Liquid silicone rubber, used in automotive, medical and other markets, is a small niche in the plastics industry, but it's growing so quickly that moulders are experiencing resin shortages, according to Rick Ziebell, vice president of technology for RD Abbott Co. Inc.
Ziebell, the first speaker at an April 9-11 open house at Boy Machine Inc. in Exton, Pennsylvania, called the shortages "the elephant in the room."
The last major shortage happened back in 1992, he said, when a lot of new applications in the automotive industry — the biggest LSR market — drove up demand for materials. New uses for LSR included coatings for airbags and parts where anti-flammability is critical.
Add in ever-growing electronic connectors, where durable silicone seals are superior to rubber ones, engine seals, and new optical silicone applications, and "the need for silicones has expanded greatly," Ziebell said.
Glues and adhesives also use the same raw materials. It adds up to a tripling of sales of silicones in the last five years, he said.
Ziebell delivered some good news: Major manufacturers are planning a total investment of about $1.4bn (€1.24bn) over the next few years.
LSR is a thermoset elastomer that gets pumped into a mould through a water-cooled nozzle and gets cured quickly inside a heated mould. The very fast curing is why LSR systems keep Part A and Part B separated, until just before they come together and go into the mould.
Medical offers big growth rates because LSR has good biocompatibility, Ziebell said.
"We're starting to see more LSR implantable medical devices," he said, especially diagnostic products.
"In about two years, you're going to see all kinds of things coming out. If you think the FitBit and the iPhone Watch is super, wait till you're taking a pill and it's measuring digestive systems. There'll be a little chip inside the pill that'll be communicating to your watch. Not only that, but on the therapeutic side, you'll get pulses back from various other devices implanted in your body to control and regulate metabolism throughout the body. It's amazing where we're headed," he said.
Ziebell, who outlined the chemistry behind liquid silicone rubber, spelled out one fundamental challenge with moulding LSR: The huge change in viscosity that goes on throughout the pumping and moulding cycle.
"The varying degree of shear mixing changes the silicone's viscosity attributes," he said. As shear increases, viscosity goes down.
When the two components come together, they start to set up and cure right away. Silicone goes from paste to water inside the injection press machine, he said, which means moulding machines have to do "phenomenal things" to compensate when running LSRs. Precise cycle times and the flow speed are very important, he added.
"A good injection press applies its force in a very repeatable manner. But LSR changes its viscosity all the time! You never know what it's going to do," Ziebell said.
RD Abbott is a full-service distributor of LSR and rubber in Cerritos, California. In addition to Ziebell's talk, representatives from pumping equipment companies, mould makers and material suppliers took a deep dive into the world of liquid silicone rubber during a conference held at the open house. The event drew 125 attendees.
Boy Machine ran five injection moulding machines at the event, moulding LSR and thermoplastic products like medical micromoulded items, baby bottle nipples and a bottle cap opener showing moulding of a metal insert with polypropylene.
A highlight was the US launch of the largest-ever Boy, the Boy 125 E, with 137 tonnes of clamping force, moulding two-component coffee mugs made of polypropylene and overmoulded with a soft thermoplastic elastomer. The bolt-on second injection unit, built by parent company Dr. Boy GmbH of Fernthal, Germany, was set up in an L-configuration, mounted horizontally at the rear of the machine.