JP2016125001A - Heat-conductive silicone composition, cured product, and composite seat - Google Patents

Abstract

SOLUTION: A heat-conductive silicone composition includes not less than 90% in a total mass part of heat conductive fillers of α-alumina having an α-transformation rate of not less than 90%, and has a weight reduction ratio of less than 1% when kept in atmospheric air at 250°C for 6 hours.EFFECT: The heat-conductive silicone composition obtained using not less than 90% in a total mass part of heat conductive fillers of α-alumina having an α-transformation rate of not less than 90% is little in weight reduction even under 250°C environment, and excellent in heat resistance. The heat-conductive silicone composition, a cured product, and a composite seat are adapted to application to places requiring heat resistance to about 250°C such as heat radiation usages of a semiconductor element using a silicon carbide substrate material, and a vehicle-mounted heater.SELECTED DRAWING: None

Description

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

  Semiconductors such as transistors and diodes used in electronic equipment such as converters and power supplies themselves generate large amounts of heat as their performance, speed, size, and integration increase. The temperature rise of equipment due to heat causes malfunction and destruction. Therefore, many heat dissipating methods for suppressing the temperature rise of the semiconductor during operation and heat dissipating members used therefor have been proposed. A general heat dissipation member has various forms such as a composition in which a polymer matrix is filled with a heat conductive filler, a cured product obtained by curing the composition, or a composite sheet in which a cured product and a reinforcing material are laminated. Things. The heat dissipating member is mounted between the heat generating member and the dissipating member, and the shape thereof is selected according to the mounting state.

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

  Silicone is often used from the viewpoints of heat resistance, cold resistance, and long-term reliability in the polymer matrix of a heat dissipation member in the field of vehicles that require a particularly large amount of heat generation and long-term reliability. In addition, silicon has been generally used as a substrate material for semiconductor elements, but recently, a substrate material using silicon carbide as a raw material is spreading. The silicon carbide-based substrate material has a higher heat resistance temperature than the silicon-based substrate material, and the allowable operating environment temperature rises to nearly 250 ° C. Also, in the in-vehicle field, hybrid cars and electric cars are becoming more popular, and it has become difficult to rely on engine heat for heating that used heat generated by the engine, and it is necessary to increase the amount of heat generated by increasing the resistance of the heater. There is sex. For example, a PTC heater requires a large current at startup, and heat generation exceeds 200 ° C.

  In such a flow, the heat-resistant temperature required for the heat dissipating member naturally increases. Since the use temperature range of the heat conductive silicone composition and its cured product, or composite sheet, which is a heat dissipating member using conventional silicone as a polymer matrix, is -40 ° C to 180 ° C, Not suitable.

  JP-A-2014-145042 is cited as a prior art related to the present invention, which is said to have heat resistance (250 ° C.). However, a heat stabilizer must be added, and in a low oxygen heating environment. There is a problem that it is limited to.

JP 2014-145042 A

  This invention is made | formed in view of the said situation, and it aims at providing the heat conductive silicone composition and hardened | cured material which can be used also in 250 degreeC atmosphere which uses silicone as a polymer matrix, and a composite sheet.

  As a result of intensive studies, the present inventors have found that by using α alumina having a particularly high α conversion rate among alumina, it is possible to provide a thermally conductive silicone composition with little weight loss even in an atmosphere at 250 ° C. I found out.

  In other words, insulation has been required for heat dissipating members, particularly in the automotive field, and as a heat conductive filler for heat dissipating members using many silicones as a polymer matrix, price, heat conductivity, etc. From the viewpoints of filling properties and insulating properties, alumina is used, but in order to achieve the above-described object, it is preferable to use silicone mainly using α-alumina as a heat conductive filler as a polymer matrix. The present inventors have found that the present invention is effective in obtaining a thermally conductive silicone composition and a cured product that can be used in an environment at 0 ° C., and have reached the present invention.

