KR102132243B1 - Thermal conductive silicone composition and cured product, and composite sheet - Google Patents

Abstract

The present invention provides a thermally conductive silicone composition in which at least 90% of the total mass parts of the thermally conductive filler is α alumina with an α conversion rate of 90% or higher, and a weight reduction rate when left in air in a 250° C. environment for 6 hours is less than 1%. .
The thermally conductive silicone composition using α alumina in which at least 90% of the total mass parts of the thermally conductive filler according to the present invention has α α ratio of 90% or more has less weight loss and excellent heat resistance even under a 250° C. environment. The thermally conductive silicone composition and the cured product and the composite sheet can cope with locations where heat resistance of about 250°C is required, such as a semiconductor device using a silicon carbide-based substrate material, and a heat dissipation application of an on-vehicle heater.

Description

THERMAL CONDUCTIVE SILICONE COMPOSITION AND CURED PRODUCT, AND COMPOSITE SHEET}

The present invention includes, for example, a heat conductive silicone composition, a heat conductive silicone cured product, and a heat conductive silicone composite sheet used for heat dissipation between a heat generating component and a heat dissipation component in an electronic device, especially when exposed to a high temperature environment of about 250°C. It is about.

Semiconductors, such as transistors and diodes used in electronic devices such as converters and power supplies, generate high amounts of heat by themselves with high performance, high speed, miniaturization, and high integration. Causes destruction. For this reason, many heat dissipation methods and heat dissipation members used therefor have been proposed to suppress the temperature rise of the semiconductor in operation. The general heat dissipation member may be of various types, such as a composition in which a polymer matrix is filled with a thermally conductive filler, a cured product obtained by curing the same, or a composite sheet obtained by laminating a cured material and a reinforcing material. The heat-dissipating member is mounted between the heat-generating member and the dissipating member, and its shape is selected according to the mounting state.

Examples of the polymer matrix of the heat-dissipating member include silicone, acrylic resin, and olefin resin, but silicone is most suitable from the viewpoints of heat resistance, cold resistance, and long-term reliability.

In particular, as a polymer matrix of a heat dissipation member in a semiconductor device having a large amount of heat generation or in a vehicle-mounted field requiring long-term reliability, silicon is often used in view of its heat resistance, cold resistance, and long-term reliability. Further, silicon has been generally used as a substrate material for semiconductor devices, but recently, a substrate material using silicon carbide as a raw material has been widely used. The silicon carbide-based substrate material has a higher heat-resistance temperature than the silicon-based substrate material, and the permissible operating environment temperature also increases to around 250°C. In addition, in the field of vehicle mounting, the spread of hybrid vehicles, electric vehicles, etc. is progressing, and it is difficult to rely on the heat of the engine for heating, which has been using the heat of the engine so far, so it is necessary to increase the resistance value of the heater to increase the heat generation amount. have. For example, the PTC heater requires a large current when driving, and the heat generation degree exceeds 200°C.

Of these flows, of course, the heat-resistant temperature required for the heat-dissipating member is also increasing. The use temperature range of the thermally conductive silicone composition which is a heat dissipation member using conventional silicone as the polymer matrix and the cured product thereof or the composite sheet is -40°C to 180°C, which is not suitable for the above situation.

Also, as a related art related to the present invention, Japanese Patent Application Publication No. 2014-145024 can be cited, and although heat resistance (250° C.) is emphasized, a problem that a heat stabilizer must be added and is limited only under a low oxygen heating environment. have.

Japanese Patent Publication No. 2014-145024

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a thermally conductive silicone composition and a cured product, and a composite sheet that can be used even in a 250°C atmosphere using silicone as a polymer matrix.

As a result of careful examination, the present inventors have found that by using α alumina, which has a high α conversion rate, among alumina, it is possible to provide a thermally conductive silicone composition with low weight loss even under an atmosphere of 250° C. in air.

