Carbon fiber composite material

Abstract

To provide a carbon fiber composite material having an electromagnetic wave shielding property and an excellent impact resistance.SOLUTION: A carbon fiber composite material has one or more carbon fiber layers and one or more carbon nanotube unwoven cloth layers, wherein at least one of the carbon fiber and carbon nanotube unwoven cloth layers in the carbon fiber composite material is impregnated with a heat-curable resin or has a heat-curable resin film laminated thereon.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to carbon fiber composite materials, and more particularly to carbon fiber composite materials that have electromagnetic wave shielding properties and excellent impact resistance, which are useful for high-speed communication equipment using millimeter-wave and terahertz electromagnetic waves, lightweight vehicles aimed at reducing carbon dioxide emissions and improving fuel efficiency, and connected cars. [Background technology]

[0002] Traditionally, fiber-reinforced composite materials, consisting of reinforcing fibers and matrix resins, have been applied in numerous fields such as aerospace, automotive, railway vehicles, ships, civil engineering and construction, and sporting goods, due to their lightweight nature while possessing excellent mechanical properties such as strength and rigidity, as well as heat resistance and corrosion resistance. Furthermore, in the automotive sector and other fields, with the advancement of electrification, there is a growing demand for fiber-reinforced composite materials that are both lighter and more impact-resistant in order to further improve fuel efficiency.

[0003] Furthermore, in recent years, high-speed communications such as 5G and 6G, which utilize electromagnetic waves in the millimeter wave and terahertz bands, are being considered for practical application. The number of wireless devices that use electromagnetic waves for communication is increasing, and the ever-increasing amount of electromagnetic waves poses risks such as electronic devices malfunctioning due to interference from surrounding electromagnetic waves, and information leakage due to electromagnetic waves emitted by the devices themselves. In addition, in order to promote the rapidly advancing autonomous driving of automobiles and other vehicles, the transmission and reception of electromagnetic waves must be carried out correctly in various electromagnetic environments ranging from low-frequency electromagnetic waves to millimeter waves. Therefore, electromagnetic wave shielding measures have become an important technical challenge, and there is a demand for electromagnetic wave shielding materials with excellent shielding performance against microwave, millimeter wave, and terahertz wave. With the advancement of electromagnetic wave utilization, there is also a growing need for new functionalities in electromagnetic wave shielding materials, such as thinning, weight reduction, and large-area applications.

[0004] Resin-impregnated carbon fiber reinforced composite materials, which use carbon fibers as reinforcing fibers, are lighter than metals and are therefore being considered as a substitute material for metals to improve fuel efficiency in electric vehicles and other applications, and are already being put into practical use in some cases. However, resin-impregnated carbon fiber reinforced composite materials have limitations in their use as vehicle body structural materials because they lack sufficient toughness and electromagnetic shielding properties compared to metals.

[0005] Numerous electromagnetic shielding technologies have been proposed using materials other than metals, such as carbon black, graphene, carbon nanotubes, conductive polymers, and dielectric oxides. Among these, carbon nanotubes, made from carbon, are attracting attention as a promising electromagnetic shielding material. Electromagnetic shielding materials using carbon nanotubes include paste materials in which carbon nanotubes are dispersed in resin (Patent Document 1) and aqueous paints in which carbon nanotubes are dispersed in aqueous solution (Patent Document 2). However, both are difficult to handle and their electromagnetic shielding performance is insufficient to be practical. Because the carbon nanotubes used are in the form of fine fibers, they have a large specific surface area and cannot be dispersed in large quantities in resin, resulting in insufficient electrical conductivity for electromagnetic shielding materials using carbon nanotubes. Furthermore, there is an electromagnetic wave shielding material that uses a sheet of carbon nanotubes formed by charged spinning (Patent Document 3), but it has the problem of being weak in strength and difficult to handle. An electromagnetic shielding material (Patent Document 4) has been disclosed in which a protonating agent such as hydronium ions or hydrochloric acid is added to a carbon nanotube sheet, and further ferromagnetic materials such as iron or cobalt are added to improve conductivity. However, the protonating agent is a strongly acidic compound, which poses a problem in terms of handling. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-144000 [Patent Document 2] Japanese Patent Publication No. 2012-174833 [Patent Document 3] Japanese Patent Publication No. 2008-218859 [Patent Document 4] Patent No. 6182176

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to provide a carbon fiber composite material having excellent electromagnetic wave shielding properties and impact resistance.

Means for Solving the Problems

[0008] As a result of intensive research to solve such problems, the present inventors have found that the following carbon fiber composite material can achieve the above object, and have completed the present invention.

[0009] That is, the present invention provides the following carbon fiber composite material. [1] A carbon fiber composite material having at least one layer of carbon fiber and at least one layer of carbon nanotube non-woven fabric, The carbon fiber composite material is obtained by impregnating at least one layer of carbon fiber and carbon nanotube non-woven fabric in the carbon fiber composite material with a thermosetting resin or laminating a thermosetting resin film. [2] At least one layer of a thermosetting resin-containing carbon fiber prepreg obtained by impregnating carbon fiber with a thermosetting resin or laminating a thermosetting resin film And At least one layer of a thermosetting resin-containing carbon nanotube non-woven fabric prepreg obtained by impregnating a carbon nanotube non-woven fabric with a thermosetting resin or laminating a thermosetting resin film The carbon fiber composite material according to [1], having. [3] The carbon fiber composite material according to [2], wherein the ratio of [the number of layers of the thermosetting resin-containing carbon fiber prepreg / the number of layers of the thermosetting resin-containing carbon nanotube non-woven fabric prepreg] in the carbon fiber composite material is 0.5 to 10. [4] A carbon fiber composite material according to any one of [1] to [3], wherein the carbon nanotube nonwoven fabric is a nonwoven fabric composed of multilayer carbon nanotubes alone, single-walled carbon nanotubes alone, or a mixture of multilayer carbon nanotubes and single-walled carbon nanotubes. [5] A carbon fiber composite material according to any one of the following [1] to [4], wherein the carbon nanotube nonwoven fabric is a carbon nanotube nonwoven fabric obtained by laminating a multi-layer carbon nanotube nonwoven fabric and a single-layer carbon nanotube nonwoven fabric. [6] Carbon nanotube nonwoven fabric with a thickness of 1 mm or less and an air permeability of 0.5 cm 3 / cm 2 A carbon fiber composite material as described in any one of the following [1] to [5], wherein the resistivity is 0.005 Ω·cm or less. [Effects of the Invention]

[0010] The carbon fiber composite material of the present invention possesses excellent electromagnetic shielding and impact resistance, does not use strong acidic compounds such as protonating agents, and is easy to handle. Therefore, the carbon fiber composite material of the present invention is a useful material for high-speed communication equipment that utilizes electromagnetic waves in the high-frequency band of millimeter waves or higher, and because the material itself is lightweight, it is also useful as a vehicle body structure material or in-vehicle material that enables weight reduction and improved fuel efficiency. [Modes for carrying out the invention]

[0011] The present invention will be described in detail below. The carbon fiber composite material of the present invention has at least one layer of carbon fibers and at least one layer of carbon nanotube nonwoven fabric, and at least one layer of the carbon fibers and carbon nanotube nonwoven fabric in the carbon fiber composite material is impregnated with a thermosetting resin or laminated with a thermosetting resin film. Preferably, it has at least one layer of thermosetting resin-containing carbon fiber prepreg, in which carbon fibers are impregnated with a thermosetting resin or laminated with a thermosetting resin film, and at least one layer of thermosetting resin-containing carbon nanotube nonwoven fabric prepreg, in which carbon nanotube nonwoven fabric is impregnated with a thermosetting resin or laminated with a thermosetting resin film.

