Electromagnetic wave absorber

Abstract

To provide an electromagnetic wave absorber that can improve electromagnetic wave absorption performance. [Solution] The electromagnetic wave absorber according to the present invention contains glass fibers and carbon nanotubes, and the glass fiber content is 80% by mass or more.

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave absorber.

Background Art

[0002] An electromagnetic wave absorber that absorbs electromagnetic waves is known. The electromagnetic wave absorber is used, for example, in offices, laboratories, hospitals, etc. to absorb electromagnetic waves emitted from electronic components such as wireless LAN (Local Area Network).

[0003] For example, Patent Document 1 describes an electromagnetic wave absorber of a conductive glass fiber mat containing a conductive material.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the electromagnetic wave absorber as described above, it is desired to improve the electromagnetic wave absorption performance.

[0006] One of the objects according to some aspects of the present invention is to provide an electromagnetic wave absorber capable of improving the electromagnetic wave absorption performance.

Means for Solving the Problems

[0007] One aspect of the electromagnetic wave absorber according to the present invention is including glass fibers and carbon nanotubes, where the content of the glass fibers is 80% by mass or more.

[0008] In one aspect of the electromagnetic wave absorber according to the present invention, the glass fibers constitute a sheet-like base material, The carbon nanotubes are attached to the glass fibers, The amount of carbon nanotubes attached to the glass fibers is 0.1 g / m 2 More than 10g / m 2 The following is also acceptable.

[0009] In one embodiment of the electromagnetic wave absorber according to the present invention, The amount of carbon nanotubes attached to the glass fibers is 0.3 g / m 2 More than 7.0g / m 2 The following is also acceptable.

[0010] In one embodiment of the electromagnetic wave absorber according to the present invention, The average fiber diameter of the glass fibers is 0.05 μm or more and 20 μm or less. The glass fibers include submicron fibers with an average fiber diameter of 0.05 μm or more and 1.0 μm or less. When the amount of glass fibers contained in the electromagnetic wave absorber is 100 parts by mass, the amount of submicron fibers may be 1.0 part by mass or more.

[0011] In one embodiment of the electromagnetic wave absorber according to the present invention, The content of the submicron fibers may be 10 parts by mass or more and 90 parts by mass or less.

[0012] In one embodiment of the electromagnetic wave absorber according to the present invention, Contains sodium carboxymethylcellulose, The carboxymethylcellulose sodium is attached to the glass fiber, The amount of sodium carboxymethylcellulose adhering to the glass fibers is 0.1 g / m². 2 More than 10g / m 2 The following is also acceptable.

[0013] In one embodiment of the electromagnetic wave absorber according to the present invention, Contains polyacrylic acid, The polyacrylic acid is attached to the glass fiber, The amount of polyacrylic acid adhering to the glass fibers is 0.1 g / m 2 More than 10g / m 2 The following is also acceptable.

[0014] In one embodiment of the electromagnetic wave absorber according to the present invention, Multiple substrates are provided, Multiple of the aforementioned substrates may be stacked. [Effects of the Invention]

[0015] The electromagnetic wave absorber according to the present invention contains glass fibers and carbon nanotubes, and since the glass fiber content is 80% by mass or more, the electromagnetic wave absorption performance can be improved. [Brief explanation of the drawing]

[0016] [Figure 1] A flowchart illustrating the manufacturing method of the electromagnetic wave absorber according to this embodiment. [Figure 2] A diagram illustrating the free-space method used to evaluate electromagnetic wave absorption performance. [Figure 3] A table showing the evaluation results for Examples 1-7 and Comparative Examples 1-4. [Modes for carrying out the invention]

[0017] Preferred embodiments of the present invention will be described in detail below with reference to the drawings. The embodiments described below are not intended to unduly limit the scope of the present invention as described in the claims. Furthermore, not all of the configurations described below are necessarily essential components of the present invention.

[0018] 1. Electromagnetic wave absorber 1.1. Ingredients First, the electromagnetic wave absorber according to this embodiment will be described. The electromagnetic wave absorber according to this embodiment includes, for example, glass fibers, carbon nanotubes (hereinafter also referred to as "CNTs"), and a dispersant.

[0019] 1.1.1. Glass fiber The average fiber diameter of the glass fiber contained in the electromagnetic wave absorber according to the present embodiment is, for example, 0.05 μm or more and 20 μm or less, preferably 0.1 μm or more and 10 μm or less, and more preferably 0.5 μm or more and 5.0 μm or less. The average fiber diameter d (μm) of the glass fiber is S total It is calculated from the following formula (1), where S is the specific surface area of the raw cotton made of glass fiber and ρ is the density of the raw cotton.

[0020] d = 4 / (S total × ρ) ··· (1)

[0021] Incidentally, the specific surface area S total (m 2 / g) is the specific surface area measured by the BET (Brunauer Emmett Teller) method by nitrogen adsorption, and is measured by, for example, an automatic specific surface area measuring device ("TriStarII3020" manufactured by Micromeritics). The density ρ is, for example, 2.49 g / cm 3 .

