Nonwoven fabric, heat dissipation structure, and production methods therefor

Abstract

A nonwoven fabric comprising fibrous carbon nanostructures having a BET specific surface area of 400 m2 / g or more and metal nanoparticles that are any one of silver nanoparticles, copper nanoparticles, and tin nanoparticles, wherein the ratio of the mass of the metal nanoparticles to the mass of the fibrous carbon nanostructures (CNT) is 0.3-250.

Description

Nonwoven fabric, heat dissipation structure, and method for manufacturing the same

[0001] This invention relates to nonwoven fabrics, heat dissipation structures, and methods for manufacturing the same.

[0002] In recent years, with the increasing integration and performance of semiconductor devices, the amount of heat generated during use has been on the rise. Furthermore, the need for miniaturization of products incorporating semiconductor devices is also leading to an increase in heat density within those products. Therefore, heat dissipation measures are becoming increasingly important in products containing semiconductor devices. Semiconductor devices, as heat sources, are typically combined with heat dissipation components such as heat sinks. Thermally conductive materials, known as TIMs (Thermal Interface Materials), are used to connect the heat source and the heat dissipation component while conducting heat. Traditionally, grease, polymer TIMs, and solder have been used as TIMs. These were applied between the heat source and the heat dissipation component to connect them in a way that allowed for heat conduction. In particular, when solder was used, the solder material was joined to both the heat source and the heat dissipation component to form a metallic bond, thereby integrating the heat source and the heat dissipation component. However, solder materials lack flexibility and cannot follow the expansion and contraction of semiconductor elements and heat dissipation components, sometimes leading to defects such as cracks. Therefore, in recent years, the use of pastes containing fine particles of metal materials different from solder materials, such as silver and copper, as TIM (Thermal Insulation Material) has been investigated.

[0003] On the other hand, thermally conductive materials that are already in sheet form have also been developed (see, for example, Patent Document 1). Patent Document 1 discloses a nonwoven fabric that contains fibrous carbon nanostructures and graphene, and is characterized in that the ratio of thermal conductivity in the plane direction to thermal conductivity in the thickness direction is 30 or more. Because such a nonwoven fabric has high anisotropy in thermal conductivity, it has excellent thermal conductivity in a specific direction.

[0004] Japanese Patent Publication No. 2019-157284

[0005] As described above, joining using metal paste containing silver or copper nanoparticles offers superior strength and flexibility compared to solder. However, precisely because it is a paste, there was room for improvement in terms of poor storage stability and difficulty in achieving uniform coating. Furthermore, while the nonwoven fabric described in Patent Document 1 does not suffer from the problem of uniform coating, it does not contain metal particles, and therefore there was room for improvement in terms of thermal conductivity.

[0006] Therefore, the present invention aims to provide a nonwoven fabric containing metal particles that has excellent thermal conductivity.

[0007] The inventors conducted diligent research to achieve the above objectives. They discovered that by using fibrous carbon nanostructures having a predetermined specific surface area, it is possible to form a nonwoven fabric that holds metal nanoparticles at a high concentration, and that such a nonwoven fabric exhibits excellent thermal conductivity, thus completing the present invention.

[0008] In other words, the purpose of this invention is to advantageously solve the above-mentioned problems, and the present invention provides the following nonwoven fabrics, etc.

[0009] [1] A fibrous carbon nanostructure comprising metal nanoparticles, wherein the metal nanoparticles comprise at least one of silver nanoparticles, copper nanoparticles, and tin nanoparticles, the ratio of the mass of the metal nanoparticles to the mass of the fibrous carbon nanostructure being 0.3 or more and 250 or less, and the BET specific surface area of ​​the fibrous carbon nanostructure being 400 m² ２ Nonwoven fabric having a density of 1 / g or more. Such nonwoven fabric has excellent thermal conductivity because it contains metal nanoparticles. In this specification, "fibrous carbon nanostructure" refers to a fibrous carbon structure with an outer diameter (fiber diameter) of less than 1 μm. In this specification, "BET specific surface area" refers to the nitrogen adsorption specific surface area measured using the BET (Brunauer-Emmett-Teller) method. The "BET specific surface area" can be determined by measuring the nitrogen adsorption isotherm at 77K and using the BET method. For example, "BELSORP®-max" (manufactured by Nippon Bell Co., Ltd.) can be used to measure the BET specific surface area.

[0010] [2] In the nonwoven fabric of [1] above, it is preferable that the metal nanoparticles are held or encapsulated within a network structure made of the fibrous carbon nanostructure. [3] In the nonwoven fabric of [1] or [2] above, it is preferable that the metal nanoparticles include silver nanoparticles or copper nanoparticles, and the ratio of the mass of the silver nanoparticles to the mass of the fibrous carbon nanostructure is 51 or more and 250 or less. [4] In the nonwoven fabric of [3] above, it is preferable that the ratio of the mass of the silver nanoparticles or copper nanoparticles to the mass of the fibrous carbon nanostructure is 51 or more and 160 or less. [5] In any of the nonwoven fabrics of [1] to [4] above, it is preferable that the metal nanoparticles include silver nanoparticles, and the change in thickness when sintered at a pressure of 10 MPa, a temperature of 180°C, and for 1 hour is 20% or more. The value of the change in thickness can be measured by the method described in the examples. [6] In any of the nonwoven fabrics of [1] to [5] above, it is preferable that the metal nanoparticles include silver nanoparticles, and the bundle diameter of the fibrous carbon nanostructure is 0.50 μm or less when the nonwoven fabric is observed at a magnification of 50,000 times. The bundle diameter of the fibrous carbon nanostructure can be measured by the method described in the examples. [7] In any of the nonwoven fabrics of [1] to [6] above, a metal nanoparticle layer mainly composed of metal nanoparticles may be provided on at least one side. [8] A method for producing a nonwoven fabric containing fibrous carbon nanostructure and metal nanoparticles, wherein the BET specific surface area is 400 m ２A method for producing a nonwoven fabric, comprising: a dispersion step of dispersing fibrous carbon nanostructures having a concentration of 1 / g or more in a dispersion medium to prepare a dispersion of fibrous carbon nanostructures; and a nonwoven fabric forming step of forming a nonwoven fabric using the dispersion of fibrous carbon nanostructures, wherein the metal nanoparticles include at least one of silver nanoparticles, copper nanoparticles, and tin nanoparticles. [9] In the production method of [8] above, it is preferable that the ratio of the mass of the metal nanoparticles to the mass of the fibrous carbon nanostructures is 0.3 or more and 250 or less.

[10] In the production method of [8] or [9] above, it is preferable that in the nonwoven fabric forming step, the metal nanoparticles are mixed with the dispersion of fibrous carbon nanostructures to obtain a mixture, the dispersion medium is removed from the mixture to form a nonwoven fabric in which the metal nanoparticles are held or enclosed within a mesh structure made of fibrous carbon nanostructures.

[11] In any of the manufacturing methods described in [8] to

[10] above, the metal nanoparticles include silver nanoparticles, and in the dispersion liquid of the fibrous carbon nanostructure obtained in the dispersion step, the dispersed particle size of the fibrous carbon nanostructure is 0.5 μm or more and 5.0 μm or less. Furthermore, in the nonwoven fabric formation step, silver nanoparticles are mixed with the dispersion liquid of the fibrous carbon nanostructure to obtain a mixed liquid, and the dispersion medium is removed from the mixed liquid to form a nonwoven fabric in which the silver nanoparticles are held or encapsulated within a network structure made of the fibrous carbon nanostructure.

[12] In the manufacturing method described in [8] above, the metal nanoparticles include copper nanoparticles, and further, in the nonwoven fabric formation step, it is preferable to perform both or either of the following operations (i) or (ii).(i) an operation to obtain a mixture by mixing copper nanoparticles with the fibrous carbon nanostructure dispersion to obtain a mixture, and to remove the dispersion medium from the mixture to form a copper nanoparticle-encapsulated nonwoven fabric in which the copper nanoparticles are encapsulated within a network structure made of the fibrous carbon nanostructure; (ii) an operation to obtain a metal nanoparticle-free nonwoven fabric by removing the dispersion medium from the fibrous carbon nanostructure dispersion to obtain a metal nanoparticle-free nonwoven fabric, and to form a copper nanoparticle layer on at least one side of the metal nanoparticle-free nonwoven fabric or the copper nanoparticle-encapsulated nonwoven fabric obtained in operation (i) by applying a copper nanoparticle dispersion in which copper nanoparticles are dispersed in a copper nanoparticle dispersion medium, and removing the copper nanoparticle dispersion medium to form a copper nanoparticle layer mainly composed of copper nanoparticles on at least one side of the copper nanoparticle-free nonwoven fabric or the copper nanoparticle-encapsulated nonwoven fabric.

[13] A heat dissipation structure comprising a heat source, one of the nonwoven fabrics from [1] to [7] above, and a heat dissipation member, laminated in this order, wherein both or at least one of the interfaces between the nonwoven fabric and the heat source, and between the nonwoven fabric and the heat dissipation member, are joined by the metal nanoparticles.

[14] A method for manufacturing a heat dissipation structure comprising a heat source, a nonwoven fabric, and a heat dissipation member, laminated in this order, comprising: a lamination step of interposing one of the nonwoven fabrics from [1] to [7] above between the heat source and the heat dissipation member to form a laminate; and a joining step of joining the laminate at a temperature of 150°C or higher and a pressure of 10 MPa or higher, so that both or at least one of the interfaces between the nonwoven fabric and the heat source, and between the nonwoven fabric and the heat dissipation member, are joined by the metal nanoparticles.

[15] In the manufacturing method of

[14] above, it is preferable that the heating rate to at least 150°C in the joining step is 4°C / second or higher.

[0011] According to the present invention, it is possible to provide a nonwoven fabric containing metal nanoparticles that has excellent thermal conductivity.

[0012] Embodiments of the present invention will be described in detail below.

