ELASTOMERIC COMPOSITIONS AND THEIR APPLICATIONS

Abstract

The present disclosure generally relates to silicone gels cured via a condensation cure chemistry and their use in encapsulating, sealing or filling of electrical and/or electronic parts, which, compared to conventional known silicone gels, exhibit good bonding to the electrical or electronic parts even when used under high-temperature conditions.

Claims

1. A multi-part condensation curable silicone composition for making a silicone material and/or elastomer, the composition comprising: (i) at least one condensation curable silyl terminated polymer having at least one, optionally at least 2 hydroxyl functional groups per molecule; (ii) a cross-linker selected from the group consisting of; silanes having at least 2 hydrolysable groups, optionally at least 3 hydrolysable groups per molecule, and/or silyl functional molecules having at least 2 silyl groups, each silyl group containing at least one hydrolysable group; (iii) a condensation catalyst selected from the group consisting of titanates and/or zirconates; and (iv) at least one chemical compound that prevents or scavenges the formation of free radicals; wherein polymer (i), cross-linker (ii) and condensation catalyst (iii) are not all in the same part; wherein the molar ratio of total silicon-bonded hydroxyl groups to total hydrolysable groups is between 0.5:1 to 2:1 for silanes (ii) and between 0.5:1 and 10:1 for silyl functional molecules (ii); and wherein the molar ratio of condensation catalyst (iii) M-OR functions to the total silicon-bonded hydroxyl groups is between 0.01:1 and 0.5:1, where M is titanium or zirconium.

2. The multi-part condensation curable silicone composition in accordance with claim 1, wherein the composition is stored in two parts and where the parts are divided as follows: a) polymer (i) and cross-linker (ii) in one part and polymer (i) and condensation catalyst (iii) in the other part; or b) cross-linker (ii) in one part and polymer (i) and condensation catalyst (iii) in the other part; or c) a first polymer (i) and cross-linker (ii) in one part and a second polymer (i) and condensation catalyst (iii) in the other part; or d) polymer (i) in one part and cross-linker (ii) and condensation catalyst (iii) in the other part.

3. The multi-part condensation curable silicone composition in accordance with claim 1, wherein the at least one chemical compound that prevents or scavenges the formation of free radicals (iv) is selected from a primary anti-oxidant, a secondary anti-oxidant, an anti-corrosive additive or a mixture thereof.

4. The multi-part condensation curable silicone composition in accordance with claim 3, wherein: the primary anti-oxidants are selected from pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate), triethylene glycol bis (3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, 4,4-thiobis (6-tert-butyl-m-cresol), (2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)ethyl]-4,6-di-tert-pentylphenyl acrylate), 2,6-di-tert-butyl-4-(4,6-bis (octylthio)-1,3,5-triazin-2-ylamino)phenol, 3,5-bis (1,1-dimethylethyl)-4-hydroxybenzenepropanoic acid thiodi-2,1-ethanediyl ester, 2,4-bis (dodecylthiomethyl)-6-methylphenol, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, N,N-hexane-1,6-diylbis (3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)), octyl-3,5-di-tert-butyl-4-hydroxy-hydrocinnamate, calcium bis (monoethyl(3,5-di-tert-butyl-4-hydroxylbenzyl)phosphonate], 2,2-methylenebis (6-tert-butyl-4-methylphenol), (2-propenoic acid,2-(1,1-dimethylethyl)-6-[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl]-4-methylphenylester), poly(dicyclopentadiene-co-p-cresol), 2,5-di(tert-amyl)hydroquinone and a mixture thereof; and/or the secondary anti-oxidants are selected from tris(2,4-ditert-butylphenyl)phosphite, 0,0-dioctadecylpentaerythritol bis (phosphite), bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphate and a mixture thereof.

5. The multi-part condensation curable silicone composition in accordance with claim 3, wherein the anti-corrosion additive is selected from cyclic compounds containing a triazole structure, a thiadiazole structure, a benzotriazole structure, a mercaptothiozole structure, a mercaptobenzothiazole structure or a benzimidazole structure.

6. The multi-part condensation curable silicone composition in accordance with claim 3, wherein the anti-corrosion additive is selected from 2,5-dimercapto-1,3,4-thiadiazole, N, N-bis (2-Ethylhexyl)-ar-methyl-1H-benzotriazole-1-methanamine, alkylated diphenylamine, zinc diamyldithiocarbamate, and/or methylene bis (dibutyldithiocarbamate).

7. A silicone material which is the condensation reaction product of the multi-part condensation curable silicone composition in accordance with claim 1.

8. A sealant for electrical or electronic parts, comprising the silicone material of claim 7.

9. An electrical or electronic part equipped with the silicone material of claim 7.

10. The electrical or electronic part according to claim 9, wherein the electrical or electronic part is a power device.

11. The electrical or electronic part according to claim 10, wherein the power device is a motor control, a motor control for transport, a power generation system, or a space transportation system.

12. A protection method for a semiconductor chip using the multi-part condensation curable silicone composition in accordance with claim 1.

13. A method of making a silicone material by intermixing the multi-part condensation curable silicone composition of claim 1 to form a mixture and curing the mixture.