[0012] <Carbon fiber> Examples of carbon fibers used in the present invention include acrylic, pitch, and rayon-based carbon fibers, with acrylic-based carbon fibers, which have particularly high tensile strength, being preferred.

[0013] Such acrylic carbon fibers can be manufactured, for example, through the following process: A spinning stock containing polyacrylonitrile obtained from a monomer mainly composed of acrylonitrile is spun by wet spinning, wet-dry spinning, dry spinning, or melt spinning. The solidified yarn after spinning is used as a precursor through a spinning process, and then carbon fibers can be obtained through processes such as flame retardation and carbonization.

[0014] The form and arrangement of the carbon fibers are not limited, and for example, continuous fibers arranged in a unidirectional direction, single tow, plain weave, satin weave, twill weave, and other woven fabrics, knits, nonwoven fabrics, mats, and braided structures can be used. Among these, the form of continuous fibers arranged in a unidirectional direction or the form of woven fabrics such as plain weave, satin weave, and twill weave are preferred, and it is preferable that a layer is formed by such carbon fibers. Here, continuous fibers refer to fibers having an average length of 10 mm or more. For continuous carbon fiber fabrics, carbon fibers may also be used, with the surface of the carbon fiber treated with a sizing agent. Examples of sizing agents include epoxy resin, polyimide resin, and bismaleimide resin. A method of sizing agent treatment involves pre-treating the carbon fiber surface with a solution of at least one of these resins in a solvent. The carbon fiber used in this invention preferably has a basis weight of 1 to 1000 g / m². 2 More preferably 10-800 g / m² 2 And more preferably 100-500 g / m² 2 The basis weight of the carbon fiber is 1 g / m². 2 A material with a basis weight of 1000 g / m² is preferable because it exhibits high mechanical strength, excellent impact resistance, and superior electromagnetic shielding properties. 2The following characteristics are preferable because they provide moderate flexibility and moderate porosity, allowing the thermosetting resin to impregnate and exhibit an anchoring effect, resulting in excellent adhesion to the thermosetting resin.

[0015] Furthermore, carbon fiber may be used alone or in combination of two or more types. Carbon fiber may also be combined with other reinforcing fibers selected from glass fiber, aramid fiber, boron fiber, PBO fiber, liquid crystal polyester fiber, high-strength polyethylene fiber, alumina fiber, and silicon carbide fiber, in which case the proportion of carbon fiber is 5% by mass or more, preferably 10 to 100% by mass.

[0016] The carbon fibers preferably have a tensile modulus in the range of 200 to 440 GPa. This range is preferable because it results in a carbon fiber composite material with high rigidity and strength, and a good balance between these properties. A more preferable tensile modulus is in the range of 230 to 400 GPa, and even more preferably in the range of 260 to 370 GPa.

[0017] The tensile elongation of the carbon fibers is preferably in the range of 0.8 to 3.0%. This range is preferable because it allows for excellent tensile strength, tensile modulus, and impact resistance of the carbon fiber composite material, as well as a good balance of these properties. A more preferable range for the tensile elongation of the carbon fibers is 1.0 to 2.5%, and even more preferably in the range of 1.2 to 2.3%.

[0018] Here, the tensile modulus and tensile elongation of the carbon fiber are values ​​measured in accordance with JIS R 7606:2000.

[0019] In the present invention, the carbon fibers used are preferably those having 2,500 to 50,000 filaments in a single fiber bundle. A filament count of 2,500 or more is preferable because it provides excellent strength. Furthermore, a filament count of 50,000 or less is preferable because it allows the thermosetting resin described later to be appropriately impregnated between the fibers. The filament count in a single fiber bundle of carbon fibers is more preferably in the range of 2,800 to 40,000.

[0020] Examples of commercially available carbon fibers include "Torayca (registered trademark)" Cross CO6343, "Torayca (registered trademark)" Cross CK6244C (both manufactured by Toray Industries, Inc.), "PYROFIL (registered trademark)" TR3110M, "PYROFIL (registered trademark)" TR6110M (both manufactured by Mitsubishi Chemical Corporation), etc., which are representative woven fabrics.

[0021] <Carbon nanotube non-woven fabric> The carbon nanotube non-woven fabric used in the present invention is one in which single-layer to multi-layer carbon nanotube fibers with a diameter of 50 nm or less and a length of 2 mm or less, preferably 10 - 500 μm, are intertwined, and the thickness of the non-woven fabric itself is preferably 1 mm or less. The carbon nanotube non-woven fabric used in the present invention may be composed of single-layer carbon nanotube fibers, multi-layer carbon nanotube fibers, or a mixture of single-layer and multi-layer carbon nanotubes. Also, the carbon nanotube non-woven fabric may be a laminate of a multi-layer carbon nanotube non-woven fabric and a single-layer carbon nanotube non-woven fabric. The carbon nanotube non-woven fabric used in the present invention preferably has a basis weight of 1 - 1000 g / m 2 and more preferably 2 - 500 g / m 2 and even more preferably 5 - 100 g / m 2 . When the basis weight of the carbon nanotube non-woven fabric is 1 g / m 2 or more, it has strong mechanical strength, excellent impact resistance and electromagnetic wave shielding properties, which is preferable. On the other hand, when the basis weight of the carbon nanotube non-woven fabric is 1000 g / m 2 or less, it is preferable because it has an excellent balance between electromagnetic wave shielding properties and flexibility. To enhance electrical conductivity, a highly conductive carbon nanotube non-woven fabric with an air permeability of 0.5 cm 3 / cm 2 ·s or less and a specific resistance of 0.005 Ω·cm or less, preferably 0.003 Ω·cm or less, is preferable. Carbon nanotube nonwoven fabrics are made by intertwining carbon nanotube fibers obtained by known methods, such as carbon nanotube fibers spun in a plasma furnace using hydrocarbon gases like methane, or carbon nanotube fibers spun from dissolved carbon nanotubes through their pores.

[0022] The degree of air permeability can be adjusted by the entanglement of carbon nanotube fibers or by applying pressure to the carbon nanotube nonwoven fabric, depending on the thickness of the nonwoven fabric. In this specification, air permeability refers to the value of the air permeability of the cloth measured using a Frazier type tester in accordance with JIS R 3420. A degree of air permeability of 0.5 cm is preferable. 3 / cm 2 • s or less, more preferably 0.1 cm 3 / cm 2 • Less than s, more preferably 0.05 cm 3 / cm 2 Nonwoven carbon nanotube fabrics with a particle size of s or less are preferred because they have good electrical conductivity and excellent electromagnetic shielding performance over a wide frequency range (10 kHz to 300 GHz).

[0023] Examples of commercially available carbon nanotube nonwoven fabrics having the above-mentioned properties include the following: (1) CNTM10 manufactured by Tortech Thickness 32 μm, air permeability 0.04 cm 3 / cm 2 ·s, specific resistance 2.22E-03(Ω·cm) (2) CNTM30 manufactured by Tortech Thickness 78 μm, air permeability 0.01 cm 3 / cm 2 ·s, specific resistance 1.51E-03(Ω·cm) (3) MIRALON® (registered trademark) manufactured by Huntsman Ltd. Thickness 20 μm, air permeability 0.05 cm 3 / cm 2 ·s, specific resistance 3.5E-03(Ω·cm) (4) Single-walled carbon nanotube nonwoven fabric, manufactured by Meijo Nanocarbon Co., Ltd. Thickness 50 μm, air permeability 0.01 cm 3 / cm 2 ·s, specific resistance 1.82E-04(Ω·cm)

[0024] <Thermosetting resin> The thermosetting resin used as a binder for carbon fiber and / or carbon nanotube nonwoven fabrics is selected from the group consisting of epoxy resins, phenolic resins, allylated epoxy resins, allylated polyphenylene ether resins, maleimide resins, bismaleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, silicone resins, acrylic resins, and polyester resins. In particular, one or more of the epoxy resins, bismaleimide resins, and cyanate ester resins listed below are preferred as the thermosetting resins used in the present invention.