[0013] (Nonwoven fabric) The nonwoven fabric of the present invention comprises fibrous carbon nanostructures and metal nanoparticles, wherein the ratio of the mass of metal nanoparticles to the mass of fibrous carbon nanostructures is 0.3 or more and 250 or less, and the BET specific surface area of ​​the fibrous carbon nanostructures is 400 m². ２ The present invention is characterized by having a ratio of 1 / g or more. The nonwoven fabric of the present invention has excellent thermal conductivity because the ratio of the mass of metal nanoparticles to the mass of fibrous carbon nanostructures is within the above predetermined range. Furthermore, by containing a considerable amount of metal nanoparticles, it also has excellent bonding properties with adherends such as heat sources and heat dissipation members. In addition, the BET specific surface area is 400 m². ２ Because the nonwoven fabric's mesh structure is formed using fibrous carbon nanostructures with a relatively high density of 1 / g or more, it exhibits excellent shape retention as a nonwoven fabric. Furthermore, the nonwoven fabric of the present invention can be efficiently manufactured according to the manufacturing method of the nonwoven fabric of the present invention described later. In addition, the nonwoven fabric of the present invention may optionally contain other components besides fibrous carbon nanostructures and metal nanoparticles. The nonwoven fabric of the present invention has excellent thermal conductivity and excellent bonding properties with adherends, making it suitable for use as a TIM (Thermal Insulation Material).

[0014] <Fibrous carbon nanostructures> In the nonwoven fabric described herein, the fibrous carbon nanostructure has a BET specific surface area of ​​400 m². ２ As long as the amount is greater than or equal to 1 / g, carbon nanostructures having a fibrous structure can be used without particular limitations. Specifically, as fibrous carbon nanostructures, for example, cylindrical carbon nanostructures such as CNTs (Carbon Nano Tubes) and non-cylindrical carbon nanostructures such as carbon nanostructures in which a network of six-membered carbon rings is formed in a flattened cylindrical shape can be used. These may be used individually or in combination of two or more. Among the above, it is more preferable that the fibrous carbon nanostructure contains CNTs.

[0015] Furthermore, the statement that a fibrous carbon nanostructure contains CNTs means that the fibrous carbon nanostructure may consist solely of CNTs, or it may be a mixture of CNTs and other fibrous carbon nanostructures.

[0016] And as the CNTs in the fibrous carbon nanostructure, there are no particular limitations, and single-walled CNTs and / or multi-walled CNTs can be used, but the CNTs are preferably CNTs from single layer to five layers.

[0017] In addition, the fibrous carbon nanostructure containing CNTs can be produced without particular limitation using known CNT synthesis methods such as the arc discharge method, the laser ablation method, the chemical vapor deposition method (CVD method), etc. Specifically, for example, when synthesizing CNTs by the CVD method by supplying a raw material compound and a carrier gas onto a substrate having a catalyst layer for CNT production on its surface, a trace amount of an oxidizing agent (catalyst activating substance) is present in the system, so that the catalytic activity of the catalyst layer is dramatically improved. According to the method (super growth method; see International Publication No. 2006 / 011655), it can be efficiently produced. Hereinafter, the CNTs obtained by the super growth method may be referred to as "SGCNTs".

[0018] And the fibrous carbon nanostructure produced by the super growth method may be composed only of SGCNTs, or may include other carbon nanostructures such as non-cylindrical carbon nanostructures in addition to SGCNTs.

[0019] The specific surface area of the above fibrous carbon nanostructure needs to be 400 m ２ / g or more, preferably 600 m ２ / g or more, more preferably 800 m ２ / g, and preferably 2500 m ２ / g or less, more preferably 1200 m ２ / g or less. If the specific surface area of the fibrous carbon nanostructure containing CNTs is above the above lower limit value, the strength as a non-woven fabric can be increased. Also, if the specific surface area of the fibrous carbon nanostructure is below the above upper limit value, the thermal conductivity of the non-woven fabric can be increased.

[0020] Furthermore, the fibrous carbon nanostructures preferably have an average diameter of 0.5 nm or more, more preferably 1 nm or more, more preferably 15 nm or less, and more preferably 10 nm or less. If the average diameter of the fibrous carbon nanostructures is within the above range, the strength and thermal conductivity of the resulting nonwoven fabric can be improved.

[0021] Furthermore, fibrous carbon nanostructures typically have an aspect ratio (length / diameter) greater than 10. In this specification, the average diameter and aspect ratio of fibrous carbon nanostructures can be determined by measuring the diameter (outer diameter) of 100 randomly selected fibrous carbon nanostructures using a transmission electron microscope. The average diameter of fibrous carbon nanostructures may also be adjusted by changing the manufacturing method or manufacturing conditions of the fibrous carbon nanostructures, or by combining multiple types of fibrous carbon nanostructures obtained by different manufacturing methods.

[0022] <Metal Nanoparticles> The metal nanoparticles contained in the nonwoven fabric according to this specification include at least one of silver nanoparticles, copper nanoparticles, and tin nanoparticles. Among these, at least one of silver nanoparticles and copper nanoparticles can be suitably used. Furthermore, the metal nanoparticles are not particularly limited, and metal particles having a nano-size, for example, a particle diameter of 900 nm or less, can be used. The particle diameter of the metal nanoparticles is preferably 700 nm or less, more preferably 500 nm or less, even more preferably 300 nm or less, and particularly preferably 100 nm or less, for example, 1 nm or more, and preferably 10 nm or more from the viewpoint of uniform dispersion of metal nanoparticles on the surface and / or inside the nonwoven fabric. If the particle diameter of the metal nanoparticles is below the above upper limit, it is not necessary to excessively increase the heating temperature when laminating the nonwoven fabric with adherends such as heat sources and heat dissipation members to manufacture the heat dissipation structure, and the heat dissipation structure can be manufactured efficiently. Here, the melting point of silver is generally known to be 961.8°C, and the melting point of copper is generally known to be 1084.5°C. However, when the size of the metal particles is on the nano-order, the melting point (sintering temperature) is known to be, for example, around 150°C to 300°C. Therefore, in the method for manufacturing the heat dissipation structure of the present invention described later, by heating the laminate of heat source-nonwoven fabric-heat dissipation member at a temperature of 150°C or higher, both or at least one of the interfaces between the heat source and the nonwoven fabric, and the interface between the nonwoven fabric and the heat dissipation part, can be joined with metal. In this specification, the particle diameter of metal nanoparticles refers to the volume-average particle diameter and can be measured using a wet particle size distribution analyzer (for example, Horiba's "SZ-100").

[0023] The shape of the metal nanoparticles is not particularly limited, but may be spherical, elliptical, rod-shaped, or plate-shaped, for example. Among these, a spherical shape is preferred.

[0024] As the metal nanoparticles, for example, metal fine particles produced by a wet reduction method (for example, reducing silver chloride, copper sulfate, etc., in a liquid) can be used. Alternatively, if commercially available metal nanoparticles are available, they may be used. As will be described in detail in the section on (Method for Manufacturing Nonwoven Fabric) below, the metal nanoparticles used in the production of the nonwoven fabric according to this specification are preferably in slurry form.

[0025] <Ratio of the mass of metal nanoparticles to the mass of fibrous carbon nanostructures> In the nonwoven fabric according to this specification, the ratio of the mass of metal nanoparticles to the mass of fibrous carbon nanostructures (amount of metal nanoparticles / amount of fibrous carbon nanostructures) must be 0.3 or more, preferably 0.4 or more, preferably 2.0 or more, preferably 6.0 or more, preferably 8.0 or more, preferably 51 or more, preferably 70 or more, preferably 90 or more, preferably 100 or more, must be 250 or less, preferably 235 or less, preferably 200 or less, may be 160 or less, may be 150 or less, may be 140 or less, or may be 120 or less. In particular, when the metal nanoparticles are copper nanoparticles, the upper limit of the above ratio may be 25.0 or less, may be 20.0 or less, or may be 15.0 or less. If the above ratio is above the lower limit, the thermal conductivity and bonding properties of the nonwoven fabric can be further improved. Furthermore, if the above ratio is below the above upper limit, it is possible to effectively suppress the detachment of metal nanoparticles from the nonwoven fabric or damage such as tearing of the sheet, thereby improving the cleanliness of the nonwoven fabric.

[0026] <Structure of Nonwoven Fabric> In the nonwoven fabric according to this specification, it is preferable that metal nanoparticles are held or embedded within a network structure made of fibrous carbon nanostructures. In this specification, "held or embedded within a network structure" of metal nanoparticles means that the metal nanoparticles are trapped not only on the surface of the nonwoven fabric, but also inside an aggregate of fibrous carbon nanostructures that are intertwined with each other to form the nonwoven fabric; that is, the metal nanoparticles are held by the network structure of fibrous carbon nanostructures that form the nonwoven fabric and exist embedded within such a network structure. If metal nanoparticles are distributed within the nonwoven fabric in this state, heat conduction in the thickness direction of the nonwoven fabric is made more efficient, and as a result the thermal conductivity of the nonwoven fabric can be increased.

[0027] Furthermore, it is preferable that the nonwoven fabric according to this specification has a metal nanoparticle layer mainly composed of metal nanoparticles on at least one side. Such a metal nanoparticle layer is particularly effective when the metal nanoparticles are copper nanoparticles. Here, "mainly composed of" in this specification means that 50% or more of the layered portion consists of metal nanoparticles. Furthermore, it is more preferable that the nonwoven fabric has metal nanoparticle layers on both sides, as this makes it possible to form bonds at each interface between the heat source and the heat dissipation member, thereby further improving the bonding properties. When the metal nanoparticle layer is laminated on the surface of the nonwoven fabric according to the manufacturing method of the present invention described later, when the cross-section of the nonwoven fabric is observed with an SEM (Scanning Electron Microscope), it can be confirmed that there is a region on the surface of the nonwoven fabric where the metal nanoparticle layer is formed where metal nanoparticles are present at a clearly higher frequency than in other parts of the nonwoven fabric (i.e., a metal nanoparticle layer). The magnification during SEM observation is not particularly limited, but it may be, for example, around 500x or 10,000x. If the nonwoven fabric has a metal nanoparticle layer on at least one side, the bonding properties with the adherend can be further improved.

[0028] <Thickness of Nonwoven Fabric> The nonwoven fabric according to this specification is preferably 155 μm or less in thickness, more preferably 150 μm or less, for example, preferably 30 μm or more, and more preferably 50 μm or more. Nonwoven fabrics with a thickness of the above upper limit or less have excellent thermal conductivity. Nonwoven fabrics with a thickness of the above lower limit or more have excellent strength as a film.

