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Polycarbonate blends for automotive body parts

Bayer MaterialScience AG : 29 March, 2006  (New Product)
Polycarbonate blends such as Makroblend and Bayblend from Bayer MaterialScience AG are increasingly suited to applications in the field of automotive body parts. For example, mineral-reinforced PC/PET and PC/PBT blends as well as unfilled and PC/ABS formulations reinforced with glass fiber are increasingly being used instead of sheet molding compounds for the production of rear spoilers and antenna covers. Examples of this trend are the rear spoilers of Volkswagen
“Our PC/PET blend is definitely a more cost-effective solution, particularly with large production runs because, unlike the corresponding SMC components, the resulting parts need no secondary finishing to remove ridges and flashes. Instead Class A surfaces are produced that can be painted without any pre-treatment”, explains Hans-Jörg Dahmen, who is an expert in processing plastics for bodywork components at Bayer MaterialScience.

Another advantage of the PC/PET blend: Due to its low density, it yields much lighter components than SMCs. In addition, being injection molded, it allows undercuts, which means greater freedom of design. This is not possible with SMCs that are processed by press molding. Its linear thermal expansion is also low enough to achieve narrow gaps between assemblies.

“Based on our positive experiences with Makroblend and Bayblend with antenna covers and spoilers, we expect to be able to use PC blends sooner or later to produce horizontal body parts”, comments Walter Köppchen from the technical product service for PC blends in the Business Development division. In his opinion, potential applications include trunk lids and roof modules with integrated inserts for antennae. Even when it comes to concepts for roof modules with large-area, transparent PC glazing, PC blends would be suitable as materials for frame components.

Another material that has come to the fore recently in the production of car body parts is Makroblend DP 7645. It has become the material of choice for the mass production of large radiator grilles, often as an alternative to polyamide. For example, the grilles of the Audi A8, Audi A6, Audi A4, Audi A3 Sportback and the Volkswagen Passat are made from this non-reinforced and elastomer-modified PC/PET blend. “Our material fulfils the complex mechanical and thermal requirements for large, striking radiator grilles” explains Dirk Loof, Key Account Manager for Volkswagen at Bayer MaterialScience. The notable characteristics of this thermoplastic are its low temperature impact resistance down to -40°C and its high stiffness and heat resistance, whose characteristic property profile meets the increased requirements with regard to pedestrian protection. A further strength of this material is its good resistance to common automotive chemicals such as oils, grease, fuel and cleaning agents.

The Volkswagen Passat is fitted with a radiator grille made of the PC/PET blend Makroblend DP 7645. The chromed frame of the grille is made of the PC/ABS blend Bayblend T45 PG (Plating Grade).

Blends of PC and ABS such as Bayblend are also firmly established in the area of automotive body parts. Non-reinforced blends are mainly used. Their heat resistance can be controlled by varying the proportion of polycarbonate in the compound. They are very pourable, stiff and remain tough over a broad range of temperatures. Typical applications include external mirror housings, small number plate indents, radiator grilles and antenna covers. Electroplatable resins such as Bayblend T45 PG (Plating Grade), which is used to produce chromed parts such as trim, emblems, handles and mirror housings are extremely successful. For example, the chromed frame of the Volkswagen Passat’s grille is made of this easy-flow material, which has a higher heat resistance than ABS and ensures an excellent bond to the electroplated layer.

A new non-reinforced blend for unpainted automobile body parts is Bayblend DP W 65 (PC/AES). In addition to its excellent weather resistance and UV resistance, its strength is its outstanding low-temperature impact strength, when compared to other weather resistance thermoplastics. Potential applications are non-painted bumper strips, air vents and radiator grilles.
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