JP2018171916A - Foaming complex - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a foaming complex having high thermal conductivity, electromagnetic wave shielding property, and flexibility.SOLUTION: A foaming complex 10 has a resin foam sheet 11, a conductive sheet 12, an adhesive layer 13 that is provided on one side of the conductive sheet 12 and bonds the conductive sheet 12 to the resin foam sheet 11, and a conductive adhesive layer 14 provided on the other side of the conductive sheet 12.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a foam composite including a resin foam sheet and used in an electronic device or the like.

  In recent years, as electronic devices have become thinner, lighter, and smaller, electronic components built into electronic devices have become more functional, denser, highly integrated, and complex, and have been affected by noise and interference from electromagnetic waves. It happens frequently. Therefore, an electromagnetic wave shielding material may be provided inside the electronic device. The electromagnetic shielding material is provided on the substrate so as to cover the electronic components in order to prevent each electronic component from emitting electromagnetic waves and receiving electromagnetic waves. Moreover, the electromagnetic wave sealing material may be provided so as to cap each electronic component individually when a high shielding property is required.

  Furthermore, with the increase in functionality and integration of electronic components, the increase in heat generated from the electronic components has become significant. If heat countermeasures are not taken, not only the function and performance of electronic components and the lifespan of the electronic parts are reduced, but also the electronic equipment itself has heat, which may cause low-temperature burns and ignition. Therefore, a heat radiating sheet may be provided inside the electronic device as a heat countermeasure. The heat dissipating sheet is disposed between the electronic component that generates heat and a metal member having a heat sink function such as a sheet metal inside the device or an electromagnetic shielding material, thereby creating a heat path, and the electronic component. The temperature rise is suppressed. In particular, electronic components such as CPUs, power amplifiers, and LEDs have a high need for heat countermeasures. Among these, the CPU is highly required to shield electromagnetic waves together with heat countermeasures.

  Conventionally, as a heat radiating sheet, a heat radiating silicone sheet, a heat radiating foam sheet obtained by blending a foam with a heat conductive filler, and the like are known. In addition, in order to reduce the size of electronic equipment and reduce the number of parts, a member having both electromagnetic shielding properties and heat dissipation properties may be required. As a member having both electromagnetic shielding properties and heat radiation properties, as disclosed in, for example, Patent Document 1, an electromagnetic wave shielding heat radiation composite sheet in which a metal layer is pressure-bonded to a graphite sheet is known.

JP 2017-28280 A

By the way, the heat-dissipating sheet and electromagnetic shielding heat-dissipating composite sheet used inside miniaturized electronic devices absorbs design tolerances of electronic parts, housings, and other parts, and follows each member with high flexibility. Is required. However, the electromagnetic wave shielding and heat radiating composite sheet disclosed in Patent Document 1 does not have high flexibility, and it is difficult to exhibit sufficient performance even when used inside a miniaturized electronic device.
This invention is made | formed in view of the above situation, and makes it a subject to provide a foam composite with high heat conductivity, electromagnetic wave shielding property, and a softness | flexibility.

As a result of intensive studies, the present inventors have found that a foamed composite having a specific layer structure can solve the above problems, and have completed the following present invention. The present invention provides the following (1) to (11).
(1) A resin foam sheet containing a thermally conductive filler, a conductive sheet, and an adhesive layer that is provided on one surface of the conductive sheet and adheres the conductive sheet to the resin foam sheet; A foam composite comprising a conductive pressure-sensitive adhesive layer provided on the other surface of the conductive sheet.
(2) The foamed composite according to (1), wherein the resin foam sheet includes 100 to 600 parts by mass of the heat conductive filler (B) with respect to 100 parts by mass of the main agent.
(3) The foamed composite according to (1) or (2), wherein the foamed resin sheet has a foaming ratio of 1.5 to 5.0.
(4) The thermally conductive filler is selected from the group consisting of aluminum oxide, magnesium oxide, boron nitride, talc, zinc oxide, silica, silicon carbide, silicon nitride, titanium oxide, carbon fiber, aluminum nitride, graphite, and graphene. The foamed composite according to any one of the above (1) to (3), which is at least one kind.
(5) The foam composite according to any one of (1) to (4), wherein the resin constituting the resin foam sheet is an elastomer resin.
(6) The foam composite according to any one of (1) to (5), wherein the conductive sheet is a conductive nonwoven fabric.
(7) The conductive sheet is a conductive resin film including a resin film and a metal film provided on at least one side of the resin film, and the conductive pressure-sensitive adhesive layer is provided on the one side of the resin film. The foamed composite according to any one of (1) to (5), which is provided.
(8) The foamed composite according to any one of (1) to (5), wherein the conductive sheet is a metal foil.
(9) The foamed composite according to any one of (1) to (8), wherein the conductive adhesive layer is composed of a conductive adhesive in which a metal filler is mixed with an adhesive.
(10) The foamed composite according to any one of (1) to (9), wherein the pressure-sensitive adhesive constituting the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer are all (meth) acrylic pressure-sensitive adhesives. body.
(11) The foamed composite according to any one of (1) to (10), which is used inside an electronic device.

  According to the present invention, it is possible to provide a foam composite having high thermal conductivity, electromagnetic wave shielding properties, and flexibility.

It is typical sectional drawing which shows one Embodiment of a foam composite. It is typical sectional drawing which shows other embodiment of a foam composite. It is typical sectional drawing which shows an example of the use condition of a foam composite. It is typical sectional drawing which shows the measuring method of thermal resistance.

Hereinafter, the present invention will be described with reference to embodiments.
As shown in FIG. 1, a foam composite 10 according to an embodiment of the present invention is provided on one surface of a resin foam sheet 11 containing a thermally conductive filler, a conductive sheet 12, and a conductive sheet 12. In addition, a pressure-sensitive adhesive layer 13 for bonding the conductive sheet 12 to the resin foam sheet 11 and a conductive pressure-sensitive adhesive layer 14 provided on the other surface of the conductive sheet 12 are provided. Hereinafter, each member will be described in more detail.

[Resin foam sheet]
The resin foam sheet is a resin foam containing a heat conductive filler. The type of resin used for the resin foam sheet is not particularly limited. For example, polypropylene resin, polyethylene resin, ethylene-vinyl acetate copolymer resin, polystyrene resin, polyvinyl chloride resin, polyamide resin, polycarbonate resin A thermoplastic resin such as a resin, a polyester-based resin, or a polymethacrylate-based resin can also be used, but an elastomer resin described below is preferable.

(Elastomer resin)
The elastomer resin that can be used for the resin foam sheet includes acrylonitrile butadiene rubber, ethylene-propylene-diene rubber, ethylene-propylene rubber, natural rubber, butyl rubber, polybutadiene rubber, polyisoprene rubber, styrene-butadiene block copolymer, hydrogenation Examples include styrene-butadiene block copolymers, hydrogenated styrene-butadiene-styrene block copolymers, hydrogenated styrene-isoprene block copolymers, and hydrogenated styrene-isoprene-styrene block copolymers. Acrylonitrile butadiene rubber and ethylene-propylene-diene rubber are preferred, and ethylene-propylene-diene rubber is more preferred.
When these elastomer resins are used, the flexibility of the resin foam sheet is easily increased. Moreover, the adhesiveness with the adhesive layer comprised from the (meth) acrylic-type adhesive mentioned later tends to become favorable.