Therefore, this invention provides the following heat conductive silicone composition and hardened | cured material, and a composite sheet.
[1]
90% or more of the total mass part of the thermally conductive filler is α-alumina having an α-izing rate of 90% or more, and the weight reduction rate when it is placed in air at 250 ° C. for 6 hours is less than 1%. A thermally conductive silicone composition characterized by the above.
[2]
The heat conductive silicone composition according to [1], wherein the heat conductivity is 0.5 W / mK or more.
[3]
The heat conductive silicone composition according to [1] or [2], which contains 250 to 2,000 parts by weight of a heat conductive filler with respect to 100 parts by weight of the organopolysiloxane main material.
[4]
A cured product obtained by curing a thermally conductive silicone composition containing α-alumina, in which 90% or more of the total mass part of the thermally conductive filler has an α conversion rate of 90% or more, is air in a 250 ° C. environment. A thermally conductive silicone cured product characterized by having a weight loss rate of less than 1% when placed therein for 6 hours.
[5]
The thermally conductive silicone cured product according to [4], wherein the thermal conductivity is 0.5 W / mK or more.
[6]
The thermally conductive silicone composition contains 100 parts by mass of an organopolysiloxane main material, 250 to 2,000 parts by mass of a thermally conductive filler, and a curing effective amount of a curing agent that cures the organopolysiloxane main material. The thermally conductive silicone cured product according to [4] or [5], wherein
[7]
A thermally conductive silicone composite sheet obtained by laminating the thermally conductive silicone cured product according to any one of [4] to [6] on one side or both sides of a reinforcing material.
[8]
The heat conductive silicone composite sheet according to [7], wherein the reinforcing material is a polyimide film.
[9]
The heat 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 [4] to [9], wherein the hardness of the thermally conductive silicone cured product is 80 to 99 in terms of durometer A hardness.

  The thermally conductive silicone composition using α-alumina in which 90% or more of the total mass part of the thermally conductive filler according to the present invention has an α conversion rate of 90% or more has little weight loss even in an environment of 250 ° C., Excellent heat resistance. This thermally conductive silicone composition, cured product, and composite sheet can be applied to places 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 for an in-vehicle heater.

  The thermally conductive silicone composition according to the present invention comprises an organopolysiloxane main material and a thermally conductive filler as main components, and the thermally conductive silicone cured product comprises the organopolysiloxane main material and the thermally conductive filler. It is formed by curing a heat conductive silicone composition to which a curing agent for curing an organopolysiloxane main material is added.

This will be described in more detail below.
[Organopolysiloxane main material]
The main part of the organopolysiloxane used in the present invention is generally composed of repeating diorganosiloxane units basically in the main chain part, but this includes a branched structure as part of the molecular structure. Although it may be a thing and a cyclic body, linear diorganopolysiloxane is preferable.

  The functional group bonded to the silicon atom is an unsubstituted or substituted monovalent hydrocarbon group such as 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, Neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl and other alkyl groups, cyclopentyl, cyclohexyl, cycloheptyl and other cycloalkyl groups, phenyl, tolyl, xylyl, naphthyl Group, aryl group such as biphenylyl group, aralkyl group such as benzyl group, phenylethyl group, phenylpropyl group, methylbenzyl group, and a part or all of hydrogen atoms in which carbon atoms are bonded to these groups are fluorine , Groups substituted by halogen atoms such as chlorine and bromine, cyano groups, etc., for example, chloromethyl 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, A typical thing is 1-10 carbon atoms, and especially a thing with 1-6 carbon atoms is typical. Preferably, an unsubstituted or substituted alkyl group having 1 to 3 carbon atoms such as a methyl group, an ethyl group, a propyl group, a chloromethyl group, a 2-bromoethyl group, a 3,3,3-trifluoropropyl group, a cyanoethyl group, and the like An unsubstituted or substituted phenyl group such as a phenyl group, a chlorophenyl group, and a fluorophenyl group. In addition, it may have an unsaturated bond such as an alkenyl group, for example, a normal carbon number of 2 to 2 such as vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, hexenyl group, cyclohexenyl group, etc. There are about 8.

  The repeating unit of the main chain siloxane is not particularly limited, and the property of the polysiloxane obtained varies depending on the number of repeating units. Therefore, the preparation method of the heat conductive silicone composition may be appropriately selected according to the property. A stirrer such as a planetary mixer is suitable if it is oily, and a stirrer that applies more shearing force, such as a two-roll or kneader, is suitable if it is raw rubber.

