INJECTION MOLDING: Mold Clear Lenses Without Yellowing, Black Specks

Plasticating system tailored for optical-grade polycarbonate.

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A new plasticating system from Nordson Xaloy, Inc., New Castle, Pa., is designed specially for molding optical-grade polycarbonate without yellowing and black specks. This system will be introduced at next month’s Fakuma 2015 show in Friedrichshafen, Germany. The package consists of four components:

• Pulsar II mixing screw modified for PC;

• Barrel with X-800 inlay (nickel-based alloy with tungsten carbide);

• Check valve designed for free flow with PC viscosity (different valves are recommended for screw sizes above and below 80-mm diam. and for flame-retardant

• Nickel-plated end cap designed to smoothly transition the PC melt from the screw to the injection nozzle.

These components are designed to deliver melt with minimum shear that can cause yellowing, and to avoid polymer sticking points or “dead spots” where black specks can form.