The above-described elastomer resin may be a solid elastomer resin at normal temperature (23 ° C.) and normal pressure (1 atm), or may be a liquid elastomer resin.
The solid elastomer resin preferably has a Mooney viscosity (ML _{1 + 4} , 125 ° C.) of 5 to 80. As for Mooney viscosity (ML1 _{+ 4} , 125 degreeC), 10-50 are more preferable, and 18-30 are more preferable. The liquid elastomer resin preferably has a viscosity at 25 ° C. of 1 to 1000 Pa · s, more preferably 2 to 500 Pa · s, and still more preferably 5 to 100 Pa · s. By setting the Mooney viscosity and the viscosity at 25 ° C. within the above ranges, foamability, moldability and the like are improved.

(Process oil)
Moreover, when using elastomer resin as resin, you may use a process oil in addition to elastomer resin. By blending the process oil, the foamability of the resin foam sheet is improved. In the present specification, the resin and the process oil are collectively referred to as “main agent”. That is, the main agent is composed of a resin or a resin and a process oil, and when the main agent is described as 100 mass, it means that the total amount of the resin and the process oil is 100 parts by mass.
When using procel 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.

  Although it does not restrict | limit especially as process oil, Vegetable oil, animal oil, mineral oil, synthetic oil etc. are mentioned. Among these, mineral oil or synthetic oil is preferable. Examples of the mineral oil include paraffinic process oil, naphthenic process oil, and aromatic process oil. The synthetic oil is not particularly limited, but is preferably a hydrocarbon oligomer. As the hydrocarbon-based oligomer, a homopolymeric oligomer obtained by polymerizing a single monomer selected from ethylene and an α-olefin such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, or the like, or Any of the copolymer oligomers obtained by copolymerization of two or more monomers may be used, but the copolymer oligomer is more preferable from the viewpoint of increasing the affinity with the elastomer resin and suppressing the generation of coarse bubbles.

From the viewpoint of improving the foamability of the resin foam sheet, the kinematic viscosity of the process oil at 40 ° C. is preferably 30000 mm ² / s or less, more preferably 20 to 20000 mm ² / s, and even more preferably 50 to It is 8000 mm < ² > / s, More preferably, it is 70-3000 mm < ² > / s. The kinematic viscosity of the process oil is measured at 40 ° C. using an Ubbelohde viscometer.

When blending procell oil, the solid elastomer resin content is preferably 80% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass, based on the total amount of the resin. That is, when blending process oil, it is preferable to use a solid elastomer resin alone as the resin.
On the other hand, when no process oil is blended, it is preferable to use a mixture of a solid elastomer and a liquid elastomer. Even if a large amount of thermally conductive filler is blended by using the mixture, the foamability can be improved. In this case, the total amount of the resin is preferably 40 to 90% by mass of the solid elastomer resin and 10 to 60% by mass of the liquid elastomer resin, and 50 to 80% by mass of the solid elastomer resin. It is preferable that the elastomer resin is 20 to 50% by mass.

(Thermal conductive filler)
The resin foam sheet contains a thermally conductive filler. Specific examples of the thermally conductive filler used in the resin foam sheet include aluminum oxide, magnesium oxide, boron nitride, talc, zinc oxide, silica, silicon carbide, silicon nitride, titanium oxide, carbon fiber, aluminum nitride, graphite, and Graphene. These heat conductive fillers may be used individually by 1 type, and 2 or more types may be mixed and used for them. Among these, boron nitride, aluminum oxide, zinc oxide, and magnesium oxide are preferable, boron nitride and magnesium oxide are more preferable, and these may be used in combination. By containing a heat conductive filler in the resin foam sheet, the heat conductivity of the resin foam sheet and the foam composite is increased. Moreover, these heat conductive fillers may be surface-treated in order to improve adhesion to the resin and processability.

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. When the thermal conductivity is within these ranges, the thermal conductivity of the resin foam sheet is sufficiently high. The upper limit of the thermal conductivity of the thermally conductive filler is not particularly limited, but is practically preferably 500 W / m · K or less, and more preferably 200 W / m · K or less.
Moreover, 1-100 micrometers is preferable, as for the average particle diameter of a heat conductive filler, 5-90 micrometers is more preferable, and 10-80 micrometers is more preferable. When the average particle size of the heat conductor is within these ranges, it is easy to make the resin foam sheet thin, and it is possible to obtain a resin foam sheet having good foamability.

Content of the heat conductive filler with respect to 100 mass parts of main agents becomes like this. Preferably it is 100-600 mass parts, 150-500 mass parts is more preferable, 200-450 mass parts is more preferable. When the content of the heat conductive filler is 100 parts by mass or more, sufficient heat conductivity can be imparted to the resin foam sheet. Moreover, when content of a heat conductive filler shall be 600 mass parts or less, it will become easy to make the softness | flexibility of a resin foam sheet, a moldability, etc. favorable.
In the resin foam sheet, the total amount of the heat conductive filler and the main agent is preferably 75% by mass or more, more preferably 85% by mass or more, and further preferably 95% by mass or more based on the total amount of the resin foam sheet.

  Although the shape of a heat conductive filler is not specifically limited, A plate-like filler and a spherical filler are preferable and these may be used together. When these are used together, it becomes easier to increase the thermal conductivity of the resin foam sheet. In addition, the spherical filler is a filler having a spherical shape and a shape close to a spherical shape, and the ratio of the major axis to the minor axis of each filler is close to 1 or 1, and the ratio is, for example, 0.6 to 1.7, preferably Is 0.8 to 1.5. Further, the plate-like filler is a filler having a flaky or flaky filler shape, and the major axis of each filler is sufficiently larger than the thickness. For example, the ratio of the thickness to the major axis is 2 or more, preferably 3. That's it.

The material for the plate-like filler and the spherical filler may be appropriately selected from those described above. Preferably, the spherical filler is at least one of aluminum oxide and magnesium oxide, and the plate-like filler is boron nitride. Preferably, the spherical filler is magnesium oxide and the plate filler is boron nitride.
When using a plate-like filler and a spherical filler together, it is better to make the content of the spherical filler larger than the content of the plate-like filler. Further, the content of the spherical filler is preferably 55 to 95% by mass, the content of the plate-like filler is 5 to 45% by mass, and more preferably the content of the spherical filler is 70 to 92% with respect to the total amount of the heat conductive filler. The content of the plate-like filler is 8 to 30% by mass.

(Optional component)
The resin foam sheet of the present invention may contain various additive components as necessary within the range in which the object of the present invention is not impaired.
The kind of the additive component is not particularly limited, and various additives usually used for foams can be used. Examples of such additives include lubricants, shrinkage inhibitors, cell nucleating agents, crystal nucleating agents, plasticizers, colorants (pigments, dyes, etc.), ultraviolet absorbers, antioxidants, anti-aging agents, and the above heat conduction agents. Examples include fillers other than the functional filler, reinforcing agents, flame retardants, flame retardant aids, antistatic agents, surfactants, vulcanizing agents, and surface treatment agents. Such additives can be used alone or in combination of two or more. In these, it is preferable to use antioxidant.
Examples of the antioxidant include phenolic antioxidants, sulfur antioxidants, phosphorus antioxidants, amine antioxidants, etc. Among them, phenolic antioxidants are preferable. 0.1-10 mass parts is preferable with respect to 100 mass parts of main agents, and, as for content of antioxidant, 0.2-5 mass parts is more preferable.

  The resin foam sheet is obtained by foaming a foamable resin sheet, as will be described later, and has a plurality of bubbles inside. The resin foam sheet is preferably obtained by adding a foaming agent to the foamable resin sheet and foaming the foamable resin sheet with the foaming agent. As the foaming agent, a pyrolytic foaming agent is preferable as described later.

