MAKROLON IN NEW APPLICATIONS: FOCUSING OPTICS MADE OF POLYCARBONATE FOR LEDS
12 August 2007 - Bayer MaterialScience AG

Bayer MaterialScience AG is one of the first plastics manufacturers to start extensive research projects into focusing optics made of polycarbonate for light-emitting diodes. The aim of the research is to be able to provide future development partners and processors with customized product grades of the polycarbonate Makrolon and comprehensive support services, ranging from optics design and mold construction to engineering and series production. “We are currently investing in a high-precision injection molding and injection-compression molding system, suitable molds, and measuring technology for assessing the quality of focusing optics. We have also purchased special rheological calculation programs designed for very thick injection moldings with extreme variations in wall thicknesses,” explains Rainer Protte, specialist for injection molding developments in the Injection Molding Technologies segment of the Polycarbonates Business Unit.

A particularly bright future is predicted for LEDs that emit white light. In future, they are expected to be used in a wide range of applications, for example in street lamps, liquid-crystal displays, advertising boards, automotive headlights and building illumination. Their main advantages over incandescent bulbs and discharge lamps are that they consume less energy and have a longer service life. Lenses with free-form surfaces that have non-symmetrical geometries make particularly suitable optics for these LEDs. Unlike multi-component classic lens systems, only one of these lenses is required to focus the LED light with very low losses.

Transparent polycarbonates such as Makrolon make ideal materials for these focusing optics because, thanks to their high heat resistance of up to 130 °C, they can cope with the maximum operating temperatures encountered in an LED. Optics with free-form surfaces typically have walls that are more than ten millimeters thick and vary greatly. As the square of the wall thickness is employed in the cooling time formula, manufacturers have to endure very long cycle times, sometimes up to several minutes, when these types of plastic optics are produced. In this respect, PC has a clear advantage over PMMA, the key competitor material among transparent plastics in that its thermal conductivity is much higher. Compared to PMMA, PC reduces cooling times, and therefore cycle times, significantly, resulting in much higher productivity. “In tests using sample sheets four millimeters thick, we showed that PC can be removed from molds up to twice as quickly as PMMA,” reports Dr. Martin Döbler, expert in Technical Product Service for optical applications using polycarbonate.

PC is much lighter than glass, and also has the advantage that complex lens geometries can be produced from it cost-effectively and with high precision by injection molding. Furthermore, the potential for functional integration can be used to integrate housing components, fastenings and guides in the lens component cost-effectively.

Bayer MaterialScience welcomes collaborations with universities and colleges, business enterprises and research institutes for its research work on PC focusing optics. For example, the company has a cooperation agreement with Light Prescriptions Innovators, a leading developer, manufacturer, and licenser of optical components for non-imaging optics.

http://www.bayermaterialscience.com

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