Electromagnetic wave shield forming material and electromagnetic wave shield

Abstract

To provide a new electromagnetic wave shielding body forming material and an electromagnetic wave shielding body which are lightweight and excellent in moldability.SOLUTION: An electromagnetic shield forming material comprising carbon nanotubes and at least one matrix selected from the group consisting of resins, elastomers and rubbers, wherein when the electromagnetic shield forming material is injection-molded or press-molded to form a molded body having a thickness of 2mm, the molded body has an absorptivity of 45% or more for electromagnetic waves having a frequency of 26. 5GHz to 110GHz. The electromagnetic wave shield is obtained by molding the electromagnetic wave shield forming material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave shielding material containing carbon nanotubes and an electromagnetic wave shielding material using the same. [Background technology]

[0002] In recent years, the frequency bands of electromagnetic waves used in communication devices, radar, etc. have been increasing at an accelerating rate. In such an electromagnetic environment, electromagnetic shielding is used to suppress malfunctions caused by electromagnetic interference between devices or between circuits inside devices.

[0003] Conventionally, electromagnetic wave shields have been made by compounding electromagnetic wave loss materials such as soft magnetic metal materials and carbon materials with rubber or resin, and molding them into sheets or the like.

[0004] For example, Patent Document 1 describes that electromagnetic waves of 1 GHz to 10 GHz can be absorbed by combining a soft magnetic metal flake powder, a Y-type hexagonal ferrite powder, and a resin. Patent Document 2 describes that an absorber made of expandable graphite and an ethylene vinyl acetate copolymer resin has good electromagnetic wave absorption properties in the range of 0.3 to 3 GHz.

[0005] In recent years, the use of carbon nanotubes as an electromagnetic wave shield has also been considered (see Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-009797 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-022937 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-118073 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, expectations have been rising for fifth-generation mobile communication systems (5G) to achieve higher capacity and faster communications than the conventional fourth-generation mobile communication systems (4G). 5G primarily uses frequency bands above 28 GHz. This has led to an increasing need for electromagnetic wave shielding to maintain a safe radio wave environment and prevent malfunctions in high-frequency bands.

[0008] However, electromagnetic wave shielding materials using soft magnetic metal materials have extremely low electromagnetic wave absorption properties for electromagnetic waves above 28 GHz, the frequency used by 5G, in accordance with Snoke's limit law. Furthermore, because soft magnetic metal materials have a high specific gravity, electromagnetic wave shielding materials using soft magnetic metal materials are heavy, which hinders efforts to reduce the weight of electromagnetic wave shielding materials. Furthermore, when using soft magnetic metal materials to create electromagnetic wave absorbers for high frequencies, a large amount of absorbing material must be added due to the low absorption properties, which increases the weight and reduces moldability.

[0009] Carbon materials have also been considered as materials for electromagnetic wave shielding, but they have not yet achieved sufficient absorption performance for electromagnetic waves in the high frequency band.

[0010] Furthermore, Patent Document 3 exemplifies the return loss of a sheet with a thickness of 1000 μm or less, but only for a frequency of 20 GHz. The electromagnetic wave absorption performance of a composite material is strongly dependent on the shape and dispersibility of the absorber, and it is necessary to verify its absorption performance in the millimeter wave band at higher frequencies.

[0011] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a novel material for forming an electromagnetic wave shield, which is lightweight and has excellent moldability, and an electromagnetic wave shield. [Means for solving the problem]

[0012] The present invention provides the following:

[0013] <1> Carbon nanotubes and At least one base material selected from resin, elastomer, and rubber; An electromagnetic wave shielding material comprising: The electromagnetic wave shielding material, when injection-molded or press-molded to form a molded body having a thickness of 2 mm, has an absorption rate of 45% or more for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz. <2> The molded body has a return loss of −2 dB or less for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz. <1> The electromagnetic wave shielding material according to claim 1. <3> The average absorption rate of the above molded body for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz is 50% or more. <1> or <2> The electromagnetic wave shielding material according to claim 1. <4> The surface resistivity of the above molded body is 2×10 4 Ω / sq. or more, <1> ~ <3> 10. The electromagnetic wave shielding material according to claim 9, wherein the first and second electromagnetic wave shielding materials are fused together. <5> The carbon nanotubes in the electromagnetic wave shielding material have an average bundle diameter of 0.5 μm or less. <1> ~ <4> 10. The electromagnetic wave shielding material according to claim 9, wherein the first and second electromagnetic wave shielding materials are fused together. <6> The specific gravity of the electromagnetic wave shielding material is 2.2 or less. <1> ~ <5> 10. The electromagnetic wave shielding material according to claim 9, wherein the first and second electromagnetic wave shielding materials are fused together. <7> <1> ~ <6> 1. An electromagnetic wave shielding body obtained by molding the material for forming an electromagnetic wave shielding body according to any one of 1 to 8, wherein the electromagnetic wave shielding body has an absorption rate of 45% or more for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz. <8> The return loss of electromagnetic waves with frequencies between 26.5 GHz and 110 GHz is -2 dB or less. <7> The electromagnetic wave shielding body according to claim 1. <9> The average absorption rate of electromagnetic waves with frequencies between 26.5GHz and 110GHz is 50% or more. <7> or <8> The electromagnetic wave shielding body according to claim 1. [Effects of the Invention]

[0014] The present invention can provide a novel material for forming an electromagnetic wave shield and an electromagnetic wave shield that are lightweight and have excellent moldability. DETAILED DESCRIPTION OF THE INVENTION

[0015] In this specification, a numerical range expressed using the symbol "to" means a range that includes the numerical values ​​before and after "to" as the lower limit and upper limit, respectively.

[0016] <Electromagnetic shielding material> The electromagnetic wave shielding material of the present invention comprises: An electromagnetic wave shielding material comprising carbon nanotubes and at least one base material selected from a resin, an elastomer, and a rubber, When the electromagnetic wave shielding material is injection molded or press molded to form a molded body having a thickness of 2 mm, the molded body has an absorption rate of 45% or more for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz.

[0017] The material for forming an electromagnetic wave shield of the present invention is lightweight and has excellent moldability, and by using this material for forming an electromagnetic wave shield, it is possible to produce an electromagnetic wave shield that has excellent absorption properties for electromagnetic waves in the high frequency band.

[0018] The molded article preferably has an absorption rate of 50% or more for electromagnetic waves with frequencies of 26.5 GHz to 110 GHz. The average absorption rate of the molded article for electromagnetic waves with frequencies of 26.5 GHz to 110 GHz is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more.

[0019] The return loss of the molded article with respect to electromagnetic waves having a frequency of 26.5 GHz to 110 GHz is preferably -2 dB or less, more preferably -3 dB or less, and even more preferably -4 dB or less. The smaller the return loss value, the smaller the reflection coefficient of the molded article. There is no particular lower limit for the return loss, but it can be -12 dB or more.

[0020] The transmission attenuation of the above-mentioned molded article for electromagnetic waves having frequencies of 26.5 GHz to 110 GHz is preferably −3 dB or less, more preferably −4 dB or less, and even more preferably −5 dB or less. The smaller the transmission attenuation value, the higher the electromagnetic wave shielding ability of the molded article.