(Foaming ratio)
The expansion ratio of the resin foam sheet is preferably 1.5 to 5.0 times. When the foaming ratio is 1.5 times or more, the flexibility becomes high, and even if the foamed composite is disposed in the gap between the members having design tolerances, the followability to the member is easily improved. Therefore, the foam composite is in close contact with each member, and it becomes easy to improve heat dissipation. Further, when the expansion ratio is 5.0 times or less, the mechanical strength is improved and the thermal conductivity is easily improved. From these viewpoints, the expansion ratio is more preferably 2.0 to 4.0 times, and further preferably 2.4 to 3.6 times. The expansion ratio can be adjusted as appropriate by changing the amount of the foaming agent used.

  The resin foam sheet is preferably one in which the above resin is crosslinked, and the crosslinking is more preferably crosslinking by ionizing radiation. The resin is usually crosslinked by a crosslinking treatment described later.

  The compression ratio when the resin foam sheet is compressed at 800 kPa is preferably 30 to 80%, preferably 40 to 70%, and more preferably 50 to 65%. When the compression ratio is not less than these lower limits, the flexibility becomes high, and even if the foamed composite is disposed in the gap between the members having design tolerances, the followability to the member can be easily improved, and the foam composite It becomes easy to improve heat dissipation. Moreover, it becomes easy to make the mechanical strength etc. of a resin foam sheet favorable as it is below an upper limit. In the present specification, the compression ratio means a value calculated by (original thickness of resin foam sheet−thickness of resin foam sheet when compressed) / original thickness of resin foam sheet × 100. .

The thickness of the resin foam sheet is preferably 100 to 700 μm, more preferably 200 to 600 μm, and still more preferably 300 to 500 μm. When the thickness of the resin foam sheet is within the above range, the resin foam sheet can be used inside a downsized electronic device.
Moreover, it is preferable that the thickness of a resin foam sheet is 0.60-0.98 with respect to the thickness of the whole foam composite. By setting the thickness ratio to 0.60 or more, the flexibility of the foamed composite can be sufficiently increased. Moreover, by setting it as 0.98 or less, it becomes possible to make thickness of a conductive sheet etc. into a fixed value or more. The thickness ratio is more preferably 0.70 to 0.95, and further preferably 0.75 to 0.92.

[Conductive sheet]
An electroconductive sheet is a sheet-like member which has electroconductivity, Comprising: A metal is contained. The metal used for the conductive sheet is not particularly limited as long as it has electromagnetic wave shielding properties, but gold, silver, copper, nickel, aluminum, iron, tin, lead, platinum, lithium, potassium, rubidium, calcium, Barium, titanium, chromium, manganese, cobalt, zinc, molybdenum, magnesium, vanadium, tantalum, alloys thereof, stainless steel, permalloy, aluminum alloy, bronze, brass, monel, invar, elinvar, inconel and the like are used. Among these, copper and nickel are preferable from the viewpoints of electromagnetic wave shielding properties, handleability, and availability. These 1 type may be used individually and may use 2 or more types together.

  The conductive sheet functions as an electromagnetic wave shielding material and serves as a support base material that holds an adhesive layer and a conductive adhesive layer described later. As specific examples of the conductive sheet, a conductive resin film or a metal mesh film in which a metal film is provided on at least one surface of each of a conductive cloth material, a resin film, and a metal mesh obtained by attaching a metal to a cloth material, Examples thereof include a metal foil made of the above metal.

(Conductive cloth material)
Examples of the cloth material used for the conductive sheet include a knitted fabric, a woven fabric, and a non-woven fabric, and a non-woven fabric is preferable. That is, the conductive sheet is preferably a conductive nonwoven fabric. By using a conductive nonwoven fabric, the conductive sheet can be made thin, and the adhesive layer and the conductive adhesive layer described later can be easily held by the conductive sheet.
The material of the cloth material such as non-woven fabric is not particularly limited. For example, natural fiber such as wood fiber and cotton, polyester such as rayon, polyolefin, polyethylene terephthalate (PET), polyamide, polyurethane, liquid crystal polymer, etc. And a mixture of natural fiber and chemical fiber. These may be used alone or in combination of two or more. Among these, polyester is preferable, and PET is more preferable.

The basis weight of the fabric material is preferably 1 to 100 g / ^{m 2,} more preferably 1.5~50g / ^{m 2,} more preferably from 2 to 20 g / ^{m 2.}
When the basis weight is equal to or more than the above lower limit, the cloth material such as the nonwoven fabric has an appropriate mechanical strength, and the laminate composed of the pressure-sensitive adhesive layer, the conductive sheet, and the conductive pressure-sensitive adhesive layer is appropriately applied to the resin foam sheet. It becomes possible to paste.
Moreover, even if metal is made to adhere to cloth materials, such as a nonwoven fabric, by making basis weight below the said upper limit, an adhesive layer and an electroconductive adhesive layer impregnate in a cloth material moderately, and an adhesive layer And it becomes possible to improve the adhesiveness of a conductive adhesive layer and a conductive sheet.

  Although the thickness of a conductive cloth material is not specifically limited, For example, it is 5-100 micrometers, Preferably it is 8-50 micrometers, More preferably, it is 10-30 micrometers. When the conductive cloth material has a thickness in such a range, the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer are appropriately held, and a laminate composed of the pressure-sensitive adhesive layer, the conductive sheet, and the conductive pressure-sensitive adhesive layer. The body can be appropriately attached to the resin foam sheet.

A method for attaching a metal to a cloth material such as a nonwoven fabric is not particularly limited, but a method of impregnating the metal with the metal by, for example, metal plating is preferable. The amount of metal attached is preferably 300 to 5000 μg / cm ² . When the adhesion amount is 300 μg / cm ² or more, the electromagnetic shielding property of the conductive sheet is good. Further, by the 5000 [mu] g / cm ² or less, the conductive sheet becomes flexible and adhesive layer, the conductive sheet, and bondability to the resin foam sheet of the stack of conductive pressure-sensitive adhesive layer and a good Become. From the above viewpoint, the adhesion amount of the metal is more preferably 500~3000μg / cm ^2, more preferably from 700~2000μg / cm ^2.

(Conductive resin film)
The conductive resin film includes a resin film and a metal film provided on one surface of the resin film. The material of the resin film is not particularly limited, but polyester such as polyolefin, polyethylene terephthalate (PET), polyamide, polyurethane, biaxially stretched polyetheretherketone (PEEK), polyimide, liquid crystal polymer, polyethylene naphthalate (PEN), polyphenylene Examples thereof include sulfide (PPS). Among these, polyester is preferable, and PET is more preferable.

The metal film may be provided on both sides of the resin film, but may be provided only on one side.
And the conductive adhesive layer mentioned later is provided in the surface side in which a metal film is provided. That is, as shown in FIG. 2, when a conductive resin film having a resin film 12A and a metal film 12B provided on one surface of the resin film 12A is used as the conductive sheet 12, the metal film of the resin film 12A. An adhesive layer 13 is provided on one surface on which 12B is not coated. Then, the conductive adhesive layer 14 is provided on the other surface on which the metal film 12B is coated. Thereby, the metal film 12B (electromagnetic wave shielding material) of the conductive sheet 12 and the conductive adhesive layer 14 can be conducted.