That is, in the conventional heat-dissipating member, especially in the vehicle-mounted field, insulation is required for the heat-dissipating member, and as a heat-conducting filler of a heat-dissipating member made of a large amount of silicone as a polymer matrix, the viewpoint of price, heat conductivity, filling property, and insulating property Although alumina is used in order to achieve the above-mentioned purpose, it is effective to obtain a thermally conductive silicone composition and a cured product that can be used under a 250° C. environment as a polymer matrix using silicone mainly composed of α alumina as a thermally conductive filler. Found out, it has come to achieve the present invention.

Accordingly, the present invention provides the following thermally conductive silicone composition and cured product, and a composite sheet.

[1] Thermally conductive silicone characterized in that at least 90% of the total mass parts of the thermally conductive filler is α alumina with an α conversion rate of 90% or more, and the weight reduction rate when left in air in a 250° C. environment for 6 hours is less than 1%. Composition.

[2] The thermally conductive silicone composition according to [1], wherein the thermal conductivity is 0.5 W/mK or more.

[3] The thermally conductive silicone composition according to [1] or [2], characterized in that it contains 250 to 2,000 parts by mass of the thermally conductive filler relative to 100 parts by mass of the organopolysiloxane base material.

[4] Weight when 90% or more of the total mass parts of the thermally conductive filler is cured by curing a thermally conductive silicone composition containing α alumina having an α amination rate of 90% or more in air at 250° C. for 6 hours A thermally conductive silicone cured product characterized in that the reduction rate is less than 1%.

[5] The thermally conductive silicone cured product according to [4], characterized in that the thermal conductivity is 0.5 W/mK or more.

[6] The thermally conductive silicone composition contains 100 parts by mass of an organopolysiloxane base, 250 to 2,000 parts by mass of a thermally conductive filler, and a curing effective amount of a curing agent for curing the organopolysiloxane base, [4] Or the cured thermally conductive silicone according to [5].

[7] A thermally conductive silicone composite sheet comprising one or both sides of a reinforcing material laminated with the thermally conductive silicone cured product according to any one of [4] to [6].

[8] The thermally conductive silicone composite sheet according to [7], wherein the reinforcing material is a polyimide film.

[9] The thermally conductive silicone composite sheet according to [7], wherein the reinforcing material is a glass cloth.

[10] The thermally conductive silicone composite sheet according to any one of [7] to [9], wherein the hardness of the thermally conductive silicone cured product is 80 to 99 in durometer A hardness.

The thermally conductive silicone composition using α alumina in which at least 90% of the total mass parts of the thermally conductive filler according to the present invention has an α conversion rate of 90% or more has less weight loss and excellent heat resistance even under a 250° C. environment. The thermally conductive silicone composition, cured product, and composite sheet can cope with locations where heat resistance of about 250°C is required, such as a semiconductor element using a silicon carbide-based substrate material and a heat dissipation application of a vehicle-mounted heater.

The thermally conductive silicone composition according to the present invention is composed of an organopolysiloxane base and a thermally conductive filler as main components, and the thermally conductive silicone cured product is a thermoelectric material in which an organopolysiloxane base and a thermally conductive filler are added with a curing agent for curing the organopolysiloxane base. It is made by curing the silicone composition.

It will be described in more detail below.

[Organopolysiloxane Presence]

In the organopolysiloxane base material used in the present invention, it is common for the main chain portion to basically include a repeat of a diorganosiloxane unit, which may include a branched structure in a part of the molecular structure, or may be annular. , Linear diorganopolysiloxanes are preferred.

