JP2019065162A - Thermally conductive foam - Google Patents

Abstract

The present invention provides a thermally conductive foam which is excellent in thermal conductivity, has a high expansion ratio, and in which abnormal foaming is suppressed. A thermally conductive foam is obtained by foaming a foamable resin composition containing a matrix component containing a resin, a thermally conductive filler, a thermal decomposition-type foaming agent, and thermally expandable fine particles. It is a thermally conductive foam whose content of the said thermally conductive filler in a resin composition is 33 volume% or more, and the expansion | swelling start temperature of the said thermally expandable microparticles | fine-particles is 120 degreeC or more. 【Selection chart】 None

Description

  The present invention relates to thermally conductive foams.

  2. Description of the Related Art With the increase in performance and integration of components in small electronic devices such as smartphones and the miniaturization of devices, the increase in heat generated from components and devices has become remarkable. Not taking measures against heat not only leads to deterioration of the function and performance of the members and the reduction of the service life, but also the apparatus itself has heat and may cause low temperature burns and fire. In particular, heat dissipation measures for members that emit heat, such as a CPU, a PA (power amplifier), and an LED, are indispensable. As a heat countermeasure of these members, the heat generating member mounted inside the device and a metal member serving as a heat sink such as a sheet metal and a shield material inside the device are brought into contact with a heat dissipation material to make a heat path, and the temperature of the heat generating member decreases. It is common to try to As a conventional heat-radiation material, the silicone resin foam sheet which mix | blended the heat conductive filler is mentioned. In addition, a thermally conductive foam sheet for electronic devices containing an elastomer resin and a thermal conductor such as magnesium oxide or aluminum oxide is also known (Patent Document 1).

International Publication No. 2014/083890

However, the conventional heat dissipating material containing the heat conductive filler contains a relatively large amount of the heat conductive filler in order to improve the heat dissipating property. On the other hand, when a large amount of thermally conductive filler is blended to try a thermally conductive foam, in many cases, it is difficult to foam well. In particular, when attempting to obtain a high expansion ratio, abnormal foaming that generates large bubbles may occur, resulting in an appearance defect.
This invention is made in view of the said conventional subject, Comprising: It aims at providing the heat conductive foam which was excellent in heat conductivity, had high foaming ratio, and abnormal foam was suppressed. .

The inventors of the present invention conducted extensive research to achieve the above object, and as a result, a foam containing a resin-containing matrix component, a thermally conductive filler, a thermal decomposition-type foaming agent and thermally expandable fine particles and satisfying specific conditions It has been found that the problem can be solved by the heat conductive foam of the water resistant resin composition, and the present invention has been completed.
That is, the present invention relates to the following [1] to [6].

[1] A thermally conductive foam formed by foaming a foamable resin composition containing a matrix component containing a resin, a thermally conductive filler, a thermal decomposition-type foaming agent and thermally expandable fine particles, which is the foamable resin The thermally conductive foam, wherein the content of the thermally conductive filler in the composition is 33% by volume or more, and the expansion start temperature of the thermally expandable fine particles is 120 ° C. or more.
[2] The thermally conductive foam according to [1], wherein the thermally decomposable foaming agent is an azo compound or a nitroso compound.
[3] The thermally conductive foam according to [1] or [2], wherein the decomposition initiation temperature of the thermal decomposition-type foaming agent is equal to or higher than the expansion initiation temperature of the thermally expandable fine particles and the difference is within 95 ° C. .
[4] The heat according to any one of [1] to [3], wherein 5 to 30 parts by mass of the thermal decomposition-type foaming agent is contained in 100 parts by mass of the matrix component in the foamable resin composition Conductive foam.
[5] The foamable resin composition according to any one of [1] to [4], wherein the thermally expandable fine particles are contained in an amount of 0.3 to 20 parts by mass with respect to 100 parts by mass of the matrix component. Thermal conductive foam.
[6] The thermally conductive foam according to any one of [1] to [5], which has an expansion ratio of 2.5 times or more.

  ADVANTAGE OF THE INVENTION According to this invention, it is excellent in heat conductivity, can have a high expansion ratio, and can provide the thermally-conductive foam by which abnormal foaming was suppressed.

