Foam, member, and heat dissipation structure

Abstract

A foam 1a includes a crosslinked rubber 11 and thermally conductive particles 12. When 50% compressive strain is generated in the foam 1a, the foam 1a has a compressive stress PC of 1.2 MPa or less. When 50% compressive strain is generated in the foam 1a, the thermal conductivity lambdaC in the compression direction of the foam 1a is 0.3 Wm-1K-1 or more.

Description

Foam, component, and heat dissipation structure

[0001] The present invention relates to a foam, a member, and a heat dissipation structure.

[0002] 2. Description of the Related Art Conventionally, a heat dissipation member that is disposed between a heat generating component and a heat dissipating component is known.

[0003] For example, Patent Document 1 describes a heat dissipation sheet having a thermally conductive silicone cured product. The thermally conductive silicone cured product is formed by curing a predetermined silicone composition. The silicone composition contains a predetermined organopolysiloxane, a predetermined organohydrogenpolysiloxane, aluminum and / or alumina, graphite, a predetermined dimethylpolysiloxane, and a platinum-based curing catalyst. The thermally conductive silicone cured product has a thermal conductivity of 5 W / m·K or more and an Asker C hardness of 60 or less.

[0004] Patent Document 2 describes a heat-dissipating resin composition. The heat-dissipating resin composition contains an epoxy resin, an epoxy resin curing agent, a specific (meth)acrylic oligomer, and thermally conductive particles. A cured product of the heat-dissipating resin composition exhibits plastic deformation and can deform in response to, for example, pressure from a semiconductor component placed on the cured product, and can retain that shape.

[0005] JP 2021-195478 A JP 2018-21163 A

[0006] When a heat dissipation member is disposed between a heat-generating component and a heat-dissipating component, the member may be compressed between the heat-generating component and the heat-dissipating component. It is important that the heat dissipation member can exhibit the desired heat dissipation properties in this state while minimizing mechanical impact on surrounding components. Furthermore, considering the ease of recycling of products that use such a member, it is also important that the member can be easily removed from between the heat-generating component and the heat-dissipating component. From this perspective, the technologies described in Patent Documents 1 and 2 have room for reexamination.

[0007] Therefore, the present invention provides a technology that is advantageous from the viewpoints of heat dissipation in a compressed state, mechanical influence on surrounding parts, and ease of recycling.

[0008] The present invention provides a foam comprising a crosslinked rubber and thermally conductive particles, wherein the foam has a compressive stress of 1.2 MPa or less when a 50% compressive strain is applied to the foam, and the thermal conductivity of the foam in the compression direction is 0.3 Wm -1 K -1 As described above, a foam is provided.

[0009] The present invention also provides a member comprising: the foam; and a pressure-sensitive adhesive layer covering one or both surfaces of the foam.

[0010] The present invention also provides a heat dissipation structure comprising: a heat-generating component; a heat-dissipating component; and the foam described above disposed in a compressed state between the heat-generating component and the heat-dissipating component.

[0011] The foamed material is advantageous in terms of heat dissipation in a compressed state, mechanical influence on surrounding parts, and ease of recycling.

[0012] Fig. 1 is a cross-sectional view schematically showing an example of a foam according to the present invention. Fig. 2 is a cross-sectional view schematically showing an example of a heat dissipation structure. Fig. 3 is a cross-sectional view schematically showing another example of a foam according to the present invention. Fig. 4 is a cross-sectional view schematically showing yet another example of a foam according to the present invention. Fig. 5 is an X-ray CT photograph of a cross section of the foam according to Example 1-2.

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0014] Fig. 1 is a cross-sectional view schematically showing an example of a foam according to the present invention. As shown in Fig. 1, the foam 1a contains a cross-linked rubber 11 and thermally conductive particles 12. In the foam 1a, the cross-linked rubber 11 forms, for example, a continuous phase. On the other hand, the thermally conductive particles 12 are, for example, dispersed in the foam 1a and form a dispersed phase. When a compressive strain of 50% is generated in the foam 1a, the foam 1a generates a compressive stress P of 1.2 MPa or less. C In addition, when a compressive strain of 50% is applied to the foam 1a, the thermal conductivity λ of the foam 1a in the compression direction is C is 0.3Wm-1 K -1 That's all.

[0015] The thermally conductive silicone cured material described in Patent Document 1 has an Asker C hardness of 60 or less, but is not a foam. For this reason, when compressed between a heat-generating component and a heat-dissipating component, for example, a relatively high compressive stress is generated in the thermally conductive silicone cured material, which is likely to have a large mechanical impact on the surrounding components. On the other hand, the compressive stress P generated in the foam 1a C is 1.2 MPa or less, so that even if the foam 1a is compressed between a heat-generating component and a heat-dissipating component, the mechanical influence on the surrounding components is likely to be small. C is 0.3Wm -1 K -1 As described above, the foam 1a tends to exhibit the desired heat dissipation properties when compressed between the heat generating component and the heat dissipating component.

[0016] It is desirable that the heat dissipation member arranged between the heat generating component and the heat dissipating component can accommodate multiple cases where the distance between the heat generating component and the heat dissipating component is different. For example, it is assumed that the distance will vary depending on the tolerances of these components. The heat dissipation sheet described in Patent Document 1 may have difficulty in accommodating multiple cases where the distance between the heat generating component and the heat dissipating component is different. On the other hand, even if a 50% compressive strain is generated in the foam 1a, the compressive stress P C Since the compressive strength is 1.2 MPa or less, the foam 1a can be easily adapted to a variety of cases where the distance between the heat generating component and the heat dissipating component is different.