[0022] The glass fiber includes, for example, submicron fibers. The electromagnetic wave absorber includes a plurality of glass fibers, and some of the plurality of glass fibers are submicron fibers. The submicron fiber is a glass fiber having an average fiber diameter of 0.05 μm or more and 1.0 μm or less. The average fiber diameter of the submicron fiber is, for example, 0.1 μm or more and 0.9 μm or less, preferably 0.3 μm or more and 0.8 μm or less.

[0023] When the glass fiber contained in the electromagnetic wave absorber is 100 parts by mass, the content of the submicron fiber is, for example, 1.0 part by mass or more and 95 parts by mass or less, preferably 10 parts by mass or more and 90 parts by mass or less, more preferably 30 parts by mass or more and 85 parts by mass or less, and even more preferably 50 parts by mass or more and 80 parts by mass or less. If the content of the submicron fiber is 1.0 part by mass or more, the texture of the electromagnetic wave absorber can be improved. If the content of the submicron fiber is 95 parts by mass or less, the strength of the electromagnetic wave absorber can be ensured.

[0024] The number-average fiber length of the glass fibers is, for example, 0.01 mm to 50 mm, preferably 0.03 mm to 5 mm, and more preferably 0.05 mm to 1 mm. If the number-average fiber length of the glass fibers is 0.01 mm or more, the strength of the electromagnetic wave absorber can be improved. If the number-average fiber length of the glass fibers is 50 mm or less, the density uniformity of the electromagnetic wave absorber can be improved. The number-average fiber length of the glass fibers is measured, for example, by a Diamscope or Diamlength manufactured by Cottonscorpe.

[0025] The glass fiber content in the electromagnetic wave absorber is 80% by mass or more, preferably 85% by mass or more, and more preferably 90% by mass or more. A glass fiber content of 80% by mass or more can improve the flame retardancy of the electromagnetic wave absorber. For example, the glass fiber content in the electromagnetic wave absorber may be 99.9% by mass or less. The glass fiber content is measured, for example, by thermogravimetric analysis (TGA).

[0026] The glass fibers constitute a sheet-like substrate. The substrate has a shape in which the length in the in-plane direction (the direction perpendicular to the thickness direction) is sufficiently longer than the thickness direction. The substrate has a porous structure. Therefore, when the substrate is impregnated with a CNT dispersion, the CNT dispersion can be uniformly absorbed into the substrate in the thickness direction.

[0027] The glass fiber sheet, which is the base material, can be manufactured using a general wet papermaking method. One wet papermaking method involves further diluting a certain amount of slurry, in which glass fibers are dispersed in an aqueous dispersion medium, with another aqueous dispersion medium, forming it on a mesh such as a wire mesh, and then drying this wet paper sheet in a dryer to form a sheet. For industrial mass production, one method involves continuously forming the dispersed slurry using a long-wire paper machine, cylinder paper machine, or inclined paper machine, drying this wet paper sheet in a hot-air dryer, infrared dryer, or drum dryer, and then winding up the dried sheet. The aqueous dispersion medium is, for example, water or an aqueous sulfuric acid solution. The aqueous dispersion medium may also contain various auxiliary agents such as pH adjusters and defoamers.

[0028] Alternatively, a slurry containing a CNT dispersion can be used for wet papermaking when dispersing glass fibers in water. The timing of adding the CNT dispersion can be either by impregnating the glass fibers before water dispersion, or by simultaneously adding the glass fibers and CNT dispersion to water and dispersing them; the order is not particularly limited.

[0029] The thickness of the base material is, for example, 0.1 mm or more and 20 mm or less, preferably 0.3 mm or more and 10 mm or less, and more preferably 0.5 mm or more and 5.0 mm or less. If the thickness of the base material is 0.1 mm or more, the strength of the base material can be improved. If the thickness of the base material is 20 mm or less This allows the CNT dispersion to penetrate uniformly in the thickness direction of the substrate when the substrate is impregnated with the CNT dispersion. The thickness of the substrate is measured, for example, by an air-type offline thickness measuring device.

[0030] The mass of the base material is, for example, 20 g / m². 2 More than 4000g / m 2 The following, preferably 60 g / m² 2 More than 3000g / m 2 The following, and more preferably 100 g / m² 2 More than 1000g / m 2 The following applies: The mass of the base material is 20 g / m². 2 If the mass of the base material is 4000 g / m², the strength of the base material can be improved. 2The following conditions can be met to reduce weight:

[0031] The base material may contain inorganic fibers other than organic fibers and glass fibers. Examples of organic fibers include polypropylene fibers, acrylic fibers, vinylon fibers, cellulose fibers, polyester fibers, and aramid fibers. Examples of inorganic fibers include rock fibers, metal fibers, alumina fibers, ceramic fibers, and silica fibers.

[0032] Multiple substrates may be provided, and these substrates may be laminated. In this case, adjacent substrates may be bonded to each other via an adhesive layer. The adhesive layer may be made of an adhesive such as a water-based adhesive, a solvent-based adhesive, a chemical reaction adhesive, a hot melt adhesive, or a wood glue. The thickness of the adhesive layer is less than the thickness of the substrate. When multiple substrates are provided, the number of substrates may be, for example, two to ten.

