JP2008053383A - Radiation heat, electric wave absorption and shield film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric wave absorbing layer on a graphite sheet having an excellent radiation heat characteristic and electromagnetic shield characteristic, thereby effectively suppressing both of heat and an electromagnetic noise generated from electronic components. <P>SOLUTION: There are provided a first layer composed of a graphite film having an anisotropy of a thermal conductivity in a face direction of a film and in a thickness direction of the film, and a second layer formed on the graphite film. The second layer contains a soft magnetic material, ferrite and carbon particles, thereby obtaining an electric wave absorption and a shield film having an excellent radiation heat characteristic. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a film having excellent heat dissipation (heat diffusion) characteristics and further having radio wave absorption and shielding effects.

In recent years, the performance of electronic devices such as personal computers, mobile phones, and PDAs has been remarkably improved due to significant performance improvements of CPU (MPUU). Along with such improvement in CPU performance, the amount of heat generated by the CPU and noise caused by the CPU increase, and how to dissipate heat and absorb electromagnetic waves in electronic devices is an important issue. In particular, due to an increase in the clock frequency of the semiconductor element, generation of high-frequency electromagnetic noise and an increase in the amount of heat generation occur at the same time, and both measures for heat dissipation inside the device and measures for noise are required. Therefore, there is a demand for a sheet capable of suppressing heat conduction and noise with a single sheet.

  As a countermeasure against heat, the method of radiating heat by spreading the heat generated by the CPU as quickly as possible is to increase the cooling efficiency, and is the most realistic cooling method for electronic devices such as mobile phones and personal computers. Is something.

  In recent years, sheet-like graphite has attracted much attention as a heat conductive sheet used for such purposes. The reason is that a high-quality graphite sheet has a very high thermal conductivity of 100 to 1200 W / mK, and the thermal conductivity (0.8 to 6.5 W / mk) of other gel-like or sheet-like heat dissipation materials. This is because it is extremely high performance in comparison with the characteristics of) and is optimal for diffusing heat.

  A representative method for producing such an artificial graphite film is a method called an expanded graphite method. This is produced by immersing natural graphite in a mixed solution of concentrated sulfuric acid and concentrated nitric acid and then rapidly heating it. The graphite produced in this manner is processed into a film by high pressure pressing after removing the acid by washing. While the thermal conductivity value of the graphite film produced in this manner is about 100 to 400 W / mK, the mechanical strength is weak, and the graphite powder has a problem of flaking off (expressed as powder falling), It is used as a heat conductive sheet because it is inexpensive and easy to manufacture thick materials.

In order to solve the above-mentioned problem of the expanded graphite method, a method of graphitizing a special polymer by direct heat treatment has been developed. Polymers used for this purpose include polyoxadiazole, polyimide, polyphenylene vinylene and the like. This method is essentially a method that does not contain impurities such as an acid, and further has a feature that a very excellent thermal conductivity in the plane direction (300 to 1200 W / mK) can be obtained. (For example, patent documents (1), (2), (3), (4), (5))
The graphite sheet itself has a conductivity similar to that of a metal, and has an excellent electromagnetic shielding effect as well as a thermal diffusion effect. Therefore, if it is installed close to an electromagnetic wave generation source, a heat dissipation effect and an electromagnetic shielding effect can be realized. However, although the graphite sheet has an electromagnetic shielding effect but does not have a radio wave absorption effect, the electromagnetic noise that is essentially generated cannot be eliminated. Therefore, there is a limit to the use of the graphite sheet for such purposes.

  In addition, the heat-dissipating graphite film has the disadvantages that it does not basically expand and contract and has no adhesiveness. For heat dissipation / heat diffusion applications, it is necessary to make sufficient contact between the heat source such as the CPU and the graphite film, which is the heat conductor, and it is also necessary to make sufficient contact with the cooling / heat dissipating member such as cooling fins and housings. Also occurs. Especially when the heat source or radiator has a rough surface, there are many cases where sufficient contact cannot be obtained. In such cases, the high thermal conductivity characteristics of the graphite film cannot be utilized. There was also a problem to say.

