JP2006135118A - Electromagnetic wave absorbing heat radiation sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorbing heat radiation sheet which has an electromagnetic absorbing property effective especially for a small-size electronic apparatus such as PDA and mobile phone which do not have enough space inside, and for an electronic apparatus including a heating element set in an closed space and also has a heat radiation property by far-infrared radiation. <P>SOLUTION: The electromagnetic wave absorbing heat radiation sheet comprises an electromagnetic wave absorption layer having a thermal conductivity of 0.7 W/mK or above and a far-infrared radiation layer formed on one face of the electromagnetic wave absorption layer either directly or via at least one different layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention has an electromagnetic wave absorbing layer and a far infrared radiation layer, and suppresses radiation of electromagnetic noise to the outside, and efficiently absorbs heat from the heating element to the outside by far infrared radiation. Related to heat-radiating sheet.

  In recent years, high density and high integration of electronic components such as CPUs and LSIs arranged inside personal computers, PDAs, mobile phones, etc., and high density of electronic components on printed circuit boards due to miniaturization of electronic devices. As mounting progresses, problems of radiation of electromagnetic noise generated from the electronic components to the outside and problems of internal electromagnetic interference have occurred.

  Conventionally, when these electromagnetic wave noise countermeasures are taken, expertise and experience of noise countermeasures are required, and the countermeasures require a lot of time. Furthermore, a mounting space for parts necessary for the countermeasure must be secured in advance in the electronic device. In order to solve these problems, an electromagnetic wave absorbing sheet is used.

  At the same time, the amount of heat generated increases with the increase in density and integration of electronic components such as CPUs and LSIs, and if the cooling is not performed efficiently, electronic devices that mount these electronic components will malfunction due to thermal runaway. There is also a problem. Conventionally, silicone grease or silicone rubber filled with a heat conductive filler has been installed between a CPU, LSI, etc. and a heat sink made of aluminum, copper or an alloy thereof as a means for efficiently releasing heat generation to the outside. There has been a method in which the contact thermal resistance is reduced, guided to the heat sink by heat conduction, and radiated from the heat sink into the air. In this method, heat transfer between the heat sink and the air is the main heat dissipation, so a large heat sink is required to increase the heat dissipation efficiency, and a fan must be provided to create the air flow. . Therefore, it has been difficult to adopt a heat dissipation structure using a heat sink in small devices such as PDAs and mobile phones and electronic devices in which heating elements are set in a sealed space.

  In such a case, a heat dissipation structure using radiant heat transfer has been attracting attention, and its practical use has begun. Patent Document 1 discloses that an electromagnetic wave is shielded and an electronic device is radiated with a heat radiating plate composed of a heat radiating layer made of a ceramic material that radiates far infrared rays and a conductive layer. Also, in Patent Document 2, a flexible heat-radiating film having an infrared radiation effect is provided on one surface of a heat-absorbing flexible heat-absorbing layer, and a heat-conductive adhesive is provided on the other surface. A heat dissipation method using a heat dissipation sheet provided with layers is shown.

However, since these heat radiating plates and heat radiating sheets cannot solve the problem of electromagnetic noise, it is necessary to consider countermeasures using an electromagnetic wave absorbing sheet and a noise suppression circuit. Therefore, electromagnetic wave noise suppression measures become complicated, and in the case of small devices, sufficient measures may not be taken due to space problems.
Japanese Patent Laid-Open No. 10-116944 JP 2004-200199 A

  The present invention has been made in view of such conventional problems, and in particular, electromagnetic wave absorption performance that works effectively when there is not enough space inside the electronic device or when the heating element is set in a sealed space. It aims at providing the electromagnetic wave absorptive thermal radiation sheet | seat which has the heat dissipation function by far infrared radiation.

  As a result of intensive studies to achieve the above object, the present inventors have laminated an electromagnetic wave absorbing layer having a thermal conductivity of 0.7 W / mK or more and a far infrared emitting layer, so that the electromagnetic wave absorbing performance and the far infrared ray are laminated. It has been found that an electromagnetic wave absorbing heat radiation sheet having a heat radiation function by radiation can be obtained.

That is, the present invention
An electromagnetic wave absorbing heat comprising an electromagnetic wave absorbing layer having a thermal conductivity of 0.7 W / mK or more, and a far infrared radiation layer provided directly on one side of the electromagnetic wave absorbing layer or via at least one other layer. Provide a radiation sheet.

