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Optical Injection Molding for Polycarbonate Plastics | Covestro

From challenging optical designs to reliable optical parts in mass production

Optical molding

The automotive lighting industry is in a highly dynamic market with high demands for materials. The unique design of each vehicle is dominated by head- and rear lamps. Recently car manufacturers were starting to use high power LEDs as efficient light source for all illumination functions in head-lamps.

Audi A8 headlamp
Headlamp made of Makrolon® LED

Lower operation temperatures up to 120°C inside LED headlamps compared to HID or halogen light sources enable transparent polymers to replace glass as material for collimator lenses. This is beneficial in several aspects: The injection molding process for thermoplastics like polycarbonate allows production of lenses with complex geometries which car manufacturers make use of to create completely new head-lamp designs.

However, LED collimator lenses cannot be considered as standard thermoplastic parts; additionally to challenging geometries raw material and molding process have to fulfill highest quality demands. Due to physical reasons collimator lenses need to have high wall thicknesses, usually between 15 and 30 mm. Those dimensions are challenging for injection molded parts. The higher the wall thickness is chosen, the higher the shrinking potential will be. That means that it is hard to mold those lenses within the required geometrical precision ranges of often less than 20µm sink mark depths. Furthermore, the needed cooling time before a thermoplastic part may be de-molded increases with the square of the wall thickness – doubling wall thickness means four times longer cooling time. Thus using “Single-Layer” molding which is todays standard lens manufacturing process leads to cycle times of up to 15 or even 20 minutes.

Covestro is supporting this trend on two tracks:

  • We have developed a group of tailor made polycarbonates, called Makrolon® LED grades with improved optical properties like purity, color and stability against high-power LED-light. 
  • On the processing side, Covestro is developing the Multi-Layer injection molding technology which allows molding thick walled lenses with both short cycle times and high precision. This is achieved by splitting up lenses in preferable three layers which are molded sequentially or parallel. For the optimum productivity and precision, Covestro has developed simulation tools which search the ideal amount and thickness of each layer.

 

Lens produced in multi-layer injection molding

Lens produced by using multi-layer
injection molding (left final lens, right preform)

    Summary

    Covestro is part of the fascinating success story of LED lenses. We are offering:

    • The tailor made product family Makrolon® LED for demanding optical systems
    • High precision optical and other material data of Makrolon® LED
    • Special injection molding technologies for optical parts
    • Simulation expertise to make Multi-Layer molding most productive. 
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