In order to solve such problems of the heat-dissipating graphite film, a composite of a graphite film and a polymer material having insulating properties and flexibility has been performed. Natural rubber and acrylic are the most common adhesives used as the adhesive layer for thermally conductive graphite films. Silicone rubber and polyimide adhesives with excellent heat resistance and adhesiveness may be used as required. . For example, a heat conductive sheet for electric parts (Patent Documents (6), (7), (8), (9)) characterized in that silicone rubber is applied to one or both surfaces of a graphite sheet, polyurethane or A heat-dissipating component (Patent Document (10)) that provides a polyurethane derivative primer layer to firmly bond graphite and the silicone composition (Patent Document (10)), and a graphite sheet and an adhesive layer with a thickness of 100 μm or less provided on the surface (Patent) An example of the document (11)) is disclosed.
JP 1-49642 JP 1-57044 JP-A-4-31069 JP-A-3-75211 JP 2000-247740 A Japanese Patent Publication No. 3-51302 JP-A-8-83990 JP-A-9-17923 JP 2001-287298 A JP-A-11-317480 JP 2002-160970

  An object of the present invention is to provide a sheet that realizes a good connection with a heat generation / noise source while taking advantage of the heat dissipation characteristics of a graphite film, and also has an excellent electromagnetic wave absorption capability.

  ADVANTAGE OF THE INVENTION According to this invention, the sheet | seat which has the outstanding electromagnetic wave absorption ability can be obtained, utilizing the heat conductivity characteristic which the graphite film originally has effectively. Furthermore, the electromagnetic wave absorption characteristics can be suppressed to a minimum, and a stable radio wave absorption capability can be exhibited. This makes it possible to obtain a sheet that is particularly effective for absorbing electromagnetic noise in the near field.

  The first of the present invention is a composite film comprising at least two layers, the first layer comprising a graphite film having anisotropy of thermal conductivity in the film surface direction and the film thickness direction, It is a heat radiation electromagnetic shielding film comprising a second layer formed on the graphite film, wherein the second layer contains soft magnetic particles.

  The second of the present invention is a composite film composed of at least two layers, the first layer comprising a graphite film having anisotropy of thermal conductivity in the film surface direction and the film thickness direction, It is a heat radiation electromagnetic shielding film comprising a second layer formed on the graphite film, wherein the second layer contains ferrite particles.

  The third of the present invention is a composite film comprising at least two layers, the first layer comprising a graphite film having a thermal conductivity anisotropy in the film surface direction and the film thickness direction, The heat radiation electromagnetic shielding film is characterized by comprising a second layer formed on the graphite film, wherein the second layer contains carbon particles.

  A fourth aspect of the present invention is characterized in that the thermal conductivity in the plane direction of the graphite film is 100 W / mK or more and is larger than the thermal conductivity in the thickness direction (1), (2), (3 ) Heat radiation electromagnetic shielding film as described.

  The fifth aspect of the present invention is to provide a heat radiation electromagnetic shielding film characterized in that the second layer described in (1), (2), (3) contains an adhesive or adhesive resin.

  A sixth aspect of the present invention is a heat radiation electromagnetic shielding film characterized in that the second layer described in (1), (2), (3) is a gel composition.

Each component of the present invention will be described.

<Graphite film>
Graphite has a structure in which carbon atoms are spread in layers, and has excellent thermal conductivity in the surface direction. With ideal graphite, the thermal conductivity in the plane direction reaches 2000 W / mK, which is five times that of copper, 398 W / mK. Further, the thermal conductivity of graphite has anisotropy, and the thermal conductivity in the thickness direction is about 1/400 in the plane direction. The graphite film used for the purpose of the present invention preferably has a thermal conductivity in the film surface direction of 100 W / mK or more and anisotropy with the thermal conductivity in the direction perpendicular to the film surface of 10 times or more. One of the objects of the present invention is heat diffusion, and it is extremely important for the present invention that the thermal conductivity in the surface direction is large. On the other hand, since the thermal conductivity in the thickness direction of the surface in the anisotropic heat conductive layer is small, it is preferable that the thickness in the thickness direction is as small as possible in the range in which sufficient heat diffusion is possible in the surface direction. In the case of using the graphite, the thickness of the anisotropic heat conductive layer is preferably 1 mm or less.

  As graphite that can be used practically for such purposes, (1) a graphite film obtained by sheeting graphite powder such as natural graphite or artificial graphite, and (2) obtained by heat-treating a polymer film. Name the graphite film.

