TW201807157A - Foamable resin sheet and thermoconductive foam sheet for electronic device - Google Patents

Abstract

A foamable resin sheet containing 100-400 parts by mass of a thermal conductor, 1-30 parts by mass of a foaming agent, and 0.10-0.50 part by mass of a foaming auxiliary with respect to 100 parts by weight of an elastomer resin containing 50-70 mass% of an elastomer (I) having a Mooney viscosity of 15-100 ML (1+4) at 100 DEG C and 30-50 mass% of an elastomer (II) having a viscosity of 3-1,000 Pa.s at 23 DEG C.

Description

Foamable resin sheet and thermally conductive foam sheet for electronic equipment

The present invention relates to a foamable resin sheet and a thermally conductive foam sheet for an electronic device obtained by foaming the foamable resin sheet.

In electronic devices such as smart phones that require miniaturization, high-density integrated electronic parts generate a large amount of heat, and this heat becomes the cause of the failure. Therefore, a heat sink is provided to dissipate the heat to the outside of the machine. The heat-radiating material is generally provided between the electronic component as a heating element and the metal case. Therefore, as the heat-radiating material, a heat-radiating grease or a heat-radiating gel with high unevenness followability may be used. Further, Patent Document 1 proposes to impregnate a radiating grease or a radiating gel into an urethane foam. Furthermore, in Patent Document 2, the present inventors have proposed a thermally conductive foam sheet for an electronic device that contains a thermal conductor in an elastomer resin portion containing a specific elastomer.

Prior art literature patent literature

Patent Document 1: Japanese Patent Application Laid-Open No. 2003-31980

Patent Document 2: Japanese Patent Application Laid-Open No. 2014-209537

Although the above-mentioned heat-dissipating grease has good heat-dissipating properties, once the grease is applied, it is difficult to re-apply, and there is a problem that the yield of the product decreases. On the other hand, there is a problem that a heat-dissipating gel is generally difficult to be processed into a sheet shape having a thickness of 1 mm or less, and the shape is deformed when compressed.

Furthermore, the urethane foam has problems in that it is difficult to process the urethane foam into a sheet shape having a thickness of 0.5 mm or less, and if it is processed into a sheet shape, the compressive stress becomes high and the flexibility is lost. In addition, with regard to sheets having a thickness of 0.5 mm or less, the thickness deviation standards of the sheets are more stringent. Therefore, there is a problem in that it cannot be incorporated into a small electronic device based on the same deviation standards as those of a sheet of 0.5 mm or more. Even if it is incorporated, the adhesion with the surface to be adhered may decrease, which may cause a decrease in heat dissipation.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a foamable resin sheet for a thermally conductive foam sheet for an electronic device that can produce a target thickness with good thickness accuracy and yield.

Another object of the present invention is to provide a thermally conductive foam sheet for an electronic device that has a thinness and flexibility that can be preferably used in an electronic device and has excellent thermal conductivity and thickness accuracy.

The present invention is based on the following [1] and [2].

[1] A foamable resin sheet containing an elastomer (I) having a Mooney viscosity of 15 to 100 ML (1 + 4) at a temperature of 100 ° C. at 50 to 70% by mass, and 30 to 50% by mass The viscosity at 23 ℃ is 3 ~ 1,000Pa. 100 parts by mass of the elastomer resin of the elastomer (II) of s, containing 100 heat conductors ~ 400 parts by mass, 1 ~ 30 parts by mass of foaming agent, and 0.10 ~ 0.50 parts by mass of foaming aid.

[2] A thermally conductive foam sheet for electronic equipment, which is obtained by foaming the foamable resin sheet, and has a thickness of 0.3 mm or less, a 25% compressive stress of 200 kPa or less, and a thickness accuracy of 20% or less .

According to the present invention, it is possible to provide a foamable resin sheet for a thermally conductive foam sheet for an electronic device that can produce a target thickness with good thickness accuracy and yield.

In addition, it is possible to provide a thermally conductive foam sheet for an electronic device that can be preferably used for the thickness and flexibility of an electronic device and has excellent thermal conductivity and thickness accuracy.