[Heat conductive foam]
The thermally conductive foam of the present invention is a foam of a foamable resin composition containing a matrix component containing a resin, a thermally conductive filler, a thermal decomposition-type foaming agent, and thermally expandable fine particles.
As described above, when only the conventional thermal decomposition-type foaming agent is used in the foamable resin composition, a high expansion ratio can be obtained if a large amount of the thermally conductive filler is blended to obtain the thermally conductive foam. It was difficult, and the appearance was sometimes impaired by abnormal foaming. On the other hand, in the thermally conductive foam of the present invention, since the foam having a cell wall is formed at the time of foaming by including the thermally expandable fine particles in the foamable resin composition, even a portion with a small amount of resin foams well. It is possible to In addition, in the portion where a large amount of resin is present, foaming by the thermal decomposition type foaming agent becomes possible. That is, due to the presence thereof, uniform foaming to the whole resin becomes possible, and a thermally conductive foam having a high expansion ratio while having good thermal conductivity even if a large number of thermally conductive fillers are blended. It is thought that can be done. Further, since the efficient foaming proceeds, abnormal foaming is also suppressed.
Hereinafter, the thermally conductive foam according to the embodiment of the present invention will be described in detail.

(Thermally expandable particles)
The thermally expandable particles generate cells having cell walls in the thermally conductive foam, and contribute to the improvement of the final expansion ratio. Therefore, from the viewpoint of obtaining a high expansion ratio, the expansion start temperature of the thermally expandable fine particles is 120 ° C. or higher, preferably 130 ° C. or higher, and more preferably 150 ° C. From the viewpoint of practical use, the temperature is preferably 270 ° C. or less.

  The expansion start temperature of the thermally expandable microparticles can be determined, for example, using a thermomechanical analyzer (TMA). That is, a predetermined sample is placed in an aluminum container, and heated from 80 ° C. to 220 ° C. at a temperature rising rate of 5 ° C./min, with a force of 0.1 N applied from above. The displacement of the measurement terminal in the vertical direction in this state is measured, and the temperature at which the displacement starts rising is taken as the expansion start temperature.

  The thermally expandable fine particles are not particularly limited as long as the expansion start temperature is 120 ° C. or higher, but it is preferable to use thermally expandable microcapsules. As the thermally expandable microcapsule, it is preferable to use a synthetic resin capsule in which a liquid or gas that is expanded by heating is contained. In particular, the microcapsules that form the outer shell are expanded by expansion of the liquid or gas contained by mixing and melting heat by screws or calenders in extrusion molding or injection molding, but they melt depending on the temperature conditions at the time of molding. It is preferable to use one that is completely molded without bursting.

  As a material of the microcapsule, a copolymer having acrylonitrile as one of monomer components is used, and as another monomer component to be copolymerized with acrylonitrile, for example, acrylic acid, methacrylic acid, acrylic ester, methacrylic ester, Examples include styrene, vinyl acetate, and vinylidene chloride.

The liquid or gas contained in the microcapsules is one that expands as a gas at a temperature below the softening point of the microcapsules, such as propane, propylene, butene, normal butane, isobutane, isopentane, neopentane, normal pentane, hexane Low boiling point liquids such as heptane, petroleum ether, halides of methane such as methyl chloride and methylene chloride, chlorofluorocarbons such as CCl ₃ F and CCl ₂ F ₂ , and tetraalkylsilanes such as tetramethylsilane and trimethylethylsilane Other examples include compounds such as AIBN which are pyrolyzed to a gaseous state by heating.

  Examples of commercially available thermally expandable microcapsules include, for example, EXPANSEL 980DU120, EXPANSEL 920DU40, EXPANSEL 920DU80, EXPANSEL 009DU80, EXPANSEL 920DU20 (manufactured by Nippon Filalight Co., Ltd.), Matsumoto Micro Sphere F-105D (manufactured by Matsumoto Yushi-Seiyaku Co., Ltd.), ADVANCEL EMH 204, ADVANCEL EM 501, ADVANCEL EM 403 (manufactured by Sekisui Chemical Co., Ltd.) and the like can be used.

  The content of the thermally expandable fine particles in the foamable resin composition is preferably 0.3 to 20 parts by mass, and more preferably 0.4 to 10 parts by mass, with respect to 100 parts by mass of the matrix component. When the content is 0.3 to 20 parts by mass, a better expansion ratio can be obtained.

  The thermally expandable fine particles preferably have a particle size of 10 μm or more after expansion, more preferably 30 μm or more, and still more preferably 100 μm or more. From the practical viewpoint, the particle diameter after expansion is preferably 200 μm or less.

(Pyrolytic foam)
The thermal decomposition-type foaming agent contributes to the improvement of the expansion ratio by the formation of air bubbles together with the thermally expandable fine particles. The foaming start temperature of the thermal decomposition type foaming agent is about 140 ° C. to 270 ° C. from the practical viewpoint, and various thermal decomposition type foaming agents such as organic type or inorganic type can be used.

