Thermally conductive silicone composition, cured product, and production method

Abstract

Provided is a thermally conductive silicone composition which is excellent in insulating properties and thermal conductivity and has an appropriate viscosity. This thermally conductive silicone composition comprises (A) an organopolysiloxane, (B) round aluminum nitride powder having an oxygen content of 0.5% by mass or less, an average particle diameter of 45-85 μm, and a ratio (D90 / D10) in the range of 8-12, (C) amorphous aluminum nitride powder having a BET specific surface area of 1.0-4.0 m2 / g and an average particle diameter of 0.5-5 μm, and (D) a silicon compound represented by general formula (1): -SiR1 a(OR2)3-a, wherein ((B):(C)) is 5:5-8:2, the total amount of component (B) and component (C) is 78%-86% by volume in the composition, and the thermally conductive silicone composition has a thermal conductivity of 8.0 W / m·K or more at 30-800 Pa·s as measured by a hot disk method in accordance with ISO 22007-2, and has excellent insulating properties, excellent thermal conductivity, and a moderate viscosity.

Description

Thermally conductive silicone composition, cured product, and manufacturing method

[0001] The present invention relates to a silicone composition with excellent thermal conductivity, and in particular to a highly thermally conductive silicone composition with excellent insulating properties that, when used as a heat dissipation member for electronic components, can be incorporated into electronic devices without damaging heat-generating electronic components such as power devices, transistors, thyristors, and CPUs (central processing units), as well as to a cured product and a method for producing the same.

[0002] In heat-generating electronic components such as power devices, transistors, thyristors, and CPUs, how to remove the heat generated during use is an important issue. Conventionally, a common method for removing heat has been to attach the heat-generating electronic components to a heat-dissipating fin or metal plate via an electrically insulating heat-dissipating sheet, and the heat-dissipating sheet used is made of silicone resin with a thermally conductive filler dispersed therein.

[0003] In recent years, the amount of heat generated by electronic components has increased with the increasing integration of circuits. For example, thermal conductivity at high temperatures, such as temperatures above 100°C, particularly 150°C, has become important. This has led to a demand for materials with even higher thermal conductivity. To improve the thermal conductivity of thermally conductive materials, a common approach has been to incorporate a filler with high thermal conductivity, such as aluminum oxide powder or aluminum nitride powder, into a matrix resin (see Patent Documents 1 and 2).

[0004] Therefore, in order to improve thermal conductivity, a method has been disclosed in which spherical aluminum oxide powder having an average sphericity, hydroxyl group content, and average particle size specified as 10 to 50 μm, and a highly thermally conductive resin composition having an average particle size specified as 0.3 to 1 μm and specified blending ratios and volume ratios of each aluminum oxide, are used. However, when the average particle size of the spherical aluminum oxide powder is a maximum of 50 μm, there is a problem that the thermal conductivity is insufficient (Patent Document 3).

[0005] Also, a thermally conductive silicone composition using an alumina powder with an average particle size of 0.1 to 100 μm has been proposed, but no specific thermal conductivity or viscosity is specified.Furthermore, a thermally conductive silicone composition has been disclosed that is specified as containing spherical alumina powder with an average particle size of 5 to 50 μm (but not including 5 μm) and spherical or irregularly shaped alumina powder with an average particle size of 0.1 to 5 μm, and in which the blending ratio and weight ratio of aluminum oxide for each is specified.However, like Patent Document 5, this also has the problem that the average sphericity or hydroxyl group content of the spherical alumina with a large average particle size is not specified, and is therefore insufficient to achieve high thermal conductivity.

[0006] Therefore, the average sphericity is 0.8 or more, and the number of hydroxyl groups is 30 / nm 2 Although a thermally conductive silicone composition using spherical aluminum oxide powder with an average particle size of 50 to 150 μm has been proposed, there are no specifications for the particle size distribution of the spherical aluminum oxide powder, and there are limitations to achieving even higher thermal conductivity while maintaining fluidity (Patent Document 4).

[0007] JP 2005-162555 A JP 2005-209765 A JP 2013-056996 A WO 2018 / 088416

[0008] The present invention has been made in view of the above circumstances, and its object is to provide a thermally conductive silicone composition that has excellent insulating properties and thermal conductivity and has an appropriate viscosity, particularly a thermally conductive silicone composition that is suitable as a heat dissipation material for electronic components, as well as a cured product thereof and a method for producing the same.

[0009] As a result of extensive research into achieving the above object, the present inventors have discovered that a silicone composition containing (A) an organopolysiloxane is provided with (B) a silicone composition having a specific oxygen content, a specific average particle size, and a ratio (D 90 / D 10The present inventors have found that the above-mentioned problems can be solved by blending (B) and (C) a rounded aluminum nitride powder having a specific BET specific surface area and average particle size, (C) an irregular-shaped aluminum nitride powder having a specific BET specific surface area and average particle size, and (D) a silicon compound having at least one silyl group per molecule and a specific viscosity in specific amounts as components (B) and (C). This composition can also be made into a curable composition by blending a curing agent therewith.