  The electromagnetic wave absorptive heat radiation sheet of the present invention is a sheet having both electromagnetic wave absorption performance and a heat radiation function by infrared radiation. In particular, since the heat conductivity of the electromagnetic wave absorption layer is 0.7 W / mK or more, the heat from the heating element can be efficiently transferred to the far-infrared radiation layer through the electromagnetic wave absorption layer. Therefore, when there is a problem of electromagnetic noise, and there is not enough space inside the device and a large heat sink cannot be installed, or when the heating element is set in a sealed space and cooling with air is not possible, The problem of electromagnetic noise and the problem of heat generation can be solved simultaneously.

  When using conventional electromagnetic wave absorbing sheet, electromagnetic wave absorbing heat conductive sheet, far infrared radiation sheet to take countermeasures against electromagnetic noise and heat, prepare each sheet separately and install it as necessary. It was necessary to do. Therefore, the mounting process takes time, and the process cost is increased. In addition, it may be necessary to attach a plurality of sheets to different places, which is a problem in terms of space particularly in a small device. On the other hand, the use of the electromagnetic wave absorbing heat radiation sheet of the present invention can simultaneously solve the problem of electromagnetic noise and the problem of heat generation with a single sheet, thereby simplifying the mounting process. And cost reduction is possible. In addition, the problem of space can be solved, and the above measures can be taken even with a small device.

  Hereinafter, the present invention will be described in more detail.

[Electromagnetic wave absorbing thermal radiation sheet]
The electromagnetic wave absorbing thermal radiation sheet of the present invention includes an electromagnetic wave absorbing layer having a thermal conductivity of 0.7 W / mK or more, and far-infrared radiation provided on one side of the electromagnetic wave absorbing layer directly or via at least one other layer. And having a layer. Here, “at least one other layer” includes, for example, a conductive layer, a reinforcing layer of mechanical strength of the sheet, and the like depending on the purpose. These layers may be used alone or in combination of two or more.

  An example of a state in which the electromagnetic wave absorbing heat radiation sheet of the present invention is mounted on a heat generating / electromagnetic noise emitting element is shown in FIG. In FIG. 1, an electromagnetic wave absorbing thermal radiation sheet 1 is composed of a far infrared radiation layer 2 and an electromagnetic wave absorbing layer 3 laminated thereunder, and the lower surface of the electromagnetic wave absorbing layer 3 is a heat generating / electromagnetic noise emitting element 10. Mounted on top of. The electromagnetic wave noise radiated from the element 10 is absorbed by the electromagnetic wave absorption layer 3, and the problem of electromagnetic interference inside the device and the problem of electromagnetic wave noise radiation to the outside can be solved. At the same time, the heat generated from the element 10 is transmitted to the far-infrared radiation layer 2 through the electromagnetic wave absorption layer 3 by heat conduction, and is emitted from the far-infrared radiation layer 2 as radiant heat. At this time, the electromagnetic wave absorbing layer 3 functions as a heat conductive layer.

[Electromagnetic wave absorption layer]
The electromagnetic wave absorbing layer of the electromagnetic wave absorbing heat radiation sheet of the present invention is not particularly limited as long as its thermal conductivity is usually 0.7 W / mK or more, preferably 2 W / mK or more. When the thermal conductivity is less than 0.7 W / mK, the heat generated from the heat-generating / electromagnetic wave noise radiation element is difficult to be transmitted to the far-infrared radiation layer, and the heat radiation effect of the electromagnetic wave absorptive heat radiation sheet of the present invention is sufficient. Disappear.

  The electromagnetic wave absorbing layer is preferably a layer comprising soft magnetic metal powder and an insulating polymer. The soft magnetic metal powder is preferably uniformly dispersed in the insulating polymer.

  The presence or absence of electromagnetic wave absorption performance can be evaluated, for example, as follows. First, the amount of electromagnetic waves radiated from the microprocessor is measured according to the 3m method of the US Federal Communications Commission (FCC) when the evaluation object (sheet or layer) is attached to the microprocessor and when it is not attached. . Next, the difference between the two measured values is calculated to determine the amount of radiated electromagnetic wave change. As a result, it is desirable that the amount of electromagnetic waves radiated when the evaluation object is attached is reduced by 2 dB or more, preferably 3 dB or more, compared to the electromagnetic wave radiated when the evaluation object is not attached.

<Soft magnetic metal powder>
Recently, the signal processing speed of electronic devices such as personal computers has been greatly increased, and the operating frequency of each element has increased from several hundred MHz to several GHz. Therefore, the frequency of electromagnetic noise generated inside electronic devices is increasing in the GHz band.

