THERMAL CONDUCTIVE SILICONE COMPOSITION

Abstract

A thermal conductive silicone composition comprises: (A) a liquid organopolysiloxane having at least two silicon atom-bonded alkenyl groups with 2 to 6 carbon atoms per molecule; (B) a thermal conductive filler with an average particle size of from 5 to 50 μm; (C) a thermal conductive filler with an average particle size of at least 0.1 μm and less than 5 μm; and (D) a carbasilatrane derivative. Optionally, the composition further comprises: (E) an organosiloxane having at least one silicon atom-bonded hydrogen atom per molecule; and/or (F) a hydrosilylation reaction catalyst. The composition exhibits excellent storage stability and handleability despite containing a large quantity of a thermal conductive filler to exhibit high thermal conductivity.

Claims

1. A thermal conductive silicone composition comprising: (A) 100 parts by mass of a liquid organopolysiloxane with a kinematic viscosity at 25° C. of 10 to 100,000 mm.sup.2/s, and having at least two silicon atom-bonded alkenyl groups with 2 to 12 carbon atoms per molecule; (B) from 100 to 500 parts by mass of a thermal conductive filler with an average particle size of from 5 to 50 μm; (C) from 10 to 100 parts by mass of a thermal conductive filler with an average particle size of at least 0.1 μm and less than 5 μm; and (D) from 0.1 to 5 parts by mass of a carbasilatrane derivative represented by the following general formula: ##STR00007##  wherein R.sup.1 is an alkyl group with 1 to 6 carbon atoms or an alkoxy group with 1 to 3 carbon atoms, R.sup.2 are the same or different hydrogen atoms or alkyl groups with 1 to 6 carbon atoms, and R.sup.3 are the same or different and are selected from groups represented by the following general formulae:
—R.sup.6—SiR.sup.4.sub.a(OR.sup.5).sub.(3-a)
—R.sup.7—O—R.sup.8  wherein R.sup.4 is an alkyl group with 1 to 6 carbon atoms, R.sup.5 is an alkyl group with 1 to 3 carbon atoms, R.sup.6 is an alkylene group with 2 to 6 carbon atoms or an alkylenoxyalkylene group with 4 to 12 carbon atoms, R.sup.7 is an alkylene group with 2 to 6 carbon atoms, R.sup.8 is an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms or an acyl group with 2 to 6 carbon atoms, and “a” is 0, 1 or 2.

2. The thermal conductive silicone composition according to claim 1, wherein component (B) is selected from the group consisting of aluminum hydroxide, aluminum oxide, and zinc oxide.

3. The thermal conductive silicone composition according to claim 1, wherein component (C) is selected from the group consisting of aluminum hydroxide, aluminum oxide, and zinc oxide.

4. The thermal conductive silicone composition according to claim 1, wherein components (B) and (C) are surface-treated with a surface treating agent in the presence of component (A), then component (D) is added to a mixture of components (A) to (C).

5. The thermal conductive silicone composition according to claim 4, wherein the surface treating agent is selected from the group consisting of hexamethyldisilazane, tetramethyl divinyl disilazane, methyl trimethoxysilane, vinyl trimethoxysilane, and dichloro dimethylsilane.

6. The thermal conductive silicone composition according to claim 1, wherein component (D) is a carbasilatrane derivative represented by the following formula: ##STR00008##

7. The thermal conductive silicone composition according to claim 1, further comprising: (E) an organosiloxane having at least one silicon atom-bonded hydrogen atom per molecule, in an amount of from 1 to 30 parts by mass relative to 100 parts by mass of component (A).

8. The thermal conductive silicone composition according to claim 1, further comprising: (F) a catalytic amount of a hydrosilylation reaction catalyst.

9. The thermal conductive silicone composition according to claim 7, further comprising: (G) a liquid organosiloxane with a kinematic viscosity at 25° C. of 1 to 100 mm.sup.2/s, and free of an alkenyl group and a silicon atom-bonded hydrogen atom, in an amount of from 1 to 30 parts by mass per 100 parts by mass of component (A).

10. The thermal conductive silicone composition according to claim 1, further defined as a curable thermal conductive silicone composition comprising a part (I) and a part (II), wherein the composition further comprises: ##STR00009## (E) from 1 to 30 parts by mass of an organosiloxane having at least one silicon atom-bonded hydrogen atom per molecule, to form part (I); and (F) a catalytic amount of a hydrosilylation reaction catalyst, to form part (II).

11. The curable thermal conductive silicone composition according to claim 10, further comprising: (G) a liquid organosiloxane with a kinematic viscosity at 25° C. of 1 to 100 mm.sup.2/s, and free of an alkenyl group and a silicon atom-bonded hydrogen atom, in an amount of from 1 to 30 parts by mass per 100 parts by mass of component (A).

12. The curable thermal conductive silicone composition according to claim 10, wherein component (B) is selected from the group consisting of aluminum hydroxide, aluminum oxide, and zinc oxide.

