JP4687887B2 - Thermally conductive silicone grease composition - Google Patents

Description

  The present invention relates to a silicone grease composition having excellent thermal conductivity.

  Since many electronic components generate heat during use, it is necessary to remove the heat from the electronic components in order for the electronic components to function properly. In particular, an integrated circuit element such as a CPU used in a personal computer has an increased amount of heat generated due to an increase in operating frequency, and countermeasures against heat are an important issue.

  Many methods have been proposed as means for removing this heat. In particular, for electronic components that generate a large amount of heat, a method for releasing heat by interposing a heat conductive grease or a heat conductive material such as a heat conductive sheet between the electronic component and a member such as a heat sink has been proposed (Japanese Unexamined Patent Application Publication No. Sho-sho). No. 56-28264: Patent Document 1, Japanese Patent Laid-Open No. 61-157487: Patent Document 2).

  Further, as this heat conductive material, there is known a heat dissipating grease based on silicone oil and blended with zinc oxide or alumina powder (Japanese Patent Publication No. 52-33272: Patent Document 3, Japanese Patent Publication No. 59-52195). Publication: see Patent Document 4).

  Furthermore, in order to improve thermal conductivity, as the one using aluminum nitride powder, the above-mentioned Japanese Patent Application Laid-Open No. 56-28264 (Patent Document 1) includes a liquid organosilicone carrier and silica fiber, and dendritic zinc oxide, A thixotropic heat conductive material comprising at least one selected from flaky aluminum nitride and flaky boron nitride is disclosed. JP-A-2-153959 (Patent Document 5) discloses a silicone grease composition prepared by blending a specific organopolysiloxane with a spherical hexagonal aluminum nitride powder having a specific particle size range. Japanese Laid-Open Patent Publication No. 10-110179 (Patent Document 7) discloses a thermally conductive silicone grease in which an aluminum nitride powder having a small particle diameter and an aluminum nitride powder having a coarse particle diameter are combined. Japanese Patent Application Laid-Open No. 2000-63872 (Patent Document 8) discloses a heat conductive grease composition using an aluminum nitride powder surface-treated with an organosilane. It is disclosed.

  Aluminum nitride has a thermal conductivity of 70 to 270 W / mK, and diamond having a thermal conductivity of 900 to 2,000 W / mK is a material having a higher thermal conductivity. Japanese Patent Laid-Open No. 2002-30217 (Patent Document 9) discloses a thermally conductive silicone composition using diamond, zinc oxide, and a dispersant as a silicone resin.

  In addition, metal is a material having high thermal conductivity, and can be used in places where electronic components do not require insulation. Japanese Unexamined Patent Publication No. 2000-63873 (Patent Document 10) discloses a thermally conductive grease composition in which a metallic aluminum powder is mixed with a base oil such as silicone oil.

  However, any heat conductive material or heat conductive grease has become insufficient for the amount of heat generated by integrated circuit elements such as recent CPUs.

  The thermal conductivity of a material in which a thermal conductive filler is blended with silicone oil can be understood from Maxwell and Bruggeman's theoretical formula, when the volume fraction of the thermal conductive filler is 0.6 or less, the thermal conductive filler. It hardly depends on the thermal conductivity. Only when the volume fraction exceeds 0.6, the influence of the thermal conductivity of the thermally conductive filler comes out. In other words, in order to increase the thermal conductivity of the thermally conductive grease, first of all, how to fill the thermally conductive filler highly, if it can be filled high, how can the filler with high thermal conductivity be used? is there. However, due to the high filling, the fluidity of the heat conductive grease is lowered, and workability such as coating property and dispensing property is deteriorated, and there is a problem that it cannot be used practically.

  As another means, since the thermal resistance is proportional to the thickness of the heat dissipation material, there is a method of reducing the thickness of the heat dissipation grease. For this purpose, a heat conductive filler having a small average particle diameter and a coarse particle is generally required, but still a sufficient heat dissipation effect cannot be obtained. The use of a heat conductive filler with a small average particle size increases the surface area, and when a metal is used as a filler, oxidation also proceeds with increasing surface area. In addition to the decrease, high filling became difficult and it was difficult to impart high thermal conductivity.

