Sprayed TPU makes padded interior trim. (Keeping up with RIM/Urethanes).

Foam-backed auto-interior trim with soft-feel surfaces can now be made in two steps instead of six, thanks to a process developed at BMW AG in Germany with the cooperation of Bayer AG. The secret is producing the outer skin and foam as one piece of thermoplastic urethane (TPU). Production costs reportedly are 30-50% lower than with standard spray and slush-molding methods.

BMW produces the black cockpit lower trim pictured here for one of its 5-Series models using the new two-step process. The entire process takes place in one injection mold. First the thermoplastic hard support is molded, then the mold is opened and the part is oversprayed with Bayer's Desmopan TPU containing a blowing agent. The mold is closed again and then opened far enough to allow foaming. The TPU next to the mold has already cooled to form a solid surface. A finished part is then ejected from the mold.

By contrast, using slush molding requires a thin outer skin layer and the hard support to be produced separately, followed by labor-intensive insertion of the skin into a mold and back-foaming between the skin and support. The resulting part has to be reworked and cleaned before assembly.

Bayer's light-stabilized Desmopan TPU adheres well to thermoplastics and can be formulated in a variety of colors. It is sold here by Bayer Corp., Polyurethanes Div., Pittsburgh.

Tel: [phone]

http://polymers-usa.bayer.com/polyurethanes