Electromagnetic wave shielding materials

Abstract

The present invention provides an electromagnetic wave blocking material that has excellent electromagnetic wave blocking ability, in particular, excellent electromagnetic wave absorbing ability in a high frequency range of several tens of GHz (in particular, with respect to near millimeter waves and millimeter waves). The present invention pertains to an electromagnetic wave blocking material including a nano wire formed from iron and nickel.

Description

[Technical Field]

[0001] The present invention relates to an electromagnetic wave shielding material that has excellent electromagnetic wave shielding properties, particularly excellent electromagnetic wave absorption properties, in the high frequency range of several tens of GHz. [Background technology]

[0002] In recent years, the use of radio waves in the quasi-millimeter and millimeter wave ranges has been rapidly increasing in fifth-generation mobile communication systems and advanced driver assistance systems. Fifth-generation mobile communication systems use radio waves in frequencies such as n257 (26.50-29.50 GHz), n258 (24.25-27.50 GHz), n259 (39.5-43.50 GHz), n260 (37.00-40.00 GHz), and n261 (27.50-28.35 GHz) for wireless communication. Millimeter-wave radar, which is part of advanced driver assistance systems, senses the area around the vehicle using radio wave beams with frequencies of 24.05-24.25 GHz for 24 GHz narrowband radar systems, 24.25-29.0 GHz for 24 GHz / 26 GHz UWB radar systems, 60.0-61.0 GHz for 60 GHz band millimeter-wave radar systems, 76.0-77.0 GHz for 76 GHz band millimeter-wave radar systems, and 77.0-81.0 GHz for 79 GHz band high-resolution radar systems. These fifth-generation mobile communication systems and the electronic components of millimeter-wave radars in advanced driver assistance systems differ from conventional systems in that they suppress the generation and impact of noise, including radio waves in the quasi-millimeter and millimeter wave ranges, and therefore there is a strong demand for suitable electromagnetic wave shielding materials.

[0003] Traditionally, the electromagnetic compatibility (EMC) of electronic devices has mainly been achieved by covering the device itself with a conductive material such as a metal case. However, with the use of quasi-millimeter and millimeter waves in fifth-generation mobile communication systems and advanced driver assistance systems, as well as the miniaturization and high integration of electronic components, a phenomenon known as intra-EMC (intra-EMC) has become a problem, in which noise generated inside the device reduces the characteristics of electronic components such as semiconductors. To prevent intra-EMC, materials that absorb radio waves are desired, rather than conventional conductive materials.

[0004] Metamaterial radio wave absorbers are known as electromagnetic wave shielding materials (radio wave absorbers) that absorb quasi-millimeter and millimeter wave bands, but their absorbing frequency band is extremely narrow, less than 0.1 GHz, making them unsuitable for systems that perform high-capacity wireless communication over a wide band, such as fifth-generation mobile communication systems and millimeter-wave radars in advanced driver assistance systems. Furthermore, cited reference 1 discloses an electromagnetic wave shielding material that uses nickel nanowires. However, the electromagnetic wave shielding material in cited reference 1 has insufficient shielding performance, and there are problems with its ability to absorb radio waves in particular. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-165996 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides an electromagnetic wave shielding material that has excellent electromagnetic wave shielding properties, particularly excellent electromagnetic wave absorption properties, in the high frequency range of several tens of GHz (particularly in the quasi-millimeter wave range and millimeter wave range). [Means for solving the problem]

[0007] The present inventors have discovered that a material containing nanowires composed of iron and nickel can achieve the above object, and have arrived at the present invention.

[0008] That is, the gist of the present invention is as follows. (1) An electromagnetic wave shielding material containing nanowires composed of iron and nickel. (2) The electromagnetic wave shielding material according to (1), wherein the mass ratio of iron to nickel (iron / nickel) in the nanowires is 20 / 80 to 65 / 35. (3) The electromagnetic wave shielding material according to (1) or (2), further comprising a dielectric. (4) The electromagnetic wave shielding material according to (3), wherein the dielectric is a binder. (5) The electromagnetic wave shielding material according to (3) or (4), wherein the ratio of the nanowires to the total of the nanowires and the dielectric material is 10% by mass or more and less than 65% by mass. (6) The electromagnetic wave shielding material according to (3) or (4), wherein the ratio of the nanowires to the total of the nanowires and the dielectric is 40% by mass or more and 60% by mass or less. (7) Volume resistivity is 10 -2 The electromagnetic wave shielding material according to any one of (1) to (6), which has a resistivity of Ω·cm or more. (8) A dispersion containing the electromagnetic wave shielding material according to any one of (1) to (7). (9) A sheet comprising the electromagnetic wave shielding material according to any one of (1) to (7). (10) A film comprising the electromagnetic wave shielding material according to any one of (1) to (7). (11) An electronic component comprising the electromagnetic wave shielding material according to any one of (1) to (7). [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an electromagnetic wave shielding material that has excellent electromagnetic wave shielding properties, particularly excellent electromagnetic wave absorption properties, in the high frequency range of several tens of GHz (particularly in the quasi-millimeter wave range and millimeter wave range). The electromagnetic wave shielding material of the present invention can be suitably used in electronic components for fifth generation mobile communication systems, advanced driver assistance systems, and the like. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing the electromagnetic wave absorption properties in the K band of Example 1. [Figure 2] 1 is a diagram showing the electromagnetic wave absorption properties in Ka band of Example 1. [Figure 3] 1 is a diagram showing the electromagnetic wave absorption properties in the U band of Example 1. [Figure 4] 1 is a diagram showing the electromagnetic wave absorption properties in E band of Example 1. [Figure 5] 1 is a diagram showing the electromagnetic wave shielding properties in the K band of Example 1. [Figure 6] 1 is a diagram showing the electromagnetic wave shielding properties of Example 1 in Ka band. [Figure 7] 1 is a diagram showing the electromagnetic wave shielding properties in the U band of Example 1. [Figure 8] 1 is a diagram showing the electromagnetic wave shielding properties in E band of Example 1. [Figure 9] 10 is a diagram showing the electromagnetic wave absorption properties in the K band of Example 5. [Figure 10] 10 is a diagram showing the electromagnetic wave absorption properties in Ka band of Example 5. [Figure 11] 10 is a diagram showing the electromagnetic wave absorption properties in the U band of Example 5. [Figure 12] 10 is a diagram showing the electromagnetic wave absorption properties in E band of Example 5. [Figure 13] 10 is a diagram showing the electromagnetic wave shielding properties in the K band of Example 5. [Figure 14] 10 is a diagram showing the electromagnetic wave shielding properties in Ka band of Example 5. [Figure 15] 10 is a diagram showing the electromagnetic wave shielding properties in the U band of Example 5. [Figure 16] 10 is a diagram showing the electromagnetic wave shielding properties in E band of Example 5. [Figure 17] 10 is a diagram showing the electromagnetic wave absorption properties in the K band of Comparative Example 2. [Figure 18] 10 is a diagram showing the electromagnetic wave absorption properties in Ka band of Comparative Example 2. [Figure 19] 10 is a diagram showing the electromagnetic wave absorption properties in the U band of Comparative Example 2. [Figure 20] 10 is a diagram showing the electromagnetic wave absorption properties in E band of Comparative Example 2. [Figure 21] 10 is a diagram showing the electromagnetic wave shielding properties in K band of Comparative Example 2. [Figure 22] 10 is a diagram showing the electromagnetic wave shielding properties in Ka band of Comparative Example 2. [Figure 23] 10 is a diagram showing the electromagnetic wave shielding properties in U band of Comparative Example 2. [Figure 24] 10 is a diagram showing the electromagnetic wave shielding properties in E band of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] The electromagnetic wave shielding material of the present invention includes nanowires composed of iron and nickel.

