JP7089322B1 - Thermally conductive sheet, its mounting method and manufacturing method - Google Patents

Abstract

The heat conductive sheet of the present invention comprises a binder component which is a mixture of a silicone matrix (A) and a hydrocarbon compound (B), and a heat conductive filler (C) dispersed in the binder component. The thermally conductive filler (C) contains an anisotropic filler oriented in the thickness direction, and has a thickness of 0.05 to 0.5 mm. According to the present invention, it is possible to provide a heat conductive sheet having a thin thickness and capable of lowering the thermal resistance value even when compressed with a low load.

Description

The present invention relates to a heat conductive sheet, for example, a heat conductive sheet arranged and used between a heating element and a radiator.

In electronic devices such as computers, automobile parts, and mobile phones, a heat sink such as a heat sink is generally used to dissipate heat generated from a heating element such as a semiconductor element or a mechanical part. It is known that a heat conductive sheet is arranged between a heating element and a heat radiating element for the purpose of increasing the heat transfer efficiency to the heat radiating element.

The heat conductive sheet is required to have followability to a heating element and a radiator in order to further improve the conduction efficiency. Therefore, a phase change type heat conductive sheet called a so-called phase change sheet, which is softened or melted by heating, has been studied. For example, Patent Document 1 discloses a heat-dissipating sheet containing at least an alkyl group-introduced silicone oil, an α-olefin, and a thermally conductive filler, which is putty-like at room temperature and softens and fluidizes by heating.

Further, as a heat conductive sheet, a heat conductive sheet using a polymer gel is also known. For example, Patent Document 2 describes a heat-dissipating sheet comprising a polymer gel, a compound that becomes a liquid when heated in the form of a solid or paste at room temperature, and a thermally conductive filler, and is softened by heating. A heat-softened heat-dissipating sheet comprising the above is disclosed.
Further, Patent Document 3 describes a heat conductive sheet including a heat conductive resin layer in which the heat conductive resin layer includes a binder resin containing wax and a heat conductive filler dispersed in the binder resin. It is disclosed that a silicone gel is used as a binder resin in a thermally conductive sheet containing the above.
The phase change sheet disclosed in each of the above Patent Documents 1 to 3 and the heat conductive sheet using a polymer gel such as a silicone gel have high flexibility, and therefore have good followability to a radiator and a heating element. Yes, it makes it possible to improve the heat conduction performance.

Japanese Unexamined Patent Publication No. 2004-331835 Japanese Patent Application Laid-Open No. 2002-234952 Japanese Unexamined Patent Publication No. 2001-291807

However, when the thickness of the conventional heat conductive sheet as described above is thin, the heating element and the heat radiating are generated when the load when the sheet is compressed and mounted between the heating element and the radiating element is low at high temperature. It has been found that there is a problem that the followability to the body is deteriorated, and therefore the thermal resistance value is increased (the thermal conductivity is decreased). On the other hand, when the heat conductive sheet is compressed with a high load, the thermal resistance value is low, but the load on the heating element and the radiator is high. Therefore, even under a low load condition, the thermal resistance value is low. Is desired.

Therefore, it is an object of the present invention to provide a heat conductive sheet having a thin thickness and capable of lowering the thermal resistance value even when compressed with a low load.

As a result of diligent studies, the present inventor has provided a binder component which is a mixture of the silicone matrix (A) and the hydrocarbon compound (B), and a thermally conductive filler (C) dispersed in the binder component. We have found that a thermally conductive sheet having a thickness of 0.05 to 0.5 mm and containing an anisotropic filler having the thermally conductive filler (C) oriented in the thickness direction can solve the above-mentioned problems. The following invention has been completed. That is, the present invention provides the following [1] to [11].

[1] The thermally conductive filler (C) comprising a binder component which is a mixture of a silicone matrix (A) and a hydrocarbon compound (B) and a thermally conductive filler (C) dispersed in the binder component (1). A thermally conductive sheet having an anisotropic filler in which C) is oriented in the thickness direction and having a thickness of 0.05 to 0.5 mm.
[2] Thermal resistance value R ₄₀ (° C. in ² / W) measured at 80 ° C. with a load of 40 psi and thickness T ₄₀ (mm) at the time of measurement, and thermal resistance value R measured at 80 ° C. with a load of 10 psi. The heat conduction according to claim 1, wherein the inclination α represented by the following formula (1) calculated by ₁₀ (° C. in ² / W) and the thickness at the time of measurement T ₁₀ (mm) is 0.4 or less. Sex sheet.
α = (R ₄₀ -R ₁₀ ) / (T ₄₀ -T ₁₀ ) ... (1)
[3] The heat conductive sheet according to the above [1] or [2], wherein the hydrocarbon compound (B) has a melting point higher than 23 ° C and 80 ° C or lower.
[4] The heat conductive sheet according to any one of the above [1] to [3], wherein the hydrocarbon compound (B) is a crystalline polyalphaolefin.
[5] The content of the hydrocarbon-based compound (B) is 0.5 to 15 parts by mass with respect to a total of 100 parts by mass of the silicone matrix (A) and the hydrocarbon-based compound (B) [1]. ] To the heat conductive sheet according to any one of [4].
[6] The heat conductive sheet according to any one of the above [1] to [5], wherein the volume filling factor of the heat conductive filler (C) is 30 to 85% by volume.
[7] A heat radiating member comprising the heat conductive sheet according to any one of the above [1] to [6] and a heat radiating body, and the heat conductive sheet is mounted on the surface of the heat radiating body.
[8] The heat conductive filler (C) comprising a binder component which is a mixture of a silicone matrix (A) and a hydrocarbon compound (B) and a heat conductive filler (C) dispersed in the binder component. A step of arranging a heat conductive sheet having an anisotropic filler in which C) is oriented in the thickness direction and having a thickness of 0.05 to 0.5 mm on the surface of the first member, and the heat. The step of heating the conductive sheet, the second member is arranged on the surface of the heat conductive sheet opposite to the surface of the first member side, and the heat conductive sheet is pressurized to obtain the above. A method for mounting a heat conductive sheet, comprising a step of assembling the heat conductive sheet between the first and second members.
[9] The method for attaching a heat conductive sheet according to the above [8], wherein the hydrocarbon compound (B) has a melting point higher than 23 ° C. and heats the heat conductive sheet to the melting point or higher.
[10] At least the curable silicone composition (A1), the hydrocarbon compound (B), the thermally conductive filler (C) containing the anisotropic filler, and the compatible substance (D) are mixed. A method for producing a thermally conductive sheet, comprising a step of obtaining a mixed composition and a step of curing the mixed composition by heating.
[11] The method for producing a thermally conductive sheet according to the above [10], wherein the compatible substance (D) is an alkoxysilane compound.

According to the present invention, it is a thin heat conductive sheet that can reduce the thermal resistance value even when it is compressed with a low load when it is attached to a heating element, a heat radiator, or the like. Can be provided.

It is a figure explaining the measuring machine which measures a thermal resistance.

[Thermal Conductive Sheet]
Hereinafter, the heat conductive sheet according to the embodiment of the present invention will be described in detail.
The heat conductive sheet of the present invention comprises a binder component which is a mixture of a silicone matrix (A) and a hydrocarbon compound (B), and a heat conductive filler (C) dispersed in the binder component. The conductive filler (C) contains an anisotropic filler oriented in the thickness direction and has a thickness of 0.05 to 0.5 mm.

By having the above configuration, the heat conductive sheet of the present invention secures a certain degree of flexibility when heated at high temperature (that is, when used), and despite its thin thickness, it can be used as a heating element, a radiator, etc. On the other hand, followability can be ensured without applying a high load, and thermal conductivity is improved.

Although the thickness of the heat conductive sheet is thin, the principle that the followability is good with a low load with respect to a heating element, a radiator, etc. is not clear, but it is estimated as follows. The heat conductive sheet of the present invention contains a hydrocarbon compound (B) as a binder component. The hydrocarbon-based compound (B) softens, melts, and has a low viscosity when heated, thereby increasing the flexibility of the thermally conductive sheet, thereby improving the followability with the heating element and the radiator. In addition to this, the heat conductive sheet of the present invention contains an anisotropic filler oriented in the thickness direction of the sheet as the heat conductive filler (C). This facilitates the formation of a heat conduction path in the thickness direction of the sheet. It is considered that these factors improve the thermal conductivity of the thermally conductive sheet.

The hydrocarbon-based compound (B) is incompatible with the silicone matrix (A), and has a sea-island structure in which the silicone matrix (A) is a sea component and the hydrocarbon-based compound (B) is an island component in the binder component. It is estimated that it will be. Since the binder component has a sea-island structure, the hydrocarbon compound (B) is continuously retained by the silicone matrix (A) even if it is softened, melted, or has a low viscosity during heating, and is pumped out while increasing its flexibility. Can also be deterred. Further, since the silicone matrix (A) constitutes a sea component, the heat conductive sheet has a predetermined rebound resilience, so that it can be stably assembled without forming an air layer between the heating element or the radiator. be able to.

