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A Comprehensive View of Transitioning to Phosphorus-Free Paint Pretreatment


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This article chronicles the experience of a large multi-national OEM (original equipment manufacturer) of home appliances in the Far East that made the transition to a phosphorus-free pretreatment process. This supplier of hot water heaters operated a conventional zinc phosphate pretreatment system for cold rolled steel and galvanized steel parts prior to powder coating application.

The OEM noted that their zinc phosphate process required weekly nitric acid descaling to remove sludge from nozzles and risers for effective operation. It was also necessary for them to dump and re-make their cleaner tanks once a month as well as pumping their zinc phosphate solution once a month to a secondary holding tank to allow the phosphate sludge to settle for removal from solution. Due to the high operating cost and increasing phosphorus regulations globally, the appliance manufacturer had a strong desire to implement a phosphorus-free pretreatment system and approached Atotech for a solution.

The multi-national OEM installed UniPrep® PF B, a phosphorus-free bioremediated cleaner, and Interlox® 5705, a phosphorus-free zirconium-based conversion coating, in November 2010. This replaced their conventional zinc phosphate process. After four weeks of testing the new system and monitoring potential cost savings, they approved Atotech as a supplier for their pretreatment system.

In the 18 months since initially installing Atotech’s phosphorus-free paint pretreatment chemistry, they have been able to lower the operating temperature of both the cleaner and adhesion promoter stages from 60°C to 35°C, eliminate the zinc phosphate conditioner stage, and reduce the burden on waste treatment. The multi-national OEM also acknowledged that their spray line remains free of significant sludge and scale, eliminating the necessity for weekly line cleanings. Lastly, they noted that both the cleaner and conversion coating stages lasted for more than a year without dumping, while their previous cleaner had to be replaced monthly and the zinc phosphate every six months.

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