[0012] In the present invention, electromagnetic wave shielding (shielding) property refers to a property that takes into consideration both the ability to reflect electromagnetic waves (electromagnetic wave reflectivity) and the ability to absorb electromagnetic waves (electromagnetic wave absorption). Electromagnetic wave reflectivity refers to the ability to reflect electromagnetic waves in the direction of the electromagnetic wave incident surface, thereby suppressing transmission of electromagnetic waves to the opposite surface. Electromagnetic wave absorption refers to the ability to convert electromagnetic wave energy into magnetism and heat, thereby suppressing transmission of electromagnetic waves to the opposite surface. Electromagnetic wave shielding and electromagnetic wave absorption can be measured by the free space method. In this specification, a high frequency band of several tens of GHz refers to a frequency range of 18 to 110 GHz (particularly 24.05 to 81.0 GHz). Quasi-millimeter waves refer to a frequency band of 20 to 30 GHz. Millimeter waves refer to a frequency band of 30 to 300 GHz.

[0013] The nanowires used in the present invention are fibrous materials with an average diameter of less than 1 μm. From the viewpoints of ease of production of the electromagnetic wave shielding material and further improving the electromagnetic wave shielding properties, particularly the electromagnetic wave absorption properties, the nanowires preferably have an average diameter of 50 to 900 nm and an average length of 5 μm or more (particularly 10 μm or more), and more preferably an average diameter of 70 to 700 nm and an average length of 15 to 500 μm. The aspect ratio of the nanowires used in the present invention is usually 10 or more (particularly 50 or more), and from the viewpoint of further improving the electromagnetic wave shielding properties (particularly the electromagnetic wave absorption properties), it is preferably 10 to 1000, more preferably 50 to 500.

[0014] In this specification, the aspect ratio of the nanowires was calculated by calculating the long axis (length) / short axis (diameter) value of each nanowire from an image taken with a SEM (scanning electron microscope), and the average value of 100 values ​​was used.

[0015] The morphology of the iron and nickel constituting the nanowires is not particularly limited, but examples thereof include a structure in which iron and nickel are randomly arranged, a core-sheath structure in which nickel is arranged around iron, a core-sheath structure in which iron is arranged around nickel, and a particle chain structure of iron particles and nickel particles. Among these, a structure in which iron and nickel are randomly arranged is preferred from the viewpoint of improving electromagnetic wave shielding properties, particularly electromagnetic wave absorption properties.

[0016] The mass ratio of iron to nickel (iron / nickel) in the nanowires is not particularly limited. Magnetic materials are advantageous for absorbing electromagnetic waves, so the mass ratio of iron to nickel is preferably 20 / 80 to 65 / 35, more preferably 20 / 80 to 50 / 50, even more preferably 20 / 80 to 40 / 60, and particularly preferably 20 / 80 to 30 / 70. To further increase the magnetic permeability, the mass ratio of Permalloy A (iron:nickel = 21.5:78.5 (mass ratio)) is most preferred.

[0017] The method for producing nanowires used in the present invention is not particularly limited, but for example, an example is a method in which an iron salt and a nickel salt are reduced in a reaction solution to produce a nanowire dispersion, and then the nanowires are collected.

[0018] Examples of methods for producing a nanowire dispersion by reducing iron salt and nickel salt in a reaction solution include electrolysis using a positron oxide film and liquid-phase reduction. The liquid-phase reduction method is a method in which iron salt and nickel salt are reduced in a reaction solution while applying a magnetic field to obtain a dispersion. Among these, the latter method is preferred because it allows for relatively inexpensive production.

[0019] The iron salt and nickel salt are preferably chlorides or acetates, and more preferably chlorides from the viewpoint of dispersibility of the resulting dispersion. Specifically, the iron salt is preferably iron(II) chloride or iron(II) chloride tetrahydrate, and the nickel salt is preferably nickel chloride or nickel chloride hexahydrate.

[0020] The total concentration of the iron salt and nickel salt in the reaction solution is preferably 10 to 1000 μmol / g, and from the viewpoint of controlling the shape of the resulting nanowires and improving the yield, it is more preferably 10 to 500 μmol / g, and even more preferably 15 to 85 μmol / g.

[0021] From the viewpoints of controlling the shape of the resulting nanowires and improving the yield, it is preferable to add a citrate to the reaction solution. The amount of citrate added is preferably 0.5 to 5 mol %, more preferably 0.5 to 3 mol %, based on the total amount of iron salt and nickel salt.

[0022] The reaction solvent used in the reaction solution is preferably a highly polar reaction solvent, such as water, alcohol, glycol, etc. Ethylene glycol, which has a high boiling point and viscosity, is preferred because it is stable to the temperature of the reduction reaction and the generated gas.