13. The curable thermal conductive silicone composition according to claim 10, wherein component (C) is selected from the group consisting of aluminum hydroxide, aluminum oxide, and zinc oxide.

14. The thermal conductive silicone composition according to claim 8, further comprising: (G) a liquid organosiloxane with a kinematic viscosity at 25° C. of 1 to 100 mm.sup.2/s, and free of an alkenyl group and a silicon atom-bonded hydrogen atom, in an amount of from 1 to 30 parts by mass per 100 parts by mass of component (A).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0032] The thermal conductive silicone composition of the present invention will be explained in detail.

[0033] Component (A) is a primary component in the present composition and is an organopolysiloxane having at least two silicon atom-bonded alkenyl groups with from 2 to 12 carbon atoms per molecule. Examples of the alkenyl groups include vinyl groups, allyl groups, butenyl groups, pentenyl groups, hexenyl groups, heptenyl groups, octenyl groups, nonenyl groups, decenyl groups, undecenyl groups, and dodecenyl groups, among which vinyl groups are preferable. In addition, examples of groups bonding to silicon atoms other than the alkenyl groups in component (A) include alkyl groups having from 1 to 12 carbon atoms such as methyl groups, ethyl groups, propyl groups, isopropyl groups, butyl groups, isobutyl groups, tert-butyl groups, pentyl groups, neopentyl groups, hexyl groups, cyclohexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecyl groups, and dodecyl groups; aryl groups having from 6 to 20 carbon atoms such as phenyl groups, tolyl groups, xylyl groups, and naphthyl groups; aralkyl groups having from 7 to 20 carbon atoms such as benzyl groups, phenethyl groups, and phenylpropyl groups; and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine atoms, chlorine atoms, or bromine atoms. Furthermore, the silicon atoms in component (A) may have small amounts of hydroxyl groups or alkoxy groups such as methoxy groups or ethoxy groups within a range that does not impair the object of the present invention.

[0034] Examples of the molecular structure of component (A) include a straight-chain structure, a partially branched straight-chain structure, a branched-chain structure, a cyclic structure, and a three-dimensional reticular structure. Component (A) may be one type of organopolysiloxane having these molecular structures or may be a mixture of two or more types of organopolysiloxanes having these molecular structures.

[0035] Examples of component (A) include a dimethylpolysiloxane capped at both molecular terminals with trimethylsiloxy groups, a dimethylpolysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups, a dimethylpolysiloxane capped at both molecular terminals with methylphenylvinylsiloxy groups, a copolymer of dimethylsiloxane and methylphenylsiloxane capped at both molecular terminals with trimethylsiloxy groups, a copolymer of dimethylsiloxane and methylphenylsiloxane capped at both molecular terminals with dimethylvinylsiloxy groups, a copolymer of dimethylsiloxane and methylvinylsiloxane capped at both molecular terminals with trimethylsiloxy groups, a copolymer of dimethylsiloxane and methylvinylsiloxane capped at both molecular terminals with dimethylvinylsiloxy groups, a methyl(3,3,3-trifluoropropyl)polysiloxane capped at both molecular terminals with dimethylvinylsiloxy groups, a copolymer of dimethylsiloxane and methylvinylsiloxane capped at both molecular terminals with silanol groups, a dimethylpolysiloxane capped at both molecular terminals with silanol groups, a copolymer of dimethylsiloxane and methylphenylsiloxane capped at both molecular terminals with silanol groups, an organopolysiloxane consisting of a siloxane unit represented by the formula: CH.sub.3SiO.sub.3/2 and a siloxane unit represented by the formula: (CH.sub.3).sub.2SiO.sub.2/2, an organopolysiloxane consisting of a siloxane unit represented by the formula: C.sub.6H.sub.5SiO.sub.3/2 and a siloxane unit represented by the formula: (CH.sub.3).sub.2SiO.sub.2/2, an organopolysiloxane consisting of a siloxane unit represented by the formula: (CH.sub.3).sub.3SiO.sub.1/2, a siloxane unit represented by the formula: CH.sub.3SiO.sub.3/2, and a siloxane unit represented by the formula: (CH.sub.3).sub.2SiO.sub.2/2, an organopolysiloxane consisting of a siloxane unit represented by the formula: (CH.sub.3).sub.3SiO.sub.1/2, a siloxane unit represented by the formula: (CH.sub.3).sub.2(CH.sub.2═CH)SiO.sub.1/2, a siloxane unit represented by the formula CH.sub.3SiO.sub.3/2, and a/ siloxane unit represented by the formula: (CH.sub.3).sub.2SiO.sub.2/2; and combinations of two or more thereof.

