JP2003183498A - Thermally conductive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally conductive sheet that is excellent in thermal conductivity, electrical insulating properties, flexibility and shape follow-up property and can easily be produced at a low cost. <P>SOLUTION: The thermally conductive sheet is produced by mold-processing into a sheet form a mixed composition prepared by blending a thermally conductive filler into a silicone rubber, wherein a silicon carbide powder having an average particle size of 50-100 μm and an aluminum oxide powder having an average particle size of 2-10 μm are blended as a thermally conductive filler. It is preferable that a graphitized carbon fiber as a thermally conductive filler is further blended, provided that the total blending amount of the thermally conductive filler as mentioned above is preferably 60-70 vol.%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a heat conductive sheet which is excellent in heat conductivity, flexibility and handleability. More specifically, various semiconductor devices and power supplies for electrical equipment,
The present invention relates to a heat conductive sheet used in contact with a heat source in order to effectively dissipate heat generated by a light source, components and the like.

[0002]

2. Description of the Related Art In recent years, in electronic equipment, high performance,
Due to the miniaturization and weight reduction of high-density packaging of semiconductor packages, high integration and high speed of LSI, etc., it is very important to take thermal measures to effectively dissipate heat generated by various electronic components to the outside. It is an issue. Therefore, heat-dissipating members such as heat sinks are attached to various electronic components of electric equipment, for example, heat-generating electronic components such as transistors and thyristors, through a sheet material having good thermal conductivity (hereinafter referred to as "heat conductive sheet"). The measure of mounting is generally adopted.

This type of heat-conducting sheet is generally attached to the heat-generating electronic component or the like in a state in which the heat-conducting electronic component or the like serving as a heat source is made to flexibly follow the irregularities of the mounting site. . The heat conductive sheet reduces the contact thermal resistance between the heat generating electronic component and the heat dissipation member,
It has the function of efficiently conducting the heat generated by the heat-generating electronic components to the heat dissipation member. In addition, this type of heat conductive sheet also functions as a protective material that prevents deformation and damage of the heat dissipation member and the heat-generating electronic component when the heat dissipation member is pressure-bonded to the heat-generating electronic component and the like. Therefore, this heat conductive sheet is required to have not only high heat conductivity but also excellent electric insulation, flexibility and shape conformability.

Conventionally, as this type of heat conductive sheet,
Silicon oxide, aluminum oxide, magnesium oxide, which has good thermal conductivity, in polymer materials such as silicone rubber.
Ceramic powders such as boron nitride, aluminum nitride, silicon nitride or silicon carbide blended as a thermally conductive filler have been widely adopted. For example, Japanese Patent Application Laid-Open No. 11-87958 discloses a heat conductive sheet in which silicon nitride and spherical alumina are mixed as a heat conductive filler in silicone rubber. Further, in Japanese Patent Laid-Open No. 2000-233452, a heat is obtained by compounding, as a thermally conductive filler, silicon carbide particles having a relatively large particle diameter and boron nitride powder having a relatively small particle diameter into a silicone gel. A conductive sheet is disclosed. These heat conductive sheets are excellent in electrical insulation, flexibility and shape conformability, and at the same time 1.0 to
The thermal conductivity was about 2.8 W / (m · K).

However, in recent years, in high-performance electronic devices such as notebook computers and mobile phones, high integration, high speed,
Along with downsizing or weight reduction, the amount of heat generated by various electronic components and the like is increasing. Against this background, there is a demand for a heat conductive sheet having higher heat conductivity than ever, and specifically, a heat conductive sheet having a high heat conductivity of 5.0 W / (m · K) or more. Is coveted. for that reason,
The above-mentioned conventional heat conductive sheet still has insufficient heat conductivity, and various improvements or proposals have been made to achieve such requirements.

For example, in Japanese Patent Laid-Open No. 2001-139733, silicon carbide powder having an average particle size of 50 to 100 μm and silicon carbide powder having an average particle size of 10 μm or less are contained in a silicone rubber as a thermally conductive filler. A heat conductive sheet has been proposed which is compounded in a weight ratio of 1: 1 to 3: 1. In this heat conductive sheet, by filling silicon carbide powder in silicone rubber to a high degree,
A thermal conductivity of 5.0 W / (mK) is achieved.

Further, Japanese Patent Laid-Open No. 9-283955 proposes a heat conductive sheet in which a specific graphitic carbon fiber is mixed as a heat conductive filler in a matrix resin. In this heat conductive sheet, the heat conductivity of 5.0 W / (m · K) or higher is achieved by using the graphite carbon fiber having extremely high heat conductivity as the heat conductive filler.

