Market For Molded Plastic - The demand for molded plastic components with special optical properties is growing. Using optical lenses as an example demonstrates how process technology innovations are helping to fulfill these high demands.

The application of optical procedures and technologies (photonics) is one of the key technologies of industrial development. Photonic components and systems are applied in areas such as vehicle manufacturing, medical technology and electronics, opening the way to novel and efficient solutions. The global market for photonics products grew from €228 billion to approximately €350 billion between 2005 and 2011. This corresponds to an annual increase of approximately 7.5%.

According to estimates, market volume will be more than €600 billion in the year 2020. In Germany, the photonics industry and its suppliers employ about 140,000 people. The rising importance of photonics naturally also affects the plastics processing industry, since the demand for molded plastic articles featuring special optical properties is significantly increasing.

Krauss Maffei has acquired an extensive store of experience in optical plastics applications over the past years, positioning itself as a qualified technology partner. New solution approaches for the photonics field are derived from process technology innovations tested and proven through the manufacture of products such as optical data carriers, automobile taillights or components for automotive glazing (figure 1).

To further developments in process engineering, Krauss Maffei is working together with numerous industrial companies and research institutes as part of research projects and development partnerships. Krauss Maffei possesses the particular advantage of offering machines and systems for thermoplastic processing as well as for reactive resin processing.

LED Optics in Automobile Headlights

Krauss Maffei is taking part in research involving the implementation of plastic lenses for LED optics in automobile headlights. The development of high-intensity LEDs has made high beams with LED technology feasible as well; there are already luxury car models equipped with full LED headlights. These headlight systems require relatively complicated lens geometries with free-form surfaces.

Transparent plastics, such as polymethylmethacrylate (PMMA) or polycarbonate (PC), offer a host of advantages over glass when used as lens materials. Because of their low density, thermoplastic lenses not only enable a reduction in total headlight weight, but the injection molding process also makes it possible to produce lenses with a high level of design freedom both cost-effectively and at high volume.
As an additional important advantage, design-related connecting elements can be integrated directly onto the lens body using the injection-molding process. This makes cost-effective installation of the module possible.

The optical requirements for LED headlight lenses result in areas with large wall thicknesses emerging in the injection-molding article. This can cause problems regarding dwell time in standard injection molding, since low-stress and dimensionally accurate lens cooling takes a relatively long time, and cycle times can extend to 20 minutes or longer. The multilayer process, in which the lens is manufactured in multiple work steps, helps remedy the situation (figure 2).

The process engineering thus corresponds to the familiar multicomponent injection-molding technology - with the exception that only a single material is processed. In the first step, the lens core is fabricated as a preform. In the second step, this core is subsequently sprayed over with a top and bottom coating of the same material.

This method can compensate for shrinkage effects and sink marks. As a result, the cycle time becomes significantly shorter, so that lenses with high optical quality can be produced in large quantities. Bayer MaterialScience AG and Evonik Industries AG are using the Krauss Maffei CX series on injection-molding machines in the scope of several research projects, in order to further develop the multilayer process.

Precise Molding

Variothermal heat-balancing of the injection mold allows further improvement in precise lens surface molding. The collaborative research project SkForm is pursuing the goal of creating functional surfaces out of polymer materials with fast variothermal mold heat-balancing.
This process has been used to manufacture precision lenses with high optical transmission using a short cycle time in a single process step, without additional cost-intensive lens coating. Optically functional structures have been accurately contoured onto the component surface. This has made it possible to shorten the cycle time considerably in comparison to conventional injection molding.

If an even finer surface structure is required for lenses or other optical components, even variothermal heat-balancing methods reach their limits after a certain point. This is because of the relatively high viscosity of the polymer melt, among other causes. The viscosity prevents the melt from fully reproducing the increasingly finer mold structures. Flow-coating of injection molding components with reactive polyurethane (PU) system, as developed by KraussMaffei, is suitable for these areas of application. The article is injection-molded, flow-coated and functionalized within a system in a two-stage process. The surfaces produced in this manner are characterized by low optical reflection, high transmission and high resistance. Since no subsequent painting is required, substantial time and cost savings can be achieved with this procedure. In cooperation with Evonik Industries AG, Krauss Maffei furthermore offers the CoverForm procedure, based on a similar principle but using a solvent-free, acrylic-based, multicomponent reactive system in place of PU (figure 3).

Outlook

LED technology is coming into increasing use in street lighting and interior lighting as well. Back at Fakuma 2012, Krauss Maffei demonstrated a 3K injection molding process with metallic circuit paths and an installed LED for fully automatic production of a complete LED table lamp in polycarbonate. Furthermore, an innovative fiber optics application for automobile interiors will stand at the center of KraussMaffei's trade show appearance during K 2013 under the title "Trendgineering."