[0029] <Change in Nonwoven Fabric Thickness> The nonwoven fabric according to this specification preferably has a thickness change of 20% or more, more preferably 30% or more, even more preferably 40% or more, and particularly preferably 50% or more when sintered at a pressure of 10 MPa, a temperature of 180°C, and for 1 hour. It may also be 100% or less, or 80% or less. Furthermore, this preferred range of thickness change can also be satisfied, for example, when the heating conditions are changed to a pulsed heat method at a pressure of 10 MPa, the heating rate is set to 4°C / second or more, the temperature is raised to 180°C, and the temperature is held for 10 minutes. Here, when a nonwoven fabric is sintered while applying a pressure of 10 MPa, the thickness of the nonwoven fabric tends to decrease. At this time, the higher the content of the predetermined fibrous carbon nanostructure, the more the restorative properties tend to be exhibited, restoring the thickness that has been compressed and thinned. If the change in thickness of the nonwoven fabric before and after sintering is above the above lower limit, it means that the bonding between metal nanoparticles progresses and a rigid structure is formed within the sheet, making it difficult for the restorative properties of the fibrous carbon nanostructure to be exhibited. Conversely, this means that the nonwoven fabric has a sufficiently high concentration of metal nanoparticles, and the bonding between the metal nanoparticles is also advanced, resulting in excellent thermal conductivity.

[0030] <Bundle diameter of fibrous carbon nanostructures in nonwoven fabrics> In the nonwoven fabrics according to this specification, the bundle diameter of the fibrous carbon nanostructures is preferably 0.50 μm or less, more preferably 0.40 μm or less, more preferably 0.30 μm or less, even more preferably 0.20 μm or less, particularly preferably 0.15 μm or less, preferably 0.01 μm or more, more preferably 0.05 μm or more, and even more preferably 0.09 μm or more. If the bundle diameter is below the above upper limit, metal nanoparticles can be well held within the network structure of the fibrous carbon nanostructures, and the amount of metal nanoparticles contained in the nonwoven fabric can be increased. As a result, a nonwoven fabric with excellent thermal conductivity can be obtained. If the bundle diameter is above the above lower limit, the network structure of the fibrous carbon nanostructures can be well formed, and the amount of metal nanoparticles contained in the nonwoven fabric can be increased.

[0031] (Method for manufacturing nonwoven fabric) According to the method for manufacturing nonwoven fabric described herein, the above-mentioned nonwoven fabric can be manufactured efficiently. The method for manufacturing nonwoven fabric described herein is for a BET specific surface area of ​​400 m². ２ The present invention is characterized by comprising a dispersion step of dispersing fibrous carbon nanostructures having a mass of 1 / g or more in a dispersion medium to prepare a fibrous carbon nanostructure dispersion, and a nonwoven fabric formation step of forming a nonwoven fabric using the obtained fibrous carbon nanostructure dispersion. In addition, when blending metal nanoparticles in the production of the nonwoven fabric, at least one of silver nanoparticles, copper nanoparticles, and tin nanoparticles is used. Furthermore, in the production method of the present invention, it is preferable that the ratio of the mass of metal nanoparticles to the mass of fibrous carbon nanostructures constituting the nonwoven fabric is 0.3 or more and 250 or less. Moreover, it is preferable that this ratio satisfies the preferred range described above for the nonwoven fabric.

[0032] Furthermore, the method for manufacturing nonwoven fabrics according to this specification may include other steps as necessary, in addition to the steps described above.

[0033] <Dispersion Process> In the dispersion process, fibrous carbon nanostructures are dispersed in a dispersion medium to prepare a dispersion of fibrous carbon nanostructures. The dispersion may optionally contain a dispersant and other components.

[0034] <<Fibrous Carbon Nanostructure>> As the fibrous carbon nanostructure, a fibrous carbon nanostructure having a BET specific surface area of 400 m ２ / g or more as described above in the section of "Non-woven fabric" is used. The preferred ranges of the BET specific surface area and the average diameter of the fibrous carbon nanostructure used for preparing the dispersion are the same as those of the fibrous carbon nanostructure constituting the non-woven fabric.

[0035] Here, the fibrous carbon nanostructure used for preparing the dispersion preferably has an average length of 1 μm or more, more preferably 100 μm or more, preferably 5000 μm or less, more preferably 3000 μm or less, and still more preferably 1000 μm or less. If the average length of the fibrous carbon nanostructure is within the above-described range, the uniformity of the obtained non-woven fabric can be enhanced, and the cleaning property of the metal nanoparticles can be improved. Further, if the length of the fibrous carbon nanostructure is within the above range, the metal nanoparticles can be well retained or encapsulated within the mesh structure of the non-woven fabric, and it becomes possible to preferably suppress the powder falling of the non-woven fabric. A non-woven fabric that is less likely to shed powder is excellent in handling properties. In this specification, the average length of the fibrous carbon nanostructure can be determined by measuring the lengths of 100 randomly selected fibrous carbon nanostructures using a transmission electron microscope.

[0036] <<Dispersion Medium>> As the dispersion medium, there is no particular limitation. For example, alcohols such as water, methanol, ethanol, n-propanol, isopropyl alcohol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, amyl alcohol, ketones such as acetone, methyl ethyl ketone, cyclohexanone, esters such as ethyl acetate, butyl acetate, ethers such as diethyl ether, dioxane, tetrahydrofuran, amide-based polar organic solvents such as N,N-dimethylformamide, N-methylpyrrolidone, aromatic hydrocarbons such as toluene, xylene, chlorobenzene, orthodichlorobenzene, paradichlorobenzene, etc. can be mentioned. These may be used alone or in combination of two or more. Among these, alcohols are preferred as the dispersion medium, and among them, water, methyl ethyl ketone, and isopropyl alcohol are preferred.

[0037] <<Dispersant>> As the dispersant, polyvinyl alcohol-based dispersants, polysaccharides such as carboxymethyl cellulose, etc. can be used. Among them, polyvinyl alcohol-based dispersants can be preferably used. The blending amount of the dispersant is preferably 2.5 times or more, preferably 4.5 times or more, preferably 10 times or less, and more preferably 7.5 times or less the mass of the fibrous carbon nanostructure from the viewpoint of effectively enhancing the dispersibility of the fibrous carbon nanostructure. In particular, when the above dispersion medium is an alcohol, if the dispersant is a polyvinyl alcohol-based dispersant, the dispersant can be well dissolved in the dispersion medium, and the dispersibility of the fibrous carbon nanostructure in the dispersion liquid can be further enhanced.

[0038] <<Dispersed Particle Size>> When silver nanoparticles are used as metal nanoparticles in the dispersion preparation, the dispersed particle size of the fibrous carbon nanostructure is preferably 0.5 μm or larger, more preferably 0.7 μm or larger, preferably 5.0 μm or smaller, and more preferably 2.5 μm or smaller. If the dispersed particle size of the fibrous carbon nanostructure is above the above lower limit, it is possible to effectively suppress the occurrence of cracks in the resulting nonwoven fabric and increase the strength of the nonwoven fabric. The reason for this is not clear, but it is presumed that if the dispersed particle size is above the above lower limit, a structure in which the fibrous carbon nanostructures intertwine with each other is formed well in the nonwoven fabric formation process. Also, when the dispersed particle size is excessively small, it is thought that the CNTs are shortened by the load during dispersion, and it is thought that it is difficult to maintain the nonwoven fabric shape with such short CNTs. In the nonwoven fabric formation process described later, the nonwoven fabric is obtained by removing the solvent from the mixed liquid containing silver nanoparticles and fibrous carbon nanostructures, but the nonwoven fabric shrinks during drying at this time. Here, if the fibrous carbon nanostructures form a good network structure, it is presumed that even when the nonwoven fabric shrinks due to drying, the fibrous carbon nanostructures will function as a buffer that absorbs stress caused by shrinkage, thereby suppressing the occurrence of cracks. Furthermore, if the dispersed particle size of the fibrous carbon nanostructures is above the lower limit, it becomes possible to incorporate more silver nanoparticles into the nonwoven fabric within the well-formed network structure of the fibrous carbon nanostructures, resulting in the formation of a nonwoven fabric with excellent thermal conductivity. On the other hand, if the dispersed particle size of the fibrous carbon nanostructures is below the upper limit, the dispersibility of the fibrous carbon nanostructures in the dispersion can be sufficiently increased, and a good network structure of fibrous carbon nanostructures can be formed in the nonwoven fabric. As a result, the amount of silver nanoparticles that can be retained in the nonwoven fabric can be increased, and a nonwoven fabric with excellent thermal conductivity can be formed.

[0039] In the dispersion process, when copper nanoparticles are used as metal nanoparticles, the dispersion liquid prepared has a dispersion particle size of fibrous carbon nanostructures that is preferably 15 μm or larger, more preferably 17 μm or larger, even more preferably 19 μm or larger, preferably 50 μm or smaller, more preferably 45 μm or smaller, even more preferably 40 μm or smaller, particularly preferably 35 μm or smaller, and even more preferably 30 μm or smaller. If the dispersion particle size of the fibrous carbon nanostructures is above the above lower limit, the strength of the resulting nonwoven fabric can be increased. Furthermore, by preventing the dispersion particle size from becoming excessively small, it is thought that the CNTs will not become excessively short due to the load during dispersion, and the shape of the nonwoven fabric can be maintained in good condition. On the other hand, if the dispersed particle size of the fibrous carbon nanostructure is less than or equal to the above upper limit in g, it is presumed that the temporary fixation of copper nanoparticles by the fibrous carbon nanostructure in the mixed liquid described later is promoted. This suppresses the rapid settling of copper nanoparticles during filtration of the mixed liquid, which clogs the porous substrate, and promotes the removal of the dispersion medium.