[0017] Compressive stress P of foam 1a C is preferably 1.1 MPa or less, more preferably 1.0 MPa or less, and even more preferably 0.95 MPa or less. C is, for example, 0.05 MPa or more, and may be 0.1 MPa or more.

[0018] The cured product of the heat-dissipating resin composition described in Patent Document 2 is described as having excellent reworkability. For example, a semiconductor component and a substrate bonded together via this cured product can be removed and reused (reworked). However, as shown in Figure 1 of Patent Document 2, the cured product is separated between the semiconductor element and the substrate, making it difficult to say that it can be easily removed from between the heat-generating component and the heat-dissipating component. On the other hand, the foam 1a can be easily removed from between the heat-generating component and the heat-dissipating component, which is advantageous from the perspective of ease of recycling.

[0019] When a 50% compressive strain is applied to the foam 1a, the ratio S1 / S0 of the size S1 of the foam 1a to the size S0 of the foam 1a is not limited to a specific value. The size S0 of the foam 1a is the size (initial size) of the foam 1a in the compression direction that causes a 50% compressive strain. The size S1 of the foam 1a is the size of the foam 1a in the compression direction one minute after the external force is released after the 50% compressive strain is applied. The ratio S1 / S0 is, for example, 0.75 (75%) or more. For example, even if the distance between the heat-generating component and the heat-dissipating component increases due to the release of the external force that caused the compressive strain in the foam 1a after the foam 1a is compressed between the heat-generating component and the heat-dissipating component, the size of the foam 1a may also increase in accordance with the increase in distance. Therefore, even in such cases, the foam 1a can occupy the desired volume between the heat-generating component and the heat-dissipating component.

[0020] The ratio S1 / S0 is preferably 78% or more, more preferably 80% or more, even more preferably 82% or more, particularly preferably 85% or more, particularly preferably 88% or more, and extremely preferably 90% or more. The ratio S1 / S0 is, for example, 99% or less.

[0021] As shown in Fig. 1, the foam 1a has a large number of bubbles 13 therein. The bubble structure of the foam 1a is such that the compressive stress P C is 1.2 MPa or less, and the thermal conductivity λ C is 0.3Wm -1 K -1As long as the above is satisfied, the foam 1a is not limited to a specific structure. The foam 1a may have an open-cell structure, a closed-cell structure, or a semi-closed-cell structure.

[0022] The ratio λ2 / λ1 of the thermal conductivity λ1 of foam 1a in the first direction when 50% compressive strain is applied to foam 1a in the first direction to the thermal conductivity λ2 of foam 1a in the second direction when 50% compressive strain is applied to foam 1a in the second direction is not limited to a specific value. The second direction is a direction perpendicular to the first direction. The ratio λ2 / λ1 is preferably 2 or greater. In this case, for example, when foam 1a is compressed in the second direction, selective heat dissipation is likely to occur in the compression direction, and heat from the heat-generating component is less likely to be transmitted through foam 1a to another component adjacent to the heat-generating component in the first direction perpendicular to the second direction. Therefore, heat from the heat-generating component is more likely to be selectively dissipated toward the heat-dissipating component.

[0023] The ratio λ2 / λ1 is more desirably 2.1 or more, and may be 2.2 or more. The ratio λ2 / λ1 is, for example, 5 or less, or may be 4 or less, or 3 or less.

[0024] The thermal conductivity λ2 is preferably 0.5 Wm -1 K -1 More preferably, 0.8 Wm -1 K -1 More preferably, it is 1.0 Wm -1 K -1 In particular, the ratio λ2 / λ1 is 2 or more, and λ2 is 1.0 Wm -1 K -1 In this case, the heat from the heat generating component is more likely to be selectively dissipated toward the heat dissipating component.

[0025] The gel fraction of the foam 1a is not limited to a specific value. The gel fraction of the foam 1a is, for example, 30% or more. In this case, even if the distance between the heat-generating component and the heat-dissipating component increases due to, for example, the removal of the external force that caused the compressive strain in the foam 1a after the foam 1a is compressed between the heat-generating component and the heat-dissipating component, the dimensions of the foam 1a may also increase in accordance with the increase in distance. Therefore, even in such cases, the foam 1a can occupy a desired volume between the heat-generating component and the heat-dissipating component. The gel fraction of the foam 1a can be determined, for example, according to the method described in the Examples.

[0026] The gel fraction of the foam 1a is preferably 35% or more, more preferably 40% or more, even more preferably 45% or more, and particularly preferably 50% or more. The gel fraction of the foam 1a is, for example, 95% or less, and may be 90% or less, 80% or less, 70% or less, or 60% or less.

[0027] The density d of the foam 1a is not limited to a specific value. The density d is, for example, 1.8 g / cm 3 The foam 1a has the following density: In this case, the foam 1a is likely to contribute to weight reduction of an article including the foam 1a. The density d is the bulk density.

[0028] The density d is preferably 1.5 g / cm 3 More preferably, it is 1.2 g / cm or less. 3 More preferably, it is 1.0 g / cm or less. 3 or less, and particularly preferably 0.8 g / cm 3 The density d is, for example, 0.1 g / cm 3 That's all.