[0036] Additionally, a kinematic viscosity at 25° C. of component (A) is in a range of from about 10 to about 100,000 mm.sup.2/s, preferably in a range from 10 to 50,000 mm.sup.2/s, alternatively in a range from 10 to 10,000 mm.sup.2/s, and alternatively in a range from 50 to 10,000 mm.sup.2/s. This is because when the kinematic viscosity of component (A) is greater than or equal to the lower limit of the aforementioned range, mechanical properties of a silicone product obtained by curing the silicone composition is improved, and when the kinematic viscosity of component (A) is less than or equal to the upper limit of the aforementioned range, handleability of the silicone composition is improved.

[0037] Component (B) is a thermal conductive filler with an average particle size of from about 5 to about 50 μm, preferably with an average particle size of from about 5 to about 40 μm, alternatively with an average particle size of from about 5 to about 30 μm, alternatively with an average particle size of from about 10 to about 40 μm, and alternatively with an average particle size of from about 10 to about 20 μm. This is because thermal conductive property of the silicone composition is improved when the average particle size of component (B) is in the range above.

[0038] Component (B) is not limited, but is preferably selected from aluminum hydroxide, aluminum oxide or zinc oxide.

[0039] The content of component (B) is in a range of from about 100 to about 500 parts by mass, preferably in a range of from about 100 to about 400 parts by mass, alternatively in a range of from about 100 to about 300 parts by mass, alternatively in a range of from about 150 to about 300 parts by mass, and alternatively in a range of from about 150 to about 250 parts by mass, relative to 100 parts by mass of component (A). This is because when the content of component (B) is greater than or equal to the lower limit of the aforementioned range, thermal conductive property of the silicone composition is improved, and when the content of component (B) is less than or equal to the upper limit of the aforementioned range, handle-ability of the curable silicone composition is improved.

[0040] Component (C) is a thermal conductive filler with an average particle size of at least 0.1 μm and less than 5 μm, preferably with an average particle size of from about 0.1 to about 4 μm, alternatively with an average particle size of from about 0.1 to about 3 μm, alternatively with an average particle size of from about 0.5 to about 4 μm, and alternatively with an average particle size of from about 0.5 to about 3 μm. This is because thermal conductive property of the silicone composition is improved when the average particle size of component (C) is in the range above.

[0041] Component (C) is not limited, but is preferably selected from aluminum hydroxide, aluminum oxide or zinc oxide.

[0042] The content of component (C) is in a range of from about 10 to about 100 parts by mass, preferably in a range of from about 20 to about 100 parts by mass, alternatively in a range of from about 30 to about 100 parts by mass, alternatively in a range of from about 40 to about 100 parts by mass, and alternatively in a range of from about 50 to about 100 parts by mass, relative to 100 parts by mass of component (A). This is because when the content of component (C) is greater than or equal to the lower limit of the aforementioned range, thermal conductive property of the silicone composition is improved, and when the content of component (D) is less than or equal to the upper limit of the aforementioned range, handle-ability of the curable silicone composition is improved.

[0043] Components (B) and (C) are typically surface-treated with a surface treating agent in the presence of component (A), preferably under heating at 60 to 250° C. or under heating at 100 to 200° C.

[0044] The surface treating agent is not limited, but is exemplified by organodisilazane, alkenyl group-containing alkoxysilane, alkyl group-containing lkoxysilane, alkoxy-functional oligosiloxane, cyclic polyorganosiloxane, hydroxyl-functional oligosiloxane, organochlorosilane, or any combination of at least two thereof. The organodisilazane may be hexamethyldisilzane, 1,3-divinyl-trimethyldisilazane, or a mixture of any two or more thereof. The alkenyl group-containing alkoxysilane may be vinyl trimethoxysilane, methylvinyl dimethoxysilane, allyl trimethoxysilane, allylmethyl dimethoxysiane, or a mixture of any two or more thereof. The alkyl group-containing alkoxysilane may be methyl trimethoxysilane, hexyl trimethoxysilane, octyl triethoxysilane, decyl trimethoxysilane, dodecyl trimethoxysilane, tetradecyl trimethoxysilane, octadecyl trimethoxysilane, octadecyl triethoxysilane, or any combination of at least two thereof. The alkoxy-functional oligosiloxane may be (CH.sub.3O).sub.3Si[(OSi(CH.sub.3).sub.2]C.sub.8H.sub.17, (CH.sub.3O).sub.3Si[(OSi(CH.sub.3).sub.2].sub.10C.sub.8H.sub.17, (CH.sub.3O).sub.3Si[OSi(CH.sub.3).sub.2]C.sub.12H.sub.25, (CH.sub.3O).sub.3Si[(OSi(CH.sub.3).sub.2].sub.10C.sub.12H.sub.25, or any combination of ate least two thereof. The hydroxyl-functional oligosiloxane may be dimethyl siloxane or methyl phenyl siloxane. The organochlorosilane may be methyltrichlorosilane, diethyldichlorosilane, or trimethylchlorosilane.

[0045] The amount of the surface treating agent is any quantity sufficient for treating component (B) and (C). The particular quantity may vary depending on factors such as the particular treating agent selected and the surface area and amount of untreated thermal conductive filler for component (B) and (C) to be treated. The treating effective amount may range from 0.01 mass % to 20 mass %, alternatively 0.1 mass % to 15 mass %, and alternatively 0.5 mass % to 5 mass %, based on the mass of components (A) to (C).