[0008]

However, in the heat conductive sheet proposed in the above-mentioned Japanese Patent Laid-Open No. 2001-139733, the silicone rubber is highly filled with 85% by weight or more of silicon carbide powder. 5.
A thermal conductivity of 0 W / (mK) is achieved. Therefore, the obtained heat conductive sheet was hard and brittle, and the handleability was poor. Further, this heat conductive sheet had a high Asker C hardness of more than 30, and was poor in flexibility and shape following ability. Furthermore, this heat conductive sheet is a material that, if used once compressed, may crack or fall off, and not only has poor reworkability, but also may deform or damage the heat dissipation member, the heat generating electronic component, and the like. there were.

On the other hand, in the heat conductive sheet proposed in the above-mentioned Japanese Patent Laid-Open No. 2001-139733, graphitic carbon fiber having extremely low electric resistance is used as a heat conductive filler. Therefore, the obtained heat conductive sheet cannot achieve electrical insulation with a volume resistivity of 10 ⁶ Ω · cm or more, and the heat conductive sheet cannot be directly contacted with heat-generating electronic components of electric equipment. It could not be used. Therefore, in order to use this heat conductive sheet in such applications, it is considered to perform an insulation treatment such as forming an insulating layer on the surface of the graphite carbon fiber or forming an insulating layer on the surface of the sheet. However, this not only makes the manufacturing process complicated and disadvantageous,
Increasing cost is inevitable.

That is, conventionally, a heat conductive sheet having a high heat conductivity of 5.0 W / (m · K) or more, flexibility and a shape following property of Asker C hardness of 30 or less has not yet been realized. Moreover, a low-cost heat conductive sheet having a low electrical insulation property of 10 ⁶ Ω · cm or more in volume resistivity has not yet been realized.

The present invention has been made to solve the above problems, and an object thereof is a heat conductive sheet which is excellent in heat conductivity, electric insulation, flexibility and shape followability, and which is easy to manufacture at low cost. To provide.

[0012]

In order to solve the above problems, the present inventor has conducted earnest research on a heat conductive filler to be blended in a silicone rubber, and as a result, a specific ceramic powder was used as a heat conductive filler. The present invention has been completed by finding that it is possible to realize a heat conductive sheet which is excellent in heat conductivity, electric insulation, flexibility and shape followability, and is low in cost and easy to manufacture by using it.

That is, the invention according to claim 1 provides a mixed composition comprising a silicone rubber and a thermally conductive filler,
In the heat conductive sheet formed into a sheet, a mixture of silicon carbide powder having an average particle diameter of 50 to 100 μm and aluminum oxide powder having an average particle diameter of 2 to 10 μm was used as the heat conductive filler. Characterize.

According to a second aspect of the present invention, in the heat conductive sheet according to the first aspect, the mixing ratio of the silicon carbide powder and the aluminum oxide powder is 1: by volume.
It is characterized by being 1 to 3: 1.

The invention according to claim 3 is characterized in that in the heat conductive sheet according to claim 1 or 2, graphitized carbon fibers are further blended as the heat conductive filler.

According to a fourth aspect of the present invention, in the heat conductive sheet according to the third aspect, the compounding ratio of the graphitized carbon fiber to the aluminum oxide powder and the silicon carbide powder is 1: 2 in volume ratio. ˜1: 5.

According to a fifth aspect of the present invention, in the heat conductive sheet according to any one of the first to fourth aspects, the total content of the heat conductive filler is 60 to 70% by volume. Is characterized in that.

According to a sixth aspect of the present invention, in the heat conductive sheet according to any one of the first to fifth aspects, the heat conductivity of the sheet is 5.0 W / (m · K) or more. And the Asker C hardness of the sheet is 30 or less.

According to a seventh aspect of the invention, in the heat conductive sheet according to any one of the first to sixth aspects, the volume resistivity of the sheet is 10 ⁶ Ω · cm or more. Is characterized by.

(Function) According to the present invention, in a heat conductive sheet obtained by molding and processing a mixed composition in which a silicone rubber is mixed with a heat conductive filler, the heat conductive filler has an average particle size of It is characterized in that 50 to 100 μm of silicon carbide powder and aluminum oxide powder having an average particle diameter of 2 to 10 μm are mixed.

When silicon carbide powder and aluminum oxide powder each having a specific average particle size are used as the heat conductive filler in this way, as shown in FIG. 1, a relatively small diameter aluminum oxide powder 11 is compared. The silicon oxide powder 11 and the silicon carbide powder 12 are filled in a gap between the large-diameter silicon carbide powder 12 so that they are closely packed to each other. Therefore, the heat transfer path is highly developed in the sheet, and high heat conductivity of the sheet can be achieved. In addition, since the high thermal conductivity is achieved without highly filling the thermally conductive filler as in the conventional case, it is possible to suppress the deterioration of the flexibility and shape conformability of the sheet.

