JP2013229591A - Heat conductive foam sheet for electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat conductive foam sheet for an electronic apparatus having thinness and flexibility which can be suitably used for an inner part of an electronic apparatus, and good thermal conductivity and good dielectric characteristic.SOLUTION: A heat conductive foam sheet for an electronic apparatus contains a heat conductor in an elastomer resin part forming the foam sheet, a content of the heat conductor to 100 pts.mass of the elastomer resin is 100 to 500 pts.mass, 25% compressive strength of the foam sheet is equal to or less than 200 kPa, a dielectric constant of the foam sheet is equal to or less than 4, and its thickness is 0.05 to 1 mm.

Description

  The present invention relates to a thermally conductive foam sheet for electronic equipment for efficiently radiating heat inside the electronic equipment to the outside.

  In electronic devices that require miniaturization, such as smartphones, electronic components that are densely integrated generate a large amount of heat, and this heat causes failure. A heat sink material is provided. Since the heat sink material is generally provided between an electronic component that is a heating element and a metal casing, a heat radiation grease or a heat radiation gel with high unevenness followability, and urethane foam are impregnated with the heat radiation material. Silicone laminates containing thermal conductive fillers such as those and boron nitride have been proposed (for example, Patent Documents 1 and 2).

JP 2003-31980 A JP 2010-260225 A

Although the heat dissipating grease has good heat dissipating property, once the grease is applied, it is difficult to reapply it, and there is a problem that the yield of the product is lowered. On the other hand, the heat-dissipating gel is generally difficult to process into a sheet having a thickness of 1 mm or less, and there is a problem that the shape is deformed when compressed. Furthermore, there is a problem that a thin sheet has high compressive strength and low flexibility.
The urethane foam is difficult to be processed into a sheet with a thickness of 1 mm or less due to its manufacturing method, and a thin sheet-like molded product is difficult to increase the expansion ratio. There is a problem of loss of sex.
On the other hand, a heat sink material including silicone as a constituent element is desired to be a heat sink material that does not use silicone because siloxane gas generated from silicone changes to silica at the contact portion of the electronic component, causing contact failure.
Furthermore, since the central processing unit (CPU) performs calculations at high speed as electronic devices become more sophisticated, the heat sink material installed in the vicinity of the central processing unit must be made of a material with a low relative dielectric constant. Is desired.

  The present invention has been made in view of the above-described conventional problems, and is an electronic device having thinness and flexibility that can be suitably used inside an electronic device, and excellent in thermal conductivity and dielectric characteristics. An object of the present invention is to provide a heat conductive foam sheet.

  The present invention is a thermally conductive foam sheet for electronic equipment that contains a thermal conductor in an elastomer resin portion constituting the foam sheet, and the content of the thermal conductor is 100 to 100 parts by mass of the elastomer resin. 500 parts by mass, 25% compressive strength of the foam sheet is 200 kPa or less, the dielectric sheet has a relative dielectric constant of 4 or less, and the thickness is 0.05 to 1 mm. The gist of the porous foam sheet.

  According to the present invention, it is possible to provide a thermally conductive foam sheet for an electronic device that has a thinness and flexibility that can be suitably used inside an electronic device, and is excellent in thermal conductivity and dielectric properties. it can.

It is a figure which shows the apparatus for measuring the thermal radiation performance of the foam sheet created in the Example and the comparative example.

  The heat conductive foam sheet for electronic equipment of the present invention is a heat conductive foam sheet for electronic equipment containing a heat conductor in an elastomer resin portion constituting the foam sheet, and is based on 100 parts by mass of the elastomer resin. The content of the heat conductor is 100 to 500 parts by mass, the 25% compressive strength of the foam sheet is 200 kPa or less, the relative dielectric constant of the foam sheet is 4 or less, and the thickness is 0.00. It is 05-1 mm.