[0040] <<Dispersion Treatment>> The dispersion is not particularly limited, but it is preferable to prepare it by a dispersion treatment that yields a cavitation effect or a disintegration effect. A dispersion treatment that yields a cavitation effect is a dispersion method that utilizes shock waves generated when vacuum bubbles in a liquid burst when high energy is applied to the liquid. Specific examples of dispersion treatments that yield a cavitation effect include dispersion treatment using an ultrasonic homogenizer, dispersion treatment using a jet mill, and dispersion treatment using a high-shear stirring device. A dispersion treatment that yields a disintegration effect is a dispersion method in which shear force is applied to a composition (crude dispersion) containing fibrous carbon nanostructures and a dispersion medium to disintegrate and disperse aggregates of fibrous carbon nanostructures, and then back pressure is applied to the crude dispersion to uniformly disperse the fibrous carbon nanostructures in the dispersion medium while suppressing the generation of bubbles. A dispersion treatment that yields a disintegration effect can be carried out using a commercially available dispersion system (for example, product name "BERYU SYSTEM PRO" (manufactured by Biryu Co., Ltd.)).

[0041] In particular, when preparing a dispersion of fibrous carbon nanostructures, a dispersion treatment using a dispersion apparatus equipped with a capillary channel is preferred, in which a crude dispersion is pumped into the capillary channel under pressure to apply shear force to the crude dispersion and disperse the fibrous carbon nanostructures. By dispersing the fibrous carbon nanostructures by pumping the crude dispersion into the capillary channel under pressure to apply shear force to the crude dispersion, it is possible to disperse the fibrous carbon nanostructures well while suppressing the occurrence of damage to the fibrous carbon nanostructures.

[0042] Examples of dispersion processing devices equipped with a narrow-tube channel include wet jet mills (e.g., product names "JN5", "JN10", "JN20", "JN100", "JN1000" (all manufactured by Jokoh Co., Ltd.)) and the aforementioned dispersion system (manufactured by Biryu Co., Ltd., product name "BERYU SYSTEM PRO").

[0043] Furthermore, the capillary channel provided in the above-mentioned dispersion processing apparatus may be a single capillary channel, or it may be a plurality of capillary channels having a confluence at any position downstream. However, from the viewpoint of more effectively causing the crude dispersions to collide with each other to impart shear force and easily controlling the particle size of the dispersed fibrous carbon nanostructure to a desired range, it is preferable that the capillary channel provided in the dispersion processing apparatus be a plurality of capillary channels having a confluence at any position downstream.

[0044] Furthermore, while the diameter of the narrow-tube channel in the dispersion processing device is not particularly limited, it is preferably 50 μm to 1000 μm, and more preferably 50 μm to 600 μm, from the viewpoint of effectively imparting high-speed flow shear to the crude dispersion without clogging the crude dispersion and easily controlling the particle size of the fibrous carbon nanostructure to the desired range.

[0045] Furthermore, the means for pumping the crude dispersion into the narrow tube channel are not particularly limited and can include a high-pressure pump or a cylinder with a piston structure.

[0046] Furthermore, the pressure used when pumping the crude dispersion into the capillary channel is not particularly limited, but is preferably between 60 MPa and 200 MPa. By keeping the pressure used when pumping the crude dispersion within the above range, it is possible to sufficiently suppress damage to the fibrous carbon nanostructures while effectively dispersing them.

[0047] <Nonwoven Fabric Formation Process> In the nonwoven fabric formation process, metal nanoparticles are mixed with a dispersion of fibrous carbon nanostructures to obtain a mixture, and the dispersion medium is removed from the mixture to form a nonwoven fabric in which the metal nanoparticles are held or encapsulated within a network structure made of fibrous carbon nanostructures. First, in this process, the dispersion obtained in the above dispersion process is mixed with metal nanoparticles to prepare a mixture containing fibrous carbon nanostructures, metal nanoparticles, and a dispersion medium. The mixture may also contain other components such as dispersants.

[0048] <<Metal Nanoparticles>> As the metal nanoparticles, the metal nanoparticles described in the "Nonwoven Fabric" section are used. Furthermore, from the viewpoint of suppressing surface oxidation, a metal nanoparticle dispersion, in which metal nanoparticles are dispersed in a solvent, may be blended with the fibrous carbon nanostructure dispersion. Here, the metal nanoparticle dispersion is preferably a slurry. By blending a slurry containing metal nanoparticles with the fibrous carbon nanostructure dispersion, the localization of the metal nanoparticles in the mixture and, consequently, in the nonwoven fabric can be effectively suppressed, making it possible to form a homogeneous nonwoven fabric. The dispersion medium of the metal nanoparticle dispersion or metal nanoparticle-containing slurry is not particularly limited, but alcohols can be suitably used. Furthermore, when the metal nanoparticles are silver nanoparticles, texanol can be suitably used among alcohols because it has a relatively high volatility point and excellent storage properties. Furthermore, when the metal nanoparticles are copper nanoparticles, methanol can be suitably used among alcohols. Furthermore, the metal nanoparticle dispersion or metal nanoparticle-containing slurry may optionally contain a protective agent to protect the metal nanoparticles in addition to the metal nanoparticles and dispersion medium. Such protective agents are thought to adhere to the surface of metal nanoparticles and also function as dispersants that exhibit an anti-aggregation effect.

[0049] <<Mixing>> It is preferable to mix the dispersion and the metal nanoparticles such that the mass ratio of metal nanoparticles to fibrous carbon nanostructures is 0.3 or more and 250 or less. This mass ratio is preferably 0.4 or more, preferably 2.0 or more, preferably 6.0 or more, preferably 8.0 or more, preferably 51 or more, preferably 70 or more, preferably 90 or more, preferably 100 or more, preferably 235 or less, preferably 215 or less, may be 200 or less, may be 160 or less, may be 150 or less, may be 140 or less, or may be 120 or less. In particular, when the metal nanoparticles are copper nanoparticles, the upper limit of the above ratio may be 25.0 or less, may be 20.0 or less, or may be 15.0 or less. If the above ratio is above the lower limit, the thermal conductivity of the nonwoven fabric can be further improved. Furthermore, if the above ratio is below the above upper limit, it is possible to effectively suppress the detachment of metal nanoparticles from the nonwoven fabric or damage such as tearing of the sheet, thereby improving the cleanliness of the nonwoven fabric. In addition, although the detailed mechanism is not clear, from the evaluation results of the thermal properties of the examples described later, it is thought that when the above ratio is below a certain upper limit, the thermal conductivity of the nonwoven fabric can be further improved. The method of mixing the dispersion and metal nanoparticles is not particularly limited, and known mixers such as homogenizers can be used.

[0050] In this step, the dispersion medium is removed from the mixture obtained above to form a nonwoven fabric in which metal nanoparticles are held or encapsulated within a network structure made of fibrous carbon nanostructures. Specifically, for example, the mixture is filtered using a porous substrate, and the resulting filtrate is dried to form a nonwoven fabric in which metal nanoparticles are held or encapsulated within a network structure made of fibrous carbon nanostructures. The filtrate obtained by filtering the dispersion may be washed with water or alcohol before drying.

[0051] Here, the porous substrate is not particularly limited and can include filter paper, cellulose, nitrocellulose, alumina, and the like. As for the filtration method, known filtration methods such as natural filtration, vacuum filtration, pressure filtration, and centrifugal filtration can be used, and among these, it is preferable to employ vacuum filtration, which is carried out under reduced pressure in the space on the lower side of the porous substrate.

[0052] Furthermore, known drying methods can be used to dry the filtered material. Specifically, drying methods include hot air drying, vacuum drying, hot roll drying, and infrared irradiation. The drying temperature is not particularly limited, but if the drying temperature is excessively high, sintering will begin between the encapsulated metal nanoparticles. Therefore, it is usually room temperature to 80°C, and the drying time is not particularly limited, but is usually 0.1 to 150 minutes. Furthermore, when drying the filtered material, it is preferable to dry the deposit formed on the filter media by vacuum filtration (i.e., the filtered material before drying) while maintaining a suction state (where the pressure on the side without filtered material is lower than the pressure on the side with filtered material, of the two spaces separated by the filter media). The drying temperature in this case may be room temperature to 80°C, preferably room temperature to 50°C. This is because drying under such a suction state can suppress the reduction in the strength of the nonwoven fabric due to drying shrinkage, resulting in a good nonwoven fabric. In this specification, "room temperature" means the temperature according to JIS Z 8703.

[0053] In the nonwoven fabric formation step, the dispersion medium may be removed from the fibrous carbon nanostructure dispersion obtained in the above dispersion step to obtain a nonwoven fabric free of metal nanoparticles. One method for doing this is to filter the fibrous carbon nanostructure dispersion using a porous substrate, for example, and dry the resulting filter to form a nonwoven fabric free of metal particles. In addition, as in the case of forming a nonwoven fabric that holds or encapsulates metal nanoparticles using the method described above, the filter obtained by filtering the dispersion may be washed with water or alcohol before drying. The types of porous substrates that can be used, the filtering method, and the method for drying the filter are as described above.

[0054] Furthermore, a metal nanoparticle dispersion, in which metal nanoparticles are dispersed in a metal nanoparticle dispersion medium, may be applied to at least one side of the metal particle-free nonwoven fabric obtained in this manner, or the nonwoven fabric that holds or encapsulates metal nanoparticles, and the metal nanoparticle dispersion medium is removed to form a metal nanoparticle layer mainly composed of metal nanoparticles on at least one side of the nonwoven fabric containing metal nanoparticles or the metal nanoparticle-free nonwoven fabric. With this configuration, the adhesion to the adherend can be further improved. The method of applying the metal nanoparticle dispersion when forming the metal nanoparticle layer is not particularly limited, but for example, it can be applied to the surface of any of the above-mentioned nonwoven fabrics or dropped. Dropping is preferred. This operation is preferably carried out according to a vacuum filtration method, similar to when forming the nonwoven fabric. Furthermore, the same drying method as when forming the nonwoven fabric can be used to dry the metal nanoparticle layer. Also, when forming metal nanoparticle layers on both sides of the nonwoven fabric, after forming the metal nanoparticle layer on one side, the same operation can be carried out on the opposite side to form metal nanoparticle layers on both sides.

