SILICONE COMPOSITIONS AND THEIR APPLICATIONS

Abstract

Provided are fast curing two-part condensation curable silicone compositions which cure by using titanium and/or zirconium based catalysts to generate cured gel materials which are suitable for encapsulating and/or potting electrical and/or electronic articles.

Claims

1. A multiple part condensation curable gel composition comprising: (i) at least one condensation curable silyl terminated polymer having at least two hydroxyl functional groups per molecule and a viscosity ≤1000 mPa.Math.s at 25° C.; (ii) a cross-linker selected from silyl functional molecules having at least two silyl groups, each silyl group containing at least two hydrolysable groups, and having a viscosity ≤1000 mPa.Math.s at 25° C., provided such viscosity is at least 75% of the viscosity of polymer (i); (iii) a condensation catalyst selected from the group consisting of titanates, zirconates, and combinations thereof; and (iv) one or more reinforcing and/or non-reinforcing filler(s); wherein: (a) catalyst (iii) and filler(s) (iv) are not stored together before cure of the composition; (b) the ratio of Si—OH groups:Si-hydrolysable groups in the composition is from 0.4:1 to 0.95:1; and which upon curing (c) upon curing the composition has a tack free time of ≤1 hour and a flip over time of ≤3 hours.

2. The multiple part condensation curable gel composition in accordance with claim 1, wherein cross-linker (ii) is a silicone or an organic polymer chain bearing alkoxy functional terminal groups.

3. The multiple part condensation curable gel composition in accordance with claim 1 wherein cross-linker (ii) is a silicone polymer chain bearing alkoxy functional terminal groups.

4. The multiple part condensation curable gel composition in accordance with claim 1, wherein polymer (i) additionally comprises polydiorganosiloxanes which have one silanol containing terminal group and one unreactive terminal group.

5. The multiple part condensation curable gel composition in accordance with claim 1, wherein cross-linker (ii) additionally comprises silyl functional molecules having at least two silyl groups, where at least one silyl group contains one hydrolysable group.

6. The multiple part condensation curable gel composition in accordance with claim 1, wherein the composition is stored in two-parts, i) a base part comprising polymer (i) and filler(s) (iv), and ii) a curing part comprising cross-linker (ii) and catalyst (iii).

7. The multiple part condensation curable gel composition in accordance with claim 1, which additionally comprises one or more thermally and/or electrically conductive filler(s).

8. The multiple part condensation curable gel composition in accordance with claim 1 which additionally comprises one or more adhesion promoters in an amount of from 0.1 to 2 wt. % of the total composition.

9. The multiple part condensation curable gel composition in accordance with any claim 1 wherein catalyst (iii) is present in a molar amount which is at least 50% of the molar amount of water present in the composition from filler(s) (iv), as determined in accordance with ISO 787-2:1981.

10. The multiple part condensation curable gel composition in accordance with claim 1, wherein cross-linker (ii) has a viscosity ≤1000 mPa.Math.s at 25° C., provided such viscosity is at least 90% of the viscosity of polymer (i).

11. A method of preparing a cured gel material from the multiple part condensation curable gel composition in accordance with claim 1, the method comprising: mixing the multiple parts of the condensation curable gel composition together to form a mixture; and applying the mixture onto a substrate and allowing to cure.

12. A cured gel material which is the reaction product of the multiple part condensation curable gel composition in accordance with claim 1, wherein: (a) catalyst (iii) and filler(s) (iv) are not stored together before cure of the composition; (b) the molar ratio of Si—OH groups:Si-alkoxy groups in the composition is from 0.4:1 to 0.95:1; and which (c) upon curing the composition has a tack free time of ≤1 hour and a flip over time of ≤3 hours.

13. An electrical or electronic part encapsulated or potted with the cured gel material in accordance with claim 12, wherein the electrical or electronic part is: i) a metal substrate selected from the group consisting of gold, silver, aluminium, copper, and electroless nickel; and/or ii) a polymeric substrate selected from the group consisting of FR4, Nylon, polycarbonate, polymethylmethacrylate, polybutylene terephthalate, and liquid crystal polymers.

14. An electrical or electronic part encapsulated or potted with the cured gel material in accordance with claim 12, comprising a light emitting device comprising one or more a light-emitting diodes (LED), or liquid crystal displays (LCD).

15. An electrical or electronic part encapsulated or potted with the cured gel material in accordance with claim 12, selected from the group consisting of a chip, one or more wires, one or more sensors, one or more electrodes, integrated circuits (ICs), power devices, insulated gate bipolar transistor (IGBT), a rectifier, a Schottky diode, a PiN diode, a merged PiN/Schottky (MPS) rectifier and Junction barrier diode, bipolar junction transistors (BJTs), a thyristor, a metal oxide field effect transistor (MOSFET), a high electron mobility transistor (HEMT), static induction transistors (SIT), and a power transistor.

16. An encapsulant or a pottant for electrical and/or electronic devices, solar photovoltaic modules and/or light emitting diodes, wherein the encapsulant or pottant is formed from the multiple part condensation curable gel composition in accordance with claim 1.

