Glazed and diffused

Automotive Design & Production, Feb, 2004 by Kermit Whitfield

What's the problem? In a word, glass. It's heavy, easily breakable and cannot be formed into the swoopy transparent panels that clothe some of the most head-turning concept cars. But it has a big advantage over the polycarbonate materials used on those one-off vehicles: abrasion resistance. Designers would love to use plastics to make their wilder dreams production realities, and the plastics industry would love to help them do it and capture the huge market in automotive glass in the process ... but then there's that scratching problem.

What's the Solution? Combining both polycarbonate and glass to get the best qualities of both. At least that's the thinking at Exatec (Wixom, MI), a joint venture between GE Plastics and Bayer Polymers. Exatec has developed a manufacturing process eponymously called Exatec 500 that uses plasma-enhanced chemical vapor deposition to apply a microns-thick layer of silicon oxide to polycarbonate panels, giving them abrasion resistance similar to glass. According to Exatec's Peter Reisinger the idea has been around for a while, but its never been done on a mass-production scale. "What we have here is a full-blown industrial process with extremely short cycle times that we can demonstrate on large pieces," he explains. (To better quantify that comment: cycle times run about two minutes for the deposition process, and the equipment can handle panels as large as 1[m.sup.2].)

[ILLUSTRATION OMITTED]

Why is it better? Glazed polycarbonate has three big advantages over glass that should make design engineers take notice. First, it is half the weight of glass, so visibility can be expanded with larger transparent panels while at the same time components like window motors can be downsized to save space and money. Second, the shape complexity that can be achieved with polycarbonate far outstrips that of glass, offering designers the potential of creating a new design language for the greenhouse. Third, unlike glass, which requires attached components be glued or bolted on, many parts like clips, strut attachments and handles can be molded in, reducing part count, assembly complexity and ultimately overall cost. Beyond that, polycarbonate panels can be frosted and textured with inexpensive in-mold appliques, or lit from within with multicolored fiber optics that diffuse light into glowing panels, or used to expose structural elements and create a "skeleton on wheels." That is, treatments that have been used to great effect by consumer product design leaders like Apple can be translated to the automobile.

What's the latest? Exatec's cause received a recent fillip of momentum from a new tool design for injection compression molding created by Summerer Technologies (Rimsting, Germany). The design allows smaller molding machines to make larger panels with low molded-in stress and at lower clamp forces. Reisinger says, "This technology changes the game. If you can use a 2,000-ton machine to make a 1[m.sup.2] window you have a very good business case." Exatec has also come up with a new ink for printing defrosters, antennae and decorations that is suited for use on complex surfaces and is bonded into the panels during production rather than being applied afterward. Reisinger thinks that these recent developments combined with the increasing maturity of the process will put Exatec 500's polycarbonate panels on production vehicles within "a few years at the maximum," and adds that several companies are now negotiating to license the technology.

By Kermit Whitfield, Senior Associate Editor