[0055] Here, the metal nanoparticle dispersion may be a commercially available product, or one prepared by dispersing metal nanoparticles in a metal nanoparticle dispersion medium. The mixing method for preparation is not particularly limited, and a general mixing method, such as a homogenizer-based mixing method, can be used. As the metal nanoparticles, the metal nanoparticles described above in the "Nonwoven Fabric" section are used. As the metal nanoparticle dispersion medium, various dispersion media listed as examples for dispersion mediums of fibrous carbon nanostructures in the "Dispersion Process" section can be used. The concentration of the metal nanoparticle dispersion is not particularly limited, but for example, 1.0% by mass or more is preferred, 1.5% by mass or more is more preferred, 5.0% by mass or less is preferred, and 4.0% by mass or less is even more preferred. If the concentration of the metal nanoparticle dispersion is above the lower limit, the bonding properties of the resulting nonwoven fabric can be efficiently improved. If the concentration of the metal nanoparticle dispersion is below the upper limit, the dust shedding resistance of the resulting nonwoven fabric can be improved.

[0056] (Heat Dissipation Structure) The heat dissipation structure according to this specification is a heat dissipation structure in which a heat source, the nonwoven fabric described above, and a heat dissipation member are laminated in this order, characterized in that both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interface between the nonwoven fabric and the heat dissipation member, are joined by metal nanoparticles. Such a heat dissipation structure has excellent heat dissipation properties.

[0057] <Heat Source and Heat Dissipation Member> The heat source is not particularly limited, but examples include semiconductor chips and semiconductor modules. The heat dissipation member is not particularly limited, but examples include heat sinks and heat dissipation substrates such as copper. Preferably, at least one of these heat source and heat dissipation member has a bonding surface made of a material that can be bonded by metal nanoparticles contained in the nonwoven fabric, such as metal and ceramic.

[0058] In the heat dissipation structure, both or at least one of the interfaces between the nonwoven fabric and the heat source, and between the nonwoven fabric and the heat dissipation member, are joined by metal nanoparticles. Joining of the metal nanoparticles themselves also occurs simultaneously. If the interface with the adherend is bonded by molten metal nanoparticles, that is, if the interface between the metal nanoparticles and the adherend is "joined", then the bonding strength and heat conduction efficiency at the interface are excellent. Therefore, the heat dissipation structure has excellent heat dissipation properties.

[0059] (Method for Manufacturing a Heat Dissipation Structure) The method for manufacturing a heat dissipation structure according to this specification is characterized by comprising: a lamination step of interposing the above-mentioned nonwoven fabric between a heat source and a heat dissipation member to form a laminate; and a bonding step of bonding the laminate under conditions of 150°C or higher, 10 MPa or higher, and an inert gas atmosphere, so that both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interface between the nonwoven fabric and the heat dissipation member, are bonded by metal nanoparticles. According to this manufacturing method, the above-mentioned heat dissipation structure can be manufactured efficiently. The method for manufacturing a heat dissipation structure may include steps other than those described above, as necessary.

[0060] <Lamination Process> In the lamination process, a nonwoven fabric is interposed between the heat source and the heat dissipation component to form a laminate. The lamination method is not particularly limited, and general methods can be used.

[0061] <<Nonwoven fabric, heat source, heat dissipation member>> The various nonwoven fabrics, heat sources, and heat dissipation members described above can be used.

[0062] <Bonding Process> In the bonding process, the laminate is bonded under conditions of 150°C or higher and 10 MPa or higher, so that both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interface between the nonwoven fabric and the heat dissipation member, are bonded by metal nanoparticles.

[0063] The heating temperature in the bonding process must be 150°C or higher, preferably 180°C or higher, more preferably 200°C or higher, preferably 300°C or lower, and more preferably 250°C or lower. If the heating temperature is above the lower limit, the metal nanoparticles can be efficiently bonded, and the interface between the adherend and the nonwoven fabric can be well bonded by the metal. Furthermore, if the heating temperature is below the upper limit, the production efficiency of the nonwoven fabric can be increased.

[0064] The pressure in the bonding process is preferably 10 MPa or more, may be 15 MPa or more, preferably 100 MPa or less, more preferably 70 MPa or less, even more preferably 20 MPa or less, and even more preferably 15 MPa or less. If the pressure is above the lower limit, the bonding strength at the interface between the adherend and the nonwoven fabric can be increased. Also, if the pressure is below the upper limit, the production efficiency of the nonwoven fabric can be increased. Here, it is preferable to apply the pressure at least in the lamination direction of the laminate.

[0065] In the bonding process, the heating rate from room temperature (JIS Z8703) to 150°C is preferably 0.5°C / second or more, more preferably 1.0°C / second or more, even more preferably 3.0°C / second or more, even more preferably 4.0°C / second or more, particularly preferably 6.0°C / second or more, and even more preferably 7.5°C / second or more. The upper limit of the heating rate is not particularly limited, but for example, it may be 15°C / second or less. If the heating rate is above the lower limit, the bonding strength in the heat dissipation structure can be increased, thereby further reducing thermal resistance. In order to control the heating rate to 4.0°C / second or more, a device capable of rapid heat input, such as a thermocompression bonding device equipped with a pulse heat device, can be used.

[0066] The atmosphere used in the bonding process is not particularly limited, but can include standard air in accordance with JIS W 0201:1990, as well as inert gases such as nitrogen gas and noble gases. In particular, when the metal nanoparticles are copper nanoparticles, it is preferable to perform the bonding process in an inert atmosphere such as nitrogen gas. This is because performing the bonding process in an inert gas atmosphere can suppress the oxidation of copper.

[0067] Furthermore, the contents disclosed herein are also characterized by the following exemplary embodiments [1] to [9].

[0068] [1] A fibrous carbon nanostructure and silver nanoparticles, wherein the ratio of the mass of the silver nanoparticles to the mass of the fibrous carbon nanostructure is 51 or more and 160 or less, and the BET specific surface area of ​​the fibrous carbon nanostructure is 400 m². ２ A nonwoven fabric with a density of 1 / g or more. Such a nonwoven fabric has excellent thermal conductivity.

[0069] [2] The nonwoven fabric described in [1] above, wherein the thickness change is 20% or more when sintered at a pressure of 10 MPa, a temperature of 180°C, and for 1 hour. Such a nonwoven fabric has low thermal resistance and even better thermal conductivity. The combustion test can be carried out in a standard atmospheric environment in accordance with JIS W 0201:1990. The thickness change can be calculated according to the method described in the examples.

[0070] [3] The nonwoven fabric according to [1] or [2] above, wherein the silver nanoparticles are held within a network structure made of the fibrous carbon nanostructures.

[0071] [4] The nonwoven fabric according to any one of [1] to [3] above, wherein the bundle diameter of the fibrous carbon nanostructure is 0.50 μm or less when the nonwoven fabric is observed at a magnification of 50,000 times. Such a nonwoven fabric has even better thermal conductivity. The bundle diameter of the fibrous carbon nanostructure can be measured according to the method described in the examples.

[0072] [5] A method for producing a nonwoven fabric containing fibrous carbon nanostructures and silver nanoparticles, wherein the BET specific surface area is 400 m ２ A method for producing a nonwoven fabric, comprising: a dispersion step of dispersing fibrous carbon nanostructures having a concentration of 0.5 μm or more / g or more in a dispersion medium to prepare a dispersion of fibrous carbon nanostructures having a dispersed particle diameter of 0.5 μm or more and 5.0 μm or less; and a nonwoven fabric formation step of mixing silver nanoparticles with the dispersion of fibrous carbon nanostructures to obtain a mixture, and removing the dispersion medium from the mixture so that the silver nanoparticles are held within a network structure made of the fibrous carbon nanostructures. According to this production method, the nonwoven fabric of the present invention can be produced efficiently. In this specification, the "dispersed particle diameter" of the fibrous carbon nanostructures in the dispersion can be measured using the method described in the examples.

[0073] [6] The method for producing a nonwoven fabric according to [5], wherein the ratio of the mass of the silver nanoparticles to the mass of the fibrous carbon nanostructure is 51 or more and 160 or less.

[0074] [7] A method for producing a nonwoven fabric according to [5] or [6] above, wherein the dispersion step includes adding a dispersant when dispersing the fibrous carbon nanostructure in the dispersion medium. By adopting this procedure, a nonwoven fabric with even better thermal conductivity can be efficiently produced.

[0075] [8] A heat dissipation structure comprising a heat source, a nonwoven fabric described in any of [1] to [4] above, and a heat dissipation member, laminated in this order, wherein both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interface between the nonwoven fabric and the heat dissipation member, are bonded by the silver nanoparticles. Such a heat dissipation structure has excellent heat dissipation properties.

[0076] [9] A method for manufacturing a heat dissipation structure in which a heat source, a nonwoven fabric, and a heat dissipation member are laminated in this order, comprising: a lamination step of interposing the nonwoven fabric described in any of [1] to [4] above between the heat source and the heat dissipation member to form a laminate; and a bonding step of bonding the laminate at a temperature of 150°C or higher and a pressure of 10 MPa or higher to such a state that both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interfaces between the nonwoven fabric and the heat dissipation member, are bonded by the silver nanoparticles. According to this manufacturing method, the heat dissipation structure of the present invention can be manufactured efficiently.

[0077] Furthermore, the contents disclosed herein are also characterized by the following exemplary embodiments <1> to <8>.

[0078] <1> A fibrous carbon nanostructure and copper nanoparticles are included, wherein the ratio of the mass of the copper nanoparticles to the mass of the fibrous carbon nanostructure is 0.3 or more and 25.0 or less, and the BET specific surface area of ​​the fibrous carbon nanostructure is 400 m². ２ A nonwoven fabric with a density of 1 / g or more. Such a nonwoven fabric exhibits excellent bonding properties with the adherend.

[0079] <2> The nonwoven fabric described in <1> above, wherein the copper nanoparticles are embedded within a network structure made of fibrous carbon nanostructures. Such a nonwoven fabric has excellent bonding properties with the adherend and also has excellent thermal properties.

[0080] <3> The nonwoven fabric according to <1> or <2> above, having a copper nanoparticle layer mainly composed of copper nanoparticles on at least one side. Such a nonwoven fabric has even better bonding properties with the adherend. In this specification, "one side" means any of the main sides of the nonwoven fabric.