[0033] 1.1.2. Carbon nanotubes (CNTs) Examples of CNTs included in the electromagnetic wave absorber according to this embodiment include single-walled carbon nanotubes (SWNTs), which are formed by winding a single six-membered ring network (graphene sheet) made of carbon into a cylindrical shape, and multi-walled carbon nanotubes (MWNTs), which are formed by winding multiple graphene sheets concentrically. The electromagnetic wave absorber may contain only one of SWNTs or MWNTs, or both. Both ends of the CNTs may be closed or open.

[0034] CNTs are fabricated by methods such as arc discharge, laser ablation, and CVD (Chemical Vapor Deposition). These methods allow CNTs to be fabricated to a predetermined size.

[0035] The diameter of the CNTs is, for example, between 1 nm and 100 nm, preferably between 5 nm and 50 nm, and more preferably between 7 nm and 20 nm. A CNT diameter between 1 nm and 100 nm improves the dispersibility of the CNTs in the CNT dispersion. The diameter of the CNTs is measured, for example, by a Scanning Electron Microscope (SEM).

[0036] The fiber length of the CNTs is, for example, 0.5 μm to 80 μm, preferably 1.0 μm to 60 μm, and preferably 10 μm to 50 μm. If the fiber length of the CNTs is 0.5 μm to 80 μm, the dispersibility of the CNTs in the CNT dispersion can be improved. The fiber length of the CNTs is measured, for example, by SEM. Note that "CNT fiber length" refers to the length of the CNTs when they are bundled together by van der Waals forces, and is the length of the CNTs before they are dispersed in the solvent.

[0037] The BET specific surface area of ​​CNT is, for example, 50m². 2 / g or more 500m 2 It is less than or equal to / g, preferably 100m 2 / g or more 300m 2 The BET specific surface area of ​​CNT is 50m². 2 / g or more 500m 2 If the value is less than / g, the dispersibility of CNTs in the CNT dispersion can be improved.

[0038] The carbon nanotubes (CNTs) are attached to the glass fibers. The CNTs may also be attached to the glass fibers via a dispersant. The amount of CNTs attached to the glass fibers is, for example, 0.1 g / m². 2 More than 10g / m 2 The following, preferably 0.3 g / m 2 More than 7.0g / m 2 The following, and more preferably 0.5 g / m 2 More than 5.0g / m 2 The following, and more preferably 0.7 g / m 2 More than 3.0g / m 2 The following is the result: The amount of CNTs attached is 0.1 g / m2 If the above conditions are met, the electromagnetic wave absorption performance and strength of the electromagnetic wave absorber can be improved. The amount of CNT attached is 10g / m 2 The following conditions can suppress the reduction in electromagnetic wave absorption performance caused by the reflection of electromagnetic waves from the surface of the electromagnetic wave absorber. The CNT content is measured, for example, by TGA.

[0039] 1.1.3. Dispersant The dispersant contained in the electromagnetic wave absorber according to this embodiment disperses CNTs in a solvent in a CNT dispersion for manufacturing the electromagnetic wave absorber. The dispersant is attached to the glass fibers. The dispersant may also be attached to the glass fibers via the CNTs. The amount of dispersant attached to the glass fibers is, for example, 0.1 g / m 2 More than 10g / m 2 The following, preferably 0.3 g / m 2 More than 7.0g / m 2 The following, and more preferably 0.5 g / m 2 More than 5.0g / m 2 The following, and more preferably 0.7 g / m 2 More than 3.0g / m 2 The following applies: The amount of dispersant attached is 0.1 g / m². 2 The above conditions can improve the dispersibility of CNTs in the CNT dispersion. Dispersant adhesion amount: 10 g / m² 2 The viscosity of the CNT dispersion can be reduced if the following conditions are met. The amount of dispersant adhering to the glass fibers may be the same as the amount of CNTs adhering to the glass fibers. The dispersant content is measured, for example, by TGA.

[0040] In a CNT dispersion, the mass M of the CNTs CNT The mass M of the dispersant relative to the dispersant DISP Ratio M DISP / M CNT The ratio is 1 / 5 to 5 (CNT:dispersant = 5:1 to 1:5), preferably 1 / 4 to 4 (CNT:dispersant = 4:1 to 1:4), and more preferably 1 / 3 to 3 (CNT:dispersant = 3:1 to 1:3). Ratio M DISP / M CNTIf the ratio is 1 / 5 or more, it is possible to enhance the performance unique to CNTs, such as electromagnetic wave absorption performance. DISP / M CNT If the value is 5 or less, the dispersibility of CNTs in the CNT dispersion can be improved.

[0041] The weight-average molecular weight of the dispersant is, for example, 5,000 to 1,000,000, preferably 6,000 to 800,000, and more preferably 7,000 to 200,000. If the weight-average molecular weight of the dispersant is 5,000 or more, the dispersant can easily entangle with the CNTs, improving the dispersibility of the CNTs in the CNT dispersion. However, if the weight-average molecular weight is too high, the dispersibility will worsen, so it is preferable that the molecular weight of the dispersant be 1,000,000 or less. Note that "weight-average molecular weight" refers to the weight-average molecular weight in polystyrene terms measured by gel permeation chromatography (GPC).

[0042] Examples of dispersants include cellulose-based polymers and polyacrylic acid. Examples of cellulose-based polymers include carboxymethylcellulose salts such as sodium carboxymethylcellulose.