[0023] In the present invention, the property of the solution for the reduction reaction is important; the reduction reaction does not proceed in the acidic to neutral range, and nanowires are not produced. Therefore, the property of the solution for the reduction reaction must be alkaline. The property of the solution can be adjusted by adding an alkaline compound, specifically, by adding an alkaline compound such as sodium hydroxide or potassium hydroxide. The amount of alkaline compound added is preferably 1 mol or less per mol of the total of the iron salt and nickel salt. From the viewpoints of the reduction reactivity of the iron salt and nickel salt, shape control of the resulting nanowires, and improving the yield, the amount is preferably 0.2 to 1 mol, and more preferably 0.5 to 0.8 mol. The alkaline compound is preferably dissolved in the reaction solvent.

[0024] When sodium hydroxide or potassium hydroxide is added, it reacts with the iron ions and nickel ions generated from each salt, resulting in the formation of a coprecipitate of salts containing iron and nickel. Because the coprecipitate is difficult to reduce, problems such as a significant delay in the reduction reaction and the formation of scaly or amorphous particles arise. In the present invention, in order to redissolve the coprecipitate, it is preferable to add ammonia to form an ammine complex. The amount of ammonia added is preferably 3 to 30 mol per mol of alkaline compound, and from the viewpoints of the reduction reactivity of iron ions and nickel ions, shape control of the resulting nanowires, and improving the yield, it is preferably 10 to 30 mol, and more preferably 20 to 30 mol. From the viewpoints of ease of handling, it is preferable to add ammonia water.

[0025] The reduction reaction is carried out using a reducing agent, such as hydrazine or hydrazine monohydrate. If a reducing agent other than hydrazines, such as a phosphorus-based reducing agent such as hypophosphorous acid or a boron-based reducing agent such as dimethylaminoborane, is used, nanowires may not be obtained.

[0026] When hydrazine monohydrate is used as the reducing agent, its concentration is preferably 1 to 20 mol, more preferably 2 to 10 mol, even more preferably 2 to 4 mol, and particularly preferably 2.5 to 3.5 mol, per 1 mol of the total of the iron salt and nickel salt, from the viewpoints of the reduction reactivity of iron ions and nickel ions, shape control of the resulting nanowires, and improving the yield. The order of addition of the nickel salt, iron salt, citrate, ammonia, reducing agent, etc. during the reduction reaction is not particularly limited, as long as the reducing agent is added last.

[0027] Nanowires can be obtained by applying a magnetic field during the reduction reaction. The magnetic field can be applied using a magnetic circuit made of a neodymium magnet, and the strength of the magnetic field is preferably about 100 mT, and more preferably 100 to 200 mT.

[0028] The temperature and reaction time of the reduction reaction are not particularly limited as long as the reduction reaction proceeds. For example, when hydrazines such as hydrazine or hydrazine monohydrate are used as the reducing agent, the temperature of the reduction reaction is preferably 70 to 100°C, more preferably 80 to 100°C, and even more preferably 80 to 95°C, from the viewpoints of the reduction reactivity of iron ions and nickel ions, shape control of the nanowires, and improved yield. The reduction time is preferably 30 minutes or longer, more preferably 60 minutes or longer, from the viewpoints of the reduction reactivity of iron ions and nickel ions, shape control of the nanowires, and improved yield.

[0029] After the reduction reaction, the nanowires can be purified and recovered by filtering or decanting the nanowire dispersion, preferably by filtering. Examples of the filtering method include suction filtration and pressure filtration.

[0030] The filter used for filtration is not particularly limited as long as it can be used with alkaline solvents or polar solvents. Even a hydrophobic filter such as a polyvinylidene fluoride (PVDF) filter can be used if the filtration surface is moistened with alcohol or the like. The pore size of the filter is not particularly limited as long as it is smaller than the length of the nanowires, and specifically, it is preferably 10 μm or less.

[0031] The electromagnetic wave shielding material of the present invention can be obtained by further mixing a dielectric with the purified and recovered nanowires. Specifically, in the electromagnetic wave shielding material of the present invention, the nanowires are dispersed and contained in the dielectric. Examples of the dielectric include compounds other than conductive and semiconductive compounds, such as organic materials such as epoxy resins, acrylic resins, styrene resins, polyester resins, alkyd resins, phenolic resins, urethane resins, polyamide resins, polyimide resins, silicone resins, fluororesins, elastomers, and rubber (especially natural rubber); and inorganic materials such as ceramics. The dielectric also functions as a binder. Mixing the nanowires with the dielectric allows them to be molded into an electromagnetic wave shielding material. Among these, epoxy resins, silicone resins, fluororesins, and ceramics are preferred due to their excellent heat resistance and low moisture absorption, and epoxy resins and silicone resins are particularly preferred due to their excellent adhesion to electronic components. From the viewpoint of further improving the electromagnetic wave shielding properties (especially the electromagnetic wave absorption properties) of the electromagnetic wave shielding material, the dielectric is preferably a styrene resin, a silicone resin, or an epoxy resin, more preferably a styrene resin or a silicone resin, and even more preferably a styrene resin. The term "resin" is used as a concept that includes polymers.

[0032] The mass ratio of nanowires to dielectric (nanowires / dielectric) in the electromagnetic wave shielding material of the present invention is not particularly limited and is usually 10 / 90 to 95 / 10, and from the viewpoint of further improving the electromagnetic wave shielding properties (particularly the electromagnetic wave absorption properties), it is preferably 10 / 90 to 90 / 10, more preferably 10 / 90 or more and less than 65 / 35, and even more preferably 40 / 60 to 60 / 40. The mass ratio can be changed as appropriate depending on whether electromagnetic waves are shielded by reflection or absorption.

[0033] When the ratio of the nanowires to the total of the nanowires and the dielectric is 10% by mass or more and less than 65% by mass, a dielectric material can be obtained. -2 Ω·cm or more (especially 4.4×10 6Ω·cm or more). Such materials are able to shield electromagnetic waves primarily by absorbing them. Generally, the higher the nanowire ratio within the allowable range, the better the electromagnetic wave shielding performance (especially electromagnetic wave absorption), but the processability becomes poorer, and processing methods may be limited to potting, dipping, screen printing, etc. Lowering the nanowire ratio enables various coating methods such as die coating and spray coating, as well as transfer and press molding. From the perspective of balancing electromagnetic wave shielding (especially electromagnetic wave absorption) and processability, the nanowire ratio is preferably between 40% and 60% by mass of the total of the nanowires and dielectric.

[0034] When the ratio of the nanowires to the total of the nanowires and the dielectric is 65% by mass or more and 90% by mass or less, a conductor can be obtained. -2 The resistivity can be less than Ω·cm. The ratio of nanowires to the total of nanowires and dielectric is more preferably 80% by mass or more and 90% by mass or less. Such materials can shield electromagnetic waves mainly by reflecting them.

