Electromagnetic wave shielding sheet

Abstract

To provide an electromagnetic wave-shielding sheet which is a cured or non-cured sheet formed by impregnating a carbon nanotube non-woven fabric with a thickness of 1 mm or less with a resin or stacking the resin on the non-woven fabric, and has excellent electromagnetic shielding property to millimeter waves or terahertz waves.SOLUTION: An electromagnetic wave-shielding sheet is formed by impregnating a carbon nanotube non-woven fabric having a thickness of 1 mm or less, air permeability of 0.5 cm3 / cm2 s or less and specific resistance of 0.005 Ω cm or less with a resin. The electromagnetic wave-shielding sheet contains an inorganic material in a gap between fibers of the carbon nanotube non-woven fabric.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave shielding sheet, and specifically, to a cured or uncured sheet obtained by impregnating and / or laminating a resin on a carbon nanotube nonwoven fabric with a thickness of 1 mm or less, and having excellent high-intensity electromagnetic wave shielding performance against millimeter waves and terahertz waves.

Background Art

[0002] In recent years, high-speed communications such as 5G and 6G that utilize high-frequency bands (1 to 300 GHz) of electromagnetic waves have become a topic of discussion. The number of wireless devices that use electromagnetic waves for communication is increasing, and the increasing electromagnetic waves can cause electronic devices to malfunction due to interference from surrounding electromagnetic waves or information leakage due to the electromagnetic waves emitted by themselves. In addition, in order to promote autonomous driving of vehicles and the like that are rapidly evolving, electromagnetic waves must be correctly transmitted and received in various electromagnetic environments from low-frequency electromagnetic waves to millimeter waves. Therefore, electromagnetic wave shielding measures have become an important technical issue, and an electromagnetic wave shielding material having excellent electromagnetic wave shielding performance against microwaves, millimeter waves, and terahertz waves is desired. In addition, due to the advancement of electromagnetic wave utilization, the needs for new functionalities such as thinning, weight reduction, and large-areaization of electromagnetic wave shielding materials are also increasing.

[0003] As electromagnetic wave shielding materials, in addition to metal materials, many electromagnetic wave shielding technologies using conductive polymers such as carbon black, graphene, and carbon nanotubes, and dielectric oxides have been proposed. Among them, carbon nanotubes made of carbon have attracted attention as promising electromagnetic wave shielding materials. As electromagnetic wave shielding materials using carbon nanotubes, there are paste materials (Patent Document 1) in which carbon nanotubes are dispersed in resin, aqueous paints (Patent Document 2) dispersed in aqueous solutions, etc. However, all of them are difficult to handle, and the electromagnetic wave shielding performance is not sufficient and not at a level that can withstand practical use. Since the carbon nanotubes used are in the form of fine fibers, they have a large specific surface area and cannot be dispersed in a large amount in resin. Therefore, the electromagnetic wave shielding materials using carbon nanotubes also have insufficient electrical conductivity. In addition, there is an electromagnetic wave shielding material (Patent Document 3) using a sheet of carbon nanotubes formed by electrospinning, but it has problems such as weak strength and difficulty in handling. An electromagnetic wave shielding material (Patent Document 4) is 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 and cobalt are added to improve conductivity. However, the protonating agent is a strongly acidic compound and handling is a problem.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object of the present invention is to provide a high-strength electromagnetic wave shielding sheet having excellent electromagnetic wave shielding performance against millimeter waves and terahertz waves.

Means for Solving the Problems

[0006] As a result of intensive research, the inventors of the present invention have found that by impregnating and / or laminating a resin on a highly conductive carbon nanotube nonwoven fabric with a thickness of 1 mm or less, an air permeability of 0.5 cm 3 / cm 2 ·s or less, and a specific resistance of 0.005 Ω·cm or less, an excellent electromagnetic wave shielding performance can be obtained, and the present invention has been completed. That is, the present invention provides the following electromagnetic wave shielding sheet.