[0010] Therefore, the present invention provides the following invention: 1. (A) organopolysiloxane (excluding component (D)), (B) an organopolysiloxane having an oxygen content of 0.5% by mass or less and a cumulative particle size distribution of 50% (D) based on a volumetric laser diffraction particle size distribution. 50 ) the average particle diameter is 45 to 85 μm and the cumulative 90 ) and cumulative 10% (D 10 ) ratio (D 90 / D 10 (C) a rounded aluminum nitride powder having a BET specific surface area of ​​1.0 to 4.0 m 2 / g and having an average particle size of 0.5 to 5 μm, and (D) an aluminum nitride powder having an irregular shape, the powder being represented by the following general formula (1): -SiR 1 a (OR 2 ) 3-a (1) (wherein, R 1 are independently unsubstituted or substituted monovalent hydrocarbon groups, R 2are independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, and a is 0, 1, or 2.) A thermally conductive silicone composition comprising a silicon compound having per molecule at least one silyl group represented by the following general formula (2): (In the formula, R 1 are independently unsubstituted or substituted monovalent hydrocarbon groups, R 2 wherein each independently represents an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, b is an integer of 5 to 100, and a is 0, 1, or 2. 3. The thermally conductive silicone composition according to 1 or 2, further comprising a curing agent. 4. The thermally conductive silicone composition according to 3, which is an addition reaction curing type, a condensation reaction curing type, or an organic peroxide curing type. 5. The thermally conductive silicone composition according to 4, which is an addition reaction curing type. 6. A cured product of the thermally conductive silicone composition according to any of 3 to 5. 7. A method for producing the thermally conductive silicone composition according to any of 1 to 5, which comprises the step of mixing components (B) and (C).

[0011] According to the present invention, it is possible to provide a highly thermally conductive silicone composition that has excellent insulating properties and thermal conductivity, and has an appropriate viscosity.

[0012] The present invention will be described in detail below. Note that the term "thermally conductive silicone composition" may sometimes be abbreviated as "simply silicone composition." [Component (A)] The organopolysiloxane of component (A) is the main component of the silicone composition of the present invention. Examples of groups bonded to silicon atoms in this organopolysiloxane include linear alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, and eicosyl groups; isopropyl, tertiary butyl, isobutyl, 2-methylundecyl, 1-hexyl, and the like; Examples of such alkyl groups include branched alkyl groups such as a xylheptyl group; cyclic alkyl groups such as a cyclopentyl group, a cyclohexyl group, and a cyclododecyl group; alkenyl groups such as a vinyl group, an aryl group, a butenyl group, a pentenyl group, and a hexenyl group; aryl groups such as a phenyl group, a tolyl group, and a xylyl group; aralkyl groups such as a benzyl group, a phenethyl group, and a 2-(2,4,6-trimethylphenyl)propyl group; halogenated alkyl groups such as a 3,3,3-trifluoropropyl group and a 3-chloropropyl group; and a hydrogen atom. Among these, alkyl groups, alkenyl groups, aryl groups, and hydrogen atoms are preferred, and methyl groups, vinyl groups, phenyl groups, and hydrogen atoms are more preferred.

[0013] The viscosity of the (A) organopolysiloxane at 25°C is not limited, but is preferably 10 to 100,000 mPa·s, more preferably 15 to 50,000 mPa·s, even more preferably 20 to 20,000 mPa·s, and particularly preferably 25 to 10,000 mPa·s. By ensuring that the viscosity is equal to or greater than the lower limit of the viscosity, the physical properties of the silicone composition are further improved, while by ensuring that the viscosity is equal to or less than the upper limit of the viscosity, the handling and workability of the silicone composition are further improved. The viscosity of each component, such as (A) or (D), at 25°C is measured using a Brookfield viscometer, and the rotor, rotation speed, and rotation time are selected appropriately in accordance with the viscosity using standard methods (the same applies hereinafter).

[0014] The molecular structure of the organopolysiloxane is not limited, and examples thereof include linear, branched, partially branched linear, and dendritic (dendrimer) structures. Of these, linear and partially branched linear structures are preferred. Examples of such organopolysiloxanes include single polymers having these molecular structures, copolymers comprising these molecular structures, and mixtures of these polymers.

[0015] More specific examples of organopolysiloxanes include dimethylpolysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylpolysiloxanes capped at both molecular chain terminals with methylphenylvinylsiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with trimethylsiloxy groups, methyl(3,3,3-trifluoropropyl)polysiloxanes capped at both molecular chain terminals with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers capped at both molecular chain terminals with silanol groups, and dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with silanol groups, and 1 / 2 and a siloxane unit represented by the formula: (CH3)2(CH2=CH)SiO 1 / 2 and a siloxane unit represented by the formula: CHSiO 3 / 2 and a siloxane unit represented by the formula: (CH3)2SiO 2 / 2organosiloxane copolymers comprising siloxane units represented by the formula: dimethylpolysiloxanes capped at both molecular chain terminals with silanol groups, dimethylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with silanol groups, dimethylpolysiloxanes capped at both molecular chain terminals with trimethoxysiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with trimethoxysilyl groups, dimethylpolysiloxanes capped at both molecular chain terminals with methyldimethoxysiloxy groups, Dimethylpolysiloxane capped at both ends with triethoxysiloxy groups, dimethylpolysiloxane capped at both molecular chain ends with trimethoxysilylethyl groups, dimethylpolysiloxane capped at both molecular chain ends with dimethylhydrogensiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both molecular chain ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer capped at both molecular chain ends with dimethylhydrogensiloxy groups, formula: (CH3)3SiO 1 / 2 and a siloxane unit represented by the formula: (CH3)2HSiO 1 / 2 and a siloxane unit represented by the formula: SiO 4 / 2 Examples of the organosiloxane copolymer include organosiloxane copolymers comprising siloxane units represented by the following formula: and these can be used alone or in appropriate combination of two or more.