[0035] The electromagnetic wave shielding material of the present invention may contain fillers, softeners, antioxidants, tackifiers, etc., within the range that does not impair the effects of the present invention. The electromagnetic wave shielding material of the present invention may be cured (or crosslinked) with a curing agent (or crosslinking agent).

[0036] The electromagnetic wave shielding material of the present invention can be produced by mixing the iron-nickel nanowires and the dielectric material. The mixing method is not particularly limited, but examples include mixing them using a solvent or the like in a planetary mixer to prepare a dispersion containing the electromagnetic wave shielding material, and then molding the dispersion.

[0037] Specifically, for example, when the dielectric is an organic material, the electromagnetic wave shielding material of the present invention can be obtained by dispersing iron-nickel nanowires in a solvent containing the organic material to form a dispersion, applying the dispersion, and drying the solvent. The organic material may be dissolved or dispersed in the dispersion. A monomer (particularly a polymerizable monomer) capable of forming the organic material may be used as the organic material. In this case, the dispersion may be applied and then polymerized (or cured). In this case, the dispersion does not need to contain a solvent. The dispersion can also be used as a paste. A sheet can be obtained by filling a plate-shaped template with the above-mentioned dispersion or paste and curing it.

[0038] Furthermore, for example, when the dielectric is an organic material, the electromagnetic wave shielding material of the present invention can be obtained by melting and mixing the organic material and iron-nickel nanowires and molding them.

[0039] Furthermore, for example, when the dielectric is an inorganic material, the inorganic material and iron-nickel nanowires can be mixed together with a solvent, and the mixture can be molded and sintered to obtain the electromagnetic wave shielding material of the present invention.

[0040] The present invention also provides a dispersion containing an electromagnetic wave shielding material. A dispersion containing an electromagnetic wave shielding material is a dispersion from which the electromagnetic wave shielding material of the present invention can be produced. The dispersion contains iron-nickel nanowires constituting the electromagnetic wave shielding material of the present invention, a solvent, and, optionally, a dielectric (e.g., an organic material or a monomer (particularly, a polymerizable monomer) capable of forming the organic material). Any solvent used in the field of nanowire dispersions can be used as the solvent, and examples of such solvents include organic solvents such as toluene, xylene, and methyl ethyl ketone. When a monomer (particularly, a polymerizable monomer) capable of forming the organic material is used as the organic material, the dispersion does not need to contain a solvent.

[0041] The shape of the electromagnetic wave shielding material of the present invention is not particularly limited, and examples thereof include a sheet and a film. The electromagnetic wave shielding material of the present invention can also be used as a coating film for various electronic components such as semiconductors. The sheet and film may have a thickness of 1 μm to 5 mm. The coating film may have a thickness of 1 to 500 μm.

[0042] The electromagnetic wave shielding material of the present invention (particularly the electromagnetic wave shielding material of the present invention in which the ratio of nanowires to the total of nanowires and dielectric is 10% by mass or more but less than 65% by mass) can also absorb electromagnetic waves (radio waves) at frequencies of 18 GHz or more. Specifically, for electromagnetic waves at frequencies of 18 GHz or more, it is preferable that the material has an average absorption of 15 dB or more in any of the following frequency ranges, and it is also preferable that the material can absorb multiple frequency bands, i.e., three or more bands, within these ranges. Furthermore, an absorption rate of 15 dB or more is preferable because it can absorb 97% of the radio wave power, and an absorption rate of 20 dB is even more preferable because it can absorb 99%. (frequency range) In the fifth generation mobile communication system, n257 (26.50-29.50GHz) used in Japan and South Korea, n258 (24.25-27.50GHz) used in the EU, n259 (39.5-43.50GHz), n260 (37.00-40.00GHz), and n261 (27.50-28.35GHz) used in the United States and China; and Millimeter-wave radar, which is part of advanced driver assistance systems, includes 24.05-24.25 GHz for 24 GHz narrowband radar systems, 24.25-29.0 GHz for 24 GHz / 26 GHz UWB radar systems, 60.0-61.0 GHz for 60 GHz millimeter-wave radar systems, 76.0-77.0 GHz for 76 GHz millimeter-wave radar systems, and 77.0-81.0 GHz for 79 GHz high-resolution radar systems.

[0043] The electromagnetic wave shielding properties of parts using the electromagnetic wave shielding material of the present invention can be determined by designing the absorption rate and shielding rate appropriate for the intended use. The shielding rate can block 90% of the electromagnetic wave power at 10 dB, 97% at 15 dB, 99% at 20 dB, 99.7% at 25 dB, and 99.9% at 30 dB.

[0044] The electromagnetic wave shielding material of the present invention can exhibit an average absorption of 15 dB or more, particularly 20 dB or more, in the following frequency bands, by adjusting the ratio of nanowires to the total of nanowires and dielectric material to 40 mass % or more and 60 mass % or less: ·n257(26.50-29.50GHz); n261 (27.50-28.35GHz); and - 77.0-81.0 GHz as a 79 GHz band high-resolution radar system.

[0045] The electromagnetic wave absorption and shielding properties of the sheet of the present invention can be changed by treating it in a magnetic field. For example, by remelting the electromagnetic wave shielding material of the present invention in a magnetic field and molding it, the absorption rate in a frequency band where the absorption rate was low can be increased.

[0046] In one embodiment of the present invention, the electromagnetic wave shielding material of the present invention absorbs electromagnetic waves at frequencies of 18 GHz or higher. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves in the frequency range of 26.5 to 29.5 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves in the frequency range of 24.5 to 27.5 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves in the frequency range of 39.5 to 43.5 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves with frequencies from 37.0 to 40.0 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves in the frequency range of 27.5 to 28.35 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves in the frequency range of 24.05 to 24.25 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves in the frequency range of 24.25 to 29.0 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves with frequencies from 60.0 to 61.0 GHz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves with a frequency of 76.0 to 77.0 Hz by an average of 10 dB or more. The electromagnetic wave shielding material of the present invention can absorb electromagnetic waves in the frequency range of 77.0 to 81.0 GHz by an average of 10 dB or more.

