Poor DOI Over Galvanized Steel

Q. I am the engineer in charge of our paint line here in Asia. We make scooters and motorcycles. I got your reference from the PF ONLINE web site. We would like to improve the Distinctness of Image (DOI) on our motorcycle fuel tanks and seek your advise for the same. The present surface texture is not very good, because the tank’s raw material is steel sheet galvanized on both sides. Presently the painting process we are using is as follows:

1. Painting—Primer coat plus Base coat plus Clear
   coat, then bake.
2. Stripping—Stripping sticker application, then Clear
   coat and bake.

Please advise us what to do to solve the problem. Your reply in this regard will be highly appreciated. V. D.

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A. Roughness in surface texture of substrates often telegraphs through paints on finished products. This could cause DOI problems. It would be especially noticeable in high gloss finishes such as Clear coats. Galvanized steel is one of the worst offenders.

Other than changing your substrate, I would try the following procedures to solve the problem. Increasing the film thickness will often cover substrate texture. Another cure is application of a sandable primer/surfacer. Although hand sanding is labor intensive, it may be the only way to cover highly textured substrates.