[Foaming resin sheet]

The foamable resin sheet of the present invention is characterized in that it has an elastomer (I) having a Mooney viscosity of 15 to 100 ML (1 + 4) and a mass of 30 to 50% by mass at a temperature of 100 ° C containing 50 to 70% by mass. The viscosity at 23 ℃ is 3 ~ 1,000Pa. 100 parts by mass of the elastomer resin of the s-elastomer (II) contains 100 to 400 parts by mass of a thermal conductor, 1 to 30 parts by mass of a foaming agent, and 0.10 to 0.50 parts by mass of a foaming aid.

The foamable resin sheet of the present invention is used by combining a specific elastomer resin and a foaming agent and a foaming assistant are used in a specific amount. Therefore, the foamable resin sheet is foamed , On the other hand, a thermally conductive foam sheet (hereinafter, also referred to as a “foam sheet”) for an electronic device with excellent thickness accuracy can be manufactured with good yield. In addition, in this specification, "thickness precision" means thickness deviation of the thermally conductive foam sheet for electronic devices manufactured by foaming a foamable resin sheet, and "excellent thickness precision" means foaming The thickness variation of the thermally conductive foam sheet for electronic equipment manufactured by foaming a flexible resin sheet is small.

<Elastomer resin>

The elastomer resin of the present invention contains 50 to 70% by mass of the elastomer (I) having a Mooney viscosity of 15 to 100ML (1 + 4) at 100 ° C, and 30 to 50% by mass of the viscosity at 23 ° C of 3 ~ 1000Pa. s's elastomer (II).

[Elastomer (I)]

The elastomer (I) is not particularly limited as long as it satisfies the aforementioned Mooney viscosity, and examples thereof include acrylonitrile-butadiene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber, and natural Rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene block copolymer, hydrogenated styrene-butadiene block copolymer, hydrogenated styrene-butadiene-styrene block Copolymers, hydrogenated styrene-isoprene block copolymers, hydrogenated styrene-isoprene-styrene block copolymers, and the like. Among these, an ethylene-propylene-diene rubber is preferable.

The Mooney viscosity of the elastomer (I) at 100 ° C is 15 ~ 100ML (1 + 4), preferably 16 ~ 80ML (1 + 4), more preferably 17 ~ 65ML (1 + 4), more preferably 18 ~ 55ML (1 + 4), more preferably 19 ~ 50ML (1 + 4), and even more preferably 20 ~ 40ML (1 + 4). As long as the Mooney viscosity of the elastomer (I) is within the above range, both moldability and foamability can be achieved.

[Elastomer (II)]

The elastomer (II) is not particularly limited as long as the viscosity is satisfied, and examples thereof include: Liquid acrylonitrile-butadiene rubber, liquid ethylene-propylene-diene rubber, liquid ethylene-propylene rubber, liquid polybutadiene rubber, liquid polyisoprene rubber, liquid styrene-butadiene Diene block copolymer, liquid hydrogenated styrene-butadiene block copolymer, liquid hydrogenated styrene-butadiene-styrene block copolymer, liquid hydrogenated styrene-isoprene block Copolymers, and liquid hydrogenated styrene-isoprene-styrene block copolymers. Among these, a liquid ethylene-propylene-diene rubber is preferable.

Elastomer (II) has a viscosity at 23 ° C of 3 to 1,000 Pa. s, preferably 4 ~ 850Pa. s, more preferably 5 ~ 600Pa. s, further preferably 5 to 300 Pa. s, and more preferably 5 ~ 150Pa. s, and more preferably 5 ~ 100Pa. s, and more preferably 5 ~ 50Pa. s. As long as the viscosity of the elastomer (II) is within the above range, the kneading property is good, and a good foam sheet can be obtained.

The content of the elastomer (I) in the elastomer resin is 50 to 70% by mass, preferably 52 to 68% by mass, and more preferably 55 to 65% by mass. The content of the elastomer (II) in the elastomer resin is 30 to 50% by mass, preferably 32 to 48% by mass, and more preferably 35 to 45% by mass. The elastomer resin of the present invention is composed of an elastomer (I) and an elastomer (II).