[0029] Compressive stress P C is 1.2 MPa or less, and the thermal conductivity λ C is 0.3Wm -1 K -1 As long as the above is satisfied, the shape and dimensions of the thermally conductive particles 12 are not limited to a specific embodiment. For example, the minimum dimension S S Maximum dimension S for L The ratio S L / S S The average value of the ratio S is not limited to a specific value.L / S S The average value of the thermal conductivity λ is, for example, 10 or more. C It is easy to arrange it in an advantageous state from the viewpoint of increasing the ratio S L / S S The average value can be calculated, for example, by eliminating combustible components such as the crosslinked rubber 11 in the foam 1a, leaving only the thermally conductive particles 12 contained in the foam 1a, and observing the remaining 50 or more thermally conductive particles 12 with an optical microscope or an electron microscope.

[0030] ratio S L / S S The average value of the ratio S is preferably 20 or more, and more preferably 30 or more. L / S S The average value of is, for example, 1000 or less, and may be 500 or less, 200 or less, or 100 or less.

[0031] The thermally conductive particles 12 are, for example, flake-shaped. In this case, the thickness of the thermally conductive particles 12 is the minimum dimension S S The maximum diameter of the thermally conductive particles 12 when viewed in plan is the maximum dimension S L It can correspond to.

[0032] The thermally conductive particles 12 may be, for example, rod-shaped or fiber-shaped. In this case, the rod diameter or fiber diameter of the thermally conductive particles 12 is the minimum dimension S S The length of the thermally conductive particles 12 corresponds to the maximum dimension S L It can correspond to.

[0033] The thermal conductivity of the thermally conductive particles 12 is higher than that of the crosslinked rubber 11. The thermally conductive particles 12 contain, for example, at least one selected from the group consisting of graphite and boron nitride. In this case, the thermally conductive particles 12 have high thermal conductivity, and the thermal conductivity λ C is likely to be high.

[0034] Compressive stress P C is 1.2 MPa or less, and the thermal conductivity λ C is 0.3Wm -1 K -1As long as the above is true, the content of the thermally conductive particles 12 in the foam 1a is not limited to a specific value. This content is, for example, 25 to 70 mass %. In this case, in the foam 1a, the compressive stress P C and thermal conductivity λ C The content of the thermally conductive particles 12 in the foam 1 a can be calculated, for example, by eliminating flammable components such as the crosslinked rubber 11 in the foam 1 a, leaving only the thermally conductive particles 12 contained in the foam 1 a, and then determining the mass of the remaining thermally conductive particles 12.

[0035] Compressive stress P C is 1.2 MPa or less, and the thermal conductivity λ C is 0.3Wm -1 K -1 As long as the above is true, the crosslinked rubber 11 is not limited to a specific crosslinked rubber. The crosslinked rubber 11 includes, for example, at least one selected from the group consisting of natural rubber, chloroprene rubber, ethylene propylene diene rubber (EPDM), acrylonitrile butadiene rubber (NBR), acrylic rubber (ACM), and silicone rubber.

[0036] The crosslinked rubber 11 preferably contains EPDM. In this case, the compressive stress P C and thermal conductivity λ C is easily adjusted to a desired range.

[0037] The crosslinked rubber 11 preferably contains ACM. In this case, the compressive stress P C and thermal conductivity λ C In addition, the heat resistance of the foam 1a is likely to be high. Since the foam 1a may be used in contact with heat-generating components, it is desirable that the foam 1a have high heat resistance.

[0038] The shape of the foam 1a is not limited to a specific shape. The foam 1a may have a thickness of, for example, 1 to 15 mm. In this case, the foam 1a can be used in a compressed state between a heat-generating component and a heat-dissipating component even if the distance between them is relatively large.

[0039] The foam 1a may be in the form of a sheet or a strip, or may be in the form of a roll.

[0040] The foam 1a may contain additives such as colorants and flame retardants, as needed. An example of a colorant is carbon black. An example of a flame retardant is a hydroxide, such as calcium hydroxide, magnesium hydroxide, or aluminum hydroxide.

[0041] A heat dissipation structure can be provided using the foam 1a. Fig. 2 is a cross-sectional view schematically showing an example of a heat dissipation structure. As shown in Fig. 2, the heat dissipation structure 5 includes, for example, a heat-generating component 3, a heat dissipation component 4, and a foam 1a. The foam 1a is disposed between the heat-generating component 3 and the heat dissipation component 4. In the heat dissipation structure 5, the foam 1a is compressed. Heat generated in the heat-generating component 3 is transferred to the heat dissipation component 4 by thermal conduction in the foam 1a, and is dissipated from the heat dissipation component 4 to the outside of the heat dissipation structure 5.

[0042] The product including the heat dissipation structure 5 is not limited to a specific product, and examples of the product include electronic devices, electrical devices, storage battery modules, and electric vehicles (EVs).

[0043] The method for producing the foam 1a is not limited to a specific method. The foam 1a can be produced, for example, by foam molding a rubber composition containing a rubber component, a cross-linking agent, a cross-linking accelerator, and thermally conductive particles 12. The foam molding may be based on physical foaming or chemical foaming. For physical foaming, for example, carbon dioxide gas or nitrogen gas is used. The foaming agent used for chemical foaming may be an organic foaming agent or an inorganic foaming agent.

