WO2018180319A1

WO2018180319A1 - Thermally conductive foam sheet

Info

Publication number: WO2018180319A1
Application number: PCT/JP2018/008858
Authority: WO
Inventors: 梨絵松井; 一平藤本; 典男神保
Original assignee: 積水化学工業株式会社
Priority date: 2017-03-30
Filing date: 2018-03-07
Publication date: 2018-10-04
Also published as: JPWO2018180319A1

Abstract

The thermally conductive foam sheet of the present invention comprises 100 parts by mass of a main ingredient comprising an elastomer resin and a process oil and 150-550 parts by mass of a thermally conductive filler, the content of the process oil being 18-75 parts by mass per 100 parts by mass of the main ingredient, the process oil having a weight-average molecular weight of 6,500 or less. The present invention can provide a thermally conductive foam sheet which is excellent in terms of thermal conductivity and foaming property, has few coarse cells, and has high product reliability.

Description

Thermally conductive foam sheet

The present invention relates to a thermally conductive foam sheet.

Due to the high performance and integration of components in small electronic devices such as smartphones, the heat generated from the components and devices is significantly increased due to the downsizing of the devices. In addition to lowering the temperature, the device itself has heat, which may cause low-temperature burns or ignition. As a heat countermeasure for these members, a heat path is created by bringing the heat generating member mounted inside the device into contact with a metal member that also serves as a heat sink, such as a sheet metal or shield material, inside the device, thereby reducing the temperature of the heat generating member. It is common to plan. As a conventional heat dissipating material, a silicone resin foam sheet containing a heat conductive filler can be used. Moreover, the heat conductive foam sheet for electronic devices containing an elastomer resin and heat conductors, such as magnesium oxide or aluminum oxide, is also known (patent document 1).

International Publication No. 2014/083890

However, the conventional thermally conductive foam sheet containing the thermally conductive filler contains a relatively large amount of thermally conductive filler in order to improve heat dissipation. In the case of contact between the member and the metal member, the adhesion tends to deteriorate. In addition, a thermally conductive foam sheet containing a thermally conductive filler tends to generate a large number of coarse bubbles, and thus there is a problem that the reliability of the product is not sufficient, such as insufficient thermal performance. It was.
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a thermally conductive foam sheet that is excellent in thermal conductivity and foamability, has few coarse bubbles, and is highly reliable as a product. And

The inventors of the present invention have made extensive studies in order to achieve the above object. As a result, it contains 100 parts by mass of a main agent composed of an elastomer resin and process oil and 150 to 550 parts by mass of a heat conductive filler, and the content of process oil in 100 parts by mass of the main ingredient is 18 to 75 parts by mass. The present invention was completed by finding that a heat conductive foam sheet having a weight average molecular weight of 6500 or less can solve the above problems.
That is, the present invention relates to the following [1] to [11].
[1] containing 100 parts by mass of a main agent composed of an elastomer resin and a process oil, and 150 to 550 parts by mass of a heat conductive filler, and the content of process oil in 100 parts by mass of the main agent is 18 to 75 parts by mass; The heat conductive foam sheet whose weight average molecular weight of the said process oil is 6500 or less.
[2] The thermally conductive foam sheet according to [1], wherein the process oil is at least one selected from the group consisting of mineral oil and synthetic oil.
[3] The thermally conductive foam sheet according to [1], wherein the process oil is a paraffinic process oil.
[4] The thermally conductive foam sheet according to the above [1], wherein the process oil is a hydrocarbon oligomer.
[5] The thermally conductive foam sheet according to any one of [1] to [4] above, wherein the process oil has a kinematic viscosity at 40 ° C. of 30000 mm ² / s or less.
[6] The thermally conductive foam sheet according to any one of the above [1] to [5], wherein the elastomer resin is ethylene propylene diene rubber.
[7] The thermally conductive filler is aluminum oxide, magnesium oxide, zinc oxide, boron nitride, talc, aluminum nitride, graphite, graphene, crystalline silica, silicon carbide, silicon nitride, beryllia, diamond, graphite, carbon nanotube, and The thermally conductive foam sheet according to any one of the above [1] to [6], which is at least one selected from the group consisting of carbon fibers.
[8] The thermally conductive foam sheet according to any one of [1] to [7], wherein the expansion ratio is 2 to 10 times.
[9] The thermally conductive foam sheet according to any one of [1] to [8] above, wherein the content of the elastomer resin is 80% by mass or more based on the total amount of the resin components.
[10] The thermally conductive foam sheet according to any one of [1] to [9] above, wherein the thermally conductive foam sheet comprises a main agent and a thermally conductive filler.
[11] An adhesive sheet comprising the thermally conductive foam sheet according to any one of [1] to [10] above and an adhesive material provided on one or both surfaces of the thermally conductive foam sheet.

