JP2024051534A - Thermally conductive silicone composition, thermally conductive silicone cured product, and electrical parts - Google Patents

Abstract

[Problem] To provide a thermally conductive silicone composition capable of providing a cured product of the thermally conductive silicone composition having high thermal conductivity and excellent compressibility. [Solution] A thermally conductive silicone composition containing specific amounts of (A) an organopolysiloxane having two or more alkenyl groups per molecule, (B) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule, (C) a thermally conductive filler consisting of spherical alumina fillers (C-1), (C-3) and (C-4) having a specific average particle size, crushed alumina filler (C-2) having a specific average particle size, and irregular aluminum nitride fillers (C-5) and (C-6) having a specific average particle size, (D) a platinum group metal-based curing catalyst, (E) an addition reaction inhibitor, and (F) a surface treatment agent. [Selected Figure] None

Description

The present invention relates to a thermally conductive silicone composition having high thermal conductivity, its cured product, and an electrical part containing the cured product.

As electrical and electronic devices continue to become smaller and more highly integrated, the impact of heat generated by electrical and electronic components such as power semiconductors and memory is becoming more serious than ever. When heat accumulates in electrical and electronic components, the temperature of the electrical and electronic components rises, which can lead to malfunctions or breakdowns. To prevent such problems, many heat dissipation methods and heat dissipation materials used for these have been proposed to efficiently dissipate the heat generated by electronic components to cooling components such as heat sinks.

Conventionally, in electrical and electronic equipment, heat sinks made of metal plates with high thermal conductivity, such as aluminum or copper, have been used to suppress temperature increases in elements during operation. The heat sink conducts heat generated by the elements and releases it from its surface due to the temperature difference with the outside air.

If the heat generating element and the heat sink are in direct contact with each other, air will be present at the interface, which will impede heat conduction, so the heat sink must be tightly attached to the element. Since each element has different heights and tolerances during assembly, a flexible and thermally conductive sheet or grease is used.

The sheets are easier to handle than grease, and thermally conductive sheets made from thermally conductive resins are used in a variety of fields.

In addition, in the automotive field, long-term reliability is required over a wide temperature range, from the lowest temperature in cold regions, around -40°C, to high temperatures of heat-generating components, such as 150°C or higher. Furthermore, properties such as flame retardancy and electrical insulation are often required. Silicone is an ideal resin that meets all of these properties, and thermally conductive silicone sheets that combine silicone with a thermally conductive filler are used.

Thermally conductive silicone sheets are often used when there is a certain amount of space between the heating element and the cooling part such as the heat sink or the housing. In such spaces, electrical insulation is often required, and insulating properties are often required for thermally conductive sheets as well. Therefore, metal particles such as aluminum, copper, and silver cannot be used as thermally conductive fillers, and insulating thermally conductive fillers such as aluminum hydroxide and alumina are often used. However, aluminum hydroxide and alumina have low thermal conductivity themselves, so that the thermal conductivity of thermally conductive silicone compositions using them as thermally conductive fillers is low.

In recent years, the amount of heat generated by electric and electronic components has increased, and the thermal conductivity required for thermally conductive sheets has also risen. Therefore, aluminum hydroxide and alumina alone cannot achieve sufficiently high thermal conductivity as thermally conductive fillers. Therefore, the use of nitrides such as boron nitride and aluminum nitride as high thermally conductive fillers has attracted attention. Ordinary scaly boron nitride has a layered crystal structure, and because there is a significant difference in thermal conductivity between the crystal plane direction and the stacking direction, it exhibits anisotropic thermal conductivity. In contrast, aluminum nitride has a wurtzite crystal structure. Therefore, aluminum nitride does not have the extreme anisotropy of boron nitride.

Therefore, various heat dissipation materials have been reported that use aluminum nitride as a highly thermally conductive filler (Patent Document 1, Patent Document 2).

However, when aluminum nitride with an average particle size of 3 μm or less is highly loaded into silicone, the material becomes highly viscous and its moldability decreases.

Patent Document 3 discloses a thermally conductive grease that suppresses viscosity increases by containing spherical alumina with an average particle size of 0.2 to 1.0 μm and aluminum nitride with an average particle size of 1 to 3 μm and a maximum particle size of 2 to 10 μm. However, because the particle size of aluminum nitride is small, it is difficult to achieve high thermal conductivity.

Therefore, Patent Document 4 proposes a composition with high thermal conductivity that contains aluminum nitride with an average particle size of 30 to 150 μm, aluminum nitride or alumina with an average particle size of 1 to 30 μm, and inorganic particles with an average particle size of 0.1 to 1 μm. However, the type and shape of inorganic particles such as aluminum nitride, and the hardness when the silicone composition is cured, have not been optimized, making it difficult to improve the thermal conductivity and compressibility of the thermally conductive cured product. Furthermore, poor compressibility makes it difficult to fit the sheet within the tolerances during assembly processing, and other parts may be damaged.

To solve this problem, Patent Document 5 proposes a highly thermally conductive composition with excellent compressibility that uses non-sintered aluminum nitride with an average particle size of 20 to 120 μm and alumina containing spherical alumina with an average particle size of 0.1 to 5 μm as thermally conductive fillers. However, since only non-sintered amorphous aluminum nitride fillers are used as the large particle size filler, the sheet is prone to becoming brittle, and cracks may occur when highly compressed, resulting in a decrease in insulation. In recent years, there has been a trend toward higher drive voltages for on-board modules, and high compression is required for thermally conductive sheets to absorb tolerances, so ensuring insulation during compression has been extremely important.

Japanese Patent Application Laid-Open No. 3-14873 Japanese Patent No. 4357064 JP 2004-91743 A Patent No. 6246986 JP 2021-195499 A

As mentioned above, the challenge is to provide a thermally conductive silicone sheet that contains aluminum nitride and has high thermal conductivity and excellent insulation properties when compressed.

The present invention has been made to solve the above problems, and aims to provide a thermally conductive silicone composition that can provide a cured product of the thermally conductive silicone composition that has high thermal conductivity and excellent compressibility, the cured product thereof, and an electrical component that includes the cured product.

（式中、Ｒ^４は独立に炭素原子数１～６のアルキル基であり、ｃは５～１００の整数である。）
で表される分子鎖片末端がトリアルコキシシリル基で封鎖されたジメチルポリシロキサン、
を含むものであることを特徴とする熱伝導性シリコーン組成物を提供する。 In order to solve the above problems, the present invention provides
(A) organopolysiloxane having two or more alkenyl groups in one molecule: 100 parts by mass,
(B) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the number of moles of hydrosilyl groups is 0.1 to 5.0 times the number of moles of alkenyl groups derived from component (A);
(C) a thermally conductive filler consisting of the following components (C-1) to (C-6): 8,600 to 9,600 parts by mass,
(C-1) Spherical alumina filler having an average particle size of more than 0.1 μm and not more than 2 μm: 1,500 to 2,500 parts by mass. (C-2) Crushed alumina filler having an average particle size of more than 0.5 μm and not more than 5 μm: 200 to 800 parts by mass. (C-3) Spherical alumina filler having an average particle size of more than 5 μm and not more than 20 μm: 1,500 to 2,500 parts by mass.
(C-4) Spherical alumina filler having an average particle size of more than 60 μm and not more than 100 μm: 500 to 1,500 parts by mass,
(C-5) irregular aluminum nitride filler having an average particle size of more than 50 μm and not more than 90 μm: 2,200 to 3,200 parts by mass,
(C-6) irregular aluminum nitride filler having an average particle size of more than 90 μm and not more than 120 μm: 500 to 1,500 parts by mass,
(D) Platinum group metal curing catalyst: 0.1 to 2,000 ppm by mass of platinum group element relative to component (A)
(E) an addition reaction inhibitor: 0.01 to 2.0 parts by mass per 100 parts by mass of the component (A); (F) a surface treatment agent which is one or more selected from the following (F-1) and (F-2): 200 to 400 parts by mass per 100 parts by mass of the component (A);
(F-1) The following general formula (1)
R ¹ _a R ² _b Si(OR ³ ) _4-a-b (1)
(In the formula, R ¹ is independently an alkyl group having 6 to 15 carbon atoms, R ² is independently a group selected from an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, R ³ is independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, b is an integer of 0 to 2, and a+b is an integer of 1 to 3.)
An alkoxysilane compound represented by the formula:
(F-2) The following general formula (2)

