Encapsulation material for light emitting diodes

Abstract

The invention relates to the use of specific organopolysilazanes as an encapsulation material for light emitting diodes (LED). The organopolysilazane polymers act as insulating filling materials and are stable over temperature and over exposure to ambient UV radiation. The encapsulating material has good thermal stability against discoloration to yellow by aging even at high temperatures which is a key factor for the long lifetime of an LED encapsulant and the LED performance.

Claims

1. A cured encapsulation material for a light emitting diode, wherein an organopolysilazane material, comprising repeating units of formulae (I) and (II) has been subjected to a curing step by treating the material to a temperature in the range of from 80 to 220 C. for a period of from 1 min to 6 h in an inert atmosphere,
[SiR.sup.1R.sup.2NR.sup.3-]x(I)
[SiHR.sup.4NR.sup.5-]y(II) wherein the symbols and indices have the following meanings: R.sup.1 is vinyl or allyl; R.sup.2 is (C.sub.1-C.sub.4)-alkyl, phenyl or H; R.sup.3 is H; R.sup.4 is (C.sub.1-C.sub.4)-alkyl, phenyl or H; R.sup.5 is H; x is 0.03 to 0.075 and y is 2*x to 0.97 with the proviso that x+y:1 and that y can be 0 if R.sup.2 is H.

2. The cured encapsulation material for a light emitting diode according to claim 1, wherein R.sup.1 is vinyl; R.sup.2 is methyl, ethyl, propyl or phenyl; R.sup.3 is H and R.sup.4 is methyl, ethyl, propyl or phenyl; R.sup.5 is H; x is 0.03 to 0.06 and y is 2*x to 0.97.

3. The cured encapsulation material for a light emitting diode according, to claim 1, wherein the organopolysilazane comprises one or more organopolysilazane comprising a repeating unit of formula (I) or formula (I) and formula (II) and one or more repeating units of formula (III) and/or (IV), ##STR00004## wherein R.sup.6, R.sup.7, and R.sup.9 are independently an organic group; R.sup.10 is H or an organic group, and R.sup.8 and R.sup.11 are independently H or an organic group.

4. The cured encapsulation material for a light emitting diode according to claim 3, wherein the symbols in formulae (III) and (IV) have the following meanings: R.sup.6, R.sup.7 and R.sup.9 are independently (C.sub.1-C.sub.8)-alkyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl, R.sup.10 is independently (C.sub.1-C.sub.8)-alkyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl, (C.sub.2-C.sub.6)-alkenyl, (C.sub.4-C.sub.6)-alkadienyl or H and R.sup.8 and R.sup.11 are H, (C.sub.1-C.sub.8)-alkyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl.

5. A crosslinked encapsulation material for a light emitting diode wherein an organopolysilazane material comprising repeating units of formulae (I) and (II) has been subjected to crosslinking by treatment with a base
[SiR.sup.1R.sup.2NR.sup.3].sub.x|(I)
[SiHR.sup.4NR.sup.5].sub.y(II) wherein the symbols and indices have the following meanings: R.sup.1 is C.sub.2-C.sub.6-alkenyl or C.sub.4-C.sub.6-alkadienyl; R.sup.2 is H or an organic group; R.sup.3 is H or an organic group; R.sup.4 is H or an organic group; R.sup.5 is H or an organic group; x is 0.001 to 0.2; and y is 2x to (1x), with the proviso that x+y1 and that y can be 0 if R.sup.2 is H.

6. The cured encapsulation material for a light emitting diode according to claim 1, wherein the molecular weight Mw of the organopolysilazanes is in the range of 2000-150,000.

7. The cured encapsulation material for a light emitting diode according to claim 1, wherein the organopolysilazane material has a viscosity of 100-100,000 mPas at 25 C.

8. The cured encapsulation material for a light emitting diode according to claim 1, wherein the amount of low molecular material with M.sub.w<500 g/mol in the organopolysilazane material is below 15 wt.-%.

