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THE RIM (REACTION INJECTION MOLDING) PROCESS has come of age. Short cycle times and improved quality have been realized utilizing RIM IMR (internal mold release) systems introduced to the industry by The Dow Chemical Company in 1982. Further improvements will maximize RIM part quality and production rates. Although the RIM process of today is competitive with other plastic molding techniques, economic sensitivity studies have shown room for improvement in the area of processing speed and post-mold handling. Development targets, including improved polymer systems and machine designs will allow RIM processing of large parts at cycle times as low as 60 seconds. Polyureas and other novel chemistries are being developed that will eliminate or control flash, reduce or eliminate post cure requirements, and produce high performance polymers with resistance to paint oven distortion. These mechanical and polymer improvements will make RIM highly competitive for molding automotive body panels.

Reaction injection Molding (R.I.M.) systems to meet the thermal resistance, physical property, and performance requirements for automotive exterior vertical body panels are under development by The Dow Chemical Company. Polymer systems designed to meet the thermal resistance requirements for a variety of paint/assembly processes from off-line painting at 250°F to full on-line painting, including E-Coat process, have been developed and are being optimized for production application. Polyurea technology and internal mold release advances have been combined to produce polymer systems such as SPECTRIM* 80S polymer (for off-line paint/assembly process), Polyurea HF (for on-line painting to 325°F) and Polyurea HF (for on-line painting through E-coat at 400°F). This paper summarizes the processing and physical property characteristics of these polymer systems with emphasis on thermal stability requirements for different assembly techniques.