08/10/2010

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Lightweight polycarbonate automotive glazing

To make the roof easy to handle and also reduce its weight, it is made of polycarbonate from Bayer MaterialScience (BMS).

The polycarbonate roof uses a new generation of infrared (IR) absorbing colours developed by BMS to meet the requirements of the Volkswagen Group, which includes the Bugatti brand. This is being used for the first time in a series application for the removable targa top. The shade of gray chosen filters the IR part of the sunlight at least as effectively as the corresponding IR colours for glass, says BMS. Thus the roof achieves a direct solar transmittance value of approximately 5 %. As a result, the vehicle interior does not heat up as much under the effects of sunshine.

The panoramic roof is made by KRD Sicherheitstechnik GmbH, a German company based in Geesthacht. The Bugatti's roof is made from solid sheets of Makrolon GP grey 722 that are 5 mm thick. Bayer Sheet Europe GmbH produces these from BMS' polycarbonate Makrolon AG2677, which is specifically formulated for auto­motive glazing. Bayer Sheet Europe has refined the extrusion process for this highly transparent material to ensure that the sheets are free of streaks, distortion, surface flaws, and impurities. As a result, they meet the high optical quality demands for glazing applications. KRD prints the sheets with a black border before thermoforming them and coating them with the AS4000 polysiloxane wet-coat system from Leverkusen-based company Momentive Performance Materials GmbH. This makes the panoramic roof highly scratch- and weather-resistant. The next step is to mill the edges. Last but not least, BBG GmbH in Mindel­heim sprays on a polyurethane edging.

Despite being 1,230 mm long and up to 1,050 mm wide, the panoramic roof weighs no more than around 5.6 kg, including the polyurethane edging. As a result, the entire targa top weighs in at just 13.5 kg. By using Makrolon instead of glass of the same thickness, a weight reduction of up to 50 % can be achieved, says BMS.

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