Heatable glass guarantees ice-free windscreen

No more icy windscreens: A research team of the Fraunhofer Institute has developed a process for the production of transparent, conducting layers on glass. Thus, car windscreens can be heated directly; embedded heating wires will be a thing of the past.

Conducting transparent layers have been around for a while. However, these layers hitherto were based on tin oxide – a material that is less than perfect for automotive applications. For instance, it is not very stable at high temperatures. In production processes where windscreens and rear windows are heated and bent into the required form, tin oxide coatings tend to crack.

The material used by the Fraunhofer Institute for Surface Engineering and Thin Films (Braunschweig, Germany) is much more stable, assures researcher Bernd Szyszka. “Temperatures up to 900 degrees Celsius are no problem; the coating remains stable even if the glass is bent.”

The Braunschweig researchers also use tin oxide, however they modified the production method: Their material is nanocrystalline tin oxide (ITO). According to the institute, this material has excellent optical and mechanical properties, including higher chemical stability compared to “normal” tin oxide. The difference lies in the production method: In order to apply the ITO coating, the researchers utilized High Power Impulse Magnetron Sputtering technology (HPIMS) with currents of up to 1000 amperes. “We ionize the sputtered material; therefore the film is build up by higher energetic particles and shows superior properties,” explains Szyszka. With this method, it is even possible to adjust texture and morphology of the ITO layer. Since the process can be executed at normal ambient temperature, the layer can even be applied to temperature-sensitive materials such as plastics.

The ITO layer is not only conductive and transparent. The low emitting properties of the outer layer ensures that the car window cools down much more slowly, preventing condensation. Thus, the windscreen or rear window remains dry and ice-free. “This makes ice scrapers redundant,” said Szyszka.

A prototype of the ITO-coated glass will be displayed at the Glasstec trade fair in Duesseldorf from September 28 through October 1.