[0044] Examples of organic blowing agents include azo blowing agents, N-nitroso blowing agents, hydrazide blowing agents, semicarbazide blowing agents, fluorinated alkane blowing agents, triazole blowing agents, and other known organic blowing agents. Examples of azo blowing agents include azodicarboxylic acid amide (ADCA), barium azodicarboxylate, azobisisobutyronitrile (AIBN), azocyclohexylnitrile, and azodiaminobenzene. Examples of N-nitroso blowing agents include N,N'-dinitrosopentamethylenetetramine (DTP), N,N'-dimethyl-N,N'-dinitrosoterephthalamide, and trinitrosotrimethyltriamine. Examples of hydrazide-based blowing agents include 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH), paratoluenesulfonylhydrazide, diphenylsulfone-3,3'-disulfonylhydrazide, 2,4-toluenedisulfonylhydrazide, p,p-bis(benzenesulfonylhydrazide) ether, and benzene-1,3-disulfonylhydrazide, allylbis(sulfonylhydrazide). Examples of semicarbazide-based blowing agents include p-toluenesulfonylsemicarbazide and 4,4'-oxybis(benzenesulfonylsemicarbazide). Examples of fluorinated alkane-based blowing agents include trichloromonofluoromethane and dichloromonofluoromethane. An example of a triazole-based blowing agent is 5-morpholyl-1,2,3,4-thiatriazole. The organic blowing agent may be thermally expandable microparticles in which a thermally expandable substance is encapsulated in microcapsules. Examples of such thermally expandable fine particles include commercially available products such as Microsphere FN (manufactured by Matsumoto Yushi Co., Ltd.). Microsphere is a registered trademark.

[0045] Examples of inorganic foaming agents include bicarbonates, carbonates, nitrites, borohydrides, inorganic azides, and other known inorganic foaming agents. Examples of bicarbonates include sodium bicarbonate and ammonium bicarbonate. Examples of carbonates include sodium carbonate and ammonium carbonate. Examples of nitrites include sodium nitrite and ammonium nitrite. Examples of borohydrides include sodium borohydride. These foaming agents may be used alone or in combination of two or more.

[0046] In chemical foaming, a predetermined amount of a foaming agent may be mixed with the rubber composition. The amount of the foaming agent is, for example, 0.1 parts by mass or more, preferably 1 part by mass or more, and more preferably 10 parts by mass or more, per 100 parts by mass of the rubber composition. The amount of the foaming agent is, for example, 50 parts by mass or less, preferably 30 parts by mass or less.

[0047] In chemical foaming, a foaming assistant is added as needed. Examples of the foaming assistant include urea-based foaming assistants, salicylic acid-based foaming assistants, benzoic acid-based foaming assistants, and metal oxides such as zinc oxide. The foaming assistants are preferably urea-based foaming assistants and metal oxides. These foaming assistants may be used alone or in combination of two or more.

[0048] The blending ratio of the foaming aid is, for example, 0.5 parts by mass or more, and preferably 1 part by mass or more, per 100 parts by mass of the rubber composition, and is, for example, 20 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the rubber composition.

[0049] The rubber composition may contain auxiliary agents such as a lubricant and a viscosity modifier, as needed.

[0050] The rubber composition may be molded into a predetermined shape such as a sheet.

[0051] For example, the crosslinking reaction of the rubber component and foam molding can be promoted by heating the rubber composition under predetermined conditions, for example, by heating the rubber composition in an environment of 150°C to 250°C for 5 to 60 minutes.

[0052] The foam 1a may be used alone. As shown in Figures 3 and 4, a member may be provided that includes the foam 1a and a pressure-sensitive adhesive layer 20 covering one or both sides of the foam 1a. This allows the member including the foam 1a to be attached to a predetermined article by pressing the pressure-sensitive adhesive layer 20 against the predetermined article. For example, in the member 2a shown in Figure 3, the pressure-sensitive adhesive layer 20 is arranged to cover only one side of the foam 1a. In the member 2b shown in Figure 4, the pressure-sensitive adhesive layer 20 is arranged to cover both sides of the foam 1a. In other words, in the member 2b, a pair of pressure-sensitive adhesive layers 20 are arranged along a pair of parallel surfaces of the foam 1a.

[0053] The adhesive layer 20 is not limited to a specific adhesive layer. The adhesive forming the adhesive layer 20 may be, for example, an acrylic adhesive, a urethane adhesive, or a rubber adhesive. The thickness of the adhesive layer 20 is, for example, 5 to 400 μm, and may be 10 to 300 μm or 50 to 250 μm. The adhesive layer 20 may have a laminated structure including a sheet or film-like substrate and adhesives attached to both sides of the substrate. The substrate is, for example, a sheet or film including a polyester resin such as polyethylene terephthalate (PET).

[0054] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0055] Example 1-1 EPDM-containing polymer blend PX-072 manufactured by Mitsui Chemicals, Inc., process oil PW-380 manufactured by Idemitsu Kosan Co., Ltd., zinc oxide manufactured by Mitsui Mining & Smelting Co., Ltd., cherry stearate manufactured by NOF Corporation, and natural graphite F#1 manufactured by Nippon Graphite Trading Co., Ltd. were blended in the amounts shown in Table 1 and kneaded in a 3-L pressure kneader to obtain a primary blend according to Example 1. PX-072 is a polymer blend containing EPDM and polyethylene. PW-380 was used as a viscosity modifier. Zinc oxide was used as a crosslinking agent or processing aid. Sakura stearate was used as a lubricant. Natural graphite F#1 was used as a thermally conductive filler. Natural graphite F#1 was in the form of flake particles. More than 50 particles of natural graphite F#1 were observed under an optical microscope to determine the aspect ratio of each particle as the ratio of the maximum diameter to the thickness of each particle. The arithmetic mean of the aspect ratios of 50 or more particles was about 44, and the arithmetic mean of the maximum diameters of 50 or more particles was 300 μm.