[0007] [1] An electromagnetic wave shielding sheet obtained by impregnating a carbon nanotube nonwoven fabric with a thickness of 1 mm or less, an air permeability of 0.5 cm 3 / cm 2 ·s or less, and a specific resistance of 0.005 Ω·cm or less with a resin. [2] The electromagnetic wave shielding sheet according to [1], which contains an inorganic material in the gaps between the fibers of the carbon nanotube nonwoven fabric. [3] The electromagnetic wave shielding sheet according to [1] or [2], wherein the impregnated resin is uncured. [4] The electromagnetic wave shielding sheet according to [1] or [2], wherein the impregnated resin is cured. [5] The electromagnetic wave shielding sheet according to any one of [1] to [4], wherein the impregnated resin is a thermoplastic resin. [6] The electromagnetic wave shielding sheet according to any one of [1] to [5], wherein the impregnation amount of the impregnated resin is 10 to 200 parts by mass with respect to 100 parts by mass of the carbon nanotube nonwoven fabric. [7] The electromagnetic wave shielding sheet according to any one of [1] to [6], wherein the carbon nanotube nonwoven fabric is treated with a coupling agent. [8] The electromagnetic wave shielding sheet according to any one of [1] to [4], wherein the impregnated resin is a thermosetting resin. [9] The electromagnetic shielding sheet according to [8], wherein the thermosetting resin is at least one selected from the group consisting of epoxy resin, allylated epoxy resin, allylated polyphenylene ether resin, maleimide resin, bismaleimide resin, cyanate resin, cyclopentadiene-styrene copolymer resin, silicone resin, bismaleimide resin, phenol resin, and acrylic resin.

[10] The electromagnetic shielding sheet according to [5], wherein the thermoplastic resin is at least one selected from the group consisting of polyethylene, polypropylene, polyphenylene ether, polyether ether ketone, polyether ketone, polyether sulfone, and fluororesin.

[11] The electromagnetic shielding sheet according to [2], wherein the inorganic material is at least one selected from the group consisting of carbon black, carbon nanotube, silica, zinc oxide, alumina, boron nitride, aluminum nitride, carbon short fiber, and alumina short fiber.

[12] The electromagnetic shielding sheet according to [2], wherein the inorganic material is copper, iron, silver, or gold, or resin particles surface-coated with these metals. [Advantages of the Invention]

[0008] The electromagnetic shielding sheet of the present invention is a high-strength electromagnetic shielding sheet, cured or uncured, obtained by impregnating and / or laminating a resin on a carbon nanotube nonwoven fabric having a thickness of 1 mm or less, an air permeability of 0.5 cm 3 / cm 2 ·s or less, and a specific resistance of 0.005 Ω·cm or less, and excellent electromagnetic shielding performance can be obtained. Therefore, the electromagnetic shielding sheet of the present invention is useful for applications such as high-speed large-capacity communication compatible devices and in-vehicle applications. [Embodiments for Carrying Out the Invention]

[0009] Hereinafter, the present invention will be described in detail.

[0010] <Carbon nanotube nonwoven fabric> The thickness of the carbon nanotube nonwoven fabric used in the present invention is 1 mm or less, the diameter is 50 nm or less, and it is a single-layer to multi-layer carbon nanotube fiber in which carbon nanotube fibers with a length of 2 mm or less are intertwined. This nonwoven fabric has 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, and is highly conductive. The carbon nanotube nonwoven fabric is made by intertwining carbon nanotube fibers spun in a plasma furnace using methane gas or carbon nanotube fibers spun from pores by dissolving carbon nanotubes.

[0011] The air permeability can be adjusted by intertwining carbon nanotubes, adjusting the thickness, and pressing the carbon nanotube nonwoven fabric. In the present invention, the air permeability refers to the value of the air permeability of the cross using a Frazier-type tester measured according to JIS R 3420. The carbon nanotube nonwoven fabric with an air permeability of 0.5 cm 3 / cm 2 ·s or less, preferably 0.1 cm 3 / cm 2 ·s or less, more preferably 0.05 cm 3 / cm 2 ·s or less has good electrical conductivity and excellent electromagnetic wave shielding performance in a wide range of frequencies (10 kHz to 100 GHz). However, since the strength of the carbon nanotube nonwoven fabric itself is insufficient, it is easily torn, and since it has no adhesiveness to the substrate, it is difficult to use as it is. In order to solve these problems, the present invention relates to a B-stage electromagnetic wave shielding sheet in which a carbon nanotube nonwoven fabric is impregnated and / or laminated with a resin and semi-cured, or a cured and strong electromagnetic wave shielding sheet. The resin impregnated and / or laminated on the carbon nanotube nonwoven fabric is preferably the following thermosetting resin and / or thermoplastic resin.

[0012] <Thermosetting resin> Examples of the thermosetting resin used in the present invention include epoxy resins, allylated epoxy resins, allylated polyphenylene ether resins, maleimide resins, bismaleimide resins, cyanate resins, cyclopentadiene-styrene copolymer resins, silicone resins, phenol resins, acrylic resins, and the like. Among them, the bismaleimide resins represented by the following general formula (1) and general formula (2) are preferable because they are excellent in heat resistance, low elasticity, toughness, and adhesiveness.