The adhesion amount of the metal film is preferably ³ to 10,000 μg / cm ² on each surface. By setting it to 3 μg / cm ² or more, it is possible to impart an appropriate electromagnetic wave shielding property to the conductive resin film. Moreover, by setting it as 10000 microgram / cm < ² > or less, it is possible to improve the softness | flexibility of a conductive resin film and to make the sticking property etc. with respect to a resin foam sheet favorable. Adhesion amount of the metal film is more preferably 5~1000μg / cm ^2, further preferably 10~500μg / cm ^2.
For example, the metal film may be formed by sputtering or metal deposition of the above metal on a resin film, but is preferably performed by sputtering.

  Further, the surface of the metal film may be appropriately subjected to a surface treatment in order to improve the adhesion with the conductive pressure-sensitive adhesive layer. Examples of the surface treatment include silicone treatment and primer treatment. Among these, silicone treatment is preferable.

(Metal foil)
The metal foil that can be used as the conductive sheet is made of the above-described metal. The thickness of the metal foil is preferably 0.5 to 70 μm. By setting the thickness to 0.5 μm or more, it is possible to impart an appropriate electromagnetic shielding property to the conductive sheet. When the thickness is 70 μm or less, the conductive sheet is prevented from becoming rigid, and the adhesiveness of the laminate composed of the pressure-sensitive adhesive layer, the conductive sheet, and the conductive pressure-sensitive adhesive layer to the resin foam sheet is improved. be able to. The thickness of the metal foil is more preferably 2 to 35 μm, still more preferably 6 to 18 μm. Further, one or both surfaces of the metal foil may be appropriately subjected to surface treatment in order to improve the adhesiveness with the pressure-sensitive adhesive layer or the conductive pressure-sensitive adhesive layer. Specific examples of the surface treatment include those listed above for the surface treatment of the metal film.

[Adhesive layer and conductive adhesive layer]
The pressure-sensitive adhesive layer is a layer for adhering the conductive sheet to the resin foam sheet, and is composed of a pressure-sensitive adhesive. In the present invention, by adhering the foam sheet and the conductive sheet by the pressure-sensitive adhesive layer, the thermal resistance in the thickness direction of the foam composite is reduced, and the thermal conductivity is improved.
The conductive pressure-sensitive adhesive layer is composed of a conductive pressure-sensitive adhesive in which a metal filler is further mixed with the pressure-sensitive adhesive. The conductive adhesive layer is a layer for adhering the foamed composite to other members. By providing the foamed sheet, the foamed composite can be bonded to another member with a high adhesive force through the conductive pressure-sensitive adhesive layer due to the compressive force thereof. Moreover, a conductive adhesive layer has electroconductivity by mix | blending a metal filler, and it becomes possible to conduct | electrically connect an electroconductive sheet and another member. Therefore, the conductive sheet can be grounded via the conductive adhesive layer.

The thickness of the pressure-sensitive adhesive layer is preferably 3 to 50 μm. The adhesiveness of an adhesive layer is securable by setting it as 3 micrometers or more. Moreover, by setting it as 50 micrometers or less, it is prevented by the adhesive layer that thermal resistance becomes large. From these viewpoints, the thickness of the pressure-sensitive adhesive layer is more preferably 8 to 30 μm, and further preferably 10 to 25 μm.
Further, the thickness of the conductive pressure-sensitive adhesive layer is preferably 3 to 50 μm, more preferably 8 to 30 μm, and still more preferably 10 to 25 μm, from the viewpoints of adhesiveness and thermal resistance.

  Examples of the pressure-sensitive adhesive used for the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer include (meth) acrylic pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, and urethane-based pressure-sensitive adhesives. A (meth) acrylic adhesive is preferred. By using the (meth) acrylic pressure-sensitive adhesive, the reliability of the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer can be easily increased. When a (meth) acrylic pressure-sensitive adhesive is used for the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer, the (meth) acrylic pressure-sensitive adhesive contained in the pressure-sensitive adhesive layer and the (meth) acrylic contained in the conductive pressure-sensitive adhesive layer The system pressure-sensitive adhesives may be the same or different.

((Meth) acrylic adhesive)
Each of the (meth) acrylic pressure-sensitive adhesives used for the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer contains a (meth) acrylic polymer.
<(Meth) acrylic polymer>
The (meth) acrylic polymer is not particularly limited, but a (meth) acrylic copolymer obtained by copolymerizing a mixed monomer containing a (meth) acrylic acid ester monomer and another copolymerizable polymerizable monomer. It is preferably a coalescence. The content of the (meth) acrylic acid ester monomer is preferably 90 to 99.5% by mass, more preferably 92 to 98% by mass, in 100% by mass of all monomers (mixed monomers) constituting the (meth) acrylic copolymer. %.
Although it does not specifically limit as said (meth) acrylic acid ester monomer, It is obtained by esterification reaction of the primary or secondary alkyl alcohol whose carbon number of an alkyl group is 1-12, and (meth) acrylic acid ( A (meth) acrylate monomer is preferable, and specific examples include ethyl (meth) acrylate, butyl (meth) acrylate, and (meth) acrylate-2-ethylhexyl. The said (meth) acrylic acid ester monomer may be used independently and may use multiple together.
Examples of other polymerizable monomers that can be copolymerized include, for example, 2-hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxyalkyl (meth) acrylate such as hydroxybutyl (meth) acrylate, Carboxyl group-containing vinyl monomers such as (meth) acrylic acid, itaconic acid, maleic anhydride, crotonic acid, maleic acid, fumaric acid, isobornyl (meth) acrylate, hydroxyalkyl (meth) acrylate, glycerin dimethacrylate, (meta ) Other functional monomers such as glycidyl acrylate and 2-methacryloyloxyethyl isocyanate. The said other polymerizable monomer which can be copolymerized may be used independently, and may use multiple together. Among these, one or both of hydroxyalkyl (meth) acrylate and a carboxyl group-containing vinyl monomer are preferable.

In order to copolymerize the mixed monomer to obtain the above-described (meth) acrylic copolymer, for example, the mixed monomer is subjected to a radical reaction in the presence of a polymerization initiator. A conventionally known method is used as a method of radical reaction of the mixed monomer, that is, a polymerization method. Examples of the polymerization method include solution polymerization method (boiling point polymerization method or constant temperature polymerization method), emulsion polymerization method, suspension polymerization method, bulk polymerization method, and UV polymerization method.
It does not specifically limit as a polymerization initiator, An organic peroxide, an azo compound, a photoinitiator, etc. are mentioned. Examples of the organic peroxide include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2, 5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylper Examples thereof include oxyisobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. Examples of the photopolymerization initiator include 2,2-dimethoxy-1,2-diphenylethane-1-one and benzophenone. The said polymerization initiator may be used independently and may use 2 or more types together.

<Crosslinking agent>
The (meth) acrylic pressure-sensitive adhesive used for the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer preferably contains a crosslinking agent. In the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer, it is preferable that crosslinking of the (meth) acrylic copolymer is advanced by a crosslinking agent.
The crosslinking agent is not particularly limited. For example, an isocyanate crosslinking agent, an epoxy crosslinking agent, a melamine crosslinking agent, a peroxide crosslinking agent, a urea crosslinking agent, a metal alkoxide crosslinking agent, a metal chelate crosslinking agent. , Metal salt crosslinking agents, carbodiimide crosslinking agents, oxazoline crosslinking agents, aziridine crosslinking agents, amine crosslinking agents, polyfunctional acrylates, and the like. The above crosslinking agents may be used alone or in combination.
The content of the crosslinking agent is preferably 0.1 to 15 parts by mass, more preferably 0.5 to 10 parts by mass, and still more preferably 0.8 to 5 parts by mass with respect to 100 parts by mass of the (meth) acrylic polymer. It is.

