JP2009066817A - Thermally-conductive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermally-conductive sheet which is extremely excellent in thermally conductive characteristics to a thickness direction. <P>SOLUTION: The thermally-conductive sheet is formed by extruding a mixture containing flaky graphite and a binder resin into sheet forms, and laminating and integrating the obtained sheets, then cutting the sheet in a lamination direction. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat conductive sheet. Specifically, the present invention relates to a heat conductive sheet used as a sheet or the like for efficiently releasing heat generated in an electronic device to the outside.

In recent years, as represented by a CPU, the speed of a semiconductor element has been increased, and accordingly, the heat generated by the potential component itself has been increasing. In addition, electronic devices that incorporate electronic components, particularly electronic devices such as mobile phones, notebook computers, and mobile phones, are becoming smaller and higher in density. Therefore, how to remove the heat generated in the device without increasing the size and weight of the device is a big problem.
In order to solve this problem, conventionally, a heat conductive sheet or a high heat conductive carbon material has been used. Here, the heat conductive sheet is a sheet that is sandwiched between a heat generating member and a heat radiating member, thereby improving adhesion and improving heat conduction efficiency. High thermal conductivity characteristics in the thickness direction are required.

As the thermal conductive sheet, for example, conventionally, an inorganic filler such as alumina, silica, or a high thermal conductive carbon material was used in a composite with a binder such as a gel, but in this thermal conductive sheet, Although the flexibility was high, the heat conduction characteristics were low.
Also, a high thermal conductivity carbon sheet is known, but the high thermal conductivity carbon fiber sheet has a very high thermal conductivity in the plane direction, but has a low thermal conductivity in the thickness direction of the core.
Therefore, research and development on a sheet having excellent thermal conductivity in the thickness direction has also been carried out, for example, a heat dissipation sheet in which a plurality of graphite sheets are laminated, and the ab plane of the graphite crystal is A heat radiating sheet characterized by being perpendicular to the sheet surface of the heat-heat sheet is known (see Patent Document 1). As a method for manufacturing such a sheet, an adhesive is applied to the sheet surface of the graphite sheet that is parallel to the ab plane of the graphite crystal, and a plurality of graphite sheets coated with the adhesive are obtained. A method is also known in which a laminate is obtained by laminating and pressing, and then cutting the laminate in a direction perpendicular to the sheet surface of the graphite sheet (see Patent Document 1).

However, the graphite sheet is made only of graphite, and as is apparent from the crystal structure of graphite, the bondability in the direction perpendicular to the surface is weak. Therefore, in this prior art, it is essential to interpose an adhesive when laminating the graphite sheets, and there is a problem that the operation of applying the adhesive is complicated, and a layer made of an adhesive is interposed between the graphite sheets. As a result, graphite cannot be directly connected to each other, and there is a problem that the heat conduction characteristic in the thickness direction is hindered.
JP 2006-303240 A

  Therefore, the problem to be solved by the present invention is to provide a heat conductive sheet that does not have the above-mentioned problems that occur when a graphite sheet is used and that is excellent in heat conduction characteristics in the thickness direction.

The present inventor has intensively studied to solve the above problems. As a result, by extruding a mixture containing scaly graphite and a binder resin into a sheet shape, the scaly graphite is regularly aligned in the surface direction during extrusion, and this is laminated and integrated. It is found that by cutting into a sheet in the stacking direction, a state in which scaly graphite is regularly aligned in the thickness direction can be realized, and a sheet having excellent heat conduction characteristics in the thickness direction can be obtained. This was confirmed and the present invention was completed.
That is, the heat conductive sheet according to the present invention is formed into a sheet by extruding a mixture containing scaly graphite and a binder resin into a sheet shape, laminating and integrating the obtained sheets, and then cutting in the laminating direction. It is characterized by.

According to the present invention, it is possible to obtain a thermally conductive sheet that is excellent in thermal conductivity characteristics in the thickness direction.
If polytetrafluoroethylene is used as the binder resin, heat resistance, chemical resistance and flame retardancy can be imparted, which is more preferable.
The sheet obtained by cutting in the laminating direction is impregnated with at least one selected from the group consisting of oil, resin solution and sol-gel solution, or the surface of the sheet obtained by cutting in the laminating direction It is preferable to coat with at least one selected from the group consisting of oil, resin solution, resin, rubber and sol-gel solution, since it is possible to exhibit even higher heat conduction characteristics.