[0013] The bismaleimide resin represented by general formula (1)

Chemical formula

[0014] The bismaleimide resin represented by general formula (2)

Chemical formula

[0015] Here, the dimer acid is a liquid dibasic acid mainly composed of a dicarboxylic acid having 36 carbon atoms, which is produced by dimerization of an unsaturated fatty acid having 18 carbon atoms using natural products such as vegetable oils as raw materials. The dimer acid skeleton is not a single skeleton but has a plurality of structures, and there are several isomers. Representative dimer acids are classified by names such as linear type (a), monocyclic type (b), aromatic ring type (c), and polycyclic type (d). In this specification, the dimer acid skeleton refers to a group derived from a dimerdiamine having a structure in which the carboxy group of such a dimer acid is substituted with a primary aminomethyl group. That is, the bismaleimide resin represented by the general formula (1) or (2) preferably has, as the dimer acid skeleton, a group in which two carboxy groups in each of the dimer acids represented by the following (a) to (d) are substituted with a methylene group. In addition, from the viewpoints of the heat resistance and reliability of the cured product, the hydrocarbon group derived from the dimer acid skeleton in the maleimide compound preferably has a structure in which the carbon-carbon double bond in the hydrocarbon group derived from the dimer acid skeleton is reduced by a hydrogenation reaction. Generally, dimer acid may contain a trimer (trimer acid) due to using natural products such as vegetable oils as raw materials. However, it is preferable that the proportion of the hydrocarbon group derived from the dimer acid among the hydrocarbon groups derived from the dimer acid and the trimer acid is, for example, 95% by mass or more, because the dielectric properties are excellent, the viscosity during heating is likely to decrease, the moldability is excellent, and the influence of moisture absorption tends to be small. In this specification, the dimer acid (trimer acid) skeleton refers to a group derived from a dimerdiamine (trimertriamine) having a structure in which the carboxy group of such a dimer acid (trimer acid) is substituted with a primary aminomethyl group.

Chemical formula

[0016] Typical bismaleimide resins include the SLK-2000 series (manufactured by Shin-Etsu Chemical Co., Ltd.), SLK-6895 (manufactured by Shin-Etsu Chemical Co., Ltd.), SLK-3000 (manufactured by Shin-Etsu Chemical Co., Ltd.), and the like. Also, a thermosetting cyclopentadiene-styrene copolymer resin can be used as a high heat resistance resin. The thermosetting resins may be used alone or in combination of two or more. Further, the bismaleimide resin represented by the general formula (1) and (2) may be used by mixing the above thermosetting resin or the following thermoplastic resin.

[0017] <Reaction initiator> A reaction initiator can be added to the bismaleimide resin to initiate and accelerate the crosslinking reaction of the maleimide compound and the reaction with a reactive group capable of reacting with the maleimide group. The reaction initiator is not particularly limited as long as it promotes the crosslinking reaction, and examples include ionic catalysts such as imidazoles, organic phosphorus 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, when the reaction group of the thermosetting resin having a reactive group capable of reacting with the maleimide group other than the bismaleimide resin promotes the reaction of the bismaleimide resin alone or is a group having a carbon-carbon double bond such as a maleimide group, an alkenyl group, and a (meth)acrylic group, organic peroxides and radical polymerization initiators are preferred. Examples of the organic peroxide include dicumyl peroxide, t-butyl peroxybenzoate, t-amyl peroxybenzoate, dibenzoyl peroxide, diuraroil peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 1,1-di(t-butylperoxy)cyclohexane, di-t-butyl peroxide, and dibenzoyl peroxide. Also, when the reaction group of the thermosetting resin having a reactive group capable of reacting with the maleimide group other than the bismaleimide resin is an epoxy group, a hydroxyl group, or an acid anhydride group, basic compounds such as imidazoles and tertiary amines and organic phosphorus compounds are preferred. Although it is also possible to use imidazole or amines for the homopolymerization of the maleimide group, in the case of imidazole or organic phosphorus compounds, a very high temperature is required, and in the case of amines, the pot life may be very short.

[0018] The reaction initiator is preferably compounded in an amount of 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, based on 100 parts by mass of the bismaleimide resin. When other thermosetting resins are compounded in the composition, it is preferably compounded in the range of 0.05 to 10 parts by mass, particularly 0.1 to 5 parts by mass, based on 100 parts by mass of the total of the bismaleimide resin and other thermosetting resin components. If outside the above range, it is not preferable because the curing may become extremely slow or fast during the molding of the bismaleimide resin composition, and the balance between the heat resistance and moisture resistance of the obtained cured product may also deteriorate. The reaction initiator may be used alone or in combination of two or more.

