JP2024022443A - Carbon nanotube aqueous dispersion and electromagnetic wave noise shielding sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carbon nanotube aqueous dispersion that contains a high content of carbon nanotubes for easy dispersion, and allows for creation of a coating layer with high adhesion to a substrate.

SOLUTION: A carbon nanotube aqueous dispersion according to the present invention includes carbon nanotubes, water, and a dispersant for dispersing the carbon nanotubes in the water. A content of the carbon nanotubes is 2.0 mass% or more. The dispersant is a polymer including at least one of a repeat unit derived from an acrylic acid and a repeat unit derived from a monomer with a sulfonic acid group.

SELECTED DRAWING: Figure 4

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to an aqueous carbon nanotube dispersion and an electromagnetic noise suppression sheet.

Carbon nanotubes have a structure similar to that of a uniformly planar graphene sheet rolled into a cylindrical shape. Because carbon nanotubes have such a unique structure, they have various properties. Therefore, carbon nanotubes are expected to be applied in a wide range of fields.

For example, Patent Document 1 describes a method of producing a carbon nanotube dispersion by pressurizing a mixture of carbon nanotube aggregates and a dispersion medium, feeding it into a plurality of thin tube channels, colliding and merging the mixture. Patent Document 1 describes that the concentration of carbon nanotube aggregates is preferably 0.01% by mass to 1% by mass. Furthermore, Patent Document 1 describes the use of, for example, carboxymethyl cellulose sodium salt as a dispersant for carbon nanotubes.

JP2013-230951A

In the carbon nanotube aqueous dispersion as described above, it is desired to increase the content of carbon nanotubes. By increasing the content of carbon nanotubes, performance specific to carbon nanotubes, such as electromagnetic noise suppression performance, can be enhanced. However, when the content of carbon nanotubes is increased, the dispersibility of carbon nanotubes becomes worse.

Furthermore, when an electromagnetic noise suppression sheet containing a coating layer and a substrate is produced by coating a carbon nanotube aqueous dispersion as described above on a substrate, the adhesion between the coating layer and the substrate is high. It is hoped that Electromagnetic noise suppression sheets are used in various places such as walls and ceilings, so they need to have sufficient adhesion.

One of the objects of some aspects of the present invention is to provide an aqueous carbon nanotube dispersion that has a large content of carbon nanotubes, has good dispersibility, and can create a coating layer that has high adhesion to a substrate. It's about doing. Further, one of the objects of some aspects of the present invention is to provide an electromagnetic noise suppression sheet that has a large content of carbon nanotubes, has good dispersibility, and has high adhesion between the coating layer and the base material. There is a particular thing.

One embodiment of the carbon nanotube aqueous dispersion according to the present invention is
carbon nanotubes,
water and,
a dispersant for dispersing the carbon nanotubes in the water;
including;
The content of the carbon nanotubes is 2.0% by mass or more,
The dispersant is a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group.

In one embodiment of the carbon nanotube aqueous dispersion,
The dispersant may be polyacrylic acid.

In one embodiment of the carbon nanotube aqueous dispersion,
The content of the dispersant may be 0.4% by mass or more.

In one embodiment of the carbon nanotube aqueous dispersion,
The content of the dispersant may be 1.0% by mass or more.

In one embodiment of the carbon nanotube aqueous dispersion,
The content of the dispersant may be 6.0% by mass or less.

In one embodiment of the carbon nanotube aqueous dispersion,
The weight average molecular weight of the dispersant may be 200,000 or less.

In one embodiment of the carbon nanotube aqueous dispersion,
The carbon nanotube may have a median diameter of 1.0 μm or less.

In one embodiment of the carbon nanotube aqueous dispersion,
The viscosity measured using a B-type viscometer at 25° C. and 60 rpm may be 300 cps or less.

In any embodiment of the carbon nanotube aqueous dispersion,
It may also be applied to a base material.

One embodiment of the electromagnetic noise suppression sheet according to the present invention is
base material and
a layer provided on the base material and containing carbon nanotubes and a polymer;
including;
In the layer, the ratio of the mass of the polymer to the mass of the carbon nanotubes is 1/10 or more and 5 or less,
The polymer includes at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group.

In one aspect of the electromagnetic noise suppression sheet,
The polymer may be polyacrylic acid.

In any aspect of the electromagnetic noise suppression sheet,
The ratio may be 1/5 or more.

In any aspect of the electromagnetic noise suppression sheet,
The ratio may be 1/2 or more.

In any aspect of the electromagnetic noise suppression sheet,
The ratio may be 3 or less.

In any aspect of the electromagnetic noise suppression sheet,
The weight average molecular weight of the polymer may be 200,000 or less.

In any aspect of the electromagnetic noise suppression sheet,
The carbon nanotube may have a median diameter of 1.0 μm or less.

The carbon nanotube aqueous dispersion according to the present invention includes carbon nanotubes, water, and a dispersant that disperses the carbon nanotubes in water. The content of carbon nanotubes is 2.0% by mass or more. The dispersant is a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group.

Therefore, in the carbon nanotube aqueous dispersion according to the present invention, a coating layer can be produced that has a large content of carbon nanotubes, has good dispersibility, and has high adhesion to the base material.

The electromagnetic noise suppression sheet according to the present invention includes a base material and a layer provided on the base material and containing carbon nanotubes and a polymer. In the layer, the ratio of the mass of the polymer to the mass of carbon nanotubes is 1/10 or more and 5 or less. The polymer includes at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group.

Therefore, in the electromagnetic noise suppression sheet according to the present invention, the content of carbon nanotubes is large, the dispersibility is good, and the adhesion between the coating layer and the base material is high.

1 is a flowchart for explaining a method for producing an aqueous carbon nanotube dispersion according to the present embodiment. FIG. 1 is a cross-sectional view schematically showing an electromagnetic noise suppression sheet according to the present embodiment. 1 is a flowchart for explaining a method for manufacturing an electromagnetic noise suppression sheet according to the present embodiment. 1 is a table showing the production conditions and experimental results of carbon nanotube aqueous dispersions of Examples 1 to 14 and Comparative Examples 1 to 9. Graph showing the median diameter of Examples 1, 5 to 9 and Comparative Examples 5 to 7. Graph showing the viscosities of Examples 1, 5 to 9 and Comparative Examples 5 to 7. Graph showing the median diameter of Examples 1 to 4 and Comparative Examples 5, 8, and 9. Graph showing the viscosities of Examples 1 to 4 and Comparative Examples 5, 8, and 9. Graph showing the median diameter of Examples 1, 13, 14 and Comparative Examples 1 to 5. Graph showing the viscosities of Examples 1, 13, and 14 and Comparative Examples 1 to 5. Table showing the experimental results of Examples 1 to 14 and Comparative Examples 1 to 9. A photo of an electromagnetic noise suppression sheet that falls under evaluation criteria A, B, and C of the Seropic test.

