||January 1, 2005
Glass run channels, belt line seals and secondary door seals for automotive applications are complex parts that are not just simple extruded profiles but require a number of finishing operations, in particular additional moldings (end caps, corners), to provide full functionality to the seal. Traditionally, a thermoset EPDM part is overmolded and cured onto EPDM vulcanized profiles. The advantage of this technique is good bonding, but this is a long and costly process in relation to the number of curing presses necessary to cope with the profile production rate and associated labor. Recent trends show an increased usage of thermoplastic overmolding onto cured EPDM profiles to provide higher total system quality at a lower cost. It offers possible reduction of cycle time, fewer post-trimming operations, preservation of surface treatment and better color stability. The critical factor for good overmolding is the bond strength to the thermoset EPDM profile over a large temperature range without the addition of primer or adhesive. Generally, thermoplastic materials have not shown good performance in that respect vis-à-vis cross-linked EPDM. In this paper, we describe a new thermoplastic vulcanizate grade that provides improved adhesion strength compared to cured EPDM rubber and can be used in critical parts like corner molding of a glass run channel. We also show that the EPDM compound can be modified to further improve this adhesion. We believe that this approach will simplify the finishing operations in weatherseal production and contribute to an overall cost reduction of the part without impairing sealing system performance.