JP-A-56-28264 JP-A 61-157487 Japanese Patent Publication No.52-33272 Japanese Patent Publication No.59-52195 Japanese Patent Laid-Open No. 2-153955 Japanese Patent Laid-Open No. 3-14873 JP-A-10-110179 JP 2000-63872 A JP 2002-30217 A JP 2000-63873 A

  This invention is made | formed in view of the said situation, and it aims at providing the heat conductive silicone grease composition which exhibits a favorable heat dissipation effect.

  In order to achieve the above object, the present inventors have conducted various studies on further improvement in thermal conductivity and workability. As a result, the oily organopolysiloxane has an average particle size of 5.0 to 15.0 μm. Yes, copper powder with an oxygen content of 0.1% by mass or less is highly filled, and the coarse particle mass of 425 mesh (32 μm opening) in this composition is 50 ppm or less, 325 mesh (45 μm opening) on By making the coarse particles of the material substantially zero, the thermally conductive silicone grease composition can make the coating thickness extremely thin, has excellent thermal conductivity, and exhibits a good heat dissipation effect. The headline and the present invention have been made.

Therefore, the present invention
(A) The following average composition formula (1)
R ¹ _a SiO _{(4-a) / 2} (1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 18 carbon atoms, and a is 1.8 ≦ a ≦ 2.2.)
An organopolysiloxane having a kinematic viscosity of 10 to 100,000 mm ² / s at 25 ° C. represented by: 10 to 60% by volume,
(B) Copper powder having an average particle diameter of 5.0 to 15.0 μm and an oxygen component of 0.1% by mass or less: 40 to 90% by volume
In the thermally conductive silicone grease composition containing, the coarse particle mass of 425 mesh (32 μm opening) ON is 50 ppm or less in the thermally conductive silicone grease composition, and 325 mesh (45 μm opening) ON There is provided a thermally conductive silicone grease composition characterized by having substantially zero coarse particles.

  The heat conductive silicone grease composition of the present invention exhibits a good heat dissipation effect.

The thermally conductive silicone grease composition of the present invention comprises:
(A) The following average composition formula (1)
R ¹ _a SiO _{(4-a) / 2} (1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 18 carbon atoms, and a is 1.8 ≦ a ≦ 2.2.)
An organopolysiloxane having a kinematic viscosity of 10 to 100,000 mm ² / s at 25 ° C. represented by: 10 to 60% by volume,
(B) Copper powder having an average particle diameter of 5.0 to 15.0 μm and an oxygen component of 0.1% by mass or less: 40 to 90% by volume
The coarse particle mass of 425 mesh (32 μm aperture) ON is 50 ppm or less in the thermally conductive silicone grease composition, and the coarse particle of 325 mesh (45 μm aperture) ON is substantially zero. belongs to.

  Here, when the coarse particle mass of 425 mesh (32 μm openings) is larger than 50 ppm with respect to the heat conductive silicone grease composition, the film thickness of the heat conductive silicone grease composition can be made sufficiently thin. Since the desired heat dissipation effect cannot be obtained, it is necessary to be 50 ppm or less, preferably 30 ppm or less. Even if the coarse particle mass of 425 mesh (32 μm aperture) ON is 50 ppm or less, one large coarse particle may be present in the thermally conductive silicone grease composition. The heat conductive silicone grease composition is not sufficiently thin and the desired heat dissipation effect cannot be obtained. Therefore, in order to obtain a desired heat radiation effect, it is necessary that the number of coarse particles having 325 mesh (45 μm openings) on is substantially zero at the same time.

  In order to remove coarse particles from the thermally conductive silicone grease composition, there is a method of directly filtering the thermally conductive silicone grease composition through a 425 mesh (aperture 32 μm). It is practically difficult to filter a material in which a heat conductive filler is contained, and it is preferable to remove coarse particles from the heat conductive filler. A method for removing coarse particles from the thermally conductive filler will be described later.

Hereinafter, each component used in the composition of the present invention will be described. The organopolysiloxane used in the component (A) of the present invention is represented by the following average composition formula (1).
R ¹ _a SiO _{(4-a) / 2} (1)

Wherein, R ¹ is one or more groups independently selected from monovalent hydrocarbon group having 1 to 18 carbon atoms. Such groups include, for example, methyl groups, ethyl groups, propyl groups, hexyl groups, octyl groups, decyl groups, alkyl groups such as dodecyl groups, tetradecyl groups, hexadecyl groups, octadecyl groups, cyclopentyl groups, cyclohexyl groups, etc. An alkenyl group such as a cycloalkyl group, a vinyl group and an allyl group; an aryl group such as a phenyl group and a tolyl group; an aralkyl group such as a 2-phenylethyl group and a 2-methyl-2-phenylethyl group; Examples thereof include halogen-substituted hydrocarbon groups such as trifluoropropyl group, 2- (perfluorobutyl) ethyl group, 2- (perfluorooctyl) ethyl group, p-chlorophenyl group, etc., particularly methyl group, phenyl group, carbon The alkyl group of several 6-18 is preferable. From the viewpoint of the consistency required for the silicone grease composition, a is preferably in the range of 1.8 to 2.2, and particularly preferably 1.9 to 2.1.