According to the present invention, it is possible to provide a thermally conductive foam sheet that has good thermal conductivity and foamability, has few coarse bubbles, and is highly reliable as a product.

[Thermal conductive foam sheet]
The thermally conductive foam sheet of the present invention contains 100 parts by mass of a main agent composed of an elastomer resin and a process oil, and 150 to 550 parts by mass of a heat conductive filler, and the content of process oil in 100 parts by mass of the main agent. The thermally conductive foam sheet is 18 to 75 parts by mass, and the process oil has a weight average molecular weight of 6500 or less.

<Main agent>
The main agent in the present invention is composed of an elastomer resin and a process oil. The content of process oil in 100 parts by mass of the main agent is 18 to 75 parts by mass, preferably 25 to 70 parts by mass, and more preferably 35 to 60 parts by mass. When the process oil content is less than 18 parts by mass, coarse bubbles are likely to be generated. When the process oil content is more than 75 parts by mass, the generation of coarse bubbles is reduced, but the foaming property is deteriorated and the expansion ratio is lowered. Tend to.

(Elastomer resin)
The elastomer resin is not particularly limited, but acrylonitrile butadiene rubber, ethylene propylene diene rubber, ethylene propylene rubber, natural rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene block copolymer, hydrogenated styrene-butadiene block copolymer. And hydrogenated styrene-butadiene-styrene block copolymer, hydrogenated styrene-isoprene block copolymer, hydrogenated styrene-isoprene-styrene block copolymer, and the like. Among these, acrylonitrile butadiene rubber and ethylene propylene diene rubber are preferable, and ethylene propylene diene rubber is more preferable from the viewpoint of improving foamability even if a relatively large amount of thermally conductive filler is blended. These elastomer resins may be used alone or in combination of two or more.
In addition, these elastomers may be liquid elastomers that are liquid at room temperature (23 ° C.) and normal pressure (1 atm), may be solid, or may be a mixture thereof. . From the viewpoint of suppressing the generation of coarse bubbles, when using a mixture, the amount of the solid elastomer resin is preferably larger than the amount of the liquid elastomer resin, and the total amount of the solid elastomer resin and the liquid elastomer resin is based on the total amount. The solid elastomer resin is preferably 80% by mass or more, more preferably 95% by mass or more, and further preferably 100% by mass. That is, from the viewpoint of suppressing the generation of coarse bubbles, it is preferable to use a solid elastomer resin alone as the elastomer resin.

The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of the solid elastomer is preferably 10 to 100, more preferably 10 to 70, and more preferably 20 to 50. Here, Mooney viscosity (ML _{1 + 4} , 100 ° C.) is a value measured in accordance with JIS K6300-1. By setting the Mooney viscosity of the solid elastomer within these ranges, it becomes easy to improve foamability.