[0025] Preferably, the epoxy resin is one having two or more glycidyl groups in one molecule. Examples of epoxy resins used in the present invention include bisphenol-type epoxy resins such as bisphenol A-type epoxy resin, bisphenol F-type epoxy resin, bisphenol AD-type epoxy resin, and bisphenol S-type epoxy resin; epoxy resins having a biphenyl skeleton; epoxy resins having a naphthalene skeleton; epoxy resins having a dicyclopentadiene skeleton; novolac-type epoxy resins such as phenol novolac-type epoxy resin and cresol novolac-type epoxy resin; polyfunctional epoxy resins; N,N,O-triglycidyl-m-aminophenol; N,N,O Examples include glycidylamine-type epoxy resins such as -triglycidyl-p-aminophenol, N,N,O-triglycidyl-4-amino-3-methylphenol, N,N,N',N'-tetraglycidyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-2,2'-diethyl-4,4'-methylenedianiline, N,N,N',N'-tetraglycidyl-m-xylylenediamine, N,N-diglycidylaniline, and N,N-diglycidyl-o-toluidine, as well as resorcinol diglycidyl ether and triglycidyl isocyanurate. These epoxy resins may be used individually or in combination.

[0026] When using epoxy resin as the thermosetting resin, it is preferable to use an epoxy resin curing agent in combination. Any curing agent can be used that has a phenolic hydroxyl group or an amino group with active hydrogen and forms a crosslinked structure with the epoxy resin. As a curing agent having a phenolic hydroxyl group, any phenolic resin having a phenolic hydroxyl group with any structure can be used. As a curing agent having an amino group, an aromatic amine curing agent that yields an epoxy resin cured product with high heat resistance and high modulus of elasticity is preferred. Specifically, such aromatic amine curing agents include 4,4'-diaminodiphenylmethane, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-4,4'-diaminodiphenylmethane, 3,3'-diethyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-dimethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, 3,3'-di-t-butyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, Examples include solid aromatic amine curing agents such as 5'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetra-t-butyl-4,4'-diaminodiphenylmethane, and 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane; diethyltoluenediamines such as 2,2'-diethyldiaminodiphenylmethane, 2,4-diethyl-6-methyl-m-phenylenediamine, and 4,6-diethyl-2-methyl-m-phenylenediamine; liquid aromatic amine curing agents such as 4,4'-methylenebis(N-methylaniline), 4,4'-methylenebis(N-ethylaniline), 4,4'-methylenebis(N-sec-butylaniline), and N,N'-di-sec-butyl-p-phenylenediamine, or mixtures of solid and liquid aromatic amine curing agents. Among these, 3,3'-diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 3,3'-diisopropyl-4,4'-diaminodiphenylmethane, 3,3',5,5'-tetramethyl-4,4'-diaminodiphenylmethane, 3,3'-diisopropyl-5,5'-diethyl-4,4'-diaminodiphenylmethane, and 3,3',5,5'-tetraethyl-4,4'-diaminodiphenylmethane are particularly preferred. The amount of phenolic resin containing phenolic hydroxyl groups is preferably 0.1 to 2.0, more preferably 0.2 to 1.8, and particularly preferably 0.4 to 1.5, of the molar equivalent of phenolic hydroxyl groups relative to 1 molar equivalent of epoxy groups contained in the epoxy resin. If the amount is less than 0.1, unreacted epoxy groups may remain, potentially leading to a decrease in adhesion. If it exceeds 2.0, unreacted phenolic hydroxyl groups may remain, potentially leading to a deterioration in strength during high-temperature storage. Furthermore, the amount of aromatic amine curing agent blended is preferably such that the total amino group equivalents in the aromatic amine curing agent are 0.7 to 1.5, more preferably 0.7 to 1.2, even more preferably 0.7 to 1.1, and particularly preferably 0.85 to 1.05, per molar equivalent of epoxy groups. If the amount is less than 0.7, unreacted epoxy groups may remain, potentially lowering the glass transition temperature or reducing adhesion. If it exceeds 1.5, the cured product becomes hard and brittle, potentially causing cracks during reflow or temperature cycling. The hardener for epoxy resin may be used alone or in combination of two or more types.

[0027] As the bismaleimide resin, the bismaleimide resin represented by formula (1) or formula (2) below is preferred because it has excellent heat resistance, low elasticity, toughness, and adhesive properties.

[0028] [ka] (In formula (1), A represents a hydrocarbon group derived from the dimer acid skeleton.) [ka] (In formula (2), B is an independent tetravalent organic group having a cyclic structure, and X is an independent divalent hydrocarbon group having 6 to 200 carbon atoms, at least one of which is a hydrocarbon group derived from a dimer acid skeleton. n is between 1 and 100.)

[0029] Dimer acid is a liquid dibasic acid mainly composed of a 36-carbon dicarboxylic acid, produced by the dimerization of 18-carbon unsaturated fatty acids derived from natural materials such as vegetable oils. Dimer acid does not have a single skeleton but possesses multiple structures and several isomers exist. Representative dimer acids are classified as linear, monocyclic, aromatic cyclic, and polycyclic. In this specification, the dimer acid skeleton refers to a group derived from a dimer amine having a structure in which the carboxyl group of a dimer acid is replaced with a primary aminomethyl group, and the hydrocarbon group derived from the dimer acid skeleton is given as its average structure -C 36 H 70 It is sometimes written as -.

[0030] A typical bismaleimide resin of formula (1) is SLK-6895; trade name, manufactured by Shin-Etsu Chemical Co., Ltd.

[0031] In formula (2), B independently represents a tetravalent organic group having a cyclic structure, and is preferably one of the tetravalent organic groups shown in the following structural formulas. [ka] (The bonds in the above structural formula that are not bonded to substituents are bonded to the carbonyl carbon that forms the cyclic imide structure in formula (2).)

[0032] Furthermore, in formula (2), X is independently a divalent hydrocarbon group having 6 to 200 carbon atoms, preferably 8 to 100, and more preferably 10 to 50 carbon atoms. In particular, it is preferable that the branched divalent hydrocarbon group is one in which one or more hydrogen atoms are substituted with an alkyl or alkenyl group having 6 to 200 carbon atoms, preferably 8 to 100, and more preferably 10 to 50 carbon atoms. The branched divalent hydrocarbon group may be either a saturated aliphatic hydrocarbon group or an unsaturated hydrocarbon group, and may have an alicyclic structure or an aromatic ring structure in the middle of the molecular chain. At least one of the X in formula (2) is a hydrocarbon group derived from a dimer acid skeleton.

[0033] In formula (2), n is between 1 and 100, preferably between 1 and 60, and more preferably between 1 and 50. If n is too large, solubility and fluidity may decrease, potentially resulting in poor moldability such as lamination and impregnation.

