If slow and steady wins the race, then we can start waving the checkered flag now under the presumption that polycarbonate (PC) window glazing, after many years of development still a "next great thing," is starting to limber up and hit its commercial stride. Two principal PC suppliers and window glazing proponents, Bayer and Sabic Innovative Plastics, continue to make steady advances and in the past days have made a number of announcements that point towards continued interest in these technologies, albeit still somewhat limited by the automotive industry’s hardships.
Bayer has invested in a new Engel press to further its PC window glazing developments.
Both suppliers, Sabic Innovative Plastics and Bayer, worked together developing glazing technology but then parted ways in August 2007 when Sabic bought Bayer’s 50% share in the two firms’ Exatec joint venture, which they had formed in 1998 to develop and promote the technology. 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 consumers’ easy access to music and movies via the Internet.
Any change as great as a switch from glass to plastics windows in automotive will take years, and so the progress has been slow, albeit steady, and recent regulations that force carmakers to drop CO2 emissions across their fleets could provide a strong push to greater PC window glazing use.
Last month Sabic Innovative Plastics announced it has been able to supply polycarbonate shielding that surrounds the driver compartments in Toronto Transit Commission (TTC) city buses. MPW understands from an interview earlier this year that the supplier is in fact molding these panels on its own molding machinery at its Exatec test lab in Wixom, MI. The driver protection enclosure consists of a 31- by 38-inch rectangular Lexan sheet window with a lower metal door.
Part of the reason holding back broader acceptance of PC window glazing is of course the need for extensive documentation on new products with regard to safety regulations involved in all things automotive. 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 have remained as to how these windows will retain the necessary transparency over the years of a car’s useful life. Now Bayer reports it has developed tests for coated polycarbonate automotive glazing to measure their resistance to windshield wipers. “This test enables us to simulate the actual stress exerted on the wiped glazing in the everyday life of a vehicle far more realistically, accurately, and with a higher reproducible quality than is possible with the Taber abrasion test stipulated in the regulations," explains Frank Buckel, who works at Bayer on the surface modification of PC automotive glazing. In the Taber test to ASTM D 1044 (DIN 52347), two abrasive rollers filled with corundum grains press with defined force against a rotating test piece. In the new test system, a wiper arm fitted with commercial wiper blades moves backwards and forwards across a fixed test sheet to which the requisite coating has been applied, with the wipers exhibiting a force of 20 g/cm2 and moving at 14 cm/second. “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,” says Buckel. Momentive Performance Materials supplies its AS 4000 polysiloxane system for the coating used by Bayer in its window glazing. According to Buckel, tests verified suitable abrasion resistance of pure polysiloxane coatings on used, series-produced polycarbonate glazing after more than six years of active use and mileages of up to 125,000 kilometers (77,500 miles).
In related news, Bayer reports it has installed a robot-equipped two-component swivel-plate Engel injection molding machine, with 2300 tonnes of clamp force, at its technical service center in Leverkusen, Germany, to help it develop new glazing applications. The molding machine is large enough to allow for processing of film insert molded components measuring up to 1.2 square meters.
Films can see use in rear windows made of polycarbonate and in the design of polycarbonate panorama roofs, where they help with the addition of decorative effects (lettering, logos or fade-outs, for example) and the integration of additional functions such as defrosters or antennas). Engel ran a similar model machine at the NPE tradeshow in Chicago in 2006. The machine in Leverkusen was unveiled during a customer symposium at which some 100 guests, included ones from virtually all the major automobile manufacturers and suppliers, attended. —[email protected]