Furthermore, if a graphitized carbon fiber is further added as a heat conductive filler, a higher heat conductivity can be achieved. And this graphitized carbon fiber,
Since it was used in combination with the silicon carbide powder and the aluminum oxide powder, which have excellent electrical insulation properties, it is possible to suppress the reduction in the electrical insulation properties of the sheet due to the blending of the graphitized carbon fibers.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments embodying the present invention will be described below. This heat conductive sheet is a heat conductive sheet obtained by molding a mixed composition in which a silicone rubber is mixed with a heat conductive filler into a sheet shape, and has an average particle diameter of 50 to 100 μm as the heat conductive filler. It is characterized in that silicon carbide powder and aluminum oxide powder having an average particle diameter of 2 to 10 μm are blended.

The silicone rubber is obtained by curing a known polyorganosiloxane. This silicone rubber, after being cured, exhibits low hardness and excellent physical properties such as flexibility, shape conformability, workability, electrical insulation and heat resistance, and is used as a matrix material constituting a heat conductive sheet. Particularly preferably used. Examples of the cured form of the silicone rubber include radical reaction type using an organic peroxide, addition reaction type using a polyorganosiloxane containing a vinyl group, an organohydrogen having a hydrogen atom bonded to a silicon atom, and a platinum-based catalyst, and condensation. Examples of the reaction type include, but are not particularly limited to.
However, in consideration of the hardness of the sheet surface, the flexibility of the sheet, the filling property of the thermally conductive filler, and the like, it is preferable to use an addition reaction type liquid silicone rubber. The silicone rubber is a mixture of known silica, flame retardant, colorant, heat resistance improver, adhesion aid, pressure sensitive adhesive, plasticizer, oil, curing retarder, etc., if necessary. It doesn't matter.

Silicon carbide powder and aluminum oxide powder to be incorporated into silicone rubber as a thermally conductive filler are
It is a ceramic powder that is particularly excellent in thermal conductivity and electrical insulation. These silicon carbide powder and aluminum oxide powder are inexpensively available on the market, for example, as a crushed abrasive. Further, the silicon carbide powder and the aluminum oxide powder have an advantage that the high-performance and homogeneous heat conductive sheet can always be stably mass-produced because there is almost no variation in characteristics depending on the production lot.

The average particle size of the silicon carbide powder is 50 to 10
It is required to be 0 μm. The larger the average particle size of the silicon carbide powder, the more the thermal conductivity of the resulting heat conductive sheet tends to improve. However, when the average particle size of the silicon carbide powder exceeds 100 μm, the sheet thickness that is normally used is When a heat conductive sheet of 1.0 mm or less is formed,
It is not suitable because unevenness is generated on the sheet surface and the sheet surface is not finished smoothly, and the adhesiveness with the heat-generating electronic component and the heat dissipation member is deteriorated. In addition, the silicon carbide powder is likely to fall off the silicone rubber, which may deform or damage the heat dissipation member, the heat-generating electronic component, and the like. Further, when the sheet is compressed, cracks or fallout occur and reworking occurs. It is not suitable because it deteriorates the sex. On the other hand, when the average particle size of the silicon carbide powder is smaller than 50 μm, the effect of improving the thermal conductivity of the resulting thermal conductive sheet becomes poor. Further, in order to achieve the desired thermal conductivity, it is required to highly fill the silicone rubber with silicon carbide powder, and in this case, as described above, the sheet has high hardness and flexibility and shape conformability. It is not suitable because the sheet becomes hard and brittle and the handleability deteriorates.

The average particle size of the aluminum oxide powder is 2 to
It is required to be 10 μm. The larger the average particle size of the aluminum oxide powder, the more the thermal conductivity of the resulting heat conductive sheet tends to improve. However, when the average particle size of the aluminum oxide powder is larger than 10 μm, the particles of the aluminum carbide powder and the silicon carbide powder are mixed. The difference in diameter is reduced, and it becomes difficult to closely fill the silicon carbide powder 0 and the aluminum oxide powder with each other, and the heat transfer path becomes insufficient and the heat conductive sheet having the desired heat conductivity. Will be difficult to achieve. On the other hand, the average particle size of the aluminum oxide powder is 2μ
When it is smaller than m, the effect of improving the thermal conductivity of the obtained thermal conductive sheet becomes poor. Further, when the average particle diameter of the aluminum oxide powder is smaller than 2 μm, the handling property is deteriorated, and the specific surface area is increased to deteriorate the filling property into the silicone rubber to achieve the desired thermal conductivity. Becomes difficult. Therefore, BE of this aluminum oxide powder
The T specific surface area is preferably smaller than 5.0 m ² / g.