[0046] Component (D) is a carbasilatrane derivative represented by the following general formula:

##STR00004##

[0047] In the formula, R.sup.1 is an alkyl group with 1 to 6 carbon atoms or an alkoxy group with 1 to 3 carbon atoms. The alkyl groups are exemplified by methyl groups, ethyl groups and propyl groups, however, methyl groups are preferred from the perspective of economic efficiency and heat resistance. The alkoxy groups are exemplified by methoxy groups, ethoxy groups and propoxy groups.

[0048] In the formula, R.sup.2 are the same or different hydrogen atoms or alkyl groups with 1 to 6 carbon atoms. The alkyl groups are exemplified by methyl groups, ethyl groups, propyl groups, butyl groups, pentyl group and hexyl groups, however, methyl groups are preferred from the perspective of economic efficiency and heat resistance.

[0049] In the formula, R.sup.3 are the same or different and are selected from groups represented by the following general formulae:

—R.sup.6—SiR.sup.4.sub.a(OR.sup.5).sub.(3-a)

—R.sup.7—O—R.sup.8.

[0050] In the formula, R.sup.4 is an alkyl group with 1 to 6 carbon atoms. The alkyl groups are exemplified by methyl groups, ethyl groups, propyl groups, butyl groups, pentyl group and hexyl groups, however, methyl groups are preferred.

[0051] In the formula, R.sup.5 is an alkyl group with 1 to 3 carbon atoms. The alkyl groups are exemplified by methyl groups, ethyl groups and propyl groups.

[0052] In the formula, R.sup.6 is an alkylene group with 2 to 6 carbon atoms or an alkylenoxyalkylene group with 4 to 12 carbon atoms. The alkylene groups are exemplified by ethylene groups, propylene groups, butylene groups, pentylene group, hexylene groups, heptylene groups and octylene groups, however, ethylene groups and propylene groups are preferred from the perspective of economic efficiency. The alkylenoxyalkylene groups are exemplified by ethylenoxyethylene groups, propylenoxyethylene groups, butylenoxypropylene groups and propylenoxypropylene group, however, ethylenoxypropylene groups and propylenoxypropylene groups are preferred from the perspective of economic efficiency.

[0053] In the formula, R.sup.7 is an alkylene group with 2 to 6 carbon atoms. The alkylene groups are exemplified by ethylene groups, propylene groups, butylene groups, pentylene group, hexylene groups, heptylene groups and octylene groups, however, ethylene groups and propylene groups are preferred from the perspective of economic efficiency.

[0054] In the formula, R.sup.8 is an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, or an acyl group with 2 to 6 carbo atoms. The alkyl groups are exemplified by vinyl groups, allyl groups, butenyl groups, pentenyl group and hexenyl groups, however, ally groups are preferred. The acyl groups are exemplified by acetyl groups, propionyl groups, acryl groups, methacryl groups, butyryl groups, isobutyryl groups, however, acetyl groups are preferred.

[0055] In the formula, “a” is 0, 1 or 2, and is preferably 0 or 1.

[0056] The carbasilatrane derivatives for component (D) are exemplified by compounds represented by the following formulae:

##STR00005##

[0057] Methods for synthesizing such carbasilatrane derivatives are known. The disclosures of Japanese Patent No. 3831481 B2 and U.S. Pat. No. 8,101,677 B2 are incorporated herein by reference to show the preparation of the carbasilatrane derivatives.

[0058] The content of component (D) is in an amount of from about 0.1 to about 5 parts by mass, preferably in an amount of from about 0.1 to about 3 parts by mass, alternatively in an amount of from about 0.1 to about 2 parts by mass, relative to 100 parts by mass of the organopolysiloxane in component (A). This is because when the content of component (D) is greater than or equal to the lower limit of the aforementioned range, the thixotropic property of the silicone composition is improved, and when the content of component (D) is less than or equal to the upper limit of the aforementioned range, thermal conductive property of the silicone material is improved.

[0059] The composition may comprise (E) an organosiloxane with at least one silicon atom-bonded hydrogen atom per molecule to form a part (I) in order to improve curability of the composition. Examples of groups bonding to silicon atoms other than hydrogen atoms in component (E) include alkyl groups having from 1 to 12 carbon atoms such as methyl groups, ethyl groups, propyl groups, isopropyl groups, butyl groups, isobutyl groups, tert-butyl groups, pentyl groups, neopentyl groups, hexyl groups, cyclohexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecyl groups, and dodecyl groups; aryl groups having from 6 to 20 carbon atoms such as phenyl groups, tolyl groups, xylyl groups, and naphthyl groups; aralkyl groups having from 7 to 20 carbon atoms such as benzyl groups, phenethyl groups, and phenylpropyl groups; and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine atoms, chlorine atoms, or bromine atoms. Furthermore, the silicon atoms in component (E) may have small amounts of hydroxyl groups or alkoxy groups such as methoxy groups or ethoxy groups within a range that does not impair the object of the present invention.