[0047] In another embodiment of the present invention, when the electromagnetic wave shielding material of the present invention is processed into a sheet with a thickness of 1 mm, the average electromagnetic wave absorption property in the frequency range of 18 to 110 GHz can be 10 dB or more. The electromagnetic wave shielding material of the present invention also has a maximum peak at any frequency between 18 and 110 GHz, and the maximum value of the maximum peak can be 50 dB or more. Furthermore, when the electromagnetic wave shielding material of the present invention is processed into a sheet with a thickness of 1 mm, the average electromagnetic wave shielding property in the frequency range of 18 to 110 GHz can be 10 dB or more. Although the reason is not clear, it is presumed that the unique electromagnetic wave shielding property is exhibited by using nanowires composed of iron and nickel, which have high magnetic permeability.

[0048] In yet another embodiment of the present invention, when the electromagnetic wave shielding material of the present invention is used as a radio wave absorber for noise and the like, the maximum electromagnetic wave absorbency at a frequency of 18 GHz or higher is preferably 20 dB or higher, and more preferably 40 dB or higher. [Example]

[0049] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0050] The evaluation was carried out by the following method. A. Evaluation of electromagnetic wave shielding materials (1) Volume resistivity The sheets obtained in the examples and comparative examples were measured at five points in accordance with JIS K 7194 (1994), and the average value was calculated.

[0051] (2) Electromagnetic wave absorption The sheets obtained in the examples and comparative examples with aluminum plates attached were used as samples, and electromagnetic wave absorption measurements were performed on the K band (18 to 26.5 GHz), Ka band (26.5 to 40 GHz), U band (40 GHz to 60 GHz), E band (60 GHz to 90 GHz), and W band (75 GHz to 110 GHz) using the free space method with a vector network analyzer. For example, the electromagnetic wave absorption measurement results of the sheet of Example 1 in K band, Ka band, U band, and E band are shown in FIGS. 1 to 4, respectively. For example, the electromagnetic wave absorption measurement results of the sheet of Example 5 in K band, Ka band, U band, and E band are shown in FIGS. 9 to 12, respectively. Further, for example, the electromagnetic wave absorption measurement results of the sheet of Comparative Example 2 in K band, Ka band, U band, and E band are shown in FIGS. 17 to 20, respectively.

[0052] The measurement results were evaluated by calculating the average absorption rate for each of the following 10 frequency bands: n257 (26.50-29.50 GHz), n258 (24.25-27.50 GHz), n259 (39.5-43.50 GHz), n260 (37.00-40.00 GHz), n261 (27.50-28.35 GHz), 24 GHz narrowband radar system (24.05-24.25 GHz), 24 GHz / 26 GHz UWB radar system (24.25-29.0 GHz), 60 GHz millimeter-wave radar system (60.0-61.0 GHz), 76 GHz millimeter-wave radar system (76.0-77.0 GHz), and 79 GHz high-resolution radar system (77.0-81.0 GHz). Each average value was evaluated according to the metal content using the following criteria. In the present invention, the greater the number of bands marked with ◯ or ⊚, the more preferable the content.

[0053] For the sample containing 50% by mass of a metal component, the average values ​​were evaluated according to the following criteria, and an overall evaluation was also performed. (Average absorption rate for each frequency band) ◎: 20dB or more; 〇: 15dB or more and less than 20dB; △: 10dB or more and less than 15dB; ×: Less than 10dB. (Comprehensive evaluation of absorption rate for each frequency band) Best: 7 or more ◎ and 〇 frequency bands; Excellent: The number of ◎ and 〇 frequency bands is 6; Good: The number of ◎ and 〇 frequency bands is 5; Acceptable: The number of ◎ and 〇 frequency bands is 3 to 4; Not allowed: The number of ◎ and 〇 frequency bands is 2 or less. In the present invention, when the metal component is contained in an amount of 50% by mass, the result of the "overall evaluation of the absorption rate in each frequency band" is required to be at a level of "fair" or higher, preferably at a level of "good" or higher, more preferably at a level of "excellent" or higher, and most preferably at a level of "best."

[0054] For the sample containing 20% ​​by mass of metal components, the average values ​​were evaluated according to the following criteria, and an overall evaluation was also performed. (Average absorption rate for each frequency band) 〇: 10dB or more; ×: Less than 10dB. (Comprehensive evaluation of absorption rate for each frequency band) Excellent: The number of 〇 frequency bands is 3 or more; Good: The number of frequency bands is 2; Acceptable: The number of frequency bands is 1; Not allowed: The number of 〇 frequency bands is 0. In the present invention, when the metal component is contained in an amount of 20 mass %, the result of the "overall evaluation of the absorption rate in each frequency band" is required to be at a level of "fair" or higher, preferably at a level of "good" or higher, and more preferably at a level of "excellent."

[0055] For the sample containing 10% by mass of a metal component, the average values ​​were evaluated according to the following criteria, and an overall evaluation was also performed. (Average absorption rate for each frequency band) 〇: 10dB or more; ×: Less than 10dB. (Comprehensive evaluation of absorption rate for each frequency band) Acceptable: The number of frequency bands marked as 〇 is 1 or more; Not allowed: The number of 〇 frequency bands is 0. In the present invention, when the metal component is contained at 10% by mass, the result of the "overall evaluation of the absorption rate in each frequency band" is required to be at a level of "fair" or higher.

[0056] Next, the average and maximum values ​​and their positions (frequency) of the absorption rate over the entire frequency band of 18 to 110 GHz were determined and evaluated according to the following criteria. (Average absorption rate in the 18-110 GHz band) ◎: 20dB or more; ○: 10 dB or more and less than 20 dB; △: 7.5 dB or more and less than 10 dB; ×: Less than 7.5dB. In practice, the average value is required to be 7.5 dB or more, preferably 10 dB or more (◯ or ⊚), and more preferably 20 dB or more (⊚). (Maximum absorption rate between 18 and 110 GHz) ◎: 40dB or more; ○: 20 dB or more and less than 40 dB; △: 10dB or more and less than 20dB; ×: Less than 10dB. In the present invention, a maximum electromagnetic wave absorbency of 10 dB or more (△) is considered to be acceptable. The maximum electromagnetic wave absorbency is preferably 20 dB or more (◯), and more preferably 40 dB or more (◎).