The particle shape of these silicon carbide powder and aluminum oxide powder is, for example, spherical, flat, granular, lumpy, fibrous, needle-like, scaly, pellet-like, fibrous, whisker-like or amorphous. However, the present invention is not limited to these. Further, the silicon carbide powder and the aluminum oxide powder may be in a form in which a plurality of particles are aggregated. Among them, a crushed shape or an amorphous shape or an aggregated shape is preferable because it can be obtained at a very low cost on the market and the cost of the sheet can be promoted. Further, the crushed shape or the amorphous shape or the agglomerated shape is preferable because they can be closely packed with each other and a heat conductive sheet having high heat conductivity can be obtained with a small amount of compounding.

In this heat conductive sheet, it is preferable to add pitch-based graphitized carbon fibers as a heat conductive filler in addition to the above silicon carbide powder and aluminum oxide powder. Here, the pitch-based graphitized carbon fiber means that the main raw material is pitch, and after each process step such as melt spinning, infusibilization and carbonization, it is heat treated at a high temperature of 2000 to 3000 ° C. or 3000 ° C. to be graphitized. I mean something. There are two types of pitch-based graphitized carbon fibers, optical isotropy and optical anisotropy, and it is particularly preferable to use mesophase pitch-based graphitized carbon fibers having optical anisotropy. This mesophase pitch-based graphitized carbon fiber has a highly developed graphite structure and has a thermal conductivity in the fiber axis direction far exceeding 500 W / (m · K). The thermal conductivity of can be dramatically improved.

The fiber shape of the graphitized carbon fiber includes, for example, short fibers, long fibers, woven cloth, non-woven cloth, felt shape, mat shape, paper shape, etc., but is not particularly limited thereto. However, since it is used as a mixture with the above-mentioned silicon carbide powder and aluminum oxide powder, it is preferable to use a columnar shape, that is, a short fiber shape rather than a plate shape in view of the filling property. When the short fibrous graphitized carbon fiber is used here, the average yarn diameter is 5 to 20.
It is preferable that the average length is 50 to 200 μm.
It is preferably m. When the average yarn diameter of the graphitized carbon fiber is less than 5 μm, the bulk specific gravity is small and the handling is difficult in production, which is not preferable. On the other hand, the average length is 20
When it exceeds 0 μm, the fibers are entangled with each other, so that the dispersibility in the silicone rubber is deteriorated and unevenness is generated on the sheet surface of the resulting heat conductive sheet, which is not preferable. A more preferable average length is 80 μm to 120 μm.

The total content of the heat conductive filler in the heat conductive sheet is not particularly limited, and in order to achieve a higher thermal conductivity, it is desirable to fill the material as high as possible. Be done. However, considering the flexibility of the sheet and the shape following property, the total content of the thermally conductive filler is preferably 60 to 70% by volume. When the total content of the thermally conductive filler exceeds 70% by volume, the sheet becomes high in hardness as described above, and the flexibility and shape conformability are deteriorated, and the sheet becomes hard and brittle to deteriorate handleability. Not preferable. On the other hand, if the total content of the thermally conductive filler is less than 60% by volume, it will be difficult to achieve the desired thermal conductivity.

The mixing ratio of the silicon carbide powder and the aluminum oxide powder is not particularly limited, but it is preferable that the volume ratio is 1: 1 to 3: 1.
The closer the mixing ratio of the silicon carbide powder and the aluminum oxide powder is, the more the respective powders tend to be packed more closely, and it is possible to realize a heat conductive sheet having more excellent thermal conductivity. it can. Further, the closer the mixing ratio of the silicon carbide powder and the aluminum oxide powder, the easier the fillers will adhere to each other when the thermally conductive sheet is compressed, and when used in such an aspect, particularly excellent thermal conductivity is obtained. You can exercise your sexuality. On the other hand, if the blending ratio of the silicon carbide powder and the aluminum oxide powder is out of this range, it becomes difficult to closely pack each powder, and the heat transfer path in the sheet becomes insufficient, which is aimed at. Achieving thermal conductivity becomes difficult.

The blending ratio of the graphitized carbon fiber to the silicon carbide powder and the aluminum oxide powder is not particularly limited, but the volume ratio is preferably 1: 2 to 1: 5. As the blending amount of the graphitized carbon fiber increases, the thermal conductivity of the resulting heat conductive sheet tends to improve. However, when the blending ratio of the graphitized carbon fiber is higher than the above percentage, the heat conductive sheet of the obtained The volume resistivity decreases, and it becomes difficult to achieve the intended electrical insulation of the sheet. On the other hand, if the blending ratio of the graphitized carbon fiber is less than this ratio, the effect of improving the thermal conductivity becomes poor and the blending effect of the graphitized carbon fiber becomes poor.