[0016] When the silicone composition cures via a hydrosilylation reaction, it is preferred that component (A) be (A-I-1) an organopolysiloxane having an average of at least 0.1 silicon-bonded alkenyl groups per molecule, and (A-I-2) an organohydrogenpolysiloxane having at least two hydrogen atoms directly bonded to silicon atoms.

[0017] (A-I-1) is preferably an organopolysiloxane having an average of 0.5 or more silicon-bonded alkenyl groups per molecule, and more preferably an organopolysiloxane having an average of 0.8 or more silicon-bonded alkenyl groups per molecule. This is because if the average number of silicon-bonded alkenyl groups per molecule is below the lower limit of the above range, the resulting silicone composition tends not to cure sufficiently. Examples of the silicon-bonded alkenyl groups in this organopolysiloxane include the same alkenyl groups as above, with vinyl groups being preferred. Furthermore, examples of groups bonded to silicon atoms other than alkenyl groups in this organopolysiloxane include the same linear alkyl groups, branched alkyl groups, cyclic alkyl groups, aryl groups, aralkyl groups, and halogenated alkyl groups as above, with alkyl groups and aryl groups being preferred, and methyl and phenyl groups being more preferred.

[0018] Component (A-I-2) is a component that functions as a crosslinking agent. Groups bonded to silicon atoms in the organohydrogenpolysiloxane (A-I-2) include the same linear alkyl groups, branched alkyl groups, cyclic alkyl groups, aryl groups, aralkyl groups, and halogenated alkyl groups as described above. Among these, alkyl groups and aryl groups are preferred, with methyl and phenyl groups being more preferred. The viscosity of component (A-I-2) at 25°C is not limited, but is preferably in the range of 10 to 100,000 mPa·s, and more preferably 15 to 5,000 mPa·s. The molecular structure of component (A-I-2) is not limited, and examples include linear, branched, partially branched linear, cyclic, and dendritic (dendrimer) structures. Examples of such organopolysiloxanes include homopolymers having these molecular structures, copolymers comprising these molecular structures, and mixtures thereof.

[0019] The amount of component (A-I-2) is the amount necessary for curing the silicone composition, and specifically, it is preferably an amount such that the number of silicon-bonded hydrogen atoms in component (A-I-2) is in the range of 0.1 to 10 moles per mole of silicon-bonded alkenyl groups in component (A-I-1), more preferably 0.2 to 5 moles, and even more preferably 0.3 to 3.0 moles. By using an amount equal to or greater than the above lower limit, greater effect can be achieved, while by using an amount equal to or less than the above upper limit, the resulting silicone cured product will be very hard, preventing the occurrence of numerous cracks on the surface.

[0020] When the silicone composition cures via a condensation reaction, component (A) is preferably (A-II) an organopolysiloxane having at least two silanol groups or silicon-bonded hydrolyzable groups per molecule, and more preferably an organopolysiloxane having at least 2 to 10 silanol groups or silicon-bonded hydrolyzable groups per molecule. Examples of silicon-bonded hydrolyzable groups in organopolysiloxanes include alkoxy groups such as methoxy, ethoxy, and propoxy; alkenoxy groups such as vinyloxy, propenoxy, isopropenoxy, and 1-ethyl-2-methylvinyloxy; alkoxyalkoxy groups such as methoxyethoxy, ethoxyethoxy, and methoxypropoxy; acyloxy groups such as acetoxy and octanoyloxy; ketoxime groups such as dimethylketoxime and methylethylketoxime; amino groups such as dimethylamino, diethylamino, and butylamino; aminoxy groups such as dimethylaminooxy and diethylaminooxy; and amide groups such as N-methylacetamide and N-ethylacetamide. Furthermore, examples of groups bonded to silicon atoms in this organopolysiloxane other than silanol groups and silicon-bonded hydrolyzable groups include the same linear alkyl groups, branched alkyl groups, cyclic alkyl groups, alkenyl groups, aryl groups, aralkyl groups, and halogenated alkyl groups as described above.

[0021] When the silicone composition cures via a free radical reaction induced by an organic peroxide, component (A) is preferably (A-III) an organopolysiloxane having at least one silicon-bonded alkenyl group per molecule. An organopolysiloxane having an average of 0.1 to 20 silicon-bonded alkenyl groups is more preferred. Examples of the group bonded to the silicon atom in this organopolysiloxane include the same linear alkyl groups, branched alkyl groups, cyclic alkyl groups, alkenyl groups, aryl groups, aralkyl groups, and halogenated alkyl groups as described above. Alkyl groups, alkenyl groups, and aryl groups are preferred, with methyl groups, vinyl groups, and phenyl groups being more preferred.

[0022] The blend amount of component (A) in the silicone composition is preferably 0.4 to 4.0 mass %, and more preferably 0.5 to 3.0 mass %.

[0023] [Component (B)] Component (B) has an oxygen content of 0.5% by mass or less, and a cumulative particle size distribution of 50% (D 50 ) the average particle diameter is 45 to 85 μm and the cumulative 90 ) and cumulative 10% (D 10 ) ratio (D 90 / D 10 ) is a rounded aluminum nitride powder having a molecular weight of 8 to 12, and can be used alone or in combination of two or more. By using component (B), the thermal conductivity of the composition of the present invention can be further increased while maintaining the fluidity.

