The current trend toward more aerodynamic body designs in the automotive industry has given rise to composite headlamp systems, which represents a major change in the marketplace worldwide. These composite headlamps have greatly enhanced design flexibility, but they have also brought about a need for sealing materials that can withstand the elevated temperatures associated with the new, smaller designs being engineered in the U.S. Further, these materials must provide good long-term adhesion to a variety of substrates.
Organic products currently in use for headlamp sealing applications have limitations, particularly in their ability to resist high and low temperatures and provide good adhesion over the lifespan of the vehicle. The majority of the headlamp systems in use today incorporate glass lenses and plastic reflectors; therefore, an engineering sealant used to adhere the components must be capable of adhering well to both materials. In addition, the adhesive/sealant must exhibit sufficient elastomeric properties to allow for the widely different thermal expansion rates of these substrates.
The development of a family of silicone sealants for the European market first satisfied the demands of this application, and since the passing of federal regulations permitting the introduction of composite headlamps in the U.S., these materials are offering several advantages to domestic car makers as well. The higher temperatures associated with emerging smaller headlamp designs require an adhesive/sealant which can resist both high and low temperature extremes. Silicone sealants retain their flexibility from -55°C to 200°C. The sealants offer excellent unprimed adhesion to a wide range of substrate materials, including glass, aluminum, steel, polycarbonate, acrylic, polyester, ABS and polyamide. In addition, silicones in general exhibit excellent UV resistance, high tensile and tear strength, and good elongation properties.
The creativity of domestic auto engineers has prompted further development of new product offerings. As the technology driving these products continues to advance, it has become apparent that silicones offer the processing and performance advantages required by today's auto manufacturers. Recent silicone research has produced some important variations in adhesives/sealants, including low-volatile versions of the material.