Next, a method for manufacturing the heat conductive sheet will be described. This heat conductive sheet is manufactured by molding a mixed composition obtained by mixing the above silicone rubber with the above various heat conductive fillers into a sheet.

When the heat conductive filler is blended in the silicone rubber, it is preferable to add a kneading operation in order to uniformly disperse the heat conductive filler in the silicone rubber.
Examples of the mixer used in this kneading operation include a hard mixer, a planetary mixer, a rotation / revolution independent rotation type mixer, and a static mixer. Among these, it is preferable to use a planetary mixer or a rotation / revolution independent rotation type mixer that can suppress the heat generation of the mixed composition during the kneading operation and can uniformly knead in a short time.

The above-mentioned various thermally conductive fillers to be added to the silicone rubber may be added, if necessary, in order to improve the dispersibility in the silicone rubber or prevent the curing reaction of the silicone rubber from being hindered. Surface treatment may be applied. As this specific surface treatment method, for example,
Examples thereof include phosphoric acid compounds, silicon compounds, sulfuric acid, silane coupling agents, titanium coupling agents, aluminum coupling agents and the like. Further, the surface of the particles of the thermally conductive filler can be coated with ceramics such as aluminum oxide or silicon dioxide, rubber, polymer, silicone oil or the like. Further, a known coupling agent, sizing agent, or the like may be used as the surface treatment of the graphitized carbon fiber. The treatment method and the number of treatments in these various surface treatments are not particularly limited.

The method of molding the mixed composition obtained as described above into a sheet is not particularly limited, and examples thereof include compression molding, extrusion molding, injection molding, and the like.
In addition to the cast molding method, blow molding method, calendar molding method and the like, in the case of a liquid mixed composition, known methods such as a coating method, a printing method, a dispenser method and a potting method can be adopted. In particular, the above-mentioned mixed composition is sandwiched between two resin films to form a sheet precursor, and the sheet precursor is rolled to a desired thickness, and then heated with an appropriate heating device. Therefore, the method of curing and molding the sheet is simple, and thus it is preferable. Examples of this rolling method include a calender molding method and a press rolling method, but the rolling method is not particularly limited thereto, and any method can be applied. In addition, in the various molding methods described above, the order of addition of raw materials and other steps can be changed as long as the sheet is not affected.

As described in detail above, according to this embodiment, the following operational effects are exhibited. In a heat conductive sheet obtained by molding a mixed composition obtained by mixing a silicone rubber with a heat conductive filler into a sheet, the heat conductive filler has an average particle size of 50 to 10
0 μm silicon carbide powder and aluminum oxide powder having an average particle size of 2 to 10 μm were blended.

By using the silicon carbide powder and the aluminum oxide powder each having a specific average particle diameter as the heat conductive filler in this way, the oxidation of the relatively small diameter of the silicon carbide powder of the relatively large diameter is performed. The aluminum powder is filled so that the aluminum oxide powder and the silicon carbide powder are closely packed to each other. Therefore, the heat transfer path is highly developed in the sheet, and the high thermal conductivity of the sheet can be achieved.

Since high thermal conductivity is achieved without highly filling the thermally conductive filler as in the prior art, even if the total content of the thermally conductive filler is 70% by volume or less,
It is possible to realize a heat conductive sheet having high heat conductivity of 5.0 W / (m · K) or more. Therefore, it is possible to suppress deterioration of the flexibility and the shape following property of the sheet, and thereby it is possible to realize a heat conductive sheet having an Asker C hardness of 30 or less and having excellent flexibility and shape following property. .

Therefore, it has a high thermal conductivity of 5.0 W / (m · K) or more, which has never been achieved before, and
It is possible to realize a heat conductive sheet having an Asker C hardness of 30 or less and having excellent flexibility and shape conformability.

Silicon carbide powder and aluminum oxide powder were used as the heat conductive filler. Since these silicon carbide powder and aluminum oxide powder are inexpensive ceramic powders which are particularly excellent in thermal conductivity and electrical insulation, it is possible to realize a thermal conductive sheet excellent in thermal conductivity and electrical insulation at low cost. You can Further, since the silicon carbide powder and the aluminum oxide powder have almost no variation in characteristics depending on the production lot, a high-performance and homogeneous heat conductive sheet can always be stably mass-produced.

Silicone rubber was used as a matrix constituting the heat conductive sheet. This silicone rubber has a low hardness, flexibility, shape conformability, and
Since it has excellent physical properties such as workability, electric insulation and heat resistance, it is possible to realize a heat conductive sheet excellent in electric insulation, flexibility and shape conformability.