(In the formula, R ⁴ is independently an alkyl group having 1 to 6 carbon atoms, and c is an integer of 5 to 100.)
a dimethylpolysiloxane having one molecular chain end blocked with a trialkoxysilyl group, represented by the formula:
The present invention provides a thermally conductive silicone composition comprising:

The thermally conductive silicone composition of the present invention can be easily made into a uniform composition by blending amorphous aluminum nitride, crushed alumina, and spherical alumina as thermally conductive fillers in a specific composition and ratio. In addition, the thermally conductive silicone cured product obtained from the thermally conductive silicone composition of the present invention has high thermal conductivity but low hardness, so it does not apply stress to the heat-generating component and has sufficient flexibility and compressibility to follow the fine unevenness of the heat-generating component and cooling component. In addition, since the sheet embrittlement during compression is suppressed, cracks are unlikely to occur even during high compression, and it can be applied to modules with high driving voltages and large tolerances. Furthermore, the cured product of the thermally conductive silicone composition of the present invention can sufficiently ensure insulation during compression. In other words, the thermally conductive silicone composition of the present invention can provide a cured product of the thermally conductive silicone composition that has high thermal conductivity and excellent compressibility.

（式中、Ｒ^５は独立に炭素数１～６のアルキル基、炭素数６～１２のアリール基、及び炭素数７～１２のアラルキル基から選ばれる基、ｄは５～２，０００の整数である。）
で表される２３℃における動粘度が１０～１００，０００ｍｍ^２／ｓのオルガノポリシロキサン：（Ａ）成分１００質量部に対し０．１～１００質量部
を含有するものであることが好ましい。 Furthermore, as the component (G),

(In the formula, ^R5 is independently a group selected from an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, and d is an integer of 5 to 2,000.)
The organopolysiloxane having a kinetic viscosity at 23° C. of 10 to 100,000 mm ² /s represented by the following formula is preferably contained in an amount of 0.1 to 100 parts by mass per 100 parts by mass of component (A).

The above component (G) can be added to impart properties such as viscosity adjuster.

The composition of the present invention is preferably one that has a maximum indentation load of 200 g or less at 23°C, measured using a texture analyzer with a cylindrical probe having a diameter of 4 mm, a compression distance of 15 mm, and a speed of 1 mm/sec.

A thermally conductive silicone composition with such a maximum indentation load can be easily molded into a desired shape.

The present invention also provides a thermally conductive silicone cured product, which is a cured product of the thermally conductive silicone composition of the present invention.

The thermally conductive silicone cured product of the present invention has high thermal conductivity yet low hardness, so it does not apply stress to the heat-generating component and has sufficient flexibility and compressibility to follow the fine irregularities of the heat-generating component and cooling component. In addition, because the sheet is prevented from becoming brittle during compression, cracks are unlikely to occur even during high compression, making it possible to apply the product to modules with high driving voltages and large tolerances. Furthermore, the thermally conductive silicone cured product of the present invention can ensure sufficient insulation during compression. In other words, the thermally conductive silicone cured product of the present invention can have high thermal conductivity and exhibit excellent compressibility.

The cured product of the thermally conductive silicone composition of the present invention is preferably in the form of a sheet.

Thermal conductive silicone cured products are easy to handle if they are in sheet form.

It is preferable that the hardness of the thermally conductive silicone cured product is 10 points or more and 40 points or less, as measured with an Asker C hardness tester.

A cured product with this hardness is easy to handle, can be deformed to fit the shape of the object to be dissipated heat, and can exhibit good heat dissipation characteristics without applying stress to the object to be dissipated heat. In addition, a cured product with this hardness can be prevented from breaking.

Thermal conductivity at 23°C measured by the hot disk method may be 10 W/mK or more.

In this way, the thermally conductive silicone cured product of the present invention can exhibit excellent thermal conductivity. Therefore, the thermally conductive silicone cured product of the present invention is useful as a heat dissipation member.

The dielectric breakdown voltage when a 2 mm thick sheet of the thermally conductive silicone cured material is compressed by 50% may be 10 kV or more.

In this way, the thermally conductive silicone cured product of the present invention can exhibit an excellent dielectric breakdown voltage upon compression of 10 kV or more, preventing cracks from occurring upon compression and ensuring stable insulation.

The present invention also provides an electrical component that is characterized by including the thermally conductive silicone cured product of the present invention as part of its configuration.

Electrical components made using the cured silicone composition of the present invention can be cooled efficiently, allowing for stable operation without loss of performance or lifespan due to heat generation.

The electrical components of the present invention can be used, for example, in vehicles.

Electrical parts made using the cured silicone composition of the present invention are able to maintain stable insulation, making them suitable for in-vehicle applications that require high insulation and long life.

As described above, the thermally conductive silicone composition of the present invention can easily be made into a uniform composition. In addition, the thermally conductive silicone cured product obtained from the thermally conductive silicone composition of the present invention has high thermal conductivity yet low hardness, so it does not apply stress to the heat-generating component and has sufficient flexibility and compressibility to follow the fine unevenness of the heat-generating component and cooling component. In addition, since the embrittlement of the sheet during compression is suppressed, cracks are unlikely to occur even during high compression, and it is possible to apply it to modules with high driving voltages and large tolerances. Furthermore, the cured product of the thermally conductive silicone composition of the present invention can sufficiently ensure insulation during compression. In other words, the thermally conductive silicone composition of the present invention can provide a cured product of the thermally conductive silicone composition that has high thermal conductivity and excellent compressibility.

Furthermore, the thermally conductive silicone cured product of the present invention has high thermal conductivity yet low hardness, so it does not apply stress to the heat-generating component and has sufficient flexibility and compressibility to follow the fine irregularities of the heat-generating component and cooling component. In addition, because the sheet is prevented from becoming brittle during compression, cracks are less likely to occur even during high compression, making it possible to apply the product to modules with high driving voltages and large tolerances. Furthermore, the thermally conductive silicone cured product of the present invention can ensure sufficient insulation during compression. In other words, the thermally conductive silicone cured product of the present invention can have high thermal conductivity and exhibit excellent compressibility.

The electrical components of the present invention allow for efficient cooling, so there is no deterioration in performance or lifespan due to heat generation, and stable operation is possible.

