PMMA for Passenger Car Glazing
From here, Evonik developed a new, impact-modified PMMA molding compound for glazing that remains crystal-clear even when large temperature fluctuations occur. The drawback of impact-modified PMMA molding compounds until now has been that they appeared slightly hazy at extremely low or high temperatures. The reason: the modifier particles which increase the impact strength of the otherwise brittle-hard PMMA. To date, this temperature-dependent, reversible haziness was observed in all known impact-modified PMMA molding compounds.
In addition, the new PMMA grade exhibits very little stress birefringence thanks to its molecular structure. This is a major benefit over other thermoplastics such as polycarbonate that were employed for glazing in the past. In injected molded PC glazing, optical distortion occurs as the result of stress-induced birefringence, a natural property of the material.
Another important requirement for glazing is scratch resistance. Standard PMMA already has the highest surface hardness of all thermoplastics even when uncoated. Nevertheless, a coating must be applied in order to meet the stringent requirements for scratch resistance. Since PMMA is inherently UV- and weathering-resistant, a single-step coating suffices. Thermoplastics that do not resistance weathering require a two-step coating system. This results in relatively high costs for coating.
The material is also interesting from the standpoint of function integration. In the future, it might be possible to incorporate lighting into rear or rooftop windows, for instance.
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