[0021] The surface resistivity of the above molded body is 2×10 4 Ω / sq. or more is preferable, and 1×10 5 Ω / sq. or more is more preferable, and it is 1×10 6 It is more preferable that the resistance is 2×10 Ω / sq. or more. 6 It is particularly preferable that the resistance is Ω / sq. or more.

[0022] The electromagnetic wave absorption rate, reflection attenuation, transmission attenuation and surface resistivity of the molded article were measured in the atmosphere at a temperature of 25°C.

[0023] In addition, when a molded article can be produced from the electromagnetic wave shielding material of the present invention only by either injection molding or press molding, or when it is difficult to produce a molded article by either method, the electromagnetic wave absorption rate, etc., are measured using a molded article molded by a method that allows the molding. For example, since it is often difficult to produce a molded article by injection molding from an electromagnetic wave shielding material using rubber as the base material, the electromagnetic wave absorption rate, etc., are measured using a molded article obtained by press molding for the electromagnetic wave shielding material using rubber as the base material. In addition, when a molded article can be produced from the electromagnetic wave shielding material of the present invention by either injection molding or press molding, the electromagnetic wave absorption rate, etc., are measured using a molded article obtained by injection molding. For example, when a resin or elastomer is used as the base material, it is often possible to produce a molded article by either injection molding or press molding. In such cases, the electromagnetic wave absorption rate, etc., are measured using a molded article obtained by injection molding.

[0024] The specific gravity of the material for forming an electromagnetic wave shield of the present invention is preferably 2.2 or less, more preferably 2.0 or less, and even more preferably 1.8 or less.

[0025] (carbon nanotubes) The electromagnetic wave shielding material of the present invention contains carbon nanotubes. Here, carbon nanotubes are substances in which graphene sheets are arranged in a single-layer or multi-layer tubular shape. In this specification, carbon nanotubes also include horn-shaped materials called carbon nanohorns.

[0026] The carbon nanotubes may be single-walled or multi-walled. From the viewpoints of various performances such as mechanical properties, electrical conductivity, and heat transfer, as well as material costs, the carbon nanotubes are preferably single-walled to 20-walled carbon nanotubes, more preferably single-walled to 15-walled carbon nanotubes, and even more preferably single-walled to 10-walled carbon nanotubes. Furthermore, both ends of the carbon nanotube may be open, or one or both ends may be closed.

[0027] The average diameter of the carbon nanotubes is preferably 0.03 to 200 nm. The lower limit of the average diameter is preferably 1 nm or more, more preferably 3 nm or more, and even more preferably 5 nm or more. The upper limit of the average diameter is preferably 150 nm or less, more preferably 100 nm or less, and even more preferably 50 nm or less.

[0028] The average length of the carbon nanotubes is preferably 0.0005 to 5 mm. The lower limit of the average length is preferably 0.0006 mm or more, more preferably 0.0008 mm or more, and even more preferably 0.001 mm or more. The upper limit is preferably 4 mm or less, more preferably 3 mm or less, and even more preferably 2 mm or less.

[0029] The average aspect ratio of the carbon nanotubes is preferably 50 to 500,000. When the average aspect ratio of the carbon nanotubes is within this range, an electromagnetic wave shielding material with excellent absorption properties for high-frequency electromagnetic waves can be produced. While the detailed reasons for this effect are unclear, it is presumed to be due to the following: It is presumed that incorporating carbon nanotubes with a high aspect ratio into the electromagnetic wave shielding material allows the formation of a three-dimensional network structure of carbon nanotubes in the electromagnetic wave shielding material. The formation of such a three-dimensional network structure is presumed to result in an increased probability of electromagnetic waves entering the electromagnetic wave shielding material colliding with the carbon nanotubes, resulting in conductive loss, and furthermore, dielectric loss due to capacitance between the dispersed carbon nanotubes, resulting in efficient absorption of electromagnetic waves. The lower limit of the average aspect ratio is preferably 100 or more, more preferably 150 or more, even more preferably 200 or more, even more preferably 1,000 or more, and particularly preferably 10,000 or more. The upper limit of the average aspect ratio is preferably 450,000 or less, more preferably 400,000 or less, and even more preferably 300,000 or less. In this specification, the average aspect ratio of carbon nanotubes refers to the ratio of the average length to the average diameter of carbon nanotubes (average length / average diameter).

[0030] In this specification, the average diameter of carbon nanotubes is a value calculated by measuring the diameters (outer diameters) of 30 randomly selected carbon nanotubes using a scanning electron microscope or a transmission electron microscope and calculating the average value thereof, and the average length of carbon nanotubes is a value calculated by measuring the lengths of 30 randomly selected carbon nanotubes using a scanning electron microscope or a transmission electron microscope and calculating the average value thereof.

[0031] The specific surface area of ​​carbon nanotubes is 100 to 800 m 2 The lower limit of the specific surface area is preferably 150 m 2 / g or more, and 200m 2 / g or more is more preferable. The upper limit of the specific surface area is 550 m 2 / g or less, and 2 / g or more is more preferable. In this specification, the specific surface area of ​​the carbon nanotubes is a value of the BET specific surface area measured by the gas adsorption method (multipoint method) based on JIS Z8830 (ISO 9277).

[0032] Carbon nanotubes can be produced by known methods such as an arc method, a laser ablation method, a chemical vapor deposition method (CVD method), etc. Carbon nanotubes can also be produced by the method described in paragraphs 0029 to 0038 of JP 2020-180251 A.

[0033] The carbon nanotubes may be modified with an oxidation treatment or polysaccharide to introduce acidic groups onto the surface, such as carboxyl groups.

[0034] The oxidized carbon nanotubes are not particularly limited, and examples thereof include carbon nanotubes oxidized by methods such as gas-phase oxidation by heating with air, oxidation by electrochemical treatment, and oxidation using an oxidizing agent. Examples of oxidizing agents include ozone; persulfates such as potassium persulfate and sodium persulfate; hypohalites such as sodium hypochlorite and potassium hypochlorite; acids such as persulfuric acid, nitric acid, sulfuric acid, and hypochlorous acid; and hydrogen peroxide. The ozone used as an oxidizing agent can be supplied in the form of gaseous ozone, liquid ozone, or ozone dissolved in an aqueous solvent such as water. The ozone-containing gas can optionally be diluted with gases such as oxygen, air, nitrogen, rare gases, and mixtures thereof. Conventional or commercially available ozone generators can be used to generate ozone or ozone-containing gases. To generate ozone or ozone-containing gases, gases such as air or pure oxygen can be supplied to the ozone generator.

[0035] Oxidized carbon nanotubes can be obtained by heating carbon nanotubes in an oxygen-containing atmosphere. Oxidized carbon nanotubes can also be obtained by mixing carbon nanotubes with an alkali metal hydroxide, heating the mixture in an oxygen-containing atmosphere, and then removing the alkali metal by washing with water. Oxidized carbon nanotubes can also be obtained by subjecting carbon nanotubes to plasma treatment, corona discharge treatment, glow discharge treatment, or oxygen bubbling treatment in water.