In addition, if the kinematic viscosity at 25 ° C. of the organopolysiloxane used in the present invention is lower than 10 mm ² / s, oil bleeding tends to occur when a silicone grease composition is used, and if it exceeds 100,000 mm ² / s. since the fluidity at the time of the silicone grease composition becomes poor, it is necessary that the kinetic viscosity at 25 ° C. is 10~100,000mm ² / s, it is particularly 10~10,000mm ² / s Is preferred.
In the present invention, the kinematic viscosity is a value at 25 ° C. measured with an Ostwald viscometer.

  If the blending ratio of the organopolysiloxane is less than 10% by volume in the heat conductive silicone grease composition, it becomes hard when the heat conductive silicone grease composition is formed, the fluidity is lost, and the workability is lowered. If it exceeds 60% by volume, the thermal conductivity is lowered and the settling of the filler proceeds, so the organopolysiloxane is in the range of 10-60% by volume in the thermally conductive silicone grease composition, preferably It is in the range of 15 to 35% by volume.

  The copper powder having an average particle size of 5.0 to 15.0 μm of the component (B) used in the present invention has a spherical or granular particle shape in order to highly fill the component (A) organopolysiloxane. Is preferably used. A dendritic powder, flake powder, needle powder, irregular powder, or the like having a large bulk density is not suitable for high filling.

  The copper powder of the component (B) is difficult to be filled when the average particle size is less than 5.0 μm, and when it exceeds 15 μm, it is difficult to reduce the thermal resistance by thinning, so the average particle size is 5.0-15. The range is 0.0 μm, preferably 7.0 to 12.0 μm. In the present invention, the average particle diameter can be determined, for example, as a volume average diameter (or cumulative average diameter: median diameter) by a laser diffraction method or the like.

  Copper is a material having a thermal conductivity of 398 W / mK at room temperature and excellent in thermal conductivity. However, in copper powder, oxidation easily proceeds on the surface, and the thermal conductivity tends to decrease. Furthermore, surface wettability also deteriorates the wettability with respect to the component (A), and irregularities are generated on the particle surface to increase the specific surface area, so that it is difficult to improve the thermal conductivity of the silicone grease composition by high filling. Since the specific surface area increases as the particle size decreases, deterioration of the thermal conductivity and wettability of the copper powder due to surface oxidation becomes significant. In copper powder having an average particle size of 5.0 to 15.0 μm, if the oxygen content is greater than 0.1% by mass, high filling becomes difficult due to deterioration of wettability and increase in specific surface area, and thermal conductivity is also deteriorated. The oxygen component is 0.1% by mass or less, preferably 0.05% by mass or less. By using a copper powder having a small oxygen component, it is possible to improve the thermal conductivity even with a small particle size by high filling. In the thermally conductive silicone grease composition of the present invention, the copper powder surface is coated with silicone, and the progress of oxidation is suppressed.

  Below, although the method of making the oxygen component of copper powder small is illustrated, this invention is not restrict | limited to this. The copper powder forms a copper oxide film on the surface when exposed to the air, so that the oxygen component increases as the specific surface area increases. If the copper powder is large in size and high in sphericity, the specific surface area is small and the oxygen component is also small. However, a thermally conductive silicone grease composition using copper powder with a large size can provide high thermal conductivity due to the high filling of copper powder, but it will not be possible to reduce the thickness during mounting, and a sufficient heat dissipation effect Cannot be obtained. When copper powder having a small size is used, the sphericity greatly contributes to the oxygen component. Examples of a method for producing a spherical powder having a high sphericity and a small specific surface area include, but are not limited to, a molten metal powdering method (atomizing method) in which molten copper is scattered and solidified by a high-speed fluid. . There is also a technique using a flux component that removes an oxide film existing on the surface of the copper powder or covers the surface to prevent contact with the atmosphere. Oxygen components can be reduced by using an organic acid or resin flux.

