|Amid rising fuel prices and growing environmental concerns, pressures are mounting on automotive makers to create lightweight, fuel-efficient and stylish vehicles. With this in view, OEMs are focusing on new technologies that facilitate weight reduction, reducing their CO2 footprint, without compromising on the design aspect. Use of plastics in automobiles is gaining as legislation, particularly in Europe and USA, apply stricter limits on emissions from new cars and demand grows for advances in motor vehicle fuel efficiency.
Polycarbonate (PC) glazing is one such development. PC glazing, you can achieve styling and design features that are just not possible with traditional materials. Also, glazing enables greater functional integration, parts consolidation and system cost advantages. Polycarbonate is an effective thermal insulator, with thermal conductivity that is one fifth that of glass. Better thermal insulation reduces fuel consumption by reducing the air conditioner load. Automotive glazing applications have quantified its potential to reduce the load on heating, ventilation and air conditioning (HVAC) systems based on the significantly lower thermal conductivity of PC versus glass. Windshields can be thinner and stronger than those made of tempered glass alone. In fact, using laminated glass can result in a typical weight savings of 11%.
Polycarbonate glazing has a number of advantages compared with glass:
It is 40-60% lighter in weight than glass, resulting in improved fuel economy, it can be injection molded into complex shapes and designs, can be produced with distinctive colors and textures, it allows parts integration. PC glazing is very tough, protecting vehicle passengers in accidents. It offers improved security against theft since it does not shatter as easily as glass.
Initially, PC glazing progress was slow due to a number of limitations like tendency of polycarbonate to scratch easily, UV sensitivity, etc. For new developments like electric cars, the light weight of polycarbonate can contribute majorly to offset the continuing heavy weight of batteries for electric cars, and significantly extend the travel range of these vehicles. Some of the newer developments include:
A roof module with glazing and integrated solar modules developed as a prototype component and concept study by Webasto AG weighs just 20 kilograms. The roof module�s low weight is thanks largely to the lightweight panoramic panel that consists of transparent polycarbonate Makrolon® AG2677, developed by Bayer MaterialScience for automotive glazing. In this car, the rear window is part of the component�s joint-free polycarbonate outer shell. Also integrated are a rear spoiler and two styling lines, which would not have been directly possible with metal and glass - in the case of the spoiler, for example, this could only have been achieved with a separate assembly operation. Tail and brake lights, directional indicators, license plate lights and high-mount brake lights are located behind the transparent outer shell so that there is no need for individual sealing of all these lights. The relevant fixings and guides can be directly integrated using the two-component back-injection method, which has a favorable impact on production costs for the assembly. Transparent tinted colors have been developed specifically for polycarbonate glazing that filter out a large proportion of the sun�s infrared (IR) rays. As a result, the vehicle interior does not heat up as much under the effects of sunshine. Appropriately treated glazing made of Makrolon® AG2677 enables IR light and energy transmission values for dark colors that are at least as low as commercial thermal insulation pigments for glass. Thus, ventilation and air conditioning systems do not need to work so intensively under the action of the sun�s heat. Polycarbonate glazing also offers benefits in terms of thermal insulation thanks to its thermal conductivity, which is roughly five times lower than that of glass. In cold weather conditions, this increases the temperature of the internal surfaces of the polycarbonate glazing inside the vehicle significantly, which in turn cuts the energy needed to heat the vehicle and also improves comfort. This feature, too, can help boost the travel range of electric vehicles. While combustion engines produce excess heat that can be used for heating, electric vehicles need to generate heat using costly electrical energy, which has a direct impact on the range that can be achieved. The climate benefits from the use of lightweight polycarbonate glazing in vehicles equipped with combustion engines too. This is because it accounts for a greater reduction in CO2 emissions when in use than result from its manufacture and recycling. The impact on the atmosphere is 14 to 22 kilograms of CO2 less per kilogram of polycarbonate used than per kilogram of glass. This is the finding of an environmental study by an independent consultancy firm using the example of a mid-class car. If all of a car�s glazings with the exception of the windshield were made of polycarbonate (a total of 15 kilograms of the plastic), the lower fuel consumption could cut CO2 emissions by up to 330 kilograms per vehicle over a vehicle�s service life of 150,000 kilometers compared to cases where glass is used.
The vario roof that collapses fully automatically into the trunk of the Mercedes SLK, transforming it into a convertible in less than 20 seconds, makes driving with the top down an incomparable experience. To give drivers an unobstructed view to the outside even with the top up, the modular roof system is optionally sold with a transparent panoramic roof element manufactured from Makrolon® AG 2677 polycarbonate. This is the first time a transparent polycarbonate is being used in an electrohydraulic hardtop of this kind. The transparent panoramic roof element is a two-component, injection-compression molding process. 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. Another advantage is the component�s low weight. Compared with a similar element made of glass, the polycarbonate roof is about 4 kilograms or 40% lighter, which reduces the SLK�s fuel consumption and CO2 emissions. 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 significantly reduces the transmission of heat to the inside of the vehicle, and is just as effective as similar IR colorants for glass. 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.
The Peugeot-Citro�n Group is now using plastic glazing made from Teijin�s Panlite polycarbonate resin in the rear quarter windows (�quarter lite�) of the Citroen DS5, a five-door hatchback unveiled at the 2011 Shanghai Motor Show. The technology was developed with Freeglass GmbH Co. The quarter window is manufactured by molding a transparent glazing and a black gloss pillar cover into an integrated piece by multi-component injection-compression and then applying hard-coating on both the internal and external sides for superior durability. Glazing weight has been reduced by 20% compared to a conventional glazing solution.