Hereinafter, preferred embodiments of the present invention will be described in detail using the drawings. Note that the embodiments described below do not unduly limit the content of the present invention described in the claims. Furthermore, not all of the configurations described below are essential components of the present invention.

1. Carbon nanotube aqueous dispersion 1.1. Components First, the carbon nanotube aqueous dispersion according to this embodiment will be explained. The carbon nanotube aqueous dispersion according to the present embodiment includes carbon nanotubes (hereinafter also referred to as "CNT"), a dispersant, and water. Each component will be explained below.

1.1.1. carbon nanotube (CNT)
The CNTs contained in the CNT aqueous dispersion according to this embodiment are single-walled carbon nanotubes (SWNTs), which are formed by winding a six-membered ring network (graphene sheet) made of carbon into a cylindrical shape. ), a multi-walled carbon nanotube (MWNT) in which a plurality of graphene sheets are concentrically wound. The CNT aqueous dispersion may contain only one of SWNT and MWNT, or may contain both. Both ends of the CNT may be closed or open.

CNTs are produced by, for example, an arc discharge method, a laser ablation method, a CVD (Chemical Vapor Deposition) method, or the like. CNTs are produced to a predetermined size by these methods.

The diameter of the CNT is, for example, 1 nm or more and 100 nm or less, preferably 5 nm or more and 50 nm or less, and more preferably 8 nm or more and 15 nm or less. If the diameter of the CNT is 1 nm or more and 100 nm or less, the dispersibility of the CNT can be improved. The diameter of the CNTs is measured using a SEM (Scanning Electron Microscope).

The fiber length of the CNT is, for example, 0.5 μm or more and 50 μm or less, preferably 15 μm or more and 35 μm or less. If the fiber length of CNT is 0.5 μm or more and 50 μm or less, the dispersibility of CNT can be improved. The fiber length of CNTs is measured by SEM. Note that the "fiber length of CNT" is the length of CNT in a state where it is bundled by van der Waals force, and is the length of CNT before being dispersed in a solvent.

The BET specific surface area of CNT is, for example, 50 m ² /g or more and 500 m ² /g or less, preferably 100 m ² /g or more and 300 m ² /g or less. When the BET specific surface area of CNT is 50 m ² /g or more and 500 m ² /g or less, the dispersibility of CNT can be improved. Note that "BET specific surface area" refers to a specific surface area measured by the BET (Brunauer Emmett Teller) method. BET specific surface area is measured by an automatic specific surface area measuring device.

In the CNT aqueous dispersion, the CNT content is 2.0% by mass or more, preferably 2.5% by mass or more, and more preferably 3.0% by mass or more. If the content of CNT is 2.5% by mass or more, performance specific to CNT such as electromagnetic noise suppression performance can be improved.

In the CNT aqueous dispersion, the CNT content is, for example, 20.0% by mass or less, preferably 10.0% by mass or less, and more preferably 5.0% by mass or less. If the content of CNT is 20.0% by mass or less, the dispersibility of CNT can be improved. The content of CNT is measured by thermogravimetric analysis (TGA).

1.1.2. Dispersant In the CNT aqueous dispersion according to the present embodiment, the dispersant disperses CNTs in water, which is a solvent. The dispersant contained in the CNT aqueous dispersion according to this embodiment is a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group. The dispersant is a polymer containing 90% by mass or more, preferably 95% by mass or more of at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group.

The dispersant may be a polymer containing repeating units derived from acrylic acid and not containing repeating units derived from a monomer having a sulfonic acid group. The dispersant may be a polymer composed of repeating units derived from acrylic acid. The dispersant may be polyacrylic acid.

The dispersant may be a polymer containing repeating units derived from a monomer having a sulfonic acid group and not containing repeating units derived from acrylic acid. The dispersant may be a polymer composed of repeating units derived from a monomer having a sulfonic acid group. Examples of monomers having a sulfonic acid group include styrene sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, sulfobutyl (meth)acrylate, 2-acrylamide-2- Examples include methylpropanesulfonic acid, 2-hydroxy-3-acrylamidopropanesulfonic acid, and 3-allyloxy-2-hydroxypropanesulfonic acid. The dispersant may be polystyrene sulfonic acid.

The dispersant may be a polymer containing both repeating units derived from acrylic acid and repeating units derived from a monomer having a sulfonic acid group. The dispersant may be a copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid, or a copolymer of acrylic acid and styrenesulfonic acid.

The weight average molecular weight of the dispersant is, for example, 5,000 or more and 1,000,000 or less, preferably 6,000 or more and 800,000 or less, and more preferably 7,000 or more and 200,000 or less. If the weight average molecular weight of the dispersant is 5000 or more, the dispersant will easily entangle with the CNTs, and the dispersibility of the CNTs can be improved. However, if the weight average molecular weight is too large, the dispersibility will deteriorate, so the molecular weight of the dispersant is preferably 1,000,000 or less. In addition, "weight average molecular weight" refers to the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

In the CNT aqueous dispersion, the content of the dispersant is, for example, 0.4% by mass or more and 10.0% by mass or less, preferably 0.5% by mass or more and 8.0% by mass or less, more preferably The content is 1.0% by mass or more and 6.0% by mass or less. If the content of the dispersant is 0.4% by mass or more and 10.0% by mass or less, the dispersibility of CNTs can be improved. The dispersant content is determined by thermogravimetric analysis.

In the CNT aqueous dispersion, the ratio of the mass of CNTs M to the mass of dispersant M _DISP to _{CNTs M DISP /} M _CNT is 1/10 or more and 5 or less (CNT: dispersant = 10:1 to 1:5), Preferably it is 1/5 or more and 4 or less (CNT: dispersant = 5:1 to 1:4), more preferably 1/3 or more and 3 or less (CNT: dispersant = 3:1 to 1:3). , and even more preferably 1/2 or more and 1 or less (CNT: dispersant = 2:1 to 1:1). When the ratio M _DISP /M _CNT is 1/10 or more, CNT-specific performance such as electromagnetic noise suppression performance can be improved. When the ratio M _DISP /M _CNT is 5 or less, the dispersibility of CNT can be improved.

1.1.3. Water The CNT aqueous dispersion according to this embodiment contains water as a solvent. Examples of water include pure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, and distilled water, and water from which ionic impurities have been removed as much as possible, such as ultrapure water. Since the CNT aqueous dispersion uses water as a solvent, it is more environmentally friendly than when an organic solvent is used as a solvent. The CNT aqueous dispersion may contain only CNTs, dispersant, and water. That is, the CNT aqueous dispersion may be composed only of CNTs, a dispersant, and water.