  As the graphite film obtained by the production method (1), a film having a thermal conductivity in the film surface direction of 100 to 400 W / mK, a thermal conductivity in the thickness direction of 5 to 20 W / mK, and a thickness of 50 to 1000 μm is obtained. It is done. The most common method for producing such graphite powder is a method called an expanding method. In this method, a graphite intercalation compound is prepared by dipping in an acid such as graphite sulfuric acid, and thereafter, this is heat-treated and foamed to separate the graphite layers. After peeling, the graphite powder is washed to remove the acid to obtain a thin film graphite powder. The graphite powder obtained by this method is further subjected to rolling roll molding or press compression to obtain film-like graphite.

  On the other hand, in the method (2), a graphite film having a thermal conductivity in the film surface direction of 400 to 1200 W / mK, a thermal conductivity in the thickness direction of 5 to 20 W / mK, and a thickness of 10 to 100 μm is obtained. Any of these graphite films is preferably used for the purpose of the present invention. This graphite film is obtained by heat-treating a raw material film made of a polymer film and / or a carbonized polymer film at a temperature of 2400 ° C. or higher. Polymer films that can be used in the present invention include sasol (PBO), polybenzobisoxazal (PBBO), polythiazole (PT polyimide (PI), polyamide (PA), polyoxadiazole (POD), and polybenzox). , Polybenzothiazole (PBT), polybenzobisthiazole (PBBT), polyparaphenylene vinylene (PPV), polybenzimidazole (PBI), and polybenzobisimidazole (PBBI). In particular, polyimide (PI), polyoxadiazole (POD), and polyparaphenylene vinylene (PPV) are preferably used as a raw material for producing graphite for this purpose. What is necessary is just to manufacture these films with a well-known manufacturing method. Among them, the polyimide described below tends to be graphitized easily and becomes graphite having excellent thermal conductivity. Furthermore, since a graphite film in an expanded state can be obtained by controlling the carbonization / graphitization process, it is a particularly preferred raw material.

As graphite used for the purpose of the present invention, a polyimide film having an average linear expansion coefficient of 2.5 × 10 ⁻⁵ cm / cm / ° C. or less in the range of 100 to 200 ° C. is heat-treated at a temperature of 2400 ° C. or more. It is preferable to produce an expanded graphite film by realizing excellent thermal conductivity.

  In addition, it is preferable to use a graphite film by heat-treating a polyimide film having a birefringence of 0.13 or more at a temperature of 2400 ° C. or more in order to realize excellent thermal conductivity and produce an expanded graphite film.

Of course, a polyimide film having an average linear expansion coefficient in the range of 100 to 200 ° C. of 2.5 × 10 ⁻⁵ cm / cm / ° C. or less and a birefringence of 0.13 or more is obtained at a temperature of 2400 ° C. or more. It is preferable to produce a graphite film by heat treatment in order to realize excellent thermal conductivity and to produce an expanded graphite film.

  The graphite sheet has an excellent electromagnetic shielding effect as well as thermal conductivity. Its performance is comparable to copper foil of the same thickness, indicating that the graphite film is a nearly perfect electromagnetic wave reflector. However, the shield effect is simply an effect of blocking electromagnetic waves by reflection, and is not an effect of absorbing and extinguishing radio waves by converting them into heat.

<Radio wave absorption layer>
The second layer formed on the graphite film includes a soft magnetic material, ferrite, and carbon particles, and as a result, forms an electromagnetic wave absorption layer.

  The electromagnetic wave absorbing layer formed on the graphite includes at least one selected from ferrite, carbon, and soft magnetic metal, and is not particularly limited. When used for the purpose of absorbing near-field electromagnetic waves, an electromagnetic wave absorbing layer corresponding to the frequency to be absorbed may be formed.

  Ferrite materials exhibit an electromagnetic absorption action due to electromagnetic loss, and the effective wavelength region is in the KHz to MHz band. The performance is expressed by magnetic permeability. For example, high-μ materials such as Mn—Zn, Ba—Fe, and Ni—Zn ferrite are candidates.

  The carbon powder exhibits an electromagnetic absorption action due to dielectric loss, and the effective wavelength region is in the MHz to GHz band. When the carbon powder is used for electromagnetic absorption, the carbon powder exists independently in the matrix, and the absorption layer itself needs to be an insulator. The graphite sheet used in the present invention is, of course, a carbon material, but is a carbon continuum and has high conductivity, so that it has an electromagnetic shielding effect but no electromagnetic absorption effect. The properties of the filler are also affected by the shape of the filler, and favorable results are often obtained by making the filler powder into flakes or, in some cases, ultrafine powder.