<Foam sheet>
The 25% compressive strength of the foam sheet used in the present invention is 200 kPa or less. When the compressive strength exceeds 200 kPa, the flexibility of the foam sheet decreases, which is not preferable. From the viewpoint of the flexibility of the foam sheet, the 25% compressive strength of the foam sheet is preferably 5 kPa or more, more preferably 50 kPa or more, further preferably 55 kPa or more, preferably 190 kPa or less, more preferably 180 kPa or less, 150 kPa or less is still more preferable, and 100 kPa or less is still more preferable.
The specific numerical value of the 25% compressive strength of the foam sheet is preferably 5 to 190 kPa, more preferably 50 to 190 kPa, still more preferably 50 to 150 kPa, and still more preferably 55 to 100 kPa.

The foam sheet used in the present invention is composed of an elastomer resin containing 10% by mass or more of a liquid elastomer, and the 50% compressive strength of the foam sheet is preferably 200 kPa or less. If the 50% compressive strength of the foam sheet is 200 kPa or less, it can be suitably used for thin electronic devices such as mobile terminals.
From the viewpoint of improving flexibility, the 50% compressive strength of the foam sheet is more preferably 150 kPa or less, and even more preferably 100 kPa or less.
The liquid elastomer content in the elastomer resin is preferably 10% by mass or more, more preferably 20% by mass or more, and preferably 90% by mass or less, more preferably 80% by mass or less.

  The thickness of the foam sheet is 0.05 to 1 mm. When the thickness of the foam sheet is less than 0.05 mm, the foam sheet is easily torn, and when it exceeds 1 mm, it is difficult to use the foam sheet in a small electronic device. From the viewpoint of the strength of the foam sheet, the thickness of the foam sheet is preferably 0.05 to 0.8 mm, more preferably 0.05 to 0.7 mm, and still more preferably 0.05 to 0.5 mm.

  The relative dielectric constant of the foam sheet is 4 or less. If the relative dielectric constant of the foam sheet exceeds 4, it may cause an operation error of the electronic device, which is not preferable. 1-3 is preferable and, as for the dielectric constant of a foam sheet, 1-2 is more preferable.

  The thermal conductivity of the foam sheet is preferably 0.3 to 10 W / m · K, and more preferably 0.4 to 2.0 W / m · K. When the thermal conductivity of the foam sheet is within the above range, it becomes possible to efficiently dissipate heat inside the electronic device to the outside.

  The expansion ratio of the foam sheet is preferably 1.5 to 5 times, more preferably 1.5 to 3 times, and still more preferably 1.5 to 2.5 times. When the foaming ratio of the foam sheet is within the above range, both the thinness and flexibility of the sheet can be achieved.

The apparent density of the foam sheet is preferably 0.4 g / cm ³ or more, more preferably 0.5 g / cm ³ or more, more preferably 0.6 g / cm ³ or more, and even more preferably 0.7 g / cm ³ or more. 0.85 g / cm ³ or more is more preferable, 1.5 g / cm ³ or less is preferable, 1.4 g / cm ³ or less is more preferable, and 1.2 g / cm ³ or less is more preferable.
Specific numerical values of apparent density of the foam sheet is preferably from 0.4 to 1.5 g / cm ^3, more preferably ^{0.4~1.4g / cm 3, 0.7~1.4g / cm} 3 More preferably, 0.85-1.2 g / cm < ³ > is still more preferable. If the apparent density of the foam sheet is within the above range, a foam sheet having a desired thickness, flexibility, and thermal conductivity can be obtained.

<Elastomer resin>
Examples of elastomer resins that can be used in the present invention include acrylonitrile butadiene rubber, liquid acrylonitrile butadiene rubber, ethylene-propylene-diene rubber, liquid ethylene-propylene-diene rubber, ethylene-propylene rubber, liquid ethylene-propylene rubber, natural rubber, liquid natural Rubber, Polybutadiene rubber, Liquid polybutadiene rubber, Polyisoprene rubber, Liquid polyisoprene rubber, Styrene-butadiene block copolymer, Liquid styrene-butadiene block copolymer, Hydrogenated styrene-butadiene block copolymer, Liquid hydrogenated styrene- Butadiene block copolymer, hydrogenated styrene-butadiene-styrene block copolymer, liquid hydrogenated styrene-butadiene-styrene block copolymer, hydrogenated styrene -Isoprene block copolymer, liquid hydrogenated styrene-isoprene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, liquid hydrogenated styrene-isoprene-styrene block copolymer, etc. Then, butyl rubber (isobutylene-isoprene rubber), ethylene-propylene rubber, and liquid ethylene-propylene rubber are preferable.