1.1.4. Other Additives The CNT aqueous dispersion according to the present embodiment may further contain various additives such as a preservative, a pH adjuster, a coloring agent, and an antifoaming agent, if necessary.

1.2. Physical properties 1.2.1. Dispersibility In the CNT aqueous dispersion, the better the dispersibility of the CNTs, the smaller the volume-based volume average particle diameter (median diameter) of the CNTs. The median diameter of CNT is a diameter at which when CNT particles are divided into two with a certain particle diameter, the larger side and the smaller side have the same amount. The median diameter is also called "d50."

In the CNT aqueous dispersion according to the present embodiment, the median diameter of the CNTs is, for example, 30.0 μm or less, preferably 15.0 μm or less, more preferably 10.0 μm or less, and even more preferably 5 μm or less. .0 μm or less, and even more preferably 1.0 μm or less.

If the median diameter of CNT is 30.0 μm or less, the dispersibility of CNT can be improved. The median diameter of the CNTs is, for example, 0.1 μm or more. The median diameter is measured by a laser diffraction/scattering particle size distribution measuring device.

1.2.2. Viscosity The viscosity of the CNT aqueous dispersion according to the present embodiment measured using a B-type viscometer at 25° C. and 60 rpm is, for example, 1000 cps or less, preferably 500 cps or less, and more preferably is 300 cps or less, and even more preferably 100 cps or less. Hereinafter, "viscosity measured using a B-type viscometer at 25° C. and 60 rpm" will also be simply referred to as "viscosity." Note that 1 cps=1 mPa·s.

If the viscosity of the CNT aqueous dispersion is 1000 cps or less, the CNT aqueous dispersion can be easily coated. Furthermore, the CNT aqueous dispersion can be coated with good uniformity.

The viscosity of the CNT aqueous dispersion is, for example, 10 cps or more, preferably 20 cps or more. If the viscosity of the CNT aqueous dispersion is 10 cps or more, the CNT aqueous dispersion can be coated more easily.

1.2.3. pH
The pH (Potential Hydrogen) of the CNT aqueous dispersion according to the present embodiment is, for example, 1.0 or more and 6.0 or less, preferably 1.5 or more and 5.0 or less, and more preferably 2.0 or more. It is 4.5 or less. If the pH of the CNT aqueous dispersion is 1.0 or more, corrosion of equipment used for producing the CNT aqueous dispersion can be reduced. "pH" refers to the hydrogen ion index. pH is measured using a commercially available pH meter under conditions of 25° C. and 1 atm.

1.3. Manufacturing method 1.3.1. Overall Flow Next, a method for producing a CNT aqueous dispersion according to the present embodiment will be described with reference to the drawings. FIG. 1 is a flowchart for explaining the method for producing a CNT aqueous dispersion according to this embodiment.

As shown in FIG. 1, the method for manufacturing a CNT aqueous dispersion according to the present embodiment includes a mixed liquid preparation step (step S11) of preparing a mixed liquid, and a CNT aqueous dispersion by dispersing CNTs contained in the mixed liquid. and a dispersion liquid preparation step (step S12). Each step will be explained below.

1.3.2. Mixed liquid preparation process (step S11)
In the liquid mixture preparation step, CNTs and a dispersant are added to water, and the CNTs, the dispersant, and water are mixed to prepare a liquid mixture. The CNTs, dispersant, and water are mixed, for example, using a homogenizer. The homogenizer may be of an ultrasonic type that causes cavitation using ultrasonic waves, a stirring type that stirs the mixed liquid, or a pressure type that applies pressure to the mixed liquid. By performing treatment with a homogenizer, aggregates caused by CNT can be reduced. Thereby, the underwater opposing collision method in the dispersion process described later can be performed smoothly.

1.3.3. Dispersion process (step S12)
In the dispersion step, a CNT aqueous dispersion is produced by dispersing the CNTs contained in the produced mixed solution by an underwater head-to-head collision method. A CNT aqueous dispersion with good CNT dispersibility can be produced by the underwater head-to-head collision method.

In the underwater head-to-head collision method, a liquid mixture containing CNTs is discharged from a nozzle hole at high pressure and collides with ceramic balls to disperse the CNTs. In the underwater facing collision method, a mixed liquid is discharged from a nozzle hole having a diameter of, for example, 50 μm or more and 250 μm or less, preferably 150 μm or more and 200 μm or less, and the mixed liquid is caused to collide with a ceramic ball. If the diameter of the nozzle hole is 50 μm or more, even a liquid mixture with high viscosity can be discharged from the nozzle hole. If the diameter of the nozzle hole is 200 μm or less, the collision energy of the mixed liquid can be increased.

In the underwater facing collision method, the mixed liquid is discharged at a pressure of, for example, 150 MPa or more and 250 MPa or less, preferably 180 MPa or more and 220 MPa or less. If the pressure is 150 MPa or more, the collision energy of the mixed liquid can be increased. When the pressure is 250 MPa or less, it is possible to prevent the collision energy from being too high and causing the CNT fibers to break and making it impossible to obtain desired characteristics.

Specifically, the underwater opposing collision method is performed using a wet atomization device "Starburst Lab" (model name: HJP-25005) manufactured by Sugino Machine Co., Ltd. The wet atomization device has a higher energy density than, for example, an ultrasonic homogenizer or a ball mill, and can produce a CNT aqueous dispersion with good dispersibility in a short time. Furthermore, the wet atomization apparatus can minimize the amount of impurities mixed in, and can produce a CNT aqueous dispersion with very little amount of impurities mixed in.

The number of passes of the mixed liquid in the wet atomization device is, for example, from 1 to 20 times, preferably from 1 time to 10 times, and more preferably from 1 time to 5 times. If the number of passes is 20 or less, it is possible to prevent the CNT fibers from being cut due to collisions between the liquid mixtures, thereby preventing desired characteristics from being obtained. Furthermore, manufacturing time can be reduced. Furthermore, energy saving can be achieved.

"The number of passes of the mixed liquid in the wet atomizer" refers to the number of times the mixed liquid is circulated in the wet atomizer. For example, "the number of passes is twice" means that the mixed liquid is circulated twice so that the CNTs that have collided with the ceramic balls once collide with the ceramic balls again. In this way, the number of passes corresponds to the number of times the mixed liquid projected from the nozzle hole collides with the ceramic ball. The number of passes is proportional to the processing time in the wet atomization device. When the processing time in the wet atomization device is long, the number of times the mixed liquid is circulated increases.

Through the above steps, the CNT aqueous dispersion according to this embodiment can be manufactured.

In addition, above, the method of dispersing CNTs by colliding a liquid mixture discharged from a nozzle hole with ceramic balls has been described as an underwater counter-impact method using a wet atomization device. However, the method is not particularly limited as long as the CNTs can be dispersed with good dispersibility, and for example, a method may be used in which two nozzle holes are arranged opposite each other and the mixed liquids collide with each other to disperse the CNTs. In this case, the number of passes corresponds to the number of collisions between the mixed liquid discharged from one nozzle hole and the mixed liquid discharged from the other nozzle hole.