[0034] A typical example of a bismaleimide resin of formula (2) is the bismaleimide resin of formula (4) (SLK-3000; trade name, manufactured by Shin-Etsu Chemical Co., Ltd.). [ka]

[0035] The bismaleimide resins of formula (1) and formula (2) may be used individually or in combination of two or more. Representative bismaleimide resins include the SLK-6895 (manufactured by Shin-Etsu Chemical Co., Ltd.) and SLK-3000 (manufactured by Shin-Etsu Chemical Co., Ltd.) mentioned above, as well as the SLK-2000 series (manufactured by Shin-Etsu Chemical Co., Ltd.).

[0036] When using bismaleimide resin as a thermosetting resin, it is preferable to use a reaction initiator for bismaleimide resin in combination as a curing catalyst. The reaction initiator for bismaleimide resin is not particularly limited as long as it promotes the crosslinking reaction, but examples include ionic catalysts such as imidazoles, organophosphorus compounds, tertiary amines, quaternary ammonium salts, boron trifluoride amine complexes, organophosphines, and organophosphonium salts; organic peroxides such as diallyl peroxide, dialkyl peroxide, peroxide carbonate, and hydroperoxide; and radical polymerization initiators such as azoisobutyronitrile. Among these, organic peroxides are preferred, and examples of organic peroxides include dicumyl peroxide, t-butyl peroxybenzoate, t-amyl peroxybenzoate, dibenzoyl peroxide, diuraloyl peroxide, 2,5-dimethyl-2,5-di(t-butyl peroxy)hexane, 1,1-di(t-butyl peroxy)cyclohexane, di-t-butyl peroxide, and dibenzoyl peroxide. The reaction initiator is preferably added in an amount of 0.05 to 10 parts by mass, and more preferably in an amount of 0.1 to 5 parts by mass, per 100 parts by mass of bismaleimide resin. The reaction initiator may be used alone or in combination of two or more types.

[0037] Cyanate ester resins are cyanate ester compounds having two or more cyanate groups in one molecule. While generally known cyanate ester compounds having two or more cyanate groups in one molecule can be used, the cyanate ester compound represented by the following formula (5) is preferred. [ka] In formula (5), R 1 and R 2 Each independently represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R 3 Each of these is a divalent linking group independently selected from the group consisting of the following formulas, and the number of p = 0 to 10. [ka] R in the above formula 4 Each of these is independently either a hydrogen atom or a methyl group.

[0038] Specific examples of cyanate ester resins include the following cyanate ester compounds: for example, bis(4-cyanatophenyl)methane, bis(3-methyl-4-cyanatophenyl)methane, bis(3,5-dimethyl-4-cyanatophenyl)methane, 1,1-bis(4-cyanatophenyl)ethane, 2,2-bis(4-cyanatophenyl)propane, 1,3-dicyanatobenzene, 1,4-dicyanatobenzene, 2-tert-butyl-1,4-dicyanatobenzene, 2,4-dimethyl-1,3-dicyanatobenzene, 2,5-di-tert-butyl-1,4- Dicyanatobenzene, tetramethyl-1,4-dicyanatobenzene, 1,3,5-tricyanatobenzene, 2,2'-dicyanatobiphenyl, 4,4'-dicyanatobiphenyl, 3,3',5,5'-tetramethyl-4,4'-dicyanatobiphenyl, 1,3-dicyanatonaphthalene, 1,4-dicyanatonaphthalene, 1,5-dicyanatonaphthalene, 1,6-dicyanatonaphthalene, 1,8-dicyanatonaphthalene, 2,6-dicyanatonaphthalene, 2,7-dicyanatonaph Talene, 1,3,6-Tricyanatonaphthalene, Bis(4-cyanatophenyl) ether, 4,4'-(1,3-phenylenediisopropylidene)diphenyl cyanate, Bis(4-cyanatophenyl) thioether, Tris(4-cyanatophenyl)phosphine, Bisphenol E type cyanate ester, Phenol novolac type cyanate, Cresol novolac type cyanate, Bis(3-ethyl-4-cyanatophenyl)methane, Bis(4-cyanatophenyl) sulfonate Examples include 1,1,1-tris(4-cyanatophenyl)ethane, 2,2-bis(4-cyanatophenyl)-1,1,1,3,3,3-hexafluoropropane, diallylbisphenol A-type cyanate ester, diallylbisphenol F-type cyanate ester, biphenyl aralkyl-type cyanate ester, dicyclopentadiene novolac-type cyanate, naphthalene ring-containing cyanate ester, aralkyl-type cyanate ester, heterocyclic cyanate ester, etc. These cyanate ester compounds can be used individually or in combination of two or more.Among these, preferred cyanate ester compounds are bis(4-cyanatophenyl)methane, bis(3-methyl-4-cyanatophenyl)methane, 1,1-bis(4-cyanatophenyl)ethane, and phenol novolac-type cyanate esters. Even more preferred cyanate ester compounds are 1,1-bis(4-cyanatophenyl)ethane and phenol novolac-type cyanate esters. Furthermore, cyanate ester compounds may be used individually or in combination of multiple types.

[0039] A viscosity of 300 Pa·s or less is preferable for the cyanate ester compound, as it provides excellent fluidity and allows for easy impregnation into carbon fiber and carbon nanotube nonwoven fabrics, resulting in uniform curing. The viscosity of the cyanate ester compounds was measured using a Type B rotational viscometer at room temperature (23-30°C) according to the method described in JIS K7117-1:1999.

[0040] When using cyanate ester resin as the thermosetting resin, it is preferable to use a curing agent for the cyanate ester resin in combination. Any curing agent that reacts with the cyanate ester compound is acceptable, and generally known curing agents can be used, such as phenolic curing agents. Examples of phenolic curing agents include phenol novolac resins, naphthalene ring-containing phenolic resins, aralkyl type phenolic resins, triphenolalkane type phenolic resins, biphenyl skeleton-containing aralkyl type phenolic resins, biphenyl type phenolic resins, alicyclic phenolic resins, heterocyclic phenolic resins, naphthalene ring-containing phenolic resins, resorcinol type phenolic resins, allyl group-containing phenolic resins, bisphenol A type resins, bisphenol F type resins, and other bisphenol type phenolic resins. The curing agent for the cyanate ester resin may be used alone or in combination of two or more types. The amount of phenolic curing agent added is preferably 0.5 to 20 parts by mass, and more preferably 1 to 10 parts by mass, per 100 parts by mass of cyanate ester resin. Furthermore, a generally known curing accelerator may be used in combination to accelerate the curing of the cyanate ester resin. Examples of curing accelerators include phosphorus compounds, tertiary amine compounds, and imidazole compounds. The curing accelerator may be used alone or in combination of two or more. The amount of curing accelerator added is preferably 0.1 to 10 parts by mass, and more preferably 0.2 to 5.5 parts by mass, per 100 parts by mass of cyanate ester resin.

[0041] <Thermosetting resin-containing carbon fiber prepreg> The thermosetting resin-containing carbon fiber prepreg constituting the carbon fiber composite material of the present invention is obtained by impregnating the above-mentioned carbon fibers with the above-mentioned thermosetting resin or laminating a thermosetting resin film onto them, preferably by impregnating them with at least one thermosetting resin selected from epoxy resin, bismaleimide resin, and cyanate ester resin, or by laminating them with at least one thermosetting resin film selected from epoxy resin, bismaleimide resin, and cyanate ester resin. Preferably, at least one thermosetting resin selected from epoxy resins, bismaleimide resins, and cyanate ester resins is contained in an amount of 10 to 200 parts by mass per 100 parts by mass of carbon fiber. Furthermore, the carbon fiber content in the thermosetting resin-containing carbon fiber prepreg is preferably 50% by mass or more, and more preferably 60% by mass or more. The thermosetting resin content in the thermosetting resin-containing carbon fiber prepreg is preferably 5 to 50% by mass, and more preferably 10 to 40% by mass. The thermosetting resin-containing carbon fiber prepreg may be manufactured by the method described below, or commercially available "PYROFIL®" TR3110-381GMX, "PYROFIL®" TR6110H331GMP (both manufactured by Mitsubishi Chemical Corporation), etc.