As described above, there has been a need to develop a thermally conductive silicone composition that can provide a cured product of the thermally conductive silicone composition that has high thermal conductivity and excellent compressibility, a cured product thereof, and an electrical component that includes the cured product.

After extensive research into the above-mentioned problems, the inventors have found that by using amorphous aluminum nitride, crushed alumina, and spherical alumina as thermally conductive fillers and skillfully combining their average particle size and compounding ratio, it is possible to ensure insulation during compression in a thermally conductive silicone sheet obtained by curing a thermally conductive silicone composition containing an organopolysiloxane. The inventors have found that the cured product of the resulting composition has high thermal conductivity yet low hardness, and therefore does not apply stress to the heat-generating component, and has flexibility and compressibility that can follow the fine unevenness of the heat-generating component and cooling component. In addition, because the embrittlement of the sheet during compression is suppressed, cracks are unlikely to occur even during high compression, and it is possible to apply the sheet to modules with high driving voltages and large tolerances. The inventors have come up with the present invention based on these findings.

（式中、Ｒ^４は独立に炭素原子数１～６のアルキル基であり、ｃは５～１００の整数である。）
で表される分子鎖片末端がトリアルコキシシリル基で封鎖されたジメチルポリシロキサン、
を含むものであることを特徴とする熱伝導性シリコーン組成物である。 That is, the present invention provides a composition comprising: (A) 100 parts by mass of an organopolysiloxane having two or more alkenyl groups in one molecule;
(B) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the number of moles of hydrosilyl groups is 0.1 to 5.0 times the number of moles of alkenyl groups derived from component (A);
(C) a thermally conductive filler consisting of the following components (C-1) to (C-6): 8,600 to 9,600 parts by mass,
(C-1) Spherical alumina filler having an average particle size of more than 0.1 μm and not more than 2 μm: 1,500 to 2,500 parts by mass. (C-2) Crushed alumina filler having an average particle size of more than 0.5 μm and not more than 5 μm: 200 to 800 parts by mass. (C-3) Spherical alumina filler having an average particle size of more than 5 μm and not more than 20 μm: 1,500 to 2,500 parts by mass.
(C-4) Spherical alumina filler having an average particle size of more than 60 μm and not more than 100 μm: 500 to 1,500 parts by mass,
(C-5) irregular aluminum nitride filler having an average particle size of more than 50 μm and not more than 90 μm: 2,200 to 3,200 parts by mass,
(C-6) irregular aluminum nitride filler having an average particle size of more than 90 μm and not more than 120 μm: 500 to 1,500 parts by mass,
(D) Platinum group metal curing catalyst: 0.1 to 2,000 ppm by mass of platinum group element relative to component (A)
(E) an addition reaction inhibitor: 0.01 to 2.0 parts by mass per 100 parts by mass of the component (A); (F) a surface treatment agent which is one or more selected from the following (F-1) and (F-2): 200 to 400 parts by mass per 100 parts by mass of the component (A);
(F-1) The following general formula (1)
R ¹ _a R ² _b Si(OR ³ ) _4-a-b (1)
(In the formula, R ¹ is independently an alkyl group having 6 to 15 carbon atoms, R ² is independently a group selected from an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, R ³ is independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, b is an integer of 0 to 2, and a+b is an integer of 1 to 3.)
An alkoxysilane compound represented by the formula:
(F-2) The following general formula (2)

(In the formula, R ⁴ is independently an alkyl group having 1 to 6 carbon atoms, and c is an integer of 5 to 100.)
a dimethylpolysiloxane having one molecular chain end blocked with a trialkoxysilyl group, represented by the formula:
The thermally conductive silicone composition is characterized by comprising:

The present invention also relates to a thermally conductive silicone cured product, which is a cured product of the thermally conductive silicone composition of the present invention.

The present invention also relates to an electrical component that includes the thermally conductive silicone cured product of the present invention as part of its configuration.

The present invention is described in detail below, but is not limited to these.

[Thermal conductive silicone composition]
As described above, the thermally conductive silicone composition of the present invention is a silicone composition comprising an organopolysiloxane having two or more alkenyl groups per molecule (hereinafter also referred to as alkenyl group-containing organopolysiloxane) (component (A)), an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule (component (B)), a thermally conductive filler (component (C)), a platinum group metal curing catalyst (component (D)), an addition reaction inhibitor (component (E)), and a surface treatment agent (component (F)).

The thermally conductive silicone composition of the present invention, which contains specific amounts of components (A) to (F), which will be described in detail below, can easily become a uniform composition. In addition, the thermally conductive silicone cured product obtained from the thermally conductive silicone composition of the present invention has high thermal conductivity yet low hardness, so it does not apply stress to the heat-generating component and has sufficient flexibility and compressibility to follow the fine irregularities of the heat-generating component and cooling component. In addition, because the sheet is prevented from becoming brittle during compression, cracks are unlikely to occur even during high compression, making it possible to apply the composition to modules with high driving voltages and large tolerances. Furthermore, the cured product of the thermally conductive silicone composition of the present invention can ensure sufficient insulation during compression.

Therefore, the thermally conductive silicone composition of the present invention can provide a cured product of the thermally conductive silicone composition that has high thermal conductivity and excellent compressibility.

The thermally conductive silicone composition of the present invention is described in more detail below.

[(A) Alkenyl-containing organopolysiloxane]
The alkenyl-containing organopolysiloxane, which is component (A), is an organopolysiloxane having two or more alkenyl groups bonded to silicon atoms in one molecule, and is the main component of the thermally conductive silicone cured product of the present invention.Normally, the main chain portion is generally composed of a repetition of diorganosiloxane units, but this may include a branched structure in a part of the molecular structure, or may be a cyclic body, but from the viewpoint of physical properties such as mechanical strength of the cured product, linear diorganopolysiloxane is preferred.

Examples of the alkenyl group include those having 2 to 8 carbon atoms, such as vinyl, allyl, propenyl, isopropenyl, butenyl, hexenyl, and cyclohexenyl groups. Of these, lower alkenyl groups such as vinyl and allyl groups are preferred, with vinyl being particularly preferred. The alkenyl group is characterized by having two or more alkenyl groups in the molecule, preferably 2 to 6, and more preferably 2 to 3. In order to provide good flexibility to the resulting cured product, it is most preferred that they are present bonded only to silicon atoms at the ends of the molecular chain.

Examples of functional groups other than the alkenyl group bonded to the silicon atom include monovalent hydrocarbon groups having 1 to 10 carbon atoms, preferably 1 to 6 carbon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl; aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl; and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Among these, methyl, ethyl, propyl, and phenyl groups are preferably used. In addition, all of the functional groups other than the alkenyl groups bonded to the silicon atom may be the same or different.

The kinematic viscosity of this organopolysiloxane at 23°C is usually in the range of 10 to 100,000 ^mm2 /s, and particularly preferably 100 to 50,000 ^mm2 /s. If the kinematic viscosity is within this range, the resulting composition will have sufficient storage stability and spreadability. In this specification, the kinematic viscosity is a value measured at 23°C using a Cannon-Fenske viscometer according to the method described in JIS Z 8803:2011.

As the organopolysiloxane of component (A), a single alkenyl group-containing organopolysiloxane may be used, or two or more alkenyl group-containing organopolysiloxanes having different kinetic viscosities may be used in combination.