As a functional group bonded to a silicon atom, an unsubstituted or substituted monovalent hydrocarbon group, for example, methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group , Hexyl group, heptyl group, octyl group, nonyl group, decyl group, alkyl group such as dodecyl group, cyclopentyl group, cyclohexyl group, cycloalkyl group such as cycloheptyl group, phenyl group, tolyl group, xylyl group, naphthyl group, Aryl groups such as biphenylyl groups, benzyl groups, aralkyl groups such as phenylethyl groups, phenylpropyl groups and methylbenzyl groups, and halogen atoms such as fluorine, chlorine and bromine are partially or entirely part of the hydrogen atoms to which these groups have carbon atoms attached , A group substituted with a cyano group, for example, chloromethyl group, 2-bromoethyl group, 3-chloropropyl group, 3,3,3-trifluoropropyl group, chlorophenyl group, fluorophenyl group, cyanoethyl group, 3,3,4,4,5,5,6,6,6-nonafluorohexyl group, etc. are mentioned, and the representative thing is 1 to 10 carbon atoms, especially the representative thing is 1 to 6 carbon atoms. Preferably, an unsubstituted or substituted alkyl group having 1 to 3 carbon atoms, such as methyl group, ethyl group, propyl group, chloromethyl group, 2-bromoethyl group, 3,3,3-trifluoropropyl group, and cyanoethyl group. , And an unsubstituted or substituted phenyl group such as a phenyl group, chlorophenyl group, and fluorophenyl group. Other than that, it may have an unsaturated bond such as an alkenyl group, for example, a vinyl group, an allyl group, a propenyl group, an isopropenyl group, a butenyl group, a hexenyl group, a cyclohexenyl group, etc., usually having 2 to 2 carbon atoms. Eight things are mentioned.

The siloxane repeating unit of the main chain is not particularly limited, and the properties of the polysiloxane obtained are changed according to the number of repeating units, so a method for preparing the thermally conductive silicone composition may be appropriately selected. If the oil phase, a stirring device such as a planetary mixer is suitable, and if it is a raw rubber phase, a stirring device such as a twin-screw roll or a kneader that takes more shear force is suitable.

In this case, it is preferable from the viewpoint of handling that the organopolysiloxane is used as a main material having a kinematic viscosity of 25°C to 100 to 40,000 kPa/s, particularly 100 to 10,000 kPa/s. In addition, kinematic viscosity can be measured with an Ostwald viscometer.

[Thermal conductive filler]

In the present invention, as the thermally conductive filler, α alumina having 90% by mass or more, preferably 95% by mass or more, of the total mass part of the thermally conductive filler is preferably 90% or more.

(Crystalline phase of alumina)

Alumina has a variety of crystal phases due to the difference in temperature, such as α, β, θ, and sintering. It was found that α alumina having the highest sintering temperature most inhibited the weight loss of the silicone polymer under the 250° C. environment. In addition, in general alumina, although there is almost no single crystal phase, it is preferable that the ratio of the α phase occupies as high as possible, and an α ratio of 90% or more, preferably 95% or more, is used.

The α ratio is the peak height (I _25.6 ) of the alumina α phase (012 plane), which appears at the position of 2θ=25.6°, from the diffraction spectrum of the fine α alumina obtained by using the X-ray diffraction apparatus, and 2θ=46° From the peak height (I ₄₆ ) of the γ phase, η phase, χ phase, κ phase, θ phase and δ phase appearing at the position of

α rate (%)=I _25.6 /(I _25.6 +I ₄₆ )×100

It is calculated by.

(Particle size of alumina)

The center particle diameter of the alumina is preferably 0.1 to 200 μm, more preferably 1 to 100 μm, and even more preferably 1 to 50 μm. When the center particle diameter is less than 0.1 µm, the filling property to the organopolysiloxane base material decreases. When the center particle diameter exceeds 200 µm, the fluidity of the composition or the strength of the cured product is difficult to obtain. In addition, it is important to select a particle size in consideration of the thickness when mounting the thermally conductive silicone composition and the thickness when curing. This is because alumina protrudes from the thermally conductive silicone composition and the cured product when alumina having a particle size larger than the thickness at the time of curing during mounting is included.

The average particle diameter of alumina is a value of a cumulative average diameter (median diameter) measured by a microtrack MT3300EX, a particle size analyzer manufactured by Nikkiso Co., Ltd.

(Figurine of alumina)

Alumina has various shapes such as spherical shape, round shape, and crushed shape according to the manufacturing method. In general, the crushed alumina has a high α-ization rate, so a crushed alumina is preferable, but if the α-ization rate is satisfied, no granularity is obtained.