<Heat conductor>
Examples of the heat conductor that can be used in the present invention include aluminum oxide, magnesium oxide, boron nitride, talc, aluminum nitride, graphite, and graphene. Among these, boron nitride and talc are preferable. These heat conductors may be used alone or in a combination of two or more.
The thermal conductivity of the thermal conductor is preferably 5 W / m · K or more, and more preferably 20 W / m · K or more. When the thermal conductivity is within the above range, the thermal conductivity of the foam sheet is sufficiently high.

  Content of the said heat conductor is 100-500 mass parts with respect to 100 mass parts of elastomer resins. When the content of the heat conductor is less than 100 parts by mass, sufficient heat conductivity cannot be imparted to the foam sheet, and when the content of the heat conductor exceeds 500 parts by mass, Flexibility is reduced. From the viewpoint of thermal conductivity and flexibility of the foam sheet, the content of the thermal conductor with respect to 100 parts by mass of the elastomer resin is preferably 120 to 400 parts by mass, and 150 to 350 parts by mass with respect to 100 parts by mass of the elastomer resin. More preferred.

<Optional component>
In the present invention, various additive components can be contained as necessary within the range in which the object of the present invention is not impaired.
The kind of the additive component is not particularly limited, and various additives usually used for foam molding can be used. Examples of such additives include lubricants, shrinkage inhibitors, cell nucleating agents, crystal nucleating agents, plasticizers, colorants (pigments, dyes, etc.), ultraviolet absorbers, antioxidants, anti-aging agents, and the above-described conductivity imparting. Examples include fillers excluding materials, reinforcing agents, flame retardants, flame retardant aids, antistatic agents, surfactants, vulcanizing agents, and surface treatment agents. The addition amount of the additive can be appropriately selected within a range that does not impair the formation of bubbles and the like, and the addition amount used for normal resin foaming and molding can be adopted. Such additives can be used alone or in combination of two or more.

  The lubricant has the effect of improving the fluidity of the resin and suppressing the thermal deterioration of the resin. The lubricant used in the present invention is not particularly limited as long as it has an effect on improving the fluidity of the resin. For example, hydrocarbon lubricants such as liquid paraffin, paraffin wax, microwax, polyethylene wax; fatty acid lubricants such as stearic acid, behenic acid, 12-hydroxystearic acid; butyl stearate, monoglyceride stearate, pentaerythritol tetrastearate And ester lubricants such as hydrogenated castor oil and stearyl stearate.

  The addition amount of the lubricant is preferably about 0.01 to 5 parts by mass, more preferably 0.05 to 4 parts by mass, and still more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the resin. If the amount added exceeds 10 parts by mass, the fluidity may become too high and the expansion ratio may decrease. There is a risk that the expansion ratio will decrease.

Examples of the flame retardant include bromine-based flame retardants such as decabromodiphenyl ether and phosphorus-based flame retardants such as ammonium polyphosphate in addition to metal hydroxides such as aluminum hydroxide and magnesium hydroxide.
Antimony compounds such as antimony trioxide, antimony tetroxide, antimony pentoxide, sodium pyroantimonate, antimony trichloride, antimony trisulfide, antimony oxychloride, antimony perchloropentane dichloride, potassium antimonate, etc. And boron compounds such as zinc metaborate, zinc tetraborate, zinc borate, basic zinc borate, zirconium oxide, tin oxide, molybdenum oxide, and the like.