(Process oil)
Process oil is used for the thermally conductive foam sheet of the present invention. By blending the process oil, the affinity with the elastomer resin is increased, the foamability is improved, and the generation of coarse bubbles is suppressed.
Although it does not restrict | limit especially as process oil, Vegetable oil, animal oil, mineral oil, synthetic oil etc. are mentioned. Among these, at least one selected from the group consisting of mineral oil and synthetic oil is preferable. Examples of the mineral oil include paraffinic process oil, naphthenic process oil, aromatic process oil, and the like, and paraffinic process oil is preferable from the viewpoint of increasing affinity with the elastomer resin and suppressing the generation of coarse bubbles. . In particular, when ethylene propylene diene rubber is used as the elastomer resin, the use of paraffinic process oil as the process oil makes it easy to suppress the generation of coarse bubbles. Products that are commercially available as paraffinic process oil include Diana Process Oil PW-32, PW-90, PW-380 manufactured by Idemitsu Kosan Co., Ltd., Super Oil M-10, M- manufactured by JX Energy Co., Ltd. 12, M-22, M-32, M-46, M-68, M-100, M-150, M-460, Nippon San Oil Co., Ltd. Thamper 107, 110, 115, 150, 2100, 2280 And Stanol LP40 manufactured by Esso Petroleum Corporation.

Although it does not restrict | limit especially as a synthetic oil which is a process oil, A hydrocarbon-type oligomer is preferable. As the hydrocarbon oligomer, a homopolymer oligomer obtained by polymerizing a single monomer selected from ethylene and α-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or the like, or Any of the copolymerization type oligomers which copolymerized 2 or more types of monomers may be sufficient. From the viewpoint of increasing the affinity with the elastomer resin and suppressing the generation of coarse bubbles, a copolymer oligomer is preferred. Among the copolymer oligomers, an ethylene α-olefin oligomer obtained by copolymerizing ethylene and an α-olefin is preferable, and an ethylene-propylene oligomer is more preferable. As a copolymer composition of the ethylene propylene oligomer, the ethylene content is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, further preferably 40 to 60% by mass, The structure is preferably amorphous. In particular, when ethylene propylene diene rubber is used as the elastomer resin, the use of ethylene propylene oligomer as the process oil makes it easy to suppress the generation of coarse bubbles. Examples of products that are commercially available as ethylene propylene oligomers include Lucant HC-40, HC-100, HC-600, and HC-2000 manufactured by Mitsui Chemicals.
Process oils may be used alone or in combination of two or more.

The weight average molecular weight of the process oil of the present invention is 6500 or less. When the weight average molecular weight is larger than 6500, the number of coarse bubbles tends to increase. The weight average molecular weight of the process oil is preferably 300 to 5000, more preferably 450 to 4000, and still more preferably from the viewpoint of improving the foamability of the thermally conductive foam sheet and suppressing the generation of coarse bubbles. Is 500-2000. The weight average molecular weight can be measured using gel permeation chromatography (GPC), and can be measured in detail by the method described in the Examples.

From the same viewpoint, the kinematic viscosity at 40 ° C. of the process oil is preferably 30000 mm ² / s or less, more preferably 20 to 10000 mm ² / s, and further preferably 70 to 3000 mm ² / s. More preferably, it is 80 to 500 mm ² / s. The kinematic viscosity can be measured by the method described in the examples.

<Thermal conductive filler>
The thermally conductive foam sheet of the present invention contains 150 to 550 parts by mass of a thermally conductive filler with respect to 100 parts by mass of the main agent composed of an elastomer resin and process oil. When the thermal conductive filler is less than 150 parts by mass, the thermal conductivity of the thermal conductive foam sheet is low, and when it exceeds 550 parts by mass, the foamability tends to be poor. Examples of the thermally conductive filler include aluminum oxide, magnesium oxide, zinc oxide, boron nitride, talc, aluminum nitride, graphite, graphene, crystalline silica, silicon carbide, silicon nitride, beryllia, diamond, graphite, and carbon nanotube ( CNT), carbon fiber, and the like, and besides these, copper powder, nickel filler, and the like can be given. Among these, magnesium oxide, aluminum oxide, zinc oxide, and boron nitride are preferable, and magnesium oxide is more preferable. A heat conductive filler may be used individually by 1 type, and 2 or more types may be mixed and used for it. These fillers may be surface-treated in order to improve adhesion to the resin and workability.