  In addition, the oxygen concentration of copper powder can be measured based on the inert gas melting-infrared absorption method of JIS Z 2613.

  If the blending ratio of the copper powder is less than 40% by volume in the heat conductive silicone grease composition, the thermal conductivity is lowered. On the other hand, if it is greater than 90% by volume, the fluidity of the heat conductive silicone grease composition is lost and the workability is reduced. Therefore, the blending amount of the copper powder is in the range of 40 to 90% by volume, preferably in the range of 50 to 85% by volume in the heat conductive silicone grease composition.

  In the present invention, in order to further improve the thermal conductivity, as the component (C), a thermal conductive powder other than the component (B) copper powder, for example, zinc oxide powder, aluminum oxide powder, boron nitride powder, aluminum nitride powder, Inorganic powders such as silicon carbide powder and diamond powder, metal powders such as silver powder, gold powder, nickel powder and stainless steel powder may be added.

  Among these, when one or more heat conductive powders having an average particle size of 0.1 to 5.0 μm are added, the filling property is improved by entering the gaps of the copper powder filled in the silicone grease. To do. Moreover, it is preferable because the stability of the thermally conductive silicone grease composition is improved and oil separation can be prevented. If the average particle size is less than 0.1 μm, the bulk density may increase, so high filling may be difficult. If the average particle size exceeds 5.0 μm, fine filling by combining with a large particle size copper powder may not be possible. The average particle size is preferably in the range of 0.1 to 5.0 μm, more preferably in the range of 0.2 to 3.0 μm.

  Further, if the blending ratio of the heat conductive powder is more than 35% by volume in the heat conductive silicone grease composition, the fluidity of the heat conductive silicone grease composition may be lost, and workability may be reduced. It is preferable that the compounding quantity of conductive powder is the range of 0-35 volume%, More preferably, it is 1-35 volume%, More preferably, it is the range of 5-30 volume%. In addition, it is preferable that the total compounding quantity of (B) and (C) component is 60-90 volume%, especially 70-85 volume%.

  In addition, as mentioned above, the heat conductive fillers of the copper powder of component (B) and the heat conductive powder of component (C) each have coarse particles of 425 mesh (32 μm openings). It is necessary that the amount of the thermally conductive silicone grease composition to be 50 ppm or less, and further, 325 mesh (45 μm opening) coarse particles are not substantially contained.

  A manufacturer that manufactures a filler such as a heat conductive filler measures the particle size distribution and puts a value on an inspection table or the like, but coarse particles with a small absolute amount cannot generally be detected by a particle size distribution measuring device. Therefore, even if the same material and the same average particle diameter are used, there is a large difference in heat dissipation characteristics depending on whether or not coarse particles are removed. It is particularly important to control the amount of coarse particles of the heat conductive filler at the time when the heat generation of the device is very large.

  There are several ways to remove coarse particles from these thermally conductive fillers. In general, there are airflow classification, mesh classification, etc. As long as coarse particles are removed to a high degree, classification of the thermally conductive filler is not limited.

  In the present invention, a wetter component (D) can be further blended as an optional component. This is because the surface of the above component (B) copper powder and (C) heat conductive powder is treated with a wetter component to improve the wettability between the powder and the organopolysiloxane of component (A) as the base oil. Assisting high filling.

As the component (D), an alkoxysilane (D-1) represented by the following general formula (2) is first mentioned.
R ² _b R ³ _c Si (OR ⁴ ) _4-bc (2)

R ² in the above formula is an alkyl group having 9 to 15 carbon atoms, and specific examples thereof include nonyl group, decyl group, dodecyl group, tetradecyl group and the like. If the carbon number is less than 9, the wettability with the powder may not be sufficient, and if it is greater than 15, the alkoxysilane solidifies at room temperature, which is inconvenient to handle and the low temperature characteristics of the resulting composition may be reduced. There is.

R ³ in the above formula is a saturated or unsaturated monovalent hydrocarbon group having 1 to 8 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, a propyl group, a hexyl group, and an octyl group. Alkyl groups, cyclopentyl groups, cyclohexyl groups such as cyclohexyl groups, alkenyl groups such as vinyl groups, allyl groups, aryl groups such as phenyl groups, tolyl groups, 2-phenylethyl groups, 2-methyl-2-phenylethyl groups, etc. And halogen-substituted hydrocarbon groups such as 3,3,3-trifluoropropyl group, 2- (perfluorobutyl) ethyl group, 2- (perfluorooctyl) ethyl group, and p-chlorophenyl group. However, a methyl group and an ethyl group are particularly preferable.

