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Coated Coil
Monday | 14 February, 2011 | 6:33 am

Coating conundrum

By Lauren Duensing

February 2011 - A recent paper by the National Coil Coating Association, Cleveland, discusses how specifying coating weights for new non-chromate coatings differs from the ASTM B449-93 standard specification for chromates on aluminum. According to the NCCA, the B449 standard is not applicable to new coatings; however, many professionals are using the standard.

According to Doug Robbins, vice president of quality and technology services for Roll Coater, Indianapolis, and chairman of the NCCA technology committee, the paper is important because it addresses the fact that customers are trying to apply chromated standards inappropriately to non-chromated treatments. "Many of these coatings are new and were not available," Robbins explains, noting the paper is important because it can assist aluminum coaters in addressing the requirements for non-chromated or ROHS-compliant coatings. "The industry is moving to address the requirements for non-chromated coatings," he says.

Chrome coatings are standardized and have been used for many years. However, new non-chrome coatings are "anything but standard and, in fact, are innovative," Robbins says. The industry currently is working toward developing treatments/coatings for non-chromates that meet requirements while meeting "the performance of a chrome treatment," he says, adding standardizing requirements before ample research can be completed could stifle development.

Toxicity risk
Tom Cape, technical manager for coil products at Henkel Technologies, believes coil coaters as a group "are very much aware of the toxicity and environmental effects of chromates and would like to eliminate their use in the passivates used on incoming metal, in pretreatments and in primers." Cape says coil coaters are "hampered by the resistance of customers to buy non-chromated products and by the need to evaluate each pretreatment and primer separately."

"Having pretreatments or primers that meet standards would help overcome the resistance," he says, adding resistance to using non-chromate coatings stems from the customers knowledge that the current chromate treatments and primers perform well, ensuring excellent paint adhesion and painted corrosion resistance.

"Conformance to ASTM B-449 is one way the industry assures the end user that excellent pretreatments and primers were applied to their product," Cape says."This assurance is lost with the use of non-chromate coatings. The coated coil customer is asked to use a product that has eliminated the chromate/chemical that they know to work well." Therefore, the product is no longer in compliance with ASTM B-449 or an equivalent ASTM standard and could cost more, he says. MM

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