[0043] 1.1.4. Other Additives The electromagnetic wave absorber according to this embodiment may further contain additives such as a binder resin, a water repellent, a surfactant, an antifoaming agent, fine fibers, or fine particles, as needed.

[0044] 1.2. Physical properties etc. The surface resistivity of the electromagnetic wave absorber according to this embodiment is, for example, 100 Ω / □ or more and 20000 Ω / □ or less, preferably 300 Ω / □ or more and 18000 Ω / □ or less, more preferably Or, it is between 500 Ω / □ and 16000 Ω / □. Surface resistivity is related to electromagnetic wave absorption performance, and basically, the lower the surface resistivity, the higher the electromagnetic wave absorption performance. However, if the surface resistivity is less than 100 Ω / □, electromagnetic waves are reflected at the surface of the electromagnetic wave absorber, and the electromagnetic wave absorption performance decreases. If the surface resistivity of the electromagnetic wave absorber is between 100 Ω / □ and 20000 Ω / □, the electromagnetic wave absorber can have high electromagnetic wave absorption performance. Surface resistivity is measured, for example, using a predetermined measuring instrument in accordance with "JIS K 7194:1994".

[0045] The density of the electromagnetic wave absorber according to this embodiment is, for example, 0.05 g / cm³. 3 More than 0.5g / cm 3 The following, preferably 0.1 g / cm³ 3 More than 0.3g / cm 3 The following, and more preferably 0.15 g / cm³ 3 More than 0.2g / cm 3 The following applies: The density of the electromagnetic wave absorber is 0.05 g / cm³. 3 If the above conditions are met, the electromagnetic wave absorption performance and strength of the electromagnetic wave absorber can be improved. 3 The possibility of cracks occurring in the electromagnetic wave absorber can be reduced if the following conditions are met. The density of the substrate to which the CNTs are attached can be calculated, for example, from the basis weight and mass.

[0046] In the electromagnetic wave absorber according to this embodiment, a metal layer may be provided on the surface opposite to the surface to which the electromagnetic waves are incident. Examples of the metal layer include a metal plate and a film on which metal has been deposited.

[0047] 1.3. Effects The electromagnetic wave absorber according to this embodiment contains glass fibers and carbon nanotubes (CNTs), with the glass fiber content being 80% by mass or more. Because the electromagnetic wave absorber according to this embodiment contains CNTs, its electromagnetic wave absorption performance can be improved. Furthermore, its strength can be improved. Without CNTs, the strength is low due to the entanglement of glass fibers alone. Moreover, because the electromagnetic wave absorber according to this embodiment has a glass fiber content of 80% by mass, it can be flame-retardant. Electromagnetic wave absorbers may be used outdoors, and flame retardancy is desirable.

[0048] In the electromagnetic wave absorber according to this embodiment, the glass fibers constitute a sheet-like substrate, and the CNTs are attached to the glass fibers, with the amount of CNTs attached to the glass fibers being 0.1 g / m². 2 More than 10g / m 2 The following, preferably 0.3 g / m 2 More than 7.0g / m 2 The following is also acceptable. If the amount of CNTs attached is within this range, the electromagnetic wave absorption performance and strength can be improved.

[0049] In the electromagnetic wave absorber according to this embodiment, the average fiber diameter of the glass fibers is 0.05 μm or more and 20 μm or less. The glass fibers include submicron fibers with an average fiber diameter of 0.05 μm or more and 1.0 μm or less. When the amount of glass fibers contained in the electromagnetic wave absorber is 100 parts by mass, the submicron fiber content is 1.0 part by mass or more, preferably 10 parts by mass or more and 90 parts by mass or less. If the submicron fiber content is within this range, the strength of the substrate can be ensured while improving the texture of the substrate. By improving the texture of the substrate, when the substrate is impregnated with a CNT dispersion, the CNTs can be attached to the glass fibers with good uniformity.

[0050] In the electromagnetic wave absorber according to this embodiment, carboxymethylcellulose sodium (hereinafter also referred to as "CMC") is included, and the CMC is attached to the glass fibers, with the amount of CMC attached to the glass fibers being 0.1 g / m 2 More than 10g / m 2The following is also acceptable. If the amount of CMC attached is within this range, the viscosity of the CNT dispersion can be lowered while improving the dispersibility of CNTs in the CNT dispersion.

[0051] In the electromagnetic wave absorber according to this embodiment, polyacrylic acid is contained, and the polyacrylic acid is attached to the glass fibers, with the amount of polyacrylic acid attached to the glass fibers being 0.1 g / m². 2 That's all. 10g / m 2 The following is also acceptable. If the amount of polyacrylic acid attached is within this range, the viscosity of the CNT dispersion can be lowered while improving the dispersibility of CNTs in the CNT dispersion.

[0052] In the electromagnetic wave absorber according to this embodiment, multiple substrates are provided, and these multiple substrates may be laminated. Laminating multiple substrates improves both electromagnetic wave absorption performance and strength.

[0053] 2. Method for manufacturing electromagnetic wave absorbers 2.1. Overall Flow Next, the method for manufacturing the electromagnetic wave absorber according to this embodiment will be described with reference to the drawings. Figure 1 is a flowchart illustrating the method for manufacturing the electromagnetic wave absorber according to this embodiment.

