KR20240054971A - Terahertz wave shielding material - Google Patents

Abstract

The present invention provides a shielding material that is excellent in heat resistance, flexibility, and shielding properties against terahertz waves. The present invention relates to a terahertz wave shielding material containing nanowires and a binder.

Description

Terahertz wave shielding material

The present invention relates to terahertz wave shielding materials.

In recent years, as a next-generation wireless communication (6G, Beyond 5G), the use of terahertz waves for the purposes of “higher speed,” “higher capacity,” “lower latency,” and/or “higher reliability” has been considered. In addition, radar, which senses the inside and outside of a car, which is an important technology for autonomous driving, is also expected to provide high-definition and three-dimensional tracking by using terahertz waves.

The mainstream of wireless communication units and sensing units that handle high frequencies such as terahertz waves is AiP (Antenna in Package), which integrates an antenna module, power unit module, RF front-end module, and MMIC module from the viewpoint of reducing transmission loss. . Therefore, there is a demand for materials that can shield terahertz waves inside the unit to prevent malfunction or deterioration of characteristics of each module from interference, oscillation, etc. of terahertz waves.

Since high frequencies such as terahertz waves have a short wavelength, shielding requires high filling of shielding filler to fill gaps, which tends to result in lack of flexibility. For this reason, shielding materials made of ferrite-based fillers such as ε-type iron oxide and resin, which can reduce the filling rate, are used (Patent Document 1). However, the shielding material of Patent Document 1, even if it is a ferrite-based filler, still needs to be blended at a high filling rate of 30% by volume (=about 67% by mass) or more. Therefore, in order to provide flexibility that can withstand processing, it is necessary to use a flexible resin with a low glass transition temperature, and because the flexible resin is used, there are problems such as poor heat resistance, limiting the usage environment, and deteriorating shielding properties due to heat. there was.

Japanese Patent Publication No. 2019-071426

The present invention seeks to solve the above problems, and aims to provide a shielding material that is excellent in heat resistance, flexibility, and shielding properties against terahertz waves.

Another object of the present invention is to provide a shielding material that is excellent in heat resistance, flexibility, and both shielding and reflection resistance to terahertz waves.

The present inventors discovered that a material containing nanowires achieves the above object, and arrived at the present invention.

That is, the gist of the present invention is as follows.

<1> Terahertz wave shielding material containing nanowires and binder.

<2> The terahertz wave shielding material according to <1>, wherein the nanowire is a nanowire containing as a main component one or more metals selected from the group consisting of iron, nickel, and cobalt.

<3> The terahertz wave shielding material according to <1> or <2>, wherein the average length of the nanowires is 5 μm or more.

<4> The terahertz wave shielding material according to any one of <1> to <3>, wherein the nanowire is a nanowire in which a plurality of particles are connected.

<5> The terahertz wave shielding material according to any one of <1> to <4>, wherein the absolute value of the transmission attenuation of electromagnetic waves with a bandwidth of 287.5 to 312.5 GHz is 20 dB/mm or more.

<6> The terahertz wave shielding material according to any one of <1> to <5>, wherein the reflectance of electromagnetic waves with a bandwidth of 287.5 to 312.5 GHz is less than 50%.

<7> The terahertz wave shielding material according to any one of <1> to <6>, wherein the nanowire content is less than 67% by mass.

<8> The terahertz wave shielding material according to any one of <1> to <7>, wherein the nanowire content is 0.5% by mass or more.

<9> The nanowire is a nanowire whose main component is iron or nickel,

The terahertz wave shielding material according to any one of <1> to <8>, wherein the nanowire content is 8 mass% or more and less than 67 mass%.

<10> Nanowire is a nanowire whose main component is iron,

The terahertz wave shielding material according to any one of <1> to <9>, wherein the nanowire content is 20 to 50 mass%.

<11> An antenna unit for wireless communication containing the terahertz wave shielding material according to any one of <1> to <10>.

<12> A sensing unit containing the terahertz wave shielding material according to any one of <1> to <10>.

According to the present invention, it is possible to provide a shielding material that is excellent in heat resistance, flexibility, and shielding properties against terahertz waves.

Since the shielding material of the present invention has sufficient shielding properties against terahertz waves even in a small mixing amount, it has excellent processability and can exhibit sufficient shielding properties even when molded from a thin material of less than 1 mm, and thus can be used for wireless applications. It can be suitably used in communication antenna units or sensing units.

Figure 1 is a diagram showing the transmission attenuation of electromagnetic waves between 0.2 and 2 THz of the shielding material of Example 2.
Figure 2 is a diagram showing the reflectance of electromagnetic waves between 0.2 and 2 THz of the shielding material of Example 2.