1.4. Effects The CNT aqueous dispersion according to the present embodiment contains CNTs, water, and a dispersant for dispersing CNTs in water, and the content of CNTs is 2.0% by mass or more, and the dispersant is , a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group. Therefore, the CNT aqueous dispersion according to the present embodiment has a large CNT content and good dispersibility, as shown in the experimental examples described later. Furthermore, a coating layer with high adhesion to the base material can be produced.

In the CNT aqueous dispersion according to this embodiment, the dispersant may be polyacrylic acid. If the dispersant is polyacrylic acid, the viscosity of the aqueous CNT dispersion can be made smaller than when, for example, sodium carboxymethyl cellulose is used as the dispersant, as shown in the experimental examples described below. Thereby, the CNT aqueous dispersion can be easily applied.

In the CNT aqueous dispersion according to this embodiment, the content of the dispersant may be 0.4% by mass or more. When the content of the dispersant is 0.4% by mass or more, the median diameter of CNTs and the viscosity of the aqueous CNT dispersion can be reduced, as shown in the experimental examples described later.

In the CNT aqueous dispersion according to this embodiment, the content of the dispersant may be 1.0% by mass or more. If the content of the dispersant is 1.0% by mass or more, as shown in the experimental example described later, even if the mixed solution is passed once in the wet atomization device, the median diameter of CNTs and CNT water The viscosity of the dispersion can be reduced.

In the CNT aqueous dispersion according to this embodiment, the content of the dispersant may be 6.0% by mass or less. If the content of the dispersant is 6.0% by mass or less, the median diameter of CNTs and the viscosity of the aqueous CNT dispersion can be reduced, as shown in the experimental examples described later.

In the CNT aqueous dispersion according to this embodiment, the weight average molecular weight of the dispersant may be 200,000 or less. If the weight average molecular weight of the dispersant is 200,000 or less, the viscosity of the CNT aqueous dispersion can be reduced as shown in the experimental examples described later.

In the CNT aqueous dispersion according to this embodiment, the median diameter of the CNTs may be 1.0 μm or less. If the median diameter of CNTs is 1.0 μm or less, a CNT aqueous dispersion with good CNT dispersibility can be produced.

The CNT aqueous dispersion according to this embodiment may have a viscosity of 300 cps or less. If the viscosity is 300 cps or less, the CNT aqueous dispersion can be easily coated using a coater.

2. Electromagnetic noise suppression sheet 2.1. Configuration Next, the electromagnetic noise suppression sheet according to the present embodiment will be described with reference to the drawings. FIG. 2 is a cross-sectional view schematically showing the electromagnetic noise suppression sheet 100 according to this embodiment.

The electromagnetic noise suppression sheet 100 includes a base material 10 and a coating layer 20, as shown in FIG. The electromagnetic noise suppression sheet 100 has a sheet shape in which the length in the direction perpendicular to the thickness direction is sufficiently large compared to the thickness. Each member will be explained below.

2.1.1. Base material The base material 10 supports the coating layer 20. The shape of the base material 10 is, for example, a sheet shape. The base material 10 may be a sheet containing pulp. The base material 10 may be composed only of pulp.

Examples of the pulp contained in the base material 10 include chemical pulps such as LBKP (hardwood bleached kraft pulp) and NBKP (softwood bleached kraft pulp), GP (groundwood pulp), PGW (pressurized groundwood pulp), and RMP (refiner mechanical pulp). pulp), mechanical pulp such as TMP (thermomechanical pulp), CTMP (chemothermomechanical pulp), CMP (chemimechanical pulp), CGP (chemiground pulp), wood pulp such as DIP (deinked pulp), or kenaf. , non-wood pulps such as bagasse, bamboo, and cotton. The base material 10 may contain only one type of these pulps, or may contain two or more types in any ratio. Furthermore, the base material 10 may contain synthetic fibers to the extent that quality is not affected.

It is preferable that the base material 10 contains LBKP. The content of LBKP in the base material 10 is, for example, 70% by mass or more, preferably 90% by mass or more, and more preferably 100% by mass. If the content of LBKP is 70% by mass or more, distortion of the base material 10 can be reduced.

When the basis weight of the base material 10 is 40 g/m ² or less, the base material 10 preferably contains NBKP. The content of NBKP in the base material 10 is, for example, 30% by mass or less. If the content of NBKP is 30% by mass or less, the smoothness and strength of the base material 10 can be maintained.

The base material 10 does not need to contain pulp. The base material 10 may be a resin film such as a PET (polyethylene terephthalate) film. The base material 10 may have translucency.

The base material 10 may contain filler, paper strength enhancer, sizing agent, bulking agent, retention improver, freeness improver, sulfate band, wet paper strength enhancer, colored dye, colored pigment, fluorescent whitening agent, if necessary. It may contain various additives such as a pitch control agent, a thickener, a preservative, and a pH adjuster.

2.1.2. Coating layer The coating layer 20 is provided on the base material 10. The coating layer 20 is coated on the base material 10. The coating layer 20 is a layer made from the CNT aqueous dispersion according to the present embodiment described above. The CNT aqueous dispersion according to this embodiment is applied to the base material 10 and then dried to form the coating layer 20. Coating layer 20 contains CNT and a polymer. The median diameter of the CNTs included in the coating layer 20 is the same as the median diameter of the CNTs included in the CNT aqueous dispersion according to this embodiment. When the CNT aqueous dispersion according to this embodiment contains an additive, the coating layer 20 may contain the additive.

The polymer contained in the coating layer 20 is constituted by the dispersant contained in the CNT aqueous dispersion according to this embodiment. Therefore, the polymer contained in the coating layer 20 contains at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group. The polymer contained in the coating layer 20 is, for example, polyacrylic acid. In the coating layer 20, the ratio of the mass of the polymer to the mass of CNTs is the mass of CNTs in the CNT aqueous dispersion according to the present embodiment described above, the mass of the dispersant to _CNTs , the ratio of _DISP , M _DISP /M _CNT , and It's the same.

2.1.3. Other Members Although not shown, the electromagnetic noise suppression sheet 100 may include an adhesive layer provided under the base material 10. Furthermore, the electromagnetic noise suppression sheet 100 may include a release layer provided under the adhesive layer. Then, the coating layer 20 may be attached to the external device via the base material 10 by peeling the release layer from the adhesive layer and bringing the adhesive layer into contact with the external device.