(Other thermally conductive fillers)

As other thermally conductive fillers, metals such as non-magnetic copper and aluminum, alumina, silica, magnesia, bengala, beryllia, titania, zirconia, and other metal oxides, metal nitrides such as aluminum nitride, silicon nitride, and boron nitride, magnesium hydroxide, and the like Materials such as metal hydroxides, artificial diamonds or silicon carbide, which are generally used as thermally conductive fillers, can be used. In addition, the center particle size may be used from 0.1 to 200㎛, it may be used in combination of one or two or more. However, since the use of the present invention is assumed to be used in an environment of 250° C., it is necessary to use a material that does not cause reactions such as melting, oxidation, and dehydration to at least 300° C. or that does not promote cracking of the organopolysiloxane. have.

(The amount of thermally conductive filler)

The blending amount of the thermally conductive filler is preferably 250 to 2,000 parts by mass, more preferably 250 to 1,000 parts by mass, and even more preferably 250 to 600 parts by mass relative to 100 parts by mass of the organopolysiloxane base material. If the amount of the thermally conductive filler is too small, there is a fear that sufficient thermal conductivity may not be obtained, and if too large, the composition itself may be difficult to prepare.

[Thermal conductive silicone composition]

As described above, the thermally conductive silicone composition is composed of an organopolysiloxane base and a thermally conductive filler as main components, but as other components, an alkoxy group-containing organopolysiloxane is used for the purpose of improving the dispersibility of the thermally conductive filler, if necessary. It can be combined. Especially as this alkoxy group containing organopolysiloxane, the following formula

(Wherein, R is an unsubstituted or substituted 1 to 30 carbon atoms, especially 1 to 10 alkyl groups, aryl groups, aralkyl groups, monovalent hydrocarbon groups such as halogenated alkyl groups, R'is 1 to 6 carbon atoms, In particular, it represents an alkyl group of 1 to 3. q is an integer from 0 to 2, preferably 0. p is an integer from 0 to 100, especially from 1 to 50.)

Diorganopolysiloxane containing one terminal alkoxy group represented by is preferable.

The blending amount of the alkoxy group-containing organopolysiloxane is preferably 1 to 30 parts by mass, particularly preferably 3 to 20 parts by mass, relative to 100 parts by mass of the organopolysiloxane.

In addition, a colorant such as an organic pigment or an inorganic pigment, a heat resistance improving agent such as iron oxide or cerium oxide, an internal additive release agent, and the like can be blended as necessary.

(Flowability of thermally conductive silicone composition)

In the present invention, the thermally conductive silicone composition can be provided for use without curing, and in this case, the fluidity of the thermally conductive silicone composition is not specifically defined, but a dispenser or metal mask called heat dissipating grease or curable heat dissipating grease is used. The viscosity when mounted in screen printing is preferably 10 to 900 Pa·s at 25° C., more preferably 10 to 400 Pa·s. When the viscosity exceeds 900 Pa·s, there is a possibility that ejection from the dispenser becomes difficult due to poor fluidity or scratches may occur in screen printing. In addition, the said viscosity is a value by a Malcolm viscometer.

(Weight reduction rate in the air at 250°C)

In the thermally conductive silicone composition according to the present invention, the weight loss ratio when left in an environment of 250° C. in air for 6 hours is less than 1%, preferably 0.8% or less. The reason for the weight reduction is that the organopolysiloxane base material is cracked by heat and becomes low-molecularized and volatilized. Therefore, if the weight-reduction ratio is large, the polymer content decreases, causing the thermally conductive silicone composition to soften or harden. In such a case, the thermal conductivity of the thermally conductive silicone composition is lost.

It was also found that the degree of cracking of silicon varied depending on the crystal phase of alumina. Alumina in a crystalline phase such as γ phase or θ phase having a low sintering temperature promotes cracking of silicon, and alumina in the α phase having the highest sintering temperature does not promote cracking of silicon, so the weight reduction rate is suppressed.