[0057] (3) Electromagnetic wave shielding property Using the sheets obtained in the examples and comparative examples as samples, electromagnetic wave shielding measurements were performed in the K band (18 to 26.5 GHz), Ka band (26.5 to 40 GHz), U band (40 GHz to 60 GHz), E band (60 GHz to 90 GHz), and W band (75 GHz to 110 GHz) using the free space method with a vector network analyzer. For example, the electromagnetic wave shielding measurement results for the sheet of Example 1 in K band, Ka band, U band, and E band are shown in FIGS. 5 to 8, respectively. For example, the electromagnetic wave shielding measurement results for the sheet of Example 5 in K band, Ka band, U band and E band are shown in FIGS. 13 to 16, respectively. Further, for example, the electromagnetic wave shielding measurement results for the sheet of Comparative Example 2 in K band, Ka band, U band and E band are shown in FIGS. 21 to 24, respectively.

[0058] To evaluate the measurement results, the average shielding rate was calculated for each of the 10 frequency bands: n257 (26.50-29.50GHz), n258 (24.25-27.50GHz), n259 (39.5-43.50GHz), n260 (37.00-40.00GHz), n261 (27.50-28.35GHz), 24GHz narrowband radar system (24.05-24.25GHz), 24GHz / 26GHz UWB radar system (24.25-29.0GHz), 60GHz millimeter-wave radar system (60.0-61.0GHz), 76GHz millimeter-wave radar system (76.0-77.0GHz), and 79GHz high-resolution radar system (77.0-81.0GHz). Each average value was evaluated according to the content of the metal component according to the following criteria: In the present invention, the more bands marked with ◯ or ⊚, the more preferable it is for any content.

[0059] For the sample containing 50% by mass of a metal component, the average values ​​were evaluated according to the following criteria, and an overall evaluation was also performed. (Average shielding rate for each frequency band) ◎: 20dB or more; 〇: 15dB or more and less than 20dB; △: 10dB or more and less than 15dB; ×: Less than 10dB. (Overall evaluation of shielding rate for each frequency band) Best: ◎ Number of frequency bands: 10; Excellent: The number of ◎ frequency bands is 9; Good: The number of ◎ frequency bands is 8; Acceptable: ◎ The number of frequency bands is 7; Not allowed: The number of ◎ frequency bands is 6 or less. In the present invention, when the metal component is contained at 50% by mass, the result of the "overall evaluation of the shielding rate for each frequency band" is required to be at a level of "fair" or higher, preferably at a level of "good" or higher, more preferably at a level of "excellent" or higher, and most preferably at a level of "best."

[0060] For the sample containing 20% ​​by mass of metal components, the average values ​​were evaluated according to the following criteria, and an overall evaluation was also performed. (Average shielding rate for each frequency band) 〇: 10dB or more; ×: Less than 10dB. (Overall evaluation of shielding rate for each frequency band) Excellent: The number of 〇 frequency bands is 9 or more; Good: The number of frequency bands is 8; Acceptable: The number of frequency bands is 7; Not allowed: The number of 〇 frequency bands is 6 or less. In the present invention, when the metal component is contained at 20% by mass, the result of the "overall evaluation of the shielding rate for each frequency band" is required to be at a level of "fair" or higher, preferably at a level of "good" or higher, and more preferably at a level of "excellent."

[0061] For the sample containing 10% by mass of a metal component, the average values ​​were evaluated according to the following criteria, and an overall evaluation was also performed. (Average shielding rate for each frequency band) 〇: 10dB or more; ×: Less than 10dB. (Overall evaluation of shielding rate for each frequency band) Best: 5 or more bands with ◯; Excellent: The number of frequency bands is 3 or 4; Good: The number of frequency bands is 2; Acceptable: The number of frequency bands is 1; Not allowed: The number of 〇 frequency bands is 0. In the present invention, when the metal component is contained at 10 mass %, the result of the "overall evaluation of the shielding rate for each frequency band" is required to be at a level of "fair" or higher.

[0062] Next, the average shielding factor for the 28 GHz band (a 1 GHz wide frequency band centered on 28 GHz), the average shielding factor for the 79 GHz band (a 1 GHz wide frequency band centered on 79 GHz), and the average and maximum shielding factors for the entire frequency band from 18 to 110 GHz were calculated and evaluated according to the following criteria. (Average shielding rate for 28GHz band, 79GHz band and 18-110GHz band) ◎:25dB or more; ○: 20 dB or more and less than 25 dB; △: 10dB or more and less than 20dB; ×: Less than 10dB. In practice, the average value is required to be 10 dB or more, preferably 20 dB or more (◯ or ⊚), and more preferably 25 dB or more (⊚). (Maximum shielding rate from 18 to 110 GHz) ◎: 70dB or more; ○: 20 dB or more and less than 70 dB; △: 10dB or more and less than 20dB; ×: Less than 10dB. In the present invention, a maximum electromagnetic wave shielding property of 10 dB or more (△) is considered to be acceptable. The maximum electromagnetic wave shielding property is preferably 20 dB or more (◯), and more preferably 70 dB or more (◎).

[0063] B. Material The nanowires and particles used in the electromagnetic wave shielding material of the present invention were prepared as follows. (1) Iron and nickel nanowires (FeNiNW1, Fe:Ni = 21.5:78.5) 15.35 g (64.58 mmol) of nickel chloride hexahydrate and 0.30 g (1.02 mmol) of trisodium citrate dihydrate were added to ethylene glycol to make a total amount of 350.0 g. The solution was heated to 90°C to dissolve the nickel chloride, yielding a nickel-citrate solution. 2.50 g (62.52 mmol) of sodium hydroxide was added to ethylene glycol to make a total amount of 388.5 g. The solution was heated to 90° C. to dissolve the sodium hydroxide, thereby obtaining a sodium hydroxide solution. 3.70 g (18.61 mmol) of iron(II) chloride tetrahydrate was added to ethylene glycol to make a total amount of 150.0 g. The mixture was stirred at room temperature to dissolve the iron(II) chloride tetrahydrate, yielding an iron solution. A reaction vessel in a magnetic circuit capable of applying a magnetic field to the center was heated to 90-95°C, and 350.0 g of nickel citrate solution, 388.5 g of sodium hydroxide solution, 100.0 g of 28% ammonia water (ammonia amount: 28.0 g), 150.0 g of iron solution, and 11.5 g (229.72 mmol) of hydrazine monohydrate were added in this order. After all additions, a magnetic field of 150 mT was applied, and the reduction reaction was carried out at 90-95°C for 90 minutes. After the reaction was completed, the nanowires were collected using a PTFE filter (T100A090C). The recovered nanowires were analyzed by ICP-MS, which revealed that the iron / nickel mass ratio was 21.5 / 78.5. The average length, diameter, and aspect ratio of the nanowires were 22.6 μm, 0.2 μm, and 113, respectively.