Examples of the material for the adhesive layer include natural rubber, synthetic rubber, urethane resin, acrylic resin, vinyl acetate resin, vinyl acetate/acrylic acid ester copolymer resin, and vinyl acetate/ethylene copolymer resin. The material of the release layer includes, for example, uncoated paper such as high-quality paper, coated paper such as general coated paper, art paper, glassine paper, film using polyethylene, polyethylene terephthalate, etc., and film laminated paper.

Although not shown, the electromagnetic noise suppression sheet 100 may include an overcoat layer provided on the coating layer 20. The overcoat layer can suppress scratches on the coating layer 20. Furthermore, the overcoat layer can increase the dielectric breakdown strength of the coating layer 20.

The material of the overcoat layer is, for example, polyethylene terephthalate, polypropylene, vinyl chloride resin, fluororesin, silicone resin, styrene-acrylic resin, acrylic resin, urethane resin, epoxy resin, polyethylene wax, polycarbonate, polyphenylene oxide, These include polysulfone, polyimide, thermoplastic polyester, phenolic resin, urea resin, epoxy resin, melamine resin, sialyl phthalate resin, furan resin, and silicone-based inorganic compounds.

2.2. Physical properties 2.2.1. Adhesion In the electromagnetic noise suppression sheet 100, the adhesion between the coating layer 20 and the base material 10 is evaluated by a Seropic test. Specifically, a cellophane tape is attached to the surface of the coating layer 20, a predetermined pressure is applied to the cellophane tape, and then the cellophane tape is peeled off from the coating layer 20. Then, the adhesion between the base material 10 and the coating layer 20 is evaluated by visually checking the state of the coating layer 20 after the cellophane tape is peeled off.

2.2.2. Electromagnetic Noise Suppression Performance The electromagnetic noise suppression sheet 100 has electromagnetic noise suppression performance that suppresses electromagnetic noise. The electromagnetic noise suppression performance is evaluated by measuring the transmission attenuation rate Rtp (dB) using the microstrip line method. The larger Rtp is, the higher the electromagnetic noise suppression performance is.

The electromagnetic noise suppression performance has a correlation with the surface resistivity of the coating layer 20. The lower the surface resistivity of the coating layer 20, the higher the electromagnetic noise suppression performance tends to be. The surface resistivity of the coating layer 20 is measured in accordance with "JIS K 7194:1994" using a predetermined measuring device.

2.3. Manufacturing method 2.3.1. Overall Flow Next, a method for manufacturing the electromagnetic noise suppression sheet 100 according to the present embodiment will be described with reference to the drawings. FIG. 3 is a flowchart for explaining the method for manufacturing the electromagnetic noise suppression sheet 100 according to the present embodiment.

As shown in FIG. 3, the method for manufacturing the electromagnetic noise suppression sheet 100 includes a base material forming step (step S21) of forming the base material 10, and a coating step (step S21) of coating the base material 10 with a CNT aqueous dispersion. S22), and a coating layer forming step (step S23) of drying the coated CNT aqueous dispersion to form the coating layer 20. Each step will be explained below.

2.3.2. Base material forming step (step S21)
In the base material forming step, for example, a slurry containing pulp but not containing CNTs is made into paper using a paper machine to form the base material 10. The slurry for forming the base material 10 has a Canadian standard freeness (CSF) of, for example, 200 ml or more and 550 ml or less, preferably 250 ml or more and 500 ml or less. CSF is determined by the method described in "JIS P 81821-2:2018". The paper-making method for the base material 10 is not particularly limited, but includes, for example, a Fourdrinier paper machine, a Fourdrinier multilayer paper machine, a cylinder paper machine, a cylinder multilayer paper machine, a Fourdrinier cylinder combination multilayer paper machine, and a twin wire paper machine. This is done using various devices such as The papermaking method may be acidic papermaking or neutral papermaking.

A size liquid containing a water-soluble polymer such as starch, polyvinyl alcohol, or polyacrylamide may be applied to the surface of the base material 10. By applying the size liquid, when the CNT aqueous dispersion is applied to the base material 10, excessive penetration of the CNT aqueous dispersion into the base material 10 can be suppressed. Furthermore, the strength of the surface of the base material 10 can be improved. The sizing liquid includes a surface sizing agent such as a styrene sizing agent, a styrene-acrylate sizing agent, an olefin sizing agent, an alkyl ketene dimer sizing agent, an alkenyl succinic anhydride sizing agent, and the like. Furthermore, the size liquid may contain auxiliary agents such as colored pigments, colored dyes, fluorescent dyes, and antifoaming agents. Examples of the method for applying the size liquid include a size press, a gate roll coater, a metering sizer, a rod coater, and a bar coater.

A paint containing a pigment and an adhesive may be applied to the surface of the base material 10. By applying the paint, when applying the CNT aqueous dispersion to the base material 10, it is possible to suppress excessive penetration of the CNT aqueous dispersion into the base material 10. Examples of pigments used in paints include inorganic pigments such as kaolin, light calcium carbonate, and titanium oxide, and organic pigments such as plastic pigments. Examples of adhesives used in paints include various copolymer latexes such as styrene-butadiene, styrene-acrylic, vinyl acetate-acrylic, and butadiene-methylmethacrylic. Furthermore, the coating material may contain auxiliary agents such as a pH adjuster, an antifoaming agent, a dispersant, a lubricant, a printability improver, a thickener, a water retention agent, a fluorescent dye, a colored pigment, and a colored dye.

Note that, as described above, a resin film such as a PET film may be used as the base material 10.

2.3.3. Coating process (step S22)
In the coating step, the CNT aqueous dispersion obtained by the method for producing a CNT aqueous dispersion according to the present embodiment described above is coated on the surface of the base material 10. The dispersion coating method is not particularly limited, and examples thereof include a die coater, a gravure coater, a wire bar coater, a knife coater, an air coater, a blade coater, a roll coater, a reverse roll coater, and the like. When applying a CNT aqueous dispersion using such a coater, if the viscosity of the CNT aqueous dispersion is too high, it becomes difficult to apply the CNT aqueous dispersion.

2.3.4. Coating layer forming step (step S23)
In the coating layer forming step, the CNT aqueous dispersion coated on the base material 10 is dried to form the coating layer 20. The method for drying the CNT aqueous dispersion is not particularly limited as long as water contained in the CNT aqueous dispersion can be evaporated, and examples thereof include hot air drying, infrared drying, natural drying, and the like.

Through the above steps, the electromagnetic noise suppression sheet 100 can be manufactured.

2.4. Effect The electromagnetic noise suppression sheet 100 includes a base material 10 and a coating layer 20 provided on the base material 10 and containing CNTs and _{a polymer} . The mass ratio M _DISP /M _CNT is 1/10 or more and 5 or less, and the polymer contains at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group _. It is a polymer containing Therefore, in the electromagnetic noise suppression sheet 100, the CNT content is large and the dispersibility is good, as shown in the experimental examples described later. Furthermore, the adhesion between the base material 10 and the coating layer 20 can be increased.