[0019] <Thermoplastic resin> Typical examples of the thermoplastic resin include polyethylene, polypropylene, polyphenylene ether, polyether ether ketone, polyether ketone, polyether sulfone, fluororesin, etc. Particularly, a thermoplastic resin soluble in a solvent is preferable. The thermoplastic resins may be used alone or in combination of two or more.

[0020] The number average molecular weight (Mn) of the resin is preferably 500 to 100,000, more preferably 800 to 50,000, and still more preferably 1,000 to 10,000. The number average molecular weight (Mn) referred to in this specification means the number average molecular weight based on polystyrene measured by GPC under the following conditions using polystyrene as a standard substance. [GPC measurement conditions] Developing solvent: Tetrahydrofuran (THF) Flow rate: 0.35 mL / min Detector: Differential refractive index detector (RI) Column: TSK Guardcolumn SuperH-L TSKgel SuperHZ4000 (4.6 mm I.D.×15 cm×1) TSKgel SuperHZ3000 (4.6 mm I.D.×15 cm×1) TSKgel SuperHZ2000 (4.6 mm I.D. × 15 cm × 2) (All are manufactured by Tosoh Corporation) Column temperature: 40 °C Sample injection volume: 5 μL (THF solution with a concentration of 0.2 mass%)

[0021] The impregnation amount and lamination amount of the resin with respect to the non-woven fabric are preferably 10 to 200 parts by mass with respect to 100 parts by mass of the carbon nanotube non-woven fabric.

[0022] <Inorganic material> In the electromagnetic shielding sheet of the present invention, by filling the gaps where the carbon nanotube fibers are intertwined with a highly conductive inorganic material, such as inorganic powder, inorganic fiber, or metal particles, the electrical conductivity can be further increased, and the electromagnetic shielding performance in the frequency band of 10 to 300 GHz can be improved. Typical examples of the inorganic powder include carbon black, carbon nanotubes, graphene, graphite, silica, zinc oxide, alumina, boron nitride, aluminum nitride, carbon short fibers, and alumina short fibers. Also, as metal particles, copper, iron, silver, gold, or resin particles surface-coated with these metals can be added. The metal particles and / or inorganic powder may be dispersed in a bismaleimide resin and laminated and / or impregnated on the carbon nanotube non-woven fabric.

[0023] Also, in order to further increase the thermal conductivity of the electromagnetic shielding sheet, inorganic particles and inorganic 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 electromagnetic shielding sheet can be made 50 to 80 W / mK.

[0024] The shape of the inorganic material is not particularly limited, but a shape close to spherical is desirable because it can be easily filled, and an average particle size of 0.5 μm to 30 μm is desirable in terms of heat dissipation and electrical conductivity.

[0025] The method of spraying the inorganic material onto the non-woven fabric can be carried out by any method. For example, a method of packing the inorganic material into the non-woven fabric using a pressing device or a laminator, a method of dispersing the inorganic material in an arbitrary solvent, spraying the dispersion liquid onto the non-woven fabric, and then drying and removing the solvent, or a combination of these methods can be mentioned. As the solvent of the dispersion liquid, any solvent can be used, but a highly volatile solvent is preferred. For example, water, alcohols such as ethanol and IPA, acetone, toluene, hydrocarbon solvents, silicone solvents, etc. can be mentioned. The concentration of the dispersion liquid is preferably 0.1 to 100 parts by mass with respect to 100 parts by mass of the inorganic material.

[0026] The spraying amount of the inorganic material onto the non-woven fabric is preferably 0.01 to 100 parts by mass with respect to 100 parts by mass of the carbon nanotube non-woven fabric.

[0027] <Method for manufacturing electromagnetic shielding sheet> The electromagnetic shielding sheet of the present invention can be manufactured by any method. However, a wet method in which a bismaleimide resin is dissolved in a solvent (volatile) to reduce its viscosity and then impregnated into a carbon nanotube non-woven fabric, a melt rolling method in which the resin is heated to reduce its viscosity and then impregnated into a carbon nanotube non-woven fabric, a transfer method in which a bismaleimide resin varnish is formed into a film by a coater or the like and then transferred and impregnated onto a carbon nanotube non-woven fabric by pressing or a laminator can be mentioned. In any case, a carbon nanotube non-woven fabric impregnated in any way is produced, and then, if necessary, a resin film is pressure laminated to produce a semi-cured B-stage or cured electromagnetic shielding sheet.