In this case, as the organopolysiloxane main material, the use of kinematic viscosity of 25 ° C. is 100~40,000mm ² / s, particularly 100~10,000mm ² / s, preferably in terms of handling. The kinematic viscosity can be measured with an Ostwald viscometer.

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

(Alumina crystal phase)
Alumina has various crystal phases depending on the sintering temperature such as α, β, θ, and γ. It has been found that α-alumina having the highest sintering temperature suppresses the weight loss of the silicone polymer most in a 250 ° C. environment. In general alumina, there is almost no single crystal phase, but it is better that the proportion of α phase is as high as possible, and the α-formation rate is 90% or more, preferably 95% or more. .

The α conversion rate is determined by the peak height (I _25.6 ) of the alumina α phase (012 plane) appearing at 2θ = 25.6 ° from the diffraction spectrum of fine α-alumina obtained by using an X-ray diffractometer for the sample. From the peak heights (I ₄₆ ) of the γ phase, η phase, χ phase, κ phase, θ phase and δ phase appearing at the position of 2θ = 46 °, the following formula: α conversion rate (%) = I _25.6 / ( I _25.6 + I ₄₆ ) × 100
The value calculated by

(Alumina particle size)
The center particle size of alumina is preferably 0.1 to 200 μm, more preferably 1 to 100 μm, and still more preferably 1 to 50 μm. When the center particle size is less than 0.1 μm, the filling property to the organopolysiloxane main material is lowered, and when the center particle size is more than 200 μm, the fluidity when the composition is used and the strength when the cured product is used. Is difficult to obtain. In addition, it is important to select the particle size in consideration of the thickness when the thermally conductive silicone composition is mounted and the thickness when it is cured. This is because if alumina having a particle size larger than the thickness at the time of curing is included when mounting, the alumina will protrude from the thermally conductive silicone composition and the cured product.
The average particle diameter of alumina is a cumulative average diameter (median diameter) measured by Microtrac MT3300EX, which is a particle size analyzer manufactured by Nikkiso Co., Ltd.

(Alumina granular)
Alumina has various granular shapes such as spherical, round, and crushed depending on the production method. In general, crushed alumina has a high alpha conversion rate, so crushed alumina is preferable. However, the granular form is not limited as long as the alpha conversion ratio is satisfied.

(Other thermally conductive fillers)
Other thermally conductive fillers include non-magnetic metals such as copper and aluminum, metal oxides such as alumina, silica, magnesia, bengara, beryllia, titania and zirconia, metals such as aluminum nitride, silicon nitride and boron nitride. A material generally used as a heat conductive filler such as a metal hydroxide such as nitride or magnesium hydroxide, artificial diamond or silicon carbide can be used. The center particle diameter may be 0.1 to 200 μm, and one or more kinds may be used in combination. However, since it is assumed to be used in an environment of 250 ° C. as an application of the present invention, reactions such as melting, oxidation and dehydration do not occur at least up to about 300 ° C., and the cracking of the organopolysiloxane main material is promoted. It is necessary to use something that does not.

(Amount of heat conductive filler)
The blending amount of the heat conductive filler is preferably 250 to 2,000 parts by mass, more preferably 250 to 1,000 parts by mass, and still more preferably 250 to 600 parts by mass with respect to 100 parts by mass of the organopolysiloxane main material. It is. If the blending amount of the heat conductive filler is too small, sufficient thermal conductivity may not be obtained, and if it is too large, preparation of the composition itself may be difficult.