[0056] ADCA-based foaming agent Vinihole AC#LQ K2 manufactured by Eiwa Chemical Industry Co., Ltd., foaming assistant Celpaste K5 manufactured by the same company, crosslinking agent Alphagran S-50EN manufactured by Tochi Corporation, and crosslinking accelerators Nocceler PZ, Nocceler EZ, Nocceler M, and Nocceler BUR manufactured by Ouchi Shinko Chemical Industry Co., Ltd. were added to the primary mixture of Example 1 in the amounts shown in Table 1, and these were kneaded in a pressure kneader having a capacity of 3 L, thereby obtaining a rubber composition of Example 1-1.

[0057] The rubber composition according to Example 1-1 was extruded into a sheet having a thickness of approximately 8 mm using a single-screw extruder having a screw diameter of 45 mm, thereby obtaining a rubber composition sheet according to Example 1-1. The rubber composition sheet according to Example 1-1 was cut along a square having a side length of 50 mm in a plan view, thereby obtaining a preliminary sheet according to Example 1-1.

[0058] Using a hot air circulation oven, the preliminary sheet according to Example 1-1 was preheated in an environment of 110°C for 1 minute, the temperature of the environment was increased to 190°C over 15 minutes, and the temperature of the environment was maintained at 190°C for 15 minutes. This promoted foaming and crosslinking reactions in the preliminary sheet according to Example 1-1. In this way, the foam according to Example 1-1 was obtained.

[0059] <Examples 1-2, 1-3, Comparative Examples 1-1, and 1-2> Foams according to Examples 1-2, 1-3, Comparative Examples 1-1, and 1-2 were obtained in the same manner as in Example 1-1, except that the blending amounts of each component in the primary admixture and the blending amounts of each component in the rubber composition were adjusted as shown in Table 1. An X-ray CT photograph of a cross section of the foam according to Example 1-2 is shown in FIG.

[0060] Comparative Example 1-3 A heat dissipation sheet 6500H provided by 3M Japan was prepared as a heat dissipation sheet according to Comparative Example 1-3.

[0061] Comparative Example 1-4 A heat-dissipating silicone pad TC-CAD-10 manufactured by Shin-Etsu Chemical Co., Ltd. was prepared as a heat-dissipating sheet according to Comparative Example 1-4.

[0062] (Compressive Stress Measurement) Rectangular compressive stress measurement samples having a thickness of 8 mm and a square surface with a side length of 10 mm in plan view were prepared from the foams according to Examples 1-1, 1-2, and 1-3, the foams according to Comparative Examples 1-1 and 1-2, and the heat dissipation sheets according to Comparative Examples 1-3 and 1-4. Using a compression tester, these compressive stress measurement samples were compressed in the thickness direction at a rate of 10 mm / min until 50% strain occurred, and the state in which 50% strain occurred in the thickness direction was maintained for 10 seconds, after which the compressive load was read. Based on the value of this compressive load, the compressive stress P when 50% compressive strain occurred was calculated. C The results are shown in Table 2. The measurements were carried out in an environment of 25°C.

[0063] (Density) The masses of the compressive stress measurement samples were measured, and the densities of the foams according to Examples 1-1, 1-2, and 1-3, the foams according to Comparative Examples 1-1 and 1-2, and the heat dissipation sheets according to Comparative Examples 1-3 and 1-4 were calculated based on the measured masses of the compressive stress measurement samples. The results are shown in Table 2.

[0064] (Thermal Conductivity Measurement) Rectangular thermal conductivity measurement samples having a thickness of 8 mm and a square surface with a side length of 20 mm in plan view were prepared from the foams according to Examples 1-1, 1-2, and 1-3, the foams according to Comparative Examples 1-1 and 1-2, and the heat dissipation sheets according to Comparative Examples 1-3 and 1-4. The thermal conductivity of the thermal conductivity measurement samples in the thickness direction was measured according to the unidirectional heat flow steady-state method in accordance with ASTM D5470, with a 50% compressive strain being generated in the thickness direction of the thermal conductivity measurement samples. In this measurement, the thermal conductivity measurement samples were sandwiched between a heating block adjusted to 100°C and a cooling block adjusted to 23°C, and the distance between the heating block and the cooling block was adjusted so that a 50% compressive strain was generated in the thickness direction of the thermal conductivity measurement samples. The results are shown in Table 2.

[0065] (Evaluation of Shape Recovery) A sample for evaluating shape recovery was prepared in the same manner as the sample for measuring compressive stress. Using a compression tester, the evaluation sample was compressed in the thickness direction at a rate of 0.5 mm / min until 50% strain occurred, and then the external force acting on the evaluation sample was released. After 1 minute had elapsed, the thickness S1 of the evaluation sample was measured, and the ratio S1 / S0 of the thickness S1 to the initial thickness S0 of the evaluation sample was calculated. The results are shown in Table 2.