As a heat conductive filler, graphitized carbon fiber was further added. By further adding the graphitized carbon fiber as the thermally conductive filler in this way, it is possible to achieve a higher thermal conductivity. Furthermore, since this graphitized carbon fiber is used in combination with the silicon carbide powder and the aluminum oxide powder, which have excellent electrical insulation properties, it is possible to suppress the reduction in the electrical insulation property of the sheet due to the blending of the graphitized carbon fibers. Therefore, excellent electrical insulating property of 10 ⁶ Ω · cm or more in volume resistivity and 7.0 W / (thermal conductivity which could not be achieved by the above-mentioned conventional thermal conductive sheet in which graphitized carbon fiber was blended alone. It is possible to realize a low-cost heat conductive sheet having high thermal conductivity of m · K) or more, excellent flexibility of Asker C hardness of 30 or less, and shape following property.

The heat conductivity of the heat conductive sheet is 5.0 W
When it is / (m · K) or more, heat can be effectively dissipated to the outside in a high-performance electronic device of recent years in which high integration, high speed, small size, and light weight have been advanced. Further, since the Asker C hardness of the heat conductive sheet is 30 or less, it can flexibly follow the complicated unevenness of the mounting site such as the heat-generating electronic component, and can be mounted in close contact with the mounting site. it can. Further, by having such a low hardness, it is possible to prevent deformation and damage of the heat radiating member and the heat generating electronic component when the heat radiating member is pressure-bonded to the heat generating electronic component. It is possible to protect parts and the like. Furthermore, since the volume resistivity of the heat conductive sheet is 10 ⁶ Ω · cm or more,
For example, it can be suitably used for heat-generating electronic components such as transistors and thyristors that require thermoelectric insulation.

(Modification) The present invention is not limited to the configuration of the above-described embodiment, and may be embodied by arbitrarily changing the configuration of each part without departing from the spirit of the present invention. .

Use of another polymer material such as a thermoplastic resin, a thermoplastic elastomer, a curable resin or rubber as a matrix constituting the heat conductive sheet. The matrix constituting the heat conductive sheet can be appropriately selected and used according to the desired performance such as desired mechanical properties, thermal properties, electrical properties or durability.
The specific polymer material is not particularly limited, but for example, an epoxy resin, a polyurethane resin, a fluorine-based rubber or the like can be preferably used.

In addition to the above various thermally conductive fillers, other thermally conductive fillers should be used in combination. The specific other thermally conductive filler is not particularly limited, but examples thereof include magnesium oxide, silicon nitride, aluminum nitride, boron nitride, aluminum hydroxide, and ferrite. Among these, from the viewpoint of electrical insulation, it is preferable to use aluminum hydroxide, magnesium oxide, boron nitride, silicon nitride, aluminum nitride, or the like.

[0049]

EXAMPLES The above embodiments will be described in more detail with reference to examples and comparative examples, but these do not limit the scope of the present invention.

The Asker C hardness of the heat conductive sheet shown below is obtained by laminating a plurality of the produced sheets to prepare a test piece having a thickness of 10 mm and measuring the Asker C hardness of the test piece. (Based on SRIS0101 (Japan Rubber Association standard) and JIS S6050). Further, the thermal conductivity of the heat conductive sheet is 60 mm in length × 120 mm in width.
A test piece having a thickness of 1 mm was prepared, and the thermal conductivity in the thickness direction of the test piece was measured by the QTM method (apparatus used: QTM-500, manufactured by Kyoto Electronics Co., Ltd.). Furthermore, the volume resistivity of the heat conductive sheet is 120 mm in length ×
A test piece having a size of 120 mm in width × 1 mm in thickness was prepared, and the volume resistivity in the thickness direction of the test piece was measured (according to JIS K 6239).

First, a heat conductive sheet is prepared by mixing liquid silicone rubber with a silicon carbide powder having an average particle size of 50 to 100 μm and an aluminum oxide powder having an average particle size of 2 to 10 μm as a heat conductive filler. It was made.

Example 1 Aluminum oxide powder (AL-170 manufactured by Showa Denko KK, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, agglomerated shape) 33% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 120 average particle size 100 μm, crushed shape) 33
Volume%, liquid silicone rubber (Toray Dow Corning
34% by volume of CY-52-290 manufactured by Silicone Co., Ltd. was mixed and kneaded with a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition was sandwiched between polyethylene terephthalate films to form a sheet precursor, which was rolled to a thickness of 1 mm, cured at 150 ° C. for 30 minutes, and then secondary vulcanized at 180 ° C. for 2 hours, followed by heat treatment. A conductive sheet was manufactured.