[0042] <Thermosetting resin-containing carbon nanotube nonwoven fabric prepreg> The thermosetting resin-containing carbon nanotube nonwoven fabric prepreg constituting the carbon fiber composite material of the present invention is obtained by impregnating the above-mentioned thermosetting resin with the above-mentioned thermosetting resin or laminating a thermosetting resin film onto the carbon nanotube nonwoven fabric, preferably by impregnating it with at least one thermosetting resin selected from epoxy resin, bismaleimide resin, and cyanate ester resin, or by laminating it with at least one thermosetting resin film selected from epoxy resin, bismaleimide resin, and cyanate ester resin. Preferably, at least one thermosetting resin selected from epoxy resins, bismaleimide resins, and cyanate ester resins is included in 10 to 200 parts by mass per 100 parts by mass of carbon nanotube nonwoven fabric. Furthermore, the carbon nanotube nonwoven fabric content in the thermosetting resin-containing carbon nanotube nonwoven fabric prepreg is preferably 50% by mass or more, and more preferably 70% by mass or more. The thermosetting resin content in the thermosetting resin-containing carbon nanotube nonwoven fabric prepreg is preferably 5 to 50% by mass, and more preferably 10 to 30% by mass. The thermosetting resin-containing carbon nanotube nonwoven fabric prepreg may be manufactured by the method described below, or a commercially available product may be used.

[0043] The carbon fiber composite material of the present invention may further contain the following components as optional components. <Thermoplastic resin> In addition to the thermosetting resins described above, a thermoplastic resin may be further impregnated into the carbon fiber and / or carbon nanotube nonwoven fabric, or a thermosetting resin film containing a thermoplastic resin may be laminated onto the carbon fiber and / or carbon nanotube nonwoven fabric. Typical examples of thermoplastic resins include polyethylene, polypropylene, polyphenylene ether, polyether ether ketone, polyether ketone, polyether sulfone, and fluororesin. Solvent-soluble thermoplastic resins are particularly preferred for impregnation into carbon fibers and carbon nanotube nonwoven fabrics. When adding a thermoplastic resin, the amount is 0 to 50 parts by mass per 100 parts by mass of the thermosetting resin.

[0044] <Coupling agent> In this invention, a coupling agent can be used to improve the wettability and adhesive strength between carbon fibers or carbon nanotube nonwoven fabrics and resins.

[0045] Examples of coupling agents include silane coupling agents and alkoxide compounds such as titanium and aluminum. Among these, silane coupling agents are preferred, and a preferred silane coupling agent is, for example, a compound represented by the general formula Y-Si-X3. Here, Y is an organic group having a functional group, such as an amino group, epoxy group, hydroxyl group, carboxyl group, vinyl group, methacrylic group, or mercapto group, and X is a hydrolyzable functional group, such as an alkoxy group. Specifically, representative examples include γ-glycidoxypropyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminobenzyltriethoxysilane, and γ-aminophenyltriethoxysilane. The appropriate amount of such coupling agent to use is in the range of 0.5 to 20 parts by mass per 100 parts by mass of thermosetting resin.

[0046] Alternatively, instead of using a coupling agent, the surfaces of carbon fibers and carbon nanotube fibers can be surface-treated with a diluted solution of thermosetting resin to improve wettability with the thermosetting resin.

[0047] <Inorganic materials> By filling the gaps between the intertwined fibers of the carbon fiber or carbon nanotube nonwoven fabric, which constitutes part of this invention, with highly conductive inorganic materials, such as inorganic powders, inorganic fibers, or metal particles, the electrical conductivity can be further enhanced, and the electromagnetic wave shielding performance in the 10-300 GHz frequency band can be improved. Typical inorganic powders include carbon black, carbon nanotubes, graphene, graphite, silica, zinc oxide, alumina, boron nitride, aluminum nitride, carbon short fibers, and alumina short fibers. Metal particles include copper, iron, silver, and gold, or resin particles coated with these metals may be added.

[0048] Furthermore, to further enhance the thermal conductivity of carbon nanotube nonwoven fabrics and carbon fibers, inorganic particles and fibers such as silica, zinc oxide, alumina, boron nitride, aluminum nitride, carbon short fibers, alumina short fibers, quartz fibers, and glass fibers may be used. By using these, the thermal conductivity of the carbon nanotube nonwoven fabric can be increased to 50-80 W / mK.

[0049] The shape of the inorganic material is not particularly limited, but an average particle size of 0.5 μm to 30 μm is preferred in terms of heat dissipation and electrical conductivity. The average particle size of the inorganic material is the D50 value measured by laser diffraction. Furthermore, when using carbon nanotubes as an inorganic material, for example, the average diameter of the carbon nanotubes is preferably 0.5 nm or more, more preferably 1 nm or more, more preferably 15 nm or less, and even more preferably 10 nm or less. The average diameter is a value obtained by measuring the diameter (outer diameter) of 100 randomly selected carbon nanotubes using a transmission electron microscope.

[0050] The inorganic material may be directly sprayed onto the carbon fiber or carbon nanotube nonwoven fabric, or the inorganic material may be dispersed in a thermosetting resin and impregnated into the carbon fiber or carbon nanotube nonwoven fabric. The inorganic material can be applied to carbon fiber or carbon nanotube nonwoven fabric by any method, but examples include packing the inorganic material into the carbon fiber or carbon nanotube nonwoven fabric using a press or laminator, dispersing the inorganic material in any solvent and spraying the dispersion onto the carbon fiber or carbon nanotube nonwoven fabric, then drying and removing the solvent, or a combination of these methods. Any solvent can be used as the solvent for the dispersion, but highly volatile solvents are preferred, such as water, alcohols such as ethanol and isopropyl alcohol, acetone, toluene, hydrocarbon solvents, and silicone solvents. The concentration of the dispersion is preferably 0.1 to 100 parts by mass per 100 parts by mass of inorganic material.

[0051] When inorganic materials are dispersed onto carbon fibers or carbon nanotube nonwoven fabrics for immobilization, the amount of immobilization is preferably 0.01 to 100 parts by mass per 100 parts by mass of carbon fibers or carbon nanotube nonwoven fabrics. When an inorganic material dispersed in a thermosetting resin is impregnated into a carbon fiber or carbon nanotube nonwoven fabric or laminated as a thermosetting resin film, the amount of the inorganic material is preferably 5 to 60 parts by mass, and more preferably 10 to 50 parts by mass, per 100 parts by mass of the thermosetting resin.

[0052] <Manufacturing method> The carbon fiber composite material of the present invention is A method for preparing a thermosetting resin-containing carbon nanotube nonwoven fabric prepreg by impregnating it with a thermosetting resin or laminating a thermosetting resin film, and laminating the thermosetting resin-containing carbon nanotube nonwoven fabric prepreg with carbon fibers. A method of preparing a thermosetting resin-containing carbon fiber prepreg by impregnating it with a thermosetting resin or laminating a thermosetting resin film, and then laminating the thermosetting resin carbon fiber prepreg with a carbon nanotube nonwoven fabric, or The product can be manufactured by either a method of preparing the thermosetting resin-containing carbon fiber prepreg and the thermosetting resin-containing carbon nanotube nonwoven fabric prepreg, and then laminating them. Examples of methods for manufacturing a thermosetting resin-containing carbon fiber prepreg include a wet method in which the thermosetting resin is dissolved in a solvent to reduce its viscosity and impregnates the carbon fibers, and a melt-rolling method in which the thermosetting resin is heated to reduce its viscosity and impregnates the carbon fibers. Methods for manufacturing a thermosetting resin-containing carbon nanotube nonwoven fabric prepreg include a wet method in which the thermosetting resin is dissolved in a solvent to reduce its viscosity and impregnates the carbon nanotube nonwoven fabric, and a melt-rolling method in which the thermosetting resin is heated to reduce its viscosity and impregnates the carbon nanotube nonwoven fabric. Alternatively, a thermosetting resin film may be prepared by coating a thermosetting resin varnish with a coater or the like, and the thermosetting resin film may be laminated on both sides of a carbon fiber or carbon nanotube nonwoven fabric to form a prepreg.

