If you’ve ever driven, you’ve likely noticed the small black band and dots along the edge of the car windshield. These black dots, which might easily be overlooked, serve several important functions.
The black band surrounding the window is called the frit or frit band. This frit band is a crucial part of the process that bonds the glass to the car’s body. The frit is created by applying liquid ceramic paint to the surface’s edge and then heat-treating it to enhance its durability. As the ceramic paint is baked into the glass, it cannot be scratched off.
Car windshields typically use laminated glass, which consists of two layers of glass with a PVB (polyvinyl butyral) film between them, bonded under heat and pressure. This is where the first purpose of the frit becomes evident. The frit acts as a primer that allows the adhesive to securely bond the windshield to the car.
The frit band strengthened through heat treatment, provides a surface that the adhesive can cling to. This ceramic paint baked into the glass is designed to stay in place without being removed.
The second role of the frit is to protect the adhesive from direct sunlight. Exposure to UV rays can degrade the adhesive, reducing its stickiness. The frit’s black color also hides the unsightly adhesive, serving an aesthetic purpose.
Simply put, the frit band provides a rough surface for adhesive bonding, protects the adhesive from UV rays, and hides the adhesive from view, enhancing the car’s visual appeal. The frit became commonplace in the 1950s and 60s when automakers began replacing metal trim with adhesive bonding.
But why are there small dots around the frit? These dots vary in size and create a gradient from the outer edge inward, which helps blur the boundary between the transparent glass and the frit, providing a smooth transition.
The dots are not just for design purposes. They also play a role in the windshield manufacturing process. The frit heats up faster than the rest of the glass due to its black color, creating a potential for optical distortion. The dots help balance this by evening out the temperature across the glass. The frit and dots help shade the interior of the car from sunlight.
Some car manufacturers even incorporate designs into the frit. For instance, the Ford F-150 Harley-Davidson edition uses the frit to feature the Harley-Davidson logo instead of simple dots.
The black dots and frit bands on car windshields are there for practical and aesthetic reasons, ensuring the windshield is securely bonded, protected from UV rays, and visually appealing.
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