New composite material, method for manufacturing composite material, and composite

Abstract

The present invention provides a composite material which has a honeycomb structure that contains cellulose nanofibers and a carbon material, wherein the carbon material is composed of at least one material which is selected from among a carbon material (a) that is composed of at least one substance that is selected from among a first shell-like body, which is a hollow particle having one hole, and a second shell-like body, which has a plurality of holes and a shape that is obtained by connecting the hollow particles, and a carbon material (b) that is composed of at least one substance that is selected from among a core-sell particle which is obtained by covering the surface of an inorganic particle with a carbon layer and a core-shell linked body which is obtained by covering the surface of a linked body of inorganic particles with a carbon layer.

Description

[Technical Field]

[0001] The present disclosure relates to novel composite materials, methods for making the composite materials, and composites including the composite materials. [Background technology]

[0002] Carbon materials have attracted considerable attention. For example, graphene, a material containing two-dimensional crystals of carbon atoms, has excellent electrical, thermal, optical, and mechanical properties. Graphene is expected to have a wide range of applications in areas such as graphene-based composites, nanoelectronics, flexible / transparent electronics, nanocomposites, supercapacitors, batteries, hydrogen storage, nanomedicine, and bioengineering materials.

[0003] Graphene needs to be dispersed to exhibit excellent electrical, thermal, optical, and mechanical properties. However, graphene tends to aggregate due to van der Waals forces. As a method for dispersing graphene, for example, Patent Document 1 discloses a method in which graphene is dispersed and stabilized in a solvent with polyvinylpyrrolidone to prepare a dispersion liquid. Patent Document 2 also describes a method for producing a porous porous material having a pore size of 1 nm to 10 μm and a specific surface area of ​​100 m 2 / g~2000m 2 / g, and the porous graphene material is said to be less prone to aggregation.

[0004] On the other hand, cellulose nanofibers have excellent properties such as morphological control (size, structure, shape, etc.), light weight, and physical properties such as strength, making them a material that is expected to be used in a variety of fields in the future. For example, Patent Document 3 discloses a nanocellulose-nanocarbon composite structure that combines nanocellulose, which is made up of cellulose nanofibers, with nanocarbon, which is made up of one or more selected from carbon nanotubes, graphene, and highly crystalline carbon black, at the nano level. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-9104 [Patent Document 2] Special Publication No. 2014-507365 [Patent Document 3] Japanese Patent Application Publication No. 2020-164378 Summary of the Invention [Problem to be solved by the invention]

[0006] In Patent Document 1, graphene is in the form of a dispersion, so the solvent needs to be evaporated or dried to form a composite. However, when the solvent is evaporated, there is a possibility that graphene may re-aggregate. The porous graphene material described in Patent Document 2 contains a mixture of graphene oxide-derived carbon and polymer-derived carbon, resulting in low graphene purity. Furthermore, the graphene oxide-derived carbon contains a large number of defects even after heat treatment, resulting in low quality and preventing the inherent effects of graphene from being fully exhibited. The nanocellulose-nanocarbon composite structure described in Patent Document 3 is prone to re-aggregation of the nanocarbon that makes up the composite structure, and therefore is unable to fully demonstrate the inherent effects of the nanocarbon.

[0007] The present disclosure has been made in view of the above circumstances, and aims to provide a novel composite material that is improved in at least one of anisotropy, electromagnetic wave absorption, weight reduction, and insulation, a method for producing the composite material, and a composite including the composite material. [Means for solving the problem]

[0008] As a result of extensive research into solving the above problems, the present inventors have found that the problems can be solved by the following invention.

[0009] That is, the present disclosure relates to the following: [1] Cellulose nanofibers and A composite material having a honeycomb structure containing a carbon material, The carbon material is at least one selected from (a) a first shell-shaped body, which is a hollow particle having one hole, and (b) a core-shell particle, which is an inorganic particle having a carbon layer coated on its surface, and (c) a core-shell linked body, which is an inorganic particle having a carbon layer coated on its surface. [2] The composite material according to [1] above, wherein the shell portions of the first shell-shaped bodies and the second shell-shaped bodies in the carbon material (a) are made of graphene having an average number of layers of 4 or less, and the carbon layers in the carbon material (b) are made of graphene having an average number of layers of 4 or less. [3] The specific surface area of ​​the carbon material (a) is 657 m 2 / g or more. [4] The composite material according to any one of [1] to [3] above, wherein the carbon material (a) has pores in the first shell-shaped bodies and pores in the second shell-shaped bodies each having a volume of 1.0 cc / g or more. [5] The composite material according to any one of the above [1] to [4], wherein the honeycomb structure has a honeycomb opening diameter of 0.2 μm or more and 200 μm or less. [6] The composite material according to any one of the above [1] to [5], wherein the content of the carbon material contained in the composite material is 5% by mass or more and 95% by mass or less. [7] The composite material according to any one of the above [1] to [6], wherein the honeycomb structure is made of the cellulose nanofibers and the carbon material. [8] The composite material according to any one of the above [1] to [6], wherein the honeycomb structure is made of the cellulose nanofibers, and the carbon material is attached to the surface of the honeycomb structure. [9] A method for producing a composite material according to the above item [7], which comprises mixing at least one carbon material (a) selected from first shell-shaped bodies which are hollow particles each having one pore and second shell-shaped bodies which are formed by interconnecting hollow particles and have a plurality of pores, and at least one carbon material (b) selected from core-shell particles in which a carbon layer is coated on the surface of inorganic particles and core-shell linked bodies in which a carbon layer is coated on the surface of linked bodies of inorganic particles, with an aqueous dispersion containing cellulose nanofibers, and freezing the mixture.

[10] A method for producing a composite material according to the above item [8], in which a honeycomb structure containing cellulose nanofibers is impregnated with a dispersion liquid containing at least one carbon material (a) selected from first shell-shaped bodies, which are hollow particles having one hole, and second shell-shaped bodies, which are in the form of connected hollow particles and have multiple holes, and at least one carbon material (b) selected from core-shell particles in which a carbon layer is coated on the surface of inorganic particles, and core-shell linked bodies in which a carbon layer is coated on the surface of linked bodies of inorganic particles.

[11] The method for producing a composite material according to [9] or

[10] above, wherein the shell portions of the first shell-shaped bodies and the second shell-shaped bodies in the carbon material (a) are made of graphene having an average number of layers of 4 or less, and the carbon layers in the carbon material (b) are made of graphene having an average number of layers of 4 or less.

[12] The composite material according to any one of the above [1] to [8], which is an electromagnetic interference suppression material.

[13] A composite material having a honeycomb structure containing cellulose nanofibers and a carbon material; At least one selected from an organic substance and an inorganic substance, The carbon material is at least one selected from carbon material (a) which is at least one selected from first shell-shaped bodies which are hollow particles having one hole and second shell-shaped bodies which are in the form of connected hollow particles and have multiple holes, and carbon material (b) which is at least one selected from core-shell particles in which a carbon layer is coated on the surface of inorganic particles and core-shell linked bodies in which a carbon layer is coated on the surface of linked inorganic particles, to form a composite.

[14] The composite according to

[13] above, wherein the organic material is a thermosetting resin.

[15] The composite according to

[13] or

[14] above, which is an electromagnetic interference suppression material. [Effects of the Invention]

[0010] According to the present disclosure, it is possible to provide a novel composite material having improved at least one of anisotropy, electromagnetic wave absorption, weight reduction, and insulation, a method for producing the composite material, and a composite including the composite material. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, the present disclosure will be described in detail with reference to an embodiment. In this specification, the lower and upper limits of numerical ranges (e.g., ranges of content, etc.) described in stages can be independently combined. In addition, in the numerical ranges described in this specification, the upper or lower limit of the numerical range may be replaced with a value shown in the examples. In this specification, "graphene" means "a graphene having 10 or fewer layers of sp 2 "A sheet of bonded carbon atoms." In this specification, the "average number of layers" of graphene is a value calculated by the following formula. Specifically, it is calculated by the method described in the examples below. Average number of graphene layers = 2627 (m 2 / g) / specific surface area (m 2 / g) The specific surface area refers to the BET specific surface area, which is a value (m 2 / g). In this specification, hollow particles refer to particles that have a shell and the interior of the particle surrounded by the shell is hollow. In this specification, the term "honeycomb structure" refers to a hollow structure in which hollow bodies of three-dimensional shape, such as polygonal pillars, circular pillars, elliptical pillars, etc., are arranged without gaps, and is not limited to regular hexagonal pillars. In this specification, the "average particle size of a carbon material" refers to the average particle size of primary particles when the carbon material is not aggregated and is in the form of primary particles, and to the average particle size of secondary particles when the carbon material aggregates and forms secondary particles. The average particle size of the carbon material can be measured by calculation from the pore volume and specific surface area, by estimation using a laser diffraction particle size distribution analyzer, or by calculation as the average particle size of particles observed in 20 to 100 fields of view using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Furthermore, the "particle size" refers to the longest distance between any two points on the particle's outline that passes through the center of the particle.

[0012] <Composite materials> The composite material of the present disclosure is a composite material having a honeycomb structure containing cellulose nanofibers and a carbon material, wherein the carbon material is at least one selected from carbon material (a) which is at least one selected from first shell-shaped bodies which are hollow particles having one hole and second shell-shaped bodies which are in the form of connected hollow particles and have multiple holes, and carbon material (b) which is at least one selected from core-shell particles in which a carbon layer is coated on the surface of inorganic particles and core-shell linked bodies in which a carbon layer is coated on the surface of linked bodies of inorganic particles. The composite material of the present disclosure has a honeycomb structure containing cellulose nanofibers and a carbon material having a specific structure, thereby improving at least one of anisotropy, electromagnetic wave absorption, weight reduction, and insulation.

[0013] The honeycomb structure of the composite material of the present disclosure is a hollow structure in which three-dimensional hollow bodies are arranged without gaps. The three-dimensional shape is not particularly limited, but examples thereof include a circular cylinder, an elliptical cylinder, a triangular prism, a square prism, and a polygonal prism such as a hexagonal prism or an octagonal prism. From the viewpoint of ease of production, the three-dimensional shape may be a polygonal prism or a hexagonal prism. Furthermore, by adding graphene to such honeycomb-shaped cellulose nanofibers, it is possible to impart anisotropy to the thermal conductivity and electromagnetic wave absorption capacity.

