The use of low-profile sheet molding compound (SMC) resins for automotive body panels is growing rapidly. Surface appearance and bonding capabilities are two major performance considerations for these body panel applications. The Owens/Corning Fibergias Atryl resin was developed specifically to meet these criteria. As with all SMC resin systems, specific formulations need to be developed for individual applications, therefore the effect of styrene, unsaturated polyester resin, and thermoplastic quantities are of major importance in formulations development. Prior to introducing this new resin system, these three parameters were varied as part of a designed experiment and studied as a function of both surface aesthetics and adhesive bonding.
From a computer generated result, the Atryl resin system was optimized to provide both smooth surface and strong bondabillty. This optimized system was then compared to other automotive SMC Class A resin systems to confirm not only that the surface was improved but also adhesive, paint primer, and in-mold coating bondabillty were maintained. From this work, the Atryl resin system, based on Owens/Corning's unsaturated polyester and thermoplastic resins, was found to meet or exceed critical performance criteria as specified by the automotive original equipment manufacturers. Based on results achieved with the recommended sheet molding compound formulation, the Owens/Corning Atryl resin system has been given a generic approval by the CPC Group of General Motors Corporation.