The terahertz wave shielding material of the present invention contains nanowires and a binder. The content of nanowires in the shielding material is not particularly limited and can be appropriately set depending on the required shielding ability and mechanical or thermal properties. Normally, the shielding performance increases as the amount of filler added increases, but the flexibility of the material decreases and becomes difficult to handle. Unlike other fillers, nanowires are characterized by a shielding effect even with a small content. If the nanowire content is 0.5% by mass or more, sufficient shielding performance can be obtained, depending on the shape (thickness). From the viewpoint of further improvement in shielding properties, the nanowire content is more preferably 1% by mass or more, more preferably 8% by mass or more, sufficiently preferably 10% by mass or more, and more preferably 20% by mass or more. . On the other hand, since the effect can be obtained even with a small content, it can be used as a shielding material that not only has excellent material strength and ease of handling, but also generates little reflected waves. Therefore, from the viewpoint of flexibility, heat resistance and reflectivity, the nanowire content is preferably less than 67% by mass, more preferably 50% by mass or less, sufficiently preferably 40% by mass or less, and 30% by mass or less. more fully desirable.

In particular, the content of nanowires mainly containing base metals such as iron, nickel, or cobalt, which will be described later, is 20 to 50% by mass when a high shielding effect is expected, and when anti-reflection (low reflectance) is expected. It is preferable that it is in the range of 1 to 20 mass% or less.

In this specification, shielding is a characteristic that sufficiently suppresses transmission of terahertz waves, 0.1 to 10 THz, especially 287.5 to 312.5 GHz.

Heat resistance is a characteristic that allows the shape to be maintained even in a high temperature environment (for example, 200°C).

Flexibility is a characteristic that allows bending without causing cracks.

Anti-reflection is a characteristic that sufficiently suppresses reflection in the terahertz range of 0.1 to 10 THz, especially in the range of 287.5 to 312.5 GHz.

Shielding properties, heat resistance, and flexibility are characteristics of the terahertz wave shielding material of the present invention.

Anti-reflection is not a property that the terahertz wave shielding material of the present invention must have, but is a property that it is desirable for the terahertz wave shielding material of the present invention to have.

The manufacturing method of the terahertz wave shielding material of the present invention is not particularly limited, but examples include methods such as melting and extrusion molding, or coating with ink or paste.

The band of terahertz waves is generally considered to be around 0.1 THz to 10 THz, and the band of 287.5 to 312.5 GHz is expected to be used in next-generation wireless communications.

The terahertz wave shielding material of the present invention shields terahertz waves. The shielding property can be evaluated by the amount of transmission attenuation using THz-TDS (terahertz time domain spectroscopy). The greater the absolute value of the transmission attenuation, the better the shielding performance. The absolute value of the transmission attenuation of terahertz waves is preferably 20 dB/mm or more, more preferably 50 dB/mm or more, and even more preferably 100 dB/mm or more. If the absolute value of the transmission attenuation is 20 dB/mm or more, it can be used as a shielding material even if it is molded from a material less than 1 mm thick. In particular, the absolute minimum value of the transmission attenuation amount is more preferably 20 dB/mm or more, more preferably 50 dB/mm or more, and 100 dB/mm in the band of 287.5 GHz to 312.5 GHz that may be used in next-generation wireless communications. It is more preferable that it is mm or more.

The transmission attenuation amount uses a value obtained by subjecting a terahertz wave shielding material having a sheet shape with a thickness of 0.4 to 1.8 mm to THz-TDS (terahertz time domain spectroscopy).

The terahertz wave shielding material of the present invention preferably has a low terahertz wave reflectance. The lower the reflectance and the greater the absolute value of transmission attenuation, the better the material's ability to absorb electromagnetic waves. If the absorption of terahertz waves is excellent, amplification of noise due to coupling of reflected waves, etc. can be suppressed. The reflectance of terahertz waves is preferably less than 50%, more preferably less than 30%, and even more preferably less than 20%. In particular, the reflectance in the band of 287.5 to 312.5 GHz is preferably less than 50%, more preferably less than 30%, and still more preferably less than 20%.

The reflectance uses a value obtained by subjecting a terahertz wave shielding material having a sheet shape with a thickness of 0.4 to 1.8 mm to THz-TDS (terahertz time domain spectroscopy). The reflectance is a value calculated as the reflectance amount of the sample/reflection amount of the gold thin film, with the reflectance amount of the gold thin film being 100%.