[0081] <4> A method for producing a nonwoven fabric containing fibrous carbon nanostructures and copper nanoparticles, wherein the BET specific surface area is 400 m ２ A method for producing a nonwoven fabric, comprising: a dispersion step of dispersing fibrous carbon nanostructures having a concentration of 1 / g or more in a dispersion medium to prepare a dispersion of fibrous carbon nanostructures; and both or either of the following steps (i) or (ii). (i) A nonwoven fabric encapsulation step of mixing copper nanoparticles with the fibrous carbon nanostructure dispersion to obtain a mixture, and removing the dispersion medium from the mixture to form a copper nanoparticle encapsulated nonwoven fabric in which the copper nanoparticles are encapsulated within a network structure made of the fibrous carbon nanostructure; (ii) A copper nanoparticle layer formation step of applying a copper nanoparticle dispersion in which copper nanoparticles are dispersed in a copper nanoparticle dispersion medium to at least one side of the copper nanoparticle encapsulated nonwoven fabric obtained in step (i), or the copper nanoparticle-free nonwoven fabric obtained by removing the dispersion medium from the fibrous carbon nanostructure dispersion obtained in the dispersion step, and removing the copper nanoparticle dispersion medium to form a copper nanoparticle layer mainly composed of copper nanoparticles on at least one side of the copper nanoparticle encapsulated nonwoven fabric or the copper nanoparticle-free nonwoven fabric. According to this manufacturing method, the nonwoven fabric of the present invention can be manufactured efficiently.

[0082] <5> The method for producing the nonwoven fabric according to <4> above, wherein the ratio of the mass of the copper nanoparticles to the mass of the fibrous carbon nanostructure is 0.3 or more and 25.0 or less.

[0083] <6> The method for manufacturing a nonwoven fabric according to <4> or <5>, wherein in step (ii), the copper nanoparticle layer is formed on at least one side of the copper nanoparticle-encapsulated nonwoven fabric obtained in step (i). By adopting this procedure, a copper nanoparticle-encapsulated nonwoven fabric having a copper nanoparticle layer on at least one side can be efficiently manufactured.

[0084] <7> A heat dissipation structure comprising a heat source, a nonwoven fabric described in any of <1> to <3> above, and a heat dissipation member, laminated in this order, wherein both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interface between the nonwoven fabric and the heat dissipation member, are bonded by copper nanoparticles. Such a heat dissipation structure has excellent bonding properties and thermal properties.

[0085] <8> A method for manufacturing a heat dissipation structure in which a heat source, a nonwoven fabric, and a heat dissipation member are laminated in this order, comprising: a lamination step of interposing the nonwoven fabric described in any of <1> to <3> above between the heat source and the heat dissipation member to form a laminate; and a bonding step of bonding the laminate under conditions of 150°C or higher, 10 MPa or higher, and an inert gas atmosphere, so that both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interfaces between the nonwoven fabric and the heat dissipation member, are bonded by the copper nanoparticles. According to this manufacturing method, the heat dissipation structure of the present invention can be manufactured efficiently.

[0086] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In each example and each comparative example, various attributes and evaluations were measured or evaluated according to the following methods.

[0087] <Thickness> The thickness of the nonwoven fabric was measured using a film thickness gauge (Mitutoyo, product name "Digimatic Indicator ID-C112XBS"). Measurements were taken at five arbitrary points on the surface of each nonwoven fabric, and the average value (mm) of the measurements was taken as the thickness of the nonwoven fabric. For Examples 1-1 to 1-9, the thickness of the nonwoven fabric was compared with the thickness of the nonwoven fabric-derived layer in the structure after the bonding process with copper foil, and the change in thickness (%) relative to the thickness of the nonwoven fabric was calculated.

[0088] <Dispersed Particle Size of Fibrous Carbon Nanostructures> The average particle size (median diameter) of fibrous carbon nanostructures in the dispersion was measured using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd., LA-960), and this value was defined as the dispersed particle size of the fibrous carbon nanostructures.

[0089] <Cracks in Nonwoven Fabrics> The appearance of the dried nonwoven fabrics obtained in the examples and comparative examples was visually evaluated, and the presence and degree of cracks were evaluated according to the following criteria: A: No cracks in the nonwoven fabric B: Cracks of 1 mm to 5 mm are observed on the surface of the nonwoven fabric C: Cracks exceeding 5 mm are observed on the surface of the nonwoven fabric, or the film cannot be formed

[0090] <Powder Shedding> The powder shedding resistance of nonwoven fabrics was evaluated. Specifically, a wet wipe was placed on the surface of the nonwoven fabric for 10 seconds, and the amount of powder adhering to the wipe surface was visually evaluated. The less powder there is (the less powder falls off), the better the nonwoven fabric is in terms of handling. A: No powder is visible on the surface of the wipe. B: Powder is visible on the surface of the wipe.

[0091] (Bonding Properties) The bonding properties between the nonwoven fabric and the copper foil as the adherend were measured using a peel analysis device (Kyowa Interface Science Co., Ltd., "VPA-H100"). First, the structure of nonwoven fabric and copper foil manufactured through the bonding process was fixed on a flat base. Next, a portion of the copper foil located on the main surface side of the nonwoven fabric was peeled off at one end of the nonwoven fabric. Then, the maximum tensile strength measured when the peeled portion of the copper foil was pulled off at a speed of 200 mm / min in a 90° direction under a 25°C atmosphere was defined as the peel strength (N), and the value obtained by dividing this value by the width was defined as the peel strength (unit: N / mm).

[0092] (Shear Strength) The obtained nonwoven fabric was cut into 5 mm squares, and a bonding process was carried out under the conditions described in Examples 10 to 12, sandwiching it between a 10 mm square copper plate as the lower base material and a 5 mm square copper plate as the upper base material, to create a copper foil-nonwoven fabric-copper foil structure. The shear strength of this structure was measured using a bonding tester (model number: PTR-1102, manufactured by Lesca Co., Ltd.) at a measurement speed of 20 μm / second. The obtained value was evaluated in MPa units by dividing it by the area of ​​the nonwoven fabric.

[0093] (Bundle Diameter) The surface of the nonwoven fabric was observed using a scanning electron microscope (SEM; Hitachi High-Tech "FE-4300") at a magnification of 50,000x to observe bundles formed by the aggregation of multiple carbon nanotubes (CNTs). The bundle diameter was measured for 50 randomly selected bundles, and the average value was taken as the average bundle diameter of the CNTs.

[0094] (Thermal Properties) The thermal properties of the nonwoven fabric were measured using a thermal properties measuring instrument (Siemens EDA Co., Ltd., "T3Ster DynTim Tester"). Specifically, the thermal properties (resistance) of the entire structure of the nonwoven fabric and copper foil obtained in the bonding process were measured. Since the overall thermal properties were evaluated, the evaluation also included the interfacial resistance between the copper foil and the nonwoven fabric. The measurement was performed with a measurement time of 200 seconds, a current of 5A, and a pressure of 1060kPa. A lower measured value indicates better thermal conductivity.

[0095] (1) Example using silver nanoparticles as metal nanoparticles (Example 1-1) <Dispersion step> Single-walled carbon nanostructures (SGCNTs, manufactured by Zeon Nanotechnology Co., Ltd., product name "ZEONANO® SG101", SGCNTs, average diameter: 3.5 nm, average length: 400 μm, BET specific surface area: 1050 m) were dispersed in isopropyl alcohol as a dispersion medium to a concentration of 0.2 mass% ２ A crude dispersion was obtained by adding 1.0% by mass (5 times the mass of CNTs) and Esrec BL-S (manufactured by Sekisui Chemical Co., Ltd.) as a dispersant to a concentration of 1.0% by mass (5 times the mass of CNTs) and stirring with a magnetic stirrer for 1 hour. Next, the crude dispersion was filled into a multi-stage step-down high-pressure homogenizer (manufactured by Miryu Co., Ltd., "BERYU SYSTEM PRO") which has a multi-stage pressure control device (multi-stage step-down converter) connected to a high-pressure dispersion processing unit (jet mill) with a 170 μm diameter tube channel. At a temperature of 25°C, a pressure of 100 MPa was intermittently and instantaneously applied to the crude dispersion and sent into the tube channel, which constituted one cycle, and this was repeated for 3 cycles. Furthermore, the previous tube channel was replaced with a tube channel with a diameter of 90 μm, and the same dispersion treatment was performed for one cycle. This was repeated for 12 cycles to obtain a dispersion. The particle size of the dispersed fibrous carbon nanostructures in this dispersion was measured. The results are shown in Table 1.

[0096] <Nonwoven Fabric Formation Process> 1.3 g of silver nanoparticle dispersion (manufactured by Admatec, texanol dispersion with a silver nanoparticle concentration of 30% by mass, volume-average particle size of silver nanoparticles: 17 nm) was added to 1.5 g of the dispersion obtained above, and after stirring with a homogenizer for 2 minutes, the mixture was filtered under reduced pressure using a Kiriyama funnel (manufactured by Kiriyama Seisakusho) as a filtration device and Kiriyama filter paper (No. 5A, diameter 3 cm) as a porous substrate, and a filtrate was obtained on the filter paper. The obtained filtrate was dried for 60 minutes in an atmosphere at a temperature of 80°C to obtain a nonwoven fabric in which silver nanoparticles are held within a mesh structure made of CNTs. The obtained nonwoven fabric was subjected to crack evaluation according to the above procedure.

[0097] <Bonding Process with Copper Foil> The obtained nonwoven fabric was cut to a size of 15 mm x 15 mm and sandwiched between two copper foils (thickness: 17 μm, no surface treatment) to form a copper foil-nonwoven fabric-copper foil structure. The obtained structure was subjected to a bonding treatment at 180°C and 10 MPa for 1 hour in an air atmosphere, creating a copper foil-nonwoven fabric-copper foil structure in which the two copper foils and the nonwoven fabric, which are the adherends, were bonded at the interface with silver. The thermal properties of this composite were evaluated. Furthermore, when the structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded with silver.