[0014] From the viewpoint of ease of manufacture, the opening diameter of the three-dimensional hollow body (honeycomb hole) constituting the honeycomb structure (hereinafter also referred to as honeycomb opening diameter) may be 0.2 μm or more and 200 μm or less, 1.0 μm or more and 180 μm or less, or 5.0 μm or more and 150 μm or less. In this specification, the term "honeycomb opening diameter" refers to the length (maximum length) when any two points on the contour line of a honeycomb hole are selected so that the distance between them is the maximum. The honeycomb opening diameter is determined as the average value of the opening diameters of 100 to 200 honeycomb holes observed in 5 to 10 fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Specifically, it can be measured by the method described in the examples.

[0015] The length of the honeycomb structure is not particularly limited, but may be 100 μm or more and 2 m or less, 200 μm or more and 1 m or less, or 500 μm or more and 0.5 m or less. When the length of the honeycomb structure is 100 μm or more, it is possible to design a honeycomb structure, and when it is 2 m or less, it is possible to apply it to a large radio wave absorber.

[0016] The honeycomb structure may be made of cellulose nanofibers and a carbon material, or may be made of cellulose nanofibers with the carbon material attached to the surface of the honeycomb structure.

[0017] (Cellulose nanofiber) Cellulose nanofiber refers to a fibrous material with a fiber diameter of 500 nm or less, produced by defibrating plant fibers to the nano level. The average fiber diameter of the cellulose nanofibers is not particularly limited, but from the viewpoint of uniforming the honeycomb structure, it may be 2 nm or more and 100 nm or less, 2 nm or more and 50 nm or less, or 2 nm or more and 30 nm or less. Furthermore, the average fiber length of the cellulose nanofibers is not particularly limited, but from the viewpoint of forming a honeycomb structure, it may be 50 nm or more and 10 μm or less, 0.1 μm or more and 5 μm or less, or 0.15 μm or more and 2 μm or less. The average fiber diameter and average fiber length of cellulose nanofibers are determined by averaging the fiber diameters and fiber lengths obtained from the observation of each fiber using an atomic force microscope (AFM). Specifically, they can be measured by the method described in the Examples.

[0018] The average aspect ratio of the cellulose nanofibers is usually at least 50. There is no particular upper limit, but it is usually no more than 1000. The average aspect ratio can be calculated using the following formula (1). Aspect ratio = average fiber length / average fiber diameter (1)

[0019] The raw material for the cellulose nanofibers is not particularly limited, but examples thereof include wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc. One type of cellulose raw material may be used, or two or more types may be used in combination.

[0020] The cellulose nanofibers may be modified. Specific examples of such modification include esterification such as acetylation, phosphorylation, urethanization, carbamidation, etherification, carboxymethylation, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl radical) oxidation, and periodate oxidation. From the viewpoint of ease of dispersion, the cellulose nanofibers may be modified by TEMPO oxidation. The cellulose nanofibers may be subjected to only one of these modification treatments, or may be subjected to two or more of these modification treatments.

[0021] The content of the cellulose nanofibers in the composite material of the present disclosure may be 5% by mass or more and 95% by mass or less, 10% by mass or more and 80% by mass or less, or 20% by mass or more and 70% by mass or less, relative to the total amount of the composite material. When the content of the cellulose nanofibers is 5% by mass or more, a honeycomb structure can be formed, and when it is 95% by mass or less, the resulting composite material can be used as an electromagnetic interference suppressor.

[0022] (carbon materials) The carbon material is at least one selected from carbon material (a), which is at least one selected from first shell-shaped bodies, which are hollow particles having one hole, and second shell-shaped bodies, which are hollow particles connected together and have multiple holes, and carbon material (b), which is at least one selected from core-shell particles in which a carbon layer is coated on the surface of inorganic particles, and core-shell linked bodies in which a carbon layer is coated on the surface of linked inorganic particles.

[0023] [Carbon material (a)] The carbon material (a) is at least one selected from first shell-shaped bodies which are hollow particles having one pore, and second shell-shaped bodies which are hollow particles connected together and have a plurality of pores. The first shell is a hollow particle having one hole. The average pore size of the pores of the first shell-shaped body may be 0.5 nm or more and 100 nm or less, 0.7 nm or more and 50 nm or less, or 1.0 nm or more and 20 nm or less.

[0024] The second shell-shaped body has a shape of interconnected hollow particles and has a plurality of pores. The number of holes that the second shell-shaped body has is not particularly limited as long as there are multiple holes. The average pore size of each pore in the second shell-shaped body may be 0.5 nm or more and 100 nm or less, 0.7 nm or more and 50 nm or less, or 1.0 nm or more and 20 nm or less.

[0025] The average pore size of the pores in the first shell-shaped body and the second shell-shaped body is a value calculated from the following formula (2) assuming cylindrical pores. Average pore diameter = 4 × pore volume / specific surface area (m 2 / g) (2) The pore volume is the value per mass of material obtained by measuring a nitrogen adsorption isotherm and determining the amount of adsorption at a relative pressure (P / P0) of 0.96. The specific surface area refers to the BET specific surface area, and is the value obtained by measuring with the BET multipoint method using nitrogen adsorption.

[0026] The average particle size of the first shell-like bodies can be considered to be the same as the average pore size of the pores of the first shell-like bodies, since the shell thickness is very thin.

[0027] From the viewpoint of ease of manufacturing, the average particle size of the second shell-shaped body may be 1.0 nm or more, 2.0 nm or more, or 5.0 nm or more, and from the viewpoint of further exerting the effects of the present disclosure, it may be 1000 nm or less, 500 nm or less, or 200 nm or less. The average particle size of the second shell-shaped bodies can be estimated using a laser diffraction particle size distribution analyzer.

[0028] When the carbon material (a) is not aggregated but is in the form of primary particles, the average particle size (primary particles) of the carbon material (a) may be 1 nm or more, 5 nm or more, or 10 nm or more from the viewpoint of ease of production, and may be 1000 nm or less, 500 nm or less, or 100 nm or less from the viewpoint of further exerting the effects of the present disclosure.

[0029] When the carbon material (a) aggregates to form secondary particles, the average particle size (secondary particles) of the carbon material (a) may be 0.1 μm or more, 1.0 μm or more, or 5.0 μm or more from the viewpoint of ease of production, and may be 200 μm or less, 100 μm or less, 50 μm or less, or 20 μm or less from the viewpoint of further exerting the effects of the present disclosure.

[0030] From the viewpoint of further exerting the effects of the present disclosure, the specific surface area of ​​the carbon material (a) is 657 m 2 / g or more, and 2 / g or more, and 2 / g or more, and 2 / g or more, and 2 / g or more. From the viewpoint of ease of production, 2 / g or less, and 2 / g or less, and 2 / g or less, and 2 / g or less. The specific surface area refers to a BET specific surface area, and is a value measured by a BET multipoint method using nitrogen adsorption.

[0031] From the viewpoint of further exerting the effects of the present disclosure, the volume of the pores of the first shell-shaped body and the second shell-shaped body may be 1.0 cc / g or more, 1.3 cc / g or more, 1.6 cc / g or more, 10.0 cc / g or less, 9.0 cc / g or less, or 8.0 cc / g or less. If the pore volume is 1.0 cc / g or more, a higher specific surface area can be obtained. The pore volume is a value obtained by measuring a nitrogen adsorption isotherm and determining the amount of adsorption at a relative pressure (P / P0) of 0.96.

[0032] The carbon material (a) is primarily composed of carbon. Here, "primarily composed of carbon" means that the carbon content in the carbon material is 50% by mass or more. The carbon content in the carbon material (a) may be 80% by mass or more, 95% by mass or more, or 98% by mass or more.

[0033] [Carbon material (b)] The carbon material (b) is at least one selected from core-shell particles in which the surface of an inorganic particle serving as a core is coated with a carbon layer serving as a shell, and core-shell linked bodies in which the surface of linked inorganic particles serving as cores is coated with a carbon layer serving as a shell. The carbon material (b) also includes inorganic particles whose pores are coated with carbon, and inorganic particles whose pores are filled with carbon.

[0034] From the viewpoint of ease of production and further exerting the effects of the present disclosure, the average particle size of the core-shell particles may be 0.0005 μm or more and 100 μm or less, 0.1 μm or more and 50 μm or less, or 0.5 μm or more and 20 μm or less. The average particle size of the core-shell particles is a value calculated from the following formula (3) assuming cylindrical pores. Average particle size of core-shell particles (m) = 6 / [specific surface area (m 2 / g) × true density of core-shell particles (g / m 3 )] (3) The specific surface area refers to a BET specific surface area, which is a value obtained by measurement by a BET multipoint method (for example, 5 to 6 points) using nitrogen adsorption.

[0035] From the viewpoint of ease of production and further exerting the effects of the present disclosure, the average particle size of the core-shell linkers may be 0.0005 μm or more and 100 μm or less, 0.1 μm or more and 50 μm or less, or 0.5 μm or more and 20 μm or less. The average particle size of the core-shell linked bodies can be estimated using a laser diffraction particle size distribution analyzer.

[0036] The average particle size of the carbon material (b) may be 100 μm or less, from the viewpoint of further exerting the effects of the present disclosure.

[0037] From the viewpoint of further exerting the effects of the present disclosure, the specific surface area of ​​the carbon material (b) is 800 m 2 / g or less, and 2 / g or less, and 2 / g or less. There is no particular lower limit, but 1m 2 / g or more, and 2 / g or more, and 2 / g or more. The specific surface area refers to a BET specific surface area, and is a value measured by a BET multipoint method using nitrogen adsorption.

[0038] [Inorganic particles] The core-shell particles and the core-shell linkers contain inorganic particles. The inorganic particles contained in the core-shell particles and the inorganic particles contained in the core-shell linkers (hereinafter collectively referred to as "inorganic particles") are not particularly limited. Examples include inorganic particles such as alumina, silica, magnesium oxide, tungsten carbide, aluminum nitride, cerium oxide, titanium oxide, and calcium carbonate; magnetic materials such as magnetic metals such as pure iron; magnetic materials such as amorphous magnetic metal alloys, Ni-Fe alloys, mild steel, silicon steel (Fe-Si alloys), Fe-Al alloys, Fe-Si-Al alloys (sendust), and Co-Fe alloys; and magnetic materials such as magnetic oxides such as carbonyl iron, magnetite, and ferrite.

[0039] Specific examples of the ferrite include Mn-Zn ferrite, Ni-Zn ferrite, Cu-Zn ferrite, Cu-Zn-Mg ferrite, Mn-Mg-Al ferrite, Y-type hexagonal ferrite, Z-type hexagonal ferrite, and M-type hexagonal ferrite.

[0040] The magnetic metal and the magnetic metal alloy may be flat.