As an organic foaming agent, azo compounds such as azodicarbonamide, metal salts of azodicarboxylate (such as barium azodicarboxylate), azobisisobutyronitrile and the like, nitroso compounds such as N, N'-dinitrosopentamethylenetetramine Examples include hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide), toluenesulfonylhydrazide, and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of inorganic foaming agents include ammonium carbonate, sodium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate and the like.

  Among the above, from the viewpoint of obtaining fine bubbles, and from the viewpoint of economy and safety, azo compounds and nitroso compounds are preferable, and azodicarbonamide, azobisisobutyronitrile, N, N'-dinitrosopentamethylene Tetramine is more preferred, and azodicarbonamide is even more preferred. These thermally decomposable blowing agents can be used alone or in combination of two or more.

  The decomposition initiation temperature of azodicarbonamide is about 200 ° C., although it depends on the particle size and the like. The decomposition initiation temperature can be lowered by mixing an azodicarbonamide with a foaming aid. Examples of the foaming aid include zinc oxide, lead oxide, cadmium oxide, magnesium oxide, zinc stearate, cadmium stearate, barium stearate, calcium stearate, zinc acetate, borax, urea, ethanolamine, biurea, dibasic acid Well-known assistants and additives such as lead phosphate, calcium hydroxide, glycerin, diethylene glycol, dibutyltin dimaleate, alkaline compounds, thioureas, thiazoles, sulpheamides, thiurams, and diocarbamic acid vulcanization accelerators, etc. Sulfur accelerators may be mentioned.

  The content of the thermal decomposition-type foaming agent in the foamable resin composition is preferably 5 to 30 parts by mass and more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the matrix component. When the content is 5 to 30 parts by mass, a better expansion ratio can be obtained.

  Moreover, it is preferable that the decomposition start temperature of the thermal decomposition type foaming agent is equal to or higher than the expansion start temperature of the thermally expandable fine particles, and the difference is within 95 ° C. When the difference is within 95 ° C., the decomposition of the thermal decomposition-type foaming agent and the expansion of the thermally expandable fine particles are easily generated uniformly. The difference is more preferably within 60 ° C.

  In addition, let the decomposition start temperature of a thermal decomposition type foaming agent be a weight loss start temperature in TG (thermogravimetric measurement) / DTA (differential thermal analysis). The temperature rise rate is about 2 ° C./min.

(Matrix component)
The “matrix component” according to the present invention is a resin, or a resin and an oil component, and for example, “elastomer resin”, “elastomer resin and polyolefin”, and “elastomer resin, polyolefin and process oil” are matrix components and Become.

<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 copolymers, hydrogenated styrene-isoprene block copolymers, hydrogenated styrene-isoprene-styrene block copolymers and the like. Among these, acrylonitrile butadiene rubber and ethylene propylene diene rubber are preferable, and ethylene propylene diene rubber is more preferable. These elastomers may be used alone or in combination of two or more.
These elastomers may be liquid elastomers which become liquid at room temperature (23 ° C.) and normal pressure (1 atm), may be solid, or may be a mixture thereof. However, it is preferred to use a mixture.

(Polyolefin)
By including a polyolefin of at least one of an ethylene-based resin and a propylene-based resin as a matrix component, the expansion ratio of the foamable resin composition is expanded to obtain a thermally conductive foam sheet in comparison with the conventional one. It can improve and improve flexibility. Moreover, it can be set as the thermally conductive foam sheet in the state which also maintained the high thermal conductivity by the thermally conductive filler. Furthermore, by improving the tensile strength of the raw fabric, the sheet is less likely to be broken, and productivity can be improved.

  The content of the polyolefin in the matrix component is preferably 25% by mass or less. It is preferable that it is 3-25 mass%.

Examples of the ethylene-based resin include low density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene and the like, and vinyl acetate or acrylic ester is contained as a monomer constituting the ethylene-based resin. Is preferred. By containing vinyl acetate or acrylic acid ester, the crosslinkability with an elastomer resin such as ethylene propylene diene rubber becomes good.
Further, the content of the monomer is preferably 2 to 45% by mass, and more preferably 2 to 35% by mass. When the content is 2 to 45% by mass, the tensile strength of the raw fabric can be improved, or the foaming ratio can be improved.