<Thickness>
The thickness of the heat conductive sheet of the present invention is 0.05 to 0.5 mm. If the thickness of the heat conductive sheet is less than 0.05 mm, the followability of the heat conductive sheet to a heating element or a heat radiator is deteriorated, and the thermal resistance value tends to be high. On the other hand, if the thickness of the heat conductive sheet exceeds 0.5 mm, it becomes difficult to use it for small electronic devices and the like. The thickness of the heat conductive sheet is preferably 0.08 to 0.5 mm, more preferably 0.1 to 0.4 mm.
The heat conductive sheet of the present invention has such a relatively thin thickness, but as described above, when it is incorporated between a heating element and a radiator, the thermal resistance value is low even with a low load. can do.

<Inclination α>
The heat conductive sheet of the present invention has a thermal resistance value R ₄₀ measured at a load of 40 psi (0.276 MPa) at 80 ° C., a thickness T ₄₀ at the time of measurement, and a thermal resistance measured at a load of 10 psi (0.069 MPa). It is preferable that the inclination α represented by the following formula (1) calculated by the value R ₁₀ and the thickness T ₁₀ at the time of measurement is 0.4 or less.
α = (R ₄₀ -R ₁₀ ) / (T ₄₀ -T ₁₀ ) ... (1)
By setting the inclination α to 0.40 or less, the followability to the heating element, the radiator, and the like is improved even at a low load, and the heat conductive sheet has excellent thermal conductivity. The slope α is preferably 0.3 or less, more preferably 0.2 or less, and further preferably 0.1 or less. The unit of the thermal resistance values R ₄₀ and R ₁₀ is ° C. in ² / W, and the unit of the thicknesses T ₄₀ and T ₁₀ is mm.
In general, the thermal resistance value of the heat conductive sheet is lower when measured at a load of 40 psi, which is a relatively high load, than when measured at a load of 10 psi, which is a relatively low load. Therefore, the slope α represented by the equation (1) showing the change in the thermal resistance value with respect to the change in the thickness is as low as the value, and as the value approaches 0, the heat is close to the same as when the load is low even when the load is low. It means to show the resistance value. Therefore, by adjusting the inclination α to a small value, it is possible to obtain a heat conductive sheet having a low thermal resistance value even with a low load.
The inclination α can be adjusted by the blending amount of the hydrocarbon compound (B) and the heat conductive filler (C), the method for producing the heat conductive sheet described later, and the like.
The thermal resistance value R ₄₀ measured at a load of 40 psi and the thermal resistance value R ₁₀ measured at a load of 10 psi can be measured by the method described in the examples.

<Compression rate>
The heat conductive sheet of the present invention preferably has a compressibility of 15% or more at 40 psi. When the compressibility of the heat conductive sheet is 15% or more, the flexibility when heated is high, the followability to the heating element and the heat radiating body at the time of use is improved, and the heat conductivity is good. The compressibility is preferably 18% or more, more preferably 20% or more, from the viewpoint of increasing flexibility during use and improving thermal conductivity.
The compression rate is preferably 50% or less. When the compression rate is 50% or less, the handleability and reliability tend to be good, the assembly to the electronic device and the cutting process become easy, and the pump-out is less likely to occur. From these viewpoints, the compression ratio is more preferably 40% or less, and further preferably 38% or less.
The compression ratio is measured by the method described in the examples.

<Silicone matrix (A)>
The silicone matrix (A) is preferably a silicone having no fluidity at both room temperature (23 ° C.) and high temperature (80 ° C.). Since the silicone matrix (A) has no fluidity, the shape retention of the heat conductive sheet can be ensured at room temperature and high temperature.
Further, as the silicone matrix (A) of the present invention, for example, silicone rubber may be used. By using silicone rubber, compression deformation becomes easy, and it becomes easy to assemble between the heating element and the radiator. Further, since a certain compression characteristic can be imparted to the heat conductive sheet, reliability can be improved.

The silicone used in the silicone matrix (A) may be either a condensation reaction type or an addition reaction type, but it is added because it is easy to highly fill the thermally conductive filler and the curing temperature can be easily adjusted by a catalyst or the like. The reaction type is preferable. The silicone matrix (A) can be obtained, for example, by curing the curable silicone composition (A1). The curable silicone composition (A1) may be composed of, for example, a main agent and a curing agent.

In the case of the addition reaction type, the curable silicone composition (A1) contains an alkenyl group-containing organopolysiloxane as a main agent and a hydrogen organopolysiloxane as a curing agent from the viewpoint of easy high filling of a heat conductive filler. Is preferably contained.
The curable silicone composition (A1) is preferably liquid before curing. Since the curable silicone composition (A1) is liquid before curing, it is easy to highly fill the heat conductive filler, and further, the hydrocarbon compound (B) is contained in the curable silicone composition (A1). It becomes easier to disperse. In the present specification, the liquid means a liquid at room temperature (23 ° C.) and 1 atm.

Further, as the silicone matrix (A), it is preferable to use a silicone matrix that is three-dimensionally crosslinked so as to ensure the shape retention of the heat conductive sheet. For this purpose, for example, in the case of an addition reaction type, curing containing an alkenyl group-containing organopolysiloxane having at least 3 or more alkenyl groups in one molecule or a hydrogen organopolysiloxane having at least 3 or more hydrogens added to a silicon atom. The sex silicone composition (A1) may be cured.

The content of the silicone matrix (A) may be, for example, about 15 to 70% by mass, preferably 17 to 50% by mass, and more preferably 20 to 39% by mass with respect to the total amount of the heat conductive sheet.

<Hydrocarbon compound (B)>
As the hydrocarbon compound (B) used in the present invention, a compound that is liquid at room temperature or melts by heating to a constant temperature (for example, a temperature higher than 23 ° C and 80 ° C or lower) may be used. By containing the hydrocarbon-based compound (B) as a liquid or a compound that melts by heating, the heat conductive sheet can increase the flexibility at the time of high-temperature heating, reduce the above-mentioned inclination α, and reduce the compressibility. It will be easier to make it higher.

The melting point of the hydrocarbon compound (B) is preferably 80 ° C. or lower, more preferably 70 ° C. or lower, still more preferably 60 ° C. or lower, still more preferably, from the viewpoint of being able to melt when heated at a high temperature (for example, 80 ° C.). It is preferably 50 ° C. or lower.
The hydrocarbon compound (B) is preferably in a solid state at room temperature and 1 atm. Being a solid at room temperature enhances handleability. For example, when the cutting process described later is performed at a temperature near room temperature, the heat conductive sheet can be easily obtained by having a predetermined rigidity. Therefore, the melting point of the hydrocarbon compound is preferably higher than normal temperature (23 ° C.), more preferably 30 ° C. or higher, and even more preferably 35 ° C. or higher. The melting point of the hydrocarbon compound is the temperature of the endothermic peak of the DTA curve measured at a heating rate of 1 ° C./min using thermal weight differential thermal analysis (TGDTA). When the hydrocarbon compound is a mixture, the melting point is the maximum endothermic peak in the above temperature range.

Specific examples of the hydrocarbon-based compound include liquid paraffin, paraffin wax, petrolatum, polyalphaolefin (PAO), polyethylene wax, polypropylene wax and the like. Among these, paraffin wax, petrolatum, polyalphaolefin (PAO), polyethylene wax, and polypropylene wax are preferable from the viewpoint of handleability at room temperature. Vaseline is a semi-solid hydrocarbon compound, and is a mixture of a plurality of hydrocarbon compounds such as isoparaffin, cycloparaffin, and naphthene. Further, as the petrolatum, for example, white petrolatum defined in the Japanese Pharmacopoeia can be exemplified.

Among the above, polyalphaolefin (PAO) is preferable, and among them, crystalline polyalphaolefin (CPAO) having crystallinity is more preferable. Polyalphaolefins are polymers of α-olefins. The type of α-olefin is not particularly limited, and may be linear, may have a branched chain, or may have a cyclic structure. The polyalphaolefin is, for example, a polymer of an α-olefin having 2 to 30 carbon atoms, preferably 6 to 20 carbon atoms. The crystalline polyalpha olefin may be, for example, a side chain crystalline polyalpha olefin by increasing the number of carbon atoms of the α-olefin.
The poly α-olefin may be a polymer of a single α-olefin or a copolymer of two or more kinds of α-olefins.

The content of the hydrocarbon-based compound (B) in the heat conductive sheet is preferably 0.5 to 15 parts by mass with respect to a total of 100 parts by mass of the silicone matrix (A) and the hydrocarbon-based compound (B).
When the content of the hydrocarbon compound (B) is 0.5 parts by mass or more, the thermally conductive sheet has a certain degree of flexibility at high temperatures and is assembled between the heating element and the radiator. It becomes easy to improve the thermal conductivity.
On the other hand, when the content is 15 parts by mass or less, the silicone matrix (A) is contained in a certain amount in the heat conductive sheet, and the shape retention of the heat conductive sheet can be improved. Further, the heat conductive sheet tends to have an appropriate rebound resilience, and an air layer is not formed between the heating element or the heat radiating element, so that the sheet can be stably assembled and the reliability is enhanced.
From these viewpoints, the content of the hydrocarbon compound (B) is more preferably 1 part by mass or more, further preferably 1.5 parts by mass or more, further preferably 2 parts by mass or more, and 40 parts by mass or less. More preferably, 10 parts by mass or less is further preferable, and 8 parts by mass or less is further preferable.