In the electromagnetic noise suppression sheet 100, the ratio M _DISP /M _CNT may be 1/5 or more. If the ratio M _DISP /M _CNT is 1/5 or more, the median diameter of the CNTs can be reduced as shown in the experimental examples described later.

In the electromagnetic noise suppression sheet 100, the ratio M _DISP /M _CNT may be 1/2 or more. If the ratio M _DISP /M _CNT is 1/2 or more, the median diameter of CNTs can be reduced even if the number of passes of the mixed liquid in the wet atomization device is one, as shown in the experimental example described later. Can be done.

In the electromagnetic noise suppression sheet 100, the ratio M _DISP /M _CNT may be 3 or less. If the ratio M _DISP /M _CNT is 3 or less, the median diameter of the CNTs can be reduced as shown in the experimental examples described later.

3. Experimental Examples Experimental examples are shown below to explain the present invention more specifically. Note that the present invention is not limited in any way by the following experimental examples.

3.1. First experimental example 3.1.1. Preparation of CNT aqueous dispersion (1) Examples 1 to 9
A mixed solution was prepared by mixing CNT, a dispersant, and water. For mixing, a homogenizer "Biomixer BM-2" manufactured by Nippon Seiki Seisakusho Co., Ltd. was used. The mixing processing time was 5 minutes.

As the CNT, "K-Nanos-100P" manufactured by KUMHO PETROCHEMICAL was used. The CNTs are MWCNTs with a diameter of 8 nm to 15 nm, a fiber length of 27 μm (bundle), and a BET specific surface area of 220 m ² /g. The content of CNT in the mixed liquid was varied in the range of 2.0% by mass to 3.5% by mass.

Polyacrylic acid was used as the dispersant. Specifically, "Aqualic HL-415" manufactured by Nippon Shokubai Co., Ltd. was used. The weight average molecular weight is 10,000. The content of polyacrylic acid in the mixed liquid was varied in the range of 0.2% by mass to 10.0% by mass.

Next, the underwater head-to-head collision method was performed on the above liquid mixture. The underwater head-to-head collision method was carried out using a wet atomization device "Starburst Lab" (model name: HJP-25005) manufactured by Sugino Machine Co., Ltd. The diameter of the nozzle hole through which the mixed liquid was discharged was set to 175 μm, the discharge pressure of the mixed liquid was set to 200 MPa, and the mixed liquid was caused to collide with the ceramic balls. The number of passes of the mixed liquid through the wet atomizer was varied in the range of 1 to 10 times. As described above, a CNT aqueous dispersion containing CNTs, a dispersant, and water was prepared.

FIG. 4 is a table showing conditions for producing CNT aqueous dispersions of Examples 1 to 9, Examples 10 to 14, and Comparative Examples 1 to 9, which will be described later. In FIG. 4, the weight average molecular weight is simply expressed as "molecular weight." "Coarse dispersion" refers to a state in which the underwater head-to-head collision method using a wet atomization device is not performed.

In FIG. 4 and the following description, polyacrylic acid is also referred to as "PAA." A copolymer of acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid is also referred to as "PAA/PSA." Polystyrene sulfonic acid is also called "PSSA". Polyoxyethylene alkyl ether is also called "POEAE". Polyacrylic acid sodium salt is also called "PAANa". Polymethacrylic acid is also called "PMA". The polycarboxylic acid polyalkylene glycol graft product is also referred to as "GRAFT". Sodium carboxymethylcellulose is also called "CMC".

(2) Examples 10 to 12
CNT dispersions of Examples 10 to 12 were prepared in the same manner as in Example 1 above, except that the weight average molecular weight of polyacrylic acid as a dispersant was changed. Specifically, "Aron A-10SL" manufactured by Toagosei Co., Ltd. was used as polyacrylic acid having a weight average molecular weight of 6,000. As polyacrylic acid having a weight average molecular weight of 200,000, "Aron A-10H" manufactured by Toagosei Co., Ltd. was used. As polyacrylic acid having a weight average molecular weight of 800,000, "Aqualic AS-58" manufactured by Nippon Shokubai Co., Ltd. was used.

(3) Example 13
Same as Example 1 above, except that a copolymer of polyacrylic acid and poly2-acrylamido-2-methylpropanesulfonic acid (PAA/PSA) was used as the dispersant instead of polyacrylic acid. Thus, a CNT dispersion liquid of Example 13 was prepared. Specifically, "Aron A-12SL" manufactured by Toagosei Co., Ltd. was used as the PAA/PSA. The weight average molecular weight is 10,000.

(4) Example 14
A CNT dispersion liquid of Example 14 was prepared in the same manner as in Example 1 described above, except that polystyrene sulfonic acid (PSSA) was used as a dispersant instead of polyacrylic acid. Specifically, PSSA manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. was used as the dispersant. The weight average molecular weight is 70,000.

(5) Comparative example 1
A CNT dispersion liquid of Comparative Example 1 was prepared in the same manner as in Example 1 described above, except that polyoxyethylene alkyl ether (POEAE) was used as a dispersant instead of polyacrylic acid. Specifically, "Emulgen 707" manufactured by Kao Corporation was used as POEAE. The weight average molecular weight is 1000 or less.

(6) Comparative example 2
As a dispersant, polyacrylic acid sodium salt (PAANa) was used instead of polyacrylic acid.
) was used, but in the same manner as in Example 1 described above, a CNT dispersion liquid of Comparative Example 2 was produced. Specifically, "Aron T-50" manufactured by Toagosei Co., Ltd. was used as PAANa. The weight average molecular weight is 6,000.

(7) Comparative example 3
A CNT dispersion liquid of Comparative Example 3 was prepared in the same manner as in Example 1 described above, except that polymethacrylic acid (PMA) was used as a dispersant instead of polyacrylic acid. Specifically, PMA manufactured by Fuji Film Wako Pure Chemical Industries, Ltd. was used as a dispersant. The weight average molecular weight is 100,000 or less.

(8) Comparative example 4
A CNT dispersion liquid of Comparative Example 4 was prepared in the same manner as in Example 1 described above, except that a polycarboxylic acid polyalkylene glycol graft (GRAFT) was used as a dispersant instead of polyacrylic acid. Specifically, "Aqualic LK-500" manufactured by Nippon Shokubai Co., Ltd. was used as GRAFT.

(9) Comparative Examples 5 to 9
CNT dispersions of Comparative Examples 5 to 9 were prepared in the same manner as in Example 1 above, except that sodium carboxymethyl cellulose (CMC) was used as a dispersant instead of polyacrylic acid. Specifically, "Celogen 5A" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. was used as the CMC. The weight average molecular weight is 15,000. The degree of etherification is 0.7. The content of CNT in the mixed liquid was varied in the range of 2.0% by mass to 3.0% by mass. Further, the content of CMC in the mixed liquid was varied in the range of 0.4% by mass to 3.0% by mass.