R ⁴ is one or more alkyl groups having 1 to 6 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, and a hexyl group, and a methyl group and an ethyl group are particularly preferable.

  Further, b is an integer of 1 to 3, but 1 is particularly preferable. c is an integer of 0 to 2, and b + c is an integer of 1 to 3.

Specific examples of the alkoxysilane represented by the general formula (2) include the following.
C ₁₀ H ₂₁ Si (OCH ₃ ) ₃ , C ₁₂ H ₂₅ Si (OCH ₃ ) ₃ ,
C ₁₀ H ₂₁ Si (CH ₃ ) (OCH ₃ ) ₂ , C ₁₀ H ₂₁ Si (C ₆ H ₅ ) (OCH ₃ ) ₂ ,
C ₁₀ H ₂₁ Si (CH ₃ ) (OC ₂ H ₅ ) ₂ ,
C ₁₀ H ₂₁ Si (CH═CH ₂ ) (OCH ₃ ) ₂ ,
C ₁₀ H ₂₁ Si (CH ₂ CH ₂ CF ₃ ) (OCH ₃ ) ₂

  It is preferable that the addition amount of this alkoxysilane is 0-5 volume% in a heat conductive silicone grease composition. Even if the addition amount is more than 5% by volume, the wetter effect may not increase, which is uneconomical and slightly volatile, so if left in an open system, the thermally conductive silicone grease composition gradually It may become hard. A more preferable addition amount is 0.1 volume% or more and 3 volume% or less in the thermally conductive silicone grease composition.

式中のＲ⁴は上記の通りであり、またｄは５〜１００の整数であり、好ましくは１０〜６０の整数である。 Moreover, as a wetter component of component (D) other than the above, the one terminal trifunctional hydrolyzable methylpolysiloxane (D-2) represented by following General formula (3) is mentioned.

R ⁴ in the formula is as described above, and d is an integer of 5 to 100, preferably an integer of 10 to 60.

  The addition amount of this one-terminal trifunctional hydrolyzable methylpolysiloxane is preferably 0 to 40% by volume in the thermally conductive silicone grease composition. In the thermally conductive silicone grease composition, when the proportion of this component is increased, the heat resistance may be lowered. Therefore, the preferable addition amount is 0.1 volume% or more and 30 volume% or less.

  In the present invention, the wetter component of component (D) can be a combination of the alkoxysilane (D-1) and the one-terminal trifunctional hydrolyzable methylpolysiloxane (D-2). It is preferable to use it in a range where the total amount of the component (A) is 40% by volume or less in the thermally conductive silicone grease composition.

  Furthermore, in the present invention, a heat resistance improver such as iron oxide and cerium oxide, a viscosity modifier such as silica, a colorant, and the like may be added within a range not impairing the object of the present invention.

  In order to produce the thermally conductive silicone grease composition of the present invention, components (A) and (B), and optional components (C), (D) and other components are mixed into a trimix, twin mix, and planetary. Mixer (registered trademark of mixer manufactured by Inoue Seisakusho Co., Ltd.), Ultramixer (registered trademark of mixer manufactured by Mizuho Kogyo Co., Ltd.), registered trademark of Hibis Disper Mix (mixer manufactured by Special Machine Industries Co., Ltd.) ) And the like. If necessary, mixing may be performed while heating to 50 to 150 ° C. Further, after mixing, it is preferable to perform a kneading operation under a high shearing force for uniform finishing. As a kneading apparatus, there are a three roll, a colloid mill, a sand grinder, etc. Among them, a method using a three roll is preferable.

  As described above, the thermally conductive silicone grease composition of the present invention needs to have a coarse particle mass of 425 mesh (32 μm aperture) ON of 50 ppm or less in the composition, and at the same time, 325 mesh. It is necessary that the coarse particles (45 μm openings) are substantially zero.

