According to an August 12 press release from BASF, its semi-rigid polyurethane foam system has made it possible for the first time to mass-produce an exterior car part featuring a honeycomb sandwich structure with a class-A film. The foam system, Elastoflex® E, was used to make the roof for a model of the new smart fortwo – an electric vehicle. The roof consists of a paper honeycomb and two surrounding glass fiber mats.

The roof, which is 30 percent lighter than the standard roof on the previous model, was developed by Fehrer Composite Components, which manufactures it in its factory in Großlangheim, Germany. Although the newer model is lighter, BASF maintains it retains the same strength and flexural rigidity.

To make the roof, honeycomb and glass fiber mats are sprayed in a single impregnation process with BASF’s Elastoflex® E 3532 and pressed together with a solid-colored 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.

“In contrast to conventional composite parts, in this roof module the individual layers are not glued together in a multi-stage process, but are instead produced in a single manufacturing step,” says Gao Kwintmeyer, Global Purchasing Fehrer. “This is much more efficient.”

In the past, the honeycomb technology was used to make interior car parts, such as loading floors, roof linings, and rear shelves. In order to make exterior car parts, however, BASF had to adjust the viscosity and reactivity of Elastoflex® E to ensure it could be optimally processed in each manufacturing step and display good adhesion properties. According to BASF, the adjusted system guarantees uniform, thin wetting of the glass fiber mats and will not drip.

For more information on Elastoflex® E, check out BASF’s product page.