[0036] The content of acidic groups on oxidized carbon nanotubes can be measured, for example, by the Boehm method (H.P. Boehm, E. Diehl, W. Heck, and R. Sappok, "Surface Oxides of Carbon," Angew. Chem. Inlernat. Edit. Vol. 3 (1964) No. 10, pp. 669-677). The Boehm method involves adding various alkalis to a sample to cause a reaction, and then back-titrating the alkali concentration after the reaction with an acid to quantify the amount of acidic functional groups present on the surface of the sample.

[0037] The polysaccharide used for surface modification of carbon nanotubes is preferably an acidic polysaccharide, such as carboxymethyl cellulose, carrageenan, pectin, gum arabic, xanthan gum, gellan gum, agar, and tragacanth gum, with carboxymethyl cellulose being preferred because it can further improve the dispersibility of carbon nanotubes in the dispersion.

[0038] In the electromagnetic wave shielding material of the present invention, the carbon nanotubes are preferably contained in the form of a masterbatch supported on a polymeric carrier material. Carbon nanotubes are bulky and prone to aggregation. However, by using the carbon nanotubes in the form of a masterbatch supported on a polymeric carrier material, aggregation of the carbon nanotubes can be suppressed during the production of the electromagnetic wave shielding material, resulting in an electromagnetic wave shielding material with excellent carbon nanotube dispersibility. Furthermore, an electromagnetic wave shielding material with excellent carbon nanotube dispersibility can be obtained without performing excessive dispersion treatment during the production of the electromagnetic wave shielding material. This prevents the carbon nanotubes from being severed by mechanical shearing, allowing the carbon nanotubes to maintain a high aspect ratio. Furthermore, the dispersibility of the carbon nanotubes in the electromagnetic wave shielding material can be increased, resulting in increased dielectric loss in the high frequency band, allowing the production of an electromagnetic wave shield with excellent absorption characteristics in the high frequency band.

[0039] The content of carbon nanotubes in the masterbatch is preferably 0.05 to 30% by mass, more preferably 0.1 to 25% by mass, and even more preferably 0.5 to 20% by mass.

[0040] Masterbatches are a step of preparing a mixed solution by mixing a carbon nanotube dispersion liquid containing carbon nanotubes and a solvent with a carrier polymer material-containing solution containing a carrier polymer material and a solvent (mixed solution preparation step); a step of solidifying the mixture to prepare a solidified product containing the carbon nanotubes and the carrier polymer material (solidification step); Each step will be explained below.

[0041] In the mixed solution preparation step, a carbon nanotube dispersion liquid and a solution containing a carrier polymer material are mixed to prepare a mixed solution.

[0042] First, the carbon nanotube dispersion liquid will be described. Examples of the carbon nanotubes contained in the carbon nanotube dispersion liquid include those mentioned above.

[0043] Examples of the solvent contained in the carbon nanotube dispersion include water, methanol, ethanol, normal propanol, isopropanol, tert-butyl alcohol, tetrahydrofuran, acetone, acetonitrile, etc., and water is preferred. Water has a high relative dielectric constant, and using water as a solvent also improves the dispersibility of carbon nanotubes in the dispersion.

[0044] The carbon nanotube dispersion preferably contains an anionic dispersant. Examples of the anionic group include a carboxy group, a sulfo group, a phospho group, and salts thereof. The carboxy group, the sulfo group, and the phospho group may have dissociated hydrogen atoms. Examples of atoms or atomic groups constituting the salt include metal ions such as alkali metal ions, alkaline earth metal ions, ammonium ions, onium ions of organic amines, copper ions, silver ions, aluminum ions, and tin ions. Specific examples of the anionic dispersant include carboxymethylcellulose, carrageenan, pectin, gum arabic, xanthan gum, gellan gum, agar, tragacanth gum, and salts thereof; anion-modified polyvinyl alcohol; and anion-modified polyacrylamide. The anionic dispersant is preferably carboxymethylcellulose or a salt thereof. The weight-average molecular weight of the anionic dispersant is preferably 1,000 to 20,000,000. The upper limit of the weight average molecular weight is preferably 15,000,000 or less, and more preferably 10,000,000 or less.The lower limit of the weight average molecular weight is preferably 10,000 or more, more preferably 50,000 or more, and even more preferably 100,000 or more.

[0045] The carbon nanotube dispersion may further contain a surfactant and a filler (carbon black, graphene, silica, talc, nanoclay, etc.).

[0046] The pH of the carbon nanotube dispersion is preferably 6 to 11, and more preferably 7 to 11. When the pH of the carbon nanotube dispersion is within the above range, the dispersibility of the carbon nanotubes is good. In this specification, the pH value is the value at 25°C.

[0047] The solid content concentration of the carbon nanotube dispersion is preferably 0.01 to 15% by mass, more preferably 0.05 to 10% by mass, and even more preferably 0.08 to 8% by mass. If the solid content concentration of the carbon nanotube dispersion is within the above range, the coagulated body can be obtained more efficiently. Furthermore, the dispersibility of the carbon nanotubes in the carbon nanotube dispersion is also good. Furthermore, the content of the carbon nanotubes in the carbon nanotube dispersion is preferably 0.01 to 10% by mass, more preferably 0.05 to 8% by mass, and even more preferably 0.1 to 5% by mass.

[0048] Next, the carrier polymer material-containing solution will be described. The carrier polymer material contained in the carrier polymer material-containing solution is not particularly limited, and examples thereof include resins, elastomers, and rubbers. The resin may be a thermoplastic resin or a thermosetting resin. Examples of the resin include known materials, such as polyester resins, polyether resins, polyolefin resins (polyethylene resins, polypropylene resins, etc.), polystyrene resins, polyamide resins, polycarbonate resins, acrylic resins, polyvinyl chloride resins, polyphenylene sulfide resins, polyphenylene ether resins, polytetrafluoroethylene resins, polyimide resins, polyamide-imide resins, polyether-imide resins, polysulfone resins, polyether sulfone resins, polyketone resins, polyether ketone resins, polyether ether ketone resins, polyarylate resins, polyether nitrile resins, phenolic resins, phenoxy resins, fluororesins, urea resins, melamine resins, benzoguanamine resins, alkyd resins, epoxy resins, silicone resins, urethane resins, furan resins, and xylene resins. Examples of elastomers include known materials, such as polystyrene elastomers, polyolefin elastomers, polyurethane elastomers, polyester elastomers, polyamide elastomers, polybutadiene elastomers, polyisoprene elastomers, fluorine-based elastomers, and silicone elastomers. Examples of rubbers include known materials, such as natural rubber (NR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), nitrile rubber, hydrogenated nitrile rubber, polyisoprene rubber (IR), butadiene rubber (BR), butyl rubber (IIR), chloroprene rubber (CR), acrylic rubber (ACM), and fluororubber (FKM, PTFE). The weight-average molecular weight of the carrier polymer material is preferably 5,000 to 15,000,000, more preferably 8,000 to 13,000,000, and even more preferably 10,000 to 10,000,000. In this specification, the weight average molecular weight of the carrier polymer material means the weight average molecular weight measured by gel permeation chromatography (GPC) in terms of polystyrene.