The nanowire used in the present invention refers to a fibrous material with a nanoscale diameter. The nanowire is preferably a nanowire containing metal as a main component from the viewpoint of increasing the dielectric constant and dielectric loss tangent of the binder material containing the nanowire and converting radio waves into heat. The metal constituting the nanowire as the main component is preferably non-metal so that the interfacial impedance of the binder material containing the nanowire does not differ from the space. The metal constituting the nanowire as a main component is preferably one or more metals selected from the group consisting of iron, nickel, and cobalt. In order to increase the permeability of the binder material containing nanowires, the nanowires are made of one or more types (particularly one type) selected from the group consisting of magnetic metals iron, nickel, and cobalt (hereinafter referred to as “group A”). It is more preferable that it is a nanowire containing a metal, and it is sufficiently preferable that it is a nanowire containing at least one type (especially one type) of metal selected from the above group A as a main component, and it is sufficiently preferable that it is a nanowire containing iron or nickel as a main component. more fully desirable. In the present invention, "consisting of a main component" refers to containing the nanowire at a content of 40% by mass or more, particularly containing it at the highest content. Additionally, by using a base metal containing the magnetic metals iron, cobalt, and nickel as the main component, it is possible to use a shielding material that can more effectively suppress reflection of terahertz waves and transmittance more effectively by forming a passivation layer on the surface. The formation of a passivation layer can be judged by X-ray photoelectron spectroscopy or Raman spectroscopy.

Nanowires containing iron as a main component, for example, have an iron content of 40% by mass or more relative to the total amount of the nanowire, and are preferably used from the viewpoint of further improvement in flexibility, heat resistance, and shielding properties and improvement in anti-reflection properties. It is 50 mass% or more, more preferably 70 mass% or more, and further preferably 70 to 90 mass%. Nanowires containing iron as a main component may contain atoms other than iron. Atoms other than iron may be, for example, one or more atoms selected from the group consisting of nickel, cobalt, and silver. The total content of atoms other than iron is usually 50 mass% or less, and may especially be 20 mass% or less.

In nanowires containing cobalt as a main component, for example, the cobalt content is preferably 40% by mass or more based on the entire amount of the nanowire, from the viewpoint of further improvement in flexibility, heat resistance, and shielding properties and improvement in anti-reflection properties. is 50% by mass or more, more preferably 70% by mass or more. Nanowires containing cobalt as a main component may contain atoms other than cobalt. Atoms other than cobalt may be, for example, one or more atoms selected from the group consisting of iron, nickel, and silver. The total content of atoms other than cobalt is usually 50 mass% or less, and may especially be 20 mass% or less.

In nanowires containing nickel as a main component, for example, the nickel content is preferably 40% by mass or more based on the entire amount of the nanowire, from the viewpoint of further improvement in flexibility, heat resistance, and shielding properties and improvement in anti-reflection properties. is 50% by mass or more, more preferably 70% by mass or more. Nanowires containing nickel as a main component may contain atoms other than nickel. Atoms other than nickel may be, for example, one or more atoms selected from the group consisting of iron, cobalt, and silver. The total content of atoms other than nickel is usually 50 mass% or less, and may especially be 20 mass% or less.

In nanowires containing silver as a main component, for example, the silver content is 40% by mass or more with respect to the total amount of nanowires, and from the viewpoint of further improvement in flexibility, heat resistance, and shielding properties and improvement in anti-reflection properties, preferably It is 50 mass% or more, more preferably 70 mass% or more. Nanowires containing silver as a main component may contain atoms other than silver. Atoms other than silver may be, for example, one or more atoms selected from the group consisting of iron, nickel, and cobalt. The total content of atoms other than silver is usually 50 mass% or less, and may especially be 20 mass% or less.

In this specification, the metal content in the nanowire is expressed as a value (% by mass) relative to the entire amount of the nanowire. The content of the metal atom is a value measured by subjecting a solution in which nanowires are dissolved to a multi-element simultaneous analysis method and a calibration curve method based on the ICP-AES method.

The nanowire used in the present invention can easily form network-structured clusters in the material due to its high shape anisotropy, so the mixing amount can be suppressed. Suppression of the compounding amount is more effective the longer the average length of the nanowires, and the average length of the nanowires is preferably 5 μm or more, and more preferably 10 μm or more. On the other hand, as the length of the nanowire increases, processability decreases, so the average length is preferably 50 μm or less, and more preferably 30 μm or less.

In this specification, the average length of nanowires is the average value of 100 arbitrary nanowires based on imaging with a scanning electron microscope (SEM).

The average diameter of the soft magnetic nanowire of the present invention is not particularly limited, but is preferably 20 to 500 nm, and more preferably 50 to 400 nm, from the viewpoint of further improvement in flexibility, heat resistance, and shielding properties and improvement in reflection resistance. It is more preferable that it is 50 to 300 nm, it is sufficiently preferable to be 50 to 200 nm, and it is more preferable to be 50 to 150 nm. The aspect ratio of the nanowire is not particularly limited, but if it is low, the effect of the nanowire cannot be obtained. For example, it may be 20 to 500, and from the viewpoint of the nanowire being sufficiently distributed in the material even in a small amount, it is preferably It is 40 to 300, and is more preferably 50 to 200 from the viewpoint of suppressing the demagnetizing field inside the nanowire.