<Tackifying resin>
Each of the (meth) acrylic pressure-sensitive adhesives used for the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer may further contain a tackifier resin. The tackifying resin is not particularly limited, for example, petroleum-based resins such as aliphatic copolymers, aromatic copolymers, aliphatic / aromatic copolymers and alicyclic copolymers, Coumarone-indene resin, terpene resin, terpene phenol resin, rosin resin such as polymerized rosin, phenol resin, xylene resin and the like. These resins may be hydrogenated resins. The tackifying resins may be used alone or in combination.
The content of the tackifying resin is preferably 5 to 50 parts by mass, more preferably 10 to 45 parts by mass, and still more preferably 15 to 40 parts by mass with respect to 100 parts by mass of the (meth) acrylic polymer.
The pressure-sensitive adhesive and the conductive pressure-sensitive adhesive may further contain conventionally known additives such as other fillers, antioxidants or ultraviolet absorbers, as necessary, within a range not impairing the effects of the present invention. Good.

<Metal filler>
Although the metal filler used for an electroconductive adhesive is not specifically limited, What is necessary is just to use various powdery metal fillers. Moreover, it is desirable that the metal filler is surface-treated.
The metal filler is not particularly limited, but as metal powder, Ni, Cu, Bi, Co, Mn, Sn, Fe, Cr, Ti, Zr, etc., as metal oxide powder, WO ₃ , SnO ₂ , ZnO ₂ , ZrO ₂ , TiO ₂ , and other metal nitrides, carbides, hydroxides, carbonates, sulfates, and other powders. These may be used alone or in combination of two or more.
The content of the metal filler is preferably 60% by mass or less with respect to the total amount of the conductive adhesive. By setting it to 60 mass% or less, it becomes possible to make the adhesiveness of a conductive adhesive layer favorable. The content of the metal filler is preferably 1% by mass or more based on the total amount of the conductive adhesive. By setting it as 1 mass% or more, appropriate electroconductivity can be provided to a conductive adhesive layer. The content of the metal filler is more preferably 5 to 50% by mass, and further preferably 12 to 35% by mass. The total amount of the conductive adhesive refers to the amount based on the solid content of the conductive adhesive.
Further, the conductive adhesive may further contain a silane coupling agent in order to improve the affinity between the metal filler and the adhesive. The content of the silane coupling agent is preferably 0.1 to 10% by mass, more preferably 0.5 to 8% by mass, and still more preferably 0.7 to 5% by mass with respect to the content of the metal filler. is there.

[Foamed composite]
As described above, the foam composite includes a resin foam sheet, a conductive sheet, a pressure-sensitive adhesive layer, and a conductive pressure-sensitive adhesive layer. The foamed composite may be composed of these four members, but may have other members as long as the object of the present invention is not violated. For example, a primer layer or the like for improving the adhesiveness with the pressure-sensitive adhesive layer may be provided on the surface of the resin foam sheet on the pressure-sensitive adhesive layer side.
Moreover, a release sheet may be bonded to the conductive pressure-sensitive adhesive layer, and the conductive pressure-sensitive adhesive layer may be protected by the release sheet. As the release sheet, a resin film, release paper or the like on which at least one surface has been release-treated may be used, and a conductive pressure-sensitive adhesive layer is bonded onto the release-treated surface. For example, the release sheet used at the time of producing the foamed composite may be used as it is.

  The total thickness of the foam composite is preferably 120 to 900 μm. When the thickness of the foam composite is 900 μm or less, the foam composite can be arranged in a narrow gap inside the downsized electronic device. Moreover, it becomes easy to exhibit various performance requested | required of a foam composite by setting it as 120 micrometers or more. From these viewpoints, the thickness of the foam composite is more preferably 200 to 700 μm, and further preferably 300 to 600 μm. When the release sheet is bonded to the conductive pressure-sensitive adhesive layer, the thickness of the entire foamed composite is the thickness excluding the release sheet.

  The surface of the foamed composite on the side of the conductive adhesive layer preferably has a surface resistance of 1000 mΩ / □ or less, preferably 500 mΩ / □ or less, and more preferably 350 mΩ / □ or less. By reducing the surface resistance of the surface of the foamed composite on the conductive adhesive layer side, the foamed composite can be grounded using the surface of the conductive adhesive layer side. The lower limit of the surface resistance is not particularly limited, but is practically 1 mΩ / □ or more, preferably 10 mΩ / □ or more.

Further, the surface of the foam composite on the foam sheet side preferably has a surface resistance of 1.0 × 10 ¹⁰ mΩ / □ or more, preferably 1.0 × 10 ¹² mΩ / □ or more. More preferably, it is 0.0 × 10 ¹⁴ mΩ / □ or more. The surface on the foamed sheet side is usually in contact with a heat sink or the like, but by increasing its surface resistance, it is possible to prevent electric leakage or the like via the heat sink or the like. The higher the surface resistance of the foam composite side surface of the foam composite, the better, but practically it is about 1.0 × 10 ²⁰ mΩ / □ or less.

  The foamed composite is preferably used inside an electronic device. Since the foamed composite of the present invention is thin and has an appropriate flexibility, it can be more suitably used inside various portable electronic devices in which the space for disposing the foamed composite is small. Examples of the portable electronic device include a mobile phone such as a smartphone, a camera, a game device, an electronic notebook, a tablet terminal, a notebook personal computer, and the like, and a mobile phone such as a smartphone is preferable.

The foam composite of the present invention, for example, is disposed between an electronic component and a heat sink, serves as a heat path, transmits heat generated by the electronic component to the heat sink, and serves as a heat dissipation sheet that dissipates heat from the heat sink. Fulfill. In addition, the electromagnetic wave emitted by the electronic component is shielded, and the electronic component is prevented from receiving the electromagnetic wave emitted by another electronic component.
The electronic component is a member that generates heat when driven or used, and specifically includes a light emitting element such as a CPU, a battery, a power amplifier, and an LED. The heat sink is composed of a metal member such as iron or stainless steel, a graphite sheet, or a laminate thereof.
The foamed composite is preferably arranged in a state in which the resin foam sheet is compressed. For example, the compression ratio of the resin foam sheet is 10 to 70%, preferably 20 to 60%, more preferably 25 to 45%. It is arranged in the state that was done.

  FIG. 3 is a sectional view showing an example of use of the foam composite of the present invention. FIG. 3 is a diagram schematically showing the inside of the electronic device, and a substrate 31 is provided on an electronic device main body 30 including a casing of the electronic device. Examples of the substrate 31 include a printed circuit board (PCB). An electronic component 32 such as a CPU is mounted on the substrate 31, and a heat conductive sheet 33 is disposed on the electronic component 32. As the heat conductive sheet 33, a conventionally known heat conductive sheet can be used. For example, a silicone sheet, an elastomer sheet, a heat radiation grease, a resin foam sheet, or the like in which a heat conductive filler is blended is used. A frame-shaped shield material 34 is provided on the outer peripheral side of the electronic component 32 so as to surround the electronic component 32 and the heat conductive sheet 33. The shield material 34 is made of a member capable of shielding electromagnetic waves, and is made of a metal such as SUS. The upper end surface 34 </ b> A of the shield material 34 is disposed on the same plane as the upper surface 33 </ b> A of the heat conductive sheet 33.