[0053] In the wet method, it is preferable to use a volatile solvent. After impregnating carbon fiber or carbon nanotube nonwoven fabric with a thermosetting resin, the solvent is removed to produce a prepreg impregnated with uncured thermosetting resin. Examples of solvents include anisole, cyclohexanone, tetralin, mesitylene, xylene, toluene, tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and acetonitrile, but are not limited to these depending on the thermosetting resin. One or more of these may be used. The amount of solvent is preferably 5 to 95% by mass. If solvent remains in the prepreg, it can adversely affect the molding process and worsen the working environment, among other problems. Therefore, the amount of solvent remaining in the prepreg should be 1% by mass or less, preferably 0.5% by mass or less. As for the method of removing the solvent, although it depends on the boiling point of the solvent used, heat treatment at 80°C to 150°C for 10 minutes to 1 hour is preferable, and solvent removal can be easily achieved by this heat treatment.

[0054] The melt rolling method has several advantages, including the fact that it does not require a solvent removal process and has relatively good work efficiency. In the melt rolling method, carbon fiber or carbon nanotube nonwoven fabric is widened to the required width using a bar or similar tool, and a film-formed thermosetting resin is placed on both or one side of it, laminated, and then heated and pressurized to produce a prepreg impregnated with uncured thermosetting resin.

[0055] Carbon fibers (thermosetting resin-containing carbon fiber prepreg) and carbon nanotube nonwoven fabric (thermosetting resin-containing carbon nanotube nonwoven fabric prepreg) can be laminated in any number and in any order as long as there is one layer of each. In particular, when both the carbon fibers and the carbon nanotube nonwoven fabric contain thermosetting resin, the ratio of [number of layers of thermosetting resin-containing carbon fiber prepreg / number of layers of thermosetting resin-containing carbon nanotube nonwoven fabric prepreg] in the carbon fiber composite material is preferably 0.5 to 10, and more preferably 1.0 to 3.0. A carbon fiber composite material having a desired shape can be obtained by laminating a thermosetting resin-containing carbon fiber prepreg (or carbon fiber) and a thermosetting resin-containing carbon nanotube nonwoven fabric prepreg (or carbon nanotube nonwoven fabric), and then molding them, for example, by the following molding methods 1) to 4). 1) Press forming This method involves layering prepreg material into a mold and then applying pressure while heating and curing it, making it suitable for mass production. 2) Autoclave molding This method involves laminating prepreg in a mold, covering it with a bagging film, reducing the pressure, and then applying pressure in an autoclave to heat-cur it. 3) Oven shaping This method involves laminating prepreg into a mold, covering it with a bagging film, reducing the pressure, and then heat-curing it under vacuum pressure. 4) Sheet wrap molding This method involves wrapping prepreg around a mandrel, taping it, and then heat-curing and removing the core.

[0056] The heat curing conditions in the above molding method are, for example, a temperature of 120 to 250°C, more preferably 140 to 200°C, and a curing time of 0.2 to 10 hours, more preferably 0.4 to 5 hours. Furthermore, the pressing conditions in press forming are preferably in the range of 1 to 10 MPa, and more preferably in the range of 3 to 8 MPa.

[0057] Various parts can be manufactured using this molding method. The carbon fiber composite material of the present invention is lightweight and has excellent electromagnetic shielding and impact resistance, making it suitable for use as a vehicle body or structural component in automobiles, drones, ships, and aircraft. Furthermore, the carbon fiber composite material of the present invention is also suitable for components requiring electromagnetic shielding, such as housings for automobile batteries that generate electromagnetic waves, motor components, and DC / DC converter encapsulants. Furthermore, the carbon fiber composite material of the present invention can be used as a component or container for communication equipment that uses high frequencies of millimeter waves or higher and requires electromagnetic wave shielding and heat resistance. Since carbon nanotube nonwoven fabrics easily generate heat when a voltage is applied to both ends, the carbon fiber composite material of the present invention can be used as a heat-generating element in a wide range of applications. [Examples]

[0058] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass". The materials used in the examples and comparative examples of the present invention are as follows.

[0059] (1) Bismaleimide resin (A-1) Bismaleimide resin represented by the following formula (SLK-3000, manufactured by Shin-Etsu Chemical Co., Ltd., number average molecular weight 5200) [ka]

[0060] (A-2) The bismaleimide resin represented by the following formula (SLK-6895, manufactured by Shin-Etsu Chemical Co., Ltd., number average molecular weight 689) [ka]

[0061] (2) Epoxy resin (A-3) Epoxy resin (ZX-1059, manufactured by Nippon Steel Chemical & Material Co., Ltd., a mixture of bisphenol A type epoxy resin and bisphenol F type epoxy resin)

[0062] (3)Thermoplastic resin (A-4) Polyethersulfone (Sumika Excel PES5003P, manufactured by Sumitomo Chemical Co., Ltd.)

[0063] <Preparation of resin film> Resin film (1) A bismaleimide resin composition was obtained by mixing 100 parts by mass of bismaleimide resin (A-1) with 1 part by mass of a curing catalyst (dicumyl peroxide, trade name "Perkmyl D", manufactured by NOF Corporation). Cyclohexanone solvent was added to this bismaleimide resin composition so that its content was 50% by mass to obtain a cyclohexanone solution (1) of the bismaleimide resin composition. The cyclohexanone solution (1) of the bismaleimide resin composition was applied to a mold-released PET film with a thickness of 38 μm using a roller coater and dried at 100°C for 10 minutes to prepare an uncured resin film (1) with a thickness of 30 μm. Resin film (2) 100 parts by mass of a bismaleimide resin composition containing 100 parts by mass of bismaleimide resin (A-2) and 1 part by mass of a curing catalyst (dicumyl peroxide, trade name "Perkmyl D", manufactured by NOF Corporation) were mixed with 5 parts by mass of carbon nanotube powder ZEONANO SG101 (manufactured by Zeon Nanotechnology Co., Ltd.) and mixed at 2000 rpm for 5 minutes using a rotary-orbit mixer to obtain a bismaleimide resin composition. Cyclohexanone solvent was added to this bismaleimide resin composition so that its content was 50% by mass to obtain a cyclohexanone solution (2) of the bismaleimide resin composition. This solution was coated onto a release-treated PET film with a thickness of 38 μm using a roller coater and dried at 100°C for 10 minutes to prepare an uncured resin film (2) with a thickness of 30 μm. Resin film (3) An epoxy resin composition was prepared by mixing 100 parts by mass of epoxy resin (A-3) with 38.3 parts by mass of aromatic amine curing agent (Kayahard AA, manufactured by Nippon Kayaku Co., Ltd.) (an amount such that the total amino group equivalent in the aromatic amine curing agent is 1.0 for every 1 molar equivalent of epoxy groups contained in the epoxy resin). Toluene was added to this epoxy resin composition to a content of 50% by mass to obtain a toluene solution (1) of the epoxy resin composition. A toluene solution (1) of the epoxy resin composition was applied to a 38 μm thick PET film that had been released using a roller coater, and dried at 120°C for 10 minutes to prepare an uncured resin film (3) with a thickness of 30 μm. Resin film (4) An epoxy resin composition was prepared by heating and kneading 100 parts by mass of epoxy resin (A-3), 38.3 parts by mass of aromatic amine curing agent (Kayahard AA, manufactured by Nippon Kayaku Co., Ltd.) (an amount such that the total amino group equivalent in the aromatic amine curing agent is 1.0 for every 1 molar equivalent of epoxy groups contained in the epoxy resin), and 20 parts by mass of (A-4) polyethersulfone. Toluene was added to this epoxy resin composition so that its content was 50% by mass to obtain a toluene solution (2) of the epoxy resin composition. A toluene solution (2) of the epoxy resin composition was applied to a 38 μm thick PET film that had been released using a roller coater, and dried at 120°C for 10 minutes to prepare an uncured resin film (4) with a thickness of 30 μm.