As for the weight reduction rate, 2 g of a thermally conductive silicone composition is weighed into a heat-resistant glass chalet having a diameter of 20 mm and put into an oven at 250°C. The atmosphere in the oven is air. It is taken out after 6 hours, returned to room temperature, weighed, and calculated from weight changes before and after input.

(Thermal conductivity)

The thermal conductivity of the thermally conductive silicone composition is preferably 0.5 W/mK or more. More preferably, it is 0.8 to 8.0 W/mK. If it is less than 0.5 W/mK, a sufficient heat dissipation effect cannot be obtained. The upper limit of the thermal conductivity is not particularly defined, but if it is desired to obtain in excess of 8.0 W/mK, filling of silicon itself becomes difficult. The thermal conductivity is a value measured by the hot disk method.

[Heat conductive silicone cured product]

The thermally conductive silicone cured product is cured by blending a curing agent with respect to the thermally conductive silicone composition containing the aforementioned organopolysiloxane base and thermally conductive filler as main components.

Examples of the curing method for the thermally conductive silicone composition include addition curing reaction using a platinum catalyst, radical reaction using an organic peroxide as a catalyst, and radical reaction using ultraviolet irradiation or electron beam irradiation. However, the curing method is not limited to these.

In this case, in order to cure the thermally conductive silicone composition using an addition curing reaction using a platinum catalyst, as an organopolysiloxane main agent, an organopolysiloxane having at least two alkenyl groups in the molecule and a silicon atom as a curing agent The organohydrogenpolysiloxane having at least two hydrogen atoms directly bonded and a platinum group metal-based curing catalyst are essential components.

In addition, when cured with an organic peroxide, the organopolysiloxane base may contain an alkenyl group, but is cured even when an organopolysiloxane base containing no alkenyl group is used.

In addition, a known technique can be employed for the amount of the curing agent for curing the organopolysiloxane base material, the curing method, and the curing conditions.

(Hardness of thermally conductive silicone cured product)

The hardness of the thermally conductive silicone cured product is preferably 80 to 99 as Durometer A hardness. More preferably, it is 90 to 96. If it is less than 80, the cured product tends to deform at the time of mounting, or the surface of the cured product may be easily damaged.

(Weight reduction rate and thermal conductivity of cured thermally conductive silicone)

The weight loss rate and the thermal conductivity of the thermally conductive silicone cured product are not the thermally conductive silicone composition itself, but the cured product cured therein as a measurement object, and the measurement method is the same as that of the aforementioned thermally conductive silicone composition.

[Thermal conductive silicone composite sheet]

The thermally conductive silicone composite sheet is obtained by laminating the thermally conductive silicone cured product on one side or both sides of a reinforcing material.

In this case, the polyimide film or glass cloth is preferable as the reinforcing material of the thermally conductive silicone composite sheet in view of practicality and processability. However, the reinforcing materials are not limited to these, and any material having sufficient strength and heat resistance can be used without problems. For example, it may be a polytetrafluoroethylene sheet.

(Polyimide film)

The thickness of the polyimide film is preferably 5 to 100 μm. More preferably, it is 7-50 micrometers, More preferably, it is 7-25 micrometers. If the polyimide film is too thin, sufficient strength or insulation is not obtained, whereas if it is too thick, the thermal conductivity is impeded. In addition, if the surface of the polyimide film is subjected to plasma treatment, adhesion to a thermally conductive silicone cured product is improved, which is preferable.

(Glass cloth)

The thickness of the glass cloth is preferably 20 to 100 μm. More preferably, it is 30 to 60 µm. If it is less than 20 µm, sufficient strength is not obtained, and if it exceeds 100 µm, there is a concern that thermal conductivity may be impeded. The method of weaving the glass cloth is not particularly limited. It is preferable that the glass cloth is silane-treated. The silane coupling agent to be treated and the treatment method are not limited.

(Thickness of thermally conductive silicone cured product)

The thickness of the thermally conductive silicone cured product is preferably 50 to 10,000 μm, particularly 200 to 800 μm. In addition, this thickness is not limited to the case of the thermally conductive silicone composite sheet, and is also applicable when the thermally conductive silicone composition or its cured product is used without reinforcing material.