17. Electronic devices, solar photovoltaic modules and/or light emitting diodes comprising an encapsulant or a pottant, wherein the encapsulant or pottant comprises the cured gel material in accordance with claim 12.

18. The electronic devices, solar photovoltaic modules and/or light emitting diodes in accordance with claim 17, selected from the group consisting of a chip, one or more wires, one or more sensors, one or more electrodes, integrated circuits (ICs), power devices, insulated gate bipolar transistor (IGBT), a rectifier, a Schottky diode, a PiN diode, a merged PiN/Schottky (MPS) rectifier and Junction barrier diode, bipolar junction transistors (BJTs), a thyristor, a metal oxide field effect transistor (MOSFET), a high electron mobility transistor (HEMT), static induction transistors (SIT), and a power transistor.

Description

EXAMPLES

[0108] The following provides details of the ingredients listed below in Tables 1 and 4: [0109] Adhesion promoter 1 was a mixture (by weight) of 53.5% of methyl trimethoxysilane, 27.4% of 3-glycidoxypropyl trimethoxy silane and 21.8% of 3-aminopropyl triethoxy silane pre-condensed; [0110] Filler 1 was untreated quartz sold under the Trade mark Sebelco® 708 Quartz having a particle size of 7 to 8 μm. The moisture content of Sebelco° 708 Quartz is around 0.24% in weight determined by ISO 787-2:1981; [0111] Filler 2 was untreated quartz sold under the Trade mark Sikron® SF600 Quartz having a particle size of about 3 μm. The moisture content of Sikron SF600 is around 0.24% in weight determined by ISO 787-2:1981; [0112] The conductive filler used was a commercially available aluminium trihydroxide, sold under the trade name HUAYA® LA4 sold by Foshan Huaya Superfine Powder Co. Ltd. It was used untreated and has a particle size of 15-17 μm, a moisture content of ≤0.4 wt. % and a pH of about 8.5. [0113] Cross-linker 1 was a polydimethylsiloxane terminated with —(Me).sub.2Si—CH.sub.2—CH.sub.2—Si(OMe).sub.3 groups having a viscosity of 450mPa.s at 25° C.; and [0114] Cross-linker 2 was a polydimethylsiloxane terminated with —(Me).sub.2Si—CH.sub.2—CH.sub.2—Si(OMe).sub.3 groups having a viscosity of 2200 mPa.s at 25° C.

[0115] All viscosity measurements were made in accordance with ASTM D4287-00 using a Brookfield. DV-III Ultra Rheometer type cone/plate rheometer with spindle No. 3 rotated at 100 rpm at room temperature (about 25° C.) unless otherwise indicated.

[0116] The terms “silanol”, “hydroxysilyl”, “SiOH” and silicon bonded hydroxyl may be used interchangeably in the scope of the present invention, to indicate a condensation curable silyl terminating group of a polymer, bearing at least one hydroxyl functional group.

[0117] The terms “alkoxy”, “SiOR” may be used interchangeably in the scope of the present invention, to indicate a condensation curable silyl terminating group of a polymer, bearing at least one hydrolysable functional group.

The terms “ratio SiOH/SiOR” and “ratio silanol/alkoxy groups” may also be used interchangeably, in the scope of the present invention.

[0118] Examples in accordance with the disclosure herein were prepared as indicated in Table 1.

[0119] The compositions identified in the above were prepared via the following process.

Part A

[0120] The polymer(s) was/were mixed for a period of 30 seconds at 2000 rpm in a speedmixer. Then the conductive filler and filler 1 were introduced and the composition was mixed for a further period of 30 seconds at 2000 rpm in a speedmixer.

Part B

[0121] Cross-linker 1 was mixed with the appropriate catalyst and, when present adhesion promoter. The components were mixed for 2×30 seconds in a speedmixer at 2000 rpm. The resulting mixture was either used immediately or was stored in a 300 ml cartridge prior to use to avoid moisture ingress.

TABLE-US-00001 TABLE 1 Compositions of Examples (wt. %) and Comp. 1 Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 1 Base, Part A Dimethylhydroxy terminated 23.53 23.53 Poly dimethyl siloxane- viscosity 75 mPa.s Dimethylhydroxy terminated 47.06 47.06 100.00 Polydimethylsiloxane- viscosity 450 mPa.s trimethyl terminated 23.53 23.53 polydimethylsiloxane viscosity 1000 mPa.s Conductive filler 35.29 35.29 35.29 35.29 Filler 1 17.65 17.65 17.65 17.65 Curing Agent, Part B Cross-linker 1 98.04 98.04 98.62 98.62 99.01 Tetra n-butyl titanate 1.37 1.38 0.50 Tetra t-butyl titanate 1.37 1.38 Adhesion Promoter 0.59 0.59 0.50

[0122] Parts A and B were mixed in the ratios as indicated in Table 2. The Si—OH:Si—OR ratios for each sample was provided as were the viscosity values of each part prior to mixing and of the final composition after parts A and B were mixed.