[0064] <Carbon nanotube nonwoven fabric> Nonwoven fabric (1) CNTM30 (manufactured by Tortech: multi-walled carbon nanotube) Thickness: 78 μm Air permeability: 0.01cm 3 / cm 2 ·s Specific resistance: 1.51E-03 (Ω cm) Nonwoven fabric (2) CNTM10 (manufactured by Tortech: multi-walled carbon nanotube) Thickness: 32 μm Air permeability: 0.04cm 3 / cm 2 ·s Specific resistance: 2.22E-03 (Ω cm) Nonwoven fabric (3) Single-layer carbon nanotube nonwoven fabric (manufactured by Meijo Nanocarbon Co., Ltd.) Thickness: 50 μm Air permeability: 0.01cm 3 / cm 2 ·s Specific resistance: 1.82E-04 (Ω cm) Nonwoven fabric (4) A carbon nanotube nonwoven fabric (3) was obtained by scattering 1 g of single-walled carbon nanotube powder (ZEONANO SG101, manufactured by Zeon Nanotechnology Co., Ltd., average diameter: 3 nm) on both sides of 0.3 g of CNTM30. 0.03 g of single-walled carbon nanotube powder was immobilized on 0.3 g of CNTM30. Thickness: 72 μm Air permeability: 0.01cm 3 / cm 2 ·s Specific resistance: 3.0E-03 (Ω cm) Nonwoven fabric (5) 0.3 g of CNTM30 was impregnated in 20 g of single-walled carbon nanotube solution (EC1.5P (NMP solution), manufactured by Meijo Nanocarbon Co., Ltd.) at 25°C for 30 minutes, and then dried at 200°C for 5 minutes to prepare a carbon nanotube nonwoven fabric consisting of single-walled and multi-walled carbon nanotubes. Thickness: 75 μm Air permeability: 0.02cm 3 / cm 2 ·s Specific resistance: 2.4E-03 (Ω cm)

[0065] <Carbon nanotube nonwoven fabric prepreg> [Reference example 1] A carbon nanotube nonwoven fabric (1) measuring 78 μm in thickness and 10 cm square was used to prepare a carbon nanotube prepreg (CNT1). A 0.23 g sheet of resin film (1) measuring 10 cm x 10 cm was placed on each side of the nonwoven fabric, laminated at 80°C for 1 minute, and then pressed at 150°C for 15 minutes.

[0066] [Reference example 2] A prepreg (CNT2) using carbon nanotube nonwoven fabric was prepared in the same manner as in Reference Example 1, except that 0.10 g of a 32 μm thick, 10 cm square carbon nanotube nonwoven fabric (2) was used instead of the carbon nanotube nonwoven fabric (1).

[0067] [Reference example 3] A prepreg (CNT3) using carbon nanotube nonwoven fabric was prepared in the same manner as in Reference Example 1, except that 1.5 g of carbon nanotube nonwoven fabric (3), which was 50 μm thick and 10 cm square, was used instead of carbon nanotube nonwoven fabric (1).

[0068] [Reference example 4] A prepreg (CNT4) using carbon nanotube nonwoven fabric was prepared in the same manner as in Reference Example 1, except that 0.22 g of carbon nanotube nonwoven fabric (4) was used instead of carbon nanotube nonwoven fabric (1).

[0069] [Reference example 5] A prepreg (CNT5) using carbon nanotube nonwoven fabric was prepared in the same manner as in Reference Example 1, except that 0.23 g of carbon nanotube nonwoven fabric (5) was used instead of carbon nanotube nonwoven fabric (1).

[0070] [Reference example 6] A prepreg (CNT6) using carbon nanotube nonwoven fabric was prepared in the same manner as in Reference Example 1, except that resin film (2) was used instead of resin film (1).

[0071] [Reference example 7] A carbon nanotube nonwoven fabric (1) was impregnated with a toluene solution (1) of the epoxy resin composition prepared above, and dried at 120°C for 30 minutes to prepare a prepreg (CNT7) using the carbon nanotube nonwoven fabric.

[0072] [Reference example 8] A carbon nanotube nonwoven fabric (1) was impregnated with a toluene solution (2) of the epoxy resin composition prepared above, and dried at 120°C for 30 minutes to prepare a prepreg (CNT8) using the carbon nanotube nonwoven fabric.

[0073] The thickness of prepregs CNT1-8, which use carbon nanotube nonwoven fabric, was measured with a micrometer, and the apparent resistivity was measured with an eddy current resistance meter (NAPSON). The results are shown in Table 1. [Table 1]

[0074] <Carbon fiber prepreg> (1) TR3110 381GMX (manufactured by Mitsubishi Chemical Corporation) Carbon fiber basis weight: 200g / m 2 Epoxy resin content: 40 wt% Thickness: 220 μm (2) TR6110H331GMP (manufactured by Mitsubishi Chemical Corporation) Carbon fiber basis weight: 280g / m 2 Epoxy resin content: 40 wt% Thickness: 320 μm

[0075] The properties of the sheets prepared in the examples and comparative examples were measured and evaluated using the following methods, and the results are shown in Tables 2 and 3. thickness The thickness of the sheet was measured with a micrometer. specific resistance The resistivity of the sheet was measured using an eddy current resistance meter (manufactured by NAPSON).

[0076] Electromagnetic wave shielding characteristics Electromagnetic shielding characteristics (SE) are defined by the following equation.

number

[0077] Impact strength Impact strength was measured using a puncture impact test in accordance with the measurement method: JIS K7211. First, two layers of carbon fiber prepreg (1) were laminated and heated and cured at 200°C for 30 minutes to produce a cured carbon fiber prepreg (1) with a thickness of 400 μm. The impact test value I of this cured carbon fiber prepreg (1) was measured. Next, the impact test value II of each sheet prepared in the example or comparative example was measured. The intensity ratio of impact test values ​​I and II was calculated using the formula: Impact test value II / Impact test value I.

[0078] [Example 1] In Reference Example 1, one carbon fiber prepreg (1) was placed on the top and bottom surfaces of the carbon nanotube nonwoven fabric prepreg (CNT1), creating a three-layer laminate. This laminate was then subjected to a heat press set to 200°C and a pressure of 7.0 MPa, and cured for 30 minutes to obtain a three-layer carbon fiber composite material (electromagnetic wave shielding sheet 1). Table 2 shows the electromagnetic shielding characteristics and impact test strength ratio of this electromagnetic shielding sheet 1.

