Monday, April 2, 2012

Membranes in the Electrocoating Process

Membrane filtration, specifically the use of ultrafiltration for the concentration cathodic paint, is a vital component to the successful operation of electrocoating processes. In the electroocoating process, an object is dipped into a paint bath and coated via electrophoretic deposition.

The electrodeposition process creates excess acid within the paint bath that must be removed in order to keep the paint chemistry in balance. Anolyte cells are the mechanism that serve both as the opposing anode to the part being coated as well as the acid removal devise. Equipped with a robust anionic membrane, the charge on these cells serves to both attract the excess acid in the paint bath and remove it through membrane filtration. Due to a constant influx of new water into the paint bath, it is essential to constantly concentrate the paint in order to maintain appropriate paint chemistry. Nearly all electrocoating processes employ ultrafiltration membrane to achieve this concentration. In this process the paint is fed through the membrane and when sufficient pressure is applied, the paint and water molecules can be separated with incredible efficiency. The resulting solutions are concentrated paint and UF quality water.

The concentrated paint is fed back into the tank to be reconstituted with water and fresh paint while the water generated during the process is used to rinse the parts after coating. The use of ultrafiltration membrane allows for incredible overall efficiency in this stage of the electrocoating process. Since the concentrated paint is reused in the paint bath and the UF permeate is used for rinsing the coated parts, this is essentially a closed loop which keeps costs down and promotes an environmentally friendly operation.


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