[Forming Method of Thermally Conductive Silicone Composite Sheet]

The method for forming the thermally conductive silicone composite sheet is prepared by preparing a thermally conductive silicone composition containing a curing agent, for example, an organic peroxide having a decomposition temperature of 120°C as a catalyst, and optionally diluting it with toluene to form a coating solution. On the reinforcing material, a coating solution is coated using an arbitrary spacer, and toluene is volatilized by putting it in an oven at 80°C for 10 minutes, and then cured by putting it in an oven at 150°C for 10 minutes. With this, a thermally conductive silicone cured product can be laminated on one side of the substrate. When it is also desired to laminate on the other side, it is coated in the same manner as described above and dried and cured. However, the method for forming the thermally conductive silicone composite sheet is not limited thereto.

[Example]

Hereinafter, 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.

[Preparation of composition]

(A) Component: Dimethylpolysiloxane represented by the following formula (1)

(X is an organic functional group, n is a number that gives the following viscosity.)

(A-1) X=methyl group, kinematic viscosity 10,000 MPa/s (25°C)

(A-2) X = methyl group, kinematic viscosity 30,000 kPa/s (25°C)

(B) Ingredient: Alumina having an average particle diameter as follows

(B-1) α-alumina with an amination rate of 99% and an average particle diameter of 5 μm

(B-2) crushed α alumina having an α ratio of 95% and an average particle diameter of 10 μm

(B-3) Spherical α alumina having an α rate of 92% and an average particle diameter of 20 μm

(B-4) Fractured γ alumina having an average particle diameter of 10 µm

(B-5) Fractured θ alumina with an average particle diameter of 10 μm

(C) Ingredient: Thermally conductive filler

(C-1) Aluminum hydroxide with an average particle size of 1.0 µm

(D) Component: Dimethylpolysiloxane in which one terminal having an average polymerization degree of 30 represented by the following formula (2) is blocked with a trimethoxy group

(E) Ingredient: C-23N (Organic peroxide-based curing agent: Shin-Etsu Chemical Co., Ltd.)

[Examples, Comparative Examples]

Using the components shown in Tables 1 and 2 in a predetermined amount shown in the table, kneading for 60 minutes with a planetary mixer, and the thermally conductive silicone compositions of Examples 1 to 7 and Comparative Examples 1 to 7 shown in Tables 1 and 2 were prepared. It was prepared, and the weight loss rate and the thermal conductivity were measured by the following method. The results are shown in Tables 1 and 2.

[How to measure]

· Weight reduction rate

The prepared thermally conductive silicone composition was weighed 2 g in a heat-resistant container having a diameter of 20 mm, and then put into an oven set at 250°C. The atmosphere in the oven is air. It is taken out after 6 hours and weighed when it returns to room temperature. The reduction is divided by the weight before input and multiplied by 100.

In addition, for Example 7 and Comparative Example 7, the prepared thermally conductive silicone composition was introduced into an oven set at 150° C. for 10 minutes to cure, and then the weight loss ratio was measured.

·Thermal conductivity

The thermal conductivity at 25°C of each thermally conductive silicone composition was measured by TPA-501 (manufactured by Kyoto Denshi Kogyo Co., Ltd.) by a hot disk method.

In addition, for Example 7 and Comparative Example 7, the thermal conductivity of the prepared thermally conductive silicone composition was cured by putting it in an oven set at 150° C. for 10 minutes to cure.

As shown in Examples 1 to 7, the thermally conductive silicone composition using α alumina [(B-1) to (B-3)] having an amination rate of 90% or more has a weight reduction rate of 1 even though it is added for 6 hours in a 250° C. atmosphere. %.

