Structure containing nano-wire having insulating film

Abstract

To provide a structure that is low in reflectivity while maintaining the performance of shutting off an electromagnetic wave in a terahertz wave region.SOLUTION: A structure contains a nano-wire coated with an insulating film consisting of a material having a volume resistivity of 1013 Ω cm or greater and resin having a volume resistivity of 1012 Ω cm or greater, in which: the material having the volume resistivity of 1013 Ω cm or greater is an inorganic material; the inorganic material is silica; the nano-wire has an average length of 3-30 μm; the nano-wire contains nickel or iron; the nano-wire is an alloy of nickel and iron; the coating has an average thickness of 50nm or smaller; the resin having the volume resistivity of 1012 Ω cm or greater is silicone resin; and the nano-wire has a mass ratio relative to a total of the nano-wire and the resin of 40 mass% or higher.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a structure containing nanowires having an insulating coating.

Background Art

[0002] As a safe non-destructive inspection electromagnetic wave that can replace X-rays and as an electromagnetic wave for 6G wireless communication, the use of electromagnetic waves in the terahertz wave region has been studied. However, since electromagnetic waves in the terahertz wave region have characteristics similar to light, they are likely to be reflected by free electrons, and amplification and attenuation are likely to occur due to interference of the reflected waves.

[0003] As a shielding material for electromagnetic waves in the terahertz region, for example, Patent Document 1 discloses an electromagnetic wave shielding material using nanowires. In recent years, an electromagnetic wave absorption material with a low reflectivity to terahertz waves has been demanded, and further reduction of the reflectivity has been required.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a structure having a low reflectivity while maintaining the shielding performance of electromagnetic waves in the terahertz wave region as compared with conventional products.

Means for Solving the Problems

[0006] As a result of intensive studies to solve such problems, the present inventors have found that the above object can be achieved by using nanowires coated with an insulating film, and have reached the present invention.

[0007] The gist of the present invention is as follows. <1>A nanostructure coated with an insulating film made of a material having a volume resistivity of 10 13 Ω·cm or more and a structure containing a resin having a volume resistivity of 10 12 Ω·cm or more. <2>The structure according to <1>, wherein the material having a volume resistivity of 10 13 Ω·cm or more is an inorganic material. <3>The structure according to <2>, wherein the inorganic material is silica. <4>The structure according to any one of <1> to <3>, wherein the average length of the nanowires is 3 to 30 μm. <5>The structure according to any one of <1> to <4>, wherein the nanowires contain nickel or iron. <6>The structure according to any one of <1> to <5>, wherein the nanowires are an alloy of nickel and iron. <7>The structure according to any one of <1> to <6>, wherein the average thickness of the film is 50 nm or less. <8>The structure according to any one of <1> to <7>, wherein the resin having a volume resistivity of 10 12 Ω·cm or more is a silicone resin. <9>The structure according to any one of <1> to <8>, wherein the mass ratio of the nanowires to the total of the nanowires and the resin is 40% by mass or more.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a structure having a low reflectance while maintaining the electromagnetic wave shielding performance in the terahertz wave region.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] The structure of the present invention contains nanowires coated with an insulating film and a resin.

[0011] The insulating film needs to have a volume resistivity of 10 13 Ω·cm or more. When the volume resistivity is less than 10 13 Ω·cm, the reflectivity becomes high, which is not preferable. As the insulating film, an inorganic material is preferable, a ceramic is more preferable, and silica is even more preferable from the simplicity of the reaction. The volume average resistivity of the insulating film is a value obtained by preparing a sheet having the same composition as the insulator film and using a resistivity meter.

[0012] The average thickness of the film is not particularly limited, but if it is too thick, the content ratio of the insulating film becomes relatively low, the shielding performance of the electromagnetic wave in the terahertz wave region deteriorates, and the reflectivity becomes high. Therefore, it is preferably 50 nm or less, more preferably 240 nm or less, and even more preferably 20 nm or less.

[0013] The nanowires preferably contain a metal, more preferably contain nickel or iron, from the ease of manufacturing and the ease of forming the film. Since a structure with a lower reflectivity can be obtained while maintaining the shielding performance of the electromagnetic wave in the terahertz wave region, it is even more preferable to contain an alloy of iron and nickel.

