LIQUID SILICONE RUBBER | INNOVATION
Material suppliers for LSR injection moulding are innovating to remove extra steps from the process, and machines are
being updated to open communications. By Peter Mapleston
Finding a cure with liquid silicone rubbers
Liquid silicone rubber is on the move. This thermo- setting polymer is already an interesting option for applications calling for flexibility, resistance to hot and cold, durability, transparency and purity. Now, material suppliers are introducing new systems that provide improved control over processing and properties, there are numerous options to choose from when it comes to mixing and dosing equip- ment to pair with injection moulding machines, and the increasing adoption of open communications protocols is helping simplify control of production systems. Elkem Silicones has commercialized a com- pletely new liquid silicone rubber system, called LSR Select, which works quite differently from traditional two-component systems. The company announced LSR Select several years ago, but began its market introduction in 2018. Silbione grade LSR Select is also available, for healthcare and medical applications. Instead of A and B components, LSR Select
works with a single standard base material to which are added the Cata platinum catalyst and “Control” curing additive at the processing machine. This is said to yield lower cycle times and curing tempera- tures. It also enables the use of one base material for diverse finished material characteristics. “LSR Select is chemically equivalent to our
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traditional two-component LSR formulations, taken apart and put back together in three components,” says a representative. “The Control and Cata are unique masterbatches, which are the levers to adjust for desired cure kinetics, ease of processing and part performance.” Cycle times are generally reduced by 15-40%, and possibly by as much as 60%, depending on the part. The company cites one customer who was able to take a cycle time on a part from 50s with traditional 2K LSR at 135°C to just 25s with LSR Select at the same temperature. Improved control over cure kinetics “helps
reduce the risk of scorching and orange-peel effect from uneven temperature distribution, air entrap- ment, and flashing resulting in less reject rates and overall improved part appearance,” the company claims.
In addition to controlling the part cure profile, LSR Select enables users to create custom durom- eter blends from 20 to 70 Shore A to achieve precise performance requirements, the company says. “With LSR Select, customers can differentiate
their offering — from productivity improvements in the range of 20 to 40%, to blending durometers for precise results, to low temperature cure for sensitive substrates,” says Chris York, president Elkem Silicones USA. Systems can cure at tempera-
April 2019 | INJECTION WORLD 33
Main image: With their complex structure, these silicone LED lenses place high demands on the injection moulding process
PHOTO:ENGEL/ACH-S
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