Teijin develops new hard-coating technology for automotive plastic glazing

Japan’s Teijin says it has developed a new hard-coating technology that can be applied evenly on large or complex-shaped automotive windows molded of polycarbonate to achieve the same level of abrasion resistance as glass windows and double the weather resistance of conventional plastics glazing.

Teijin initially will produce small-lot samples of actual windows for selected car models using the technology at a pilot plant in Matsuyama, Japan. Going forward, it will gradually verify production technologies for the manufacture of a wider range of windows on a mass-production basis, aiming at an early launch of full-scale commercial manufacturing operations.

To further reduce automobile mass, automakers are targeting deployment of lightweight but highly abrasion-resistant back and side windows made of plastic. However, when used in glazing that contacts windscreen wipers, conventional polycarbonate (PC) plastic glazing, which are less abrasion-resistant than glass, can be scratched by operating the windshield wipers, or even by merely raising or lowering them.

According to Japanese automobile safety standards, plastic glazing in car models released from July 2017 must offer enhanced abrasion resistance. The conventional wet method used for hard coating, however, does not meet the required level of resistance. Furthermore, plastic glazing in new cars also will be required to be sufficiently weather resistant to prevent yellowing after long-term exposure to sunlight.

Although a technology known as plasma-enhanced chemical vapor deposition (plasma CVD) already exists to enhance the abrasion and weather resistance of wet coated PC to the level of glass, the size of the window is restricted to around 0.3 square meter, and it is also hard to apply plasma CVD to complex curved surfaces. Consequently, this technology does not offer a practical solution for plastics glazing under the new auto standards.

In response, Teijin collaborated with fellow Japanese company Tsukishima Kikai to develop a plasma CVD pilot plant that is capable of treating large and moreover three-dimensional molded resin products with a uniform coating of plasma CVD. Actual-size plastics glazing exceeding one square meter, including those with complex curves for back windows, are being treated at the pilot plant. The plasma CVD method achieves abrasion resistance on the level as glass, satisfying not only the new Japanese standards but also those of the USA and EU.

The new hard-coating technology firmly applies a plasma CVD layer to the wet hard-coat layer, thereby preventing oxygen or water vapor from penetrating and subsequently degrading the underlying wet hard-coat layer. Further, since the wet hard-coat layer absorbs the ultraviolet rays which cause resin degradation, the time until discoloration or degradation using the new technology is double that of solely wet hard-coated glazing.