Silicone composition based on both condensation/curing reaction and organic-peroxide curing reaction

Abstract

Provided is a thermally conductive silicone composition which need not be stored with cooling or freezing and needs neither a heating nor a cooling step during mounting to bring about a high production efficiency and which gives cured objects that, during heating or cold/heat cycling, can be inhibited from suffering a change in hardness or a deterioration caused by cracking or dislocation. The composition includes a conventional condensation-curable silicone composition, and is cured by a combination of the condensation and curing with an organic peroxide.

Claims

1. A silicone composition relying on both condensation curing reaction and organic peroxide curing reaction, comprising as essential components, (A) 100 parts by weight of an organopolysiloxane capped with hydroxyl at both ends and represented by the general formula (1): ##STR00012## wherein R.sup.1 is each independently an unsubstituted or halogen or cyano-substituted C.sub.1-C.sub.5 alkyl or C.sub.6-C.sub.8 aryl group, and n is such a number that the organopolysiloxane of formula (1) may have a viscosity at 25 C. of the value defined below, the organopolysiloxane having a viscosity at 25 C. of 0.1 to 1,000 Pa.Math.s, (B) 1 to 40 parts by weight of at least one compound selected from a silane compound represented by the general formula (2):
R.sup.2.sub.aSiX.sub.(4-a)(2) wherein R.sup.2 is an unsubstituted or halogen or cyano-substituted C.sub.1-C.sub.3 alkyl, vinyl, or phenyl group, X is a hydrolyzable group, and a is 0 or 1, a (partial) hydrolysate and a (partial) hydrolytic condensate thereof, (C) 0.01 to 20 parts by weight of a condensation catalyst selected from alkyltin ester compounds, titanic acid esters, titanium chelate compounds, organozinc compounds, organoiron compounds, organocobalt compounds, organomanganese compounds, organoaluminum compounds, hexylamine, dodecylamine phosphate, quaternary ammonium salts, alkali metal salts of lower fatty acids, dialkylhydroxylamines, and guanidyl-containing silanes and siloxanes, (D) 0.01 to 10 parts by weight of an organic peroxide selected from peroxy ketals, hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxy esters, and peroxy dicarbonates, (E) 100 to 8,000 parts by weight of a heat-conductive filler having a thermal conductivity of at least 10 W/m.Math.K, and (F) an organopolysiloxane represented by the general formula (3): ##STR00013## wherein R.sup.3 is each independently an unsubstituted or halogen or cyano-substituted monovalent hydrocarbon group, R.sup.4 is each independently an alkyl, alkoxyalkyl, alkenyl, or acyl group, m is an integer of 2 to 100, and b is an integer of 1 to 3, in an amount of 75 to 400 parts by weight per 100 parts by weight of component (A).

2. The silicone composition of claim 1, further comprising (G) at least one compound selected from a silane compound having a group bonded to a silicon atom via a carbon atom and selected from the group consisting of an amino, epoxy, mercapto, acryloyl, and methacryloyl group, and a silicon-bonded hydrolyzable group and a partial hydrolytic condensate thereof, in an amount of 0.01 to 30 parts by weight per 100 parts by weight of component (A).

3. The silicone composition of claim 1, wherein X in formula (2) is an alkenyloxy group.

4. The silicone composition of claim 1, wherein component (C) is selected from the group consisting of tetramethylguanidylpropyltrimethoxysilane, tetramethylguanidylpropylmethyldimethoxysilane, and tetramethylguanidylpropyltris(trimethylsiloxy)silane.

5. The silicone composition of claim 1, component (D) is selected from the group consisting of 1,1-di(t-butylperoxy)cyclohexane, 2,2-di(4,4-di-(t-butylperoxy)cyclohexyl)propane; p-menthanehydroperoxide, diisopropylbenzenehydroperoxide; dicumyl peroxide, t-butyl cumyl peroxide; dibenzoyl peroxide, disuccinic acid peroxide; t-butylperoxy acetate, t-butylperoxy benzoate; and diisopropylperoxy dicarbonate.

6. The silicone composition of claim 1, which cures at room temperature in moist atmosphere.

7. The silicone composition of claim 1, wherein component (A) is a dimethylpolysiloxane capped with hydroxyl at both ends and having a viscosity of 0.7 Pa-s at 25 C.