[(B) Organohydrogenpolysiloxane]
The organohydrogenpolysiloxane of component (B) is an organohydrogenpolysiloxane having an average of 2 or more, preferably 2 to 100, hydrosilyl groups (hydrogen atoms directly bonded to silicon atoms) per molecule. Component (B) is a component that acts as a crosslinking agent for component (A). That is, the hydrosilyl groups in component (B) and the alkenyl groups in component (A) are added by a hydrosilylation reaction promoted by the platinum group metal curing catalyst of component (D) described below, to give a three-dimensional network structure having a crosslinked structure. Note that if the number of hydrosilyl groups is less than 2, the composition will not cure.

（式中、Ｒ^６は独立に水素原子、又は炭素数１～１２のアルキル基、炭素数６～１２のアリール基、及び炭素数７～１２のアラルキル基から選ばれる１価炭化水素基である。ただし、１分子中の２個以上、好ましくは２～１０個のＲ^６は水素原子である。また、ｅは１以上の整数、好ましくは１０～２００の整数である。） As the organohydrogenpolysiloxane, for example, one represented by the following average structural formula (4) is used, but it is not limited thereto.

(In the formula, R ⁶ is independently a hydrogen atom or a monovalent hydrocarbon group selected from an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms. However, at least two, preferably at least two and at most ten, R ^6s in one molecule are hydrogen atoms. Also, e is an integer of 1 or more, preferably an integer of 10 to 200.)

In formula (4), examples of monovalent hydrocarbon groups other than hydrogen atoms for R ⁶ include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, and dodecyl, cycloalkyl groups such as cyclopentyl, cyclohexyl, and cycloheptyl, aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl, and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl. Among these monovalent hydrocarbon groups, those having 1 to 10 carbon atoms, and particularly preferably having 1 to 6 carbon atoms, are preferably used, and among these, alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, and propyl, and phenyl groups are preferably used.

The amount of component (B) added is characterized in that the number of moles of hydrosilyl groups is 0.1 to 5.0 times the number of moles of alkenyl groups derived from component (A). Preferably, the number of moles of hydrosilyl groups is 0.3 to 2.0 times, more preferably 0.5 to 1.0 times, the number of moles of alkenyl groups derived from component (A). If the amount of hydrosilyl groups derived from component (B) is less than 0.1 mole per mole of alkenyl groups derived from component (A), the composition may not cure, or the strength of the cured product may be insufficient to maintain the shape of the molded product and make it difficult to handle. If the amount exceeds 5.0 moles, the cured product loses flexibility and becomes brittle.

[(C) Thermally conductive filler]
The thermally conductive silicone composition of the present invention uses, as the thermally conductive filler, a filler consisting of amorphous aluminum nitride filler (component (C-5) and component (C-6)), crushed alumina filler (component (C-2)), and spherical alumina filler (component (C-1), component (C-3), and component (C-4)).

[Components (C-5) and (C-6): amorphous aluminum nitride]
There are granulated and amorphous bodies. Granulated bodies are spherical particles, so they have better filling properties in silicone polymers than amorphous bodies. On the other hand, the thermal conductivity of granulated bodies is inferior to that of amorphous bodies. This is because a few percent of yttria is added to aluminum nitride during granulation, resulting in a mixture of aluminum nitride phases and yttria phases. Granulated bodies are also very expensive because of the granulation process. Therefore, amorphous aluminum nitride is essential in the present invention.

[Component (C-2): crushed alumina and components (C-1), (C-3) and (C-4): spherical alumina]
Alumina has various crystal phases such as α, β, θ, and γ depending on the sintering temperature. α-alumina, which has the highest sintering temperature, is chemically stable, so it is preferable to use α-alumina. In addition, although general alumina rarely has a single crystal phase, it is better to use one with a high α-phase ratio, and it is preferable to use one with an α-phase ratio of 90% or more, preferably 95% or more. Alumina has various granular shapes such as spherical, rounded, and crushed depending on the manufacturing method. In general, crushed alumina has a high α-phase ratio, so crushed alumina is preferred. On the other hand, spherical alumina has good filling properties in silicone polymers and can increase the fluidity of a composition that is extremely highly filled with filler. In addition, by blending spherical alumina of different particle size ranges, when the cured product is compressed, the spherical alumina flows effectively at each compression thickness, suppressing the occurrence of cracks. Therefore, crushed alumina and spherical alumina are essential in the present invention.

The thermally conductive filler, which is the component (C), specifically consists of the following components (C-1) to (C-6). Each of the fillers may be used alone or in combination of two or more.
(C-1) Spherical alumina filler having an average particle size of more than 0.1 μm and not more than 2 μm: 1,500 to 2,500 parts by mass. (C-2) Crushed alumina filler having an average particle size of more than 0.5 μm and not more than 5 μm: 200 to 800 parts by mass. (C-3) Spherical alumina filler having an average particle size of more than 5 μm and not more than 20 μm: 1,500 to 2,500 parts by mass.
(C-4) Spherical alumina filler having an average particle size of more than 60 μm and not more than 100 μm: 500 to 1,500 parts by mass,
(C-5) irregular alumina nitride filler having an average particle size of more than 50 μm and not more than 90 μm: 2,200 to 3,200 parts by mass,
(C-6) Irregular alumina nitride filler having an average particle size of more than 90 μm and not more than 120 μm: 500 to 1,500 parts by mass.

In the present invention, the average particle size is the volume-based cumulative 50% particle size (D ₅₀ ) value measured using a particle size distribution measuring device MT3000II manufactured by Microtrac Bell.

The spherical alumina filler of component (C-1) also plays a role in improving the thermal conductivity of the composition, but its main role is to adjust the viscosity of the composition, improve smoothness, and improve filling properties. The average particle size of component (C-1) is more than 0.1 μm and 2 μm or less, and 0.2 to 1.5 μm is more preferable in order to express the above-mentioned characteristics.

The amount of component (C-1) to be blended is 1,500 to 2,500 parts by mass, and preferably 1,700 to 2,300 parts by mass, per 100 parts by mass of component (A). If the amount is too small, it is difficult to improve the thermal conductivity, and if the amount is too large, the composition loses its fluidity and its moldability is impaired.

The crushed alumina filler of component (C-2), when used in combination with the spherical alumina filler of component (C-1), plays a role in improving the thermal conductivity, smoothness, and filling properties of the composition. Because it is crushed, there are more contact points with other fillers, and it is more effective at improving thermal conductivity than spherical alumina filler. The average particle size of component (C-2) is more than 0.5 μm and 5 μm or less, and 0.7 to 3 μm is more preferable in order to express the above-mentioned characteristics.

The amount of component (C-2) to be blended is 200 to 800 parts by mass, and preferably 300 to 700 parts by mass, per 100 parts by mass of component (A). If the amount is too small, it is difficult to improve the thermal conductivity, and if the amount is too large, the composition loses its fluidity and its moldability is impaired.

The spherical alumina fillers of the (C-3) and (C-4) components play a role in improving the thermal conductivity, smoothness, and filling properties of the composition. The use of spherical alumina fillers with multiple particle size distributions over a wide particle size range significantly improves filling properties. Furthermore, when the cured product is compressed, these spherical aluminas flow during deformation, allowing smooth compression and suppressing the occurrence of cracks in the cured product. The average particle size of the (C-3) component is more than 5 μm and 20 μm or less, and more preferably 7 to 15 μm, in order to express the above-mentioned characteristics. Furthermore, the average particle size of the (C-4) component is more than 60 μm and 100 μm or less, and more preferably 75 to 95 μm, in order to express the above-mentioned characteristics.