[0066] As shown in Table 2, the foams according to Examples 1-1, 1-2, and 1-3 had a compressive strain of 0.3 Wm -1 K -1 The foams according to the examples had a thermal conductivity of 100% or more. It is believed that the desired heat dissipation properties are easily exhibited even when the foams are compressed between a heat-generating component and a heat-dissipating component. The compressive stress P CThe compressive stress P C Therefore, it is considered that when the foam according to Comparative Example 1-1 is used, the compression stress P C Although the thermal conductivity was low, it was difficult to say that the desired thermal conductivity was exhibited when a 50% compressive strain was generated.

[0067] The heat dissipation sheets according to Comparative Examples 1-3 and 1-4 exhibit high thermal conductivity when subjected to a 50% compressive strain, but the compressive stress P C In addition, the ratio S1 / S0 of the heat-dissipating sheets according to Comparative Examples 1-3 and 1-4 was small, suggesting that these heat-dissipating sheets would be unlikely to return to their original shape even after the external force that caused the compressive strain was removed.

[0068] Example 2-1 A rubber composition according to Example 2-1 was obtained in the same manner as Example 1-1, except that the blending amounts of each component in the primary admixture and the blending amounts of each component in the rubber composition were adjusted as shown in Table 3. A rubber composition sheet according to Example 2-1 was obtained in the same manner as Example 1-1, except that the rubber composition according to Example 2-1 was used instead of the rubber composition according to Example 1-1. A laminate of multiple rubber composition sheets according to Example 2-1 was pressed using a vacuum press to obtain a thick sheet. The foaming and crosslinking reaction of the sheet was promoted to obtain a thick foam in the same manner as Example 1-1, except that this thick sheet was used instead of the spare sheet according to Example 1-1. This thick foam was cut to a width of approximately 8 mm along a direction corresponding to the thickness direction of the rubber composition sheet, and a foam according to Example 2-1 was obtained, with the cut surface being the main surface.

[0069] Examples 2-2 to 2-6 Foams according to Examples 2-2, 2-3, 2-4, 2-5, and 2-6 were obtained in the same manner as Example 2-1, except that the blending amounts of each component in the primary admixture and the blending amounts of each component in the rubber composition were adjusted as shown in Table 3. In Example 2-6, spherical graphite CGB-90R manufactured by Nippon Graphite Industries Co., Ltd. was used as the thermally conductive filler instead of natural graphite F#1.

[0070] Example 2-7 EPDM-containing polymer blend PX-072, zinc oxide, and Sakura stearate (NOF Corporation) were placed in a pressure kneader in the amounts shown in Table 3 and kneaded for 3 minutes at 90°C and 38 rotations per minute (rpm). Next, natural graphite F#1 and process oil PW-380 were gradually added to the pressure kneader and kneaded for 6 minutes under the same conditions. Next, ADCA-based foaming agent Vinihol AC#LQ K2 and foaming aid Cellpaste K5 (NOF Corporation) were further added and kneaded for 3 minutes to obtain a rubber composition sheet according to Example 2-7.

[0071] The rubber composition sheet according to Example 2-7 was molded into a sheet having a thickness of about 8 mm using a vacuum press. Next, both sides of the rubber composition sheet according to Example 2-7 were irradiated with electron beams at an acceleration voltage of 250 kV and a dose of 100 kGy using an electron beam irradiation device EC300 manufactured by Iwasaki Electric Co., Ltd., to obtain a preliminary sheet according to Example 2-7.

[0072] Using a hot air circulation oven, the preliminary sheet according to Example 2-7 was heated in an environment of 130°C for 1 minute. Next, the ambient temperature of the preliminary sheet according to Example 2-7 was increased to 180°C over 10 minutes, and then the ambient temperature was maintained at 180°C for 10 minutes to promote foaming of the preliminary sheet. Thereafter, the foam according to Example 2-7 obtained by foaming the preliminary sheet was removed from the hot air circulation oven.

[0073] Example 3-1 Nipol® AR12 acrylic rubber manufactured by Zeon Corporation, Adeka plasticizer Adeka Cizer RS700PW-380 manufactured by ADEKA Corporation, Sakura stearate manufactured by NOF Corporation, Greg G-8205 ester wax manufactured by Nisshin Trading Co., Ltd., and natural graphite F#1 manufactured by Nippon Graphite Trading Co., Ltd. were blended in the amounts shown in Table 4 and kneaded in a 3-L pressure kneader to obtain a primary blend according to Example 3-1. Adeka Cizer RS700PW-380 was used as a viscosity modifier. Sakura stearate and Greg G-8205 were used as lubricants. Natural graphite F#1 was used as a thermally conductive filler.

[0074] ADCA-based foaming agent Vinihole AC#LQ K2 manufactured by Eiwa Chemical Industry Co., Ltd., foaming aid Celpaste K5 manufactured by the same company, antioxidant Nocrac CD manufactured by Ouchi Shinko Chemical Industry Co., Ltd., crosslinking accelerator Noccela DT manufactured by the same company, and crosslinking agent Sanfel 6-MC manufactured by Sanshin Chemical Industry Co., Ltd. were added to the primary mixture according to Example 3-1 in the amounts shown in Table 1, and these were kneaded in a pressure kneader having a capacity of 3 L to obtain the rubber composition according to Example 3-1.

[0075] A thick sheet according to Example 3-1 was obtained in the same manner as in Example 2-1, except that the rubber composition according to Example 3-1 was used instead of the rubber composition according to Example 2-1.