[0098] (Example 1-2) In the <Dispersion Process>, the capillary channel was replaced with a capillary channel with a diameter of 90 μm, and the subsequent dispersion process was stopped after 8 cycles to obtain a dispersion. In the <Nonwoven Fabric Formation Process>, when mixing the dispersion and the silver nanoparticle dispersion, the amount of CNTs and silver nanoparticles were adjusted to the amounts shown in Table 1. Except for this point, various operations and evaluations were carried out in the same manner as in Example 1-1. The results are shown in Table 1. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by silver.

[0099] (Example 1-3) In the <Dispersion Process>, the amount of dispersant was adjusted to a concentration of 0.6% by mass (three times the mass of CNTs). In the <Nonwoven Fabric Forming Process>, when mixing the dispersion and the silver nanoparticle dispersion, the amount of CNTs and silver nanoparticles were adjusted to the amounts shown in Table 1. Except for these points, various operations and evaluations were carried out in the same manner as in Example 1-2. The results are shown in Table 1. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by silver.

[0100] (Examples 1-4) The fibrous carbon nanostructure to be blended in the <Dispersion Process> is Tuball (manufactured by OCSiAl, product name "TUBALL", average diameter: 2.0 nm, average length: 500 μm, BET specific surface area: 980 m²) ２ The ratio was changed to / g). Except for this point, various operations and evaluations were carried out in the same manner as in Examples 1-2. The results are shown in Table 1. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by silver.

[0101] (Examples 1-5) In the <Dispersion Step>, the dispersion medium used was changed to a mixed solvent (EtOH / water = 8 / 2) obtained by mixing ethanol and water in a volume ratio of 8:2. In the <Nonwoven Fabric Formation Step>, when mixing the dispersion and the silver nanoparticle dispersion, the amount of CNTs and silver nanoparticles were adjusted to the amounts shown in Table 1. Except for these points, various operations and evaluations were carried out in the same manner as in Examples 1-2. The results are shown in Table 1. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by silver.

[0102] (Example 1-6) In the nonwoven fabric formation process, the amount of CNTs and silver nanoparticles were adjusted to the amounts shown in Table 1 when mixing the dispersion and the silver nanoparticle dispersion. Except for this point, various operations and evaluations were carried out in the same manner as in Example 1-2. The results are shown in Table 1. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by silver.

[0103] (Examples 1-7 to 1-9) In the nonwoven fabric formation process, when mixing the dispersion and the silver nanoparticle dispersion, the amount of silver nanoparticles was adjusted to the amounts shown in Table 1. For drying, the filtrate obtained on filter paper after vacuum filtration was left to dry for 60 minutes under vacuum suction to obtain a nonwoven fabric in which the silver nanoparticles were held within a mesh structure made of CNTs. Except for the above, various operations and evaluations were carried out in the same manner as in Example 1-1. The results are shown in Table 1. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by silver.

[0104] (Example 1-10) No dispersant was added in the <Dispersion step>. Except for this point, various operations and evaluations were carried out in the same manner as in Example 1-2. The results are shown in Table 1.

[0105] (Examples 1-11 to 1-12) In the <Joining Process with Copper Foil>, a thermocompression bonding device equipped with a pulse heat device (Flip Chip Bonder, a heating and firing machine manufactured by Flip Chip Japan Co., Ltd.) was used. Under an atmospheric environment, the temperature was raised to 180°C from 20°C over 20 seconds using a pulse heat method at 10 MPa, with the heating rate during the bonding process set to 8°C / second (Example 1-11) and 4°C / second (Example 1-12). After raising the temperature, the temperature was held for 10 minutes, and then the bonding process was completed by natural cooling for 30 seconds. Through this bonding process, a copper foil-nonwoven fabric-copper foil structure was fabricated in which two copper foils and a nonwoven fabric were bonded at the interface with silver. Thermal properties and shear strength were evaluated for this composite. The results are shown in Table 2. Furthermore, when the structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded with silver.

[0106] (Example 1-13) In the <Joining process with copper foil>, an oven was used, and under an atmospheric environment, the temperature was raised to 180°C over approximately 300 seconds at 10 MPa, with the heating rate during the joining process set to about 0.5°C / second. The temperature was then held for 1 hour. Through this joining process, a copper foil-nonwoven fabric-copper foil structure was fabricated, in which two copper foils and a nonwoven fabric were joined at the interface by silver. Thermal properties and shear strength were evaluated for this composite. The results are shown in Table 2. Furthermore, when the structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was joined by silver.

[0107] (Reference Example) In the nonwoven fabric formation process, when mixing the dispersion and the silver nanoparticle dispersion, the amount of CNTs and silver nanoparticles were adjusted to the amounts shown in Table 1. Except for this point, various operations and evaluations similar to those in Example 1-2 were attempted. However, unlike the nonwoven fabric formation process in Examples 1-7 to 1-9 described above, the operation of drying the filtrate obtained on the filter paper after vacuum filtration under vacuum suction was not performed, and under the conditions of this reference example with a large amount of silver nanoparticles, the nonwoven fabric tore and film formation was not possible. Therefore, although the CNT bundle diameter was evaluated using fragments of the nonwoven fabric, the thickness and thermal properties of the nonwoven fabric were not evaluated. The results are shown in Table 1.

[0108] In Tables 1 and 2, "CNT" refers to carbon nanotubes, "SGCNT" refers to carbon nanotubes produced by the supergrowth method, "IPA" refers to isopropyl alcohol, and "EtOH" refers to ethanol.

[0109]

[0110]

[0111] From Tables 1-2, the BET specific surface area is 400 m². ２ The nonwoven fabrics of Examples 1-1 to 1-13, which contain fibrous carbon nanostructures at a concentration of 1 / g or more and silver nanoparticles, and in which the ratio of the mass of silver nanoparticles to the mass of fibrous carbon nanostructures (CNTs) is 0.3 to 250, were found to have low resistance and excellent thermal properties.

[0112] (2) Example using copper nanoparticles as metal nanoparticles (Example 2-1) <Dispersion step> Single-walled carbon nanostructures (SWCNTs) (manufactured by Zeon Nanotechnology, product name "ZEONANO® SG101", SGCNT, average diameter: 3.5 nm, average length: 400 μm, BET specific surface area: 1050 m) were dispersed in methyl ethyl ketone as a dispersion medium to a concentration of 0.2 mass% ２A crude dispersion was obtained by adding ( / g) and stirring with a magnetic stirrer for 1 hour. Next, the crude dispersion was filled into a multi-stage step-down high-pressure homogenizer (BERYU SYSTEM PRO, manufactured by Miryu Co., Ltd.) which has a multi-stage pressure control device (multi-stage step-down converter) connected to a high-pressure dispersion processing unit (jet mill) with a 170 μm diameter tube channel. At a temperature of 25°C, a pressure of 100 MPa was intermittently and instantaneously applied to the crude dispersion and fed into the tube channel, which constituted one cycle. This was repeated for three cycles. Furthermore, the previous tube channel was replaced with a 90 μm diameter tube channel, and the same dispersion treatment was performed for one cycle. This was repeated for three cycles to obtain a dispersion. The particle size of the dispersed fibrous carbon nanostructures in this dispersion was measured. The results are shown in Table 3.

[0113] <Process for forming a nonwoven fabric with embedded copper nanoparticles ((i) process)> 2 g of copper nanoparticle dispersion (manufactured by Kyoritsu Chemical Industry, methanol solution with a copper nanoparticle concentration of 10% by mass, volume-average particle size of copper nanoparticles: 80 nm) was added to 5 g of the dispersion obtained in the above mixing process, and the mixture was stirred for 2 minutes using a homogenizer. Then, the mixture was filtered under reduced pressure using a Kiriyama funnel (manufactured by Kiriyama Seisakusho) as a filtration device and Kiriyama filter paper (No. 5A, diameter 3 cm) as a porous substrate, and the filtrate was obtained on the filter paper. The obtained filtrate was dried for 60 minutes in an atmosphere at a temperature of 80°C to obtain a nonwoven fabric with embedded copper nanoparticles. The dust shedding resistance of the obtained nonwoven fabric was evaluated according to the above.

[0114] <Bonding process with copper foil> The obtained nonwoven fabric was cut to a size of 15 mm x 15 mm and sandwiched between two copper foils (thickness: 17 μm, no surface treatment) to form a copper foil-nonwoven fabric-copper foil structure. The obtained structure was subjected to a bonding treatment at 300°C and 20 MPa for 1 hour under a nitrogen atmosphere, and a copper foil-nonwoven fabric-copper foil structure was fabricated in which the two copper foils and the nonwoven fabric, which are the adherends, were bonded by copper at the interface. Bondability and thermal properties were evaluated for this composite. Furthermore, when the structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by copper.

[0115] (Example 2-2) Except for changing the amount of copper nanoparticle dispersion added in the <Encapsulated Nonwoven Fabric Formation Process ((i))> to 1 g, various operations and evaluations were carried out in the same manner as in Example 2-1. The results are shown in Table 3. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by copper.

[0116] (Example 2-3) A nonwoven fabric was formed by laminating copper nanoparticle layers on both surfaces of an encapsulated nonwoven fabric as described below. Specifically, the copper nanoparticle encapsulated nonwoven fabric obtained in the <encapsulated nonwoven fabric formation process ((i))> was subjected to the copper nanoparticle layer formation process ((ii)) as described below. Except for this point, various operations and evaluations were carried out in the same manner as in Example 2-1. The results are shown in Table 3. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by copper. <Copper Nanoparticle Layer Formation Process ((ii) Process)> While the space on the lower side of the copper nanoparticle-encapsulated nonwoven fabric was kept under reduced pressure, 0.2 g of copper nanoparticle dispersion (manufactured by Kyoritsu Chemical Industry, methanol solution with a copper nanoparticle concentration of 2% by mass, volume-average particle size of copper nanoparticles: 80 nm) was dropped onto the surface of the nonwoven fabric so as to uniformly cover it, and then filtered under reduced pressure. The nonwoven fabric obtained in this way, with a copper nanoparticle layer arranged on one side of the encapsulated nonwoven fabric, was dried at 80°C for 1 hour. Then, the same operations as above—dropping of copper nanoparticle dispersion, filtration under reduced pressure, and drying—were sequentially performed on the surface of the dried nonwoven fabric where the copper nanoparticle layer was not present, to obtain a non-encapsulated nonwoven fabric with copper nanoparticle layers on both sides. The dust shedding resistance of the obtained nonwoven fabric was evaluated according to the above. Furthermore, observation by SEM at magnifications of 10,000x and 500x confirmed the presence of copper nanoparticle layers on both surfaces of the nonwoven fabric.

