PC+ABS roof element. The roof PC+ABS (polycarbonate/acrylonitrile butadiene styrene) element, which is coated in the body color offline, demonstrates that this high-performance material makes it possible to take thermoplastic exterior bodywork parts installed horizontally to an entirely new dimension with respect to size while still satisfying the very stringent requirements for comfort, optical quality and dimensional accuracy, Bater MaterialScience says.

The PC+ABS roof element is manufactured by Peguform GmbH, a leading manufacturers of plastic parts, complete systems and modules for automotive interiors and exteriors. The company is based in Bötzingen, Germany.

The roof module element exhibits high energy absorption in crash situations. This benefits safety, because the component does not break and fail. The PC+ABS blend retains break resistance even at temperatures well below freezing. With a temperature of deflection under load of 127 °C (0.45 MPa, ISO 75-1, -2), the unreinforced material is able to satisfy the high thermal requirements placed on horizontal bodywork parts. Other strengths include high chemical and stress-cracking resistance, plus 10&ndash:15% better flowability compared with the standard material.

Transparent panorama roof element. The modular roof system is optionally sold with a transparent panoramic roof element from Webasto, manufactured from Makrolon AG 2677 polycarbonate.

It’s the first time a transparent polycarbonate is being used in an electrohydraulic hardtop of this kind. Our custom material for automotive glazing sets standards in terms of weight reduction, comfort, surface quality and heat protection.

—Dr. Sven Gestermann, key account manager on Bayer MaterialScience’s Automotive Glazing team

The transparent panoramic roof element is manufactured by Webasto in a two-component, injection-compression molding process at its Plastics Competence Center in Schierling, Germany. In the first step, the transparent external polycarbonate surface is fabricated with an average wall thickness of 5.5 mm. In the second step, the interior black margin is back-injected with colored Bayblend T95 MF.

The mineral-reinforced PC+ABS blend was customized for this process and its properties precisely adapted to the Makrolon AG 2677. The roof element, measuring 1063 x 727 millimeters, can therefore be manufactured to close tolerances, with extremely low interior stresses and warpage.

Compared with a similar element made of glass, the polycarbonate roof is about four kilograms or 40 percent lighter, which reduces the SLK’s fuel consumption and CO₂ emissions. What’s more, it improves vehicle handling, because the vehicle’s center of gravity is lower.

—Detlef Penczek, project manager for Daimler

The roof element is darkened with a special IR-absorbing gray tone. The driver and front passenger have an unobstructed, undistorted panoramic view, but are not blinded by the sun. This eliminated the need for a shading system, such as an interior roller blind, which means more headroom for passengers.

The colorant developed for the Makrolon AG 2677 used in this application reduces the transmission of heat to the inside of the vehicle, and is just as effective as similar IR colorants for glass, Gestermann says. Light transmission and direct energy transmission each amount to only about 6%; the car interior does not heat up as much as in the sun, and the radiant heat passengers feel from the sunlight is effectively suppressed.

The panoramic roof element made of polycarbonate has a polysiloxane hardcoat from Momentive Performance Materials GmbH in Leverkusen.