The blending amount of the heat conductive filler is preferably 200 to 500 parts by mass, more preferably 230 to 400 parts by mass, and further preferably 250 to 350 parts by mass with respect to 100 parts by mass of the main agent. . By setting the thermal conductive filler in such a range, the thermal conductivity of the thermal conductive foam sheet is improved, and the foaming property is likely to be excellent.
The particle size of the heat conductive filler is preferably 0.1 to 200 μm, more preferably 5 to 150 μm, and still more preferably 8 to 50 μm.
For the measurement method of the average particle size, a laser diffraction / scattering particle size distribution measuring device (HELOS / BFM, manufactured by Sympatec GmbH) is used. With this apparatus, the particle size distribution is measured by a conventional method to determine the average particle size, and the average value when five measurements are taken is taken as the average particle size.
The thermal conductivity of the thermally conductive filler is preferably 5 W / m · K or more, more preferably 20 W / m · K or more, and preferably 2000 W / m · K or less.
The shape of the heat conductive filler is not particularly limited, and may be any shape such as a spherical shape, a hollow shape, a plate shape, a scaly shape, a needle shape, and a fiber shape.

In the thermally conductive foam sheet, from the viewpoint of weight reduction, the filler volume% is preferably 25 to 60 volume%, more preferably 30 to 50 volume%, and still more preferably 35 to 50 volume%. It is preferable to mix.
The volume% of the heat conductive filler is calculated on the basis of the total volume of the heat conductive foam sheet, but the volume of the heat conductive foam sheet is, for example, that of the foamable resin composition described later. It is possible to calculate by subtracting the volume of the additive (foaming agent) that decomposes and disappears during foaming from the total volume. Moreover, the volume of the above-described heat conductive filler can be calculated from the mass of each component to be blended, and can be calculated, for example, by multiplying the mass of each component by the density at 23 ° C. of each component.

<Other resins>
The heat conductive foam sheet may contain other resins other than the elastomer resin as long as the effects of the present invention are not hindered. The content of the elastomer resin is preferably 80% by mass or more, more preferably 95% by mass or more, and 97% by mass or more with respect to the resin component total amount standard (total amount of the elastomer resin and other resins). More preferably, it is more preferably 100% by mass.
Examples of other resins other than the elastomer resin include thermoplastic resins such as polypropylene, polyethylene, polymethylpentene, ethylene-propylene copolymer, and polystyrene.
In addition, it is preferable that the elastomer resin and process oil which comprise the main ingredient of this invention, and other resin mix | blended as needed are mutually compatible in a heat conductive foam sheet. In addition, being compatible means that a phase separation structure such as a sea-island structure is not formed.

<Optional component>
The thermally conductive foam sheet may be composed of a main agent and a thermally conductive filler, but in addition to these, various additive components are contained as necessary within the range in which the object of the present invention is not impaired. be able to. Specifically, these additive components are contained in an amount of, for example, 50 parts by mass or less, preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and further preferably 5 parts by mass or less, with respect to 100 parts by mass of the main agent. The
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 copper damage prevention. Agents, fillers excluding the above-mentioned conductivity-imparting materials, reinforcing agents, flame retardants, flame retardant aids, antistatic agents, surfactants, vulcanizing agents, surface treatment agents and the like. 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.