[0076] Using a hot air circulation oven, the thick sheet according to Example 3-1 was heated in an environment of 130°C for 1 minute, the temperature of the environment was raised to 170°C over 10 minutes, and the temperature of the environment was maintained at 170°C for 20 minutes. This promoted foaming and crosslinking reactions in the thick sheet according to Example 3-1. Further, secondary crosslinking was carried out at 170°C for 2 hours to obtain a thick foam. This thick foam was cut to a width of approximately 8 mm along the direction corresponding to the thickness direction of the rubber composition sheet, to obtain a foam according to Example 3-1 with the cut surface as the main surface.

[0077] Example 3-2 A foam according to Example 3-2 was obtained in the same manner as in Example 3-1, except that the blending amount of each component in the primary admixture and the blending amount of each component in the rubber composition were adjusted as shown in Table 4.

[0078] (Measurement of compressive stress, density, and evaluation of shape recoverability) For the foams of Examples 2-1 to 2-7, 3-1, and 3-2, measurement of compressive stress, measurement of density, and evaluation of shape recoverability were performed in the same manner as for the foam of Example 1-1. The results are shown in Table 5.

[0079] (Thermal Conductivity Measurement) Thermal conductivity measurement samples according to these examples were prepared in the same manner as in Example 1-1, except that the foams according to Examples 2-1 to 2-7, Example 3-1, and Example 3-2 were used instead of the foam according to Example 1-1. The thermal conductivity measurement sample was subjected to a 50% compressive strain in the thickness direction (second direction) of the thermal conductivity measurement sample, and the thermal conductivity λ2 in the thickness direction (second direction) of the thermal conductivity measurement sample was measured according to the unidirectional heat flow steady-state method in accordance with ASTM D5470. In this measurement, the thermal conductivity measurement sample was sandwiched between a heating block adjusted to 100 ° C and a cooling block adjusted to 23 ° C, and the distance between the heating block and the cooling block was adjusted so that a 50% compressive strain was generated in the thickness direction (second direction) of the thermal conductivity measurement sample. The results are shown in Table 5.

[0080] The thick foam of Example 2-1 was sliced ​​along the in-plane direction of the rubber composition sheet immediately after extrusion molding to a thickness of approximately 8 mm to obtain a reference foam of Example 2-1. Reference foams of Examples 2-2 to 2-6, 3-1, and 3-2 were obtained in the same manner, except that the rubber composition sheets of Examples 2-2 to 2-6, 3-1, and 3-2 were used. Each of the foams of Example 2-7 was cut to a width of approximately 8 mm, and the resulting multiple pieces having cut surfaces were stacked so that the cut surfaces were connected in a plane to obtain an accumulation of Example 2-7. Furthermore, the heat-dissipating sheets of Comparative Examples 1-3 and 1-4 were cut to a width of approximately 8 mm, and the resulting multiple pieces having cut surfaces were stacked so that the cut surfaces were connected in a plane to obtain accumulations of these comparative examples. Thermal conductivity measurement samples were prepared in the same manner as in Example 1-1, except that the foam of Example 1-1 was replaced with the reference foams of Examples 2-1 to 2-6, 3-1, and 3-2, or the above-mentioned aggregates. These thermal conductivity measurement samples were subjected to a 50% compressive strain in the thickness direction (first direction) of the thermal conductivity measurement samples, and the thermal conductivity λ1 in the thickness direction of the thermal conductivity measurement samples (first direction) was measured according to the unidirectional heat flow steady-state method in accordance with ASTM D5470. In this measurement, the thermal conductivity measurement sample was sandwiched between a heating block adjusted to 100 ° C and a cooling block adjusted to 23 ° C, and the distance between the heating block and the cooling block was adjusted so that a 50% compressive strain was generated in the thickness direction (first direction) of the thermal conductivity measurement sample. The results are shown in Table 5.

[0081] (Gel fraction) Each of the foams according to Examples 2-1 to 2-7, 3-1, and 3-2 was heat-treated at 800° C. for 1 hour in a nitrogen atmosphere, and the weight W of the residue obtained thereafter was A The weight of the residue W relative to the initial weight W of the foam was measured. A The ratio A [%] of the insoluble matter remaining after immersing each of the foams according to Examples 2-1 to 2-7, 3-1, and 3-2 in toluene at 23° C. for 168 hours was calculated. BThe weight of the insoluble matter W relative to the initial weight W of the foam was measured. B The ratio B [%] of the above was calculated. The gel fraction of each foam was determined according to the following formula (1). The results are shown in Table 5. Gel fraction [%] = 100 × (B - A) / (100 - A) Formula (1)

[0082] As shown in Table 5, the foams according to Examples 2-1 to 2-7, 3-1, and 3-2 had a compressive strain of 0.3 Wm -1 K -1 The foams according to the examples had a thermal conductivity of 100% or more. It is believed that the desired heat dissipation properties are easily exhibited even when the foams are compressed between a heat-generating component and a heat-dissipating component. The compressive stress P C This suggests that even when these foams are compressed between the heat-generating and heat-dissipating components, the mechanical impact on the surrounding components is likely to be small.

[0083] For example, the thermal conductivity ratio λ2 / λ1 was high in Examples 2-1 to 2-5, 2-7, 3-1, and 3-2. When these foams are compressed in the second direction, heat dissipation is likely to occur selectively in the compression direction, and it is expected that heat from the heat-generating component will be less likely to be transmitted through the foam to another component adjacent to the heat-generating component in the first direction perpendicular to the second direction.