[0054] As shown in Figure 1, the method for manufacturing an electromagnetic wave absorber according to this embodiment includes, for example, a CNT dispersion preparation step (step S1) for preparing a CNT dispersion, an impregnation step (step S2) for impregnating a substrate made of glass fibers with the CNT dispersion, and a drying step (step S3) for drying the substrate impregnated with the CNT dispersion.

[0055] 2.2. Process for preparing CNT dispersion (Step S1) In the CNT dispersion preparation process, CNTs and a dispersant are added to water as a solvent, and the CNTs, dispersant, and water are mixed to prepare a mixture. The mixing of CNTs, dispersant, and water is performed, for example, by a homogenizer. The homogenizer may be an ultrasonic type that causes cavitation with ultrasound, an agitator type that stirs the mixture, or a pressure type that applies pressure to the mixture. By performing the homogenization process, the aggregation of CNTs can be reduced. This allows the underwater counter-impact method described later to be carried out smoothly.

[0056] In the mixture, the CNT content is, for example, 0.05% by mass or more and 10% by mass or less, preferably 1% by mass or more and 5% by mass or less. If the CNT content is 0.05% by mass or more, the electromagnetic wave absorption performance of the electromagnetic wave absorber 100 can be improved. If the CNT content is 10% by mass or less, the viscosity of the dispersion can be reduced. If the viscosity of the dispersion is too high, the nozzle holes in the wet atomization device described later may become clogged. In the mixture, the dispersant content is, for example, the same as the CNT content.

[0057] The water in the mixture may be pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, and distilled water, or ultrapure water from which ionic impurities have been removed as much as possible, or it may be tap water. Since the mixture uses water as a solvent, it is more environmentally friendly than when an organic solvent is used. The mixture may contain only CNTs, a dispersant, and water. In other words, the mixture may consist only of CNTs, a dispersant, and water.

[0058] Next, the CNTs contained in the mixture are dispersed using a wet atomization device, for example, one that has a ball impact chamber, by an underwater counter-impact method. Specifically, the mixture is sprayed from the nozzle of the wet atomization device and impacted against ceramic balls. The CNTs contained in the mixture are dispersed by the shear force as they pass through the nozzle holes, cavitation caused by spraying into the liquid, and the impact force when the CNTs collide with the ceramic balls.

[0059] The diameter of the nozzle hole is, for example, 100 μm or more and 600 μm or less, preferably 120 μm or more and 350 μm or less. If the diameter of the nozzle hole is 100 μm or more, clogging of the nozzle hole with the mixed liquid can be suppressed. If the diameter of the nozzle hole is 600 μm or less, impact of the mixed liquid Energy can be increased.

[0060] The pressure applied to the mixed liquid sprayed from the nozzle is, for example, 100 MPa to 300 MPa, preferably 150 MPa to 250 MPa. If the pressure is 100 MPa or higher, the collision energy of the mixed liquid can be increased. If the pressure is 300 MPa or lower, it is possible to suppress the collision energy from being too high, which would cause the CNT fibers to break and prevent the desired properties from being obtained.

[0061] The processing rate of the mixed liquid sprayed from the nozzle is, for example, 20 L / hr to 400 L / hr, preferably 25 L / hr to 100 L / hr. If the processing rate is 20 L / hr or more, the processing time in the wet atomization device can be shortened. If the processing rate is 400 L / hr or less, clogging of the nozzle holes with the mixed liquid can be suppressed.

[0062] In a wet atomization apparatus, the number of passes of the mixed liquid is, for example, 1 to 10 times, preferably 2 to 5 times. If the number of passes is 10 or less, it is possible to suppress the breakage of CNT fibers due to collisions with the mixed liquid, which can prevent the acquisition of desired properties. Furthermore, it is possible to shorten the manufacturing time and save energy.

[0063] Note that "number of passes of the mixed liquid in the wet atomization device" refers to the number of times the mixed liquid is circulated in the wet atomization device. For example, "2 passes" means that the mixed liquid is circulated twice so that a CNT that has already collided with a ceramic ball will collide with the ceramic ball again. Thus, the number of passes corresponds to the number of times the mixed liquid sprayed from the nozzle hole collides with the ceramic ball. The number of passes is proportional to the processing time in the wet atomization device. If the processing time in the wet atomization device is long, the number of times the mixed liquid is circulated increases.

[0064] The CNT content in the CNT dispersion can be adjusted by diluting it with water as appropriate. The CNT content in the CNT dispersion is, for example, 0.05% by mass or more and 1% by mass or less, preferably 0.1% by mass or more and 0.6% by mass or less. If the CNT content is 0.05% by mass or more, the amount of CNTs adhering to the electromagnetic wave absorber can be increased, thereby improving the electromagnetic wave absorption performance. If the CNT content is 1% by mass or less, the possibility of the amount of CNTs adhering too much and the electrical resistance of the electromagnetic wave absorber becoming too low, thereby impairing the electromagnetic wave absorption performance, can be reduced.

[0065] Based on the above, a CNT dispersion can be prepared.

[0066] Furthermore, the form of the wet atomization apparatus is not particularly limited as long as the CNTs can be dispersed in water. Alternatively, the CNTs may be dispersed in water without using a wet atomization apparatus.

