Windscreen bonding and sealing on vehicles has evolved at an accelerated pace. Although traditional rubber mounted gaskets and butyl products can still be found on some older vehicles, liquid adhesives, also known as direct glazing compounds (DGC) are now the method of choice for both the original equipment manufacturer (OEM) and remains as the automotive glass replacement (AGR) professional’s most important product.
DGC adhesives are usually single-component moisture-cure polyurethanes (PUR) which offer superior performance in torsional stiffness, cohesive strength, initial holding strength and sealing ability. These materials offer improved vehicle aesthetics and safety; have lowered manufacturing costs and facilitate a much more simplified assembly process for car builders. DGC products eliminate – or reduce – mechanical fastening methods; they reduce inventory requirements and costs; improve operator safety and enhance vehicle performance. But as car designs and manufacturing processes have changed over the years, product development and design engineers have demanded faster, safer, more consistent (and convenient) adhesive solutions.
Despite their many advantages for bonding windscreens, traditional polyurethane based DGC compounds have significant limitations which restrict their use in vehicle assembly processes. To ensure good adhesion to glass, plastic and paint, DGC adhesives rely upon solvent-based glass (and paint) primers which add steps to the assembly process; they also contain hazardous isocyanates, and thus, introduce health and safety issues for the handlers of those products. Since the adhesive itself requires ambient humidity to cure, curing times can vary greatly depending on temperature and humidity levels in the manufacturing environment, causing potential bottle necks in the overall vehicle assembly process.
Recent advances in primerless windscreen adhesive systems have minimised these limitations and helped vehicle manufactures increase line speeds, eliminate hazardous solvent-based primers from the workplace; climate control chambers are no longer essential enabling a more consistent and controlled assembly process. Whilst the basic elements of bonding glass units to motor vehicles remain the same, there are some differences between the vehicle manufacturer processes, and those used by the aftermarket glass replacement industry. For the OEM the emphasis is on reducing downtime, and increasing efficiency. The glass replacement industry is consumer driven and focuses on mostly on safe drive away times (SDAT).
Windscreen Bonding Evolution
Bonding a windscreen to a vehicle using direct glazing technology is much more complicated than attaching a windscreen on a car’s aperture using a gasket or adhesive tape. There is a critical scientific process involved in properly applying direct glazing adhesives. This, in turn, is a crucial component in the car’s structural integrity.
Typically, windscreens are made of either float, laminated or tempered glass (or a synthetic material like polycarbonate). In the bond line area, the windscreen will coated with an opaque black material (known as a frit) which is applied during manufacture. This frit – or silkprint – is usually a specific ceramic paint and provides a suitable substrate which improves adhesion, protects the adhesive from being damaged by UV radiation, and generally provides an aesthetically-pleasing finish.