  Soft magnetic metal exhibits an electromagnetic absorption effect due to conduction loss, and its effective band is the GHz band. Specific materials include Fe, Co, FeSi, Fe—Ni, FeCo, FeSiAl, FeCrSi, and FeBSiC.

  These electromagnetic wave absorbing materials are usually used as powders dispersed in a matrix resin. As the matrix, heat-resistant acrylic, chloroprene, silicone rubber, butadiene rubber, urethane rubber, acrylic rubber and other rubber materials, elastic epoxy, silicone resin, melamine foam, and the like are used. It is preferable for the purpose of the present invention that the matrix resin has adhesiveness or tackiness.

<Production of composite membrane>
In the present invention, a layer having the above-mentioned radio wave absorption capability is further provided on graphite having excellent electromagnetic shielding characteristics and heat dissipation characteristics to solve the problem of reducing near-field electromagnetic noise in electronic parts and the problem of heat. It is well known that near-field electromagnetic noise increases as the heat generated by electronic components such as CPUs increases. Since noise may increase due to heat generation or the nature of the noise may change, noise must be completely suppressed. Was difficult.

  However, the composite film of the present invention has an extremely excellent thermal diffusion characteristic of 50 W / mK to 600 W / mK, and this characteristic works extremely effectively for heat dissipation of electronic parts. Radio wave absorption / shield films that take heat conduction into account have already been developed and marketed, but these have improved heat dissipation characteristics by increasing the amount of filler, and their thermal diffusion characteristics are at most about 2 W / mK. Is insufficient. Since the composite film of the present invention has extremely excellent thermal diffusion, the radio wave absorption characteristics are stable.

  The electromagnetic absorption layer is formed on graphite having heat dissipation / electromagnetic shielding ability, but the formation method may be to apply a liquid electromagnetic absorbing paint, or may be bonded to an electromagnetic absorbing sheet. . The heat dissipation / electromagnetic absorption film of the present invention can be produced by laminating a film or sheet having an electromagnetic absorption capability with graphite through an adhesive layer, but in some cases, the thermal resistance increases through the adhesive layer. However, there may be a problem that the heat dissipation characteristics are impaired. Therefore, it is more preferable for the purpose of the present invention that the matrix resin layer has tackiness and adhesiveness, is in a gel form, and can form an electromagnetic absorption layer directly on the graphite layer.

Hereinafter, the present invention will be described more specifically with reference to examples.
<Graphite film>
First, the following four types of graphite films were used as examples of the present invention, but of course the present invention is not limited to these examples.

(1) Graphite film-A
Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and p-phenylenediamine were synthesized in a molar ratio of 4/3/1 to 100 g of a 18 wt% polyamic acid DMF solution from 20 g of acetic anhydride and 10 g of isoquinoline. The resulting curing agent was mixed, stirred, defoamed by centrifugation, and cast onto an aluminum foil. The process from stirring to defoaming was performed while cooling to 0 ° C. The laminate of the aluminum foil and the polyamic acid solution was heated at 120 ° C. for 150 seconds to obtain a gel film having self-supporting properties. This gel film was peeled off from the aluminum foil and fixed to the frame. This gel film was heated at 300 ° C., 400 ° C., and 500 ° C. for 30 seconds each to produce a polyimide film having an average linear expansion coefficient of 100 × 200 ° C. to 1.6 × 10 ⁻⁵ cm / cm / ° C. The film thickness is 75 μm. The birefringence of the film produced by these methods was 0.14.

  The obtained film was pretreated by raising the temperature in a nitrogen gas to 1200 ° C. using an electric furnace and keeping the temperature at 1200 ° C. for 1 hour. The obtained carbonized film was set inside a cylindrical graphite heater so that it could freely expand and contract, and treated at 2800 ° C.

  It was found that this polyimide film can be converted to high-quality graphite at 2800 ° C. The obtained graphite film-A is in a foamed state, the thickness in the foamed state is 80 μm, the thickness when compressed at 17 MPa and the pressure is released is 40 μm, and the thermal conductivity in the surface direction of the compressed film is 1200 W. The thermal conductivity in the thickness direction was 6 W / mK.