[0067] Furthermore, although the above example described a CNT dispersion where water is the solvent, any solvent can be used instead of water as long as the CNTs can be dispersed in the solvent.

[0068] 2.3. Impregnation process (Step S2) In the impregnation process, the substrate is impregnated with a CNT dispersion. The substrate is formed from raw cotton made of glass fibers, for example, by a flame process or a centrifugal process. Methods of impregnation include, for example, bar coating, curtain coating, die coating, spray coating, etc., to allow the CNT dispersion to soak into the substrate, or to impregnate the entire substrate with the CNT dispersion. Through this process, CNTs adhere to the glass fibers of the substrate.

[0069] 2.4. Drying process (Step S3) In the drying process, the substrate impregnated with the CNT dispersion is dried. The drying method is not particularly limited as long as the water contained in the CNT dispersion is evaporated, but examples include hot air drying, infrared drying, and natural drying. When using a drying oven, the temperature of the oven is, for example, 70°C to 160°C, preferably 100°C to 140°C. If the temperature of the drying oven is 70°C or higher, the water can be sufficiently evaporated. If the temperature of the drying oven is 160°C or lower, the melting of the glass fibers can be suppressed.

[0070] By following the above steps, the electromagnetic wave absorber according to this embodiment can be manufactured.

[0071] 3. Examples and Comparative Examples The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited in any way by the following examples and comparative examples.

[0072] 3.1. Sample Preparation <Example 1> A mixture was prepared by mixing CNTs, a dispersant, and water. A homogenizer, "Biomixer BM-2," manufactured by Nippon Seiki Seisakusho Co., Ltd., was used for mixing. The mixing process time was set to 5 minutes.

[0073] For the carbon nanotubes (CNTs), we used "LUCAN.BT1003M" manufactured by LG Chem. These CNTs are MWCNTs, with a diameter of 8nm to 17nm, a fiber length of 10μm to 50μm (bundle), and a BET specific surface area of ​​165m². 2 / g~205m 2 The value is / g. The CNT content in the mixture was set to 3.0% by mass.

[0074] CMC was used as a dispersant. Specifically, "Selogen 5A" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was used as the CMC. Its weight-average molecular weight is 15,000. Its degree of etherification is 0.7. The CMC content in the mixture was set to 3.0% by mass.

[0075] The CNTs contained in the above mixture were dispersed using a wet atomization apparatus equipped with a ball impact chamber. The wet atomization apparatus used was the "Starburst Lab" wet atomization apparatus (model name: HJP-25005) manufactured by Sugino Machine Co., Ltd. The diameter of the nozzle hole from which the mixture was sprayed was set to 0.17 mm, and the pressure applied to the mixture was set to 200 MPa, causing the mixture to impact the ceramic balls. The wet atomization apparatus passed the mixture four times. In this way, a CNT dispersion containing CNTs, a dispersant, and water was prepared.

[0076] Sixty parts by mass of glass fibers with an average fiber diameter of 0.65 μm, forty parts by mass of glass fibers with an average fiber diameter of 2.44 μm, and an aqueous dispersion medium pre-mixed with dilute sulfuric acid to pH 3 were placed in a disintegrating pulper, and the raw materials were dispersed to a concentration of 1% by mass to prepare a raw material slurry. Next, the raw material concentration was diluted to 0.1% by mass with water adjusted to pH 3 with concentrated sulfuric acid, and continuous papermaking was performed on an inclined paper machine, followed by a drying process to produce a sheet-like substrate. "B-06-F" manufactured by Unifrax Corporation was used as the glass fiber with an average fiber diameter of 0.65 μm. "B-26-R" manufactured by Unifrax Corporation was used as the glass fiber with an average fiber diameter of 2.44 μm.

[0077] The above substrate was impregnated by diluting a 3.0% CNT dispersion (CNT: 3.0% by mass, CMC: 3.0% by mass) to 0.1% (CNT: 0.1% by mass, CMC: 0.1% by mass) and immersing it in the diluted CNT dispersion. After that, the substrate, from which the excess CNT dispersion was removed by vacuum, was heat-dried at 130°C to produce a substrate with attached CNTs.

[0078] Based on the above, the sample for Example 1 was prepared.

[0079] <Example 2> Sample for Example 2 was prepared in the same manner as in Example 1 described above, except that three substrates with CNTs attached were made and the three substrates were laminated together. Franklin's woodworking adhesive "Titebond III Ultimate" was used as the adhesive for the substrates.

[0080] <Example 3> Sample for Example 3 was prepared in the same manner as in Example 1 described above, except that five substrates with CNTs attached were prepared and the five substrates were laminated together. The adhesive used was the same as in Example 2.

[0081] <Example 4> The sample for Example 4 was prepared in the same manner as in Example 1 described above, except that the CNT dispersion was diluted to 0.5% (CNT: 0.5% by mass, CMC: 0.5% by mass).

[0082] <Example 5> Sample for Example 5 was prepared in the same manner as in Example 1 described above, except that the CNT dispersion was diluted to 0.3% (CNT: 0.3% by mass, CMC: 0.3% by mass), and the substrate was prepared using 50 parts by mass of glass fibers with an average fiber diameter of 0.65 μm, 40 parts by mass of glass fibers with an average fiber diameter of 2.44 μm, and 10 parts by mass of organic binder fibers.

