Momentive Performance Materials is introducing a new line of highly transparent liquid silicon rubber (LSR) for optical applications. These new materials are characterised by their high transparency (up to 95 per cent), low opaqueness and excellent physical stability. According to the company, the material will be of interest for the manufacture of ancillary LED lenses for automotive applications.
The increasing use of high-power LEDs, especially in the automotive industry, 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 high temperatures of up to 150 degrees C, in conjunction with a high proportion of hard blue light radiation. This combination of temperature and radiation leads to accelerated ageing of the optical thermoplastics typically used today, as well as a shortened LED system life of only a few thousand hours. However, the new LSR 7000 series from Momentive offers an innovative alternative for such increased demands.
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, which enables economical moulding. At the same time, the good mechanical characteristics of the material permits easy moulding of complex geometries and even straightforward undercuts, hence more complex optical components can be produced 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 are well proven in this field. 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 been launched.
An Eschenbach Optik feasibility study demonstrated the considerable potential of LSR 7070. Erik Schalle, head of plastics technology, commented: "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.
"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."
Thorsten Häuser, head of LSR automotive application technology at Momentive, adds: "The concept of manufacturing lenses from an elastomer at first sounds a little absurd, as this market is traditionally dominated by rigid materials. 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."LSR 7000