A Couple of Questions About Touch-Up Paints
Q1: We are working with a new sheet metal fabricator who also will be finishing our products with Powder Coat Paint. What is the best way to do touch-up to the power coated surface should there be slight damage occurring from shipping?? (i.e. nicks, chips) Can enamel paints be used, as there is no powder painting processes are done at this plant? J. P.
Q2: When using the liquid touch up paint, what salt spray test results can I expect? Will failures originate around the powder coat? How much less time to failure (powder vs. liquid paint) can I expect? V. H.
A. There are many liquid touch-up paints available for powder coating. Everything from spray cans containing air-dried enamels to more sophisticated two-component urethanes. Choosing a liquid touch-up paint should only be done in consultation with the powder formulator to ensure compatibility with the powder coating material. If you do not do this then you risk lifting the powder from the part or having adhesion problems between the touch-up and the powder coating. Choose a coating that you can easily apply in your operation and yet still provides the performance you need.
Touch-up should only be performed to fix minor surface scratches, nicks, etc. Don’t try to use touch-up to fix large-scale areas that have corrosion problems. Your best bet here is to strip the part and start over. Remember, as the name implies you are trying to “touch-up” a small area on the part, not repaint it.
As far as salt spray resistance is concerned, this really depends upon the pretreatment on the part before the powder coating was applied. If the scratch has removed the pretreatment, then corrosion resistance will suffer. Furthermore, the liquid touch-up paint formulation will have a great deal to do with corrosion performance. For instance, two component urethane liquid paints are more corrosion resistant than air-dried enamels.
Failure will always occur at the weakest link on a chain. Therefore, any failures are likely to occur where the pretreatment was damaged and the liquid paint was applied. For a wild guess, you can expect up to a 50% reduction in corrosion resistance for the liquid touch-up areas on the part.
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Powder coating is one of the most durable finishes that can be applied to industrial manufactured products, and offers excellent corrosion protection and is very safe because of its lack of volatile organic compounds.