[0028] In the wet method, after impregnating the resin, the solvent is removed to produce an electromagnetic shielding sheet impregnated with the resin. If the solvent remains in the electromagnetic shielding sheet, there are problems such as adverse effects during molding and deterioration of work efficiency. Therefore, the amount of the solvent remaining in the electromagnetic shielding sheet is 1% by mass or less, preferably 0.5% by mass or less. As a method for removing the solvent, although it depends on the boiling point of the solvent used, heat treatment at 80 to 150 °C for about 10 minutes to 1 hour is preferable, and the removal of the solvent can be easily achieved by this heat treatment.

[0029] In the melt rolling method, there is no particular need for a step of removing the solvent, and it is advantageous in various aspects such as relatively good working efficiency. In the melt rolling method, the carbon nanotube nonwoven fabric is widened to a required width with a bar or the like, and after sandwiching the resin (thermosetting resin and / or thermoplastic resin) formed into a film from above and below with release paper, it is nipped with several pairs of heating metal rolls installed at substantially the same height with respect to the traveling direction of the carbon nanotube nonwoven fabric, so that the carbon nanotube nonwoven fabric can be impregnated with the thermosetting resin and / or thermoplastic resin to produce an electromagnetic shielding sheet. In the melt rolling method, since the nip pressure is a linear pressure, it is preferable to increase the number of nip rolls in order to obtain sufficient impregnability. Further, pressure molding may be performed with a molding press such as a pressure multi-stage press that can be heated without using a heating metal roll.

[0030] In the transfer method, a resin varnish is coated on a base film, the solvent is dried to obtain a resin film, and then both sides of the carbon nanotube nonwoven fabric are sandwiched with the resin film and pressure-bonded with a laminator or a press to transfer and impregnate the resin film into the carbon nanotube nonwoven fabric. Any film can be used as the base film, but a resin film that is easy to peel off, such as a PET film, a PE film, a PP film, a Teflon film, or an Afflex film, is preferable. The surface of the above base film can be subjected to various surface treatments such as corona treatment, plasma treatment, or silicone treatment as required. Any solvent can be used as the solvent used in the resin varnish, but a highly volatile solvent is preferred, and examples thereof include alcohols such as ethanol and IPA, acetone, toluene, xylene, anisole, hydrocarbon solvents, and silicone solvents. The concentration of the resin varnish is preferably 0.1 to 200 parts by mass with respect to 100 parts by mass of the resin. As a method of coating a resin varnish on a base film, any method can be used, but it is preferable to use a spin coater or a bar coater because it is easy to use. As the temperature for drying the resin film on the base film, a temperature at which the thermosetting resin does not react is preferable, and a temperature of 30°C to 120°C is preferable. In addition, when sandwiching both sides of the carbon nanotube nonwoven fabric with a resin film and pressing them by a laminator or a press to transfer the resin film to the carbon nanotube nonwoven fabric, pressurization and heating can be performed as necessary.

[0031] As the electromagnetic wave shielding sheet of the carbon nanotube nonwoven fabric using a thermosetting resin, an electromagnetic wave shielding sheet in which the resin is completely cured and an electromagnetic wave shielding sheet in a semi-cured state can be manufactured. By selecting the chemical structure, impregnation amount, lamination amount, and curing method of the thermosetting resin, the cured electromagnetic wave shielding sheet can be made into an electromagnetic wave shielding sheet that is hard and tough or flexible and can follow the shape. The electromagnetic wave shielding sheet in a semi-cured state can be adhered to the housing or container by pressure-bonding the electromagnetic wave shielding sheet according to the shape of the container containing the housing or communication equipment by pressurization and heat pressing. Since the electromagnetic wave shielding sheet of the present invention can be freely manufactured in a sheet size from a small area to a large area, there is no limit to the area for electromagnetic wave shielding. Even when a thermoplastic resin is used, an electromagnetic wave shielding sheet can be produced in the same manner as when a thermosetting resin is used.

[0032] In the present invention, when impregnating the carbon nanotube nonwoven fabric with a resin, by surface-treating the surface of the carbon nanotube nonwoven fabric with a coupling agent, the carbon nanotube nonwoven fabric and the resin are adhered to each other, and the durability of the electromagnetic wave shielding sheet can be improved. As the coupling agent, alkoxide compounds such as silane coupling agents, titanium, and aluminum can also be used. Among them, silane coupling agents are preferred, and preferred silane coupling agents include, for example, compounds represented by the general formula Y-Si-X3. Here, Y is an organic group having a functional group such as an amino group, an epoxy group, a hydroxyl group, a carboxyl group, a vinyl group, a methacryl group, a mercapto group, etc., and X is a hydrolyzable functional group such as an alkoxy group. Specific examples of the compound represented by the general formula Y-Si-X3 include, for example, γ-glycidoxypropyltrimethoxysilane, vinyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-aminobenzyltriethoxysilane, γ-aminophenyltriethoxysilane, etc.

