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New polycarbonate-ABS blend roof element debuts with new Mercedes SLK; transparent panorama roof an option

A new application of polycarbonate-ABS blends (PC+ABS) is premiering together with the new Mercedes SLK. The base version of the convertible is equipped with an electrohydraulic vario roof system having a roughly 0.8 square meter roof element of Bayblend T85 XF from Bayer MaterialScience.

The modular vario roof system for the SLK is offered in two additional versions besides the base version with the roof element of Bayblend T85 XF: a transparent panorama roof element made of Makrolon AG 2677, a Bayer MaterialScience polycarbonate tailored for automotive glazing, and a glass roof element that changes from transparent to dark and vice-versa in just a few seconds at the push of a button. All three roof elements are bonded to the same roof module frame featuring a lightweight design.

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.



Why not incorporate high efficiency transparent solar cells in it. Two similar panels (separated by the rolling bar) could supply almost enough energy for the car e-ancillaries.


Solar cells would make it too expensive for - Oh, wait - never mind.

Good suggestion.


How will this polycarbonate handle Florida sun for 10 years?.. if it can be be made to last it may remove a lot of lbs from all the glazing in a car.


Plastic does not conduct heat as good as glass. This means it will insulate the car better in winter, reducing heating requirements and increasing the range of BEV's in winter.


With air on both sides, any solid material in the middle makes little difference for heat transfer.

The real downside is you lose the scratch resistance of glass - which you can clean with a razor blade.



You are probably referring to the boundary layer of air that creates extra insulation. That is perhaps true for a house, but a car is not a house.

The air on the outside of the car is moving very fast. On the inside, air is forced over the windows to keep them defrosted. Especially along the huge windshields of modern cars. This boundary layer effect is virtually non-existent in a car.

And I forgot to mention that plastic even may enable double pane glazing for cars since it is much lighter.

HarveyD treated/hardened plastic eye glasses are cleaned twice a day without scratches. This material many be even better. Using better insulation for all car windows and ultra high efficiency heat pump could certainly reduce the energy required to keep the relative small volume cab (104 c.f.) at +20C to +24C.


I am referring to forced convection and the boundary layer that exist for any surface, house or car.

The difference between the heat load for this size sunroof at a 25C differential (inside to OAT) is about 500W for glass and 25W less for polycarbonate-ABS, assuming forced convection on both sides – that’s about 5%.

And don't forget double glazing can have fogging problems if not hermetic (glass).

Try wiping road dust off your glasses with a dry rag, Harvey, or maybe remove tree sap or road tar with a razor blade.


TT...use appropriate non-abrasive cleaning liquid and soft cloth (not razor blades) and your car roof will look new 10+ years down the road. You can also refinish with protective coating once a year or so.

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