[0041] The inorganic particles may be appropriately selected depending on the application. From the viewpoint of improving volume resistivity, the inorganic particles may contain at least one selected from alumina, silica, magnesium oxide, tungsten carbide, and aluminum nitride, or may contain at least one selected from alumina, silica, and magnesium oxide, or may contain alumina. The inorganic particles may also contain silica from the viewpoint of thermal expansion coefficient. Furthermore, from the viewpoint of thermal conductivity, the inorganic particles may contain at least one selected from alumina, magnesium oxide, and aluminum nitride, and may contain alumina. Furthermore, the inorganic particles may be magnetic, from the viewpoint of improving the thermal conductivity and improving the electromagnetic wave absorption ability over a wide frequency range, and the magnetic material may contain at least one selected from magnetic metals, magnetic metal alloys, and magnetic oxides, or may contain amorphous magnetic metal alloys, or may contain at least one selected from Fe-Si-Al alloys (sendust), ferrite, and magnetite, or may contain at least one selected from ferrite and magnetite.

[0042] The inorganic particles may be composed of only one type, or may contain two or more types. The inorganic particles may be nanoparticles from the viewpoint of further exerting the effects of the present disclosure.

[0043] [Graphene] The carbon material (a) may be such that the shell portions of the first shell-shaped bodies and the second shell-shaped bodies are made of graphene having an average layer number of 4 or less. The carbon material (b) may be such that the carbon layers are made of graphene having an average layer number of 4 or less. By adopting such a structure, the carbon materials (a) and (b) can more effectively exhibit the excellent thermal conductivity and electromagnetic wave absorption performance that graphene itself possesses.

[0044] The graphene is a sheet-like substance having a hexagonal lattice structure in which carbon atoms are bonded. The graphene may be in a single-layer state having a thickness equivalent to one carbon atom, or in a multi-layer state of two or more layers, up to four layers. The graphene may contain oxygen atoms, hydrogen atoms, etc. in addition to carbon atoms.

[0045] In the carbon material (a), the graphene content (% by mass) in the first shell-shaped bodies and the second shell-shaped bodies is not particularly limited, but from the viewpoint of further exerting the effects of the present disclosure, it may be 90% by mass or more, 95% by mass or more, or 98% by mass or more.

[0046] In the carbon material (b), the graphene content (% by mass) in the core-shell particles and the core-shell linked bodies is not particularly limited, but from the viewpoint of further exerting the effects of the present disclosure, it may be 0.1% by mass or more and 70% by mass or less, 0.5% by mass or more and 45% by mass or less, or 1% by mass or more and 20% by mass or less.

[0047] [Method of manufacturing carbon materials] [Method for producing carbon material (a)] The carbon material (a) can be produced by a method including a first step of using particles of alumina, magnesium oxide, or the like as a template, coating the template with a carbon layer to prepare carbon-coated particles, and a second step of dissolving and removing the template. By using such a method, a carbon material with a high specific surface area can be easily obtained.

[0048] [1st process] (template) The template used in synthesizing the carbon material (a) must be capable of introducing organic substances into the surface and pores, must maintain the original structure stable during CVD treatment, and must be easily separated from the resulting carbon material. For this reason, the template must be heat-resistant and removable using an acid or alkali. The resulting carbon material (a) has pores that reflect the shape of the template itself. In other words, the carbon material (a) is synthesized in a state where the shape of the template is transferred. Therefore, the template may be a material with a uniform structure and composition, with a uniform particle size. By using such a material, a carbon material with pores of controlled size can be prepared. Furthermore, in order to achieve a high specific surface area, the template may be a material that can control the average number of layers of the resulting graphene to four or less.

[0049] Examples of such templates include particles of alumina, silica, magnesium oxide, tungsten carbide, aluminum nitride, cerium oxide, titanium oxide, calcium carbonate, etc. These particles may be nanoparticles. From the viewpoint of the material properties that the template should have and the properties of the resulting carbon material (a), the template may be at least one particle selected from alumina and magnesium oxide, or may be alumina particles or alumina nanoparticles. The type of alumina is not particularly limited, but may be θ-alumina or γ-alumina.

[0050] The average particle size of the particles used for the template is not particularly limited, but may be 4 nm to 100 nm, or 5 nm to 20 nm. An average particle size of 4 nm or more provides easy handling and good carbon coverage. Furthermore, the gas permeability of the carbon source is improved when coating the carbon source, facilitating uniform carbon coverage. On the other hand, an average particle size of 100 nm or less can provide a carbon material (a) with a high specific surface area (BET specific surface area). Furthermore, a decrease in the yield of the carbon material (a) due to a relative increase in the amount of template dissolved in a subsequent process can be reduced.

[0051] The particles may be mixed with granular spacers. The use of spacers ensures adequate voids between the particles, reducing pressure loss due to over-packing. The spacers may be particles with an average particle size of, for example, 100 μm to 5,000 μm. The material of the spacers is not particularly limited as long as they can be sieved after carbon coating, and may be one that does not decompose at 900°C to 1,000°C. Alternatively, they may be one that can be dissolved and removed simultaneously with the mold. Examples of suitable spacers include quartz sand, silica, alumina, silica-alumina, and titania. For example, when using quartz sand, it may be washed with acid and calcined at 600°C to 1,000°C for 1 hour to 5 hours to adjust the particle size to the above range.

[0052] The compounding ratio of the particles to the spacers is not particularly limited, but may be, for example, a mass ratio of (particles:spacers) of 0.1:10 to 10:10, or 1:10 to 10:10. When the mass ratio is within the above range, the carbon material (a) can be obtained in high yield.

[0053] (carbon layer coating) There are no particular limitations on the method for coating the surface of the template particles with a carbon layer, and either a wet method or a dry method can be used. Furthermore, by using chemical vapor deposition (CVD), a carbon layer made of graphene with an average number of layers of 4 or less can be formed.

[0054] The CVD method, used to introduce organic compounds and deposit a carbon layer on a template, is an industrial technique for producing a thin film (e.g., a thin film made of carbon) of a specific element or elemental composition on a substrate such as a template. Typically, the technique involves applying energy to a gas containing the source material using heat or light, or converting it into plasma using high frequency waves, which converts the source material into radicals through a chemical reaction or thermal decomposition, making it highly reactive, and allowing the source material to be adsorbed and deposited on the substrate.

[0055] The organic compound used in the CVD method may be a gas at room temperature (25°C) or may be vaporizable. Vaporization methods include heating above the boiling point or reducing the pressure of the atmosphere. The organic compound used can be appropriately selected from carbon source substances. In particular, it may be a compound that decomposes thermally upon heating, or a compound that can deposit a carbon layer on the surface of particles used as a template.

[0056] The organic compound used may also be an organic compound containing hydrogen, an organic compound containing unsaturated or saturated hydrocarbons, or a mixture thereof. The organic compound used may be an unsaturated linear or branched hydrocarbon having a double bond and / or a triple bond, a saturated linear or branched hydrocarbon, or a saturated cyclic hydrocarbon, or an aromatic hydrocarbon such as benzene or toluene. The organic compound may be an alcohol such as methanol or ethanol, or a nitrogen-containing compound such as acetonitrile or acrylonitrile. Examples of the organic compound include acetylene, methylacetylene, ethylene, propylene, isoprene, cyclopropane, methane, ethane, propane, benzene, toluene, vinyl compounds, ethylene oxide, methanol, ethanol, acetonitrile, and acrylonitrile. One organic compound may be used alone, or two or more organic compounds may be used in combination. Among these, organic compounds that can penetrate into the voids between particles, such as acetylene, ethylene, propylene, methane, and ethane, may be used. From the viewpoint of depositing highly crystalline carbon, methane, propylene, and benzene may be used. Methane may also be used from the viewpoint of obtaining highly crystalline carbon due to its high thermal decomposition temperature. The organic compounds used in the higher temperature CVD and the lower temperature CVD may be the same or different, for example, acetylene, ethylene, etc. may be used in the lower temperature CVD, and propylene, isoprene, benzene, etc. may be used in the higher temperature CVD.

[0057] When introducing the organic compound onto the particles, the particles may be decompressed in advance, or the system itself may be decompressed. Any method that deposits carbon by CVD may be used. For example, carbon produced by chemical reaction or thermal decomposition of an organic compound may be deposited (or adsorbed) on alumina particles to coat the alumina particles with a carbon layer.

[0058] The pressure during the CVD treatment is not particularly limited and may be, for example, 1 kPa to 200 kPa or 50 kPa to 150 kPa. The heating temperature during the CVD treatment may be any temperature that can form several or fewer carbon layers on the particles, and an appropriate temperature can be selected depending on the organic compound used. The heating temperature may be 400°C to 1500°C, 450°C to 1100°C, or 550°C to 950°C. For example, when propylene is used as the organic compound, the heating temperature may be 700°C to 900°C, and when methane is used, the heating temperature may be 900°C to 1100°C. However, the temperature may be approximately 50°C to 200°C lower than the decomposition temperature of the organic compound. Heating to a temperature above the decomposition temperature of the organic compound causes significant vapor phase carbon deposition, but by doing so, for example, unevenness in the amount of carbon deposition between the particle surface and interior can be reduced, allowing for uniform deposition. The heating temperature can be appropriately selected depending on the CVD processing time and / or the pressure in the reaction system. Alternatively, the product may be analyzed, and the temperature required to achieve the desired number of layers may be set based on the results.

[0059] The temperature rise rate during CVD treatment is not particularly limited, but may be 1°C / min or more and 50°C / min or less, or 5°C / min or more and 20°C / min or less. The treatment time in CVD treatment (CVD treatment time at a predetermined heating temperature) can be appropriately selected depending on the organic compound or temperature used. For example, the treatment time in CVD treatment may be 5 minutes to 8 hours, 0.5 hours to 6 hours, or 1 hour to 5 hours. In addition, the product may be analyzed, and the time required for sufficient carbon deposition may be set based on the results.

[0060] The CVD treatment may be carried out under reduced pressure, vacuum, or pressure, or may be carried out in an inert gas atmosphere, such as nitrogen, helium, neon, or argon, and nitrogen may also be used. In the CVD method, carbon can be easily deposited or adsorbed onto particles in the gas phase by heating a gaseous organic compound together with a carrier gas while flowing the compound in contact with the particles. The type, flow rate, flow rate, and heating temperature of the carrier gas are appropriately adjusted depending on the type of organic compound used. Examples of the carrier gas include the inert gases listed above, and may be nitrogen or a mixture with oxygen gas or hydrogen gas.