（式中、Ｒは非置換又は置換の炭素原子数１〜３０、特に１〜１０のアルキル基、アリール基、アラルキル基、ハロゲン化アルキル基等の１価炭化水素基、Ｒ’は炭素原子数１〜６、特に１〜３のアルキル基を示す。ｑは０〜２の整数であり、好ましくは０である。ｐは０〜１００、特に１〜５０の整数である。）
で示される片末端アルコキシ基含有ジオルガノポリシロキサンが好ましい。 [Heat conductive silicone composition]
As described above, the thermally conductive silicone composition is mainly composed of an organopolysiloxane main material and a thermally conductive filler, but as other components, the dispersibility of the thermally conductive filler can be increased as necessary. For the purpose of improving, an alkoxy group-containing organopolysiloxane can be blended. As the alkoxy group-containing organopolysiloxane, in particular, the following formula

(In the formula, R is an unsubstituted or substituted carbon atom having 1 to 30, particularly 1 to 10 monovalent hydrocarbon groups such as an alkyl group, aryl group, aralkyl group, halogenated alkyl group, etc., and R ′ is the number of carbon atoms. An alkyl group of 1-6, especially 1-3, q is an integer of 0-2, preferably 0. p is an integer of 0-100, especially 1-50.)
The one end alkoxy group containing diorganopolysiloxane shown by these is preferable.

  1-30 mass parts is preferable with respect to 100 mass parts of organopolysiloxane main materials, and, as for the compounding quantity of the said alkoxy group containing organopolysiloxane, it is especially preferable that it is 3-20 mass parts.

  Furthermore, if necessary, a colorant such as an organic pigment or an inorganic pigment, a heat resistance improver such as iron oxide or cerium oxide, and an internal release agent can be blended.

(Flowability of thermally conductive silicone composition)
In the present invention, the thermally conductive silicone composition is not cured and can be used as it is. In this case, the fluidity of the thermally conductive silicone composition is not particularly specified, When mounted by screen printing using a so-called dispenser or metal mask, the viscosity 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 the fluidity is poor and it becomes difficult to discharge with a dispenser, and the screen printing may be curled. In addition, the said viscosity is a value by a Malcolm viscometer.

(Weight reduction rate in air at 250 ° C)
In the thermally conductive silicone composition according to the present invention, the weight loss rate when it is placed in an air atmosphere at 250 ° C. for 6 hours is less than 1%, preferably 0.8% or less. The reason for the weight reduction is that the organopolysiloxane main material is cracked by heat and becomes low molecular weight and volatilizes. Therefore, if the weight reduction rate is large, the polymer content decreases and the thermally conductive silicone composition becomes It becomes brittle or hard. In such a case, the thermal conductivity of the thermally conductive silicone composition is lost.

  It has also been found that the degree of silicone cracking varies depending on the crystalline phase of alumina. Alumina in a crystalline phase having a low sintering temperature such as a γ phase or a θ phase promotes silicone cracking, and an α phase alumina having the highest sintering temperature does not promote silicone cracking.

  For the weight reduction rate, 2 g of the thermally conductive silicone composition is weighed in a heat-resistant glass petri dish having a diameter of 20 mm and put into an oven at 250 ° C. The atmosphere in the oven is air. It is a value calculated from the change in weight before and after charging after taking out after 6 hours, returning to room temperature, weighing.

(Thermal conductivity)
The thermal conductivity of the thermally conductive silicone composition is preferably 0.5 W / mK or more. More preferably, it is 0.8-8.0 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 specified, but if it exceeds 8.0 W / mK, it is difficult to fill the silicone itself. The thermal conductivity is a value measured by a hot disk method.

[Heat conductive silicone cured product]
The thermally conductive silicone cured product is obtained by blending a curing agent with the above-mentioned thermally conductive silicone composition containing the above-described organopolysiloxane main material and a thermally conductive filler as the main components and curing it.

Examples of the curing method of the thermally conductive silicone composition include an addition curing reaction using a platinum catalyst, a radical reaction using an organic peroxide as a catalyst, and a radical reaction using ultraviolet irradiation or electron beam irradiation. However, the curing method is not limited to these.
In this case, when the thermally conductive silicone composition is to be cured using an addition curing reaction using a platinum catalyst, an organopolysiloxane having at least two alkenyl groups in the molecule is used as the organopolysiloxane main material. Siloxane, organohydrogenpolysiloxane having at least two hydrogen atoms directly bonded to silicon atoms as a curing agent, and a platinum group metal curing catalyst are essential components.
Further, when curing with an organic peroxide, the organopolysiloxane main material may contain an alkenyl group, but the organopolysiloxane main material containing no alkenyl group can also be cured.
In addition, a well-known technique can be employ | adopted for the compounding quantity of the hardening | curing agent which hardens such an organopolysiloxane main material, a hardening method, hardening conditions, etc.

