There's a change afoot when it comes to the silicones used in medical devices. "The silicone portfolio is shifting toward liquids," reports Andres Pugi, general manager of GE Advanced Materials-Silicones (http://rbi.ims.ca/3848-504). And that shift should come as no surprise. For high-volume products, injection-molded liquid silicone rubber offers a significant productivity edge over the heat cure silicones traditionally used in medical devices. New liquid silicone formulations can extend that advantage even further—by streamlining the assembly process.
Medical devices typically combine the silicone with thermoplastics or metal components, and bonding these disparate materials usually requires secondary operations. Sometimes, the components are joined mechanically. Or if they are adhesively bonded, the substrate needs primers or surface treatments for the silicone to stick, reports Sharon Shatto, GE's industry manager for healthcare.
GE has recently come up with two, self-bonding formulations that allow silicone components to stick to plastic or metal components during two-shot or overmolding processes--without a secondary assembly step. "The heat of the silicone cure helps generate the bond," Shatto explains.
As for bond strength, the company has tested the grades on a variety of engineering thermoplastics and metals; Shatto says the materials have passed 200 psi lap shear tests. So far, GE has developed two Class VI self-bonding grades. One of them, LIM 8040, offers a hardness of 40 Shore A. The other, 8070, has a 70 Shore A durometer.