1994-03-01

New Developments in Low Density RIM Composites for Interior Trim 940703

The use of low density reinforced Reaction Injection Molded (RIM) substrates for covered interior automotive articles continues to increase globally. Reduced party mass, consolidation of manufacturing steps (labor), and the use of aluminum tooling, instead of steel, are cited advantages that LD-RIM offers when compared to traditional wood based and thermoplastic materials.
Two RIM processes are successfully being used to produce covered interior door panels. Low density structural RIM (LD-SRIM), utilizing conventional RIM equipment, involves the placement of a pre-cut fiberglass mat in the tool cavity prior to open-pour injection of the 2-stream liquid urethane components. Low density reinforced RIM (LD-RRIM), utilizing lance cylinder RIM equipment, incorporates reinforcing fibers, such as milled fiberglass or wollastonite, in the liquid resin component. The liquid resin containing reinforcing filler is injected with the isocyanate component into a closed mold. Both LD-SRIM and LD-RRIM covered door panels meet OEM performance specifications.
Little difference exists between LD-SRIM and LD-RRIM substrates, aside from tool design considerations and processing with either glass mat or reinforcing filler. In-mold polymer cure times and pressure/temperature profiles are essentially the same for both processes, and are dependent on the polyurethane components (i.e. polyol, catalysts etc.) employed, polyurethane wall thickness, and polyurethane density (1). Aluminum production tools are preferred because: 1) the polyurethane substrates are “class B surfaces” and do not have the distinctness of image requirements which “class A” parts obtain from steel surfaces, 2) the low level of reinforcement (< 20 percent by weight of the substrate) is non-abrasive to the tool surface, and 3) the low tonnage (<100 ton) RIM clamps which are used.
Advancements have been made in LD-RIM substrates to reduce weight further, to proliferate the LD-RIM substrate to other automotive applications, to demonstrate the recyclability of both PVC covered LD-SRIM and LD-RRIM substrates, and to impart “self-release” properties of the LD-RIM substrate from aluminum production tools.

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