[0083] <Example 6> The sample for Example 6 was prepared in the same manner as in Example 5 described above, except that two substrates with CNTs attached were prepared and the two substrates were laminated together. The adhesive used was the same as in Example 2.

[0084] <Example 7> Sample for Example 7 was prepared in the same manner as in Example 1 described above, except that polyacrylic acid was used as a dispersant. As the polyacrylic acid, "Aquaric HL-415" manufactured by Nippon Shokubai Co., Ltd. was used. Its weight-average molecular weight is 10,000.

[0085] <Comparative Example 1> A sample for Comparative Example 1 was prepared in the same manner as in Example 1 described above, except that the substrate was not impregnated with the CNT dispersion.

[0086] <Comparative Example 2> A sample for Comparative Example 2 was prepared in the same manner as in Example 1 described above, except that the substrate was impregnated with a mixture of CMC (0.1% by mass) and water instead of a CNT dispersion.

[0087] <Comparative Example 3> A sample for Comparative Example 3 was prepared in the same manner as in Example 1 described above, except that the substrate was impregnated with a mixture of CMC (0.5% by mass) and water instead of a CNT dispersion.

[0088] <Comparative Example 4> A sample for Comparative Example 4 was prepared in the same manner as in Example 1 described above, except that the substrate was impregnated with a mixture of polyacrylic acid (0.3% by mass) and water instead of a CNT dispersion.

[0089] 3.2. Evaluation Method 3.2.1. Amount of adhesion In a substrate to which CNTs are attached, the amount of CNTs attached to the glass fibers, and the amount of CMC or polyacrylic acid attached to the glass fibers are measured in terms of the mass of the substrate after impregnation (g / m²). 2 ) and the mass of the substrate before impregnation (g / m²) 2The difference between ) and was used to calculate the ratio of CNTs, CMC, and polyacrylic acid. The ratio of was allocated according to the mixing ratio. The mass was measured using a balance.

[0090] 3.2.2. Thickness The thickness of the sample was measured using an air-type offline thickness measuring device manufactured by Yamabun Electric Co., Ltd. The measurement pressure was set to 0.4 kPa.

[0091] 3.2.3. Surface resistivity The surface resistivity of the substrate to which CNTs were attached was measured in accordance with "JIS K 7194". A "Loresta-AX MCP-T370" (4 terminals) manufactured by Mitsubishi Chemical Analytec Corporation was used as the measuring device. In Examples 2, 3, and 6, the measurement was performed on the substrate to which the CNTs were attached before lamination.

[0092] 3.2.4. Tensile Strength The tensile strength of the substrate with attached carbon nanotubes (CNTs) was measured in accordance with "JIS P8113:2006 Paper and cardboard - Test methods for tensile properties". The measuring device used was the "Auto Bluff AGX" manufactured by Shimadzu Corporation. Examples 2, 3, and 6 measured the substrate before lamination.

[0093] 3.2.5. Density The density of the substrate with attached CNTs was calculated from the basis weight and mass. In Examples 2, 3, and 6, the substrate with attached CNTs was measured before lamination.

[0094] 3.2.6. Flame retardancy The flame retardancy of the sample was evaluated in accordance with the UL94 standard. Specifically, as part of the V-0 vertical combustion test method, the lower end of the vertically held sample was exposed to the flame of a gas burner for 10 seconds. If combustion stopped within 30 seconds, the flame was applied for another 10 seconds.

[0095] The evaluation criteria were as follows: an "A" was given if all of the following five criteria were met, and a "D" was given if even one criterion was not met.

[0096] <Standards> 1. None of the samples continued to burn for more than 10 seconds after any of the flame exposures. 2. The total burning time for 10 flame applications to 2.5 samples does not exceed 50 seconds. 3. There is no sample burning up to the position of the fixing clamp. 4. There is no sample to cause burning particles to fall that would ignite the cotton wool placed below the sample. 5. After the second flame application, no sample remained red-hot for more than 30 seconds.

[0097] 3.2.7. Electromagnetic wave absorption performance The electromagnetic wave absorption performance was assessed by measuring the return loss of the sample based on the free-space method. The measurement device used was the "DPS-10-03" manufactured by Keycom Co., Ltd. In the free-space method, the sample is placed between two opposing antennas, and the reflection and transmission measurements can be evaluated by inducing electromagnetic waves radiated from one of the antennas onto the sample. Figure 2 is a diagram illustrating the free-space method used to evaluate the electromagnetic wave absorption performance.

[0098] As shown in Figure 2, the sample S was placed between antennas A1 and A2 of the measuring device. A metal plate M was set on the back surface of the sample S (the surface opposite to the incident surface of the electromagnetic wave). Next, A Electromagnetic waves were irradiated from antenna A1 towards sample S. The electromagnetic waves irradiated from antenna A1 do not reach antenna A2 due to the metal plate M. Then, by receiving the electromagnetic waves reflected from the sample S side with antenna A1, the ratio of the amount of electromagnetic waves incident on sample S to the amount of electromagnetic waves reflected (reflection attenuation) was derived as the amount of electromagnetic wave absorption. Sample S diffusely reflects the electromagnetic waves internally, converting the electromagnetic waves into heat. As a result, the electromagnetic waves are attenuated. The electromagnetic waves irradiated from antenna A1 are plane waves, also called orthogonal polarization.