[0084] As shown in Table 5, the foams of Examples 2-1 to 2-6, 3-1, and 3-2 had a high S1 / S0 ratio, suggesting that these foams easily return to their original shape when the external force that generates compressive strain is removed. The foams of Examples 2-1 to 2-6, 3-1, and 3-2 had a relatively high gel fraction, which is thought to be related to the high S1 / S0 ratio.

[0085]

[0086]

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[0089]

[0090] A first aspect of the present invention is a foam comprising a crosslinked rubber and thermally conductive particles, wherein the foam has a compressive stress of 1.2 MPa or less when a 50% compressive strain is applied to the foam, and the foam has a thermal conductivity of 0.3 Wm in the compression direction. -1 K -1 As described above, a foam is provided.

[0091] A second aspect of the present invention provides the foam of the first aspect, wherein when a 50% compressive strain is applied to the foam, the ratio of the dimension of the foam in the compression direction before the compressive strain is applied to the dimension of the foam one minute after the external force is released after the compressive strain is applied is 0.75 or more.

[0092] A third aspect of the present invention provides the foam of the second aspect, wherein the ratio is 0.80 or greater.

[0093] A fourth aspect of the present invention provides the foam according to any one of the first to third aspects, wherein the foam has a gel fraction of 30% or more.

[0094] A fifth aspect of the present invention provides a foam according to any one of the first to fourth aspects, wherein the ratio of the thermal conductivity of the foam in a first direction when a 50% compressive strain is applied to the foam in the first direction to the thermal conductivity of the foam in a second direction when a 50% compressive strain is applied to the foam in the second direction perpendicular to the first direction is 2 or greater.

[0095] A sixth aspect of the present invention is the method for manufacturing a heat-resistant foam according to the fifth aspect, wherein when a compressive strain of 50% is applied to the foam, the thermal conductivity of the foam in the compression direction is 1.0 Wm -1 K -1 As described above, a foam is provided.

[0096] A seventh aspect of the present invention is any one of the first to sixth aspects, wherein the density is 1.8 g / cm3 A foam is provided having the following density:

[0097] An eighth aspect of the present invention provides the foam according to any one of the first to seventh aspects, wherein the average ratio of the maximum dimension to the minimum dimension of the thermally conductive particles is 10 or more.

[0098] A ninth aspect of the present invention provides the foam according to any one of the first to eighth aspects, wherein the thermally conductive particles include at least one selected from the group consisting of graphite and boron nitride.

[0099] A tenth aspect of the present invention provides the foam according to any one of the first to ninth aspects, wherein the content of the thermally conductive particles in the foam is 25 to 70 mass %.

[0100] An eleventh aspect of the present invention provides the foam according to any one of the first to tenth aspects, wherein the crosslinked rubber includes an ethylene propylene diene rubber.

[0101] A twelfth aspect of the present invention provides the foam according to any one of the first to eleventh aspects, wherein the crosslinked rubber includes an acrylic rubber.

[0102] A thirteenth aspect of the present invention provides a member comprising: a foam according to any one of the first to twelfth aspects; and a pressure-sensitive adhesive layer covering one or both sides of the foam.

[0103] A fourteenth aspect of the present invention provides a heat dissipation structure comprising: a heat-generating component; a heat-dissipating component; and a foam according to any one of the first to twelfth aspects, arranged in a compressed state between the heat-generating component and the heat-dissipating component.

Claims

1. A foam comprising a crosslinked rubber and thermally conductive particles, wherein when a 50% compressive strain is applied to the foam, the foam has a compressive stress of 1.2 MPa or less and a thermal conductivity in the compression direction of the foam of 0.3 Wm -1 K -1 That's it, foam.

2. The foam according to claim 1, wherein, when a 50% compressive strain is applied to the foam, the ratio of the size of the foam in the compression direction before the compressive strain is applied to the size of the foam in the compression direction one minute after the compressive strain is applied and the external force is released is 0.75 or more.

3. The foam of claim 2, wherein the ratio is 0.80 or greater.

4. The foam according to claim 1, wherein the foam has a gel fraction of 30% or more.

5. The foam described in claim 1, wherein the ratio of the thermal conductivity of the foam in a first direction when a 50% compressive strain is applied to the foam in the first direction to the thermal conductivity of the foam in a second direction when a 50% compressive strain is applied to the foam in the second direction perpendicular to the first direction is 2 or greater.

6. When a 50% compressive strain is applied to the foam, the thermal conductivity of the foam in the compression direction is 1.0 Wm -1 K -1 The foam according to claim 5 , wherein 7. 1.8 g / cm 3 10. The foam of claim 1 having a density:

8. The foam of claim 1, wherein the thermally conductive particles have an average ratio of their maximum dimension to their minimum dimension of 10 or greater.

9. The foam of claim 1, wherein the thermally conductive particles include at least one selected from the group consisting of graphite and boron nitride.

10. The foam according to claim 1, wherein the content of the thermally conductive particles in the foam is 25 to 70 mass %.

11. The foam of claim 1, wherein the crosslinked rubber comprises ethylene propylene diene rubber.

12. The foam according to claim 1, wherein the crosslinked rubber comprises an acrylic rubber.

13. A member comprising the foam according to any one of claims 1 to 12 and an adhesive layer covering one or both sides of the foam.

14. A heat dissipation structure comprising: a heat-generating component; a heat-dissipating component; and the foam according to any one of claims 1 to 12, disposed in a compressed state between the heat-generating component and the heat-dissipating component.

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