As the above-mentioned elastomer resin, an ethylene-propylene-diene rubber having a Mooney viscosity of 15 to 100 ML (1 + 4) at 100 ° C. and a viscosity of 3 to 1000 Pa at 23 ° C. are more preferable. s liquid ethylene-propylene-diene rubber mixture.

<Thermal conductor>

The foamable resin sheet of the present invention contains 100 to 400 parts by mass of a thermal conductor with respect to 100 parts by mass of the elastomer resin. If the content of the thermal conductor is less than 100 parts by mass, sufficient thermal conductivity cannot be imparted to the foam sheet, and if the content of the thermal conductor exceeds 400 parts by mass, the flexibility of the foam sheet is reduced.

From the viewpoint of the thermal conductivity and flexibility of the foam sheet, the amount of the thermal conductor with respect to 100 parts by mass of the elastomer resin is preferably 120 to 380 parts by mass, more preferably 140 to 350 parts by mass, and more preferably It is 160 to 320 parts by mass, and more preferably 180 to 290 parts by mass.

Examples of the heat conductor that can be used in the present invention include alumina, magnesium oxide, boron nitride, talc, aluminum nitride, graphite, and graphene. Among these, it is preferably selected from alumina, magnesium oxide, One or more kinds of boron nitride, talc, and aluminum nitride, and more preferably one or more kinds selected from alumina, magnesium oxide, and boron nitride. These heat conductors may be used individually by 1 type, and may mix and use 2 or more types.

The thermal conductivity of the thermal conductor is preferably 8 W / m. Above K, more preferably 15W / m. K or more, and more preferably 20 W / m. K or more, and more preferably 35W / m. K or more. As long as the thermal conductivity is within the above range, the thermal conductivity of the foam sheet is sufficiently high.

The average particle diameter of the heat conductor is preferably 50 μm or less, more preferably 30 μm or less, still more preferably 15 μm or less, and even more preferably 10 μm or less. When the particle diameter of the heat conductor is within the above range, it is easy to reduce the thickness of the foam and obtain a foamed sheet having good foamability. In addition, the average particle diameter of the said heat-conducting body is a value measured by the particle size distribution meter Microtrac HRA using the laser diffraction scattering method.

<Foaming agent>

In the present invention, a foaming agent is used to foam a foamable resin sheet. The foaming agent is not particularly limited, but a thermally decomposable foaming agent is preferably used.

Specific examples of the thermally decomposable foaming agent include organic or inorganic chemical foaming agents having a decomposition temperature of about 160 ° C to 270 ° C.

Examples of the organic blowing agent include azodimethylformamide and metal azodicarboxylic acid salt (couple Barium azadicarboxylate, etc.), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine, hydrazine dimethylformamide, 4,4 '-Oxobis (benzenesulfenylhydrazine), hydrazine derivatives such as tosylhydrazine, amine urea compounds such as tosylhydrazine, and the like.

Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and anhydrous sodium citrate.

Among these, from the viewpoint of obtaining fine bubbles, and from the viewpoint of economics and safety, azo compounds and nitroso compounds are preferred, and azomethoxamine and azodiisobutyl are more preferred. Nitrile, N, N'-dinitrosopentamethylenetetramine, particularly preferred is azodimethylformamide. These thermally decomposable foaming agents can be used alone or in combination of two or more.

From the viewpoint of manufacturing a foamed sheet having a high thickness accuracy, the amount of the foaming agent relative to 100 parts by mass of the elastomer resin is 1 to 30 parts by mass, preferably 5 to 25 parts by mass, and more preferably 10 to 20 parts by mass, more preferably 12 to 20 parts by mass. If the amount of the foaming agent with respect to 100 parts by mass of the elastomer resin is outside the above-mentioned range, it cannot be sufficiently foamed or the softness of the foamed sheet is impaired, which is not preferable.

<Foaming aid>

In order to improve the thickness accuracy of the foamable resin sheet, the foamable resin sheet of the present invention uses a foaming aid. As the foaming aid, from the viewpoint of improving the thickness accuracy of the foamable resin sheet, a higher fatty acid metal salt having 10 to 18 carbon atoms in the alkyl group is preferred.

Examples of higher fatty acids having 10 to 18 carbon atoms in the alkyl group include, from the viewpoint of foamability, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, and linoleic acid. Among them, higher fatty acids having 14 to 18 carbon atoms are more preferred.