[0049] Examples of the solution containing the carrier polymer material include latex, emulsion, and resin particle dispersion.

[0050] The latex or emulsion used as the carrier polymer material-containing solution can be prepared, for example, by using a reaction solution obtained by synthesizing a carrier polymer material such as a resin, elastomer, or rubber by emulsion polymerization in the presence of an emulsifier, either as is or after appropriate dilution or by adding an emulsifier. Alternatively, the latex or emulsion can be prepared by subjecting a reaction solution obtained by synthesizing a carrier polymer material such as a resin, elastomer, or rubber by solution polymerization to phase inversion in the presence of an emulsifier into an aqueous system.

[0051] The resin particle dispersion liquid used as the carrier polymer material-containing solution can be prepared by dispersing resin particles in a solvent in the presence of a surfactant or a dispersant.

[0052] Examples of the solvent contained in the carrier polymer material-containing solution include water, methanol, ethanol, normal propanol, isopropanol, tert-butyl alcohol, tetrahydrofuran, acetone, and acetonitrile, with water being preferred.

[0053] The solution containing the carrier polymer material may further contain a surfactant and a filler (carbon black, graphene, silica, talc, nanoclay, etc.).

[0054] The pH of the carrier polymer material-containing solution is preferably 6-11, and more preferably 7-11.

[0055] The solids concentration of the carrier polymer material-containing solution is preferably 0.5 to 70% by mass, more preferably 1 to 65% by mass, and even more preferably 2 to 60% by mass. If the solids concentration of the carrier polymer material-containing solution is within the above range, a coagulated body can be obtained more efficiently. Furthermore, the content of the carrier polymer material in the carrier polymer material-containing solution is preferably 0.5 to 60% by mass, and even more preferably 1 to 50% by mass.

[0056] The pH of the mixture obtained in the mixture preparation step is preferably 6 to 11, and more preferably 7 to 11.

[0057] The solids concentration of the mixture obtained in the mixture preparation step is preferably 0.5 to 15 mass%, more preferably 1 to 10 mass%, and even more preferably 2 to 8 mass%. The ratio of carbon nanotubes to carrier polymer material in the mixture is preferably 200 to 9900 mass parts, more preferably 250 to 9800 mass parts, and even more preferably 300 to 9700 mass parts of carrier polymer material per 100 mass parts of carbon nanotubes.

[0058] The coagulation step can be carried out by adding an acid or a salt to the mixture obtained in the mixture preparation step.

[0059] Examples of acids include formic acid, sulfuric acid, hydrochloric acid, acetic acid, etc. Examples of salts include monovalent to trivalent metal salts such as calcium salts such as sodium chloride, magnesium chloride, calcium nitrate, calcium chloride, etc. Among these, calcium chloride is preferred.

[0060] In the coagulation step, it is preferable to add an acid or a salt to the mixed solution and then add the cationic polymer to the mixed solution, or to add the cationic polymer to the mixed solution and then add the acid or salt to the mixed solution. It is particularly preferable to add the cationic polymer to the mixed solution and then add the acid or salt to the mixed solution. By linking the carbon nanotubes and the carrier polymer material with the cationic polymer and then adding the acid or salt, a coagulated body can be obtained more efficiently.

[0061] Examples of cationic polymers include polymers having cationic groups. Examples of cationic groups include amino groups, ammonium groups, imino groups, and salts thereof. Examples of atoms or atomic groups that constitute salts include hydroxide ions, halogen ions, carboxylate ions, sulfonate ions, fluoride ions, cyanide ions, silicate ions, borate ions, and condensed phosphate ions. The amino group given as an example of the cationic group is not limited to -NH2, but also includes substituted amino groups and cyclic amino groups. Examples of substituted amino groups include monoalkylamino groups, dialkylamino groups, monoarylamino groups, diarylamino groups, and alkylarylamino groups. Examples of the cyclic amino group include a pyrrolidine group, a piperidine group, a piperazine group, a morpholine group, a pyrrole group, a pyrazole group, an imidazole group, a pyridine group, a pyridazine group, a pyrimidine group, a pyrazine group, an oxazole group, an isoxazole group, a thiazole group, an isothiazole group, a pyrrolidone group, a piperidone group, a 3-morpholinone group, and a morpholinedione group.

[0062] The cationic polymer may be a block polymer or a random polymer. Examples of the cationic polymer include a polymer having a repeating unit derived from allylamine such as polyallylamine, a condensation polymer of epichlorohydrin with at least one selected from ammonia and an amine compound, a Hoffmann-modified polyacrylamide obtained by Hoffmann-modifying polyacrylamide, and a cation-modified polyvinyl alcohol. Among these, a polymer having a repeating unit derived from allylamine and a condensation polymer of epichlorohydrin with at least one selected from ammonia and an amine compound are preferred.

[0063] It is also preferable to use a polymer having an oxazoline group as the cationic polymer. According to this embodiment, it is possible to produce a masterbatch in which the carbon nanotubes and the carrier polymer material are firmly bonded together.

[0064] The polymer having an oxazoline group may be a polymer having a repeating unit derived from a 2-oxazoline monomer and a repeating unit derived from a nitrogen-containing heterocyclic monomer. In the polymer having an oxazoline group, the content of the repeating unit derived from the 2-oxazoline monomer is preferably 1 to 90 mol %, and the content of the repeating unit derived from the nitrogen-containing heterocyclic monomer is preferably 10 to 99 mol %.

[0065] Examples of 2-oxazoline monomers include 2-vinyl-2-oxazoline, 4-methyl-2-vinyl-2-oxazoline, 5-methyl-2-vinyl-2-oxazoline, 4-ethyl-2-vinyl-2-oxazoline, 5-ethyl-2-vinyl-2-oxazoline, 4,4-dimethyl-2-vinyl-2-oxazoline, 4,4-diethyl-2-vinyl-2-oxazoline, 4,5-dimethyl-2-vinyl-2-oxazoline, 4,5-diethyl-2-vinyl-2-oxazoline, and 2-isopropenyl-2-oxazoline. Examples of oxazoline include 4-methyl-2-isopropenyl-2-oxazoline, 5-methyl-2-isopropenyl-2-oxazoline, 4-ethyl-2-isopropenyl-2-oxazoline, 5-ethyl-2-isopropenyl-2-oxazoline, 4,4-dimethyl-2-isopropenyl-2-oxazoline, 4,4-diethyl-2-isopropenyl-2-oxazoline, 4,5-dimethyl-2-isopropenyl-2-oxazoline and 4,5-diethyl-2-isopropenyl-2-oxazoline. Examples of the nitrogen-containing heterocyclic monomer include N-vinylpyrrolidone, N-methylvinylpyrrolidone, N-vinylpyridine, N-vinylpiperidone, N-vinylpyrimidine, N-vinylpiperazine, N-vinylpyrazine, N-vinylpyrrole, N-vinylimidazole, N-vinyloxazole, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylmorpholine, N-vinylmorpholine, N-vinylpiperidone, N-vinyl-3-morpholinone, N-vinylcaprolactam, N-vinyl-1,3-oxazin-2-one, N-vinyl-3,5-morpholinedione, N-vinylpyrazole, N-vinylisoxazole, N-vinylthiazole, N-vinylisothiazole, and N-vinylpyridazine.