3.1.2. Experimental Method The dispersibility of the CNTs contained in the CNT aqueous dispersion was evaluated by measuring the median diameter of the CNTs contained in the CNT aqueous dispersion prepared as described above. The median diameter of the CNTs was measured using a laser diffraction/scattering particle size distribution measuring device "LA-960V2" manufactured by Horiba, Ltd.

Furthermore, the viscosity of the CNT aqueous dispersion prepared as described above was measured. The viscosity of the CNT aqueous dispersion was measured using a B-type viscometer "BM" manufactured by Tokyo Keiki Co., Ltd. at 25° C. and a rotation speed of 60 rpm.

Furthermore, the pH of the mixture before the CNT aqueous dispersion was dispersed was measured. The pH of the mixed solution was measured under conditions of 25° C. and 1 atm using a “desktop pH meter” manufactured by Horiba, Ltd.

3.1.3. Experimental results (1) Evaluation when the CNT content is 2.0% by mass and the dispersant content is varied Median diameter, viscosity, and pH are shown in FIG. FIG. 5 is a graph showing the median diameter of Examples 1, 5 to 9 and Comparative Examples 5 to 7 in which the CNT content is 2.0% by mass. FIG. 6 is a graph showing the viscosities of Examples 1, 5 to 9 and Comparative Examples 5 to 7. The graphs in FIGS. 5 and 6 are plots of the values shown in FIG.

Note that the viscometer used in this experimental example cannot measure a viscosity of 10,000 cps or more. For example, even if the viscosity is originally 20,000 cps, it is expressed as "10,000 cps" by the viscometer used in this experimental example. In FIG. 4, the case where "10000 cps" was written in the viscometer used in this experimental example was set as "10000↑".

Further, for convenience, in FIGS. 5 and 6 and FIGS. 7 and 8 described later, "% by mass", which is the unit of content of the dispersant, is simply expressed as "%".

As shown in Figures 5 and 6, when the PAA content was 0.2% by mass, both the median diameter and viscosity were extremely large compared to when the PAA content was 0.4% or more. . Furthermore, when the PAA content was 10.0% by mass, both the median diameter and viscosity were larger than when the PAA content was 6.0% by mass. When the PAA content was 1.0% by mass or more and 6.0% by mass or less, the median diameter and viscosity were particularly small.

When the PAA content was 0.4% by mass, the median diameter was smaller than when the CMC content was 0.4% by mass. From this, it was found that when PAA was used as a dispersant, the dispersibility was better than when CMC was used.

As the number of passes through the wet atomization device increased, the median diameter and viscosity tended to decrease.

(2) Evaluation when the content ratio of CNTs and dispersant is 1:1 and the content is varied. Figure 7 shows Example 1 in which the ratio of CNTs and dispersant content is 1:1. 4 is a graph showing the median diameter of Comparative Examples 5, 8, and 9. FIG. 8 is a graph showing the viscosities of Examples 1 to 4 and Comparative Examples 5, 8, and 9. The graphs in FIGS. 7 and 8 are plots of the values shown in FIG. 4.

As shown in FIGS. 7 and 8, the median diameter and viscosity tended to increase as the contents of CNT and dispersant increased.

As shown in FIG. 8, when CMC is used as a dispersant, when the content of CNT and CMC is 2.5% by mass, the viscosity is too high and the wet atomization device is passed twice or more. I couldn't do it. The same was true when the content of CNT and CMC was 3.0% by mass. On the other hand, when PAA was used as a dispersant, even if the content of CNT and PAA was 3.0% by mass, the wet atomization device could be passed 10 times. From this, it was found that when PAA was used as a dispersant, the viscosity was lower than when CMC was used. However, even when PAA is used as a dispersant, if the content of CNT and PAA is 3.5% by mass, the viscosity is too high and the pass through the wet atomization device must be performed two or more times. I couldn't do it.

(3) Evaluation of type of dispersant FIG. 9 is a graph showing the median diameter of Examples 1, 13, and 14 and Comparative Examples 1 to 5 in which the content of CNT and dispersant is 2.0% by mass. FIG. 10 is a graph showing the viscosity of Examples 1, 13, and 14 and Comparative Examples 1 to 5. The graphs in FIGS. 9 and 10 are plots of the values shown in FIG.

Examples 1, 13, and 14 using PAA, PAA/PSA, and PSSA as dispersants had a lower median diameter and viscosity than Comparative Examples 1 to 5 using POEAE, PAANa, PMA, and GRAFT. It tended to become smaller. Furthermore, when PAA or PAA/PSA was used as a dispersant, the median diameter was equal to or smaller than when CMC was used. Furthermore, when PAA or PAA/PSA was used as a dispersant, the viscosity was lower than when CMC was used.

(4) Evaluation of weight average molecular weight When PAA is used as a dispersant, as shown in Figure 4, the viscosity of Example 11 with a weight average molecular weight of 200,000 cps is the same as that of Example 11 with a weight average molecular weight of 800,000 cps. Compared to Example 12, there was a tendency to become smaller. Furthermore, the viscosity of Example 1 with a weight average molecular weight of 10,000 cps tended to be smaller than that of Example 11 with a weight average molecular weight of 200,000 cps.

3.2. Second experimental example 3.2.1. Preparation of Electromagnetic Noise Suppression Sheet The CNT aqueous dispersions of Examples 1 to 14 and Comparative Examples 1 to 9 described above were applied to a base material using a die coater. As the base material, a paper base material "Hamayu" (registered trademark) manufactured by Hokuetsu Corporation was used. The basis weight is 30g/ ^m2 . Next, the coated CNT aqueous dispersion was dried at 60° C. to 70° C. by hot air drying to evaporate water. Then, an electromagnetic noise suppression sheet consisting of a base material and a coating layer was produced.

3.2.2. Experimental method The surface resistivity of the coating layer of the electromagnetic noise suppression sheet produced as described above was measured. As a measuring instrument, "Loresta-AX MCP-T370" manufactured by Mitsubishi Chemical Analytech Co., Ltd. was used. The measurement was performed in accordance with "JIS K 7194:1994".

Furthermore, the transmission attenuation rate Rtp (dB) of the electromagnetic noise suppression sheet produced as described above was measured. The measuring device used was a network analyzer "ZVA67" manufactured by ROHDE & SCHWARZ, connected to a test fixture "TF-18C" or "TF-30A" manufactured by KEYCOM. The measurement was performed by a microstrip line method in accordance with "IEC62333". The measurement frequency was 500 MHz to 30 GHz.

