Car manufacturers and their suppliers impose particularly
stringent demands on surface coating systems. The fact that the latest
environmentally compatible, waterborne polyurethane coatings are able to
comply with these strict specifications is illustrated by the example of
the cardan shafts that are being built into some of the top models. They
are coated with an aqueous one-component system containing Bayhydrol® B
130, a binder supplied by Bayer MaterialScience AG.
The Bayhydrol® based system provides the cardan shafts with outstanding
corrosion protection. It can withstand 240 hours in a salt spray
environment and six cycles of the alternating climate test (VDA 621-415).
The coating also has excellent stone-chip resistance, due mainly to the
fact that it adheres very well on the substrate - but then that is not
really surprising as Bayhydrol® B 130 is also frequently used as a
waterborne adhesion promoter. "It has to be said that this particular
application is especially challenging for the coating system because of the
production process: the components of the cardan shaft first undergo an
alkaline degreasing operation, are then welded together and subsequently
coated without any additional pretreatment," says Dr. Ulrich Freudenberg,
an expert for polyurethane coatings at Bayer MaterialScience.
Almost as soon as the coating operation has finished, the cardan shafts are
packed into transport frames, where they are secured with the aid of
rubber-covered clamps. It is only because Bayhydrol® B 130 is such a
fast-drying binder that the paint film can withstand this mechanical stress
Until now, components for the automotive industry like cardan shafts, shock
absorbers, axles etc. were usually coated with conventional solvent-based
systems. The changeover to waterborne coatings makes it possible to comply
with planned VOC guidelines, which aim to further reduce emissions of
volatile organic compounds.
Information about polyurethane coatings, including detailed descriptions of
applications, and contact details can be found on the Internet at