[0066] The polymer having an oxazoline group may further contain a repeating unit derived from a vinyl monomer such as a (meth)acrylate having an alkyl group having 1 to 12 carbon atoms, an N-alkyl(meth)acrylamide having an alkyl group having 1 to 12 carbon atoms, an N,N-dialkyl(meth)acrylamide having the same or different two alkyl groups having 1 to 12 carbon atoms, a (meth)acrylate or (meth)acrylamide having an aromatic substituent, a hydroxyalkyl (C1-12) (meth)acrylate or (meth)acrylamide, (meth)acrylonitrile, or (meth)acrylic acid.

[0067] The weight average molecular weight of the cationic polymer is preferably 500 to 2,500,000, more preferably 600 to 2,000,000, and even more preferably 700 to 1,500,000.

[0068] In addition, as a preferred embodiment of the cationic polymer, it is preferable to use at least one selected from cationic polymer cp1 having a weight-average molecular weight of 500 to 10,000 and cationic polymer cp2 having a weight-average molecular weight of 500,000 to 2,500,000. Among these, it is more preferable to use cationic polymer cp1 because the particle size of the aggregated particles produced by the cationic polymer becomes smaller. It is also preferable to use cationic polymer cp1 and cationic polymer cp2 in combination. When cationic polymer cp1 and cationic polymer cp2 are used in combination, the effect of easily controlling the size of the aggregated particles and the aggregation rate is obtained. When cationic polymer cp1 and cationic polymer cp2 are used in combination, the ratio of cationic polymer cp2 to 100 parts by mass of cationic polymer cp1 is preferably 0.5 to 15 parts by mass, more preferably 1 to 10 parts by mass.

[0069] The weight average molecular weight of the cationic polymer cp1 is preferably 500 to 9,000, more preferably 600 to 8,500, and even more preferably 700 to 8,000.

[0070] The weight average molecular weight of the cationic polymer cp2 is preferably 550,000 to 2,500,000, more preferably 600,000 to 2,000,000, and even more preferably 700,000 to 1,500,000.

[0071] In this specification, the weight average molecular weight of the cationic polymer means the weight average molecular weight in terms of polyethylene glycol measured by gel permeation chromatography (GPC).

[0072] Commercially available cationic polymers include the PAA series (polyallylamine) available from Nittobo Medical Co., Ltd., and the Unisense series available from Senka Corporation (for example, Unisense FCA1000L, Unisense FCA1001L, Unisense FCA5000L (each an aqueous solution of a copolymer of acrylamide and diallyldimethylammonium chloride); Unisense FPA100L, Unisense FPA101L, Unisense FPA102L, Unisense FPA1000L, Unisense FPA1001L, Unisense FPA1002L (each an aqueous solution of poly(diallyldimethylammonium chloride)); Unisense KHF10P (dicyandiamide-formalin condensate); Unisense KHP10L, Unisense KHP10P (each an aqueous solution of dicyandiamide-diallyldimethylammonium chloride)). ethylenetriamine condensate); Unisense KHE100L, Unisense KHE101L, Unisense KHE102L, Unisense KHE105L, Unisense KHE1000L, Unisense KHE1001L (all aqueous solutions of condensation product of dimethylamine, ammonia and epichlorohydrin); Unisense KHE104L (aqueous solution of condensation product of dimethylamine and epichlorohydrin); Unisense FPV1000L (aqueous solution of poly(trimethylaminoethyl methacrylate-methyl sulfate)); Unisense ZCA100L (aqueous solution of acrylate-acrylamide-diallylamine hydrochloride copolymer), etc.), the DiaCatch series available from Mitsubishi Chemical Corporation, and Epocross WS-300 (oxazoline group-containing polymer) available from Nippon Shokubai Co., Ltd.

[0073] The amount of cationic polymer added is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 8 parts by mass, and even more preferably 0.1 to 5 parts by mass, relative to 100 parts by mass of solids in the mixed liquid containing the carbon nanotube dispersion and the carrier polymer material-containing solution. If the amount of cationic polymer added is within the above range, a coagulated body can be obtained efficiently.

[0074] After the coagulation step, the resulting aggregated mass is separated, washed with water, dehydrated, and dried at about 80 to 110°C to obtain a masterbatch. Various drying devices, such as a single-screw extruder, oven, vacuum dryer, and air dryer, can be used for the drying process. Drying may be performed under normal pressure, but is preferably performed under reduced pressure (about 10 to 1000 Pa). The drying time varies depending on the size of the dryer used, but is typically about 30 to 180 minutes under reduced pressure. The drying temperature is typically about 50 to 150°C.

[0075] In the electromagnetic wave shielding material, carbon nanotubes exist in a bundle state called a bundle. The average bundle diameter of the carbon nanotubes in the electromagnetic wave shielding material is preferably 1.5 μm or less, more preferably 1.0 μm or less, even more preferably 0.5 μm or less, even more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less. The bundle diameter of carbon nanotubes refers to the diameter of a bundle of carbon nanotubes. In this specification, the average bundle diameter of carbon nanotubes in the electromagnetic wave shielding material is calculated by press-molding a 1 mm thick molded body using the electromagnetic wave shielding material, cutting the molded body, measuring the diameters (outer diameters) of 50 randomly selected carbon nanotubes from the cross section using a scanning electron microscope, and calculating the average value.

[0076] The content of carbon nanotubes in the material for forming the electromagnetic wave shield is preferably 0.1 to 1.5% by mass. The lower limit is preferably 0.2% by mass or more, more preferably 0.4% by mass or more. The upper limit is preferably 1.4% by mass or less, more preferably 1.2% by mass or less. If the carbon nanotube content is too high, electromagnetic waves incident on the electromagnetic wave shield tend to be more easily reflected near the surface of the electromagnetic wave shield, making it difficult for the electromagnetic waves to be absorbed into the electromagnetic wave shield. When the carbon nanotube content is within the above range, a three-dimensional network structure of carbon nanotubes is easily formed in the electromagnetic wave shield. The formation of such a three-dimensional network structure in the electromagnetic wave shield allows for efficient absorption of electromagnetic waves due to conductive loss caused by an increased probability of electromagnetic waves incident on the electromagnetic wave shield colliding with the carbon nanotubes, and dielectric loss due to capacitance between the carbon nanotubes, resulting in an electromagnetic wave shield with excellent absorption properties for electromagnetic waves in the high-frequency band.