Example 2 Aluminum oxide powder (AL-150SG manufactured by Showa Denko KK, average particle size 2.0 μm)
m, BET specific surface area 4 m ² / g, agglomerated shape) 33% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 120 average particle size 100 μm, crushed shape) 33% by volume, liquid silicone rubber (Toray CY-52-290 manufactured by Dow Corning Silicone Co., Ltd.)
34% by volume was mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

Example 3 Aluminum oxide powder (AL-170 manufactured by Showa Denko KK, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, aggregate shape 33% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 240 average particle size 64 μm, crushed shape) 33% by volume, liquid silicone rubber (Toray Dow Corning)・ Silicone CY-52-290) 34% by volume
Were mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

Example 4 Aluminum oxide powder (AL-170 manufactured by Showa Denko KK, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, agglomerated shape) 33% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 280 average particle diameter 55 μm, crushed shape) 49.
5% by volume and 34% by volume of liquid silicone rubber (CY-52-290 manufactured by Toray Dow Corning Silicone Co., Ltd.) were mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

(Comparative Example 1) Aluminum oxide powder (AL-45-2 manufactured by Showa Denko KK, average particle size 1.8 μm)
m, BET specific surface area 1.7 m ² / g, amorphous) 33% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 120 average particle size 100 μm, crushed shape) 33% by volume, liquid silicone rubber ( CY-52-290 manufactured by Toray Dow Corning Silicone Co., Ltd.)
34% by volume was mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

(Comparative Example 2) Aluminum oxide powder (manufactured by Showa Denko KK, AS-20, average particle size 21 μm, BE
T specific surface area 0.7 m ² / g, spherical 33% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 120 average particle size 100 μm, crushed shape) 33% by volume, liquid silicone rubber (Toray Dow Corning Silicone Co., Ltd. CY-52-290) 34% by volume
Were mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

(Comparative Example 3) Aluminum oxide powder (AL-170 manufactured by Showa Denko KK, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, agglomerated shape 33% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 360 average particle size 42 μm, crushed shape) 33% by volume, liquid silicone rubber (Toray Dow Corning)・ Silicone CY-52-290) 34% by volume
Were mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

Table 1 shows the results of evaluation of Asker C hardness, thermal conductivity and volume resistivity of the heat conductive sheets obtained in Examples 1 to 4 and Comparative Examples 1 to 3, respectively. Show.

[0060]

[Table 1] From the above, the average particle size of the thermally conductive filler is 50
~ 100 μm silicon carbide powder and average particle size 2.0 ~ 1
By using 0 μm aluminum oxide powder,
High thermal conductivity of 5.0 W / (m · K) or more, excellent flexibility and shape followability of Asker C hardness of 30 or less, and excellent volume resistivity of 10 ⁶ Ω · cm or more. It was confirmed that a heat conductive sheet having electric insulation could be realized.

Next, on the liquid silicone rubber, as a thermally conductive filler, silicon carbide powder having an average particle diameter of 50 to 100 μm, aluminum oxide powder having an average particle diameter of 2 to 10 μm, and further graphitized carbon fiber. A heat conductive sheet containing the above was prepared.

Example 5 Aluminum oxide powder (AL-170 manufactured by Showa Denko KK, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, agglomerated shape) 23% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 180 average particle size 80 μm, crushed shape) 24% by volume, pitch-based graphitized carbon fiber (stock) Company Petka L
359 Trade name: Melbronn milled, average yarn diameter 9.0μ
m, average length 100 μm) 17% by volume, liquid silicone rubber (manufactured by Toray Dow Corning Silicone Co., Ltd.
36% by volume of CY-52-290) was mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition.
The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

Example 6 Aluminum oxide powder (AL-170 manufactured by Showa Denko KK, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, agglomerated shape) 23% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 180 average particle size 80 μm, crushed shape) 27% by volume, pitch-based graphitized carbon fiber (stock) Company Petka N
Y252 Brand name: Melbronn milled, average thread diameter 10μ
m, average length 90 μm) 12% by volume of liquid silicone rubber (manufactured by Toray Dow Corning Silicone Co., Ltd.)
38% by volume of CY-52-290) was mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition.
The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

(Comparative Example 4) Aluminum oxide powder (Showa Denko KK AL-170, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, agglomerated shape) 30% by volume, silicon carbide powder (Green Densic GC # 180 manufactured by Showa Denko KK, average particle size 80 μm, crushed shape) 30% by volume, pitch-based graphitized carbon fiber (stock) Company Petka L
359 Trade name: Melbronn milled, average yarn diameter 9.0μ
m, average length 100 μm) 5% by volume, liquid silicone rubber (Toray Dow Corning Silicone Co., Ltd. C
Y-52-290) 35% by volume was mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition. The obtained mixed composition is treated in the same manner as in Example 1 above,
A heat conductive sheet was manufactured.