[0014] The shape of the nanowire is not particularly limited as long as it can be mixed with the resin. However, if the average length is too long, the nanowire will be cut during mixing with the resin and a structure cannot be fabricated, which is not preferable. The average length of the nanowire is preferably 3 to 30 μm, and more preferably 5 to 25 μm. The aspect ratio (average length / average diameter) of the nanowire is preferably 60 or more, and more preferably 70 or more. The larger the aspect ratio, the lower the reflectivity of the structure can be obtained while maintaining the shielding performance of the electromagnetic wave in the terahertz wave region.

[0015] The nanowire used in the present invention can be obtained by fabricating the nanowire in a magnetic field and then coating it with an insulating film.

[0016] When the nanowire is a metal nanowire such as nickel, iron, or an alloy of iron and nickel, the nanowire can be obtained by reducing each metal ion with a reducing agent in a reaction solution while applying a magnetic field.

[0017] The total concentration of the metal salts in the reaction solution is preferably 10 to 100 mmol / kg, and more preferably 30 to 60 mmol / kg. When the concentration is less than 10 mmol / kg, the production efficiency may deteriorate. When the concentration exceeds 100 mmol / kg, the obtained nanowires may aggregate and the dispersibility may be poor. The total concentration of the above metal salts is the concentration in the reaction solution when a magnetic field is applied and stirred.

[0018] The reaction solution preferably has a boiling point of 80°C or higher and is a highly polar solvent, and polyols such as ethylene glycol and propylene glycol, and water are more preferable.

[0019] From the viewpoints of the reduction potential and the removal of the solvent after the production of the nanowires, it is preferable to use hydrazine monohydrate as the reducing agent. When a boron-based or phosphorus-based reducing agent is used, boron or phosphorus may be incorporated into the metal and nanowires may not be obtained. The concentration of the reducing agent is preferably 1.1 molar ratio with respect to the total concentration of the metal salts. The concentration of the reducing agent is preferably 25 to 150 mmol / kg, and more preferably 30 to 70 mmol / kg. When the concentration of the reducing agent is less than 25 mmol / kg, metal ions may not be reduced and the yield may be significantly reduced. On the other hand, when the concentration of the reducing agent exceeds 150 mmol / kg, the reduction efficiency saturates. The concentration of the reducing agent described above is the concentration in the reaction solution when stirring is performed with a magnetic field applied.

[0020] When reducing metal ions, it is preferable to use sodium hydroxide and ammonia in addition to the metal salts and the reducing agent. By using sodium hydroxide, the reaction solution can be made alkaline and the reduction reaction can be promoted. On the other hand, sodium hydroxide reacts with some metal ions to form hydroxide precipitates, reducing the yield and the purification efficiency. To suppress the decrease in the yield and the purification efficiency, it is preferable to use ammonia. By using ammonia, complexes can be formed and the hydroxides can be redissolved. Sodium hydroxide is preferably added so that the pH of the reaction solution becomes 11 to 13, and the concentration of ammonia is preferably 0.5 to 5% by mass in the reaction solution, and more preferably 0.8 to 3% by mass.

[0021] By adding sodium hydroxide to make the pH of the reaction solution 11 to 13, a passive layer can be formed on the surface immediately after the formation of the nanowires.

[0022] When producing nanowires, it is preferable to use trisodium citrate as the complexing agent, and the concentration of the nucleating agent is preferably 5 to 20 molar ratio with respect to the total concentration of the metal salts.

[0023] The temperature of the reduction reaction is preferably 85 to 95°C, more preferably 90 to 95°C. When the temperature of the reduction reaction is lower than 85°C, the reaction may take a long time. On the other hand, when the temperature is higher than 95°C, nanowires may not be generated.

[0024] During the reduction reaction, a magnetic field is applied. The application of the magnetic field can be carried out by a magnetic circuit or the like, and it is preferably carried out with a magnetic field of about 50 to 150 mT, more preferably with a magnetic field of about 100 to 150 mT.

[0025] The obtained nanowires are purified to remove impurities such as by-products and unreacted substances, and then recovered.