<Physical properties of thermally conductive foam sheet>
The expansion ratio of the thermally conductive foam sheet is preferably 2 to 10 times, more preferably 3 to 8 times, still more preferably 4 to 8 times, and further preferably 4.5 to 7 times. When the expansion ratio is 2 times or more, the thermally conductive foam sheet becomes light. In addition, flexibility is increased, and for example, adhesion to a member inside the electronic device is increased. When the expansion ratio is 10 times or less, the thermal conductivity is good.
The thickness of the thermally conductive foam sheet is appropriately selected depending on the intended use and is not particularly limited, but is preferably 0.05 to 2 mm, more preferably 0.1 to 1.5 mm, and still more preferably 0.2. ~ 1 mm.
The thermal conductivity at 50% compression of the thermally conductive foam sheet is preferably 0.3 to 5.0 W / m · K, and more preferably 0.4 to 3.0 W / m · K.
The number of coarse bubbles having a maximum diameter of 2.0 mm or more in the thermally conductive foam sheet is preferably 3 or less per 1 m ³ , and more preferably 2 or less. The number of coarse bubbles can be measured by the method described in Examples.

The heat conductive foam sheet of the present invention is suitably used inside an electronic device. That is, the thermally conductive foam sheet of the present invention is, for example, a mobile phone such as a smartphone, a camera, a game machine, an electronic notebook, a tablet terminal, a notebook personal computer or the like, preferably a mobile phone such as a smartphone. Is preferably used as a heat dissipation sheet. More specifically, for example, it is appropriately compressed between the heat source and the heat radiating member, and is arranged without a gap. Moreover, when it falls, it also becomes possible to absorb the impact provided to an electronic component etc.

<The manufacturing method of a heat conductive foam sheet>
The thermally conductive foam sheet is formed from a foamable resin composition obtained by blending and kneading the above-mentioned main agent, thermally conductive filler, foaming agent, and other additives as necessary. It is preferable to prepare a foamable resin sheet by the above method, then cross-link with ionizing radiation or the like, and then heat and foam in a heating apparatus such as a heating furnace or an oven.
A thermal decomposition type foaming agent is preferable as the foaming agent. Specific examples of the pyrolytic foaming agent include organic or inorganic chemical foaming agents having a decomposition temperature of about 140 ° C. to 270 ° C.
Organic foaming agents include azodicarbonamide, azodicarboxylic acid metal salts (such as barium azodicarboxylate), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N, N′-dinitrosopentamethylenetetramine, And hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate, and the like.
Among these, azo compounds and nitroso compounds are preferable from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety, and azodicarbonamide, azobisisobutyronitrile, N, N′-dinitrosopentamethylene. Tetramine is more preferred, and azodicarbonamide is particularly preferred. These pyrolytic foaming agents can be used alone or in combination of two or more.
The blending amount of the pyrolytic foaming agent is preferably 1 to 30 parts by mass with respect to 100 parts by mass of the main agent. By setting it as such a compounding quantity, it can foam appropriately, without the bubble of a sheet | seat exploding. Moreover, if the compounding quantity of a thermal decomposition type foaming agent is increased, a foaming ratio will become high and it is possible to improve a softness | flexibility. Therefore, the blending amount of the pyrolytic foaming agent is more preferably 5 to 25 parts by mass, and further preferably 10 to 25 parts by mass.

(Method for producing foamed resin sheet)
As a method for producing the foamable resin sheet, for example, the foamable resin composition is kneaded using a kneader such as a Banbury mixer or a pressure kneader, and then continuously extruded by an extruder, calendar, conveyor belt casting or the like. The method of manufacturing a foamable resin sheet by this is mentioned.

(Method for crosslinking foamable resin sheet)
Next, examples of the crosslinking method of the foamable resin sheet include crosslinking by ionizing radiation, crosslinking by organic peroxide, and the like, and crosslinking by ionizing radiation is preferable.
In the case of crosslinking with ionizing radiation, examples of the ionizing radiation include light, γ-rays, and electron beams. The irradiation dose of ionizing radiation is preferably 0.5 to 10 Mrad, more preferably 0.7 to 5.0 Mrad.
When cross-linking is performed by ionizing radiation, a thermally conductive foam sheet having uniform bubbles with a small diameter can be obtained. Such a thermally conductive foam sheet having small diameters and uniform bubbles has a smooth surface, a large contact area with respect to the adherend surface, and improved adhesion.