In the electronic device, a heat sink 37 is disposed above the heat conductive sheet 33 at a certain distance from the heat conductive sheet 33. Between the heat sink 37 and the heat conductive sheet 33, the foam composite A body 10 is arranged. In the foamed composite 10, the conductive adhesive layer 14 is directed toward the heat conductive sheet 33, and the conductive adhesive layer 14 adheres to the upper surface 33 A of the heat conductive sheet 33 and the upper end surface 34 A of the shield material 34. The The foam composite 10 is placed between the heat sink 37 and the heat conductive sheet 33 in a state where the resin foam sheet 11 is compressed as described above, and the upper surface 11A of the resin foam sheet 11 is placed on the heat sink 37. It will be in close contact. Therefore, even if there is a design tolerance in the gap between the heat conductive sheet 33 and the heat sink 37, the resin foam sheet 11 can follow the heat sink 37. Therefore, the foamed composite 10 can efficiently transmit the heat generated by the electronic component to the heat sink 37 and dissipate the heat from the heat sink 37. Further, the foamed composite 10 closes the opening of the frame-shaped shield material 34 whose upper surface is opened, and can effectively shield electromagnetic waves together with the shield material 34. Furthermore, since the conductive sheet 12 is electrically connected to the shield material 34 via the conductive adhesive layer 14, it is grounded via the shield material 34.
Note that the usage example illustrated in FIG. 3 is an example, and various modifications are possible. For example, the electronic component may be other than the CPU.

[Method for producing resin foam sheet]
The resin foam sheet is obtained by foaming a foamable resin sheet, and is produced, for example, by the following production method.
Although a foaming resin sheet is not specifically limited, For example, other additive components, such as resin, a heat conductive filler, and a foaming agent, are supplied to an extruder, it melt-kneads, and it manufactures by extruding from an extruder. Or you may obtain the expandable resin sheet which has predetermined thickness by conveying the said material continuously, kneading | mixing using a calendar | calender, conveyor belt casting, etc. Moreover, you may obtain a foamable resin sheet by pressing what knead | mixed resin, a heat conductive filler, and another additive component.

Moreover, although the method of foaming a foamable resin sheet is not specifically limited, It is preferable to foam with the foaming agent mix | blended with the foamable resin sheet. Here, it is preferable to use a pyrolytic foaming agent as the foaming agent. Specific examples of the pyrolytic foaming agent include organic or inorganic chemical foaming agents having a decomposition temperature of about 160 ° 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, Examples thereof include 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 3 to 25 parts by mass, more preferably 5 to 20 parts by mass with respect to 100 parts by mass of the main agent so that the foam of the resin foam sheet can be appropriately foamed without rupturing. preferable.
The method for decomposing and foaming the pyrolytic foaming agent is not particularly limited. For example, the foamable resin sheet is heated with hot air, the infrared heat is heated, the salt bath is heated, or the oil bath is heated. These may be used, and these may be used in combination. The heating temperature is preferably 200 to 320 ° C, more preferably 250 to 300 ° C.
In addition, the manufacturing method of a resin foam sheet is not limited to the said method, You may manufacture by another method.

  Moreover, in this manufacturing method, it is preferable to perform a crosslinking treatment on the foamable resin sheet before foaming. As a method for crosslinking the foamable resin sheet, for example, a method of irradiating the foamable resin sheet with ionizing radiation such as electron beam, α ray, β ray, γ ray, etc., an organic peroxide is previously applied to the foamable resin sheet. And a method of decomposing an organic peroxide by heating the foamable resin sheet. These methods may be used in combination. In these, the method of irradiating ionizing radiation is preferable. The irradiation dose of ionizing radiation is preferably 0.5 to 10 Mrad, and more preferably 1 to 5 Mrad.

[Method for producing foam composite]
The foamed composite may be obtained by appropriately laminating a pressure-sensitive adhesive layer, a conductive sheet, and a conductive pressure-sensitive adhesive layer on the resin foam sheet produced as described above. Among them, a pressure-sensitive adhesive layer is laminated on one surface of a conductive sheet, and a conductive pressure-sensitive adhesive layer is laminated on the other surface to obtain a double-sided pressure-sensitive adhesive sheet based on the conductive sheet. A method is preferred in which is bonded to one surface of a resin foam sheet via an adhesive layer.

The method of forming the pressure-sensitive adhesive layer or the conductive pressure-sensitive adhesive layer on the conductive sheet is not particularly limited. For example, the method of directly applying the pressure-sensitive adhesive or the conductive pressure-sensitive adhesive to the surface of the conductive sheet, or on the release sheet Examples include a method of transferring the formed pressure-sensitive adhesive layer or conductive pressure-sensitive adhesive layer to the surface of the conductive sheet. In addition, what is necessary is just to perform formation of the adhesive layer or the electroconductive adhesive layer on a peeling sheet by apply | coating an adhesive or an electroconductive adhesive to the peeling process surface of a peeling sheet.
Application of the adhesive or the conductive adhesive may be performed using various coaters, sprays, brushes, and the like. The pressure-sensitive adhesive and the conductive pressure-sensitive adhesive may be applied after appropriately diluting with an organic solvent to obtain a pressure-sensitive adhesive diluted solution or a conductive pressure-sensitive adhesive diluted solution. Moreover, after apply | coating an adhesive, a conductive adhesive, or these dilution liquids, you may heat, dry, etc. as needed. The pressure-sensitive adhesive layer or the conductive pressure-sensitive adhesive layer may be crosslinked by heating with a crosslinking agent contained in the pressure-sensitive adhesive or the conductive pressure-sensitive adhesive.

  The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

In the present invention, methods for measuring and evaluating various physical properties are as follows.
[Thermal resistance measurement]
As shown in FIG. 4, the sample 42 was placed on the cold plate 41. In addition, heat radiation grease 43 (manufactured by Shin-Etsu Chemical Co., Ltd., trade name “G-776”) is applied on the sample 42, and a heat source 44 is placed through the heat radiation grease 43, so that the thermal resistance ( Total R) was measured. In the examples, the foamed composite was compressed as a sample 42 so that the resin foam sheet had a predetermined compression rate (37.5%). Regarding the foamed composite used for the sample 42, the surface provided with the conductive adhesive layer was bonded to the cold plate 41. On the other hand, in Comparative Example 1, the conductive adhesive tape is bonded to the cold plate with the conductive adhesive layer, and the resin foam sheet is compressed so as to have a predetermined compression rate (37.5%). It mounted on the tape and the thermal resistance was measured similarly to the Example. In Comparative Example 2, the conductive adhesive tape was bonded to the cold plate with the conductive adhesive layer, and the heat-dissipating silicone sheet was placed on the conductive adhesive tape without being compressed. It was measured.
The thermal resistance was measured according to JESD51-14 by using transient heat measurement under the following conditions using T3Ster manufactured by Mentor Graphics.
Heating current / measurement current: 2 A / 10 mA, heat source: IPP029N06N (NchMOSFET), measurement mode: MOS-diode mode, heating time / measurement time: 150 s / 150 s

[Surface resistance]
In the examples, the surface resistance of each surface of the foamed composite (the surface on the conductive adhesive layer side and the surface on the resin foam sheet side) was measured. Also in the comparative example, in the laminate in which the foam sheet or the heat radiation silicone sheet and the conductive adhesive tape are overlapped, the surface resistance of the surface on the conductive adhesive layer side and the surface on the resin foam sheet or heat radiation silicone sheet side is measured. did.
The surface of the conductive pressure-sensitive adhesive layer side was measured by a four-terminal method using an ASP probe terminal with a resistance measuring machine “Loresta” manufactured by Mitsubishi Analytech Co., Ltd. The surface of the resin foam sheet or the heat dissipation silicone sheet side was obtained by using a resistance measuring machine “Hiresta” manufactured by Mitsubishi Analytech Co., Ltd.