(Hardness of thermally conductive silicone cured product)
The hardness of the thermally conductive silicone cured product is preferably 80 to 99 in terms of durometer A hardness. More preferably, it is 90-96. If it is less than 80, the cured product may be easily deformed during mounting, or the surface of the cured product may be easily damaged.

(Weight reduction rate and thermal conductivity of thermally conductive silicone cured product)
The weight reduction rate and the thermal conductivity of the thermally conductive silicone cured product are not the thermally conductive silicone composition itself, but only the cured product obtained by curing the composition. The same as in the case of the 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 reinforcing material of the thermally conductive silicone composite sheet is preferably a polyimide film or glass cloth in view of practicality and workability. However, the reinforcing material is not limited to these, and can be used without any problem as long as it has sufficient strength and heat resistance. For example, a polytetrafluoroethylene sheet may be used.

(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 and insulating properties cannot be obtained. Conversely, if the polyimide film is too thick, thermal conductivity is hindered. Moreover, when the polyimide film surface is subjected to plasma treatment, adhesion to the thermally conductive silicone cured product may be improved.

(Glass cloth)
The thickness of the glass cloth is preferably 20 to 100 μm. More preferably, it is 30-60 micrometers. If it is less than 20 μm, sufficient strength cannot be obtained, and if it exceeds 100 μm, thermal conductivity may be hindered. The method of weaving the glass cloth is not particularly limited. The glass cloth is preferably 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 preferably 200 to 800 μm. This thickness is not limited to the case of the heat conductive silicone composite sheet, and is also applicable to the case where the heat conductive silicone composition or its cured product is used as it is without a reinforcing material.

[Method of forming thermally conductive silicone composite sheet]
The heat conductive silicone composite sheet is molded by preparing a heat 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 with toluene to obtain a coating solution. . A coating solution is applied onto the reinforcing material using an optional spacer, and is placed in an oven at 80 ° C. for 10 minutes to volatilize toluene, and then is placed in an oven at 150 ° C. for 10 minutes to be cured. Thereby, the heat conductive silicone hardened | cured material can be laminated | stacked on the single side | surface of a base material. When it is desired to laminate on the other side, the same method is applied, followed by drying and curing. However, the molding method of the heat conductive silicone composite sheet is not limited to this.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

（Ｘは有機官能基であり、ｎは下記粘度を与える数である。）
（Ａ−１）Ｘ＝メチル基で、動粘度１０，０００ｍｍ²／ｓ（２５℃）
（Ａ−２）Ｘ＝メチル基で、動粘度３０，０００ｍｍ²／ｓ（２５℃） [Preparation of composition]
(A) Component: Dimethylpolysiloxane represented by the following formula (1)

(X is an organic functional group, and n is a number giving the following viscosity.)
(A-1) X = methyl group, kinematic viscosity 10,000 mm ² / s (25 ° C.)
(A-2) X = methyl group, kinematic viscosity 30,000 mm ² / s (25 ° C.)

Component (B): Alumina (B-1) having a mean particle size as shown below is 99%, and crushed α-alumina (B-2) having a mean particle size of 5 μm is 95%. Crushed α-alumina (B-3) having an average particle diameter of 10 μm and spherical α-alumina (B-4) having an average particle size of 20 μm and an α conversion of 92%, and a crushed γ-alumina (B-5) having an average particle diameter of 10 μm Crushed θ-alumina with an average particle size of 10 μm

(C) Component: Thermally conductive filler (C-1) Aluminum hydroxide having an average particle size of 1.0 μm

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

(E) Component: C-23N (Organic peroxide type curing agent: manufactured by Shin-Etsu Chemical Co., Ltd.)

[Examples and Comparative Examples]
The components shown in Tables 1 and 2 were used in predetermined amounts shown in the table, and kneaded 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 A product was prepared, and the weight loss rate and thermal conductivity were measured by the following methods. The results are shown in Tables 1 and 2.