[0061] The flow rate of the carrier gas may be 0.05 m / min or more and 1.0 m / min or less, or 0.32 m / min or more and 0.64 m / min or less. By setting the flow rate of the carrier gas within the above range, a carbon layer made of graphene with an average layer number of 4 or less can be obtained. Furthermore, the amount of the organic compound introduced may be 1 vol% or more and 30 vol% or less, or 5 vol% or more and 20 vol% or less, based on the total amount of the carrier gas and the organic compound.

[0062] The method for coating the particles with a carbon layer may involve introducing an organic compound by a wet method such as impregnation and carbonizing the particles. Alternatively, the particles may be impregnated with the organic compound and carbonized before introducing the organic compound and performing CVD. For example, a thermally polymerizable monomer such as furfuryl alcohol, which has a high carbonization yield, may be used as the organic compound to be impregnated. The impregnation method for the organic compound can be any known method, such as contacting the particles with the organic compound directly or mixed with a solvent if the organic compound is liquid, or dissolving the organic compound in a solvent if the organic compound is solid.

[0063] After the first step, the carbon-coated particles may be heat-treated to carbonize the carbon layer and deposit highly crystalline carbon on the particle surface, thereby providing the resulting carbon material (a) with higher crystallinity and a larger specific surface area.

[0064] Since carbonization of the carbon layer can also proceed by CVD treatment, the heat treatment may be carried out during CVD treatment or by other methods.

[0065] The method of heat treatment is not particularly limited, and the heat treatment may be carried out using a high-frequency induction heating furnace or the like.

[0066] [Second process] The second step, which is a step of dissolving and removing the template, is a step of dissolving and removing the template from the carbon-coated particles to obtain shell-like bodies. To dissolve and remove the template, an alkaline solution such as NaOH, KOH, LiOH, RbOH, or CsOH may be used. The alkaline solution may have a concentration of, for example, 1 to 5 M. The alkaline solution may be present at a concentration of 30 times or more, or even 50 times or more, relative to the particle mass. A concentration of 30 times or more relative to the particle mass can reduce the amount of template particles remaining. For dissolution and removal, for example, carbon-coated particles may be placed in the alkaline solution and heat-treated at a temperature between 200°C and 300°C. To ensure uniform contact of the sample with the alkaline solution, the carbon-coated particle sample may be pulverized beforehand. The heating rate during heat treatment is not particularly limited, for example, 200 to 300°C / hour. The heat treatment time (retention time at the specified heat treatment temperature) is also not particularly limited, for example, 1 hour to 5 hours. This dissolution and removal process may be performed multiple times. The product may be analyzed, and the conditions required for sufficient template removal may be determined based on the results.

[0067] After dissolving and removing the template, the shells may be recovered by, for example, filtration or may be dried by vacuum heat drying. The conditions for vacuum heat drying are not particularly limited, and for example, the vacuum heat drying temperature can be 100°C or higher and 200°C or lower. The vacuum heat drying time can be, for example, 1 hour or higher and 10 hours or shorter. By the method having the above-mentioned first and second steps, it is possible to obtain a first shell-shaped body, which is a hollow particle having one hole, and a second shell-shaped body, which is a structure in which hollow particles are connected and has multiple holes, i.e., carbon material (a).

[0068] [3rd step] The method for producing the carbon material (a) may include a third step of heat treatment after the second step. By performing the third step after the second step, the crystallinity of the coated carbon is enhanced and stabilized. As a result, the carbon material (a) (graphene) has higher levels of electrical conductivity, corrosion resistance, and a large specific surface area. The heat treatment temperature is not particularly limited, but may be 1100°C or higher and 1850°C or lower, or 1550°C or higher and 1830°C or lower. When the heat treatment temperature is 1100°C or higher, the effects of the present disclosure can be more significantly obtained. Furthermore, when the heat treatment temperature is 1850°C or lower, the reaction between the remaining template and carbon can be prevented. The heat treatment time (the holding time at a predetermined heat treatment temperature) may be from 0.1 to 10 hours, from 0.2 to 5 hours, or from 0.5 to 2 hours. The heat treatment step may be carried out under reduced pressure.

[0069] [Method for producing carbon material (b)] The carbon material (b) can be produced, for example, by a method of coating inorganic particles with a carbon layer.

[0070] (Inorganic particles) Examples of inorganic particles include those described in the above section "Inorganic Particles." When the inorganic particles are coated with a carbon layer by CVD or the like, the inorganic particles may be those that maintain their original structure stably during CVD or the like. Therefore, the inorganic particles may have good heat resistance. The inorganic particles may be made of a material with a uniform particle size, structure, and composition, or may be made of a material that allows the average number of layers of the resulting graphene to be controlled to 4 or less in order to achieve a high specific surface area. From this viewpoint, the inorganic particles may be at least one selected from alumina, silica, magnesium oxide, tungsten carbide, aluminum nitride, and magnetic materials such as magnetic metals, magnetic metal alloys, and magnetic oxides. From the viewpoint of improving electrical insulation performance, the inorganic particles may be alumina or silica, and from the viewpoint of improving thermal conductivity and heat dissipation, the inorganic particles may be a magnetic material, such as at least one selected from Fe-Si-Al alloys (sendust), ferrite, and magnetite.

[0071] The average particle size of the inorganic particles is not particularly limited, but may be 0.0005 μm or more and 100 μm or less, 0.1 μm or more and 50 μm or less, or 0.5 μm or more and 20 μm or less. When the average particle size is 0.0005 μm or more, handling is easy and carbon coating properties are good. Furthermore, when coating a carbon source, the gas permeability of the carbon source is good, facilitating uniform carbon coating. On the other hand, when the average particle size is 100 μm or less, a carbon material (b) with a high specific surface area (BET specific surface area) can be obtained.

[0072] The inorganic particles may be mixed with granular spacers. The use of spacers ensures adequate voids between the particles, reducing pressure loss due to over-packing of the particles. The spacers may be particles with an average particle size of, for example, 100 μm to 5000 μm. The spacer material is not particularly limited as long as it can be sieved after carbon coating, and may be one that does not decompose at temperatures between 900°C and 1000°C.

[0073] The compounding ratio of the particles to the spacers is not particularly limited, but may be, for example, a mass ratio of (particles:spacers) of 0.1:10 to 10:10, or 1:10 to 10:10. When the mass ratio is within the above range, the carbon material (b) can be obtained in high yield.

[0074] (carbon layer coating) The method for coating the surface of inorganic particles with a carbon layer is not particularly limited, and either a wet method or a dry method can be used. Alternatively, a carbon layer made of graphene with an average layer number of 4 or less can be obtained by using a chemical vapor deposition (CVD) method or a method in which naphthalene molecules are introduced onto the surface of inorganic particles such as silica by chemical modification and then calcined.

[0075] The CVD method used to introduce an organic compound and deposit a carbon layer on inorganic particles is as explained in the section [Method for producing carbon material (a)].

[0076] The inorganic particles coated with the carbon layer may be heat-treated to carbonize the carbon layer and deposit highly crystalline carbon on the surface of the inorganic particles, thereby providing the resulting carbon material (b) with higher crystallinity and a larger specific surface area. Since carbonization of the carbon layer can also proceed by CVD treatment, the heat treatment may be carried out during CVD treatment or by other methods. The method of heat treatment is not particularly limited, and the heat treatment may be carried out using a high-frequency induction heating furnace or the like. By the above method, it is possible to obtain core-shell particles in which the surfaces of inorganic particles are coated with a carbon layer, and core-shell linked bodies in which the surfaces of linked inorganic particles are coated with a carbon layer, i.e., carbon material (b).

[0077] The composite material of the present disclosure may be one in which the carbon material is attached to the surface of the cellulose nanofiber from the viewpoint of exhibiting anisotropic electromagnetic wave absorption performance, or one in which the carbon material is dispersed in the cellulose nanofiber from the viewpoint of improving electrical insulation. Furthermore, by changing the compounding ratio of the cellulose nanofibers and the carbon material, the electrical properties of the composite material can be controlled over a wide range, from good conductivity to insulation.

[0078] The content of the carbon material in the composite material of the present disclosure may be 5% by mass or more and 95% by mass or less, 10% by mass or more and 80% by mass or less, or 20% by mass or more and 65% by mass or less, relative to the total amount of the composite material. When the carbon material content is 5% by mass or more, the resulting composite material can be used as an electromagnetic interference suppressor, and when the carbon material content is 95% by mass or less, the resulting composite material can be formed into a honeycomb structure.

[0079] Furthermore, when the composite material alone is used as an electromagnetic interference suppressor, the content of the carbon material contained in the composite material may be 5% by mass or more and 50% by mass or less, relative to the total amount of the composite material. Within this range, insulating properties are exhibited. When the composite material is made into a composite and used as an electromagnetic interference suppressor, the content of the carbon material contained in the composite material may be 5% by mass or more and 95% by mass or less, relative to the total amount of the composite material. When the composite material is contained in a composite, insulating properties are exhibited even within this range. Furthermore, when the composite material alone is used as a conductive material, the content of the carbon material contained in the composite material may be more than 50% by mass or more and 95% by mass or less, relative to the total amount of the composite material. Within this range, conductivity is exhibited.

[0080] <Method of manufacturing composite materials> The method for producing the composite material of the present disclosure is not particularly limited. [Manufacturing method-1] When the composite material of the present disclosure is formed by adhering the carbon material to the surface of the cellulose nanofibers, a method for producing the composite material includes a method of impregnating a honeycomb structure containing cellulose nanofibers with a dispersion containing at least one carbon material (a) selected from first shell-shaped bodies, which are hollow particles with one hole, and second shell-shaped bodies, which are in the form of connected hollow particles and have multiple holes, and at least one carbon material (b) selected from core-shell particles in which a carbon coating layer is coated on the surface of inorganic particles, and core-shell linked bodies in which a carbon coating layer is coated on the surface of linked bodies of inorganic particles.

[0081] The method for obtaining the honeycomb structure containing the cellulose nanofibers is not particularly limited, but examples include the ice crystal templating method. The ice crystal templating method is a unidirectional freezing method that controls the growth of ice that serves as a template. When the dispersion is frozen, phase separation occurs, and the dispersion is separated into two phases: a phase of solidified almost pure water and a phase of concentrated colloidal particles. This concentration causes the colloidal particles that have gathered in the gaps between the ice to bond together, even at an extremely low temperature of -196°C. In this process, the ice acts as a template, and the frozen shape is maintained after drying. The ice crystal templating method may be carried out, for example, by the steps of preparing an aqueous dispersion, freezing it, and freeze-drying it.