[0024] The oxygen content of component (B) is 0.5% by mass or less, preferably 0.2% by mass or less. The lower limit is not particularly limited and may be 0.01% by mass or even 0% by mass. If the oxygen content, which is an indicator of the nitriding rate of component (B), exceeds 0.5% by mass, the crystallite size becomes smaller and the chemical purity of component (B) deteriorates, which may result in a decrease in the thermal conductivity of the composition and poor thermal properties after moisture resistance. The oxygen content of component (B) can be measured using an oxygen / nitrogen analyzer and analyzed by comparison with a standard silicon nitride. An oxygen / nitrogen analyzer such as the Shimadzu EMGA-920 can be used.

[0025] In the volume-based laser diffraction particle size distribution, the cumulative 50 The average particle size of the hydroxyl group hydroxyl group (H) is 45 to 85 μm, preferably 50 to 78 μm, and more preferably 50 to 70 μm. If the average particle size is less than 45 μm, the fillability into the resin will be poor and the viscosity will be high. On the other hand, if the average particle size exceeds 85 μm, this is preferable from the viewpoint of increasing the thermal conductivity of the composition, but oil separation will easily proceed over time, and the target viscosity will not be achieved.

[0026] The cumulative figure is 90% (D 90 ) and cumulative 10% (D 10 ) ratio (D 90 / D 10 By adjusting the viscosity of the resin, it is possible to achieve both the desired viscosity and high thermal conductivity. 90 / D 10 is 8 to 12, preferably 8.5 to 12.0, more preferably 8.5 to 11.5, and even more preferably 9 to 11. 90 / D 10 If D is less than 8, the desired thermal conductivity cannot be obtained. 90 / D 10 If D exceeds 12, the desired viscosity may not be obtained. 90 is preferably 90 to 250 μm, and D 10 The particle size distribution is preferably 8 to 30 μm. 90 / D 10 becomes larger, and if the particle size distribution is narrow, D 90 / D 10 becomes smaller.

[0027] The BET specific surface area (nitrogen gas adsorption method) of component (B) is preferably as low as possible, and is preferably 0.3 m or less, from the viewpoint of increasing the thermal conductivity of the composition. 2 / g or less is preferable, and 0.2m 2 Although there is no particular lower limit for the BET specific surface area, the average particle diameter (D 50 ) and the cumulative upper limit in the volume-based laser diffraction particle size distribution is 90% (D 90 ) and cumulative 10% (D 10 ) ratio (D 90 / D 10 ) to 0.05m 2 The BET specific surface area of ​​the component (B) can be analyzed using, for example, a Macsorb (registered trademark) HM Model-1201 manufactured by Mountech.

[0028] The shape of component (B) is rounded; if it is an irregular shape, the desired viscosity may not be obtained. A rounded shape is preferred because it reduces the initial viscosity of the composition, minimizes viscosity change even when treated at 200°C, and further improves heat resistance. In the present invention, "rounded" refers to a shape having an aspect ratio (average major axis length / average minor axis length) of 2.0 or less, preferably 1.2 to 1.9. The aspect ratio can be measured by dynamic image analysis, for example, using a "Dynamic Particle Image Analysis System iSpect DIA-10" manufactured by Shimadzu Corporation.

[0029] The component (B) can be obtained by any method that satisfies the requirements of the present invention, including reduction nitriding and direct nitriding. Of these, direct nitriding is preferred from the viewpoint of making it easier to obtain a material with an oxygen content of 0.5% by mass or less. The direct nitriding improves the chemical purity, thereby further improving the thermal properties after moisture resistance.

[0030] The method for producing component (B) is not particularly limited and may be carried out according to a known direct nitriding method (including combustion synthesis). For example, a method in which metallic aluminum powder is nitrided alone in a nitrogen atmosphere at 0.2 to 3 MPa is exemplified. If necessary, the resulting powder can be pulverized according to known methods, such as a ball mill, jet mill, or crusher.

[0031] Another example is a method that includes a heat treatment step of component (B) obtained by direct nitriding in a non-oxidizing atmosphere at 1,600 to 2,000°C. This method removes the corners of particles with angular, irregular shapes and turns them into rounded particles, which is suitable for reducing the viscosity of the composition. Note that if the temperature is lower than 1,600°C, it is difficult to obtain a rounded shape, and if the temperature exceeds 2,000°C, component (B) particles may sinter together, resulting in an undesired average particle size.

[0032] It is preferable to add component (B) in a range that does not impair the present invention, and specifically, in order to avoid a significant decrease in the thermal conductivity of the thermally conductive silicone composition, the amount of component (B) relative to the total amount of the silicone composition is preferably 40 to 70 volume %, and more preferably 45 to 65 volume %. By setting the amount to 40 volume % or more, the thermal conductivity of the silicone composition will be increased, and by setting it to 70 volume % or less, it is possible to further prevent the viscosity of the silicone composition from becoming too high.

[0033] [Component (C)] Component (C) is a sintered body having a BET specific surface area of ​​1.0 to 4.0 m 2 / g and an average particle size of 0.5 to 5 μm, and can be used alone or in combination of two or more. The aspect ratio of the irregular shaped aluminum nitride powder is not particularly limited, but is preferably 10.0 or less, and more preferably 5.0 or less. Shapes other than spherical are considered irregular.

