DSM proposes a way to reduce SMC density with its low-profile additive

For many years composite material solutions based on SMC have greatly contributed to creating light weight components and assemblies for automotive markets. A major improvement in weight reduction is now possible by using a combination of DSM’s (Schaffhausen, Switzerland) high-performance low profile trademarked additive Palapreg H2700-01 and surface modified hollow glass spheres, says a new white paper written by DSM’s Asal Hamarneh, Blazej Gorzolnik, and Andreas Horback.DSM was able to reduce the density of sheet molding compound (SMC) moldings to ~1.3 g/cm3 compared to the conventional “Class A” formulation of 1.85 g/cm3 (i.e. a 30 percent reduction), while maintaining surface quality and mechanical performance. This combination allows the production of even lighter parts, supporting automotive OEM’s targets of reducing carbon emissions.Fuel savings and the reduction of carbon emissions are high on the agenda of automotive OEMs, driven by strict legislation and the increasingly greener purchasing behavior of car users. At the same time, drivers want more car functionality and performance for less money, causing OEMs to keep a close eye on manufacturing costs. For that reason car makers have been looking for effective ways to reduce weight and make their manufacturing more consistent at the same time.DSM is one of the leading suppliers of synthetic resins used in SMC systems. Besides working on new SMC systems that bring better performance, DSM has a track record of introducing novel solutions for improved sustainability. Recent examples include the commercial introduction of styrene-free, cobalt-free, and bio-based material systems.

To obtain lighter weight SMC formulations, high-density inorganic fillers such as calcium carbonate (CaCO3) can be partially replaced by hollow glass spheres (HGS). However, only a fraction of the fillers can be exchanged by these spheres. When higher HGS quantities are added the processability of the SMC paste is normally troublesome due to much lower paste viscosity.Another challenge is the selection of the right HGS type. Choosing a wrong HGS type will result in crushing of the HGS during the SMC molding process, leading to lower mechanical performance and bad surface quality. In addition to these issues, HGS are known to have poor adhesion to the matrix and to the paint. This is a challenge for parts with high demands on surface quality and for applications where painting is required.

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