[0079] [Example 2] One sheet of carbon nanotube nonwoven fabric prepreg (CNT1) manufactured in Reference Example 1 was placed on the top and bottom surfaces of a carbon fiber prepreg (1), and after laminating it into three layers, one more sheet of carbon fiber prepreg (1) was placed on the top and bottom surfaces of each of the three layers, resulting in five layers of laminated material. This material was then heated in a press set to 200°C and subjected to a pressure of 7.0 MPa, and cured for 30 minutes to obtain a five-layer carbon fiber composite material (electromagnetic wave shielding sheet 2). Table 2 shows the electromagnetic shielding characteristics and impact test strength ratio of electromagnetic shielding sheet 2.

[0080] [Example 3] In Reference Example 1, one carbon fiber prepreg (2) was placed on the top and bottom surfaces of the carbon nanotube nonwoven fabric prepreg (CNT1), creating a three-layer laminate. This laminate was then subjected to a heat press set to 200°C and a pressure of 7.0 MPa, and cured for 30 minutes to obtain a three-layer carbon fiber composite material (electromagnetic wave shielding sheet 3). Table 2 shows the electromagnetic shielding characteristics and impact test strength ratio of electromagnetic shielding sheet 3.

[0081] [Example 4] In Reference Example 2, one carbon fiber prepreg (1) was placed on the top and bottom surfaces of the carbon nanotube nonwoven fabric prepreg (CNT2), creating a three-layer laminate. This laminate was then subjected to a heat press set to 200°C and a pressure of 7.0 MPa, and cured for 30 minutes to obtain a three-layer carbon fiber composite material (electromagnetic wave shielding sheet 4). Table 2 shows the electromagnetic shielding characteristics and impact test strength ratio of electromagnetic shielding sheet 4.

[0082] [Example 5] Similar to Example 1, one carbon fiber prepreg (1) was placed on the top and bottom surfaces of the carbon nanotube nonwoven fabric prepreg (CNT3) manufactured in Reference Example 3, creating a three-layer laminate. This laminate was then subjected to a pressure of 7.0 MPa using a heated press set to 200°C and cured for 30 minutes to obtain a three-layer carbon fiber composite material (electromagnetic wave shielding sheet 5). Table 2 shows the electromagnetic shielding characteristics and impact test strength ratio of electromagnetic shielding sheet 5.

[0083] [Example 6] A carbon nanotube nonwoven fabric prepreg (CNT1) manufactured in Reference Example 1 was placed on the upper surface of a carbon fiber prepreg (1), creating a two-layer laminate. This laminate was then subjected to a heat press set to 200°C and a pressure of 7.0 MPa, and cured for 30 minutes to obtain a two-layer carbon fiber composite material (electromagnetic wave shielding sheet 6). Table 2 shows the electromagnetic shielding characteristics and impact test strength ratio of the electromagnetic shielding sheet 6.

[0084] [Examples 7-11] Except for using the carbon nanotube nonwoven fabric prepregs (CNT4-CNT8) manufactured in Reference Examples 4-8 instead of the carbon nanotube nonwoven fabric prepreg (CNT1) manufactured in Reference Example 1, the process was the same as in Example 1, and the materials were pressed at a pressure of 7.0 MPa in a heated press set to a temperature of 200°C and cured for 30 minutes to obtain three-layer carbon fiber composite materials (electromagnetic wave shielding sheets 7-11). Table 2 shows the electromagnetic shielding characteristics and impact test strength ratios of electromagnetic shielding sheets 7 to 11.

[0085] [Example 12] A carbon nanotube nonwoven fabric (1) was placed on the upper surface of a carbon fiber prepreg (1), and the two layers were laminated. The two layers were then heated in a press set to 200°C and subjected to a pressure of 7.0 MPa, and cured for 30 minutes to obtain a two-layer carbon fiber composite material (electromagnetic wave shielding sheet 12). The electromagnetic shielding characteristics of the electromagnetic shielding sheet 12 (value at 80 GHz) were 80 dB, and the impact test strength ratio was 1.1.

[0086] [Comparative Example 1] Two layers of carbon fiber prepreg (1) were laminated and heat-cured at 200°C for 30 minutes to produce a sheet-like cured material (sheet 13) with a thickness of 400 μm.

[0087] [Comparative Example 2] Two layers of carbon nanotube nonwoven fabric prepreg (CNT1) prepared in Reference Example 1 were laminated and heat-cured at 200°C for 30 minutes to produce a sheet-like cured material (sheet 14) with a thickness of 270 μm.

[0088] [Comparative Example 3] A carbon nanotube nonwoven fabric (1) was used as sheet 15.

[0089] [Comparative Example 4] A carbon nanotube nonwoven fabric (2) was used as sheet 16.

[0090] [Table 2]

[0091] [Table 3]

[0092] As shown in Examples 1 to 12, the electromagnetic shielding sheets of Examples 1 to 12 have an impact test strength ratio of 1.0 or higher compared to the sheet made of two-layer carbon fiber prepreg of Comparative Example 1, clearly demonstrating superior impact resistance. Furthermore, the electromagnetic shielding sheets of Examples 1 to 12 exhibit impact resistance equivalent to or better than that of the sheet made of two-layer carbon nanotube nonwoven fabric prepreg of Comparative Example 2. Moreover, the electromagnetic shielding characteristics of the electromagnetic shielding sheets of Examples 1 to 12 at 80 GHz are also superior to those of Comparative Examples 1 and 2. The carbon fiber composite material of the present invention improves impact strength without reducing electromagnetic shielding properties compared to an electromagnetic shielding sheet made of carbon fiber alone, resulting in a highly reliable electromagnetic shielding sheet. [Industrial applicability]

[0093] The carbon fiber composite material of the present invention has excellent electromagnetic wave shielding properties and strength, making it suitable for use in high-speed, high-capacity communication equipment and automotive applications.

Claims

1. A carbon fiber composite material having at least one layer of carbon fiber and at least one layer of carbon nanotube nonwoven fabric, The carbon fiber composite material comprises at least one layer of carbon fibers and carbon nanotube nonwoven fabric impregnated with a thermosetting resin or laminated with a thermosetting resin film, A carbon fiber composite material in which the carbon nanotube nonwoven fabric is 1 mm or less in thickness, has an air permeability of 0.05 cm³ / cm²·s or less, and a resistivity of 0.005 Ω·cm or less.

2. At least one layer of a thermosetting resin-containing carbon fiber prepreg, which is obtained by impregnating carbon fibers with a thermosetting resin or laminating a thermosetting resin film onto carbon fibers. and At least one layer of a thermosetting resin-containing carbon nanotube nonwoven fabric prepreg, which is obtained by impregnating a carbon nanotube nonwoven fabric with a thermosetting resin or laminating a thermosetting resin film onto it. A carbon fiber composite material according to claim 1, having the properties of the carbon fiber composite material described in claim 1.

3. The carbon fiber composite material according to claim 2, wherein the ratio of [number of layers of thermosetting resin-containing carbon fiber prepreg / number of layers of thermosetting resin-containing carbon nanotube nonwoven fabric prepreg] in the carbon fiber composite material is 0.5 to 10.

4. The carbon fiber composite material according to any one of claims 1 to 3, wherein the carbon nanotube nonwoven fabric is a nonwoven fabric made of multilayer carbon nanotubes alone, single-walled carbon nanotubes alone, or a mixture of multilayer carbon nanotubes and single-walled carbon nanotubes.

5. The carbon fiber composite material according to any one of claims 1 to 3, wherein the electromagnetic wave shielding characteristic at 80 GHz is 83 dB or more.

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