Coating to Hide Blemishes

Is powder coating suitable for a polypropylene part with deep recesses?


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Q. We have an automobile hood grill with honeycomb segments around 10 mm deep. It needs to be painted to hide rib marks and blemishes.  It is polypropylene in material and needs to have a good overall finish (no orange peel), as it is prominent at the front end of the car. Paint will not be able to penetrate correctly into the depths of the part, so would powder coating suffice? —M.G.

A. It is hard to be certain without seeing a part and having a standard for the level of orange peel, but I do not think powder will be the right answer. Powder is applied by charging the material electrostatically, and therefore recesses can be challenging to penetrate in some cases. Also, powder is very nearly 100-percent solids, so there may be more orange peel than with a liquid paint. Maybe the biggest issue is the substrate. Polypropylene will not tolerate the needed cure temperatures that are typical for powder coating.

Hiding blemishes with a coating is not easy. It needs to be thick enough to round out the blemish, and that usually will reduce the distinctness of image (DOI). I suggest you consider a liquid primer to help hide the defects and get some coverage in the recesses. Then apply a good liquid topcoat over that to provide the smooth appearance.

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