In this specification, the average diameter of nanowires is the average value at 100 arbitrary points based on imaging with a scanning electron microscope (SEM). In addition, when the nanowire has a particle connection shape described later, the average diameter of the nanowire was set as the average value A of the maximum diameters described later.

The nanowire used in the present invention may have any shape as long as it has a fibrous shape. Fibrous shape means that one nanowire has a linear shape as a whole, and includes a “particle connected shape” in which particles are one-dimensionally connected and a simple “rod shape”.

The nanowire used in the present invention preferably has a particle-connected shape from the viewpoint of improving anti-reflection properties. Because the nanowire has a particle-connected shape, irregularities are created on the surface of the nanowire, which promotes the diffusion of incoming electromagnetic waves. As a result, terahertz waves become easier to absorb, suppressing reflection and increasing shielding properties. . It is possible to determine whether a nanowire has a particle-connected shape by SEM.

In detail, the particle connected shape refers to a linear shape as a whole formed by connecting a plurality of particles in series and continuously. Each particle at both ends is connected to one adjacent particle, and each other particle is connected to two adjacent particles on both sides. In such a particle connection shape, a concave portion is usually formed at the connecting portion (boundary portion between two particles), a convex portion is formed at the particle portion, and the concave portion and the convex portion are formed in the particle connection direction (longitudinal direction of the nanowire). The parts are repeated continuously. Each particle that makes up a nanowire has an approximately spherical shape. A roughly spherical shape is meant to include not only a spherical shape with a circular cross section, but also a three-dimensional shape with a triangular or larger polygonal shape, an elliptical shape, or a composite shape thereof.

Nanowires having a particle-connected shape are, specifically, when the average value of the maximum diameters in the nanowires is set to A (nm) and the average value of the minimum diameters in the nanowires is set to B (nm), the following In order to satisfy the formula (1-1), improve reflection resistance, and make it difficult to fold, it is preferable to satisfy the formula (1-1') below, and to satisfy the formula (1-1'') below: It is more preferable.

1.1≤A/B≤2.5 (1-1)

1.1≤A/B≤2 (1-1')

1.1≤A/B≤1.75 (1-1'')

In a nanowire having a particle-connected shape, the diameter means the diameter in a cross section perpendicular to the longitudinal direction of the nanowire, and the maximum and minimum values of the diameter can be read in the SEM image of the nanowire. Nanowires with particle-connected shapes provide a maximum diameter at locations other than the ends of the nanowire. The end is within 100 nm from the end of the nanowire. The average value A of the maximum diameter is the average value of the maximum diameter for 100 arbitrary nanowires. The average value B of the minimum diameter value is the average value of the minimum diameter values for 100 arbitrary nanowires. Based on these values, A/B is calculated.

In nanowires having a particle-connected shape, the average value A of the maximum diameter is usually 50 to 500 nm, especially 50 to 400 nm, and from the viewpoint of further improvement in flexibility, heat resistance and shielding properties and improvement in anti-reflection properties, it is preferable. is 50 to 300 nm, more preferably 50 to 200 nm, further preferably 60 to 200 nm, and most preferably 60 to 150 nm.

In nanowires having a particle-connected shape, the average value B of the minimum diameter is usually 10 to 200 nm, especially 20 to 200 nm, and from the viewpoint of further improvement in flexibility, heat resistance and shielding properties and improvement in anti-reflection properties, it is preferable. is 30 to 150 nm, more preferably 30 to 100 nm, further preferably 40 to 100 nm, and sufficiently preferably 40 to 90 nm.

The manufacturing method of the nanowire used in the present invention is not particularly limited, but can be obtained by reducing metal ions in a solution under specific conditions. A method for producing a nanowire having a particularly preferable particle connection shape and containing as a main component a metal selected from the group consisting of iron, nickel, and cobalt is shown below.

Metal ions that serve as raw materials for nanowires are supplied as metal salts such as hydrochloride, sulfate, and nitrate. Examples include iron chloride, cobalt chloride, nickel chloride, iron sulfate, cobalt sulfate, nickel sulfate, iron nitrate, cobalt nitrate, and nickel nitrate. There is no problem with these even if they are hydrated.

The metal salt of the raw material is supplied to the reaction system as a solution. To turn a metal salt into a solution, a highly polar organic solvent such as monoalcohol, glycol, NMP, DMSO, or water is required. There is no problem whether these are single solvents or mixed solvents.

To the solution of the metal salt, a complexing agent such as EDTA or citric acid may be added depending on the needs of the reaction. Usually, adding a complexing agent lowers the reaction activity, making it easier to control the reaction, which affects shape control.

