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Press Releases

WACKER Presents High-Transparency LED-Encapsulants with High-Refractive-Index

Munich, Oct 19, 2016

At the 20th International Trade Fair for Rubber and Plastics K2016, WACKER, the Munich-based chemical company, is showcasing high performance silicones for the encapsulation of light emitting diodes (LED) and optical components. When cured, the encapsulants
LUMISIL® 590 and LUMISIL® 591 transform into highly transparent elastomers with a high refractive index. The products withstand high operating temperatures and strong light radiation without yellowing. That makes them ideal encapsulants for LEDs with a high light efficiency. They also protect the LED chip against corrosive gases, which greatly extends the component’s service life. The silicone compounds can be processed in industrial metering processes such as dispensing. K 2016 takes place in Düsseldorf, Germany, from October 19 to 26.

Silicone Einkapselung Leuchtdioden
At the K 2016 Trade Fair for Rubber and Plastics, WACKER, the Munich-based chemical company, will present LUMISIL® 590 und LUMISIL® 591, two highly transparent LED encapsulants. They have a refractive index of 1.53 which boosts the efficiency of the lighting unit. They also protect the LED chip from damage and corrosive gases which prolongs its service life.

LUMISIL® 590 and LUMISIL® 591 are highly transparent, addition-curing silicone encapsulants. They form elastomers with a refractive index of 1.53 which ranks them among the high-refractive-index (HRI) encapsulants. Compounds of this kind are particularly suitable for manufacturing high performance LEDs. The HRI silicone protects the sensitive LED chip against mechanical influences and corrosive gases. At the same time, its high refractive index enables optimum light efficiency.

Semiconductor chips used to generate light in LEDs usually 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.

This is exactly what the new silicone encapsulants offer: their refractive index is 1.53, which is roughly the value of most LED chips. Due to this, LUMISIL® 590 and LUMISIL® 591 improve the efficiency of the LED significantly. What’s more, the highly transparent silicones are almost completely transparent for light in the visible spectral range (approx. 400 to 700 nm). Also, they do not yellow, even when radiation is extremely intense. Transmission tests with LUMISIL® 590 show that a one-millimeter-thick layer lets over 91 percent of visible light through.

LUMISIL® 590 and LUMISIL® 591 protect the LED chip reliably against environmental influences. Corrosive gases such as hydrogen sulfide can damage the LED chip and reduce its performance. Tests show that LED chips encapsulated with LUMISIL® 590 and LUMISIL® 591 are protected against such damage longer and have a prolonged service life.

Both encapsulants are easy to process, heat-resistant and absolutely tack-free after curing. They also exhibit optimized flow and cross-linking 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. LUMISIL® 590 and LUMISIL® 591 form cured rubber grades of varying hardness. With a hardness of 65 Shore A, LUMISIL® 590 is relatively soft, whereas LUMISIL® 591 is formulated to be significantly harder at 40 Shore D.


The LUMISIL® product line comprises optical high-performance silicones for LED manufacturers with high requirements. WACKER offers highly transparent silicone elastomers for applications with a high (HRI) and normal (NRI) refractive index. All products enable very efficient, cost-effective production and exhibit optimized flow and crosslinking characteristics, as well as high photostability. As an encapsulation material, they protect the LED chip reliably against environmental influences and thereby extend its service life.

Visit WACKER at K 2016 in Hall 6, Booth A10.


Wacker Chemie AG
Media Relations & Information
Florian Degenhart

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