[0034] The BET specific surface area of ​​component (C) (as measured by nitrogen gas adsorption) is 1.0 to 4.0 m 2 / g, and 1.1 to 3.5 m 2 / g is preferred. 2 If the specific surface area is less than 4.0 m / g, the unevenness of the sheet surface becomes large, the interface thermal resistance increases, and the thermal conductivity deteriorates. 2If it exceeds 1 / g, contact between particles will be reduced, increasing interparticle contact thermal resistance and resulting in poor thermal conductivity. The average particle size of component (C) is 0.5 to 5 μm, preferably 0.7 to 4.8 μm. If it is less than 0.5 μm, contact between particles will be reduced, increasing interparticle contact thermal resistance and resulting in poor thermal conductivity. If it exceeds 5 μm, the sheet surface will have large irregularities, increasing interfacial thermal resistance and resulting in poor thermal conductivity. The average particle size and BET specific surface area are measured using the same methods as for component (B).

[0035] The volume ratio ((B):(C)) of the above-mentioned components (B) and (C) is 5:5 to 8:2, preferably 5:5 to 8.0:2.0, and more preferably 6:4 to 7:3. If the volume ratio of component (B) is less than 5 (10 for the total of components (B) and (C), the packing properties of components (B) and (C) may be poor. On the other hand, if the volume ratio of component (B) exceeds 8, it becomes difficult to pack components (B) and (C) densely, and oil separation may easily occur over time. Furthermore, the total amount of components (B) and (C) is 78 to 86% by volume of the composition, preferably 79 to 85% by volume, and more preferably 80 to 84% by volume. If the total amount of components (B) and (C) is less than 78% by volume, the desired thermal conductivity may not be obtained, and if the total amount of components (B) and (C) exceeds 86% by volume, the filling properties may be poor.

[0036] [Component (D)] The component (D) is a compound represented by the following general formula (1): —SiR 1 a (OR 2 ) 3-a (1) (wherein, R 1 are independently unsubstituted or substituted monovalent hydrocarbon groups, R 2 are independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, and a is 0, 1, or 2.) These silicon compounds can be used alone or in combination of two or more. It is preferred that components (B) and (C) have been surface-treated with component (D).

[0037] R 1are independently unsubstituted or substituted monovalent hydrocarbon groups, preferably monovalent hydrocarbon groups having 1 to 10 carbon atoms, more preferably 1 to 6 carbon atoms, and even more preferably 1 to 3 carbon atoms. Specific examples include linear alkyl groups, branched alkyl groups, cyclic alkyl groups, alkenyl groups, aryl groups, aralkyl groups, and halogenated alkyl groups. Examples of linear alkyl groups include methyl groups, ethyl groups, propyl groups, hexyl groups, octyl groups, and decyl groups. Examples of branched alkyl groups include isopropyl groups, isobutyl groups, tert-butyl groups, and 2-ethylhexyl groups. Examples of cyclic alkyl groups include cyclopentyl groups and cyclohexyl groups. Examples of alkenyl groups include vinyl groups and aryl groups. Examples of aryl groups include phenyl groups and tolyl groups. Examples of aralkyl groups include 2-phenylethyl groups and 2-methyl-2-phenylethyl groups. Examples of halogenated alkyl groups include 3,3,3-trifluoropropyl, 2-(nonafluorobutyl)ethyl, and 2-(heptadecafluorooctyl)ethyl groups, among which methyl and phenyl groups are preferred.

[0038] R 2 are independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, and are preferably an alkyl group. Examples of alkyl groups include R 1 Examples of the alkoxyalkyl group include a methoxyethyl group and a methoxypropyl group. Examples of the alkenyl group include R 1 Examples of the acyl group include the same groups as those exemplified in R. The group having 1 to 8 carbon atoms is preferred. Examples of the acyl group include an acetyl group and an octanoyl group. 2 is preferably an alkyl group, more preferably a methyl group or an ethyl group.

[0039] Examples of the component (D) include (D-1) organopolysiloxanes represented by the following general formula (2): (In the formula, R 1are independently unsubstituted or substituted monovalent hydrocarbon groups, R 2 are independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, b is an integer of 5 to 100, and a is 0, 1, or 2.

[0040] R 1 and R 2 is the same as above. b is an integer of 5 to 100, preferably 5 to 50. a is 0, 1 or 2, preferably 0.

[0041] Specific examples of suitable organopolysiloxanes for component (D-1) include the following: (In the formula, Me is a methyl group.)

[0042] When component (D-1) is added, the amount is preferably 5 to 1,000 parts by mass, more preferably 10 to 900 parts by mass, and even more preferably 20 to 800 parts by mass, per 100 parts by mass of component (A).

[0043] (D-2) Component (D) also includes a silane coupling agent (D-2). Examples of the silane coupling agent include vinyl silane coupling agents, epoxy silane coupling agents, acrylic silane coupling agents, and long-chain alkyl silane coupling agents. These can be used alone or in appropriate combinations of two or more in combination with component (D-1). Among these, long-chain alkyl silane coupling agents having 5 to 20 carbon atoms are preferred, and decyltrimethoxysilane is more preferred.

[0044] When component (D-2) is added, the amount is preferably 0.05 to 5 parts by mass, more preferably 0.07 to 4.5 parts by mass, and even more preferably 0.09 to 4 parts by mass, per 100 parts by mass of the total of components (B) and (C). By using it in this range, the effect can be more effectively exhibited.