Nanowires can be obtained by reducing metal ions in solution. As a reduction method, hydrazine, sodium borohydride, dimethylamine borane, sodium hypophosphite, etc., which are common reducing agents in the electroless plating method, may be used, and the reduction may be performed under conditions recommended for each reducing agent and the metal ion to be reduced.

The method of supplying the reducing agent to the reaction system may be appropriately selected depending on the state of the reducing agent and the conditions of the reaction system. For example, if it is a liquid such as hydrazine, it can be supplied to the reaction system as is. In the case of solids such as sodium borohydride, it is preferable to supply them in solution.

The reaction after supplying the reducing agent may follow each reduction condition. For example, in the case of hydrazine with a medium reducing power, the pH is adjusted to alkaline with sodium hydroxide or the like, and the reduction reaction is performed at about 90°C. In the case of sodium borohydride, which has high reducing power, the reduction reaction is carried out at room temperature (eg, 20°C).

The reduction reaction may be performed by a batch method or a flow method.

In order to produce nanowires in the particle-connected form, a magnetic field of about 100 to 150 mT is applied during the reduction reaction in either the batch method or the flow method. The method for applying the magnetic field may be an appropriate method selected depending on the size of the reaction vessel or reaction channel.

The concentration of each material can be appropriately selected based on the capacity of the reaction system or the mixing method of each raw material. In the case of a reaction capacity of about several L, the metal salt of the raw material can be adjusted to a concentration of about 50 mmol/L, and the reducing agent can be added at a higher concentration than that concentration.

According to one of the purposes of the present invention, nanowires that provide shielding properties for terahertz radio waves exhibit excellent shielding effects even when their mixing ratio is low. For this reason, the terahertz wave shielding material of the present invention does not impair the heat resistance, flexibility, etc. of the binder itself.

The binder is not particularly limited and may be either organic or inorganic. Organic substances generally refer to polymers, and specific examples thereof include polyacrylic resin; polyurethane resin; epoxy resin; polyimide resin; fluororesin; Various rubbers, such as silicone rubber, etc. are mentioned. Examples of inorganic materials include water glass and silica.

When various types of rubber such as acrylic resin, urethane resin, and silicone rubber are used as the organic material, the terahertz wave shielding material of the present invention has excellent flexibility and becomes a material that is easy to process.

Additionally, for example, if epoxy resin is used, the terahertz wave shielding material of the present invention becomes a material with excellent adhesiveness.

Additionally, for example, if polyimide resin is used, the terahertz wave shielding material of the present invention becomes a material with excellent heat resistance.

Additionally, for example, if fluorine resin is used, the terahertz wave shielding material of the present invention becomes a material with excellent stain resistance.

When water glass, silica, etc. are used as the inorganic material, the terahertz wave shielding material of the present invention can have a low coefficient of thermal expansion, making it a material suitable for combination with ceramics and metals.

Various additives may be added to the terahertz wave shielding material of the present invention within a range that does not impair the effect of the present invention.

The shape of the terahertz wave shielding material of the present invention is not particularly limited, but examples include plate shape, sheet shape, coating film, and box shape. In detail, the terahertz wave shielding material of the present invention may have a so-called pellet form, or may have the form of a molded product having any shape. For example, the terahertz wave shielding material of the present invention may have a so-called pellet form formed by melting and kneading nanowires and a binder. Additionally, for example, the terahertz wave shielding material of the present invention may have the form of a molded product obtained by molding the pellet. Additionally, for example, the terahertz wave shielding material of the present invention may have the form of a molded product obtained by directly molding and processing nanowires and a binder. The molding processing method is not particularly limited, and examples include compression molding, injection molding, casting, melt kneading, and coating.

The terahertz wave shielding material of the present invention is excellent in heat resistance, flexibility, and terahertz wave shielding (preferably additional anti-reflection resistance), so it can be used for antenna units and sensing units in wireless communication. Specifically, the terahertz wave shielding material of the present invention is used to cover parts other than the transmitting and receiving parts of the antenna unit and the sensing unit to suppress noise coupling, etc.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

A. Various evaluations

(1) Qualitative and quantitative determination of metal species in nanowires

The sufficiently vacuum-dried nanowires were subjected to qualitative and quantitative analysis by ICP-AES.

(2) Average length of nanowires

As in (1), sufficiently vacuum-dried nanowires were photographed with SEM at 2000x magnification. The length of 100 random nanowires was measured, and the average value was calculated.

(3) Shape of nanowire

The nanowires were photographed with SEM at 100,000x magnification and their shape was evaluated.

When the nanowire had a particle-connected shape, the following measurements were performed.

The nanowire dispersion was dried on a grid with a support membrane, the obtained nanowires were photographed with a transmission electron microscope at a magnification of 100,000 to 1 million times, and the maximum and minimum diameters for one nanowire were arbitrarily set to 100. Measurements were made for the bone. From the average of those values, the A value, B value, and A/B value of the nanowire were calculated.