The silicone matrix (A) is formed from the curable silicone composition (A1) described later. Therefore, in the mixed composition described later, the content of the hydrocarbon compound (B) with respect to a total of 100 parts by mass of the curable silicone composition (A1) and the hydrocarbon compound (B) is the above-mentioned hydrocarbon compound ( It becomes the same as the content of B). The same applies to the contents of the thermally conductive filler (C), the anisotropic filler, and the non-anisotropic filler, which will be described later.
The binder component may be composed of a silicone matrix (A) and a hydrocarbon-based compound (B), but as long as the effect of the present invention is not impaired, a resin component other than the silicone matrix (A) or a hydrocarbon-based component can be used. A plasticizer other than the compound (B) may be contained as a binder component.

<Thermal conductive filler (C)>
The thermally conductive sheet of the present invention further comprises a thermally conductive filler (C). The thermally conductive filler (C) may be dispersed in a binder component which is a mixture of the silicone matrix (A) and the hydrocarbon-based compound (B), and may be retained in the binder component.
The thermally conductive filler contains an anisotropic filler that is oriented in the thickness direction of the thermally conductive sheet. This makes it easier for the heat conductive sheet to increase the heat conductivity. When oriented in the thickness direction, it becomes difficult to increase the above-mentioned compression rate. However, in the present invention, the hydrocarbon-based compound (B) is dispersed in the silicone matrix (A) to increase the compression rate in the thickness direction. can.
When the anisotropic filler is oriented in the thickness direction, the major axis direction does not have to be strictly parallel to the thickness direction, and even if the major axis direction is slightly tilted with respect to the thickness direction. It shall be oriented in the thickness direction. Specifically, an anisotropic filler whose major axis direction is tilted by less than 20 ° is also an anisotropic filler which is oriented in the thickness direction, and such an anisotropic filler is large in the heat conductive sheet. If it is a part (for example, more than 60%, preferably more than 80% with respect to the number of total anisotropic fillers), it shall be oriented in the thickness direction.

The content of the thermally conductive filler (C) is preferably 150 to 3000 parts by mass, more preferably 200 to 2000 parts by mass with respect to 100 parts by mass of the total of the silicone matrix (A) and the hydrocarbon compound (B). Parts, more preferably 300 to 1000 parts by mass. By setting the heat conductive filler (C) to 150 parts by mass or more, a certain heat conductivity can be imparted to the heat conductive sheet. Further, by setting the content to 1500 parts by mass or less, the heat conductive filler (C) can be appropriately dispersed in the binder component. In addition, it is possible to prevent the viscosity of the mixed composition described later from becoming higher than necessary.
The volume filling ratio of the heat conductive filler with respect to the total amount of the heat conductive sheet is preferably 30 to 85% by volume, more preferably 50 to 83% by volume, and further preferably 61 to 80% by volume. .. By setting the volume filling factor to the above lower limit value or more, a certain thermal conductivity can be imparted to the thermal conductivity sheet. Further, by setting the value to the upper limit or less, the production of the heat conductive sheet becomes easy.

(Anisotropic filler)
The anisotropic filler is a filler having anisotropy in shape and can be oriented. Examples of the anisotropic filler include a fiber material and a scaly material. The anisotropic filler has a high aspect ratio, specifically, the aspect ratio exceeds 2, and the aspect ratio is preferably 5 or more. By making the aspect ratio larger than 2, it becomes easy to orient the anisotropic filler in one direction such as the thickness direction, and it is easy to increase the thermal conductivity in one direction such as the thickness direction of the heat conductive sheet. The upper limit of the aspect ratio is not particularly limited, but is practically 100.
The aspect ratio is the ratio of the length in the major axis direction to the length in the minor axis direction of the anisotropic filler, which means the fiber length / fiber diameter in the fiber material and in the scaly material. Means the length / thickness of the scaly material in the longitudinal direction.

The content of the anisotropic filler in the heat conductive sheet is preferably 10 to 500 parts by mass, preferably 30 to 300 parts by mass, based on 100 parts by mass of the total of the silicone matrix (A) and the hydrocarbon-based compound (B). It is more preferably parts by mass, and even more preferably 50 to 250 parts by mass.
By setting the content of the anisotropic filler to 10 parts by mass or more, it becomes easy to increase the thermal conductivity. Further, when the content is 500 parts by mass or less, the viscosity of the mixed composition described later is likely to be appropriate, and the orientation of the anisotropic filler is good. Further, the dispersibility of the anisotropic filler in the silicone matrix (A) is also improved.

When the anisotropic filler is a fiber material, the average fiber length thereof is preferably 10 to 500 μm, more preferably 20 to 350 μm, and further preferably 50 to 300 μm. When the average fiber length is 10 μm or more, the anisotropic fillers appropriately contact each other inside the heat conductive sheet, a heat transfer path is secured, and the heat conductivity of the heat conductive sheet is improved.
On the other hand, when the average fiber length is 500 μm or less, the bulk of the anisotropic filler becomes low, and the binder component can be highly filled.
Further, the average fiber length of the fiber material is preferably shorter than the thickness of the heat conductive sheet. Being shorter than the thickness prevents the fibrous material from protruding more than necessary from the surface of the thermally conductive sheet.
The average fiber length can be calculated by observing the anisotropic filler with a microscope. More specifically, the fiber length of 50 arbitrary anisotropic fillers can be measured using, for example, an electron microscope or an optical microscope, and the average value (arithmetic mean value) can be used as the average fiber length. can.

When the anisotropic filler is a scaly material, the average particle size thereof is preferably 10 to 400 μm, more preferably 15 to 300 μm, still more preferably 20 to 200 μm. By setting the average particle size to 10 μm or more, the anisotropic fillers are likely to come into contact with each other in the heat conductive sheet, a heat transfer path is secured, and the heat conductivity of the heat conductive sheet is improved. On the other hand, when the average particle size is 400 μm or less, the bulk of the thermally conductive sheet becomes low, and it becomes possible to highly fill the binder component with the anisotropic filler.
The average particle size of the scaly material can be calculated by observing the anisotropic filler with a microscope and using the major axis as the diameter. More specifically, the major axis of 50 arbitrary anisotropic fillers can be measured using, for example, an electron microscope or an optical microscope, and the average value (arithmetic mean value) thereof can be used as the average particle size. ..

As the anisotropic filler, a known material having thermal conductivity may be used, but when it is oriented by magnetic field orientation as described later, it may have diamagnetism. On the other hand, if it is oriented by flow orientation or if the anisotropic filler is not oriented, it does not have to have diamagnetism.
Specific examples of the anisotropic filler include carbon fibers, carbon-based materials represented by scaly carbon powder, metal materials and metal oxides represented by metal fibers, boron nitride and metal nitrides, and metal carbides. Examples thereof include metal hydroxides and polyparaphenylene benzoxazole fibers. Among these, the carbon-based material is preferable because it has a small specific gravity and good dispersibility in the binder component, and among them, a graphitized carbon material having a high thermal conductivity is more preferable. The graphitized carbon material has diamagnetism when the graphite surfaces are aligned in a predetermined direction.
Boron nitride is also preferable as the anisotropic filler. Boron nitride is not particularly limited, but is preferably used as a scaly material. The scaly boron nitride may or may not be aggregated, but it is preferable that part or all of the boron nitride is not aggregated. Boron nitride and the like also have diamagnetism when their crystal planes are aligned in a predetermined direction.

The anisotropic filler is not particularly limited, but has a thermal conductivity of generally 30 W / m · K or more along the direction having anisotropy (that is, the long axis direction), preferably 60 W / m / K. It is m · K or more, more preferably 100 W / m · K or more, still more preferably 200 W / m · K or more. The upper limit of the thermal conductivity of the anisotropic filler is not particularly limited, but is, for example, 2000 W / m · K or less. The thermal conductivity can be measured by a laser flash method or the like.

The anisotropic filler may be used alone or in combination of two or more. For example, as the anisotropic filler, at least two anisotropic fillers having different average particle sizes or average fiber lengths may be used. When anisotropic fillers of different sizes are used, the anisotropic filler is densely filled in the binder component by allowing the small anisotropic filler to enter between the relatively large anisotropic fillers. At the same time, it is thought that the heat conduction efficiency can be improved.

The carbon fiber used as the anisotropic filler is preferably graphitized carbon fiber. Further, as the scaly carbon powder, scaly graphite powder is preferable. As the anisotropic filler, it is also preferable to use graphitized carbon fiber and scaly graphite powder in combination.
The graphitized carbon fiber has a crystal plane of graphite connected in the fiber axis direction and has a high thermal conductivity in the fiber axis direction. Therefore, by aligning the fiber axial directions in a predetermined direction, the thermal conductivity in a specific direction can be increased. Further, the scaly graphite powder has graphite crystal planes connected in the in-plane direction of the scaly plane, and has high thermal conductivity in the in-plane direction. Therefore, by aligning the scale faces in a predetermined direction, the thermal conductivity in a specific direction can be increased. The graphitized carbon fiber and the scaly graphite powder are preferably those having a high degree of graphitization.