When crosslinking with an organic peroxide, examples of the organic peroxide include diisopropylbenzene hydroperoxide, 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, t-butyl perbenzoate, cumyl hydroperoxide, tyl -Butyl hydroperoxide, 1,1-di (t-butylperoxy) -3,3,5-trimethylhexane, n-butyl-4,4-di (t-butylperoxy) valerate, α, α ' -Bis (t-butylperoxyisopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3, t-butylperoxycumene and the like.
The compounding amount of the organic peroxide is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 7 parts by mass with respect to 100 parts by mass of the main agent.

[Foaming method of foamable resin sheet]
Examples of the method for foaming the foamable resin sheet include a batch system such as an oven and a continuous foaming system in which the foamable resin sheet is formed into a long sheet shape and continuously passed through a heating furnace. The heating temperature is preferably 200 to 320 ° C, more preferably 250 to 300 ° C.

[Adhesive sheet]
In the present invention, a pressure-sensitive adhesive sheet may be provided by providing a pressure-sensitive adhesive on one side or both sides of the thermally conductive foam sheet. The pressure-sensitive adhesive sheet is a pressure-sensitive adhesive sheet comprising a heat conductive foam sheet and a pressure-sensitive adhesive material provided on one or both sides of the heat conductive foam sheet. The pressure-sensitive adhesive material includes at least a pressure-sensitive adhesive layer, and the thermally conductive foam sheet is adhered to another member by the pressure-sensitive adhesive layer. More specifically, the pressure-sensitive adhesive material may be a single pressure-sensitive adhesive layer directly laminated on the surface of the heat conductive foam sheet, or a double-sided pressure-sensitive adhesive tape attached to the surface of the heat conductive foam sheet. There may be.
The double-sided pressure-sensitive adhesive tape includes a base material and a pressure-sensitive adhesive layer provided on both surfaces of the base material. In the double-sided pressure-sensitive adhesive tape, one pressure-sensitive adhesive layer is bonded to the thermally conductive foam sheet, and the other pressure-sensitive adhesive layer is bonded to another member.

The adhesive layer is composed of an adhesive. There is no restriction | limiting in particular as an adhesive, For example, an acrylic adhesive, a urethane type adhesive, a rubber-type adhesive, etc. are mentioned, Among these, an acrylic adhesive is preferable. Moreover, as a base material of a double-sided adhesive tape, a resin film is used, for example. The pressure-sensitive adhesive may have different specifications on both sides, and a silicon-based pressure-sensitive adhesive can be used on the surface that does not contact the foam.

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.

[Elastomer resin]
(Ethylene-propylene-diene rubber (solid))
Product name “EP21” manufactured by JSR Corporation
Ethylene content: 61% by mass, diene content: 5.8% by mass
Mooney viscosity: 35 (ML _{1 + 4} , 100 ° C.)
(Liquid ethylene-propylene-diene rubber (a))
Product name “PX-068” manufactured by Mitsui Chemicals, Inc.
Number average molecular weight: 920
Viscosity at 23 ° C .: 10 Pa · s
Ethylene content 50% by mass, diene content 11% by mass
(Liquid ethylene-propylene-diene rubber (b))
Product name “T-65” manufactured by Lion Elastomer Co., Ltd.
Number average molecular weight: 7000
Viscosity at 20 ° C .: 11000 Pa · s
Diene content 10.5% by mass

