Polycarbonate rear window 35% lighter than glass version

With the automotive industry focused on hitting future fuel economy and emission targets, the Ford Motor Company has revealed a drivable multi-material lightweight vehicle (MMLV) with polycarbonate (PC) glazing from Sabic's Innovative Plastics business. This solution reportedly realizes a 35% weight reduction compared to the same window on a 2013 model year Ford Fusion production vehicle. The weight savings total 7.4 pounds, even though the rear window is over one millimeter thicker than the production glass window it replaces, whose density is double that of PC.

The lightweight concept vehicle was developed with the U.S. Department of Energy's Vehicle Technologies Program, together with Cosma International (Sindelfingen, Germany) - a subsidiary of Magna International (Aurora, ON)- to illustrate long-term potential light-weighting solutions. Sabic contributed PC glazing materials, advanced coatings technology and engineering design expertise to support the rear window's development and production.

The solution used in the concept's rear window combines Lexan resin, a PC material said to be characterized by its light weight, high optical clarity and impact resistance, with Exatec E900 plasma coating for glass-like scratch and UV resistance. The E900 coating is designed to deliver a high level of weatherability and abrasion resistance over the life of the vehicle and enable automakers to meet homologation requirements for driver visibility - including U.S. standards such as the Federal Motor Vehicle Safety Standard (FMVSS) 205 regulations, as governed by the NHTSA AS2 specification, and the American National Standards Institute Z26.1, which covers the visibility, strength and abrasion resistance of glazing materials.

"Sabic is committed to spread the adoption of  PC glazing technology, which offers styling and weight saving benefits to help  increase fuel efficiency and lower emissions," said Scott Fallon, general manager, Automotive, Sabic's Innovative Plastics business. "To date, several OEMs have validated the technology for use on rear quarter windows and roofs on production vehicles. At the same time, real-world demonstration programs like Ford's drivable multi-material lightweight vehicle concept are valuable to further highlight the performance gains that can come from an advanced approach like PC glazing and to ultimately help validate and speed up its wide-scale adoption."

Besides weight reduction, PC also allows automakers to improve energy efficiency via improved thermal insulation of the passenger cabin, a consequence of PC's five-fold lower thermal conductivity relative to glass. Sabic's advanced computer analyses have quantified PC's potential to reduce the load on HVAC (heating, ventilating and air conditioning) systems: emissions can be cut by as much as three grams of carbon dioxide per kilometer, and the range of electric and hybrid vehicles can be extended by two to three percent.

Design flexibility

The rear window of Ford's MMLV is identical in geometry to the part used in the Fusion production vehicle. This design approach allows Ford to test the two parts and compare the performance differences between them based strictly on the change in materials.

The material's ability to be injection-molded means windows can be designed to reduce even more weight, increase aerodynamic performance and enhance styling. Designs can go beyond the shape and complexity limitations of glass to glazing with geometric effects that can make possible relatively thin PC surfaces, potentially adding to the weight-out total. Also, 3D styling possibilities and aerodynamic features enabled by PC glazing can minimize drag and contribute to fuel efficiency.

Integration opportunities, enabled by PC glazing, can also contribute to enhanced efficiency - and cost savings - by reducing the number of parts and materials associated with joining otherwise discrete components.

Another consideration for automotive OEMs and suppliers is the maturity of PC glazing technology and its suitability for mass production according to Sabic IP. In collaboration with Japan's ULVAC (Chigasaki), Sabic has helped develop an advanced vacuum equipment technology for the automotive industry to develop lightweight, plasma-coated PC glazing components cost-effectively and efficiently on a broad scale.