As the graphitized carbon material such as the graphitized carbon fiber and the scaly graphite powder described above, the following raw materials that have been graphitized can be used. Examples thereof include condensed polycyclic hydrocarbon compounds such as naphthalene, condensed heterocyclic compounds such as PAN (polyacrylonitrile) and pitch, and graphitized mesophase pitch, polyimide and polybenzazole having a particularly high degree of graphitization should be used. Is preferable. For example, by using the mesophase pitch, in the spinning process described later, the pitch is oriented in the fiber axis direction due to its anisotropy, and graphitized carbon fibers having excellent thermal conductivity in the fiber axis direction can be obtained.
The mode of use of the mesophase pitch in the graphitized carbon fiber is not particularly limited as long as it can be spun, and the mesophase pitch may be used alone or in combination with other raw materials. However, the use of mesophase pitch alone, that is, graphitized carbon fiber having a mesophase pitch content of 100% is most preferable from the viewpoint of high thermal conductivity, spinnability and quality stability.

As the graphitized carbon fiber, one obtained by sequentially performing each treatment of spinning, insolubilization and carbonization and then pulverized or cut to a predetermined particle size and then graphitized, or one which is pulverized or cut after carbonization and then graphitized may be used. can. When crushing or cutting before graphitization, the shrink polymerization reaction and cyclization reaction are likely to proceed during the graphitization treatment on the surface newly exposed by crushing, so the degree of graphitization is increased and heat conduction is further increased. Graphitized carbon fibers with improved properties can be obtained. On the other hand, when the spun carbon fibers are granulated and then crushed, the carbon fibers after graphitization are rigid and easily crushed, and carbon fiber powder having a relatively narrow fiber length distribution can be obtained by crushing in a short time.

As described above, the average fiber length of the graphitized carbon fibers is preferably 10 to 500 μm, more preferably 20 to 350 μm, and even more preferably 50 to 300 μm. Further, the aspect ratio of the graphitized carbon fiber exceeds 2 as described above, and is preferably 5 or more. The thermal conductivity of the graphitized carbon fiber is not particularly limited, but the thermal conductivity in the fiber axial direction is preferably 400 W / m · K or more, more preferably 800 W / m · K or more.

When the heat conductive sheet contains an anisotropic filler, the anisotropic filler may or may not be exposed on the surface of the sheet, but it is preferable that the thermally conductive sheet is exposed. The surface of the heat conductive sheet can be made a non-adhesive surface by exposing the anisotropic filler. The heat conductive sheet is the main surface of the sheet, and the anisotropic filler may be exposed on only one of both surfaces of the sheet, or the anisotropic filler may be exposed on both surfaces. It may be exposed. Since the surface of the heat conductive sheet is non-adhesive, it can be slid when assembling to an electronic device or the like, and the assembling property is improved.

(Nonisotropy filler)
The thermally conductive filler (C) in the present invention further contains a non-anisotropic filler, and the above-mentioned anisotropic filler and the non-anisotropic filler may be used in combination.
When the non-anisotropic filler is used in combination with the anisotropic filler oriented in one direction, the non-anisotropic filler can be interposed in the gap between the oriented anisotropic fillers to further increase the thermal conductivity. The non-anisotropic filler is a filler having substantially no anisotropy in shape, and is under an environment in which the anisotropic filler is oriented in a predetermined direction, such as under the generation of magnetic field lines or the action of shearing force, which will be described later. However, it is a filler that does not orient in the predetermined direction.

The non-anisotropic filler has an aspect ratio of 2 or less, preferably 1.5 or less. When the non-anisotropic filler having such a low aspect ratio is used in combination with the anisotropic filler, it is likely to be arranged in the gap of the anisotropic filler, and the thermal conductivity is easily improved. Further, by setting the aspect ratio to 2 or less, it is possible to prevent the viscosity of the mixed composition described later from increasing and to achieve high filling.

Specific examples of the non-asymmetric filler include metals, metal oxides, metal nitrides, metal hydroxides, carbon materials, non-metal oxides, nitrides, carbides and the like. The shape of the non-anisotropic filler may be spherical or amorphous powder.
In the non-asymmetric filler, examples of the metal include aluminum, copper, nickel and the like, examples of the metal oxide include aluminum oxide typified by alumina, magnesium oxide and zinc oxide, and examples of the metal nitride include aluminum nitride and the like. can do. Examples of the metal hydroxide include aluminum hydroxide. Further, examples of the carbon material include spheroidal graphite. Examples of oxides, nitrides and carbides other than metals include quartz, boron nitride and silicon carbide.
Among these, aluminum oxide and aluminum are preferable because they have high thermal conductivity and spherical ones are easily available.
As the non-anisotropic filler, one of the above-mentioned ones may be used alone, or two or more of them may be used in combination.

The average particle size of the non-anisotropic filler is, for example, 0.1 to 200 μm. For example, when used in combination with an anisotropic filler, the average particle size of the non-anisotropic filler is preferably 0.1 to 50 μm, more preferably 0.5 to 35 μm, and 1 to 15 μm. Is more preferable. By setting the average particle size to 50 μm or less, problems such as disturbing the orientation of the anisotropic filler are less likely to occur even when used in combination with the anisotropic filler. Further, by setting the average particle size to 0.1 μm or more, the specific surface area of the non-anisotropic filler does not become larger than necessary, and the viscosity of the mixed composition does not easily increase even if a large amount is blended. It becomes easier to highly fill the anisotropic filler.
As the non-anisotropic filler, for example, as the non-anisotropic filler, at least two non-anisotropic fillers having different average particle sizes may be used.

The average particle size of the non-anisotropic filler is preferably 0.1 to 200 μm, more preferably 0.5 to 100 μm, and even more preferably 1 to 70 μm.
The average particle size of the non-anisotropic filler can be measured by observing with an electron microscope or the like. More specifically, the particle size of 50 arbitrary non-anisotropic fillers is measured using, for example, an electron microscope or an optical microscope, and the average value (arithmetic mean value) is used as the average particle size. Can be done.

The content of the non-anisotropic filler is preferably 50 to 2500 parts by mass, preferably 100 to 1500 parts by mass with respect to 100 parts by mass of the total of the silicone matrix (A) and the hydrocarbon compound (B). It is more preferably present, and further preferably 200 to 750 parts by mass. By setting the amount to 50 parts by mass or more, the heat conductivity of the heat conductive sheet can be improved. On the other hand, when the content is 1500 parts by mass or less, the non-anisotropic filler is appropriately dispersed in the binder component, and the effect of increasing the thermal conductivity according to the content can be obtained. In addition, it is possible to prevent the viscosity of the mixed composition from increasing more than necessary.

The mass ratio of the content of the non-anisotropic filler to the content of the anisotropic filler is not particularly limited, but is preferably 0.5 to 5, more preferably 1 to 3. It is preferably 1.1 to 2.5. By setting the mass ratio within the above range, the non-anisotropic filler can be appropriately filled between the anisotropic fillers to form an efficient heat transfer path, so that the heat conductive sheet can be formed. The thermal conductivity of the can be further improved.

(Additive)
In the heat conductive sheet, various additives may be further added to the binder component as long as the function as the heat conductive sheet is not impaired. Examples of the additive include at least one selected from a dispersant, a coupling agent, a pressure-sensitive adhesive, a flame retardant, an antioxidant, a colorant, an antioxidant and the like. Further, when the curable silicone composition (A1) is cured as described above, a curing catalyst or the like that accelerates the curing may be blended as an additive. Examples of the curing catalyst include platinum-based catalysts.
Further, as will be described later, the compatible substance (D) may be blended in the mixed composition. The compatible substance (D) does not have to be volatilized in the process of producing the heat conductive sheet and does not remain in the heat conductive sheet, but at least a part of the blended compatible substance (D) remains. May be good.

[Manufacturing method of heat conductive sheet]
The heat conductive sheet of the present invention can be manufactured, for example, by a manufacturing method including the following steps X and Y.
Step X: At least the curable silicone composition (A1), the hydrocarbon compound (B), the thermally conductive filler (C) containing the anisotropic filler, and the compatible substance (D) are mixed. Step Y: Step of curing the mixed composition obtained in Step X by heating Hereinafter, each step will be described in detail.

(Process X)
In step X, in addition to the heat conductive filler (C) containing the curable silicone composition (A1), the hydrocarbon compound (B), and the anisotropic filler, the compatible substance (D) is mixed. To obtain a mixed composition. The compatible substance (D) is a substance that is compatible or soluble in the hydrocarbon compound (B) and the curable silicone composition (A1). The hydrocarbon compound (B) has low compatibility with the curable silicone composition (A1), but can be uniformly mixed in the curable silicone composition (A1) by using the compatible substance (D). .. Therefore, the hydrocarbon compound (B) is uniformly mixed in the silicone matrix (A) obtained by curing the curable silicone composition (A1).

In step X, as long as each of the above components can be mixed to obtain a mixed composition, the mixing method and mixing order are not particularly limited, and the curable silicone composition (A1) and the hydrocarbon compound (B) are not particularly limited. , The heat conductive filler (C), the compatible substance (D), and other components optionally added may be appropriately mixed in any order to obtain a mixed composition.
Further, as described above, the curable silicone composition (A1) is composed of, for example, a main agent and a curing agent. In such a case, the main agent, the curing agent, the hydrocarbon compound (B), and the heat conductive filler (the heat conductive filler). C), the compatible substance (D), and other components optionally added may be mixed in any order to obtain a mixed composition.