[0026] It is necessary to form an insulating film such as a silica film on the recovered nanowires. For example, when forming a silica film, it can be formed by treating the obtained nanowires with tetraethoxysilane and an alkali. The film thickness of the film can be controlled by the treatment time. The treatment time is preferably 1 hour or more.

[0027] The structure of the present invention can be manufactured by mixing and molding the nanowires and a resin. For example, a method of mixing nanowires and a resin with a mixer, adding a curing agent, and then defoaming and molding can be mentioned. Examples of the shape of the structure include a sheet shape, a film shape, and a rod shape.

[0028] The resin needs to have a volume resistivity of 10 12 Ω·cm or more. When the volume resistivity is less than 10 12 Ω·cm, the shielding performance of electromagnetic waves in the terahertz wave region deteriorates and the reflectivity increases, which is not preferable. From the viewpoints of flexibility and heat resistance, a silicone resin is preferable as the resin. Examples of the silicone resin include TSE3450(A) and TSE3450(B) manufactured by Momentive.

[0029] It is preferable that the mass ratio of the nanowire to the total of the nanowire and the resin is 40% by mass or more. When the mass ratio is less than 40% by mass, it may be difficult to distill off a solvent or the like, or bubbles may be generated in the structure, resulting in a performance degradation.

[0030] Compared with conventional products, the structure of the present invention can be suitably used as a shielding material for electromagnetic waves in the terahertz wave region because it maintains the shielding performance of electromagnetic waves in the terahertz wave region while having a low reflectance.

Examples

[0031] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto. (1) Composition of Nanowire The nanowire was vacuum-dried at room temperature for 24 hours. The vacuum-dried nanowire was dissolved in a mixed solution of dilute hydrochloric acid and dilute nitric acid. The obtained solution was quantitatively analyzed for the contents of Fe and Si by a calibration curve method using an ICP-AES method with aqueous solutions of nickel (Ni) and iron (Fe) as standard solutions.

[0032] (2) Average Fiber Diameter and Average Length of Nanowire The nanowire sufficiently vacuum-dried in the same manner as in (1) was photographed with a scanning electron microscope (SEM). For any 10 fields of view, the fiber length and fiber diameter were measured at any 10 points in each field of view (a total of 100 points), and the respective averages were taken as the average length and average diameter.

[0033] (3) Average Thickness of Coating The nanowire sufficiently vacuum-dried in the same manner as in (1) was photographed with a TEM. The film thickness of silica was measured at any 10 points, and the average value was taken as the average thickness of the silica coating.

[0034] (4) Volume Resistivity of Coating A 10 cm square sheet was prepared using a metal having the same composition as the coating used, and the resistivity was measured using a resistivity meter (Hi-Rester-UX MCP-HT800).

[0035] (5) Volume resistivity of the resin A 10 cm square sheet was fabricated using the resin used, and the volume resistivity was measured with a resistivity meter (High Resista-UX MCP-HT800).

[0036] (6) Transmission attenuation (shielding property) The molded sheet was cut into 2 cm × 2 cm pieces, and the transmission attenuation was measured using THz-TDS (terahertz time-domain spectroscopy). The minimum value of the absolute value of the transmission attenuation in the frequency band of 0.2875 to 0.3125 THz was obtained. The minimum value of the absolute value of the transmission attenuation was evaluated according to the following evaluation criteria by comparing with the same structure except using nanowires without an insulating film, and the value obtained from the following (Equation 1). (Equation 1) (Minimum value of the absolute value of the transmission attenuation of the structure using nanowires with an insulator film / Minimum value of the absolute value of the transmission attenuation of the same structure except using nanowires without an insulating film) × 100

[0037] (Evaluation criteria) ◎: 95% or more (excellent); ○: 90% or more and less than 95% (good); ×: Less than 90% (problematic in practical use).

[0038] (6) Reflectance The molded sheet was cut into 2 cm × 2 cm pieces, and the reflectance was measured using THz-TDS with a gold thin film as a blank. The maximum value of the reflectance in the frequency band of 0.2875 to 0.3125 THz was obtained. The maximum value of the reflectance was evaluated according to the following evaluation criteria by comparing with the same structure except using nanowires without an insulating film, and the value obtained from the following (Equation 2). (Equation 2) 100 - (Maximum value of the reflectance of the structure using nanowires with an insulator film - Maximum value of the reflectance of the same structure except using nanowires without an insulating film) × 100

[0039] (Evaluation criteria) ◎: 30% or more (excellent); ○: More than 5% and less than 30% (good); ×: Less than 5% (problematic in practical use).

