Friday, October 21, 2011: 05:59:17 PM

Plastics for Electric Cars: Greater Range Thanks to Lightweight Polycarbonate Glazing

The need to reduce fuel consumption and carbon dioxide emissions is driving the development of alternative drive systems for vehicles. One example is electric mobility, which makes it possible to eliminate the use of fossil fuels all together. One challenge here, though, is the still short range of electric vehicles. The key to solving this challenge lies primarily in even lighter weight automobile construction. Bayer MaterialScience is developing innovative and sustainable material solutions based on polycarbonate and polyurethane, which can be in the areas of glazing and the roof structure, for example. There, these materials enable weight reductions of upto 50 per cent compared to glass, as already demonstrated by the use of polycarbonate panoramic roofs or fixed side windows in series production.

A roof module with glazing and integrated solar modules developed as a prototype component and concept study by Webasto AG and exhibited in an electric car at the IAA, for example, weighs just 20 kilograms. The roof module’s low weight is thanks largely to the lightweight panoramic panel. This consists of the transparent polycarbonate Makrolon® AG2677, developed by Bayer MaterialScience for automotive glazing.

‘Automotive glazing made using our polycarbonate can make a key contribution to offsetting the continuing heavy weight of batteries for electric cars,’ says Dr. Sven Gestermann, Key Account Manager - Automotive Glazing, Bayer MaterialScience. ‘A key aim of current developments is to significantly extend the travel range of vehicles. Automotive manufacturers are therefore showing great interest in glazing systems based on our plastic.’

Wealth of Design Options with Polycarbonate
New design freedom are being opened up for developing electric vehicles, as fundamentally different concepts can be used for the drive chain. The existing engine compartment in conventional vehicles could thus be dispensed with altogether, allowing completely new vehicle designs. Polycarbonate can also benefit from this, as its moulding properties, which are more extensive than glass and metal, allow large, complex moulding of 3D external bodywork parts with integrated glazing elements. ‘As distinctive stylistic elements, these components can determine the brand design of vehicles,’ says Gestermann.

The styling options this allows are demonstrated by Bayer MaterialScience using the example of a prototype concept for a complete, one-piece tailgate. 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 favourable impact on production costs for the assembly.

System-Based Colouring and Heat Management
Further freedom in vehicle design results from the virtually unlimited choice of options for polycarbonate colouring. Glazing for cars, on the other hand, is only available in a few standard colours. Bayer MaterialScience has developed transparent tinted colours 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 colours that are at least as low as commercial thermal insulation pigments for glass. ‘Ventilation and air conditioning systems thus don’t need to work so intensively under the action of the sun’s heat, which cuts power consumption and extends the range that electric vehicles can travel,’ says Gestermann.

Polycarbonate glazing also offers benefits in terms of thermal insulation thanks to the plastic’s 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.

Significant Contribution to Climate Protection for Conventional Vehicles, Too
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 glazing 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.

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