[0099] Specifically, the amount of electromagnetic wave absorption was calculated using the following formula (2).

[0100] Electromagnetic wave absorption amount = 10 × log(Pm / Pa) ... (2)

[0101] In equation (2), Pm is the amount of incident electromagnetic wave (in watts). Pa is the amount of reflected electromagnetic wave (in watts). The amount of electromagnetic wave absorption is expressed in decibels (dB). If the amount of electromagnetic wave absorption is -10 dB, 90% of the electromagnetic wave is absorbed; at -20 dB, 99% is absorbed; and at -30 dB, 99.9% is absorbed.

[0102] The evaluation criteria for electromagnetic wave absorption performance are as follows:

[0103] <Evaluation Criteria> A: Electromagnetic wave absorption is -11dB or less B: Electromagnetic wave absorption is greater than -11dB and less than or equal to -6dB. C: Electromagnetic wave absorption is greater than -6dB and less than or equal to -3dB. D: Electromagnetic wave absorption is greater than -3dB

[0104] 3.3. Evaluation Results Figure 3 is a table showing the evaluation results for Examples 1-7 and Comparative Examples 1-4.

[0105] As shown in Figure 3, Examples 1-7, which included CNTs, had higher electromagnetic wave absorption performance compared to Comparative Examples 1-4, which did not include CNTs.

[0106] Comparing Examples 1-3 with Comparative Example 2, the amount of CMC adhering was the same at 0.7 g / m². 2 Even so, Examples 1-3, which contained CNTs, had greater tensile strength than Comparative Example 2, which did not contain CNTs. Comparing Examples 4-6 with Comparative Example 3, the amount of CMC attached was the same at 3g / m². 2 Even so, Examples 4-6, which contained CNTs, had greater tensile strength than Comparative Example 3, which did not contain CNTs. Comparing Example 7 and Comparative Example 4, the amount of polyacrylic acid attached was the same at 1.6 g / m². 2 Nevertheless, Example 7, which included CNTs, had a higher tensile strength than Comparative Example 4, which did not include CNTs.

[0107] Based on the above, it was found that including CNTs can improve electromagnetic wave absorption performance and intensity.

[0108] By comparing Examples 1 to 3, it was found that the electromagnetic wave absorption performance increased with a greater number of substrate layers. Furthermore, by comparing Examples 1 and 4, it was found that the electromagnetic wave absorption performance increased with a greater thickness of the substrate layer.

[0109] Regarding flame retardancy, all samples in Examples 1-7 and Comparative Examples 1-4 showed good results.

[0110] The embodiments and variations described above are examples only and are not limited thereto. For example, each embodiment and each variation can be combined as appropriate.

[0111] The present invention is not limited to the embodiments described above, and various further modifications are possible. For example, the present invention includes configurations that are substantially identical to those described in the embodiments. A substantially identical configuration is, for example, a configuration that has the same function, method, and result, or a configuration that has the same purpose and effect. The present invention also includes configurations in which non-essential parts of the configuration described in the embodiments are replaced. Furthermore, the present invention includes configurations that produce the same effects or achieve the same purpose as the configuration described in the embodiments. Furthermore, the present invention includes configurations that add known technology to the configuration described in the embodiments.

Claims

1. It contains glass fibers and carbon nanotubes, An electromagnetic wave absorber having a glass fiber content of 80% by mass or more.

2. The glass fibers constitute a sheet-like substrate, The carbon nanotubes are attached to the glass fibers, The amount of carbon nanotubes attached to the glass fibers is 0.1 g / m ２ 10g / m or more ２ The electromagnetic wave absorber according to claim 1, which is as follows:

3. The amount of carbon nanotubes attached to the glass fibers is 0.3 g / m ２ 7.0g / m or more ２ The electromagnetic wave absorber according to claim 2, which is as follows:

4. The average fiber diameter of the glass fibers is 0.05 μm or more and 20 μm or less. The glass fibers include submicron fibers with an average fiber diameter of 0.05 μm or more and 1.0 μm or less. The electromagnetic wave absorber according to claim 2 or 3, wherein, when the amount of glass fibers contained in the electromagnetic wave absorber is 100 parts by mass, the amount of submicron fibers is 1.0 part by mass or more.

5. The electromagnetic wave absorber according to claim 4, wherein the content of the submicron fibers is 10 parts by mass or more and 90 parts by mass or less.

6. Contains sodium carboxymethylcellulose, The carboxymethylcellulose sodium is attached to the glass fiber, The amount of sodium carboxymethylcellulose adhering to the glass fibers is 0.1 g / m ２ 10g / m or more ２ The electromagnetic wave absorber according to claim 2 or 3, which is as follows:

7. Contains polyacrylic acid, The polyacrylic acid is attached to the glass fiber, The amount of polyacrylic acid adhering to the glass fibers is 0.1 g / m ２ 10g / m or more ２ The electromagnetic wave absorber according to claim 2 or 3, which is as follows:

8. Multiple substrates are provided, The electromagnetic wave absorber according to claim 2 or 3, wherein the plurality of substrates are laminated together.

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