[0082] (Preparation of aqueous dispersion) First, the raw material cellulose nanofibers are added to water and mixed to obtain an aqueous dispersion in which the cellulose nanofibers are dispersed in water. The cellulose nanofibers that can be used are those described in the <Composite Materials> section. The raw material may further contain a resin other than the cellulose nanofiber. Examples of the resin other than the cellulose nanofiber include polyurethane. When polyurethane is used as the resin other than the cellulose nanofiber, the flexibility of the resulting honeycomb structure is improved.

[0083] When the raw material contains a resin other than the cellulose nanofibers, the blending ratio of the cellulose nanofibers (X) to the resin (Y) other than the cellulose nanofibers [(Y):(X)] may be 1:9 to 9:1, or 1:4 to 4:1, on a mass basis.

[0084] The aqueous dispersion can be prepared by thoroughly stirring manually or with a stirrer. The solids concentration of the aqueous dispersion may be 0.5% by mass or more and 10% by mass or less, 0.8% by mass or more and 8% by mass or less, or 1% by mass or more and 6% by mass or less, based on the total amount (100% by mass) of the aqueous dispersion. In the present disclosure, the term "solid content concentration" refers to the content (concentration) of components other than the solvent.

[0085] The aqueous dispersion may be allowed to stand at a temperature of 0° C. or higher and 50° C. or lower for 1 minute or longer and 10 hours or shorter.

[0086] (frozen) Next, the aqueous dispersion is transferred into a tubular cell and frozen. The aqueous dispersion may be frozen by gradually inserting the entire cell into a refrigerant such as liquid nitrogen at a predetermined insertion speed using a constant speed motor, etc. By inserting the aqueous dispersion into the refrigerant, ice in the portion inserted into the refrigerant grows into a columnar shape along the insertion direction.

[0087] Furthermore, by changing the freezing conditions, the diameter of the ice pillars that serve as templates can be changed, and the honeycomb pore diameter of the resulting honeycomb structure can be adjusted appropriately. The freezing temperature may be -196°C or higher and -10°C or lower, -196°C or higher and -50°C or lower, or -196°C or higher and -100°C or lower. The speed of inserting the cells into the refrigerant may be 2.5cm / h or higher and 50cm / h or lower, 5cm / h or higher and 40cm / h or lower, or 7.5cm / h or higher and 30cm / h or lower.

[0088] (Lyophilization) Next, the frozen aqueous dispersion is freeze-dried. The freeze-drying is carried out under reduced pressure (vacuum) to sublimate the water (ice), thereby obtaining a honeycomb structure containing cellulose nanofibers. The freeze-drying may be performed using a vacuum freeze-dryer. The freeze-drying may be performed, for example, at a temperature of −20° C. to 30° C. for 24 hours or more. There is no particular upper limit to the freeze-drying time, but it may be within 72 hours.

[0089] (Impregnation) Next, the obtained honeycomb structure containing the cellulose nanofibers is impregnated with a dispersion containing the carbon material, thereby obtaining a composite material in which the carbon material adheres to the inner and outer walls of the honeycomb pores of the honeycomb structure containing the cellulose nanofibers.

[0090] The carbon material may be one that has been described in the section on <Composite Material>. Examples of the solvent for dispersing the carbon material include water and ethanol. The solid content concentration of the dispersion may be 0.5% by mass or more and 10% by mass or less, 0.8% by mass or more and 8% by mass or less, or 1% by mass or more and 6% by mass or less, based on the total amount (100% by mass) of the dispersion.

[0091] The honeycomb structure may be impregnated with the dispersion containing the carbon material, for example, at a temperature of 0° C. to 50° C. for 1 minute or more. There is no particular upper limit to the impregnation time, but it may be within 72 hours.

[0092] [Manufacturing method-2] When the composite material of the present disclosure is formed by dispersing the carbon material in the cellulose nanofibers, examples of a method for producing the composite material include a method of mixing at least one carbon material selected from the group consisting of (a) first shell-shaped bodies, which are hollow particles with one hole, and (b) second shell-shaped bodies, which are hollow particles connected together and have multiple holes, and (b) core-shell particles, which are inorganic particles with a carbon coating layer on the surface thereof, and core-shell linked bodies, which are inorganic particles with a carbon coating layer on the surface thereof, with an aqueous dispersion containing cellulose nanofibers, and freezing the mixture.

[0093] The carbon material and the cellulose nanofibers can be those described in the <Composite material> section. The method for freezing the aqueous dispersion includes the above-mentioned ice crystal template method.

[0094] (Preparation of aqueous dispersion) First, the raw material cellulose nanofibers are added to water and mixed to obtain an aqueous dispersion in which the cellulose nanofibers are dispersed in water. The raw material may further include a resin other than the cellulose nanofibers. Examples of the resin other than the cellulose nanofibers include those listed in [Production Method-1]. Furthermore, when the raw material contains a resin other than the cellulose nanofiber, the blending amount thereof is as explained in [Production Method-1].

[0095] Next, a carbon material is added to the aqueous dispersion and mixed to obtain an aqueous dispersion in which the cellulose nanofibers, a resin other than the cellulose nanofibers that is blended as needed, and the carbon material are dispersed.

[0096] The aqueous dispersion can be prepared by thoroughly stirring manually or with a stirrer. The solids concentration of the aqueous dispersion may be 0.5% by mass or more and 10% by mass or less, 0.8% by mass or more and 8% by mass or less, or 1% by mass or more and 6% by mass or less, based on the total amount (100% by mass) of the aqueous dispersion.

[0097] The aqueous dispersion may be allowed to stand for 1 minute or more at a temperature of 0° C. to 50° C. There is no particular upper limit to the time for which the aqueous dispersion is allowed to stand, but it may be within 72 hours.

[0098] (frozen) Next, the aqueous dispersion is transferred into a tubular cell and frozen. The aqueous dispersion may be frozen by gradually inserting the entire cell into a refrigerant such as liquid nitrogen at a predetermined insertion speed using a constant speed motor, etc. By inserting the aqueous dispersion into the refrigerant, ice in the portion inserted into the refrigerant grows into a columnar shape along the insertion direction.

[0099] Furthermore, by changing the freezing conditions, the diameter of the ice pillars that serve as templates can be changed, and the honeycomb pore diameter of the resulting honeycomb structure can be adjusted appropriately. The freezing temperature may be -196°C or higher and -10°C or lower, -196°C or higher and -50°C or lower, or -196°C or higher and -100°C or lower. The speed of inserting the cells into the refrigerant may be 2.5cm / h or higher and 50cm / h or lower, 5cm / h or higher and 40cm / h or lower, or 7.5cm / h or higher and 30cm / h or lower.

[0100] (Lyophilization) Next, the frozen aqueous dispersion is freeze-dried. The freeze-drying is carried out under reduced pressure (vacuum) to sublimate the water (ice), thereby obtaining a honeycomb structure in which the carbon material is dispersed in the cellulose nanofibers. The freeze-drying may be performed using a vacuum freeze-dryer. The freeze-drying may be performed, for example, at a temperature of -10°C to 50°C for 1 minute or longer. There is no particular upper limit to the freeze-drying time, but it may be within 72 hours.

[0101] (annealing treatment) The honeycomb structure may be subjected to an annealing treatment. By subjecting the honeycomb structure to an annealing treatment, it is possible to improve the mechanical strength and water resistance. The annealing treatment may be performed, for example, at a temperature of 60°C to 250°C for 1 hour to 24 hours, or at a temperature of 100°C to 250°C for 1 hour to 10 hours.

[0102] The composite material obtained in this manner has a honeycomb structure containing cellulose nanofibers and a carbon material having a specific structure, and therefore has improved anisotropy, electromagnetic wave absorption, weight reduction, and insulation properties. Furthermore, the composite material has improved electromagnetic wave interference reduction performance and can be used as an electromagnetic interference suppressor.

[0103] <Composite> The composite of the present disclosure includes the aforementioned composite material and at least one selected from organic and inorganic materials. By including the aforementioned composite material, the composite of the present disclosure improves at least one of anisotropy, electromagnetic wave absorption, weight reduction, and insulation. Furthermore, the composite has enhanced electromagnetic wave interference reduction performance and can be used as an electromagnetic interference suppressor.

[0104] The composite material used is the one explained in the <Composite Material> section. The composite material may be used as it is, or may be pulverized to an appropriate size using a cutting mill, ball mill, cyclone mill, hammer mill, vibration mill, cutter mill, grinder mill, speed mill, or the like. In order to further exert the effects of the present disclosure, the content of the composite material may be 0.05 mass% or more and 50 mass% or less, 0.08 mass% or more and 30 mass% or less, or 0.10 mass% or more and 20 mass% or less, relative to the total amount of the composite.

[0105] (organic matter) The organic material used in the present disclosure is not particularly limited, and examples thereof include thermosetting resins, thermoplastic resins, etc. Examples of thermosetting resins include epoxy resins, phenolic resins, imide resins, etc. Examples of thermoplastic resins include polyamide resins, polycarbonates, etc.

[0106] The organic material may be a thermosetting resin from the viewpoint of reliability of the molded body using the composite, or may be an epoxy resin or an imide resin from the viewpoint of the molded body using the composite further exhibiting the effects of the present disclosure. The organic substances may be used alone or in combination of two or more.

[0107] In the present disclosure, the epoxy resin used as the organic substance is not particularly limited in terms of molecular structure, molecular weight, etc., as long as it has two or more epoxy groups in one molecule and is one that is commonly used in electronic components. Examples of the epoxy resin include aliphatic epoxy resins such as phenol novolac epoxy resins, cresol novolac epoxy resins, and dicyclopentadiene derivatives; and aromatic epoxy resins such as biphenyl, biphenyl aralkyl, naphthyl, and bisphenol epoxy resins. These epoxy resins may be used alone or in combination. There are no particular limitations on their state, and they may be liquid or solid at room temperature (25°C). For example, the epoxy resin may be a solid cresol novolac epoxy resin. The solid cresol novolac epoxy resin is commercially available, and examples include N670 (manufactured by DIC Corporation). Furthermore, the epoxy resin may be a liquid epoxy resin. Specific examples include bisphenol A epoxy resins and bisphenol F epoxy resins, and the epoxy resin may be a liquid bisphenol A epoxy resin. Liquid bisphenol A type epoxy resins are available as commercial products, and examples thereof include Epomic (registered trademark) R140 (manufactured by Mitsui Chemicals, Inc.). In the present disclosure, a liquid epoxy resin refers to an epoxy resin that is liquid at 25°C.

