TPE touch makes a great gasket

Compounds from Kraiburg TPE (Waldkraiburg, Germany) are helping BMW enhance the performance of its new 7 series sedan. The material supplier’s TPE-S series, part of its Thermolast-K product group, for example, has been used in a single-component overmolding process involving glass windows to form a gasket that offers not only reliable sealing without the need for a separate bonding step, but also effective noise absorption while serving as a compensating buffer between the glass and the steel body.

The TPE need not be predried and it cools down quickly after injection. Both factors significantly shorten manufacturing cycles. The process runs at temperatures up to 250ºC.

TPE-S resins also offer a further advantage in terms of processing safety. The dimensional tolerance of the glass insert is lower than that of the tool steel. This makes for more critical conditions both when inserting the glass in the mold and during overmolding itself, during which the pressure has to be kept uniform. In comparison with conventional TPEs, the Kraiburg compounds require lower injection pressure on account of their better flow properties compared with traditional TPEs or even PVC, thus reducing the probability of glass breakage.

Aesthetics are another area in which TPE-S series compounds shine, particularly compared with PVC. The good flow properties, for instance, eliminate the so-called “gramophone record effect” (grooves perpendicular to the direction of flow); a homogenous surface is created, showing no ridges or ripples. Thanks to its superior elasticity, TPE-S resins allow the manufacture of any desired window geometry, translating to enhanced design freedom. Furthermore, the compounds offer outstanding resistance to weathering and ultraviolet light. —[email protected]