  In the present invention, in order to measure the coarse particle mass in the heat conductive silicone grease composition, any solvent that can dissolve the silicone content of the heat conductive silicone grease composition may be used. After dissolving, the solution is passed through 325 mesh (aperture 45 μm) and 425 mesh (aperture 32 μm), washed well, and 325 mesh (aperture 45 μm) ON is visually observed and 425 mesh (aperture 32 μm) ) For the ON, the coarse particles that have been turned ON are dried, collected on a medicine wrapping paper, etc., and the mass thereof may be measured.

  The viscosity of the thermally conductive silicone grease composition of the present invention is preferably less than or equal to 1,000 Pa · s, more preferably less than or equal to 500 Pa · s. It is. Dispensing property indicates workability when a thermally conductive silicone grease composition is applied to a substrate, and if this is poor, use of a syringe or dispensing device having means for extruding the thermally conductive silicone grease composition. Discharge becomes difficult and it becomes difficult to apply thinly on the substrate.

The heat conductive silicone grease composition of the present invention preferably has a thermal resistance at 25 ° C. of 6 mm ² · K / W or less, particularly 4 mm ² · K / W or less as measured by a laser flash method. When the thermal resistance exceeds 6 mm ² · K / W, application to a heating element having a large calorific value may be impossible.

  The thermally conductive silicone grease composition of the present invention obtained as described above can have a significant improvement in thermal conductivity and good workability.

  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.

[Examples 1-5, Comparative Examples 1-5]
First, the components used in the thermally conductive silicone grease composition according to the present invention and the production method thereof are shown below.

Ingredient (A)
A-1: Organopolysiloxane represented by the following composition formula

ここで、成分（Ａ）の動粘度は、オストワルド粘度計により測定した２５℃における値である。 A-2: Organopolysiloxane represented by the following composition formula

Here, the kinematic viscosity of the component (A) is a value at 25 ° C. measured by an Ostwald viscometer.

Ingredient (B)
B-1: Copper powder (average particle size 10.1 μm, airflow classified product, oxygen component 0.03% by mass)
B-2: Copper powder (average particle size 10.1 μm, airflow classified product, oxygen component 1.4 mass%)
B-3: Copper powder (average particle size 12.3 μm, no classification, 0.2 mass% oxygen component)
Here, the oxygen concentration measurement of a component (B) was performed based on the inert gas melting-infrared absorption method of JISZ2613. The analyzer used was OXYGEN / NITROGEN ANALYZER EMGA-523 manufactured by Horiba. Moreover, the average particle diameter of a component (B) and the following component (C) is the value of the cumulative average diameter (median diameter) measured by Microtrac MT3300EX which is a particle size analyzer made by Nikkiso Co., Ltd.

Ingredient (C)
C-1: Aluminum powder (average particle size 1.4 μm, 425 mesh pass product)
C-2: Zinc oxide powder (average particle size: 0.5 μm, airflow classification product)
C-3: Aluminum powder (average particle size 6.5 μm, no classification)

Ingredient (D)
D-1: Alkoxysilane C ₁₀ H ₂₁ Si (OCH ₃ ) ₃ represented by the following composition

D-2: Hydrolyzable methylpolysiloxane represented by the following composition formula

[Production method]
Components (A) to (D) are weighed in the ratios shown in Tables 1 and 2, and the whole amount is charged into a planetary mixer (manufactured by Inoue Seisakusho Co., Ltd.). Manufactured.

[Test method]
The characteristics of the obtained heat conductive silicone grease composition were measured by the following test methods. The results are shown in Tables 1 and 2.

〔viscosity〕
The thermally conductive silicone grease composition was allowed to stand in a thermostatic chamber at 25 ° C. for 24 hours, and then the viscosity at a rotation speed of 10 rpm was measured using a Malcolm viscometer.

[Test piece production]
A test piece was prepared by sandwiching a heat conductive silicone grease composition having a thickness of 75 μm between two aluminum plates having a diameter of 12.6 mm and a thickness of 1 mm, and applying a pressure of 0.15 MPa for 60 minutes.

[Measurement of thickness of thermally conductive silicone grease composition]
The thickness of the test piece was measured with a micrometer (manufactured by Mitutoyo Corporation), and the thickness of the thermally conductive silicone grease composition was calculated by subtracting the thickness measured in advance for two aluminum plates.

(Thermal resistance measurement)
After measuring the thickness of the thermally conductive silicone grease composition, the thermal resistance of the thermally conductive silicone grease composition at 25 ° C. was measured using the test piece. As a measuring instrument, a model Microflash 300 manufactured by Holometrix micromet was used.

