CLEVELAND — Standard plastics are seeing competition from liquid silicone rubber in medical parts and other injection molding applications.
LSR has been able to make inroads in these areas because of its good physical properties and great chemical and heat resistance, Qure Medical general manager Jim Miller said May 7 at Plastics in Medical Devices, a conference hosted by Plastics News in Cleveland.
Qure was formed from the merger of three manufacturing companies in 2012. The Twinsburg, Ohio-based firm operates several plants in the U.S. and recently opened a plant in Dongguan, China. Qure employs almost 1,000 worldwide and has annual sales of about $150 million.
In the medical field, Qure has used LSR in a wide range of applications, including 0-ring seals, duckbill valves and internal wound drains.
In O-ring seals, Miller said that LSR offers good compression set performance and competitive pricing because of good cycle times. For duckbill valves, the material can provide excellent bounce-back properties and is biocompatible for intravenous fluids.
Internal wound drains made from LSR can be overmolded onto silicone tubing, Miller said. Holes also can be punched into the tubing to increase flow from the wound.
LSR feeding tubes also have proven to be resistant to stomach acids and feeding solutions. Other fluid management applications for LSR include plunger tips and other applications that deliver or remove fluids from the body.
Miller added that the use of heat with LSR injection molding is the opposite of what it is with plastics. "We're heating molds and chilling barrels," he explained.
Although LSR molds can be more difficult to clean and maintain than plastic molds, Miller said the material offers other advantages such as transparency, easy sterilization and biocompatibility. LSR also has proven popular, Miller said, because its soft feel is similar to that of skin, allowing it to be used in devices that contact the body.
Longtime plastics injection molder GW Plastics opened its GW Silicones unit in Royalton, Vt., in 2008. At PMD, unit general manager Mark Hammond said that silicones continue to challenge PVC and traditional rubber materials in medical and other markets. LSR also can compete with thermoplastic elastomers in those applications, he said.
LSR can offer more consistent pricing than TPEs, added Hammond, whose firm operates four plants in the U.S., as well as single plants in Mexico and China. The materials also are easily colored and are approaching the same cycle times as plastics in the molding process, he said.
Hammond cited a Freedonia Group study showing that by percentage, medical was the fastest-growing end market for silicones in the 2001-11 time period. But a possible downside of LSR use, according to Hammond, is the material's high air permeation and need for specialized equipment and expertise.
LSR also has been used in two-shot silicone molding, which Hammond said can produce complex parts with fine detail and tight tolerances.