Further, it is preferable that the hydrocarbon compound (B) is dissolved in the compatible substance (D) and then mixed with the curable silicone composition (A1) and other components.
In this case, a mixture of the hydrocarbon compound (B) and the compatible substance (D), the curable silicone composition (A1) (or the main agent and the curing agent), the thermally conductive filler (C), and if necessary. It is advisable to mix the other components to be optionally added in any order to obtain a mixed composition.
As described above, when the hydrocarbon-based compound (B) is dissolved in the compatible substance (D) in the step X, the hydrocarbon-based compound (B) can be mixed more uniformly in the silicone matrix (A).
When the hydrocarbon compound (B) is dissolved in the compatible substance (D), it may be appropriately heated. At this time, the heating temperature is preferably heated to a temperature higher than the melting point of the compatible substance (D), and may be heated to, for example, 40 ° C. or higher to melt. Further, the upper limit of the heating temperature can be a temperature at which the thermally conductive silicone does not substantially cure in the process of mixing when the main agent and the curing agent are mixed. On the other hand, when the compatible substance (D) is mixed with the main agent and the curing agent, the temperature can be set so that the compatible substance (D) does not easily volatilize. May be good.
Further, the state in which the silicone matrix (A) and the hydrocarbon compound (B) are mixed is a transparent or slightly cloudy uniform mixture due to the presence of the compatible substance (D). On the other hand, when the compatible substance (D) is not contained, the solid hydrocarbon-based compound is dispersed or the liquid hydrocarbon-based compound is separated into two layers.

<Compatible substance (D)>
The compatible substance (D) used in the present invention is preferably a substance that is soluble in the hydrocarbon compound (B) and compatible with the curable silicone composition (A1). The compatible substance (D) is preferably a substance that is liquid at room temperature (23 ° C.) and 1 atm. As will be described later, the compatible substance (D) is a component that volatilizes, for example, by heating in step Y at about 50 to 180 ° C. The compatible substance (D) volatilizes by heating during curing, so that the content ratio of the heat conductive filler (C) in the heat conductive sheet can be increased. Further, the mixed composition contains the compatible substance (D), so that the viscosity is lowered. Therefore, it becomes easy to increase the blending amount of the heat conductive filler (C), and further, it becomes easy to orient the anisotropic filler in a predetermined direction by magnetic field orientation or the like described later.

Examples of the compatible substance (D) include an alkoxysilane compound, a hydrocarbon solvent, and an alkoxysiloxane compound. Since these compounds have high solubility or compatibility with the hydrocarbon compound (B) and the curable silicone composition (A1), the hydrocarbon compound (B) with respect to the curable silicone composition (A1) in the mixed composition. ) Can be enhanced. As a result, the hydrocarbon compound (B) is appropriately dispersed even in the heat conductive sheet, and it becomes easy to secure shape retention, reliability, flexibility at high temperature and the like.
The compatible substance (D) may be used alone or in combination of two or more.

As the compatible substance (D), it is preferable to use an alkoxysilane compound. By using the alkoxysilane compound, bubbles and the like are not seen on the surface of the heat conductive sheet obtained by curing, and the appearance is improved.
In the alkoxysilane compound used as the compatible substance (D), 1 to 3 of the 4 bonds of the silicon atom (Si) are bonded to the alkoxy group, and the remaining bonds are bonded to the organic substituent. It is a compound having a structure. Since the alkoxysilane compound has an alkoxy group and an organic substituent, the dispersibility of the hydrocarbon compound (B) with respect to the curable silicone composition (A1) can be enhanced.
Examples of the alkoxy group contained in the alkoxysilane compound include a methoxy group, an ethoxy group, a protoxy group, a butoxy group, a pentoxy group, and a hexatoxy group. The alkoxysilane compound may be contained as a dimer in the curable silicone composition (A1).

Among the alkoxysilane compounds, an alkoxysilane compound having at least one of a methoxy group and an ethoxy group is preferable from the viewpoint of availability. The number of alkoxy groups contained in the alkoxysilane compound is preferably 2 or 3 from the viewpoint of compatibility and solubility with the curable silicone composition (A1) and the hydrocarbon compound (B). It is more preferable to have. The alkoxysilane compound is preferably at least one selected from a trimethoxysilane compound, a triethoxysilane compound, a dimethoxysilane compound, and a diethoxysilane compound.

Examples of the functional group contained in the organic substituent of the alkoxysilane compound include an acryloyl group, an alkyl group, a carboxyl group, a vinyl group, a methacrylic group, an aromatic group, an amino group, an isocyanate group, an isocyanurate group and an epoxy group. Examples include a hydroxyl group and a mercapto group. Here, when a platinum catalyst is used as the curing catalyst of the curable silicone composition (A1), it is preferable to select and use an alkoxysilane compound that does not easily affect the curing reaction of the organopolysiloxane. Specifically, when an addition reaction type organopolysiloxane using a platinum catalyst is used, the organic substituent of the alkoxysilane compound shall not contain an amino group, an isocyanate group, an isocyanurate group, a hydroxyl group, or a mercapto group. Is preferable.

The alkoxysilane compound has an alkylalkoxysilane compound having an alkyl group bonded to a silicon atom, that is, an alkyl group as an organic substituent from the viewpoint of enhancing the dispersibility of the hydrocarbon compound (B) in the silicone matrix (A). It preferably contains an alkoxysilane compound. Therefore, a dialkyldialkoxysilane compound and an alkyltrialkoxysilane compound are preferable, and an alkyltrialkoxysilane compound is particularly preferable.
The number of carbon atoms of the alkyl group bonded to the silicon atom may be, for example, 1 to 16. Further, in a trialkoxysilane compound such as a trimethoxysilane compound and a triethoxysilane compound, the number of carbon atoms of the alkyl group is preferably 6 or more, preferably 8 or more, from the viewpoint of enhancing the dispersibility of the hydrocarbon-based compound. It is more preferably 12 or less, and more preferably 10 or less.
On the other hand, in the dialkoxysilane compound such as the dimethoxysilane compound and the triethoxysilane compound, the number of carbon atoms of the alkyl group may be 1 or more from the viewpoint of enhancing the dispersibility of the hydrocarbon-based compound, and the number of carbon atoms may be 1. 10 or less is preferable, 6 or less is more preferable, and 4 or less is further preferable.

Examples of the alkyl group-containing alkoxysilane compound include methyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, ethyltrimethoxysilane, and n-propyltrimethoxysilane. Di-n-propyldimethoxysilane, di-n-propyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane , Methylcyclohexyldimethoxysilane, methylcyclohexyldiethoxysilane, n-octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, n-decyltriethoxysilane and the like.
Among the alkyl group-containing alkoxysilane compounds, n-decyltrimethoxysilane, dimethyldimethoxysilane, and n-octyltriethoxysilane are more preferable, and hydrocarbon-based compounds are more preferable from the viewpoint of improving the dispersibility of the hydrocarbon-based compound (B). From the viewpoint of solubility with the compound (B), n-decyltrimethoxysilane and n-octyltriethoxysilane are even more preferable.

The alkoxysiloxane compound used as the compatible substance (D) has two or more siloxane bonds and has a structure in which an alkoxy group is bonded to at least one silicon atom. The alkoxysiloxane compound has a structure in which an organic substituent is bonded to at least one silicon atom among the silicon atoms constituting the siloxane bond. The alkoxysiloxane compound has an alkoxy group and an organic substituent, so that the dispersibility of the hydrocarbon-based compound (B) can be enhanced.
Examples of the alkoxy group and the organic substituent contained in the alkoxysiloxane compound include those exemplified in the above description of the alkoxysilane compound, which have at least an alkyl group from the viewpoint of enhancing the dispersibility of the hydrocarbon-based compound (B). Is preferable.

Examples of the alkoxysiloxane compound include methylmethoxysiloxane oligomer, methylphenylmethoxysiloxane oligomer, methylepoxymethoxysiloxane oligomer, methylmercaptomethoxysiloxane oligomer, and methylacryloylmethoxysiloxane oligomer.
As the alkoxysiloxane compound, one kind or two or more kinds can be used.

Examples of the hydrocarbon solvent used as the compatible substance (D) include aromatic hydrocarbon solvents. Of these, an aromatic hydrocarbon solvent is preferable from the viewpoint of compatibility with the curable silicone composition (A1). Examples of the aromatic hydrocarbon solvent include aromatic hydrocarbon solvents having about 6 to 10 carbon atoms, and examples thereof include toluene, xylene, methylene, ethylbenzene, propylbenzene, butylbenzene, t-butylbenzene and the like. , Preferably toluene, xylene and the like.

