New legislations in Western countries have been introduced to limit pollution caused by vehicles. European legislations such as EC 715/2007 (Euro 5, 6 standards) and US regulations such as EPA 2010 are applying stricter rules to reduce CO2 emissions from new cars. US President Barack Obama announced a plan to increase fuel efficiency by more than 5% pa starting in 2012. These requirements necessitate lighter vehicles and improved fuel efficiency. Thus, auto makers increasingly hinge on the plastics industry to help create lighter vehicles and improve fuel efficiency. Lightweight materials may find exciting opportunities in the automotive industry as a means of increasing fuel efficiency. With 75% of fuel consumption relating directly to vehicle weight, potential weight reductions that result in improved price-performance ratio promote use of lightweight materials. Plastics are light weight materials ideal to improve fuel efficiency and design flexibility without compromising on performance or safety. The automotive industry can expect an impressive 6-8% improvement in fuel usage with only 10% reduction in vehicle weight. This translates into a reduction of around 20 kg of CO2 per kilogram of weight reduction over the vehicle's lifetime. Compared to traditional materials, plastic bumpers, engine covers and fuel tanks are currently 10.4 kg, 4.2 kg, and 5 kg lighter, respectively. With newer advances in plastics materials, the weight of these parts is bound to reduce. Lighter vehicles facilitate easier braking, reduced collision impact and superior driving experience.
One of the key plastics used in automotive sector is polycarbonate (PC). PC has dominated the market for vehicle headlamp covers for 15 years, and now it challenges glass in windows. The primary advantages of PC automotive glazing are lowered weight and associated CO2 emissions reductions along with greater styling freedom and simpler functional integration.
European regulation currently permits polycarbonate (PC) use in all automotive glazing applications except the windshield. An amendment to EU standard ECE43R, which would allow PC to be used in front windshields, is expected to be passed by 2010. In the United States, the US Department of Transportation's National Highway Traffic Safety Administration (NHTSA) has approved the use of PC for all non-windshield glazing applications provided that it meets all existing auto glazing specifications for laminated glass as prescribed in the Federal Motor Vehicle Safety Standard (FMVSS) No. 205. This includes < 2% delta haze in the all-important Taber 1000 abrasion test. However, uncertainty over long term weathering and compliance with the ANSI regulation has held back adoption of PC glazing in the US.
Advances in this application have been slowed by UV sensitivity of the material and its tendency to scratch easily, which makes it less weatherable than glass. Coating technology is developed to provide scratch resistance as well as UV resistance. Polysiloxane coating to enhance PC's UV stability in automotive glazing has been developed by Exatec. The correct application of such wet-coat systems is important to ensure that PC glazing components retain their clarity throughout the vehicle's life.
The wide choice of styling options with PC is testing conventional assumptions of automotive window design and creating whole new opportunities for advanced vehicle styling. Features such as colored glazing are now possible along with gaps in the window, sharp corners, smooth corner radii or complex 3D shapes. These features are undesirable, unmoldable or cost-prohibitive with laminated or tempered glass. PC auto glazing permits parts integration previously not possible. Using two-shot injection compression molding (ICM), it is possible to create a roof-module frame and optical panel in one piece. Prototypes have also been produced in which two color molding integrates the window into the tailgate together with taillight assembly connections, wiring and interior trim. PC glazing can also be molded to incorporate ribs or brackets used to attach parts onto the vehicle or support additional features. Rear view mirrors can be mounted on the side window, rather than on the door panel. Molding heating/defrosting elements and fractal antennas into a PC window panel is also possible using in-mold films with preprinted circuitry.
Two principal PC suppliers and window glazing proponents, Bayer and Sabic Innovative Plastics, continue to make steady advances. Window glazing is a crucial part of growth plans for both companies as the market for compact discs and digital video discs has dropped due to consumers’ easy access to music and movies via the Internet as per MPW. One of the factors inhibiting broader acceptance of PC window glazing is need for extensive documentation on new products with regard to safety regulations involved. In 2005, the U.S. Dept. of Transportation’s National Highway Traffic Safety Administration (NHTSA) confirmed that Exatec E900-coated polycarbonate may be used in vehicle areas specified for Item 2 glazing (safety glazing material for use anywhere in a motor vehicle except windshields), provided that the product satisfies the existing performance standards for Item 2 glazing.
But questions persist regarding retention of the necessary transparency over the useful lifetime of the vehicle. Bayer has developed tests for coated polycarbonate automotive glazing to measure their resistance to windshield wipers. This test enables simulation of the actual stress exerted on the wiped glazing far more realistically, accurately, and with a higher reproducible quality than is possible with the Taber abrasion test stipulated in the regulations. Initial tests have shown that, when dirty panes with a polysiloxane coating are wiped under primarily wet conditions, they exhibit virtually no clouding that is visible to the naked eye - even after 30,000 double-wiper cycles. |
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