The amount of component (C-3) is 1,500 to 2,500 parts by mass, preferably 1,700 to 2,300 parts by mass, per 100 parts by mass of component (A). The amount of component (C-4) is 500 to 1,500 parts by mass, preferably 700 to 1,300 parts by mass, per 100 parts by mass of component (A). If the amount is too small, it is difficult to improve the thermal conductivity, and cracks may occur when the cured product is compressed. If the amount is too large, the composition loses its fluidity and its moldability is impaired.

The amorphous aluminum nitride fillers of the (C-5) and (C-6) components are responsible for increasing the thermal conductivity of the composition, and the thermal conductivity of the composition is greatly improved by filling the composition. The average particle size of the (C-5) component is more than 50 μm and not more than 90 μm, and more preferably 55 to 85 μm, in order to express the above-mentioned characteristics. The average particle size of the (C-6) component is more than 90 μm and not more than 120 μm, and more preferably 95 to 110 μm, in order to express the above-mentioned characteristics.

The amount of component (C-5) is 2,200 to 3,200 parts by mass, and preferably 2,400 to 3,000 parts by mass, per 100 parts by mass of component (A). The amount of component (C-6) is 500 to 1,500 parts by mass, and preferably 700 to 1,300 parts by mass, per 100 parts by mass of component (A). If the amount is too small, it is difficult to improve the thermal conductivity, and if the amount is too large, the composition loses its fluidity and its moldability is impaired.

By using component (C) in the above blending ratio, the above-mentioned effects of the present invention, particularly excellent thermal conductivity and excellent compressibility (excellent insulation when compressed), can be achieved more advantageously and reliably.

The content of the thermally conductive filler, component (C), is 8,600 to 9,600 parts by mass per 100 parts by mass of component (A). Outside this range, it is not possible to obtain a composition or a cured product that exhibits high thermal conductivity.

[(D) Platinum group metal curing catalyst]
The platinum group metal curing catalyst of component (D) is a catalyst for promoting the addition reaction between the alkenyl group derived from component (A) and the hydrosilyl group derived from component (B), and examples of catalysts well known for use in hydrosilylation reactions include platinum group metals such as platinum (including platinum black), rhodium, and palladium, H ₂ PtCl _{4.nH 2} O, H ₂ PtCl _{6.nH 2} O, NaHPtCl _6.nH 2 O, KaHPtCl _{6.nH 2} O, _{Na 2} PtCl _{6.nH 2 O} , K ₂ PtCl _{4.nH 2} O, PtCl 4.nH ₂ O, PtCl ₂ , and Na ₂ HPtCl _{4.nH 2 O.} O (wherein, n is an integer of 0 to 6, preferably 0 or 6), chloroplatinic acid and chloroplatinate salts, alcohol-modified chloroplatinic acid (see U.S. Pat. No. 3,220,972), complexes of chloroplatinic acid and olefins (see U.S. Pat. Nos. 3,159,601, 3,159,662 and 3,775,452), platinum black, platinum group metals such as palladium supported on a support such as alumina, silica or carbon, rhodium-olefin complexes, chlorotris(triphenylphosphine)rhodium (Wilkinson's catalyst), complexes of platinum chloride, chloroplatinic acid or chloroplatinate salts with vinyl group-containing siloxanes, particularly vinyl group-containing cyclic siloxanes.

The amount of component (D) used is 0.1 to 2,000 ppm, preferably 50 to 1,000 ppm, calculated as the mass of platinum group metal element relative to component (A).

[(E) Reaction control agent]
The addition reaction inhibitor of component (E) is not particularly limited as long as it is a known addition reaction inhibitor used in a normal addition reaction curing silicone composition. For example, acetylene compounds such as 1-ethynyl-1-cyclohexanol, 3-butyn-1-ol, 2-methyl-3-butyn-2-ol, and 3-methyl-1-tridecyne-3-ol, various nitrogen compounds, organic phosphorus compounds, oxime compounds, organic chloro compounds, and vinyl group-containing siloxanes such as 1,3-divinyl-1,1,3,3-tetramethyldisiloxane and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, are included. When component (E) is blended, the amount used is preferably about 0.01 to 2.0 parts by mass, particularly about 0.1 to 1.2 parts by mass, per 100 parts by mass of component (A). If the blended amount is too large, the curing reaction does not proceed, and molding efficiency may be impaired.

[(F) Surface treatment agent]
The purpose of the surface treatment agent of component (F) is to hydrophobize component (C) during the preparation of the composition, improve the wettability with component (A), and uniformly disperse component (C) in the matrix of component (A). Component (F) is at least one selected from components (F-1) and (F-2) shown below.

The component (F-1) is an alkoxysilane compound represented by the following general formula (1).
R ¹ _a R ² _b Si(OR ³ ) _4-a-b (1)
(In the formula, R ¹ is independently an alkyl group having 6 to 15 carbon atoms, R ² is independently a group selected from an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, R ³ is independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, b is an integer of 0 to 2, and a+b is an integer of 1 to 3.)

In the above general formula (1), examples of the alkyl group represented by ^R1 include a hexyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group, a tetradecyl group, etc. When the number of carbon atoms of the alkyl group represented by ^R1 is in the range of 6 to 15, the wettability of component (A) is sufficiently improved, the handleability is good, and the low-temperature properties of the composition are excellent.

Examples of the alkyl group having 1 to 5 carbon atoms represented by ^R2 include, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, a pentyl group, and a neopentyl group. Examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, and a biphenylyl group. Examples of the aralkyl group having 7 to 12 carbon atoms include a benzyl group, a phenylethyl group, a phenylpropyl group, and a methylbenzyl group. Among these, preferred are alkyl groups having 1 to 3 carbon atoms, such as a methyl group, an ethyl group, and a propyl group, and a phenyl group. Examples of ^R3 include a methyl group, an ethyl group, a propyl group, a butyl group, and a hexyl group.

（式中、Ｒ^４は独立に炭素原子数１～６のアルキル基であり、具体的には前記Ｒ^３で例示されたアルキル基と同じものが例示できる。ｃは５～１００、好ましくは５～７０、特に好ましくは１０～５０の整数である。） Component (F-2) is a dimethylpolysiloxane having one molecular chain end blocked with a trialkoxysilyl group, as represented by the following general formula (2).

(In the formula, R ⁴ is independently an alkyl group having 1 to 6 carbon atoms, and specific examples thereof include the same alkyl groups as those exemplified for R ³ above. c is an integer of 5 to 100, preferably 5 to 70, and particularly preferably 10 to 50.)

As the surface treatment agent for component (F), either component (F-1) or component (F-2) may be used alone or in combination with both.

When component (F) is added, the amount is 200 to 400 parts by mass, and preferably 250 to 350 parts by mass, per 100 parts by mass of component (A). If the proportion of this component is too high, it may induce oil separation.

