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Dow silicone adhesives are specially formulated to provide unprimed adhesion to many reactive metals, ceramics and glass, as well as to selected laminates, resins and plastics. However, good adhesion cannot be expected on non-reactive metal substrates or non-reactive plastic surfaces such as Teflon®, polyethylene or polypropylene. Special surface treatments such as chemical etching or plasma treatment can sometimes provide a reactive surface and promote adhesion to these types of substrates.
Dow brand primers can be used to increase the chemical activity on difficult substrates. For best results, the primer should be applied in a very thin, uniform coating and then wiped off after application. After application, primers should be thoroughly air dried prior to application of the silicone elastomer. Additional instructions for primer usage can be found in the Dow literature, "Dow brand Primers, Prime Coats and Adhesion Promoters” (Form 10-909) and in the information sheets specific to the individual primers. Alternatively, use a low-viscosity primerless adhesive to pot your components.
Poor adhesion can be experienced on plastic or rubber substrates that are highly plasticized since the mobile plasticizers act as release agents. Small-scale laboratory evaluation of all substrates is recommended before production trials are made.
In general, increasing the cure temperature and/or cure time will improve the ultimate adhesion.
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