  Examples of the ethylene-based resin containing the above monomer include an ethylene-vinyl acetate copolymer (EVA resin) containing ethylene as a main component, an ethylene-alkyl acrylate copolymer containing ethylene as a main component, and the like. In addition, "an ethylene is a main component", Preferably ethylene content says 55 mass% or more.

  As ethylene-vinyl acetate copolymer (EVA resin) which has ethylene as a main component, ethylene-vinyl acetate copolymer such as ethylene-vinyl acetate copolymer and ethylene-vinyl acetate copolymer saponification of high temperature crosslinking type is modified Body resin etc. are mentioned.

The ethylene-alkyl acrylate copolymer containing ethylene as the main component (ethylene content is preferably 55% by mass or more) is a random copolymer even if it is an alternating copolymer of ethylene and alkyl acrylate, Also, it may be a block copolymer.
Specific examples of the alkyl acrylate include acrylates of alkyl having 1 to 4 carbon atoms such as methyl acrylate, ethyl acrylate, propyl acrylate and butyl acrylate. Preferred ethylene-alkyl acrylate copolymers include ethylene methyl acrylate copolymer (EMA), ethylene ethyl acrylate copolymer (EEA) and the like.

  Examples of the propylene-based resin include homopolypropylene, maleic acid modified polypropylene, chlorinated polypropylene, ethylene-propylene copolymer, butylene-propylene copolymer and the like. The propylene-based resin may be used alone, or a plurality of types of propylene-based resins may be used in combination.

  The melt flow rate of the polyolefin is 2 to 45 g / 10 min. Preferably 2 to 35 g / 10 min. More preferably, 2 to 10 g / 10 min. It is further preferred that Melt flow rate is 2 to 45 g / 10 min. Can prevent the bubbles from breaking.

(Process oil)
It is preferable to mix a process oil as a matrix component. By blending the process oil, the affinity with the elastomer resin is enhanced, the foamability becomes good, and the generation of coarse cells is suppressed.
The process oil is not particularly limited, and examples include vegetable oil, animal oil, mineral oil, synthetic oil and the like. Among these, at least one selected from the group consisting of mineral oil and synthetic oil is preferable. Examples of mineral oils include paraffinic process oils, naphthenic process oils, aromatic process oils and the like, and paraffinic process oils are preferred from the viewpoint of enhancing the affinity with the elastomer resin and suppressing the generation of coarse cells. . In particular, when ethylene propylene diene rubber is used as the elastomer resin, the generation of coarse bubbles is easily suppressed by using paraffinic process oil as the process oil. Products commercially available as paraffinic process oils include Diana Process Oil PW-32, PW-90, PW-380 manufactured by Idemitsu Kosan Co., Ltd., Super Oil M-10 manufactured by JX Energy Co., Ltd., M- 12, M-22, M-32, M-46, M-68, M-100, M-150, M-460, sunpers 107, 110, 115, 150, 2100, 2280 manufactured by Japan Sun Oil Co., Ltd. And Stanol LP40 manufactured by Esso Oil Co., Ltd.

The synthetic oil that is the process oil is not particularly limited, but hydrocarbon oligomers are preferable. As a hydrocarbon-based oligomer, a homopolymer-based oligomer obtained by polymerizing one kind of monomer selected from ethylene and α-olefins such as propylene, 1-butene, 1-pentene, 1-hexene and 1-octene, or Although any copolymerized oligomer obtained by copolymerizing two or more kinds of monomers may be used, a copolymerized oligomer is preferable from the viewpoint of enhancing the affinity with the elastomer resin and suppressing the generation of coarse cells. Among copolymerized oligomers, ethylene α-olefin oligomers obtained by copolymerizing ethylene and α-olefins are preferable, and ethylene-propylene oligomers are more preferable. As a copolymerization composition of ethylene propylene oligomer, it is preferable that ethylene content is 20-80 mass%, It is more preferable that it is 30-70 mass%, It is more preferable that it is 40-60 mass%, Crystal The structure is preferably amorphous. In particular, when ethylene propylene diene rubber is used as the elastomer resin, the generation of coarse bubbles is easily suppressed by using an ethylene propylene oligomer as the process oil. As a product marketed as an ethylene propylene oligomer, Mitsui Chemicals make Lucanto HC-40, HC-100, HC-600, HC-2000, etc. are mentioned.
The process oils may be used alone or in combination of two or more.