<Method for producing foam sheet>
The heat conductive foam sheet for electronic devices of the present invention can be produced by a known chemical foaming method or physical foaming method, and the production method is not particularly limited.
In addition, the foaming processing method can use a well-known method including the method described in the plastic foam handbook (Makihiro, Atsushi Kosaka edit Nikkan Kogyo Shimbun 1973).

Examples The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
The materials used in the following examples and comparative examples are as follows.
(1) Butyl rubber Exxon, isobutylene-isoprene rubber, trade name “butyl 065”
Density: 0.92 g / cm ³
Mooney viscosity (100 ° C) = 47 (ML)
Unsaturation = 2.0
(2) Ethylene-propylene rubber JSR Corporation model number “EP21”
Mooney viscosity (125 ° C) = 26 (ML)
(3) Ethylene-propylene rubber-diene rubber (EPDM)
Product name “EP21” manufactured by JSR Corporation
Density: 0.86 g / cm ³
Propylene content: 34% by mass
(4) Liquid ethylene-propylene-diene rubber (liquid EPDM)
Product name “PX-068” manufactured by Mitsui Chemicals, Inc.
Density: 0.9 g / cm ³
Propylene content: 39% by mass
(5) Azodicarbonamide, trade name “SO-L” manufactured by Otsuka Chemical Co., Ltd.
(6) Talc Nippon Talc Co., Ltd., trade name “P-6”
Average particle size: 4 μm
(7) Boron nitride, manufactured by Denki Kagaku Kogyo Co., Ltd., trade name “DENCABORON NITRIDE SGP”
Average particle size: 15 μm
(8) Phenol antioxidant manufactured by Ciba Specialty Chemicals Co., Ltd., trade name “Irganox 1010”

<Examples 1-4, Comparative Examples 1 and 2>
Example 1
100 parts by weight of butyl rubber, 16 parts by weight of azodicarbonamide, 200 parts by weight of talc and 0.1 parts by weight of phenolic antioxidant are melt-kneaded and then pressed to obtain a foamable resin sheet having a thickness of 0.4 mm. It was.
The foamable resin sheet was cross-linked by irradiating an electron beam of 2.5 Mrad at an acceleration voltage of 500 keV on both surfaces of the obtained foamable resin sheet. Next, the foamable resin sheet was foamed by heating the sheet to 250 ° C. to obtain a foam sheet having an apparent density of 0.74 g / cm ³ and a thickness of 0.5 mm.

Example 2
100 parts by weight of butyl rubber, 16 parts by weight of azodicarbonamide, 220 parts by weight of boron nitride, and 0.1 parts by weight of a phenolic antioxidant are melt-kneaded and then pressed to obtain a foamable resin sheet having a thickness of 0.4 mm. It was.
The foamable resin sheet was cross-linked by irradiating an electron beam of 2.5 Mrad at an acceleration voltage of 500 keV on both surfaces of the obtained foamable resin sheet. Next, the foamable resin sheet was foamed by heating the sheet to 250 ° C. to obtain a foam sheet having an apparent density of 0.76 g / cm ³ and a thickness of 0.5 mm.

Example 3
Foam with a thickness of 0.4 mm is obtained by melting and kneading 100 parts by mass of ethylene-propylene rubber, 17.5 parts by mass of azodicarbonamide, 220 parts by mass of boron nitride, and 0.1 parts by mass of a phenolic antioxidant, and then pressing. A functional resin sheet was obtained.
Both surfaces of the foamable resin sheet were irradiated with an electron beam of 2.5 Mrad at an acceleration voltage of 500 keV to crosslink the foamable resin sheet. Next, the foamable resin sheet was foamed by heating the sheet to 250 ° C. to obtain a foam sheet having an apparent density of 0.74 g / cm ³ and a thickness of 0.5 mm.

