Malte Röbig

High Precision Optics for LED Applications Made of Liquid Silicone Rubber (LSR)

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.

Multi-technology products

Development of technical solutions that lead to widening the use of multi-technological products as well as in assessing ecological and economic potentials of multi-technological products have not yet been studied intensively. The activities conducted in the context of this research area focus on these aspects. The aforementioned aspects have been examined, evaluated and quantified on the basis of three example products resulting from the first funding period. The research activities conducted on the example components deliver the basis for the layout of different integrated multi-technology production systems. Technical solutions that enable coupling of different process steps with each other as well as the integration of different functionalities and different materials in final multi-technology products have been proposed. The complex interdependencies of the products themselves and their associated production processes have been researched and evaluated intensively. Finally, a profitability assessment of the proposed solutions was conducted and future research topics identified.

Injection moulding of high precision optics for light-emitting diodes made of liquid silicone rubber

In the market of lighting technologies, light-emitting diodes (LEDs) gradually substitute conventional light sources. Because of their high energy efficiency and long lifetime, they are increasingly used in consumer products, interior and exterior lighting applications in the home and mobility sector as well as in industrial applications. The material properties in the surrounding area of the light-emitting semiconductor chip are crucial to the performance of LED. Although the energy efficiency of LED is higher compared to conventional light sources, temperatures exceed about 150°C close to the semiconductor chip. Especially in combination with high amounts of blue ultraviolet (UV) radiation, the materials for encapsulation cannot meet the requirements and reduce the lifetime of an LED significantly. Contrary to conventional materials, high transparent liquid silicone rubber (LSR) can resist high temperatures as well as UV radiation and offer a great freedom in design. This enables the combination of the encapsulation (primary optics) and the secondary optics in one component. The objective of an ongoing joint research project with various partners from the industry is the development of an innovative injection moulding process for high precision optics in LED applications made of LSR, which is analysed at the Institute of Plastics Processing (IKV), Aachen, Germany. Therefore, the LED board is placed in the injection mould and overmoulded with LSR. The goal is a highly integrated process with major emphasis on the reduction of components, mounting steps and costs. Furthermore, the combination of primary and secondary optics promises an improved effectiveness because losses in light power due to the transition of the primary and secondary optics are reduced.

Injection molding of high precision optics for LED applications made of liquid silicone rubber

Light Emitting Diodes (LED) conquer the growing global market of lighting technologies. Due to their advantages, they are increasingly used in consumer products, in lighting applications in the home and in the mobility sector as well as in industrial applications. Particularly, with regard to the increasing use of high-power LED (HP-LED) the materials in the surrounding area of the light emitting semiconductor chip are of utmost importance. While the materials behind the semiconductor chip are optimized for maximum heat dissipation, the materials currently used for the encapsulation of the semiconductor chip (primary optics) and the secondary optics encounter their limits due to the high temperatures. In addition certain amounts of blue UV radiation degrade the currently used materials such as epoxy resins or polyurethanes for primary optics. In the context of an ongoing joint research project with various partners from the industry, an innovative manufacturing method for high precision optics for LED app...

Application of a multilayer injection molding process for thick-walled optical components

Abstract Nowadays, the injection molding of optical components is becoming more and more important. A process which constructs the injection-molded part in layers offers considerable potential for productivity increases in the manufacturing of thick-walled optical components. The so-called multilayer injection molding, also known as overmolding technology enables a considerable reduction of the normally long cycle times and improves the optical properties. It is even possible to increase the molding accuracy due to the lower shrinkage potential of the single layers. Contrary to experience, the influence of the mold temperature on the bonding strength is very low. So, the temperature control of the mold can be adapted to the process consideration in regard to optical characteristics.

Improved molding of micro structures using PVD-coated mold inserts

Abstract Micro structured optical plastics components are intensively used, i.e. in consumer electronics, for optical sensors in metrology, innovative LED-lighting, or laser technology. Injection molding has been proven successful for the large-scale production of these parts. However, the production of these parts still causes difficulties due to challenges in the molding and demolding of plastics parts created with laser-structured mold inserts. A complete molding of the structures often leads to increased demolding forces, which then cause a breaking of the structures and a clogging of the mold. An innovative approach is to combine physical vapor deposition (PVD)-coated, laser-structured inserts and a variothermal molding process to create functional micro structures in a one-step process. Therefore, a PVD coating is applied after the laser-structuring process in order to improve the wear resistance and the anti-adhesive properties against the plastics melt. In a series of molding trials with polycarbonate (PC) and polymethyl methacrylate (PMMA) using different coated molds, the mold temperature during injection was varied in the range of the glass transition and the melt temperature of the polymers. Subsequently, the surface topography of the molded parts was evaluated by digital three-dimensional laser-scanning microscopy. The influence of the molding parameters and the coating of the mold insert on the molding accuracy and the demolding behavior were analyzed. It was shown that micro structures created by ultra-short pulse laser ablation can be successfully replicated in a variothermal molding process. Due to the mold coating, significant improvements could be achieved in producing micro structured optical plastics components.