[Visual observation on 325 mesh (aperture 45 μm)]
50 g of the thermally conductive silicone grease composition was placed in a 200 ml plastic bottle together with 100 g of toluene, capped and shaken until the thermally conductive silicone grease composition was completely dispersed. After dispersion, the dispersion was poured into a 325 mesh test sieve (standard sieve: JIS Z 8801) (aperture 45 μm), thoroughly washed with toluene for washing, and the mesh was placed in a dryer and dried. After drying, 325 mesh-on coarse particles were transferred to the medicine wrapping paper, visually observed, and evaluated according to the following criteria.
<Criteria>
◯: Coarse particles with 325 mesh (aperture 45 μm) are not found visually.
X: 325 mesh (aperture 45 μm) ON coarse particles can be confirmed by visual observation.

[425 mesh (aperture 32 μm) on mass measurement]
325 mesh (aperture 45 μm) ON 50 g of thermally conductive silicone grease composition in which coarse particles were not confirmed by visual observation was placed in a 200 ml plastic bottle together with 100 g of toluene, stoppered and thermally conductive silicone grease composition Shake until all is dispersed. After the dispersion, the dispersion was poured into a 425 mesh test sieve (standard sieve: JIS Z 8801) (mesh size: 32 μm), thoroughly washed with washing toluene, and the mesh was placed in a dryer and dried. After drying, 425 mesh-on coarse particles were transferred to a medicine wrapping paper and weighed to calculate the ppm of 425 mesh-on coarse particles for the thermally conductive silicone grease composition.

＊１）：比較例１はプラネタリーミキサーで攪拌混合してもペースト状にならなかった。

* 1): Comparative Example 1 did not become a paste even when stirred and mixed with a planetary mixer.

Claims (7)

(A) The following average composition formula (1)
R ¹ _a SiO _{(4-a) / 2} (1)
(In the formula, R ¹ is independently a monovalent hydrocarbon group having 1 to 18 carbon atoms, and a is 1.8 ≦ a ≦ 2.2.)
An organopolysiloxane having a kinematic viscosity at 25 ° C. of 10 to 100,000 mm ² / S represented by: 10 to 60% by volume,
(B) Copper powder having an average particle diameter of 5.0 to 15.0 μm and an oxygen component of 0.1% by mass or less: 40 to 90% by volume
In the thermally conductive silicone grease composition containing, the coarse particle mass of 425 mesh (32 μm opening) ON is 50 ppm or less in the thermally conductive silicone grease composition, and 325 mesh (45 μm opening) ON A heat conductive silicone grease composition characterized by having substantially zero coarse particles. 2. The thermally conductive silicone grease composition according to claim 1, wherein R ^{1 in the} formula (1) contains an alkyl group having 6 to 18 carbon atoms.   Furthermore, as a component (C), heat conductive powder other than the component (B) whose average particle diameter is 0.1-5.0 micrometers is contained: 1-35 volume%, The characterized by the above-mentioned. The thermally conductive silicone grease composition described in 1. Furthermore, as a component (D-1), following General formula (2)
R ² _b R ³ _c Si (OR ⁴ ) _4-bc (2)
(Wherein R ² is an alkyl group having 9 to 15 carbon atoms, R ³ is a monovalent hydrocarbon group having 1 to 8 carbon atoms, R ⁴ is an alkyl group having 1 to 6 carbon atoms, and b is an integer of 1 to 3) C is an integer from 0 to 2, and b + c is an integer from 1 to 3.)
The thermally conductive silicone grease composition according to any one of claims 1 to 3, wherein an alkoxysilane represented by the formula: Furthermore, as a component (D-2), following General formula (3)

(In the formula, R ⁴ is an alkyl group having 1 to 6 carbon atoms, and d is an integer of 5 to 100.)
5. The thermally conductive silicone grease composition according to claim 1, wherein the hydrolyzable methylpolysiloxane having a trifunctional group at one end is represented by the formula:   The thermally conductive silicone grease composition according to any one of claims 1 to 5, wherein the thermally conductive silicone grease composition has a viscosity at 25 ° C of 1,000 Pa · s or less. The thermal conductivity according to any one of claims 1 to 6, wherein the thermal resistance of the thermally conductive silicone grease composition at 25 ° C measured by a laser flash method is 6 mm ² · K / W or less. Silicone grease composition.