Liquid silicone rubber has provided a profitable growth path for GW Silicones, a unit of injection molder GW Plastics Inc. of Bethel, Vt.
At the recent Plastics in Medical Devices conference in Westlake, GW Silicones General Manager Mark Hammond, along with officials of Engel Machinery Inc. and Roembke Manufacturing & Design Inc., offered tips for plastics firms that might be considering LSR work.
GW Silicones, based in Royalton, Vt., has put its money behind its intentions, recently adding at least a dozen molding machines dedicated to LSR work, and spending $3 million on a clean room for LSR applications.
LSR applications for GW include health-care uses such as surgical instruments and drug-delivery devices. Hammond said working with LSR “is all about preparation and reducing risk.” He urged prospective LSR users to concentrate on automatic and flashless molding and to have a dedicated facility with dedicated resources for LSR work.
LSR's advantages include being odorless, tasteless, stainless, bacteria-resistant and easy to clean and sterilize, Hammond said during the June 13 session on LSR molding.
The material also is biocompatible and good with implantable devices, as well as being easily colored, temperature-flexible and chemical-resistant.
But LSR is more expensive to buy and work with than are thermoplastic elastomers, which Hammond said many molders use “because they don't know other options.”
“Silicone processing has come a long way in the past 10 years,” Hammond said.
“Processors can use off-the-shelf grades, with no in-house formulation needed.”
And although LSR has some limits in overmolding applications — where the thermoplastic substrate needs to be heat resistant — that hasn't stopped U.S. silicone demand from growing. It is currently estimated at $250 million per year and was the fastest-growing medical market between 2001 and 2011. Demand is expected to grow through 2016 as the material continues to take market share away from rubber and PVC.
Other medical uses for LSR include long-term implants such as pacemakers and heart valves, as well as short-term contact and disposable applications such as seals and gaskets, catheter tips and balloons.
LSR's compressible nature also can be an advantage, according to Steve Broadbent, an LSR process engineer with York, Pa.-based Engel. Typical LSR materials can be 5-7 percent compressible, depending on the supplier.
LSR also provides very low variation. Recent Engel test molds for a four-cavity umbrella mold showed variation of only around 0.04 percent. LSR also offers “a better material mix” for micromolding in color dispersion and other areas, according to Broadbent.
Greg Roembke, president of Ossian, Wis.-based Roembke, pointed out that LSR is expandable and requires higher mold temperatures than typical plastics. Plastic mold temperatures typically range from 70°-150° F, while typical LSR ranges are 320°-450° F.