  The weight average molecular weight of the process oil is preferably 6500 or less. When the weight average molecular weight is 6500 or less, the number of coarse cells can be reduced, and the foamability of the thermally conductive foam sheet can be improved. From the viewpoint of suppressing the generation of coarse cells, it is preferably 300 to 5,000, more preferably 450 to 4,000, and still more preferably 500 to 2,000. 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 point of view, 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 still more preferably 70 to 3000 mm ² / s. More preferably, it is 80-500 mm < ² > / s. The kinematic viscosity can be measured by the method described in the examples.
70 mass% or less is preferable, and, as for content of the process oil in a matrix component, 20-50 mass% is more preferable.
The process oil may be substituted as long as it is compatible with an elastomer resin such as ethylene propylene diene rubber, and as such, a liquid elastomer such as liquid ethylene propylene diene rubber can be mentioned. Therefore, the preferred content of the liquid elastomer in this case is the same as the process oil. Moreover, when using together liquid elastomer and process oil, 70 mass% or less is preferable, and 20-50 mass% of the sum total of these in a matrix component is more preferable.

(Heat conductive filler)
Examples of the heat conductive filler include aluminum oxide, magnesium oxide, zinc oxide, boron nitride, talc, aluminum nitride, graphite, graphene, silica, silicon carbide, silicon nitride, titanium oxide, carbon fiber and the like, and others Also copper powder, nickel filler and the like. Among these, magnesium oxide, aluminum oxide, zinc oxide and boron nitride are preferable, and boron nitride and magnesium oxide are more preferable. The thermally conductive fillers may be used alone or in combination of two or more. These heat conductive fillers may be surface-treated to improve adhesion to resin and processability.
By adding the thermally conductive filler, the thermal conductivity of the thermally conductive foam sheet can be improved, but furthermore, the variation in the thermal conductivity between samples can be reduced, and the physical properties are stabilized. Improve the reliability of

From the viewpoint of excellent thermal conductivity, the content of the thermally conductive filler in the foamable resin composition is 33% by volume or more. If the content is less than 33% by volume, high thermal conductivity can not be obtained. The content of the heat conductive filler is more preferably 33 to 60% by volume.
The volume percent of the thermally conductive filler is calculated on the basis of the total volume of the foamable resin composition, but the volume of the thermally conductive filler described above can be calculated from the mass of the component to be blended. For example, it can be calculated by multiplying the mass of the component by the density at 23 ° C. of the component.

  It is preferable that it is 20-600 mass parts with respect to 100 mass parts of matrix components, as for the compounding quantity of a heat conductive filler, 100-450 mass parts is more preferable, and 150-450 mass parts is still more preferable.

2.0-8.0 g / cm < ³ > is preferable, as for the density of a heat conductive filler, 2.0-6.0 g / cm < ³ > is more preferable, and 2.0-5.0 g / cm < ³ > is still more preferable.
0.1-200 micrometers is preferable, as for the particle size of a heat conductive filler, 5-150 micrometers is more preferable, and 10-100 micrometers is still more preferable.
A laser diffraction / scattering particle size distribution analyzer (HELOS / BFM, manufactured by Sympatec GmbH) is used as a method of measuring the average particle size. With this apparatus, the particle size distribution is measured by a conventional method to determine the average particle size, and the average value of five measurements is taken as the average particle size.
The thermal conductivity of the thermally conductive filler is preferably 5 W / m · K or more, and more preferably 20 W / m · K or more.
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, and a needle shape, and different shapes may be mixed.

(Higher fatty acid derivative)
In the thermally conductive foam sheet according to the present invention, it is preferable to include a higher fatty acid derivative containing at least one of an ester structure and an amide structure in a matrix component. By adding the higher fatty acid derivative, the appearance can be kept good even when the content of the heat conductive filler is high. The higher fatty acid derivative is preferably contained in an amount of 0.5 to 12 parts by mass, and more preferably 1 to 10 parts by mass, with respect to 100 parts by mass of the matrix component.
It is preferable that carbon number of the fatty acid which comprises a higher fatty acid derivative is 16-24, and it is more preferable that it is 16-20. Moreover, it is preferable that the higher fatty acid derivative has an unsaturated bond.
Specific examples of the higher fatty acid derivative include Dai-Ichi Kogyo Seiyaku Co., Ltd. product name "Nuygen ES-99D" and NOF Corporation Co., Ltd. product name "Falpac L-1014".

