Aug 3 2004
BASF has patented a process for colouring aluminium in baths containing methanesulphonic acid (WO 2002/04717). This innovative new process makes it possible to obtain a realistic gold finish on aluminium surfaces.
In conventional processes, gold effects are obtained by anodising the aluminium and then applying the colour. Dyes are often used to colour the surface, but there are limitations on the performance of the dyes used to obtain gold effects. The shade often appears too yellow or too brown, and the lightfastness of the dyes is not always up to standard. “Much better results can be obtained if baths based on our high purity methanesulphonic acid are used instead of dyes”, explained Dr. Helmut Witteler, Head of Development and Applications Technology for Surface Finishing at BASF. “Instead of dyes, finely divided metal crystals are deposited in the aluminium oxide layer. This results in a realistic gold finish with excellent lightfastness. The metal crystals are deposited very evenly if the bath is based on methanesulphonic acid, and this does not depend on the position of the parts in the bath”, explained the chemist Dr. Witteler. BASF’s patented process enables aluminium finishers to obtain very level shades, especially gold shades, even on complex shapes. Another advantage is that the methanesulphonic acid process enables aluminium to be coloured up to 50 % more quickly compared to other processes.
BASF supplies methanesulphonic acid world-wide under the trade name of Lutropur® MSA in various different grades though to an ultra-pure electronic grade. Methanesulphonic acid is readily biodegradable. It can be employed in all processes in metal finishing in which acids are used. Its advantage over sulphuric acid and ordinary, less pure grades of methanesulphonic acid is that tin, silver and copper compounds can be prevented from forming sludge – which saves money and energy. BASF also manufactures and distributes Lutropur® MSA for use as an electrolyte in electroplating baths. For instance, methanesulphonic acid is used in the manufacture of tinplate and in the production of printed circuit boards. BASF is currently working in close cooperation with several companies in the surface finishing sector, and Dr. Witteler invites other companies to join in: “BASF is looking for more partners in the industry to develop new processes for treating metal surfaces with methanesulphonic acid”.
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