[0060] Examples of the molecular structure of component (E) include straight-chain, partially branched straight-chain, branched chain, cyclic, and three-dimensional reticular structures, and the molecular structure is preferably a partially branched straight-chain, branched chain, or three-dimensional reticular structure.

[0061] Examples of such component (E) include methylhydrogenpolysiloxanes capped at both molecular terminals with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers capped at both molecular terminals with trimethylsiloxy groups, dimethylpolysiloxanes capped at both molecular terminals with dimethylhydrogensiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers capped at both molecular terminals with dimethylhydrogensiloxy groups, methylhydrogensiloxane-diphenylsiloxane copolymers capped at both molecular terminals with trimethylsiloxy groups, methylhydrogensiloxane-diphenylsiloxane-dimethylsiloxane copolymers capped at both molecular terminals with trimethylsiloxy groups, copolymers consisting of (CH.sub.3).sub.2HSiO.sub.1/2 units and SiO.sub.4/2 units, copolymers consisting of (CH.sub.3).sub.2HSiO.sub.1/2 units, SiO.sub.4/2 units, and (C.sub.6H.sub.5)SiO.sub.3/2 units, and mixtures of two or more types thereof.

[0062] The content of component (E) is in a range of from 1 to 30 parts by mass, preferably in a range of from 1 to 25 parts by mass, alternatively in a range of from 1 to 20 parts by mass, and alternatively in a range of from 5 to 25 parts by mass, relative to 100 parts by mass of component (A). This is because when the content of component (E) is less than or equal to the upper limit of the aforementioned range, mechanical properties of the silicone material are good, whereas when the content of component (E) is greater than or equal to the lower limit of the aforementioned range, curability of the composition is good.

[0063] The composition may comprise (F) a hydrosilylation catalyst to form a part (II) in order to accelerate the curing of the present composition. Examples of component (F) include platinum group element catalysts and platinum group element compound catalysts, and specific examples include platinum-based catalysts, rhodium-based catalysts, palladium-based catalysts, and combinations of at least two types thereof. In particular, platinum-based catalysts are preferable in that the curing of the present composition can be dramatically accelerated. Examples of these platinum-based catalysts include finely powdered platinum; platinum black; chloroplatinic acid, alcohol-modified chloroplatinic acid; chloroplatinic acid/diolefin complexes; platinum/olefin complexes; platinum/carbonyl complexes such as platinum bis(acetoacetate), and platinum bis(acetylacetonate); chloroplatinic acid/alkenylsiloxane complexes such as chloroplatinic acid/divinyltetramethyl disiloxane complexes, and chloroplatinic acid/tetravinyl tetramethyl cyclotetrasiloxane complexes; platinum/alkenylsiloxane complexes such as platinum/divinyltetramethyl disiloxane complexes, and platinum/tetravinyl tetramethyl cyclotetrasiloxane complexes; complexes of chloroplatinic acid and acetylene alcohols; and mixtures of two or more types thereof. In particular, platinum-alkenylsiloxane complexes are preferable in that the curing of the present composition can be accelerated.

[0064] Examples of the alkenylsiloxane used in the platinum-alkenylsiloxane complex include 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, alkenylsiloxane oligomers in which some of methyl groups of these alkenylsiloxanes are substituted with ethyl groups, phenyl groups, or the like, and alkenylsiloxane oligomers in which vinyl groups of these alkenylsiloxanes are substituted with allyl groups, hexenyl groups, or the like. In particular, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane is preferable in that the stability of the platinum-alkenylsiloxane complex that is produced is good.

[0065] In order to improve the stability of the platinum-alkenylsiloxane complexes, it is preferable to dissolve these platinum-alkenylsiloxane complexes in an alkenylsiloxane oligomer such as 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, 1,3-diallyl-1,1,3,3-tetramethyldisiloxane, 1,3-divinyl-1,3-dimethyl-1,3-diphenyldisiloxane, 1,3-divinyl-1,1,3,3-tetraphenyldisiloxane, or 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane or an organosiloxane oligomer such as a dimethylsiloxane oligomer, and it is particularly preferable to dissolve the complexes in an alkenylsiloxane oligomer.

[0066] The content of component (F) is catalytic amount to to accelerate the curing of the present composition, but it is preferably in an amount of from about 0.01 to about 1,000 ppm of the platinum group metal in this component in terms of mass units with respect to this composition. Specifically, the content is preferably an amount such that the content of platinum group metal in component (F) is in the range of from about 0.01 to about 500 ppm, alternatively in the range of from about 0.1 to about 100 ppm in terms of mass units with respect to the present composition. This is because when the content of component (F) is greater than or equal to the lower limit of the aforementioned range, curability of the composition is good, whereas when the content of component (F) is less than or equal to the upper limit of the aforementioned range, coloration of the cured product is suppressed.

