Practical wear resistance tests developed for coated polycarbonate automotive glazing

Bayer MaterialScience's technical service center has developed a practical wear resistance tests for coated polycarbonate automotive glazing. The newly developed windshield wiper test checks the scratch and abrasion resistance of the polycarbonate glazing to see whether it can withstand a car wash and windshield wiper usage. Dr. Frank Buckel, expert in the surface modification of polycarbonate automotive glazing at Bayer MaterialScience, says, "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." 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. A force of 20 g/cm2 is applied and the wipers move at a speed of 14 cm/s. As drivers tend to have very different "wiper habits", the test can be adjusted accordingly. For example, the tests can be performed dry and/or wet with or without standard dirt (ISO 6255). "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. In order to check the precise correlation between laboratory wiper test and conditions during practical usage, a wiper test bench for large polycarbonate rear windows has also been set up. Bayer MaterialScience has been able to show that the Taber test does not provide reliable data on the actual abrasion resistance of unwiped polycarbonate glazing on the road. Unwiped glazing includes fixed side windows and panorama roofs. For this purpose, test sheets with commercial coatings were attached to the roof of a car. Once a week over a period of more than three years, the vehicle was put through a car wash - no "protective" substances such as car waxes were used. The tests showed that the AS 4000 polysiloxane system from Momentive Performance Materials GmbH is significantly more resistant than wetcoats with a plasma topcoat. Even after over 150 wash cycles, the Makrolon® glazing coated with AS 4000 displayed no visible clouding. The team was also able to verify the good 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.