[0033] The appropriate amount of such a coupling agent to be used is in the range of 0.5 to 20 parts by mass with respect to 100 parts by mass of the bismaleimide resin. The electromagnetic wave shielding sheet of the present invention has electromagnetic wave shielding characteristics of 50 dB or more, preferably 60 dB or more, in the frequency band of 10 to 300 GHz.

[0034] This electromagnetic wave shielding sheet may be laminated on the upper and lower surfaces of the electromagnetic wave shielding sheet using a thermoplastic film such as polyester as a protective film to form a laminate.

Examples

[0035] Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples. In the examples, "parts" means "parts by mass". Each material used in the examples and comparative examples is shown below. Also, the physical property values and characteristic values in the present invention were measured by the following methods.

[0036] (1) Specific resistance The specific resistance was calculated by the following formula. Specific resistance (Ω·cm) = Surface resistivity (Ω / sq) × Thickness (cm) The surface resistivity was measured using Loresta-GX MCP-T700 (low resistance resistivity meter, manufactured by Nitto Seiko Analytic Co., Ltd.) and Hi-Rester-UX MCP-HT800 (high resistance resistivity meter, manufactured by Nitto Seiko Analytic Co., Ltd.). The specific resistance was calculated using the measured values.

[0037] (2) Electromagnetic shielding characteristics The electromagnetic shielding characteristics (SE) are defined by the following formula. A larger SE value indicates a higher shielding effect.

Equation

[0038] The value obtained from the above calculation formula at 100 GHz and the qualitative judgment of the value were performed according to the following criteria. SE of 50 dB or more: ○ SE less than 50 dB: ×

[0039] (3) Tensile strength The tensile strength of the electromagnetic shielding sheets produced in the examples and comparative examples was measured in accordance with the measurement method: "6.3 Tensile strength and elongation" of JIS L1913:2010 "General test methods for nonwovens".

[0040] 1. Carbon nanotube nonwoven fabric (1) CNTM30 manufactured by Tortech Thickness 62 μm, air permeability 0.01 cm 3 / cm 2 ·s, specific resistance 1.46E-03 (Ω·cm) (2) CNTM10 manufactured by Tortech Thickness 40 μm, air permeability 0.04 cm 3 / cm 2 ·s, specific resistance 2.44E-03 (Ω·cm) (3) Carbon nanotubes (for comparative example) Thickness 40 μm, air permeability 0.7 cm 3 / cm2 · s, specific resistance 8.32E-03 (Ω·cm)

[0041] 2. Inorganic materials (1) Carbon nanotube powder; manufactured by ZEONANO TECHNOLOGY Co., Ltd. (ZEONANO SG101, average particle size 100 μm) (2) Carbon black powder; manufactured by Denka Co., Ltd. (Denka Black, average particle size 35 μm) (3) Silver particles; manufactured by Fukuda Metal Foil & Powder Co., Ltd. (AgC-HWQ, average particle size 1.5 μm)

[0042] <Thermosetting resin · Thermoplastic resin> (1) Bismaleimide resin · (A-1): Linear alkylene group-containing bismaleimide resin represented by the following formula (SLK-3000, manufactured by Shin-Etsu Chemical Co., Ltd., number average molecular weight 5200)

Chemical formula

Chemical formula

Examples

[0043] 100 parts by mass of the bismaleimide resin (A-1) (SLK-3000, manufactured by Shin-Etsu Chemical Co., Ltd.) represented by the above formula (1) and 1 part by mass of a curing catalyst (dicumyl peroxide (trade name: "Perkyl D"), manufactured by NOF Corporation) were used to prepare a resin film with a thickness of 30 μm. Both sides of the carbon nanotube nonwoven fabric CNTM30 with a thickness of 62 μm and an air permeability of 0.01 cm 3 / cm 2 ·s were laminated with the above resin film at 80°C for 1 minute, and then pressed at 150°C for 15 minutes for impregnation to prepare a semi-cured solid sheet. Thereafter, it was heated at 150°C for 4 hours to produce Electromagnetic Wave Shielding Sheet 1. The shielding characteristics and mechanical strength of Electromagnetic Wave Shielding Sheet 1 are shown in Table 1.

Example

[0044] Instead of the CNT nonwoven fabric CNTM30 in Example 1, Electromagnetic Wave Shielding Sheet 2 was produced in the same manner as in Example 1 except that CNTM10 with a thickness of 40 μm and an air permeability of 0.04 cm 3 / cm 2 ·s was used. The shielding characteristics and mechanical strength of Electromagnetic Wave Shielding Sheet 2 are shown in Table 1.