Hereinafter, the thermal conductive sheet according to the present invention will be described in detail, but the scope of the present invention is not limited by these descriptions, and other than the following exemplifications, changes are made as appropriate without departing from the spirit of the present invention. Can do.
[Scaly graphite]
The flaky graphite exhibits excellent anisotropy in the finally obtained heat conductive sheet.
The scaly graphite is not particularly limited, and those having a length of 5 to 500 μm and a thickness of 0.1 to 10 μm can be used.
[Binder resin]
Binder resin has the role which combines scaly graphite, provides moldability, and provides adhesiveness between sheets and other materials.

  The ratio of the binder resin used is not particularly limited. For example, the binder resin is preferably used so that the ratio of the flake graphite to 100 parts by weight of the binder resin is 100 to 1200 parts by weight. If the proportion of the binder resin is high and the proportion of the flaky graphite is less than 100 parts by weight, the high thermal conductivity may be hardly exhibited, the proportion of the binder resin is small, and the proportion of the flaky graphite is 1200 weight. If it exceeds the portion, the sheet strength may be greatly reduced. More preferably, it is 300-900 weight part. In addition, since binder resin does not have electroconductivity, the electroconductivity of the heat conductive sheet obtained as the use ratio increases, and the electroconductivity of the heat conductive sheet obtained increases as the use ratio decreases. Therefore, in consideration of this point, it is preferable to set the usage ratio according to the characteristics of the target thermal conductive sheet.

The binder resin is not particularly limited. Examples thereof include polyamide resin, polyimide resin, phenol resin, epoxy resin, acrylic resin, urethane resin, silicone resin, cellulose resin, vinyl acetate resin, and polycarbonate resin.
Among the above, a fluororesin is preferable, and polytetrafluoroethylene is particularly preferable.
[Other materials]
Other materials may be used for the heat conductive sheet according to the present invention as long as the effects of the present invention are not impaired. Specifically, for example, metals such as copper and aluminum, carbon materials such as diamond and carbon nanotubes, rubbers such as silicon rubber and chloroprene rubber, resins such as PET and PVA, magnetic alloy metals such as sendust and permalloy, Examples thereof include glass such as ferrite and low-melting glass, ceramics such as silicon carbide and boron nitride, inorganic thin films such as silicon dioxide and titanium dioxide, and semiconductor thin films such as gallium arsenide and gallium nitride.

Furthermore, you may add 1 type (s) or 2 or more types as needed, a solvent, a dispersing agent, a plasticizer, a crosslinking agent, anti-aging agent, a crosslinking accelerator, a pigment.
[Manufacture of thermal conductive sheet]
In the method for producing a heat conductive sheet according to the present invention, the above-described scaly graphite and a binder resin are used as essential components, and other materials are used as appropriate, and a mixture containing them is extruded into a sheet shape. After the sheets are laminated and integrated, they are cut into a lamination direction to form sheets. The “sheet” here includes a thin film.
Specifically, for example, the thermal conductive sheet according to the present invention can be manufactured through steps A to D shown in FIG.

  In the process A, as a mixture essentially containing flaky graphite and binder resin, a dispersion liquid of binder resin and a stirred mixture 2 of flaky graphite 1 are used, and this is formed into a sheet by extruding with a roll 3 to obtain a sheet 4 Have gained. The sheet formation by the extrusion molding can be performed at a molding temperature of 10 to 80 ° C., for example, and can be a continuous sheet having a width of 20 to 300 mm and a thickness of 10 to 2000 μm. By this extrusion molding, the scaly graphite 2 that did not have a constant orientation in the state of the mixture before extrusion molding is in a state of being regularly oriented in the sheet surface direction under the pressure of the roll 3, and in the sheet surface direction. Thermal conductivity is extremely excellent.

  As described above, when a dispersion liquid containing a binder resin is prepared and mixed with flaky graphite to obtain a mixture of flaky graphite and a binder resin, the dispersion medium used for the dispersion liquid After the flaky graphite and the binder resin are sufficiently homogenized by mixing means such as stirring, they may be removed in advance before extrusion by known means such as centrifugation, or while extruding. The dispersion medium contained in the extruded sheet can be removed by drying by heating or the like. Further, it may be removed by pressure at the time of steps B and C (sheet lamination and integration) described later. In this way, if the dispersion medium is sufficiently removed, the adhesion between the sheets after extrusion molding becomes good, and the thermally conductive sheet obtained by cutting in the laminating direction becomes stable.

