FT Archives

Roobol On Painting

Keep Sending Mail

I purchased the third edition of your Industrial Painting and Powdercoating book and enjoyed it very much. In the front of the book you indicated that anyone who had comments could contact you. Would you be interested in additional information on the hydrographics process that our company is developing? It involves general process details and doesn't include our company name, so I'm not trying to advertise here. Let me know and I'll send it. By the way, I sent this email to drroobol@ flash.net because I couldn't reach the norm@roobol.net address nor find your Web site.

Please send the hydrographics information. Since I've spent my life in the finishing field, all such material keenly interests me.

I have shut down my Web site, so that old e-mail address is no longer valid; please use the drroobol@flash.net address instead. It is my intention to reduce my consulting workload this year and that is why the Web site was closed. Rest assured I plan to continue writing this column, which I have enjoyed writing ever since I started back in 1980. Part of the pleasure derives from having readers such as you submit helpful ideas and information to me. Thank you very much for sending it.

Wrinkling on Recoated Parts

Any idea what would cause wrinkling on recoats? A local coater paints with a three-booth disk system. They do not get wrinkling on the raw parts but they get it very badly when they attempt to put a second coat on a part that had a repaired defect. The parts' electrical grounding is poor. A lot of paint is attracted to the booth walls and ceiling. This problem is new and began after a two-week shutdown period.

Wrinkling of liquid paint (and I assume this is not powder paint) is nearly always caused by excessively thick application, which can be aggravated by conditions that create fast skinning over of the film. But poor grounding should result in a lower film thickness. If the repaired parts do not go through the pretreatment dry-off oven, they may be cooler and thus have more solvent remaining in the film when they enter the bake oven.

The other cause for wrinkling can be incomplete baking of the initial application coat, resulting in retention of some slow-evaporating solvents. That this problem arose after shutdown suggests that settings on fluid flows, line speeds or bake-oven temperatures are different from before the shutdown. Have the painter reduce the film build on recoats; this will certainly lessen or possibly completely eliminate this defect.

Water-based vs. Waterborne

I am a Japanese translator specializing in translating Japanese specifications for patent applications. I have been wondering whether there is any difference among the terms aqueous, water-based and waterborne with respect to various coating compositions, e.g., paints, clear lacquers and inks. I'm unsure about which term I should use when I encounter a Japanese term corresponding to aqueous, water-based or waterborne.

In an Industrial Paint & Powder magazine article, you state that the term water-based should not be used for any aqueous paints, although it often is, and that the term waterborne is far more accurate. Why is this?

The terms "water-based" and "solvent-based" are not scientifically accurate adjectives in English or Japanese. Paints and similar coatings contain resins that are the essential film formers in their composition. Solvents and water in paints are used as carriers for the resins, and are designed to evaporate after application of the wet film. The resins remain behind to form the coating layer. So to say that coatings are "based" on water or solvent is inaccurate. The coatings are based on the vinyl, acrylic, urethane, epoxy, etc., resins that create the final paint film.

For this reason, "aqueous," "waterborne" and "solventborne" are proper descriptions of paints that use water or solvents as a volatile carrier of the resins; but "water-based" and "solvent-based" are not.

Here is a subsequent response from this Japanese lady:

Your explanation was so understandable that I was convinced to use the term "waterborne" instead of "water-based" for paints or coatings. Thank you very much.