[0067] The composition may comprise (G) an organosiloxane free of alkenyl groups and silicon atom-bonded hydrogen atoms in a molecule. Examples of groups bonding to silicon atoms in component (G) include alkyl groups having from 1 to 12 carbon atoms such as methyl groups, ethyl groups, propyl groups, isopropyl groups, butyl groups, isobutyl groups, tert-butyl groups, pentyl groups, neopentyl groups, hexyl groups, cyclohexyl groups, heptyl groups, octyl groups, nonyl groups, decyl groups, undecyl groups, and dodecyl groups; aryl groups having from 6 to 20 carbon atoms such as phenyl groups, tolyl groups, xylyl groups, and naphthyl groups; aralkyl groups having from 7 to 20 carbon atoms such as benzyl groups, phenethyl groups, and phenylpropyl groups; and groups in which some or all of the hydrogen atoms of these groups are substituted with halogen atoms such as fluorine atoms, chlorine atoms, or bromine atoms. Furthermore, the silicon atoms in component (G) may have small amounts of hydroxyl groups or alkoxy groups such as methoxy groups or ethoxy groups within a range that does not impair the object of the present invention.

[0068] Examples of the molecular structure of component (G) include straight-chain, partially branched straight-chain, branched chain, cyclic, and three-dimensional reticular structures, and the molecular structure is preferably a partially branched straight-chain, branched chain, or three-dimensional reticular structure.

[0069] Examples of such component (G) include dimethylsiloxanes capped at both molecular terminals with trimethylsiloxy groups, dimethylsiloxanes capped at both molecular terminals with dimethylhydoxysiloxy groups, methylphenylsiloxanes capped at both molecular terminals with trimethylsiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers capped at both molecular terminals with trimethylsiloxy groups, and mixtures of two or more types thereof.

[0070] The content of component (G) is not limited, but it is preferably in an amount of about 1 to about 100 parts by mass, alternatively about 5 to about 100 parts by mass, and alternatively about 1 to about 50 parts by mass, relative to 100 parts by mass of component (A). This is because the viscosity of the composition can be reduced if the content of component (G) is not less than the lower limit of the above-mentioned range and mechanical properties of the silicone material is improved if the content of component (H) is not more than the upper limit of the above-mentioned range.

[0071] The composition may comprise (H) a hydrosilylation reaction inhibitor in order to prolong the usable time at ambient temperature and to improve storage stability. Examples of component (H) include acetylenic alcohols such as 1-ethynyl-cyclohexan-1-ol, 2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, 2-ethynyl-isopropan-2-ol, 2-ethynyl-butan-2-ol, and 3,5-dimethyl-1-hexyn-3-ol; silylated acetylenic alcohols such as trimethyl (3,5-dimethyl-1-hexyn-3-oxy) silane, dimethyl bis(3-methyl-1-butyn-oxy) silane, methylvinyl bis(3-methyl-1-butyn-3-oxy) silane, and ((1,1-dimethyl-2-propynyl)oxy)trimethylsilane; unsaturated carboxylic esters such as diallyl maleate, dimethyl maleate, diethyl fumarate, diallyl fumarate, and bis(2-methoxy-1-methylethyl) maleate, mono-octylmaleate, mono-isooctylmaleate, mono-allyl maleate, mono-methyl maleate, mono-ethyl fumarate, mono-allyl fumarate, and 2-methoxy-1-methylethylmaleate; ene-yne compounds such as 2-isobutyl-1-buten-3-yne, 3,5-dimethyl-3-hexen-1-yne, 3-methyl-3-penten-1-yne, 3-methyl-3-hexen-1-yne, 1-ethynyl cyclohexene, 3-ethyl-3-buten-1-yne, and 3-phenyl-3-buten-1-yne; and mixtures of two or more types thereof.

[0072] The content of component (H) is in an amount of from about 0.1 to 10,000 ppm in this component in terms of mass units with respect to this composition. Specifically, the content is preferably an amount of from about 1 to about 5,000 ppm, alternatively an amount of from about 10 to about 500 ppm in this component in terms of mass units with respect to the present composition. This is because when the content of component (H) is greater than or equal to the lower limit of the aforementioned range, storage stability of the present composition is good, whereas when the content of component (H) is less than or equal to the upper limit of the aforementioned range, curability of the present composition at low temperatures is good.

[0073] The composition may comprise a reinforcing and/or non-reinforcing filler. Examples of the fillers include one or more of finely divided treated or untreated precipitated or fumed silica; precipitated or ground calcium carbonate, zinc carbonate; clays such as finely divided kaolin; quartz powder; zirconium silicate; diatomaceous earth; wollastonite; pyrophylate; and metal oxides such as fumed or precipitated titanium dioxide, cerium oxide, magnesium oxide powder, zinc oxide, and iron oxide. These may also include glass fiber; talc; aluminite; calcium sulphate (anhydrite); gypsum; calcium sulphate; magnesium carbonate; magnesium hydroxide (brucite); graphite; barite, a form of barium sulphate; copper carbonate, e.g., malachite; nickel carbonate, e.g., zarachite; barium carbonate, e.g., witherite; strontium carbonate e.g., strontianite, or a similar inorganic filler.