As a metal salt of a higher fatty acid, the thickness accuracy of the foamable resin sheet is improved. In terms of liters, alkali metal salts, alkaline earth metal salts, and zinc salts are preferred. Specific examples of the alkali metal salt, alkaline earth metal salt, and zinc salt of the higher fatty acid include, for example, sodium laurate, potassium laurate, sodium myristate, potassium myristate, calcium myristate, magnesium myristate, Zinc myristate, sodium palmitate, potassium palmitate, magnesium palmitate, calcium palmitate, zinc palmitate, sodium stearate, potassium stearate, magnesium stearate, calcium stearate, zinc stearate, Sodium linoleate, potassium linoleate, calcium linoleate, magnesium linoleate and zinc linoleate.

Among these, calcium, magnesium and zinc salts of stearic acid and palmitic acid are preferred, and zinc stearate is more preferred.

From the viewpoint of improving the thickness accuracy of the foamable resin sheet, the amount of the foaming assistant relative to 100 parts by mass of the above-mentioned elastomer resin is 0.10 to 0.50 parts by mass, preferably 0.20 to 0.40 parts by mass, and more preferably It is 0.30 to 0.40 parts by mass. If the amount of the foaming aid relative to 100 parts by mass of the elastomer resin is less than 0.10 parts by mass, sufficient flexibility cannot be imparted to the foamed sheet, and if the content of the foaming aid exceeds 0.50 parts by mass, foamability The moldability of the resin sheet is reduced.

<Thickness accuracy of foamable resin sheet>

The thickness accuracy of the foamable resin sheet of the present invention is preferably 15% or less. If the thickness accuracy is 15% or less, a foam sheet having a high thickness accuracy can be obtained when it is foamed. From the viewpoint of obtaining a foamed sheet excellent in thickness accuracy, the thickness accuracy of the foamable resin sheet of the present invention is preferably 14% or less, and more preferably 13% or less.

The thickness accuracy of the foamable resin sheet refers to a value measured by a method described in Examples.

<Optional component>

In the present invention, as long as the object of the present invention is not impaired, various additives may be contained as necessary.

The type of the additive component is not particularly limited, and various additives commonly used in foam molding can be used. Examples of such additives include antioxidants, lubricants, anti-shrinking agents, bubble nucleating agents, crystal nucleating agents, plasticizers, colorants (pigments, dyes, etc.), ultraviolet absorbers, anti-aging agents, Fillers, reinforcing agents, flame retardants, flame retardant additives, antistatic agents, surfactants, vulcanizing agents, and surface treatment agents other than the above-mentioned heat conductors. The amount of the additive can be appropriately selected within a range such as the formation of non-destructive bubbles, and an ordinary amount of resin used for foaming and molding can be used. This additive may be used alone or in combination of two or more.

Examples of the antioxidant include phenol-based antioxidants, sulfur-based antioxidants, phosphorus-based antioxidants, and amine-based antioxidants. Among these, phenol-based antioxidants are preferred.

Examples of the phenolic antioxidant include 2,6-di-tert-butyl-p-cresol, 3- (3,5-di-tert-butyl-4-hydroxyphenyl) propanoic acid n-octadecyl ester, 2-tert-butyl-6- (3-tert-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenylacrylate, tetrakis [methylene-3- (3,5 -Di-tert-butyl-4-hydroxyphenyl) propionate] methane and the like. The antioxidant may be used alone or in combination of two or more kinds.

In the case of using an antioxidant, the amount is preferably 0.05 to 10 parts by mass, and more preferably 0.08 to 5 parts by mass relative to 100 parts by mass of the elastomer resin.

The lubricant has the effect of improving the fluidity of the resin and suppressing the thermal degradation of the resin. The lubricant used in the present invention is not particularly limited as long as it exhibits an effect on improving the fluidity of the resin. Examples include hydrocarbon lubricants such as liquid paraffin, paraffin, micro-paraffin, and polyethylene wax; fatty acid lubricants such as stearic acid, behenic acid, and 12-hydroxystearic acid; butyl stearate, and stearic acid Ester-based lubricants such as monoglyceride, pentaerythritol tetrastearate, hydrogenated castor oil, and stearate.

