Sheet Molding Compounds (SMCs) are a type of prepreg made with short fibers (15 to 50 mm). They present a lighter alternative to aluminum, and offer a good compromise between performance and cost. SMCs are ideal for interior parts such as C-pillar reinforcements and partition walls. Huntsman provides components for formulating SMC epoxy matrices, as well as semi-formulated epoxy systems.
Epoxy short-fiber prepregs are used to make parts requiring higher thermomechanical performance than polyester Sheet Molding Compound. An additional benefit of epoxy matrices is that, unlike polyester and vinyl ester matrices, they do not release harmful volatile compounds during processing or after polymerization, and therefore can be used for parts located inside a vehicle.
Glass transition temperature (Tg):
130 - 140°C
Cure time:
3 min 150°C
Suitable for:
Fast cure B-stage SMC system for serial production of automotive parts. VOC free. Resulting SMC retains very good drapability for 3 weeks at 23°C.
Glass transition temperature (Tg):
115 - 135°C
Cure time:
5 - 10 min 150°C
Suitable for:
Medium Tg B-stage epoxy SMC system for body in white parts. VOC free. The system can be compounded on large sized SMC rolls and the resulting SMC retains very good drapability for 6 weeks at 23°C. A wide range of part thicknesses can be processed.
Glass transition temperature (Tg):
160 - 190°C
Cure time:
5 - 10 min 160°C
Suitable for:
High Tg B-stage epoxy SMC system for parts close to the engine. VOC free. The system can be compounded on medium sized SMC rolls and the resulting SMC retains very good drapability for 6 weeks at 23°C. Allows processing up to medium part thicknesses.
The semi-formulated solutions offered by Huntsman must be completed with fibers and fillers by the compounders. The rheology of the matrix is the key to delivering a cost-effective preparation of the final epoxy SMC formulation. Based on long experience in standard long-fiber prepreg epoxy formulations, Huntsman chemists have focused on a winning combination to deliver optimal systems for SMC processes: optimized rheological behavior and conservation of thermomechanical performance.
Huntsman’s internal simulation tools allow cure time, Tg and maximum temperature during the process to be predicted. This allows the customer to select the right resin system for a particular application, adapt process parameters to reduce part production time, and decrease the number of trials before getting an optimal part.
Our leading composite expertise, broad product range and unique simulation capabilities can reduce development cycles by up to 50 %.
SMC finds applications in transportation when parts must be designed and produced at lower cost compared to long-fiber composite parts. Recent developments show that epoxy SMC could be considered for more structural parts such as chassis to significantly reduce costs.
Polyester and vinyl ester matrices release styrene, whereas epoxy matrices produce zero outgassing, so the latter are suitable for applications in which no release of volatile products can be tolerated. Epoxy carbon SMCs also exhibit low shrinkage compared to polyester and vinyl ester SMCs, so they are preferred for cosmetic parts.
ARALDITE® LY 3569 resin / ARADUR® 1571 hardener / Accelerator 1573 / XB 50021 B is a medium-Tg B-stage epoxy SMC system for body-in-white parts. A wide range of part thicknesses can be processed.
XB 50021 A / ARADUR® 1571 hardener/ Accelerator 1573 / XB 50021 B is a high-Tg B-stage epoxy SMC system specially formulated for parts located close to engines. It allows processing up to medium part thickness.
Both systems can be compounded on large SMC rolls, and the resulting SMC retains an out life of 6 weeks at 23° C.