[Process oil]
(Paraffinic process oil (a))
Product name “Diana Process Oil PW-32” manufactured by Idemitsu Kosan Co., Ltd.
Weight average molecular weight (Mw): 400
Kinematic viscosity (40 ° C.): 31 mm ² / s
(Paraffinic process oil (b))
Product name "Diana Process Oil PW-90" manufactured by Idemitsu Kosan Co., Ltd.
Weight average molecular weight (Mw): 530
Kinematic viscosity (40 ° C.): 91 mm ² / s
(Paraffinic process oil (c))
Product name “Diana Process Oil PW-380”, manufactured by Idemitsu Kosan Co., Ltd.
Weight average molecular weight (Mw): 750
Kinematic viscosity (40 ° C.): 409 mm ² / s
(Hydrocarbon oligomer (a))
Product name "Lucanto HC-40" manufactured by Mitsui Chemicals, Inc.
Ethylene-propylene oligomer Ethylene / propylene composition ratio 50/50
Crystal structure: amorphous Weight average molecular weight (Mw): 1030
Kinematic viscosity (40 ° C.): 400 mm ² / s
(Hydrocarbon oligomer (b))
Product name "Lucant HC-100" manufactured by Mitsui Chemicals, Inc.
Ethylene-propylene oligomer Ethylene / propylene composition ratio 50/50
Crystal structure: amorphous Weight average molecular weight (Mw): 2400
Kinematic viscosity ^{(40 ℃): 1300mm 2 /} s
(Hydrocarbon oligomer (c))
Product name "Lucant HC-600" manufactured by Mitsui Chemicals, Inc.
Ethylene-propylene oligomer Ethylene / propylene composition ratio 50/50
Crystal structure: amorphous Weight average molecular weight (Mw): 4700
Kinematic viscosity (40 ° C.): 10,000 mm ² / s
(Hydrocarbon oligomer (d))
Product name "Lucant HC-2000" manufactured by Mitsui Chemicals, Inc.
Ethylene-propylene oligomer Ethylene / propylene composition ratio 50/50
Crystal structure: amorphous Weight average molecular weight (Mw): 7000
Kinematic viscosity (40 ° C.): 37500 mm ² / s

[Thermal conductive filler]
(Magnesium oxide)
Product name “RF-10C” manufactured by Ube Material Co., Ltd.
Particle size: 10 μm
Density: 3.65 g / cm ³
Thermal conductivity (λ): 42-60W / m · K
Shape: Spherical (boron nitride)
Product name “PT131” manufactured by Momentive
Particle size: 10 μm
Density: 2.2 g / cm ³
Thermal conductivity (λ): 30 to 150 W / m · K
Shape: scaly

[Foaming agent]
Azodicarbonamide Ebina Kasei Kogyo Co., Ltd. trade name “Vinole Hall AC-K3-TA”, decomposition temperature: 210 ° C.
[Phenolic antioxidant]
Product name "Irganox 1010", manufactured by BASF Corporation

The measurement methods of average molecular weight, Mooney viscosity, viscosity, and kinematic viscosity are as follows.
[Average molecular weight]
The weight average molecular weight of the process oil was calculated as a polystyrene equivalent value using gel permeation chromatography (GPC). The GPC measurement was performed at the apparatus name (2690 Separations Model manufactured by Waters), the column used KF-806L (manufactured by Showa Denko), the measurement solvent THF, and the temperature of 40 ° C.
[Mooney viscosity (100 ° C), viscosity (25 ° C)]
The Mooney viscosity (ML _{1 + 4} , 100 ° C.) of ethylene propylene diene rubber at 100 ° C. is a value measured according to JIS K6300-1. The viscosity at 20 ° C. or 25 ° C. of the liquid ethylene propylene diene rubber is a value measured with a B-type rotational viscometer at a rotational speed of 1 rpm.
[Kinematic viscosity]
The kinematic viscosity of the process oil is measured at 40 ° C. using an Ubbelohde viscometer.

Example 1
80 parts by mass of ethylene propylene diene rubber, 20 parts by mass of paraffinic process oil (c), 300 parts by mass of magnesium oxide, 17.5 parts by mass of azodicarbonamide, and 3 parts by mass of antioxidant are melt-kneaded and then thickened by pressing. A foamable resin sheet having a thickness of 0.5 mm was obtained.
Both surfaces of the obtained foamable resin sheet were irradiated with an electron beam of 1.2 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 thermally conductive foam sheet.
About the said heat conductive foam sheet, the expansion ratio, the thermal conductivity, and the number of coarse bubbles were evaluated as shown below. The results are shown in Table 1.