When a lubricant is used, the amount is preferably about 0.01 to 5 parts by mass, more preferably about 0.05 to 4 parts by mass, and even more preferably about 0.1 to 3 parts by mass relative to 100 parts by mass of the elastomer resin. If the added amount exceeds 10 parts by mass, the fluidity may become too high and the expansion ratio may decrease. If it is less than 0.5 parts by mass, the fluidity may not be improved, and the elongation at the time of foaming may cause a problem. Concerns about the decrease in bubble magnification.

Examples of the flame retardant include metal hydroxides such as aluminum hydroxide and magnesium hydroxide, bromine-based flame retardants such as decabromodiphenyl ether, and phosphorus-based flame retardants such as ammonium polyphosphate.

Examples of the flame retardant aid include antimony trioxide, antimony tetraoxide, antimony pentoxide, sodium pyroantimony, antimony trichloride, antimony trisulfide, antimony oxychloride, antimony dichloride, perchloropentane, and antimony. Antimony compounds such as potassium acid, boron compounds such as zinc metaborate, zinc tetraborate, zinc borate, and basic zinc borate; zirconium oxide, tin oxide, and molybdenum oxide.

[Thermal conductive foam sheet for electronic equipment]

The thermally conductive foam sheet for electronic equipment of the present invention is obtained by foaming the foamable resin sheet of the present invention, and has a thickness of 0.3 mm or less, a 25% compressive stress of 200 kPa or less, and a thickness accuracy of 20% or less. .

<Thickness of foam sheet>

The thickness of the foam sheet is 0.3 mm or less. If the thickness of the foamed sheet exceeds 0.3 mm, it is difficult to use the foamed sheet in a void 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 0.28 mm, and more preferably 0.05 to 0.25 mm.

<25% compressive stress>

The 25% compressive stress of the foam sheet is 200 kPa or less. If the 25% compressive stress exceeds 200 kPa, the flexibility of the foam sheet is reduced, which is not preferable. From the viewpoint of the softness of the foam sheet In other words, the 25% compressive stress of the foam sheet is preferably 10 to 150 kPa, more preferably 15 to 150 kPa, still more preferably 20 to 150 kPa, and even more preferably 25 to 100 kPa.

<50% compressive stress>

The 50% compressive stress of the foam sheet is preferably 400 kPa or less, more preferably 300 kPa or less, still more preferably 50 to 190 kPa, and even more preferably 55 to 180 kPa. When the 50% compressive stress is in the above range, the flexibility of the foam sheet is improved.

<Thickness Accuracy of Foam Sheet>

The thickness accuracy of the foam sheet of the present invention is 20% or less. If the thickness accuracy is 20% or less, the foam sheet cannot be incorporated into a void in a small electronic device, and a void may be generated between the device and the foam sheet during assembly, thereby reducing thermal conductivity. Situation. In the present invention, the thickness accuracy is preferably 18% or less, and more preferably 17% or less, from the viewpoint of being preferably used for a small electronic device and for improving the thermal conductivity when incorporated into a small electronic device. , And more preferably 16% or less.

The thickness accuracy of the foam sheet refers to a value measured by the method described in the examples.

<Thermal resistance of the foam sheet during assembly and / or 50% compression>

The thermal resistance of the foam sheet during assembly and / or 50% compression is preferably 10 ° C / W or less, more preferably 8 ° C / W or less, more preferably 6 ° C / W or less, and further preferably 5 ° C. / W or less. As long as the thermal resistance of the foam sheet during assembly and / or 50% compression is equal to or less than the upper limit value, the heat inside the electronic device can be efficiently radiated to the outside.

In addition, the thermal resistance at the time of assembly of the present invention refers to a value measured by a method described in the examples.

<Foaming ratio of foam sheet>

The foaming ratio of the foam sheet is preferably 2 to 4 times, more preferably 2.5 to 3.7 times, and even more preferably 2.5. ~ 3.6 times. When the foaming ratio of the foam sheet is within the above range, the flexibility and thermal conductivity of the foam sheet can be taken into consideration.