9. An LED encapsulated with a cured encapsulation material for a light emitting diode wherein an organopolysilazane material comprising repeating units of formula (I) and (II)
[SiR.sup.1R.sup.2NR.sup.3].sub.x(I)
[SiHR.sup.4NR.sup.5].sub.y(II) wherein the symbols and indices have the following meanings: R.sup.1 is C2-C6-alkenyl or C4-C6-alkadienyl; R.sup.2 is H or an organic group; R.sup.3 is H or an organic group; R.sup.4 is H or an organic group; R.sup.5 is H or an organic group; x is 0.001 to 0.2; y is 2x to (1x), and with the proviso that x+y1 and that y can be 0 if R.sup.2 is H, is applied as a layer in a thickness of from 200 m to 5 mm, and wherein the encapsulation material is a thermally stable, insulating transparent filling material.

10. A process for encapsulating an LED, comprising the steps of a) applying an organopolysilazane material to the LED as an encapsulation layer and b) curing the organopolysilazane of the invention for 1 min to 6 h at a temperature of from 80 C. to 220 C. in an inert atmosphere or air: wherein the organopolysilazane material comprises repeating units of formulae (I) and (II):
[SiR.sup.1R.sup.2NR.sup.3].sub.x(I)
[SiHR.sup.4NR.sup.5].sub.y(II) wherein the symbols and indices have the following meanings: R.sup.1 is C.sub.2-C.sub.6-alkenyl or C.sub.4-C.sub.6-alkadienyl; R.sup.2 is H or an organic group; R.sup.3 is H or an organic group; R.sup.4 is H or an organic group; R.sup.5 is H or an organic group; x is 0.001 to 0.2; and y is 2x to (1x), with the proviso that x+y1 and that y can be 0 if R.sup.2 is H.

11. The process according to claim 10, wherein the curing step b) is carried out in the presence of a catalyst selected from peroxy compounds, azo compounds, Pt-compounds and Pd-compounds.

12. The process according to claim 10, wherein the organopolysilazane material is applied as a layer in a thickness of from 200 nm to 5 mm.

13. An encapsulation material for LED, obtainable by a) providing a crosslinked organopolysilazane material as described in claim 5, b) thermal curing the crosslinked organopolysilazane material by treating the material to a temperature in the range of from 80 C. to 220 C. for a period of from 1 min to 6 h in an inert atmosphere or air.

14. An LED, comprising the material as described in claim 1 as an encapsulating material.

15. An LED, comprising the material as described in claim 13 as an encapsulating material.

16. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein R.sup.1 is (C.sub.2-C.sub.6)-alkenyl or (C.sub.4-C.sub.6)-alkadienyl; R.sup.2 is (C.sub.1-C.sub.8)-alkyl, (C.sub.2-C.sub.6)-alkenyl, (C.sub.3-C.sub.6)-cycloalkyl, (C.sub.6-C.sub.10)-aryl or H; R.sup.3 is H or (C.sub.1-C.sub.8)-alkyl, (C.sub.2-C.sub.6)-alkenyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl; R.sup.4 is H or (C.sub.1-C.sub.8)-alkyl, (C.sub.2-C.sub.6)-alkenyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl; R.sup.5 is H or (C.sub.1-C.sub.8)-alkyl, (C.sub.2-C.sub.6)-alkenyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl; x is 0.02 to 0.1 and y is 2*x to 0.98.

17. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein R.sup.1 is vinyl or allyl; R.sup.2 is (C.sub.1-C.sub.4-alkyl, phenyl or H; R.sup.3 is H; R.sup.4 is (C.sub.1-C.sub.4)-alkyl, phenyl or H; R.sup.5 is H; x is 0.03 to 0.075 and y is 2*x to 0.97.

18. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein R.sup.1 is vinyl; R.sup.2 is methyl, ethyl, propyl or phenyl; R.sup.3 is H and R.sup.4 is methyl, ethyl, propyl or phenyl; R.sup.5 is H; x is 0.03 to 0.06 and y is 2*x to 0.97.

19. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein the organopolysilazane comprises one or more organopolysilazane comprising a repeating unit of formula (I) or formula (I) and formula (II) and one or more repeating units of formula (III) and/or (IV), ##STR00005## wherein R.sup.6, R.sup.7, R.sup.8, R.sup.9, R.sup.10 are independently an organic group; R.sup.10 is H or an organic group, and R.sup.8 and R.sup.11 are independently H or an organic group.

20. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein the symbols in formulae (Ill) and (IV) have the following meanings: R.sup.6, R.sup.7 and R.sup.9 are independently (C.sub.1-C.sub.8)-alkyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl, R.sup.10 is independently (C.sub.1-C.sub.8)-alkyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl, (C.sub.2-C.sub.6)-alkenyl, (C.sub.4-C.sub.6)-alkadienyl or H and R.sup.8 and R.sup.11 are H, (C.sub.1-C.sub.8)-alkyl, (C.sub.3-C.sub.6)-cycloalkyl or (C.sub.6-C.sub.10)-aryl.

21. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein the molecular weight Mw of the organopolysilazanes is in the range of 2000-150,000.

22. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein the organopolysilazane material has a viscosity of 100-100,000 mPas at 25 C.

23. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein the amount of low molecular material with Mw <500 g/mol in the organopolysilazane material is below 15 wt.-%.

24. The crosslinked encapsulation material for a light emitting diode according to claim 5, wherein the organopolysilazane material is applied as a layer in a thickness of from 200 m to 5 mm.

Description

EXAMPLES

Synthesis Examples

(1) The following examples are meant to demonstrate the base-catalyzed crosslinking of low molecular weight oligomeric organosilazanes to produce higher molecular weight polysilazanes useful for application as bulk encapsulant. Besides the higher molecular weight, these polysilazanes are distinguished by a high-viscous oil-like appearance and a low weight loss on heating.

(2) The following examples demonstrate the base catalyzed crosslinking of the organosilazanes Durazane 1033 (formerly ML-33) and DURAZANE-1800 (formerly HTT 1800) available from AZ Electronic Materials Germany GmbH, Wiesbaden, Germany.

Example No. 1

(3) A 250 ml flask was purged with dry nitrogen and charged with 50 g HTT-1800 and 100 g n-heptane. After cooling down to 0 C., 0.5 g of potassium-hexamethyldisilazane were added. After addition of the catalyst, gas formation could be observed. The mixture was stirred for 2 h at 0 C. and for additional 2 h at 20 C. Then 0.5 g chlorotrimethylsilane were added. The precipitate was removed by filtration and all of the solvent was removed by evaporation under reduced pressure.

(4) Yield: 47 g of a colorless to slightly yellow viscous oil.

Example No. 2

(5) A 250 ml flask was purged with dry nitrogen and charged with 25 g HTT-1800, 25 g ML-33 and 100 g THF. After cooling down to 0 C., 0.5 g of potassium-hexamethyldisilazane were added. After addition of the catalyst, gas formation could be observed. The mixture was stirred for 2 h at 0 C. and for additional 2 h at 20 C. Then 0.5 g chlorotrimethylsilane were added. The precipitate was removed by filtration and all of the solvent was removed by evaporation under reduced pressure.

(6) Yield: 48 g of a colorless viscous oil.

Example No. 3

(7) A 250 ml flask was purged with dry nitrogen and charged with 16.7 g HTT-1800, 33.3 g ML-33 and 100 g 1,4-Dioxane. After cooling down to 0 C., 0.5 g of potassium-hexamethyldisilazane were added. After addition of the catalyst, gas formation could be observed. The mixture was stirred for 2 h at 0 C. and for additional 2 h at 20 C. Then 0.5 g chlorotrimethylsilane were added. The precipitate was removed by filtration and all of the solvent was removed by evaporation under reduced pressure.

(8) Yield: 47 g of a colorless viscous oil.

Example No. 4

(9) A 250 ml flask was purged with dry nitrogen and charged with 12.5 g HTT-1800, 37.5 g ML-33 and 100 g THF. After cooling down to 0 C. 0.3 g of sodium-amide were added. After addition of the catalyst, gas formation could be observed. The mixture was stirred for 2 h at 0 C. and for additional 2 h at 20 C. and finally another 2 h at 40 C. Then 0.5 g chlorotrimethylsilane were added. The precipitate was removed by filtration and all of the solvent was removed by evaporation under reduced pressure.

(10) Yield: 46 g of a colorless viscous oil.