  In order to suppress these electromagnetic noises, plate-like bodies obtained by firing powders of spinel cubic ferrite such as manganese zinc ferrite and nickel zinc ferrite, and these powders are dispersed uniformly in the polymer. The obtained sheet may be applied. However, the electromagnetic wave absorption performance of such a ferrite plate or ferrite sheet is high mainly for electromagnetic waves in the MHz band, but low for electromagnetic waves in the GHz band.

  On the other hand, since soft magnetic metal powder has high electromagnetic wave absorption performance for electromagnetic waves from MHz band to GHz band, in recent electronic devices, in order to suppress electromagnetic noise, electromagnetic wave absorption including soft magnetic metal powder is required. The layer is particularly effective. The soft magnetic metal powder is also suitable for the present invention in that it has a higher thermal conductivity than ferrite.

  As the soft magnetic metal powder, it is preferable to use a powder containing 15% by mass or more of iron element from the viewpoint of supply stability, cost, and the like. For example, carbonyl iron, electrolytic iron, Fe—Cr alloy, Fe—Si alloy, Fe—Ni alloy, Fe—Al alloy, Fe—Co alloy, Fe—Al—Si alloy, Fe—Cr— Although metal powders, such as Si type alloy, Fe-Cr-Al type alloy, Fe-Si-Ni type alloy, and Fe-Si-Cr-Ni type alloy, are mentioned, it is not limited to these. These soft magnetic metal powders may be used alone or in combination of two or more.

  Examples of the shape of the soft magnetic metal powder include a flat shape and a spherical shape. The soft magnetic metal powder may include only particles having the same shape, or may include particles having different shapes.

  The average particle size of the soft magnetic metal powder is preferably 0.1 to 100 μm, and particularly preferably 1 to 50 μm. If the average particle diameter is within this range, the soft magnetic metal powder can be easily filled because the specific surface area is kept at an appropriate size, and the electromagnetic wave absorbing performance of the electromagnetic wave absorbing layer is sufficiently exhibited. The

  The content of the soft magnetic metal powder in the electromagnetic wave absorbing layer is preferably 10 to 80% by volume, particularly preferably 15 to 70% by volume, based on the total amount of the electromagnetic wave absorbing layer. If the content is within this range, sufficient electromagnetic wave absorbing performance can be obtained, and the electromagnetic wave absorbing layer can be prevented from becoming brittle.

<Polymer>
The insulating polymer of the electromagnetic wave absorbing layer is a layer in which the matrix constitutes a matrix, in which soft magnetic metal powder, a heat conductive filler, etc. are dispersed. For example, silicone, acrylic rubber, ethylene propylene rubber , Fluororubber, chlorinated polyethylene and the like can be mentioned, and can be appropriately selected according to the intended use. These polymers may be used individually by 1 type, and may be used in combination of 2 or more type.

<Thermal conductive filler>
By increasing the thermal conductivity of the electromagnetic wave absorbing layer, heat can be efficiently transferred from the heat generating / electromagnetic noise emitting element to the far infrared emitting layer, and the heat radiation effect of the electromagnetic wave absorbing thermal radiation sheet of the present invention is enhanced. Therefore, the electromagnetic wave absorbing layer may preferably contain a heat conductive filler.

  Examples of the thermally conductive filler include metal powders such as aluminum and copper; metal oxide powders such as aluminum oxide and silicon oxide; metal nitride powders such as silicon nitride, boron nitride and aluminum nitride. However, it is not limited to these. These heat conductive fillers may be used alone or in combination of two or more.

  The average particle size of the thermally conductive filler is preferably 0.1 to 100 μm, and particularly preferably 1 to 50 μm. If the average particle diameter is within this range, the heat conductive filler can be easily filled because the specific surface area is kept at an appropriate size, and the heat conductivity of the electromagnetic wave absorbing layer can be kept high. Furthermore, the electromagnetic wave absorbing layer can be prevented from becoming brittle.

The content of the heat conductive filler in the electromagnetic wave absorption layer is preferably relative to the total amount of the electromagnetic wave absorption layer in consideration of the balance with the content of the soft magnetic metal powder so that the electromagnetic wave absorption layer can obtain a predetermined electromagnetic wave absorption performance. Is 60% by volume or less, particularly preferably 40% by volume or less. If the content is within this range, the content of the soft magnetic metal powder can be relatively maintained, and sufficient electromagnetic wave absorbing performance can be maintained.
<Mixing of soft magnetic metal powder and / or thermally conductive filler and polymer>

  The mixing of the soft magnetic metal powder and / or the heat conductive filler and the polymer can be performed by a mixer such as a homomixer, a kneader, a two-roll mill, or a planetary mixer until they are uniformly dispersed. The invention is not particularly limited to this. At this time, if necessary, an appropriate amount of a powder surface treatment agent such as a silane coupling agent, a flame retardant, a crosslinking agent, a control agent, and a crosslinking accelerator may be appropriately blended.

