Improvements in RIM Processing for Automotive Fascia 900425

Improved reaction injection molded (RIM) polyurea polymers for fascia have been developed which provide significantly longer mold fill times while maintaining the fast cure times sought by molders. These polymers have been formulated for use with or without fillers. In either case (filled or unfilled), surface quality comparable to painted steel can be achieved.

Material performance data such as heat sag, low temperature impact, coefficient of linear thermal expansion and moisture absorption are compared for RIM polyurea and a commercial thermoplastic copolyester. The data illustrate that RIM polyurea fascia can be processed on existing equipment. These polymers provide superior performance over polyurethane/urea and equal performance with an economic advantage over injection molded engineering thermoplastic.

POLYurethane/urea RIM fascia systems have become the dominant materials in North America for molding plastic fascia because they economically meet the performance requirements of the automotive industry. However, the industry is seeking improved dimensional stability and surface quality for fascia on full sized and luxury vehicles; properties that can be obtained with RIM polyurea chemistry at a cost below engineering thermoplastics.

With improved polyurea chemistry offered by The Dow Chemical Company, fascia can now be molded under processing conditions similar to RIM polyurethane/urea (PU/UREA) systems. While initial RIM polyurea candidates reduced in-mold cure times from 30 seconds to 20 seconds, they also gelled much faster than PU/UREA systems, thus requiring less than 1 second for mold fill. Recent developments have extended the gel time for polyureas without sacrificing other process conditions or performance. The improved resins are formulated with zinc stearate internal mold release [1] and the isocyanate prepolymers incorporate new polyether technology [2]. These systems have been designated polyurea HT30 and polyurea HT55. The details of this development work, which compare the mold fill times of the improved polyurea systems with the initial polyureas and PU/UREA hybrids, are given in this paper. A contrast is also made with the mechanical performance and cost of a commercial thermoplastic copolyester fascia material.