Abstract
Light Emitting Diodes (LED) conquer the growing global market of lighting technologies. Due to their advantages regarding efficiency and lifetime, they are increasingly used in consumer products, for lighting applications in the home and in the mobility sector as well as in industrial applications. Conventionally, LED chips are encapsulated by so-called primary optics and the optical function is given by an optical head. In the context of a joint research project in cooperation with the partners Hella KGaA Hueck & Co., Lippstadt, Momentive Performance Materials GmbH, Leverkusen, all Germany, and ELMET Elastomere Produktions- und Dienstleistungs-GmbH, Oftering, Austria, an injection molding process of combined primary optics and optical heads made of liquid silicone rubber (LSR) was investigated. Due to the material-specific advantages of highly transparent LSR especially regarding the excellent high temperature resistance and the great freedom in design the optics can meet both the requirements for the encapsulation of LED chips as well as the realization of an optical function. An integrated injection mold concept was realized in order to reduce mounting steps, where a LED circuit-board is inserted and directly overmolded with LSR. Processing studies have shown that a reproducible replication of LSR optics with good optical properties and molding accuracy is possible. Moreover, for the use in an automotive application long term properties are crucial. Therefore, a temperature cycling test between −40°C and 125°C for 1,000 cycles as well as a continuous operation of the LED with permitted maximum current for 2,000 h were carried out.
Additionally, the application of optical micro structured LED optics made of LSR was examined. For this purpose appropriate optics and mold inserts were designed and manufactured.
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