(2) Graphite film-B
Pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, and p-phenylenediamine were synthesized at a molar ratio of 3/2/1 to 100 g of a 18 wt% polyamic acid DMF solution from 20 g of acetic anhydride and 10 g of isoquinoline. The resulting curing agent was mixed, stirred, defoamed by centrifugation, and cast onto an aluminum foil. The process from stirring to defoaming was performed while cooling to 0 ° C. The laminate of the aluminum foil and the polyamic acid solution was heated at 120 ° C. for 150 seconds to obtain a gel film having self-supporting properties. This gel film was peeled off from the aluminum foil and fixed to the frame. This gel film was heated at 300 ° C., 400 ° C., and 500 ° C. for 30 seconds each to obtain a polyimide film (thickness 75 μm) having an average linear expansion coefficient of 100 × 200 ° C. to 1.0 × 10 ⁻⁵ cm / cm / ° C. Manufactured. The birefringence of this film was in the range of 0.15 to 0.16. Using this film, graphitization was performed at 2800 ° C. as in the case of (1). The obtained graphite film-B is in a foamed state, the film thickness in the foamed state is 75 μm, the film thickness after pressure compression is 45 μm, the thermal conductivity in the surface direction of the compressed film is 1400 W / mK, the thickness direction The thermal conductivity of was 5 W / mK.

(3) Graphite film-C
Panasonic (PGS graphite sheet, product number: EYGS182310) thickness 70 μm, surface direction thermal conductivity 700 W / mK, thickness direction 5 W / mK.

(4) Graphite film-D
Graphtec Corp. (eGRAF-HiTherm, product number 1205AP) thickness 130 μm, surface direction thermal conductivity 200 W / mK, thickness direction 7 W / mK.

<Electromagnetic wave absorbing layer>
As described above, the electromagnetic wave absorbing layer may be selected depending on the type of electromagnetic wave to be absorbed, and is not particularly limited. In the present invention, the following four types ((α) (β) (γ) (δ) The usefulness of the present invention was demonstrated using the electromagnetic wave absorbing layer forming material. Of course, the present invention is not limited to this embodiment.

(1) Electromagnetic wave absorber (α)
Application type electromagnetic wave absorbing material (EMISeal EM-330) manufactured by Aika Kogyo Co., Ltd. The filler is special composite hard magnetic particles and the binder resin is modified polyimide. Corresponding frequency is several tens of MHz to several GHz.

(2) Electromagnetic wave absorber (β)
An electromagnetic absorber (Ortas Doutite OLS-9014) manufactured by Nippon Radio Wave Absorber Co., Ltd. In the black liquid paint, soft magnetic metal and carbon are used as fillers, and the binder is urethane resin. Corresponding frequency is 1GHz ~ 3GHz.

(3) Electromagnetic wave absorber (γ)
Sea Isope AEM2.5G manufactured by Japan Radio Absorption Band Co., Ltd. Thickness 1mm. The purpose is to absorb frequencies of 2.5 GHz for carbonyl iron, ferrite and rubber.

(4) Electromagnetic wave absorber (δ)
FDK gel ferrite sheet (GE45B). Initial permeability 6μiac, thickness 0.5mm. Rubber strength 28
<Measurement of electromagnetic shielding characteristics of graphite film>
The electromagnetic shielding characteristics of the graphite sheet were measured. As a result, it was found that the shield performance was comparable to that of the copper foil having the same thickness, and showed excellent performance in a wide frequency range of 10 MHz to 50 GHz. Measurement is performed by transmitting and receiving electromagnetic waves between 10 MHz and 1 GHz using a spectrum analyzer (Advantest, Spectrum Analyzer R3361C), and measuring S21 (corresponding to the transmission coefficient) using Anritsu as an amplifier and Pre Amplifier MH648A. did. A region of 1 GHz or higher was measured by the lens method, and S21 and S11 (corresponding to the reflection coefficient) were measured.

  In a 75 μm thick graphite film (A), the shield effect S21 at 1 MHz is −45 MHz, S21 at 10 MHz is −65 dB, S21 at 100 MHz is −80 dB, S21 at 1 GHz is −80 dB, and S21 at 30 GHz. Is −80 dB, and S11 is almost zero. This indicates that the graphite film is an almost perfect electromagnetic wave reflector in the above frequency range.