<Adhesiveness>
As shown in FIG. 1, the electromagnetic wave absorptive heat radiation sheet of the present invention has an electromagnetic wave absorption layer disposed on the side close to the heat generating / electromagnetic wave noise radiation element, and the far infrared radiation layer sandwiches the electromagnetic wave absorption layer and the element. Are mounted to the element so that they are arranged on the opposite side. In this case, a mechanical mechanism may be provided so that the electromagnetic wave absorbing heat radiation sheet of the present invention is pressed against the element, but the electromagnetic wave absorbing layer itself is not adhesive in a place where there is little space, such as inside a small device. As described above, it is preferable to adhere and fix the electromagnetic wave absorbing heat radiation sheet of the present invention to the element from the viewpoints of space saving, cost reduction, and workability.

  Examples of the method for making the electromagnetic wave absorbing layer tacky include, but are not limited to, a method using an acrylic pressure-sensitive adhesive or a silicone pressure-sensitive adhesive as a polymer, and a method of mixing these pressure-sensitive adhesives with a polymer. It is not something.

[Far infrared radiation layer]
Although the far-infrared radiation layer of the electromagnetic wave absorptive heat radiation sheet of the present invention is not particularly limited as long as it has a heat radiation function by far-infrared radiation, it is preferably a layer comprising a far-infrared radiation oxide ceramic. Examples of the far-infrared emitting oxide ceramics include silicon oxide, aluminum oxide, cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ), and the like.

  Examples of the method for producing the far-infrared radiation layer include, but are not limited to, the following methods. The far-infrared radiation layer is manufactured by applying an organic solvent solution in which a powder containing far-infrared radiation oxide ceramics and a binder such as silicone resin are mixed to a predetermined substrate and curing to form a layer. be able to. The far-infrared radiation layer can also be produced by baking a powder containing far-infrared radiation oxide ceramics into a plate shape. In addition, an appropriate amount of a powder surface treatment agent such as a silane coupling agent, a flame retardant, a cross-linking agent, a control agent, a cross-linking accelerator and the like may be appropriately added to the far-infrared emitting layer as necessary.

  The presence / absence of a heat radiation function by far-infrared radiation can be evaluated, for example, as follows. First, an evaluation object (sheet or layer) is mounted on a microprocessor in a sealed casing, and a thermocouple having a diameter of 50 μm is sandwiched between the microprocessor and the evaluation object. Next, the microprocessor is operated, and the temperature after 30 minutes when the microprocessor is in a steady state is measured. On the other hand, the surface temperature of the microprocessor is measured in the same manner except that the evaluation target is not attached to the microprocessor. As a result, it is desirable that the temperature when the evaluation target is mounted is 10 ° C. or more, preferably 20 ° C. or more lower than the temperature when the evaluation target is not mounted.

[Conductive layer]
In the electromagnetic wave absorptive heat radiation sheet of the present invention, a conductive layer can be laminated between the electromagnetic wave absorption layer and the far infrared ray radiation layer as necessary. Depending on the nature of the electromagnetic wave noise radiating element and its arrangement inside the device, electromagnetic wave noise may be more effectively suppressed by providing a conductive layer, that is, an electromagnetic wave shielding layer, laminated with the electromagnetic wave absorbing layer. . The conductive layer has a volume resistivity of 1 × 10 ⁻² Ω · m or less, preferably 1 × 10 ⁻⁴ Ω · m or less.

  Further, the conductive layer preferably has a large thermal conductivity, for example, a thermal conductivity of 0.5 W / mK or more, so as not to prevent heat transfer from the electromagnetic wave absorbing layer to the far infrared radiation layer, More preferably, it has a thermal conductivity of mK or more.

  Examples of the conductive layer include foils, plates and meshes of metals such as aluminum and copper or alloys thereof, graphite sheets, and conductive rubber sheets.

[Adhesive layer]
In order to fix the electromagnetic wave absorptive heat radiation sheet of the present invention to an exothermic and electromagnetic noise radiation element, in addition to making the electromagnetic wave absorbing layer adhesive as described above, an adhesive layer may be separately provided. In the electromagnetic wave absorptive heat radiation sheet of the present invention, the far infrared radiation layer is provided directly on one side of the electromagnetic wave absorption layer or via at least one other layer, but the adhesive layer is on one side opposite to the one side. It is preferable to provide it. In places where there is little space, such as inside small devices, it is also possible to save space, reduce costs, and work by separately providing an adhesive layer in this way and bonding and fixing the electromagnetic wave absorbing heat radiation sheet of the present invention to the element. From the viewpoint of sex.