[Shielding property]
The shielding characteristics for each frequency (10 to 100 MHz and 100 to 1000 MHz) were measured according to the KEC shielding method.
[Maximum compression ratio]
In Examples 1 to 5 and Comparative Example 3, the foamed composite was cut into 50 mm × 50 mm, and the compressibility at 800 kPa was measured using Tensilon (manufactured by A & D Co., Ltd.). In Comparative Examples 1 and 2, a conductive adhesive tape and a resin foam sheet or a heat-dissipating silicone sheet, each cut to 50 mm × 50 mm, were overlapped, and the compressibility at 800 kPa was measured using Tensilon.

[SUS adhesive strength]
In Examples 1 to 5 and Comparative Example 3, the foamed composite was cut to 25 × 150 mm, and attached to a SUS304 mirror-finished plate with a 2 kg roller using a conductive adhesive layer. After pasting, it was left for 20 minutes in an environment of 23 ° C. and a relative humidity of 50%, and then peeled off the foamed composite in the direction of 180 ° at a peeling speed of 300 mm / min in an environment of 23 ° C. and a relative humidity of 50%. SUS adhesive strength was obtained. In Comparative Examples 1 and 2, a similar test was performed using a conductive adhesive tape instead of the foamed composite to obtain SUS adhesive strength.

[Foaming ratio]
The expansion ratio of the resin foam sheet was calculated by gradually decreasing the specific gravity of the foamable resin sheet before foaming with the specific gravity of the resin foam sheet after foaming. Specific gravity was measured based on JISK7222.
[Inorganic filler diameter]
Using a laser diffraction / scattering particle size distribution measuring device (HELOS / BFM, manufactured by Sympatec GmbH), the particle size distribution was measured by a conventional method, and the average value of the average particle size when measured five times was taken as the diameter of the inorganic filler. .
[Mooney viscosity and viscosity at 25 ° C.]
The Mooney viscosity (ML _{1 + 4} , 125 ° C.) of the elastomer is a value measured according to JIS K6300-1. The viscosity at 25 ° C. is a value measured with a B-type rotational viscometer at a rotational speed of 1 rpm.

The materials used in the foamable resin sheets of Examples and Comparative Examples are as follows.
Ethylene-propylene-diene rubber: “EMB-EPT 4021” manufactured by Mitsui Chemicals, Mooney viscosity (ML _{1 + 4} , 125 ° C.) = 26
Liquid ethylene-propylene-diene rubber: “PX-068” manufactured by Mitsui Chemicals, viscosity at 25 ° C. = 10 Pa · s
Azodicarbonamide: “SO-L” manufactured by Otsuka Chemical Co., Ltd.
Phenol antioxidant: BASF Japan Ltd., trade name “Irganox 1010”
Magnesium oxide: manufactured by Ube Materials Co., Ltd., trade name “RF-50C”, average particle size 50 μm, thermal conductivity 50 W / m · K
Boron nitride: “PTX25” manufactured by Momentive Co., Ltd., average particle size 25 μm, thermal conductivity 60 W / m · K)

[Example 1]
(Production of foam sheet (1))
After melt-kneading 55 parts by mass of ethylene-propylene-diene rubber, 45 parts by mass of liquid ethylene-propylene-diene rubber, 7 parts by mass of azodicarbonamide, 300 parts by mass of magnesium oxide, 45 parts by mass of boron nitride and 1 part by mass of phenolic antioxidant The foamed resin sheet having a thickness of 0.42 mm was obtained by pressing. The foamable resin sheet was cross-linked by irradiating 3.0 Mrad of an electron beam at an acceleration voltage of 500 keV on both surfaces of the obtained foamable resin sheet. Next, the foamable resin sheet was foamed by heating the foamable resin sheet to 250 ° C. to obtain a resin foam sheet having a foaming ratio of 3 times and a thickness of 0.40 mm.

(Conductive non-woven fabric)
A polyester non-woven fabric (basis weight: 8 g / m ² ) manufactured by Hirose Paper Co., Ltd. was used which was plated with nickel after copper plating (mass ratio: copper / nickel = 3/1). The total adhesion amount of copper and nickel was 1200 μg / cm ² , and the thickness of the conductive nonwoven fabric was 18 μm.

(Preparation of adhesive diluent)
A reactor equipped with a stirrer, a cooler, a thermometer, and a nitrogen gas inlet was prepared. The reactor is mixed with 62 parts by mass of butyl acrylate (BA), 35 parts by mass of 2-ethylhexyl acrylate (2EHA), 3 parts by mass of acrylic acid (AAc), and 0.1 parts by mass of 2-hydroxyethyl acrylate (HEA). A reaction solution containing the mixed monomer and 100 parts by mass of ethyl acetate as a solvent was charged. The reaction solution was bubbled with nitrogen gas for 30 minutes to remove dissolved oxygen.
Thereafter, the inside of the apparatus was replaced with nitrogen gas, and the temperature of the reaction solution was increased with an oil bath while stirring the reaction solution until the reaction solution reached the reflux temperature. When the reaction solution reaches the reflux temperature, a polymerization initiator solution in which 0.1 part by mass of azobisisobutyronitrile is dissolved in 1.35 parts by mass of cyclohexane is added to the reaction solution over 7 hours, and the mixed monomer is added. Copolymerized. To the acrylic copolymer solution obtained after completion of the polymerization, 1.5 parts by mass of an isocyanate-based crosslinking agent (trade name “Coronate L-55” manufactured by Nippon Polyurethane Industry Co., Ltd.) and a rosin-modified resin (Arakawa) as a tackifying resin 30 parts by mass of Chemical Industry Co., Ltd., trade name “KE388”) was added and stirred to prepare an adhesive diluent.
(Adjustment of conductive adhesive diluent)
In addition to the above adhesive diluent, 40 parts by mass of nickel powder (“Type 255” manufactured by VALE) (23% by mass with respect to the total amount of conductive adhesive (solid content)), silicone coupling agent (Shin-Etsu Chemical Co., Ltd.) 0.5 part by mass (trade name “KBM403”, manufactured by Co., Ltd.) was added to prepare a conductive adhesive diluent.

(Production of foam composite)
A release sheet made of a PET film having one surface subjected to a release treatment was prepared. The pressure-sensitive adhesive solution obtained above is applied to the release-treated surface of this release sheet so that the thickness after drying is 15 μm, dried at 110 ° C. for 3 minutes, and the acrylic co-polymer in the pressure-sensitive adhesive diluent is dried. Cross-linking of the polymer was advanced to produce a laminated sheet in which an adhesive layer was provided on the release treatment surface of the release sheet. The surface of the laminated sheet on which the pressure-sensitive adhesive layer was provided was bonded to one surface of the conductive nonwoven fabric to obtain a laminate composed of the pressure-sensitive adhesive layer / conductive nonwoven fabric. In this laminate, the pressure-sensitive adhesive layer was protected by the release sheet while the release sheet was still bonded to the pressure-sensitive adhesive layer.
Subsequently, in the same manner as described above, the conductive adhesive diluent is applied to the release treatment surface of the release sheet so as to have a predetermined thickness and dried, and the conductive adhesive layer is applied to the release treatment surface of the release sheet. A laminated sheet provided with was prepared. The side of the laminated sheet on which the conductive pressure-sensitive adhesive layer is provided is bonded to the other surface of the conductive nonwoven fabric to obtain a double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer / conductive nonwoven fabric / conductive pressure-sensitive adhesive layer. It was. In addition, both sides of this double-sided pressure-sensitive adhesive sheet were bonded to each other and protected by the release sheet.
Thereafter, the release sheet for protecting the pressure-sensitive adhesive layer is removed, the foamed sheet is bonded to the exposed pressure-sensitive adhesive layer, and cured in an oven at 40 ° C. for 24 hours, and a resin foam sheet / pressure-sensitive adhesive layer as shown in FIG. A foamed composite in which the respective layers were laminated in the order of / conductive nonwoven fabric / conductive adhesive layer was obtained. Both the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer had a thickness of 15 μm, and the thickness of the entire foamed composite was 448 μm. In addition, the release adhesive sheet was affixed and the conductive adhesive layer of this foam composite was protected. However, the release sheet was removed from the foamed composite before each evaluation was performed.

