Bayer MaterialScience is confident that the automotive market for polycarbonate glazing is set to grow rapidly. Applications include panoramic and lamella roofs and fixed side windows, but these are likely to expand and look set to include rear windshields.
Lighter than glass, polycarbonate offers greater design freedom and exhibits high break and shatter resistance. Bayer’s product in this area is Makrolon, for which the company has invested in manufacturing systems for the development of new glazing technologies and to improve its customer service. At its technical laboratory for scratch-resistant coatings, it also has a program in place to test the effects of windshield wipers on the material. The measures come under the company’s BayVision brand.
Bayer MaterialScience’s manufacturing systems at its pilot plant in Leverkusen, Germany, now include a 2300-t (2535-ton), two-component injection-molding machine produced by Engel, having a swivel platen and an injection compression-molding function. It can produce 3-D roof modules measuring up to 1.2 m2 (13 ft2), together with other complex glazing components. Clean-room conditions are central to Bayer’s production environment and the machine’s process is fully automated.
The new Leverkusen facility can back-inject pre-formed, printed plastic films. Known as FIM (film insert molding), the process can integrate additional functions, including heating antennae and infrared reflection in roof modules and windows.
Volkhard Krause, Head of Bayer MaterialScience’s Automotive Glazing team, said: “The new facility enables us to precisely reproduce our customers’ entire production process and help them with mold proving or production problems.”
At a recent customer seminar, Uwe Renz, Head of the Glass and Wiper Systems Division at Daimler, stated that communication with experts in the polycarbonate area would help utilize the potential of the material for future automotive applications.
Bayer has also invested in extending its coating plant at Uerdingen. The company is focusing on polysiloxane wetcoats, which are “proving their worth,” Bayer claims, in series applications. In a clean-room facility at its pilot plant, it is applying flow coatings to 3-D molded polycarbonate components measuring up to 1.4 m2 (15 ft2).
However, abrasion- and scratch-resistance are essential for polycarbonate components, particularly for future use as rear windshields. Injection compression molding is very effective in manufacturing for series production because at reduced injection pressure it delivers low stress and low distortion results with required surface quality that are highly suitable for wetcoats.
Commenting on the wiper test program, Dr. Frank Buckel, an expert in the modification of polycarbonate automotive glazing, explained: “The test enables us to simulate the actual stress exerted on the wiped glazing in everyday use of a vehicle far more realistically, accurately, and with a high reproducible quality than is possible with the Taber abrasion test.”
The Taber test involves two abrasive rollers filled with corundum grains, pressing with a specifically defined force against a rotating test piece. In the new system at Bayer, a wiper arm fitted with a commercial wiper blade moves back and forth across a fixed test sheet that has the required coating. Force applied is 20 g/cm2 and the wipers’ speed is 14 cm/s.
Said Buckel: “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.”
Testing of unwiped surfaces (panoramic roofs, side windows) have involved the use of test sheets attached to the roof of a vehicle that was subjected to a car wash every week over a three-year period. No protective substances were used. Bayer claims that its tests showed that the AS4000 polysiloxane system supplied by Momentive Performance Materials was “significantly more resistant” than wetcoats with a plasma topcoat, with the Makrolon glazing displaying no visible clouding.
The tests also verified the good abrasion resistance of the coating on series-produced polycarbonate glazing after more than six years of active use and up to 125,000 km (77,700 mi).