ELASTOMERIC COMPOSITIONS AND THEIR APPLICATIONS

Abstract

A room temperature curable composition is disclosed. The composition can be used as an encapsulation/potting material. The composition comprises: (i) at least one condensation curable silyl terminated polymer having at least one silicon bonded hydroxyl functional group per molecule; (ii) a cross-linker having at least two hydrolysable groups and selected from certain silanes and/or silyl functional molecules; and (iii) a condensation catalyst selected from the group of titanates and/or zirconates. The molar ratio of the sum of moisture present in the composition and total silicon bonded hydroxyl groups: the catalyst (the molar ratio) is >7:1. When the molar ratio is from >7:1 to 10:1, the molar ratio of total silicon bonded hydroxyl groups:total hydrolysable groups is between 0.1:1 to 0.3:1. When the molar ratio is >10:1, the molar ratio of total silicon bonded hydroxyl groups:total hydrolysable groups is between 0.1:1 to 0.5:1.

Claims

1. A room temperature curable encapsulation/potting material composition; the composition comprising: (i) at least one condensation curable silyl terminated polymer having at least one, optionally at least two, silicon bonded hydroxyl functional group(s) per molecule; (ii) a cross-linker selected from the group consisting of silanes having at least two hydrolysable groups, optionally at least three hydrolysable groups, per molecule; and/or silyl functional molecules having at least two silyl groups, each silyl group containing at least one hydrolysable group; and (iii) a condensation catalyst selected from the group consisting of titanates and/or zirconates; wherein the molar ratio of the sum of moisture present in the composition, as determined in accordance with ISO 787-2:1981, and total silicon bonded hydroxyl groups:the catalyst is >7:1; and (a) when the molar ratio of the sum of moisture present in the composition and total silicon bonded hydroxyl groups:the catalyst is from >7:1 to 10:1, the molar ratio of total silicon bonded hydroxyl groups:total hydrolysable groups is between 0.1:1 to 0.3:1; and (b) when the molar ratio of the sum of moisture present in the composition and total silicon bonded hydroxyl groups:the catalyst is >10:1, the molar ratio of total silicon bonded hydroxyl groups:total hydrolysable groups is between 0.1:1 to 0.5:1.

2. The composition in accordance with claim 1, wherein the molar ratio of total silicon bonded hydroxyl groups:total hydrolysable groups is between 0.1:1 to 0.5:1, and the molar ratio of the sum of moisture present in the composition and total silicon bonded hydroxyl groups: the catalyst is >10:1.

3. The composition in accordance with claim 1, in the form of a gel or an elastomer.

4. The composition in accordance with claim 1, wherein the composition is stored in two parts, the parts having: polymer (i) and cross-linker (ii) in a base part and polymer (i) and catalyst (iii) in a cure part; or having polymer (i) in a base part and cross-linker (ii) and catalyst (iii) in a cure part; or having a first polymer (i) and cross-linker (ii) in a base part and a second polymer (i) and catalyst (iii) in a cure part.

5. The composition in accordance with claim 4, wherein the two parts are mixed in a base part:cure part weight ratio of from 10:1 to 1:1.

6. The composition in accordance with claim 5, wherein polymer (i) and filler are in the base part and cross-linker (ii) and catalyst (iii) are in the cure part.

7. The composition in accordance with claim 6, wherein the filler comprises, or consists of, light scattering particles.

8. The composition in accordance with claim 1, wherein cross-linker (ii) is a silicone or organic polymer chain bearing alkoxy functional terminal groups.

9. The composition in accordance with claim 8, wherein cross-linker (ii) is a polydimethylsiloxane having at least one trialkoxy terminal group.

10. The composition in accordance with claim 1, further comprising at least one adhesion promoter in an amount of from 0.1 to 2 wt. % of the total composition.

11. A silicone encapsulation potting material, wherein the material is the condensation reaction product of the composition in accordance with claim 1.

12. An encapsulation/potting material for electrical or electronic parts, comprising a composition and/or the condensation reaction product of the composition, wherein the composition is in accordance with claim 1.

13. The silicone encapsulation/potting material in accordance with claim 11, which is optically clear.

14. An electrical or electronic part encapsulated and/or potted with the silicone encapsulation/potting material of claim 11.

15. The electrical or electronic part in accordance with claim 14, wherein the electrical or electronic part comprises a metal substrate selected from the group consisting of gold, silver, aluminum, copper, electroless nickel, and combinations thereof; and/or a polymeric substrate selected from the group consisting of FR4, Nylon, polycarbonate, polymethylmethacrylate, polybutylene terephthalate, liquid crystal polymers, and combinations thereof.

16. The electrical or electronic part in accordance with claim 14, comprising a light emitting device comprising one or more a light-emitting diodes (LED), or liquid crystal displays (LCD).

17. The electrical or electronic part in accordance with claim 14, selected from the group consisting of chips, wires, sensors, electrodes, integrated circuits (ICs), power devices, insulated gate bipolar transistors (IGBTs), rectifiers, Schottky diodes, PiN diodes, merged PiN/Schottky (MPS) rectifiers, junction barrier diodes, bipolar junction transistors (BJTs), thyristors, metal oxide field effect transistors (MOSFETs), high electron mobility transistors (HEMTs), static induction transistors (SITs), power transistors, and combinations thereof.

