A Makrolon® lamella roof proven in the current Mercedes-Benz A-Class now features in the Mercedes-Benz B-Class. Its five transparent, gray-tinted lamella are made of the Makrolon® AG2677 polycarbonate from Bayer MaterialScience AG. The innovative panoramic roof was developed by Webasto AG, which also acts as system supplier for the complete assembly and is based in Stockdorf near Munich, Germany. "We opted for polycarbonate as the material for the lamella because it offers a weight saving over a purely steel-based solution of around 3.5 kilograms and gives more freedom in terms of the 3D component layout and therefore more freedom in the design. What's more, polycarbonate is extremely resistant to chipping from stones and, in the event of a crash, will not shatter like glass. That means increased safety for passengers," explains Ralf Schwaighofer, Group Manager, Plastics Technology, at Webasto.
The lamella design means the roof opening can be made around 60 percent larger than with traditional sunroofs. When opened, the roof gives passengers a generous panoramic view and, when closed, ensures the inside of the automobile has a bright, welcoming and open atmosphere.
The lamella panels are manufactured by freeglass GmbH & Co. KG of Schwaikheim, Germany, using a dual-component injection molding technique.
Firstly, the transparent panel exterior is manufactured from Makrolon® AG
2677 and a surrounding black border made of plastic is then molded to the inside. A finally applied polysiloxane coating protects the lamella roof panels from scratching and weathering.
In terms of its property profile, Makrolon® AG2677 is a specially optimized grade of polycarbonate for automotive glazing. The material is extremely pure and can be colored in various thicknesses in the specific colors required by the customer. Further strengths of the material include its high toughness, transparency and heat resistance. "Thanks to several successful projects, such as the panoramic roof on the smart forfour, we have garnered extensive development, design, material and processing expertise for polycarbonate automotive glazing. Our customers can leverage this know-how if, for example, they are looking to achieve optimal levels of dimensional accuracy and surface quality," says Volkhard Krause, Head of the Automotive Glazing Team at Bayer MaterialScience. Krause believes a fundamental advantage of polycarbonate over glass is its high integration
potential: "For example, it's even possible to develop panoramic roofs that incorporate sun visors or roof modules with integrated solar cells and illumination elements."
Bayer MaterialScience has taken great pains to ensure that polycarbonate glazing can be integrated into surrounds suitable for plastics and has, for example, developed modified Makrolon® grades for the frame components.
Grades of the transparent copolycarbonate Apec® are available for applications that have to be particularly heat resistant. The company is also in the process of developing polycarbonate grades with IR protection.
These materials can be used to create glazing that largely absorbs the sun's heat radiation so that the inside of the automobile remains cooler.