(Optional ingredient)
The thermally conductive foam sheet can contain various additive components as needed in addition to the above, as long as the object of the present invention is not impaired. Specifically, these additive components are contained, for example, 50 parts by mass or less, preferably 20 parts by mass or less, with respect to 100 parts by mass of the matrix component.
The type of the additive component is not particularly limited, and various additives generally used for foam molding can be used. As such additives, for example, lubricants, internal lubricants, shrinkage inhibitors, foam nucleating agents, crystal nucleating agents, plasticizers, colorants (pigments, dyes, etc.), UV absorbers, antioxidants, anti-aging agents, The filler except the said conductivity imparting material, a reinforcing agent, a flame retardant, a flame retardant adjuvant, an antistatic agent, surfactant, a vulcanizing agent, a surface treatment agent etc. are mentioned. The addition amount of the additive can be appropriately selected within a range that does not impair the formation of air bubbles and the like, and the addition amount used for foaming and molding of a normal resin can be adopted. Such additives can be used alone or in combination of two or more.

(Physical properties of thermally conductive foam)
The apparent density of the thermally conductive foam is preferably 0.17 to 1.0 g / cm ³ , more preferably 0.2 to 1.0 g / cm ³ , still more preferably 0.2 to 0.8 g / cm ^3. More preferably, it is 0.2 to 0.5 g / cm ³ . By setting it as 1.0 g / cm ³ or less, the heat conductive foam sheet is reduced in weight, and when it is 0.2 g / cm ³ or more, many heat conductive fillers can be blended, and it is easy to make the heat conductivity good. Become.
The expansion ratio of the thermally conductive foam is preferably 2.5 times or more, preferably 2.5 to 8 times, and more preferably 2.5 to 5 times. While the thermal conductivity is good when the expansion ratio is 2.5 times or more, flexibility can be imparted to the foam.
The thickness of the thermally conductive foam sheet is appropriately selected depending on the use application 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.
0.3-2.0 W / m * K is preferable and, as for the heat conductivity at the time of 35% compression of a heat conductive foam, 0.5-2.0 W / m * K is more preferable.

  The heat conductive foam of the present invention is suitably used in the inside of an electronic device, for example, used as a heat dissipation sheet in a smartphone. More specifically, for example, the heat source and the heat dissipation member are appropriately compressed and disposed without a gap. In addition, when dropped, it is also possible to absorb an impact applied to the electronic component or the like.

[Method of producing thermally conductive foam]
The manufacturing method of the heat conductive foam sheet as one aspect of a heat conductive foam is demonstrated. First, a foamable resin composition obtained by blending and kneading the above-mentioned matrix component, thermal decomposition-type foaming agent and thermally expandable fine particles, thermally conductive filler, and other additives is formed into a sheet. Prepare a foamable resin sheet. Next, the foamable resin sheet is preferably crosslinked by ionizing radiation or the like and then manufactured by a method of heating and foaming in a heating apparatus such as a heating furnace or an oven.

(Production method of foamable resin sheet)
As a method of producing the foamable resin sheet, for example, after the foamable resin composition is kneaded using a kneading machine such as a Banbury mixer or a pressure kneader, it is continuously extruded by an extruder, a calender, a conveyor belt casting, etc. The method of manufacturing a foamable resin sheet by this is mentioned.

(Cross-linking method of foamable resin sheet)
Next, as a crosslinking method of the foamable resin sheet, crosslinking by ionizing radiation, crosslinking by organic peroxide, etc. may be mentioned, but crosslinking by ionizing radiation is preferable.
In the case of crosslinking by ionizing radiation, examples of the ionizing radiation include light, γ-rays, and electron beams. 0.5-10 Mrad is preferable and, as for the irradiation amount of ionizing radiation, 0.7-5.0 Mrad is more preferable.
When crosslinking is carried out by ionizing radiation, a thermally conductive foam sheet having a small diameter and uniform cells can be obtained. The thermally conductive foam sheet having such a small diameter and uniform cells has a smooth surface and a large contact area with respect to the adherend surface, thereby improving adhesion.

In the case of crosslinking with an organic peroxide, examples of the organic peroxide include diisopropylbenzene hydroperoxide, 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, t-butyl perbenzoate, cumyl hydroperoxide, t -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.
0.05-10 mass parts is preferable with respect to 100 mass parts of matrix components, and, as for the compounding quantity of an organic peroxide, 0.1-7 mass parts is more preferable.