14. The silicone material in accordance with claim 7, as an encapsulant or a pottant for electronic devices, solar photovoltaic modules and/or light emitting diodes.

15. (canceled)

16. (canceled)

17. The method in accordance with claim 13, wherein the mixture is applied onto a substrate prior to cure using a dispenser selected from curtain coaters, spray devices, die coaters, dip coaters, extrusion coaters, knife coaters and screen coaters.

18. A gel made from the silicone material of claim 7, for sealing, potting, encapsulating or filling electrical or electronic parts.

19. The multi-part condensation curable silicone composition in accordance with claim 1, wherein polymer (i) has at least 2 hydroxyl functional groups per molecule.

20. The multi-part condensation curable silicone composition in accordance with claim 1, wherein cross-linker (ii) is selected from the group consisting of silanes having at least 3 hydrolysable groups per molecule.

Description

EXAMPLES

[0112] In the following examples the silicone material is solely cured via a condensation pathway. All parts are by weight unless otherwise indicated. All viscosity values were measured at 23 C. using a Brookfield cone plate viscometer (RV DIII) adapting the cone plate and the speed according to the polymer viscosity.

[0113] Materials used: [0114] Polymer (i): OH terminated polydimethylsiloxane (viscosity ca 13,500 mPa.Math.s) [0115] Crosslinker (ii): 1,6 bisBis (trimethoxysilyl) hexane, or 3-mercaptopropyltrimethoxy silane, or Trimethoxysilyl terminated polydimethylsiloxane (viscosity ca 56,000 mPa.Math.s) [0116] Catalyst: tetra n-butyl titanate [0117] Antioxidant: Songnox 11B (Phenol-Phosphite Antioxidant Blend available from Songwon Int.) [0118] Corrosion inhibitor: Cuvan 826 (2,5-dimercapto-1,3,4-thiadiazole derivative available from Vanderbilt Chemicals) [0119] Comparative 2-parts hydrosilylation gel: Sylgard 527 Silicone Dielectric, available from Dow Corning Corporation

[0120] Examples 1 to 4 features compositions in accordance of the present invention. Comparative examples 1 and 2 feature condensation curable compositions which do not contain a chemical compound that prevents or scavenges the formation of free radicals. Comparative examples 3 and 4 feature hydrosilylation curable compositions. The compositions are detailed in Table 1, where the amounts are measured in parts by weight. The total amount is not expected to necessarily be =100 parts total.

[0121] The compositions are stored in two parts until immediately prior to use when they are appropriately mixed.

[0122] The compositions in Examples 1 to 4 were unexpectedly found to be cured in bulk overnight.

TABLE-US-00001 TABLE 1 Comp Comp Comp Comp Ex 1 Ex 2 Ex 3 Ex 4 Ex 1 Ex 2 Ex 3 Ex 4 Part A OH terminated 50 50 50 50 50 50 polydimethylsiloxane (viscosity ca 13,500 mPa .Math. s) Dow Corning 527 Part A 50 50 1,6 bisBis 0.4 0.4 (trimethoxysilyl) hexane Songnox 11B 0.2 0.12 0.2 Cuvan 826 0.3 3- 0.3 mercaptopropyltrimethoxy silane Part B OH terminated 50 50 polydimethylsiloxane (viscosity ca 13,500 mPa .Math. s) Dow Corning 527 50 50 Part B Trimethoxysilyl 12 12 12 12 terminated polydimethylsiloxane (viscosity ca 56,000 mPa .Math. s) tetra n-butyl titanate 0.08 0.04 0.04 0.04 0.08 0.04

[0123] Each prepared composition was evaluated after 7 days to determine penetration and softness, using the texture analyser method: A TA XT plus texture analyser was used to monitor the hardness of the cured elastomer. The probe used is a polycarbonate cylinder terminated by a spherical end. The diameter of the probe and sphere is inch. A return to start program was used. The pre-test speed is 5 mm/s and the trigger force is 0.1 g. The test speed is 1 mm/s. The probe is inserted to a distance of 5 mm in the product and then removed to a distance where no significant force is measured. The maximum positive and negative force is measured and the positive force is reported in Table 2. A higher positive force is representative of a harder gel/elastomer. A higher negative force is representative of a more tacky gel/elastomer.

TABLE-US-00002 TABLE 2 Texture analyser strength (g) Comp Comp Comp Comp (positive force) Ex 1 Ex 2 Ex 3 Ex 4 Ex 1 Ex 2 Ex 3 Ex 4 7 days room 514 139 129 146 195 124 44 Not temperature (RT) cured 7 days RT + 2012 1296 910 3600 Hard Hard Hard NA 3000 h at 225 C. Crust Crust Crust 7 days RT + 5998 6161 673 Hard Hard Hard Hard NA 1000 h at 225 C. Crust Crust Crust Crust

[0124] The results in Table 2 indicate the compositions of Examples 1 to 4 according to the invention provide for gels with improved temperature resistance. Indeed, the gels remain in good shape and do not form a crust on the surface as fast as the Comparative examples 1 and 2 which do not contain the antioxidant or anticorrosion additives. Comparative example 3 is not suitable for purpose as it does not withstand the test conditions, while Comparative example 4 does not cure at all in presence of the selected antioxidant.