08/13/2008, Düsseldorf / Germany
More than 10 years of Henkel-experience with chrome-free pretreatment of aluminium
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Perfect protection against corrosion
Aluminium surfaces must be protected against corrosion prior to painting by a suitable chemical treatment. For this surface treatment, chromate containing chemicals have been in use for decades.
The discussion on environmental and health risks has encouraged the coating industry’s search for „cleaner“ solutions. In particular, the implementation of the new chemical policy REACH will boost the replacement of the chromate processes that are proven, but hazardous to human health and environment.
Henkel has far outpaced this trend together with its industry partners. While the idea of an integrated chemicals’ safety policy like REACH was not born over a decade ago, chromates were already known to pose a health problem. Yet they seemed to be irreplaceable for their anti-corrosive performance. Henkel, however, had already taken up research in the 1980s, to develop chrome-free pre-treatment processes for architectural applications. Together with our partner companies, we made these processes capable for industrial use. This applies to the coating of single work pieces (batch painting) e.g. window frame profiles and façade parts, as well as to the industrial painting of metal coil (coil coating) that is used for large wall claddings or roofing, but also for garage doors or sun blinds and roller shutters.
As early as 1996, non-chrome technology was introduced into the European batch painting market. An administration building on Henkel’s headquarter premises in Düsseldorf, Germany, was chosen as pioneer object. Henkel cooperated with various partners in the German batch painting industry, ranging from family-owned Dörner Co. of Alpenrod to market leader Gartner Co. of Gundelfingen, to introduce non-chrome technology based on titanium and zirconium compounds. After struggling with authorities and market obstacles in the early days, nowadays non-chrome pre-treatments are standard in the aluminium batch painting market. Today some 250 painting companies throughout Europe use non-chrome technology from Henkel like Alodine® 4830 or Alodine® 400. When designing a new painting line (as the majority of lines are over the zenith of their age or capacity), non-chrome technology has become the standard choice that even serves well under marine conditions.To gain acceptance in the batch coating market each new process requires a quality approval from European wide operating quality associations, as GSB or Qualicoat. Henkel obtained both approvals very early in 1996/97. Even more, development has advanced over the years. The processes of the early years that were sensitive to operating conditions have been improved to robust industry standards.
For the coil coating of aluminium, Alodine® NR 1453, another chrome-free process was introduced in the same period. This process comprises the so-called no-rinse application of an aqueous pre-treatment chemical. In this process, a solution of the Cr-free treatment chemical is applied onto the moving metal strip by roller coaters, forming a liquid film of a few micrometres. This liquid film is dried, whereby a corrosion preventing, adhesion promoting solid layer is formed. The process does not require the removal of excess chemicals and unwanted by-products. It saves chemicals and water, and virtually removes the need of waste treatment and discharge. The metal coil surfaces pre-treated in this way are ready for immediate coating with a variety of lacquers.
When some of Henkel’s laboratory buildings were refurbished in 1998, another project was born to create a reference object also for the new chrome-free coil pre-treatment. In cooperation with VAW AG of Grevenbroich (today Hydro Aluminium Deutschland GmbH), aluminium coil stock for wall cladding and sun blinds was treated with Alodine® NR 1453 and top-coated with a single-layer, high-durable polyester paint. V-groove façade sheet and sun shades were made from this coil material, and mounted in October 1998 on the walls of the staircases and the south-facing rows of windows of both buildings. The surface area amounted to some 400 square metres of V-groove sheet and 800 square metres of sun stores. The façades have been in use now for 10 years, facing sun, wind and rain in this industrial environment, and also encountering mechanical damage around the loading areas. The silver metallic paint coating, however, does not show any corrosion even at critical points like punch-holes, bolt and screw joints or dripping edges. This demonstrates the high performance standard of Cr-free pre-treated, coil coated aluminium sheets for building applications.
Henkel AG & Co. KGaA
Head of Corporate Communications
Ernst Primosch, Corporate Vice President