[0077] (base material) The electromagnetic wave shielding material of the present invention includes at least one base material selected from resins, elastomers, and rubbers. The resin may be a thermoplastic resin or a thermosetting resin. Examples of the resin include known materials such as polyester resins, polyether resins, polyolefin resins (such as polyethylene resins and polypropylene resins), polystyrene resins, polyamide resins, polycarbonate resins, acrylic resins, polyvinyl chloride resins, polyphenylene sulfide resins, polyphenylene ether resins, polytetrafluoroethylene resins, polyimide resins, polyamideimide resins, polyetherimide resins, polysulfone resins, polyethersulfone resins, polyketone resins, polyetherketone resins, polyetheretherketone resins, polyarylate resins, polyethernitrile resins, phenolic resins, phenoxy resins, fluororesins, urea resins, melamine resins, benzoguanamine resins, alkyd resins, epoxy resins, silicone resins, urethane resins, furan resins, and xylene resins. Examples of elastomers include known materials, such as polystyrene elastomers, polyolefin elastomers, polyurethane elastomers, polyester elastomers, polyamide elastomers, polybutadiene elastomers, polyisoprene elastomers, fluorine-based elastomers, silicone elastomers, etc. Examples of rubbers include known materials, such as natural rubber (NR), styrene butadiene rubber (SBR), acrylonitrile butadiene rubber (NBR), nitrile rubber, hydrogenated nitrile rubber, polyisoprene rubber (IR), butadiene rubber (BR), butyl rubber (IIR), chloroprene rubber (CR), acrylic rubber (ACM), fluororubber (FKM, PTFE), etc.

[0078] The base material is preferably a resin. The resin is preferably a polyolefin resin, more preferably a polypropylene resin. According to this embodiment, an electromagnetic wave shielding body having excellent absorption properties for electromagnetic waves in the high frequency band can be produced.

[0079] When the carbon nanotubes are used in the form of a masterbatch, the type of the base material may be the same as or different from the carrier polymer material of the masterbatch.

[0080] The content of the base material in the electromagnetic wave shielding material is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit is preferably 99.9% by mass or less, more preferably 99.8% by mass or less, and even more preferably 99.6% by mass or less. Furthermore, when carbon nanotubes are used in the form of a masterbatch, the total content of the base material and the carrier polymer material contained in the masterbatch in the electromagnetic wave shielding material is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. The upper limit is preferably 99.9% by mass or less, more preferably 99.8% by mass or less, and even more preferably 99.6% by mass or less.

[0081] (Other additives) The electromagnetic wave shielding material of the present invention may further contain additives as needed, such as antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, crosslinking agents, pigments, colorants, foaming agents, antistatic agents, flame retardants, lubricants, softeners, tackifiers, plasticizers, release agents, deodorizers, and fragrances.

[0082] The content of the additive in the electromagnetic wave shielding material is preferably 0.01 to 30% by mass. The lower limit is preferably 0.05% by mass or more, and more preferably 0.1% by mass or more. The upper limit is preferably 25% by mass or less, and more preferably 20% by mass or less.

[0083] <Electromagnetic shielding material> The electromagnetic wave shield of the present invention is an electromagnetic wave shield obtained by molding the electromagnetic wave shield-forming material of the present invention described above, and is characterized by having an absorption rate of 45% or more of electromagnetic waves at frequencies from 26.5 GHz to 110 GHz.

[0084] The method for molding the electromagnetic wave shielding material is not particularly limited, and known methods can be used, such as injection molding, press molding, blow molding, vacuum molding, and compression molding.

[0085] The electromagnetic wave shield preferably has an absorption rate of 50% or more for electromagnetic waves with frequencies of 26.5 GHz to 110 GHz. The average absorption rate of the electromagnetic wave shield for electromagnetic waves with frequencies of 26.5 GHz to 110 GHz is preferably 50% or more, more preferably 55% or more, and even more preferably 60% or more.

[0086] The return loss of the electromagnetic wave shielding material for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz is preferably −2 dB or less, more preferably −3 dB or less, and even more preferably −4 dB or less. There is no particular lower limit, but it can be −12 dB or more.

[0087] The transmission attenuation of the electromagnetic wave shield for electromagnetic waves with frequencies of 26.5 GHz to 110 GHz is preferably −3 dB or less, more preferably −4 dB or less, and even more preferably −5 dB or less.

[0088] The surface resistivity of the electromagnetic wave shield is 2 x 10 4 Ω / sq. or more is preferable, and 1×10 5 Ω / sq. or more is preferable, and 1×10 6 It is more preferable that the resistance is 2×10 Ω / sq. or more. 6 It is particularly preferable that the resistance is Ω / sq. or more.

[0089] The electromagnetic wave absorption rate, return loss and surface resistivity of the electromagnetic wave shielding material are values ​​measured in the atmosphere at a temperature of 25°C.

[0090] The average bundle diameter of the carbon nanotubes in the electromagnetic wave shield is preferably 1.5 μm or less, more preferably 1.0 μm or less, even more preferably 0.5 μm or less, even more preferably 0.3 μm or less, and particularly preferably 0.1 μm or less.

[0091] The electromagnetic wave shield of the present invention can be used to counter radiation noise from electronic devices such as communication devices, computers, home appliances, automotive electrical equipment, and medical electrical equipment, as well as to counter radio wave reflection in ETC (Electronic Toll Collection Systems) and radar. [Example]

[0092] The present invention will be explained in more detail below with reference to examples. The materials, amounts used, ratios, processing details, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[0093] <Manufacturing of carbon nanotubes> (Production Example 1-1) A support film was formed on one surface of a silicon substrate by sputtering using an aluminum target, and then a catalyst film was formed on the support film by sputtering using an iron target.

[0094] Next, the substrate with the catalyst film formed thereon was placed upright in the reaction vessel of the CVD apparatus. Next, the reaction vessel was closed, and the pressure was reduced to 1 Pa while simultaneously energizing the heater to start heating inside the reaction vessel. Next, when the temperature inside the reaction vessel approached 700°C, nitrogen gas was supplied into the reaction vessel, and the reaction vessel was continuously evacuated with a pump so that the pressure inside the reaction vessel could be maintained at 90 kPa.

[0095] Next, the inside of the reaction vessel was heated to 750°C, and both nitrogen gas and hydrogen gas were supplied into the reaction vessel, maintaining the pressure inside the reaction vessel at 30 kPa. After the temperature inside the reaction vessel reached 750°C, nitrogen gas, hydrogen gas, and acetylene gas were supplied along the surface of the catalyst film from the upper end to the lower end of the substrate inside the reaction vessel while preheating with the heater. While maintaining the pressure inside the reaction vessel at 30 kPa, carbon nanotubes were synthesized on the substrate, with a length of 0.1 to 2 mm, an average length of 2.0 mm, a number of walls of 3 to 8, an average number of walls of 6, a diameter of 5 to 12 nm, an average diameter of 9 nm, and a specific surface area of ​​225 m. 2 Straight carbon nanotubes with almost no waviness were obtained, with a G / D ratio of 0.8 and a metal impurity content of 250 ppm.

[0096] The length of the carbon nanotubes was evaluated from SEM images taken with a scanning electron microscope (JEOL Ltd., model JSM-7800F) either on the substrate or after the carbon nanotubes were cut from the substrate. The average length of the carbon nanotubes was determined by randomly selecting 30 carbon nanotubes from the SEM image and calculating the average length of the 30 carbon nanotubes.