<Apparent Density of Foam Sheet>

The apparent density of the foam sheet is preferably 0.2 to 1.5 g / cm ³ , preferably 0.3 to 1.2 g / cm ³ , and more preferably 0.4 to 1.2 g / cm ³ . As long as 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.

<Manufacturing method of foam sheet>

The thermally conductive foam sheet for an electronic device of the present invention can be produced, for example, by a production method including the following steps (I) to (II).

Step (I): a step of manufacturing a foamable resin sheet, the foamable resin sheet having a Mooney viscosity of 15 to 100 ML (1 + 4) relative to an elastomer having a Mooney viscosity of 50 to 70% by mass at 100 ° C ), And the viscosity at 23 ° C of 30-50% by mass is 3 ~ 1,000Pa. 100 parts by mass of the elastomer resin of the s-elastomer (II) contains 100 to 400 parts by mass of a thermal conductor, 1 to 30 parts by mass of a foaming agent, and 0.10 to 0.50 parts by mass of a foaming aid.

Step (II): A step of manufacturing the thermally conductive foam sheet for an electronic device by foaming the above-mentioned foamable resin sheet, the thermally conductive foam sheet for an electronic device having a plurality of bubbles and having a thickness of 0.3 mm or less , 25% compressive stress is 200kPa or less, and thickness accuracy is 20% or less.

Each step will be described in detail below.

<Step (I)>

The foamable resin sheet used in step (I) can be supplied to the extruder, for example, by supplying a heat conductor, a foaming agent, a foaming aid, and other added components to the extruder, melt-kneading the elastomer resin, and self-extruding Obtained by extrusion. In addition, elastomer resins, The heat conductor, the foaming agent, the foaming aid, and other added components are continuously conveyed while being kneaded, thereby obtaining a foamable resin sheet having a specific thickness. Furthermore, a foamable resin sheet can also be obtained by pressurizing an elastomer resin, a heat conductor, a foaming agent, a foaming aid, and other added components.

<Step (II)>

In step (II), the foamable resin sheet is foamed to produce a thermally conductive foam sheet for an electronic device. The thermally conductive foam sheet for an electronic device has a plurality of bubbles and has a thickness of 0.3 mm or less. , 25% compressive stress is 200kPa or less, and thickness accuracy is 20% or less.

As a method of foaming the said foamable resin sheet, it is preferable to foam using the said thermal decomposition type foaming agent.

Examples of the method of decomposing and decomposing the thermally decomposable foaming agent and foaming include a method of heating a foamable resin sheet by hot air, a method of heating by infrared rays, a method of heating by a salt bath, and oil. The method of heating a bath, etc., may be used together.

The temperature at which the foamable resin sheet is foamed also depends on the type of foaming agent used, and is preferably 200 to 300 ° C, and more preferably 220 to 280 ° C.

Moreover, the manufacturing method of a foamed sheet is not limited to the said method, It can also manufacture by other methods. The foaming method includes a method described in a manual on plastic foams (edited by Makihiro and Atsushi Kosaka, published by the Nikkan Kogyo Shimbun, 1973), and known methods can be used.

<Crosslinking treatment>

In the present invention, it is preferable to perform a crosslinking treatment on the foamable resin sheet before foaming. Examples of the method for cross-linking the foamable resin sheet include a method of irradiating the foamable resin sheet with free radiation such as electron beam, α-rays, β-rays, and γ-rays, and pre-treating the foamable resin sheet. A method of preparing organic peroxide and heating a foamable resin sheet to decompose the organic peroxide, etc. may be used in combination. Among these, a method of radiating free radiation is preferable. The radiation dose of the free radiation is preferably 5 to 100 kGy, and more preferably 10 to 50 kGy.

<How to use thermally conductive foam sheet for electronic equipment>

The thermally conductive foam sheet for electronic equipment of the present invention is used for electronic equipment. As the electronic device, portable devices such as a mobile phone, a tablet terminal, an electronic paper, a notebook PC, a video camera, and a digital camera are preferred.

The thermally conductive foam sheet for electronic equipment is arranged near the heat source inside the electronic equipment, and is used as a heat sink for diffusing or radiating heat generated from the heat source. The thermally conductive foam sheet for electronic devices has high flexibility and is thin. Therefore, it can be placed in a narrow space.