[0040] Example 1 10.0 parts by mass (0.0421 mol parts) of nickel chloride hexahydrate and 0.935 parts by mass (0.00318 mol parts) of trisodium citrate dihydrate were dissolved in ethylene glycol and adjusted to 500 parts by mass. 2.50 parts by mass (0.0625 mol parts) of sodium hydroxide were dissolved in ethylene glycol and adjusted to 442 parts by mass. The two solutions were mixed, placed in a magnetic circuit with a central magnetic field of 130 mT, and 55.0 parts by mass (0.904 mol parts) of 28% aqueous ammonia and 2.50 parts by mass (0.0499 mol parts) of hydrazine monohydrate were added in this order, followed by heating and stirring at 90 - 95 °C for 15 minutes. In the reaction solution, the concentration of nickel salt was 42.1 mmol / kg and the concentration of reducing agent was 49.9 mmol / kg. The pH of the reaction solution was 12, and the addition amount of ammonia in the reaction solution was 1.54% by mass. Thereafter, the application of the magnetic field was stopped, and the resulting black solid was filtered using a PTFE filter with the trade name "T100A090C" (manufactured by Advantec) and washed three times with water to obtain nickel nanowires. 25.0 parts by mass of the washed nanowires were immersed in a solution of 475 parts by mass of isopropanol, 40.0 parts by mass of water, 5.00 parts by mass of tetraethoxysilane, and 2.00 parts by mass of aqueous ammonia at room temperature for 3 days. After immersion, it was filtered and recovered using a PTFE filter of T100A090C, washed with water and isopropanol, and vacuum dried at 500 °C for 24 hours to obtain nanowires. 15.8 parts by mass of the obtained nanowires were mixed with 76.6 parts by mass of TSE3450(A) and 7.6 parts by mass of TSE3450(B), degassed under vacuum, and made into a sheet with a thickness of 0.5 mm.

[0041] Example 2 9.21 parts by mass (38.4 mol parts) of nickel chloride hexahydrate and 0.100 parts by mass (0.340 mol parts) of trisodium citrate dihydrate were dissolved in ethylene glycol and adjusted to 400 parts by mass. 1.50 parts by mass (37.5 mol parts) of sodium hydroxide was dissolved in ethylene glycol and adjusted to 410 parts by mass. 2.22 parts by mass (11.2 mol parts) of iron(II) chloride tetrahydrate was dissolved in ethylene glycol and adjusted to 100 parts by mass. The three liquids were mixed, placed in a magnetic circuit with a central magnetic field of 130 mT, and 75.0 parts by mass (1230 mol parts) of 28% aqueous ammonia and 15.0 parts by mass (300 mol parts) of hydrazine monohydrate were added in this order, followed by heating at 90 - 95 °C for 45 minutes. Thereafter, the application of the magnetic field was stopped, and the resulting black solid was filtered and recovered using a PTFE filter of T100A090C, then washed three times each with water and methanol, and dried in vacuo for 24 hours to obtain nanowires. With respect to 25.0 parts by mass of the washed nanowires, they were immersed in a solution of isopropanol 475 parts by mass, water 40.0 parts by mass, tetraethoxysilane 5.00 parts by mass, aqueous ammonia 2.00 parts by mass = 65:16:2:0.7 (mass ratio) at room temperature for 3 days. After immersion, they were filtered and recovered using a PTFE filter of T100A090C, then washed with water and isopropanol, and dried in vacuo at 500 °C for 24 hours to obtain nanowires. To 15.5 parts by mass of the obtained nanowires, 76.8 parts by mass of TSE3450(A) and 7.7 parts by mass of TSE3450(B) were mixed, degassed in vacuo, and made into a sheet with a thickness of 0.5 mm.

