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Results Show Pure Wetcoats are More Resistant than Wetcoats with a Plasma Topcoat

Published on 2009-04-09. Author : SpecialChem

PITTSBURGH -- The abrasion resistance of plastic or glass automotive glazing is determined by means of the Taber test on test pieces. Two abrasive rollers press with a defined force against the test piece, which rotates at a defined speed as a function of the type of glazing. The extent of the resulting haze determines whether the test is passed. Though standard, the test does not represent the actual abrasion resistance that automobile glazing faces in everyday conditions. For that reason, Bayer MaterialScience has tested common coating systems under realistic conditions in a commercial car wash - and the results are clear.

"Pure polysiloxane wetcoats are significantly more abrasion resistant than wetcoats with a plasma topcoat. There is no visible hazing, even after 100 wash cycles. We were also able to verify the successful abrasion resistance of the pure wetcoat coatings on used, series-produced polycarbonate glazing," said Peter Capellen, a coatings expert in the Automotive Glazing team at Bayer MaterialScience.

For the car wash test, polycarbonate test sheets with various coatings were attached to the roof of a car. Once a week over a period of more than three years, the vehicle went through the car wash of a gas station and was otherwise in normal use at the ChemPark in Leverkusen, Germany. The unit's brushes had x-shaped, spliced polyethylene bristles. The vehicle was washed with water without the addition of wax. After 10 wash cycles, the test sheets on the roof were moved in order to obtain position-independent results.

"After more than 150 wash cycles and more than three years of weekly trips to the car wash, test sheets coated with the pure wetcoat AS 4000 from Momentive Performance Materials GmbH exhibited less than 1 percent haze, which is not visible to the naked eye," said Capellen.

In contrast, the haze exhibited by wetcoat plasma coatings intended especially for automotive glazing exceeded this critical value after only about 50 wash cycles. This is due in part to the fact that, at just under 1 percent, the initial haze value of plasma systems is higher. Furthermore, spot delamination of the plasma coating occurs relatively quickly, resulting in greater light scatter and thus visible haze.

To test the validity of these results, Bayer MaterialScience studied a number of "used" polycarbonate glazing elements coated with pure wetcoats from series-produced vehicles. Among these was the fixed side window made of Bayer MaterialScience's Makrolon® polycarbonate resin from a compact car. Only glazing elements more than two years old were examined.

"Even after six years on the road, all of the parts exhibited less than 1 percent haze in the transparent areas," observed Capellen. The surface gloss of the black region of the glazings was also barely diminished.

"The expertise gleaned from these and other tests in the coating of polycarbonate glazing elements is part of BayVision®. This brand represents a comprehensive package of service, materials and know-how that we use to support systems suppliers and OEMs in projects involving automotive glazing made from Makrolon polycarbonate resin," noted Volkhard Krause, head of the Automotive Glazing team. "This includes aspects of polycarbonate glazing ranging from the selection of customized materials, through the provision of plastic- and coating-compatible designs for glazing elements, to suitable processing technologies such as injection-compression molding," he added.

About Bayer MaterialScience:

Bayer MaterialScience LLC is one of the leading producers of polymers and high-performance plastics in North America and is part of the global Bayer MaterialScience business with nearly 15,100 employees at 30 sites around the world and 2008 sales of 9.7 billion euros. Business activities are focused on the manufacture of high-tech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction, medical, and sports and leisure industries.

About Bayer Corporation:

Bayer Corporation, headquartered in Pittsburgh, is a subsidiary of Bayer AG, an international health care, nutrition and high-tech materials group based in Leverkusen, Germany. In North America, Bayer had 2008 net sales of approximately 8 billion euros (about $12 billion) and employed 17,000 at year end. Bayer's three subgroups, Bayer HealthCare, Bayer CropScience and Bayer MaterialScience, improve people's lives through a broad range of essential products that help diagnose, prevent and treat diseases; protect crops and enhance yields; and advance automobile safety and durability.

Source: Bayer MaterialScience


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