  As the adhesive layer, a layer containing a known adhesive can be used. Examples of such pressure-sensitive adhesives include acrylic pressure-sensitive adhesives and silicone pressure-sensitive adhesives, but are not particularly limited thereto.

  Since the thermal conductivity of normal adhesive is about 0.1 to 0.2 W / mK, in order to transfer heat from the heating element to the electromagnetic wave absorbing layer more efficiently, the adhesive layer is filled with a heat conductive filler. By doing so, the thermal conductivity of the adhesive layer is preferably 0.5 W / mK or more, and more preferably 1 W / mK or more. If the thermal conductivity is within this range, the heat generated from the heating element is more efficiently transmitted to the far infrared radiation layer, and the heat radiation effect of the electromagnetic wave absorbing thermal radiation sheet of the present invention is further enhanced.

  Examples of the heat conductive filler in the adhesive layer include metal powders such as aluminum and copper; metal oxide powders such as aluminum oxide and silicon oxide; metal nitride powders such as silicon nitride, boron nitride and aluminum nitride However, it is not limited to these. These heat conductive fillers may be used alone or in combination of two or more.

  The average particle size of the thermally conductive filler is preferably 0.1 to 100 μm, and particularly preferably 1 to 50 μm. If the average particle diameter is in this range, the heat conductive filler can be easily filled with a high specific surface area because the specific surface area is maintained at an appropriate size, and the adhesive layer has a smooth surface. Therefore, sufficient adhesive strength can be maintained, and the electromagnetic wave absorptive heat radiation sheet of the present invention can be reliably fixed on the exothermic and electromagnetic noise radiation element.

  The content of the heat conductive powder in the adhesive layer is preferably 70% by volume or less, particularly preferably 50% by volume or less, based on the total amount of the adhesive layer. When the content is within this range, the adhesive layer retains sufficient adhesive strength, and the electromagnetic wave absorbing heat radiation sheet of the present invention can be reliably fixed on the heat generating / electromagnetic noise emitting element.

[Production method]
As a method for laminating the far-infrared radiation layer and the electromagnetic wave absorption layer, for example, (1) the electromagnetic wave absorption layer is previously molded by coating molding or press molding, and directly on the far infrared radiation material powder (for example, A method of laminating a solution obtained by mixing a far-infrared radiation oxide ceramic) and a binder such as a silicone resin in an organic solvent, or (2) a far-infrared radiation material powder and silicone. Far-infrared radiation obtained by curing a solution obtained by mixing a binder such as a resin in an organic solvent on a glass cloth, or a foil, plate, or mesh of a metal such as aluminum or copper or an alloy thereof. There are methods such as laminating an electromagnetic wave absorbing layer on a layer or a fired plate of a far-infrared radioactive material powder by coating molding, press molding, etc., especially these methods The present invention is not limited. Moreover, in order to strengthen the adhesion between the two layers, the bonding surface of each layer before lamination may be subjected to a primer treatment.

  As a method of creating a three-layer structure in which a far-infrared radiation layer, a conductive layer, and an electromagnetic wave absorption layer are laminated, a solution obtained by mixing a far-infrared radiation material powder and a binder such as silicone resin in an organic solvent is used. The far-infrared radiation layer is laminated after being applied and cured on a conductive layer (for example, a foil, plate, mesh, etc. of a metal such as aluminum or copper or an alloy thereof, cured, etc.) Includes a method of laminating an electromagnetic wave absorbing layer on one side of the conductive layer on the opposite side by coating molding, press molding, or the like, but is not particularly limited to these methods.

  As a method for producing a four-layer structure in which a far-infrared radiation layer, a conductive layer, an electromagnetic wave absorption layer, and an adhesion layer are laminated, or a three-layer structure in which a far-infrared radiation layer, an electromagnetic wave absorption layer, and an adhesion layer are laminated, Although the method of laminating | stacking an adhesion layer directly by coating molding, press molding, etc. on the electromagnetic wave absorption layer created by the method is mentioned, It does not specifically limit to these methods.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not limited to these Examples.

