It is known that plastics/polymers age owing to the effect of environmental influences such as moisture, temperature, radiation, chemicals or owing to the effect of mechanical stresses. The use of plastic in technical products is compromised by the effect of electromagnetic radiation. Such electromagnetic radiation primarily involves the high-energy radiation component in the sunlight spectrum with a wavelength <500 nm. The effect of this radiation can lead to photochemical degradation of plastics, and therefore to shortening of the lifetime of plastics in outdoor applications and in opto-electronics. Protective layers made of polymer films with UV absorbers such as titanium oxide or zinc oxide are therefore often used for metals, see WO 98/06575. Further UV absorbers for UV-stable plastics can be found, for example, in CN 1307072.
The light emitted by light-emitting diodes (LEDs) is generated by recombination of electrons and holes in the junction of a semiconductor, the energy released during the recombination being radiated as light. LEDs, and especially luminescent diodes, are often encapsulated using high-purity, water-clear and non-yellowing epoxy resin systems/epoxy casting resins. Such encapsulated light-emitting diodes are used, for example, with polymer-based light-conversion elements as SCW (single chip white) LEDs, also referred to as luminescence-conversion LEDs, in the automobile industry. UV- and blue-emitting luminescent diodes consist of semiconductors based on GaN or InGaN, which can also be used in conjunction with known phosphors (primarily such as cerium-doped garnets of the rare earths Y, Gd, La, Lu and Tb) in order to achieve a white mixed color and special colors.
The lifetimes currently being achieved for wavelength-converting potting compounds in blue and SCW LEDs are insufficient for the SCW light-conversion concept to be used in general lighting with bright light-emitting semiconductors based on GaN (also Al and/or In, especially InGaN).
Ageing of the plastic matrix/polymer matrix covering a semiconductor in light-emitting diodes, due to environmental effects as well as the short-wavelength radiation emitted by the semiconductors, can lead to changes in the range of emitted wavelengths, and therefore to a color shift of the light-emitting diodes, to a change in the radiation characteristics as well as to a change in the brightness of the emitted light.
This ageing leads to an insufficient long-term operating time of the light-emitting diodes, and currently restricts their use significantly, particularly in general lighting.
The opto-electronic semiconductor component is already known from WO 01/50540. Specifically, it describes a potting compound which is based on epoxy resin systems or similar materials, such as epoxy-novolac blends. In this case, particularly, a UV light-stabilizing component is also included with a proportion of up to 2% by weight. But stabilizers used in this capacity have hitherto exclusively been organic materials, which are described in more detail in CA 2 185 878 and U.S. Pat. No. 5,824,722, for example. These are pure radical traps, however, which only partly fulfill their function. Under the operating conditions in which thermal, moisture and radiation stresses occur in combination, these stabilizers are not sufficiently long-term stable, lose their effectiveness owing to migration, or become chemically modified.