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Test developed for checking resistance to windshield wipers

Published on 2009-07-02. Author : SpecialChem

Polycarbonate is already used in the automotive industry as a series-production glazing material for panorama and lamella roofs and fixed side windows. As polycarbonate is lighter than glass, offers greater design freedom, and exhibits high break and shatter resistance, it is also ideal for rear windows. In this application, too, the surfaces require high scratch and abrasion resistance and must be able to withstand car wash and windshield wiper usage. This prevents visibility from being impaired due to wear on the surfaces. That's why the company's technical service center added a windshield wiper test to cater specifically to this area of application. "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," explains Dr. Frank Buckel, expert in the surface modification of polycarbonate automotive glazing at Bayer MaterialScience. "With the results of the work we have carried out to check resistance to windshield wipers, we are able to expand the service package we offer system suppliers and the automotive industry as part of BayVision®."

In the Taber test to ASTM D 1044 (DIN 52347), two abrasive rollers filled with corundum grains press with defined force against a rotating test piece. "This hardly reflects the stress exerted during normal vehicle operation," comments Buckel. 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/cm2is 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 the individual test conditions in this laboratory wiper test and conditions during practical usage, a wiper test bench for large polycarbonate rear windows has also been set up.

Car wash test confirms high abrasion resistance of polysiloxane coatings

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.

BayVision® - customized service for glazing coatings

After withdrawing from the Exatec joint venture some two years ago, Bayer MaterialScience has been consistently building up its technological expertise in coatings for polycarbonate automotive glazing and systematically investing in the expansion of the technical service center for coatings at its Uerdingen site. Special attention has been paid to flow coating. Of all of the available coating technologies, flow coating exhibits the optimal optical surface quality. For example, the technical service center is equipped with a system that can be used to flow coat 3D components measuring up to 1.4 m2 in a cleanroom with laminar flow (cleanroom class 100, air exchange up to 700 times per hour). Additional equipment includes various convection ovens and a UV through-type system for hardening various coatings, and equipment for the surface analysis of polycarbonate panes. "In addition to our own development work, the service center is dedicated primarily to our comprehensive range of application-related customer services, which takes in all aspects of coating for large 3D panes made of polycarbonate," says Buckel. These services are part of BayVision®, the competence brand that brings together the complete expertise of Bayer MaterialScience in automotive glazing with Makrolon®. For example, the experts from the technical service center provide support in determining which component geometries, design elements and types of function integration are suitable for coating in line with the relevant specifications. In addition they also assist in designing coating systems and identifying appropriate process parameters for flow coating large 3D parts. The team can also provide detailed support on questions relating to bonding these components.

About Bayer MaterialScience:

With 2008 sales of EUR 9.7 billion, Bayer MaterialScience is among the world's largest polymer companies. 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 and the sports and leisure industries. At the end of 2008, Bayer MaterialScience had 30 production sites and employed approximately 15,100 people around the globe. Bayer MaterialScience is a Bayer Group company.

Source: Bayer MaterialScience

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