[0074] The content of the reinforcing and/or non-reinforcing filler is not limited, but it is preferably in an amount of about 1 to about 200 parts by mass, alternatively about 5 to about 150 parts by mass, and alternatively about 10 to about 150 parts by mass, relative to 100 parts by mass of component (A). This is because the heat resistance and mechanical properties of the silicone material can be improved if the content of the reinforcing and/or non-reinforcing filler is not less than the lower limit of the above-mentioned range and the viscosity of the composition can be reduced if the content of the reinforcing and/or non-reinforcing filler is not more than the upper limit of the above-mentioned range.

[0075] The thermal conductive silicone compositions of this invention can be prepared by combining all of ingredients at ambient temperature. Any of the mixing techniques and devices described in the prior art can be used for this purpose. The particular device used will be determined by the viscosity of the ingredients and the final composition. Cooling of the ingredients during mixing may be desirable to avoid premature curing.

EXAMPLES

[0076] The thermal conductive silicone composition of the present invention will be described in detail hereinafter using Practical Examples and Comparative Examples. However, the present invention is not limited by the description of the below listed Practical Examples.

Viscosity

[0077] Viscosity was measured using a rotational viscometer such as a Brookfield Synchro-lectric viscometer. Since virtually all materials measured are non-Newtonian in nature, no correlation should be expected between results obtained using different spindles or speeds. The results are generally reported in centipoise. This method is based on ASTM D 1084: HBDV-III, NO. 3 SPINDLE, AT 100 RPM.

Shore A Hardness

[0078] A cured silicone material was obtained by heat curing the curable thermal conductive silicone composition for 1 hour at 120° C. in an air circulating oven. The cured silicone materials were stacked to be at least 6 mm in thickness for durometer measurement. The Shore A hardness of the cured silicone material at 25° C. was determined according to test method ASTM D2240-05(2010) (Standard Test Method for Rubber Property Durometer Hardness).

Adhesion

[0079] The adhesion is determined by measuring the amount of pull required to separate a lap shear laminate. The adhesion of the cured silicone material at 25° C. was determined according to test method ASTM 1002: Add Mix A & B(1:1) and degas by using vacuum. Clean 8 lap shear A1 panels (Alclad 2024T3, 1 in.×3 in. (2.5 cm×7.6 cm) and known thickness, Q Panel Company, Cleveland, Ohio). With IPA, place 4 panels on the lower level of the mould, apply mixed sample to each panel, lay a second panel directly on top of each panel to give the specified gap(0.9 mm), then put them into 120C oven for 1 hour. Take them out and trim any excess material from the edges of the test sample after the sample is cured (Bonding area is 10 mm*25.4 mm), then teste with Instron equipment. The results are reported in pounds per square inch. The amount of adhesive or cohesive failure is estimated.

Settle Check

[0080] The settlement check for the presented material is not a standard method. The procedure can be described as below: put 5 kg material in a 5 L pail, leave the container at RT for a period time (1 M/3 M . . . ), then check the material settlement at each planned time. For the settlement check, use a ruler to dip into the material in the container, and stop when the ruler touch a hard material layer, and read the ruler mark (H1) as the soft material height. Second step is to dip the ruler entirely to the pail bottom, to get a whole material layer height (H2). The hard-caking settlement lay can be achieved as H=H2−H1.

[0081] The following components were used to prepare the thermal conductive silicone compositions in Practical and Comparative Examples.

Component (a-1): a dimethylpolysiloxane having a viscosity of about 450 mm.sup.2/s and endblocked at both molecular chain terminals with dimethylvinylsiloxy groups.
Component (a-2): a dimethylpolysiloxane having a kinematic viscosity of about 70 mm.sup.2/s and endblocked at both molecular chain terminals with dimethylvinylsiloxy groups.
Component (b-1): an aluminum hydroxide powder having an average particle diameter of about 15 μm.
Component (c-1): an aluminum hydroxide powder having an average particle diameter of about 1 μm.
Component (d-1):a carbasilatrane derivative represented by the following formula:

##STR00006##

Component (e-1): a dimethylsiloxane-methylhydrogensiloxane co-oligomer having a kinematic viscosity of about 7 mm.sup.2/s and endblocked at both molecular chain terminals with trimethylsiloxy groups.
Component (e-2): a dimethylpolysiloxane having a kinematic viscosity of about 65 mm.sup.2/s and endblocked at both molecular chain terminals with dimethylhydrogensiloxy groups.
Component (f-1): a platinum complex with 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane in a 1,3-diethenyl-1,1,3,3-tetramethyldisiloxane solution (platinum content=0.1 mass %)
Component (g-1): 1,1,1,3,3,5,5,7,7,7-decamethyltetrasiloxane methyltrimethoxysilane
3-acryloxypropyl trimethoxysilane
1,3,5,7-tetramethyl-1,3,5,7-tetravinyltetracyclosiloxane