(4) Heat resistance

The molded sheet was cut into 2 cm x 2 cm and left in an oven heated to 200°C for 5 minutes.

After standing still, the shape was observed and evaluated based on the following standards.

○: The shape was maintained.

×: The shape could not be maintained.

(5) Flexibility

The molded sheet was cut into 2 cm x 10 cm and bent in the 90° direction at 5 cm from the 10 cm direction.

The bent portion was visually observed in the bent state, and evaluated based on the following criteria.

○: No cracks were formed.

×: Cracks were forming.

(6) Transmission attenuation (shielding)

The molded sheet was cut into 2 cm x 2 cm pieces, and the transmission attenuation was measured using THz-TDS (terahertz time domain spectroscopy).

From the measurement results, the minimum absolute value of the transmission attenuation in the band of 287.5 to 312.5 GHz was taken as the minimum transmission attenuation.

The lowest transmission attenuation was evaluated based on the following standards.

◎◎: 100dB/mm or more (maximum);

◎: 50 dB/mm or more, less than 100 dB/mm (excellent);

○: 20dB/mm or more, less than 50dB/mm (positive);

×: Less than 20dB/mm (practically problematic).

(7) Reflectance (reflection resistance)

The molded sheet was cut into 2 cm x 2 cm and measured with THz-TDS. A gold thin film was used as a blank, and its reflectance was set to 100%.

From the measurement results, the highest value in the band of 287.5 to 312.5 GHz was taken as the highest reflectance.

The highest reflectance was evaluated based on the following standards.

◎◎: less than 20% (maximum);

◎: 20% or more, less than 30% (excellent);

○: 30% or more, less than 50% (positive);

×: 50% or more (practically problematic).

B. Raw materials

B-1. nanowires or particles

(1) Fe20NW

9.21 parts by mass (38.4 mole parts) of nickel chloride hexahydrate and 0.100 parts by mass (0.340 mole parts) of trisodium citrate dihydrate were dissolved in ethylene glycol to prepare 400 parts by mass.

1.50 parts by mass (37.5 mole parts) of sodium hydroxide was dissolved in ethylene glycol to prepare 410 parts by mass.

2.22 parts by mass (11.2 mole parts) of iron(II) chloride tetrahydrate was dissolved in ethylene glycol to prepare 100 parts by mass.

The three liquids are mixed, placed in a magnetic circuit with a central magnetic field of 130 mT, 75.0 parts by mass (1230 mole parts) of 28% aqueous ammonia and 15.0 parts by mass (300 mole parts) of hydrazine monohydrate are added in that order, and the temperature is 45°C at 90 to 95°C. Heated for a minute.

After that, the application of the magnetic field was stopped, and the resulting black solid was collected by filtration using a T100A090C PTFE filter, washed three times each with water and methanol, and vacuum dried for 24 hours to obtain nanowires.

(2) Fe80NW

26.0 parts by mass (131 mole parts) of iron (II) chloride tetrahydrate and 7.78 parts by mass (32.7 mole parts) of nickel chloride hexahydrate were dissolved in 1556.22 parts by mass of water, placed in a magnetic circuit with a central magnetic field of 130 mT, and bubbling with nitrogen gas. started. Ten minutes after the start of bubbling, dropwise addition of 310 parts by mass of an aqueous solution containing 12.4 parts by mass (327 parts by mole) of sodium borohydride dissolved in water was started. It was added dropwise at room temperature over 15 minutes and left to stand for an additional 10 minutes.

After that, application of the magnetic field and bubbling of nitrogen gas were stopped, and the reaction solution was poured into 1000 parts by mass of water and diluted. The resulting black solid was collected by filtration using a T100A090C PTFE filter, washed three times each with water and methanol, and vacuum dried for 24 hours to obtain nanowires.

(3) FeNW

34.2 parts by mass (172 parts by mol) of iron (II) chloride tetrahydrate was dissolved in 1195.8 parts by mass of water, placed in a magnetic circuit with a central magnetic field of 130 mT, and bubbling of nitrogen gas was started. Ten minutes after the start of bubbling, 730 parts by mass of an aqueous solution containing 28.0 parts by mass (740 mole parts) of sodium borohydride dissolved in water began to be added dropwise. It was added dropwise at room temperature over 15 minutes and left to stand for an additional 10 minutes.

After that, application of the magnetic field and bubbling of nitrogen gas were stopped, and the reaction solution was poured into 1000 parts by mass of water and diluted. The application of the magnetic field and the bubbling of nitrogen gas were stopped, and the resulting black solid was collected by filtration using a T100A090C PTFE filter, washed three times each with water and methanol, and vacuum dried for 24 hours to obtain nanowires.

