PU Foam System Can also Be Used Outdoors
Honeycomb on the Car Roof
The Elastoflex E polyurethane (PU) foam system from BASF SE, Ludwigshafen, Germany, supports mass-production of an exterior car component featuring a honeycomb sandwich technology with a Class A film. The roof module in the standard model of the new Smart Fortwo from Daimler AG, Stuttgart, Germany, consists of a paper honeycomb and two surrounding glass fiber mats, which in an impregnation process are sprayed with the low-density, heat-activatable Elastoflex E 3532 polyurethane foam system and pressed together with a solid-colored Class A film. A single operation thus produces a roof module that is claimed to be 30 % lighter than the standard roof on the predecessor model – but retains the same strength and flexural rigidity. The lightweight roof was developed by F. S. Fehrer Automotive GmbH, Kitzingen, Germany, which manufactures it at its plant in Großlangheim, Germany.
The honeycomb technology has previously been is used in car interiors, e. g. for loading floors, roof linings and rear shelves. For use in exterior components, the chemical company has adjusted the viscosity and reactivity of the semi-rigid polyurethane system which was developed specially for the honeycomb technology, so that it can be optimally processed in each manufacturing step and exhibits good adhesion properties: it guarantees uniform, thin wetting of the glass fiber mats and does not drip. After the semi-finished product has been impregnated, it is pressed into shape in a heated mold together with the Class A film. This causes the polyurethane system to foam up slightly at the edge of the sandwich and creates a solid material composite between film, reinforcing mats and paper honeycomb core.
The reactivity of the PU foam system has been adjusted so that long spray times of up to 120 s for large-scale parts as well as short demolding times of up to 60 s are possible. The company maintains that decorative materials and films can be directly back-foamed in the mold, as the material adheres well to many materials. The roof module is fitted on the outside with a Class-A film while a textile covering is attached on the inside.
Translated from Kunststoffe 9/15, p. 13
F.S. Fehrer Automotive GmbH
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