[0064] (2) Nanowires composed of iron and nickel (FeNiNW2, Fe:Ni=55:45) 8.18 g (34.43 mmol) of nickel chloride hexahydrate and 0.30 g (1.02 mmol) of trisodium citrate dihydrate were added to ethylene glycol to make a total amount of 350.0 g. The solution was heated to 90°C to dissolve the nickel chloride, yielding a nickel-citrate solution. 2.50 g (62.52 mmol) of sodium hydroxide was added to ethylene glycol to make a total amount of 388.5 g. The solution was heated to 90° C. to dissolve the sodium hydroxide, thereby obtaining a sodium hydroxide solution. 9.24 g (46.48 mmol) of iron(II) chloride tetrahydrate was added to ethylene glycol to make a total amount of 150.0 g. The mixture was stirred at room temperature to dissolve the iron(II) chloride tetrahydrate, yielding an iron solution. A reaction vessel in a magnetic circuit capable of applying a magnetic field to the center was heated to 90-95°C, and 350.0 g of nickel citrate solution, 388.5 g of sodium hydroxide solution, 100.0 g of 28% ammonia water (ammonia amount: 28.0 g), 150.0 g of iron solution, and 11.5 g (229.72 mmol) of hydrazine monohydrate were added in this order. After all additions, a magnetic field of 150 mT was applied, and the reduction reaction was carried out at 90-95°C for 90 minutes. After the reaction was completed, the nanowires were collected using a PTFE filter (T100A090C). The recovered nanowires were analyzed by ICP-MS, revealing that the iron / nickel mass ratio was 54.8 / 45.2. The average length, diameter, and aspect ratio of the nanowires were 24.6 μm, 0.2 μm, and 123, respectively.

[0065] (3) Nanowires composed of iron and nickel (FeNiNW3, Fe:Ni=64:36) 6.89 g (28.99 mmol) of nickel chloride hexahydrate and 0.30 g (1.02 mmol) of trisodium citrate dihydrate were added to ethylene glycol to make a total amount of 350.0 g. This solution was heated to 90°C to dissolve the nickel chloride and obtain a nickel-citrate solution. 2.50 g (62.52 mmol) of sodium hydroxide was added to ethylene glycol to make a total amount of 388.5 g. The solution was heated to 90° C. to dissolve the sodium hydroxide, thereby obtaining a sodium hydroxide solution. 10.78 g (54.17 mmol) of iron(II) chloride tetrahydrate was added to ethylene glycol to make a total amount of 150.0 g. The mixture was stirred at room temperature to dissolve the iron(II) chloride tetrahydrate, yielding an iron solution. A reaction vessel in a magnetic circuit capable of applying a magnetic field to the center was heated to 90-95°C, and 350.0 g of nickel citrate solution, 388.5 g of sodium hydroxide solution, 100.0 g of 28% ammonia water (ammonia amount: 28.0 g), 150.0 g of iron solution, and 11.5 g (229.72 mmol) of hydrazine monohydrate were added in this order. After all additions, a magnetic field of 150 mT was applied, and the reduction reaction was carried out at 90-95°C for 90 minutes. After the reaction was completed, the nanowires were collected using a PTFE filter (T100A090C). The recovered nanowires were analyzed by ICP-MS, which revealed that the iron / nickel mass ratio was 64.0 / 36.0. The average length, diameter, and aspect ratio of the nanowires were 23.2 μm, 0.2 μm, and 116, respectively.

[0066] (4) Particles composed of iron and nickel (FeNiP) 15.35 g (64.58 mmol) of nickel chloride hexahydrate and 0.30 g (1.02 mmol) of trisodium citrate dihydrate were added to ethylene glycol to make a total amount of 350.0 g. The solution was heated to 90°C to dissolve the nickel chloride, yielding a nickel-citrate solution. 2.50 g (62.52 mmol) of sodium hydroxide was added to ethylene glycol to make a total amount of 388.5 g. The solution was heated to 90° C. to dissolve the sodium hydroxide, thereby obtaining a sodium hydroxide solution. 3.70 g (18.61 mmol) of iron(II) chloride tetrahydrate was added to ethylene glycol to make a total amount of 150.0 g. The mixture was stirred at room temperature to dissolve the iron(II) chloride tetrahydrate, yielding an iron solution. The reaction vessel was heated to 90-95°C, and 350.0 g of nickel citrate solution, 388.5 g of sodium hydroxide solution, 100.0 g of 28% aqueous ammonia (ammonia amount: 28.0 g), 150.0 g of iron solution, and 11.5 g (229.72 mmol) of hydrazine monohydrate were added in this order. After all the ingredients were added, the reduction reaction was carried out at 90-95°C for 90 minutes. After the reaction was completed, the nanowires were collected using a PTFE filter (T100A090C). The collected particles were analyzed by ICP-MS, and the iron / nickel mass ratio was found to be 21.5 / 78.5. Because the particles were in particulate form, the aspect ratio was 1.

[0067] (5) Nickel nanowires (NiNWs) 4.00 g (16.8 mmol) of nickel chloride hexahydrate and 0.375 g (1.27 mmol) of trisodium citrate dihydrate were added to ethylene glycol to make a total amount of 500.0 g. This solution was heated to 90°C and dissolved to obtain a nickel-citrate solution. In a separate container, 1.00 g of sodium hydroxide was added to ethylene glycol to make a total amount of 499.0 g. The solution was heated to 90°C and dissolved to obtain a sodium hydroxide solution. A reaction vessel placed in a magnetic circuit capable of applying a magnetic field to the center was heated to 90-95°C, and 500.0 g of nickel citrate solution, 499.0 g of sodium hydroxide solution, and 1.0 g (229.72 mmol) of hydrazine monohydrate were added in that order. After all the components were added, a magnetic field of 150 mT was applied, and the reduction reaction was carried out at 90-95°C for 90 minutes. After the reaction was completed, the nanowires were collected using a T100A090C PTFE filter. The average length, diameter, and aspect ratio of the nanowires were 24 μm, 0.1 μm, and 240, respectively.