In the mixed composition, the content of the compatible substance (D) is preferably 6 to 60 parts by mass with respect to a total of 100 parts by mass of the curable silicone composition (A1) and the hydrocarbon compound (B). When it is 6 parts by mass or more, the uniformity of mixing of the hydrocarbon compound (B) with respect to the curable silicone composition (A1) can be sufficiently enhanced. Further, by setting the content to 60 parts by mass or less, an effect commensurate with the amount of the compatible substance (D) used can be obtained. From these viewpoints, the content of the compatible substance (D) is more preferably 10 to 50 parts by mass, further preferably 15 to 45 parts by mass.
At this time, if the mixing of the hydrocarbon compound (B) is not uniform, the hydrocarbon compound remains undissolved, and for example, a solid hydrocarbon compound is dispersed. Such a dispersed solid substance may have properties as a filler in the mixed composition. That is, since the undissolved solid matter becomes a part of the filler that increases the viscosity, it may be difficult to increase the blending amount of the thermally conductive filler as a result.
Further, in the mixed composition, from the viewpoint of enhancing the dispersibility of the hydrocarbon-based compound (B), the content of the compatible substance (D) is preferably higher than the content of the hydrocarbon-based compound (B). ..
It is preferable that part or all of the compatible substance (D) is volatilized by heating in step Y. Therefore, the compatible substance (D) may not be contained in the heat conductive sheet, but may be contained in the heat conductive sheet in an amount smaller than the content in the mixed composition.

In the mixed composition, components other than the compatible substance (D) (that is, curable silicone composition (A1), hydrocarbon compound (B), thermally conductive filler (C), other additives, etc. ) Is as described above. Further, the contents of the hydrocarbon compound (B) and the heat conductive filler (C) in the mixed composition are also as described above. However, in the above, the content of each component is shown based on a total of 100 parts by mass of the silicone matrix (A) and the hydrocarbon compound (B), but in the mixed composition, the curable silicone composition is shown. The amount is based on a total of 100 parts by mass of the substance (A1) and the hydrocarbon compound (B).

(Step Y)
Step Y is a step of curing the mixed composition by heating. The temperature at which the mixed composition is heated is not particularly limited as long as the curable silicone composition (A1) can be cured by heating, and may be higher than room temperature (23 ° C.), but is preferably at a temperature of 50 ° C. or higher. It is good to heat. The heating temperature is not particularly limited, but may be any temperature as long as the heat conductive sheet and the mixed composition are not thermally deteriorated, and are, for example, 180 ° C. or lower, preferably 150 ° C. or lower. Further, the heating of the mixed composition may be carried out in one step or in two or more steps. When performing in two or more steps, the heating temperature may be within the above range at least in any one step, but it is preferable that the heating temperature is within the above range in all steps. The total heating time is, for example, about 10 minutes to 3 hours. In the case of performing in two or more steps, for example, it is preferable to semi-cure the mixed composition in the first step and completely cure the mixed composition by heating in the second step transition.

In step Y, the mixed composition may be formed into a predetermined shape such as a block shape or a sheet shape, and may be heated and cured. Further, in step Y, the mixed composition may be cured by heating after the anisotropic filler used as the thermally conductive filler (C) is oriented in one direction. The anisotropic filler can be oriented by a magnetic field orientation method or a flow orientation method, but it is preferably oriented by a magnetic field orientation method.

In the magnetic field orientation method, it is preferable to inject the mixed composition into a mold or the like and place it in a magnetic field to orient the anisotropic filler along the magnetic field. Then, it is preferable to obtain an oriented molded product by curing the curable silicone composition (A1). The mixing composition may be cured under the heating conditions as described above.
The oriented molded body is preferably block-shaped, but may be sheet-shaped. By forming the sheet, the oriented molded body can be used as it is as a heat conductive sheet without slicing. On the other hand, the block shape enhances the orientation of the anisotropic filler.

In the magnetic field orientation method, a release film may be placed in a portion of the mold that comes into contact with the mixed composition. As the release film, for example, a resin film having good peelability or a resin film whose one side is peeled with a release agent or the like is used. By using the release film, the oriented molded body can be easily released from the mold.

The viscosity of the mixed composition used in the magnetic field orientation method is preferably 10 to 300 Pa · s in order to align the magnetic field. When it is set to 10 Pa · s or more, the heat conductive filler (C) is less likely to settle. Further, when the content is 300 Pa · s or less, the fluidity is improved, the anisotropic filler is appropriately oriented by a magnetic field, and there is no problem that the orientation takes too long. The viscosity is a viscosity measured at a rotation speed of 10 rpm at 25 ° C. using a rotational viscometer (Brookfield viscometer DV-E, spindle SC4-14).
However, when the thermally conductive filler (C) which is difficult to settle is used or when an additive such as a settling inhibitor is combined, the viscosity of the mixed composition may be less than 10 Pa · s.

In the magnetic field orientation method, examples of the magnetic force line generation source for applying the magnetic force lines include superconducting magnets, permanent magnets, and electromagnets, but superconducting magnets are preferable because they can generate a magnetic field having a high magnetic flux density. The magnetic flux density of the magnetic field generated from these magnetic force line generation sources is preferably 1 to 30 tesla. When the magnetic flux density is 1 tesla or more, the above-mentioned anisotropic filler made of a carbon material or the like can be easily oriented. Further, by setting the content to 30 Tesla or less, it becomes possible to practically manufacture the product.

In the flow orientation method, a shearing force is applied to the mixed composition to produce a primary sheet in which the anisotropic filler is oriented along the plane direction. More specifically, in the flow orientation method, first, the mixed composition prepared in the step X is stretched flat while applying a shearing force to form a sheet (primary sheet). By applying a shearing force, the anisotropic filler can be oriented in the shearing direction. As a sheet forming means, for example, a coating applicator such as a bar coater or a doctor blade, extrusion molding, ejection from a nozzle, or the like is used to apply the mixed composition onto the base film, and then, if necessary. It may be dried, the mixed composition may be semi-cured, or it may be fully cured. The thickness of the primary sheet is preferably about 50 to 5000 μm. In the primary sheet, the anisotropic filler is oriented in one direction along the surface direction of the sheet.
The mixed composition used in the flow orientation method has a relatively high viscosity so that a shearing force is applied when the mixed composition is stretched into a sheet. Specifically, the viscosity of the mixed composition is preferably 3 to 500 Pa · s.

As will be described later, the primary sheet may be used as it is as a heat conductive sheet without forming a block. Further, after stacking a plurality of primary sheets so that the orientation directions are the same, the primary sheets are bonded to each other by a hot press or the like while being cured by heating as necessary to form a laminated block (block-shaped). An oriented molded body) may be formed.
Further, when forming a laminated block, the primary sheets may be overlapped after irradiating at least one of the surfaces of the primary sheets to be overlapped with each other with vacuum ultraviolet rays. When the primary sheets are overlapped with each other through the surface irradiated with the vacuum ultraviolet rays, the primary sheets can be firmly adhered to each other. Further, when irradiating with vacuum ultraviolet rays, the mixed composition may be completely cured when the primary sheet is produced, and when the primary sheets are laminated to form a laminated block, the mixed composition is cured by heating or the like. No need.
Also in the flow orientation method, the curing of the mixed composition may be performed under the heating conditions as described above.

As described above, when forming a block-shaped oriented molded body, the obtained oriented molded body is cut by a slice or the like perpendicular to the direction in which the anisotropic filler is oriented to form a sheet. Good for the body. Slicing may be performed with, for example, a shear blade. In the sheet-shaped molded product, the tip of the anisotropic filler is exposed from the binder component on each surface which is the cut surface by cutting the slice or the like.
The sheet-shaped molded product obtained by cutting may be used as it is as a heat conductive sheet, or may be further treated. For example, each surface which is a cut surface may be polished. The surface may be polished using, for example, abrasive paper.

[How to use the heat conductive sheet]
The heat conductive sheet of the present invention is used inside an electronic device or the like. Specifically, the heat conductive sheet is interposed between the two members and is used to conduct heat from one member to the other. Specifically, the heat conductive sheet is interposed between the heating element and the heat radiating element, conducts heat generated by the heating element, transfers the heat to the radiating element, and dissipates heat from the radiating element. Here, examples of the heating element include various electronic components such as a CPU, a power amplifier, and a power supply used inside an electronic device. Examples of the radiator include a heat sink, a heat pump, and a metal housing of an electronic device. The heat conductive sheet may be used with both surfaces in close contact with each of the heating element and the heat radiating element and compressed.

[How to attach the heat conductive sheet]
The present invention also provides a method for mounting a heat conductive sheet. As described above, the heat conductive sheet of the present invention comprises a binder component which is a mixture of a silicone matrix (A) and a hydrocarbon compound (B), and a heat conductive filler (C) dispersed in the binder component. The thermally conductive filler (C) contains an anisotropic filler oriented in the thickness direction, and has a thickness of 0.05 to 0.5 mm.
The heat conductive sheet of the present invention can be stably mounted between two members (between the first and second members) by the mounting method having the following steps 1 to 3.

Step 1: Place the heat conductive sheet on the surface of the first member Step 2: Step to heat the heat conductive sheet Step 3: The side opposite to the surface of the heat conductive sheet on the first member side The process of arranging the second member on the surface of the surface and pressurizing the heat conductive sheet to assemble the heat conductive sheet between the first and second members. In this mounting method, the first and second members are Although not particularly limited, it is preferable that one is a heating element and the other is a radiator. The detailed description of the heating element and the radiator is as described above.

(Step 1)
In step 1, the heat conductive sheet is placed on the surface of the first member. The method of arranging the heat conductive sheet is not particularly limited, but it is preferable to arrange the heat conductive sheet so that one surface of the heat conductive sheet comes into contact with the first member.
In this method, as will be described later, it is preferable to perform step 2 after step 1. In that case, since the heat conductive sheet is arranged on the surface of the first member in a state where there is elasticity before heating, the workability of the step 1 is improved.

