Cars primarily use glass for windshields rather than plastic due to several key reasons:
Optical clarity: Glass provides excellent optical clarity, which ensures a clear and distortion-free view of the road ahead. Plastic materials, such as acrylic or polycarbonate, can be prone to scratches and yellowing over time, impairing visibility. While there are specialized coatings available to mitigate these issues, glass still offers superior long-term clarity.
Durability: Automotive windshields need to withstand various stresses, including impacts from rocks, debris, and temperature changes. Glass is a highly durable material that resists scratching and maintains its structural integrity under normal driving conditions. It is also more resistant to UV radiation, preventing degradation and yellowing over time.
Safety considerations: In the event of a collision or impact, glass windshields provide better protection. They are designed to shatter into small, blunt pieces that are less likely to cause severe injuries. Plastic materials, on the other hand, can crack or break into sharp shards, posing a greater risk of harm to occupants.
Resistance to environmental factors: Glass windshields offer better resistance to chemical exposure and harsh weather conditions. They are less prone to damage from exposure to sunlight, rain, snow, and cleaning agents compared to some plastics that may degrade or discolor under certain conditions.
However, it's worth noting that some modern cars do incorporate plastic elements in windshields. For instance, the inner layer of laminated glass windshields often contains a plastic interlayer for safety purposes. This layer helps hold the shattered glass pieces together upon impact, reducing the risk of injury to occupants.
In summary, while plastic materials have their advantages in certain applications, glass windshields remain the preferred choice for automotive use due to their optical clarity, durability, safety features, and resistance to environmental factors.