（式中、Ｒ^５は独立に炭素数１～６のアルキル基、炭素数６～１２のアリール基、及び炭素数７～１２のアラルキル基から選ばれる基、ｄは５～２，０００の整数である。）
で表される２３℃における動粘度が１０～１００，０００ｍｍ^２／ｓのオルガノポリシロキサンを添加することができる。（Ｇ）成分としては、１種のオルガノポリシロキサンを単独で用いても良いし、または２種以上のオルガノポリシロキサンを併用してもよい。 [(G) Organopolysiloxane]
The thermally conductive silicone composition of the present invention may contain an optional component (G) of organopolysiloxane for the purpose of imparting properties such as viscosity adjusting properties to the thermally conductive silicone composition. Component (G) is, for example, an organopolysiloxane represented by the following general formula (3):

(In the formula, ^R5 is independently a group selected from an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, and d is an integer of 5 to 2,000.)
It is possible to add an organopolysiloxane having a kinetic viscosity at 23° C. of 10 to 100,000 mm ² /s, as represented by the following formula: As component (G), one type of organopolysiloxane may be used alone, or two or more types of organopolysiloxanes may be used in combination.

In the above general formula (3), ^R5 is independently a group selected from an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms. Specific examples of ^R5 include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, and pentyl groups, cycloalkyl groups such as cyclopentyl and cyclohexyl groups, aryl groups such as phenyl, tolyl, xylyl, naphthyl, and biphenylyl groups, and aralkyl groups such as benzyl, phenylethyl, phenylpropyl, and methylbenzyl groups. Among these, alkyl groups having 1 to 3 carbon atoms such as methyl, ethyl, and propyl groups, and phenyl groups are preferred, with methyl and phenyl groups being particularly preferred.

From the viewpoint of the required viscosity, the above d is preferably an integer between 5 and 2,000, and particularly preferably an integer between 10 and 1,000.

Furthermore, the kinetic viscosity of component (G) at 23° C. is preferably 10 to 100,000 mm ² /s, and especially preferably 100 to 10,000 mm ² /s. If the kinetic viscosity is within this range, the cured product of the resulting composition can be prevented from oil-bleeding, and a thermally conductive silicone composition with excellent flexibility can be obtained.

When component (G) is added to the thermally conductive silicone composition of the present invention, there are no particular limitations on the amount added, so long as the desired effect is obtained, but the amount is preferably 0.1 to 100 parts by mass, and more preferably 1 to 50 parts by mass, per 100 parts by mass of component (A). When the amount added is within this range, it is easy to maintain good fluidity and workability in the thermally conductive silicone composition before curing, and it is also easy to fill the composition with the thermally conductive filler of component (C).

[Other ingredients]
The thermally conductive silicone composition of the present invention may further contain other components, such as a heat resistance improver such as iron oxide, a viscosity modifier such as silica, a colorant, a release agent, and other optional components.

[Preparation of Thermally Conductive Silicone Composition]
The thermally conductive silicone composition of the present invention can be prepared by uniformly mixing the above-mentioned components according to a conventional method. The method for producing the silicone composition is not particularly limited, but it can be obtained, for example, by kneading the above-mentioned components in a predetermined amount using a known kneading machine such as a two-roll mill, a kneader, or a Banbury mixer. If necessary, it may be heat-treated (kneaded under heating).

[Maximum indentation load of thermally conductive silicone composition]
The maximum indentation load of the thermally conductive silicone composition of the present invention, measured at 23° C. using a texture analyzer with a cylindrical probe having a diameter of 4 mm, a compression distance of 15 mm, and a speed of 1 mm/sec, is preferably 200 g or less, and more preferably 150 g or less. If the maximum indentation load is 200 g or less, the composition can be sufficiently molded into the desired shape.

[Thermal conductive silicone cured product]
The thermally conductive silicone cured product of the present invention is a cured product of the thermally conductive silicone composition of the present invention described above.

The thermally conductive silicone cured product of the present invention has high thermal conductivity yet low hardness, so it does not apply stress to the heat-generating component and has sufficient flexibility and compressibility to conform to the minute irregularities of the heat-generating component and cooling component. In addition, because the embrittlement of the sheet during compression is suppressed, cracks are less likely to occur even under high compression, making it applicable to modules with high driving voltages and large tolerances. Furthermore, the thermally conductive silicone cured product of the present invention can ensure sufficient insulation during compression.

In other words, the thermally conductive silicone cured product of the present invention can have high thermal conductivity and exhibit excellent compressibility.

[Method for producing thermally conductive silicone cured product]
The curing conditions for molding the thermally conductive silicone composition of the present invention may be the same as those for known addition reaction curing type silicone rubber compositions. For example, the composition will cure sufficiently at room temperature, but may be heated and pressurized as necessary. Addition curing is preferably performed at 100 to 120°C for 5 to 20 minutes. Such a silicone cured product of the present invention has excellent thermal conductivity. If the cured product is in sheet form, it will be easier to handle, such as for transportation and mounting.

[Hardness of cured thermally conductive silicone product]
The hardness of the thermally conductive silicone cured product in the present invention is preferably 40 or less, more preferably 35 or less, and more preferably 10 or more, as measured at 23°C using an Asker C hardness tester. If the hardness is 40 or less, the product can deform to fit the shape of the heat-dissipating body, and can exhibit good heat dissipation characteristics without applying stress to the heat-dissipating body. If the hardness is 10 or more, the product can be prevented from becoming too tacky and from decreasing in handleability. In addition, the hardness can be prevented from breaking. Such hardness can be adjusted by changing the ratio of the (A) component and the (B) component to adjust the crosslinking density.

[Thermal Conductivity of Cured Thermally Conductive Silicone Product]
The thermal conductivity of the thermally conductive silicone cured product of the present invention, measured by the hot disk method at 23° C., should desirably be at least 10 W/mK, and especially at least 11.0 W/mK. A thermal conductivity of 10 W/m K or more will provide excellent thermal conductivity for use as a heat dissipation member.

[Dielectric breakdown voltage of thermally conductive silicone cured product under compression]
The dielectric breakdown voltage of the thermally conductive silicone cured product of the present invention is preferably 10 kV or more, more preferably 12 kV or more, as measured in accordance with JIS K 6249: 2003 when a 2 mm thick sheet-like cured product is compressed by 50%. A dielectric breakdown voltage of 10 kV or more can prevent cracks from occurring during compression, ensuring stable insulation.

[Electrical component]
The electrical part of the present invention contains the thermally conductive cured silicone product of the present invention as part of its configuration.

The cured product of the silicone composition of the present invention can also be used in general electronic components, without being limited to the term "electrical components."

Electrical and electronic components using the cured product of the silicone composition of the present invention can be cooled efficiently, and therefore can operate stably without loss of performance and lifespan due to heat generation. In addition, electrical and electronic components using the cured product of the silicone composition of the present invention can maintain stable insulation, making them suitable for automotive applications that require high insulation and long lifespan.

The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[Preparation of Composition]
Components (A) to (G) used in the following Examples and Comparative Examples are shown below.

