Dynamic automotive door seals are complex components generally constituted of a low-density sponge profile co-extruded onto a dense metal carrier. These seals contribute to the comfort inside the car by insulating from water and aerodynamic noises. They control the door closing force, assessed by load deflection measurements; and the long term sealing performance, assessed through compression set testing. Thermoplastic elastomers have started penetrating automotive weather seal applications, offering light weight, easier processing and recyclability vs. traditional material. But TPV sponge seals have been limited in comparison to existing technology by several issues like rough surface aspect, high water absorption, compression load deflection, and compression set. In this paper, the authors will describe general principles of a foaming technology suitable for thermoplastic elastomers, focusing on a new technique of foaming TPV by super critical fluid that creates a closed microcellular structure, and thus dramatically reduces water absorption and offers a better surface aspect. In addition, TPV compositions adapted to this supercritical foaming technique can provide controlled cell morphology and improved performance. It can be shown that selected TPV compositions optimized for the Mucell technique and using N2 as SCF can achieve a cell morphology which is comparable to the one obtained with a chemically blown EPDM; therefore, similar dynamic compression load deflection can be expected. Another benefit of the Mucell technique is the ability to on-line control the cell structure by the amount of injected gas. This is an improvement over the chemical blow system for a more capable extrusion process. TPV has a constant and better long term compression set in comparison with EPDM. This is a key advantage for designing door profiles with a better sealing performance over the lifetime of the car. With Mucell SCF technique, TPV foamed seals can be produced with tight tolerances, thin walls and consistent density over long extrusion runs. This is a potential for scrap reduction for the transformer. A higher overall quality can be perceived by the consumer for TPV door seal foamed with SCF, since the potential odor from chemical residues of the blow system is eliminated. The authors believe that this new foaming process used in combination with such an adapted TPV grade can offer the performance required for dynamic automotive sealing systems.
TPV sponge materials and foaming systems for dynamic automotive weatherseals
2005
14 Seiten, 15 Bilder, 4 Tabellen, 2 Quellen
Aufsatz (Konferenz)
Englisch
WEATHERSEALS IN AUTOMOTIVE APPLICATIONS
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