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

[Adhesive sheet]
In the present invention, an adhesive material may be provided on one side or both sides of the thermally conductive foam sheet to form an adhesive sheet. The pressure-sensitive adhesive material comprises at least a pressure-sensitive adhesive layer, and the heat-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 laminated directly on the surface of the thermally conductive foam sheet, or a double-sided pressure-sensitive adhesive tape attached to the surface of the thermally conductive foam sheet. It may be.
The double-sided pressure-sensitive adhesive tape comprises a substrate and a pressure-sensitive adhesive layer provided on both sides of the substrate. The double-sided pressure-sensitive adhesive tape bonds one pressure-sensitive adhesive layer to the heat-conductive foam sheet and the other pressure-sensitive adhesive layer to the other member.

  The pressure-sensitive adhesive layer is composed of a pressure-sensitive adhesive. There is no restriction | limiting in particular as an adhesive, For example, although an acrylic adhesive, a urethane adhesive, a rubber 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 it is also possible to use a silicon-based pressure-sensitive adhesive on the side not in contact with the foam.

The present invention will be described in more detail by way of examples, but the present invention is not limited by these examples.
The materials used in the following examples and comparative examples are as follows.
(1) Ethylene-propylene-diene rubber (1) (solid EPDM (1))
Product name "EP21" manufactured by JSR Corporation
(2) Ethylene-propylene-diene rubber (2) (solid EPDM (2))
Product name "EP22" manufactured by JSR Corporation
(3) Process oil Idemitsu Kosan Co., Ltd., trade name "Diana Process Oil PW-380"
Weight average molecular weight (Mw): 750
Dynamic viscosity (40 ° C): 409 m ² / s

(4) Magnesium oxide (i) Magnesium oxide (1) (MgO (1))
Ube Material Co., Ltd., trade name "RF-50-SC"
Average particle size: 50 μm
Density: 3.65 g / cm ³
Thermal conductivity (λ): 42 to 60 W / m · K
Shape: Spherical (ii) Magnesium oxide (2) (MgO (2))
Kyowa Chemical Industry Co., Ltd. product name "Pyroquisma (registered trademark) 3320"
Average particle size: 20 μm
Density: 3.65 g / cm ³
Thermal conductivity (λ): 42 to 60 W / m · K
Shape: spherical

(5) Boron nitride (BN)
(I) Boron nitride (1) (BN (1))
Made of Momentive, product name "PT131"
Average particle size: 10 μm
Density: 2.2 g / cm ³
Thermal conductivity (λ): 30 to 150 W / m · K
Shape: scale-like (ii) boron nitride (2) (BN (2))
Made by Momentive Co., Ltd., trade name "PTX60S"
Aggregate average particle size: 60 μm
Density: 2.2 g / cm ³
Thermal conductivity (λ): 30 to 150 W / m · K
Shape: scale-like aggregate

(6) Thermally Expandable Fine Particles, Thermally Expandable Fine Particles (1): Nippon Philalight Co., Ltd., trade name "Expancel 980DU120"
Particle size 25 to 40 μm (120 μm after foaming)
Expansion start temperature 158-173 ° C
Thermally expandable particles (2): Nippon Philalight Co., Ltd., trade name "Expancer 920 DU 40"
Particle size 10 to 16 μm (40 μm after foaming)
Expansion start temperature 123 to 133 ° C
· Thermally expandable particles (3): Nippon Philalight Co., Ltd., trade name "Expancel 920 DU 20"
Particle size 5 to 10 μm (20 μm after foaming)
Expansion start temperature 120 ° C
· Thermally expandable fine particles (4): Sekisui Chemical Co., Ltd. product name, "Advancel EMH 204"
Particle size 35-45 μm
Expansion start temperature 110 ° C
· Thermally expandable particles (5): manufactured by Sekisui Chemical Co., Ltd., trade name "ADVANCEL EM304"
Particle size 23 to 29 μm
Expansion start temperature 135 ° C
· Thermally expandable fine particles (6): manufactured by Sekisui Chemical Co., Ltd., trade name "ADVANSEL EM501"
Particle size 22-28 μm
Expansion start temperature 160 ° C
· Thermally expandable particles (7): Sekisui Chemical Co., Ltd. product name, "Advancel EM 403"
Particle size 25-35 μm
Expansion start temperature 150 ° C

(7) Foaming agent (i) Azodicarbonamide (1) (ADCA (1))
Otsuka Chemical Co., Ltd. product name "# 1305-I", decomposition start temperature: 200 ° C, particle diameter 3.2μm
(Ii) azodicarbonamide (2) (ADCA (2))
Otsuka Chemical Co., Ltd. product name "3245I", decomposition start temperature: 210 ° C, particle diameter 25μm
(Iii) Dinitrosopentamethylenetetramine (DPT)
Otsuka Chemical Co., Ltd. product name "Cellular D", decomposition start temperature: 205 ° C
(Iv) azodicarbonamide (A) (ADCA (A))
Eiwa Kasei Kogyo Co., Ltd. product name, "DW 6", decomposition start temperature: 170 ° C., containing assistant (v) 4,4'-oxybis (benzenesulfonyl hydrazide) (OBSH)
Nagaha Kasei Kogyo Co., Ltd., trade name “N11000S”, decomposition start temperature: 170 ° C.