Component (A):
An organopolysiloxane represented by the following formula (5):

(wherein f is a number giving the following viscosity):
(A-1) Dynamic viscosity: 400 mm ² /s
(A-2) Dynamic viscosity: 30,000 mm ² /s

Component (B):
Organohydrogenpolysiloxane represented by the following formula (6):

Component (C):
Spherical alumina, crushed alumina, and aluminum nitride having the following average particle sizes: (C-1-1) Spherical alumina having an average particle size of 0.3 μm (C-1-2) Spherical alumina having an average particle size of 1.0 μm (C-2) Crushed alumina having an average particle size of 2.3 μm (C-3) Spherical alumina having an average particle size of 10 μm (C-4) Spherical alumina having an average particle size of 90 μm (C-5-1) Irregular aluminum nitride having an average particle size of 60 μm (C-5-2) Irregular aluminum nitride having an average particle size of 80 μm (C-6) Irregular aluminum nitride having an average particle size of 100 μm

The average particle size is the cumulative 50% particle size (D ₅₀ ) on a volume basis measured by a particle size distribution measuring device MT3000II manufactured by Microtrac Bell.

Component (D):
5% by mass solution of chloroplatinic acid in 2-ethylhexanol.

Component (E):
As an addition reaction regulator, 3-methyl-1-tridecyn-3-ol.

Component (F): Component (F-2) A dimethylpolysiloxane represented by the following formula (7), having an average degree of polymerization of 30 and one end blocked with a trimethoxysilyl group.

Component (G) A plasticizer, which is a dimethylpolysiloxane represented by the following formula (8):

[Examples 1 to 4, Comparative Examples 1 to 4]
In Examples 1 to 4 and Comparative Examples 1 to 4, compositions were prepared as follows using the above components (A) to (G) in the amounts shown in Table 1 below, molded and cured, and the viscosity of the compositions, the thermal conductivity, hardness, and dielectric breakdown voltage when compressed of the cured products were measured according to the methods described below. The results are also shown in Table 1.

[Preparation of Composition]
Component (A), component (C), component (F), component (F), and component (G) were mixed in the respective prescribed amounts shown in the columns for Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1 below, and the mixture was kneaded for 60 minutes with a planetary mixer. Component (D) was then added in the respective prescribed amounts shown in the columns for Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1 below, and methylphenyl silicone oil (product name: KF-54, manufactured by Shin-Etsu Chemical Co., Ltd.) was further added as an internal release agent to promote release from the separator, and the mixture was kneaded for 30 minutes.

The components (B) and (E) were then added in the respective amounts shown in the columns for Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1 below, and the mixture was kneaded for 30 minutes to obtain a composition.

[Molding method]
The compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were poured into a mold having a length of 60 mm, a width of 60 mm, and a thickness of 6 mm or 2 mm, and molded at 120° C. for 10 minutes using a press molding machine.

[Evaluation method]
Composition maximum pressing load:
The indentation load of the compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was measured in an environment of 23°C using a texture analyzer (product name: TA.XTplus100C, manufactured by Eiko Seiki Co., Ltd.). The measurements were performed using a cylindrical probe with a diameter of 4 mm, at an indentation speed of 1 mm/sec and a compression distance of 15 mm. The results are shown in Table 1.

Hardness of cured product:
The compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were cured under the above conditions using a press molding machine to form two 6 mm thick sheets, which were then measured for hardness using an Asker C hardness tester. The results are shown in Table 1.

Thermal conductivity of cured product:
The compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were cured under the above conditions using a press molding machine to obtain two 6 mm-thick sheets, and the thermal conductivity of the sheets was measured using a thermal conductivity meter (product name: TPS-2500S, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) The results are shown in Table 1.

Dielectric breakdown voltage when cured product is compressed:
The compositions obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were cured under the above conditions using a press molding machine to produce a 2 mm thick sheet. This sheet was then compressed by 50% using the press machine to obtain a 1 mm thick sheet. The dielectric breakdown voltage of this sheet was measured in accordance with JIS K 6249:2003. The results are shown in Table 1.

In Examples 1 to 4, the flexibility and moldability of the composition, the hardness of the cured product, and the thermal conductivity were all good. In addition, the occurrence of cracks during compression was suppressed, and high insulation properties were maintained even under high compression conditions.

When the amount of thermally conductive filler was too high, as in Comparative Example 1, a composition could not be obtained. On the other hand, when the amount of thermally conductive filler was too low, as in Comparative Example 2, high thermal conductivity could not be achieved. When the amount and ratio of the thermally conductive filler was outside the range of the present invention, as in Comparative Example 3, the cured product became brittle and cracks occurred due to high compression, and a decrease in insulation properties was observed.

As in Comparative Example 4, when the number of moles of hydrosilyl groups derived from component (B) was less than 0.1 of the number of moles of alkenyl groups derived from component (A), the compound did not cure sufficiently and sheet molding was not possible.

（式中、Ｒ^４は独立に炭素原子数１～６のアルキル基であり、ｃは５～１００の整数である。）
で表される分子鎖片末端がトリアルコキシシリル基で封鎖されたジメチルポリシロキサン、
を含むものであることを特徴とする熱伝導性シリコーン組成物。
［２］更に、（Ｇ）成分として、下記一般式（３）

（式中、Ｒ^５は独立に炭素数１～６のアルキル基、炭素数６～１２のアリール基、及び炭素数７～１２のアラルキル基から選ばれる基、ｄは５～２，０００の整数である。）
で表される２３℃における動粘度が１０～１００，０００ｍｍ^２／ｓのオルガノポリシロキサン：（Ａ）成分１００質量部に対し０．１～１００質量部
を含有するものであることを特徴とする［１］に記載の熱伝導性シリコーン組成物。
［３］テクスチャーアナライザーにおいて、直径４ｍｍの円柱プローブを用い、圧縮距離を１５ｍｍとし、速度を１ｍｍ／秒として測定した２３℃における前記組成物の押し込み最大荷重が２００ｇ以下のものであることを特徴とする［１］又は［２］に記載の熱伝導性シリコーン組成物。
［４］［１］～［３］のいずれか１つに記載の熱伝導性シリコーン組成物の硬化物であることを特徴とする熱伝導性シリコーン硬化物。
［５］形状がシート状である［４］に記載の熱伝導性シリコーン硬化物。
［６］前記熱伝導性シリコーン硬化物のアスカーＣ硬度計で測定した硬さが１０ポイント以上、４０ポイント以下である［４］又は［５］に記載の熱伝導性シリコーン硬化物。
［７］ホットディスク法により測定した２３℃における熱伝導率が、１０Ｗ／ｍＫ以上である［４］～［６］の何れか１つに記載の熱伝導性シリコーン硬化物。
［８］前記熱伝導性シリコーン硬化物の２ｍｍ厚のシートを５０％圧縮した時の絶縁破壊電圧が１０ｋＶ以上である［４］～［７］の何れか１つに記載の熱伝導性シリコーン硬化物。
［９］［４］～［８］の何れか１つに記載の熱伝導性シリコーン硬化物を構成の一部として含むものであることを特徴とする電気部品。
［１０］車載用である［９］に記載の電気部品。 The present specification includes the following aspects.
[1] (A) an organopolysiloxane having two or more alkenyl groups per molecule: 100 parts by mass,
(B) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the number of moles of hydrosilyl groups is 0.1 to 5.0 times the number of moles of alkenyl groups derived from component (A);
(C) a thermally conductive filler consisting of the following components (C-1) to (C-6): 8,600 to 9,600 parts by mass,
(C-1) Spherical alumina filler having an average particle size of more than 0.1 μm and not more than 2 μm: 1,500 to 2,500 parts by mass. (C-2) Crushed alumina filler having an average particle size of more than 0.5 μm and not more than 5 μm: 200 to 800 parts by mass. (C-3) Spherical alumina filler having an average particle size of more than 5 μm and not more than 20 μm: 1,500 to 2,500 parts by mass.
(C-4) Spherical alumina filler having an average particle size of more than 60 μm and not more than 100 μm: 500 to 1,500 parts by mass,
(C-5) irregular aluminum nitride filler having an average particle size of more than 50 μm and not more than 90 μm: 2,200 to 3,200 parts by mass,
(C-6) irregular aluminum nitride filler having an average particle size of more than 90 μm and not more than 120 μm: 500 to 1,500 parts by mass,
(D) Platinum group metal curing catalyst: 0.1 to 2,000 ppm by mass of platinum group element relative to component (A)
(E) an addition reaction inhibitor: 0.01 to 2.0 parts by mass per 100 parts by mass of the component (A); (F) a surface treatment agent which is one or more selected from the following (F-1) and (F-2): 200 to 400 parts by mass per 100 parts by mass of the component (A);
(F-1) The following general formula (1)
R ¹ _a R ² _b Si(OR ³ ) _4-a-b (1)
(In the formula, R ¹ is independently an alkyl group having 6 to 15 carbon atoms, R ² is independently a group selected from an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, R ³ is independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, b is an integer of 0 to 2, and a+b is an integer of 1 to 3.)
An alkoxysilane compound represented by the formula:
(F-2) The following general formula (2)