8. The silicone composition of claim 1, wherein component (B) is selected from the group consisting of phenyltri(isopropenoxy)silane, vinyltri(isopropenoxy)silane, and combinations thereof.

9. The silicone composition of claim 1, wherein component (E) is selected from the group consisting of an aluminum oxide powder with an average particle size of 40 m (thermal conductivity: 27 W/m-K), an aluminum oxide powder with an average particle size of 1.0 m (thermal conductivity: 27 W/m-K), and combinations thereof.

10. The silicone composition of claim 1, wherein component (F) is an organopolysiloxane of the following formula: ##STR00014##

11. The silicone composition of claim 1, wherein component (G) is 3-aminopropyltriethoxysilane.

12. The silicone composition of claim 1, wherein component (H) is a dimethylpolysiloxane capped with trimethylsilyl at both ends and having a viscosity of 0.1 Pa s at 25 C.

13. The silicone composition of claim 1, wherein the composition is cured to form a cured composition, and wherein the cured composition does not exhibit cracking/slipping upon standing at 232 C. and 505% RH for 7 days, followed by keeping horizontal at 160 C. for 500 hours.

14. The silicone composition of claim 1, wherein the composition is cured to form a cured composition, and wherein the cured composition does not exhibit cracking/slipping upon placing vertically and thermal cycling between 40 C./30 minutes and 160 C./30 minutes over 500 cycles.

15. The silicone composition of claim 1, wherein the composition further comprises an unreactive organo(poly)siloxane.

16. The silicone composition of claim 1, wherein the composition further comprises at least one additive selected from the group consisting of antioxidants, reinforcing or non-reinforcing fillers, thixotropy enhancing agents, colorants, and combinations thereof.

17. The silicone composition of claim 16, wherein the antioxidant is 2,6-di-t-butyl-4-methylphenol.

18. The silicone composition of claim 16, wherein the reinforcing or non-reinforcing filler is calcium carbonate.

19. The silicone composition of claim 16, wherein the thixotropy enhancing agent is a polyether.

Description

EXAMPLES

(1) The invention is specifically described below with reference to Examples and Comparative Examples, but not limited thereto.

(2) First there were furnished the following components, from which silicone compositions of the invention were prepared.

(3) [Component (A)]

(4) A-1: dimethylpolysiloxane capped with hydroxyl at both ends and having a viscosity of 0.7 Pa-s at 25 C.
[Component (B)] B-1: phenyltri(isopropenoxy)silane

(5) ##STR00006## B-2: vinyltri(isopropenoxy)silane

(6) ##STR00007##
[Component (C)] C-1: tetramethylguanidylpropyltrimethoxysilane

(7) ##STR00008##
[Component (D)] D-1: 1,1-di(t-butylperoxy)cyclohexane

(8) ##STR00009##
[Component (E)] E-1: aluminum oxide powder with an average particle size of 40 m (thermal conductivity: 27 W/m-K) E-2: aluminum oxide powder with an average particle size of 1.0 m (thermal conductivity: 27 W/m-K)
[Component (F)] F-1: organopolysiloxane of the following formula

(9) ##STR00010##
[Component (G)] G-1: 3-aminopropyltriethoxysilane

(10) ##STR00011##
[Other component (H)] H-1: dimethylpolysiloxane capped with trimethylsilyl at both ends and having a viscosity of 0.1 Pa s at 25 C.

Examples 1 to 5 and Comparative Examples 1 to 6

(11) Preparation of Silicone Compositions

(12) Silicone compositions were prepared by mixing the foregoing components (A) to (E) and optionally components (F), (G), and other component (H) in the amounts shown in Tables 1 and 2 according to the following procedure. Specifically, a 5-liter Planetary Mixer (Inoue Mfg., Inc.) was charged with components (A), (E), (F), and (H), which were mixed at 130 C. for 3 hours. The mixture was cooled to room temperature, to which components (B), (C), (D), and (G) were added. The mixture was uniformly mixed to give a silicone composition. Each of the compositions thus obtained was measured for viscosity and heat conductivity, and the cured product thereof measured for hardness and hardness change, by the test methods described below. In addition, hardness change upon 160 C. heat exposure, and resistance to cracking/slipping upon 160 C. heat exposure and thermal cycling between 40 C./30 minutes and 160 C./30 minutes were evaluated. The results are shown in Tables 1 and 2.