Practical Example 1

[0082] 1185 parts by mass of component (a-1), 1610 parts by mass of component (a-2), and 119 parts by mass of methyl trimethoxysilane were combined in a mixer at room temperature. Next, 2489 parts by mass of component (c-1) was combined with the mixture for 10 minutes. Next, total 5808 parts by mass of component (b-1) divided into three times was combined with the mixture for 80 minutes. Next, the mixture was mixed and heated from room temperature to 120° C. in an atmosphere of nitrogen gas, then was mixed at 120° C. for 1 hour under reduced pressure. Next, the mixture was cooled down to 40° C. under reduced pressure. Finally, 742 parts by mass of component (a-2), 23.7 parts by mass of component (d-1), 24.65 parts by mass of component (f-1), and 300 parts by mass of component (g-1) were combined prepared by combining for 20 minutes to produce a thermal conductive silicone composition (1). The characteristics of the thermally conductive silicone composition (1) were determined and the results were listed in Table 1.

Practical Example 2

[0083] 1950 parts by mass of component (a-1), 464 parts by mass of component (a-2), and 59 parts by mass of methyl trimethoxysilane were combined in a mixer at room temperature. Next, 2497 parts by mass of component (c-1) was combined with the mixture for 10 minutes. Next, total 5827 parts by mass of component (b-1) divided into three times was combined with the mixture for 80 minutes. Next, the mixture was mixed and heated from room temperature to 120° C. in an atmosphere of nitrogen gas, then was mixed at 120° C. for 1 hour under reduced pressure. Next, the mixture was cooled down to 40° C. under reduced pressure. Finally, 24 parts by mass of component (d-1), 308 parts by mass of component (e-1), 768.3 parts by mass of component (e-2), 300 parts by mass of component (g-1), 30 parts by mass of methyl trimethoxysilane, 36 parts by mass of 3-acryloxypropyl trimethoxysilane, and 6.5 parts by mass of 1,3,5,7-tetramethyl-1,3,5,7-tetravinyltetracyclosiloxane were combined prepared by combining for 20 minutes to produce a thermal conductive silicone composition (2). The characteristics of the thermally conductive silicone composition (2) were determined and the results were listed in Table 1.

[0084] Curable thermal conductive silicone compositions were prepared by mixing the thermal conductive silicone compositions (1) and (2) before and after aging in a mass ratio of 1:1. The characteristics of silicone materials of the curable thermally conductive silicone compositions were determined and the results were listed in Table 1.

Comparative Example 1

[0085] A thermally conductive silicone composition (3) was prepared in the same way as Practical Example 1, except component (d-1) was not added. The characteristics of the thermally conductive silicone composition (3) were determined and the results were listed in Table 1.

Comparative Example 2

[0086] A thermally conductive silicone composition (4) was prepared in the same way as Practical Example 2, except component (d-1) was not added. The characteristics of the thermally conductive silicone composition (4) were determined and the results were listed in Table 1.

[0087] A curable thermal conductive silicone composition was prepared by mixing the thermal conductive silicone compositions (3) and (4) before and after aging in a mass ratio of 1:1. The characteristics of silicone materials of the curable thermally conductive silicone compositions were determined and the results were listed in Table 1.

TABLE-US-00001 TABLE 1 Examples Practical Comparative Examples Examples Parameters 1 2 1 2 Intial Viscosity (mPa .Math. s) 3056 2368 1960 1816 Shore A Hardness 68 66 Adhesion (psi) 218 279 After aging Viscosity (mPa .Math. s) 2528 2024 1768 1736 50° C. for 1 Shore A Hardness 69 66 week Adhesion (psi) 212 259 After aging Viscosity (mPa .Math. s) 2496 2120 1800 1888 50° C. for 2 Shore A Hardness 67 64 weeks Adhesion (psi) 222 297 After aging Viscosity (mPa .Math. s) 2308 2104 1780 1692 50° C. for 3 Shore A Hardness 68 67 weeks Adhesion (psi) 278 257 Settle check after storage at 0 cm 0 cm 1.0 cm 1.0 cm 25° C. for 1 month caking caking caking caking (Jell- (Jell- like) like) Settle check after storage at 0 cm 0 cm 3.0 cm 2.0 cm 25° C. for 3 months caking caking caking caking (Jell- (Jell- like) like)

INDUSTRIAL APPLICABILITY

[0088] The thremal conductive silicone composition of the present invention exhibits excellent storage stability and handleability despite containing a large quantity of a thermal conductive filler to exhibit high thermal conductivity. Therefore, the thermal conductive silicone composition is useful, in thermal conductive materials for an electric/electronic apparatus.