(In the formula, R ⁴ is independently an alkyl group having 1 to 6 carbon atoms, and c is an integer of 5 to 100.)
a dimethylpolysiloxane having one molecular chain end blocked with a trialkoxysilyl group, represented by the formula:
A thermally conductive silicone composition comprising:
[2] Furthermore, as the component (G),

(In the formula, ^R5 is independently a group selected from an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, and d is an integer of 5 to 2,000.)
The thermally conductive silicone composition according to [1], characterized in that it contains 0.1 to 100 parts by mass of an organopolysiloxane having a kinetic viscosity at 23°C of 10 to 100,000 ^mm2 /s represented by the following formula per 100 parts by mass of component (A).
[3] The thermally conductive silicone composition according to [1] or [2], characterized in that the maximum indentation load of the composition at 23°C is 200 g or less, as measured in a texture analyzer using a cylindrical probe having a diameter of 4 mm at a compression distance of 15 mm and a speed of 1 mm/sec.
[4] A thermally conductive silicone cured product, which is a cured product of the thermally conductive silicone composition according to any one of [1] to [3].
[5] The thermally conductive silicone cured product according to [4], which is in the form of a sheet.
[6] The thermally conductive silicone cured product according to [4] or [5], wherein the hardness of the thermally conductive silicone cured product as measured with an Asker C hardness scale is 10 points or more and 40 points or less.
[7] The thermally conductive silicone cured product according to any one of [4] to [6], which has a thermal conductivity of at least 10 W/mK at 23° C. as measured by the hot disk method.
[8] The thermally conductive silicone cured product according to any one of [4] to [7], wherein a breakdown voltage when a 2 mm thick sheet of the thermally conductive silicone cured product is compressed by 50% is 10 kV or more.
[9] An electrical part comprising, as part of its configuration, the thermally conductive silicone cured product according to any one of [4] to [8].
[10] The electrical component according to [9], which is for mounting on a vehicle.

The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included within the technical scope of the present invention.

Claims (10)

(A) organopolysiloxane having two or more alkenyl groups in one molecule: 100 parts by mass,
(B) an organohydrogenpolysiloxane having two or more hydrosilyl groups per molecule: an amount such that the number of moles of hydrosilyl groups is 0.1 to 5.0 times the number of moles of alkenyl groups derived from component (A);
(C) a thermally conductive filler consisting of the following components (C-1) to (C-6): 8,600 to 9,600 parts by mass,
(C-1) Spherical alumina filler having an average particle size of more than 0.1 μm and not more than 2 μm: 1,500 to 2,500 parts by mass. (C-2) Crushed alumina filler having an average particle size of more than 0.5 μm and not more than 5 μm: 200 to 800 parts by mass. (C-3) Spherical alumina filler having an average particle size of more than 5 μm and not more than 20 μm: 1,500 to 2,500 parts by mass.
(C-4) Spherical alumina filler having an average particle size of more than 60 μm and not more than 100 μm: 500 to 1,500 parts by mass,
(C-5) irregular aluminum nitride filler having an average particle size of more than 50 μm and not more than 90 μm: 2,200 to 3,200 parts by mass,
(C-6) irregular aluminum nitride filler having an average particle size of more than 90 μm and not more than 120 μm: 500 to 1,500 parts by mass,
(D) Platinum group metal curing catalyst: 0.1 to 2,000 ppm by mass of platinum group element relative to component (A)
(E) an addition reaction inhibitor: 0.01 to 2.0 parts by mass per 100 parts by mass of the component (A); (F) a surface treatment agent which is one or more selected from the following (F-1) and (F-2): 200 to 400 parts by mass per 100 parts by mass of the component (A);
(F-1) The following general formula (1)
R ¹ _a R ² _b Si(OR ³ ) _4-a-b (1)
(In the formula, R ¹ is independently an alkyl group having 6 to 15 carbon atoms, R ² is independently a group selected from an alkyl group having 1 to 5 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, R ³ is independently an alkyl group having 1 to 6 carbon atoms, a is an integer of 1 to 3, b is an integer of 0 to 2, and a+b is an integer of 1 to 3.)
An alkoxysilane compound represented by the formula:
(F-2) The following general formula (2)

(In the formula, R ⁴ is independently an alkyl group having 1 to 6 carbon atoms, and c is an integer of 5 to 100.)
a dimethylpolysiloxane having one molecular chain end blocked with a trialkoxysilyl group, represented by the formula:
A thermally conductive silicone composition comprising: Furthermore, as the component (G),

(In the formula, ^R5 is independently a group selected from an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, and an aralkyl group having 7 to 12 carbon atoms, and d is an integer of 5 to 2,000.)
The thermally conductive silicone composition according to claim 1, characterized in that it contains 0.1 to 100 parts by mass of an organopolysiloxane having a kinetic viscosity at 23°C of 10 to 100,000 ^mm2 /s, represented by the formula: The thermally conductive silicone composition according to claim 1, characterized in that the maximum indentation load of the composition at 23°C measured using a texture analyzer with a cylindrical probe having a diameter of 4 mm, a compression distance of 15 mm, and a speed of 1 mm/sec is 200 g or less. A thermally conductive silicone cured product, which is a cured product of the thermally conductive silicone composition according to any one of claims 1 to 3. The thermally conductive silicone cured product according to claim 4, which is in the form of a sheet. The thermally conductive silicone cured product according to claim 4, wherein the hardness of the thermally conductive silicone cured product measured with an Asker C hardness tester is 10 points or more and 40 points or less. The thermally conductive silicone cured product according to claim 4, which has a thermal conductivity of 10 W/mK or more at 23°C as measured by the hot disk method. The thermally conductive silicone cured product according to claim 4, wherein the dielectric breakdown voltage when a 2 mm thick sheet of the thermally conductive silicone cured product is compressed by 50% is 10 kV or more. An electrical component comprising the thermally conductive silicone cured product according to claim 4 as part of its configuration. The electrical component according to claim 9, which is for vehicle use.