[0108] The epoxy equivalent of the epoxy resin may be 140 or more from the viewpoint of thermomechanical properties of a molded article using the composite. Furthermore, from the viewpoint of further exerting the effects of the present disclosure, it may be 200 or more. From the viewpoint of thermomechanical properties, the upper limit of the epoxy equivalent may be 400 or less, or 380 or less.

[0109] The epoxy resin is (R 1 O)m and a polyoxyalkylene structure represented by (R 2 The epoxy resin may be an epoxy resin having a polyoxyalkylene structure represented by the formula (O)n. where R 1 and R 2each independently represents an alkylene group having one or more carbon atoms. m+n may be 1 or more and 50 or less, or 1 or more and 20 or less. m may be 0 or more and 49 or less, or 0 or more and 19 or less. n may be 1 or more and 50 or less, or 1 or more and 20 or less.

[0110] R 1 and R 2 Examples of the alkylene group represented by the formula (I) include alkylene groups having 1 to 6 carbon atoms, and specific examples include a methylene group, an ethylene group, a trimethylene group, a propylene group, a tetramethylene group, a hexamethylene group, etc. From the viewpoint of further exerting the effects of the present disclosure, the alkylene group may be a methylene group or an ethylene group. m R 1 In the O group, multiple R 1 may be the same alkylene group or may be alkylene groups with different carbon numbers. 2 In the O group, multiple R 2 may be the same alkylene group or may be alkylene groups with different carbon numbers.

[0111] Examples of epoxy resins having a polyoxyalkylene structure include liquid epoxy resins having a bisphenol A skeleton, polyethylene glycol diglycidyl ether, etc. Commercially available liquid epoxy resins having a bisphenol A skeleton include Rikaresin BEO-60E (manufactured by New Japan Chemical Co., Ltd.) represented by the following general formula (1), and commercially available polyethylene glycol diglycidyl ethers include Epolite 400E (manufactured by Kyoeisha Chemical Co., Ltd.), whose main component is a compound represented by the following general formula (2).

[0112] [ka]

[0113] [ka]

[0114] In the present disclosure, examples of imide resins used as organic substances include bisallylnadiimide, etc. Bisallylnadiimide is available as a commercially available product, such as BANI-M (manufactured by Maruzen Petrochemical Co., Ltd.) and BANI-X (manufactured by Maruzen Petrochemical Co., Ltd.).

[0115] When the composite of the present disclosure contains the organic substance, from the viewpoint of further exerting the effects of the present disclosure, the content thereof may be 1% by mass or more and 40% by mass or less, 3% by mass or more and 30% by mass or less, 4% by mass or more and 25% by mass or less, or 5% by mass or more and 20% by mass or less, relative to the total amount of the composite.

[0116] When the organic material contains a thermosetting resin, the composite of the present disclosure may further contain a curing agent, a curing accelerator, and the like. Examples of the curing agent include aliphatic amines, aromatic amines, dicyandiamide, dihydrazide compounds, acid anhydrides, phenolic resins, etc. These may be used alone or in combination of two or more.

[0117] Examples of the curing accelerator include organic peroxides such as dicumyl peroxide and dibutyl peroxide; imidazole compounds such as 2-methylimidazole and 2-ethylimidazole; organic phosphorus compounds such as trimethylphosphine, triethylphosphine, tributylphosphine, and triphenylphosphine; diazabicycloalkene compounds such as 1,8-diazabicyclo[5,4,0]undecene-7 (DBU) and 1,5-diazabicyclo[4,3,0]nonene-5; and tetraphenylboron compounds such as 2-ethyl-4-methylimidazole tetraphenylborate. These may be used alone or in combination of two or more.

[0118] When the composite of the present disclosure contains a curing agent, the content thereof may be 1.0 mass % or more and 20.0 mass % or less, 2.0 mass % or more and 18.0 mass % or less, or 3.0 mass % or more and 15.0 mass % or less, based on the total mass of the composite.

[0119] Furthermore, when the composite of the present disclosure contains a curing accelerator, the content thereof may be 0.01 mass% or more and 10.0 mass% or less, 0.05 mass% or more and 5.0 mass% or less, or 0.1 mass% or more and 3.0 mass% or less, relative to the total amount of the composite.

[0120] (inorganic) The inorganic substance used in the present disclosure is not particularly limited as long as it is an inorganic substance used in electronic components, and examples of the inorganic substance include silica, alumina, magnesium oxide, titanium oxide, barium titanate, silicon nitride, aluminum nitride, silicon carbide, tungsten carbide, and ceramics.

[0121] The ceramics are not particularly limited, but specific examples include sintered bodies mainly composed of metal oxides, nitrides, carbides, etc. Specific examples of metal oxides include alumina, zirconia, magnesium oxide, etc. Specific examples of metal nitrides include aluminum nitride, boron nitride, silicon nitride, etc. Specific examples of metal carbides include silicon carbide, boron carbide, etc. The ceramic may be a sintered body of at least one kind selected from alumina and aluminum nitride.

[0122] From the viewpoint of further exerting the effects of the present disclosure, the inorganic substance may be at least one selected from silica, alumina, and silicon carbide, and may be silica.

[0123] The shape of the inorganic substance is not particularly limited, and examples thereof include powder, fiber, scale, etc. The shape of the inorganic substance may be powder or spherical.

[0124] The average particle size of the inorganic substance is not particularly limited, but may be 0.1 μm or more and 100 μm or less, 0.2 μm or more and 75 μm or less, or 0.2 μm or more and 50 μm or less. In this specification, the average particle size refers to the volume average particle size, and the average particle size of an inorganic substance can be calculated as the average value of the major axis of the particles measured using a laser diffraction particle size distribution analyzer.

[0125] When the composite of the present disclosure contains the inorganic substance, from the viewpoint of further exerting the effects of the present disclosure, the content thereof may be 30% by mass or more and 95% by mass or less, 40% by mass or more and 90% by mass or less, or 50% by mass or more and 88% by mass or less, relative to the total amount of the composite.

[0126] (Other ingredients) In addition to the above components, the composite of the present disclosure may contain additives, as needed, that are commonly added to this type of composite, such as release agents such as synthetic waxes, natural waxes, higher fatty acids, and esters of higher fatty acids; colorants such as cobalt blue; modifiers such as silicone oils and silicone rubbers; hydrotalcites; ion scavengers; charge control agents; and flame retardants such as phosphazene, within the scope of the present disclosure. Each of these additives may be used alone or in combination of two or more.

[0127] The content of each of these additives in the composite of the present disclosure may be, relative to the total amount of the composite, 0.05 mass% or more and 30.0 mass% or less, or 0.2 mass% or more and 20.0 mass% or less.

[0128] In the composite of the present disclosure, the total content of the composite material, organic substance, and inorganic substance may be 70% by mass or more, or may be 80% by mass or more.

[0129] [Composite manufacturing method] The composite of the present disclosure may be obtained by thoroughly and uniformly mixing a composite material having a honeycomb structure containing cellulose nanofibers and a carbon material, at least one selected from organic and inorganic materials, and additives added as needed using a mixer or the like, and then kneading the mixture using a disperse mixer, kneader, three-roll mill, twin-screw heated roll, twin-screw heated extrusion kneader, or the like. The kneading may be performed under heating. The temperature may be 70°C or higher and 150°C or lower, or 75°C or higher and 120°C or lower.

[0130] The composite of the present disclosure may be used, for example, after the kneading treatment, by cooling and solidifying, and then pulverized to an appropriate size using a cutting mill, ball mill, cyclone mill, hammer mill, vibration mill, cutter mill, grinder mill, speed mill, or the like.

[0131] The mixture obtained after the kneading treatment may be pressed in a molding machine at a temperature of 50° C. to 100° C. and a pressure of 0.5 MPa to 1.5 MPa to form a sheet.

[0132] [Composite properties] From the viewpoint of preventing transmission signal loss when the composite molded article of the present disclosure is present on a transmission line of an electronic component, the real part of the complex permittivity (ε') at 25°C and 10 GHz may be 30 or less, 25 or less, or 20 or less. There is no particular lower limit for ε', but it may be 2 or more.

[0133] From the viewpoint of electromagnetic wave absorption performance, the composite molded article of the present disclosure may have an imaginary part (ε'') of the complex permittivity at 25°C and 10 GHz of 0.5 or more, 0.8 or more, or 1.0 or more. The upper limit of ε'' is not particularly limited, but may be 30 or less. The ε′ and ε″ can be measured by a waveguide method, specifically by the method described in the examples.

[0134] The electromagnetic wave absorption performance of the composite molded article of the present disclosure may be −2 dB or less, −4 dB or less, or −6 dB or less. The electromagnetic wave absorption performance is measured by placing a compression-molded molded body having a thickness of 0.5 mm between a high-frequency oscillation device and a receiving antenna, generating electromagnetic waves with a measurement frequency of 10 GHz, measuring the electromagnetic wave intensity with and without the molded body, and expressing the ratio (electromagnetic wave intensity when electromagnetic waves are absorbed by the molded body / electromagnetic wave intensity when the molded body is not present) in dB units. The electromagnetic wave intensity can be measured in accordance with the Transactions of the Institute of Electronics, Information and Communication Engineers, Vol. J97-B, No. 3, pp. 279-285.

[0135] The volume resistivity of the composite molded body of the present disclosure is 1.0 × 10 6 It may be 1.0×10 Ω·cm or more. 8 The upper limit is not particularly set, but it is 1.0×10 16 It may be Ω·cm or less. The volume resistivity can be measured in accordance with JIS K-6911:2006, specifically by the method described in the examples.

[0136] The composite of the present disclosure can be used as an electromagnetic wave absorbing material, an electromagnetic wave absorbing sheet, a semiconductor encapsulant, an encapsulating sheet, a covering material for electric wires, a transparent electrode, a coating material, a paint, and the like. [Example]

[0137] The present disclosure will now be described in detail with reference to examples, but the present disclosure is not limited to these examples in any way.

[0138] [Production Example 1: Production of carbon material] (Production of carbon-coated alumina nanoparticles) Alumina nanoparticles (manufactured by Taimei Chemical Industry Co., Ltd., TM300, crystalline phase: γ-alumina, average particle size: 7 nm, specific surface area: 220 m 2Alumina nanoparticles (10 ...