(13) [Viscosity]

(14) An absolute viscosity of each composition was measured at 25 C. by a Malcolm viscometer (type PC-1T).

(15) [Thermal Conductivity]

(16) Each composition was wrapped with food wrap and measured for thermal conductivity by TPA-501 (Kyoto Electronics Manufacturing Co., Ltd.).

(17) [Hardness and Hardness Change]

(18) Each composition was shaped into sheets of 2.0 mm thick, which were allowed to stand at 232 C. and 505% RH for 7 days, and a laminate of 6 sheets was measured by an Asker C Durometer. After the hardness measurement, the sheets were further held in 160 C. environment for 500 hours, following which hardness was measured by Asker C Durometer.

(19) [Cracking/Slipping Test]

(20) Each composition, 0.2 mL, was coated on a glass plate and overlaid with another glass plate via a spacer of 1.0 mm, and the assembly was secured by a clip. The assembly was subjected to test (1) of allowing to stand at 232 C. and 505% RH for 7 days, and then keeping horizontally at 160 C. for 500 hours, and test (2) of placing vertically and thermal cycling between 40 C./30 minutes and 160 C./30 minutes over 500 cycles. Each specimen was observed for cracks or slipping.

(21) TABLE-US-00001 TABLE 1 Formulation Example (parts by weight) 1 2 3 4 5 (A) A-1 100 100 100 100 100 (B) B-1 11.3 11.3 11.3 11.3 B-2 9.2 (C) C-1 2.5 2.5 2.5 2.5 2.5 (D) D-1 3.8 3.8 1.9 3.8 3.8 (E) E-1 1,688 1,688 1,688 1,688 1,688 E-2 1,125 1,125 1,125 1,125 1,125 (F) F-1 75 75 75 75 150 (G) G-1 2.5 (H) H-1 75 75 75 75 Total of component (E) 2,813 2,813 2,813 2,813 2,813 Test results Viscosity (Pa .Math. s) 50 52 54 60 35 Thermal conductivity (W/m .Math. K) 3.4 3.3 3.5 3.4 3.4 Hardness: initial 56 60 56 65 50 Hardness: 160 C./500 hours 36 48 33 44 34 Cracking/slipping: (1) not not not not not 160 C./500 hours observed observed observed observed observed Cracking/slipping: (2) not not not not not 40 C./30 min .Math. 160 C./30 min, observed observed observed observed observed 500 cycles

(22) TABLE-US-00002 TABLE 2 Formulation Comparative Example (parts by weight) 1 2 3 4 5 6 (A) A-1 100 100 100 100 100 100 (B) B-1 11.3 11.3 11.3 11.3 11.3 11.3 B-2 (C) C-1 2.5 2.5 2.5 25 2.5 (D) D-1 3.8 3.8 3.8 15 (E) E-1 1,688 1,688 5,000 1,688 1,688 1,688 E-2 1,125 1,125 3,332 1,125 1,125 1,125 (F) F-1 75 75 300 75 75 75 (G) G-1 2.5 (H) H-1 75 75 75 75 75 Total of component (E) 2,813 2,813 8,332 2,813 2,813 2,813 Test results Viscosity (Pa .Math. s) 71 73 not 45 putty 54 Thermal conductivity (W/m .Math. K) 3.4 3.4 become 3.4 form (un- 3.3 Hardness: initial 49 53 greasy not measurable) 60 Hardness: 160 C./500 hours 54 59 cured 46 Cracking/slipping: (1) observed observed observed 160 C./500 hours Cracking/slipping: (2) observed observed observed 40 C./30 min .Math. 160 C./30 min, 500 cycles

(23) The silicone composition of the invention eliminates not only a need for refrigeration or freezing during storage, but also a need for heating/cooling steps in its application since it cures at room temperature when allowed to stand in moist atmosphere. The results in Tables 1 and 2 reveal that blending a specific amount of organic peroxide as component (D) is successful in improving deep section cure and preventing a cured product from deteriorating owing to hardness changes and cracking/slipping upon heat exposure and thermal cycling.

(24) The invention is not limited to the forgoing embodiments. The embodiments are for illustrative purpose only, and any embodiment which has substantially the same constitution as the technical ideas set forth in the claims and which exerts equivalent functions and results is included within the technical scope of the invention.