Whitepapers

This paper will demonstrate the ability of silicone adhesives, with the aid of primers, to adhere to low surface energy plastics and to high strength metals. In general, some plastics are difficult to adhere to because of their low surface energy, available bond sites, and chemical interaction. Most plastic have...

This paper will demonstrate the ability of silicone adhesives, with the aid of primers, to adhere to low surface energy plastics and to high strength metals. In general, some plastics are difficult to adhere to because of their low surface energy, available bond sites, and chemical interaction. Most plastic have a surface energy under 50 dynes/cm while aluminum, an easier substrate to adhere to, is closer to 825 dynes/cm. Surface energy is a thermodynamic effect of how a liquid will ‘wet out’ on a surface. Low surface energy materials, like plastics, do not allow a liquid, like an adhesive, to ‘wet out’ on its surface. Adhesion chemistry tells us that the better an adhesive can ‘wet out’ on a substrate, the more surface area it can cover and allow more reactive groups to bond, making a stronger bond. Several low surface energy plastics and high strength metals were tested with silicone adhesives and primers to achieve cohesive bond failure when performing lap-shear testing. This list of substrates evaluated include polycarbonate, polyetherimide, polyamide, polyurethane, polymethylmethacrylate, polysulphone, titanium, stainless steel, and aluminum.

This paper will demonstrate the availability of dramatically ccelerating the cure of certain silicone adhesives and their advantage to the manufacturing process. A ‘fast cure’ adhesive is defined as full cure in less than ten minutes—or partial cure for handling under five minutes and full cure at room temperature in...

This paper will demonstrate the availability of dramatically ccelerating the cure of certain silicone adhesives and their advantage to the manufacturing process. A ‘fast cure’ adhesive is defined as full cure in less than ten minutes—or partial cure for handling under five minutes and full cure at room temperature in 8 hours or one shift. Using a specific cure system and materials that have been developed to obtain fast-cure with heat acceleration, an experiment was performed to determine how fast, and at what temperatures these adhesives will cure. In conclusion, to obtain fast-cure at low temperature, 65ºC, R31-2186 can be fully cured in one minute. When adhering to temperature sensitive substrates, this provides a fast-cure choice. Although needing a higher temperature to obtain ‘fast-cure’, R32-2186 fully cures in 2 minutes at 100ºC. This can be useful because of R32-2186’s extended worktime. LSR-9820-20 proves the best choice for high temperature cure, 185ºC. In just 30 seconds it has a 300psi lap shear. Although this figure reaches optimum over time, for many applications this is a great partial cure.