[Example 1]
As materials for coating the far infrared radiation layer, 200 parts by mass of silicone varnish KR271 (trade name, Shin-Etsu Chemical Co., Ltd.), 60 parts by mass of crystalline silica powder (average particle size: 1 μm), alumina powder (average) (Particle size: 4 μm) A mixture comprising 100 parts by mass and 40 parts by mass of toluene was prepared. This coating material was spray-coated on one side of an aluminum foil having a thickness of 50 μm used as a conductive layer so that the far-infrared radiation layer had a thickness of 80 μm and air-dried at room temperature. Thereafter, the coating material was cured by drying the sample at 80 ° C. for 10 minutes in a warm air dryer, and an aluminum foil on which a far infrared radiation layer was laminated was produced.

  Next, an organic peroxide curable silicone composition (KE520u (trade name, Shin-Etsu Chemical Co., Ltd.)) and an organic peroxide vulcanizing agent C were prepared to prepare a material for coating the electromagnetic wave absorbing layer. -24 (trade name, kneaded product with Shin-Etsu Chemical Co., Ltd. (mass ratio 100 / 1.5)), flat Fe-Si-Cr-Ni alloy powder (composition: Fe80 mass) %, Si 15% by mass, Cr 3% by mass, Ni 2% by mass; average particle size: 20 μm) were mixed to obtain a mixture. 100 parts by mass of this mixture was dissolved in 100 parts by mass of toluene to prepare a coating material for preparing an electromagnetic wave absorption layer. This coating material was bar-coated on one side opposite to the one side of the aluminum foil on which the far-infrared radiation layer was laminated, so that the thickness of the electromagnetic wave absorbing layer was 0.1 mm, and air-dried at room temperature. After that, this sample was dried at 60 ° C. for 10 minutes with a hot air dryer, and finally crosslinked and cured by heating at 150 ° C. for 10 minutes to obtain a far-infrared radiation layer, an aluminum foil, and an electromagnetic wave absorption layer. A three-layer laminate was produced. In addition, content of the Fe-Si-Cr-Ni type alloy powder in this electromagnetic wave absorption layer was 37 volume% with respect to the electromagnetic wave absorption layer whole quantity.

  Furthermore, silicone adhesives (KR101-10 (trade name, Shin-Etsu Chemical Co., Ltd.) and Nyper BMT-K40 (trade name, Nippon Oil & Fats Co., Ltd.) A mixture of 170 parts by mass (mass ratio 97/3)), 300 parts by mass of alumina powder (average particle size: 4 μm), and 80 parts by mass of toluene was prepared. This coating material was bar-coated on the electromagnetic wave absorbing layer in the three-layer laminate so that the thickness of the heat conductive adhesive layer was 30 μm, and air-dried at room temperature. Then, the electromagnetic wave absorbing heat according to the present invention is formed as a four-layer structure in which a far infrared radiation layer, an aluminum foil, an electromagnetic wave absorbing layer, and a heat conductive adhesive layer are laminated by heating at 150 ° C. for 5 minutes. A radiation sheet was obtained. The content of alumina powder in this heat conductive adhesive layer was 43% by volume with respect to the total amount of the heat conductive adhesive layer.

[Example 2]
In order to prepare a material for coating and molding the electromagnetic wave absorbing layer, instead of the mixture of Example 1, spherical Fe—Cr— was used with respect to 100 parts by mass of the organic peroxide-curable silicone composition having the same composition. Si-based alloy powder (composition: Fe 85% by mass, Cr 12% by mass, Si 3% by mass; average particle size: 9 μm) 1200 parts by mass and alumina powder (average particle size: 1 μm) 300 parts by mass were kneaded to obtain a mixture. Example 1 except that 100 parts by mass of this mixture was dissolved in 40 parts by mass of toluene to prepare a coating material for preparing an electromagnetic wave absorbing layer, and that the thickness of the electromagnetic wave absorbing layer was 0.2 mm. In the same manner as above, an electromagnetic wave absorbing heat radiation sheet according to the present invention was obtained as a four-layer structure in which a far infrared radiation layer, an aluminum foil, an electromagnetic wave absorption layer, and a heat conductive adhesive layer were laminated. In addition, content of the Fe-Cr-Si type alloy powder in this electromagnetic wave absorption layer was 46 volume% with respect to the electromagnetic wave absorption layer whole quantity.