Example 4
After melt-kneading 70 parts by mass of ethylene-propylene-diene rubber, 30 parts by mass of liquid ethylene-propylene-diene rubber, 17.5 parts by mass of azodicarbonamide, 220 parts by mass of boron nitride, and 0.1 parts by mass of phenolic antioxidant, A foamable resin sheet having a thickness of 0.38 mm was obtained by pressing.
The foamable resin sheet was crosslinked by irradiating 3.0 Mrad of an electron beam at an acceleration voltage of 500 keV on both surfaces of the obtained foamable resin sheet. Next, the foamable resin sheet was foamed by heating the sheet to 250 ° C. to obtain a foam sheet having an apparent density of 0.44 g / cm ³ and a thickness of 0.5 mm.

Comparative Example 1
A heat-dissipating silicone pad (“TC-CAS-10” manufactured by Shin-Etsu Chemical Co., Ltd., thickness 0.5 mm, thermal conductivity 1.8 W / m · K) was used as Comparative Example 1.

Comparative Example 2
Resin having a thickness of 0.5 mm and an apparent density of 1.5 g / cm ³ by melting and kneading 100 parts by mass of ethylene-propylene rubber, 220 parts by mass of boron nitride, and 0.1 parts by mass of a phenolic antioxidant, A compound sheet was obtained.

<Physical properties>
The physical properties of the obtained foam sheet were measured as follows. Each measurement result is shown in Table 1.
[Foaming ratio]
The expansion ratio was calculated by dividing the specific gravity of the foam sheet by the specific gravity of the foamable sheet. [Apparent density]
It measured based on JISK7222.
[25% compressive strength]
The 25% compressive strength in the thickness direction of the foam sheet was measured based on JIS K6767-7.2.3 (JIS2009).
[Measurement of relative permittivity]
The relative dielectric constant of the foam sheet was measured by an automatic equilibrium bridge method using an LCR meter under the conditions of 1 MHz and a main electrode diameter of 28φ (attached with tin foil).
[Thermal conductivity of foam sheet]
The thermal conductivity was measured at 25 ° C. using “TC-7000” manufactured by ULVAC-RIKO Co., Ltd. by a laser flash method.
[Heat conduction performance]
As shown in FIG. 1, a 25 mm × 25 mm × 2 mm heater (Sakaguchi Electric Heat Co., Ltd. micro ceramic heater, model number “MS5”) was placed on the heat insulating material, and a 25 mm × 25 mm sample was stacked thereon. An aluminum plate of 50 mm × 100 mm × 2 mm was placed thereon to form a structure in which the heat transmitted through the sample diffuses into the aluminum plate. In this state, 1 W of electric power was applied to the heater, and when the temperature became constant after 15 minutes, the temperature [T] (° C.) of the heater was measured. A smaller value indicates better heat conduction performance.

  From the results of Examples and Comparative Examples, the thermally conductive foam sheet for electronic devices according to the present invention has a low relative dielectric constant, has thinness and flexibility, and has thermal conductivity equivalent to that of a silicone sheet. I understand that.

Claims (5)

  A heat conductive foam sheet for an electronic device containing a heat conductor in an elastomer resin portion constituting the foam sheet, wherein the content of the heat conductor with respect to 100 parts by mass of the elastomer resin is 100 to 500 parts by mass The 25% compressive strength of the foam sheet is 200 kPa or less, the relative permittivity of the foam sheet is 4 or less, and the thickness is 0.05 to 1 mm. .   2. The thermally conductive foam sheet for an electronic device according to claim 1, wherein the thermal conductor is at least one selected from the group consisting of boron nitride, talc, aluminum oxide, magnesium oxide, aluminum nitride, graphite, and graphene.   The thermally conductive foam sheet for electronic equipment according to claim 1 or 2, wherein the foaming ratio of the foam sheet is 1.5 to 5 times.   The thermally conductive foam sheet according to claim 1, wherein the foam sheet has a thermal conductivity of 0.3 to 10 W / m · K.   The thermally conductive foam sheet for electronic equipment according to any one of claims 1 to 4, wherein the elastomer resin is butyl rubber or ethylene-propylene rubber.