18. An encapsulant or pottant for electrical and/or electronic devices, solar photovoltaic modules, and/or light emitting diodes, wherein the encapsulant or pottant comprises a composition and/or the condensation reaction product of the composition, and wherein the composition is in accordance with claim 1.

Description

EXAMPLES

[0109] All viscosity measurements were made using a Brookfield cone plate viscometer RV DIII with the most appropriate cone plate at 23 C. unless otherwise indicated.

[0110] Polydimethylsiloxanes having terminal groups containing SiOH (viscosity ca 2,000 mPa.Math.s) exhibit a typical number average molecular weight (Mn) of 22,000 g/mol determined by Gel permeation chromatography (GPC). Cross-linker, trimethoxysilyl terminated polydimethylsiloxane (viscosity ca 2,000 mPa.Math.s) exhibits a typical number average molecular weight (Mn) of 22,000 g/mol determined by GPC.

[0111] Part B was prepared by mixing stepwise ingredients of the table directly after their addition in a speedmixer for 30 seconds at 2300 rpm.

[0112] The compositions used in the following examples were made by mixing part A and part B together in a speedmixer. The part A and Part B were introduced into a speedmixer and were then mixed for four periods of 30 seconds at a speed of 2300 revolutions per minute (rpm). The resulting mixture was poured into an aluminium cup and onto a glass substrate surface and left to cure for 7 days at room temperature.

TABLE-US-00001 TABLE 1a Example Example Example Example Example 1 2 3 4 5 Part A OH terminated 100 100 100 100 100 polydimethylsiloxane (viscosity ca 2,000 mPa .Math. s) Part B Trimethoxysilyl 100 100 100 100 100 terminated polydimethylsiloxane (viscosity ca 2,000 mPa .Math. s) Aminopropyl 0.2 0.2 0.2 0.4 triethoxysilane tetra n-butyl titanate 0.2 0.2 0.3 0.3 0.4 Transparent upon Yes Yes Yes Yes Yes visual inspection Mixing ratio weight 1 1 1 0.7 1 SiOH/SiOR mol 0.36 0.33 0.33 0.23 0.29 ratio SiOH/Ti mole ratio 15.5 15.5 10.3 7.3 7.8

TABLE-US-00002 TABLE 1b Comparatives Comparative Comparative Comparative example 1 Example 2 Example 3 Part A OH terminated 100 100 100 polydimethylsiloxane (viscosity ca 2,000 mPa .Math. s) Part B Trimethoxysilyl 100 100 100 terminated polydimethylsiloxane (viscosity ca 2,000 mPa .Math. s) Aminopropyl 0.2 0.2 triethoxysilane tetra n-butyl titanate 0.4 0.3 0.4 Mixing ratio weight 1 0.5 1 SiOH/SiOR mol ratio 0.36 0.16 0.33 SiOH/Ti mole ratio 7.8 5 7.8

[0113] It will be appreciated that none of these compositions contained filler and as such the moisture value for said compositions upon mixing is zero. Upon visual inspection each sample was considered transparent both before and after cure. Adhesive failure (AF) refers to the situation when the coating detaches cleanly (peels off) from the substrate. Cohesive failure (CF) is observed when the coating itself breaks without detaching form the substrate plate.

TABLE-US-00003 TABLE 2a Example Example Example Example Example 1 2 3 4 5 Bubbles in no no no no no aluminium cup Adhesion to glass CF CF CF CF CF after 7 day cure at room temperature Adhesion to CF CF CF CF CF anodized aluminum after 7 days cure at room temperature Adhesion to epoxy AF CF CF CF CF printed circuit board after 7 days cure at room temperature

[0114] As previously discussed, addition cure materials do not develop sufficient adhesion at room temperature to substrates. Each of examples 1 to 5 exhibit adhesion on glass and aluminium at room temperature. Moreover, good adhesion results were obtained when samples had been placed on printed circuit boards after 7 days of cure at room temperature in respect of examples 2 to 5. Example 1 did not contain any adhesion promoter, which, it is believed, consequently resulted in its adhesive failure on epoxy printed circuit boards after a 7 day cure at room temperature. This indicates that, in the absence of adhesion promoter, whilst the composition of Example 1 is perfectly adequate for adhering to many substrates it has a comparatively limited adhesion profile, compared to examples 2 to 5 which suggests that it may have limited potential use in the absence of an adhesion promoter.

TABLE-US-00004 TABLE 2b Comparative Comparative Comparative example 1 example 2 example 3 Bubbles in yes yes no aluminium cup Adhesion to glass CF CF CF after 7 day cure at room temperature Adhesion to anodized CF CF CF aluminum after 7 days cure at room temperature Adhesion to epoxy AF CF AF printed circuit board after 7 days cure at room temperature

[0115] Unwanted bubbling was observed in comparative examples 1 and 2. Without being bound to any current theory, it was thought that this would appear be due to the low SiOH/Ti molar ratio. Whilst bubbles are not observed in comparative example 3, comparative example 3 does contain adhesion promoter and it was found that even with adhesion promotor present, comparative Example 3 failed to show any improvement over example 1 (no adhesion promoter) with respect to adhesion to epoxy circuit board as it too exhibited adhesion failure, despite containing said adhesion promoter. This is unlike examples 2, 3, 4 and 5.