(Step 2)
In step 2, the heat conductive sheet is heated. Step 2 may be performed after step 1, before step 1, or in parallel with step 1, but step 2 may be performed after step 1 as described above. preferable. That is, in step 2, it is preferable to heat the heat conductive sheet arranged on the surface of the first member.

In step 2, the heat conductive sheet may be heated to a temperature equal to or higher than the melting point of the hydrocarbon compound (B). Therefore, the thermal conductivity sheet should be heated to a temperature higher than normal temperature (23 ° C.), but the hydrocarbon-based compound (B) is surely melted and thermally conductive at the time of assembly (step 3 described later). From the viewpoint of increasing the flexibility of the sheet, it is preferable to heat the sheet to 40 ° C. or higher, more preferably 50 ° C. or higher, still more preferably 60 ° C. or higher.
Further, from the viewpoint of preventing the heat conductive sheet from being heated more than necessary, the heat conductive sheet may be heated to 100 ° C. or lower, preferably 90 ° C. or lower, more preferably 85 ° C. or lower. It is good.
In step 2, when the heat conductive sheet is heated to a temperature equal to or higher than the melting point of the hydrocarbon compound (B), the first and second heat-conducting sheets are pressurized in step 3 through the molten hydrocarbon compound (B). Can be easily fixed to the member of.

The method for heating the heat conductive sheet is not particularly limited, and the heat conductive sheet may be heated by a heating device such as an infrared heater, a hot air heater, or a heat transfer heater.
Conventionally, the phase change sheet is generally softened or melted by heating a heating element constituting either the first or second member, but in this mounting method, the heat conductive sheet generates heat. It is preferable that the heating device is heated by a heating device separate from the body before being sandwiched between the first and second members. According to such an aspect, the heat conductive sheet can be fixed to the first and second members before the use of the electronic device. Therefore, it is possible to compress and assemble the heat conductive sheet at the compression rate as designed.

(Step 3)
In step 3, the second member is arranged on the surface of the heat conductive sheet opposite to the surface of the first member side, and the heat conductive sheet is pressurized to be between the first and second members. Assemble the heat conductive sheet.
In step 3, it is preferable to further arrange the second member on the heat conductive sheet arranged on the surface of the first member, whereby the heat conductive sheet is made of the first and second members. It will be in a state of being sandwiched between them.
Step 3 may be performed in parallel with step 2, but is preferably performed after step 2. Therefore, in step 3, it is preferable to further arrange the second member on the heat conductive sheet that has been arranged on the surface of the first member and has already been heated.
In this mounting method, it is more preferable to perform the steps 1, step 2, and step 3 in this order. If each process is performed in such an order, workability is improved.

The heat conductive sheet sandwiched between the first and second members in step 3 is heated by step 2, and therefore, in step 3, the heated state is further pressurized in the thickness direction. It is good. Here, the pressurization may be performed, for example, by further pressing the heat conductive sheet sandwiched between the first and second members in the thickness direction by the first and second members.
Further, the heat conductive sheet has a temperature equal to or higher than the melting point of the hydrocarbon compound (B) at the time of pressurization in step 3, and the hydrocarbon compound (B) is melted. The heat conductive sheet may be fixed to the first and second members by the compound (B).

As described above, since the heat conductive sheet of the present invention has a certain degree of flexibility in a heated state, it can be made to follow the first and second members by the pressurization in step 3. Therefore, even if the first and second members have irregularities, the heat conductive sheet can be brought into close contact with the first and second members to prevent the thermal resistance from increasing. Further, the heat conductive sheet can be assembled without applying high stress to the first and second members. Further, since the heat conductive sheet has shape retention even when heated, pump-out is suppressed and reliability is enhanced even when used in a compressed state as described above. Further, since the heat conductive sheet has a certain elasticity before heating, the workability at the time of assembly can be improved.

[Heat dissipation member]
The present invention also provides a heat-dissipating member provided with the above-mentioned heat-conducting sheet and a heat-dissipating body, and the heat-conducting sheet is mounted on the surface of the heat-dissipating body. Such a heat radiating member can be obtained, for example, by arranging a heat conductive sheet on the surface of the heat radiating body and fixing the heat conductive sheet to the surface of the heat radiating body. Here, the heat conductive sheet may be fixed to the surface of the radiator by heating to a temperature equal to or higher than the melting point of the hydrocarbon compound (B) and pressurizing, for example. At this time, the heat conductive sheet may be placed on the surface of the heat radiating body after being heated, or may be placed on the surface of the heat radiating body and then heated.

Further, as the heat radiating member, the heat conductive sheet can be mounted between the heat radiating body and the heat generating body by arranging the heat generating body on the surface of the heat conductive sheet opposite to the surface of the heat radiating body side. As the mounting method, the method including the above steps 2 and 3 may be performed, and the details thereof are as described above and will be omitted.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples.

The heat conductive sheets obtained in this example and comparative example were evaluated by the following methods.

[Thermal resistance value, slope α]
The thermal resistance value was measured by the method shown below using a thermal resistance measuring machine as shown in FIG. Specifically, for each sample, a test piece S having a size of 30 mm × 30 mm was prepared for this test. Then, each test piece S is attached onto a copper block 22 having a measurement surface of 25.4 mm × 25.4 mm and whose side surface is covered with a heat insulating material 21, sandwiched between the upper copper blocks 23, and pressured by a load cell 26 (40 psi). A load of 0.276 MPa) was applied. Here, the lower copper block 22 is in contact with the heater 24. Further, the upper copper block 23 is covered with a heat insulating material 21 and connected to a heat sink 25 with a fan. Next, 10 minutes after the heater 24 is heated to a substantially steady state, the temperature of the upper copper block 23 (θ _j0 ), the temperature of the lower copper block 22 (θ _j1 ), and the calorific value of the heater (Q). ) Was measured, and the thermal resistance value _R40 of each sample was obtained from the following formula (2). The temperature was adjusted so that the heat conductive sheet had a calorific value of 80 ° C.
Thermal resistance value = (θ _j1 -θ _j0 ) / Q ・ ・ ・ Equation (2)
In the formula (2), θ _j1 is the temperature of the lower copper block 22, θ _j0 is the temperature of the upper copper block 23, and Q is the calorific value.

Further, the thermal resistance value R ₁₀ was calculated in the same manner as above except that a load of 10 psi (0.069 MPa) was applied by the load cell 26.
The thermal resistance value R ₄₀ (° C. in ² / W) measured at a load of 40 psi calculated as described above, the thickness of the heat conductive sheet at the time of measurement at a load of 40 psi T ₄₀ (mm), and the thermal resistance measured at a load of 10 psi. From the value R ₁₀ (° C. in ² / W) and the thickness T ₁₀ (mm) of the heat conductive sheet at the time of measurement at a load of 10 psi, the inclination α was obtained by the following formula (1).
α = (R ₄₀ -R ₁₀ ) / (T ₄₀ -T ₁₀ ) ... (1)

The thermal resistance value at low load was evaluated according to the following criteria based on the value of the slope α.
A Slope α is 0.1 or less B Slope α is more than 0.1 0.4 or less C Slope α is more than 0.4 1 or less D Slope α is more than 1

[Compression rate]
The heat conductive sheet was cut into a size of 10 mm × 10 mm, and the compression ratio when compressed at 0.276 MPa (= 40 psi) in an environment of 80 ° C. was measured. Specifically, the test piece is sandwiched between a pedestal having a size of 10 mm × 10 mm and a flat surface and a presser that presses in parallel, and the thickness T2 when the test piece is compressed at 0.276 MPa is measured, and the initial thickness is measured. The compression ratio (%) [100 × (T1-T2) / T1] with respect to the thickness T1 was calculated.

[Example 1]
Side-chain crystalline polyalphaolefin (CPAO, melting point (Tm): 42 ° C.) as the hydrocarbon compound (B) and n-decyltrimethoxysilane as the compatible substance (D) are added according to the blending amounts in Table 1. The mixture was mixed at 23 ° C. to obtain a mixture in which the hydrocarbon compound (B) was dissolved in the compatible substance (D). Uniformly the obtained mixture, the silicone main agent 1 (alkenyl group-containing organopolysiloxane) as the curable silicone composition (A1), the silicone curing agent (hydrogen organopolysiloxane), and the catalyst (platinum-based catalyst). After mixing, the heat conductive filler (C) was mixed according to the blending amounts shown in Table 1 to obtain a mixed composition.

As the thermally conductive filler (C), aluminum powder (spherical, average particle size 3 μmm, aspect ratio 1 to 1.5, thermal conductivity 236 W / m · K) was used as the non-anisotropic filler. .. Further, as an anisotropic filler, scaly graphite powder (average particle size 40 μm, aspect ratio 10, thermal conductivity 550 W / m · K), graphitized carbon fiber 1 (average fiber length 77 μm, aspect ratio 8, thermal conductivity 1200 W). / M · K) and graphitized carbon fiber 2 (average fiber length 150 μm, aspect ratio 15, thermal conductivity 900 W / m · K) were used. The volume filling factor of the heat conductive filler (C) in each Example and Comparative Example was 66% by volume.
The melting point is the temperature of the endothermic peak of the DTA curve measured under the condition of a heating rate of 1 ° C./min by thermal weight differential thermal analysis (TGDTA, "DTG-60" manufactured by Shimadzu Corporation).