[Example 2]
It implemented similarly to Example 1 except having used the foam sheet (2) produced as follows as a resin foam sheet. The total thickness of the foamed composite was 448 μm.
(Preparation of foam sheet (2))
By melt-kneading and pressing 70 parts by mass of ethylene-propylene-diene rubber, 30 parts by mass of liquid ethylene-propylene-diene rubber, 7 parts by mass of azodicarbonamide, 300 parts by mass of magnesium oxide, and 1 part by mass of phenolic antioxidant A sheet-like foamable resin sheet having a thickness of 0.45 mm was obtained. The foamable resin sheet was cross-linked by irradiating 3.0 Mrad of an electron beam at an acceleration voltage of 500 keV on both surfaces of the obtained foamable resin sheet. Next, the foamable resin sheet was foamed by heating the foamable resin sheet to 250 ° C. to obtain a foam sheet having a foaming ratio of 3 times and a thickness of 0.40 mm.

[Example 3]
The following conductive resin film was used instead of the conductive nonwoven fabric, and the same procedure as in Example 2 was performed except that the thickness of the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer was 18 μm. The foam composite of Example 3 had a laminated structure in which the layers were laminated in the order of resin foam sheet / adhesive layer / resin film / metal film / conductive adhesive layer as shown in FIG. . The total thickness of the foamed composite was 448 μm.
(Conductive resin film)
A metal film was formed by sputtering copper and nickel at a mass ratio (copper / nickel = 3/1) on one surface of a PET film having a thickness of 12 μm (trade name “E5200” manufactured by Toyobo Co., Ltd.). Sputtering performed nickel sputtering after copper sputtering. The adhesion amount of the metal film was 50 μg / cm ² .

[Example 4]
The same operation as in Example 3 was performed except that the foamed sheet (1) produced in the same manner as in Example 1 was used as the resin foam sheet.

[Example 5]
It implemented similarly to Example 4 except having used the 12-micrometer-thick copper foil as a conductive sheet instead of the conductive resin film. The total thickness of the foamed composite of Example 5 was 448 μm.

[Comparative Example 1]
A foam sheet (2) was produced in the same manner as in Example 2. In addition to the foam sheet (2), the thickness of the conductive resin film produced by the same method as in Examples 3 and 4 on the surface on which the metal film was formed was the same as in Examples 3 and 4. An 18 μm conductive adhesive layer was formed to obtain a conductive adhesive tape comprising PET film / metal film / conductive adhesive layer. The foamed sheet (2) was superposed on the surface of the conductive adhesive tape on the PET film side, and various evaluations were performed.

[Comparative Example 2]
It implemented similarly to the comparative example 1 except the point which used the commercially available heat radiation silicone sheet (Joinset company make, brand name "Joinpad4") instead of the foam sheet (2).

[Comparative Example 3]
First, similarly to Example 1, the foam sheet (1), the laminated sheet provided with the pressure-sensitive adhesive layer on the release treatment surface of the release sheet, and the conductive pressure-sensitive adhesive layer provided on the release treatment surface of the release sheet. A laminated sheet was produced. Subsequently, the surface in which the adhesive layer of the laminated sheet which has an adhesive layer was provided in the foam sheet (1) was bonded together. After peeling the release sheet from the pressure-sensitive adhesive layer, the surface of the laminated sheet having the conductive pressure-sensitive adhesive layer provided with the conductive pressure-sensitive adhesive layer is bonded to the exposed pressure-sensitive adhesive layer and cured in an oven at 40 ° C. for 24 hours. Thus, a foam composite having a layer configuration of foam sheet (1) / adhesive layer / conductive adhesive layer was obtained. Various evaluations were performed on the foamed composite as in Example 1.

  As described above, the foamed composites of Examples 1 to 5 have high electromagnetic shielding properties by having a laminated structure in which a resin foam sheet, an adhesive layer, a conductive sheet, and a conductive adhesive layer are laminated in this order. It has become possible to ensure thermal conductivity and flexibility. On the other hand, Comparative Examples 1, 2, and 3 did not have the above laminated structure, and therefore at least one of electromagnetic shielding properties, thermal conductivity, and flexibility could not be sufficiently increased. .

DESCRIPTION OF SYMBOLS 10 Foam composite 11 Resin foam sheet 12 Conductive sheet 12A Resin film 12B Metal film 13 Adhesive layer 14 Conductive adhesive layer 30 Electronic equipment main body 31 Substrate 32 Electronic component (CPU)
33 Thermal conductive sheet 34 Shielding material
37 Heat Sink 41 Cold Plate 42 Sample 43 Heat Dissipation Grease 44 Heat Source

Claims (11)

  A resin foam sheet containing a thermally conductive filler, a conductive sheet, a pressure-sensitive adhesive layer that is provided on one surface of the conductive sheet, adheres the conductive sheet to the resin foam sheet, and the conductive material. A foam composite comprising a conductive pressure-sensitive adhesive layer provided on the other surface of the sheet.   The foam composite according to claim 1, wherein the resin foam sheet contains 100 to 600 parts by mass of the heat conductive filler (B) with respect to 100 parts by mass of the main agent.   The foam composite according to claim 1 or 2, wherein the resin foam sheet has an expansion ratio of 1.5 to 5.0 times.   The thermally conductive filler is at least one selected from the group consisting of aluminum oxide, magnesium oxide, boron nitride, talc, zinc oxide, silica, silicon carbide, silicon nitride, titanium oxide, carbon fiber, aluminum nitride, graphite, and graphene. The foam composite according to any one of claims 1 to 3, which is a seed.   The foamed composite according to any one of claims 1 to 4, wherein the resin constituting the resin foam sheet is an elastomer resin.   The foamed composite according to any one of claims 1 to 5, wherein the conductive sheet is a conductive nonwoven fabric.   The conductive sheet is a conductive resin film including a resin film and a metal film provided on at least one side of the resin film, and the conductive adhesive layer is provided on the one side of the resin film. Item 6. The foamed composite according to any one of Items 1 to 5.   The foamed composite according to any one of claims 1 to 5, wherein the conductive sheet is a metal foil.   The foamed composite according to any one of claims 1 to 8, wherein the conductive pressure-sensitive adhesive layer is composed of a conductive pressure-sensitive adhesive in which a metal filler is mixed with a pressure-sensitive adhesive.   The foamed composite according to any one of claims 1 to 9, wherein each of the pressure-sensitive adhesives constituting the pressure-sensitive adhesive layer and the conductive pressure-sensitive adhesive layer is a (meth) acrylic pressure-sensitive adhesive.   The foam composite according to any one of claims 1 to 10, which is used inside an electronic device.