<Method for measuring thermophysical properties of composite film>
The thermal diffusivity was measured at 10 Hz in an atmosphere of 20 ° C. using a thermal diffusivity measuring device by an optical alternating current method. The thermal conductivity was calculated from the measured thermal diffusivity using values of density and specific heat. The density of the graphite film was calculated by dividing the weight (g) of the graphite film by the volume (cm ³ ) calculated by the product of the vertical, horizontal and thickness of the graphite film. The thermal conductivity values of the four types of graphite films are those obtained by this method.

<Measurement of electromagnetic absorption characteristics of composite film>
The radio wave absorption characteristics of the composite film material were measured using the microstrip line method. An evaluation sample for characteristic evaluation is shown in FIG. The sample has a size of 100 × 20 mm, the distance between the SMA connector and the sample is 50 mm, and the impedance of the microstrip line is 50Ω. The S parameter (transmission attenuation (S21) and reflection attenuation (S11)) and characteristic impedance were measured for such a sample.

  Further, the measurement of the integrated suppression level in the near field was performed by a measurement method as schematically shown in FIG. 2 using a loop antenna. That is, two micro-loop antennas pulled out from a network analyzer via a coaxial cable were set apart from each other by a predetermined distance, and electromagnetic waves radiated from one antenna were received by one antenna. The measuring device is a device based on a near-field noise suppression sheet measuring device (fixture FS-21, loop antenna IT-IB-6B) manufactured by KEYCOM.

A graphite film-A cut to a size of 100 × 20 mm ² was prepared. An electromagnetic noise absorbing paint (α) was applied to one side of this graphite film so that the thickness after drying was about 100 μm, and a composite film was produced. Curing conditions were 80 ° C. for 30 minutes and then heat-treated at 150 ° C. for 30 minutes.

  The radio wave absorption characteristics of the obtained composite film were measured using a microstrip line method, and S parameters and characteristic impedance characteristics were measured. As a result, S21 decreased to -6 dB or less at both 2 GHz and 3 GHz. Compared to 2 GHz at -3 dB and 3 GHz at -5 GHz without a graphite film, it was found that the transmission attenuation characteristics were excellent, and the shield characteristics were excellent. Moreover, S11 did not change with and without the graphite film. Furthermore, the characteristic impedance was 48Ω, which was found to be hardly affected as compared with 50Ω in the case of the blank.

  The thermal diffusivity of the composite film was measured using the optical alternating current method. As a result, the thermal diffusivity of the composite film of Example 1 was 330 W / mK, and it was found that the composite film had excellent heat dissipation characteristics.

Furthermore, in order to estimate the heat dissipation characteristics of the obtained composite film (area 100 × 20 mm ² ), a ceramic heater (Sakaguchi Electric Heat Co., Ltd. micro ceramic heater, MS-3 (size 10 × 10 mm ² ) is placed in the center of the substrate. A constant electric power (16W) was applied, and the temperature rise of the heater was measured with a thermocouple (the measured value includes an error of about ± 2 to 3 ° C). The substrate has good heat conduction and excellent heat dissipation characteristics. The temperature of the ceramic heater does not rise as much, and the obtained result is 87 ° C., compared with 150 ° C. when the electromagnetic absorption layer (A) having the same thickness as the polyimide film and the graphite film is provided. And found that it has a very good heat dissipation effect.

  A similar experiment was performed using graphite films (B), (C), and (D) instead of graphite film (A). There was no difference in electromagnetic absorption and shielding characteristics, but there was a difference in heat conduction characteristics.

  Similarly, the thermal diffusivity of each composite film was measured using the optical alternating current method. As a result, the thermal diffusivity of graphite film (B) is 430 W / mK, the thermal diffusivity of graphite film (C) is 280 W / mK, and the thermal diffusivity of graphite film (D) is 100 W / mK. It has been found that it has heat dissipation characteristics.

  Further, the heat dissipation characteristics were measured in the same manner as in Example 1. The heater temperature in the state where each composite film was adhered was 80 ° C. in (B), 87 ° C. in (C), and 98 ° C. in (D). This indicates that any graphite film has excellent heat dissipation and shielding properties.

A graphite film-A cut to a size of 100 × 20 mm ² was prepared. An electromagnetic noise absorbing paint (β) was applied to one side of this graphite film so that the thickness after drying was about 100 μm, and a composite film was produced.

  The electromagnetic absorption characteristics of the obtained composite film were evaluated in the same manner as in Example 1. S21 was −6 dB or less at GHz and −6 dB or less even at 3 GHz. Compared with 2 GHz at −3 dB and 3 GHz at −4 GHz without a graphite film, it showed excellent transmission attenuation characteristics and was found to have excellent shielding characteristics. Moreover, S11 hardly changed with or without the graphite film. Furthermore, the characteristic impedance was 48Ω, which was found to be unaffected compared to 50Ω in the case of the blank.