Subsequently, the mixed composition is injected into a mold set to a thickness sufficiently larger than that of the heat conductive sheet, and an 8T magnetic field is applied in the thickness direction to apply the anisotropic filler in the thickness direction. After orientation, the curable silicone composition (A1) was cured by heating at 80 ° C. for 60 minutes to obtain a block-shaped oriented molded body.
Next, the block-shaped oriented molded product is sliced into a sheet using a shear blade to obtain a sheet-shaped molded product in which the anisotropic filler is exposed, and then heated at 150 ° C. for 2 hours. Then, the sheet-shaped molded body was used as a heat conductive sheet. Two types of heat conductive sheets, one having a thickness of 0.2 mm and the other having a thickness of 0.3 mm, were produced.
For each heat conductive sheet, the heat resistance value R ₄₀ measured at a load of 40 psi and the thickness T ₄₀ at the time of measurement, and the heat resistance value R ₁₀ measured at a load of 10 psi and the thickness T ₁₀ at the time of measurement are described above. The measurement was performed as per, and the inclination α was calculated and the thermal resistance at low load was evaluated. The results are shown in Table 1.

[Examples 2 to 4]
A heat conductive sheet was obtained in the same manner as in Example 1 except that the blending amount of each component was changed to the amount shown in Table 1. Two types of heat conductive sheets, one having a thickness of 0.2 mm and the other having a thickness of 0.3 mm, were produced.
For each heat conductive sheet, the heat resistance value R ₄₀ measured at a load of 40 psi and the thickness T ₄₀ at the time of measurement, and the heat resistance value R ₁₀ measured at a load of 10 psi and the thickness T ₁₀ at the time of measurement are described above. The measurement was performed as per, and the inclination α was calculated and the thermal resistance at low load was evaluated. The results are shown in Table 1.

[Example 5]
A heat conductive sheet was obtained in the same manner as in Example 1 except that the blending amount of the side chain crystalline polyalphaolefin (CPAO) was as shown in Table 1 and dimethyldimethoxysilane was used as the compatible substance (D). .. In Example 5, the hydrocarbon-based compound (B) tended to be difficult to dissolve in the compatible substance (D), and it took time to dissolve, but a heat conductive sheet could be obtained without any problem. Two types of heat conductive sheets, one having a thickness of 0.2 mm and the other having a thickness of 0.3 mm, were produced.
For each heat conductive sheet, the heat resistance value R ₄₀ measured at a load of 40 psi and the thickness T ₄₀ at the time of measurement, and the heat resistance value R ₁₀ measured at a load of 10 psi and the thickness T ₁₀ at the time of measurement are described above. The measurement was performed as per, and the inclination α was calculated and the thermal resistance at low load was evaluated. The results are shown in Table 1.

[Example 6]
A heat conductive sheet was obtained in the same manner as in Example 1 except that white petrolatum according to the Japanese Pharmacopoeia was used as the hydrocarbon compound (B) in the blending amounts shown in Table 1. Two types of heat conductive sheets, one having a thickness of 0.2 mm and the other having a thickness of 0.3 mm, were produced.
For each heat conductive sheet, the heat resistance value R ₄₀ measured at a load of 40 psi and the thickness T ₄₀ at the time of measurement, and the heat resistance value R ₁₀ measured at a load of 10 psi and the thickness T ₁₀ at the time of measurement are described above. The measurement was performed as per, and the inclination α was calculated and the thermal resistance at low load was evaluated. The results are shown in Table 1.

[Comparative Examples 1 and 2]
The same procedure as in Example 1 was carried out except that a heat conductive sheet was prepared from a mixed composition obtained by mixing each component according to the formulation shown in Table 1 without using the hydrocarbon compound (B). Table 1 shows the evaluation results of the heat conductive sheet obtained in Comparative Example 1.

[Comparative Example 3]
The same procedure as in Example 1 was carried out except that the mixed composition obtained by mixing each component according to the formulation shown in Table 1 was used without using the compatible substance (D), but the hydrocarbon compound (B) was used. Was not dispersed in the curable silicone composition (A1), and a block-shaped oriented molded body could not be obtained.

The heat conductive sheets of Examples 1 to 6 were heat conductive sheets satisfying the requirements of the present invention, had a high compressibility at high temperatures, and were excellent in flexibility. Further, although the thickness is thin, the value of the inclination α is small, the followability to the heating element and the heat radiating element is excellent under a low load, and the thermal resistance value is low. In particular, Examples 2, 3 and 6 obtained by blending the hydrocarbon compound (B) in the range of 2 parts by mass or more and 8 parts by mass or less and using n-decyltrimethoxysilane as the compatible substance (D). The heat conductive sheet of No. 1 had a lower value of inclination α and a particularly low heat resistance value under a low load.
Since the heat conductive sheet obtained in each example was a relatively rigid sheet at room temperature lower than the melting point of the hydrocarbon compound (B), the heat conductive sheet is obtained by slicing as described above. It was possible and was excellent in handleability. Further, even at 80 ° C., the liquid did not become liquid and the liquid material did not flow out, so that pump-out did not occur even when compressed for a long period of time, and the reliability was good. Furthermore, no bubbles were observed on the surface of the heat conductive sheet, and the appearance was good.
The heat conductive sheets of Comparative Examples 1 and 2 had a low compressibility at high temperatures and did not have a certain degree of flexibility. In addition, the value of the slope α was larger than that of the examples, and at a low load, the followability to the heating element and the radiator was insufficient, and the thermal resistance value was high.
In Comparative Example 3, since the compatible substance (D) was not used, a heat conductive sheet could not be obtained.

21 Insulation material 22 Lower copper block 23 Upper copper block 24 Heater 25 Heat sink 26 Load cell S Test piece θ _j0 Upper copper block temperature θ _j1 Lower copper block temperature

Claims (10)

A binder component that is a mixture of the silicone matrix (A) and the hydrocarbon compound (B),
A heat conductive filler (C) dispersed in the binder component is provided.
The thermally conductive filler (C) contains an anisotropic filler that is oriented in the thickness direction.
It has a thickness of 0.05 to 0.5 mm and has a thickness of 0.05 to 0.5 mm.
Thermal resistance value R ₄₀ (° C. in ² / W) measured at 80 ° C. with a load of 40 psi and thickness T ₄₀ (mm) at the time of measurement, and thermal resistance value R ₁₀ (° C. ) measured at 80 ° C. with a load of 10 psi. The inclination α represented by the following equation (1) calculated by in ² / W) and the measured thickness T ₁₀ (mm) is 0.4 or less.
Thermally conductive sheet.
α = (R ₄₀ - R ₁₀ ) / (T ₄₀ -T ₁₀ ) ... (1) The heat conductive sheet according to claim 1, wherein the hydrocarbon compound (B) has a melting point higher than 23 ° C and 80 ° C or lower. The heat conductive sheet according to claim 1 or 2 , wherein the hydrocarbon compound (B) is a crystalline polyalphaolefin. The content of the hydrocarbon compound (B) is 0.5 to 15 parts by mass with respect to a total of 100 parts by mass of the silicone matrix (A) and the hydrocarbon compound (B). The heat conductive sheet according to any one item. The heat conductive sheet according to any one of claims 1 to 4 , wherein the heat conductive filler (C) has a volume filling rate of 30 to 85% by volume. A heat radiating member comprising the heat conductive sheet according to any one of claims 1 to 5 and a heat radiating body, and the heat conductive sheet is mounted on the surface of the heat radiating body. The heat conductive filler (C) comprises a binder component which is a mixture of a silicone matrix (A) and a hydrocarbon compound (B), and a heat conductive filler (C) dispersed in the binder component. It contains an anisotropic filler oriented in the thickness direction, has a thickness of 0.05 to 0.5 mm, and has a thermal resistance value of R ₄₀ (° C. in ² / W) measured at 80 ° C. with a load of 40 psi. The following formula calculated by the measured thickness T ₄₀ (mm), the thermal resistance value R ₁₀ (° C in ² / W) measured at 80 ° C with a load of 10 psi, and the measured thickness T ₁₀ (mm). The step of arranging the heat conductive sheet having the inclination α of 0.4 or less shown in (1) on the surface of the first member, and
The step of heating the heat conductive sheet and
The second member is arranged on the surface of the heat conductive sheet opposite to the surface of the first member side, and the heat conductive sheet is pressurized to be between the first and second members. A method for mounting a heat conductive sheet, which comprises a step of assembling the heat conductive sheet.
α = (R ₄₀ - R ₁₀ ) / (T ₄₀ -T ₁₀ ) ... (1) The method for attaching a heat conductive sheet according to claim 7 , wherein the hydrocarbon compound (B) has a melting point higher than 23 ° C. and heats the heat conductive sheet to the melting point or higher. At least the curable silicone composition (A1), the hydrocarbon-based compound (B), the thermally conductive filler (C) containing the anisotropic filler, and the compatible substance (D) are mixed and mixed. The process of obtaining the composition and
The method for producing a thermally conductive sheet according to any one of claims 1 to 5, further comprising a step of curing the mixed composition by heating. The method for producing a thermally conductive sheet according to claim 9 , wherein the compatible substance (D) is an alkoxysilane compound.

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