[0097] The number of walls and diameter of carbon nanotubes were evaluated from TEM images taken with a transmission electron microscope (Hitachi High-Tech Corporation, Model: HF2200) on the substrate or after carbon nanotubes were cut from the substrate. The average number of walls of carbon nanotubes was determined by randomly selecting 30 fields from the TEM image where the number of walls of the carbon nanotubes could be determined, and rounding off the decimal point of the average number of walls of the 30 carbon nanotubes. The average diameter of carbon nanotubes was determined by randomly selecting 30 fields from the TEM image, and rounding off the decimal point of the average diameter of the 30 carbon nanotubes.

[0098] The specific surface area (BET value) of the carbon nanotubes was measured by a gas adsorption method (multipoint method) using a specific surface area measuring device (Shimadzu Corporation, model: 3Flex) based on JIS Z8830 (ISO 9277).

[0099] The G / D ratio of the carbon nanotubes was determined using a Raman microscope (manufactured by Renishaw, model: inVia). Specifically, the G-band (1590 cm ) of the Raman spectrum measured using the Raman microscope was measured. -1 ) peak intensity of the D-band (1350 cm -1 ) was divided by the peak intensity to obtain the value.

[0100] <Production of carbon nanotube dispersion liquid> (Production Example 2-1) 120 g of carboxymethyl cellulose (product name Cellogen WS-C, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was dissolved in 5,880 g of ion-exchanged water to prepare 6 kg of CMC solution. 120 g of the carbon nanotubes obtained in Production Example 1-1 and 23.8 kg of ion-exchanged water were added to the CMC solution and stirred, and then treated with a cutter mixer (Robocoupe R-10E, manufactured by FMI) at 3,000 rpm for 10 minutes to produce carbon nanotube dispersion 1.

[0101] (Production Example 2-2) Carbon nanotube dispersion liquid 1 was passed through a high-pressure homogenizer (Starburst Lab HJP-25003, manufactured by Sugino Machine Co., Ltd.) once at a pressure of 150 MPa to produce carbon nanotube dispersion liquid 2.

[0102] <Masterbatch manufacturing> (Production Example 3-1) A mixed solution was prepared by adding 8352 g of polypropylene emulsion (trade name: Arrowbase YA-6010, manufactured by Unitika Ltd., solid content concentration: 25% by mass, pH 9.93) to 30 kg of carbon nanotube dispersion 1. 3600 g of a 2% by mass solution of cationic polymer (trade name: Diacatch CHP295, manufactured by Mitsubishi Chemical Corporation, weight average molecular weight: 702,000) was added to this mixed solution and stirred. 20% formic acid solution was further added until the mixed solution solidified. The resulting solid was filtered through a mesh with 149 μm openings and collected. The solid was dehydrated and then dried at 110°C to produce masterbatch 1 (carbon nanotube content: 5% by mass).

[0103] (Production Example 3-2) Masterbatch 2 (carbon nanotube content: 5% by mass) was produced in the same manner as in Production Example 3-1, except that Carbon Nanotube Dispersion 2 was used instead of Carbon Nanotube Dispersion 1.

[0104] (Production Example 3-3) A mixed liquid was prepared by adding 655 g of acrylonitrile butadiene rubber (NBR) latex (product name Nipol LX531B, manufactured by Zeon Corporation, solid content concentration 66 mass%, pH 11) to 6 kg of carbon nanotube dispersion liquid 2. Next, a 20% formic acid solution was added to the mixed liquid until the mixed liquid solidified. The obtained solid was filtered through a mesh with a mesh opening of 149 μm, and the solid was collected. The solid was dehydrated and then dried at 110°C to produce masterbatch 3 (carbon nanotube content 5 mass%).

[0105] <Production of electromagnetic wave shielding material> (Manufacturing Examples 4-1 to 4-4) The materials for forming an electromagnetic wave shield of Production Examples 4-1 to 4-4 were produced by melt-kneading the raw materials in the blending ratios shown in the following Table 1 using a twin-screw extruder (Omega30H manufactured by STEER). The kneading temperature was 190°C.

[0106] (Manufacturing Examples 4-5 to 4-7) Using a mixer (Labo Plastomill, manufactured by Toyo Seiki Co., Ltd.), the raw materials were kneaded for 5 minutes at the blending ratio shown in the Kneading A column of Table 2 to obtain Kneaded Mixture A, and then using the mixer, the raw materials were kneaded for 3 minutes at the blending ratio shown in the Kneading B column of Table 2 to obtain Kneaded Mixture B. The obtained Kneaded Mixture A and Kneaded Mixture B were kneaded using mixing rolls (manufactured by Nippon Roll Mfg. Co., Ltd.) (gap between rolls: 1 mm) to produce electromagnetic wave shielding body-forming materials (rubber compositions) of Production Examples 4-5 to 4-7.

[0107] In Tables 1 and 2, the content of carbon nanotubes in the electromagnetic wave shielding material is shown in the "CNT concentration" column. The bundle diameter of carbon nanotubes in the electromagnetic wave shielding material is shown in the "CNT bundle diameter" column. The specific gravity of the electromagnetic wave shielding material is shown in the "Specific gravity" column. The specific gravity increase rate of the electromagnetic wave shielding material is shown in the "Specific gravity increase rate" column.

[0108] The bundle diameter of the carbon nanotubes in the electromagnetic wave shielding material was calculated by press-molding a 1 mm thick molded body using the electromagnetic wave shielding material, cutting the molded body, and measuring the diameters (outer diameters) of 50 randomly selected carbon nanotubes on the resulting cross section using a scanning electron microscope, and then calculating the average value. The materials of Production Examples 4-1 to 4-4 were pressed in a hydraulic heating and cooling press (model 1811, Imoto Manufacturing Co., Ltd.) at a set temperature of 200°C, followed by pressing at 20°C to produce molded bodies. The materials of Production Examples 4-5 to 4-7 were pressed in a hydraulic heating and cooling press (model 1811, Imoto Manufacturing Co., Ltd.) at a set temperature of 170°C, followed by pressing at 20°C to produce molded bodies. The specific gravity increase rate of the electromagnetic wave shielding material was calculated using the following formula. Specific gravity increase rate = (specific gravity of electromagnetic wave shielding material / specific gravity of electromagnetic wave shielding material excluding carbon nanotubes) x 100

[0109] [Table 1] [Table 2]

[0110] Details of the materials listed with the abbreviations in Tables 1 and 2 are as follows: MB1: Masterbatch 1 mentioned above MB2: Masterbatch 2 as mentioned above MB3: Masterbatch 3 mentioned above PP: Polypropylene resin (product name: Novatec PP BC03GS, manufactured by Japan Polypropylene Corporation) MAPP: Maleic acid-modified polypropylene resin (product name: Umex 1001, manufactured by Sanyo Chemical Industries, Ltd.) Antioxidant: Adeka Stab AO-60 (product name, manufactured by ADEKA Corporation) NBR: Acrylonitrile butadiene rubber (product name: Nipol DN2850, manufactured by Zeon Corporation) Zinc oxide: "No. 1 zinc oxide" manufactured by Hakusui Chemical Co., Ltd. Processing oil: JX Nippon Oil & Gas Corporation "T-DAE", low-aroma oil Sulfur: Karuizawa Refinery Co., Ltd. Vulcanization accelerator A: 1,3-diphenylguanidine (trade name: Noccela D, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) Vulcanization accelerator B: N-tert-butyl-2-benzothiazolylsulfenamide (trade name: Noccela NS, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.)