[0139] Methane CVD was performed by heating alumina nanoparticles from room temperature (20 ° C) to 900 ° C at a heating rate of 10 ° C / min under conditions where the N gas flow rate was adjusted to 224 ml / min, and then holding at 900 ° C for 30 minutes. Then, using N gas as a carrier gas, 20 volume % methane (based on the total amount of carrier gas and methane) was introduced into the reaction tube, and chemical vapor deposition (CVD) processing was performed at 900 ° C for 2 hours. At this time, the flow rate of methane gas was adjusted to 45 ml / min and the flow rate of N gas was adjusted to 179 ml / min. Then, the introduction of methane gas was stopped, and the N gas flow rate was adjusted to 224 ml / min. The mixture was held at 900 ° C for 30 minutes, and then cooled to obtain carbon-coated alumina nanoparticles 1.

[0140] (Dissolving and removing the mold) Carbon-coated alumina nanoparticles 1 and 5 M NaOH (50 times or more the stoichiometric ratio) were placed in a Teflon (registered trademark) autoclave container, heated at a rate of 250°C / hour using a muffle furnace, and held at 250°C for 2 hours. After natural cooling, the nanoparticles were collected by filtration and dried by vacuum heating at 150°C for 6 hours to obtain carbon material 1 (shell-like body).

[0141] [Measurement and evaluation of carbon materials] The following items were measured and evaluated for the obtained carbon material 1. The results of these measurements and evaluations are summarized in Table 1.

[0142] <Specific surface area (BET specific surface area)> The obtained carbon material 1 was dried by heating under vacuum at 150°C for 6 hours, and then the specific surface area (m 2 / g) was calculated.

[0143] <Average number of graphene layers> The average number of graphene layers was calculated from the specific surface area calculated by the above-mentioned method using the following formula. Average number of graphene layers = 2627 (m 2 / g) / specific surface area (m 2 / g)

[0144] <Pore volume> The obtained carbon material 1 was dried by heating under vacuum at 150°C for 6 hours, and then a nitrogen adsorption isotherm was measured using a high-precision automatic gas / vapor adsorption measuring device "BEL SORP MAX" (manufactured by BEL Japan Co., Ltd.). The pore volume per mass of material (cc / g) was calculated from the adsorption amount at a relative pressure (P / P0) of 0.96.

[0145] [Table 1]

[0146] [Production Example 2: Production of TEMPO-oxidized cellulose nanofibers] Bleached softwood kraft pulp (NBKP, containing 12 g of cellulose) was added to 700 ml of deionized water and stirred for 20 minutes at 300 rpm using a simple mixer (K-2RN, AS ONE Corporation). To the resulting NBKP solution, 20 ml of an aqueous solution containing 0.15 g of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO, Wako Pure Chemical Industries, Ltd.) and 20 ml of an aqueous solution containing 1.5 g of sodium bromide (Kanto Chemical Co., Ltd.) were slowly added. To the resulting mixture, an aqueous solution of sodium hypochlorite (Wako Pure Chemical Industries, Ltd.) adjusted to a Cl concentration of 8% by mass was slowly added to initiate the TEMPO oxidation reaction. Subsequently, the mixture was adjusted to pH 10.5 with the addition of a 3 M aqueous solution of sodium hydroxide (Wako Pure Chemical Industries, Ltd.). The resulting TEMPO-oxidized cellulose fibers were washed three times with 1200 ml of pure water to remove residual sodium hypochlorite, sodium hydroxide, etc., yielding a wet paste with a concentration of 3% by mass. The resulting wet paste was processed in a blender (MX1000XTX, manufactured by Waring Corporation) to break down the oxidized cellulose fiber bundles into nanofibers. This mechanical processing was repeated several times with the addition of water to obtain TEMPO-oxidized cellulose nanofibers. One hundred of the resulting TEMPO-oxidized cellulose nanofibers were observed using an atomic force microscope (AFM), and the average fiber diameter and average fiber length were calculated. The average fiber diameter was 5 nm and the average fiber length was 1.25 μm.

[0147] [Manufacturing of composite materials] Example 1 An aqueous dispersion with a solids concentration of 3% by mass was prepared by dispersing the TEMPO-oxidized cellulose nanofibers produced in Production Example 2 in water. A water-based urethane resin (DAOTAN VTW 1265 / 36WA, manufactured by Daicel-Allnex Corporation) was added to the aqueous dispersion so that the resin component was 3% by mass and the carbon material 1 produced in Production Example 1 was 2.6% by mass, and the mixture was thoroughly mixed. The mixture was then transferred to a tubular cell, which was then immersed in a -196°C refrigerant at a rate of 10 cm / h and frozen in one direction. Next, the cell was removed, and the mixture was freeze-dried in a sealed chamber by reducing the pressure at -5°C for 24 hours and then at 0°C for a further 24 hours, to obtain Composite Material 1, a cylindrical honeycomb structure in which carbon material 1 was dispersed in TEMPO-oxidized cellulose nanofibers and urethane. Next, the obtained composite material 1 was subjected to an annealing treatment at 200° C. for 6 hours. The composite material 1 after the annealing treatment was cut into a size of 440 mm×440 mm×25 mm to prepare an evaluation sample.

[0148] Example 2 An aqueous dispersion with a solids concentration of 3% by mass was prepared by dispersing the TEMPO-oxidized cellulose nanofibers produced in Production Example 2 in water. A water-based urethane resin (DAOTAN VTW 1265 / 36WA, manufactured by Daicel-Allnex Corporation) was mixed with the aqueous dispersion so that the resin content was 3% by mass. The mixture was then transferred to a tubular cell, which was then immersed in a -196°C refrigerant at a rate of 10 cm / h and frozen in one direction. Next, the cell was removed and freeze-dried in a sealed chamber by reducing the pressure at -5°C for 24 hours, and then at 0°C for another 24 hours to obtain a cylindrical honeycomb structure containing TEMPO-oxidized cellulose nanofibers and urethane. Next, the carbon material 1 produced in Production Example 1 was dispersed in water to prepare an aqueous dispersion with a solid content concentration of 2 mass%, and the honeycomb structure was immersed in this at room temperature (20°C) for 30 minutes, and then heated and dried at 120°C for 120 minutes to obtain a composite material 2 in which the carbon material 1 was adhered to the surface of the honeycomb structure. The obtained composite material 2 was cut into a size of 440 mm x 440 mm x 25 mm to prepare an evaluation sample.

[0149] Example 3 An aqueous dispersion with a solids concentration of 3% by mass was prepared by dispersing the TEMPO-oxidized cellulose nanofibers produced in Production Example 2 in water. A water-based urethane resin (DAOTAN VTW 1265 / 36WA, manufactured by Daicel-Allnex Corporation) was added to the aqueous dispersion so that the resin component was 3% by mass and the carbon-coated alumina nanoparticles 1 produced in Production Example 1 were 8.2% by mass. After thorough mixing, the mixture was transferred to a tubular cell, which was then immersed in a -196°C refrigerant at a rate of 10 cm / h and frozen in one direction. Next, the cell was removed, and the mixture was freeze-dried in a sealed chamber by reducing the pressure at -5°C for 24 hours, and then at 0°C for another 24 hours. This yielded composite material 3, a cylindrical honeycomb structure composed of TEMPO-oxidized cellulose nanofibers and carbon-coated alumina nanoparticles 1 dispersed in urethane. Next, the obtained composite material 3 was subjected to an annealing treatment at 200° C. for 6 hours. The composite material 3 after the annealing treatment was cut into a size of 440 mm×440 mm×25 mm to prepare an evaluation sample.

[0150] Example 4 An aqueous dispersion with a solids concentration of 3% by mass was prepared by dispersing the TEMPO-oxidized cellulose nanofibers produced in Production Example 2 in water. A water-based urethane resin (DAOTAN VTW 1265 / 36WA, manufactured by Daicel-Allnex Corporation) was mixed with the aqueous dispersion so that the resin content was 3% by mass. The mixture was then transferred to a tubular cell, which was then immersed in a -196°C refrigerant at a rate of 10 cm / h and frozen in one direction. Next, the cell was removed and freeze-dried in a sealed chamber by reducing the pressure at -5°C for 24 hours, and then at 0°C for another 24 hours to obtain a cylindrical honeycomb structure containing TEMPO-oxidized cellulose nanofibers and urethane. Next, the carbon-coated alumina nanoparticles 1 produced in Production Example 1 were dispersed in water to prepare an aqueous dispersion with a solid content of 6 mass%, and the honeycomb structure was immersed in this at room temperature (20°C) for 30 minutes, and then heated and dried at 120°C for 120 minutes to obtain a composite material 4 in which the carbon-coated alumina nanoparticles 1 were attached to the surface of the honeycomb structure. The obtained composite material 4 was cut into a size of 440 mm x 440 mm x 25 mm to prepare an evaluation sample.

[0151] (Comparative Example 1) Adipic acid, diethylene glycol, and trimethylolpropane were placed in a flask and mixed by heating at 120°C. Triisopropyl titanate was then added, and the mixture was dehydrated under reduced pressure at 240°C to prepare an adipic acid-based polyester polyol. A polyol mixture was obtained by mixing 10 parts by mass of the above adipic acid-based polyester polyol, 70 parts by mass of terephthalic acid-based polyester polyol "Terol 250" (manufactured by OXID Corporation), 20 parts by mass of ethylenediamine-based polyether polyol "AE-300" (manufactured by Mitsui Chemicals Polyurethanes Inc.), 15 parts by mass of flame retardant "TMCPP" (manufactured by Daihachi Chemical Industry Co., Ltd.), 1 part by mass of foam stabilizer "L-5340" (manufactured by Nippon Unicar Co., Ltd.), 2.5 parts by mass of catalyst "KL-31" (manufactured by Kao Corporation), 35 parts by mass of blowing agent "HFC-245fa", and 1.5 parts by mass of water. The resulting polyol mixture and isocyanate "Sumidur 44V20" (manufactured by Sumika Bayer Urethane Co., Ltd.) were mixed and stirred to a urethane index of 105. The resulting mixture was placed in a mold and molded into a size of 440 mm x 440 mm x 25 mm to obtain a rigid polyurethane foam (polyurethane foam). The resulting rigid polyurethane foam was then cut into a size of 440 mm x 440 mm x 25 mm. Next, mixed dispersion 1 was prepared by mixing 1 part by mass of carbon black (TPK1227R; manufactured by Cabot Corporation, average particle size: 0.1 μm) with 10,000 mL of urethane emulsion "Superflex" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), and the resulting foamed polyurethane was immersed in mixed dispersion 1 at room temperature (20°C) for 30 minutes, and then heated and dried at 120°C for 120 minutes to obtain composite material 5 in which powdered carbon material was present on the surface of the foamed polyurethane. The resulting composite material 5 (440 mm x 440 mm x 25 mm) was used as an evaluation sample.