[0045] The surface treatment method for components (B) and (C) with component (D) can be a spraying method using a fluid nozzle, a stirring method using shear force, a dry method using a ball mill or mixer, or a wet method using an aqueous or organic solvent. Stirring is performed at a temperature that does not cause destruction of the aluminum nitride powder. In a dry method, the temperature in the system or the drying temperature after treatment is determined appropriately depending on the type of surface treatment agent so as not to volatilize or decompose the surface treatment agent, but is, for example, 80 to 180°C.

[0046] The viscosity of the organopolysiloxane of component (D) at 25°C is 0.01 to 100 mPa·s, preferably 1 to 50 mPa·s. If the viscosity is less than 0.01 mPa·s, the silicone composition may be prone to oil bleeding and dripping. If the viscosity exceeds 100 mPa·s, the resulting silicone composition may have poor fluidity, which may worsen application workability.

[0047] The amount of component (D) in the silicone composition is preferably 2 to 6.5 mass %, more preferably 3 to 6 mass %, and even more preferably 3.5 to 5.5 mass %.

[0048] [Curable Composition] The highly thermally conductive silicone composition of the present invention may be used as is, or may be further blended with a curing agent to form a curable composition.

[0049] Curable thermally conductive silicone compositions can be prepared in the following three forms. The organopolysiloxane (A), which is the base polymer, can be one of the organopolysiloxanes of components (AI) to (A-IV) above, blended with the thermally conductive fillers (B), (C), and (D) described above. [I] Addition reaction-curable thermally conductive silicone composition [II] Condensation reaction-curable thermally conductive silicone composition [III] Organic peroxide-curable thermally conductive silicone composition Of these, the addition reaction-curable thermally conductive silicone composition [I] is preferred because it cures quickly and does not produce by-products. Each of these compositions is described in detail below.

[0050] [I] Addition-reaction-curable heat-conductive silicone composition When the silicone composition is an addition-reaction-curable heat-conductive silicone composition that cures via a hydrosilylation reaction, the above-described components (A-1) and (A-1-2) are used as the above-described (A), and the composition further contains the following component, where the curing agent is the following (E): (E) a platinum group metal-based curing catalyst (F) optionally an addition reaction inhibitor

[0051] (E) The platinum group metal curing catalyst is a catalyst for accelerating the curing of the silicone composition, and examples thereof include chloroplatinic acid, an alcohol solution of chloroplatinic acid, an olefin complex of platinum, an alkenylsiloxane complex of platinum, and a carbonyl complex of platinum.

[0052] The amount of component (E) is the amount necessary for curing the silicone composition, and specifically, it is preferably an amount such that the platinum metal in component (F) is 0.01 to 1,000 ppm (by mass), and more preferably 0.1 to 500 ppm, by mass, relative to component (A-I-1). If the amount of component (F) is less than the lower limit of the above range, the resulting silicone composition may not cure sufficiently, while adding an amount exceeding the upper limit of the above range does not significantly improve the cure rate of the resulting silicone composition.

[0053] (F) Curing Reaction Inhibitor In order to adjust the curing rate of the silicone composition and improve handling and workability, a curing reaction inhibitor can be blended in. Examples of curing reaction inhibitors include acetylene-based compounds such as 2-methyl-3-butyn-2-ol, 2-phenyl-3-butyn-2-ol, and 1-ethynyl-1-cyclohexanol; ene-yne ​​compounds such as 3-methyl-3-penten-1-yne and 3,5-dimethyl-3-hexen-1-yne; and other hydrazine-based compounds, phosphine-based compounds, and mercaptan-based compounds. These can be used alone or in appropriate combinations of two or more.

[0054] Although there are no particular restrictions on the amount of component (F), it is preferable that the amount be 0.0001 to 1.0% by mass of the silicone composition. By setting the amount within this range, the workability and curing speed of the silicone composition become more favorable.

[0055] [II] Condensation-Curable Thermally Conductive Silicone Composition When the silicone composition is a condensation-curable thermally conductive silicone composition, the above-described component (A-II) is used as the above-described (A), and the following components are further included, with the curing agent being the following component (G): (G) a silane having at least three silicon-bonded hydrolyzable groups per molecule or a partial hydrolyzate thereof, and (H) optionally a condensation reaction catalyst.

[0056] Examples of the silicon-bonded hydrolyzable group in component (G) include the same alkoxy group, alkoxyalkoxy group, acyloxy group, ketoxime group, alkenoxy group, amino group, aminoxy group, and amide group as described above.In addition to the above-mentioned hydrolyzable groups, the silicon atom of this silane may be bonded with, for example, the same linear alkyl group, branched alkyl group, cyclic alkyl group, alkenyl group, aryl group, aralkyl group, or halogenated alkyl group as described above.Examples of such silanes or their partial hydrolyzates include methyltriethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, and ethylorthosilicate.

[0057] The amount of component (G) blended is the amount necessary for curing the silicone composition, and specifically, it is preferably 0.01 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of component (A-II). If the content of this silane or its partial hydrolysate is below the lower limit of the above range, the storage stability of the resulting silicone composition may be reduced, while if the content exceeds the upper limit of the above range, the curing of the resulting silicone composition may be significantly slowed.