The state of the mixture is, for example, a gel.
The dispersion medium used in the dispersion liquid is not particularly limited, and examples thereof include water and an organic solvent, and it is particularly preferable to use water in view of the environment. When an organic solvent is used, for example, acetone or the like may be used alone, or two or more kinds may be used in combination.
The amount of the dispersion medium used is not particularly limited, but is preferably 10 to 500 parts by weight with respect to 100 parts by weight of the binder resin, for example. If the amount of the dispersion medium used is less than 10 parts by weight, it may be difficult to make the binder resin uniform on the surface of the filler (flaky graphite), and if it exceeds 500 parts by weight, it is difficult to obtain a gel-like mixture. There is a risk. More preferably, it is 20-300 weight part.

Next, in step B, the extruded sheet 4 is laminated on the compression mold 5 for supporting the sheet subjected to pressure during the lamination integration. At this time, when the sheet 4 is a continuous sheet, the sheet 4 may be cut to an appropriate size before lamination. As a lamination | stacking number of sheets, it can be set as 5-1000 sheets, for example.
After the lamination in the process B, the laminated body 6 is obtained by pressure bonding in the process C. The pressure bonding can be performed, for example, by applying a pressure of 2 to 30 MPa.
In addition, in this lamination | stacking integration in this invention, since the binder resin contained as an essential material shows the outstanding adhesiveness, it is not necessary to interpose an adhesive agent etc. between each sheet | seat.

Finally, in step D, the laminate 6 is cut in the stacking direction by the cutter 7 so as to have a desired thickness, so that the scaly graphite is oriented in the thickness direction, and the heat conduction characteristics in the thickness direction are obtained. An extremely excellent thermal conductive sheet 8 is obtained.
Although the said heat conductive sheet 8 is not specifically limited, For example, it is preferable to set it as a sheet | seat of length 20-300 mm, width 20-300 mm, and thickness 5-5000 micrometers. If the thickness is less than 5 μm, the sheet strength becomes too weak, and there is a risk of breakage or cracking. If the thickness exceeds 5000 μm, the heat conduction distance becomes too long, and the heat transfer effect is lowered, so that there is a possibility that the practicality may be lacking. . More preferably, the thickness is 50 to 2000 μm, and even more preferably, the thickness is 100 to 1000 μm.

After cutting in the laminating direction as described above, it is preferable to impregnate oil, a resin solution, a sol-gel solution, or the like because a heat conductive sheet with more excellent heat conductivity can be obtained.
Further, by coating the surface of the sheet obtained by cutting in the laminating direction as described above with oil, resin solution, resin, rubber, sol-gel solution, etc., it is possible to obtain a heat conductive sheet with more excellent heat conductivity. This is preferable because it is possible. The coating method is not particularly limited, and examples thereof include spin coating and doctor blade.
Examples of the oil include, but are not limited to, liquid paraffin, silicone oil, and fluorine oil.

The resin solution is not particularly limited, and examples thereof include the following resins and rubber solutions and dispersion liquids, and examples of the solvent and dispersion medium include acetone and thinner. be able to.
Although it does not necessarily limit as said resin, For example, reaction hardening type liquid resins, such as an epoxy resin and a phenol resin, etc. can be mentioned.
Examples of the rubber include, but are not limited to, reaction curable rubber such as silicone RTV rubber.
Although it does not necessarily limit as said sol-gel solution, For example, a silane alkoxide solution, a titanium alkoxide solution, etc. can be mentioned.

A clear coating layer or a colored coating layer may be formed on the heat conductive sheet for the purpose of protecting the sheet.
In addition, since the heat conductive sheet concerning this invention has electroconductivity, it is an electroconductive part, ie, on the wiring in which the electrical continuity is taken on a board | substrate, and the lead terminal of MPU. It cannot be applied directly to such places. Therefore, in order to maintain insulation on the sheet surface, an insulating sheet may be laminated on one side or both sides of the thermally conductive sheet. Although it does not specifically limit as said insulating sheet, Resin, such as a fluororesin and a silicone resin, Ceramics, such as a silica and a titanium oxide, etc. are mentioned, According to the use and the objective, the 1 type (s) or 2 or more types are selected suitably Just do it. The thickness of the insulating sheet can be 5 to 100 μm.

  The heat conductive sheet manufactured in this way is interposed between a heat generator such as an electronic component and a heat sink such as a heat sink or a heat pipe to effectively conduct heat between them. Is suitable. Examples of the covering object include a mobile phone and a circuit board.

Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples. Hereinafter, for convenience, “parts by weight” may be simply referred to as “parts” and “% by weight” may be referred to as “%”.
The measurement methods and evaluation methods in the examples are shown below.
<Measurement method of heat conduction characteristics>
Thermal conductivity characteristics were evaluated by thermal conductivity and thermal resistance. Specifically, it measured as follows.
As shown in FIG. 2, while compressing the sample with two copper plates on the heater side and heat sink side, the heater is heated by applying electric power to reach the thermal equilibrium, the temperature of each copper plate, the compression force of the sample, the sample The thickness was measured. And thermal conductivity was computed by following formula (1), and thermal resistance was computed by following formula (2).

Thermal conductivity (W / m · K) = W × t / s × (T ₁ −T ₂ ) (1)

Thermal resistance (° C./W)=(T ₁ −T ₂ ) / W (2)

In the above equation, T ₁ (° C.) is the heater side temperature, T ₂ (° C.) is the heat sink side temperature, W is the heating value of the heater (W) = heater applied voltage (V) × current (A), t (m ) Is the sample thickness (when compressed), and s (m ² ) is the heat transfer area.

[Example 1]
Polytetrafluoroethylene was used as a binder resin, and 100 parts of polytetrafluoroethylene was diluted with 467 parts of water to prepare 567 parts of a polytetrafluoroethylene dispersion. The dispersion liquid and 400 parts of scaly graphite SP20 (manufactured by Nippon Graphite Co., Ltd.) were stirred and mixed to obtain a gel-like product. This gel-like product was formed into a sheet by extrusion molding at a temperature of 30 ° C. to obtain a continuous sheet having a width of 100 mm and a thickness of 500 μm.
The continuous sheet is cut to a width of 50 mm and cut to an appropriate length in the extrusion direction, and then cut into strips, and after stacking 80 strips of sheets, they are laminated and integrated while dehydrating at a pressure of 5 MPa. By cutting this in the laminating direction, a thermally conductive sheet according to the present invention was obtained.

The obtained sheet had a length of 30 mm, a width of 50 mm, and a thickness of 893 μm.
[Example 2]
The thermally conductive sheet obtained in Example 1 was impregnated with liquid paraffin to obtain a thermally conductive sheet according to Example 2.
The obtained sheet had a length of 30 mm, a width of 50 mm, and a thickness of 883 μm.
[Comparative Example 1]
In the same manner as in Example 1, a sheet obtained by extrusion molding (without processing after lamination integration) was used as Comparative Example 1.

The obtained sheet was a continuous sheet having a width of 100 mm and a thickness of 350 μm.
[Comparative Example 2]
An aluminum foil having a thickness of 50 μm was used as Comparative Example 2.
[Comparative Example 3]
A commercially available thermal conductive sheet “lambda gel” (trade name, manufactured by Geltech Co., Ltd.) having a thickness of 860 μm was used as Comparative Example 3.
[Evaluation]
Based on the evaluation of the thermal conductivity, thermal conductivity and thermal resistance were measured. The results are shown in Table 1. When evaluating the thermal conductivity, the sheets finally obtained in each example and comparative example were cut into the dimensions shown in Table 1 in accordance with the dimensions of the copper plate of the measuring device. Using.

  As is clear from Table 1, the thermal conductive sheets according to Examples 1 and 2 have extremely excellent thermal conductivity in the thickness direction as compared with the sheets according to other Comparative Examples 1 to 3. I understand that. In particular, it can be seen that the thermal conductive sheet according to Example 2 impregnated with liquid paraffin has a very high thermal conductivity in the thickness direction.

  The heat conductive sheet according to the present invention can be suitably used as a sheet for improving adhesiveness and heat conduction efficiency by being sandwiched between a heat generating member and a heat radiating member.

It is a figure which shows the outline | summary of one Embodiment of this invention. It is a figure which shows the outline | summary of the apparatus for measuring a heat conductive characteristic.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mixture 2 Scale-like graphite 3 Roll 4 Extruded sheet 5 Compression mold 6 Laminate 7 Cutter 8 Thermally conductive sheet

Claims (4)

  A method for producing a thermally conductive sheet, in which a mixture containing scaly graphite and a binder resin is extruded into a sheet shape, the obtained sheets are laminated and integrated, and then cut into a lamination direction to form a sheet.   The manufacturing method of the heat conductive sheet of Claim 1 whose said binder resin is polytetrafluoroethylene.   The method for producing a thermally conductive sheet according to claim 1 or 2, wherein the sheet is cut in the laminating direction and then impregnated with at least one selected from the group consisting of oil, resin solution and sol-gel solution.   The heat conduction according to claim 1 or 2, wherein the sheet surface is coated with at least one selected from the group consisting of oil, resin solution, resin, rubber and sol-gel solution after cutting in the laminating direction to form a sheet. Manufacturing method of adhesive sheet.

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