Momentive: New highly transparent LSR types for automotive LED lens systems

Momentive Performance Materials (www.momentive.com) presents a new line of highly transparent liquid silicon rubber (LSR) for innovative optical applications. These new materials are characterised by their high transparency (up to 95%), low opaqueness and excellent physical stability. Therefore the material is of interest for the manufacture of ancillary LED lenses in the automotive applications.

Increasing demands on transparent polymer materials
The increasing use of “high-power” LEDs, especially in automotive technology, places increasing demands on the materials used. The new generation of LED systems are characterised by a high light output with lower power consumption in comparison to traditional light systems. Despite the effectiveness of the lamps, their very compact construction gives rise to extremely high temperatures of up to 150°C, in conjunction with a high proportion of hard blue light radiation. This combination of temperature and radiation leads to accelerated ageing of the up to now used optical thermoplastics and shortened LED system life-span of only a few thousand hours. The new LSR 7000 series from Momentive offers an innovative alternative for such increased demands.

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Special material qualities
Alongside the outstanding optical qualities highlighted above, the LSR 7000 series material is characterised in particular by its low mixing viscosity, which leads to shorter dosing and injection times while at the same time maintaining a low injection pressure. In conjunction with the short vulcanisation times that are typical for LSR, comparatively short cycle times can be expected, thus allowing very economical manufacturing of optical components. At the same time, the good mechanical characteristics of the material permits easy molding of very complex geometries and even straightforward undercuts, thus allowing manufacturing of considerably more complex optical components than is the case with thermoplastic materials or glass.

The LSR 7000 series was originally developed for the manufacture of light conductor systems for mobile telephone backlighting. The qualities of this material have been put to the test and have proven themselves a million times over in this area of application. The LSR 7000 series is commercially available in a hardness range from 60-80 Shore A. Furthermore, an ultra-soft 5 Shore A version has recently become available.

First implementation in LED systems
An Eschenbach Optik GmbH feasibility study demonstrated the considerable potential of LSR 7070. “For the manufacture of lenses for high-power LEDs we really struggled with transparent thermoplastics, such as PC and PMMA. With regard to temperature stability, LSR 7070 offers plentiful reserves compared to the thermoplastics and also permits short cycle times and low-waste manufacturing”, says Erik Schalle, Head of Plastics Technology at Eschenbach.

“The new LSR 7070 really can be processed with an almost complete lack of waste, as no large sprue is required to generate holding pressure, which is the case with thermoplastics. This means that material losses encountered during the manufacture of optical elements are reduced to a minimum.”

“The concept of manufacturing lenses from an elastomer at first sounds a little absurd, as this market is traditionally dominated by rigid materials”, adds Thorsten Häuser, Head of LSR Automotive Application Technology at Momentive. “But facts such as transparency, no expected stress cracks, and the possibility of economically manufacturing complex geometries (including even undercuts) speak clearly in favour of the considerable innovative potential offered by highly transparent LSRs in the application area of future LED systems. We are convinced that our customers will bring about many new and interesting developments with the new LSR 7000 series.”

About Eschenbach Optik
Eschenbach Optik (www.eschenbach-optik.de) was founded in 1913 by Josef Eschenbach as an optical products wholesale business. Today the company with headquarter in Nuremberg includes the three divisions eyewear, vision technology and technical optics. In the division technical optics Eschenbach Optik develops and manufactures customized optical components, assemblies and appliances. The company also produces specialized solutions in the field of technical plastics.

Photo: Various LSR 7070 lenses for high-power LEDs in the automobile sector

Momentive Performance Materials GmbH, Leverkusen, Germany

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