[0042] Comparative Example 1 10.0 parts by mass (0.0421 mol parts) of nickel(II) chloride hexahydrate and 0.935 parts by mass (0.00318 mol parts) of trisodium citrate dihydrate were dissolved in ethylene glycol and adjusted to 500 parts by mass. 2.50 parts by mass (0.0625 mol parts) of sodium hydroxide was dissolved in ethylene glycol and adjusted to 442 parts by mass. Mix two liquids, place them in a magnetic circuit with a central magnetic field of 130 mT, and add 55.0 parts by mass (0.904 mole parts) of 28% aqueous ammonia and 2.50 parts by mass (0.0499 mole parts) of hydrazine monohydrate in this order. Heat and stir at 90 - 95 °C for 15 minutes. In the reaction solution, the concentration of nickel salt was 42.1 mmol / kg, and the concentration of the reducing agent was 49.9 mmol / kg. The pH of the reaction solution was 12, and the addition amount of ammonia in the reaction solution was 1.54% by mass. After that, stop applying the magnetic field, filter the resulting black solid using a PTFE filter with the trade name "T100A090C" (manufactured by Advantec), and wash it three times with water to obtain nickel nanowires. Mix 15 parts by mass of the obtained nanowires with 77.3 parts by mass of TSE3450(A) and 7.7 parts by mass of TSE3450(B). After vacuum degassing, prepare a sheet with a thickness of 0.5 mm.

[0043] Comparative Example 2 Dissolve 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 in ethylene glycol and adjust to 400 parts by mass. Dissolve 1.50 parts by mass (37.5 mole parts) of sodium hydroxide in ethylene glycol and adjust to 410 parts by mass. Dissolve 2.22 parts by mass (11.2 mole parts) of iron(II) chloride tetrahydrate in ethylene glycol and adjust to 100 parts by mass. Mix the three liquids, place them in a magnetic circuit with a central magnetic field of 130 mT, and add 75.0 parts by mass (1230 mole parts) of 28% aqueous ammonia and 15.0 parts by mass (300 mole parts) of hydrazine monohydrate in this order. Heat at 90 - 95 °C for 45 minutes. After that, stop applying the magnetic field, filter and collect the resulting black solid using a PTFE filter of T100A090C, wash it three times each with water and methanol, and vacuum dry for 24 hours to obtain nanowires. Mix 15.0 parts by mass of the obtained nanowires with 77.3 parts by mass of TSE3450(A) and 7.7 parts by mass of TSE3450(B). After vacuum degassing, prepare a sheet with a thickness of 0.5 mm.

[0044] Table 1 shows the configurations of the structures obtained in Examples 1 and 2 and Comparative Examples 1 and 2, the characteristic values of the nanowires used, the characteristic values of the resin, and the characteristic values of the obtained structures.

[0045]

Table 1

[0046] The structures obtained in Examples 1 and 2, when compared with the structures obtained in Comparative Examples 1 and 2 which are the same except that they use nanowires without an insulating film which is a conventional product, maintained almost the same electromagnetic wave shielding performance in the terahertz region (the value of (Equation 1) is 90% or more), while the reflectivity decreased by 5% or more (the value of (Equation 2) is 5% or more).

Claims

Claim 1 An insulating film made of a material with a volume resistivity of 10 １３ Ω·cm or more, and a nanostructure coated with the insulating film, and a structure containing a resin with a volume resistivity of 10 １２ Ω·cm or more. Claim 2 The structure according to claim 1, wherein the material having a volume resistivity of 10 １３ Ω·cm or more is an inorganic material. Claim 3 The structure according to claim 2, wherein the inorganic material is silica. Claim 4 The structure according to claim 1 or 2, wherein the average length of the nanowires is 3 to 30 μm. Claim 5 The structure according to claim 1 or 2, wherein the nanowires contain nickel or iron. Claim 6 The structure according to claim 1 or 2, wherein the nanowires are an alloy of nickel and iron. Claim 7 The structure according to claim 1 or 2, wherein the average thickness of the coating is 50 nm or less. Claim 8 The resin having a volume resistivity of 10 １２ Ω·cm or more is a silicone resin, and the structure according to claim 1 or 2. Claim 9 The structure according to claim 1 or 2, wherein the mass ratio of the nanowires to the total of the nanowires and the resin is 40% by mass or more.

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