[0068] Example 1 10 g of FeNiNW1, 10 g of styrene resin (St, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), and 10 g of toluene were mixed in a planetary mixer to obtain a dispersion liquid. The resulting dispersion was cast onto a Teflon sheet, dried at 40°C, and the coating was peeled off from the Teflon sheet to obtain a sheet with a thickness of 1 mm.

[0069] Example 2 10 g of FeNiNW1 and 9 g of TSE3450 (Si, silicone resin manufactured by Momentive) were mixed in a planetary mixer, and then 1 g of TSE3450 (a curing agent for silicone resin manufactured by Momentive) was further mixed to obtain a dispersion. The obtained dispersion was cast onto a polycarbonate resin sheet, cured at room temperature for 24 hours or more, and the coating was peeled off from the polycarbonate resin sheet to obtain a sheet with a thickness of 1 mm.

[0070] Examples 3 and 4 (Reference example) A sheet was obtained by the same procedure as in Example 1, except that the mass ratio of the FeNiNW1 to the styrene resin used was changed so that the mass ratio of the FeNiNW1 to the styrene resin was the mass ratio in Table 2A or 3A.

[0071] Example 5 Teflon sheets were laminated on both sides of the sheet produced in Example 1 to produce a laminate consisting of Teflon sheet / sheet obtained in Example 1 / Teflon sheet. The thickness of the obtained laminate was fixed at the edge with a 1 mm spacer plate, and then the laminate was sandwiched between two ferrite magnet plates and heat-treated for 4 hours at 130°C. After that, the laminate was removed and the Teflon sheet was peeled off to obtain a sheet with a thickness of 1 mm.

[0072] Example 6 13 g of FeNiNW1 and 9 g of jER (Ep, an epoxy resin manufactured by Mitsubishi Chemical Corporation) were mixed in a planetary mixer, and then 4 g of trimethylhexamethylenediamine was added to obtain a dispersion liquid. The resulting dispersion was cast onto a Teflon sheet and cured at 120°C for 30 minutes or more, and the coating was peeled off from the Teflon sheet to obtain a sheet with a thickness of 1 mm.

[0073] Examples 7 and 8 (Reference example) A sheet having a thickness of 1 mm was obtained in the same manner as in Example 6, except that FeNiNW1 was changed to FeNiNW2 or FeNiNW3.

[0074] Comparative Example 1 A sheet was obtained in the same manner as in Example 1, except that FeNiNW was changed to FeNiP.

[0075] Comparative Example 2 A sheet was obtained in the same manner as in Example 1, except that FeNiNW was replaced with NiNW.

[0076] Comparative Example 3 A sheet was obtained in the same manner as in Example 2, except that FeNiNW was replaced with NiNW.

[0077] Comparative Example 4 A sheet was obtained in the same manner as in Example 3, except that FeNiNW was replaced with NiNW.

[0078] Comparative Example 5 A sheet was obtained in the same manner as in Example 4, except that FeNiNW was replaced with NiNW.

[0079] Comparative Example 6 A sheet was obtained by carrying out the same operation as in Example 1, except that FeNiNW was replaced with AgNW (manufactured by Aldrich).

[0080] The compositions and evaluation results of the electromagnetic wave shielding materials obtained in the examples and comparative examples are shown in Tables 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B, 3C, 4A, 4B and 4C.

[0081] [Table 1A]

[0082] [Table 1B]

[0083] [Table 1C]

[0084] [Table 2A]

[0085] [Table 2B]

[0086] [Table 2C]

[0087] [Table 3A]

[0088] [Table 3B]

[0089] [Table 3C]

[0090] [Table 4A]

[0091] [Table 4B]

[0092] [Table 4C]

[0093] Examples 1, 2, and 6, which contained 50% metal components, had an electromagnetic wave absorption rate of 15 dB or more in at least 6 of the 10 frequency bands used, and were excellent in terms of electromagnetic wave shielding properties. On the other hand, Comparative Examples 1 to 3 and 6 had the same metal component content as Examples 1, 2, and 6, but did not contain nanowires made of iron and nickel, so the number of bands in which they could absorb 15 dB or more was less than 3 (particularly 2 or less), and there were many frequency bands in which they could not adequately absorb, limiting their use as materials.

[0094] Example 3, which contained 20% metal components, had four frequency bands in which it could absorb 10 dB or more, and was also excellent in terms of electromagnetic wave shielding properties. In contrast, Comparative Example 4 did not have any frequency bands in which it could absorb 10 dB or more.

[0095] Example 4 containing 10% of metal components was able to absorb 10 dB or more in one frequency band, whereas Comparative Example 5 was unable to absorb 10 dB or more in any frequency band.

[0096] Example 5 has the same composition as Example 1, but by melting and remolding in a magnetic field, it was possible to confirm a high absorption rate of 20 dB or more for n258 (24.25-27.5 GHz) and a 24 GHz narrowband radar system (24.05-24.25 GHz), which Example 1 was unable to absorb, and for a 24 GHz / 26 GHz UWB radar system (24.25-29.0 GHz), for which the absorption rate was less than 15 dB. [Industrial Applicability]

[0097] The electromagnetic wave shielding material of the present invention has excellent electromagnetic wave shielding properties, particularly electromagnetic wave absorption properties, in the high frequency range (particularly the quasi-millimeter wave range and millimeter wave range), and can therefore be suitably used in electronic components for fifth generation mobile communication systems, advanced driver assistance systems, etc.

Claims

1. nanowires and a dielectric material composed of iron and nickel; the mass ratio of iron to nickel (iron / nickel) in the nanowires is 20 / 80 to 40 / 60; An electromagnetic wave shielding material, wherein the ratio of the nanowires to the total of the nanowires and the dielectric is 40% by mass or more and 60% by mass or less.

2. 2. The electromagnetic wave shielding material according to claim 1, wherein the mass ratio of iron to nickel (iron / nickel) in the nanowires is 20 / 80 to 30 / 70.

3. 3. The electromagnetic wave shielding material according to claim 1, wherein the dielectric is a binder.

4. Volume resistivity is 10 －２ 4. The electromagnetic wave shielding material according to claim 1, wherein the resistivity is Ω·cm or more.

5. A dispersion comprising the electromagnetic wave shielding material according to any one of claims 1 to 4.

6. A sheet comprising the electromagnetic wave shielding material according to any one of claims 1 to 4.

7. A film comprising the electromagnetic wave shielding material according to any one of claims 1 to 4.

8. An electronic part comprising the electromagnetic wave shielding material according to any one of claims 1 to 4.

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