Material for Good Shape Maintenance & Surface Appearance in Air Bag Covers

Advantages of Vandar® over other Thermoplastic Ester
Autoliv, a global leader in automotive safety, selected Vandar® thermoplastic polyester alloy over thermoplastic ester for a large, passenger-side, automotive air bag cover, because it is better able to satisfy shape maintenance requirements and still meet those for surface appearance, paintability and thermal performance. The thermoplastic ester was unable to provide the shape needed because of differential shrinkage between the layers of this two-shot part.

Processing
The part is made in a rotary molding machine with two injection units and two molds. Each cycle injects the first shot in one mold and the second shot in the other. The machine then ejects the completed part, flips the tools 180° and repeats the cycle.The first shot uses Vandar® 9114 polyester to form a stiff, 4-mm-thick structural member that mounts to the deployment canister and shapes the part. This structural member is overmolded with a 2-mm layer of Vandar® AB100 polyester, a softer grade that allows for texturing and receives a two-component, soft-touch urethane paint without the need for primers or adhesion promoters. The two polyester layers form a strong bond, so no adhesive is needed.

Vandar® 9114 and AB100: High Compatibility
Vern Phillips, Principal Engineer at Autoliv, says the success of part is due to the material used and the tool they designed. “The two Vandar® grades are highly compatible and give us a smooth profile and superior dimensional consistency,” he says. “The result is a good looking surface that conforms to the instrument panel. In addition, test after test has verified that the built-in seam tears properly, even at extreme temperatures and after prolonged exposure to UV radiation.”