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Automotive sheet. New processing technology for coated aluminum units - forming of powder pre-coated aluminum sheets

Neue Verarbeitungstechnologie für beschichtete Aluminiumbaugruppen - Verformung von mit Pulver vorbeschichteten Aluminiumblechen
: Edelmann, M.; Gedan-Smolka, M.; Demmler, M.

Hirsch, J. ; Deutsche Gesellschaft für Materialkunde e.V. -DGM-, Oberursel:
Aluminium Alloys. Their Physical and Mechanical Properties. Vol.2 : Proceedings of the 11th International Conference on Aluminium Alloys, 22 - 26 Sept. 2008, Aachen, Germany; ICAA 11
Weinheim: Wiley-VCH, 2008
ISBN: 978-3-527-32367-8
ISBN: 3-527-32367-8
International Conference on Aluminium Alloys <11, 2008, Aachen>
Conference Paper
Fraunhofer IWU ()
Aluminiumlegierung; beschichteter-Werkstoff; Blechumformen; chemische Reaktion; Polymerreaktion; Polyurethan

Polyurethane powder coatings are known for their excellent properties such as weathering resistance, superior flow characteristics, high flexibility and resistance to chemicals. The curing or polyurethane powder coatings proceeds by reaction between an OH-functionalized polyester and an isocyanate cross-linker. Due to the high reactivity of the isocyanate groups it is necessary to use blocked isocyanate cross- linkers to prevent the premature reaction of the NCOgroups and the OH- groups of the polyester. Todays state of the art is the use of two different kinds of blocking mechanisms for PU powder coatings. In case of externally blocked isocyanate cross-linkers the blocking agent, e.g. epsilon-caprolactam, is set free at temperatures above 170 deg C. The liberation of the blocking agent improves the flow properties of the coating but the mam disadvantage is its emission during the curing process. In contrast, internally blocked uretdione cross-linkers are completely emission-free. The initial disadvantage of the high curing temperatures greater than 190 deg C due to the dissociation of the uretdione ring was eliminated using various catalysts which enable curing temperatures of 130 deg C.