(4) NiNW

10.0 parts by mass (42.1 mole parts) of nickel chloride hexahydrate and 0.935 parts by mass (3.18 mole parts) of trisodium citrate dihydrate were dissolved in ethylene glycol to prepare 500 parts by mass.

2.50 parts by mass (62.5 mole parts) of sodium hydroxide was dissolved in ethylene glycol to prepare 442 parts by mass.

The two liquids are mixed, placed in a magnetic circuit with a central magnetic field of 130 mT, 55.0 parts by mass (904 mole parts) of 28% aqueous ammonia and 2.50 parts by mass (49.9 mole parts) of hydrazine monohydrate are added in that order, and the temperature is 15% at 90 to 95°C. Heated for a minute.

Afterwards, the application of the magnetic field was stopped, and the resulting black solid was collected by filtration using a T100A090C PTFE filter, washed three times each with water and methanol, and vacuum dried for 24 hours to obtain nanowires.

(5) AgNWs

The Ag nanowire dispersion liquid manufactured by Sigma-Aldrich was collected by filtration using a T100A090C PTFE filter, washed three times each with water and methanol, and vacuum dried for 24 hours to obtain nanowires.

(6) NiP

Ni particles manufactured by Sigma-Aldrich (diameter 1 μm or less)

Table 1 shows the characteristic values of the nanowires and particles used.

In Table 1, the average length of NiP is the maximum length of the particles.

The aspect ratio of NiP is the maximum length/minimum length of the particle.

Meanwhile, the maximum and minimum lengths of the particle are the maximum and minimum lengths relative to the diameter passing through the center of gravity of the particle in the SEM image. The center of gravity is the point when a material of the same quality (e.g., paper) is cut along the outline of the particle, balanced, and supported at the point.

B-2. bookbinder

(1) Silicone mixed resin

Resin mixed with Momentive TSE3450/Momentive TSE3450=10/1 (mass ratio)

(2) Epoxy resin

Resin mixed with DIC EXA-4850-150/triethylenetetramine = 12/1 (mass ratio)

(3) Fluororesin

AGC company EA-2000. In the present invention, one suspended in toluene is used.

Example 1

65.0 parts by mass of Fe20NW and 35.0 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.5 mm in thickness.

Example 2

3.00 parts by mass of Fe20NW and 7.00 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press (RC-2000, manufactured by Noda) to produce a sheet (shielding material) of 12 cm x 12 cm x 0.4 mm thick.

Example 3

1.00 parts by mass of Fe20NW and 9.00 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.7 mm in thickness.

Example 4

0.500 parts by mass of Fe20NW and 9.50 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.4 mm thick.

Example 5

0.100 parts by mass of Fe20NW and 9.90 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.4 mm thick.

Example 6

3.00 parts by mass of Fe80NW and 7.00 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.4 mm thick.

Example 7

1.00 parts by mass of Fe80NW and 9.00 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 1.8 mm thick.

Example 8

1.00 parts by mass of FeNW and 9.00 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 1.6 mm thick.

Example 9

1.00 parts by mass of NiNW and 9.00 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 1.6 mm thick.

Example 10

3.00 parts by mass of AgNW and 7.00 parts by mass of silicone mixed resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.4 mm thick.

Example 11

3.00 parts by mass of Fe20NW and 7.00 parts by mass of epoxy resin were mixed and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.4 mm thick.

Example 12

3.00 parts by mass of AgNW were mixed with 7.00 parts by mass of epoxy resin, and molded using a tabletop hand press to produce a sheet (shielding material) of 12 cm x 12 cm x 0.4 mm thick.

Example 13

3.00 parts by mass of Fe20NW and 7.00 parts by mass of fluororesin were mixed, dried (toluene removed) in a 10 cm x 10 cm mold, and heat cured at 350°C to produce a sheet (shielding material) with a thickness of 0.4 mm.

Example 14

1.00 parts by mass of Fe20NW and 9.00 parts by mass of fluororesin were mixed, dried (toluene removed) in a 10 cm x 10 cm mold, and heat cured at 350°C to produce a sheet (shielding material) with a thickness of 0.4 mm.

Example 15

3.00 parts by mass of NiNW and 7.00 parts by mass of fluororesin were mixed, dried (toluene removed) in a 10 cm x 10 cm mold, and heat cured at 350°C to produce a sheet (shielding material) with a thickness of 0.4 mm.

Example 16

1.00 parts by mass of NiNW and 9.00 parts by mass of fluororesin were mixed, dried (toluene removed) in a 10 cm x 10 cm mold, and heat cured at 350°C to produce a sheet (shielding material) with a thickness of 0.4 mm.