(11) TABLE-US-00001 TABLE 1 Summary of the Synthesis Examples Molecular Viscosity Example Raw material Solvent Catalyst Temperature weight* Appearance [mPas]/25 C. 1. HTT-1800 Heptane KN(SiMe.sub.3).sub.2 0-20 C. 4230 liquid/oil 21300 2. HTT-1800:ML-33 = 1:1 THF KN(SiMe.sub.3).sub.2 0-20 C. 5750 liquid/oil 42400 3. HTT-1800:ML-33 = 1:2 Dioxane KN(SiMe.sub.3).sub.2 0-20 C. 4980 liquid/oil 37600 4. HTT-1800:ML-33 = 1:3 THF NaH 0-40 C. 6100 liquid/oil 50600 ML-33 2210 liquid 19 (reference) HTT- 2390 liquid 80 1800 (reference) *the molecular weight was analyzed by GPC (size exclusion chromatography) using Polystyrene standards

(12) By comparing Examples 1 to 4, it can be demonstrated that it is possible to synthesize liquid oil-like polysilazanes by base catalyzed crosslinking. The viscosity is controlled by adjusting the amount and type of catalyst, the solvent and the reaction temperature and time. By using different types and mixtures of the raw materials, it is possible to determine the organic moieties at the silicon and the nitrogen atom of the silazane backbone. In Examples 1 to 4 the ratio of hydrogen, methyl and vinyl bound to the silicon was varied.

Application Examples

Example No. 5 FT-IR Spectrum

(13) FIG. 1 shows the FT-IR spectrum of the above described specimen:

(14) FT-IR trace of surface in contact with air

(15) FT-IR trace of material 500 m below the surface

(16) peak assignment: #1: SiN

(17) #2: SiO #3: SiCH.sub.3 #4: SiH #5: CH #6: NH

(18) Example No. 5 shows two FT-IR traces of the cured material of a specimen exposed to 420 nm radiation in combination with a temperature of 140 C. for 3 days. One is the spectrum of the surface and the second one is of the material 500 m below the surface. Only a small amount of SiO signals is detectable at the surface. The major signals of the SiN, SiH and NH groups still remain unchanged, which proves that only a minor oxidation occurred. The FT-IR of the material 500 m below the surface is almost unchanged polysilazane.

Example No. 6 Curing Process of an Encapsulant on an LED Board

(19) In Example No. 6 the curing process of an encapsulant on an LED board is described.

(20) The mother board of the experiment consisted of 20 LEDs which were mounted on a circuit board. Each LED was connected to a temperature sensor. Two types of LEDs (white and UV (400 nm)) were used. Half of the number of LEDs was coated with the encapsulation material of Synthesis Example 4. The encapsulation material was cured after addition of 0.5% of Peroxan PK 234 (2,2-di(t.-butylperoxy)butane) on the board. Half of the number of LEDs stayed uncoated (for reference).

(21) The curing of the encapsulant involved several steps. The mother board was heated on a hotplate up to 80 C. whilst the encapsulation material was degased in an ultrasonic bath. Then the encapsulation material was also heated up to 80 C. on the hotplate to decrease viscosity and the encapsulation material was filled into a pipette without making air bubbles. The encapsulant material was dispensed slowly and uniformly on the LEDs with the pipette under avoiding of further building of air bubbles. The mother board with the encapsulated LEDs and the uncoated reference LEDs was heated at 120 C. up to 3.5 h in an oven under standard pressure nitrogen.

Example No. 7 Optical Transmission Vs. Wavelength (Before and after UV Radiation and Temperature Exposure)

(22) FIG. 2 shows the optical transmission versus wavelength of cured material of 3 mm thickness. The encapsulation material was cured in two Teflon forms 32 cm with a depth of ca. 3 mm at 120 C. for about 4 h in an oven under standard pressure nitrogen. The cured material was taken out of the Teflon form after cooling up to room temperature.

(23) One cured material was hold back as reference. The other one was treated for 72 h with 120 C. and UV radiation at 400 nm. The optical spectrum of both materials was measured with spectral photometry in an Ulbricht sphere:

(24) before treatment

(25) after treatment at 120 C. and UV radiation for 72 h.

Example No. 8 UV Resistance and Non-Yellowing Properties

(26) The encapsulated LEDs and uncoated LEDs from Example No. 6 were operated (lighting) for 500 h at controlled ambient temperatures.

(27) The change of the emitted light of each LED was monitored periodically.

(28) FIG. 3 shows the emission of the coated white LEDs before and after 500 h of UV radiation treatment. The spectra were corrected for the spectra of the reference LEDs:

(29) mission spectra before temperature and UV radiation treatment

(30) emission spectra after temperature and UV radiation treatment for 500 h.