[0058] The component (H) is an optional component and is not essential when, for example, a silane having a hydrolyzable group such as an aminoxy group, an amino group, or a ketoxime group is used as the curing agent. Examples of such condensation reaction catalysts include organic titanate esters such as tetrabutyl titanate and tetraisopropyl titanate; organic titanium chelate compounds such as diisopropoxybis(acetylacetate)titanium and diisopropoxybis(ethylacetoacetate)titanium; organic aluminum compounds such as aluminum tris(acetylacetonate) and aluminum tris(ethylacetoacetate); organic aluminum compounds such as zirconium tetra(acetylacetonate) and zirconium tetrabutylate; dibutyltin dioctoate and dibutyltin dioctoate; metal salts of organic carboxylic acids such as tin naphthenate, tin oleate, tin butyrate, cobalt naphthenate, and zinc stearate; amine compounds and salts thereof such as hexylamine and dodecylamine phosphate; quaternary ammonium salts such as benzyltriethylammonium acetate; lower fatty acid salts of alkali metals such as potassium acetate and lithium nitrate; dialkylhydroxylamines such as dimethylhydroxylamine and diethylhydroxylamine; and guanidyl group-containing organosilicon compounds.

[0059] When component (H) is added, the amount thereof need only be the amount necessary to cure the silicone composition, and specifically, it is preferably 0.01 to 20 parts by mass, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of component (A-II). This is because, when this catalyst is essential, if the content of this catalyst is below the lower limit of the above range, the resulting silicone composition tends to not cure sufficiently, and conversely, if the content exceeds the upper limit of the above range, the storage stability of the resulting silicone composition tends to decrease.

[0060] [III] Organic Peroxide-Curable Thermally Conductive Silicone Composition When the silicone composition is an organic peroxide-curable thermally conductive silicone composition, the silicone composition uses the component (A-III) shown above as the component (A) and further contains the following component, where the curing agent is the component (I) shown below: (I) Organic Peroxide

[0061] (I) Examples of organic peroxides include benzoyl peroxide, dicumyl peroxide, 2,5-dimethylbis(2,5-t-butylperoxy)hexane, di-t-butyl peroxide, and t-butyl perbenzoate.

[0062] The amount of component (I) is the amount necessary for curing the silicone composition, and specifically, it is preferably in the range of 0.1 to 5 parts by mass per 100 parts by mass of the organopolysiloxane of component (A-III) above. If the amount of component (I) is less than the lower limit of this range, the resulting silicone composition tends to not cure sufficiently, while if the amount added exceeds the upper limit of this range, the cure rate of the resulting silicone composition does not improve significantly and may even cause voids.

[0063] Furthermore, the silicone composition of the present invention may contain other optional components, as long as the object of the present invention is not impaired, such as fillers such as fumed silica, precipitated silica, and fumed titanium oxide, fillers whose surfaces have been hydrophobized with an organosilicon compound, adhesion promoters such as 3-glycidoxypropyltrimethoxysilane and 3-methacryloxypropyltrimethoxysilane, and other flame retardants and plasticizers such as pigments, dyes, fluorescent dyes, heat-resistant additives, and triazole-based compounds. Furthermore, thermally conductive fillers other than components (B) and (C) may also be blended within limits that do not impair the effects of the present invention, such as aluminum powder, copper powder, silver powder, nickel powder, gold powder, zinc oxide powder, magnesium oxide powder, aluminum oxide powder, boron nitride powder, diamond powder, and carbon powder.

[0064] [Production Method] The silicone composition of the present invention can be prepared by uniformly mixing the predetermined amounts of the above-mentioned components. For example, a method that includes a step of mixing components (B) and (C) is preferred. It may also include a step of mixing optional components.

[0065] [Thermal Conductive Silicone Composition] The thermal conductivity of the thermally conductive silicone composition is a high thermal conductivity of 8.0 W / m K or more, preferably 9.0 W / m K or more, as measured by the hot disk method in accordance with ISO 22007-2. There is no particular upper limit, and the upper limit may be higher, but it can be set to 16.0 W / m K or less. The measurement temperature is 25°C.

[0066] The viscosity at 25°C, measured at 10 rpm using a spiral viscometer, is 30 to 800 Pa·s, preferably 30 to 600 Pa·s, and more preferably 100 to 400 Pa·s. Within this range, a silicone composition with good handleability can be obtained.

[0067] [Cured Product] When the silicone composition is curable, the curing method is not limited. Examples include molding the silicone composition and then leaving it at room temperature, or molding the silicone composition and then heating it to 40 to 200°C. These methods result in a silicone elastomer molded product or silicone rubber. The properties of the silicone rubber thus obtained are not limited, but examples include gel, low-hardness rubber, and high-hardness rubber. The cured product preferably has a thickness of 150 μm or more. There is no particular upper limit, but considering the size of heat-generating electronic components using this silicone composition, a thickness of 5 mm or less is preferred. The hardness of the cured product is preferably 3 to 90, more preferably 5 to 80, and even more preferably 30 to 80, when the silicone composition is poured into a mold that will give a cured thickness of 6 mm, cured at 100°C for 1 hour, and then measured with a Shore 00 hardness tester 30 seconds after pressing the 6 mm-thick cured product.

[0068] The present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited to the following examples. In the following formulas, Me is a methyl group, and the bonding order of the siloxane units does not matter. % in the composition is by mass unless otherwise specified.

