow the advice with care and caution. A little defoamer addition may help, but too much can be harmful potentially disrupting the delicate chemical balance of the coating, affecting performance.
In conclusion, there are as you have now read, a number of factors that contribute to and cause foaming when coatings are used. Some of these you can control by following the recommended coating practices outlined above.
If you have any questions about foaming with the Aqueous Coatings you use, please do not hesitate to contact the expert help at Cork Industries, your partner in print and packaging coatings.