[0111] <Production of Molded Body (Electromagnetic Wave Shielding Body)> [Production Examples 5-1 to 5-8] Production of polypropylene molded body The materials for forming an electromagnetic wave shielding body shown in the table below (Production Examples 4-1 to 4-4) were injection molded or press molded to produce plate-shaped molded bodies (electromagnetic wave shielding bodies) with the thickness shown in the table below and dimensions of 15 cm in length and 15 cm in width. The injection molding conditions and press molding conditions were as follows. The surface resistivity of the obtained molded bodies (electromagnetic wave shielding bodies) is also shown.

[0112] (Injection molding conditions) A molded body was produced using an electric injection molding machine (FNX140, manufactured by Nissei Plastic Industrial Co., Ltd.) at a molding temperature of 190°C, a mold temperature of 50°C, and an injection pressure of 30 MPa.

[0113] (Press molding conditions) The mixture was pressed at a set temperature of 170°C using a hydraulic heating and cooling press (model 1811, Imoto Manufacturing Co., Ltd.), and then pressed at 20°C to produce a compact.

[0114] [Production Examples 5-9 to 5-11] Production of NBR molded body The electromagnetic wave shielding material (Production Examples 4-5 to 4-7) shown in the table below was press-molded and vulcanized (170°C, 5 minutes) using a hydraulic molding machine to produce molded bodies (electromagnetic wave shielding bodies) with the thicknesses shown in the table below.

[0115] (Method for measuring surface resistivity) Three square test pieces measuring 100 mm x 100 mm were cut out from the molded body produced in each manufacturing example and used as measurement samples. A probe was pressed against the center of the measurement sample to measure the resistance value (Ω). The resistance values ​​(Ω) of five measurement samples were measured, and the average value was used as the resistance value (Ω) of the molded body. The obtained resistance value (Ω) was then converted into surface resistivity (Ω / sq.) according to the usual method. 4 In the case of high resistance of Ω or more, the resistance value (Ω) was measured at room temperature (25°C) according to JIS K 6911 using a high resistivity meter (manufactured by Mitsubishi Chemical Analytical Co., Ltd., Hiresta (registered trademark) MCP-HT800, probe: URS probe) using the double ring method. 4 In the case of low resistance less than Ω, the resistance value (Ω) was measured at room temperature (25°C) in accordance with JIS K 7194 using a low resistivity meter using the four-point probe method (Loresta (registered trademark) MCP-610T, manufactured by Mitsubishi Chemical Analytical Co., Ltd., probe: ASP probe).

[0116] [Table 3]

[0117] (Measurement of electromagnetic wave absorption rate, reflection loss, and transmission loss) Measurements were made in the atmosphere at room temperature (25°C) using a PNA microwave network analyzer N5227 (Keysight Technologies). The molded body of each manufacturing example was placed in the center of the transmitting antenna and the receiving antenna, and electromagnetic waves were irradiated perpendicularly onto the molded body. The reflected and transmitted waves (reflection coefficient S 11 , the transmission coefficient S 21 ) was measured, and the electromagnetic wave absorption rate, reflection attenuation, and transmission attenuation were measured using the following equations. Absorption rate (%) = (1 - |S 11 | 2 -|S 21 | 2 ) x 100 Return loss (dB) = 20log 10 |S 11 | Transmission attenuation (dB) = 20log 10 |S 21 | S 11 is the reflection coefficient of the molding, and S 21 is the permeability coefficient of the molded body.

[0118] The measurement frequencies were divided into the following categories depending on the antenna used: (1) 26.5 GHz to 45 GHz (Ka band), (2) 45 GHz to 67 GHz (V band), (3) 67 GHz to 75 GHz (V band), and (4) 75 GHz to 110 GHz (W band). The division of each band conformed to IEEE Std. 521-2002.

[0119] [Table 4]

[0120] [Table 5]

[0121] The molded articles of Production Examples 5-1 to 5-3 and 5-5 to 5-10 are molded articles of the Examples. The electromagnetic wave shielding material-forming materials of Production Examples 4-1, 4-3, 4-4, 4-5, and 4-6 used to produce the molded articles of Production Examples 5-1 to 5-3 and 5-5 to 5-10 were lightweight and had excellent moldability. Furthermore, the molded articles of Production Examples 5-1 to 5-3 and 5-5 to 5-10 all had an absorption rate of 45% or more for electromagnetic waves with frequencies of 26.5 GHz to 110 GHz, and were excellent in absorbing properties for electromagnetic waves in the above frequency range. Furthermore, the molded articles of Production Examples 5-1 to 5-3 and 5-5 to 5-10 had a return loss of -2 dB or less for electromagnetic waves at frequencies of 26.5 GHz to 110 GHz, and thus had low reflection of electromagnetic waves at these frequencies. The molded articles of Production Examples 5-1 to 5-3 and 5-5 to 5-10 have excellent absorption properties for electromagnetic waves in the high-frequency band, and by using these molded articles in communication devices and the like, malfunctions due to electromagnetic interference between circuits within the devices can be effectively suppressed.

Claims

1. Carbon nanotubes and At least one base material selected from a resin, an elastomer, and a rubber; An electromagnetic wave shielding material comprising: The electromagnetic wave shielding material, when injection molding or press molding the electromagnetic wave shielding material to form a molded body having a thickness of 2 mm, has an absorption rate of 45% or more of electromagnetic waves having a frequency of 26.5 GHz to 110 GHz of the molded body.

2. 2. The electromagnetic wave shielding material according to claim 1, wherein the molded article has a return loss of −2 dB or less for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz.

3. 3. The electromagnetic wave shielding material according to claim 1, wherein the average absorption rate of the molded body for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz is 50% or more.

4. The surface resistivity of the molded body is 2×10 ４ The electromagnetic wave shielding material according to any one of claims 1 to 3, wherein the resistivity is Ω / sq. or more.

5. 5. The material for forming an electromagnetic wave shield according to claim 1, wherein the carbon nanotubes in the material for forming an electromagnetic wave shield have an average bundle diameter of 0.5 μm or less.

6. The electromagnetic wave shielding material according to any one of claims 1 to 5, wherein the specific gravity of the electromagnetic wave shielding material is 2.2 or less.

7. 7. An electromagnetic wave shield obtained by molding the material for forming an electromagnetic wave shield according to claim 1, wherein the electromagnetic wave shield has an absorption rate of 45% or more for electromagnetic waves having a frequency of 26.5 GHz to 110 GHz.

8. 8. The electromagnetic wave shield according to claim 7, wherein the return loss of electromagnetic waves at frequencies of 26.5 GHz to 110 GHz is −2 dB or less.

9. 9. The electromagnetic wave shield according to claim 7, wherein the average absorption rate of electromagnetic waves having a frequency of 26.5 GHz to 110 GHz is 50% or more.

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