[Measuring method]
Weight reduction rate 2 g of the prepared thermally conductive silicone composition is weighed in a heat-resistant container having a diameter of 20 mm and put into an oven set at 250 ° C. The atmosphere in the oven is air. Remove after 6 hours and weigh after returning to room temperature. Divide the decrease by the weight before charging and multiply by 100.
Regarding Example 7 and Comparative Example 7, the prepared thermally conductive silicone composition was put into an oven set at 150 ° C. for 10 minutes and cured, and then the weight loss rate was measured.
-Thermal conductivity The thermal conductivity in 25 degreeC of each heat conductive silicone composition was measured by TPA-501 (made by Kyoto Electronics Industry Co., Ltd.) with the hot disk method.
In addition, regarding Example 7 and Comparative Example 7, the prepared thermal conductive silicone composition was put into an oven set at 150 ° C. for 10 minutes, and the thermal conductivity of the cured product was measured.

As shown in Examples 1 to 7, the thermally conductive silicone composition using α-alumina [(B-1) to (B-3)] having an α conversion rate of 90% or more is 6 in a 250 ° C. atmosphere. Even if time is added, the weight reduction rate is suppressed to less than 1%.
On the other hand, as shown in Comparative Example 1, when γ alumina is used, the weight reduction rate becomes 1% or more, and heat resistance cannot be imparted. As shown in Comparative Example 2, when θ alumina is used, the weight reduction rate is 1% or more, and heat resistance cannot be imparted. As shown in Comparative Example 3, when the proportion of α-alumina in the total mass part of the thermally conductive filler is less than 90%, the weight reduction rate becomes 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 heat conductive filler is less than 90%, and when aluminum hydroxide is used as the heat conductive filler to be further used, the weight is further reduced. The rate increases. This is because aluminum hydroxide caused a dehydration reaction and the weight of aluminum hydroxide itself decreased. In Comparative Example 5, the amount of γ alumina to be filled was reduced as compared with Comparative Example 1, but the weight reduction rate was increased. This is because the proportion of the silicone polymer is relatively increased. As shown in Comparative Example 6, when aluminum hydroxide was used as the thermally conductive filler, the weight reduction of the aluminum hydroxide itself due to the dehydration reaction of the aluminum hydroxide occurred rather than the weight reduction of the silicone, and the weight reduction rate was Especially big. 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)

  90% or more of the total mass part of the thermally conductive filler is α-alumina having an α-izing rate of 90% or more, and the weight reduction rate when it is placed in air at 250 ° C. for 6 hours is less than 1%. A thermally conductive silicone composition characterized by the above.   The heat conductive silicone composition according to claim 1, wherein the heat conductivity is 0.5 W / mK or more.   The thermally conductive silicone composition according to claim 1 or 2, comprising 250 to 2,000 parts by mass of a thermally conductive filler with respect to 100 parts by mass of the organopolysiloxane main material.   A cured product obtained by curing a thermally conductive silicone composition containing α-alumina, in which 90% or more of the total mass part of the thermally conductive filler has an α conversion rate of 90% or more, is air in a 250 ° C. environment. A thermally conductive silicone cured product characterized by having a weight loss rate of less than 1% when placed therein for 6 hours.   The thermally conductive silicone cured product according to claim 4, wherein the thermal conductivity is 0.5 W / mK or more.   The thermally conductive silicone composition contains 100 parts by mass of an organopolysiloxane main material, 250 to 2,000 parts by mass of a thermally conductive filler, and a curing effective amount of a curing agent that cures the organopolysiloxane main material. The thermally conductive silicone cured product according to claim 4 or 5, wherein:   A thermally conductive silicone composite sheet obtained by laminating the thermally conductive silicone cured product according to any one of claims 4 to 6 on one side or both sides of a reinforcing material.   The thermally conductive silicone composite sheet according to claim 7, wherein the reinforcing material is a polyimide film.   The thermally conductive silicone composite sheet according to claim 7, wherein the reinforcing material is a glass cloth.   The thermally conductive silicone composite sheet according to any one of claims 4 to 9, wherein the hardness of the thermally conductive silicone cured product is 80 to 99 in terms of durometer A hardness.