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New Clarity For Plastic Glazing
NHTSA clarifies position on polycarbonate for automotive windows
Joseph Ogando -- Design News, December 5, 2005
The best thing about polycarbonate automotive glazing is that it's not glass. But that's also the worst thing about it, at least from a regulatory standpoint. Federal safety regulations and tests related to glazing understandably revolve around glass and its unique failure modes, which have left plastic glazing in a bit of a legal fog.
" 'Can we use it?' is always one of the first questions that comes up," says Alex Scholten, a product developer for Exatec, the joint venture formed by Bayer Material-Science and GE Advanced Materials to develop polycarbonate glazing.
Now, it looks like the answer is yes. The National Highway Traffic Safety Administration (NHTSA) issued a letter clarifying its position on Exatec's polycarbonate glazing, which weighs in at roughly 40 percent less than glass. The administration found that Exatec 900 glazing can be used anywhere on the vehicle other than windshield as long as it passes the tests proscribed in the Federal Motor Vehicle Safety Standard (FMVSS) No. 205.
That standard only names four specific types of safety glazing—laminated glass, tempered glass, and two classes of multiple glazed units. But the standard also includes a provision for new materials whose properties allow them to meet prescribed groups of glazing tests. Citing that provision, NHTSA's letter makes it possible for Exatec to certify its glazing system as AS2, the designation used for safety glass suitable for the side and rear locations on the car. "It's really big news for us," says Scholten.
NHTSA did, however, announce its intention to propose some additional tests for polycarbonate glazing because it possesses different failure modes than glass. The NHSTA letter mentions three in particular—weathering, chemical resistance, and flammability. The letter expresses some concern, for example, about weathering-induced haze that would diminish visibility over time.
But Scholten believes that any new tests won't pose a problem. The Exatec 900 system coats the polycarbonate with a proprietary plasma-deposited hardcoat that helps the plastic ward off UV damage as well as scratches. And he points to a recent Batelle Laboratories study that predicts a lifespan of at least 10 years for the Exatec 900 glazing.
In other news, Exatec has developed a new product aimed specifically at the tops of vehicles. Called Exatec 900 VT, the system lacks some of the scratch- and abrasion-resistance of Exatec 900. "It doesn't need as much because visibility isn't as much of an issue," says Scholten.
The loss of some scratch resistance, though, goes hand in hand with a gain in design freedom. As Scholten explains, the new system lacks an interior flow coat, which makes it easier to integrate interior assemblies and features that would otherwise have interfered with the application of a coating. "You lose some scratch resistance but gain absolute design freedom," says Scholten.
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