LSR provides a clear choice for optical molding

In a market traditionally dominated by rigid materials, a new series of highly transparent liquid silicone rubbers (LSRs) showcased at the Fakuma show in Germany has proven successful in manufacturing lenses for high-power LEDs. The LSR7000 Series from Momentive Performance Materials (Albany, NY) offers designers high transparency, high elasticity, and is said to be easy to process. With transparency levels typically of 98%, this LSR is aimed at replacing materials such as transparent polycarbonate and polymethyl methacrylate (PMMA) in mobile phones, optical systems, and light-guide applications.

Temperatures of up to 150°C and blue light radiation in high-power LED applications lead to accelerated aging in thermoplastics, shortening the lifespan to a few thousand hours. But Momentive’s new LSR7000 can meet these increased demands. The addition-cured, platinum-catalyzed LSR series already is commercially available in a hardness range from 60-80 Shore A, and an ultrasoft 5 Shore A version has recently been released.

A feasibility study by optical product developer and manufacturer Eschenbach Optik GmbH (Nürnberg, Germany) found that, compared to transparent thermoplastics such as PC and PMMA, LSR7070 offers good temperature stability and permits short cycle times. And it can be processed with an almost complete lack of waste as no large sprue is required to generate holding pressure. The LSR offers the possibility of manufacturing complex geometries, including undercuts, without the expected stress cracks.

At Fakuma, Momentive also made further improvements to its FFSL 70x1 range of fully fluorinated LSR products. With resistance to fuels, lubricants, and oils similar to conventional fluorovinylmethyl silicone (FVMQ), a poly addition system developed for the new material allows much faster polymerization. This optimized version has been used in new projects involving items coming into contact with flex fuels like E85 and E22. The FFSL is offered commercially in 30-70 Shore A hardness, plus a self-lubricating 40 Shore A version.

Momentive Performance Materials
www.momentive.com