[Example 3]
In order to prepare a material for coating the electromagnetic wave absorbing layer, an organic peroxide curable silicone composition (KE520u (supra) and an organic peroxide vulcanizing agent C-8 (trade name, Shin-Etsu Chemical Co., Ltd.) Co.)) and 100% by mass of the kneaded product (mass ratio 100 / 1.5)) with a flat Fe-Si-Cr-Ni alloy powder (composition: Fe 80 mass%, Si 15 mass%, Cr 3 mass%, A mixture was obtained by kneading 400 parts by mass of Ni 2 mass%; average particle size: 20 μm). This mixture was dispensed with a two-roll mill to a thickness slightly thicker than 0.5 mm, and then press-molded at 170 ° C. for 10 minutes to produce an electromagnetic wave absorbing layer having a thickness of 0.5 mm. In addition, content of the Fe-Si-Cr-Ni type alloy powder in this electromagnetic wave absorption layer was 37 volume% with respect to the electromagnetic wave absorption layer whole quantity.

  The same coating material for preparing the far infrared radiation layer as that prepared in Example 1 was spray-coated on one surface of the electromagnetic wave absorption layer so that the thickness of the far infrared radiation layer was 80 μm and air-dried at room temperature. . Then, this coating material was hardened by drying this sample for 10 minutes at 80 degreeC in a warm air dryer, and produced the two-layered laminate of a far-infrared radiation layer and an electromagnetic wave absorption layer.

  Further, the same heat conductive adhesive layer as that prepared in Example 1 was formed in the same manner as in Example 1 on the side opposite to the one side of the electromagnetic wave absorbing layer on which the far infrared radiation layer was laminated, with a thickness of 30 μm. Thus, an electromagnetic wave absorbing thermal radiation sheet according to the present invention was obtained as a three-layer structure in which a far infrared radiation layer, an electromagnetic wave absorption layer, and a heat conductive adhesive were laminated.

[Comparative Example 1]
A sheet having a three-layer structure in which a far-infrared radiation layer, an aluminum foil, and a heat conductive adhesive were laminated was obtained in the same manner as in Example 1 except that the electromagnetic wave absorbing layer was not laminated.

[Comparative Example 2]
A sheet having a two-layer structure in which an electromagnetic wave absorbing layer and a heat conductive adhesive were laminated was obtained in the same manner as in Example 3 except that the far infrared radiation layer was not laminated.

[Comparative Example 3]
The far-infrared radiation layer, the electromagnetic wave absorption layer, and the heat conduction are the same as in Example 3 except that the amount of the flat Fe-Si-Cr-Ni alloy powder is 200 parts by mass instead of 400 parts by mass. A sheet having a three-layer structure laminated with a pressure-sensitive adhesive was obtained.

[Measurement]
The thermal conductivity of the electromagnetic wave absorbing layer and the adhesive layer in the sheets obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the heat dissipation performance of the entire sheet, and the radiated electromagnetic wave variation as the electromagnetic wave absorption characteristics are as follows. The results are shown in Table 1.

"Thermal conductivity"
The thermal conductivity was measured based on ASTM E 1530.

<Heat dissipation performance>
FIG. 2 is a longitudinal sectional view showing an apparatus for measuring the heat dissipation performance of the evaluated sheet. As shown in FIG. 2, a microprocessor 22 fixed on a printed wiring board 21 was set in a sealed casing 13 composed of an aluminum alloy lid 11 and an insulating plastic container 12. The microprocessor 22 operates at a frequency of 1 GHz. Further, an evaluation sheet 31 was installed on the upper surface of the microprocessor 22. A far-infrared absorbing layer 41 is coated on the inner surface of the aluminum alloy lid 11 facing the evaluation sheet 31. A thermocouple having a diameter of 50 μm was sandwiched between the microprocessor 22 and the sheet to be evaluated 31, and the microprocessor 22 was operated to measure the temperature 30 minutes after the substantially steady state was reached. For comparison, the surface temperature of the microprocessor 22 without the evaluation sheet 31 was also measured.

<Change in radiated electromagnetic wave>
FIG. 3 is an explanatory diagram showing an apparatus for measuring the amount of change in radiated electromagnetic wave of the sheet to be evaluated and its operation. First, a device similar to that shown in FIG. 2 was installed in the anechoic chamber 51, and a receiving antenna 52 was installed at a position 3 m away from it. That is, this is a method that matches the FCC-compliant 3m method. The antenna 52 was connected to the EMI receiver 54 (spectrum analyzer) in the shield room 53. Next, the microprocessor 22 was operated, and the generated electromagnetic wave noise with a frequency of 1 GHz was measured by the EMI receiver 54 via the receiving antenna 52. The difference between the measured value of electromagnetic noise when the evaluated sheet was installed and the measured value of electromagnetic noise when the evaluated sheet was not installed was defined as the amount of radiated electromagnetic wave change. The negative radiated electromagnetic wave change amount represents that the evaluated sheet 31 installed on the microprocessor 22 attenuated electromagnetic wave noise, and the positive radiated electromagnetic wave change amount was that the evaluated sheet 31 increased electromagnetic wave noise. Represents that.