Examples 2 to 16, Comparative Examples 1 to 7
Except that the formulation was changed as described in Tables 1 and 2, a thermally conductive foam sheet was produced in the same manner as in Example 1, and the following evaluation was performed. The results are shown in Tables 1 and 2.

[Evaluation of the physical properties]
The physical properties of the obtained heat conductive foam sheet were measured as follows. The measurement results are shown in Tables 1 and 2.
(Foaming ratio)
The specific volume (unit: cm ³ / g) of the foamable resin sheet before foaming and the heat conductive foam sheet is measured, and the specific volume of the heat conductive foam sheet / the specific volume of the foamable resin sheet before foaming Calculated.
(Thermal conductivity)
The thermal conductivity of the conductive foam sheet is 10 mm or more from a 25 mm × 25 mm thermal conductive foam sheet using a hot disk thermophysical property measuring apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., model name “TPS1500”). Thus, the test piece was compressed by 50% to be a test piece, the sensor was sandwiched between the two test pieces, the sensor was heated, and the thermal conductivity was measured from the temperature rise.
(Number of coarse bubbles)
A thermally conductive foam sheet was passed over the light box, and the presence of bubbles was confirmed visually. The maximum diameter of the bubbles was measured with a microgauge, and the number of coarse bubbles present in the thermally conductive foam sheet 1 m ³ was confirmed with the bubbles having a length of 2 mm or more as coarse bubbles.

As is clear from the results in Table 1, the thermally conductive foam sheet of the present invention in which a certain amount of process oil having a specific range of weight average molecular weight is blended has high thermal conductivity, good foamability, and coarse bubbles. It turns out that there are few. On the other hand, in the comparative example which does not use the process oil specified by the present invention shown in Table 2, it was found that coarse bubbles increase or foamability is not good.

Claims

100 parts by mass of a main agent composed of an elastomer resin and a process oil and 150 to 550 parts by mass of a heat conductive filler, and the content of the process oil in 100 parts by mass of the main agent is 18 to 75 parts by mass. The heat conductive foam sheet whose weight average molecular weight is 6500 or less.
The heat conductive foam sheet according to claim 1, wherein the process oil is at least one selected from the group consisting of mineral oil and synthetic oil.
The heat conductive foam sheet according to claim 1, wherein the process oil is a paraffinic process oil.
The heat conductive foam sheet according to claim 1, wherein the process oil is a hydrocarbon oligomer.
The thermally conductive foam sheet according to any one of claims 1 to 4, wherein the process oil has a kinematic viscosity at 40 ° C of 30000 mm 2 / s or less.
The thermally conductive foam sheet according to any one of claims 1 to 5, wherein the elastomer resin is ethylene propylene diene rubber.
The thermally conductive filler is made of aluminum oxide, magnesium oxide, zinc oxide, boron nitride, talc, aluminum nitride, graphite, graphene, crystalline silica, silicon carbide, silicon nitride, beryllia, diamond, graphite, carbon nanotube, and carbon fiber. The thermally conductive foam sheet according to any one of claims 1 to 6, which is at least one selected from the group consisting of:
The thermally conductive foam sheet according to any one of claims 1 to 7, wherein the expansion ratio is 2 to 10 times.
The thermally conductive foam sheet according to any one of claims 1 to 8, wherein the content of the elastomer resin is 80% by mass or more based on the total amount of the resin components.
The thermally conductive foam sheet according to any one of claims 1 to 9, wherein the thermally conductive foam sheet comprises a main agent and a thermally conductive filler.
An adhesive sheet comprising the thermally conductive foam sheet according to any one of claims 1 to 10 and an adhesive material provided on one side or both sides of the thermally conductive foam sheet.