LSR material cures at low temperatures

ANAHEIM, Calif.—At first, LSR Select, a base polymer material commercialized in 2018, was touted for saving production time by reducing cure times for liquid silicone rubber.

Oslo, Norway-based Elkem A.S.A., a global silicones materials supplier, said it optimized the cure kinetics of the LSR Select brand and improved cycle times by between 15 and 40 percent.

More recently, the material is proving to be a breakthrough by achieving low-temperature curing, according to J. Christopher York, president of Elkem Silicones USA Corp., a New Jersey-based division.

LSR Select can cure at 80°C compared to 160°C for traditional two-component LSR, York told Rubber & Plastics News. This means LSR Select can be used in a wider range of applications without damaging temperature-sensitive components, such as plastics, electronics and batteries, in both the two-shot and overmolding processes.

"The thought of running at 80°C has been a wow factor because it's so unique to the marketplace," York said at the Medical Design & Manufacturing West trade show in Anaheim.

Founded in 1904, Elkem supplies silicon-based materials from quartz to specialty silicones to the health care, aerospace, automotive, construction and other markets. The company has 6,300 employees and nine manufacturing sites. Sales were $2.1 billion in 2019.

Elkem put a spotlight on LSR Select's capabilities at the medical trade show, calling it a next-generation LSR for formulation flexibility in addition to productivity and low-temperature cure.

The wider cure range opens doors to using silicone rubber in heat-sensitive applications, such as medical wearable devices, according to Elkem officials. They said LSR that cures at 160°C can't be used for products with electronics or overmolded with parts made of certain plastics such as polypropylene because it would melt.

The whole idea of low-temperature cure is to allow overmolding on sensitive polymers and also electronic components," said Mehdi Abbadi, Elkem's global business unit director. "With this feature, LSR can be used in a completely different way targeting completely different applications. You no longer need mechanical tricks to bind together rigid plastics, such as PP and PE (polyethylene), with an elastomer like LSR. It saves time and expense to directly overmold these plastics."

LSR Select is a suitable material for wearable medical devices controlled with printed circuit boards that help patients manage their health by monitoring parameters, such as blood and glucose levels, added Julie Harber, Elkem's business development manager.

The advancement of wearable medical technology, which gathers data for patients to monitor for themselves or forward to their doctor, is growing along with demand from consumers to take control of their own health. The wearable medical device market was valued at $10.6 billion in 2019 and is growing at a compounded annual rate of 18.3 percent, according to the India-based market research firm P&S Intelligence. Market revenue is projected to reach $67.2 billion by 2030.

In addition to trials related to different substrates, LSR Select fared well when tested and compared to other LSRs used with sensitive electronics, Harber said.

"If you try to overmold a printed circuit board at 165°C, which we did prove out, it destroys the board. It's nonfunctioning," Harber said. "But in our trials, we were able to overmold that at 110°C, and it functions with the software program. We've proven that out in a couple trials, which is industry-changing."

Customized durometers
LSR Select also has in-line blending capabilities and can be customized to obtain precise durometers on the Shore A Hardness Scale, which begins at zero for very soft materials and goes up to 100 for hard materials, like rigid plastics.

The Shore A scale measures the hardness of flexible rubbers from very soft and flexible—like a rubber band—at the low end, to somewhat flexible like a pencil eraser at the mid-point, to hard and semi-rigid like a tire tread at the high end.

LSR Select is available in 25, 35, 50 and 70 Shore A hardness. Any two of these base polymers can be blended to target specific measurements, mechanical forces, product functions and performance requirements. For example, a mixture with 20 percent LSR Select 35 and 80 percent LSR Select 50 yields a 40 Shore A hardness.

Elkem said the ability to create and repeat a specific durometer recipe can offer competitive advantages in terms of meeting demanding specifications, producing consistent parts, and offering a hardness that isn't easily duplicated.

Being able to achieve a wide durometer range from four base polymers also means a business can reduce its inventory, which saves space, money and time, Abbadi said.

Quick to cure
Elkem demonstrated how LSR Select is processed by producing baby bottle nipples in three different colors and durometers. In a traditional two-component system, which is also known as an A and B component system, the pink, blue and white nipples would cure in about 25 seconds, but Elkem got it down to 11-15 seconds.

"That's significant. We saw that right off the bat," York said. "We thought our biggest opportunities with LSR Select would be on the productivity of a unit, and that was our initial focus, but since then we've learned a lot more."

Elkem switched baby nipple colors and durometers within six shots that took less than 90 seconds during the demonstration, which used the Elmet Top 5000 dosing system built by Austria-based Elmet Elastomere Produktions.

"Elmet did a great thing when they redesigned the Elmet 3000 and upgraded to Elmet 5000," York said. "It enabled them to run a two-component system and put software into the program for those that want to run LSR Select."

While standard LSR systems use a drum of A material and a drum of B material that crosslink when heated, the LSR Select demonstration essentially showed two drums of LSR Select material with 20 and 70 durometers. The pump on the Elmet 5000 can adjust the ratios up to 100 percent on one side and 0 percent on the other or 50/50 or any other durometer ratio in between, according to Bob Pelletier, president of the U.S. division, Elmet North America Inc. Additives, catalysts and control agents for coloring and curing also are mixed in.

"People see pink parts and then blue parts because we're changing colors within six shots. That alone is a game changer," Pelletier said. "We also can custom-formulate durometer and cure at 80°C, so now we can start bonding some polyolefin and other plastic that can't handle the traditional heat. This has been a very exciting material."

One of the early adopters is a processor in South Carolina that makes silicone bite devices for people with sensory disorders such as autism.

"They originally were made with (thermoplastic elastomers), but they wanted a more medically approved material so they went into LSR Select," Pelletier said. "Now they can custom formulate the colors and durometers and make their own."