[Evaluation]
As shown in Table 1, it can be seen that the sheets of Examples 1 to 3 which are the electromagnetic wave absorbing thermal radiation sheet of the present invention attenuated electromagnetic wave noise by 2 dB or more in the measurement of the radiated electromagnetic wave variation. Therefore, it is recognized that the sheet has a sufficiently high electromagnetic wave absorption performance. In the sheet, since the electromagnetic wave absorption layer has a high thermal conductivity of 0.7 W / mK or more, heat generated from the microprocessor can be efficiently transmitted to the far-infrared radiation layer. Therefore, it turns out that the heat dissipation performance as the whole sheet | seat which has an electromagnetic wave absorption layer is also high.

  Comparing Examples 1 and 2 with Comparative Example 1, it can be seen that the conventional heat radiation sheet (Comparative Example 1) in which the electromagnetic wave absorbing layer is not laminated has no electromagnetic wave absorbing performance. Rather, electromagnetic wave noise is increased due to the influence of the conductive layer of the sheet (Comparative Example 2).

  When Example 3 and Comparative Example 2 are compared, it can be seen that only a conventional electromagnetic wave absorbing sheet having no far-infrared radiation layer has no heat dissipation effect.

  When Example 3 and Comparative Example 3 are compared, it can be seen that a sufficient heat dissipation effect cannot be obtained when the thermal conductivity of the electromagnetic wave absorbing layer is smaller than 0.7 W / mK.

It is a figure showing an example of the state with which the electromagnetic wave absorption heat radiation sheet of this invention was mounted | worn with the exothermic and electromagnetic noise radiation element. It is a longitudinal cross-sectional view showing the apparatus for measuring the thermal radiation performance of the to-be-evaluated sheet. It is explanatory drawing showing the apparatus for measuring the emitted electromagnetic wave variation | change_quantity of a to-be-evaluated sheet | seat, and its operation | movement.

Explanation of symbols

1 Electromagnetic wave absorbing thermal radiation sheet
2 Far-infrared radiation layer
3 Electromagnetic wave absorption layer
10 Heat-generating / electromagnetic noise emitting element
11 Aluminum alloy lid
12 Insulating plastic container
13 Sealed enclosure
21 Printed circuit board
22 Microprocessor
31 Evaluated sheet
41 Far-infrared absorbing layer
51 Anechoic chamber
52 Receive antenna
53 Shield Room
54 EMI receiver

Claims (10)

  An electromagnetic wave absorbing heat comprising an electromagnetic wave absorbing layer having a thermal conductivity of 0.7 W / mK or more, and a far infrared radiation layer provided directly on one side of the electromagnetic wave absorbing layer or via at least one other layer. Radiant sheet.   The electromagnetic wave absorbing thermal radiation sheet according to claim 1, wherein the electromagnetic wave absorbing layer is a layer comprising a soft magnetic metal powder and an insulating polymer.   The electromagnetic wave absorbing heat radiation sheet according to claim 2, wherein the soft magnetic metal powder contains 15 mass% or more of iron element.   The electromagnetic wave absorbing thermal radiation sheet according to claim 2 or 3, wherein the polymer is silicone, acrylic rubber, ethylene propylene rubber, fluoro rubber, chlorinated polyethylene, or a combination of two or more thereof.   The electromagnetic wave absorbing thermal radiation sheet according to any one of claims 1 to 4, wherein the electromagnetic wave absorbing layer contains a thermally conductive filler.   The electromagnetic wave absorptive heat radiation sheet according to claim 1, wherein the far infrared radiation layer is a layer comprising a far infrared radiation oxide ceramic.   The electromagnetic wave absorptive thermal radiation sheet according to any one of claims 1 to 6, wherein the far infrared radiation layer is provided on a conductive layer provided on the one surface of the electromagnetic wave absorption layer.   The electromagnetic wave absorbing thermal radiation sheet according to any one of claims 1 to 7, wherein the electromagnetic wave absorbing layer is adhesive.   The electromagnetic wave absorptive thermal radiation sheet according to any one of claims 1 to 7, wherein an adhesive layer is provided on one side of the electromagnetic wave absorbing layer opposite to the one side. The electromagnetic wave-absorbing thermal radiation sheet according to claim 9, wherein the adhesive layer contains a thermally conductive filler, and the thermal conductivity of the adhesive layer is 0.5 W / mK or more.

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