  Furthermore, for the purpose of estimating the heat dissipation characteristics of the obtained composite film, the heat dissipation characteristics were measured by the same method as in Example 1. The better the heat dissipation characteristics, the more the temperature of the ceramic heater does not rise. The obtained result is 93 ° C., and the polyimide film having the same thickness as the graphite film has a very excellent heat dissipation effect compared to 150 ° C. when the electromagnetic absorption layer (β) having the same thickness is provided. I understood.

  The graphite film (A) and the electromagnetic wave absorbing material (γ) were bonded together with an acrylic adhesive of 10 μm, and the electromagnetic wave absorption characteristics were measured. The measurement method is the loop antenna method described in FIG. When the absorption characteristic at 2.5 GHz was measured, the maximum attenuation rate at the radio wave absorption center at 2.5 GHz was -40 dB. This is a characteristic equal to or greater than the value of -35 dB when the electromagnetic wave absorbing sheet is used alone.

  Furthermore, for the purpose of estimating the heat dissipation characteristics of the obtained composite film, the heat dissipation characteristics were measured by the same method as in Example 1. The better the heat dissipation characteristics, the more the temperature of the ceramic heater does not rise. The obtained result is 115 ° C., and it has a very good heat dissipation effect compared to 148 ° C. of the sample laminated with the same thickness of polyimide film as the graphite film and the electromagnetic absorption layer (β) of the same thickness. I understood.

  A gel-like electromagnetic wave absorbing material (δ) was attached to the graphite film (A) to prepare a composite film consisting of two layers. The thickness of the gel-like electromagnetic wave absorbing material (δ) is 1 mm. The integrated suppression level in the near field was measured using a loop antenna as shown in FIG. The result is shown in FIG. As a result, excellent attenuation characteristics of −2 dB or more were obtained in the range of 100 MHz to 1 GHz.

  The thermal conductivity of the gel electrolyte alone was 1.0 W / mK, but the thermal conductivity of the composite film with graphite is about 50 W / mK, and excellent heat dissipation and electromagnetic absorption characteristics can be realized. I understood.

  The usefulness of the present invention was proved by the above examples.

The conceptual diagram of the electromagnetic wave absorption characteristic measurement using a microstrip line. The conceptual diagram of the electromagnetic wave absorption characteristic measurement using a loop antenna. Measurement result of integrated suppression level in the near field

Explanation of symbols

11 Heat Dissipation / Electromagnetic Wave Absorption Composite Film 12 Microstrip Line 13 SMA Connector 21 Network Analyzer 22 Loop Antenna 23 Heat Dissipation / Electromagnetic Wave Absorption Composite Film

Claims (6)

A composite film composed of at least two layers, formed on the graphite film, a first layer comprising a graphite film having anisotropy of thermal conductivity in the film surface direction and the film thickness direction. An electromagnetic wave absorbing / shielding film excellent in heat dissipation characteristics, characterized in that it comprises a second layer and the second layer contains a soft magnetic material. A composite film composed of at least two layers, formed on the graphite film, a first layer comprising a graphite film having anisotropy of thermal conductivity in the film surface direction and the film thickness direction. An electromagnetic wave absorbing / shielding film with excellent heat dissipation characteristics, characterized by comprising a second layer and the second layer containing ferrite. A composite film composed of at least two layers, formed on the graphite film, a first layer comprising a graphite film having anisotropy of thermal conductivity in the film surface direction and the film thickness direction. An electromagnetic wave absorbing / shielding film excellent in heat dissipation characteristics, characterized in that it comprises a second layer and the second layer contains carbon particles. The radio wave absorption / excellence in heat dissipation characteristics according to claim 1, 2, or 3, wherein the thermal conductivity in the surface direction of the graphite film is 100 W / mK or more and is larger than the thermal conductivity in the thickness direction. Shield film. An electromagnetic wave absorbing / shielding film excellent in heat dissipation characteristics, wherein the second layer according to claim 1, 2 or 3 contains an adhesive or tacky resin. A radio wave absorption / shield film excellent in heat radiation characteristics, wherein the second layer according to claim 1, 2 or 3 is a gel composition.

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