(Comparative Example 5) Aluminum oxide powder (AL-170 manufactured by Showa Denko KK, average particle size 2.2 μm,
BET specific surface area 3 m ² / g, aggregate shape 11% by volume, silicon carbide powder (Showa Denko KK Greendensic GC # 180 average particle size 80 μm, crushed shape) 10% by volume, pitch-based graphitized carbon fiber (stock) Company Petka L
359 Trade name: Melbronn milled, average yarn diameter 9.0μ
m, average length 100 μm) 45% by volume, liquid silicone rubber (manufactured by Toray Dow Corning Silicone Co., Ltd.
34% by volume of CY-52-290) was mixed and kneaded in a rotation / revolution independent rotation type mixer to prepare a mixed composition.
The obtained mixed composition was treated in the same manner as in Example 1 above to produce a heat conductive sheet.

Table 2 shows the results of evaluation of Asker C hardness, thermal conductivity and volume resistivity of the heat conductive sheets obtained in Examples 5 and 6 and Comparative Examples 4 and 5. Show.

[0067]

[Table 2] From the above, the average particle size of the thermally conductive filler is 50
~ 100 μm silicon carbide powder and average particle size 2.0 ~ 1
By using 0 μm aluminum oxide powder and graphitized carbon fiber, high thermal conductivity of 7.0 W / (m · K) or more, excellent flexibility and shape following of Asker C hardness of 30 or less. And volume resistivity of 10 ⁶ Ω · c
It was confirmed that a heat conductive sheet having excellent electrical insulation of m or more can be realized.

(Supplementary Note) Next, the technical idea understood from the above-described embodiments and examples will be described below.

(A) In a heat conductive sheet obtained by molding and processing a mixed composition obtained by mixing a polymer material with a heat conductive filler, the heat conductive filler has an average particle size of 50 to 100 μm. Of the first ceramic powder and the second ceramic powder having an average particle diameter of 2 to 10 μm are blended together.

(B) The ceramic powder is at least one selected from the group consisting of silicon carbide, aluminum oxide, magnesium oxide, silicon nitride, aluminum nitride, boron nitride, aluminum hydroxide and ferrite. The heat conductive sheet according to (A) above.

[0071]

As described in detail above, according to the present invention,
As a heat conductive filler, a silicon carbide powder having an average particle diameter of 50 to 100 μm and an aluminum oxide powder having an average particle diameter of 2 to 10 μm are blended to obtain a thermal conductivity of 5.
High thermal conductivity of 0 W / (m · K) or higher and Asker C
It is possible to realize a low-cost, easy-to-manufacture heat conductive sheet having excellent flexibility and shape following property with hardness of 30 or less.
The thermal conductivity is 7.0 W / (m · K) by further blending graphitized carbon fiber as the thermally conductive filler.
The above high thermal conductivity can be achieved. Moreover, since the graphitized carbon fiber was used in combination with the above-mentioned silicon carbide powder and aluminum oxide powder, the volume resistivity was 10 ⁶ Ω.
A low-cost and easy-to-manufacture heat conductive sheet having excellent electrical insulation of cm or more can be realized.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a dispersed state of a heat conductive filler in a heat conductive sheet of the present invention.

[Explanation of symbols]

11 ... Aluminum oxide powder, 12 ... Silicon carbide powder.

Claims (7)

[Claims] 1. A thermally conductive sheet obtained by molding a mixed composition of silicone rubber and a thermally conductive filler into a sheet, wherein the thermally conductive filler has an average particle size of 50 to 100 μm.
A silicon carbide powder of m and an aluminum oxide powder having an average particle size of 2 to 10 μm are blended, which is a heat conductive sheet. 2. The heat conductive sheet according to claim 1, wherein the volume ratio of the silicon carbide powder to the aluminum oxide powder is 1: 1 to 3: 1. 3. The heat conductive sheet according to claim 1, further comprising a graphitized carbon fiber as the heat conductive filler. 4. The heat according to claim 3, wherein a blending ratio of the graphitized carbon fiber to the silicon carbide powder and the aluminum oxide powder is 1: 2 to 1: 5 by volume ratio. Conductive sheet. 5. The total content of the thermally conductive filler is 60.
It is-70 volume%, The heat conductive sheet of any one of Claim 1 to 4 characterized by the above-mentioned. 6. The thermal conductivity of the sheet is 5.0 W / (m
・ K) or above and the Asker C hardness of the sheet is 3
It is 0 or less, The heat conductive sheet of any one of Claim 1 to 5 characterized by the above-mentioned. 7. The volume resistivity of the sheet is 10 ⁶ Ω.multidot.
It is more than cm, Claim 1 to Claim 6 characterized by the above-mentioned.
The heat conductive sheet according to any one of 1.