Mixture of Part A and Part B

[0123] Part A and part B were mixed in accordance to the weight ratio indicated in Table 2 below for a period of 30 seconds at 2000 rpm in a speedmixer 4 times.

TABLE-US-00002 TABLE 2 Features of Examples in Table 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Comp. 1 A:B mix ratio (wt.) 6:1 2:1 6:1 2:1 1:1 OH/SiOR ratio (mol) 0.6 0.5 0.6 0.5 Viscosity of Part A (mPa.s) 3000 2600 3000 2600 450 Viscosity of Part B (mPa.s) 600 600 550 550 460 Viscosity of Mixed (mPa.s) 3200 3400 3200 3300 500

[0124] The resulting compositions were then allowed to cure and a series of physical property tests were undertaken. [0125] (i) The flowability test evaluated the flowability of the sample by allowing a small ball of the material (about 4.7 g) to stand undisturbed on a glass plate at room temperature and 50% relative humidity for a period of an hour and analyzing the base circle caused by the resulting flow. Samples having a diameter measured to be ≥35 mm after the one hour period were considered to have “good” flowability. [0126] (ii) The Tack free time was determined by spreading an uncured sample having a thickness of about 0.35 cm on a clean smooth surface at 25° C. and 50% relative humidity and periodically touching the surface of the sample with a fingertip until the sample does not adhere to the fingertip. [0127] (iii) Flip over time was determined by filling standard sized aluminium cups with samples of the final composition after mixing to a height of about 15 mm. The samples were then cured at either room temperature (about 25° C.) or at 65° C. Periodically a cup was inverted or “flipped-over”. The point in time when the composition had cured sufficiently so that upon inversion there was no substantial movement of the curing composition was deemed to be the Flip over Time and was noted. [0128] (iv) Shore A Hardness samples tested had a 10 mm thickness and were allowed to cure for 7 days at room temperature before testing.

[0129] The results of the physical property testing of the examples are depicted in Table 3 below.

TABLE-US-00003 TABLE 3 Physical Properties of Examples Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Flowability Good Good Good Good Good Tack-Free-Time 1 hr 0.5 hr 50 mins 0.5 hr 55 mins (RT) Flip over time (RT) <3 hrs <3 hrs <3 hrs <3 hrs 6 hrs Flip over 1 hr 1 hr 50 mins 45 mins 1 hr time (65° C.) Shore A 0022 0035 0021 0032 0018 Hardness (ASTM D2240)

[0130] It can be seen from Comp. 1 that it is necessary to include filler, which will provide moisture in the bulk of the composition in order to generate appropriate Flip over times at room temperature.

[0131] A series of further comparative examples were also prepared. They were prepared in accordance with the processes indicated above for the examples using the amounts indicated in Table 4 below.

TABLE-US-00004 TABLE 4 Compositions of Comparative Examples (wt. %) Comp Comp Comp Comp Ex. 2 Ex. 3 Ex. 4 Ex. 5 Base, Part A Dimethylhydroxy terminated 41.49 57.14 47.06 100.00 Polydimethylsiloxane- viscosity-2500 mPa.s) Conductive filler 35.29 Filler 1 42.86 17.65 Filler 2 58.51 Curing Agent, Part B Cross-linker 2 99.01 99.01 99.01 99.01 Tetra n-butyl titanate 0.99 0.99 0.99 0.50 Adhesion promoter 0.49

[0132] Parts A and B of the comparative examples were analogously mixed as described above for the examples in the amounts indicated in Table 5 below. Again, the Si—OH:Si—OR ratios are provided as are the viscosity of each part prior to mixing and of the final composition after parts A and B were mixed.

TABLE-US-00005 TABLE 5 Features of Comparative Examples in Table 4 Comp Comp Comp Comp Ex. 2 Ex. 3 Ex. 4 Ex. 5 A:B mix ratio (wt.) 10:1 7:1 7:1 1:1 OH/SiOR ratio (mol) 1.5 1.1 1.1 Viscosity of Part A (mPa.s) 26,000 7000 18,000 2500 Viscosity of Part B (mPa.s) 2100 2100 2100 2200 Viscosity of Mixed (mPa.s) 18,000 4200 12,000 2350

[0133] The resulting compositions were then allowed to cure and a series of physical property tests were undertaken using the same processes as used in the examples above.

TABLE-US-00006 TABLE 6 Physical Properties of Comparative Examples Comp Comp Comp Comp Ex. 2 Ex. 3 Ex. 4 Ex. 5 Flow-ability Poor Good Poor Good Tack-Free-Time (RT) 8 hrs 3 hrs 2 hrs 50 mins Flip over time (RT) >12 hrs >5 hrs 4 hrs 6 hrs Flip over time (65° C.) >5 hrs >3 hrs 2 hrs 1 hr Hardness (Shore) 00016 00022 0020 0040

[0134] It can be seen that one or both of the flip over time and tack free times of the comparative examples were significantly greater than those of the results in Table 3 above.

[0135] It can also be seen from Comp. Examples 1 and 5 that the absence of a filler has a negative effect on the results. This is thought to be because of the reduction in moisture presence within the composition from the quartz when present.