Example

[0045] On the surface of CNTM30 used in Example 1, a 5 mass% carbon nanotube powder ethanol dispersion (ZEONANO SG101, manufactured by ZEON NANO TECHNOLOGY Co., Ltd.) as a conductive powder was spray-sprayed on both sides, and the solvent was dried at 100°C for 10 minutes. Then, it was laminated with a resin film in the same manner as in Example 1, and then pressed at 150°C for 15 minutes for impregnation to prepare a semi-cured solid sheet. Thereafter, it was heat-cured at 150°C for 4 hours to produce Electromagnetic Wave Shielding Sheet 3. The shielding characteristics and mechanical strength of Electromagnetic Wave Shielding Sheet 3 are shown in Table 1.

Example

[0046] Similar to Example 3, a 5 mass% carbon black ethanol dispersion (Denka Black, manufactured by Denka Co., Ltd.) as the conductive powder was spray-coated on both sides, and after drying the solvent at 100 °C for 10 minutes, it was laminated with a resin film, and then pressed at 150 °C for 15 minutes for impregnation to prepare a semi-cured solid sheet. Thereafter, it was heat-cured at 150 °C for 4 hours to produce an electromagnetic wave shielding sheet 4. The shielding characteristics and mechanical strength of the electromagnetic wave shielding sheet 4 are shown in Table 1.

Example

[0047] Similar to Example 3, a 10 mass% silver particle toluene dispersion (AgC-HWQ, manufactured by Fukuda Metal Foil Powder Industry Co., Ltd., average particle size 1.5 μm) as the conductive powder was spray-coated on both sides, and after drying the solvent at 100 °C for 10 minutes, it was laminated with a resin film, and then pressed at 150 °C for 15 minutes for impregnation to prepare a semi-cured solid sheet. Thereafter, it was heat-cured at 150 °C for 4 hours to produce an electromagnetic wave shielding sheet 5. The shielding characteristics and mechanical strength of the electromagnetic wave shielding sheet 5 are shown in Table 1.

Example

[0048] To 100 parts by mass of a bismaleimide resin composition containing 100 parts by mass of the bismaleimide resin (A-2) (SLK-6895, manufactured by Shin-Etsu Chemical Co., Ltd.) represented by the above formula 2 and 1 part by mass of a curing catalyst (dicumyl peroxide; trade name "Perk Mill D", manufactured by NOF Corporation), 5 parts by mass of carbon nanotube powder (ZEONANO SG101, manufactured by ZEON NanoTech Co., Ltd.) was added, and it was mixed at 2000 rpm for 5 minutes using a planetary mixer. Using the obtained mixture, it was formed into a resin film with a thickness of 30 μm by a bar coater and dried by heating at 100 °C for 10 minutes. Hereinafter, in the same manner as in Example 1, a semi-cured solid sheet using a carbon nanotube nonwoven fabric CNTM30 was prepared and heat-cured to produce an electromagnetic wave shielding sheet 6. The shielding characteristics and mechanical strength of the electromagnetic wave shielding sheet 6 are shown in Table 1.

Example

[0049] Instead of the bismaleimide resin (A-1) of Example 1, an electromagnetic wave shielding sheet 7 was produced in the same manner as in Example 1 using a silicone resin (A-3). The shielding properties and mechanical strength of the electromagnetic wave shielding sheet 7 are shown in Table 1.

Examples

[0050] A fluororesin (A-4) was molded into a resin film with a thickness of 30 μm by pressing at 200°C. Both sides of the carbon nanotube nonwoven fabric CNTM30 were sandwiched between the above fluororesin films and crimped by pressing at 200°C for 30 minutes to produce an electromagnetic wave shielding sheet 8. The shielding properties and mechanical strength of the electromagnetic wave shielding sheet 8 are shown in Table 1. Comparative Example 1

[0051] In the same manner as in Example 1, a resin film with a thickness of 30 μm composed of the bismaleimide resin composition of Example 1 was prepared. Using this resin film, both sides of a carbon nanosheet with a thickness of 40 μm and an air permeability of 0.7 cm 3 / cm 2 ·s and a specific resistance of 8.32E-03 (Ω·cm) were laminated at 80°C for 1 minute, and then pressed at 150°C for 15 minutes to prepare a semi-cured solid sheet. Then, it was heated at 150°C for 4 hours to produce an electromagnetic wave shielding sheet 9. The shielding properties and mechanical strength of the electromagnetic wave shielding sheet 9 are shown in Table 2. Comparative Example 2

