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Silicone Enhancements
Technology advances improve these versatile plastics
By Design News Staff -- Design News, August 14, 2005
Silicones have their share of desirable qualities, especially in medical applications. Silicone elastomers pair biocompatibility with good chemical resistance, clarity, compression set, and tensile properties. Coatings and adhesives based on silicones have likewise found a home in medical devices and medical electronics. But these materials have their share of hassles too. For example, liquid silicone rubbers have a high coefficient of friction that has made them difficult to use in some applications. And some two component formulations have a limited shelf life. Technology advances, however, now make silicones easier to use. Here's a look at three such products from one of the major silicones suppliers, GE Advanced Materials.
Tufel I
Many high consistency silicone rubbers, or HCRs, have had what amounts to a chemistry problem. These rubbers are two-component formulations and have a limited shelf life. And they sometimes use peroxide catalysts that have raised some safety questions lately. Tufel I addresses both issues. This patented one-component formulation uses a platinum-based catalyst. And it lasts for three months on the shelf, rather than the two weeks associated with a traditional two-component formulation, according to Eric Luftig, GE's manager for silicones in healthcare applications. Despite the new chemistry, this elastomer hasn't sacrificed silicone's mechanical property advantages. An extrusion material, Tufel I is suited to a variety of other tubing applications. For more information, visit www.gesilicones.com.
WE ARE HERE!!!SilCool LTR3292
Getting more functionality out of an adhesive is the point of SilCool LTR3292. With a low thermal resistance of 28 mm2 K/W and a thermal conductivity of 1.56 W/mK, this one-component, low-viscosity adhesive offers higher thermal conductivity than traditional silicone adhesives, according to Gail Riley, GE's manager for microelectronics. Proprietary fillers are the key to the thermal performance, and they also help LTR3292 work with very thin bond lines typically 1 to 2 mil. This adhesive remains in a liquid state at room temperature and heat-cures into an elastomer with a hardness of 85 Shore A and a tensile strength of 375 psi. Applications for this new adhesive include electronic components and devices with high heat transfer. It bonds to a wide variety of substrates, including ceramics, glass, and most metals, including aluminum, copper, and nickel plate. In addition, it also offers excellent adhesion to a broad range of high performance thermoplastics, such as PPS and PBT. For more information, go to GE Silicones.
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LSR Top Coat
Silicones are sticky. And their inherently high coefficient of friction (COF) has made them less desirable in applications where the elastomer comes in contact with human skin or moving components. The traditional solution to this friction problem has been chemical coatings, but these can wear off over time or crack under stress. TopCoat takes a different approach to making silicone rubber parts less sticky. This coating is actually a two-component silicone itself. So it offers a chemical bond with its silicone substrates. As for the surface friction reduction, it offers a 32-43 percent reduction in silicone-on-silicone COF. And Bernie Powell, GE's silicones product manager, reports that the range of COF reduction corresponds to the application method; TopCoat can be applied through spraying, brushing, or dipping, with each method resulting in a different reduction in surface friction. Applications for the new coating have so far included orthopedic inserts for shoes—the reduced friction makes it easier for feet to slide in and out. The material also targets medical applications, particularly where the device has to come in contact with the patient's skin or where silicone tubing parts come in contact with one another. These include a variety of respiratory products and well as components for fluid and drug delivery. For more information go to www.gesilicones.com.