The thermally conductive foam sheet for an electronic device is arranged, for example, between a heat source and a heat sink, and together with the heat sink, constitutes a heat radiation mechanism that dissipates heat from the heat source. The thermally conductive foam sheet for an electronic device is preferably arranged so as to be in contact with a heat source, and more preferably arranged so as to be in contact with both a heat source and a heat sink. The heat source is an electronic component that generates heat when driven or used. Specifically, the heat source is a CPU, a battery, a power amplifier, or the like. Examples of the heat sink include metal members such as iron and stainless steel, and it is preferable to constitute a housing of an electronic device.

Examples

The present invention will be further described in detail by 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) Elastomer (I)

‧Elastomer (I-1)

Solid EPDM (ethylene-propylene-diene rubber)

Made by JSR, "EP21"

Mooney viscosity at 100 ℃: 35ML (1 + 4)

‧Elastomer (I-2)

Solid EPDM (ethylene-propylene-diene rubber)

Manufactured by Mitsui Chemicals, Inc., Model: 8030M

Mooney viscosity at 100 ℃: 32ML (1 + 4)

‧Elastomer (I-3)

Solid EPDM (ethylene-propylene-diene rubber)

Manufactured by Mitsui Chemicals, Inc., Model: 4050M

Mooney viscosity at 100 ℃: 45ML (1 + 4)

(2) Elastomer (II)

Liquid EPDM (liquid ethylene-propylene-diene rubber)

Manufactured by Mitsui Chemicals, Inc., "PX-068"

Viscosity at 23 ° C: 10Pa. s

(3) Foaming agent

Azodimethylamine, manufactured by Otsuka Chemical Co., Ltd. under the trade name "SO-L"

(4) Foaming aid

‧Manufactured by Kawamura Chemical Industry (Co., Ltd.), zinc stearate

‧Reagents manufactured by Sanjin Chemical Co., Ltd., zinc laurate

(5) Thermal conductor (magnesium oxide)

Manufactured by UBE MATERIALS (Co., Ltd.), trade name "RF-10-SC", flat

Average particle size: 3 ~ 5μm

Thermal conductivity: 55W / m. K

(6) Phenol antioxidant

Manufactured by BASF under the trade name "Irganox 1010"

<Examples 1 to 8 and Comparative Examples 1 and 2>

Example 1

60 parts by mass of elastomer (I-1), 40 parts by mass of elastomer (II), 17 parts by mass of azomethoxamine, 0.35 parts by mass of zinc stearate, 250 parts by mass of magnesium oxide, and phenolic antioxidant 0.1 After the mass parts were melt-kneaded, a foamable resin sheet having a thickness of 0.15 mm was obtained by a sheeting roll.

On both sides of the obtained foamable resin sheet, an electron beam of 15 kGy was irradiated at an acceleration voltage of 500 keV to crosslink the foamable resin sheet. Next, the foamable resin sheet was heated to 250C, and thereby foamed to obtain a foamed sheet having a thickness of 0.2 mm (central product) and an apparent density of 0.62 g / cm ³ (central product).

Examples 2, 3

A foamed sheet was obtained in the same manner as in Example 1 except that the blending amounts of the elastomer (I-1) and the elastomer (II) were changed as shown in Table 1 below.

Example 4

A foamed sheet was obtained in the same manner as in Example 1 except that the elastomer (I-1) was changed to the elastomer (I-2).

Example 5

Except changing the elastomer (I-1) to the elastomer (I-3), it is the same as in Example 1 In the same manner, a foam sheet was obtained.

Example 6

A foamed sheet was obtained in the same manner as in Example 1 except that the zinc stearate was changed to zinc laurate as a foaming aid.

Example 7

A foamed sheet was obtained in the same manner as in Example 1 except that 0.35 parts by mass of zinc stearate was set to 0.1 parts by mass.

Example 8

A foamed sheet was obtained in the same manner as in Example 1 except that 0.35 parts by mass of zinc stearate was set to 0.5 parts by mass.

Comparative Example 1

A foamed sheet was obtained in the same manner as in Example 1 except that no foaming aid (zinc stearate) was added.