(8) Other Additives Internal Lubricant ・ ・ ・ Polymerized Wax Polymer Clariant Co., Ltd., trade name "PP1302"
Phenolic antioxidant ・ ・ ・ BASF Japan Ltd., trade name "Irganox 1010"

Example 1
50 parts by mass of ethylene-propylene-diene rubber (1), 50 parts by mass of liquid ethylene-propylene-diene rubber, 15 parts by mass of azodicarbonamide (1), 5 parts by mass of thermally expandable fine particles (1), 2 parts by mass of internal lubricant After melt-kneading 3 parts by mass of the agent, pressing was performed to obtain a foamable resin sheet having a thickness of 0.6 mm.
The surface of the obtained foamable resin sheet was irradiated with 1.2 Mrad of an electron beam 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 (thermally conductive foam).
The expansion ratio, the density and the thermal conductivity of the thermally conductive foam sheet were evaluated as follows.

Examples 2 to 18 and Comparative Examples 1 to 5
A thermally conductive foam sheet was produced in the same manner as in Example 1 except that the composition was changed as shown in Tables 1 to 3, and the following evaluation was performed. The results are shown in Table 1.

<Physical evaluation>
Physical properties of the obtained thermally conductive foam sheet were measured as follows. The measurement results are shown in Tables 1 and 2.
[Presence or absence of abnormal foaming]
Abnormal foam measurement method: Whether or not a large cell diameter of 3 mm or more in diameter is present on the surface of a 100 mm square sample sheet after foaming was confirmed by scale and visual observation. The case where there were less than 20 large bubbles having a diameter of 3 mm or more was regarded as no abnormal foaming (〇), and the case where 20 or more were present was regarded as abnormal bubbles (×).

[Expansion ratio]
The specific volume (unit: cm ³ / g) of the foamable resin sheet and the heat conductive foam sheet before foaming is measured, and the specific volume of the heat conductive foam sheet / the specific volume of the foamable resin sheet before foam Calculated.

〔Thermal conductivity〕
The thermal conductivity of the thermally conductive foam sheet is set to a thickness of 10 mm or more of a thermally conductive foam sheet of 25 mm × 25 mm using a hot disk thermal physical property measuring apparatus (manufactured by Kyoto Electronics Industry Co., Ltd., model name “TPS1500”). The test pieces were stacked in 35% compression to form test pieces, and the two test pieces were used to hold the sensor, heat the sensor, and measure the thermal conductivity from the temperature rise.

  As apparent from the results in Tables 1 to 3, it was found that the thermally conductive foam sheet of the present invention is excellent in thermal conductivity, has a high expansion ratio, and suppresses abnormal foaming.

Claims (6)

A thermally conductive foam obtained by foaming a foamable resin composition containing a matrix component containing a resin, a thermally conductive filler, a thermal decomposition type foaming agent, and thermally expandable fine particles,
The content of the thermally conductive filler in the foamable resin composition is 33% by volume or more,
The heat conductive foam whose expansion | swelling start temperature of the said thermally expandable microparticles | fine-particles is 120 degreeC or more.   The heat conductive foam according to claim 1, wherein the thermally decomposable foaming agent is an azo compound or a nitroso compound.   The thermally conductive foam according to claim 1 or 2, wherein the decomposition initiation temperature of the thermal decomposition-type foaming agent is equal to or higher than the expansion initiation temperature of the thermally expandable fine particles, and the difference is within 95 ° C.   The thermally conductive foam according to any one of claims 1 to 3, wherein 5 to 30 parts by mass of the thermal decomposition-type foaming agent is contained in 100 parts by mass of the matrix component in the foamable resin composition. body.   The thermal conductivity according to any one of claims 1 to 4, wherein the thermally expandable fine particles are contained in an amount of 0.3 to 20 parts by mass with respect to 100 parts by mass of the matrix component in the foamable resin composition. Foam.   The thermally conductive foam according to any one of claims 1 to 5, which has an expansion ratio of 2.5 times or more.