Lumisil 590 and 591
High-Refractive-Index Silicones for LEDs
Wacker Chemie AG, Munich, Germany, has developed new encapsulants for light emitting diodes (LED) and optical components. Lumisil 590 and Lumisil 591 are highly transparent, addition-curing silicone elastomers with a refractive index of 1.53, which means they rank among the high-refractive-index (HRI) encapsulants.
Such grades are particularly suitable for manufacturing highly efficient LEDs. The HRI silicone protects the sensitive LED chip against mechanical influences and corrosive gases. At the same time, the silicone’s high refractive index enables optimum light efficiency. Semiconductor chips used to generate light in LEDs have a high refractive index. To maximize the amount of light emitted by the LED chip that can pass through the encapsulation, the refractive index of the chip and encapsulant must be roughly the same value. Thanks to their refractive index of 1.53, Lumisil 590 and Lumisil 591 make LEDs highly efficient. What’s more, the highly transparent silicones are almost completely transparent for light in the visible spectral range (approx. 400 to 700 nm) and do not yellow even when radiation is extremely intense. Transmission tests with Lumisil 590 show that a one-millimeter-thick layer lets over 91 % of visible light through.
The new HRI silicones are easy to process, heat-resistant and absolutely tack-free after curing. They also exhibit optimized flow and crosslinking characteristics. With a viscosity of the mix of 2,000 and 2,500 mPa*s respectively, they enable efficient, cost-effective processing. Both products are suitable for encapsulating the LED chip via contact-free dispensing processes.
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