Comparative Example 1

The silicone mixed resin was molded using a tabletop hand press to produce a sheet of 12 cm x 12 cm x 0.6 mm thick.

Comparative Example 2

1.00 parts by mass of NiP and 9.00 parts by mass of silicone mixed resin were molded using a tabletop hand press to produce a sheet of 12 cm x 12 cm x 0.6 mm thick.

Comparative Example 3

3.00 parts by mass of NiP and 7.00 parts by mass of silicone mixed resin were molded using a tabletop hand press to produce a sheet of 12 cm x 12 cm x 0.4 mm thick.

Comparative Example 4

8.00 parts by mass of NiP and 2.00 parts by mass of silicone resin were molded using a tabletop hand press to produce a sheet of 12 cm x 12 cm x 0.4 mm thick.

Comparative Example 5

3.00 parts by mass of NiP and 7.00 parts by mass of epoxy resin were molded using a tabletop hand press to produce a sheet of 12 cm x 12 cm x 0.4 mm thick.

Comparative Example 6

8.00 parts by mass of NiP and 2.00 parts by mass of epoxy resin were molded using a tabletop hand press to produce a sheet of 12 cm x 12 cm x 0.4 mm thick.

The composition and evaluation of the obtained sheets are shown in Tables 2 and 3.

Since the sheets (shielding materials) of Examples 1 to 16 were shielding materials containing nanowires and a binder, the attenuation properties (i.e., shielding properties) of terahertz waves were excellent. In addition, since the shielding performance was high even when the amount of nanowires added was low, the material had excellent flexibility and heat resistance.

Furthermore, since the sheets (shielding materials) of Examples 1 to 9, 11, and 13 to 16 used nanowires whose main components are metals selected from the group consisting of iron, nickel, and cobalt, they have low reflectivity and cannot transmit terahertz waves. was able to be more sufficiently attenuated inside the molded body.

Since the sheets of Comparative Examples 1 to 5 did not contain nanowires, the terahertz wave attenuation properties were poor.

In Comparative Examples 4 and 6, the amount of Ni particles added was increased in order to shield terahertz waves, so flexibility became insufficient, and since the amount added was large, the materials became materials with high reflectivity.

From comparison of Examples 1 to 3, 6 to 9, 11 and 13 to 16 with Examples 4 to 5, 10 and 12, the terahertz wave shielding material of the present invention satisfies the following conditions (A1) and (A2) It is clear that it has better shielding and anti-reflection properties (all above the “good” level) by satisfying:

(A1) The nanowire is a nanowire whose main component is iron or nickel;

(A2) The nanowire content is 8 mass% or more and less than 67 mass%.

From a comparison of Example 6 with Examples 1 to 5, 7 to 12, and 13 to 16, the terahertz wave shielding material of the present invention satisfies the following conditions (B1) and (B2), thereby providing further performance. It is clear that it has excellent shielding and anti-reflection properties (both at the “best” level):

(B1) The nanowire is a nanowire whose main component is iron;

(B2) The nanowire content is 20 to 50 mass%.

The terahertz wave shielding material of the present invention is useful for all applications that require at least one (preferably all properties) of heat resistance, flexibility, and shielding and anti-reflection properties for terahertz waves. Such uses include, for example, antenna units for wireless communication; sensing unit; Magnetic field shield for high frequencies; Examples include electromagnetic wave absorbing materials.

Claims (12)

Terahertz wave shielding material containing nanowires and binders. According to claim 1,
A terahertz wave shielding material, wherein the nanowire is a nanowire containing as a main component one or more metals selected from the group consisting of iron, nickel, and cobalt. According to claim 1,
A terahertz wave shielding material whose nanowires have an average length of 5μm or more. According to claim 1,
A terahertz wave shielding material in which nanowires are nanowires in which multiple particles are connected. According to claim 1,
A terahertz wave shielding material whose absolute value of transmission attenuation of electromagnetic waves with a bandwidth of 287.5 to 312.5 GHz is 20 dB/mm or more. According to claim 1,
A terahertz wave shielding material with a reflectance of less than 50% of electromagnetic waves in the bandwidth of 287.5 to 312.5 GHz. According to claim 1,
A terahertz wave shielding material with a nanowire content of less than 67% by mass. According to claim 1,
A terahertz wave shielding material with a nanowire content of 0.5% by mass or more. According to claim 1,
A nanowire is a nanowire whose main component is iron or nickel,
A terahertz wave shielding material with a nanowire content of 8 mass% or more and less than 67 mass%. According to claim 1,
A nanowire is a nanowire whose main component is iron,
A terahertz wave shielding material with a nanowire content of 20 to 50 mass%. An antenna unit for wireless communication containing the terahertz wave shielding material according to any one of claims 1 to 10. A sensing unit comprising the terahertz wave shielding material according to any one of claims 1 to 10.