3.2.3. Experimental Results FIG. 11 is a table showing the surface resistivity and transmission attenuation rate Rtp of the electromagnetic noise suppression sheets of Examples 1 to 14 and Comparative Examples 1 to 9. FIG. 11 shows Rtp at 5 GHz, 14 GHz, and 28 GHz.

As shown in FIG. 11, electromagnetic noise suppression performance was confirmed in Examples 1 to 14. Example 1 using PAA (content 2.0% by mass) as a dispersant had the same Rtp as Comparative Example 5 using CMC (content 2.0% by mass) as a dispersant. Surface resistivity was generally correlated with Rtp.

3.2. Third experimental example 3.3.1. Preparation of Electromagnetic Noise Suppression Sheet The CNT aqueous dispersions of Examples 1, 5 to 14 and Comparative Examples 1 to 7 described above were applied to a base material using a die coater. As the base material, a PET (Polyethylene Terephthalate) film "A4360" manufactured by Toyobo Co., Ltd. was used. In this experimental example, a CNT aqueous dispersion was used which was subjected to an underwater head-to-head collision method with five passes through a wet atomization device. Next, the coated CNT aqueous dispersion was dried at 60° C. to 70° C. by hot air drying to evaporate water. Then, an electromagnetic noise suppression sheet consisting of a base material and a coating layer was produced.

In Comparative Examples 5 to 9 in which CMC was used as a dispersant, isopropyl alcohol (IPA) was added to the CNT aqueous dispersion and then applied to the substrate. If IPA was not applied, the CNT aqueous dispersion would be repelled by the base material, making it impossible to apply the CNT aqueous dispersion. In Examples 1 to 14, the CNT aqueous dispersion could be coated without adding IPA.

3.3.2. Experimental Method The adhesion between the base material and the coating layer of the electromagnetic noise suppression sheet produced as described above was evaluated. Adhesion was evaluated by Seropic test. Specifically, cellophane tape was attached to the coating layer, and the cellophane tape was strongly pressed five times with a finger. Thereafter, the cellophane tape was removed all at once, and the peeling of the coating layer was visually confirmed. As the cellophane tape, cellotape (registered trademark) "CT405AP-15" manufactured by Nichiban Co., Ltd. was used.

The evaluation criteria for the Seropic test are as follows.
A: The coating layer was not peeled off from the base material at all.
B: The coating layer was slightly peeled off from the base material, and the base material was slightly visible.
C: The coating layer was completely peeled off from the base material, and the base material was completely visible.

FIG. 12 is a photograph of an electromagnetic noise suppression sheet that corresponds to evaluation criteria A, B, and C of the Seropic test.

3.3.3. Experimental Results FIG. 11 shows the results of the seropic test of the electromagnetic noise suppression sheets of Examples 1, 5 to 14 and Comparative Examples 1 to 7.

As shown in FIG. 11, Examples 1 and 5 to 14 had better results in the seropic test than Comparative Examples 1 to 7, and the adhesion between the coating layer and the base material was high.

Example 10, in which the content of PAA is 0.2% by mass, is similar to Example 9, in which the content of PAA is 0.4% by mass, and Example 8, in which the content of PAA is 1.0% by mass. In comparison, the adhesion between the coating layer and the base material was low.

Among Comparative Examples 1 to 7, Comparative Example 3 using PMA as a dispersant had the best results in the seropic test. However, in Comparative Example 3, as shown in FIGS. 4 and 9 described above, the median diameter of the CNTs was small and the dispersibility of the CNTs was poor.

The above experimental examples show that by using a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group as a dispersant, the CNT content can be increased. It was found that an electromagnetic noise suppression sheet with good CNT dispersibility and high adhesion between the coating layer and the base material could be produced.

Regarding the electromagnetic noise suppression sheet using PET film as the base material, Rtp was measured by the microstrip line method in the same way as in the second experimental example. Comparable electromagnetic noise suppression performance was confirmed.

The above-described embodiments and modifications are merely examples, and the present invention is not limited thereto. For example, it is also possible to combine each embodiment and each modification as appropriate.

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes configurations that are substantially the same as those described in the embodiments. Substantially the same configurations are, for example, configurations that have the same function, method, and result, or configurations that have the same purpose and effect. Further, the present invention includes a configuration in which non-essential parts of the configuration described in the embodiments are replaced. Further, the present invention includes a configuration that has the same effects or a configuration that can achieve the same purpose as the configuration described in the embodiment. Further, the present invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

DESCRIPTION OF SYMBOLS 10... Base material, 20... Coating layer, 100... Electromagnetic noise suppression sheet

Claims (16)

carbon nanotubes and
water and,
a dispersant that disperses the carbon nanotubes in the water;
including;
The content of the carbon nanotubes is 2.0% by mass or more,
The dispersant is a carbon nanotube aqueous dispersion, which is a polymer containing at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group. The carbon nanotube aqueous dispersion according to claim 1, wherein the dispersant is polyacrylic acid. The carbon nanotube aqueous dispersion according to claim 1, wherein the content of the dispersant is 0.4% by mass or more. The carbon nanotube aqueous dispersion according to claim 1, wherein the content of the dispersant is 1.0% by mass or more. The carbon nanotube aqueous dispersion according to claim 1, wherein the content of the dispersant is 6.0% by mass or less. The carbon nanotube aqueous dispersion according to claim 1, wherein the weight average molecular weight of the dispersant is 200,000 or less. The carbon nanotube aqueous dispersion according to claim 1, wherein the carbon nanotubes have a median diameter of 1.0 μm or less. The carbon nanotube aqueous dispersion according to claim 1, having a viscosity of 300 cps or less as measured using a B-type viscometer at 25° C. and a rotation speed of 60 rpm. The carbon nanotube aqueous dispersion according to any one of claims 1 to 8, which is applied to a substrate. base material and
a layer provided on the base material and containing carbon nanotubes and a polymer;
including;
In the layer, the ratio of the mass of the polymer to the mass of the carbon nanotubes is 1/10 or more and 5 or less,
The electromagnetic noise suppression sheet, wherein the polymer includes at least one of a repeating unit derived from acrylic acid and a repeating unit derived from a monomer having a sulfonic acid group. The electromagnetic noise suppression sheet according to claim 10, wherein the polymer is polyacrylic acid. The electromagnetic noise suppression sheet according to claim 10 or 11, wherein the ratio is 1/5 or more. The electromagnetic noise suppression sheet according to claim 10 or 11, wherein the ratio is 1/2 or more. The electromagnetic noise suppression sheet according to claim 10 or 11, wherein the ratio is 3 or less. The electromagnetic noise suppression sheet according to claim 10 or 11, wherein the weight average molecular weight of the polymer is 200,000 or less. The electromagnetic noise suppression sheet according to claim 10 or 11, wherein the carbon nanotubes have a median diameter of 1.0 μm or less.

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