Optics: Creating optical parts for LED applications with multi-layer injection molding technology

The revolution in automotive headlamp design probably serves as the best example of the use of polycarbonates for optical parts: For physical reasons, the collimator lenses in headlamps need to have high wall thicknesses, usually between 15 and 30 mm (or more). These dimensions are challenging for injection molded parts because as the wall thickness increases, so does the shrinking potential. Molding lenses reliably within the required geometric precision range of, often, sink mark depths of less than 20µm, can therefore be very difficult. Another challenge is productivity, since the required cooling time before demolding of a thermoplastic part increases by the square of the wall thickness – so doubling wall thickness means four times more cooling time. Thus, using “single-layer” molding, today’s standard lens manufacturing process, leads to cycle times of up to 15 or even 20 minutes.

Lower operation temperatures inside LED headlamps – compared to HID or halogen light sources – enable transparent polymers to replace glass as the material for collimator lenses. Which is why more and more car manufacturers are using injection-molded thermoplastics to produce lenses with complex geometries for their innovative new headlamp designs. We support this trend in two ways. First, we have developed a group of tailor-made polycarbonates, our Makrolon® LED grades, with improved optical properties like purity, color and stability against high-power LEDs. Second, on the processing side, we developed multi-layer injection molding technology that allows the molding of thick-walled lenses with high precision and short cycle times. The success of this technique lies in splitting up lenses into several layers which are then molded in parallel.

In summary, we offer:
• Tailor-made Makrolon® LED grades for demanding optical systems
• High-precision optical and other material data for Makrolon® LED
• Special injection-molding technologies for optical parts