On the other hand, as shown in Comparative Example 1, when γ alumina is used, the weight reduction ratio becomes 1% or more, and heat resistance cannot be imparted. As shown in Comparative Example 2, even when θ alumina is used, the weight reduction ratio becomes 1% or more, and heat resistance cannot be imparted. As shown in Comparative Example 3, if the proportion of α alumina in the total mass part of the thermally conductive filler is less than 90%, the weight reduction rate is 1% or more, and sufficient heat resistance cannot be obtained. As shown in Comparative Example 4, the proportion of α alumina in the total mass part of the thermally conductive filler is less than 90%, and further, when aluminum hydroxide is used as a thermally conductive filler to be used in combination, the weight reduction rate is greater. This is because aluminum hydroxide causes a dehydration reaction, and the weight of aluminum hydroxide itself is reduced. Comparative Example 5 reduced the amount of γ alumina to be filled compared to Comparative Example 1, but, on the contrary, the weight reduction ratio increased. This is because the proportion of the silicone polymer has increased relatively. As shown in Comparative Example 6, when aluminum hydroxide is used as the thermally conductive filler, the weight of the aluminum hydroxide itself is reduced by the dehydration reaction of aluminum hydroxide rather than the weight of silicon, and the weight reduction rate is particularly large. As shown in Comparative Example 7, even when the thermally conductive silicone composition is cured, the weight reduction rate increases when γ alumina is used.

Claims (10)

Contains 100 parts by mass of an organopolysiloxane base having a dynamic viscosity of 100 to 40,000 kPa/s at 25°C, 250 to 2,000 parts by mass of a thermally conductive filler, and 1 to 30 parts by mass of a diorganopolysiloxane containing one terminal alkoxy group represented by the following formula , 90% or more of the total mass parts of the thermally conductive filler is α alumina with a crushing rate of 90% or more, a viscosity of 10 to 900 Pa·s at 25° C., a thermal conductivity of 0.5 W/mK or more, and 250° C. A thermally conductive silicone composition characterized in that the weight loss rate when left in the air for 6 hours in an environment is less than 1%.

(Wherein, R is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms, R'is an alkyl group having 1 to 6 carbon atoms, q is an integer from 0 to 2, p is an integer from 0 to 100 to be.) The method of claim 1, wherein the functional group bonded to the silicon atom based on the organopolysiloxane is selected from an unsubstituted or halogen substituted or cyano group substituted alkyl group having 1 to 10 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group. Thermally conductive silicone composition. 100 parts by mass of an organopolysiloxane base having a kinematic viscosity of 100 to 40,000 Pa/s at 25°C, 250 to 2,000 parts by mass of a thermally conductive filler, and 1 to 30 parts by mass of a diorganopolysiloxane containing one terminal alkoxy group represented by the following formula , Containing a curing effective amount of the organic peroxide curing agent to cure the organopolysiloxane base material, 90% or more of the total mass parts of the thermally conductive filler is crushed α alumina having an α conversion rate of 90% or more, and a viscosity of 10 at 25° C. When the cured product formed by curing the thermally conductive silicone composition, which is from 900 to 900 MPa·s, is left in the air at 250° C. for 6 hours, the weight reduction rate is less than 1%, the thermal conductivity is 0.5 W/mK or more, and the hardness is durometer. A thermally conductive silicone cured product, characterized in that it is 80 to 99 in meters A hardness.

(Wherein, R is an unsubstituted or substituted monovalent hydrocarbon group having 1 to 30 carbon atoms, R'is an alkyl group having 1 to 6 carbon atoms, q is an integer from 0 to 2, p is an integer from 0 to 100 to be.) The method according to claim 3, wherein the functional group bound to the silicon atom based on the organopolysiloxane is selected from an unsubstituted or halogen substituted or cyano group substituted alkyl group having 1 to 10 carbon atoms, a cycloalkyl group, an aryl group, or an aralkyl group. Cured thermally conductive silicone. A thermally conductive silicone composite sheet, characterized in that the thermally conductive silicone cured product according to claim 3 or 4 is laminated on one side or both sides of a reinforcing material. The thermally conductive silicone composite sheet according to claim 5, wherein the reinforcing material is a polyimide film. The thermally conductive silicone composite sheet according to claim 5, wherein the reinforcing material is a glass cloth. delete delete delete