[0069] The components used in the examples and comparative examples are shown below. The viscosity of each component at 25°C was measured using a Brookfield viscometer, and the rotor, rotation speed, and rotation time were selected appropriately according to the viscosity in accordance with conventional methods. Component (A) A-1: ​​A dimethylpolysiloxane having a viscosity (25°C) of 400 mPa·s, a specific gravity (25°C) of 0.98, both ends of which are terminated with dimethylvinylsilyl groups, and a vinyl group content of 0.018 mol / 100 g. A-2: A dimethylsiloxane-diphenylsiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups, having a specific gravity (25°C) of 1.07 and a viscosity (25°C) of 400 mPa·s. A-3: A dimethylsiloxane-diphenylsiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups, having a specific gravity (25°C) of 1.00 and a viscosity (25°C) of 1,000 mPa·s. A-4: Organohydrogenpolysiloxane represented by the following formula, having a specific gravity (25°C) of 0.97 and a viscosity (25°C) of 28 mPa·s

[0070]

[0071] Component (B): Rounded aluminum nitride powder (specific gravity: 3.32) having the properties shown in the table below.

[0072] D 90 / D 10 In the volume-based laser diffraction particle size distribution, the cumulative 90 ) and cumulative 10% (D 10 ) means the ratio of

[0073] Component (C): Irregular shaped aluminum nitride powder (specific gravity: 3.32) having the properties shown in the table below.

[0074]

[0075] Component (D) D-1: an organopolysiloxane represented by the following formula, having a specific gravity (25°C) of 0.97 and a viscosity (25°C) of 30 mPa·s

[0076]

[0077] Component (E) E-1: chloroplatinic acid-1,3-divinyltetramethyldisiloxane complex having a specific gravity (25°C) of 1.00 and a platinum concentration of 1% by mass

[0078] Component (F) F-1: 50% toluene solution of 1-ethynyl-1-cyclohexanol, with a specific gravity (25°C) of 0.92

[0079] [Examples and Comparative Examples] Using the above components, silicone compositions were prepared by the methods described below, and thermally conductive molded articles were obtained using these silicone compositions. These were then evaluated by the methods described below. The results are also shown in the tables.

[0080] The above components were mixed in the amounts shown in Tables 3 to 6 below to obtain silicone compositions. Specifically, (A), (B), (C), and (D) were placed in a 5-liter gate mixer (manufactured by Inoue Seisakusho Co., Ltd., product name: 5-liter planetary mixer) in the amounts shown in the tables, and the mixture was heated and degassed at 150°C for 2 hours. The mixture was then cooled to room temperature (25°C), and component (F) was added. The mixture was then mixed at room temperature (25°C) until uniform. Component (E) was then added, and the mixture was degassed and mixed at room temperature until uniform. The initial viscosity, post-cure hardness, and thermal conductivity before and after curing of the silicone compositions obtained in this manner were evaluated using the methods described below. The results are also shown in the tables.

[0081] [Evaluation of viscosity (initial)] The initial viscosity of the silicone composition was measured at 25°C using a spiral viscometer: Malcom viscometer (Type PC-10AA, rotation speed 10 rpm), and the value was read after 10 minutes. Note that in Comparative Examples 3 and 9, oil separation was severe immediately after production, and the viscosity changed unstably, so it was determined that measurement was impossible.

[0082] [Evaluation of hardness after curing] The silicone composition was poured into a mold to give a cured thickness of 6 mm and cured at 100°C for 1 hour. The resulting 6 mm thick cured product was then measured using a Shore OO hardness tester. [Evaluation of thermal conductivity] The silicone composition was poured into a mold to give a cured thickness of 6 mm and cured at 100°C for 1 hour. The resulting 6 mm thick cured product was then measured for thermal conductivity at 25°C using a hot disc method thermal property measuring device TPS 2500 S manufactured by Kyoto Electronics Manufacturing Co., Ltd. (hot disc method in accordance with ISO 22007-2).

[0083]

[0084]

[0085]

[0086]

Claims

1. (A) Organopolysiloxane (excluding component (D)), (B) an oxygen content of 0.5% by mass or less, and a cumulative particle size distribution of 50% (D) based on a volume-based laser diffraction particle size distribution. 50 ) the average particle diameter is 45 to 85 μm and the cumulative 90 ) and cumulative 10% (D 10 ) ratio (D 90 / D 10 (C) a rounded aluminum nitride powder having a BET specific surface area of ​​1.0 to 4.0 m 2 / g and having an average particle size of 0.5 to 5 μm, and (D) an aluminum nitride powder having an irregular shape, the powder being represented by the following general formula (1): -SiR 1 a (OR 2 ) 3-a (1) (wherein, R 1 are independently unsubstituted or substituted monovalent hydrocarbon groups, R 2 wherein each of the following is independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group, and a is 0, 1, or 2:

2. The component (D) is represented by the following general formula (2): (In the formula, R 1 are independently unsubstituted or substituted monovalent hydrocarbon groups, R 2 are independently an alkyl group, an alkoxyalkyl group, an alkenyl group, or an acyl group; b is an integer of 5 to 100; and a is 0, 1, or 2.

3. The thermally conductive silicone composition of claim 1, further comprising a curing agent.

4. The thermally conductive silicone composition according to claim 3, which is an addition reaction curing type, a condensation reaction curing type, or an organic peroxide curing type.

5. The thermally conductive silicone composition of claim 4, which is an addition reaction curing type.

6. A cured product of the thermally conductive silicone composition according to any one of claims 3 to 5.

7. A method for producing the thermally conductive silicone composition according to any one of claims 1 to 5, comprising the step of mixing components (B) and (C).

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