• Field Notes 20.09.2010

    One of the adjustments in switching jobs in the last 18 months was getting used to a new coating technology/product. Coming from as far back when everything was anodized – either clear, black or different shades of bronze – then moving to Kynar paints took some getting used to. But moving from an aluminum world to a steel curtain wall world required another shift:  the liquid applied paint of the aluminum world is not very friendly to some steel curtain wall products. At TGP, we’re using powder coatings in a majority of our product lines.

    And while the steel world has been using liquid-applied paints for quite some time, just not always the PVDF paints that are used in aluminum, there are some similarities between the two paints and the two metals.

    The beauty of either finish is that it can be applied to either metal. Some of the aluminum finishers out there can’t paint the steel in the same manner they paint the aluminum. For one, the steel’s obviously heavier, and some of the cleaning operations aren’t configured to handle steel.

    The major difference between the liquid applied and powder coating is that the liquid paints have a high percentage of VOC solvents that allow the paint to be spray-applied to the object being painted, while the powder coatings don’t have those solvents. The powder is just that, a dried resin basically that is sprayed onto the metal. The powder particles are less than 35 microns in diameter, and are spray-applied using air, not solvents to move the material through the paint lines.

    But everything else about the two applications of paint products is very similar:  The metals still have to be cleaned, the material sent through paint lines where the metals are electrostaticly charged to attract the paint material, then are sent through ovens. In the case of the liquid-applied paints, it’s heated to burn off the solvents. In the case of powders, it melts the powder and when cooled forms the durable surface powders are becoming known for.

    Most of what you see in architectural metals other than curtain walls is receiving powder coatings. Playground equipment, light poles, as well as handrails are being given powder coatings. A lot of metal parts in lawn and garden equipment receive powder coatings, as well. They have the potential to match very high gloss, with smoother finishes than what they had when first introduced to the architectural finishing arena.

    The primary attraction of the powder finishes is the absence of the solvents, which have some environmental issues. By comparison, with the liquid applied paints, the solvents make up around 70% of the coating material. These solvents are burned off in the heating of the material after the paint is applied, but some still escape to the environment.

    Some of the initial concerns with powder coats that small quantities and custom colors were difficult have since been resolved by the manufacturers. For example, Tiger Drylac, our largest supplier, has a large variety of standard colors, with some metallic finishes, also. Some of TGP’s projects are for one or two punched opening type windows, with finish areas of less than 200 square feet. The manufacturers can all do custom colors, usually at a 15-20% premium.

    Most of the powder coatings offer 1-5 year warranties on the finish, depending on whether or not a 1-, 2- or 3-coat application is used. Generally speaking, in 2- or 3-coat applications, the first coat is a primer, the second coat the finish color coat, and the third coat (when required) is a clear sealer.

    What’s coming on line now is that Spraylat, PPG and Tiger Drylac – three of the big manufacturers in the powder coating world – are introducing powder coatings with PVDF resin. These finishes have warranties of up to 15 years, and have many of the characteristics of their liquid applied cousins. Such paints are meeting AAMA 2603/2604/2605 specs, as well.

    One drawback, and somebody might take exception to this:  The liquid applied paints are easily applied to sheet metal in the coil coating process. That’s not necessarily true yet of the powder coatings.

    So there’s a lot happening in the world of finishes. While it’s been a long time since the last anodized curtain wall I’ve worked on, liquid applied finishes have some competition now.

    The powder paint manufacturers, as well as the coating and glazing trade magazines, have a lot of good articles about these coatings, their advantages, and their limitations. As the architects spec powder finishes, those resources can provide useful insights.

    Posted by Blogger @ 9:45 am

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