ABS Plastic Rework

Q. I’m the paint manager at my plant. We produce a number of plastic parts for various industries. One of the parts we are painting is an ABS plastic substrate finished with acrylic and polyurethane paints. This product requires a very nice quality finish. Every once in a while, we must repaint one of these parts. Our current procedure is to sand the paint off of the ABS.

This is not only tedious but very time consuming. I have been having a difficult time finding a more efficient process to remove paint from the ABS substrate without damaging the surface. Can a conventional paint stripper be utilized, and if so what type would you recommend? – S.S.

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A. ABS (acrylonitrile butadiene styrene) is a strong thermoplastic derived from petroleum-based products. The short and unfortunate but honest answer is ABS is next to impossible to safely strip with out of some type of damage to the surface. The physical property of ABS is easily attacked with most solvent-based products used to strip or remove paint, such as acetone, MEK (methyl ethyl ketone) or conventional strippers.

There is a technical term called “amalgamation” which is to combine, merge, or coalesce. In essence, when one of these types of chemicals is used, it is actually bonding to the surface, often melting or tacking the substrate in the process, i.e. the damage you already mentioned. Using any of the previously mentioned chemicals typically involves a very messy process, involving rags, steel wool, and or scotch-brite pads soaked in the solution of choice as they scrub off the paint. But you may win the battle but loose the war on this one.

I have, however, heard that there are several types of citrus-based strippers used to remove paint from various substrates as well. I have used citrus strippers on wood, metal, and glass products with success, but I have honestly never tried them on plastic.

Another thing to note is the timeframe in which you try to remove the material(s) in question. The longer you wait, the more difficult the removal process will be, due to the curing process. Typically, acrylic and urethane products have an initial cure time of three days to a week. After this time, these coatings become much more resistant to a stripping process. Even if you were to catch it very early, you will more than likely still be left with a mess to deal with.

One last thought would be to sand blast with a very light-blasting medium such as ground pecan or walnut shell, or even cornstarch. This may offer an easier solution then conventional sanding procedures, as they typically remove paint without damaging many types of substrates. This process would also re-etch the surface for repainting. In any event, I hope you find a solution that works best for your operation.