Comparative Example 2

A silicon-based resin (trade name "TC-20TAG-3" manufactured by Shin-Etsu Silicones (Co., Ltd.)) was press-molded to obtain a sheet having a thickness of 120 μm.

<Physical properties>

The physical properties of the obtained foamable sheet and foamed sheet were measured in the following manner. Each measurement result is shown in Table 1 or Table 2.

[Thickness accuracy of foamable sheet, and thickness accuracy of foam sheet]

The thickness accuracy of the foamable sheet and the thickness accuracy of the foamed sheet are calculated based on JIS K 7248 and measured at 2000 locations on a 1000 mm wide × 200 m foamed sheet in units of 10 cm. Here, the so-called The central product refers to the average thickness, the minimum product thickness is the minimum, and the maximum product thickness is the maximum.

[Apparent density]

The measurement was performed in accordance with JIS K 7222.

[Foaming ratio]

The expansion ratio is calculated by dividing the specific gravity of the foamed sheet by the specific gravity of the foamable resin sheet.

[25% compressive stress and 50% compressive stress]

The 25% compressive stress and 50% compressive stress in the thickness direction of the foam sheet are measured in accordance with JIS K 6767-7.2.3 (JIS 2009).

[Thermal resistance of foam sheet]

The thermal resistance of the foam sheet is conventionally used in a compressed state or a 50% compressed state when the foam sheet is assembled, using a brand name "T3Ster (registered trademark) DynTIM Tester" manufactured by Mentor Graphics, The measurement was performed according to ASTM D5470.

As can be seen from the results of the examples and comparative examples, as long as it is the foamable resin of the present invention Sheet, it is possible to produce a thermally conductive foam sheet for an electronic device with a desired thickness accuracy and yield.

In addition, the thermally conductive foam sheet for an electronic device of the present invention has a thinness and flexibility that can be preferably used in an electronic device, and has excellent thermal conductivity and thickness accuracy.

Claims (10)

A foamable resin sheet containing 50 to 70% by mass of an elastomer (I) having a Mooney viscosity of 15 to 100ML (1 + 4) at 100 ° C and 30 to 50% by mass of 23 ° C The viscosity is 3 ~ 1,000Pa. 100 parts by mass of the elastomer resin of the s-elastomer (II) contains 100 to 400 parts by mass of a thermal conductor, 1 to 30 parts by mass of a foaming agent, and 0.10 to 0.50 parts by mass of a foaming aid. For example, the foamable resin sheet according to item 1 of the patent application scope, wherein the thickness accuracy of the foamable resin sheet is 15% or less. For example, the foamable resin sheet according to item 1 or 2 of the patent application range, wherein the foaming assistant is a higher fatty acid metal salt having a carbon number of 10 to 18 in the alkyl group. For example, the foamable resin sheet according to any one of claims 1 to 3, wherein the elastomer resin is an ethylene-propylene-diene having a Mooney viscosity of 15 to 100 ML (1 + 4) at 100 ° C. The viscosity of rubber and 23 ℃ is 3 ~ 1000Pa. A liquid ethylene-propylene-diene rubber mixture. For example, the foamable resin sheet according to any one of claims 1 to 4, wherein the thermally conductive system is at least one selected from the group consisting of alumina, magnesium oxide, boron nitride, talc, and aluminum nitride. For example, the foamable resin sheet according to any one of claims 1 to 5, wherein the thermal conductivity of the thermal conductor is 8 W / m. K or more. For example, the foamable resin sheet according to any one of claims 1 to 6, wherein the average particle diameter of the heat conductor is 50 μm or less. A thermally conductive foam sheet for electronic equipment, which is obtained by foaming a foamable resin sheet according to any one of claims 1 to 7, and has a thickness of 0.3 mm or less and 25% compression The stress is 200 kPa or less, and the thickness accuracy is 20% or less. For example, the thermal conductive foam sheet for electronic equipment in the scope of patent application No. 8 has a thermal resistance at 50% compression of 10 ° C / W or less. For example, the thermally conductive foam sheet for electronic equipment in the scope of patent application No. 8 or 9, its 50% compressive stress is 400kPa or less.