[0152] [Measurement and evaluation of composite materials] The composite material thus obtained was subjected to the following measurement and evaluation. The results of these measurements and evaluations are summarized in Table 2.

[0153] <Honeycomb opening diameter> The honeycomb pores of the honeycomb structures of Composite Materials 1 to 4 were observed using a scanning electron microscope (SEM), and the average value of the opening diameters of 100 honeycomb pores observed in five fields of view was calculated and taken as the honeycomb opening diameter.

[0154] <Carbon material content or adhesion amount> The content of carbon material contained in the composite materials obtained in Examples 1 and 3 was calculated from the amounts of cellulose nanofibers, urethane resin, and carbon material charged. The amount of carbon material attached to the composite materials obtained in Examples 2 and 4 was calculated from the difference in mass between the honeycomb structure containing cellulose nanofibers and urethane after it was impregnated with a dispersion containing the carbon material and the honeycomb structure containing the cellulose nanofibers and urethane before it was impregnated. The amount of carbon material attached to the composite material obtained in Comparative Example 1 was calculated from the difference in mass between the polyurethane foam after it was impregnated with a dispersion containing the carbon material and the polyurethane foam before it was impregnated.

[0155] <Electromagnetic wave absorption performance (frequency 5GHz, far-field measurement system)> A 1 mm thick copper plate (600 mm × 600 mm) was placed on the anti-reflection wave absorber, and an evaluation sample (440 mm × 440 mm × 25 mm) was placed on the metal plate. Next, antennas were attached to a network analyzer via cables. Electromagnetic waves with a frequency of 5 GHz were transmitted from one antenna, reflected by the evaluation sample and the metal plate placed underneath, and received by the other antenna to measure the electromagnetic wave intensity. In addition, electromagnetic waves were radiated in the same manner as above without the evaluation sample placed on the metal plate, and the electromagnetic wave intensity was measured. The ratio of these values ​​(electromagnetic wave intensity when absorbed by the evaluation sample / electromagnetic wave intensity without the evaluation sample) was used to represent the electromagnetic wave absorption performance in dB. To evaluate the anisotropy of the electromagnetic wave absorption performance, the electromagnetic wave was transmitted at two angles: 10°, which was nearly perpendicular to the evaluation sample, and 45°, which was oblique. The electromagnetic wave intensity was measured in accordance with "Kagoshima Prefectural Industrial Technology Center Research Report No. 15 (2001), pp. 53-61."

[0156] [Table 2]

[0157] As shown in Table 2, Examples 1 to 4, which used a composite material having a honeycomb structure containing cellulose nanofibers and a carbon material with a specific structure, had better electromagnetic wave absorption performance than general urethane foam-based radio wave absorbers, and the electromagnetic wave absorption performance was strongly anisotropic. In the composite material of the present disclosure, a particularly large absorption performance can be expected in the frequency range where the length of half the wavelength of electromagnetic waves coincides with the honeycomb opening diameter or honeycomb opening circumferential diameter.

[0158] [Composite Manufacturing] The details of each component used in the preparation of the composites are listed in Table 3 below. [Organic matter] Epoxy resin: EPICLON N670; cresol novolac epoxy resin; manufactured by DIC Corporation, epoxy equivalent: 210 [Inorganic substances] Silica: FB105; manufactured by Denka Co., Ltd., average particle size: 12 μm

[0159] [Carbon materials] Composite material 1: Composite material prepared in Example 1 Composite material 2: Composite material prepared in Example 2 Composite material 3: Composite material prepared in Example 3 Composite material 4: Composite material prepared in Example 4 Cellulose nanofiber (CNF): TEMPO-oxidized cellulose nanofiber produced in Production Example 2. Average fiber diameter: 5 nm, average fiber length: 1.25 μm Carbon nanotubes (CNTs): LUCAN; manufactured by LG; average fiber length: 30 μm, average fiber diameter: 0.02 μm

[0160] [Other ingredients] Hardener: BRG-557; phenol novolac resin; manufactured by Aica Kogyo Co., Ltd. Curing accelerator: Curesol C11Z; imidazole compound; manufactured by Shikoku Kasei Co., Ltd. Flame retardant: Rabitol (phosphazene flame retardant) FP100; manufactured by Mitsui Chemicals Fine Chemicals, Inc.

[0161] (Examples 5 to 8, Comparative Examples 2 to 4) The components of the types and amounts listed in Table 3 were charged into a Henschel mixer and mixed, then charged into a twin-screw roll mixer heated to 110°C and heated and mixed until homogenous. The heated and mixed mixture was then charged into a cold roll, stretched into a sheet, and pulverized to obtain a composite.

[0162] [Composite measurement evaluation] The resulting composites were compression molded (temperature: 175°C, pressure: 10 MPa) to form bodies with a thickness of 0.5 mm or 1.0 mm. The complex dielectric constant and electromagnetic wave absorption performance were measured by the following methods. The evaluation results are shown in Table 3.

[0163] <Complex permittivity (real part: ε′, imaginary part: ε′′)> The dielectric properties were measured using a 1.0 mm thick molded body at a temperature of 25°C using a network analyzer (Agilent PNA E8363B) and a rectangular waveguide (WRJ-10) in the frequency range of 8.20 GHz to 12.40 GHz, and the respective values ​​at 10 GHz were obtained.

[0164] <Electromagnetic wave absorption performance (frequency 10GHz)> A molded body molded to a thickness of 0.5 mm was placed between a high-frequency oscillator device and a receiving antenna, and the electromagnetic wave intensity when an electromagnetic wave with a frequency of 10 GHz was generated was measured with and without the molded body, and the ratio (electromagnetic wave intensity when electromagnetic wave is absorbed by the molded body / electromagnetic wave intensity when the molded body is not present) was taken as the electromagnetic wave absorption performance in dB. The electromagnetic wave intensity was measured in accordance with the Transactions of the Institute of Electronics, Information and Communication Engineers, Vol. J97-B, No. 3, pp. 279-285.

[0165] <Volume resistivity> Using a molded body molded to a thickness of 1.0 mm, the volume resistivity at 150°C was measured in accordance with JIS K-6911:2006.

[0166] [Table 3]

[0167] As shown in Table 3, the composites of Examples 5 to 8, which contained a composite material having a honeycomb structure containing cellulose nanofibers and a carbon material having a specific structure, had good electromagnetic wave absorption performance, high volume resistivity, and good insulation properties.

Claims

1. Cellulose nanofibers, A composite material having a honeycomb structure containing a carbon material, the carbon material is at least one selected from (a) a carbon material which is at least one selected from first shell-shaped bodies which are hollow particles having one hole and second shell-shaped bodies which are in the form of linked hollow particles and have a plurality of holes; and (b) a carbon material which is at least one selected from core-shell particles in which the surfaces of inorganic particles are coated with a carbon layer and core-shell linked bodies in which the surfaces of linked bodies of inorganic particles are coated with a carbon layer; The carbon material (a) is a composite material in which the shell portions of the first shell-shaped body and the second shell-shaped body are made of graphene having an average number of layers of 4 or less, and the carbon material (b) is a composite material in which the carbon layers are made of graphene having an average number of layers of 4 or less.

2. The specific surface area of ​​the carbon material (a) is 657 m ２ The composite material of claim 1, wherein the tensile strength is 1 / g or more.

3. 2. The composite material according to claim 1, wherein the carbon material (a) has pores in the first shell-shaped bodies and pores in the second shell-shaped bodies each having a volume of 1.0 cc / g or more.

4. 2. The composite material according to claim 1, wherein the honeycomb structure has a honeycomb opening diameter of 0.2 μm or more and 200 μm or less.

5. The composite material according to claim 1 , wherein the content of the carbon material contained in the composite material is 5% by mass or more and 95% by mass or less.

6. The composite material according to claim 1 , wherein the honeycomb structure is made of the cellulose nanofibers and the carbon material.

7. The composite material according to claim 1 , wherein the honeycomb structure is made of the cellulose nanofibers, and the carbon material is attached to the surface of the honeycomb structure.

8. 7. The method for producing a composite material according to claim 6, wherein at least one carbon material selected from the group consisting of first shell-shaped bodies, which are hollow particles having one hole, and second shell-shaped bodies, which are in the form of linked hollow particles and have a plurality of holes, and at least one carbon material selected from the group consisting of core-shell particles in which the surfaces of inorganic particles are coated with a carbon layer, and core-shell linked bodies in which the surfaces of linked inorganic particles are coated with a carbon layer, are mixed with an aqueous dispersion containing cellulose nanofibers and frozen, wherein the shell portions of the first shell-shaped bodies and the second shell-shaped bodies in the carbon material (a) are made of graphene having an average number of layers of 4 or less, and the carbon layers of the carbon material (b) are made of graphene having an average number of layers of 4 or less.

9. 8. The method for producing a composite material according to claim 7, wherein a honeycomb structure containing cellulose nanofibers is impregnated with a dispersion containing at least one carbon material selected from the group consisting of first shell-shaped bodies, which are hollow particles having one hole, and second shell-shaped bodies, which are in the form of connected hollow particles and have a plurality of holes, and the carbon material (b), which is at least one carbon material selected from the group consisting of core-shell particles in which the surfaces of inorganic particles are coated with a carbon layer, and core-shell linked bodies in which the surfaces of linked inorganic particles are coated with a carbon layer.

9. The method for producing a composite material according to claim 7, wherein the shell portions of the first shell-shaped bodies and the second shell-shaped bodies in the carbon material (a) are made of graphene having an average number of layers of 4 or less, and the carbon layers of the carbon material (b) are made of graphene having an average number of layers of 4 or less.

10. The composite material according to any one of claims 1 to 7, which is an electromagnetic interference suppression material.

11. a composite material having a honeycomb structure containing cellulose nanofibers and a carbon material; At least one selected from an organic substance and an inorganic substance, the carbon material is at least one selected from (a) a carbon material which is at least one selected from first shell-shaped bodies which are hollow particles having one hole and second shell-shaped bodies which are in the form of linked hollow particles and have a plurality of holes; and (b) a carbon material which is at least one selected from core-shell particles in which the surfaces of inorganic particles are coated with a carbon layer and core-shell linked bodies in which the surfaces of linked bodies of inorganic particles are coated with a carbon layer; The carbon material (a) is a composite in which the shell portions of the first shell-shaped body and the second shell-shaped body are made of graphene having an average number of layers of 4 or less, and the carbon material (b) is a composite in which the carbon layers are made of graphene having an average number of layers of 4 or less.

12. The composite of claim 11 , wherein the organic material is a thermosetting resin.

13. 13. The composite of claim 11 or 12, which is an electromagnetic interference suppressor.

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