[0117] (Example 2-4) A dispersion was obtained by performing the same <dispersion process> as in Example 2-1. The obtained dispersion was filtered under reduced pressure using a Kiriyama funnel (manufactured by Kiriyama Seisakusho) as a filtration device and Kiriyama filter paper (No. 5A, 3 cm in diameter) as a porous substrate, and a filtrate was obtained on the filter paper. The obtained filtrate was dried for 60 minutes in an atmosphere of 80°C to obtain a copper nanoparticle-free nonwoven fabric. The obtained copper nanoparticle-free nonwoven fabric was subjected to the same <copper nanoparticle layer formation process ((ii) process)> as in Example 2-3 described above to obtain a copper nanoparticle-free nonwoven fabric (referred to as "laminated" nonwoven fabric in Table 3) with copper nanoparticle layers arranged on both sides. The dust shedding resistance of the obtained nonwoven fabric was evaluated according to the above. Except for these points, various operations and evaluations were performed in the same manner as in Example 2-1. The results are shown in Table 3. Furthermore, observation by SEM at magnifications of 10,000x and 500x confirmed the presence of copper nanoparticle layers on both surfaces of the nonwoven fabric. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by copper.

[0118] (Examples 2-5 to 2-7) 5 g of dispersion obtained by the same method as in the <Dispersion Step> of Example 2-1 was mixed with 0.8 g (Example 2-5), 0.5 g (Example 2-6), and 1.2 g (Example 2-7) of copper nanoparticle dispersion (manufactured by Kyoritsu Chemical Industry, methanol solution with a copper nanoparticle concentration of 10% by mass, volume-average particle size of copper nanoparticles: 80 nm), respectively. The mixture was stirred for 2 minutes using a homogenizer, and then filtered under reduced pressure using a Kiriyama funnel (manufactured by Kiriyama Seisakusho) as a filtration device and Kiriyama filter paper (No. 5A, 3 cm in diameter) as a porous substrate to obtain a filtrate on the filter paper. The obtained filtrate was dried by leaving it under reduced pressure for 60 minutes to obtain a nonwoven fabric in which copper nanoparticles were held (encapsulated) within a mesh structure made of CNTs. The dust-shedding resistance of the obtained nonwoven fabric was evaluated according to the above. Various operations and evaluations were carried out using the obtained nonwoven fabric in the same manner as in Example 2-1. The results are shown in Table 3. Furthermore, when the obtained copper foil-nonwoven fabric-copper foil structure was observed by SEM at magnifications of 10,000x and 500x, it was confirmed that the interface between the copper foil and the nonwoven fabric was bonded by copper.

[0119] (Comparative Example 2-1) <Dispersion Process> As a fibrous carbon nanostructure, the specific surface area is 400 m² ２ Multilayer CNTs with a density of less than 1 / g (KUMHO PETROCHEMICAL Co., Ltd., product name "K-NANO", MWCNT, average diameter: 13 nm, average length: 30 μm, BET specific surface area: 266 m²) ２ Except for using (g), the same operations as in Example 2-4 were attempted. However, in step (ii), when attempting to form a copper nanoparticle layer to form a laminated nonwoven fabric, the nonwoven fabric collapsed when attempting to form the copper nanoparticle layer on the surface, making it impossible to continue the operation, and the operation was discontinued.

[0120] (Reference Example) In the <Encapsulated Nonwoven Fabric Formation Process ((i))>, the amount of copper nanoparticle dispersion added was changed to 1.5 g, but various operations were attempted in the same manner as in Example 2-1. However, cracks appeared in the nonwoven fabric during drying in (i), and although the thickness of the nonwoven fabric could be measured, subsequent operations and evaluations could not be carried out. This is thought to be because the filtrate obtained on the filter paper after vacuum filtration was not dried under vacuum suction, and therefore the nonwoven fabric could not be given the mechanical strength to support a high content of metal nanoparticles.

[0121]

[0122] From Table 3, the BET specific surface area is 400 m². ２ The nonwoven fabrics in Examples 2-1 to 2-7, which contain fibrous carbon nanostructures and copper nanoparticles at a concentration of 1 / g or more, and in which the ratio of the mass of copper nanoparticles to the mass of fibrous carbon nanostructures (CNTs) is 0.3 to 250, exhibited excellent thermal conductivity.

[0123] According to the present invention, it is possible to provide a nonwoven fabric containing metal nanoparticles that has excellent thermal conductivity.

Claims

1. A fibrous carbon nanostructure comprising metal nanoparticles, wherein the metal nanoparticles comprise at least one of silver nanoparticles, copper nanoparticles, and tin nanoparticles, the ratio of the mass of the metal nanoparticles to the mass of the fibrous carbon nanostructure being 0.3 or more and 250 or less, and the BET specific surface area of ​​the fibrous carbon nanostructure being 400 m². ２ Nonwoven fabric with a weight of 1g or more.

2. The nonwoven fabric according to claim 1, wherein the metal nanoparticles are held or encapsulated within a network structure made of fibrous carbon nanostructures.

3. The nonwoven fabric according to claim 1, wherein the metal nanoparticles include silver nanoparticles or copper nanoparticles, and the ratio of the mass of the silver nanoparticles to the mass of the fibrous carbon nanostructure is 51 or more and 250 or less.

4. The nonwoven fabric according to claim 3, wherein the ratio of the mass of the silver nanoparticles or copper nanoparticles to the mass of the fibrous carbon nanostructure is 51 or more and 160 or less.

5. The nonwoven fabric according to claim 1, wherein the metal nanoparticles include silver nanoparticles, and the thickness change when sintered at a pressure of 10 MPa, a temperature of 180°C, and for 1 hour is 20% or more.

6. The nonwoven fabric according to claim 1, wherein the metal nanoparticles include silver nanoparticles, and the bundle diameter of the fibrous carbon nanostructures is 0.50 μm or less when the nonwoven fabric is observed at a magnification of 50,000 times.

7. The nonwoven fabric according to claim 1, having a metal nanoparticle layer mainly composed of metal nanoparticles on at least one side.

8. A method for producing a nonwoven fabric containing fibrous carbon nanostructures and metal nanoparticles, wherein the BET specific surface area is 400 m². ２ A method for producing a nonwoven fabric, comprising: a dispersion step of dispersing fibrous carbon nanostructures having a concentration of 1 / g or more in a dispersion medium to prepare a dispersion of fibrous carbon nanostructures; and a nonwoven fabric forming step of forming a nonwoven fabric using the dispersion of fibrous carbon nanostructures, wherein the metal nanoparticles include at least one of silver nanoparticles, copper nanoparticles, and tin nanoparticles.

9. The method for producing a nonwoven fabric according to claim 8, wherein the ratio of the mass of the metal nanoparticles to the mass of the fibrous carbon nanostructure is 0.3 or more and 250 or less.

10. The method for producing a nonwoven fabric according to claim 8, wherein in the nonwoven fabric forming step, metal nanoparticles are mixed with the fibrous carbon nanostructure dispersion to obtain a mixed solution, and the dispersion medium is removed from the mixed solution to form a nonwoven fabric in which the metal nanoparticles are held or encapsulated within a network structure made of the fibrous carbon nanostructure.

11. The method for producing a nonwoven fabric according to claim 8, wherein the metal nanoparticles include silver nanoparticles, the dispersion of fibrous carbon nanostructures in the dispersion liquid of fibrous carbon nanostructures obtained in the dispersion step has a particle diameter of 0.5 μm or more and 5.0 μm or less, and further, in the nonwoven fabric forming step, silver nanoparticles are mixed with the dispersion liquid of fibrous carbon nanostructures to obtain a mixed solution, the dispersion medium is removed from the mixed solution to form a nonwoven fabric in which the silver nanoparticles are held or encapsulated within a network structure made of fibrous carbon nanostructures.

12. A method for producing a nonwoven fabric according to claim 8, wherein the metal nanoparticles include copper nanoparticles, and further, in the nonwoven fabric forming step, both or either of the following operations (i) or (ii) are performed: (i) an operation to mix copper nanoparticles with the fibrous carbon nanostructure dispersion to obtain a mixture, and remove the dispersion medium from the mixture to form a copper nanoparticle-encapsulated nonwoven fabric in which the copper nanoparticles are encapsulated within a network structure made of the fibrous carbon nanostructure; (ii) an operation to remove the dispersion medium from the fibrous carbon nanostructure dispersion to obtain a metal nanoparticle-free nonwoven fabric, and apply a copper nanoparticle dispersion in which copper nanoparticles are dispersed in a copper nanoparticle dispersion medium to at least one side of the metal nanoparticle-free nonwoven fabric or the copper nanoparticle-encapsulated nonwoven fabric obtained in operation (i), and remove the copper nanoparticle dispersion medium to form a copper nanoparticle layer mainly composed of copper nanoparticles on at least one side of the copper nanoparticle-free nonwoven fabric or the copper nanoparticle-encapsulated nonwoven fabric.

13. A heat dissipation structure comprising a heat source, a nonwoven fabric according to any one of claims 1 to 7, and a heat dissipation member, laminated in this order, wherein both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interface between the nonwoven fabric and the heat dissipation member, are joined by the metal nanoparticles.

14. A method for manufacturing a heat dissipation structure comprising a heat source, a nonwoven fabric, and a heat dissipation member laminated in this order, comprising: a lamination step of interposing the nonwoven fabric described in any one of claims 1 to 7 between the heat source and the heat dissipation member to form a laminate; and a bonding step of bonding the laminate at a temperature of 150°C or higher and a pressure of 10 MPa or higher to a state in which both or at least one of the interfaces between the nonwoven fabric and the heat source, and the interfaces between the nonwoven fabric and the heat dissipation member, are bonded by the metal nanoparticles.

15. The method for manufacturing a heat dissipation structure according to claim 14, wherein in the bonding step, the heating rate up to at least 150°C is 4°C / second or more.

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