[0052] The carbon nanotube nonwoven fabric CNTM30 alone was used as the electromagnetic wave shielding sheet 10. The shielding properties and mechanical strength of the electromagnetic wave shielding sheet 10 are shown in Table 2. Comparative Example 3

[0053] The carbon nanotube nonwoven fabric CNTM10 alone was used as the electromagnetic wave shielding sheet 11. The shielding properties and mechanical strength of the electromagnetic wave shielding sheet 11 are shown in Table 2. Comparative Examples 4 to 6

[0054] The bismaleimide resin film, silicone resin film, and fluororesin film with a thickness of 30 μm used in Example 1, Example 7, and Example 8 were used as the electromagnetic wave shielding sheets 12 to 14, respectively. The shielding properties and mechanical strength of the electromagnetic wave shielding sheets 12 to 14 are shown in Table 2. Comparative Example 7

[0055] The carbon nanotube powder-containing bismaleimide resin film with a thickness of 30 μm used in Example 6 alone was used as the electromagnetic shielding sheet 15. Table 2 shows the shielding characteristics and mechanical strength of the electromagnetic shielding sheet 15.

[0056]

Table 1

[0057]

Table 2

[0058] From Examples 1 to 2, 7 to 8 and Comparative Examples 2 to 7, the electromagnetic shielding sheet combining the organic resin and the carbon nanotube nonwoven fabric has improved tensile strength without degrading the electromagnetic shielding characteristics, resulting in a highly reliable electromagnetic shielding sheet. From Example 1 and Comparative Example 1, the electromagnetic shielding sheet made of an organic resin and a carbon nanotube nonwoven fabric with an air permeability within a predetermined range has excellent tensile strength and high electromagnetic shielding performance. From Examples 3 to 6 and Comparative Example 7, the electromagnetic shielding sheet combining the organic resin, the inorganic powder, the metal particles and the carbon nanotube nonwoven fabric has excellent tensile strength compared to the electromagnetic shielding sheet made of the organic resin, the inorganic powder and the metal particles without the carbon nanotube nonwoven fabric, and has high electromagnetic shielding performance.

[0059] As described above, the electromagnetic shielding sheet in which the carbon nanotube nonwoven fabric with a thickness of 1 mm or less, an air permeability of 0.5 cm 3 / cm 2 ·s or less, and a specific resistance of 0.005 Ω·cm or less is impregnated with a resin, and in particular, by containing an inorganic material (inorganic powder and / or metal particles) in the gaps between the carbon nanotube fibers, it has excellent electromagnetic shielding performance against millimeter waves and terahertz waves.

Claims

1. An electromagnetic wave shielding sheet obtained by impregnating a carbon nanotube nonwoven fabric having a thickness of 1 mm or less, an air permeability of 0.5 cm 3 / cm 2 ·s or less, and a specific resistance of 0.005 Ω·cm or less with a resin.

2. The electromagnetic wave shielding sheet according to claim 1, containing an inorganic material in the gaps between the fibers of the carbon nanotube nonwoven fabric.

3. The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the impregnated resin is uncured.

4. The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the impregnated resin is cured.

5. The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the impregnated resin is a thermoplastic resin.

6. The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the impregnation amount of the impregnated resin is 10 to 200 parts by mass with respect to 100 parts by mass of the carbon nanotube nonwoven fabric.

7. The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the carbon nanotube nonwoven fabric is treated with a coupling agent.

8. The electromagnetic wave shielding sheet according to claim 1 or 2, wherein the impregnated resin is a thermosetting resin.

9. The electromagnetic wave shielding sheet according to claim 8, wherein the thermosetting resin is one or more selected from the group consisting of epoxy resin, allylated epoxy resin, allylated polyphenylene ether resin, maleimide resin, bismaleimide resin, cyanate resin, cyclopentadiene·styrene copolymer resin, silicone resin, bismaleimide resin, phenol resin, and acrylic resin.

10. The electromagnetic shielding sheet according to claim 5, wherein the thermoplastic resin is one or more selected from the group consisting of polyethylene, polypropylene, polyphenylene ether, polyether ether ketone, polyether ketone, polyether sulfone, and fluororesin.

11. The electromagnetic shielding sheet according to claim 2, wherein the inorganic material is one or more selected from the group consisting of carbon black, carbon nanotube, silica, zinc oxide, alumina, boron nitride, aluminum nitride, carbon short fiber, and alumina short fiber.

12. The electromagnetic shielding sheet according to claim 2, wherein the inorganic material is copper, iron, silver, or gold, or resin particles surface-coated with these metals.

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