Bayer MaterialScience AG is adding two new mineral-filled PC+ABS grades – Bayblend® DP T90 MF-20 and Bayblend® DP T95 MF – to its range of polycarbonate blends for bodywork parts . “Both materials represent an attractive alternative to sheet molding compounds in terms of surface quality, coatability and cost-effectiveness. The properties of each blend are geared to specific bodywork applications,” explains Dr. Eckhard Wenz, head of the Bayer MaterialScience technical product service for polycarbonate and blends in Europe.
Particular strengths of Bayblend® DP T95 MF include a heat resistance temperature of 142 °C (Vicat/B 120) and very good toughness for a reinforced PC+ABS blend. At room temperature and under multi-axial stress, for example, the material demonstrates ductile fracture behavior. Furthermore, it has an Izod impact strength of over 150 kJ/m2, measured under ISO 180-1U test conditions. “This makes our material ideal for components that need to satisfy tough crash requirements – for example off-line coated fenders, bumpers and frames for polycarbonate glazing elements,” continues Wenz. The material is already used together with Makrolon® AG2677 – a polycarbonate developed for automotive glazing – in the large roof module of the smart fortwo. “We have adapted the shrinkage behavior of Bayblend® DP T95 MF to that of the polycarbonate so that, despite its size of over one square meter, the roof module can be manufactured using 2-component injection molding with very limited internal component stresses and distortion. This enabled us to achieve the excellent crash behavior required for the application and take into account the high demands in terms of the component’s surface quality and dimensional stability,” explains Dr. Andreas Seidel, a member of the Global Innovation Blends team responsible for Bayblend® product development in the Polycarbonates Business Unit.
The outstanding features of Bayblend® DP T90 MF-20 are its excellent flowability and very low, largely isotropic thermal linear expansion. “Coefficients of linear thermal expansion in the range of 0.4 x10-4 K-1 are achieved in actual components, a figure that sets the benchmark for mineral-filled polycarbonate blends,” observes Seidel. The PC+ABS blend is the material of choice for components such as trunk lids, antenna covers, rear spoilers, tailgates and rear valance panels where toughness is less important than small gap dimensions that produce a seamless look. With an elasticity modulus of 5,200 MPa, Bayblend® DP T90 MF-20 features excellent stiffness that only glass-fiber-reinforced PC+ABS grades have so far been able to achieve. Cutting the melt viscosity by around half can also result in flow paths up to 50 percent longer than with Bayblend® DP T95 MF. “This makes the blend ideal for large components with complex geometries,” explains Wenz.
Like Makroblend® – the PC+PBT and PC+PET blends that are tailor-made for such applications – the two new PC+ABS blends for bodywork parts represent a cost-effective alternative to sheet molding compounds (SMCs), in particular where larger quantities are involved. Unlike with SMC components, no additional finishing is required on parts made from these blends because there is no burring or flashing. Both blends produce Class A surfaces straight off that can be coated without any pretreatment. Because they have a lower density than SMCs, they allow lighter components to be manufactured. Use of the injection molding method also enables undercuts to be produced, something that is not possible with SMCs processed by compression molding.