Specialty chemicals company Lanxess says it foresees considerable potential for the use of PBT and polyamide compounds in production of vehicle exterior body parts like bumpers, sills, front grilles, door handles, fuel tank flaps, spoilers and mirror housings. "That is why we are building up a wide range of Durethan and Pocan materials for this use segment. The development work is focusing on application-specific, optimized mechanical properties, as well as good surface qualities and good paintability," says Frank Krause, design expert at Lanxess.

Lanxess has an innovative material for fuel tank flaps in Pocan B 5220 XF reinforced with a glass bead content of 20 percent. The product is an alternative to blends of polyphenylene ethers and polyamide (PPE+PA), which are often used in series-produced fuel tank flaps because they can be painted online. A disadvantage of such blends, however, is their high degree of moisture absorption, which has an undesirable effect on the required dimensional accuracy. PBT, by contrast, stands out by virtue of its high degree of dimensional stability.

"Our Pocan B 5220 XF also withstands the usual temperatures required for cathodic dip coating (CDC). That means the part can be mounted to the vehicle body and go through online coating and the CDC process along with it, which yields savings on logistics and coating costs," adds Krause. Mineral-filled PBT and PA compounds, on the other hand, which fuel tank flaps are also made of, are not suitable for CDC.

Lanxess says it has intensively studied the new material's thermal expansion behavior, using fuel tank flaps that were produced on a series-production tool. "Even after one hour at 200degC, the expansion of the freely suspended parts was negligible," says Krause. Another strength of the new PBT is the good surface quality and paintability, which is due to the absence of glass fibres in the material. Compared to similar glass bead-reinforced standard materials, its bears the promise of much improved melt flow properties and approximately 50 percent greater toughness.

New (PC+PBT) blend for radiator grilles
Lanxess has developed Pocan TP 406-001 for radiator grilles. "The non-reinforced polycarbonate+PBT blend material was conceived primarily for parts with Class A surfaces, which are given a high-gloss coating," says Krause. The material displays very low and uniform shrinkage and hardly any tendency to distortion at all. Thanks to the blend's extreme toughness even in cold temperatures, the radiator grille does not shatter into shards in the event of a collision,

which helps protect nearby pedestrians. The high heat deflection temperature ensures that long, horizontal grille fins do not sag as a result of exposure to the radiator heat.

For exterior bodywork parts that are not coated online, the Lanxess product line continues to feature materials including non-reinforced (PBT+PC) and (PET+PC) blends, and reinforced (PBT+PET) blends.

A good choice for spoilers, for example, is Pocan TP 957-001, which consists of up to 25 percent post-consumer recyclate from PET bottles. The mineral-reinforced (PET+PC) blend is very impactresistant and displays minimal distortion, among other properties.

Durethan DP 2131/20 W1 EF, a heat-stabilized polyamide 6 with easy flow characteristics, says Lanzess, is ideal for substructures of spoilers, exterior mirror housings and door handles. It provides non-coated exterior bodywork parts with excellent resistance to weathering.