Massive growth leading to LSR resin shortages

Exton, Pa. — 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 molders are experiencing resin shortages, according to Rick Ziebell, vice president of technology for R.D. Abbott Co. Inc.

Ziebell, the first speaker at an April 9-11 open house at Boy Machine Inc. in Exton, 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 $1.4 billion over the next few years.

LSR is a thermoset elastomer that gets pumped into a mold through a water-cooled nozzle and gets cured quickly inside a heated mold. 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 mold.

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 molding LSR: The huge change in viscosity that goes on throughout the pumping and molding 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 molding 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.

R.D. Abbott is a full-service distributor of LSR and rubber in Cerritos, Calif. In addition to Ziebell's talk, representatives from pumping equipment companies, mold 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 molding machines at the event, molding LSR and thermoplastic products like medical micromolded items, baby bottle nipples and a bottle cap opener showing molding of a metal insert with polypropylene.

A highlight was the U.S. launch of the largest-ever Boy, the Boy 125 E, with 137 tons of clamping force, molding two-component coffee mugs made of polypropylene and overmolded 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.

Bob and Mike Pelletier, brothers who work for competing pumping equipment companies, explained the importance of metering the two components.

"You have to look at the big picture when you look at silicon processing," said Bob Pelletier, operations manager for Elmet North America Inc.

Pelletier said the company's new Top 5000 P dosing system makes sure you use 99 percent of the LSR components in the drums.

For clean room molding, a molder can gain space by isolating the pumping system outside the room, set up on levels above and below.

One big issue is the skill level of operators, who may have come from thermoplastics molding — the exact opposite of thermoset LSR processing, Pelletier said.

"We spend a lot of money on machinery, we spend a lot on the dosing system and molds, and then we pull someone off the street to run it," he said.

Elmet set up a timer on its controller, giving operators advance notice that levels are getting low and it's time to get materials prestaged in new drums. Another feature allows only authorized employees to set up production and shows who made what changes. He said video instructions show how to hook up the A and B components, and a bar code scanner checks the drums before they ever get hooked up — making sure the system is set up correctly.

Elmet North America is in Dimondale, Mich., near Lansing.

Mike Pelletier, business development manager for LSR and medical systems at Graco-Fluid Automation Inc., said the company's F4-5 and F4-55 metering systems automatically adjust the pumping ratio to ensure equal material consumption of the two components.

Graco-Fluid Automation is based in North Canton, Ohio.

Officials from two LSR mold makers described their craft.

Dana King, business development manager of Kipe Molds Inc., said some critical areas are a balance of fill and valve gate control and proper mold venting on parting lines. By minimizing the pressure drop across the cavity, the mold maker can minimize the possibility of trapping air and flash, he said.

Kipe Molds is in Placentia, Calif.

Rick Finnie, president of M.R. Mold & Engineering Corp. in Brea, Calif., said silicone can tear when it's too hot and not fully cured. "It can be easily damaged when coming out of the tools," he said. Deformation can also be a problem.

"The most common defect with silicone is flash, and it's hard to stop because silicone can flash easily," Finnie said. "It's an ongoing challenge." Other challenges include air-trap, non-fill or short shot areas, as well as "backrind" a ragged indention at the parting line.

Finnie said gate location and the parting line are very important. Sharp corners in the mold can cause tearing of the part, he said. A mold maker can add undercuts, if they're properly designed, he added.

Careful mold design is also needed for venting. One option could be adding a small reservoir or "dump area" for excess material, he said.

"We don't need draft. In fact, you can have negative draft in the mold and it wouldn't hurt anything at all if it wasn't too bad. Silicone does an excellent job of replicating texture that's in the tool," Finnie said.

Vincent Colarossi, senior application development engineer of elastomers for Momentive Performance Materials Inc., said several techniques can be used for two-component LSR molding, including chemical bonding of the two materials or a mechanical interlock with holes and undercuts.

Two-component parts can be molded in one injection press, with a mold rotating between two injection units — one for thermoplastic and the other overmolding silicone. Or a molder could use two machines, molding the substrate on one press and moving or over to another machine for LSR processing, Colarossi said.

"The real driver is the high-performance products — waterproofing and durability," he said.